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BACKGROUND: A dielectric barrier discharge reactor coupled with a series of activated carbon (AC) catalysts was applied to remove low concentrations of chlorobenzene. The catalysts were prepared via an impregnation method and their adsorption capacity and plasma-catalytic ability examined in a sequential adsorption–plasma oxidation process. RESULTS: Ag/AC had the longest breakthrough time and highest breakthrough capacity among the catalysts studied. At the discharge stage, the Ag/AC catalyst had the highest CO2 yield, chlorobenzene mineralization rate and carbon balance, and the lowest emission of chlorobenzene when compared with the other catalysts under the same conditions. However, the Ag/AC catalyst exhibited the worst reducing ozone generation performance, while the Mn/AC catalyst showed the best ozone decomposition ability. The organic intermediates produced using Ag/AC and Ce/AC were simpler and in lower concentrations than those formed using Mn/AC.The adsorption capacity and catalytic activity of the Ag/AC catalyst showed no obvious decrease after five cycles. Fourier transform infrared and scanning electron microscopy–energy dispersive spectroscopy analyses after the reaction showed that some nitrogen organic intermediates and chlorine substances produced via the degradation of chlorobenzene were adsorbed onto the catalyst surface. CONCLUSIONS: Ag/AC exhibited a longer breakthrough time, higher breakthrough capacity, higher CO2 yield, less chlorobenzene emission and better carbon balance when compared with the other catalysts.

Keratoconus (KC) is an ectatic corneal disease characterized by progressive thinning and irregular astigmatism, and a leading indication for corneal transplantation. KC-associated changes have been demonstrated for the entire cornea, but the pathological thinning and mechanical weakening is usually localized. We performed quantitative proteomics using Sequential Windowed Acquisition of All Theoretical Fragment Ion Mass Spectrometry (SWATH-MS) to analyze epithelial and stromal changes between the topographically-abnormal cone and topographically-normal non-cone regions of advanced KC corneas, compared to age-matched normal corneas. Expression of 20 epithelial and 14 stromal proteins was significantly altered (≥2 or ≤0.5-fold) between cone and non-cone in all 4 KC samples. Ingenuity pathway analysis illustrated developmental and metabolic disorders for the altered epithelial proteome with mitochondrion as the significant gene ontology (GO) term. The differential stromal proteome was related to cellular assembly, tissue organization and connective tissue disorders with endoplasmic reticulum protein folding as the significant GO term. Validation of selected protein expression was performed on archived KC, non-KC and normal corneal specimens by immunohistochemistry. This is the first time to show that KC-associated proteome changes were not limited to the topographically-thinner and mechanically-weakened cone but also non-cone region with normal topography, indicating a peripheral involvement in KC development. NRF (Natl Research Foundation, S’pore) NMRC (Natl Medical Research Council, S’pore) MOH (Min. of Health, S’pore) Published version

Mitochondrial dysfunction underscores aging and diseases. Mitophagy (mitochondria + autophagy) is a quality control pathway that preserves mitochondrial health by targeting damaged mitochondria for autophagic degradation. Hence, molecules or compounds that can augment mitophagy are therapeutic candidates to mitigate mitochondrial-related diseases. However, mitochondrial stress remains the most effective inducer of mitophagy. Thus, identification of mitophagy-inducing regimes that are clinically relevant is favorable. In this study, pomegranate extract (PE) supplementation is shown to stimulate mitophagy. PE activates transcription factor EB (TFEB) to upregulate the expression of autophagy and lysosomal genes for mitochondrial quality control under basal and stress conditions. Basally, PE alters mitochondrial morphology and promotes recruitment of autophagosomes to the mitochondria (mitophagosome formation). Upon onset of mitochondrial stress, PE further augments mitophagosome formation, and engages PINK1 and Parkin to the mitochondria to potentiate mitophagy. This cellular phenomenon of PE-induced mitophagy helps to negate superfluous mitochondrial reactive oxygen species (ROS) production and mitochondrial impairment. Overall, our study highlights the potential of PE supplementation as a physiological therapy to modulate TFEB activity to alleviate mitochondrial dysfunction in aging and mitochondrial-related diseases.

Efficient electrocatalysts for hydrogen evolution reaction are key to realize clean hydrogen production through water splitting. As an important family of functional materials, transition metal oxides are generally believed inactive towards hydrogen evolution reaction, although many of them show high activity for oxygen evolution reaction. Here we report the remarkable electrocatalytic activity for hydrogen evolution reaction of a layered metal oxide, Ruddlesden−Popper-type Sr2RuO4 with alternative perovskite layer and rock-salt SrO layer, in an alkaline solution, which is comparable to those of the best electrocatalysts ever reported. By theoretical calculations, such excellent activity is attributed mainly to an unusual synergistic effect in the layered structure, whereby the (001) SrO-terminated surface cleaved in rock-salt layer facilitates a barrier-free water dissociation while the active apical oxygen site in perovskite layer promotes favorable hydrogen adsorption and evolution. Moreover, the activity of such layered oxide can be further improved by electrochemistry-induced activation., Water may serve as a renewable hydrogen fuel source to replace fossil fuels, although such electrolysis requires highly active catalysts. Here, authors explore Ruddlesden−Popper oxides as hydrogen evolution electrocatalysts that feature an unusual synergistic effect to promote high activity.

The complement system serves as the frontline of host defense for the human body against foreign entities, and is triggered via one or more of several signaling cascades that consist of interactions between soluble and cell surface-bound complement proteins. In this thesis, the objective is to explore how lipid membranes influence the initiation, amplification, termination and regulation of complement activation, utilizing supported lipid bilayer platforms as a model experimental system. The overall hypothesis of this work is that the supported lipid bilayer platform provides a useful model system to recapitulate key protein-lipid and protein-protein interactions involved in complement activation at lipid membrane interfaces, thereby establishing an experimental framework to decipher key trigger factors (e.g., membrane surface charge) as well as evaluate candidate inhibitors acting against complement convertases and membrane attack complex assemblies. Within this scope, four different experimental studies were conducted, leading to new insights into the mechanisms by which lipid membranes influence complement activation. In the first study, the influence of membrane surface change on the adsorption properties of different pattern recognition proteins involved in initiation of complement activation was investigated. In the second study, the effects of covalent and noncovalent tethering strategies on the self-assembly of the alternative pathway C3 convertase was monitored. It was identified that the C3b immobilization scheme is a critical factor governing convertase assembly, further enabling successful evaluation of a clinically relevant complement inhibitor, compstatin. In the third study, the assembly of the complement-terminating membrane attack complex was monitored onto supported lipid bilayer platforms, with particular attention to the influence of membrane surface charge. It was determined that the membrane attack complex assembly preferentially forms on negatively charged lipid membranes, indicating the importance of membrane electrostatics. In the fourth study, the inhibitory action of vitronectin and clusterin against the membrane attack complex assembly was evaluated, offering insight into the different mechanisms by which these two regulatory proteins inhibit complement activation. In summary, the findings presented in this thesis significantly contribute to the fundamental understanding of complement activation occurring at lipid membrane interfaces, and offer a new platform to characterize the mechanisms of action for a wide range of complement inhibitors including small molecules, antibodies, and peptides. Doctor of Philosophy (MSE)

This thesis concerns the study of amorphous photonic crystal structures: disordered photonic lattices possessing short-range but not long-range order. In the first part of the thesis, I study amorphous structures intended for electrically-pumped random quantum cascade lasers (QCLs). Random lasers are a class of lasers which, unlike traditional lasers, have no well-defined and well-structured cavity; lasing takes place through multiple scattering from a random medium. I design and analyze amorphous lattices of dielectric rods, joined by dielectric veins, which support high quality factor (Q factor) lasing for transverse magnetic (TM) modes. Simulations show that these structures can achieve 2D Q-factors of as large as 10^5, which is not possible using previous designs based on air holes etched in dielectric slabs. In the second part, I perform a numerical study of an amorphous variant of a “photonic topological insulator” (PTI). PTIs are photonic crystal structures with band structures analogous to topological insulator materials, supporting robust electromagnetic edge states that propagate unidirectionally along the edge. Although the existence of these edge states is justified by theoretical arguments that assume long-range order, I show that similarly robust edge states exist in amorphous lattices, which possess only short-range order. This study opens new possibilities for studying disorder in PTIs. In the third and final part, I develop a computational method called "FLAME-slab", which is capable of efficiently solving the wave scattering problem for amorphous slab structures, where scattering elements are distributed within a slab with short-range order. Compared to standard finite element or finite difference methods, the FLAME-slab method allows for much coarser meshes, with as few as three grid layers spanning the thickness of the slab. Solutions are generated based on the Flexible Local Approximation Method (FLAME), using Rigorous Coupled Wave Analysis (RCWA) as a subroutine to generate local basis functions. ​Doctor of Philosophy (SPMS)

The development of ultrafast charging electrochemical energy storage (EES) devices with long cycle life is of great importance to the advancement of modern society with sustainable energy generation and consumption. Lithium-ion based EES devices offer high power, high energy and exceptional lifetime and are consistently pursued for such applications. In particular, TiO2 (B) material is promising anode candidate owing to its fast lithium diffusion kinetics and open channel structure. However, the high rate performance of TiO2 (B) is hindered by its poor electrical conductivity originated from large band gap (> 3.0 eV), therefore a large amount of conductive additives (> 15 wt%) are required to unleash the high power capabilities, which decreases the overall energy of the electrode since these additives are electro inactive within the operation window (1-3 V) of TiO2 (B). To address such issues, this thesis aims to improve the high rate performances of TiO2 (B) electrode while maximizing the total contents of active materials through integration of anatase phase. The ultimate scope is to develop fast charging TiO2 electrodes with maximum loading amount of active materials for high power and long life EES devices. To achieve such goal, the properties of TiO2 materials are investigated first in half cells with lithium metal as counter electrode. Applying the additive-free all TiO2 nanotube electrodes as platform, a systematic investigation of the electrodes conduction behavior via in situ electrochemical impedance study (EIS) indicates that much higher lithiation-induced conductivity is achieved in dual phase TiO2 nanotubes than pure phase TiO2 (B) at early stage of reaction, owing to the high conductivity of lithiated anatase. The resultant dual phase TiO2 nanotubes feature superior rate performances: a specific capacity of 112.1 mAh g-1 can be delivered at 24 A g-1 (~72 C), and higher capacity of 131.1 mAh g-1 can be achieved after 10,000 cycles at 30 C. Furthermore, even mechanical mixture of anatase particles to TiO2 (B) nanotubes exhibits much higher rate performances at 24 A g-1 (91.2 mAh g-1) than pure phase TiO2 (B) nanotubes (13.7 mAh g-1). Followed by the discovery of high lithiation-induced conductivity in dual phase TiO2 materials, a pre-lithiation process is carried out to improve the electrical conductivity and first cycle Columbic efficiency of the pristine TiO2 materials for applications in high power lithium-ion hybrid capacitor (LIC). The LIC cells with pre-lithiated TiO2 anode could achieve high energy density of 50.77 Wh kg-1 and high power density of 8.98 kW kg-1 at 20.7 Wh kg-1, compared to only 10.9 Wh kg-1 delivered by pristine TiO2 electrode at power density of 4550 W kg-1. Furthermore, the cycling stability of the pre-lithiated TiO2 materials is also improved with 73% capacity retention after 10,000 cycles. Finally, a water soluble sericin binder is developed for the first time to assist in formation of stable passivation layer in high voltage LiNi0.5Mn1.5O4 cathode to fabricate high energy and high power battery cells with TiO2 anode. The highest energy density of the full cell formulated with sericin binder can reach 687.6 Wh kg-1 (based on TiO2 mass). At higher power of 18.26 kW kg-1, the energy density can still reach 233.4 Wh kg-1, much higher than that of the PVDF binder (89.7 Wh kg-1). Furthermore, the full cell could be cycled at 10 C for 1,000 cycles with 80% capacity retention, further indicating the long-term stability of TiO2 and the sericin binder. In conclusion, this thesis unravels the importance of dual phase TiO2 electrode for ultrafast charging EES devices with ultralong cycle life. The lithiation-induced conductivity plays important roles in the utilization of TiO2-based electrode materials with fast charging capabilities. These findings provide guidance towards commercial adoption of TiO2-based electrode, in fact, large scale prismatic and cylindrical cells have already been fabricated for commercialization evaluation. Doctor of Philosophy (MSE)

Noble metal nanoparticles are fundamental to modern science and technology and have been utilized in many applications such as sensing, energy, biology, and medicine. Manipulation of the morphology and composition of noble metal nanoparticles enables the control over their optical/electrochemical properties and also to improve their performance in targeted applications. Among different classes of morphology-engineered nanoparticles, branched nanoparticles have attracted tremendous research attention recently due to their unique optical and electrochemical properties. The high charge density and charge polarization at tip extremities of branched nanoparticles generate a huge enhancement of the local electromagnetic (EM) field and a tunable localized surface plasmon resonance (LSPR) response over a wide spectral range. In addition, branched nanoparticles also exhibit pronounced electrocatalytic efficiency attributed to their large surface area, the exposure of certain high-index facets at tip edges/corners, and the synergetic effect arisen from the alloying character. However, the anisotropic growth of highly branched nanoparticles is not energetically favored in solution because of their large surface energy and the high crystalline symmetry of face centered cubic (fcc) metal nanocrystals. The growth of highly branched nanoparticles often required multi-steps, high pressure/temperature treatment, or the addition of capping agents which led to tedious and time-consuming purification steps. Besides, the synthesis of alloy nanoparticles composing of multi-metals is also challenging because of the mismatches in the reduction potential, solubility, and lattice of all metal precursors. Therefore, my aim is to develop new and facile routes for the synthesis of complex branched metallic particles and further explore their applications in plasmonics and electrocatalysis. Herein, I developed a one-step, aqueous-based, and surfactant-free method to synthesize highly branched gold mesoflowers (AuMFs) with multilevel long and sharp tips. The method enables me to control the size, morphology, and the optical properties of the AuMFs by manipulating the reaction condition. I also demonstrated that chlorite ions Clˉ played a critical role in the formation of long and sharp tips and the tip branching by regulating the formation of multiple twin defects in the crystal structure of growing particles. The branched AuMFs exhibit a LSPR peak maximum in the NIR to MIR region (~1800-3000 nm), depending on the tip morphology. The simulation analysis based on finite-difference time domain (FDTD) model was also conducted to elucidate the effect of tip morphology on the optical property of the AuMFs. The simulation was done in collaboration with researchers in prof. Li Shuzou’s group, MSE, NTU with the assistance on the simulation. Besides, the galvanic replacement reaction was often used in the seed mediated growth approaches to form hollow alloy metallic nanoparticles. I also established a new way to synthesize highly branched trimetallic hollow PdAgCu nanoparticles by coupling galvanic replacement with co-reduction reaction. The particles exhibited a high density of multiple tips on the surface, hollow interiors, and a tunable LSPR response in the NIR region. I also investigated the refractive index (RI) sensitivity and electrocatalytic activity of branched trimetallic PdAgCu nanoparticles towards ethanol oxidation reaction (EOR). The results showed that highly branched trimetallic PdAgCu nanoparticles exhibited a higher RI sensitivity and pronounced electrocatalytic improvement compared to that of branched bimetallic PdAg and PdCu nanoparticles. This work was done in collaboration with researchers in Prof. Jason’s group, MSE, NTU with the assistance on electrocatalytic measurement and discussion. Doctor of Philosophy (MSE)

The aim of this thesis is to study a new kind of energy storage solution known as “Hybrid Electrochemical capacitor” which allows for the integration of two existing technologies Lithium ion batteries and supercapacitors. The resulting device has the promising properties of both these devices, and can further be fine-tuned to meet the demands of autonomous industry vehicles and Plug-in Hybrid Electric Vehicles. The thesis achieves the above aim by the development and study of electrode materials that can meet the requirements of hybrid electrochemical capacitors. Initial studies are based on the narrowing down of appropriate intercalation materials which can be used as electrodes for a hybrid capacitor. This is achieved in three steps. A benchmark is set using a high Lithium ion conducting type electrode followed by fundamental understanding of the effect of electrode polarity on the energy density of hybrid capacitors. A working prototype cell is constructed using the above rule. Further improvements on the hybrid capacitor are planned by the use of high capacity Lithium rich layered materials. Apart from battery electrode, the thesis looks to develop activated carbon from a biodegradable source with low cost and low environmental impact. The biowaste material chosen in this thesis is human hair. Human hair was chosen because it is cheap to obtain and environmentally benign also the hair follicles are composed of loosely attached flakes which present a possibility of high surface area activated carbon. Dependence of the activation mechanism on the surface area and pore size distribution is studied. The final aim of this section is to develop a supercapacitor material with a high surface and optimum pore size distribution so that the energy stored in the capacitor electrode can be maximised. All the materials studied during the course of this thesis were carefully characterised to study structural morphological and electrochemical properties Doctor of Philosophy (MSE)

Hybrid materials in general could be classified into three categories : (i) mixed metal oxides (MMO), (ii) MMO with noble metal hybrid, and (iii) MMO with nanocarbon hybrid. Ln this research work, layered double hydroxides (LDH) mediated route is utilized to synthesize the three types of multifunctional hybrid materials . Studies will focus on understanding how the LDH mediated route lead to the intimately mixed morphology and strong interfacial interaction of the hybrid materials . The impact of these features on the functional property improvement is discussed thoroughly. This research begins with a systematic investigation on the properties of ZnGaFe ternary MMO prepared via LDH mediated route , and non-LDH route (solid state reaction method) is used as a comparison. Detailed analysis reveals that the MMO derived from LDH mediated approach not only has uniform and well mixed morphology, but also possesses strong metal to metal interactions. All of these characteristic properties are reflected in the study of photocatalytic reactions. To synthesis MMO-noble metal hybrid material , the noble metal ion ([AuCI4D intercalated ZnFe LDH is used as a solid state molecular precursor. Intimately mixed ZnFe MMO with uniformly decorated Au nanoparticles is obtained after low temperature calcination. In this work, the evolution of direct intercalated LDH structure is discussed in details. The intra-layer merging mechanism is proposed for the MMO growth during heat treatment. The morphology created is intimately mixed as compared with that of MMO obtained from inter-layer merging mechanism . The intimate interface could lead to favorable band alignment and excellent synergistic interactions for photocatalytic reactions . The LDH mediated route for synthesis of MMO-CNT hybrid material is also attempted . NiFe LDH nano-plates were firstly deposited on CNT through electrostatic force . With controlled calcination process , NiFe MMO and CNT hybrid material is obtained. The nano sized NiFe MMO obtained from the LDH precursor is intimately mixed, which ensures the strong interaction between Ni and Fe in MMO. More importantly, the hybrid is featured with a unique in-grown structure which is formed due to the carbon reduction reaction during calcination. Instead of coupling through organic ligand or electrostatic force, the in-grown structure results to strong chemical bonding between MMO and CNT, The strong coupling is very favorable for the charge transfer process, and hence significantly improved the electrochemical property. This thesis concludes the outcomes and findings from the three connected works. Some extended works that could benefit from the concept of LDH mediated synthesis route are proposed. Doctor of Philosophy (MSE)

The use of sunlight to drive organic reactions constitutes a green and sustainable strategy for organic synthesis. In such reactions, the photoredox requirements of organic reactions are typically fulfilled through using wide band gap semiconductors or redesigning the photocatalyst. Herein, we demonstrated the use of a reverse strategy; instead of redesigning the dye as per convention, the reactant is chemisorbed on the Brønsted base sites of Al2O3 to form a surface complex, causing an upshift in its HOMO to a level accessible for electron abstraction by the dye. This enables the highly selective oxidation of benzylic alcohols to aldehydes by a large variety of dyes, even though negligible reaction occurred in the absence of Al2O3 or with other metal oxides. The charge-transfer surface complex formed between the dye and Al2O3 is also essential in facilitating the transport of electrons from BnOH to O2. Next, we further extended the use of Al2O3 complexation in conjunction with photocatalysis to drive the selective aerobic oxidation of phenylboronic acids. It was discovered that all metal oxides with Brønsted basicity can also enable high yields of phenols. The proximity and strength of the Brønsted base sites appear to be crucial towards the reaction; there seems to be a positive relationship between the yields of alcohol and the quantity of strong Brønsted base sites, rather than with the quantity of weak or all Brønsted base sites. Lastly, we explored the idea of rendering Al2O3 photocatalytically active through carbon-modification, which would eliminate the need for a dye. The resultant carbon doped Al2O3 enables the selective oxidation of benzylic amines to form imines under visible light irradiation. We believe that our aforementioned discoveries may subvert our understanding of the role of Al2O3 in photocatalytic reactions. It may also bring forth a new methodology of utilizing surface complexation mechanisms between the reactants and earth-abundant materials to effectively achieve a wider range of photoredox reactions. Doctor of Philosophy (MSE)

TiN-based nanocomposite coatings were prepared using physical vapor deposition to deliver enhanced mechanical, tribological and thermal character that can be exploited for superhard cutting tool surfacing. These properties are controlled by tailoring processing methods to tune the microstructure and microchemistry. This thesis examined three coating systems, which are Ti-Al-N, Ti-Al-Y-N and Ti-Si-N, configured variously as multilayer superlattices and nanocomposites to comprehensively correlate hardness, wear resistance and oxidation resistance with deposition parameters. Combining X-ray diffraction and transmission electron microscopy with physical-mechanical testing, over a wide range of coating configurations, permitted construction of a predictive process-performance matrix to guide the fabrication of hardened surfaces. In multilayer TiN/TixAl1-xN coatings prepared by cathodic arc deposition, the mechanical properties were controlled by the layer period that was adjusted by varying substrate rotation speed. A hardness of 38.9 ± 3.6 GPa was achieved for a superlattice period of 13 nm, where the coatings contain columnar textured rock salt – type crystals connected by low-angle grain boundaries. When yttrium was introduced to the multilayers, by adding a Y - metal target powered by DC magnetron sputtering, the morphology changed from columnar to acicular grains with smaller grain size. Specifically, by fixing the period at 5.5 nm and incorporating Y from 0 to 2.4 at% the grain size decreased (100-200 nm to 20-30 nm) and hardness increased (28.7 ± 7.3 GPa to 40.8 ± 2.8 GPa). The improved performance was a consequence of solid solution hardening that arises from the misfit strain field introduced by Y (element radii 2.12 Å) substitution for Ti (1.76 Å) or Al (1.18 Å), and a nanosize effect, where finer grains result in a greater volume fraction of grain boundaries that block dislocation movement. Higher Y additions also retard oxidation as high temperature (800 ºC) annealing generates Ti2O3, rather than TiO2 as in Y-free coatings, and also affects Al oxidation. Adhesion and wear resistance were not compromised by higher Y contents demonstrating that TiN/TixAl1-xN coatings can enhance mechanical properties and thermal stability. Notably, this work employed a pure Y target, instead of an Ti-Al-Y alloy target, and substrate holder rotation speed was the critical parameter, where faster substrate rotation lead to smaller periods and more uniform Y distribution. However, an Y-rich layer became progressively thicker at slower rotation with the period increasing from 5.5 nm to 24 nm. These Y-rich regions seeded crystal nucleation that reduced coherency at layer interfaces and grain boundaries to significantly degrade mechanical properties (40.8 ± 2.8 GPa to 29.7 ± 4.9 GPa). Therefore, the period and Y content work in tandem in multilayered TiN/TixAl1-xN coatings and the optimized Y content was to be 2.4 at% at a period of 5.5 nm. Nanocrystallite TiN / amorphous (a)-Si3N4 nanocomposites were fabricated by high power impulse magnetron sputtering. The introduction of silicon by controlling the Si target current can be used to modify the coating structure, tailor mechanical properties, improve wear resistance and passivate oxidation. Smaller crystal sizes promoted at higher Si content lead to TiN / amorphous (a)-Si3N4 nanocomposites, with ~10 at% Si/(Si+Ti) yielding maximum hardness (41.31 ± 2.93 GPa). Compared to TiN, Ti0.903Si0.097N showed enhanced resistance to oxidation and wear resistance, however, the TiN crystallites were not completely encapsulated by a-Si3N4 intergranular films and further optimization of the structure and property relationship can be realised. Doctor of Philosophy (IGS)

In order to detect small analytes with high specificity and efficiency that cannot otherwise be achieved by antibody–based immunoassays, the development of a new Photochrome Aptamer Switch Assay (PHASA) was explored. In this assay, aptamer which can be synthesized chemically and can bind small molecules specifically is utilized as the molecular recognition element. Stilbene compounds having a unique reporting power via an instant conformational change upon irradiation, and whose decay rate change depends on medium viscosity are used as the photochrome probe. Two scopes–competitive binding and adaptive binding were proposed and were applied on malachite green (MG)-MG aptamer model system. The competitive binding scope involves the competition for the aptamer binding pocket between MG analyte and stilbene-MG conjugate. The conjugate needs to possess both strong binding affinity and fluorescence decay. Four stilbene-MG conjugates: “fused” stilbene-MG, MG-CH2-NH-Stilb-OMe, MG-CH2-NAc-Stilb-OMe and MG-COO-Stilb-NO2 were synthesized. Their binding experiments with MG aptamer and decay kinetics measurements in MG aptamer binding buffer based aqueous mixtures were conducted. Results of the measured dissociation constant demonstrate that Kd(MG) (200 nM) < Kd(“fused” stilbene MG) (500 nM) < Kd(– CH2-NAc –) (1.7 µM) < Kd(– CH2-NH –) (2.4 µM) < Kd(– COO –) (6.6 µM). That is, “fused” stilbene-MG conjugate has the strongest binding affinity, and there is literally no binding of MG-COO-Stilb-NO2 to MG aptamer among the studied stilbene-MG conjugates. For the decay kinetics, the decay of both “fused” stilbene-MG and MG-COO-Stilb-NO2 conjugates are quenched while the decay of MG-CH2-NH-Stilb-OMe and MG-CH2-NAc-Stilb-OMe are preserved. Combining the binding affinity and decay kinetics, the MG-CH2-NAc-Stilb-OMe conjugate is the most promising candidate for PHASA competitive binding scope. The adaptive binding scope requires the conjugation between stilbene compounds and MG aptamer, and thiol-maleimide click chemistry was chosen as the cross-linker. The dissociation constant Kd value of four SH-modified MG aptamers are measured in the range of 700~900 nM, preserving their binding ability towards MG analyte. Thiol conjugation of stilbene maleimides proves to restore their quenched fluorescence decay in DMSO (v% ≤ 10%) and MG aptamer binding buffer solution mixtures, allowing subsequent detection based on decay rate change in stilbene-MG complex without further separation. Three stilbene maleamic acid compounds were also synthesized for better water solubility, their decay rates’ dependences on medium viscosity are confirmed and decay kinetics in DMSO and buffer solution mixtures are preserved instead of being quenched. Besides medium viscosity probing, further applications of studied stilbene compounds were also explored. The fluorescence decay rate of dimethylamino-stilbene-maleamic acid (DMASMA) is linearly quenched by EtOH in the concentration range of 0.004~0.1 mol L-1 where no effect from methanol and isopropanol (IPA) is observed. The photophysical properties of all three stilbene maleimic acids are sensitive to the solution pH. That is, the studied stilbene compounds can have promising applications in pH or EtOH sensing apart from medium viscosity probing. Doctor of Philosophy (MSE)

Noxious pollutants such as endocrine disrupting compounds (EDCs) are associated with rapid industrial and urban development. They are difficult to remove using conventional wastewater treatments and thus pose new challenges in environmental remediation. These concerns necessitate more effective and efficient approaches for emerging pollutant removal from wastewater treatment units. (Aim) This study evaluated various strategies for the removal of one of these emerging endocrine disruptor compounds, bisphenol A (BPA). (Scope) In particular, to improve the removal of BPA from aqueous environments, we investigated processes of physical separation of BPA from an aqueous solution through adsorption and then investigated the subsequent integration of adsorption with biological degradation. Among the emerging adsorbent materials, biosorbents predominate due to their low cost and abundance. However, these products have low adsorption capacity. Therefore, to improve these abilities, amphiphilic surfactant treated biosorbent was developed and studied, and the factors affecting its ability to remove BPA were assessed. In the first study, we evaluated pre-treatment of bamboo powder waste, a kind of biosorbents, to remove BPA. Despite the marked increase in removal capacity after treatment with cationic surfactant, its kinetics and adsorption capacity are still considered inferior in comparison to other emerging adsorbent materials. A comparison study was conducted among treated bamboo powder, commercial graphene nanoplatelets, and single- and multi-walled carbon nanotubes (MWCNTs) for the removal of BPA. Our study deduced that carbon nanomaterial (CNM) variants in general possess faster adsorption capacities and kinetics for BPA removal. Indeed, CNM variants have gained tremendous interest as adsorbents due to their high adsorption capacity and improved re-usability through multiple regeneration cycles. However, there are concerns regarding their environmental toxicity, which brings into question about their application as environmentally safe and sustainable adsorbent materials. To overcome this, the second part of our study focused on the development of composite sorbents such as entrapped MWCNTs and TiO2 inside alginate beads to reduce environmental toxicity and to facilitate the recovery of the used sorbent. Because wastewater treatment plants are operated in continuous mode with limited contact time to reach equilibrium, it was necessary to assess the capability of a sorbent during continuous flow mode to assess its practical application. BPA removal from the composite beads in the column reactors was affected by the feed flow rate, bed depth and initial inlet concentrations. The BPA sorption performance was predicted with good correlation using a dose-response model. We showed that photolytic degradation of BPA desorbed from the beads, and thus the regeneration of the spent adsorbent beads can be achieved simultaneously. Results showed that the alginate beads alone, however, were easily abraded and susceptible to destruction by phosphate, rendering their use in their pure form unsuitable for the containment of MWCNTs in water treatment. Therefore, in the next part of our study, we designed a macro-bead platform comprised of a calcium-alginate core and a polysulfone (Psf) layer as an immobilization matrix for MWCNTs. We hypothesized that the additional Psf layer would improve BPA removal and reduce the percentage of MWCNTs that leaked from the beads. We tested these fabricated beads for adsorption of BPA in a batch reactor and tested their re-usability in a column reactor. The physical and chemical properties of the fabricated beads were characterized using electron microscopy, zeta potential, BET surface area, FTIR and Instron microtester. Bioluminescence assay was used as a means to detect the leakage of MWCNTs from the beads. Several accepted kinetic and isotherm models were utilized to characterize the adsorption behavior of the hybrid beads. Our observations show that BPA removal increased with the content of MWCNTs. Also, the addition of the Psf layer improved the amount of adsorbed BPA at lower MWCNT amounts but was less significant with higher counts of MWCNTs. Moreover, the hybrid beads were relatively stable over a wide range of pHs. The BPA adsorption profile of the hybrid beads correlates well with the pseudo-second order kinetic model and the Langmuir isotherm monolayer adsorption model. Addition of a Psf layer on composite beads that contained MWCNTs improved the compressive load capacity of the composite beads up to twelvefold at 40% compression. The improved compressive load capacity in beads layered in Psf could be applicable to both shield and improve the stability of the composite calcium alginate-MWCNT beads in reactors, where the bead sorbents may be subjected to abrasion that could affect bead integrity. Building from our previous studies, in the last part of our work, we attempted to integrate the biodegrading component into the hybrid bead. We used a novel BPA tolerant bacteria strain PBPA2 that was isolated from the environment and embedded it within the calcium-alginate/MWCNT/Psf beads with the purpose of integrating the adsorption performance of MWCNTs and the biodegradation capability of the PBPA2 strain. The effects of enrichment and mineral media composition, bead diameter and cell loading were studied in a batch reactor. It was observed that the addition of 0.05% yeast extract into the mineral medium and the reduction of the bead’s diameter enhanced the removal of BPA. Subsequent experiments in continuous-flow column reactors resulted in enhanced BPA removal, reinforcing the potential of integrating biodegrading bacteria with CNTs. In summary, this work reveals the development of a novel composite sorbent platform for the removal of BPA and elucidates upon its sorption mechanisms and efficiencies. Doctor of Philosophy (MSE)

Reliability of smart cards depends extensively on the corrosion resistance of the electrical contacts they contain as these contacts are primarily exposed to the environment. Although corrosion as an entirety is a century old problem, the corrosion of thin electrical contacts has been rarely studied in a systematic manner. Cu is typically used as substrate material for electrical contacts and nickel based barrier layer coating have been essential to suppress copper diffusion through the gold topcoat. This thesis aims to bridge knowledge gaps in literature with regards to the corrosion behaviour of Ni and Ni-P barrier coated electrical contacts. Much work has been dedicated to the corrosion resistance of electroless Ni-P deposits but research on electrolytic deposits is limited. The impact of electrodepositing parameters on corrosion resistance has not been well documented. This thesis aids the understanding of the electrodepositing parameters and their implications on corrosion resistance. Moreover, corrosion behaviour due to different arrangement of thin Ni and Ni-P stacks (< 3 μm) is unknown. This thesis also explores different thin Ni and Ni-P stacks and its corrosion resistance to salt spray (SS) and mixed flowing gas (MFG) environments. The corrosion behaviour of these stacks, corrosion mechanism and causes of corrosion disparity have been also discussed in this report. The thesis is bounded by three main considerations viz., method and type of deposition, and corrosion testing methods. Electrodeposition was the choice of deposition technique, Ni and Ni-P electrodeposits were chosen barrier layers and lastly, accelerated tests which simulate atmospheric corrosion were employed. The research starts with a systematic study on the electrodepositing parameters and their influence on the corrosion resistance of electrical contacts. Corrosion products due to the neutral salt spray (NSS) and mixed flowing gas (MFG) tests were characterised through spectroscopic and diffractions studies. Electrical contacts exposed to NSS tests produced green corrosion residues which consist of CuCl (nantokite) and CuCl2(OH)3 (clinoatacamite) and brown residues which consist of Cu2O (cuprite). Electrical contacts exposed to MFG test produces copper sulfides (major) and nickel sulfides (minor). Also increasing the thickness of Ni consistently improved the corrosion resistance in both neutral NSS and MFG corrosion tests. However, the influence of Ni thickness on corrosion was overshadowed by the Ni-P thickness. Increasing the thickness of Ni-P deposits resulted in higher corrosion in the NSS environment and decreased corrosion under the MFG environment. Although initial results pointed towards a disparity that Ni-P may not be suitable for corrosion protection in environments with heavy chlorine concentration but appropriate for sulfur-containing corrosion media, subsequent in-depth studies revealed that this disparity was due to the high edge porosity caused by fast plating. Subsequently, the arrangement of Ni and Ni-P on Cu was hypothesised to affect the eventual corrosion resistance of an electrical contact. The thickness of the overall barrier layer was kept constant and different stacks such as Ni/Au (NA), Ni-P/Ni/Au (PNA), Ni-P/Au (PA), Ni/Ni-P/Au (NPA) and Ni-P/Ni/Ni-P/Au (PNPA) stacks were examined. The discrete and coalesced pits formed due to MFG were explained with a proposed dominant pit concept. Results showed that multi-layer stacks, such as PNA, NPA, PNPA, displayed worse corrosion resistance than single-layered stacks (NA, PA). Removing Ni and Ni-P interfaces was effective in inhibiting corrosion in NSS and MFG environments as Ni/Ni-P interfaces accelerate corrosion due to galvanic coupling. Corrosion pits propagated horizontally and vertically through Ni and Ni-P films, depending on the way Ni and Ni-P were arranged within a stack. Tunnelling corrosion through Ni-P turned distinct with a reduction in Ni-P thickness. This was attributed to possibly higher percentages of discontinuities (i.e. porosity) with decreasing thickness. The reducing thickness coupled with the galvanic coupling between Ni and Ni-P layers further worsened the corrosion in stacks such as Ni-P/Ni/Ni-P/Au. Based on the two aforementioned studies, disparity in corrosion resistance of Ni and Ni-P barrier layers under NSS and MFG corrosion tests was a recurring observation. When corrosion resistance of Ni/Au and Ni-P/Au stacks was assessed using NSS and MFG corrosion tests, each stack emerged superior in only one test. To explain this disparity, factors that could influence corrosion resistance were examined first, namely: internal stress, surface wettability and sulfur co-deposition. None of these factors could explain for the disparity in corrosion performance. Corrosion product analysis was then performed to understand the corrosion product formation due to NSS and MFG. Detailed pits analysis revealed that the disparity was caused by the porosity and corrosion product migration. These concepts were supported experimentally. Based on the understandings generated from the three main studies, some guidelines are proposed to improve the corrosion resistance of electronic contacts under the MFG and NSS corrosion tests. Optimisation of various parameters to generate the current stacking arrangement (i.e. Ni/Ni-P/Au) offer important but limited solution to enhance corrosion protection as individuals layers behave differently when coupled. Different stacking arrangements studied in this thesis show that single-layered stacks such as Ni/Au or Ni-P/Au offer better corrosion protection. The failure of bi-layered and tri-layered stacks does not necessarily stem from the design of such stacks but stem from the industrial practice to layer very thin coatings (such as Ni-P at 500 nm) on Ni under-plates. The increased defects in such thin Ni-P coatings accelerate galvanic corrosion due to difference in corrosion potentials and the small-anode-large-cathode phenomenon. The study on single layered stacks points to the most important aspect of this thesis. Ni-P as a single barrier layer deposited at lower current densities (≤ 1 ASD) and at higher thicknesses (≥ 2 µm) can improve overall good corrosion protection in both NSS and MFG corrosion tests. Doctor of Philosophy (MSE)

As the demand for energy increases day by day, the future relies more on clean renewable energy resources. Wind turbines have a promising active contribution to meet this future demand. Wind industries are more interested to have bigger turbines to produce more power economically from a single turbine unit. Glass and carbon fiber composite materials are largely used in the light weight turbine blade manufacturing due to their high strength to weight ratio. The spar-cap is considered as the back bone of a wind turbine blade and it consists of significant amount of unidirectional laminates. Manufacturing defects are unavoidable due to their nature and involvement in the structure. Some of these defects may affect the life expectancy of the blade as well as the whole turbine unit. Focus of the present study is related to a common manufacturing defect found in spar cap regions, ‘fiber waviness’, and its influence towards the failure initiation and propagation under compression and bending loads. Despite its wide spread occurrence, in-plane fiber waviness defect found throughout the thickness of composite laminates is not well studied. Therefore, a coupon level in-plane fiber waviness defect was induced in unidirectional composite samples and tested under numerous loading conditions. Variations in both mechanical strength and failure modes of waviness induced samples were characterized. In addition, double cantilever beam experiments were conducted to study the effect of fiber waviness on the fracture energy and crack propagation. Further, an analytical model has been prepared by adding sinusoidal waviness into the laminate to estimate the reduction in modulus based on the constitutive relations. Also, finite element analysis was used to predict the compressive strength and failure modes under the static compression loads based on a physical based failure theory (LaRC02) using ABAQUS 6.13TM software. Finally, a 6-m wind turbine blade shell model was designed using NuMAD software. Fiber waviness was introduced at various locations of the spar-cap region and a static flap-wise bending analysis was performed at designed maximum bending moment of the blade. The longitudinal strain deformation during flap-wise bending analysis at the fiber waviness region of those blade models was validated with the help of four-point bending test of a composite I - beam consisting of waviness defect. Doctor of Philosophy (IGS)

The thesis demonstrates for the first time coexistence of write once read many memory (WORM) with resistive random access memory (RRAM). This is the first time such coexistence phenomena are reported in organic materials system. Furthermore, better understanding of working mechanism in resistive switching phenomena in organic materials particularly conjugated polymer has been achieved. Two materials systems are chosen, namely, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT PSS) and Polyvinyl alcohol (PVA) where PEDOT PSS is a conducting polymer and PVA is an insulator polymer. For a device with 5 μm thick PEDOT PSS sandwiched between two Au electrodes, the coexistence of WORM memory and RRAM memory can be achieved (Chapter 4). The WORM result was attributed to dedoping of the conducting PEDOT + PSS- segments to insulating PEDOT 0 segments. The RRAM was explained due to Proton H+ conductive properties of PSS acid domains inside the film after dedoping. This points to a general feature: resistive switching behavior of a whole device is the result of additive/summative resistive switching characteristic of its components. Based on this, we reveal the coexistence of RRAM memory and WORM memory demonstrated in PEDOT PSS blend with PVA (Chapter 5). The WORM memory is again attributed to PEDOT PSS while RRAM memory is attributed to the charge trapping characteristic of PVA. The device performance is improved significantly as compared to the earlier PEFOT PSS system, with more than 1000 cycling stability and much more than 10^4 s retention for RRAM mode. Additional I-V characteristic of this device is further studied in chapter 6 which reveals a new type of WORM memory. This type of WORM memory is driven by metallic migration of Au electrodes. Doctor of Philosophy (MSE)

In recent years the bio-detection and bio-imaging are hot research areas, more and more probes have been reported to monitor intracellular and intercellular substances, which are highly sensitive, high-resolution and low-cost. Though they have many advantages, these probes have some main limitations such as short lifetime, small penetration depth, damage to the samples and autofluorescence.Therefore new probes should be developed to overcome these shortcomings.On the other hand, upconversion nanoparticles (UCNPs) have got considerable interest and have many potential applications in this field. Compared with conventional fluorescent probes, UCNPs have many advantages: chemical stability, non-autofluorescence from bio-samples, large light penetration depth, long lifetime (millisecond scale) and less damage to samples. To better understand the development of UCNPs, this thesis introduces basic principles and applications of the UCNPs,followed by some experimental methodologies such as synthetic methods, purification methods, basic characterization techniques, spectroscopy and electrochemical techniques and bio-applications. This thesis focused on developing new UCNP-based probes,using Luminescence Resonance Energy Transfer(LRET) processfor bio-detection and bio-imaging, and this thesis contains two parts. In the first part, a Hg2+ UCNP-based probe is elaborated. Hg2+ is an extremely toxic ion, which will accumulate in human bodies and cause severe nervous system damage. Therefore, the sensitive and efficient monitoring of Hg2+ is of great importance. In this part, a thiazole-derivative-functionalized NaYF4 probe is demonstrated, and upconversion emission intensity ratio of 540 nm to 803 nm (I540/I803) is employed as a ratiometric signal to detect Hg2+ in living cells and showed excellent photostability and high selectivity, with detection limit to be 0.21 μM. The structure of nano-probe was characterized by transmission electron microscopy (TEM), Powder X-ray diffraction (Powder XRD) and the low cytotoxicity was confirmed by an MTT assay. The UCL (upconversion luminescence) test in Hela cells was carried out by confocal microscopy. The results demonstrated that organic-dye-functionalized UCNPs should be a good strategy to detect toxic metal ions when studying cellular bio-systems. In the second part, an improved Cu2+-NaYF4-based probe is demonstrated. Cu2+ plays a key role in metabolism. Its disequilibrium in human body will cause several severe diseases. Therefore, sensitively and efficiently monitoring Cu2+ in both environment and human body is of great importance. In addition, developing an inorganic-organic hybrid probe with multi-channel responses to more accurately detect ions in living systems is very challenging but highly desirable. In this part, for the first time, electrically-active ferrocene group was attached onto the framework of optically-active Rhodamine to form a new dye (RB-FC), which could be further loaded onto the surface of silica-coated UCNPs to construct a novel nano probe (RB-FC-UCNPs) to detect Cu2+ through both electrochemical method and optical ways. Upon the interaction with Cu2+, this as-prepared nano-probe showed obvious changes in absorption, emission and electrochemical parameters. The detection employed absorption intensity at 558 nm (A558), emission intensity ratio of 540 nm to 654 nm (I540/I654) as spectral signals, and oxidation peak of cyclic voltammetry curve as electrochemical signal, demonstrating high stability and low detection limit of this novel probe. In addition, bio-imaging test revealed that this probe could be applied in detecting and visualizing Cu2+ in A549 cells with low cytotoxicity. Doctor of Philosophy (MSE)

Transparent glasses are hotly pursued as premium construction materials in transport vehicles and architectural buildings for its aesthetic appeal. Due to widespread usage of transparent glasses, 43% of global world primary energy are spent on heating, ventilation and air-conditioning in buildings. Moreover, individual can also experience uncomfortable situations, such as glaring sunlight, skin and thermal discomfort. Current practice of using multi-layered optical solar films for solar shielding requires costly fabrication process and further results in low visibility and disruption of communication signals. Although solar modulation system driven by external stimuli have been demonstrated, these systems usually involve costly installation, complex device fabrication process and rely on external mechanical or electrical stimuli. Hence, an autonomous system driven by solar heating itself to exhibit broadband solar modulation would be ideal. The closest class of material that could perform in such manner is the thermally responsive hydrogel, a material containing around 90% of water. Unfortunately, their chances of commercialization are largely detracted by their inherent shrinking and aqueous characteristics. In this thesis, a new class of phase transition material that can respond to temperature change was developed. With the increase in temperature, different degree of reversible solar modulation can be achieved and tailored accordingly to a wide range of operating temperatures. The components in this new material consists of ionic liquids which are intrinsically stable and polyurethane elastomer which is not only cost effective, but further endow the material with mechanical robustness. The distinct advantages of broad transition range tunability, cyclic stability and functional versatility in the material system is unattainable by any existing solar modulation solution. This is the first time where ionic liquids were explored as material for thermotropic smart window and the resulting new material super cyclic stability with critical non-volatile and non-freezing properties can be attributed to the superior intrinsic characteristics of ionic liquids. This new material also allows facile and unparalleled tuning range of transition temperature (tuning via multiple parameters). The mechanism of the underlying thermally responsive interactions in this new class of material was extensively elucidated and applied in smart window application for the very first time. In a parallel study, plasmonic particles which exclusively absorb in near infrared region was coupled with thermally responsive hydrogel. Experimental results show that both the response speed and solar modulation of the thermotropic composite could be enhanced. Photothermal characteristics endowed by the plasmonic particle not only enhance the thermal insulation features for tropical climates but further enable optical switching in cold weather climates. The mechanism of plasmonic heating coupled with thermally responsive polymer for smart window was reported for the very first time. Combination of the above novel technologies offers a unique competitive advantage and result in a new class of thermally responsive organic/inorganic hybrid which can be affixed as an interlayer laminate for a fully autonomous smart window to achieve energy conservation. Apart from their application in transport vehicles and architectural buildings, this new material may also find itself in other numerous optical applications, such as over-heating protector for solar panels and other smart devices with memory or sensing functions. It is believed that the novel outcomes from this research thesis will fit neatly into the technological gap concerning green and smart buildings. It will also be propelled by the rapid development and pressing demand of innovative solutions in a highly competitive automotive industry. Doctor of Philosophy (MSE)

Lithium ion battery (LIB) is currently one of the most widely used forms of rechargeable energy storage system in portable electronics. To achieve LIB with enhanced lithium storage properties, better safety aspects and lower cost, extensive research has been conducted on the various components of a LIB for the past few decades. Although graphite is currently used as the anode material in most commercial LIB, its limited capacity and the safety issues related to its low electrochemical potential (vs. Li/Li+) have prompted scientists to search for alternative materials. Amongst the various conversion-typed materials, metal sulfides are particularly interesting as sulfur (S) has a rich and versatile chemistry, thus providing the possibility of altering the lithium storage properties of the materials by simply varying the stoichiometric ratio between the metal and sulfide ion in the compound. However, as with all sulfur and sulfide electrodes, polysulfides will be formed during their partial reduction, resulting in poor capacity retention and cycling performance in lithium and lithium ion batteries. In view of this, more study needs to be carried out to find approaches that can be undertaken to improve the lithium storage performance of metal sulfide electrodes. Hence, this thesis aims to gain an insight into how the amount of sulfide ion in the stoichiometry of a metal sulfide compound affects its lithium storage properties, with the focus placed on two metal sulfide systems, namely, iron sulfides (intercalation-conversion material) and tin sulfides (conversion-alloying material). To investigate the effect of how the amount of sulfide ion in the stoichiometry of an iron sulfide compound affects its lithium storage properties, pyrrhotite Fe1-xS and pyrite FeS2 with good purity have been successfully synthesized via a solution-based chemical synthesis method and their electrochemical properties were characterized. It was found that pyrite FeS2 exhibits better lithium storage capability than pyrrhotite Fe1-xS because of: (1) the lower polarization, better electron and Li+ ion transport at the interface between the active material and electrolyte at the pyrite FeS2 electrode and (2) the reversible lithiation and delithiation of iron sulfide (FeSy) during the galvanostatic cycling of the pyrite FeS2 electrode. SnS and SnS2 with good purity have also been successfully prepared via a solution-based chemical synthesis method to investigate the effect of how the amount of sulfide ion in the stoichiometry of a tin sulfide compound affects its lithium storage properties and the electrochemical properties of these compounds were characterized. It was found that SnS2 displayed a higher capacity and better cycling stability than SnS after prolonged cycling particularly at higher current densities. Since the SnS2 electrode was found to have a poorer electronic and ionic conductivity than the SnS electrode, its superior lithium storage performance is attributed to its chemical and structural properties. As evidenced by the higher discharge capacity attained from the intercalation and conversion reaction throughout the 100 cycles, more Li2S is formed during the lithiation of SnS2, thus providing a thicker layer to buffer the large volume change during the lithiation and delithiation of Sn. This can result in a reduction in the pulverization and better capacity retention of the electrode after prolonged cycling, as verified by the slower alloying capacity fading rate observed in the SnS2 electrode compared to the SnS electrode. It is found in this dissertation that for both iron and tin sulfides, the compound with a higher sulfide ion content in its stoichiometry i.e. FeS2 and SnS2 exhibits better lithium storage performance than its counterpart with lower sulfide ion content i.e. Fe1-xS and SnS when cycled in a voltage window of 0.001 – 3 V. For the pyrite FeS2 electrode, which undergoes intercalation and conversion reaction during cycling, the superior lithium storage performance is attributed to its better conductivity and reversibility of the lithiation and delithiation of FeSy. On the other hand, the SnS2 electrode, which undergoes conversion and alloying reaction during cycling, displayed a better lithium storage performance due to its ability to form a thicker Li2S layer which provides better buffering for the large volume change in the Sn particles during their alloying reaction, thus maintaining structural integrity of the electrode and result in slower capacity fading. Doctor of Philosophy (MSE)

Water splitting utilizing solar energy is an attractive way to produce clean and sustainable energy. Among various approaches, photoelectrochemical cell (PEC) has proven to be a promising route to achieve highly efficient artificial photosynthesis. In general, there are three types ofPEC: single absorber PEC, dualabsorber PEC and Photovoltaic (PV)-assisted PEC. Between these three types, dual-absorber PEC has the most advantages as it has higher photon absorption efficiency compared to single absorber PEC. Meanwhile, it also has simpler configuration and lower manufacture cost compared with PV -assisted PEC. The performance of a PEC depends on the photocatalytic performance of its photoelectrodes. Hence, fabricating photoelectrodes with high photocatalytic efficiencies is the most important objective. In this work, high performance W03 photoanode was achieved through optimizing the nanostructure. A triple layered W03 was prepared using a one-step controllable anodizing method. The anodization was carried out in a heated acidic solution containing NH4F as the surfactant for morphology control. Results show that with this unique triple layer structure, light generated charge carriers can be efficiently separated and migrated to the electrode surface for the chemical reactions. This triple layered W03 is able to generate photocurrent as high as 0.9 mA.cm-2 at 1.2 V vs RHE. By the time we reported this work, this was the highest photocurrent achieved by pure W03 photo anode without any cocatalyst deposition. Moreover, it has been greatly reported that the stability of W03 is a main limiting factor in its photoelectrochemical application, even in neutral electrolyte. Thus, an ultrathin (10 nm) Ti02 protective overlayer was added on top of triple layered W03 enhanced the stability of the triple-layer W03 photoanodes considerably. Meanwhile, efficient CU20 photocathodes have been prepared through depositing a thin layer of NiFe layered double hydroxide (LDH) co-catalyst on top of CU20. Both materials were prepared using simple electrodeposition methods without any post treatment. Through modifying CU20 with NiFe-LDH co-catalyst,the photocurrent of CU20 photocathode has been greatly improved, especially in the low bias range. It is observed that under as low as -0.2 V vs Ag/ AgCl applied voltage, photocurrent increases almost seven times with the assist of NiFe-LDH cocatalyst. The origin of such a pronounced effect is the improved electron transportation towards the electrolyte as the NiFe-LDH overlayer induces an appropriate energy level alignment. LDH are known to be used as oxygen evolution cocatalyst, and it was the first time for NiFe-LDH to be reported as a photocathode cocatalyst. Moreover, It is well known that the electrochemical instability of CU20 poses a serious challenge to its PEC application. The stability of CU20 has shown great improvement after coating with NiFe-LDH. Results show that there is almost zero photocurrent loss after 40 hours continuous illumination at -0.2 V vs Ag/ AgCI condition. To explore other semiconductor oxide systems, BiV04 was also prepared as an alternative photoanode in the current work. Results indicate that an ultra-thin layer of NiCo-LDH improves the photocurrent by three-folds. Finally, by combining the synthesized photoelectrodes (i.e. W03-based photoanode, CU20-based photocathode and BiV04-based photoanode) with commercially available semiconductors (i.e. p-type Si, and p-type GaP) and another commonly used photoanode (a-Fe203), the mechanisms behind the voltage generation of a dual-absorber PEC was investigated. It is clear that the important factors for the overall voltage generation are the photoanode and photocathode photocurrent, especially under low bias conditions. In conclusion, modification of the nanostructure and deposition of a cocatalyst are two efficient approaches in improving the photo electrode activities. In general, the nanostructure increases the light harvesting efficiency and reduces the charge recombination rate; the co-catalyst improves the reaction kinetics and increases the charge transportation and inject rate towards the electrolyte. Meanwhile, in order to achieve high efficiency dual-absorber PEC, the voltage generated within the integrated dual-absorber PEC upon illumination is very important. This can be improved by increasing the efficiencies of the photoelectrodes especially their charge separation and injection rate. Doctor of Philosophy (MSE)

The increasing demand of clean and sustainable energy drives the development of energy storage devices. Rechargeable batteries, including lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), have been considered as one of the most promising energy storage systems. However, it is still desirable to develop LIBs and SIBs with high energy storage, fast rate capability and long stability to meet their potential applications in portable electronic devices, electric vehicles (EVs) and hybrid electric vehicles (HEVs). Phosphorene, mono- or few-layer black phosphorus (BP), has attracted much attention as a promising anode for rechargeable batteries, due to its high theoretical specific capacity (2596 mAh g-1) and ultrafast Li/Na ions diffusion along the zigzag direction. However, it faces major challenges of low-yield preparation of phosphorene and the poor air-stability. In addition, phosphorene exhibits low initial reversible capacities and fast capacity fading when tested as anodes for LIBs and SIBs, due to the sluggish reaction kinetics and large volume change (-300%). Therefore, large-scale preparation methods, effective passivation approaches and advanced strategies towards improved electrochemical performance are necessary before the direct application of phosphorene into these areas. In our studies, we aim to address the problems aforementioned. Firstly, we identify formamide as an appropriate solvent to produce high-yield phosphorene with good crystallinity and tunable size distributions via liquid-phase sonication of bulk BP, which largely outperforms the commonly used ones (e.g., NMP, DMF, IPA) in previous reports. In addition, phosphorene obtained in formamide can be stable for further processing and applications. Furthermore, a densely-packed graphene-phosphorene composite (PG-SPS) is designed and prepared via a facile spark plasma sintering (SPS) method, during which densification and reduction process take place simultaneously. As a result, the PG-SPS sample exhibits much improved air-stability due to effectively suppressing the permeation of water or oxygen molecules into the sample. Importantly, the densely packed PG-SPS sample shows improved volumetric capacities due to its high packing density (0.6 g cm-3) without scarifying its electrochemical performance. In addition, to enhance the charge transfer kinetics and surface wettability with electrolyte, nanoscale surface engineering of exfoliated few-layer BP is performed by homogeneous deposition of horizontally aligned PEDOT nanofibers on surface-modified BP nanosheets. The as-obtained BP/PEDOT composites exhibit much improved wettability towards the electrolyte compared to that of the pure BP nanosheets. Accordingly, the purposely engineered E-BP/PEDOT architecture exhibits significantly enhanced reversible specific capacities compared to that of the pure few-layer BP electrode. Importantly, due to the high mass percentage of the BP in the sample, the Na storage properties of E-BP/PEDOT outperform that of the E-BP/graphene composites based on the overall mass of whole electrodes. Furthermore, a OD-2D heterostructure of Ni2P nanocrystals (NCs)-BP nanosheets (denoted as NhP@BP) was also constructed via a facile strategy. In such a heterostructure, the 2D morphology of BP nanosheets is well maintained and Ni2P NCs display an average diameter of ~ 5nm. As a demonstration of its viability, the Ni2P@BP shows much improved Li storage properties versus the bare BP when evaluated as electrode materials for LIBs. Doctor of Philosophy (IGS)

The emergence of soft energy devices provides new possibilities for various applications, it also creates significant challenges in the selection of structural design and material compatibility. Herein, we demonstrate a stretchable transmissive electrochromic energy storage device by inkjet-printing single layer of WO3 nanoparticles on an elastomeric transparent conductor. Such hybrid electrode is highly conductive and deformable, making it an excellent candidate for the application: large optical modulation of 40%, fast switching speed (

Honeycomb-like lignin-derived carbon (LC) foams doped with reduced graphene oxide (RGO) are fabricated via unidirectional ice-templating followed by freeze-drying and carbonization. The dimensions, constituent contents, and density of the foams could be easily adjusted. By manipulating the density, high electrical conductivity and good mechanical properties could be achieved at relatively low RGO contents. In addition to the high conductivity and interfaces between LC and RGO, aligned pores also boost electromagnetic interference (EMI) shielding effectiveness (SE) of the foams owing to induced multiple reflections. X-band EMI SE of the LC-based foams with 2-mm thickness could reach 28.5 to 70.5 dB at very low densities. Furthermore, the normalized surface specific SE (SE divided by density and thickness) could be as high as 28750 dB·cm2/g, which is much higher than those of other types of carbon foams and most shielding materials ever reported. With the outstanding EMI shielding performance, good mechanical properties and more sustainable raw material, the biomass-based carbon foams offer promising prospects for lightweight, robust and high-performance EMI shielding materials. ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

Dye-sensitized solar cells (DSSCs) belong to the group of thin-film solar cells which have been under extensive research for more than two decades due to their low cost, simple preparation methodology, low toxicity and ease of production. Still, there is lot of scope for the replacement of current DSSC materials due to their high cost, less abundance, and long-term stability. The efficiency of existing DSSCs reaches up to 12%, using Ru(II) dyes by optimizing material and structural properties which is still less than the efficiency offered by first- and second-generation solar cells, i.e., other thin-film solar cells and Si-based solar cells which offer ~ 20–30% efficiency. This article provides an in-depth review on DSSC construction, operating principle, key problems (low efficiency, low scalability, and low stability), prospective efficient materials, and finally a brief insight to commercialization. Published version

Bioresorbable scaffolds (BRS) were introduced to overcome limitations of current metallic drug-eluting stents and poly-L-lactide (PLLA) has been used in the fabrication of BRS due to its biodegradability and biocompatibility. However, such polymers have weaker mechanical properties as compared to metals, limiting their use in BRS. We hypothesized that nanofillers can be used to enhance the mechanical properties considerably in PLLA. To this end, polymer-matrix composites consisting of PLLA reinforced with 5–20 wt% barium sulfate (BaSO4) nanofillers as a potential BRS material was evaluated. Stearic-acid (SA) modified BaSO4 nanofillers were used to examine the effect of functionalization. Rigid nanofillers improved the tensile modulus and strength of PLLA (60% and 110% respectively), while the use of SA-BaSO4 caused a significant increase (~110%) in the elongation at break. Enhancement in mechanical properties is attributed to functionalization which decreased the agglomeration of the nanofillers and improved dispersion. The nanocomposites were also radiopaque. Finite element analysis (FEA) showed that scaffold fabricated from the novel nanocomposite material has improved scaffolding ability, specifically that the strut thickness could be decreased compared to the conventional PLLA scaffold. In conclusion, BaSO4/PLLA-based nanocomposites could potentially be used as materials for BRS with improved mechanical and radiopaque properties.

Stretchable energy storage devices are prerequisites for the realization of autonomous elastomeric electronics. Microsupercapacitors (MSCs) are promising candidates for this purpose due to their high power and energy densities, potential for miniaturization, and feasibility of embedding in circuits; however, efforts to realize stretchable MSCs have mostly relied on strain-accommodating materials and have suffered from limited stretchability, low conductivity, or complicated patterning processes. Here, we designed and fabricated a stretchable MSC based on reduced-graphene-oxide/Au heterostructures patterned by facile and versatile direct laser patterning. An interconnected and stable 3D network composed of vertically oriented heterostructures was realized by high-repetition-rate femtosecond laser pulses. Upon transferring to polydimethylsiloxane (PDMS), the 3D network achieved a high conductivity of ~105 S m−1, and the conductivity could be maintained at ~104 S m−1 even at 50% strain. A fully laser-patterned stretchable electronics system was integrated with embedded MSCs, which will find applications in soft robotics, wearable electronics, and the Internet of Things. By transforming flat graphene oxide films into vertically oriented sheets, researchers have constructed an energy storage device that may power wearable electronics. Graphene oxide’s ability to quickly store and release charge from its surface makes it attractive for supercapacitors, which recharge significantly faster than conventional batteries. Young-Jin Kim and Pooi See Lee from the Nanyang Technological University in Singapore and colleagues have now used ultrafast lasers to controllably heat graphene oxide into a spiky 3D network that accommodates large amounts of mechanical strain. Following deposition of a gold coating and subsequent transfer to an elastomeric substrate, the team’s supercapacitor retained its high energy output even after being rolled, bent, twisted, and crumpled hundreds of times. The laser-based fabrication enabled production of customized patterns, such as wavy electrode ‘fingers’ that can attach to curved surfaces. An intrinsically stretchable and highly conductive graphene electrode based on vertically oriented graphene/Au bilayer flakes are successfully fabricated by a direct-laser-patterning at a very high-repetition rate and fast scanning speed of laser with a femtosecond pulse, allowing micro-supercapacitors to be integrated with the complete soft electronics systems that can be standalone and be customized by user’s circuit designs.

A combined experimental and computational study was carried out to investigate ballistic performance of laterally preload compressed SiC tile against long rod impact. A 100 × 100 b y 20 mm thick SiC tile was pushed into a 5 mm thick steel frame at high temperature of 430 °C so that after cool down to room temperature, the lateral preload compressive stress was developed in the SiC tiles. Depth of penetration tests of the SiC tiles with and without pre-stress were performed, where tungsten alloy long rods at a nominal velocity of 1240 m/s were launched to hit the SiC tiles backed by the steel blocks. Compared with the SiC tiles without any pre-stress, the pre-compressed SiC tiles were found to reduce significantly the residual penetration in the backing block. Simulations were carried out using the LS-dyna hydrocode, taking account of preload stress. The simulations showed that the lateral preload compression strengthened the intact SiC tiles and dwell occurred in the early penetration stage, eroding the striking long rod efficiently. Keywords: Pre-compressed SiC tile, DOP test, WHA long rod

A new type of dipole plasmon excitations in colloidal highly doped ZnO nanocrystals has been studied by means of many-body quantum mechanical approach. We demonstrate that in photodoped ZnO nanocrystals, the conduction band electrons are localized close to the surface and the plasmon oscillations are induced by their angular motion. The transition of this plasmon mode from classical to quantum regime is defined by the nanocrystal size. The size dependence of the resonance frequency which results from quantum effects is in remarkable agreement with experimental observations. Published version

The creation of crystal phase heterostructures of transition metal chalcogenides, e.g., the 1T/2H heterostructures, has led to the formation of metal/semiconductor junctions with low potential barriers. Very differently, post-transition metal chalcogenides are semiconductors regardless of their phases. Herein, we report, based on experimental and simulation results, that alloying between 1T-SnS2 and 1T-WS2 induces a charge redistribution in Sn and W to realize metallic Sn0.5W0.5S2 nanosheets. These nanosheets are epitaxially deposited on surfaces of semiconducting SnS2 nanoplates to form vertical heterostructures. The ohmic-like contact formed at the Sn0.5W0.5S2/SnS2 heterointerface affords rapid transport of charge carriers, and allows for the fabrication of fast photodetectors. Such facile charge transfer, combined with a high surface affinity for acetone molecules, further enables their use as highly selective 100 ppb level acetone sensors. Our work suggests that combining compositional and structural control in solution-phase epitaxy holds promises for solution-processible thin-film optoelectronics and sensors., Controlling the composition and crystal phase of layered heterostructures is important. Here, the authors report the liquid-phase epitaxial growth of Sn0.5W0.5S2 nanosheets with 83% metallic phase on SnS2 nanoplates, which are used as 100 ppb level chemiresistive gas sensors at room temperature.

We report an environmentally benign and cost‐effective method to produce Fe and Co magnetic metal nanoparticles as well as the Fe/Cao and Co/CaO nanocomposites by using a novel, dry mechanochemical process. Mechanochemical milling of metal oxides with a suitable reducing agent resulted in the production of magnetic metal nanoparticles. The process involved grinding and consequent reduction of low‐costing oxide powders, unlike conventional processing techniques involving metal salts or metal complexes. Calcium granules were used as the reducing agent. Magnetometry measurements were performed over a large range of temperatures, from 10 to 1273 K, to evaluate the Curie temperature, blocking temperature, irreversibility temperature, saturation magnetization, and coercivity. The saturation magnetizations of the iron and cobalt nanoparticles were found to be 191 and 102 emu g−1, respectively. The heating abilities of these nanoparticles suspended in several liquids under alternating magnetic fields were measured and the specific loss power was determined. Our results suggest that the dry mechanochemical process is a robust method to produce metallic nanoparticles and nanocomposites. NRF (Natl Research Foundation, S’pore) Published version

A major challenge of maintaining primary hepatocytes in vitro is progressive loss of hepatocyte-specific functions, such as protein synthesis and cytochrome P450 (CYP450) catalytic activity. We developed a three-dimensional (3D) nanofibrous scaffold made from poly( l -lactide-co-glycolide) (PLGA) polymer using a newly optimized wet electrospinning technique that resulted in a highly porous structure that accommodated inclusion of primary human hepatocytes. Extracellular matrix (ECM) proteins (type I collagen or fibronectin) at varying concentrations were chemically linked to electrospun PLGA using amine coupling to develop an in vitro culture system containing the minimal essential ECM components of the liver micro-environment that preserve hepatocyte function in vitro. Cell-laden nanofiber scaffolds were tested in vitro to maintain hepatocyte function over a two-week period. Incorporation of type I collagen onto PLGA scaffolds (PLGA-Chigh: 100 µg/mL) led to 10-fold greater albumin secretion, 4-fold higher urea synthesis, and elevated transcription of hepatocyte-specific CYP450 genes (CYP3A4, 3.5-fold increase and CYP2C9, 3-fold increase) in primary human hepatocytes compared to the same cells grown within unmodified PLGA scaffolds over two weeks. These indices, measured using collagen-bonded scaffolds, were also higher than scaffolds coupled to fibronectin or an ECM control sandwich culture composed of type I collagen and Matrigel. Induction of CYP2C9 activity was also higher in these same type I collagen PLGA scaffolds compared to other ECM-modified or unmodified PLGA constructs and was equivalent to the ECM control at 7 days. Together, we demonstrate a minimalist ECM-based 3D synthetic scaffold that accommodates primary human hepatocyte inclusion into the matrix, maintains long-term in vitro survival and stimulates function, which can be attributed to coupling of type I collagen. Statement of Significance Culturing primary hepatocytes within a three-dimensional (3D) structure that mimics the natural liver environment is a promising strategy for extending the function and viability of hepatocytes in vitro. In the present study we generate porous PLGA nanofibers, that are chemically modified with extracellular matrix proteins, to serve as 3D scaffolds for the in vitro culture of primary human hepatocytes. Our findings demonstrate that the use of ECM proteins, especially type I collagen, in a porous 3D environment helps to improve the synthetic function of primary hepatocytes over time. We believe the work presented within will provide insights to readers for drug toxicity and tissue engineering applications.

A bilayer swellable drug-eluting ureteric stent (BSDEUS) is engineered and implemented, as a sustained drug delivery platform technology that enhances localized drug delivery to the highly impermeable urothelium, for the treatment of urothelial diseases such as strictures and carcinomas. On deployment, the device swells to co-apt with the ureteric wall and ensure drug availability to these tissues. BSDEUS consists of a stent spray-coated with a polymeric drug containing polylactic acid-cocaprolactone (PLC) layer which is overlaid by a swellable polyethylene glycol diacrylate (PEGDA) based hydrogel. In-vitro quantification of released drug demonstrated a tunable time-profile, indicating sustained delivery over 1-month. The PEGDA hydrogel overlayer enhanced drug release and transport into explanted porcine ureteric tissues ex-vivo, under a simulated dynamic fluid flow. A preliminary pilot invivo feasibility study, in a porcine model, demonstrated that the swollen hydrogel co-apts with the urothelium and thus enables localized drug delivery to the target tissue section. Kidney functions remained unaffected and device did not result in either hydronephrosis or systemic toxicity. This successful engineering of a bilayer coated stent prototype, demonstrates its feasibility, thus offering a unique solution for drug-based urological therapy. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) NMRC (Natl Medical Research Council, S’pore) Accepted version

Additive manufacturing (AM) technologies provide more freedom to functional part design in various industries. One of the unique capabilities of AM is that multi-material parts can be produced with material compositional and geometric complexity. Multi-material parts have the advantage of achieving multiple performance requirements. In the research, we propose a framework for designing multi-material parts using AM processes. The proposed framework is composed of four interacting modules, including design requirement identification, primary material selection, AM process selection, material composition, and part geometry determination. Rules and guidelines for AM are integrated into the proposed framework with AM processes’ capabilities and constraints compiled in databases. We also introduce databases to assist in decision-making and ensure manufacturability of the designed multi-material part in various product design phases. The proposed framework is applied to a case study involving a conceptual design of a multi-material battery pack cooling plate. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version

The coupling of the localized surface plasma resonance (LSPR) between noble metals of Au, Ag and Cu and semiconductors of Cu2 xE (E ¼ S, Se, Te) opens new regime to design photothermal (PT) agents with enhanced PT conversion efficiency. However, it is rarely explored on fabricating of engineered dual plasmonic hybrid nanosystem for combinatory therapeutic-diagnostic applications. Herein, rattle-type Au@Cu2 xS hollow mesoporous nanoparitcles with advanced PT conversion efficiency are designed for cellular vehicles and chemo-photothermal synergistic therapy platform. The LSPR coupling between the Au core and Cu2 xS shell are investigated experimentally and theoretically to generate a PT conversion efficiency high to 35.2% and enhanced by 11.3% than that of Cu2 xS. By conjugating microRNA (miRNA) gene probe on the surface, it can realize the intracellular oncogenic miRNA detection. After loading of anticancer drug doxorubicin into the cavity of the Au@Cu2 xS, the antitumor therapy efficacy is greatly enhanced in vitro and in vivo due to the NIR photoactivation chemo- and photothermal synergistic therapy. The rattle-type metal-semiconductor hollow mesoporous nanostructure with efficient LSPR coupling and high cargo loading capability will be beneficial to future design of LSPR-based photothermal agents for a broad range of biomedical application. MOE (Min. of Education, S’pore) Accepted version

Ice accretion and accumulation pose serious challenges for maintaining the operation and performance of outdoor facilities in cold climate. Epoxy resin, with a wide range of formulation possibilities, is widely used as protective coatings for outdoor facilities. However, bisphenol A (BPA), a key ingredient of conventional epoxy, is known to interfere with human's natural hormones and cause various disorders in the body system. Reduction or complete elimination of the usage of BPA is therefore high in the agenda of the coatings industries. In this study, a transparent, anti-icing, bio-based epoxy coating was developed for room-temperature processing. As a result of hydrophobic treatment with addition of silanes, the glass-transition temperature and anti-icing performance of bio-based epoxy resin increased significantly. The optimum coating exhibited good water repellency and ice-adhesion strength as low as 50 kPa at −20°, which was half of the widely accepted threshold value of 100 kPa for icephobic coatings. The icing delay time was much delayed compared with that of an uncoated glass substrate. To further demonstrate the anti-icing performance of the optimized coating, supercooled-water dripping on coated wooden outdoor floors and wooded boards was conducted at −15 °C, superior anti-icing performance was observed on the coated substrates. Keywords: Anti-icing, Icephobic, Transparent coating, Bio-epoxy, Ice adhesion, Icing delay, Water repellent

In5SnSbO12 is being considered for use in thermoelectric applications. It has a satisfactory electrical conductivity and is expected to possess low thermal conductivity. However, it is difficult to densify In5SnSbO12 by conventional solid-state reaction method. In this work, we demonstrated that Ga doping could increase the relative density of In5SnSbO12, from ~ 60% (x = 0) to ~ 90% (x = 0.1). The improved densification may be attributable to the increased cationic occupancy after the addition of Ga and the reduced grain size induced by the presence of the secondary phase Ga2In6Sn2O16. The improved relative density led to a significant reduction in electrical resistivity; for example, for x = 0.1, the lowest electrical resistivity was ~ 0.002 Ω cm at 973 K, which was five times lower than that of the undoped sample (x = 0). The resultant power factor of this sample had a value of 3.4 × 10−4 Wm−1 K−2 at 973 K, which was nearly four times higher than that of the undoped sample. Although thermal conductivities were increased with Ga doping due to the enhanced densification, they were lower than that of In2O3. The highest thermoelectric performance was achieved in the sample with x = 0.05, specifically zT ~ 0.17 at 973 K. These results indicate that the addition of Ga to In5SnSbO12 results in a material which is more promising for thermoelectric applications.

Titanium dioxide nanotubes (TNTs) have drawn wide attention and been extensively applied in the field of biomedicine, due to their large specific surface area, good corrosion resistance, excellent biocompatibility, and enhanced bioactivity. This review describes the preparation of TNTs and the surface modification that entrust the nanotubes with better antibacterial property and enhanced osteoblast adhesion, proliferation, and differentiation. Considering the contact between TNTs’ surface and surrounding tissues after implantation, the interactions between TNTs (with properties including their diameter, length, wettability, and crystalline phase) and proteins, platelets, bacteria, and cells are illustrated. The state of the art in the applications of TNTs in dentistry, orthopedic implants, and cardiovascular stents are introduced. In particular, the application of TNTs in biosensing has attracted much attention due to its ability for the rapid diagnosis of diseases. Finally, the difficulties and challenges in the practical application of TNTs are also discussed. Accepted version

Oil-water separation is critically important for the water treatment of oily wastewater or oil-spill accidents. The oil contamination in water not only induces severe water pollution but also threatens human beings’ health and all living species in the ecological system. To address this challenge, different nanoscale fabrication methods have been applied in endowing biomimetic porous materials, which provides a promising solution for oily-water remediation. In this review, we present the state-of-the-art developments on the rational material interface design on special wettability for the intelligent separation immiscible/emulsified oil-water mixture. Mechanism understanding towards oil-water separation is firstly described, following with the summary of separation solutions for traditional oil-water mixture and special oil-water emulsion enabled by the self-amplified wettability due to nanostructures. Guided by the basic theory, rational interface design at nanoscale on various porous materials with special wettability towards superhydrophobicity-superoleophilicity, superhydrophilicity-superoleophobicity, and superhydrophilicity-underwater superoleophobicity is discussed in details. Although the above nanoscale fabrication strategies are able to address most of current challenges, intelligent superwetting materials developed to meet special oil-water separation demands and to further promote the separation efficiency are also reviewed for various special application demands. Finally, challenges and the future perspectives on the development of more efficient oil-water separation materials and devices by nanoscale control are provided. It is expected that the biomimetic porous materials with nanoscale interface engineering will overcome the current challenges of oil-water emulsion separation, realizing in practical applications in the near future with continuous efforts in this field. Accepted version

Vanadium dioxide (VO2) nanoparticles with reversible semiconductor-metal phase transition holds the tremendous potential as a thermochromic material for the energy-saving smart glazing. However, the trade-off between improving the luminous transmittance (Tlum) while sacrificing the solar modulation ability (ΔTsol) hampers its bench-to-market translation. Previous studies of anti-reflection coatings (ARCs) focused primarily on increasing Tlum while neglecting ΔTsol, which is a key energy-saving determinant. The intrinsically low ΔTsol (

The monoclinic scheelite‐type BiVO4 is recognized as one of the promising candidate materials for a photoanode because of its 9.1 % theoretical efficiency for half‐cell solar‐to‐hydrogen conversion. Although significant research efforts have been devoted to improving the performance of the photoelectrochemical cell (PEC) of this material, they have mainly been in small anode areas with only a handful of studies on scaled‐up sizes. Herein, a facile metal–organic decomposition synthesis method was used to produce scaled‐up Mo‐doped BiVO4 photoanodes. Multiple modifications were explored and incorporated to enhance the performance of the photoanode. A large‐area (5 cm×5 cm) photoanode was successfully prepared with all modifications. The resulting photoanode gave rise to an initial photocurrent density of 2.2 mA cm−2 at 1.23 V versus reversible hydrogen electrode, under AM 1.5G illumination in a PEC, which remained at 79 % of this value after 1 h of operation. A deleterious effect of the increased anode surface area on the photocurrent density was observed, which we termed the “areal effect”. Understanding the reasons for the areal effect is indispensable for the development of large‐scale PEC devices for water splitting. NRF (Natl Research Foundation, S’pore) Accepted version

Choroid thinning occurs in age-related macular degeneration (AMD). However, it remains unclear whether the reduction is due to reduction in choroidal vessels or shrinkage of choroidal stroma, or both. The purpose of this study was to evaluate the changes of the choroidal vascular and stromal area in 118 patients with typical AMD (t-AMD) and polypoidal choroidal vasculopathy (PCV) over a 12-month period. We used spectral-domain optical coherence tomography (SD-OCT) with enhanced depth imaging (EDI) mode to measure the subfoveal choroidal thickness (CT), central retinal thickness (CRT) and choroidal vascularity index (CVI - ratio of luminal area to total choroidal area). At baseline, PCV eyes had higher CRT (471.6 µm vs 439.1 µm, p = 0.02), but comparable subfoveal CT and CVI, compared to t-AMD. Eyes with high CVI at baseline showed marked reduction in stromal area compared with eyes with average or low CVI. Over 12 months, CRT and subfoveal CT significantly decreased (p

This paper attempts to identify key factor(s) for highly reflective silver (Ag) coatings. Investigation was made over the crystal orientation and surface roughness, using several types of surfaces, including electroplated Ag polycrystal films, physical vapour deposited polycrystal Ag films, and single crystal Ag foils with different crystal orientations. In each type of the surfaces, surface roughness was varied so that, for different combinations of crystal orientation, roughness would elucidate the key factors towards highly reflective Ag coatings. It is found that surface roughness plays a critical role in determining the reflectance, while the crystal orientation has negligible effect. The mean reflectance and one-way ANOVA analysis indicate that the single crystal Ag foils with three orientations performed statistically the same in the same roughness group at significance levelα= 0.05. Moreover, correlation between the surface reflectance and surface roughness has been proposed for the benefit of coating design. Refection data obtained from the polycrystalline silver samples are used to verify the accuracy of the proposed correlations. It was observed that the development surface area ratio,Sdr, is a better roughness indicator in predicting the reflectance of polycrystalline silver films than the arithmetic average roughness,Ra.

In this work, the effect of fine grain sizes on the mechanical and bio-corrosion properties of AZ31 magnesium alloy was studied. Bio-corrosion refers to the accelerated degradation of metal within the human body. Fine-grained (~1.5 µm) AZ31 was obtained through Severe Plastic Deformation (SPD) via three cycles of Constrained Groove-Pressing (CGP) under elevated temperature. The effects of CGP and post-annealing (at 473 K for 15 and 30 min) on bio-corrosion were preliminarily investigated by potentiodynamic polarization measurements and constant immersion tests. Results obtained show that the as-processed samples with annealing exhibited improvements in yield strength and ductility while the bio-corrosion rate in Hank’s solution remains fairly similar during the early stage. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

Artificial photosynthesis, i.e. solar water splitting, has been recognized as a green and promising way to produce clean energy fuel, hydrogen, and solve the fossil fuel shortage problem. My PhD study explores the strategies of improving the efficiency of artificial photosynthesis, and my work mainly focuses on using cheap and abundant materials to design efficient composite photoelectrode and nano-photocatalyst via enhancing light absorption and charge separation. In my first strategy, a novel design consisting of a sandwich structure of Fe2O3/Au/Fe2O3 was implemented and expected to work as an efficient photoanode for solar water splitting. Fe2O3 is a well-known cheap semiconductor which can utilize visible light energy. However, the efficiency is highly limited due to the poor charge separation. In the new design, the charge separation and photo-response are expected to be significantly improved by inserting one thin intermediate layer of Au within layers of Fe2O3 to form a tandem composite configuration. The SPR absorption from the intermediate Au layer and the resulted Plasmon-excitation induced electron transfer may enable wider light harvesting range and more efficient charge separation. All these may contribute to improve photocurrent response compared to Fe2O3 alone. The tandem layers were constructed by spin-coating of pre-synthesized Fe2O3 nanoparticles and sputtering of the gold intermediate layer. Tests on photo-current response proved that this sandwich structure exhibited much higher photo-activity efficiency as compared to the Fe2O3 photoanode. Mechanism studies on functions of Au intermediate layer well explained this enhancement. The results indicated that the Au intermediate layer was able to contribute in electron transfer as well as visible-light harvesting due to its plasmonic excitation. Such sandwich structure may be applied to other semiconductors to improve their performance in solar water splitting. DOCTOR OF PHILOSOPHY (MSE)

Polyvinylidene Fluoride (PVDF) is one type of semicrystalline fluoropolymers that has been widely used in automotive and chemical industries, semiconductor, biomedical and sensor applications; owing to its superior chemical resistance, excellent mechanical properties and unique electronic properties. Polymeric composites containing nanoscale fillers, such as graphene, carbon nanotube (CNTs) or nanoclay often render polymers with interesting mechanical, structural, electrical, optical and many other functional properties. The objective of this work is to improve mechanical and functional properties of PVDF by the advantageous introduction of CNTs. Studies will focus on the preparation methodology of PVDF/CNTs composites with uniform morphology, the interaction between CNTs and polymer matrix and surface treatment of CNTs. The surface properties of CNTs often play an important role in determining the performance of polymer/CNTs composites. Therefore, in the first study, we focused on studying the surface functionalization of CNTs. Controlled thermal annealing in air was employed in order to oxidize CNTs. It was found that longer time/higher temperature can effectively increase the oxygen content in CNTs. Shorter duration/higher temperature annealing results in more C-O-C groups than longer duration/lower temperature annealing, while the latter yields more C=O groups. The mechanism of CNT surface functionalization by air annealing was proposed. In the following work, PVDF/CNTs composites with well dispersed and distributed CNTs were fabricated using both solution mixing and melt extrusion strategies. The introduction of low content of CNTs lead to an unusual observation of large enhancement in ductility; while marginal increase were observed for Young’s modulus and tensile strength. Systematic characterizations lead to the conclusion that the unexpected phenomenon is correlated with the change of polymorphs because of the existence of CNTs. Mechanism of phase transformation and pinning effect are proposed to further elucidate the phenomenon. In the third study, we explore the possibility using PVDF and its CNTs composites for oil/water separation applications. PVDF and PVDF/CNTs aerogel were fabricated through a vapor induced phase inversion process. Contributed by the hierarchical micro-nano structure that is tailorable by PVDF concentration, both surfactant-free and surfactant-stabilized oil-in-water emulsion could be effectively separated by the fabricated PVDF aerogel simply under gravity, with good flux and high filtrate purity up to 99.99%. PVDF aerogel also exhibited moderate oil absorption capacity and almost instantaneous oil up-taking when tested using various types of oil. Furthermore, PVDF aerogel is highly stable towards concentrated alkaline solution owing to its superhydrophobicity, and shows good reusability in both oil/water separation and oil absorption. The influence of introduction of CNT on the mechanical and porous microstructure was examined. With 0.1 wt. % CNTs, the mechanical performance could be improved without impairing the surface properties of aerogel. In the last part of this thesis, the findings are summarized and potential future works are suggested. DOCTOR OF PHILOSOPHY (MSE)

224 p. Nonlinear optical (NLO) polymers have attracted extensive attention because of their potential applications in integrated optical devices such as optical switching, frequency conversion and high-speed electro-optic (EO) devices. However, the stability and optical loss of currently used polymers limit their applications. It is very important to develop NLO polymers with better transparency and higher stability without sacrificing other properties. This study focused on the development of new side-chain NLO polyimides based on the novel fluoronitroaryl diaminoazobenzene chromophores and polyimide/silicon composites. The effects of the fluorine and the fluorine position in the chromophores on the structures and properties of the chromophores and polyimides were studied. The influences of the silicon network on the properties of the composite films were also investigated. DOCTOR OF PHILOSOPHY (MSE)

Crystalline silicon (Si) nanowires are important building blocks in devices of photonics, quantum-dots, optoelectronics, and energy. Thermal annealing of metal-covered Si wafers gives rise to clean Si nanowires without metallic catalyst at the tip. The process does not need flammable or toxic gases. However, the growth mechanism is yet elucidated. This project grows Si nanowires by adopting the thermal annealing method: nickel (Ni) is sputtered on Si wafers as catalyst and thereafter a layer of carbon is sputtered to protect Si nanowires from oxidation during thermal annealing. Careful studies via transmission electron microscopy and selected area electron diffraction patterns elucidate the growth process and the relationship between the seeding Ni particle and the grown Si nanowire. The seeding Ni particles are embedded in the Ni-Si-O nanoclusters that are connected with the grown Si nanowires at the end of the nanowire growth. The growth orientation of Ni-seeded Si nanowires is not dictated by surface energy of the various nanocrystal planes, but follows specific structure sensitive principle with the seeding Ni nanoparticles to minimize the mismatch in lattice spacing and dihedral angle at the wire/particle interface. It is inferred that the growth orientation of Si nanowires is determined by the ordered planes of the Ni catalyst particle at the wire/particle interface. The various morphologies of the nanowires are controlled by the diameter and vibration of the Ni-Si-O droplet, the distribution of the Ni-Si, Ni-Si-Oy (y≈1) and Ni-Si-Ox (x≈2) phases, and the supersaturated content in the Ni-Si-O droplet. DOCTOR OF PHILOSOPHY (MAE)

Solar fuels derived from solar energy are envisioned to replace fossil fuels for a sustainable earth and society. Photocatalytic carbon dioxide (CO2) reduction for gaseous or liquid fuels production is one of the most promising processes to not only solve the energy crisis, but also reduce the environmental issues such as greenhouse effect. However, advancement of CO2 reduction for solar fuels production is largely hindered by the lack of efficient photocatalysts. In this thesis, the work was focused on surface modification of semiconductor metal oxide photocatalyst to increase the affinity between CO2 and catalysts as well as preventing the electron hole pair recombination toward optimize the reaction efficiency. Firstly, methanolamine was utilized to functionalize the TiO2 surface by a facile one-step solvothermal method. Surface amine group can greatly increases the affinity of CO2 on TiO2 surfaces through chemisorption by formation of carbamate. This process can also activate the CO2 molecules, which allows more efficient charge transfer from TiO2. As a results, amine-functionalize TiO2 can significantly enhances the CO and CH4 production yield by photocatalytic CO2 reduction. Secondly, to further apply this amine group surface modification method, amine-functionalized ZnO was synthesized via a facile one-step hydrothermal method. The CO2 adsorption ability is greatly increased after surface amine group modification. After activation of CO2 molecules upon chemisorptions, the photoexicited electrons generated under UV-light irradiation can more efficiently reduce the CO2, thus significantly enhance the photocatalytic CO2 reduction rate. Finally, to prevent electron-hole pair recombination of semiconductor, Cu was decorated on ZnO nanowire single crystal by photodeposition method. The Cu exists in Cu2O form and act as a cocatalyst. By trapping the photogenerated electrons, this Cu cocatalyst can effectively reduce electron-hole pair recombination toward efficient CO2 photoreduction. The selectivity towards CO2 reduction is also increased by this Cu cocatalst. DOCTOR OF PHILOSOPHY (MSE)

High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in both thermal ablation for solid tumor/cancer therapy and soft-tissue fragmentation. Mechanical as well as thermal effects play an important role in the HIFU treatment simultaneously. Further understanding the underlying mechanisms of HIFU ablation is critical for its safety and efficiency in the clinical application as well as developing new technology. In order to achieve our goals, nonlinear acoustic propagation of a HIFU burst was first simulated using KZK equation. Then bubble dynamics at the focal plane of the HIFU transducer, where a soft tissue is located, was simulated by the Gilmore model and its diffusion in the interval time by a static diffusion model with the progress of HIFU ablation. The simulation results show that the bubble dynamics is not consistent for each burst exposure and in general the maximum bubble size reached and the associated radiation acoustic pressure in the collapse increase with the number of delivered bursts although there are significant variations. This finding has a good agreement with the erosion on the soft tissue during histotripsy, starting at the focus, extending laterally and then reaching the threshold for the erosion area. Secondly, a novel lesion production strategy was developed and tested in both gel phantom and ex vivo tissue with the HIFU pulse duration much longer than that of histotripsy but shorter than boiling histotripsy. The characteristics of bubble cavitation by passive cavitation detection (PCD) for the inertial and stable cavitation and temperature elevation by a thermocouple were measured during the therapeutic procedure. Lesion would vary from a mechanical erosion in the shape of a “squid” to a “dumbbell” lesion with DOCTOR OF PHILOSOPHY (MAE)