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The application of a built-in electric field due to piezoelectric potential is one of the most efficient approaches for photo-induced charge transport and separation. However, the efficiency of converting mechanical energy to chemical energy is still very low, and the enhancement of photocatalysis, thus, is limited. To overcome this problem, here, we propose sonophotocatalysis based on a new hybrid photocatalyst, which combines ferroelectric nanocrystals (BaTiO3) and dendritic TiO2 to form an urchin-like TiO2/BaTiO3 hybrid photocatalyst. Under periodic ultrasonic excitation, a spontaneous polarization potential of BaTiO3 nanocrystals in response to ultrasonic waves can act as an alternating built-in electric field to separate photoinduced carriers incessantly, which can significantly enhance the photocatalytic activity and cyclic performance of the urchin-like TiO2/BaTiO3 catalyst. More importantly, the significant enhancement of photocatalytic hydrogen evolution is due to the coupling effect of two types of piezoelectric potential in the presence of BaTiO3 nanocubes as well as the semiconductor and optical properties of TiO2 nanowires of the urchin-like TiO2/BaTiO3 hybrid structure under simulated sunlight and periodic ultrasonic irradiation, which can significantly improve the efficiency of converting mechanical energy to chemical energy.

The application of a built-in electric field due to piezoelectric potential is one of the most efficient approaches for photo-induced charge transport and separation. However, the efficiency of converting mechanical energy to chemical energy is still very low, and the enhancement of photocatalysis, thus, is limited. To overcome this problem, here, we propose sonophotocatalysis based on a new hybrid photocatalyst, which combines ferroelectric nanocrystals (BaTiO

This thesis focuses on the development and application of a new type of nanowire growth where ultrathin metal nanowires selectively grow from the interface between seeds and oxide substrate. Under this active-surface growth mode, surface-bound metal nanowires can achieve nanowire-substrate hierarchical structures such as vertically aligned metal nanowires which show excellent performance in fixed-bed catalysis. By modifying the reaction conditions, this unique growth mode can also be applied in the growth of bimetallic segmented nanowires as well as chiral nanostructures. The synthesis of these surface-bound nanowires is carried out at room temperature in aqueous solution using solid seeds. This approach of promoting anisotropic growth of nanocrystals into nanowires is novel and previously unknown in the literature (Chapter 1). It shows potential for fabrication of complex nanostructures as building blocks in nanodevices. By employing strong thiol ligands, the nanowires grow from only one side of the seeds. Interestingly, the width of emerging nanowires is independent of the size of the seeds but dependent on the dynamic competition between the ligand diffusion and metal deposition processes (Chapter 2). By carrying out designed experiments, a mechanism is proposed that can explain these unusual phenomena. The strong binding of thiol ligands in this system blocks the deposition of metal on the exposed surface of the seeds, while in turn forcing selective deposition of metal at the ligand-deficient interface between metal seeds and oxide substrates. Subsequently, the instant binding of ligands inhibits the growth of newly-formed surface at the perimeter of the interface, thus conferring the interface higher “activity” for metal deposition. This method for growing surface-bound metal nanowires is facile and scalable. It can be applied on different kinds of oxide substrates and even trumpet shells to form conductive films. By growing Au nanowires on glass fibres, they can be used in a column for fixed-bed catalysis (Chapter 3). With the high loading Au surface and loose packing of glass fibres, both high catalytic capability and fast flow of reaction solutions can be achieved in the system. For the conversion reaction of 4-nitrophenol to 4-aminophenol, the continuous flow catalysis can be achieved with a processing rate about 100 times that of the best literature rate. This active-surface growth is not limited to the fabrication of Au nanowires. For example, it can also be applied to the growth of surface-bound ultrathin Pd nanowires which cannot be synthesized by any reported methods (Chapter 4). With the understanding of the growth mechanism, it is demonstrated that the “active” metal-substrate interface allows the deposition of another metal even when their lattices mismatch. The growth of Pd nanowires can be controlled from the interface of Au seeds and substrate, as well as the interface of Au nanowires and substrate, thus producing Pd nanowires with Au tips or Au-Pd bimetallic segmented nanowires. Fabricating chiral nanostructures is one of the important research objectives in nanoscience and nanotechnology. Metallic chiral nanowires are rarely reported because the assembly of symmetric metal atoms in an asymmetric way is difficult. Chapter 5 demonstrates that the strong binding of ligands (4-mercaptobenzoic acid) in the current system can be made use of to induce the growth of chiral nanowires such as spiral nanowires when the reaction conditions are altered. When excess ligands are present in the system, the uneven binding of ligands at the seed-substrate interface is proposed to induce imbalanced growth rate of Au at this interface. This imbalanced rate makes the growth of emerging nanowires to tilt towards another direction. Thus, the propagation of the curving results in the final chiral structures. Based on the analysis, it is also shown that other thiol ligands can also be used to synthesize chiral nanowires. With the additional understanding of active-surface growth mechanism, further insights can be gained on how different nanocrystals are formed. This active-surface growth mode is facile as it is able to be applied to different substrates. It can also fabricate a variety of nanowires such as pure metal, bimetallic, chiral nanowires. One of its potential applications in fixed-bed catalysis has also been explored. Active-surface growth mode shows promising capabilities for the fabrication of complex nanostructures as building blocks in future nanodevices. DOCTOR OF PHILOSOPHY (SPMS)

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another "bad" ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized. Published version

The growth of a zeolitic imidazolate framework (ZIF-8) on Au nanoparticles (NPs) is controlled through tuning of the Au NP surface structure using competitive ligands, which results in concentric core–shell, eccentric core–shell or Janus nano-hybrids. With these three types of controlled structures, we demonstrated the influence of the ZIF-8 shell on the catalytic performance of Au NPs.

We expand the scope of the previously developed Active Surface Growth mode for growing substrate-bound ultrathin Pd (d = 4 nm) and Ag nanowires (d = 30 nm) in aqueous solution under ambient conditions. Using Au nanorods as the seeds, selective growth at the contact line between the rod and the substrate eventually leads to an attached Pd nanoplate. The unique growth mode also allows sequential growth of different materials via a single seed, giving substrate-bound Au-Pd diblock nanowires. The new abilities to use seed shape to pre-define the active sites and to apply sequential growth open windows for new pathways to hybrid nanostructures.

We show that spiral and helical Au nanowires can be directly grown via the active surface growth mechanism. The formation of spiral nanowires as opposed to straight nanowires is not triggered by the presence of a particular reactant, but controlled by the ratio of reactant concentrations. We propose that the asymmetric blocking of the Au–substrate interface induces imbalanced growth of the nanowire, causing it to curve. Blocking a single corner of the active interface leads to spiral nanowires whereas blocking two corners leads to helical nanowires. Spiral and helical nanowires become more frequent when the diffusion of Au is the limiting factor, as the reactant ratio falls below a critical value. The transition from helices to spirals and finally to nearly straight nanowires indicates a gradual loss of the blocked sites, hence supporting the asymmetric blocking mechanism.

Thiolated ligands are seldom used as morphology-directing reagent in the synthesis of Au nanostructures due to their low selectivity toward the different facets. Recently, we developed a thiolated ligands-induced synthesis of nanowires where the selective Au deposition only occurs at the ligand-deficient Au-substrate interface. Herein, the structural effect of thiolated ligands in this active surface growth is systematically investigated. It is revealed that their ability of rendering surface is closely related to the molecular structure. Ligands with aromatic backbones are capable of inducing nanowire formation, whereas those with aliphatic backbones cannot, likely because the former can pack better at short time scale of the rapid growth. The substituents of the ligands are critical for the colloidal stability of the final structure. It is further demonstrated that aromatic and aliphatic ligands could be mixed to turn on the continual lateral growth, leading to nanowires with tapered ends. The ligand generality in this growth mode also allows the creation of superhydrophobic surface, with the nanowire forest providing the nanoscale surface roughness and the hydrophobic ligand offering the surface property. These applications of the thiolated ligands in the nanosynthesis open a new approach for controlled synthesis of Au-based nanostructures with various morphologies and properties.

Metallic nanohelices are extremely rare and, to date, have never been synthesized by a direct solution method. In this work, we report ultralong Au nanohelices grown in solution under ambient conditions. They are ultralong with several tens of micrometers in length, with extraordinary aspect ratio (length/diameter greater than 22 300) and the number of pitches (more than 22 000 pitches). The pitch and width are uniform within each helix but vary widely among the helices. Crystal analyses showed that the facets, twin boundaries, grain sizes, and orientations are aperiodic along the helices. The apparent smooth curving is only possible with a large number of surface steps, suggesting that these structural features are the mere consequence of the helix formation rather than the cause. We propose that the nanowires are formed by the active surface growth mechanism and that the helicity originates from the random and asymmetrical blocking of nuclei embedded within the floccules of ligand complexes, in the form of either asymmetric binding of ligands or asymmetric diffusion of growth materials through the floccules. The separate growth environment of these nuclei causes constant helicity within each helix but differing helicity among the individuals. The embedding also provides a robust environment for the sustained growth of the nanohelices, leading to their record length and consistency.

Ein Werkzeug aus Stein kann moglicherweise durch Zufall entdeckt werden, aber es erfordert mehr als nur Gluck, um ein Auto oder ein Handy zu entwickeln. Mit zunehmenden Fortschritten der Nanowissenschaften verlangt die Synthese der immer aufwendigeren Nanostrukturen nach einem rationalen Design und einem systematischen Ansatz. In diesem Aufsatz pladieren wir fur eine Unterscheidung zwischen thermodynamisch und kinetisch kontrollierten Szenarien, oder anders gesagt, nach einer Unterscheidung, ob sich ein Produkt bildet, weil es sich um den stabilsten Zustand handelt oder weil der dahin fuhrende Weg die geringste Barriere aufweist. Unser Ziele sind eine genaue Beschreibung der vielen, gleichzeitig ablaufenden Prozesse bei typischen Nanosynthesen und die Einordnung von mechanistischen Vorschlagen in der Literatur in einen gemeinsamen Rahmen, damit diese sich leichter vergleichen lassen.

Growing oxide shells on seed nanoparticles requires the control of several processes: (a) the nucleation and growth of the shell material; (b) the "wetting" of the shell material on the seeds; and (c) the aggregation of the nanoparticles. These processes are influenced by a number of factors, many of which are related. Without understanding the interdependence of these contributing factors, it is difficult to circumvent problems and achieve rational synthesis. We first did a case study on encapsulating Au nanoparticles with ZnO to understand the multiple roles of polyvinylpyrrolidone (PVP) and their dependence on other factors. We developed a general method for coating ZnO on a variety of seeds, including metals, oxides, polymer nanoparticles, graphene oxide, and carbon nanotube. This method can be further extended to include Fe3O4, MnO, Co2O3, TiO2, Eu2O3, Tb2O3, Gd2O3, β-Ni(OH)2, ZnS, and CdS as the shell materials. The understanding obtained in this systematic study will aid rational design and synthesis of other core-shell nanostructures.

We report a nanowire growth that is highly unconventional: (1) nanowires can grow from substrate-bound seeds but cannot from colloidal seeds under otherwise the same conditions; (2) the nanowires grow from only one side of the seeds, with their diameter independent of the size of the seeds; and (3) vertically aligned ultrathin nanowires are obtained on substrates, using aqueous solution and ambient conditions. With carefully designed experiments, we propose and test a new mechanism that can explain these unusual phenonmena. It turns out that the strong binding of ligands in this system forces selective deposition of Au at the ligand-deficient interface between Au seeds and oxide substrates. This means of promoting anisotropic growth of nanocrystals into nanowires is previously unknown in the literature. We are able to pinpoint the site of active growth and explain the control of nanowire width. The sustained growth at the active site and the inhibited growth at its parameter push the nanocrystals upward into wires; their diameter is dependent on the dynamic competition of the two processes. The site-specific growth from substrate-anchored seeds provides a rare means to create substrate-nanowire hierarchical structures in aqueous solution under ambient conditions. Rendering a surface conductive, particularly one with complex surface morphology, is now made easy.

Photocatalytic materials comprised of semiconductor nanostructures have attracted tremendous scientific and technological interest over the last 30 years. This is due to the fact that these photocatalytic materials have unique properties that allow for an effective direct energy transfer from light to highly reactive chemical species which are applicable in the remediation of environmental pollutants and photocatalytic hydrogen generation. Heterostructured photocatalysts are a promising type of photocatalyst which can combine the properties of different components to generate a synergic effect, resulting in a high photocatalytic activity. In this work, a heterostructured photocatalyst comprised of few-layered MoS2 nanosheets coated on a TiO2 nanobelts surface was synthesized through a simple hydrothermal treatment. The hybrid heterostructures with enhanced broad spectrum photocatalytic properties can harness UV and visible light energy to decompose organic contaminants in aqueous solutions as well as split water to hydrogen and oxygen. The mechanism of the enhancement is that the MoS2/TiO2 nanobelts heterostructure can enhance the separation of the photo-induced carriers, which results in a higher photocurrent due to the special electronic characteristics of the graphene-like layered MoS2 nanosheets. This methodology is potentially applicable to the synthesis of a range of hybrid nanostructures with promising applications in photocatalysis and other relevant areas.

One-dimensional assembly of gold nanoparticles (see picture)is achieved by a sphere-to-cylinder transformation of polymer shells. A large amount of monomers remains after the assembly, which is characteristic of the chain-growth “polymerization”. Single-line chains can be converted to double-line chains, thus substantiating the unique role of the polymer shell.

Two solution processable π-conjugated triphenylamine-based dendrimers, Tr-TPA3 and Tr-TPA9 were served as hole-transporting materials (HTMs) for organic light-emitting devices (OLEDs). The two dendrimers exhibit similar absorption and emission behaviors in solutions and thin films, which demonstrate that these dendrimers can form amorphous states in their films. The dendrimers showed excellent solubility, which are soluble in common organic solvents such as chloroform, tetrahydrofuran, and 1,1,2,2-tetrachloroethane, high thermal stability with high glass-transition temperature (Tg) of 115 °C for Tr-TPA3 and 140 °C for Tr-TPA9, high the highest unoccupied molecular orbital (HOMO) energy level (−5.12 eV for Tr-TPA3 and −4.95 eV for Tr-TPA9, respectively) and good film forming property. When we employed these dendrimers as hole transport layer (HTL) in tris-(8-hydroxyquinoline) aluminum (Alq3)-emitting electroluminescence (EL) devices, the Tr-TPA9-based double-layer device exhibited the turn-on voltage of 2.5 V, the maximum luminance of about 11,058 cd m−2 and the maximum current efficiency of 4.01 cd A−1. The comparison of the properties between the EL devices with dendrimers as HTL and the EL device with 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) as HTL indicated that this series of dendrimers can be good candidates for HTM in OLEDs.

A symmetrical D-π-A-π-D organic dye molecule 2-{2,6-bis-[2-(4-diphenylamino-phenyl)-vinyl]-pyran-4-ylidene}-malononitrile (DADP) has been introduced into solution-processable organic solar cells (S-P OSCs). Detailed investigations on the relationship between its molecular structure and thermal, photophysical, electrochemical properties and electronic structure are described. The optimized bulk heterojunction solar cell based on DADP as donor and PCBM as acceptor with the configuration of ITO/PEDOT/DADP:PCBM/LiF/Al exhibits a Voc of 0.98 V, Isc of 4.16 mA/cm2, FF of 0.37, and power conversion efficiency (PCE) of 1.50% under the illumination of AM 1.5 simulated solar light (100 mW/cm2). It was noted that the PCE of the device based on DADP is almost double that of the device based on TPA-DCM-TPA, an analogue of DADP, although there is only a small difference between their molecular structures; DADP has a shorter distance between the triphenylamine (TPA) group and the 2-pyran-4-ylidenemalonitrile (PM) group ...

We have studied the crystal structures and photophysical properties of four 9,10-distyrylanthracene (DSA) derivatives. Their crystal structures exhibit nonplanar conformations due to the supramolecular interactions resulting in rigid molecules and relative tight stacking. The four DSA derivatives possess a typical aggregation-induced emission (AIE) property, i.e., they exhibit faint emission in their solutions but intense emission in their crystals as a result of the dominant nonradiative decay by free intramolecular torsion in the solution and the restricted torsional motion by supramolecular interaction in the crystal. The investigation of the relationship between the crystal structures and AIE properties of the four DSA derivatives indicates that DSA moiety is the key factor of AIE property because of the restricted intramolecular torsion between the 9,10-anthrylene core and the vinylene moiety.

A planar-diffused photovoltaic device based on Poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) has been prepared by a simple solution process, in which the PCBM organic solution was spin-coated onto the underlying MEH-PPV layer to fabricate the MEH-PPV/PCBM planar-diffused active layer. Investigation of the effects of active layer thicknesses and solvents on the performance of planar-diffused photovoltaic devices indicates that, with increasing the underlying MEH-PPV layer thickness, a gradual transition from absolutely penetrated to planar-diffused active layer structure occurs and the best power conversion efficiency is obtained for the device prepared by spin-coating a non-aromatic chloroform solution of PCBM onto the MEH-PPV layer, rather than device prepared by spin-coating the mixed solution of chloroform and chlorobenzene or aromatic chlorobenzene solution of PCBM onto MEH-PPV layer. Based on the photovoltaic performance, a structural model of planar-diffused active layer is proposed.

A simple convergent procedure has been developed for the preparation of triphenylamine dendrons containing an alkene at the center, which can be coupled in a single step to give dendrimers that contain truxene for the core without any protection–deprotection chemistry. These conjugated dendrimers exhibit similar absorption and emission behaviors in solutions and in thin films, which are indicative of the high isolation effect of well-organized three-dimensional dendrimers. They also have high fluorescence quantum yields and high glass transition temperatures, which indicate that these dendrimers are candidates for the application in OLED as light emitting materials.

Over the last few decades, the excess exploitation of our planet and degradation of environment have gone up at an alarming rate. Environmental problems, especially air and water pollution, which takes a huge number of years to recover, have become the major concern affecting the progress of human society. The overwhelming threats have driven global research and innovation in the development of advanced technology and devices toward a cleaner environment. In this context, the generation of functional one-dimensional (1-D) nanomaterials has become an area of intense interest from both academia and industry due to their unique advantages for environmental applications. Electrospinning is recognized as the most powerful technique for producing 1-D composite nanofibers via facile incorporation of active ingredients in the solutions for electrospinning or by some posttreatment process. In this review, we give an overview on the latest research progress in the fabrication and utilization of functional polymer/ceramic/carbon nanofibers generated by electrospinning for air and water purification, as well as their applications as sensors for pollutant monitoring and control. We also present the perspectives and challenges of the current electrospinning technique for environmental applications.

New types of nanowire arrangements are explored via active surface growth, where the use of Au seeds at room temperature means that the seed shape has major impacts on the subsequent nanowire growth. When Au nanorods are used as seeds, the original stripe-shape contact line with the substrate (the active surface) splits into a series of circular dots as the result of Rayleigh instability, giving coplanar nanowire bundles. The influence of a solid system by Rayleigh instability is exceptional, permitted by the dynamic active surface. The splitting is driven by the tendency to minimize the surface of the newly emerged nanowire section, whereas Rayleigh instability is responsible for overcoming the kinetic barriers. As a result, the average distance between the nanowires is only a few nanometers, much smaller than conventional lithographic methods. Conical and tubular bundles of nanowires are formed at low seed density, where the excessive growth material available for each seed leads to expansion and splitting of the active surface under the influence of both the diffusion limited growth and Rayleigh instability. Further designs of nanowire-based Au architectures demonstrate the feasibility of combining the multiple control of the system for new synthetic advances.

One may discover a stone tool by chance but it takes more than luck to make a car or cell phone. With the advance of nanoscience, the synthesis of increasingly sophisticated nanostructures demands a rational design and a systems approach. In this Review, we advocate the distinction between thermodynamically and kinetically controlled scenarios, that is, whether a product forms because it is the most stable state or because the pathway leading to it has the lowest energy barrier. Great endeavours have been made to describe the multiple concurrent processes in typical nanosynthesis phenomena, so that the mechanistic proposals in the literature are brought into a common framework for easy contrast and comparison.

A Boerdijk–Coxeter–Bernal (BCB) helix is made of linearly stacked regular tetrahedra (tetrahelix). As such, it is chiral without nontrivial translational or rotational symmetries. We demonstrate here an example of the chiral BCB structure made of totally symmetrical gold atoms, created in nanowires by direct chemical synthesis. Detailed study by high-resolution electron microscopy illustrates their elegant chiral structure and the unique one-dimensional “pseudo-periodicity”. The BCB-type atomic packing mode is proposed to be a result of the competition and compromise between the lattice and surface energy.

Amphiphilic block copolymers such as polystyrene-block-poly(acrylic acid) (PSPAA) give micelles that are known to undergo sphere-to-cylinder shape transformation. Exploiting this polymer property, core–shell nanoparticles coated in PSPAA can be “polymerized” into long chains following the chain-growth polymerization mode. This method is now extended to include a variety of different nanoparticles. A case study on the assembly process was carried out to understand the influence of the PAA block length, the surface ligand, and the size and morphology of the monomer nanoparticles. Shortening the PAA block promotes the reorganization of the amphiphilic copolymer in the micelles, which is essential for assembling large Au nanoparticles. Small Au nanoparticles can be directly “copolymerized” with empty PSPAA micelles into chains. The reaction time, acid quantity, and the [Au nanoparticles]/[PSPAA micelles] concentration ratio played important roles in controlling the sphere–cylinder–vesicle conversion of the PSPAA micelles, giving rise to different kinds of random “copolymers”. With this knowledge, a general method is then developed to synthesize homo, random, and block “copolymers”, where the basic units include small Au nanoparticles (d = 16 nm), large Au nanoparticles (d = 32 nm), Au nanorods, Te nanowires, and carbon nanotubes. Given the lack of means for assembling nanoparticles, advancing synthetic capabilities is of crucial importance. Our work provides convenient routes for combining nanoparticles into long-chain structures, facilitating rational design of complex nanostructures in the future. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version

For industry applications of nano-catalysts, the main bottlenecks are the low loading per unit support area and the slow flow rate through the support particles. By growing a dense Au nanowire forest on a loose network of glass fibers, continuous-flow catalysis can be achieved with a processing rate about 100 times that of the best literature rate.

Parallel-stacked gold nanowires (NWs) in a ring conformation are induced to coalesce, forming solid seamless rings. The axial lattice orientation of the original Au NWs is preserved in the coalesced rings (see picture; scale bars 2 nm, insets 50 nm). A zipper mechanism is proposed to reconcile the three major events in coalescing nanocrystals: ligand loss, lattice alignment, and coalescence.

Selective gas adsorption plays an important role in adsorptive separation of gases and scavenging unfavorable or hazardous gases. The use of cost-effective and environmentally friendly materials for selective gas adsorption has become one of the most pressing needs today. The development of new adsorbents is essential but difficult due to the selectivity and efficiency requirements for practical application. As potential scavengers, metal–organic frameworks (MOFs) have drawn great attention. In this review, the current progress of science and technology development of MOFs on selective gas scavenging will be highlighted. Future perspectives for exploring MOFs for practical application will also be put forward.

Food packaging has been changing from bulky and rigid form in the past to different variation of lights and plastic packagings. Regardless of the changes, the packaging must be able to uphold its original function which is to serve as food containment as well as to protect the food from the external environment. Coupled with the increasing consumer’s awareness on food waste, higher standard of living, technological developments are underway to enhance the shelf-life of packed food as well as methods to provide indications of food packaging environment. There are many different indicators for food spoilage, but two commonly found gases in food packaging are oxygen and carbon dioxide. Oxygen is the main mechanism for food spoilage, while carbon dioxide is often used in modified-atmosphere-packaging. There are also different methods of gas scavenging and/or sensing techniques based on different concepts in the literature. In this review, the focus will be on nano-materials, namely titanium dioxide, silica, zeolites and metal organic frameworks. This review is structured in a manner to highlight how each material can be used in both gas scavenging and/or indicators applications. The last part of the review focuses on the approach and some key considerations when integrating nano-materials into the plastic film.

We show that embedding of a surface ligand can dramatically affect the metal–metal interfacial energy, making it possible to create nanostructures in defiance of traditional wisdom. Despite matching Au–Ag lattices, Au–Ag hybrid NPs can be continuously tuned from concentric core–shell, eccentric core–shell, acorn, to dimer structures. This method can be extended to tune even Au–Au and Ag–Ag interfaces.

is not available in fulltext. Published version

We demonstrate a facile colloidal method for synthesizing Janus nanoparticles, whose eccentric polymer shells are exploited to fabricate eccentric bimetallic cores.

Three functionalized 9,10-distyrylanthracene (DSA) derivatives, namely, 9,10-bis(4-hydroxystyryl)anthracene (2), 9,10-bis{4-[2-(diethylamino)ethoxy]styryl}anthracene (4), and 9,10-bis{4-[2-(N,N,N-triethylammonium)ethoxy]styryl}anthracene dibromide (5), were synthesized and their fluorescence properties were investigated. The three DSA derivatives possess a typical aggregation-induced emission (AIE) property (i.e., they are nonluminescent in dilute solutions but are efficiently fluorescent as induced by molecular aggregation). Different AIE properties were tuned through molecular structure control. Dye 2 is a phenol-moiety-containing compound, which shows aggregation at pH values smaller than 10, resulting in a high fluorescence intensity. Thus, dye 2 has a pK(a) of 9.94. 4 is an amine-containing compound that starts to aggregate at slightly basic conditions, resulting in a pK(a) of 6.90. Dye 5 is an ammonium-salt-containing compound. Because it is very soluble in water, this compound has no AIE phenomenon but can interact strongly with protein or DNA to amplify its emission. Therefore, 5 is a fluorescent turn "on" biological probe for protein and DNA detection and it is also selective, which works for native BSA and ct DNA but not their denatured forms. Therefore, we not only developed a few new compounds showing the AIE phenomena but also controlled the AIE through environmental stimulation and demonstrated that the new AIE molecules are suitable for pH and biomacromolecule sensing.

Over the last 50 years, remarkable improvements in mechanical and barrier properties of polymer composites have been realized. Their improved properties have been widely studied and employed for food packaging to keep food fresh, clean and suitable for consumption over sufficiently long storage period. In this paper, the current progress of science and technology development of polymer composites for intelligent food packaging will be highlighted. Future directions and perspectives for exploring polymer composites for intelligent food packaging to reveal freshness and quality of food packaged will also be put forward.

Three DSA (9,10-distyrylanthracene) derivatives, 9,10-bis(3,5-dimethylstyryl)anthracene (TMDSA), 9,10-bis(3,5-bis(trifluoromethyl)styryl)anthracene (TFMDSA) and 9,10-bis(3,5-difluorostyryl)anthracene (TFDSA) were synthesized and characterized. Here we report their crystal structures, structure-property relationships, and nanowire fabrication. The crystal structures indicate that the three compounds with varying substituents exhibit different molecular packing modes. In particular, introducing a F substituent to generate weak intermolecular C–H⋯F interactions benefits the formation of intermolecular π–π stacking in the TFMDSA and TFDSA crystals. Photophysical investigations and crystal structure analysis indicate that inhibition of vibrational relaxation in the aggregate state should be the origin for the high fluorescence and blueshift in crystals of our materials. By controlling the experimental conditions, TFDSA could easily achieve perfect regular 1D nanowires, in which the weak intermolecular C–H⋯F interaction together with effective π–π interaction play a significant role. High quantum efficiency (75% for TFDSA) and regular 1D nanowires suggest that this kind of material may have potential applications in optoelectronic device applications.

Conjugated oligocarbazoles with a 9,10-divinylanthracene core have been synthesized, and exhibit the transition from aggregation-induced emission (AIE) to aggregation-induced emission enhancement (AIEE) behaviour with extending conjugation length; self-assembly of the Cz4 molecule affords nanorings with high fluorescent efficiency.

Binary nanoassembly was realized by mixing gold@polyaniline nanoparticles with diblock copolymers in the DMF/H(2)O system and the products present a controlled transformation from symmetrical shells into spatially distributed petal-like polymer shells on gold cores.

Composite vesicles with embedded Au nanoparticles are directly prepared from thiophene and Au nanoparticles in aqueous solution in the presence of H2O2 and a catalytic amount of FeCl3. The number, shape, and structure of the vesicles thereof can be readily controlled. We provide evidence that these vesicles contain an aqueous phase in their cavities. The direct synthesis offers an economical route to nanoscale containers and also a rare example for the minimal conditions of vesicle formation.

Three π-conjugated dendrimers (Ph-G0, Ph-G1 and Ph-G2) bearing triphenylamine moieties have been synthesized through a convergent synthetic strategy without any protection–deprotection chemistry. The linear photophysical properties, two-photon absorption (TPA), and optical limiting behavior of the dendrimers were investigated in solution at room temperature. Linear absorption and emission spectra revealed a bathochromic shift and decreased fluorescence quantum yields with increasing dendrimer generation. A strong cooperative effect in the TPA absorption of these dendrimers was observed. The TPA cross-sections increase gradually with the proportion of triphenylamine units and the maximum value of the TPA cross-section can reach 5690 GM for Ph-G2. These triphenylamine-based dendrimers exhibited efficient two-photon optical limiting under femtosecond excitation.