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A high flow rate, low-pressure microfluidic photocatalytic microreactor was created and demonstrated here.

Stormwater runoff management and treatment are significant topics for designing a sustainable city. Therefore, photocatalytic, permeable, and removable concrete is a promising solution to reduce pollution through leaching with permeable and scalable road. The objective of this work was to develop cost-effective and greener photocatalytic concretes that can be easily scaled-up, and to demonstrate their photocatalytic activities. To achieve this, seedless hydrothermal ZnO nanostructures (NSs) in 2 h were employed to functionalize a concrete surface by a soft functionalization process, avoiding overconsumption of energy and chemical products. In this work, two different concretes were studied and used for the degradation of organic dye in water. The results demonstrated the universality of the proposed functionalization process by showing similar gap values, ZnO NSs morphologies, and XRD pattern, compared to the concrete functionalized by the traditional two-step hydrothermal synthesis. The XRD results certified the presence of the ZnO Würtzite phase on the concrete surface. The synthesis feasibility was attributed to the basic pH and O− groups’ presence in concrete. Then, their photocatalytic efficiency was proved for organic dye removal in water. An almost total degradation was recorded after 5 h under artificial solar light, even after several uses, demonstrating a similar efficiency to the photocatalytic concrete functionalized by the traditional two-step synthesis.

International audience; We report on a new class of metamaterials, which consists of meta-foams, optimized for high performance in enhanced solar steam generation. The design of these meta-foams involves precise dimensional control of a periodic two-dimensional micro-pore array. Proof-of-concept of meta-foams efficiency is demonstrated using two fabrication technologies. The first one involves microscale plasma etching onto a nanostructured black silicon substrate. As an alternative low-cost technique, we also use 3D printing of a graphene-containing polymer material. The experimental validation shows that the best evaporation rate reaches 1.34 kg/(h·m2) under 1 sun illumination, in open-air conditions under normal temperature and relative humidity conditions of 20 °C and 58%, an unmatched value so far under similar conditions, while the theoretical limit is estimated at 1.5 kg/(h·m2). This corresponding to a 89% conversion efficiency. Experimental data concur well with the predicted performance obtained by numerical simulations. The proposed model simultaneously accounts for both heat and mass transfer, including photothermal conversion and water phase change, to guide the optimization towards the maximization of the evaporation rate, an important figure of merit in many applications, including solar heat harvesting and solar water purification.

Co-integration of nanomaterials into microdevices poses several technological challenges and presents numerous scientific opportunities that have been addressed in this paper by integrating zinc oxide nanowires (ZnO-NWs) into a microfluidic chamber. In addition to the applications of these combined materials, this work focuses on the study of the growth dynamics and uniformity of nanomaterials in a tiny microfluidic reactor environment. A unique experimental platform was built through the integration of a noninvasive optical characterization technique with the microfluidic reactor. This platform allowed the unprecedented demonstration of time-resolved and spatially resolved monitoring of the in situ growth of NWs, in which the chemicals were continuously fed into the microfluidic reactor. The platform was also used to assess the uniformity of NWs grown quickly in a 10-mm-wide microchamber, which was intentionally chosen to be 20 times wider than those used in previous attempts because it can accommodate applications requiring a large surface of interaction while still taking advantage of submillimeter height. Further observations included the effects of varying the flow rate on the NW diameter and length in addition to a synergetic effect of continuous renewal of the growth solution and the confined environment of the chemical reaction.

In an effort to scale-up nanomaterial growth over large surface areas, we aim to effectively study the structural non-homogeneities within the arrays of zinc oxide nanowires (ZnO-NWs). The assessment of the lateral gradient of the nanowires' characteristics is presented including their height and surface density. To this end, spectroscopic ellipsometry and the rather recently reported technique of spectral domain attenuated reflectometry are used as two fast, simple and non-invasive characterization methods with further capabilities of scanning over the sample surface. Simple models are proposed by considering ZnO-NWs as the equivalent of thin stratified layers based on the effective medium approach. The methodology not only reveals the presence of gradients, but also enables quantitative analysis for all the samples grown using the hydrothermal method with different growth times ranging from 0.5 h up to 4 h. The gradients are confirmed using scanning electron microscopy (SEM) observations taken as a reference. The results also suggest that the sample orientation during the growth influences the NW growth besides the other parameters already known to affect the growth mechanisms.

Structured and functional microfluidic channels make microfluidic chips and devices more powerful in a variety of applications. In situ decoration of nanostructures on the channel wall is a low-cos...

To shift towards the greener city, photocatalytic urban infrastructures have emerged as a promising solution for pollution remediation. To reach this goal, the large bandgap semiconductors, such as nontoxic Zinc Oxide (ZnO), already proved their excellent photocatalytic performances. However, integrating and developing cost-effective and greener photocatalytic surfaces with an easily scaled-up synthesis method and without energy and chemical product overconsumption is still challenging. Therefore, this work proposes to develop a depolluting Zinc (Zn) roof covered by ZnO nanostructures (NSs) using a one-step seedless hydrothermal growth method in 2 h. The feasibility of this synthesis was firstly studied on small areas of Zn (1.25 cm2) before being scaled up to medium-sized areas (25 cm2). The efficiency of this functionalization route for ZnO NSs grown without seed layer was attributed to the presence of Zn2+ sites and the native oxide film on the Zn surface. Their photocatalytic efficiency was demonstrated by removing in less than 3 h the Methylene Blue (MB) and Acid Red 14 (AR14) in both DI water and rainwater under UV-light. Promising results were also recorded under solar light. Therefore, the photocatalytic Zn roof functionalized by ZnO NSs is a promising route for rainwater purification by photocatalysis.

Atmospheric pollution is a major issue affecting environment and health. Therefore, semi-conductor-nanoparticles-based photocatalytic infrastructures appeared as a promising solution to improve urban air quality due to their abilities to mineralize toxic organic compounds. To avoid the direct use of free nanoparticles, as nanomaterials are suspected to be carcinogenic, this work intends to develop civil engineering materials functionalized by direct growth of ZnO nanostructures as a more environmentally friendly and biocompatible approach to reduce the air pollution. By scaling-up an innovative and low-cost hydrothermal direct growth synthesis, a few square meters paved with tiling and bitumen road were easily produced in order to evaluate their photocatalytic activity at large scale under solar lamp in a climatic chamber (Sense-City, 3200 m3) to reflect real atmospheric air purification situations. Observations provide insights into their ability to simultaneously remove various pollutants from a real car exhaust (O3, COX, NOX, VOCs) and their durability, as well as understandings of the weather conditions impact on the photocatalytic degradation of these pollutants and of the relationships between pollutants trend evolution. This study also seems to prove that, when exposed to sunlight, bitumen roads are responsible of pollutants emission and causes modifications in the Chapman cycle.

In this study, iron oxide cocatalysts were deposited on the surface of ZnO nanostructures by a simple “drop, evaporation, calcination” method. Different deposition concentrations were studied, allowing to extend the photocatalyst absorption spectral range from UV to visible light, improving the photocatalytic efficiency under natural sunlight. An optimal deposition concentration of 0.06% molar percentage of iron against zinc led to improve by 11% the Methyl Orange (MO) photocatalytic degradation after 5 h under natural sunlight. No iron leaching was detected by ICP-MS analysis after the water purification by photocatalysis. By studying the lifetime stability of the optimal sample under a powerful UV light source, no losses of photocatalytic efficiency were recorded after several degradation cycles. Nevertheless, under this powerful light source, photocorrosion damages were observed with two antagonistic effects: (1) no photocorrosion effect for the ZnO regions covered by iron oxide and (2) ZnO photocorrosion and an acceleration of the dissolution of the ZnO nanostructures in uncovered regions. Thus, we assume the electron/hole delocalisation, which is responsible of the photocatalytic activity improvement, is also the reason justifying the ZnO photocorrosion acceleration of uncovered part. The photocorrosion phenomena was observed only under the powerful UV light source, not under natural sunlight.

Photocatalysis is proven to be the most efficient and environmentally friendly method for the degradation of organic pollutants in water purification. To meet the requirement of large-scale water treatment, there are two important points: One is the lifetime and chemical stability of the photocatalyst material, especially in the complex and harsh aqueous conditions. The other is the ease of synthesis of such photocatalysts with specific nano-morphology. In this work, two common photocatalyst materials, zinc oxide (ZnO) and titanium dioxide (TiO2), are selected to form more sustainable photocatalysts with high chemical stability. This involves the combination of both TiO2 and ZnO in a two-step simple synthesis method. It appears advantageous to exploit the conformal deposition of atomic layer deposition (ALD) to achieve nanometer-thick TiO2 coating on ZnO nanowires (NWs) with a high aspect ratio, which are firmly anchored to a substrate and exhibit a large specific surface area. The high chemical stability of the ALD TiO2 coating has been investigated in detail and proven to be effective under both strong acid and strong alkaline aqueous solutions. In addition, photocatalysis experiments with organic dyes show that via this simple two-step synthesis method, the produced ZnO/TiO2 tandem photocatalysts does indeed exhibit improved chemical stability in a harsh environment, while allowing efficient photodegradation.

ZnO nanowire (NW) arrays were successfully grown on pre-seeded indium Tin oxide (ITO)-coated glass substrate using hydrothermal synthesis. Herein, the effects of ZnO seed layer density on the performance of ZnO NWs were investigated in details. The orientation and the dimension of ZnO NWs were found to depend on seeded substrate density as shown by scanning electron microscopy (SEM) micrographs which revealed that the typical morphology with the most uniform size can be obtained. From the X-ray diffraction (XRD) measurement, it can be seen that hexagonal c -axis oriented NWs were grown. The resonant Raman scattering was also investigated in details. It confirmed the wurtzite structure of the NW arrays and expected for good optical properties. The optical band gaps of synthesized ZnO NWs were found to decrease comparing to bulk ZnO and as function of seed layer. The photoluminescence (PL) spectra at room temperature have shown strong UV excitonic emission and weak deep-level emissions which reveal that the as-grown NW arrays have good optical properties with limited deep-level defects.

Structures of the two-dimensional atomic nuclei on ZnO (0001)-Zn and ( 000 1 ¯ )-O polar surfaces were studied by first principles density functional theory. The polarity-dependent nucleation dynamics was investigated by simulating two-dimensional (2D) nuclei consisting of 1-8 ZnO monomers on both polar surfaces. According to total energy calculations, average binding energy per ZnO monomer of the surface nuclei was analyzed to investigate if the nucleation and growth will proceed reasonably in physics. We found nucleation on (0001)-Zn surface was easier than that on ( 000 1 ¯ )-O surface. By using atomistic thermodynamics analysis, we calculated the Gibbs free energy of formation of these nuclei and made a comparison between the two polar surfaces. On (0001)-Zn surface, the critical Gibbs free energy of formation is much lower than that on ( 000 1 ¯ )-O surface under the same supersaturation, which leads to a much larger ZnO growth rate and rougher morphology, in accordance with experimental results. In addition, energetic analysis of nucleation at real thermodynamic conditions was achieved by introducing the temperature- and pressure-dependent chemical potentials of ZnO precursors.

We present online monitoring of nanowires growth within a microfluidic chamber. This achievement is introduced for the first time thanks to simple and noninvasive real-time optical method, where the results were confirmed later by scanning electron microscopy (SEM). Nanowire length and diameter could be monitored versus growth time thanks to remote optical measurement. In this work, we also report kinetics study and online monitoring of in-situ growth of Zinc-Oxide nanowires (ZnO-NWs) within a microfluidic chamber showing the impact of different growth parameters on the NWs characteristics. It appeared that growth within a microfluidic reactor provides 4-times faster growth rate compared to macroscopic growth due to the confined environment of the chemical reaction. It also appears that varying the flow rate has more influence on the NWs diameter rather than the NWs length.

Environmental chemical pollution in water and air is induced by increasing human activity such as industry, transportation, intensive agriculture and growing urbanization. These global environmental issues are now listed among the sustainable development goals (SDGs), hence the increasing scientific and technological interests on water depollution and air purification, besides the needs for selective measurement of pollutants. ZnO nanostructures have been widely studied as a very promising material to rise such challenge of depollution/purification. Online monitoring of air purification is presented, where purification is made by photo-catalysis using ZnO nanowires, while monitoring is achieved by a MEMS-FTIR spectrometer operating in the mid-infrared MIR spectral range. The experiment was conducted on toluene, acetone as well as tobacco smoke. The whole system appears as an efficient and cheap solution for indoor and outdoor purification and monitoring of air.

Photocatalysis is one of the most promising processes for treating air and water pollution. Innovative civil engineering materials for environmental depollution by photocatalysis have already been synthesized by incorporating TiO2 or ZnO nanoparticles in cement. This method suffers from two flaws: first, most of the NPs are incorporated into the cement and useless for photocatalysis; second, rain and wind could spread the potentially carcinogenic nanoparticles from the cement surface into nature. Thus, we propose the efficient synthesis of nontoxic and biocompatible ZnO nanostructures solely onto the surface of commercially available concrete and tiling pavements by a low-cost and low-temperature hydrothermal method. Our samples exhibited enhanced photocatalytic activity for degrading organic dyes in aqueous media, and dye molecules are commonly used in the pharmaceutical, food, and textile industries. Durability studies showed no loss of efficiency after four photocatalysis experiments. Such supported structures, which are easy to implement onto the varying surfaces of commercially available materials, are promising for integration into civil engineering surfaces for environmental depollution in our daily life., Photocatalysis: Synthesizing safe zinc oxide nanowires for civil engineering materials An easy, low-cost method has been developed for successfully synthesizing zinc oxide (ZnO) nanostructures onto commercially available materials for environmentally safe use in civil engineering. Photocatalysis is the process whereby light accelerates a chemical reaction, and it holds promise as a means of tackling pollution caused by civil engineering materials. Previous efforts to produce such materials by incorporating ZnO and titanium oxide (TiO2) nanoparticles for photocatalysis have suffered drawbacks, notably the nanoparticles being incorporated within the cement and thus useless for photocatalysis. A team headed by Yamin Leprince-Wang at Université Paris-Est, France developed a low-cost, low-temperature hydrothermal method for efficiently synthesizing nontoxic, biocompatible ZnO nanowires solely onto the surface of commercially available concrete, which allowed for excellent photocatalytic efficiency. The team believes that its method has good potential for environmentally safe application on road surfaces.

We propose spectral domain attenuated reflectometry (SDAR) for fast characterization of nanomaterial growth. The method is demonstrated here for zinc oxide (ZnO) nanowires (NWs) which are grown vertically in random forest fashion showing that it is not limited to well-ordered NWs. We show how SDAR can provide, on the basis of a single measured spectrum, simultaneous information on nanowire length, nanowire density (through nanowire/air filling ratio), and crystalline quality (through band gap). The robustness of the proposed method is assessed first through comparison with information obtained from SEM and XRD taken as reference. In SDAR, the process for fast extraction of NW thickness and filling ratio values makes use of the interference pattern contrast and the spectral periodicity in the reflection response which involve a best fit of the measured spectra with simple theoretical modeling based on the effective medium approach, achieved with a mean square error down to 0.1%. The results also suggest the existence of either 2 or 3 layers of different effective refractive index, hence providing insight on possible growth mechanisms.

Air pollution is used to refer to the release of pollutants into the air, where these pollutants are harmful to the human health and our planet. The main source of these pollutants comes from energy production and consumption that release Volatile Organic Compounds (VOCs) such as BTEX and Aldehydes group. Real time monitoring of these VOCs in factories, stations, homes and in the street is important for analysis of the pollution sources fingerprint and for alerting, when exceeding the harmful limits. In this work we report the use of a MEMS FTIR spectrometer in the mid-infrared for this purpose. The spectrometer works in the wavelength range of 1.6 μm - 4.9 μm with a resolution down to 33 cm-1. This covers the absorption spectrum of water vapour, BTEX, Aldehydes and CO2 around 2.65 μm, 3.27 μm, 3.6 μm and 4.3 μm, respectively. The spectra of Toluene with different concentrations are measured, using a multipass gas cell with a physical length of 50 cm and an optical path length of 20 m, showing excellent sensor linearity. The minimum concentration measured is 350 ppb limited by the interference of the side lobes of the strong absorption of water vapour, which can be overcome in the future by humidity compensation. The SNR is measured and found to be 5000:1, corresponding to a detection limit of about 90 ppb. The achieved results open the door for a compact and low-cost solution targeting air pollution monitoring.

International audience

In this work, we propose a simple and time-saving method for the characterization of the ZnO-NWs. The method is based on the measurement of the spectral reflection of the ZnO-NWs in the UV-VIS-NIR ranges. Then the ZnO-NWs effective refractive index, and subsequently the density, and the length are obtained making use of the interference pattern contrast and periodicity in the reflection response versus wavelength. The extracted NWs length and density using the proposed method show good agreement with the SEM results. This characterization method opens the door for easy and cheap monitoring of the growth within microfluidic environment.

In this paper, different contents of molybdenum oxide/tungsten oxide (MoO3/WO3) composite nanostructures were synthesized by hydrothermal method. Field emission scanning electron microscopy images revealed that the morphologies of WO3 nanostructures were significantly influenced by the Mo amount. Furthermore, the introduction strategy of MoO3 into WO3 could effectively improve the gas sensing properties. Especially, the sensor based on the 4 mol% MoO3/WO3 composite nanostructures exhibited enhanced gas sensing performance, giving a low limit of detection (500 ppb). It shows high responses of 28.5 and 18.2–100 ppm ethanol and acetone at the operating temperature of 320 °C, which were about 2.3 and 1.7 times higher than those of the pure WO3, respectively. The enhanced sensing properties of MoO3/WO3 gas sensor can be attributed to the addition of MoO3, which has been discussed in relation to the gas sensing mechanism.

Two types of ZnO nanostructure have been fabricated to make a comparative study on their gas sensing performance: the conventional ZnO nanowire arrays were synthesized by hydrothermal method and the hierarchical ZnO nanowires/nanofibers nanostructures were prepared through a combination of the hydrothermal and electrospinning methods. Field emission scanning electron microscopy study showed a quiet homogeneous morphology both for both nanostructures. Three kinds of commonly used gases, such as ethanol, acetone and ammonia were chosen for ZnO nanostructure gas sensing property study. The UV-Visible spectroscopy measurements showed a higher detection sensitivity of ZnO NWs for ammonia compared to ethanol and acetone, and an enhanced sensing performance for the hierarchical nano- structure, which has a higher surface to volume ratio. On the other hand, the enhancement was more obviously in the case of ethanol sensing. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A study of the ZnO nanowire array photocatalysis performance has been carried out under UV radiation for the degradation of the toxic organic compounds such as methylene blue (MB), methyl orange (MO), and acid red 14 (AR14) dyes, which are commonly used in textile and pharmaceutics industries. UV–Vis spectrometry has been used to follow the dye degradation characterization. The degradation mechanism has been proposed for each dye, which will give a reasonable explanation about different degradation degree under same experimental conditions. MB and AR14 showed a better degradation performance than MO.

Developing and designing smart civil engineering materials for environmental depollution in our daily life is a major issue. ZnO nanostructures implemented onto civil engineering material surfaces by low cost hydrothermal growth could be one of the most promising solutions, and already showed a good water purification efficiency by photocatalysis under UV light. Nevertheless, there are two main factors to work out in order to simplify and intensify the photocatalyst production on engineering materials. The first one is the reduction of the growth time. The second one is the use of sunlight, which is the most abundant, clean, and renewable light source available. However, reducing the growth time might have an impact on the photocatalytic efficiency due to the surface/volume ratio modification. In this work, a short and efficient hydrothermal synthesis (2 h or 1 h 30 min vs 4 h) was used to grow ZnO nanostructures directly on non-conventional substrates such as tiling and concrete, demonstrating an excellent photocatalytic activity for organic pollutant degradation in water under natural sunlight, even during cloudy days. Decreasing the growth time showed no significant influence on tiling samples and even increased their photocatalytic efficiency until the optimal value obtained with a growth time of 2 h. A strong impact of the shorter growth time was observed on concrete samples, as reducing the growth time leads to complex ZnO nanosheet structures with a lower gap value (3.11 eV for 1 h 30 min against 3.17 eV for 4 h) due to a possible influence of the surface pH value and the complex chemical composition of concrete.

Lipid droplets have gained strong interest in recent years to comprehend how they function and coordinate with other parts of the cell. However, it remains challenging to study the regulation of lipid droplets in live preadipocytes using conventional microscopic techniques. In this paper, we study the effects of fatty acid stimulation and cell starvation on lipid droplets using optical diffraction tomography and Raman spectroscopy by measuring size, refractive index, volume, dry mass and degree of unsaturation. The increase of fatty acids causes an increase in the number and dry mass of lipid droplets. During starvation, the number of lipid droplets increases drastically, which are released to mitochondria to release energy. Studying lipid droplets under different chemical stimulations could help us understand the regulation of lipid droplets for metabolic disorders, such as obesity and diabetes. NRF (Natl Research Foundation, S’pore) Published version

A chiral metasurface, which obtains chirality through a subwavelength artificial structure, is essential for realizing asymmetric transmission in the application of enantioselective sensing, spin-dependent light emission, and other polarization control systems. Here, we studied a split Archimedean spiral metasurface, which can control the propagating wave from asymmetric transmission to symmetric transmission for linear polarized light. As a proof of concept, a dual-band asymmetric transmission is demonstrated in the GHz region using the coupling of the split spiral structures. The maximum asymmetric transmission parameter reaches 53%. By manipulating the height of the split spiral structures using microfluidic technology, a broadband asymmetric transmission is obtained with the bandwidth of 25.9%. Meanwhile, the asymmetric transmission can be controlled from 50% to 0%, enabling the propagation wave from asymmetric transmission to symmetric transmission. Furthermore, the asymmetric transmission is maintained when the metasurface is bent into different curvatures, promising high potential applications for optical isolation, one-way glass, and optical interconnects. NRF (Natl Research Foundation, S’pore) Published version

This paper reports a paper-based electrostatic kinetic energy harvester (e-KEH) implementing multilayered electret films based on electrospun nanofibrous material. It is the first time that a fully flexible electret-based e-KEH is reported. The proposed electret, PVDF-PTFD nanofibrous covered by Parylene C, has a faster stabilization of surface potential than a planar thin film of Parylene C, and a higher stability of charge storage. With a maximum force of 0.5 N and a 3-layer electret, the device capacitance increases from 25 pF to 100 pF during a pressing operation. Working with the optimal resistive load of 16 MΩ, the device pressed manually delivers a peak instantaneous power up to 45.6 μW and an average energy of 54 nJ/stroke, corresponding to a peak instantaneous power density of 7.3 μWcm-2 and an average energy density of 8.6 nJcm-2/stroke. Within 450 manual strokes, a 10-nF capacitor is charged up to 8.5 V by the prototype through a full-wave diode bridge. On a 1-μF capacitor, the energy delivery of 9.9 nJ/stroke has been obtained with a 10 Hz pressing movement excited by a vibrator with a maximum force of 0.5 N.

This paper reports fast and efficient chemical decontamination of water within a tree-branched centimeter-scale microfluidic reactor. The microreactor integrates Zinc oxide nanowires (ZnO NWs) in situ grown acting as an efficient photocatalytic nanomaterial layer. Direct growth of ZnO NWs within the microfluidic chamber brings this photocatalytic medium at the very close vicinity of the water flow path, hence minimizing the required interaction time to produce efficient purification performance. We demonstrate a degradation efficiency of 95% in

In this paper, electrospun piezoelectric PVDF-TrFE nanofibers were used for the fabrication of two types of flexible nanogenerator (NG) devices based on the direct piezoelectric effect, allowing the conversion of mechanical energy into electrical energy. The first one is composed of quite well aligned thin film nanofibers of about 35 μm and the second one is composed of random nanofibers of about 50 μm. The influence of the applied stress and strain rate on the output for both types of NG was studied. It is shown that the pulse peaks generated by NG increase with the applied mechanical strain frequency, the generated output is also proportional to the applied stress amplitude. The first NG loaded in bending mode can generate a maximum voltage of 270 mV. By connecting two devices in series/parallel, the voltage/current value could be multiplied by two. The second NG which was biased in compression mode using a shaker controlled by a force sensor, can generate a potential of about 7 V under 3.6 N applied force.

The impact on environment and on health of different pollutants, especially chemical pollutants, is becoming critical due to their drastic consequences on our main vital resource: water. In recent years, extensive efforts of fundamental research and developing practical processes have been devoted to the polluted water treatment. The semiconductor-based photocatalytic process has shown a great potential as an environmental-friendly and sustainable treatment technology due to its low-cost, and its ability to decompose the wide spectrum of contaminants in wastewater at room temperature without residual deposits requiring further post-treatment [1,2]. With high surface/volume ratio, the nanostructured semiconductor shows enhanced photocatalytic efficiency leading to very promising advances in drinking water and wastewater treatment [3,4]. Among the photocatalytic materials, nanostructured ZnO is a promising candidate for its easy-controllable synthesis, its chemical and thermal stability. On the other hand, microfluidic systems can overcome the main limit of the mass transfer during the photo-degradation process of polluted water due to the shorter diffusion lengths within microscale chambers [5]. In this work, we present a high efficiency microfluidic system decorated inside by ZnO nanostructure as a micro-reactor for threes dyes (MB, MO & AR14) as well as for VOCs-polluted water purification. ZnO nanowire array (NWA) samples have been prepared using two-step hydrothermal method as descripted in our previous work [6]. The SEM images show a quite homogenous NWA with the c-axis preferential growth direction of Wurtzite structure according to the X-ray diffractogram (Fig.1). Fig.2 shows the photodegradation effect of three dyes, it is worth noting that the degradation time is quite long in static mode: after ~3h UV irradiation, the degradation rate (X = (A0-A/A0) *100%) reach 86%, 49% and 93% for MB, MO & AR14 respectively. However, by using the micro-reactor with integrated ZnO NWA (Fig. 3), the same degradation efficiency was reached after only 6-7 min photocatalysis process (Fig. 4). In order to confirm the photocatalysis efficiency of the ZnO-based microfluidics system, an even smaller micro-reactor including a micro-pillar array has been realized. This micro-reactor also co-integrates in-situ grown ZnO nanostructures. The same initial concentration dye-polluted water needs only one-pass (with 250 µL/min flow-rate) to reach quasi total degradation (not shown in the figure). This microfluidic system has also been used to test the VOCs-polluted water purification efficiency. The contaminated water sample contains mixture of six VOC pollutants: Benzene, Toluene, Ethylbenzene and m-p-o Xylenes (BTEX) diluted in water at 10 ppm concentration of each. Fig 6 shows superimposition of two chromatograms before and after one-pass degradation (with 50 µL/min flow-rate). This enables in a selective manner to prove that all VOCs have been dropped below the threshold concentration level of 1 ppm of the maximum allowed contamination level.

Electromagnetic (EM) absorption plays a foremost important role in the area of energy harvesting, stealth technology, interference shielding and biological imaging etc. Perfect metamaterial/metasurface absorber, which obtains near-unity EM absorption through subwavelength artificial structure, usually suffers from narrow bandwidth. Here, for the first time, we demonstrate a curved water-based metasurface which functions as an active ultra-broadband absorbing material working across the entire Ku, K and Ka bands. Distinct from conventional metallic metamaterial/metasurface, the proposed water-based metasurface acquires broadband absorption property from the dielectric Mie resonance and periodic grating effect, which exhibits an experimental absorptivity of ∼99% and an absorption bandwidth (absorptivity higher than 90%) that covers 71.4% of the central frequency. Furthermore, near-unity absorption is maintained when the soft metasurface is bent into different curvatures, promoting its potential applications on non-planar circumstances.

This paper presents a new optofluidic detection system to measure the absolute refractive index map of host cells. This new system: cell refractive index tomography, can measure the absolute refractive index map of host cells. During virus infection, cell morphology and the intracellular contents of the host cells are changed. Such changes can be monitored by detecting the refractive index variation. By monitoring of the cell’s refractive index, the detection of virus infection in real-time and label-free is determined.

The impact on environment and on health of different pollutants, especially chemical pollutants, is becoming critical due to their drastic consequences on our main vital resource: water. In recent years, extensive efforts of fundamental research and developing practical processes have been devoted to the polluted water treatment. The semiconductor based photocatalytic process has shown a great potential as an environmental friendly and sustainable treatment technology due to its low-cost, and its ability to decompose the wide spectrum of contaminants in wastewater at room temperature without residual deposits that may require further post-treatment. With high surface/volume ratio, the nanostructured semiconductor shows enhanced photocatalytic efficiency in advancing water and wastewater treatment. Among the photocatalytic materials, ZnO nanostructure is a promising candidate for their easy-controllable synthesis, chemical and thermal stability. On the other hand, its further integration in a microfluidic system can overcome the main limitation of low speed mass transfer during the photo-degradation process of polluted water due to the shorter diffusion length within confined micro-chambers. Here we show a high efficiency microfluidic system decorated inside by ZnO nanostructures leading to a high throughput micro-reactor for water purification.

In this work we report, a novel Fabry-Perot architecture and its implementation on silicon leading to an ultra-wideband spectral range, where the latter is not limited to the infrared range, but extended below 1100 nm and even to the visible range. The microcavity is constructed of two flat slotted mirrors. The microcavity is fabricated using deep reactive ion etching (DRIE) of silicon wafer. The structure is metalized with Aluminum to improve the mirrors reflectivity, while the mirror is partially transmitting; thanks to the slots in the mirrors. The characterization is carried out using tunable laser sources (TLS) around 1575 nm and 914 nm. The measured free spectral range (FSR) is 6.7 nm around 1575 nm and 2.2 nm around 914 nm. Two microcavities are characterized having 2-pm and 4-pm slot widths, and their quality factor is about 1300 and 2000, respectively at 1575 nm. The quality factor is 2555 for the 2 pm slotted mirrors structure at 914 nm demonstrating the operation below 1100 nm. The reported results open the door for MEMS microcavity operating below 1100 nm, which is a range of high interest for biomedical and food spectroscopy applications.

Terahertz metasurface absorption materials, which absorb terahertz wave through subwavelength artificial structures, play a key role in terahertz wave shielding and stealth technology, etc. However, most of the metasurface absorption materials in terahertz suffer from limited tuning range and narrow incident angle characteristics. Here, we demonstrate a liquid-metal-based metasurface through microfluidic technology, which functions as a terahertz absorption material with broadband tunability and wide-angle features. The proposed terahertz metasurface absorption material exhibits an experimental tuning range from 0.246 THz to 0.415 THz (the tuning range of central frequency reaches 51.1%), and the tuning range maintains at high level with wide-angle response up to 60°. NRF (Natl Research Foundation, S’pore) Published version

This paper presents a biophysical method to characterize single bacterium in water by using an on-chip optofluidic immersion refractometer. Water safety is a major factor in the well-being of people, but the presence of bacteria such as Escherichia coli (E. coli), bacillus subtilis, Shigella flexneri and vibrio cholera in drinking water can lead to infectious diseases such as typhoid fever. Hence, it is crucial to detect and identify bacteria to prevent bacterial outbreaks. In this paper, an optofluidic immersion refractometer is developed to measure three biophysical parameters, i.e. size, shape and refractive index. The refractive index of a single bacterium is measured in high sensitivity of 0.005 RIU. This system is an innovative method to allow on-site real-time detection of single bacterium in water. It significantly reduces the amount of detection time and do not require trained personnel or additional chemical and biological reagents. © 2014 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of Eurosensors 2014.

In this paper, for the first time, an on-chip optofluidic imaging system is innovated to measure the biophysical signatures of single waterborne bacteria, including both their refractive indices and morphologies (size and shape), based on immersion refractometry. The key features of the proposed optofluidic imaging platform include (1) multiple sites for single-bacterium trapping, which enable parallel measurements to achieve higher throughput, and (2) a chaotic micromixer, which enables efficient refractive index variation of the surrounding medium. In the experiments, the distinctive refractive index of Echerichia coli, Shigella flexneri and Vibrio cholera are measured with a high precision of 5 × 10(-3) RIU. The developed optofluidic imaging system has high potential not only for building up a database of biophysical signatures of waterborne bacteria, but also for developing single-bacterium detection in treated water that is in real-time, label-free and low cost.