UV Light Source Research Articles

NaFeS2 as a new photocatalytic material for the degradation of industrial dyes

A new photocatalytic material sodium iron disulfide (NaFeS2) has been synthesized via a hydrothermal method for the degradation of methylene blue (MB) and indigo carmine (IC). This material has been subjected to various analytical, electrochemical and photocatalytic studies to understand its morphology, crystallinity, band gap, oxidation-reduction potential and ability to catalyse the rate of dye degradation. The material exists as nanorods with a thickness of 30–100 nm and a monoclinic phase with an average crystallite size of 25–30 nm. The energy bandgap of the prepared photocatalyst has been calculated using the Kubelka-Munk function and is found to be 2.01 eV. Using a UV light source, the photocatalytic activity of NaFeS2 has been carried out, where the time of irradiation determined the ability of the catalyst to degrade the dye under investigation. With a degradation efficiency of 97% in 105 min for MB and 99% in 45 min for IC, NaFeS2 appears as an excellent photocatalytic material. The electrochemical studies also act as a testament for NaFeS2’sadmirable photocatalytic property. The photocatalytic and electrochemical activities of NaFeS2 offer an innovative platform for the treatment of various other environmental pollutants as well.

Low Concentration Acetone Sensing with ZnO-TiO2 Composites Nanoarrays: A Comparative Study Under Light Illumination

1.Introduction In the past decade, numerous efforts have been taken to develop one-dimensional nanomaterials with specific morphologies such as nanowires and/or NAs because of their large surface to volume ratio. These morphologies also offer a possibility for surface modification so their versatile material properties can be used for different applications. ZnO NAs has been widely used as a sensing layer but the major drawbacks of metal-oxide based sensitive layers are their lack of sensitivity at low operating temperatures. In this work, the ZnO NAs are coated with a thin TiO2 layer to form ZnO-TiO2 composite materials. The combination of ZnO and TiO2 has attained significant attention because of the synergistic advantages these materials could contribute [1]. Several studies have used ZnO-TiO2 composites as a gas sensing layer, however there is a void in the literature, especially in NAs structures for acetone sensing. Hence, this work centres on the investigation of tailored ZnO and TiO2 composites in NAs structures under light illumination for their sensing capability towards low concentrations of acetone (<100 ppm). 2.Experimental In this work ZnO-TiO2 based composite NAs were synthesised by coating a thin layer of (~50 nm) TiO2 using low-temperature CVD on the ZnO NAs grown by hydrothermal synthesis. The composition of TiO2 and ZnO added, the annealing temperature and time plays a crucial role in determining the crystal phase of the material [2]. The TiO2 coated ZnO NAs were annealed at 550 °C (1h, air) to form ZnO-TiO2 core-shell NAs and further annealed at 650 °C (1h, air) to form a mixed metal oxide, hence ZnTiO3 NAs. The surface morphology of the sensitive layers developed were studied using FEI Verios 460L SEM instrument. The acetone vapor sensing event included acetone exposure and recovery (under dry air) steps, each set at 5 minutes. All sensors developed were tested toward different acetone concentrations (ranging from 1.2 to 12.5 ppm). The acetone sensing performance was tested under operating temperatures 45 - 350 °C by applying a potential bias of 6 V DC. A UV light source with a wavelength of 365 nm (maximum intensity up to 2024 µW·cm-2) was used for light-assisted gas sensing. 3.Results and discussion The synthesis procedure schematic and the corresponding SEM images are presented in Figure. 1a-e. The ZnO NAs had an average length and diameter of 1.5 µm and ~30 nm, respectively. The images (Figure. 1d-e) suggest that the thicknesses of the NAs increased significantly after the ~50 nm TiO2 coating. The gas sensing performance of the developed sensors showed a poor dynamic range (Figure. 2a) at 85 °C in dark conditions. When illuminated with light, the sensors showed enhanced response magnitudes and dynamic range (Figure. 2b and 2c). The photo excitation of the sensitive layers has been shown to increase the electron carrier density of the layer, which in turn is hypothesized to facilitate the formation of oxygen ions on the surface of the sensor, which results in a significant increase in sensor response magnitude [3]. In comparison to the pristine ZnO control sensor, the ZnO-TiO2 composite NAs had much higher response magnitude. The annealing of the ZnO NAs coated with TiO2 initiates the diffusion of Ti from the titania shell to the zinc core and vice versa. The Zn2+ ions get substituted with Ti4+ ions in the core thereby the ZnO core becomes electron rich and also increases the affinity to adsorb more oxygen on the surface [4]. The possible reason for the ZnO-TiO2 core-shell NAs to have higher response than the ZnO NAs could be the reactivity of TiO2 in tailored NAs morphology with high surface to volume ratio. Further, the formation of ZnTiO3 NAs introduces structural defects and oxygen deficiencies which results in higher oxygen adsorption on their surface in comparison to pure ZnO sensors. The LoD of the ZnO NAs, ZnO-TiO2 core-shell NAs and ZnTiO3 NAs sensors calculated to be 90, 70, 30 ppb respectively and the sensitivity, adsorption (t90-ads) and desorption (t90-des) time are presented in Table. 1. 4.Acknowledgements The support of the Australian Research Council Discovery Project DP150101939 is acknowledged. All authors acknowledge the RMIT Microscopy and Microanalysis Facility (RMMF) for their scientific and technical assistance and for providing access to their comprehensive infrastructure and research facilities.

Investigating the in-Situ Doping Effect of Niobium Pentoxide Nanostructures on Their Electronic Surface Properties

The release of large quantities of effluents to the environment as wastewater affects the quality of drinking water and it is a serious concern for the environment and for the public health. Often wastewater contains substances that are toxic, carcinogenic and resistant to biodegradation [1]. Thereby, the stringent regulations imposed by environmental and governmental agencies to improve the quality of water, require more efficient wastewater treatment techniques. Advanced oxidative processes (AOPs) consist of non-selective and efficient oxidative degradation of organic pollutants using chemical species with high oxidative power such as hydroxyl radicals [1]. In one of the AOP methods, light interacts with semiconductors generating excitons by the transfer of electrons from the valence band to the conduction one. The excitons react with oxygen and water forming hydroxyl radicals, which degrade organic molecules. Actually, photodegradation is an effective-cost method to treat industrial effluents [1]. However, this technology suffers from some challenges such as insufficient utilization of visible-light. Therefore, advances in photodegradation processes require the development of new semiconductors, the evaluation of their electronic and surface properties, to enhance the efficiency of hydroxyl radicals’ generation in presence of UV light and broad spectrum light source. [2][3]. Different metal oxides, were exploited for such a purpose like TiO2, SnO2, ZnO2, Fe3O2, Al2O3, showing different performances in terms of degradation rates [1]. Niobium pentoxide has been investigated for different applications such as humidity, gas and chemical sensing, electrochromic devices and catalysis due to its thermodynamic stability, high corrosion resistance, biocompatibility and Bronsted acidic properties [2]. At the same time, is one of the least studied metal oxides, which makes it attractive for fundamental studies. Nb2O5 is a wide band-gap semiconductor, with a band gap of 3.4 - 4 eV depending on its morphological features, meaning that it can be used as a photocatalyst only when activated with ultraviolet irradiation [4][5][6]. In this work, we investigate the impact of the nature and content of the doping element on the electronic surface properties of Nb2O5 nanostructures aiming at widen its photon absorption in the electromagnetic spectrum.The Nb2O5 nanoparticles were synthesized by hydrothermal synthesis at 150°C, for 2h, by mixing ammonium niobium oxalate with the different percentages of dopant precursors: N, Cu, and Ta. The structural and morphological characterization of the samples was carried out by X-ray diffraction (XRD) and Scanning electronic microscopy (SEM). The optical properties were investigated by UV-Visible-NIR diffuse-reflectance spectroscopy (DRS) to define the effective optical band gap, Ultraviolet photoelectron spectroscopy (UPS) to calculate the work function of the materials and by X-ray photoelectron spectroscopy (XPS) to determine the valence band edge, leading to the complete construction of the energy diagram of the different synthesized nanoparticles. The successful doping of Nb2O5 nanostructures with 1 wt% of Ta, Cu or N lead to a narrowing of the optical band gap as illustrated in Figure 1. The reduction of the optical band gap of Nb2O5 is at least of 0.5 EV through the doping with tantalum but around 1 eV with nitrogen. The correlation between the electronic surface properties and the structure of the materials will be discussed.AcknowledgementsThe authors would like to thank the funding from NSERC (Strategic partnership program, Canada) and FAPESP (BEPE 2018/17279-1, Brazil).

Stress Relaxation via Covalent Dynamic Bonds in Nanogel-Containing Thiol-Ene Resins.

Functional nanogels are attractive additives for use in polymer composites. In this study, nanogels with internal allyl sulfide moieties throughout their network structure were prepared via a thiol-Michael addition reaction. The excess thiol-functionalized nanogels were less than 60 nm as discrete particles but act as room-temperature liquids in the bulk state. The reactive nanogels can be dispersed in and swollen by a thiol-ene matrix resin, which upon photopolymerization yields dramatically decreased levels of polymerization shrinkage stress. Furthermore, the postcured nanogel-modified polymers effectively relaxed applied stresses as well as enhanced toughness during exposure to a UV light source that activated the addition-fragmentation as a means for dynamic bond exchange. These nanogels provide a generic approach to introduce adaptable network performance that significantly improves a number of key properties of glassy cross-linked polymer.

Construction and Photocatalytic Properties of TiO2@HNb3O8-NS

TiO2 loaded HNb3O8 nanocomposite (TiO2@HNb3O8-NS) was successfully prepared by an exfoliation-assembled method at the moderate conditions. The physicochemical properties were characterized by means of XRD, HRTEM, LRS, N2 adsorption-desorption measurement and UV–vis DRS. The characterization results indicated that TiO2 were highly dispersed on the HNb3O8 nanosheet (HNb3O8-NS) and there was an obvious interaction between host HNb3O8-NS and guest TiO2. The photocatalytic performance of the as-prepared materials was investigated through degradation of methylene blue (MB). The results showed that the as-prepared TiO2@HNb3O8-NS composite owns excellent photodegradation performance under UV light source. The role of TiO2 dispersed on HNb3O8-NS in degradation of methylene blue (MB) was mainly attributed to the change of band gap structure and the improvement of separation of photogenerated carriers. And the photocatalytic mechanism was discussed in the article.

A fluorescence signal amplification strategy for modification-free ratiometric determination of tyrosinase in situ based on the use of dual-templated copper nanoclusters.

A fluorescence resonance energy transfer (FRET)-based in situ fluorescence signal amplification strategy is described for the determination of tyrosinase (TYR). In this assay, a dual-templated copper nanocluster (CuNCs) stabilized by bovine serum albumin (BSA) and glycylglycine (Gly-Gly) was used as an energy donor. Metyrosine was employed as a TYR substrate because its enzyme catalytic product (methyldopa) was able to function as a monomer molecule to form fluorescent polymethyldopa (PMeDP) with the assistance of BSA/Gly-Gly CuNCs. In this process, PMeDP can combine with BSA/Gly-Gly CuNCs without extra modification and then acts as an energy receptor, which leads to a remarkable FRET from BSA/Gly-Gly CuNCs to PMeDP. Interestingly, the fluorescence intensity of PMeDP was strengthened greatly in the FRET-based sensor compared tothe separate excitation, which provided good sensitivity for TYR sensing. Illuminated under a UV light source, the fluorescence signal change is observed from dark violet to bright green. Therefore, the present sensing system affords a reliable ratiometric assay for TYR determination. Also, the ratio of fluorescence intensity between PMeDP (λem at 505nm, F505) and BSA/Gly-Gly CuNCs (λem at 415nm, F415) was used for quantitative determination of TYR. The sensing system was easily operated in aqueous media with an exciting detection limit of 44.0UL-1. This sensing strategy has been applied tothe screening of inhibitors. Graphical abstract Schematic representation of the strategy for the determination of tyrosinase.

Photocatalytic Reduction of AuCl4- by Fe3O4/SiO2/TiO2 Nanoparticles

&lt;p&gt;Metallurgy and recovery of gold in electronic waste sometimes involve the reduction of tetrachloroaurate ion (AuCl4-) to elemental gold form. Currently, for the reduction of tetrachloroaurate ion, people use reducing agents such as hydroquinone and sodium borohydride. Photocatalysts of Fe3O4/SiO2/TiO2 nanoparticles were prepared and tested for the reduction of tetrachloroaurate ion under UV light illumination. The magnetite (Fe3O4) nanoparticle was first prepared by coprecipitation and sonication, followed by SiO2 and TiO2 coatings via the sol-gel process and calcination. The products were confirmed by XRD and TEM. The photocatalytic reduction of tetrachloroaurate ion was performed in a closed reactor equipped with a UV light source. The results indicated that Fe3O4/SiO2/TiO2 nanoparticles were successfully prepared, which retained good magnetic and photocatalytic properties. The photocatalytic reaction is best performed at a pH of 5 under UV irradiation for 2 h, which is capable of reducing 96% of the tetrachloroaurate present in the mixture. The co-presence of Ni2+ and Cu2+ ions in the solution leads to a decrease in yield due to competitive reduction and adsorption. The photocatalyst is recoverable by the use of a magnetic bar and may find application for gold recovery and metallurgy.&lt;/p&gt;&#x0D;

Modification of photocatalyst Ti-Pillared clay by Zn metal addition for decolorization process of organic liquid waste

Black liquor produced from a pretreatment process of bioethanol using the lignocellulose material, such as an empty palm bunch. Black liquor is organic liquid waste and should be treated before release to the environment. One of the degradation processes of black liquor is by the photocatalytic reaction using the Ti-Pillared Clay (Ti-PiLC) catalyst. However, there is a limitation of process condition if using a Ti-PiLC catalyst; the degradation process should be conducted under a UV light source. This study is focused on the modification of photocatalytic catalyst Ti-PiLC by adding Zn metal (Ti-Zn/PiLC), thus the degradation process of black liquor could be conducted on a visible light source. Characterizations of the prepared photocatalysts were obtained using XRD, BET, TPD, TGA, SEM, TEM and UV-Vis spectrophotometer for the degradation degree. Although the degradation process of black liquor could be conducted on the visible light source, the degradation degree was still minor compared with only using Ti-PiLC photocatalyst. It is assumed that combination Ti and Zn as the active metals of the photocatalyst was not good enough to enhance the degradation process of black liquor even on the visible light source, perhaps using other metal, such as cerium (Ce).

High-efficiency AlGaN/GaN/AlGaN tunnel junction ultraviolet light-emitting diodes

AlGaN is the material of choice for high-efficiency deep UV light sources, which is the only alternative technology to replace mercury lamps for water purification and disinfection. At present, however, AlGaN-based mid- and deep UV LEDs exhibit very low efficiency. Here, we report a detailed investigation of the epitaxy and characterization of LEDs utilizing an AlGaN/GaN/AlGaN tunnel junction structure, operating at ∼ 265 nm , which have the potential to break the efficiency bottleneck of deep UV photonics. A thin GaN layer was incorporated between p + and n + -AlGaN to reduce the tunneling barrier. By optimizing the thickness of the GaN layer and thickness of the top n -AlGaN contact layer, we demonstrate AlGaN deep UV LEDs with a maximum external quantum efficiency of 11% and wall-plug efficiency of 7.6% for direct on-wafer measurement. It is also observed that the devices exhibit severe efficiency droop under low current densities, which is explained by the low hole mobility, due to the hole hopping conduction in the Mg impurity band and the resulting electron overflow.

Optical characterization of photocatalytic copper doped thin films of anodized titanium

Titanium oxide is used in a myriad of applications such as in capacitors, insulation paints among others. It is a prime candidate for water splitting due to its photocatalytic properties. In this work, undoped TiO2 thin films were prepared by anodizing titanium foils cut into pieces measuring 60 mm by 20 mm. The specimens were anodized in an electrolyte consisting of 0.5 M H2SO4 and 0.075% wt HF at room temperature. The anodizing voltages ranged from 50 V to 100 V. Anion doping of copper in as anodized TiO2 was done electrochemically. The as anodized Ti foils were dipped in a 1 M Cu2SO4 solution. All samples were annealed at 450 °C for 3 h. Near-normal total reflectance was measured on as anodized and copper pigmented samples in the solar (300–2500 nm) wavelength range. Spectrophotometric reflectance data was analyzed to obtain the absorption coefficient and using the same to determine the band gap of the films. It was noted that the films exhibited reduced solar integrated reflectance for TiO2 samples prepared at lower anodic voltages of 50, 60 and 70 V. The copper pigmented, and annealed, TiO2 samples exhibited both direct and indirect energy band gaps in the ranges, 3.38–3.86 and 2.50–2.74, respectively. Further, annealing and copper doping of the films lead to increased absorption. The photocatalytic activity of the films was assessed by measuring the rate of degradation of 10ppm methylene blue in UV light source. Copper doped TiO2 exhibited enhanced photocatalytic performance in compared to pure TiO2. An increase in the anodization voltage caused subsequent increase in photocatalytic activity of films with 70 V as the optimum voltage above which photo degradation of methylene blue decreased.

Synthesis of magnetic nanoparticles using Parkia speciosa Hassk pod extract and photocatalytic activity for Bromophenol blue degradation

Green synthesis of magnetic nanoparticles using Parkia speciosa Hassk pod extract and their photocatalytic activity were studied. Heterogeneous magnetic nanoparticles were prepared by a reduction reaction between iron (II) and iron (III) solution in the presence of P. speciosa Hassk pod extract. The physicochemical characteristics of the nanoparticles were identified using X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) techniques. Bromophenol blue (BPB) degradation via photocatalytic activity of the nanoparticles was evaluated under UV and visible light sources. The nanoparticles obtained consisted of a combination of Fe3O4 and Fe2O3 particles, with sizes in the range of 10–80 nm. The particles exhibited magnetic properties, as well as excellent photocatalytic degradation of BPB under both UV and visible light exposure, with degradation efficiency of about 98%. The results imply that the nanoparticles have potential use as photocatalysts, with applications in dye-containing wastewater degradation.

Dynamically Coated Photocatalytic Zeolite–TiO2 Membrane for Oil-in-Water Emulsion Separation

This paper evaluated the effectiveness of polyester (PS)/poly(vinyl alcohol) (PVA) dynamic membrane (DM) incorporating photocatalytic zeolite/TiO2 for oil-in-water (O/W) emulsion separation. The photocatalytic zeolite/TiO2 was established onto the membrane surface via self-forming and pre-coating method with the aims of reducing membrane fouling during O/W emulsion treatment. The results obtained showed that the pre-coated composite DM could decrease support membrane fouling by improving flux recovery rate by 5.8%, while the use of the self-forming composite DM exhibited lower flux recovery rate after three filtration cycles in O/W emulsion treatment. The results were confirmed by cleaning and oil removal efficiency. The cleaning efficiency of composite DM was further enhanced by substitution of deionized water with sodium dodecyl sulfate as a cleaning agent in the treatment of O/W emulsion. Using sodium dodecyl sulfate, the pre-coated composite DM showed higher flux recovery rate (81%) than the self-forming composite DM. In addition, the photocatalytic effects of zeolite/TiO2 on the DM with respect to flux recovery rate and oil rejection under UV light source were investigated. It was found that by combining cleaning process and UV irradiation, the fouling of DM was further decreased, recording high flux recovery rate (up to 83.6%) without compromising oil rejection rate (85.3%).

Three Dimensional Maskless Ultraviolet Exposure System Based on Digital Light Processing

This paper reports the development of a three dimension maskless photolithography system with an oblique scanning method based on digital light processing technology. The system consists of a UV light source, a digital micromirror device (DMD), a microlens/pinhole array, two optical projection lenses, and a three-axis (xyz) servo-controlled stage. The optical system can form a rectangular array of UV spots with a diameter of few μm directly on the surface of a sample sitting on the stage. A photoresist (PR) layer is coated on the sample surface. Using an oblique scanning approach, the whole area of PR layer can be exposed by this UV exposure system in a maskless manner. Since the energy intensity of each UV spot can be independently modulated by a corresponding group of micromirrors in the DMD, and a three-dimensional (3D) UV dosage distribution can be achieved through computer programming on the DMD and the xyz stage. After developing processes, 3D PR microstructures with arbitrary patterns and/or surface profiles can be readily formed by this maskless lithography system. Experimental results will be addressed as well as potential applications for 2D and 3D microfabrication.

Photodegradation of contaminants in bathroom wastewater under UV illumination source

Photocatalytic water treatment is well known advanced oxidation method which produces hydroxyl radicals by using nanocrystaline catalyst titanium dioxide. Titanium dioxide can mineralize a toxic organic compound into inoffensive end products such as co2 and water. Surfactants or Surface active agents (SAA) are released from various households and industrial activities. SAA present in the effluent stream create the bioaccumulation and serious negative impacts on biotic and abiotic elements of ecosystem. A wide range of SAA found in residential bathroom waste water, SAA can be minimized by using photocatalytic treatment. Photocatalysis process in reactor takes place in the presence of photons and catalyst. Photons are illuminated from UV light source and hence enhance the reaction speed by using suspension state catalyst. Anatase structure titanium dioxide nanoparticles catalysts are activated by UV light source under 180 mins of irradiation time. Surfactants degradation of treated effluent water by photocatalytic treatment can be monitored by total organic carbon degradation. After the treatment the TOC removal efficiency was about 93%.

Thiol-ene coupling reaction achievement and monitoring by "in situ" UV irradiation NMR spectroscopy.

In this study, the possibilities of a new “in situ” LED UV illumination NMR spectroscopic technique for performing an initiator-free thiol–ene “click” coupling reaction of an allyl-functionalized poly(allyl glycidyl ether) (PAGE) prepolymer with a number of mono- and di-oligo polyethylene glycol (PEG) thiols is demonstrated. The state-of-the-art setup constructed with LEDs as UV light sources that illuminate through optical fibers directly into an NMR testing tube at a fixed wavelength of 365 nm is appropriate for various polymeric materials and biologically active substances. The selected experimental protocol uses a series of periods of irradiation and dark periods, thus providing opportunities to conduct an effective thiol–ene “click” reaction and simultaneously study the kinetics of the photochemical reaction with the exposure time, as well as macromolecular association directly in a solution applying the whole types of NMR methods: from conventional 1H or 13C NMR to diffusion NMR spectroscopy (DOSY). In addition, the molecular mass characteristics of the prepared copolymers were studied by gel-permeation chromatography (GPC). The observed differences in the reaction rates as well as in the size of species formed (the corresponding hydrodynamic radiuses Rh of aggregates) as a result of the coupling process of parent PAGE prepolymers and model PEG thiols were thoroughly discussed and the reaction pathway proposed.

Alternative Bi precursor effects on the structural, optical, morphological and photocatalytic properties of BiOI nanostructures

BiOI nanostructures were synthetized through a hydrothermal process using either bismuth acetate or subsalicylate as Bi precursor. Regardless of the used Bi source, the same crystalline structure of BiOI was obtained; nevertheless, the nature of the Bi precursor had an evident impact in the color appearance of the obtained sample. Another notable difference was observed in the resulting morphology, where ∼1.6 μm flower- and dandelion-like shapes were obtained for acetate and subsalicylate, respectively; both structures assembled by around 30 nm thick nanoflakes with rounded and straight edge, respectively. UV–vis diffuse reflectance shows an energy gap around 1.8 eV. Raman spectroscopy confirms also the tetragonal phase of BiOI. The photocatalytic activity was evaluated through degradation of methyl orange dye using visible and UV light sources, comparing results with P25 TiO2. Both BiOI nanostructures presented an improvement of photocatalytic activity when irradiated with visible light, having the best photoactivity the sample synthetized with bismuth acetate.

Using LED Powered UV Light Sources for Printing

Using LED Powered UV Light Sources for Printing

Comparative Evaluation of the Photodegradation of Stearic Acid by TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; - Modified Cement Under UV Irradiation Through Water Contact Angle and Absorbance Studies

The photodegradation of stearic acid has been studied through evaluation of changes in the contact angles of water and from absorbance measurements. The photodegradation of 0.02 M stearic acid coatings and solutions were initiated by TiO2 nanoparticles of average size of 9.80 ± 2.92 nm embedded in cements in 1.66 wt.%, 3.33 wt.%, 5.0 wt.% and 6.67 wt.% to generate modified cement composites with photocatalytic capability. It was noted that the photodegradation efficiencies increased with the increase in the weight-percent of TiO2 present in the modified cement samples. A modified Cassie-Baxter and the Langmuir-Hinselwood models were used to compute the rate constants, based on changes in the contact angles of water and in the concentration of the stearic acid respectively, on exposure to the UV light source. The modified Cassie-Baxter model successfully provided a route to relate the changes in water contact angle to the rate of photodegradation of a hydrophobic, long-chain stearic acid. The values of the rate constant estimated from both models increased with increase in the amount of TiO2 present in the modified cement samples. However, the rate constant values obtained from the modified Cassie-Baxter model were lower than those obtained from the Langmuir-Hinselwood model. The values of these rate contants were in the range of 0.11-0.50 hr-1 and 0.78-1.33 hr-1 as btained from the modified Cassie-Baxter and Langmuir-Hinselwood models respectively. This disparity in the values was attributed to a higher mobility of the charge carriers and free-radicals that induced the photodegradation in liquid medium as compared to the solid medium.

Cost-effective smart microfluidic device with immobilized silver nanoparticles and embedded UV-light sources for synergistic water disinfection effects.

A novel microfluidic-device for water disinfection via diverse physiochemical effects has been demonstrated. Firstly, a microfluidic device with embedded, multiple germicidal UV-LEDs was fabricated through the innovatively modified cost-effective soft-lithography process. Further, synthesised silver nanoparticles were immobilized within its inner microchannel surface. Disinfection results proved the synergistic bactericidal effect of coated AgNPs and coupled UV-light, while a suspension of bacterial strains, were passed through the micro-device.

Boosted ultraviolet electroluminescence of InGaN/AlGaN quantum structures grown on high-index contrast patterned sapphire with silica array

Epitaxially grown high crystalline quality InGaN/AlGaN multiple quantum structures on patterned sapphire with silica array (PSSA) have been successfully demonstrated. In comparison to conventional epilayers grown on patterned sapphire substrate (PSS), we observed a reduced threading dislocation density in the films grown on PSSA, attributing to the preferable vertical growth mode and reduced misfit at the coalescence boundary. Furthermore, a significant enhancement in light extraction efficiency can be achieved from InGaN/AlGaN-based ultraviolet light-emitting diodes (UVLEDs) built on PSSA owing to the large refractive index contrast between the epilayers and PSSA. More photons can escape from the top and bottom of the device, which was confirmed by numerically modeling light propagation within such device architecture. Benefiting from the reduced threading dislocation density and enhanced light extraction efficiency, the external quantum efficiency (EQE) of the fabricated UVLEDs on PSSA was more than two times higher than that of devices on the conventional flat sapphire substrate and it was additionally enhanced by 26.1% in comparison to the devices fabricated on PSS under an injection current of 150 mA. Therefore, the successful demonstration of UVLED on PSSA provides an unprecedented opportunity in achieving higher electroluminescence performance in future solid-state UV light sources.