UV LED Illumination Research Articles

Photocatalytic degradation of diclofenac amide in a fixed-bed reactor using TiO2/β-Bi2O3: Process optimization and stability analysis

In this study, we employed a recirculating photocatalytic fixed-bed reactor featuring a TiO2/β-Bi2O3 (TB) composite as a photocatalyst immobilized onto borosilicate glass beads for the degradation of the water-dissolved pharmaceutical compound diclofenac amide (DCFA) under UV-LED illumination. Our findings from the DCFA degradation runs revealed that the initial concentration (Co) and the volumetric recirculation flow rate (Q) exert minimal influence on the DCFA degradation rate, indicating the absence of mass transfer limitations at the chosen Q.A kinetic model, developed in alignment with the experimental data, facilitated the calculation of kinetic adsorption (k1 = 0.15 (ppm h)-1, Keq = 15 ppm−1, St = 4.3 ppm) and reaction rate constants (kr = 0.015 h−1). These constants were pivotal in determining the photocatalytic space yield (PSTY—0.45 × (10-6 m3 water m−3 reactor day−1 kW−1 lamp)) for the employed reactor system.The results from three consecutive cycles of DCFA degradation, conducted with the same TB-coated glass beads, demonstrated that the adsorption of DCFA in the dark primarily occurs through the glass material of the beads. Upon exposure to light, the DCFA degradation rate remained constant across all three oxidation cycles. Analysis of the kobs values for cycle 1 (0.0041 ± 0.00067 h−1, R2 = 0.91), cycle 2 (0.0083 ± 0.0013 h−1, R2 = 0.93), and cycle 3 (0.0073 ± 0.001 h−1, R2 = 0.94) indicated an initial excessive leaching of weakly bound TB powder during the first DCFA degradation cycle, potentially resulting in light scattering and reduced photon absorption. Nevertheless, the coatings exhibited reusability over three DCFA degradation cycles, highlighting their stability and reproducible activity.Furthermore, the long-term stability of the coated TB beads was demonstrated by comparing the photocatalytic activity between the present day and two years ago. Remarkably, comparable activity levels were achieved both today (kobs = 0.0085 ± 0.0035 h−1, R2 = 0.71) and two years ago (kobs = 0.0071 ± 0.0014 h−1, R2 = 0.90). These obtained results offer valuable insights for the refinement and optimization of fixed-bed photoreactors in the context of wastewater treatment.

Crime Light Imaging (CLI): A Novel Sensor for Stand-Off Detection and Localization of Forensic Traces.

Stand-off detection of latent traces avoids the scene alteration that might occur during close inspection by handheld forensic lights. Here, we describe a novel sensor, named Crime Light Imaging (CLI), designed to perform high-resolution photography of targets at a distance of 2-10 m and to visualize some common latent traces. CLI is based on four high-power illumination LEDs and one color CMOS camera with a motorized objective plus frontal filters; the LEDs and camera could be synchronized to obtain short-exposure images weakly dependent on the ambient light. The sensor is integrated into a motorized platform, providing the target scanning and necessary information for 3D scene reconstruction. The whole system is portable and equipped with a user-friendly interface. The preliminary tests of CLI on fingerprints at distance of 7 m showed an excellent image resolution and drastic contrast enhancement under green LED light. At the same distance, a small (1 µL) blood droplet on black tissue was captured by CLI under NIR LED, while a trace from 15 µL semen on white cotton became visible under UV LED illumination. These results represent the first demonstration of true stand-off photography of latent traces, thus opening the way for a completely new approach in crime scene forensic examination.

Radiation modeling and performance evaluation of a UV-LED photocatalytic reactor for water treatment

A photocatalytic reactor under UV-LED illumination is presented. It is an annular, packed-bed reactor filled with TiO2-coated glass rings. The reactor is irradiated both internally and externally in order to minimize the presence of dark zones. The knowledge of the radiation distribution inside the reactor is a key aspect to optimize its design and improve its efficiency. A three-dimensional model has been developed to describe the distribution of the local rate of photon absorption inside the reactor. The Monte Carlo method was applied to solve the radiation model. Simulation results were validated with experimental measurements. The model was able to predict the influence of the catalyst film thickness and the illumination conditions on the radiation distribution and on the total rate of photon absorption. Also, degradation assays of the pharmaceutical clofibric acid were carried out in the reactor and the performance of different illumination conditions was evaluated by means of the quantum efficiency parameter.

(Invited, Digital Presentation) Photoactivated In2O3/GaN NW Sensors for Monitoring NO2 with High Sensitivity and Low Power

We report and discuss our results on the performance of our photoactivated In3O2/GaN NW sensors, for monitoring NO2 at various levels of relative humidity and operating power. A 1ppm sensitivity as high as 29% was demonstrated at operating power of 5 mW and relative humidity 40%.Nanostructure-based semiconductor gas sensors such as nanowires, nanotubes or nanorods have seen significant progress in recent years, owning to their large surface-to-volume ratio proprieties, which lead to considerably increased sensitivity and improve the time response to analyte gases. In particular, Gallium Nitride (GaN) nanostructure-based gas sensors have generated a lot of interest due to its unique combination of sensor “friendly” properties such as, direct bandgap, excellent carrier mobility, high heat capacity and high breakdown voltage. These properties combined with suitable surface engineering make GaN and GaN-based nanostructures an excellent candidate for portable gas sensors.In this work, Gallium Nitride (GaN) nanowire (NW)-based NO2 sensors, functionalized with either pure In2O3 or In2O3 covered with an evaporated Au nanolayer, were developed for low operating power and high sensitivity. An AlGaN buffer layer was first deposited on a Si substrate to minimize lattice mismatch and improve adhesion between the Si substrate and the GaN NWs. Then the GaN NWs were patterned by stepper lithography-assisted dry-etching, followed by Induced Coupled Plasma etching using a metal hard mask to protect the GaN NW. The nanowire width target ranged between 200-600nm. Subsequently, electrodes composed of Ti/Al/Ti/Au metal stacks were deposited on top of the GaN to form Ohmic contacts. A thin In2O3 layer metal oxide receptor was deposited on all devices, using RF magnetron sputtering on top of the exposed GaN NW and this was followed for a subgroup of devices by coating the In2O3 with an evaporated Au nanolayer. Finally, rapid thermal annealing (RTA) at 700 0C was performed to crystalize the receptor layers and improve the ohmic contact. The surface quality of the resulting sensors was inspected with the help of Scanning Electron Microscope (SEM) micrographs.Several devices of each group (In2O3 and In2O3/Au ) were wire bonded and mounted onto an array board chamber. The devices were biased under 5V DC. Photoconductivity measurements, humidity testing and NO2 gas testing (1ppm and 10ppm concentration) were conducted. The sensors were illuminated under constant UV LED illumination throughout the duration of the testing at two wavelengths, 265 nm and 365 nm and three irradiance levels, 5mW, 30mW and 60mW. In general, the In3O2 GaN NW sensors where characterized by low sensitivity levels, whereas the In3O2/Au GaN NW sensors achieved excellent sensitivity levels. Fig.1 shows typical dynamic responses to 1ppm NO2 of the In3O2/Au GaN NW sensors under illumination at 265 nm and 365 nm, respectively, and Fig.2 the response at various relative humidity (RH) levels. An increase in resistance upon exposure to NO2 is observed, confirming the oxidizing nature of the NO2 gas. At this NO2 concentration level, the highest response value (29%) was obtained under (5mW, 265 nm) illumination, whereas the sensitivity under (5mW, 365nm) illumination was lower. For (30mW, 265nm) illumination, the sensitivity was 23% and for (30mW, 365nm) illumination it dropped to 15%. This phenomenon has been observed in the past by other authors also, and although its origins are not yet understood unambiguously, it may be caused by a higher rate of phonon energy relaxation at the surface at higher wavelengths, thereby reducing the effectiveness of chemisorption at the surface. In conclusion, room-temperature low-power photoactivated In3O2/Au GaN NW sensors with excellent levels of sensitivity at elevated relative humidity were designed, fabricated and tested. Figure 1

AlGaOx nanowires obtained by wet oxidation as a visible white phosphor under UV-LED illumination

We obtain white luminescence by the oxidation of GaAs/Al-rich Al0.87Ga0.13As nanowire which is visible to the eye. The oxidized amorphous AlGaOx shell emits light over a wide spectral range covering entire visible wavelengths between 400–700 nm. The emission intensity depends on the oxidation temperature and time. Through the optimization of those conditions, we observe clear white light from the sample by the eye under the illumination of ultraviolet light-emitting diodes, which would be applicable as a white light phosphor.

Comparison of UV-A photolytic and UV/TiO2 photocatalytic effects on Microcystis aeruginosa PCC7813 and four microcystin analogues: A pilot scale study

To date, the high cost of supplying UV irradiation has prevented the widespread application of UV photolysis and titanium dioxide based photocatalysis in removing undesirable organics in the water treatment sector. To overcome this problem, the use of UV-LEDs (365 nm) for photolysis and heterogeneous photocatalysis applying TiO2 coated glass beads under UV-LED illumination (365 nm) in a pilot scale reactor for the elimination of Microcystis aeruginosa PCC7813 and four microcystin analogues (MC-LR, -LY, -LW, -LF) with a view to deployment in drinking water reservoirs was investigated. UV-A (365 nm) photolysis was shown to be more effective than the UV/TiO2 photocatalytic system for the removal of Microcystis aeruginosa cells and microcystins. During photolysis, cell density significantly decreased over 5 days from an initial concentration of 5.8 × 106 cells mL−1 until few cells were left. Both intra- and extracellular microcystin concentrations were significantly reduced by 100 and 92 %, respectively, by day 5 of the UV treatment for all microcystin analogues. During UV/TiO2 treatment, there was great variability between replicates, making prediction of the effect on cyanobacterial cell and toxin behavior difficult.

Solvent‐Free Photobiocatalytic Hydroxylation of Cyclohexane

AbstractThe use of neat reaction media, that is the avoidance of additional solvents, is the simplest and the most efficient approach to follow in biocatalysis. Here, we show that unspecific peroxygenase from Agrocybe aegerita (AaeUPO) can hydroxylate the neat model substrate cyclohexane. H2O2 was photocatalytically generated in situ by nitrogen‐doped carbon nanodots (N−CNDs) and UV LED illumination. AaeUPO entrapment in alginate beads increased enzyme stability and facilitated the reaction in neat cyclohexane. N−CNDs absorption in beads containing AaeUPO created a 2‐in‐1 heterogeneous photobiocatalyst that was active for up to seven days under reaction conditions and produced cyclohexanol, 2.5 mM. To increase productivity, the bead size and the photocatalyst‐to‐enzyme ratio have been identified as promising targets for optimisation.

P.668 Visual working memory as a possible endophenotypic schizophrenia marker

Poor efficiency of TiO2 by visible light and the fast recombination rate of electron/hole pairs remain significant challenges in photocatalytic applications of TiO2 in water treatment. In this study, graphene was used to enhance TiO2 photocatalytic activity by reducing electron-hole pair recombination. Nanocomposites were formed by combining TiO2 nanoparticles (P25) with graphene oxide (GO) though simultaneous hydrothermal synthesis and GO reduction. Nanocomposite characterization confirmed that the GO was successfully reduced and P25 nanoparticles evenly dispersed in the graphene surface. The band gap of the nanocomposite was determined to be 2.74 eV, which is a promising shift to the visible spectrum in graphene-TiO2 photocatalysts. The photocatalytic performance of the TiO2/G nanocomposites was then evaluated by quantifying the formation of 2-hydroxyterephthalic acid (HTPA) (probe molecule) under UV-LED illumination. To further optimize the photocatalytic efficiency of the TiO2/G nanocomposites, the response surface methodology (RSM) with central composite design (CCD) was used. Out of the 6 variables including stirring time, stirring speed, the amount of TiO2, the amount of GO, hydrothermal reaction time, and ethanol/water ratio, it was determined that the last three are substantially affected the HTPA formation rate. The optimum conditions were found to be GO 0.48 wt%, ethanol/water 51.49 v/V%, and a reaction time 19 h. Predicted values for HTPA formation were found to be in good agreement with experimental values (R2 = 0.93 and adj-R2 = 0.87). The optimized nanocomposite showed 125% enhancement in photocatalytic efficiency over pure P25.

Photocatalytic degradation using TiO2-graphene nanocomposite under UV-LED illumination: Optimization using response surface methodology

Poor efficiency of TiO2 by visible light and the fast recombination rate of electron/hole pairs remain significant challenges in photocatalytic applications of TiO2 in water treatment. In this study, graphene was used to enhance TiO2 photocatalytic activity by reducing electron-hole pair recombination. Nanocomposites were formed by combining TiO2 nanoparticles (P25) with graphene oxide (GO) though simultaneous hydrothermal synthesis and GO reduction. Nanocomposite characterization confirmed that the GO was successfully reduced and P25 nanoparticles evenly dispersed in the graphene surface. The band gap of the nanocomposite was determined to be 2.74 eV, which is a promising shift to the visible spectrum in graphene-TiO2 photocatalysts. The photocatalytic performance of the TiO2/G nanocomposites was then evaluated by quantifying the formation of 2-hydroxyterephthalic acid (HTPA) (probe molecule) under UV-LED illumination. To further optimize the photocatalytic efficiency of the TiO2/G nanocomposites, the response surface methodology (RSM) with central composite design (CCD) was used. Out of the 6 variables including stirring time, stirring speed, the amount of TiO2, the amount of GO, hydrothermal reaction time, and ethanol/water ratio, it was determined that the last three are substantially affected the HTPA formation rate. The optimum conditions were found to be GO 0.48 wt%, ethanol/water 51.49 v/V%, and a reaction time 19 h. Predicted values for HTPA formation were found to be in good agreement with experimental values (R2 = 0.93 and adj-R2 = 0.87). The optimized nanocomposite showed 125% enhancement in photocatalytic efficiency over pure P25.

Design of UV LED illumination system for direct imaging lithography

UV LED, which can be used as the illumination source in the direct imaging (DI) exposure equipment, has the advantages of rich wavelengths and low cost. It has a good application prospect in the field of printed circuit board (PCB) manufacturing. In practical application, there are high requirements for output power density, stray light control, and luminance uniformity of DI system to improve the productivity and exposure performance. We present an optical structure of the illumination system for DI lithography to provide uniform illumination low stray light for digital micromirror device (DMD), which combines Kohler illumination and double telecentric imaging. In this design, the high luminance illumination can be obtained by LED etendue analysis, fly’s eye condenser is not needed, and the stray light on the DMD caused by light outside the effective angle of the LED can be mostly filtered out. Based on this idea, a lithographic illumination system with the numerical aperture of 0.1 is designed and fabricated for 0.95-in. DMD. According to experimental measurements, the effective illumination power is up to 10 W, the stray light accounts for 10.7%, and the illuminance uniformity is about 90%, which meet the requirements of DI lithography equipment used in PCB manufacturing.

Application driven key wavelengths mining method for aflatoxin detection using hyperspectral data

The first step of developing Aflatoxin intelligent sorter is to determine the key wavelengths for aflatoxin detection. In order to find more accurate wavelengths, in this paper, three kinds of sensor system are built separately: the first sensor is hyper-spectrometer by ASD spectrometer, the second is the multispectral camera system based on Liquid crystal tunable filter (LCTF) and the third one is the hyperspectral camera based on Grating spectrometer module (GSM). Under 365 nm UV LED illumination, using these three systems, three hypersepctral datasets of 45, 41 and 73 peanut samples before and after aflatoxin contaminated have be collected separately. In order to select the best key wavelengths, four feature selection methods (Fisher, SPA, BestFist and Ranker) and four classifier models (KNN, SVM, BP-ANN, RandomForest) were analyzed and compared. Using all selected wavelengths based on different datasets, a weighted voting method was proposed and 10 key wavelengths (440 380 410 460 420 370 450 490 700 600 nm) were selected. Based on the best model (Random Forest), the best integrated average recognition rate is 94.5%. And then, using these key wavelengths and the best classification model, a new design system for aflatoxin sorter base on a Ploygon mirror was proposed. The structure of this system is simple, detection accuracy is high, which can be applied to online sorting of aflatoxin detection.

Nanocomposites of Perovskite Quantum Dots Embedded in Magnesium Silicate Hollow Spheres for Multicolor Display

Organometal halide perovskite quantum dots (PQDs) have recently received much attention as a very promising family of materials with excellent performance in electronic and optoelectronic fields, but these perspectives are being restrained by the severe stability, such as chemical and optical degradations. Herein, we propose and demonstrate a facile solution synthesis of nanocomposites of CH3NH3PbX3 (X = Cl, Br, I) PQDs embedded in magnesium silicate hollow spheres. The resultant nanocomposites preserved the strong photoluminescence of the CH3NH3PbX3 PQDs, and the emission peak can be tunable from blue to red region. Photostability tests demonstrated that the nanocomposite samples were obviously more stable than the bare CH3NH3PbX3 PQDs. The photoluminescence (PL) of the nanocomposite sample still remained at 80% after 72 h UV LED illumination, which was much higher than the remnant PL (30%) of the pure CH3NH3PbX3 PQDs. With their high thermal stability and photostability, we demonstrated that these nanoc...

35.4: UV LED ILLUMINATION STEPPER OFFERS HIGH PERFORMANCE AND LOW COST OF OWNERSHIP

Flat panel displays (FPD) are electronic viewing technologies used to let people see content in media and entertainment, consumer electronics, personal computer and mobile devices. Other applications and industries are medical, transportation and industrial equipment. FPD is often the preferred choice due to lower weight and less power consumption. Common types of FPD are liquid crystal display (LCD), plasma display panels (PDP) and organic light‐emitting diode (OLED).The global market for FPD continues to grow due to the high demand in the automobile and smartphone industries. As a result of the high demand, the FPD manufacturing industry continues to remain highly competitive. In this cost sensitive arena, FPD manufacturers need to find new ways to reduce the cost of ownership of lithography equipment.Most lithography systems in FPD manufacturing plants use high power mercury ARC lamps to generate i‐line (365nm) wavelength for the photoresist exposure process. This is a costly process as the mercury ARC lamps have a limited lifetime, typically less than one month, which results in downtime to swap lamps.. The cost of replacing the high power mercury ARC lamp, together with the high electricity consumption, and disposal of mercury waste, turns out to be a substantial operating cost.This paper will demonstrate how the use of ultraviolet light emitting diode (UV LED), in replacing the high power mercury lamp, will reduce the overall operating cost which therefore lowers the cost of ownership of the stepper. The breakdown of cost structure will be discussed in detail and show that UV LED is a good replacement solution for the high power mercury ARC lamp.The throughput improvement by using UV LED will also be discussed and compared to the conventional high power mercury arc lamp. The analysis will also show that the consistency of throughput, as compared to the degradation of mercury arc lamp intensity, as well as the time saved for replacement further reduces operating costs.This paper also demonstrates the improved performance of dose accuracy and repeatability, as well as the capability to achieve extremely low exposure doses without compromising dose accuracy. The improvement in stepper reliability by removing the conventional shutter moving parts will also be discussed.The performance data for illumination intensity, dose accuracy, uniformity, spectral line width, CD uniformity and cost reduction will be discussed in detail. The final analysis will show that moving to UV LED illumination offers lower cost and better performance.

Porous silica/TiO2 Nanocomposite for Collective Adsorption and Degradation Functionalities

The performance of photocatalytic oxidation of volatile organic compounds (VOCs) generally depends on two properties: VOCs adsorption abilities as well as the degradation functionalities. In this work, a hybrid system of silicon dioxide (SiO2) and titanium dioxide (TiO2) was synthesized for enhanced degradation functionalities. The reasons for high demand of porous silica in the applications are attributed to the low cost, high surface area and the feasibility of obtaining various pore sizes. A simple aqueous-phase method was used to synthesize different structures of porous silica for VOC adsorption capabilities. Porous SiO2 rods of the highest surface area (1238 m2g-1) was chosen to incorporate with the TiO2 sheets for enhanced degradation. Hydrothermal TiO2 growth on SiO2 was optimized by varying the amount of precursors used. The synthesized materials were characterized with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and photocatalytic performance for VOC degradation under UV-LED illumination. The optimized SiO2rods@TiO2 sample showed enhancement of degrading up to 60 % in 120 min of degradation. Furthermore, CuO acts as an effective co-catalyst to enhance charge separation and the degradation performance was improved by loading the SiO2rods@TiO2 sample with CuO. A loading amount of 5% was found to be the optimum for enhanced degradation performance.

UV activated hollow ZnO microspheres for selective ethanol sensors at low temperatures

UV activated metal oxides for chemiresistive-type gas sensors have been recently studied aiming to lower the working temperature and thus lower the power consumption. In this work, the mesoporous hollow ZnO microspheres were prepared by template-assisted method and examined for VOCs detection with UV LED illumination at lower temperatures than 150°C. The as-synthesized ZnO based sensor indicated an excellent response and selectivity to different concentrations of ethanol (10–1000ppm) with low-powered UV LED (2mW) at 80°C. The response time is only ∼6s while the recovery is a little sluggish (∼94s). The enhanced sensing performance could be attributed to the mesoporous hollow microstructure of the synthesized ZnO and UV activated differential photoctalytic oxidation reactions at the shallow oxide surface regions. The repeatability and long term stability of the sensor and the sensor response were also investigated. A comparison with the conventional thermal-activated gas sensing of the hollow ZnO was also conducted and the photo-activated gas sensing mechanism was discussed.

Mathematical modelling of quantum yield enhancements of methyl orange photooxidation in aqueous TiO2 suspensions under controlled periodic UV LED illumination

Quantum yields of the photocatalytic degradation of methyl orange under controlled periodic illumination (CPI) have been modelled using existing models. A modified Langmuir–Hinshelwood (L–H) rate equation was used to predict the degradation reaction rates of methyl orange at various duty cycles and a simple photocatalytic model was applied in modelling quantum yield enhancement of the photocatalytic process due to the CPI effect. A good agreement between the modelled and experimental data was observed for quantum yield modelling. The modified L–H model, however, did not accurately predict the photocatalytic decomposition of the dye under periodic illumination.

Validation of a newly developed FTIR in situ reactor: Real time study of photocatalytic degradation of nitric oxide

For many years, photocatalysis has been proposed as one of the promising techniques to abate environmental pollutants. To improve these reactions it is vital to know the reaction mechanisms of the photocatalytic degradation. This new reactor will make it possible to study the catalytic surface at the moment the reactions occur. By the means of UV LED illumination there is no need of an external UV lamp and thus lowers the cost. The validation of this newly developed reactor is done by investigating the photocatalytic reaction mechanism of nitric oxide (NO) and comparing these findings with those already discussed in literature. From these results, it became clear that the newly developed FTIR in situ reactor allows real time study of photocatalytic degradations.

Focus on spectroscopy

Focus on spectroscopy