Ultraviolet A Light-emitting Diode Research Articles

Insight into wavelength-dependent UVA-LED/chlorine process for micropollutant degradation: Performance, mechanism, and effects of water matrix

Ultraviolet A light-emitting diode (UVA-LED)-activated chlorine effectively degraded micropollutants at different irradiation wavelengths. Quenching experiments indicated that OH, reactive chlorine species (RCS), and O3 were the main reactive species for degradation of atenolol (ATL). Bezafibrate and ibuprofen, were used for the first time to jointly quantify the concentrations of Cl2− and ClO. Notably, O3 contributed most to the degradation of ATL (38.9%), following by OH (30.2%) and RCS (27.6%) at pH 7.0 by the UVA-LED/chlorine at 385 nm. ATL degradation increased with the decrease of wavelengths, due to the higher quantum yields of chlorine. The kobs of ATL was positively correlated to the quantum yield of chlorine at the UVA wavelength band. Higher light intensity could enhance the photolysis of chlorine, leading to enhanced ATL degradation. The protonated chlorine is more conducive to the degradation of ATL. Specifically, the contributions of OH, O3, and RCS to ATL degradation changed from 40.9%, 6.53%, and 41.0% at pH 4.0 to 11.6%, 59.9%, and 26.6% at pH 9.0, respectively. Cl− had no significant influence on ATL degradation, mainly due to the synergistic effect of different reactive species. HCO3− and HA inhibited ATL degradation owing to the quenching effect for reactive species and/or UV filtering effect. The primary transformation pathway of ATL included hydroxylation, chlorination, and bond-cleavage pathways based on the structures of the eight identified transformation products. Seven chlorinated disinfection by-products decreased as wavelengths and pH increased. The above results show that UVA-LED/chlorine might be an efficient process for water treatment.

Generation of hydroxyl radicals via activation of Cr(VI) by UVA-LED for rapid decontamination: The important role of Cr(V).

Hexavalent chromium (Cr(VI)) was activated by ultraviolet-A light-emitting diode (UVA-LED), resulting in efficient removal of various pollutants, including dye, pharmaceuticals, and pesticides, with pseudo-first-order rate constants of 0.0610-0.159min-1. Comparatively, UVA-LED or Cr(VI) alone barely degraded selected pollutants. Both HO• and Cr(V) were produced in the UVA-LED/Cr(VI) system based on scavenging and probing experiments, UV-visible and electron spin resonance spectra analysis. HO• was demonstrated to be the dominant reactive species via stepwise regeneration of Cr(V) to Cr(VI). The quantum yield of HO• was determined to be 7.79×10-4 mol Es-1 at a Cr(VI) dosage of 0.5mM and pH of 6.0. Additionally, the degradation efficiency of sulfamethoxazole (SMX) as a model compound decreased linearly as UVA-LED wavelengths increased from 365 to 405nm, while SMX was barely degraded at visible light irradiation wavelength ranges (449-505nm). SMX degradation efficiency increased from 71.0 % to 97.5 % as Cr(VI) dosage increased from 0.05 to 0.7mM. pH displayed a negative impact on SMX degradation with its removal efficiency decreasing from 99.4 % to 13.3 % as pH increased from 3.0 to 9.0. This study first reported that HO• was generated via activation of Cr(VI) by UVA-LED, which is instructive for the removal of pollutants co-existed in chromium-containing wastewater.

Combination system of pulsed ohmic heating and 365-nm UVA light-emitting diodes to enhance inactivation of foodborne pathogens in phosphate-buffered saline, milk, and orange juice

This study developed and investigated the combination system of pulsed ohmic heating (POH) and ultraviolet A light-emitting diode (UVA-LED) to enhance inactivation of pathogens in phosphate-buffered saline, milk, and orange juice. When Escherichia coli O157:H7 and Salmonella Typhimurium (6–8 log CFU/ml) in samples were subjected to the simultaneous combination of POH and UVA-LED at 50–65°C, the reduction levels increased >1 log CFU/ml compared with each treatment alone. After pathogens in PBS were subjected to the combination treatment at 65°C (50 s), the degree of intracellular ROS generation and lipid peroxidation were increased approximately 1.6 times than each treatment alone. Moreover, propidium iodide uptake values, which indicated cell membrane damage, for E. coli O157:H7 were 0.92, 14.22, and 19.92 after UVA-LED, POH, and their combination treatment, respectively. Therefore, the combination of POH and UVA-LED may possibly be applied as an effective hurdle technology for food safety. Industrial relevanceIt was identified that the combination treatment induced the generation of intracellular ROS; thereby causing lipid peroxidation and cell membrane damage of pathogens. However, the combination system has no effect on DNA damage of pathogens. In addition, there was no significant difference in the content of vitamin and malondialdehyde in milk and orange juice before and after the combination treatment. Thus, this research provides a fundamental database for the applicability of the combination system of POH and UVA-LED to the pasteurization process in the food industry.

Penicillium growth inhibition, fruit decay reduction, and polymethoxyflavones and scoparone induction in satsuma mandarin irradiated with ultraviolet-A light-emitting diodes

In this study, we investigated the effects of ultraviolet (UV)-A light-emitting diodes (LEDs) on the inhibition of fungal spore germination, fruit decay, and accumulation of secondary metabolites, including phytoalexins, in satsuma mandarin. We examined the growth and development of blue (Penicillium italicum) and green (Penicillium digitatum) molds exposed to UV-A LED irradiation in vitro and found that UV-A LEDs with an emission peak of 375 nm and light intensity of 9.4 W m−2 significantly reduced the growth of both these fungi. In addition, wounded fruits inoculated with P. digitatum were irradiated with UV-A LEDs for 6 days, and we monitored the subsequent changes in green mold symptoms. The results indicated that low-intensity UV-A LED treatment significantly reduced green mold symptoms in fruit, being the effect most pronounced inhibitory on Penicillium sporulation. Furthermore, wounded fruits subjected to UV-A LED treatment were found to have significantly higher contents of the coumarin compound scoparone than fruits maintained in the dark. Contrastingly, scoparone was barely detectable in non-wounded fruits, irrespective of UV-A LED irradiation. The contents of nobiletin, tangeretin, and hesperidin were likewise found to be higher in wounded fruits treated with UV-A LED than in either non-wounded or non-irradiated fruits. These results indicate that treatment with low-intensity UV-A LED irradiation is sufficient to reduce mold symptom development, and accordingly could represent a promising safe approach to the control of post-harvest decay in citrus fruits. On the basis of our observations, we speculate that the biosynthesis of scoparone, polymethoxyflavones, and flavanones could be induced when the peel is injured and irradiated with UV-A contributing to a reduction in fruit decay.

Highly Transparent p‐AlGaN‐Based (326–341 nm)‐Band Ultraviolet‐A Light‐Emitting Diodes on AlN Templates: Recent Advances and Perspectives

The epitaxial growth of transparent p‐AlGaN‐based ultraviolet‐A (UVA), light‐emitting diodes (LEDs) may solve the problems of UVA light absorption through the GaN buffers and p‐GaN contact layers at (326–341 nm)‐band emission, respectively. Herein, first, an idea of conventional n‐AlGaN buffer layer (BL) and n‐AlGaN electron source layer (ESL) for the suppression of threading dislocation density (TDD) and enhancement of internal quantum efficiency (IQE) of UVA emitters, using low‐pressure metalorganic vapor‐phase epitaxy (LP‐MOVPE) is attempted. As a result, the total‐TDDs is reduced from ≈ 3 × 109 cm−2 to ≈ 1 × 109 cm−2 in the n‐AlGaN ESL of a 326 nm‐band UVA multiquantum‐wells (MQWs), and IQE is also improved from 30% to 52% at room temperature (RT). Second, an idea of Si‐doped n‐AlGaN Superlattices (SLs)‐based BL, using LP‐MOVPE is challenged. Subsequently, a record IQE of 56% at RT and high crystal quality in 341 nm‐band UVA MQWs are observed. Finally, using a well thickness ≈ 2 nm in SLs‐based UVA MQWs, the light power and external quantum efficiency (EQE), respectively, are remarkably enhanced from 3.5 mW and 0.5% to 7.5 mW and 1.4% on wafer in 341 nm‐Band UVA LED. The perspective for the improvements of UVA emitter's performances is also discussed.

UVA-LED-Assisted Activation of the Ferrate(VI) Process for Enhanced Micropollutant Degradation: Important Role of Ferrate(IV) and Ferrate(V).

This paper investigated ultraviolet A light-emitting diode (UVA-LED) irradiation to activate Fe(VI) for the degradation of micropollutants (e.g., sulfamethoxazole (SMX), enrofloxacin, and trimethoprim). UVA-LED/Fe(VI) could significantly promote the degradation of micropollutants, with rates that were 2.6-7.2-fold faster than for Fe(VI) alone. Comparatively, UVA-LED alone hardly degraded selected micropollutants. The degradation performance was further evaluated in SMX degradation via different wavelengths (365-405 nm), light intensity, and pH. Increased wavelengths led to linearly decreased SMX degradation rates because Fe(VI) has a lower molar absorption coefficient at higher wavelengths. Higher light intensity caused faster SMX degradation, owing to the enhanced level of reactive species by stronger photolysis of Fe(VI). Significantly, SMX degradation was gradually suppressed from pH 7.0 to 9.0 due to the changing speciation of Fe(VI). Scavenging and probing experiments for identifying oxidative species indicated that high-valent iron species (Fe(V)/Fe(IV)) were responsible for the enhanced degradation. A kinetic model involving target compound (TC) degradation by Fe(VI), Fe(V), and Fe(IV) was employed to fit the TC degradation kinetics by UVA-LED/Fe(VI). The fitted results revealed that Fe(IV) and Fe(V) primarily contributed to TC degradation in this system. In addition, transformation products of SMX degradation by Fe(VI) and UVA-LED/Fe(VI) were identified and the possible pathways included hydroxylation, self-coupling, bond cleavage, and oxidation reactions. Removal of SMX in real water also showed remarkable promotion by UVA-LED/Fe(VI). Overall, these findings could shed light on the understanding and application of UVA-LED/Fe(VI) for eliminating micropollutants in water treatments.

Assessing an Integral Treatment for Landfill Leachate Reverse Osmosis Concentrate

An integral treatment process for landfill leachate reverse osmosis concentrate (LLROC) is herein designed and assessed aiming to reduce organic matter content and conductivity, as well as to increase its biodegradability. The process consists of three steps. The first one is a coagulation/flocculation treatment, which best results were obtained using a dosage of 5 g L−1 of ferric chloride at an initial pH = 6 (removal of the 76% chemical oxygen demand (COD), 57% specific ultraviolet absorption (SUVA), and 92% color). The second step is a photo-Fenton process, which resulted in an enhanced biodegradability (i.e., the ratio between the biochemical oxygen demand (BOD5) and the COD increased from 0.06 to 0.4), and an extra 43% of the COD was removed at the best trialed reaction conditions of [H2O2]/COD = 1.06, pH = 4 and [H2O2]/[Fe]mol = 45. An ultra violet-A light emitting diode (UVA-LED) lamp was tested and compared to conventional high-pressure mercury vapor lamps, achieving a 16% power consumption reduction. Finally, an optimized 30 g L−1 lime treatment was implemented, which reduced conductivity by a 43%, and the contents of sulfate, total nitrogen, chloride, and metals by 90%. Overall, the integral treatment of LLROC achieved the removal of 99.9% color, 90% COD, 90% sulfate, 90% nitrogen, 86% Al, 77% Zn, 84% Mn, 99% Mg, and 98% Si; and significantly increased biodegradability up to BOD5/COD = 0.4.

Photocatalytic inactivation of viral particles of human norovirus by Cu-doped TiO2 non-woven fabric under UVA-LED wavelengths

Metal-doped TiO2 photocatalysis are recognized as effective materials for eliminating human norovirus (HuNoVs). In recent years, the airborne transmission of viral particles of HuNoVs has been a cause for concern. In this study, we evaluated the virucidal effects of a Cu/TiO2 non-woven fabric (NWF) on viral particles of HuNoV genogroup II genotype 4 (HuNoV GII.4) under an ultraviolet A light-emitting diode (UVA-LED) source. For the optimized parameters, a multivariate statistical analysis using the Box-Behnken design (BBD) technique combined with the response surface methodology (RSM) was applied. The experimental results showed that the Cu/TiO2-based NWF degraded HuNoV viral particles in the air samples. The BBD-based RSM indicated that the optimum treatment conditions for inactivating the HuNoV GII.4 droplets with the Cu/TiO2 NWF were a 1:7.7 ratio of Cu:TiO2 and the use of a 373-nm UVA-LED source for 48.08 min. The optimal conditions for the photocatalytic efficacy in HuNoV GII.4 of Cu/TiO2 NWF were verified experimentally, giving a value of 2.89 ± 0.11 log10 genomic copies, which was the same as the predicted value (2.91611) within experimental uncertainty. This result adequately validated the predicted model and confirmed that viral particles of HuNoVs could efficiently be disinfected using Cu/TiO2 NWF stimulated by UVA-LED light.

Beyond 53% internal quantum efficiency in a AlGaN quantum well at 326 nm UVA emission and single-peak operation of UVA LED

AlGaN-based ultraviolet-A (UVA) light-emitting-diodes (LEDs) at emission under 330 nm are of great importance for numerous applications, including medicine and photochemical technologies. In this Letter, a highly relaxed n-AlGaN electron injection layer (EIL) underneath the multi-quantum wells (MQWs) for the suppression of both threading dislocation densities and piezoelectric effect was attempted. When the Ga-rich n-AlGaN EIL in the UVA LED was relaxed up to 75%, the full width at half-maximum values of the X-ray rocking curves for the (10–12) planes were reduced from our previous value of approximately 793 to 564 arcsec. Subsequently, a maximum light power of 3.1 mW was achieved in the 326 nm band UVA LED. However, carrier confinement and transport issues in the MQWs were observed. To resolve these issues of carrier confinement and transport, we provide a short roadmap for experimental efforts to realize an internal quantum efficiency (IQE) beyond 53% in AlGaN UVA-MQWs.

Novel Radiation Device for Application in the UV-A and UV-B Range

This work concerns an ultraviolet-A (UV-A) and UV-B emitting radiation unit. To this end, UV-A emitting light emitting diodes (LEDs) were combined with a Lu3Al5O12:Gd3+ (LuAG:Gd) coated Xe excimer discharge lamp. Prior to the application, the single-phase phosphor was optimized w.r.t particle size distribution and reflection spectrum before the photoluminescence properties were recorded. It turned out that LuAG:Gd is an intense emitting material in the UV-B spectral range. Afterwards, a phosphor paint was made and applied with an up-flush technique to a fused silica tube to create a uniform coating. For the excimer lamp a high voltage pulse generator in flyback topology was developed which allows to adjust the UV-B output from 1% to 100% without affecting the lamp efficiency. To maximize the UV output power the pulse width, pulse amplitude as well as the duty cycle of lamp was tuned. At last the complete set up was measured in front of an BaSO4 coated integrating sphere to record the radiation pattern and to show the scalability of the UV-A LEDs and UV-B excimer lamp. Overall, a fully adjustable and versatile radiation device for medical treatment, photochemistry and tanning purposes was engineered which could be an alternative to (coated) mercury discharge lamps and UV-B LEDs.

Optical characteristics of highly conductive n-type GaN prepared by pulsed sputtering deposition

We have characterized highly conductive Si-doped GaN films with a high electron mobility of 112 cm2V−1s−1 at an electron concentration of 2.9 × 1020 cm−3, prepared using pulsed sputtering deposition (PSD). With an increase in the doping concentration, the absorption edge was found to shift toward a higher energy level, owing to the Burstein-Moss effect, thus making this material suitable for the transparent conductive tunneling electrodes of visible and ultraviolet-A light-emitting diodes. The full width at half maximum value of the near-band-edge (NBE) emissions in a photoluminescence spectrum measured at 77 K was as small as 185 meV, even for the sample with the highest electron concentration of 2.9 × 1020 cm−3. Such sharp NBE emissions from PSD-grown heavily Si-doped GaN films can be explained by an analytical model with a low compensation ratio θ of around 0.1, which is consistent with the exceptionally high observed electron mobility. These results indicate the strong potential of the low-temperature PSD growth technique for the formation of high-quality, heavily Si-doped GaN.

Response of Mustard Microgreens to Different Wavelengths and Durations of UV-A LEDs.

Ultraviolet A (UV-A) light-emitting diodes (LEDs) could serve as an effective tool for improving the content of health-promoting bioactive compounds in plants in controlled-environment agriculture (CEA) systems. The goal of this study was to investigate the effects of UV-A LEDs at different wavelengths (366, 390, and 402 nm) and durations (10 and 16 h) on the growth and phytochemical contents of mustard microgreens (Brassica juncea L. cv. “Red Lion”), when used as supplemental light to the main LED lighting system (with peak wavelengths of 447, 638, 665, and 731 nm). Plants were grown for 10 days under a total photon flux density (TPFD) of 300 µmol m−2 s−1 and 16-h light/8-h dark period. Different UV-A wavelengths and irradiance durations had varied effects on mustard microgreens. Supplemental UV-A radiation did not affect biomass accumulation; however, the longest UV-A wavelength (402 nm) increased the leaf area of mustard microgreens, regardless of the duration of irradiance. The concentration of the total phenolic content and α-tocopherol mostly increased under 402-nm UV-A, while that of nitrates increased under 366- and 390-nm UV-A at both radiance durations. The contents of lutein/zeaxanthin and β-carotene increased in response to the shortest UV-A wavelength (366 nm) at 10-h irradiance as well as longer UV-A wavelength (390 nm) at 16 h irradiance. The most positive effect on the accumulation of mineral elements, except iron, was observed under longer UV-A wavelengths at 16-h irradiance. Overall, these results suggest that properly composed UV-A LED parameters in LED lighting systems could improve the nutritional quality of mustard microgreens, without causing any adverse effects on plant growth.

Photocatalytic performance and application outlook of 3D TiO2/titanium mesh modified by GO-Ag joined-deposition

Abstract In this paper, in-situ growth of titanium dioxide nanotubes on titanium mesh and deposition of silver (Ag) and graphene (GO) were combined to construct 3D catalysts. By introducing ultraviolet-A/Light emitting diodes (UVA-LEDs), the GO-Ag-TNTs/UVA-LEDs photocatalytic system was setup for methyl orange (MO) degradation. Herein, Ag and GO were doped by photoreduction deposition and hydrothermal reduction respectively, which the doping amount of Ag and GO was optimized, the optimal silver nitrate precursor concentration was 5 mM, and the optimal concentration of GO was 25 mg added into 90 mL of ethanol and deionized water. Additionally, Field emission scanning electron microscopy (FESEM), Raman, Fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectrophotometer (UV–vis-DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS) were utilized to directly and indirectly clarify the structural characteristics of the catalysts before and after loading, while photoelectric properties were checked by Electrochemical Workstation. Results showed that GO-Ag joint-doped TNTs sample exhibited the highest photocurrent response and lowest transfer charge resistance compared to other TNTs samples. As for MO degradation and TOC mineralization, GO-Ag optimally doped-TNTs sample enhanced photocatalytic effects (about 20% and 30% improvement respectively) compared with bare TNTs sample.

Determining optimum wavelength of ultraviolet rays to pre-exposure of non-uniformity error correction in Gafchromic EBT2 films

Abstract Gafchromic films have been used to measure X-ray doses in diagnostic radiology such as computed tomography. The double-exposure technique is used to correct non-uniformity error of Gafchromic EBT2 films. Because of the heel effect of diagnostic x-rays, ultraviolet A (UV-A) is intended to be used as a substitute for x-rays. When using a UV-A light-emitting diode (LED), it is necessary to determine the effective optimal UV wavelength for the active layer of Gafchromic EBT2 films. This study evaluated the relation between the increase in color density of Gafchromic EBT2 films and the UV wavelengths. First, to correct non-uniformity, a Gafchromic EBT2 film was pre-irradiated using uniform UV-A radiation for 60 min from a 72-cm distance. Second, the film was irradiated using a UV-LED with a wavelength of 353-410 nm for 60 min from a 5.3-cm distance. The maximum, minimum, and mean ± standard deviation (SD) of pixel values of the subtraction images were evaluated using 0.5 inches of a circular region of interest (ROI). The highest mean ± SD (8915.25 ± 608.86) of the pixel value was obtained at a wavelength of 375 nm. The results indicated that 375 nm is the most effective and sensitive wavelength of UV-A for Gafchromic EBT2 films and that UV-A can be used as a substitute for x-rays in the double-exposure technique.

Comparison of standard light-emitting diode (LED) and 385 nm ultraviolet A LED (UVA-LED) for disinfection of Escherichia coli

UV light has become an integral part of human life especially in performing wide range of disinfection. Most of the research on UVLEDs is limited to UVC region because of comparison with mercury based UV lamps which work typically at 254 nm. Limited research is found on the use of UVA-LEDs for inactivation of microorganisms in healthcare. In this study a standard 3 mm LED has been compared with 385 nm UVA-LED for inactivation of Escherichia coli. E. coli strains were swabbed on control, LED and UVA-LED petri dishes using cotton bud. The LED and UVA-LED samples were exposed to standard LED light and UVA light respectively for 1 h. The analysis of bacteria by determining Colony forming units (CFU) and log inactivation were carried out to calculate the number of colonies present in each sample. Result showed negligible to none disinfection properties in standard LED light. LED samples had CFU/ml colonies compared to control which is CFU/ml. UVA-LED samples achieved maximum inactivation and only had CFU/ml. Log inactivation results showed that LED samples observed 0.1-log inactivation whereas the UVA-LED had significant inactivation of 3.8-log inactivation corresponding to approximately 99.99 % E. coli reduction. The results demonstrate that UVA-LED at 385 nm is capable of efficiently providing inactivation of bacteria E. coli.

Decomposition of acetaminophen (Ace) using TiO2/UVA/LED system

For photocatalytic degradation of organic pharmaceutical pollutants in wastewater, an important limitation is low photonic efficiency. To solve this problem, using periodic illumination is a good option. However, due to the nature of widely applied traditional mercury lamp, which cannot be turned on and off efficiently, the study of periodic illumination was limited. In this research, ultraviolet-A/light emitting diode (UVA/LED) lamp was introduced and a TiO2/UVA/LED photocatalytic system was setup for acetaminophen (Ace) degradation study. The background study was conducted, which included the effects of H2O2, humic acid and bicarbonate ion concentrations. Different periodic pulse frequencies were applied, results in this study shows that smallest duty cycle (0.2) and shortest cycle time (20ms) gave the highest photonic efficiency for photocatalytic degradation of Ace in the studied range. The effect of additional H2O2 was also studied. H2O2 added into the heterogeneous reaction system enhanced both decomposition rate and photonic efficiency under both continuous illumination mode and periodic illumination mode. The enhancement effect of H2O2, however, was found more obvious for controlled periodic illumination, especially for small duty cycles and short cycle times. In addition, by the addition of H2O2, the mineralization of Ace was accelerated probably due to the increase of hydroxyl radical concentration.

Effects of UV-A LED light irradiation on growth of cultured RAW 264.7 cells

The aim of this study was to examine the effects of ultraviolet A (UV-A) irradiation-induced damage on cultured macrophage RAW 264.7 cells and determine which components produced these manifestations. RAW 264.7 cells were irradiated with 365 nm UV-A using a light-emitting diode (LED). Cell viability and damage were determined using a calcein-AM and propidium iodide dual-staining assay and lactate dehydrogenase leakage, respectively. Intracellular reactive oxygen species (ROS) were measured by H2DCF-DA. The components of ROS in each medium were measured using an electron paramagnetic resonance (EPR) spectrometer in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide (TPC). While UV-A irradiation for 2 min significantly suppressed cell growth, LDH leakage did not occur. Addition of N-acetyl cysteine restored inhibition of cell proliferation, and reduced intracellular ROS levels. The EPR signal in the presence of TPC increased with time but was decreased by sodium azide. In addition, a typical EPR spectrum was obtained in the presence of DMPO, indicating the presence of a hydroxyradical. The spectrum was diminished by L-histidine. Data suggest that ROS generated in cells or culture medium by UV-A irradiation is predominantly singlet oxygen, and this singlet oxygen suppressed cell proliferation.

Vegetable surface sterilization system using UVA light-emitting diodes.

Surface sterilization of fresh produce has been needed in the food manufacturing/processing industry. Here we report a UVA-LED (Ultra Violet A-Light Emitting Diode) system for surface sterilization that is safe, efficacious, low cost, and apparently harmless to fresh produce. To test the system, Escherichia coli strain DH5α was spot-inoculated onto vegetable tissues, and treated under UVA-LED. Tissues were homogenized and bacteria quantified by colony-forming assay. Possible effects of UVA-LED on vegetable quality were evaluated by HPLC. Tissue weight changes were checked after treatment at 4℃, 15℃, and 30℃. Bacterial inactivation by UVA-LED radiation was observed after a 10 min treatment and increased with increasing time of irradiation. The log survival ratio reached -3.23 after a 90 min treatment. Bacterial cells surviving treatment grew slowly compared to non-irradiated control cells. Cabbage tissue lost weight over time after treatment, and weight loss increased with increasing incubation temperature, but there was no difference between losses by UVA-LED treated and control tissues at any temperature tested. In addition, no differences of Vitamin C content in cabbage tissue were detected by HPLC after UVA-LED treatment. These results suggest that UVA-LED treatment has great potential for vegetable surface sterilization in the food manufacturing/processing industry.

Degradation of acetaminophen by UVA/LED/TiO2 process

Photocatalytic process that uses traditional low pressure mercury lamp and TiO2 as catalyst has attracted numerous attentions recently for the degradation of organic pollutants in water environment. However, there are several important drawbacks to this mercury lamp such as high energy cost and the production of toxic mercury waste. Compared to traditional mercury lamp, the newly emerging UVA/LED is more efficient in converting electricity into light. It has longer lifetime and no toxic waste generation problem exists. Therefore, the purpose of this research was to study the ability of high power ultraviolet A light-emitting diode (UVA/LED) as a light source in the degradation of organic pollutants. The optimal operational conditions were also determined. In this study, a new device equipped with high-energy 365nm UVA/LED using TiO2-P25 as the catalyst was developed and evaluated for photolytic/photocatalytic oxidation of acetaminophen (Ace). The results showed that the chosen UVA/LED alone degraded negligible amount of Ace, while in the presence of TiO2, the concentration of Ace decreased substantially. In most experiments of this study, Ace could be degraded to non-detectable level within 20min. The degradation rate was found to be related to the dosage of TiO2, initial Ace concentration and light intensity. Based on the experimental data, the following kinetic equation was achieved by kinetic modeling: rs=-2.4168×I0.5732×[Ace]1+0.1523×[Ace]0, which was also in agreement with the Langmuir–Hinshelwood (L–H) law.

New water disinfection system using UVA light-emitting diodes

To evaluate the ability of high-energy ultraviolet A (UVA) light-emitting diode (LED) to inactivate bacteria in water and investigate the inactivating mechanism of UVA irradiation. We developed a new disinfection device equipped with high-energy UVA-LED. Inactivation of bacteria was determined by colony-forming assay. Vibrio parahaemolyticus, enteropathogenic Escherichia coli, Staphylococcus aureus and Escherichia coli DH5alpha were reduced by greater than 5-log(10) stages within 75 min at 315 J cm(-2) of UVA. Salmonella enteritidis was reduced greater than 4-log(10) stages within 160 min at 672 J cm(-2) of UVA. The formation of 8-hydroxy-2'-deoxyguanosine in UVA-LED irradiated bacteria was 2.6-fold higher than that of UVC-irradiated bacteria at the same inactivation level. Addition of mannitol, a scavenger of hydroxyl radicals (OH(*)), or catalase, an enzyme scavenging hydrogen peroxide (H(2)O(2)) to bacterial suspensions significantly suppressed disinfection effect of UVA-LED. This disinfection system has enough ability to inactivate bacteria and OH(*) and H(2)O(2) participates in the disinfection mechanism of UVA irradiation. We newly developed UVA irradiation system and found that UVA alone was able to disinfect the water efficiently. This will become a useful disinfection system.