UV-A LED Research Articles

Performance of a UV-A LED system for degradation of aflatoxins B1 and M1 in pure water: kinetics and cytotoxicity study

The efficacy of a UV-A light emitting diode system (LED) to reduce the concentrations of aflatoxin B1, aflatoxin M1 (AFB1, AFM1) in pure water was studied. This work investigates and reveals the kinetics and main mechanism(s) responsible for the destruction of aflatoxins in pure water and assesses the cytotoxicity in liver hepatocellular cells. Irradiation experiments were conducted using an LED system operating at 365 nm (monochromatic wave-length). Known concentrations of aflatoxins were spiked in water and irradiated at UV-A doses ranging from 0 to 1,200 mJ/cm2. The concentration of AFB1 and AFM1 was determined by HPLC with fluorescence detection. LC–MS/MS product ion scans were used to identify and semi-quantify degraded products of AFB1 and AFM1. It was observed that UV-A irradiation significantly reduced aflatoxins in pure water. In comparison to control, at dose of 1,200 mJ/cm2 UV-A irradiation reduced AFB1 and AFM1 concentrations by 70 ± 0.27 and 84 ± 1.95%, respectively. We hypothesize that the formation of reactive species initiated by UV-A light may have caused photolysis of AFB1 and AFM1 molecules in water. In cell culture studies, our results demonstrated that the increase of UV-A dosage decreased the aflatoxins-induced cytotoxicity in HepG2 cells, and no significant aflatoxin-induced cytotoxicity was observed at UV-A dose of 1,200 mJ/cm2. Further results from this study will be used to compare aflatoxins detoxification kinetics and mechanisms involved in liquid foods such as milk and vegetable oils.

Novel laser induced fluorescence with hyperspectral imaging of amplifying fluorescent melamine resin for TNT vapor detection

Terrorism by means of explosive is an imminent threat; instant detection of explosive vapors is a vital demand. Explosives are electron deficient molecules; the vicinity of explosives to fluorescent material could hinder excitation migration resulting in fluorescence quenching. This study reports on the facile synthesis of porous melamine–formaldehyde–diethylenetriaminepentaacetic acid (MF–DTPA) resin with surface area of 162 m2/g, and average pore diameter is 94.7 (Å). MF–DTPA resin demonstrated unique ability to capture TNT vapors with complete change in its color from white to reddish. Furthermore, MF–DTPA resin demonstrated novel fluorescence properties over visible band (400–560 nm) and infrared band (700–760 nm) when stimulated with UVA LED source at 385 nm of 100 mW power. These two emission bands were completely quenched when MF–DTPA was subjected to TNT vapors. Amplified chemosensory response was archived via wired receptors in a series. Hyperspectral imaging associated with 2D moving average filter was employed to develop enhanced color intensity maps.

Coupling Persulfate-Based AOPs: A Novel Approach for Piroxicam Degradation in Aqueous Matrices

The activated persulfate degradation of piroxicam, a non-steroidal anti-inflammatory drug (NSAID) belonging to oxicams, was investigated. Persulfate was activated with thermal energy or (UV-A and simulated solar) irradiation. Using 250 mg/L sodium persulfate at 40 °C degraded almost completely 0.5 mg/L of piroxicam in 30 min. Increasing piroxicam concentration from 0.5 to 4.5 mg/L decreased its removal. The observed kinetic constant was increased almost ten times from 0.077 to 0.755 min−1, when the temperature was increased from 40 to 60 °C, respectively. Process efficiency was enhanced at pH 5–7. At ambient conditions and 30 min of irradiation, 94.1% and 89.8% of 0.5 mg/L piroxicam was removed using UV-A LED or simulated solar radiation, respectively. Interestingly, the use of simulated sunlight was advantageous over UV-A light for both secondary effluent, and 20 mg/L of humic acid solution. Unlike other advanced oxidation processes, the presence of bicarbonate or chloride in the range 50–250 mg/L enhanced the degradation rate, while the presence of humic acid delayed the removal of piroxicam. The use of 0.5 and 10 g/L of methanol or tert-butanol as radical scavengers inhibited the reaction. The coupling of thermal and light activation methods in different aqueous matrices showed a high level of synergy. The synergy factor was calculated as 68.4% and 58.4% for thermal activation (40 °C) coupled with either solar light in 20 mg/L of humic acid or UV-A LED light in secondary effluent, respectively.

Mechanistic insights into UV-A mediated bacterial disinfection via endogenous photosensitizers

UV-A and visible light are thought to excite endogenous photosensitizers in microbes, thereby initiating complex chemical interactions that ultimately kill cells. Natural solar-based disinfection methods have been adapted into commercial lighting technologies with varying degrees of reported efficacy and associated safety hazards for human exposure. Here we utilize a narrow-spectrum UV-A LED prototype (currently in development for health care applications) to investigate the mechanism of bacterial photoinactivation using 365 nm light. Using a combination of reverse genetics and biochemical investigation, we report mechanistic evidence that 365nm light initiates a chain-reaction of superoxide-mediated damage via auto-excitation of vitamin-based electron carriers, specifically vitamin K2 menaquinones and the FAD flavoprotein in Complex II in the electron transport chain. We observe that photoinactivation is modifiable through supplementation of the environment to bypass cell damage. Lastly, we observe that bacteria forced into metabolic dormancy by desiccation become hypersensitized to the effects of UV-A light, thereby permitting photoinactivation at fluences that are significantly lower than the industry threshold for safe human exposure. In total, these results substantiate the mechanism and potential application of narrow- spectrum UV-A light for bacterial disinfection purposes.

Photocatalytic degradation of an agro-industrial wastewater model compound using a UV LEDs system: kinetic study

An ultraviolet light emitting diode (UV-A LED) system was built to test the capability of performing heterogeneous photocatalysis using TiO2 P25. The LEDs maximum wavelength is 365 nm with an irradiance power of 85 W m−2. The device was tested in batch and continuous (CSTR) mode in a laboratorial scale reactor. The degradation of an agro-industrial wastewater model compound (p-hydroxybenzoic acid, pHBA) was investigated, assessing the effect of different experimental conditions such as pH, pHBA and TiO2 concentration keeping constant the UV-A LEDs power and temperature. The photodegradation of different concentrations of pHBA with [TiO2] = 500 mg L−1, IUV = 85 W m−2 and a T = 21 °C were analysed by pseudo-first order kinetics. The results were applied to the Langmuir-Hinshelwood model yielding kc = 0.885 mg L−1 min−1 and kLH = 0.217 L mg−1. In a comparative experiment the UV-A LEDs system showed faster kinetics (k = 0.0134 min−1) than solar radiation (IUV = 23 W m−2; k = 0.0077 min−1), with [pHBA] = 75 mg L−1 and [TiO2] = 500 mg L−1. The values of the Electric Energy per Order (EEO) = 115 kWh m−3 order−1 and the Specific Applied Energy (ESAE) = 318 kWh mol−1 order−1 were obtained with [TiO2] = 1000 mg L−1 and [pHBA] = 50 mg L−1. Analogous results were obtained ([TiO2] = 500 mg L−1) in a CSTR with a slight decrease in the first order kinetic constant due to the “non-ideal” reactor: from 0.0284 to 0.0158 min−1 and from 0.0143 to 0.00825 min−1 with [pHBA] = 50 mg L−1 and 75 mg L−1, respectively. This work shows that photocatalytic reactors with UV-A LEDs can advantageously replace conventional UV mercury lamps based reactors in the photodegradation of phenolic compounds.

Beyond 53% internal quantum efficiency in a AlGaN quantum well at 326 nm UVA emission and single-peak operation of UVA LED: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 495 (2020)OPLEDP0146-959210.1364/OL.376894.

Development of A Novel High Throughput Photo-catalyst Screening Procedure: UV-A Degradation of 17α-Ethinylestradiol with Doped TiO2-Based Photo-catalysts.

The rising pollution of surface water by endocrine disruptive chemicals (EDCS) could lead to the persistent harm of aquatic wildlife. Addressing this concern, advanced waste water treatment techniques should be established in addition to the present sewage treatment. Therefore, the promising advanced oxidation process of photocatalysis is discussed. With the aim of establishing a novel high throughput screening approach for photocatalysts, a workflow resting upon the use of a self-constructed 60-fold parallel stirring UV-A LED photoreactor, followed by parallel sample extraction by SPE and sequential automated analysis by GC-MS, was developed, and is presented in this article. With the described system, TiO2-based photocatalysts, doped with different amounts of zinc, and synthesised by a sol-gel-route, were tested regarding their activity in the photocatalytic degradation of the synthetic estrogen 17α-ethinylestradiol. Thereby, the functional behavior of the photoreactor system and its applicability in a high throughput process could be evaluated. As a result of the catalyst screening, TiO2 catalysts with low amounts of zinc were found with a significantly higher activity, compared to undoped TiO2. In conclusion, the presented system provides an easily accessible high throughput method for a variety of photocatalytic experiments.

Physiological and Metabolomic Responses of Kale to Combined Chilling and UV-A Treatment.

Short-term abiotic stress treatment before harvest can enhance the quality of horticultural crops cultivated in controlled environments. Here, we investigated the effects of combined chilling and UV-A treatment on the accumulation of phenolic compounds in kale (Brassica oleracea var. acephala). Five-week-old plants were subjected to combined treatments (10 °C plus UV-A LED radiation at 30.3 W/m2) for 3-days, as well as single treatments (4 °C, 10 °C, or UV-A LED radiation). The growth parameters and photosynthetic rates of plants under the combined treatment were similar to those of the control, whereas UV-A treatment alone significantly increased these parameters. Maximum quantum yield (Fv/Fm) decreased and H2O2 increased in response to UV-A and combined treatments, implying that these treatments induced stress in kale. The total phenolic contents after 2- and 3-days of combined treatment and 1-day of recovery were 40%, 60%, and 50% higher than those of the control, respectively, and the phenylalanine ammonia-lyase activity also increased. Principal component analysis suggested that stress type and period determine the changes in secondary metabolites. Three days of combined stress treatment followed by 2-days of recovery increased the contents of quercetin derivatives. Therefore, combined chilling and UV-A treatment could improve the phenolic contents of leafy vegetables such as kale, without growth inhibition.

Effectiveness of visible and ultraviolet light emitting diodes for inactivation of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli: A comparative study

The rapid use of ultraviolet light emitting diodes (UV-LEDs) in various disinfection applications is growing tremendously due to their advantages unachievable using UV lamps. In this study, a comparison of standard LED at 460 nm wavelength and UVA LED at 385 nm was conducted to determine their effectiveness in disinfection of frequently isolated pathogens in hospitals (Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli). Determination of disinfection efficiency was carried out by measuring inhibition zone. Effects of varied exposure time on the inactivation of pathogenic microorganisms was studied. The results demonstrated that LED does not have germicidal activities. The highest inactivation for UVA LED was achieved for Pseudomonas aeruginosa. Linear relationship was found between exposure time and log reduction. This study showed that UVA LEDs can effectively inactivate significantly higher number of microorganisms hence can be used in disinfection of various applications.

Micropollutant removal in real WW by photo-Fenton (circumneutral and acid pH) with BLB and LED lamps

In this study, photo-Fenton treatment was performed to remove a target compound (propranolol, PROP) from wastewaters of secondary effluents coming from WWTP. Two different radiation sources were tested: BLB and UV-A LEDs, which implies low electrical power and no mercury content. The differences observed in the PROP removal with both lamps may be due to the different radiation distribution, absorption inside the reactor, emission angle and wavelength emission, which are key parameters in the radiation field of the photoreactor. Four wastewaters (IFAS, MBR, CAS and CAS-NE) and ultrapure water were tested to determine the influence of water matrix. Instead the propranolol degradation using UV-A LEDs was smaller than using BLB lamps, in ultrapure water the degradation was very similar. The matrices with more organic matter and turbidity achieved low propranolol removals due to the competition for hydroxyl radicals and the effect of the light scattering. In addition, photo-Fenton at neutral pH (to avoid the acidification/basification) was also carried out using two chelating agents (EDDS and EDTA). Two molar ratios ligand-Fe(II) were tested (1:1 and 1.5:1). EDDS with L:Fe(II) molar ratio 1:1 was selected based on studies of MP degradation, biodegradability and toxicity. Comparisons between conventional photo-Fenton and photo-Fenton with EDDS-Fe(II) were performed with UV-A LEDs. For Milli-Q and IFAS best results were achieved in conventional photo-Fenton (32.9% for IFAS instead of 14.3% in EDDS-Fe(II)). Contrary, for the MBR, CAS and CAS-NE the best results were shown for EDDS-Fe(II) photo-Fenton. In IFAS, biopolymers and humic substances were the responsible of the different behavior of IFAS than other WW. Finally, for conventional photo-Fenton, dark Fenton plays an important role during the first 30 s, then, photo-Fenton controls the process. For circumneutral photo-Fenton, dark Fenton is not so important during the initial time. These observations have been corroborated by different kinetic fittings for different reaction times.

A Study of Lens Design Technique for Proximity Exposure Using a UVA LED

A Study of Lens Design Technique for Proximity Exposure Using a UVA LED

Synergies, radiation and kinetics in photo-Fenton process with UVA-LEDs

The photo-Fenton process, with UV-A LED (λ = 380–390, 390–400 and 380–400 nm) has demonstrated to be effective in the abatement of a target micropollutant, such as diphenhydramine hydrochloride (DPH). Different concentrations of iron (Fe2+) and H2O2 were tested and monitored, and the best results in DPH removal were obtained for the highest concentrations of both iron (II) and H2O2 (10 mg Fe2+/L - 150 mg H2O2/L). The evolution of iron and peroxide concentration was also monitored. Kinetic studies showed that dark Fenton process prevails at the beginning of the experiment, when Fe2+ concentration is higher. However, after these initial moments, the prevailing process is photo-Fenton and, in addition, wavelength radiation plays an important role. Concerning the effect of radiation, four LEDs (4.2 W total power) were used, emitting radiation in the wavelength range between 380–390 or 390–400 nm. Similar results were obtained in both cases in DPH removal by photo-Fenton (30 min for total elimination). However, a synergistic effect was observed when two LEDs of 380–390 nm and two LEDs of 390–400 nm were used. Total power was the same (4.2 W) in each experimental condition, but the increase in the wavelength range to 20 nm (380–400 nm) produces an increase in the rate of DPH removal, achieving its total elimination at 15 min. This fact, with the use of a simple radiation model, reveals the important role that radiation plays in the photo-Fenton process. Finally, the formed intermediates were determined and some reaction pathways were proposed.

EBT3-based dosimeter in characterizing UVA–LEDs with lambertian radiation pattern

PurposeThis paper aims to propose an area under the curve model to represent ultraviolet (UV) exposure doses on EBT3 films (in mJ/cm2). The model was developed on a cross-section of the exposed films using visible absorbance method. Ultraviolet–A light emitting diodes (UVA–LEDs) with 20° and 60° half angle with distinctive peak emission wavelengths between 365 to 405 nm are used in this experiment. No similar experimental setup or findings have been reported thus far, though the various application of EBT3 for the measurement of solar UV (A + B) have been published since EBT3 is commercially available.Design/methodology/approachTwo sets of UVA–LEDs were used as the UV radiation source in the experiment. The first set contains of four 5 mm low power UVA–LEDs with the 20° half angle and peak emission wavelength at 365, 375, 385 and 400 nm. The second set contains of five surface mount high power UVA–LEDs with the 60° half angle and peak emission wavelength at 365, 375, 385, 305 and 400 nm. The illumination setup for the two sets of LEDs is different between each other to obtain sufficient dose distribution on the films for spectroscopy analysis. This is due to the different illumination angle and irradiance intensity by each set of LEDs.FindingsUV–LED with a peak emission of 365, 375 and 385 nm able to produce UV doses accurately measurable using EBT3 films, UVA–LEDs with peak emission at 395 nm and above produced much lower accuracy with R2. From both set of LEDs, it can be concluded that peak emission wavelength of UVA–LED does influence the discoloration of the films. Shorter wavelength (higher energy) of UVA–LEDs discolors EBT3 films much intense compared to longer wavelength for a given UV dose exposure.Originality/valueDespite various practical applicability and advantages of UV–LEDs, there are still no standard methods in measuring UV–LED radiation output. The proposed approach not only allows us to obtain the dose of UV–LED, where the sensitivity of measurement is wavelength (energy) depended but also allows us to visually observe the illumination pattern of invisible UV radiation through the application of EBT3 films.

Realization of p-GaN ohmic contact by using a strained p-AlInGaN interlayer and its application in UVA LEDs

We use a p+-AlInGaN strained interlayer to form ohmic contact between p-GaN and indium tin oxide, and achieve a specific contact resistance of 6.06 × 10−2 Ω · cm2, similar to that with a p+-InGaN interlayer. When applied in a 365 nm UV LED, it shows a 0.5 V reduction of working voltage and an 18.1% enhancement of light output power, compared with those of the reference LED. Furthermore, the light output power is 12.8% higher than that of a LED with a p+-InGaN interlayer. These results indicate that a strained p-AlInGaN interlayer is a favorable choice for UVA LEDs.

Front Cover Picture: Gold Catalyzed Photoredox C1‐Alkynylation of N‐Alkyl‐1,2,3,4‐tetrahydroisoquinolines by 1‐Bromoalkynes with UVA LED Light (Adv. Synth. Catal. 6/2019)

Front Cover Picture: Gold Catalyzed Photoredox C1‐Alkynylation of <i>N</i>‐Alkyl‐1,2,3,4‐tetrahydroisoquinolines by 1‐Bromoalkynes with UVA LED Light (Adv. Synth. Catal. 6/2019)

Terephthalic acid decomposition by photocatalytic ozonation with VxOy/ZnO under different UV-A LEDs distributions

In this work, the degradation of terephthalic acid (TA) by vanadium oxide (VxOy) supported on zinc oxide (ZnO) was evaluated in a photocatalytic ozonation treatment based on two UV-A LEDs distributions. TEM analysis and specific surface area measurement suggest that VxOy is not supported on ZnO, while the EDXRF and XPS analysis indicated the presence of VxOy. The XPS analysis on VxOy/ZnO catalyst showed non-significant surface change between fresh and used catalyst. However, ozone decomposition showed a higher reaction rate constant for catalytic (230%) and photocatalytic ozonation (310%) in comparison with single ozone treatment. Photocatalytic ozonation with central and external irradiation arrays was evaluated in TA elimination by a kinetic study. The irradiation arrays had not statistical differences in the TA decomposition or oxalic acid formation. These results suggest that the construction of central bodies inside the reactor could be not necessary for photocatalytic processes.

Effect of catalyst coated surface, illumination mechanism and light source in heterogeneous TiO2 photocatalysis using a mili-photoreactor for n-decane oxidation at gas phase

This work evaluates the effect of the catalyst coated surface per reactor volume, illumination mechanism (back side (BSI) or front side (FSI) illumination) and light source on heterogeneous TiO2 photocatalysis using a mili-photoreactor, for the oxidation of a volatile organic compound in a gas stream. A thin film of TiO2-P25 was uniformly deposited on the front borosilicate window of the mili-photoreactor (BSI mechanism) or on the network of channels and chambers imprinted in the back stainless steel slab (FSI mechanism) using a spray system. BSI and FSI mechanisms were assessed using two different UVA LED systems (9 LEDs – LED9 and 18 LEDs – LED18), UVA lamps and simulated solar light as radiation sources. Under BSI and solar light the maximum reaction rate (rdec) obtained was 1.0 µmol min−1, whereas a 1.7-fold increase was attained using BSI-LED9. Although under FSI mechanism the catalyst coated surface per reactor volume is three times higher than under BSI, the maximum rdec for FSI showed only a 1.4 and 1.1-fold increase using simulated solar light and LED9, respectively, when compared with BSI. In order to provide a better light distribution over the catalyst coated surface, a new LED plate with 18 LEDs was designed and tested. Under FSI or BSI mechanisms and using the LED18 system, a ∼3.6 fold increase on the maximum rdec was observed when compared to the LED9 system. However, even for the LED18 system, similar maximum reaction rates are observed for BSI and FSI mechanisms. This means, that regardless of the light source configuration used, ∼60% of the catalyst coated surface is not illuminated.

Sensitized [2 + 2] intramolecular photocycloaddition of unsaturated enones using UV LEDs in a continuous flow reactor: kinetic and preparative aspects

A photocatalysed cycloaddition by benzophenone derivatives under flow and UVA LED irradiation is described.

Photodegradation of 4-aminoantipyrine over nano-titania heterojunctions using solar and LED irradiation sources

The non-doped and non-metal tri-doped TiO2 were prepared and used as photocatalysts activated by low-cost and low powered irradiation sources (LED) for the degradation of 4-aminoantipyrine (4-AAP) for the first time. The nano-spindle-like brookite phase with high-quality was hydrothermally synthesized at 200 °C for 20 h, in the absence of glycine. The nano-spherical-like anatase mixed with nano-rod-like brookite TiO2 were synthesized using different molarities of glycine. The N-C-S tridoped B/A TiO2 was synthesized by mixing optimum non-doped TiO2 with thiourea followed by calcination at 450 °C. The findings exhibited that the absorption edges of the obtained TiO2 shifted from UV to visible region as a result of non-metal tri-doping. The N-C-S tri-doped/TiO2 was confirmed by XPS analysis. The effect of pH values, the catalyst loadings and 4-AAP concertation were performed for degradation of 4-AAP employing solar and LED irradiation sources (UV-A and visible light). The complete degradation of 4-AAP (pH 3, 0.02 g L−1) under solar, UV-A LED, and visible light sources was achieved using N-C-S-tri-doped B/A TiO2 photocatalyst (0.4 g L−1). PL spectra confirmed that tri-doped TiO2 hetrojunction reduce the e-/h+ recombination.

CFD modeling of a UV-A LED baffled flat-plate photoreactor for environment applications: a mining wastewater case.

The use of ultraviolet light in photoreactors for wastewater treatment has become popular as an alternative of known chemical oxidative substances. UV LED light represents cheaper, robust, and versatile alternative to traditional UV lamps. In this study, it was designed and evaluated a photoreactor with an approach of chemical fluid dynamics (CFD) and experimental validation. The evaluation consisted of (1) CFD velocity profile analysis, (2) characterization of the average light distribution with potassium ferrioxalate actinometry, (3) degradation of a typical recalcitrant metallic cyanocomplex Fe(CN)63-, and (4) scavenger effect analysis in the photodegradation using potassium persulfate. Actinometrical essay concluded that the system was able to receive 1.93μE/s. The reactor operated under turbulent regime and best result for Fe(CN)63- degradation was obtained at 4h of operation, using 5-W UV-A LEDs, with pH ~ 7 and 10mM de S2O82-. Baffled photoreactor demonstrated to be useful for this type of illumination and wastewater treatment.