UV-A Light-emitting Diodes Research Articles

Spectral Dependence of Bovine Coronavirus Photoinactivation under Irradiation by UV-A, UV-B, and UV-C Light-Emitting Diodes

Spectral Dependence of Bovine Coronavirus Photoinactivation under Irradiation by UV-A, UV-B, and UV-C Light-Emitting Diodes

UV-A Flexible LEDs Based on Core-Shell GaN/AlGaN Quantum Well Microwires.

Nanostructured ultraviolet (UV) light sources represent a growing research field in view of their potential applications in wearable optoelectronics or medical treatment devices. In this work, we report the demonstration of the first flexible UV-A light emitting diode (LED) based on AlGaN/GaN core-shell microwires. The device is based on a composite microwire/poly(dimethylsiloxane) (PDMS) membrane with flexible transparent electrodes. The electrode transparency in the UV range is optimized: namely, we demonstrate that single-walled carbon nanotube electrodes provide a stable electrical contact to the membrane with high transparency (70% at 350 nm). The flexible UV-A membrane demonstrating electroluminescence around 345 nm is further applied to excite Zn-Ir-BipyPDMS luminophores: the UV-A LED is combined with the elastic luminophore-containing membrane to produce a visible amber emission from 520 to 650 nm. The obtained results pave the way for flexible inorganic light-emitting diodes to be employed in sensing, detection of fluorescent labels, or light therapy.

Photocatalytic oxidation of n-decane in a NETmix photoreactor: Insights into the reactor geometry and illumination mechanism

This study focuses on the gas-phase photocatalytic degradation of n-decane using a NETmix photoreactor illuminated by UVA light-emitting diodes. The photoreactor is a static mixer composed of a network of cylindrical chambers interconnected by prismatic channels imprinted in a stainless-steel slab sealed with a borosilicate glass slab (reactor window with 55.7 cm2 of illuminated area). Photocatalytic performance was evaluated as a function of the flow rate (0.67 to 15 L min−1), corresponding to Reynolds number (Re) from 54 to 1209, using NETmix plates with 1 mm (92.3 cm2) and 3 mm depth (165.4 cm2), under back-side (BSI) and front-side (FSI) illumination mechanisms. The TiO2-P25 loading over the borosilicate slab (25–100 mg; BSI optimal: 75 mg) and stainless-steel slabs (100–400 mg; FSI-1/FSI-3 optimal: 200/400 mg) was optimized. Within system constraints, higher Re corresponds to increased reaction rate, apparent quantum yield, and reactivity, with decreased degradation efficiency, due to a reduction in the residence time, regardless of the reactor geometry and illumination. Moreover, operating at the same Re, the NETmix plate with 3 mm depth achieves reaction rates 2.2-/1.9-fold higher than 1 mm, considering FSI/BSI mechanisms. The results were consistent with applied experimental conditions and ray tracing simulations, indicating superior kinetic performance with higher catalyst superficial area. Ray tracing was coupled with Computational Fluid Dynamics (CFD) simulations to evaluate n-decane single-pass oxidation. A 94 % n-decane maximum experimental conversion was attained for a Re of 54, representing an error of ∼ 6.6 % compared to CFD simulation. In these conditions, only 1 % of n-decane was not mineralized, being identified aldehydes, alkanes, carboxylic acids, and ketones as the main reaction by-products. The influence of relative humidity (2 %-40 %) and n-decane inlet concentration (15–114 ppm) were also investigated.

Refractive Index Engineering as a New Degree of Freedom for Designing High‐Performance AlGaN‐Based Ultraviolet C Light‐Emitting Diodes

This study delves into a profound exploration, using simple yet effective Monte Carlo ray‐tracing simulations, of the influence of the refractive indices of multiple quantum wells (MQWs) and p‐type electron blocking layer (p‐EBL) on the photon propagation and subsequent light extraction behavior in AlGaN‐based ultraviolet‐C (UVC) light‐emitting diodes (LEDs), covering both transverse‐electric (TE) and transverse‐magnetic (TM) polarized light. Remarkably, the refractive index contrasts at the heterointerfaces of p‐EBL/MQWs/n‐AlGaN have a relatively minor impact on the extraction efficiency of TE‐polarized light but exert a significant influence on TM‐polarized light. This discrepancy arises from the substantial effect of total internal reflection at these heterointerfaces on the propagation of photons emitted at large angles. Thus, this observation elucidates the oversight of photon propagation in the conventional design of MQWs and p‐EBL in AlGaN‐based UVA and UVB LEDs, where TE‐polarized emission predominates. Building upon simulation results, a highly effective strategy for extracting TM‐polarized light in AlGaN‐based UVC LEDs is further demonstrated by combining refractive index engineering with inclined sidewalls. The findings suggest refractive index engineering can serve as a novel design parameter for AlGaN‐based UVC LEDs dominated by TM‐polarized emission, expanding the range of techniques available for enhancing device performance.

Distinct Impacts of UV-A Light Wavelengths on Nutraceutical and Mineral Contents in Green and Purple Basil Cultivated in a Controlled Environment

Controlled environment agricultural (CEA) systems create technological opportunities for the higher nutritional value of vegetables and herbs. It was hypothesized that UV-A light, supplementing basal light emitting diode (LED) illumination in CEA, would enhance growth and nutritional value (nutraceutical compounds and mineral element contents) in purple and green basil in a UV-A wavelength-specific manner. Therefore, blue (452 nm) and red (662 nm) 1:10 basal LED lighting (250 μmol m−2 s−1, 16 h) was supplemented with 1 mW cm−2 of 343, 366, 386, or 402 nm UV-A LED light for green ‘Italiano classico’ and purple ‘Red rubin’ basil cultivation. Different wavelengths have specific impacts for two basil genotypes, and certain light wavelengths should be selected to boost growth or to alter the contents of specific nutraceutical compounds. UV-A/violet 402 nm light enhanced growth, chicoric acid, β carotene, lutein, and zeaxanthin contents in green basil, while 343 nm UV-A light increased fresh weight, ascorbic acid, and carotenoid content in purple basil. UV-A light of 386 nm has the most negligible impact on reducing mineral element (P, Ca, Fe, K, Mg, Mn, and Zn) contents in basil. Understanding the wavelength dependence of plant responses to UV-A is essential for optimizing quality preservation and improving basil cultivation in controlled environment systems.

A UVA light-emitting diode microreactor for the photocatalytic degradation of humic acids and the control of disinfection by-products formation potential

Chlorination is one of the most applied technologies for drinking water disinfection. However, the generation of disinfection by-products (DBPs) in the chlorination process is threatening drinking water safety, especially when the concentration of natural organic matter (NOM) is high in source water. Climate change increases the fluctuation of NOM in source water, which further challenges water safety in small and rural communities. In this study, environmental microfluidics was introduced to a UVA-LED photocatalytic oxidation system for a rapid oxidation of NOM. The results showed that HA adsorption and degradation, and DOC degradation were more favored in low pH. At pH 5, 56.9% of HA and 58.1% of dissolved organic carbon (DOC) were removed in 3.4 min by the microreactor. DBP formation potential was efficiently reduced, with the highest reduction of THM and HAA formation potentials by 76% and 70.7%, respectively. Compared with the bottle reactor, the degradation rate constants of HA and DOC by UVA-LED microreactor were increased by 2.99 – 15.8 times, and 6.8 – 170.2 times, respectively. Homogenous irradiation and rapid mass transfer in the microreactor accelerated the inhibited oxidation of HA in acidic and base solutions and increased the apparent quantum yields of photocatalysis. Further, the microfluidic photocatalytic oxidation was much more efficient in the reduction of DPBs formation potential in a source water sample. The process was rapid and had low chemical and energy consumption. Approaches on system scale-up, system simplification, and energy conservation would increase potential of microfluidic photocatalytic oxidation in water purification for households and small communities.

Supplementary White, UV-A, and Far-Red Radiation Differentially Regulates Growth and Nutritional Qualities of Greenhouse Lettuce.

Light is a crucial environmental signal and a form of photosynthetic energy for plant growth, development, and nutrient formation. To explore the effects of light quality on the growth and nutritional qualities of greenhouse-grown lettuce (Lactuca sativa L.), lettuce was cultivated under supplementary white (W) light-emitting diodes (LEDs); white plus ultraviolet A LEDs (W+UV); white plus far-red LEDs (W+FR); and the combination of white, far-red, and UV-A LEDs (W+FR+UV) for 25 days, with lettuce grown under natural sunlight used as the control. The results indicate that the leaf length and leaf width values for lettuce grown under the W+FR+UV treatment were significantly higher than those of lettuce grown under other supplementary light treatments. The highest values of shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight were recorded under the W+FR treatment (4.0, 6.0, 8.0, and 12.4 times higher than those under the control treatment, respectively). Lettuce grown under the W+FR treatment exhibited the highest total chlorophyll content (39.1%, 24.6%, and 16.2% higher than that under the W, W+UV, and W+FR+UV treatments, respectively). The carotenoid content of lettuce grown under the W+FR treatment was the highest among all treatments. However, the root activity of greenhouse-grown lettuce was the highest under the W+FR+UV treatment. Soluble sugar content, cellulose content, and starch content in the lettuce responded differently to the light treatments and were highest under the W+UV treatment. In summary, supplementary light promoted growth and nutrient accumulation in lettuce. Specifically, white plus far-red light promoted lettuce growth, and white plus UV increased some specific compounds in greenhouse-grown lettuce. Our findings provide valuable references for the application of light-supplementation strategies to greenhouse lettuce production.

Biochemical and functional characteristics of stored (double-dose) buffy-coat platelet concentrates treated with amotosalen and a prototype UVA light-emitting diode illuminator.

Pathogen reduction of platelet concentrates (PCs) using amotosalen and broad-spectrum UVA illumination contributes to the safety of platelet transfusion by reducing the risk of transfusion-transmitted infections. We evaluated the in vitro quality of stored buffy-coat (BC) PCs treated with amotosalen and a prototype light-emitting diode (LED) illuminator. Double-dose BC-PCs collected into PAS-III/plasma or SSP+ /plasma (55/45%) were treated with amotosalen in combination with either conventional UVA lamps (INT100 Illuminator 320-400 nm) or LED illuminators at 350 nm. Platelet quality and function were evaluated over 7 days. Platelet counts were conserved during storage in all groups, as was platelet swirling without appearance of macroscopic aggregates. Integrin αIIbβ3 and glycoprotein (GP) VI expression remained stable, whereas GPIbα and GPV declined similarly in all groups. UV lamp- and LED-treated PCs displayed similar glucose consumption, lactate generation, and pH variation. Comparable spontaneous and residual P-selectin and phosphatidylserine exposure, activated αIIbβ3 exposure, mitochondrial membrane potential, lactate dehydrogenase release, and adhesive properties under flow conditions were observed during storage. The use of SSP+ /plasma compared with PAS-III/plasma better preserved most of these parameters, especially during late storage, irrespective of the type of illuminator. Replacing the UVA lamp for photochemical treatment by LED illuminators had no impact on platelet metabolism, spontaneous activation, apoptosis or viability, or on the in vitro function of BC-PCs stored for 7 days in SSP+ or PAS-III/plasma. These findings support improved procedures for the pathogen reduction and storage of PCs, to ensure transfusion safety and retention of platelet functional properties.

Effect of Different Monochromatic LEDs on the Environmental Adaptability of Spathiphyllum floribundum and Chrysanthemum morifolium.

Light-emitting diodes (LEDs) can be programmed to provide specialized light sources and spectra for plant growth. UV-A (397.6 nm), blue (460.6 nm), green (520.7 nm), and red (661.9 nm) LED light sources were used to study the effects of different monochromatic lights on the growth, antioxidant system, and photosynthetic characteristics of Spathiphyllum floribundum 'Tian Jiao' (a shade-loving species) and Chrysanthemum morifolium 'Huang Xiu Qiu' (a sun-loving species). This research revealed that green and blue light could enhance the morphological indicators, Chl a/b, photosynthetic electron transfer chain performance, and photosystem activity of S. floribundum, blue and red light could enhance the solution protein, Chl a, and photosynthetic electron transfer chain performance of C. morifolium, red and UV-A light viewed the highest SOD and CAT activities of S. floribundum (275.56 U·min·g-1; 148.33 U·min·g-1) and C. morifolium (587.03 U·min·g-1; 98.33 U·min·g-1), respectively. Blue and green light were more suitable for the growth and development of the shade-loving plant S. floribundum, while red and blue light were more suitable for the sun-loving plant C. morifolium. UV-A light could be used for their stress research. The research revealed the different adaptation mechanism of different plants to light environmental conditions.

UVA LED Light Promoted Cross‐Coupling of Tertiary α‐Silylamines with 1‐Iodoalkynes

AbstractA synthetic strategy that exploits the formation of an electron donor‐acceptor (EDA) complex between a tertiary α‐silylamine and 1‐iodoalkyne under UVA LED (light emitting diode) light (λmax=365 nm) to prepare propargyl amines is described. The site‐ and chemoselective synthetic method was shown to tolerate a wide range of functional groups to give the α‐alkynylation product in good to excellent yields. The usefulness of the C(sp)–C(sp3) bond formation protocol was also exemplified by the late‐stage functionalisation of a variety of natural products and bioactive compounds.

Inactivation of the waterborne marine pathogen Vibrio alginolyticus by photo-chemical processes driven by UV-A, UV-B, or UV-C LED combined with H2O2 or HSO5−

Ultraviolet (UV) radiation is a well-implemented process for water disinfection. The development of emergent UV sources, such as light-emitting diodes (LEDs), has afforded new possibilities for advanced oxidation processes. The emission wavelength is considered to be an important factor for photo-chemical processes in terms of both biological damage and energetic efficiency, as the inactivation mechanisms and mode-of-action may differ according to the wavelength that is applied. In addition, these processes merit exploration for inactivating emerging pathogens, such as marine vibrios, that are important bacteria to control in maritime activities. The main goal of this study was to compare the disinfection efficacy of several UV-LED driven processes with different modes of action. First, the effect of UV-LEDs was assessed at different UV ranges (UV-A, UV-B, or UV-C). Second, the possible enhancement of a combination with hydrogen peroxide (H2O2) or peroxymonosulfate salt (HSO5−) was investigated under two different application strategies, i.e. simultaneous or sequential. The results obtained indicate a high sensitivity of Vibrio alginolyticus to UV radiation, especially under UV-B (kobs = 0.24 cm2/mJ) and UV-C (kobs = 1.47 cm2/mJ) irradiation. The highest inactivation rate constants were obtained for UV/HSO5− (kobs (cm2/mJ)=0.0007 (UV-A); 0.39 (UV-B); 1.79 (UV-C)) with respect to UV/H2O2 (kobs (cm2/mJ)=0.0006 (UV-A); 0.26 (UV-B); and 1.54 (UV-C)) processes, however, regrowth was avoided only with UV/H2O2. Additionally, the disinfection enhancement caused by a chemical addition was more evident in the order UV-A > UV-B > UV-C. By applying H2O2 (10 mg/L) or HSO5− (2.5 mg/L) in a sequential mode before the UV, negligible effects were obtained in comparison with the simultaneous application. Finally, promising electrical energy per order (EEO) values were obtained as follows: UV/HSO5− (EEO (kWh/m3)=1.68 (UV-A); 0.20 (UV-B); 0.04 (UV-C)) and UV/H2O2 (EEO (kWh/m3)=2.15 (UV-A); 0.32 (UV-B); 0.04 (UV-C)), demonstrating the potential of UV-LEDs for disinfection in particular activities such as the aquaculture industry or maritime transport.

Photocatalytic treatment as a polishing step for the degradation of bio‐recalcitrant fractions of winery wastewater under solar, UVA‐LED, and blacklight irradiation

AbstractBACKGROUNDThis study investigates, for the first time, the most beneficial conditions for photocatalytic oxidation under ultraviolet (UV) irradiation provided by either a solar simulator, UVA light‐emitting diode (UVA‐LED), or UVA blacklight lamp (UVA‐BL) as a post‐treatment step for the degradation of the residual COD and color in winery wastewater (WiWW) after biological treatment.RESULTSThe effect of WiWW dilution (0, 50%), TiO2 concentration (0–1000 mg/L), catalyst type (TiO2, ZnO), pH (3, 6, 8.4), H2O2 addition (0–1000 mg/L), and treatment time on process efficiency was evaluated. At the best‐assayed conditions (1000 mg/L TiO2, 1000 mg/L H2O2), COD removal percentages in the range of 94–97% were obtained and color was removed by 99% within 180 min of treatment under all irradiation sources. The process was enhanced when the WiWW was subjected to 50% dilution and its pH was adjusted to 6. Among the three irradiation sources, UVA‐BL led to a marginally higher photocatalytic performance than solar and UVA‐LED, both of which achieved similar removal efficiencies. Regarding energy efficiency, UVA‐LED was found to be up to 1.7 times more energy efficient than UVA‐BL/TiO2. Finally, in most cases, the phytotoxicity of secondary effluent was eliminated during solar photocatalytic treatment.CONCLUSIONAlteration of basic operating parameters significantly improved process efficiency. In all cases, LED‐driven photocatalysis combined high removal performance and energy efficiency, proving to be an appropriate and sustainable alternative to solar photocatalysis for 24 h operation or for supplementary application during the harvest, when the majority of WiWW is generated. © 2022 Society of Chemical Industry (SCI).

Combination of Zinc Oxide Photocatalysis with Membrane Filtration for Surface Water Disinfection.

Increase water usage has led to its deterioration. Pollutants are easily found in the aquatic environment and treatment techniques must keep improving to meet the current needs and future demands. Membranes are attractive for water treatment, but limitations like fouling and the highly concentrate produced affect their performance. Combining membrane filtration with photocatalysis provides the opportunity to integrate a self-cleaning step during membrane filtration. In this work, we studied two simple and efficient approaches to combine membrane filtration with zinc oxide nanoparticles (using the catalyst in suspension and immobilized) activated by light emitting diodes (LED) emitting light at 365 nm. Both systems were used to test the disinfection efficiency in real surface water, compared in terms of catalyst concentration in the permeate stream (below the limit of detection) and its recovery after filtration (higher that 74%). The system's capability to retain and inactivate target bacteria (total coliforms and E. coli) in the retentate stream was tested with samples of real surface water. The results obtained show that both configurations led to an improved performance in comparison to the membrane treatment alone with a higher retention of the bacteria (not detected in the permeate samples) and higher treatment of the retentate. For the modified membranes, different catalyst concentrations and thermal treatments were tested. The performance of all the processes was evaluated in terms of the level of treatment achieved and the permeate flux. All the modified membranes showed an efficient retention of the target bacteria from surface water, with higher performances than the unmodified membrane (96.2% for total coliforms and 94.9% for E. coli). Remarkable retention and treatment of the retentate was achieved using a membrane modified with a catalyst load of 125 mg subject during two hours to a thermal treatment of 300 °C. This modification has a performance comparable to the system with the same catalyst load in suspension. During operation, the permeate flux reduction is lower with the modified membranes which could lead to longer operation times without the need of further cleaning or replacement. The combined system, ceramic membranes modified with zinc oxide and UV-A LEDs proved to be effective to retain and disinfect water quality indicator bacteria present in real surface water matrices.

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.

The Combinations of White, Blue, and UV-A Light Provided by Supplementary Light-Emitting Diodes Promoted the Quality of Greenhouse-Grown Cucumber Seedlings

Insufficient solar light in winter inside the greenhouse may lead to a lower quality of vegetable seedlings, and supplemental light is an effective technique to solve this problem. This study evaluated the impacts of supplementary white (W)-light-emitting diodes (LEDs), ultraviolet A LEDs (UV-A), white and blue LEDs (WB), the combinations of white and UV-A LEDs (W-UVA), and white, blue, and UV-A LEDs (WB-UVA) on the leaf morphology, photosynthetic traits, biomass accumulation, root architecture, and hormone content of cucumber (Cucumis sativus L. cv. Tianjiao No. 5) seedlings grown in the greenhouse. The results indicated that supplementary LED lighting led to a decreased plant height, shorter hypocotyl length, bigger leaf area, and thicker leaf compared with those grown with solar light only, regardless of light quality. The shoot fresh weight, root fresh weight, and seedling quality index of cucumber seedlings grown under the combinations of white, blue, and UVA radiations increased by 30.8%, 3.2-fold, and 1.8-fold, respectively, compared with those grown with natural light only. However, no significant differences were exhibited in the biomass accumulation of greenhouse-grown cucumber seedlings between the control and the UVA treatment. The cellulose content and stem firmness of greenhouse-grown cucumber seedlings grown under the combinations of white, blue, and UVA radiations increased by 49.9% and 13.1%, respectively, compared with those grown under white light only. Additionally, the cytokinin content of cucumber seedlings was promoted by over 36.7% by applying supplementary light. In summary, the combinations of white, blue, and UVA radiations led to compact morphological characteristics, superior mechanical properties, and preferable growth performance, which could be applied as an available lighting strategy to obtain the desired morphological and quality properties of vegetable seedlings.

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.

Preliminary investigation of the UV LED photodegradation of methylene blue using TiO2–carbonized medium-density fiberboard

This preliminary study aimed to realize the potential use of titanium dioxide–carbonized medium-density fiberboard (TiO2–cMDF) as a biomaterial for dye wastewater treatment. TiO2–cMDF, which was prepared by carbonizing MDF treated with titanium tetraisopropoxide in isopropyl alcohol, was investigated for adsorption and then photodegradation of methylene blue (MB) under UV-A (390 nm, 19 W) and UV-C (280 nm, 12 W) light emitting diodes (LEDs). After two full cycles of adsorption, four successive cycles of photodegradation were conducted under UV-A LED. For every adsorption or photodegradation cycle, TiO2–cMDF practically removed MB. Both adsorption and photodegradation followed pseudo-first-order kinetics. The rate constants for adsorption decreased by half. The rate constants for photodegradation were similar. This finding suggests that UV-A LED is a robust and steady source of UV light. Photodegradation under UV-C LED was also performed. However, due to its high-energy output, the UV-C LED module overheated even though a cooling fan was present. Although the results indicate a slow photodegradation under UV LEDs, because of the limited number of specimens, increasing the number of specimens and UV LED modules will improve its performance.

Short-Term Pre-Harvest Supplemental Lighting with Different Light Emitting Diodes Improves Greenhouse Lettuce Quality

Winter–spring greenhouse vegetable production is limited by low-level natural light, resulting in decreased growth and quality. To investigate whether short-term pre-harvest supplemental lighting (SL) with light emitting diodes (LEDs) can address this issue, a study was conducted in a greenhouse in Dallas, Texas. Red leaf lettuce (Lactuca sativa L. ‘Red Mist’) plants grown in a hydroponic system were treated with daytime or nighttime SL with red (R) and blue (B) LEDs (RB-LED), blue and UVA LEDs (B/UVA-LED), or white LEDs (W-LED) for three days before harvest and compared to those without SL (control). All SL treatments provided a photon flux density of 167 μmol·m−2·s−1 for 12 h daily. Compared with the control, SL treatments increased leaf thickness and greenness, antioxidant capacity, and concentrations of phytonutrients such as anthocyanins, carotenoids, and total phenolics; however, shoot fresh biomass and total leaf area were generally not affected by SL. There were no differences in all of the above traits among W-LED, RB-LED and B/UVA-LED. Compared with daytime SL, nighttime SL increased leaf greenness and carotenoid concentration. In summary, all three LEDs with different spectra were effective in improving lettuce quality as short-term pre-harvest SL sources and nighttime SL was more effective than daytime SL; however, plant fresh weight and total leaf area were not affected.

Visible-Light Driven Photocatalytic Degradation of 4-Chlorophenol Using Graphitic Carbon Nitride-Based Nanocomposites

4-chlorophenol (4-CP), a hydroxylated aromatic compound (HAC), is a recalcitrant and toxic organic pollutant found in industrial wastewater and various environmental media. In this paper, visible-light-activated photocatalysis using graphitic carbon nitride (GCN) was used to treat 4-CP in an aqueous media. Graphitic carbon nitride from different precursors (dicyanamide, urea, and melamine), as well as GCN/silver nanocomposites (AgBr, Ag3PO4, Ag2CrO4, and Ag), were successfully synthesized and characterized by BET, XRD, SEM, EDS, and UV-Vis DRS. The band gaps of the photocatalysts were estimated using the UV-Vis DRS characterization results and Tauc plots. The evaluation of the efficacy of the GCN-based catalysts in degrading 4-CP was conducted with different photoreactors such as a royal blue light-emitting diode (LED), a UV-A LED, LUZCHEM cool white lamps, and a solar simulator. The results showed that GCNs with royal blue LED can effectively degrade 4-CP from aqueous media. Among the different precursors, urea-derived GCN showed the best performance in degrading 4-CP due to its large surface area. GCN/0.3Ag2CrO4 nanocomposite showed a synergistic effect for the enhanced photocatalytic degradation of 4-CP. The degradation of 4-CP with a rate constant of 2.64 × 10−2 min−1 was achieved with a GCN/0.3Ag2CrO4 nanocomposite under royal blue LED irradiation.

Growth and biochemical responses of kale to supplementary irradiation with different peak wavelengths of UV-A light-emitting diodes

Growth and biochemical responses of kale to supplementary irradiation with different peak wavelengths of UV-A light-emitting diodes