Ultraviolet (UV)-A light-emitting diode (LED) light sources are strongly demanded for both medical and photochemical applications. In our previous report, we investigated the conventional n-AlGaN ...buffer layer (BL)-based UV-A LED devices and a very low output power was achieved. In this work, we aim for the suppression of vertically propagating threading dislocation densities (TDDs) in the n-AlGaN BL including the current spreading layer (CSL) by introducing Si-doped n-Al0.37Ga0.63N/n-Al0.27Ga0.73N superlattices (SLs) between the AlN template and n-AlGaN BL for the demonstration of 341 nm UV-A LEDs. When the conventional n-AlGaN BLs were replaced with n-AlGaN SL-based BLs (with a suitable number of periods up to ~70) in the UV-A multi-quantum wells, then the full width at half maximum of the x-ray rocking curves in the n-AlGaN CSL for the (0 0 0 2) and (10-12) planes, respectively, were reduced to 346 and 431 arcsec and the total TDDs were suppressed to approximately ~1 × 109 cm−2. Finally, when the conventional Ni (20 nm)/Au (150 nm) p-electrodes were replaced with new Ni (1 nm)/Mg (200 nm) p-electrodes in the n-AlGaN SL-based UV-A LEDs, the maximum output power was improved from 2.1 to 2.5 mW.
To test the hypotheses that (1) protective mycobiont tissues and/or (2) medullary UV-B-absorbing carbon-based secondary compounds (CBSCs) protect lichen photobionts against UV-B radiation, we ...quantified cortical UV-transmittance and ran a three-way factorial lab experiment with (1) three UV radiation regimes, (2) photobiont layers with/without a screening cortex, and (3) with natural/reduced CBSC-concentration. We used melanin-deficient Lobaria pulmonaria from shaded forests. Maximum photochemical efficiency of photosystem II (Fv/Fm) in photobionts inside thalli with natural CBSC-concentrations was not affected by any UV-regime, consistent with close to 0% measured cortical transmittance of wavelengths <325 nm. Exposing photobiont layers to direct radiation strongly aggravated photoinhibition (P < 0.001), as did an increase in UV-exposure (P < 0.001). The effect of CBSC-removal was weaker (yet significant at P = 0.001), mainly affecting exposed photobiont layers given short-wavelength UV radiation. Based on these findings, we conclude that the primary role of extrolites in L. pulmonaria is not to screen excess solar radiation.
In this work, the photolysis of enrofloxacin (ENR), pefloxacin (PEF), and sulfaquinoxaline (SQX) in aqueous solution by UV combined with H2O2 or ferrous ions (Fe(II)), as well as Fenton (Fe(II)/H2O2) ...processes, was investigated. In addition, the toxicity of the final reaction solution after UV/H2O2/Fe(II) treatment toward zebrafish embryos was determined. The degradation of the test compounds followed pseudo-first-order reaction kinetics. The optimum concentrations of H2O2 for ENR, PEF and SQX removal under UV/H2O2 treatment were 20, 20 and 5 mM, respectively. The optimum concentrations of Fe(II) for ENR, PEF and SQX removal in the UV/Fe(II) system were 0.25, 10, and 1 mM, respectively. For the UV/H2O2/Fe(II) system, pH = 3 is the best initial pH for the degradation of ENR, PEF and SQX with the degradation efficiencies at 100%, 79.1% and 100% after 180 min, respectively. Considering the degradation rate and electrical energy per order of the test compounds, the UV/H2O2/Fe(II) process was better than the UV/H2O2 and UV/Fe(II) processes because of the greater OH generation. Based on major transformation products of ENR, PEF, and SQX detected during UV/H2O2/Fe(II) treatment, the probable degradation pathway of each compound is proposed. The fluorine atom of ENR and PEF was transformed into fluorine ion, and the sulfur atom was transformed into SO2/SO42−. The nitrogen atom was mainly transformed into NH3/NH4+. Formic acid, acetic acid, oxalic acid, and fumaric acid were identified in the irradiated solutions and all the test compounds and their intermediates can be finally mineralized. In addition, after the UV/H2O2/Fe(II) process, the acute toxicity of the final reaction solutions on zebrafish embryos was lower than that of the initial solution without any treatment. In summary, UV/H2O2/Fe(II) is a safe and efficient technology for antibiotic degradation.
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•ENR, PEF and SQX can be finally mineralized under UV/H2O2/Fe(II)•OH played a vital role for the UV/H2O2/Fe(II) degradation of pollutants.•The degradation pathways for ENR, PEF and SQX were proposed under UV/H2O2/Fe(II).•The acute toxicity on zebrafish embryos decreased after UV/H2O2/Fe(II) treatment.
The accumulation of ultraviolet (UV)‐absorbing compounds (flavonoids and related phenylpropanoids) and the resultant decrease in epidermal UV transmittance (TUV) are primary protective mechanisms ...employed by plants against potentially damaging solar UV radiation and are critical components of the overall acclimation response of plants to changing solar UV environments. Whether plants can adjust this UV sunscreen protection in response to rapid changes in UV, as occurs on a diurnal basis, is largely unexplored. Here, we use a combination of approaches to demonstrate that plants can modulate their UV‐screening properties within minutes to hours, and these changes are driven, in part, by UV radiation. For the cultivated species Abelmoschus esculentus, large (30–50%) and reversible changes in TUV occurred on a diurnal basis, and these adjustments were associated with changes in the concentrations of whole‐leaf UV‐absorbing compounds and several quercetin glycosides. Similar results were found for two other species (Vicia faba and Solanum lycopersicum), but no such changes were detected in Zea mays. These findings reveal a much more dynamic UV‐protection mechanism than previously recognized, raise important questions concerning the costs and benefits of UV‐protection strategies in plants and have practical implications for employing UV to enhance crop vigor and quality in controlled environments.
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•Advanced oxidation of municipal wastewater by UV/H2O2, UV/PDS and UV/Chlorine.•Oxidation performance followed the order of UV/Chlorine > UV/H2O2 ≈ UV/PDS.•UV absorbance (UVA), total ...fluorescence (TF) revealed highest R2 values with TOrCs.
UV-based advanced oxidation processes (AOPs) have been widely explored to remove organic contaminants from water streams. In this lab-scale study, the removal of 17 trace organic chemicals (TOrCs) by UV/H2O2, UV/PDS and UV/Chlorine was investigated at equimolar radical promoter concentrations in municipal wastewater. Direct comparison of the UV-AOPs was conducted with eight TOrCs being resistant to direct oxidation by H2O2, PDS and chlorine and revealed a general oxidation performance following the order of UV/Chlorine > UV/H2O2 ≈ UV/PDS while UV/PDS and UV/Chlorine exhibited higher compound selectivity than UV/H2O2. However, although oxidation performance of UV/Chlorine is outstanding in comparison of the three UV-AOPs, it has to be noted that oxidation by-product (OBP) formation potential might be substantially higher during both UV/PDS and UV/Chlorine compared to UV/H2O2 which was not investigated in this study. Evaluating potential optical surrogates to predict trace organic chemical (TOrCs) removal in UV-AOPs, nine parameters were selected representing chromophore and fluorophore features of DOM including components derived by parallel factor analysis (PARAFAC) of excitation-emission matrices. UV absorbance (UVA), total fluorescence (TF) and the selected fluorescence peak P_IV revealed highest linear correlation coefficients and were therefore identified as surrogates representing underlying mechanistic reactions of each UV-AOP. As none of the surrogates directly reacted with UV irradiation, slopes of surrogate-indicator correlations for photo-susceptible TOrCs decreased towards higher oxidant dosages. Correlations for these compounds should therefore only be determined for a limited range of oxidant dosage.
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•The degradation behaviors and differences of chiral pollutants (OFLO and LEV) were firstly identified.•UV/PS process was much more effective than the UV/H2O2 process for antibiotic ...degradation.•The second-order rate constants of SO4•−/•OH with OFLO and LEV were derived, respectively.•The acute toxicity of OFLO and LEV and their intermediate products was evaluated by TTC dehydrogenase activity assay.•Economic comparison of AOPs was based on energy and oxidant consumption.
Chiral quinolone antibiotics, as racemate and in enantiomerically form, have been attracted extensive attention due to their same molecular structure and different pharmacological properties and toxicity in environment. The present study focused on the difference of degradation efficiency and pathway of chiral antibiotics by different AOPs technology. The degradation behaviors and differences of chiral pollutants were firstly identified. Among them, UV/PS process exhibited the best performance for the elimination of chiral pollutants removal and reduction of total organic carbon (TOC). The degradation of ofloxacin and levofloxacin revealed pronounced pH dependence in UV/H2O2 and UV/PS processes, where the impact on Levofloxacin (LEV) was greater than that on Ofloxacin (OFLO). Only a slight variation of TOC was observed to be less than 50%, where the removal efficiencies were all above 96%. SO4•− generated in UV/PS process yields a greater mineralization of antibiotics than •OH in UV/H2O2 process. Cl−, NO3− and NOM had inhibitory effects on OFLO and LEV degradation in both processes, while SO42− showed positive effect on UV/PS degradation. Meanwhile, chairal antibiotics removal was dominated by •OH with the second-order rate constants of 3.97 × 109 and 2.48 × 109 M−1s−1 in UV/H2O2 process, while SO4•− played the key role in UV/PS system with second-order rate constants of 2.19 × 1010 and 2.66 × 1010 M−1s−1, respectively. The results of acute toxicity assay shown that OFLO exhibited higher acute toxicity than LEV, while TTC dehydrogenase activity of intermediate products of OFLO was lower than LEV. This study demonstrated that AOPs (especially UV/PS) were efficient for removing fluoroquinolone antibiotics, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.
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•The H2O2 and Fe(II) addition can enhance TCs mineralization under UV.•Environmental-level water constituents promoted TCs attenuation under UV.•UV light, ·OH, DOM*, H2O2, and Fe(II) ...complexation can attenuate TCs.•A tentative degradation pathway of TCs under UV-based treatment was proposed.•The evaluation for toxicity of treated solutions to zebrafish embryos was conducted.
The pollution of tetracyclines (TCs) in waters has caused public concern and scientific interest. This study investigates the effect of low-level hydrogen peroxide (H2O2) and ferrous ion (Fe(II) concentrations on the UV treatment of four TCs: oxytetracycline (OTC), tetracycline (TC), chlorotetracycline (CTC), and doxycycline (DXC). The optimum addition of Fe(II) (0.05 mM) and H2O2 (0.5 mM) promoted the attenuation and mineralization of test TCs, and a higher pH was conducive to their attenuation. Environmental-level water constituents (CO32−, HCO3−, NO3−, SO42−, NH4+, fulvic acid (FA), and humic acid (HA)) promoted test TCs attenuation under UV treatment, but inhibited their attenuation under H2O2/UV and Fe(II)/UV treatments (with the exception of HCO3− and FA). The attenuation of test TCs was attributed to UV and DOM* under UV treatment, UV, DOM*, H2O2, and ·OH under H2O2/UV treatment, and UV, DOM*, Fe-complexation, and ·OH under Fe(II)/UV treatment. A tentative degradation pathway of test TCs was proposed based on the detected intermediates and the degradation mechanisms. Additionally, an evaluation of the toxicity of treated solutions to zebrafish embryos showed that, solutions treated by only Fe(II) or H2O2 caused great toxicity, and Fe(II) or H2O2 combining with UV treatment could decrease the toxicity but required a longer irradiation time (>4h). Overall, our findings provide a scientific assessment of UV-based methods to remove antibiotics from aquatic systems.
The instability and rapid consumption of H2O2 limit the application of UV/H2O2 in water treatment. Recently, calcium peroxide (CaO2) has been demonstrated as an effective source of H2O2. However, the ...performance and mechanism of UV/CaO2 are still unknown. Herein, UV/CaO2 and UV/H2O2 were compared for degradation of aniline. The removal efficiency of aniline by UV/CaO2 was slightly lower than that by UV/H2O2, which could be attributed to the light scavenger by CaO2 suspended particles. HO‧ was identified to participate in aniline degradation in both UV/CaO2 and UV/H2O2, while O2-· was only involved in UV/CaO2. The efficiency of aniline degradation in UV/CaO2 was affected by the released H2O2 in the system. The release and decomposition rate of H2O2 in UV/CaO2 system were influenced by the CaO2 dosage and reaction pH, but slightly related with water matrix. Excessive CaO2 would scavenge aniline degradation through the released H2O2 to react with HO‧. Acidic condition would enhance the concentration of H2O2 in UV/CaO2 and promote the degradation of aniline. Cl– showed slight and almost no effect on aniline degradation in UV/CaO2 and UV/H2O2 systems, respectively, while HCO3– scavenged aniline degradation in UV/CaO2. NO3– inhibited aniline degradation in both UV/CaO2 and UV/H2O2. Compared to UV/H2O2, UV/CaO2 shows the similar efficiency on organics removal but conquers the limitations in UV/H2O2, which is a promising alternative choice in water treatment.
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•Aniline removal by UV/CaO2 was slightly lower than that by UV/H2O2.•Aniline degradation was affected by the released H2O2 in UV/CaO2.•Acidic pH enhanced H2O2 concentration and aniline degradation.•HO‧ and O2-‧ were involved in the degradation process.
In this study, ultraviolet based advanced oxidation processes (UV-AOPs) including UV/persulfate (UV/PS), UV/chlorine, and UV/H2O2 were employed to alleviate ultrafiltration membrane fouling during ...the treatment of algae-laden water. The results show that UV/PS pretreatment exhibited the best performance on fouling control, followed by the UV/H2O2 pretreatment. The fouling mitigation performance improved with the increase of oxidant dose. However, UV/chlorine pretreatment aggravated membrane fouling, and the irreversible fouling resistance increased by five times compared with that of raw water. The dissolved organic carbon (DOC) in the algae-laden solution was reduced after UV/PS pretreatment, while either UV/chlorine or UV/H2O2 pretreatment had little influence on the DOC of feed water. UV/PS and UV/H2O2 pretreatments were effective in the degradation of fluorescent compounds, thus reducing the deposition of organic matter on the membrane surface. Additionally, the decreased concentration of hydrophobic organics, algal cells, and debris in feed water after UV/PS pretreatment was also contributed to the fouling alleviation. The aggravated irreversible fouling after UV/chlorine pretreatment was probably ascribed to the increased accumulation of hydrophobic fractions in the membrane pores. Modeling result indicates that membrane fouling during the filtration of raw algae-laden water was dominated by intermediate blocking and cake filtration mechanisms. Both UV/PS and UV/H2O2 pretreatments transformed the combined fouling mechanism into standard blocking, while UV/chlorine pretreatment aggravated the pore blocking in the initial filtration period.
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•UV/PS pretreatment effectively mitigated fouling caused by algae-laden water.•UV/H2O2 pretreatment reduced fouling at high H2O2 dose.•UV/chlorine pretreatment significantly aggravated irreversible fouling.•Intrinsic mechanisms of membrane fouling after UV-AOPs pretreatment were proposed.
The degradation of pharmaceuticals and personal care products (PPCPs) by the UV/H2O2 and UV/chlorine processes was compared at practical concentrations in simulated drinking water and wastewater. In ...pure water, the UV/chlorine process performed better than the UV/H2O2 process for the degradation of 16 PPCPs among the investigated 28 PPCPs under neutral conditions. Interestingly, the UV/chlorine approach was superior to the UV/H2O2 approach for the removal of all PPCPs in simulated drinking water and wastewater at the same molar oxidant dosage. The radical sink by oxidants and/or H2O was 2–3 orders of magnitude higher in UV/chlorine than UV/H2O2 in pure water. Thus, the UV/chlorine process was less affected by the water and wastewater matrices than UV/H2O2. In UV/chlorine, the concentration of ClO• was calculated to be ∼3 orders of magnitude greater than that of HO• in pure water, and the reactivities of ClO• with some PPCPs were as high as > 108 M−1 s−1. ClO• was mainly scavenged by the effluent organic matter (EfOM) with a rate constant of 1.8 × 104 (mg L−1)−1 s−1 in wastewater. Meanwhile, secondary radicals such as Br•, Br2•-, ClBr•- and CO3•- further contributed to PPCP degradation by the UV/chlorine process in wastewater, whose concentrations were at least 2 orders of magnitude higher than that in UV/H2O2. Compared with the UV/H2O2 process, the UV/chlorine process saved 3.5–93.5% and 19.1%–98.1% electrical energy per order (EE/O) for PPCP degradation in simulated drinking water and wastewater, respectively.
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•UV/chlorine and the UV/H2O2 were compared for the abatement of 28 PPCPs at neutral pH.•The concentration of HO.• was lower in UV/chlorine, but Cl• and ClO• compensated it.•UV/chlorine was less affected by water matrices than UV/H2O2 for PPCP degradation.•The secondary radicals such as Br.•, ClBr•- and CO3•- were higher in UV/chlorine in wastewater.•EE/O was lower in UV/chlorine than UV/H2O2 in simulated drinking water and wastewater.
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