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Photocatalytic degradation of Microcystin-LR by visible light active and magnetic, ZnFe2O4-Ag/rGO nanocomposite and toxicity assessment of the intermediates
摘要： In this work, we aimed to study photocatalytic degradation of Microcystin-LR (MC-LR), a cyanotoxin known to cause acute as well as chronic toxicity and even mortality. The nanocomposite (NC) based on zinc ferrite (ZnFe2O4) was modified with graphene oxide (GO) and Ag nanoparticles (NPs) to enhance its photocatalytic properties under visible light. The so-formed ZnFe2O4-Ag/rGO NC exhibited superior performance in visible light allowing complete degradation of MC-LR within 120 mins of treatment with pseudo rate constant, k = 0.0515 min-1, several times greater than other photocatalysts, TiO2 (k = 0.0009 min-1), ZnFe2O4 (k = 0.0021 min-1), ZnFe2O4-Ag (k = 0.0046 min-1) and ZnFe2O4/rGO (k = 0.007 min-1) respectively. The total organic carbon analysis revealed that only 22% of MC-LR was mineralized on 120 mins of treatment time indicating presence of different intermediate by-products. The intermediates formed during photocatalytic treatment were identified using liquid chromatography–mass spectrometry (LCMS) based on which probable degradation pathways were proposed. The attack from ?OH radicals formed during the photocatalytic process resulted to hydroxylation and subsequent cleavage of diene bond. The toxicity assessment with Daphnia magna revealed that the degradation process has alleviated toxicity of the MC-LR and no toxic intermediates were formed during the treatment which is very important from eco-toxicological view point. Therefore, ZnFe2O4-Ag/rGO has a good potential in the field of environmental applications as visible light active and magnetic photocatalyst with enhanced performance.
关键词： Photocatalytic degradation,Toxicity,Daphnia magna,Microcystin,Intermediates
更新于2025-09-23 15:23:52
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Construction of precious metal-loaded BiOI semiconductor materials with improved photocatalytic activity for microcystin-LR degradation
摘要： The composite photocatalyst of precious metal loaded on BiOI (M/BiOI, M = Pt, Au, Ag) was prepared by photochemical deposition and used for the photocatalytic degradation of microcystins (MC-LR). The material was characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet visible (UV-vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence spectra (PL). The effect of photodegradation of MC-LR and the possible mechanism were investigated. It turned out that, among precious metals of Pt, Au, and Ag, Ag had the most significant improvement for photocatalytic activity of BiOI and Au was the least. The Ag/BiOI catalyst was illuminated 2 h under the simulated visible-light condition with the optimal load ratio of Ag catalyst (1.0 wt%) and the 2-h illumination under simulated visible-light condition, the degradation rate of MC-LR was 61.26% ± 0.12%. In addition, through the experiment of trapping agent and the analysis of electron spin resonance (ESR), we could conclude that the main active species is O2? in the process of the degradation of MC-LR by three precious metal-loaded BiOI semiconductor materials.
关键词： Microcystin-LR,Photocatalysis,Precious metals,BiOI
更新于2025-09-19 17:15:36
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Fluorescence as a Surrogate for the Release of Intracellular Material From Cyanobacteria
摘要： Water treatment plants that apply preoxidation before physical cell removal can compromise cyanobacterial cell integrity and cause the release of intracellular organic matter (IOM) containing toxic or odorous metabolites. In this study, fluorescence was evaluated as a surrogate for IOM released from cyanobacterial cells following oxidation with ozone, chlorine, chlorine dioxide, or monochloramine. Oxidation of 200,000 cells/mL of Microcystis aeruginosa led to a significant increase in both the fluorescence index (FI) and the fluorescent dissolved organic matter (FDOM) intensity (excitation wavelength, 370 nm; emission wavelength, 460 nm). FI and FDOM proved impractical for detecting weakly fluorescing IOM released from Oscillatoria sp. and Lyngbya sp., indicating that the viability of fluorescence monitoring is cyanobacteria-specific. For strongly fluorescing IOM, FI and FDOM can serve as qualitative surrogates for the concomitant release of metabolites. Elevated FI and FDOM were not sensitive to the concentration of microcystin-LR but can provide an early warning that a utility’s source water is at risk for metabolite release and accumulation.
关键词： fluorescence index,cyanobacteria,Microcystis aeruginosa,fluorescent dissolved organic matter,intracellular organic matter,microcystin-LR
更新于2025-09-19 17:15:36
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Degradation of cyanotoxins (microcystin) in drinking water using photoelectrooxidation
摘要： The discharge of sewage and industrial effluents containing high concentrations of pollutants in water bodies increases eutrophication. Cyanobacteria, some of the organisms whose growth is promoted by high nutrient concentrations, are resistant and produce several types of toxins, known as cyanotoxins, highly harmful to human beings. Current water treatment systems for the public water supply are not efficient in degradation of toxins. Advanced oxidation processes (AOP) have been tested for the removal of cyanotoxins, and the results have been positive. This study examines the application of photoelectrooxidation in the degradation of cyanotoxins (microcystins). The performance of the oxidative processes involved was evaluated separately: Photocatalysis, Electrolysis and Photoelectrooxidation. Results showed that the electrical current and UV radiation were directly associated with toxin degradation. The PEO system is efficient in removing cyanotoxins, and the reduction rate reached 99%. The final concentration of toxin was less than 1 μg/L of microcystin in the treated solution.
关键词： microcystin,advanced oxidation process,photoelectrooxidation,cyanotoxin
更新于2025-09-10 09:29:36
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Label-free Identification of Trace Microcystin-LR with Surface-Enhanced Raman Scattering Spectra
摘要： The analysis of trace microcystin-LR (MC-LR) plays important roles in environmental fields, especially in monitoring domestic water quality and safety, since it has particularly harmful effect on wild and domestic animals as well as humans at low doses. Herein, we combine confocal Raman spectroscopy with SERS-AG substrate to characterize the “fingerprint” information of MC-LR directly. High sensitivity of SERS-AG substrates was verified by utilizing the probe molecule Rhodamine 6G. Mapping spectra demonstrated good reproducibility of MC-LR identification with label-free surface-enhanced Raman scattering (SERS) strategy. Differences between SERS spectra of MC-LR and R6G, microcystin-RR were evaluated by calculating their scores and loading weights with an unsupervised exploratory principal component analysis method. Then, relationship between Raman intensities and concentrations was preliminary analyzed with SERS spectra of MC-LR and the lowest concentration of MC-LR identification was 10-6 mg.L-1 while using SERS-AG substrate. Thereafter, 68.6% quantitative recovery of 10-3 mg.L-1 MC-LR in tap water samples was obtained by the proposed label-free SERS method. These results showed that confocal Raman spectroscopy with label-free surface-enhanced Raman scattering strategy can handle the identification of trace MC-LR for monitoring water quality and safety worldwide in future.
关键词： principal component analysis,microcystin-LR,surface-enhanced Raman scattering
更新于2025-09-09 09:28:46