Effective degradation of tetracycline by mesoporous Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript> under visible light irradiation

Bi₂WO₆ was synthesized with a hydrothermal method at different pHs and used for the degradation of tetracycline (TC) in water. The mesoporous Bi₂WO₆ prepared at pH 1 (BWO-1) displayed the highest adsorption and degradation capacity to TC due to its large surface area and more efficient capacity to separate photogenerated electrons and holes. 97% of TC at 20 mg·L^?1 was removed by BWO-1 at 0.5 g·L^?1 after 120 min irradiation under simulated solar light. Only 31% of the total organic carbon (TOC) was removed after 360 min irradiation although the TC removal reached 100%, suggesting that TC was mainly transformed to intermediate products rather than completely mineralized. The intermediates were identified by high-performance liquid chromatography-time of flight-mass spectrometry (HPLC-TOF-MS) and possible photodegradation pathways were proposed.     

Photodegradation of Ibuprofen,Cetirizine, and Naproxen by PAN-MWCNT/TiO<Subscript>2</Subscript>–NH<Subscript>2</Subscript> nanofiber membrane under UV light irradiation

Background

In this study, the photodegradation of three pharmaceuticals, namely Ibuprofen (IBP), Naproxen (NPX), and Cetirizine (CIZ) in aqueous media was investigated under UV irradiation. The photocatalyst used in this work consists of surface functionalized titanium dioxide (TiO₂–NH₂) nanoparticles grafted into Polyacrylonitrile (PAN)/multi-walled carbon nanotube composite nanofibers. Surface modification of the fabricated composite nanofibers was illustrated using XRD, FTIR, and SEM analyses.

Results

Sets of experiments were performed to study the effect of pharmaceuticals initial concentration (5–50 mg/L), solution pH (2–9), and irradiation time on the degradation efficiency. The results demonstrated that more than 99% degradation efficiency was obtained for IBP, CIZ, and NPX within 120, 40, and 25 min, respectively.

Conclusions

Comparatively, the photocatalytic degradation of pharmaceuticals using PAN-CNT/TiO₂–NH₂ composite nanofibers was much more efficient than with PAN/TiO₂–NH₂ composite nanofibers.

     

Effect of natural aquatic humic substances on the photodegradation of bisphenol A

The photochemical degradation of bisphenol A (BPA) was studied in the presence of natural humic substances from different origins under simulated solar irradiation. BPA underwent insignificant direct photolysis in neutral water, but rapid photosensitized degradation in four humic substances solutions via pseudo-first-order reaction occurred. The photo-degradation rate of BPA was insensitive to the different initial BPA concentrations and was inhibited in aerated solution compared with the deoxygenated medium. The reactive oxygen species (ROS) such as ·OH and ¹O₂ produced from excitation of humic substances under irradiation was determined from the quenching kinetic experiment using molecular probe. The five main intermediate photoproducts of BPA in Nordic lake fulvic acid (NOFA) were tentatively identified using gas chromatography/mass spectrometer (GC/MS). Based on the identification of ROS and the analysis of photoproduct formation, the possible phototransformation pathways of BPA were proposed, involving the direct photolysis due to the energy transfer from the triplet state humic substance (³HS*) to BPA molecules and hydroxyl radical addition and oxidation as well.     

TiO2 photocatalyzed degradation of diazinon in an aqueous medium

The photocatalytic degradation of diazinon was studied over TiO₂ catalysts. The kinetics obtained demonstrated that powder titania (t_1/2 = 9.7 min) was more efficient compared to pure titania thin film catalysts (t_1/2 = 29.4 min). Mineralization of organic carbon to CO₂ after 360 min of irradiation was found to be 75% while heteroatoms (P, S, N) were mineralized into phosphate, sulfate and nitrate ions, respectively. A microtox test was performed to evaluate the toxicity of solutions treated by catalysts. Illumination of diazinon in the presence of TiO₂ gave rise to several intermediates that have been identified by means of solid phase extraction and gas chromatography-mass spectrometry, while a simple degradation pathway is proposed.     

Electrochemical degradation of Acid Red I dye and its treatment by UV light

Degradation of Acid Red I (ARI) dye by electrochemical treatment and UV light irradiation was studied in this work. The effect of the current density and the concentration of NaCl and dye on the decoloration and degradation efficiency were studied and optimized. The UV irradiation was monitored by UV-Vis spectrophotometry and chemical oxygen demand. The kinetic constants for decoloration and degradation were calculated. Degradation of 86% was achieved in 160?min and the first-order kinetic constant was 0.013?min^?1. Degradation products were identified by gas chromatography/mass spectrometry. The mechanism for the degradation of ARI was proposed.     

Rose Bengal‐sensitized photooxygenation of chlorohydroxyaromatic contaminants in water: A kinetic study

A kinetic study of the RB‐sensitized photooxygenation of a series of chlorohydroxyaromatic (ClArOH) water contaminants (phenolic and dihydroxybenzene derivatives) has been carried out. In addition, an exhaustive study on the possible interactions of RB electronically excited triplet and singlet states with ClArOH was also developed. The determination of relative rates of oxygen uptake upon sensitized irradiation, employing auxiliar selective quenchers of oxygen active species, indicate the contribution of both singlet molecular oxygen (ca. 71%) and Superoxide ion (ca. 26%) as the reactive pathways for ClArOH degradation. The substitution by chlorine atoms in position meta greatly decrease the photooxygenation rate of the phenolic derivatives. For the dihydroxybenzene series, increase in nuclear chlorination parallels a decrease in the photodegradation rate.

Outdoors sensitized solar irradiation experiments on different ClArOH mixtures leads to measurable levels of oxygen after a few minutes exposure. From the environmental point of view, and ruling out the possibility of direct‐irradiation photoreactions, sensitized photooxygenation appears as an alternative pathway for ClArOH degradation, in competence with other naturally‐occurring photoprocesses involving reactive transient species.     

Preparation of CuO/SiO<Subscript>2</Subscript> and photocatalytic activity by degradation of methylene blue

A photocatalyst based on CuO/SiO₂ was prepared, and evaluated for the degradation of methylene blue in aqueous medium. The photocatalyst was obtained by calcination method of copper salt, in the presence of silica. The characterization by XRD, FTIR, and TPR techniques confirmed the formation of CuO as active phase. SEM studies showed CuO deposited on the surface of SiO₂. By ESI-MS, it was demonstrated that the degradation of methylene blue occurs through successive hydroxylations. Photodegradation assays showed that CuO/SiO₂ was efficient for degradation, and that the material worked better in the presence of UV light.     

Efficient oxidation of bisphenol A with oxysulfur radicals generated by iron-catalyzed autoxidation of sulfite at circumneutral pH under UV irradiation

There is actually a need for efficient methods to clean waters and wastewaters from pollutants such as the bisphenol A endocrine disrupter. Advanced oxidation processes currently use persulfate or peroxymonosulfate to generate sulfate radicals. There are, however, few reports on the use of sulfite to generate sulfate radicals, instead of persulfate or peroxymonosulfate, except for dyes. Here we studied the degradation of the bisphenol A using iron(III) as catalyst and sulfite as precursor of oxysulfur radicals, at initial pH of 6, under UV irradiation at 395 nm. The occurrence of radicals was checked by quenching with tert-butyl alcohol and ethanol. Bisphenol A degradation products were analyzed by liquid chromatography coupled with mass spectrometry (LC–MS). Results reveal that iron(III) or iron(II) have a similar oxidation efficiency. Quenching experiments show that the oxidation rate of bisphenol A is 47.7 % for SO ₄ ^·? , 37.3 % for SO ₅ ^·? and 15 % for HO^·. Bisphenol A degradation products include catechol and quinone derivatives. Overall, our findings show that the photo-iron(III)–sulfite system is efficient for the oxidation of bisphenol A at circumneutral pH.     

Photoinduced degradation of sulfonamides,kinetic, and structural characterization of transformation products and assessment of environmental toxicity

This study focuses on the degradation of the sulfonamide antibiotics, sulfadiazine, sulfamethazine, sulfamethoxazole, and sulfathiazole, using ultraviolet irradiation in various conditions. Different pHs were investigated in combination with the addition of hydrogen peroxide and further oxygen removal. High-performance liquid chromatography electrospray ionization ion-trap mass spectrometry was used to identify and elucidate degradation products and to establish concentration–time curves. Previously unknown degradation products could be characterized. Reaction rate constants of all compounds and transformation products were determined. The parent sulfonamides decayed according to first-order kinetics, while the concentrations of the transformation products varied with time according to a subsequent reaction of an intermediate product. Quantum efficiencies were analyzed for mechanistic purposes. As example, sulfamethoxazole was added to effluents from a wastewater treatment plant and irradiated. Phototoxicity and environmental hazard were assessed through quantitative structure-activity relationship computations. In addition, the minimal inhibition concentrations were determined for Pseudomonas fluorescens and Bacillus subtilis. Conclusions for UV-C irradiation as a fourth purification wastewater treatment stage were derived.     

Kinetik und Mechanismen beim photochemischen Abbau von Fluorphenolen

The results of a study of the photolytic degradation of mono- and difluorophenols as a function of oxidation agent and temperature are reported. The effects of the position of fluorine are discussed. Fluorinated aromatic compounds have been mineralized to CO₂, fluoride, acetate and formate by irradiation (l=254nm) over various intermediate steps. The degradation of fluorophenols apparently followed first-order kinetics. A proposed degradation pathway for the photolytic oxidation of fluorophenols is presented. A complete mineralization as generally proposed in the literature cannot be supported by our results.     

Degradation of bisphenol A by photo-fenton processes

The photo-Fenton reactions, which could yield hydroxyl radicals via the catalytic degradation of H₂O₂ by Fe(II), were focused as one of the abiotic degradation processes of bisphenol A (BPA) in surface waters. At pH 6, in the presence of H₂O₂ only, 32% of BPA was degraded after 120?min of irradiation. However, 97% of BPA was degraded in the presence of both H₂O₂ and Fe(II). Without light irradiation, no BPA degradation was observed even in the presence of Fe(II) and H₂O₂. These results show that photo-Fenton processes are effective in the natural attenuation of BPA in surface water. In addition, the presence of humic acids (HAs), which were of more aliphatic nature, resulted in enhancing BPA degradation via the photo-Fenton processes. Therefore, HAs can be one of the important factors in enhancing the degradation of BPA in surface water via the photo-Fenton processes.     

Degradation of azo dye reactive violet 5 by TiO2 photocatalysis

The photocatalytic degradation of hydrolyzed reactive violet 5 (RV5) using titanium dioxide (TiO₂) was investigated in this study. The effects of various factors including the amount of photocatalyst, RV5 concentration, light intensity, and pH on photocatalytic degradation were evaluated. The photodegradation efficiency was 90% after 20 min of irradiation and reached nearly 100% after 80 min under the condition of pH 4 and temperature of 25°C. The decolorization rate typically followed first-order reaction, and increased markedly with increasing amount of photocatalyst, pH as well as light intensity. The total mineralization, based on total organic carbon (TOC) concentration was 53% after 20 min of UV light exposure and approached nearly 100% after 140 min. The final mineralization product was formylformamide. The photodegradation was faster than the mineralization, indicating that the intermediate products of decolorization were resistant to photodegradation. In this study, we found that toxicity of RV5 significantly decreased after decolorization. Our study suggests that the photocatalytic degradation treatment of RV5 with TiO₂ in wastewater is a simple and fast method.     

Selective photoreduction of acetonitrile to acetaldehyde in dilute aqueous solutions

Acetonitrile is a commonly used solvent in both industry and research. The treatment of acetonitrile wastes in dilute aqueous solutions with visible light offers advantages to chemical treatment and ultraviolet (UV) irradiation. This study presents the degradation of acetonitrile via a photoinduced electron transfer reaction in the presence of a photosensitizer (dye) and a sacrificial reductant under visible light. Acetonitrile photodegradation (photoreduction) was investigated utilizing a variety of sacrificial reductants and photosensitizers. Optimal results were observed in the presence of methylene green and tri-isopropanolamine with a decrease of acetonitrile in solution to 86% in 24 hours. The only photoreaction product observed was acetaldehyde and a plausible mechanism for the photochemical degradation of acetonitrile is proposed.     

三硝基甲苯的γ-辐照降解实验研究

基于三硝基甲苯(TNT)溶液采用常规处理方法难以降解,采用60Co-γ射线对三硝基甲苯溶液进行辐照降解,研究了吸收剂量、初始浓度、溶液初始pH值、双氧水(H2O2)等因素对辐照降解效果的影响.实验结果表明,60Co-γ射线辐照能够有效地降解三硝基甲苯.三硝基甲苯溶液初始浓度为5—50 mg.L-1,当接受不超过15 kGy剂量时,三硝基甲苯的降解率可达100%,化学需氧量(COD)去除率可达55%;弱酸性和碱性环境更有利于三硝基甲苯的降解和COD的去除;加入少量H2O2时,三硝基甲苯降解率和COD去除速率均随之增加,但过高的H2O2加入量将会抑制三硝基甲苯的去除,并且加入H2O2的量愈大其抑制作用愈明显.     

几种环境激素酞酸酯的光催化降解研究

在紫外光照射下,以TiO2为催化剂,研究邻苯二甲酸二丁酯(DBP)、邻苯二甲酸二环己酯(DCHP)和邻苯二甲酸丁基苄基酯(BBP)水溶液的光催化降解规律,不同结构特征的酞酸酯在降解过程中pH值均表现为先升高,再降低的趋势.降解为表观一级反应.采用色质联用技术(GC-MS)分别对上述物质降解过程中生成的中间体进行分析,提出了可能的降解机理.     

Enhanced photocatalytic activity of electrospun TiO2/polyacrylonitrile membranes in a crossflow reactor using dual lights

Photocatalytic membranes reactors have become one of the most efficient technologies to treat polluted waters. However, a major drawback is the unilateral irradiation of the membrane, where only one side of the membrane is exploited. To overcome this issue, we developed a reactor where the membrane can be irradiated on both sides. Polyacrylonitrile membranes containing different amounts of TiO₂ nanoparticles up to 60% were first prepared by electrospinning. These membranes were used in a 3D-printed crossflow photocatalytic membrane reactor for the degradation of methylene blue under different combinations of lights. The use of both sides of the photocatalytic membrane significantly enhanced the photocatalytic activity for the decolorization of methylene blue in water. The prepared membranes showed the best decolorization rate for a loading of 60% of TiO₂ and the use of dual ultraviolet lights, where the methylene blue solution was completely discolored after 90 min. This is the first report of a such system configuration, and this new irradiation concept is promising for photocatalytic membrane reactions and water cleaning.

     

Photocatalytic degradation of methyl orange using ZnO/TiO composites

ZnO/TiO₂ composites were synthesized by using the solvothermal method and ultrasonic precipitation followed by heat treatment in order to investigate their photocatalytic degradation of methyl orange (MO) in aqueous suspension under UV irradiation. The composition and surface structure of the catalyst were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). The degradation efficiencies of MO at various pH values were obtained. The highest degradation efficiencies were obtained before 30min and after 60min at pH 11.0 and pH 2.0, respectively. A sample analysis was conducted using liquid chromatography coupled with electrospray ionization ion-trap mass spectrometry. Six intermediates were found during the photocatalytic degradation process of quinonoid MO. The degradation pathway of quinonoid MO was also proposed.     

Photocatalytic degradation of methyl orange using ZnO/TiO2 composites

ZnO/TiO₂ composites were synthesized by using the solvothermal method and ultrasonic precipitation followed by heat treatment in order to investigate their photocatalytic degradation of methyl orange (MO) in aqueous suspension under UV irradiation. The composition and surface structure of the catalyst were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and transmission electron microscopy (TEM). The degradation efficiencies of MO at various pH values were obtained. The highest degradation efficiencies were obtained before 30 min and after 60 min at pH 11.0 and pH 2.0, respectively. A sample analysis was conducted using liquid chromatography coupled with electrospray ionization ion-trap mass spectrometry. Six intermediates were found during the photocatalytic degradation process of quinonoid MO. The degradation pathway of quinonoid MO was also proposed.     

Experimental and computational assessment of 1,4-Dioxane degradation in a photo-Fenton reactive ceramic membrane filtration process

• 1,4-Dioxane was degraded via the photo-Fenton reactive membrane filtration. • Degradation efficiency and AQY were both enhanced in photocatalytic membrane. • There is a tradeoff between photocatalytic degradation and membrane permeation flux. • Degradation pathways of 1,4-Dioxane is revealed by DFT analysis. The present study evaluated a photo-Fenton reactive membrane that achieved enhanced 1,4-Dioxane removal performance. As a common organic solvent and stabilizer, 1,4-Dioxane is widely used in a variety of industrial products and poses negative environmental and health impacts. The membrane was prepared by covalently coating photocatalyst of goethite (α-FeOOH) on a ceramic porous membrane as we reported previously. The effects of UV irradiation, H₂O₂ and catalyst on the removal efficiency of 1,4-Dioxane in batch reactors were first evaluated for optimized reaction conditions, followed by a systematical investigation of 1,4-Dioxane removal in the photo-Fenton membrane filtration mode. Under optimized conditions, the 1,4-Dioxane removal rate reached up to 16% with combination of 2 mmol/L H₂O₂ and UV₃₆₅ irradiation (2000 µW/cm²) when the feed water was filtered by the photo-Fenton reactive membrane at a hydraulic retention time of 6 min. The removal efficiency and apparent quantum yield (AQY) were both enhanced in the filtration compared to the batch mode of the same photo-Fenton reaction. Moreover, the proposed degradation pathways were analyzed by density functional theory (DFT) calculations, which provided a new insight into the degradation mechanisms of 1,4-Dioxane in photo-Fenton reactions on the functionalized ceramic membrane.     

Photoelectrocatalytic degradation of camphor on TiO2/RuO2 electrodes

The degradation of camphor using titanium/ruthenium dioxide (TiO₂/RuO₂; 70:30) electrodes was investigated in a photoelectrochemical thin-film reactor under near UV light irradiation. Two different electrolytes (Na₂SO₄ and NaCl) were used in this work. Camphor degradation was monitored by solvent extraction methods and gas chromatography (GC) analysis. Comparative studies between photoelectrochemical, electrochemical, photolytic, and heterogeneous photocatalytical process were carried out. When NaCl was used, the degradation efficiency of camphor was improved, probably on account of electrochemical generation of active chlorine species and their photochemical conversion to chlorine radicals. Under these conditions camphor was completely mineralized at reaction times of 30 min.