Kinetics of photocatalytic degradation of diuron in aqueous colloidal solutions of Q-TiO2 particles

The Fabrication and Property Characterization of a Ho2YSbO7/Bi2MoO6 Heterojunction Photocatalyst and the Application of the Photodegradation of Diuron under Visible Light Irradiation

A novel photocatalytic nanomaterial, Ho2YSbO7, was successfully synthesized for the first time using the solvothermal synthesis technique. In addition, a Ho2YSbO7/Bi2MoO6 heterojunction photocatalyst (HBHP) was prepared via the hydrothermal fabrication technique. Extensive characterizations of the synthesized samples were conducted using various instruments, such as an X-ray diffractometer, a Fourier transform infrared spectrometer, a Raman spectrometer, a UV-visible spectrophotometer, an X-ray photoelectron spectrometer, and a transmission electron microscope, as well as X-ray energy dispersive spectroscopy, photoluminescence spectroscopy, a photocurrent test, electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. The photocatalytic activity of the HBHP was evaluated for the degradation of diuron (DRN) and the mineralization of total organic carbon (TOC) under visible light exposure for 152 min. Remarkable removal efficiencies were achieved, with 99.78% for DRN and 97.19% for TOC. Comparative analysis demonstrated that the HBHP exhibited markedly higher removal efficiencies for DRN compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.13 times, 1.21 times, or 2.95 times higher, respectively. Similarly, the HBHP demonstrated significantly higher removal efficiencies for TOC compared to Ho2YSbO7, Bi2MoO6, or N-doped TiO2 photocatalyst, with removal efficiencies 1.17 times, 1.25 times, or 3.39 times higher, respectively. Furthermore, the HBHP demonstrated excellent stability and reusability. The mechanisms which could enhance the photocatalytic activity remarkably and the involvement of the major active species were comprehensively discussed, with superoxide radicals identified as the primary active species, followed by hydroxyl radicals and holes. The results of this study contribute to the advancement of efficient heterostructural materials and offer valuable insights into the development of sustainable remediation strategies for addressing DRN contamination.

Assessment of Various Toxicity Endpoints in Duckweed (Lemna minor) at the Physiological, Biochemical, and Molecular Levels as a Measure of Diuron Stress

The common, broad-spectrum herbicide diuron poses some risks to the environment due to its long persistence and high toxicity. Therefore, the effective monitoring of diuron residues will inform efforts to assess its impacts on ecosystems. In this study, we evaluated the toxicity targets of diuron in the model aquatic macrophyte Lemna minor at the physiological (growth and photosynthetic efficiency), biochemical (pigment biosynthesis and reactive oxygen species (ROS) levels), and molecular (rbcL transcript) levels. The toxicity of diuron was detectable after 48 h of exposure and the order of sensitivity of toxicity endpoints was gene transcription > maximum electron transport rate (ETR_max) > non-photochemical quenching (NPQ) > maximum quantum yield (F_v/F_m) > ROS > fresh weight > chlorophyll b > chlorophyll a > total frond area > carotenoids. Under diuron stress, pigment, ROS, and gene transcript levels increased while frond area, fresh weight, and photosynthesis (F_v/F_m and ETR_max) gradually decreased with the increasing duration of exposure. Notably, ROS levels, F_v/F_m, frond area, and fresh weight were highly correlated with diuron concentration. The growth endpoints (frond area and fresh weight) showed a strong negative correlation with ROS levels and a positive correlation with F_v/F_m and ETR_max. These findings shed light on the relative sensitivity of different endpoints for the assessment of diuron toxicity.

Removal of alachlor, diuron and isoproturon in water in a falling film dielectric barrier discharge (DBD) reactor combined with adsorption on activated carbon textile: Reaction mechanisms and oxidation by-products

A falling film dielectric barrier discharge (DBD) plasma reactor combined with adsorption on activated carbon textile material was optimized to minimize the formation of hazardous oxidation by-products from the treatment of persistent pesticides (alachlor, diuron and isoproturon) in water. The formation of by-products and the reaction mechanism was investigated by HPLC-TOF-MS. The maximum concentration of each by-product was at least two orders of magnitude below the initial pesticide concentration, during the first 10 min of treatment. After 30 min of treatment, the individual by-product concentrations had decreased to values of at least three orders of magnitude below the initial pesticide concentration. The proposed oxidation pathways revealed five main oxidation steps: dechlorination, dealkylation, hydroxylation, addition of a double-bonded oxygen and nitrification. The latter is one of the main oxidation mechanisms of diuron and isoproturon for air plasma treatment. To our knowledge, this is the first time that the formation of nitrificated intermediates is reported for the plasma treatment of non-phenolic compounds.

Visible light-assisted photocatalytic mineralization of diuron pesticide using novel type II CuS/Bi2W2O9 heterojunctions with a hierarchical microspherical structure

A hierarchical CuS/Bi₂W₂O₉ heterojunction photocatalyst exhibits excellent photocatalytic activity for the degradation of diuron achieving 95% mineralization within 3 h of irradiation.

Photocatalytic Degradation of Organic Pollutants: A Review

Water pollution is increasing at an ever increasing pace and the whole world is in the cancerous grip of this pollution. Various industries are discharging their untreated effluents into the nearby water resources; thus, adding to the existing water pollution to a great extent. Hence, there is a pressing demand to develop an alternate technology for wastewater treatment and in this context; photocatalysis has emerged as an Advanced Oxidation Process with green chemical approach for such a treatment. This chapter deals with photocatalytic degradation of different kinds of organic pollutants; mainly surfactants, pesticides, dyes, phenols, chloro compounds, nitrogen containing compounds etc. Mechanisms of their degradation have also been discussed with hydroxyl and allied radicals as the main active oxidizing species.

Efficient degradation of methabenzthiazuron photoinduced by decatungstate anion in water: kinetics and mechanistic studies

This study concerns the elimination of methabenzthiazuron (MBTU) photocatalysed by sodium decatungstate salts W10O32(4-)·(DTA) in aqueous solution under irradiation at 365 nm. Ninety percentage of MBTU (10(-4) M) is mineralised in the presence of the photocatalyst (2×10(-4) M) after 7 d under exposure and the formation of nitrate, sulphate and ammonium confirmed this phenomenon. In aerated conditions, the photodegradation rate of MBTU clearly increased in the presence of DTA by a factor of 40 when compared to direct photolysis with ΦMBTU=2.5×10(-2) and t1/2 (MBTU)=1.4 h. Oxygen appeared essential since 2 times inhibition of MBTU disappearance and the photocatalytic cycle interrupt were observed in the absence of oxygen. The degradation mechanism has been elucidated through the photoproducts identification by LC-ESI-MS analysis. Two processes were implied in the degradation: electron transfer and H atom abstraction reactions both involving W10O32(4-∗) excited state species. In the primary steps of the degradation, the aromatic ring hydroxylation was observed by electron transfer leading to OH-MBTU isomers and H atom abstraction reaction gave benzthiazuron and a supposed demethylated product. Secondary oxidations permitted the hydroxylation of both products.

Evolution of algal toxicity during (photo)oxidative degradation of diuron

In the aquatic environment and in engineered water treatment systems, organic contaminants can undergo oxidative and photochemical transformations. For an overall risk assessment, the toxicity of the resulting transformation products has to be investigated. In this study, the toxicity of degradation products of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) formed during its degradation by four (photo)oxidative processes (direct phototransformation, triplet-induced photosensitized oxidation, oxidation by hydroxyl radicals and ozone) was investigated in buffered aqueous solution. The toxicity was evaluated using the combined algae test with Pseudokirchneriella subcapitata that determines both, specific inhibition of photosynthesis and inhibition of the growth rate. The comparison between evolution of toxicity and degradation kinetics indicated that the toxicity during all studied processes was caused predominantly by diuron whereas the formation of degradation products did not contribute to the mixture toxicity. This implies that, if any more toxic transformation products than diuron were formed, their concentration was not sufficiently high to affect the mixture toxicity, which was dominated by the parent compound diuron. On this account, no further studies on identification of degradation products and their toxicity are needed. This study presents an example of a systematic and simple first tier method to assess the toxicity of degradation products.

Photocatalytic activity of boron-modified titania under UV and visible-light illumination

Nanosized boron(III) oxide-doped titania was prepared by homogeneous hydrolysis of titanium oxo-sulfate with urea in aqueous solutions in the presence of amorphous boron. The prepared samples were annealing at 700 degrees C. The structure of as-prepared samples was characterized by X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) and surface area (BET) and porosity determination (BJH). The morphology and microstructure characteristics were obtained by scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM). The method of UV/vis diffuse reflectance spectroscopy was employed to estimate band gap energies of the boron-doped titania. The photoactivity of the prepared samples was assessed by the photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 and 400 nm wavelength. The prepared titania samples doped with boron(III) oxide showed better photocatalytic activity in comparison with the reference TiO(2) sample. These photocatalysts showed better photocatalytic performance under visible-light irradiation.

Photocatalytic properties of Ru-doped titania prepared by homogeneous hydrolysis

Nanocrystalline titania particles doped with ruthenium oxide have been prepared by the homogenous hydrolysis of TiOSO4 in aqueous solutions in the presence of urea. The synthesized particles were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), High Resolution Transmission Electron Microscopy (HRTEM), Selected Area Electron Diffraction (SAED) and Nitrogen adsorption-desorption was used for surface area (BET) and porosity determination (BJH). The photocatalytic activity of the Ru-doped titania samples were determined by photocatalytic decomposition of Orange II dye in an aqueous slurry during irradiation at 365 nm and 400 nm wavelengths.

Mechanisms of photocatalytical degradation of monomethylarsonic and dimethylarsinic acids using nanocrystalline titanium dioxide

Photodegradation mechanisms of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) with nanocrystalline titanium dioxide under UV irradiation were investigated. In the presence of UV irradiation and 0.02 g/L TiO2, 93% MMA (initial concentration is 10 mg-As/L) was transformed into inorganic arsenate, [As(V)], after 72 h of a batch reaction. The mineralization of DMA to As(V) occurred in two steps with MMA as an intermediate product. The photodegradation rate of MMA and DMA could be described using first-order kinetics, where the apparent rate constant is 0.033/h and 0.013/h for MMA and DMA, respectively. Radical scavengers, including superoxide dimutase (SOD), sodium bicarbonate, tert-butanol, and sodium azide, were used to study the photodegradation mechanisms of MMA and DMA. The results showed that hydroxyl radicals (HO*) was the primary reactive oxygen species for the photodegradation of MMA and DMA. The methyl groups in MMA and DMAweretransformed into organic carbon, including formic acid and possibly methanol, also through photochemical reactions. The results showed that nanocrystalline TiO2 can be used for the photocatalytical degradation of MMA and DMA and subsequent removal of the converted As(V), since the high adsorption capacity of the material for inorganic arsenic species has been demonstrated in previous studies.

Radiation-induced reduction of diuron by gamma-ray irradiation

Diuron degradation efficiencies and the proposed mechanism by gamma-ray irradiation were investigated. Several factors that might affect the degradation values were further examined. The UV absorbances at 200-400 nm and diuron concentration decreased with the increase of radiation dose. When diuron initial concentration was 18.5 mg L(-1) and 1.0 kGy was selected as the radiation dose, diuron removal value and loss of total organic carbon were 100 and 34.1%, respectively. However, the concentration of Cl- ion increased with the increase of radiation dose. The process could be depicted by first order reaction kinetics and the reaction was mainly caused by the reaction of diuron with .OH and eaq-. The degradation efficiency decreased with the increase of initial concentration at the same radiation dose. H2O2, HCO3-, NO3-, NO2-, CH3OH and humic acid as additives reduced the degradation efficiency. Furthermore, the increase of NO3-, NO2-, CH3OH and humic acid would result in the decrease of the degradation values. The pH value could affect the removal efficiency and the degradation process was enhanced in acid condition. The pH value became lower with increasing radiation dose after gamma-ray irradiation.

Zinc Oxide Prepared by Homogeneous Hydrolysis with Thioacetamide, Its Destruction of Warfare Agents, and Photocatalytic Activity

Zinc sulfide (ZnS) nanoparticles were prepared by homogeneous hydrolysis of zinc sulfate and thioacetamide (TAA) at 80 degrees C. After annealing at a temperature above 400 degrees C in oxygen atmosphere, zinc oxide (ZnO) nanoparticles were obtained. The ZnS and ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Brunauer-Emmett-Teller (BET)/Barrett-Joyner-Halenda (BJH) methods were used for surface area and porosity determination. The photocatalytic activity of as-prepared zinc oxide samples was determined by decomposition of Orange II dye in aqueous solution under UV irradiation of 365 nm wavelength. Synthesized ZnO were evaluated for their non-photochemical degradation ability of chemical warfare agents to nontoxic products.

Photo-induced degradation of diuron in aqueous solution by nitrites and nitrates: kinetics and pathways

The photo-induced degradation of diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in aqueous solution under simulated solar irradiation has been investigated in the presence of NO3-/NO2- ions. The degradation rates were compared by varying environmental parameters including substrate and inducer concentrations, oxygen content and pH. The photoproducts were identified by extensive LC-ESI-MS and LC-ESI-MS-MS studies after SPE preconcentration on prepacked cartridges. In both NO3- and NO2- conditions, oxidation of the N-(CH3)2 terminus group is the main process leading to the N-monodemethylated (NHCH3), N-formyl (N(CH3)CHO) and the uncommon and unstable carbinolamine (N(CH3)CH2OH) by-products. Cl/OH substituted and nitrated phenylureas are formed minorily. Degradation pathways involving OH* and NO2* (or dimer) radicals as reactive species are proposed.

Photocatalytic degradation of phenyl-urea herbicides chlortoluron and chloroxuron: characterization of the by-products by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

The first stages of the photocatalytic degradation of the compounds chlortoluron [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] and chloroxuron [3-[4-(4-chlorophenoxy)phenyl]-1,1-dimethylurea], belonging to the class of phenyl-urea herbicides, were investigated using high-performance liquid chromatography (HPLC) coupled to electrospray ionization ion trap tandem mass spectrometry (ESI-IT-MS/MS). Degradation was accomplished under solar radiation, using TiO2 embedded into a polyvinylidene fluoride (PVDF) transparent matrix as a heterogeneous photocatalyst. Aliquots of the chlorinated herbicide solutions were withdrawn at different times and subjected to gradient elution, reversed-phase HPLC separations, specifically optimized to obtain the highest resolution between peaks related to the herbicide degradation by-products. The latter were then investigated using MS detection; in particular, MS/MS measurements were made and structural information was obtained from the interpretation of fragmentation data. Several by-products were identified; the most important ones are hydroxylated compounds arising from the interaction between the two chlorinated herbicides and OH radicals generated at the TiO2 surface under irradiation. Other by-products were generated by slightly different processes, namely demethylation, dearylation and dechlorination, eventually followed by interaction with OH radicals.

Mechanisms of Direct and TiO2-Photocatalysed UV Degradation of Phenylurea Herbicides

Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another.

Photocatalytic degradation of the herbicide isoproturon: characterisation of by-products by liquid chromatography with electrospray ionisation tandem mass spectrometry

By-products arising from immobilised TiO2-catalysed photodegradation of the herbicide isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] in aqueous solution under solar radiation were analysed by reversed-phase liquid chromatography combined with electrospray ionisation ion trap mass spectrometry. Structural information on by-products, formed at different degradation times, was then obtained from interpretation of the relevant MS/MS spectra. Several species were identified through this approach, and in many cases several isomers were found. As expected, most by-products resulted from single or multiple hydroxylation (by photo-generated OH* radicals) of the isoproturon molecule at different positions. However, substitution of some functional groups of the herbicide (isopropyl or methyl) by OH* was also observed. A possible degradation scheme is hypothesised.