Photocatalytic degradation of dimethoate using LbL fabricated TiO2/polymer hybrid films

Preparation of wavy three-dimensional graphene-like biochar and its adsorption mechanism of embedded separation for dimethoate

In this study, graphene-like biochar (IZBC) was prepared by pyrolysis of wheat straw in the presence of catalyst and activator. The formation of graphene in IZBC could be divided into three stages: shell core generation, carburization, and carbon precipitation. When the pyrolysis temperatures were in the ranges of 500-600 ℃, 600-700 ℃, 700-800 ℃ and 800-900 ℃, 17%, 32%, 13% and 38% of graphene were produced, respectively. The contribution ratios of graphene by FeCl₃, ZnCl₂ and HCl were 64%, 23% and 13%, respectively. Moreover, IZBC was filled with porous wavy three-dimensional graphene nanosheets that enabled self-aggregation to be effectively prevented, which was superior to the striped two-dimensional structure. The adsorption of IZBC for dimethoate was a spontaneous exothermic reaction with the adsorption capacity of 980 μmol/g, which was consistent with the pseudo-second-order and intraparticle diffusion models. The adsorption was inhibited by coexisting cations, anions, and humic acid in water. Dimethoate was adsorbed on graphene through embedded separation, with pore filling, cation-π and electrostatic attraction as the key driving forces. In addition, the adsorbed saturated IZBC could be effectively regenerated for many times by 2 mol/L HCl solution.

Heterogeneous photocatalytic oxidation for the removal of organophosphorus pollutants from aqueous solutions: A review

Organophosphorus pollutants (OPs), which are compounds containing carbon‑phosphorus bonds or phosphate derivatives containing organic groups, have received much attention from researchers because of their persistence in the aqueous environment for long periods of time and the threat they pose to human health. Heterogeneous photocatalysis has been widely applied to the removal of OPs from aqueous solutions due to its better removal effect and environmental friendliness. In this review, the removal of OPs from aqueous matrices by heterogeneous photocatalysis was presented. Herein, the application and the heterogeneous photocatalysis mechanism of OPs were described in detail, and the effects of catalyst types on degradation effect are discussed categorically. In particular, the heterojunction type photocatalyst has the most excellent effect. After that, the photocatalytic degradation pathways of several OPs were summarized, focusing on the organophosphorus pesticides and organophosphorus flame retardants, such as methyl parathion, dichlorvos, dimethoate and chlorpyrifos. The toxicity changes during degradation were evaluated, indicating that the photocatalytic process could effectively reduce the toxicity of OPs. Additionally, the effects of common water matrices on heterogeneous photocatalytic degradation of OPs were also presented. Finally, the challenges and perspectives of heterogeneous photocatalysis removal of OPs are summarized and presented.

Identification of photodegradation product of organophosphorus pesticides and elucidation of transformation mechanism under simulated sunlight irradiation

Organophosphorus pesticides (OPs) are posing great threat to the environment and human health, due to their overuse and persistence in the environment. Photolysis has been established as an effective method to degrade OPs. The influence of pH value, the initial concentration of pesticides and the light source on the photolysis of two OPs, including chlorpyrifos and dimethoate, was investigated. The optimal reaction condition for OPs degradation was under pH 9, with xenon lamp as the light source, in which the photodegradation efficiencies of chlorpyrifos and dimethoate (500 mg/L) were 75.12% and 94.31%, respectively. The photodegradation products of chlorpyrifos and dimethoate were identified by GC-MS. Also, density functional theory (DFT) calculations were used to characterize the molecular properties of chlorpyrifos and dimethoate, as well as predicting potential photolysis reactions. Photodegradation mechanisms of chlorpyrifos and dimethoate were proposed, in which 3,5,6-trichloropyridinol (TCP), O,O-diethyl thiophosphate (DETP), 2,3,5-Trichloro-6-methoxypyridine (TMP) and O,O,S-trimethyl phosphorothioate were identified as the main products of chlorpyrifos degradation. Omethoate, O,O,S-trimethyl thiophosphorothioate, N-methyl-2-sulfanylacetamide, O,O,O-trimethyl thiophosphate, O,O,S-trimethylphosphorothiate, and O,O,O-trimethyl phosphoric ester as the main photodegradation products for dimethoate. The main degradation mechanisms included ring opening, cleavage, oxidation and demethylation. This work demonstrated the feasibility of combining chemical analysis with quantum chemical calculation in unraveling degradation mechanisms of OPs. Also, it is of great significance for evaluating the environmental fate of OPs in aquatic system and further environmental risk assessment.

Rapid degradation of dimethoate and simultaneous removal of total phosphorus by acid-activated Fe(VI) under simulated sunlight

Ferrate (Fe(VI)) is usually effective for oxidizing a variety of organic pollutants within a few seconds, but some recalcitrant asorganophosphorus pesticides such as dimethoate require higher dose of Fe(VI) and inorganic phosphorus produced by mineralization is difficult to remove. In this study, acid-activated ferrate (Fe(VI)) was firstly used to degrade organophosphorus pesticides dimethoate and simultaneously remove total phosphorus (TP) from solution under simulated sunlight. At a Fe(VI):dimethoate molar radio of 15:1, dimethoate was almost completely removed within 20 min and 47% of TP in the solution was removed by the reduction product of Fe(VI) within 240 min. Electron paramagnetic resonance (EPR) and terephthalic acid (TA) fluorescence experiments showed that •OH radicals were continuously generated in the system, and •OH formation pathway was proposed. Importantly, the involvement of •OH in acid-activated Fe(VI) process was confirmed for the first time by EPR. In the acid-activated Fe(VI)/simulated sunlight system, the removal of dimethoate and TP gradually increased with the decrement of activation pH, whereas the increase of molar ratio of Fe(VI):dimethoate enhanced the removal of dimethoate and TP. The addition of inorganic anions (HCO₃^- and NO₂^-) had obvious inhibitory effects on dimethoate and TP removal. Eight degradation products including O,O,S-trimethylphosphorothiate, omethoate and 2-S-methyl-(N-methyl) acetamide were determined by gas chromatography mass spectrometry (GC-MS) analysis, and two possible degradation pathways were proposed. The insights gained from this study open a new avenue to simultaneously degrade and remove organic contaminants.

Oxidative degradation and mineralization of bentazone from water

Bentazone degradation efficiency and mineralization in water solutions using chlorine dioxide treatment were evaluated. Double distilled water and a river water sample spiked with bentazone were studied and compared after chlorine dioxide treatment. Degradation efficiency was determined using high-performance liquid chromatography (HPLC). Daphnia magna toxicity testing and total organic carbon (TOC) analysis were used to ascertain the toxicity of the degraded solutions and mineralization degree. Bentazone degradation products were identified using gas chromatography with a triple quadrupole mass detector (GC-MS-MS). A simple mechanistic scheme for oxidative degradation of bentazone was proposed based on the degradation products that were identified. Decrease in D. magna mortality, high degradation efficiency and partial bentazone mineralization were achieved by waters containing bentazone degradation products, which indicate the formation of less toxic compounds than the parent bentazone and effective removal of bentazone from the waters. Bentazone degraded into four main degradation products. Humic acid from Sava River water influenced bentazone degradation, resulting in a lower degradation efficiency in this matrix (about 10% lower than in distilled water). Chlorine dioxide treatment of water to degrade bentazone is efficient and offers a novel approach in the development of new technology for removal of this herbicide from contaminated water.

Evaluation of azamethiphos and dimethoate degradation using chlorine dioxide during water treatment

Chlorine dioxide (ClO₂) degradation of the organophosphorus pesticides azamethiphos (AZA) and dimethoate (DM) (10 mg/L) in deionized water and in Sava River water was investigated for the first time. Pesticide degradation was studied in terms of ClO₂ level (5 and 10 mg/L), degradation duration (0.5, 1, 2, 3, 6, and 24 h), pH (3.00, 7.00, and 9.00), and under light/dark conditions in deionized water. Degradation was monitored using high-performance liquid chromatography. Gas chromatography coupled with triple quadrupole mass detector was used to identify degradation products of pesticides. Total organic carbon was measured to determine the extent of mineralization after pesticide degradation. Real river water was used under recommended conditions to study the influence of organic matter on pesticide degradation. High degradation efficiency (88-100% for AZA and 85-98% for DM) was achieved in deionized water under various conditions, proving the flexibility of ClO₂ degradation for the examined organophosphorus pesticides. In Sava River water, however, extended treatment duration achieved lower degradation efficiency, so ClO₂ oxidized both the pesticides and dissolved organic matter in parallel. After degradation, AZA produced four identified products (6-chlorooxazolo[4,5-b]pyridin-2(3H)-one; O,O,S-trimethyl phosphorothioate; 6-chloro-3-(hydroxymethyl)oxazolo[4,5-b]pyridin-2(3H)-one; O,O-dimethyl S-hydrogen phosphorothioate) and DM produced three (O,O-dimethyl S-(2-(methylamino)-2-oxoethyl) phosphorothioate; e.g., omethoate; S-(2-(methylamino)-2-oxoethyl) O,O-dihydrogen phosphorothioate; O,O,S-trimethyl phosphorodithioate). Simple pesticide degradation mechanisms were deduced. Daphnia magna toxicity tests showed degradation products were less toxic than parent compounds. These results contribute to our understanding of the multiple influences that organophosphorus pesticides and their degradation products have on environmental ecosystems and to improving pesticide removal processes from water.

Examination of degradation and ecotoxicology of pethoxamid and metazachlor after chlorine dioxide treatment

Chlorine dioxide has been reported as very efficiently removing pesticides and other organic compounds from water matrixes. Due to pesticide toxicity and potential toxicity of their degradation products, it is important to monitor these compounds as environmental pollutants in ground and surface waters. Evaluating the effects of chlorine dioxide treatment is necessary, and toxicity studies are used to ascertain the severity of effects of intermediates due to incomplete degradation of the parent compounds. In this paper, for the first time, chlorine dioxide is applied and evaluated for the removal of chloroacetamide herbicides (pethoxamid and metazachlor) from waters (deionized water and Sava River water). The degradation degree of herbicides was measured by high-performance liquid chromatography, the main degradation products were identified using gas chromatography with a triple quadrupole mass detector, and the degree of mineralization was monitored by total organic carbon analysis. Four and two degradation products were identified after pethoxamid and metazachlor degradation, respectively. Total organic carbon analysis showed mineralization occurred, but it was incomplete. The mineralization and the characteristics of the degradation products obtained were tested using Daphnia magna and showed lower toxicity than the parent herbicides. The advantage of the applied treatment was a very high degradation percentage for pethoxamid removal from deionized water and Sava River water (100% and 97%, respectively), with higher mineralization efficiency (65%) than metazachlor. Slightly lower degradation efficiency in the Sava River water was due to chlorine dioxide oxidizing the herbicides and dissolved organic matter simultaneously.

Recent Advances in Hybrid Biomimetic Polymer-Based Films: from Assembly to Applications

Biological membranes, in addition to being a cell boundary, can host a variety of proteins that are involved in different biological functions, including selective nutrient transport, signal transduction, inter- and intra-cellular communication, and cell-cell recognition. Due to their extreme complexity, there has been an increasing interest in developing model membrane systems of controlled properties based on combinations of polymers and different biomacromolecules, i.e., polymer-based hybrid films. In this review, we have highlighted recent advances in the development and applications of hybrid biomimetic planar systems based on different polymeric species. We have focused in particular on hybrid films based on (i) polyelectrolytes, (ii) polymer brushes, as well as (iii) tethers and cushions formed from synthetic polymers, and (iv) block copolymers and their combinations with biomacromolecules, such as lipids, proteins, enzymes, biopolymers, and chosen nanoparticles. In this respect, multiple approaches to the synthesis, characterization, and processing of such hybrid films have been presented. The review has further exemplified their bioengineering, biomedical, and environmental applications, in dependence on the composition and properties of the respective hybrids. We believed that this comprehensive review would be of interest to both the specialists in the field of biomimicry as well as persons entering the field.

KOH modified Thevetia peruviana shell activated carbon for sorption of dimethoate from aqueous solution

Modified Thevetia peruviana shell activated carbon for sorption of dimethoate from aqueous solution derived with potassium hydroxide (KOH) was studied at different concentrations for its potential application in water treatment. The batch sorption was investigated using dimethoate solution of 10-100 mg/L concentrations. Proximate analysis was determined and changes on the surfaces and structure of the TPS were characterized after chemical activation with KOH using XRD, FTIR, SEM-EDAX, pH_pzc, BET. The quantum chemical calculation for dimethoate yielded molecule associated energies of -9.8421 (HOMO) and -2.3879 (LUMO) and a total energy of -53,376.2. The kinetic of the sorption was modeled which indicated the sorption equilibrium time as 90 min and pseudo-first order kinetics model showing R² = 0.994 provided a better description of the process. Analysis of sorption equilibrium revealed that the data fitted well to Freundlich sorption isotherm model (R² = 0.966), indicating multi-layer sorption of dimethoate on the surface of sorbent. The sorption of dimethoate onto KOHTPS shows 92.60% removal efficiency.

Photocatalytic degradation of dimethoate in Bok choy using cerium-doped nano titanium dioxide

Dimethoate, a systemic insecticide, has been used extensively in vegetable production. Insecticide residues in treated vegetables, however, pose a potential risk to consumers. Photocatalytic degradation is a new alternative to managing pesticide residues. In this study, the degradation of dimethoate in Bok choy was investigated under the field conditions using cerium-doped nano titanium dioxide (TiO₂/Ce) hydrosol as a photocatalyst. The results show that TiO₂/Ce hydrosol can accelerate the degradation of dimethoate in Bok choy. Specifically, the application of TiO₂/Ce hydrosol significantly increased the reactive oxygen species (ROS) contents in the treated Bok choy, which speeds up the degradation of dimethoate. Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) analysis detected three major degradation products, including omethoate, O,O,S-trimethyl thiophosphorothioate, and 1,2-Bis (acetyl-N-methyl-) methane disulfide. Two potential photodegradation pathways have been proposed based on the intermediate products. To understand the relationship between photodegradation and the molecular structure of target insecticides, we investigated the bond length, Mulliken atomic charge and frontier electron density of dimethoate using ab initio quantum analysis. These results suggest the P = S, P-S and S-C of dimethoate are the initiation sites for the photocatalytic reaction in Bok choy, which is consistent with our empirical data.

Fluoride Removal from Aqueous Solutions Using Poly(Styrene Sulfonate)/Nanoalumina Multilayer Thin Films

In the present study, fluoride removal from drinking water is investigated using layer-by-layer (LbL) fabricated poly(sodium 4-styrene-sulfonate) (PSS)/Al2O3 thin films. The surface morphology of the fabricated thin films is characterized using atomic force microscopy and field emission-scanning electron microscopy. Optical profilometry is used to determine the self-assembly of the multilayer thin films. The effect of various parameters such as adsorbent dosage, contact time, initial fluoride content, number of bilayers, surface area, and pH is thoroughly studied. Fluoride removal increases with the number of bilayers and number of slides (total surface area). The amount of fluoride adsorbed increases from 11.32 to 26 mg L-1 when the number of substrates increases from 1 to 5. A 68% removal of fluoride is observed when 20 bilayers of PSS/Al2O3 thin films with three slides at an initial fluoride concentration of 5 mg L-1 are used, thereby bringing down the fluoride concentration level below the World Health Organization permissible limit. Slide reusability studies reveal that the fabricated thin films can be used for ten cycles without affecting the fluoride removal properties of the film. This study demonstrates the potential application of immobilized PSS/Al2O3 thin films as an effective adsorbent for drinking water purification.

Synergistic toxicity of zno nanoparticles and dimethoate in mice: Enhancing their biodistribution by synergistic binding of serum albumin and dimethoate to zno nanoparticles

The extensive applications of ZnO nanoparticles (nano ZnO) and dimethoate (DM) have increased the risk of humans' co-exposure to nano ZnO and DM. Here, we report the synergistic effect of nano ZnO and DM on their biodistribution and subacute toxicity in mice. Nano ZnO and DM had a synergistic toxicity in mice. In contrast, bulk ZnO and DM did not cause an obvious synergistic toxicity in mice. Although nano ZnO was low toxic to mice, coexposure to nano ZnO and DM significantly enhanced DM-induced oxidative damage in the liver. Coadministration of nano ZnO with DM significantly increased Zn accumulation by 30.9 ± 1.9% and DM accumulation by 45.6 ± 2.2% in the liver, respectively. The increased accumulations of DM and Zn in the liver reduced its cholinesterase activity from 5.65 ± 0.32 to 4.37 ± 0.49 U/mg protein and induced hepatic oxidative stress. Nano ZnO had 3-fold or 2.4-fold higher binding capability for serum albumin or DM, respectively, than bulk ZnO. In addition, serum albumin significantly increased the binding capability of nano ZnO for DM by approximately four times via the interaction of serum albumin and DM. The uptake of serum albumin- and DM-bound nano ZnO by the macrophages significantly increased DM accumulation in mice. Serum albumins play an important role in the synergistic toxicity of nano ZnO and DM. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1202-1212, 2017.

Microfluidic-based photocatalytic microreactor for environmental application: a review of fabrication substrates and techniques, and operating parameters

This article gives an overview of photocatalytic microreactors with an application in environmental science, in particular, the degradation of different toxic dyes within microchannels.

Effects of ZnO Nanoparticles on Dimethoate-Induced Toxicity in Mice

The extensive applications of ZnO nanoparticles (nano ZnO) and dimethoate have increased the risk of people's coexposure to nano ZnO and dimethoate. Therefore, we evaluated in this study the effects of nano or bulk ZnO on dimethoate-induced toxicity in mice. The serum biochemical parameters, biodistributions, oxidative stress responses, and histopathological changes in mice were measured after intragastric administration of nano or bulk ZnO and/or dimethoate for 14 days. Oral administration of nano or bulk ZnO at a dose of 50 mg/kg did not cause obvious injury in mice. In contrast, oral administration of dimethoate at a dose of 15 mg/kg induced observable oxidative damage in mice. Co-administration of nano or bulk ZnO with dimethoate significantly increased Zn accumulation by 30.7 ± 1.7% or 29.7 ± 2.4% and dimethoate accumulation by 42.8 ± 2.1% or 46.6 ± 2.9% in the liver, respectively. The increased accumulations of dimethoate and Zn in the liver reduced its cholinesterase activity from 5.64 ± 0.45 U/mg protein to 4.67 ± 0.42 U/mg protein or 4.76 ± 0.45 U/mg protein for nano or bulk ZnO, respectively. Furthermore, the accumulations of dimethoate and Zn in liver also increased hepatic oxidative stress, resulting in severe liver damage. Both nano and bulk ZnO dissolved quickly in acidic gastric fluid, regardless of particle size; therefore, they had nearly identical enhanced effects on dimethoate-induced toxicity in mice.

Fabrication of an inexpensive and high efficiency microphotoreactor using CO2 laser technique for photocatalytic water treatment applications

In this study, a micro-photoreactor with catalyst-immobilized micro-channels was designed and fabricated using CO2 laser as a simple and inexpensive technique. The micro-photoreactor is composed of an array of micro-channels, a quartz plate, and an array of UV-LEDs. The micro-channels with the dimension of 400 µm width, 50 µm depth, and 80 cm length were inscribed on a flat plate of poly(methyl methacrylate) (PMMA). The illuminated specific surface area for the designed micro-reactor was calculated to be 25000 m(-1). To examine the performance of miniaturized photoreactor, the photocatalytic degradation of 4-Nitrophenol as a refractory pollutant was investigated. The effects of operational variables on the performance of micro-photoreactor were studied. Higher photocatalytic degradation is obtained for low flow rates, high light intensities, long micro-channels lengths, and low inlet concentrations. Also, the performance of micro-photoreactor was examined in the presence of different types of TiO2 catalysts with an average particle size between 5 and 27 nm (such as P25, PC500, Merck, and UV100) and textile dyes with different chemical structures (such as Acid Orange 7, Acid Violet 19, Basic Red 46, Methyl Orange, and Malachite Green). Finally, the reusability of miniaturized photoreactor was evaluated and the results showed satisfactory stability and reusability for the designed micro-reactor in the photocatalytic degradation of organic pollutants.

Compound specific isotope analysis of organophosphorus pesticides

Compound-specific isotope analysis (CSIA) has been established as a tool to study the environmental fate of a wide range of contaminants. In this study, CSIA was developed to analyse the stable carbon isotope signatures of the widely used organophosphorus pesticides: dichlorvos, omethoate and dimethoate. The linearity of the GC-C-IRMS system was tested for target pesticides and led to an acceptable isotope composition within the uncertainty of the instrument. In order to assess the accuracy of the developed method, the effect of the evaporation procedure on measured carbon isotope composition (δ(13)C) values was studied and showed that concentration by evaporation of solvents had no significant isotope effect. The CSIA was then applied to investigate isotope fractionation of the hydrolysis and photolysis of selected pesticides. The carbon isotope fractionation of tested pesticides was quantified by the Rayleigh model, which revealed a bulk enrichment factor (ε) of -0.2±0.1‰ for hydrolysis of dichlorvos, -1.0±0.1‰ and -3.7±1.1‰ for hydrolysis and photolysis of dimethoate respectively. This study is a first step towards the application of CSIA to trace the transport and degradation of organophosphorus pesticides in the environment.