Search Results (6)

Persulfate-based advanced oxidation process has been proven to be a promising method for the toxic pesticide chlorpyrifos (CPY) degradation in wastewater treatment. However, due to the limitation for the short-lived intermediates detection, a comprehensive understanding for the degradation pathway remains unclear. To address this issue, density functional theory was used to analyze the degradation mechanism of CPY at the M06-2X/6-311++G(3df,3pd)//M06-2X/6-31+G(d,p) level, and computational toxicology methods were employed to explore the toxicity of CPY and its degradation products. Results show that hydroxyl radicals (·OH) and sulfate radicals (SO₄^•−) initiate the degradation reactions by adding to the P=S bond and abstracting the H atom on the ethyl group, rather than undergoing α-elimination of the pyridine ring in the persulfate oxidation process. Moreover, the addition products were attracted and degraded by breaking the P–O bond, while the abstraction products were degraded through dealkylation reactions. The transformation products, including 3,5,6-trichloro-2-pyridynol, O,O-diethyl phosphorothioate, chlorpyrifos oxon, and acetaldehyde, obtained through theoretical calculations have been detected in previous experimental studies. The reaction rate constants of CPY with ·OH and SO₄^•− were 6.32 × 10⁸ and 9.14 × 10⁸ M⁻¹·s⁻¹ at room temperature, respectively, which was consistent with the experimental values of 4.42 × 10⁹ and 4.5 × 10⁹ M⁻¹ s⁻¹. Toxicity evaluation results indicated that the acute and chronic toxicity to aquatic organisms gradually decreased during the degradation process. However, some products still possess toxic or highly toxic levels, which may pose risks to human health. These research findings contribute to understanding the transformation behavior and risk assessment of CPY in practical wastewater treatment. Full article

Using municipal sewage as a source of reclaimed water is an important way to alleviate the shortage of water resources. At present, advanced oxidation technology (AOPs), represented by ozone oxidation, is widely used in wastewater treatment. In this study, γ-Al₂O₃, a low-cost traditional ozone catalyst, was selected as the matrix. By modifying magnetic γ-Fe₂O₃ with a titanate coupling agent, in situ deposition, and calcination, the final formation of a γ-Al₂O₃/TiO₂/γ-Fe₂O₃ micrometer ozone catalyst was achieved. A variety of material characterization methods were used to demonstrate that the required material was successfully prepared. The catalyst powder particles have strong magnetic properties, form aggregates easily, and have good precipitation and separation properties. Subsequently, ibuprofen was used as the degradation substrate to investigate the ozone catalytic performance of the prepared catalyst, and this proved that it had good ozone catalytic activity. The degradation process was also analyzed. The results showed that in the ozone system, some of the ibuprofen molecules will be oxidized to form 1,4-propanal phenylacetic acid, which is then further oxidized to form 1,4-acetaldehyde benzoic acid and p-phenylacetaldehyde. Finally, the prepared catalyst was applied to the actual wastewater treatment process, and it also had good catalytic performance in this context. GC–MS detection of the water samples after treatment showed that the types of organic matter in the water were significantly reduced, among which nine pollutants with high content, such as bisphenol A and sulfamethoxazole, were not detected after treatment. Full article

Acetaldehyde is a typical toxic substance of the petrochemical industry. Dissolved organic carbon (DOC) plays an important role in wastewater treatment. Therefore, the molecular weight, hydrophilicity, and chemical composition of DOC in acetaldehyde wastewater were evaluated. First, the molecular weight (MW) distribution was investigated; the results showed that acetaldehyde wastewater was mainly composed of components with a MW less than 1 kDa, and possessed higher proportion of protein-like substances that were dominant contributors to membrane fouling. Then, the distribution of hydrophobicity was evaluated; hydrophobic bases were reported to be slowly biodegradable fractions due to the high humic content. Finally, gas chromatography–mass spectrometry (GC-MS) was utilized to determine chemical composition, and 30 pollutants were detected. Aldehydes, hydrocarbons, ketones, alcohols, furans, phenols, and organic acids were the dominant pollutants. Most of them were moderately toxic compounds. The comprehensive characterization of acetaldehyde wastewater will contribute to control strategies and sustainable development. Full article

Wastewaters from precious metal industries contain high amounts of noble metals, but their efficient recycling is hindered by the wastewater complex composition. Here, we propose an innovative approach for the efficient recovery of noble metals contained in these metal-enriched wastewaters as precursors for the synthesis of noble metal nanoparticles (NPs) and supported metal catalysts. Silver NPs were synthesized from Ag-enriched wastewater and then deposited on TiO₂ to prepare photocatalysts. Then, further promotion of the photocatalytic activity of Ag-modified TiO₂ was achieved by the addition of as little as 0.5 wt.% of Au. STEM-EDS analyses proved that Au NPs were located on Ag or AgO_x nanoparticles. The contact between the two metal-containing NPs results in charge transfer effects, appreciable both in terms of oxidation states determined by XPS and of optical properties. In particular, the plasmon band of Au NPs shows photochromic effects: under UV light irradiation, bimetallic samples exhibit a blue-shift of the plasmon band, which is reversible under dark storage. The activity of the materials was tested towards ethanol photodegradation under UV light. Adding 0.5 wt.% Au NPs resulted in a promoted activity compared to Ag-TiO₂, thus showing synergistic effects between Au and Ag. Ethanol was completely converted already after 1 h of UV irradiation, acetaldehyde was formed as the main oxidation product and fully degraded in less than 180 min. Notably, bimetallic samples showed ethylene formation by a parallel dehydration mechanism. Full article

This work recovered Ni or Cu cations from simulated electroplating wastewater to synthesize Ni/Cu nano-catalysts for H₂ generation by ethanol steam reforming (ESR). Aluminum lathe waste was used as a framework to prepare the structured catalyst. Li–Al–CO₃ layered double hydroxide (LDH) was electrodeposited on the surface of the framework. The LDH was in a platelet-like structure, working as a support for the formation of the precursor of the metal catalysts. The catalytic performance and the coke properties of a 6Cu_6Ni two-stage catalyst configuration herein used for ESR catalytic reaction were studied. The Cu–Ni two-stage catalyst configuration (6Cu_6Ni) yielded more H₂ (~10%) than that by using the Ni-based catalyst (6Ni) only. The 6Cu_6Ni catalyst configuration also resulted in a relatively stable H₂ generation rate vs. time, with nearly no decline during the 5-h reaction. Through the pre-reaction of ethanol-steam mixture with Cu/LiAlO₂ catalyst, the Ni/LiAlO₂ catalyst in the 6Cu_6Ni catalyst configuration could steadily decompose acetaldehyde, and rare acetate groups, which would evolve condensed coke, were formed. The Ni nanoparticles were observed to be lifted and separated by the carbon filaments from the support and had no indication of sintering, contributing to the bare deactivation of the Ni/LiAlO₂ catalyst in 6Cu_6Ni. Full article

The development of immobilized photocatalyst as a strategy for problematic electronics wastewater reuse is described in this study. The strategy was to perform separate rinsing, mostly consisting of low molecular weight compounds, and to decompose them with a simple process, based on the advanced oxidation process (AOP). Extensive studies were performed on the preparation conditions of immobilized photocatalysts by sol-gel method under various amount of precursor and support, water to precursor ratio, pH, aging time, and calcination conditions. The optimized preparation conditions were chosen by measuring removal efficiencies of isopropyl alcohol as a representative target compound with supportive SEM and XRD analyses. Removal efficiencies with photocatalyst and UV irradiation in synthetic wastewater simulating electronics wastewater were evaluated over time. Removal efficiencies of alcohol, acetone, ethanol, and acetaldehyde reached 97.2%, 71.2%, 99.0%, and 99.0%, respectively, in 2 h. Reaction constants of each compound were determined by fitting experimental data to the first order kinetic equation and the trial and error method with consecutive reaction pathway. As analysis results of reaction constants, UV with prepared photocatalyst was found to be effective and the decomposition of acetone was found to be the rate-determining step. The immobilized photocatalyst developed in this study would be useful for application of wastewater reuse with high removal efficiencies, mild preparation conditions, and mechanical stability. Full article