Mechanism of significant enhancement of VO2-Fenton-like reactions by oxalic acid for diethyl phthalate degradation

Phthalate esters: occurrence, toxicity, bioremediation, and advanced oxidation processes

Phthalic acid esters are emerging pollutants, commonly used as plasticizers that are categorized as hazardous endocrine-disrupting chemicals (EDCs). A rise in anthropogenic activities leads to an increase in phthalate concentration in the environment which leads to various adverse environmental effects and health issues in humans and other aquatic organisms. This paper gives an overview of the research related to phthalate ester contamination and degradation methods by conducting a bibliometric analysis with VOS Viewer. Ecotoxicity analysis requires an understanding of the current status of phthalate pollution, health impacts, exposure routes, and their sources. This review covers five toxic phthalates, occurrences in the aquatic environment, toxicity studies, biodegradation studies, and degradation pathways. It highlights the various advanced oxidation processes like photocatalysis, Fenton processes, ozonation, sonolysis, and modified AOPs used for phthalate removal from the environment.

Degradation kinetics and transformation pathway of methyl parathion by δ-MnO2/oxalic acid reaction system

Methyl parathion (MP) is a typical organophosphorus pesticide that is widely used worldwide, and hydrolysis, oxidation and reduction are the main abiotic degradation processes. Manganese dioxide (MnO₂) and organic acid can participate in various geochemical processes of pollutants, a reaction system was constructed to degrade MP using δ-MnO₂ and oxalic acid. The δ-MnO₂/oxalic acid reaction system could efficiently degrade MP, and the removal rate of MP (20 μM) reached 67.83% within 30 h under the optimized conditions (pH 5, [δ-MnO₂] = 2 mM, [oxalic acid] = 100 mM). MP was hydrolyzed by substitution reactions of S_N@P and S_N@C, and reduced by conversion of the nitro groups (-NO₂) in MP and its hydrolysates to amino groups (-NH₂). The primary active substance produced in the reaction system was the complexes dominated by Mn(III)-oxalic acid. This study provides a scientific basis for the degradation of organophosphorus pesticides using MnO₂ and an organic acid. The results have important theoretical significance and application value for pollution control and remediation of organophosphorus pesticides.

Enhanced paper sludge dewatering and in-depth mechanism by oxalic acid/Fe2+/persulfate process

As a typical advanced oxidation process, Fe²⁺-persulfate (PDS) oxidation technology has been widely and efficiently reported for enhancing sludge dewaterability. However, higher dosage of Fe²⁺ must be added, which will restrain the oxidation efficiency of Fe²⁺-PDS process. In this work, the oxalic acid (OA)/Fe²⁺-PDS process was studied to improve paper sludge dewatering. With the OA dosage of 6 μmol (g total solid (TS))^-1, Fe²⁺ dosage of 0.3 mmol (g TS)^-1, and PDS dosage of 0.6 mmol (g TS)^-1, sludge dewaterability was improved more efficiently. The specific resistance to filtration and water content of sludge cake were decreased by 70.7% and 8.0%, respectively. In comparison with Fe²⁺-PDS process, the viscosities of sludge suspension and supernatant were further reduced by 3.73% and 51.77%, respectively, and the contents of extracellular polymeric substances fractions were increased. The improved sludge dewaterability in OA/Fe²⁺-PDS process was mainly contributed by the synergistic effect of oxidative disintegration by free radicals and flocs re-flocculation, the contributions of which were the orders: metal cations > sulfate radical > hydroxyl radical. OA enhanced the efficient disintegration of sludge flocs, released more bound water, generated more Fe³⁺-oxalate complexes, and finally increased the sludge particle size significantly, forming a larger aggregation and obvious cracks. Additionally, the stabilization of several heavy metals was improved due to the chelating capacity of OA. These works will provide a novel approach for sludge dewatering in the PDS oxidation process.

Contribution of photocatalytic and Fenton-based processes in nanotwin structured anodic TiO2 nanotube layers modified by Ce and V

In the present work, nanotwin structured TiO₂ nanotube (TNT) layers are prepared by the electrochemical anodization technique to form the anatase phase and by surface modification via spin-coating of Ce and V precursors to form Ce-TNT and V-TNT, respectively. The surface and cross-sectional images by SEM revealed that the nanotubes have an average diameter of ∼130 nm and a length of ∼14 μm. In addition, the TEM images revealed the nanotwin structures of the nanotubes, especially the anatase (001) and (112) twin surfaces, that increase the transport of photogenerated charges. The photoinduced degradation of caffeine (CAF) by TNT, Ce-TNT, and V-TNT led to a degradation extent of 16%, 26% and 33%, respectively, whereas it increased to 26%, 38%, and 46% in the presence of H₂O₂, owing to the involvement of Fenton-based processes (in addition to photocatalysis). The effect of the Fenton-based processes accounts for about 10% of the total degradation extent of CAF. Finally, the mechanism of the photoinduced degradation of CAF was investigated. The main oxidative species were the hydroxyl radicals, and the better efficiency of V-TNT over Ce-TNT and TNT was ascribed to its negative surface, thus improving the interactions with CAF.