Thermodynamic study of the electrochemical oxidation of some aminophenol derivatives: Experimental and theoretical investigation

Environmental fate and ecotoxicity of diclofenac degradation products generated by photo-assisted advanced oxidation processes

Diclofenac (DCF), a widely used non-steroidal anti-inflammatory drug (NSAID), poses environmental concerns due to its persistence, bioaccumulation potential, and transformation into toxic byproducts during oxidative and chlorination processes. This study investigated the photodegradation of DCF, both directly and in the presence of oxidants, to characterize the resulting degradation products and assess their potential environmental impact. The highest efficiency for direct UV photodegradation of DCF was observed at pH 5, while the addition of oxidants significantly accelerated the degradation rate. Among the advanced oxidation processes (AOPs) examined, the H₂O₂/UV system, with a DCF:H₂O₂ molar ratio of 1:30, exhibited the most effective performance in terms of DCF removal and total organic carbon (TOC) reduction. However, ecotoxicity assessments using Alivibrio fischeri, Daphnia magna, and Lemna minor revealed that AOPs generally increased the toxicity of the resulting solutions compared to untreated DCF. Toxicity analyses showed that post-reaction mixtures from AOPs involving NaOCl exhibited the highest toxic effects, consistent with forming specific transformation products identified as highly toxic by ECOSAR modeling. Additionally, the analysis of the physicochemical properties of DCF and its transformation products, including solubility and organic matter affinity, suggests a limited potential for long-range transport. These compounds are more likely to bind to sediments, reducing their mobility in groundwater.

Transformation of m-aminophenol by birnessite (δ-MnO2) mediated oxidative processes: Reaction kinetics, pathways and toxicity assessment

The m-aminophenol (m-AP) is a widely used industrial chemical, which enters water, soils, and sediments with waste emissions. A common soil metal oxide, birnessite (δ-MnO₂), was found to mediate the transformation of m-AP with fast rates under acidic conditions. Because of the highly complexity of the m-AP transformation, mechanism-based models were taken to fit the transformation kinetic process of m-AP. The results indicated that the transformation of m-AP with δ-MnO₂ could be described by precursor complex formation rate-limiting model. The oxidative transformation of m-AP on the surface of δ-MnO₂ was highly dependent on reactant concentrations, pH, temperature, and other co-solutes. The UV-VIS absorbance and mass spectra analysis indicated that the pathway leading to m-AP transformation may be the polymerization through the coupling reaction. The m-AP radicals were likely to be coupled by the covalent bonding between unsubstituted C2, C4 or C6 atoms in the m-AP aromatic rings to form oligomers as revealed by the results of activation energy and mass spectra. Furthermore, the toxicity assessment of the transformation productions indicated that the toxicity of m-AP to the E. coli K-12 could be reduced by MnO₂ mediated transformation. The results are helpful for understanding the environmental behavior and potential risk of m-AP in natural environment.