Electrochemical mineralization of uric acid with boron-doped diamond electrode: Factor analysis and degradation mechanism

Investigation into the electrochemical advanced oxidation of p-arsanilic acid: Peculiar role of electrolytes and unexpected formation of coupling byproducts

Although banned in some countries, p-arsanilic acid (ASA) is still widely used as feed additive in poultry production. As a result, ASA is usually released into the aquatic environment without any treatments. Although ASA exhibits low toxicity, it can be transformed into highly toxic aromatic amines and inorganic arsenic species (As (V) as H2AsO4- and HAsO42-) under natural environmental conditions. Hence, it is necessary to develop efficient technologies for its removal or degradation. In this contribution, electrochemical advanced oxidation technology with boron-doped diamond (BDD) had been initially used to degrade ASA pollutants. A five-level central composite rotatable design (CCRD) was implemented to optimize the various influencing factors involved, among applied current density, NaCl concentration, Na2SO4 concentration and NaHCO3 concentration on the oxidation efficiency; the latter was assessed in terms of ASA degradation percentage. The results obtained highlighted the unique and important roles of electrolytes during the electrolytic oxidations. Meanwhile, the major degradation byproducts detected were also strongly dependent on the electrolyte adopted. In particular, several oligomer byproducts with novel structures were initially identified in BDD-treated ASA solutions. Two different electrochemical transformation pathways of ASA on BDD anode were thus proposed. This study demonstrated the effectiveness of BDD technology in the degradation of ASA, as well as the potential minor risk of its application in actual ASA wastewater treatment.

Enhanced thyroxine removal from micro-polluted drinking water resources in a bio-electrochemical reactor amended with TiO2@GAC particles: Efficiency, mechanism and energy consumption

A three-dimensional bioelectrochemical system (3D-BES) with both electrocatalytic and biodegradation functions was designed and developed to enhance iodine-containing hormone removal from micro-polluted oligotrophic drinking water sources and to reduce energy consumption. Thyroxine (T4) removal efficiency was 99.0% in the 3D-BES amendment with TiO2@GAC as the particle electrodes, which was 20.5% higher than the total efficiency of single biodegradation (28.7%) plus electrochemical decomposition (49.8%). The high T4 removal efficiency was a result of biochemical synergistic degradation, enhancement of electron transfer and utilization, enrichment of functional microorganisms, and the expression of dehalogenation functional genes. The electron transfer was increased by 1.63 times in 3D-BES compared to the 2D-BES, which contributed to: (i) ∼17.8% enhancement of dehalogenation, (ii) 2.35 times enhancement of the attenuation rate, and (iii) 60% reduction in energy consumption. Moreover, the aggregation of microorganisms and the hydrophobic T4 onto TiO2@GAC shortened the transfer distance of matter and energy, which induced the degradation steps to be shortened and the toxic decay to be accelerated from T4 and its metabolites. These comprehensive functions also enhanced the 31.8% ATPase activity, 7.3% abundance of the functional reductive dehalogenation genera, and 52.3% dehalogenation genes expression for Pseudomonas, Ancylobacter, and Dehalogenimonas, which contributed to an increase in T4 removal. This work provides an environmental-friendly biochemical synergistic method for the detoxification of T4 polluted water.

Exploration for cobalt/nitrogen-doped catalyst to creatinine degradation via peroxymonosulfate activation: toxicity evaluation, statistical modeling, and mechanisms study

Developing multifunctional catalysts applied in diversiform modes via advanced oxidation processes (AOPs) is a promising and attractive approach for organic pollution degradation. Herein, a novel hollow bamboo-like structural cobalt/nitrogen-doped carbonized material (CoC/N) was employed as a catalyst for AOPs, in which CoC/N was prepared in situ through calcining a Co-based coordination polymer. When CoC/N was utilized as a peroxymonosulfate (PMS) activator, the catalyst stood out prominent activities for effective CA oxidation. Furthermore, a five-level central composite rotatable design (CCRD) model describing CA decay as a function of PMS concentration, CoC/N dosage, and solution pH value was successfully constructed and engaged to explore the optimal operating conditions. Finally, the possible degradation mechanism of CA in CoC/N-PMS system was proposed by quantum chemistry calculation and LC/MS analysis. This work shed light on the structural morphology of the catalyst and its PMS synergy degradation pathway, which promotes its applications in miscellaneous pollutant degradation. A new Co/N-doped material was used to degrade unconventionality organic pollutant creatinine (CA) for the first time, in which the scientific approaches of five-level central composite rotatable design (CCRD) model, response surface methodology (RSM) and density function theory (DFT) were employed to evaluate the material performance and CA degradation pathway. The toxicity evaluation, statistical modeling and mechanisms study have been investigated meticulously.

Electrochemical degradation and mineralisation of organic dyes in aqueous nitrate solutions

Electrochemical treatment of organic matter for environmental remediation necessitates the development of cheap and robust electrodes that are chemically and structurally stable. To address this challenging requirement, we demonstrate a new electrochemical approach using a simple copper electrode under cathodic conditions to electrochemically generate reactive nitrosonium ions for the degradation of different classes of synthetic organic dyes. This could be achieved in an aqueous HNO₃/KNO₃ electrolyte at a relatively low cathodic potential of -0.5 V RHE at room temperature. UV-visible absorption spectroscopy, Raman spectroscopy, liquid chromatography - mass spectrometry and total organic carbon measurements revealed the rapid decolorisation and mineralisation of several dye types such as triarylmethane dyes (crystal violet, cresol red), an azo dye (methyl orange) as well as a sulfur containing thiazine dye (toluidine blue). The total organic carbon content of a 50 mg L^-1 methyl orange solution was found to decrease by 83% after 1 h of electrolysis. Promisingly, locally sourced river and creek water samples spiked with 50 mg L^-1 methyl orange were also successfully treated for up to 6 cycles at a simple Cu electrode, demonstrating potential for the remediation of polluted waterways.

Optimized Mo-doped IrOx anode for efficient degradation of refractory sulfadiazine

Electrochemical advanced oxidation processes (EAOPs) is considered to be an efficacious method to degrade antibiotics. However, the performance of the anode has become the main limiting factor of this technology. In this study, due to the electron-deficient characteristics and the improvement of OER performance of Mo, we chose to use thermal decomposition to incorporate Mo into IrO₂ to prepare anodes with industrial applicability. Under the optimal ratio of Ir to Mo is 7:3, (Ir_0.7Mo_0.3)O_x electrode's particular pore structure can expose more active sites and create a channel for the transportation of electrons, thereby promoting the formation of free radicals and degrading pollutants more efficiently. (Ir_0.7Mo_0.3)O_x electrode also has a higher mass activity (6.332 A g^-1, three times that of the IrO₂ electrode) and a larger electrochemical active area (ECSA, 375.43 cm², seven times that of the IrO₂ electrode). In addition, the optimal conditions of (Ir_0.7Mo_0.3)O_x electrode for degrading sulfadiazine(SDZ) were explored, which achieved a higher removal than traditional electrodes (90% removal within 4 h) when the Ti plate was the substrate. Through the intermediate products of SDZ degradation and related literatures, two possible degradation pathways of SDZ were speculated. This research provides a new type of anode catalyst for the degradation of sulfonamide antibiotics, which is possible for industrial application.