Enhanced photoelectrocatalytic oxidation of hypophosphite and simultaneous recovery of metallic nickel via carbon aerogel cathode

Progress and challenges in the use of electrochemical oxidation and reduction processes for heavy metals removal and recovery from wastewaters

Heavy metals-laden industrial wastewater represents both a threat to ecosystems and human health and, in some instances, a potential source of valuable metals however the presence of organic ligands that bind the metals in heavy metal complexes (HMCs) renders metal removal (and, where appropriate, recovery) difficult. Electrochemical-based oxidation and reduction processes represent a potentially promising means of degrading the organic ligands and reducing their ability to retain the metals in solution. In this state-of-the-art review, we provide a comprehensive overview of the current status on use of electrochemical redox technologies for organic ligand degradation and subsequent heavy metal removal and recovery from industrial wastewaters. The principles and degradation mechanism of common organic ligands by various types of electrochemical redox technologies are discussed in this review and consideration given to recent progress in electrode materials synthesis, cell architecture, and operation of electrochemical redox systems. Furthermore, we highlight the current challenges in application of electrochemical redox technologies for treatment of HMC-containing wastewaters including (i) limited understanding of the chemical composition of industrial wastewaters, (ii) constrained mass transfer process affecting the direct/indirect electron transfer, (iii) absence of approaches to convert recovered metal into high-value-added products, and (iv) restricted semi-or full-industrial-scale application of these technologies. Potential strategies for improvement are accordingly provided to guide efforts in addressing these challenges in future research.

Superior performance of oxygen vacancy-enriched Cu-Co3O4/urushiol-rGO/peroxymonosulfate for hypophosphite and phosphite removal by enhancing singlet oxygen

The treatment of wastewater containing hypophosphite [P(I)] and phosphite [P(III)] is challenged by limitations of traditional Fenton oxidation such as low efficiency, secondary pollution and high costs. This study introduced a facile solvent-thermal method to synthesize Cu-Co3O4 nanoparticles uniformly loaded on graphene (Cu-Co3O4/U-rGO) through the reduction and coordination effects of urushiol (U). As prepared Cu-Co3O4/U-rGO exhibited excellent activity in activating peroxymonosulfate (PMS) for the oxidation of P(I)/P(III) to phosphate [P(V)] (0.229 min-1), along with high stability and reusability (91.5 % after 6 cycles), low metal leaching rate (Co: 0.2 mg/L, Cu: 0.05 mg/L), insensitivity to common anions in water and a wide pH range (3-11). The activation mechanism involved the synergistic effects from both urushiol and graphene, which promoted redox of Cu+/Cu2+ and Co2+/Co3+ and induced abundant oxygen vacancies for PMS activation to produce singlet oxygen. Furthermore, the Cu-Co3O4/U-rGO/PMS was also excellent in the oxidative removal of organic phosphorus. This study is expected to advance strategies for the treatment of P(I)/P(III)-rich wastewater and provide new insights for the development of low-cost, highly efficient heterogeneous catalysts with abundant oxygen vacancies.

Electro-intensified simultaneous decontamination of coexisting pollutants in wastewater

The treatment of wastewater has become increasingly challenging as a result of its growing complexity. To achieve synergistic removal of coexisting pollutants in wastewater, one promising approach involves the integration of electric fields. We conducted a comprehensive literature review to explore the potential of integrating electric fields and developing efficient electro-intensified simultaneous decontamination systems for wastewater containing coexisting pollutants. The review focused on comprehending the applications and mechanisms of these systems, with a particular emphasis on the deliberate utilization of positive and negative charges. After analyzing the advantages, disadvantages, and application efficacy of these systems, we observed electro-intensified systems exhibit flexible potential through their rational combination, allowing for an expanded range of applications in addressing simultaneous decontamination challenges. Unlike the reviews focusing on single elimination, this work aims to provide guidance in addressing the environmental problems resulting from the coexistence of hazardous contaminants.