Polymerization-driven removal of pollutants in advanced oxidation processes (AOPs) offers a sustainable way for the simultaneous achievement of contamination abatement and resource recovery, supporting a low-carbon water purification approach. However, regulating such a process remains a great challenge due to the insufficient microscopic understanding of electronic structure-dependent reaction mechanisms. Herein, this work probes the origin of catalytic pollutant polymerization using a series of transition metal (Cu, Ni, Co, and Fe) single-atom catalysts and identifies the d-band center of active site as the key driver for polymerization transfer of pollutants. The high-valent metal-oxo species, produced via peroxymonosulfate activation, are found to trigger the pollutant removal via polymerization transfer. Phenoxyl radicals, identified by the innovative spin-trapping and quenching approaches, act as the key intermediate in the polymerization reactions. More importantly, the oxidation capacity of high-valent metal-oxo species can be facilely tuned by regulating their binding strength for peroxymonosulfate through d-band center modulation. A 100% polymerization transfer ratio is achieved by lowering the d-band center. This work presents a paradigm to dynamically modulate the electronic structure of high-valent metal-oxo species and optimize pollutant removal from wastewater via polymerization.

Water contamination has become a critical issue, resulting in a decline in global water quality that harms both human health and the environment. Biochar, a porous carbon-rich material produced through the thermochemical decomposition of biomass, has attracted significant attention in wastewater treatment. This review provides a comprehensive overview of biochar preparation methods, modification strategies, characterization techniques, and environmental applications in wastewater treatment. Relevant information was gathered from peer-reviewed articles published in reputable databases. Among various production methods, pyrolysis is the most commonly employed technique for biochar production. The type of biomass and operational conditions, such as residence time, heating rate, and temperature, significantly impact the yield, structure, and composition of biochar. Advanced techniques, including FTIR, XRD, XPS, SEM, TGA, and BET, play a crucial role in characterizing biochar and evaluating its potential environmental applications. This review emphasizes the effectiveness of biochar in removing organic and inorganic contaminants from wastewater and highlights its growing role in environmental remediation. However, there is an ongoing debate regarding its long-term stability and potential release of adsorbed pollutants, which may pose risk if not properly managed. Therefore, this review suggests that future research should also consider its environmental safety, lifecycle sustainability, and regeneration potential. Moreover, establishing quality standards and a regulatory framework for safe and effective biochar use is important to ensure its role as a long-term solution for sustainable water management.