Electron paramagnetic resonance (EPR) has been extensively used for the identification of free radicals that are generated from advanced oxidation processes (AOPs) so as to establish the reaction mechanism. However, some misinterpretations or controversies on the identity of detected EPR signals remain in the literature. This study, with Cu(II)-based AOPs as examples, comprehensively investigated the origin of 5,5-dimethyl-l-pyrroline N-oxide (DMPO) adducts in Cu(II) alone, Cu(II)/H2O2, Cu(II)/peroxymonosulfate (PMS), and Cu(II)/peroxydisulfate (PDS) systems. In most Cu(II) systems, DMPO-OH signals can be detected even without any peroxygens, indicating the presence of other origins of this adduct in addition to the genuine spin trapping of •OH by DMPO. According to the formed secondary radical adducts (DMPO-OCH3 from a nonradical process or DMPO-CH2OH from a radical oxidation) derived from methanol quenching, we propose that CuO+, instead of free radicals, is involved in the Cu(II)/PMS system, while •OH is indeed generated in the Cu(II)/H2O2 and Cu(II)/PDS systems under neutral conditions. Notably, 17O-incorporation experiments demonstrate that -OH in the detected DMPO-OH adduct originates 100% from water in the Cu(II) alone system but the amount of -OH is over 99.8% from the oxidant while peroxygens are added. In addition, DMPO-O2- appears only in the Cu(II)/PDS system under highly alkaline conditions and H2O is not involved in superoxide formation.

EPR Evidence for Mechanistic Diversity of Cu(II)/Peroxygen Oxidation Systems by Tracing the Origin of DMPO Spin Adducts.

Water pollution is a major concern for public health and a sustainable future. It is urgent to purify wastewater with effective methods to ensure a clean water supply. Most wastewater remediation techniques rely heavily on functional materials, and cost-effective materials are thus highly favorable. Of great environmental and economic significance, developing waste-derived materials for wastewater remediation has undergone explosive growth recently. Herein, the applications of waste (e.g., biowastes, electronic wastes, and industrial wastes)-derived materials for wastewater purification are comprehensively reviewed. Sophisticated strategies for turning wastes into functional materials are firstly summarized, including pyrolysis and combustion, hydrothermal synthesis, sol–gel method, co-precipitation, and ball milling. Moreover, critical experimental parameters within different design strategies are discussed. Afterward, recent applications of waste-derived functional materials in adsorption, photocatalytic degradation, electrochemical treatment, and advanced oxidation processes (AOPs) are analyzed. We mainly focus on the development of efficient functional materials via regulating the internal and external characteristics of waste-derived materials, and the material’s property-performance correlation is also emphasized. Finally, the key future perspectives in the field of waste-derived materials-driven water remediation are highlighted. 

Recent advances in waste-derived functional materials for wastewater remediation

Co-hydrothermal carbonization of rape straw and microalgae: pH-enhanced carbonization process to obtain clean hydrochar

Energetic properties of new nanothermites based on in situ MgWO4-rGO, CoWO4-rGO and Bi2WO6-rGO

Electrosorption of cadmium and arsenic from wastewaters using nitrogen-doped biochar: Mechanism and application

Green quaternary ammonium nitrogen functionalized mesoporous biochar for sustainable electro-adsorption of perchlorate

Catalytic enhancement of hydrogenation reduction and oxygen transfer reaction for perchlorate removal: A review.

Mechanistic insights into enhanced waste activated sludge dewaterability with Cu(II) and Cu(II)/H2O2 treatment: Radical and non-radical pathway.

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Green quaternary ammonium nitrogen functionalized mesoporous biochar for sustainable electro-adsorption of perchlorate

Catalytic enhancement of hydrogenation reduction and oxygen transfer reaction for perchlorate removal: A review.

Mechanistic insights into enhanced waste activated sludge dewaterability with Cu(II) and Cu(II)/H2O2 treatment: Radical and non-radical pathway.