In this review, we systematically summarized the origins, development, basic mechanism and limits of reductant-enhanced iron-based peroxide activation processes (including H2O2, peroxymonosulfate and peroxydisulfate). Notably, the use of reductants would simultaneously accelerate the reduction of Fe3+ and quench the production of reactive species. This trade-off between Fe3+ reduction and reactive species consumption is mainly determined by two aspects, i.e. (i) intrinsic chemical properties like electron transfer pathways and reaction rates with reactive species, and (ii) experimental conditions like reagent dosage ratio, dissolved O2 and pH. Therefore, we first reviewed the characteristics of different iron/peroxide/reductant systems in terms of the above two aspects. Then, we evaluated the practical application potential of different reductants based on their toxicity, costs and self-transformation products. Finally, newly-emerging enhancement strategies like multiple dosing and regulation of phase and crystalline degree were summarized, and future research needs were proposed.

Critical review of reductant-enhanced peroxide activation processes: Trade-off between accelerated Fe3+/Fe2+ cycle and quenching reactions

Effect of phosphate on pollutant removal was widely investigated in various peroxumonosulfate-based advanced oxidation processes (AOPs) but the role of phosphate was controversial. Many studies also used phosphate as buffer in PMS-based AOPs. This study shows that phosphate promoted PMS activation for pollutants removal. Therefore, PMS activation capacity of some strategies may be overestimated when conducted in the phosphate buffer. Importantly, the results of radical quenching tests, radical probes and reaction stoichiometries indicated that the yields of SO4 − was elevated by the presence of phosphate and linearly depended on phosphate concentration, while the yields of OH remained constant. Density Functional Theory (DFT) calculation confirmed that PO43− and HPO42− could efficiently break O O bond of PMS, promoting the generation of SO4 − for contaminants decomposition. These results illuminated the role of phosphate in AOPs utilizing PMS and uncovered the underlying mechanism of PMS activation by phosphate.

Effect of phosphate on peroxymonosulfate activation: Accelerating generation of sulfate radical and underlying mechanism

Heterogeneous photocatalyst-driven persulfate activation process under visible light irradiation: From basic catalyst design principles to novel enhancement strategies

Synthesis, application and catalytic performance of layered double hydroxide based catalysts in advanced oxidation processes for wastewater decontamination: A review

Yuling Zhang

Papers

An old story with new insight into the structural transformation and radical production of micron-scale zero-valent iron on successive reactivities