Flow line of density functional theory in heterogeneous persulfate-based advanced oxidation processes for pollutant degradation: A review

Persulfate-based advanced oxidation processes (P-AOPs), as the commonly used technologies, attract intensive attention, because persulfate is stable and safe with various activation methods, and the generated reactive oxygen species (ROS) are highly active. Density functional theory (DFT) calculations can analyze the intrinsic mechanism and specific pathways of P-AOPs at microscopic level, which is difficult to be realized in experiments. Recent DFT discoveries for P-AOPs have induced tremendous interest in persulfate activation or pollutant degradation pathways, and the corresponding mechanism. However, there is no systemic and comprehensive flow line for DFT calculations to evaluate the performance and understand the mechanism of P-AOPs. In this review, flow line of DFT calculations on heterogeneous P-AOPs is systematically summarized in the following aspects: (i) sites for persulfate activation or pollutant degradation; (ii) persulfate activation process; (iii) pollutant degradation process; and (iv) influential factors. Specially, primary evaluation criteria of radical or nonradical mechanism of persulfate activation are ultimately proposed, aiming to boost the development of P-AOPs. It not only provides systemic flow line to utilize DFT calculations to explore heterogeneous P-AOPs at microscopic level, but also guides and helps more researchers to instantly analyze their results and interpret the phenomena occurred in experiments or DFT calculations.