The structure and composition of the heterogeneous Fenton catalyst itself facilitate the electron transfer from the electron donor to Fe3+, accelerating the reduction of Fe3+ to Fe2+, achieving the efficient cycling of Fe3+ and Fe2+ on the heterogeneous Fenton catalyst (Sohn et al., 1971; Zhong et al., 2013; Lyu et al., 2016). The reaction mechanism for the heterogeneous Fenton process is shown in Fig. 2.