Efficient mineralization of coal pyrolysis wastewater in a heterogeneous electro-Fenton system using a novel Fe₃O₄-LaFeO₃/C/GF heterojunction cathode

A bifunctional electro-Fenton (EF) cathode with Fe₃O₄-LaFeO₃/C embedded graphite felt (GF) was synthesized through a hydrothermal process, which was used for in situ electrochemical formation of active oxygen species (ROS) for coal pyrolysis wastewater (CPW) removal. Experimental results illustrated that the mineralization efficiency of dimethylphenol (DMP) was achieved at 90.7 % within 150 min reaction. On the basis of quenching test and free radical detection, the ∙OH and ∙O₂⁻ were the detectable ROS in the hetero-EF system for DMP removal. Meanwhile, the formed oxygen vacancies (OVs) and the redox of Fe²⁺/Fe³⁺ promoted the oxygen adsorption and H₂O₂ activation. Density functional theory (DFT) calculations further discussed that the Fe₃O₄-LaFeO₃ interface possessed more downward spin density of states in the conduction band, resulting in a higher total density of states (DOS) value near the Fermi level. Moreover, the Fe₃O₄-LaFeO₃/C/GF cathode displayed good recyclability with low metal ion dissolution for 5 times (99.5 % DMP removal and 78.6 % TOC removal) and underlying actual CPW application potential (80.2 % of COD removal and 100 % of total phenol (Tph) removal). Overall, this work invented a novel and stable bifunctional cathode for the efficient removal of refractory CPW in the hetero-EF system.