Cobalt anchored on porous N, P, S-doping core-shell with generating/activating dual reaction sites in heterogeneous electro-Fenton process

Abstract

A novel controllable mesoporous core–shell microsphere (Co/Fe3O4@PZS) is synthesized by polycondensation, and used as ORR electrocatalyst in the heterogeneous electro-Fenton (hetero-EF) reaction. Characteristic analysis indicated that PZS offered massive reactive sites for anchoring Co ions on the shell. Heteroatom Lewis acidic active sites, related with pyridinic N (4.15%), P = N/P-N (6.46%) and S = O (3.19%) bonds, were formed through the replacement of C = C groups with the N-P-S doped at the shell, which benefited the activating/generating reactive oxygen species (ROS), and capturing/degrading the target pollutant substrates. Moreover, PZS shells prevent the nano-Fe3O4 crystals in the core from direct contact with the solution, which would greatly improve the stability of electrode with almost no leaching of Fe/Co ions after six successive runs. Electrochemical experiments confirmed the accelerating electron transfers among ≡FeII/III/≡CoII/III by the direct electric activation, as evidenced by the decreasing potential discrepancy (from 0.175 to 0.123 V) and sharply increasing ring current (from 35 to 200μA), markedly improved the ORR toward two-electron process (n = 2.01). ESR and radical scavenging experiments verified that •OH and 1O2 served as the main ROS in the Co/Fe3O4@PZS hetero-EF system. In addition to the two-electron reduction (O2→H2O2→·OH), O2 could also be directly electro-activated to 1O2 via one-electron reduction (O2→·O2-/·HO2-→1O2). Additionally, the regenerating/reducing of ≡FeIII/CoIII could get the electron directly from the cathode without excess consumption of H2O2, all these could eventually facilitate BPA degradation with lower energy consumption (1.318 kWh m−3). This study provides a reliable and facile route to prepare mesoporous core–shell microsphere, and developed as doped cathode in the field of electro-Fenton electrocatalysis process.