Biochar as an electron shuttle loaded with Fe/Ni bimetallic nanoparticles for efficient removal of 2,4-dichlorophenols: Performance, degradation pathway and mechanism

Biochar can be served as a substrate for immobilizing bimetallic particles and applied in the pollutant removal, however, its specific role and mediated electron shuttle mechanism against 2,4-dichlorophenol (2,4-DCP) have not been elucidated. In this study, biochar loaded with Fe/Ni bimetallic nanoparticles (BC@Fe/Ni) was optimally synthesized, and its dechlorination performance, pathway and mechanism towards 2,4-DCP were investigated. The results showed that BC@Fe/Ni was more effective compared to Fe/Ni nanoparticles in the 2,4-DCP removal due to its well-dispersed Fe/Ni nanoparticles and increased electron-shuttling capability. The optimal parameters for 2,4-DCP removal by BC@Fe/Ni were assessed, the highest removal efficiency equivalent to 50 mg L−1 of 2,4-DCP was achieved at pH 4.0 with a dosage of 2 g L−1. The 2,4-DCP removal was an adsorption-dechlorination-adsorption pathway, primarily through para-Cl elimination, ortho-Cl elimination and finally phenol adsorption. The removal mechanism of 2,4-DCP by BC@Fe/Ni may involve the 2,4-DCP reductive dechlorination by nZVI, atomic hydrogen and biochar-mediated electron transfer, and final adsorption by biochar. In summary, this study demonstrates that biochar is a promising electron shuttle for immobilizing bimetallic particles and serves as a reference for the dechlorination mechanism of chlorinated organic pollutants by biochar-based bimetallic nanomaterials.