CO2-assisted synthesis of Fe/N-doped biochar for efficient Fenton-like process

Abstract

Persulfate (PS)-based Fenton-like process is effective for degrading organic pollutants in aqueous systems. Given that iron is earth abundant and inexpensive, Fe-loaded biochar has attracted particular attention as a PS-activating catalyst. However, mass production of Fe-loaded biochar is hindered by the low energy recovery from the conventional pyrolysis process. Here, Fe-impregnated rice husk (RH) was pyrolyzed under CO2 to convert condensable oxygenated compounds (derived from RH) into syngas. Time-resolved gas evolution (CO, H2, CH4, and C2 hydrocarbons (HCs)) showed that Fe species enhanced the formations of CO and H2 from CO2-assisted pyrolysis of Fe-impregnated RH. The reduced abundance of oxygenated compounds in bio-oil indicated an enhanced conversion of condensable volatiles into syngas. For Fe-loaded biochar synthesized under the CO2 condition (Fe/RHB_CO2), its characterizations confirmed the immobilization of Fe3O4 active sites, an increased mesopore volume, and enrichment of N functionalities within the structure of biochar. Consequently, Fe/RHB_CO2 exhibited higher bisphenol A adsorption capacity and superior peroxydisulfate/peroxymonosulfate activation compared with Fe-free RHBs prepared under N2 or CO2, achieving >99% BPA removal. By linking energy-efficient catalyst production with effective organic pollutant degradation, this work outlines a practical route to couple biomass valorization with advanced water-treatment processes.