Exploring the effect of different precursor materials on Fe-loaded biochar catalysts for toluene removal

Abstract

Rice husks, camphor tree leaves, and corn stalks were selected as raw materials from shell, leaf, and stem biomass, respectively, to prepare Fe-loaded biochar catalysts, and the removal efficiency of toluene by the three catalysts was determined. The removal efficiencies of shell catalyst (ARHB-Fe) and stem catalyst (ACSB-Fe) were 89.68% and 90.97%, respectively, both lower than that of leaf catalyst (ACLB-Fe), which was 92.01%. ARHB-Fe and ACSB-Fe exhibited a fibrous structure, while ACLB-Fe exhibited a three-dimensional honeycomb structure. ARHB-Fe had the largest specific surface area at 284.65 m²/g, exhibiting excellent physical adsorption performance for toluene. A cross-comparison of the existing forms of Fe in the three catalysts was conducted. The highest Fe2+ content in ARHB-Fe was 45.64%. The highest Fe3+ content in ACLB-Fe was 46.76%. Fe3+ underwent electrostatic reactions with the benzene ring, enhancing the adsorption of toluene. The highest Fe3C content in ACSB-Fe was 18.20%. At high temperatures, Fe3C decomposed to produce Fe0, possessing strong reducing ability and high reactivity, which effectively promoted the catalytic cracking of toluene. ARHB-Fe and ACSB-Fe were mainly influenced by n–π interactions (C–O functional groups). ACLB-Fe exhibited the combined effects of hydrogen bonding interactions (–OH functional groups), n–π interactions, and π–π interactions (CC functional groups). Furthermore, ACLB-Fe possessed the most abundant acidic sites and the highest acidity.