Insight into synthesis and catalytic performance of mesoporous electroactive biochar for aqueous sulfide adsorptive oxidation

Pristine biochar (PBC) is flourishing in adsorptive oxidation for pollutants remediation as an alternative to carbon adsorbents derived from coal/petroleum carbon sources, multistep, and hash synthesis. However, it is widely overlooked for aqueous S 2- remediation because the rational design of biochar with proper conductive and porous structure is challenging. Cobalt or iron ion was impregnated in biomass to produce biochar with different porous and conductive structures and explore S 2- adsorptive oxidation mechanism. Finding suggests cobalt and iron ions facilitate biomass decomposition to remove volatile matter, which transforms them into elemental cobalt (Co 0 ) or magnetite (Fe 3 O 4 ) on biochars (BC-Co) or (BC-Fe) and improves the porous structure. BC-Co benefitted from superior mesopores to adsorb S 2- 2.4 and 35 times faster than PBC and BC-Fe, achieving 811 ± 146 mg-S 2- /g maximum capacity. BC-Fe removed S 2- far less than PBC because Fe 3 O 4 on its surface blocked S 2- diffusion channel to the active site. It is postulated that S 2- was removed from water via external and internal diffusion and adsorption and oxidation at active sites. S 2- diffuses from bulk liquid to film near the biochar pore and into the pores via pore and surface diffusion to the active site, where it is adsorbed and oxidized to elemental sulfur or sulfate by quinone , semiquinone, or hydroxyl radicals at the wall of biochars. This study has documented fundamental information for developing mesoporous electroactive biochar for contaminant removal.