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 S2- 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 S2- adsorptive oxidation mechanism. Finding suggests cobalt and iron ions facilitate biomass decomposition to remove volatile matter, which transforms them into elemental cobalt (Co0) or magnetite (Fe3O4) on biochars (BC-Co) or (BC-Fe) and improves the porous structure. BC-Co benefitted from superior mesopores to adsorb S2- 2.4 and 35 times faster than PBC and BC-Fe, achieving 811 & PLUSMN; 146 mg-S2-/g maximum capacity. BC-Fe removed S2- far less than PBC because Fe3O4 on its surface blocked S2- diffusion channel to the active site. It is postulated that S2- was removed from water via external and internal diffusion and adsorption and oxidation at active sites. S2- 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.