Sulfur-engineered corncob biochar via pyrolysis-hydrothermal strategy: A sustainable bio-product for metal removal

Abstract

Sustainable biomass valorization is increasingly explored as a pathway for developing functional materials for environmental applications, although its broader environmental implications require careful validation. In this study, the effect of post-pyrolysis hydrothermal treatment and sulfur-assisted modification on adsorption performance was investigated. Corncob biomass was converted into a porous carbonaceous material via pyrolysis at 600 degrees C under an inert atmosphere. The resulting biochar was further modified through acid washing and hydrothermal treatment (100-220 degrees C) to tailor surface chemistry and structural properties. Sulfur incorporation was achieved using H2SO4-assisted post-modification, enabling the introduction of sulfur-containing functional groups onto the carbon matrix. Comprehensive characterization using FTIR, SEM-EDX, N-2 adsorption-desorption, TGA-DTA, and pH(p)zc analyses demonstrated that hydrothermal and sulfur treatments significantly altered surface functionality, porosity, and thermal stability. The functional performance of the modified biochar was evaluated via Pb(II) and Ni(II) adsorption to establish structure-property relationships under controlled batch conditions. The sulfur-doped biochar exhibited high and stable metal uptake across a broad pH range, with maximum adsorption capacities exceeding similar to 100 mg g(-1) for Pb(II) and values consistent with the experimental mass balance for Ni(II). Preliminary regeneration experiments indicated that the adsorbent retained more than 80% of its initial adsorption capacity after multiple cycles, suggesting reasonable reusability. The findings demonstrating the potential of sulfur-functionalized biochar derived from agricultural residues as a low-cost adsorbent for aqueous heavy metal removal.