Efficient removal of Sb(III) from aqueous solution using TiO₂ precipitated onto waste herb-residue biochar

Increasing antimony (Sb) pollution has become a global concern, but there is still a lack of economically efficient adsorbents for its remediation. In this study, a novel remediation material was developed by precipitating TiO₂ onto waste herb-residue biochar (named TBC). The effectiveness and adsorption mechanisms of the material for Sb(III) removal were investigated through adsorption experiments, and the enhancement pathway of traditional herb decoction on the effectiveness of modified biochar was analyzed. The findings revealed that the rapid release of volatile contents in the herbal residue due to the herb decoction that improved the pore structure of the biochar, thereby promoting a synergistic effect between the TiO₂ nanoparticles and biochar, and enhancing its adsorption capacity for Sb(III). This synergy allowed the modified biochar, with a TiO₂ loading ratio of only 6.88 wt%, to achieve excellent adsorption efficiency. Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and zeta potential analysis confirmed that the hydroxyl groups in Ti-OH underwent ligand exchange with the antimony species, forming internal coordination complexes that were immobilized on TBC. The adsorption mechanism of Sb(III) onto TBC was a combination of direct adsorption and photocatalytic oxidation adsorption, with photocatalytic oxidation being influenced primarily by ·OH and O₂^-, and by ·OH as the dominant factor. The q_m of TBC was 136.159 mg/g. Overall, TBC exhibited wide pH adaptability, strong resistance to interference from ions, and excellent reusability.