Synergistic enhancement in ultra-trace thallium(I) removal using the titanium dioxide/biochar composite

Thallium (Tl), recognized for its high toxicity, is subject to stringent international regulations regarding its permissible concentrations at ultra-trace levels. In this study, titanium dioxide (TiO₂) was integrated with potassium (K)-rich biochar to create TiO₂/biochar (TiO₂/BC) composites for synergistic enhancement in ultra-trace Tl(I) removal, focusing on achieving concentration below the rigorous local threshold of 0.1 μg/L for drinking water. The Tl(I) adsorption behavior of TiO₂/BC was thoroughly investigated, along with characterizing the mechanisms behind Tl(I) removal. The material prepared at a TiO₂/BC mass ratio of 1:2 demonstrated high efficiency in lowering Tl(I) concentrations, showing resilience against interference from coexisting ions at concentrations ranging from 1 to 100 mM. Actual wastewater from polluted river water containing Tl was successfully treated to meet regulatory limits, highlighting the practical applicability of the composites. The composites displayed a remarkable maximum adsorption capacity of 1152 mg/g at a material dosage of 0.1 g/L, surpassing most materials reported. The underlying Tl(I) removal mechanisms include inner-sphere surface complexation, cation exchange between K⁺ and Tl⁺, and electrostatic adsorption. Superior to individual components, the TiO₂/BC composite benefits from an enlarged specific surface area and K⁺-based ion-exchange interactions. Tl capture was also found to have a linearly positive correlation with the K release from the composites. Overall, this study contributes to a better understanding of the interaction between titanium oxides and K-rich biochar, offering a promising approach for remediating water sources contaminated with ultra-trace levels of Tl.