Mechanistic Study of Pb(II) Removal by TiO₂ and Effect of PO₄

As a commercial adsorbent, TiO₂ shows a high adsorption capacity for lead (Pb(II)). However, the molecular structure of Pb(II) adsorption on TiO₂ is still unknown. Meanwhile, as a widely used corrosion inhibitor, phosphate (PO₄) is usually added into drinking water, and its influential mechanism on Pb(II) removal by TiO₂ remains unknown. Here, the mechanisms of Pb(II) adsorption on TiO₂ and the effect of PO₄ were systematically investigated using a combination of spectroscopic analyses and surface complexation modeling. The adsorption structure of Pb(II) on TiO₂ was revealed as a tridentate mononuclear configuration by the extended X-ray absorption fine structure (EXAFS) analysis. In the presence of 0.1-5 mg/L PO₄, Pb(II) was removed mainly by adsorption on TiO₂ rather than precipitation. Ternary complexation between Pb(II) and PO₄ on TiO₂ surfaces was found based on EXAFS and in situ Fourier transform infrared characterizations. These complexation structures were used to build a surface complexation model to accurately simulate and predict Pb(II) removal under different conditions. This study provides essential information about the mechanisms of Pb(II) removal by TiO₂ and develops a model to predict adsorption behaviors, especially in the presence of PO₄.