Application of titanium dioxide in arsenic removal from water: A review

Natural arsenic pollution is a global phenomenon and various technologies have been developed to remove arsenic from drinking water. The application of TiO ₂ and TiO ₂-based materials in removing inorganic and organic arsenic was summarized. TiO ₂-based arsenic removal methods developed to date have been focused on the photocatalytic oxidation (PCO) of arsenite/organic arsenic to arsenate and adsorption of inorganic and organic arsenic. Many efforts have been taken to improve the performance of TiO ₂ by either combing TiO ₂ with adsorbents with good adsorption property in one system or developing bifunctional adsorbents with both great photocatalytic ability and high adsorption capacity. Attempts have also been made to immobilize fine TiO ₂ particles on supporting materials like chitosan beads or granulate it to facilitate its separation from water. Among the anions commonly exist in groundwater, humic acid and bicarbonate have significant influence on TiO ₂ photocatalyzed oxidation of As(III)/organic arsenic while phosphate, silicate, fluoride, and humic acid affect arsenic adsorption by TiO ₂-based materials. There has been a controversy over the TiO ₂ PCO mechanisms of arsenite for the past 10 years but the adsorption mechanisms of inorganic and organic arsenic onto TiO ₂-based materials are relatively well established. Future needs in TiO ₂-based arsenic removal technology are proposed.