Removal of arsenate from aqueous solution by adsorption onto titanium dioxide nanoparticles

Titanium dioxide (TiO2) was investigated for the removal of pentavalent arsenate from aqueous solution. Kinetic results revealed that arsenate adsorption was almost instantaneous. The extent of arsenate adsorption decreased with increasing pH owing to the decrease of positively charged binding sites on the TiO2 surface. Adsorption isotherms measured at pH 3 and 7 generally followed the Langmuir model. The maximum uptake capacity ranged from 8 mg g-1 at pH 3 to 2.7 mg g-1 at pH 7. Addition of phosphate resulted in a significant reduction in arsenate adsorption, indicating that phosphate-a molecular analogue of arsenate-competes with arsenate for the same surface binding sites. By contrast, bicarbonate had little effect on arsenate adsorption, whereas sulfate exhibited a moderate suppression effect. A considerable reduction in arsenate adsorption was also observed in the presence of relatively high concentrations of background electrolytes (>50 mmol L-1).