Influence of ionic strength, electrolyte type, and NOM on As(V) adsorption onto TiO2.

As(V) adsorption onto a commercially available TiO2 (Degussa P25) in NaCl or NaClO4 at various concentrations (0.001-0.1 M) was investigated. The effect of natural organic matter (NOM) on As(V) removal through the adsorption by TiO2 was also examined. In either electrolyte, As(V) adsorption onto TiO2 increased with the increase of ionic strength under alkaline conditions (pH 7.0-11.0). Under acidic conditions (pH 4.0-6.0), the adsorption of As(V) onto TiO2 was insensitive to ionic strength in NaClO4 electrolyte but decreased with increasing ionic strength in NaCl electrolyte. The presence of 2-15 mg/L NOM as C significantly decreased the fraction of As(V) adsorbed onto TiO2 at pH 6.0 regardless of the initial As(V) concentration (1-15 microM). The measurement of zeta potential of TiO2 with and without As(V) suggests that the presence of As(V) can shift the point of zero charge (pH(pzc)) of TiO2 to a lower pH value. The overall data presented in this study suggest that As(V) can form both inner-sphere and outer-sphere complexes on TiO2 surface, and NOM is an important factor controlling As(V) adsorption onto TiO2.