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

Abstract

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 μM). 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.

Keywords:

• As(V)
• adsorption
• TiO₂
• NOM
• electrolyte type
• ionic strength

Acknowledgments

This study was funded by the Notre Dame Environmental Molecule Scientific Institute through the National Science Foundation (NSF EAR02–21966). The TiO₂ used in this study was provided as a gift by Degussa Company. We thank Jennifer Forsyther and Jennifer Szymanowski for lab and instrument maintenance.

This paper was presented at the SETAC Asia/Pacific 2006 conference held at Peking University, China on September 18–20, 2006.