Adsorption of As(V) and As(III) by nanocrystalline titanium dioxide

Abstract

This study evaluated the effectiveness of nanocrystalline titanium dioxide (TiO 2) in removing arsenate [As(V)] and arsenite [As(III)] and in photocatalytic oxidation of As(III). Batch adsorption and oxidation experiments were conducted with TiO 2 suspensions prepared in a 0.04 M NaCl solution and in a challenge water containing the competing anions phosphate, silicate, and carbonate. The removal of As(V) and As(III) reached equilibrium within 4 h and the adsorption kinetics were described by a pseudo-second-order equation. The TiO 2 was effective for As(V) removal at pH<8 and showed a maximum removal for As(III) at pH of about 7.5 in the challenge water. The adsorption capacity of the TiO 2 for As(V) and As(III) was much higher than fumed TiO 2 (Degussa P25) and granular ferric oxide. More than 0.5 mmol/g of As(V) and As(III) was adsorbed by the TiO 2 at an equilibrium arsenic concentration of 0.6 mM. The presence of the competing anions had a moderate effect on the adsorption capacities of the TiO 2 for As(III) and As(V) in a neutral pH range. In the presence of sunlight and dissolved oxygen, As(III) (26.7 μM or 2 mg/L) was completely converted to As(V) in a 0.2 g/L TiO 2 suspension through photocatalytic oxidation within 25 min. The nanocrystalline TiO 2 is an effective adsorbent for As(V) and As(III) and an efficient photocatalyst.