Arsenic sorption on TiO 2 nanoparticles: Size and crystallinity effects

Abstract

Single solute As (III) and As (V) sorption on nano-sized amorphous and crystalline TiO 2 was investigated to determine: size and crystallinity effects on arsenic sorption capacities, possible As (III) oxidation, and the nature of surface complexes. Amorphous and crystalline nanoparticles were prepared using sol-gel synthesis techniques. For amorphous TiO 2, solute pH in the range of 4–9 had a profound impact on only As (V) sorption. As (III) and As (V) sorption isotherms indicated that sorption capacities of the different TiO 2 polymorphs were dependent on the sorption site density, surface area (particle size) and crystalline structure. When normalized to surface area, As (III) surface coverage on the TiO 2 surface remained almost constant for particles between 5 and 20 nm. However, As (V) surface coverage increased with the degree of crystallinity. X-ray absorption spectroscopic analysis provided evidence of partial As (III) oxidation on amorphous TiO 2 rather than crystalline TiO 2. The data also indicated that As (III) and As (V) form binuclear bidentate inner-sphere complexes with amorphous TiO 2 at neutral pH.