pH effects of the arsenite photocatalytic oxidation reaction on different anatase TiO2 facets.

TiO2 is one of the most cheap materials which can both adsorb arsenic and oxidize arsenite [As(III)] to arsenate [As(V)]. In this study, anatase TiO2 crystals with different main facets such as {101}, {001} and {100} are synthesized and used to investigate arsenic adsorption kinetics, adsorption isotherms, photocatalytic oxidation (PCO) process and the pH effects. The adsorption kinetics of arsenic on TiO2 crystals can be described by the pseudo second-order kinetic model. For the adsorption isotherms, the Langmuir model is better than the Freundlich model for arsenic on these TiO2 crystals. For the PCO process, the rate of As(III) oxidation can be denoted by the pseudo first-order kinetic model. It should be noted that at neutral condition the adsorption and PCO rates of the three kinds of TiO2 crystals follow the order of {101} > {001} > {100}. The pH effect is above all important for both the arsenic adsorption and its PCO. The highest PCO speed appears at high pH values such as at pH 11 or 12.