Experimental and computational studies of nitrogen doped Degussa P25 TiO2: application to visible-light driven photo-oxidation of As(iii)

Abstract

Degussa P25 TiO2 doped with nitrogen via NH3 treatment at 400–600 °C was found to be capable of catalyzing the photo-oxidation of aqueous As(III) to As(V) under visible light. Substitutional doping of N for O creates N–Ti–O surface linkages, as confirmed by XPS. Kinetic studies have been performed in batch systems with 40 μM As(III) and 0.05 g L−1 TiO2. Photocatalytic oxidation of As(III) in the presence of N-doped TiO2 annealed at 500 °C was complete within 4 hours of irradiation at λ > 435 nm. The presence of titanium oxynitride (or similar surface moieties) is linked with the good photooxidation catalytic activity toward As(III). Zeta potentials of the N-doped TiO2 showed negative shifts at low pH values, which became more pronounced when measured after photocatalytic testing, suggesting at least partial retention of As(V). First principles DFT calculations were also carried out for a model anatase (101) surface, in both the pristine and N-doped condition. Dissociation of water is energetically favoured over the N-TiO2 surface. This surface activation mechanism provides the rationale for increased As(V) retention. Enhanced adsorptive properties in TiO2 would render it a more versatile remediation agent.