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

Degussa P25 TiO 2 doped with nitrogen via NH 3 treatment at 400600 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 NTiO surface linkages, as confirmed by XPS. Kinetic studies have been performed in batch systems with 40 M As( iii ) and 0.05 g L 1 TiO 2 . Photocatalytic oxidation of As( iii ) in the presence of N-doped TiO 2 annealed at 500 C was complete within 4 hours of irradiation at > 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 TiO 2 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-TiO 2 surface. This surface activation mechanism provides the rationale for increased As( v ) retention. Enhanced adsorptive properties in TiO 2 would render it a more versatile remediation agent. Model of the anatase (101) surface with NH and OH groups: red spheres = O, green spheres = Ti, blue sphere = N, grey spheres = H.