Nitrate can be effectively photoreduced to NH 3 on TiO2 using oxalic acid as sacrificial electron donor.
The reduction is favored at low oxalic acid concentration, when both reactants are adsorbed on the TiO2 surface.
It seems that noble metal coated TiO2 is only necessary, if no reductants are available in solution.
In this case, photochemically produced hydrogen acts as electron donor.