Light driven water oxidation on silica supported NiO-TiO₂ heteronanocrystals yields hydrogen peroxide

Decomposition of nickel nitrate hexahydrate in the presence of rod-shape anatase TiO₂ nanocrystals led to the formation of NiO-TiO₂ heteronanocrystals confirmed with powder X-ray diffraction and electron microscopy. The heteronanocrystals were supported on amorphous fumed silica to provide a heterogeneous photocatalyst material SiO₂/NiO-TiO₂. The aqueous suspension of the catalyst, under argon atmosphere, irradiated with a Xe arc lamp led to the formation of H₂O₂ with trace gaseous product formation. We observed an initial rate of formation of H₂O₂ of 1.8 μmol g^-1 min^-1 that decays toward a steady-state concentration of 52 μM. Addition of AgNO₃ to the aqueous suspension gave fast reduction of silver ion, and higher initial rates of formation and steady state concentrations of H₂O₂. We report the concentration dependence of water oxidation versus [AgNO₃] with the fastest initial rate of formation of H₂O₂ as 9.1 μmol g^-1 min^-1 and a steady-state concentration of 174 μM.