Enhanced photocatalytic H2-production activity of TiO2 using Ni(NO3)2 as an additive.

Herein, we for the first time report the production of H₂ using Degussa P25 TiO₂ powder (P25) from a mixed aqueous solution of methanol and Ni(NO₃)₂. The effect of the amount of Ni(NO₃)₂ on the photocatalytic H₂-production activity of TiO₂ was investigated and discussed. The results indicate that the photocatalytic H₂-production activity of TiO₂ is significantly enhanced in the presence of Ni(NO₃)₂. The optimal Ni(NO₃)₂ amount (the molar ratio of Ni(NO₃)₂ to TiO₂ and Ni(NO₃)₂) was found to be 0.32 mol%, giving a H₂-production rate of 2547 μmol h⁻¹ g⁻¹ with a quantum efficiency (QE) of 8.1% at 365 nm, exceeding that of pure TiO₂ by 135 times. This high photocatalytic H₂-production activity is due to the adsorption of Ni²⁺ on the surface of TiO₂. The potential of Ni²⁺/Ni (Ni²⁺ + 2e⁻ = Ni, E^o = −0.23 V) is slightly lower than the conduction band (CB) of anatase TiO₂ (−0.26 V), but higher than the reduction potential of H⁺/H₂ (2H⁺ + 2e⁻ = H₂, E^o = −0.00 V), which favors electron transfer from TiO₂ to Ni²⁺ and reduction of Ni²⁺ to Ni⁰. The role of metallic Ni is to help charge separation and to act as a co-catalyst for H₂ production, thus enhancing the photocatalytic H₂-production activity of TiO₂. [ABSTRACT FROM AUTHOR]