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

Herein, we for the first time report the production of H-2 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 H-2-production activity of TiO2 was investigated and discussed. The results indicate that the photocatalytic H-2-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 H-2-production rate of 2547 mu mol 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 H-2-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+/H-2 (2H(+) + 2e(-) = H-2, E-o = -0.00 V), which favors electron transfer from TiO2 to Ni2+ and reduction of Ni2+ to Ni-0. The role of metallic Ni is to help charge separation and to act as a co-catalyst for H-2 production, thus enhancing the photocatalytic H-2-production activity of TiO2.