Enhanced photocatalytic H₂-production activity of TiO₂using Ni(NO₃)₂as an additive

Abstract

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 Ni(2+) on the surface of TiO2. The potential of Ni(2+)/Ni (Ni(2+) + 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 Ni(2+) and reduction of Ni(2+) to Ni(0). 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.