Photocatalytic hydrogen production from aqueous glycerol solution using NiO/TiO2 catalysts: Effects of preparation and reaction conditions

The photocatalytic H-2 production from a mixture of glycerol and water over NiO/TiO2 catalysts was investigated. Effects of preparation and reaction conditions were examined, including TiO2 materials, NiO loading, glycerol concentration, and pH value. The rate of H-2 production was observed to be maximized at a certain NiO loading and at a pH value close to the zero-point charge of TiO2. The influence of NiO loading may be explained by a decrease in the band gap energy and a decrease in the exposed area of TiO2, which were of importance in the ranges of small and larger NiO loading, respectively. At such a pH value, the amount of surface hydroxyl groups was likely to be maximized, which could promote the adsorption of glycerol molecules via hydrogen bonding. The change of the H-2 production rate with the glycerol concentration was explained assuming a Langmuir adsorption model. Both water and glycerol are involved in the photocatalytic H-2 production with NiO/TiO2 catalysts. The reaction results with D2O instead of H2O indicate that glycerol may be a main H-2 source. In addition, it has been found that NiO is a good choice in preparing active TiO2 based catalysts as compared with the other transition metal oxides of Cob and Cub. (C) 2015 Elsevier B.V. All rights reserved.