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

The photocatalytic H2 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 H2 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 H2 production rate with the glycerol concentration was explained assuming a Langmuir adsorption model. Both water and glycerol are involved in the photocatalytic H2 production with NiO/TiO2 catalysts. The reaction results with D2O instead of H2O indicate that glycerol may be a main H2 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 CoO and CuO.