| dc.description.abstract | Develop a photocatalyst system for solar energy conversion to electric energy or chemical energy is a topic of great interest for fundamental and practical importance. In this study, photocatalytic activities of InVO4, InTaO4, InNbO4, In6WO12, K4Nb6O17 catalysts for water splitting under visible light irradiation were investigated. Photocatalytic activities of NaTaO3 catalysts for water splitting were studied under UV light irradiation. The effect of different preparation parameters, such as type of cocatalyst and amount of NiO loading, doping metal and pretreatment process on the photocatalysis reaction was investigated. The photocatalysts was synthesized by solid-state reaction method using metal oxide as the starting materials. The catalysts were characterized by powder X-ray diffraction (XRD), scanning electron spectroscopy (SEM), ultraviolet-visible spectroscopy (UV-Vis) and X-ray photoelectron spectroscopy (XPS). The photocatalytic reaction was carried out in a Pyrex reactor with a 500 W halogen light as visible light source and 400 W high pressure mercury lamp as UV light source. All of the catalysts were fully crystallized. SEM results In6WO12 catalysts had the smallest particle size were ca. 1~2 μm. In addition, many pin-holes appeared on InVO4 particles, after loading NiO, CoOx and RuOx. The band gap of InVO4, InTaO4, InNbO4, In6WO12, K4NB6O17 and NaTaO3 were 1.8 eV, 2.7 eV, 2.6 eV, 2.6 eV, 3.0 eV and 3.3 eV, respectively, showing that these catalysts had ability to split water into H2 and O2.
For InVO4 catalyst, NiO was the best cocatalyst for water splitting, which gave the highest activity (750 μmolh-1gcat.-1 for H2 evolution and 375 μmolh-1gcat.-1 for O2) when the loading was 0.3 wt%. The pretreatment method had a great effect on the activity of the catalyst. The NiO/InVO4 catalyst which was reduced at 500oC for 2 h and oxidized at ambient condition for 48 h gave the highest activity with a rate of 896μmolh-1gcat.-1. It demonstrated that the pretreatment process plays a key role in creating high catalytic performance for the NiO/InVO4 catalyst.
For InTaO4 catalysts, we also have tested various metal oxides as the additive and NiO gave the highest activity. The yields of H2 and O2 on NiO-InTaO4 were 842 μmolh-1gcat.-1 and 420 μmolh-1gcat.-1, respectively. Similarly, NiO was found to be best catalyst on InNbO4 catalyst. However, the negative of reduction-oxidation treatment was observed on NiO/InTaO4 and NiO/InNbO4.
For In6WO12 catalyst, RuO2 additive gave the highest activity. The pretreatment method had a little effect on the activity of the catalyst. The yields of H2 and O2 were 774 μmolh-1gcat.-1 and 365 μmolh-1gcat.-1, respectively. K4Nb6O17 is a very active catalyst. The yields of H2 and O2 were 839 μmolh-1g cat.-1 and 415 μmolh-1g cat.-1, respectively.
Photocatalytic activities of La-NaTaO3 catalysts for water splitting were studied under UV light irradiation. The yields of H2 and O2 were 1476 μmolh-1gcat.-1 and 738 μmolh-1gcat.-1, respectively. | en_US |