| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程研究所 === 94 === Developing a photocatalytic system for solar energy conversion to electric energy or chemical energy is a topic of great interest with fundamental and practical importance. Semiconductor photocatalysts such as InTaO4, InNbO4 and InVO4, have been extensively used for water splitting under visible light irradiation and demonstrated very high activity. According to the band structures of InTaO4, InNbO4 and InVO4, the photoreduction of carbon dioxide on InTaO4, InNbO4 and InVO4 catalysts should be feasible. However, they have not been applied for photoreduction of carbon dioxide.
The photocatalysts were 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 Microscope (SEM), Ultraviolet-Visible Spectroscope (UV-Vis) and X-ray Photoelectron Spectroscope (XPS). The photocatalytic reduction was carried out in a Pyrex reactor with KHCO3 or NaOH aqueous solution bubbled with ultra pure CO2 gas under visible light illumination (500W halogen light as the light source). All the catalysts were fully characterized. SEM micrographs showed the appearance of many pellets on InTaO4 and InNbO4 particles, whereas many pinholes were observed on the InVO4 particles with NiO and CoO cocatalysts. The band gap of InTaO4, InNbO4 and InVO4 were observed to be 2.7 eV, 2.6 eV and 1.8 eV, respectively, showing that these catalysts have the ability to reduce CO2 into methanol.
In this study, photocatalytic activity of InTaO4, InNbO4 and InVO4 catalysts for carbon dioxide reduction under visible light irradiation was investigated. The effect of adding different species and various amounts of cocatalysts, pretreatment process and diverse aqueous solutions on the photocatalytic reduction was a top priority to investigate. InTaO4 catalysts were tested by varying several conditions such as different species and various amounts of cocatalysts and diverse aqueous solutions. The methanol yield was increasing with the amount of cocatalysts. Also, the pretreatment method has a good effect on the catalyst. The activity of the photocatalyst performs better in KHCO3 aqueous solution. It was found that the reaction of InTaO4 catalyst with 1.0 wt. % NiO cocatalyst after pretreatment in KHCO3 aqueous solution gave the highest activity and the yield of methanol was 1.394 �慆ol．h-1．gcatal.-1. However, InNbO4 and InVO4 catalysts showed the highest activity at 1.615 �慆ol．h-1．gcatal.-1 and 2.028 �慆ol．h-1．gcatal.-1, respectively, with 0.5 wt. % NiO cocatalyst after pretreatment.
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