On sol–gel derived Au-enriched TiO2 and TiO2-ZrO2 photocatalysts and their investigation in photocatalytic reduction of carbon dioxide

Gold-enriched TiO2 and TiO2-ZrO2 and their parent counterparts were prepared by using the sol–gel process controlled within the reverse micelles environment, followed by impregnation in AuCl3 solution. Catalysts were characterized by organic elementary analysis (OEA), inductively coupled plasma mass spectrometry (ICP MS), N2 physisorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) combined with electron diffraction, UV–vis spectroscopy, and tested in CO2 photocatalytic reduction. The performance of photocatalysts iluminated by UV-lamp with the wavelenght maximum at 254 nm was decreasing in the order TiO2-ZrO2 > Au/TiO2-ZrO2 > TiO2 > Au/TiO2 > TiO2 Evonic P25. The photocatalytic performance decrease over Au/TiO2-ZrO2 and Au/TiO2, compared to their parent counterparts, can be explained by the presence of too large Au particles, which block the oxide surface and either reduce the light absorption capability of the catalysts, or serve as the recombination centres. Higher photocatalytic performance of the amorphous TiO2-ZrO2 than of the nanocrystalline TiO2 can be ascribed to the enlarged surface area and higher photoactivity of titania-zirconia oxide mixture under the UV lamp with the wavelenght maximum at 254 nm. With regard to crystalline materials the appropriate anatase crystallite-size plays a key role in performance of CO2 photocatalytic reduction. Moreover, correlation between the adsorption edge and the anatase crystallite-size was revealed.