Sol-gel synthesis of photoactive kaolinite-titania: Effect of the preparation method and their photocatalytic properties

Supporting TiO2 on different materials is a potential strategy to improve the photochemical properties of the resulting composites. Kaolinite (K) was used as a support to synthesize a series of kaolinite-titania (K-TiO2) photocatalysts with desirable properties for decolorization of organic contaminants. Initially, TiO2 sol was formed through gelation of titanium oxychloride using ammonium hydroxide solution and subsequent peptization of the preformed gel in a low concentration of nitric acid. The sol was reacted with different concentrations of kaolinite at different pH conditions to yield K-TiO2 composites with different TiO2 compositions. The physicochemical properties of the photocatalysts were examined by XRD, FTIR, TGA, SEM-EDAX, XRF, UV-visible DRS, TEM and nitrogen gas physisorption studies analyses. XRD results revealed that through varying pH of the reaction a mixture of TiO2 crystals can be attained in the sintered samples. A simple photocatalytic experiment of the calcined photocatalysts was carried out to evaluate the decolorization of methylene blue in the presence of an artificial UV source. The obtained results were exquisitely compared to those of the ZrO2-TiO2 based composites obtained in our previous study. It was revealed that the amount of TiO2 in the composites and the calcination temperature had a profound effect on the microstructure and photocatalytic performance of the samples. Thus, the KT34-600 sample exhibited the highest activity of all due to its superior properties. This study provides a criterion for selection of precursors, synthetic routes and support suitable for the formation of metal oxides composites with desirable properties for heterogeneous catalysis.