Comparison of the pure TiO2 and kaolinite/TiO2 composite as catalyst for CO2 photocatalytic reduction

The kaolinite/TiO2 composite was prepared using thermal hydrolysis of kaolinite/titanyl sulphate suspension and characterized by XRFS, XRPD, SEM and N2 physical adsorption. Its photocatalytic properties were evaluated by photocatalytic reduction of CO2 by water and compared with commercial TiO2 photocatalyst Degussa P25. Results showed that the yields of CO2 photocatalytic reduction products methane and methanol were higher over a kaolinite/TiO2 composite than over commercial TiO2 (Degussa P25) in spite of smaller proportion of TiO2 in the composite. Introducing of TiO2 nanoparticles into the kaolinite structure caused a decrease of anatase crystallite size. Kaolinite can also change acidobasic properties of catalyst surface, inhibit the recombination of electron–hole pairs and prevent the formation of TiO2 aggregates in suspension. These facts can contribute to the observed higher photocatalytic efficiency of kaolinite/TiO2 compared to the commercial TiO2 photocatalyst.