Solvothermal preparation of TiO₂/saponite nanocomposites and photocatalytic activity

A saponite-rich clay sample from western Macedonia, Greece was used for the preparation of TiO₂-saponite nanocomposites by solvothermal reaction of a mixture of water and ethanol as the solvent, hexamethylene tetramine as the precipitant and titanium trichloride as the TiO₂ precursor. Phase composition was determined by X-ray diffraction (XRD) and particle morphology and elemental content was characterized by scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). These samples were also characterized by attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR). Particle-size analysis was carried out using dynamic light scattering method (DLS) and specific surface area and pore-size distribution analyses using BET N₂ adsorption-desorption isotherms. The composite photocatalysts showed a mesoporous structure with the distribution of pore diameters centered at 3.8 and at 5.7-9.8 nm, with high specific surface areas. The photocatalytic activities of titania-saponite nanocomposites in decomposing NOx gas were measured as a function of two different TiCl₃-saponite ratios. TiO₂:saponite with a mass ratio of 0.2:1 (Ti-Sap1) showed the highest photocatalytic activity because of its relatively large specific surface area and higher TiO₂ content. Both the TiO₂-saponite nanocomposites showed higher photocatalytic activity than the standard titania (Degussa P25) based on TiO₂ content because the titania was well dispersed on saponite.