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.