Sepiolite-TiO₂ nanocomposites for photocatalysis: Synthesis by microwave hydrothermal treatment versus calcination

Sepiolite-TiO₂ nanocomposites were synthesized by conventional calcination process and microwave hydrothermal (M-H) treatment and were tested and compared for their photocatalytic activity. XRD analysis indicated that nanocomposites after calcination at 500 °C or M-H treatment for 40 min at about 200 °C appear to be the optimal conditions, which assured the amorphous TiO₂ to crystalline anatase phase transition. The deposition of the TiO₂ on the surface of sepiolite by M-H treatment yielded small dispersed nanoparticles at all treatment times used in this study. However, TiO₂ particle size increased with increasing calcination temperature, which was confirmed by SEM and TEM. N₂-adsorption-desorption isotherms indicated that calcination process reduced the specific surface areas of the nanocomposites while the M-H treatment led to a higher surface area with better photocatalytic performance for the degradation of Orange G. The intact structure of sepiolite and the homogeneous dispersion of the TiO₂ nanocrystals on sepiolite surfaces led to enhanced photocatalytic activity in M-H treated samples.