Halloysite–TiO2 nanocomposites: Synthesis, characterization and photocatalytic activity

Abstract

Two halloysite–TiO2 nanocomposites were prepared with two different tubular halloysite clays by depositing anatase-TiO2 on the halloysite surfaces using titanium isopropoxide under hydrothermal treatment at 180°C. The nanocomposites were characterized by X-Ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR), absorption properties by UV–vis spectroscopy and N2 specific surface area (SSA) analysis by BET method. Good dispersion of 3–10nm TiO2 particles on halloysite external surfaces was achieved in both the halloysite–TiO2 nanocomposites and ATR-FTIR results showed the formation of hydrogen bonding between TiO2 and the outer surfaces of halloysite tubes. After treating with TiO2, both halloysite samples largely showed interparticle mesopores of about 5.7nm. However, the macropores of halloysite (lumen or central hole in halloysite tubes) were not detected probably as a result of plugging of the lumens in halloysite tubes by TiO2 nanoparticles. These nanocomposites were tested for their photocatalytic activities in decomposing NOx gas and toluene. The halloysite–titania samples showed significantly higher activity in decomposing NOx gas under visible-light irradiation (λ>510nm) and UV–visible light irradiation (λ>290nm) compared to that of the standard commercial titania photocatalyst, P25. In addition, composite photocatalyst showed larger catalytic activity either under sunlight or pure UV irradiation in decomposing toluene compared to the commercial titania, P25. Our experimental data suggest that the enhanced photocatalytic activity is related with the good dispersion of the TiO2 nanocrystals on the surface of the clay minerals.