The effects of synthesis procedures on the morphology and photocatalytic activity of multi-walled carbon nanotubes/TiO2 nanocomposites

This study investigates the microstructures of multi-walled carbon nanotubes (MWNTs)/TiO2 nanocomposites, obtained by sol-gel and hydrothermal processes. The synthesized nanocomposite materials were characterized by x-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) adsorption analysis, transmittance electron microscopy (TEM), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, and x-ray photoelectron spectroscopy (XPS). The effects of the synthetic procedures and MWNTs on the morphology and photocatalytic activity of the nanocomposites were studied. The photocatalytic activity of the MWNTs/TiO2 nanocomposite was elucidated based on the photooxidation of NOx under UV light illumination. A fleck-like and well dispersed TiO2 microstructure on the surface of the MWNTs was observed in the sol-gel system, while compact and large aggregated particles were found in the hydrothermal procedure. The nanocomposite prepared by the sol-gel system exhibits better photocatalytic activity for NO oxidation (from 20.52 to 32.14%) than that prepared by the hydrothermal method (from 22.58 to 26.51%) with the same MWNT loading (from 0 to 8 wt%), respectively. The optimal MWNT content in the nanocomposite was considered at 8 wt%. Additionally, results confirm that the introduction of MWNTs will cause the NO2 to be more consumed than NO in the photocatalytic experiments, leading to more complete NOx photooxidation. These observations indicate that the different TiO2 distributions on the MWNT surfaces and MWNT contents in the materials would determine the morphology, the physicochemical and photocatalytic characteristics for the nanocomposite materials.