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

Abstract

This study investigates the microstructures of multi-walled carbon nanotubes(MWNTs)/TiO2 nanocomposites, obtained by sol–gel and hydrothermal processes. The synthesizednanocomposite materials were characterized by x-ray diffractometry (XRD),Brunauer–Emmett–Teller (BET) adsorption analysis, transmittance electronmicroscopy (TEM), scanning electron microscopy (SEM), photoluminescence(PL) spectroscopy, and x-ray photoelectron spectroscopy (XPS). The effects ofthe synthetic procedures and MWNTs on the morphology and photocatalyticactivity of the nanocomposites were studied. The photocatalytic activity of theMWNTs/TiO2 nanocomposite was elucidated based on the photooxidation ofNOx under UV light illumination. A fleck-like and well dispersedTiO2 microstructure on the surface of the MWNTs was observed in the sol–gel system, whilecompact and large aggregated particles were found in the hydrothermal procedure. Thenanocomposite prepared by the sol–gel system exhibits better photocatalytic activity forNO 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 theNO2 to be more consumed than NO in the photocatalytic experiments, leading to more completeNOx photooxidation. These observations indicate that the differentTiO2 distributions on the MWNT surfaces and MWNT contents in the materials woulddetermine the morphology, the physicochemical and photocatalytic characteristics for thenanocomposite materials.