Carbon nanotubes/titanium dioxide (CNTs/TiO2) nanocomposites prepared by conventional and novel surfactant wrapping sol–gel methods exhibiting enhanced photocatalytic activity

Abstract

In this work, a conventional sol–gel method was used to prepare CNTs/TiO2 nanocomposites with different carbon loading in the range up to 20% CNTs/TiO2 by weight. The bare CNTs (multi-walled), and the composites were characterized by a range of analytical techniques including TEM, XRD, BET and TGA–DSC. The results show the successful covering of the CNTs with discrete clusters of TiO2 and bare CNTs surfaces which after annealing at 500°C led to mesoporous crystalline TiO2 (anatase) clusters. The photocatalytic activities of the nanocomposites were monitored from the results of the photodegradation of methylene blue (MB). The optimum CNTs/TiO2 ratio in the composites prepared by conventional sol–gel method was found to be in the range from 1.5% to 5% by weight under the experimental conditions investigated. The maximum increase in activity was found to be 12.8% compared to the pure TiO2 sample.In contrast, the synthesis of CNTs/TiO2 nanocomposites by a novel surfactant wrapping sol–gel method [B. Gao, C. Peng, G.Z. Chen, G. Li Puma, Appl. Catal. B: Environ. 85 (2008) 17.] led to a uniform and well-defined nanometer-scale titania layer on individual CNTs. The nanocomposites were found to enhance the initial oxidation rate of methylene blue by onefold compared to the pure TiO2 sample. This larger degree of rate enhancement is attributed to the supporting role of the CNTs and surface properties prepared by this novel modified sol–gel method.