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

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.