Synthesis and characterization of carbon nanotubes supported Au nanoparticles encapsulated in various oxide shells

Abstract

A novel supported catalyst with various oxide shells (SiO₂, TiO₂, ZnO) assembled on Au nanoparticles with carbon nanotubes as support has been successfully fabricated. This process involves preparation of modified MWCNTs, sequential deposition of Au and then oxide shells, and finally calcination at high temperature to remove the organics. The obtained samples were characterized by several techniques, including N₂ adsorption–desorption isotherms, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), UV-Vis spectra, X-ray diffraction and thermogravimetric analysis (TGA). The results established that all the oxide shells could serve as effective barriers to prevent the migration and aggregation of Au NPs during calcination. Moreover, different oxide layers have an obvious influence on the distribution of Au nanoparticles. Additionally, the prepared catalyst exhibited a mesoporous structure because of the preservation of carbon nanotubes. In our experiments, the catalytic activities of MO_x/Au/CNTs were investigated by photo-metrically monitoring the reduction of p-nitrophenol (p-NPh) by an excess of NaBH₄. It was found that the prepared TiO₂/Au/CNTs catalyst revealed excellent catalytic activity and the sample could be easily recycled without a decrease of the catalytic activity in the reaction.