Effect of carbon nanotubes loading on the photocatalytic activity of zinc oxide/carbon nanotubes photocatalyst synthesized via a modified sol-gel method

Abstract

Environmental crisis caused by constantly discharged of anthropogenic pollutants into the water bodies has been increasingly arousing the concern of public. Semiconductor metallic oxide such as zinc oxide with photocatalytic ability can serve as an auspicious alternative in tackling the issues mentioned. Nevertheless, massive recombination rate of photo-induced charge carriers, agglomeration and photocorrosion of zinc oxide often reduce its photocatalytic degradation performance. Therefore, this study aimed to elucidate the effect of carbon nanotubes loading on the photocatalytic activity of zinc oxide/carbon nanotubes photocatalyst that synthesized via a modified sol-gel method whereby the synthesis pathway excludes the necessity for organic additive and subsequence annealing treatment. Besides, the carbon nanotubes were added and ultrasonicated with precursor prior to the formation of zinc oxide which can enable the carbon nanotubes to serve as nucleation sites for the growth of zinc oxide. The zinc oxide was found to be attached on carbon nanotubes surface through the formation of zinc carboxylate group and morphologies of the zinc oxide/carbon nanotubes photocatalyst showed that the aggregation of zinc oxide was reduced in the presence of carbon nanotubes. The band gap energy of zinc oxide photocatalyst was slightly blue shifted after hybridized with carbon nanotubes. The zinc oxide/carbon nanotubes photocatalyst demonstrated greater photocatalytic activity than pure zinc oxide in degrading methylene blue under irradiation of sunlight and the photocatalytic activity of the zinc oxide/carbon nanotubes photocatalyst was increased with increasing carbon nanotubes loading. An optimum photocatalytic activity was obtained using zinc oxide/carbon nanotubes with 10 wt.% carbon nanotubes.