Formation of chemical heterojunctions between ZnO nanoparticles and single-walled carbon nanotubes for synergistic enhancement of photocatalytic activity

Abstract

A series of nanocomposites composed of spherical ZnO nanoparticles (ZNPs, average diameter of 119 nm) and single-walled carbon nanotubes (average diameter of 1.1 nm) (ZNP–SWCNT) were synthesized. The synergistic effect of the SWCNTs on the photocatalytic efficiency of the ZNPs for the degradation of methylene blue dye under UV-light was demonstrated. The as-synthesized nanocomposites, pure ZNPs, and the pristine SWCNTs exhibited pseudo-first-order kinetic behavior in the decomposition of the dye. The decomposition rate constant in the presence of the nanocomposite varied with the amount of SWCNTs. The maximum rate constant was 680 % and 2570 % greater than those of the pure ZNPs and the pristine SWCNTs, respectively. It was found that the optical bandgap of the pure ZNPs was considerably narrowed, and their maximum UV absorbance was red-shifted upon composite formation between the SWCNTs and ZNPs. Those results suggested that the SWCNTs played a crucial role in the improvement of the catalytic activity of the ZNPs. Such a synergistic effect was due to the creation of a chemical heterojunction between the SWCNTs and the ZNPs. Moreover, the prepared nanocomposite demonstrated remarkable reusability: the photocatalytic efficiency was reduced by only 3.62 % after the fifth cycle.