ZnO supported Au/Pd bimetallic nanocomposites for plasmon improved photocatalytic activity for methylene blue degradation under visible light irradiation

Abstract

Recently, photocatalysis has attracted great attention due to its potential applications in the environmental sector. Visible light driven metal-semiconductor photocatalysts with efficient light absorption, high charge separation, enhanced surface plasmon resonance, and utilized active sites have emerged as promising materials for the degradation of organic pollutants. Here, plasmonic ZnO/Au/Pd nanocomposites, with various concentrations of Au (5, 10, and 15 wt%) and 5 wt% of Pd nanoparticles (NPs) were prepared by a facile and eco-friendly three-step pulsed laser ablation in liquid and photodeposition technique without utilizing any surfactants or capping agents to enhance the photocatalytic performance under visible light illumination. The plasmonic properties of Au NPs and an excellent trapping of photogenerated electrons on the surface of Pd led to the improved photocatalytic activity (PCA). The as-prepared ZnO/Au/Pd nanocomposites were characterized by numerous spectroscopic and microscopic techniques, and the results confirmed the fabrication of Au and Pd NPs homogeneously decorated on the surface of ZnO nanospheres. The effect of plasmon improved photocatalytic activity of the ZnO/Au/Pd photocatalysts was investigated by the degradation of methylene blue dye under visible light illumination. The optimum ZnO/Au/Pd nanocomposite was ca. 5.4 times more efficient at degrading methylene blue than pure ZnO. This exceptional improvement of photocatalytic activity for the ZnO/Au/Pd catalysts was due to the enhanced surface plasmon resonance effect of the Au NPs under visible light illumination, and the deposited Pd NPs assisted as an electron storage chamber for the degradation of methylene blue, thus, enabling the separation of charge carriers. Based on the experimental results, a possible photocatalytic mechanism for the degradation of methylene blue catalyzed by the ZnO/Au/Pd nanocomposite was proposed.