High Density Unaggregated Au Nanoparticles on ZnO Nanorod Arrays Function as Efficient and Recyclable Photocatalysts for Environmental Purification

Abstract

Photodegradation of organic pollutants in aqueous solution is a promising method for environmental purification. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. Unfortunately, the separation of these semiconductor-metal nanopowders from the treated water is very difficult and energy consumptive, so their usefulness in practical applications is limited. Here, a precisely controlled synthesis of a large-scale and highly efficient photocatalyst composed of monolayered Au nanoparticles (AuNPs) chemically bound to vertically aligned ZnO nanorod arrays (ZNA) through a bifunctional surface molecular linker is demonstrated. Thioctic acid with sufficient steric stabilization is used as a molecular linker. High density unaggregated AuNPs bonding on entire surfaces of ZNA are successfully prepared on a conductive film/substrate, allowing easy recovery and reuse of the photocatalysts. Surprisingly, the ZNA-AuNPs heterostructures exhibit a photodegradation rate 8.1 times higher than that recorded for the bare ZNA under UV irradiation. High density AuNPs, dispersed perfectly on the ZNA surfaces, significantly improve the separation of the photogenerated electron-hole pairs, enlarge the reaction space, and consequently enhance the photocatalytic property for degradation of chemical pollutants. Photoelectron, photoluminescence and photoconductive measurements confirm the discussion on the charge carrier separation and photocatalytic experimental data. The demonstrated higher photodegradation rates demonstrated indicate that the ZNA-AuNPs heterostructures are candidates for the next-generation photocatalysts, replacing the conventional slurry photocatalysts.