Au/ZnS and Ag/ZnS nanoheterostructures as regenerated nanophotocatalysts for photocatalytic degradation of organic dyes

Abstract

Although several groups have reported the synthesis of ZnS quantum dots, only a few have developed methods to prepare potentially nontoxic, noble metal loaded ZnS QDs. In this study, we devised a gram scale, environmentally benign, room temperature, aqueous solution based method for the synthesis of renewable and eco-friendly, well dispersed ZnS quantum dots along with noble metal loaded ZnS QDs (loading amount 4 wt%). The properties of the nanophotocatalysts were determined by using XRD, XPS, TEM and SEM techniques. The ZnS QDs were found to have small sizes of ca. 4.5 nm and to display quantum effects in terms of blue shifts in their absorption maxima associated with an optical band gap, Eg, of 4.63 eV. The photocatalytic activities of ZnS QDs, Au/ZnS and Ag/ZnS were assessed using photodegradation of methylene blue. The results demonstrate that a significant increase in the photocatalytic efficiency takes place upon the loading of Ag and Au nanoparticles on ZnS QDs. An in-depth investigation was carried out to uncover information about the effects of noble metals on band gap energies and surface charges of the QDs. Finally, a new surface reactivation procedure was developed for the reactivation of nanophotocatalysts. Consequently, the newly synthesized photocatalysts are renewable, a property that should make their use in practical applications cost effective.