Facile synthesis of UCNPs/ZnxCd1-xS nanocomposites excited by near-infrared light for photochemical reduction and removal of Cr(VI)

Photocatalysis driven by near-infrared (NIR) light is of scientific and technological interest for exploiting solar energy. In this study, we demonstrate a facile hydrothermal process to synthesize core-shell nanoparticles combining upconversion nanoparticles (UCNPs) and alloyed Zn x Cd 1- x S, which can be excited using NIR or visible light. Morphologies, phase, and chemical composition have been investigated using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and atomic absorption spectroscopy. Moreover, we found that amorphous TiO 2 layers existing in the final samples play an important role in formation of UCNPs@Zn x Cd 1- x S yolk-shell nanoparticles, which bind the as-prepared Zn x Cd 1- x S nanoparticles tightly to form yolk-shell nanoparticles. The chemical composition of alloyed Zn x Cd 1- x S can be tunable by adjusting the amount of the Cd and Zn source compounds. The photochemical reduction of Cr(VI) in water has been performed to study the photocatalytic performance under irradiation by NIR light or a simulated solar light, showing efficient photoreduction and Cr(VI) removal over the as-prepared UCNPs@Zn x Cd 1- x S/TiO 2 yolk-shell nanoparticles. The as-prepared UCNPs@Zn x Cd 1- x S/TiO 2 nanoparticles show excellent production of hydroxyl radicals, which are responsible for the photochemical reduction of Cr(VI) to Cr(III). This study will provide an alternative strategy for environmental wastewater treatment , making full use of solar energy.