Sm doped ZnO-SnO2 nanocomposites with improved photo-degradation strength and antibacterial properties

Abstract

In this work, we devoted our effort to synthesize rare-earth (Sm3+) doped ZnO-SnO2 nanocomposites by sol-gel method to address issues like wastewater treatment and minimization of bacterial infection. Successful formation of multi-phase nanocomposites of hexagonal ZnO and tetragonal SnO2 has been confirmed by x-ray diffraction (XRD) analysis. The effect of Sm doping is understood from the enhancement in ZnO grain growth and shift in diffraction peaks. The morphology study by FESEM reveals the variation in sample morphology with Sm doping with energy-dispersive analysis of x-ray (EDAX) study providing the confirmation on the existence of Sm ions in the crystal lattice of ZnO-SnO2 heterostructure. Transmission electron microscopic (TEM) study manifests the formation of two distinct types of particles (hexagonal & spherical) corresponding to ZnO and SnO2 which has been further clarified from the measurement of lattice spacing from the high-resolution TEM images and indexing of selected area electron diffraction (SAED) pattern. The near band edge emission (NBE) of ZnO is blue shifted along with the evolution of oxygen vacancy defects which induced new bands at 488 nm and 613 nm upon Sm doping. Further, intra-4f transitions of Sm3+ ions have also been observed at 560 nm, 590 nm and 638 nm linked to 4G5/2– 6HJ (J = 5/2, 7/2, 9/2) transitions. The Zn, Sn, O, and Sm elements are confirmed to exist in the nanocomposite according to the X-ray photoelectron spectroscopy (XPS) investigation which provided information on the chemical composition and electronic states of the material. Photocatalytic degradation study of toxic environmental dyes like methylene blue (MB), Congo red (CR) and methyl orange (MO) shows that Sm3+ ions in ZnO/SnO2 helps to enhance the degradation efficiency by the formation of Z-scheme heterojunctions between ZnO and SnO2. This allows the delay in recombination rate of the photoinduced electron/hole pairs. The antibacterial behavior of the prepared nanocomposites against E. Coli and S. Aureus has also been studied in detail which demonstrates improved antibacterial efficiency of the samples.