Direct Hydrothermally Synthesized Novel Z-Scheme Dy3+ Doped ZnO/SnS Nanocomposite for Rapid Photocatalytic Degradation of Organic Contaminants

Abstract

Different concentrations (1, 3 and 5 wt%) of dysprosium (Dy3+)-doped ZnO/SnS (ZSD) nanophotocatalysts using the one-step facile hydrothermal method at 230 ℃ are presented. Their structure, morphological appearance, inclusion of constituent elements, bandgap engineering and luminescent nature are confirmed by the XRD, TEM, XPS, UV-DRS and PL techniques. The photocatalytic activity (PCA) of the prepared nano photocatalysts is studied in the presence of a model pollutant MB under solar light illumination. The degradation kinetics and charge separation mechanism of the ZSD photocatalysts are also presented. Our XRD analysis showed the mixed-phase occurrence of ZnO (hexagonal) and SnS (orthorhombic) from their JCPDS numbers with no additional traces of a doping element, which in turn indicates the purity, substantial crystal structure and high dispersion of the samples. TEM micrographs revealed the appearance of a flake structure and more agglomeration when increasing the dopant concentration. The XPS spectra confirmed the Zn2+, Sn2+, S2−, O2− and Dy3+ oxidation states of the constituent elements along with carbon and nitrogen peaks. The Tauc plots showed a decreasing trend in the optical bandgap, i.e., a redshift due to the loading of Dy3+ ions into Sn2+ ions. The lower recombination rate of photoinduced e−-h+ pairs is noted when increasing the Dy3+ ion content; i.e., the luminescent intensity is suppressed when increasing the concentration of Dy3+ ions. The obtained degradation efficiency of the MB dye using the ZSD3 nano photocatalyst is around 98% for a duration of 120 min under solar light irradiation. The prepared ZSD photocatalyst follows pseudo first-order kinetics, and the evidence for attaining a robust Z-scheme PCA is presented in the form of the charge separation mechanism.