Synthesis of SnO₂-ZnO heterojunction composites for effective degradation of methylene blue and chromium (VI) under solar light irradiation

In this work, SnO₂/ZnO nanocomposites were synthesized via hydrothermal treatment, and their structural, optical, and morphological properties were characterized using various techniques, including powder X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, UV–visible (UV–vis) spectroscopy, and photoluminescence (PL) spectra. The photocatalytic performance of the SnO₂/ZnO nanocomposites was evaluated for the degradation of dual pollutants, specifically chromium (VI) (Cr (VI)) and methylene blue (MB), under solar light irradiation. The results demonstrated an enhanced degradation efficiency for both Cr (VI) and MB, achieving degradation rates of 89 and 92%, respectively, within 90 min of exposure to solar light. The rate constant for the decomposition of Cr (VI) was determined to be 0.0059 min⁻¹ while the rate constant for the degradation of MB was found to be 0.0071 min⁻¹. These values compare favorably with existing standards in the field, where typical rate constants for similar photocatalysts range between 0.0020 and 0.0065 min⁻¹ for Cr (VI) and 0.0030 and 0.0068 min⁻¹ for MB degradation. These findings underscore the potential of SnO₂/ZnO nanocomposites for effective photocatalytic treatment of industrial pollutants under solar light, outperforming several existing photocatalysts in terms of degradation efficiency and rate constants.