Surface texture dependency of photocatalytic behavior of facile synthesized mesoporous ZnS-ZnO heterostructure under LED illumination

Employing three porous semiconductor particles, the impact of the surface area on dynamic photocatalytic degradation of methylene blue has been investigated under an LED light source. At first, porous ZnS with a relatively high surface area was synthesized via an innovative method in ethanol, which is insoluble for Sulphur precursor (Na₂S). This semiconductor was used for the synthesis of porous ZnO and ZnS-ZnO nanocomposites through a simple oxidation treatment in the air atmosphere. The characterization of the synthesized compounds was conducted through different techniques including X-ray diffraction, physisorption of nitrogen, simultaneous thermal analysis, field emission scanning and high-resolution transmission electron microscopy, photoluminescence spectroscopy, FT-IR spectroscopy, Mott-Schottky technique, and visible-ultraviolet spectroscopy. Based on the results, the specific surface areas were reported as 165 m² g^-1, 35 m² g^-1, and 10 m² g^-1 for ZnS, ZnS-ZnO, and ZnO, respectively. Despite ZnS having a higher bandgap (3.3 eV) and lower charge carrier density (9.21⋅10¹⁵ cm^-3) than ZnS-ZnO, it exhibits better photocatalytic efficiency which emphasizes on the pronounced impact of surface area on the photocatalytic degradation of the selected dye. The efficiency of ZnS in removing organic pollutants is 88%, while ZnO achieves only 43% removal, and the ZnS-ZnO composite exhibits a removal efficiency of 55%. This superior efficiency of ZnS is further supported by its higher surface area, reduced PL intensity and visible-range emissions due to defect states, along with Mott-Schottky analysis confirming trap states that enhance charge separation under LED light. The degradation followed a dynamic process driven by efficient charge transfer and surface interactions.