Heterojunction PdO/CoS as a high-performance visible-light active photocatalyst in elimination of methylene blue from in aqueous media

Abstract

Abstract In this research, the photocatalytic degradation of methylene blue dye was investigated using cobalt sulfide and palladium oxide nanoparticles, as well as the composite PdO/CoS, under visible light irradiation. The structural and morphological properties were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Mott-Schottky analysis, and transmission electron microscopy (TEM). The hexagonal structure was observed for cobalt sulfide, and the XRD analysis revealed a multi-faceted structure for the composite. The Mott-Schottky analysis confirmed the formation of a p-n heterojunction, and the flat band potential values for the n-type and p-type semiconductors were found to be -1 and 1.3, respectively. The bandgap of the composite was determined to be 3 eV using Diffuse Reflectance Spectroscopy (DRS). Various conditions such as temperature and pH, as well as the percentage of palladium doping, significantly influenced the degradation of methylene blue. Both CoS and PdO alone exhibited some degradation ability, but when palladium oxide was deposited on cobalt sulfide to form the composite, a remarkable 91% degradation efficiency was achieved. When 0.1 grams of the synthesized composite was used for 90 minutes, it successfully degraded 91% of methylene blue with an initial concentration of 10 ppm. In the Design of Experiments (DOE) approach, the optimum conditions for this research were found to be a catalyst mass of 0.06 g, an initial dye concentration of 8 ppm, and 2% palladium doping at pH 10, resulting in a 92.38% degradation efficiency in 110 minutes. To model the degradation of methylene blue using the synthesized composite, the Fritz-Schlunder and Koble-Corrigan models achieved the highest correlation coefficients (0.995 and 0.992, respectively) and the lowest error functions (0.024, 0.0008) and (0.032, 0.002), respectively. Additionally, the Langmuir-Hinshelwood and Intra-particle diffusion control kinetic models showed the highest correlation coefficient (98%). In summary, the study demonstrated that the PdO/CoS composite exhibited excellent photocatalytic activity for methylene blue degradation, and the optimized conditions resulted in high degradation efficiency. The proposed kinetic models provided valuable insights into the degradation mechanism of methylene blue using the synthesized composite.