Efficient Photocatalytic Degradation of Rhodamine B With Heterostructured CdS/Mn-MOF Composite

Abstract

A highly efficient photocatalyst, the CdS/Mn-MOF composite, was synthesized by first preparing a new 2D Mn-MOF (Mn(L)·H₂O, H₂L = 5-(2-benzothiazolyl)isophthalic acid) precursor through the solvothermal method and subsequently growing CdS nanoparticles. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, and other techniques were utilized to characterize the structural, morphological, textural, compositional, and optical properties of the composites. The prepared photocatalysts, designated as X-CdS/Mn-MOF (where X = 50, 25, and 10, represents the mass percentage of CdS), were tested for photocatalytic performance. Among them, the 50-CdS/Mn-MOF sample exhibits the optimized degradation efficiency of 99.1% for Rhodamine B (RhB, 20 mg/L) in 50 min under visible light irradiation, which is 7.3 times and 2.4 times higher than that of Mn-MOF and CdS, respectively. Various test results indicate that the improved photocatalytic activity of CdS/Mn-MOF composites can be attributed to the formation of heterojunctions. Specifically, the heterojunctions enhance the separation efficiency of photogenerated carriers and effectively suppress the recombination of electrons and holes, thereby improving the overall efficiency of the photocatalytic reaction. Moreover, the presence of heterojunctions optimizes the material's band structure, facilitating more efficient carrier transport, which further enhances photodegradation performance. Radical quenching experiments confirmed hydroxyl radicals (·OH⁻) and superoxide radical anions (·O₂⁻) played dominant roles in the photodegradation process. Additionally, the composite material also demonstrates good stability and reproducibility. The research further provides evidence that the efficiency of dye degradation can be significantly improved by the rational design of composite catalysts consisting of other semiconductors and MOFs.