Synthesis, characterization, and photocatalytic degradation of toxic dyes from wastewater using AgI@Sn-BDC-NH2 heterojunction nanocomposites

Metal-organic frameworks (MOFs) have attracted significant research interest as promising innovative platforms for designing heterojunction photocatalysts. Herein, we report the rational design and preparation of an AgI@Sn-BDC-NH₂ heterojunction composite via a simple and facile in-situ route to degrade organic dyes (RhB). The AgI@Sn-BDC-NH₂ structural, surface, and optical characteristics were thoroughly examined by means of XRD, FTIR, SEM, EDS, UV-Vis DRS, VB-XPS, N₂ physisorption, TG, XPS, PL, transient photocurrent, and EIS techniques. The experimental results confirmed that AgI particles were dispersed on the surface of flower-like Sn-BDC-NH₂, and the introduction of AgI significantly boosts the photocatalytic performance of the nanocomposites. Under the operating parameters (catalyst dosage of 0.5 g/L, RhB concentration of 30 mg/L, volume of 40 mL, and illumination time of 60 min), the 30-AgI@Sn-BDC-NH₂ with the AgI loading of 30% exhibited the highest degradation efficiency in RhB, reaching 94.7%, with a photocatalytic rate constant of 0.039 min^{- 1}, which was 3.22 times and 26.0 times that of pure AgI and Sn-BDC-NH₂, respectively. The enhanced activity can be originated from the formation of Z-scheme heterojunction between AgI and Sn-BDC-NH₂ with intimate interfacial contact and the synergistic effects among the components, thereby providing a mesoporous structure and larger relative surface area (27.9 m²/g), improving utilization of visible light, more charge transfer channels, and lower electron-hole pair recombination rates. More crucially, it retained 78.1% degradation efficiency after five cycles, confirming excellent stability. Furthermore, trapping analyses suggest that e^-, •O₂^-, and h⁺ radicals dominate the degradation reaction pathway, and then a possible mechanism of 30-AgI@Sn-BDC-NH₂ Z-scheme heterojunction was proposed. Overall, this research work highlights the potential of using Sn-MOF-based heterojunction composites as practical photocatalysts for sustainable dye-contaminated wastewater treatment.