Synthesis, characterization, and application of mixed-addenda silicon vanado tungstate polyoxometalate integrated into nanoporous MIL-101(Cr) for the quick removal of organic dyes from water

In this work, a polyoxometalate, namely, [SiW₉V₃O₄₀]^-7, was successfully encapsulated into the pores of a MIL-101(Cr) metal organic framework (MOF) <i>via</i> a water-based, eco-friendly impregnation method. This was supported by diverse characterization techniques, such as FT-IR spectroscopy, XRPD, FE-SEM, EDX spectroscopy, N₂ adsorption-desorption method, and TGA. The resulting composite, SiW₉V₃@MIL-101(Cr), denoted as SiW₉V₃@MC, exhibited a high specific surface area (1463.3 m² g^-1), indicating a large capacity for dye adsorption. The composite demonstrated excellent performance in the removal of cationic dyes, such as Rhodamine B (RhB) and methylene blue (MB), from aqueous solutions. The adsorption efficiency was systematically studied using varying factors, including adsorbent amount, dye concentration, pH level, and temperature. The adsorption kinetics were observed to adhere to a pseudo-second-order model, while the adsorption isotherms conformed to the Langmuir model, suggesting the realization of monolayer adsorption onto the surface of the adsorbent. Furthermore, SiW₉V₃@ MC displayed exceptional reusability, maintaining its activity and selectivity after multiple adsorption-desorption cycles without significant structural degradation. This stability throughout the experiments underscores its ability as a sustainable and affective adsorbent for waste-water treatment applications. The high adsorption capacity, combined with its environmentally friendly synthesis method, positions SiW₉V₃@MC as a potential option for efficient water purification methods.