Metal–organic frameworks for high-performance removal of sunset yellow dye: Combined Box-Behnken design and theoretical insights into adsorption

The development of efficient and reusable adsorbents for dye removal from wastewater is crucial for sustainable environmental management. In this study, two highly porous and chemically stable metal–organic frameworks, MOF-808(Zr) and MIL-101(Cr), were investigated for the adsorption of the anionic dye Sunset Yellow (SY) from aqueous media. PXRD confirmed the successful synthesis and stability of both MOFs, even after adsorption. Their large surface areas, 756.62 m² g⁻¹ for MOF-808(Zr) and 1858.04 m² g⁻¹ for MIL-101(Cr), contributed directly to the high adsorption capacities observed. Zeta potential measurements revealed a strong pH-dependence of surface charge and adsorption efficiency. Process optimization using a Box–Behnken design led to SY removal rates above 99 %. Kinetic data followed a pseudo-second-order model, indicating chemisorption as the dominant mechanism. X-ray photoelectron spectroscopy (XPS) provided further insights, showing π–π interactions between SY and aromatic linkers in MOF-808, while in MIL-101 the data suggested delocalization, polarization, or charge transfer. FTIR spectra before and after adsorption corroborated these interactions. Density functional theory (DFT) calculations supported the experimental findings, highlighting the strong affinity of SY molecules for the framework nodes and linkers. UV–vis diffuse reflectance analysis offered complementary information on the electronic environment during adsorption. Importantly, MIL-101(Cr) maintained high efficiency over four cycles, and ICP-OES confirmed negligible metal leaching, underscoring the material's robustness. Both MOFs also performed efficiently in real textile wastewater, demonstrating their potential as sustainable adsorbents for environmental remediation.