Lignin-Based Cationic Hydrogels Incorporating MIL-100(Fe) for Combined Adsorption and Photo-Fenton Degradation of Naproxen Sodium

The occurrence of persistent pharmaceutical residues, such as nonsteroidal anti-inflammatory drugs (NSAIDs), in aquatic environments requires treatment strategies that combine high removal efficiency with operational practicality. Herein, a hybrid lignin-based cationic hydrogel incorporating the iron-based metal-organic framework MIL-100(Fe) (LS-pAAm-DAC/MIL-100(Fe)) is reported as a multifunctional material for the integrated adsorption and heterogeneous photo-Fenton degradation of naproxen sodium (NPX-Na) in water. The composite is synthesized via in situ radical polymerization, leading to the uniform immobilization of crystalline MIL-100(Fe) within a sustainable, lignin-derived polymer network. Structural and morphological analyses (XRD, ATR-FTIR, SEM/EDS) confirm the preservation of the MOF structure and its homogeneous dispersion throughout the hydrogel matrix. The composite exhibits rapid NPX-Na uptake and enhanced adsorption capacity (39 mg/g) compared with the pristine hydrogel, attributable to combined electrostatic interactions in the cationic network and additional adsorption sites on MIL-100(Fe). Under UVA irradiation in the presence of H2O2, the material promotes complete NPX-Na degradation via a heterogeneous photo-Fenton process, with HPLC/MS evidence of progressive transformation into oxidized phthalic acid-type by-products. Importantly, ICP-OES analysis reveals no detectable iron leaching, demonstrating robust immobilization of MIL-100(Fe) and operational stability. The composite retains substantial adsorption performance over multiple regeneration cycles, highlighting its reusability. Overall, LS-pAAm-DAC/MIL-100(Fe) represents a recoverable and sustainable platform that integrates capture and oxidative degradation of anionic pharmaceuticals, offering promising prospects for advanced water treatment applications.