Xanthan Gum/Lignin Double-Interpenetrating Network Cryogels: Preparation, Characterization, and Water Purification...

The development of multifunctional, bio-based materials capable of simultaneously addressing microbial contamination and inorganic pollutants is of increasing interest for sustainable water purification. In this study, xanthan gum (XG)/lignin(LN) double-interpenetrating network (DN) cryogels were prepared and investigated as porous, multifunctional materials for antimicrobial applications and water purification. The cryogel architecture combines the abundant oxygen-containing functional groups of XG and LN with an interconnected porous network generated under cryogenic conditions. The prepared networks were comprehensively characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), dynamic vapor sorption (DVS), swelling analysis, and uniaxial mechanical testing to evaluate their structural, morphological, physicochemical, and mechanical properties. Their Cu²⁺ sorption performance was subsequently assessed by atomic absorption spectroscopy (AAS), and the experimental equilibrium data were analyzed using the Langmuir, Freundlich, and Sips isotherm models. The single-network (SN) XG-based materials exhibited Cu²⁺ sorption capacities of 62.13-109.81 mg/g, whereas the DN cryogels showed higher capacities of 111.87-120.84 mg/g. The Sips model provided the best description of the equilibrium data, with (R²) values of 0.991-0.994 and substantially lower (χ²) values than the Langmuir and Freundlich models, indicating heterogeneous sorption sites with finite saturation capacity. Importantly, the Cu²⁺-loaded SN and DNs exhibited sorption efficiency toward sulfate ions, demonstrating their potential for sequential contaminant removal. Sulfate sorption capacities reached 694.53 mg/g for the SN.X2/Cu²⁺ composite and up to 812.53 mg/g for the DN.XL3/Cu²⁺ composite. In addition, the prepared materials demonstrated antimicrobial activity against two Gram-negative (Escherichia coli, Salmonella Typhimurium) and two Gram-positive (Staphylococcus aureus, Listeria monocytogenes) bacterial strains. The results demonstrate that XG/LN DN cryogels combine effective metal-ion and sulfate sorption with antimicrobial activity, providing promising bio-based platforms for water purification and potentially extending the functional lifetime of the material through sequential contaminant removal.