Tailoring the macromolecular architecture of covalently crosslinked xanthan gum/polyvinyl alcohol hydrogels for wastewater treatment: From nanometer mesh sieve to macroporous trap.

This study investigates the nanostructured network architecture, thermodynamic behavior, rheological and dye adsorption properties of chemically crosslinked Xanthan Gum/polyvinyl alcohol (XG/PVA) hydrogels synthesized at varying blending ratios (1:3, 1:1 and 3:1). Using gravimetric swelling analysis coupled with the Peppas-Merrill approach, the true molecular mesh size and volumetric crosslinking density were quantified in pure water to map out network transport pathways. Exposing the crosslinked networks to ethanol and isopropanol anti-solvents triggered severe solvent-induced phase syneresis and provided experimental evidence of a macroporous trapping mechanism. The structural divergence across the synthesized matrix series enables targeted environmental remediation based on the molecular geometry of pollutants. These findings provide design rules for tuning hydrogel matrices, establishing the 1:1 mixing ratio as an ideal candidate for highly constrained barrier systems and the 3:1 ratio for macroscopic fluid uptake or macromolecular drug delivery cascades. The sorption capacity of the hydrogels towards cationic dyes Nile Blue Chloride and Methylene Blue was investigated by varying the sorbent dosage, pH, contact time, and initial dye concentration. Analysis of adsorption data with different kinetic and isotherm models revealed that dye adsorption occurs by both physical diffusion and specific binding, with the best fit of the data for the Sips model. A hydrogel matrix with a 3:1 mixing ratio led to a maximum adsorption capacity of 324.47 (in MB) and 300.16 (in NB).