Thermoresponsive and reusable chitosan/hydroxypropyl cellulose monolithic hydrogel with interconnected porosity...

In this study, a novel thermoresponsive blend monolithic hydrogel was synthesized using the chemical cross-linking of chitosan (CS) and hydroxypropyl cellulose (HPC), and further modified through freezing and thawing treatment to form the FCS/HPC hydrogel. The hydrogel analysis revealed that this modification created an interconnected macroporous network with a surface area of 75.31 m². g^-1, which is significantly greater than that of the unmodified CS/HPC hydrogel (2.18 m².g^-1) with smooth surface morphology and no apparent pores. Furthermore, the mixing speed during initial cross-linking markedly influences the morphological characteristics, pore architecture, and textural properties of the resulting hydrogel. The FCS/HPC hydrogel exhibits a lower critical solution temperature (LCST) of approximately 42 °C and reversible temperature-responsive swelling-deswelling properties. Adsorption studies showed high dye removal efficiency for both cationic (methylene blue) and anionic (reactive red 2) dyes below the LCST, whereas selective adsorption for anionic dyes was observed above this temperature. The adsorption behaviour of the FCS/HPC hydrogel was found to be best described by the pseudo-first-order kinetic model and the Freundlich isotherm, indicating multilayer adsorption on a heterogeneous surface through physical interactions. The hydrogel also demonstrated notable reusability after five adsorption-desorption cycles, highlighting its potential as a sustainable, thermo-responsive material for the selective separation of pollutants in industrial wastewater treatment.