Development of Blended Thermosensitive <scp>NIPAM</scp> /Acrylic Acid and <scp>NIPAM</scp> /Chitosan Hydrogels for the Simultaneous Cation–Anion Adsorption

ABSTRACT Thermosensitive hydrogels based on N ‐isopropylacrylamide (NIPAM) copolymerized with acrylic acid (AA) and chitosan (Chi) were synthesized at 30°C and 50°C and evaluated for their structural, thermal, swelling, and adsorption properties. FTIR spectroscopy confirmed successful copolymerization, revealing temperature‐dependent changes in the intensity of functional groups. XRD analysis showed predominantly amorphous structures, with a slight increase in crystallinity at higher synthesis temperatures due to enhanced molecular ordering above the lower critical solution temperature. TGA revealed two main degradation stages for both blends, with a residual mass of ~4.72%. Hydrogels synthesized at 30°C exhibited higher equilibrium swelling, reaching a maximum swelling ratio of 5.8, due to a more expanded polymer network. SEM and BET analyses indicated a more porous structure and a higher specific surface area (27.83 m 2 g −1 ) at the lower synthesis temperature. CdCl 2 adsorption studies (100 mg L −1 ) showed rapid equilibrium within 4 h and a maximum removal efficiency of 91.90% at a low adsorbent dosage (0.2 g L −1 ). Maximum adsorption capacities were 13.25 mg g −1 for Cd 2+ and 17.41 mg g −1 for Cl − . Freundlich isotherm and Avrami kinetic models indicated heterogeneous adsorption involving combined physical and chemical interactions, highlighting the potential of this hydrogel for efficient heavy‐metal remediation.