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

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 m² g⁻¹) at the lower synthesis temperature. CdCl₂ 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 Cd²⁺ 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.