Development and Characterization of Carboxyl‐Functionalized Chitosan Hydrogels: Integrating Maleic Anhydride and Acrylic/Itaconic Acid Grafting With <scp>PVP</scp> and <scp>PVA</scp> for Enhanced Dye Adsorption

ABSTRACT This study reports the synthesis and characterization of two novel porous chitosan‐based hydrogels with carboxyl functionalization, aimed at efficient cationic dye removal from aqueous solutions. BET and Nano‐measurer analysis revealed that CMAP@PVA exhibited a higher micropore proportion and larger pore size, while thermogravimetric analysis demonstrated excellent thermal stability for both hydrogels. Adsorption experiments showed that CMAP@PVA achieved maximum removal efficiencies of 97.62% for methylene blue (MB), 96.67% for malachite green (MG), 98.12% for crystal violet (CV), and 99.32% for basic fuchsin (BF). Correspondingly, CMIP@PVA achieved 98.74%, 95.49%, 95.55%, and 98.42% for these dyes. Zeta potential and adsorption data indicate preferential removal of cationic dyes via electrostatic interactions, with additional contributions from hydrogen bonding and n –π interactions. Even in the presence of interfering ions, the hydrogels maintained strong adsorption for CV and BF, indicating good ion tolerance. Kinetic and isotherm studies revealed that the adsorption process followed the pseudo‐second‐order model and conformed well to the Langmuir isotherm, suggesting chemisorption and monolayer adsorption behavior. Notably, both hydrogels retained &gt; 80% adsorption capacity after 5 cycles. This carboxyl‐functionalized hydrogel strategy offers a sustainable, efficient platform for treating dye‐laden wastewater.