Preparation of citric acid-modified β-cyclodextrin/poly (acrylic acid-co- acrylamide) composite hydrogel for enhanced methylene blue adsorption

Water pollution poses a severe threat to human health and ecological systems, thereby demanding high-performance adsorbents for wastewater treatment. Herein, a novel composite hydrogel (CA-β-CD/P(AA-co-AM)) was synthesized via radical polymerization using citric acid-modified β-CD (CA-β-CD). Citric acid modification introduced functional sites, tuned cavity structure, and linked β-CD units into oligomer, overcoming native β-CD’s limitations to serve as an ideal hydrogel component. The incorporation of CA-β-CD into P(AA-co-AM) formed a porous network, enabled synergistic interactions, enhanced stability, and integrated CA-β-CD’s adsorption superiority with the polymer’s robust matrix. The structure and properties of the composite hydrogel were characterized by FT-IR, ¹ H NMR, SEM, TGA, GPC, and XPS. It showed outstanding methylene blue (MB) adsorption via host–guest inclusion, hydrogen bonding, and electrostatic interactions, with a maximum capacity of 3743.23 mg/g. Adsorption followed pseudo-second-order kinetics and Langmuir isotherm, with rate controlled by intra-particle and liquid film diffusion. Importantly, the composite hydrogel maintained excellent reusability — after 10 consecutive adsorption–desorption cycles, the MB removal rate (R) remained above 92%. This work provides a promising strategy for cyclodextrin-derived adsorbents in dye wastewater treatment.