TiO2-embedded κ-carrageenan-based copolymer hydrogel: synthesis, characterization and pH-responsive dye adsorption applications

Abstract

This study presents the synthesis and characterization of a novel pH-responsive hydrogel nanocomposite based on κ-carrageenan-g-poly(crotonic acid-co-sodium 4-vinylbenzenesulfonate) [κC-g-(CA-co-VBS)] reinforced with TiO₂ nanoparticles. κ-Carrageenan, a hydrophilic and biodegradable polysaccharide, was chemically modified through graft copolymerization with CA and VBS monomers, using potassium persulfate (KPS) as the initiator and N,N′-methylene bisacrylamide (MBA) as the crosslinker. The incorporation of TiO₂ enhanced the hydrogel’s swelling capacity (up to 3700%) and pH sensitivity. Structural and morphological analyses (FTIR, XRD, FE-SEM/EDX, HRTEM, BET) confirmed successful grafting and TiO₂ integration. The nanocomposite was evaluated as an adsorbent for Orange G dye, achieving a maximum adsorption efficiency of 677.4 mg/g and removal efficiency of 90.3% under optimal conditions (pH 7, 600 mg/L, 60 min). Adsorption followed the Freundlich isotherm model and pseudo-second-order kinetics, indicating multilayer chemisorption. Thermodynamic parameters suggested that the adsorption of OG dye onto the hydrogel composite was spontaneous (ΔG < 0), and endothermic (ΔH > 0). The hydrogel retained 82.7% efficiency after six regeneration cycles, demonstrating excellent stability and reusability. The novelty of this work lies in the incorporation of TiO₂ nanoparticles into a κ-carrageenan-based hydrogel matrix, which significantly enhances swelling capacity, adsorption efficiency, and reusability compared to conventional hydrogels, thereby offering an innovative and sustainable approach for dye-contaminated wastewater treatment.

Graphical abstract