Chitosan/kaolinite composite hydrogel with high mechanical strength for efficient and selective removal of copper...

To address the urgent need for Cu²⁺ pollution remediation in wastewater, this study developed an inorganic-organic composite hydrogel adsorbent (CKNH) through a three-dimensional assembly strategy, integrating abundantly available kaolinite nanosheets (KN) with low-cost natural chitosan. The CKNH-0.2 material, synthesized via energy-efficient free radical polymerization, demonstrated exceptional adsorption performance: a maximum Cu²⁺ adsorption capacity of 261.69 mg/g (pH = 5, 25 °C) and retained 72 % selective Cu²⁺ removal efficiency in the presence of coexisting Ni²⁺/Co²⁺/Zn²⁺/Mn²⁺ ions. Characterization analyses revealed that KN incorporation enhanced the hydrogel's thermal stability (18 % reduction in weight loss at 300 °C) and mechanical strength (tensile strain >300 %) through physical crosslinking, while its layered structure significantly increased specific surface area and active site density. Notably, the material maintains over 85 % adsorption efficiency even after five consecutive adsorption-desorption cycles, demonstrating excellent regeneration performance. XPS, FTIR, and density functional theory (DFT) calculations confirmed that Cu²⁺ preferentially formed strong coordination bonds with -NH₂/-OH/-COOH groups on the adsorbent, with adsorption further facilitated by electrostatic attraction and ion exchange. This triple synergistic mechanism ensures highly efficient and selective adsorption.