Carboxymethyl Cellulose-Based Composite Polymer Hydrogels Cross-Linked with Epichlorohydrin and Application for Cu(II) Removal

In this work, CMC-ECH/PAM hydrogels with perfect compressive strength were prepared by epichlorohydrin (ECH) cross-linking sodium carboxymethyl cellulose (CMC) grafted with polyacrylamide (PAM) to remove the copper ion (Cu2+) from water. The chemical and structural morphology of the product was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. The compressive strength was measured by successive compression–decompression cycles and up to 70 kPa. Adsorption was studied at different pH values 1–5, adsorbent doses (0.2–8) g/L, and initial Cu2+ concentrations from (50 to 400) mg/L to obtain the optimum conditions for maximum removal of Cu2+. The experimental adsorption data were well fitted by the pseudo-second-order kinetics model, Langmuir isotherm model, and Freundlich isotherm model. The maximum adsorption capacity calculated by the Langmuir model was 75.930 mg/g at 338.15 K. In addition, the negative ΔG° and positive ΔH° also indicated that the adsorption of Cu2+ is a spontaneous, endothermic, and chemical process. The adsorption mechanism was further verified by X-ray photoelectron spectroscopy analysis. CMC-ECH/PAM hydrogels also exhibited excellent reusability after five adsorption–desorption cycles, maintaining about 80% Cu2+ removal efficiency.