A novel hydrogel for highly efficient adsorption of Cu(II): synthesis, characterization, and mechanisms

Synthesis and Characterization of Novel Magnetic Nano-Biocomposite Hydrogels Based on Starch-g-poly(acrylic acid) Reinforced by Cellulose Nanofibers for Cu2+ Ion Removal

One of the crucial challenges of the adsorption process is to recapture the adsorbent from the solution, especially for adsorbents in powder form. This study synthesized a novel magnetic nano-biocomposite hydrogel adsorbent to successfully remove Cu²⁺ ions, followed by convenient recovery and reusability of the adsorbent. The Cu²⁺ adsorption capacity of starch-g-poly(acrylic acid)/cellulose nanofibers (St-g-PAA/CNFs) composite hydrogel and magnetic composite hydrogel (M-St-g-PAA/CNFs) was investigated and compared in both bulk and powder forms. Results showed that Cu²⁺ removal kinetics and swelling rate were improved by grinding the bulk hydrogel into powder form. The kinetic data and adsorption isotherm were best correlated with the pseudo-second-order and Langmuir models, respectively. The maximum monolayer adsorption capacity values of M-St-g-PAA/CNFs hydrogels loaded with 2 and 8 wt % Fe₃O₄ nanoparticles in 600 mg/L Cu²⁺ solution were found to be 333.33 and 555.56 mg/g, respectively, compared to 322.58 mg/g for the St-g-PAA/CNFs hydrogel. Vibrating sample magnetometry (VSM) results demonstrate that the magnetic hydrogel that included 2 and 8 wt % magnetic nanoparticles exhibited paramagnetic behavior with the magnetization of 0.6-0.66 and 1-1.04 emu/g at the plateau, respectively, which showed a proper magnetic property and good magnetic attraction in the magnetic field for separating the adsorbent from the solution. Also, the synthesized compounds were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and Fourier transform infrared spectroscopy (FTIR). Finally, the magnetic bioadsorbent was successfully regenerated and reused for four treatment cycles.