Ultrasonic Method to Synthesize Glucan‑g‑poly(acrylic acid)/Sodium Lignosulfonate Hydrogels and Studies of Their Adsorption of Cu2+ from Aqueous Solution

In the paper, a green ultrasonic method was applied to prepare glucan-g-poly­(acrylic acid) (GL-g-PAA), sodium lignosulfonate-g-poly­(acrylic acid) (SLS-g-PAA), and glucan-g-poly­(acrylic acid) /sodium lignosulfonate (GL-g-PAA/SLS) hydrogels with the participation of initiator ammonium persulfate (APS) and cross-linker N′,N-methylenebis­(acrylamide) (NMBA), and these hydrogels were taken as absorbents to remove the Cu2+ ion from aqueous solutions. The structure, morphology, and stability of hydrogels were confirmed by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The various experimental conditions that influence the adsorption capacity were investigated such as temperature (25–50 °C), pH (1.0–6.0), adsorbent dosage (10–60 mg), foreign ions (300 mg·L–1), and contact time (0–180 min) as well as the initial concentration of the Cu2+ ion solution (100–600 mg·L–1). In addition, the experimental results indicated that the adsorption isotherms of the hydrogels for Cu2+ ions was in line with the Freundlich model, and the adsorption kinetics of the lyogels for Cu2+ ions were in good agreement with the pseudo-second-order model. The maximum adsorption capacities were 195.6, 188.5, and 221.4 mg·g–1 for GL-g-PAA, SLS-g-PAA, and GL-g-PAA/SLS, respectively. The thermodynamic parameters of Cu2+ ion adsorption onto preceding hydrogels were calculated. The positive ΔS° value reflected that adsorption is a process of entropy increase. The ΔG° was negative, revealing that the adsorption was a spontaneous process, and the ΔH° was positive value, suggesting that the adsorption was endothermic in nature.