Efficient methylene blue elimination from water media by nanocomposite adsorbent-based carboxymethyl cellulose-grafted poly(acrylamide)/magnetic biochar decorated with ZIF-67

A free radical polymerization approach was applied to synthesize different carboxymethyl cellulose-grafted poly(acrylamide) hydrogels (Hyd) composited with biochar, magnetic biochar, and magnetic biochar decorated with ZIF-67 to decontaminate methylene blue (MB) from water media. Biochar was obtained from walnut shells (WS) by a pyrolysis method, and magnetic biochar (WS/CoFe₂O₄) and biochar-decorated ZIF-67 (WS/CoFe₂O₄/ZIF-67) were prepared by chemical co-precipitation and hydrothermal methods, respectively. An increase in the amount of these particles by up to 10 wt% enhanced the removal performance. The maximum removal performance by Hyd, Hyd/WS, Hyd/WS/CoFe₂O₄, and Hyd/WS/CoFe₂O₄/ZIF-67 was computed to be 85.74%, 91.74%, 95.83%, and 97.72%, respectively, at optimum conditions of pH = 10, adsorbent dose = 1 g L⁻¹, contact time = 50 min, initial concentration = 10 mg L⁻¹, and temperature = 25 °C. Pseudo-second-order kinetic and the Freundlich isotherm models had the highest desirability in the kinetic and equilibrium data regression, respectively. The thermodynamic study showed the spontaneity and exothermic nature of the MB decontamination process. Ultimately, the synthesized adsorbents, specifically Hyd/WS/CoFe₂O₄/ZIF-67, could be used for wastewater treatment.