The effect of grafting a hydrogel with an activated biochar/Fe₃O₄ nanocomposite derived from rice straw

This study used the co-precipitation method to graft activated biochar derived from rice straw with Fe₃O₄ nanocomposite at different doses of acrylic acid (AAc) and acrylamide (AAm) by using ⁶⁰Co gamma irradiation of 15 kGy. The copolymer hydrogel adsorbents (RS4-RS5-RS6) were prepared and characterized, and X-ray diffractions (XRD), scanning electron microscope (SEM) and (EDX), transmittance electron microscope (TEM), BET, Zeta potential, and particle size distribution (PSD). The maximum grafting efficiency for RS6 (89.48%) was achieved at 25 °C, while grafting efficiency for RS4 and RS5 was 75.6% and 80.69%, respectively. The maximum swelling percentage recorded for RS4, RS5, and RS6 were 3215%, 2375%, and 1610% at 60 °C and pH 9, respectively. The maximum adsorption capacity (qmax) of RS4, RS5, and RS6 was calculated to be 218.76, 215.33, and 364.22 mg/g, respectively with a contact time of 480 min, a temperature of 25 °C, an adsorbent dose of 100 mg, a pH of 7, a concentration of the dye solution of 100 ppm, and a volume of dye solution of 50 mL. The experimental data was fitted to nonlinear pseudo-second order (PSO). The equilibrium adsorption data fitted well to both Freundlich and Langmuir models. The thermodynamic properties, including entropy (ΔS), enthalpy (ΔH), and free energy (ΔG), were determined.