Resource utilization of oak fruit peel as biomass waste for the synthesis of carbon with graphene oxide-like composition and its composite with Mg1−xCaxFe2O4 for Cd(ii) removal from water: characterization, magnetic properties, and potential adsorption study†

In this study, carbon with graphene oxide (GO)-like composition (C_GO) was prepared from oak fruit peel (OFP) using a room-temperature method. C_GO was decorated with sol–gel synthesized Mg_1−xCa_xFe₂O₄ (x = 0.2 (MCF2) and 0.8 (MCF8)) via a hydrothermal method to obtain C_GO/MCF nanocomposites. The samples were characterized using XRD, RS, FTIR, FESEM, EDX, TEM, BET, and VSM analysis. C_GO/MCF nanocomposites were assessed for their Cd²⁺ adsorption capacity from aqueous solutions via flame AAS. Factors such as contact time (1–60 min); nanocomposite dose (0.002–0.01 g); initial Cd²⁺ concentration (5–60 mg L⁻¹); and coexisting ions of Pb²⁺, Co²⁺, and Ni²⁺ (10 mg L⁻¹ each) at pH 7 were examined. The results indicated that the Cd²⁺ adsorption capacity of C_GO/MCF2 (357.5 mg g⁻¹) was higher (30%) than that of C_GO/MCF8 (250 mg g⁻¹) at a contact time of 1 h, nanocomposite dose of 0.002 g, and initial Cd²⁺ concentration of 60 mg L⁻¹. The Cd²⁺ adsorption capacity of C_GO/MCF nanocomposites was fitted with pseudo-second-order kinetics (R² > 0.99) and the Langmuir isotherm (R² > 0.99). The adsorption mechanisms involved pore filling, electrostatic attraction, surface complexation, ion exchange, and cation–π attraction. However, coexisting metal ions affected Cd²⁺ removal by C_GO/MCF2, reducing the efficiency by 33%. Using wastewater from a plating metal restoration workshop, it was demonstrated that the C_GO/MCF2 nanocomposite exhibits high removal efficiencies of 71% for Cd, 100% for Pb, 32% for Zn, and 28% for Fe. This study suggests that C_GO prepared from green biomass of OFP, in combination with MCF2, can be a promising adsorbent for removing metal contaminants from water and wastewater.