Functionalized biochar-supported magnetic MnFe2O4 nanocomposite for the removal of Pb(ii) and Cd(ii)

In this study, a novel magnetic biochar-MnFe2O4 nanocomposite (BC/FM) was prepared using low-cost corn straw and MnFe2O4 by sol-gel/pyrolyzing route using egg white, which has abundant functional groups (-NH2 and -COOH). Following that, its composition, morphology and structure was characterized by various techniques including SEM-EDX, BET, XRD, and VSM. Batch experiment of the adsorption for Pb(ii) and Cd(ii) including influence of pH, kinetics, isotherm and thermodynamics was also studied. The results demonstrated that biochar could effectively support MnFe2O4, which displayed high dispersion on the surface of the biochar and possessed abundant functional groups and high surface area contributing to superior performance on Pb(ii) and Cd(ii) removal. Therein, MnFe2O4 with high magnetism is convenient for separating the magnetic BC/FM from an aqueous medium. Adsorption experiment results indicate that Pb(ii) and Cd(ii) removal by BC/FM was closely related to pH with the best value of pH 5.0, and the process reached equilibrium in 2 h. The adsorption process is well-described by the pseudo-second-order kinetic model and Sips (Freundlich-Langmuir) model. Thermodynamic studies suggest that the adsorption process is spontaneous and exothermic. The maximum experimental adsorption capacity of BC/FM is 154.94 and 127.83 mg g-1 for Pb(ii) and Cd(ii), respectively, in single-solute system, which is higher than that of some of the other adsorbents of biochar or biochar-based composites. In bi-solute system, the preferential adsorption order of BC/FM for the two metals is Pb(ii) prior to Cd(ii). Finally, FTIR and XPS analysis verified that the main mechanism of Pb(ii) and Cd(ii) removal by BC/FM is by forming Pb/Cd-O or complexation of carboxyl and hydroxyl and ion exchange. Therefore, the prepared magnetic BC/FM composite, as an excellent adsorbent, exhibited potential applications for the removal of Pb(ii) and Cd(ii) from wastewater.