Pb(II) and Co(II) Decontamination in Aqueous Systems by Magnesium-Enriched Bismuth Ferrite and Its Hybrid Materials

A novel magnesium-incorporated bismuth ferrite along with its composites, including bentonite and activated carbon hybrids, were synthesized via a self-ignition technique where glycine acted as a combustion agent. The efficiency of these materials to eliminate Pb(II) and Co(II) species in polluted water was comprehensively evaluated. Characterizations were performed through BET surface area measurement, SEM observation, FTIR analysis, and XRD examination. FTIR spectra confirmed the presence of metal–oxygen bond vibrations in the 400–1000 cm⁻¹ region, highlighting an Fe–O stretching mode near 419 cm⁻¹, Mg–O bands between 469 and 548.18 cm⁻¹, and Bi–O vibrations ranging from 673 to 730.28 cm⁻¹ for the ferrite and its composites. SEM micrographs revealed irregular, porous morphologies featuring surface microcavities that favor heavy metal diffusion. BET results indicated mesoporous structures with specific surface areas of 23.694 m²/g, 25.0 m²/g, and 20.289 m²/g for the ferrite, ferrite/bentonite, and ferrite/activated carbon composites, respectively. Pore diameters varied between 4.94 and 15.5 nm, with pore capacities ranging from 0.029 to 0.0456 cm³/g, underscoring their promising capacity for heavy metal adsorption. Co²⁺ ions required a longer time to reach equilibrium (up to 180 minutes) compared to Pb²⁺ ions (120 minutes), suggesting faster interaction or diffusion of lead ions onto the adsorbents. Kinetic experiments demonstrated that adsorption obeyed a second-order kinetic equation, indicating a rate-controlling step primarily determined by the abundance of available active centers and by the concentration of metallic cations on the sorbent interface, rather than by simple transport of ions. The sorption behavior was assessed using Langmuir and Freundlich models, showing that findings from both models were consistent with each other: the Langmuir approach highlighted single-layer adsorption over a uniform interface, whereas the Freundlich approach revealed increasing heterogeneity of adsorption sites, particularly in the composites, explaining their superior performance relative to the pure ferrite. The highest metal ion removal capacities reached 181.8 mg/g (Pb) and 166.666 mg/g (Co) using the ferrite, 191.975 mg/g (Pb) and 188.643 mg/g (Co) with the ferrite/bentonite composite, and 195.198 mg/g (Pb) and 190.839 mg/g (Co) when employing the ferrite/activated carbon composite. According to thermodynamic findings, metal ion capture was spontaneous and exothermic. Low isosteric heat values indicated a physisorption-dominated mechanism with weak adsorbate–adsorbent interactions. The research reported herein supports the progress of sustainable chemistry and development in Africa by providing novel approaches to address environmental pollution and resource management challenges.