Mg–Fe layered double hydroxides as multifunctional materials for manganese removal and methanol electrooxidation

Abstract

This study evaluated how well Mg–Fe layered double hydroxides (LDH) removed manganese (Mn²⁺) from aqueous media and electrocatalytic methanol oxidation. The structural and physicochemical properties of the materials both prior to and after the adsorption process were characterized by X-ray diffraction, infrared analysis, particle size analysis, and field emission scanning electron microscopy. Adsorption was evaluated at different pH levels and adsorbent dosages, revealing that surface hydroxyl groups and interlayer anions are crucial for manganese uptake. The equilibrium data were well fitted by the Langmuir–Freundlich isotherm model, whereas the kinetic results followed those of the mixed 1,2-order and intraparticle diffusion models, indicating that monolayer adsorption was dominated by chemisorption mechanisms. Thermodynamic parameters confirmed that the adsorption process is spontaneous and exothermic, suggesting strong interactions between Mn²⁺ ions and the LDH surface through surface complexation and chemical bonding. The Mg–Fe LDH achieved a manganese removal efficiency exceeding 70%, and q_max was 198.99 mg g⁻¹. Furthermore, electrochemical studies demonstrated that both pristine LDH and Mn-loaded LDH (LDH/Mn) exhibit enhanced electrocatalytic activity toward methanol oxidation. The improved LDH/Mn performance was attributed to a larger electroactive surface area and improved charge-transfer kinetics. These results highlight the dual functionality of Mg–Fe LDH for environmental remediation and electrochemical energy conversion applications.