Hierarchical ternary ZnCoFe layered double hydroxide as efficient adsorbent and catalyst for methanol electrooxidation
E.E. Abdel‐Hady, Rehab Mahmoud, Sarah H.M. Hafez, Hamdy F. M. Mohamed
Abstract
Layered double hydroxide (LDH) was developed as a strong adsorbent material for the removal of organic dyes from wastewater. In this study, Zn–Co–Fe/LDH with a molar ratio of 2:2:1 was synthesized by the co-precipitation method. The characterization revealed a high degree of crystallinity as well as a lamellar structure. Additionally, Zn–Co–Fe/LDH was examined for wastewater treatment from cationic methylene blue (MB) under different adsorption parameters. When the initial concentration of MB was 100 mg/L, the adsorptivity reached 88.6% at pH 7 using 0.1 g of LDH. The pseudo-second-order kinetic model best described MB adsorption onto Zn–Co–Fe/LDH. The equilibrium adsorption data were obeyed by both the Langmuir and Freundlich models. The equilibrium parameter (RL) value for MB adsorption onto Zn–Co–Fe/LDH was calculated to be 0.571 indicating that the adsorption is favorable. The adsorption capacity of MB (58.26 mg/g) has been successfully obtained by Zn–Co–Fe/LDH from wastewater. Temperature experiments were conducted at 25, 35, 45, and 55 °C to investigate the thermodynamic parameters ΔH°, ΔS°, and ΔG°. The calculated values show exothermic and non-spontaneous adsorption processes. The results revealed that MB removal mechanisms involved physical and chemical adsorption. After calcining the waste material at different temperatures, Zn–Co–Fe/LDH/MB at 400 °C showed the highest pore radius (6.387 nm) and indicated the highest performance for methanol oxidation with a current density of 41.11 mA/cm2 at 50 mV/s and 3 M methanol. This study presented a novel method for employing LDH residue as a catalyst in direct methanol fuel cells (DMFCs).