Hierarchical ternary ZnCoFe layered double hydroxide as efficient adsorbent and catalyst for methanol electrooxidation

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).

Keywords

• Layered double hydroxide
• Methylene blue
• Adsorption
• Zn–Co–Fe
• Adsorbent material
• Non-expensive catalyst