Synthesis and characterization of Zn/Fe layered double hydroxide and its composites for copper adsorption from aqueous solution

Application of zinc-iron layered double hydroxide (ZnFe-LDH) and its composites with single-wall carbon nanotubes (LDH/CNT) and biochar derived from orange peel biomass (LDH/OPb) for batch adsorption of Cu2+ was extensively studied. The X-ray diffraction (XRD) patterns and energy-dispersive X-ray (EDX) analyses confirmed some chemical changes and successful adsorption of Cu2+. An equilibrium contact time of 60 min was adopted for the optimum removal of the Cu2+ using all the adsorbents. LDH/OPb demonstrated a greater affinity for the Cu2+ than LDH/CNT and ZnFe-LDH due to its large surface area. The adsorption capacity decreased with increasing removal efficiency as the adsorbents dose increased from 0.2 to 0.9 g. However, both the adsorption capacity and removal efficiency increased as pH increased from 2.0 to 5.0 with an optimum pH of approximately 6.0. The removal efficiency decreased with a higher increase in the sorption capacity of LDH/OPb than other adsorbents as the initial Cu2+ concentration increased from 10 to 100 mg L-1. The Langmuir model demonstrated a better estimation and a better fit to the adsorption data than the Freundlich and D-R isotherms. The pseudo-second-order kinetic model demonstrated the best fitting to the adsorption data compared with other kinetic models.