Adsorptive Removal of Congo Red Using Organically Modified Zinc–Copper–Nickel Ternary Metal Hydroxide: Kinetics, Isotherms and Adsorption Studies

Abstract

In the current study synthesis of composite material consisting of ethylene glycol (EG) functionalized Zinc-Copper-Nickel (Zn–Cu–Ni) ternary metal hydroxide was successfully carried out and was characterized using various techniques. The formation of layered structure was confirmed using Powder X-Ray Diffraction (PXRD), Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) while thermal stability was assessed using Thermogravimetric Analysis (TGA). The presence of metal ions and their respective oxidation states was confirmed using Energy Dispersive X-Ray Analysis (EDX), elemental mapping, and X-Ray Photoelectron Spectroscopy (XPS). Pore size of the synthesized material, estimated using Brunauer–Emmett–Teller (BET) analysis technique, was found to be 15.08 nm g⁻¹. The synthesized material was subsequently utilized for the sequestration of toxic Congo red (CR) dye from untreated water. Investigation of controlling parameters i.e. concentration, contact time and pH was undertaken to see their influence on the adsorption performance. The maximum dye removal efficacy of the adsorbent was observed at pH 7, suggesting good buffering ability of EG functionalized Zn–Cu–Ni composite material. The experimental data for equilibrium studies was favoured by the Langmuir model, suggesting monolayer adsorption while the kinetic study was best-correlated with the model of pseudo-second order. The capacity of synthesized material for dye uptake was ascertained to be 127.71 mg g⁻¹ along with the good reutilization capacity even after five consecutive cycles. These results demonstrate that EG functionalized Zn–Cu–Ni ternary metal hydroxide may be effectively used as an adsorbent for the separation of dye effluents from aqueous medium.