High performance nanohybrid ZnO-α-FeOOH nanocomposite prepared for toxic metal ions removal from wastewater: Combined sorption and desorption studies

Abstract

ZnO-α-FeOOH Nanohybrid (NH) was synthesized from zinc nitrate hexahydrate and hydrothermally synthesized α-FeOOH nanoparticles. X-ray diffraction (XRD) confirmed the composition, while Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) methods were used to determine the functional groups, morphology, crystallinity and particle sizes of the synthesized mineral respectively. The results showed crystalline material in spherical shape with some rod-like structures embedded in the structures. The average sizes was determined from DLS as 41.11 nm. The NH was used in batch mode at different experimental conditions, and optimum adsorption capacity of Cd(II) and Pb(II) onto the NH were 279.2 mg/g and 538.9. mg/g at pH 6 in 180 min at 318 K. The Langmuir isotherm and pseudo-second-order models fitted well for the adsorption process. The negative values of ΔG◦ indicated spontaneity of the adsorption process, while the positive values of ΔH (+12.48 and +15.85 kJ/mol) and ΔS (+0.418 and +0.536 kJ/mol/K) for Cd(II) and Pb(II) respectively, revealed endothermic and randomness of the adsorption process. The activation energy, Ea, were found to be +7.982 and +4.771 kJ/mol for adsorption of Cd(II) and Pb(II) respectively, which showed that adsorption onto ZnO-α-FeOOH NH were physical process (Ea < +40 kJ/mol). The adsorption–desorption studies revealed that the adsorption efficiency of ZnO-α-FeOOH NH in the third cycles were 90.18 % and 93.87 % Cd(II) and Pb(II) respectively. These suggest that the adsorbent could be reused in up to three cycles without remarkable losses in its adsorption capacity.