Carbon quantum dots/layered double hydroxide hybrid for fast and efficient decontamination of Cd(II): The adsorption kinetics and isotherms

Novel carbon quantum dots/zinc aluminum layered double hydroxide (CQD/ZnAl-LDH) composite was prepared through the precipitation of metal nitrates in the presence of CQD by a facile and simple method and further applied to remove excessive Cd(II) ions from water. The chemical composition and morphology of the CQDs/ZnAl-LDH hybrid was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and Energy-dispersive X-ray spectroscopy. Batch studies were done to evaluate the effects of the adsorption of Cd(II) by CQDs/ZnAl-LDH to optimize the major parameters such as pH, contact time, and initial concentration. The maximum uptake capacity of Cd(II) on CQDs/ZnAl-LDH was only 12.60 mg/g at 20 min due to the available exterior sites on the adsorbent. The adsorption kinetics and isotherms of Cd(II) on CQDs/ZnAl-LDH were also investigated. The experimental data indicated that the adsorption kinetics and adsorption isotherms of Cd(II) on CQDs/ZnAl-LDH were well-fitted by the pseudo-second-order kinetic model and the Freundlich isotherm model, respectively. (C) 2017 Elsevier B.V. All rights reserved.