Controllable preparation of porous Ca-Mg-Al hydroxides based adsorbents and their CO2 adsorption performances

Abstract

A series of porous Ca-Mg-Al hydroxides based adsorbents of layered structure were successfully prepared with CaCl2, MgCl2·6H2O and AlCl3·6H2O as the precursors and urea as the precipitant through a hydrothermal method and subsequent KOH alkaline etching treatment, in order to investigate the effects of molar ratio of Mg/Ca, addition amount of graphene oxide and alkaline etching time of KOH solution on the CO2 uptake performance of the resulting adsorbents. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), and scanning electron microscope (SEM), respectively, and the results showed that the Ca-Mg-Al hydroxides-derived adsorbents presented a hexagonal and layered structure, which conformed to the structure of hydrotalcite-like compounds. CO2 adsorption properties of the adsorbents were measured using a thermogravimetric analyzer, and the adsorption data of the samples were fitted by the first-order kinetic model, pseudo-second-order kinetic model and Elovich model, respectively. Taking advantage of the amphoteric nature of Al species, the adsorbent LTH/GO-12 displayed the favorable uptake performance of 20.04 mg/g and cyclic stability with the retention rate of 93.4% over five cycles. The improving capture performance of LTH/GO-12 was mainly contributed by the development of pore structure and the increase of adsorption active sites because of the removal of Al species by alkaline etching and the adding of graphene oxide.