Nanoconfinement of metal oxide MgO and ZnO in zeolitic imidazolate framework ZIF-8 for CO2 adsorption and regeneration

Abstract

Microporous materials exhibit fast CO2 adsorption rate with possible sacrificed capacity, while CO2 chemisorption on metal oxides is remarkable but kinetics and reactive area are critical. In order to adopt the advantages of both microporous sorbent zeolitic imidazolate framework (ZIF) and metal oxide (MO), in this research, magnesium oxide (MgO) and zinc oxide (ZnO) were doped to ZIF-8 (MO@ZIF) using infiltration and calcination processes. The powder X-ray diffraction patterns showed retained ZIF-8 integrity after MO addition. Broad MgO peaks implied well-dispersed nanoparticles, while sharp ZnO diffractions indicated oxide agglomeration, supported by the field emission transmission electron microscope images. ZIF pore size was expanded due to confined MgO without sacrificing the framework porosity. Because of nanoconfinement, the MgO@ZIF-8 room temperature CO2 adsorption, as well as the adsorption rate constant in pseudo-second order model, were two-fold higher than expectation. In addition, the decarbonation temperature in MgO@ZIF-8 was reduced by 40 degrees. In general, it was found that metal oxide nanoconfinement in microporous zeolitic imidazolate frameworks performed improved CO2 uptake, facilitated adsorption kinetics at ambient temperature, and lowered regeneration temperature to release CO2.