CO₂ adsorption behavior of amine-functionalized ZIF-8, graphene oxide, and ZIF-8/graphene oxide composites under dry and wet conditions

Development and optimization of solid adsorbents is highly sought after toward establishment of energy-efficient and high-throughput CO₂ capture processes in industry. Herein, graphene oxide (GO), zeolitic imidazolate framework ZIF-8, and composite ZIF-8/GO adsorbents were developed and further functionalized using various amine functionalities, namely, 3-aminopropyl-triethoxysilane (APTES), polyethyleneimine (PEI), and ethylene diamine (ED). Following structural and morphological evaluation, the resulting adsorbents were tested and compared for CO₂ adsorption capacity and kinetics, while their performance under the presence of pre-adsorbed water was evaluated as well. GO functionalization by APTES resulted in a 36% increase in adsorption capacity at 1 bar and 30 °C compared to unmodified GO, and a further 33% increase under the presence of pre-adsorbed water (10% RH) compared to the corresponding APTES-GO capacity under dry conditions. Amine functionalization of ZIF-8 resulted in a capacity increase of up to 43% at 1 bar compared to unmodified ZIF-8, while ZIF-8/GO post-functionalization in water enhanced the capacity of this type of composite adsorbent compared to non-functionalized ZIF-8/GO and the pure ZIF-8 particularly at lower pressures. The reported results can be valuable towards devising optimum paths of functionalization and performance enhancement of these types of adsorbents that can pave the way toward design of highly efficient materials and processes for the current and future CO₂ capture needs.