Preparation of N-Enriched GO Adsorbents and Their Properties for Selective CO₂ Capture

In this work, GO adsorbents were fabricated based on the Hummers’ procedure and further chemically modified with 3-aminopropyl-triethoxysilane (APTS) as primary amino-silane, piperazine (PIP) as a secondary cyclic diamine, and ethanolamine (EA) as primary amine to enhance their CO₂ adsorption/separation properties. The adsorption characteristics of the amine-functionalized adsorbents were assessed at different temperatures and pressures. It was found that the aforementioned functionalities highly influence the physical–chemical and textural properties of the prepared adsorbents. The experimental isotherm data were analyzed by the Sips isotherm equation to describe the CO₂ adsorption isotherm. GO/APTS exhibited the maximum CO₂ adsorption capacity of 43.114 mmol/g, based on the Sips isotherm model at 298 K. Accordingly, GO/APTS showed ideal adsorbed solution theory selectivity (CO₂/N₂) of 33.7. The adsorption mechanism of GO and amine-modified GO adsorbents can be described a physico-chemical adsorption, driven by the cooperation between nitrogen functional groups and the filling of micropores. It was found that the CO₂ adsorption capacity for GO/APTS was 2.3 times higher than the sorption capacity for unmodified GO, confirming the contributions of electron-donor amine and methyl groups, the high molecular weight of APTS, and the high surface area of GO/APTS in enhancing CO₂ adsorption capacity.