CO2 Adsorption by Amino-Functionalized Graphene–Silica Gels

Abstract

This work evaluates the CO2-adsorption relevance and cycling stability of graphene oxide–silica (GO-SiO2) and reduced graphene oxide–silica (rGO-SiO2) gels after amine functionalization, demonstrating high-capacity retention under repeated adsorption–desorption cycles: rGO-SiO2-APTMS retains ≈96.3% of its initial uptake after 50 cycles, while GO-SiO2-APTMS retains ≈90.0%. The use of surfactants to control the organization of inorganic and organic molecules has enabled the development of ordered mesostructures, such as mesoporous silica and organic/inorganic nanocomposites. Owing to the outstanding properties of graphene and its derivatives, synthesizing mesostructures intercalated between graphene sheets offers nanocomposites with novel morphologies and enhanced functionalities. In this study, GO-SiO2 and rGO-SiO2 gels were synthesized and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), mass spectrometry (MS), N2 adsorption–desorption isotherms, and transmission electron microscopy (TEM). The resulting materials exhibit a laminar architecture, with mesoporous silica domains grown between graphene-based layers; the silica contents are 83.6% and 87.6%, and the specific surface areas reach 446 and 710 m2·g−1, respectively. The laminar architecture is retained regardless of the surfactant-removal route; however, in GO-SiO2 obtained by solvent extraction, a fraction of the surfactant remains partially trapped. Together with their high surface area, hierarchical porosity, and amenability to surface functionalization, these features establish amine-grafted graphene–silica gels, particularly rGO-SiO2-APTMS, as promising CO2-capture adsorbents.