Interrogating the Carbon and Oxygen K-Edge NEXAFS of a CO2-Dosed Hyperbranched Aminosilica

Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, we shed light on the nature of the interaction between CO2 and the amine moieties in a hyperbranched aminosilica (HAS) material, a porous aminosilica composite with great potential for postcombustion carbon capture applications. We show that after dosing a pristine (annealed) HAS sample with CO2, the C K-edge NEXAFS spectrum presents a new π* resonance at 289.9 eV, which can be attributed to the formation of a C═O (carbonyl) bond. Additional analyses of the O K-edge using model samples containing carbamate, carbonate, and bicarbonate functional groups as reference demonstrate a carbamate bonding mechanism for the chemical adsorption of CO2 by the HAS material under the conditions employed. These findings show the capability of the C and O K-edge NEXAFS technique to identify CO2-adsorbate species despite the high concentration of C and O atoms inherently present in the sample (prior to CO2 dosing) and the significant similarities between the possible adsorbates.