Revealing nanoscale sorption mechanisms of gases in a highly porous silica aerogel

J Appl Crystallogr. 2024 Aug 19;57(Pt 5):1311-1322. doi: 10.1107/S1600576724006794. eCollection 2024 Oct 1.

Abstract

Geological formations provide a promising environment for the long-term and short-term storage of gases, including carbon dioxide, hydrogen and hydro-carbons, controlled by the rock-specific small-scale pore structure. This study investigates the nanoscale structure and gas uptake in a highly porous silica aerogel (a synthetic proxy for natural rocks) using transmission electron microscopy, X-ray diffraction, and small-angle and ultra-small-angle neutron scattering with a tracer of deuterated methane (CD4) at pressures up to 1000 bar. The results show that the adsorption of CD4 in the porous silica matrix is scale dependent. The pore space of the silica aerogel is fully accessible to the invading gas, which quickly equilibrates with the external pressure and shows no condensation on the sub-nanometre scale. In the 2.5-50 nm pore size region a classical two-phase adsorption behaviour is observed. The structure of the aerogel returns to its original state after the CD4 pressure has been released.

Keywords: carbon dioxide sequestration; contrast-matched small-angle neutron scattering; gas uptake; methane adsorption; silica aerogels.

Grants and funding

This research is funded by grants from the Australian Research Council (ARC CE230100032, LE200100209 and DP200102517).