Molecular Modeling of the Adsorption-Induced Expansion of Graphene Oxide Frameworks

Adsorbent materials such as activated carbons (AC) have potential for gas storage or separation. ACs are often modeled as slit-shaped pores: parallel graphene-like sheets of very high surface area. In almost all adsorption analyses adsorbent is assumed structurally inert. It has been long known that liquids adsorption produces structural deformations. More recently gate opening transitions have been observed in Metal Organic Frameworks during subcritical adsorption of gases. The deformation arises from large solid-liquid interactions and depend on the nature of the adsorbent-adsorbate interaction, sometimes contracting or expanding. More recently, a monotonic increase ~4% in the d-spacing of benzene diboronic acid (DBA) Graphene Oxide Frameworks (GOF) was observed by in situ neutron diffraction during supercritical adsorption of various gases [1]. We present the results of molecular dynamics simulations based on ab initio models of GOFs. Our results suggest that a model of randomly oriented covalently bonded DBA linkers is consistent with experimental observations.

[1] Previous talk, and J. Schaeperkoetter, et al., Adsorption-Induced Expansion of Graphene Oxide Frameworks: Observation by in Situ Neutron Diffraction. ACS Omega (DOI: 10.1021/acsomega.9b02589).