Hexagonal Mesoporous Silica for carbon capture: Unrevealing CO2 microscopic dynamics by Nuclear Magnetic Resonance

Global warming and environmental concerns have triggered global efforts to reduce anthropogenic carbon emission. Against this background, mesoporous silica materials have experienced a great expansion in the latest years due to their interesting carbon capture properties. Despite the very vast literature currently available in synthetic strategies and adsorption behaviour of MSs, the internal arrangement and diffusion properties of carbon dioxide (CO2) inside silica mesopores, to date, have been barely clarified. Here, mesoporous silica material with hexagonal framework (MCM-41) has been synthesized by a modified Srober process, and its CO2 capture properties were assessed yielding a maximum amount of CO2 adsorbed of 18 wt% at 15 bar and RT. Fort the first time, microscopic distribution of CO2 and its mobility in the MCM-41 mesopores have been investigated by C-13 NMR techniques. Peak fitting analysis of the C-13 NMR spectra and T-1-relaxometry data revealed a multiple component configuration for CO2 adsorbed in the silica mesopores with at least two physisorbed species coexisting. C-13 PFG NMR self-diffusion study showed anisotropic long-range mobility for carbon dioxide adsorbed in MCM-41. The fastest self-diffusion coefficient, ascribed CO2 molecules diffusing parallel to the axis of the MCM-41 channels, was in the order of 10(-5) cm(2) s(-1), i.e., two order of magnitude higher that of gas diffusing perpendicular to the mesopore. This study is crucial to properly address the future design and preparation of mesoporous silica materials with improved CO2 capture performances.

Automated summary

Global warming and environmental concerns have led to global efforts to reduce anthropogenic carbon emissions, leading to a focus on mesoporous silica materials for their carbon capture properties. A recent study investigated the internal arrangement and diffusion properties of CO2 in silica mesopores, revealing multiple physisorbed species coexisting. Through C-13 NMR and C-13 PFG NMR analysis, it was found that CO2 in mesopores exhibited anisotropic long-range mobility with different diffusion coefficients depending on direction.