Solid State NMR for Mechanistic Exploration of CO₂ Adsorption on Amine-Based Silica Adsorbents

Mitigating atmospheric carbon dioxide concentrations is crucial because elevated CO₂ levels drive climate change by enhancing the greenhouse effect, leading to global warming, extreme weather events, ocean acidification, loss of biodiversity, and significant socioeconomic and health challenges for ecosystems and human populations. The necessity to reduce atmospheric carbon dioxide levels has led to the creation of novel materials designed to effectively capture and convert CO₂ using carbon capture and utilization methods. A diverse array of materials such as metal-organic frameworks, covalent organic frameworks, porous carbon, zeolites, and amine functionalized silica has been reported for efficient carbon dioxide capture. Notably, amine-functionalized silica has emerged as one of the most extensively studied materials in the field of carbon dioxide capture. Solid-state NMR is a powerful spectroscopic technique for analyzing amine-based silica adsorbents, as it provides detailed, nondestructive molecular insights into structure, interactions, and adsorption mechanisms that are challenging to resolve using traditional techniques like infrared spectroscopy and BET (Brunauer-Emmett-Teller). Solid-state NMR, particularly magic angle spinning (MAS) NMR, demonstrates significant potential in providing high-resolution insights into atomic-level interactions and dynamics. This minireview will explore how solid-state NMR spectroscopy and its advancements are effective in investigating the amine immobilization and stabilization mechanism on silica, probing the local structures of CO₂ adsorption species, and assessing the influence of varying conditions on the performance of adsorbents. The information obtained through the application of various solid-state NMR experiments is emphasized, along with strategies for further enhancing this knowledge.