(30e) Hierarchically-Structured Porous Materials for Enhanced Greenhouse Gas Capture

Owing to global concern on climate change, the technologies for capturing greenhouse gases such as CO₂, SF₆ and chlorofluorocarbons from anthropogenic sources have attracted a great amount of interests. In this work, a series of hierarchical LTA zeolites possessing various mesopore spaces that are decorated with alkylamines was designed and synthesized for an enhanced CO₂ adsorption. The highest CO₂ uptake capacity was observed when (3-aminopropyl)trimethoxysilane (APTMS) was grafted onto the hierarchical LTA zeolite having the largest mesopores. Owing to the contributions of both alkylamine groups grafted on the mesopore surfaces and active sites in zeolites LTA, the amount of CO₂ uptake on such material was observed to be much higher than those for conventional aminosilicas such SBA-15 and MCM-41. Furthermore, the adsorbent showed good CO₂ uptake capacity and recyclability under a dynamic flow condition.

Meanwhile, HKUST-1, an inexpensive metal-organic framework possessing open metal sites, has a great potential for capture and recovery of SF₆. In this work, the structural property of HKUST-1 was modified to yield a hierarchically-structured HKUST-1 nanocrystal exhibiting a superior performance with higher SF₆ uptake, better SF₆/N₂ selectivity, faster SF₆ adsorpton kinetics and lower energy penalty for regeneration than bulk HKUST-1 crystal as well as conventional zeolite and porous carbon adsorbents. Higher surface area and the presence of mesoporosity to facilitate the transport of SF₆ to active sites residing in microporous spaces were found to be key factors contributing to such enhancement. An outstanding potential utility of our HKUST-1 crystal in industrial applications was also validated with an idealized vacuum swing adsorption model.