Crystal engineering of hybrid ultramicroporous materials for study of direct air capture of carbon dioxide

Global atmospheric CO2 levels are currently 409 ppm, an increase of 130 ppm since the pre-industrial era. Efficient mitigation strategies combined with advanced carbon capture technologies are required to address this global threat. Direct air capture (DAC) offers an attractive proposition that would facilitate onsite technologies that use CO2 as a feedstock, eliminating the need for storage and transportation. Currently, CO2 scrubbers based on aqueous alkanolamine solutions and amine grafted mesoporous materials are being used for DAC, but they suffer from high regeneration energy. CO2 selective physisorbents have the potential to reduce energy costs of DAC but have until recently not exhibited appropriate selectivity and hydrolytic stability. Crystal engineering, defined as “the field of chemistry that studies the design, properties and application of crystals” has recently enabled the design of a new generation of physisorbents with the pore size and pore chemistry suited for DAC. Specifically, hybrid ultramicroporous materials (HUMs) with inorganic anion pillars that offer strong electrostatics and tight binding sites for CO2 can offer precise control over pore size/chemistry to afford order of magnitude improvement in the carbon capture performance of physisorbents. A pyrazine based HUM, (Zn(pyrazine)2SiF6)n, SIFSIX-3-Zn, reported in 2013 was found to exhibit a new benchmark for CO2/N2 selectivity (> 1800). The primary objective of this study is to prepare and characterise a platform of related HUMs by systematically varying the metal node or the inorganic pillar in order to develop HUMs with the following characteristics: a) high thermal and hydrolytic stability, b) better DAC performance and c) cost-effective synthesis (high yield/low waste). A secondary objective is to gain insight into the reasons for the exceptional carbon capture performance of HUMs.