Ph. D defense – Sajjad Ghojavand – Synthesis of nano sized chabazite zeolite for CO2 capture

Chabazite (CHA) type zeolite is one of the most promising zeolitic frameworks for CO2 capture and separation due to its large cages and high microscopic flexibility. In this thesis we showed that CHA particle sizes can be tuned by altering the incubation time during the synthesis using inorganic cations (Na+, K+, and Cs+) as structure directing agent. Cs+ cations are necessary to stabilize CHA structure. By combining GCMC modeling, adsorption and FTIR spectroscopy it was illustrated that different alkali forms of nanosized CHA are of great potential for CO2 capture and separation due to high CO2 capacities (up to 4.5 mmol g-1). Furthermore, by using FTIR and high resolution 1H MAS NMR spectroscopy combined with DFT calculations it was shown that silanol sites (defect sites) of nanosized CHA crystals depend on the Cs+ content. Increasing the Cs+ population can heal the CHA defects up to 26 %. We also observed a linear correlation between concentration of silanol sites and the CO2 adsorption capacities in different alkali forms of nanosized CHA. Afterwards and by developing a new post-synthetic concurrent dealumination and silylation method, Si/Al ratio of nanosized CHA was tuned from 2.0 to 4.0. During preparation of these new nanosized CHA samples, the silanol sites concentrations were almost doubled; however, all internal silanol sites were healed after the treatment. The additional silanol sites were due to generation of isolated and weak/medium hydrogen bonded silanol sites.

Keywords: nanosized zeolites, chabazite, crystallization, CO2 capture, silanol sites, dealumination, silylation, glioblastoma, cytotoxicity.