Department of Chemistry - PhD Student Seminar - When Less is More: Sorption Properties in Ultra-microporous Materials

Student: Mr. Kwan Shing LAU

Department: Department of Chemistry, HKUST

Supervisor: Prof. Ian Duncan Williams

Co-supervisor: Prof. Yangjian QUAN

Abstract

The study of porous solids has exploded in the past 25 years with the advent of MOF materials such as HKUST-1, which showed a number of attractive properties versus classical zeolite metal oxides, especially with a view to chemical modification and engineering of the channel pores. This was recognized in 2025 with the most recent award of the Nobel prize for Chemistry to Robson, Yaghi and Kitagawa.

Early MOF work focussed on the idea of increasing the large specific surface areas of such porous MOFs as measured by BET physisorption measurements using N2 gas. These open MOFs having greater scope for storage capacity, or diffusion of larger guest molecules in/out of catalytic sites. 

More recently however there has been a growing realization that engineering very small pores (ultra-microporous solids) can allow stronger interactions between guests and the interior channel walls, as well as more highly selective sorptions, with optimal separation properties.  A MOF with small channel size based on aluminum formate [Al(O2CH)3] has been studied by Cheetham and co-workers for its capacity to separate N2 and O2 mixtures as well as capture CO2 and store H2.

Finally, the trapping of very small gas in the ultimate microporous solids can be considered for ScF3 or CaZrF6 which demonstrate uptake of He atoms to form clathrate solids with modified solid-state properties versus the parent solid phase.

We will discuss the way in which such ultrapore materials can be prepared and their sorption and desorption properties can be established.