Porous organic materials for gas sorption

Nano-structured materials with well-defined pores are the subject of intensive research and development for use in the sensing, storage and separation of gases. Zeolites, clays, metal-organic frameworks and mesoporous metal oxides are among the materials under development for applications in sectors such as environmental, energy and biomedical.

Porous molecular solids may be an important alternative. These organic compounds can be tailored in terms of pore size and functional groups lining the pores for very high selectivity. Further, dynamic molecular structural changes could be exploited in macromolecular switches or actuators. The EU-funded project 'Synthesis and characterization of porous molecular solids' (POMOS) is focusing on calixarenes and cyclopeptoids as building blocks of devices relying on gas-solid interactions at the atomic level.

Calixarenes and cyclopeptoids are both macrocyclic organic compounds that form cavities capable of holding small molecules or ions forming a host-guest system. Calixarenes have already been successfully employed as building blocks of nano-structured materials whereas cyclopeptoids are relatively unexplored.

Novel calixarenes and cyclopeptoids have already been synthesised and characterised in preliminary experiments. Results from characterisation of calixarenes using single-crystal and powder X-ray diffraction as well as thermal analysis were presented at the European Crystallographic Meeting in 2013 and in two publications.

Calixarene-based compounds have also been tested for gas adsorption properties under non-ambient conditions using a tailor-made gas cell. The set-up is allowing scientists to characterise the host-guest interactions with atomic resolution in order to characterise adsorption mechanisms.

Data obtained using the gas cell at large facilities for synchrotron radiation and neutron diffraction are supplementing the other methods of characterisation. These facilities are able to perform in situ single-crystal X-ray diffraction when only very small (10 microns) single crystals are obtained and/or to perform in situ high-resolution X-ray powder diffraction when only crystalline powders are obtained.

The effective strategies for characterisation of the gas sorption and release of novel molecular porous materials will be instrumental in development of novel devices for sensing, separation and storage of gases. Such devices are of tremendous commercial interest and thus the project will contribute to a strong EU position in an important global market.