Carbon sponges

Tim Mays
Nigel Seaton
Geoff Moggridge

New carbon sponges created by UK scientists using a molecular moulding approach could be used to selectively absorb specific gases. The geometry of the pores of the new materials has been precisely controlled at the nanometer scale by Tim Mays of Bath, Nigel Seaton of Edinburgh and Geoff Moggridge of Cambridge Universities.

Carbon is a common enough material for absorbing gases for separation and purification purposes but creating activated carbons is normally a matter of trial and error given that the starting materials are usually natural materials, such as coconut husk and wood.

Mays and his colleagues are now using a templating approach to create specific pore geometries. The templates are based on synthetic clay minerals with layered or laminar microstructure. The precursor is produced by templating the formation of the carbon during the mineral synthesis and then blasting out the mineral with heat to anneal the material and finally dissolve away the mineral to leave behind the carbon skeleton using acid.

Electron microscopy and X-ray diffraction have demonstrated the control possible at the nanometer scale, say the researchers. The team has looked at several synthetic clays with potentially useful microstructures that might be used to template carbon. Among them are pillared clays � where the layers of mineral are held apart by small stacks. "It is a little like having coins in between the cards of a deck," says Mays, "It offers a way of controlling the space between the layers and hence the depth of the carbon layers once the mould has been taken."