Developing Switchable and Self-Accelerating MOFs for Toxic Gas Adsorption

Metal-organic frameworks are some of the most exciting new materials to have been prepared over the last two decades. They comprise metals ions or metal clusters linked by organic groups to provide highly porous materials with surface areas approaching 6000m2/g. These materials have aroused great interest in many different areas, from hydrogen and methane storage for energy to drug and medical gas delivery agents. Of particular relevance to the defense industries is their ability to adsorb toxic gases in large amounts.

In St Andrews we have developed a particularly interesting MOF called STAM-1 (Figure 1), which shows some very unusual properties.1 We published a paper in Nature Chemistry that showed 'switchable' adsorption, a unique property where the adsorption between two channels can be controlled. We have since followed up this work by showing that a composite STAM-1/silica material is the only MOF that shows increased adsorption of toxic gases like ammonia in the presence of water (Figure 2), which is usually a limiting feature of MOF adsorption as the water competes very successfully against other gases for adsorption sites. STAM-1 is also much more stable than other materials of its type, and so the material shows great promise for further application.
1. To prepare a series of materials with the STAM-1 topology but different chemistry
2. To understand how toxic gases interact with the materials. In particular we will complete mechanism studies using in situ X-ray diffraction and other techniques to study whether it is the switchable nature of the pores that causes the observed improvement.
3. To understand how the preparation of silica/MOF composites improves the properties of the materials, especially in the presence of moisture