Department of Materials Science & Metallurgy

Tom Bennett

Tom Bennett portrait

Royal Society University Research Fellow

MSci University of Cambridge
PHD University of Cambridge

+44 (0)1223 334342
tdb35@cam.ac.uk
www.fihm.msm.cam.ac.uk/directory/tdb35@cam.ac.uk

Metal-Organic Frameworks (MOFs)

Metal-organic frameworks (MOFs) are network solids in which inorganic nodes (clusters or metal ions) are linked via organic ligands in an infinite array.  The synthesis of novel MOF materials has been the subject of intense research and debate over the last decade, mainly because of their potential for application in gas storage and separation, catalysis and chemical sensing.  A small but growing number of cases of MOFs which lack the long-range order characteristic of crystalline structures are steadily capturing scientific interest.  Most of this work has been done on a sub-family of MOFs called Zeolitic Imidazolate Frameworks (ZIFs).

Synthesis and Structure of Amorphous Metal-Organic Frameworks

The disordered nature of amorphous MOFs (αMOFs) is probed using total scattering experiments, which gives information on both Bragg and diffuse scattering.  After suitable data treatment, the Fourier transform of S(Q) yields the pair distribution function (PDF), G(r), which is in effect a map of the distances between atom pairs.  The PDF can then be used to provide insight into structural behavior, though accurate structural modeling based on the PDF using programs such as RMC Profile.  Recently, we discovered that amorphous MOFs can be synthesized from the application of stress (pressure, heat, electrical discharge or ball-milling) on existing frameworks, and exhibit substantially stronger mechanical properties than their crystalline counterparts.  In many cases, their structures were found to be much like that of conventional silica glass.

Properties and Applications of Amorphous Metal-Organic Frameworks

The mechanical properties of αMOFs have been found to be superior to those of their crystalline counterparts.  I have been exploring the design and use of MOFs to selectively adsorb different harmful molecules (e.g. I2 – one of the major radioactive isotopes released during the Fukushima nuclear incident in 2011), followed by subsequent collapse of the frameworks to irreversibly trap the harmful molecule within the porous interior.  I have also looked at possibility for tailored long term delivery of drugs inside the human body by trapping them inside porous MOF frameworks, whilst super strong hybrid glasses have also been synthesized by melting frameworks, raising possibilities for the manufacture of electroluminescent and optically active glasses.

Crystalline MOF structures
Figure 1: Crystalline MOF Structures. Carbon – green, Nitrogen – blue, Oxygen – red, Chlorine – yellow, Zinc – pink, Hydrogen – omitted for clarity.
Figure 2: The improvement in retention of I2 upon heating in amorphous MOFs compared to crystalline ones.
  • TD Bennett, PJ Saines, DA Keen, J-C Tan and AK Cheetham, "Ball-Milling Induced Amorphization of Novel and Existing Zeolitic Imidazolate Frameworks (ZIFs) for the Irreversible Trapping of Iodine" Chem. Eur. J. 19 7049-7055 (2013)
  • TD Bennett, S Cao, J-C Tan,  DA Keen, EG Bithell, PJ Beldon, T Friscic, AK Cheetham, "Facile Mechanosynthesis of Amorphous Zeolitic Imidazolate Frameworks", J. Am. Chem. Soc. 133 14546-14549 (2011)
  • TD Bennett, DA Keen, J-C Tan, ER Barney, AL Goodwin, AK Cheetham, " Thermal Amorphization of Zeolitic Imidazolate Frameworks" Angew. Chem. Int. Ed. 50 3067 (2011)
  • TD Bennett, AL Goodwin, MT Dove, DA Keen, MG Tucker, ER Barney, AK Soper, EG Bithell, J-C Tan, A K Cheetham, " Structure and Properties of an Amorphous Metal-Organic Framework" Phys. Rev. Lett. 104 115503 (2010)