Stable metal organic frameworks for the catalytic destruction of chemical warfare agents

Abstract

The work described within this Thesis has focused on the preparation and characterisation of metal-organic frameworks (MOFs) as catalysts for the hydrolysis of the nerve agent simulant dimethyl 4-nitrophenyl phosphate (DMNP).

Mixed-metal MOFs were explored for this application using a combination of zirconium and hafnium in known MOFs in order to investigate the role of Lewis-acidity on catalysis. A series of mixed-metal MOFs were prepared and successfully catalysed the hydrolysis of DMNP. For UiO-66 and NU-1000 the highest rates were seen for the Zr 100% samples. For MOF-808 the most successful catalyst was found to be the Zr 33% Hf 66% sample. Further investigations compared properties of each sample and concluded that a change in Lewis-acidity plays a role in the catalytic activity, despite differences in material characteristics.

Mixed-linker MOFs were also investigated through the addition of di-topic linkers to a MOF-808 synthesis. For each sample, ca. 10\% of a chosen di-topic linker, as a proportion of linker present, was incorporated into the MOF-808 structure. Further investigations using the 5-amino isophthalic acid di-topic linker found up to 25% of 5-amino isophthalic acid could be incorporated into MOF-808. All samples successfully hydrolysed DMNP, with the 20% 5-amino isophthalic acid MOF-808 sample giving the highest rate and out-performing the parent MOF-808 sample.

Investigations into preparing MOF-composite materials were also carried out. This focused on incorporating MOF-808 into the materials PET, cotton, silk and nylon, using a range of synthesis methods. Loading estimates were calculated through q-NMR measurements. All materials saw MOF-808 successfully deposited on the surface, with the exception of one sample. All materials tested as catalysts for the hydrolysis of DMNP outperformed the blank samples. MOF-808 had therefore retained catalytic properties within the composite material. The hydrothermal synthesis method using PET displayed the highest initial rate for all composite materials prepared.