Two dimensional metal-organic frameworks for gas sensing

The aim of the work in this project is to develop sensing technology that can be readily miniaturised and provide lightweight mobile or networked molecular detection of chemicals in the vapour phase. A further requirement is that the sensor is cheap, light, and does not require much power. Ultimately such gas sensors could be incorporated into mobile devices to provide constant monitoring of gasses hazardous to health. This project is to develop such sensors through the use of conducting networks operating near the electrical percolation threshold, which are referred to as percolation sensors. Percolation sensors have been shown to provide orders of magnitude increased sensitivity relative to thin film sensors made from the same materials. As the conducting element conducting polymers have previously been used, but this project is to grow percolation devices using two dimensional (2D) conducting metal-organic frameworks (MOFs). 2D MOFs will be grown both in the liquid phase and onto a substrate in a vacuum environment. Conductive 2D MOF networks are recently discovered materials, resulting from square planar complexation of late transition metals and some simple polyaromatic hydrocarbon ligands. The interaction with gas phase analytes can readily change the local electrical conductivity of the MOF. The MOFs will be grown or deposited onto insulating substrates so that they can be used for as chemiresistors for high sensitivity gas sensing of volatile organic compounds.

This project falls within the EPSRC Physical Sciences research area.

The aims are:
- To grow 2D MOFs in the liquid and vacuum phases and to characterise the resultant materials using electrical conductivity measurements, X-ray diffraction, and Raman spectroscopy.
- To create 2D MOF percolation networks by depositing sub-monolayers on electrically insulating substrates decorated with interdigitated noble metal electodes, and to evaluate these through dc resistance and lock-in techniques.
- To use the percolation networks for gas phase sensing of volatile organic compounds such as C3H8 and common hazardous gasses including CO and NH3. This will include establishing the limit of detection of the networks.
- To investigate the optimised device architecture for integration into a mobile device. This may involve setting up the MOF percolation network as a transistor and investigating the temperature and humidity limitations of the device.