Metal-Organic Frameworks (MOFs) are a special type of porous polymers made up of metal nodes linked to organic struts. As their numerous pores offer to house guest molecules, MOFs have found applications in gas storage, separation, and catalysis.

This metal-organic framework hosts a conducting polymer; the resulting composite material sees a billion fold increase in electrical conductivity (Image Courtesy: Nirmalya Ballav)

Most commonly, MOFs are poor conductors of electricity because of ineffective orbital overlap between the insulating organic linker and the metal node. And even on occasions when this has earlier been achieved, it has not been possible to increase conductivity by more than a million-fold.

In a new report that raises the bar to a billion-fold increase in electrical conductivity, a team of researchers from IISER Pune including PhD student Barun Dhara and led by faculty member Nirmalya Ballav has developed a new concept to modulate electrical conductivity of MOFs.

They achieved this by filling the 1D nano-channels of a cadmium-based MOF with chains of polypyrrole (PPy), a conducting polymer. Noticeably, the composite material continued to display fluorescence properties, a useful characteristic to possess for an optoelectronic material.

The MOF-PPy composite was realized to be an n-type semiconductor with high-carrier density and mobility, closely matching with those of inorganic-based semiconductors like doped-GaAs. The key behind such an unusual increment in the electrical conductivity was attributed to non-covalent interactions between the guest (PPy) and host (MOF) moieties as well as confinement effect.

PhD student Barun Dhara (right) and Dr. Nirmalya Ballav at work

Ballav said “The void-space in MOFs can be used not only for gas/liquid adsorption and separation but can also be accessed as confined-space to perform novel host-guest chemistry. This could pave the way for rational design of various MOF-based functional-materials for future applications”.

The paper titled “Increase in electrical conductivity of MOF to billion-fold upon filling the nanochannels with conducting polymer” and authored by Barun Dhara, S.S. Nagarkar, J. Kumar, V. Kumar, P.K. Jha,  S.K. Ghosh, S. Nair,  and Nirmalya Ballav (all from IISER Pune) has appeared in the Journal of Physical Chemistry Letters (7:2945-2950). 

This work received funding from IISER Pune.

- Reported by Shanti Kalipatnapu with inputs from Nirmalya Ballav

Read here a highlight of this work in Chemistry World magazine.