Water transport in boron nitride nanotube membranes

Lennard-Jones Centre discussion group seminar by Sritay Mistry from the University of Edinburgh.

Carbon nanotubes (CNTs) have been heralded as the material of choice for next-generation membranes for more than a decade. Meanwhile, simulation studies on boron nitride nanotubes (BNNTs) showed they potentially offer faster water transport than CNTs, contradicting the few recent experiments and some simulations which claim the opposite. This talk describes a combination of simulations and experimental data to address the causes of these contradictions in literature by analysing BNNTs through the framework of resistance to flow. Dividing the resistance into the components of end resistance and nanotube flow resistance, the role of factors such as pore end configuration, membrane length, and BNNT atom partial charges, affecting both the resistance terms can be studied independently. Molecular simulations of nanotube membranes in literature often use very short nanotubes connected to high and low-pressure reservoirs, to reduce computational time. Resistance in these short nanotubes is found to be dominated by the end resistance arising at the pore, hiding the flow resistance within the nanotube. For microscale-thick laboratory-scale membranes, the flow resistance inside the nanotubes dominates, with the end resistance nearly negligible compared to the nanotube flow resistance. CNTs are found to consistently have a lower nanotube flow resistance, indicating they will provide faster water transport at the laboratory scale. The choice of partial charge on the BN atoms is also shown to play a large role in determining the nanotube flow resistance, with higher charges presenting higher resistance. A more accurate approach to comparing simulation results with experiments for nanotube membranes is highlighted.

The seminar was held on 9th May 2022.

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