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Nanoconfinement; Water clusters; Carbon nanotubes; Density functional theory.

An ab initio investigation on water clusters confined to armchair carbon nanotubes (CNT) with varying diameters has been performed using the density functional theory-based calculations. Different parameters have been investigated including structure, hydrogen bonding pattern and vibrational spectra of water-CNT complexes. Our results reveal that one-dimensional water chain parallel to CNT axis is formed in narrow nanotubes CNT(4,4) and CNT(5,5), whereas in CNT(6,6), zigzag structure is observed. An increase in the CNT diameter results in more symmetric structures similar to the gas phase. The vibrational analysis shows a redshift in stretching frequency of the hydrogen bond assisted O–H in CNT(6,6) due to the reduction in O—O separation whereas a significant blue shift in stretching frequency mode is observed in highlyconfined CNT(4,4) and CNT(5,5). It implies that the hydrogen bond strength between water molecules is strongest in CNT(6,6). It is also observed that water cluster tends to be near CNT wall due to H...p interaction between water molecule and the p-electron cloud of CNT. An inverse relation between the electronic charge transfer (from CNT to water) and the diameter is also established. This study demonstrates that the degree of confinement is extremely important in deciding the properties of confined water molecules.

MANOJ K TRIPATHY^{1 2} DEVENDRA K MAHAWAR³ K R S CHANDRAKUMAR^{2 4}

1. Research Reactor Services Division, Bhabha Atomic Research Centre, Mumbai 400 085, Maharashtra, India
2. Homi Bhabha National Institute, Mumbai 400 094, Maharashtra, India
3. Department of Chemistry, University of Rajasthan, Jaipur 302 004, Rajasthan, India
4. Theoretical Chemistry Section, Bhabha Atomic Research Centre, Mumbai 400 085, Maharashtra, India

Published

January 2020

Manuscript received

17 May 2019

Manuscript revised

13 August 2019

Accepted

15 August 2019