Title of Paper:Formation Mechanism of the Spiral-Like Structure of a Hydrogen Bond Network Confined in a Fluorinated Nanochannel: A Molecular Dynamics Simulation

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Date of Publication:2017-06-29

Journal:JOURNAL OF PHYSICAL CHEMISTRY C

Included Journals:SCIE、EI、Scopus

Volume:121

Issue:25

Page Number:13840-13847

ISSN No.:1932-7447

Abstract:The structure of the hydrogen bond network inside of the proton conductive channel is of significant importance to proton transfer confined in a nanochannel. In order to investigate the independent effects of fluorination and confinement dimension on the hydrogen bond network, a one-dimensional carbon nanotube decorated with fluorine was built to mimic the environment of the proton conductive channel in the perfluorosulfonic membrane (Phys. Chem. Chem. Phys. 2016, 18(35), 24198-24209). It was found that a fluorinated nanochannel helps to form a spiral-like sequential hydrogen bond network with few branched hydrogen bonds in the central region, which is believed to promote unidirectional proton transfer along the channel axis without random movement. To explore the mechanism of the formation of the spiral-like hydrogen bond structure, molecular dynamics simulation was conducted to analyze the hydrogen bonding properties of water and a hydrated proton confined in the fluorinated CNT with chirality of (10,10). The hydrogen bond criteria were initially evaluated for the water-water and hydronium-water hydrogen bonds. It was found that the confined hydrated protons help maintain the connectivity of the hydrogen bond network along the axis of the fluorinated nanochannel at different temperatures. The hydronium ion prefers to form hydrogen bonds with two neighboring water molecules, resulting in a continuous hydrogen bond network. The non-hydrogen-bonded hydrogen atom of the hydronium ion has strong attraction with the fluorinated channel surface, stabilizing the hydrogen bond structure and making space in the central region of the nanochannel. The connectivity of the hydrogen bond network and the interaction between hydronium and the channel surface produce the spiral-like structure of the hydrogen bond network along the axis of the fluorinated nanochannel with few branched hydrogen bonds.