Two-dimensional monolayer salt nanostructures can spontaneously aggregate rather than dissolve in dilute aqueous solutions

Authors

Wenhui Zhao, Ningbo University
Yunxiang Sun, Ningbo University
Weiduo Zhu, University of Science and Technology of China, Hefei
Jian Jiang, University of Nebraska-LincolnFollow
Xiaorong Zhao, Ningbo University
Dongdong Lin, Ningbo University
Wenwu Xu, Ningbo University
Xiangmei Duan, Ningbo University
Joseph S. Francisco, University of PennsylvaniaFollow
Xiao Cheng Zeng, University of Nebraska - LincolnFollow

ORCID IDs

Wenwu Xu http://orcid.org/0000-0002-0651-9562

Joseph S. Francisco http://orcid.org/0000-0002-5461-1486

Xiao Cheng Zeng http://orcid.org/0000-0003-4672-8585

Date of this Version

9-23-2021

Citation

NATURE COMMUNICATIONS (2021) 12:5602

https://doi.org/10.1038/s41467-021-25938-0

Comments

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,

© The Authors 2021

Abstract

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal ring and/or zigzag chain patterns. These structural patterns appeared to be quite generic, regardless of the water and ion models used in the MD simulations. The generic patterns formed by 2D monolayer NaCl and LiCl nanostructures were also confirmed by ab initio MD simulations. The formation of 2D salt structures in dilute aqueous solution at room temperature is counterintuitive. Free energy calculations indicated that the unexpected spontaneous salt nucleation behavior can be attributed to the nanoscale confinement and strongly compressed hydration shells of ions.

Supplementary files, including 6 movies, attached below.