Investigations of structural and dynamical mechanisms of ice formation regulated by graphene oxide nanosheets.

Shengkai Zhang,Zhixin Wang,Jingjing Han,Victoria Garcia Sakai,Na Li,Xudong Gu,Xiang Luo,Nicolas R De Souza,Xiang-Qiang Chu

doi:10.1063/4.0000111

Abstract

Recent research indicates that graphene oxide (GO) nanosheets can be used to regulate ice formation by controlling critical ice nucleus growth in water at supercooling temperatures. In addition, the study of ice formation mechanisms regulated by GO nanosheets, a good model system for antifreeze proteins (AFPs), will shed light on how AFPs regulate ice formation in nature. In this work, time-resolved small-angle x-ray scattering (TR-SAXS) and quasi-elastic neutron scattering (QENS) experiments were carried out to investigate the structural and dynamical mechanisms of ice formation regulated by GO nanosheets. Strikingly, a transient intermediate state was observed in TR-SAXS experiments that only exists in the aqueous dispersions with a larger GO size (11 nm). This serves as evidence that the size of GO is critical for regulating ice formation. Elastic neutron scattering results indicate that ice is formed in all samples and thermal hysteresis occurs in GO aqueous dispersions in both H2O and D2O. The structural and dynamics information about water molecules in GO, extracted from QENS, reveals different dynamical behaviors of water molecules in GO aqueous dispersions when approaching the ice formation temperature.

Highlights

Nature has unique ways of regulating ice formation; for example, antifreeze proteins (AFPs) protect organisms from freeze damage by regulating the formation of ice[1] via controlling the arrangement of hydroxyl groups
quasi-elastic neutron scattering (QENS) enables us to study the dynamics of water molecules in graphene oxide (GO) aqueous dispersions and we compared them with that of pure water
From the analysis of the QENS data in the energy domain, the diffusive process of water molecules is shown to be slower at lower temperatures in GO aqueous dispersions, and the motion of H-atoms within water molecules has been suppressed during the ice formation, which is consistent with the elastic scattering results

Summary

Introduction

Nature has unique ways of regulating ice formation; for example, antifreeze proteins (AFPs) protect organisms from freeze damage by regulating the formation of ice[1] via controlling the arrangement of hydroxyl groups. The GO nanosheets in water droplets have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets Both experimental results[13] and theoretical calculations[14] have shown the coexistence of large oxidized and unoxidized graphene regions on the surface of GOs. Hydroxy(-OH) and epoxy(-O-) groups are located at oxidized regions of the basal plane of GOs, whereas the carboxyl groups mainly localize at the periphery of GOs.[15]. The plane of GO consists of repeat honeycomb hexagonal carbon rings, forming a scaffold structure to arrange the hydroxy groups on GOs and facilitate the ice crystal lattice matching It is reminiscent of the hydroxy group organization on the ice-binding surface of AFPs. Previous study indicates that GOs induce a thermal hysteresis

Methods

Results

Conclusion