Heterogeneity of Water Molecules on the Free Surface of Thin Reduced Graphene Oxide Sheets

Abstract

Reduced graphene oxide (rGO) has numerous potential applications, such as molecular sensor, gas separation membrane, etc. The performance of these devices is often subject to the environment humidity due to the interaction of rGO with water. However, the atomically detailed information on the dynamical and thermodynamic properties of water on the surface of graphene-based materials as well as its underlying molecular mechanism is largely unknown. By performing neutron scattering on hydrated rGO powders, composed by well separated monolayer and few-layer rGO sheets, we found three components of surface water. One remains liquid at −80 °C, while the other two freeze into ice in a stepwise manner above −40 °C. Although slightly slower than the other two, the nonfreezing water diffuses an order of magnitude faster on rGO than those confined in the hydrophilic bulk phase, such as compact powder or membrane. Complementary molecular dynamics simulation revealed that the heterogeneity of surface water arises from the gradual attenuation of the electrostatic interaction between water and oxide groups on rGO within a few hydration layers. These findings are fundamental for understanding of interfacial hydration and ice formation in many materials, and valuable for various applications using graphene-based materials.

The ω3 scaling of the vibrational density of states in quasi-2D nanoconfined solids

“…Nanometer confinement is ubiquitous in the frontiers of biotechnology, electronic engineering, and material sciences to achieve unprecedented advantage, e.g. applications of graphene or graphene-based materials for electron conduction 14 – 16 , seawater desalination 17 , 18 and biosensoring 19 , 20 . Atomic vibrations in confined environments play a crucial role in a plethora of phenomena such as facilitating electron conduction in graphene-based electronic devices 21 , 22 , enhancing proton delivery through the ion channel across the cell membrane 23 , 24 and conducting energy via the power enzymatic motion of protein molecules 25 , 26 .…”

Universal dynamical onset in water at distinct material interfaces

“…The biomaterials, polymers and rGO are in the form of powders, while GO is prepared as a membrane where water molecules are sandwiched between the GO sheets. 17 To highlight the dynamics of water, fully deuterated proteins and PEG were used and hydrated in H 2 O. For simplicity, the perdeuterated proteins and PEG are labeled as D-protein and D-PEG, respectively, while regular ones are denoted as H-protein and H-PEG.…”

“…[1][2][3][4][5][6][7][8][9][10] The material surfaces, exhibiting a large degree of heterogeneity in their structure, chemistry and morphology, can signicantly perturb the structure and dynamics of the water located inside the hydration shell. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] One such consequence is the prevention of ice formation upon cooling, with interfacial water remaining in a liquid phase and mobile at temperatures much below 0 C. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] This non-freezing interfacial water imparts a great amount of exibility and mobility to the underlying substrate materials, such as protein, 4 DNA, 19 RNA, 20 polymers…”

Controlling the Substrate Specificity of an Enzyme through Structural Flexibility by Varying the Salt-Bridge Density

“…Both elastic and quasi-elastic incoherent neutron scattering spectra were collected on ligand-free CYP101 and CYP2C9 samples at h = 0.4 (0.4 gram water per gram protein) using the NG2 high-flux backscattering spectrometer at NIST Center for Neutron Research at National Institute of Standard and Technology with a fixed energy resolution of ~0.8 μeV (corresponding to a time resolution of ~1 ns) [ 27 , 58 ]. Elastic scans were performed for both protein samples in the temperature range of 4~290 K at a heating rate of 1.0 K/min.…”