Self-assembled rhomboidal ammonia monolayer confined in two vertically stacked graphene oxide/graphene nanosheets

Abstract

Confined water molecules have attracted widespread research interest due to its versatile phase behaviors. Ammonia (NH3, isoelectronic with water) molecules are also expected to realize the delicate self-assembled hydrogen-bonded network...

First-Principles Study on Out-of-Plane Piezoelectricity of Self-Assembled Ammonia Layers Confined in Two Vertically Stacked Graphene Oxide Nanosheets

“…All the NH 3 molecules still adopt a Y-shaped configuration observed in our previous study. 19 Further considering from their top-view structures in Figure 3b′,c′, the rhomboidal pattern within NH 3 monolayers still remains unchanged, and their difference in N•••N distances of two corresponding short adjacent sides can be negligible and that of two corresponding long sides is smaller than 0.018 Å. Noticeably, some NH 3 molecules own more space, when the interlayer distance between two GO nanosheets becomes larger under the 6% tensile strain.…”

“…We know that the oxygen-containing functional groups in GO sheets are diverse, mainly involving hydroxyl, epoxy, ether, or carbonyl in the basal plane and hydroxyl or carboxyl at the edge. , However, the synthesis conditions can be controlled to realize GO sheets with desirable O-containing groups . Hence, it is acceptable to build more ideal GO models with relatively uniform O-containing groups in computational simulations. ,, Based on that, the computational models of NH 3 monolayer@GO systems were generated and confirmed in our previous study . In order to further explore their piezoelectricity, five various GO monolayers are first considered here involving different oxygen-containing functional groups, such as hydroxyl/carbonyl, hydroxyl, ether, and epoxy, the same as in previous treatments .…”

“…19 In order to further explore their piezoelectricity, five various GO monolayers are first considered here involving different oxygen-containing functional groups, such as hydroxyl/carbonyl, hydroxyl, ether, and epoxy, the same as in previous treatments. 19 After geometry optimization, two functionalized GO monolayers are then vertically stacked to make their functional groups hang inside to interact with the confined rhomboidal NH 3 monolayer, whose structures have been verified in our previous work, 19 to generate five different super cells of NH 3 monolayer@GO (see Table S1 of the Supporting Information) with a 60 Å c-axis length to ensure their sufficiently thick vacuum layers. Noticeably, two ether-functionalized GO with different C/O ratios (R C/O 's) of 8 versus 4 are considered here to explore the influence of oxygen content in GO plates on the piezoelectric properties of these systems.…”

“…Further considering their side views in Table S1, we cannot recognize the change of orderly rhomboidal monolayers of confined NH 3 molecules, in line with the previously observed pattern. 19 Noticeably, the lattice parameters in the rhomboidal pattern of NH 3 monolayers vary a lot due to the changed interaction with ether O atoms in GO layers based on the the top-view structures in Table S1. The N•••N distances of two short adjacent sides remain unchanged for two NH 3 monolayer@ ether-functionalized GO systems (R C/O = 8 versus 4), but those of the two long sides change from about 3.8 to about 4.3 Å as the C/O ratios in GO layers decrease.…”

Puckered Zigzag Monolayer Ice: Does a Confined Flat Four-Coordinated Monolayer Ice Always Have a Corresponding Puckered Phase?

“…However, as the simulated graphene confined 2D ice crystals are slightly rhomboidal, it was suggested that these structures may be an artifact of the presence of sodium chloride contamination. Later, six stable mono-, bi-, and tri-layer ices or amorphous ices were revealed by classical molecular dynamics (MD) simulations of water confined by graphene sheets. − Very recently, both ab initio and machine learning potential based MD simulations of water within graphene nanocapillaries shown that a flat zigzag monolayer ice (ZZMI) consisting of an array of zigzag water chains is stable at high pressures. , …”