Cluster-associated filling of water molecules in graphene-based mesopores

Abstract

Graphene monoliths were prepared through unidirectional freeze-drying method of graphene oxide colloids-KOH mixed solution and successive reduction by heating at 573 K in Ar. The porosity-and crystallinitycontrolled graphene monoliths were prepared by the KOH activation at different temperature and the post-heating in Ar. These activated graphene monoliths were characterized by N 2 adsorption at 77 K, X-ray diffraction and Raman spectroscopy. Water adsorption isotherms show a typical hydrophobicity below P/P 0 = 0.5 and a marked hydrophilicity above P/P 0 = 0.6, which depends on the pore width. In the water adsorption isotherms of porous graphene monoliths activated at different temperature, the higher the activation temperature, the larger the rising P/P 0 . No essential change in the shape of the water adsorption isotherm for the post-heated nanoporous graphene monoliths is observed except for the decrease in water adsorption amount with higher post-heating temperature. The linear relationship between the saturated water adsorption and pore volume whose width is smaller than 4 nm indicates clearly that water molecules are adsorbed in small mesopores by the clusterassociated filling mechanism.

Structural behaviors in water adsorbing phenomena on nanoporous carbon fabricated from waste rice husk

“…The scattering intensity decreased due to the reduction of electron deviation occurred by uniform adsorption; on the contrary, the intensity increased due to the density biasing in pores, which happened by the cluster formation. 50,51) Figure 8 presents the scattering intensity as a function of water content since the fractional filling could be considered as 1 under the assumption in this study. From above, the initial decrease of intensity with water content indicates the bias of electron density in the space, which was alleviated by the discrete entry of water molecules into nanopores.…”

On the growth of argon clusters on a weak adsorbent decorated with patches

“…The dispersion interaction between water and graphite is extremely weak and water would not adsorb on a bare graphite surface at ambient temperatures; the weak quadrupole at each C site does not contribute any significant electrostatic addition to the potential energy because the close proximity of the sites means that positive and negative terms tend to cancel out. Nevertheless, the presence of functional groups at the edges of graphene layers or at surface defects facilitate wetting since these act as strong adsorption sites for water molecules [1,2] and it is well-known that water molecules cluster around functional groups carrying electrostatic partial charges [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The interaction between water and these strong sites is greater than or, at least comparable to, the interaction between water molecules and is significantly stronger than the interaction between water and the basal plane of graphite.…”

Development and application of kinetic Monte Carlo for the simulation of bulk fluids and gaseous adsorption

“…The dispersion interaction between water and graphite is extremely weak and water would not adsorb on a bare graphite surface at ambient temperatures ( Figure 2-1a); the weak quadrupole at each carbon site does not contribute any significant electrostatic addition to the potential energy because the close proximity of the sites means that positive and negative terms tend to cancel out. Nevertheless, the presence of functional groups at the edges of graphene layers or at surface defects facilitate wetting since these act as strong adsorption sites for water molecules [26,27] and it is well-known that water molecules cluster around functional groups carrying electrostatic partial charges [11,14,21,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40].…”