On the influence of heterogeneity of graphene sheets in the determination of the pore size distribution of activated carbons

Abstract

We model carbon-based microporous materials, such as activated carbons, taking into account surface defects in the form of geometrical rugosity in the inner surface of each graphitic slit pore. The used model is a simplified variation of the randomly etched graphite (REG) pore model (Seaton et al., Langmuir 13:1199-1204.When subcritical Ar or N 2 is used as probe-gas to simulate the adsorption process in slit pores assembled with ideally perfect graphene walls, the resulting pore size distribution (PSD) rather consistently shows a relatively low population of pores around 12-13 Å. This feature is supposed to be an artifact introduced by the perfect graphene sheets modeling assumptions.In this study, we particularly examine to which extent the gap of the PSD around 12-13 Å is linked to the perfect graphene sheet model and the effects of surface rugosity in the determination of the PSD. Adsorption isotherms of nitrogen at 77 K and local density distributions are studied simultaneously in the simulation. We found that, by mixing a complete series of heterogeneous pores with 25% of repulsive sites, a noticeable improvement in the fitting between the theoretical and the experimental isotherms was achieved and the PSD gap was eliminated. The mixed model with 25% of repulsive sites provided a more realistic estimate of the internal structure of microporous carbons.

Prediction of chlorophenols adsorption on activated carbons by representative pores method

“…Among the models proposed in the literature for activated carbon (Do and Do 2006;Lucena et al 2008Lucena et al , 2017Nguyen et al 2008;Oliveira et al 2011), we choose the most used model. The molecular representation of activated carbon is then de ned as slits of graphene layers walls.…”

Monte Carlo Simulation Strategies for Predicting CO2/CH4 Adsorption onto Activated Carbons from Pure Gas Isotherms

“…where, for one-component adsorption, the bulk gas phase composition y is equal to one (Heuchel et al 1999); N i ex (H,T,P,y) is the excess number of adsorbed molecules of species i in a model pore of width H at temperature T, pressure P and bulk gas-phase composition y; N i abs (H,T,P,y) is the N H T P y N H T P y y is the bulk fluid density of species i at the temperature and pressure of concern; and V bf (H) is the volume in the model pore of width H accessible to the bulk fluid (Oliveira et al 2011). The calculations were performed at a defined temperature and pressure by using the equation of state for ideal gases at low pressures (up to 0.1 MPa) and the Peng-Robinson equation of state (1976) for high pressures, employing the parameters listed in Table 2 (Sandler 1989).…”

Modeling of Alcohol/Water Separation in Graphene-Based Membranes: The Roles of Interfacial Adsorption and the Effective Transfer Path

“…In porous membranes, the pore flow model describes pervaporation as liquid permeation under a pressure difference, such as the Hagen–Poiseuille (HP) equation. − Most of these conventional models tend to describe the flow behavior based on the assumption of homogeneous fluids ,, and using their bulk properties. However, the fluid is inhomogeneous when confined within nanometer or subnanometer spaces (<2 nm), and their properties, such as density, diffusion coefficient, and viscosity, significantly differ from those observed in bulk phases when confined within nanometer or subnanometer spaces (<2 nm). − This is because, according to the molecular collision theory, the interaction between fluids and solids cannot be ignored for the fluids passing through 2D nanochannels. , For example, early studies have mentioned the classical coupling effects of two phenomena during the multicomponent pervaporation process, i.e., the coupling of flow and thermodynamic interactions leads to preferential adsorption . Experimentally, the measurements of attenuated total reflection (ATR) infrared spectroscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM) also revealed an ice-like structure of the water molecules near the surface.…”