Evaluation of methods for determining the pore size distribution and pore-network connectivity of porous carbons

Graphene Oxide: Study of Pore Size Distribution and Surface Chemistry Using Immersion Calorimetry

In this work, the textural parameters of graphene oxide (GO) and graphite (Gr) samples were determined. The non-local density functional theory (NLDFT) and quenched solid density functional theory (QSDFT) kernels were used to evaluate the pore size distribution (PSD) by modeling the pores as slit, cylinder and slit-cylinder. The PSD results were compared with the immersion enthalpies obtained using molecules with different kinetic diameter (between 0.272 nm and 1.50 nm). Determination of immersion enthalpy showed to track PSD for GO and graphite (Gr), which was used as a comparison solid. Additionally, the functional groups of Gr and GO were determined by the Boehm method. Donor number (DN) Gutmann was used as criteria to establish the relationship between the immersion enthalpy and the parameter of the probe molecules. It was found that according to the Gutmann DN the immersion enthalpy presented different values that were a function of the chemical groups of the materials. Finally, the experimental and modeling results were critically discussed.

The effect of different organic solvents on sodium ion storage in carbon nanopores

GCMC atomistic simulation to study the coupled effects of nanoporous hard carbon and different organic solvents on Na ion storage.

Effects of pore size and surface charge on Na ion storage in carbon nanopores

Na ion batteries (NIBs) are considered as a promising low cost and sustainable energy storage technology.

To the pore and through the pore: thermodynamics and kinetics of helium in exotic cubic carbon polymorphs

Applying pore size analysis, Monte Carlo simulations, and transition state theory, we study the molecular sieving properties of recently discovered crystalline exotic cubic carbon allotropes (Hu et al., J. Phys. Chem. C, 2012, 116, 24233-24238) at 298 K and infinite dilution. The fcc-C10 cubic carbon crystal shows unusual molecular sieving characteristics. The carbon cavities of the fcc-C10 cubic carbon polymorph (with an effective size of ~3.5-4 Å) are kinetically closed to common gaseous contaminants of He fluid (including: Ne, Ar, H2, and CO). Because the sizes of nanowindows connecting carbon cavities are comparable with the effective size of a He atom (~2.556 Å), we predict a significant resistance to self-diffusion of the He in the fcc-C10 crystal. Computed self-diffusion coefficients ~1.3 × 10(-6)-1.3 × 10(-7) cm(2) s(-1) for He inside fcc-C10 fall in the range characteristic of molecular diffusion in zeolites. Infrequent "jumps" of He atoms between neighboring carbon cavities and kinetic rejection of other gaseous particles indicate potential application of the fcc-C10 carbon polymorph for kinetic molecular sieving of He near ambient temperatures. The theoretical results presented here are useful for correct interpretation of the pore volumes of carbon molecular sieves measured from helium porosimetry.

Characterization of micro- and mesoporous materials using accelerated dynamics adsorption

Porosimetry is a fundamental characterization technique used in development of new porous materials for catalysis, membrane separation, and adsorptive gas storage. Conventional methods like nitrogen and argon adsorption at cryogenic temperatures suffer from slow adsorption dynamics especially for microporous materials. In addition, CO2, the other common probe, is only useful for micropore characterization unless being compressed to exceedingly high pressures to cover all required adsorption pressures. Here, we investigated the effect of adsorption temperature, pressure, and type of probe molecule on the adsorption dynamics. Methyl chloride (MeCl) was used as the probe molecule, and measurements were conducted near room temperature under nonisothermal condition and subatmospheric pressure. A pressure control algorithm was proposed to accelerate adsorption dynamics by manipulating the chemical potential of the gas. Collected adsorption data are transformed into pore size distribution profiles using the Horvath-Kavazoe (HK), Saito-Foley (SF), and modified Kelvin methods revised for MeCl. Our study shows that the proposed algorithm significantly speeds up the rate of data collection without compromising the accuracy of the measurements. On average, the adsorption rates on carbonaceous and aluminosilicate samples were accelerated by at least a factor of 4-5.

The influence of the carbon surface chemical composition on Dubinin-Astakhov equation parameters calculated from SF6 adsorption data-grand canonical Monte Carlo simulation

Using grand canonical Monte Carlo simulation we show, for the first time, the influence of the carbon porosity and surface oxidation on the parameters of the Dubinin-Astakhov (DA) adsorption isotherm equation. We conclude that upon carbon surface oxidation, the adsorption decreases for all carbons studied. Moreover, the parameters of the DA model depend on the number of surface oxygen groups. That is why in the case of carbons containing surface polar groups, SF(6) adsorption isotherm data cannot be used for characterization of the porosity.

Can carbon surface oxidation shift the pore size distribution curve calculated from Ar, N(2) and CO(2) adsorption isotherms? Simulation results for a realistic carbon model

Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbon surface oxidation on the pore size distribution (PSD) curve determined from simulated Ar, N(2) and CO(2) isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton, and that all pores are accessible for studied molecules (i.e., only the effect of the change of surface chemical composition is studied). The results obtained show two important things, i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculated from the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curves calculated from simulated isotherms are to a greater or lesser extent affected by the presence of surface oxides. The most reliable results are obtained from Ar adsorption data. Not only is adsorption of this adsorbate practically independent from the presence of surface oxides, but, more importantly, for this molecule one can apply the slit-like model of pores as the first approach to recover the average pore diameter of a real carbon structure. For nitrogen, the effect of carbon surface chemical composition is observed due to the quadrupole moment of this molecule, and this effect shifts the PSD curves compared to Ar. The largest differences are seen for CO(2), and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms of this molecule contain artificial peaks and the average pore diameter is strongly influenced by the presence of electrostatic adsorbate-adsorbate as well as adsorbate-adsorbent interactions.