Structural Modelling of Silicon Carbide-Derived Nanoporous Carbon by Hybrid Reverse Monte Carlo Simulation

Abstract

An atomistic model of the nanoparticle size Silicon Carbide Derived Carbon (SiC-CDC) is constructed using the Hybrid Reverse Monte Carlo (HRMC) simulation technique through a two-step modeling procedure. Pore volume and three-membered ring constraints are utilized in addition to the commonly used structure factor and energy constraints in the HRMC modeling to overcome the challenges arising from uncertainties involved in determining the structure. The final model is characterized for its important structural features including pore volume, surface area, pore size distribution, physical pore accessibility, and structural defects. It is shown that the microporous structure of SiC-CDC 800 possesses a high pore volume and surface area, making it potentially a good candidate for gas adsorption applications. The HRMC model reveals the SiC-CDC 800 structure to be highly amorphous, largely comprising twisted graphene sheets. It is found that these distorted graphene-like carbon sheets comprising the carbon structure present a higher value for the solid–fluid potential strength compared to that of graphite, which is crucial in correct interpretation of experimental adsorption data. Furthermore, the constructed model is validated by comparing predictions of Ar, CO2 and CH4 adsorption against experimental data over a wide range of temperatures and pressures. It is demonstrated that our model is able to predict the experimental isotherms of different simple gases over various thermodynamic conditions with acceptable accuracy. The model also suggests the presence of ultramicroporosity that is accessible to CO2 but only partially accessible to CH4.

Hybrid Reverse Monte Carlo simulation of amorphous carbon: Distinguishing between competing structures obtained using different modeling protocols

“…Nevertheless, despite moderate success, this method is unable to satisfactorily capture topological and morphological characteristics of the experimental sample. In contrast, it is well-demonstrated that realistic modeling of disordered porous materials is better achieved using the Hybrid Reverse Monte Carlo modeling (HRMC) technique, so that the final constructed model can reproduce many characteristic properties of the experimental sample including structural features, equilibrium gas adsorption and transport properties of the fluid in the target material [18,[25][26][27][28][29].…”

“…This constraint controls the pore volume of the model by mimicking the experimental porosity of the target experimental sample through grid occupancy of the simulation cell, with associated error [27,31] …”

“…The quenching scheme can be designed in different ways. In general, a linear quenching procedure, where the temperature is linearly decreased with the number of trial MC moves may be used, however for more amorphous structures application of exponential functions with very slow quenching rate is advisable [27]. Here the key point is the use of an appropriate reactive force field, which should be able to capture interatomic interactions at different length scales.…”

“…The models are constructed based on a unique set of static structure factor data obtained from neutron scattering experiment with the sample, covering a wave vector range 0.2 < q < 50 Å -1 using the SANDALS small angle neutron diffractometer at ISIS -Rutherford Appleton Laboratory, U.K. Details of the synthesis process of the carbon sample, as well as the diffraction experiment at ISIS are given elsewhere [27,29,36]. The radial distribution function of the sample is obtained by the Fourier inverse transform of the experimental structure factor data [8]:…”

Raman spectroscopy study of the transformation of the carbonaceous skeleton of a polymer-based nanoporous carbon along the thermal annealing pathway

“…Apart from the abundance of inter-layer boundaries due to their nanoscale size, intra-layer defects have also been observed in recent atomic-resolution electron microscopy studies [12][13][14], including in the form of non-hexagonal rings. Structural models, that captures microporosity as well as defective carbonaceous skeleton have been proposed of this material [1,9,10,12,15,16] although there is still debate over their validity [1]. A quantitative understanding of this defective structure is important for tailoring NPCs to have desired characteristics in the contexts of adsorption [14], thermal [17] and electrical [18] conductivity, and…”