(665j) Atomistic Models of Activated Carbons

Activated carbons are porous materials synthesized from organic carbonaceous precursors such as woods, coconut shell and coal. Due to their low cost of production and their excellent adsorptive properties, these materials are widely used in industrial applications ranging from electrolyte storage to gas and fluid purification. Several strategies have been employed to generate realistic structural models for activated carbons. Reconstructive methods, such as the Hybrid Reverse Monte Carlo (HRMC) method, generate models from X-ray or neutron diffraction density profiles, while methods such as Quenched Molecular Dynamics (QMD) are capable of predicting structural characteristics strictly from thermodynamic considerations. We have used both of these approaches to generate structural models for several activated carbons. We present a detailed structural and thermodynamic characterization of these model structures. In particular, the structural features of the models are compared by examining atomic radial distribution functions, ring size distributions, ring network connectivity analysis and pore size distributions. The adsorptive properties of the models are also examined by calculating simulated adsorption isotherms for a wide range of adsorbates, such as argon, methane and water, using Grand Canonical Monte Carlo (GCMC) simulations. Finally, the diffusive behaviors of the adsorbates are examined using Equilibrium Molecular Dynamics (EMD) simulations. We demonstrate that despite some structural differences between the models generated using HRMC and QMD, the adsorptive and diffusive properties of the models are remarkably similar.