Abstract
Characterization of carbon materials to determine surface area and pore size distribution conventionally uses models based on the Steele 10-4-3 potential (with Crowell-Steele molecular parameters) and the assumptions: (1) the collision diameter of a carbon atom in a grapheme layer is 0.34nm and (2) the interlayer distance between the adjacent layers is 0.335nm. However, there is growing evidence from experiments and from quantum mechanical calculations, that challenges the parameters used in the Crowell-Steele 10-4-3 model. Experimentally, low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) have shown that molecules are closer to the graphite surface than predicted by the Steele model, and theoretically, quantum DFT calculation of the van der Waal C6 coefficient per carbon for a single grapheme layer has been found to be much greater than that for C in bulk graphite. On these grounds, the speaker proposed an improved model for graphite that gives good descriptions of adsorption isotherms and isosteric heats, especially in describing the various transitions and the spike in the plot of the isosteric heat versus loading. The features of this new model are: (1) the collision diameter of carbon atom in the top grapheme layer is 0.28nm: smaller than that for grapheme layers in the bulk solid of 0.34nm, (2) the interlayer distance between the top layer and the second layer is 0.299nm compared to the spacing of 0.3365nm for lower layers, supported with transmission electron microscopy (TEM) images, (3) the corrugation of the grapheme surface is taken into account by using discrete carbon atom, rather than solid continuum calculations, and (4) the anisotropy of polarisability of carbon in graphite parallel and normal to the surface, is included in the potential model.
The speaker has used grand canonical Monte Carlo (GCMC) and kinetic canonical Monte Carlo (k-CMC) simulations to evaluate the effects of the above modeling on the adsorption isotherm and isosteric heats of adsorbates commonly used for the characterization of carbon materials: argon, nitrogen, krypton, methane and water. His proposed model successfully captures many fundamental features of how adsorbed molecules are structured on graphite. For simple gases he considered: (1) the gas-liquid transition, (2) the transition of 2D liquid to 2D solid, (3) the transition from commensurate to incommensurate packing, and (4) the cusp-spike signature in the isosteric heat versus loading. Water, which is an associating fluid, shows several distinct features: (1) formation of water-oxygen functional group complexes (at the edges of grapheme layers), (2) growth of water clusters, and (3) merging of clusters, followed by filling of the interstices with condensate between graphite micro-crystallites. Simulation results for simple gases and water were validated with high resolution experimental data.
About the speaker
Prof Duong D Do got his BE and PhD from The University of Queensland in 1976 and 1980 respectively. He then started his academic career at The University of Queensland as a tutor and senior research assistant. After a period of Research Fellowship at California Institute of Technology in the US, he joined The University of Queensland again as a lecturer in 1981 and was promoted to Senior Lecturer in 1985, Associate Professor in 1986 and eventually Professor in 1991.
Prof Do is an international authority in adsorption, modelling, applied mathematics and computer simulation. He is the editorial board members of four journals, including Adsorption Journal, Adsorption Science & Technology, Journal of Non-equilibrium Thermodynamics and Frontiers of Chemical Engineering in China. He is also a prolific researcher himself, with over 400 journal publications in high impact journals, more than 50 book chapters, over 300 conference papers, giving more than 50 plenary/keynote lectures at international conferences and published 5 books including 2 textbooks in applied mathematics and chemical engineering.
Prof Do has been recognized as a fellow of the International Adsorption Society (2016). He is also honored with the Esso Award of Excellence in Chemical Engineering (1999). Besides, he has been the members of American Institute of Chemical Engineers and International Adsorption Society since 1980 and 1989 respectively.
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