Impact of Metal Oxides Functionalization on the Structural Stability of Kaolin–Carbon Quantum Dot Shale Models for Pentane Adsorption: A Molecular Dynamics Study
Description
Molecular simulation techniques were used to examine the adsorption characteristics of pentane on pristine and metal oxide-functionalized (CuO, ZnO, TiO2) shale materials. Molecular dynamics (MD) simulations were first performed at 298, 308, and 318 K to examine the thermodynamic stability of pristine and modified shale systems. Results showed successful equilibration of all the systems, with average temperatures all being close to the target temperatures and stable energy fluctuations during the simulation time. The total and potential energies of the shale framework were reduced by metal oxide functionalization, suggesting increased stabilization of the shale framework in comparison with the pristine shale model. Compared with the other unfunctionalized shale systems, slightly higher peak intensities were observed in the RDF for the functionalized shale systems, which could indicate improved local adsorbate–adsorbent interaction. The metal oxides incorporation was found to enhance the mobility of pentane in the shale matrix by analysis of mean square displacement (MSD) and self-diffusion coefficient. The diffusion coefficients were in the order ZnO@SHALE > CuO@SHALE > TiO2@SHALE > SHALE, which was found to be the most favorable transport environment provided by the ZnO functionalization. The adsorption energies were calculated to verify that the adsorption of pentane is thermodynamically favorable on all the surfaces studied. The functionalized systems showed adsorption energies between −34.526 and −35.491 kcal/mol, while the pristine shale showed the highest adsorption affinity with the adsorption energy of −49.163 kcal/mol. While their molecular adsorption strength was slightly lower, the metal-oxide-functionalized systems exhibited better molecular transport and lower structural deformation energies.