August 1, 2016.
Metal organic frameworks are synthetic porous materials with great capacity for adsorption of carbon dioxide and methane. They chemically appear as a chain-link fence with nodes of metal connected by organic linkers. The pores between the nodes define the characteristics of the material, allowing gas particles of specific size to pass through while blocking larger particulates. While there has been success in synthesizing small amounts of metal organic frameworks, the mechanistic details behind their assembly remain unknown. Understanding the synthesis mechanism is necessary to understand the kinetics involved and be able to produce this useful material on an industrial scale. Using a well-known metal organic framework as a prototypical system, we calculated the energy barriers needed to join intermediate species in the synthesis of a metal organic framework with non-equilibrium molecular dynamics simulations. The umbrella sampling technique is used, where classical dynamics simulations with high spatial force constraints on the reaction coordinate of the system are performed. A potential of mean force at all points along the reaction coordinate is obtained revealing the free energy required, which determines the rate for joining intermediates together. The simulation protocol developed will be employed to obtain the energy barriers to join possible intermediates, and these barriers combined into a kinetic model of overall metal organic framework formation.
Materials Chemistry | Organic Chemistry | Polymer Chemistry
Pacific Northwest National Laboratory (PNNL)
*This material is based upon work supported by a grant from the S.D. Bechtel, Jr. Foundation and the California State University STEM Teacher Researcher Program. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Foundation.