NSF-DFG Confine: Diffusion of Water Confined in Patterned Hydrophilic-Hydrophobic Nanopores

点击翻译按钮获取中文摘要

With support from the Chemical Structure, Dynamics and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professors Laura Gagliardi of the University of Chicago and Omar Yaghi of the University of California at Berkeley are combining advanced molecular simulation and chemical analysis tools such as nuclear magnetic resonance (NMR) to explore and characterize the motion of water molecules inside metal-organic frameworks (MOFs). Water is essential to life and understanding how water molecules move in confined spaces is of fundamental interest. This research focuses on MOFs with well-defined patterns of alternating water attracting (hydrophilic) and water repelling (hydrophobic) grid-like tiled regions. This project seeks to reveal for the first time the molecular level details of the diffusion of water within this patterned space and the interplay between the hydrophilic and hydrophobic regions. Professor Gagliardi, her student and a collaborator in Germany (Professor Joachim Sauer, Humboldt University) will perform quantum mechanical calculations to predict water-MOF interactions, and Professor Yaghi and his student will characterize the water-MOF interactions with NMR spectroscopic techniques. The discoveries of this project could lead to a variety of useful applications of MOF materials, including liquid and gas separations and purification, water harvesting, and CO2 capture. In addition to formal research training activities, the Gagliardi group also seeks to inspire future generations of internationally aware scientists through the Chicago chapter of Expanding Your Horizons. This collaborative project will provide the students involved with a rich interdisciplinary and international experience. Professor Gagliardi and her student compute chemically accurate adsorption constants for water molecules on a lattice of adsorption sites from ab initio free energies; they also compute chemically accurate diffusion rate constants for jumps of water molecules between adsorption sites using ab initio transition state theory. To define elementary diffusion steps, they define adsorption cells and consider all possible jump pathways between sites in neighbored cells in all crystallographic directions. Finally, they predict adsorption isotherms and diffusivities as a function of loading using Grand Canonical Monte Carlo (GCMC) and kinetic Monte Carlo (kMC) simulation, respectively, on a lattice of sites. Professor Sauer is providing ab initio-calculated potential energy surfaces to augment the accuracy of the GCMC and kMC simulations. Professor Yaghi and his student will synthesize MOF materials and study the water self-diffusion at different water loadings in the MOF pores using pulsed magnetic field gradient NMR measurements. This should allow for a direct comparison with the predicted intrapore diffusion constants. Additionally, they will employ quasi-elastic neutron scattering (QENS) to gain more insight about the water mobility in the nanopores at different loadings. Importantly, QENS would provide exclusive information about the diffusion model and mechanism in the MOF pores.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.