ERI: Creating Stable and Periodic Arrays of Molecular-Scale Liquid:Liquid Interfaces for Chemical Reactions

Chemical interfaces are formed when two liquids with different polarities cannot mix, e.g., immiscible liquids. In heterogeneous systems, these interfaces provide unique chemical environments with molecular structures and thermodynamic and chemical properties that are different from those far from the interface. For example, the interfacial properties can facilitate molecular self-assembly (i.e., molecular rearrangement) to form micro- and nano-structured thin films, which are potentially useful for industrial chemical processes.

However, harnessing this phenomenon in an application requires generating a large interfacial contact area, which is challenging because the contact areas between bulk solutions are self-minimizing. A class of porous materials called metal-organic frameworks (MOFs) consists of a group of continuous hollow or liquid-containing networks of uniformly sized or hierarchically cross-connecting channels.

Hierarchically cross-connecting channels are larger structures formed from building blocks that have their own distinct molecular structure. Hierarchically nanoporous channels are expected to create nanoconfined interfacial spaces that distribute polar and nonpolar molecules to form stable and periodic arrays of molecular-scale interfaces, overcoming the limited interfacial contact area challenge.

This project aims to develop nanosized liquid-liquid interfaces in MOFs, enabling select chemical reactions to occur at the interface between the nanoconfined immiscible liquids. The fundamental knowledge gained here will provide insight into the distribution of polar and nonpolar molecules in a hierarchically nanoporous environment and build a foundation for studying important industry-relevant chemical processing, nanoconfinement-enabled reactions, molecular separations, and energy conversion processes.

This research program is integrated with course development that bridges advanced undergraduate and graduate content across science and engineering disciplines. The project also creates opportunities for undergraduate and graduate research student training.

The project’s research goals are to (1) examine polar and nonpolar molecular adsorption/desorption thermodynamics and kinetics and demonstrate the formation of liquid:liquid interfaces in hierarchically nanoporous MOFs and (2) develop reaction systems for the manipulation of these interfaces in nanoconfined space by investigating model chemical reactions, such as the interfacial synthesis of nanomembranes and catalytic phenol alkylation with olefin, and use combined experimental and computational tools to obtain structure-function relationships. The project will explore the self-sorting phenomenon of polar and nonpolar molecules in hydrophilic and hydrophobic channels in hierarchically nanoporous MOFs.

The sitting location of molecules in MOFs will be determined using difference electron (envelope) density (DED) mapping from powder X-ray diffraction data. Neutron scattering measurements combined with computational simulations will enable further characterization of the liquid:liquid interfaces. The results from this project will be used to develop new systems where the periodic nanosized interfaces will enable efficient reactions for those rate-limited by the liquid:liquid contact areas.

A bridge course for undergraduate seniors and graduate students majoring in science and engineering will be delivered at Rochester Institute of Technology. The research results will be integrated into this course to foster interdisciplinarity across chemistry and engineering fields. Three elements will be incorporated into the course to maximize the potential impact on students and the broader community: delivery of core concepts of porous structured materials, analysis of high-impact research articles, and guest lectures from neighboring academic institutions.

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.