Date of Award

Fall 12-12-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Ning Fang

Second Advisor

Gangli wang

Abstract

Single-molecule fluorescence (SMF) microscopy imaging was employed to understand the nanoconfinement in porous materials. The changes in chemical and physical properties of molecules in nanoconfined space are often termed as the confinement effects. The single-molecule approach unveils the static and dynamic heterogeneities from seemingly equal molecules by removing the ensemble averaging effect. Physicochemical processes, including mass transport, surface adsorption/desorption, and chemical conversions within the confining space inside porous materials, have been studied at nanometer spatial resolution, at the single nanopore level, with millisecond temporal resolution, and under real chemical reaction conditions. Understanding these physicochemical processes provides the ability to quantitatively measure the inhomogeneities of nanoconfinement effects from the confining properties, including morphologies, spatial arrangement, trapping domains, etc. By employing SMF imaging, nanoconfinement effects on molecular transport and reaction kinetics in heterogeneous catalysis under variable nanopore morphologies were studied. Our results revealed higher catalytic activity on the confined metal reaction centers, which was enhanced further with longer and narrower nanopores. Experimental evidence, including molecular orientation, activation energy, and intermediate reactive species, has been gathered to provide a molecular-level explanation of the physical constraints on molecular orientation and enrichment of reaction intermediates. Moreover, Reaction rates, molecular adsorption strength, and product molecule dissociation kinetics are experimentally quantified at the single-molecule level for a mechanistic understanding of catalytic reaction behaviors in hydrophilic and hydrophobic nanopores. Furthermore, a molecular-level understanding of separation processes/mechanism under nanoconfinement using 3D single-molecule tracking to resolve molecular diffusion was used to obtain the capacity factor and to lay a general foundation for further work in modifying stationary phases to improve the separation performance. Prospects and limitations of current single-molecule imaging studies on nanoconfinement are also discussed.

DOI

https://doi.org/10.57709/32647744

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