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Add to Calendar 9/5/2018 4:00 pm 9/5/2018 America/Chicago Physics Colloquium: “New Eyes for Nanocatalysts: Atomic Scale Investigations of TiO2 Chemistry” DESCRIPTION:

Earth-abundant metal oxides have attracted a great deal of attention for environmental remediation and photocatalysis. These materials are attractive because they are inexpensive, they are typically very stable under reactive conditions, and their semiconducting nature enables efficient generation of long-lived photocarriers that can initiate chemical reactions. Nevertheless, an atomic-scale understanding of their reactivity under real-world conditions has proven elusive, in part because of the complex milieu of reactants in ambient environments.

Over the past few years, researchers around the world have observed the formation of mysterious molecularly ordered structures on the surface of TiO2 photocatalysts in air and solution. These structures have been attributed to many causes, including a new state of ordered H2O. Using a combination of atomic-scale microscopy and spectroscopy, we show that these structures are due to the highly selective adsorption of atmospheric acids that are typically present in parts-per-billion concentrations. These surfaces effectively repel other adsorbates, such as alcohols, present in much higher concentrations. The self-assembled monolayers have the unusual property of being both hydrophobic and highly water soluble, which may contribute to the self-cleaning properties of TiO2. Interestingly, these monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

In related work, we investigate the structure of solution-deposited monolayers on TiO2 and demonstrate a rational approach to tuning intermolecular interactions and enabling long-range ordering. We show simple electrostatic insights can be used to engineer away unfavorable intermolecular interactions, producing monolayers with exceptional long-range ordering. Quantitative measurements show that the long-range interactions that lead to this regularity are much stronger than predicted by conventional surface simulations based on density functional theory  and suggest a new path to the production of highly ordered monolayers and superstructures of large molecules.

\n\nSPEAKER: Melissa A. Hines, Department of Chemistry and Chemical Biology, Cornell University
141 Loomis Lab false

Physics Colloquium: “New Eyes for Nanocatalysts: Atomic Scale Investigations of TiO2 Chemistry”

Speaker Melissa A. Hines, Department of Chemistry and Chemical Biology, Cornell University
Date: 9/5/2018
Time: 4 p.m.
Location: 141 Loomis Lab
Event Contact: Suzanne Hallihan
217-244-7151
shalliha@illinois.edu
Cost: None
Sponsor: Department of Physics
Event Type: Other
 

Earth-abundant metal oxides have attracted a great deal of attention for environmental remediation and photocatalysis. These materials are attractive because they are inexpensive, they are typically very stable under reactive conditions, and their semiconducting nature enables efficient generation of long-lived photocarriers that can initiate chemical reactions. Nevertheless, an atomic-scale understanding of their reactivity under real-world conditions has proven elusive, in part because of the complex milieu of reactants in ambient environments.

Over the past few years, researchers around the world have observed the formation of mysterious molecularly ordered structures on the surface of TiO2 photocatalysts in air and solution. These structures have been attributed to many causes, including a new state of ordered H2O. Using a combination of atomic-scale microscopy and spectroscopy, we show that these structures are due to the highly selective adsorption of atmospheric acids that are typically present in parts-per-billion concentrations. These surfaces effectively repel other adsorbates, such as alcohols, present in much higher concentrations. The self-assembled monolayers have the unusual property of being both hydrophobic and highly water soluble, which may contribute to the self-cleaning properties of TiO2. Interestingly, these monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

In related work, we investigate the structure of solution-deposited monolayers on TiO2 and demonstrate a rational approach to tuning intermolecular interactions and enabling long-range ordering. We show simple electrostatic insights can be used to engineer away unfavorable intermolecular interactions, producing monolayers with exceptional long-range ordering. Quantitative measurements show that the long-range interactions that lead to this regularity are much stronger than predicted by conventional surface simulations based on density functional theory  and suggest a new path to the production of highly ordered monolayers and superstructures of large molecules.

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