2013 Fall Seminar Series

Tuesday, December 10, 2013

Understanding and Controlling Selectivity in Heterogeneous Catalysis of Biomass Derivatives
Will Medlin
University of Colorado, Dept. of Chemical and Biological Engineering


2:00 PM
Tuesday, December 10, 2013
CEB 218 (810 South Clinton Street)
Performing specific transformations of reactants with multiple functional groups is a challenging objective, since each functional group can potentially adsorb and react on a catalytic surface. Addressing this problem is particularly important for the conversion of biomass to chemicals and fuels, because carbohydrates and their downstream intermediates contain multiple reactive functional groups. For example, furfural and hydroxymethyl furfural, which can be produced in high volumes from dehydration of sugars, contain one or more oxygenate (alcohol or aldehyde) functions together with a furan ring. Alcohols, aldehydes, and furan in isolation are all reactive on Pt-group metal surfaces, and the individual reaction pathways of each group are observable when these functions are located on the same molecule. Furthermore, as will be demonstrated in this presentation, the multiple functions on furfuryl oxygenates have synergistic effects on reactivity, opening up additional reaction pathways not available to reactants containing only a single functional group. Thus, controlling selectivity through heterogeneous catalyst design is highly complex.Our group has conducted surface-level investigations of a number of reactions important for the conversion of biomass to fuels and chemicals. This presentation will focus on how these studies can be used to understand key aspects of reaction mechanisms on surfaces, and furthermore how this understanding can lead to design of catalysts with improved performance. Several examples will be presented. In the selective conversion of furfurals to fuel-grade products, we have found that selectivity can be drastically improved by preparing catalysts that control crowding of reactants on the surface. For the selective oxidation of biomass-derived polyols to key renewable chemicals, local surface composition can be controlled to influence reactant binding in a way that improves desired product yields. Finally, reforming of biomass-derived “tars” can be improved by using atomic layer deposition to make catalysts with precise control over both surface structure and composition. A general approach for approaching catalyst design in reactions of complex oxygenated chemicals will also be discussed.

Thursday, November 14, 2013

Water: The Killer App for Diamond
J.A. Carlisle
Advanced Diamond Technologies, Inc., Co-Founder & CTO


11:00 AM
Thursday, November 14, 2013
CEB 218 (810 South Clinton Street)
In this presentation our work to develop boron-doped UNCD (Ultrananocrystalline Diamond) thin films for water-related environmental applications will be highlighted. Over the past ten years there has been considerable work to develop diamond-based electrochemical water treatment & sensing technologies. The surface of diamond has many desirable electrochemical properties that make it attractive for the disinfection and remediation of water as well as for the electrochemical detection of toxins and pathogens such as endocrine inhibitors and legionella. Despite years of study there are many fundamental questions that remain unanswered regarding the electrochemical reactions that may occur during oxidant generation or waste destruction, as well has how the hydrolytic stability of clean and functionalized diamond surfaces can impact the electrochemical transduction of information for sensing targets in aqueous media. Also, a major challenge for the successful commercialization of electrodes based on thin film diamond has been their long-term durability as well as the perceived high cost of the technology. UNCD combined with UDD (ultra-disperse diamond) seeding has led to a major improvement in the overall dimensional stability of UNCD/Nb and UNCD/Ta electrodes. Most importantly, operation of these electrodes can now be sustained at very high current densities (300-1000 mA/cm2) with projected lifetimes of years. This has opened up opportunities for the use of diamond-based electrodes for the optimized generation of concentrated oxidant solutions suitable for a number of water treatment applications. In particular, the on-site generation (OSG) of mixed oxidants, which contain a mixture of chlorine- and oxygen-based chemicals with high oxidation potentials, are particularly attractive for a number of disinfection applications, including water used for cooling towers (largest user of water in the US), commercial swimming pools, and oil & gas mining. OSG is also attractive as a green technology as it eliminates the shipment & storage of hazardous chemicals such as chlorine. Also presented will be work to develop boron-doped UNCD MEMS devices that can enable the real-time, continuous monitoring of water for chemical and biological contaminants. Amperometric sensors based on boron-doped UNCD have proved very effective at sensing Contaminants of Emerging Concern (CECs) such as endocrine inhibitors. Biosurfaces based on the covalent immobilization of antibodies on BD-UNCD that selectively target bacterial pathogens such as Escherichia coli can function for periods of days-weeks while continuously monitoring for the presence of these impurities with ppb sensitivities. Co-integration of electrochemical detection and destruction technologies could open up new areas of application.

Thursday, October 10, 2013

Effects of Nanoscale Confinement in Polymer Films: Glass Transition Temperature and Diffusion
John M. Torkelson
Chemical and Biological Engineering & Materials Science and Engineering, Northwestern University


11:00 AM
Thursday, October 10, 2013
CEB 218 (810 South Clinton Street)
In 1995, Philip Anderson wrote, "The deepest and most interesting unsolved problem in solid state theory is … the nature of glass and the glass transition” (Science 1995, 267, 1615). One year earlier, Keddie, Jones and Cory (Europhys. Lett. 1994, 27, 59) discovered that a 15-nm-thick polystyrene film supported on silica exhibits a glass transition temperature, Tg, that is reduced by more than 20 K relative to bulk Tg. Since then, dozens of studies have characterized how Tg values of polymers are modified by nanoscale confinement. However, most studies characterized only average Tgs across films and focused on a single polymer -- polystyrene. In 2000, Pierre de Gennes (Eur. Phys. J. E 2000, 2, 201) challenged the glass transition and confinement research communities by stating, “Future experiments should aim not at the determination of a single Tg, but at a distribution of Tgs.” In response to this challenge, we developed a simple fluorescence/multilayer method to determine distributions of Tg in polymer films and nanocomposites. We have found that perturbations to Tg at a free surface or polymersubstrate interface (with attractive interactions) can propagate several tens to hundreds of nanometers into a film and that the strength of the gradient in Tg is strongest at the free surface or interface. Our studies of a dozen different polymer species also indicate which fundamental polymer properties play key roles in defining the Tg-confinement effect, with fragility being an important example. Finally, we have discovered that translational diffusion coefficients of small dye molecules dispersed in polymer can be reduced by as much as a factor of 1000 with confinement. Our studies have led to understanding why the effects of surfaces and interfaces in perturbing Tg depend strongly on polymer species. We have found that the Tg reduction associated with free surface effects is enhanced with an increasing requirement for cooperativity of segmental mobility associated with Tg; that is, the free-surface effect is enhanced with increasing polymer fragility. In contrast, H-bond formation between chain segments and hydroxyl groups on nanofiller or substrate surfaces results in increasing values of Tg with nanoconfinement. Novel experiments involving templated nanorods and nanotubes will also be discussed. With this geometry, it is possible to explore Tg-confinement effects by conventional differential scanning calorimetry, which is the technique used to characterize thermal transitions in bulk polymers in both industry and academia. We will show that confinement in this novel geometry leads to Tg confinement effects similar to those observed in polymer films via non-calorimetric techniques.

Thursday, October 3, 2013

Theory and Simulation of Biomolecular Systems: Surmounting the Challenge of Bridging the ScalesOn
Gregory A. Voth
Department of Chemistry, James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, University of Chicago


2:00 PM
Thursday, October 3, 2013
CEB 218 (810 South Clinton Street)
A multiscale theoretical and computational methodology will be discussed for studying biomolecular systems across multiple length and time scales. The approach provides a systematic connection between all-atom molecular dynamics, coarse-grained modeling, and mesoscopic phenomena. At the heart of the approach is a method for deriving coarse-grained models from protein structures and their underlying molecular-scale interactions. This particular aspect of the work has strong connections to the theory of renormalization, but it is more broadly developed and implemented for heterogeneous biomolecular systems. A critical component of the methodology is also its connection to experimental structural data such as cryo-EM or x-ray, thus making it “hybrid” in its character. Important applications of the multiscale approach to study key features of large multi-protein complexes such as the HIV-1 virus capsid, actin filaments, and protein-mediated membrane remodeling will be presented as time allows.

 
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