Chemistry, Department of

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A Convenient, Effective, and Safer Flame Demonstration

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-08-07
Abstract: 

The well-described flame demonstration illustrates different aspects of energy, electronic transition, atomic structure, and the electromagnetic spectrum. Burning salts dissolved in a solvent produces visually appealing and vividly colored flames but many incidents have been reported from improper use of solvents and further use of this method has been strongly discouraged. Although alternative approaches have been developed to address some of the safety concerns, they do not match the convenience of use and vibrant colors produced using this new method. Presented, is a new approach on the standard flame demonstration that mitigates all concern regarding solvent use and restores the convenient aspects and brilliance of color of the traditional flame demonstration without compromising safety.

Document type: 
Article

Physical Modeling of the Proton Density in Nanopores of PEM Fuel Cell Catalyst Layers

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-08-10
Abstract: 

In polymer electrolyte fuel cells, a foremost goal is to design catalyst layers with high performance at markedly reduced platinum loading. As a contribution towards this objective, we explore a simplified pore geometry to capture the impact of ionomer structure and metal charging properties on the proton density distribution and conductivity in relevant nanopores. The basic model is a cylindrical tubular pore confined by an ionomer shell and a solid platinum-coated core. The gap region between metal and ionomer is filled with water. We study how the surface charge density at the ionomer and the metal charging relation as well as geometric pore parameters affect the electrochemical performance. The density of charged side chains at the ionomer shell exerts a pronounced impact on the surface charge density at the Pt surface and thereby on the activity of the pore for the oxygen reduction reaction. The key parameter controlling the interplay of surface and bulk charging phenomena is the overlap of the Debye lengths of ionomer and metal surfaces in relation to the width of the gap. It allows distinguishing regions with weak and strong correlation between surface charge densities at ionomer shell and Pt core.

Document type: 
Article
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Introducing Complex NMR Mixtures at the Undergraduate Level: Analysis of the Diels-Alder Reaction Between Methylcyclopentadiene and Maleic Anhydride (Part I)

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019
Abstract: 

Analysis of a simple NMR spectrum is fairly easy and straight forward for undergraduate students but analyzing a fairly complex NMR can be very daunting and requires a methodical approach. This work uses the ubiquitous Diels-Alder reaction of methylcyclopentadiene and maleic anhydride to introduce students to an NMR spectrum that consist of inseparable mixtures of isomers and their analysis using advanced NMR spectroscopic techniques. This laboratory experiment further outlines the use of derivatization techniques for the separation of isomeric mixtures by preparing diastereomers and using NMR spectroscopy for their identification.

Document type: 
Article
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Binary Silanization and Silver Nanoparticle Encapsulation to Create Superhydrophobic Cotton Fabrics with Antimicrobial Capability

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-06-05
Abstract: 

Cotton fabrics are functionalized with a binary solution of fluorine-free organosilanes and “encapsulated” with silver nanoparticles to achieve both superhydrophobic and antimicrobial properties. Derived from cellulose, cotton is one of the most abundant biologically generated materials and has been used in a wide variety of consumer goods. Nonetheless, cotton fabrics are not waterproof and prone to microbial contamination. Herein we report the rapid functionalization of cotton fabrics with a binary hexane solution of methyltrichlorosilane (MTS) and octadecyltrichlorosilane (OTS) at low concentration (0.17% v/v) followed by coating with colloidal silver nanoparticles (AgNP). The combined effects of binary silanization and AgNP encapsulation produced a surface that has remarkable water contact angle of 153 ± 2° and antimicrobial properties (against gram-negative Escherichia coli). The superior performance of the modified cotton fabrics produced with fluorine-free organosilanes and silver nanoparticles augments the potential of improving the functionality of abundant biopolymers to be waterproof and contamination-resistant.

Document type: 
Article
File(s): 

Towards the Organic Double Heterojunction Solar Cell

Author: 
Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-04-04
Abstract: 

A perspective on the operating principles of organic bulk heterojunction solar cells is outlined and used to suggest an alternative device configuration, employing two type II semiconductor heterojunctions in series. Guiding principles to the implementation of this configuration, called a double heterojunction, are summarized. Assuming an exciton binding energy of 0.3 eV or less, results in a maximum achievable power conversion efficiency of well over 25 %. Achieving a high efficiency organic double heterojunction requires a specific energy level alignment, charge separation in the absence of driving forces, high phase purity and excellent diode quality. Fully conjugated triblock polymers of the form [D1-A1]-[D1-A2]-[D2-A2] appear to be a system that can fulfill these requirements. Going forward, the primary challenge is the identification and development of synthetically tractable materials which have the necessary properties.

Document type: 
Article
File(s): 

Poly(Bis-Arylimidazoliums) Possessing High Hydroxide Ion Exchange Capacity and High Alkaline Stability

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-05-24
Abstract: 

Solid polymer electrolyte electrochemical energy conversion devices that operate under highly alkaline conditions afford faster reaction kinetics and the deployment of inexpensive electrocatalysts compared with their acidic counterparts. The hydroxide anion exchange polymer is a key component of any solid polymer electrolyte device that operates under alkaline conditions. However, durable hydroxide-conducting polymer electrolytes in highly caustic media have proved elusive, because polymers bearing cations are inherently unstable under highly caustic conditions. Here we report a systematic investigation of novel arylimidazolium and bis-arylimidazolium compounds that lead to the rationale design of robust, sterically protected poly(arylimidazolium) hydroxide anion exchange polymers that possess a combination of high ion-exchange capacity and exceptional stability.

Document type: 
Article
File(s): 

Mesoporous Platinum Prepared by Electrodeposition for Ultralow Loading Proton Exchange Membrane Fuel Cells

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-03-11
Abstract: 

The porosity and utilization of platinum catalysts have a direct impact on their performance within proton exchange membrane fuel cells. It is desirable to identify methods that can prepare these catalysts with the desired features, and that can be widely implemented using existing and industrially scalable techniques. Through the use of electrodeposition processes, fuel cell testing, and electron microscopy analyses before and after fuel cell testing, we report the preparation and performance of mesoporous platinum catalysts for proton exchange membrane fuel cells. We found that these mesoporous platinum catalysts can be prepared in sufficient quantities through techniques that also enable their direct incorporation into membrane electrode assemblies. We also determined that the mesoporous catalysts achieved a high porosity, which was retained after assembly and utilization within fuel cells. In addition, these mesoporous platinum catalysts exhibited an improved platinum mass specific power over catalysts prepared from commercially available platinum nanocatalysts.

Document type: 
Article
File(s): 

18F-Fluorination of Unactivated C-H Bonds in Branched Aliphatic Amino Acids: Direct Synthesis of Oncological PET Imaging Agents

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-03
Abstract: 

A mild and selective photocatalytic C-H 18F-fluorination reaction has been developed that provides direct access to 18F-fluorinated amino acids. The biodis-tribution and uptake of three 18F-labelled leucine ana-logues via LAT1 mediated transport in several cancer cell lines is reported. PET imaging of mice bearing PC3 (pros-tate) or U87 (glioma) xenografts using 5-[18F]-fluoro-homoleucine showed high tumor uptake and excellent tumor visualization, highlighting the utility of this strat-egy for rapid tracer discovery for oncology.

Document type: 
Article
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Design Principles for Block Polymer Organic Double Heterojunction Solar Cells

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-09
Abstract: 

An organic double heterojunction photovoltaic device is described and the limits of its power conversion efficiency are investigated via numerical calculation. In the absence of exciton binding energy, fully conjugated block polymer devices exhibit power conversion efficiencies slightly exceeding the Shockley-Queissar limit. As exciton binding energy increases, a decrease in efficiency occurs, but remains over 20% for binding energies less than 0.5 eV. Further calculations show that devices require a high degrees of phase purity to leverage the full benefit of the double heterjunction structure. Synthetic targets are identified and their maximum efficiency is calculated based on experimentally measured energy levels, leading to a generalized structural motif.

Document type: 
Article
File(s): 

Surface Configuration and Wettability of Nickel (Oxy)Hydroxides: A First-Principles Investigation

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-07
Abstract: 

This article explores the wetting behavior of b-type nickel hydroxide, b-Ni(OH)2, and nickel oxyhydroxide, b-NiOOH, by means of first-principles calculations. Water is found to interact weakly with b-Ni(OH)2(001), but strongly with b-NiOOH(001). As unveiled with the use of ab initio molecular dynamics simulations, surface water layers at b-NiOOH(001) show a high degree of ordering correlated with a large surface polarization effect. In comparison, interfacial water at b-Ni(OH)2(001) exhibits enhanced disorder and higher mobility. The weak interaction of water with b-Ni(OH)2(001) is consistent with the small dipole moment of this surface. On the surface of b-NiOOH(001), in addition to the significantly increased surface dipole moment, unsaturated O atoms increase the number of hydrogen bonds between water molecules and the surface, resulting in strong water binding. The wettability trends found in this simulation study are consistent with experimental observations. Another theoretical observation is the increased work function of b-NiOOH(001) relative to b-Ni(OH)2(001) that agrees with experimental results reported in the literature.

Document type: 
Article
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