Chemistry, Department of

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Optimization of the Synthesis of n-Phthalimidoalkylthiols as Precursors for w-Aminoalkylthiols as Prepared by Undergraduate Chemistry Students

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2015-04-20
Abstract: 

The synthesis of n-phthalimidoalkylthiols from phthalimide and n,m-dibromoalkane was demonstrated as a general approach to short and medium chain (x = 1 to 12) functional alkylthiols in an undergraduate laboratory setting. The reaction conditions were demonstrated to be mild enough to directly synthesize nphthalimidoalkylthiols with a carbon chain containing either double or triple bonds. The syntheses of each of these alkylthiols can be completed in less than 24 h (over a few laboratory periods) with at least a 50% overall yield. Reactivity of n,m-dibromoalkane with phthalimide was monitored with 1 H-NMR to determine the length of time needed for the reaction to reach completion avoiding the inaccurate use of thin layer chromatography. Based on this result, reaction times were reduced by two-thirds from those previously reported in the literature, which was necessary to prepare a method that will accommodate the duration of second year introductory organic or organic spectroscopy courses.

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Article
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Determining the Thickness of Aliphatic Alcohol Monolayers Covalently Attached to Silicon Oxide Surfaces Using Angle-Resolved X-ray Photoelectron Spectroscopy

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-04-01
Abstract: 

The thickness of alcohol based monolayers on silicon oxide surfaces were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS). Advantages of using alcohols as building blocks for the formation of monolayers include their widespread availability, ease of handling, and stability against side reactions. Recent progress in microwave assisted reactions demonstrated the ease of forming uniform monolayers with alcohol based reagents. The studies shown herein provide a detailed investigation of the thickness of monolayers prepared from a series of aliphatic alcohols of different chain lengths. Monolayers of 1-butanol, 1-hexanol, 1-octanol, 1-decanol, and 1-dodecanol were each successfully formed through microwave assisted reactions and characterized by ARXPS techniques. The thickness of these monolayers consistently increased by ∼1.0 Å for every additional methylene (CH2) within the hydrocarbon chain of the reagents. Tilt angles of the molecules covalently attached to silicon oxide surfaces were estimated to be ∼35° for each type of reagent. These results were consistent with the observations reported for thiol based or silane based monolayers on either gold or silicon oxide surfaces, respectively. The results of this study also suggest that the alcohol based monolayers are uniform at a molecular level.

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Article
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Nanoscale Thin Films of Niobium Oxide on Platinum Surfaces: Creating a Platform for Optimizing Material Composition and Electrochemical Stability

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-12-18
Abstract: 

A nanoscale thin film of niobium oxide on a platinum substrate was evaluated for its influence on the electronic and chemical properties of the underlying platinum towards the oxygen reduction reaction with applications to proton exchange membrane fuel cells. The nanoscale thin film of niobium oxide was deposited using atomic layer deposition onto the platinum substrate. A film of niobium oxide is a chemically stable and electronically insulating material that can be used to prevent corrosion and electrochemical degradation when layers are several nanometers thick. These layers can be insulating if sufficiently thick and may not be sufficient to protect the platinum from corrosion if too thin. An ∼3 nm thin film of niobium oxide was fabricated on the platinum surface to determine its influence on the electronic and chemical properties at the interface of these materials. The atomic layer deposition process enabled a precise control over the material composition, structure, and layer thickness. The niobium oxide film was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy to evaluate whether a balance could be found between the inhibition of platinum degradation and electronic insulation of the platinum for use in proton exchange membrane fuel cells. The 3 nm thin niobium oxide film was found to be sufficiently thin to permit electronic conductivity while reducing the incidence of platinum dissolution.

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Article
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Synthesis of Lithium Niobate Nanocrystals with Size Focusing through an Ostwald Ripening Process

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-03-06
Abstract: 

A simple surfactant assisted solution-phase approach is demonstrated here for the preparation of lithium niobate (LiNbO3) nanoparticles with an average size of 30 nm. This solution-phase process results in the formation of crystalline, uniform nanoparticles of LiNbO3 at 220 °C with an optimal reaction time of 36 h. Advantages of this method also include the preparation of crystalline nanoparticles of LiNbO3 without the need for further heat treatment or the use of an inert atmosphere. The growth of these nanoparticles began with a controlled agglomeration of nuclei. The reaction subsequently underwent a process of oriented attachment and Ostwald ripening, which dominated and controlled the further growth of the nanoparticles. These processes produced single-crystalline nanoparticles of LiNbO3. The average dimensions of the nanoparticles were tuned from 30 to 95 nm by increasing the reaction time of the solvothermal process. The LiNbO3 nanoparticles were characterized using transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution TEM, X-ray diffraction, and Raman spectroscopy techniques. The nanoparticles were also confirmed to be optically active for second harmonic generation (SHG). These particles could enable further development of SHG based microscopy techniques.

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Article
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Regular Dimpled Nickel Surfaces for Improved Efficiency of the Oxygen Evolution Reaction

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-04-02
Abstract: 

Persistent bubble accumulation during the oxygen evolution reaction (OER) can effectively block catalytically active surface sites and reduce overall system performance. The OER is an essential half-reaction with relevance to metal–air batteries, fuel cells, and water electrolysis for power to gas applications. The renewable energy sector could benefit from the identification of surface morphologies that can effectively reduce the accumulation of bubbles on electrocatalytic surfaces. In this work, regular dimpled nickel (Ni) features were prepared to investigate how electrode morphology and therefore its roughness and wetting properties may affect the efficiency of the OER. The dimpled Ni features were prepared using spherical poly(styrene) (PS) templates with a diameter of 1 μm. The electrodeposition against regular, self-assembled arrays of PS templates was tuned to produce four types of dimpled features each with a different depth. Enhancements to the OER efficiency were observed for some types of dimpled Ni features when compared to a planar electrodeposited Ni electrode, while the dimpled features that were the most recessed demonstrated reduced efficiencies for the OER. The findings from this study emphasize the influences of electrode surface morphology on processes involving electrocatalytic gas evolution.

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Article
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Modifying the Surface Properties of Indium Tin Oxide with Alcohol-Based Monolayers for Use in Organic Electronics

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-04-25
Abstract: 

Transparent conductive oxides (TCOs) serve a critical function in many devices, such as organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). To optimize the performances of these devices, it is desirable to tune the interface between the TCO and the next functional layer of these devices. Self-assembled monolayers prepared from phosphonic acids and silanes are commonly used to tune the properties and performance of this interface, including its surface energy, work function, and durability. Here, we report a new form of self-assembled monolayers for modifying indium tin oxide (ITO), a standard TCO used in OLEDs and OPVs. The ITO surfaces were modified with a series of distinct alcohol reagents. Stabilities of these alcohol-based monolayers were compared with modifications derived from silanes and phosphonic acids, which are commonly used in the literature and industrial processes. Work functions and surface energies of these modified substrates were determined using ultraviolet photoelectron spectroscopy and contact angle measurements. Stability of these monolayers was assessed using cyclic voltammetry, X-ray photoelectron spectroscopy, and transmission spectroscopy techniques. On the basis of the results of these studies, alcohol-based monolayers are promising candidates to modify ITO substrates for use in OLEDs and OPVs.

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Article
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Template Assisted Preparation of High Surface Area Macroporous Supports with Uniform and Tunable Nanocrystal Loadings

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-01-01
Abstract: 

The incorporation of catalytic nanocrystals into macroporous support materials has been very attractive due to their increased catalyst mass activity. This increase in catalytic efficiency is attributed in part to the increased surface area to volume ratio of the catalysts and the use of complementary support materials that can enhance their catalytic activity and stability. A uniform and tunable coating of nanocrystals on porous matrices can be difficult to achieve with some techniques such as electrodeposition. More sophisticated techniques for preparing uniform nanocrystal coatings include atomic layer deposition, but it can be difficult to reproduce these processes at commercial scales required for preparing catalyst materials. In this study, catalytic nanocrystals supported on three dimensional (3D) porous structures were prepared. The demonstrated technique utilized scalable approaches for achieving a uniform surface coverage of catalysts through the use of polymeric sacrificial templates. This template assisted technique was demonstrated with a good control over the surface coverage of catalysts, support material composition, and porosities of the support material. A series of regular porous supports were each prepared with a uniform coating of nanocrystals, such as NaYF4 nanocrystals supported by a porous 3D lattice of Ti1−xSixO2, Pt nanocrystals on a 3D porous support of TiO2, Pd nanocrystals on Ni nanobowls, and Pt nanocrystals on 3D assemblies of Au/TiO2 nanobowls. The template assisted preparation of high surface area macroporous supports could be further utilized for optimizing the use of catalytic materials in chemical, electrochemical, and photochemical reactions through increasing their catalytic efficiency and stability.

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Article
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Veronicastrum axillare Alleviates Ethanol-Induced Injury on Gastric Epithelial Cells via Downregulation of the NF-kB Signaling Pathway

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-01-15
Abstract: 

We used human gastric epithelial cells (GES-1) line in an ethanol-induced cell damage model to study the protective effect of Veronicastrum axillare and its modulation to NF-κB signal pathway. The goal was to probe the molecular mechanism of V. axillare decoction in the prevention of gastric ulcer and therefore provide guidance in the clinical application of V. axillare on treating injuries from chronic nephritis, pleural effusion, gastric ulcer, and other ailments. The effects of V. axillare-loaded serums on cell viability were detected by MTT assays. Enzyme-linked immunosorbent assay (ELISA) and Real-Time PCR methods were used to analyze the protein and mRNA expression of TNF-α, NF-κB, IκBα, and IKKβ. The results showed that V. axillare-loaded serum partially reversed the damaging effects of ethanol and NF-κB activator (phorbol-12-myristate-13-acetate: PMA) and increased cell viability. The protein and mRNA expressions of TNF-α, NF-κB, IκBα, and IKKβ were significantly upregulated by ethanol and PMA while they were downregulated by V. axillare-loaded serum. In summary, V. axillare-loaded serum has significantly protective effect on GES-1 against ethanol-induced injury. The protective effect was likely linked to downregulation of TNF-α based NF-κB signal pathway.

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Construction of an Array of Photonic Crystal Films for Visual Differentiation of Water/Ethanol Mixtures

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-11-14
Abstract: 

A photonic crystal film (PCF) which consists of a porous layered structure with a highly ordered periodic arrangement of nanopores has been used to differentiate between various mixtures of water and ethanol (EtOH). The refractive index difference between the wall (silica) of the empty nanopore and air which occupies it results in the structural color of the PCF. This color disappears when the nanopores are infiltrated by a liquid with a similar refractive index to silica (or silicon dioxide). The disappearance of the structural color provides a means to construct a colorimetric sensor to differentiate between various water/EtOH mixtures based on their wettability of the nanopores in the PCF. In this study, an array of silica-based PCFs was synthesized on a silicon substrate with a precise control of nanopore properties using the co-assembly/sedimentation method. Using this method, we benefitted from having different PCFs on a single substrate. Chemical coatings, neck angles, and film thicknesses on each PCF were the three factors used to adjust the wettability of the pores. Nanopore wetting by water/EtOH mixtures was studied in a systematic manner based on the three factors, and the findings were used to develop a sensor for visual differentiation of various water/EtOH mixtures. The final developed sensor consisting of an array of six PCFs was able to differentiate between seven different water/EtOH mixtures: W10, W20, W30, W40, W50, W60, and W70, in which W10 means 10% of water in EtOH.

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Article
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The Influence of Electrochemical Aging on Bead-Blasted Nickel Electrodes for the Oxygen Evolution Reaction

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2019-04-16
Abstract: 

The oxygen evolution reaction (OER) is of importance to both electrochemical energy conversion and energy storage. Low-cost, non-precious metal electrocatalysts that can withstand high operational current densities will likely be the best candidates for meeting the commercial needs for a range of OER applications. In addition to electrode composition, the surface morphology of gas evolving electrodes can affect their efficiency and performance. In this work, we demonstrate the influence of electrochemical aging on the performance of micro- and nanoscale textures for the OER. A series of textured Ni electrodes were prepared by rapid, scalable techniques, which included the use of bead-blasting. Two distinct approaches to induce the formation of the active Ni (oxy)hydroxide phase were conducted by electrochemical aging using cyclic voltammetry (CV) methods. The influence of the aging technique was assessed and correlated to the performance of these surface textures. Differences in the morphology of these textures and their resulting surface areas were estimated using three-dimensional (3D) reconstructions obtained from electron microscopy analyses. Focused ion beam (FIB) milling was also performed on the bead-blasted electrodes to visualize buried cracks and voids. The potential required for the OER at an applied current density of 500 mA/cm2 exhibited a reduction of 0.7 V for the electrodes aged by the steady-state treatment. The OER performance of the textured electrodes were found to correlate to both the electrode surface morphology and the type of electrochemical aging applied to the electrodes.

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