Chemistry, Department of

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Surface-Initiated Atom Transfer Radical Polymerization Induced Transformation of Selenium Nanowires into Copper Selenide@Polystyrene Core-Shell Nanowires

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-09-02
Abstract: 

This Article reports the first preparation of cuprous and cupric selenide nanowires coated with a ∼5 nm thick sheath of polystyrene (copper selenide@polystyrene). These hybrid nanostructures are prepared by the transformation of selenium nanowires in a one-pot reaction, which is performed under ambient conditions. The composition, purity, and crystallinity of the copper selenide@polystyrene products were assessed by scanning transmission electron microscopy, electron energy-loss spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy techniques. We determined that the single crystalline selenium nanowires are converted into polycrystalline copper selenide@polystyrene nanowires containing both cuprous selenide and cupric selenide. The product is purified through the selective removal of residual, non-transformed selenium nanowires by performing thermal evaporation below the decomposition temperature of these copper selenides. Powder X-ray diffraction of the purified copper selenide nanowires@polystyrene identified the presence of hexagonal, cubic, and orthorhombic phases of copper selenide. These purified cuprous and cupric selenide@polystyrene nanowires have an indirect bandgap of 1.44 eV, as determined by UV–vis absorption spectroscopy. This new synthesis of polymer-encapsulated nanoscale materials may provide a method for preparing other complex hybrid nanostructures.

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Article
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Platinum Ordered Porous Electrodes: Developing a Platform for Fundamental Electrochemical Characterization

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-07-09
Abstract: 

High surface area platinum electrodes with an ordered porous  structure (Pt-OP electrodes) have been prepared and characterized by  electrochemical methods. This study builds a foundation upon which we can  seek an in-depth understanding of the limitations and design considerations  to make efficient and stable Pt-OP electrodes for use in electrochemical  applications. A set of Pt-OP electrodes were prepared by controlled  electrodeposition of Pt through a self-assembled array of spherical particles  and subsequent removal of the spherical templates by solvent extraction. The  preparation method was shown to be reproducible and the resulting electrodes  were found to have clean Pt surfaces and a large electrochemical surface area  (A ecsa) resulting from both the porous structure, as well as the nano- and  micro-scale surface roughness. Additionally, the Pt-OP electrodes exhibit a  surface area enhancement comparable to commercially available  electrocatalysts. In summary, the Pt-OP electrodes prepared herein show  properties of interest for both gaining fundamental insights into  electrocatalytic processes and for use in applications that would benefit  from enhanced electrochemical response. 

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Article
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Optically Active Nanoparticle Coated Polystyrene Spheres

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-05-13
Abstract: 

Nanoparticles (NPs) with either plasmonic or upconverting properties have been selectively coated onto the surfaces of polystyrene (PS) spheres, imparting their optical properties to the PS colloids. These NP coated PS spheres have many potential applications, such as in medicine as drug-delivery systems or diagnostic tools. To prepare the NP coated PS spheres, gold or core-shell NaYF4Tm0.5Yb30/NaYF4 NPs were synthesized and separately combined with amino-functionalized PS spheres. The mechanism by which the NPs adhered to the PS spheres is attributed to interactions of the NP and a polyvinylpyrrolidone additive with the surfaces of the PS spheres. Two-photon fluorescence microscopy and SERS analysis demonstrate the potential applications of these NP coated PS spheres.

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Article
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A Tunable Loading of Single-Stranded DNA on Gold Nanorods through the Displacement of Polyvinylpyrrolidone

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-09-09
Abstract: 

A quantitative and tunable loading of single-stranded (ss-DNA) molecules onto gold nanorods was achieved through a new method of surfactant exchange. This new method involves the exchange of cetyltrimethylammonium bromide surfactants for an intermediate stabilizing layer of polyvinylpyrrolidone and sodium dodecylsulfate. The intermediate layer of surfactants on the anisotropic gold particles was easily displaced by thiolated ss-DNA, forming a tunable density of single-stranded DNA molecules on the surfaces of the gold nanorods. The success of this ligand exchange process was monitored in part through the combination of extinction, X-ray photoelectron, and infrared absorption spectroscopies. The number of ss-DNA molecules per nanorod for nanorods with a high density of ss-DNA molecules was quantified through a combination of fluorescence measurements and elemental analysis, and the functionality of the nanorods capped with dense monolayers of DNA was assessed using a hybridization assay. Core–satellite assemblies were successfully prepared from spherical particles containing a probe DNA molecule and a nanorod core capped with complementary ss-DNA molecules. The methods demonstrated herein for quantitatively fine tuning and maximizing, or otherwise optimizing, the loading of ss-DNA in monolayers on gold nanorods could be a useful methodology for decorating gold nanoparticles with multiple types of biofunctional molecules.

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Article
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Measuring Shear-Induced Adhesion of Gecko-Inspired Fibrillar Arrays Using Scanning Probe Techniques

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2013-07-30
Abstract: 

The natural ability of geckos and spiders to climb almost all surfaces using the compliant, nano‐structured components on their feet provides motivation for making bio‐inspired adhesives. The goal of the studies in this paper is to create an analytical technique for improving the ability to characterize dry adhesives modeled after these biological systems. The technique described herein uses a scanning probe microscope to manipulate a flat test surface in contact with biomimetic fibrillar arrays while monitoring the adhesion forces. Adhesion forces were measured after both normal contact and shear‐induced contact between the nano‐structured fibrils and the test surface. Results confirm that the adhesion forces are higher for bio‐inspired adhesives after a shear‐induced contact. Variations in these forces can be measured across the sample with micrometer‐scale lateral resolution. This method of analysis can be extended to evaluate bio‐inspired dry adhesives with realistic mechanisms of attachment utilized in robotic and similar applications of these materials.

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Article
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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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