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

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

A Proposed Mechanism of the Influence of Gold Nanoparticles on DNA Hybridization

A combination of gold nanoparticles (AuNPs) and nucleic acids has been used in biosensing applications. However, there is a poor fundamental understanding of how gold nanoparticle surfaces influence the DNA hybridization process. Here, we measured the rate constants of the hybridization and dehybridization of DNA on gold nanoparticle surfaces to enable the determination of activation parameters using transition state theory. We show that the target bases need to be detached from the gold nanoparticle surfaces before zipping. This causes a shift of the rate-limiting step of hybridization to the mismatch-sensitive zipping step. Furthermore, our results propose that the binding of gold nanoparticles to the single-stranded DNA segments (commonly known as bubbles) in the duplex DNA stabilizes the bubbles and accelerates the dehybridization process. We employ the proposed mechanism of DNA hybridization/dehybridization to explain the ability of 5 nm diameter gold nanoparticles to help discriminate between single base-pair mismatched DNA molecules when performed in a NanoBioArray chip. The mechanistic insight into the DNA–gold nanoparticle hybridization/dehybridization process should lead to the development of new biosensors

Enhanced CO Tolerance with PtRuAuPd/C Anode Catalyst in Proton Exchange Membrane Fuel Cells

Platinum poisoning in the presence of even trace amounts of carbon monoxide (CO) within a hydrogen fuel degrades the activity of a proton exchange membrane (PEM) fuel cell. Herein, we report a quadmetallic alloy, PtRuAuPd/C, prepared by a water-in-oil microemulsion method for CO tolerant hydrogen oxidation reaction (HOR). The obtained spherical nanoparticles were 3.4 ± 0.5 nm in size with a Pt:Ru:Au:Pd atomic ratio of 22:34:22:22. The X-ray diffraction confirmed the alloy formation through a shift in the Pt peaks. The compositions and oxidation states were elucidated via X-ray photoelectron spectroscopy. The comparison catalysts, PtRu/C, PtRuAu/C, and PtRuPd/C alloys, were also similarly prepared and analyzed. Among all these alloys, PtRuAuPd/C demonstrated the highest electrochemically active surface area of 123.2 m2/g and a CO oxidation peak potential merely 20 mV higher than the PtRu/C catalyst, as measured using CO stripping voltammetry in a 0.5 M H2SO4 electrolyte. The evaluation of CO tolerance through a 30 s exposure to 5% CO at a constant potential revealed PtRuAuPd/C recovery of 93.6% in HOR current density outperforming PtRu/C at 91.5%. Following the durability test cycling, wherein a reduction in surface Ru concentration was observed through cyclic voltammetry, the CO oxidation potential of PtRuAuPd/C remained unchanged, while that of PtRu/C significantly shifted to higher potentials by 270 mV. Single fuel cell assessments at 70 °C revealed higher cell performance of PtRuAuPd/C with pure H2 fuel and higher oscillating potentials during self-oxidation with 80 ppm of CO contamination in comparison to commercial PtRu/C catalyst demonstrating its high CO tolerance

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

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

Optimizing the Quality of Monoreactive Perfluoroalkylsilane-Based Self-Assembled Monolayers

Self-assembled monolayers (or SAMs) created from monoreactive perfluoroalkylsilanes by deposition from a toluene solution are investigated for the dependence of their quality on processing conditions. Surface-sensitive spectroscopic techniques are used to provide feedback on the processing conditions in which solution temperature, silane concentration, and reaction time are optimized to improve the quality of these SAMs. For these analyses, monolayers are formed at 20, 40, 60, or 80 °C from solutions containing between 0.5 and 5 mM perfluoroalkylsilane over a period of up to 5 h. Physically adsorbed molecules are removed from these surfaces by extraction to determine the quality of the covalently bound monolayer. Water contact angle measurements, spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), respectively, are used in combination to assess the uniformity of the surface hydrophobicity, monolayer thickness, composition of the assembled perfluoroalkylsilane molecules, and topography of these monolayers. A comparison is also presented for two approaches to fill defects within these solvent extracted monolayers with more perfluoroalkylsilane molecules, aiming to improve the quality of these SAMs. A detailed XPS analysis is used to assess both the relative changes in density and average tilt of molecules within the monolayers as the process temperature is increased in increments from 20 to 80 °C. The observed differences in quality of the SAMs are attributed to temperature- and time-dependent organization and reactivity of the silane molecules. Although the assembly of these monoreactive perfluoroalkylsilanes is driven by thermodynamics, the quality of the monolayer is ultimately limited by the kinetics and mass transport during this assembly process. Lessons from these studies can be exploited for improving the quality of monolayers composed of other alkylsilane molecules that are covalently bound to the surfaces of oxides

Electrochemically Active Nickel Foams as Support Materials for Nanoscopic Platinum Electrocatalysts

Platinum is deposited on open-cell nickel foam in low loading amounts via chemical reduction of Pt cations (specifically, Pt²⁺ or Pt⁴⁺) originating from aqueous Pt salt solutions. The resulting Pt-modified nickel foams (Pt/Ni foams) are characterized using complementary electrochemical and materials analysis techniques. These include electron microscopy to examine the morphology of the deposited material, cyclic voltammetry to evaluate the electrochemical surface area of the deposited Pt, and inductively coupled plasma optical emission spectrometry to determine the mass of deposited Pt on the Ni foam substrate. The effect of potential cycling in alkaline media on the electrochemical behavior of the material and the stability of Pt deposit is studied. In the second part of this paper, the Pt/Ni foams are applied as electrode materials for hydrogen evolution, hydrogen reduction, oxygen reduction, and oxygen evolution reactions in an aqueous alkaline electrolyte. The electrocatalytic activity of the electrodes toward these processes is evaluated using linear sweep voltammetry curves and Tafel plots. The results of these studies demonstrate that nickel foams are acceptable support materials for nanoscopic Pt electrocatalysts and that the resulting Pt/Ni foams are excellent electrocatalysts for the hydrogen evolution reaction. An unmodified Ni foam is shown to be a highly active electrode for the oxygen evolution reaction

Comprehensive Structural, Surface-Chemical and Electrochemical Characterization of Nickel-Based Metallic Foams

Nickel-based metallic foams are commonly used in electrochemical energy storage devices (rechargeable batteries) as both current collectors and active mass support. These materials attract attention as tunable electrode materials because they are available in a range of chemical compositions, pore structures, pore sizes, and densities. This contribution presents structural, chemical, and electrochemical characterization of Ni-based metallic foams. Several materials and surface science techniques (transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), focused ion beam (FIB), and X-ray photoelectron spectroscopy (XPS)) and electrochemical methods (cyclic voltammetry (CV)) are used to examine the micro-, meso-, and nanoscopic structural characteristics, surface morphology, and surface-chemical composition of these materials. XPS combined with Ar-ion etching is employed to analyze the surface and near-surface chemical composition of the foams. The specific and electrochemically active surface areas (<i>A</i>_s, <i>A</i>_ecsa) are determined using CV. Though the foams exhibit structural robustness typical of bulk materials, they have large <i>A</i>_s, in the range of 200–600 cm² g^–1. In addition, they are dual-porosity materials and possess both macro- and mesopores