10 research outputs found
Microwave Assisted Formation of Monoreactive Perfluoroalkylsilane-based Self-Assembled Monolayers
We demonstrate the use of microwave radiation as a tool to accelerate the formation of perfluoroalkylsilane based self-assembled monolayers (SAMs) on silicon oxide surfaces. Surface coverage of these SAMs of monoreactive perfluoroalkylsilanes increased in proportion to the duration over which the solutions were heated by microwave radiation. 
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
Ordered Porous Electrodes by Design: Towards Enhancing the Effective Utilization of Platinum in Electrocatalysis
Platinumânanoparticleâfunctionalized, ordered, porous support electrodes are prepared and characterized as a potential new class of oxygen reduction reaction (ORR) electrocatalysts. This study aims to develop electrode materials that enhance the effective utilization of Pt in electrocatalytic reactions through improved mass transport properties, high Pt mass specific surface area, and increased Pt electrochemical stability. The electrodes are prepared using modular sacrificial templates, producing a uniform distribution of Pt nanoparticles inside ordered porous Au electrodes. This method can be further fineâtuned to optimize the architecture for a range of characteristics, such as varying nanoparticle properties, pore size, or support material. The Ptâcoated Au, ordered, porous electrodes exhibit several improved characteristics, such as enhanced Pt effective utilization for ORR electrocatalysis. This includes a nearly twofold increase in Pt mass specific surface area over other ultrathin designs, superior mass transport properties in comparison to traditional catalyst layers of C black supported Pt nanoparticles mixed with ionomer, good methanol tolerance and exceptional stability toward Pt chemical and/or electrochemical dissolution through interfacial interactions with Au. The methods to prepare Ptâcoated ordered porous electrodes can be extended to other architectures for enhanced catalyst utilization and improved performance of Pt in electrochemical processes
Self-Assembly of Nanoparticles onto the Surfaces of Polystyrene Spheres with a Tunable Composition and Loading
Functional colloidal materials were prepared by design through the self-assembly of nanoparticles (NPs) on the surfaces of polystyrene (PS) spheres with control over NP surface coverage, NP-to-NP spacing, and NP composition. The ability to control and fine tune the coating was extended to the first demonstration of the co-assembly of NPs of dissimilar composition onto the same PS sphere, forming a multi-component coating. A broad range of NP decorated PS (PS@NPs) spheres were prepared with uniform coatings attributed to electrostatic and hydrogen bonding interactions between stabilizing groups on the NPs and the functionalized surfaces of the PS spheres. This versatile two-step method provides more fine control than methods previously demonstrated in the literature. These decorated PS spheres are of interest for a number of applications, such as catalytic reactions where the PS spheres provide a support for the dispersion, stabilization, and recovery of NP catalysts. The catalytic properties of these PS@NPs spheres were assessed by studying the catalytic degradation of azo dyes, an environmental contaminant detrimental to eye health. The PS@NPs spheres were used in multiple, sequential catalytic reactions while largely retaining the NP coating
Template Assisted Preparation of High Surface Area Macroporous Supports with Uniform and Tunable Nanocrystal Loadings
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 Ti1âxSixO2, 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
Colloidal CoreâShell Materials with âSpikyâ Surfaces Assembled From Gold Nanorods
A series of coreâshell materials with âspikyâ surfaces are prepared through the self-assembly of gold nanorods onto polystyrene microspheres. Loading of the nanorods is finely tuned and the assemblies exhibit surface plasmon resonance properties. The âspikyâ surface topography of the assembled structures could serve as a versatile substrate for surface-enhanced Raman spectroscopy based sensing applications
Stabilization of Oil-in-Water Emulsions with Noninterfacially Adsorbed Particles
Classical (surfactant stabilized)
and Pickering (particle stabilized)
type emulsions have been widely studied to elucidate the mechanisms
by which emulsion stabilization is achieved. In Pickering emulsions,
a key defining factor is that the stabilizing particles reside at
the liquidâliquid interface providing a mechanical barrier
to droplet coalescence. This interfacial adsorption is achieved through
the use of nanoparticles that are partially wet by both liquid phases,
often through covalent surface modification of or surfactant adsorption
to the nanoparticle surfaces. Herein, we demonstrate particle-induced
stabilization of an oil-in-water emulsion with fully water wet nanoparticles
(no interfacial adsorption) via synergistic interaction with low concentrations
of surfactants. Laser scanning confocal microscopy analysis allows
for unique and vital insights into the properties of these emulsions
via both three-dimensional imaging and real-time monitoring of particle
dynamics at the oilâwater interface. Investigation of these
ânon-Pickeringâ particle stabilized emulsions suggests
that the nonadsorbed particles impart stability to the emulsion primarily
via entropic forces imparted by the accumulation of silica nanoparticles
in the coherent phase between dispersed oil droplets
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, Pt<sup>2+</sup> or Pt<sup>4+</sup>) 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