10 research outputs found
WO<sub>3</sub>‑Enhanced TiO<sub>2</sub> Nanotube Photoanodes for Solar Water Splitting with Simultaneous Wastewater Treatment
Composite
WO<sub>3</sub>/TiO<sub>2</sub> nanostructures with optimal properties
that enhance solar photoconversion reactions were developed, characterized,
and tested. The TiO<sub>2</sub> nanotubes were prepared by anodization
of Ti foil and used as substrates for WO<sub>3</sub> electrodeposition.
The WO<sub>3</sub> electrodeposition parameters were controlled to
develop unique WO<sub>3</sub> nanostructures with enhanced photoelectrochemical
properties. Scanning electron microscopy (SEM) images showed that
the nanomaterials with optimal photocurrent density have the same
ordered structure as TiO<sub>2</sub> nanotubes, with an external tubular
nanostructured WO<sub>3</sub> layer. Diffuse reflectance spectra showed
an increase in the visible absorption relative to bare TiO<sub>2</sub> nanotubes and in the UV absorption relative to bare WO<sub>3</sub> films. Incident simulated solar photon-to-current efficiency (IPCE)
increased from 30% (for bare WO<sub>3</sub>) to 50% (for tubular WO<sub>3</sub>/TiO<sub>2</sub> composites). With the addition of diverse
organic pollutants, the photocurrent densities exhibited more than
a 5-fold increase. Chemical oxygen demand measurements showed the
simultaneous photodegradation of organic pollutants. The results of
this work showed that the unique structure and composition of these
composite WO<sub>3</sub>/TiO<sub>2</sub> materials enhance the IPCE
efficiencies, optical properties, and photodegradation performance
compared with the parent materials
Composite WO<sub>3</sub>/TiO<sub>2</sub> Nanostructures for High Electrochromic Activity
A composite
material consisting of TiO<sub>2</sub> nanotubes (NT) with WO<sub>3</sub> electrodeposited on its surface has been fabricated, detached
from its Ti substrate, and attached to a fluorine-doped tin oxide
(FTO) film on glass for application to electrochromic (EC) reactions.
Several adhesion layers were tested, finding that a paste of TiO<sub>2</sub> made from commercially available TiO<sub>2</sub> nanoparticles
creates an interface for the TiO<sub>2</sub> NT film to attach to
the FTO glass, which is conductive and does not cause solution-phase
ions in an electrolyte to bind irreversibly with the material. The
effect of NT length and WO<sub>3</sub> concentration on the EC performance
were studied. The composite WO<sub>3</sub>/TiO<sub>2</sub> nanostructures
showed higher ion storage capacity, better stability, enhanced EC
contrast, and longer memory time compared with the pure WO<sub>3</sub> and TiO<sub>2</sub> materials
Effect of Ordered Intermediate Porosity on Ion Transport in Hierarchically Nanoporous Electrodes
The high surface area of nanoporous electrodes makes
them promising
for use in electrochemical double-layer supercapacitors, desalination
and pollution remediation, and drug delivery applications. When designed
well and operating near their peak power, their charging rates are
limited by ion transport through their long, narrow pores. This can
be alleviated by creating pores of intermediate diameter that penetrate
the electrode. We have fabricated electrodes featuring these by creating
colloidal crystal-templated opals of nanoporous gold formed by dealloying.
The resulting electrodes contain a bimodal pore-size distribution,
with large pores on the order of several 100 nm and small pores on
the order of 10 nm. Electrochemical impedance spectrometry shows that
porous gold opals sacrifice some capacitance, but possess a lower
internal resistance, when compared to a porous gold electrode with
only the smaller-diameter pores. The architectural flexibility of
this approach provides a greater ability to design a balance between
power density and energy density
Analysis of existing approaches at the bank's competitiveness
Викладений аналіз найпоширеніших сучасних підходів до аналітичного оцінювання конкурентоспроможності банку.The article analyzes the most common approaches of building the model of the bank's competitiveness
Atomic-Layer Electroless Deposition: A Scalable Approach to Surface-Modified Metal Powders
Palladium
has a number of important applications in energy and
catalysis in which there is evidence that surface modification leads
to enhanced properties. A strategy for preparing such materials is
needed that combines the properties of (i) scalability (especially
on high-surface-area substrates, e.g. powders); (ii) uniform deposition,
even on substrates with complex, three-dimensional features; and (iii)
low-temperature processing conditions that preserve nanopores and
other nanostructures. Presented herein is a method that exhibits these
properties and makes use of benign reagents without the use of specialized
equipment. By exposing Pd powder to dilute hydrogen in nitrogen gas,
sacrificial surface PdH is formed along with a controlled amount of
dilute interstitial hydride. The lattice expansion that occurs in
Pd under higher H<sub>2</sub> partial pressures is avoided. Once the
flow of reagent gas is terminated, addition of metal salts facilitates
controlled, electroless deposition of an overlayer of subnanometer
thickness. This process can be cycled to create thicker layers. The
approach is carried out under ambient processing conditions, which
is an advantage over some forms of atomic layer deposition. The hydride-mediated
reaction is electroless in that it has no need for connection to an
external source of electrical current and is thus amenable to deposition
on high-surface-area substrates having rich, nanoscale topography
as well as on insulator-supported catalyst particles. STEM-EDS measurements
show that conformal Rh and Pt surface layers can be formed on Pd powder
with this method. A growth model based on energy-resolved XPS depth
profiling of Rh-modified Pd powder is in general agreement. After
two cycles, deposits are consistent with 70–80% coverage and
a surface layer with a thickness from 4 to 8 Å
Direct <i>in Situ</i> Observation of Nanoparticle Synthesis in a Liquid Crystal Surfactant Template
Controlled and reproducible synthesis of tailored materials is essential in many fields of nanoscience. In order to control synthesis, there must be a fundamental understanding of nanostructure evolution on the length scale of its features. Growth mechanisms are usually inferred from methods such as (scanning) transmission electron microscopy ((S)TEM), where nanostructures are characterized after growth is complete. Such <i>post mortem</i> analysis techniques cannot provide the information essential to optimize the synthesis process, because they cannot measure nanostructure development as it proceeds in real time. This is especially true in the complex rheological fluids used in preparation of nanoporous materials. Here we show direct <i>in situ</i> observations of synthesis in a highly viscous lyotropic liquid crystal template on the nanoscale using a fluid stage in the STEM. The nanoparticles nucleate and grow to ∼5 nm particles, at which point growth continues through the formation of connections with other nanoparticles around the micelles to form clusters. Upon reaching a critical size (>10–15 nm), the clusters become highly mobile in the template, displacing and trapping micelles within the growing structure to form spherical, porous nanoparticles. The final products match those synthesized in the lab <i>ex situ</i>. This ability to directly observe synthesis on the nanoscale in rheological fluids, such as concentrated aqueous surfactants, provides an unprecedented understanding of the fundamental steps of nanomaterial synthesis. This in turn allows for the synthesis of next-generation materials that can strongly impact important technologies such as organic photovoltaics, energy storage devices, catalysis, and biomedical devices
Direct <i>in Situ</i> Observation of Nanoparticle Synthesis in a Liquid Crystal Surfactant Template
Controlled and reproducible synthesis of tailored materials is essential in many fields of nanoscience. In order to control synthesis, there must be a fundamental understanding of nanostructure evolution on the length scale of its features. Growth mechanisms are usually inferred from methods such as (scanning) transmission electron microscopy ((S)TEM), where nanostructures are characterized after growth is complete. Such <i>post mortem</i> analysis techniques cannot provide the information essential to optimize the synthesis process, because they cannot measure nanostructure development as it proceeds in real time. This is especially true in the complex rheological fluids used in preparation of nanoporous materials. Here we show direct <i>in situ</i> observations of synthesis in a highly viscous lyotropic liquid crystal template on the nanoscale using a fluid stage in the STEM. The nanoparticles nucleate and grow to ∼5 nm particles, at which point growth continues through the formation of connections with other nanoparticles around the micelles to form clusters. Upon reaching a critical size (>10–15 nm), the clusters become highly mobile in the template, displacing and trapping micelles within the growing structure to form spherical, porous nanoparticles. The final products match those synthesized in the lab <i>ex situ</i>. This ability to directly observe synthesis on the nanoscale in rheological fluids, such as concentrated aqueous surfactants, provides an unprecedented understanding of the fundamental steps of nanomaterial synthesis. This in turn allows for the synthesis of next-generation materials that can strongly impact important technologies such as organic photovoltaics, energy storage devices, catalysis, and biomedical devices
Direct <i>in Situ</i> Observation of Nanoparticle Synthesis in a Liquid Crystal Surfactant Template
Controlled and reproducible synthesis of tailored materials is essential in many fields of nanoscience. In order to control synthesis, there must be a fundamental understanding of nanostructure evolution on the length scale of its features. Growth mechanisms are usually inferred from methods such as (scanning) transmission electron microscopy ((S)TEM), where nanostructures are characterized after growth is complete. Such <i>post mortem</i> analysis techniques cannot provide the information essential to optimize the synthesis process, because they cannot measure nanostructure development as it proceeds in real time. This is especially true in the complex rheological fluids used in preparation of nanoporous materials. Here we show direct <i>in situ</i> observations of synthesis in a highly viscous lyotropic liquid crystal template on the nanoscale using a fluid stage in the STEM. The nanoparticles nucleate and grow to ∼5 nm particles, at which point growth continues through the formation of connections with other nanoparticles around the micelles to form clusters. Upon reaching a critical size (>10–15 nm), the clusters become highly mobile in the template, displacing and trapping micelles within the growing structure to form spherical, porous nanoparticles. The final products match those synthesized in the lab <i>ex situ</i>. This ability to directly observe synthesis on the nanoscale in rheological fluids, such as concentrated aqueous surfactants, provides an unprecedented understanding of the fundamental steps of nanomaterial synthesis. This in turn allows for the synthesis of next-generation materials that can strongly impact important technologies such as organic photovoltaics, energy storage devices, catalysis, and biomedical devices
Direct <i>in Situ</i> Observation of Nanoparticle Synthesis in a Liquid Crystal Surfactant Template
Controlled and reproducible synthesis of tailored materials is essential in many fields of nanoscience. In order to control synthesis, there must be a fundamental understanding of nanostructure evolution on the length scale of its features. Growth mechanisms are usually inferred from methods such as (scanning) transmission electron microscopy ((S)TEM), where nanostructures are characterized after growth is complete. Such <i>post mortem</i> analysis techniques cannot provide the information essential to optimize the synthesis process, because they cannot measure nanostructure development as it proceeds in real time. This is especially true in the complex rheological fluids used in preparation of nanoporous materials. Here we show direct <i>in situ</i> observations of synthesis in a highly viscous lyotropic liquid crystal template on the nanoscale using a fluid stage in the STEM. The nanoparticles nucleate and grow to ∼5 nm particles, at which point growth continues through the formation of connections with other nanoparticles around the micelles to form clusters. Upon reaching a critical size (>10–15 nm), the clusters become highly mobile in the template, displacing and trapping micelles within the growing structure to form spherical, porous nanoparticles. The final products match those synthesized in the lab <i>ex situ</i>. This ability to directly observe synthesis on the nanoscale in rheological fluids, such as concentrated aqueous surfactants, provides an unprecedented understanding of the fundamental steps of nanomaterial synthesis. This in turn allows for the synthesis of next-generation materials that can strongly impact important technologies such as organic photovoltaics, energy storage devices, catalysis, and biomedical devices
Effect of Rhodium Distribution on Thermal Stability of Nanoporous Palladium–Rhodium Powders
Powders of nanoporous palladium and palladium alloy particles
are
of potential value for storage of hydrogen isotopes, as long as the
pores remain stable over a useful range of temperatures and chemical
environments. Rhodium alloys are known to have enhanced hydrogen storage
and improved thermal stability versus pure palladium. However, the
distribution of rhodium on pore and particle surfaces is critical
to this. Pores are more ordered and thermally stable in rhodium-rich
regions. Treatment of particles at elevated temperature under reducing
conditions can cause rearrangement of Rh and Pd at the surface, but
not a major change in Rh distribution throughout the particle. Heating
in the presence of hydrogen causes more rapid pore rearrangement than
heating in vacuum subsequent to hydrogen exposure, suggesting a direct
chemical influence of hydrogen on mobility of surface atoms. These
results provide a clear path to future improvements in the stability
of nanoporous metals in reducing atmospheres