192 research outputs found
Rayleigh Instability Driven Nodular Cu<sub>2</sub>O Nanowires via Carbothermal Reduction of CuO Nanowires
Nodular cuprous oxide (Cu<sub>2</sub>O) vertical nanowire (NW)
arrays with a length of more than 20 Îźm and diameter of âź300
nm have been synthesized by the carbothermal reduction of thermally
grown cupric oxide (CuO) NWs. The transformation initiates at a low
temperature of 350 °C. Two important effects are observed: First,
the CuO â Cu<sub>2</sub>O reduction occurs by oxygen out diffusion
under a highly reducing atmosphere afforded by the presence of carbon
monoxide (CO). Second, the surface reduction creates instabilities,
which propagate and grow into a string of nodules along the length
of the Cu<sub>2</sub>O NWs. This effect is determined to be due to
Rayleigh instability, but initiated via Cu<sub>2</sub>O phase transformation
Excess Electron and Hole in 1âBenzylpyridinium-Based Ionic Liquids
The
study of ionic liquids that may be compatible with the type
of radiation chemistry events occurring in nuclear separation processes
is a topic of high current interest. In this article, we focus on
two ionic liquids based on the benzylpyridinium cation. This cation
has been proposed to be able to capture either an excess electron
or hole without undergoing fast dissociation. Shkrob, Wishart, and
collaborators (J. Phys.
Chem. B 2013, 117 (46), 14385â14399) have indicated that the
stabilization is likely in the form of dimers in solution with the
excess electron localized on adjacent pyridinium rings and the excess
hole localized on phenyl rings. Our first-principles dynamical studies
support these ideas but present a more nuanced view of the time-dependent
behavior that is likely to occur at short time for systems at room
temperature
Role of Organic Solvents in Immobilizing Fungus Laccase on Single-Walled Carbon Nanotubes for Improved Current Response in Direct Bioelectrocatalysis
Improving bioelectrocatalytic current
response of redox enzymes
on electrodes has been a focus in the development of enzymatic biosensors
and biofuel cells. Herein a mediatorless electroreduction of oxygen
is effectively improved in terms of a remarkable enhancement by ca.
600% in maximum reductive current by simply adding 20% ethanol into
laccase solution during its immobilization onto single-walled carbon
nanotubes (SWCNTs). Conformation analysis by circular dichroism and
attenuated total reflectance infrared spectroscopy demonstrate promoted
laccase-SWCNTs contact by ethanol, thus leading to favorable enzyme
orientation on SWCNTs. Extended investigation on acetone-, acetonitrile-, <i>N</i>,<i>N</i>-dimethylformamide (DMF)-, or dimethyl
sulfoxide (DMSO)-treated laccase-SWCNTs electrodes shows a 400% and
350% current enhancement at maxima upon acetone and acetonitrile treatment,
respectively, and a complete diminish of reductive current by DMF
and DMSO. These results together reveal the important role of organic
solvents in regulating laccase immobilization for direct bioelectrocatalysis
by balancing surface wetting and protein denaturing
A two-step approach for fluidized bed granulation in pharmaceutical processing: Assessing different models for design and control
<div><p>Various modeling techniques were used to understand fluidized bed granulation using a two-step approach. First, Plackett-Burman design (PBD) was used to identify the high-risk factors. Then, Box-Behnken design (BBD) was used to analyze and optimize those high-risk factors. The relationship between the high-risk input variables (inlet air temperature X<sub>1</sub>, binder solution rate X<sub>3</sub>, and binder-to-powder ratio X<sub>5</sub>) and quality attributes (flowability Y<sub>1</sub>, temperature Y<sub>2</sub>, moisture content Y<sub>3</sub>, aggregation index Y<sub>4</sub>, and compactability Y<sub>5</sub>) of the process was investigated using response surface model (RSM), partial least squares method (PLS) and artificial neural network of multilayer perceptron (MLP). The morphological study of the granules was also investigated using a scanning electron microscope. The results showed that X<sub>1</sub>, X<sub>3</sub>, and X<sub>5</sub> significantly affected the properties of granule. The RSM, PLS and MLP models were found to be useful statistical analysis tools for a better mechanistic understanding of granulation. The statistical analysis results showed that the RSM model had a better ability to fit the quality attributes of granules compared to the PLS and MLP models. Understanding the effect of process parameters on granule properties provides the basis for modulating the granulation parameters and optimizing the product performance at the early development stage of pharmaceutical products.</p></div
(a) VIP and (b) coefficients for the PLS model.
<p>(a) VIP and (b) coefficients for the PLS model.</p
Indirect Phase Transformation of CuO to Cu<sub>2</sub>O on a Nanowire Surface
The
reduction of CuO nanowires (NWs) to Cu<sub>2</sub>O NWs undergoes
an indirect phase transformation on the surface: from single crystalline
CuO, to a disordered Cu<sub>2âδ</sub>O phase, and then
to crystalline Cu<sub>2</sub>O. A 9â12 nm disordered Cu<sub>2âδ</sub>O is formed on the NW surface by exposing CuO
NWs to CO at 1 Torr, 300 °C for 30 min. After 60 min, this layer
decreases to 2â3 nm and is eliminated after 180 min. Energy
dispersive X-ray spectroscopy using a scanning tunneling electron
microscope and across a single NW reveals the disordered layer to
be O-rich with respect to Cu<sub>2</sub>O with a maximum at. % Cu:O
= 1.8. X-ray photoelectron spectroscopy shows adsorbed CO on the surface
as evidence of the reduction reaction. Micro-Raman spectroscopy tracks
the transformation in NWs as a function of reduction time. A CO enabled
surface reduction reaction coupled to diffusion-limited transport
of ânonlatticeâ O to the surface is proposed as a mechanism
for Cu<sub>2âδ</sub>O formation. The initial buildup
of out-diffusing O to the surface appears to aid the formation of
the disordered surface layer. The transformation follows OstwaldâLussacâs
law which predicts formation of unstable phases over stable phases,
when phase transformation rates are limited by kinetic or diffusional
processes. The study provides a generalized approach for facile growth
of few nanometer transient layers on multivalent, metal oxide NW surfaces
MLP neural network architecture used for modeling granule properties.
<p>MLP neural network architecture used for modeling granule properties.</p
Plasmonic Metal-to-Semiconductor Switching in Au Nanorod-ZnO nanocomposite films
We
demonstrate conductivity switching from a metal to semiconductor using
plasmonic excitation and charge injection in Au-nanorod (AuNRs)-ZnO
nanocomposite films. ZnO films 12.6, 20.3, and 35.6 nm were deposited
over AuNRs using atomic layer deposition. In dark conditions, the
films transitioned from metallic to semiconducting behavior between
150 and 200 K. However, under sub-bandgap, white light illumination,
all films behaved as semiconductors from 80 to 320 K. Photoresponse
(light/dark conductivity) was strongly dependent on the thickness
of ZnO, which was 94.4 for AuNRâ12.6 nm ZnO and negligible
for AuNRâ35.6 nm ZnO. Conductivity switching and thickness
dependence of photoresponse were attributed to plasmonically excited
electrons injected from AuNRs into ZnO. Activation energies for conduction
were extracted for these processes
Contour plots showing the effects of X<sub>1</sub> and X<sub>3</sub> on granule compactability obtained by using: (a) RSM, (b) PLS, and (c) MLP (X<sub>5</sub> = 11.5).
<p>Contour plots showing the effects of X<sub>1</sub> and X<sub>3</sub> on granule compactability obtained by using: (a) RSM, (b) PLS, and (c) MLP (X<sub>5</sub> = 11.5).</p
Standard Pareto chart showing the effects of various process factors on (a) flowability, (b) temperature, (c) moisture, (d) aggregation index, and (e) compactability.
<p>Standard Pareto chart showing the effects of various process factors on (a) flowability, (b) temperature, (c) moisture, (d) aggregation index, and (e) compactability.</p
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