28 research outputs found
Confining Sulfur Species in Cathodes of Lithium–Sulfur Batteries: Insight into Nonpolar and Polar Matrix Surfaces
To alleviate the polysulfides shuttle
effect in lithium–sulfur
batteries (LSBs), the use of a functionalized carbon matrix with a
polar surface has been widely reported to chemically bind the soluble
polysulfides. However, whether and how such a polar carbon surface
affects the overall cathode performance, particularly the initial
discharge corresponding to the reduction of cyclooctasulfur (S<sub>8</sub>), has not caught enough attention. By combining polar and
nonpolar carbon matrix surfaces in different configurations through
sandwiching sulfur species between two carbon matrix membranes, we
found cells with dramatically different performance. The discharge
process at different states, particularly the charge-transfer resistances
corresponding to nonpolar S<sub>8</sub> and polar polysulfide intermediates
and the final Li<sub>2</sub>S, were investigated. The experimental
results, further supported by first-principles density functional
theory calculations, indicate that the adsorption energy and barrier
for electron transfer together affect the electrochemical performance
of LSBs, and therefore, a rational design that combines polar and
nonpolar surfaces should be adopted
Comparing Graphene-TiO<sub>2</sub> Nanowire and Graphene-TiO<sub>2</sub> Nanoparticle Composite Photocatalysts
We demonstrate that uniform dispersion of TiO<sub>2</sub> on graphene
is critical for the photocatalytic effect of the composite. The hydrothermal
method was employed to synthesize TiO<sub>2</sub> nanowires (NW) and
then fabricate graphene-TiO<sub>2</sub> nanowire nanocomposite (GNW).
Graphene oxide (GO) reduction to graphene and hybridization between
TiO<sub>2</sub> NWs and graphene by forming chemical bonding was achieved
in a one-step hydrothermal process. Graphene-TiO<sub>2</sub> nanoparticle
(NP) nanocomposite (GNP) was also synthesized. Photocatalytic performance
and related properties of NP, NW, GNP, and GNW were comparatively
studied. It was found that by incorporation of graphene, GNP and GNW
have higher performance than their counterparts. More importantly,
it was found that NWs, in comparison with NPs, have more uniform dispersion
on graphene with less agglomeration, resulting in more direct contact
between TiO<sub>2</sub> and graphene, and hence further improved electron–hole
pairs (EHPs) separation and transportation. The adsorbability of GNW
is also found to be higher than GNP. The result reveals that the relative
photocatalytic activity of GNW is much higher than GNP and pure NWs
or NPs
Rationally Designed Porous MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> Nanoneedles for Low-Temperature Selective Catalytic Reduction of NO<sub><i>x</i></sub> by NH<sub>3</sub>
In this work, a novel
porous nanoneedlelike MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> catalyst (MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> nanoneedles) was developed
for the first time by rationally heat-treating metal–organic
frameworks including MnFe precursor synthesized by hydrothermal method.
A counterpart catalyst (MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> nanoparticles) without porous nanoneedle
structure was also prepared by a similar procedure for comparison.
The two catalysts were systematically characterized by scanning and
transmission electron microscopy, X-ray diffraction, thermogravimetric
analysis, X-ray photoelectron spectroscopy, hydrogen temperature-programmed
reduction, ammonia temperature-programmed desorption, and in situ
diffuse reflectance infrared Fourier transform spectroscopy (in situ
DRIFT), and their catalytic activities were evaluated by selective
catalytic reduction (SCR) of NO<sub><i>x</i></sub> by NH<sub>3</sub>. The results showed that the rationally designed MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> nanoneedles
presented outstanding low-temperature NH<sub>3</sub>-SCR activity
(100% NO<sub><i>x</i></sub> conversion in a wide temperature
window from 120 to 240 °C), high selectivity for N<sub>2</sub> (nearly 100% N<sub>2</sub> selectivity from 60 to 240 °C),
and excellent water resistance and stability in comparison with the
counterpart MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> nanoparticles. The reasons can be attributed not
only to the unique porous nanoneedle structure but also to the uniform
distribution of MnO<sub><i>x</i></sub> and FeO<sub><i>x</i></sub>. More importantly, the desired Mn<sup>4+</sup>/Mn<sup><i>n</i>+</sup> and O<sub>α</sub>/(O<sub>α</sub> + O<sub>β</sub>) ratios, as well as rich redox sites and abundant
strong acid sites on the surface of the porous MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> nanoneedles, also
contribute to these excellent performances. In situ DRIFT suggested
that the NH<sub>3</sub>-SCR of NO over MnO<sub><i>x</i></sub>–FeO<sub><i>x</i></sub> nanoneedles follows both
Eley–Rideal and Langmuir–Hinshelwood mechanisms
Highly Efficient Photocatalyst Based on a CdS Quantum Dots/ZnO Nanosheets 0D/2D Heterojunction for Hydrogen Evolution from Water Splitting
A novel
CdS/ZnO heterojunction constructed of zero-dimensional (0D) CdS quantum
dots (QDs) and two-dimensional (2D) ZnO nanosheets (NSs) was rationally
designed for the first time. The 2D ZnO NSs were assembled into ZnO
microflowers (MFs) via an ultrasonic-assisted hydrothermal procedure
(100 °C, 12 h) in the presence of a NaOH solution (0.06 M), and
CdS QDs were deposited on both sides of every ZnO NS in situ by using
the successive ionic-layer absorption and reaction method. It was
found that the ultrasonic treatment played an important role in the
generation of ZnO NSs, while NaOH was responsible to the assembly
of a flower-like structure. The obtained CdS/ZnO 0D/2D heterostructures
exhibited remarkably enhanced photocatalytic activity for hydrogen
evolution from water splitting in comparison with other CdS/ZnO heterostructures
with different dimensional combinations such as 2D/2D, 0D/three-dimensional
(3D), and 3D/0D. Among them, CdS/ZnO-12 (12 deposition cycles of CdS
QDs) exhibited the highest hydrogen evolution rate of 22.12 mmol/g/h,
which was 13 and 138 times higher than those of single CdS (1.68 mmol/g/h)
and ZnO (0.16 mmol/g/h), respectively. The enhanced photocatalytic
activity can be attributed to several positive factors, such as the
formation of a Z-scheme photocatalytic system, the tiny size effect
of 0D CdS QDs and 2D ZnO NSs, and the intimate contact between CdS
QDs and ZnO NSs. The formation of a Z-scheme photocatalytic system
remarkably promoted the separation and migration of photogenerated
electron–hole pairs. The tiny size effect effectively decreased
the recombination probability of electrons and holes. The intimate
contact between the two semiconductors efficiently reduced the migration
resistance of photogenerated carriers. Furthermore, CdS/ZnO-12 also
presented excellent stability for photocatalytic hydrogen evolution
without any decay within five cycles in 25 h
Development of Multifunctional Nanoencapsulated <i>trans</i>-Resveratrol/Chitosan Nutraceutical Edible Coating for Strawberry Preservation
Phytochemical nanoencapsulation for nutrient delivery
and edible
coatings for perishable food preservation are two emerging technologies.
Leveraging the strong antimicrobial function of phytochemical nutrients,
we propose convergent research to integrate the two technologies by
embedding phytochemical-encapsulated nanoparticles in an edible coating
on fresh fruits to achieve multiple functions. In particular, we report
the study of an edible coating on strawberries that is composited
of trans-resveratrol (R)-encapsulated nanoparticles
(RNPs) embedded in a chitosan (CS) matrix. The biodegradable and biocompatible
RNPs significantly increased the aqueous solubility of R by 150-fold
and bioavailability by 3.5-fold after oral administration. Our results
demonstrated the abilities of the RNP-embedded CS edible coating to
diminish dehydration, prevent nutrient loss, inhibit microbe growth,
increase nutraceutical value, preserve strawberry quality, and extend
shelf life during storage at both 22 and 4 °C. Such a phytochemical
nanoencapsulation-based edible coating is promising for the dual purposes
of enhancing nutrient delivery and preserving perishable foods
Polarization and Dielectric Study of Methylammonium Lead Iodide Thin Film to Reveal its Nonferroelectric Nature under Solar Cell Operating Conditions
Researchers
have debated whether methylammonium lead iodide (MAPbI<sub>3</sub>), with a perovskite crystal structure, is ferroelectric and
therefore contributes to the current–voltage hysteresis commonly
observed in hybrid perovskite solar cells (PSCs). We thoroughly investigated
temperature-dependent polarization, dielectric, and impedance spectroscopies,
and we found no evidence of ferroelectric effect in a MAPbI<sub>3</sub> thin film at normal operating conditions. Therefore, the effect
does not contribute to the hysteresis in PSCs, whereas the large component
of ionic migration observed may play a critical role. Our temperature-based
polarization and dielectric studies find that MAPbI<sub>3</sub> exhibits
different electrical behaviors below and above ca. 45 °C, suggesting
a phase transition around this temperature. In particular, we report
the activation energies of ionic migration for the two phases and
temperature-dependent permittivity of MAPbI<sub>3</sub>. This study
contributes to the understanding of the material properties and device
performance of hybrid perovskites
An example image including FSD (a), QISS (b), and CE-MRA (c) from which the SNR, CNR, and vessel sharpness were derived.
<p>The circles drawn in the cross-section of arterial segments (yellow circles) and the adjacent tissue (red circles) indicated the representative ROIs for the calculation of signal intensity of arterial blood and tissue, respectively. The circles drawn in the background (green circles) indicated the representative large air ROI for the calculation of noise. The line drawn perpendicularly to the vessel wall indicated the representative user-selected line for the calculation of vessel sharpness.</p
Comparison of image quality of three calf arterial segments for NCE-MRA in 26 patients with diabetes.
<p><sup>a</sup>Wilcoxon signed rank test.</p><p>Comparison of image quality of three calf arterial segments for NCE-MRA in 26 patients with diabetes.</p
The number of different kinds of artifacts for NCE-MRA in 26 patients with diabetes.
<p>The number of different kinds of artifacts for NCE-MRA in 26 patients with diabetes.</p
Comparison of the time efficiency of SNR (SNR <sub>eff</sub>) and CNR (CNR <sub>eff</sub>) between QISS and FSD with only dark and bright blood scan (a, b) or adding the phase-contrast and m1-scout scan (c, d)) in three arterial segments of the calf.
<p>Each column represents average measurements and error is shown as standard deviation. Asterisks indicated significant difference (P < 0.05). SNR: signal-to-noise ratio; CNR: contrast-to-noise ratio; QISS: quiescent-interval single-shot; FSD: flow-sensitive dephasing.</p