15 research outputs found
Controlling Surface Termination and Facet Orientation in Cu<sub>2</sub>O Nanoparticles for High Photocatalytic Activity: A Combined Experimental and Density Functional Theory Study
Cu<sub>2</sub>O nanoparticles with
controllable facets are of great significance for photocatalysis.
In this work, the surface termination and facet orientation of Cu<sub>2</sub>O nanoparticles are accurately tuned by adjusting the amount
of hydroxylamine hydrochloride and surfactant. It is found that Cu<sub>2</sub>O nanoparticles with Cu-terminated (110) or (111) surfaces
show high photocatalytic activity, while other exposed facets show
poor reactivity. Density functional theory simulations confirm that
sodium dodecyl sulfate surfactant can lower the surface free energy
of Cu-terminated surfaces, increase the density of exposed Cu atoms
at the surfaces and thus benefit the photocatalytic activity. It also
shows that the poor reactivity of the Cu-terminated Cu<sub>2</sub>O (100) surface is due to the high energy barrier of holes at the
surface region
Media 1: Multiple-soliton dynamic patterns in a graphene mode-locked fiber laser
Originally published in Optics Express on 12 March 2012 (oe-20-6-6685
Dye-Assisted Transformation of Cu<sub>2</sub>O Nanocrystals to Amorphous Cu<i><sub>x</sub></i>O Nanoflakes for Enhanced Photocatalytic Performance
Amorphous Cu<i><sub>x</sub></i>O nanoflakes with a thickness
of 10ā50 nm were synthesized through dye-assisted transformation
of rhombic dodecahedral Cu<sub>2</sub>O nanocrystals using a facile
solution process. The morphology evolution observed by electron microscopy
is highly dependent on the reaction between the surface and the dye.
The crystal grain shrinks during the process until the formation of
a purely amorphous nanoflake. The amorphous Cu<i><sub>x</sub></i>O nanoflake consists of a combination of CuĀ(I) and CuĀ(II)
with a ratio close to 1:1. It shows enhanced photocatalytic reactivity
toward the degradation of methyl orange compared to that of rhombic
dodecahedral Cu<sub>2</sub>O nanocrystals with all active (110):Cu
facets. The chemical composition and architecture remain the same
after repeating degradation tests. The high surface-to-volume ratio
contributes to its superior photocatalytic performance, whereas its
low surface energy, confirmed by density functional theory simulations,
explains its improved stability. The nanoflakes also show the ability
of degrading nitrobenzene effectively, thus demonstrating great promise
as a highly stable and active photocatalyst for environmental applications
Improving the Fire Performance of Nylon 6,6 Fabric by Chemical Grafting with Acrylamide
Our previous study has demonstrated that photografting
can enhance
the flame retardancy of both polyamide and polyester fabric. In this
work, efforts to use chemical grafting with acrylamide (AM) as the
monomer and dibenzoyl peroxide (BPO) as the initiator were made to
improve the homogeneity of the grafting chains and the flame retardancy
of nylon 6,6 fabric. The effects of reaction time, reaction temperature,
and monomer concentration on the percentage of grafting (PG) were
investigated. The effect of PG on the fire performance of AM-<i>g</i>-nylon 6,6 fabric was also studied. The flame retardancy
and thermal behavior were characterized in terms of the limiting oxygen
index (LOI), UL 94 test, cone calorimetry, thermogravimetric analysis
(TGA), and differential thermal analysis (DTA). The results showed
that the after-flame time and char length were significantly reduced
after grafting. The heat release rate (HRR) of grafted sample was
decreased by 28% compared to that of the ungrafted sample. The optimal
grafting conditions were obtained as follows: reaction time, 1.5 h;
reaction temperature, 70 Ā°C; and concentration of total monomer,
15 wt %. The chemical structure and microstructure of AM-<i>g</i>-nylon 6,6 fabric were analyzed by attenuated-total-reflection Fourier
transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy
(SEM), respectively. A possible grafting mechanism is proposed and
discussed
Tetrahedral Silver Phosphate/Graphene Oxide Hybrids as Highly Efficient Visible Light Photocatalysts with Excellent Cyclic Stability
The
degradation efficiency and recyclability of photocatalysts
are the key for their practical applications. Tetrahedral silver phosphate
(Ag<sub>3</sub>PO<sub>4</sub>) is a superior visible-light photocatalyst,
while graphene oxide (GO) sheets with high specific surface area and
abundant functional groups are expected to further enhance the photocatalytic
efficiency and improve the recyclability of Ag<sub>3</sub>PO<sub>4</sub>. Herein, we demonstrate an eco-friendly and kinetically controlled
approach to synthesize Ag<sub>3</sub>PO<sub>4</sub>/GO hybrids. Tetrahedral
Ag<sub>3</sub>PO<sub>4</sub> are grown in situ on the GO sheets in
mixed solvents, and their microstructures are controlled by the slow
dissolution and ionization of H<sub>3</sub>PO<sub>4</sub> and the
adjustment of the volume ratios of ethanol/water solvents. The hybrid
with 5 wt % of GO exhibits an extraordinary photocatalytic efficiency
and satisfactory recyclability for the degradation of organic dyes.
Approximately 99% of methylene blue could be degraded in 4 min, and
the degradation percentage is still as high as 97% even after 5 cycles
of photocatalytic degradations. The mechanism of reinforcement of
the photocatalytic performance was also studied. This hybridization
of tetrahedral Ag<sub>3</sub>PO<sub>4</sub> with GO sheets provides
an efficient solution to the photocorrosion of Ag<sub>3</sub>PO<sub>4</sub> and is an efficient approach for synthesizing Ag<sub>3</sub>PO<sub>4</sub>-based semiconducting hybrids as highly efficient and
recyclable photocatalysts
Fine Tuning Water States in Hydrogels for High Voltage Aqueous Batteries
Hydrogels
are widely used as quasi-solid-state electrolytes
in
aqueous batteries. However, they are not applicable in high-voltage
batteries because the hydrogen evolution reaction cannot be effectively
suppressed even when water is incorporated into the polymer network.
Herein, by profoundly investigating the states of water molecules
in hydrogels, we designed supramolecular hydrogel electrolytes featuring
much more nonfreezable bound water and much less free water than that
found in conventional hydrogels. Specifically, two strategies are
developed to achieve this goal. One strategy is adopting monomers
with a variety of hydrophilic groups to enhance the hydrophilicity
of polymer chains. The other strategy is incorporating zwitterionic
polymers or polymers with counterions as superhydrophilic units. In
particular, the nonfreezable bound water content increased from 0.129
in the conventional hydrogel to >0.4 mg mgā1 in
the fabricated hydrogels, while the free water content decreased from
1.232 to ā¼0.15 mg mgā1. As a result, a wide
electrochemical stability window of up to 3.25 V was obtained with
the fabricated hydrogels with low concentrations of incorporated salts
and enhanced hydrophilic groups or superhydrophilic groups. The ionic
conductivities achieved with our developed hydrogel electrolytes were
much higher than those in the conventional highly concentrated salt
electrolytes, and their cost is also much lower. The designed supramolecular
hydrogel electrolytes endowed an aqueous K-ion battery (AKIB) system
with a high voltage plateau of 1.9 V and contributed to steady cycling
of the AKIB for over 3000 cycles. The developed supramolecular hydrogel
electrolytes are also applicable to other batteries, such as aqueous
lithium-ion batteries, hybrid sodium-ion batteries, and multivalent-ion
aqueous batteries, and can achieve high voltage output
Rational Design and Modification of Highā<i>k</i> Bis(double-stranded) Block Copolymer for High Electrical Energy Storage Capability
High dielectric constant (high-<i>k</i>) polymers have
important application in advanced electronic devices such as energy
storage, wearable electronics, artificial muscles, and electrocaloric
cooling because of their excellent flexibility and ease of processing.
However, most of the commercially available polymers have low-<i>k</i> values and the designed strategies for enhancing <i>k</i> are usually at the cost of the increase of dielectric
loss. In this work, novel high-<i>k</i> and low loss bisĀ(double-stranded)
block copolymers, containing the ionic-conjugated hybrid conductive
segments (HCS) with narrow band gap and the insulating segments with
wide band gap, were synthesized by tandem metathesis polymerizations.
The novel copolymers exhibited enhanced dielectric constant of 33ā28
accompanied by low dielectric loss of 0.055ā0.02 at 10<sup>2</sup>ā10<sup>6</sup> Hz, and thus greatly increased stored
energy density of 9.95 J cm<sup>ā3</sup> was achieved at relatively
low electric field of 370 MV m<sup>ā1</sup>, which is significantly
higher than that of the commercial biaxially oriented polypropylene (BOPP) (about 1.6 J cm<sup>ā3</sup> at 400 MV m<sup>ā1</sup>). In addition, by doping with I<sub>2</sub>, the <i>k</i> values of the HCS-contained block
copolymer can increase further to 36.5ā29 with low dielectric
loss of 0.058ā0.026, and the stored energy density maintained
at a high level of 8.99 J cm<sup>ā3</sup> at 300 MV m<sup>ā1</sup> with suitable I<sub>2</sub> content. The excellent dielectric and
energy storage capability were attributed to the unique macromolecular
structure and well-defined nanomorphology, which not only enhanced
the dipolar, electronic, and interfacial polarizations but also significantly
suppressed the leakage current and increased the breakdown strength
by wrapping the narrow band gap segments in the wide band gap segments
Vertically Aligned Carbon Nanotubes on Carbon Nanofibers: A Hierarchical Three-Dimensional Carbon Nanostructure for High-Energy Flexible Supercapacitors
Hierarchical
structures enable high-performance power sources.
We report here the preparation of vertically aligned carbon nanotubes
directly grown on carbon nanofibers (VACNTs/CNFs) by combining electrospinning
with pyrolysis technologies. The structure and morphology of VACNTs/CNFs
could be precisely tuned and controlled by adjusting the percentage
of reactants. The desired VACNTs/CNFs could not only possess high
electric conductivity for efficient charge transport but could also
increase surface area for accessing more electrolyte ions. When using
an ionic liquid electrolyte, VACNTs/CNFs-based electric double layer
(EDL) flexible supercapacitors can deliver a high specific energy
of 70.7 Wh/kg at a current density of 0.5 A/g and at 30 Ā°C, and
an ultrahigh-energy density of 98.8 Wh/kg at a current density of
1.0 A/g and at 60 Ā°C. Even after 20āÆ000 charging/discharging
cycles, the EDL capacitor still retains 97.0% of the initial capacitance.
The excellent performance highlights the important role of the branched
VACNTs in storing and accumulating charge and the CNF backbone in
transporting charge, thereby boosting both power density and energy
density
Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman
High load-bearing capacity is one of the crucial indicators
for
liquid superlubricants to move toward practicality. However, some
of the current emerging systems not only have low contact pressures
but also are highly susceptible to further degradation due to water
adsorption and even superlubricity failure. Herein, a novel choline
chloride-based ionic liquid analogues (ILAs) of a superlubricant with
triethanolamine (TEOA) as the H-bond donor is reported for the first
time; it obtains an ultralow coefficient of friction (0.005) and high
load-bearing capacity (360 MPa, more than 2 times that of similar
systems) due to adsorption of a small amount of water (<5 wt %)
from the air. In situ Raman combined with 1H NMR and FTIR
techniques reveals that adsorbed water competes with the hydroxyl
group of TEOA for coordination with Clā, leading
to the conversion of some strong H-bonds to weak H-bonds in ILAs;
the localized strong H-bonds and weak H-bonds endow the ILAs with
high load-bearing capacity and the formation of ultralow shear-resistance
sliding interfaces, respectively, under the shear motion. This study
proposes a strategy to modulate the interactions between liquid species
using adsorbed water from air as a competing ligand, which provides
new insights into the design of ILA-based macroscopic liquid superlubricants
with a high load-bearing capacity
Flexible Waterproof Rechargeable Hybrid Zinc Batteries Initiated by Multifunctional Oxygen Vacancies-Rich Cobalt Oxide
Although
both are based on Zn, Znāair batteries and Znāion
batteries are good at energy density and power density, respectively.
Here, we adopted Arāplasma to engrave a cobalt oxide with abundant
oxygen vacancies (denoted as Co<sub>3</sub>O<sub>4ā<i>x</i></sub>). The introduction of oxygen vacancies to cobalt
oxide not only promotes its reversible CoāO ā CoāOāOH
redox reaction but also leads to good oxygen reduction reaction and
oxygen evolution (ORR/OER) performance (a half-wave potential of 0.84
V, four-electron transfer process for ORR, and 330 mV overpotential,
58 mVĀ·dec<sup>ā1</sup> Tafel slope for OER). We then constructed
a battery system based on both ZnāCo<sub>3</sub>O<sub>4ā<i>x</i></sub> and Znāair electrochemical reactions. The
hybrid battery reveals both a high-power density of 3200 WĀ·kg<sup>ā1</sup> and high-energy density of 1060 WhĀ·kg<sup>ā1</sup>. Furthermore, the developed flexible solid-state hybrid batterydemonstrates
good waterproof and washable ability (99.2% capacity retention of
after 20 h water soaking test and 93.2% capacity retention after 1
h washing test). Interestingly, the fabricated flexible battery can
work under water, and after the power is exhausted, the battery can
automatically recover electricity output as long as it is exposed
to air. The developed device is suitable for wearable applications
considering its electrochemical performances, great environmental
adaptation, and āair recoverabilityā. In addition, this
study underscores the approach to develop hybrid energy-storage technologies
through modification of electrode materials