9 research outputs found
Flat-Band Potentials of Molecularly Thin Metal Oxide Nanosheets
Exfoliated
nanosheets derived from DionāJacobson phase layer perovskites
(TBA<sub><i>x</i></sub>H<sub>1ā<i>x</i></sub>A<sub>2</sub>B<sub>3</sub>O<sub>10</sub>, A = Sr, Ca, B = Nb,
Ta) were grown layer-by-layer on fluorine-doped tin oxide and gold
electrode surfaces. Electrochemical impedance spectra (EIS) of the
five-layer nanosheet films in contact with aqueous electrolyte solutions
were analyzed by the MottāSchottky method to obtain flat-band
potentials (<i>V</i><sub>FB</sub>) of the oxide semiconductors
as a function of pH. Despite capacitive contributions from the electrodeāsolution
interface, reliable values could be obtained from capacitance measurements
over a limited potential range near <i>V</i><sub>FB</sub>. The measured values of <i>V</i><sub>FB</sub> shifted
ā59 mV/pH over the pH range of 4ā8 and were in close
agreement with the empirical correlation between conduction band-edge
potentials and optical band gaps proposed by Matsumoto (<i>J. Solid State Chem.</i> <b>1996</b>, <i>126</i> (2), 227ā234). Density functional
theory calculations showed that A-site substitution influenced band
energies by modulating the strength of AāO bonding, and that
subsitution of Ta for Nb on B-sites resulted in a negative shift of
the conduction band-edge potential
Rheotaxis of Bimetallic Micromotors Driven by ChemicalāAcoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Rheotaxis of Bimetallic Micromotors Driven by ChemicalāAcoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Rheotaxis of Bimetallic Micromotors Driven by ChemicalāAcoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
Rheotaxis of Bimetallic Micromotors Driven by ChemicalāAcoustic Hybrid Power
Rheotaxis
is a common phenomenon in nature that refers to the directed
movement of micro-organisms as a result of shear flow. The ability
to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality
to enable their applications in biomedicine and chemistry. Here, we
present a hybrid strategy that can achieve both positive and negative
rheotaxis of synthetic bimetallic micromotors by employing a combination
of chemical fuel and acoustic force. An acoustofluidic device is developed
for the integration of the two propulsion mechanisms. Using acoustic
force alone, bimetallic microrods are propelled along the bottom surface
in the center of a fluid channel. The leading end of the microrod
is always the less dense end, as established in earlier experiments.
With chemical fuel (H<sub>2</sub>O<sub>2</sub>) alone, the microrods
orient themselves with their anode end against the flow when shear
flow is present. Numerical simulations confirm that this orientation
results from tilting of the microrods relative to the bottom surface
of the channel, which is caused by catalytically driven electro-osmotic
flow. By combining this catalytic orientation effect with more powerful,
density-dependent acoustic propulsion, both positive and negative
rheotaxis can be achieved. The ability to respond to flow stimuli
and collectively propel synthetic microswimmers in a directed manner
indicates an important step toward practical applications
High Yield Exfoliation of WS<sub>2</sub> Crystals into 1ā2 Layer Semiconducting Nanosheets and Efficient Photocatalytic Hydrogen Evolution from WS<sub>2</sub>/CdS Nanorod Composites
Monolayer
WS<sub>2</sub> has interesting properties as a direct bandgap semiconductor,
photocatalyst, and electrocatalyst, but it is still a significant
challenge to prepare this material in colloidal form by liquid-phase
exfoliation (LPE). Here, we report the preparation of 1ā2 layer
semiconducting WS<sub>2</sub> nanosheets in a yield of 18ā22
wt % by a modified LPE method that involves preintercalation with
substoichometric quantities of <i>n-</i>butyllithium. The
exfoliated WS<sub>2</sub> nanosheeets are n-type, have a bandgap of
ā¼1.78 eV, and act as a cocatalyst with CdS nanorods in photocatalytic
hydrogen evolution using lactate as a sacrificial electron donor.
Up to a 26-fold increase in H<sub>2</sub> evolution rate was observed
with WS<sub>2</sub>/CdS hybrids compared with their pure CdS counterpart,
and an absorbed photon quantum yield (AQE) of >60% was measured
with the optimized photocatalyst
Fast and Efficient Preparation of Exfoliated 2H MoS<sub>2</sub> Nanosheets by Sonication-Assisted Lithium Intercalation and Infrared Laser-Induced 1T to 2H Phase Reversion
Exfoliated 2H molybdenum disulfide
(MoS<sub>2</sub>) has unique properties and potential applications
in a wide range of fields, but corresponding studies have been hampered
by the lack of effective routes to it in bulk quantities. This study
presents a rapid and efficient route to obtain exfoliated 2H MoS<sub>2</sub>, which combines fast sonication-assisted lithium intercalation
and infrared (IR) laser-induced phase reversion. We found that the
complete lithium intercalation of MoS<sub>2</sub> with butyllithium
could be effected within 1.5 h with the aid of sonication. The 2H
to 1T phase transition that occurs during the lithium intercalation
could be also reversed by IR laser irradiation with a DVD optical
drive
Controlled Exfoliation of MoS<sub>2</sub> Crystals into Trilayer Nanosheets
The controlled exfoliation of transition
metal dichalcogenides
(TMDs) into pristine single- or few-layer nanosheets remains a significant
barrier to fundamental studies and device applications of TMDs. Here
we report a novel strategy for exfoliating crystalline MoS<sub>2</sub> into suspensions of nanosheets with retention of the semiconducting
2H phase. The controlled reaction of MoS<sub>2</sub> with substoichiometric
amounts <i>n</i>-butylĀlithium results in intercalation
of the edges of the crystals, which are then readily exfoliated in
a 45 vol % ethanolāwater solution. Surprisingly, the resulting
colloidal suspension of nanosheets was found (by electron microscopy
and atomic force microscopy) to consist mostly of trilayers. The efficiency
of exfoliation of the pre-intercalated sample is increased by at least
1 order of magnitude relative to the starting MoS<sub>2</sub> microcrystals,
with a mass yield of the dispersed nanosheets of 11ā15%
Confined Chemical Fluid Deposition of Ferromagnetic Metalattices
A magnetic, metallic
inverse opal fabricated by infiltration into
a silica nanosphere template assembled from spheres with diameters
less than 100 nm is an archetypal example of a āmetalatticeā.
In traditional quantum confined structures such as dots, wires, and
thin films, the physical dynamics in the free dimensions is typically
largely decoupled from the behavior in the confining directions. In
a metalattice, the confined and extended degrees of freedom cannot
be separated. Modeling predicts that magnetic metalattices should
exhibit multiple topologically distinct magnetic phases separated
by sharp transitions in their hysteresis curves as their spatial dimensions
become comparable to and smaller than the magnetic exchange length,
potentially enabling an interesting class of āspin-engineeredā
magnetic materials. The challenge to synthesizing magnetic inverse
opal metalattices from templates assembled from sub-100 nm spheres
is in infiltrating the nanoscale, tortuous voids between the nanospheres
void-free with a suitable magnetic material. Chemical fluid deposition
from supercritical carbon dioxide could be a viable approach to void-free
infiltration of magnetic metals in view of the ability of supercritical
fluids to penetrate small void spaces. However, we find that conventional
chemical fluid deposition of the magnetic late transition metal nickel
into sub-100 nm silica sphere templates in conventional macroscale
reactors produces a film on top of the template that appears to largely
block infiltration. Other deposition approaches also face difficulties
in void-free infiltration into such small nanoscale templates or require
conducting substrates that may interfere with properties measurements.
Here we report that introduction of āspatial confinementā
into the chemical fluid reactor allows for fabrication of nearly void-free
nickel metalattices by infiltration into templates with sphere sizes
from 14 to 100 nm. Magnetic measurements suggest that these nickel
metalattices behave as interconnected systems rather than as isolated
superparamagnetic systems coupled solely by dipolar interactions