7 research outputs found
Rheotaxis of Bimetallic Micromotors Driven by Chemical–Acoustic 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 Chemical–Acoustic 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 Chemical–Acoustic 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 Chemical–Acoustic 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
Electrolysis of CO<sub>2</sub> to Syngas in Bipolar Membrane-Based Electrochemical Cells
The electrolysis of CO<sub>2</sub> to syngas (CO + H<sub>2</sub>) using nonprecious metal electrocatalysts
was studied in bipolar
membrane-based electrochemical cells. Electrolysis was carried out
using aqueous bicarbonate and humidified gaseous CO<sub>2</sub> on
the cathode side of the cell, with Ag or Bi/ionic liquid cathode electrocatalysts.
In both cases, stable currents were observed over a period of hours
with an aqueous alkaline electrolyte and NiFeO<sub><i>x</i></sub> electrocatalyst on the anode side of the cell. In contrast,
the performance of the cells degraded rapidly when conventional anion-
and cation-exchange membranes were used in place of the bipolar membrane.
In agreement with earlier reports, the Faradaic efficiency for CO<sub>2</sub> reduction to CO was high at low overpotential. In the liquid-phase
bipolar membrane cell, the Faradaic efficiency was stable at about
50% at 30 mA/cm<sup>2</sup> current density. In the gas-phase cell,
current densities up to 200 mA/cm<sup>2</sup> could be obtained, albeit
at lower Faradaic efficiency for CO production. At low overpotentials
in the gas-phase cathode cell, the Faradaic efficiency for CO production
was initially high but dropped within 1 h, most likely because of
dewetting of the ionic liquid from the Bi catalyst surface. The effective
management of protons in bipolar membrane cells enables stable operation
and the possibility of practical CO<sub>2</sub> electrolysis at high
current densities
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>-butylÂlithium results in intercalation
of the edges of the crystals, which are then readily exfoliated in
a 45 vol % ethanol–water 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 11–15%
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