Flat-Band Potentials of Molecularly Thin Metal Oxide Nanosheets

Exfoliated nanosheets derived from Dion–Jacobson phase layer perovskites (TBA_<i>x</i>H_1–<i>x</i>A₂B₃O₁₀, 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 Mott–Schottky method to obtain flat-band potentials (<i>V</i>_FB) of the oxide semiconductors as a function of pH. Despite capacitive contributions from the electrode–solution interface, reliable values could be obtained from capacitance measurements over a limited potential range near <i>V</i>_FB. The measured values of <i>V</i>_FB shifted −59 mV/pH over the pH range of 4–8 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), 227–234). Density functional theory calculations showed that A-site substitution influenced band energies by modulating the strength of A–O 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 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 (H₂O₂) 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 (H₂O₂) 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 (H₂O₂) 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 (H₂O₂) 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 WS₂ Crystals into 1–2 Layer Semiconducting Nanosheets and Efficient Photocatalytic Hydrogen Evolution from WS₂/CdS Nanorod Composites

Monolayer WS₂ 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 1–2 layer semiconducting WS₂ nanosheets in a yield of 18–22 wt % by a modified LPE method that involves preintercalation with substoichometric quantities of <i>n-</i>butyllithium. The exfoliated WS₂ nanosheeets are n-type, have a bandgap of ∼1.78 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 H₂ evolution rate was observed with WS₂/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 MoS₂ Nanosheets by Sonication-Assisted Lithium Intercalation and Infrared Laser-Induced 1T to 2H Phase Reversion

Exfoliated 2H molybdenum disulfide (MoS₂) 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 MoS₂, which combines fast sonication-assisted lithium intercalation and infrared (IR) laser-induced phase reversion. We found that the complete lithium intercalation of MoS₂ 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 MoS₂ 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 MoS₂ into suspensions of nanosheets with retention of the semiconducting 2H phase. The controlled reaction of MoS₂ with substoichiometric amounts <i>n</i>-butyl­lithium 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 MoS₂ microcrystals, with a mass yield of the dispersed nanosheets of 11–15%

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 “metalattice”. 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 “spin-engineered” 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 “spatial confinement” 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