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

Electrolysis of CO₂ to Syngas in Bipolar Membrane-Based Electrochemical Cells

The electrolysis of CO₂ to syngas (CO + H₂) using nonprecious metal electrocatalysts was studied in bipolar membrane-based electrochemical cells. Electrolysis was carried out using aqueous bicarbonate and humidified gaseous CO₂ 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_<i>x</i> 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 CO₂ 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/cm² current density. In the gas-phase cell, current densities up to 200 mA/cm² 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 CO₂ electrolysis at high current densities

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%

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