Fuel‐Free Synthetic Micro‐/Nanomachines

Inspired by the swimming of natural microorganisms, synthetic micro‐/nanomachines, which convert energy into movement, are able to mimic the function of these amazing natural systems and help humanity by completing environmental and biological tasks. While offering autonomous propulsion, conventional micro‐/nanomachines usually rely on the decomposition of external chemical fuels (e.g., H₂O₂), which greatly hinders their applications in biologically relevant media. Recent developments have resulted in various micro‐/nanomotors that can be powered by biocompatible fuels. Fuel‐free synthetic micro‐/nanomotors, which can move without external chemical fuels, represent another attractive solution for practical applications owing to their biocompatibility and sustainability. Here, recent developments on fuel‐free micro‐/nanomotors (powered by various external stimuli such as light, magnetic, electric, or ultrasonic fields) are summarized, ranging from fabrication to propulsion mechanisms. The applications of these fuel‐free micro‐/nanomotors are also discussed, including nanopatterning, targeted drug/gene delivery, cell manipulation, and precision nanosurgery. With continuous innovation, future autonomous, intelligent and multifunctional fuel‐free micro‐/nanomachines are expected to have a profound impact upon diverse biomedical applications, providing unlimited opportunities beyond one's imagination.     

Pistachio‐Shuck‐Like MoSe2/C Core/Shell Nanostructures for High‐Performance Potassium‐Ion Storage

Potassium‐ion batteries (KIBs) have recently attracted intensive attention because of the abundant potassium resources and their low cost and high safety. However, the major challenge faced by KIBs lies in the lack of stable and high‐capacity materials for the intercalation/deintercalation of large‐size potassium ions. A unique pistachio‐shuck‐like MoSe₂/C core/shell nanostructure (PMC) is synthesized herein as an advanced anode for boosting the performance of KIBs. This PMC is featured with a few layers of molybdenum selenide as the core with an expanded interlayer spacing of ≈0.85 nm, facilitating the intercalation/deintercalation of K ions, and a thin amorphous carbon as the shell, which can confine the active molybdenum selenide nanosheets during cycling for maintaining the high structural stability. Most importantly, as a whole, the PMC has the advantages of reducing the surplus hollow interior space for improving its packing density and buffering the volume expansion during the K‐ion intercalation for further enhancing the stability. As a consequence, the PMC shows a very high capacity of 322 mAh g^?1 at 0.2 A g^?1 over 100 cycles, and can still remain 226 mAh g^?1 at 1.0 A g^?1 for a long period of 1000 cycles, which is among the best‐reported KIBs anodes.     

MoS2/ta‐C‐Kombinationsschichten hergestellt durch Laser‐Arc‐Technologie

MoS₂/ta‐C coatings produced by laserarc‐technology A series of MoS₂ and combined MoS₂/ta‐C coatings were prepared by lasercontrolled arc evaporation (Laser‐Arc) in order to study the tribological coating behaviour under vacuum and atmospheric conditions. Very low friction coefficients down to 0.005 were measured under high vacuum. By using a ta‐C underlayer beneath the MoS₂ a increased lifetime up to 5×10⁵ load cycles could be obtained. Also under atmospheric conditions the underlayer had a beneficial effect on coating performance.     

Bruchmechanische Untersuchung der Titan‐PEEK‐Grenzfläche in thermoplastischen Titan‐CF/PEEK‐Laminaten durch Mixed‐Mode‐Bending‐Versuche

The adhesion and failure mechanism at well‐designed titanium‐PEEK interfaces within Ti‐CF/PEEK laminates are investigated by superposed mode I‐ and mode II‐loading before and after hydrothermal aging. The laser‐induced columnar structured oxide layer enhances the adhesion at the Titanium‐PEEK interface. PEEK‐Polymer that is locked mechanically in the capillary gaps of the columnar oxide structure are stretched and stiffed in the case of loading resulting in good adhesion. The adhesion at the oxide structure reduces by the influence of hydrothermal aging. Basically, the failure mechanism is not changed. Thus, the columnar oxide structure leads to enhanced humidity resistance of the adhesion between titanium and PEEK. The PEEK‐Polymer is also locked in the undercuts between the depressions and rims of the laser‐induced dot‐like surface structure resulting in adhesion. The adhesion at the dot‐like structured surface is nearly completely reduced by the influence of hydrothermal aging. The failure mechanism is changed from ductile failure within the PEEK‐Polymer to party disrupted rims and melt spatter.     

Single‐Mode Lasing from Colloidal Water‐Soluble CdSe/CdS Quantum Dot‐in‐Rods

Core–shell CdSe/CdS nanocrystals are a very promising material for light emitting applications. Their solution‐phase synthesis is based on surface‐stabilizing ligands that make them soluble in organic solvents, like toluene or chloroform. However, solubility of these materials in water provides many advantages, such as additional process routes and easier handling. So far, solubilization of CdSe/CdS nanocrystals in water that avoids detrimental effects on the luminescent properties poses a major challenge. This work demonstrates how core–shell CdSe/CdS quantum dot‐in‐rods can be transferred into water using a ligand exchange method employing mercaptopropionic acid (MPA). Key to maintaining the light‐emitting properties is an enlarged CdS rod diameter, which prevents potential surface defects formed during the ligand exchange from affecting the photophysics of the dot‐in‐rods. Films made from water‐soluble dot‐in‐rods show amplified spontaneous emission (ASE) with a similar threshold (130 μJ/cm²) as the pristine material (115 μJ/cm²). To demonstrate feasibility for lasing applications, self‐assembled microlasers are fabricated via the “coffee‐ring effect” that display single‐mode operation and a very low threshold of ～10 μJ/cm². The performance of these microlasers is enhanced by the small size of MPA ligands, enabling a high packing density of the dot‐in‐rods.     

Multilayer Amorphous‐Si‐B‐C‐N/γ‐Al2O3/α‐Al2O3 Membranes for Hydrogen Purification

The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H₂ can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single‐step under high temperature conditions. In the present work, the multilayer amorphous‐Si‐B‐C‐N/γ‐Al₂O₃/α‐Al₂O₃ membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H₂/CO permeance. The α‐Al₂O₃ support has a bimodal pore‐size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate γ‐Al₂O₃ layer—deposited from boehmite colloidal dispersion—has an average pore‐size of 8 nm being mesoporous. The results obtained by the N₂‐adsorption method indicate a decrease in the volume of micropores—0.35 vs. 0.75 cm³ g^?1—and a smaller pore size ?6.8 vs. 7.4 Å—in membranes with the intermediate mesoporous γ‐Al₂O₃ layer if compared to those without. The three times Si‐B‐C‐N coated multilayer membranes show higher H₂/CO permselectivities of about 10.5 and the H₂ permeance of about 1.05 × 10^?8 mol m^?2 s^?1 Pa^?1. If compared to the state of the art of microporous membranes, the multilayer Si‐B‐C‐N/γ‐Al₂O₃/α‐Al₂O₃ membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high‐temperature and high‐pressure stability.     

Electric‐Field‐Tunable Conductivity in Graphene/Water and Graphene/Ice Systems

This study demonstrates that the application of an external electrical potential to a phenyl‐sulfonic functionalized graphene (SG)/water suspension distinctly enhances its electrical conductivity via the structural transition from isolated clusters to a 3D SG network. Microstructural and alternating current impedance spectroscopy studies indicate that the surface charge plays an important role in the state of dispersion and connectivity of the SG in the suspension due to the potential‐dependent interactions with functional groups on the SG surface in the presence of an external electrical potential. In addition, the conductive SG/ice can be produced via liquid–solid phase transition of the SG/water suspension in the presence of an external electrical potential, which shows a one‐order magnitude improvement in electrical conductivity compared with pure ice. The electric‐field‐tunable property advances the understanding of nanofluid systems and has many potential applications.