Li-Min Liu

Iced photochemical reduction to synthesize atomically dispersed metals by suppressing nanocrystal growth

Photochemical solution-phase reactions have been widely applied for the syntheses of nanocrystals. In particular, tuning of the nucleation and growth of solids has been a major area of focus. Here we demonstrate a facile approach to generate atomically dispersed platinum via photochemical reduction of frozen chloroplatinic acid solution using ultraviolet light. Using this iced-photochemical reduction, the aggregation of atoms is prevented, and single atoms are successfully stabilized. The platinum atoms are deposited on various substrates, including mesoporous carbon, graphene, carbon nanotubes, titanium dioxide nanoparticles, and zinc oxide nanowires. The atomically dispersed platinum on mesoporous carbon exhibits efficient catalytic activity for the electrochemical hydrogen evolution reaction, with an overpotential of only 65u2009mV at a current density of 100u2009mAu2009cm−2 and long-time durability (>10u2009h), superior to state-of-the-art platinum/carbon. This iced-photochemical reduction may be extended to other single atoms, for example gold and silver, as demonstrated in this study.Photochemical synthesis is a popular approach to fabricate metallic nanoparticles, however stabilizing individually-dispersed atoms by this method remains challenging. Here, the authors freeze their precursor solution prior to UV irradiation to obtain atomically-dispersed platinum catalysts with high electrocatalytic performance.

Tuning defects in oxides at room temperature by lithium reduction

Defects can greatly influence the properties of oxide materials; however, facile defect engineering of oxides at room temperature remains challenging. The generation of defects in oxides is difficult to control by conventional chemical reduction methods that usually require high temperatures and are time consuming. Here, we develop a facile room-temperature lithium reduction strategy to implant defects into a series of oxide nanoparticles including titanium dioxide (TiO2), zinc oxide (ZnO), tin dioxide (SnO2), and cerium dioxide (CeO2). Our lithium reduction strategy shows advantages including all-room-temperature processing, controllability, time efficiency, versatility and scalability. As a potential application, the photocatalytic hydrogen evolution performance of defective TiO2 is examined. The hydrogen evolution rate increases up to 41.8u2009mmolu2009g−1u2009h−1 under one solar light irradiation, which is ~3 times higher than that of the pristine nanoparticles. The strategy of tuning defect oxides used in this work may be beneficial for many other related applications.Defective oxides are attractive for energy conversion and storage applications, but it remains challenging to implant defects in oxides under mild conditions. Here, the authors develop a versatile lithium reduction strategy to engineer the defects of oxides at roomxa0temperature leading to enhanced photocatalytic properties.

Tunable dipole and carrier mobility for a few layer Janus MoSSe structure

Transition metal chalcogenides have attracted considerable attention for the further development of nanoscale devices, however low carrier mobility seriously prevents its further application. Here, the first-principles calculations are used to explore the structural, electronic, and carrier mobility properties of few layer Janus MoSSe in different types of stacking. The result shows that AC-stacking is the most favored stacking regardless of combination mode. Besides the band gap regulation, the dipole moment perpendicular to the x–y plane can be effectively modified through varying of the combination mode and thickness of few layers, which is further evidenced by the plane electrostatic potential energy difference between the two sides. Furthermore, the carrier mobility in these Janus structures can be greatly affected by the dipole and thickness. Although the carrier mobility in monolayer MoSSe is relatively low, the bilayer or trilayer structures have a quite high electron carrier mobility of 1194 cm2 V−1 s−1 and hole carrier mobility of 5894 cm2 V−1 s−1, mainly determined by the deformation potential. The results presented here show that the few layer Janus MoSSe has a potential in designing electronic devices or photocatalysts such as for water splitting with the intrinsic built-in electronic field.

Structural resolution of inorganic nanotubes with complex stoichiometry

Determination of the atomic structure of inorganic single-walled nanotubes with complex stoichiometry remains elusive due to the too many atomic coordinates to be fitted with respect to X-ray diffractograms inherently exhibiting rather broad features. Here we introduce a methodology to reduce the number of fitted variables and enable resolution of the atomic structure for inorganic nanotubes with complex stoichiometry. We apply it to recently synthesized methylated aluminosilicate and aluminogermanate imogolite nanotubes of nominal composition (OH)3Al2O3Si(Ge)CH3. Fitting of X-ray scattering diagrams, supported by Density Functional Theory simulations, reveals an unexpected rolling mode for these systems. The transferability of the approach opens up for improved understanding of structure–property relationships of inorganic nanotubes to the benefit of fundamental and applicative research in these systems.Structural determination of inorganic nanotubes has lagged far behind that of their carbon-based counterparts. Here, the authors present a transferable methodology, combining wide angle X-ray scattering and computation, to quantitatively resolve the atomic structure of inorganic nanotubes with complex stoichiometry.

Self-hydrogenated shell promoting photocatalytic H 2 evolution on anatase TiO 2

As one of the most important photocatalysts, TiO2 has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO2 at microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO2 are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO2 nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO2 surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO2 interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H2 (H–H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.Photocatalytic water splitting on TiO2 is a promising route to H2 fuel production, but the mechanistic pathway at the water–TiO2 interface remains poorly understood. Here, using liquid environmental TEM and first-principles calculations, the authors unveil the formation of a self-hydrogenated shell on the TiO2 surface that further promotes H2 production.

Mechanical Properties of AISI 1045 Steel Subjected to Combined Loads of Tension and Torsion

AbstractThe quasi-static standard tensile, torsional, and combined tension and torsion tests were performed at room temperature to investigate the mechanical properties of normalized AISI 1045 steel specimens. The performance of yielding, Young’s modulus, and modulus of elasticity in shear were analyzed via two kinds of experiments with sequence-given loading paths, such as tension-torsion (torsional response after tension) and torsion-tension (tensile response after torsion) tests, under various preloads. Additionally, time-variant coupled effects between the shear stress and normal stress responded similarly in tension-torsion and torsion-tension experiments. Results demonstrate that ultimate strengths of torsion and tension obtained by combined tension and torsion tests were consistent with those strengths achieved by standard uniaxial tests. Yield strengths derived by the Von Mises criterion and combined tension and torsion test were compared, and results showed maximum deviations of 23.01% and 43.28% in shear and normal stress, respectively. Results indicated that the material exhibited quite different mechanical properties under combined loads of tension and torsion from those under uniaxial loads.n Graphical Abstractᅟ

Ice Melting to Release Reactants in Solution Syntheses

Aqueous solution syntheses are mostly based on mixing two solutions with different reactants. It is shown that freezing one solution and melting it in another solution provides a new interesting strategy to mix chemicals and to significantly change the reaction kinetics and thermodynamics. For example, a precursor solution containing a certain concentration of AgNO3 was frozen and dropped into a reductive NaBH4 solution at about 0u2009°C. The ultra-slow release of reactants was successfully achieved. An ice-melting process can be used to synthesize atomically dispersed metals, including cobalt, nickel, copper, rhodium, ruthenium, palladium, silver, osmium, iridium, platinum, and gold, which can be easily extended to other solution syntheses (such as precipitation, hydrolysis, and displacement reactions) and provide a generalized method to redesign the interphase reaction kinetics and ion diffusion in wet chemistry.