High‐Yield Synthesis of Crystal‐Phase‐Heterostructured 4H/fcc Au@Pd Core–Shell Nanorods for Electrocatalytic Ethanol Oxidation

Noble‐metal nanomaterials are attracting increasing research interest due to their promising applications in electrochemical catalysis, for example. Although great efforts have been devoted to the size‐, shape‐, and architecture‐controlled synthesis of noble‐metal nanomaterials, their crystal‐phase‐controlled synthesis is still in its infancy. Here, for the first time, this study reports high‐yield synthesis of Au nanorods (NRs) with alternating 4H/face‐centered cubic (fcc) crystal‐phase heterostructures via a one‐pot wet‐chemical method. The coexistence of 4H and fcc phases is relatively stable, and the 4H/fcc Au NRs can serve as templates for crystal‐phase‐controlled epitaxial growth of other metals. As an example, bimetallic 4H/fcc Au@Pd core–shell NRs are synthesized via the epitaxial growth of Pd on 4H/fcc Au NRs. Significantly, the 4H/fcc Au@Pd NRs show superior mass activity toward the ethanol oxidation reaction, i.e., 6.2 and 4.9 times those of commercial Pd black and Pt/C catalysts, respectively. It is believed that this new synthetic strategy can be used to prepare other novel catalysts for various promising applications.     

Quasi‐Epitaxial Growth of Magnetic Nanostructures on 4H‐Au Nanoribbons

Phase engineering of nanomaterials is an effective strategy to tune the physicochemical properties of nanomaterials for various promising applications. Herein, by using the 4H‐Au nanoribbons as templates, four novel magnetic nanostructures, namely 4H‐Au @ 14H‐Co nanobranches, 4H‐Au @ 14H‐Co nanoribbons, 4H‐Au @ 2H‐Co nanoribbons, and 4H‐Au @ 2H‐Ni nanoribbons, are synthesized based on the quasi‐epitaxial growth. Different from the conventional epitaxial growth of metal nanomaterials, the obtained Co and Ni nanostructures possess different crystal phases from the Au template. Due to the large lattice mismatch between Au and the grown metals (i.e., Co and Ni), ordered misfit dislocations are generated at the Co/Au and Ni/Au interfaces. Notably, a new super‐structure of Co is formed, denoted as 14H. Both 4H‐Au @ 14H‐Co nanobranches and nanoribbons are ferromagnetic at room temperature, showing similar Curie temperature. However, their magnetic behaviors exhibit distinct temperature dependence, resulting from the competition between spin and volume fluctuations as well as the unique geometry. This work paves the way to the templated synthesis of nanomaterials with unconventional crystal phases for the exploration of phase‐dependent properties.     

Syntheses and Properties of Metal Nanomaterials with Novel Crystal Phases

In recent decades, researchers have devoted tremendous effort into the rational design and controlled synthesis of metal nanomaterials with well‐defined size, morphology, composition, and structure, and great achievements have been reached. However, the crystal‐phase engineering of metal nanomaterials still remains a big challenge. Recent research has revealed that the crystal phase of metal nanomaterials can significantly alter their properties, arising from the distinct atomic arrangement and modified electronic structure. Until now, it has been relatively uncommon to synthesize metal nanomaterials with novel crystal phases in spite of the fact that these nanostructures would be promising for various applications. Here, the research progress regarding the fine control of noble metal (Au, Ag, Ru, Rh, Pd) and non‐noble metal (Fe, Co, Ni) nanomaterials with novel crystal phases is reviewed. First, synthesis strategies and their phase transformations are summarized, while highlighting the peculiar characteristics of each element. The phase‐dependent properties are then discussed by providing representative examples. Finally, the challenges and perspectives in this emerging field are proposed.     

Synthesis of Hierarchical 4H/fcc Ru Nanotubes for Highly Efficient Hydrogen Evolution in Alkaline Media

Hierarchical metal nanostructures containing 1D nanobuilding blocks have stimulated great interest due to their abundant active sites for catalysis. Herein, hierarchical 4H/face‐centered cubic (fcc) Ru nanotubes (NTs) are synthesized by a hard template‐mediated method, in which 4H/fcc Au nanowires (NWs) serve as sacrificial templates which are then etched by copper ions (Cu²⁺) in dimethylformamide. The obtained hierarchical 4H/fcc Ru NTs contain ultrathin Ru shells (5–9 atomic layers) and tiny Ru nanorods with length of 4.2 ± 1.1 nm and diameter of 2.2 ± 0.5 nm vertically decorated on the surface of Ru shells. As an electrocatalyst for the hydrogen evolution reaction in alkaline media, the hierarchical 4H/fcc Ru NTs exhibit excellent electrocatalytic performance, which is better than 4H/fcc Au‐Ru NWs, commercial Pt/C, Ru/C, and most of the reported electrocatalysts.     

Ligand-Exchange-Induced Amorphization of Pd Nanomaterials for Highly Efficient Electrocatalytic Hydrogen Evolution Reaction

Various kinds of amorphous materials, such as transition metal dichalcogenides, metal oxides, and metal phosphates, have demonstrated superior electrocatalytic performance compared with their crystalline counterparts. Compared to other materials for electrocatalysis, noble metals exhibit intrinsically high activity and excellent durability. However, it is still very challenging to prepare amorphous noble-metal nanomaterials due to the strong interatomic metallic bonding. Herein, the discovery of a unique thiol molecule is reported, namely bismuthiol I, which can induce the transformation of Pd nanomaterials from face-centered-cubic (fcc) phase into amorphous phase without destroying their integrity. This ligand-induced amorphization is realized by post-synthetic ligand exchange under ambient conditions, and is applicable to fcc Pd nanomaterials with different capping ligands. Importantly, the obtained amorphous Pd nanoparticles exhibit remarkably enhanced activity and excellent stability toward electrocatalytic hydrogen evolution in acidic solution. This work provides a facile and effective method for preparing amorphous Pd nanomaterials, and demonstrates their promising electrocatalytic application.     

Identifying Phase‐Dependent Electrochemical Stripping Performance of FeOOH Nanorod: Evidence from Kinetic Simulation and Analyte–Material Interactions

Metal hydroxide nanomaterials are widely applied in the energy and environment fields. The electrochemical performance of such materials is strongly dependent on their crystal phases. However, as there are always multiple factors relating to the phase‐dependent electrochemistry, it is still difficult to identify the determining one. The well‐defined crystal phases of α‐ and β‐FeOOH nanorods are characterized through the transmission electron microscopy by a series of rotation toward one rod, where the cross‐section shape and the growth direction along the [001] crystalline are first verified for 1D FeOOH nanostructures. The electrosensitivity of the two materials toward Pb(II) is tested, where α‐FeOOH performs an outstanding sensitivity whilst it is only modest for β‐FeOOH. Experiments via Fourier transform infrared spectroscopy, X‐ray absorption fine structure (XAFS), etc., show that α‐FeOOH presents a larger Pb(II) adsorption capacity due to more surficial hydroxyl groups and weaker Pb? O bond strength. The reaction kinetics are simulated and the adsorption capacity is found to be the determining factor for the distinct Pb(II) sensitivities. Combining experiment with simulation, this work reveals the physical insights of the phase‐dependent electrochemistry for FeOOH and provides guidelines for the functional application of metal hydroxide nanomaterials.     

Plasmon‐Driven Rapid In Situ Formation of Luminescence Single Crystal Nanoparticle

Single crystal nanomaterials are very important for the fundamental investigation and application of luminescence. However, a very critical growth condition or high temperature treatment is always required for their preparation. Here, an easy and rapid in situ achievement of a single crystal luminescent material is realized by taking advantage of plasmon‐induced thermal and catalysis effects. With the assistance of localized surface plasmon resonance of Au nanoparticles, polycrystalline NaYF₄ transforms to single crystal Y₂O₃ in tens of milliseconds, resulting in remarkable improvement of luminescence emission. It is important to point out that the single crystal transformation is also achieved even at a very low temperature, which is impossible with conventional approaches. Such a convenient and efficient plasmon assisted scheme provides a new technology for the rapid achievement of single crystal materials and extends the application of surface plasmon to a much broader field.     

Revealing the Role of Electrocatalyst Crystal Structure on Oxygen Evolution Reaction with Nickel as an Example

Establishing a correlation between the crystal structure and electrocatalytic activity is crucial to the rational design of high performance electrocatalysts. In this work, taking the widely investigated nickel (Ni) based nonprecious oxygen evolution reaction (OER) catalyst as an example, for the first time, it is reported that the crystal structure plays a critical role in determining the OER performance. Similar‐sized nickel nanoparticles but in different hexagonal close‐packed phase and face‐centered cubic phase coated with N‐doped carbon shells, noted as hcp‐Ni@NC and fcc‐Ni@NC, are successfully prepared, respectively, in which the N‐coated carbon shell structures were also similar. Surprisingly, a dramatically enhanced OER performance of hcp‐Ni@NC in comparison with fcc‐Ni@NC is observed. The hcp‐Ni@NC only requires 305 mV overpotential to achieve the current density of 10 mA cm^?2, which is 55 mV lower than that of fcc‐Ni@NC, which can be ascribed to the influence of nickel crystal phase on the electron structure of N‐doped carbon shell. This finding will bring new thinking toward the rational design of high performance non‐noble metal electrocatalysts.     

Miscible-Solvent-Assisted Two-Phase Synthesis of Monolayer-Ligand-Protected Metal Nanoclusters with Various Sizes

Effective yet versatile synthetic strategies for size-tunable metal nanoclusters (NCs) are scarce. This has hampered the development of this unique class of nanomaterials. Here, a general protocol is reported for the synthesis of high-quality metal NCs protected by a variety of organic ligands (e.g., selenolate, thiolate, and phosphine) based on a miscible-solvent-assisted phase transfer between water and organic solution. This method is demonstrated to be facile, rapid (≤3 h), scalable (gram-scale), and versatile. The size of the selenolated and thiolated Au NCs can be tuned from Au₁₀ to Au₆₁ by simply varying the miscible solvent in proportions and types. The advantages of this method, such as quick phase separation and no need for purification treatment, enable real-time monitoring of metal NC growth within the NaBH₄ reduction system. The results show that the size of Au NCs gradually increases with increasing valence electron count by a stepwise 2x e^- hopping mechanism (x = 0–5), i.e., 0 e^- → 2 e^- → 4 e^- → 8 e^- → 18 e^- → 22 e^- → 32 e^-.     

Oxidation Etching-Induced Post-Crystallization of Palladium Nanosheets for Efficient Catalytic Hydrogenation

The performances of catalysts are highly dependent on their crystallinities. It is a significant challenge to successively manipulate the crystallinities of noble metal nanocatalysts due to the strong metallic bonds, especially under ambient conditions. Herein, a post-crystallization approach is developed for successive control of the crystallinity of Pd nanosheets via selective oxidation etching of the amorphous domains. This strategy can be extended to crystallize other Pd and Ru nanomaterials. By carefully modulating the crystallinity of Pd nanosheets, the time for the complete conversion of 4-nitrostyrene via hydrogenation is reduced by 20 times. Also, crystallization can turn the selectivity of the products and improve the stability of Pd nanosheets. These findings may advance the crystal engineering of metal nanomaterials for wide applications.     

Amorphous/Crystalline Hetero‐Phase Pd Nanosheets: One‐Pot Synthesis and Highly Selective Hydrogenation Reaction

Similar to heterostructures composed of different materials, possessing unique properties due to the synergistic effect between different components, the crystal‐phase heterostructures, one variety of hetero‐phase structures, composed of different crystal phases in monometallic nanomaterials are herein developed, in order to explore crystal‐phase‐based applications. As novel hetero‐phase structures, amorphous/crystalline heterostructures are highly desired, since they often exhibit unique properties, and hold promise in various applications, but these structures have rarely been studied in noble metals. Herein, via a one‐pot wet‐chemical method, a series of amorphous/crystalline hetero‐phase Pd nanosheets is synthesized with different crystallinities for the catalytic 4‐nitrostyrene hydrogenation. The chemoselectivity and activity can be fine‐tuned by controlling the crystallinity of the as‐synthesized Pd nanosheets. This work might pave the way to preparing various hetero‐phase nanostructures for promising applications.     

A General and Straightforward Route to Noble Metal‐Decorated Mesoporous Transition‐Metal Oxides with Enhanced Gas Sensing Performance

Controllable and efficient synthesis of noble metal/transition‐metal oxide (TMO) composites with tailored nanostructures and precise components is essential for their application. Herein, a general mercaptosilane‐assisted one‐pot coassembly approach is developed to synthesize ordered mesoporous TMOs with agglomerated‐free noble metal nanoparticles, including Au/WO₃, Au/TiO₂, Au/NbO_x, and Pt/WO₃. 3‐mercaptopropyl trimethoxysilane is applied as a bridge agent to cohydrolyze with metal oxide precursors by alkoxysilane moieties and interact with the noble metal source (e.g., HAuCl₄ and H₂PtCl₄) by mercapto (? SH) groups, resulting in coassembly with poly(ethylene oxide)‐b‐polystyrene. The noble metal decorated TMO materials exhibit highly ordered mesoporous structure, large pore size (≈14–20 nm), high specific surface area (61–138 m² g^?1), and highly dispersed noble metal (e.g., Au and Pt) nanoparticles. In the system of Au/WO₃, in situ generated SiO₂ incorporation not only enhances their thermal stability but also induces the formation of ε‐phase WO₃ promoting gas sensing performance. Owning to its specific compositions and structure, the gas sensor based on Au/WO₃ materials possess enhanced ethanol sensing performance with a good response (R_air/R_gas = 36–50 ppm of ethanol), high selectivity, and excellent low‐concentration detection capability (down to 50 ppb) at low working temperature (200 °C).     

Microstructural characterization of gold nanoparticles synthesized by solution plasma processing

Microstructural characteristics of gold nanoparticles (Au NPs) fabricated by solution plasma processing (SPP) in reverse micelle solutions have been studied by high-resolution transmission electron microscopy (HRTEM). The synthesized Au NPs, with an average size of 6.3 ± 1.4?nm, have different crystal characteristics; fcc single-crystalline particles, multiply twinned particles (MTPs), and incomplete MTPs (single-nanotwinned fcc configuration). The crystal structure characteristics of the Au NPs synthesized by the SPP method were analyzed and compared with similar-size Au NPs obtained by the conventional chemical reduction synthesis (CRS) method. The TEM analysis results show that the Au NPs synthesized by the CRS method have shapes and crystal structures similar to those nanoparticles obtained by the SPP method. However, from the detailed HRTEM analysis, the relative number of the Au MTPs and incomplete MTPs to the total number of the Au NPs synthesized by the SPP method was observed to be around 94%, whereas the relative number of these kinds of crystal structures fabricated by the CRS method was about 63%. It is most likely that the enhanced formation of the Au MTPs is due to the fact that the SPP method generates highly reaction-activated species under low environmental temperature conditions.     

Misorientation‐Angle‐Dependent Phase Transformation in van der Waals Multilayers via Electron‐Beam Irradiation

Misorientation‐angle dependence on layer thickness is an intriguing feature of van der Waals materials, which causes stark optical gain and electrical transport modulation. However, the influence of misorientation angle on phase transformation is not determined yet. Herein, this phenomenon in a MoS₂ multilayer via in situ electron‐beam irradiation is reported. An AA′‐stacked MoS₂ bilayer undergoes structural transformation from the 2H semiconducting phase to the 1T′ metallic phase, similar to a MoS₂ monolayer, which is confirmed via in situ transmission electron microscopy. Moreover, non‐AA′ stacking, which has no local AA′ stacking order in the Moiré pattern, does not reveal such a phase transformation. While a collective sliding motion of chalcogen atoms easily occurs during the transformation in AA′ stacking, in non‐AA′ stacking it is suppressed by the weak van der Waals strength and by the chalcogen atoms interlocked at different orientations, which disfavor their kinetics by the increased entropy of mixing.     

Thermodynamic Functions and Phase Transformation of Metal Nanocrystals

1.IntroductionNanocrystalline materials have attracted increasingscientific interests since they emerged in the late80s',be-cause of their unusual physical and chemical propertiesthat are normally attributed to the ultrafine grains.Thespecial properties of nanocrystalline materials are essen-tially connected with both thermodynamics and dynam-ics of the formation of nano materials.However,it hasshown that traditional thermodynamic and phase trans-formation models cannot satisfactorily describe…     

铜纳米杆弯曲行为动态特性的模拟

采用分子动力学方法模拟金属铜纳米杆的弯曲力学性能，研究了从准静态加载到快速加载范围内不同加载速率的行为。结果表明，金属纳米杆的弯曲力学行为表现出显著的加载速率相关性和非线性变形行为。在弹性弯曲过程中，一种变形机制是发生从面心立方到密排六方的晶结构转变。转变发生后横截面增大和长度减小导致抗弯能力显著增强，另一种变形是纳米杆不发生晶格结构转变，位错的产生和运动导致塑性行为。     

One-dimensional TiO2 nanomaterials: preparation and catalytic applications

This work reports on the syntheses of one-dimensional (1D) H2Ti3O7 materials (nanotubes, nanowires and their mixtures) by autoclaving anatase titania (Raw-TiO2) in NaOH-containing ethanol-water solutions, followed by washing with acid solution. The synthesized nanosized materials were characterized using XRD, TEM/HRTEM, BET and TG techniques. The autoclaving temperature (120-180 degrees C) and ethanol-to-water ratio (V(EtOH)/V(H2O) = 0/60 approximately 30/30) were shown to be critical to the morphology of H2Ti3O7 product. The obtained H2Ti3O7 nanostructures were calcined at 400-900 degrees C to prepare 1D-TiO2 nanomaterials. H2Ti3O7 nanotubes were converted to anatase nanorods while H2Ti3O7 nanowires to TiO2(B) nanowires after the calcination at 400 degrees C. The calcination at higher temperatures led to gradual decomposition of the wires to rods and phase transformation from TiO2(B) to anatase then to rutile. Photocatalytic degradation of methyl orange was conducted to compare the photocatalytic activity of these 1D materials. These 1D materials were used as new support to prepare Au/TiO2 catalysts for CO oxidation at 0 degrees C and 1,3-butadiene hydrogenation at 120 degrees C. For the CO oxidation reaction, Au particles supported on anatase nanorods derived from the H2Ti3O7 nanotubes (Au/W-180-400) were 1.6 times active that in Au/P25-TiO2, 4 times that in Au/Raw-TiO2, and 8 times that on TiO2(B) nanowires derived from the H2Ti3O7 nanotubes (Au/M-180-400). For the hydrogenation of 1,3-butadiene, however, the activity of Au particles in Au/M-180-400 was 3 times higher than those in Au/W-180-400 but similar to those in Au/P25-TiO2. These results demonstrate that the potential of 1D-TiO2 nanomaterials in catalysis is versatile.     

Grain refinement of biomedical Co-27Cr-5Mo-0.16N alloy by reverse transformation

Advanced grain refinement of a biomedical Ni-free Co-27Cr-5Mo-0.16N alloy without hot or cold plastic deformation was successfully achieved by a reverse transformation from a lamellar (hcp + Cr₂N) phase to an fcc phase. The technique consisted of a two-step heat treatment. First, the solution-treated specimen was subjected to isothermal aging at 1073 K for 90 ks, forming a lamellar structure of hcp and Cr₂N phases. Then, the aged specimen having a completely lamellar microstructure was reverse-treated at temperatures from 1273 to 1473 K, where the fcc phase is stable. The resultant grains were approximately 1/10 of their initial size. Moreover, tensile testing after reverse transformation showed excellent strength with good ductility compared to samples examined before the reverse transformation. Our results will contribute to the development of biomedical Ni-free Co-Cr-Mo-N alloys with refined grain size and good mechanical properties, without requiring any hot workings.     

Discovery of and Insights into DNA “Codes” for Tunable Morphologies of Metal Nanoparticles

The discovery and elucidation of genetic codes has profoundly changed not only biology but also many fields of science and engineering. The fundamental building blocks of life comprises of four simple deoxyribonucleotides and yet their combinations serve as the carrier of genetic information that encodes for proteins that can carry out many biological functions due to their unique functionalities. Inspired by nature, the functionalities of DNA molecules have been used as a capping ligand for controlling morphology of nanomaterials, and such a control is sequence dependent, which translates into distinct physical and chemical properties of resulting nanoparticles. Herein, an overview on the use of DNA as engineered codes for controlling the morphology of metal nanoparticles, such as gold, silver, and Pd‐Au bimetallic nanoparticles is provided. Fundamental insights into rules governing DNA controlled growth mechanisms are also summarized, based on understanding of the affinity of the DNA nucleobases to various metals, the effect of combination of nucleobases, functional modification of DNA, the secondary structures of DNA, and the properties of the seed employed. The resulting physical and chemical properties of these DNA encoded nanomaterials are also reviewed, while perspectives into the future directions of DNA‐mediated nanoparticle synthesis are provided.     

Facet‐Dependent Optical Properties Revealed through Investigation of Polyhedral Au–Cu2O and Bimetallic Core–Shell Nanocrystals

The ability to prepare Au–Cu₂O core–shell nanocrystals with precise control over particle size and shape has led to the discovery of facet‐dependent optical properties in cuprous oxide crystals. The use of Au cores not only allows the successful formation of Au–Cu₂O core–shell nanocrystals with tunable sizes, but also enables the observation of facet‐dependent optical properties in these crystals through the Au localized surface plasmon resonance (LSPR) absorption band. By tuning the Cu₂O shell morphology from rhombic dodecahedral to octahedral and cubic structures, and thus the exposed facets, the Au LSPR band position can be widely tuned. Such facet‐dependent optical effects are not observed in bimetallic Au–Ag and Au–Pd core–shell nanocrystals with the same precisely tuned particle sizes and shapes. It is believed that similar facet‐dependent optical properties could be observed in other ionic solids and other metal–metal oxide systems. The unusually large degree of plasmonic band tuning covering from the visible to the near‐infrared region in this type of nanostructure should be quite useful for a range of plasmonic applications.