Abstract: Well shaped single crystalline Mn3O4 nano-octahedra with exposed highly active {011} facets at different particle sizes have been synthesized and used as anode materials for lithium ion batteries. The electrochemical results show that the smallest sized Mn3O4 nano-octahedra show the best cycling performance with a high initial charge capacity of 907 mA h g−1 and a 50th charge capacity of 500 mA h g−1 at a current density of 50 mA g−1 and the best rate capability with a charge capacity of 350 mA h g−1 when cycled at 500 mA g−1. In particular, the nano-octahedra samples demonstrate a much better electrochemical performance in comparison with irregular shaped Mn3O4 nanoparticles. The best electrochemical properties of the smallest Mn3O4 nano-octahedra are ascribed to the lower charge transfer resistance due to the exposed highly active {011} facets, which can facilitate the conversion reaction of Mn3O4 and Li owing to the alternating Mn and O atom layers, resulting in easy formation and decomposition of the amorphous Li2O and the multi-electron reaction. On the other hand, the best electrochemical properties of the smallest Mn3O4 nano-octahedra can also be attributed to the smallest size resulting in the highest specific surface area, which provides maximum contact with the electrolyte and facilitates the rapid Li-ion diffusion at the electrode/electrolyte interface and fast lithium-ion transportation within the particles. The synergy of the exposed {011} facets and the smallest size (and/or the highest surface area) led to the best performance for the Mn3O4 nano-octahedra. Furthermore, HRTEM observations verify the oxidation of MnO to Mn3O4 during the charging process and confirm that the Mn3O4 octahedral structure can still be partly maintained after 50 dischargecharge cycles. The high Li-ion storage capacity and excellent cycling performance suggest that Mn3O4 nano-octahedra with exposed highly active {011} facets could be excellent anode materials for high-performance lithium-ion batteries.

Abstract: Tuning the lattice degree of freedom in nanoscale functional crystals is critical to exploit the emerging functionalities such as piezoelectricity, shape-memory effect, or piezomagnetism, which are attributed to the intrinsic lattice-polar or lattice-spin coupling. Here it is reported that a mechanical probe can be a dynamic tool to switch the ferroic orders at the nanoscale multiferroic phase boundaries in BiFeO3 with a phase mixture, where the material can be reversibly transformed between the soft tetragonal-like and the hard rhombohedral-like structures. The microscopic origin of the nonvolatile mechanical switching of the multiferroic phase boundaries, coupled with a reversible 180 degrees rotation of the in-plane ferroelectric polarization, is the nanoscale pressure-induced elastic deformation and reconstruction of the spontaneous strain gradient across the multiferroic phase boundaries. The reversible control of the room-temperature multiple ferroic orders using a pure mechanical stimulus may bring us a new pathway to achieve the potential energy conversion and sensing applications.

Abstract: Hole diggers: The hierarchically structured porous solid-acid catalyst described in this report possess a remarkable pore system, encompassing well-defined macrochannels, interconnected mesopores, intracrystalline mesopores, and tunable zeolite micropores. Importantly, the catalyst exhibits very strong acidity and superior catalytic activity for esterification reactions.

Abstract: Size-controlled, catalytically active nanoparticles are successfully encapsulated in a one-pot synthesis to form novel hierarchical macroporous core@mesoporous shell structures, where macroporous cores are connected by uniform and ordered mesoporous channels. Most importantly, the encapsulated nanoparticles can be used as nanoreactors, with high activities and excellent long-term recycling stability.

Abstract: We report on one-pot synthesis of various morphologies of CuO nanostructures. PEG200 as a structure directing reagent under the synergism of alkalinity by hydrothermal method has been employed to tailor the morphology of CuO nanostructures. The CuO products have been characterized by XRD, SEM, and TEM. The morphologies of the CuO nanostructures can be tuned from 10 (nanoseeds, nanoribbons) to 2D (nanoleaves) and to 3D (shuttle-like, shrimp-like, and nanoflowers) by changing the volume of PEG200 and the alkalinity in the reaction system. At neutral and relatively low alkalinity (OH-/Cu2+ <= 3), the addition of PEG200 can strongly influence the morphologies of the CuO nanostructures. At high alkalinity (OH/Cu2+ >= 4), PEG200 has no influence on the morphology of the CuO nanostructure. The different morphologies of the CuO nanostructures have been used for the photodecomposition of the pollutant rhodamine B (RhB) in water. The photocatalytic activity has been correlated with the different nanostructures of CuO. The 10 CuO nanoribbons exhibit the best performance on the RhB photodecomposition because of the exposed high surface energy {-121} crystal plane. The photocatalytic results show that the high energy surface planes of the CuO nanostructures mostly affect the photocatalytic activity rather than the morphology of the CuO nanostructures. Our synthesis method also shows it is possible to control the morphologies of nanostructures in a simple way. (C) 2012 Elsevier Inc. All rights reserved.

Abstract: Ultralong Cu(OH)(2) and CuO nanowire bundles with lengths ranging from tens to hundreds of micrometers have been selectively synthesized on a large scale by a facile solution-phase method, using PEG200 as growth-directing agent. The growth mechanisms were investigated by monitoring the nanowire evolution process. The results showed that under the action of PEG200 molecules, the Cu(OH)(2) and CuO nanowires were first formed through oriented attachment of colloidal particles, then through side self-assembly leading to nanowire bundles, and finally to CuO nanoleaves. PEG200 plays a critical role in the synthesis of nanowires as it not only prevents the random aggregation of colloidal particles toward CuO nanoleaves but also helps to orientate nanowire growth by the coalescence and alignment in one direction of the colloidal particles. The concentration of OH(-) in the reaction system is also important for nanowire growth. In the absence of PEG200, nanoleaves are formed by an Ostwald ripening process. The band-gap value estimated from a UV-Vis absorption spectrum of CuO nanowire bundles is 2.32 eV. The photodegradation of a model pollutant, rhodamine B, by CuO nanowires and nanoleaves was compared with commercial nanopowders, showing that the as-synthesized ultralong CuO polycrystalline nanowire bundles have an enhanced photocatalytic activity with 87% decomposition of rhodamine B after an 8-h reaction, which was much higher than that of single-crystal nanoleaves (61%) and commercial nanopowders (32%). The origin of the high photocatalytic activity of these new polycrystalline CuO nanowire bundles has been discussed. This present work reveals that the (0 0 2) crystallographic surface is more favorable for photocatalytic decomposition of organic compounds and that these ultralong CuO nanowire bundles are potential candidates for photocatalysts in wastewater treatment. (C) 2010 Elsevier Inc. All rights reserved.

Abstract: Very uniform and well shaped Mn3O4 nano-octahedra are synthesized using a simple hydrothermal method under the help of polyethylene glycol (PEG200) as a reductant and shape-directing agent. The nano-octahedra formation mechanism is monitored. The shape and crystal orientation of the nanoparticles is reconstructed by scanning electron microscopy and electron tomography, which reveals that the nano-octahedra only selectively expose {101} facets at the external surfaces. The magnetic testing demonstrates that the Mn3O4 nano-octahedra exhibit anomalous magnetic properties: the Mn3O4 nano-octahedra around 150 nm show a similar Curie temperature and blocking temperature to Mn3O4 nanoparticles with 10 nm size because of the vertical axis of [001] plane and the exposed {101} facets. With these Mn3O4 nano-octahedra as a catalyst, the photodecomposition of rhodamine B is evaluated and it is found that the photodecomposition activity of Mn3O4 nano-octahedra is much superior to that of commercial Mn3O4 powders. The anomalous magnetic properties and high superior photodecomposition activity of well shaped Mn3O4 nano-octahedra should be related to the special shape of the nanoparticles and the abundantly exposed {101} facets at the external surfaces. Therefore, the shape preference can largely broaden the application of the Mn3O4 nano-octahedra.

Abstract: A series of BiVO4/3DOM TiO2 nanocomposites have been synthesized and their photocatalytic activity was investigated under visible light irradiation using the RhB dye as model pollutant molecule in an aqueous solution. The effect of the amount of BiVO4 as visible light sensitizer on the photocatalytic activity of BiVO4/3DOM TiO2 nanocomposites was highlighted. The heterostructured composite system leads to much higher photocatalytic efficiencies than bare 3DOM TiO2 and BiVO4 nanoparticles. As the proportion of BiVO4 in BiVO4/3DOM TiO2 nanocomposites increases from 0.04 to 0.6, the photocatalytic performance of the BiVO4/3DOM TiO2 nanocomposites increases and then decreases after reaching a maximum at 0.2. This improvement in photocatalytic perfomance is related to 1) the interfacial electron transfer efficiency between the coupled materials, 2) the 3DOM TiO2 inverse opal structure with interconnected pores providing an easy mass transfer of the reactant molecules and high accessibility to the active sites and large surface area and 3) the effect of light sensitizer of BiVO4. Intensive studies on structural, textural, optical and surface properties reveal that the electronic interactions between BiVO4 and TiO2 lead to an improved charge separation of the coupled BiVO4/TiO2 system. The photogenerated charge carrier densities increase with increasing the BiVO4 content, which acts as visible light sensitizer to the TiO2 and is responsible for the enhancement in the rate of photocatalytic degradation. However, the photocatalytic activity is reduced when the BiVO4 amount is much higher than that of 3DOM TiO2. Two reasons could account for this behavior. First, with increasing BiVO4 content, the photogenerated electron/hole pairs are accumulated at the surface of the BiVO4 nanoparticles and the recombination rate increases as shown by the PL results. Second, decreasing the amount of 3DOM TiO2 in the nanocomposite decreases the surface area as shown by the BET results. Moreover, the poor adsorptive properties of the BiVO4 photocatalyst also affect the photocatalytic performance, in particular at higher BiVO4 content. The present work demonstrates that BiVO4/3DOM TiO2 is a very promising heterojunction system for visible light photocatalytic applications.

Abstract: Tunable transport properties and Fano resonances are predicted in a circular bilayer phosphorene nanoring. The conductance exhibits Fano resonances with varying incident energy and applied perpendicular magnetic field. These Fano resonance peaks can be accurately fitted with the well known Fano curves. When a magnetic field is applied to the nanoring, the conductance oscillates periodically with magnetic field which is reminiscent of the Aharonov-Bohm effect. Fano resonances are tightly related to the discrete states in the central nanoring, some of which are tunable by the magnetic field.

Abstract: The effect of Ag addition on the precipitation evolution and interfacial segregation for Al-Mg-Si alloys was systematically investigated by atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), atom probe tomography (APT) and density functional theory (DFT) calculation. At the early aging stage, Ag atoms could enter clusters and refine the distribution of these clusters. Then, Ag atoms preferentially segregate at the GP zone/alpha-Al and beta ''/alpha-Al interfaces at the peak aging stage by the replacement of Al atoms in FCC matrix. With prolonging aging time, Ag atoms generally incorporate into the interior of beta '' precipitate, facilitating the formation of QP lattice (a hexagonal network of Si atomic columns) and the local symmetry substructures, Ag sub-unit (1) and Ag sub-unit (2). At the over-aged stage, the Ag sub-unit (1) and Ag sub-unit (2) could transform to the beta'(Ag) (i.e. beta'(Ag1) and beta'(Ag2).) and Q'(Ag) unit cells, respectively. All the precipitates at the over-aging stage have a composite and disordered structure due to the coexistence of different unit cells (beta'(Ag1), beta'(Ag2), Q'(Ag) and beta') and the non-periodic arrangement of Ag atoms within the precipitate. In the equilibrium stage, the incorporated Ag atoms in the precipitates release into the alpha-Al matrix as solute atoms or form Ag particles. In general, Ag atoms undergo a process of “segregate at the precipitate/matrix interface -> incorporate into the interior of precipitate -> release into the alpha-Al matrix” during the precipitation for Al-Mg-Si-Ag alloys. Besides, Ag segregation is found at the interfaces of almost all metastable phases (including GP zone, beta '', beta'/beta'(Ag) phase) in Al-Mg-Si-Ag alloys. The Ag segregation at the beta'/alpha-Al interface could increase the length/diameter ratio of beta' phase and thus promote the additional strengthening potential of these alloys. These findings provide a new route for precipitation hardening by promoting the nucleation and morphology evolution of precipitates. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Abstract: Nano-width martensite plates in a fully martensitic Ni50Ti50 alloy are indexed successfully by using the off-axis transmission Kikuchi diffraction in scanning electron microscope (i.e., SEM-based TKD). The data obtained by SEM-TKD are effectively interpreted using an improved approach based on the framework of the theoretical groupoid structure method, where the equivalent variants transformed from the monoclinic variants are introduced to calculate all theoretical axis/angle pairs of rotation, and to formulate a complete list of source martensite to target martensite pairs. Consequently, B19' monoclinic martensite variants in NiTi alloys are identified unambiguously, by using numerical comparison between the experimental and theoretical rotation components, without the reference of retained parent phase. (C) 2020 Elsevier B.V. All rights reserved.

Abstract: The three-dimensional (3D) nanostructure of Ni4Ti3 precipitates in a porous Ni50.8Ti49.2 alloy has been re-constructed by “Slice-and-View” in a Focused Ion Beam/Scanning Electron Microscope (FIB/SEM). The 3D configuration of these precipitates forming a network structure in the B2 austenite matrix has been characterized via 3D visualization and quantitative analysis including volume fraction, skeleton, degree of anisotropy and local thickness. It is found that dense Ni4Ti3 precipitates occupy 54% of the volume in the B2 austenite matrix. Parallel Ni4Ti3 precipitates grow alongside the surface of a micro-pore, yielding an asymmetric structure, while nano voids do not seem to affect the growth of Ni4Ti3 precipitates. The small average local thickness of the precipitates around 60 nm allows their coherency with the matrix, and further induces the R-phase transformation in the matrix. On the other hand, the B2 matrix exhibits a winding and narrow structure with a skeleton of 18.20 mm and a thickness similar to the precipitates. This discontinuous matrix segmented by the Ni4Ti3 network and pores is responsible for the gradual transformation by stalling the martensite propagation.