Nanometer-sized Building Blocks Research Articles

Hybrid hierarchical nanolattices with porous platinum coating

Nanolattices, defined as lattice structures composed of nanometer-sized building blocks, exhibit a wide range of unique properties and represent a new and rapidly growing class of mechanical metamaterials. In this work, we fabricated a core-shell polymer-platinum nanolattice by combining several fabrication techniques. The CAD-designed polymer nanolattices were fabricated by a two-photon lithography technique to achieve the required architecture. The lattices were then coated with a thin film of platinum using the atomic layer deposition (ALD) method. The unique interaction of the gaseous ALD precursor with the polymer surface resulted in a porous nanogranular film, providing a structural hierarchy ranging from the micrometer-size overall dimensions down to the microstructural features of a few nanometers. The nanoporous structure of platinum coating caused its creep-like shrinkage and buckling of the polymer struts during the initial stages of platinum ALD, thus weakening the whole structure. Increasing the thickness of the platinum layer eliminated the porosity and strengthened the lattices, indicating the load-bearing capacity of the architected platinum coating. The yield stress of platinum coating estimated from the results of microcompression tests was comparable to the yield stress of annealed bulk platinum and much lower than the flow stress of solid nanocrystalline platinum nanopillars.

Phase Behavior and Aggregate Transition in Aqueous Mixtures of Negatively Charged Carbon Dots and Cationic Surfactants

To prepare supramolecular structures with interesting dimensions and morphologies using nanometer-sized building blocks is highly challenging. Herein, negatively charged carbon dots (n-CDs), which bear carboxy and hydroxyl groups on the surfaces, are mixed, respectively, with two cationic surfactants in water, i.e., 1-tetradecyl-3-methylimidazolium bromide (C14mimB) and tetradecyltrimethylammonium bromide (TTAB). The phase behavior and aggregate transition in n-CDs/C14mimB and n-CDs/TTAB mixtures were investigated in detail. At a fixed concentration of n-CDs (cn-CDs, 0.1 mg·mL–1), both systems exhibit a phase sequence of an isotropic phase (I1), a turbid phase (T1), a precipitated phase (P), a second turbid phase (T2), and a second isotropic phase (I2) with increasing concentration of the surfactant (cs). While only vesicles were observed in the T1 phase, hexosomes were also detected in the T2 phase in addition to vesicles. The phase transition obtained by the experiments gains solid support from computer simulations using a dissipative particle dynamics method, which give structural details of the hexosomes and evidence of anion−π interaction in an n-CDs/C14mimB system. The results obtained in the current study reinforce the conclusion that CDs/surfactant is a good combination for facile construction of supramolecular structures. The aggregates with diverse morphologies open up the possibility of a variety of future applications.

Self-assembly of water-soluble silver nanoclusters: superstructure formation and morphological evolution.

Supramolecular self-assembly, based on non-covalent interactions, has been employed as an efficient approach to obtain various functional materials from nanometer-sized building blocks, in particular, [Ag6(mna)6]6-, mna = mercaptonicotinate (Ag6-NC). A challenging issue is how to modulate the self-assembly process through regulating the relationship between building blocks and solvents. Herein, we report the controlled self-assembly of hexanuclear silver nanoclusters into robust multilayer vesicles in different solvents, DMSO, CH3CN, EG and MeOH. Their unique luminescence enables them to be bifunctional probes to sense Fe3+ and dl-dithiothreitol (DTT). By protonating the Ag6-NC to Ag6-H-NC using hydrochloric acid (HCl), the multilayer vesicles survive in aprotic solvents, DMSO and CH3CN, but are transformed to nanowires in protic solvents, water, EG and MeOH. Our results demonstrated that the solvent-bridged H-bond plays a key role in the evolution of the morphologies from vesicles to nanowires. Moreover, the nanowires could further hierarchically self-assemble in water into hydrogels with high water content (99.5%), and with remarkable mechanical strength and self-healing properties. This study introduces a robust cluster-based building block in a supramolecular self-assembly system and reveals the significance of aprotic and protic solvents for the modulation of the morphologies of cluster-based aggregates.

Coherent 3D nanostructure of γ-Al2O3: Simulation of whole X-ray powder diffraction pattern

The structure and nanostructure features of nanocrystalline γ-Al2O3 obtained by dehydration of boehmite with anisotropic platelet-shaped particles were investigated. The original models of 3D coherent nanostructure of γ-Al2O3 were constructed. The models of nanostructured γ-Al2O3 particles were first confirmed by a direct simulation of powder X–Ray diffraction (XRD) patterns using the Debye Scattering Equation (DSE) with assistance of high-resolution transmission electron microscopy (HRTEM) study. The average crystal structure of γ-Al2O3 was shown to be tetragonally distorted. The experimental results revealed that thin γ-Al2O3 platelets were heterogeneous on a nanometer scale and nanometer-sized building blocks were separated by partially coherent interfaces. The XRD simulation results showed that a specific packing of the primary crystalline blocks in the nanostructured γ-Al2O3 particles with formation of planar defects on {001}, {100}, and {101} planes nicely accounted for pronounced diffuse scattering, anisotropic peak broadening and peak shifts in the experimental XRD pattern. The identified planar defects in cation sublattice seem to be described as filling cation non-spinel sites in existing crystallographic models of γ-Al2O3 structure. The overall findings provided an insight into the complex nanostructure, which is intrinsic to the metastable γ-Al2O3 oxide.

Synthesis of hierarchical MoS2 microspheres composed of nanosheets assembled via facile hydrothermal method as anode material for lithium-ion batteries

A hierarchical MoS2 architecture composed of nanosheet-assembled microspheres with an expanded interplanar spacing of the (002) planes was successfully prepared via a simple hydrothermal reaction. Electron microscopy studies revealed formation of the MoS2 microspheres with an average diameter of 230 nm. It was shown that the hierarchical structure of MoS2 microspheres possesses both the merits of nanometer-sized building blocks and micrometer-sized assemblies, which offer high surface area for fast kinetics and buffers the volume expansion during lithium insertion/deinsertion, respectively. The micrometer-sized assemblies were found to contribute to the enhanced electrochemical stabilities of the electrode materials. The mentioned advantages of the MoS2 electrode prepared in this work allowed enhanced cyclability and high rate capability of the material. Along with this, the material delivered a high initial discharge capacity of 1206 mAh g−1 and a reversible discharge capacity of 653 mAh g−1 after 100 cycles at a current density of 100 mA g−1. Furthermore, the material delivered a high reversible capacity of 480 mAh g−1 at a high current density of 1000 mA g−1.

Electrophoretic deposition of fluorescent Cu and Au sheets for light-emitting diodes.

Electrophoretic deposition (EPD) is a conventional method for fabricating film materials from nanometer-sized building blocks, and exhibits the advantages of low-cost, high-efficiency, wide-range thickness adjustment, and uniform deposition. Inspired by the interest in the application of two-dimensional (2D) nanomaterials, the EPD technique has been recently extended to building blocks with 2D features. However, the studies are mainly focused on simplex building blocks. The utilization of multiplex building blocks is rarely reported. In this work, we demonstrate a controlled EPD of Cu and Au sheets, which are 2D assemblies of luminescent Cu and Au nanoclusters. Systematic investigations reveal that both the deposition efficiency and the thickness are determined by the lateral size of the sheets. For Cu sheets with a large lateral size, a high ζ-potential and strong face-to-face van der Waals interactions facilitate the deposition with high efficiency. However, for Au sheets, the small lateral size and ζ-potential limit the formation of a thick film. To solve this problem, the deposition dynamics are controlled by increasing the concentration of the Au sheets and adding acetone. This understanding permits the fabrication of a binary EPD film by the stepwise deposition of Cu and Au sheets, thus producing a luminescent film with both Cu green emission and Au red emission. A white light-emitting diode prototype with color coordinates (x, y) = (0.31, 0.36) is fabricated by employing the EPD film as a color conversion layer on a 365 nm GaN clip and further tuning the amount of deposited Cu and Au sheets.

Electrostatic Assembly of Sandwich-like Ag-C@ZnO-C@Ag-C Hybrid Hollow Microspheres with Excellent High-Rate Lithium Storage Properties.

Herein, we introduce a facile electrostatic attraction approach to produce zinc-silver citrate hollow microspheres, followed by thermal heating treatment in argon to ingeniously synthesize sandwich-like Ag-C@ZnO-C@Ag-C hybrid hollow microspheres. The 3D carbon conductive framework in the hybrids derives from the in situ carbonation of carboxylate acid groups in zinc-silver citrate hollow microspheres during heating treatment, and the continuous and homogeneous Ag nanoparticles on the outer and inner surfaces of hybrid hollow microspheres endow the shells with the sandwiched configuration (Ag-C@ZnO-C@Ag-C). When applied as the anode materials for lithium ion batteries, the fabricated hybrid hollow microspheres with sandwich-like shells reveal a very large reversible capacity of 1670 mAh g(-1) after 200 cycles at a current density of 0.2 A g(-1). Even at the very large current densities of 1.6 and 10.0 A g(-1), the high specific capacities of about 1063 and 526 mAh g(-1) can be retained, respectively. The greatly enhanced electrochemical properties of Ag-C@ZnO-C@Ag-C hybrid microspheres are attributed to their special structural features such as the hollow structures, the sandwich-like shells, and the nanometer-sized building blocks.

Porous Sulfur/Polypyrrole/Multiwalled Carbon Nanotube Ternary Composite Cathode for Lithium/Sulfur Batteries

Introduction Lithium batteries have the highest energy density among the commercialized secondary batteries and they are leading the path for energy storage and sources for portable applications, including electric vehicle transportation. Commercial lithium batteries are based on oxide cathodes such as LiCoO2, LiFePO4 and LiMn2O4, which can deliver only up to 200 mAh g-1 of capacity, limiting their use for energy demanding applications. The elemental sulfur could be a best choice for the cathode due its theoretical capacity of 1672 mAh g-1, which is one of the highest among all known cathode materials. Combined with its abundant availability, this makes sulfur a most promising cathode for lithium batteries. However, this cathode material suffers from its low conductivity and capacity fading due to the dissolution of electrochemical reaction products [1, 2]. In this work, we report on the preparation of a novel hierarchical porous sulfur/polypyrrole/multiwalled carbon nanotube composite (S/PPy/MWNT), and on its physical and electrochemical properties as a cathode for lithium secondary batteries. Experimental The S/PPy/MWNT composite preparation is schematically presented in Fig.1. The porous S/PPy/MWNT composite was synthesized via in situpolymerization of pyrrole monomer with nano-sulfur and MWNT aqueous suspension followed by a low temperature heat-treatment. The S/PPy/MWNT composite was characterized using chemical analysis, XRD, SEM and HRTEM. The composite cathode electrode was prepared by mixing S/PPy/MWNT composite with conductive carbon and PVdF binder and coating this mixture on Al foil. The electrochemical properties of the composite cathode were investigated in a lithium half cell (coin-type CR2032) by cyclic voltammetry (CV) and galvanostatic cycling. Results and Discussion Figure 2 a present that SEM result, which reveal that a porous structure with interconnected spherical pores has been formed. While the pore sizes are about 500-1000 nm in diameter, the holes with the diameters of about 20-30 nm connect them with each other in the sample structure. This S/PPy/MWNT composite with hierarchical nano/microstructures can utilize the advantages of both nanometer-sized building blocks and micro- or submicrometer-sized assemblies. While the former could provide negligible lithium ion diffusion time and distances, and possibly a new Li storage mechanism for the favorable kinetics and high capacities, the latter could be beneficial to afford good stability of the electrode materials, which are important for enhancing the cycle performance of the electrodes. The elemental analysis (mapping) of the S/PPy/MWNT composite carried out by EDS is shown in Fig. 2 (b and c), demonstrating the existence and homogeneous distribution of sulfur and MWNT in the composite. Further development of this research will be presented at the Meeting.

Synthesis of ZnO–ZnCo2O4 hybrid hollow microspheres with excellent lithium storage properties

ZnO–ZnCo2O4 hybrid hollow microspheres are successfully produced via an annealing process of the pre-fabricated zinc–cobalt citrate hollow microspheres in air. ZnO and ZnCo2O4 have homogeneous distribution within the whole hollow microspheres. The gained hybrid hollow microspheres deliver outstanding lithium storage properties when utilized as the anode material in lithium ion batteries. A high reversible capacity of 1199mAhg−1 can be retained after 200 cycles. The exceptional electrochemical properties of the hybrid hollow microspheres are ascribed to the synergetic effect between ZnO and ZnCo2O4 nanoparticles, the catalytic effect of Co nanocrystals, the favorable hollow structures together with the nanometer-sized building blocks of hybrid microspheres.

Facile synthesis of Mn–Co oxide nanospheres with controllable interior structures and their catalytic properties for methane combustion

Uniform Mn–Co mixed oxide solid, hollow and yolk–shell nanospheres with nanometer-sized building blocks have been successfully fabricated by heat-treatment of their Mn–Co alkoxyacetate precursors at a proper ramping rate. The formation of the hollow and yolk–shell structures during the thermal decomposition is mainly based on the heterogeneous contraction caused by non-equilibrium heat treatment. In virtue of the unique structural features, the resultant Mn–Co oxide nanospheres with different interiors were used as catalysts in CH4 combustion, and showed an excellent catalytic activity. Catalytic results suggest that the (Co,Mn)(Co,Mn)2O4 yolk–shell nanospheres show relatively higher activity.

Template-free synthesis of novel, highly-ordered 3D hierarchical Nb3O7(OH) superstructures with semiconductive and photoactive properties

3D hierarchical Nb3O7(OH) mesocrystals can be formed by self-organization from nanometer sized building blocks. The present study focuses on the synthesis and detailed investigation of mesocrystals, which can be achieved from a one-step, template-free hydrothermal synthesis approach. The obtained cubic superstructures consist of a periodic nanowire-network and combine a large surface area, high crystallinity, with a band gap of 3.2 eV and photocatalytic activity. Their easy processability in combination with the named excellent properties makes them promising candidates for a large number of applications. These include photochemical and photophysical devices where the Nb3O7(OH) mesocrystals can be used as electrode material since they are semiconducting and possess a large surface area. Generally the forces involved in the self-organized formation of mesocrystals are not fully understood. In this regard, the assembly of the Nb3O7(OH) mesocrystals was investigated in-depth applying transmission electron microscopy, scanning electron microscopy, UV/Vis measurements and electron energy-loss spectroscopy. Based on the achieved results a formation mechanisms is proposed, which expands the number of mechanisms for mesocrystal formation reported in literature. In addition, our study reveals different types of nanowire junctions and investigates their role at the stabilization of the networks.

Zeolitic Imidazolate Framework 67‐Derived High Symmetric Porous Co3O4 Hollow Dodecahedra with Highly Enhanced Lithium Storage Capability

High symmetric porous Co3O4 hollow dodecahedra constructed by nanometer-sized building blocks are rationally synthesized by templating against Co-containing zeolitic imidazolate framework-67. The well-defined hollow structure and highly porous framework render these hollow dodecahedra exhibit high specific capacity, excellent cycling stability and superior rate capability when evaluated as an anode material for lithium-ion batteries.

Bi-component MnO/ZnO hollow microspheres embedded in reduced graphene oxide as electrode materials for enhanced lithium storage

Novel composite of bi-component MnO/ZnO (denoted as MZO) hollow microspheres embedded in reduced graphene oxide (RGO) as a high performance electrode material for Lithium ion batteries (LIBs) is prepared via one-pot hydrothermal method and subsequent annealing. The structures and morphologies of as-prepared hybrid materials are characterized by X-ray diffraction, scanning electron microscopy, Raman spectra, FTIR and transmission electron microscopy. The results reveal that the MZO hollow microspheres with nanometer-sized building blocks are well dispersed in the RGO support. The electrochemical tests show that the hybrid material has a reversible capacity of 660mAh/g at a current density of 100mA/g with a coulombic efficiency of 98% after 100 cycles. Besides, a specific capacity of about 207mAh/g is retained even at a current density as high as 1600mA/g, exhibiting high reversibility and good capacity retention. Our results suggest that the composite of bi-component MZO hollow microspheres embedded in RGO will be promising electrode materials for low-cost, environmentally friendly and high-performance LIBs.

Local Structure Analysis of BaTiO3 Nanoparticles

The atomic-scale structure of nanocrystalline BaTiO3 powders has been studied using high-energy X-ray diffraction, X-ray absorption fine structure, and atomic pair-distribution function analysis techniques. Studies show that the materials are well-ordered at nanometer distances. The three-dimensional atomic ordering in BaTiO3 is cubic on average, but locally shows slight tetragonal distortions, similarly to that occurring in coarse-grained bulk crystals. Ferroelectric coherence is facilitated in part by control of the particle morphology. The spatial extent of cooperative ferroelectric distortions is found to be degraded in nanometer-sized building blocks. The new structural information obtained helps one to understand better the dielectric properties of these nanomaterials.

Double‐Shelled CoMn2O4 Hollow Microcubes as High‐Capacity Anodes for Lithium‐Ion Batteries

New double-shelled CoMn2O4 hollow microcubes with nanometer-sized building blocks are prepared by annealing Co0.33Mn0.67CO3 (600 °C, 5 h in air) obtained by coprecipitation from aqueous solutions of Co(NO3)2, MnSO4, EtOH, (NH4)2SO4, and NH4HCO3 (50 °C, 9 h).

Biomolecule-assisted in situ route toward 3D superhydrophilic Ag/CuO micro/nanostructures with excellent artificial sunlight self-cleaning performance

Three-dimensionally (3D) hierarchical micro/nano oriented arrays constructed from nanometer-sized building blocks represent an important group of materials and have received enormous attention for a series of applications because they can offer both the advantages of nanosized building blocks and micro- or submicrometer-sized ordered arrays. In this work, 3D flower-like superhydrophilic CuO micro/nanostructures decorated by Ag nanoparticles were synthesized via an amino acid-assisted biomimetic hydrothermal method. Experiments reveal that the product demonstrates excellent sunlight self-cleaning performance in terms of wettability (without the help of high-free-energy compounds and in the absence of UV irradiation) and enhanced photocatalytic activities, which portends a bright future for this material as self-cleaning photovoltaic coatings. It is also a good example for the organic combination of green chemistry and functional materials.

3-D mesoporous nano/micro-structured Fe3O4/C as a superior anode material for lithium-ion batteries

Urchin-like nano/micro-structured Fe3O4/C composite has been successfully synthesized using inexpensive starting materials. The urchin-shaped nano/micro-structure consisted of several oriented nanorods. TEM analysis revealed that there is a large number of pores and uniform amorphous carbon distribution at a nanoscale in the nanorods walls. As used in lithium-ion batteries, the mesoporous Fe3O4/C anode delivered a higher reversible capacity of about 830 mAh g−1 at 0.1 C up to 50 cycles, as well as enhanced high-rate capability compared with urchin-like Fe2O3 and commercial Fe3O4. The improvements can be attributed to the combined effects of the nano/micro-architecture, the porosity, and the ultra-fine carbon matrix, where the three factors would contribute to possess both the merits of nanometer-sized building blocks and micro-sized assemblies and provide high electronic conductivity. It is believed that the results of this study offer new prospects for improving the lithium storage capacity of metal oxides by controlling both architecture and composition.

Simultaneous Targeted Immobilization of Anti-Human IgG-Coated Nanotubes and Anti-Mouse IgG-Coated Nanotubes on the Complementary Antigen-Patterned Surfaces via Biological Molecular Recognition

Introduction of self-assembly in nanometer-sized building blocks is expected to accomplish bottom-up fabrications in a more reproducible, efficient, and economic manner; however, it is necessary to selectively place multiple types of nano-building blocks (e.g., metal nanotubes and semiconductor nanotubes) at specific locations on surfaces with high precision and reproducibility for more complex nanometer-scale device assemblies. Biological molecular recognition such as antibody-antigen bindings may be suitable to use in the building-block assembly since nature always assembles materials with complex functions and structures at room temperature reproducibly. Our approach is to immobilize antibody-coated nanotubes at specific complementary binding positions patterned on surfaces. To demonstrate this hypothesis, two types of nanotubes coated with different antibodies were anchored selectively onto their complementary antigen areas, patterned by tips of atomic force microscope (AFM). Because those nanotubes can be coated by various metals and semiconductors with controlled morphologies, this outcome opens the possibility to accomplish the proposed unconventional device fabrication methodology that antibody nanotubes coated with different types of metals/semiconductors can be self-assembled on antigen-patterned surfaces via biological molecular recognition.

Electrical and optical effects in molecular nanoscopic-sized building blocks

A biomimetic strategy is used to bridge the gap from the molecular scale to the microscale. Dendritic, conformationally rigid ruthenium(II)polypyridyl complexes have been synthesized to form a set of nanometer-sized building blocks (NBBs) (1.6– 5.0 nm ) with discrete ‘tertiary’ structures. We postulate that thin films constructed from NBBs with differing tertiary structures will form ordered arrays with differing ‘quaternary’ structures and, presumably, differing electronic properties. Experimental studies show that thin films of these molecules are conductive, display electric field-modulated conductivity, and enhanced conductivity upon visible irradiation. Significantly, changes in the molecule's overall shape (tertiary structure) have a measurable effect on the electrical properties of the films prepared from them. Importantly, these NBBs are chemically robust and structurally tunable. We intend to exploit these properties as well as their newly discovered electronic, optical, and, potentially even, chiro-optical properties so as to provide a new, added dimension in molecular electronics and chiral optical devices.

Directed self-assembly of two kinds of nanoparticles utilizing monolayer films of diblock copolymer micelles.

We demonstrated a self-assembly of two different kinds of nanoparticles simultaneously directed on a monolayer film of diblock copolymer micelles via physical and chemical arrangements. We first incorporated gold nanoparticles physically around the micelles of a monolayer film of PS-PVP micelles having a short-range hexagonal order. Iron oxide nanoparticles were then synthesized chemically in the PVP core area of the ordered micelles, resulting in a mosaic nanopattern of magnetic iron oxide nanoparticles surrounded by metallic gold nanoparticles. Thus, we were able to direct two kinds of nanoparticles to self-assemble in the specific positions as an example of controlled fabrication of nanometer-sized building blocks.