Hollow Nano Research Articles

Hollow Microspherical and Microtubular [3 + 3] Carbazole-Based Covalent Organic Frameworks and Their Gas and Energy Storage Applications.

Covalent organic frameworks (COFs) are a family of crystalline porous networks having applications in various fields, including gas and energy storage. Despite respectable progress in the synthesis of such crystalline materials, examples of the use of template-free methods to construct COFs having hollow nano- and microstructures are rare. Furthermore, all reported methods for synthesizing these hollow structural COFs have involved [4 + 2] and [3 + 2] condensations. Herein, we report the synthesis of hollow microspherical and microtubular carbazole-based COFs through template-free, one-pot, [3 + 3] condensations of the novel triamine 9-(4-aminophenyl)-carbazole-3,6-diamine (Car-3NH2) and triformyl linkers with various degrees of planarity. Depending upon the monomer's planarity, a unique morphological variety was observed. A time-dependent study revealed that each COF formed through an individual mechanism depended on the degree of planarity of the triformyl linker; it also confirmed that the hollow structures of these COFs formed through inside-out Ostwald ripening. Our COFs exhibited high Brunauer-Emmett-Teller surface areas (up to ca. 1400 m2 g-1), excellent crystallinity, and high thermal stability. Moreover, the CO2 uptake capacities of these COFs were excellent: up to 61 and 123 mg g-1 at 298 and 273 K, respectively. The high surface areas facilitated greater numbers of strong interactions with CO2 molecules, leading to high CO2 uptake capacities. Moreover, the prepared COFs exhibited redox activity because of their redox-active triphenylamine and pyridine groups, which can be utilized in electrochemical energy storages. Accordingly, such hollow COFs having high surface areas appear to be useful materials for industrial and biological applications.

Zinc acetate activation-enhanced performance of hollow nano silica/carbon composite nanofibers for lithium-sulfur batteries

Here we develop a facile and scalable method to prepare silica/activated carbon nanofibers (SiO2/ACNFs) via electrospinning a mixture of PAN and hollow SiO2 nanospheres with following heat treatment, during which Zn(CH3COO)2 activation and PAN carbonization are simultaneously completed. When applied in lithium sulfur battery, the coin cells using S/SiO2/ACNF composites as cathode material exhibit a high discharge specific capacity and long cycling life. The specific capacity at 0.5 and 1 C rates after 300 cycles still remains at 584 and 513 mA h g−1, respectively, and the corresponding capacity decay is just 0.09% at 0.5 C and 0.13% at 1 C per cycle. The Zn(CH3COO)2 activation benefits sulfur loading and volume expansion suppression by creating numerous hierarchical pores in carbon nanofibers. Additionally, hollow SiO2 nanospheres contribute to restrain the “shuttle effects” by adsorbing and releasing polysulfides reversibly. This kind of SiO2/ACNF material and its fabrication method hold high potential for Li-S battery.

Hollow Mesoporous Functional Hybrid Materials: Fascinating Platforms for Advanced Applications

AbstractFunctionalized hollow nano‐ and microspheres containing both hollow and mesoporous structures are fascinating materials for a broad range of applications, such as nanoparticle collectors, catalysis, drug delivery systems, immobilization of biomolecules, and the adsorption and separation of gas and pollutants, because of their empty interior. These hollow mesoporous silica materials are synthesized mainly via soft‐ and hard‐templating routes and are usually modified with a range of organic functional groups (SH, NH2, CN, CH3, CC, benzene, fluorine linked organoalkylsilanes, and ethane‐, amine, benzene, and biphenyl‐bridged silanes) to improve their performance in many applications. This article outlines the most advanced applications of silica‐based and functionalized hollow mesoporous materials that are reported in the last 3 years (January 2014–June 2017). The high applicability of hollow materials in various fields is discussed, including drug delivery and cancer therapy, bioimaging, adsorption/separation, catalysis, thermal and electrical insulators, anticorrosion, sensors, fuel cells, proton conductors, membrane, optics, superhydrophobic surfaces, and fire safety.

Nano-CaCO3 synthesis by jet flow

A new methodology was introduced to produce hollow nano calcite particles in homogenous size distribution without aggregation. The design consisted of a jet flow system in which the crystallization region was separated from the stabilization region. The newly produced nano CaCO3 particles of about 140nm were removed from the crystallization region as quickly as possible into the stabilization region before aggregation or crystal growth. In the stages of crystallization, the particles started to dissolve from their edges which opened-up the pores inside the particles. At the late stages of crystallization, the open pores closed. These particles were stable in Ca(OH)2 solution and no aggregation was detected. Different particles with different morphologies can be produced by adjusting the stages in the crystallization.

Hollow Nano- and Microstructures as Catalysts.

Catalysis is at the core of almost every established and emerging chemical process and also plays a central role in the quest for novel technologies for the sustainable production and conversion of energy. Particularly since the early 2000s, a great surge of interest exists in the design and application of micro- and nanometer-sized materials with hollow interiors as solid catalysts. This review provides an updated and critical survey of the ever-expanding material architectures and applications of hollow structures in all branches of catalysis, including bio-, electro-, and photocatalysis. First, the main synthesis strategies toward hollow materials are succinctly summarized, with emphasis on the (regioselective) incorporation of various types of catalytic functionalities within their different subunits. The principles underlying the scientific and technological interest in hollow materials as solid catalysts, or catalyst carriers, are then comprehensively reviewed. Aspects covered include the stabilization of catalysts by encapsulation, the introduction of molecular sieving or stimuli-responsive "auxiliary" functionalities, as well as the single-particle, spatial compartmentalization of various catalytic functions to create multifunctional (bio)catalysts. Examples are also given on the applications which hollow structures find in the emerging fields of electro- and photocatalysis, particularly in the context of the sustainable production of chemical energy carriers. Finally, a critical perspective is provided on the plausible evolution lines for this thriving scientific field, as well as the main practical challenges relevant to the reproducible and scalable synthesis and utilization of hollow micro- and nanostructures as solid catalysts.

In situ X-ray tomographic microscopy of Kirkendall pore formation and evolution during homogenization of pack-aluminized Ni–Cr wires

The Kirkendall effect, usually associated with the formation of undesirable fields of micron-size pores, can be used to fabricate hollow nano- and microstructures, where all pores have coalesced into a single cavity. Here, this concept is used with the goal of converting 50 μm diameter Ni-20wt.%Cr wires into Ni–Cr–Al tubes by diffusion of a surface-deposited aluminide coating. The formation and evolution of Kirkendall pores, created by imbalanced diffusion fluxes of Al, Ni and/or Cr, are investigated using both in situ X-ray tomographic microscopy and ex situ annealing studies. The tomography results indicate that the pores nucleate near the interface between the Ni–Cr core and β-NiAl(Cr) reaction layer that develops upon homogenization. They then grow and coalesce near the center of the radial cross-section of the wire. This is followed by a stagnation period until the pores migrate longitudinally due to the influence of a temperature gradient imposed by the laser heating used for annealing. The ex situ experiments are in qualitative agreement with the tomography study with the exception of the secondary pore migration along the wire length, as expected because the ex situ study is conducted under isothermal conditions. Detailed features of the microstructure were discernable only upon metallographic preparation and include Cr-rich precipitates and an α-Cr(Al,Ni) rejection region that formed during coating and homogenization, respectively. In situ X-ray tomographic microscopy is thus demonstrated to be a viable technique to use in conjunction with more conventional ex situ metallographic techniques to conduct interdiffusion and Kirkendall pore studies.

Theory of semiconductor solid and hollow nano‐ and microwires with hexagonal cross‐section under torsion (Phys. Status Solidi B 4/2015)

Theory of semiconductor solid and hollow nano‐ and microwires with hexagonal cross‐section under torsion (Phys. Status Solidi B 4/2015)

Theory of semiconductor solid and hollow nano‐ and microwires with hexagonal cross‐section under torsion

The effect of torsion on ‐oriented wurtzite and ‐oriented zincblende nanowires with hexagonal cross‐section is discussed. The stresses (and strains) are determined via calculation of Prantl's stress function. The spatial variation of the valence band structure in the cross‐section is evaluated in the framework of the valence band Hamiltonian and deformation potential theory. The shear strain induced potential leads to additional localization of holes in the center of the facets. In wurtzite wires, torsion does not evoke piezoelectric charges or potentials and thus does not impact the signal in piezotronic sensors. In zincblende wires, the second order piezoelectric effect causes piezoelectric charges with threefold symmetry. The strain distribution in hexagonal nanowires with rounded corners depends on the curvature radius of the corners. For finite corner radius, the strain does no longer vanish at the corners. Also hexagonal nanotubes are discussed; here the inner and outer boundary exhibit different strain distributions.Visualization of the distribution of shear stress in the hexagonal cross‐section of a ‐oriented wurtzite nanowire under torsion.

Optical, structural and morphological properties of zirconia nanoparticles prepared by laser ablation in liquids

Absorption, fluorescence and Raman spectra, the structural composition and morphology of zirconia nanoparticles synthesised via the laser ablation of a metal in water and aqueous solutions of the sodium dodecyl sulphate (SDS) surfactant have been studied using absorption spectroscopy, Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The results demonstrate that, exposing zirconium to intense nanosecond laser pulses at a high repetition rate in these liquids, one can obtain stable cubic, tetragonal and monoclinic crystalline phases of nanozirconia with a particle size in the range and a Zr – SDS organic – inorganic composite. The absorption and fluorescence of the synthesised zirconia strongly depend on the SDS concentration in the starting solution. The gas – vapour bubbles forming during ablation are shown to serve as templates for the formation of hollow nano- and microstructures.

Designing hollow nano gold golf balls.

Hollow/porous nanoparticles, including nanocarriers, nanoshells, and mesoporous materials have applications in catalysis, photonics, biosensing, and delivery of theranostic agents. Using a hierarchical template synthesis scheme, we have synthesized a nanocarrier mimicking a golf ball, consisting of (i) solid silica core with a pitted gold surface and (ii) a hollow/porous gold shell without silica. The template consisted of 100 nm polystyrene beads attached to a larger silica core. Selective gold plating of the core followed by removal of the polystyrene beads produced a golf ball-like nanostructure with 100 nm pits. Dissolution of the silica core produced a hollow/porous golf ball-like nanostructure.

Hollow nano silicon prepared by a controlled template direction and magnesiothermic reduction reaction as anode for lithium ion batteries

In this work, nanostructured, hollow Si has been prepared by a combined template direction and magnesiothermic reduction reaction. Fe2O3 nanorings are used as templates to synthesize hollow SiO2 nanorings, the precursor for hollow Si. After carbon coating by chemical vapor deposition, the hollow Si–C composite shows high capacity and stable cycling due to its unique hollow structure and nanoscale size that endow Si–C with enhanced electrode kinetics. This work provides a controllable method to synthesize hollow nano Si and Si–C nanocomposites as high-performance anodes for Li-ion batteries.

Promoter Induced Rapid Synthesis of Hollow Silica Nano Cuboids from Octadecyltrichloro Silane

Promoter Induced Rapid Synthesis of Hollow Silica Nano Cuboids from Octadecyltrichloro Silane

Template‐Free Fabrication of Mesoporous Hollow ZnMn2O4 Sub‐microspheres with Enhanced Lithium Storage Capability towards High‐Performance Li‐Ion Batteries

In this work, we rationally designed an efficient template‐free synthetic strategy to fabricate hierarchical mesoporous hollow ZnMn2O4 sub‐microspheres (HZSMs) constructed entirely from nanoparticle (NP) building blocks of size ≈15 nm. The well‐known inside‐out Ostwald ripening process was tentatively proposed to shed light on the formation mechanism of the mesoporous hollow nano‐/microarchitecture. In favor of the intrinsic structural advantages, these resulting HZSMs exhibited superior electrochemical lithium‐storage performance with high specific capacity, excellent cyclability, and good rate capability when evaluated as an anode material for advanced Li‐ion batteries (LIBs). The excellent electrochemical performance should be reasonably ascribed to the porous and hollow structure of the unique HZSMs with nanoscale subunits, which reduced the diffusion length for Li+ ions, improved the kinetic process and enhanced the structural integrity with sufficient void space for tolerating the volume variation during the Li+ insertion/extraction. These results further revealed that the as‐prepared mesoporous HZSMs would be a promising anode for high‐performance LIBs.

Synthesis of Hollow Nano Silica Particles with Methyl Groups

Synthesis of hollow nano silica particles with methyl groups based on inorganic template method. Typically, silica coating on calcium carbonate template is formed via sol-gel reaction, and then template is removed by addition of diluted hydrochloric acid solution. When a methyltriethoxysilane （MTES） having one methyl group was used for silica coating, hollow structures were not obtained because of its slow reactivity and low affinity with calcium carbonate surface. Therefore, when MTES was mixed with tetraethoxysilane （TEOS） for silica coating, hollow structures were obtained for enough reaction time and optimum MTES/TEOS rate. The hybrid hollow particles exhibited hydrophobic so that high affinity with dispersing medium and matrix can be achieved.

Pyrene-Loaded Polypyrrole Microvessels

The encapsulation of guest molecules within polymeric hollow nano- or microscale structures is a rapidly developing field of interdisciplinary research due to a variety of applications ranging from drug delivery and sensor fabrication to nanoscale synthesis and bioinspired mineralization. We report on the encapsulation of pyrene within three-dimensional polypyrrole microvessels synthesized by precipitation polymerization of pyrrole onto toluene droplets that contain pyrene. Steady state and time-resolved fluorescence measurements show that the optical response and dynamics of encapsulated pyrene is significantly different from that in the free solution, likely due to interactions with oligomeric species generated during the polymerization process that partition into the organic core of the microvessel. Our results indicate that the encapsulation process can have a significant influence on the local environment of encapsulated species, an issue that is critical from the perspective of potential synthetic or medical applications.

Selective Hydrogenation of Acetylene Over Egg-Shell Palladium Nano-Catalyst

A novel egg-shell Pd/PHSNs nano-catalyst was prepared by a wet impregnation method using self-synthesized porous hollow silica nanoparticles (PHSNs) as support and applied in selective hydrogenation of acetylene to remove acetylene from the ethylene feed. By controlling the preparing conditions and calcining temperature, the active metal particles were loaded evenly on the support with a size about 5 nm. Compared with conventional catalysts prepared with solid silica nanoparticles, solid Al2O3 millispheres and a commercial catalyst, the Pd/PHSNs catalyst showed higher acetylene conversion rates at same reaction temperatures, and the porous hollow nano structure of PHSNs allowed smoother diffusion of ethylene molecules within the catalyst matrix so that ethylene could migrate away from the active sites in time to avoid turning into ethane, which resulted in superior ethylene selectivity at high acetylene conversion rates.

Fabrication of Hollow Nano Particles of Metallic Oxides through Oxidation Process

The formation mechanisms of hollow metal oxide through the oxidation of several metal nanoparticles have been studied by transmission electron microscopy. For Zn, Al, Cu, Ni and Fe nanoparticles, hollow oxide nanoparticles were obtained as a result of vacancy aggregation in the oxidation processes. The formation of the hollow morphology is attributed to the faster outward diffusion of metal ions through the oxide layer in the oxidation processes. Further changes in morphology during the annealing of hollow Cu, Ni and Fe oxides at higher temperatures in air were examined.

Polycondensation in tetradecaethoxyhexasiloxane adsorption layers at the methylene chloride/water interface under alkaline conditions: application to the formulation of hollow microcapsules

Polycondensation in tetradecaethoxyhexasiloxane adsorption layers at the methylene chloride/water boundary under alkaline conditions has been studied by interfacial dilational rheometry in view of the formulation of hollow nano- and microcapsules.

Designed Self‐Assembled β‐Sheet Peptide Fibrils as Templates for Silica Nanotubes

AbstractSol–gel condensation of tetraethoxysilane in the presence of designed self‐assembled β‐sheet peptide fibril templates, followed by template extraction, yields hollow silica nanotubes. The nanotubes are hundreds of nanometers long and possess a central pore of ∼ 3.5 nm, determined by the fibril template diameter. The effects of synthesis conditions have been investigated and the resultant silica materials characterized by various techniques.Silica nanostructures with various morphologies have been produced previously using supramolecular organic assemblies as templates. Hollow nano‐ or microtubes, which may have applications in separations, catalysis, nano‐optics, and ‐electronics have been of particular interest. Peptide‐based templates are especially interesting because of their relevance to biological silica microstructure formation. The new fibrillar peptide templates described here have the advantages of prescribed diameter, twist pitch, and handedness, which should impart chirality on the resulting silica nanotubes, providing control of the internal surface architecture by appropriate peptide design.

Solid and Hollow Micro and Nano Spherical Structures: in Polysilicon and Phosphosilicate Glass

Fabrication of three dimensional micro structures in silicon and silicon related materials is becoming increasingly important for the realisation of micro systems comprising of sensors, actuators, transducers and analytical assemblies. Fabrication of such devices so far has been mostly in form of structures defined by the crystal planes of silicon, or has involved sophisticated technologies such as ion beam machining, replication using LIGA, or micromachining techniques involving a sequence of alignment and etch stages using binary masks. Structures with circular symmetry are of great interest as micro optical components amongst others, and these are not easily amenable to microfabrication techniques commonly employed.