Formation Of Hollow Structure Research Articles

The Mechanism of the One‐Step Synthesis of Hollow‐Structured Li3VO4 as an Anode for Lithium‐Ion Batteries

In recent years, the controlled synthesis of inorganic micro- and nanostructures with hollow interiors has attracted considerable attention because of their widespread potential applications. A feasible method for synthesizing Li3 VO4 by a template-free, solution synthesis of single-crystalline microboxes with well-defined non-spherical morphologies has been reported. This study provides the useful information to produce other hollow structure materials to the broad audience of readers. The formation of hollow structure and the influence of raw materials have been presented. The thus-synthesized Li3 VO4 exhibited significantly improved conductivity, rate capability, and cycling life compared to commercial graphite, synthesized Li4 Ti5 O12 , and previously reported Li3 VO4 .

General One-Pot Template-Free Hydrothermal Method to Metal Oxide Hollow Spheres and Their Photocatalytic Activities and Lithium Storage Properties

A general and facile one-pot template-free hydrothermal strategy has been developed to synthesize various metal oxide (TiO2, SnO2 and α-Fe2O3) hollow spheres with unified morphologies. The formation of hollow structure involves a trifluoroacetic acid (TFA)-assisted Ostwald ripening process. Photocatalytic activities of the as-prepared TiO2 product are evaluated by the photodegradation of Rhodamine B (RhB), which the TiO2 hollow spheres obtained from 450 °C thermal treatment exhibit higher photocatalytic activity than Degussa P25. In addition, electrochemical measurements demonstrate that all of the as-prepared metal oxides hollow spheres have the potential applications in lithium-ion battery. We have a great expectation that this synthesis strategy can afford a new universal route for functional metal oxide hollow materials preparation without using template.

Influence of morphologies and pseudocapacitive contributions for charge storage in V2O5 micro/nano-structures

Three pure V2O5 micro/nano-structures including rods, hierarchical wires and porous tubes are synthesized via a chemical vapor deposition process by adjusting the oxidation temperature. Their surface-to-volume ratio increases significantly because of particle size decrease, pore quantity increase and hollow structure formation. Lithium-ion storage investigation in aqueous electrolyte indicates that the enlargement of surface area can suppress irreversible phase transition and lead to significant improvement of cycling stability, storage capacity and electrochemical kinetics. Furthermore, scan-rate dependence cyclic voltammetry analysis demonstrates that both pseudocapacitive and bulk Li+ storage are within these V2O5 electrodes and the relative contributions of them depend strongly on the scan rate. In porous V2O5 micro/nano-tubes, the surface pseudocapacitive storage dominates the total storage capacity at scan rates above 0.06Vs−1, whereas the bulk Li+ storage is the domination effect for V2O5 micro/nano-rods at the scan rate ranging from 0.02 to 0.3Vs−1. At the special scan rate, the maximum and minimum capacity is observed in V2O5 porous micro/nano-tubes and micro/nano-rods, respectively. These studies should be useful for elucidating the morphological effects on Li-ion storage for V2O5-based electrodes. By varying key morphological parameters, the pseudocapacitive properties of V2O5 micro/nano-structure electrodes are expected to be affected.

Synthesis of various magnetite nanoparticles through simple phase transformation and their shape-dependent magnetic properties

Shape-controlled synthesis of magnetite nanoparticles has been successfully carried out through simple phase transformation via a modified polyol process using akaganeite (β-FeOOH) as the precursor. Different shapes of magnetite nanoparticles, including solid nanospheres and solid and hollow nanoellipsoids, could be obtained by either adding the appropriate amount of sodium acetate (NaOAc) or using the anion exchange of β-FeOOH. NaOAc makes it possible to retain the rod-like shape of the precursor material during the phase transformation by coordinating the surface and controlling the basic pH to slow down dissolution–recrystallization mechanism. It is also proposed that chloride ions in the β-FeOOH structure play a key role in the formation of hollow structure. The shape-dependent magnetic properties were investigated using a magnetic property measurement system at 300 K. All magnetite nanoparticles exhibited ferromagnetic behaviour with different values of saturation magnetization (Ms) and coercivity (Hc), and these values were highly depend on the shape of the nanoparticles due to their different grain size, spin disorder, shape, and surface anisotropy.

Electromagnetic properties of hollow PAN/Fe<SUB align="right">3O<SUB align="right">4 composite nanofibres via coaxial electrospinning

Fe3O4 nanoparticles were prepared by the chemical by using Triton X-100 as dispersant. Hollow polyacrylonitrile (PAN)/Fe3O4 magnetic composite nanofibres were fabricated through coaxial electrospinning and post-treatment. The effect of sheath feed rate on the formation of hollow structure was investigated and hollow structures of composite nanofibres were characterised by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Fe3O4 nanoparticles existed in composite nanofibres was proved by X-ray diffraction (XRD). The magnetic properties and microwave absorbing properties of hollow composite nanofibres were respectively characterised through superconducting quantum interference device (SQUID) and vector network analyser. The study revealed that the magnetic properties of hollow composite nanofibres were closely related to the contents of Fe3O4 nanoparticles. The microwave absorbing properties of hollow PAN/Fe3O4 composite nanofibres were better than those of solid PAN/Fe3O4 composite nanofibres.

One-pot facile synthesis of hierarchical hollow microspheres constructed with MnO2 nanotubes and their application in lithium storage and water treatment

Semiconductor α-MnO2 hierarchical hollow microspheres constructed with nanotubes have been facilely synthesized through a bubble template-based self-scrolling solution route. An energy-minimizing-driven self-assembly of α-MnO2 nanoparticles on the base of O2 bubbles is responsible for the formation of hierarchical hollow microsphere structure. The as-obtained α-MnO2 products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and UV-vis-NIR spectrophotometry. The Li ion storage and water treatment performances of these α-MnO2 hierarchical hollow microspheres constructed with nanotubes were tested. A discharge capacity as high as 983 mA h g−1 during the 30th cycle has been delivered at a current density of 300 mA g−1. These as-prepared samples were also used as adsorbents in water treatment, and showed an excellent ability to remove organic pollutants without any other additives.

Preparation and Characterization of Magnetic SiO2/PSt Hollow Composite Microspheres via Miniemulsion Polymerization

In this work, a facile method was presented for the preparation of magnetic SiO2/PSt hollow composite micro- spheres via double in situ miniemulsion polymerization. Our approach was based on the in situ miniemulsion polymerization of organic monomers and in situ formation of silica from precursor (tetraethoxysilane, TEOS) within miniemulsion mono- mers droplets simultaneously. Firstly, monodisperse hydrophobic magnetic nanoparticles were synthesized by coprecipitation method as the literature reported. Then the as-prepared magnetic nanoparticles (MNP) were added in the mixtures of styrene (St), divinyl benzene (DVB), TEOS, and γ-methacryloxypropyl trimethoxy silane (MPS) to be used as the oil phase. Mag- netic nanoparticles were restricted in miniemulsion microreactor droplets via the miniemulsification process by sodium do- decyl sulfate (SDS) aqueous solution as a water phase. After the monomers polymerized, TEOS phase is compressed and restricted as a liquid core due to phase separation between TEOS and the growing polystyrene. When the ammonia was added, silica was in situ formed by the hydrolysis-condensation of TEOS under basic conditions. Because the volume of TEOS decreased dramatically, the original TEOS phase shrank into silica and led to the formation of hollow structure. Hol- low composite microspheres were characterized by Fourier-transformed infrared spectrum (FT-IR), transmission electron microscopy (TEM), thermogravimetry and differential analyses (TGA/DSC) and vibrating sample magnetometer (VSM), respectively. The results showed that in the absence of magnetic nanoparticles SiO2/PSt hollow composite microspheres with particle sizes in range of 300~600 nm were prepared successfully. With the addition of hydrophobic magnetic nanoparticles, the magnetic SiO2/PSt composite microspheres were fabricated conveniently with magnetic nanoparticles embedded in the polymeric shell, which remained the same hollow structure as the SiO2/PSt hollow composite microspheres. The inner void size of composite microspheres could be easily controlled by using varied TEOS contents in the miniemulsion formulation. The entrapment efficiency of magnetic nanoparticles in SiO2/PSt composite microspheres reached up to 86%. The magnetic SiO2/PSt hollow composite microspheres were superparamagnetic and their saturation magnetizations were 14.7 emu/g. The magnetic hollow composite microspheres may provide a very promising vehicle for drug delivery, catalysis, and photoelectric materials.

Autocatalytic-assembly based on self-decomposing templates: a facile approach toward hollow metal nanostructures

Hollow metal nanostructures have received increasing interest because they exhibit unique chemical and physical properties different from their solid counterparts. In this work, the autocatalytic-reduction approach based on the self-decomposing of metal hydroxides and oxides is reported, which is distinct from the traditional template methods. Under solution conditions of a reducing atmosphere, metal hydroxides can serve as both the autocatalytic reagent and the sacrificial templates in the reaction process. It is demonstrated that the autocatalytic-reduction method is a general approach to fabricate a series of metal hollow structures, including hollow Ni nanospheres (NSs), Ni nanotubes (NTs), bead-like Ni NSs, and hollow Cu microspheres. Moreover, the structural diversity of original M(OH)x or MOx/2 (M = metal) templates allows the preparation of size and shape-adjustable templates. A possible mechanism for hollow structure formation is also proposed.

Morphology Study of New Shaped Porous Nanotubes of LiFePO4 by Electrospinning

Abstract Porous nanotubes of lithium iron phosphate (LiFePO4) were synthesized from a metal oxide precursor by the electrospinning method. After calcination of the above precursor nanotube at 800 °C, LiFePO4 nanotubes with a diameter in the range of 150–500 nm, were obtained. Poly(vinylpyrrolidone) had an important role in the formation of hollow structure. The obtained nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), videoscopy, and transmission electron microscopy (TEM), respectively. The results showed that porous and hollow morphologies of nanotubes were successfully formed by electrospinning parameters and calcination temperature.

Facile synthesis of hollow Cu2O octahedral and spherical nanocrystals and their morphology-dependent photocatalytic properties

Herein, we report that octahedral and spherical Cu2O samples with hollow structures are synthesized in high yield by reducing Cu(EDA)22+ complex with hydrazine. A series of experiments are carried out to investigate the factors which impact on the morphology of the Cu2O samples. It is observed that ethylenediamine (EDA) serves as a molecular template in the formation of hollow structure. Octahedral Cu2O with solid structure is prepared without EDA. When EDA is added, Cu2O sample with hollow structure is formed. Different morphologies of Cu2O such as spherical and octahedral could be obtained by adjusting the concentration of EDA and NaOH. The temporal crystal growth mechanism is proposed. Furthermore, the photocatalytic activities of the as-prepared Cu2O nanoparticles are evaluated by monitoring two dyes (methyl orange and congo red) using UV-visible spectrophotometer. Results show that the order of photocatalytic activity of Cu2O with different morphologies is as follows: hollow octahedral morphology > hollow sphere morphology > solid octahedral morphology. The hollow octahedral Cu2O nanoparticles would be a promising material on applications for photocatalytic degradation of organic pollutants.

基于动态溶胀法制备中空聚合物微球

Hollow polymer microspheres about 5 m in diameter were synthesized by dynamic swelling method using micron-sized polystyrene spheres with positive charges on surfaces as seeds. The synthesis process included swelling by organic solvents such as toluene and divinylbenzene, polymerizing and coating. The influences of variety and dosage of organic solvents on diameter, size distribution and hole structure of hollow microspheres were investigated, and the formation mechanism of hollow microspheres was discussed. It is indicated that some volatile organic solvents, such as toluene and dimethylbenzene, are crucial to hollow structure formation. Experimental results show that, more toluene leads to larger hollow structure after swelling, and dimethylbenzene is good for hollow structure formation, owing to its low solubility.

Facile preparation of carbon-supported PtNi hollow nanoparticles with high electrochemical performance

To design Pt-based materials with a hollow structure via a galvanic reaction would be one of the effective ways to prepare electro- catalysts with high activity. The galvanic reaction between Pt ions and metal template is usually conducted under limited conditions, which makes the preparation of Pt hollow nanoparticles laborious. Here, we introduce a one-step and one-pot synthetic approach for the preparation of carbon-supported PtNi alloy hollow nanoparticles with a narrow size distribution. Prepared PtNi alloys were characterized by a nonporous shell consisting of a Pt-enriched surface layer and an inner alloy layer of Pt and Ni. Due to its unique structural advantages, this material showed excellent electrocatalytic performance for oxygen reduction (3.3- and 7.8-fold enhanced mass and specific activities compared to those of a commercial carbon-supported Pt nanoparticle). A possible mechanism for the formation of PtNi hollow structure is suggested.

Hollow Structure Formation Mechanism of Calcium Carbonate Particles Synthesized by the CO2 Bubbling Method

The hollow structure formation mechanism of calcium carbonate particles synthesized by the CO2 bubbling method has been investigated. Samples were sequentially taken during the bubbling process to be structurally evaluated by X-ray diffraction and scanning electron microscopy. As a result, it has been elucidated that there are three development stages (A, B, and C) in the formation of the hollow structure. In stage A, amorphous CaCO3 precipitates as primary particles with the decreasing pH by CO2 bubbling. The primary particles then aggregate around pH 9.1 to form secondary particles, and turbidity ensues. Furthermore, because of the decreasing pH, the primary particles on the surface of the secondary particles begin to transform into the vaterite phase and form a shell. During stage B, the surface potential decreases along with a steep decrease in the pH, interparticle attraction of the primary particles on the surface of the secondary particles becomes stronger, and a highly compacted shell is formed. A...

Synthesis of hollow titania microspheres by using microfluidic droplet-template

Droplet-based microfluidics is of great interest due to its particular characteristics compared with the conventional methods, such as reduced reagent consumption, rapid mixing, high-throughput, shape controlled, etc. A novel method using microfluidic droplet as soft template for the synthesis of hollow titania microspheres was developed. A typical polydimethylsiloxane (PDMS) microfluidic device containing "flow-focusing" geometry was used to generate water/oil (W/O) droplet. The mechanism for the hollow structure formation was based on the interfacial hydrolysis reaction between the continuous phase containing titanium butoxide precursor and the dispersed containing water. The continuous phase mixed with butanol was added in the downstream of the channel after the hydrolysis reaction. This step was used for drawing the water out of the microgels for further hydrolysis. The microgels obtained through a glass pipe integrated were washed, dried under vacuum and calcined after aging for a certain time. The fluorescence and scanning electron microscope (SEM) image of the microspheres indicated the hollow structure and the thickness of the shell. In addition, these microspheres with thin shell (about 2 microm) were apt to rupture and collapse. Droplet-based microfluidic offered a gentle and size-controllable manner to moderate this problem. Moreover, it has potential applications in photocatalysis combined with some modification realized on the chip simultaneously.

One-pot synthesis of uniform hollow cuprous oxide spheres fabricated by single-crystalline particles via a simple solvothermal route

Uniform Cu2O hollow spheres fabricated by single-crystalline particles (smaller than 20 nm) are facile synthesized in ethylene glycol (EG) solution by a simple solvothermal route without using pre-fabricated templates and reductive agents. EG in this protocol is not only used as a solvent, complexing agent, and reducing agent, but also served as a structure-directing agent for the formation of hollow structure. By control of reaction conditions, such as reaction time, temperature, and the anions, the morphology and structure of the hollow spheres can be tuned. A coordination adsorption and oriented attachment and Ostwald ripening mechanism is proposed for explaining the formation process of hollow Cu2O spheres in EG solution; and importantly, the hollow Cu2O spheres exhibit an excellent property for the electro-catalytic oxidization of ascorbic acid in acetic acid buffer solution. Moreover, the hollow spherical Cu2O particles could be potentially applied in catalysis, sensor, and as model for fundamental research.

Synthesis of molybdenum oxide hollow microspheres by ethanol and PEG assisting hydrothermal process

Molybdenum oxide hollow microspheres were successfully synthesized via a combination of a hydrothermal method with ethanol and PEG assisting technique. The as-obtained products were characterized by SEM, XRD. The SEM results showed that the sizes of molybdenum oxide hollow spheres were 1–2 μm, and the spherical shape of the hollow microsphere products remained almost unaltered after calcination at 500 °C for 2 h. The XRD results showed that a purity phase of α-MoO 3 could be obtained after calcination. It was also found that the reaction temperature played a key role in the formation of hollow microshphere structure.

Template-free hydrothermal synthesis of hollow hematite microspheres

Hollow hematite (α-Fe2O3) microspheres with an average diameter of 3-4 μm and a shell thickness of approximate 150 nm was synthesized by a simple hydrothermal route using FeCl3·6H2O solution and acetic acid without using any templates. The hollow microspheres were composed of α-Fe2O3 nanoparticles with the diameter range from 20 to 40 nm. The effects of reaction parameters such as reaction time, temperature, concentration of FeCl3·6H2O solution, and initial pH on the morphology of the final products were investigated. A possible formation mechanism of hollow α-Fe2O3 microspheres was also proposed, where the acetic acid played a role of etching in the formation of hollow structure.

General Synthesis of 2D Ordered Hollow Sphere Arrays Based on Nonshadow Deposition Dominated Colloidal Lithography

A general strategy, nonshadow deposition dominated colloidal lithography (NSCL), was proposed for the synthesis of two-dimensional (2D) ordered hollow sphere arrays of conductive materials. Gold, polypyrrole, CdS, and ZnO were taken as model materials to demonstrate the NSCL strategy, and built as 2D hollow sphere arrays successfully. In this strategy, a thin gold coating is first introduced on a polystyrene sphere (PS) colloidal monolayer via ion-sputtering deposition, and a hollow sphere array can thus be obtained by further electrochemical deposition on such a monolayer and by subsequent removal of PSs. The proposed strategy is flexible and facile to control the microstructure and size of the hollow sphere array, and the features are as follows: (i) controllable shell of the hollow sphere from single-layer to multilayer with single or multiple compositions, (ii) tunable morphology from simple structure to hierarchical micro/nanostructure, and (iii) changeable arrangement of hollow spheres from close-packing to non-close-packing. Besides these, the hollow sphere size and the shell thickness can also be controlled by changing the colloidal sphere and deposition time, respectively. Further investigation indicates that the success of NSCL should be owed to a key step, that is, an ion-sputtering induced nonshadow deposition surrounding the whole surfaces of colloidal spheres. This allows an equipotential face and thus homogeneous deposition surrounding the surfaces of PSs in an electrochemical deposition process, and final formation of hollow sphere structure. The 2D ordered hollow sphere arrays with controllable microstructure and size could exhibit importance both in fundamental research and in practical applications.

Synthesis and formation mechanism of hematite hollow microspheres by a one-pot templateless surfactant-free hydrothermal process

Hollow microspheres of hematite (α-Fe 2O 3) were prepared by a simple hydrothermal treatment of ferrous ammonium sulphate hexahydrate ((NH 4) 2Fe(SO 4) 2·6H 2O) aqueous solution without any surfactants and additives at 180–200 °C. The products were characterized by XRD, FE-SEM and TEM. The results show that α-Fe 2O 3 hollow microspheres are about 1 μm in diameters and are composed of α-Fe 2O 3 nanoparticles with a diameter range from 50 nm to 150 nm. The effects of reaction parameters such as reaction time, temperature and [(NH 4) 2Fe(SO 4) 2·6H 2O] on the morphology of the final product were investigated. A potential formation mechanism of α-Fe 2O 3 hollow microspheres was also proposed, where the intermediate, urchin-like goethite, served as a sacrificial template for the formation of hollow structure. The reaction parameters-depended morphologies of the final products consisted well with the proposed formation mechanism.

Hollow Sodium Tungsten Bronze (Na0.15WO3) Nanospheres: Preparation, Characterization, and Their Adsorption Properties

We report herein a facile method for the preparation of sodium tungsten bronzes hollow nanospheres using hydrogen gas bubbles as reactant for chemical reduction of tungstate to tungsten and as template for the formation of hollow nanospheres at the same time. The chemical composition and the crystalline state of the as-prepared hollow Na0.15WO3nanospheres were characterized complementarily, and the hollow structure formation mechanism was proposed. The hollow Na0.15WO3nanospheres showed large Brunauer–Emment–Teller specific area (33.8 m2 g−1), strong resistance to acids, and excellent ability to remove organic molecules such as dye and proteins from aqueous solutions. These illustrate that the hollow nanospheres of Na0.15WO3should be a useful adsorbent.