Formation Of Hollow Spheres Research Articles

Template-free synthesis of Ni7S6hollow spheres with mesoporous shells for high performance supercapacitors

Ni7S6 hollow spheres with mesoporous shells were successfully synthesized by a novel and facile hydrothermal process without any template or surfactant using nickel chloride hexahydrate and sodium thioglycolate as starting materials. The morphology and microstructure of the samples were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), energy dispersive spectroscopy (EDS), and N2 adsorption–desorption isotherm measurement. A bubble template-based ripening process was proposed for the formation of Ni7S6 hollow spheres with mesoporous shells. When applied as electrode materials for supercapacitors, the as-prepared Ni7S6 hollow spheres with mesoporous shells exhibited tremendous pseudocapacitance of 2329.5 F g−1 at 2 mV s−1 and 2283.2 F g−1 at 1 A g−1. A capacity retention of 97.1% was achieved even after 1000 cycles. The maximum energy density is 50.7 W h kg−1 at a current density of 1 A g−1. The excellent capacitive performance is attributed to their unique hollow structure with mesoporous shells providing fast ion and electron transfer, and high electronic conduction. These results suggest that the Ni7S6 hollow spheres with mesoporous shells are highly promising candidates for supercapacitor electrodes.

An external template-free route to uniform semiconducting hollow mesospheres and their use in photocatalysis.

Solid amorphous TiO2 mesospheres were synthesized by controlled hydrolysis of Ti-containing precursors. Subsequently, solid TiO2 mesospheres were exploited as scaffolds and subjected to a one-step external template-free hydrothermal treatment, yielding intriguing hollow anatase TiO2 mesospheres. The synthetic protocol was optimized by investigating the effect of buffer reagents and fluoride ions on the formation of hollow TiO2 spheres. The diameter of hollow mesospheres, ranging from 308 to 760 nm, can be readily tailored by varying the precursor concentration. The average thickness of a shell composed of TiO2 nanocrystals was approximately 40 nm with a mean crystal size of 12.4-20.0 nm. Such hollow TiO2 mesospheres possessed a large surface area and were employed in photocatalytic degradation of methylene blue under UV irradiation. Interestingly, the synthetic conditions were found to exert a significant influence on the photocatalytic ability of hollow TiO2 mesospheres. The correlation between the degradation ability of hollow TiO2 mesospheres and the precursor concentration as well as the hydrothermal time was scrutinized. The optimal photocatalytic performance of hollow TiO2 mesospheres was identified.

Self‐Templated Formation of Uniform NiCo2O4 Hollow Spheres with Complex Interior Structures for Lithium‐Ion Batteries and Supercapacitors

AbstractDespite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template‐based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed‐metal‐oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium‐ion batteries and supercapacitors. This approach can be an efficient self‐templated strategy for the preparation of mixed‐metal‐oxide hollow spheres with complex interior structures and functionalities.

Self-templated formation of uniform NiCo2O4 hollow spheres with complex interior structures for lithium-ion batteries and supercapacitors.

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities.

Effects of Urea/Al3+ Ratios and Hydrothermal Treated Time on the Formation of Self-Assembled Boehmite Hollow Sphere

Using Al2(SO4)3 and urea [CO(NH2)2] as the starting materials, the self-assembled boehmite (γ-AlOOH) sphere with hollow structure was successfully synthesized by hydrothermal process. The effects of urea/Al3+ molar ratios and hydrothermal treated time on the crystal structure, morphology and specific surface area were investigated in detail. It showed that the boehmite (γ-AlOOH) formed when the urea/Al3+ molar ratio was 1:1, 2:1 and 3:1 hydrothermally treated at 180°C for 24 h. The synthesized particles formed a hollow sphere structure with nano-flakelets surface and had the large specific area of 208 m2 g−1 and high pore volume of 1.23cm3 g−1 respectively.

A Novel double-shelled C@NiO hollow microsphere: Synthesis and application for electrochemical capacitor

Herein, double-shelled hollow architecture composed of carbon inner shell and flower-like NiO exterior shell has been prepared through a facile hydrothermal process, followed by a heat treatment. Taking SiO2@RF (resorcinol–formaldehyde resin, RF) sphere as template, the flower-like NiSilicate shell was grown on the surface of RF during the formation of hollow inner structure. The calcination process in the inert atmosphere gives rise to the carbonization and decomposition simultaneously, leading to the formation of carbon-based NiO hollow spheres (C@NiO HSs) with similar structure to that of the parent precursor, which possess large specific surface area (217m2g−1) and favorable pore structure for supercapacitor application. It is found that C@NiO composite shows higher electrochemical performance than that of pure NiO hollow sphere without interior carbon shell. The C@NiO hollow spheres have high specific capacitance of 211F/g at the current density of 1A/g and good cycle stability (84.6%) after 1000 cycles at the current density of 5A/g, which are superior to NiO HSs without carbon shell. The synthetic strategy can be expanded to fabricate other functional hybrid materials, which should be potential in diverse fields.

A general and rapid synthesis of metal sulphides hollow spheres that have properties enhanced by salt-assisted aerosol decomposition: a case of ZnS and other multicomponent solid solutions

Synthesis of hollow structures of metal sulphides generally involves various templates and complex chemical processing. In the present study, a general and rapid method of salt-assisted aerosol decomposition (SAD) is presented for the synthesis of hollow spheres of various metal sulfides, including ZnS, ternary sulfides, and solid solutions. The NaCl salt plays a critical role in the formation of hollow spheres of metal sulfides. The hollow spherical microstructure was formed from solid by using a small amount of water soluble NaCl salt. The formation of metal sulphide hollow spheres differs from previous mechanisms and is referred to as molten salt heterogeneous nucleation (MSHN). The present method offers the most promising advantage for controlling the multicomponent composition of hollow spheres. Furthermore, hollow spheres of sulphides have much enhanced properties such as photoluminescence of ZnS:Mn2+ and photocatalytic dye degradation of ZnIn2S4 due to the role of molten salt in the promotion of crystallization, The present method could be explored further by applying the process to other compounds such as sulfides, oxides, and nitrides.

Fabrication of hollow silica spheres and their application in polyacrylate film forming agent

Polystyrene (PS)/silica core/shell spheres were fabricated using mono-dispersed PS as templates by hydrolysis and condensation of two different silica precursors. The PS cores of PS/silica core/shell spheres were dissolved subsequently in the tetrahydrofuran medium to form mono-dispersed hollow silica spheres. The structures and morphologies of hollow silica spheres were characterized by scanning electron microscopy and transmission electron microscopy. Then, polyacrylate/hollow silica composite film forming agents were prepared via physical blending of polyacrylate and two different hollow silica spheres, and the water vapor permeability of their films were compared. The results showed that the structure of hollow silica spheres were very typical and obvious. The silica shell was continuous and uniform using tetraethylorthosilicate as precursor, which was accumulated by many silica seeds with size of 10–20 nm, and the thickness of silica shell was about 16.7 nm. However, the hollow silica spheres using tetraethylorthosilicate and vinyl triethoxysilane as precursors had mesoporous structure in the shell. The introduction of hollow silica spheres could significantly improve the water vapor permeability of polyacrylate film. At last, a possible mechanism for the formation of hollow silica spheres was proposed and the process of water vapor through polyacrylate/hollow silica composite films was modeled.

Uniform hollow magnetite spheres: Facile synthesis, growth mechanism, and their magnetic properties

Hierarchical porous Fe3O4 hollow spheres with high saturation magnetization were synthesized through a simple solvothermal process in ethylene glycol (EG) in the presence of Tetrabutylammonium chloride (TBAC) and urea. By investigating the effect of reaction temperature, time, the amount of urea, and concentration of iron ion on the formation of hollow spheres, it was proposed that the main formation mechanism of hollow spheres is Ostwald ripening process combined with assembly-then-inside-out evacuation process. Additionally, it is found that the morphology of Fe3O4 with nanoparticles, hollow, and irregular structures could be adjusted by changing the above factors. The resulting products were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometer (VSM). The hierarchical porous Fe3O4 hollow spheres exhibited enhanced saturation magnetization as compared with Fe3O4 nanoparticles.

Preparation and studies on properties of porous epoxy composites containing microscale hollow epoxy spheres

In this work, a series of porous epoxy composites containing microscale, hollow epoxy spheres were synthesized and characterized. First, microscale epoxy spheres were produced using amino-modified silica (AMS) particles with diameters of ∼1μm through a base-catalyzed sol–gel route. The as-synthesized AMS particles were then characterized through Fourier-transform infrared, 13C nuclear magnetic resonance (NMR), and 29Si-NMR spectroscopy. The prepared core–shell particles were immersed into a 1wt.% of HF solution for 24h to remove the inner part of the silica core, leading to the formation of hollow spheres of epoxy with a wall thickness of ∼100nm. These hollow epoxy spheres (HES) were characterized by scanning electron microscopy (SEM), Transmission electron microscopy, and thermogravimetric analysis (TGA). Finally, a series of hybrid materials was synthesized by performing thermal ring-opening polymerization reactions of epoxy resin in the presence of as-synthesized HES. Based on SEM observations on the morphology, the HES showed good dispersion capability in the polymer matrices, which led to a significantly reduced thermal conductivity and slightly decreased dielectric constant based on the transient plane source and LCR measurements, respectively. For example, the thermal conductivity and dielectric constant decreased by 49.3% and 12.6%, respectively, in the porous epoxy material synthesized with a final HES loading of about 10%. One possible reason was the large amount of air present in the material. Other physical characteristics such as the thermal and mechanical properties based on the results of TGA, differential scanning calorimetry, and dynamic mechanical analysis were investigated.

Hollow sphere formation from a three-dimensional structure composed of an adamantane-based cage.

An adamantane-based cage with a three-dimensional (3D) framework was synthesized by the copper-mediated acetylene coupling reaction, in which two 1,3,5-triethynyladamantane units were linked by phenyldiacetylenic bridges possessing ester groups. X-ray crystallography revealed that the cage has an internal space and accommodates a solvent molecule, which afforded molecular networks through CH/O interactions between cage molecules. Furthermore, the cage containing six ester groups spontaneously self-assembled into hollow spherical aggregates with an average diameter of 230 nm in a mixed solvent.

Hollow spherical rare-earth-doped yttrium oxysulfate: A novel structure for upconversion

A facile biomolecule-assisted hydrothermal route followed by calcination has been employed for the preparation of monoclinic yttrium oxysulfate hollow spheres doped with other rare-earth ions (Yb3+ and Eu3+ or Er3+). The formation of hollow spheres may involve Ostwald ripening. The resulting hybrid materials were used for upconversion applications. The host crystal structure allows the easy co-doping of two different rare-earth metal ions without significantly changing the host lattice. The luminescent properties were affected by the ratio and concentration of dopant rare-earth metal ions due to energy transfer and the symmetry of the crystal field. The type of luminescent center and the crystallinity of samples were also shown to have a significant influence on the optical properties of the as-prepared products.

Development of a scalable spray pyrolysis process for the production of non-hollow battery materials

Spray pyrolysis typically produces hollow particles when the particles are larger than about 2 microns. In this work, a scalable spray pyrolysis process was developed for the production of electrochemically active materials in a way that overcomes hollow sphere formation. With this new slurry spray pyrolysis process particles greater than 6 μm have been successfully produced with a solid, yet porous interior morphology. Results indicate that the process shows great potential for the production of high quality, electrochemically active materials, as demonstrated by the electrochemical performance of layered Li1.2Mn0.54Ni0.13Co0.13O2 materials. The materials are phase pure, as observed by powder X-ray diffraction (XRD), and discharge capacities greater than 200 mAh g−1 after 100 cycles at C/3 rate (where 1 C = 200 mAh g−1) are consistently obtained. The standard deviation in discharge capacity for 5 batches of material produced under identical conditions was 11 mAh g−1. These promising electrochemical results were obtained at a scale of 50 g h−1 and with minimal process optimization, indicating the potential for commercial scale production.

Self-Assembly of Methyl Substituted Polyaniline Hollow Nanospheres in a Polyelectrolyte Solution

Hollow nanospheres of poly(m-toluidine), poly(o-toluidine), and poly(N-methylaniline) were successfully prepared in a solution of poly(methyl vinyl ether-alt-maleic acid) by using ammonium persulfate as the oxidant. The polymerization processes of methyl substituted aniline were monitored by recording pH and temperature changes of the reaction medium. The experimental results showed that the substitution position of methyl group affected the characteristics of formed hollow nanospheres. The formation mechanism of such hollow nanospheres was suggested. The produced hydrophobic oligomers self-assembled at the interface of water/droplet of monomers and acted as the soft template for the formation of hollow spheres.

An acid-free route for the facile synthesis of iron-functionalized mesoporous silicas: Transformation between hollow nanospheres and cage-like mesostructures

Iron-substituted silicas with hollow nanospherical morphology and cage-like mesostructure have been synthesized using triblock copolymer F127 as surfactant and tetramethoxysilane (TMOS) as silica source with no necessary addition of mineral acids. Iron-functionalized hollow nanospheres were obtained using Fe(acac)3 as iron source. When Fe(NO3)3 was employed as iron source, iron-containing cage-like FDU-12 mesostructure and hollow nanospheres were formed with Fe/Si molar ratio lower than 0.008 and higher than 0.015, respectively. The formation of hollow spheres at high Fe/Si ratio can be regarded as gradually dissociation of nanocages from Fe-FDU-12. The structure of the iron centers was determined by spectroscopic methods (UV–vis and UV–Raman measurements) and by elemental analyses. The facile structural evolution between cage-like and nanospherical structures may be helpful for further understanding the formation mechanism of mesoporous silicas.

Preparation of CdO hollow microspheres via H2O2 pre-oxidation

Cadmium oxide (CdO) hollow microspheres were prepared by pre-oxidizing Cd powders and subsequent thermal oxidation under normal atmospheric pressure. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to characterize the microstructures. A layer of Cd(OH)2 shell was formed on the surface of the cadmium core during the pre-oxidation process, and the shell transformed into a dense CdO layer at relatively low temperature, which resulted in the formation of CdO hollow sphere during the thermal oxidation. The growth of hollow sphere was mainly affected by the thickness of pre-oxidized layer (the time of pre-oxidation) and the thermal oxidation temperature.

Surfactant-Free Synthesis, Luminescent Properties, and Drug-Release Properties of LaF3 and LaCO3F Hollow Microspheres

Uniform LaF3 and LaCO3F hollow microspheres were successfully synthesized through a surfactant-free route by employing La(OH)CO3 colloidal microspheres as a sacrificial template and NaBF4 as the fluorine source. The synthetic process consists of two steps: the preparation of a La(OH)CO3 precursor via a facile urea-based precipitation and the following formation of lanthanide fluoride hollow microspheres under aqueous conditions at low temperature (50 °C) and short reaction time (3 h), without using any surfactant and catalyst. The formation of hollow spheres with controlled size can be assigned to the Kirkendall effect. It is found that the phase and structure of the products can be simply tuned by changing the pH values of the solution. Time-dependent experiments were employed to study the possible formation process. N2 adsorption/desorption results indicate the mesoporous nature of LaF3 hollow spheres. Yb(3+)/Er(3+) (Ho(3+)) and Yb(3+)/Tm(3+)-doped LaF3 hollow spheres exhibit characteristic up-conversion (UC) emissions of Er(3+) (Ho(3+)) and Tm(3+) under 980 nm laser-diode excitation, and Ce(3+)/Tb(3+)-doped LaF3 and LaCO3F emit bright yellow-green and near-white light under UV irradiation, respectively. In particular, LaF3:Yb/Er and LaCO3F:Ce/Tb hollow microspheres exhibit obvious sustained and pH-dependent doxorubicin release properties. The luminescent properties of the carriers allow them to be tracked or monitored during the release or therapy process, suggesting their high potential in the biomedical field.

Submicrometer-Sized Hierarchical Hollow Spheres of Heavy Lanthanide Orthovanadates: Sacrificial Template Synthesis, Formation Mechanism, and Luminescent Properties

Hollow spheres of heavy lanthanide orthovanadates (LnVO4, Ln = Tb, Dy, Er, Tm, Yb, Lu) and yolk-shell structures of Ho(OH)CO3@HoVO4 have been successfully prepared by employing Ln(OH)CO3 colloidal spheres as a sacrificial template and NH4VO3 as a vanadium source. In particular, the as-obtained LuVO4 hollow spheres are assembled from numerous hollow-structured elliptic nanoparticles, and their textural parameters such as the inner and outer diameters, shell thicknesses, and number of shells could be finely tuned through introducing different amounts of NH4VO3 and employing Lu(OH)CO3 templates with different sizes. The possible mechanisms for the formation of hollow spheres and yolk-shell structures, and also the hollow-structured elliptic nanoparticles of LuVO4, i.e., building blocks of LuVO4 hollow spheres, are proposed and discussed in detail. Under ultraviolet excitation, the obtained LuVO4:Eu(3+) hollow spheres show strong red emissions located in the saturated color region, and the modulation of emission intensity and color purity could be realized by tuning the textural parameters of the obtained hollow spheres. It was found that the nanostructure of the building blocks of LuVO4:Eu(3+) hollow spheres also had an effect on the luminescent properties of the as-obtained materials. Moreover, the quantum efficiency could be affected by the textural parameters of the as-obtained LuVO4:Eu(3+) hollow spheres, and the double-shelled LuVO4:Eu(3+) hollow sphere has the highest quantum efficiency. In addition, the excellent biocompatibility indicates the potential biological applications of LuVO4 hollow spheres.

Synthesis of hollow CdS micro-/nanospheres by CoSP technique and their visible light photocatalytic activities

CdS hollow micro-/nanospheres with high yield, purity, and photocatalytic property have been successfully synthesized by a continuous spray pyrolysis (CoSP) technique. The experimental conditions mainly the temperature and the nature of solvent are found to influence the creation of hollow spheres. The synthesized products have been characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), UV–vis and photoluminescence spectra. The XRD analysis confirmed the hexagonal crystal structure of the CdS microspheres supported by the measured lattice spacing from HR-TEM. The effects of synthesis temperature and the electric field applied during the spray on the formation of hollow spheres and their visible light photocatalytic properties are reported. Photodegradation of methylene blue (MB) dye under visible light was used to evaluate the performance of these CoSP made CdS micro-/nanospheres. The MB photodegradation efficiency was maximum, ∼90% in 2h, for CdS microspheres prepared at 500°C. The importance of hollow morphology over solid morphology is also proven; the hollow sphere sample (CdS5) is about twice efficient than solid sphere sample (CdS7). The results show that the CoSP method is a simple and inexpensive technique for preparing highly photo-active CdS hollow spheres which can be extended to prepare other sulphide and oxide hollow spheres at a large scale. Typically 100mg of the powder can be prepared from ∼100ml of spray solution.

A novel approach to synthesize hollow α-Fe2O3 spheres via hydrothermal treatment

Novel α-Fe2O3 hollow crystal spheres were formed on a large scale by a facile and efficient hydrothermal process. In this paper, the inorganic anions are important in the formation of α-Fe2O3. And the concentration of H2PO4− is important for forming hollow spheres. The coordination effect of phosphate ions with Fe3+ ions is another important aspect in the formation of hollow spheres. H2PO4− is important for forming hollow structures. The samples were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction.