Preparation and electrochemical characteristics of mesoporous carbon spheres for supercapacitors

Mesoporous carbon spheres serving as electrode materials for supercapacitors were synthesized by a facile polymerization-induced colloid aggregation method using melamines as a carbon precursor and commercial colloidal silica as a silica source for hard template. After the carbonization of as-formed resins-template composites at 1000 °C and the removal of the silica template by hydrofluoric acid, the resulting mesoporous carbon spheres with a diameter size of ∼5 μm, specific surface area (up to 1280 m²/g) and uniform pore size as large as 30 nm could be obtained. Due to the enriched nitrogen content and the large pore size of the mesoporous carbon spheres affecting the surface wettability, resistance, and ion diffusion process in the pores, the mesoporous carbon spheres showed a high specific capacitance of 196 F/g in 5 mol/l H₂SO₄ electrolytes at a discharge current density of 1 A/g.     

The size modulation of hollow mesoporous carbon spheres synthesized by a simplified hard template route

Hollow mesoporous carbon spheres (HMCSs) have been prepared by a simplified replication route from a solid silica core/mesoporous silica shell aluminosilicate (SCMS-Al) template, which was synthesized by directly incorporating aluminum species into the mesoporous framework during template synthesis. The size of HMCSs can be tuned between 80 and 470 nm by simply changing the diameters of SCMS-Al. The HMCSs have uniform mesopores with a narrow pore size distribution (3.4-4.1 nm), and high surface area, (890-1150 m²/g) and total pore volumes (0.75-1.15 cm³/g). The techniques of N₂ sorption isotherms, TEM, EDX and SEM were used to characterize the as-synthesized spheres.     

Solvothermal synthesis of the special shape (deformable) hollow g-C3N4 nanospheres

Special shaped (deformable) hollow g-C₃N₄ nanospheres were synthesized by the solvothermal technique using silica spheres as template. The X-ray diffraction (XRD) peaks of the product were indexed to g-C₃N₄ materials. Field-Emission Scanning Electron Microscopy and Transmission Electron Microscopy confirmed that the external diameter of the hollow nanospheres is about 130-150 nm and thickness of the wall is about 20-30 nm. The FTIR spectrum showed absorption peak at 810 cm^-1 can be attributed to the s-triazine (C₃N₃) breathing mode. Raman spectrum exhibited two broad peaks approximately at 1360 cm^-1 (D band) and 1580 cm^-1 (G band). The deformed pie shape or mortars like hollow spheres were first reported. The flexility of the deformable hollow g-C₃N₄ nanospheres may be used in special field such as drug delivery carriers adjusting the delivery ratio by the external pressure, and a good material for studying the mechanical properties of the sp² hybrid g-C₃N₄. The photoluminescence spectrum of the product indicates that the deformable hollow g-C₃N₄ nanospheres may have potential applications in nano-optical device fields.     

Facile one-pot synthesis and luminescence of hexagonal TbPO4·nH2O hollow spheres

Monodisperse hexagonal TbPO₄·nH₂O hollow spheres were successfully obtained by utilizing Tb(OH)CO₃ colloidal spheres as the precursor and NH₄H₂PO₄ as the phosphorus source through the hydrothermal process. The obtained hollow spheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), respectively. They have the average diameter of 200 nm. There are a number of tiny nanorods with the length of about 60 nm on the surface of the spheres. The obtained TbPO₄ hollow spheres exhibit green color emission from ⁵D₄ − ⁷F_J (J = 6, 5, 4, 3) transitions of the Tb³⁺ ions, which are expected to be applied in display applications and biological applications.     

Synthesis and photoluminescence properties of CaSiO3:Eu spheres prepared by the reverse micelles soft template

We report here the successful synthesis of CaSiO₃:Eu³⁺ spheres using the reverse micelles soft template. The influence of the calcination temperature on the shape, crystallization and photoluminescence properties of the prepared spheres was investigated by DTA-TG, XRD, IR, SEM and PL. The results showed that the temperature of crystallization (from amorphous phase to β-CaSiO₃) is 668 °C. The temperature of phase transition (from β-CaSiO₃ to α-CaSiO₃) is 790 °C. The average size of CaSiO₃:Eu³⁺ spheres calcined at 700 °C was about 350 nm. The radiation was dominated by the red emission peak at 613 nm and the highest emission intensity was observed when the spheres were calcined at 700 °C. When calcined at 800 °C, the spheres are almost cracked and melted down, due to the high temperature.     

Sol-gel synthesis of titania hollow spheres

TiO₂ hollow spheres are prepared by a convenient sol-gel method at room temperature. The products were characterized by XRD, FESEM, TEM and FT-IR. It was found that these spheres are hollow inside with outer diameters of 200-500 nm. The average mesoporous diameter is about 9.8 nm. And the BET surface area and specific pore volume are about 161.9 m²/g and 0.441 cm³/g, respectively.     

Crystalline diamond/graphite nanoflake hybrid films

Freestanding crystalline diamond/graphite nanoflake hybrid films have been deposited in H₂/CH₄ gas mixtures using a high pressure (1.3 × 10⁴ Pa) direct current plasma discharge. Sacrificial layers of close-packed silica microspheres were used as a matrix to produce dual gas chemistries on the plasma-facing and reverse sides of the microspheres. A continuous polycrystalline diamond film was formed on the front surface whilst graphite was deposited in the form of nanoflakes as a thinner hemispherical layer on the reverse side of the silica spheres respectively. Chemical etching of the silica matrix yielded crystalline diamond/well-aligned graphite nanoflakes hybrid films.     

Simple synthesis of hollow carbon spheres from glucose

Hollow carbon spheres were prepared by the reaction between glucose and Zn particles at 550 °C. Scanning and transmission electron microscopies reveal that most of the spheres are about 1-2 µm in diameter, similar to the sizes of the Zn particle. The shells of the spheres are comprised of numerous hollow nanospheres with the diameter of 10-100 nm. The specific surface area of the spheres is 207 m²/g. The Zn particles act as both the reactant and the template for the micron-scale spheres, and the H₂ bubbles generated during the reaction as the template for the hollow nanospheres.     

A novel synthetic route to Y2O3:Tb phosphors by bicontinuous cubic phase process

This study applies a novel approach to prepare the terbium-doped yttrium oxide phosphors (Y₂O₃:Tb³⁺) using the bicontinuous cubic phase (BCP) process. The experimental results show that the prepared precursor powder was amorphous yttrium hydroxide Y_1−xTb_x(OH)₃ with a spherical shape and primary size 30–50 nm. High crystallinity phosphors with body-centered cubic structures were obtained after heat treatment above 700 °C for 4 h. The primary size of the phosphors grew to 100–200 nm, and dense agglomerates with a size below 1 μm were formed during the calcination. The obtained Y₂O₃:Tb³⁺ phosphor had a strong green emitting at 542 nm. The optimum Tb³⁺ concentration was 1 mol% to obtain the highest PL intensity. This study indicates that the calcining temperature of 700 °C needed for high luminescence efficiency in this work is much lower than 1000 °C or above needed for the conventional solid-state method.     

Vapor-phase synthesis of uniform silica spheres through two-stage hydrolysis of SiCl4

We report, for the first time, a vapor-phase synthesis of nearly monodispersed silica spheres 250-300 nm in size through a two-stage hydrolysis of SiCl₄. In the first stage, SiCl₄ vapor was partially hydrolyzed with water vapor in a batch reactor at 150 °C to form silicon oxychloride particles, nearly monodispersed and spherical. In the second stage, these oxychloride particles were converted into silica particles through further hydrolysis at 1000 °C in a tubular reactor, while the morphology and size after the first-stage reaction remained virtually unchanged.     

Template-free fabrication of SnO2 hollow spheres with photoluminescence from Sni

SnO₂ hollow spheres with interstitial Sn²⁺ defect were fabricated by the hydrothermal method without any surfactant or polymer, whose shell is constructed by two layers of tetragonal prism nanorod arrays. The growth mechanism of the hollow spheres was investigated and attributed to the nucleation and arrangement of SnO₂ tetragonal prism nanorods on the surface of the hydrothermal reaction formed NO bubbles in the aqueous solution. After illumination by 275 nm wavelength light, narrow peak emissions centered at about 587-626 nm have been found in the photoluminescence spectrum, which have been ascribed to the interstitial Sn²⁺ defect in the SnO₂ hollow spheres.     

Preparation and formation mechanism of nano-sized MnOx-CeO2 hollow spheres via a supercritical anti-solvent technique

Manganese and cerium composite oxide (MnO_x-CeO₂) hollow nanospheres were successfully prepared by precipitating manganese acetylacetonate and cerium acetylacetonate from their mixed methanol solution using supercritical carbon dioxide as an anti-solvent. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the precursor and as-prepared MnO_x-CeO₂. XRD analysis reveals the cubic fluorite structure of the MnO_x-CeO₂. HRTEM results indicate that the MnO_x-CeO₂ hollow spheres have an average diameter of about 50 nm, and a wall thickness of 10-20 nm. A new formation mechanism of these nano-sized hollow spheres has also been proposed based on the experimental results.     

Uniform lanthanide-doped Y2O3 hollow microspheres: Controlled synthesis and luminescence properties

Lanthanide-doped uniform pure cubic phase Y₂O₃ hollow microspheres have been successfully synthesized via a facile, high yield urea-based coprecipitation route with assistant of carbon spheres templates. The diameter and shell thickness of the microspheres can be manipulated by adjusting carbon sphere templates. Under a 980 nm excitation, Yb³⁺/Er³⁺, Er³⁺, Yb³⁺/Tm³⁺-doped Y₂O₃ hollow microspheres emit bright upconversion red, green, blue light with high purity, respectively, while Eu³⁺, Eu³⁺/Tb³⁺-doped Y₂O₃ hollow microspheres exhibit intense downconversion red light under the excitation of 254 nm ultraviolet light. Especially, the 610 nm emission intensity of Eu³⁺ in the Eu³⁺/Tb³⁺-codoped Y₂O₃ hollow microspheres is almost 5 times of that in the Y₂O₃:Eu³⁺ hollow microspheres indicating the occurring of the energy transfer from Tb³⁺ to Eu³⁺ ions.     

Layered δ-MnO2 as positive electrode for lithium intercalation

Layer structured δ-MnO₂ was synthesized by a microwave-assisted hydrothermal method. The morphology of the product consists of flower-like spheres that range from about 200 nm to 3 μm in diameter and are composed of sheets about 5-10 nm in thickness. When tested in the voltage range of 2 to 4.5 V vs. Li⁺/Li in coin cells, the separator is blocked, handicapping Li⁺ conductivity and leading to cell failure. When tested in the voltage range of 2 to 4 V in ethylene carbonate/dimethyl carbonate (EC/DMC), the δ-MnO₂ delivers an initial reversible capacity of 143.7 mAh g⁻¹ and can maintain 120 mAh g⁻¹ at the 60th cycle. The δ-MnO₂ electrode shows good cycling stability at different current densities and delivers a discharge capacity of about 90 mAh g⁻¹ at 1 C, indicating that it is a promising cathode material for lithium ion batteries.     

Synthesis of large-pore periodic mesoporous organosilica

Periodic mesoporous organosilica (PMO) materials with large pores have been successfully synthesized using a combinational strategy by decreasing both the synthesis temperature and acidity. Herein, we use a tri-block copolymer EO106PO70EO106 [Pluronic F127, where EO is poly(ethylene oxide) and PO is poly(propylene oxide)] as the template, bis(trimethoxysilyl)ethane (BTME) as a silica source and 1,3,5-trimethylbenzene (TMB) as a pore expander. The PMO material synthesized in this approach has a face-centered cubic (fcc) structure. When the synthesis temperature is 0 °C and the acidity is 0.1 M HCl, the pore diameter of the PMO material reaches 33.6 nm, which is the largest among cubic PMO materials to our knowledge.     

Strong broad green UV-excited photoluminescence in rare earth (RE = Ce, Eu, Dy, Er, Yb) doped barium zirconate

The wet synthesis hydrothermal method at 100 °C was used to elaborate barium zirconate (BaZrO₃) unpurified with 0.5 mol% of different rare earth ions (RE = Yb, Er, Dy, Eu, Ce). Morphological, structural and UV-photoluminescence properties depend on the substituted rare earth ionic radii. While the crystalline structure of RE doped BaZrO₃ remains as a cubic perovskite for all substituted RE ions, its band gap changes between 4.65 and 4.93 eV. Under 267 nm excitation the intrinsic green photoluminescence of the as synthesized BaZrO₃: RE samples is considerably improved by the substitution on RE ions. For 1000 °C annealed samples, under 267 nm, the photoluminescence is dominated by the intrinsic BZO emission. It is interesting to notice that Dy³⁺, Er³⁺ and Yb³⁺ doped samples present whitish emissions that might be useful for white light generation under 267 nm excitation. CIE color coordinates are reported for all samples.     

Fabrication of silica monolithic columns with ordered meso/macropore structure

Recently, much effort has been focused on the materials with ordered meso/macropores, because of their potential applications in catalysis, separations, coatings, microelectronics and electro-optics. In this paper, silica monoliths with well-defined columnar shape more than 1 cm in length are successfully fabricated by using the micelles of triblock copolymer F127 and colloidal crystals composed of polystyrene (PS) latex microspheres as mesopore and macropore template, respectively. The column templated by PS microspheres 870 nm in diameter and 0.5 g F127 (MCL-0.5-870) shows uniform ordered macropores, contact pores connecting macropores together, and assembled and inter-particle pores increasing the BET specific surface area and adsorption capability of the monolithic column. The backpressure curve and hydraulic permeability experiment exhibit its good penetrability and mechanical stability. These excellent characteristics, together with high BET specific surface area (387.4 m² g⁻¹) and porosity (80%), may endow its potential application for chromatography separation. In addition, the size of macropores and mesopores can be easily regulated by changing the diameter of PS spheres and F127 weight, respectively. This indicates that this method is a facile and universal protocol to fabricate the applied monolithic column with ordered meso/macropores.     

Silica@Carbon mesoporous nanorattle structures synthesised by means of a selective etching strategy

A facile route for the fabrication of nanorattles composed of tunable silica spherical nanoparticles confined inside mesoporous carbon shells is presented. The synthetic strategy involves several steps: i) the synthesis of solid core/mesoporous shell silica microspheres, ii) the infiltration of the mesoporous shell with a carbon precursor and its conversion to carbon through a carbonization process and iii) the controlled dissolution of the silica by means of a soft etching agent (NaOH 1.5 M). Following this procedure, a variety of Silica@Carbon nanorattles of diameter ∼ 430 nm is produced. The diameter of the silica core can be uniformly tuned between 330 nm and 160 nm by varying the etching time in a range of 2 h-44 h. The rate constant for the dissolution process of the silica core was estimated to be k ≈ 1.2 × 10^− 10 g cm^− 2 s^− 1. These nanorattles have a high BET surface area and a large pore volume, depending on the amount of silica in the composite.     

Influence of 150 MeV Ni swift heavy ion irradiation on CuFe2O4 thin films prepared by radio frequency magnetron sputtering: Modification on structure and surface morphology

The bulk copper ferrite nanomaterials are synthesized by co-precipitation technique. The vibrating sample magnetometer measurement for bulk CuFe₂O₄ reveals its unsaturated superparamagnetic behavior. The crystallites of the synthesized nanomaterial are in cubic form having an average size of ~ 100 Å and are used as target to prepare thin films of various thicknesses (600, 900 and 1100 nm) by radio frequency magnetron sputtering technique. X-ray peaks arise only when films are annealed at 1200 °C and also they are found to be in tetragonal structure. The magnetic characteristics of 900 nm unirradiated CuFe₂O₄ thin film exhibit superparamagnetic behavior and have an unsaturated magnetic moment at high field. Magnetic force microscopy images of unirradiated CuFe₂O₄ thin films confirm the soft nature of the magnetic materials. The 150 MeV Ni¹¹⁺ swift heavy ion irradiation on these thin films at the fluence of 1 × 10¹⁴ ions/cm² modifies the polycrystalline nature due to electron-phonon coupling. Atomic force microscopy image shows that the swift heavy ion irradiation induces agglomeration of particles in 600 and 900 nm thin films and increases rms surface roughness from 33.43 to 39.65 and 69.7 to 102.46 nm respectively. However, in 1100 nm film, holes are created and channel-like structures are observed along with a decrease in the rms surface roughness from 75.12 to 24.46 nm. Magnetic force microscopy images of 900 nm irradiated thin film explain the formation of domains on irradiation and are also supported by the ferromagnetic hysteresis observed using vibrating sample magnetometer.     

Silica-[Fe(bpy)3] composite particles with photo-responsive change of color and magnetic property

Photo-induced complex formation of tris-2,2′-bipyridine iron(II) complex ([Fe(bpy)₃]²⁺) from the mixture of FeCl₃ and 2,2′-bipyridine was achieved in silica gel containing 150-300 μm silica particles, derived from a complex emulsion with HCl aqueous solution and tetraethyl orthosilicate (TEOS). More than 95% of Fe(III) and 2,2′-bipyridine were incorporated in silica particles. Yellow-red color change, due to [Fe(bpy)₃]²⁺, was observed by irradiation with 365 nm UV beam at 0.3 mW cm⁻² for 120 s. The complex formation accompanies simultaneous spin transition from the high-spin state of Fe(III) to the low-spin state of Fe(II).