Carbon Sphere Template Research Articles

Synthesis of SiC Macroscopic Spheres from Fly Ash

SiC macroscopic spheres have been synthesized by a microwave heating and carbothermal reduction method with commercial carbon spheres as template and fly ash as silica source. The morphology and structure of SiC hollow spheres were characterized using X-ray diffraction, N2 adsorption isotherms, scanning electron microscope and energy-dispersive. The results show that the SiC hollow spheres have retained the similar size with the original carbon sphere template. The shell of SiC hollow sphere is composed of curving SiC wires, and the shell thickness can be modulated by the ratio between C and SiO2. The formation of curving SiC wires attribute to the VLS mode, the Fe catalyst is indispensable reason of it.

Preparation and Photocatalytic Property of Porous CuO Hollow Microspheres via Carbon Sphere Templates

Porous copper oxide (CuO) hollow microspheres have been successfully fabricated by using carbon spheres as templates. The products were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). The influences of different experimental parameters on the morphology of CuO structures have been investigated in detail and the possible formation mechanism of porous CuO hollow microspheres has also been proposed. The specific surface area of the hollow spheres with 74.805 m2/g is measured by BET method. Barrett-Joyner-Halenda (BJH) calculations for the pore size distribution, derived from desorption data, reveal that the average pore radius is 8.56 nm, and the total pore volume (r = 1686.1 A, P/P0 = 0.994296) is 0.107257 cc/g. UV-vis absorption spectrum shows quantum size effect of porous CuO hollow microspheres. Furthermore, the porous CuO hollow microspheres exhibit high efficiency for photodegradation of a sample organic dye, Rhodamine B (RhB), under UV light.

General Synthesis Route to Fabricate Uniform Upconversion Luminescent Gadolinium Oxide Hollow Spheres

Uniform upconversion luminescent gadolinium oxide hollow spheres were successfully synthesized via a homogeneous precipitation method with carbon spheres as template followed by a calcination process. During the annealing process, the carbon spheres template can be effectively removed and the amorphous precursor has converted to crystalline Gd2O3, which can be confirmed by the XRD and TG-DSC analysis. SEM and TEM images indicate that the Gd2O3 hollow spheres with diameters of 300-400 nm are uniform in size and distribution. The rare earth activator ions Ln3+-doped Gd2O3 hollow spheres exhibit intense upconversion luminescence with different colors under 980 nm light excitation, which may find potential applications in the fields such as drug delivery or biological labeling. Moreover, the upconversion luminescent mechanisms of the hollow spherical phosphors were investigated in detail.

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

► Uniform and size-controlled lanthanide-doped pure cubic phase Y 2 O 3 hollow microspheres. ► Bright up-conversion red, green, blue emission with high purity. ► Intense high-purity red down-conversion light emission. ► The energy transfer from Tb 3+ to Eu 3+ ions. Lanthanide-doped uniform pure cubic phase Y 2 O 3 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, Yb 3+ /Er 3+ , Er 3+ , Yb 3+ /Tm 3+ -doped Y 2 O 3 hollow microspheres emit bright upconversion red, green, blue light with high purity, respectively, while Eu 3+ , Eu 3+ /Tb 3+ -doped Y 2 O 3 hollow microspheres exhibit intense downconversion red light under the excitation of 254 nm ultraviolet light. Especially, the 610 nm emission intensity of Eu 3+ in the Eu 3+ /Tb 3+ -codoped Y 2 O 3 hollow microspheres is almost 5 times of that in the Y 2 O 3 :Eu 3+ hollow microspheres indicating the occurring of the energy transfer from Tb 3+ to Eu 3+ ions.

Preparation and Up-Conversion Luminescence of Hollow La2O3:Ln (Ln = Yb/Er, Yb/Ho) Microspheres

Hollow La(2)O(3):Ln (Ln = Yb/Er, Yb/Ho) microspheres with up-conversion (UC) luminescence properties were successfully synthesized via a facile sacrificial template method by employing carbon spheres as hard templates followed by a subsequent heating process. The structure, morphology, formation process, and fluorescent properties are well investigated by various techniques. The results indicate that the hollow La(2)O(3):Ln microspheres can be well indexed to the hexagonal La(2)O(3) phase. The hollow La(2)O(3):Ln microspheres with uniform diameter of about 270 nm maintain the spherical morphology and good dispersion of the carbon spheres template. The shell of the hollow microspheres consists of numerous nanocrystals with the thickness of approximately 40 nm. Moreover, the possible formation mechanism of evolution from the carbon spheres to the amorphous precursor and to the final hollow La(2)O(3):Ln microspheres has also been proposed. The Yb/Er and Yb/Ho codoped La(2)O(3) hollow spheres exhibit bright up-conversion luminescence with different colors derived from different activators under the 980 nm NIR laser excitation. Furthermore, the doping concentration of the Yb(3+) is optimized under fixed concentration of Er(3+)/Ho(3+). This material may find potential applications in drug delivery, hydrogen and Li ion storage, and luminescent displays based on the uniform hollow structure, dimension, and UC luminescence properties.

Influence of carbon templates and Yb 3+ concentration on red and green luminescence of uniform Y 2O 3:Yb/Er hollow microspheres

Uniform Yb 3+ and Er 3+-codoped Y 2O 3 hollow microspheres were synthesized via urea co-precipitation using carbon spheres as templates. Intense red emission ( 4F 9/2→ 4I 15/2) and weak green emission ( 2H 11/2, 4S 3/2→ 4I 15/2) of Er 3+ were observed for the Yb 3+ and Er 3+-codoped Y 2O 3 hollow microspheres under 980 nm infrared excitation. The integrated intensity of visible emission and the ratio of red to green were found to be strongly dependent on the amount of carbon sphere templates and the concentration of Yb 3+ ions. The amount of carbon sphere templates also plays an important role in adjusting the size of crystallite. Multi-phonon relaxation resulted from the absorbents (OH − and CO 3 2−) on the surface of the crystallite, and efficient occur of energy transfer processes and cross-relaxation between Er 3+ and Yb 3+ are responsible for the enhancement of intensity ratio of red to green emission. Interestingly, for higher concentration of Yb 3+ ions, the green emission is assigned to a three-phonon process in Y 2O 3:Yb/Er hollow microspheres, which also could result in the increase of the red to green emission ratio. An explanation to account for these behaviors was presented.

Preparation of Three Different Sphere-Like Au/CeO<sub>2</sub> Catalysts and their Activity for the CO Oxidation

Three different CeO2 sphere nanomaterials (hollow sphere, flowerlike sphere, spherical cluster) were controllably synthesized by carbon sphere template method, hydrothermal and solvothermal method respectively. Then 2.5 wt% Au was doped on the supports by the deposition precipitation method and Au/CeO2 catalysts with three different morphologies were obtained. Composition, morphology and structure of these catalysts were characterized by the techniques of XRD, Raman, TPR, SEM and TEM, and the activity for CO oxidation of the catalysts was investigated. The catalytic test results indicated that the addition of Au could remarkably improve catalytic performance on CO oxidation. The activities of the three catalysts differ largely, the flowerlike Au/CeO2 catalyst had the highest activity for CO oxidation and its T100% was 29°C. The mechanism for the different activity of the catalysts was investigated. H2-TPR result indicated flowerlike had a more intensive peak at 125°C than others and it implied more reducible Au species in this case, that plays a vital role in the CO oxidation.

Porous α-Fe 2O 3 hollow microspheres and their application for acetone sensor

Porous α-Fe 2O 3 hollow microspheres were synthesized through a simple and efficient carbon sphere template method. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and N 2 adsorption–desorption. Structural characterization indicated that as-prepared α -Fe 2O 3 hollow microspheres had porous structure with around 200 nm in diameter and thin shell about 10 nm thick. The average pore size and Brunauer–Emmett–Teller specific surface area of α-Fe 2O 3 hollow microspheres were 6.5 nm and 111.6 m 2/g, respectively. The gas sensing behavior investigation showed that as-synthesized α-Fe 2O 3 hollow microspheres exhibited very good gas sensing property to acetone vapor.

SnO2 monolayer porous hollow spheres as a gas sensor

The authors report on gas sensing properties ofSnO2 hollow spheres with diverse microstructures, which are synthesized through controlled precipitationof Sn(OH)4 layers on carbon sphere templates, followed by heat treatment at differenttemperatures. Hollow spheres derived at 973 K consist of monolayerSnO2 grains, which lead to a huge activated surface area. The sensitivity of sensors based onSnO2 monolayer hollow spheres is up to 51 at 100 ppm ethanol, which is much higher than that oftwo other samples. We attribute this enhancement mostly to the enhanced depletion effectarising from the increased exposed surface. Our results suggest a direction forimproving the performance of gas sensors by using monolayer porous hollow spheres.

Porous ceria hollow microspheres: Synthesis and characterization

Porous hollow microspheres of crystalline ceria were synthesized via a simple carbon sphere template method. The as-synthesized products were characterized by techniques of XRD, XPS, SEM, TEM and N 2 adsorption–desorption. Structural characterization indicated that as-prepared ceria hollow microspheres (150 nm in diameter) possess porous structure (average pore diameter of 6.5 nm), high surface area (144.1 m 2/g), large pore volume (0.23 cm 3 g −1) and thin shell (16 nm in thickness) composed of small nanoparticles (mean particle diameter of 4.9 nm). It is expected that as-prepared ceria hollow microspheres have potential applications in several fields as catalysts, catalyst supports, chemical sensors, storage hydrogen devices and optical or electrical materials. A possible mechanism for the formation of ceria hollow spheres was discussed in detail.

Bottom-Up Routes to Porous Silicon Carbide

We report on constructive methods providing a large range of high purity porous SiC products. All methods are based on modified sol-gel processes combined with carbothermal re¬duction. We obtain monodisperse regular pores of well defined diameters by using carbon sphere templates which are removed after SiC infiltration. A different way is a sol-gel based conversion of graphite bodies into SiC, which transfers the porosity from the graphite matrix into the final SiC product. Thus a large variety of porosity features are available, originating either from natural poro¬sity of graphite or from priorly created nano-/ microstructures in the carbonaceous base material. Whereas all our pristine porous sol-gel derived silicon carbide products are semi-insulating, doping is possible, during the growth to modifiy the electrical and optical properties.

Highly sensitive gas sensors based on hollow SnO 2 spheres prepared by carbon sphere template method

Hollow SnO 2 spheres were prepared in dimethylfomamide (DMF) by controlled hydrolysis of SnCl 2 using newly made carbon microspheres as templates. The phase composition and morphology of the material particles were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The gas sensing properties of sensors based on the hollow SnO 2 spheres were investigated. It was found that the sensor exhibited good performances, characterized by high response, good selectivity and very short response time to dilute (C 2H 5) 3N operating at 150 °C, especially, the response to 1 ppb (C 2H 5) 3N attained 7.1 at 150 °C. It was noteworthy that the response to 0.1 ppm C 2H 5OH of the sensor was 2.7 at 250 °C.