Carbon Sphere Template Research Articles

Synthesis of Hollow Iron Oxide Nanospheres and Their Application to Gas Sensors

Hollow nanomaterials have attracted great interest because of their many applications in catalysis, nanoreactors, drug delivery systems, for lubrication and in gas sensors. Here, carbon sphere templates were prepared from glucose under hydrothermal conditions to facilitate the synthesis of hollow Fe2O3 nanospheres. Thermal decomposition of an iron precursor in benzylalcohol with the carbon spheres resulted in the deposition of Fe3O4 nanoparticles on the carbon sphere templates. The nanoparticles on the carbon surface naturally agglomerate and form a dense oxide shell during the calcination step, which produces typical Fe2O3 hollow structures. The gas sensing performance of the hollow Fe2O3 nanospheres was investigated at an operating temperature of 300 °C. The hollow Fe2O3 nanospheres showed high sensitivity (R = 10.766 at 1 ppm formaldehyde) with a linear response to formaldehyde gas concentration in the range of 0.8~2.4 ppm, and good selectivity to formaldehyde gas in volatile organic compounds, compared to commercial Fe2O3 nanoparticles.

Synthesis of Br-doped TiO2 hollow spheres with enhanced photocatalytic activity

The Br-doped hollow TiO2 photocatalysts were prepared by a simple hydrothermal process on the carbon sphere template following with calcination at 400 °C. The structure and properties of photocatalysts were characterized by X-ray diffraction, Raman spectrum, scanning electron microscope, transmission electron microscopy, N2 desorption–adsorption, UV–Vis spectroscopy, and X-ray photoelectron spectroscopy. The TiO2 hollow spheres are in diameter of 500 nm with shell thickness of 50 nm. The shell is composed of small anatase nanoparticles with size of about 10 nm. The TiO2 hollow spheres exhibit high crystalline and high surface area of 89.208 m2/g. With increasing content of Br doping, the band gap of TiO2 hollow spheres decreased from 2.85 to 1.75 eV. The formation of impurity band in the band gap would narrow the band gap and result in the red shift of absorption edge from 395 to 517 nm, which further enhances the photocatalytic activity. The appropriate Br doping improves the photocatlytic activity significantly. The TiO2 hollow spheres with 1.55% Br doping (0.5Br-TiO2) exhibit the highest photocatalytic activity under full light. More than 98% of RhB, MO, and MB can be photodegraded using 0.5Br-TiO2 with concentration of 10 mg/L in 40, 30, and 30 min, respectively. The degradation rate of Br-doped photocatalysts was 40% faster than undoped ones.

Carbon sphere templates for TiO2 hollow structures: Preparation, characterization and photocatalytic activity

TiO2 hollow structures (HS) were synthesized by carbon sphere template removal method. Nanometer sized carbon spheres (CS) were prepared by mild hydrothermal treatment of ordinary table sugar (sucrose). The size of these spheres can be controlled by the parameters of the hydrothermal treatment (e.g. time and pH). The obtained CSs were characterized by scanning electron microscopy (SEM), Raman spectroscopy, infrared spectroscopy (IR), X-ray diffraction (XRD) and thermogravimetry (TG). CSs were successfully coated with TiO2 via sol–gel method. The phase composition of the TiO2 hollow spheres were controlled by the annealing temperature during crystallization and CSs template removal. TiO2 hollow structures (HSs) were characterized by SEM, XRD, Raman spectroscopy, TG and energy-dispersive X-ray spectroscopy (EDX). Photocatalytic performance of the TiO2 HSs was evaluated by phenol degradation in a batch-type foam reactor under low powered UV‐A irradiation. The degradation reaction was followed by high‐performance liquid chromatography (HPLC) and total organic carbon (TOC) measurement techniques. Photocatalytic activity test results pointed out that increased rutile content up to a certain extent (resulting mixed phase anatase-rutile TiO2) effects advantageously the photocatalytic performance of TiO2 HSs and the unique morphology proved to enhance the photocatalytic activity (six times) as well as TOC removal efficiency (twelve times) compared to the sample which was prepared by the same method without the CSs.

Facile Synthesis and High Photocatalytic Degradation Performance of ZnO-SnO2 Hollow Spheres.

ZnO-SnO2 hollow spheres were successfully synthesized through a hydrothermal method-combined carbon sphere template. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). The average diameter of hollow spheres is about 150 nm. The photocatalytic activity of the as-prepared samples was investigated by photodegrading Rhodamine B. The results indicated that the photocatalytic activities of ZnO-SnO2 hollow spheres are higher than ZnO hollow spheres. The degradation efficiency of the hollow spheres could reach 99.85% within 40 min, while the ZnO hollow spheres need 50 min.

Highly enhanced acetone sensing performance of porous C-doped WO3 hollow spheres by carbon spheres as templates

WO3-based gas sensors have received considerable attention in breath acetone analysis for their great potential in the clinical diagnosis of diabetes. However, several key challenges, especially sensitivity, selectivity and stability, should be further addressed before WO3-based materials are capable of applying for acetone analysis. Herein, C-doped WO3 sensing materials were synthesized by coupling carbon sphere templates with post-heat treatment method. The resulting materials are composed mainly of ε-WO3, a phase with high selectivity to acetone, and featured with porous hollow sphere structure. The as-fabricated sensors based on the C-doped WO3 materials show high sensitivity to acetone down to 0.2ppm. By contrast, the sensors show substantially lower response to other gases including ethanol, methanol, toluene, NH3, NO and CO. In addition, the effect of the relative humidity (RH) on the sensing property was studied and it was found that the response distinction to acetone even at 90% RH was sufficient to separate diabetics from healthy people. More attractively, the ε-phase WO3 could maintain its acetone sensing activity at 350°C over 3 months, suggesting excellent long-term stability. The results gained herein may be useful for rational design of new types of highly selective and stable acetone sensing materials.

Controlled Synthesis of Hollow Manganese Oxide Nanocrystals.

Carbon spheres have been prepared from glucose under hydrothermal conditions to facilitate the synthesis of hollow manganese oxides. The phases of manganese oxide are controlled by changing annealing temperature of the manganese monoxide on a carbon sphere template. The particles on the carbon surface get an agglomeration and make dense oxide shell during the calcination step, which result in typical hollow structures. The electrochemical properties of hollow manganese oxides have been investigated to elucidate their relative catalytic activities.

ChemInform Abstract: Chemical Approach to a New Crystal Structure: Phase Control of Manganese Oxide on a Carbon Sphere Template.

AbstractHexagonal wurtzite MnO (space group P6mc) on a carbon sphere template is prepared by heating a slurry of Mn(acac)2 in benzylamine with carbon spheres (obtained from an aqueous glucose solution in an autoclave at 160—180 °C for 5—18 h) at 185 °C for 3 h under argon.

Preparation of Gd-doped TiO2 hollow spheres with enhanced photocatalytic performance

Using (C16H36O4)Ti, Gd2O3 and HNO3 as raw materials, TiO2 and TiO2:Gd3+ hollow spheres with different Gd dopant concentrations of 0.25, 0.5, 1, 1.5 and 2 mol% were obtained with the assistance of the carbon sphere templates. The morphology, structure, specific surface area and photocatalytic properties of the prepared hollow spheres were studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller and UV–Vis 2550 spectrophotometer, respectively. Several factors influencing the photocatalytic activities of the samples were studied, which include pH value of the solutions, Gd dopant concentrations, amount of the additive catalysts and types of the dyes. In this work, fabrication of TiO2:Gd3+ hollow spheres (b) was obtained with the assistance of the carbon sphere template (a). Characterization of the samples was also reported in this paper.

Catalyst Layer Architectures with Supportless Pt Hollow Spheres for Polymer Electrolyte Fuel Cells (PEFCs)

Supportless Pt black is an attractive oxygen reduction reaction (ORR) catalyst for polymer electrolyte fuel cells (PEFCs) due to its merits such as no concern of support corrosion at high potentials and high durability against Pt dissolution at frequent potential change conditions. However, when the Pt black catalysts were fabricated as MEAs the performance is still lower than the current Pt/C catalysts and they have difficulty in reducing Pt content in the MEAs. In the present study, we have prepared sub-micron size Pt hollow spheres as an alternative catalyst layer architecture for PEFC MEAs. The big Pt spheres were employed to make 3-dimensional catalyst layer architectures and to enhance oxygen transport in catalyst layers, and hollow type Pt was made to reduce Pt content and to facilitate water management. 200 nm Pt hollow spheres with 10 nm shell thickness were prepared using carbon sphere templates. The Pt hollow spheres revealed comparable ORR performance with commercial Pt/C catalyst in a half cell test. Catalyst layer fabrication was also performed using the catalysts by optimizing the catalyst slurries and its fuel cell performance at different operating conditions and durability will be discussed based on single cell test results.

An electrochemical sensing platform based on hollow mesoporous ZnO nanoglobules modified glassy carbon electrode: Selective detection of piperidine chemical

Hollow mesoporous ZnO nanoglobules were synthesized through carbon spheres template assisted sonochemical process followed by annealing at 600°C. The synthesized hollow mesoporous ZnO nanoglobules was applied as a working electrode or electron mediator electrode for the fabrication of reproducible, highly sensitive and reliable chemical sensors for the detection of piperidine chemical. The synthesized nanomaterials possessed the porous hollow globular morphology due to the radial arrangement of nanoparticles on the outer shell of nanoglobules. The formation of hollow mesoporous ZnO nanoglobules was confirmed by analyzing the structural, crystalline and the compositional properties. The electrochemical behavior was examined by performing the cyclic voltammetry using hollow mesoporous ZnO nanoglobules based glassy carbon electrode (GCE) towards the detection of piperidine chemical. The performance of piperidine chemical sensor based on hollow mesoporous ZnO nanoglobules GCE was analyzed by measuring the current (I)–voltage (V) characteristics of different piperidine concentrations in phosphate buffer solution. The hollow ZnO nanoglobules GCE based piperidine chemical sensor exhibited the high sensitivity of ∼59.9μAmM−1cm−2 and a detection limit of ∼3.3μM with a correlation coefficient (R) of ∼0.98782 and a short response time of 10s.

Synthesis, morphology, photoluminescence and photocatalytic properties of yolk–shell Au@Y2O3:Eu3+ sub-microspheres

Uniform yolk–shell Au@Y2O3:Eu3+ sub-microsphere phosphors were successfully prepared through urea-assisted homogeneous precipitation method by using carbon spheres as templates. The structure, morphology, photoluminescence and photocatalytic properties of the as-prepared Au@Y2O3:Eu3+ microspheres were subsequently investigated. The results indicate that the Y2O3:Eu3+ microspheres can be well indexed to the cubic Y2O3 phase. Furthermore, the Au@Y2O3:Eu3+ microsphere is able to maintain the spherical morphology and good dispersion of the carbon sphere template. The yolk–shell Au@Y2O3:Eu3+ spheres exhibit the bright luminescence of Eu3+. The photocatalysis of the Y2O3:Eu3+ shell and the Au core occur simultaneously, thereby significantly decreasing the absorbance of rhodamine B solutions. This work provides a strategy for inhibiting aggregation of noble metal nanoparticles during high-temperature calcinations and leaching of noble metal nanoparticles into a solution through a mesoporous shell. Ultimately, a multifunctional nanostructure was obtained by combining a specific metal core with an oxide shell.

TiO2/SnO2 double-shelled hollow spheres-highly efficient photocatalyst for the degradation of rhodamine B

TiO2/SnO2 double-shelled hollow spheres are successfully synthesized by two-step liquid-phase deposition method using carbon sphere templates. The formation process of TiO2/SnO2 hollow spheres is discussed. The samples are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis absorption spectroscopy. The behavior of photogenerated charges in the TiO2/SnO2 heterojunction structures has been investigated through surface photovoltage spectroscopy. The TiO2/SnO2 hollow spheres which are realized show significantly enhanced photocatalytic activities, with respect to the cases of SnO2 and TiO2 hollow spheres. Furthermore, TiO2/SnO2 hollow spheres show good recyclable photocatalytic activities.

Chemical approach to a new crystal structure: phase control of manganese oxide on a carbon sphere template.

The stabilization and growth of a non-native structure, hexagonal wurtzite MnO (h-MnO), is explored via kinetic control of manganese precursor on a carbon sphere template. MnO is most stable in the cubic rock-salt structure (c-MnO), and a number of studies have focused on the synthesis and properties of this rock-salt phase. However, h-MnO has not been fully characterized before our work. Prolonged heating at a relatively low temperature yields c-MnO, whereas rapid heating of the reaction mixture at reflux produces h-MnO in the presence of carbon spheres. The effect of benzyl amine concentration on the formation of two different oxidation states (c-MnO and t-Mn3O4) was examined as well. Moreover, the structural stability of the manganese oxides and phase transition of MnO in terms of the wurtzite to rock-salt structural transformation have been investigated.

CaO-based meshed hollow spheres for CO2 capture

This paper describes the synthesis of CaO-based meshed hollow spheres using colloidal carbon as a template via a urea hydrolysis method for CO2 absorption. The features of meshed hollow spheres and the CO2 absorption performance of the absorbent in calcinations/carbonation cycles were investigated employing scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), and thermo gravimetric analyzer (TGA). The absorbent had an excellent performance with a higher capacity and a better stability compared to the reference absorbents, which were prepared without using the carbon sphere templates or the urea hydrolysis. The initial capacity of the absorbent was about 75% that maintained 63% after the 28th cycle absorption/desorption process. It was suggested that the meshed hollow sphere structure was favorable for absorption capacity and stability of the absorbent due to the formation of uniform, disperse, and loose CaO particles.

Facile hard template approach for synthetic hectorite hollow microspheres

A facile route for the synthesis of synthetic hectorite hollow microspheres (SHHMS) having a diameter of 4–6µm and wall thickness of 30–50nm has been demonstrated. Carbon spheres obtained from the autogenic pyrolysis of polypropylene have been utilized as a template for the synthesis of SHHMS. The formation of the hectorite architecture was confirmed by X-ray diffraction and infrared spectroscopy. The scanning and transmission electron microscopic studies reveal their spherical and hollow nature. The morphology of the obtained product was dependent on the amount of carbon spheres template. The obtained SHHMS showed the mesoporous textural property with enhanced carbon dioxide adsorption capacity (19.2cm3/g) as compared to that of calcined hectorite (15.3cm3/g) at 303K.

High specific surface area LaMO3(M = Co, Mn) hollow spheres: synthesis, characterization and catalytic properties in methane combustion

LaMO3(M = Mn, Co) hollow spheres were synthesized by a carbon sphere template method, while a slow heating rate resulted in multishelled hollow spheres.

Facile one-pot synthesis of uniform TiO2–Ag hybrid hollow spheres with enhanced photocatalytic activity

TiO(2)-Ag hybrid hollow spheres (about 700 nm in diameter) with a highly uniform morphology and good structural stability were facilely prepared via a one-pot hydrothermal method, using carbon spheres as templates followed by an annealing treatment. Through this route, the as-prepared hybrid hollow spheres preserved the uniformity of the initial carbon sphere templates and the loading amount of the Ag nanocrystals can be conveniently varied or controlled by the concentration of the Ag precursor. The investigation of the photocatalytic ability demonstrated that the as-prepared TiO(2)-Ag hybrid hollow spheres possess excellent photocatalytic activity, superior to commercial TiO(2) nanoparticles (Degussa P25), for the degradation of rhodamine B (RhB) and methyl orange (MO) dyes under visible-light illumination. Furthermore, the ˙OH radicals formed during photocatalysis with different Ag content hybrids were revealed by means of a terephthalic acid fluorescence probe method, which uncovers that the Ag content in the TiO(2)-Ag hybrids was crucial to obtain an optimal synergistic effect between the Ag and TiO(2) for the degradation of organic pollutants. Accordingly, the optimum matching for the best photocatalytic activity was investigated thoroughly and a reasonable mechanism was also proposed.

Construction and enhanced gas sensing performances of CuO-modified α-Fe2O3 hybrid hollow spheres

Abstract The well-defined three-dimensional (3D) CuO-modified α-Fe 2 O 3 hybrid hollow sphere (HS) nanostructures, with thin shell of about 10 nm, were one-pot constructed by the facile carbon sphere template method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. Using several volatile organic compounds (VOCs) including methanol, ethanol and acetone as probe gases, gas sensing performance of the sensor based the prepared CuO-modified α-Fe 2 O 3 hybrid HSs was systematically investigated. The results showed that the CuO-modified α-Fe 2 O 3 HS sensor had a remarkably enhanced response to VOCs compared with the single α-Fe 2 O 3 HS sensor. The enhanced sensor properties could be attributed to the unique hollow structure with porous shell and the synergic electronic interaction between p-type CuO and n-type α-Fe 2 O 3 . The 3D hybrid HS sensor exhibited not only high response to ppm level VOCs, but also short response and recovery times within 10 s, demonstrating its potential application as gas sensor.

Solvothermal-assisted synthesis of hollow Ni 0.5 Zn 0.5 Fe 2 O 4 microspheres through carbon spheres templating

This Letter presents a facile solvothermal-assisted carbon spheres template method to fabricate hollow Ni 0.5 Zn 0.5 Fe 2 O 4 microspheres. The key strategy of the hollow structure is absorbing sol at the inside surface layer of pores in carbon templates driven by vigorous internal thermal motion of molecules. The formation mechanism of hollow structure can be attributed to Ostwald ripening. The thermogravimetric analysis results reveal that the presented method provides the possibilities to prepare hollow inorganic microspheres with a high productivity. A series of hollow structural inorganic materials can be prepared through the presented approach, and new opportunities will be opened up to control the structures, morphologies and particle sizes of nanomaterials, as well as their properties.

Synthesis, Characterization and Gas Sensing Properties of In(OH)3 and In2O3 Nanorods through Carbon Spheres Template Method

Poly-crystalline In(OH) 3 nanorods have been successfully prepared via a urea-based precipitation using the colloidal carbon spheres as the templates. After calcinations, the resulted In 2 O 3 nanorods with poly-crystalline structure were fabricated. Structure and morphology of the product were characterized by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The possible formation process was schemed. The sensor gas properties towards C 2 H 5 OH and CO were examined.