Porous MoS2 synthesized by ultrasonic spray pyrolysis

The hydrodesulfurization (HDS) activity of molybdenum sulfide-based catalysts is localized to the edges of this layered solid and is, therefore, highly dependent on the technique used to prepare the material. Here, ultrasonic spray pyrolysis (USP) was used to synthesize porous, nanostructured MoS2. Low surface area powders, not useful for catalysis, are generally produced by USP. This work shows that when combined with a dissolvable template, USP is capable of producing high surface area materials. An aqueous solution of ammonium tetrathiomolybdate and colloidal silica was nebulized and pyrolyzed to give a MoS2/SiO2 composite material. Leaching with HF removed the sacrificial SiO2, resulting in a highly porous MoS2 network with surface areas as high as 250 m2/g. Cobalt-promoted MoS2 networks were also synthesized. The thiophene HDS activities of these materials were substantially higher than those of unsupported MoS2 and RuS2 standards, illustrating the enhanced dispersion of the HDS active phase achieved by this synthetic technique.     

Porous carbon powders prepared by ultrasonic spray pyrolysis

New, thermally robust meso- and macroporous carbon powders were prepared by ultrasonic spray pyrolysis (USP) of aqueous solutions using an inexpensive high-frequency ultrasound generator from a household humidifier. We choose our molecular precursors rationally, so that the expected decomposition pathways produce only remnant carbon atoms. Specifically, our rational design criterion led to halo-organic carboxylate salts, whose pyrolysis yields well-defined carbon solids with a temporary template being generated in situ, simply an inorganic salt, which is easily dissolved during aqueous workup. The materials have been characterized by SEM, TEM, XRD, 13C NMR MAS, XPS, FTIR spectroscopy, and BET surface area measurements. Changing the alkali metal alters the morphology and pore structure of the final material, which can be explained in terms of the observed differences in the DSC and TGA of the various precursors. This preparatory method provides an extremely facile and versatile method for the generation of meso- and macroporous carbons.     

Solar photocatalytic activities of porous Nb-doped TiO2 microspheres prepared by ultrasonic spray pyrolysis

Ultrasonic spray pyrolysis method was used to prepare Nb-doped TiO₂ porous microspheres with an average diameter of 500 nm for solar photocatalytic applications. The effect of Nb-doping on morphology, structure, surface area, as well as spectral absorption properties of TiO₂ microspheres was investigated with SEM, TEM, XRD, Raman spectra, BET, and UV-Vis absorption spectra. The Nb-doping decreased the grain size of TiO₂ porous microsphere, and influenced its surface area and pore size distribution dependent on the doping concentration, but changed negligibly the morphology and size of TiO₂ microspheres. Moreover, the Nb-doping was observed to extend the spectral absorption of TiO₂ into visible spectrum, and the absorption onset was red-shifted for about 88 nm at a doping level of 5% compared to pristine TiO₂ microspheres. Under solar or visible irradiation, Nb-doped TiO₂ microspheres showed higher photocatalytic activity for methylene blue degradation compared with TiO₂ microspheres, which could be ascribed to the extended light absorption range and the suppression of electron-hole pair recombination.     

Thin films of ZnO:M synthesized by ultrasonic spray pyrolysis

High optical quality ZnO:M@Si nanocomposites (where M is the doping element) were obtained by ultrasonic spray pyrolysis. The variation of experimental conditions, the use of various precursors and dopants demonstrated that the morphology of zinc oxide nanoparticles is mainly determined by the sort of the doping element. The luminescence spectra confirm indirectly the isomorphous incorporation of the dopant ions into the zinc oxide lattice.     

Designing of nanostructured hollow TiO2 spheres obtained by ultrasonic spray pyrolysis

Theoretical model describing the mechanism of droplet formation and structure of hollow TiO2 spheres prepared by the process of ultrasonic spray pyrolysis, using colloidal solution consisting of the 2.5-nm TiO2 nanoparticles as a precursor, is developed. The proposed model quantitatively defines each line in the size distribution spectrum. The mechanism of droplet formation and/or particle genesis is fully determined by harmonization between the physical fields inherent to the system as the consequence of its physical characteristics: external, e.g., ultrasound, and internal. Agreement between theoretically obtained basic structural parameters (size distribution and geometry) and experimentally determined values was found.     

Synthesis and characterization of alumina- and zirconia-based powders obtained by the ultrasonic spray pyrolysis

The ultrasonic spray pyrolysis (USP) technique was used for synthesis of alumina- and zirconia-based powders. The starting agents were aqueous solutions, atomized by the ultrasonic spray generator and pyrolized in the furnace under the open-air conditions. The powders prepared by USP were in the form of solid and hollow aggregates (spheres) consisted of nanosize amorphous grains as determined by the microscopy and the X-ray diffraction techniques. The alumina-based powders were consolidated by the pulse plasma sintering resulting in single-phase materials. Different behavior of solid and hollow particles during the isostatic sintering is found; a higher degree of deformation of spheres is observed in the second case.     

Synthesis of spherical porous carbon by spray pyrolysis and its application in Li-S batteries

A spherical porous carbon (SPC) with high specific surface area is prepared by spray pyrolysis at 800 °C followed by removing silica template. The prepared SPC is employed as a conductive matrix in the sulfur cathode (S-SPC) for lithium–sulfur secondary batteries. The BET surface area of the prepared SPC sample is as high as 1,133 m² g^?1 and the total pore volume is 2.75 cm³ g^?1. The electrochemical evaluations including charge–discharge tests, cyclic voltammograms (CV), and electrochemical impedance spectrum suggest that the prepared S-SPC composite presents superior electrochemical stability when compared to the S-SP cathode. The as-prepared S-SPC composite shows improved cycle performance. The reversible discharge capacity is about 637 mAh g^?1 after 50 cycles, which is much better than that of the as-prepared sulfur–Super P carbon black composite. It may be attributed to the high porosity and excellent conductive structure of the SPC.     

Synthesis of porous wires from directed assemblies of nanospheres

A method is reported for the fabrication of wires with extended pore structures. Nanospheres are initially infiltrated into the one-dimensional channels of alumina or polymer porous membranes. Metal is then electrochemically deposited within the channels. Removal of the membrane and nanospheres results in porous wires. The production of 1-mum diameter wires with 300- or 500-nm diameter pores and 300-nm diameter wires with 140-nm pores illustrates the utility of this approach. Contacts between the spheres and the channel wall result in openings on the surface of the wires, and contacts between the spheres themselves produce openings between adjacent pores. Some short-range ordering of the spheres within the channels, as reflected in the wire pore structure, is evident. Characterization of the porous wires by electron microscopy is presented, and the potential applications of materials is discussed.     

Battery performance of nanostructured lithium manganese oxide synthesized by ultrasonic spray pyrolysis at elevated temperature

Nanostructured lithium manganese oxide with spherical particles was synthesized via ultrasonic spray pyrolysis technique. The material shows a pronounced stability upon prolonged cycling at room temperature at high charge–discharge rates up to 10C. The electrochemical performance of the cell at elevated temperature was remarkably improved by addition of AlPO₄ to the electrolyte. The AC impedance spectroscopy study showed the interface stabilization by the AlPO₄ additives and the suppression of the interface impedance development upon prolonged cycling.     

Visible light-induced water oxidation on mesoscopic alpha-Fe2O3 films made by ultrasonic spray pyrolysis

Alpha-Fe(2)O(3) films having a mesoscopic leaflet type structure were produced for the first time by ultrasonic spray pyrolysis (USP) to explore their potential as oxygen-evolving photoanodes. The target of these studies is to use translucent hematite films deposited on conducting fluorine doped tin oxide (FTO) glass as top electrodes in a tandem cell that accomplishes the cleavage of water into hydrogen and oxygen by sunlight. The properties of layers made by USP were compared to those deposited by conventional spray pyrolysis (SP). Although both types of films show similar XRD and UV-visible and Raman spectra, they differ greatly in their morphology. The mesoscopic alpha-Fe(2)O(3) layers produced by USP consist mainly of 100 nm-sized platelets with a thickness of 5-10 nm. These nanosheets are oriented mainly perpendicularly to the FTO support, their flat surface exposing (001) facets. The mesoscopic leaflet structure has the advantage that it allows for efficient harvesting of visible light, while offering at the same time the very short distance required for the photogenerated holes to reach the electrolyte interface before recombining with conduction band electrons. This allows for water oxidation by the valence band holes even though their diffusion length is only a few nanometers. Distances are longer in the particles produced by SP favoring recombination of photoinduced charge carriers. Open-circuit photovoltage measurements indicate a lower surface state density for the nanoplatelets as compared to the round particles. These factors explain the much higher photoactivity of the USP compared to the SP deposited alpha-Fe(2)O(3) layers. Addition of hydrogen peroxide to the alkaline electrolyte further improves the photocurrent-voltage characteristics of films generated by USP indicating the hole transfer from the valence band of the semiconductor oxide to the adsorbed water to be the rate-limiting kinetic step in the oxygen generation reaction.     

Core-shell microspherical Ti(1-x)Zr(x)O2 solid solution photocatalysts directly from ultrasonic spray pyrolysis

A series of Ti(1-x)Zr(x)O(2) solid solutions photocatalysts (x = 0.000, 0.045, 0.090, 0.135, and 0.180) was directly obtained by an ultrasonic spray pyrolysis method. Compared with previous methods for solid solutions, our preparation was very fast. The resulting samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, nitrogen adsorption, and UV-vis diffuse reflectance spectroscopy. The characterizations revealed core-shell spherical structures of the resulting solid solutions. We evaluated photocatalytic activities of the solid solutions on degradation of rhodamine B in aqueous solution under simulated solar light. It was found that Ti(0.91)Zr(0.09)O(2) solid solution exhibited the highest photocatalytic activity among all the as-prepared samples. Its activity was much higher than that of P25. The formation mechanism of core-shell spherical structures was proposed. Moreover, we successfully extended this method to prepare microspheres of ceria and ceria-zirconia solid solutions. We think this general method may be easily scaled up for industrial production of microspherical solid solutions photocatalysts and catalysts.     

Synthesis of porous ZnO nanospheres for gas sensor and photocatalysis

Monodispersed porous ZnO nanospheres with diameters about 400–600 nm were successfully fabricated by a facile and effective cationic surfactant assisted selective etching strategy. The as-synthesized ZnO materials were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N₂ adsorption–desorption. These samples were used as the gas sensor, showing the high, stable and fast response to acetone, revealing the potential application as gas sensor to detect acetone. In addition, the photocatalytic degradation property of the porous ZnO nanospheres for methyl orange (MO) under UV irradiation was investigated. The degradation efficiency of MO reaches 96 % of the porous ZnO samples after 50 min of UV-light irradiation.     

One-step catalyst-free generation of carbon nanospheres via laser-induced pyrolysis of anthracene

Carbon nanospheres with diameters between 100 and 400 nm have been successfully synthesized via low-power laser-assisted pyrolysis of anthracene in a nitrogen atmosphere. The developed facile route yields homogeneous nanoparticles and requires no supplementary carbon feedstock or catalyst. The sharp thermal gradient afforded by the laser results in two kinds of carbon products that differ in crystallinity and mean particle size. Our detailed findings point to the carbon nanospheres being comprised of small-unclosed aromatic layers that are connected together by simple organic linkers. C-H bonds in the anthracene molecules are partially broken by the laser beam energy, and as the newly created large radicals aggregate, carbon nanospheres are formed.     

Preparation and properties of nitrogen-containing hollow carbon nanospheres by pyrolysis of polyaniline-lignosulfonate composites

Polyaniline-lignosulfonate composite hollow spheres were synthesized by using one-step unstirred polymerization of aniline in the presence of lignosulfonate. Novel nitrogen-containing hollow carbon nanospheres were prepared by direct pyrolysis of the polyaniline-lignosulfonate composite spheres at different temperatures under a nitrogen atmosphere. Thermal behavior of the polyaniline-lignosulfonate composite spheres was studied by TG-DTG, FTIR and element analyze instruments. The resultant carbon spheres were characterized by SEM, XRD and nitrogen adsorption-desorption measurement. It was found that the pyrolysis products of the polyaniline-lignosulfonate composite spheres were made up of uniform hollow carbon nanospheres with an average diameter of 135 nm. Furthermore, the hollow carbon nanospheres exhibit high BET surface area range from 381.6 m² g⁻¹ to 700.2 m² g⁻¹. The hollow carbon nanospheres could be used as adsorbents of papain. The papain adsorption capacity for the carbon spheres prepared at 1200 °C was up to 1161 mg g⁻¹ at an initial papain concentration of 10 mg mL⁻¹ at 25 °C.     

Photocatalytic formation of porous CdS/ZnO nanospheres and CdS nanotubes

It was found that ZnO nanocrystals have photocatalytic activity in the formation of CdS during the reduction of sulfur in the presence of cadmium acetate. It was shown that mesoporous spheres measuring 150–170 nm and consisting of CdS/ZnO particles measuring 5–8 nm are formed during the irradiation of ZnO particles measuring 5.5 nm. During the photodeposition of CdS by the action of light on nanorods produced by ultrasonic treatment of microcrystalline zinc oxide nanotubes of CdS 0.5–0.8 μm in length and 15–110 nm in internal diameter are formed. A mechanism, in which they appear at the ends of the ZnO nanorods and grow on the surface of the CdS/ZnO heterojunction, is proposed for the formation of the CdS nanotubes. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 215–219, July–August, 2007.     

XPS depth profile study of porous zirconia films deposited on stainless steel by spray pyrolysis: the problem of substrate corrosion

Zirconia (ZrO₂) films of tissue‐like structure and narrow pore size distribution have been deposited by spray pyrolysis using aqueous zirconyl chloride octahydrate (ZrOCl₂·8H₂O) precursor solutions. Stainless‐steel sheets, protected or unprotected by a ZnO barrier layer, have been used as the substrate material held at 473 K. The ZnO barrier layers have been deposited on the stainless steel held at 523 K by spray pyrolysis using a zinc acetate precursor. Their property of corrosion protection to stainless steel has been proved by electrochemical polarization measurements in 0.5 M NaCl solution. A complementary study of XPS (depth profiling, mapping) and x‐ray diffraction has shown that the unprotected steel substrates were corroded during ZrO₂ film post‐annealing in air at T ≥ 773 K, whereas steel substrates protected with a compact barrier layer of crystalline ZnO before ZrO₂ film deposition did not show surface corrosion even after annealing up to 997 K. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of porous C/Fe3O4 microspheres by spray pyrolysis with NaNO3 additive for lithium-ion battery applications

In this work, we successfully synthesized porous C/Fe₃O₄ microspheres by spray pyrolysis at 700ºC with a sodium nitrate (NaNO₃) additive in the precursor solution. Furthermore, we studied their electrochemical properties as anode material for Li-ion batteries. The systematic studies by various characterization techniques show that NaNO₃ catalyzes the carbonization of sucrose and enhances the crystallization of Fe₃O₄. Moreover, an aqueous etching can easily remove sodium compounds to produce porous C/Fe₃O₄ microspheres with large surface areas and pore volumes. The porous C/Fe₃O₄ microspheres exhibit a reversible capacity of ~780 mAh g^–1 in the initial cycles and ~520 mAh g^–1 after 30 cycles at a current density of 50 mA g^–1. Moreover, a reversible capacity of ~400 mAh g^–1 is attainable after 200 cycles, even at a high current density of 500 mA g^–1. The wide range of pores produced from the removal of sodium compounds might enable easy electrolyte penetration and facilitate fast Li-ion diffusion, while the N-doping can promote the electronic conductivity of the carbon. These features of porous C/Fe₃O₄ microspheres led to the improved electrochemical properties of this sample.

Graphical Abstract

     

Evaluation of the porous structure development of chars from pyrolysis of rice straw: Effects of pyrolysis temperature and heating rate

The effects of pyrolysis temperature and heating rate on the porous structure characteristics of rice straw chars were investigated. The pyrolysis was done at atmospheric pressure and at temperatures ranging from 600 to 1000 °C under low heating rate (LHR) and high heating rates (HHR) conditions. The chars were characterized by ultimate analysis, field emission scanning electron microscope (FESEM), helium density measurement and N₂ physisorption method. The results showed that temperature had obvious influence on the char porous characteristics. The char yield decreased by approximately 16% with increasing temperature from 600 to 1000 °C. The carbon structure shrinkage and pore narrowing occurred above 600 °C. The shrinkage of carbon skeleton increased by more than 22% with temperatures rising from 600 to 1000 °C. At HHR condition, progressive increases in porosity development with increasing pyrolysis temperature occurred, whereas a maximum porosity development appeared at 900 °C. The total surface area (S_total) and micropore surface area (S_micro) reached maximum values of 30.94 and 21.81 m²/g at 900 °C and decreased slightly at higher temperatures. The influence of heating rate on S_total and S_micro was less significant than that of pyrolysis temperature. The pore surface fractal dimension and average pore diameter showed a good linear relationship.     

The structural characteristics of Zn-Mn ferrite synthesized by spray pyrolysis

The applicability of IR spectroscopy in studies of the structural characteristics of the ferrite spinel phase was shown for Zn_0.5Mn_0.5Fe₂O₄ samples prepared by the pyrolysis of aerosols of aqueous solutions of metal nitrates. The IR spectra of synthesized (ZnMn)Fe₂O₄ ferrites, Fe₂O₃, ZnO, MnO, and Mn₂O₃ pure oxides, and mixtures of these oxides in the region of characteristic M-O stretching vibration and M-O-H bending vibration frequencies were compared to determine the degree of concentration and structural uniformity of the ferrite spinel phase.