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.     

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.     

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.     

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.     

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.     

Magnetic and porous nanospheres from ultrasonic spray pyrolysis

We have used an inexpensive high-frequency ultrasound generator from a household humidifier to create a useful source for ultrasonic spray pyrolysis and produced submicrometer silica particles that are porous on the nanometer scale. By using two heated zones, we first initiate polymerization of organic monomers in the presence of silica colloid, which creates in situ a composite of silica with an organic polymer, followed by a second heating to pyrolyze and remove the polymer. The morphology and surface area of the final porous silica are controlled by varying the silica-to-organic monomer ratio. In a single flow process, ferromagnetic cobalt nanoparticles can be easily encapsulated in the porous silica, and the resulting nanospheres are extremely resistant to air oxidation. Products were characterized by SEM, (S)TEM, EDS, XPS, and SQUID.     

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.     

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.     

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.     

Thermal behaviour of precursors for CuInS2 thin films deposited by spray pyrolysis

The thermal decomposition of precursors for copper indium disulphide (CuInS₂) thin films obtained by drying aqueous solutions of copper chloride (CuCl₂), indium chloride (InCl₃) and thiourea (SC(NH₂)₂) at the Cu:In:S molar ratios of 1:1:3 (1) and 1:1:6 (2) was monitored by simultaneous thermogravimetry /differential thermal analysis/ evolved gas analysis-mass spectrometry (TG/DTA/EGA-MS) measurements in a dynamic 80 %Ar + 20 %O₂ atmosphere. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to characterise the dried precursors and products of the thermal decomposition. The precursors 1 and 2 are mixtures of copper and indium chloride thiourea complex compounds, whilst 1 can also contain unreacted InCl₃. The thermal degradation of 1 and 2 in the temperature range of 30–800 °C consists of six steps with a total mass loss of 71.5 and 89.8 %, respectively. According to XRD, CuInS₂ is formed below 300 °C. Decomposition of 1 and 2 is completed at 620 and 600 °C, respectively. The final decomposition product of 1 at 800 °C consists of a mixture of In₂O₃ and CuO phases, whilst 2 consists of In₂O₃, CuO and Cu₂In₂O₅ phases. EGA by MS revealed the release of CS₂, NH₃, H₂NCN and HNCS, which upon their oxidation also yield COS, SO₂, HCN and CO₂.     

Porous microfibers and microhoneycombs synthesized by ice templating

Recently we introduced the “ice templating” method, a new method which allows the synthesis of nanoporous materials with unique morphology, such as microfibers and microhoneycombs. In this method, materials are synthesized by freezing their parent hydrosols or hydrogels unidirectionally. Ice crystals which grow within the precursor during freezing act as the template. Therefore, the template can be easily removed through simple thawing and drying, which is a unique and beneficial feature of this method. This paper will first describe the outline of this new method and next, the details about methods to control the dimensions of the materials obtained through it. Comments about the range of applicability of this method will also be provided.     

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.     

Amperometric CO<Subscript>2</Subscript> gas sensor based on interconnected web-like nanoparticles of La<Subscript>2</Subscript>O<Subscript>3</Subscript> synthesized by ultrasonic spray pyrolysis

Thin films of La₂O₃ were deposited onto glass substrates by ultrasonic spray pyrolysis. Their structural and morphological properties were characterized by X-ray diffraction, Fourier transform Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photo-electron spectroscopy, Brunauer-Emmett-Teller and optical absorption techniques. The sensor displays superior CO₂ gas sensing performance at a low operating temperature of 498 K. The signal change on exposure to 300 ppm of CO₂ is about 75%, and the signal only drops to 91% after 30 days of operation.

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Graphical abstract Schematic diagram of the CO₂ gas sensing mechanism of an interconnected web-like La₂O₃ nanostructure in presence of 300 ppm of CO₂ gas and at an operating temperature of 498 K.

     

RuO2/Co3O4 thin films prepared by spray pyrolysis technique for supercapacitors

RuO₂/Co₃O₄ thin films with different RuO₂ content were successfully prepared on fluorine-doped tin oxide coated glass plate substrates by spray pyrolysis method, and their capacitive behavior was investigated. Electrochemical property was performed by cyclic voltammetry, constant current charge/discharge, and electrochemical impedance spectra. The capacitive performance of RuO₂/Co₃O₄ thin films with different RuO₂ content corresponded to a contribution from a main pseudocapacitance and an additional electric double-layer capacitance. The specific capacitance of pure Co₃O₄, 15.5%, 35.6%, and 62.3% RuO₂ composites at the current density of 0.2 A g⁻¹ were 394 ± 8, 453 ± 9, 520 ± 10, and 690 ± 14 F g⁻¹, respectively; 62.3% RuO₂ composite presented the highest specific capacitance value at various current densities, whereas 35.6% RuO₂ composite exhibited not only the largest specific capacitance contribution from RuO₂ (C _sp ^RuO2) at the current density of 0.5, 1.0, 1.5, and 2.0 A g⁻¹ but also the highest specific capacitance retention ratio (46.3 ± 2.8%) at the current density ranging from 0.2 to 2.0 A g⁻¹. Electrochemical impedance spectra showed that the contact resistance dropped gradually with the decrease of RuO₂ content, and the charge-transfer resistance (R _ct) increased gradually with the decrease of RuO₂ content.     

Characterization of Al/Al2O3/NiOx solar absorber obtained by spray pyrolysis

The aim of this paper is to obtain high efficient and inexpensive spectral selective solar absorbers, for solar thermal flat plat collectors using a simple technique – spray pyrolysis deposition (SPD). To achieve maximum solar absorptance and minimum thermal emittance, the following parameters are optimized: the precursor solution concentration and composition, substrate temperature and annealing treatment. The structural and morphological properties of the films were investigated by X-ray diffraction, atomic force microscopy and contact angle measurements. The thermal emittance and solar absorptance of as-deposited films were correlated with the chemical composition, crystalline structure and morphology. The results prove that coatings with excellent spectral selective properties (normal solar absorptance of 0.92 and a normal thermal emittance of 0.03) can be obtained by SPD.     

聚合物前驱体热解制备SiC纳米线研究

采用催化剂辅助聚合物前驱体热解工艺制备出宏量碳化硅纳米线(Si CNW),研究了基底材料、热处理温度及催化剂加载量等参数对所制备Si CNW微观结构形貌的影响规律.借助扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射分析(XRD)等分析测试手段对Si CNW的晶体结构和微观形貌进行表征,并分析了其生长机制.研究结果表明:制备的Si CNW为面心立方单晶结构的β-Si C,平均直径约为400 nm.随着热处理温度的提高,Si CNW的形貌由弯曲状生长转变为直线状生长,纳米线的直径也随之增加,在高温出现链珠状形貌纳米线;随着催化剂加载量的增加,纳米线的直径逐渐提高,产量却有所减小.纳米线的生长过程主要遵循VLS机制.当热解温度为1 600℃,基底材料为碳纤维布,催化剂加载量为5%(质量分数)时制备的Si C纳米线的直径、数量和分布状况较为理想.     

表面活性剂辅助水热制备形貌结构可控的MoS2及其蒽加氢性能

随着原油资源重质化和劣质化的加剧以及对清洁燃料油品需求的不断增加,将重质油加工成清洁燃料成为现代炼厂面临的挑战.悬浮床加氢是重质油转化为清洁液体燃料的先进技术,其核心难题是高效加氢催化剂的开发.MoS2在石油化工领域油品加氢提质研究中表现出非常好的催化加氢性能.MoS2晶体结构中有两种面:沿S-Mo-S层间的剥离面,又称基面,化学性质稳定;沿Mo-S的断裂面,又称棱面,具有大量的不饱和键,化学性质不稳定,可做催化活性中心.由于MoS2结构和形貌对其物理化学性能有重要影响,所以通过合理设计和调控MoS2的结构和形貌可增加暴露的催化活性位,进而改善其催化性能.本文以七钼酸铵和硫代乙酰胺为原料,水合肼做还原剂,采用不同表面活性剂(包括PEG,PVP,P123,SDS,AOT和CTAB)辅助的水热合成法制备了结构及形貌可控的MoS2,并提出不同表面活性剂条件下MoS2催化剂的生长机理,进一步研究了重油模型化合物稠环芳烃蒽的催化加氢性能.结果表明,在不同表面活性剂辅助的条件下分别制得了由MoS2纳米片组装而成的球形、块状和花状的MoS2产物;通过改变表面活性剂种类可调变MoS2纳米片的长度、堆积层数、层间距以及最终产物的形貌.在PEG或PVP辅助下得到了球形MoS2产物,其中MoS2纳米片长<15 nm,堆积层数<6.在PEG辅助下制备的球形MoS2粒径约为250 nm,尺寸均一且分散性好.在PVP辅助下MoS2粒径在200–450 nm,粒径分布范围宽且有明显团聚.在P123或SDS辅助下得到了团聚较明显的块状微米级MoS2产物.在P123辅助下得到的MoS2纳米片长<15 nm,层数<6.在SDS辅助下制备的MoS2纳米片长>20 nm,堆积层数>8.在AOT或CTAB辅助下得到团聚比较严重的花状微米级MoS2产物,其中MoS2纳米片长>20 nm,堆积层数>8.另外,水热反应过程中,高温高压的环境促进了反应体系中游离的NH4+插入到MoS2层状结构中,导致MoS2纳米片层间距增大.基于此,本文提出了不同表面活性剂辅助的水热过程中不同结构和形貌MoS2产物的形成机理.对不同结构和形貌的MoS2样品进行了悬浮床蒽加氢催化性能评价.结果表明,PEG辅助制备的MoS2催化剂具有最高催化加氢活性.该MoS2催化剂中纳米片层短,堆积层数少,暴露了更多的加氢活性位.单分散的球形MoS2颗粒粒径小,分散性好,有利于加氢活性位的充分暴露,进而表现出较好的催化性能.本文所采用的表面活性剂辅助的水热法为可控合成不同结构和形貌的过渡金属硫化物提供了有效指导和借鉴.     

Hydroxyapatite of platelet morphology synthesized by ultrasonic precipitation from solution

Hydroxyapatite (HA) synthesis by precipitation with urea from aqueous solutions of calcium nitrate and ammonium hydrogenphosphate is studied. Ultrasonication during the synthesis decreases the size of platelet HA crystals from several micrometers to 200–300 nm. At low calcium concentrations in solution, the crystallizing phase is carbonate-hydroxyapatite, whereas at high calcium concentrations, octacalcium phosphate (OCP) precedes hydroxyapatite crystallization.     

Self-Assembly Approach Towards MoS2-Embedded Hierarchical Porous Carbons for Enhanced Electrocatalytic Hydrogen Evolution

Transition metal-based nanoparticle-embedded carbon materials have received increasing attention for constructing next-generation electrochemical catalysts for energy storage and conversion. However, designing hybrid carbon materials with controllable hierarchical micro/mesoporous structures, excellent dispersion of metal nanoparticles, and multiple heteroatom-doping remains challenging. Here, a novel pyridinium-containing ionic hypercrosslinked micellar frameworks (IHMFs) prepared from the core–shell unimicelle of s-poly(tert-butyl acrylate)-b-poly(4-bromomethyl) styrene (s-PtBA-b-PBMS) and linear poly(4-vinylpyridine) were used as self-sacrificial templates for confined growth of molybdenum disulfide (MoS₂) inside cationic IHMFs through electrostatic interaction. After pyrolysis, MoS₂-anchored nitrogen-doped porous carbons possessing tunable hierarchical micro/mesoporous structures and favorable distributions of MoS₂ nanoparticles exhibited excellent electrocatalytic activity for hydrogen evolution reaction as well as small Tafel slope of 66.7 mV dec⁻¹, low onset potential, and excellent cycling stability under acidic condition. Crucially, hierarchical micro/mesoporous structure and high surface area could boost their catalytic hydrogen evolution performance. This approach provides a novel route for preparation of micro/mesoporous hybrid carbon materials with confined transition metal nanoparticles for electrochemical energy conversion.