Synthesis of highly crystalline hexagonal cesium tungsten bronze nanoparticles by flame-assisted spray pyrolysis

Highly crystalline and hexagonal single-phase cesium tungsten bronze (Cs_0.32WO₃) nanoparticles were successfully synthesized by a flame-assisted spray pyrolysis followed by annealing under a reducing gas atmosphere. The resulting Cs_0.32WO₃ nanoparticles featured a pure hexagonal Cs_0.32WO₃ phase with a high crystallinity and homogeneous chemical composition. Unlike conventional methods, the proposed process in this paper has several advantages, including a short reaction time and the ability to yield products with high purity and good energy efficiency. Furthermore, the Cs_0.32WO₃ nanoparticles produced in this research showed a remarkable near-infrared shielding ability with a 97.7% cut-off at 1500?nm.     

Direct synthesis of highly crystalline transparent conducting oxide nanoparticles by low pressure spray pyrolysis

In this article, we firstly reported a general preparation method for the production of highly crystallized and single crystalline transparent conducting oxide (TCO) nanoparticles: tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), aluminum-doped zinc oxide (AZO), and gallium-doped zinc oxide (GZO). Low-pressure spray pyrolysis was applied by means of a modified-atomizer and preheated carrier gas. The effects of pyrolysis pressure, temperature and carrier gas temperature on the size and morphology of the synthesized TCO nanoparticles were systematically investigated. The synthesized TCO nanoparticles were 17 nm large with crystallite size of 8–11 nm. The resistivities of the formed pellets were measured and compared. These results showed that this method successfully produces various TCO nanoparticles using neither dispersing agents nor post-heating treatments, which allows rapid, continuous, single-step preparation.     

High rate flame synthesis of highly crystalline iron oxide nanorods

Single-step flame synthesis of iron oxide nanorods is performed using iron probes inserted into an opposed-flow methane oxy-flame. The high temperature reacting environment of the flame tends to convert elemental iron into a high density layer of iron oxide nanorods. The diameters of the iron oxide nanorods vary from 10 to 100?nm with a typical length of a few microns. The structural characterization performed shows that nanorods possess a highly ordered crystalline structure with parameters corresponding to cubic magnetite (Fe(3)O(4)) with the [100] direction oriented along the nanorod axis. Structural variations of straight nanorods such as bends, and T-branched and Y-branched shapes are frequently observed within the nanomaterials formed, opening pathways for synthesis of multidimensional, interconnected networks.     

Surfactant controlled synthesis of crystalline phosphovanadate nanorods

Phosphovanadate nanorods were obtained in a reaction of vanadium (V) oxide as a precursor and a cationic surfactant, dodecylpyridinium chloride, as structure directing template at pH ∼3 at room temperature. The composition and morphology of the nanorods was established by powder X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The obtained nanorods have diameters of 40-60 nm with lengths up to 1 μm. The effect of reaction parameters such as concentration of surfactant and pH of the solution on the growth of nanorods has been investigated. A plausible mechanism involving the coalescence of nanoparticle ‘seeds’ leading to one-dimensional nanorods is also discussed. The same reaction when performed under hydrothermal condition, keeping other reaction parameters unchanged, resulted in the formation of phosphovanadate nanospheres of diameter 10-15 nm.     

Nano-sized manganese oxide particles prepared by low-pressure spray pyrolysis using FEAG process

Nano-sized manganese oxide particles were prepared by low-pressure spray pyrolysis using the new type of liquid aerosol generator called as FEAG process. The particles prepared from polymeric precursors spray solution with organic additives had large size, hollow and fractured morphologies due to the gas evolution from the decomposition of the organic additives. The precursor particles with micron size, hollow and thin wall structures turned to nano-sized manganese oxide particles after post-treatment at temperatures of 700 and 800 °C. The optimum concentrations of citric acid (CA) and ethylene glycol (EG) to prepare the nano-sized manganese oxide particles by spray pyrolysis using the FEAG process were 0.3 M each. The manganese oxide particles prepared from the polymeric precursors spray solutions with high concentrations of CA and EG had spherical shape and porous morphologies.     

Direct synthesis of maghemite,magnetite and wustite nanoparticles by flame spray pyrolysis

Magnetic iron-oxide nanoparticles have been prepared by flame spray pyrolysis (FSP) under controlled atmosphere. This way controlled and direct flame synthesis of Fe₂O₃ (maghemite), Fe₃O₄ (magnetite) and FeO (wustite) particles is possible by a scalable process. The Fe oxidation state was controlled by varying the fuel to air ratio during combustion as well as by varying the valence state of the applied Fe precursor. The as-prepared materials were characterized by electron microscopy, nitrogen adsorption, X-ray diffraction and Raman spectroscopy. Magnetic properties were investigated with SQUID, which unravelled superparamagnetic behaviour for all materials and typical features for the corresponding crystal structures and particle sizes. Maximum magnetisation was achieved for a mixture of maghemite and magnetite.     

Effect of chloride ion on crystalline phase transition of iron oxide produced by ultrasonic spray pyrolysis

Ultrafine spherical Fe₂O₃ powders with controllable morphology and crystal phase were synthesized by ultrasonic spray pyrolysis. In this experiment, we chose three common ferric salts (Fe(NO₃)₃·9H₂O, FeSO₄·7H₂O or FeCl₂·4H₂O) as precursor solution and regulated the concentration of chlorine ion (Cl^?) in precursor solution to produce Fe₂O₃ particles. The morphology, crystal structure and magnetic property of prepared Fe₂O₃ particles were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vibrating sample magnetometer (VSM). The diameter of the obtained Fe₂O₃ products ranged from 0.2 to 2?μm. And the product obtained from FeCl₂ precursor solution was magnetic, which was composed of hexagonal α-Fe₂O₃ and cubic γ-Fe₂O₃ from XRD results. We also calculated the weight percent of α-Fe₂O₃ and γ-Fe₂O₃ in the product through XRD quantitative analysis. However, with the addition of Cl^? in Fe(NO₃)₃ or FeSO₄ precursor solution, the products turned from non-magnetic to magnetic, whose pure α-Fe₂O₃ phase became to α-Fe₂O₃ and γ-Fe₂O₃ multi-phase. Besides, the weight percent of γ-Fe₂O₃ and the amount of M_s increased with the Cl^? concentration in precursor solution improving. According to the research, it can be inferred that the presence of Cl^? inhibits the phase transition of γ-Fe₂O₃ to α-Fe₂O₃ at high temperature.     

Direct synthesis of strontium titanate phosphor particles with high luminescence by flame spray pyrolysis

SrTiO₃:Pr, Al phosphor particles with high luminescence intensities were directly prepared by flame spray pyrolysis without post-treatment. They had better crystallinity than those prepared by general spray pyrolysis with post-treatment and solid-state reaction methods. In addition, they had complete spherical shape and narrow size distribution. On the other hand, the particles prepared by general spray pyrolysis had irregular shape, and poorer brightness than those prepared by solid-state reaction method, while the particles prepared by flame spray pyrolysis had comparable photoluminescence and cathodoluminescence intensities with those of particles prepared by solid-state reaction method. The photoluminescence intensity of SrTiO₃:Pr, Al particles prepared by flame spray pyrolysis was as much as 4.7 times higher than that of particles prepared by general spray pyrolysis.     

Synthesis and characterization of crystalline hexagonal bipods of zinc oxide

The preparation of nano- and submicrometre-sized one-dimensional (1D) zinc oxides (ZnOs) from zinc nitrate was performed by precipitation with urea in two types of solvents (water and water/polyol mixtures). The influence of different polyols (ethylene glycol, diethylene glycol and tetraethylene glycol) on the size of the final particles (length and diameter) is presented for the first time. As well as the influence of the solvents used, the ratio of water/polyol, temperature, pH and time of synthesis was correlated with the size and morphology of the final particles. In all cases crystalline ZnO was synthesized in the form of hexagonal bipods. The morphological and crystalline properties of the samples obtained were characterized by SEM, IR, and XRD.     

Single step synthesis of indium tin oxide by ultrasonic spray and microwave assisted pyrolysis

Ultrafine indium tin oxide (ITO) powders were successfully synthesised by the combined methods of ultrasonic spray and microwave assisted pyrolysis, which is a single step, facile, rapid and continuous method without post-heating treatment. Crystallinity, morphology and microstructure of the samples were investigated by X-ray diffractometer, scanning electron microscope, transmission electron microscope, energy dispersive X-ray spectroscope, selected area electron diffraction pattern and laser grain size analyser. Results indicate that pure solid solution ITO ultrafine powders with homogeneous and narrow size distribution, highly dense and smooth surface morphology can be obtained under optimum conditions. Each uniform spherical particle consisted of many smaller crystallites with diameter of <10 nm.     

Direct synthesis of ultralong carbon nanotube bundles by spray pyrolysis and investigation of growth mechanism

A mass of ultralong aligned carbon nanotube (CNT) bundles up to about 8?mm in length was synthesized by utilizing the spray pyrolysis of ferrocene/xylene solutions in the absence of promoters, such as thiophene or pure sulfur, and etching agents, such as plasma, oxygen, ethanol or water. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) results indicated the continuous and multi-walled nanotube structure for the CNTs in the macroscopical bundles. A graph demonstrating the correlation between growth time and length of CNT arrays revealed that the maximum growth rate reaches approximately 4612?nm?s(-1). Based on the experimental phenomena and results, a continuous rapid growth mechanism in both directions was proposed, which suggests that longer CNT arrays can be synthesized at this rapid growth rate if the growth time is extended.     

Hierarchical nanostructures of ZnO obtained by spray pyrolysis

A two step spray pyrolysis deposition method was applied in order to grow ZnO nanorod core/ZnO shell hierarchical nanostructures with various surface morphologies, such as a highly organised platelet network on the side facets of the ZnO rod and bundles of nanoneedles on the top plane of the rod. First, well-shaped ZnO nanorods with lengths of ca. 1 μm and average diameters of 150–300 nm were deposited from zinc chloride (ZnCl₂·2H₂O) aqueous solutions onto TCO/glass substrates. Then, zinc acetate (Zn(CH₃COO)₂·2H₂O) solution was pulverised over the surface of the sprayed ZnO nanorods at a growth temperature of approximately 330 °C within 6–10 min. The obtained structures were characterised by high resolution SEM, UV–VIS and XRD. To estimate the surface areas and photocatalytic ability of the bare rods and hierarchical structures, their adsorption ability and activity of photocatalytic oxidation of doxycycline were measured. It was found that the surface area of hierarchical structures comprised of a network of platelets is at least 4 times larger than that of a bare rod. The structural and morphological properties of sprayed hierarchical structures largely depend on the spraying rate of the zinc acetate solution and on the ZnO nanorod top plane shape.     

Solid-state synthesis of tungsten carbide from tungsten oxide and carbon, and its catalysis by nickel

Tungsten carbide has been produced by heating a mixture of tungsten oxide and carbon powder at 1300 °C for 2 h. Further batches were made with additional KCl, KCl + Ni, or KCl + Fe. The products were compared by XRD and SEM. A mixture of WC and W₂C was produced from the plain WO₃/carbon reaction, but adding 1 wt.% nickel assisted the formation of a pure WC phase. Both Ni and Fe assisted the growth of larger WC crystals.     

Hydrothermal synthesis of oriented MnS nanorods on anodized aluminum oxide template

High-density aligned MnS nanorods with a narrow length distribution were prepared on an anodized aluminum oxide (AAO) template under a hydrothermal condition. MnS nanomaterials with different shapes were obtained using different precursor concentrations in the reaction solution. The porous surface of the AAO template and the precursor concentrations may play key roles in the initial nucleation stage of growing oriented MnS nanorods.     

Direct synthesis of submicron FeNi particles via spray pyrolysis using various reduction agents

Preparing spherical and submicron FeNi particles in a simple, rapid, and harmless process is highly desirable for various applications yet severely challenging. Herein, we successfully synthesized the FeNi particles from their metal salts in a relatively low reduction atmosphere using three types of reduction agent, i.e., ethanol, ethylene glycol, and formic acid, via spray pyrolysis. The reduction agents were tested over a concentration range of 0–30 vol%. The type and concentration of reduction agents show a crucial role in the formation of FeNi particles. At higher concentrations (25 vol%), ethanol and ethylene glycol produced smooth and spherical FeNi particles of submicron size, 284 ± 1.6 and 399 ± 1.5 nm respectively, whereas formic acid produced particles with an irregular and Janus shape comprising FeNi and FeO, with a size of 396 ± 1.5 nm. A plausible metal salt reduction mechanism was proposed for the different reduction agents. The reduction agent type not only influences the reduction degree but also particle morphology during synthesis. This finding opens new opportunities to adjust the FeNi particles with respect to varied purposes by manipulating reduction agents.     

Low substrate temperature synthesis of carbon nanowalls by ultrasonic spray pyrolysis

In this paper, we report the synthesis of two-dimensional wall like carbon nanostructures (i.e. carbon nanowalls) by ultrasonic spray pyrolysis of ethanol and fullerene mixture. At higher temperature carbon nanofibers were formed on the substrate placed at the center of the reactor tube, whereas carbon nanowalls were observed on the substrate placed downstream of the tube below 100 °C. Spaces between the nanowalls changed with distance of the substrates from the furnace. Qualitative analysis of materials was performed using scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.     

Temperature dependence of Fluorine-doped tin oxide films produced by ultrasonic spray pyrolysis

Fluorine-doped tin oxide (FTO) films were prepared at different substrate temperatures by ultrasonic spray pyrolysis technique on glass substrates. Among F-doped tin oxide films, the lowest resistivitiy was found to be 6.2 × 10^− 4 Ω-cm for a doping percentage of 50 mol% of fluorine in 0.5 M solution, deposited at 400 °C. Hall coefficient analyses and secondary ion mass spectrometry (SIMS) measured the electron carrier concentration that varies from 3.52 × 10²⁰ cm^− 3 to 6.21 × 10²⁰ cm^− 3 with increasing fluorine content from 4.6 × 10²⁰ cm^− 3 to 7.2 × 10²⁰ cm^− 3 in FTO films deposited on various temperatures. Deposition temperature on FTO films has been optimized for achieving a minimum resistivity and maximum optical transmittance.     

Optical and electrical properties of zinc oxide films prepared by spray pyrolysis

Zinc oxide thin films were prepared on glass substrates from an aqueous solution of zinc acetate by spray pyrolysis. These films were characterized using X-ray diffraction, scanning electron microscopy and optical transmission. The films were highly transparent to the visible radiation and electrically conductive. Films deposited at optimum conditions exhibited a resistivity of 3·15×10⁻³ Ωm along with a transmittance of 98% at 550 nm.     

Growth and characterization of indium oxide thin films prepared by spray pyrolysis

Highly transparent and conducting indium oxide thin films are prepared on glass substrates from precursor solution of indium chloride. These films are characterized by X-ray diffraction, scanning electron microscopy and optical transmission. The preferential orientation of these films is found to be sensitive to deposition parameters. A comparative study has been made on the dependence on the thickness of the film on substrate temperatures with aqueous solution and 1:1 C₂H₅OH and H₂O as precursors. Films deposited at optimum conditions have 167 nm thickness and exhibited a resistivity of 2.94 × 10⁻⁴ Ω m along with transmittance better than 82% at 550 nm. The analytical expressions enabling the derivation of the optical constants of these films from their transmission spectrum only have successfully been applied. Finally, the refractive index dispersion is discussed in terms of the single-oscillator Wemple and Didomenico model.     

Low temperature synthesis of single crystalline ZnO nanorods by oblique angle deposition

The authors report the growth of single crystalline ZnO nanorods by direct current magnetron sputtering in the oblique angle deposition configuration near room temperature. These isolated nanorods have a diameter of  40 nm, an inter-rod spacing of  20 nm, and a height of  100 nm. The nanorods show a (002) orientation along the rod-axis which is normal to the substrate. The low temperature fabrication of single crystal ZnO nanorods may find potential applications in optoelectronics and energy conversion devices.