Synthesis of nanosized vanadium pentoxide/carbon composites by spray pyrolysis for electrochemical capacitor application

Nanostructured vanadium pentoxide/carbon (V₂O₅/carbon) composite powders with enhanced specific capacitance were synthesized by the spray pyrolysis technique. Electrochemical properties were examined by the cyclic voltammetry technique. Following analysis of powders sprayed at different temperatures, composite powders obtained at an optimum temperature of 450 °C yielded a maximum specific capacitance of 295 F g⁻¹ in 2 M KCl electrolyte at a 5-mV s⁻¹ scan rate. The weight percentage of carbon-related species was 2.7 wt% in this V₂O₅/carbon composite, as detected by thermogravimetric analysis (TGA) and confirmed by transmission electron microscope energy dispersive spectroscopy (TEM-EDS) analysis. Following initial X-ray diffraction (XRD) characterization, scanning electron microscope (SEM), TEM and high-resolution TEM (HRTEM) imaging revealed a specific morphology of spherical shell agglomerates of V₂O₅ nanorods and nanoribbons, with each shell comprising a network of these one- and two-dimensional nanoparticles in an amorphous carbon matrix. The V₂O₅ network was not fully dense, and the majority of the nanorod sizes were in the range of 50-150 nm, with additional long nanoribbons extending from the outsides of the spherical shells. The specific surface area was 18 m² g⁻¹ for the composite powders, and the pore size distribution revealed that the majority of pores had diameters in the range of 40-50 Å, which was relatively larger than the pore diameters obtained at 500 °C and would be beneficial for electrochemical performance. The enhancement of the specific capacitance in V₂O₅/carbon composites was attributed to the distribution of amorphous carbon throughout the V₂O₅ and the particular open nanostructure.     

Synthesis, characterization and microbiological response of silver doped bioactive glass nanoparticles

Glass nanoparticles containing 1, 3, 5, and 10 wt% of Ag₂O (coded; GAg1%, GAg3%, GAg5%, and GAg10%, respectively) were synthesized through a quick alkali mediated sol-gel method and were characterized by TEM, XRF, FT-IR, XRD, TGA, and DSC. Thermal analysis showed that all organic and inorganic by-products were completely decomposed before 700 °C and, hence, all glass samples were stabilized at this temperature. XRD confirmed the amorphous nature of all glasses after stabilization. TEM micrographs showed that the average particle sizes of all samples were less than 100 nm in diameter and the XRF showed that the compositions of the obtained glasses were almost consistent with the designed ones. The samples GAg1%, GAg3%, GAg5%, and GAg10%, showed average pore diameters of 19.85, 18.22, 13.32, and 19.62 nm and specific surface areas of 73.18, 100.38, 192.6, and 55.7 m²/g, respectively. In addition, their porosity% was 76.53, 83.20, 77.97, and 79.61%, respectively. The FT-IR spectra of all glasses showed bands located in the range of 1000-1200, 725-800, and 450-480 cm⁻¹ that correspond to the Si-O-Si asymmetric stretching vibration, the Si-O-Si symmetric stretching vibration, and the Si-O-Si bending mode, respectively. Finally, all samples had an anti-bacterial effect against different types of bacteria and the extraction of silver ions from them followed a diffusion-controlled mechanism, which could demonstrate their ability to treat bone infection.     

Influence of glass phase on Al2O3 fiber-reinforced Al2O3 composites processed by slip casting

The present work describes the processing of alumina fiber reinforced alumina ceramic preforms consisting of chopped Al₂O₃ fibers (33 wt%) and Al₂O₃ (67 wt%) fine powders by slip casting. The preforms were pre-sintered in air at 1100 °C for 1 h. A lanthanum based glass was infiltrated into these preforms at 1250 °C for 90 min. Linear shrinkage (%) was studied before and after glass infiltration. Pre-sintered and infiltrated specimens were characterized by scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, porosimetry and flexural strength. The alumina preforms showed a narrow pore size distribution with an average pore size of ∼50 nm. It was observed that introducing Al₂O₃ fibers into Al₂O₃ particulate matrix produced warp free preforms with minor shrinkage during pre-sintering and glass infiltration. It was observed that the infiltration process fills up the pores and considerably improves the strength and reliability of alumina preform.     

Properties of sol–gel derived Al2O3–15 wt.% ZrO2 (3 mol% Y2O3) nanopowders using two different precursors

An alumina–15 wt.% zirconia (3 mol% yttria) nanopowder was synthesized by sol–gel method using salt and alkoxide as precursors. Al(NO₃)₃·9H₂O, ZrOCl₂·8H₂O and Y(NO₃)₃·6H₂O were used as salt precursors and Al(OC₄H₉)₃ and Zr(OC₄H₉)₄ were used as alkoxide precursors. The dried gels of two precursors were heat treated in the range of 450–1350 °C. The powders produced by alkoxide precursors calcined at 750 °C were in the range of 15–75 nm, while those prepared by salt precursors had the size in the range of 30–90 nm. The former powders had a higher surface area and smaller mean pore diameter compared with the later powder, i.e. 152 m²/g and 5.63 nm comparing with 121 m²/g and 9.79 nm, respectively. Therefore phase transformation in the former occurred in lower temperatures.     

In situ preparation of SiC/Si3N4-NW composite powders by combustion synthesis

Large-scale composite powders containing silicon carbide (SiC) particles and silicon nitride nanowires (Si₃N₄-NWs) were synthesized in situ by combustion synthesis (CS). In this process, a mixture of silicon, carbon black, polytetrafluoroethylene (PTFE) and a small amount of iron powders was used as the precursor. The products were characterized by XRD, SEM, EDS and TEM. The particles are equiaxed with diameters in the micron range, and the in situ formed nanowires are straight with uniform diameters of 20-350 nm and lengths of tens of microns. The Si₃N₄-NWs are characterized to be α-phase single crystals grown along the [1 0 1] or [1 0 0] direction. VLS and SLGS processes are proposed as the growth mechanisms of the nanowires. The as-synthesized powders have great potential for use in the preparation of high-performance SiC/Si₃N₄-NW composites.     

Diameter control of carbon nanotubes by changing the concentration of catalytic metal ion solutions

We have developed a simple new method to control the diameter of carbon nanotubes (CNTs) using catalytic nanoparticle arrays fabricated by filling the pores of well-ordered porous anodic aluminum oxide (AAO) templates with a metal ion solution. Fe ion solution was used to fill the pores in which Co had been deposited electrochemically, and then the template was dried naturally on a magnet. After this process, the pores were widened in NaOH solution. Well-graphitized multi-walled CNTs were grown from almost all the pores and were very long in length and homogeneous in diameter. We were able to control the diameter of CNTs, simply, by changing the concentration of iron ion solution. For example, the average outer diameters of the CNTs are 7 ± 1.5, 13 ± 1, and 17 ± 1 nm when the concentrations of Fe ion in their mother solutions were 1.0 × 10⁻³, 3.0 × 10⁻³, and 6.0 × 10⁻³ M, respectively. The inner diameters of these CNTs corresponded to the calculated diameters of Fe nanoparticles by assuming that all Fe ions contained in each pore are reduced to a single nanoparticle. This means that homogeneous nanoparticles are made in each pore. Our new method could be used to fabricate homogeneous nanoparticles from most metal ion solutions.     

Agglomeration of α-Al2O3 powders prepared by gel combustion

Ultrafine α-Al₂O₃ powders were prepared by a gel combustion method and the agglomeration characteristic of the resultant powders was studied. A variety of fine crystallite α-Al₂O₃ powders with different agglomeration structures could be obtained by altering the citrate-to-nitrate ratio γ and calcining the precursors at 1050 °C for 2 h. All the powders were of nearly equivalent crystallite size (60–80 nm) except for the P1 powder (113 nm) from the gel with γ = 0.033. The primary crystallites of the obtained α-Al₂O₃ powders were formed into large secondary particles with different degree of agglomeration. Except for the powder P1, the mean particle sizes from specific surface area and particle size distribution measurement increase with increasing citrate-to-nitrate ratio in the fuel-lean condition and decrease in the fuel-rich condition. Densities of alumina ceramics from powders P4 and P5 sintered at different temperatures were relatively low due to the wide particle size distribution.     

Synthesis of nanocrystalline ytterbium-doped yttria by citrate-gel combustion method and fabrication of ceramic materials

Nanosized ytterbium doped yttria powders were prepared by citrate-gel combustion techniques. As-synthesized precursor and calcined powders were characterized for their crystalline structure, particle size and morphologies. Nanocrystalline Yb³⁺:Y₂O₃ powders with pure cubic yttria crystal structure were obtained by calcination of as-prepared precursors at 1100 °C for 3 h. Powders obtained were well dispersed with an average particle size of 60 nm. By using the obtained powders, nearly full dense Yb³⁺:Y₂O₃ ceramics were produced by vacuum sintering at 1800 °C for 12 h. The emission spectrum of the sintered ceramics under the excitation wavelength of 905 nm illustrates that there are three fluorescence peaks locating at 976 nm, 1030 nm and 1075 nm respectively, all corresponding to the ²F_5/2 → ²F_7/2 transitions of ytterbium ion.     

Effect of heat treatment on 7Na2O-23B2O3-70SiO2 glass

Porous 7Na₂O-23B₂O₃-70SiO₂ glass was successfully fabricated by acid leaching treatment and phase-separation. The 2 mol/l hydrochloric acid (HCl) solution treatment was used for 24 h. Thermal analysis and X-ray diffraction were used to identify the temperature range of heat-treatment. The average pore size and the pore volume were investigated by a nitrogen adsorption instrument, and SEM was used to characterize the appearance of the porous glass. The results show that the average size of pores changed from 3.75 nm to 3.03 nm when heat treated at 640-680 °C for 6 h. In addition, when heat treated at 640 °C for 6-24 h, the pore size fell from 3.75 nm to 3.66 nm. The surface area and pore volume become larger with the increase in both temperature and heat treatment time.     

Low-temperature solution synthesis of carbon nanoparticles, onions and nanoropes by the assembly of aromatic molecules

Graphitic carbon nanostructures were prepared in solution by two methods: solvothermal synthesis and hot injection. Small carbon nanoparticles with uniform diameters of 3-6 nm, carbon onion particles with larger diameters of 30-80 nm, and carbon nanoropes with a length of hundreds of nm and a width of 3-20 nm, were formed using commercial mesophase pitches as a carbon precursor through solution-phase synthesis below 200 °C. In the solvothermal synthesis, organic-organic assemblies of aromatic molecules from the pitches could be constrained into different stacking arrangements directed by varying the concentration of the block copolymer P123 template in toluene solution at 200 °C. In the hot injection method, when oleic acid was used as a solvent at 180 °C, the assemblies of the aromatic building blocks were controlled by varying the reaction time (5-30 min) or the concentration of H₂SO₄ catalyst (0.015-0.061 mol L⁻¹) in the nucleation and growth process.     

Synthesis of carbon nanotubes over gold nanoparticle supported catalysts

The synthesis of carbon nanotubes (CNTs) through the catalytic decomposition of acetylene was carried out over gold nanoparticles supported on SiO₂-Al₂O₃. Monodispersed gold nanoparticles with 1.3-1.8 nm in diameter were prepared by the liquid-phase reduction method with dodecanethiol as protective agent. The carbon products formed after acetylene decomposition consist of multi-walled carbon nanotubes with layered graphene sheets, carbon nanofilaments (CNFs), and carbon nanoparticles encapsulating gold particles. The observed CNTs have outer diameters of 13-25 nm under 850 °C. The influence of several reaction parameters, such as kind of carriers, reaction temperature, gas flow rate, was investigated to search for optimum reaction conditions. The CNTs were observed at a relatively low temperature (550 °C). The silica-alumina carrier showed higher activity for the formation of CNTs than others used in the screening test. With increasing temperature, the CNTs showed cured structures having thick diameters and inside compartments. When Au content on the support was over 5 wt.%, the gold nanoparticles coagulated to form large ones >20 nm in diameter and became encapsulated with graphene layers after decomposition of acetylene.     

Formation of carbon nanotubes through ethylene decomposition over supported Pt catalysts and silica-coated Pt catalysts

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

Preparation and characterization of transparent Tm:YAG ceramics

Polycrystalline (Y_3−xTm_x)Al₅O₁₂ (x = 0, 0.18, 0.9, 1.5, 3) ceramics were fabricated by a solid-state reaction method using high-purity micrometer-sized powders. Tm-doped ceramics with an almost perfect pore-free structure and high transparency were obtained by advanced ceramic processing. The average grain size and grain boundary width were 15 μm and 1 nm, respectively. The Y_2.82Tm_0.18Al₅O₁₂ (6 at.% Tm:YAG) ceramic slab (5 mm × 5 mm × 3.5 mm) was end-pumped by a Ti:sapphire laser at 785 nm and the maximum output power of 725 mW was obtained with a slope efficiency of 36.2% at 2012 nm.     

Phase separation and mechanical responses of polyurethane nanocomposites

Nanocomposites of a diamine-cured polyurethane with nanofillers of different kinds, sizes, and surfaces were studied. Atomic force microscopy, scanning electron microscopy, X-ray diffraction, tensile tests, and dynamic mechanical thermal analysis were employed in the experiments. Experimental results suggest that mechanical properties are strongly correlated to polymer phase separation, which depends on the nature of the interface between the polymer and the nanoparticles. Two stages of phase separation were observed: the first stage involves the self-assembly of the hard segments into small hard phases of about 10 nm in width; the second stage involves the assembly of the 10 nm wide hard phases into larger domains of about 40-100 nm in width. In the case of polyurethane/ZnO nanocomposites with 5 wt% (less than 1 vol%) 33 nm ZnO nanoparticles, the covalent bonds that were formed between the polymer and ZnO surface hydroxyl groups constrain both stages of phase separation in polyurethane, resulting in approximately 40% decrease in the Young's modulus, 80% decrease in the strain at fracture, and 11 °C increase in the glass transition temperature of the soft segments. In the case of polyurethane/Al₂O₃ nanocomposites with 5 wt% 15 nm Al₂O₃ nanoparticles, hydrogen bonds between the particles and the polymer mainly constrain the second step of the phase separation, resulting in about 30% decrease in the Young's modulus and 12 °C increase in the glass transition temperature, but only a moderate decrease in the strain at fracture. The most striking results come from polyurethane/clay composites, where only van der Waals type interactions exist between polyurethane and the organically modified clay (Cloisite 20A). With the addition of 5 wt% surface modified clay (Cloisite 20A), both the Young's modulus and the strain at fracture decrease more than 80%, but the glass transition temperature increases by about 13 °C. Adding 10 wt% Cloisite 20A into polyurethane almost totally disrupts the phase separation, resulting in a very soft composite that resembles a “viscous liquid” rather than a solid.     

Silver nanoparticles distributed into polyaniline bridged silica network: A functional nanocatalyst having synergistic influence for catalysis

A novel organic–inorganic hybrid nanocatalyst, Ag nanoparticles supported poly[N-(3-Trimethoxy silyl)propyl]aniline (Ag@PTMSPA), was prepared by a simple one-step method. X-ray diffraction analysis, field emission transmission electron microscopy and X-ray photo electron spectroscopy reveal the coexistence of Ag nanoparticles (average size ∼ 10 nm) and PTMSPA in Ag@PTMSPA. N₂ adsorption–desorption experiments provide the textural properties of the catalyst, such as surface area (86.6 m²/g), pore volume (1.3 × 10^− 1 cm³/g) and pore size (4.2 nm). UV–visible spectroscopy was used to follow the kinetics of reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH₄) in the presence of Ag@PTMSPA catalyst.     

Adsorption of vitamin B12 on ordered mesoporous carbons coated with PMMA

Ordered mesoporous carbons CMK-3 and CMK-1 were prepared from SBA-15 and MCM-48 materials with pore diameters 3.9 nm and 2.7 nm, respectively. When both mesoporous carbons were coated with about 10 wt.% poly(methyl methacrylate) (PMMA), the pore diameters decreased from 3.9 nm to 3.4 nm for CMK-3 and from 2.7 nm to 2.5 nm for CMK-1. These mesoporous carbons containing about 10 wt.% PMMA were studied as adsorbents of Vitamin B 12 (VB12) from water solutions, and their performances were compared with that of pristine CMK-3, CMK-1. Compared with CMK-1, CMK-3 showed higher vitamin B12 adsorption due to a larger mesopore volume, a higher BET surface and a larger pore diameter. After coated with PMMA, both mesoporous carbons showed higher adsorption capacity than pristine materials. The adsorption properties were influenced by the pore structure and surface properties of mesoporous carbons.     

Enhanced electrochromic performance of macroporous WO3 films formed by anodic oxidation of DC-sputtered tungsten layers

Self-organized macroporous tungsten trioxide (WO₃) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10 mm × 25 mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO₃ films with a thickness of ca. 350 nm are formed. The film shows a connected network with average pore size of 100 nm and a pore wall thickness of approximately 30 nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1 M H₂SO₄, the macroporous WO₃ films show enhanced electrochromic properties with a coloration efficiency of 58 cm² C⁻¹. Large modulation of transmittance (∼50% at 632.8 nm) and a switching speed of about 8 s are also achieved with this macroporous film.     

A simple aqueous solution based chemical methodology for synthesis of Ag nanoparticles dispersed on mesoporous silicate matrix

A simple chemical method has been developed for preparation of Ag nanoparticles dispersed on mesoporous silicate matrix, SBA-15. Ag nanoparticles were uniformly dispersed on SBA-15 matrix by using the reduction reaction of AgNO₃ with trisodium citrate. The synthesized materials were characterized by using room temperature powder XRD analysis, N₂ adsorption-desorption isotherm, high resolution TEM and SEM. It was observed that the synthesized SBA-15 and Ag-SBA-15 have a surface area of 778 and 151 m²/g respectively. The synthesized materials have long range ordering of pores with narrow pore size distribution centered at ∼ 7 nm. Pore structure of SBA-15 remains preserved even after deposition of Ag nanoparticle. This chemical route reported here offers a simple method for preparation of Ag-SBA-15, where unagglomerated Ag nanoparticles (∼ 20 nm) are uniformly dispersed on SBA-15.     

Tin oxide nanoparticles synthesized by gel combustion and their potential for gas detection

Tin oxide nanoparticles were synthesized starting from SnCl₄·5H₂O with the aid of polyacrylamide gel. The pyrolysis of the gel and the influence of the calcination temperature were discussed based on thermogravimetric analysis and X-ray powder diffraction. The decomposition of the polyacrylamide gel occurred mainly in the temperature range of 220–600 °C, after which resulting in a heap of fine powders. The average grain size of the nanoparticles synthesized at 600, 700 and 800 °C were calculated to be 8.1, 19.2 and 27.9 nm, respectively. The prepared SnO₂ nanoparticles were sphere-like and uniform in size, weakly aggregated in thin platelets as indicated by scanning electron microscope (SEM) images. Thick-film sensor samples based on the as-synthesized SnO₂ nanoparticles without specific additives showed response sensitivity of around 28.8 at the optimal detection temperature of 150 °C to 30 ppm H₂S gas, while their responses to 1000 ppm of CO or CH₄ were negligible.