Effects of precursor concentration on crystalline morphologies and particle sizes of electrospun WO3 nanofibers

Tungsten oxide (WO₃) nanofibers with different crystalline morphologies and various particle sizes were fabricated using an electrospinning technique. The nanofibers were prepared from mixtures of polyvinyl alcohol (PVA) and ammonium metatungstate hydrate (AMH) of various concentrations ranging from 4.2%w/v to 50.0%w/v. After calcination at 500 °C for 2 h, the nanofibers were observed to have a monoclinic crystal structure with diameters ranging from 30 to 250 nm. AMH concentration had a large influence on the resulting nanofiber morphology. Very low AMH concentration of 4.2%w/v led to the formation of WO₃ nanofibers having a very large area of monocrystalline structure. Higher AMH concentrations result in polycrystalline WO₃ nanofibers with joined nanoparticles along the fiber axis. The average particle size within the nanofibers increased from 29 to 66 nm as the AMH concentration increased from 8.3%w/v to 50%w/v. At these precursor concentration levels, primary particles were formed before PVA was completely burnt off, resulting in agglomeration of primary particles along the nanofiber axis.     

Effects of PVA content on the synthesis of LaFeO3 via sol-gel route

LaFeO₃ were synthesized via a sol-gel route based on polyvinyl alcohol (PVA). Differential scanning calorimetry (DSC), Thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy and field emission scanning electron microscopy (FESEM) techniques were used to characterize precursors and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mⁿ⁺/-OH) on the formation of LaFeO₃ was investigated. XRD analysis showed that single-phase and well-crystallized LaFeO₃ was obtained from the Mⁿ⁺/-OH = 4:1 molar ratio precursor at 700 °C. For the precursor with Mⁿ⁺/-OH = 2:1, nanocrystalline LaFeO₃ with average particle size of ∼50 nm was formed directly in the charring procedure. With increase of PVA content to Mⁿ⁺/-OH = 1:1, phase pure LaFeO₃ was obtained at 500 °C.     

Supercritical fluid extraction of flavonoids from Maydis stigma and its nitrite-scavenging ability

Supercritical fluid carbon dioxide (SF-CO₂) extraction (SFE) of flavonoids from Maydis stigma and its nitrite-scavenging ability were investigated. The effects of extraction time, particle size and co-solvent composition in terms of water content in ethanol were first optimized. Then, a Box-Behnken design combined with response surface methodology (RSM) was employed to study the effects of three independent variables (temperature, pressure and co-solvent amount) on the extraction yield of flavonoids. A maximal extraction yield of flavonoids of approximately 4.24 mg/g of M. stigma by SFE was obtained under optimal conditions (a temperature of 50.88 °C, a pressure of 41.80 MPa, a co-solvent amount of 2.488 mL/g and an extraction time of 120 min with 0.4-mm particle sizes and 20% aqueous ethanol as the co-solvent). Furthermore, the nitrite-scavenging ability of the flavonoid-enriched SFE extracts was assessed using the Griess reagent. The flavonoid-enriched SFE extracts exhibited the highest scavenging ability on nitrite (88.1 ± 3.04%) at the concentration of 500 μg/mL and at pH 3.0. The nitrite-scavenging ability of the extracts appeared to be concentration dependent but negatively correlated with the pH.     

Effect of the stirring rate on physical and electrochemical properties of LiMnPO4 nanoplates prepared in a polyol process

In a polyol approach to make olivine-typed LiMnPO₄ nanoplates, the effect of the stirring rate on physical and electrochemical properties of the obtained sample has been symmetrically investigated for the first time. The as-prepared powders exhibit well crystalline olivine structure as presented by X-ray diffraction analysis. The secondary particles with a size of 2–3 μm are composed of aggregated nanoplates as verified by particle size analysis and field emission scanning electron microscopy measurement. Transmission electron microscopy presents that the nanoplate is about 18 nm thick along a-axis. The discharge capacity of the sample prepared under a stirring rate of 700 rpm reaches 150 mAh g⁻¹ when cycled at 0.05C after a few cycles.     

High permeability Ni-Cu-Zn ferrites through additive-free low-temperature sintering of nanocrystalline powders

Nanocrystalline Ni-Cu-Zn ferrite powders Ni_0.20Cu_0.20Zn_0.62Fe_1.98O_3.99 were prepared by thermal decomposition of an oxalate precursor. The particle size is 6 nm and 350 nm, respectively, for powders obtained through calcinations at 350 °C or 750 °C. The shrinkage behavior significantly changes with particle size; the temperature of maximum shrinkage rate is T_MSR = 700 °C for particles of 6 nm size and increases to T_MSR = 880 °C for particles 350 nm in size. Dense samples with a permeability of μ = 780 are obtained by sintering at 900 °C for 2 h. Mixtures of nanocrystalline and sub-micron powders allow tailoring of the shrinkage behavior. A maximum permeability of μ = 840 is obtained after sintering of a 1:1-mixture at 900 °C. This demonstrates the potential of nanocrystalline ferrites for co-firing without additives at 900 °C and integration of ferrite inductors into LTCC modules.     

Dispersion polymerization of 2-hydroxyethyl methacrylate stabilized by a hydrophilic/CO2-philic poly(ethylene oxide)-b-poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) (PEO-b-PFDA) diblock copolymer in supercritical carbon dioxide

Dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) has been successfully performed in supercritical carbon dioxide at P=370 bar and T=65 °C with azobis(isobutyronitrile) as initiator and a hydrophilic/CO₂-philic poly(ethylene oxide)-b-poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) (PEO-b-PFDA) block copolymer as steric stabilizer. The PEO-b-PFDA (2K/21K) block copolymer was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Spherical particles of poly(HEMA) were obtained in the range of 200-400 nm diameter size with a narrow particle size distribution (D_w/D_n<1.1). The effect of the stabilizer concentration on the dispersion polymerization was investigated from 20 w/w% down to 3.5 w/w% versus HEMA. Precipitation polymerization in the absence of stabilizer lead to the formation of large aggregates of partially coalesced particles whereas discrete spherical particles of poly(HEMA) were obtained by dispersion polymerization even at low concentration of PEO-b-PFDA (3.5 w/w% versus HEMA).     

Gasification reaction kinetics on biomass char obtained as a by-product of gasification in an entrained-flow gasifier with steam and oxygen at 900-1000 °C

The purpose of this study was to investigate the gasification kinetics of biomass char, such as the wood portion of Japanese cedar char (JC), Japanese cedar bark char (JB), a mixture of hardwood char (MH) and Japanese lawngrass char (JL), each of which was obtained as a by-product of gasification in an entrained-flow type gasifier with steam and oxygen at 900-1000 °C. Biomass char was gasified in a drop tube furnace (DTF), in which gasification conditions such as temperature (T_g), gasifying agent (CO₂ or H₂O), and its partial pressure (P_g) were controlled over a wide range, with accompanying measurement of gasification properties such as gasification reaction ratio (X), gasification reaction rate (R_g), change of particle size and change of surface area. Surfaces were also observed with a scanning electric microscope (SEM). By analyzing various relationships, we concluded that the random pore model was the most suitable for the biomass char gasification reaction because of surface porosity, constant particle size and specific surface area profile, as well as the coincidence of R_g, as experimentally obtained from Arrhenius expression, and the value is calculated using the random pore model. The order of R_g was from 10⁻² to 10⁻¹ s⁻¹, when T_g = 1000 °C and P_g = 0.05 MPa, and was proportional to the power of P_g in the range of 0.2-0.22 regardless of gasifying agent. Reactivity order was MH > JC > (JB, JL) and was roughly dependent on the concentration of alkali metals in biomass feedstock ash and the O/C (the molar ratio of oxygen to carbon) in biomass char.     

Formation of nanosize ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate

Formation of ZnO particles by thermal decomposition of zinc acetylacetonate monohydrate in air atmosphere has been investigated using XRD, DTA, FT-IR, and FE-SEM as experimental techniques. ZnO as a single phase was produced by direct heating at ≥200 °C. DTA in air showed an endothermic peak at 195 °C assigned to the ZnO formation and exothermic peaks at 260, 315 and 365 °C, with a shoulder at 395 °C. Exothermic peaks can be assigned to combustion of an acetylacetonate ligand released at 195 °C. ZnO particles prepared at 200 °C have shown no presence of organic species, as found by FT-IR spectroscopy. Particles prepared for 0.5 h at 200 °C were in the nanosize range from ∼20 to ∼40 nm with a maximum at 30 nm approximately. The crystallite size of 30 nm was estimated in the direction of the a₁ and a₂ crystal axes, and in one direction of the c-axis it was 38 nm, as found with XRD. With prolonged heating of ZnO particles at 200 °C the particle/crystallite size changed little. However, with heating temperature increased up to 500 or 600 °C the ZnO particle size increased, as shown by FE-SEM observation. Nanosize ZnO particles were also prepared in two steps: (a) by heating of zinc acetylacetonate monohydrate up to 150 °C and distillation of water and organic phase, and (b) with further heating of so obtained precursor at 300 °C.     

Gas permeability, solubility and diffusivity in 1,2-polybutadiene containing brookite nanoparticles

Brookite (i.e., titanium dioxide) nanoparticles having a nominal diameter of 3 nm were dispersed in 1,2-polybutadiene (PB) via solution processing to form polymer nanocomposites. Atomic force microscopy and scanning transmission electron microscopy were used to characterize particle dispersion. A significant population of nanoparticle aggregates exhibited characteristic dimensions below 50 nm. However, some aggregates were over 1 μm in size. At high nanoparticle loadings (e.g., 27 nominal volume percent TiO₂), the permeability coefficients of CO₂, CH₄, N₂ and H₂ were more than 3 times higher than that in unfilled PB, which is opposite to the trend typically observed when impermeable particles are added to rubbery polymers. Gas solubility coefficients generally increased with increasing particle loading, whereas diffusion coefficients decreased with increasing particle loading. Therefore, the increase in permeability was due to an increase in gas solubility upon incorporating highly sorbing nanoparticles into the polymer. Interestingly, there was virtually no change in pure gas selectivity in the nanocomposites as compared to unfilled PB.     

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.     

Low surface area nanosilica from an agricultural biomass for fabrication of dental nanocomposites

This study aimed to obtain nanosilica with desirable characteristics from an agricultural biomass waste using an organic acid. The effect of the feed rate of the precipitant and the mixing speed on the morphology and characteristics of nanosilica from rice husk for use as fillers in dental nanocomposites has been explored. The feed rate showed considerable effects on the agglomeration and the size of the silica nanoparticles. At a feed rate of 0.2 ml/min, the particles were bigger and highly agglomerated with a mean particle size of 261 nm. The mean particle sizes for the feed rates of 1 ml/min and 5 ml/min were 213 nm and 174 nm, respectively, exhibiting a decrease in the mean particle size with increasing feed rate. The shape of the silica nanoparticles depended on the mixing speed and it was possible to obtain spherical, dense, low surface area silica particles suitable for use in the fabrication of dental nanocomposites using this simple technique.     

Synthesis of nanocrystalline lithium niobate powders via a fast chemical route

Lithnium niobate (LiNbO₃) can be obtained by mixing lithium nitrate (LiNO₃), ammonium niobate oxalate hydrate (C₄H₄NNbO₉) and glycine and then calcining at 600 °C for 1 h. The thermal analysis, structure, and morphology of the as-prepared LiNbO₃ were characterized by thermogravimetric and differential thermal analyses (TG/DTA), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The crystallization temperature of LiNbO₃ precursor is 580 °C based on the TG/DTA results. After being calcined at 600 °C, the structure of the LiNbO₃ synthesized using various ratios of glycine to metal nitrates (Ψ-value) was formed with a particle size of about 29-38 nm, as found by XRD analysis. The crystal size has the lowest value at Ψ = 2, and the highest level of crystallization is at Ψ = 3.     

A flat premixed flame reactor to study nano-ash formation during high temperature pulverized coal combustion and oxygen firing

This paper deals with the development of a laboratory reactor to study ultrafine (D < 100 nm) and nano (D < 30 nm) ash formation during pulverized coal combustion and oxy-firing. The reactor consists of an atmospheric pressure flat laminar premixed flame homogeneously doped with pulverized coal particles, monodisperse in size. It is accessible to diagnostics and sampling systems and it allows investigating the early stage of particle formation in a wide range of pulverized coal combustion operative conditions, in terms of gas composition and temperature. Coal combustion in an oxygen enriched gas mixture was investigated by performing on-line high resolution differential mobility analyses (DMA) and thermophoretic samplings for atomic force microscopy (AFM) image analyses. Ultrafine particle size distribution functions in a size range extending down to 1 nm have been measured. Three types of high volatile bituminous coals have been tested. Ultrafine particles, commonly neglected at the exhaust of pulverized coal combustors, form with huge number concentration and they represent a not negligible fraction of total ashes also in volume/mass. Nano-ashes are the most abundant in number and they also significantly contribute to ultrafine particle mass concentration. This not negligible contribution slight increases with the coal chlorine content while the shape of the nano-ash size distribution function is quite unaffected by the used coal type.     

Controllable and SDA-free synthesis of sub-micrometer sized zeolite ZSM-5. Part 2: Influence of sodium ions and ageing of the reaction mixture on the chemical composition, crystallinity and particulate properties of the products

In this work, the influences of excess amount of sodium ions and the way/duration of ageing of the reaction mixture (hydrogel) on structural, particulate, morphological and chemical properties of the crystalline end products obtained by hydrothermal treatment (heating at 483 K for 2 h) of the TPA-free reaction mixture: 1.0Al₂O₃/100SiO₂/xNa₂O/4000H₂O/yNa₂SO₄ (0.4 ? (x + y) ? 100) seeded by silicalite-1 nanocrystals (260 nm, 4 wt.% of silica in gel mixture), was investigated by different characterization methods such as, powder X-ray diffraction (XRD), scanning-electron microscopy (SEM), particle size distribution (PSD) measuring by laser light scattering (LLS) and X-ray fluorescence (XRF). The obtained results showed that addition of sodium sulfate in low-alkaline reaction mixture enhances the aggregation of the particles of colloidal silica and formation of gel by the action of sulfate oxy-anions while in high-alkaline reaction mixtures the condensation process takes place on the surface of the crystalline end products. Excess amount of sodium ions do not increase the crystallization rate thus showing that the rate-determining factor is concentration of “free” low-molecular weight silicate species, determined by the alkalinity of system. On the other hand, addition of sodium sulfate considerably reduces the formation of crystal aggregates, by combined chemical and electrical interactions. Ageing of the reaction mixture (hydrogel) mainly influences the particle size distribution of the crystalline end products, which is explained by the change in the relative rates of crystal growth and crystal aggregation with the time of ageing. However, hydrogel ageing does not affect the size and number of crystals in the crystalline end product, showing that the growth precursor particles form during hydrothermal treatment of the reaction mixture and not during its room-temperature ageing.     

Radical-scavenging activity of extracts from Cordia verbenacea DC obtained by different methods

The possibility of using the leaves of Cordia verbenacea as a new source of natural antioxidant compounds was investigated. In the present work, extracts from C. verbenacea were obtained using different extraction methods: supercritical fluid extraction (SFE), Soxhlet (SE), hydrodistillation and maceration, with the objective to evaluate the methods in terms of yield and antioxidant potential. The high-pressure technique was applied using pure CO₂ and CO₂ with co-solvent at different temperatures and pressures (30, 40 and 50 °C and 100, 200, and 300 bar). Organic solvents with different polarities were used to obtain extracts by low-pressure extraction processes. The extracts were evaluated according to their antioxidant activity using total phenolic content, scavenging abilities on DPPH radical, total antioxidant activities (ABTS^•+), superoxide anion radical-scavenging (O₂^•) and protection against lipid peroxidation in vitro (LPO). Ethyl acetate fraction obtained by maceration and extract isolated by SE using 25% aqueous mixture of ethanol possessed the highest scavenger activity against DPPH radical (IC₅₀ = 9.2 ± 0.4 μg/ml, IC₅₀ = 27.4 ± 0.1 μg/ml, respectively). The SFE with 8% ethanol as a co-solvent produced extracts with distinguished increase in the antioxidant activity. The Soxhlet extract with ethyl acetate exhibited a strong reduction of lipid peroxidation (IC₅₀ = 209 ± 3 μg/ml) value comparable to the standard rutin (IC₅₀ = 203 ± 2 μg/ml). The results indicate that extracts of C. verbenacea have important potential as a source of bioactive compounds with antioxidant activity.     

Synchrotron SAXS 〈in situ〉 identification of three different size modes for soot nanoparticles in a diffusion flame

The high photon flux (10¹⁴ photons/s) and high spatial resolution (∼100 μm) of synchrotron radiation available at ID09b/ESRF facility has been exploited in an in situ investigation of the early stages of soot formation in an ethylene-air diffusion flame. SAXS data demonstrate in situ evidence that the size distribution of soot nanoparticles within the flame exhibits three distinct modes at different heights above the burner z’s. In particular, at z ∼ 3 mm, small particles (4-6 nm size), called sub-primary particles, are observed to come into existence. The corresponding monomodal distribution is observed to evolve to bimodal one at z > 5 mm, with the sub-primary particle mode being progressively depleted in favor of the growth of a mode corresponding to larger primary particles (10-12 nm size). The sub-primary peak vanishes completely at about z ∼ 20 mm where distribution is again single mode about 12 nm diameter. Porod’s plots show that the sub-primaries are born as configurational flat entities similar to discs or lamellae with a small aspect ratio (Porod’s exponent about 2), and upon going to higher z’s, they approach a spherical form with a smooth surface (Porod’s exponent about 4). Moreover, the careful use of Kratky plots has allowed to demonstrate the presence within the flame of very small nuclei, sized about 1.5-2 nm, which have a nucleation burst at about z ∼ 5 mm, whose number concentration progressively decreases at larger z, finally disappearing around z ∼ 15 mm. The relative increase of primary particles (size larger than 12 nm) is found to correspond to the progressive decrease of these very small nuclei (∼2 nm) concentration. At heights larger than 15 mm a strong ionization signal is observed that increases with height. These findings are in agreement with previous experimental works in the literature performed by Transmission Electron Microscopes and Differential Mobility Analyzers as well as with theoretical studies of dimer-dominated stochastic coagulation.     

Characterization and magnetic coercivity of nanostructured (Fe50Co50)100-XVX= 0,2,4 powders containing a small amount of Co3V intermetallic obtained by mechanical alloying

(Fe₅₀Co₅₀)_100−XV_X = 0,2,4 alloy powders were prepared by mechanical alloying. The milling times were 4 h, 8 h, 16 h, 24 h, 36 h, 55 h and 125 h, respectively. Structural, micro-structural and magnetic studies were carried out by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and a Vibration Sample Magnetometer (VSM). The XRD results showed that the inter-metallic compound (Co₃V) appears during milling and affects the coercivity, lattice parameter and micro-strain. Crystallite size decreases and reaches approximately 10 nm at 125 h. The coercivity increases during the milling and reaches a maximum at 55 h and then decreases slightly.     

Particle size design of digitoxin in supercritical fluids

Bioavailability of the pharmaceutical substances is very important for their activity. In case of necessity, bioavailability can be improved by reducing the particle size of the drugs. In this study, particle size of digitoxin was reduced by the Rapid Expansion of Supercritical Solutions (RESS). The effects of pre-expansion temperature (90-110 °C), flow rate (2.5-7.5 ml/min), spray distance (3-7 cm) on the size and size distribution of the precipitated digitoxin particles were carried out. The particles were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and LC-MS analysis.While the particle size range of the original digitoxin was 0.2-8 μm, it was decreased to 68-458 nm and determined that 97% of the particles were below 200 nm depending on the different experimental conditions.Response surface method (RSM) was used to optimize the process parameters. The flow rate, 7 ml/min; spray distance, 7 cm; pre-expansion temperature, 95 °C were found to be the optimum conditions to achieve the minimum particle size of digitoxin.     

Influence of precursor Bi/Fe ion concentration on hydrothermal synthesis of BiFeO3 crystallites

In this study we investigated the effect of precursor Bi³⁺/Fe³⁺ ion concentration on the hydrothermal synthesis of BiFeO₃ crystallites. It is demonstrated that the phase-purity and morphology of the products is highly dependent on the metal ion concentration. Phase-pure BiFeO₃ crystals can be prepared at the Bi³⁺/Fe³⁺ ion concentration ranging from 0.025 to 0.0625 M. The samples prepared at n(Bi³⁺/Fe³⁺)=0.025, 0.0375, 0.05, and 0.0625 M, are composed, respectively, of cuboid-like particles (100–200 nm), regular spherical agglomerates (30–40 μm) made up of irregular grains with size about several hundred nanometers, irregular flower-like clusters formed from irregular grains of several hundred nanometers in size, and octahedron-shaped particles (500–600 nm). These samples have a similar bandgap energy of 2.20 eV and exhibit a typical antiferromagnetic behavior at room temperature.     

A simple and efficient preparation of LaFeO3 nanopowders by glycine-nitrate process: Effect of glycine concentration

LaFeO₃ perovskites have been prepared by the glycine-nitrate process (GNP) at various glycine-to-nitrate molar ratios. The perovskites have been systematically characterized by X-ray diffraction, BET surface area, scanning electron microscopy, transmission electron microscopy and temperature-programmed reduction to study the effect of glycine concentration on various properties of LaFeO₃. The X-ray diffraction patterns of the as-prepared and calcined samples show the formation of orthorhombic phase without any impurities. The BET specific surface areas of various perovskites increased with an increase in glycine-to-nitrate ratio (GNR) of 2.0 but were nearly constant at higher ratios. The scanning electron microscopy indicates that the prepared material is flake-like at GNRs ≤1.5 and exists as agglomerated particles at GNRs ≥2.0. The particle size of the as-prepared samples was in the range of 30-130 nm depending on the GNR and the calcined samples exhibited particle size in the range of 60-160 nm. The samples that were prepared at GNR < 1.5 did not show any peaks in temperature-programmed reduction, but the samples prepared at a GNR of 2.0 and above showed the reduction of Feⁿ⁺.