Nanoparticles In Air Research Articles

Structural and thermal properties of boron nanoparticles synthesized from B2O3 + 3Mg + kNaCl mixture

Amorphous boron nanoparticles were synthesized by heating a B2O3+3Mg+kNaCl (k is the number of moles of NaCl) exothermic mixture in a laboratory oven at 800°C under argon flow. NaCl was used as inert material to decrease the maximum combustion temperature of the reaction mixture when it was self-ignited after the melting of Mg at 650°C. The size of the boron nanoparticles extracted from the final product by acid leaching ranged between 30 and 300nm for k values ranging from 1 to 5. Moreover, increasing the value of k from 1 to 5 resulted in an increase in the specific surface area of the nanoparticles from 40 to 74m2g−1. However, at k=10, a decrease in the specific surface area to 47.56m2g−1 was recorded due to incomplete reduction of B2O3. The ignition point of boron nanoparticles in air as estimated using a thermocouple was approximately 300°C. Digital camera recording of the combustion process of boron nanoparticles in air revealed that the burning speed of the nanoparticles increased significantly from 0.3 to 15cm/s when k increased from 1 to 5.

Double-walled core-shell structured Si@SiO2@C nanocomposite as anode for lithium-ion batteries

Double-walled core-shell structured Si@SiO2@C nanocomposite has been prepared by calcination of silicon nanoparticles in air and subsequent carbon coating. The obtained Si@SiO2@C nanocomposite demonstrates a reversible specific capacity of about 786 mAh g−1 after 100 cycles at a current density of 100 mA g−1 with a capacity fading of 0.13 % per cycle. The enhanced electrochemical performance can be due to that the double walls of carbon and SiO2 improve the electronic conductivity and enhance the compatibility of electrode materials and electrolyte as a result of accommodating the significant volumetric change during cycles. The interlayer SiO2 may release the mechanical strain and enhance the interfacial adhesion between carbon shell and silicon core.

Preparation of Extremely Small Pt Nanoparticle Catalysts and Their Electrocatalytic Activity for Oxygen Reduction Reaction

Introduction Polymer electrolyte fuel cells (PEFCs) have attracted great attention as the next generation energy device for electric vehicles due to their high energy conversion efficiency and low emission of pollutants. Pt nanoparticles-loaded carbon black (Pt/CB) is widely used as an electrocatalyst in PEFCs. However, it is necessary to minimize the consumption of Pt because of its high cost and diminishing reserves.CO is known to be strongly adsorbed on Pt atoms. If Pt nanoparticles are prepared in a CO atmosphere, the growth of Pt may be suppressed. Based on the above idea, we have prepared a Pt-carbonyl cluster complex ([Pt3(CO)3 (μ-CO)3]3 2−) by bubbling CO in an acetonitrile-water (1:1 in volume ratio) mixed solution containing PtCl6 2−.1 The complex spontaneously adsorbed on CB, and oxidatively broke and aggregated to form Pt nanoparticles in air. The resultant Pt nanoparticles had the monodispersed particle size of 1.8±0.3 nm. If the Pt-carbonyl cluster complex were fixed on CB with a stabilizer, the aggregation of the resultant Pt nanoparticles could be suppressed. In this study, we designed to inhibit the growth of Pt nanoparticles by electrostatically binding several kinds of stabilizers with the anionic complex on CB before converting to Pt. We characterized the resultant extremely small Pt nanoparticles-loaded CB and evaluated its catalysis for oxygen reduction reaction. Experimental Several cationic molecules, polydiallyldimethylammonium-chloride (PDDA), methyl-viologen(MV), benzyl-viologen(BV), cetyltrimethylammonium-bromide(CTA), pyridine(Pyr), bipyridine(Bpy) and terpyridine (Tpy), were used as a stabilizer in this study. They were mixed after the Pt-carbonyl cluster complex dianion was adsorbed on CB, leading to the production of ionic couples due to electrostatic interaction. Results and Discussion Pt nanoparticles prepared with stabilizers except CTA were smaller in mean size than conventional Pt nanoparticles (ca. 1.8 nm) prepared without stabilizer, suggesting that each stabilizer inhibited the growth of Pt nanoparticles on CB.In ORR, specific activity (SA), activity per unit electrochemical surface area of Pt, and mass activity (MA), activity per mass of Pt, for the Pt/CB catalyst prepared with bipyridine (Pt/CB+Bpy) were ca. 1.4 and 1.6 times higher than those of the commercial catalyst (Pt/CB-TKK(Tanaka Kikinzoku Kogyo TEC10E50E)), respectively. X-ray photoelectron spectra exhibited that in Pt(4f) core level spectra of Pt/CB+Bpy, a peak assigned to metallic Pt shifted to higher binding energy because of the final state effect and a decrease in electron density of Pt surface atoms due to adsorption of electron-withdrawing stabilizers, which seems to weaken Pt-O bond and increase SA and MA. Reference 1. E. Higuchi, A. Taguchi, K. Hayashi, H. Inoue, J. Electroanal. Chem., 663, 83-89 (2011).

Fabrication of Si nanoparticles from Si swarf and application to solar cells

Abstract Si nanoparticles with diameter of 1–20 nm have been fabricated from Si swarf by use of a beads milling method. Treatment with dilute hydrofluoric acid stabilizes Si nanoparticles, and the thickness of the SiO2 layer formed by leaving nanoparticles in air for one week is only 1.2 nm. p-Si nanoparticles/crystalline n-Si structure shows rectifying behavior, indicating formation of pn-junction. Treatment with nitric acid followed by heating at 900 °C greatly decreases series resistance, showing that the ultrathin SiO2 layer formed by nitric acid oxidation melts and is bound to surrounding nanoparticles. p-type Si nanoparticles/n-type crystalline Si structure shows rectifying behavior and the photovoltaic effect, indicating that Si nanoparticles are applicable to solar cells.

Electrochemical Preparation of N‐Doped Cobalt Oxide Nanoparticles with High Electrocatalytic Activity for the Oxygen‐Reduction Reaction

Nitrogen-doped CoO (N-CoO) nanoparticles with high electrocatalytic activity for the oxygen-reduction reaction (ORR) were fabricated by electrochemical reduction of CoCl2 in acetonitrile solution at cathodic potentials. The initially generated, highly reactive nitrogen-doped Co nanoparticles were readily oxidized to N-CoO nanoparticles in air. In contrast to their N-free counterparts (CoO or Co3 O4 ), N-CoO nanoparticles with a N content of about 4.6 % exhibit remarkable ORR electrocatalytic activity, stability, and immunity to methanol crossover in an alkaline medium. The CoNx active sites in the CoO nanoparticles are held responsible for the high ORR activity. This work opens a new path for the preparation of nitrogen-doped transition metal oxide nanomaterials, which are promising electrocatalysts for fuel cells.

Comparative STM studies of mixed ligand monolayers on gold nanoparticles in air and in 1-phenyloctane.

Scanning tunnelling microscopy (STM) studies have found stripe-like domains on gold nanoparticles (NPs) coated with certain binary mixtures of ligand molecules. The majority of these NPs' properties have been investigated for particles in solvents. Yet, most STM studies are for NPs in a dry state. Images of the same particles in air and liquid have not been obtained yet. In this work, a judicious choice of ligand molecules led to NPs with close-to-ideal STM imaging conditions in air and in 1-phenyloctane (PO). Large datasets under both conditions were acquired and rapidly evaluated through power spectral density (PSD) analysis. The result is a quantitative comparison of stripe-like domains in air and PO on the same NPs. PSD analysis determines a characteristic length-scale for these domains of ~1.0 nm in air and in PO showing persistence of striped domains in these two media. A length scale of ~0.7 nm for homoligand NPs was found.

Photocatalytic properties of SnS2/SnO2 nanocomposite prepared by thermal oxidation of SnS2 nanoparticles in air

An alternative in situ chemical method, which was based on thermal oxidation of SnS2 nanoparticles in air at 300°C for 3h, was proposed for the preparation of SnS2/SnO2 nanocomposite (SnS2/SnO2-TO). The photocatalytic properties of SnS2/SnO2-TO were tested by the reduction of aqueous Cr(VI) under visible-light (λ>420nm) irradiation, and compared with those of SnS2 nanoparticles, SnO2 nanoparticles and SnS2/SnO2-PM (which denotes the physically mixed SnS2/SnO2 nanocomposite with the same composition as SnS2/SnO2-TO). Besides, the effects of the coexistence of some organic compounds (e.g., phenol, rhodamine B (RhB) and methyl orange (MO)) on SnS2/SnO2-TO-mediated photocatalytic reduction of aqueous Cr(VI) were also studied. It was observed that (i) SnS2/SnO2-TO not only displayed higher visible-light-activated photocatalytic activity than SnS2, SnO2 and SnS2/SnO2-PM, but also displayed good reusability in the reduction of aqueous Cr(VI); and (ii) the coexistence of phenol and RhB enhanced the photocatalytic reduction of Cr(VI), whereas the coexistence of MO retarded the photocatalytic reduction of Cr(VI) over SnS2/SnO2-TO. The reasons accounting for the photocatalytic results were also discussed.

Water purification and toxicity control of chlorophenols by 3D nanofiber membranes decorated with photocatalytic titania nanoparticles

Highly photocatalytic water purification three-dimensional nanofiber membranes were fabricated. We identified the optimal fabrication process of nylon-6 nanofiber membranes suspending titania nanoparticles for potential water purifications and toxicity control of chlorophenols. Nanofibers and nanoparticles were deposited on a soda lime glass substrate by electrospinning and electrospraying, respectively. Titania nanoparticles were used to induce the UV light driven photocatalytic effect and nanofibers were used to tightly suspend the nanoparticles in air. Both batch and continuous deposition processes were introduced in the membrane fabrication process and their water purification performances were compared and quantified using a methylene blue solution, which is often used as a model pollutant. Surface morphologies and characteristics of the membranes fabricated at various process conditions were also provided. The membrane fabricated by the continuous means yielded 100% degradation of the methylene blue solution within 90min under a relatively weak UV irradiation (0.6mW/cm2), which promises its potential indoor application. The nano-textured membranes developed in this work was also applied to the real pollutants, such as chlorophenols, and showed a promising performance in their toxicity control.

Preparation and Optical Properties of YH2:Er2+ and Y2O3:Er3+ Nanoparticles

The rare earth hydride nanoparticles have been prepared successfully by a novel method of hydrogen plasma-metal reaction. The YH2:Er2+ nanoparticles of 40-50 nm were polycrystalline and in hexagonal shape. The Y2O3:Er3+ nanoparticles were fabricated by annealing the hydride nanoparticles in air at 300, 500 and 700 degrees C, respectively. The influence of the sintering temperature on the size, crystal structure and optical properties of these nanoparticle samples were investigated. After annealing, the Y2O3:Er3+ nanoparticles became single crystalline and spherical shape, and the mean particle size of these particles did not change apparently upon the annealing temperature up to 700 degrees C. With the increase of the annealing temperature, the absorption intensity of YH2 in the Fourier transform infrared spectroscopy spectra decreased and the peak position moved to high-frequency, whereas the absorption intensity of Y2O3 was enhanced. The intensity of the near-IR fluorescence spectra of the Y2O3:Er3+ nanoparticles increased remarkably with the increase of the annealing temperature from 300 to 700 degrees C. The Y2O3:Er3+ sample sintered at 700 degrees C exhibited a strong photoluminescent intensity at the wavelength of about 1535 nm, with a narrow full width of 6 nm at the half maximum. This makes the Y2O3:Er3+ nanoparticles promising for the applications in the optical communication devices.

Highly Selective Adsorption of Plants' Leaves on Nanoparticles

Adsorption of fine particles in air by a leaf is studied experimentally. It is found that each leaf can absorb only a kind of particles with almost same size, and it also exhibits high selectivity over other particles. The SEM study reveals that the size of nanopore on the epidermis is a main factor of the highly selective adsorption; the smaller nanopores can absorb larger nanoparticles in air. The morphology of a lotus leaf, which is waterproof and dustproof, has, on the other hand, many short nanofibrils instead of nanopores. It is concluded that the nanoscale geometrical structure of a surface affects its attraction/repulsion property. The experiment also shows that one square millimeter surface with nanopores in diameter of 18 nm can absorb 2 million nanoparticles of about 200 nm in diameter from air in 24 hours. A better understanding of the adsorption/repulsion mechanism could help the further design of bio-mimetic waterproof/dustproof artificial materials and artificial porous materials/fabrics/nonwovens for adsorption of nanoparticles in air.

Intrinsic and impurity defects in chromium‐doped SrTiO3 nanopowders: EPR and NMR study

AbstractElectron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) spectra were studied in solvothermal‐ and citrate sol–gel‐grown (CSGG) SrTiO3:Cr(0.1%) crystalline nanopowders. Various growth conditions and thermal treatments were used to determine defects and to tailor nanoparticles structure and crystallization processes. Solvothermal‐grown nanopowders with 5 nm particle size revealed the dominant presence of the single perovskite‐type phase. Annealing of the CSGG nanoparticles in air up to 800 °C leads to an increase of the particles size and the amount of the titanium dioxide (rutile and/or anatase) phase, which is initially present in small amounts in CSGG powders. It was found that paramagnetic Cr3+, Cr5+, ${\rm Cr}_{{\rm surf}}^{{\rm 3 + }} $, O−, O2− ions are present in solvothermal‐grown nanopowders and in all CSGG powders. In the annealed particles the majority of paramagnetic centers (PC) are located in the particle surface and in the TiO2 phase. The nature of the PC in nanopowders exhibiting different degrees of catalytic activity in nanopowders was studied too. A correlation between O− and O2− content, synthesis conditions and particle size was found. The NMR spectra of 47Ti (I = 5/2) and 49Ti (I = 7/2) reveal a pronounced dependence of the spectral line intensity on synthesis conditions, evidencing coexistence of Ti3+ and Ti4+ ions in SrTiO3:Cr nanoparticles.

Photoluminescence of silicon nanoparticles chemically modified by alkyl groups and dispersed in low-polar liquids

A detailed comparative analysis of photoluminescence behavior of silicon nanoparticles in air and dispersed in low-polar liquids is reported. Efficient dispersion and excellent stability of the chemically modified nanoparticles in low-polar liquids are achieved. Influence of the chemical functionalization and of the low-polar liquids on steady-state and time-resolved photoluminescence of the silicon nanoparticles is investigated. Role of low-polar liquids on recombination mechanisms taking place in the nanoparticles is discussed in terms of Forster resonant energy transfer processes. Effect of exciting laser power on photoluminescence spectra of the silicon nanoparticles both in air and in low-polar liquids is investigated and the electronic mechanisms involved into the observed phenomena are discussed.

Facile synthesis of porous bifunctional Fe3O4@Y2O3:Ln nanocomposites using carbonized ferrocene as templates

Porous magnetic-luminescent Fe3O4@Y2O3:Ln (Ln = Eu, Yb/Er) nanoparticles (NPs) have been fabricated using carbonized ferrocene as templates. Through hydrothermal carbonization of ferrocene, carbon-coated Fe3O4 NPs were obtained, providing both a magnetic core and a good depositing surface to establish a uniform layer of Ln(OH)CO3:Ln. After annealing the pre-synthesized Fe3O4@C@Y(OH)CO3:Ln NPs in air, core–shell Fe3O4@Y2O3:Ln NPs with a porous morphology were synthesized. The as-synthesized NPs are uniform in size with a core diameter of 140 nm and a shell thickness of 20 nm. N2 adsorption–desorption isotherms reveal that these porous NPs possess a large surface area of 32 m2 g−1. After being doped with different lanthanide ions, these NPs can exhibit various down- and up-conversion emissions. Magnetic measurements also indicate that these NPs display superparamagnetic behavior and high magnetization at room temperature.

Microstructure and superconducting properties in air-properties GdBa2Cu3O7-δ superconductor with the additives of nano particles

It is regarded as an effective method to improve the flux pinning performance by the additives of the secondary phase inclusions in nano sizes into high temperature superconductor bulks. We prepared the single domain superconductor GdBa2Gi3O7-δ bulks with variable additions of (ZrO2+SnO2+ZnO) nano-particles in air by using top seed melt-textured growth process. The effect of nano-particle additions on superconductivity properties has been investigated. An enhancement of the critical current JC in low and intermediate field at 77K and trapped field was discovered by the additions of the nano-particles. At the same time, the superconductor transition temperature, TC, slightly decreases from 93.5K to 91.5K The microstructure measurements show that the nano-particle inclusions enhance with the increase of the content of nano-particles, which may illuminate the JC enhancement of the specimens.

Nearly full-dense and fine-grained AZO:Y ceramics sintered from the corresponding nanoparticles

Aluminum-doped zinc oxide ceramics with yttria doping (AZO:Y) ranging from 0 to 0.2 wt.% were fabricated by pressureless sintering yttria-modified nanoparticles in air at 1,300°C. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, a physical property measurement system, and a densimeter were employed to characterize the precursor nanoparticles and the sintered AZO ceramics. It was shown that a small amount of yttria doping can remarkably retard the growth of the as-received precursor nanoparticles, further improve the microstructure, refine the grain size, and enhance the density for the sintered ceramic. Increasing the yttria doping to 0.2 wt.%, the AZO:Y nanoparticles synthetized by a coprecipitation process have a nearly sphere-shaped morphology and a mean particle diameter of 15.1 nm. Using the same amount of yttria, a fully dense AZO ceramic (99.98% of theoretical density) with a grain size of 2.2 μm and a bulk resistivity of 4.6 × 10−3 Ω·cm can be achieved. This kind of AZO:Y ceramic has a potential to be used as a high-quality sputtering target to deposit ZnO-based transparent conductive films with better optical and electrical properties.

Highly sensitive laser-based sensor for nanoparticles in air using a dual-ring-mirror setup

One of the most frequently applied techniques to detect nanoparticles in air is analyzing laser light scattering. This technique is very flexible while offering high accuracy and reliability. Yet its functionality highly depends on the sensitivity of the measurement system components. Especially for miniaturized sensor devices with limited space, additional techniques are needed to preserve high intensity of scattered light. In our work we demonstrate a technique using two spherical ring mirrors to identify nanoparticles with diameters below 100 nm in a forward-scattering setup. We succeeded measuring polystyrene particles with diameters of 92 nm with a signal-to-noise-ratio of more than 10.

Deodorization of a gas stream containing dimethyl disulfide with zero-valent iron nanoparticles

In this work, zero-valent iron nanoparticles (50–200nm) were synthesized for the complete reduction of dimethyl disulfide (DMDS) to give methane and iron sulfide. Iron quantity and pH were varied to study their influence on the reaction. A 60% reduction in DMDS was achieved, but it was observed that the desired reaction to give methane only occurred at the very first stage of the experiment. The production of sulfur byproducts was subsequently observed. The evidence suggests that there are two mechanisms of the reaction which compete simultaneously. In the first, CS and SS bonds are broken to give methane and FeS. This mechanism is more rapid, but results in lower conversion of DMDS. In the second mechanism, only SS bonds are broken. It results in a lower reaction velocity and higher conversion of DMDS. The evidence also suggests that the oxidation of iron nanoparticles in air acts to limit the quantity of iron that can be employed. It was also shown that the reaction did not occur at basic pH, and that acid addition did not improve DMDS reduction. Bimetallic nanoparticles were synthesized to minimize the production of byproducts; Ni/Fe provided the best results. The reduction of sulfur compounds by nanoparticles offers great opportunities for odor removal and environmental applications, but more studies need to be performed to improve the selectivity of the reaction to yield methane.

Femtosecond Laser‐Induced Formation of Wurtzite Phase ZnSe Nanoparticles in Air

We demonstrate an effective method to prepare wurtzite phase ZnSe nanoparticles from zincblende ZnSe single crystal using femtosecond pulse laser ablation. The fabricated ZnSe nanoparticles are in spherical shape and uncontaminated while synthesized under ambient environment. By controlling the laser fluences, the average size of ZnSe nanoparticles can be varied from ~16 nm to ~22 nm in diameter. In Raman spectra, the surface phonon mode becomes dominant in the smaller average particle size with uniform size distribution. The interesting phase transition from the zinc blende structure of ZnSe single crystal to wurtzite structure of ZnSe nanoparticles may have been induced by the ultrahigh ablation pressure at the local area due to the sudden injection of high energy leading to solid‐solid transition.

Zinc oxide nanoparticles: A study of defect level blue–green emission

Systematic investigation of the structural, morphological and optical properties of hexylamine capped zinc oxide (ZnO) nanoparticles is presented. Optical properties indicate the presence of sufficient amount of surface defects. These defects in highly dispersed ZnO nanoparticles have been studied by annealing the nanoparticles in air at various temperatures and recording the photoluminescence spectra. The annealing temperature was found to strongly influence the UV band edge emission and the blue–green defect level emission (DLE). At low annealing temperatures an increase in UV emission with temperatures is observed and this emission is proposed to be a result of desorption of surface adsorbed water and hydroxyl groups. The DLE of the synthesized sample is likely due to the presence of oxygen vacancies on the surface resulting in green emission.

“Magnetic Force Microscopy and Energy Loss Imaging of Superparamagnetic Iron Oxide Nanoparticles”

We present quantitative, high spatially resolved magnetic force microscopy imaging of samples based on 11 nm diameter superparamagnetic iron oxide nanoparticles in air at room temperature. By a proper combination of the cantilever resonance frequency shift, oscillation amplitude and phase lag we obtain the tip-sample interaction maps in terms of force gradient and energy dissipation. These physical quantities are evaluated in the frame of a tip-particle magnetic interaction model also including the tip oscillation amplitude. Magnetic nanoparticles are characterized both in bare form, after deposition on a flat substrate, and as magnetically assembled fillers in a polymer matrix, in the form of nanowires. The latter approach makes it possible to reveal the magnetic texture in a composite sample independently of the surface topography.