Single Charging of Nanoparticles by UV Photoionization at High Flow Rates

The feasibility of UV photoionization for single unipolar charging of nanoparticles at flow rates up to 100 l· min ^?1 is demonstrated. The charging level of the aerosol particles can be varied by adjusting the intensity of the UV radiation. The suitability of a UV photocharger followed by a DMA to deliver monodisperse nanoparticles at high aerosol flow rates has been assessed experimentally in comparison to a radioactive bipolar charger ( ⁸⁵ Kr, 10 mCi). Monodisperse aerosols with particle sizes in the range of 5 to 25 nm and number concentrations between 10 ⁴ and 10 ⁵ cm ^?3 have been obtained at flow rates up to 100 l· min ^?1 with the two aerosol chargers. In terms of output particle concentration, the UV photoionizer performs better than the radioactive ionizer with increasing aerosol flow rate. Aerosol charging in the UV photoionizer is described by means of a photoelectric charging model that relies on an empirical parameter and of a diffusion charging model based on the Fuchs theory. The UV photocharger behaved as a quasi-unipolar charger for polydisperse aerosols with particles sizes less than 30 nm and number concentrations ～10 ⁷ cm ^?3 . Much reduced diffusion charging was observed in the experiments, with respect to the calculations, likely due to ion losses onto the walls caused by unsteady electric fields in the irradiation region.     

A Differential Mobility Analyzer (DMA) for Size Selection of Nanoparticles at High Flow Rates

This article demonstrates the feasibility of scaling-up the technique for particle size selection in the gas phase based on differential mobility analysis. Nano-DMAs used to select the particle size in processes for the synthesis of nanomaterials in the laboratory operate at aerosol flow rates of a few liters per minute. A new DMA capable of classifying nanoparticles of up to 30 nm in size at aerosol flow rates as high as 100 l· min ^?1 will be presented (HF-DMA). A major advantage of the HF-DMA over current nano-DMAs covering the same particle size is that its resolution is almost unaffected by Brownian diffusion for particles as small as 3 nm. Monodisperse nanoparticles in the 5 to 25 nm size range have been produced at flow rates of up to 90 l· min ^?1 . The spread in particle size and the particle number concentration were studied with respect to their dependency on the flow rates in the HF-DMA. The measurements reflect the behavior predicted by the theory. The HF-DMA makes it possible to deliver nanoparticles of a well-defined size at yields two orders of magnitude higher than with current nano-DMAs.     

Synthesis and characterisation of nanocrystalline Ca–Al layered double hydroxide {[Ca2Al(OH)6]NO3.nH2O}: in vitro study

Abstract

Abstract

In this study, Ca–Al–NO₃ layered double hydroxide (LDH) nanoparticles of varying sizes were synthesised by a process involving co-precipitation under hydrothermal condition. This method produces stable homogeneous LDH suspensions under variable hydrothermal treatment conditions with particle size in the range of 7·5–2·5 μm. Layered double hydroxides were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, thermal gravimetric/differential thermal analysis, scanning electron microscopy and transmission electron microscopy (TEM) and nanosizer analyses. By increasing the hydrothermal treatment time, the crystallinity and the particle size of obtained LDH increased. Scanning electron microscopy and TEM observations showed uniform hexagonal flake-like particles with high aspect ratio. Finally, Ca–Al–NO₃ LDH did not show any acute cytotoxic effect up to 100 μg mL^?1 as measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.     

Characterization of a dimer preparation method for nanoscale organic aerosol

Nanoscale dimers have application in studies of aerosol physicochemical properties such as aerosol viscosity. These particle dimers can be synthesized using the dual tandem differential mobility analyzer (DTDMA) technique, wherein oppositely charged particle streams coagulate to form dimers that can be isolated using electrostatic filtration. Although some characterization of the technique has been published, a detailed thesis on the modes and theory of operation has remained outside the scope of prior work. Here, we present new experimental data characterizing the output DTDMA size distribution and the physical processes underlying its apparent modes. Key experimental limitations for both general applications and for viscosity measurements are identified and quantified in six distinct types of DTDMA experiments. The primary consideration is the production of an adequate number of dimers, which typically requires high mobility-selected number concentration in the range 25,000–100,000?cm^?3. The requisite concentration threshold depends upon the rate of spontaneous monomer decharging, which arises predominately from interactions of the aerosol with ionizing radiation within the coagulation chamber and is instrument location dependent. Lead shielding of the coagulation chamber reduced the first-order decharging constant from ～2.0?×?10^?5 s^?1 to ～0.8?×?10^?5 s^?1 in our laboratory. Dimer production at monomer diameters less than 40?nm is hindered by low bipolar charging efficiency. Results from the characterization experiments shed light on design considerations for general applications and for characterization of viscous aerosol phase transitions.

Copyright © 2019 American Association for Aerosol Research     

Al2O3–Ag nanopowders: new method of synthesis,characterisation and biocidal activity

Abstract

Abstract

The present paper describes an innovative method of producing silver nanoparticles incorporated into an aluminium nano‐oxide substrate. The method utilises thermal decomposition and reduction, which yields an Al₂O₃–Ag nanopowder with the average size of particles ranging from 43 to 60?nm and the average size of agglomerates between 330 and 870?nm. The average size of the silver nanoparticles incorporated in the aluminium nano‐oxide carrier ranges from 22 to 60?nm. The Al₂O₃–Ag nanopowders thus produced have a largely developed surface area (above 200?m²?g^?1) with a great number of open pores (above 5×10^?4?m³?g^?1), which gives evidence that their tendency to agglomeration is only slight and that the possible agglomerates have a loose structure. Moreover, the nanopowders show good bactericidal and fungicidal properties. The results obtained in the present experiments show that the Al₂O₃–Ag nanopowders produced by the proposed method can be used successfully as the raw material in the production of biocidal biomaterials.     

Synthesis of spherical lead zirconate titanate (PZT) nanoparticles by electrohydrodynamic atomisation

Abstract

This paper describes the production of spherical-shaped lead zirconate titanate (PZT) nanoparticles by the electrohydrodynamic atomisation (EHDA) process in order to make inks suitable for ink jet printing applications. PZT sols with different concentrations (0·1–0·6 M) were used as starting materials. Two different heating systems, gas heating and direct heating, were used in order to remove the solvent, reduce the particle size and stabilise the PZT particles. Several aspects have been considered, such as liquid flow rate, sol concentration and heat system temperature, and their influence on the particle dimension is determined. Using optimised processing parameters of direct heating at 520°C, 0·2 M precursor sol, flow rate of 0·2 mL h^?1 and field of 3 kV cm^?1, particles of 100–300 nm in diameter were synthesised. Following stabilisation at 300°C, the particles were suspended in a PZT sol to produce an ink suitable for ink jet printing.     

Condensation Particle Counter Proportionality Calibration from 1 Particle·cm−3 to 104 Particles·cm−3

This article presents a process to calibrate a condensation particle counter (CPC) over the concentration range from 1 particle·cm^?3 to 10⁴ particles·cm^?3 with traceability to SI units as realized by the National Institute of Standards and Technology (NIST). The process combines two independent steps: a proportionality assessment over the range of the CPC using a consistent diluter and an absolute calibration of the CPC with an aerosol electrometer (AE) at high concentrations. The proportionality assessment, which is the focus of the article, is analogous to the attenuation method for testing the proportionality of high-power laser detectors. This procedure tests the proportionality of one CPC by itself and does not require the use of a calibrated reference CPC. The primary calibration of the CPC with the AE at high concentrations allows for an absolute calibration with NIST traceability, resulting in a simple one-parameter correction to the measured CPC data. The proportionality test enables uncertainties to be assigned to the CPC over an extended range of concentration beyond the lower detection limit of the AE, thereby establishing measurement traceability for low concentrations. The relative expanded uncertainty of the CPC with a coverage factor of k = 2 is 2.8% over the range of about 1 particle·cm^?3 to 10⁴ particles·cm^?3.     

Effect of skimmed milk powder concentrations on the biological characteristics of microencapsulated Saccharomyces cerevisiae by vacuum-spray-freeze-drying

Abstract

The effects of skimmed milk powder (SMP) concentrations on the biological characteristics of microencapsulated Saccharomyces cerevisiae prepared by employing vacuum-spray-freeze-drying (VSFD) technology are evaluated. Results show that the live bacteria rate of S. cerevisiae embedded with 11% SMP is 76.36%, which is higher than that in other concentrations. Scanning electron microscope (SEM) photographs indicate that the SMP concentration exhibits a significant impact on the surface morphology of microencapsulation. Moreover, microparticles with SMP at the concentration of 11% provide the highest stability levels in both high and low temperature conditions. Cell counts in the microparticles with 11% SMP show a reduction of 3.9 (60?°C, 20?min) log CFU mL^?1, 3.13 (50?°C, 20?min) log CFU mL^?1, 0.23 (40?°C, 20?min) log CFU mL^?1, 2.74 (4?°C, week) and 0.72 (10?°C, week) log CFU mL^?1, respectively, which are all lower than that of powders with 3% SMP. Furthermore, the best-quality icewine exhibiting the typical features of a fresh fragrance and a delicate taste is used for the in vivo fermentation process. Fermentation is initialized by the microencapsulated cells with 11% SMP. These results indicate that the complex materials containing an SMP concentration of 11% as a carrier can be considered as a better choice for improving the stability and survival rate of S. cerevisiae.     

A novel miniature inverted-flame burner for the generation of soot nanoparticles

Lab-scale soot nanoparticle generators are used by the aerosol research community to study the properties of soot over a broad range of particle size distributions, and number and mass concentrations. In this study, a novel miniature inverted-flame burner is presented and its emitted soot particles were characterized. The burner consisted of two co-annular tubes for fuel and co-flow air and the flame was enclosed by the latter. The fuel used was ethylene. A scanning mobility particle sizer (SMPS) and an aerodynamic aerosol classifier (AAC) were used to measure mobility and aerodynamic size distribution of soot particles, respectively. Particle morphology was studied using transmission electron microscopy (TEM). The elemental carbon (EC) and organic carbon (OC) content of the soot were measured using thermal-optical analysis (TOA). The burner produced soot particles with mobility diameter range of 66–270?nm, aerodynamic diameter range of 56–140?nm, and total concentration range of 2?×?10⁵–1?×?10⁷?cm^?3. TEM images showed that most soot particles were sub-micron soot aggregates. Some soot superaggregates, typically larger than 2?µm in length, were observed and their abundance increased with ethylene flow rate. TOA showed that the concentration of EC in the generated soot increased with ethylene flow rate, and the soot was observed to have high EC fraction at high ethylene flow rates. The miniature inverted-flame burner was demonstrated to produce soot nanoparticles over a range of concentrations and sizes with high EC content, making it a practical device to study soot nanoparticle properties in different applications.

Copyright © 2019 American Association for Aerosol Research     

Emissions and radiative impacts of sub-10 nm particles from biofuel and fossil fuel cookstoves

Abstract

Combustion sources have been shown to directly emit particles smaller than 10?nm. The emission of 1-3?nm particles from biofuel or fossil fuel cookstoves has not been studied previously, nor have the radiative impacts of these emissions been investigated. In this work, emissions (number of particles) were measured during a water boiling test performed on five different cookstoves (three-stone fire, rocket elbow, gasifier, charcoal, and liquified petroleum gas [LPG]) for particle diameters between ～1 and ～1000?nm. We found significant emissions of particles smaller than 10?nm for all cookstoves (>5?×?10¹⁵ # kg-fuel^?1). Furthermore, cleaner (e.g., LPG) cookstoves emitted a larger fraction of sub-10?nm particles (relative to the total particle counts) than traditional cookstoves (e.g., three-stone fire). Simulations performed with the global chemical transport model GEOS-Chem-TOMAS that were informed by emissions data from this work suggested that sub-10?nm particles were unlikely to significantly influence number concentrations of particles with diameters larger than 80?nm that can serve as cloud condensation nuclei (CCN) (<0.3%, globally averaged) or alter the cloud-albedo indirect effect (absolute value <0.005?W m^?2, globally averaged). The largest, but still relatively minor, localized changes in CCN-relevant concentrations (<10%) and the cloud-albedo indirect effect (absolute value <0.5?W m^?2) were found in large biofuel combustion source regions (e.g., Brazil, Tanzania, Southeast Asia) and in the Southern Ocean. Enhanced coagulation-related losses of these sub-10?nm particles at sub-grid scales will tend to further reduce their impact on particle number concentrations and the aerosol indirect effect, although they might still be of relevance for human health.

Copyright © 2020 American Association for Aerosol Research     

Assessment of a Cylindrical and a Rectangular Plate Differential Mobility Analyzer for Size Fractionation of Nanoparticles at High-Aerosol Flow Rates

An existing differential mobility analyzer (DMA) of cylindrical electrodes and a novel DMA of rectangular plate electrodes are demonstrated for size fractionation of nanoparticles at high-aerosol flow rates in this work. The two DMAs are capable of delivering monodisperse size selected nanoparticles (SMPS σ_g < 1.1) at gas flow rates ranging from 200 slm to 500 slm. At an aerosol flow rate of 200 slm, the maximum attainable particle mean size is of about 20 nm for the cylindrical DMA and of nearly 50 nm for the rectangular plate DMA. The number concentration of the monodisperse nanoparticles delivered by the high-flow DMAs spans from 10⁴ cm^?3 to 10⁶ cm^?3 depending upon the particle mean size and particle size dispersion.

Copyright 2014 American Association for Aerosol Research     

Ozone-free post-DBD aerosol bipolar diffusion charger: Evaluation as neutralizer for SMPS size distribution measurements

A postplasma neutralizer for submicron particles size measurements by mobility analysis has been evaluated. Bipolar ion currents have been measured downstream a dielectric barrier discharge (DBD) to estimate the ion fluxes at the inlet of charging volume and the n_i·τ product that define the theoretical maximal concentration that can be neutralized. Charge distributions were measured versus DBD voltage, aerosol diameter and concentration for monodisperse aerosols. It is confirmed that the charge distribution of particles depends on the ratio of initial positive and negative ion currents controlled by the DBD voltage leading to a tuneable mean charge of aerosol in this post-DBD bipolar charger. As expected from Gunn's law, the mean charge and the variance are proportional to particle diameter above 50 nm and independent of the aerosol concentration. The size distributions measured with ⁸⁵Kr and post-DBD neutralizer present the same modal diameters and a maximal overestimation of the total concentration of 10%, for aerosol from 15 to 730 nm with concentrations up to 6 × 10¹² m^?3. This post-DBD bipolar charger can be used for submicron aerosol neutralization and thus for scanning mobility particle sizer size distribution measurements in air as well as in nitrogen to suppress ozone downstream DBD.

Copyright © 2017 American Association for Aerosol Research     

First measurements of the number size distribution of 1–2 nm aerosol particles released from manufacturing processes in a cleanroom environment

This study was conducted to observe a potential formation and/or release of aerosol particles related to manufacturing processes inside a cleanroom. We introduce a novel technique to monitor airborne sub 2 nm particles in the cleanroom and present results from a measurement campaign during which the total particle number concentration (>1 nm and >7 nm) and the size resolved concentration in the 1 to 2 nm size range were measured. Measurements were carried out in locations where atomic layer deposition (ALD), sputtering, and lithography processes were conducted, with a wide variety of starting materials. During our campaign in the clean room, we observed several time periods when the particle number concentration was 10⁵ cm^?3 in the sub 2 nm size range and 10⁴ cm^?3 in the size class larger than 7 nm in one of the sampling locations. The highest concentrations were related to the maintenance processes of the manufacturing machines, which were conducted regularly in that specific location. Our measurements show that around 500 cm^?3 sub 2 nm particles or clusters were in practice always present in this specific cleanroom, while the concentration of particles larger than 2 nm was less than 2 cm^?3. During active processes, the concentrations of sub 2 nm particles could rise to over 10⁵ cm^?3 due to an active new particle formation. The new particle formation was most likely induced by a combination of the supersaturated vapors, released from the machines, and the very low existing condensation sink, leading to pretty high formation rates J_{1.4 nm} = (9 ± 4) cm^?3 s^?1 and growth rates of particles (GR_{1.1–1.3 nm} = (6 ± 3) nm/h and GR_{1.3–1.8 nm} = (14 ± 3) nm/h).

Copyright © 2017 American Association for Aerosol Research     

Thermoresponsive and acid-cleavable amphiphilic copolymer micelles for controlled drug delivery

Thermoresponsive and acid-cleavable amphiphilic block copolymers poly(N-isopropylacrylamide)-acetal-poly(4-substituted-ε-caprolactones) (PNiPAAm-a-PXCLs) containing an acidic-cleavable acetal linkage at the junction between the temperature-sensitive hydrophilic PNiPAAm and the degradable hydrophobic block PXCL were synthesized through ring-opening polymerization and electrophilic addition reactions. These polymer solutions showed reversible changes in optical properties and a lower critical solution temperature in the range of 32.0–46.4°C. The copolymers formed micelles in aqueous solution with critical micelle concentrations in the range of 0.83–15.95?mg?L^?1 had hydrodynamic sizes of <200?nm and were spherical. Under the combined stimulation of temperature and pH, the micellar nanoparticles could be dissociated; the loaded molecules could be released from the assemblies more efficiently than that under only one stimulus or without stimulus. In addition, the nanoparticles exhibited low toxicity against human cervical cancer (HeLa) cells at concentrations ≤1000?µg?mL^?1. Doxorubicin-loaded PNiPAAm₁₁-a-PCL₂₈ micelles also effectively inhibited the proliferation of HeLa cells with a half-maximal inhibitory concentration (IC₅₀) of 1.60?µg?mL^?1.     

Synthesis,and characterization folate-conjugated photocleavable poly(4-substituted-ε-caprolactone) polymers for drug delivery

Abstract

Photo-cleavable polymers containing 5-hydroxy-2-nitrobenzyl alcohol (ONB) junction point between the target molecule of folic acid (FA) and the hydrophobic poly(4-substituted-?-caprolactone) (PXCL_n) chain were synthesized. FA –terminated ONB-PXCL_n polymers formed micelles with critical micelle concentration (CMC) 1.2 – 64.3?mg L^?1. Fluorescence emission spectroscopy indicated the release of Nile red encapsulated FA-ONB-PXCL_n micelles in response to irradiation. Light-triggered bursts released were observed for drug-loaded FA-ONB-PXCL_n micelles. The nanoparticles exhibited nonsignificant toxicity at concentrations up to 300?µg mL^?1. Flow cytometry revealed that the uptake of folate-targeted doxorubicin (DOX) -encapsulated micelles by HeLa cells was faster than that of free DOX.     

Direct Determination of Ultra-trace Plutonium Nanoparticles in Downstream of a Six-Stage HEPA Filter by Inductively-Coupled-Plasma Mass Spectrometry: A Field Application

In this work, plutonium aerosol generated from a plutonium reprocessing facility is filtered by a six-stage High Efficiency Particulate Air (HEPA) filter system and analyzed in laboratory within a week. Through on-line monitoring of number concentration of particles above 10 nm by a commercial condensation particle counter and off-line monitoring of ²³⁹Pu activity concentration by ²⁴²Pu isotope dilution Inductively-Coupled Plasma Mass Spectrometry (ICP-MS), it is confirmed that the HEPA filter system works properly during the field operation. Direct determination of plutonium aerosol by two types of ICP-MS, Finnigan ELEMENT ICP-MS and Nu MC-ICP-MS, has been conducted. The results show that the detection limits of ELEMENT and Nu for plutonium concentration are 5.0 × 10^?3 Bq/m³ and 5.5 × 10^?4 Bq/m³, respectively. Plutonium concentrations in the filtered gas samples are on the order of 2.0 × 10^?2 Bq/m³ while the blank value is 5.7 × 10^?3 Bq/m³. It's discovered that some plutonium nanoparticles have penetrated the six-stage HEPA filter system. This phenomenon is also observed in the repeated works of last two years. The size of the penetrated plutonium nanoparticles is investigated by ELEMENT in single particle mode. The preliminary results indicate that the penetrated plutonium nanoparticles are smaller than 10 nm and assume the form of ²³⁹PuO₂.     

Investigation of soot nanoparticles during combustion of liquid hydrocarbons with injection of a superheated steam jet into the reaction zone

The characteristics of soot particles formed during combustion of liquid hydrocarbons in a laboratory model of an original burner with injection of a superheated steam jet into the reaction zone are experimentally studied. The concentration and size distribution of soot particles formed in the burner flame are measured by a diffusion aerosol spectrometer. It is shown that the majority of the primary particles have sizes ranging from 20 to 60 nm. The particle concentration in the external flame rapidly decreases with distance from the burner exit from 10⁸ to 5 · 10⁶ cm^?3. The images obtained by transmission electron microscopy demonstrate a chain-branched (fractallike) structure of aggregates. The primary particles composing these aggregates have a union-like structure with the interplane distance between the layers smaller than 1 nm. Compact aggregates with sizes up to 500 nm are observed in cooled combustion products. The content of soot in combustion products is 35 mg/m³, and the mean particle mass is 7 · 10^?12 mg. Results obtained in the combustion modes with injection of a superheated steam jet and with injection of an air jet are compared.     

Particle Charging and Transmission Efficiencies of Aerosol Charge Neutralizes

ABSTRACT

Diffusion losses and charging efficiency were measured for three types of charge neutralizers commonly used in aerosol research: two with ⁸⁵Kr and one with ²¹⁰Po as radiation sources. The diffusion losses were characterized at flows of 0.5 -6 1 min^?1 typically used in atmospheric aerosol physics measurements. All of the neutralizers tested exhibited high transmission efficiencies, with losses up to 25% at the smallest tested size of 3 nm, varying with size and flow in general agreement with diffusion loss theory. Charging efficiency was measured for a singly charged, monodisperse aerosol at the same flows and at concentrations of 10³-10⁴ particles cm^?3. Neither of the ⁸⁵Kr chargers brought the charge distribution close to equilibrium at 2 1 min^?1, except at concentrations ≤ 10³ cm^?3. The ²¹⁰Po charger produced the theoretically expected fraction of singly charged particles within the uncertainty of the experiment.     

Elaboration and characterisation of low cost ceramic support membrane

Abstract

A porous tubular ceramic membrane was prepared from low cost Tunisian clay. The characterisation of the raw material and the effect of the sintering temperature on the morphology, pores size distribution and the mechanical properties of the ceramic membrane were studied. A ceramic membrane fired at 1000°C for 1?h presented a mean pore diameter of ～1·04?μm. The porosity was equal to 38?vol.-%. The filtration of a 0·5?g?L^?1 bovine serum albumin solution indicated that the limiting flux of permeate was 245?L?h^?1?m^?2?bar^?1, which corresponded to a retention rate of about 13%.     

Design and optimization of a medium flow differential mobility analyzer (MF-DMA) for classification of high-density particles

A new design of a Differential Mobility Analyzer (DMA) was tested with medium aerosol flow rates ranging from 1.5 to 10 slm and high-density particles. The vacuum-tight construction makes it possible to classify pure metal nanoparticles from production processes. The selectable electrical mobility range is comparable to the TSI Long and Nano DMA and covers the full nanometer scale from 15–600?nm. The Medium Flow-DMA (MF-DMA) is characterized by its transfer function, which was determined by a tandem DMA setup using a SMPS with Long DMA downstream. Silver nanoparticles with a density of 10.49?g cm^?3 were used to demonstrate the size-selecting performance of high-density particles. The transfer function was calculated for aerosol to sheath gas flow ratios of 1/10, 1/5, and 1/3 directly from the SMPS data by a new method using modeling approach and comparison to the theory. Sufficiently high resolution was reached by increasing the SMPS scan time of the classified size distribution to 300?s. During the investigation, a broadened transfer function could be attributed to an inhomogeneous flow field resulting from the aerosol inlet design. The aerosol inlet of the MF-DMA was optimized by the number of inlet drillings and the opening of the inlet slit to achieve a more homogeneous flow field. CFD simulations of the MF-DMA also confirmed this. The modification improved the transfer function especially for medium aerosol flow rates above 5 slm.

Copyright © 2019 American Association for Aerosol Research