A Granular Bed for Use in a Nanoparticle Respiratory Deposition Sampler

A granular bed was designed to collect nanoparticles as an alternative to nylon mesh screens for use in a nanoparticle respiratory deposition (NRD) sampler. The granular bed consisted of five layers in series: a coarse mesh, a large-bead layer, a small-bead layer, a second large-bead layer, and a second coarse mesh. The bed was designed to primarily collect particles in the small-bead layer, with the coarse mesh and large-bead layers designed to hold the collection layer in position. The collection efficiency of the granular bed was measured for varying depths of the small-bead layer and for test particles with different shape (cuboid, salt particles; and fractal, and stainless steel and welding particles). Experimental measurements of collection efficiency were compared to estimates of efficiency from theory and to the nanoparticulate matter (NPM) criterion, which was established to reflect the total deposition in the human respiratory system for particles smaller than 300 nm. The shape of the collection efficiency curve for the granular bed was similar to the NPM criterion in these experiments. The collection efficiency increased with increasing depth of the small-bead layer: the particle size associated with 50% collection efficiency, d₅₀, for salt particles was 25 nm for a depth of 2.2 mm, 35 nm for 3.2 mm, and 45 nm for 4.3 mm. The best-fit to the NPM criterion was found for the bed with a small-bead layer of 3.2 mm. Compared to cubic salt particles, the collection efficiency was higher for fractal-shaped particles larger than 50 nm, presumably due to increased interception.

Copyright 2015 American Association for Aerosol Research     

Design and development of a self-contained personal electrostatic bioaerosol sampler (PEBS) with a wire-to-wire charger

Here, we present a concept of a personal electrostatic bioaerosol sampler (PEBS), which is an open channel collector consisting of a novel wire-to-wire particle charger and a collection section housing a double-sided and removable metal collection plate and two quarter-cylinder ground electrodes. The charger consists of a tungsten wire (25.4 mm long and 0.076 mm in diameter) connected to high voltage and positioned in the center of the charging section (a cylinder 50.8 mm long and 25.4 mm in diameter); a ring of stainless steel wire 0.381 mm in diameter surrounds the hot electrode at its midpoint and is grounded. The newly designed wire-to-wire charger produces lower ozone concentrations compared to traditional wire-to-plate or wire-to-cylinder charger designs. The particles captured on the collection plate are easily eluted using water or other fluids. The sampler was iteratively optimized for optimum charging and collection voltages, and collection electrode geometry. When tested with polystyrene latex particles ranging from 0.026 µm to 3.1 µm in diameter and 10 L/min collection flow rate, the sampler's collection efficiency was approximately 70%–80% at charging and collection voltages of +5.5 kV and ?7 kV, respectively. The PEBS showed this collection efficiency at sampling times ranging from 10 min to 4 h. Preliminary tests with Bacillus atrophaeus bacterial cells and fungal spores of Penicillium chrysogenum showed similar collection efficiency. The use of a unique wire-to-wire charger resulted in ozone production below 10 ppb. Due to low ozone emissions, this sampler will allow maintaining desirable physiological characteristics of the collected bioaerosols, leading to a more accurate sample analysis.

© 2017 American Association for Aerosol Research     

3D Electrodes from aluminium foams prepared by replication process

Aluminium foams with pores displaying both regular size and distribution have been prepared by replication methods. Their volumetric density and electrical conductivity were 0.65 g cm^?3 and 2.44 MS m^?1, respectively. This method represents a simple way to produce 3D metal macroporous electrodes. In addition, the aluminium foam has been employed as support to produce 3D platinum electrodes (Pt/Al foam) by electrodeposition. The conditions for platinum electrodeposition have been established, and the electrodes were characterized by scanning electron microscopy and cyclic voltammetry. The electrocatalytic behaviour of the Pt/Al foam electrodes to methanol oxidation has been tested in 1 M CH₃OH + 0.5 M H₂SO₄ solutions.     

Development and Evaluation of a High Loading PM2.5 Speciation Sampler

A high loading sampler for the chemical characterization of fine particles (PM _2.5 ) was developed and validated through laboratory and field experiments. This speciation sampler consists of two identical serially connected impaction stages to remove particles larger than 2.5 μm, following by a chamber to allow use of one or two all-glass honeycomb diffusion denuders, and a holder for a 47 mm filter. Two configurations of the sampler allow sampling at flows of 10 lpm and 16.7 lpm. System performance was evaluated in laboratory experiments using artificially generated polydisperse aerosols. This novel sampler provides a much larger mass loading capacity than previous impactors that use flat, rigid substrate surfaces. The polyurethane foam (PUF) substrate maintains adequate performance characteristics (retention of size cut-off, sharpness of cut-off curve, and minimal particle bounce and re-entrainments) at loadings of at least 35 mg. This is equivalent to 728 μg/m³ for a 48 h sampling period (or 500 h of sampling at 70 μg/m³). System performance was also evaluated in a series of field intercomparison experiments for both flow configurations (10 and 16.7 lpm). Measurements of PM _2.5 mass and sulfate concentrations showed excellent agreement between the US EPA Federal Reference Method (FRM) Sampler and the speciation sampler.     

Development and Optimization of the Electrostatic Precipitator with Superhydrophobic Surface (EPSS) Mark II for Collection of Bioaerosols

We recently developed an electrostatic collector for bioaerosols that electrostatically deposits biological particles onto a 3.2 mm electrode covered by a superhydrophobic substance. The deposited biological particles are removed and collected by rolling water droplets (20 or 40 microliter) which results in high concentration rates. The collector has been improved further by integrating it with an electrical charger. Here, we describe the development and optimization of the charger and collection chamber, while maximizing collection efficiency and minimizing particle loss. The resulting sampler is made of static dissipative material (e.g., Delrin), is shaped as a closed half cylinder, and is integrated with a charger. The sampler's round top section contains eight carbon fiber brushes (ion sources to charge particles), while its flat bottom section holds a rectangular collection electrode (254 × 3.2 mm) made of pressed carbon fiber and coated with a superhydrophobic material.

The optimized configuration of the EPSS Mark II had a collection efficiency of up to 84% when sampling airborne Escherichia coli at 10 L/min and for 10 min. The bacteria were accumulated in rolling water droplets as small as 20 microliters, and the sampler achieved sample concentration rates of up to 4.2 × 10⁵/min. When the sampler was operated for a longer time period (60 min), its collection efficiency was 72%. The efficiency decrease was most likely due to a reduced particle removal from the electrode, but the difference was not statistically significant. Since the EPSS Mark II shows satisfactory collection efficiency and high sample concentration rate, it could serve as a basis for developing a field-deployable version of the sampler.

Copyright 2015 American Association for Aerosol Research     

Design of Porous Banana Foam Mat to Resist Moisture Migration Using a 2-D Stochastic Pore Network and Its Textural Property

The high porosity of dried banana foam allows it to quickly adsorb moisture from the air during storage, leading to a loss of quality and textural properties. Therefore, the main purpose of this research was to design and study banana foam structure at the pore level to limit moisture migration using a 2-D stochastic pore network. A 2-D network formed by the interconnection of cylindrical pores was used to represent the voids inside the banana foam and the moisture movement inside the individual pore segments during adsorption was described by Fick's law. The pore network was divided into two layers with different banana foam densities and the top surface of the network was exposed to humid air. The upper layer was assigned with pore sizes from the banana foam density of 0.31 g/cm³, having a void area fraction of 0.22, or from a density of 0.21 g/cm³, having a void area fraction of 0.31; the lower layer was assigned specifically with the pore sizes from the banana foam density of 0.26 g/cm³, having a void area fraction of 0.26. The predictions agreed well with the experimental results, with an R² value above 0.95. The two-layered banana foam mat with high banana foam density (characterized by mostly small pores) on the upper layer could limit the transport of moisture, with a rate relatively lower than that of a single-layered banana foam mat, and also exhibited more crispiness than the single banana foam. However, when the low banana density was in the upper layer, the two-layered sample adsorbed moisture quickly and its texture was less crispy.     

CONFINEMENT EFFECTS ON ADSORPTION AND DIFFUSION OF HEXANE IN NANOPOROUS MCM-41 WITH DIFFERENT PORE SIZES: A MOLECULAR DYNAMICS STUDY

We report the results of molecular dynamics (MD) simulations using a new semi-empirical intermolecular interaction potential on the adsorption and diffusion of hexane in siliceous MCM-41 at 300 K. The potential function is tuned to give an adsorption energy of ? 9.1 kcal/mol, reproducing the experimental value for a corresponding pore size. We investigated MCM-41 models with four different pore sizes and studied loadings from one molecule of hexane up to a loading corresponding to the density of liquid hexane. As a result of confinement in MCM-41, the free energy of adsorption of hexane increases when the pore sizes decrease; for example, the adsorption energy increases from ? 9.1 to 13.7 kcal/mol for the largest to the smallest pore size for a loading of one molecule. Also, the adsorption energy increases by 3–4 kcal/mol for all pore sizes when the loading is increased from one hexane molecule to the density of liquid hexane. The calculated self-diffusion coefficients of hexane in MCM-41 with a pore diameter of 27 Å are in the order of 1 × 10^?5 cm²/s, depending on the loading, which is in reasonable agreement with available experimental data. The self-diffusion coefficients decrease with increasing loadings and when the pore sizes decrease. The average distance between the centers of the mass of hexane molecules in the smallest pores is only marginally less than in the larger pores and in the liquid phase. For low loadings the hexane molecules lie parallel to the pore channel for every pore size. When the loading is increased, they build up concentric rings. These rings of hexane molecules are less well separated from each other in the larger models, and thus their structure more resembles the liquid phase.     

Use of Polyurethane Foam as the Impaction Substrate/Collection Medium in Conventional Inertial Impactors

Open pore polyurethane foam (PUF) can be used effectively as a substrate for conventional inertial impactors with both high particle collection efficiency and minimal vaporization of semi-volatile particle components. The collection characteristics of PUF as an impaction substrate were studied as a function of PUF density, Reynolds number, impaction substrate diameter, and nozzle-toplate distance. The conventional impaction substrate of the PM_2.5 Harvard Impactor sampler was replaced with the PUF substrate. The use of PUF resulted in significant changes in the collection efficiency curve, with the 50% cut-off size (     

A novel membrane-assisted fermentation coupling with foam separation for improving the titer of polymyxin E

In this paper, a novel membrane-assisted fermentation coupling with foam separation (M-FCFS) technology was developed to separate polymyxin E from its broth immediately. The effects of starting aeration time, membrane, volumetric airflow rate in foam column, and nitrogen source (i.e. peptone, also known as foam stabilizer) on the production of polymyxin E were studied. Under the optimal conditions, the total titer (TT) of polymyxin E reached 1.29 × 10⁶ IU, resulting in a 50.4% improvement compared with the uncoupling experiment (8.60 × 10⁵ IU). This work combined the advantages of foam separation and membrane filtration, and provided a promising technology for the production of polymyxin E.     

Development and application of a simultaneous measurement method for gaseous ammonia and particulate ammonium in ambient air

Ammonia gas is one of the precursors contributing to the formation of secondary particulate ammonium via reactions with atmospheric acids, such as sulfuric and/or nitric acids, which are present in ambient air. In this study, a new instrument that is suitable for measuring ammonia gas and fine particulate ammonium (PM_2.5 NH₄⁺) concentrations simultaneously under ambient conditions was developed. A wetted frit sampler was connected in the back of a counter-current flow tube (CCFT) sampler, and the NH₃ gas and PM_2.5 NH₄⁺ samples were collected by CCFT and wetted frit samplers, respectively. An air sample was drawn through the samplers at a flow rate of 1.0 dm³ min^?1 and an absorption water flow rate of 120 mm³ min^?1. Then, the ammonium that formed in the absorption solution was detected by the indophenol method using a continuous flow analysis system. The estimated detection limits were 43 and 49 ng m^?3 for ammonia gas and PM_2.5 NH₄⁺, respectively. Notably, the ammonia gas was collected on the CCFT sampler with a collection efficiency of 98.5%, but most of the PM_2.5 NH₄⁺ passed through it and was captured on the wetted frit sampler with a collection efficiency of approximately 100%. The present method was applied to measure NH₃ gas and PM_2.5 NH₄⁺ at two urban sites: Osaka, Japan and Ho Chi Minh City, Vietnam. It was found that the simultaneous measurement method performed very well and that the measured concentrations were comparable with those obtained with the annular denuder method.

Copyright © 2016 American Association for Aerosol Research     

Biogenic Separation,Accumulation and Cellular Distribution of Cu,Co, and Ni in Medicago sativa under Idealized Conditions

The limits of uptake of Co, Ni, and Cu by the common metallophyte, Medicago sativa, were assessed using hydroponic growth and metal uptake experiments. The influence of the growth substrate metal concentration (500 and 1000 ppm) and exposure time, i.e., the time plants were exposed to the metal solution (24, 48, or 72 h) was investigated. The combined roots and shoots of Medicago sativa accumulated up to 2.2 wt-% Co, 2.0 wt-% Ni, and 3.5 wt-% Cu, when exposed to aqueous solutions containing 1000 ppm Co for 48 h, 1000 ppm Ni for 72 h, and 1000 ppm Cu for 72 h, respectively. The distribution of the sequestered metals was assessed using proton induced that X-ray emission spectroscopy (μ-PIXE), which indicated that translocation mechanism was most likely xylem loading. However, the rate of translocation of the metal from the roots to the plant stem was different for each metal, suggesting differing mechanisms for each. Collectively, these results suggest the separation and removal of the heavy metals Cu, Co, and Ni from contaminated substrates using Medicago sativa is a viable technology.     

Physicochemical Characterization of Simulated Welding Fumes from a Spark Discharge System

This study introduces a spark discharge system (SDS) as a way to simulate welding fumes. The SDS was developed using welding rods as electrodes with an optional coagulation chamber. The size, morphology, composition, and concentration of the fume produced and the concentration of ozone (O₃) and nitrogen oxides (NO_X) were characterized. The number median diameter (NMD) and total number concentration (TNC) of fresh fume particles were ranged 10–23 nm and 3.1×10⁷ ? 6×10⁷ particles/cm³, respectively. For fresh fume particles, the total mass concentration (TMC) measured gravimetrically ranged 85–760 μg/m³. The size distribution was stable over a period of 12 h. The NMD and TNC of aged fume particles were ranged 81–154 nm and 1.5×10⁶?2.7×10⁶ particles/cm³, respectively. The composition of the aged fume particles was dominated by Fe and O with an estimated stoichiometry between that of Fe₂O₃ and Fe₃O₄. Concentrations of O₃ and NO_X were ranged 0.07–2.2 ppm and 1–20 ppm, respectively. These results indicate that the SDS is capable of producing stable fumes over a long-period that are similar to actual welding fumes. This system may be useful in toxicological studies and evaluation of instrumentation.

Copyright 2014 American Association for Aerosol Research     

Potassium geopolymer foams made with silica fume pore forming agent for thermal insulation

Porous potassium based geopolymers with a mutli-scale porosity were synthesized. Silica fume is introduced as an additive to the geopolymer formulation. The free silicon contained inside this silica fume is oxidized in alkaline solution, releasing molecular hydrogen which generates the porosity. Previous work has shown how the porosity can be controlled with temperature, repeated temperature cycles and the mass introduced. Using this protocol, homogeneous foams were made and then studied with scanning electron microscopy. In particular the foam expansion has been followed with time in relation to the microstructure. The thermal conductivity values of the foams were evaluated using a fluxmeter method. The effective thermal conductivities are comprised between 0.12 and 0.35 W m^?1 K^?1 for apparent densities ranging from 0.40 to 0.85 g cm^?3. The corresponding calculated pore volume fractions are in the range of 65–85%. The interest of this material is that it combines the advantages of low bulk density and insulating properties with the characteristics of a geopolymer skeleton. Literature reports a very good fire and acid/base resistance, a low cost of production and the possibility of recycling industrial waste in the form of silica fume.     

Synthesis,characterization and antibacterial activity of Pd(II), Pt(II) and Ag(I) complexes of 4-ethyl and 4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazides

Pd(II), Pt(II) and Ag(I) ions were found to form stable complexes with 4-(p-tolyl)- or 4-ethyl-1-(pyridin-2-yl)thiosemicarbazides (Hp-TPTS or HEPTS). The complex structure was elucidated by analysis (elemental and thermal), spectroscopy (electronic, IR and ¹H NMR spectra) and physical measurements (magnetic susceptibility and molar conductance). The ligands coordinate to the metal ions as monobasic bidentate through nitrogen and sulfur atoms. The electronic spectra of the Pt(II) complexes in DMF showed a metal to ligand charge transfer transition at 11,935–13,260 cm^?1. The structural, electronic and vibrational features of HEPTS and Hp?TPTS were discussed on the basis of semi-empirical quantum mechanic calculations [ZINDO/S and semi-empirical parameterization (PM3)]. The simulated IR and electronic spectra are found reasonable in accordance with the experimental data. Finally, the antibacterial activities of the ligands and their complexes were investigated and some were found promising.     

Mechanical properties of a particle‐strengthened polyurethane foam

Quasi‐static compression tests have been performed on polyurethane foam specimens. The modulus of the foam exhibited a power‐law dependence with respect to density of the form: E* ∝ (ρ*)ⁿ, where n = 1.7. The modulus data are described well by a simple geometric model (based on the work of Gibson and Ashby) for a closed‐cell foam in which the stiffness of the foam is governed by the flexure of the cell struts and cell walls. The compressive strength of the foam is also found to follow a power‐law behavior with respect to foam density. In this instance, Euler buckling is used to explain the density dependence. The modulus of the foam was modified by addition of gas‐atomized, spherical, aluminum powder. Additions of 30 and 50 wt % Al measurably increased the foam modulus, but without a change in the density dependence. However, there was no observable increase in modulus with 5 and 10 wt % additions of the metal powder. Strength was also increased at high loading fractions of powder. The increase in modulus and strength could be predicted by combining the Gibson–Ashby model, referred to above, with a well‐known model describing the effect on modulus of a rigid dispersoid in a compliant matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2724–2736, 1999     

Effects of a sheet metal stamping lubricant on static strength of adhesive-bonded aluminum alloys

Stamping lubricant is often applied to sheet metal surface to improve the formability. In this study, the effect of stamping lubricant on the strength of adhesive-bonded 1.0-mm-thick bare aluminum (Novelis X610-T4PD) and 0.9-mm-thick bare aluminum (Novelis X626-T4P) joints was investigated. It was found that while a proper amount of lubricant (~2.21 g/m², 1.5?μL lubricant on the 25?×?25 mm coupon) applied on the surface of the substrate had little effect on the joint strength, levels more than 2.21 g/m² lubricant significantly decreased the joint strength. When the lubricant amount exceeds the adhesive’s compatibility with the lubricant, the negative effects of pores from lubricant evaporation during curing on the strength overrides the positive effect of increased adhesion energy. Furthermore, the presence of 2.21 g/m² lubricant minimized the reduction of the strength of the joints pre-exposed to neutral salt spray (i.e. a concentration of 50?±?5 g/L sodium chloride solution). Careful analyses of the results indicated that corrosion of aluminum substrate surfaces of the pre-exposed joints led to the degradation in bond adhesion between the adhesive and substrates, and consequently resulted in the decrease of the joint strength. The hydrophobic lubricant protected the aluminum substrate from electrochemical reaction by damage of the bond adhesion between the adhesive and substrates leading to the lubricated joints having better corrosion resistance than the unlubricated joints.     

The influence of cooling rate on the fracture properties of a glass reiforced/nylon fiber-metal laminate

The effect of varying cooling rate on the microstructure and resulting mechanical properties of a novel fiber-metal laminate (FML) based on a glass fiber-reinforced nylon composite has been investigated. Polished thin sections removed from plain glass fiber/nylon composites and their corresponding fiber-metal laminates indicated that the prevailing microstructure was strongly dependent on the rate of cooling from the melt. Mode I and Mode II interlaminar fracture tests on the plain glass fiber reinforced nylon laminates indicated that the values of G_Ic and G_IIc averaged approximately 1100 J/m² and 3700 J/m² respectively at all cooling rates. The degree of adhesion between the aluminum alloy and composite substrates was investigated using the single cantilever beam geometry. Here, the measured values of G_c were similar in magnitude to the Mode I interlaminar fracture energy of the composite, tending to increase slightly with increasing cooling rate. The tensile and flexural fracture properties of the plain composites and the fiber metal laminates were found to increase by between 10% and 20% as the cooling rate was increased by two orders of magnitude. This effect was attributed to over-aging of the aluminum alloy plies at elevated temperature during cooling. Finally, fiber metal laminates based on glass fiber/nylon composites were shown to exhibit an excellent resistance to low velocity impact loading. Damage, in the form of delamination, fiber fracture, matrix cracking in the composite plies, and plastic deformation and fracture in the aluminum layer, was observed under localized impact loading. Here, the fast-cooled fiber metal laminates offered superior post-impact mechanical properties at low and intermediate impact energies, yet very similar results under high impact energies.     

Surface-collection efficiency of Nuclepore filters for nanoparticles

The flat surface of Nuclepore filters is suitable for observing collected particles with a scanning electron microscope (SEM). However, experimental data on surface-collection efficiency are limited because surface-collection efficiencies cannot be measured directly using aerosol measuring instruments. In this study, the surface-collection efficiencies of Nuclepore filters were determined by establishing the ratio of the number of particles deposited on the surface of the filter visually counted with an SEM to the number of inflow particles counted by a condensation particle counter, using monodispersed polystyrene latex particles (30–800 nm) and silver particles (15–30 nm). Because Nuclepore filters with smaller pore sizes would be expected to produce higher minimum surface-collection efficiency and a higher pressure-drop, 0.08 and 0.2 µm Nuclepore filters were chosen as the test filters in view of both collection efficiency and pressure drop. The results showed that the minimum surface-collection efficiencies of the 0.08 µm pores at face velocities of 1.9 and 8.4 cm·s^?1 were approximately 0.6 and 0.7, respectively, and those of the 0.2 µm pores at face velocities of 1.5 and 8.6 cm·s^?1 were approximately 0.8 and 0.6, respectively. Because the pressure drop of the 0.2 µm pore filter was lower than that of the 0.08 µm pore filter under the same flow-rate conditions, the 0.2 µm pore filter would be more suitable considering the pressure drop and collection efficiency. The obtained surface collection efficiencies were quantitatively inconsistent with theoretical surface-collection efficiencies calculated using conventional theoretical models developed to determine the collection efficiency of filters with larger pores.

© 2016 American Association for Aerosol Research     

Ozone Solubility in Aqueous Solutions of NaCl,Na2SO4, and K2SO4: Application of the Weisenberger-Schumpe Model for Description of Regularities and Calculation of the Ozone Molar Absorption Coefficient

The ozone solubility in aqueous solutions of salts, NaCl (up to 5 М) and Na₂SO₄ (up to 2 М) and their mixtures, was studied. The results are adequately described by the semi-empirical model proposed by Weisenberger and Schumpe for calculation of the solubilities of atmospheric gases in concentrated solutions of electrolytes. By comparing the data obtained experimentally and calculated in terms of the Weisenberger and Schumpe model, the ozone molar absorption coefficient was found to be ε = 2860 ± 200 M^?1 cm^?1 at 260 nm.     

Statistical Optimization of Culture Conditions and Characterization for Ligninolytic Enzymes Produced from Rhizopus Sp. Using Prickly Palm Cactus Husk

Dry prickly palm cactus (Nopalea cochenillifera) husk was investigated as a substrate for Rhizopus sp. cultivation in the solid state, aiming at the production of laccase (Lac), lignin peroxidase (LiP), and manganese peroxidase (MnP). The optimization of fermentation was evaluated by an experimental design and it was obtained, for each enzyme, maximum productivities (U g^?1 h^?1) of: 0.085 ± 0.02 (MnP), 0.066 ± 0.001 (LiP), and 0.023 ± 2.3.10^?4 (Lac), at the conditions of 10 g of substrate, 72 h of fermentation, a_w = 0.865, and 30°C. The enzymes thermal and pH stabilities were evaluated and it was observed better results at temperatures no higher than 60°C and pH of 5.0; in addition, the storage of these enzymes was better at ? 25°C than at 4°C. Since the prickly palm cactus is an agricultural substrate and specially because of its low cost, it is important to propose different applications for it as, for example, an alternative substrate for biotechnological processes.