Nanoparticle Collection Efficiency Research Articles

Multifactorial evaluation of an ultra-fast process for electrospinning of recycled expanded polystyrene to manufacture high-efficiency membranes for nanoparticle air filtration

The increased production of polystyrene waste has led to the need to find efficient ways to dispose of it. One possibility is the use of solid waste to produce filter media by the electrospinning technique. The aim of this work was to develop an ultra-fast electrospinning process applied to recycled polystyrene, with statistical evaluation of the influence of polymeric solution parameters (polymer concentration and percentage of DL-limonene) and process variables (flow rate, voltage, and type of support) on nanoparticle collection efficiency, air permeability, and fiber diameter. An extensive characterization of the materials and evaluation of the morphology of the fibers was also carried out. It was found that recycled expanded polystyrene could be used in electrospinning to produce polymeric membranes. The optimized condition that resulted in the highest nanoparticle collection efficiency was a polymer concentration of 13.5%, percentage of DL-limonene of 50%, voltage of 25 kV, and flow rate of 1.2 mL/h, resulting in values of 99.97 ± 0.01%, 2.6 ± 0.5 × 10−13 m2, 0.19 Pa-1, and 708 ± 176 nm for the collection efficiency of nanoparticles in the range from 6.38 to 232.9 nm, permeability, quality factor, and mean fiber diameter, respectively. All the parameters were found to influence collection efficiency and fiber diameter. The use of DL-limonene, a natural solvent, provided benefits including increased collection efficiency and decreased fiber size. In addition, the electrostatic filtration mechanism was evaluated using the presence of a copper grid as a support for the nanofibers. The findings demonstrated that an electrospinning time of only 5 min was sufficient to obtain filters with high collection efficiencies and low pressure drops, opening perspectives for the application of polystyrene waste in the development of materials with excellent characteristics for application in the area of atmospheric pollution mitigation.

Influence of wire spacing and plate spacing on electrostatic precipitation of nanoparticles: An approach involving electrostatic shielding and diffusion charging

Electrostatic precipitation is a process widely used as gas cleaning device, to removal particles from gas flows. However, in a conventional and well-sized precipitator, the collection efficiency decreases for ultrafine particles, making it difficult to employ this equipment for controlling nanoparticle pollution. This paper investigates the influence of plate spacing (4 and 6.5 cm) and wire spacing (4, 6, and 12 cm) on the electric current and nanoparticle collection efficiency, considering the effect of diffusion charging and electrostatic shielding. Two laboratory-scale dry wire-plate electrostatic precipitators with different plate spacings were tested for the collection of nanoparticles (6.15–241.4 nm) at three air velocities (1.9, 2.9, and 3.9 cm/s). The results demonstrated the effectiveness of the equipment in removing nanoparticles (99.9%) under the highest electric fields. Higher values of the wire spacing led to increases in the current and the collection efficiency. This was associated with reduced electrostatic shielding, which is more evident in smaller ducts with a higher density of field lines. It is expected that the findings should improve knowledge on electrostatic precipitation of nanoparticles, enabling optimization of collection efficiency by considering the effects of geometric parameters.

An Investigation of Factors Affecting Measurement Accuracy of Nanoparticles Real-time Sensor using Corona Discharge integrated with Quartz Crystal Microbalance

A nanoparticles real-time sensor in the present study was designed using corona discharge integrated with quartz crystal microbalance (QCM) or Nano-QCM detector. We investigated the following factors affecting the measurement accuracy of the detector; needle to plate distance, flow rate, and number of particles on QCM. DC high voltage power supply of 7 kV was used to maintain the positive corona voltages difference in the charger. The mass sensitivity of 10 MHz AT-cut QCMs coated by plate rigid gold film were investigated. The monodisperse aerosol particles smaller than 300 nm were initially used for the testing of the system. They were charged with negative corona voltages and then deposited on the surface of QCM electrode. Sauerbrey equation was used to describe the frequency-mass relationship at the QCM surface. Results show that the above factors significantly affect the accuracy of the detector measurement. The particles can be collected on a QCM electrode using the partial breakdown high voltage (reach to breakdown points) in terms of needle-to-plate corona discharge. The optimal needle-to-plate distance is 6 mm with maximum mass change (frequency shift) on QCM electrode of 0.607μg/min. The QCM collection efficiency of nanoparticles on the QCM electrode surface using corona discharge technique can be as high as 95% of total particles. Collection efficiency of PM0.1 is under investigation.

Uncertainty assessment for the airborne nanoparticle collection efficiency of a TEM grid-equipped sampling system by Monte-Carlo calculation

A mini particle sampler (MPS) equipped with a transmission electron microscopy (TEM) grid enables convenient particle sampling to subsequent analysis. However, its sampling efficiency involves uncertainties, and accurate sampling efficiency is required for particle collection applications. In this study, the sampling efficiency uncertainties from measured data and models are quantified using Monte-Carlo methods. The Sobol variance-based sensitivity analysis is used to determine the contributions of parameters to the sampling efficiency uncertainties. The results reveal that the sampling efficiency uncertainties from experimental dispersion calibration and theoretical models are generally less than 1% and 9%, respectively. Most sampling efficiency measured data are covered by the efficiency uncertainty range simulated by theoretical models. Pore size and flowrate contribute significantly to the sampling efficiency uncertainties and require control to improve the sampling efficiency precision. Besides, the Cunningham correction factor is also a sensitivity parameter. The utilization of proper models is crucial to support simulations for further process optimization. This study offers a quantitative method for nanoparticle collection efficiency analysis, which will help assess nanomaterials’ workplace exposure.

Discharge electrode influence on electrostatic precipitation of nanoparticles

Electrostatic precipitators (ESPs) can achieve high collection efficiencies. However, their application for nanoparticle removal has not been widely discussed, largely because the charging mechanism is affected by the small diameter of these particles. Therefore, this work evaluated the influence of the discharge electrode parameters such as number (1–4), diameter (0.3 and 0.4 mm) and spacing (6.5 and 12 cm) on the electric characteristics of a wire-plate ESP and the nanoparticle collection efficiency (5.94–224.7 nm). A greater number of wires and a smaller wire diameter improved particle collection almost three-fold but under some operating conditions was reduced by the shielding effect. On the other hand, the wire spacing had a small influence on the particle collection. The highest collection efficiency (99.99%) was achieved using 4 discharge wires and wire diameter of 0.4 mm, although similar collection efficiencies were achieved with the configuration of 2 wires and wire diameter of 0.3 mm.

Preparation of TiO2 compact layer by heat treatment of electrospun TiO2 composite for dye-sensitized solar cells

The power conversion efficiency (PCE) of the dye-sensitized solar cell was improved by using titanium dioxide (TiO2) compact layer prepared via heat treatment assisted electrospinning. Titanium tetraisopropoxide mixed with polyvinyl-alcohol was used as the electrospun solution. In this study, TiO2 photoanode with TiO2 compact layer was compared with TiO2 photoanode without TiO2 compact layer where the PCE was improved by 76.88%. Electrochemical impedance spectroscopy proved that the TiO2 compact layer can reduce the series resistance and improved the short circuit current density, resulting in a low recombination effect that leads to a higher PCE. The electron lifetime and charge collection efficiency of TiO2 nanoparticles with TiO2 compact layer displayed a higher value compared to TiO2 nanoparticles without TiO2 compact layer.

Efficient nanoparticles removal and bactericidal action of electrospun nanofibers membranes for air filtration

Human exposure to air pollution and especially to nanoparticles is increasing due to the combustion of carbon-based energy vectors. Fibrous filters are among the various types of equipment potentially able to remove particles from the air. Nanofibers are highly effective in this area; however, their utilization is still a challenge due to the lack of studies taking into account both nanoparticle collection efficiency and antibacterial effect. The aim of this work is to produce and evaluate novel silver/polyacrylonitrile (Ag/PAN) electrospun fibers deposited on a nonwoven substrate to be used as air filters to remove nanoparticles from the air and also showing antibacterial activity. In order to determine the optimum manufacturing conditions, the effects of several electrospinning process parameters were analyzed such as solution concentration, collector to needle distance, flow rate, voltage, and duration. Ag/PAN nanofibers were characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infra-Red spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and Scanning Electron Microscopy (SEM). In addition, filtration performances were determined by measuring the pressure drop and collection efficiency of sodium chloride (NaCl) aerosol particles (9 to 300 nm diameters) using Scanning Mobility Particle Sizers (SMPS). Filters with high filtration efficiency (≈100%) and high-quality factor (≈0.05 Pa−1) were obtained even adding different concentrations of Ag nanoparticles (AgNPs) to PAN nanofibers. The resultant Ag/PAN nanofibers showed excellent antibacterial activity against 104 CFU/mL E. coli bacteria.

Filtration of nanoaerosols through a granular layer

Diffusion deposition of nanoparticles in model granular filters with different structures has been considered at low Reynolds numbers. On the basis of a three-dimensional flow field calculated for layers of granules, nanoparticle-collection efficiences have been determined for the granules in a wide range of the Peclet diffusion numbers. The interference of the layers has been studied, and approximation equations have been derived for calculating the pressure drop and the nanoparticle-collection efficiency.

Enhanced Collection Efficiency of Nanoparticles by Electrostatic Precipitator with Needle-Cylinder Configuration

Enhanced Collection Efficiency of Nanoparticles by Electrostatic Precipitator with Needle-Cylinder Configuration

Nebulization of Nanocolloidal Suspensions for the Growth of Nanocomposite Coatings in Dielectric Barrier Discharges

The nebulization of colloidal suspensions is analyzed by dynamic light scattering, scanning, and transmission electron microscopies. While primary agglomeration can be important for many nanoparticle‐solvent couples, our results indicate that for TiO2 nanoparticles dispersed in water, secondary agglomeration also occurs during nebulization. When nebulization is realized immediately after sustaining a plane‐to‐plane dielectric barrier discharge at atmospheric pressure, the collection efficiency of TiO2 nanoparticles increases due to the presence of a remanent electric field between the two electrodes. Finally, these findings are used to deposit SiO2–TiO2 nanocomposite thin films by alternating the deposition of dense silica‐like layers in a Townsend discharge and the collection of TiO2 nanoparticles through nebulization of the nanocolloidal suspension.

An efficient wet electrostatic precipitator for removing nanoparticles, submicron and micron-sized particles

An efficient wire-to-plate single-stage wet electrostatic precipitator (WESP) was designed and tested to control nanoparticles, submicron and micron-sized particles emitted from semiconductor manufacturing processes. Tungsten-wires of 0.36mm in diameter were used as discharge electrodes and a fixed voltage of −15kV was supplied to generate the electric field and corona ions. Fine water mist at room temperature was used to quench the high temperature exhaust gas to enhance particle condensation growth and improve the collection efficiency of nanoparticles. Experimental results showed that without fine water mist, nanoparticle collection efficiency was 67.9–92.9%, which was greatly enhanced to 99.2–99.7% when the WESP was operated with fine water mist. A predictive method was developed to calculate the particle collection efficiency equation η(%) in the form as η(%)=[1−exp(−α(NDe)β+γ)]×100%, in which α, β and γ are regression coefficients and NDe is the Deutsch number. Good agreement was obtained between present predictions and experimental data. For longer term operation, the periodic wall-cleaning water was used to clean discharge electrodes and collection electrodes regularly. In the field tests, the total collection efficiencies (40⩽dp⩽8100nm) of the WESP were found to maintain greater than 98.7% and 97.3% for continuous operation for 35 and 22day at fab A and fab B, respectively.

Intrathecal Magnetic Drug Targeting Using Gold-Coated Magnetite Nanoparticles in A Human Spine Model

We aimed to magnetically guide and locally confine nanoparticles in desired locations within the spinal canal to achieve effective drug administration for improved treatment of chronic pain, cancers, anesthesia and spasticity. We developed a physiologically and anatomically consistent in vitro human spine model to test the feasibility of intrathecal magnetic drug targeting. Gold-coated magnetite nanoparticles were infused into the model and targeted to specific regions using external magnetic fields. Experiments and simulations aiming to determine the effect of key parameters, such as magnet strength, duration of magnetic field exposure, magnet location and ferrous implants, on the collection efficiency of superparamagnetic nanoparticles in targeted regions were performed. An 891% increase in nanoparticle collection efficiency within the target region was achieved using intrathecal magnetic drug targeting when compared with the control. Nanoparticle collection efficiency at the target region increased with time and reached a steady value within 15 min. Ferrous epidural implants generated sufficiently high-gradient magnetic fields, even when magnets were placed at a distance equal to the space between a patient's epidermis and spinal canal. Our experiments indicate that intrathecal magnetic drug targeting is a promising technique for concentrating and localizing drugs at targeted sites within the spinal canal for treating diseases affecting the CNS.

Investigation of the effect of nozzle shape on supersonic/hypersonic impactors designed for size discrimination of nanoparticles

In this study the flow field and the nanoparticle collection efficiency of supersonic/hypersonic impactors with different nozzle shapes were studied using a computational modeling approach. The aim of this study was to develop a nozzle design for supersonic/hypersonic impactors with the smallest possible cut-off size d50 and rather sharp collection efficiency curves. The simulation results show that the changes in the angle and width of a converging nozzle do not alter the cut-off size of the impactor; however, using a conical Laval nozzle with an L/Dn ratio less than or equal to 2 reduced d50. The effect of using a cap as a focuser in the nozzle of a supersonic/hypersonic impactor was also investigated. The results show that adding a cap in front of the nozzle had a noticeable effect on decreasing the cut-off size of the impactor. Both flat disks and conical caps were examined, and it was observed that the nozzle with the conical cap had a lower cut-off size.

Amorphous carbon encapsulation of metal aerosol nanoparticles for improved collection and prevention of oxidation

A technique to encapsulate silver nanoparticles in an amorphous carbon matrix to facilitate nanoparticle collection and limit nanoparticle oxidation is presented. A carbon source added to the metal salt precursor solution decomposes to generate amorphous carbon, which forms large aggregates that are efficiently collected by filtration. The carbon matrix can be removed by oxidation with hydrogen peroxide without damaging the silver nanoparticles within it. X‐ray diffraction showed no evidence of oxidation of encapsulated particles over a two‐week period, whereas bare particles showed oxidation after 1 day. Slight oxidation was observed following carbon removal, but no further oxidation was detected over a subsequent two‐week period. Carbon encapsulation improves nanoparticle collection efficiency, relative to direct collection of unagglomerated silver nanoparticles with membrane filters. The yield of metal nanoparticles is increased by a factor 1.5 to 3 using this approach. The encapsulating carbon itself forms dendritic nanostructures that may also be of interest. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4116–4123, 2013

Development of a dose-controlled multiculture cell exposure chamber for efficient delivery of airborne and engineered nanoparticles

In order to study the various health influencing parameters related to engineered nanoparticles as well as to soot emitted by Diesel engines, there is an urgent need for appropriate sampling devices and methods for cell exposure studies that simulate the respiratory system and facilitate associated biological and toxicological tests. The objective of the present work was the further advancement of a Multiculture Exposure Chamber (MEC) into a dose-controlled system for efficient delivery of nanoparticles to cells. It was validated with various types of nanoparticles (Diesel engine soot aggregates, engineered nanoparticles for various applications) and with state-of-the-art nanoparticle measurement instrumentation to assess the local deposition of nanoparticles on the cell cultures. The dose of nanoparticles to which cell cultures are being exposed was evaluated in the normal operation of the in vitro cell culture exposure chamber based on measurements of the size specific nanoparticle collection efficiency of a cell free device. The average efficiency in delivering nanoparticles in the MEC was approximately 82%. The nanoparticle deposition was demonstrated by Transmission Electron Microscopy (TEM). Analysis and design of the MEC employs Computational Fluid Dynamics (CFD) and true to geometry representations of nanoparticles with the aim to assess the uniformity of nanoparticle deposition among the culture wells. Final testing of the dose-controlled cell exposure system was performed by exposing A549 lung cell cultures to fluorescently labeled nanoparticles. Delivery of aerosolized nanoparticles was demonstrated by visualization of the nanoparticle fluorescence in the cell cultures following exposure. Also monitored was the potential of the aerosolized nanoparticles to generate reactive oxygen species (ROS) (e.g. free radicals and peroxides generation), thus expressing the oxidative stress of the cells which can cause extensive cellular damage or damage on DNA.

Collection efficiency and interstage loss of nanoparticles in micro-orifice-based cascade impactors

In this study, two micro-orifice-based cascade impactors, including the micro-orifice uniform deposit impactor (MOUDI, MSP Model 110) and the NCTU micro-orifice cascade impactor (NMCI), were tested for the collection efficiency and interstage loss of nanoparticles. In the NMCI, new nozzle plates with smooth nozzle shape made by the LIGA (Lithography, Electroplating, and Molding) process were used to replace the 7th–10th stages in one of the MOUDI. Test results show that after adjusting proper S/W ratios (S: jet to plate distance, W: nozzle diameter) to 2.52, 3.01, 13.44, and 24.75 for the 7th, 8th, 9th and 10th stage of the NMCI, respectively, and 5.56, 11.18, 9.3, and 10.9 for the 7th, 8th, 9th and 10th stage of the MOUDI, respectively, the cutoff aerodynamic diameters (dpa50) are close to the nominal values given in Marple et al. (1991). Different S/W ratios are needed due to differences in the nozzle shape and nozzle diameter between two cascade impactors. Total interstage loss of nanoparticles from the inlet to the 6th–10th stage of the MOUDI exists due to the convection-diffusion mechanism, which increases with decreasing dpa. For the MOUDI, total loss is 2.9–15.3 % (dpa: 105.8 to 15.4 nm) for the inlet to the 6th stage and it increases to 20.1–26.1 % (dpa: 23 to 15.4 nm) for the inlet to the 10th stage, respectively. Similar but slightly lower loss also exists in the NMCI. Field comparison tests in the ambient air show that mass size distributions measured by the MOUDI agree well with those of the NMCI. Finally, nozzle clogging tests using high concentration incense smokes indicate that the NMCI has a much less tendency for particles to clog in the nozzles than the MODUI.

Numerical Study for Nanoparticle Removal in Vacuum Conditions

LES turbulent models were employed to study the gas-solid two phase characteristics in an axial flow cyclone. Predicted data of velocity and pressure distributions of gas phase and the separation efficiency of the dispersed droplets were listed in this paper. The results showed that there are much differences between the LES turbulent model and RANS turbulent models; the velocities of the gas phase depended mostly on the direction of guide vane, and the operating pressure had a great effect on the collection efficiency of nanoparticles in vacuum conditions.

Evaluation of environmental filtration control of engineered nanoparticles using the Harvard Versatile Engineered Nanomaterial Generation System (VENGES)

Applying engineering controls to airborne engineered nanoparticles (ENPs) is critical to prevent environmental releases and worker exposure. This study evaluated the effectiveness of two air sampling and six air cleaning fabric filters at collecting ENPs using industrially relevant flame-made engineered nanoparticles generated using a versatile engineered nanomaterial generation system (VENGES), recently designed and constructed at Harvard University. VENGES has the ability to generate metal and metal oxide exposure atmospheres while controlling important particle properties such as primary particle size, aerosol size distribution, and agglomeration state. For this study, amorphous SiO(2) ENPs with a 15.4 nm primary particle size were generated and diluted with HEPA-filtered air. The aerosol was passed through the filter samples at two different filtration face velocities (2.3 and 3.5 m/min). Particle concentrations as a function of particle size were measured upstream and downstream of the filters using a specially designed filter test system to evaluate filtration efficiency. Real time instruments (FMPS and APS) were used to measure particle concentration for diameters from 5 to 20,000 nm. Membrane-coated fabric filters were found to have enhanced nanoparticle collection efficiency by 20-46 % points compared to non-coated fabric and could provide collection efficiency above 95 %.

A Modified Deutsch-Anderson Equation for Predicting the Nanoparticle Collection Efficiency of Electrostatic Precipitators

It is of great importance to mitigate nanoparticle exposure in the environment by using effective control devices. For controlling nanoparticles with the particle diameter (dp) ＜ 100 nm in the air environment, electrostatic precipitators (ESPs) are widely used in many industries because of their low pressure drop and high removal efficiency. However, existing models cannot predict the nanoparticle collection efficiency very well. This is due to the partial charging effect, when some nanoparticles are not charged but penetrate through the ESPs, resulting in a decrease in the collection efficiency. In this study, a modified Deutsch-Anderson model was developed to predict the nanoparticle collection efficiency (η, %), as well as that for particles with dp ＞ 100 nm. The present model is η(%) = [1 - exp(-A(N(subscript De))B) + C(N(subscript De)) - (1 - α)] × 100%, where A, B, and C are regression coefficients, N(subscript De) is the modified Deutsch number, and α is the partial charging factor. Good agreement was obtained between the present predictions and experimental data published in the literature. It is expected that the modified equation can facilitate the design and scale-up of the ESPs for controlling nanoparticle emissions, as well as particle in all size ranges.

전기집진기의 10 nm 급 초미세 나노입자의 하전 및 집진 특성

전기집진에서의 10 nm 급 초미세 나노입자의 하전 및 집진 특성을 파악하였고, 나노입자의 확산효과와 비교해 보았다. 나노입자의 하전율과 확산손실 효과의 지배력에 따라 전기집진기에서의 나노입자 집진효율이 결정되는 것을 확인할 수 있었다. 10nm 급 영역에서는 입자 크기가 작아질수록 지속적으로 집진효율이 감소하였다. 10 nm 이하의 영역에서는 나노입자의 부분적 하전효과가 전기집진기 내의 확산손실 효과보다 지배적인 것을 알 수 있었다. 10 nm 이하의 나노입자에 대하여 집진효율 실험 결과가 단극 확산 하전 이론을 적용한 입자하전율 계산 결과와도 잘 일치하였다.