Electrofiltration of Aqueous Suspensions

Electrofiltration of hydrosols in fixed-bed filters was studied experimentally. The experimental variables examined included media type, electric field strength, and suspension pH values. The extent of particle removal was found to improve with the application of the electric field, and lower pH values favor particle collection. The filtrate quality displayed the transient behavior of increasing particle concentration with time. A simple model which assumes that the filter coefficient decreases linearly with the extent of deposition was developed and found capable of predicting the observed behavior. Copyright 2000 Academic Press.     

Examination of a procedure for the production of a simulated filter-based air particulate matter reference material

An approach for producing simulated air particulate matter (APM) deposited on filters has been developed and investigated as to its usefulness for yielding large batches of filters as a future reference material. The APM deposited on the filters was a material collected from an urban industrial area, and had been milled to approximate a material of PM-2.5 particle size distribution. The milled APM material was loaded onto filter substrates (Nuclepore) through the deposition of aliquots from a liquid suspension via vacuum filtration. It should be noted that these filters do not represent a typical PM-2.5 elemental composition, since the milling increased the proportion of crustal materials and the suspension in liquid decreased the sulfate content. Homogeneity between filters was tested using INAA (whole filter analysis) and ED-XRF and PIXE and was estimated to be in the 5% range (relative standard deviation). Homogeneity within the filters and among the filters was also tested using micro-XRF and found to be acceptable for the elements tested. The results of the tests carried out on the filters indicate that this approach is appropriate for large-scale production of similar filters for distribution as reference materials.     

Electrophoretic deposition strategy for the fabrication of highly stable functionalized silica nanoparticle coatings onto nickel‐titanium alloy wires for selective solid‐phase microextraction

A new strategy for the immobilization of phenyl‐functionalized silica nanoparticles onto nickel‐titanium alloy wires is presented. The homogeneous and compact silica nanoparticle coating was achieved on the hydrothermally treated nickel‐titanium wires with large surface area by electrophoretic deposition, and followed by self‐assembled modification of phenyltrichlorosilane. Coupled to high‐performance liquid chromatography with ultraviolet detection, the extraction performance of the fabricated fiber was evaluated using typical aromatic compounds in direct‐immersion mode of solid‐phase microextraction. Due to its high extraction efficiency and good selectivity for ultraviolet filters, the novel fiber was employed to investigate the key factors affecting the extraction of ultraviolet filters. Under the optimized conditions, the proposed method presented linear ranges from 0.05 to 300 μg/L with correlation coefficients higher than 0.999 and limits of detection from 0.005 to 0.058 μg/L. Relative standard deviations were below 4.3 and 5.6% for intraday and interday analyses at the spiking level of 50 μg/L ultraviolet filters with the single fiber, respectively. The proposed method was successfully applied to the selective concentration and sensitive detection of target ultraviolet filters from environmental water samples. Furthermore, the developed fiber can be used at least 200 times, and fabricated in a precisely controllable manner.     

Environmental thin-layer reference materials of urban particulate matter on filter media

The Institute of Non-Ferrous Metals, Gliwice (Poland) has developed a process for uniform deposition of urban particulate matter on filter media which enables the production of reference materials for X-ray calibration by depositing certified reference materials on filters at different mass loadings. This process has been used to prepare the SRM 2783 for the National Institute of Standards and Technology, which consists of a set of five such filters based on the use of the SRM 1648 for the deposition.     

Inertial Deposition of Aerosol Particles on Fiberous Filters

The inertial deposition of aerosol particles on model filters at low and intermediate Stokes numbers and low Reynolds numbers was studied. It was shown that the efficiency of the inertial deposition of submicron particles is markedly affected by retarded van der Waals forces and the gas slip in the vicinity of thin fibers.     

Hollow-fiber membrane adsorber: Mathematical model

Two opposite design strategies for ultrafiltration/microfiltration filters: (1) reduction of concentration polarization and particle deposition to increase permeate velocity and (2) utilization of particle deposition on membrane surface to produce an additional (to permeate) volume of clarified water, are analyzed. It is shown that the first strategy is always associated with additional expenditures in power or other material resources, making it not enough cost-effective to be competitive with non-membrane filtration processes in some water treatment applications. At the same time, the second strategy does not require additional power expenditures and provides high water recovery and cost-effectiveness. The mathematical model describing the performance of hollow-fiber membrane adsorber, which represents a second-strategy filter, is studied. A general form of the particle-deposition equation is introduced, and its terms are analyzed. As a result, its linearized form, looking like a linear equation of reversible adsorption, is chosen. A numerical solution to the system of governing equations is obtained and used to assess the accuracy of approximate solutions. A new approximate solution allowing one to evaluate the adsorber particle retentions with an acceptable accuracy is suggested.     

Gravitational Deposition of Aerosol Particles on a Fibrous Filter with Account for the Effect of Van der Waals Force

The deposition of inertialess aerosol particles with a finite radius is investigated on fibrous filters under the effect of gravitational and molecular forces. It is shown that particles are deposited on fibers from an upgoing slow flow as a result of the action of van der Waals forces that balance the gravitational particle displacement from the flow lines near the fibers     

Quality control materials for the determination of trace elements in airborne particulate matter

The development of quality control materials for the determination of selected trace elements in air pollution studies is described. Three types of test samples were prepared for proficiency testing: (1) filters loaded with PM10 fraction of urban air particulate matter (APM) using high-volume air samplers, which were subsequently divided into smaller sections, (2) a bulk sample of APM collected in an automobile tunnel in Prague, and (3) simulated air filters loaded with APM using a wet deposition process. Homogeneity of the test samples was studied using instrumental neutron activation analysis, proton induced X-ray emission and atomic absorption spectrometry, and inductively coupled plasma optical emission spectrometry and mass spectrometry. Sufficiently homogeneous samples were prepared by all three procedures. The simulated air filters appeared to be the most suitable test samples for proficiency testing.     

Stokes flow and deposition of aerosol nanoparticles in model filters composed of elliptic fibers

The calculation is implemented for the fiber collection efficiencies due to diffusion of nanoparticles in model filters, i.e., separate rows of fibers with an elliptic cross section located normal to the flow at different orientations of the ellipse axes with respect to the flow. The Stokes flow field in the system of the fibers is found by the method of fundamental solutions. The concentration field of Brownian particles and the efficiency of their deposition onto the fibers are determined from the numerical solution of the equation for the convective diffusion. The dependence of the capture coefficient on the Peclet number for elliptic fibers is shown to have the form η = APe^−m, where exponent m changes from 2/3 to 3/4 at the parallel and normal orientation of the major axes of the ellipses with respect to the flow, respectively. It is shown that, from the viewpoint of aerosol nanoparticle capture, the best filters are those in which the fibers have a maximum midsection at the same cross-sectional area.     

Study of the adsorption of americium on manganese-dioxide-impregnated filters

Adsorption of americium with manganese-dioxide-impregnated filters has been studied. The adsorption of americium decreases as the pH increases due to its hydrolysis. From the reported laboratory experiments, it can be concluded that the adsorption on manganese-dioxide filters is not a reliable method to determine americium in natural waters.     

Influence of Gravity on Filtration of Submicron Aerosols of Heavy Metals

Colloid Journal - The influence of gravity on the deposition of high-density submicron aerosol particles in fibrous filters from vertical and horizontal (relative to the gravity vector direction)...     

Electroblotting of polypeptides onto glass fiber filters for direct sequence analysis after sodium dodecyl sulfate-polyacrylamide gel electrophoresis

The technique of electroblotting polypeptides onto Polybrene-treated glass fiber filter discs after protein detection with potassium chloride is evaluated further with different proteins in separate applications. The number of proteins analyzed with this method is now more than double that previously reported. Reproducible results in good yield are obtained. Average overall yield--including the electrophoretic step before blotting--is 26%, with maximal recoveries through all steps up to 60%. High sensitivity radiosequence analysis is also applicable. Recent modifications of the previously described procedure include use of Whatman glass fiber filters, removal of air in the Polybrene-impregnated filters by buffer penetration under reduced pressure, and use of widely different times for electrotransfer. Special advantages with this method are low extent of protein alpha-amino group destruction, direct use of the entire filter in the sequencer, and insensitivity to variations in electroblotting time. Gas-phase hydrolysis in situ of blotted proteins followed by amino acid analysis is known to give a low yield of polar amino acids, and often artifacts, but can still give an estimate of the amount of polypeptide immobilized on the filter. A wash with n-butyl chloride is now shown to reduce the Polybrene-associated artifacts, and an addition of sodium chloride to increase the recovery of polar amino acids. These two steps therefore appear interesting in schemes for compositional analyses of electroblotted proteins.     

Collection of Nanoaerosols by Filters Composed of Nanofibers

Colloid Journal - The collection of aerosol nanoparticles by filters composed of nanofibers has been theoretically investigated. The convective diffusion deposition of point particles from a Stokes...     

Deposition of nanoparticles in filters composed of permeable porous fibers

The diffusion deposition of nanoparticles is studied from a flow at low Reynolds numbers in model filters composed of permeable circular porous fibers. The field of particle concentration is calculated and the capture coefficient is determined for a cell, as well as the isolated row of parallel fibers within a wide range of Peclet numbers (Pe) depending on the fiber permeability. It is shown that at Pe > 1, the diffusion capture coefficient η increases with permeability, while at Pe → ∞, it tends toward the limiting value, which is equal to the gas flow rate through the porous fiber. The capture coefficients calculated from a cell model and for a row of fibers are almost equal to each other. The diffusion deposition of aerosol particles in the highest penetration range is calculated with an allowance for their finite sizes and it is shown that the radii of most penetrable particles decrease with an increase in fiber permeability.     

Deposition of Aerosol Nanoparticles in Fibrous Filters

The deposition of aerosol nanoparticles on model fibrous filters of different porosity at small Reynolds numbers was considered. The efficiency of particle deposition on a fiber was determined by the numerical solution of the convective diffusion equation in the ordered systems of parallel fibers located perpendicularly to a flow. The calculation results agree with the known experiments on the model filters over the Peclet number (Pe) range from 0.05 to 1000. It was shown that the Natanson–Stechkina formula for the coefficient of capture obtained in the limit of thin diffusion boundary layer at Pe 1 is valid within a wide range of the Peclet numbers up to Pe 1.     

Molecular dynamics simulations of polyelectrolyte multilayering on a charged particle

Molecular dynamics simulations of polyelectrolyte multilayering on a charged spherical particle revealed that the sequential adsorption of oppositely charged flexible polyelectrolytes proceeds with surface charge reversal and highlighted electrostatic interactions as the major driving force of layer deposition. Far from being completely immobilized, multilayers feature a constant surge of chain intermixing during the deposition process, consistent with experimental observations of extensive interlayer mixing in these films. The formation of multilayers as well as the extent of layer intermixing depends on the degree of polymerization of the polyelectrolyte chains and the fraction of charge on its backbone. The presence of ionic pairs between oppositely charged macromolecules forming layers seems to play an important role in stabilizing the multilayer film.     

The effect of gas slip on pressure drop and deposition of submicron particles in model granular filters

The Stokes flow field and aerosol particle deposition from flows in model filters, i.e., separate layers of granules with square and hexagonal structures, have been calculated taking into account the effect of gas slip at granule surface. Approximating formulas have been derived for granule drag forces to a flow. The efficiencies of diffusion collection of particles have been calculated in a wide range of Peclet numbers with allowance for a finite particle size and the existence of a Knudsen boundary layer, the layer thickness being comparable with the particle sizes. The applicability of the cell model to the calculation of granular filters has been discussed.     

Computer simulations of particle-bubble interactions and particle sliding using Discrete Element Method

Polymer coatings on nano-sized remediation agents and subsurface heterogeneity will affect their transport, likely in a pH-dependent manner. The effect of pH on the aggregation of polymer-coated nanoscale zerovalent iron (nZVI) and its deposition onto sand and clay (kaolinite) surfaces was studied. nZVI coatings included a high molecular weight (90 kg/mol) strong polyanion, poly(methacrylic acid)-b-(methy methacrylate)-b-(styrenesulfonate) (PMAA-PMMA-PSS) and a low molecular weight (2.5 kg/mol) weak polyanion, polyaspartate. Aggregation and deposition increased with decreasing pH for both polyelectrolytes. The extent was greater for the low MW polyaspartate coated nZVI. Enhanced deposition at lower pH was indicated because the elutability of polyaspartate-modified hematite (which did not aggregate) also decreased at lower pH. The greater deposition onto clay minerals compared to similar sized silica fines is attributed to charge heterogeneity on clay mineral surfaces, which is sensitive to pH. Heteroaggregation between kaolinite particles and nZVI over the pH range 6-8 confirmed this assertion. Excess unadsorbed polyelectrolyte in solution (100mg/L) enhanced the transport of modified nZVI by minimizing aggregation and deposition onto sand and clay. These results indicate that site physical and chemical heterogeneity must be considered when designing an nZVI emplacement strategy.     

A model of a dust-loaded filter with asymmetric deposit of particles on fibers

Results of numerical simulation have been reported for the flow field and diffusion deposition of nanoparticles in a model dust-loaded fibrous filter, i.e., a row of parallel fibers coated with porous permeable shells shifted toward an incident flow. The flow field and point particle collection efficiency on fibers coated with the shells have been calculated by combining the Stokes, Brinkman, and convective diffusion equations. It has been shown that the pressure drops and efficiencies of nanoparticle deposition in the filters composed by fibers with coaxial and asymmetric porous shells are almost identical.     

Deposition of aerosol nanoparticles in filters composed of fibers with porous shells

The diffusion deposition of submicron aerosol particles in model filters consisting of fibers covered with permeable porous shells is studied. An ordered system of parallel cylinders arranged perpendicular to the flow is used as a model filter. The results of calculations are given for the dependences of the capture coefficient on the shell radius, the shell permeability, the packing density of the filters, the particle radius, and the flow velocity. Calculations are performed within a wide range of Peclet numbers. It is shown that the capture coefficient and the quality criterion γ of a filter increase with the diffusion mobility of particles and shell permeability, as well as that the dependence of the quality criterion on the radius of permeable shells has a maximum. It is also shown that the capture coefficients for fibers with porous shells, calculated using the cell model and the isolated row of fibers, almost coincide with one another.