Filtration Of Nanoparticles Research Articles

Filtration of nano-particles by a gas–solid fluidized bed

The filtration of 80 nm SiO 2 and Al 2O 3 particles in a gas stream using fluidized beds was studied. Silica sand and activated carbon (A.C.) were adopted as bed materials to filtrate 80 nm SiO 2 and Al 2O 3 particles. The collected particles were elutriated from the fluidized bed, so the filtration was a dynamic process and the variations of the removal efficiency with time were studied. Experimental results showed that the filtrations of 80 nm SiO 2 and Al 2O 3 particles with a bed material of silica sand were not dynamic processes but the filtration by A.C. was. The removal efficiencies for SiO 2 and Al 2O 3 particles using silica sand as bed material were held steady and found to be equal, between 86 and 93%. A.C. is considered to be more efficient than silica sand because it has a high specific surface area. However, the experimental data yield conflicting results. The removal efficiency of Al 2O 3 particles fell from 92% initially to 80% at the end of test—a little lower than that obtained by filtration using silica sand. A higher voidage of A.C. than silica sand weakens the removal of nanoparticles since the diffusion mechanism dominates. The removal efficiency of SiO 2 by A.C. decayed from 83 to 40% with time passed. The huge differences between the filtration efficiency of SiO 2 and that of Al 2O 3 particles by A.C. was associated with the extensive segregation of SiO 2 and A.C. particles, which caused more SiO 2 particles to move to the top of the bed, where they were elutriated. The weak inter-particle force for SiO 2 decreased the removal efficiency also.

A Practical Approach to the use of Nanoparticles for Vaccine Delivery

The objective of this work was to obtain a nanoparticle formulation that could be sterile filtered, lyophilized, and resuspended to the initial size with excipients appropriate for use as a vaccine formulation. Poly(lactide-co-glycolide) (PLG) polymers were used to create nanoparticles ranging in size from 110 to 230 nm. Protein antigens were adsorbed to the particles; the protein-nanoparticles were then lyophilized with the excipients. Vaccine compatible excipient combinations of sugars alone, surfactants alone, and sugars and surfactants were tested to find conditions where initial particle size was recovered. Sterile filtration of smaller nanoparticles led to minimal PLG losses and allowed the particle preparation to be a nonaseptic process. We found that the smaller nanoparticles of size ~ 120 nm required higher surfactant concentration to resuspend postlyophilization than slightly larger (~220 nm) particles. To resuspend 120 nm nanoparticles formulations of poly(vinyl alcohol) (PVA) with sucrose/mannitol or dioctyl sodium sulfosuccinate (DSS) with trehalose/mannitol were sufficient. The protein-nanoparticles resuspension with the same excipients was dependent on the protein and protein loading level. The nanoparticle formulations in vivo were either similar or had enhanced immunogenicity compared to aluminum hydroxide formulations. A lyophilized nanoparticle formulation with adsorbed protein antigen and minimal excipients is an effective vaccine delivery system.

Modeling of filtration efficiency of nanoparticles in standard filter media

The goal of this study is to model the data from the experiments of nanoparticle filtration performed at the Particle Technology Lab, University of Minnesota and at the 3M Company. Comparison shows that the experimental data for filter efficiency are bounded by the values computed from theoretical expressions which do not consider thermal rebound. Therefore thermal rebound in the tested filter media is not detected down to 3 nm particles in the present analysis. The efficiency measured experimentally is in good agreement with the theoretical expression by Stechkina (1966, Dokl. Acad. Nauk SSSR 167, 1327) when the Pectlet number Pe is larger than 100; it agrees well with the theoretical expression by Kirsch and Stechkina (1978, Fundamentals of Aerosol Science. Wiley, New York) when Pe is of the order of unit. We develop an empirical power law model for the efficiency depending on the Peclet number, which leads to satisfactory agreement with experimental results.

Experimental study of nanoparticles penetration through commercial filter media

In this study, nanoparticle penetration was measured with a wide range of filter media using silver nanoparticles from 3 nm to 20 nm at three different face velocities in order to define nanoparticle filtration characteristics of commercial fibrous filter media. The silver particles were generated by heating a pure silver powder source via an electric furnace with a temperature of 870°C, which was found to be the optimal temperature for generating an adequate amount of silver nanoparticles for the size range specified above. After size classification using a nano-DMA, the particle counts were measured by an Ultrafine Condensation Particle Counter (UCPC) both upstream and downstream of the test filter to determine the nanoparticle penetration for each specific particle size. Particle sampling time continued long enough to detect more than 105 counts at the upstream and 10 counts at the downstream sampling point so that 99.99% efficiency can be detected with the high efficiency filter. The results show a very high uniformity with small error bars for all filter media tested in this study. The particle penetration decreases continuously down to 3 nm as expected from the classical filtration theory, and together with a companion modeling paper by␣Wang et al. in this same issue, we found no significant evidence of nanoparticle thermal rebound down to 3 nm.

Coagulation and Filtration of Nanoparticles in Wastewater from Hsinchu Science‐Based Industrial Park (HSIP)

The Hsinchu Science‐based Industrial Park (HSIP) is a “high‐tech” manufacturing base in Taiwan. Wastewater from the HSIP contains numerous nanoparticles, which are difficult to remove by conventional coagulation‐sedimentation processes, and are the main foulants to ultrafiltration (UF) and reverse‐osmosis (RO), membrane in filtration. This investigation observed that the coagulation rates of nanoparticles in wastewater could be significantly increased by raising the solution temperature to over 65°C, thus yielding large and compact aggregates. The proposed thermal treatment could considerably reduce the fouling potentials of UF and RO membranes, and thus represents a suitable pre‐treatment for producing clean water from HSIP wastewater.

Filtration Efficiency of Aerosol Particles Below 20 Nanometers

The current work examines the filtration of both charged and uncharged NaCl nanoparticles in the size range of 2.5–20 nm on grounded metal filters and meshes, and on plastic mesh. The methodology thus allows electrostatic and other effects to be differentiated from true thermal rebound effects (Wang and Kasper 1991). The work also compares measurements under identical conditions made with a number of different condensation particle counters, and a number of different experimental methodologies, in order to allow exclusion of certain measurement errors from the results. It was found that even for particle sizes as small as 2.5 nm there was no measurable deviation from the classical single-fiber-efficiency theory. This conflicts with recently published work (Balazy et al. 2004) which claimed that the thermal bounce of nanometer sized aerosol particles begins to occur at a much larger particle size than previously thought. However, peculiarities or artifacts in CPC counting efficiency at small particle sizes...

The Formation of Porous Membranes by Filtration of Aerosol Nanoparticles

Flame-generated aerosol particles of Al2O3 were deposited by gas filtration on two types of porous and ceramic tubes of α-Al2O3 with mean pore diameters of 450 and 2700 nm, respectively. The particles were aggregates with average mobility diameters in the range of 30–100 nm and primary particle diameters of 4–8 nm. The particles are characterized by differential mobility analysis, transmission electron microscopy, and by their specific surface area. The deposited membranes are characterized by gas permeability measurements, scanning electron microscopy, and by their pore size distribution from nitrogen capillary condensation. The particles form a distinct, homogeneous membrane layer with a porosity of ∼90% on top of the substrate surface and only penetrate slightly into the substrate structure. The mean pore sizes of the deposited membranes determined by nitrogen condensation agree approximately with those determined by gas permeation and the specific surface area. The mean pore diameter varies in the range of 30–70 nm. The gas permeability of the deposited membranes is related to the specific surface area but influenced by the high porosity. The mean pore size and the permeability of the membranes are almost independent of the substrate structure.

Adhesion of elastic spheres

Bradley (1932) showed that if two rigid spheres of radii R 1 and R 2 are placed in contact, they will adhere with a force 2πΔ R γ, where R is the equivalent radius R 1 R 1 /( R 1 + R 2 ) and Δγ is the surface energy or ‘work of adhesion’ (equal to γ1+γ2-γ12). Subsequently Johnson et al. (1971) (JKR theory) showed by a Griffith energy argument (assuming that contact over a circle of radius a introduces a surface energy -π a 2 Δγ) how the Hertz equations for the contact of elastic spheres are modifed by surface energy, and showed that the force needed to separate the spheres is equal to (3/2)πΔ R γ, which is independent of the elastic modulus and so appears to be universally applicable and therefore to conflict with Bradley9s answer. The discrepancy was explained by Tabor (1977), who identified a parameter 3 Δγ 2 / 3 / E * 2 / 3 \e governing the transition from the Bradley pull-off force 2π R Δ|γ to the JKR value (3/2)π R Δγ. Subsequently Muller et al. (1980) performed a complete numerical solution in terms of surface forces rather than surface energy, (combining the Lennard–Jones law of force between surfaces with the elastic equations for a half-space), and confirmed that Tabor9s parameter does indeed govern the transition. The numerical solution is repeated more accurately and in greater detail, confirming the results, but showing also that the load–;approach curves become S-shaped for values of μ greater than one, leading to jumps into and out of contact. The JKR equations describe the behaviour well for values of μ of 3 or more, but for low values of μ the simple Bradley equation better describes the behaviour under negative loads.

Filtration of Nanoparticles with Dimethyldioctadecylammonium Bromide Treated Microporous Polypropylene Filters

Microporous polypropylene membrane filters are modified with a cationic surfactant, dimethyldioctadecylammonium bromide (DDAB), to create a charged surface. Negatively charged nanoparticles can then be filtered by utilizing the electrostatic interaction between the charged particles and the polar heads of the surfactants adsorbed on the filters. The study focuses on particle adsorption and particle filtration. Particle adsorption studies have shown that particle adsorption can be increased significantly with this treatment due to Coulombic attraction. Filtration results for 60 nm negatively charged particles (carboxylate modified copolymer) filtered through DDAB treated filters show a significant increase in particle capture efficiency. Capture efficiency is dependent on the pH of the suspension due to competitive adsorption between the hydroxide ions and the negatively charged nanoparticles. As the mean pore diameter increases, capture efficiency decreases due to the increase in distance between the part...