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.     

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.     

Deposition of aerosol nanoparticles on filters coated with layer of carbon nanotubes

Problems concerning intensification of fine gas purification from suspended particles by coating filter fibers with permeable layers of carbon nanotubes, as well as problems relevant to the rebound of Brownian nanoparticles from nanofibers, are discussed. When passing nanoaerosols of sodium chloride through different filtering partitions, the internal surface of which is coated with a thin layer of carbon nanotubes, no peculiarities are observed for deposition of nanoparticles with diameters of larger than 3.5 nm.     

Deposition of charged aerosol nanoparticles in diffusion batteries

The deposition of weakly charged aerosol nanoparticles onto fibers in a diffusion battery designed to measure the diffusion coefficients of particles is considered. The fiber collection efficiancies as functions of particle size and charge are determined by the numerical solution of the equation of convective diffusion in a system of parallel uncharged fibers located normal to a flow. It is shown of effect of the single charge of nanoparticles produced by a differential mobility analyzer on their deposition is negligible and may be ignored when calibrating diffusion batteries.     

Permeability of medium composed of cylindrical fibers with fractal porous adlayer

The flow of viscous liquid in the porous medium formed by cylindrical fibers coated with a fractal porous adlayer is considered. Based on the Happel-Brenner cell method, the hydrodynamic permeability of a medium is calculated using the Brinkman equations. The analysis is performed for boundary conditions on cell surfaces of four types corresponding to the Happel, Kuwabara, Kvashnin, and Cunningham models. Different (transversal, longitudinal, and random) orientations of fibers with respect to liquid flow are considered.     

Diffusion deposition of aerosol nanoparticles in model granular filters

The diffusion deposition of point aerosol particles from a flow in model granular (grained) filters, i.e., separate layers composed of parallel chains of spherical granules, has been studied at small Reynolds numbers. Numerical solution of the Stokes and convective diffusion equations has been employed to determine the drag forces and granule collection efficiencies as depending on the Peclet diffusion number in a range Pe = 0.02–2 × 10⁴ and the ratio between the granule diameter and the distance between chain axes. Layers of closed chains with square and hexagonal packings have been considered. Approximation formulas have been derived for calculation of nanoparticle penetration in model granular filters.     

Preparation of pickering-emulsion-based capsules with shells composed of titanium dioxide nanoparticles and polyelectrolyte layers

A procedure has been proposed for the preparation of capsules with shells composed of titanium dioxide nanoparticles and polymers via the formation of Pickering emulsions (colloidosomes) followed by layer-by-layer deposition of polyelectrolytes. The feasibility of stabilizing oil droplets of emulsions by spontaneous adsorption of partly hydrophobized nanoparticles of anatase-form titanium dioxide at the oil/water interface has been studied. Conditions have been determined for the formation of stable colloidosomes and the subsequent layer-by-layer deposition of oppositely charged polyelectrolytes onto their surfaces. It has been shown that hydrophobic dyes may be encapsulated using the procedure developed for the preparation of the capsules. The photocatalytic activity of TiO₂ particles occurring in the shell has been demonstrated by the example of degradation of Nile red which is incorporated in the oil core of a capsule.     

Deposition of continuous platinum shells on gold nanoparticles by chemical precipitation

Continuous platinum shells consisting of ~5 atomic layers were deposited onto preformed gold seeds in aqueous medium by reducing hexachloroplatinic acid with ascorbic acid. By controlling the reduction kinetics of Pt(IV) species and the properties of the substrate, it was possible to ensure a slow and controlled deposition of platinum atoms onto the gold cores. Electrochemical evaluations revealed the presence of a compact platinum shell. The mass specific oxygen reduction activity of platinum in the AuPt core-shell nanoparticles was found to be four times higher than that of platinum black and comparable to that of polycrystalline bulk metal.     

Efficiency of inertial deposition of aerosol particles in fibrous filters with regard to particle rebounds from fibers

The inertial deposition of submicron aerosol nanoparticles onto fibers during gas filtration through fine-fiber filters is considered. It is shown that there is critical filtration velocity U* below which the energy loss upon collisions has no influence on the filtration efficiency. Above this critical velocity, the filtration efficiency depends on the mechanism of the inelastic energy loss and can be noticeably lower than the result of its estimation with no allowance for the particle rebound. For a rather dense fibrous medium, when not all particles that have rebounded from a fiber have time to attain the flow velocity before the next collision with another fiber, the filtration efficiency depends on the velocity distribution of the rebounding particles. It is shown that, in this case, the filtration efficiency must increase with the packing density of a filter.     

Deposition of silver nanoparticles on cellulosic fibers via stabilization of carboxymethyl groups

The stabilizing role of carboxymethyl groups on the conformal deposition of Ag NPs over cellulosic fibers was elucidated while developing a method for the deposition of silver nanoparticles (NPs) on cellulose acetate (CA), cellulose and partially carboxymethylated cellulose (CMC) electrospun fibers. CMC fibers were prepared through judicious anionization of deacetylated cellulose acetate fibers. Ag NPs were chemically reduced from silver nitrate using sodium borohydride and further stabilized using citrate. Ag NPs were directly deposited onto CA, cellulose and CMC electrospun fibers at pH conditions ranging from 2.5 to 9.0. The resulting composites of Ag/fiber were characterized by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The results revealed that the amount of Ag agglomerates and NPs deposited on CMC fibers was higher than that deposited on cellulose fibers at similar pH conditions, and that barely any Ag agglomerates or NPs were deposited on the CA fibers. These results implied that functional groups on the cellulose backbone played two important roles in the deposition of NPs as follows: (1) Hydrogen bonding was the main driving force for agglomeration of NPs when the medium pH was below 4.4, which corresponds to the pKa of carboxylic acid groups; (2) Carboxymethyl groups could replace citrate groups as stabilizers allowing the fabrication of a uniform and evenly distributed Ag NPs layer over CMC fibers at higher pH values. This report also highlights the importance of the substrate’s surface charge and that of the pH of the medium used, on the deposition of NPs. The composite of Ag NPs on CMC electrospun fibers appears to be a promising candidate for wound dressing applications due to its superior antibacterial properties originated by the uniform and even distribution of Ag NPs on the surface of the fibers and the wound healing aptness of the CMC fibers.     

Synthesis of porous zinc gallate prisms composed of highly oriented nanoparticles by an in situ conversion reaction

Porous ZnGa(2)O(4) prisms assembled by highly oriented nanoparticles have been fabricated by an in situ chemical conversion approach. We report, for the first time, that a solid α-Ga(2)O(3) precursor can be directly converted into ZnGa(2)O(4) rather than through the intermediate GaOOH. Based on a detailed study of the evolution of ZnGa(2)O(4) prisms, a growth mechanism is proposed for the in situ conversion reaction. During this conversion process, the precursor morphology can be highly retained, which is attributed to the similar atomic arrangements of the Ga and O atoms and excellent matching of the lattice spacing between the α-Ga(2)O(3) and ZnGa(2)O(4) prisms. The direct reaction between the precursor α-Ga(2)O(3) and Zn(2+) ions is more efficient than that between the byproduct GaOOH and Zn(2+) ions. Moreover, the photoluminescent color of the ZnGa(2)O(4) phosphor can be tuned by doping with Mn(2+) ions. Efficient energy transfer (ET) from the host lattice to the Mn(2+) centers is observed, whereas ET from the defects to the Mn(2+) ions is prohibited. The fabricated ZnGa(2)O(4) products have potential in the field of display applications.     

Cellulose fibers modified with silver nanoparticles

Cellulose fibers modified with silver nanoparticles were prepared using N-methylmorpholine-N-oxide as a direct solvent and analyzed in this study. Silver nanoparticles were generated as a product of AgNO₃ reduction by means of three methods under varying light conditions (daylight and darkroom). Influence of generating conditions on the size, the type and the number weighting of created nanoparticles was examined. Dynamic Light Scattering technique (DLS) was used for determination of those parameters. DLS analysis showed that the best method, i.e. the one that allowed the generation of the greatest number of silver nanoparticles with the smallest diameter and the smallest agglomerates, was incubation of cellulose pulp with AgNO₃ in a darkroom for 24 h. Mechanical and hydrophilic properties of all obtained fibers were also determined. Results showed that the method of silver nanoparticles generation did not influence significantly mechanical and hydrophilic properties of the modified fibers, because in all cases only small decreases of the studied parameters were observed.     

Ultra-low background measurements of decayed aerosol filters

Aerosol samples collected on filter media were analyzed using HPGe detectors employing varying background-reduction techniques in order to experimentally evaluate the opportunity to apply ultra-low background measurement methods to samples collected, for instance, by the Comprehensive Test Ban Treaty International Monitoring System (IMS). In this way, realistic estimates of the impact of low-background methodology on the sensitivity obtained in systems such as the IMS were assessed. The current detectability requirement of stations in the IMS is 30 μBq/m³ of air for ¹⁴⁰Ba, which would imply ~10⁶ fissions per daily sample. Importantly, this is for a fresh aerosol filter. One week of decay reduces the intrinsic background from radon daughters in the sample allowing much higher sensitivity measurement of relevant isotopes, including ¹³¹I. An experiment was conducted in which decayed filter samples were measured at a variety of underground locations using Ultra-Low Background (ULB) gamma spectroscopy technology. The impacts of the decay and ULB are discussed.     

Water-soluble amphiphilic gold nanoparticles with structured ligand shells

Highly water-soluble mixed monolayer protected "rippled" gold nanoparticles were synthesized through a one step reaction with sodium 11-mercaptoundecanesulfonate and octanethiol ligands at various ratios.     

Cell models of porous media composed of impenetrable spherical particles coated with nonuniform porous layers

The liquid flow through a set of nonuniform porous cylinders with a impenetrable core are studied by the Happel—Brenner cell method. Different orientations of cylinders relative to the liquid flow, such as transverse, longitudinal, and random, are considered. Brinkman equations are used to describe the flow of liquid in the porous layer. All known boundary conditions on the cell surface (Happel, Kuwabara, Kvashnin, and Cunningham conditions) are considered. The models proposed can be used to describe the processes of reverse osmosis, as well as nano-and ultrafiltration.     

Compositions of the shells of nanoparticles with pentagonal symmetry

A method of calculation of the number of atoms in the structure of nanoforms with pentagonal symmetry (fullerenes, nanoparticles, clusters) depending on the arrangement of atoms on the symmetry elements of the I _h group has been developed. The formulas for calculation of the number of particles in all possible shells, including multilayer ones, are reported. The numbers of atoms in the shells of pentagonal symmetry are determined by four structurally invariant numbers and the “quantum number” of the order n of the group. The classification of all possible atomic shells S _{? + 60z} (z = 0, 1, ...) is presented, and the constructions of the basic shells S _? (? = 12, 20, 30, 50, 60) are given. For each basic shell, the sum rule is met: the sum of the coordination numbers of the elements of subshells is equal to 60. In clusters with magic numbers, basic shells are periodically repeated. In addition to the known shells of nanostructures, the formulas of new structures that are expected to be stable—B₂₀O₃₀, B₆₀O₉₀ (B₂O₃), and B₉₀O ₁₃₀ ¹⁰⁺ (borate)—are reported for the first time. The same is valid for similar compounds of Group III elements.     

Permeability of media composed of impenetrable cylinders covered with porous layer

The liquid flow through a set of nonuniform porous cylinders with a impenetrable core are studied by the Happel—Brenner cell method. Different orientations of cylinders relative to the liquid flow, such as transverse, longitudinal, and random, are considered. Brinkman equations are used to describe the flow of liquid in the porous layer. All known boundary conditions on the cell surface (Happel, Kuwabara, Kvashnin, and Cunningham conditions) are considered. The models proposed can be used to describe the processes of reverse osmosis, as well as nano-and ultrafiltration.     

Polyaniline-coated cellulose fibers decorated with silver nanoparticles

Cellulose fibers of 20 μm in diameter and aspect ratio of 2 or 10 were coated with protonated polyaniline (PANI) during the oxidation of aniline hydrochloride with ammonium peroxydisulfate in an aqueous medium. The presence of PANI has been proved by FTIR spectroscopy. The conductivity increased from 4.0 × 10⁻¹⁴ S cm⁻¹ to 0.41 S cm⁻¹ after coating the fibers with PANI. The percolation threshold in the mixture of original uncoated and PANI-coated fibers was reduced from 10 mass % PANI to 6 mass % PANI, as the aspect ratio changed from 2 to 10. The subsequent reaction with silver nitrate results in the decoration of PANI-coated cellulose fibers with silver nanoparticles of about 50 nm average size. The content of silver of up to 10.6 mass % was determined as a residue in thermogravimetric analysis. FTIR spectra suggest that the protonated emeraldine coating changed to the pernigraniline form during the latter process and, consequently, the conductivity of the composite was reduced to 4.1 × 10⁻⁴ S cm⁻¹, despite the presence of silver.     

New multifunctional nanoparticles with mesoporous cores and silver shells

The feasibility of preparing continuous silver shells of different thicknesses on mesoporous silica particles is demonstrated for the first time. The resulting composite nanoparticles with a tuned localized surface plasmon resonance can simultaneously be used as containers for a number of compounds, e.g., drugs for combined therapy of tumors.