Ivan Volkov

Filtration of nanosized particle aerosols by electret fibrous filters

Results of studying the filtration efficiency of various nanoaerosols in an air-cleaning system in which particles are charged in the integrated corona discharge unit and polymer fibers with electret properties serve as the filtration material are presented. The total filtration efficiency for titanium oxide (TiOx), diethyl-hexylsebacate (DEHS), and bovine serum albumin (BSA) aerosols and anti-mosquito smoke (AMS) is 99.9, 99.3, 98.6, and 98.7%, respectively. A significant (5–10%) drop in the filtration efficiency has been observed for DEHS and BSA aerosols and AMS in a particle size range of less than 80 nm. It has been demonstrated that the filtration efficiency can be substantially increased by activating the electrostatic particle-capture mechanism through the charging of particles in the corona discharge unit. In connection with this, the electrostatic mechanism is the dominant one for particles larger than 80 nm, while its contribution decreases in the particle size range of less than 80 nm with a decrease in particle size and a simultaneous increase in the contribution of the capture mechanism due to diffusion. It has also been found that the increase in the filter solidity by a factor of higher than 1.5 has a negligible effect on the filtration efficiency, thus making it reasonable to utilize low-solidity electret filters whose quality factor reaches the maximal values.

Reducing Humidity Response of Gas Sensors for Medical Applications: Use of Spark Discharge Synthesis of Metal Oxide Nanoparticles

The application of gas sensors in breath analysis is an important trend in the early diagnostics of different diseases including lung cancer, ulcers, and enteric infection. However, traditional methods of synthesis of metal oxide gas-sensing materials for semiconductor sensors based on wet sol-gel processes give relatively high sensitivity of the gas sensor to changing humidity. The sol-gel process leading to the formation of superficial hydroxyl groups on oxide particles is responsible for the strong response of the sensing material to this factor. In our work, we investigated the possibility to synthesize metal oxide materials with reduced sensitivity to water vapors. Dry synthesis of SnO2 nanoparticles was implemented in gas phase by spark discharge, enabling the reduction of the hydroxyl concentration on the surface and allowing the production of tin dioxide powder with specific surface area of about 40 m2/g after annealing at 610 °C. The drop in sensor resistance does not exceed 20% when air humidity increases from 40 to 100%, whereas the response to 100 ppm of hydrogen is a factor of 8 with very short response time of about 1 s. The sensor response was tested in mixtures of air with hydrogen, which is the marker of enteric infections and the marker of early stage fire, and in a mixture of air with lactate (marker of stomach cancer) and ammonia gas (marker of Helicobacter pylori, responsible for stomach ulcers).

Tin Acetylacetonate as a Precursor for Producing Gas-Sensing SnO2 Thin Films

To expand the range of precursors used in the sol–gel technology for applying nanostructured SnO2 thin films promising as components of semiconductor chemical gas sensors, the efficiency of using tin acetylacetonate solutions with various precursor concentrations was demonstrated. It was determined that finely divided SnO2 with a crystallite size of 3–4 nm (cassiterite) can be obtained by hydrolysis by atmospheric moisture in the course of solvent evaporation at room temperature. Using tin acetylacetonate solutions with various precursor concentrations for applying SnO2 thin films by dip coating to the surface of rough ceramic Al2O3-based substrates with platinum interdigital electrodes and a microheater resulted in significant differences in microstructure, continuity, thickness, and porosity of the produced coatings. In a lower-concentration (0.13 mol/L) tin acetylacetonate solution, a multilayer dense continuous SnO2 coating was applied, whereas in a higher-concentration (0.25 mol/L) solution, the formed layer comprised aggregated nanoparticles 30–60 nm in size and had much more defects and higher porosity. The sensitivity of the obtained thin-film nanostructures to the most practically important gaseous analytes: CO, H2, CH4, CO2, and NO2. The produced two-dimensional nanomaterials were shown to be promising for detecting carbon monoxide at 200–300°C in dry air.

Determination of the critical values of flow parameters characteristic of the alignment of cylindrical nano-objects in suspensions

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