Hye Moon Lee

Al-Coated Conductive Fibrous Filter with Low Pressure Drop for Efficient Electrostatic Capture of Ultrafine Particulate Pollutants.

Here, we demonstrate a new strategy of air filtration based on an Al-coated conductive fibrous filter for high efficient nanoparticulate removals. The conductive fibrous filter was fabricated by a direct decomposition of Al precursor ink, AlH3{O(C4H9)2}, onto surfaces of a polyester air filter via a cost-effective and scalable solution-dipping process. The prepared conductive filters showed a low sheet resistance (<1.0 Ω sq-1), robust mechanical durability and high oxidative stability. By electrostatic force between the charged fibers and particles, the ultrafine particles of 30-400 nm in size were captured with a removal efficiency of ∼99.99%. Moreover, the conductive filters exhibited excellent performances in terms of the pressure drop (∼4.9 Pa at 10 cm s-1), quality factor (∼2.2 Pa-1 at 10 cm s-1), and dust holding capacity (12.5 μg mm-2). After being cleaned by water, the filtration efficiency and pressure drop of the conductive filter was perfectly recovered, which indicates its good recyclability. It is expected that these promising features make the conductive fibrous filter have a great potential for use in low-cost and energy-efficient air cleaning devices as well as other relevant research areas.

Fabrication of Reference Filter for Measurements of EC (Elemental Carbon) and OC (Organic Carbon) in Aerosol Particles

Reference filters with uniformly deposited, known masses of elemental carbon (EC) and organic carbon (OC) were produced by a spray-drying method and a carbon aerosol sampling system. Submicrometer carbon particles were produced by nebulizing a carbon black hydrosol and a potassium hydrogen phthalate (KHP; C 6 H 4 (COOK)(COOH)) solution. Total carbon (TC) concentrations measured at three different locations on the filter showed that the carbon particles were uniformly distributed on the filter. Reference filters were analyzed using thermal optical analysis methods (TOA) IMPROVE and NIOSH 5040-NIIH, and the measured concentrations of TC, EC, and OC were compared to the gravimetrically measured concentrations. TC measurements by both TOA methods used were in excellent agreement with gravimetrically measured TC. It was found that the IMPROVE method produced approximately 3.5 times as much pyrolytically generated elemental carbon (PEC) as did the NIOSH 5040-NIIH method. However, no PEC was detectable on reference filters when both EC and OC were present. This led to discrepancies in EC and OC measurement between the TOA and gravimetric methods. Better agreement was found when PEC generation of pure OC reference filters was taken into account and measurements on filters with both EC and OC deposited were corrected for PEC generation. These data imply that, when both EC and OC are present on the filter, TOA methods are often inaccurate in correctly measuring the amount of PEC generated, with the magnitude of measurement error dependent upon the type of EC and OC present in the sample. In addition, reference filters with OC deposited on top of EC and EC deposited on top of OC were generated and analyzed. From these reference filters, it was found that PEC measurements are also affected by the way in which the EC and OC deposit on the filter. Overall, the method devised here to create reference EC/OC filters is a simple technique in which EC, OC, and mixed EC-OC particles of a controlled size and chemical composition can be deposited uniformly onto filters and such reference filters will be invaluable in evaluation of TOA methods of EC/OC measurement.

Al-Coated Conductive Fiber Filters for High-Efficiency Electrostatic Filtration: Effects of Electrical and Fiber Structural Properties

Through the direct decomposition of an Al precursor ink AlH3{O(C4H9)2}, we fabricated an Al-coated conductive fiber filter for the efficient electrostatic removal of airborne particles (>99%) with a low pressure drop (~several Pascals). The effects of the electrical and structural properties of the filters were investigated in terms of collection efficiency, pressure drop, and particle deposition behavior. The collection efficiency did not show a significant correlation with the extent of electrical conductivity, as the filter is electrostatically charged by the metallic Al layers forming electrical networks throughout the fibers. Most of the charged particles were collected via surface filtration by Coulombic interactions; consequently, the filter thickness had little effect on the collection efficiency. Based on simulations of various fiber structures, we found that surface filtration can transition to depth filtration depending on the extent of interfiber distance. Therefore, the effects of structural characteristics on collection efficiency varied depending on the degree of the fiber packing density. This study will offer valuable information pertaining to the development of a conductive metal/polymer composite air filter for an energy-efficient and high-performance electrostatic filtration system.

Roll-to-roll processed, highly conductive, and flexible aluminum (Al) electrodes based on Al precursor inks

In this study, a roll-to-roll (R2R) process for the large-scale fabrication of aluminum thin films on flexible polyimide (PI) films is proposed. The R2R machine for Al-film coating assembled in the current work uses a previously reported Al etherate-based precursor ink as the source. After the PI substrate is exposed to a diluted catalyst, the Al precursor ink is coated directly on to the substrate by a slit-die coating method. To optimize the injection of the Al precursor ink, a low-flow limit was established. At a film speed of 5 cm s−1, the width of the fabricated Al film was 130 mm. Such Al-coated films exhibit many advantageous features, including 5.87 × 106 S m−1 of high electrical conductivity at 60.9 nm film thickness and high durability with good adhesion. There was only a minor change in the resistance of the film when it was heated at 100 °C in an oven for 10 days or when it was exposed to H2O or ethyl alcohol. Flexibility and tape testing was also conducted and the film showed robustness in both cases. Touch panels (7 cm × 9 cm) were fabricated using the fabricated Al-coated film as one side of the panel; the panel showed enough sensitivity to write recognizable letters on the computer. This indicates that the fabricated Al films can be applied in actual electronic devices without further complicated processing.