Removing air pollution with nanogenerator-enhanced air filters

(Nanowerk Spotlight) A triboelectric nanogenerator (TENG) is a device that converts mechanical energy into electricity using the coupling effects between triboelectrification and electrostatic induction through the contact separation or relative sliding between two materials that have opposite tribo-polarity.
TENGs utilize charges arising from friction similar to the static we experience on dry winter days. Going back to the 18th century, Benjamin Franklin found that when a piece of glass and a piece of silk cloth, neither of which exhibit any electrical properties, attract each other after rubbing against each other due to the build up of charges.
In other words, a TENG is based on a physical process of converting mechanical agitation to an electric signal through the triboelectrification (in the inner circuit) and electrostatic induction processes (in the outer circuit).
Researchers have now utilized a rotating triboelectric nanogenerator (R-TENG) to enhance a polyimide (PI) nanofiber air filter for particulate matter (PM) removal. The international research team from Georgia Institute of Technology and the Chinese Academy of Sciences published their findings in ACS Nano ("Triboelectric Nanogenerator Enhanced Nanofiber Air Filters for Efficient Particulate Matter Removal").
Triboelectric Nanogenerator Enhanced Nanofiber Air Filters for Efficient Particulate Matter Removal
(a) Schematic illustration of the setup for PM removal efficiency measurement. The inset is the FE-SEM image of PI nanofiber film (b-c) Schematic image of the filtration mechanism of the filter, (a) without R-TENG, (b) with R-TENG. (d) Rectified voltage of the RTENG. (e) Comparison of PM2.5 removal efficiency of air filters with different meshes and different electrospinning time. (© American Chemical Society) (click on image to enlarge)
As the team demonstrates, their PI nanofiber filter exhibited high removal efficiency for the PM particles with diameter larger than 0.5 µm. When working with the R-TENG, the removal efficiency of the filter is enhanced, especially in the region with the diameter of the particles in the PM smaller than 100 nm.
The highest enhancement is 207.8% at the diameter of 76.4 nm where the removal efficiency enhances from 27.1% to 83.6% and the highest removal efficiency is 90.6% at the diameter of 33.4 nm. What is more, the pressure drop of the filter does not increase and there is no ozone produced.
The later is significant as nowadays, electrostatic precipitation and fibrous filter are widely utilized to remove PM. The electrostatic precipitators capture PM through generating high electric field and charging the particles electrically. One major drawback of the electrostatic precipitators is that they inevitably ionize air, and hence produce ozone, which cause negative effects on human health with the possibility of causing cancer.
As for fibrous filters, they use different types of fibrous filters, such as high efficiency particulate air filter (HEPA), polymer nanofiber films, and so forth to remove the PM. The fibrous filters have the advantage of high efficiency to remove the particles larger than the holes because of the multilayer microfiber/nanofiber structure.
However, the pressure drop increases with the dust loading. Moreover, the removal efficiency for ultrafine particles (UFPs), whose diameters are much smaller than the holes of the fibrous filter, decreases significantly. The removal efficiency for UFPs can be improved through increasing the thickness of the filter, but the pressure drop will increase dramatically.
The scientists conclude that their work may propose an approach of air cleaning and haze management by introducing TENGs to the filters.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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