Chinese scientists have made efficient and reliable air filter for nanosized particles. It consists of a sponge impregnated with the composition and the ionic liquid through which current is passed. The invention, in addition to the ability to filter particles smaller than a micron, differs from existing analogues by durability, adaptability to regeneration and stability at high speeds the air flow. Article published in the journal Nature Communications.
In the result of fuel combustion and other industrial processes are emitted into the air of micro – and nanoparticles with sizes ranging between ten microns and less. They are dangerous carcinogens that are able to penetrate even into the brain, their harm is one of the common arguments of the supporters of green energy. But even if we assume that humanity will be able to reduce the use of fossil fuels several times, emissions from some factories is still inevitable. Therefore, they need filtering, but the smaller the particle, the harder it is to do so a fine sieve.
A group of scientists from Sichuan University, under the leadership of Guo-Hao Zhang (Guo-Hao Zhang) has decided to produce a compact and inexpensive filter that uses electrostatic force. Unlike a normal filter where the dirt linger a little long in such construction the particles settle on the surface due to electrostatic forces, just as the dust was attracted to the screen of the old televisions with cathode ray tubes.
There is a class of chemicals called ionic liquids. By and large, any salt composed of ions — electrically charged particles, but ordinary salt melts when heated to several hundred degrees. To change this, over the past decade emerged salt remains liquid at room temperature, among which the most common compounds of imidazole. For filters ionic liquids are of interest because of their high electrostatic capacity.
As the basis for the filter was used melanin-formaldehyde sponge with fine pores. As the ionic liquid made a few acetates methylimidazole, which mixed with different liquid polymers (in the end, the scientists chose the most efficient pair). The mixture of polymers was necessary, first, to increase adhesion to the sponge, second, hydrophilic polymers well attract fine dust, which is itself wet, as it absorbs water from the atmosphere.
The mixture was applied to a sponge and tested. The filter worked well for particles larger than one micron, its efficacy was approximately equal to 98-99 percent, which roughly corresponds to that of the existing analogues. But when it came to nanoparticles having a size less than a micron, he managed to remove no more than 36 percent, which is not enough. Therefore, the researchers decided to increase the electrostatic force of the filter, by submitting to it the voltage.
Current has reduced the number of non-filtered large particles three to six times, bringing the total efficiency to approximately 99.7 per cent, but the most significant impact on the sequestration of nanoparticles. By increasing the voltage to three volts on the sponge settled 94 percent of dust with a diameter less than a micron. In addition, the filter does not lose efficiency with increasing speed of the passage through it of air, and it can be reused after cleaning.