They will require replacement about every four months. Others rely on the air moving through the plastic filter to generate the static charge. Filters that use static electricity function somewhat like an electrostatic precipitator, but since they use no 110 volt electricity they don't produce ozone. They probably fall somewhere between low and medium efficiency filters in their ability to remove particulates. The media is usually activated carbon, but it can also be activated alumina, a zeolite, or other miscellaneous materials.
Activated carbon is the most common, and it works something like a sponge.
The carbon is usually in granule form, and under a microscope it can be seen as very porous, having many tiny chambers. This gives it a tremendous surface area for gases to adhere to. Standard activated carbon can easily remove dozens of gases from the air, but it isn't particularly good at adsorbing formaldehyde. Specially processed carbons are available that are actually designed to attract formaldehyde, and activated alumina works well at adsorbing it. For industrial applications, carbons can be produced that work very well at adsorbing specific pollutants like mercury gas or ammonia.