What Are the Main Filter Media Used in Air Purifiers?

HEPA filtration is one of the most common technologies used in mainstream air purifiers. A HEPA filter meets the relevant HEPA standard. The original specifications cite an efficiency of 99.7% for particles of 0.1 µm (1 µm = 0.0001 cm) and 0.3 µm, and a removal efficiency of more than 99.97% for particles 0.3 µm in diameter or larger, about one two-hundredth the diameter of a human hair. It is an effective medium for filtering smoke, dust, bacteria, and other airborne pollutants. HEPA filters feature relatively high airflow resistance, high dust-holding capacity, and fine filtration accuracy. They can be made in different sizes and shapes to suit different air-purifier models.

2. Photocatalysts

A photocatalyst is a general term for semiconductor materials with photocatalytic properties, typically represented by nanoscale titanium dioxide. Under light, titanium dioxide can generate strongly oxidizing substances, such as hydroxyl radicals and reactive oxygen species. These substances can break down organic compounds, some inorganic compounds, bacteria, and viruses. In daily use, photocatalysts can help degrade harmful airborne gases such as formaldehyde, kill various bacteria, and break down toxins released by bacteria or fungi.

3. Activated carbon

Activated carbon is specially processed carbon. Organic raw materials such as nut shells, coal, or wood are heated without air to reduce non-carbon components through carbonization. The material then reacts with gas so that its surface is etched, creating a highly developed microporous structure through activation. Because activation causes countless point-like areas of surface erosion, activated carbon contains a vast number of tiny pores. Its adsorption performance depends on the size and structure of these pores. In general, smaller particles allow faster pore diffusion and stronger adsorption. Activated carbon used for air purification should be hard, strong, and rich in micropores.

4. Negative-ion generators

A negative-ion generator produces negative air ions. Incoming direct or alternating current passes through an EMI processing circuit and lightning-protection circuit. Pulse circuitry, overvoltage and current-limiting protection, and high/low-voltage isolation then raise it to high-voltage alternating current. Special electronic materials rectify and filter this current to produce clean, high-voltage negative direct current. The current is connected to a metal or carbon discharge tip, where the high voltage creates a strong corona and releases many electrons. Because free electrons cannot remain in the air for long, they are quickly captured by oxygen molecules, forming negative air ions. Large negative ions can help settle dust, freshen the air, and reduce smoke.