Air Purification: Filtration, Adsorption & Catalytic…

Filtration

Filtration involves capturing airborne particles using physical barriers. High-Efficiency Particulate Air (HEPA) filters are designed to capture at least 99.97% of particles as small as 0.3 micrometers, making them highly effective in removing dust, pollen, and other particulates from the air.

The efficiency of a filter is often measured by its ability to remove specific sizes of particles, which can be quantified using the filtration efficiency curve.

Adsorption

Adsorption involves the adhesion of gas molecules or dissolved substances onto a surface. Activated carbon filters are commonly used in air purifiers due to their high surface area and ability to adsorb volatile organic compounds (VOCs) and odors.

The mechanism of adsorption is driven by van der Waals forces, which allow for the accumulation of pollutants on the surface of the adsorbent material.

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Catalytic Oxidation

Catalytic oxidation uses a catalyst to convert harmful gases into less toxic substances. In air purifiers, this process often involves UV-C light activating a photocatalyst like titanium dioxide (TiO2), which then oxidizes pollutants such as formaldehyde and benzene.

The reaction can be represented by the equation: TiO2 + hν → TiO2* + e-; followed by 2H2O → 4OH-, where the excited state of TiO2 reacts with water to produce hydroxyl radicals that oxidize pollutants.

CADR and Room Volume Balance

The Clean Air Delivery Rate (CADR) is a measure of how effectively an air purifier can remove specific types of contaminants from the air. It is calculated based on the volume of clean air delivered per minute.

For effective purification, the CADR must be sufficient to handle the total volume of the room being purified and the rate at which pollutants are generated.

Frequently asked questions

How does a HEPA filter work?

A HEPA filter works by forcing air through a fine mesh that traps particles as small as 0.3 micrometers, effectively filtering out dust, pollen, and other particulates.

What is the difference between adsorption and catalytic oxidation?

Adsorption involves capturing gases or liquids on a surface, while catalytic oxidation uses a catalyst to convert harmful gases into less toxic substances through an oxidative reaction.

Why are activated carbon filters effective for removing odors?

Activated carbon filters are highly effective at removing odors because their porous structure provides a large surface area for adsorption of volatile organic compounds (VOCs) that cause unpleasant smells.

How does UV-C light contribute to air purification?

UV-C light activates photocatalysts like titanium dioxide, which then oxidize pollutants such as formaldehyde and benzene, effectively breaking down harmful substances into less toxic compounds.

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