• Consists of a pure or doped metal oxide semiconductor material.
• Most Common Photocatalyst is Ti02 (titanium dioxide).
• Activated by a UV light source.
• UV-A (400-315nm)
• UV-C (280-200nm
• UV-V (under 200nm) Ozone can be formed at UV-V wavelengths.
• Light mediated, redox reaction of gases and biological particles absorbed on the surface.
• Some units claim disinfection from gaseous hydrogen peroxide.
• Possible by-products formed by incomplete oxidizing.
• Some air cleaners using PCO remove harmful contaminants to levels below limits for reducing health risks set by recognized cognizant authorities.
• Some are ineffective in reducing concentrations significantly; manufacturer data should be considered carefully.

More information can be gathered here https://www.ashrae.org/technical-resources/filtration-disinfection#uvc