Abstract: The present invention discloses an air filter cartridge for use in an air-purifying device for removing formaldehyde (methanal, HCHO) and other aldehyde-like VOCs (Volatile Organic Compounds), and in certain embodiments amine-like VOCs, from indoor air. The air filter cartridge is made up of a casing containing a plurality of filament-like elements as a support and a mixture of one or more natural polyphenols and a catalyst integrated in said support as a powder, forming a sponge-like mesh. The air filter acts as an absorption filter, the sponge-like mesh reacting irreversibly with the aldehyde-like VOCs present in the air, generating a polymer in the form of a polyphenol-aldehyde resin inside the air filter. Due to this irreversible reaction, the air filter is capable of capturing formaldehyde, as well as other aldehyde-like VOCs that are less reactive than formaldehyde, amine-like VOCs and ammonia.