In various embodiments, an air purifier capable of destroying and deactivating airborne contaminants such as SARS-CoV-2 is described. The air purifier comprises a photocatalytic system comprising at least one photoactivated semiconductor photocatalyst and a lamp configured to irradiate and excite the at least one photoactivated semiconductor photocatalyst to generate reductive and/or oxidative reactive species from oxygen and/or water on the photocatalyst surface. In various embodiments, the photocatalytic system comprises a stack of PCB cards, each card having a photocatalytic layer disposed thereon, or a 3-dimensionally ordered macroporous (3-DOM) structure comprising an open cell lattice.