Because TiO2 shows low solar light activity and a high recombination rate of electron–hole pairs, researchers have developed second-generation photocatalysts in which TiO2 is used in combination with other components, such as metals. This new generation of photocatalysts shows high efficiency of inactivation of a wide range of bacteria and some viruses. Among them, S-doped and N-doped TiO2 show photocatalytic properties when exposed to visible light and, therefore, would possibly be effective under interior lightning. The antimicrobial properties of these photocatalysts have been tested with a variety of bacteria, sometimes indicating good disinfection efficiency (for reviews, see refs (192) and (193)), but to our knowledge, they have not been tested on viruses. Moreover, depositing some Ag NPs on the surface of TiO2 NPs increases their antiviral efficiency against MS2 by means of increased production of hydroxyl radicals.196 A Ag- and Cu-doped TiO2 nanowire membrane is more active in eliminating bacteriophage MS2 from drinking water than are TiO2, Ag-TiO2, or Cu-TiO2 membranes, both in the dark and when exposed to UV light. The underlying mechanism is thought to combine both enhanced photoactivity due to the lower band gap of (Ag, Cu)-TiO2 than that of TiO2197 and antimicrobial activity of free Ag and Cu ions released into the treated water.198 Another strategy to improve the antiviral capability of TiO2 is by increasing its potential to absorb viruses, which has successfully been achieved by mixing TiO2 NPs with SiO2 NPs. Due to the large specific surface area of SiO2, the mixture of NPs inactivated bacteriophage MS2 more effectively than did TiO2 alone, in spite of reduced hydroxyl production.199 Glass slides coated with TiO2 doped with Pt show slightly better efficiency in inactivating aerosols containing influenza A (H3N2) virus than do surfaces coated with only TiO2 when irradiated with UV-A,200 owing to their increased oxidizing photocatalytic properties. Finally, as described by Byrnes et al.,193 new photocatalytic materials that show efficient antibacterial activity have been developed and could be tested for the inactivation of SARS-CoV-2. These new materials include (among others) BiVO4, CuFeO2, CuYxFe2–xO4, LaFeO8, CuMn2O4, ZnMn2O4, BaCr2O4, SrCr2O4, NiCo2O4, CuCo2O4, LaCoO3, and La0.9Sr0.1CoO3. Importantly, before being used for SARS-CoV-2 inactivation, their nontoxicity should be ensured.