Degradation of 2-naphthol and antiviral activities of Bi<sub>2</sub>Sn<sub>2</sub>O<sub>7</sub> doped with La or Ce under dark and visible-light conditions

La- or Ce-substituted Bi2Sn2O7 (BSO) powders were synthesized via a hydrothermal method, and correlations between their structural, compositional, and adsorption properties and their 2-naphthol decomposition and antiviral activities under dark and visible-light conditions were investigated. Ten mol % of Bi was substituted with La or Ce, and all samples were confirmed to be single-phase BSO, exhibiting lattice parameter changes consistent with the ionic radii of the dopant ions. All samples were found to decompose 2-naphthol in aqueous solution at room temperature even in the dark, and the activity was further enhanced under visible-light irradiation. Antiviral performance was evaluated against two structurally distinct viruses, a non-enveloped virus and an enveloped virus, using test procedures with reference to ISO methods. Visible-light irradiation enhanced the antiviral activity of all samples, with La-substituted BSO exhibiting the highest performance against both viruses under both dark and visible-light conditions. The observed antiviral activity is attributed primarily to interactions between rare-earth elements and viral proteins, leading to virus immobilization on the material surface, followed by structural damage to viral components, including capsid disruption, envelope oxidation, and spike protein denaturation, driven by the intrinsic oxidative properties of BSO and the presence of rare-earth elements. It was suggested that La substitution is more effective than Ce substitution at promoting virus immobilization, resulting in superior antiviral activity.