The effect of Ag, Au, Pt, and Pd on the surface properties, photocatalytic activity and toxicity of multicomponent TiO2-based nanomaterials

Multicomponent TiO2-based nanomaterials (MC-NMs) show better physicochemical properties than their individual components or bulk materials. However, the same unique properties that offer innovative applications might also pose unknown risks to human health and the environment. In this context, TiO2-based nanomaterials with a mixture of noble metal precursors (Ag, Au, Pt, and Pd) for large-scale technological applications in air purification were designed, synthesized and characterized. The influence of the type and amount of noble metal precursor on the optical properties and photocatalytic activity of MC-NMs and their toxicity to mouse embryo fibroblast cell line (BALB/3T3), human lung cell line (A549) and human liver cell line (HepG2) was investigated. A hazard assessment of the designed TiO2-based MC-NMs was performed for the first time according to the standards developed under the Joint Research Center and NANoReg2 project (Horizon 2020). The threshold concentration of monometallic NPs that ensure high photocatalytic activity without increasing hazard to humans and the environment was determined. The results indicated that the most effective sample is represented by the 0.1Ag_0.1Au_0.1Pt_1Pd/TiO2 photocatalyst, in which noble metal NPs demonstrated a synergistic effect on photocatalytic activity without increasing the toxicity (safe MC-NMs with 86% toluene degradation after 1 h of irradiation, efficiency 5 times higher than that of pristine TiO2). The obtained results confirm that systematic knowledge and proper manipulation of component concentration may lead to rational design of safe TiO2-based MC-NMs with wide application in air purification under solar energy.