Remarkable improvement of visible light photocatalytic activity of TiO₂ nanotubes doped sequentially with noble metals for removing of organic and microbial pollutants

Highlights: • Ordered TiO₂ nanotubes (NTs) were synthesized using anodic oxidation. • TiO₂ NTs were modified with Ag and Au NPs that settled separately to widen visible absorption. • TiO₂ NTs modified with Ag and Au NPs is superior visible light photocatalyst. • TiO₂ NTs modified with Ag and Au NPs shows superior antibacterial activity. • Annealing temperature played important role in photocatalytic activity of TiO₂ NTs. - Abstract: The aim of this study was to show that Ag and Au nanoparticles (NPs) can have a synergistic effect on the photocatalytic and antibacterial activity of TiO₂ nanotubes (NTs) under visible irradiation. TiO₂ NTs were grown on Ti substrate by anodic oxidation and modified with Ag and Au NPs by dip coating and sputtering methods, respectively. The spherical 5–20 nm Ag and Au NPs were deposited on TiO₂ NTs with diameter of 50–80 nm. In contrast to obtained results under UV irradiation, visible-light absorption range and visible photocatalytic activity of Ag and Au co-modified TiO₂ NTs were much higher than TiO₂ NTs without modification and TiO₂ NTs modified with monometallic NPs. Photocatalytic activity of modified TiO₂ NTs increased with increasing annealing temperature and appearing rutile phase. Antibacterial activity of Ag and Au-comodified TiO₂ NTs against E. coli was noticeably more than that of TiO₂ NTs modified with monometallic NPs.