Black TiO2 nanotube arrays decorated with Ag nanoparticles for enhanced visible-light photocatalytic oxidation of salicylic acid

Abstract Novel forms of black TiO 2 nanotubes-based photocatalysts for water purification were prepared. Two features were combined: decoration of TiO 2 nanotube arrays with Ag nanoparticles (sample TiO 2 -NT's@Ag) and further hydrogenation of this material (TiO 2 -NT's@Ag-HA). Obtained photocatalysts show high efficiency for degradation of salicylic acid, a typical water-borne pollutant. The photocatalysts considerably exceed the photocatalytic properties of TiO 2 nanotubes and commercial TiO 2 P25 taken as a reference for modeling of the photocatalytic process. The comparison of photocatalytic activities between novel photocatalyst was based on a numerical approach supported by the complex kinetic model. This model allowed a separate study of different contributions on overall degradation rate. The contributions include: salicylic acid photolysis, photocatalysis in UVB, UVA and in the visible part of applied simulated solar irradiation. The superior photocatalytic performance of the photocatalyst TiO 2 -NT's@Ag-HA, particularly under visible irradiation, was explained by the combined effect of a local surface plasmon resonance (LSPR) due to Ag nanoparticles and creation of additional energy levels in band-gap of TiO 2 due to Ti 3+ states at nanotube surfaces. The presence of Ag also positively influence charge separation of created electron-holes pairs. The synergy of several effects was quantified by a complex kinetic model through the factor of synergy, f Syn . Stability testing indicated that the catalysts were stable for at least 20 h. The novel design of catalysts, attached on Ti foils, presents a solid base for the development of more efficient photocatalytic reactors for large-scale with a long-term activity.