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

Novel forms of black TiO2 nanotubes-based photocatalysts for water purification were prepared. Two features were combined: decoration of TiO2 nanotube arrays with Ag nanoparticles (sample TiO2-NT's@Ag) and further hydrogenation of this material (TiO2-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 TiO2 nanotubes and commercial TiO2 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 TiO2-NT's@AgHA, 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 TiO2 due to Ti3+ 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. (C) 2018 Elsevier B.V. All rights reserved.