Visible light sensitization of TiO2/Ag/N nanostructures synthesized by microwave irradiation for oxidative degradation of organic dyes

The synthesis of photocatalysts for organic pollutants degradation is a topic of fundamental interest and practical importance, in particular if using green methodologies. In this study, Methyl Orange (MO) and Indigo Carmine (IC) photodegradation on composite TiO2 nanostructures containing silver or nitrogen was examined. TiO2 nanotubes (NTs), TiO2 nanoparticles (NPs) and Ag NPs were prepared by microwave-assisted chemistry (MWAC) using different precursors. The photocatalysts were characterized by XRD, TEM, UV-Vis, BET, XPS and EIS techniques. The degradation rate of MO by the TiO2 NTs@Ag NPs photocatalyst, under UV-Vis illumination, was about six times higher than that exhibited by the pristine TiO2 NTs. Additionally, the photodegradation rate of MO on TiO2 NTs@Ag NPs under visible light (lambda >= 400 nm) was more than three times higher than pristine TiO2 NTs irradiated with UV-Vis light. TiO2 NPs prepared using a water-soluble titanium complex [TALH: Titanium(IV) bis(ammoniumlactato)dihydroxide] as precursor, presents high photodegradation rate for IC and MO under UV-Vis and only visible light irradiation. The presence of nitrogen in the TiO2 NPs lead to lower band gap values, compared to pristine NTs, which may explain the visible light activity of this photocatalyst. Additionally, Mott-Schottky analysis gave information about the donor density and the absolute position of the flatband potential of the nanostructured TiO2 thin film electrodes showing a correlation between those parameters and the photocatalytic observed activity. The present work also shows that a green methodology, such as MWAC, coupled to a mild water-soluble precursor, like TALH, may lead to its use in environmental remediation applications with direct utilization of solar light as a sustainable technology.