Mechanism of the Photoactivity under Visible Light of N-Doped Titanium Dioxide. Charge Carriers Migration in Irradiated N-TiO₂ Investigated by Electron Paramagnetic Resonance.

Abstract

The generation of surface charge carriers in N-doped TiO 2 under various types of irradiation has been investigated by electron paramagnetic resonance using an approach consisting in scavenging surface migrated electrons and holes using oxygen and hydrogen, respectively. N-doped TiO 2 , which is moderately active in photocatalytic processes under visible light, forms surface electrons and, at lower extent, surface holes due to the synergistic effect of visible components (around 400 nm) and near-infrared ones. The visible radiation excites electrons from intra band gap NO x− states to the conduction band, while NIR frequencies excite electrons from the valence band to the NO x− centers. The limited concentration of such centers explains the moderate efficiency of the whole process and, consequently, of the photocatalytic activity of N-TiO 2 in visible light with respect to the case of UV light irradiation. Despite the mentioned limits this material remains a fundamental starting point for a new generation of photocatalytic systems exploiting solar light.

The interaction of oxygen with the surface of CeO2–TiO2mixed systems: an example of fully reversible surface-to-molecule electron transfer

“…4) prompted us to test the photochemical properties of the 85 systems. It was therefore investigated, using a methodology already illustrated in previous work from some of us 63 , the presence of photogenerated electrons and holes at the surface of the solid under irradiation with visible light. No trace of photogenerated charge carriers was observed.…”

Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates

“…Doping NTO with metals and non-metals creates new energy levels between the VB and CB of TiO 2 [121], which in turn reduces its band gap and helps the doped catalyst to absorb in the visible region (Figure 4). Recently, researchers have reported the successful doping of vanadium [122], iron [123], rhodium [50], palladium [124], and silver [125] metals, and carbon [105,126], nitrogen [51,96,105,121,124,127,128], sulfur [98,129], fluorine [96], and iodine [130] non-metals in NTO to achieve the visible light photocatalytic degradation of various chemicals and Escherichia coli in aqueous solution (Table 3). In all reports, except in silver doping, the visible light photocatalytic activity was mainly attributed to the associated red shift that originated from the creation of local bands between the VB and CB of NTO (Figure 4).…”

Photocatalytic degradation of tetracycline using nanosized titanium dioxide in aqueous solution

“…Doping TiO 2 with metals or non-metals can decrease the band gap of the doped catalyst and makes possible the light absorption in the visible region. The improved catalysts seem to be photo-stable in aqueous solution and can be used in photocatalytic water purification (Kuvarega et al 2011;Barolo et al 2012). 5.…”