Evaluating the Mechanism of Visible Light Activity for N,F-TiO₂ Using Photoelectrochemistry

Abstract

The improvement of the solar efficiency of photocatalytic materials is important for solar driven environmental remediation and solar energy harvesting applications. Photoelectrochemical characterization of nitrogen and fluorine codoped titanium dioxide (N,F-TiO2) was used to probe the mechanism of visible light activity. The spectral photocurrent response under visible irradiation did not correlate with the optical absorption spectrum of the N,F-TiO2; however, open-circuit photopotential measurements provided better correlation to the optical absorption spectra. These observations suggest that electrons excited to the conduction band from the N-induced midgap state are rapidly trapped by defect levels below the conduction band. Reactive oxygen species (ROS) can be produced via the reduction of molecular oxygen by conduction band electrons leading to the oxidative degradation of organic pollutants, and singlet oxygen may play a role. If there is no loss in the band gap activity, as compared to undoped titania, then any additional visible light activity may give an overall improvement in the solar efficiency. The photocurrent response should not be used as a direct measure of photocatalytic activity for doped titania as the oxygen reduction pathway is vitally important for the generation of ROS, whereas hole transfer from dopant midgap states may not be so critical.

A review of solar and visible light active TiO2 photocatalysis for treating bacteria, cyanotoxins and contaminants of emerging concern

“…It was also suggested that despite the decrease in band gap energy, metals were not always successfully introduced into the TiO 2 framework, and that the remaining metals on the outside surface sheltered the photoreaction sites [44]. Significant attention has been directed at reducing the band gap and in turn increasing the visible light activity of TiO 2 by doping with a range of non-metal elements including nitrogen [34,[45][46][47][48][49], carbon [43,[50][51][52][53], sulphur [54][55][56], phosphorous [57], boron [58,59], oxygen [60], and fluorine [61,62], along with heterojunctions [63][64][65][66][67] and combinations of these elements [68][69][70][71][72][73].…”

Enhancement of the intrinsic photocatalytic activity of TiO2 in the degradation of 1,3,5-triazine herbicides by doping with N,F

“…Previous research has shown improvement of TiO 2 optical characteristic in degrading organic pollutant by the incorporation of nitrogen and fluorine atoms into its crystal lattice [20,[27][28][29][30][31][32][33][34][35][36][37][38]. In addition, the foreign atom incorporation has proven to improved TiO 2 particle dispersion, inhibit particle size agglomeration and retard phase transformation [15].…”

Recent Progress in Self-Cleaning Materials with Different Suitable Applications

“…This particular experiment showed the constant hydrophobicity of the film and photocatalytic properties of stains for up to 1800 h. The photocatalytic potential of TiO 2 , in addition to its photo induced amphiphilic property can be explained by the self-cleaning action of the hydrophobic film (Liu et al, 2013b;Katsanaki et al, 2013;Pelaez et al, 2012). There was an increase in the Ti/oxygen volume and consequently, the value of hydroxyl group due to exposure to UV light (Hamilton et al, 2014;Weng and Huang, 2013). A group of scientists carried out a survey to test the self-cleaning ability of some materials by using graphite powder on the surface.…”