Abstract
The doping of Au/TiO2 with FeOx is shown to result in a strong enhancement of its photocatalytic activity in the degradation of the azo dye Orange II. In order to examine the source of this enhancement, Au-FeOx/TiO2 nanocomposites containing different molar ratios of Au:Fe were synthesized, and X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and high-resolution transmission electron microscope (HRTEM) analyses indicated that the TiO2-supported Au nanoparticles were partially covered with an amorphous layer of FeOx species, in which the iron was present as Fe2+ and Fe3+. The metal-semiconductor system, i.e., Au/TiO2, showed only a moderate degradation rate, whereas doping with FeOx strongly enhanced the degradation activity. The bandgap energy decreased gradually from Au/TiO2 (3.13 eV) to the catalyst with the highest FeOx loading Au-FeOx (1:2)/TiO2 (2.23 eV), and this decrease was accompanied by a steady increase in the degradation activity of the catalysts. XPS analyses revealed that compared to Au/TiO2, on Au-FeOx/TiO2 a much higher population density of chemisorbed and/or dissociated oxygen species was generated, which together with the decreased bandgap resulted in the highest photocatalytic activity observed with Au-FeOx (1:2)/TiO2. The processes occurring during reaction on the catalyst surface and in the bulk liquid phase were investigated using operando attenuated total reflection IR spectroscopy (ATR-IR) combined with modulation excitation spectroscopy (MES), which showed that the doping of Au/TiO2 with FeOx weakens the interaction of the dye with the catalyst surface and strongly enhances the cleavage of the azo bond.
Highlights
Increasing public concern about the detrimental environmental impact of organic pollutants in wastewater effluents from industrial and domestic sources has urged the development of suitable technologies for their cleaning
For the first time, operando modulation excitation attenuated total reflection IR spectroscopy (ATR-IR) spectroscopy (MES-ATR-IR) of the catalyst surface and the liquid phase was employed to shed some light on the molecular processes occurring in this catalytic system
This is supported by the fact that the Au-Fe(1:2)/TiO2 photocatalysts with abundant oxygen species (OC) species exhibited the highest activity in the photocatalytic degradation of Orange II
Summary
Increasing public concern about the detrimental environmental impact of organic pollutants in wastewater effluents from industrial and domestic sources has urged the development of suitable technologies for their cleaning. Photocatalytic degradation of organic pollutants in wastewaters is driven by photogenerated electrons and holes on the semiconductor surface, which act as electron donors and acceptors, respectively, initiating the formation of highly active radicals that degrade the pollutant into water, carbon dioxide, and inorganic salts [1,6]. The mechanisms of these processes have been the subject of extensive research, which has been covered in several reviews [1,6,7,8,9]. For the first time, operando modulation excitation ATR-IR spectroscopy (MES-ATR-IR) of the catalyst surface and the liquid phase was employed to shed some light on the molecular processes occurring in this catalytic system
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