Visible light activity of rare earth metal doped (Er3+, Yb3+ or Er3+/Yb3+) titania photocatalysts

• Er/Yb co-doping enhanced the photocatalytic activity under visible irradiation.
• Oxygen vacancies and surface defects are created due to TiO2 substitution by RE3+.
• Phenol oxidation over Er/Yb-TiO2 under visible light leads to formation of benzoquinone.
• Er/Yb-TiO2 could be excited under visible light in the range from 420 to 475 nm.

A series of Er3+-TiO2, Yb3+-TiO2 and Er3+/Yb3+-TiO2 photocatalysts were obtained via sol–gel method, using lanthanides precursor ranging from 0.25 to 10 mol%. The experiments demonstrated that phenol in aqueous solutions was successfully degraded under visible light (λ > 450 nm) using Er/Yb-TiO2. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS), UV–vis absorption measurement, BET surface area analysis and luminescent spectroscopy. XPS analysis revealed that erbium and ytterbium were present in the form of oxides. The sample showing the highest photoactivity was in the form of anatase, its surface area equalled to 125 m2/g, average crystals size was 13 nm, and it was prepared introducing 1 mol% of Yb3+ into reaction medium. 3 h of irradiation resulted in 89% of phenol degradation under visible light. Action spectra analysis performed for the selected Er/Yb-TiO2 samples, revealed that irradiation from 420 to 475 nm is responsible for visible light photoactivity.

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