Rare earth oxides in zirconium dioxide: How to turn a wide band gap metal oxide into a visible light active photocatalyst

Unraveling the Charge State of Oxygen Vacancies in ZrO2–x on the Basis of Synergistic Computational and Experimental Evidence

“…Zirconium oxide (ZrO2) occurs in three polymorphs: the monoclinic structure is thermodynamically stable at room temperature and reversibly transforms to the tetragonal polymorph (T-ZrO2) at 1150 °C, whereas the cubic phase is stable at temperatures in excess of 2370 °C 1 . Despite its large band gap (Eg) characterized by two direct transitions at 5.2 and 5.79 eV 2 , ZrO2 was recently proposed as a photocatalyst [3][4][5] . The visible-light photoresponsivity of zirconia-based materials was obtained either by doping with rare-earth metals, such as Ce 3 and Er 4 , using wet synthesis methods, or by magnesiothermic reduction of commercial monoclinic ZrO2 5 .…”

“…Despite its large band gap (Eg) characterized by two direct transitions at 5.2 and 5.79 eV 2 , ZrO2 was recently proposed as a photocatalyst [3][4][5] . The visible-light photoresponsivity of zirconia-based materials was obtained either by doping with rare-earth metals, such as Ce 3 and Er 4 , using wet synthesis methods, or by magnesiothermic reduction of commercial monoclinic ZrO2 5 . Oxygen vacancies are the main intrinsic defects in ZrO2 and they play a key role in defining its functional and structural properties such as the ionic conductivity at elevated temperature 6 , the luminescence 7,8 and the stabilization of metastable T-ZrO2 at room temperature.…”

Considerations of Trends in Heterogeneous Photocatalysis. Correlations between Conduction and Valence Band Energies with Bandgap Energies of Various Photocatalysts

“…In some other cases, photoexcitation was achieved with the use of a mediator . Further development into creating visible‐light‐active photocatalysts involves the up‐conversion phenomenon with rare‐earth ions to sensitize wide‐bandgap semiconductors (even for such dielectrics as ZrO 2 ; E bg ≈5.0 eV). A discussion of the advantages and/or disadvantages of such strategies was beyond the scope of the present study.…”

Erbium Salts as Non-Toxic Catalysts Compatible with Alternative Reaction Media

“…Er(III) doped photocatalysts are a special case concerning the use of Er(III) cations in a heterogeneous phase. In this very recent application, Er(III) is far from playing an active catalytic role in photocatalysis, but it is essential to change the structural and electronic characteristics of well-known photocatalysts, thus improving their performances, especially under solar insulation [87][88][89][90][91][92][93][94][95][96][97]. It is well known, for example, that titania (Ti 2 O) is a semiconductor active as a photocatalyst in the UV range, and its applications in water splitting, pollutant removal and conversion of carbon dioxide into useful chemicals have been extensively studied [87].…”

“…Moreover, the incorporation of Er(III) into YVO 4 improved its photocatalytic activity by inducing a change in morphology and a better electron-hole separation mechanism, thus making this catalyst a promising candidate for water splitting reactions [96]. Er(III) was finally used as a dopant to transform a wide band gap metal oxide (ZrO 2 ) into a visible light active photocatalyst [97].…”