Preparation of Dumbbell-like Er/ZnO Microrods with Efficient Energy Upconversion for the Catalytic Degradation of Tartaric Acid in Water

Cerium-, Europium- and Erbium-Modified ZnO and ZrO2 for Photocatalytic Water Treatment Applications: A Review

“…From a structural point of view, most manuscripts sustain the notion of replacement of a reticular Zn 2+ cation with a Er 3+ cation at a regular atomic site in the lattice. This description aroused from the fact that, except in few cases [173][174][175], the Er 2 O 3 crystal phase was not detected via XRD or TEM analysis, also for concentration up to 5% molar [104,176,179]. Rather, it was clearly highlighted a progressive shift at lower 2θ angles of the ZnO reflection corresponding to the (111) crystallographic plane, visible in Figure 13 [175,177,178,180,182].…”

“…However, what emerges from the analysed literature is an enhanced photocatalytic behaviour when erbium was added in the synthesis of zinc oxide, also if, very frequently, the band gap of the final material doesn't exhibit a noticeable redshift, as appreciable in Table 6. For this reason, the Er-modified ZnO engineered material has been mainly tested upon UV light rather than under visible photon irradiation for the mineralization of commercial dyes [173][174][175][176][177][178][179][180][181] and phenolic compounds [121,182,183].…”

“…As previously mentioned, the incorporation of erbium in ZnO doesn't markedly deviate the absorption edge of the prepared material respect that of ZnO; nevertheless, the optical properties of the Er-ZnO system greatly differs from that of the bare zinc oxide. Very often, the Uv-vis and photoluminescence spectroscopies highlighted the presence of erbium by means its peculiar absorptions assigned to the discrete f-f transitions occurring in the visible-NIR regions of the electromagnetic spectrum [104,176,182]. However, in the investigations in which a moderate red shift was detected for Er-doped ZnO it has mainly explained with an electronic transition from the valence bands to impurity levels generated by Er in substitutional position, placed just below the CB minimum.…”

“…Almost all the authors reported photoluminescence measurements in which the emission in the visible range (pointed in the range 550-650 nm) increases with the increase in Er content: the so called deep level emission (DLE) in ZnO is attributed to the recombination of photoinduced holes with ionized intrinsic defects generating defect levels in the material band gap, such as oxygen vacancies, zinc vacancies and zinc interstitials. This would imply that the introduction of erbium leads to a larger amount of this kind of defects that might actively participate in the charge carrier separation as electron trapping centres or directly in the photocatalytic process promoting the charge transfer at the surface of the material [174][175][176]179,182,184].…”

Synthesis and Characterization of a Novel Rambutan‐like ZnO@SrTiO3/TiO2 Microsphere

“…[15][16][17] On the one hand, it can increase the adsorption capacity of the sample on the contaminant, on the other hand, the recombination rate of the hole electron pair can be reduced by the gradient energy level regulation and the interface between different semiconductors, thereby improving the photocatalytic performance. [18][19][20] The band gap position of ZnO is located in the middle level of the conduction band and the valence band energy of TiO 2 and SrTiO 3 , which provides a gradient energy band distribution. [21,22] In this work, an environmentally friendly design scheme is used to prepare composite samples with a band-matching structure and a large specific surface area with a certain hierarchical structure.…”