Synthesis, structure, and visible-light-driven activity of o-YbFeO₃/h-YbFeO₃/CeO₂ photocatalysts

Abstract

Photo-Fenton-like oxidation of organic substances is one of the key advanced oxidation processes based on the reversible Fe2+↔Fe3+ transition and the generation of a strong oxidant ·OH in the presence of H2O2 and is currently considered as a promising method for the purification of polluted aqueous media. However, the absence of effective and stable photocatalysts of this process, operating under the action of visible light, necessitates the exploratory studies, mainly among iron oxides and ferrites of various compositions and structures. In this work, using the method of solution combustion followed by heat treatment in air the heterojunction nanocomposites based on ytterbium orthoferrite and cerium dioxide of the composition o-YbFeO3/h-YbFeO3/CeO2 (0–20 mol.%) with high absorption in the visible region and advanced photo-Fenton-like activity were obtained. The nanocomposites were studied by EDS, SEM, XRD, BET, and DRS methods. The photo-Fenton-like activity of the nanocomposites was investigated during the degradation of methyl violet under the action of visible (λmax = 410 nm) radiation. As a result, the formation of I-type heterojunction based on stable rhombic (55.4–79.0 nm) and metastable hexagonal (19.5–24.0 nm) modifications of ytterbium orthoferrite (o-YbFeO3 and h-YbFeO3, respectively) and cubic cerium dioxide CeO2 (13.2–19.2 nm) nanocrystals was established. It was shown that the obtained nanocomposites had foamy morphology and were characterized by a specific surface in the range of 9.1–25.0 m2/g, depending on the CeO2 content. It was found that nanocrystalline components were chemically and phase-pure, uniformly spatially distributed over the nanocomposite, and had multiple contacts with each other. Based on this fact and the established electronic structure of the nanocomposite components, the formation of I-type heterojunction with the participation of o-YbFeO3 (Eg = 2.15 eV), h-YbFeO3 (Eg = 2.08 eV), and CeO2 (Eg = 2.38 eV) was shown, the presence of which increased photocatalytic activity of the resulting nanocomposite. The optimal content of CeO2 in the nanocomposite was 5%, and the o-YbFeO3/h-YbFeO3/CeO2–5% sample was characterized by the highest rate constant of photo-Fenton-like degradation of methyl violet under the action of visible light equal to k = 0.138 min–1, which was 2.5 to 5 times higher than for nanocomposites based on ytterbium orthoferrite. The obtained results obtained indicate that the developed nanocomposites can be considered as a promising basis for the advanced oxidation processes for the purification of aqueous media from organic pollutants.

Effect of TiO2 Additives on the Stabilization of h-YbFeO3 and Promotion of Photo-Fenton Activity of o-YbFeO3/h-YbFeO3/r-TiO2 Nanocomposites

“…However, the stabilization effect of the second phase addition has never been reported. Recently, we confirmed the possibility of the stabilization of h-YbFeO 3 by the CeO 2 extra phase [32]. In the present work, for the first time, the possibility of creating additional spatial restrictions due to the insertion of the second TiO 2 phase was demonstrated and the synthesis of novel I-type heterojunction nanocomposites of o-YbFeO 3 /h-YbFeO 3 /r-TiO 2 was performed.…”

“…As was previously reported, the presence of an inert phase prevents mass transfer and interrupts the structural transition hexagonal → orthorhombic ytterbium orthoferrite [32]. It can be surmised that the formation of o-YbFeO 3 was interrupted by r-TiO 2 particles on the board between shaped and foam-like areas.…”

“…On the other hand, h-YbFeO 3 shows high instability and a tendency to transform easily in the stable o-YbFeO 3 phase [32,33].…”

Synthesis of highly active and visible-light-driven PrFeO3 photocatalyst using solution combustion approach and succinic acid as fuel

“…According to the obtained data, in all spectra, there is a single absorption peak corresponding to 550 nm, which naturally decreases with time during prolonged irradiation with a light source, which confirms the photocatalytic activity of the synthesized sample. The most intense decrease in the dye concentration is observed in the first 10 minutes of irradiation, then the intensity of discoloration decreases, which is associated with a gradual decrease in the generation of hydroxyl radicals caused by the processes of recombination of electron-hole pairs [13,32] and the peculiarity of the filling of catalytically active centers on the catalyst surface.…”

Mesoporous nanocomposites based on CeO2 and MgO: preparation, structure and photocatalytic activity

“…The synthesis of nanostructured CeO 2 with a given morphology is a laborious process that includes several steps: the choice of precursors, cosolvents, a structureforming agent and optimal conditions. Sol-gel, 4,18 citrate, 19 hydrothermal, [20][21][22][23] precipitation 24,25 and self-propagating hightemperature synthesis (SHS) [26][27][28][29] methods are used to synthesize CeO 2 . Among these methods, the SHS method has special advantages associated with the possibility of obtaining a solid material with a small particle size (up to 10 nm) from chemically homogeneous precursors.…”