Magnetically recoverable catalyst based on porous nanocrystalline HoFeO3 for processes of n-hexane conversion

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

Nanostructured hexagonal rare-earth orthoferrites (h-RfeO₃, R = Sc, Y, Tb-Lu) are well known as a highly effective base for visible-light-driven heterojunction photocatalysts. However, their application is limited by metastability, leading to difficulties in synthesis due to the irreversible transformation to a stable orthorhombic structure. In this work, we report on a simple route to the stabilization of h-YbFeO₃ nanocrystals by the synthesis of multiphase nanocomposites with titania additives. The new I-type heterojunction nanocomposites of o-YbFeO₃/h-YbFeO₃/r-TiO₂ were obtained by the glycine-nitrate solution combustion method with subsequent heat treatment of the products. An increase in the mole fraction of the h-YbFeO₃ phase in nanocomposites was found with the titanium addition, indicating its stabilizing effect via limiting mass transfer over heat treatment. The complex physicochemical analysis shows multiple contacts of individual nanocrystals of o-YbFeO₃ (44.4-50.6 nm), h-YbFeO₃ (7.5-17.6 nm), and rutile r-TiO₂ (~5 nm), confirming the presence of the heterojunction structure in the obtained nanocomposite. The photocatalytic activity of h-YbFeO₃/o-YbFeO₃/r-TiO₂ nanocomposites was evaluated by the photo-Fenton degradation of the methyl violet under visible light (λ ≥ 400 nm). It was demonstrated that the addition of 5 mol.% of TiO₂ stabilizes h-YbFeO₃, which allowed us to achieve a 41.5 mol% fraction, followed by a three-time increase in the photodecomposition rate constant up to 0.0160 min^-1.

Recovery/Reuse of Heterogeneous Supported Spent Catalysts

The rapid separation and efficient recycling of catalysts after a catalytic reaction are considered important requirements along with the high catalytic performances. In this view, although heterogeneous catalysis is generally less efficient if compared to the homogeneous type, it is generally preferred since it benefits from the easy recovery of the catalyst. Recycling of heterogeneous catalysts using traditional methods of separation such as extraction, filtration, vacuum distillation, or centrifugation is tedious and time-consuming. They are uneconomic processes and, hence, they cannot be carried out in the industrial scale. For these limitations, today, the research is devoted to the development of new methods that allow a good separation and recycling of catalysts. The separation process should follow a procedure economically and technically feasible with a minimal loss of the solid catalyst. The aim of this work is to provide an overview about the current trends in the methods of separation/recycling used in the heterogeneous catalysis.

Low-Temperature Co-Precipitation Synthesis of HoFeO3 Nanoparticles

In this research, we investigate and discuss the characteristics of HoFeO3 nanoparticles synthesized by the co-precipitation method at low temperature (t° ≤ 4 °C). The single-phase HoFeO3 samples with the orthorhombic structure formed after annealing of the precipitates at different temperatures up to 950 °C. The annealed HoFeO3 nanoparticles have an average crystal size of 10–20 nm (SEM, TEM). UV-Vis spectrum of HoFeO3 sample annealed at 750 °C showed strong UV and Vis absorption with small optical energy gap (Eg = 1.56 eV). In the range temperature of 100–300 K, the HoFeO3 samples showed superparamagnetic behaviour at 5 kOe with high magnetization (Ms = 1.3–2.4 emu/g) and very low susceptibility (χ << 1).

The synthesis of novel heterojunction h-YbFeO3/o-YbFeO3 photocatalyst with enhanced Fenton-like activity under visible-light

A simple solution combustion approach followed by heat treatment was used to successfully synthesize a novel h-YbFeO₃/o-YbFeO₃ nanocrystalline heterojunction with an enhanced photo-Fenton-like activity in the decolorization process of methyl violet.