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The article focused on a new method (colloidal solution combustion synthesis, CSCS) for obtaining TiO2/YFeO3 nanocomposites and the photocatalytic activity (methyl violet oxidation) of the synthesized samples depending on the TiO2 content (0–10 wt%). The obtained photocatalysts' properties were examined by means of EDXS, PXRD, nitrogen physisorption, Raman spectroscopy, and UV-Vis DRS. With the CSCS method, the phase transformation of TiO2 from anatase (a-TiO2) to amorphous (am-TiO2) was observed as a result of the combustion process. The am-TiO2 grains were found to be well dispersed on the surface of orthorhombic YFeO3 (o-YFeO3) with an average diameter of about 138 nm and 1.5 μm, respectively. The calculated average size (D) of o-YFeO3 crystals was in the range of about 35–56 nm; the largest D belonged to the case of pure YFeO3. All of the samples were shown to be mesopore adsorbents with pore widths of 40–50 nm. A synergistic effect between TiO2-added and YFeO3-based components was discovered. In comparison to pure YFeO3, TiO2/YFeO3 composites were developed for methyl violet photodegradation. The optimal TiO2 content for YFeO3-based photocatalysts was 2.5 wt%, with a dye removal efficiency of 38.6% and a TOF of 3.31·10−5 min–1. The TiO2-2.5/YFeO3 sample demonstrated the possibility of repeated use with the dye. The findings enable the creation of novel heterogeneous nanocomposites containing am-TiO2 and o-YFeO3 phases as well as their potential use in the photocatalytic oxidation of synthetic dyes. Highlights: am-TiO2/o-YFeO3 photocatalysts were obtained by using the colloidal solution combustion method. am-TiO2 particles demonstrated a synergistic effect on the resulting photocatalytic activity. The average size of o-YFeO3 crystals and the sample's specific surface area depended on the am-TiO2-containing phase. am-TiO2/o-YFeO3 samples exhibited high activity on the oxidation of methyl violet. Optimal am-TiO2-content was determined as 2.5 wt%. [ABSTRACT FROM AUTHOR]

BACKGROUND: Self‐propagating high‐temperature synthesis was used to create mesoporous CeO2 and MgO powders as well as nanocomposites based on them for efficient degradation of organic dyes. RESULTS: It has been investigated how magnesium oxide and cerium oxide interact to affect the crystal structure, morphology and microstructure of the materials produced. It was assumed that CeO2 forms on the surface of MgO while the material's developed surface is preserved. The values of the specific surface area and average pore diameter of the studied samples depend on the composition and vary in the ranges of 16–41 m2 g−1 and 11.919 nm, respectively. CONCLUSION: It has been established that the sizes of CeO2 crystallites in the composition of nanocomposites change insignificantly and range from 6.5 to 7.4 nm. The photocatalytic activity of the studied samples is at least two times higher compared to analogs. The samples MgO–CeO2 (30 mol%) and MgO–CeO2 (50 mol%) showed the maximum photodegradation efficiency of acid telon blue and direct bright blue dyes at levels of 98.5% and 92.5%, respectively. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Superparamagnetic nanocrystals of gadolinium orthoferrite (GdFeO3) with close to isometric morphology were successfully synthesized by heat treatment of gadolinium and iron(III) hydroxides obtained by direct co-precipitation with and without ultrasonic irradiation. The obtained samples were investigated by PXRD, low-temperature nitrogen adsorption–desorption isotherm measurements, HRTEM and VSM. It was established that ultrasonication during co-precipitation led to a decrease in the average size of GdFeO3 crystallites obtained after heat treatment by approximately 19%, an increase in their BET specific surface area by more than two times, a decrease in the degree of their aggregation by about five times and an improvement in their magnetic properties due to the increase in phase homogeneity. The colloidal solutions of the GdFeO3 nanoparticles synthesized using ultrasound were investigated by 1H NMR to measure the T1 and T2 relaxation times of water protons at 0.47 T. The resulting relaxivities r1 and r2 were approximately recalculated at 1.5, 3 and 4.7 T on the basis of a semi-statistical ad hoc method by analyzing the literature data for a number of structurally similar compounds with reported relaxivity values at different NMR frequencies. According to the experimental and predicted values of the r2/r1 ratio, the investigated GdFeO3 sample may be classified as a T1-contrast agent for MRI at 0.47 and 1.5 T, as a T1–T2 dual-modal contrast agent at 3 T and as a T2-contrast agent at 4.7 T. [ABSTRACT FROM AUTHOR]

The volume of dye production in the chemical industry is growing rapidly every year. Given the global importance of clean water resources, new wastewater treatment solutions are required. Utilizing photocatalysis by harvesting solar energy represents a facile and promising solution for removing dangerous pollutants. This study reports the possibility of increasing the photocatalytic activity of g-C3N4 by creating nanocomposites with ZnO. Exfoliated g-C3N4/ZnO nanocomposites were synthesized by heat treatment of urea and subsequent ultrasonic exfoliation of the colloidal solution by introducing zinc acetate. The uniformity of the distribution of ZnO nanoparticles is confirmed by the method of elemental mapping. The obtained X-ray diffractograms of the obtained nanocomposites show typical X-ray reflections for g-C3N4 and ZnO. It was found that the introduction of oxide into g-C3N4 leads to an increase in the specific surface area values due to the developed ZnO surface. The maximum value of the specific surface area was obtained for a sample containing 7.5% ZnO and was 75.2 m2/g. The g-C3N4/7.5% ZnO sample also demonstrated increased photocatalytic activity during the decomposition of methylene blue under the influence of visible light, which led to a twofold increase in the reaction rate compared to initial g-C3N4. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, a simple solution combustion synthesis followed by heat treatment was proposed to produce nanocrystalline h-YbFeO3/o-YbFeO3 heterojunction and phase-pure o-YbFeO3. A detailed investigation on the formation process of h-YbFeO3 and o-YbFeO3 nanocrystals was carried out using a wide variety of methods, including EDS, SEM, PXRD, 57Fe Mössbauer spectroscopy, DRS. The most prospective samples of the h-YbFeO3/o-YbFeO3 nanocomposite and o-YbFeO3 nanopowder were examined towards the photo-Fenton decolorization of methyl violet (MV) under visible light. It was shown that the proposed approach allows for obtaining h-YbFeO3 and o-YbFeO3 nanocrystals with an average size of 15.7–21.1 nm and 41.1–65.5 nm, respectively, and with a specific surface area of up to 16 m2 g−1. It was found that the h-YbFeO3/o-YbFeO3 nanocomposite has a mesoporous structure and foam-like morphology, while the o-YbFeO3 nanopowder is non-porous and represented by agglomerates of individual nanoparticles with isometric morphology. Based on the DRS results, it was found that the band gap value was 2.05 eV and 2.16 eV for the h-YbFeO3/o-YbFeO3 and o-YbFeO3 samples, respectively, providing strong visible-light absorption of the samples. It was shown that the electron structure of the h-YbFeO3/o-YbFeO3 nanocomposite refers to I type heterojunction, leading to effective electron and hole transfer from o-YbFeO3 to h-YbFeO3 bands. This feature determines the higher photocatalytic activity of the h-YbFeO3/o-YbFeO3 nanocomposite as compared to pure o-YbFeO3 in the process of the Fenton-like decolorization of methyl violet under visible light with the pseudo-first-order reaction rate of 0.004848 min−1 and 0.003123 min−1, respectively. In conclusion, the mechanism of the photocatalytic decolorization of MV over the heterojunction nanocomposite was proposed to explain its high activity in the Fenton-like process. [ABSTRACT FROM AUTHOR]

Nanocrystals of gadolinium orthoferrite (GdFeO3) with morphology close to isometric and superparamagnetic behavior were successfully synthesized using direct, reverse and microreactor co-precipitation of gadolinium and iron(III) hydroxides with their subsequent heat treatment in the air. The obtained samples were investigated by PXRD, FTIR, low-temperature nitrogen adsorption-desorption measurements, HRTEM, SAED, DRS and vibration magnetometry. According to the X-ray diffraction patterns, the GdFeO3 nanocrystals obtained using direct co-precipitation have the smallest average size, while the GdFeO3 nanocrystals obtained using reverse and microreactor co-precipitation have approximately the same average size. It was shown that the characteristic particle size values are much larger than the corresponding values of the average crystallite size, which indicates the aggregation of the obtained GdFeO3 nanocrystals. The GdFeO3 nanocrystals obtained using direct co-precipitation aggregate more than the GdFeO3 nanocrystals obtained using reverse co-precipitation, which, in turn, tend to aggregate more strongly than the GdFeO3 nanocrystals obtained using microreactor co-precipitation. The bandgap of the obtained GdFeO3 nanocrystals decreases with decreasing crystallite size, which is apparently due to their aggregation. The colloidal solutions of the obtained GdFeO3 nanocrystals with different concentrations were investigated by 1H NMR to measure the T1 and T2 relaxation times. Based on the obtained r2/r1 ratios, the GdFeO3 nanocrystals obtained using microreactor, direct and reverse co-precipitation may be classified as T1, T2 and T1–T2 dual-modal MRI contrast agents, respectively. [ABSTRACT FROM AUTHOR]

Superparamagnetic nanocrystals of gadolinium orthoferrite (GdFeO 3 ) with close to isometric morphology were successfully synthesized by heat treatment of gadolinium and iron(III) hydroxides obtained by direct co-precipitation with and without ultrasonic irradiation. The obtained samples were investigated by PXRD, low-temperature nitrogen adsorption-desorption isotherm measurements, HRTEM and VSM. It was established that ultrasonication during co-precipitation led to a decrease in the average size of GdFeO 3 crystallites obtained after heat treatment by approximately 19%, an increase in their BET specific surface area by more than two times, a decrease in the degree of their aggregation by about five times and an improvement in their magnetic properties due to the increase in phase homogeneity. The colloidal solutions of the GdFeO 3 nanoparticles synthesized using ultrasound were investigated by 1 H NMR to measure the T 1 and T 2 relaxation times of water protons at 0.47 T. The resulting relaxivities r 1 and r 2 were approximately recalculated at 1.5, 3 and 4.7 T on the basis of a semi-statistical ad hoc method by analyzing the literature data for a number of structurally similar compounds with reported relaxivity values at different NMR frequencies. According to the experimental and predicted values of the r 2 / r 1 ratio, the investigated GdFeO 3 sample may be classified as a T 1 -contrast agent for MRI at 0.47 and 1.5 T, as a T 1 - T 2 dual-modal contrast agent at 3 T and as a T 2 -contrast agent at 4.7 T.