Mechanistic Insight into the Precursor Chemistry of ZrO2 and HfO2 Nanocrystals; towards Size-Tunable Syntheses

One can nowadays readily generate monodisperse colloidal nanocrystals, but a retrosynthetic analysis is still not possible since the underlying chemistry is often poorly understood. Here, we provide insight into the reaction mechanism of colloidal zirconia and hafnia nanocrystals synthesized from metal chloride and metal isopropoxide. We identify the active precursor species in the reaction mixture through a combination of nuclear magnetic resonance spectroscopy (NMR), density functional theory (DFT) calculations, and pair distribution function (PDF) analysis. We gain insight into the interaction of the surfactant, tri-n-octylphosphine oxide (TOPO), and the different precursors. Interestingly, we identify a peculiar X-type ligand redistribution mechanism that can be steered by the relative amount of Lewis base (L-type). We further monitor how the reaction mixture decomposes using solution NMR and gas chromatography, and we find that ZrCl4 is formed as a by-product of the reaction, limiting the reaction yield. The reaction proceeds via two competing mechanisms: E1 elimination (dominating) and SN1 substitution (minor). Using this new mechanistic insight, we adapted the synthesis to optimize the yield and gain control over nanocrystal size. These insights will allow the rational design and synthesis of complex oxide nanocrystals.

Synthesis and thermal behavior of nanoceramic material based on Bi13Fe5Ti6O39

The process of formation by the chemical coprecipitation method of nanoceramic material based on layered perovskite-like complex oxide Bi13Fe5Ti6O39 with the structure of the Aurivillius phase has been described. The temperatures of the onset of formation, the onset of decomposition, and activation of sintering, as well as the coefficient of linear thermal extension of the material, have been determined. Technological parameters for the synthesis of the material with a high yield of the target product and the ability to vary the crystallite size in the range of 70‒85 nm have been determined.

Preparation of complex oxide (Pr0.8Y0.2)0.6Ca0.4CoO3 from Pr–Y–Ca–Co gel synthesized by ultrasonic irradiation and its metal-insulator transition characteristics

We previously reported that a swollen gel possessing a uniform composition and prolonged stability can be conveniently prepared by simple ultrasonic irradiation of an ethanol suspension of calcium acetate, which is poorly soluble in ethanol. In this study, the same gel synthesis method was applied to prepare the multicomponent oxide (Pr1−yYy)1−xCaxCoO3 (PYCCO), which undergoes a metal-insulator phase transition. Calcination of the Pr–Y–Ca–Co swollen gel at 800 °C for 12 h in air afforded PYCCO nanoparticles with good crystallinity, representing a faster and more convenient route compared with conventional solid-phase reaction methods or sol–gel methods.

Evolution of Chemical Composition and Modeling of Growth Nonmetallic Inclusions in Steel Containing Yttrium

The programs WYK_Stal and Bi-Growth, developed at AGH-UST, Kraków, Poland, were used for simulating the refining process, the formation of non-metallic inclusions, and their growth. The Fe-Y-Al-O-S-Ca system in pre-oxidized steel was analyzed, where yttrium formed precipitates from both O and S. When first Al and second Y were added to steel, the proportion of Al2O3 inclusions remained constant. This resulted in higher yttrium losses for oxide formation, whereas the sulfur content promoted sulfide phase formation. The introduction of yttrium at the end of refining contributed to reducing the consumption of this element in the non-metallic phase formation. The addition of aluminum and then calcium were sufficient to achieve a high degree of deoxidation and desulfurization. Calculations performed with WYK_Stal for both (a) and (c) versions of the model showed that the sulfide phase was constituted by CaS and FeS (model c) and CaS (model (a)). The participation of the calcium sulfide phase turned out to be dominant in the inclusions. Their presence was also identified in the slag phase. Simulations of the growth of complex oxide and oxo-sulfide inclusions using the Bi_Growth program showed that the yttrium content of the steel has a decisive role in the formation of complex oxide inclusions and the final oxygen content of the steel. In contrast, for the growth of oxide-sulfide inclusions, the character of growth is determined by the sulfur content of steel.

Upcycling Waste Plastics into Multi-Walled Carbon Nanotube Composites via NiCo2O4 Catalytic Pyrolysis

In this work, multi-walled carbon nanotube composites (MWCNCs) were produced by catalytic pyrolysis of post-consumer plastics with aluminium oxide-supported nickel, cobalt, and their bimetallic (Ni/α–Al2O3, Co/α–Al2O3, and NiCo/α–Al2O3) oxide-based catalysts. The influence of catalyst composition and catalytic reaction temperature on the carbon yield and structure of CNCs were investigated. Different temperatures (800, 900, 950, and 1000 °C) and catalyst compositions (Ni, Co, and Ni/Co) were explored to maximize the yield of carbon deposited on the catalyst. The obtained results showed that at the same catalytic temperature (900 °C), a Ni/Co bimetallic catalyst exhibited higher carbon yield than the individual monometallic catalysts due to a better cracking capability on carbon-hydrogen bonds. With the increase of temperature, the carbon yield of the Ni/Co bimetallic catalyst increased first and then decreased. At a temperature of 950 °C, the Ni/Co bimetallic catalyst achieved its largest carbon yield, which can reach 255 mg g−1plastic. The growth of CNCs followed a “particle-wire-tube” mechanism for all studied catalysts. This work finds the potential application of complex oxide composite material catalysts for the generation of CNCs in catalytic pyrolysis of wasted plastic.