Low-Temperature Synthesis of Magnetic Pyrochlores (R2Mn2O7, R = Y, Ho-Lu) at Ambient Pressure and Potential for High-Entropy Oxide Synthesis.

Rare-earth manganese pyrochlores (R2Mn2O7) are frustrated magnetic materials, which previously have only been accessed using expensive high-pressure and high-temperature synthesis. In the present work, we demonstrate a convenient synthetic approach to synthesize R2Mn2O7 pyrochlores at ambient pressure. A series of pyrochlores (R = Y, Ho-Lu) were prepared by a simple and cost-effective molten salt method using NaCl and KCl as the flux. Moreover, phase-selectivity was demonstrated for yttrium manganese oxides (YMnO3 and Y2Mn2O7) by a simple variation of synthesis temperature and precursors-to-chlorides ratio. The synthetic procedure does not require high pressures or temperatures nor oxygen flow. All synthesized pyrochlores demonstrated ferromagnetic behavior at low temperature, and the magnetic properties were in good agreement with those of high-pressure-synthesized materials. The versatility of the method was confirmed by the preparation of a mixed-rare earth Y0.4Er0.4Tm0.4Yb0.4Lu0.4Mn2O7 solid solution─a compositionally complex high-entropy oxide.

Tuning the structural properties of cadmium-aluminum layered double hydroxide for enhanced photocatalytic dye degradation.

The distinctive layered structure, chemical stability and tunability of layered double hydroxides (LDHs) have led to extensive investigations in various areas of photocatalysis, including photocatalytic water splitting, carbon dioxide photoreduction, and degradation of organic pollutants. Here, a series of visible light active cadmium-aluminum layered double hydroxides (CdAl LDHs) with various Cd2+ : Al3+ ratios is synthesized via the reaction-diffusion framework (RDF) leading thereby to a hierarchal spherical structure of the LDH. The aim of this study is to develop an optimal CdAl LDH photocatalyst that is activated by solar light irradiation and tested for methylene blue (MB) degradation. The structural and physicochemical properties of the synthesized materials are determined by several imaging and spectroscopic techniques. The photocatalytic study reveals a strong dependence of the photocatalytic activity of the CdAl LDH on the cationic ratio with an optimal performance at a ratio Cd2+ : Al3+ equal to 3 : 1. A mechanism is proposed whereby the activity is ascribed to the formation of intermediate reactive oxidative species (ROS) during the photodegradation reactions and scrutinised by invoking different ROS quenchers and corroborated by density functional theory (DFT) calculations.