Magnetochemistry

With the acceleration of industrialization and urbanization, heavy metals, organic pollutants, microplastics, and emerging contaminants are continuously entering the environment, posing a serious threat to ecosystems and human health [...]

SiCN ceramics, doped with transition metal ions Fe and Mn, are very promising functional materials for applications in electronics, spintronics and tunable soft magnetics for MEMS/NEMS (micro–nanoelectromechanical system) applications. EPR studies of nanostructured superparamagnetic compounds provide essential information on their chemical composition, homogeneity and size distribution. EPR measurements on Fe- and Mn-doped SiCN samples, annealed at various temperatures, revealed that they were superparamagnetic. In addition, their EPR spectra depended significantly on the sizes of the nanoparticles. The magnetism of SiCN/Fe is mainly due to the presence of Fe₅Si₃ nanoparticles distributed within the SiCN matrix. There may be minor contributions from Fe_xSi_yC_z and α-Fe superparamagnetic nanoparticles. It is suggested that the main source of magnetism in SiCN/Mn ceramics is the presence of Mn₅Si₃C_x. Magnetization experiments on SiCN/Fe reveal that the difference between the ZFC (zero-field cooling) and FC (field cooling) magnetizations decreased with the increasing annealing temperatures of the samples, implying that the homogeneity in the distribution of the sizes of nanoparticles increased with increasing annealing temperature. This result can be exploited for practical applications of Fe-doped SiCN nanoceramics as functional materials by annealing these samples at temperatures even higher than 1400 °C. Polymer-derived SiCN/Fe and SiCN/Mn ceramics are prospective materials that can be used in MEMS/NEMS applications, requiring homogeneous and uniform material.

Water affects the local structure, dynamics, and adsorption properties of metal–organic frameworks (MOFs), yet the molecular-level characterization of confined water remains difficult due to the lack of long-range ordering. Here, we study the water adsorption in microporous MOF Al(HCOO)₃ using multinuclear solid-state NMR spectroscopy combined with ab initio molecular dynamics (AIMD) simulations. ¹H NMR resolves two distinct confined-water environments and reveals water–framework and water–water contacts. ¹³C and ²⁷Al NMR further show that water adsorption perturbs the local environments of the formate linkers and AlO₆ coordination units. Powder X-ray diffraction shows that the long-range crystalline framework is preserved after water loading, whereas ¹³C NMR detects a minor mobile formate-containing species that disappears upon re-dehydration, consistent with the partial local hydrolysis of the framework. ²H NMR distinguishes both highly mobile and confined water undergoing rapid anisotropic reorientation. The effective quadrupolar line shape is consistent with rapid anisotropic reorientation, for which C₂-axis flips provide one possible motional model. ¹H–²H CP-HETCOR NMR further suggests dipolar contacts between restricted water molecules, the formate framework, and neighboring water molecules. AIMD simulations support water–framework interactions associated with the two pore environments and the formation of an interconnected water network. These results provide molecular-level insights into the water adsorption sites and dynamics in Al(HCOO)₃ and the previously unreported partial hydrolysis of this MOF.