Chemical Synthesis of Magnetic Nanoparticles for Permanent Magnet Applications

Permanent magnets are a class of critical materials for information storage, energy storage, and other magneto-electronic applications. Compared with conventional bulk magnets, magnetic nanoparticles (MNPs) show unique size-dependent magnetic properties, which make it possible to control and optimize their magnetic performance for specific applications. The synthesis of MNPs has been intensively explored in recent years. Among different methods developed thus far, chemical synthesis based on solution-phase reactions has attracted much attention owing to its potential to achieve the desired size, morphology, structure, and magnetic controls. This Minireview focuses on the recent chemical syntheses of strongly ferromagnetic MNPs (H_c >10 kOe) of rare-earth metals and FePt intermetallic alloys. It further discusses the potential of enhancing the magnetic performance of MNP composites by assembly of hard and soft MNPs into exchange-coupled nanocomposites. High-performance nanocomposites are key to fabricating super-strong permanent magnets for magnetic, electronic, and energy applications.

Embedding Ultrasmall Au Clusters into the Pores of a Covalent Organic Framework for Enhanced Photostability and Photocatalytic Performance

Gold clusters loaded on various supports have been widely used in the fields of energy and biology. However, the poor photostability of Au clusters on support interfaces under prolonged illumination usually results in loss of catalytic performance. Covalent organic frameworks (COFs) with periodic and ultrasmall pore structures are ideal supports for dispersing and stabilizing Au clusters, although it is difficult to encapsulate Au clusters in the ultrasmall pores. In this study, a two-dimensional (2D) COF modified with thiol chains in its pores was prepared. With -SH groups as nucleation sites, Au nanoclusters (NCs) could grow in situ within the COF. The ultrasmall pores of the COF and the strong S-Au binding energy combine to improve the dispersibility of Au NCs under prolonged light illumination. Interestingly, Au-S-COF bridging as observed in this artificial Z-scheme photocatalytic system is deemed to be an ideal means to increase charge-separation efficiency.

Ingestible Contrast Agents for Gastrointestinal Imaging

Gastrointestinal (GI) ailments cover a wide variety of diseases involving the esophagus, stomach, small intestine, large intestine, and rectum. They bring about many inconveniences in daily life in chronic diseases and can even be life threatening in acute cases. Rapid and safe detection approaches are essential for early diagnosis and timely management. Contrast agents for GI imaging can enhance contrast to distinguish abnormal lesions from normal structures. Computed tomography and magnetic resonance imaging are two important diagnostic tools for the evaluation of GI conditions. This review mainly involves several common GI diseases, including inflammatory diseases, intestinal tumors, diarrhea, constipation, and gastroesophageal reflux diseases. Selected contrast agents, such as barium sulfate, iodine-based agents, gadolinium-based agents, and others, are summarized. Going forward, continued endeavors are being made to develop more emerging contrast agents for other imaging modalities.