Gd₂O(CO₃)₂ · H₂O Particles and the Corresponding Gd₂O₃: Synthesis and Applications of Magnetic Resonance Contrast Agents and Template Particles for Hollow Spheres and Hybrid Composites

The solution approach was employed to yield multifunctional amorphous Gd 2 O(CO 3 ) 2 · H 2 O colloidal spheres by reflux of an aqueous solution containing GdCl 3 · 6H 2 O and urea. By elongating the reaction time, crystalline rhombus‐ shaped Gd 2 O(CO 3 ) 2 · H 2 O with at least 87% yield could be formed and were also accompanied by some rectangular particles. High‐resolution synchrotron powder X‐ray diffraction provides crystal structure information, such as cell dimensions, and indexes the exact crystal packing with hexagonal symmetry, which is absent from the Joint Committee on Powder Diffraction Standards file, for the crystalline rhombus sample. Particle formation was studied based on the reaction time and the concentration ratio of [urea]/[GdCl 3 · 6H 2 O]. After a calcination process, the amorphous spheres and crystalline rhombus Gd 2 O(CO 3 ) 2 · H 2 O particles convert into crystalline Gd 2 O 3 at temperatures above 600 °C. For in vitro magnetic resonance imaging (MRI), both Gd 2 O(CO 3 ) 2 · H 2 O and Gd 2 O 3 species show the promising T 1 ‐ and T 2 ‐weighted effects and could potentially serve as bimodal T 1 ‐positive and T 2 ‐negative contrast agents. The amorphous Gd 2 O(CO 3 ) 2 · H 2 O contrast agent further demonstrates enhanced contrast of the liver and kidney using a dynamic contrast‐enhanced MR imaging (DCE‐MRI) technique for in vivo investigation. The multifunctional capability of the amorphous Gd 2 O(CO 3 ) 2 · H 2 O spheres was also evidenced by the formation of nanoshells using these amorphous spheres as the template. Surface engineering of the amorphous Gd 2 O(CO 3 ) 2 · H 2 O spheres could be performed by covalent bonding to form hollow silica nanoshells and hollow silica@Fe 3 O 4 hybrid particles.