Controllable Synthesis of Manganese Oxide Nanostructures from 0-D to 3-D and Mechanistic Investigation of Internal Relation between Structure and T1 Relaxivity

Since manganese oxide nanomaterials attract wide attention in the biomedical and energy fields, understanding the inner relationship between their properties and structures is fundamental and urgently needed. However, controllable synthesis of metal oxide nanomaterials with diverse morphologies is still a persistent challenge. Herein, various anisotropic manganese oxide nanostructures from zero-dimensional (0-D) to three-dimensional (3-D) were successfully fabricated through thermal decomposition. We observed that chloride ions can assist the formation of 0-D nanooctaherals, nanocubes, and nanooctapods due to its binding capacity to the manganese ions on the nanocrystal surface. Interestingly, the procedural heating process can affect the decomposition rate of the manganese–oleate, which drives a substantial reduction in the surface free energy by sharing a common crystallographic orientation and leads to the formation of 1-D and 3-D nanostructures by oriented attachment growth. On the basis of systematic analyses, surface-to-volume ratio, surface manganese ion density, and geometrical confinement determined by specific morphology are found to be the key parameters to achieve high-performance T1 relaxivity. Moreover, the screened out manganese oxide nanocubes with high r1 value exhibit good contrast ability in T1-weighted MRI imaging in vitro and in vivo, showing a great potential for lesion detection in T1 contrast imaging. This study builds a link between controllable synthesis of manganese oxide nanomaterials and its property and, thus, provides a rational design clue to develop high-performance magnetic oxide nanomaterials, especially in the biomedical and energy fields.