Colorless Magnetic Colloidal Particles Based on an Amorphous Metal-Organic Framework Using Holmium as the Metal Species.

Holmium (Ho) is a lanthanide element with a high magnetic moment. Here, we create an amorphous metal-organic framework (MOF) that has no long-range periodic order but retains the basic components of MOF by using isophthalic acid as an organic linker and Ho as a metal species. The resulting spherical Ho-MOF particles disperse well in a solvent and exhibit excellent magnetic properties in response to magnets. Since Ho has almost no coloring, Ho-MOF particles are a colorless magnetic material, unlike conventional iron oxide particles. Taking advantage of the colorless property, the selective adsorption of dyes on Ho-MOF particles can be easily visually confirmed by magnetically separating the particles. In addition, present versatile processes that enable adaptation of lanthanide elements other than Ho enable the development of colorless multifunctional MOF particles.