Preparation and application of hydroxylated magnetic covalent organic framework material

The invention discloses a magnetic nanoparticle and a preparation method and application thereof, the nanoparticle comprises: a core body formed by ferroferric oxide; the shell covers at least part of the surface of the core body, the shell is composed of repeated multi-element ring units shown in the formula I, and R is H or hydroxyl. The magnetic nanoparticle takes a ferroferric oxide nanoparticle as a core body, has magnetism and is easy to adsorb and separate, so that the problems that a covalent organic framework material is poor in stability, inconvenient to use and operate, difficult to recycle and the like are solved; the covalent organic framework material composed of a multi-element ring unit shown in the formula I serves as a shell, and the covalent organic framework material has the advantages of being large in specific surface area and good in stability, has wide application prospects in the enrichment aspect of trace pollutants and is especially suitable for steroid hormone extraction, and the e