Fe₃O₄ Nanoparticles Decorated with UIO-66 Metal–Organic Framework Particles and Encapsulated in a Triazine-Based Covalent Organic Framework Matrix for Photodegradation of Anionic Dyes

A type of magnetic composite Fe3O4@MOFUIO-66@TzDa-COF with a matryoshka structure was successfully synthesized by following a specific synthesis order. The Fe3O4@MOFUIO-66@TzDa-COF still has an efficient and rapid photocatalytic degradation effect irrespective of the concentration of the Malachite Green and Congo Red dyes, respectively. Even with 100 mg/L Malachite Green and Congo Red aqueous solutions, they can be completely degraded by the prepared composite within 40 and 120 min with removal rates of Malachite Green and Congo Red of up to 99 and 97%, respectively. In addition, the composite Fe3O4@MOFUIO-66@TzDa-COF has high photocatalytic activities of 1.21 and 0.65 min–1 for Malachite Green and Congo Red with a concentration of 20 mg/L, as far as we all know, which are the fastest degradation rates of Malachite Green and Congo Red among the reported nanoporous adsorbents. More interestingly, the photodegradation performance of the Fe3O4@MOFUIO-66@TzDa-COF was influenced by the order of the embedded nanoparticles, that is, the kind of inner core metal. This research provides an idea for constructing a type of photocatalyst with both enhanced functionality and magnetic separability by combining the advantages of covalent organic frameworks (COFs), metal–organic frameworks (MOFs), and magnetic nanoparticles, which is of great significance to the field of environmental protection.