Metallic nanoparticles immobilized in magnetic metal–organic frameworks: preparation and application as highly active, magnetically isolable and reusable catalysts

Separation and recycling of catalysts after catalytic reactions are critically required to reduce the cost of catalysts as well as to avoid the generation of waste in industrial applications. In this paper, ultrafine noble metallic nanoparticles are incorporated into cauliflower-like porous magnetic metal–organic frameworks (MOFs). With the restriction effects of the pore/surface structure in the MOFs, “surfactant-free” metallic nanoparticles are successfully obtained on a 2–3 nm scale. In addition, both the thickness of MOFs shell and the content of noble metallic NPs are tunable on the MOFs coating. Moreover, the microspheres exhibit excellent performance for the catalytic reduction of p-nitrophenol with a turnover frequency of 3094 h−1. The uniform cavities in the MOFs shell provide docking sites for p-nitrophenol and act as confinement nanoreactors, which greatly improves the catalytic performance. Most importantly, the magnetically responsive microspheres can be easily recovered by a magnetic field and show excellent reusability. The as-prepared catalyst also shows good activity for the reduction of other nitrobenzenes. Consequently, this work provides a highly active, magnetically isolable, and recyclable catalyst, which can be used for various catalytic industrial processes. The fundamental model can be further employed in a variety of biomedical fields including drug delivery and biological molecules separation.