Controlled synthesis of Fe₃O₄/ZIF-8 nanoparticles for magnetically separable nanocatalysts

Fe₃O₄/ZIF-8 nanoparticles were synthesized through a room-temperature reaction between 2-methylimidazolate and zinc nitrate in the presence of Fe₃O₄ nanocrystals. The particle size, surface charge, and magnetic loading can be conveniently controlled by the dosage of Zn(NO₃)₂ and Fe₃O₄ nanocrystals. The as-prepared particles show both good thermal stability (stable to 550 °C) and large surface area (1174 m²g^-1). The nanoparticles also have a superparamagnetic response, so that they can strongly respond to an external field during magnetic separation and disperse back into the solution after withdrawal of the magnetic field. For the Knoevenagel reaction, which is catalyzed by alkaline active sites on external surface of catalyst, small Fe₃O₄/ZIF-8 nanoparticles show a higher catalytic activity. At the same time, the nanocatalysts can be continuously used in multiple catalytic reactions through magnetic separation, activation, and redispersion with little loss of activity.