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

Graphical Increasing attraction : Fe 3 O 4 /zeolite imidazolate framework (ZIF-8) nanoparticles were synthesized through a room-temperature reaction between 2-methylimidazolate (MeIM) and zinc nitrate in the presence of Fe 3 O 4 nanocrystals (see figure; PAA=polyacrylic acid). The particles have a superparamagnetic response and can be separated by means of a magnetic field and redispersed into the solution after withdrawal of the field. Fe 3 O 4 /ZIF-8 nanoparticles were synthesized through a room-temperature reaction between 2-methylimidazolate and zinc nitrate in the presence of Fe 3 O 4 nanocrystals. The particle size, surface charge, and magnetic loading can be conveniently controlled by the dosage of Zn(NO 3 ) 2 and Fe 3 O 4 nanocrystals. The as-prepared particles show both good thermal stability (stable to 550 °C) and large surface area (1174 m 2 g −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 Fe 3 O 4 /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.