Fe3O4@SiO2–SO3H Nanoparticles: An efficient magnetically retrievable catalyst for esterification reactions

In this study, magnetite nanoparticles were obtained from Fe(II) and Fe(III) salts in an alkaline medium. The nanoparticles were then protected from oxidation by a silica shell formed by the sol-gel method using tetraethoxy orthosilicate (TEOS) in an EtOH/H2O mixture. The synthesized Fe3O4@SiO2-SO3H magnetic nanocatalyst was characterized with Fourier transform infrared (FT-IR) spectroscopy, wide angle X-ray diffraction (WXRD), thermal gravimetric analysis (TGA), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Hammett acidity function and pH analysis as well as Brunauer-Emmett-Teller surface area measurement (SBET). Finally, the esterification reaction of phthalic anhydride, mono- and dicarboxylic acids with various alcohols was chosen to show the catalytic activity of the magnetic nanocatalyst. The reaction conditions were optimized and catalyst recovery was also demonstrated. The nanocatalyst was magnetically separated and reused several times without significant loss of activity.