Immobilization of phosphotungstic acid on the surface of chemically modified magnetite nanoparticles: An efficient heterogeneous acid catalyst for alcoholysis of epoxides

Abstract

A new magnetically recoverable heterogeneous acid catalyst was easily synthesized by electrostatic interaction of phosphotungstic acid (HPW) species with 3-aminopyridine (Ampy) modified magnetite-silica heterostructure (Fe3O4/SiO2-Ampy-HPW). The step by step modification of magnetite nanoparticles along with structural stability, and maintenance of magnetization and morphology of bare magnetite nanoparticles after chemical functionalization steps were confirmed by various physicochemical techniques. The size of these nanoparticles was obtained to be 10–30 nm from TEM analysis, which was in accordance with the data estimated from XRD technique. Also, it was observed that the presence of HPW on the surface of catalyst has increased the acid content of catalyst. Catalytic property of Fe3O4/SiO2-Ampy-HPW catalyst was assessed in acid-catalyzed ring opening of epoxides with alcohols. According to the results obtained at optimum reaction condition, the prepared catalyst exhibited good performance (conversion of 93%) with high selectivity (100%) in methanolysis of styrene oxide compared to the unfunctionalized Fe3O4/SiO2, which is definitely due to the presence of HPW acidic species on the surface of Fe3O4/SiO2. Moreover, other epoxides and alcohols were tested in this catalytic system, which subsequently, reasonable results with more or less conversion were obtained based on the types of the epoxides and alcohols used.