Magnetic Chitosan-Supported Polyoxometalates and Its Catalytic Oxidation of Tetrahydrothiophene

Firstly, Fe₃O₄ nanospheres were prepared by solvothermal method, which were used as magnetic cores and coated with chitosan (CS) crosslinked by glutaraldehyde. Then, polyoxometalate (POM) was supported onto the magnetic CS carriers by electrostatic bonding and three magnetic polyoxometalates microspheres (Fe₃O₄@CS@POM) were prepared, including Keggin type magnetic phosphotungstic acid (Fe₃O₄@CS@PW₁₂) and Dawson type magnetic phosphotungstic acid (Fe₃O₄@CS@P₂W₁₇ and Fe₃O₄@CS@P₂W₁₈). Their structures and morphologies were characterized by FT-IR、UV-Vis、EA and TEM. The catalytic activity of Fe₃O₄@CS@POM on tetrahydrothiophene (THT) was investigated in detail. It is shown that all the three kinds of Fe₃O₄@CS@POM microspheres have good catalytic oxidation abilities to THT, among which Fe₃O₄@CS@PW₁₂ shows the best catalytic activity. The conversion of THT could reach 100% at room temperature after 105 min with a small amount of Fe₃O₄@CS@PW₁₂ (0.01 g). The catalytic oxidation process follows the quasi-first order kinetic model. The catalyst could be separated quickly and efficiently in the external magnetic field. In addition, Fe₃O₄@CS@PW₁₂ has good reusability, and the catalytic activity remains stable after 5 cycles.