Water-dispersible magnetic catalysts based on metal ferrite for selective oxidation of thiols

Abstract

Heterogenous magnetic photocatalyst, so-called multifunctional catalyst, has been of an intensive interests for using in many research fields. It can be also reused for several times after catalyzed the reaction by using magnetic field for separation. Magnetic metal- ferrite nanoparticles were synthesized by thermal decomposition method of iron (III) oleate in 1-octadecene in the presence of oleic acid leads to a simple, cost effective synthesis route for large scale monodisperse ferrite nanoparticles. Herein, Spherical magnetic metal ferrite (MFe₂O₄) with the diameter 6-13 nm, where M represents Mg, Fe, Co, Ni, Cu, and Mn, while maintaining the spinel crystal structure. The as-synthesized metal ferrites nanoparticles were characterized by using TEM, SEM-EDX, and XRD for their composition, size, shape, and structure. Moreover, MgFe₂O₄@TiO₂ core-shell structure was created by reverse-microemulsion for using in the selective oxidation of thiols. However, MgFe₂O₄@TiO₂ nanocomposites effectively catalyzed the aerobic oxidation of 4-chlorothiophenol under dark condition as well as MgFe₂O₄ without TiO₂ shell decoration within an hour reaction time. Therefore, the single metal ferrite with various metal would be interesting to further utilize instead of MgFe₂O₄@TiO₂ core-shell structure. Among all of metal ferrite nanoparticles, CuFe₂O₄ nanoparticles would be outstanding candidates for using under ambient condition in aqueous solution within 2 day to complete the aerobic oxidation of 4-chlorothiophenol to disulfide products. Magnetic metal ferrites can be magnetically recovered after finishing the reaction and reused up to forth runs without any significantly loss of catalytic activity. Therefore, these magnetic catalysts were effectively used in the selective oxidation of thiols that perform the catalytic property and magnetic property within the same materials.