서강대학교

초록/요약

Synthesis of recyclable polyoxomolybdate catalysts in which Keggin-type polyoxoanion, PMo12O403- (POM) was immobilized on the superparamagnetic mesoporous microspheres(POM/NiFe2O4@SiO2 SMSs). Superparamagnetic NiFe2O4 nanoparticles(NPs) were grown within mesoporous shell/solid core silica spheres, followed by covering the surface of NPs with silica. They can separate simply by a magnet which can be used recyclable catalyst. The silica coated magnetic spheres were functionalized with APTMS(3-aminopropyl triethoxysilane) molecules. Then, these were then reacted with POM molecules to yield the POM catalysts supported on magnetic micro spheres. The POM catalysts were throughly characterized by powder X-ray diffraction, SEM, TEM and magnetization measurements using a SQUID magnetometer. When dimethyl sulfoxide was used as a solvent and oxygen donor, the POM catalysts afforded over 99 % yield to benzylic aldehyde in the selective oxidation of benzylic alcohol. For the purpose of comparison, we also carried out the same reaction with homogeneous POM catalysts. Indeed the oxidation activity of the POM/NiFe2O4@SiO2 SMSs was much higher than that of POM alone. When pure POM was dissolve in solvent, reaction condition was became acidic. This pH dependency disturb that oxygen molecule of DMSO supply to substrate. POM immobilized on magnetic silica spheres are very effective and recyclable hybrid catalysts. TiO2 colloids are very valuable photocatalytic systems, efficient of converting solar energy to chemical or electrical energy. For enhancive photoinduced interfacial electron transfer, a photoreactive polyoxometalate such as H3PMo12O40 was immobilized on the surface of commercial TiO2 (Degussa P25). The heterogeneous photocatalysts TiO2-APTMS-POM have been prepared using APTMS(3-aminopropyl triethoxysilane) molecules which link to POM and TiO2 successfully. The physicochemical properties of composites characterized by FT IR, Solid UV-vis, TEM, ICP-MS demonstrated that PMo12O403- were anchored on the surface of support TiO2, and that the PMo12O403- still retained their Keggin structure. Upon irradiation of the POM/TiO2 system with near-UV and visible light (λ≥300nm) in methyl alcohol (0.1%) aqueous solution, interfacial electron transfer takes place from the conduction band of TiO2 to the immobilized POM, which is also excited to catalyze photoreduction of methyl orange. The photoinduced charge-carrier generation at the heterojunction is very useful. Moreover, we observed the catalytic phororeduction activity of POM-immobilized on TiO2 for methyl orange has been synergistically improved under visible light irradiation (λ≥380nm).