Fabrication of Bifunctional TiO2/POM Microspheres Using a Layer-by-Layer Method and Photocatalytic Activity for Methyl Orange Degradation

Bifunctional films of Keggin-type polyoxometalates H 3 PW 12 O 40 (PW 12 ), H 4 SiW 12 O 40 (SiW 12 ), H 3 PMo 12 O 40 (PMo 12 ), and TiO 2 were successfully built on Fe 3 O 4 @SiO 2 microspheres using a layer-by-layer method. The characterization by field emission scan electronic microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) shows that TiO 2 nanoparticles and polyoxometalate (POM) anions are successfully assembled. The photodegradation of methyl orange (MO) was used to test the photocatalytic efficiency of magnetic catalysts under UV irradiation. For MO decomposition, multilayer films that combine PW 12 and SiW 12 with TiO 2 show high efficiency, which can be attributed to the synergistic effect between POMs and TiO 2 . The degradation of the model contaminant was also systematically checked under different conditions such as bilayer number deposited on magnetic microspheres, catalyst concentration, inorganic oxidants, and salts. The oxidation process of MO follows an apparent first-order reaction. Furthermore, the composite catalysts deposited on Fe 3 O 4 @SiO 2 magnetic microspheres can be conveniently, quickly, and efficiently separated by an external magnet from a solution.