Synthesis and visible light photocatalytic properties of polyoxometalate–thionine composite films immobilized on porous TiO2 microspheres

Abstract

Multilayer films (PW12–TH)n (PW12=PW12O403-, TH=thionine) were immobilized on porous anatase TiO2 microspheres by layer-by-layer (LbL) self-assembly method. The porous structure of TiO2 was confirmed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that TiO2 template particles had a round shape with an average diameter of 250nm. The composite films were characterized by FTIR spectroscopy, UV diffuse reflectance spectroscopy and XRD spectroscopy. The results confirmed the successful immobilization of (PW12–TH)n composite films onto TiO2 microspheres, and the growth of PW12–TH layer pair was uniform. SEM and TEM were also used to characterize the morphology. When PW12–TH composite films were assembled on the template, the surface became rougher with the increasing number of layer pair. The lattice fringe of TiO2 became weaker when immobilized (PW12–TH)n. The photocatalytic properties of the microspheres toward a rhodamine B (RhB) solution were investigated under visible light irradiation. The combination of TiO2 and PW12 showed an excellent photocatalytic performance. Both TH sensitization and PW12 adsorption played important roles during the process of photocatalysis. Moreover, the catalytic property and reusability of as-prepared catalyst were relevant to the number of PW12–TH bilayer. The kinetics of the photodecomposition to rhodamine B followed the first-order reaction.