Magnetic, monodisperse titania microspheres with bimodal pore size distribution by a new sol–gel templating method and their photocatalytic activity

A new sol gel templating method was developed for the synthesis of magnetic monodisperse-porous titania microspheres 5.5 µm in size. A bimodal pore size distribution including both mesoporous and macroporous regions was first reported for magnetic titania microspheres. The product obtained by developed method and its AuNP decorated forms were evaluated as photocatalyst for textile-dye degradation in batch fashion. Different from the photocatalytic degradations performed by titania nanoparticles (i.e. P25 or similar types), a decolorization process including two serial stages was observed with the magnetic-porous titania microspheres. In the first stage, the low intraparticular diffusion resistance originated from macropores and the high surface area originated from mesopores provided fast dye adsorption onto the magnetic photocatalyst and a sudden decrease in the dye concentration (i.e. fast decolorization) that was not observed with titania nanoparticles. In the second stage, a slower decolorization occurred due to the slower photochemical degradation of adsorbed dye molecules on the magnetic photocatalyst. Complete removal of dye was achieved at acidic pH, using magnetic titania microspheres. A marked enhancement in the decolorization rate was obtained by the decoration of magnetic titania microspheres with AuNPs synthesized by Martin method.