Synthesis of magnetically separable N, La-doped TiO2 with enhanced photocatalytic activity

•The magnetic photocatalyst possesses the performance of SiO2 and N,La-TiO2.•N, La-co-doped enhances the photocatalytic activity of TiO2 under visible light.•SiO2 inter-layer is crucial for retention of photocatalytic activity of N,La-TiO2.•SiO2 inter-layer is a good adsorbent for dye molecules in water.•Composite photocatalyst can be recovered effectively and be put into cyclic use.

A magnetically separable nitrogen and lanthanum co-doped photocatalyst γ-Fe2O3@SiO2@N,La-TiO2 (FST) with a typical superparamagnetic property was prepared by an effective three-step approach. Specifically, the preformed monodisperse γ-Fe2O3 nanoparticles were used as templates for directing the sequential deposition of SiO2 layer by modified Stöber method and subsequent N,La-TiO2 layer by hydrothermal method. During the hydrothermal assisted TiO2 deposition, the interior black Fe3O4 nanoparticles were converted into dark-brown γ-Fe2O3 nanoparticles. FST showed a ternary structure with a core of γ-Fe2O3, a SiO2 mesosphere and a N,La-TiO2 (anatase) crust. SiO2 layer can prevent effectively the transfer of charges from TiO2 to γ-Fe2O3, which avoids electrons and holes recombination at the interface. SiO2 inter-layer is also a good adsorbent for dye molecules, FST showed higher photocatalytic activity than γ-Fe2O3@N,La-TiO2 (FT). FST is photoactive under both UV and visible light irradiation and can be easily separated from a slurry in photoreactor by the application of an external magnetic field.