Preparation and photocatalytic properties of rutile TiO2 with a unique morphology and SrTiO3–TiO2 composites obtained by acid treatment of SrTiO3

•Anatase- and rutile-phase TiO2 was formed by SrTiO3 acid dissolution.•The crystalline phase of the formed TiO2 is dependent on the HNO3 concentration.•SrTiO3–TiO2 composite particles can be prepared by a short-duration acid treatment.•In the composite, fine TiO2 (anatase) particles formed on the SrTiO3 core.•SrTiO3–TiO2 composites exhibited higher photocatalytic activities.