Sol–gel synthesis of mesoporous anatase–brookite and anatase–brookite–rutile TiO2 nanoparticles and their photocatalytic properties

TiO2 photocatalysts with a mixture of different TiO2 crystal polymorphs have customarily been synthesized hydrothermally at high temperatures using complicated and expensive equipment. In this study TiO2 nanoparticles with a mixture of TiO2 crystals were synthesized using a modified sol–gel method at low temperature. In order to form nanoparticles with different polymorphs a series of samples were obtained at pH 2, 4, 7 and 9. Raw samples were calcined at different temperatures ranging from 200 to 800 °C to evaluate the effect of the calcination temperature on the physico-chemical properties of the samples. XRD results revealed that a mixture of anatase and brookite can be obtained in the as-synthesized samples and in those calcined up to 800 °C depending on the pH used to obtain the final product. Indeed, a mixture of anatase brookite and rutile; or a sample with only rutile phase can be yielded through further calcination of the as-prepared samples at temperatures ⩾600 °C due to phase transformation. The photocatalytic performance of the samples with a mixture of anatase–brookite; anatase–brookite–rutile; and anatase–rutile (Degussa P25 TiO2) was exquisitely investigated in the degradation of methylene blue solutions. The samples obtained at pH 2 and calcined at 200 °C possessed the highest activity of all due to its superior properties. This study elucidates a facile method suitable for the synthesis of TiO2 with different mixtures of TiO2 polymorphs with desirable properties for various applications.