Photocatalytically active titanium dioxide nanopowders: Synthesis, photoactivity and magnetic separation

Two approaches were used to obtain nanocrystalline titanium dioxide (TiO₂) photocatalyst powders. Firstly, low-temperature synthesis method and secondly liquid flame spraying. The structural properties of the produced powders were determined with X-ray diffraction, transmission electron microscopy and nitrogen adsorption tests. The photocatalytic properties of the powders were studied with methylene blue (MB) discoloration tests. After discolorations tests, TiO₂ was coagulated with magnetite particles using FeCl₃·6 H₂O at a fixed pH value. Magnetic separation of coagulated TiO₂ and magnetite was carried out by a permanent magnet. The obtained results showed that the particle size of the powders synthesized at low-temperature was very small and the specific surface area high. The phase content of the powder was also shown to depend greatly on the acidity of the synthesis solution. Powder synthesized by liquid flame spraying was mixture of anatase and rutile phases with essentially larger particle size and lower specific surface area than those of low-temperature synthesized powders. The MB discoloration test showed that photocatalytic activity depends on the phase structure as well as the specific surface area of the synthesized TiO₂ powder. The magnetic separation of TiO₂–magnetite coagulate from solution proved to be efficient around pH:8.