Synthesis of Cross-like TiO2 Thermally Derived from Ammonium Oxofluorotitanate Mesocrystals Under Different Calcination Temperatures and Their Photocatalytic Activity

Synthesis of anatase titanium dioxide (TiO 2 ) catalysts with excellent photocatalytic activity is of great importance in photocatalytic application. In this work, a cross-like anatase TiO 2 structure is obtained by thermal treatment of precursors synthesized in an electrochemical cell with mixed phases of (NH 4 ) 2 TiOF 4 and NH 4 TiOF 3 . When calcined at various temperatures, these obtained anatase TiO 2 products could preserve their original morphologies and structures until 750 °C and kept anatase phase from rutile till 900 °C showing better thermal and structural stability, which was probably associated with fluoride contents on the surface of anatase TiO 2 products after conversion from (NH 4 ) 2 TiOF 4 and NH 4 TiOF 3 precursors. The photocatalytic activity of prepared TiO 2 samples over methyl orange is investigated. The photocatalytic activity of mesocrystalline TiO 2 cross decreases with the increase of the calcination temperature of ammonium oxofluorotitanates except for a best performance at 600 °C. The calcination temperature-dependent catalytic performance of the products could be ascribed to the removal of fluorine, nitrogen, or hydroxyl radicals on the surface, and the change of crystallinity and crystallite size with varying heating temperatures. The results indicated that anatase TiO 2 mesocrystals calcined at 600 °C showed the highest photocatalytic performance more likely owing to well-defined morphology, good microstructure, and suitable crystallite size. Graphical Abstract