Investigation of phase transitions for the hydrothermal formation of TiO2 in the presence of F− ions

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 214; no. 1; pp. 229 - 236
• Main Authors: Yang, Hongyun, Chen, Feng, Jiao, Yanchao, Zhang, Jinlong
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier B.V 01-01-2013; Elsevier
• Subjects: ammonia; Anatase; Applied sciences; Brookite; Catalysis; Catalytic reactions; Chemical engineering; Chemistry; condensation; electrolytes; Exact sciences and technology; F− ion; General and physical chemistry; ions; Phase transition; Photocatalytic activity; photolysis; Reactors; scanning electron microscopy; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; X-ray diffraction; Photocatalytic activity; Brookite; F− ion; Anatase; Phase transition; Scanning electron microscopy; Phase composition; Photocatalysis; F; Electrostatic interaction; ion; Condensation; X ray diffraction; Phase transitions; Electrolyte; Morphology; Titanium oxide; Photochemical degradation
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2012.10.045

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► Presence of F− ion affects the phase transition of ammonium titanate into TiO2. ► Pure brookite TiO2 was prepared in a wide Na+ concentration range with F−. ► F− ion catalyzes the condensation reaction of TiOH to produce TiOTi linkage. ► F− regulates the intercalation/de-intercalation of Na+ in the titanate layers. ► TiO2 prepared in the presence of F− showed superior photocatalytic activity.
The hydrothermal phase transition of ammonium titanate into TiO2 in aqueous ammonia media was investigated in the presence of F− ions by adding various kinds of electrolytes such as NaCl, NH4Cl, NaF, and NH4F. The phase composition and the morphologies of the products were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). With the assistance of F− ions, pure brookite TiO2 can be hydrothermally prepared with a wide range of Na+ ion concentrations from 0.25M to 1.5M in just 24h, which has obvious advantages over the previous NaCl scheme [1,2]. Moreover, photocatalytic degradation of MO shows that both anatase and brookite prepared in the presence of F− ions show superior photocatalytic activities than those prepared in the absence of F− ions. The phase transition mechanism from ammonium titanate into TiO2 was also proposed. Besides the introduction of Na+ ions that benefits the phase transition from titanate to brookite, F− ions are suggested to play two key roles during the hydrothermal process: catalyzing the condensation reaction of TiOH to produce TiOTi linkages by forming TiF and regulating the intercalation and the de-intercalation of Na+ ions by counteracting the electrostatic interaction between the Na+ ions and the titanate layers.