Study of the decomposition of aqueous citratoperoxo-Ti(IV)-gel precursors for titania by means of TGA-MS and FTIR

Abstract

An aqueous solution-gel route is developed for the preparation of TiO2. In this report, we study an aqueous citratoperoxo-Ti(IV)-precursor at pH 2.0, which is compatible with polyvinyl alcohol (PVA) and therefore can be applied for the preparation of a thick mesoporous TiO2 film. With regard to deposition of films, it is important to gain insight in the behaviour of the precursor during thermal treatment. Therefore, the thermal decomposition mechanism of a citratoperoxo-Ti(IV)-gel and a PVA modified citratoperoxo-Ti(IV)-gel is studied. Weight losses and evolved gasses are characterized by TGA-MS (5 degrees C min(-1)), while gel structure and changes in the solid upon heating are studied by means of FTIR. For both gels, decomposition in dry air can be divided into five regions. After drying of the samples in the first region (similar to 100 degrees C), decomposition of the organic matter not coordinated to the metal ions occurs (similar to 200 degrees C). The third region (similar to 310 degrees C) involves the decomposition of citrato ligands. Finally, the residual organic matter is combusted in the last two regions. Only in dry air it is possible to fully remove the organic matrix in both gels at temperatures below 600 degrees C. It is also proven that the citratoperoxo-Ti(IV)-complexes, seen at pH 7.0, exist in the precursor gel already at pH 2.0. (c) 2007 Elsevier B.V. All rights reserved.