An aqueous solution–gel citratoperoxo–Ti(IV) precursor: synthesis, gelation, thermo-oxidative decomposition and oxide crystallization

A watersoluble citratoperoxo–Ti(IV) complex was synthesized and the chemical reactions that occur during the different synthesis steps were studied. A crystalline complex could be obtained by slow evaporation of highly concentrated precursor solutions, while fast evaporation led to the preparation of a homogeneous, amorphous glassy solid, the gel. The chemical structure of the crystallized complex ion and of the gel were shown to be related, but differed due to the presence of a crosslinked ammonium citrate network in the gel, which prevents crystallization. The thermo-oxidative decomposition pathway of the crystalline complex and the gel to the metal oxide is described based on in-situ thermal analysis techniques combined with Fourier transform infrared and mass spectrometry, diffuse reflection infrared by Fourier transform as well as high-temperature X-ray diffraction. The study offers a fundamental understanding of the behavior of the aqueous solution gel Ti(IV) precursor which is applicable in the preparation of all kinds of multimetal oxide systems containing Ti(IV) ions.