Comprehensive evolved gas analysis (EGA) of amorphous precursors for S-doped titania by in situ TG-FTIR and TG/DTA-MS in air: Part 2. Precursor from thiourea and titanium(IV)-n-butoxide

Thermal decomposition of an amorphous precursor for sulfur-doped titania (S:TiO2) nanopowders, prepared by controlled sol-gel hydrolysis-condensation of titanium(IV) tetrabutoxide and thiourea in aqueous butanol, has been studied in situ up to 850 degrees C in flowing air by simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR) for analysis of gases and their evolution dynamics in order to explore and simulate thermal annealing processes of fabrication techniques aimed S:TiO2 photocatalysts with photocatalytic activities under visible light. The studied S-doped precursor's decomposition course remembers to that of non-doped xerogel from Ti(IV)-n-butoxide, which seems to retard a considerable amount of organics in the solid phase even at high temperature, probably in polymeric forms, proven by evolution of CO2 in several temperature regions of decomposition stages. The incorporation form of thiourea in the original xerogel seems to be chemically bounded, resulting lower decomposition temperature than that of pure thiourea, and producing evolution of carbonyl sulfide (COS) already between 120 and 190 C. Nevertheless, evolution of SO2, and that of CO2 is also observed above 500 degrees C by both EGA detection methods. The latter observation implies that the blackish grey samples obtained even at 750 degrees C might be simultaneously S- and C-doped ones. (C) 2008 Elsevier B.V. All rights reserved.