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| - Preparation, Testing and Characterization of Doped TiO2 Active in the Peroxidation ofBiomolecules under Visible Light
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| - Doped TiO2 samples using different preparative procedures were synthesized using either urea or thiourealeading to N- or S-doped TiO2. Photocatalytic peroxidation and oxidation (mineralization) of phosphatidylethanolamine (PE) lipid with doped TiO2 were carried out under light irradiation λ > 410 nm. The formationof conjugated double bonds in PE molecules was followed to detect the formation of peroxy radicals(peroxidation index) under light excitation (λ > 410 nm) when doped TiO2 was used. The kinetics of CO2production was monitored during the mineralization of PE. Colored TiO2 powders were studied in detail bydifferent and complementary physicochemical techniques. The band gap energies of colored TiO2 weredetermined by diffuse reflectance spectroscopy (DRS). The visible absorption shoulder of TiO2 was observedto follow Urbach's law. The variation of the transient decay after 354 nm laser pulse excitation does notcorrelate with the different N− and S−TiO2 doping levels introduced by the addition of urea or thiourea.This suggests that the states (recombination centers or traps) introduced by the doping are not effective invarying the decay kinetics within the nanosecond and microsecond time scale. Elemental analysis showscomparable amounts of S- and N-doping of TiO2 when thiourea is used as dopant. X-ray diffraction revealsno rutile in S−TiO2 samples heated to 600 °C, suggesting that the addition of sulfur precludes rutilizationduring sample crystallization. X-ray photoelectron spectroscopy (XPS) of the S−TiO2 samples confirms thepreferential localization of S on the 20 topmost layers of S−TiO2 upon calcination at 500 °C for 2 h.
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