科研之友
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摘要
The photoinduced processes of pristine and Mg2+-doped anatase nanopowders with the exposed {001} facets synthesized by a solvothermal method, using HF as the capping agent, were investigated by EPR spectroscopy. The adsorbed fluoride ions on the (001) facets of the as-prepared anatase samples have been removed by NaOH washing (washed samples) or calcination at 600 degrees C (calcined samples). EPR spectra monitored at 100 K for the as-prepared and washed anatase nanopowders characterized with high percentage of the exposed {001) facets, evidenced the presence of paramagnetic signals attributed to the intrinsic Ti3+ centers with narrow-line axially symmetric spectrum (g(perpendicular to) = 1.988, g(parallel to) = 1.956) and holes (O-) characterized with g-tensor g(perpendicular to) = 2.006, g(parallel to) = 2.003 already before exposure. Upon in situ UV exposure under air, the intensity of EPR signals of Ti3+ and O- increased significantly and two additional signals compatible with the photogenerated O-2 is approximately equal to and (O2H)-O-center dot were observed. A series of indirect EPR techniques, e.g., spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO), hindered amine oxidation, or reduction of radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate), were applied to follow the reactions in the irradiated TiO2 dispersions. While in the irradiated aerated aqueous media all anatase samples revealed the generation of (DMPO)-D-center dot-OH spin-adduct, upon UV exposure of the as-prepared samples in deaerated acetonitrile, the formation of a unique EPR spectrum attributed to (DMPO)-D-center dot-F was found. The (DMPO)-D-center dot-F spin-adduct is most probably produced by the inverted spin trapping mechanism via interaction of DMPO radical anion with the surface fluorides.
- 出版日期2015-11
