We have studied the photoinduced transformation of a colloidal solution of TiS2 nanodisks into TiS2/TiO2 heterostructures via partial oxidation of TiS2 to TiO2. Combined with the large absorption coefficient of TiS2 in the visible spectral range, the type II quantum well structure of TiS2/TiO2 can be efficient for photocatalysis. We have measured changes to the electronic structure using both steady state and time resolved absorption spectroscopy, as well as elucidated a mechanism for the photo-oxidation process. Photo-oxidation occurs only when the sample is irradiated with high intensity pulsed laser light, and is a highly non-linear process requiring a large number of excitations. Irradiation with CW laser light of similar intensity does not cause photo oxidation. During oxidation, TiS2 particles become thinner, as TiS2 is converted to TiO2 on the basal plains. Oxidation causes the particle bandgap to shift towards shorter wavelength, and increases the relaxation time of electrons photoexcited near the band gap transition. Interestingly, during initial oxidation, the overall particle volume remains constant, indicating that S is directly substituted for O, however in the limit of complete oxidation, the particles convert into a toroid structure. Oxidation was confirmed through XRD and EDS, which show the growth of amorphous TiO2, and an increase in the Ti/S ratio from 1/2 in the as synthesized particles to roughly 1/1 is partially oxidized particles.

Photoinduced transformation of colloidal layered TiS2 nanodiscs into TiS2/TiO2 hetero structures

247th National Meeting (2014)

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