Rod shape anatase TiO2 nanocrystals can be prepared easily in multi-gram quantities according to the procedure reported by the Hyeon group. The nanocrystals are an ideal platform for the design of photoelectrochemical catalysts if the issues of visible light absorption and bottle-necks in electron transfer catalysis can be addressed. We demonstrate three routes to modify the surface and electronic structure of TiO2 nanocrystals. With the use of inexpensive metal chloride hydrates, quantitative control of the adsorption of transition metal ions (Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+) onto the surface of TiO2 nanocrystals was demonstrated. The adsorption is self-limiting up to one monolayer. It is even possible to partially titrate the nanocrystal with one metal ion then fill the remaining surface sites with a second metal, which affords 15 bimetal combinations of the 6 metal ions above. We also show that it is possible to ‘push’ the surface bound metal ions into the nanocrystal to make metal-doped TiO2 nanocrystals with precise control of the dopant concentration, which is limited by the solubility of the metal in the TiO2 and the amount of metal ion on the nanocrystal surface. Finally, we demonstrate a straightforward concept for the preparation of a wide range of metal-semiconductor hybrid nanocrystals. So far, we have prepared Ag-TiO2, Co-TiO2, Ni-TiO2, and Cu-TiO2 hybrid nanocrystals. We find that spontaneous air oxidation occurs with the first-row metals to afford CoO-TiO2, NiO-TiO2, and Cu2O-TiO2 hybrid nanocrystals. In this way, we could also prepare a ternary-phase hybrid nanocrystal upon formation of a Ag-TiO2-Ni sample that (in air) oxidizes to Ag-TiO2-NiO. In particular, this sample may possess key features of a photoelectrochemical catalyst, namely longitudinal separation of the electron/hole pair within the TiO2 nanorod, electron collection and catalysis at Ag, and hole collection and catalysis at NiO.

Systematic approaches to modify the surface and electronic structure of TiO2 nanocrystals

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.