Manipulating nanocrystal doping, structure, and photocatalytic activity with organic ligands

Org. ligands (or surfactants) are key in detg. colloidal nanocrystal structure and, therefore, function. In addn. to their more traditional role as surface passivating agents impacting nanocrystal size and shape, surfactants can also behave as active reagents during the synthesis, hence influencing reaction paths and chem. potential. Herein, we highlight the crit. role of surfactants in controlling doping kinetics and granting access to metastable cryst. phases by considering two different photocatalytic oxide systems as examples: TiO2 and BiVO4. In both cases controlling doping, cryst. phase and surface chem. is essential to manipulate their photocatalytic function. Infact, substitutional anion doping (i.e. N, S and C) in TiO2 and other binary metal oxides (WO3, Ta2O5) and cation doping (i.e. Sb, Pb) in BiVO4 have been shown to contribute reducing the band gap and enhancing the absorption in the visible range of these classes of metal oxides. In the case of binary oxides, we show that it is possible to intentionally position nitrogen in interstitial or substitutional sites depending on the amines used as surfactants during the synthesis. Our UPS/XPS measurements and UV-Vis absorption spectroscopy, supported by d. functional theory calcns., highlight the importance of both nitrogen content and location in detg. the defect states position within the oxide band gap and, consequently, the oxide band gap redn. expected in case of hybridization of nitrogen and oxygen 2p orbitals. In BiVO4 doping, it is important not only to effectively substitute bismuth with the dopant cations but also to stabilize the more catalytically active monoclinic phase vs. the thermodynamically stable tetragonal phase. We demonstrate that the choice of proper reaction conditions and, esp., of surfactants is crucial to this purpose. Finally, we will briefly discuss preliminary results illustrating the impact of post-synthetic surface treatment on the photoelectrochem. activity of doped TiO2 and BiVO4 nanocrystal-based electrodes.

Published in:
Abstracts of Papers, 248th ACS National Meeting & Exposition, San Francisco, CA, United States, August 10-14, 2014, COLL-703
American Chemical Society
Copyright (C) 2016 American Chemical Society (ACS). All Rights Reserved.

 Record created 2016-12-22, last modified 2018-09-13

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