Selective suppression of {112} anatase facets by fluorination for enhanced TiO particle size and phase stability at elevated temperatures

• Published in: Nanoscale advances Vol. 3; no. 21; pp. 6223 - 623
• Main Authors: Kohlrausch, Emerson C, dos Reis, Roberto, Lodge, Rhys W, Vicente, Isabel, Brolo, Alexandre G, Dupont, Jairton, Alves Fernandes, Jesum, Santos, Marcos. J. L
• Format: Journal Article
• Published: 27-10-2021
• ISSN: 2516-0230
• DOI: 10.1039/d1na00528f

Generally, anatase is the most desirable TiO
2
polymorphic phase for photovoltaic and photocatalytic applications due to its higher photoconductivity and lower recombination rates compared to the rutile phase. However, in applications where temperatures above 500 °C are required, growing pure anatase phase nanoparticles is still a challenge, as above this temperature TiO
2
crystallite sizes are larger than 35 nm which thermodynamically favors the growth of rutile crystallites. In this work, we show strong evidence, for the first time, that achieving a specific fraction (50%) of the {112} facets on the TiO
2
surface is the key limiting step for anatase-to-rutile phase transition, rather than the crystallite size. By using a fluorinated ionic liquid (IL) we have obtained pure anatase phase crystallites at temperatures up to 800 °C, even after the crystallites have grown beyond their thermodynamic size limit of
ca.
35 nm. While fluorination by the IL did not affect {001} growth, it stabilized the pure anatase TiO
2
by suppressing the formation of {112} facets on anatase particles. By suppressing the {112} facets, using specific concentrations of fluorinated ionic liquid in the TiO
2
synthesis, we controlled the anatase-to-rutile phase transition over a wide range of temperatures. This information shall help synthetic researchers to determine the appropriate material conditions for specific applications.
Fluorinated ionic liquids are used to finely control the exposure of {112} facets on the TiO
2
surface enabling an exquisite temperature control of the anatase-to-rutile phase transition.