Highly photoactive anatase nanoparticles obtained using trifluoroacetic acid as an electron scavenger and morphological control agent

Abstract

Fluorine species adsorbed on the surface of TiO 2 anatase nanoparticles improve their photocatalytic performance by reducing the recombination rate of photogenerated electrons and holes. Trifluoroacetic acid (TFAA) has been recently proposed as a promising harmless substitute for hydrofluoric acid (HF) in preparing fluorine-modified anatase with good scavenger properties. However the photocatalytic performance of the TiO 2 nanoparticles also depends on their specific morphology, by which the number and type of crystal facets, which remain exposed, are determined. A comprehensive study is presented in this contribution which for the first time describes the role of TFAA in stabilizing the highly photoactive {001} TiO 2 facets. Furthermore, by reducing the amount of water incorporated into the reaction medium, a simple one-step synthesis method is also proposed that allows the preparation of TFAA-modified anatase nanoparticles with specific morphology and selected stabilized facets, eventually yielding a semiconductor material with excellent photocatalytic properties.

Defects in Metal Oxide Nanoparticle Powders

“…A comprehensive study addressed the role of trifluoro acetic acid in stabilizing the highly photoactive {001} TiO 2 facets. Corresponding results substantiated the hypothesis that fluorine species adsorbed on the surface of TiO 2 anatase nanoparticles improve their photocatalytic performance by reducing the recombination rate of photogenerated electrons and holes [166].…”

Adsorption properties of trifluoroacetic acid on anatase (101) and (001) surfaces: a density functional theory study

“…101) surface. Interestingly, the resulting bridging adsorption mode is in agreement with the suggestion from analysis of the infrared spectra of TFAA on TiO 2 anatase nanoparticles 23. Thus, orientations with the molecule parallel or perpendicular to the surface were considered and each case initial geometries were tried with the molecule placed above different surface sites.…”

“…To complete the discussion we will now focus on the interpretation of the XPS experiments reported by Calatayud et al 23 These authors find two well separated contributions corresponding to the F(1s) core level binding energies. The first peak appears at 684 eV and is attributed to F species adsorbed above Ti surf sites, the second peak exhibits larger intensity and appears at a rather higher binding energy of 688 eV and is attributed to F atoms on the -CF 3 moiety of the TFAA molecule.…”

“…TiO 2 anatase single crystal mesoparticles with controlled size, well-defined polyhedral facets, 18 , 19 and high-level photocatalytic activities have been synthetized in the past few years. 23 Moreover, the use of TFAA enormously reduces the presence of water in the reaction medium allowing for a better control. Yet, this understanding is 3 critical in order to promote the development of large-scale production facilities that can produce a low-cost/high-efficiency TiO 2 -based material and create a competitive advantage in the industry by leveraging the nanoscale morphology control.…”

“…The geometry optimization procedure was started from almost all possible coordination modes and orientations of the TFAA molecule to the surface. Nevertheless, this can play a role on the semi solvo-thermal synthesis conditions used by Calatayud et al23 and may be the reason why a too high temperature results in nanoparticles with less well-defined facets. The parallel initial geometry always evolves to a perpendicular one with the O atoms pointing towards the surface.…”