Raman and XRD study on brookite–anatase coexistence in cathodic electrosynthesized titania

Abstract

Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy‐hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solid–liquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium‐tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X‐ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile‐free mixture of brookite and anatase at temperatures as low as 200 °C that persists up to 800 °C, when pure anatase dominates. The amount of brookite in the brookite–anatase mixture reaches a maximum at 400 °C. This very simple method for obtaining a brookite–anatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright © 2011 John Wiley & Sons, Ltd.