2.1. Preparation of the Materials. Bi2WO6 was
synthesized by following a procedure reported elsewhere.27
Briefly, two solutions with the corresponding amounts of
Bi(NO3)3·5H2O and Na2WO4·2H2O were prepared. The Bi
precursor (0.005 mol) was dissolved in 5 mL of glacial acetic
acid and the W solution (0.0025 mol) in 45 mL of Milli-Q
water. These solutions were mixed to form a white suspension
which was kept under stirring for 1 h. Then, this mixture was
transferred to a Teflon liner inside a stainless steel autoclave
and submitted to hydrothermal treatment at 140 °C for 20h.
Finally, the precipitate was filtered, repeatedly washed, dried
overnight, and calcined at 300 °C for 4h.
An analogous procedure was used for the preparation of
BiVO4. In this case, the vanadium precursor was anhydrous
NaVO3, which was added in a stoichiometric proportion (0.005
mol) to Bi.
The coupled Bi2WO6/TiO2−P25 sample was synthesized
with the same method. The corresponding amount of
commercial TiO2 (Evonik, P25) was added to the white
suspension of Bi−W prior to the hydrothermal treatment, with
a TiO2/Bi2WO6 ratio of 50% wt. This material was named
BW−Ti.