Structure and Properties of Visible-Light Active Binary TiO2&Au Nanocomposites

The synthesis of gold-modified TiO
2
powders was carried out by a chemical method using titanium tetraisopropoxide (TTIP) and HAuCl
4
in the presence of additional substances. It is shown that the introduction of glucose and NaOH into the system affects the phase composition of TiO
2
powders. According to TG-DTA, the transformation of lyophilized precipitates includes first the formation of anatase and brookite phases (T < 460 °C) followed by the crystallization of an intermediate
$\bold{\upbeta}-\mathbf{TiO}_{2}$
phase (460–550 °C) before transformation of TiO
2
polymorphs into rutile (680-920 °C). The formation of each phase is confirmed by XRD on thermal annealing samples. Anatase and brookite (T = 600 °C) present a CSR of 7.6-9.9 nm and 29.8-30.2 nm, respectively. The distortion of the tetragonality of the anatase crystal lattice and the shift of
$d$
(110) to larger angles suggest the inclusion of gold in the TiO
2
structure. According to XRD data, nanopowders processed at T = 1000 °C contain
$\bold{\upbeta}-\mathbf{TiO}_{2}$
and rutile
$([\mathbf{Au}]\ =2.0-3.5\ \mathbf{wt}.\%)$
or only
$\bold{\upbeta}-\mathbf{TiO}_{2}$
([Au] = 0.5-1.0 wt.%). The CSR of rutile is 28.9-35.7 nm while it ranges from 25.8-34.9 nm for
$\bold{\upbeta}-\mathbf{TiO}_{2}$
. The photocatalytic activity of these TiO
2
&Au nanopowders was assessed through the decolorization of malachite green (MG) solutions. The best result (up to 99%) was obtained for the anatase-brookite system (600 °C) with an Au content of 2.0 wt. %. Increasing the powder processing temperature to 1000 °C reduces the decolorization activity to 54%. Therefore, the studies indicate that dispersed binary systems based on titanium dioxides, in particular, anatase-brookite or amorphous TiO
2
are promising for the creation of catalysts active in visible light.