drop wise into mixture till reached pH
value approximately 1.8. Thiourea (Tu: CH4SN2, as a precursor
of nitrogen and sulfur) can transfer the photocatalytic
activity of TiO2 to visible region due to synergetic
effect by S and N. Thus, after few minutes, while stirring
solution, 0.25 g Tu (to make 0.45 M ratio of Tu:TiO2)
was dissolved into the TiO2 sol under vigorous stirring.
The molar ratio 0.45 was selected based upon our previous
work which highest photodecomposition efficiency was
reported (Behpour and Atouf, 2012). Finally, the obtained
yellow solution was stirred continuously for 2 h at room
temperature until it forms homogeneous solution.