Mixture design optimization of the composition of S, C, SnO2-codoped TiO2 for degradation of phenol under visible light

We have applied mixture design and response surface techniques to prepare visible light-active TiO2 photocatalysts codoped with sulfur, carbon, and tin oxide using titanium tetraisopropoxide (TTIP), tin(IV) chloride, and thiourea, respectively, as precursors. During calcination, the S atoms replaced the Ti or O atoms in the TiO2 structure to maintain the anatase form, whereas doping with SnO2 promoted the anatase-to-rutile transformation. O–Ti–C bonds and carbonaceous species were present in the prepared samples; together with the S atoms, they were responsible for the visible light activity, which was boosted by moderate doping SnO2 due to a declined e−–h+ recombination rate. A synergic effect induced by dopants SnO2 and S, C on the visible light activity of TiO2 was quantitatively established for the first time through mixture design techniques and response surface methodologies. The obtained empirically quartic models describe well the main and interactive influences of the precursors on the specific surface area and visible light activity of the S, C, SnO2-codoped TiO2 samples.