Study on vapor-thermal synthesis and sulfur-doping of TiO2/graphene composites

Intimately contacted TiO 2 (nanoflake)/graphene composites were synthesized and doped with sulfur (S) at varying S/Ti molar ratios ( R S/Ti ) via a vapor-thermal method. S-doping led to a change in TiO 2 morphology from nanoflakes to nanoparticles. The dopant S in TiO 2 exhibits the multiple valence states of S 2− (replacing O 2− ), namely S 0 , S 4+ , and S 6+ (replacing Ti 4+ ), and introduces electronic states above the valence band of TiO 2 , simultaneously distorting the crystal lattice of TiO 2 . S-doping increases the degradation rate to methylene blue pollutant from 7.7 ×   10 −2  min −1 to 10.7 × 10 −2  min −1 due to the increase in OH/ O 2 − free radicals, which play an important role in methylene blue degradation.