Improved adsorption and degradation performance by S-doping of (001)-TiO(2)

In this work, sulfur-doped (S-doped) TiO(2) with the (001) face exposed was synthesized by thermal chemical vapor deposition at 180 or 250 °C using S/Ti molar ratios R(S/Ti) of 0, 0.5, 1, 2, 3, 4 and 5. The S-doped samples synthesized at 250 °C exhibit a significantly improved photocatalytic performance. More precisely, S-doping has the following effects on the material: (1) S can adopt different chemical states in the samples. Specifically, it exists in the form of S(2−) replacing O(2−) at a ratio of R(S/Ti) = 1 and also in the form of S(6+) replacing Ti(4+) at R(S/Ti) ≥ 2. As a result, S-doping causes a lattice distortion, because the ionic radii of S(2−) and S(6+) differ from that of the O(2−) and Ti(4+) ions. (2) S-doping increases the adsorption coefficient A(e) for methylene blue (MB) from 0.9% to 68.5% due to the synergistic effects of the oxygen vacancies, increased number of surface chemical adsorption centers as a result of SO(4)(2−) adsorption on the TiO(2) surface and the larger pore size. (3) S-doping increases the MB degradation rate from 6.9 × 10(−2) min(−1) to 18.2 × 10(−2) min(−1) due to an increase in the amount of •OH and •O(2−) radicals.