The influence of titanium dioxide modification by sulfur and carbon on physico-chemical and photocatalytic properties

The nanocomposites based on TiO 2 doped with sulfur (S/TiO 2 ), carbon (C/TiO 2 ), carbon and sulfur (S/C/TiO 2 ) have been obtained. The powders were characterized by XRD, XPS, BET, SEM, EDX, TEM and UV-VIS spectroscopy. EDX and XPS spectroscopies prove that titanium dioxide powder includes only Ti and O elements, composites C/TiO 2 include the elements Ti, O, C, composites S/TiO 2 - Ti, O, S and composites C/S/TiO 2 - Ti, O, C, and S. XRD analysis revealed phase of anatase in all composites, rutile phase appeared with increasing of sulfur amount in sulfur-containing powders. It has been found that composites consist of roundish agglomerates in the range of 5–30 mm. Sulfur additives decrease grain growth of titanium dioxide particles from 14 to 9–10 nm in S/TiO 2 composites, carbon leads to increase in particle size from 14 to 19 nm, simultaneous modification of titanium dioxide by carbon and sulfur leads to the formation of particles with sizes of 7–8 nm. Analysis of nitrogen sorption–desorption isotherms for all synthesized samples has shown the presence of a hysteresis loop which is the evidence for mesoporous structure of the powders. The isotherms correspond to type IV of IUPAC classification for mesoporous materials with H1 type for C/TiO 2 and H 2 type for S/TiO 2 , and C/S/TiO 2 of hysteresis loop. The modification of TiO 2 by carbon and sulfur leads to increase of specific surface area (of about 1.8 times in the case of C/TiO 2 , about 3.3 times for S/TiO 2 and about 4.7 times for C/S/TiO 2 ), average pore volume and decrease of radius pore volume compared with TiO 2 . Absorption spectra of nanocomposites showed a bathochromic shift as compared with the absorption band of pure TiO 2 . It has been found that modification leads to band gap narrowing. Nanocomposite samples showed higher photocatalytic activity in the destruction of safranine T under UV and visible irradiation compared to pure TiO 2 . It may be related to the participation of dopants in the inhibition of electron-hole recombination, prolongation of charges lifetime, increasing efficiency of interfacial charge separation and formation of doping electronic states.