Nanocomposites and nanomaterials

Properties of TiO2 mechanochemically modified with carbon and sulfur

Khalyavka T.A.1, Shapovalova M.V.1, Shcherban N.D.2, Camyshan S.V.1, Dulian P.3,
Khyzhun O.Y.4, Permyakov V.V.5 

1Institute for Sorption and Problems of Endoecology, NAS of Ukraine, General Naumov str., 13, Kyiv, Ukraine, 03164, takhalyavka@ukr.net
2 L.V. Pisarzhevskii Institute of Physical Chemistry, NAS of Ukraine, Prospekt Nauky, 31, Kyiv, Ukraine, 03028 
3 Institute of Technology, Pedagogical University of Cracow, 2 Podchorążych Str., 30-084 Cracow, Poland  
4 І.М. Fratsevich Institute for Problems in Materials Science , NAS of Ukraine, Krzhizhanovsky str., 3, Ukraine, 03142
5Institute of Geological Sciences, NAS of Ukraine, O. Honchar str., 55-b., Ukraine, 01054

It is known, that photocatalytic application of pure TiO2 has inherent limitation due to its wide band gap in the near-UV spectrum rendering inactivity under visible light [1-3]. To shift the light absorption edge of TiO2 into visible range, doping is considered to be an effective procedure. In most cases, doping of TiO2 with non-metals leads to increase the efficiency of photocatalytic activity. The aim of our work is obtaining the nanocomposites based of TiO2, their doping with carbon (C/TiO2), sulfur (S/TiO2) and co-doping with carbon and sulfur simultaneously (C/S/TiO2) by mechanochemical technique and investigation their properties. As a source of carbon for modification we used activated carbon, thiourea was a sulfur source.    
Analysis of SEM-images of the synthesized samples shows that they consist of fragmented agglomerates in the range of 1–21 µm. Modification in all cases leads to a decrease in particles size. It was confirmed by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) study. During doping and co-doping of titanium dioxide with carbon and sulfur using mechanochemical treatment the formation of new phases does not occur. 
N2 ad(de)sorption isotherms of all the composites possess 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/TiO2 and H2 type for S/TiO2, and C/S/TiO2 of hysteresis loop. The modification of TiO2 by carbon and sulfur leads to increase of specific surface area (of ca. 3.3 times for S/TiO2 and ca. 4.7 times for C/S/TiO2), total pore volume and decrease of pore radius compared to TiO2. 
C=O bonds on the surface of C/TiO2, S/TiO2 and C/S/TiO2 samples and S2– and -NH2 on the surface of S/TiO2 and C/S/TiO2 powders were identified. Absorption spectra of the nanocomposites showed a bathochromic shift as compared with the absorption band of pure TiO2. Adsorption and photocatalytic activity of nanocomposite samples under UV irradiation increase in comparison with pure titanium dioxide which is associated with a decrease in particle size, increase in specific surface area. It was found that the samples of titanium dioxide modified with carbon and sulfur show photocatalytic activity under visible irradiation in the destruction reaction of Safranin T, which is explained by their sensitization to visible light by the adsorbed dye (table 1).

Table 1. Photocatalytic activity of the powders in the destruction of Safranin T
Sample	UV, % destruction	Visible, % destruction	
3ТіО2	46	–	
1С2/3ТіО2	52	25	
2С2/3ТіО2	71	29	
1S/3TiO2	22	18	
1S/C2/3TiO2	59	40	

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