Nanocomposites and nanomaterials

Experimental study and quantum chemical modeling on the effect of tin impurity sites in titanium dioxide on its electronic properties

Smirnova O.1, Grebenyuk A. 1, Khalyavka T.2, Shapovalova M.2, Permyakov V.3, Korzhak G.4, Lobanov V. 1

1 Chuiko Institute of Surface Chemistry NAS of Ukraine, General Naumov Str. 17, Kyiv, Ukraine, 03164
2 Institute for Sorption and Problems of Endoecology, NAS of Ukraine, General Naumov str., 13, Kyiv-03164, Ukraine, bondarenkomaryna91@gmail.com 
3 Institute of Geological Sciences NAS of Ukraine, O. Gonchar Str. 55-b, Kyiv, Ukraine, 01054
4 L.V. Pisarzhevskii Institute of Physical Chemistry, NAS of Ukraine, Prospekt Nauky, 31, Kyiv-03028, Ukraine.

Doping titanium dioxide with different metals is effective method for change of its properties in particular photocatalytic [1, 2]. Mesoporous nanocomposite materials based on TiO2 with different tin content were synthesized using titanium (IV) tetrabutoxide, SnCl2, citric acid and castor oil. The energy-dispersive spectroscopy based on energy-dispersive technique proves that these materials have a uniform distribution of Ti, Sn and O. All the composite samples revealed weak peaks which belong to the anatase phase and intense peaks corresponding to the rutile phase. Absorption spectra of nanocomposites showed a bathochromic shift as compared with the absorption band of pure TiO2 (Fig 1) and band gap narrowing. Nanocomposites Sn/TiO2 exhibit higher photocatalytic activity than pure TiO2 in the reactions of dyes (Safranine T, Rodamine B) photodestruction in water solutions and photocatalytic hydrogen evolution from alcohol-aqueous solutions. 

	
Fig. 1. UV-Vis diffuse reflectance spectra of samples: 
1 – TiO2, 2 – 0.1Sn/TiO2, 3 – 0.5Sn/TiO2, 4 - 1Sn/TiO2, 
5 - 2Sn/TiO2	Fig. 2. Sn-doped titania clusters.	

To explain the changes of physico-chemical properties of TiO2 due to Sn modification it is necessary to elucidate the mechanism of formation of nanocomposites with different amounts of tin. The quantum mechanical calculations are a useful tool to investigate this question.
The calculations of electron absorption spectra of pure and Sn-doped titania clusters (Fig. 2) have been carried out by TDDFT method using the basis set 6-31G (d, p) by means of the PC GAMESS software package (FireFly version 8.2.0 by A. Granovsky) [3]. When comparing experimental and calculated spectra, one can conclude that admixting Sn atoms results in a broadening and complication of the spectra observed in the region of 250-300 nm. Nevertheless there is no definite correlation between the energy gap (it can increase or decrease due to presence of Sn atoms) and calculated absorption spectra.

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