Preparation Of Microstructure-controlled Sn⁴⁺-doped TiO₂ Nanocrystals And Their Photoactivities

In our work, Sn⁴⁺ doped TiO₂ nanocrystals with controlled crystalline phase and morphology had been successfully prepared using Ti(SO₄)₂ and SnCl4·5H₂O as precursors, H₂O₂ as peptizing agent from the peroxo-metal-complex precursor by hydrothermal and solvothermal methods. The obtained materials were investigated by several characterization tests. The photocatalytic activities of the synthesized materials were tested by using the liquid-phase photocatalytic degradation of phenol as a model reaction.(1) Ti_1-xSn_xO₂ (x=0～0.1) nanocrystal colloids had been successfully prepared using H₂O as solvent from the peroxo-metal-complex precursor by hydrothermal method. The obtained materials were investigated by means of XRD, Raman, TEM, XPS, ICP-AES, N2 adsorption–desorption measurements (BET), PL and UV–vis spectroscopies technology. The results indicated that Ti_1-xSn_xO₂ nanocrystal colloids were obtained in the nanometer scale (less than 10 nm) and the crystalline size was smaller than pure TiO₂. Anatase phase, mixture phase (anatase and rutile) and rutile phase of Sn-doped TiO₂ samples were formed, when x < 0.04, 0.04 < x < 0.06 and x≥0.06, respectively. The Sn⁴⁺ dopants presented substitution Ti⁴⁺ into the lattice of TiO₂ alongside increasing the surface oxygen vacancies and the surface hydroxyl groups. Regarding photocatalytic activity, Sn-doped TiO₂ samples (TiSn3) were nearly four times higher than undoped samples. This obvious beneficial effect could be attributed to high surface area, optimal crystalline phase and surface state modifications.(2) Ti_1-xSn_xO₂ (x=0～0.1) nanocrystals with various amounts of dopant Sn⁴⁺ ions were prepared using n-butanol as solvent from peroxo-metal-complex precursor by solvothermal method and characterized by XRD, TEM, HRTEM, XPS, ICP-AES and UV–vis spectrophotometer. The experimental results indicated that the dopant Sn⁴⁺ substituted Ti⁴⁺ in the lattice of TiO₂, which reflected in the lattice expansion in both a- and c-direction and change of the binding energy. All the Ti_1-xSn_xO₂ nanocrystal samples appeared to be anatase evenly with dopant level up to 10 mol%. The effect of dopant Sn⁴⁺ ions and reaction solvents on physicochemical properties of the obtained anatase Ti_1-xSn_xO₂ nanocrystals had been discussed. In addition, the growth mechanism and microstructure evolution of Ti_1-xSn_xO₂ nanocrystals had been suggested. The photocatalytic activity of the anatase Ti_1-xSn_xO₂ nanocrystals was tested by the degradation of phenol. Compared with the undoped TiO₂ sample, the enhanced photocatalytic activity of the anatase Ti_1-xSn_xO₂ nanocrystals could be attributed to modification of the optical propertiesand surface state by doping the optimum concentration of Sn⁴⁺ ions.(3) Ti_0.9Sn_0.1O₂ nanocrystals with controlled crystalline phase and morphology had been successfully prepared through easily adjusting the solvent system from the peroxo-metal-complex precursor by solvothermal method. Ti_0.9Sn_0.1O₂ nanocrystals were characterized by XRD, Raman, TEM, HRTEM, XPS, ICP-AES, BET, UV-Vis. The experimental results indicated that the Ti_0.9Sn_0.1O₂ nanocrystals prepared in pure water or the predominant water system trend to form rod-like rutile, while cubic-shaped anatase Ti_0.9Sn_0.1O₂ nanocrystals can be obtained in alcohol system. The growth mechanism and microstructure evolution of Ti_0.9Sn_0.1O₂ nanocrystals prepared in different solvent systems are discussed. The liquid-phase photocatalytic degradation of phenol was used as a model reaction to test the photocatalytic activity of the synthesized materials. It was found that sample Ti_0.9Sn_0.1O₂ prepared in 1-butanol (TSB) showed the maximum photoactivity, which attributed to the higher band gap, optimal crystalline phase and surface state modifications.