Study On Visible-light-Driven Photocatalytic K₂La₂Ti₃O₁₀ Nanocomposites

Photo-catalytic reactions of semiconductors such as splitting of water have received much attention from researchers because of their possible application to the conversion of solar energy into chemical energy. Especially, more and more layered compounds have been used as catalysts owing to their unique structural feature and excellent photo catalytic activities.In this Ph.D. dissertation, the ultrafine layered K₂La₂Ti₃O₁₀ photo-catalyst was fabricated, and the photo-catalytic activity of K₂La₂Ti₃O₁₀ was improved by doping metal ion and nonmetal, pillaring, intercalating oxide. Then the samples obtained were characterized by theoretical calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravity - differential scanning calorimeters analysis (TG-DSC), Fourier transform infrared spectroscopy (FT-IR), ultra violet-visible spectroscopy (UV-vis), specific surface area (BET), fluorescence spectrophotometer, etc, experiments. The performance of K₂La₂Ti₃O₁₀ such as structure, reaction mechanism, photo catalytic activity, was studied. The dissertation was mainly discussed as follows:The density of states and electronic structures of K₂La₂Ti₃O₁₀ perovskites were calculated by first-principles calculations with ultrasoft pseudopotentials plane-wave method based on the density functional theory. It is shown that the valance band has the contributions from the 2p orbital of O atom, and the conduction band has the contributions from the 3d orbital of Ti. From the observed parameters, it appears that K₂La₂Ti₃O₁₀ hasΔE≥3.2 eV.The micrometer-sized K₂La₂Ti₃O₁₀ was hydrothermally synthesized in the titanium (IV) isopropoxide, lanthanum trioxide and potassium hydroxide system under mild conditions. The results show that the products are dependent on some factors, such as Ti/ La molar ratio, crystallization temperature and time, pH value in reaction mixture. It was showed that it has a high purity, larger surface area than the solid state reaction sample. The hydrothermal sample has higher photo catalytic comparison the samples synthesized by the solid state reaction. The band gap of product is 3.72 eV. The growth unit mechanism may be used to explain the synthesis process.Ultrafine layered K₂La₂Ti₃O₁₀ was successfully fabricated by stearic acid method under relatively lower temperature and shorter reaction time, which were usually used for the preparation of nanoparticles. The possible mechanism was primarily brought forward with the assistant of XRD, TG-DSC, FT-IR, etc. It was showed that it has a high purity, larger surface area than the solid state reaction sample. The hydrothermal sample has higher photo catalytic activity comparison the samples synthesized by the solid state reaction. The band gap of product is 3.71 eV.K_2-xLa₂Ti_3-xM_xO₁₀ (M=V, Nb, Ta; x=0.0¹.0) photo catalyst were fabricated by doping transition metals V, Nb, Ta in K₂La₂Ti₃O₁₀. The phase of K_2-xLa₂Ti_3-xM_xO₁₀ (M=V, Ta) were changed from Ruddlesden-Popper (K_2–xLa₂Ti_3–xM_xO₁₀, x = 0.8; K_2-xLa₂Ti_3-xTa_xO₁₀, x = 0.7) to Dion-Jacobson except for K2-xLa2Ti3-xNbxO10. The influence of doping with M on the photo catalytic property and band gap of photo catalyst were studied. The results reveal that the photo catalytic property of K_1.9La₂Ti_2.9M_0.1O₁₀ is higher than other samples owing to the appropriately doping with M ion.Nitrogen-doped K₂La₂Ti₃O_10-xN_x was successfully prepared by wet chemical method. The absorption threshold was transferred to long wavelength. Because the nitrogen element was introduced in the crystal lattice of K₂La₂Ti₃O_10-xN_x, so the energy gap declined. The photo activity of K₂La₂Ti₃O_10-xN_x has higher photo catalytic activity comparison K₂La₂Ti₃O₁₀ and TiO₂(P25). The possible mechanism was primarily brought forward with the assistant of XRD, UV-vis, FT-IR, etc.Intercalation behavior of n-alkylamines into a protonated from of a layered perovskite, H₂La₂Ti₃O₁₀ has been investigated. The interlayer distance increase to 2.15 (n = 3), 2.53 (n = 4), 2.68 (n = 6) and3.15 (n = 9) nm. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains.TiO₂, CdS-ZnS, Fe₂O₃ and Pt into the interlayer of H₂La₂Ti₃O₁₀has been investigated. A serial of layered nanocomposites were synthesized by lots of reaction processes. The gallery height of interlayer was less than 1.0 nm.Photo catalytic activities of H₂La₂Ti₃O₁₀/TiO₂, H₂La₂Ti₃O₁₀/CdS and H₂La₂Ti₃O₁₀/Fe₂O₃ were superior to those of unsupported H₂La₂Ti₃O₁₀, TiO₂ and Fe₂O₃ and were greatly enhanced by co-incorporation of Pt. Especially H₂La₂Ti₃O₁₀/CdS and H₂La₂Ti₃O₁₀/Fe₂O₃ showed photo catalytic activity under visible light irradiation. Under irradiation withλ> 290 nm from a Hg lamp of 450 W for 5 h, about 404μmol hydrogen was produced form 1250 ml methanol solution 10 vol. % containing 1g of dispersed H₂La₂Ti₃O₁₀/(Pt, TiO₂). Furthermore,12μmol hydrogen was produced by 1g of dispersed H₂La₂Ti₃O₁₀/(Pt, Fe₂O₃) under irradiation withλ> 400 nm light for 5 h, and the photocorrosion of CdS was suppressed effectively when it was incorporated in the interlayer of H₂La₂Ti₃O₁₀. Finally, the concentration of the photocatalysts and productivities of hydrogen were discussed. The results showed that the productivities of hydrogen decreased with the concentration of the photocatalysts'increasing when them were beyond the optimal concentration, which might be due to the particle's dispersion was strengthened when the concentration of the photocatalysts increased.