【作者】 黄昀昉；

【导师】 吴季怀；

【作者基本信息】 华侨大学 ， 材料学， 2008， 博士

【摘要】 将太阳能转换为氢能是解决未来能源问题的理想方法之一,光催化技术是实现其转换过程最有希望的途径。具有层状结构的半导体光催化剂因其特有的空间结构优势已成为目前光催化研究领域最为活跃的方向之一。本论文主要研究了超细层状K₂La₂Ti₃O₁₀光催化剂的制备,并通过金属离子和非金属离子的掺杂、柱撑、氧化物插层等方式对其进行改性,提高其光催化性能。通过理论计算,X射线衍射光谱、热谱、扫描电子显微镜、紫外-可见-红外光谱和荧光光谱表征,研究K₂La₂Ti₃O₁₀光催化剂的组成—结构—合成—性质之间的关系,探讨其反应机理和光催化活性,主要内容如下:结合能带计算方法,如赝势法的第一原理计算方法,计算了K₂La₂Ti₃O₁₀的电子密度分布和能带结构等基态物理性质,其价带主要由O的2p轨道构成,导带主要由Ti的3d轨道构成,理论带隙ΔE≥3.2eV。在温和的水热条件下,通过控制反应摩尔比、晶化温度和时间以及体系矿化剂浓度等重要因素,以Ti（O-iPr）₄、La₂O₃和KOH为原料合成了亚微米级的K₂La₂Ti₃O₁₀。水热法合成的K₂La₂Ti₃O₁₀粒径小、纯度高、比表面积大、能隙为3.72 eV,光催化活性是固相合成法的2倍多,其生长机理为基元模型。采用硬脂酸法在1000℃下烧结2小时可生成纯的K₂La₂Ti₃O₁₀粒子,该法所制备的K₂La₂Ti₃O₁₀比表面积大,能隙为3.71 eV,其光催化活性接近固相合成法的3倍,通过表征,初步提出了反应历程。将适量的过渡金属V、Nb、Ta掺杂于K₂La₂Ti₃O₁₀中,获得K_2–xLa₂Ti_3–xM_xO₁₀ （M = V, Nb, Ta; x = 0.0 1.0）系列的光催化剂。当掺杂浓度增加至一定值时,K_2–xLa₂Ti_3–xM_xO₁₀ （M = V, Ta; x = 0.8 1.0）体系由Ruddlesden-Popper （RP）相转变为Dion-Jacobson （DJ）,而K_2–xLa₂Ti_3–xNb_xO₁₀体系由于Nb⁵⁺的半径与Ti⁴⁺相近,没有发生相转变。研究了过渡金属M5+浓度对K_2–xLa₂Ti_3–xM_xO₁₀能隙和催化活性的影响,当掺杂量为x = 0.1时获得最佳光催化效果。通过湿化学法有效的N将掺杂到K₂La₂Ti₃O₁₀中,K₂La₂Ti₃O₁₀–xNx样品的吸收边向可见光方向发生红移,能隙降至3.44 eV,并对其形成机理做了初步的探讨。在紫外光辐照下K₂La₂Ti₃O_10–xN_x的产H2活性大于K₂La₂Ti₃O₁₀和TiO₂（P25）,可见光照射下K₂La₂Ti₃O_10–xN_x的降解染料的催化活性要高于K₂La₂Ti₃O₁₀和TiO₂（P25）。不同有机胺的预柱撑对层状H₂La₂Ti₃O₁₀的层间距有着较大的影响,采用分子链较长的有机胺柱撑对增大H₂La₂Ti₃O₁₀层间距和半导体的插入更有利。n-C₃H₇NH₂、n-C₄H₉NH₂、n-C₆H₁₃NH₂和n-C₉H₁₉NH₂柱撑后的H₂La₂Ti₃O₁₀,其层间距分别可达到2.15纳米、2.53纳米、2.68纳米和3.15纳米。通过酸交换和预柱撑的方法,将Pt、TiO₂、Fe₂O₃和CdS等客体有效地插入到H₂La₂Ti₃O₁₀的层间,且以粒径小于1纳米的状态存在于H₂La₂Ti₃O₁₀的层状空间,构建光催化纳米插层材料,光催化性能得到进一步提高。实验结果表明,以CH3OH作为空穴清除剂,每克H₂La₂Ti₃O₁₀/（Pt, TiO₂）在紫外光辐照下5小时光解水产H2达404微摩尔;Fe₂O₃和CdS插入到H₂La₂Ti₃O₁₀层间后所形成的层状纳米复合材料不仅在紫外光辐照下有较强的光催化活性,并且在可见光辐照下也有一定的光催化水活性,每克H₂La₂Ti₃O₁₀/（Pt, Fe₂O₃）在可见光照射下5小时光解水产H2达12微摩尔;CdS插入到H₂La₂Ti₃O₁₀的层间能有效地提高其抗光腐蚀的性能;光催化剂在光解水反应中存在一个最佳使用浓度,本实验条件下,当催化剂的用量为1克时,产H2量达到最大,当用量超过这一浓度时,产H2效率又会随着用量的增加而减小。更多还原

【Abstract】 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.更多还原