【作者】 高强；

【导师】 周曦亚； 樊粤明；

【作者基本信息】 华南理工大学 ， 材料学， 2014， 博士

【摘要】 现阶段能源危机和环境污染已成为人类面临和亟待解决的重大课题。TiO2纳米材料的出现提供了一种有效的解决能源和环境问题的新思路。由于TiO2具有光催化、光电转换、高反射率等性质，使其在环境净化、光电池、传感器及涂料等方面拥有重要的应用价值。TiO2基光催化材料可以直接利用太阳光降解空气和水中的污染物,是解决环境问题的重要手段之一,具有巨大的应用潜力；而TiO2基高反射颜料在隔热涂料中的应用则是降低炎热地区建筑物空调能耗的有效手段。但是TiO2光催化降解污染物在实际应用中遇到一些认识或技术难题，如金红石氧化钛光催化活性为什么较低；氧化钛光响应范围较窄，不能有效利用太阳光；光催化剂回收困难等问题。此外，氧化钛薄膜的组成、微结构与太阳光谱反射率关系的理论研究尚不完善，也阻碍了氧化钛基反射隔热材料性能的提高。本论文采用非均相化学沉淀法在云母表面构筑了不同组成和微结构的纳米氧化钛薄膜，系统研究了氧化钛薄膜的组成（晶型）、微结构对光催化性能、漫反射性能以及润湿性的影响。具体内容包括以下几个方面。第一，云母表面锐钛矿氧化钛薄膜的构筑及其性能的研究。系统研究了pH值对云母表面氧化钛薄膜组成和成膜方式的影响，对比了钛源浓度和负载量对薄膜组成、微结构和紫外光催化性能的影响。研究发现，在pH值在1~7的范围内，均会生成锐钛矿型的纳米氧化钛薄膜。但pH值对氧化钛纳米粒子在云母表面的沉积方式有较大的影响：当pH为1时，非均匀成核占优，氧化钛纳米颗粒在云母表面整齐排列形成薄膜；而当pH为3~7时，均匀成核占优，氧化钛纳米颗粒会在云母表面堆积形成零星岛状聚集体。随着钛盐浓度的降低氧化钛薄膜的颗粒尺寸明显变小，样品的紫外光催化活性逐渐增强，尤其是钛酸四丁酯浓度为1/400时所合成样品的光催化降解常数是P25的2.2倍。随着氧化钛负载量的增加，氧化钛薄膜的光催化性能呈现先增强后降低的趋势。对于云母负载锐钛矿型氧化钛，氧化钛负载量为10%时光催化活性最强。第二，云母表面成核剂的预沉积对薄膜组成的影响。在云母表面预先沉积了SnO2、MnO2或Fe2O3做成核剂，研究了成核剂的种类和用量对薄膜组成的影响。通过预先在云母表面沉积SnO2或MnO2作成核剂，可在70℃的低温下构筑出结晶良好的金红石型氧化钛薄膜。通过控制SnO2（或MnO2）与云母的质量比，可以构筑出不同锐钛矿、金红石比例的氧化钛薄膜。而Fe2O3的预沉积只能得到混晶氧化钛。SnO2或MnO2能够促进金红石型氧化钛低温形成的机理在于金红石型TiO2与SnO2或MnO2沿a轴和c轴方向的晶格常数非常接近。因此，SnO2或MnO2可以作为金红石型氧化钛的成核剂，大大降低了金红石氧化钛晶核的成核位垒，促进金红石TiO2的成核生长。第三，云母表面成核剂的预沉积对薄膜微结构的影响。通过控制成核剂种类和用量、四氯化钛乙醇溶液的用量可以制备出不同微结构的氧化钛薄膜，并揭示出了不同微结构氧化钛薄膜的生长机制。SnO2的预沉积可以获得单分散的纳米棒状或纳米花状的金红石氧化钛薄膜，MnO2的预沉积可以获得纳米颗粒、纳米棒以及纳米花组成的金红石氧化钛薄膜，Fe2O3的预沉积可以获得颗粒状、片状、花瓣状等多种形貌的混晶氧化钛薄膜。此外，Fe2O3预沉积形成的氧化钛薄膜中金红石纳米棒表面还附着了许多1~3nm的无定型态突起。第四，薄膜组成和微结构对其光学性能的影响。SnO2预沉积获得的低温金红石氧化钛薄膜在400~1300nm的可见光区和近红外区具有比锐钛矿氧化钛薄膜更高的反射率，而在紫外区则具备更强的紫外线吸收能力。云母表面金红石型氧化钛的负载量和颗粒尺寸对薄膜漫反射性能有较大的影响。随着金红石氧化钛负载量的增大，薄膜的紫外-可见反射光谱出现了明显的红移，能隙由2.85eV增大到2.95eV。在400~700nm的可见光区，薄膜的反射率随金红石TiO2负载量的增大而增大；而在1300~2500nm的近红外光区，薄膜的反射率随金红石TiO2负载量的增大而降低。这是由于随着负载量的增大，金红石型氧化钛的颗粒尺寸逐渐增大。根据K-M理论，当氧化钛颗粒尺寸增大时，颗粒边界处的反射就会减少，从而导致散射系数减小，进而导致在1300~2500nm的近红外光区的反射率降低。而MnO2、Fe2O3的预沉积则使薄膜出现了明显的可见光吸收，该波段的吸收可以归因于Mn4+、Fe3+离子的d-d跃迁。第五，薄膜组成和微结构对其光催化性能的影响。在SnO2预沉积的情况下，金红石型TiO2薄膜的紫外光光催化活性高于锐钛矿TiO2薄膜和P25；而MnO2的预沉积则明显降低了薄膜的紫外光催化活性，所得金红石薄膜的光催化降解常数只有锐钛矿薄膜的74%。这是由于金红石TiO2在成核剂SnO2或MnO2表面成核生长，在两者的界面处形成了TiO2/SnO2或TiO2/MnO2复合半导体结构。TiO2/SnO2复合半导体结构有效促进了电子和空穴的分离，从而促进了金红石氧化钛薄膜紫外光催化活性的提高；TiO2/MnO2复合半导体结构促使了电子、空穴的复合，导致金红石氧化钛薄膜紫外光催化活性较低。Fe2O3的预沉积对混晶TiO2薄膜在可见光下的催化活性影响很大。低Fe2O3沉积量下，可见光催化活性随Fe2O3沉积量增加而增强，但Fe2O3沉积量太大催化活性反而下降。在制备样品中mica-1.47%Fe2O3-TiO2具有最强的可见光光催化活性，其光催化降解常数是P25的9.1倍，这是由于Fe2O3附着在TiO2晶体表面改变了可见光下光激发路径，光生电子从Fe2O3d子带激发到二氧化钛导带上引发了光催化反应。第六，薄膜微结构对其润湿性的影响。通过控制云母表面金红石氧化钛薄膜的粗糙度和表面羟基含量可以构筑出不同亲水程度的表面（无紫外光激发条件下）。mica-2.07%MnO2-TiO2经过800℃煅烧后，金红石薄膜的粗糙度增加了0.6倍，并且表面羟基含量增加了5.5%，使得样品由亲水状态变为超亲水状态（无紫外光激发条件下）。此外，该超亲水表面能够在黑暗条件下长时间的保持超亲水性。更多还原

【Abstract】 Nowadays, energy and environmental issues are the biggest challenges. TiO2basedmaterials exhibit great potentials in environmental protection and solar energyconversion. Due to their physical properties of photocatalytic activities, photoelectricconversion characteristics, and high reflectance properties, TiO2have been widelyused in environment purification system, solar cells, sensors and coatings. TiO2basedphotocatalytic materials can decompose pollutes in water and air with the help ofsolar irradiation, making them good candidates for environment purification. Besides,it’s an effective way to apply TiO2based reflective materials to reduce the energyconsumption of air conditioning in Southern China. However, owing to its lowquantum efficiency and relatively wide band gap, which can only absorb the UV light,their practical applications are restricted. What’s more, the theory study ofrelationships between compositon, structure and solar reflectance of TiO2is notthorough, which restricts the improving of reflectance properties of TiO2.In this dissertation, we constructed TiO2coatings on mica substrates with differentcompositions and microstructures, and study the effect of compositions andmicrostructures on the photocatalytic properties, reflectance properties and wettingability. The main points could be summarized as following.Firstly, anatase TiO2was coated onto mica substrates. We studied the effect ofconcentration and TiO2loading on constitutions, microstructures and photocatalyticproperties of TiO2coated mica particles. The results showed that anatase TiO2coatings could be obtained at pH of1to7and pH showed a great influence on themicrostructure of TiO2coatings. TiO2coating composed of nanoparticles could beprepared at low pH, while island-shaped TiO2coating could be prepared at high pH.Raman spectra verified that Si-O-Ti and Al-O-Ti formed between the interface ofmica and TiO2coating, which leaded to the close coating of TiO2onto mica. Particlesize decreases as the decrease of concentration, leading to the increase ofphtocatalytic properties. What’s more, the photocatalytic activities increased firstlyand then dropped with increasing TiO2loadings. Secondly, effect of prior deposition of metal dioxides on the phase compositons ofTiO2coatings. Rutile TiO2coated mica particles were prepared by hydrosis of TiCl4ethanolic solution in water at70℃with a prior depositon of SnO2or MnO2. Wecould control the ratio of anatase to rutile by controlling the mass ratio of SnO2(orMnO2) to mica. The rutile promoting effects of SnO2or MnO2could be ascribed tothe structural similarity of rutile and cassiterite (or pyrolusite). Besides, the priordepositon of Fe2O3lead to the formation of mixed-phase TiO2.Thirdly, effect of prior deposition of metal dioxides on the microstructures of TiO2coatings. The various microstructures of TiO2coatings could be obtained by adjustingthe usage of seed and TiCl4ethanolic solution. The prior depositon of SnO2lead to theformation of nanorod-like or nanoflower-like rutile TiO2coatings, the prior depositonof rutile TiO2coating composed of nanoparticles, nanaorods and nanoflowers, whilethe prior depositon of Fe2O3lead to the formation of nanorod-like, nanoplate-like ornanoflower-like rutile TiO2coatings. MnO2lead to the formation of nanorod-like ornanoflower-like rutile TiO2coatings. Moreover, amorphous Fe2O3were absorbed onthe surface of rutile TiO2nanorods after the prior depositon of Fe2O3.Fourthly, effect of phase compositions and microstructures on the optical propertiesof TiO2coatings. Rutile TiO2showed stronger UV shielding ability and higher NIRreflectance compared to anatase TiO2. We studied the effect of rutile TiO2loadings onthe band gap, visible reflectance and NIR reflectance. The decrease of TiO2loadingleads to the increase of reflectance in the region of1300-2500nm. This increasedreflectance property can be ascribed to a decrease in the mean particle size inaccordance with the KM theory.The results showed that the particle size andmorphology had a great influence on the photocatalytic properties. Besidew, the priordepositon of MnO2or Fe2O3lead to obvious visible absorbance due to the d-dtransition of Mn4+or Fe3+.Fifthly, effect of phase compositions and microstructures on the photocatalyticproperties of TiO2coatings. Due to the different band structures of TiO2/SnO2orTiO2/MnO2, the prior depositon of SnO2lead to the high photocatalytic properties ofrutile TiO2, while the prior deposition of MnO2lead to the low photocatalytic properties of rutile TiO2. The band structures of TiO2/SnO2favored the separation ofelectrons and holes, leading to the high photocatalytic properties of rutile TiO2coating.The band structures of TiO2/MnO2favored the recombine of electrons and holes,leading to the low photocatalytic properties of rutile TiO2coating. The priordeposition of Fe2O3also had a great influence on the photocatalytic activity of thesamples under visible irradiation. The photocatalytic activity increased firstly andthen dropped with increasing Fe2O3loadings. mica-1.47%Fe2O3-TiO2showed thestrongest visible photocatalytic property, which was almost9.1times as high as thatof Degussa P25. The high visible photocatalytic activity could be ascribed to thetransition of electron from d sub-band of Fe2O3to the conduct band of TiO2undervisible irradiation.Sixthly, effect of phase compositions and microstructures on the wettabilities ofTiO2coatings. Interestingly, rutile TiO2coated mica particles can be directly appliedas a general kind of building blocks to construct large-area superhydrophilic surfaceswithout UV irradiation by the simple spin-coating technique. The superhydrophilicityoriginates from the combination of the special rough structures of hierarchicalnanorods and nonoflowers and the increased hydroxyl content caused by calcinations.More importantly, this property is very stable for half a year and could be used inself-cleaning surfaces.更多还原