【作者】 周艺；

【导师】 黄可龙；

【作者基本信息】 中南大学 ， 应用化学， 2010， 博士

【摘要】 TiO2半导体纳米功能材料由于独特的光学、电学、磁学、催化与化学特性,在光电子技术领域起着越来越重要的作用,因而被广泛应用于太阳能转换、光致发光、光催化与纳米电子学等方面。纳米TiO2的合成、表征与改性已经成为TiO2半导体功能材料光电化学与光催化的核心内容,TiO2纳米材料的功能化研究一直是其应用基础研究领域的热点。针对具有重要应用背景的TiO2纳米功能材料,进行维度、尺寸、形貌与组分的综合控制以及机理研究,通过不同的制备方法来获取各种功能导向的TiO2纳米材料具有重要意义。基于此,我们展开了TiO2纳米功能材料的研究工作,通过溶胶-凝胶法、水热法、阳极氧化法以及模板法等不同的合成手段制备了不同形貌和功能的纳米TiO2材料,研究了不同形貌TiO2纳米材料(如纳米颗粒、纳米管、纳米纤维及纳米阵列薄膜)的可控合成及功能化改性影响。对上述目标合成物通过X射线衍射(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)和紫外-可见漫反射光谱(UV-Vis)等手段进行表征。采用自制的光催化反应系统对其光催化活性进行了评价；组装了TiO2染料敏化太阳能电池(DSSC),采用1.5AM的Newport太阳模拟光源测试其光电转换性能。有关研究工作如下：制备了系列掺杂的TiO2纳米颗粒、纳米纤维及纳米管,对功能掺杂TiO2纳米材料的可控制备及性能进行了深入研究。实验发现,掺杂适量稀土RE(RE为Pr,La,Gd,Ho,Nd)能够显著提高纳米TiO2的光催化活性,其催化活性与RE性质、掺杂方式及掺杂量有关,其中适量Gd掺杂样品在自然光下具有更强的催化活性；采用水热法制备了管径约为5nm,壁厚为1nm的Gd3+掺杂及B3+掺杂的TiO2纳米管,并对其微观形貌、晶型结构及光吸收性等进行表征分析,同时研究了制备工艺中的各种影响因素；以碳酸钾和二氧化钛为原料,用两步合成法,掺杂适量的Gd3+,制得掺杂的四钛酸钾纤维前驱体,在甘油溶剂中加热回流合成锐钛矿型的Gd3+掺杂TiO2纳米纤维,纤维平均长度为几十微米,直径为50nm左右,实验结果表明,Gd3+掺杂的TiO2纤维具有较高的光催化活性,自然光下对甲基橙的降解率可达70%以上；用溶胶-凝胶法制备Gd／N双元素共掺杂的纳米TiO2复合光催化材料,自然光下甲基橙为目标降解物,评价了Gd／N双元素共掺杂纳米TiO2的光催化活性,结果表明：Gd／N双元素掺杂样品为锐钛型结构,颗粒平均粒径为13nm左右,样品在可见光范围内光响应增强,Gd、N共掺杂具有协同效应,比较了几种不同的掺杂方式对Gd／N共掺杂纳米TiO2的光催化活性的影响,其中以尿素为氮掺杂源所得Gd／N共掺杂样品有较高的光催化活性,其对甲基橙的降解率达92%。在阳极氧化法制备TiO2纳米管阵列实验中,通过控制一定反应条件在纯钛表面获得了结构规整有序的纳米管阵列；在氧化过程中加入硝酸锌,控制反应条件,使纳米管负载一定量Zn2+,考察了氧化电压、温度、时间、pH值、电解液浓度及Zn2+负载等对纳米管的形貌和尺寸的影响。通过电化学工作站扫描纳米管生长过程中电流-时间曲线,对纳米管的生长过程进行量化监控,研究其生长机理；用XRD表征TiO2纳米管阵列的晶型；SEM表征纳米管阵列的形貌；交流阻抗(EIS)研究材料的光电性能。结果表明：在pH值为1,HF浓度为0.5wt%,电压为20V,氧化温度为20℃等条件下氧化2h,所得TiO2纳米管阵列晶型为锐钛型,管长70-100nm、管壁厚约10nm,管径分布均匀,无坍塌现象；交流阻抗(EIS)结果表明：Zn2+的载入减少了界面之间的阻抗,使得载流子的流动更加迅速,有利于提高光电性能。研究了PS模板法制备稀土掺杂TiO2基纳米多孔阵列薄膜。通过控制反应条件,如苯乙烯单体浓度、引发剂浓度以及表面活性剂浓度制备粒径不同、大小均一的胶体颗粒以获取具有一定孔隙结构的模板,然后采用溶胶-凝胶工艺进行组装,获得了稀土掺杂TiO2基纳米多孔阵列薄膜,并对有序多孔TiO2薄膜结构的影响因素进行了分析。结果表明,在制备过程中控制稀土掺杂浓度、占据位(晶格位、间隙位)以及TiO2前驱体的浓度可以获得高功能有序多孔TiO2薄膜。采用电化学分析测试系统对样品进行光电活性分析,分析了掺杂与TiO2多孔基质相互作用的本质因素,并用此薄膜材料组装了染料敏化太阳能电池,在模拟太阳光下进行了光电性能测试。结果表明：掺杂0.5%Gd3+的纳米TiO2在紫外及可见光区的吸收均有所增强。光电性能测试结果表明,掺杂0.5%Gd3+的有序多孔TiO2薄膜电极的短路电流为0.618mA,开路电压为0.538V,均比纯TiO2薄膜电极及有序多孔纯TiO2薄膜电极有所提高,而0.5%Gd3+、0.3%La3+共掺杂有序多孔TiO2薄膜电极由于Gd3+、La3+二者的协同作用,光电性能更优,其短路电流为0.696mA,开路电压为0.539V。分别用水热法和溶胶-凝胶法制备了Gd3+和Eu3+共掺杂纳米TiO2/MWCNT(multi-walled carbon nanotube)复合光催化剂,用SEM、TEM、FL(光致荧光光谱仪)对光催化剂进行表征,以甲基橙为目标降解物对催化剂进行活性评价。结果表明：水热法制得的复合光催化剂样品中,TiO2颗粒基本均匀分布在碳纳米管上,同时,其光催化活性也比溶胶-凝胶法制得的样品高；Gd3+和Eu2+共掺杂能有效提高其光催化活性,当Gd3+和Eu2+掺杂量为分别为0.1%和1.0%时,TiO2／MWCNT复合光催化剂具有较高的光催化活性。上述研究结果极有可能推进TiO2光电性能的提升和突破,深入研究纳米TiO2的制备工艺及其功能化改性,探讨掺杂离子与基质的作用机制,有望为探索纳米材料基质与界面中电子的传输行为、光电特性等物理性质的尺寸和维度效应等提供新的思路和理想的研究系统,同时本文的研究成果可有望为绿色能源TiO2染料敏化太阳能电池的研制以及TiO2光催化应用提供理论依据及技术支持。更多还原

【Abstract】 Titanium dioxide (TiO2) as a well-known wide band gap semiconductor, has a lot of applications such as solar energy conversion, photoluminescence, photocatalytic and nano-electronics because of its unique optical, electrical, magnetic, catalytic and chemical properties. The synthesis, characterization and modification of nano-TiO2 has become core contents in semiconductor photoelectrochemical and photocatalytic for TiO2 material application, the functionalization of TiO2 nano-materials has alwaysly been a focus research area in basic research. Preparation mechanism investigation of nano-TiO2 materials was carried out to optimize the dimensions, size, morphology and composition of nano-TiO2 materials, which has important significance to obtain functional oriented nano-TiO2 materials. Based on that state, we prepared nano-TiO2 materials with different morphologies and functions by different methods such as sol-gel, hydrothermal, anodic oxidation and template methods. Different morphologies of nano-Ti02 materials such as nano-particle, nano-tube, nano-fiber and ordered porous film were studied for the functional modification of nano-TiO2 materials. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-Vis spectroscopy were employed to characterize the structures and properties of nano-TiO2 materials. Photocatalytic activity of nano-TiO2 materials was evaluated using self-made photocatalysis reaction system. Optoelectronic property of nano-TiO2 materials was investigated under simulated solar illumination (Newport 1.5AM) by using TiO2 film an electrode in dye-sensitized solar cells (DSSC) with a sandwich structure.A series of doping TiO2 nano-particles, nano-fibers and nano-tubes were prepared with above methods. The controllability in preparation and the performance of the functional doping nano-TiO2 materials were also investigated. Experiment results showed that:(1) The RE-doped nano-TiO2 materials were prepared by sol-gel method using tetrabutyl titanate and rare-earth salts as precursors. Photocatalytic ability of nano-TiO2 materials doped with RE (Pr, La, Gd, Ho, Nd) has improved significantly. And its photocatalysis activity was closely related to different kind of RE, its adding amount and the doping approach. Among all the RE employed, Gd doped specimen compound possessed the highest photocatalysis activity. (2) The Gd3+and B3+co-doping TiO2 nanotubes prepared by hydrothermal method, where the caliber is approximately 5nm and the wall thickness is 1nm. The micro-morphology, crystalline structure and photo-absorption of the as-produced samples were also characterized. Various influence factors on preparation process were also discussed. (3) A two-step synthesis method was also used. First, Potassium tetratitanate (K2Ti4O9) nano-fibers doped with gadolinium were prepared by mixing P25 and K2CO3 with Gd(NO)3 solution through the kneading-drying-calcination method (KDC). Then, using K2Ti4O9 fibers as the precursor, the doping nano-TiO2 fiber consist of primary anatase crystallites were synthesized after dispersed in glycerine and heat treated under reflux. The average length of the formed TiO2 nano-fiber was tens of microns and the average diameter was approximately 50nm. The results showed that the TiO2 nano-fiber doped Gd3+exhibits high photocatalysis activity, the degrading rate of methyl orange could be above 70% under natural light. (4) Gd/N co-doped nano-TiO2 photocatalyst was synthesized by sol-gel method. The photocatalytic activity was evaluated by the photodegradation of methyl orange in an aqueous solution under natural light irradiation.The results indicated that Gd/N co-doped simple was anatase, had synergistic effect and increased absorption in visible range, its average particle diameter was about 13nm; Several different doping method were carried in preparation of Gd/N co-doped TiO2 samples and their photocatalytic activity was compared, the sample with urea as nitrogen source had higher photocatalytic activity than other’s, the degradation rate for methyl orange was 92%.Ordered nano-tube arrays with regular structure were prepared by the electrochemical anode oxidation method with control of certain reaction conditions. Zn (NO3)2 was added during the oxidation process to load a certain amount of Zn in the nano-tube. The influence of the oxidation voltage, temperature, time, pH value, electrolyte concentration, and content of Zn, as well as the photoelectric effect, on the structure and morphologies of the TiO2 nanotubes were investigated as well. The current-time curves scanned by an electrochemical workstation were adopted to quantitatively monitor the growth process of TiO2 nano-tube arrays and investigate their growth mechanism. Scanning electron microscopy (SEM) and x-ray diffraction spectroscopy (XRD) were applied to characterise their morphology and crystalline structures. The photo-electrochemical properties were studied by electrochemical impedance spectrum (EIS). The optimum working conditions for TiO2 nano-tube arrays were found to be pH 1,0.5wt%HF concentration, and 20 V anodized oxidation for 2 h. The produced sample was in anatase form, with a length of around 70～100 nm, a thickness of 10 nm, uniform diameter, and structure that does not collapse at the preparation conditions. The EIS results showed that TiO2 nano-tube arrays prepared with 0.5wt%HF concentration presented low resistance and the TiO2 nano-tube arrays loaded by Zn could decrease the resistance. This decrease could likely accelerate the transfer of carriers and even increase photoelectric conversion.Ordered porous TiO2 film doped with Gd3+and La3+were prepared by PS template. The influence of concentration of styrene, initiator (K2S2O8), surfactant (SDBS) to the particle size PS beads and the void structure of the template was studied. Based on the template, an ordered porous TiO2 film doped with Gd3+and La3+was deposited on a conductive glass. The results shown that rare earth dopant, the lattice of PS template and the TiO2 precursor exhibit influences on the performance of ordered porous TiO2 film. The photoelectric properties of TiO2 film were characterized by electrochemical analysis system to investigate the mechanism of dopant and TiO2. The as-produced film was used as an electrode in dye-sensitized solar cells (DSSC) with a sandwich structure. Under simulated solar illumination, a short circuit current of 0.618 mA and an open circuit voltage of 0.538 V were attained by the ordered porous TiO2 electrode doped with 0.5% Gd3+, which were better than the performances of TiO2 film electrode and ordered porous TiO2 film electrode. As the synergistic effect of Gd3+and La3+, the photoelectric properties of ordered porous TiO2 electrode co-doped with 0.5%Gd3+and 0.3%La3+is the best, which attained a short circuit current of 0.696 mA and an open circuit voltage of 0.539 V.Gd3+/Eu3+-codoped TiO2-multi walled carbon nano-tubes (Gd3+/Eu3+-codoped MWCNTs/TiO2) multiplex photocatalysts were successfully synthesized with sol-gel method and hydrothermal method respectively. SEM, TEM and FL (photoluminescence) spectra were applied to characterise their morphology and properties. Methyl orange was employed as a modal pollutant to investigate the photocatalytic activity of the obtained photocatalysts. The experiment results shown that nano-TiO2 particles distribute evenly along MWCNT in samples prepared with the hydrothermal method. Meanwhile, their photocatalysis activity is higher than that prepared with the sol-gel method. Co-doping proper proportioning Gd3+/Eu3+can increase the photocatalysis activity of multiplex photocatalyst, and the optimal dopant contents for Gd3+, Eu3+are 0.1 wt%and 1.0wt%respectively.The above mentioned results were possible to promote the photoelectric properties of TiO2 nano-materials and even make breakthrough in this filed. Studies on the preparation technology and functional modification, investigate the effect mechanism between doped ions and TiO2 matrix, which were hopeful to provide new ideas and ideal research systems for the exploration of the photoelectric properties and electron transmission between nano-materials matrix and the interface. Meanwhile, the results were hopeful to provide theoretical basis and technical support for the development of TiO2 dye-sensitized solar cells (DSSC) and the application of TiO2 nano-materials in photocatalysis filed.更多还原