【作者】 陶海军；

【导师】 陶杰；

【作者基本信息】 南京航空航天大学 ， 材料加工工程， 2007， 博士

【摘要】 纳米TiO₂是一种重要的无机功能材料,在光催化降解大气和水中的污染物、染料敏化太阳能电池（DSSC）、气敏传感器、光解水等方面有着广阔的应用前景。与其它形态的TiO₂相比,TiO₂纳米管阵列具有更大的比表面积、更强的吸附能力、高效的电子传输通道,有望在提高TiO₂已知性能的同时,获得新的功能特性。因此,对TiO₂纳米管阵列的制备及应用进行系统深入的研究具有重要的实际意义。本文采用恒压阳极氧化法制备TiO₂纳米管阵列,通过FE-SEM、XRD、TEM等对纳米管阵列的形貌和结构进行表征,并研究了阳极氧化电压、时间及电解液种类对管阵列形貌、结构的影响。结果表明:对于同一电解液体系,TiO₂纳米管阵列的形成需要特定的氧化电压、时间参数范围。纳米管的平均管径、管壁厚度、管长随氧化电压的提高而增大,氧化时间只对纳米管长度有显著影响;电解液种类是获得大长径比TiO₂纳米管阵列的关键。在具有高的介电常数和粘度系数的有机电解液中,可以制备出更长的纳米管。阳极氧化法制备的TiO₂纳米管阵列为无定型态,经过热处理可获得锐钛矿、金红石等不同晶型。纳米管阵列中TiO₂的结晶过程有别于其它形态的TiO₂。管中锐钛矿晶粒在达到一定尺度后不再增大,也不转变为金红石相。只有当纳米管坍塌,管中的小尺寸锐钛矿相晶粒才会消失。此外,本文对TiO₂纳米管阵列在光催化降解甲基橙、直接甲醇燃料电池阳极电催化剂、DSSC的光阳极三个方面的应用进行了探索性研究。得出以下结论:将空气热处理的TiO₂纳米管阵列作为光催化剂,对甲基橙溶液进行光催化降解试验,研究了阳极氧化电压、氧化时间、热处理温度对光催化性能的影响。结果表明,0.5wt%HF电解液（20V、20min）中制备的TiO₂纳米管阵列400℃热处理后具有较好的光催化性能,其经高压汞灯照射40min,对10mg/L甲基橙溶液的降解率可达到99.6%。通过直流电沉积和超声辅助直流电沉积,成功制备出Pt/TiO₂纳米管阵列/Ti复合电极。沉积过程中超声波及纳米管的存在促进了Pt在电极表面的分散。同等制备条件下,超声辅助电沉积制备的Pt/TiO₂纳米管阵列/Ti复合电极对甲醇具有最强的电催化氧化能力,普通电沉积的其次,直接沉积在Ti上的最差,但它们的性能都优于同等面积的纯Pt片状电极。利用TiO₂纳米管阵列作为光阳极材料,成功组装制备了DSSC。TiO₂纳米管阵列的比表面积对电池性能有着重要影响。比表面积越大,其组装的太阳能电池的性能越好。例如,含有1vol%水的0.25wt% NH₄F/乙二醇电解液（20V、2h）中制备的大比表面积TiO₂纳米线/带/管阵列镶段复合结构,经过450℃空气热处理后,组装成的DSSC（1cm×1cm）具有最佳的光电性能(J_sc=3.53mA/cm²、V_oc=0.81V、η=1.508%)。更多还原

【Abstract】 Nano titania, an important inorganic functional material, finds wild use in the field of photocatalysis, dye-sensitized solar cells （DSSC）, gas sensing, water photolysis, and so on. Compared with any other morphologic form of titania, TiO₂ nanotube arrays are expected to exhibit novel and improved functional characteristics, due to their higher specific surface area, stronger adsorbability and efficient electron transfer path. Thus the systematical studies on the preparation and application of TiO₂ nanotube arrays have both scientific and engineering significances.TiO₂ nanotube arrays were fabricated by anodic oxidation at a constant potential in this paper. The morphology and the structure of TiO₂ nanotubes were characterized respectively by means of FE-SEM, XRD, TEM, and so on. The effects of anodic potential, anodic time and electrolyte composition on the nanotube morphology were investigated. The results indicate that TiO₂ nanotube arrays can be regularly formed at the specific anodic voltage and anodic time. Furthermore, the pore size, wall thickness and length of the nanotube become bigger with the increasing anodic voltage, while anodic time only obviously influences the nanotube length. The appropriate electrolyte is the key aspect to achieve high-aspect-ratio TiO₂ nanotube arrays. Longer nanotubes can be formed in organic electrolytes because of their large dielectric constants and coefficient of viscosities.The anatase and the rutile crystallites from amorphous as-fabricated TiO₂ nanotube arrays can be formed inside the tube walls at elevated temperatures. The crystallization process of nanotubes is different to the other morphologic form of titania. Anatase crystallite in the tubes does not transform to rutile and its size keeps unchanged at elevated temperatures after reaching a special size of anatase crystallite. The small anatase crystallites can disappear, only following the collapse of nanotube structure.Moreover, the properties of such novel nano-architecture, used for methyl orange photolysis, the anode electrocatalyst of direct methanol fuel cells, and the photoelectrode of DSSC, were investigated individually. The TiO₂ nanotube arrays were used as photocatalyst to degrade the methyl orange. The effects of anodic potential, anodic time, annealing temperature on the photocatalysis of TiO₂ nanotube arrays were also studied. The results show that TiO₂ nanotube arrays, fabricated with anodic voltage of 20V for 20 minutes in 0.5wt%HF electrolyte and then annealed at 400℃, possess a better photo-catalytic activity, i.e. 99.6% decolourisation of 10mg/L methyl orange after irradiation with high-pressure Hg-lamp for 40 minutes.Furthermore, Pt/TiO₂ nanotube arrays/Ti composite electrodes were fabricated by direct current electrodeposition with or without ultrasonic vibration. The results show that both ultrasonic vibration and nanotube array itself can promote the dispersion of Pt particles onto the electrode. The Pt/TiO₂ nanotube arrays/Ti composite electrode with ultrasonic vibration is of the best electrocatalytic property, while the Pt/TiO₂ nanotube arrays/Ti composite electrode without ultrasonic vibration is better than the Pt/Ti composite electrode. Anyway, the three kinds of composite electrodes have better electrocatalytic properties than Pt electrode with the same working area. Their high electrocatalytic activities for methanol oxidation can be attributed to the high dispersion of Pt particles.Finally, TiO₂ nanotube arrays were successfully used as photoelectrodes to build DSSC. The specific surface area of TiO₂ nanotube arrays has an important influence on the photovoltaic properties of the cells. It is found that the dye-sensitized solar cell （1cm×1cm）, composed with TiO₂ composite nanostructures prepared in 1vol% water/0.25wt% NH₄F/glycol electrolyte with an anodic voltage of 20V for 2h and annealed at 450℃, exhibits the best performance with the short-circuit photocurrent density (J_sc) 3.53mA/cm², the open-circuit photovoltage (V_oc) 0.81V, and the photo-current conversion （η） 1.508%.更多还原