【作者】 田国辉；

【导师】 付宏刚；

【作者基本信息】 黑龙江大学 ， 无机化学， 2008， 博士

【摘要】 近年来,半导体催化剂因其在空气净化、有害污染物治理和水清洁等环境方面的广泛应用而备受关注。在众多的半导体氧化物光催化剂中,TiO₂因其氧化能力强、廉价、物理化学性质稳定而成为被广泛应用的光催化剂之一。然而,TiO₂在实际应用中仍然存在着量子效率和可见光利用率低等问题,极大的限制了TiO₂的发展。本论文针对TiO₂光催化领域存在的这些问题,通过改善合成方法和优化实验条件制备出不同系列的光催化剂,研究了晶相结构、比表面积等性质对光催化活性的影响本质,为进一步发展高活性纳米TiO₂光催化剂的制备方法积累经验。本论文的主要内容如下:发展了以十六烷基三甲基溴化铵（CTAB）和氨水协同作用制备高活性纳米TiO₂光催化剂的方法。用该方法制备的TiO₂具有小晶粒、大比表面积、晶化程度高的优点,从而大大提高了光催化剂的催化活性。这种方法是在钛酸四丁酯水解得到的纳米晶和CTAB共存的条件下,经过水热和氨水回流处理,焙烧后制得小晶粒尺寸、大比表面积、晶化程度好的高活性纳米TiO₂光催化剂。在制备的过程中,CTAB抑制纳米粒子聚集并组装TiO₂纳米晶,氨水除与TiO₂纳米粒子有较强的相互作用外,在回流处理过程中还增强了CTAB与TiO₂纳米粒子的相互作用,这种CTAB与氨水间的协同作用极大地阻碍了TiO₂纳米粒子间的进一步接触,提高了TiO₂的热稳定性,抑制了在焙烧过程中晶粒的增长、聚集、比表面积降低和相转变的发生,使TiO₂在保持较小晶粒和较大比表面积的同时,仍然具有较适宜的晶化度,通过这种方法制备的TiO₂显示出了比Degussa P25更高的光催化活性。发展了CTAB和乙二胺协同作用制备高活性纳米TiO₂光催化剂的方法。采用这种方法同样制备了小晶粒、大比表面积、晶化程度高的纳米TiO₂,这种方法中用乙二胺代替氨水主要是为了克服氨水易分解、成本高以及所带来的操作繁琐等缺点,并对CTAB和乙二胺协同作用制备高活性纳米TiO₂的合成机理进行了分析。所制备的纳米TiO₂的光催化活性显著高于Degussa P25,这为进一步制备高活性的纳米TiO₂提供了新的合成思路。发展了改变溶剂极性制备晶相组成可控的介孔TiO₂的合成方法。该方法通过改变溶剂的极性（水和乙醇的比例）制备了纯锐钛矿以及锐钛矿和板钛矿比例可调的一系列介孔TiO₂。结果表明溶剂极性的不同会引起TiO₂中锐钛矿和板钛矿的相对含量、晶粒尺寸和比表面积的变化,研究了晶相结构、组成、比表面积等性质对光催化活性的影响。发展了以高热稳定性、小晶粒、大比表面积TiO₂作为原材料制备氮掺杂TiO₂可见光催化剂的方法。这种方法是将按照本论文第5章的实验方法制备的锐钛矿TiO₂在空气中800℃焙烧后直接降至某一温度,通入NH3/N2的混合气,并在此温度下保持一定时间制备了氮掺杂TiO₂。结果表明,该方法可以有效地掺氮而同时保持原有的锐钛矿结构以及小晶粒、大比表面积的优点。氮掺杂后的TiO₂明显拓展了可见光响应范围,制备的适当氮掺杂量的TiO₂在保持较高的紫外光催化活性的基础上显著提高了可见光催化活性,显现出比同样条件下进行氮掺杂的Degussa P25高很多的光催化活性。发展了ZrO₂改性的硫掺杂介孔TiO₂可见光催化剂的制备方法。该方法是在蒸发诱导自组装的基础上,通过加入硫脲和氧氯化锆制得具有可见光响应的硫掺杂介孔TiO₂,而ZrO₂的引入则显著的抑制了晶粒的生长和聚集,阻碍了锐钛矿向金红石的转变,同时也抑制了硫元素在焙烧时的过度损失。因此,所制备的ZrO₂改性的硫掺杂TiO₂相对于未改性的硫掺杂TiO₂具有更小的粒径、更大的比表面积和孔体积,并显示出比未改性的硫掺杂TiO₂更高的可见光响应和催化活性。更多还原

【Abstract】 In recent years, a great deal of effort has been devoted to developing heterogeneous semiconductor photocatalysts with high photocatalytic activity for their wide environmental applications such as air purication, water disinfection, hazardous waste remediation and water purication. Among various oxide semiconductor photocatalysts, titanium dioxide has been proved to be one of the best photocatalysts due to its high oxidative ability, cost-effectiveness, physical and chemical inertness for widespread environmental applications. However, there still remain some problems in practical applications, such as the preparation of photocatalyst with high photocatalytic activity, the light utilization ratio. The photocatalytic activity of titania must be further enhanced from the point of practical use and commerce. In the present work, aiming at the the existing problems,we try to improve on the fabrication methods and conditions so as to synthesize a serial of TiO₂ photocatalyst with high photocatalytic activity. Lots of studies were done to explain the effect of crystal structure, surface area and other properties on the photocatalytic activity. This can accumulate experience for the development of synthetic methods of high photocatalytic activity. The main results of the present work were as follows:A method was developed to prepare superior photoactive TiO₂ nanopowders under synergistic effect of CTAB and ammonia. The prepared TiO₂ has a characteristic of small crystal size, large surface area and high crystallinity, which can improve the photocatalytic activity. In this method, nano TiO₂ particles were synthesized by a hydrothermal process in the presence of cetyltrimethylammonium bromide （CTAB） and a post-treatment with ammonia. During the hydrothermal process, CTAB can make the agglomeration resulting from the amorphous phase after the hydrolysis dispersed, along with the transformation from amorphous to TiO₂ crystallites, and further induce the assembly of the as-prepared TiO₂ crystallites to form mesoporous titania. The ammonia post treatment can maintain the porous structure and suppress the phase transformation from anatase to rutile, moreover, there is a synergistic effect of CTAB and ammonia. All the effects make it possible to obtain nano-sized TiO₂ simultaneously with fine particle size and high crystallinity. The photocatalytic activity of prepared photocatalysts was obviously higher than that of commercial Degussa P25, and therefore is a promising photocatalyst with high photocatalytic performance.A method was developed to prepare superior photoactive TiO₂ nanopowders under synergistic effect of CTAB and ethylenediamine. The prepared TiO₂ also has a characteristic of small crystal size, large surface area and high crystallinity. It is well known that ammonia is alkalescent, not stable, and apt to decompose during the refluxing treatment; this would bring much discommodity to the work. To overcome the shortcomings of ammonia, ethylenediamine was used as a base during the post treatment. Stable porous TiO₂ photocatalysts, with higher photocatalytic activity than Degussa P25, were also synthesized via a hydrothermal process using CTAB as the template, the post-treatment considerably increased the thermal stability of the porous framework and inhibited the undesirable grain growth and phase transformation during calcinations, and one possible formation mechanism of the stable porous titania was proposed. This work may provide a new insight into preparing high photoactive TiO₂ photocatalysts. A method was developed to prepare a series of TiO₂ samples with stable, controllable crystalline phase content mesoporous TiO₂ by means of the change of solvent polarity. Results demonstrate that crystal phase content of anatase and brookite, particle size can vary with the change of solvent polarity （H2O/EtOH ratios）. The effects of crystal structure, composition and surface area on the photocatalytic activity were also studied. A method was developed to prepare nitrogen doped TiO₂ with visible light activity on the basis of TiO₂ with high thermal stability, large surface area and small crystal size. Nitrogen doped TiO₂ powders were prepared by annealing anatase TiO₂ at 800℃in air, subsequently under NH3/N2 flow in a suitable temperature for a certain time. The results revealed that, a proper nitrogen concentration can enhance photocatalytic activity, the catalyst prepared at the best condition showed higher photocatalytic activity than the nitrogen doped Degussa P25 under the same condition.ZrO₂ modified mesoporous S-TiO₂ has been successfully synthesized via the evaporation-induced self-assembly （EISA） in the presence of Thiourea and zirconium oxychloride. Results revealed that Sulphor was doped into the lattice of TiO₂ by the thermal treatment of mixed TiO₂ gels, converting the TiO₂ into a visible-light responsive catalyst. The introduction of ZrO₂ strongly inhibited the undesirable crystallite growth and aggregation, and the crystal phase transformation from anatase-to-rutile structure. Consequently, the ZrO₂ modified S-TiO₂ showed larger BET surface area, higher pore volume, and an improved thermal stability over the corresponding unmodified S-TiO₂ sample. The photocatalytic activity of mesoporous ZrO₂ modified S-TiO₂ composites was superior than that of unmodified S-TiO₂ under visible light irridiation.更多还原