【作者】 夏晓红；

【导师】 贾志杰；

【作者基本信息】 华中师范大学 ， 凝聚态物理， 2007， 博士

【摘要】 纳米技术、信息技术及生物技术将成为世纪社会经济发展的三大支柱。纳米材料是纳米技术的基础，功能纳米材料是纳米材料科学中最富有活力的领域，它对信息、生物、能源、环境、宇航等高科技领域，将产生深远的影响并具有广阔的应用前景。光催化是光化学反应的一个前沿领域，它能使许多在通常情况下难以实现的反应可以在比较温和的条件下进行，而光催化材料的开发则是通过光催化技术实现各种光催化化学反应的关键之一。纳米TiO₂光催化材料是当前最有潜力的一种光催化剂，它的优点是：光照后不发生光腐蚀，耐酸碱性好，化学性质稳定，对生物无毒性，来源丰富，能隙较大，有很强的氧化性和还原性。本文采用不同方法制备了不同形貌与结构的纳米TiO₂材料，分别用碳纳米管（CNTs）负载和用Cu²⁺掺杂两种方法来对TiO₂进行修饰，研究了光催化剂形貌、结构及修饰对其光催化性能的影响。具体总结如下：1．用五种方法制备了纳米TiO₂粉体材料，包括气相法、溶胶-凝胶法、MgO沉淀法、超声法和水热法，选择活性艳红为降解对象研究了所制备纳米TiO₂的光催化性能，得到如下结论：（1）用改进气相法制备了纯度较高的锐钛矿型TiO₂微球。反应温度越高，TiO₂颗粒越致密，尺寸均匀性越差。载气流量对产物形貌和结构的影响较小，对产量影响较大，最佳载气流量为200sccm。该方法制备的TiO₂尺寸较大，大部分为微米球，且结构致密，光催化效果差。（2）用传统的溶胶-凝胶法得到无定形小颗粒TiO₂，为提高其结晶度，改善其稳定性，需对其进行高温烧结。但烧结后TiO₂小颗粒发生了团聚，光催化效果较差。（3）对传统的溶胶-凝胶法进行改进，用MgO沉淀法制备了颗粒状的纳米TiO₂。其粒径小、分布均匀，颗粒间的团聚有所改善，光催化活性优于溶胶-凝胶法制备的TiO₂。（4）以TiCl₄为前驱体，用超声法，通过调整TiCl₄的浓度和超声时间制备了束状和棒状的金红石型纳米TiO₂。产物均匀分散，比表面积较大，热稳定性能好，束状TiO₂的光催化效率比棒状TiO₂的高。（5）采用水热法，通过调整TiCl₄的浓度、反应温度和初始压强，制备了不同形貌和结构的纳米TiO₂粉体材料。80℃加压和不加压时得到的分别是棒状锐钛矿型和颗粒状无定形TiO₂；160℃时得到的是花状锐钛矿型TiO₂；320℃时得到的是片状金红石型TiO₂。锐钛矿型TiO₂的光催化活性比金红石型TiO₂高；花状TiO₂的光催化活性比颗粒状TiO₂高，棒状TiO₂的光催化活性低于颗粒状TiO₂但高于片状TiO₂。总结上述方法制备的不同形貌和结构的TiO₂及其光催化结果，可以得出如下结论：（1）TiO₂的形貌决定其分散性和稳定性。颗粒状的产物虽然尺寸很小，表面活性高，但是易团聚；花状、束状和棒状TiO₂的分散性较好，表面积较高；片状的产物最稳定，分散性最好。（2）TiO₂的结构影响其光催化性能，锐钛矿型TiO₂的光催化活性比金红石型TiO₂高；溶胶-凝胶法制备的无定形TiO₂基本不具有光催化活性，必须经过450℃高温烧结后形成锐钛矿型TiO₂才具有光催化活性；超声法直接得到的金红石型TiO₂的束状形貌以及表面的小孔，使其光催化活性比水热法制备的金红石型TiO₂高。虽然气相法得到的产物是锐钛矿型TiO₂，但是TiO₂的尺寸太大，没有表现出优异的光催化性能。比较几种制备方法，水热法可以制备出尺寸小、分散性好、结构稳定、具有优异光催化性能的锐钛矿型TiO₂，优于其他的制备方法。2．以CNTs作载体材料，用溶胶-凝胶法制备了CNTs负载TiO₂纳米材料。首先研究了CNTs制备过程中的工艺参数，包括：裂解温度、时间、气源流量和碳源等因素对CNTs制备的影响。对于C₂H₂作碳源，Fe/Al₂O₃催化剂制备CNTs，最佳反应温度为640℃，气源流量为200sccm，反应时间为30min。用CO₂作碳源，Cr/Fe/MgO催化剂，气源流量为200sccm，反应时间为30min，裂解温度为930℃，得到的产物是纳米碳棒而不是CNTs。用水热法，以FeCl₃·6H₂O为原料，制备了直径在60-80nm，长度在200nm左右的均匀分散的棒状纳米Fe₂O₃。用该棒状Fe₂O₃作催化剂，C₂H₂作碳源，640℃制备出了直径约30nm，长度在微米级的CNTs。纯化处理后的CNTs中，棒状催化剂的残余量少于颗粒状催化剂。以TiCl₄为原料，用溶胶-凝胶法制备了CNTs负载TiO₂纳米材料，并应用于光催化还原CO₂和H₂O的实验中。结果显示，CNTs的加入提高了TiO₂的光催化效率，但CNTs加入量过多会妨碍TiO₂光催化剂对光的吸收。相对于活性炭来说，CNTs更有助于增强TiO₂的光催化活性。在循环利用过程中，CNTs负载TiO₂催化剂的光催化活性比纯TiO₂高。在CNTs负载TiO₂纳米材料的制备过程中进行水热处理有助于催化还原产物的选择，经水热处理后的催化剂能催化生成更多的甲酸，而溶胶-凝胶法制备的产物更有利于生成乙醇。3、采用Cu²⁺对TiO₂进行修饰，使TiO₂的光吸收向可见光方向扩展。用TiCl₄和CuCl₂为原料制备了Cu²⁺掺杂的金红石型TiO₂。随着Cu²⁺加入量的增加，TiO₂的晶体尺寸逐渐减小，超过20％的Cu²⁺掺杂对TiO₂的晶体结构影响和20％掺杂的样品相似。2％Cu²⁺掺杂的TiO₂的光吸收向可见光方向移动，超过5％的Cu²⁺掺杂引起了TiO₂吸收峰的蓝移。Cu²⁺的掺入有利于提高光催化降解活性艳红的效率，2％的Cu²⁺掺杂的金红石TiO₂的光催化活性最高，约为没有掺杂样品的3倍，不掺杂的样品光催化活性最低。4、以Cu（NO₃）₂和NaOH为原料，分别用溶胶-凝胶法和水热法制备了纳米CuO。与溶胶-凝胶法相比，水热法可以制备出晶格缺陷少、表面能低、自分散的片状纳米CuO。增大压力是减小纳米CuO尺寸的主要途径，适当控制溶液的pH值也有利于减小纳米CuO的尺寸。用水热法制备的纳米CuO比表面积大，用于锂离子电池负极可以提高电池的比能量；工作稳定；嵌锂平稳、脱锂容易；可克服衰减，延长电池使用寿命。更多还原

【Abstract】 Nano materials have attracted much attention since they have excellent performance in information, biology, energy, and environment. Photocatalysis is also a hot research area in recent years, because it can explode many reactions which can not take place in normal environment. The development of photocatalyst is one of the key factors to realize the photocatalytic reactions. Among the various semiconductor photocatalysts, titania is widely used because of its strong oxidizing power, absence of toxicity and long-term photostability.In this thesis, we first synthesized and investigated the photocatalytic performance of the TiO₂ with different morphology and structure prepared by chemical vapor deposition （CVD）, sol-gel, MgO deposition, ultrasonic and hydrothermal methods. And then, we studied the effect of modifying with carbon nanotubes （CNTs） and Cu²⁺ on the photocatalytic performance of TiO₂. The detailed contents are as follows:（1） Five methods were used to prepare nano TiO₂ photocatalyst and the catalysts were tested in the photocatalytic degradation of X-3B. Firstly, we prepared TiO₂ microspheres using the CVD method. At lower temperature, the spheres were composed of small rods grown from the center. At higher temperature, the rods melt together to form more smooth spheres. Since the spheres are in micrometers, the photocatalytic efficiency of them was very low. The optimal flux is 200sccm considering the quality of the product. Secondly, we had prepared TiO₂ nano particles by sol-gel method and an improve sol-gel method. The particles prepared by the sol-gel methods are very small but they agglomerated badly. The improved sol-gel method could some extent improve the photocatalytic efficiency of TiO₂ but the agglomeration still exist. Thirdly, TiO₂ nanorod and arrays were successfully prepared by the ultrasonic method, the TiO₂ arrays exhibited better photocatalytic efficiency than the TiO₂ rods since there are some small holes on the surface of the arrays which results in bigger surface area. The increase of the surface area is beneficial to promote the photocatalytic degradation of the dyes. Fourthly, we have successfully prepared TiO₂ particles, rods, flowers and sheets by hydrothermal method under acidic condition. The morphology of the samples could be controlled by adjusting the temperature, pressure and the concentration of TiCl₄. Pressure is helpful for the formation of the nanorods at 80℃and the nanoflowers at 160℃. It is also favorable for the crystallization of the as-prepared TiO₂ nanostructures. The flower-like structure has the best and the sheet-like structure shows the worst photocatalytic activity. With the increase of TiCl₄ concentration, the particle size increases and the surface area as well as the photocatalytic efficiency of the samples decrease except for the flower-like structure. In conclusion, TiO₂ with different morphology and structures were prepared by the five methods. The differences in the morphology and structure result in the differences in the photocatalytic efficiency of the products.（2） CNTs have attracted much attention since its discovery. Through the previous research results, CNTs are suitable for supporting TiO₂. So we had prepared CNTs in our lab and studied the factors affecting the preparing of CNTs.As for acetylene, iron catalyst can effectively catalyze the growth of CNTs. 640℃is the best temperature and 200sccm should be the most suitable gas flux, 30 minutes is enough for 500mg catalyst to prepare CNTs. When CO₂ was used as the carbon source, it broke to C atoms at 930℃, and the products are carbon nanorods rather than CNTs on the Fe/Cr/MgO catalyst.Rod-like Fe₂O₃ was prepared by hydrothermal method and it was used as the catalyst to prepared CNTs. XRD result shows that the product isα-Fe₂O₃ crystal and the SEM images show that they are rod-like which are about 60-80nm in diameter and 200nm in length. CNTs with diameter of about 30nm and micrometers in length were successfully produced by chemical vapor deposition method using the rod-like Fe₂O₃ catalyst. Formation mechanism of rod-like nano Fe₂O₃ was also discussed. The CNTs prepared by the rod like catalyst is easier to be purified than the particle like catalyst.The purified CNTs were then used as support for TiO₂ by sol-gel method. The CNT supported TiO₂ composites have been used as photocatalyst in the reduction of CO₂ with H₂O. The results show that the addition of CNTs could obviously improve the photocatalytic efficiency of TiO₂ and the CNTs have better effect than active carbon. C₂H₅OH can be selectively produced by the sol-gel method prepared CNT supported TiO₂, while HCOOH is the main product catalyzed by the hydrothermal treated one and P25. The CNT supported TiO₂ prepared by the sol-gel method exhibits higher efficiency than pure TiO₂ in the reusing cycles. Taking into account of the semiconducting properties of TiO₂, these CNT supported TiO₂ nanocomposites can also be applied to sensors, high-density electronic devices and lithium ion batteries as well as photocatalytic decomposition of pollutants. Moreover, the photocatalytic products CH4, HCOOH, C₂H₅OH can be reused as energy sources.（3） Cu²⁺ doped TiO₂ were prepared via a simple aqueous-phase stirring for 24h at a low temperature of 85℃, employing only TiCl₄, HCl and CuCl₂ as the starting materials. The results show that addition of copper influences the structure of TiO₂. The crystallite size decreased sharply with the increase of the copper content up to 10%. While there was no significant change in the crystallite size of titania particles as the copper content exceeded 20%. It confirms that the embedding of some portion of copper into titania particle inhibits the growth of rutile crystal of titania particles. This inhibition is correlated with the segregation of copper oxide at the boundaries of TiO₂. The embedded copper influences the photocatalytic activity of TiO₂ as well as the structure. The 2% copper-doped rutile TiO₂ exhibited relatively the highest photocatalytic activity which is about 3 times of the undoped TiO₂ in the photodegradation of aqueous brilliant red X-3B solution. The imbedding of the 2% Cu²⁺ also caused the red-shift of the absorption of TiO₂. Excessive of Cu²⁺ imbedding could not promote the photocatalytic efficiency of TiO₂, which also should be due to the morphology and structure of the TiO₂ photocatalyst.（4） Nano CuO was prepared by hydrothermal method using Cu（NO₃）₂ and NaOH as the source materials. Particle like CuO prepared by sol-gel method was also used for compare. The morphology of the sheet like CuO kept stable after 500℃sintering, while the particle like CuO agglomerated even after 200℃sintering. And the sheet like CuO has larger surface area and dispersed better than the particle like CuO. The two kinds of CuO were used in the negative electrode of Li-ion battery. The Li-ion battery using sheet like CuO as the negative electrode has higher specific energy and worked more stable than using the particle like CuO.更多还原