摘要
随着经济的发展,环境污染尤其是水污染越来越成为全球最迫切的问题之一。由于水源安全直接威胁人类的生存,因此,治理污水已成为世界各国的共识,污水处理也由此成为各国科研工作者的重要研究内容。虽然人类已经掌握了多种处理污水的方法,但是这些存在着不同程度的成本高、降解不彻底、工艺复杂、二次污染等问题,因此探索和研究更为经济和有效的处理污水的新方法是十分有意义的。
上世纪70年代发展起来的半导体光催化是一种降解污水和净化空气的新方法,具有成本低,无毒,降解彻底等众多优点。其中纳米TiO_2光催化剂因其活性高、稳定性好、对人体无害、持续作用时间长、成本低、等优良特性,成为使用最广泛的光催化剂。但是TiO_2量子效率较低,且其只能吸收占太阳能4%的紫外光,严重制约了TiO_2光催化的应用。为了解决以上两个问题,各国研究人员提出过许多途径来提高光催化效率,如贵金属沉积、复合半导体、离子修饰、寻找替代光催化剂等。
本文主要研究以下两个方面:
(1)寻找可替代传统TiO_2的光催化剂
ZnO具有比TiO_2更高的量子效率,且无毒廉价,是有希望代替TiO_2的材料之一。银/银卤化物是基于纳米金属表面等离子体效应和半导体光催化效应的新型可见光光催化材料,其对有机染料的可见光分解速度是普通可见光光催化剂(掺氮TiO_2)的8倍,因此银/银卤化物体系也是很有希望代替TiO_2的光催化材料之一。
(2)制备三维有序大孔结构的TiO_2结构
三维有序大孔结构的良好通透性和高的比表面积对光催化非常有利,此外三维有序大孔结构具有独特的慢光子效应,如果慢光子的能量与材料的吸收所处的能量区域有交叠,那么将会导致材料光吸收的提高。因此,与普通TiO_2纳米晶相比,TiO_2三维有序大孔结构的光催化性能将有望有较大的提高。
本文的主要工作及结果如下:
(1)利用水热法制备了花型ZnO微纳结构,研究了该花型结构的形成机理及形貌演变。该花型结构的形貌可以通过调节反应时间来控制。发现所制备的花型ZnO微纳结构具有较好的光催化性能,并且热处理对其光催化性能影响很大,最佳热处理温度为200度。
(2)利用自制的二氧化硅胶体晶体,通过改进过的快速垂直沉降法制备了二氧化硅蛋白石结构模板。用四氯化钛取代钛酸四丁酯作为前驱体浸渍提拉制备了具有光子禁带的反蛋白石结构,所制备的反蛋白石结构表面光滑,裂纹很少,与传统的钛酸四丁酯前驱体提拉制备的二氧化钛反蛋白石相比有了很大的改进。同时发现可以通过调节垂直沉降的温度来控制所制备的二氧化钛反蛋白石的膜厚。
(3)用简单的方法制备了Ag@AgI复合结构,该结构是一种稳定的表面等离子体光催化剂。改变合成AgI时的反应温度,可以调节其Ag粒子的表面等离子体吸收强度,进而控制材料的光催化能力。
With the development of the economy, the environmental pollution, especially the water pollution, more and more become one of the most urgent problem of the world. Sewage treatment has already been a global consensus, as well as a research hot spot. Although various methods had been used to treat sewage, the application of these methods is restricted due to high cost, poor degradation efficiency, second-pollution and complicated technology. As a result, it is significant to develop the new method which is more economical and efficient.
The semiconductor photocatalysis is a new method of sewage treatment which was developed in 1972. It has attracted much attention for its advantages such as low cost, nontoxic, high degradation efficiency. TiO_2 nanophotocatalyst became the most widely used photocatalyst for it possesses many characteristics such as high photocatalysis activity, excellent stability, harmless to human beings, low cost and so on. However, the photocatalysis application of the TiO_2 is restricted due to the poor quantum efficiency and the fact that it could only absorb the UV light which is just the 4% of sunlight. To solve these problem, many mechods, including noble metal deposition, coupled semiconductor, ion modification, were proposed to enhance the photocatalysis efficiency by scientist.
This paper focuses to the follow two aspects:
(a) Search for the new photocatalyst which could replace the conventional TiO_2 photocatalyst.
ZnO could be a substitute for the superior quantum efficiency than TiO_2 as well as the nontoxic and cheapness. The plasmonic photocatalyst Ag@Ag halidesis is efficient and stable under visible light and is promising candidates for the development of highly efficient and stable photocatalysts active under visible light.
(b) Prepare the three-dimensionally ordered macroporous TiO_2 structure
Three-dimensionally ordered macroporous TiO_2 structure possess high surface area which is favorable for photocatalysis. In addition the slow photons effect, a characteristic of the three-dimensionally ordered macroporous structure, could enhance the optical absorption of material. Therefore, compared with the conventional TiO_2, the photocatalysis activity of three-dimensionally ordered macroporous TiO_2 structure is promising to improve largely.
The main content of my paper are as follow:
(a) The flowerlike ZnO nano/microstructures had been successfully prepared in high yield via a hydrothermal process at 95°C. The possible formation mechanism of this nano/microstructure has been proposed. Our experimental results demonstrated that the flowerlike morphology could be controlled by adjusting reaction time. Heat treatment, as well as reducing the size of the rods of flowerlike ZnO nano/microstructures could obviously enhance their photocatalytic activity. Our results demonstrated that flowerlike ZnO nano/microstructures had a promising application for photocatalytic degradation.
(b) SiO_2 opal structure was prepared by vertical deposition method. Then, TiO_2 inverse opal which has photonic band gap was obtained via dip-coating method. the tetrabutyl titanate was replaced by titanium tetrachloride to use as precursor. The prepareed inverse opal has smooth surface and few crack was observed in a large range. It is found that the film thickness of the TiO_2 inverse opal could be controlled by adjusting the deposition temperature.
(c) The plasmonic photocatalyst Ag@AgI had been successfully synthesized by a simple method. The synthesized Ag@AgI was stable under light and exhibit excellent photocatalytic activity. We found that the surface plasmonic intensity which could enhance photocatalysis activity could be controlled via adjusting the prepare reaction temperature of the AgI.
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