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基于ZnO的甲醛光降解反应微观机理研究
李玲
学位类型硕士
导师王传义
2017-05-28
学位授予单位中国科学院大学
学位授予地点北京
学位专业物理化学
关键词光降解 氧化锌 甲醛 氧气
摘要

近年来,随着现代工业的不断发展,大量与甲醛相关的工业产品(如粘合剂,复合木质产品等)出现在我们的生活中,室内甲醛污染已经成为人们生活中无法回避的威胁。甲醛对人体的神经系统及呼吸系统有很强的刺激作用,并且具有致癌、致敏、破坏免疫系统等危害。如何有效快速的降解室内甲醛已经成为人们研究的热点。半导体光催化技术由于可以直接利用太阳能且没有二次污染等优点,在环境污染治理等领域得到了广泛的应用,被认为是最有前景的环境净化技术之一。而作为二氧化钛以外最常用的光催化剂之一,氧化锌(ZnO)由于具有合适的带隙,良好的电子迁移率与化学稳定性,以及较好的甲醛吸附能力等特点,使其在光催化降解甲醛研究中备受关注。本论文采用溶胶-凝胶法(sol-gel)制备纳米ZnO和Ag复合的ZnO(Ag/ZnO)样品,并研究了不同条件对纳米ZnO表面发生的甲醛光催化降解微观过程的影响,研究内容主要包括:(1)纳米ZnO不同煅烧(或真空退火)温度的影响实验中我们发现,制备过程中的不同煅烧温度或者在真空环境下的退火对ZnO晶面分布及光催化降解甲醛效率有着显著的影响。高温退火使ZnO纳米颗粒表面暴露的极性面减少,非极性面增多。由于极性方向上光生电子-空穴对更容易分离,甲醛在ZnO极性面上表现出优于非极性面的光催化活性。(2)环境的影响这部分工作中我们研究了不同浓度氧气、水蒸气以及反应温度对ZnO光催化降解甲醛的影响。气相水主要是以吸附在样品表面的羟基形式参与反应,由于光催化反应过程中产生的羟基自由基较低的移动性,水蒸气对光催化降解甲醛没有明显的促进作用;而氧气则是以光活化的氧直接参与反应,氧气压力的提高可以显著提高光催化效率。另外,在不同反应温度下所得到的结果表明,在ZnO表面发生的光催化降解甲醛反应最佳温度是323 K,说明在反应温度为323 K以下时,电子-空穴的分离与迁移过程是整个反应的速控步骤,而在反应温度为323 K以上时,电子/空穴参与的表面反应为整个反应的速控步骤。(3)金属复合的影响通过研究不同含量Ag修饰的ZnO对光催化降解甲醛的影响,发现Ag的修饰提高了ZnO在可见光区的光吸收;在323 K,PCH2O:PO2=1:30(PCH2O=5 mbar)条件下ZnO-2%Ag光催化降解甲醛的反应活性最好。

其他摘要

With the fast development of industry related with formaldehyde in recent years, indoor air pollution has become one of the major threats to human health as the formaldehyde being the typical case. Formaldehyde can cause serious health problems, such as immune system damagement, cancer and sensitization hazards etc. So, it’s a relevant issue to carry out research work on removing gaseous formaldehyde.Photocatalytic technique is one of the promising methods to remove gaseous pollutants with a lot of superiorities such as utilizing the natural energy of sunlight, no secondary pollution to the environment and sustainable development. As a popular photocatalyst in addition to TiO2, ZnO has suitable bandgap (3.3 eV), large excitonic binding energy (60 meV), high carrier mobility and well formaldehyde adsorption ability, which makes ZnO very unique in photocatalytic degradation of gaseous formaldehyde.In this thesis, nano-sized ZnO sample was synthetized by sol-gel method. The photocatalytic degradation of gaseous formaldehyde under different conditions has been systematically studied:(1) effect of annealing (calcining) temperature It was found that annealing the ZnO nanoparticles at high temperature results in a slight redistribution of crystal faces with partial transformation from polar to nonpolar facets. Compared to the nonpolar facets on ZnO, the polar facets exhibit higher photoactivities toward formaldehyde photocatalytic degradation, revealing that photoactivity can be strongly affected by facet polarities.(2) the influence of environmentIn this part we focused on the influence of the coexistence of oxygen and steam on the photocatalytic degradation efficiency. It was found that formaldehyde adsorbed on ZnO nanoparticles can be oxidized to carbon dioxide under UV light irradiation with the coexistence of either oxygen or steam. However, different from aqueous condition where water molecules are first oxidized to be free radicals then react with formaldehyde, direct photoactivation of oxygen becomes the dominant step in promoting photocatalytic degradation efficiency of gaseous formaldehyde. In addition, we have studied the temperature dependence of the photocatalytic reaction and found that the optimized temperature for photocatalytic removing of gaseous formaldehyde was 323 K, indicating that the rate determining step below 323 K was the separation of electron hole pairs and above 323 K the surface reaction induced by electron/holes.(3) the influence of silver modification on ZnO nanoparticlesIt was found that the modification of silver particles notably improve the light absorption in visible light region. A systematic comparison study of different molar ratio of silver reveals that the best photocatalytic efficiency comes from the ZnO-2%Ag sample with PCH2O:PO2=1:30(PCH2O=5 mbar)under 323 K.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4979
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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李玲. 基于ZnO的甲醛光降解反应微观机理研究[D]. 北京. 中国科学院大学,2017.
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