载银纳米TiO₂-Al₂O₃球粒光催化室内甲醛的研究

【作者】 陈小开；

【导师】 彭兵；

【作者基本信息】 中南大学 ， 环境工程， 2006， 硕士

【摘要】 室内空气污染是当今人们最关注的重要环境问题之一，HCHO是一种无色的具有强烈刺激性的有毒气体，为引起室内空气污染的最主要的物质，对人体健康的危害极大。目前治理室内空气甲醛污染的方法有吸附法、纳米TiO₂光催化技术、臭氧催化（O₃／Catalysis）技术、非平衡等离子体技术、植物净化法等等，每一种方法都有缺点且效果不是很明显。本研究基于吸附和光催化的原理，首次将氧化铝球粒的优良吸附性能、纳米二氧化钛的光催化性能、银离子的光催化促进功能，很好地结合起来，制备出一种兼有吸附及光催化双重功能的载银纳米TiO₂-Al₂O₃球粒，用于光催化降解甲醛；获得了一些创新性成果，主要体现在：1)以活性氧化铝和二氧化硅为主要原料，添加助烧剂（氧化镁）、成孔剂（碳酸氢铵）、粘结剂（羧甲基纤维素纳），控制AL₂O₃、SiO₂、MgO、NH₄HCO₃和CMCNa的含量分别为60％、10％、5％、20％和5％，制备出粒径为5mm的球粒，在1150℃烧结获得具有良好吸附性能的产品；再通过浸渍载银纳米TiO₂在400℃温度下焙烧活化，得到兼有吸附及催化功能的最终产品。通过扫描电镜分析，产品内部的微孔很发达，孔的形态不太规则；孔隙分布比较均匀，内表面凹凸不平，具有很高的比表面；孔径大致呈三个系列分布，微孔由二部分构成，其中大气孔为造孔剂碳酸氢铵受热分解或矿化剂分解所致。2)确定了与甲醛光催化降解相关的因素有：电光源功率、活化温度、活化时间和载银量。当银的掺杂量为1.0％，焙烧活化温度为400℃所得的载银纳米TiO₂-Al₂O₃球粒的光催化性能最好，其原因是在400℃的焙烧温度下，掺杂的Ag⁺可提供电子、空穴的浅势捕获陷阱，同时抑制电子和空穴的复合，有利于提高纳米TiO₂的光催化性能，光催化降解甲醛的效率可达到90％以上。3)初步探讨了球粒吸附催化甲醛的机理，HCHO在Al₂O₃上的吸附等温线可分成三段，（I）低压时，吸附量与气体分压成正比，压力的影响十分显著：（Ⅱ）压力升高，吸附量的增加开始变慢，而且出现转折；（Ⅲ）当压力达到足够高时，曲线近于水平，吸附渐趋饱和。等温线的这种形态的改变应当归因于单分子层吸附的完成。光催化反应机理是甲醛通过光催化降解反应过程中生成的中间产物甲酸，进一步被氧化为二氧化碳和水。更多还原

【Abstract】 Indoor air pollution is one of the most concerned environmentalproblems. Air pollutant formaldehyde is a colorless and strongly incentivepoisonous gas, which is harmful to human health. Some methodsfrequently used to treat the pollution of indoor HCHO are adsorption,photocatalytic degradation, o₃/catalysis, non-equilibrium plasma andplant removal. But every one of them has some drawbacks and its effectis not strong.The experiment based on the principle of adsorption andphotocatalysis was conducted by combining excellent adsorbingcapability of alumina with photocatalytic capability of nano-TiO₂improved by Ag⁺ to produce an adsorbing and photocatalysising silverloaded spheroid of TiO₂-Al₂O₃. It could be used to degradateformaldehyde by photocatalysising and the achievements obtained in thisstudy were as follows:1) Al₂O₃ and SiO₂ are primary materials with some helping sinterreagent （MgO）, holing reagent （NH₄HCO₃） and felting reagent （CMCNa）in the product. Under the content of Al₂O₃, SiO₂, MgO, NH₄HCO₃ andCMCNa 60％, 10％, 5％, 20％and 5％respectively, diameter ofspheroid 5mm treated at 1150℃, an excellent adsorbing capability ofalumina particle was achieved successfully and then loaded TiO₂ on thespheroid by thermal treated at 400℃. There were many different shapesof small uniformal holes present in alumina particle. The holes weredistributed in the interior and exterior facies. Aperture showed three seriesdistribution, small hole constitute with two parts and decomposingNH₄HCO₃ and mineration reagent bring about the large hole.2) It was found in this study that the factores influencingphotocatalytic degradation were strength of light, activated temperatureand activated time. The result showed the silver loaded spheroid ofTiO₂-Al₂O₃ had fairly good quality and the degradation percentage offormaldehyde was over 90％after treated at 400℃and silver loaded just1％. Silver loaded could prevent complex between electrons and cavitys, which improved photocatalytic capability of nano-TiO₂.3) Tish paper delivered an elementarily discussion about themechanism of the alumina granule adsorbing and photocatalyticdegrading formaldehyde. There are three status in adsorption isotherm ofHCHO on the surface of Al₂O₃. （Ⅰ） The pressure is strongly affected theadsorption capacity under low pressure condition. （Ⅱ） Adsorptioncapacity increases and transition appears at high pressure. （Ⅲ）Adsorption isotherm gets to a high level when the pressure becomes highenough, and then the adsorption is in saturated condition. The chang ofconfiguration of adsorption isotherm attributes to achievement of thesingle molecule adsorption. HCHO is photocatalytically degraded to CO₂and H₂O through the middle outcome HCOOH.更多还原