【作者】 刘亚兰；

【导师】 李坚；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2009， 博士

【摘要】 室内空气质量对人们的生活和工作质量有着重要影响,有机污染物是室内空气中重要的污染源,因为甲醛、甲苯、二甲苯和VOC等是致癌物质,室内空气中有机污染物的超标将严重危害室内人员的健康,研究室内空气的有效净化与控制技术十分必要。目前,纳米TiO₂光催化技术和活性炭吸附净化技术作为净化手段,由于各自的优缺点,将两者结合起来将是室内空气净化中最具前景的技术之一。本研究采用结合理论分析和实验验证方法,对纳米TiO₂协同活性炭纤维降解室内空气中的有机污染物的效果进行了评价。采用溶胶-凝胶法和超临界流体干燥技术制成了TiO₂/ACF复合材料,在自行设计的光催化反应仓中,以甲醛为目标污染物,系统地研究和评价了各参数对TiO₂/ACF复合材料去除有机污染物性能的影响,并结合SEM和XRD技术,分析复合材料表面相貌和晶相结构,确定了TiO₂/ACF制备的最佳条件。以GC-MS联用技术检测了鉴定了复合材料对甲苯和二甲苯去除过程中所产生的中间产物的存在和种类。其研究结果和创新的学术思想如下:（1）在溶胶-凝胶制备过程中,采用超临界干燥技术,制得了具有典型气凝胶特点的二氧化钛。从而强化了TiO₂/ACF复合材料的功能。通过扫描电镜（SEM）观察,其粒径大小均匀,尺寸均在40-50nm范围内,空隙率大,具有网络结构。在自然光下为乳白色半透明块状固体,比表面积在500 m²/g以上。（2）TiO₂醇凝胶被浸渍到活性炭纤维毡（ACF）内,使ACF的每根纤维上均匀负载TiO₂醇凝胶,将负载TiO₂凝胶的ACF放入低温环境下陈化,然后置于超临界干燥器中进行干燥。通过SEM观察,活性炭纤维毡的每根纤维表面上都载有TiO₂,且呈“蛋壳”型分布,其厚度可通过浸渍后的离心时间来控制,同时在相邻纤维之间留有一定的空隙,有利于紫外光的透射。该“蛋壳”型分布,活性组分主要分布在载体的外表面上。这种分布对快速反应较为有利,能提高反应的选择性。这种技术路线设计新颖,具有创新性。（3）将TiO₂/ACF置于真空下煅烧,使处于无定形态的TiO₂向锐钛矿相和金红石相转变ACF,在450℃时保温2小时。XRD图谱表明,此时TiO₂处于混晶形态,即锐钛矿型TiO₂和金红石型相混合的形态。金红石与锐钛矿晶型的比例基本与P25相一致。（4）模拟试验结果表明,以甲醛为为目标污染物,在波长为245nm的紫外光照射下,经超临界干燥的TiO₂/ACFsd的光催化降解效果好于普通干燥方法制得的TiO₂/ACFnd的效果,当然也好于ACF的单独使用。这是由于负载了具有三维多孔的网络结构的块体材料的光催化剂（TiO₂/ACF sd）,还具有较大的孔径和空隙率,有利于有机物分子的内扩散和紫外光能的透射,当紫外光照射时激发的空穴量高,参与氧化反应的活性点位增多,提高了光催化效率。（5）试验结果表明,当甲醛浓度较高时,负载量越大,降解速度越快;而当污染物甲醛浓度较低时,负载量对污染物的降解率影响不明显。适当的负载量可以加大比表面积,光催化剂的比表面积（BET）大小顺序为:TiO₂/ACF-388>TiO₂/ACF-88>ACF>TiO₂/ACF-254>TiO₂/ACF-546>TiO_/ACF-788。同时仅一次负载即可达到较大的负载量,简化了操作工艺。（6）在光催化剂使用寿命的试验结果表明:可以重复使用而不降低使用效果。经过5次充分使用后,其光催化效果好于市售（BUY）。（7）由于优化了光催化剂的分布及其与载体的接合关系,成功的实现了ACF的吸附作用与TiO₂的光催化作用的协同效应。在控制其他污染物方面,TiO₂/ACF光催化剂的降解效果也非常显著。以VOCs为目标污染物,TiO₂/ACF在紫外光的作用下,对VOCs的降解率远远高于ACF的单独作用。以甲苯和二甲苯为目标污染物时,TiO₂/ACF光催化剂对甲苯和二甲苯的降解效果非常好,并且甲苯好于二甲苯。（8）经过色谱一质谱分析,光催化甲苯与二甲苯过程产生的中间产物可能是:（9）制备的TiO₂/ACF复合材料,除具有优越的吸附和降解室内有机污染物的功能以外,还兼有显著的消毒灭菌作用。本课题旨在研究TiO₂/ACF的制备及其光催化性能,其研究结果为净化室内空气污染物提供了新的有效途径,对提升人类生活质量和保证环境安全有着重要意义。更多还原

【Abstract】 Anatase-type Titanium dioxide （TiO₂）has attracted much attention for its potential application in decomposition of various environmental pollutants in both gaseous and liquid phases. The photocatalytic degradation systems using fine TiO₂ powder under UV irradiation have been widely investigated . However, separation of the fine TiO₂ powder from the solution after degradation is time consuming and costly . Development of TiO₂ photocatalysts anchored on supporting materials with large surface areas, by which dilute polluted substances could be condensed, would be of great significance, not only to avoid the disadvantages of filtration and suspension of fine photocatalyst particles, but to lead to high photodecomposition efficiency . Recently, supported TiO₂ photocatalysts on various porous materials were prepared by a pasting treatment,a sol-gel method,or an ionized cluster beam （ICB） method.Activated carbon fibers （ACFs） are one kind of highly microporous carbon materials, having a larger pore volume and a more uniform micropore size distribution than granular activated carbons. Generally, activated carbon fibers are considered to have larger adsorption capacity and greater rates of adsorption and desorption process than granular activated carbons. However, so far there have been only a few reports to study preparation methods and applications of activated carbon fibers supported TiO₂ photocatalysts. Reported methods of depositing TiO₂ photocatalysts on ACFs include an ionized cluster beam , an impregnation method , and a coating treatment by loading commercial TiO₂ powder on ACFs with polymer binders. Precipitation of titania coating on microporous carbon surface by a molecular adsorption-deposition method was once studied by Matsumoto et al.to modify carbon surface to improve its adsorptive properties for gases. In this paper, this method will be introduced as a new way to prepare ACFs supported TiO₂ photocatalyst with the expectation of combining the effects of high adsorption capacity of ACFs and photocatalytic reactivity of anatase-type TiO₂.In the present study, the preparation of activated carbon fibers supported TiO₂ photocatalyst and its characterization are addressed in detail. The effective photocatalytic reactivity of the photocatalyst produced has been demonstrated by its photocatalytic degradation of volatile organic compounds in air.Activated carbon fibers （ACFs） supported TiO₂ photocatalyst was successfully prepared by an sol-gel , soakage-adsorption and supercritical fluid dry method followed by calcination in vaccum.The amount of deposited TiO₂ could be adjusted by controlling the centrifugal time. Titanium dioxide was found to be loaded on almost all carbon fibers. And a combination（ TiO₂/ACFsd） had aerogel properties be obtained.The photocatalyst developed was characterized by SEM, XRD, BET surface area. SEM observation showed the particles of TiO₂ are uniform with an average size of about 40nm ,and TiO₂ was deposited on almost each carbon fiber ,and the space between adjacent fibers was remained unfilled after coating , to allow UV light to penetrate into the felt-form photocatalyst to a certain depth, to form a three-dimensional environment for photocatalytic degradation. BET surface area of TiO₂ aerogol was above 500m²/g,however , BET surface area of TiO₂ xerogel was only 0.1828 m²/g.And after the supercritical fluid CO₂ dry and calcination process, TiO₂/ACFsd could have large BET surface area, BET surface area of TiO₂/ACF-388 could be up to 1604.2 m²/g,was higher than ACF’s. As confirmed by XRD examinations, after TiCVACFsd was calcined at temperature 450℃in vaccum stove,Tight contact of thin TiO₂ coating to carbon fibers surfaces was supposed to transformation from anatase to rutile-form, and to keep high crystallinity and rate of anatase. All those exhibited the very good photocatalytic actvity of TiO₂/ACFsd, and make it very suitable for configurating an efficient photoreactor for purification of polluted water and air.The comparative experiments indicated the photocatalyst prepared had a combined effect of photocatalytic reactivity of TiO₂ with adsorptive property of activated carbon fibers. After the supercritical fluid CO₂ dry and calcination process, ,the photocatalytic activity of TiO₂/ACFsd was higher than TiO₂/ACFnd that was prepared on normal dry condition. Moreover, it can be used repeatedly without any deline as confirmed by photodegradation of formaldehyde indoor air. In addition, For the photocatalytic degradation of other organic pollutants , toluene, dimethylbenzene and VOCs , the photocatalytic activity of TiO₂/ACFsd was also effective.Therefore, the combination of photocatalytic activity of TiO₂ and ACF was effective for degration organic pollutants in air.更多还原