【作者】 孙秀云；

【导师】 王连军；

【作者基本信息】 南京理工大学 ， 环境工程， 2007， 博士

【摘要】 二氧化钛光催化作为一种高级氧化技术，正被广泛深入研究，研究的核心内容集中在TiO₂催化性能的提高，以及分离回用催化剂，二者是二氧化钛光催化技术实际应用的前提与基础。论文以2，4，6-三硝基间苯二酚（2，4，6-Trinitroresorcinol，又称斯蒂酚酸）为目标降解物；采用在TiO₂表面复合电子捕获剂SnO₂，提高其光生电子和光生空穴的分离效率，提高光催化效率；采用在TiO₂晶格掺入少量N，提高催化剂的可见光活性；以Fe₃O₄为磁核，制备磁性复合光催化剂，实现催化剂的磁分离；将膜分离与光催化技术有机地结合起来，组成光催化-膜分离反应器，实现光催化悬浮体系中催化剂的回用及反应连续运行。主要研究工作结果：（1）TiO₂光催化悬浆体系可有效降解有毒有机污染物三硝基间苯二酚（斯蒂酚酸），在一定的紫外光强度下，TiO₂投加量存在最佳值，本实验条件下最佳投加量为1g·L^-1；采用二元线性回归分析可知，反应时间对于评估ln（C₀／C）是显著变量；增加降解底物初始浓度，光催化降解反应速率下降；适量加入电子受体，如O₂、H₂O₂、Fe³⁺、Cu²⁺和Zn²⁺等可提高体系的降解效率；低pH有利于斯蒂酚酸的降解；斯蒂酚酸紫外扫描特征峰随光催化反应的进行不断降低，体系TOC去除率的变化趋势与斯蒂酚酸的基本符合，说明斯蒂酚酸被光催化降解，体系TOC的降低是降解最终产物CO₂离开体系所致。（2）采用均匀沉淀法，在TiO₂表面沉积SnO₂，制备TiO₂-SnO₂复合光催化剂，最佳制备条件为：沉淀剂NH₄HCO₃的浓度和加入速度分别为1.0 mol·L^-1和0.2 mL·s^-1；Sn⁴⁺浓度为0.02 mol·L^-1；搅拌速度200 r·min^-1；反应温度20℃；TiO₂与SnO₂质量比为9：1，焙烧温度为600℃，对50 mg·L^-1斯蒂酚酸的去除率达93.2％，而相同条件下，商品TiO₂对斯蒂酚酸的去除率为79.9％。SnO₂-TiO₂复合催化剂由锐钛矿相TiO₂和四方晶型SnO₂所组成，样品表面的Sn／Ti原子比高于体相的Sn／Ti原子比，形成复合型SnO₂-TiO₂光催化剂；SnO₂的引入使复合半导体带隙增加0.1 eV，在半导体n-p复合作用下，表面形成的Sn-O-Ti键，促进光生载流子在复合半导体上的传递，实现光生电子和空穴的有效分离，提高了光催化效率。（3）采用均匀沉淀法，制备出N掺杂型氧化钛光催化剂。硫酸钛与碳酸氢铵反应产生的沉淀，经过超声波洗涤分离后，在氮气气氛下经300℃焙烧，制得N掺杂氧化钛光催化剂，在不损失紫外段催化能力的情况下，提高了催化剂的可见光活性，光吸收区发生红移，其吸收带边拓展至468 nm。洗涤对于非金属N的掺杂至关重要，经洗涤后焙烧的样品，呈现特殊的黄色，实现了N的掺杂，未经洗涤而直接焙烧的样品无黄色出现。由于非金属N的掺杂，造成了Ti-O成键的变化，可能形成了N-Ti-O的不对称伸缩振动峰，同时掺杂的N高度分散在TiO₂中，并在TiO₂中形成N-Ti-O网络，O原子的电子结合能减小。N掺杂催化剂中的TiO₂以混晶的形式存在，N的掺杂可以弥补催化剂颗粒低温焙烧条件下在晶型上的不足，呈现出良好的光催化活性。（4）以Fe₃O₄为磁核，采用机械力化学法制备TiO₂／Fe₃O₄磁性复合光催化剂，其质量比为m（TiO₂）：m（Fe₃O₄）=3：1，Fe³⁺离子部分取代了Ti-O-Ti网络中的Ti⁴⁺离子，形成Ti-O-Fe桥氧结构。磁性复合催化剂与纯TiO₂光催化性能接近。由于采用的球磨设备为陶瓷材料，在球磨过程中有少量SiO₂杂质的掺入，但并未影响催化剂的光催化性能与磁分离性能。催化剂的光催化反应为动力学一级反应。采用自制的磁分离器，对复合催化剂进行磁分离实验，分离率可达93％左右。（5）在光催化-膜分离反应器中，选用孔径为0.1μm～0.2μm的聚丙烯中空纤维微滤膜，可实现对粒径为20nm二氧化钛能达到很好的截留效果。本实验的最佳操作压力为0.020 MPa，在光催化反应常用的二氧化钛浓度范围内，催化剂浓度对膜通量的影响不大，增大曝气量可以减缓沉积层污染，降低膜阻力，本实验的经济曝气量为0.4 m³·h^-1；当料液pH值接近二氧化钛的等电点时，膜通量较大，pH值偏离等电点时，膜通量减小；料液中不同电解质的存在，影响TiO₂颗粒表面电荷性质，CaCl₂的加入使膜阻力减小，Na₂SO₄的加入使膜阻力增大，NaCl的加入对膜通量影响不大。膜可逆阻力是造成膜污染的主要因素，可通过控制膜抽吸压力、合理选择曝气量、间歇抽吸等工艺条件减缓膜可逆污染；污染的膜依次用清水冲洗、超声波清洗、0.5％NaOH+0.2％NaClO浸泡，0.5％HCl浸泡后可使膜通量恢复99％以上。采用光催化-膜分离反应器降解斯蒂酚酸模拟污水，二氧化钛浓度为1.5 g·L^-1，滤膜操作压力为0.02 MPa，采用抽吸13 min，停抽2 min的运行模式，水力平均停留时间为2 h，在30 d的运行时间内，出水浊度去除率＞99.9％。更多还原

【Abstract】 As a kind of advanced oxidation processes, TiO₂ photocatalysis is being deeply andwidely studied recently. The key of the research focuses on the improvement ofphotoreaction activity of TiO₂ catalyst, and the separation and recycle of the catalyst. Bothare the precondition and foundation of the practical applications of TiO₂ photocatalysis.To evaluate the photocatalytic activity of samples, the photooxidation of 2, 4,6-Trinitroresorcinol （styphnic acid） was carried out in a series of experiments. To improvephotocatalytic efficiency of TiO₂ catalyst, SnO₂ acted as electron captor was coupled on thesurface of TiO₂ to heighten separation ratio of photo-generated electrons and holes.Nonmetal ion N was involved in the crystal lattice of TiO₂ which brought about thevisible-light sensitization of TiO₂. Magnetic photocatalyst （TiO₂/Fe₃O₄）, which are liableto be separated and recycled, were prepared using Fe₃O₄ as support. To accomplish therecycle of catalyst membrane filtration technology was combined with Photooxidation andmake the system run continuously. The primary study was listed as following:（1） Poisonous organic pollutant 2, 4, 6-Yrinitroresorcinol （styphnic acid） could bedegraded effectively in TiO₂ photocatalytic suspension system. An optimal concentration ofTiO₂ existed under a definite irradiation degree of UV, 1g·L^-1 in the experiment. The resultsof duality linear regression indicated that the reaction time was an important variable forthe evaluation of ln（C₀/C）. Reaction velocity of photocatalytic degradation decreased withthe accretion of the initial consistence of the pollutant. The fitting addition of O₂, H₂O₂,Fe³⁺, Cu²⁺ and Zn²⁺ which played the role as electron acceptor could raise the degradationrate of the reaction. And a lower pH was favorable to the degradation of styphnic acid. Theabsorption of character peek of styphnic acid was reduced with the operation of thereaction, which was consistent with the trend of TOC degradation rate. It indicated thedegradation of the organic pollutant.（2）TiO₂-SnO₂ coupled catalytic particles have been prepared with SnO₂ aggrading onTiO₂ in the method of symmetrical precipitation. The best way to obtain the catalysts shouldbe: 1.0 mol·L^-1 NH₄HCO₃ acted as precipitator dropped at the velocity of 0.2 mL·s^-1 intothe solution with the initial concentration of Sn⁴⁺ 0.02 mol·L^-1, and pulsator stirred at aspeed of 200 r·min^-1 simultaneously, the whole reaction acted at 20℃, the mass ratio ofTiO₂ and SnO₂ was 9:1. Then the deposition should be calcined at 600℃. The degradationrate of 50 mg·L^-1 2, 4, 6-Trinitroresorcinol was 93.2％in compared with 79.9％when economical TiO₂ was used as catalyst. TiO₂-SnO₂ coupled catalyst were composed withanatase TiO₂ and square crystalline SnO₂. Sn/Ti atom ratio on the samples surface washigher than which was in the inner phase and coupled SnO₂-TiO₂ was formed. Because ofthe involvement of SnO₂, the energy gap of the coupled catalyst was increased by 0.1 eV.Effectively separation of photo-generated electrons and holes was accomplished andphotocatalytic efficiency was improved because of the photo carrier transmitted in coupledcatalyst on the surface of which Sn-O-Ti bond was shaped.（3） N-doped photocatalyst was prepared by symmetrical precipitating action. N-dopingcould be carried out at a lower temperature （300℃）, and NH₄HCO₃ was chosen asprecipitating agent and source of nitrogen. N-doped photocatalyst was obtained throughultrasonic separation and calcinations in N₂ atmosphere of the deposit, which was generatedin the reaction of Ti（SO₄）₂ and NH₄HCO₃. Moreover, the catalyst showed excellentphotocatalytic activity under the irradiation of UV and visible light, light absorptionshowed red-shift and absorption region has been enlarged to 468nm. Washing determine thepossibility of N-doped. The samples calcined after washing was specially yellow whichindicated N was doped, while the samples without treatment of washing showed white. TheTi-O bond changed because of the doping of nonmetal ions N. It was estimated theformation of N-Ti-O asymmetric deformation vibrations band. Doped N was dispersed intothe TiO₂ crystal lattice simultaneously, and the N-Ti-O net was shaped consequencely. Theelectron binding energy of O atom decreased. Photocatalyst existed in the formation ofdifferent crystal phase. N-doping could counteract the disadvantages of the crystal shape ofobtained catalyst calcined under lower temperatures, and the catalyst showed goodperformance of photoreaction.（4）Magnetic photocatalyst TiO₂/Fe₃O₄ （the mass ratio is 3:1） has been prepared in themethod of mechanochemistry using Fe₃O₄ as magnetic support. Ti⁴⁺ in the crystal lattice ofTi-O-Ti has been partially substituted by Fe³⁺, which brought about the structure of Ti-O-Febridging oxygen. The photocatalytic ability of obtained coupled catalyst was close to theability of purchased TiO₂. The doping of SiO₂ impurity brought in the process ofmechanical attrition, which was ascribed to the equipment by chinaware material, has notinfluenced the photocatalytic ability and magnetic separation ability of catalyst.Photocatalytic reaction was first-order reaction kinetics. The experiments have been carriedout to test the ability of magnetic separation of catalyst with magnetic reactor which weremade by ourselves. The separation rate was as high as 93％which meant the bettermagnetic separate ability of prepared catalyst. （5）TiO₂ particles of 20nm diam. in suspension liquor could be intercepted very well inphotocatalysis-membrane separation reactor, in which polypropylene hollow fibermembrane of 0.1μm～0.2μm diam. has been used. The optimum pressure in the operationwas 0.02MPa. The concentration of catalysts effects lightly to membrane flux in theaverage concentration range of photocatalytic reaction. Increasing aeration intensity couldmitigate the pollution degree on deposit layer and reduce the resistance of membrane, theeconomical aeration intensity is 0.4m³·h^-1 in the system. Membrane flux would increasewhen solution pH approach to the equipotential point of TiO₂, vice versa. Differentelectrolyte in the solution made influence to the property of charge on the surface ofparticles: CaCl₂ make the resistance decreased, Na₂SO₄ increased and the exist of NaCleffected slightly. Studies showed that the reversible resistance is the main reason causingmembrane fouling. Controlling suction pressure, choosing logical aeration intensity andperiodic running can greatly alleviate membrane reversible fouling. Flux of pollutedmembrane could be recovered up to 99％by means of washing by water, ultrasoniccleaning, dipping in 0.5％NaOH+0.2％NaClO liquid, and then 0.5％HCl in turn.The photocatalytic of 2, 4, 6-Trinitroresorcinol experiments was carried out inphotocatalysis-membrane separation reactor. The concentration of 20 nm diam. TiO₂ was1.5 g·L^-1, operation press 0.02 MPa, 13 minutes of suction time 2 minutes of suctionsuspended time, about 2h of waterpower average settle time. The continuous operation for30 days is described, the results showed that turbidity removal of out water was＞99.9％.更多还原