【作者】 辛柏福；

【导师】 王鹏；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2009， 博士

【摘要】 锐钛矿相的TiO₂由于具有光稳定性好、无毒、价格低廉及氧化能力强等特性而成为首选的光催化剂。但TiO₂光催化效率受到光生载流子复合率高和太阳光利用率低这两个关键因素限制。在本论文中采用了Cu、Sn两种金属元素对TiO₂进行了改性，试图解决光生载流子的复合率高和太阳光的利用率低这两个关键问题。Cu离子掺杂对TiO₂光催化活性的影响已经被广泛研究，但具有多价态的Cu离子在光催化反应过程中所起的作用仍不明确。在本研究中，首先采用溶胶-凝胶法制备了一系列Cu-TiO₂光催化剂。利用TG、XRD、DRS、SPS及XPS等分析技术对所制备的样品进行了表征。并以罗丹明B（RhB）为光催化目标降解物，研究了Cu-TiO₂纳米粒子的光催化性能。探讨了在纳米TiO₂的制备和改性过程中，焙烧温度、焙烧时间、不同金属Cu元素加入量等因素对光催化活性的影响。通过DRS、SPS及XPS表征探讨了Cu掺杂对TiO₂的改性机制：在铜掺杂量适宜条件时，由于Cu-TiO₂纳米粒子中的氧空位和铜组分能够捕获光生电子，抑制了光生载流子的复合，此外，适量的Cu掺杂使TiO₂表面-OH数量增加，这些因素改善了催化剂的活性；但在铜的掺杂量较高时，过量的氧空位及铜组分则成为光生电子-空穴的复合中心。同时，过量的铜组分会覆盖TiO₂表面从而阻碍其对光的吸收，并且，在铜掺杂浓度较大时TiO₂的导电类型由N型变成P型，导致TiO₂光催化剂中毒，从而降低了催化剂光催化活性。利用氢还原处理可以使光生电子-空穴的有效分离从而改善TiO₂的光催化性能。但氢还原法工艺较复杂，存在着易燃易爆等不安全因素及制备时间长、成本高等缺点，因而限制了其实际应用。为了克服上述缺点，本研究采用工艺简单的Sn²⁺化学还原方法制备了Sn还原纳米TiO₂光催化剂（Sn-TiO₂-X）。利用UV-Vis-DRS，SPS，XPS，EIS等测试手段探讨了Sn对TiO₂的改性机制：Sn²⁺还原后的TiO₂中生成了Ti3+离子，导致TiO₂的费米能级升高，活性氧组分的数量增多；Sn²⁺还原增加了TiO₂表面氧空位密度，能更有效的捕获光生电子，抑制了光生电子-空穴的复合；Sn²⁺还原TiO₂后，在TiO₂粒子表面生成SnO2，SnO2的费米能级低于TiO₂费米能级，导致光生电子从TiO₂导带向SnO2迁移，起光生电子捕获阱作用，抑制光生载流子的复合从而改善其光催化活性；Sn²⁺还原后引入Ti3+、SnO2等掺杂能级，这些能级可以导致催化剂发生亚带隙跃迁，即掺杂能级也参与了光化学过程，光催化剂的吸光范围拓展到了可见光区。Sn²⁺化学还原改性方法兼具氢还原法和Sn4+掺杂改性方法的优点，有效的改善了光催化剂的活性。三氟羧草醚是一种广泛应用于大豆及水稻出苗后期选择性去除阔叶杂草的含氯除草剂。三氟羧草醚足够长的半衰期使其能够被冲进地表水（江河和湖泊），对环境造成危害。本研究以Cu、Sn改性TiO₂为光催化剂，考查了光强、催化剂用量、pH值、农业生产中经常使用的一些阴、阳离子及降解目标物初始浓度等各种因素对三氟羧草醚光催化降解的影响。实验结果表明：由于三氟羧草醚的解离状态及TiO₂表面电性，相对于三氟羧草醚原液，调节pH值后的三氟羧草醚溶液的降解率均有所下降；阴离子的加入对以Cu-TiO₂为催化剂的反应体系影响显著，但对以Sn-TiO₂-X为催化剂的反应体系无明显影响；K+、Ca2+的加入对于光催化降解三氟羧草醚影响不大，但加入Cu2+的影响较为明显。此外，利用光生电子、空穴捕获剂，判断识别了二种改性机制不同的催化剂光催化反应中的活性组分作用的大小。实验结果表明，以Cu-TiO₂为催化剂的反应体系·OH为主要活性组分，而以Sn-TiO₂-X为催化剂的反应体系的活性氧组分的作用比Cu-TiO₂为催化剂的反应体系大。最后，研究了三氟羧草醚降解动力学、降解过程的中间产物及降解途径。光催化实验结果表明三氟羧草醚降解反应为0级反应。更多还原

【Abstract】 The anatase crystalline form of TiO₂has been the best photocatalyst of choice.It has been found to have the best overall properties in terms of photo-stability,toxicity, cost, availability and redox efficiency. However, the efficiency ofphotocatalytic reactions is limited by the high recombination rate of photoinducedelectron-hole pairs formed in photocatalytic processes and by the absorptioncapability for visible light of photocatalysts. The aim of this research is to solvethese key problems using Cu or Sn elements to modifiy TiO₂photocatalyst.The effects of copper ions have been studied on the photodegradation oforganic pollutant, but many aspects with regard to the role of copper species withmultivalent states in the photocatalytic reaction remain unclear. In this research, aseries of Cu-TiO₂catalysts have been synthesized by sol-gel method. The obtainedsamples were characterized in detail via TG, XRD, DRS, SPS and XPS methods.The photocatalytic activity of Cu-TiO₂was studied by degrading the RhodamineBextra solution （RhB）. Meanwhile, the effects of different metal content，calcination temperature，and calcination time on the photocatalytic activity ofsamples were investigated. The modified mechanism of the Cu doping TiO₂wasinvestigated via DRS, SPS and XPS technologies: when the Cu concentration isfeasible, oxygen vacancies and Cu species could trap the photoinduced electronsand effectively inhibit the recombination of the photoinduced charges consequentlyin the photocatalytic process, in addition, the content of surface hydroxyl on thesurface of the0.06mol%Cu-TiO₂was increased remarkably in contrast to that ofpure TiO₂, these factors were favor to the increase of the photocatalytic activity forsamples. When copper dopant content exceeds0.06mol%, however, excessiveoxygen vacancies and Cu species could be the recombination centers of thephotoinduced electrons and holes. Meanwhile, at heavy Cu doping concentration,excessive P-type Cu2O can cover the surface of TiO₂, which leads to decrease in thephotocatalytic activity of photocatalyst.The thermal hydrogen （H2） treatment of TiO₂was also found to be capable toaccelerate the e-h separation and improved photocatalytic activity of the TiO₂catalyst. However, there were many insufficiencies in the process of the thermalhydrogen （H2） treatment of TiO₂, such as, there were the factors of inflammable and explosive, the technologies route was complicated, furthermore, this method wastoo time-consuming and expensive. These factors limited its practical application.To overcome these difficulties and disadvantages, in this thesis, a rapid andsimple method, the so-called stannous chemical reducing method was developed toprepare the nanocrystalline Sn-TiO₂-X. The mechanism of the Sn modified TiO₂wasinvestigated via DRS, SPS, XPS and EIS methods. Firstly, that is deu to theexistence of Ti3+ions, which can elevate the Femi energy level and increase thenumber of the the active oxygen species. Secondly, the amount of oxygen vacanciesis increased, which can effectively trap photoinduced carriers and inhibit therecombination of the photoinduced electrons and holes. Thirdly, Sn species areformed as SnO2on the surface of TiO₂, the Fermi levels of SnO2is lower than thatof TiO₂, which leads to the photoinduced electrons transfer from the conductiveband of TiO₂to that of SnO2on the surface of TiO₂, not to the bulk of TiO₂, whichcan also trap photoinduced electrons and inhibit the recombination of thephotoinduced electrons and holes. At last, Sn-modified TiO₂introduce the doppingenergy level of Ti3+and Sn species, which can result in the sub-band gap transitionof catalysts, the doped energy level participate in the photochemistry process, thelight whose energy is less than the Eg can be absorbed by catalysts, so, theabsorption range of photocatalyst could beexpanded to visible region. Thephotocatalyst prepared by the stannous chemical reducing method have efficacies ofboth the thermal hydrogen （H2） treatment and Sn4+doping modification.Acifluorfen is a diphenyl ether herbicide contained chlorine used inpostemergence for the selective control of most broadleaf weeds in soybeans andrice. The half-life of Acifluorfen is sufficiently long that it may be washed awaytoward surface waters （rivers and lakes） and had caused great damage to theenvironment.In present work, the experiments of the photocatalytic degradation ofAcifluorfen were carried out using Cu-TiO₂and Sn-TiO₂-Xas photocatalysts. Ourobjective was to explore the effects of the irradiation intensity, the catalyst dosage,pH values, the type and the amount of anions and cations often used in agriculture,and the initial concentration on the degradation of Acifluorfen. The experimentalresults indicate that:The smaller activities found at acidic and basic pH are explained byconsidering the ionisation state of Acifluorfen and the charge density of TiO₂; Effect of the anions addition on the degradation of Acifluorfen is remarkable for thereaction system using Cu-TiO₂as photocatalyst, but there is less effect forSn-TiO₂-X; The influence of metal ions like K+and Ca2+on the photocatalyticefficiency of TiO₂in the elimination of Acifluorfen is unnoticeable, but adetrimental effect of the presence of Cu2+is observed.In addition, the roles of the active species generated in TiO₂systems areidentified using i-PrOH and dissolved oxygen as·OH and photoinduced electronsscavenging reactant, and the role of the main active species in the photodegradationof Acifluorfen is determined. The experimental results indicate that·OH is the mainactive specie for Cu-TiO₂, and the amount of the active oxygen species in thereaction system using Sn-TiO₂-Xas photocatalyst are more than that of Cu-TiO₂.Finally, the removal kinetics of Acifluorfen, and established the primaryintermediate products and degradation pathways of Acifluorfen have been studied.The results of photocatalytic experiment reveal that the decline of Acifluorfenconcentration in the solution followed a zero-order kinetics.更多还原