摘要
由于无毒、稳定、强氧性以及良好的光催化性能等优点,在近年来TiO_2材料得到了广泛研究。锐钛矿TiO_2光催化材料的禁带宽度为3.2 eV,只有在紫外光的作用下才能显示出明显的活性,而地球表面太阳光谱中,紫外光大约占5%,严重地影响了TiO_2光催化材料、基于TiO_2染料敏化太阳能电池的应用。因此,有效地利用可见光,拓宽TiO_2应用范围,改善其在可见光谱的吸收,使光吸收边向可见光区发生较大的红移,增强TiO_2光催化材料在可见光区的光催化性能,是TiO_2光催化材料的主要研究方向之一。本文针对目前TiO_2光催化材料改性研究中的一些难点,借助计算机模拟了不同的非金属和过渡金属元素掺杂对锐钛矿相Ti0_2电子结构和光学性能的影响,得到最佳的非金属和金属光学性质改性元素,然后对最佳非金属和金属掺杂元素进行组合,共同掺杂进而增强锐钛矿TiO_2在可见光区的吸收。本文工作运用第一性密度泛函理论平面波赝势方法,对非金属元素C、N、F和金属元素Cr、Cu、Zn、V、Sc分别掺杂以及C、Cu共掺杂锐钛矿相Ti0_2的电子结构和光学性质进行了计算和分析。
第一章综述了TiO_2的分类、现状以及研究意义,着重介绍了TiO_2光催化材料光学性质的各种改性方式,论述了本论文的选题目的和意义。
第二章系统论述了第一性原理密度泛函理论和计算方法。介绍了局域密度近似和广义梯度近似;对密度泛函理论的数值计算方法如线性组合原子轨道法和赝势方法做了说明;对常用的第一性原理软件Gaussian、Material Studio、VASP、WIEN、PWSCF、SIESTA、ADF、ABINIT、CPMD、Octopus做了简要介绍,对CASTEP软件的使用进行了详细说明。
第三章采用非金属元素C、N、F分别掺杂锐钛矿相Ti0_2,对其能带结构、态密度、电荷密度和光学性质进行了计算分析。计算结果表明,C/N掺杂锐钛矿相Ti0_2属于受主掺杂,C/N的2p态与O的2p态、Ti 3d态杂化形成杂质能级,光学带隙变窄,光吸收边红移到可见光区;F掺杂锐钛矿相Ti0_2属于施主掺杂,由于F的负电性较强,能级较低,使得价带下移,光学带隙变宽,导致掺杂后光吸收边发生微弱蓝移;三种非金属掺杂元素中以C掺杂锐钛矿TiO_2光学改性效果最佳。
第四章采用金属元素Cr、Cu、Zn、V、Sc分别掺杂锐钛矿相Ti0_2,对其能带结构、态密度、电荷差分密度和光学性质进行了计算分析。计算结果表明,Cr掺杂锐钛矿相Ti0_2属于电子掺杂,Cr的3d态电子形成施主杂质能级,导致掺杂后的TiO_2的禁带宽度变窄,光吸收曲线红移到可见光区;Cu掺杂锐钛矿相Ti0_2属于空穴掺杂,这部分空穴态来自于O的2p态,空穴态在带隙中间形成受主杂质能级,光学带隙减小,光吸收边红移到可见光区;Zn掺杂锐钛矿相Ti0_2属于受主掺杂,掺杂Zn后O 2p态和Ti 3d态之间的光学带隙和未掺杂时相比没有大的改变,因此Zn掺杂锐钛矿TiO_2后光吸收边基本保持不变;V掺杂锐钛矿相Ti0_2属于施主掺杂,并在带隙中间引入了杂质能级,光学带隙减小,使得掺杂后锐钛矿Ti0_2光吸收边发生红移; Sc掺杂锐钛矿相Ti0_2属于受主掺杂,掺杂后的TiO_2的禁带宽度没有发生大的变化,光吸收边基本不变。五种金属掺杂锐钛矿TiO_2的元素中以Cu掺杂光学改性效果最佳。
第五章运用C、Cu共掺杂锐钛矿相Ti0_2,对其能带结构、态密度、电荷密度和光学性质进行了计算分析。计算结果表明C、Cu共掺杂属于受主掺杂,C的2p态在带隙中间引入了3条杂质能级,Cu由于本身3d态能量较低,所以在其周围O的2p态上留下空穴,在带隙中间引入了一条O 2p态的间隙杂质能级,使得掺杂后的TiO_2光学带隙减小,光吸收边发生红移。因此C、Cu共掺杂锐钛矿TiO_2的光学改性效果要好于其各自单相掺杂。
Titanium oxide semiconductors have attracted increasingly attention in recent years due to its many advantages including of non-toxic, stable, strong oxidizing character and excellent photoelectron-chemical effect. However, TiO_2 can only be activated by the ultraviolet irradiation due to its relatively large band gap about 3.2eV for the anatase phase. Ultraviolet in the nature light is about 5%, which is difficult to develop photochemical materials and dye sensitized solar cells of TiO_2. The effective use of visible light to expand TiO_2 scope of application and improve the TiO_2 absorption in the visible spectrum, so that its visible absorption edge occur red shift to enhance the TiO_2 photocatalytic ability in the visible region, which is one of the main research for TiO_2. In this thesis, according to some hot and difficult questions of TiO_2 photocatalytic research, computer simulations have been made to predict the electronic structures and optical properties for doped anatase TiO_2 with the different non-metallic and transition metal elements. The first-principles density functional calculation was chose to investigate the electronic structures and optical properties of non-metallic C/N/F-doped, transition metal Cr/Cu/Zn/V/Sc-doped and C-Cu co-doped anatase TiO_2. In chapter one, the categories, progress in research, research meaning and optical modified methods on photocatalytic performance of TiO_2 were reviewed. The works on this topic and research meaning are introduced.
In chapter two, the first-principles density functional theory and calculation methods are descussed. Density functional theory with local density approximation and generalized gradient approximation was explained. Numerical methods for density functional theory such as Linear Combination of Atomic Orbitals and Pseudopotential methods were illustrated. The common packages for the first-principles, such as Gaussian, Material Studio, VASP, WIEN, PWSCF, SIESTA, ADF, ABINIT, CPMD and Octopus, were given a brief introduction. Some operational techniques and features for CASTEP program were described in detail.
In chapter three, the energy band structures, density of states, electronic density and optical properties were calculated for non-metallic C/N/F-doped anatase TiO_2, respectively. The results show that, C/N in the anatase TiO_2 is acceptor impurity. It is clear that forbidden band is narrowing due to the formation of impurity energy levels by hybridized with O 2p states, Ti 3d states, and C/N 2p states, which lead to red-shift of the absorption edges toward visible-light region. F atom in the anatase TiO_2 is donor impurity. F doped anatase TiO_2 has lower energy levels because of strong electronegativity, which cause the valence band to shift toward lower energy levels, the optical band gap to narrow and the absorption edges to slightly blue-shift toward ultraviolet region. C doped anatase TiO_2 has better improved effects in the non-metallic C/N/F elements.
In chapter four, the energy band structures, density of states, electronic density and optical properties were calculated for the Cr/Cu/Zn/V/Sc-doped anatase TiO_2, respectively. The results show that Cr in the anatase TiO_2 is a donor impurity. It is clear that optical band gap is narrowing due to the formation of impurity energy levels by hybridized with O 2p states, Ti 3d states, and Cr 2p states leading to red-shift of the absorption edges toward visible-light region. Cu in the anatase TiO_2 is an acceptor impurity. The holes originated from O 2p states. The optical band gap is narrowing due to the formation of the impurity energy levels from the O 2p hole states, which result in red-shift of the absorption edges toward visible-light region. Zn atom in the anatase TiO_2 is acceptor impurity. The optical band gap between O 2p states and Ti 3d states is basically the same in the both Zn-doped and pure anatase TiO_2. As a result optical absorption edges are essentially unchanged. V atom in the anatase TiO_2 is donor impurity. It is clear that optical band gap is narrowing due to the formation of the impurity energy levels from the V 3d states leading to red-shift of the absorption edges toward the visible-light region. Sc atom in the anatase TiO_2 is acceptor impurity. The optical band gap is essentially unchanged, which is for that reason absorption edges of Sc-doped TiO_2 don’t red-shift toward the visible-light region. Cu-doped TiO_2 has better improved optical effects in five doping metallic elements.
In chapter five, the electronic structures and the optical properties were calculated for metallic C-Cu-codoped anatase TiO_2. The results show that both of C and Cu elements in the anatase TiO_2 are donor impurity. Three impurity levels originating from C 2p states appear in the forbidden band. An impurity level from O 2p states appear in the band gap. The narrowing optical band gap is obviously observed due to the formation of impurity energy levels, which lead to red-shift of the absorption edges toward visible-light region. Therefore, C-Cu-doped anatase TiO_2 has better improved optical effects than theirs single doped.
引文
[1] Vainshtein B K, Fridkin W M, Indenbom V L. Structure of Crystals. Berlin:Macmil-lan India Ltd, 1994, 749-750
[2] Fujishima A, Honda K. Electrochemical photolysis of water at a semi-conductor electrode. Nature, 1972: 37-38
[3] Wang R, Hashimoto K, Fujishima A. Light-induced amphiphilic surfaces. Nature, 1997, 388: 431-432
[4] Fujishima A. Recentprogress in titanium dioxide photocatalysis. National Conference on Photocatalysis Con-fernece Corpus, 2002:1-3
[5] O’Regan B, Gr?tzel M. A low cost high efficiency solar cell based on dye-sensitized colloidal TiO_2 films. Nature, 1991, 353(24): 737-740
[6] Nazeeruddin M K, Kay A, Gratzel M. Conversion of light to electricity bycis-X-bis-(2,2'-bipyridyl-4,4'-dicarboxylat-e) ruthenium(Ⅱ) charge-transfer sensitizers (X=Cl-, Br-, I-, CN- and SCN-) on nanocrystalline titanium dioxide electrodes. J Am Chem Soc, 1993, 115(14): 6382-6390
[7] Nazeeruddin M K, Comte P, Gratzel M. Engineering of efficient panchromatic sensitizers for nanocrystalline TiO_2-based solar cells. J Am Chem Soc, 2001, 123(8): 1613-1624
[8] Yasuo C, Ashrafui I, Yuki W, et a1. Dye sensitized solar cells with conversion efficiency of 11.1%. Japanese Journal of Applied Physics, 2006, 45(60): 638-640
[9]曹江林. TiO_2和过渡金属掺杂TiO_2薄膜电极的制备及光电化学性能研究:[博士学位论文].杭州:浙江大学材化学院,2004
[10] Asahi R, Morikawa T, Ohwaki T, et a1. Visible-light photocatalysis in nitrogen doped titanium oxides. Science, 2001, 293(13): 269-271
[11]邱炜,陈爱平,刘威等.掺氮光敏化纳米晶TiO_2的研制.华东理工大学学报(自然科学版), 2005, 31(1): 79-82
[12]张莉,任焱杰,蔡生民.染料敏化La3+掺杂的TiO_2纳米多孔膜光电化学.电化学, 2002, 8(1): 27-31
[13] Choi W, Termin A, Hoffmann M R. The role of metalion dopants in quantumsizedTiO_2: Correlation between photoreactivity and chargecarried recombination dynamics. Phys Chem, 1994, 98 (5): 13669-13679.
[14] Antonino Sclafani, Leonardo Palmisano, Eugenio Davì. Photocatalytic degradaton of phenol in aqueous polycrystalline TiO_2 dispersions: the influence of Fe3+, Fe2+ and Ag+ on the reaction rate. Journal of Photochemistry and Photobiology A: Chemistry, 1994, 56(1): 113-123
[15]余锡宾,王桂华,罗衍庆等. TiO_2微粒的掺杂改性与催化活性.上海师范大学学报(自然科学版), 2000, 29(1): 75-82
[16]余家国,赵修建,林立等.超亲水TiO_2/SiO_2复合薄膜的制备与表征.无机材料学报, 2001, 16 (3): 529-534
[17]陈文梅,余家国,赵修建等. TiO_2/SiO_2纳米薄膜的光催化活性和亲水性.物理化学报, 2001, 17 (3): 261-264
[18]赵修建,韩建军. TiO_2/SiO_2复合薄膜的晶粒尺寸研究.硅酸盐学报, 2001, 29(3): 286-290
[19] Miyashita K , Kuroda S , Ubukata T , et al. Enhanced effect of vacuum-deposited SiO_2 overlayer on photo-induced hydrophilicity of TiO_2 film. Mater Sci, 2001, 36: 3877-3884
[20] Jiang H, Gao L. Enhancing the UV inducing hydrophilicity TiO_2 thin film by doping Feions. Mater.Chem.Physi, 2002, 77: 878-881
[21] Kang M G, Han H E, Kim K J. Enhanced photodecomposition of chlorophenol in aqueous solution by deposition of CdS on TiO_2. Photochem Photobiol A: Chem, 1999, 125:119-125
[22] Li X Z, Li F B, Yang C L, et al. Photocatalytic activity of WOx-TiO_2 under visible light irradiation. Photochem PhotobioA: Chem, 2001, 141(2): 209-217
[23]郝彦忠,王伟.聚3-甲基噻吩修饰量子点硫化镉连接纳米结构TiO_2复合膜电极光电化学研究.功能材料,2007,38(1):11-13
[24]张晨宁,胡志强,刘丽红等. FeS2/TiO_2复合薄膜光电性.功能材料与器件学报, 2007, 13(2): 139-144
[25]王传义,刘春艳,沈涛.半导体光催化剂的表面修饰.高等学校化学学报, 1998, 19(12): 2013-2019
[26]柳闽生,杨迈之,郝彦忠等.纳米尺度TiO_2/聚吡咯多孔膜电极光电化学研究.高等学校化学学报, 1997, 18(6): 938-942
[27]李卫华,郝彦忠,乔学斌等.硫化物/Ru(Ⅱ)络合物复合敏化TiO_2纳米多孔膜.物理化学学报, 1998, 14(9): 841-845
[28]安立超,曾桁,李海燕等.载银TiO_2催化剂的制备与性能研究.环境污染治理技术与设备, 2001, 2(4): 30-33
[29] Andrew Burns, Hayes G, Li W, et al. Neodymium ion dopant effects on the phase transformation in sol-gel de-rived titanium nanostructures. Mat. Sci. Eng B, 2004, 111: 150-155
[30] Lin J, Yu J C. An investigation on photocatalytic activities of mixed TiO_2 rare earth oxides for the oxidation of acetone in air. J Phot PhotA: Chem, 1998, 116: 63-67
[31] Xu W X, Schierbaum K D, Goepe W. Ab initio study of the effect of oxygen defect on the strong-metal-support interaction between Pt and TiO_2(Rutile)(110) surface. J Sol State Chem, 1995, 119: 237-245
[32] Xue W D, Cai J, Wang M X, et al. First-principle study on SrTiO_3 film oxygen imperfection.J. At.Mol. Phys, 2007, 24(4): 875
[33] LIU Peng LI Rong-ping DONG Hai-cheng LI Zhong-xian Influence of Ce and Y Doping on Nano-TiO_2's Optical Characteristic. Chinese Rare Earths. 2008, 29(5)
[34] DAI Shi-Jun, HU Chang-Wei, DU Lin, et al. Investigation on Electrocatalytic Degradation of Methyl Orange on Ti/TiO_2 Anode Doped with Ru-Pd. ACTA CHIMICA SINICA, 2008, 66(14): 1620-1626
[35] Le Saux G, Kruger P, Domenichini B, et al. Dynamics of molybdenum nano structure formation on the TiO_2 (110) surface: a kinetic Monte Carlo approach. Appl Sur Sci., 2006, 252: 5399-5424
[36] XU Xiao-hong, TIAN Yue, WU Jian-feng, et al. Influence of La3+ and Fe3+ Co-doping on Photocatalytic Properties of TiO_2 Nanoparticles. Journal of wuhan university of technology. 2008, 30(6): 1-5
[37]李晓辉刘守新. N、F共掺杂TiO_2可见光响应光催化剂的酸催化水解制备及表征.物理化学学报. 2008, 24(11):2019-2024
[38] Zongyan Zhao Qingju Liu. Designed highly effective photocatalyst of anatase TiO_2 Co-doped with Nitrogen and Vanadium Under Visible-light Irradiation Using First-principles. Catal Lett, 2008, 124:111–117
[39]陈琦丽,唐超群. N/F掺杂和N-F双掺杂锐钛矿相TiO_2(101)表面电子结构的第一性原理计算. ACTA PHYSICO-CHIMICA SINICA , 2009 , 25(5):915-912
[40] Chatterjee D, Mahata A. Photoassisted detoxification of organic poll utants on the surface modified TiO_2 semiconductor particulate system. Catal Commun, 2001, 2 (1): 1-3
[41]吴迪,沈珍,薛兆历,等.卟啉类光敏剂在染料敏化太阳能电池中的应用.无机化学学报, 2007, 23(1): 1-14
[42]谭芳.氧化锌纳米晶\卟啉复合材料的制备及能量和电子转移过程的研究:[硕士学位论文] .长春:东北师范大学物理学院, 2006
[43]谭芳,韩也,刘益春.氧化锌纳米晶\卟啉复合材料的制备及性质研究.长春大学学报, 2006, 16(5): 27-30
[44]杨朝晖.酞菁敏化纳米二氧化钛电极制备及光电性能研究:[硕士学位论文].南京:东南大学化学化工学院,2006
[45] L Giribabu, Ch Vijay Kumar, V Gopal Reddy, et al. Unsymmetrical alkoxy zinc phthlocyanine for sensitization of nanocrystalline TiO_2 films. Solar Energy Materials Solar Cells, 2007, 91:1611-1617
[46] J He,B Gaboro, K Ferenc, et al. Modified Phthalocyanines for Efficient Near-IR Sensitization of Nanostructured TiO_2 Electrode. J Am Chem Soc, 2002, 124(17): 4922-4932
[47] D J Calvin, F F Fan, A J Bard. Spectral sensitization of the semiconductors phthalocyanine. J Am Chem Soc, 1980, 102(8): 2592-2598
[48] Y Shen, L Wang.Z Lu, et al. Fabrication characterization and photovoltaic study of a TiO_2 microporous electrode. Thin Solid Film, 1995, 257: 144-146
[49]郝三存.天然色素敏化TiO_2多孔膜太阳能电池的研究:[硕士学位论文].泉州:华侨大学材料科学与工程学院,2004
[50] Calogero G, Marco G DI. Red Sicilian orange and purple eggplant fruits as natural sensitizers for dye-sensitized solar cells. Sol Energy Mater Sol Cells, 2008, 92(11): 1341-1346
[51]管自生,马颖,曹亚安等.预处理对TiO_2表面超亲水性的影响.感光科学与光化学, 2000, 18 (3): 204-207
[52] Yu J C, Yu J, Zhao J .Enhanced photocatalytic activity of mesoporousand ordinary TiO_2 thin films by sulfuric acid treatment. Appl CatalB: Environ, 2002, 36 (1): 31-43
[53] Kozlov D V, Paukshtis E A, Savinov E N. The comparative studies of titanium dioxide in gas-phase ethanol photocatalytic oxidation by the FTIR in situ method. Appl Catal B: Environ, 2000, 24 (1): 7-12
[54] Muggli D S, Ding L. Photocatalytic performance of sulfated TiO_2 and De-gussa P225 TiO_2 during oxidation of organic. Appl Catal B: Environ, 2001, 32 (3): 181-194
[55]付贤智,丁正新,苏文悦等.二氧化钛基固体超强酸的结构及其光催化氧化性能.催化学报, 1999, 20(3): 321-324
[56]姜勇,张平,刘祖武.高活性多孔纳米TiO_2的制备及协同光催化作用机理的探讨.材料科学与工程学报, 2004, 22(4): 584-587
[57]步绍静,靳正国,刘晓新等.聚乙二醇含量对纳米TiO_2多孔薄膜性质的影响.半导体学报, 2005, 26(2): 329-334
[58] M. Born, K Huamg, M Lax. Dynamical Theory of Crystal Lattices. American Journal of Physics, 1955, 23(7): 474-478
[59] K. Capelle. A bird’s-eye view of density functional theory. Braz J Phys, 2006, 36:1318-1343
[60] J. C. Slater. Wave functions in a periodic potential. Phys Rev. 1937, 51: 846-851.
[61] R. M. Martin. Electronic Structure: Basic Theory and Practical Methods. Cambridge University Press, 2004
[62] J P Perdew, K Burke, M Ernzerhof. Generalized Gradient Approximation Made Simple. Phys Rev Lett, 1996, 77: 3865-3868
[63] C Filippi, C J Umrigar, M Taut. Comparison of exact and approximate density functionals for an exactly soluble model. J Chem Phys, 1994, 100: 1290-1296
[64] Xin Xu, William A. Goddard lll. The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties. Proc. Nati. Acad. Sci, 2004, 101: 2673-2677.
[65]李正中,固体物理,高等教育出版社,北京, 200_2
[66] J C Slater. An Augmented Plane Wave Method for the Periodic Potential Problem. Phys Rev, 1953, 92: 603-608
[67] D Vanderbilt. Soft self-consistent pseudopotentials in a generalized eigenvalue formalism. Phys Rev B, 1990, 41: 7892-7895
[68] Jing-bo Li and Su-Huai Wei. Design of shallow acceptors inZnO: First principles band structurecalculations. PHYSICALREVIEWB , 2006 , 74: 0812011-0812014
[69] Daimei Chen, Zhongyi Jiang, Jiaqing Geng, et al. Carbon and Nitrogen Co-doped TiO_2 with Enhanced Visible-Light Photocatalytic Activity. Ind. Eng. Chem. Res. 2007, 46 (9): 2741–2746
[70] ZHANG Xiao-Yan, CUI Xiao-Li. Preparation and Photocatalytic Hydrogen Evolution Performance of C-N-Codoped Nano TiO_2 Photocatalysts. Acta Phys Chim Sin, 2009, 25(9): 1829-1834
[71]冯庆,王渭华. Fe—N共掺杂锐钛矿相Ti0_2电子性质与光学性质的第一性原理研究.原子与分子物理学, 2010, 27(2): 345-352
[72] ZHANG Xiao, Ru LIN Yan-Hong, ZHANG Jian-Fu. Photoinduced Charge Carrier Properties and Photocatalytic Activity of N-Doped TiO_2 Nanocatalysts. Acta Phys Chim Sin, 2010, 26(10):2733-2738
[73] LIU Shou-Xin, CHEN Xiao-Yun, LI Xiao-Hui. Effect of N doping on Structure Chracteristics and Photocatalytic Activity of Ti0_2 Photocatalyst. CHINESE JOURNAL OF INORGANIC CHEMISTRY, 2008, 24(2): 253-259
[74] FENG Qing, WANG Wei-Hua. First-principles study of electronic and optical property of Fe-N codoped anatase TiO_2. JOURNAL OF ATOMIC AND MOLECULAR PHYSICS, 2010, 27(2): 345-352
[75] LIAO Bin, QIN Li-Zhao, WU Xian-Ying, et al. Calculation of Electronic Structure of Anatase TiO_2 Doped with Transition Metal V, Cr, Fe and Cu Atoms by the Linearized Augmented Plane Wave Method. CHINESE JOURNAL OF STRUCTURAL CHEMISTRY, 2009, 28(7): 869-873
[76]侯兴刚,刘安东. V注入锐钛矿TiO_2第一性原理研究.物理学报. 2007, 56(8) : 4896-4900
[77]徐凌,唐超群,黄宗斌. V掺杂锐钛矿相TiO_2的光吸收特性.物理化学学报, 2010, 26(5): 1401-1407
[78]廖斌,覃礼钊,侯兴刚等.线性缀加平面波法计算掺杂钨和钒锐钛矿二氧化钛的电子结构.化学学报, 2008, 66(2) : 28l-284
[79] CHENG Ken, LIAO Bin, HOU Xinggang, et al. ANALYSIS ON ELECTRONIC STRUCTURE OF ANATASE TiO_2 DOPED WITH Ni, Cu, Pt UTILIZING THE FULL-POTENTIAL LINEARIZED AUGMENTED PLANE-WAVE METHOD. JOURNAL OF BEIJING NORMAL UNIVERSITY, 2008, 44(6): 591-594
[80]赵宗彦,柳清菊,朱忠其等.非金属阳离子掺杂锐钛矿相TiO_2的第一性原理研究.功能材料, 2008, 39(6):953-956
