含氧空位锐钛矿表面的非金属杂质对其吸附NH_3特性的影响
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摘要
【目的】金属氧化物光学气敏材料可用来灵敏检测环境气体成分及浓度,而对这一材料的掺杂是改善其光学气敏特性的一种重要途径。【方法】基于密度泛函理论的平面波超软赝势方法,模拟计算了含氧空位锐钛矿TiO_2(101)表面掺杂非金属C、N、F对NH_3分子吸附,对掺杂后锐钛矿TiO_2(101)表面结构的稳定性、NH_3分子吸附后表面结构的稳定性、态密度、电荷分布、差分电荷密度、光学性质给以理论分析。【结果】分析发现:非金属杂质C,N,F易掺杂于有氧空位的TiO_2(101)表面,且有基底的稳定性从大到小依次为C,N,F;杂质元素掺杂于基底表面提高了基底表面氧空位的氧化性,更有助于NH_3分子的吸附,且杂质元素对基底氧空位氧化性的贡献从小到大依次为C,N,F;通过态密度和光学性质分析,NH_3分子吸附在C和N掺杂于含氧空位TiO_2(101)基底表面相对于无掺杂含氧空位TiO_2(101)基底表面降低了材料在可见光范围内的利用率;而吸附在F元素掺杂于含氧空位TiO_2(101)基底表面对可见光范围内的利用率相对于吸附在无掺杂含氧空位TiO_2(101)基底表面的利用率提高了5倍。【结论】掺杂F元素显著的提高了材料的光学气敏传感能力。
[Purposes]The sensitive detection composition and concentration of environmental gas by metal oxide optical gas sensing materials has become a hot spot in recent research,and doping is an important way to improve the optical gas sensing properties.[Methods]By applying the first-principles plane-wave ultrasoft pseudopotential method based on density functional theory,the paper simulated the process which anatase TiO_2(101)surface doped nonmetal C,N,F with oxygen vacancies absorbed NH_3 and calculated the stability,density of state,charge distribution,electron density difference,and optical properties by theoretical analysis.[Findings]The results show that nonmetallic C,N and F are easily doped on TiO_2(101)surface with oxygen vacancies and the stability is C>N>F.Additionally,the impurity elements doped on the surface has improved the oxidation of the surface oxygen vacancies and the adsorption to NH_3 molecules.The order of impurity elements contributing to the oxidation of oxygen vacancies is:C>N>F.Through the analysis of states density and optical properties,it shows that TiO_2(101)substrates with oxygen vacancies doped C and N reduces the visible light utilization rate compared with un-doped surface.Moreover,TiO_2(101)substrates with oxygen vacancies doped with F increased about 5 times in visible light utilization rate than un-doped surface.[Conclusions]Doping F significantly improves the optical gas sensing ability of the material.
[Purposes]The sensitive detection composition and concentration of environmental gas by metal oxide optical gas sensing materials has become a hot spot in recent research,and doping is an important way to improve the optical gas sensing properties.[Methods]By applying the first-principles plane-wave ultrasoft pseudopotential method based on density functional theory,the paper simulated the process which anatase TiO_2(101)surface doped nonmetal C,N,F with oxygen vacancies absorbed NH_3 and calculated the stability,density of state,charge distribution,electron density difference,and optical properties by theoretical analysis.[Findings]The results show that nonmetallic C,N and F are easily doped on TiO_2(101)surface with oxygen vacancies and the stability is C>N>F.Additionally,the impurity elements doped on the surface has improved the oxidation of the surface oxygen vacancies and the adsorption to NH_3 molecules.The order of impurity elements contributing to the oxidation of oxygen vacancies is:C>N>F.Through the analysis of states density and optical properties,it shows that TiO_2(101)substrates with oxygen vacancies doped C and N reduces the visible light utilization rate compared with un-doped surface.Moreover,TiO_2(101)substrates with oxygen vacancies doped with F increased about 5 times in visible light utilization rate than un-doped surface.[Conclusions]Doping F significantly improves the optical gas sensing ability of the material.
引文
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[2]CECILIAIN M,CHAITO I V.Theoreticaland experimental analysis of the oxidation of CO on Pt catalysts supported on modified TiO2(101)[J].Journal of Molecular Catalysis A:Chemical,2015,407:102-112.
[3]汪洋.用分子轨道理论研究NO气体在TiO2表面吸附[J].化学学报,2005,63(11):1023-1027.WANG Y.Study of NO adsorption on TiO2(110)surface by molecular orbital theory[J].Acta Chimica Sinic,2005,63(11):1023-1027.
[4]汪洋,孟亮.TiO2表面氧空位对NO分子吸附的作用[J].物理学报,2005,54(5):6820-6824.WANG Y,MENG L.Effects of the oxygen vacancy on NO adsorption at the TiO2 surface[J].Acta Physica Sinica,2005,54(5):6820-6824.
[5]汪洋,刘祥.利用GAUSSIAN计算NO在TiO2(110)吸附和脱附[J].兰州交通大学学报,2006,25:47-50.WANG Y,LIU X.Calculation of adsorption and desorption of NO on TiO2(110)surface by GAUSSIAN[J].Journal of Lanzhou Jiaotong University,2006,25:47-50.
[6]马新国,唐超群,黄金球等.锐钛矿TiO2(101)面原子几何及弛豫结构的第一性原理计算[J].物理学报,2006,55(8):4208-4212.MA X G,TANG C Q,HUANG J Q.First-principle calculations on the geometry and relaxation structure of anatase TiO2(101)surface[J].Acta Physica Sinica,2006,55(8):4208-4212.
[7]马新国,江建军,梁培.锐钛矿TiO2(101)面本征点缺陷的理论研究[J].物理学报,2008,57(5):3120-3125.MA X G,JIANG J J,LIANG P.Theoretical study on intrinsic point defects of anatase TiO2(101)surface[J].Acta Physica Sinica,2008,57(5):3120-3125.
[8]MA X G,TANG C Q,YANG X H.Electronic tructures of S-doped anatase and rutile TiO2[J].Journal of Theoretical and Computational Chemistry,2011,6(1):23-32.
[9]马新国.锐钛矿型TiO2表面的理论研究[D].武汉:华中科技大学,2006.MA X G.Theoretical research on the surface of the TiO2anatase type[D].Wuhan:Huazhong University of Science and Technology,2006.
[10]FENG Q,YUE Y X,WANG W H,et al.First-principles study on anatase TiO2(101)surfaceadsorption of NO[J].Chinese Phys B,2014,4:215-222.
[11]朱洪强,冯庆,周晴,等.SP3杂化的气体分子在金红石相二氧化钛(110)面吸附规律与特性[J].中国科学:物理学力学天文学,2015,45(7):077301-077309ZHU H Q,FENG Q,ZHOU Q,et al.A study on adsorption law and characteristics of SP3hybrid gas molecules in the rutile titanium dioxide(110)surface[J].Scientia Sinica Physica,Mechanica and Astronomica,2015,45(7):077301-077309.
[12]CHEN Q L,TANG C Q,Zheng G.First-principles study of TiO2anatase(101)surfaces doped with N[J].Physica B,2009,404(8):1074-1078.
[13]Chen Q L,Tang C Q.First-principles calculations on electronic structures of N/F-doped and N-F-codoped TiO2anatase(101)surfaces[J].Acta Physico-Chimica Sinica,2009,25(5):915-920.
[14]RAINA W,PETER D,THOMAS F.First principles theoretical study of the hole-assisted conversion of CO to CO2on the anatase TiO2(101)surface[J].The Journal of chemical physics,2011,134(10):104701-104707.
[15]PERDEW J P.Restoring the Density-Gradient expansion for exchange in solids and surfaces[J].Phys Rev Lett,2008,100(13):136406-136410.
[16]FELIX R,RALF B,FLEMMING B,et al.Vicinal rutile TiO2 surfaces and their interactions with O2[J].Phys Chem C,2014,118(7):3620-3628.
[17]DIEBOLD U,LEHMAN J,MAHMOUD T,et al..Intrinsic defects on a TiO2(110)(1x1)surface and their reaction with oxygen:a scanning tunneling microscopy study[J].Surf Sci,1998,411(1/2):137-153.
[18]HEBENSTREIT E L D,HEBENSTREIT W,DIEBOLD U.Adsorption of sulfur on TiO2(110)studied with STM,LEED and XPS:temperature-dependent change of adsorption site combined with O-S exchange[J].Surf Sci,2000,461(1):87-97.
[19]PERDEW J P.Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces[J].Phys Rev Lett,2008,100(13):136406-136410.
[21]LIU B,GU M,LIU X L,et al.First-principles study offluorine-doped zinc oxide[J].Applied Physics Letters,2010,97(12):122101-1-122101-3.
[22]HAN Y,LIU C J,GE Q F.Interaction of Pt clusters with the Anatase surface:A First Principles Study[J].Phys Chem B,2006,110:7463-7472.
[23]沈学础.半导体光谱与光学性质[M].第二版.北京:科学出版社,1992.SHEN X C.Semiconductor spectrum and optical properties[M].2nd edition.Beijing:Science Press,1992.