稀土金属Y掺杂锐钛矿TiO_(2)(101)表面的改性

为了掌握Y原子掺杂在锐钛矿TiO_(2)(101)表面的稳定吸附位置和电子结构变化,提高其表面光催化活性,本文利用基于密度泛函理论的第一性原理计算研究了Y原子掺杂在完美的、带有亚表层氧空位和带有表层氧空位的锐钛矿TiO_(2)(101)表面的结构稳定性和电子性能。结构优化和电荷密度结果表明,Y原子可以稳定吸附在三种不同的表面上。在完美表面吸附时,Y原子最稳定的吸附位置是两个三配位O原子之间的空位;与完美表面类似,在带有亚表层氧空位表面吸附时,Y原子最稳定吸附位置是与氧空位邻近的两个三配位O原子之间的空位;而在带有表层氧空位表面吸附时,Y原子则停留于氧空位邻近的四配位Ti原子位置上最稳定。电荷密度计算结果也表明Y原子与这三种表面结合非常稳固。电子态密度计算结果表明,在带有表层氧空位的锐钛矿TiO_(2)(101)表面引入Y原子会在费米面附近的带隙中引入缺陷态,带隙从1.67 eV降至1.44 eV,这有可能引起电子的分级跃迁,提高表面光催化能力。本文的研究为利用单原子Y掺杂提高TiO_(2)(101)表面光催化能力提供了理论支持。

过渡金属掺杂锐钛矿TiO2(101)表面的改性

采用密度泛函理论的平面波超软赝势方法,对过渡金属Fe,Ni,Pd,Pt,Cu,Ag和Au的中性原子在锐钛矿TiO_2(101)面上的掺杂改性开展了系统深入的理论研究.通过比较分析锐钛矿TiO_2(101)面掺杂前后的几何结构、电子结构和光学性质等,揭示了宏观催化活性与电子结构、光电子特性之间的关联.结果表明:过渡金属掺杂能减小禁带宽度或引入杂质能级,从而提高TiO_2(101)面的可见光响应;杂质能级通常位于禁带内,这主要是由过渡金属原子的d电子态贡献形成的;不同过渡金属掺杂的TiO_2(101)面具有不同的光催化性能,这与掺杂后的禁带宽度、费米能级位置、杂质能级的形成位置以及过渡金属原子的最外层电子排布等有关.本研究为TiO_2光催化剂结构设计与改性提供了指导性参考,并有利于加深人们对其他材料的过渡金属掺杂的理解.

Photo-depositing Ru and RuO2 on Anatase TiO2 Nanosheets as Co-catalysts for Photocatalytic O2 Evolution from Water Oxidation

TiO2 nanosheets mainly exposed （001） facet were prepared through a hydrothermal process with HF as the morphology-directing agent. Ru and RuO2 species were loaded by photo-deposition methods to prepare the photocatalysts. The structural features of the catalysts were characterized by X-ray di raction, transmission electron microscopy, inductively cou-pled plasma atomic emission spectrum, and H2 Temperature-programmed reduction. The photocatalytic property was studied by the O2 evolution from water oxidation, which was examined with respect to the in uences of Ru contents as well as the oxidation and reduction treatments, suggesting the charge separation effect of the Ru species co-catalysts on di erent facets of TiO2 nanosheets. In contrast to Ru/TiO2 and RuO2/TiO2 with the single deposited co-catalyst, the optimized catalyst 0.5%Ru-1.0%RuO2/TiO2 with dual co-catalysts achieved a much improved catalytic performance, in terms of the synergetic effect of dual co-catalysts and the enhanced charge separation effect.

Impact of Oxygen Vacancy on Band Structure Engineering of n-p Codoped Anatase TiO2

Doping with various impurities is an effective approach to improve the photoelectrochemical properties of TiO2. Here, we explore the effect of oxygen vacancy on geometric and elec- tronic properties of compensated （i.e. V-N and Cr-C） and non-compensated （i.e. V-C and Cr-N） codoped anatase TiO2 by performing extensive density functional theory calculations. Theoretical results show that oxygen vacancy prefers to the neighboring site of metal dopant （i.e. V or Cr atom）. After introduction of oxygen vacancy, the unoccupied impurity bands located within band gap of these codoped TiO2 will be filled with electrons, and the posi- tion of conduction band offset does not change obviously, which result in the reduction of photoinduced carrier recombination and the good performance for hydrogen production via water splitting. Moreover, we find that oxygen vacancy is easily introduced in V-N codoped TiO2 under O-poor condition. These theoretical insights are helpful for designing codoped TiO2 with high photoelectrochemical performance.

Effects of crystallinity, {001}/{101} ratio, and Au decoration on the photocatalytic activity of anatase TiO_2 crystals

Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800℃. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800℃.

La掺杂TiO2(101)面的电子结构和光学性质的第一性原理研究

本文利用基于密度泛函理论的第一性原理方法研究了La掺杂TiO2(101)面的电子结构和光学性质,并讨论了其内部的微观机制.研究结果表明:La掺杂TiO2(101)面时,可以引起晶格畸变和偶极矩的产生.La@in1、La@O■和La@O2-O■模型为N型半导体,La@Ti5和La@Ti5-Ti6模型为P型半导体.La@O■和La@O2-O■模型的带隙减小和带隙中出现了杂质能级,杂质能级主要归因于Ti 3d轨道、O 2p轨道及它们之间的杂化作用.La@O2-O■模型在可见光区的吸收能力最强,主要归因于晶格畸变、带隙减小和杂质能带的出现.这些因素可以促进电子空穴对的产生和分离,从而使其在可见光区的光催化能力得到显著增强.

The adsorption and activation of formic acid on different anatase TiO2 surfaces

Formic acid photodegradation is one of the most important reactions in organic pollution control, and helps to improve the hydrogen generation efficiency in titanium dioxide catalyzed water photodecomposition. Based on density functional theory and Reax FF molecular dynamics, the adsorption, diffusion and activation of formic acid on the different anatase TiO（101）,（001）,（010） surfaces are investigated.The result shows that the adsorption of COOH on anatase TiOsurface shrinks the energy gap between the dehydrogenation intermediate COOH and HCOO. On the anatase TiO（101） surface, the formic acid breaks the O–H bond at the first step with activation energy 0.24 eV, and the consequent break of α-H become much easier with activation energy 0.77 eV. The dissociation of α-H is the determination step of the HCOOH decomposition.

Quasiparticle Band Structures of Defects in Anatase TiO2 Bulk

Quasiparticle band structures of the defective anatase TiO2 bulk with O vacancy, Ti interstitial and H interstitial are investigated by the GW method within many-body Green＇s function theory. The computed direct band gap of the perfect anatase bulk is 4.3 eV, far larger than the experimental optical absorption edge （3.2 eV）. We found that this can be ascribed to the inherent defects in anatase which drag the conduction band （CB） edge down. The occupied band-gap states induced by these defects locate close to the CB edge, exclud- ing the possible contribution of these bulk defects to the deep band-gap state below CB as observed in experiments.

First-principles study on anatase TiO_2 (101) surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.

Ultrasonic Degradation of Methyl Orange in Presence of Y2O3 Doping Anatase TiO2 Catalyst

Various affecting factors and degradation mechanism were studied on ultrasonic degradation of methyl orange adopting Y2O3 doping anatase TiO2 catalyst prepared in laboratory.In the experiment, the UV-VIS spectrophotometer was used to follow and inspect the degradation process of methyl orange.The results indicate that the ultrasonic degradation ratios of methyl orange in the presence of anatase TiO2 catalyst are much better than those without catalyst.Moreover, the catalytic performance of Y2O3 doping anatase TiO2 catalyst is obviously higher than that of anatase TiO2 catalyst without doping.The optimal conditions were adopted in this work and the degradation and COD elimination ratio of methyl orange got to98% and 99.0% in 90 min, respectively.

Adsorption Regularity and Characteristics of sp^3-Hybridized Gas Molecules on Anatase TiO_2(101) Surface

We report the anatase titanium dioxide （101） surface adsorption of sp3-hybridized gas molecules, including NH3, 1-12 0 and CH4, using first-principles plane-wave ultrasoft pseudopotential based on the density functional theory. The results show that it is much easier for a surface with oxygen vacancies to adsorb gas molecules than it is for a surface without oxygen vacancies. The main factor affecting adsorption stability and energy is the polarizability of molecules, and adsorption is induced by surface oxygen vacancies of the negatively charged center. The analyses of state densities and charge population show that charge transfer occurs at the molecule surface upon adsorption and that the number of transferred charge reduces in the order of N, 0 and C. Moreover, the adsorption method is chemical adsorption, and adsorption stability decreases in the order of NH3, tt2 0 and CH4. Analyses of absorption and reflectance spectra reveal that after absorbed CH4 and H2 O, compared with the surface with oxygen vacancy, the optical properties of materials surface, including its absorption coefficients and reflectivity index, have slight changes, however, absorption coefficient and reflectivity would greatly increase after NH3 adsorption. These findings illustrate that anatase titanium dioxide （101） surface is extremely sensitive to NH3.

Role of Reduced Defects for Coupling Reactions of Acetaldehyde on Anatase TiO2（001）-（1×4） Surface

The chemistry of acetaldehyde (CH3CHO) adsorbed on the anatase TiO2(001)-(1×4) surface has been investigated by temperature-programmed desorption (TPD) method. Our experimental results provide the direct evidence that the perfect lattice sites on the anatase TiO2(001)-(1×4) surface are quite inert for the reaction of CH3CHO, but the reduced defect sites on the surface are active for the thermally driven reductive carbon-carbon coupling reactions of CH3CHO to produce 2-butanone and butene. We propose that the coupling reactions of CH3CHO on the anatase TiO2(001)-(1×4) surface should undergo through the adsorption of paired CH3CHO molecules at the reduced defect sites, since the existing reduced Ti pairs provide the suitable adsorption sites.

Dependence of Nonlinear Optical Response of Anatase TiO2 on Shape and Excitation Intensity

Nonlinear optical （NLO） properties of anatase TiO2 with nanostructures of nanopaxticle （NP）, nanowire （NW） and annealed nanowire （NWA） are studied by open-aperture and closed-aperture Z-scan techniques with a fem- tosecond pulsed laser at wavelengths of 532 nm and 780 nm simultaneously. At 532 nm, when increasing excitation intensity, NLO absorption of TiO2 NPs transforms from saturable absorption to reverse-saturable absorption. However, NWs and NWAs exhibit the opposite change. At 780nm, all samples show reverse-saturable absorption, but have different sensitivities to excitation intensity. Due to the larger surface-to-volume ratio of NPs and less defects of NWAs by annealing, nonlinear optical absorption coet^icients follow the order NPs≥ NWs≥ NWAs. The results also show that these shape and annealing effects axe dominant at low excitation intensity, but do not exhibit at the high excitation intensity. The NLO refractive index of NPs shows a positive linear relationship with the excitation intensity, whereas NW and NWAs exhibit a negative linear relationship. The results could provide some foundational guidance to applications of anatase TiO2 in optoelectronic devices or other aspects.

轻稀土掺杂TiO2(101)面的电子结构和光学性质的理论研究

利用基于密度泛函理论的第一性原理方法研究了轻稀土掺杂TiO2(101)面的电子结构和光学性质,并讨论了其内部的微观机制.研究结果表明:稀土掺杂TiO2(101)面时,掺杂原子诱导掺杂体系的价带顶和导带底出现了显著的不对称,掺杂体系形成了兼并型的P型或N型半导体.掺杂体系的价带和导带出现了明显的移动,平均带隙相比未掺杂体系均出现了不同程度的增加,但是在带隙中出现了浅杂质能级.稀土原子替代O原子或以插入原子形成掺杂体系的光吸收强度明显高于稀土原子替代Ti原子形成的掺杂体系.La@O13体系和Ce@O13体系的光吸收能力最强,其可以归因于净磁矩的产生和浅杂质能级的形成,从而致使电子空穴对的产生和分离,进一步提高了掺杂体系在可见光区域的光催化吸收强度.研究结果可为二氧化钛在光电子器件领域的应用开发提供有益的理论依据.

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(英文)

采用密度泛函理论(DFT)平面波赝势方法计算了N/F掺杂和N-F双掺杂锐钛矿相TiO2(101)表面的电子结构.由于DFT方法存在对过渡金属氧化物带隙能的计算结果总是与实际值严重偏离的缺陷,本文也采用DFT+U(Hubbard系数)方法对模型的电子结构进行了计算.DFT的计算结果表明N掺杂后,N2p轨道与O2p和Ti3d价带轨道的混合会导致TiO2带隙能的降低,而F掺杂以及氧空位的引入对材料的电子结构没有明显的影响.DFT+U的计算却给出截然不同的结果,N掺杂并没有导致带隙能的降低,而只是在带隙中引入一个孤立的杂质能级,反而F掺杂以及氧空位的引入带来明显的带隙能降低.DFT+U的计算结果与一些实验测量结果能够较好地符合.

锐钛矿型(101)晶面吸附SF_6局部放电分解组分的气敏机理分析

气体绝缘组合开关(GIS)内部的局部放电会导致绝缘气体SF_6分解,生成多种特征气体。通过检测特征气体的成分和浓度能够及早发现GIS设备内部潜伏性绝缘缺陷,在设备绝缘状况恶化前提前预警,避免突发性故障发生。作为气敏传感领域的研究热点,TiO_2纳米管在GIS故障气体监测领域应用前景广阔。该文从微观层面上研究TiO_2纳米管气体传感器的气敏机理。利用Materials Studio软件仿真计算了锐钛矿型TiO_2(101)晶面的完美晶面、缺陷晶面以及Pt掺杂晶面对特征气体SO_2、SOF_2、SO_2F_2的吸附参数,理论分析了气体分子与晶面的作用过程,建立起晶面导电性能与气体分子吸附的联系。此外,通过气敏实验研究了本征及Pt掺杂TiO_2纳米管传感器对SO_2、SOF_2、SO_2F_2的气敏响应,并基于仿真结果解释实验现象,完善了TiO_2纳米管的气敏机理,为制备GIS设备局部放电监测的气敏传感器奠定了基础。

纳米TiO_2添加剂对ZL101A铝合金微弧氧化膜耐蚀性能的影响

目前,关于纳米TiO_2含量对铝合金微弧氧化膜耐蚀性的影响报道较少。在硅酸盐电解液中加入不同浓度纳米TiO_2,在ZL101A铝合金表面制备微弧氧化膜。采用扫描电镜(SEM)、X射线衍射仪(XRD)、电化学极化曲线及交流阻抗等,研究了纳米TiO_2浓度对微弧氧化膜耐蚀性能的影响。结果表明:纳米TiO_2进入到微弧氧化膜中,膜层表面变得更加致密;随着纳米TiO_2浓度的增加,膜层在3.5%Na Cl溶液中的腐蚀电流密度不断减小,交流阻抗不断增大,膜层的耐蚀性明显提高;综合考虑形貌和耐蚀性,本工作中纳米TiO_2最佳浓度为20 g/L。

锐钛矿型TiO_(2)(101)面对常见还原性气体CO、SO_(2)、H_(2)S吸附的微观机制与光学气敏特性研究

利用密度泛函理论体系下第一性原理平面波超软赝势方法,研究了锐钛矿型TiO_2(101)面吸附CO、SO_2、H_2S气体的微观机制与光学气敏性质。研究表明,这3种气体分子均能被TiO_2(101)面吸附,综合考虑吸附距离,吸附后结构的稳定性,吸附后电子的转移,与吸附后的光学性质,在这3种气体中,H_2S气体被TiO_2(101)面吸附后结构更稳定,电荷转移更明显,光学气敏特性较明显。