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.

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。

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.

Effect of TiO_2 surface properties on the SCR activity of NOx emission abatement catalyst

NOx emission abatement catalysts V 2O 5 supported on various TiO 2 including anatase, rutile and mixture of both were investigated with various physico\|chemical measurements such as BET, NH\-3\|TPD, NARP, XRD and so on, and the effect of TiO\-2 surface properties on the SCR(selective catalytic reduction) activity of V\-2O\-5/TiO\-2 catalysts was studied. It was found that the TiO\-2 surface properties had strong affect on the SCR activity of V\-2O\-5/TiO\-2 catalysts. The stronger acidic property resulted in the higher exposure of active sites as well as the higher SCR activity.

Building surface defects by doping with transition metal on ultrafine TiO_2 to enhance the photocatalytic H_2 production activity

Inefficient charge separation and limited light absorption are two critical issues associated with high‐efficiency photocatalytic H2production using TiO2.Surface defects within a certain concentration range in photocatalyst materials are beneficial for photocatalytic activity.In this study,surface defects(oxygen vacancies and metal cation replacement defects)were induced with a facile and effective approach by surface doping with low‐cost transition metals(Co,Ni,Cu,and Mn)on ultrafine TiO2.The obtained surface‐defective TiO2exhibited a3–4‐fold improved activity compared to that of the original ultrafine TiO2.In addition,a H2production rate of3.4μmol/h was obtained using visible light(λ>420nm)irradiation.The apparent quantum yield(AQY)at365nm reached36.9%over TiO2‐Cu,significantly more than the commercial P25TiO2.The enhancement of photocatalytic H2production activity can be attributed to improved rapid charge separation efficiency andexpanded light absorption window.This hydrothermal treatment with transition metal was proven to be a very facile and effective method for obtaining surface defects.

Effects of Sintering Atmosphere on the Microstructure and Surface Properties of Symmetric TiO2 Membranes

The effects of sintering atmosphere on the properties of symmetric TiO2 membranes are studied with regard to sintering behavior, porosity, mean pore size, surface comPosition. and surface charge properties. The exerimental results show that the symmetric TiO2 membranes display better sintering activity in the air than in argon, and the mean pore diameters and porosities of the membrane sintered in argon are higher than those of the membrane sintered in the air at the same temperature. The surface compositions of the symmetric TiO2 membrane sintered in the air and in argon at different temperatures, as studied by X-ray photoelectron spectroscopy, are discussed in terms of their chemical composition, with particular emphasis on the valence state of the titanium ions. The correlation between the valence state of the titanium ions at the surface and the surface charge properties is examined.It is found that the presence of Ti^3＋, introduced at the surface of the symmetric TiO2 membranes by sintering in a lower partial pressure of oxygen, is related to a significant decrease in the isoelectric point. TiO2 with Ti^4＋ at the interface has an isoelectric point of 5.1, but the non-stoichiometric TiO2-x with Ti^3＋ at the interface has a lower isoelectric point of 3.6.

Fabrication of TiO_2(B)/anatase heterophase junctions in nanowires via a surface-preferred phase transformation process for enhanced photocatalytic activity

Heterojunction fabrication is one of the most effective strategies for enhancing the photocatalytic performance of semiconductor photocatalysts. Here, TiO2（B）/anatase nanowires with interfacial heterostructures were prepared through a three-step synthesis method, including hydrothermal treatment, H＋ exchange, and annealing. The phase structures of the nanowires in the bulk and on the surface during the annealing process were monitored by XRD and UV-Raman spectroscopy, respectively. SEM and TEM results indicate that the TiO2（B） nanowires partially collapse and transform into anatase during the annealing process and the heterophase junction structure is formed simultaneously. On the basis of the phase structure together with morphology data, a phase-transformation mechanism was proposed. Photocatalytic activity was evaluated by hydrogen production and pollutant-degradation assays. The optimized structure of the photocatalyst contains 24% TiO2（B） in the bulk and 100% anatase on the surface. The charge-carrier behavior during the photocatalytic process was investigated by photocurrent, electrochemical impedance spectroscopy（EIS）, and photoluminescence（PL） spectroscopy, which revealed that the heterophase-junction structure in the bulk was responsible for the highly efficient charge separation and transportation, etc.; the anatase on the surface took control of the high surface-reaction activity.

Growth mechanism of palladium clusters on rutile TiO_2 (110) surface

Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal.Thus in this paper,we embark on a systematic study for Pd n （n=1-5） clusters adsorbed on TiO2 （110） surface based on DFT-GGA calculations utilizing periodic supercell models.A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction,while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface.According to the transition states （TSs） search,the adsorbed Pd trimer tends to triangular growth mode,rather than linear mode,while the Pd4 and Pd5 clusters prefer three-dimensional （3D） models.However,the oxygen vacancy has almost no influence on the promotion of Pd n cluster nucleation.Additionally,of particular significance is that the Pd-TiO2 interaction is the main driving force at the beginning of Pd nucleation,whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger.It is hoped that our theoretical study would shed light on further designing high-performance TiO2 supported Pd-based catalysts.

Synthesis and Optimization of TiO_(2)/Graphene with Exposed {001} Facets Based on Response Surface Methodology and Evaluation of Enhanced Photocatalytic Activity

Response surface methodology(RSM)was employed to optimize the control parameters of TiO_(2)/graphene with exposed{001}facets during synthesis,and its enhanced photocatalytic activities were evaluated in the photodegradation of toluene.Experimental results were in good agreement with the predicted results obtained using RSM with a correlation coefficient(R^(2))of 0.9345.When 22.06 mg of graphite oxide(GO)and 2.09 mL of hydrofluoric acid(HF)were added and a hydrothermal time of 28 h was used,a maximum efficiency in the degradation of toluene was achieved.X-ray diffraction(XRD),transmission electron microscopy(TEM),and scanning electron microscopy(SEM)were employed to characterize the obtained hybrid photocatalyst.The electron transferred between Ti and C retarded the combination of electron–hole pairs and hastened the transferring of electrons,which enhanced the photocatalytic activity.

Surface Texturing of TiO_2 Film by Mist Deposition of TiO_2 Nanoparticles

Unique and various microstructures of titanium oxide(TiO_2 ) film including macroporous structure, chromatic veins and rings, have been easily fabricated by mist deposition method on silicon substrate with mild preparation conditions. Rutile phase TiO_2 nanoparticles were directly used as starting material to prepare film and led to a simple preparation process. It was found that several different microstructures existed in the sample and changed with the varied positions from the center to the edge of the film when the concentration of the TiO_2 suspension is 0.06 mol/l, the deposition time is 30 min, the flow rate is 1 l/min and the temperature is150. The surface texturing shows apparent distinction as the concentration of the TiO_2 suspension decreased to 0.03 mol/l and 0.01 mol/l.

Surface Microstructure Characterization of Sol-gel Derived Porous TiO_2 Thin Films

Porous TiO2 thin films were prepared from alkoxide solutions with and without polyethylene glycol (PEG) by sol-get route on soda lime glass, and were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that TiO2 film prepared from precursor solution without PEG is composed of spherical particles of about 100 nm and several nanometer mesoporous pores. With the increase of the amount of PEG added to the precursor solution, the diameter and the depth of the pores in the resultant films increas on the decomposition of PEG during heat-treatment, which lead to them increase of the surface roughness of the films. XRD and TEM results show that the single anatase phase is precipitated and there are some orientation effects in (101) direction.

Photocatalytic reaction kinetics model based on electrical double layer theory Ⅲ.Surface complexation model of methyl orange adsorption on TiO_2 surface

Based on the infrared characterization of methyl orange adsorption on TiO 2 surface and the titration of TiO 2, the triple layer model of methyl orange adsorption on TiO 2 was established according to electric double theory. The software FITEQL3.1 was applied to calculate the distribution of organic adsorption on TiO 2 surface by introducing dummy components to help to overcome mathematical difficulties. It is shown that the chem. adsorption species of methyl orange have a great adsorption amount. The adsorption constants of three kinds of surface complexation expressed as SOH +org -,SOH 2org 2 and SOHorg - are 5.98, 17.57 and -4.2, respectively.

TiO_2/Ag composite nanowires for a recyclable surface enhanced Raman scattering substrate

Multifunctional TiO2/Ag composite nanowires are fabricated with a hydrothermal method by precipitating Ag nanoparticles （NPs） on the surfaces of TiO2 nanowires. This hierarchical one-dimensional （1D） nanostructure can be used as a surface enhanced Raman scattering （SERS） substrate with high sensitivity, for detecting the rhodamine 6G （R6G） in a wide range of low concentrations （from 1 × 10 6 M to 1 × 10-12 M）. In addition, the substrate can be self-cleaned under the irradiation of ultraviolet （UV） light due to the superior photocatalytic capacity of the TiO2/Ag composite nanostructure, making the recycled use of SERS substrates closer to reality. With both the evident SERS performance and high efficiency of photocatalytic capacity, such TiOz/Ag composite nanowires demonstrate considerable potential in the chemical sensing of organic pollutants.

Surface constructions of nano TiO_2 as the environmental and energy materials

TiO_2 has attracted an increasing attention because of its variety of potential applications in environments and energies,such as gas sensing,self-cleaning,solar energy conversion, wettability and photo-catalysis applications.In this presentation,we summarize some progress in surface constructions of nano TiO_2 and its characterizations of physicochemistry and properties. (1)Superhydrophobic nanostructure TiO_2 films Superhydrophobic nanotube,nanopore and sponge-like structure TiO_2 films are fabricated ...

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.

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。

The Ab Initio Studies of NO Chemisorption on TiO_2(110) Surface

The studies of NO chemisorption on TiO2(110) surface are the base of research to NO decomposed to N2O on TiO2 surface. In this paper, 12 kinds of possible models of NO adsorbed on TiO2 perfect and defect surface were calculated by use of ab initio cluster method. We carried out optimization of the geometry, calculation of the chemisorption energy and analysis of the Mulliken population to those adsorption models. According to the calculation results, it can be got that the adsorbed decomposition of NO on defect surface is more advantageous and M6 and M12 are the important models to NO chemisorption and decomposition on TiO2 surface.

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.