金红石TiO2纳米团簇与铀酰相互作用的相对论密度泛函理论计算

采用全电子相对论密度泛函理论方法探索金红石型Ti O_2纳米团簇与铀酰的相互作用。考察金红石团簇模型(包括层数和表面积大小)变化对吸附铀形成复合物结构、吸附作用能等性质的影响,确定2层、表面积为1.1 nm×0.6 nm、包括63个原子的纳米团簇(标记为2L-Ti15)能够合理描述金红石纳米粒子性质的同时,还能节约计算资源。对2L-Ti15-[(UO_2)(H_2O)_3]~(2+)复合物计算表明,纳米团簇和铀酰存在共价键作用;优化得到U-O_(surf)键长0.233~0.238 nm,这一距离在已发现铀酰基配合物U-O距离范围内。在气相条件下,纳米团簇对铀酰吸附反应为放热过程(-3.02 e V);考虑溶剂介质环境的影响,反应则需要吸收少许能量(0.16e V)。U-O_(surf)键的能量分解发现,纳米团簇和铀酰的化学键作用为轨道相互作用主导的(占94%),它的静电吸引略大于Pauli排斥。基于电子密度的QTAIM(quantum theory of atoms in molecule)分析揭示,U-O_(surf)作用是介于离子和共价之间的配位键,其强度高于复合物中的U-OH_2键作用,但比U=O键弱。波函数分析表明,来自纳米团簇的O(2p)贡献HOMO轨道,并混有σ(U=O)成键性质,而LUMO轨道则为Ti(3d)修饰的U(5f)性质,复合物HOMO-LUMO带隙为2.40 e V,相对吸附前的纳米团簇半导体粒子的3.35 e V变窄。从吸收光谱角度而言,复合物体系可能在可见光区域具有更强的捕光性能。     

An ONIOM and DFT study of water adsorption on rutile TiO2 (110) cluster

Density functional theory (DFT) calculations performed at ONIOM DFT B3LYP/6‐31G**‐MD/UFF level are employed to study molecular and dissociative water adsorption on rutile TiO₂ (110) surface represented by partially relaxed Ti₂₅O₃₇ ONIOM cluster. DFT calculations indicate that dissociative water adsorption is not favorable because of high activation barrier (23.2 kcal/mol). The adsorption energy and vibration frequency of both molecularly and dissociatively adsorbed water molecule on rutile TiO₂ (110) surface compare well with the values reported in the literature. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Structure and properties of polymer modified TiO2 pillared montmorillonite

With the aim of improving the microstructures and properties of TiO₂ pillared montmorillonite (MMT), a long-chain polymer (polyoxypropylenediamine, PPO-D 2000) was used as a template to synthesize composite pillared MMT. The materials were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectrophotometer, Fourier Raman (FT-Raman) spectrophotometer, thermo-gravimeter/differential thermogravimeter (TG/DSC), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) methods. The results show that as compared to low-molecular weight surfactant, this polymer significantly expanded the interlayer spacing and thus more TiO₂ could be intercalated into MMT. The specific surface area of polymer/TiO₂ pillared MMT was increased by 13% with comparison to TiO₂ pillared MMT and rose to 241.52 m²/g. Both the pore diameter and volume are doubled, and thus the pore structure is optimized markedly. The investigation on the photo-catalytic degradation of methyl orange in aqueous solution show that the modulation of polymer molecules raise the adsorption content of montmorillonite and improve the photo-catalytic activity. Therefore, this process provides a novel alternative to design and prepare the advanced eco-catalytic materials with high adsorption capacity and photo-catalytic activity. __________ Translated from Huaxue Tongbao, 2007, 12: 936–941 [译自: 化学通报]     

Active Sites for Adsorption and Reaction of Molecules on Rutile TiO2(110) and Anatase TiO2(001) Surfaces (cited: 1)

The reactivity of specific sites on rutile TiO₂(110)-(1×1) surface and anatase TiO₂(001)-(1×4) surface has been comparably studied by means of high resolution scanning tunneling microscopy. At the rutile TiO₂(110)-(1×1) surface, we find the defects of oxygen vacancy provide distinct reactivity for O₂ and CO₂ adsorption, while the terminal fivefold-coordinated Ti sites dominate the photocatalytic reactivity for H₂O and CH₃OH dissociation. At the anatase TiO₂(001)-(1×4) surface, the sixfold-coordinated terminal Ti sites at the oxidized surface seem to be inert in both O₂ and H₂O reactions, but the Ti-rich defects which introduce the Ti³⁺ state into the reduced surface are found to provide high reactivity for the reactions of O₂ and H₂O. By comparing the reactions on both rutile and anatase surfaces under similar experimental conditions, we find the reactivity of anatase TiO₂(001) is actually lower than rutile TiO₂(110), which challenges the conventional knowledge that the anatase (001) is the most reactive TiO₂ surface. Our findings could provide atomic level insights into the mechanisms of TiO₂ based catalytic and photocatalytic chemical reactions.     

用分子轨道理论研究NO气体在TiO2表面吸附

根据一氧化氮(NO)气体在二氧化钛(TiO₂)表面吸附和脱附的实验结果, 揭示了气体脱附量的变化规律. 利用MOPAC 和GAUSSIAN分子轨道理论计算了在TiO₂(110)表面上吸附NO分子的原子簇模型, 电荷分布以及原子簇的能级, 推断了NO在TiO₂(110)表面吸附的稳定性.     

水对甲醇在Rutile-TiO2(110)-(1 ×1)表面光催化解离的影响简

采用程序升温脱附方法研究了甲醇分子吸附在真空退火后的二氧化钛（110）表面的光催化过程,对比分析了单独吸附甲醇分子以及甲醇分子与水分子共吸附情况下的光催化解离过程. 结果表明,在二氧化钛（110）表面吸附的甲醇分子对共吸附水分子的光催化解离过程并没有直接的帮助作用. 共吸附状态下的水分子也同样没有影响到甲醇的光致解离过程,但是水分子的存在抑制了甲醇光解产物甲醛的光致脱附过程,同时促进了甲酸甲酯的形成.     

Photocatalytic degradation of methylene blue on Fe3+-doped TiO2 nanoparticles under visible light irradiation

Fe³⁺-doped TiO₂ composite nanoparticles with different doping amounts were successfully synthesized using sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultravioletvisible spectroscopy (UV-Vis) diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue was used as a model reaction to evaluate the photocatalytic activity of Fe³⁺/TiO₂ nanoparticles under visible light irradiation. The influence of doping amount of Fe³⁺ (ω: 0.00%–3.00%) on photocatalytic activities of TiO₂ was investigated. Results show that the size of Fe³⁺/TiO₂ particles decreases with the increase of the amount of Fe³⁺ and their absorption spectra are broaden and absorption intensities are also increased. Doping Fe³⁺ can control the conversion of TiO₂ from anatase to rutile. The doping amount of Fe³⁺ remarkably affects the activity of the catalyst, and the optimum efficiency occurs at about the doping amount of 0.3%. The appropriate doping of Fe³⁺ can markedly increase the catalytic activity of TiO₂ under visible light irradiation. __________ Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(6): 55–56 [译自: 西北师范大学学报(自然科学版)]     

Unique adsorption behaviors of NO and O2 at hydrogenated anatase TiO2(101)

The extra electron on the hydrogenated anatase TiO₂(101) is localized at the nearest Ti_5c only, and the chargetransfer promoted NO and O₂ adsorptions are also site-selective. These results are totally different from those at hydrogenated rutile TiO₂(110).     

Adsorption of uranyl species onto the rutile (110) surface: a periodic DFT study

To model the structures of dissolved uranium contaminants adsorbed on mineral surfaces and further understand their interaction with geological surfaces in nature, we have performed periodic density funtional theory (DFT) calculations on the sorption of uranyl species onto the TiO₂ rutile (110) surface. Two kinds of surfaces, an ideal dry surface and a partially hydrated surface, were considered in this study. The uranyl dication was simulated as penta‐ or hexa‐coordinated in the equatorial plane. Two bonds are contributed by surface bridging oxygen atoms and the remaining equatorial coordination is satisfied by H₂O, OH^?, and CO₃^2? ligands; this is known to be the most stable sorption structure. Experimental structural parameters of the surface–[UO₂(H₂O)₃]²⁺ system were well reproduced by our calculations. With respect to adsorbates, [UO₂(L1)_x(L2)_y(L3)_z]ⁿ (L1=H₂O, L2=OH^?, L3=CO₃^2?, x≤3, y≤3, z≤2, x+y+2z≤4), on the ideal surface, the variation of ligands from H₂O to OH^? and CO₃^2? lengthens the U? O_surf and U? Ti distances. As a result, the uranyl–surface interaction decreases, as is evident from the calculated sorption energies. Our calculations support the experimental observation that the sorptive capacity of TiO₂ decreases in the presence of carbonate ions. The stronger equatorial hydroxide and carbonate ligands around uranyl also result in U?O distances that are longer than those of aquouranyl species by 0.1–0.3 Å. Compared with the ideal surface, the hydrated surface introduces greater hydrogen bonding. This results in longer U?O bond lengths, shorter uranyl–surface separations in most cases, and stronger sorption interactions.     

Characterization of Titania/Silica Gel by Means of Low-Pressure Nitrogen Adsorption

Adsorbents synthesized by grafting of titania onto mesoporous silica gel surfaces at different temperatures were studied by means of nitrogen adsorption–desorption and water desorption. The pore size distribution f(R_p) of titania/silica gel depends on the titania concentration (C_TiO2) and the temperature of titania synthesis. Nonuniformity of TiO₂ phase is maximal at a low C_TiO2 value (3.2 wt.% anatase deposited at 473 K), and two peaks of the fractal dimension distribution f(D) are observed at such a concentration of titania, but at larger C_TiO2 values, only one f(D) peak is seen. More ordered filling of pores and adsorption sites by nitrogen, reflecting in the shape of adsorption energy distributions f(E) at different pressures of adsorbate, is observed for adsorbent with titania (rutile+anatase) grafted on silica gel at a higher temperature (673 K).     

Adsorption of CO2 in metal organic frameworks of different metal centres: Grand Canonical Monte Carlo simulations compared to experiments

A Grand Canonical Monte Carlo study has been performed in order to compare the different CO₂ adsorption mechanisms between two members of the MIL-n family of hybrid metal-organic framework materials. The MIL-53 (Al) and MIL-47 (V) systems were considered. The results obtained confirm that there is a structural interchange between a large pore and narrow pore forms of MIL-53 (Al), not seen with the MIL-47 (V) material, which is a consequence of the presence of μ ₂-OH groups. The interactions between the CO₂ molecules and these μ ₂ OH groups mainly govern the adsorption mechanism in this MIL-53 (Al) material. The subsequent breaking of these adsorption geometries after the adsorbate loading increases past the point where no more preferred adsorption sites are available, are proposed as key features of the breathing phenomenon. After this, any new adsorbates introduced into the MIL-53 (Al) large pore structure experience a homogeneous adsorption environment with no preferential adsorption sites in a similar way to what occurs in MIL-47 (V).     

Adsorption of acetonitrile and its reaction with oxygen on TiO2-supported Au — Rh bimetallic catalysts

The adsorption of acetonitrile and its surface reactions with oxygen on TiO₂-supported Au — Rh bimetallic catalysts were studied by FTIR and mass spectrometry at 300–673 K. The band due to CH₃CN on Lewis acid centres shifted to lower wavenumbers with the increase of the Rh content, which shows that the strength of Lewis acid sites weakens with the increase of the Rh content of the catalysts. CH₃CN, on the other hand, dissociates producing CN_(a) species. From the shift to higher wavenumbers of the band due to CN_(a), strengthening of the C — N bond with increasing Rh content has been established. During the heat treatments of the adsorbed CH₃CN layer, methylamine (CH₃NH₂) was detected in the gas phase, the amount of which depended on the composition of the catalysts. Dehydrogenation of the adsorbed acetonitrile also depends on the Rh content: the higher the Rh content of the sample, the lower the temperature of the first appearance of gaseous H₂, and the higher the amount of H₂ evolved. The presence of gaseous oxygen affects the formation of isocyanate (NCO) surface species only on 1% Au/TiO₂ and on 1% (0.75Au–0.25Rh)/TiO₂ catalysts.     

胶溶-水热晶化过程中纳米TiO2相稳定性研究

The phase stability of nanocrystaline anatase and rutile TiO2 in sols peptized at different temperature has been studied by X-ray Diffraction (XRD) and thermodynamical analysis. The results show that the stability of nanocrystaline TiO2 of different crystal types is a function of particle size. According to the thermodynamical analysis, anatase TiO2 becomes more stable than rutile TiO2 when the particle size is less than ca. 14 nm, which coincides with the experimental data obtained by XRD. Both surface Gibbs free energy and surface stress play important roles in the thermodynamically phase stability. Comparing the data calculated thermodynamically with the experimental results obtained under different temperatures, it is found that the constant K in the function relation, f=KGS, between surface free energy GS and surface stress f is temperature dependent and equal to 1 at 333 K and 2 at 453 K, respectively.     

NO adsorption on the stoichiometric and reduced SnO2(110) surface

The adsorption of NO molecules on the perfect and defective (110) surfaces of SnO₂ was studied with first-principles methods at the density-functional theory level. It was found that NO mainly interacts via the nitrogen atom with the bridging oxygens of the stoichiometric surface while the coordinatively unsaturated surface Sn atoms are less reactive. On the oxygen-deficient surface, NO is preferentially adsorbed at the vacancy positions, with the nitrogen atom close to the former surface oxygen site. Regardless of the adsorption site, the unpaired electron is located mainly on the NO molecule and only partly on surface Sn atoms. The results for the SnO₂ surface are compared to literature results on the isostructural TiO₂ rutile (110) surface. Dedicated to Professor Karl Jug on the occasion of his 65th birthday     

Thermal evolution of mesoporous titania prepared by CO2 supercritical extraction

Porous anatase is attractive because of its notable photo-electronic properties. Titania wet gel prepared by hydrolysis of Ti-alkoxide was immersed in the flow of supercritical CO₂ at 60°C and the solvent was extracted (aerogel). Mesoporous TiO₂ consisting of anatase nano-particles, about 5 nm in diameter, have been obtained. Thermal evolution of the microstructure of the aerogel was evaluated by TGA-DTA, N₂ adsorption, TEM and XRD, and discussed in comparison with that of the corresponding xerogel. The diffraction peaks of anatase were found for the as-extracted gel while the xerogel dried at 90°C was amorphous. After calcination at 600°C, the average pore size of the aerogel, about 20 nm in diameter, was 4 times larger than that of the xerogel, and the pore volume, about 0.35 cm³ g⁻¹, and the specific surface area, about 60 m² g⁻¹, were 2 times larger than those of the xerogel. XRD peaks of rutile have been found after calcination at 600°C. The particle sizes of anatase and rutile are about 13 and 25 nm in diameter, respectively. The surface morphology of TiO₂ nano-particles has been discussed in terms of their surface fractal dimensions estimated from the N₂ gas adsorption isotherms.     

An ONIOM and DFT study of water and ammonia adsorption on anatase TiO2 (001) cluster

Density functional theory (DFT) calculations at ONIOM DFT B3LYP/ 6‐31G**‐MD/UFF level are employed to study molecular and dissociative water and ammonia adsorption on anatase TiO₂ (001) surface represented by partially relaxed Ti₂₀O₃₅ ONIOM cluster. DFT calculations indicate that water molecule is dissociated on anatase TiO₂ (001) surface by a nonactivated process with an exothermic relative energy difference of 58.12 kcal/mol. Dissociation of ammonia molecule on the same surface is energetically more favorable than molecular adsorption of ammonia (?37.17 kcal/mol vs. ?23.28 kcal/mol). The vibration frequency values also are computed for the optimized geometries of adsorbed water and ammonia molecules on anatase TiO₂ (001) surface. The computed adsorption energy and vibration frequency values are comparable with the values reported in the literature. Finally, several thermodynamical properties (ΔH°, ΔS°, and ΔG°) are calculated for temperatures corresponding to the experimental studies. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Topotaxial formation of titanium-rich barium titanates during solid state reactions on (110) TiO2 (rutile) and (001) BaTiO3 single crystals

The orientation relationships of Ti-rich barium titanate phases formed by solid state reactions at high temperatures were studied using (110) TiO₂ (rutile) and (001) BaTiO₃ single-crystal substrates. Well-oriented Ba₆Ti₁₇O₄₀ islands were observed after a vapor–solid reaction of a BaO quantity equivalent to a nominal BaO film thickness of 1 nm with the TiO₂ substrate, whereas a thin film consisting of well-oriented BaTiO₃ and Ba₆Ti₁₇O₄₀ grains was formed after vapor–solid reaction of a BaO quantity equivalent to a nominal BaO film thickness of 50 nm with the rutile substrate. A topotaxial orientation relationship between Ba₆Ti₁₇O₄₀ and TiO₂ was found. Topotaxy is facilitated by a certain similarity in the oxygen sublattices of TiO₂ and Ba₆Ti₁₇O₄₀. The mechanism of the reaction occurring between BaO vapor and the TiO₂ surface at high temperature is discussed. On the other hand, several well-oriented Ba₄Ti₁₃O₃₀, Ba₆Ti₁₇O₄₀ and Ba₂Ti₅O₁₂ phases were observed to be embedded in the mainly forming Ba₂TiSi₂O₈ phase after a solid–solid reaction of amorphous SiO₂ thin films with (001) BaTiO₃ substrates at temperatures above 1000 °C. They were formed by a topotaxial reaction involving the transformation of (111) planes of BaTiO₃ into (001) planes of the Ti-rich phases by removal of BaO and insertion of TiO₂. Cross-sections of the interfaces between the substrates and the various reaction products are studied by (high-resolution) transmission electron microscopy.     

Influence of Gemini Surfactant with Modified TiO2 Nanoparticles on the Interfacial Tension of Oil/Water

The research on the impacts of modified TiO₂ nanoparticles (NPs) on interfacial tension (IFT) is in its infancy. Our work focuses on the IFT of the modified TiO₂ and Gemini surfactant N,N,N′,N′-tetramethyl-N,N′-dimyristyl-1,2-ethane diammonium dichlone (YND1233) complex solutions for reservoir stimulation purposes. The factors of YND1233, modified TiO₂ NPs, temperature, aging stability, adsorption loss, and mineralized degree were explored with the comparison of unmodified TiO₂ NPs and YND1233 as contrast samples. The results indicate that the dynamic IFTs decrease and then increase with the concentrations of YND1233 and modified TiO₂ NPs, and the minimum IFT appears at 0.200 and 0.010 wt%, respectively. YND1233/modified TiO₂ complex solutions show lower and more stable IFTs, better temperature resistance, longer aging time, and lower adsorption on the surface of quartz sand. The modified TiO₂ NPs and YND1233 in the YND1233/modified TiO₂ complex solution can be adsorbed to the interface and decrease the IFTs through synergistic effect. A mixed diffusion-kinetic mechanism is provided for the adsorption and interactions with Ca²⁺/Mg²⁺ involved in YND1233/modified TiO₂ complex solution.     

H2分子在LaFeO3表面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,通过计算表面能确定LaFeO₃(010)表面为最稳定的吸附表面,研究了H₂分子在LaFeO₃(010)表面的吸附性质。LaFeO₃(010)表面存在LaO和FeO₂两种终止表面,但吸附主要发生在FeO₂终止表面,由于LaFeO₃(010)表面弛豫的影响,使得凹凸不平的表面层增加了表面原子与H原子的接触面积,表面晶胞的纵向体积增加约2.5%,有利于H原子向晶体内扩散。研究发现,H₂分子在LaFeO₃(010)表面主要存在3种化学吸附方式:第一种吸附发生在O-O桥位,2个H原子分别吸附在2个O原子上,形成2个-OH基,这是最佳吸附位置,此时H原子与表面O原子的作用主要是H1s与O2p轨道杂化作用的结果,H-O之间为典型的共价键。H₂分子的解离能垒为1.542 eV,说明表面需要一定的热条件,H₂分子才会发生解离吸附;第二种吸附发生在Fe-O桥位,1个H原子吸附在O原子上形成1个-OH基,另一个H原子吸附在Fe原子上形成金属键;第三种吸附发生在O顶位,2个H原子吸附在同一个O原子上,形成H₂O分子,此时H₂O分子与表面形成物理吸附,H₂O分子逃离表面后容易形成氧空位。此外,H₂分子在LaFeO₃(010)表面还可以发生物理吸附。     

Facet Dependence of Photochemistry of Methanol on Single Crystalline Rutile Titania

The crystal phase, morphology and facet significantly influence the catalytic and photocatalytic activity of TiO₂. In view of optimizing the performance of catalysts, extensive efforts have been devoted to designing new sophisticate TiO₂ structures with desired facet exposure, necessitating the understanding of chemical properties of individual surface. In this work, we have examined the photooxidation of methanol on TiO₂(011)-(2×1) and TiO₂(110)-(1×1) by two-photon photoemission spectroscopy (2PPE). An excited state at 2.5 eV above the Fermi level (E_F) on methanol covered (011) and (110) interface has been detected. The excited state is an indicator of reduction of TiO₂ interface. Irradiation dependence of the excited resonance signal during the photochemistry of methanol on TiO₂(011)-(2×1) and TiO₂(110)-(1×1) is ascribed to the interface reduction by producing surface hydroxyls. The reaction rate of photooxidation of methanol on TiO₂(110)-(1×1) is about 11.4 times faster than that on TiO₂(011)-(2×1), which is tentatively explained by the difference in the surface atomic configuration. This work not only provides a detailed characterization of the electronic structure of methanol/TiO₂ interface by 2PPE, but also shows the importance of the surface structure in the photoreactivity on TiO₂.