H2O和OH在UO(100)表面吸附的密度泛函研究

运用密度泛函理论中的广义梯度近似(GCA)的PW91方法结合周期性平板模型,研究了H2O分子和OH在UO(100)表面上的吸附.通过对不同吸附位的吸附能和几何结构参数的计算和比较发现:水分子在UO(100)表面的吸附为化学吸附,水分子平面与UO(100)表面夹角为15°的吸附构型最稳定,吸附能最大,近89 kJ·mol-1.对H2O吸附前后的态密度分析可知,H2O通过其O原子的P轨道与底物U原子的d轨道作用.本文还进一步探讨H2O在UO(100)表面的解离机理.     

水分子和二氧化铈(111)表面相互作用的DFT+U研究

采用引入Hubbard参数U修正的密度泛函理论(DFT+U)方法, 对水分子在二氧化铈(111)表面的吸附作用进行了研究. 计算结果表明: 在氧化的二氧化铈(111)表面, 水分子以单氢键构型吸附在二氧化铈表面, 但是不能自发解离; 在还原的二氧化铈(111)表面, 水分子或化学吸附在衬底上, 或自发解离成表面羟基结构. 与氢气在氧化的二氧化铈(111)表面上物理吸附体系的总能相比, 羟基化表面构型是能量更低的构型, 所以羟基解离形成氢气, 从而使表面被氧化的过程需要有外部条件, 反应不能自发进行. 因此, 水分子在还原的二氧化铈(111)表面有两个可能的状态, 即无氢键结构的化学吸附和表面羟基结构的解离吸附. 在一定的外部条件下, 表面羟基结构进一步解离形成氢气, 并使还原的二氧化铈(111)表面得以氧化.     

Impurity atom

气体分子与光催化剂之间的相互作用对于光催化反应的触发非常重要.对于Ti O2, ZnO和WO3等传统金属氧化物光催化剂上的水分解反应而言,已有许多报道研究了水分子在它们表面的吸附行为.结果表明,水分子与催化剂表面的原子形成了O–H…O氢键.石墨相氮化碳(g-C3N4)是一种具有可见光响应且化学性质稳定的光催化剂,对其进行修饰以增强其分解水产氢性能的研究非常多.本文通过密度泛函理论计算,全面研究了水分子在均三嗪(s-triazine)基g-C3N4上的吸附情况.首先构建了一系列初始吸附模型,考察了各种吸附位和水分子的朝向.通过比较分析计算得到的吸附能,确定了一种最优的吸附构型,即水分子以竖直的朝向吸附于褶皱的单层g-C3N4表面.水分子中的一个极性O–H键与g-C3N4中一个二配位富电子的氮原子结合形成了分子间的O–H…N氢键.其中, H原子与N原子的间距为1.92?, O–H键的键长由0.976?增至0.994?.进一步通过计算Mulliken电荷,态密度和静电势曲线分析了该吸附体系的电子性质.结果发现在分子间氢键的桥接作用下, g-C3N4上的电子转移至水分子,由此导致g-C3N4的费米能级降低,功函数由4.21 eV增至5.30 eV.在该吸附模型的基础上,考查了不同的吸附距离.当水分子与g-C3N4的间距设为1至4?时,几何优化后总是能得到相同的吸附构型,吸附能和氢键长度也十分相近.随后,通过改变吸附基底g-C3N4的大小和形状,验证了这种吸附构型具有很强的重复性.将2?2单层g-C3N4吸附基底替换为2?2多层g-C3N4 (2至5层), 3?3和4?4单层g-C3N4,以及具有不同管径的单壁g-C3N4纳米管后,水分子的吸附能随着体系原子数的增多而增大,但吸附模型的几何结构和电子性质基本不变,包括O–H…N氢键的形成和键长,以及电子转移和增大的功函数.另外还研究了非金属元素(P, O, S, Se, F, Cl和Br)掺杂对吸附能的影响.构建模型时,杂质原子以取代二配位氮原子的方式进行掺杂,水分子放置于杂质原子上方.结果显示,引入杂质原子后水分子的吸附能增大,在理论上从吸附的角度解释了元素掺杂增强g-C3N4分解水活性.总之,本文揭示了一种在分子间氢键的作用下,具有高取向性的水分子吸附的g-C3N4构型,这有助于g-C3N4基光催化剂上水分解过程的理解和优化设计.     

表面增强拉曼光谱研究银电极/乙腈界面微量水的吸附行为

利用表面增强拉曼散射技术研究了含微量水的乙腈溶液中银电极 /乙腈界面水分子的吸附行为 ,详细考察了随电极电位的改变及微量水浓度对其的影响 .研究表明 ,银电极双电层中存在多种吸附模式下的水分子结构 .在较正电位下 ,水分子主要与乙腈形成弱的氢键共吸附于电极表面上 ,ν(O— H)伸缩振动出现在3 487cm- 1左右 ,一定范围内增加体相水的浓度对其影响较小 ;在较负电位下 ,随着乙腈解离反应的进行 ,水分子转为与表面配合物 [Ag(CN) n]( n- 1 ) - 作用而共吸附于电极表面 ,其有序性地增加导致 ν(O— H)频率出现在更高的波数 3 5 83 cm- 1 .增加水的浓度加强了界面水分子间的氢键作用 ,致使 ν(O— H)红移 ;在极负电位下 ,水分子发生解离 ,ν(O— H)的振动主要来自 Li OH微晶 ,其波数为 3 665 cm- 1 .随着体相水含量的增加 ,电极表面进一步形成水合 Li OH· H2 O,特征 ν(O— H)的波数为 3 5 63 cm- 1 .     

银表面甲醇氧化反应机理的ab initio计算研究 1: 银表面静态吸附物种的几何构型和吸附性质

本文用原子簇模型(CM)的从头计算方法, 计算了银表面甲醇氧化反应中的静态吸附物种的优化几何构型及吸附性质。计算表明在清洁银表面甲醇、甲醛只存在物理吸附; 当表面存在吸附氧原子时, 甲醇可在银表面形成两种分子态吸附;甲醛与表面羟基OH(a)或氢原子H(a)共存时在银表面能够形成化学吸附, 且CH2O(a)极易与O(a)反应生成深度氧化中间体η^2-甲二氧基; 中间产物甲氧基在无氧的银表面能够形成稳定吸附, 在富氧银表面极易进一步氧化脱氢生成产物甲醛。通过计算与实验结果的对照, 我们对反应机理作了初步讨论。     

银表面甲醇氧化反应机理的ab initio计算研究 1: 银表面静态吸附物种的几何构型和吸附性质

本文用原子簇模型(CM)的从头计算方法, 计算了银表面甲醇氧化反应中的静态吸附物种的优化几何构型及吸附性质。计算表明在清洁银表面甲醇、甲醛只存在物理吸附; 当表面存在吸附氧原子时, 甲醇可在银表面形成两种分子态吸附;甲醛与表面羟基OH(a)或氢原子H(a)共存时在银表面能够形成化学吸附, 且CH2O(a)极易与O(a)反应生成深度氧化中间体η^2-甲二氧基; 中间产物甲氧基在无氧的银表面能够形成稳定吸附, 在富氧银表面极易进一步氧化脱氢生成产物甲醛。通过计算与实验结果的对照, 我们对反应机理作了初步讨论。     

(C_5H_7N_2)_3AsMo_(12)O_(40)·5H_2O的合成、表征及光催化性能研究

合成了配合物(C5H7N2)3AsMo12040·5H2O,对其进行了IR和TG/DTA分析,并用X-射线单晶衍射仪测定了晶体结构。配合物晶体属于单斜晶系,P-1空间群。配合物经N—H…N和N—H…O氢键相连组成超分子化合物,氢键稳定了晶体结构。将该配合物掺杂TiO2制备复合催化剂(C5H7N2)3AsMo12040·5H2O/TiO2,以甲醇、丙酮气体消除反应为模式反应评价该配合物和复合催化剂的光催化性能。结果表明,复合催化剂的催化活性优于配合物本身和TiO2。配合物中的有机分子,对有机物有强的亲和性,更容易吸附有机分子利于光催化反应的进行。     

水分子在均三嗪基g-C3N4上的吸附

气体分子与光催化剂之间的相互作用对于光催化反应的触发非常重要.对于TiO2,ZnO和WO3等传统金属氧化物光催化剂上的水分解反应而言,已有许多报道研究了水分子在它们表面的吸附行为.结果表明,水分子与催化剂表面的原子形成了O-H…O氢键.石墨相氮化碳(g-C3N4)是一种具有可见光响应且化学性质稳定的光催化剂,对其进行修饰以增强其分解水产氢性能的研究非常多.本文通过密度泛函理论计算,全面研究了水分子在均三嗪(s-triazine)基g-C3N4上的吸附情况.首先构建了一系列初始吸附模型,考察了各种吸附位和水分子的朝向.通过比较分析计算得到的吸附能,确定了一种最优的吸附构型,即水分子以竖直的朝向吸附于褶皱的单层g-C3N4表面.水分子中的一个极性O-H键与g-C3N4中一个二配位富电子的氮原子结合形成了分子间的O-H…N氢键.其中,H原子与N原子的间距为1.92?,O-H键的键长由0.976?增至0.994?.进一步通过计算Mulliken电荷,态密度和静电势曲线分析了该吸附体系的电子性质.结果发现在分子间氢键的桥接作用下,g-C3N4上的电子转移至水分子,由此导致g-C3N4的费米能级降低,功函数由4.21 eV增至5.30 eV.在该吸附模型的基础上,考查了不同的吸附距离.当水分子与g-C3N4的间距设为1至4?时,几何优化后总是能得到相同的吸附构型,吸附能和氢键长度也十分相近.随后,通过改变吸附基底g-C3N4的大小和形状,验证了这种吸附构型具有很强的重复性.将2′2单层g-C3N4吸附基底替换为2′2多层g-C3N4(2至5层),3′3和4′4单层g-C3N4,以及具有不同管径的单壁g-C3N4纳米管后,水分子的吸附能随着体系原子数的增多而增大,但吸附模型的几何结构和电子性质基本不变,包括O-H…N氢键的形成和键长,以及电子转移和增大的功函数.另外还研究了非金属元素(P,O,S,Se,F,Cl和Br)掺杂对吸附能的影响.构建模型时,杂质原子以取代二配位氮原子的方式进行掺杂,水分子放置于杂质原子上方.结果显示,引入杂质原子后水分子的吸附能增大,在理论上从吸附的角度解释了元素掺杂增强g-C3N4分解水活性.总之,本文揭示了一种在分子间氢键的作用下,具有高取向性的水分子吸附的g-C3N4构型,这有助于g-C3N4基光催化剂上水分解过程的理解和优化设计.     

纳米TiO_2的有机酸改性

纳米TiO2粉体独特的光催化作用、颜色效应以及紫外屏蔽等功能使其在汽车工业、防晒化妆品、环保等方面有着广阔的应用前景[1-3]。未经表面处理的纳米TiO2表面疏油,不易在有机介质中分散,直接影响到TiO2性能的发挥。锐钛矿型TiO2晶体中[4], Ti—O键距离短且不等长,分别为1·937A°和1·964A°,这种不平衡使TiO2分子极性很强,强极性使得TiO2表面易吸附水分子并使水分子极化而形成表面羟基。本文选用月桂酸和棕榈酸作为改性剂,让羧基与TiO2的羟基以化学吸附的形式连接起来,使纳米TiO2表面改性为亲油性。结果表明棕榈吸的改性效果较月桂…     

甲酸在Au（997）台阶表面的氧化反应

金催化是纳米催化的代表性体系之一,但对金催化作用的理解还存在争议,特别是金颗粒尺寸对其催化作用的影响.金颗粒尺寸减小导致的表面结构主要变化之一是表面配位不饱和金原子密度的增加,因此研究金原子配位结构对其催化作用的影响对于理解金催化作用尺寸依赖性具有重要意义.具有不同配位结构的金颗粒表面可以利用金台阶单晶表面来模拟.我们研究组以同时具有Au(111)平台和Au(111)台阶的Au(997)台阶表面为模型表面,发现Au(111)台阶原子在CO氧化、NO氧化和NO分解反应中表现出与Au(111)平台原子不同的催化性能.负载型Au颗粒催化甲酸氧化反应是重要的Au催化反应之一.本文利用程序升温脱附/反应谱(TDS/TPRS)和X射线光电子能谱(XPS)研究了甲酸在清洁的和原子氧覆盖的Au(997)表面的吸附和氧化反应,观察到Au(111)台阶原子和Au(111)平台原子不同的催化甲酸根氧化反应行为.与甲酸根强相互作用的Au(111)台阶原子表现出比与甲酸根弱相互作用的Au(111)平台原子更高的催化甲酸根与原子氧发生氧化反应的反应活化能.在清洁Au(997)表面,甲酸分子发生可逆的分子吸附和脱附.甲酸分子在Au(111)台阶原子的吸附强于在Au(111)平台原子的吸附. TDS结果表明,吸附在Au(111)台阶原子的甲酸分子的脱附温度在190 K,吸附在Au(111)平台原子的甲酸分子的
　　脱附温度在170 K. XPS结果表明,分子吸附甲酸的C 1s和O 1s结合能分别位于289.1和532.8 eV.利用多层NO2的分解反应在Au(997)表面控制制备具有不同原子氧吸附位和覆盖度的原子氧覆盖Au(997)表面,包括氧原子吸附在(111)台阶位的0.02 ML-O(a)/Au(997)、氧原子同时吸附在(111)台阶位和(111)平台位的0.12 ML-O(a)/Au(997)、氧原子和氧岛吸附在(111)平台位和氧原子吸附在(111)台阶位的0.26 ML-O(a)/Au(997). TPRS和XPS结果表明,甲酸分子在105 K与Au(997)表面原子氧物种反应生成甲酸根和羟基物种,但甲酸根物种的进一步氧化反应依赖于Au原子配位结构和各种表面物种的相对覆盖度.在0.02 ML-O(a)/Au(997)表面暴露0.5 L甲酸时, Au(111)台阶位氧原子完全反应,甲酸过量.表面物种是Au(111)台阶位吸附的甲酸根、羟基和甲酸分子.在加热过程中,甲酸分子与羟基在181 K反应生成甲酸根和气相水分子(HCOOH(a)+ OH(a)= H2O + HCOO(a)),甲酸根在340 K发生歧化反应生成气相HCOOH和CO2分子(2HCOO(a)= CO2+ HCOOH).在0.12 ML-O(a)/Au(997)和0.26 ML-O(a)/Au(997)表面暴露0.5 L甲酸时,甲酸分子完全反应,原子氧过量.表面物种是Au(111)平台位和Au(111)台阶位吸附的甲酸根、羟基和原子氧.在加热过程中, Au(111)平台位和Au(111)台阶位的甲酸根分别在309和340 K同时发生氧化反应(HCOO(a)+ O(a)= H2O + CO2)和歧化反应(2HCOO(a)= CO2+ HCOOH)生成气相CO2, H2O和HCOOH分子.在0.26 ML-O(a)/Au(997)表面暴露10 L甲酸时,甲酸分子和原子氧均未完全消耗.表面物种是Au(111)平台位和Au(111)台阶位吸附的甲酸根、羟基、甲酸分子和原子氧.在加热过程中,除了上述甲酸根的氧化反应和歧化反应,还发生171 K的甲酸分子与羟基的反应(HCOOH(a)+ OH(a)= H2O + HCOO(a))和216 K的羟基并和反应(OH(a)+ OH(a)= H2O + O(a)).     

Probing defect sites on TiO2 with [Re3(CO)12H3]: spectroscopic characterization of the surface species

Samples of the anatase phase of titania were treated under vacuum to create Ti(3+) surface-defect sites and surface O(-) and O(2) (-) species (indicated by electron paramagnetic resonance (EPR) spectra), accompanied by the disappearance of bridging surface OH groups and the formation of terminal Ti(3+)-OH groups (indicated by IR spectra). EPR spectra showed that the probe molecule [Re(3)(CO)(12)H(3)] reacted preferentially with the Ti(3+) sites, forming Ti(4+) sites with OH groups as the [Re(3)(CO)(12)H(3)] was adsorbed. Extended X-ray absorption fine structure (EXAFS) spectra showed that these clusters were deprotonated upon adsorption, with the triangular metal frame remaining intact; EPR spectra demonstrated the simultaneous removal of surface O(-) and O(2) (-) species. The data determined by the three complementary techniques form the basis of a schematic representation of the surface chemistry. According to this picture, during evacuation at 773 K, defect sites are formed on hydroxylated titania as a bridging OH group is removed, forming two neighboring Ti(3+) sites, or, when a Ti(4+)-O bond is cleaved, forming a Ti(3+) site and an O(-) species, with the Ti(4+)-OH group being converted into a Ti(3+)-OH group. When the probe molecule [Re(3)(CO)(12)H(3)] is adsorbed on a titania surface with Ti(3+) defect sites, it reacts preferentially with these sites, becoming deprotonated, removing most of the oxygen radicals, and healing the defect sites.     

As(V)在TiO2表面的吸附机理

用延展X射线吸收精细结构(EXAFS)光谱和密度泛函理论(DFT)研究了As(V)-TiO2体系的吸附机理. 离子强度变化对As(V)-TiO2体系吸附无显著影响, 表明吸附后形成了内层络合物. EXAFS结果表明, As(V)原子主要通过—AsO4上的O原子结合到TiO2表面上, 平均As-O原子间距(R)在吸附前后无明显变化, 保持在(0.169±0.001) nm. As-Ti层的EXAFS分析结果与DFT计算的吸附构型的As-Ti原子间距对照表明, 体系存在两种主要亚稳平衡吸附(MEA)结构, 即对应于R1=(0.321±0.002) nm 的双角(DC)强吸附构型和R2=(0.360±0.002) nm的单角(SC)弱吸附构型. 而且随着吸附量由9.79 mg·g-1增加至28.0 mg·g-1, 吸附样品中双角构型配位数与单角构型配位数的比值(CN1/CN2)从3.3降低到1.6, 说明双角亚稳平衡吸附结构在低覆盖度时占优势, 而在高表面覆盖度时单角亚稳平衡吸附结构占优势, 即在表面覆盖度较大时, As(V)在TiO2表面上倾向于形成单角构型.     

The adsorption and reaction of a titanate coupling reagent on the surfaces of different nanoparticles in supercritical CO2

The adsorption and reaction in supercritical CO2 of the titanate coupling reagent NDZ-201 on the surfaces of seven metal oxide particles, SiO2, Al2O3, ZrO2, TiO2 (anatase), TiO2 (rutile), Fe2O3, and Fe3O4, was investigated. FTIR and TG analysis indicated that the adsorption and reaction were different on different particle surfaces. On SiO2 and Al2O3 particles, there was a chemical reaction of the titanate coupling reagent on the surfaces. On the surfaces of ZrO2 and TiO2 (anatase) particles, there were two kinds of adsorption, weak and strong adsorption. On the surfaces of TiO2 (rutile), Fe2O3, and Fe3O4 particles, there was only weak adsorption. The acidity or basicity of the OH groups on the particle surface was the key factor that determined if a surface reaction occurred. When the OH groups were acidic, the titanate coupling reagent reacted with these, but otherwise, there was no reaction. The surface density of OH groups on the original particles and the amount of titanate coupling reagent adsorbed and reacted were estimated from TG analysis. The reactivity of the surface OH groups of Al2O3 particles was higher than that of the SiO2 particles.     

Mechanism of photoinduced superhydrophilicity on the TiO2 photocatalyst surface

The physicochemical properties of the H(2)O molecules adsorbed on TiO(2) surfaces during UV light irradiation were fully investigated by near-infrared (NIR) absorption spectroscopy. It was found that the H(2)O molecules adsorbed on the TiO(2) surfaces desorb during UV light irradiation by the heating effect of the light source. Since the amount of the H(2)O adsorbed on the TiO(2) surfaces decreased, the distribution of the hydrogen bonds within the H(2)O molecules decreased, resulting in a decrease in the surface tension of the H(2)O clusters. The decrease in the surface tension of H(2)O under UV light irradiation was found to be one of the most important driving forces in which the H(2)O clusters on the TiO(2) surface spread out thermodynamically, forming H(2)O thin layers. The partial elimination of the hydrocarbons from the TiO(2) surface by the photocatalytic complete oxidation was seen to be the other important factor, providing free spaces on the surface where the H(2)O clusters could spill over and spread out to form the thin H(2)O layers. Moreover, the temperature changes of the TiO(2) powder samples during UV light irradiation were found to show a good correspondence with the changes in the contact angle of the H(2)O droplets on the TiO(2) thin film surfaces. Especially the time scale for the hydrophilic conversion on the TiO(2) surfaces under UV light irradiation was in good agreement with the decrease in the amount of H(2)O molecules adsorbed on the TiO(2) surfaces but not the amount of the hydrocarbons eliminated by the photocatalytic oxidation reactions, showing that the adsorption and desorption of H(2)O molecules are generally quite sensitive to the temperature changes of solid surfaces.     

Adsorption and solar light decomposition of acetone on anatase TiO2 and niobium doped TiO2 thin films

Adsorption and solar light decomposition of acetone was studied on nanostructured anatase TiO2 and Nb-doped TiO2 films made by sol-gel methods (10 and 20 mol % NbO2.5). A detailed characterization of the film materials show that films contain only nanoparticles with the anatase modification with pentavalent Nb oxide dissolved into the anatase structure, which is interpreted as formation of substituted Nb=O clusters in the anatase lattice. The Nb-doped films displayed a slight yellow color and an enhanced the visible light absorption with a red-shift of the optical absorption edge from 394 nm for the pure TiO2 film to 411 nm for 20 mol % NbO2.5. In-situ Fourier transform infrared (FTIR) transmission spectroscopy shows that acetone adsorbs associatively with eta1-coordination to the surface cations on all films. On Nb-doped TiO2 films, the carbonyl bonding to the surface is stabilized, which is evidenced by a lowering of the nu(C=O) frequency by about 20 cm(-1) to 1672 cm(-1). Upon solar light illumination acetone is readily decomposed on TiO2, and stable surface coordinated intermediates are formed. The decomposition rate is an order of magnitude smaller on the Nb-doped films despite an enhanced visible light absorption in these materials. The quantum yield is determined to be 0.053, 0.004 and 0.002 for the pure, 10% Nb:TiO2, and 20%Nb:TiO2, respectively. Using an interplay between FTIR and DFT calculations we show that the key surface intermediates are bidentate bridged formate and carbonate, and H-bonded bicarbonate, respectively, whose concentration on the surface can be correlated with their heats of formation and bond strength to coordinatively unsaturated surface Ti and Nb atoms at the surface. The oxidation rate of these intermediates is substantially slower than the initial acetone decomposition rate, and limits the total oxidation rate at t>7 min on TiO2, while no decrease of the rate is observed on the Nb-doped films. The rate of degradation of key surface intermediates is different on pure TiO2 and Nb-doped TiO2, but cannot explain the overall lower total oxidation rate for the Nb-doped films. Instead the inferior photocatalytic activity in Nb-doped TiO2 is attributed to an enhanced electron-hole pair recombination rate due to Nb=O cluster and cation vacancy formation.     

Effect of Hydrogen on O2 Adsorption and Dissociation on a TiO2 Anatase (001) Surface

The effect of hydrogen on the adsorption and dissociation of the oxygen molecule on a TiO₂ anatase (001) surface is studied by first‐principles calculations coupled with the nudged elastic band (NEB) method. Hydrogen adatoms on the surface can increase the absolute value of the adsorption energy of the oxygen molecule. A single H adatom on an anatase (001) surface can lower dramatically the dissociation barrier of the oxygen molecule. The adsorption energy of an O₂ molecule is high enough to break the O?O bond. The system energy is lowered after dissociation. If two H adatoms are together on the surface, an oxygen molecule can be also strongly adsorbed, and the adsorption energy is high enough to break the O?O bond. However, the system energy increases after dissociation. Because dissociation of the oxygen molecule on a hydrogenated anatase (001) surface is more efficient, and the oxygen adatoms on the anatase surface can be used to oxidize other adsorbed toxic small gas molecules, hydrogenated anatase is a promising catalyst candidate.     

Density functional study of the interfacial electron transfer pathway for monolayer-adsorbed InN on the TiO(2) anatase (101) surface

Density functional theory (DFT) in connection with ultrasoft pseudopotential (USP) and generalized gradient spin-polarized approximations (GGSA) is applied to calculate the adsorption energies and structures of monolayer-adsorbed InN on the TiO(2) anatase (101) surface and the corresponding electronic properties, that is, partial density of states (PDOS) for surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN, to shed light on the possible structural modes for initial photoexcitation within the UV/vis adsorption region followed by fast electron injection through the InN/TiO(2) interface for an InN/TiO(2)-based solar cell design. Our calculated adsorption energies found that the two most probable stable structural modes of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are (1) an end-on structure with an adsorption energy of 2.52 eV through N binding to surface 2-fold coordinated O (O(cn2)), that is, InN-O(cn2), and (2) a side-on structure with an adsorption energy of 3.05 eV through both N binding to surface 5-fold coordinated Ti (Ti(cn5)) and In bridging two surface O(cn2), that is, (O(cn2))(2)-InN-Ti(cn5). Our calculated band gaps for both InN-O(cn2) and (O(cn2))2-InN-Ti(cn5) (including a 1.0-eV correction using a scissor operator) of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are red-shifted to 1.7 eV (730 nm) and 2.3 eV (540 nm), respectively, which are within the UV/vis adsorption region similar to Gratzel's black dye solar cell. Our analyses of calculated PDOS for both surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN on the TiO(2) anatase (101) surface suggest that the (O(cn2))(2)-InN-Ti(n5) configuration of monolayer-adsorbed InN on the TiO(2) anatase (101) surface would provide a more feasible structural mode for the electron injection through the InN/TiO(2) interface. This is due to the presence of both occupied and unoccupied electronic states for monolayer-adsorbed InN within the band gap TiO(2) anatase (101) surface, which will allow the photoexcitation within the UV/vis adsorption region to take place effectively, and subsequently the photoexcited electronic states will overlap with the unoccupied electronic states around the lowest conduction band of the TiO(2) anatase (101) surface, which will ensure the electron injection through the InN/TiO(2) interface. Finally, another thing worth our attention is our preliminary study of double-layer-adsorbed InN on the TiO(2) anatase (101) surface, that is, (O(cn2))(2)-(InN)(2)-Ti(cn5), with a calculated band gap red-shifted to 2.6 eV (477 nm) and a different overlap of electronic states between double-layer-adsorbed InN and the TiO(2) anatase (101) surface qualitatively indicated that there is an effect of the thickness of adsorbed InN on the TiO(2) anatase (101) surface on both photoexcitation and electron injection processes involved in the photoinduced interfacial electron transfer through InN/TiO(2). A more thorough and comprehensive study of different layers of InN adsorbed in all possible different orientations on the TiO(2) anatase (101) surface is presently in progress.     

TiO2晶面依赖的Ir-TiOx相互作用对Ir/TiO2催化剂巴豆醛选择性加氢性能的影响

α,β-不饱和醇是一类重要的精细化学品,主要通过α,β-不饱和醛选择性加氢获得.由于α,β-不饱和醛分子中含有共轭的C=C键和C=O键,且后者键能更大,在热力学和动力学上均不利于C=O键的选择性加氢生成α,β-不饱和醇.因此,提高α,β-不饱和醛中C=O的加氢选择性是催化领域中一项挑战性的课题.巴豆醛属于典型的α,β-不饱和醛,研究其选择性加氢生成巴豆醇具有广泛的代表意义;Ir负载在具有还原性载体(如TiO2)上时,表现出很好的C=O加氢选择性,因此,成为近年来的研究热点.由于暴露不同晶面的TiO2具有不同的形貌和电子结构,因此研究Ir-TiO2相互作用的晶面依赖性及其对巴豆醛选择性加氢反应的影响具有重要意义.本文以分别暴露{101}、{100}和{001}晶面的锐钛矿TiO2纳米晶为载体,制备了负载型Ir/TiO2催化剂,系统研究了催化剂经过不同的预处理过程(在不同温度下H2还原和O2再氧化)后对巴豆醛的气相选择性加氢的性能.利用高分辨透射电镜、原位X射线光电子能谱和原位漫反射红外光谱及氨程序升温脱附等技术研究发现,预处理条件显著改变了Ir-TiOx的相互作用,包括Ir金属的几何、电子性质及催化剂表面酸性.这种相互作用与TiO2的暴露晶面密切相关,从而改变了不同Ir/TiO2催化剂上不同加氢反应行为.研究结果表明,经300℃预还原的Ir/TiO2-{101}催化剂催化性能最好,在80℃下初始反应速率为166.1 μmol g-Ir-1 s-1,巴豆醇的生成转化频率为0.022 s-1.与其他催化剂相比,Ir/TiO2-{101}催化剂表面Ir0浓度最高,表面酸度适中,因此表现出最佳的催化性能.同时Ir-TiOx界面在反应中的协同作用,对H2和巴豆醛分子中C=O键的吸附和活化起到了关键作用.然而当催化剂经过400℃的H2预还原后,由于产生了强的金属-载体相互作用使得TiOx对Ir粒子进行了包裹从而导致Ir-TiOx界面缺失,因而催化剂催化巴豆醛加氢性能降低.本文为理解金属-载体相互作用对巴豆醛选择性加氢反应的影响提供了新的见解,并为设计高性能α,β-不饱和醛选择性加氢催化剂提供了理论依据.     

Effect of calcination temperature on the structure of a Pt/TiO2 (B) nanofiber and its photocatalytic activity in generating H2

Hydrogen trititanate (H 2Ti 3O 7) nanofibers were prepared by a hydrothermal method in 10 M NaOH at 403 K, followed by acidic rinsing and drying at 383 K. Calcining H 2Ti 3O 7 nanofibers at 573 K led to the formation of TiO 2 (B) nanofibers. Calcination at 673 K improved the crystallinity of the TiO 2 (B) nanofibers and did not cause any change in the morphology and dimensions of the nanofibers. TiO 2 (B) and H 2Ti 3O 7 nanofibers are 10-20 nm in diameter and several micrometers long, but FE-SEM reveals that several of these nanofibers tend to bind tightly to each other, forming a fiber bundle. Calcination at 773 K transformed TiO 2 (B) nanofibers into a TiO 2 (B)/anatase bicrystalline mixture with their fibrous morphology remaining intact. Upon increasing the calcination temperature to 873 K, most of the TiO 2 (B) nanofibers were converted into anatase nanofibers and small anatase particles with smoother surfaces. In the photocatalytic dehydrogenation of neat ethanol, 1% Pt/TiO 2 (B) nanofiber calcined at 673 K was the most active catalyst and generated about the same amount of H 2 as did 1% Pt/P-25. TPR indicated that the calcination of 1% Pt/TiO 2 (B) nanofiber at 573 K produced a poor Pt dispersion and poor activity. Calcination at a temperature higher than 773 K (in ambient air) resulted in an SMSI effect similar to that observed over TiO 2 in the reductive atmosphere. As suggested by XPS, such an SMSI effect decreased the surface concentration of Pt metal and created Pt (delta) sites, preventing Pt particles from functioning as a Schottky barrier and leading to a lower activity. Because of the synergetic effect between TiO 2 (B) and anatase phases, the bicrystalline mixture, produced by calcining at 773 K, was able to counter negative effects such as the reduction in surface area and the SMSI effect and maintained its photocatalytic activity.     

Computational study on the reactions of H2O2 on TiO2 anatase (101) and rutile (110) surfaces

This study investigates the adsorption and reactions of H(2)O(2) on TiO(2) anatase (101) and rutile (110) surfaces by first-principles calculations based on the density functional theory in conjunction with the projected augmented wave approach, using PW91, PBE, and revPBE functionals. Adsorption mechanisms of H(2)O(2) and its fragments on both surfaces are analyzed. It is found that H(2)O(2) , H(2)O, and HO preferentially adsorb at the Ti(5c) site, meanwhile HOO, O, and H preferentially adsorb at the (O(2c))(Ti(5c)), (Ti(5c))(2), and O(2c) sites, respectively. Potential energy profiles of the adsorption processes on both surfaces have been constructed using the nudged elastic band method. The two restructured surfaces, the 1/3 ML oxygen covered TiO(2) and the hydroxylated TiO(2), are produced with the H(2)O(2) dehydration and deoxidation, respectively. The formation of main products, H(2)O(g) and the 1/3 ML oxygen covered TiO(2) surface, is exothermic by 2.8 and 5.0 kcal/mol, requiring energy barriers of 0.8 and 1.1 kcal/mol on the rutile (110) and anatase (101) surface, respectively. The rate constants for the H(2)O(2) dehydration processes have been predicted to be 6.65 × 10(-27) T(4.38) exp(-0.14 kcal mol(-1)/RT) and 3.18 × 10(-23) T(5.60) exp(-2.92 kcal mol(-1)/RT) respectively, in units of cm(3) molecule(-1) s(-1).