CH3OH在ZnO(0001)表面的光催化解离

本文利用266 nm波长的激光及程序升温脱附的方法研究了甲醇在ZnO(0001)表面的光催化反应. TPD结果显示部分的CH₃OH以分子的形式吸附在ZnO(0001)表面,而另外一部分在表面发生了解离. 实验过程中探测到H₂,CH₃^·,H₂O,CO,CH₂O,CO₂和CH₃OH这些热反应产物. 紫外激光照射实验结果表明光照可以促进CH₃OH/CH₃O^·解离形成CH₂O,在程序升温或光照的过程中它又可以转变为HCOO^-. CH₂OH_Zn与OH_ad反应在Zn位点上形成H₂O分子. 升温或光照都能促进CH₃O^·转变为CH₃^·. 该研究对CH₃OH在ZnO(0001)表面的光催化反应机理提供了一个新的见解.     

甲醇在Pt (100)表面吸附与解离的第一性原理研究.

采用基于第一性原理的密度泛函理论结合周期模型方法对甲醇在Pt(100)完整表面的吸附与解离进行了研究. 通过比较不同吸附位置的吸附能与构型参数发现,表面top吸附位为最稳定吸附位,甲醇分子通过氧原子吸附于Pt(100)表面. 同时计算了甲醇分子在top吸附位可能的解离路径,发现在解离过程中OH键首先断裂的路径为最低能量路径. 分解生成的若干产物其吸附稳定性排序为CH₃O>CH₂OH>CH₃>CH₂O.     

甲胺水合离子团簇的结构模型及红外光谱研究

本文利用量子化学计算方法，研究了甲胺和水复合离子团簇[(CH₃NH₂)(H₂O)_n]⁺的几何结构、能量和红外光谱，揭示了结构生长模型、氢键作用机制和质子转移机理. 研究结果表明，在[(CH₃NH₂)(H₂O)_n]⁺团簇中，甲胺甲基上的一个氢原子转移到氨基上，形成分子内质子转移的CH₂NH₃⁺离子核心结构模型，水分子作为氢键受体，与质子化氨基NH₃⁺形成氢键. CH₃NH₂⁺离子核心结构模型没有CH₂NH₃⁺离子核心结构模型稳定. 在团簇的红外光谱中，CH振动、自由NH振动、氢键结合的NH振动和OH振动模式在CH₃NH₂⁺和CH₂NH₃⁺两种离子核心结构模型的理论计算红外光谱中明显不同，因此可用于鉴别甲胺水合离子团簇的结构模型，有助于理解甲胺和水复合团簇的氢键网络结构.     

Pd修饰Cu电极的电化学CO2还原

利用微分电化学质谱和电化学原位衰减全反射红外光谱技术探究了Cu和CuPd催化剂上CO₂和CO的电化学还原行为. 红外光谱观察到了生成甲醇、甲烷与乙烯的CH_x中间物种. 在CuPd电极CO₂还原过程中，红外光谱的CO吸附峰起始电位比Cu正移大约300 mV，说明CuPd能够有效促进CO₂还原；CO饱和溶液中，Cu和CuPd电极CO起始吸附电位基本相同；两电极上CO谱带出现的电位与CO₃^2-的谱带降低的电位基本相同，说明CO的吸附需要CO₃^2-的脱附. 利用电化学在线质谱发现在CuPd电极上CO还原产生CH₄和CH₃OH的起始电位比Cu电极正移约200 mV. 推测催化活性的提升可能是由于Pd的引入改变了Cu的d能带，且Pd吸附更多的H，从而促进CO₂还原，使CO能够与H结合并被深度还原.     

二氧化碳对质子化甲醇的溶剂化作用 (cited: 1)

利用团簇模型研究了二氧化碳对质子化甲醇的溶剂化作用．H⁺(CH₃OH)(CO₂)_n⁺(n=1～7)的量子化学计算结果表明,需要3个或4个二氧化碳分子完成甲醇的羟基第一溶剂层．除了氢键,二氧化碳分子间的相互作用对大团簇的稳定性也起到了重要的作用．在这些溶剂化作用的早期阶段,不容易发生质子从甲醇到二氧化碳的转移过程．模拟的红外光谱揭示了自由O-H伸缩振动、氢键作用后的O-H伸缩振动、以及二氧化碳的O-C-O伸缩振动频率是研究质子化甲醇溶剂化过程的灵敏探针．     

基于差频中红外激光的痕量气体高分辨光谱检测研究

研究了基于差频光源的高分辨中红外激光光谱检测系统,差频中红外光源使用两台近红外半导体激光器作为种子光源,采用PPLN晶体作为非线性混频器件,结合准相位匹配技术实现了3.2~3.7 μm中红外相干光源输出,最大差频输出功率约为1 μW.以CH₄为例检验了系统的高分辨红外光谱检测特性,选择CH₄分子3 028.751 cm^-1 v₃基频吸收线作为分析谱线,10 cm光程的检测限为0.8 ppm.光谱数据分析表明,系统检测限主要受到标准具光学噪音的限制.     

密度泛函理论研究α-MoC(100)在甲醇水蒸汽重整中的催化作用

本文通过密度泛函理论计算方法探究了α-MoC催化甲醇水蒸气重整(CH₃OH+H₂O→CO₂+3H₂)反应,系统地研究了甲醇水蒸气重整反应中相关中间体的吸附行为和基本步骤的动力学. 结果表明,在α-MoC(100)表面,甲醇容易裂解形成CH₃O中间体,CH₃O进一步脱氢为CH₂O. 通过比较CH₂O和OH缔合过程和CH₂O直接分解过程,发现CH₂O和OH之间更容易形成CH₂OOH而不是分解成CHO和H. 计算结果表明,CH₂OOH中间体的连续脱氢对CO₂有很高的选择性. 相反,在α-MoC(111)表面,由于CH₂O中间体的强吸附使其更偏向于脱氢生成CHO,最后生成产物CO. 此外,高水解离产生的OH物种可以促进中间体O-H键的断裂,并显著降低反应能垒. 本文不仅揭示了α-MoC(100)晶面在甲醇水蒸气重整反应中的催化作用,也为α-MoC基催化剂的设计提供了理论指导.     

密度泛函理论研究黄曲霉素B1的表面增强拉曼散射效应

用密度泛函理论B3LYP方法和6-311G(d,p)/Lanl2DZ优化得到黄曲霉素B₁(AFB₁)分子及其复合物AFB₁-Ag的稳定结构,并计算了复合物的表面增强拉曼光谱和预共振拉曼光谱. 结果表明,AFB₁分子的拉曼光谱很大程度依赖于吸附位点以及入射光的激发波长. 与分子的常规拉曼光谱相比,复合物表面增强拉曼光谱中C=O伸缩振动模的增强因子约为10²～10³复合物的极化率增强而导致的静态化学增强,并分析了振动模式的振动方向与其拉曼强度的关系．选择复合物最大吸收峰附近激发光266和482 nm以及远离共振吸收波长785和1064 nm作为入射光,计算得到不同入射光激发下复合物的预共振拉曼光谱．结果表明其增强因子最大达到10⁴量级,主要是由电荷转移产生的共振增强引起的．     

CH2和CH3自由基吸附在Cun (n=1-6)团簇上C-H对称振动模式的软化

利用密度泛函理论中杂化泛函理论方法计算了CH₂和CH₃自由基吸附在Cu_n(n=1～6)团簇上时C?H对称伸缩振动模式的软化性质,结果表明,CH₂在Cun团簇上的吸附要比CH₃的吸附强. 计算得到的C-H键的振动频率与实验上测量的这两个自由基吸附在Cu(111)表面的结果符合得很好,随着团簇尺寸的增加,C-H对称伸缩振动频率的软化(红移)越来越大.     

高灵敏度集成光偏振干涉仪特性及生化传感应用研究

利用射频溅射技术在平面单模玻璃波导表面局部淀积一层Ta₂O₅梯度薄膜, 形成复合光波导芯片, 结合棱镜耦合法制备了一种集成光偏振干涉传感器. 基于四层平板波导模型理论分析了复合光波导表面折射率灵敏度S_RI与Ta₂O₅梯度薄膜等效厚度T_eq的关系, 结合实验测定的S_RI得出了本工作中所使用Ta₂O₅梯度薄膜的T_eq ≈ 33.021 nm, 进一步得出芯片吸附层厚度灵敏度S_ab≈ (2.412× 2π) nm^-1. 利用该复合波导偏振干涉仪结合Lorentz-Lorenz有效介质理论测得了市售食用白醋中醋酸的浓度, 并以市售牛栏山二锅头酒为例进行了白酒掺水和掺甲醇的测试, 结果表明, 白酒掺水或甲醇前后的折射率改变量与掺杂量成准线性变化关系; 原位实时监测了丁酰胆碱酯酶的动态吸附过程及细胞色素c/聚苯乙烯磺酸钠的分子自组装过程, 并利用测得的位相差变化结合芯片吸附层厚度灵敏度S_ab 获得了蛋白质表面覆盖度.     

Cr2O3催化合成气转化至甲醇的微观动力学研究

Cr₂O₃是双功能催化合成气转化的重要氧化物组分,其可将合成气转化为重要的中间物种甲醇. 结合密度泛函理论计算和微观动力学模拟,本文系统研究了干净Cr₂O₃(001)和(012)表面,以及氢覆盖或含有氧空位的还原(012)表面的结构及催化合成气转化至甲醇的活性. 本文探讨了合成气转化为甲醇的分步或协同反应路径,并确定CO或CHO氢化是决速步骤. 微观动力学分析表明,Cr₂O₃(001)表面难以催化合成气转化为甲醇,在673 K 时,两个还原性(012)表面的反应速率(25∽28 s^-1)比干净的(012)表面(4.3 s^-1)高出约五倍. 计算结果表明了Cr₂O₃表面还原性对催化活性的重要性,或许可以为双功能催化体系中氧化物组分的设计提供参考.     

甲醇分子在金红石TiO2(110)和锐钛矿TiO2(001)表面吸附和反应的活性位点

通过高分辨的扫描隧道显微术研究并比较了金红石型TiO₂(110)-(1×1)和锐钛矿型TiO₂(001)-(1×4)两种表面的活性位点． 在金红石型TiO₂(110)-(1×1)表面, 观察到氧空位缺陷是O₂和CO₂分子的活性吸附位点,而五配位的Ti原子是水分子和甲醇分子的光催化反应活性位点．在锐钛矿型TiO₂(001)-(1×4)表面,观察到完全氧化的表面,Ti原子更可能是六配位的,H₂O和O₂分子均不易在这些Ti原子上吸附．经还原后表面出现富Ti的缺陷位点, 这些缺陷位点对H₂O和O₂分子表现出明显的活性． 锐钛矿型TiO₂(001)-(1×4)表面的吸附和反应活性并不具有很高的活性,某种程度上其表现出的活性似乎低于金红石型TiO₂(110)-(1×1)表面．     

IR spectroscopy of CH2CBrF adsorbed on TiO2 and quantum-mechanical studies

The adsorption at room temperature of 1-bromo-1-fluoroethene (CH₂CBrF) on TiO₂ has been investigated by Fourier-transform infrared spectroscopy after a preventive assignment of the fundamentals in the gas-phase, carried out for the first time. The spectrum resulting from the adsorption has been compared with the gas-phase one and the most important differences consist in a red-shift of the CH₂ stretching vibration and in the presence of two distinct absorptions for both the C=C and C–F stretching modes. Basing on the observed features it has been inferred that there is the formation of an H-bond between the CH₂ group and a surface Lewis basic site and that the adsorption can occur through the double C=C bond or the F atom. Two proposed adsorbate-substrate structures have been investigated by periodic quantum-mechanical calculations at DFT/B3LYP level considering the rutile (110) surface. In the case of the adsorption by the F atom, also the formation of the H-bond has been considered. The interaction energy resulting from the adsorption through the double C = C bond is smaller than that arising from the interaction by means the F atom and the H-bond. The shifts due to the adsorption of the calculated vibrational frequencies well reproduce the experimental data.     

Surface state of TiO2 treated with low ion energy plasma

The effect of low pressure radio frequency (rf) plasma treatment on TiO₂ surface states has been studied using X-ray photoelectron spectroscopy. Three different oxidation states of oxygen in untreated TiO₂ powder were observed, which suggests the existence of adsorbed water and carbon on the surface. The ratio of oxygen to titanium (O/Ti) was decreased for the low ion dose plasma treated samples due to desorption of water from the surface. In the case of Ti 2p about 20% of surface states were converted to Ti³⁺ 2p_3/2 state after plasma treatment with a very good stability, whereas untreated TiO₂ remained mostly as Ti⁴⁺ state. A rapid decrease in the ratio of carbon to titanium (C/Ti) at TiO₂ surface was also observed after plasma treatment and more than 90% of carbon atoms were removed from the surface. Therefore, the plasma treatment of TiO₂ has advantages to surface carbon cleaning, increasing O⁻ and Ti³⁺ surface states, hence improving the activity of TiO₂ for different environmental, energy and biological applications.     

S180 cell growth on low ion energy plasma treated TiO2 thin films

X-ray photoelectron spectroscopy (XPS) was used to characterise the effects of low energy (<2 eV) argon ion plasma surface modification of TiO₂ thin films deposited by radio frequency (RF) magnetron sputter system. The low energy argon ion plasma surface modification of TiO₂ in a two-stage hybrid system had increased the proportion of surface states of TiO₂ as Ti³⁺. The proportion of carbon atoms as alcohol/ether (COX) was decreased with increase the RF power and carbon atoms as carbonyl (CO) functionality had increased for low RF power treatment. The proportion of C(O)OX functionality at the surface was decreased at low power and further increase in power has showed an increase in its relive proportion at the surface. The growth of S180 cells was observed and it seems that cells are uniformly spreads on tissue culture polystyrene surface and untreated TiO₂ surfaces whereas small-localised cell free area can be seen on plasma treated TiO₂ surfaces which may be due to decrease in C(O)OX, increase in CO and active sites at the surface. A relatively large variation in the surface functionalities with no change in the surface roughness was achieved by different RF plasma treatments of TiO₂ surface whereas no significant change in S180 cell growth with different plasma treatments. This may be because cell growth on TiO₂ was mainly influenced by nano-surface characteristics of oxide films rather than surface chemistry.     

甲醛在金红石型TiO2(100)-(1×1)表面的光解离

We have investigated the photoinduced decomposition of formaldehyde (CH₂O) on a rutile TiO₂(100)-(1×1) surface at 355 nm using temperature-programmed desorption. Products, formate (HCOO^-), methyl radical (CH₃·), ethylene (C₂H₄), and methanol (CH₃OH) have been detected. The initial step in the decomposition of CH₂O on the rutile TiO₂(100)-(1×1) surface is the formation of a dioxymethylene intermediate in which the carbonyl O atom of CH₂O is bound to a Ti atom at the five-fold-coordinated Ti⁴⁺ (Ti_5c) site and its carbonyl C atom bound to a nearby bridge-bonded oxygen (O_b) atom, respectively. During 355 nm irradiation, the dioxymethylene intermediate can transfer an H atom to the O_b atom, thus forming HCOO^- directly, which is considered as the main reaction channel. In addition, the dioxymethylene intermediate can also transfer methylene to the O_b row and break the C-O bond, thus leaving the original carbonyl O atom at the Ti_5c site. After the transfer of methylene, several pathways to products are available. Thus, we have found that O_b atoms are intimately involved in the photoinduced decomposition of CH₂O on the rutile TiO₂(100)-(1×1) surface.     

锐钛矿型TiO2(101)面原子几何及弛豫结构的第一性原理计算

采用平面波超软赝势方法计算了锐钛矿型TiO₂(101)面的表面能和表面原子弛豫结构.首先对TiO₂(101)面的6种不同的表面原子终止结构的体系总能量进行了计算,结果表明终止原子为两配位的O原子、次层为五配位的Ti原子的表面结构最为稳定.针对该表面研究了表面能和原子弛豫与模型中原子层数和真空厚度的关系,当原子层数为12层,真空厚度为0.4nm时,表面能收敛度小于0.01J/m².研究发现:表面上两配位的O原子向里移动约0.0012nm,五配 关键词： 第一性原理 2')" href="#">TiO₂ 表面结构 弛豫     

Photocatalytic decomposition of methylene blue and 4-chlorophenol on nanocrystalline TiO2 films under UV illumination: A ToF-SIMS study

The photocatalytic degradation of methylene blue and 4-chlorophenol on nanocrystalline TiO₂ (nc-TiO₂) under UV irradiation was investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Nanocrystalline TiO₂ films were prepared from suspensions containing TiO₂-crystallites of different average sizes, the smallest one being 12 nm. The organic substances (either methylene blue or 4-chlorophenol) were applied to these films. The specimens were studied in the pristine state and upon UV exposure. The UV illuminations were carried out both under atmospheric conditions and in situ under ultrahigh vacuum in the ToF-SIMS instrument. Distinct mass signals from the parent molecules and from fragment ions are observed for the as-prepared samples. Upon irradiation with UV light under atmospheric conditions, the surface composition is significantly changed, an observation ascribed to photocatalytic reactions induced by UV photons: the parent molecule signals are strongly diminished whereas fragmentation products are identified to be present at the TiO₂ surfaces. UV irradiations carried out under different vacuum conditions in the ToF instrument (ultrahigh vacuum, air or oxygen adsorption) indicate that varying ambient conditions may influence the photocatalytic reaction on the nanocrystalline TiO₂ films.     

Selective desorption from the binary coadsorbate C2H6CH3FNaCl by resonant vibrational excitation with laser infrared radiation

After measuring the linear infrared absorption spectrum of the coadsorbate, selective desorption of CH₃F from the binary coadsorbate C₂H₆CH₃FNaCl under ultrahigh vacuum conditions at 12o K stimulated by resonant CO₂ laser pulses of small fluence ～ 0.1 J·cm^t?2 has been carried out. No desorption of ethane, which is slightly more volatile, but has no significant infrared absorption at the laser frequency, was observed. The primary activation step is the resonant multiphoton excitation of the most intense internal CH₃FNaCl adsorbate vibration, the CF stretching mode ν₃. The substance separation seems to indicate high localisation of the activation in this desorption and could be of interest for applications.     

CH3OH/TiO2(110)界面的光电子能谱研究

Methanol/TiO₂(110) is a model system in the surface science study of photocatalysis where methanol is taken as a hole capture. However, the highest occupied molecular orbital of adsorbed methanol lies below the valence band maximum of TiO₂, preventing the hole transfer. To study the level alignment of this system, electronic structure of methanol covered TiO₂(110) surface has been measured by ultraviolet photoelectron spectroscopy and the molecular orbitals of adsorbed methanol have been clearly identified. The results indicate the weak interaction between methanol and TiO₂ substrate. The static electronic structure also suggests the mismatch of the energy levels. These static experiments have been performed without band gap excitation which is the prerequisite of a photocatalytic process. Future study of the transient electronic structure using time-resolved UPS has also been discussed.