Al-C60-Al分子结电子输运特性的第一性原理计算

利用基于密度泛函理论的格林函数方法, 计算了Al-C60-Al分子结的电子输运特性. 考虑了C60分子在铝电极表面的原子结构弛豫, 计算结果表明共振传导是Al-C60-Al分子结电子输运的主要特征, 在费米能级附近的电导约为1.14G0 (G0=2e2/h). 投影态密度(PDOS)分析表明, Al-C60-Al分子结的电子输运主要通过C60分子的最低空分子轨道(LUMO)和次低空分子轨道(LUMO+1)进行. 讨论了C60分子和铝电极之间距离的变化对其电子输运特性的影响.     

结构转变方式对光致变色分子开关输运性能影响的从头计算研究(英文)

采用密度泛函理论方法系统地研究了由不同结构转变方式引发的一系列光致变色分子在用于分子开关时的电子输运性质.对各种分子结构转变前后的最高占据轨道(HOMO)与最低空轨道(LUMO)的能级间隙(HLG)、前线轨道的空间分布、电子透射谱和投影电子态密度(PDOS)谱进行了计算和讨论.结果表明,相似的结构转变方式通常造成分子具有相似的电流开关性质,这与分子的共轭程度又有一定的关系.比较各种分子的电流开关比后发现偶氮苯结构单元具有最大的电流开关比.     

分子线电导问题的密度泛函研究: 分子-电极耦合形貌以及分子间相互作用对传输特性的影响

采用基于密度泛函(DFT)的非平衡态Green函数方法(non-equilibrium Green functions, NEGF), 计算了耦合于两个面心立方Au(111)表面间的对苯二硫酚(Di-thiol benzene, DTB)分子的电导性质. 讨论了偏压、分子-表面耦合形貌、分子间相互作用等因素对电荷传输特性的影响. 结果显示, DTB分子顶端H原子的存在会显著降低分子的透射系数, 减小分子的微分电导(dI/dV). 当在两极间移动分子时, 电导存在极大值. 分子间的相互作用会显著改变分子的输运性质.     

基于离子修饰簇模型的单分子结的拉曼光谱-电导关联性的理论研究

在分子电子学中,金属电极-分子-金属电极分子结的单分子电导性质强烈依赖于分子锚定基团和电极的成键性质.然而其成键性质难以在室温下获得.前期本课题组结合钓鱼模式针尖增强拉曼光谱(FM-TERS)和电导测量联用系统,在室温下同时获得单分子的拉曼光谱和电导值,进而发现了单分子电导值与拉曼强度随偏压变化同增同减的关联现象.本文尝试发展一种离子修正的簇模型并计算不同偏压下模型分子4-4′联吡啶(BPy)的分子电导和拉曼光谱,再现实验观察到的关联现象.进一步基于最高占据轨道和最低非占据轨道近似的两能级模型,从理论上推导出Au-BPy-Au分子结中单分子电导和单分子拉曼光谱的关联性函数,从而揭示了这种关联性的内在物理化学本质.     

由激光诱导荧光确定对称陀螺分子定向和取向的理论研究

采用密度矩阵方法推导了从激光诱导荧光强度中抽出对称陀螺分子定向和取向参数的一般表达式. 分子定向和取向由分子态多极矩描述. 激发激光和探测荧光分别为圆偏振和线偏振光. 在一般情况下, 激光诱导荧光强度是初始分子态多极矩、动力学因子和激发-探测几何因子的复杂函数. 它包含一个布居(population)、10个定向(orientation)和14个取向(alignment)态多极矩. 讨论了如何从分辨荧光强度中抽出所有初始分子态多极矩问题.     

硅掺杂的氮化硼纳米管对氯化氰吸附性能的理论研究

为了探索氮化硼纳米管(BNNT)在化学传感器件领域的潜在应用,我们利用密度泛函理论研究了(8,0)单壁BNNT和硅掺杂的(8,0)BNNT对毒性气体氯化氰分子(ClCN)的吸附性能.结果表明,硼位或氮位硅掺杂的BNNT,均对ClCN分子存在较强的化学吸附,而纯氮化硼纳米管对ClCN仅有较弱的物理吸附.态密度的计算进一步表明硅掺杂使纳米管费米能级附近的电子结构发生显著变化,由于杂化态的引入,使带隙明显减小,增强了对毒性ClCN分子的吸附敏感性.硅掺杂的BNNT有望成为检测毒性ClCN分子的潜在资源.     

Ni(100)表面吸附SO2的密度泛函研究

以原子簇Ni14为模拟表面,采用DFT/B3LYP方法研究了二氧化硫(SO2)分子在Ni(100)表面的吸附构型、能量、电荷及态密度。结果表明,SO2分子通过S原子平铺吸附在Ni(100)的桥位最有利,计算结果与实验相符。电荷密度及态密度分析表明,Ni原子的d轨道与SO2分子的空p轨道之间存在明显的s-p作用和电荷转移,这一作用可能导致SO2分子发生解离。     

氧在CuCl(111)表面吸附的密度泛函理论研究

运用广义梯度密度泛函理论的PW91方法结合周期平板模型,在DNP基组下研究了氧分子和氧原子在CuCl(111)表面上的吸附.对氧分子在CuCl(111)表面吸附的相关计算和比较发现,覆盖度为0.25单层时的吸附构型为稳定的吸附构型,氧分子倾斜地吸附在CuCl(111)表面的顶位时比较稳定,吸附后O2分子的伸缩振动频率与自由O2分子相比发生了红移.态密度和Mulliken电荷布居分析结果表明,整个吸附体系发生了由Cu原子向O2分子的电荷转移.氧原子在CuCl(111)表面吸附的计算结果表明,氧原子倾向于以穴位(hollow)吸附在CuCl(111)表面,通过Mulliken电荷布居和态密度分析对氧原子在CuCl表面的吸附行为作了进一步探讨.     

间甲基苯甲醚分子旋转异构体的质量分辨阈值电离光谱

间甲基苯甲醚分子有顺式和反式两个转动异构体.利用单光共振双光子电离技术和质量分辨阈值电离技术,研究了间甲基苯甲醚分子顺反异构体的基态到第一电子激发态(S1←S0)的跃迁和阈值电离.得到顺式、反式间甲基苯甲醚分子S1态的激发能(E1)分别为(36049±2)和(36117±2)cm-1,绝热电离能(Ip)分别为(64859±5)和(65110±5)cm-1.结合从头算法和密度泛函理论的量子化学计算,解释了顺式、反式间甲基苯甲醚分子E1和Ip存在差异的原因,并且对S1态和离子基态D0态出现的谱峰进行了标识.间甲基苯甲醚分子顺反异构体在S1态和D0态的活性振动主要是甲基转动、面内环的运动和与取代基相关的弯曲振动.间甲基苯甲醚分子的S1态振动光谱、D0态离子光谱以及理论计算均表明这两个转动异构体在D0态的几何构型与S1态的中性几何构型相比有较大改变,取代基与取代基、取代基与苯环间的相互作用强度高低次序为:S0S1D0.     

量化方法研究分子结BEMP和TEMP的电子输运特性

通过结合杂化密度泛函和前线轨道理论与弹性散射格林函数方法研究了BE- MP(benzene-1,4-di-ethynyl-4-mercaptophenyl)和TEMP(thiophene-2,5-di-ethynyl-4- mercaptophenyl)两分子结的输运性质。基于杂化密度泛函方法计算两扩展分子电子结构的基础上,计算了两分子的输运性质．计算结果显示:电流增加来源于电极和分子轨道的共振;电导曲线呈现出平台特征．在此基础上从扩展分子A(Au-BEMP-Au)中间的苯环的旋转而引起电流减小的角度解释了负微分电阻现象．     

Biocompatible, lactide-based surfactants for the CO2-water interface: high-pressure contact angle goniometry, tensiometry, and emulsion formation

The unique properties of compressed CO2, including its low cost, nontoxicity, easily tunable solvent strength, and favorable transport properties, make it an environmentally attractive alternative to volatile organic solvents. Suitable surface-active species can be utilized to realize the full potential of clean, CO2-based technologies, by helping to overcome the low solubility typically associated with many solutes of interest in CO2. In this work we synthesize and investigate the interfacial activity of a series of nonionic amphiphiles with a biocompatible and biodegradable CO2-phile at both the CO2-water (C|W) and CO2-water-solid (C|W|S) interfaces. We developed a high-pressure pendant drop tensiometer and contact angle goniometer that allows us to measure both tension and contact angle in tandem. The tension of the C|W interface was measured in the presence of the lactide (LA)-based surface active agents with varying molecular weight and hydrophilic-to-CO2-philic ratios. Emulsion studies with an optimum balanced surfactant were performed. The contact angle of water droplets against a silane-modified (hydrophobic) substrate under CO2 atmosphere was also measured in presence of a selected LA-based amphiphile. The results demonstrate that the nonionic copolymers with the biodegradable and biocompatible LA-based group can significantly reduce the tension of the C|W interface. The LA-based surface active species are also capable of forming stable emulsions of water and CO2 and reducing the angle of the three-phase C|W|S contact line.     

原位制备氧化钛/氮掺杂石墨烯空心球光催化剂及其光催化CO2还原性能研究

利用光催化技术将二氧化碳转化为化学燃料是缓解温室效应以及能源危机的理想途径之一.因此,开发高效的光催化剂是当务之急.氧化钛由于具有优异的物理化学稳定性、成本低廉、无毒性以及环境友好等优点,近年来被广泛关注.此外,空心球结构光催化剂具有短的载流子扩散距离、良好的光散射性以及较大的比表面积等优点,从而成为光催化二氧化碳还原最有潜力的候选材料.但纯的氧化钛空心球由于较快的光生载流子复合速率从而导致低的光催化效率.因此,为了应对这一挑战,我们尝试在氧化钛空心球表面负载助催化剂用以促进光生载流子的分离,从而提高光催化二氧化碳还原转换效率.在各种助催化剂中,贵金属被证明是有效的.然而,高成本以及稀缺性限制了贵金属的广泛应用.因此,有必要设计成本低廉的助催化剂替代品.石墨烯以其优异的导电性、较大的功函数以及来源丰富而备受关注.当石墨烯与n型半导体光催化剂结合在一起时,能够显著促进光生电子从半导体光催化剂向石墨烯的定向迁移,从而有效地抑制光生电子与空穴的复合.当石墨烯中掺杂氮元素时,石墨烯骨架中的电子密度会进一步提高,同时,氮原子中的孤对电子更加有利于石墨烯骨架中的电子传输.此外,氮掺杂石墨烯中不同的氮位点(吡啶氮、吡咯氮和石墨氮)作为路易斯碱位点,能够用以二氧化碳分子的吸附以及活化.然而,迄今为止,最常用的制备半导体/氮掺杂石墨烯纳米复合光催化剂的方法是在氮掺杂石墨烯表面生长半导体光催化剂.所制备的光催化剂与氮掺杂石墨烯之间界面接触有限,不利于光生载流子的快速传递与分离.此外,助催化剂和光催化剂之间建立高质量的界面接触可以有效地抑制光生电子与空穴的复合.因此,有必要绕开传统制备方法的弊端,从而设计与光催化剂之间具有大的接触面积和紧密的界面接触以及具有丰富活性位点的高质量氮掺杂石墨烯助催化剂.本文提出了一种新的策略,以吡啶为氮掺杂石墨烯的前驱体,通过化学气相沉积方法在氧化钛空心球表面原位生长超薄氮掺杂石墨烯层(1～2层).此外,在高温状态下,吡啶分子脱氢生成具有优异扩散性质的脱氢吡啶自由基气相分子,随着反应的进行,氧化钛表面的每个纳米颗粒基元表面都能够与吡啶分子充分接触,从而保障两者之间大面积以及紧密的界面接触.光催化二氧化碳还原性能测试结果表明,优化后的氧化钛/氮掺杂石墨烯空心球纳米复合材料的二氧化碳光催化总转化率(一氧化碳、甲醇和甲烷的总产率)为18.11 μmol g-1 h-1,是空白氧化钛空心球的4.6倍和商业P25的10.7倍.高分辨透射电子显微镜、X射线光电子能谱以及拉曼光谱结果表明,成功构建了氧化钛与氮掺杂石墨烯之间紧密接触的界面.同时,氮掺杂石墨烯的引入能够显著增强复合光催化剂的表面光热效应以及氧化钛与氮掺杂石墨烯界面肖特基势垒的形成均有助于促进光催化二氧化碳还原反应的进行.因此,本文为石墨烯基光助催化剂的原位构建提供了一种行之有效的策略.     

Pressure dependence of the contact angle in a CO2-H2O-coal system

Carbon dioxide injection into coal layers serves the dual purpose to enhance coal bed methane production (ECBM) and to store CO2. The efficiency of this process is expected to be much higher if water is the non-wetting phase in the coal-water-gas system. Therefore, contact angles in the coal-water-CO2 system have been measured using the captive bubble technique in the pressure range between atmospheric pressure and 141 bar at a temperature of 45 degrees C. At atmospheric pressure the contact angle of a shrinking CO2 droplet increases with time, but stays below 90 degrees . At higher pressures (>2.6 bar) the contact angle increases beyond 90 degrees . The pressure dependence of the contact can be represented by theta=(111 degrees +/-10.5 degrees )+(0.17+/-0.14)P [bar]. The exceptional behavior at atmospheric pressure is possibly related to the stability of water patches on the coal surface. It is concluded that water is the non-wetting phase in this coal-water-CO2 system.     

Nucleation of the CO2 hydrate from three-phase contact lines

Using molecular dynamics simulations on the microsecond time scale, we investigate the nucleation and growth mechanisms of CO(2) hydrates in a water/CO(2)/silica three-phase system. Our simulation results indicate that the CO(2) hydrate nucleates near the three-phase contact line rather than at the two-phase interfaces and then grows along the contact line to form an amorphous crystal. In the nucleation stage, the hydroxylated silica surface can be understand as a stabilizer to prolong the lifetime of adsorbed hydrate cages that interact with the silica surface by hydrogen bonding, and the adsorbed cages behave as the nucleation sites for the formation of an amorphous CO(2) hydrate. After nucleation, the nucleus grows along the three-phase contact line and prefers to develop toward the CO(2) phase as a result of the hydrophilic nature of the modified solid surface and the easy availability of CO(2) molecules. During the growth process, the population of sI cages in the formed amorphous crystal is found to increase much faster than that of sII cages, being in agreement with the fact that only the sI hydrate can be formed in nature for CO(2) molecules.     

IR spectroscopic observation of molecular transport through Pt@CoO yolk-shell nanostructures

FTIR spectroscopy has been used to monitor the transport of CO to the Pt cores of Pt@CoO nanoparticles forming CO/Pt species. It was found that external Pt sites are not present on the outer surfaces of the approximately 10 nm diameter nanostructures and that CO transports to Pt adsorption sites by an activated surface diffusion process through the CoO shells surrounding approximately 2 nm diameter Pt cores. The CO transport process is not due to gas-phase transport below 300 K. The weakly bound adsorbed CO/CoO species responsible for transport was directly observed at approximately 2147 cm(-1) during transport through the CoO shells.     

Contact angle of water on polystyrene thin films: effects of CO(2) environment and film thickness

We examine the contact angle of water droplets on polystyrene (PS) thin films of varying thicknesses supported by silicon wafers under both air and pressurized carbon dioxide (CO2) environments. At 23 degrees C, the contact angle is found to increase upon increasing CO2 pressure in the vapor regime and then levels off in the liquid CO2 regime. A macroscopic model based on Young's equation and the geometric-mean method for interfacial tensions, and long-range van der Waals interactions, correctly predicts the trends and the magnitude of the contact angle dependence on pressure, although deviations occur at high CO2 activities. The contact angle was also found to depend on film thickness, h, when h was comparable to or smaller than 50 nm. Specifically, the contact angle decreases with decreasing PS film thickness. This behavior could be accounted for with the use of a model that incorporates the effects of film thickness, CO2 pressure, and the long-range van der Waals potential.     

十七氟癸基修饰的有机-无机杂化二氧化硅膜材料的制备及气体分离性能

以十七氟癸基三乙氧基硅烷(PFDTES)和1,2-双(三乙氧基硅基)乙烷(BTESE)为前驱体, 通过溶胶-凝胶法制备了十七氟癸基修饰的SiO₂溶胶, 采用浸渍提拉法在γ-Al₂O₃/α-Al₂O₃多孔陶瓷支撑体上涂膜, 然后在N₂气氛保护下烧结成完整无缺陷的有机-无机杂化SiO₂膜. 利用扫描电子显微镜对膜材料的形貌进行观察, 通过动态光散射技术对溶胶粒径及分布进行测试, 利用视频光学接触角测量仪、 红外光谱仪和热分析仪表征了十七氟癸基修饰对有机-无机杂化SiO₂膜疏水性的影响. 结果表明, 十七氟癸基已经成功修饰到SiO₂膜材料中, 且随着PFDTES加入量的增大, 溶胶粒径和膜材料对水的接触角不断增大. 当n(PFDTES): n(BTESE)=0.25: 1时, 溶胶粒径分布较窄, 平均粒径为3.69 nm, 膜材料对水的接触角为(112.0±0.4)º. 在修饰后的有机-无机杂化SiO₂膜中H₂的输运遵循微孔扩散机理, 在300℃时, H₂的渗透率达到5.99×10^-7 mol·m^-2·Pa^-1·s^-1, H₂/CO和H₂/CO₂的理想分离系数分别达到9.54和5.20, 均高于Knudsen扩散的理想分离因子, 表明膜材料具有良好的分子筛分效应.     

Structural changes of the gold-support interface during CO oxidation catalyzed by mononuclear gold complexes bonded to zeolite NaY: evidence from time-resolved X-ray absorption spectroscopy

Mononuclear gold complexes synthesized from AuIII(CH3)2(acac) in zeolite NaY were characterized by time-resolved X-ray absorption spectroscopy and infrared spectroscopy as they catalyzed CO oxidation at 298 K and 760 Torr in flow systems. Initial contact with a CO + O2 mixture led to the rapid formation of cationic gold complexes in which Au was bonded to approximately two zeolite O atoms, on average. Further contact with CO + O2 led to breaking of an Au-surface oxygen bond, giving a gold carbonyl anchored to approximately one O atom. The process was reversed in the absence of CO and O2.     

Interaction of UV radiation and inorganic carbon supply in the inhibition of photosynthesis: spectral and temporal responses of two marine picoplankters

The effect of ultraviolet radiation (UVR) on inhibition of photosynthesis was studied in two species of marine picoplankton with different carbon concentration mechanisms: Nannochloropsis gaditana Lubian possesses a bicarbonate uptake system and Nannochloris atomus Butcher a CO2 active transport system. Biological weighting functions (BWFs) for inhibition of photosynthesis by UVR and photosynthesis vs irradiance (PI) curves for photosynthetically active radiation (PAR) were estimated for both species grown with an enriched CO2 supply (high dissolved inorganic carbon [DIC]: 1% CO2 in air) and in atmospheric CO2 levels (low DIC: 0.03% CO2). The response to UVR and PAR exposures was different in each species depending on the DIC treatment. Under PAR exposure, rates of maximum photosynthesis were similar between treatments in N. gaditana. However, the cultures growing in high DIC had lower sensitivity to UVR than the low DIC cultures. In contrast, N. atomus had higher rates of photosynthesis under PAR exposure with high DIC, but the BWFs were not significantly different between treatments. The results suggest that one or more processes in N. gaditana associated with HCO3- transport are target(s) for UV photodamage because there was relatively less UV inhibition of the high DIC-grown cultures in which inorganic carbon fixation is supplied by passive CO2 diffusion. Time courses of photochemical efficiency in PAR, during UV exposure and during subsequent recovery in PAR, were determined using a pulse amplitude modulated fluorometer. The results were consistent with the BWFs. In all time courses, a steady state was obtained after an initial decrease, consistent with a dynamic balance between damage and repair as found for other phytoplankton. However, the relationship of response to exposure showed a steep decline in activity that is consistent with a constant rate of repair. A novel feature of a model developed from a constant repair rate is an explicit threshold for photosynthetic response to UV.     

Influence of surfactant transport suppression on dynamic contact angle hysteresis

The influence of local and nonlocal transport processes of cetyltrimethylammonium bromide (CTAB) molecules on dynamic contact angles and contact angle hysteresis was studied in a rotating drum setup. The influence of long-range surfactant transport was analyzed by hindering selectively the surface or the bulk transport via movable barriers. With increasing hindrance of the surfactant transport, the receding contact angle decreased at all withdrawing velocities in the presence of CTAB. The control experiment with pure water was unaffected by the presence of the barriers. Dynamic contact angles are, therefore, not only influenced by short-range effects like Marangoni stresses close to the contact line, but also by long-range transport processes (like diffusion and advection) between the regions close to the receding and advancing contact lines.