Adsorption of sodium ions and hydrated sodium ions on a hydrophobic graphite surface via cation-π interactions

Using density functional theory computation, we show that sodium ions and hydrated sodium ions can be strongly adsorbed onto a hydrophobic graphite surface via cation-π interactions. The key to this cation-π interaction is the coupling of the delocalized π states of graphite and the empty orbitals of sodium ions. This finding implies that the property of the graphite surface is extremely dependent on the existence of the ions on the surface, suggesting that the hydrophobic property of the graphite surface may be affected by the existence of the sodium ions.     

H2NO·自由基和顺-2-丁烯反应机理的理论研究

采用UB3LYP/6-311++G(d,p)//UB3LYP/6-31G(d)方法对H2NO·自由基和顺-2-丁烯反应的势能面进行了研究, 发现了三类共5条可能的反应通道: L4-Ⅰ和L4-Ⅱ(夺氢-加成), L4-Ⅲ和L4-Ⅳ(加成-加成-消除), L4-Ⅴ(加成-加成-消除-催化转换). 动力学分析表明, 该反应为加成-加成-消除过程.     

双取代铵氧化物(R2HNO)与双取代羟胺(R2NOH)的相互转换机制的理论研究——取代基的电负性和立体效应影响

在B3LYP/6-311++G(d,p)水平下, 对一系列双取代铵氧化物(R2HNO)与双取代羟胺(R2NOH){R=NH2, N(CH3)2, N(CH2CH3)2, N[C(CH3)3]2, OH, OCH3, OCH2CH3, OC(CH3)3}的相互转换机制进行了理论研究. 研究结果表明, 双取代铵氧化物R2HNO的热力学和动力学稳定性受电负性和立体效应的综合控制. 其中胺基系列热力学稳定性以空间位阻的影响为主, 而烷氧基系列热力学稳定性以电负性的影响为主. 而两者的动力学稳定性均以电负性影响为主.     

双取代铵氧化物(R2HNO)与双取代羟胺(R2NOH)的 相互转换机制的量子化学研究

在B3LYP/6-311＋＋G(d,p)水平下, 首次对一系列双取代铵氧化物(R2HNO)与双取代羟胺(R2NOH) [R＝CH3, NH2, OH, F, CH2CH3, CH(CH3)2, C(CH3)3]同分异构体的相互转换机制进行了理论计算研究, 并与已知的H3NO和H2NOH进行了比较. 结果表明, 相对于双取代羟胺(R2NOH), 按照H＜CH3＜NH2＜OH＜F的顺序, 增加取代基R的电负性有助于提高双取代铵氧化物(R2HNO)的热力学和动力学稳定性. 此外, 对烷基取代基R [R＝CH3, CH2CH3, CH(CH3)2, C(CH3)3], 其空间位阻越大越能增加双取代铵氧化物(R2HNO)的热力学稳定性, 动力学稳定性也有相应增加, 但不显著. 对所研究的7种取代基[R＝CH3, NH2, OH, F, CH2CH3, CH(CH3)2, C(CH3)3], R2HNO向R2NOH转换的能垒介于27.0～56.3 kcal/mol之间, 表明在气相条件下极有可能观测到双取代铵氧化物(R2HNO).     

Preparation of graphene oxides with different sheet sizes by temperature control

The sheet size of a graphene oxide(GO) can greatly influence its electrical, optical, mechanical, electrochemical and catalytic property. It is a key challenge to how to control the sheet size during its preparation in different application fields. According to our previous theoretical calculations of the effect of temperature on the oxidation process of graphene,we use Hummers method to prepare GOs with different sheet sizes by simply controlling the temperature condition in the process of the oxidation reaction of potassium permanganate(KMn O_4) with graphene and the dilution process with deionized water. The results detected by transmission electron microscopy(TEM) and atomic force microscopy(AFM)show that the average sizes of GO sheets prepared at different temperatures are about 1 μm and 7 μm respectively. The ultraviolet–visible spectroscopy(UV-vis) shows that lower temperature can lead to smaller oxidation degrees of GO and less oxygen functional groups on the surface. In addition, we prepare GO membranes to test their mechanical strengths by ultrasonic waves, and we find that the strengths of the GO membranes prepared under low temperatures are considerably higher than those prepared under high temperatures, showing the high mechanical strengths of larger GO sheets. Our experimental results testify our previous theoretical calculations. Compared with the traditional centrifugal separation and chemical cutting method, the preparation process of GO by temperature control is simple and low-cost and also enables large-size synthesis. These findings develop a new method to control GO sheet sizes for large-scale potential applications.     

Potentials of classical force fields for interactions between Na~+ and carbon nanotubes

Carbon nanotubes(CNTs) have long been expected to be excellent nanochannels for use in desalination membranes and other bio-inspired human-made channels owing to their experimentally confirmed ultrafast water flow and theoretically predicted ion rejection. The correct classical force field potential for the interactions between cations and CNTs plays a crucial role in understanding the transport behaviors of ions near and inside the CNT, which is key to these expectations. Here,using density functional theory calculations, we provide classical force field potentials for the interactions of Na+/hydrated Na+with(7,7),(8,8),(9,9), and(10,10)-type CNTs. These potentials can be directly used in current popular classical software such as nanoscale molecular dynamics(NAMD) by employing the tcl BC interface. By incorporating the potential of hydrated cation-π interactions to classical all-atom force fields, we show that the ions will move inside the CNT and accumulate, which will block the water flow in wide CNTs. This blockage of water flow in wide CNTs is consistent with recent experimental observations. These results will be helpful for the understanding and design of desalination membranes, new types of nanofluidic channels, nanosensors, and nanoreactors based on CNT platforms.     

[GeCN2]分子异构化势能面的理论研究

在CCSD(T)/6-311＋G(2df)//B3LYP/6-311＋G(d)水平下, 研究了四原子分子 [GeCN2]的各个异构体的几何结构、红外振动光谱、相对能量及异构化和解离稳定性, 构建了[GeCN2]势能面. 我们得到了7个[GeCN2]异构体, 包括5个直线型结构GeNCN (1), GeNNC (2), NGeCN (3), NGeNC (4), GeCNN (5)和2个环形结构Ge-cCNN (6)和Ge-cNCN (7). 其中异构体5, 6, 7是我们新找到的构型, 而且GeCNN (5)是整个势能面上稳定性仅次于GeNCN (1)的异构体. 几何和电子结构分析表明, GeCNN (5)具有共轭三键结构: Ge≡C—N≡N:. 由于具有良好的热力学和动力学稳定性, 异构体GeCNN (5)有望在实验中观测到. 我们建议利用过渡金属羰基化合物的络合作用可以进一步稳定GeCNN (5). 本研究为寻找新型含高周期元素的多重键化合物提供了理论线索.     

SnCNN: 一个包含SnC三重键的分子

在CCSD(T)//B3LYP方法下, 研究了四原子分子[SnCN₂]的势能面, 发现线性异构体SnCNN具有良好的动力学稳定性. 几何分析与键分析表明, 该异构体包含Sn≡C三重键, 并可以用过渡金属络合物配合稳定来增加其稳定性.     

A Theoretical Study of a Single-Walled ZnO Nanotube as a Sensor for H_2 O Molecules

We have studied the property of single-walled ZnO nanotubes with adsorbed water molecules, and theoretically designed a new sensor for detecting water molecules using single-walled ZnO nanotubes using a combination of density functional theory and the non-equilibrium Green's function method. Details of the geometric structures and adsorption energies of the H 2 O molecules on the ZnO nanotube surface have been investigated. Our computational results demonstrate that the formation of hydrogen bonding between the H 2 O molecules and the ZnO nanotube, and adsorption energies of the H 2 O molecules on the ZnO nanotube are larger than the adsorption energies of other gas molecules present in the atmospheric environment. Moreover, the current-voltage curves of the ZnO nanotube with and without H 2 O molecules adsorbed on its surface are calculated, the results of which showed that the H 2 O molecules form stable adsorption configurations that could lead to the decrease in current. These results suggest that the single-walled ZnO nanotubes are able to detect and monitor the presence of H 2 O molecules by applying bias voltages.     

双取代铵氧化物(R2HNO)与取代羟胺(R2NOH)的相互转换机制的量子化学研究

在B3LYP/6-311 G(d,p)水平下,首次对一系列双取代铵氧化物(R2HNO)与双取代羟胺(R2NOH)[R=CH3,NH2,OH,F,CH2CH3,CH(CH3)2,C(CH3)3]同分异构体的相互转换机制进行了理论计算研究,并与已知的H3NO和H2NOH进行了比较.结果表明,相对于双取代羟胺(R2NOH),按照H相似文献