Experimental and computational studies on the solvation of lithium tetrafluorobrate in dimethyl sulfoxide

Solvation structures of the lithium cation and tetrafluorobrate anion in dimethyl sulfoxide (DMSO) were investigated by Raman spectroscopy and ab initio calculations at various salt concentrations. The SO and C S stretching bands were used to monitor the structural change of the solvation shell. It has been shown that the solvation number of Li⁺, calculated by the changes in intensities of the C S asymmetric and symmetric stretching bands, is consistent with the value predicted by ab initio calculations. The wavenumber shift of the C H stretching band is suggested to be the result of the anion solvation and the dissociation of the associated DMSO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

LDH of NiZnFe and its composites with carbon nanotubes and data-palm biochar with efficient adsorption capacity for RB5 dye from aqueous solutions: Isotherm,kinetic, and thermodynamics studies

In the study, the layered double hydroxide (LDH) of NiZnFe and its composites with date-palm biochar (LDH-DPb) and carbon nanotubes (LDH-cnt) were synthesized for adsorbing reactive black 5 (RB5) dye from aqueous solutions. In the first 5 min, rapid adsorption was followed by a gradual increase in both dye uptake and removal efficiency of up to 60 min of starting time. In the investigated pH range (3.0–8.0), the removal efficiency linearly decreased while the sorption capacity linearly increased for all three adsorbents as their doses increased to 0.3 or 0.4 g following a decreasing trend up to 0.6 g. By increasing the initial RB5 concentration from 10 to 100 mg L⁻¹, the removal efficiency linearly decreased. A nearly perfect fitting of the pseudo-second-order kinetic model to the adsorption data was observed; however, the Elovich kinetic model showed the heterogeneous surface of adsorbents with chemisorption. At the solid–liquid interface, from a thermodynamics point of view, we obtained the nonspontaneous nature of the adsorption of RB5 dye of the studied adsorbents with an increased disorder, which supported the endothermic nature onto the studied adsorption process. Furthermore, a nearly perfect fitting of the Langmuir model was obtained to the adsorption data, thereby suggesting the monolayer adsorption of RB5 dye onto the studied adsorbents. In the Dubinin–Radushkevich model, a good agreement of the calculated adsorption capacities to the experimental values were observed and the chemical adsorption of RB5 dye on to the studied adsorbents was proposed based on E (8 – 16 kJ mol⁻¹).     

氧吸附对单壁碳纳米管的电子结构和光学性能的影响

用密度泛函理论计算了氧分子物理吸附在半导体型单壁碳纳米管的束缚能，能带结构和吸收 光谱.计算结果指出氧分子吸附在碳纳米管表面的优先位置，研究发现氧吸附对碳管的电子 输运特性和吸收光谱有着重要的影响，并对光致氧分子解吸附的现象进行了理论分析. 关键词： 单壁碳纳米管 氧物理吸附 能带结构 吸收光谱     

Real-space visualization of intercalated water phases at the hydrophobic graphene interface with atomic force microscopy

The phase behavior of water is a topic of perpetual interest due to its reinai kable anomalous properties and importance to biology,material science,geoscience,nanoscience,etc.It is predicted confined water at interface can exist in large amounts of crystalline or amorphous states.However,the experimental evidence of coexistence of liquid water phases at interface is still insufficient.Here,a special folding few-layers graphene film was elaborate prepared to form a hydrophobic/hydrophobic interface,which can provide a suited platform to study the structure and properties of confined liquid water.The real-space visualization of intercalated water layers phases at the folding interface is obtained using advanced atomic force microscopy(AFM).The folding graphene interface displays complicated internal interfacial characteristics.The intercalated water molecules present themselves as two phases,low-density liquid(LDL,solid-like)and high-density liquid(HDL,liquid-like),according to their specific mechanical properties taken in two multifrequency-AFM(MF-AFM)modes.Furthermore,the water molecules structural evolution is demonstrated in a series of continuous MF-AFM measurements.The work preliminary confirms the existence of two liquid phases of water in real space and will inspire further experimental work to deeply understanding their liquid dynamics behavior.     

Effects of textural and surface characteristics of microporous activated carbons on the methane adsorption capacity at high pressures

The objective of this study is to relate textural and surface characteristics of selected microporous activated carbons to their methane storage capacity. In this work, a magnetic suspension balance (Rubotherm, Germany) was used to measure methane adsorption isotherms of several activated carbon samples. Textural characteristics were assessed by nitrogen adsorption on a regular surface area analyzer (Autosorb-MP, by Quantachrome, USA). N₂ adsorption was analysed by conventional models (BET, DR, HK) and by Monte Carlo molecular simulations. Elemental and surface analyses were performed by X-ray photoelectronic spectroscopy (XPS) for the selected samples. A comparative analysis was then carried out with the purpose of defining some correlation among the variables under study. For the system under study, pore size distribution and micropore volume seem to be a determining factor as long as the solid surface is perfectly hydrophobic. It was concluded that the textural parameters per se do not unequivocally determine natural gas storage capacities. Surface chemistry and methane adsorption equilibria must be taken into account in the decision-making process of choosing an adsorbent for gas storage.     

Nanofibrous membrane of polyacrylonitrile with efficient adsorption capacity for cadmium ions from aqueous solution: Isotherm and kinetic studies

The nanofibrous membrane of polyacrylonitrile (NMP) was successfully synthesized after NaOH and NaHCO₃ treatment aiming its functionalization using electrospinning for cadmium ion (Cd²⁺) adsorption. Field emission scanning electron microscopy (FE-SEM) revealed that small particles attached to the surface of functionalized PAN nanofibers. Equilibrium was attained after 60 min following a rapid uptake of Cd²⁺ with maximum adsorption capacity and percentage removal at an optimum solution pH of 7.0. The adsorbent dose of 0.3 g and 90 mg L⁻¹ of initial Cd²⁺ concentration yielded the maximum adsorption capacity. The pseudo-second-order kinetic model was the best fitted to the adsorption data, indicating that the chemisorption is the controlling mechanism of adsorption. The physisorption was proposed based on the calculated values of the mean free energy of adsorption from the D–R isotherm (E < 8 kJ mol⁻¹). Furthermore, three-parameter isotherm models indicated the homogeneous and heterogeneous Cd²⁺ adsorption onto NMP adsorbent.     

Improving the surface properties of multi-walled carbon nanotubes after irradiation with gamma rays

The effects of gamma-irradiation on the modification of the surface and structure of multi-walled carbon nanotubes were studied. Gamma-irradiation affected the graphitization properties of functional groups, and decreased the diameter of multi-walled carbon nanotubes. The irradiated multi-walled carbon nanotubes with the absorbed dose of 100 kGy exhibited a larger specific surface area and microporous volume as compared with the other samples. The Raman spectroscopy and X-ray photoelectron spectroscopy showed that the interaction between the gamma-irradiation and the multi-walled carbon nanotubes with the absorbed dose of 150 kGy destroyed the nanostructure of carbons, leading to the formation of diamond-like structures and carbon oxides. In addition, gamma-irradiation with the absorbed dose of 100 kGy improved multi-walled carbon nanotubes graphitization and surface properties while at higher absorbed dose (150 kGy), it induced damaged structures (sp³ bonds and oxygen compositions).     

A Raman spectroscopic study on the active site of sodium cations in the structure of Na2Ti3O7 during the adsorption of Sr2+ and Ba2+ cations

A detailed study on the structural deformation of trititanate nanofibers after the adsorption of divalent strontium (Sr) and barium (Ba) cations was conducted by using Raman spectroscopy, X‐ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that the Raman bands at 309 cm⁻¹ corresponding to very long Ti O bonds (2.2 Å) and at 883 cm⁻¹ corresponding to the very short Ti O bonds (1.7 Å) decreased in intensity after the adsorption of Ba²⁺ and Sr²⁺ cations. Additionally, the band at 922 cm⁻¹ corresponding to an intermediate length Ti O bond was observed to weaken with the adsorption of divalent cations, indicating that the TiO₆ octahedra in Na₂Ti₃O₇ are more regular. These results suggest that the active sodium (Na⁺) cations in Na₂Ti₃O₇ should be located at the corner of the TiO₆ octahedral slabs, i.e. the plane (003). This was further confirmed by a large decrease of diffraction intensity of the plane (003) observed in the XRD pattern. Copyright © 2010 John Wiley & Sons, Ltd.     

Exploring acetylene chemistry in superbasic media: A theoretical study of the effect of water on vinylation and ethynylation reactions with acetylene in KOH/DMSO and NaOH/DMSO systems

A rapidly developing approach adding new dimensions to acetylene chemistry relying on employment of high basicity media such as alkali metal hydroxide suspensions in dimethyl sulfoxide (DMSO) has been, for the first time, investigated theoretically using ab initio models. Extending our recently introduced model of superbase catalysis with a nondissociated KOH (or NaOH) participation, we present here a model for a superbasic reaction center with the first solvation shell explicitly included. The alkali metal hydroxides in a DMSO solution were found to form KOH·5DMSO and NaOH·4DMSO complexes that are stabilized due to the interligand interaction. Our present MP2/6‐311++G**//B3LYP/6‐31+G* computations show that 1 and 2 water molecules can build themselves into the MOH close surrounding without substantially perturbing the DMSO ligands and easily travel between different insertion positions. Our results predict that the activation energies in the series of reactions of nucleophilic addition to a triple bond with water, methanol, methanethiol, sodium hydrosulfide, and acetone in the presence of dihydrated complexes should be larger than those obtained with the participation of monohydrated ones, which is in fair agreement with the experimental findings. The present model also explains an increase in the ethynylation reaction yield in the presence of water by suppression of the competitive enolization reaction.     

不同密度氢吸附金刚石(100)表面的微观结构

利用基于广义梯度近似的密度泛函理论,计算了金刚石(100)表面不同氢吸附密度的平衡态几何结构和态密度.结果表明对于2×1构型,在平行和垂直表面两个方向上发生弛豫,而1×1构型仅在垂直表面方向上发生弛豫.另外,清洁2×1,2×1 ∶0.5H和1×1 ∶1.5H表面,带隙中存在空表面态;而对于1×1 ∶2H和2×1 ∶H两种表面结构,空表面态上移进入导带,带隙中不存在表面态.结合电荷密度分布,探讨了金刚石(100)不同构型和氢吸附密度表面的表面态诱发机理. 关键词： 氢吸附 金刚石 弛豫 表面态     

硼原子掺杂对碳纳米管吸附Ne原子影响的第一性原理计算

采用基于第一性原理的密度泛函理论（DFT）和局域密度近似（LDA）方法,优化计算得到碳纳米管（CNT）,硼原子取代碳原子及其吸附氖原子前后系统的几何结构,能量,电子能带和态密度。结果显示,碳纳米管的能带结构与石墨的层状几何结构相似,能量的变化只在kz=0和kz=0.5平面之间沿着c轴方向出现。B原子取代C原子使价带和导带分别分裂为两个和三个能带。对Ne原子的吸附使价带能量沿着c轴方向升高并导致Fermi面附近的态密度下降。Ne原子的吸附在谷位H最稳定,顶位A其次。C-C间σ键的弯曲使Ne原子吸附在桥位b1比桥位b2处更为稳定。Ne原子在管外的吸附均为放热过程,而管内则为吸热过程。结构分析表明Ne原子对C原子有排斥作用,对B原子却具有吸引作用。B原子取代C原子的位置略凸出于CNT的管壁之外,使Ne原子的吸附能增加。     

含Nb或Ge的锆合金表面氧吸附行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 研究了纯锆表面和含Nb或Ge锆合金表面上氧的吸附性质. 结果表明, Nb和Ge对Zr(0001), (1120)和(1010)表面吸附性质的影响各不相同. 根据计算得到的偏聚能结果, Nb和Ge迁移到Zr(0001)表面比迁移到其他两个表面更容易, 而Nb和Ge 都可以降低Zr(0001)表面对氧原子的吸附能力, 因此这两种元素都能抑制锆合金的初始氧化. 进一步的电子结构分析发现, Nb和Ge改变表面对氧原子的吸附能力是通过改变表面d能带的分布来实现的.     

硼原子掺杂对碳纳米管吸附Ne原子影响的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)和局域密度近似(LDA)方法,优化计算得到碳纳米管(CNT),硼原子取代碳原子及其吸附氖原子前后系统的几何结构,能量,电子能带和态密度.结果显示,碳纳米管的能带结构与石墨的层状几何结构相似,能量的变化只在kz=0和kz=0.5平面之间沿着c轴方向出现.B原子取代C原子使价带和导带分别分裂为两个和三个能带.对Ne原子的吸附使价带能量沿着c轴方向升高并导致Fermi面附近的态密度下降.Ne原子的吸附在谷位H最稳定,顶位A其次.C-C间σ键的弯曲使Ne原子吸附在桥位b1比桥位b2处更为稳定.Ne原子在管外的吸附均为放热过程,而管内则为吸热过程.结构分析表明Ne原子对C原子有排斥作用,对B原子却具有吸引作用.B原子取代C原子的位置略凸出于CNT的管壁之外,使Ne原子的吸附能增加.     

DFT calculations for Au adsorption onto a reduced TiO2 (110) surface with the coexistence of Cl

Residual chlorines, which originate from HAuCl₄, enhance the aggregation of gold (Au) nanoparticles and clusters, preventing the generation of highly active supported Au catalysts. However, the detailed mechanism of residual-chlorine-promoted aggregation of Au is unknown. Herein to investigate this mechanism, density functional theory (DFT) calculations of Au and Cl adsorption onto a reduced rutile TiO₂ (110) surface were performed using a generalised gradient approximation Perdew, Burke, and Ernzerhof formula (GGA–PBE) functional and plane-wave basis. Although both Au and Cl atoms prefer to mono-absorb onto oxygen defect sites, Cl atoms have a stronger absorption onto a reduced TiO₂ (110) surface, abbreviated as rTiO₂ (110) in the following, than Au atoms. Additionally, co-adsorption of a Cl atom and a Au atom or Au nanorod onto a rTiO₂ surface was investigated; Cl adsorption onto an oxygen defect site weakens the interaction between a Au atom or Au nanorod and rTiO₂ (110) surface. The calculation results suggest that the depletion of interaction between Au and rTiO₂ surface is due to strong interaction between Cl atoms at oxygen defect sites and neighbouring bridging oxygen (O^B) atoms.     

Coating curly carbon nanotubes with monocrystalline Zn(BO2)2 and the mechanism of straightening the tubes

We overgrew single-crystalline Zn(BO2)2 coatings on carbon nanotubes (CNTs) for the first time. Scanning electron microscopy and transmission electron microscopy analyses revealed that the carbon nanotube-zinc borate composite rods are from tens to hundreds of nm in diameter. It is notable that the original curly tubes were straightened by the monocrystalline coatings. In addition, the crystal nucleation and growth on the surface of CNT were explained. We set a two-dimensional model, which is based on our experimental result, to qualitatively explain the mechanism of straightening the curly tubes by coating them with single-crystals.     

基于密度泛函理论研究掺杂Pd石墨烯吸附O2及CO

基于第一性原理的密度泛函理论研究了单个O₂和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O₂和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O₂后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.     

A new force field for the adsorption of H2, O2, N2, CO,H2O,and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H₂, O₂, N₂, CO, H₂O, and H₂S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li⁺, Na⁺_, K⁺ and Cs⁺ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the β/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical Monte Carlo (GCMC) simulation of the H₂ adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H₂ adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions.     

氮掺杂及水分子吸附碳纳米管电子场发射第一性原理研究

对闭口碳纳米管(CNT)顶端分层掺氮及吸附不同数目水分子体系,运用第一性原理研究了有电场存在时的电子场发射性能.结果表明：掺氮并吸附水分子的CNT结构稳定;外电场愈强、水分子数愈多,体系态密度(DOS)向低能端移动幅度愈大且最高分子占据轨道(HOMO)/最低分子空轨道(LUMO)能隙愈小.吸附能,DOS/LDOS,HOMO/LUMO及其能隙分析一致表明,第三层氮掺杂CNT吸附不同数目水分子体系的场发射性能最佳. 关键词： 氮掺杂 水吸附 密度泛函理论 电子场发射     

Determination of the K adsorption site on Fe(1 1 0) with XSW

We have used X-ray standing waves (XSW) in near normal incidence to determine the K–Fe bond length and the adsorption site of K at the saturation coverage at room temperature on the Fe(1 1 0) surface. Three different scattering geometries were used to enable the determination of the adsorption site by triangulation. From the results we conclude that the potassium atoms adsorb in a distorted hexagonal overlayer. The Fe–K distance, as determined from the measurements in the (2 2 0) Bragg reflection, is 3.4±0.2 Å. The long bridge site seems to be the preferred adsorption site for the potassium atoms in the distorted hexagonal overlayer. This geometry not only fits all the XSW data, but also explains all spots in the LEED pattern without the need to introduce multiple scattering. Comparison of the measured and simulated XSW data, based on the distorted hexagonal overlayer, enables a more accurate determination of the Fe–K bond length to 3.36±0.14 Å. This corresponds to a potassium hard sphere radius of r_K=2.12±0.14 Å. This radius is among the largest reported for potassium on a metal, which is attributed to the high coverage and coordination of the K atoms in this overlayer arrangement.