铀酰离子在羟基化α-石英(101)表面的吸附

采用周期性密度泛函理论研究羟基化α-石英(101)面的铀酰离子吸附行为.通过对铀酰离子的水合作用考虑水溶剂对结构的短程溶剂化效应,并通过类导体屏蔽模型(COSMO)考虑水溶剂对结构的远程溶剂化效应.吸附能计算结果和电子结构数据均表明水合铀酰离子吸附构型比氢氧化铀酰吸附构型稳定,并且在液相中两种类型的稳定吸附位均为dia-Os1Os2位.两种形式在电子结构上有很大的差异,主要是由于铀与表面作用后成键强弱程度不同,使5f轨道宽化和略微红移存在差异.在铀酰离子吸附的基础上利用卤素离子改变铀酰离子配位环境可调整体系的带隙.     

密度泛函理论研究十二烷硫醇在Au(111)面上的吸附

采用第一性原理方法研究了十二烷硫醇(C₁₂H₂₅SH)分子在Au(111)面上未解离和解离吸附的结构、能量和吸附性质,在此基础上分析判断长链硫醇分子在Au(111)面吸附时S―H键的解离, 以及分子链长度对吸附结构和能量的影响. 计算了S原子在不同位置以不同方式吸附的系列构型, 结果表明在S―H键解离前和解离后,均存在两种可能的表面结构, 直立吸附构型和平铺吸附构型; 未解离的C₁₂H₂₅SH分子倾向于吸附在top位, 吸附能为0.35-0.38 eV; H原子解离后C₁₂H₂₅S基团倾向于吸附在bri-fcc位, 吸附能量为2.01-2.09 eV. 比较分析未解离吸附和解离吸附, 发现C₁₂H₂₅SH分子未解离吸附相较于解离吸附要稳定, 未解离吸附属于弱化学吸附.局域电子态密度和差分电荷密度分析进一步验证了S―H解离后S原子与表面之间成键的数目增加, 而且键合更强. 同时我们发现长链硫醇的吸附能量较短链硫醇的吸附能量略大, S原子与表面Au原子之间的距离略小.     

UO22＋•nH2O和PuO22＋•nH2O (n＝2, 4, 5, 6)密度泛函理论研究

首先用密度泛函理论(DFT)方法研究了铀酰和钚酰离子的几何与电子结构, 计算结果与实验基本符合, 表明DFT方法也能用于含铀和钚重原子的化合物计算. 然后对铀酰和钚酰水合离子的几何构型、Mulliken集居数分布以及铀酰(钚酰)与配体水分子的结合能进行计算, 计算结果表明UO₂^2＋•5H₂O和PuO₂^2＋•5H₂O分别为铀酰和钚酰系列水合离子中最稳定的配合物.     

基于含双吡唑的四羧酸配体构筑的Fe(Ⅱ)/Co(Ⅱ)同构配合物的合成、晶体结构及磁性质

本文报道了2种二维同构配位聚合物{（NH₂（CH₃）₂）₂[M（L）]}_n（M=Fe （1）、Co （2）,H₄L=1,1''-（1,4-苯基双（亚甲基））双（1H-吡唑-3,5-二羧酸））的合成、晶体结构和磁性。X射线单晶衍射结构分析表明,2种配合物属于相同的单斜晶系P2₁/n空间群,中心金属离子M（Ⅱ）是六配位的八面体构型。该配合物的特点是配离子带有2个负电荷,溶剂DMF分解形成的二甲基胺离子作为阳离子而使配合物保持电中性。在聚合物中,每个配体通过吡唑环上的N、O原子和该吡唑环上的单齿O原子桥联2个金属离子,形成···M-L-M-L···一维链,此一维链相交形成包含M₄L₄单元的无限二维网络结构。磁性研究表明,配合物1和2具有反铁磁性。     

基于1-(3，5-二羧基苄基)-1H-吡唑-3，5-二羧酸的钴(Ⅱ)配位聚合物的合成、结构、磁性和荧光传感性质

以1-（3,5-二羧基苄基）-3,5-吡唑二羧酸（H₄L）为配体,采用水热法合成了1个三维钴配位聚合物[Co₅（L）₂（μ₃-OH）₂（H₂O）₈]_n（1）,并通过单晶X射线衍射分析、元素分析、红外光谱分析和热重分析对其结构进行了表征。单晶结构分析表明配合物1属于三斜晶系,空间群为P1。配合物1具有三维网状结构。分子中的3个Co （Ⅱ）离子都采取六配位模式,构成了轻微扭曲的八面体配位构型。通过变温磁化率测量发现,配合物1中的Co （Ⅱ）离子之间存在反铁磁相互作用。荧光传感实验表明配合物1对Hg²⁺有高度的灵敏性和选择性荧光猝灭。此外,Co （Ⅱ）-CP传感器可用于延河水样中Hg²⁺含量的测定。     

甲硫醇在Cu(111)表面的解离吸附: 密度泛函理论研究

采用基于密度泛函理论的第一性原理方法和平板模型研究了CH₃SH分子在Cu(111)表面的吸附反应.系统地计算了S原子在不同位置以不同方式吸附的一系列构型, 第一次得到未解离的CH₃SH分子在Cu(111)表面顶位上的稳定吸附构型,该构型吸附属于弱的化学吸附, 吸附能为0.39 eV. 计算同时发现在热力学上解离结构比未解离结构更加稳定. 解离的CH₃S吸附在桥位和中空位之间, 吸附能为0.75-0.77 eV. 计算分析了未解离吸附到解离吸附的两条反应路径, 最小能量路径的能垒为0.57 eV. 计算结果还表明S―H键断裂后的H原子并不是以H₂分子的形式从表面解吸附而是以与表面成键的形式存在. 通过比较S原子在独立的CH₃SH分子和吸附状态下的局域态密度, 发现S―H键断裂后S原子和表面的键合强于未断裂时S原子和表面的键合.     

两个三核钴(Ⅱ)Salamo型配合物的合成、晶体结构、溶剂效应和荧光性质

通过四水乙酸钴（Ⅱ）和Salamo型双肟配体4,4''-二硝基-2,2''-（1,2-乙二氧双（氮次甲基））二酚（H₂L）在不同溶剂中的配位反应,合成了2种不同溶剂参与配位的三核钴（Ⅱ）配合物,即[Co₃L（OAc）₂（CH₃CH₂OH）]·2CH₃CH₂OH·2CHCl₃（1）和[Co₃L（OAc）₂（C₃H₇OH）]（2）,并通过元素分析、红外光谱、紫外-可见光谱和单晶X射线衍射法对其进行了性质表征。在配合物1和2中,存在2个配体单元（提供N₂O₂配位原子）,2个乙酸根离子,2个配位的乙醇或正丙醇分子。虽然2个配合物是在不同溶剂中合成的,但配合物中的钴（Ⅱ）离子均采用稍微扭曲的八面体几何构型。结果表明,溶剂效应在配合物的配位环境中起了关键的作用。另外,配合物1和2在激发波长为450 nm时能表现出强烈的光致发光,其最大发射波长分别为568和566 nm。     

对乙酰氨基苯甲酸和含氮配体构筑铜、锌配合物的合成、结构及性质研究

利用对乙酰氨基苯甲酸（HPABA）和邻菲咯啉（phen）、硝酸铜在DMF/CH₃OH/H₂O溶液中合成了单核铜配合物[Cu（PABA）（phen）（H₂O）₂]·（NO₃）·H₂O（1）,然后又和4,4’-联吡啶（4,4’-bpy）、硝酸锌在DMF/CH₃OH/H₂O溶液中获得配位聚合物{[Zn（PABA）₂（4,4’-bpy）]·4H₂O}_n（2）。根据X射线衍射分析结果,配合物1中每个铜离子周围有2个氮原子和3个氧原子与之配位形成畸变的四方锥配位构型,然而在配合物2中,六配位八面体构型的锌离子通过配体4,4’-联吡啶扩展为一维Zigzag型链。分别对这两个配合物的热稳定性和电化学性质进行了研究。     

两个三核钴(II)Salamo型配合物的合成、晶体结构、溶剂效应和荧光性质

通过四水乙酸钴（Ⅱ）和Salamo型双肟配体4,4''-二硝基-2,2''-（1,2-乙二氧双（氮次甲基））二酚（H₂L）在不同溶剂中的配位反应,合成了2种不同溶剂参与配位的三核钴（Ⅱ）配合物,即[Co₃L（OAc）₂（CH₃CH₂OH）₂]·2CH₃CH₂OH·2CHCl₃（1）和[Co₃L（OAc）₂（C₃H₇OH）₂]（2）,并通过元素分析、红外光谱、紫外-可见光谱和单晶X射线衍射法对其进行了性质表征。在配合物1和2中,存在2个配体单元（提供N₂O₂配位原子）,2个乙酸根离子,2个配位的乙醇或正丙醇分子。虽然2个配合物是在不同溶剂中合成的,但配合物中的钴（Ⅱ）离子均采用稍微扭曲的八面体几何构型。结果表明,溶剂效应在配合物的配位环境中起了关键的作用。另外,配合物1和2在激发波长为450 nm时能表现出强烈的光致发光,其最大发射波长分别为568和566 nm。     

噻吩在M(111)(M=Pd,Pt, Au)表面的吸附

采用密度泛函理论(DFT), 选取DMol³程序模块, 对噻吩在M(111) (M=Pd, Pt, Au)表面上的吸附行为进行了探讨. 通过对噻吩在不同底物金属上的吸附能、吸附构型、Mulliken 电荷布居、差分电荷密度以及态密度的分析发现, 噻吩在Pd(111)面上的吸附能最大, Pt(111)面次之, Au(111)面最小. 吸附后, 噻吩在Au(111)面上的构型几乎保持不变, 最终通过S端倾斜吸附于top 位; 噻吩在Pd(111)及Pt(111)面上发生了折叠与变形, 环中氢原子向上翘起, 最终通过环平面平行吸附于hollow 位. 此外, 噻吩环吸附后芳香性遭到了破坏, 环中碳原子发生sp³杂化, 同时电子逐渐由噻吩向M(111)面发生转移, M(111)面上的部分电子也反馈给了噻吩环中的空轨道, 这种协同作用最终导致了噻吩分子稳定吸附于M(111)面.     

Modeling adsorption of the uranyl dication on the hydroxylated alpha-Al2O3(0001) surface in an aqueous medium. Density functional study

As a first step toward modeling the interaction of dissolved actinide contaminants with mineral surfaces, we studied low-coverage adsorption of aqueous uranyl, UO2(2+), on the hydroxylated alpha-Al2O3(0001) surface. We carried out density functional periodic slab model calculations and modeled solvation effects by explicit aqua ligands. We explored the formation of both inner- and outer-sphere complexes and estimated the corresponding adsorption energies. Effects of solvation were accounted for by explicit consideration of the first hydration shell of uranyl and by means of a posteriori corrections for long-range solvent effect. With energetics described at the GGA-PW91 level and under the assumption of a fully protonated ideal surface, we predict a weakly bound outer-sphere adsorption complex.     

Molecular dynamics simulation of uranyl(VI) adsorption equilibria onto an external montmorillonite surface

We used molecular dynamics simulations to study the adsorption of aqueous uranyl species (UO(2)(2+)) onto clay mineral surfaces in the presence of sodium counterions and carbonato ligands. The large system size (10,000 atoms) and long simulation times (10 ns) allowed us to investigate the thermodynamics of ion adsorption, and the atomistic detail provided clues for the observed adsorption behavior. The model system consisted of the basal surface of a low-charge Na-montmorillonite clay in contact with aqueous uranyl carbonate solutions with concentrations of 0.027 M, 0.081 M, and 0.162 M. Periodic boundary conditions were used in the simulations to better represent an aqueous solution interacting with an external clay surface. Uranyl adsorption tendency was found to decrease as the aqueous uranyl carbonate concentration was increased, while sodium adsorption remained constant. The observed behavior is explained by physical and chemical effects. As the ionic strength of the aqueous solution was increased, electrostatic factors prevented further uranyl adsorption once the surface charge had been neutralized. Additionally, the formation of aqueous uranyl carbonate complexes, including uranyl carbonato oligomers, contributed to the decreased uranyl adsorption tendency.     

Adsorption of dimethyl methylphosphonate and trimethyl phosphate on calcium oxide: an ab initio study

Ab initio study of the adsorption of dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) on three types of models simulating the calcium oxide surface (non-hydroxylated Ca₄O₄, completely hydroxylated Ca₄O₄(OH)₂H₂, and partially hydroxylated Ca₄O₄(OH)H) was performed. The target molecule and the surface hydroxyl groups were optimized while the CaO fragment was kept frozen. The intermolecular interactions were investigated applying Bader’s Atoms in Molecules theory. The maps of electrostatic potential of the studied adsorption systems were also produced. The interaction energies of studied adsorption systems corrected by the basis set superposition error were obtained. The most energetically favorable adsorption of DMMP and TMP was found at the configuration where the oxygen atoms of the P=O and methoxy groups point toward the Ca cation of the surface. The P atom points toward the O atom of the surface and forms a P–O chemical bond. This configuration was revealed for the non-hydroxylated and partially hydroxylated CaO-DMMP and CaO-TMP systems. The presence and number of surface hydroxyl groups on the CaO models play a key role in the adsorption of the studied compounds. DMMP and TMP were found to be much less stable on the completely hydroxylated CaO surface where they are adsorbed only via weak electrostatic interactions and H-bonding to the surface oxygen atoms and hydroxyl groups. TMP was found to be slightly more stable on this type of surface than DMMP. The difference in stability is even larger if one compares this TMP system with the complex of tabun adsorbed on completely hydroxylated CaO surface model (Michalkova et al. Chem Phys Lett 438:72, 2007).

CeO2(110)表面上CO氧化反应的密度泛函理论研究

利用密度泛函理论系统研究了O2与CO在CeO2(110)表面的吸附反应行为. 研究表明, O2在洁净的CeO2(110)表面吸附热力学不利, 而在氧空位表面为强化学吸附, O2分子被活化, 可能是重要的氧化反应物种. CO在洁净的CeO2(110)表面有化学吸附与物理吸附两种构型, 前者形成二齿碳酸盐物种, 后者与表面仅存在弱的相互作用. 在氧空位表面, CO可分子吸附或形成碳酸盐物种, 相应吸附能均较低. 当表面氧空位吸附O2后(O2/Ov), CO可吸附生成碳酸盐或直接生成CO2, 与原位红外光谱结果相一致. 过渡态计算发现,O2/Ov/CeO2(110)表面的三齿碳酸盐物种经两齿、单齿过渡态脱附生成CO2. 利用扩展休克尔分子轨道理论分析了典型吸附构型的电子结构, 说明表面碳酸盐物种三个氧原子电子存在离域作用, 物理吸附的CO及生成的CO2电子结构与相应自由分子相似.     

Exploration of the (ethanol)4–water heteropentamers potential energy surface by simulated annealing and Ab initio molecular dynamics

A DFT electronic structure study of the (ethanol)₄–water heteropentamers at the B3LYP/6‐31+G(d) model chemistry was carried out. To get determine possible configurations, the potential energy surface (PES) was explored with two methods: simulated annealing and ab initio molecular dynamics. The results suggest that the PES is very flat. A total of 81 stable structures were determined. These structures were classified into 16 different geometric patterns according to geometric criteria like the number of hydrogen bonds and their spatial arrangement: cyclic, bicyclic, or lineal patterns. Thermodynamic stability was used for defining the order of such classification. Hydrogen bonds are mutually disturbed due to the existence of cooperative effects. Cooperativity affects the nature of the hydrogen bonds and the overall stability of the ethanol–water system given that the strongest interactions are markedly covalent and the most stable geometric pattern corresponds to the pentagonal arrangement. These observations were supported by the analysis of the loss of atomic charge of the hydrogen atoms involved in hydrogen bonds. These hydrogen bonds were classified as primary and secondary hydrogen bonds: O? H ··· O and C? H ··· O, respectively. For comparative purposes, some (ethanol)₅, (methanol)₅, and (methanol)₄–water clusters were characterized in this study. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Adsorption of Uranyl Ions into Poly(Acrylamide‐co‐Acrylic Acid) Hydrogels Prepared by Gamma Irradiation

Acrylamide (AAm)/Acrylic Acid (AAc) copolymers have been prepared by gamma irradiation of binary mixtures at three different compositions where the acrylamide/acrylic acid mole ratios varied around 15, 20, and 30%. Threshold dose for 100% conversion of monomers into hydrogels was found to be 8.0 kGy. Poly(Acrylamide‐co‐Acrylic Acid) (poly(AAm‐co‐AAc)) hydrogels have been considered for the removal of uranyl ions from aqueous solutions. Swelling behavior of these hydrogels was determined in distilled water at different pH values and in aqueous solutions of uranyl ions. The results of swelling tests at pH 8.0 indicated that poly(AAm‐co‐AAc) hydrogel, containing 15% acrylamide showed maximum % swelling. Diffusion of water and aqueous solutions of uranyl ion into hydrogels was found to be non‐Fickian in character and their diffusion coefficients were calculated. The effect of pH, composition of hydrogel, and concentration of uranyl ions on the adsorption process were studied at room temperature. It was found that one gram of dry poly(AAm‐co‐AAc) hydrogel adsorbed 70–320 mg and 70–400 mg uranyl ions from aqueous solutions of uranyl nitrate and uranyl acetate in the initial concentration range of 50–1500 mg UO₂ ²⁺L^?, depending on the amount of AAc in the hydrogels, respectively. Adsorption isotherms were constructed for poly(AAm‐co‐AAc)–uranyl ion system indicating an S type of adsorption in the Giles classification system. It is concluded that crosslinked poly(AAm‐co‐AAc) hydrogels can be successfully used for the removal of uranyl ions from their aqueous solutions.     

Nitrogen-rich carbon nitrogen polymers for enhancing the sorption of uranyl

Nitrogen enrichment and increased nitrogen content is an effective strategy for enhancing adsorption of uranium by carbon nitride polymers. Herein, we reported the uranium absorption by using a structurally well-defined and nitrogen-rich carbon nitride polymer with C₃N₅ stoichiometry for the first time. In comparison with the adsorption performance of g-C₃N₄ for U(VI), the conjugation system of the material was increased by connecting the heptazine unit through the azo bridge in the structure of C₃N₅, so that C₃N₅ exhibited several times higher adsorption performance than that of g-C₃N₄. The C₃N₅ has high kinetics for uranyl ions, which can adsorb 100 mg/g U(VI) in only 10 min and reach complete adsorption equilibrium in 60 min; the theoretical maximum adsorption capacity is 207 mg/g, meanwhile, the material exhibits high selectivity. The results of spectral analysis and theoretical calculations indicate that the process of uranyl ion capture by C₃N₅ is a combination of physical and chemical adsorption, and its higher density of electronic states makes the electrostatic binding ability enhanced, which is favorable to the adsorption of uranyl ions by C₃N₅. This work indicates that C₃N₅ has great promise and application in the separation and enrichment of uranyl ions, and also provides a reference for the systematic investigation of the adsorption ability of nitrogen-rich carbon nitrogen polymers on uranyl ions.     

Structural environment of uranium (VI) species sorbed onto ZrP2O7: X-ray absorption spectroscopy study

The structure of the surface complex formed during the sorption of UO₂²⁺_aq ion onto the selected phosphate solid has been investigated mainly using X-ray absorption spectroscopy. Samples were prepared by batch experiments. L_III U edge measurements have shown that uranyl ions are sorbed on the phosphate surface as a mononuclear bidentate inner-sphere complex.