DNA模板荧光金属纳米团簇的合成及应用

荧光金属纳米团簇的尺寸介于金属原子和纳米颗粒之间，特殊的结构和尺寸赋予了金属纳米团簇一系列优异的荧光特性，如荧光强度高、抗光漂白性能强、较大的斯托克斯位移。脱氧核糖核酸(DNA)由于其独特的结构和可设计的序列而成为合成金属纳米簇的理想模板。DNA模板的金属纳米簇主要包括DNA模板的银纳米团簇(DNA-AgNCs)、铜纳米团簇(DNA-CuNCs)、金纳米团簇(DNA-AuNCs)等。DNA模板的金属纳米团簇作为一种新型的荧光纳米探针在生物传感和生物成像等领域具有较大潜在应用价值。基于先前对DNA模板的金属纳米团簇的研究，系统总结了DNA模板的金属纳米簇的制备、性质和在生物传感以及生物成像中的应用。最后，讨论了DNA模板的金属纳米簇的未来发展研究重点和前景。     

NaPn（n=1～9）团簇结构和稳定性的研究

在前人所研究的磷团簇基础上设计出NaPn（n=1～9）团簇的各种结构模型,并在B3LYP／6—311G（d）水平上对它们进行优化和频率分析,得到NaPn（n=1—9）每种团簇的各种稳定结构,并对每种团簇的最稳定结构进行二阶能量有限差分分析。结果表明：与纯磷团簇相比,NaPn（n=1～9）团簇的对称性与稳定性都有所降低;n=3,6时NaPn（n=1～9）团簇的最稳定结构存在幻数结构,它们在所有NaPn（n=1～9）团簇中最稳定。     

复合镍基催化剂表面纳米团簇结构的调控及其催化应用

利用新型等离子体技术,将常压放电冷等离子体炬应用于催化剂制备,研究了制备方法、载体、活性组分和助剂对复合镍基催化剂表面纳米团簇结构的调控效果;并分析了催化剂表面纳米团簇结构的形成机理和催化剂性能的构效关系。结果表明:采用冷等离子体炬直接焙烧还原可调控表面纳米团簇;以-γAl2O3为载体的Ni催化剂(PCR)具有较高的活性和稳定性;活性组分Ni对表面纳米团簇结构的调控效果较好,添加量为12%(质量分数)时,表面纳米团簇高度分散,其尺寸约5 nm;助剂Mg添加可有效提高催化剂活性,合适的添加量为1%,且催化剂仍保持良好的表面纳米团簇结构,尺寸约5 nm;表面纳米团簇结构优化后的催化剂抗积炭能力明显提高。     

(ZrO2)n(1≤n≤5)团簇的结构及其光谱特征

应用密度泛函理论方法计算了各种可能的(ZrO2)n(1≤n≤5)团簇结构,同时模拟了对应团簇结构的红外光谱.氧化锆团簇中,锆氧原子间最大程度的交互连接是最稳定的结构.团簇的红外光谱表明:600～700 cm-1附近的峰对应着氧化锆团簇的Zr-O-Zr-O四元环振动,800 cm-1附近的峰对应着氧化锆团簇的Zr-O-Zr-O-Zr-O六元环振动,大于900 cm-1的峰对应着氧化锆团簇的自由氧原子的Zr-O振动.实验分析与理论计算结果表明:500 cm-1附近较强的特征振动峰对应着四方氧化锆的特征振动.     

团簇Co4P的自旋布居数及磁学性质研究

以团簇Co4P作为非晶态合金Co-P体系的局域结构,对其进行全参数优化计算,最终得到6种优化构型.通过对团簇Co4P 6种优化构型的Mulliken自旋布居数(包括团簇原子各轨道自旋布居数、团簇轨道自旋布居数及团簇原子自旋布居数)进行分析,对团簇Co4P各优化构型的成单电子进行研究,发现Co原子的d轨道成单电子数最多;...     

微波电场对甘油水溶液体系中氢键的影响

通过分子动力学模拟考察微波电场对不同水含量甘油溶液中氢键的影响。研究发现：甘油含量高时,甘油分子在溶液中以较大的团簇结构存在,水分子以较小的团簇结构或游离状态存在,电场作用下,大的甘油分子团簇变成较小的团簇并且变得更加有序;随着电场强度继续增加,甘油分子整体结构变化不大,但是团簇结构边缘甘油分子氢键断裂,变成游离状态。对于水分子而言,其较小的团簇结构在电场作用下被打开,团簇结构消失,水分子在电场方向上整齐排布,且电场强度继续增大,其结构变化不大,同样个别水分子氢键断裂变成游离状态。因此,甘油浓度高时,水分子间氢键数减少,甘油分子氢键数先增大后略微减少;甘油浓度低时,水分子氢键数先增大后略有减少,甘油分子间氢键减少。     

疏水性钯纳米团簇的合成及其作为表面增强拉曼散射基底的应用

以醋酸钯为前体、有机氢硅烷为还原剂开发了一种简单温和的疏水性钯纳米颗粒制备方法。通过调节前体、保护剂和还原剂的配比,在氯仿溶液中室温条件下合成了疏水性的钯纳米团簇和钯纳米球。运用透射电子显微镜（TEM）、X射线衍射（XRD）、光学接触角测试仪、循环伏安法（CV）、表面增强拉曼光谱（SERS）对这两种钯纳米材料进行了测试表征。TEM观察表明这两种钯纳米材料粒径分布均匀,分散性良好。接触角测试表明钯纳米团簇与钯纳米球均具有疏水性。CV测定结果显示这两种钯纳米材料具有良好的电催化稳定性,钯纳米团簇比钯纳米球对乙醇氧化具有更突出的电催化性能,表明钯纳米团簇结构稳定并具有更大的比表面积。SERS测试表明钯纳米团簇是一种优良的疏水性表面增强拉曼散射基底,利用这种基底对疏水性致癌物3,4-苯并芘和联苯胺进行了SERS快速检测,检测限为0.1mg/mL。     

微波电场对甘油水溶液体系中氢键的影响

通过分子动力学模拟考察微波电场对不同水含量甘油溶液中氢键的影响。研究发现:甘油含量高时,甘油分子在溶液中以较大的团簇结构存在,水分子以较小的团簇结构或游离状态存在,电场作用下,大的甘油分子团簇变成较小的团簇并且变得更加有序;随着电场强度继续增加,甘油分子整体结构变化不大,但是团簇结构边缘甘油分子氢键断裂,变成游离状态。对于水分子而言,其较小的团簇结构在电场作用下被打开,团簇结构消失,水分子在电场方向上整齐排布,且电场强度继续增大,其结构变化不大,同样个别水分子氢键断裂变成游离状态。因此,甘油浓度高时,水分子间氢键数减少,甘油分子氢键数先增大后略微减少;甘油浓度低时,水分子氢键数先增大后略有减少,甘油分子间氢键减少。     

Ag/SiO_2复合颗粒的溶胶-凝胶法制备与表征

采用溶胶-凝胶法(Sol-gel)制备了不同形貌结构的纳米掺银复合颗粒.分析了掺银二氧化硅复合颗粒的形成机理,并采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、红外(FT-IR)及紫外可见(UV-Vis)光谱仪等手段对Ag/SiO_2复合颗粒的形貌结构进行了表征和分析.结果表明:复合颗粒(290 nm)尺寸均匀,近似球状,银颗粒(4 nm)均匀分布在二氧化硅表面,硅烷偶联剂KH-550影响了银粒子在复合颗粒中的分布状态,对Si-O-Si网络结构也有一定的影响,同时有效抑制了复合颗粒的团簇程度.     

CdSe和HgTe团簇基态性质的第一性原理计算

基于密度泛函理论的第一性原理方法,在广义梯度近似下,计算了团簇(CdSe)n和(HgTe)n (原子数n=1～7)的结构和电子性质,以及团簇(CdSe)n和 (HgTe)n的最高占据轨道和最低未占据轨道的能隙、结合能.结果表明:团簇(CdSe)n能隙与结合能均在n=5时出现了极小值,n=4时出现极大值;团簇(HgTe)n只是在n=4时出现了较大能隙,没有出现极小值.能隙随结合能变化而变化.比较了团簇(CdSe)n和(HgTe)n (n=4,5和7)的基态结构,发现同种结构对称性的不同团簇对应着不同的稳定性,这是导致块体材料CdSe形成闪锌矿结构和HgTe形成纤锌矿结构的原因.     

Enhancement of NO-elimination activity of Co-silicate catalyst by high-temperature calcination in steam-containing air

H–Co-silicate having an MFI structure (CoMFI), calcined in steam-containing air at 800°C (CoMFI-800S), was characterized by XRD and diffuse reflectance electron absorption (EA). The calcination educed some of the Co ions from the CoMFI framework to make small clusters nearby. The CoMFI-800S performance in NO elimination in the presence of excess O₂ was compared with that of Co supported on siliceous MFI zeolite ([Co]SiMFI), Co supported on H–Co-silicate ([Co]CoMFI), and a physical mixture of CoMFI and [Co]SiMFI (Co+[Co]). The educed Co ions enhanced NO elimination due to the uniform and isolated dispersion of oxidized Co clusters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural stabilisation of (CoO)x clusters in ZSM5 zeolites

The structure and stability of (CoO) _x clusters in siliceous ZSM5 (silicalite) and on SiO₂ have been investigated using atomistic simulation techniques. The deconvolution of the energy into distortion and interaction contributions revealed that the improved stability of the supported clusters is due to the energy gained from the cluster-host interaction. (CoO) _x clusters in ZSM5 of between 4 and 6 Co atoms showed an enhanced stability, while clusters larger than 18 Co atoms were sterically limited inside the zeolite lattice.     

Advances in the study of nano-structured Co/MCM-41 materials: surface and magnetic characterization

Co-modified mesoporous supports with MCM-41 structure and several metal loadings were successfully synthesized by a fast wet impregnation method. The nature and location of different Co species formed on the solids were inferred by TEM/SEM, XPS, XANES/EXAFS, adsorption of pyridine coupled to FT-IR spectroscopy and temperature dependence of magnetization. The presence of Co oxide species (clusters and Co₃O₄ nanoparticles) inside the channels of all the samples could be evidenced by TEM, XPS and XANES/EXAFS. In this sense, the surface Co/Si atomic ratios obtained by XPS were notably lower than the corresponding bulk Co/Si ratios obtained by ICP, indicating that the Co atoms are mostly incorporated inside the mesopores channels of the silica matrix. Nevertheless, by TEM, Co₃O₄ nanoparticles of small size segregated on the external surface of the silicate were also observed for the higher metal loadings. The temperature dependence of the magnetization performed for the Co/M(2.5) sample allowed to assign its superparamagnetic behavior to the presence of clusters and Co₃O₄ nanoparticles of very small size that grow inside the MCM-41 mesopores. Therefore, the analyses presented in this work indicate that a Co theoretical loading of 2.5 wt% leads to the formation of Co oxide nanospecies in the MCM-41 support with a particular superparamagnetic behavior. This sample with improved structural and magnetic properties result an attractive porous solid for drug hosting, to be applied in the field of the controlled release of medicaments.     

Structures and Stabilities of the Metal Doped Gold Nano-Clusters: M@Au10 (M = W,Mo, Ru,Co)

The structures and stabilities of a series of endohedral gold clusters containing ten gold atoms M@Au₁₀ (M = W, Mo, Ru, Co) have been determined using density functional theory. The gradient-corrected functional BP86, the Tao-Perdew-Staroverov-Scuseria TPSS meta-GGA functional, and the hybrid density functionals B3LYP and PBE1PBE were employed to calculate the structures, binding energies, adiabatic ionization potentials, and adiabatic electron affinities for these clusters. The LanL2DZ effective core potentials and the corresponding valence basis sets were employed. The M@Au₁₀ (M = W, Mo, Ru, Co) clusters have higher binding energies than an empty Au₁₀ cluster. In addition, the large HOMO–LUMO gaps suggest that the M@Au₁₀ (M = W, Mo, Ru, Co) clusters are all likely to be stable chemically. The ionization potentials and electron affinities for these clusters are very high, and the W@Au₁₀ and Mo@Au₁₀ clusters have electron affinities similar to the super-halogen Al₁₃.     

Hydrodesulfurization activity of highly dispersed Co sulfide clusters prepared in zeolite cages

Zeolite-supported highly dispersed Co sulfide clusters are synthesized using Co(CO)₃ (NO) as a precursor. The amount of Co inCoS_x/zeolite anchored by a CVD technique increases as the Al/Si ratio of the zeolite increases, whereas the activity per Co atomdecreases for thiophene hydrodesulfurization (HDS). When an Na-exchanged USY zeolite is used, the Co sulfide catalyst shows a muchhigher HDS activity than a conventional Co—Mo/Al₂ O₃ catalyst. It is considered from XAFS and NO adsorption techniques that thehigh HDS activity of CoS_x/USY-Na is due to an extremely high dispersion of Co sulfide clusters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Controlling the size and the stability of magnetic clusters formed in polyacrylamide hydrogels via cobalt‐anionic fluoroprobe interactions

Polyacrylamide (PAAm)‐Cobalt(II)acetate (Co) composite materials were synthesized with and without pyranine (8‐hydroxypyrene‐1, 3,6‐trisulfonic acid, trisodium salt; POH) anionic fluoroprobe having a reactive group, OH, and three ionic groups, SO, as peripheral. Magnetization and fluorescence measurements showed that addition of POH molecules into the pregel solution results in stable clusters between Co⁺² ions and POH molecules via ionic interactions. The cluster formation, which decreases magnetization of the composites considerably, can occur only during the polymerization. When the POH molecules are diffused into the PAAm‐Co gel after the preparation, no change in the magnetization is observed. But, they behave like flocculants and decrease the average size of the Co‐clusters by dispersing them via attractive electrostatic interactions. Change in the fluorescence spectra of POH molecules gives direct information about the cluster formation and the stability of the clusters. SEM images showed that the size of the clusters formed in composites depends roughly on Co‐POH composition. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Structure of Co and Co oxide clusters in MCM-41

The structural properties of Co/MCM-41 with pore diameters between 2.9 and 3.6 nm prepared by direct synthesis and impregnation were investigated. For both preparation methods, the size of the metal particles decreased with the pore diameter. For Co/MCM-41 with the same pore diameter we observed that the direct synthesis method led to significantly smaller metal clusters compared to the impregnation method. For all Co/MCM-41 samples constraints of the metal cluster sizes were observed, which are speculated to result from influences of the micro structure during the formation of the catalyst precursor.     

Scanning tunneling microscopy investigations of cluster sizes of molybdenum-based catalysts on graphite

Surface morphologies of molybdenum-based catalysts supported on graphite were investigated with a scanning tunneling microscope. The oxide phases of Mo, Co, and Mo-Co were observed to form distinct types of clusters on graphite. MoOx clusters appeared to be elliptical, with sizes ranging from 100 to 200 Å in length and 60 Å in width, while CoOx formed round and needle-shaped clusters, about 200 Å in size. Oxidized Co-Mo was observed to form ringtype structures which were uniformly 100 Å in diameter. This ring-type structure was attributed to the CoMoOx structure with Co decorating the edges of Mo. Sulfided phases of these catalysts were observed to form large slabs on graphite. Sulfided MoOx formed large islands (100 Å × 150 Å). These may be formed from the aggregation of small MoS₂ crystallites. Besides forming large patches, CoS also formed needle-type clusters similar to CoOx, but smaller (120 Å) in length. These clusters and patches are believed to be bulk Co₉S₈. Sulfided CoMoOx formed CoMoS islands similar to the needle-type clusters observed in CoS, but much larger in size, from 300 to 600 Å. No MoS₂ and CoS types of clusters were observed on this sample. No apparent movement of the clusters was observed during repeated scanning, suggesting that there is an interaction between the cluster and the graphite support.     

Structure of Pt–Co/Al2O3 and Pt–Co/NaY Bimetallic Catalysts: Characterization by In Situ EXAFS,TPR, XPS and by Activity in Co (Carbon Monoxide) Hydrogenation

Temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and in situ extended X-ray absorption fine structure (EXAFS) studies were performed to investigate Pt-Co/NaY and Pt-Co/Al₂O₃ bimetallic catalysts. The EXAFS experiments were carried out at the Pt L_III and Co K edges of the same sample. This particular approach allows a precise determination of the electronic and structural characteristics of the metallic part of the catalyst. For both systems in situ reduction under pure H₂ results in the formation of nanometer-scale metallic clusters. For both Co and Pt, nearest neighbors are Co atoms. The complete set of parameters implies the presence of two families of nanometer-scale metallic clusters: monometallic Co nanosized particles and Pt-Co bimetallic clusters, in which only Pt-Co bonds exist (no Pt-Pt bonds). TPR and XPS results indicating a reduction of Co²⁺ ions in Pt-Co/NaY to a greater extent than in Pt-Co/Al₂O₃ give evidence of a facilitated reduction. XRD also shows the presence of nanometer-scale particles with only a very small fraction of larger bimetallic particles. In subsequent mild oxidation of the reduced systems the Co nanoparticles are still present inside the supercage of NaY zeolite in bimetallic form and the oxidation of the metallic particles is slowed down. Catalytic behavior is in good agreement with the structure of the Pt-Co bimetallic system.     

Fischer–Tropsch synthesis: effect of water on Co/Al2O3 catalysts and XAFS characterization of reoxidation phenomena

Both low loaded 15% Co/Al₂O₃ and more highly loaded 25% Co/Al₂O₃ catalysts are studied, in order to explore the impact of cluster size on the stability of the cobalt cluster to support-influenced reoxidation processes at high H₂O/CO ratios. XAFS and activity data suggest that there are two regions for the water effect: at lower H₂O/CO ratios water influences CO conversion by reversible kinetic effects while at higher H₂O/CO ratios cobalt re-oxidation processes occur. The latter regime where water was added at and above 25% are examined. Synthesis conditions were maintained constant while argon balancing gas was replaced by added water. Catalyst samples were withdrawn from the reactor during synthesis at different partial pressures of added water and cooled in the wax product under inert gas. The EXAFS results suggest that, unlike the smaller clusters on unpromoted and, especially noble-metal promoted, 15% Co/Al₂O₃ catalysts, the larger crystallites (>10 nm by chemisorption and XRD) on 25% Co/Al₂O₃ undergo oxidation by H₂O to CoO, most likely confined to the surface. The clusters are re-reduced when H₂O was switched off, and the activity displayed an important recovery.