Sulfated and phosphated mesoporous Nb oxide in the benzylation of anisole and toluene by benzyl alcohol

Materials possessing the high acidities of sulfated zirconia and the diffusion properties of mesoporous oxides are predicted to have numerous applications in the petrochemical industry. Because of surface deactivation and loss of structure under highly acidic conditions, there are few examples of materials which meet these specifications. In this work, mesoporous Nb oxide was treated with 1 M sulfuric acid or phosphoric acid and evaluated for their catalytic activities in the benzylation of toluene or anisole with benzyl alcohol. Characterization by XRD, nitrogen adsorption/desorption, and TEM demonstrated that the mesostructure was surprisingly stable to acid treatment. Pyridine adsorption and infrared spectroscopy (IR) showed a mixture of Lewis and Bronsted sites before and after acid treatment. Titration with a series of indicators demonstrated that sulfated mesoporous Nb oxide possesses a pKa of -8.2 and 31.784 mmol/g acid sites, roughly 100 times stronger than either bulk phosphated or sulfated niobia, which both possess pKa values in the range of -3.0. The best catalytic results in this study were achieved when using mesoporous Nb oxide treated with sulfuric acid; the conversion of benzyl alcohol with anisole to the benzylation product was 100% in 30 min, which is 200 times faster than the bulk catalyst. The extremely high activity was rationalized by the high number of strong Br?nsted sites on the surface coupled with the superior diffusion properties of the mesoporous system.     

Selected-control hydrothermal synthesis and formation mechanism of monazite- and zircon-type LaVO(4) nanocrystals

Selective-controlled structure and shape of LaVO(4) nanocrystals were successfully synthesized by a simple hydrothermal method without the presence of catalysts or templates. It was found that tuning the pH of the growth solution was a crucial step for the control of the structure transformation, that is, from monoclinic (m-) to tetragonal (t-) phase, and morphology evolution of LaVO(4) nanocrystals. Further studies demonstrated that the morphology of the product had a strong dependence on the initial lanthanum sources. In the La(NO(3))(3) or LaCl(3) reaction system, pure t-LaVO(4) nanorods with uniform diameters about 10 nm could be obtained. But when using La(2)(SO(4))(3) as the lanthanum source, we can get t-LaVO(4) nanowiskers with broomlike morphology. The detailed systematic study had shown that a special dissolution-recrystallization transformation mechanism as well as an Ostwald ripening process was responsible for the phase control and anisotropic morphology evolution of the LaVO(4) nanocrystals. As a result, the controlled synthesis of m- and t-LaVO(4) not only has great theoretical significance in studying the polymorph control and selective synthesis of inorganic materials but also benefits the potential applications based on LaVO(4) nanocrystals owing to the unusual luminescent properties induced by structural transformation.     

溶液中离子－偶极子俘获力常数及离子内氛重组能标度

本文基于重组现象改进的自交换模型及离子－偶极子俘获力场势，提出了描述外氛电子转移机理中溶液离子内氛重组织效应的能量指标的一种新的标度方法，并对公式中所含参数利用离子－偶极子俘获力场势进行了确定。结果表明该方法有效地改进了前人的工作，取得了与实验光谱标度数据一致的结论，并与光发射实验结果吻合较好。它避免了因缺乏溶液中可信的振动光谱数据在计算内氛重组能上的困难，通过易得的离子和配体的性质参数给出了一种简便而精确的计算方案。     

Probing the imine silylenoid HN=SiNaF and its insertions reaction with R–H (R=F,OH, NH<Subscript>2</Subscript>, CH<Subscript>3</Subscript>) using DFT

The geometries and isomerization of the imine silylenoid HN=SiNaF as well as its insertion reactions with some R–H molecules have been systematically investigated theoretically, where R=F, OH, NH₂, and CH₃, respectively. The barrier heights for the four insertion reactions are 67.7, 115.6, 153.5, and 271.5 kJ/mol at the B3LYP/6-311+G* level of theory, respectively. Here, all the mechanisms of the four reactions are identical to each other, i.e., a stable intermediate has been formed during the insertion reaction. Then, the intermediate could dissociate into the substituted silylene (HN=SiHR) and NaF with a barrier corresponding to their respective dissociation energies. Correspondingly, the reaction energies for the four reactions are 71.8, 95.5, 123.3, and 207.6 kJ/mol, respectively, which are linearly correlated with the calculated barrier heights. Furthermore, the effects of halogen substitutions (F, Cl, and Br) on the reaction activity have also been discussed. As a result, the relative reactivity among the four insertion reactions should be as follows: H–F > H–OH > H–NH₂ > H–CH₃.     

Preparation and field emission properties of carbon nanotubes cold cathode using melting Ag nano-particles as binder

A new preparation process for carbon nanotubes (CNTs) cold cathode was studied through the replacement of traditional organic or inorganic binder with Ag nano-particles. This method has the advantages of low preparation temperature and fine electrical contact between CNTs paste and substrate. A mixture paste of CNTs, Ag nano-particles and other organic solvents was spreaded on Si substrate. By melting and connecting of Ag nano-particles after sintered 30 min at 250 °C, a flat CNTs films with good field emission properties was obtained. The measurements reveal that the turn on electric field and the threshold electric field of as-prepared CNTs cathode are 2.1 and 3.9 V/μm respectively and the field emission current density is up to 41 mA/cm² at an applied electric field of 4.7 V/μm.     

Femtosecond time-resolved difference absorption spectroscopy of all-<Emphasis Type="Italic">trans</Emphasis>-β-Apo-8′-carotenal

The femtosecond time-resolved difference absorption spectra of all-trans-β-Apo-8′-carotenal have been recorded and analyzed by the singular-value decomposition (SVD) method followed by global fitting using a sequential model for the excited-state energy relaxation. With this model, we have obtained the excited-state absorption spectra and the lifetimes of the corresponding excited states both in nonpolar solvent n-hexane and polar solvent methanol. Three excited states, namely S₃(170fs), S₂(2.32ps) and S₁(26ps) in n-hexane, and two excited states S₂(190fs) and S₁(9.4ps) in methanol have been observed. The excited-state absorption spectra of all-trans-β-Apo-8′-carotenal in methanol display a red shift and broadeness, while the lifetime of S₁ state becomes shorter. It is proposed that these effects are related to the presence of a carbonyl functional group that leads to the solvent effect on the excited-state energy level. At the same time, it is shown that the SVD method is a useful tool in resolving the time-resolved absorption spectra.     

Blow-up for semilinear parabolic equations with nonlinear memory

In this paper, we consider the semilinear parabolic equation with homogeneous Dirichlet boundary conditions, where p, q are nonnegative constants. The blowup criteria and the blowup rate are obtained.     

ClO/ClO~-耦合体系结构性质及反应通道研究

利用从头算法和密度泛函理论对ClO/ClO~-体系进行了研究。首先应用密度泛 函理论的六种方法(B3LYP,BLYP,B3P86,BP86,BHLYP,LSDA)和从头算理论的CCSD方法 在6-3+G~*,6-311+G~*及6-311+G(3df)基组水平上对单体进行了优化,选出最适合 该体系的方法和基组B3LYP/6-311+G(3df);然后在B3LYP/6-311+G(3df)水平上计算 了沿各种反应通道的离解能,并且进行了校正。找出了存在的中间体及中间体异构 化的过渡态,并进行了IRC路径解析。对各稳定体进行了频率分析和成键分析。结 果表明,单体ClO和单体ClO~-结合为稳定的中间体后,其离解方式主要是向着 ClOO+Cl~-和ClOO~-+Cl两种方式进行,两种离解方式的离解能分别为-33.39和82. 88kJ/mol,并且前者是一个离解性电子转移过程,经历一个电子转移过渡态。     

六苄基六氮杂异伍兹烷五种氢解脱苄化合物的合成及工业制备

综述了六苄基六氮杂异伍兹烷(HBIW)五种氢解脱苄化合物的合成条件和工业制备工艺。这五种化合物是:四乙酰基二苄基六氮杂异伍兹烷(TADBIW)、四乙酰基二甲酰基六氮杂异伍兹烷(TADFIW)、四乙酰基六氮杂异伍兹烷(TAIW)、四乙酰基二乙基六氮杂异伍兹烷(TADEIW)和六乙酰基六氮杂异伍兹烷(HAIW)。其中的TADBIW系由HBIW经一次氢解合成,其它四种都系由HBIW经两次氢解合成。HBIW的这五种氢解脱苄化合物均可经硝解合成六硝基六氮杂异伍兹烷(HNIW)。另外,本文总结了HBIW及其五种氢解脱苄产物的红外、核磁和质谱数据及它们的基本性能参数。     

Characterization of self-assembled decyl bis phosphonate-Collagen layers on titanium by QCM-D and osteoblast-compatibility

Quartz crystal microbalance dissipation (QCM-D) was used to monitor the layer by layer (LBL) self-assemble process of decyl bis phosphonate (DBP) and Collagen on titanium. The mass and viscoelastic properties of self-assembled layers were obtained using QCM-D. The stability of DBP and Collagen layer on titanium was tested to be very good. Osteoblasts cell culture was performed on LBL modified samples and that after BSA adsorption. The morphology of cells was observed by a scanning electron microscope (SEM). The total metabolic activity and differentiation of osteoblasts were evaluated by a metabolic assay and alkaline phosphatase (ALP) activity, respectively. These tests showed that osteoblasts have better activity, proliferation, and differentiation on Collagen terminated samples and BSA adsorbed samples.These results, along with the good biomineralization and protein adsorption abilities of Ti/DBP/Collagen surface (tested in our previous work), suggest titanium modified by this layer by layer technique has the potential application for medical implants.