缓冲体系中高热和水热稳定性的MCM-48介孔分子筛的合成

利用混合阳离子-非离子表面活性剂为模板剂在缓冲体系中成功地合成出具有高热和水热稳定性的MCM-48介孔材料. 通过XRD, N₂吸附-脱附, ²⁹Si MAS NMR和 ³¹P MAS NMR等手段对样品进行了表征. 结果表明, 合成的MCM-48材料具有高的比表面积和高度有序的孔道系统. 样品在空气中于900 ℃下焙烧15 h和在600 ℃ 100%水蒸气下处理8～10 h, 仍能保持良好的立方孔道结构, 显示很高的热稳定性和极好的水热稳定性.     

Structures and stabilization energies of methyl anions with main group substituents from the first five periods

The effects of substituents (X) on the structures and stabilities of CH₂X^? anions for groups comprised of fourth- and fifth-period main group elements (X = K, CaH, GaH₂, GeH₃, AsH₂, SeH, Br, Rb, SrH, InH₂, SnH₃, SbH₂, TeH, and I) have been investigated by ab initio pseudopotential calculations. Full geometry optimizations have been carried out on the CH₂X^? anions and the corresponding neutral parent molecules, CH₃X, at HF/DZP + and MP2/DZP + levels. Results for substituents from the second (X = Li? F) and third (X = Na? Cl) periods provide comparisons of substituent effects of the main group elements of the first four rows of the periodic table on methyl anions. Frequency calculations characterize the nature of stationary points and show pyramidal CH₂X^? anion structures to be the most stable unless π acceptor interactions (e.g., with BH₂, AlH₂, GaH₂, and InH₂ favor planar geometries. The CH₂X^? stabilization energies [at QCISD(T)/DZP + /MP2/DZP + + ZPE level for X = K? I and QCISD(T)/6?31 + G*/MP2/6?31 + G* + ZPE level] for X = Li? Cl) also show strong π-stabilizing effects for the same substituents. With the exception of CH₃ and NH₂, all substituents stabilize methyl anions, although the σ stabilization by OH and F is small. The SiH₃? PH₂? SH? Cl, GeH₃? AsH₂? SeH? Br, and SnH₃? SbH₂? TeH? I sets of substituents give stabilization energies between 19 and 30 kcal/mol. The stability of methyl anions substituted by the halogens and the chalcogens (X = OH, SH, SeH, and TeH) increases down a group in accord with the increasing substituent polarizability, while for π acceptors (BH₂, AlH₂, GaH₂, and InH₂) the stability decreases down a group in line with their π-accepting ability. © 1994 by John Wiley & Sons, Inc.     

含锡介孔分子筛MCM-48的合成、表征及催化性能

自M41S问世以来[1],其在吸附、催化及催化剂载体等领域的应用成为人们研究的热点。但纯硅M41S本身不具有催化活性中心,不能直接应用于催化反应中,将具有催化活性的金属掺杂在分子筛骨架中是赋予M41S系列介孔分子筛催化性能的重要手段。文献[2,3]已报道了一些金属掺杂在MCM-41中     

Facile H2O2 Hydrothermal Synthesis of Bimodal Mesoporous Silica MCM-48 Spheres

The ordered bimodal mesoporous silica MCM-48 spheres were facile synthesized by mild-temperature post-synthesis H₂O₂ hydrothermal treatment of as-synthesized MCM-48. The results showed that H₂O₂ is indispensable for simultaneously removing organic templates and forming ordered bimodal mesoporous silica MCM-48 spheres. The bimodal mesoporous MCM-48 was characterized by X-ray diffraction, transmission electron micrographs, FT-IR, and N₂ adsorption-desorption, and a possible mechanism was proposed for the formation of bimodal mesoporous MCM-48.     

Study by fluorescence of calix[4]arenes bearing heterocycles with anions: highly selective detection of iodide

The present work describes a study of complexation efficiency of calix[4]arenes bearing benzoimidazolyl, benzothiazolyl, and benzoxazolyl heterocycles (5–7) towards several anions. The binding ability of calixarene derivatives 5–7 towards selected anions of different molecular geometries such as: F^?, HSO₄ ^?, I^?, N₃ ^?, NO₃ ^?, NO₂ ^?, SCN^?, ClO₄ ^?, Br^?, CN^?, Cl^?, CH₃COO^? CF₃SO₃ ^? in methanol, has been investigated by fluorescence spectroscopic techniques, all anions were used as tetrabutylammonium salts to avoid possible complexation of cationic species by the derivative calix[4]arenes. Fluorescent chemosensor ability of these three calixarene derivatives was highly selective for iodide in contrast with other anions studied. The best chemosensor found, corresponds to compound 7, with an association constant of 2.01 × 10⁴ mol^?1 L and a detection limits of 0.22 ppm for iodide.     

Electrocatalytic oxidation of nickel amalgam in aqueous solutions of halogen and pseudohalogen ions

The voltammetric oxidation of nickel amalgam from the hanging mercury drop electrode in aqueous solutions of F^?, Cl^?, Br^?, I^?, N₃^?, SCN^?, and ClO₄^? ions have been investigated. Concentrations of these anions were sufficiently low to depress the formation of complexes with nickel(II) in the bulk of the solution.An increase in the rate of anodic oxidation with increase of concentration of anions was observed both without and with correction for the φ₂ potential. This increase is explained as due to a catalytic effect of anions adsorbed on the electrode surface.Using the concept of changes of the activity coefficient of the activated complex it was possible to show that the oxidation of the nickel amalgam in thiocyanates and azides proceeds by the formation of the activated complex with bound SCN^? and N₃^? anions. These complexes form only in the activated state and decompose when products leave the double layer.In chlorides and bromides a similar mechanism is suggested only at larger surface concentration of anions. At lower surface concentration and in iodides the oxidation proceeds by the activated complex with no anions bound to the nickel, only long-range interactions of adsorbed anions with activated complex then exist.The order of these electrode reactions was calculated using the concept of the surface activity.The two-step mechanism of the charge transfer is also discussed.     

Aqueous Solutions of Ionic Liquids: Microscopic Assembly

Aqueous solutions of ionic liquids are of special interest, due to the distinctive properties of ionic liquids, in particular, their amphiphilic character. A better understanding of the structure–property relationships of such systems is hence desirable. One of the crucial molecular‐level interactions that influences the macroscopic behavior is hydrogen bonding. In this work, we conduct molecular dynamics simulations to investigate the effects of ionic liquids on the hydrogen‐bond network of water in dilute aqueous solutions of ionic liquids with various combinations of cations and anions. Calculations are performed for imidazolium‐based cations with alkyl chains of different lengths and for a variety of anions, namely, [Br]^?, [NO₃]^?, [SCN]^?, [BF₄]^?, [PF₆]^?, and [Tf₂N]^?. The structure of water and the water–ionic liquid interactions involved in the formation of a heterogeneous network are analyzed by using radial distribution functions and hydrogen‐bond statistics. To this end, we employ the geometric criterion of the hydrogen‐bond definition and it is shown that the structure of water is sensitive to the amount of ionic liquid and to the anion type. In particular, [SCN]^? and [Tf₂N]^? were found to be the most hydrophilic and hydrophobic anions, respectively. Conversely, the cation chain length did not influence the results.     

新型三脚架苯甲醛苯腙醋酸根选择性比色化学传感器

本文合成了一个新的基于三脚架苯甲醛苯腙的能够选择地检测醋酸根离子的比色化学传感器1。用紫外可见吸收光谱证实了受体1在二甲基亚砜溶液中对醋酸根离子高选择的键合能力超越了其它阴离子。和其他所研究的阴离子相比,其在二甲基亚砜中紫外可见吸收光谱对具有高选择性醋酸根离子的存在显示了应答,当存在（2´10^-5mol·dm^-3）醋酸根离子时其溶液的颜色也由黄色变化到蓝色。当用其他不同的客体阴离子（F^-, Cl^-, Br^-, I^-, H₂PO₄ ^–和 OH^-）处理受体1时,仅出现了很小的紫外可见吸收光谱变化。受体1对醋酸根的结合常数 K_ass为1.69´ 10⁴。     

Novel N,N＇-Diacylhydrazine-Based Colorimetric Receptors for Selective Sensing of Fluoride and Acetate Anions

Three novel and simple N,N＇-diacylhydrazine-based colorimetric receptors have been prepared. The binding properties of the receptors to anions such as F^-, Cl^-, Br^-, AcO^-, HSO4^- and HEPO4^- in acetonitrile solution were examined by UV-Vis spectroscopy methods, which show high sensitivity and selectivity to F^- and AcO^- over other anions. The results indicated that a 1 ： 1 stoichiometry complex was formed between the receptors and the anions, while ^1H NMR titrations confirmed hydrogen binding interaction between the receptors and the anions.     

The Application of Cryptand 22 as a Bifunctional Stationary Phase for Ion Chromatography

Poly (styrene/divinyl benzene) with cryptand 22 as an anchoring group was synthesized and applied as a bifunctional packing material for the separation of both cations and anions. At pH < 2, the resin can be protonated and applied as an anion exchanger for the separation of anions; with water as eluent, inorganic anions such as F^?, Cl^?, Br^?, NO₃^?”, I^? were well separated. After deprotonation at pH> 10, the resin became a cation exchanger and successfully separated alkali metal ions such as Li⁺, K⁺ and Cs⁺ with methanol as eluent. The effects of solvents, flow rate and temperature on the separation of various ions were also investigated.     

Ion‐Specific Aggregation of Hydrophobic Particles

This work shows that colloidal stability and aggregation kinetics of hydrophobic polystyrene (PS) nanospheres are extremely sensitive to the nature of the salt used to coagulate them. Three PS latices and four aggregating electrolytes, which all share the same cation (Na⁺) but have various anions located at different positions in the classical Hofmeister series depending on their kosmotropic or chaotropic character, are used. The present study focuses on analyzing different aggregating parameters, such as critical coagulation concentrations (CCC), cluster size distributions (CSD), initial kinetic constants K₁₁, and fractal dimensions of the aggregates d_f. While aggregation induced by SO₄^2? and Cl^? behaved according to the predictions of the classical Derjaguin–Landau–Verwey–Overbeek theory, important discrepancies are found with NO₃^?, which become dramatic when using SCN^?. These discrepancies among the anions were far more significant when they acted as counterions rather than as co‐ions. While SO₄^2? and Cl^? trigger fast diffusion‐limited aggregation, SCN^? gives rise to a stationary cluster size distribution in a few aggregation times when working with cationic PS particles. Clear differences are found among all analyzed parameters (CCC, CSD, K₁₁, and d_f), and the experimental findings show that particles aggregate in potential wells whose depth is controlled by the chaotropic character of the anion. This paper presents new experimental evidence that may help to understand the microscopic origin of Hofmeister effects, as the observations are consistent with appealing theoretical models developed in the last few years.     

SXI route to mesostructured materials from Fau and Beta zeolite precursors: A comparative study of their assembly behaviors in extremely acidic media

Mesoporous molecular sieves were synthesized from Beta and Fau zeolite precursors through S⁺X⁻I⁺ route under extremely acidic conditions in parallel (designated as M_Beta and M_Fau, respectively). The textural properties of M_Fau were different from its M_Beta counterpart but resembled normal MCM-41 silica from TEOS. Al content in M_Beta was almost equivalent to that in the initial Beta zeolite precursors, whereas only trace Al species was present in M_Fau from elemental analysis results. The hydrothermal stability of M_Beta after post-synthesis ammonia treatment was considerably improved compared with normal MCM-41 aluminosilicates, whereas the M_Fau after the same procedure was as unstable as normal MCM-41 silica. Thus, the assembly behaviors of Beta and Fau zeolite precursors were comparatively studied based on these results. The microstructure of Fau zeolite precursors were degraded by the extremely acidic condition, and Al species was dissolved into the synthesis mixture. However, Beta zeolite precursors survived the chemical attack of extremely acidic media and were incorporated into mesostructured framework as primary building units.     

Effect of the catalyst MCM-41 on the kinetic of the thermal decomposition of poly(ethylene terephthalate)

The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min^?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol^?1, for the pure polymer (PET), to 195 kJ mol^?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process.     

Hydration numbers of ions in aqueous solutions of KOH, KCl, KI, and KIO3 according to refractometric data

Ion hydration in aqueous solutions of KOH, KCl, KI, and KIO₃ was studied by refractometry. The sum of the hydration numbers of the potassium ion and each anion in these compounds and the hydration numbers of OH^?, Cl^?, I^?, and IO ₃ ^? anions were determined by the Lorentz-Lorenz equation at different salt concentrations. The model suggests that the polarizability of the hydrated ion is proportional to the cube of the ion radius and the volume of the hydrated ion equals the sum of the nonhydated ion and hydration shell volumes. The hydration numbers of the anions calculated by the proposed procedure increase with their radii in the sequence: OH^?, Cl^?, I^?, and IO ₃ ^? .     

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part V. Case of a charged adsorbed reactant. Trichloroacetate electroreduction in the presence of Br−, l−, SCN−, N3−, Ti+ and C(NH2)3+

The rate constant k_f for CCl₃COO^? electroreduction at constant applied potential, once corrected for diffuse-layer effects according to Frumkin, still depends on the charge density q_i due to specifically adsorbed supporting ions. Thus, in the presence of the adsorbed anions Br^?, I^?, SCN^? and N₃^?, the logarithm Φ of the rate constant corrected for diffuse-layer effects decreases linearly with |q_i|, albeit slightly. In the presence of the adsorbed cations Tl⁺ and C(NH₂)₃⁺, Φ increases with the positive charge density q_i due to the cation at a rate which is 3 to 8 times greater than the corresponding rate of decrease in the presence of the adsorbed anions. This behaviour has been interpreted on the basis of the theoretical treatment of ref. 22 by considering that the time of adsorption of the electroactive anion CCl₃COO^? is long enough to permit a perturbation in the distribution of the adsorbed supporting ions in the immediate vicinity of the adsorbed reactant.     

Complexation of inorganic anions by β-cyclodextrin studied by polarography and 1H NMR

Abstract

Complexation of o-chloronitrobenzene with β-cyclodextrin has been studied in 0.1 M aqueous solutions containing PF₆ ^?, ClO₄ ^?, C₂O₄ ^2-, SCN^?, SO₄ ^2- and F^? anions by a polarographic method. Using an equation which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the anion, both stability constants have been calculated. Interaction of the ClO₄ ^? anion with β-cyclodextrin has been confirmed by ¹H NMR techniques. It has been found that the ClO₄ ^? anion is trapped in the β-cyclodextrin cavity. The stability constant has been calculated. Results of polarographic and ¹H NMR studies have been compared.     

Strongly decussated π-stacking in a Ag(I)–Co(III) complex containing a Ag2Co2 44 square tile motif

A mixed Co–Ag complex with 2,6-dicarboxypyridine (H₂PDC), AgCo(PDC)₂, was synthesized under hydrothermal conditions. The complex adopts a 2D layer structure formed by intramolecular π-stacking. Each Co(III) ion is chelated by two 2,6-dicarboxypyridine anions to give the [Co(PDC)₂]^? anion that is further extended by Ag⁺ to form 4⁴ square grids.     

Halide anions driven self-assembly of haloperfluoroarenes: Formation of one-dimensional non-covalent copolymers

The supramolecular organization in six solid assemblies involving iodo- and bromoperfluoroarene derivatives is described. Single crystal X-ray analyses show that the formation of the supramolecular architectures is controlled by I⁻?Br–Ar_F, I⁻?I–Ar_F, Br⁻?I–Ar_F, and Cl⁻?I–Ar_F halogen bondings thus proving the X⁻?X′–Ar_F supramolecular synthon, where X can be the same as or different from X′, is particularly robust. In five of the described architectures halide anions form two halogen bondings and form infinite chains wherein dihaloperfluoroarenes, which function as bidentate electron acceptors, and halide anions, which function as bidentate electron donors, alternate. This behaviour shows halide anions have a fair tendency to work as bidentate halogen bonding acceptors.     

Towards a Molecular Understanding of Cation–Anion Interactions—Probing the Electronic Structure of Imidazolium Ionic Liquids by NMR Spectroscopy,X‐ray Photoelectron Spectroscopy and Theoretical Calculations

Ten [C₈C₁Im]⁺ (1‐methyl‐3‐octylimidazolium)‐based ionic liquids with anions Cl^?, Br^?, I^?, [NO₃]^?, [BF₄]^?, [TfO]^?, [PF₆]^?, [Tf₂N]^?, [Pf₂N]^?, and [FAP]^? (TfO=trifluoromethylsulfonate, Tf₂N=bis(trifluoromethylsulfonyl)imide, Pf₂N=bis(pentafluoroethylsulfonyl)imide, FAP=tris(pentafluoroethyl)trifluorophosphate) and two [C₈C₁C₁Im]⁺ (1,2‐dimethyl‐3‐octylimidazolium)‐based ionic liquids with anions Br^? and [Tf₂N]^? were investigated by using X‐ray photoelectron spectroscopy (XPS), NMR spectroscopy and theoretical calculations. While ¹H NMR spectroscopy is found to probe very specifically the strongest hydrogen‐bond interaction between the hydrogen attached to the C² position and the anion, a comparative XPS study provides first direct experimental evidence for cation–anion charge‐transfer phenomena in ionic liquids as a function of the ionic liquid’s anion. These charge‐transfer effects are found to be surprisingly similar for [C₈C₁Im]⁺ and [C₈C₁C₁Im]⁺ salts of the same anion, which in combination with theoretical calculations leads to the conclusion that hydrogen bonding and charge transfer occur independently from each other, but are both more pronounced for small and more strongly coordinating anions, and are greatly reduced in the case of large and weakly coordinating anions.     

Anions as Triggers in Controlled Release Protocols from Mesoporous Silica Nanoparticles Functionalized with Macrocyclic Copper(II) Complexes

Three different mesoporous silica nano‐sized materials ( SC1 , SC2 , and SC3 ), loaded with [Ru(bipy)₃]²⁺ dye (bipy=bipyridine) and functionalized on the external surface with three macrocyclic copper(II) complexes ( C1 , C2 , and C3 ), were synthesized and characterized. When SC1 , SC2 , and SC3 were suspended in water, the entrapped [Ru(bipy)₃]²⁺ dye was free to diffuse from the inner pores to the solution. However, addition of anions induced certain degrees of pore blockage, with subsequent dye release inhibition. Small monovalent and divalent anions were unable to induce complete pore blockage, whereas bulky and highly charged anions induced marked reductions in [Ru(bipy)₃]²⁺ delivery. The best [Ru(bipy)₃]²⁺ delivery inhibitors were ATP and hexametaphosphate anions. Inhibition was ascribed to the interaction of the anions with the grafted Cu^II complexes on the surface of the SC1 , SC2 , and SC3 supports. The hexametaphosphate anion was selected to prepare two capped materials ( SC1‐mPh and SC3‐mPh ). Studies of the [Ru(bipy)₃]²⁺ dye release from solids SC1‐mPh and SC3‐mPh alone and in the presence of a collection of selected anions (HS^?, F^?, Br^?, Cl^?, I^?, CN^?, HPO₄^2?, AcO^?, citrate, NO₃^2?, HCO₃^?, SO₄^2?, and S₂O₈^2?), amino acids (alanine and histidine), thiol‐containing biomolecules (cysteine, methylcysteine, homocysteine, and glutathione (GSH)), and oxidants (H₂O₂) were performed. None of the chemicals tested, except hydrogen sulphide, was able to induce remarkable cargo delivery in both solids. The observed dye release was ascribed to a demetalation reaction of the C1 and C3 complexes induced by the hydrogen sulphide anion.