Dielectric properties and Fourier transform IR analysis of MCM-48, Al-MCM-48 and Ti-MCM-48 mesoporous materials

 Broad-band dielectric spectroscopy was used to investigate the dielectric properties of the meso- porous materials MCM-48, Al-MCM-48 and Ti-MCM-48. The samples were examined in the frequency range from 20 Hz to 1 MHz and in the temperature range from −100 to 250 °C. The dielectric relaxation of the materials has a complex nonexponential behavior with some common features for all the samples. The dielectric spectroscopy and Fourier transform IR measurements identified the relaxation process related to percolation of H⁺ ions associated with silanol groups and water adsorbed in the materials. The non-Debye behavior of the macroscopic dipole correlation functions related to the percolation process allowed us to extract the fractal dimensions of the paths of excitation transfer within the porous medium, and the porosity of each sample was estimated. Received: 7 September 1999 Accepted: 10 December 1999     

Synthesis and properties of novel liquid crystalline materials with super high birefringence: styrene monomers bearing diacetylenes, naphthyl, and nitrogen-containing groups

Three new liquid crystal asymmetrical styrene monomers bearing diacetylenes, naphthyl, and nitrogen-containing groups were successfully synthesized from 2-(bromoethynyl)-6-(hexyloxy)naphthalene, 4-(4-bromo-2-vinylphenyl)-2-methylbut-3-yn-2-ol, and derivatives of 4-ethynylaniline. The molecular structures of these compounds were confirmed by FTIR, ¹H NMR spectroscopy, elemental analysis, and mass spectrometry. The liquid crystalline properties of monomers were characterized by differential scanning calorimetry and polarized light microscopy. Results indicated that all the compounds exhibited the nematic phase in liquid crystal state and super high optical birefringence of 0.5-0.8. The change of terminal nitrogen-containing group affected the birefringence values in the order of -N(CH₃)₂<-NH₂<-NCS. Moreover, measurements using UV-vis and fluorescence spectroscopy showed their good photoluminescence properties and high quantum efficiency of 0.4-1.0.     

One‐pot synthesis of polymer/inorganic hybrids: toward readily accessible,low‐loss,and highly tunable refractive index materials and patterns

The realization that modulated light pulses can be transported in a confined fashion over long distances within a structure that comprises a controlled spatial distribution of the refractive index n—as in optical fibres and waveguides—has, without doubt, underpinned the telecommunications revolution witnessed during the 20th century. The refractive index n, quantifying how light propagates in a given medium, as a consequence, has become one of the most important materials properties in designing photonics products. The other key characteristic for most optical and photonic applications is the amount of light that is absorbed by a material, expressed as the extinction coefficient κ. Although a range of organic/inorganic hybrid materials have been advanced with tunable refractive index, only a few systems combine a high n, sufficiently low κ and straightforward sample preparation to allow simple fabrication of highly transparent, low‐loss structures. Here, we present a hybrid material that can be readily produced in water via a one‐pot synthesis directly from commercially available, low‐cost precursors. Moreover, our hybrid material can be solution‐processed, yielding systems of an extinction coefficient <0.01, and a refractive index, which can be controlled to adopt values between 1.5 to at least 2.1. Unprecedentedly, simple post‐deposition procedures such as thermal annealing or irradiation with high‐intensity UV‐light allow adjusting n also after film fabrication, offering an exceptional degree of freedom in designing and tailoring also more complex photonic architectures or planar wave‐guides, for example, through creation of in‐plane refractive index patterns. As a proof‐of‐concept, we demonstrate fabrication of waveguides based on local heating. The versatility of our materials is further illustrated by the production of lenses and dielectric filters of ～100% reflectivity in a given wavelength regime. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 000: 000–000, 2011     

Epoxidation of unsaturated FAMEs obtained from vegetable source over Ti(IV)-grafted silica catalysts: A comparison between ordered and non-ordered mesoporous materials

The liquid-phase epoxidation of mixtures of fatty acid methyl esters (FAMEs) over titanium-containing silica materials, using tert-butylhydroperoxide (TBHP) as oxidant, is here reported. The mixtures were obtained from vegetable renewable source, i.e. from high-oleic sunflower oil, coriander oil, castor oil and soya-bean oil. The influence of the nature and the position of functional groups on the C-18 chain of the FAMEs was studied. Very high activity and selectivity were obtained in the epoxidation of castor and soya-bean oil methyl esters in a reaction medium free from organic acids. Ti–MCM-41 (an ordered mesoporous titanium-grafted silica) displayed in this case, for the first time, superior performances, from a synthetic point of view, with respect to non-ordered mesoporous titanosilicates.     

Study on the controllable synthesis of SH-MCM-41 mesoporous materials and their adsorption properties of the La3+, Gd3+ and Yb3+

SH-MCM-41 was examined in adsorption and desorption experiments to investigate the adsorption capacities of La³⁺, Gd³⁺ and Yb³⁺ and the reusability.     

A review of self-organising 2,5- and 2,4-disubstituted 1,3-thiazole-containing materials: synthesis,mechanisms and tactics

ABSTRACT

2,5- and 2,4-disubstituted 1,3-thiazoles have been incorporated as core units in thermotropic liquid crystalline materials. However, synthetic approaches to these systems have been somewhat limited, and this is reflected in the relatively few reports of these mesogenic systems. This paper highlights both recent and well-established synthetic approaches to these systems using ring closure (Gabriel- and Hantzsch-type approaches) methodology and modifications of an intact 1,3-thiazole ring. The scope and limitations of each of these approaches are discussed.     

Mesoporous silicas by self-assembly of lipid molecules: ribbon, hollow sphere, and chiral materials

Using lipids (N-acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0 degrees C to 10, 15, or 20 degrees C. The structures were studied by electron microscopy. It was found that 1) the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2) these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid-solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3) the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L-form N-acyl amino acid was used as the lipid template; 4) the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries.     

Improving surface‐analysis methods for characterization of advanced materials by development of standards,reference data,and interlaboratory comparisons

This paper summarizes the results of two surveys examining current needs for improved analyses of surfaces. Surfaces and interfaces are increasingly important to science and technologies associated with nanoparticles, nano‐structured materials and other complex materials including those associated with information systems and medical or biological applications. Adequate characterization of advanced materials frequently requires application of more than one analysis method along with the need to analyze data in increasingly sophisticated and sometimes interrelated ways. It is useful for both new and experienced analysts to have ready access to best practices for obtaining accurate and useful information from a variety of different analysis tools. The International Organization for Standardization (ISO) Committee TC 201 on surface chemical analysis and the ASTM Committee E‐42 on surface analysis are working to address these needs by assembling guides and standards reflecting the collective experience and wisdom of experts in this community. Published in 2007 by John Wiley & Sons, Ltd     

Preparation and properties of luminous materials of CaSiO3: Pb, Mn by sol-gel method

The luminous materials of CaSiO₃: Pb, Mn were synthesized by sol-gel method and ultrasound technology. The properties of the phosphors were characterized by luminescence spectrum, differential thermal analysis and thermal gravimetry analysis (DTA-TG), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and transmission electron microscopy (TEM). The effects of factors such as the synthetic material compositions, ultrasound time and annealed temperature on phosphorescent brightness of sample were studied and the optimum synthetic conditions were determined. The results show that, compared with the sample made by the high temperature solid-state reaction, the luminescent intensity of the CaSiO₃: Pb, Mn sample increased by about 200% and the mean diameter of particles of the sample decreased by about 300 nm. __________ Translated from Chemical Research and Application, 2007, 19(2): 140–144 [译自: 化学研究与应用]     

Supersonic molecular beam growth of thin films of organic materials: A novel approach to controlling the structure,morphology, and functional properties

Thin films of semiconducting molecular materials can be grown with a seeded supersonic molecular beam epitaxy (SuMBE), which provides unprecedented control over structural, morphological, and, therefore, functional properties. This novel technique of deposition takes full advantage of its ability to regulate the initial state of the molecular precursors in the beams and, in particular, the kinetic energy, to control the morphology, structure, and functional properties of growing films. This article reviews the state of the art of SuMBE, discussing the basic aspects of the technique and the major achievements so far. The major results obtained with respect to growth on dielectrics and metal substrates of films of oligothiophenes and pentacene and with respect to the codeposition of phthalocyanines and fullerenes are discussed and compared with the state of the art of more conventional organic molecular beam deposition. The potential impact of SuMBE in the field of π‐conjugated materials and devices is also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2501–2521, 2003     

Using polyethyleneimine (PEI) as a scaffold to construct mimicking systems of [FeFe]‐hydrogenase: preparation,characterization of PEI‐based materials,and their catalysis on proton reduction

Ten branched polymeric materials (PEI‐P‐Fe₂s) derived from polyethyleneimine (PEI) functionalized with [Fe₂(CO)₅]‐units to mimic [FeFe]‐hydrogenase were prepared. Before the functionalization, PEI was first premodified using diphenylphosphinamine (NPPh₂) group. In the premodification, three approaches were employed: (i) using PEI with an average molecular weight of 1800 and 600, respectively; (ii) grafting NPPh₂ group by either direct reaction of chlorodiphenylphosphine with PEI or Br(CH₂)₁₁OPPh₂; and (iii) further premodification with BrCH₂COOH after immobilization of the NPPh₂ group. Reaction of the premodified PEI with diiron hexacarbonyl complexes, [Fe₂(μ‐S)₂(CO)₆] (1), or [Fe₂(μ‐S₂C₂H₄)(CO)₆] (3) produced 10 functionalized materials, PEI‐P‐Fe₂s. These materials were characterized using a variety of spectroscopic techniques, FTIR, NMR, TGA, and cyclic voltammetry. Spectral comparison with two control complexes, [Fe₂(μ‐S)₂(CO)₅PPh₃] (2) and [Fe₂(μ‐S₂C₂H₄)(CO)₅PPh₃] (4), suggested that the immobilized diiron units of PEI‐P‐Fe₂s were dominantly pentacarbonyl analogous to complexes 2 and 4, although tetracarbonyl units may also exist because the amine groups of PEI could also be involved in substituting CO, as was the NPPh₂ group. The catalysis of these materials on proton reduction was examined in 0.1 mol l^?1 [NBut₄]BF₄/DMF containing acetic acid by using cyclic voltammetry. Our results indicated that both the presence of carboxylic acid and dangling the diiron units at the end of a long aliphatic chain improved catalytic efficiency by one‐fold. The improvement was attributed to the increase in flexibility of the catalytic center and enhancement of proton transfer during the catalysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Enantiomeric Enrichments via the Self‐Disproportionation of Enantiomers (SDE) by Achiral,Gravity‐Driven Column Chromatography: a Case Study Using N‐(1‐Phenylethyl)acetamide for Optimizing the Enantiomerically Pure Yield and Magnitude of the SDE

This work explores the self‐disproportionation of enantiomers (SDE) via achiral, gravity‐driven column chromatography as typically used in laboratory settings for the purpose of enantiomeric enrichment using N‐(1‐phenylethyl)acetamide (PEA) as a case study. The major finding of this work is the very large magnitude of the SDE for PEA across a variety of conditions and broad range of starting ee values, thereby facilitating a simple, reliable, and predictable means of obtaining enantiomerically pure samples. For example, starting with a sample of PEA of ee as low as 28%, a single column run yielded an enantiomerically pure sample (>99.9% ee) from the first fractions and a significantly enantiomerically depleted sample (<17% ee) from the final fractions. An assessment of SDE via achiral, gravity‐driven column chromatography was also rendered with regard to the differing objectives that workers might target – a large magnitude of the SDE, obtaining an optimum sample of desired ee, or preparative‐scale separation of the excess enantiomer. Overall, it can be considered that the SDE phenomenon via achiral, gravity‐driven column chromatography – readily applicable in the usual laboratory settings – is a simple and convenient method for enantiomeric enrichment with a high degree of proficiency. Advantages of SDE via achiral, gravity‐driven column chromatography over conventional fractional recrystallization for the enantiomeric enrichment of amides/amines, and applicable also to many other classes of compounds as well, are discussed.