Etude comparative des hydro- et deuteroaluminates de lithium LiAlH4 et LiAlD4 II - Spectres de diffusion raman des composes solidesComparative study of hydro- and deuteroaluminates of lithium LiaAlH4 and LiAlD4

The Raman spectra of lithium tetrahydroaluminate (LiAlH₄) and tetradeuteroaluminate (LiAlD₄) in their room pressure phases have been investigated at room temperature. Internal vibrational modes as well as lattice modes have been observed. As the cristallographic structure of LiAlH₄-α is not fully determined, a partial vibrational analysis has been performed. Using deuteration as a spectroscopic probe, the separation between librational and translational phonon modes has been established. Raman spectra of the new LiAlD₄-α′ form have been analysed. They have confirmed the irreversible transformation of LiAlD₄-α′ into the well known LiAlD₄- α form, at ca.65°C.     

Recent Progress on Microfine Design of Metal–Organic Frameworks: Structure Regulation and Gas Sorption and Separation

Metal–organic frameworks (MOFs) have emerged as an important and unique class of functional crystalline hybrid porous materials in the past two decades. Due to their modular structures and adjustable pore system, such distinctive materials have exhibited remarkable prospects in key applications pertaining to adsorption such as gas storage, gas and liquid separations, and trace impurity removal. Evidently, gaining a better understanding of the structure–property relationship offers great potential for the enhancement of a given associated MOF property either by structural adjustments via isoreticular chemistry or by the design and construction of new MOF structures via the practice of reticular chemistry. Correspondingly, the application of isoreticular chemistry paves the way for the microfine design and structure regulation of presented MOFs. Explicitly, the microfine tuning is mainly based on known MOF platforms, focusing on the modification and/or functionalization of a precise part of the MOF structure or pore system, thus providing an effective approach to produce richer pore systems with enhanced performances from a limited number of MOF platforms. Here, the latest progress in this field is highlighted by emphasizing the differences and connections between various methods. Finally, the challenges together with prospects are also discussed.     

Design and synthesis of metal-carboxylate frameworks with permanent microporosity

Metal-carboxylate clusters are ideally suited as secondary building units (SBU) for the assembly of extended open frameworks. Examples extracted from the chemistry of the multidentate building block 1,4-benzenedicarboxylate (BDC) show that Zn(BDC) clusters lead to the formation of rigid, stable and truly microporous metal-carboxylate networks. Gas sorption isotherms measured for this class of materials show type (I) gas uptake that is analogous to those observed for zeolites and molecular sieves. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cellular uptake and cytotoxic impact of chemically functionalized and polymer-coated carbon nanotubes

The impact of nanomaterials such as carbon nanotubes on biological matter is a topic of increasing interest and concern and requires a multifaceted approach to be resolved. A modified cytotoxic (lactate dehydrogenase (LDH)) assay is developed in an attempt to offer a valid and reliable methodology for screening carbon nanotube toxicity in vitro. Two of the most widely used types of surface-modified multiwalled carbon nanotubes (MWNTs) are tested: ammonium-functionalized MWNTs (MWNT-NH3+ ) and Pluronic F127 coated MWNTs (MWNT:F127). Chemically functionalized MWNTs show significantly greater cellular uptake into lung epithelial A549 cells compared to the non-covalently Pluronic F127-coated MWNTs. In spite of this, MWNT:F127 exhibit enhanced cytotoxicity according to the modified LDH assay. The validity of the modified LDH assay is further validated by direct comparison with other less reliable or accurate cytotoxicity assays. These findings indicate the reliability of the modified LDH assay as a screening tool to assess carbon nanotube cytotoxicity and illustrate that high levels of carbon nanotube cellular internalization do not necessarily lead to adverse responses.     

Modular chemistry: secondary building units as a basis for the design of highly porous and robust metal-organic carboxylate frameworks

Secondary building units (SBUs) are molecular complexes and cluster entities in which ligand coordination modes and metal coordination environments can be utilized in the transformation of these fragments into extended porous networks using polytopic linkers (1,4-benzenedicarboxylate, 1,3,5,7-adamantanetetracarboxylate, etc.). Consideration of the geometric and chemical attributes of the SBUs and linkers leads to prediction of the framework topology, and in turn to the design and synthesis of a new class of porous materials with robust structures and high porosity.     

Conformation‐Controlled Molecular Sieving Effects for Membrane‐Based Propylene/Propane Separation

Membrane‐based separation is poised to reduce the operation cost of propylene/propane separation; however, identifying a suitable molecular sieve for membrane development is still an ongoing challenge. Here, the successful identification and use of a metal–organic framework (MOF) material as fillers, namely, the Zr‐fum‐ fcu ‐MOF possessing an optimal contracted triangular pore‐aperture driving the efficient diffusive separation of propylene from propane in mixed‐matrix membranes are reported. It is demonstrated that the fabricated hybrid membranes display a high propylene/propane separation performance, far beyond the current trade‐off limit of polymer membranes with excellent properties under industrial conditions. Most importantly, the mechanism behind the exceptional high propylene/propane selectivity is delineated by exploring theoretically the efficiency of sieving of different conformers of propane through the hypothesized triangular rigid pore‐aperture of Zr‐fum‐ fcu ‐MOF.     

Fullerene membrane transport mediated by γ‐cyclodextrin immobilised in poly(vinyl alcohol) films

This paper reports on fullerene C₆₀ and C₇₀ transport across hydrophilic membrane materials consisting of a poly(vinyl alcohol) matrix on which γ‐cyclodextrin moieties were attached as molecular recognition sites. The rate‐limiting step of the membrane transport was demonstrated to be dissociation of the inclusion complex at the stripping interface. Copyright © 2003 Society of Chemical Industry     

Etude spectrometrique infrarouge et raman du tetrahydridoaluminate de sodium NaAlH4 solideRaman and infrared spectroscopy study of sodium tetrahydridoaluminate,NaAlH4

Synthesis of sodium tetrahydridoaluminate has been optimized to allow the formation of a polycrystalline powder with crystallites of about 0.5 mm dia. This material showed very good optical properties for Raman scattering and lattice modes has been obtained by spectral analysis. This work which has been performed from 150 to 300 K shows that spectral parameters do not vary in this temperature range. In contrast, IR spectra show only very broad bands and an accurate analysis was not possible. Vibrational analysis of internal modes and lattice modes agrees very well with the crystalline structure and confirms the ionic character of the crystal.     

Valuing Metal–Organic Frameworks for Postcombustion Carbon Capture: A Benchmark Study for Evaluating Physical Adsorbents

The development of practical solutions for the energy‐efficient capture of carbon dioxide is of prime importance and continues to attract intensive research interest. Conceivably, the implementation of adsorption‐based processes using different cycling modes, e.g., pressure‐swing adsorption or temperature‐swing adsorption, offers great prospects to address this challenge. Practically, the successful deployment of practical adsorption‐based technologies depends on the development of made‐to‐order adsorbents expressing mutually two compulsory requisites: i) high selectivity/affinity for CO₂ and ii) excellent chemical stability in the presence of impurities. This study presents a new comprehensive experimental protocol apposite for assessing the prospects of a given physical adsorbent for carbon capture under flue gas stream conditions. The protocol permits: i) the baseline performance of commercial adsorbents such as zeolite 13X, activated carbon versus liquid amine scrubbing to be ascertained, and ii) a standardized evaluation of the best reported metal–organic framework (MOF) materials for carbon dioxide capture from flue gas to be undertaken. This extensive study corroborates the exceptional CO₂ capture performance of the recently isolated second‐generation fluorinated MOF material, NbOFFIVE ‐1‐Ni, concomitant with an impressive chemical stability and a low energy for regeneration. Essentially, the NbOFFIVE ‐1‐Ni adsorbent presents the best compromise by satisfying all the required metrics for efficient CO₂ scrubbing.     

Nanosheets of Nonlayered Aluminum Metal–Organic Frameworks through a Surfactant‐Assisted Method

During the last decade, the synthesis and application of metal–organic framework (MOF) nanosheets has received growing interest, showing unique performances for different technological applications. Despite the potential of this type of nanolamellar materials, the synthetic routes developed so far are restricted to MOFs possessing layered structures, limiting further development in this field. Here, a bottom‐up surfactant‐assisted synthetic approach is presented for the fabrication of nanosheets of various nonlayered MOFs, broadening the scope of MOF nanosheets application. Surfactant‐assisted preorganization of the metallic precursor prior to MOF synthesis enables the manufacture of nonlayered Al‐containing MOF lamellae. These MOF nanosheets are shown to exhibit a superior performance over other crystal morphologies for both chemical sensing and gas separation. As revealed by electron microscopy and diffraction, this superior performance arises from the shorter diffusion pathway in the MOF nanosheets, whose 1D channels are oriented along the shortest particle dimension.