Flexible microporous coordination polymers

In a decade, many porous coordination polymers have been synthesized, providing a variety of properties ranging from storage, separation and exchange of guests in their cavities, magnetism, conductivity and catalysis by their frameworks. Recent advent of flexible porous coordination polymers, which exhibit elastic guest accommodation in contrast to rigid three-dimensional (3-D) frameworks of conventional porous materials, have acquired a position as a new class of porous materials. Such flexible porous properties induce highly selective guest accommodation and magnetic modulation, which could now be a unique class of practical materials. In this review, we introduce recent flexible porous coordination polymers (3-17) and their functional properties, categorizing with the four types of pores with framework deformation.     

Determination of microporous adsorbents heterogeneity with the condensation approximation method

Using the condensation approximation method the distribution function of adsorption energy for microporous adsorbents has been defined. Due to application of proper equations for the isotherm of global adsorption, the considerations include differencies in the shape of the distribution function of the structural heterogeneity for the microporous adsorbents studied.

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Die Bestimmung der Heterogenität mikroporöser Adsorbentien mit der Kondensationsnäherung

Zusammenfassung Mit Hilfe der Methode der Kondensationsnäherung wurde die Verteilungsfunktion der Adsorptionsenergie für mikroporöse Adsorbentien bestimmt. Die Anwendung entsprechender Gleichungen für die Globalisotherme gestattet die Berücksichtigung von Differenzen in der Gestalt der Verteilungsfunktionen der Strukturheterogenität.

     

Distribution functions of structural heterogeneity of microporous adsorbents

The distribution functions of structural heterogeneity of microporous adsorbents have given. Influences of adsorbents and adsorbates types on this heterogeneity have been studied.

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Verteilungsfunktionen für die Struktur-Heterogenität von mikroporösen Adsorbentien

Zusammenfassung Es werden Verteilungsfunktionen für die strukturelle Heterogenität von mikroporösen Adsorbentien angegeben. Die Einflüsse der Adsorbens- und Adsorbatarten auf diese Heterogenität wurden untersucht.

     

Adsorption of volatile organic compounds in porous metal–organic frameworks functionalized by polyoxometalates

The functionalization of porous metal–organic frameworks (Cu₃(BTC)₂) was achieved by incorporating Keggin-type polyoxometalates (POMs), and further optimized via alkali metal ion-exchange. In addition to thermal gravimetric analysis, IR, single-crystal X-ray diffraction, and powder X-ray diffraction, the adsorption properties were characterized by N₂ and volatile organic compounds (VOCs) adsorption measurements, including short-chain alcohols (C<4), cyclohexane, benzene, and toluene. The adsorption enthalpies estimated by the modified Clausius–Clapeyron equation provided insight into the impact of POMs and alkali metal cations on the adsorption of VOCs. The introduction of POMs not only improved the stability, but also brought the increase of adsorption capacity by strengthening the interaction with gas molecules. Furthermore, the exchanged alkali metal cations acted as active sites to interact with adsorbates and enhanced the adsorption of VOCs.     

Exploitation of a microporous organic polymer as a stationary phase for capillary gas chromatography

Microporous organic polymers (MOPs) have emerged as a new class of functional porous materials with unique characteristics and potential uses in diverse areas. However, the field of MOPs for gas chromatographic (GC) separations has not been well explored. Herein, a MOP namely KAPs-1 was dynamic coated onto a capillary column for the first time. The fabricated column exhibited a nonpolar nature and the column efficiency for n-dodecane was up to 7769 plates m⁻¹. The KAPs-1 coated column showed high GC separation performance for a series of volatile organic compounds (VOCs) including the challenging ethylbenzene and xylene isomers, which could not be resolved at baseline on the commercial 5% phenyl polysiloxane stationary phase. Moreover, the relative standard deviations for five replicate determinations of the studied analytes were 0.0–0.6%, 0.9–3.2%, 1.1–5.9%, 0.8–3.7% for retention time, peak area, peak height and peak width, respectively. To investigate the interaction between some analytes and the stationary phase, thermodynamic and kinetic parameters were also evaluated. The results of this study show it is very promising to utilize MOPs as stationary phases for capillary GC.     

In situ fabrication of microporous organic network coated capillary column for high resolution gas chromatographic separation of hydrocarbons

Microporous organic networks (MONs) are a new class of porous materials synthesized via Sonogashira coupling reactions between organic building blocks. Here we report an in situ synthesis approach to fabricate MONs coated capillary column for high resolution GC separation of hydrocarbons. The McReynolds constant evaluation reveals the MONs coated capillary is a non‐polar column. The MONs coated capillary column shows good resolution for GC separation of diverse important industrial hydrocarbons such as linear and branched alkanes, alkylbenzenes, pinene isomers, ethylbenzene and styrene, cyclohexane and benzene. The MONs coated capillary column gave a high column efficiency of 1542 plates per meter for hexane and good precision for replicate separations of the selected hydrocarbons with the RSDs of 0.2–0.3, 1.5–3.1, and 1.9–3.3% for retention time, peak height and peak area, respectively. The MONs coated capillary also offered better resolution than commercial Inert Cap‐1 and Inert Cap‐5 capillary columns for hexane and heptane isomers. These results reveal the potential of MONs as novel stationary phases in GC.     

Fabrication of microporous organic network@silica composite for high-performance liquid chromatographic separation of drugs and proteins

Microporous organic networks (MONs) that exhibit good stability and hydrophobicity are promising candidates for performing HPLC separation of small organic compounds. However, their applications in separating large analytes as well as biomolecules are still limited by the microporous nature of MONs. Herein, we demonstrated the fabrication of a MON-functionalized silica (MON@SiO₂), exhibiting micro and mesopores for the HPLC separations of small drugs as well as large analytes, such as flavones, nonsteroidal anti-inflammatory drugs (NSAIDs), endocrine disrupting chemicals (EDCs), and proteins. MON was successfully modified on SiO₂ microspheres to yield the uniform and mono-dispersed MON@SiO₂. The separation mechanisms and performance of the MON@SiO₂ packed column were evaluated for a wide range of analytes, including neutral, acidic, basic compounds, drugs, and proteins. Compared with commercial C18 and SiO₂–NH₂ packed columns, the proposed MON@SiO₂ column afforded superior performance in the separations of flavones, NSAIDs, EDCs, and proteins. Moreover, the MON@SiO₂ column also offered good repeatability with intraday RSDs (n = 7) of <0.1%, <2.0%, <2.3%, and <0.7% for the retention time, peak height, peak area, and half peak width, respectively, for separating EDCs. This work proved the potential of using MONs in the HPLC separations of drugs and proteins.     

Crosslinked sulfonated polyimide networks as polymer electrolyte membranes in fuel cells

Sulfonated polyimides with tertiary nitrogen in the polymer backbone were synthesized with 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid, 2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, and diaminoacrydine hemisulfate. They were crosslinked with a series of dibromo alkanes to improve the hydrolytic stability. The crosslinked sulfonated polyimide films were characterized for their thermal stability, ion‐exchange capacity (IEC), water uptake, hydrolytic stability, and proton conductivity. All the sulfonated polyimides had good thermal stability and exhibited a three‐step degradation pattern. With an increase in the alkyl chain length of the crosslinker, IEC decreased as 1.23 > 1.16 > 1.06 > 1.01, and the water uptake decreased as 7.29 > 6.70 > 6.55 > 5.63. The order of the proton conductivity of the crosslinked sulfonated polyimides at 90 °C was as follows: polyimide crosslinked with dibromo butane (0.070) > polyimide crosslinked with dibromo hexane (0.055) > polyimide crosslinked with dibromo decane (0.054). The crosslinked polyimides showed higher hydrolytic stability than the uncrosslinked polyimides. Between the crosslinked polyimides, the hydrolytic stability decreased with an increase in the alkyl chain length of the crosslinker. The crosslinked and uncrosslinked sulfonated polyimides exhibited almost the same proton conductivities. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2370–2379, 2005     

Solid-phase microcolumn extraction and gas chromatography-mass spectrometry identification of volatile organic compounds emitted by paper

A rapid non-destructive sampling technique for the analysis of volatile organic compounds (VOCs) emitted by paper sheets is described. A capillary, which is connected to a microcolumn packed with Tenax TA, is inserted between two sheets at the centre of a paper stack encapsulated inside a PET/Al/PE composite foil. The other end of the microcolumn is connected to a gas-tight syringe and an appropriate volume of gaseous phase is aspirated. The microcolumn is then thermally desorbed in a modified GC inlet (modification is presented) and analysed by gas chromatography-mass spectrometry (GC-MS). In the chromatogram from the analysis of artificially aged paper sample 21 compounds were identified. Advantages of the method including the short sampling time (1 min), simplicity and economic aspect are discussed.     

A simple isotherm equation for describing gas adsorption on heterogeneous microporous solids

A simple isotherm equation for describing gas adsorption on solids showing heterogeneity of microporous structure is proposed. It is shown that this equation gives a good representation of the experimental data of argon, nitrogen and benzene adsorption on different types of activated carbons. Its parameters may be used to characterize heterogeneity of microporous structure of the solids.

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Eine einfache Isotherme zur Beschreibung der Gas-Adsorption an heterogenen mikroporösen Feststoffen

Zusammenfassung Es wird eine einfache Isotherme zur Beschreibung der Gasadsorption an Feststoffen mit heterogener mikroporöser Struktur vorgeschlagen. Es wird gezeigt, daß diese Gleichung die experimentellen Daten für die Adsorption von Argon, Stickstoff und Benzol an verschiedenen Typen von Aktivkohle gut beschreibt. Die Parameter der Isotherme können zur Charakterisierung der Heterogenität der mikroporösen Struktur von Festkörpern herangezogen werden.

     

Fabrication and evaluation of a polymer Li-ion battery with microporous gel electrolyte

This paper introduces an easy method for the fabrication of polymer Li-ion batteries with microporous gel electrolyte (MGE). The MGE is a multiphase electrolyte, which is composed of liquid electrolyte, gel electrolyte, and polymer matrix. The MGE not only has high ionic conductivity and good adhesion to the electrodes at low temperatures, but also retains good mechanical strength at elevated temperatures. Therefore, the MGE batteries are able to operate over a wide temperature range. During battery fabrication, the MGE is formed in situ by introducing liquid electrolyte into a swellable microporous polymer membrane and then heating or cycling the battery. In this work, the chemical compatibility of MGE with metal lithium during 60 °C storage and with LiMn₂O₄ cathode during cycling was studied. In addition, graphite/MGE/LiMn₂O₄ Li-ion batteries were made and evaluated.     

A microfluidic chip based liquid-liquid extraction system with microporous membrane

A robust and simple approach for microfabricated chip based liquid-liquid extraction was developed for on-chip sample pretreatment. The chip based extraction system was composed of two microfabricated glass plates with a microporous membrane sandwiched in between. A simple bonding approach using epoxy was used to achieve bonding and sealing of the L-L extraction chip. Gravity was employed to drive the aqueous and organic flows through separate channels in the extraction system, separated by the membrane. During extraction, the analyte in an aqueous sample stream was transferred through the membrane into the organic stream. The fluorescence intensity of the analyte extracted into the organic stream was monitored in situ by a laser induced fluorescence detection system. The performance of the system was demonstrated using an aqueous solution of butyl rhodamine B (BRB) and isobutanol as sample and extractant, respectively. The system proved to be an efficient means for achieving chip based microporous membrane liquid-liquid extraction. The precision of fluorescence measurements was 1.5% R.S.D. (n = 4). A linear response range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M BRB was obtained with a regression equation: I = 8.00 × 10⁶ C + 4.91. An enrichment factor of ca. 3 was obtained with an extraction efficiency of 69%.     

Prediction of single component adsorption isotherms on microporous adsorbents

The adsorption of gases on microporous solids is a fundamental physical interaction which occurs in many technical processes, e.g. the heterogeneous catalysis or the purification of gases. In this context the adsorption equilibrium can determine the velocity and/or the capacity of the process. Therefore, it has to be known for designing purposes. The aim of this work has been the a priori prediction of the adsorption equilibria of arbitrary gases on microporous solids like zeolites and active carbon based only on the molecular properties of the adsorptive and the adsorbent. The adsorption isotherm is described completely from the Henry region over the transition zone to the saturation region. The quality of the model permits a first approximation of the planned process without further experimental effort.     

Sorption of water and organic solutes in polyimide films and its effects on dielectric properties

The effect of structure on the sorption kinetics of water and of various organic solutes into polyimide (PMDA-ODA) thin films was studied. The major techniques employed include measurements of sorption kinetics, density, and dielectric relaxation. More solute uptake, lower densities and higher diffusivities were observed for films cured at lower temperatures. By measuring both changes of mass and of density, the volume expansion of the polymer due to each solute was obtained; this was found to be proportional to the molar volume of the solute. The two dielectric relaxation peaks (denoted by γ₁ and γ₂) due to water (and other solutes) were studied in detail to obtain the relevant activation energies and the separate dipole moments. While water and methylene chloride appear in both γ₁ and γ₂ configurations, methyl and ethyl alcohol appear mainly as γ₂, while acetic acid is primarily γ₁. It was concluded that the γ₁ configurations are relatively homogeneously distributed throughout the polymer, involving loose bonding to the polymer structure, while the γ₂ configurations involve small clusters, probably chains of molecules. © 1993 John Wiley & Sons, Inc.     

Interactions of volatile organic compounds with syndiotactic polystyrene crystalline nanocavities

The interaction of some volatile organic compounds, namely, 1,2-dichloroethane, 1,2-dibromoethane, and 1,1,2,2-tetrachloroethane, included in the δ crystalline phase of syndiotactic polystyrene (sPS) has been studied in terms of conformation, orientation, and dynamical behavior. By combination of X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and solid-state (2)H NMR analyses, it has been shown that despite the differences in guest molecular properties (mass, boiling temperature, and volume), stable sPS/guest δ-clathrate cocrystals are formed since the nanoporous δ crystalline form has a flexible structure able to adapt itself to the guest molecule. As a consequence of inclusion, it has been shown that the guest diffusivity is strongly reduced and the dynamical processes are constrained, particularly when these guests are in trans conformation. This suggests the nanoporous sPS δ form to be an efficient tool for water and air purification through volatile organic compound absorption.     

Mesoporous TiO2 microspheres with improved efficiency for photooxidation of volatile organic compounds

Research on Chemical Intermediates - Mesoporous hierarchical TiO2 microspheres have been prepared using titanium alkoxide and crown ether as a structure-directing agent in combination with a small...     

Headspace needle-trap analysis of priority volatile organic compounds from aqueous samples: application to the analysis of natural and waste waters

Combining headspace (HS) sampling with a needle-trap device (NTD) to determine priority volatile organic compounds (VOCs) in water samples results in improved sensitivity and efficiency when compared to conventional static HS sampling. A 22 gauge stainless steel, 51-mm needle packed with Tenax TA and Carboxen 1000 particles is used as the NTD. Three different HS-NTD sampling methodologies are evaluated and all give limits of detection for the target VOCs in the ng L⁻¹ range. Active (purge-and-trap) HS-NTD sampling is found to give the best sensitivity but requires exhaustive control of the sampling conditions. The use of the NTD to collect the headspace gas sample results in a combined adsorption/desorption mechanism. The testing of different temperatures for the HS thermostating reveals a greater desorption effect when the sample is allowed to diffuse, whether passively or actively, through the sorbent particles. The limits of detection obtained in the simplest sampling methodology, static HS-NTD (5 mL aqueous sample in 20 mL HS vials, thermostating at 50 °C for 30 min with agitation), are sufficiently low as to permit its application to the analysis of 18 priority VOCs in natural and waste waters. In all cases compounds were detected below regulated levels.     

Single-walled carbon nanohorns immobilized on a microporous hollow polypropylene fiber as a sorbent for the extraction of volatile organic compounds from water samples

We have evaluated the behavior of single-walled carbon nanohorns as a sorbent for headspace and direct immersion (micro)solid phase extraction using volatile organic compounds (VOCs) as model analytes. The conical carbon nanohorns were first oxidized in order to increase their solubility in water and organic solvents. A microporous hollow polypropylene fiber served as a mechanical support that provides a high surface area for nanoparticle retention. The extraction unit was directly placed in the liquid sample or the headspace of an aqueous standard or a water sample to extract and preconcentrate the VOCs. The variables affecting extraction have been optimized. The VOCs were then identified and quantified by GC/MS. We conclude that direct immersion of the fiber is the most adequate method for the extraction of VOCs from both liquid samples and headspace. Detection limits range from 3.5 to 4.3 ng L^?1 (excepted for toluene with 25 ng L^?1), and the precision (expressed as relative standard deviation) is between 3.9 and 9.6 %. The method was applied to the determination of toluene, ethylbenzene, various xylene isomers and styrene in bottled, river and tap waters, and the respective average recoveries of spiked samples are 95.6, 98.2 and 86.0 %.

Sampling and determination of volatile organic compounds with needle trap devices

In this study, a sorbent was immobilized inside a needle resulting in the development of a needle trap (NT) device. This device was applied to extract organic components from gaseous samples and to introduce an enriched mixture into a conventional gas chromatography (GC) injector. Construction of this simple and integrated sampling/extraction/sample introduction device was optimized by considering different ways to immobilize a sorbent in the needle, packing single and multiple-layer sorbent beds, and applying different desorption strategies into the GC injector. A carrier gas system was modified to minimize the carryover for the needle trap with a sealed tip (NT-1), and a narrow-neckliner was used for the blunt-tip needle trap (NT-2). Breakthrough in the device was investigated by connecting two NT-2 devices in series. The needle trap performed very well as an exhaustive spot sampler, as well as in a time-weighted average (TWA) operation. The linear velocity of the mobile phase has no influence on the sampling rate of the needle trap. Validation results against the standard NIOSH 1501 method using charcoal tubes for indoor air surveys demonstrated good accuracy for the NT approach. The reproducibility of the NT-2 was about 1% for benzene. The detection limits for FID detection and for 25 ml gas sample were 0.23 ng/l, 2.10 ng/l and 1.12 ng/l for benzene, ethylbenzene and o-xylene, respectively.