Gas sorption analysis

S. Surble, F. Millange, C. Serre, T. Duren, M. Latroche, S. Bourrelly, P. L. Llewellyn, and G. Ferey, Synthesis of MIL-102, a chromium carboxylate metal-organic framework, with gas sorption analysis, J. Am. Chem. Soc., 128, 14889-14896(2006). 

The pore network connectivity is usually determined by gas sorption analysis [2-4] or mercury intrusion [5] based on percolation theory. Recently, Ismadji and Bhatia [6] have successfully employed the liquid phase adsorption isotherms to determine the pore network connectivity and the pore size distribution of three commercial activated carbons. In our recent study [7], the pore network connectivity of three commercial activated carbons was characterized using liquid phase adsorption isotherms of eight different compounds. In that study we used ester molecules with complex structure, as probe molecules. 

For the purposes of this review, we restrict the definition of PIMs to organic polymers which have interconnected pore structures and which exhibit appreciable apparent inner surface areas by gas sorption analysis. PIMs can be linear polymers (Sect. 2.2.1) or networks (Sect. 2.2.2). While other network polymers may be microporous (e.g. Sect. 2.1 and 2.4), it is this porosity of the linear analogues that distinguishes PIMs. Again, the area of PIMs has been reviewed quite recently [41,42] so relatively brief details are given here. 

Gas sorption analysis probes the interaction between a gas or vapor (adsorptive) and the adsorbent this interaction can occur upon adsorption in micropores, mono- and multilayer adsorption at the inner surface of the specimen or via liquid/solid interaction when the adsorptive is condensing in the pores of the adsorbent. The probe most commonly used to characterize aerogels is N2 sorption at 77.3 K. When varying the gas pressure from vacuum to 0.1 MPa (1 bar) rel. gas pressures from almost 0 to 1 can be covered hereby typically information on specific surface areas down to 0.01 m /g and pore widths in the range from 0.3 to 100 nm can be derived. 

Comment. Gas sorption analysis is a well-established tool for the characterization of open porous solids. For aerogels the method provides reliable information on the surface area. However, care has to be taken in case of microporous aerogels here a well-equilibrated isotherm in combinatiOTi with the right choice of the evaluation range will still yield reliable values for the microporosity and the specific surface area. For detailed analysis of microporosity measurements with CO2 at 273 K are recommended. 

According to Verweij et al. [14], the transport through the membiane pore depends on the pore radius and the interaction of the permeant and the membrane material. According to the lUPAC terminology and the gas sorption analysis the pores are classified as follows. Micorpore (p <2 nm mesopore l<(p <50 nm and macropore ) >50 nm. Verweij et al. also classified the membrane pore transport, depending on the pore size, as shown in Table 8.11. 

Through PXRD and TGA measurements, it was determined that 28 was stable to loss of 80% of the included DMF molecules, which inferred porosity. CO2 and N2 gas sorption analysis gave BET surface areas of 216 m /g and 209 m /g, respectively. Upon complete loss of DMF, a loss of order was observed by PXRD, but order was regained upon resolvation. The addition of two hydroxyl groups ortho to the phosphonate groups provided sufficient steric effects to disrupt the formation of the layered motif and form an open structure in 28. Stability in this structure is sustained by the ID chains of phosphonate-bridged tetrahedral Zn ions, with no solvent molecules coordinating Zn. Stability is evidenced by the permanent porosity of 28. 

Classical characterization methods (gas sorption, TEM, SEM, FTIR, XPS and elemental analysis) were used to describe the resulting porous carbon structures. Temperature-dependent experiments have shown that all the various materials kept the nitrogen content almost unchanged up to 950 °C, while the thermal and oxidation stability was found to be significantly increased with N-doping as compared to all pure carbons. Last but not least, it should be emphasized that the whole material synthesis occurs in a remarkably energy and atom-efficient fashion from cheap and sustainable resources. 

In Section I we introduce the gas-polymer-matrix model for gas sorption and transport in polymers (10, LI), which is based on the experimental evidence that even permanent gases interact with the polymeric chains, resulting in changes in the solubility and diffusion coefficients. Just as the dynamic properties of the matrix depend on gas-polymer-matrix composition, the matrix model predicts that the solubility and diffusion coefficients depend on gas concentration in the polymer. We present a mathematical description of the sorption and transport of gases in polymers (10, 11) that is based on the thermodynamic analysis of solubility (12), on the statistical mechanical model of diffusion (13), and on the theory of corresponding states (14). In Section II we use the matrix model to analyze the sorption, permeability and time-lag data for carbon dioxide in polycarbonate, and compare this analysis with the dual-mode model analysis (15). In Section III we comment on the physical implication of the gas-polymer-matrix model. 

Monitoring fast pressure changes in gas transport and sorption analysis... 

This review does not aim for an encyclopedic coverage of the rapidly expanding field of membrane science. The topics treated do, however, present a reasonable sampling of the current literature on membrane science. The subfects treated reflect directly the interests of the authors and many of the topics are fundamentally related to the fact that the membrane is a high polymer. Indeed, the transport and sorption theories presented provide parameters whose physical interpretation often is a useful complement to other methods of physical analysis of the polymeric state. The study of gas sorption and transport in rubbery polymers is petbaps the simplest example of such a case and will be treated first. 

A. H. Chan, W. J. Koros, D. R Paul, Analysis of hydrocarbon gas sorption and transport in ethyl cellulose using the dual mode sorption/partial immobilization modes, J. Membr. Sci. 3 (1978) 117-130. 

A customized Cu(I)Y zeolite is employed as a sorbent to actively collect CO in air samples to measure the concentration of CO in ambient air.The interaction is selective to CO only, but not to N2, O2, and CO2. The sorption process is facilitated by formation of Cu(l)-CO complexes, while CO can be desorbed at 300°C under helium flow for 2 min. Before the gas chromatographic analysis, a methanizer is used to reduce CO to CH4, which can then be quantified by FID. Detection limit of methane by this method is approximately 0.2 ppm. The laboratory data shows the capacity of the Cu(I)Y zeolite sorbent as 2.74 mg CO/g of sorbent. For a typical sorbent tube containing 0.5 g of treated zeolite sampling at the PEF of 50 ppm with a nominal flow rate of 100 ml/min, sampling can last as long as approximately 4 h before a breakthrough point is reached. Furthermore,... 

CON Conforti, R.M. and Barbari, T.A., A thermodynamic analysis of gas sorption-desorption hystereses in glassy polymers. Macromolecules, 26, 5209, 1993. 

Bhole YS, Karadkar PB, Kharul UK. Nitration and amination of polyphenylene oxide synthesis, gas sorption and permeation analysis. Eur Polym J 2007 43(4) 1450-9. 

Reichenauer G, Fella H J, Fricke J (2002) Monitoring fast pressure changes in gas transport and sorption analysis. Characterization of Porous Solids VI 144 443 49... 

S. Kanehashi and K. Nagai, Analysis of dual-mode model parameters for gas sorption in glassy polymers, J. Membr. Sci., 253 (2005) 117-138. 

Recently, NMR cryoporometry has been applied to study structural details of mesoporous sihcon (Dvoyashkin et al. 2008 Khokhlov 2009 Khokhlov et al. 2007, 2008a, b). It is well known that different characterization techniques may reveal different information. Therefore, comparative analysis of identical samples using different approaches is beneficial not only for a better characterization but also for the understanding of the pros and cons of the techniques apphed. In this chapter, we provide such a comparative study of two selected mesoporous silicon samples (see Table 1) using classical nitrogen gas sorption and NMR cryoporometry techniques. 

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