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Comesana-Gandara, B.,Hernandez, A.,de la Campa, J.G.,de Abajo, J.,Lozano, A.E.,Lee, Y.M. Elsevier Scientific Pub. Co 2015 Journal of membrane science Vol.493 No.-
Ortho-hydroxypolyimides (HPIs) undergo thermal rearrangement processes in a solid state at high temperatures to produce thermally rearranged polybenzoxazoles (TR-PBOs), which are promising materials for gas separation membranes due to their exceptional permeability-selectivity performance. The strong dependence between the structure of HPIs and the final properties of the TR-PBOs and the high cost of the HPI precursors are considered excellent reasons for their continued study. In this work, a set of low-cost HPIs were synthetized via the reaction of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) with 2,4-diaminophenol dihydrochloride (DAP-Cl) and 4,6-diaminoresorcinol dihydrochloride (DAR-Cl). The polyimide made from 6FDA and m-phenylene diamine (MPD) was also obtained for comparison purposes. The polyimide precursors and the corresponding TR-PBOs, which were tested as films, were thoroughly characterized. The glass transition temperature of these precursor polyimides was shown to be a function of the number of hydroxyl groups such that the lowest value corresponded to the polyimide from MPD and the highest value corresponded to that derived from DAR. The conversion rate of HPIs to PBO at different processing temperatures was determined, and the highest conversion rate matched the DAP derived polyimide. With respect to their gas separation properties after thermal treatment at 450<SUP>o</SUP>C, these HPIs gave rise to TR-PBOs with very high permeability and satisfactory permselectivity values for several gas pairs.
Comesañ,a-Gandara, B.,Ansaloni, L.,Lee, Y.M.,Lozano, A.E.,De Angelis, M.G. Elsevier 2017 Journal of membrane science Vol.542 No.-
<P><B>Abstract</B></P> <P>We studied in this work the properties of a new membrane (TR-PBO) obtained by solid state thermal rearrangement at 450°C of a recently developed polyimide precursor, (mHAB-6FDA), which was synthesized by reaction of (3,3-diamino-4,4-dihydroxybiphenyl, mHAB) with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The mHAB monomer is an isomer of the commercial 3,3′-dihydroxybenzidine (pHAB), used to form the more popular polyimide precursor pHAB-6FDA. TR-PBO membranes obtained from mHAB-6FDA showed excellent CO<SUB>2</SUB> permeability (720 Barrer) and good CO<SUB>2</SUB>/CH<SUB>4</SUB> ideal selectivity of 23. We found out that the thermal rearrangement enhances the solubility and diffusion coefficients of CO<SUB>2</SUB> at 10bar by factors as high as 1.3 and 5, respectively. Larger enhancements, however, were observed in the case of CH<SUB>4</SUB>, causing the diffusivity selectivity to decrease by a factor of 2.6 and the solubility selectivity to decrease by a factor of ~1.5 upon rearrangement. The pure gas solubility was modeled with the Dual Sorption Mode model and the NELF model. The two models were then used to predict the mixed gas behavior in terms of solubility-selectivity, highlighting the effects of competition that are consistent with those observed in other glassy polymers.</P> <P>We also performed moisture sorption tests and gas permeability measurements in the presence of humidity. It was observed that the thermal rearrangement increases the membrane hydrophobicity and, consistently, the CO<SUB>2</SUB> and CH<SUB>4</SUB> permeability of mTR-PBO membranes is much more stable in the presence of humidity than that of the precursor polyimide membranes. Finally, the effect of aging on the membrane performance was analyzed. A 30% decrease in the CO<SUB>2</SUB> permeability of TR polymer membranes (around 50µm thick) was observed after 6 months, while the selectivity increased by 20%. These results indicate that, even after 6 months, the performance of the TR polymer membrane was outstanding and close to Robeson's upper bound.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The properties of a new TR membrane based on mHAB-6FDA were characterized in detail. </LI> <LI> The sorption and diffusion of gases are enhanced after conversion. </LI> <LI> Sorption and solubility-selectivity were modeled with the NELF model. </LI> <LI> Humidity and ageing lower the gas permeability and enhance the selectivity. </LI> <LI> The thermal rearrangement makes membranes less sensitive to humidity and ageing. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
The Taxonomy of Psilocybe fagicola-complex
Gaston Guzman,James Q. Jacobs,Florencia Ramirez-Guillen,Dulce Murrieta,Etelvina Gandara 한국미생물학회 2005 The journal of microbiology Vol.43 No.2
Psilocybe fagicola comprises a complex of more than eight species, six of them in Mexico, and all of them possessing a long pseudorhiza, a characteristic not listed by Heim and Cailleux in 1959 in the original description of the type species, but described by Guzmán in 1978 and 1983. The description of Psilocybe fagicola s.s. is here emended to include the length of the cheilocystidia of (6-) 12-20 (-30) μm, as well as the absence or scarcity of pleurocystidia. Psilocybe xalapensis and P. wassoniorum are considered to be synonymous with P. fagicola s.s. However, Psilocybe banderillensis and P. herrerae from Mexico, P. columbiana from Colombia, and P. keralensis from India are considered to be valid species within this complex. Moreover, P. novoxalapensis and P. teofilae, both from Mexico, are described as new species. Length of spores, presence or absence of pleurocystidia and their variations, and type of cheilocystidia constitute the principal defining characteristics of the species. Setaceous hyphae at the base of the stipe, as well as caulocystidia, lack taxonomic value, as do other morphological characteristics, including pileipellis and subpileipellis. A key to the eight considered species is also presented within the paper.
Large-Pore Apertures in a Series of Metal-Organic Frameworks
Deng, H.,Grunder, S.,Cordova, K. E.,Valente, C.,Furukawa, H.,Hmadeh, M.,Gandara, F.,Whalley, A. C.,Liu, Z.,Asahina, S.,Kazumori, H.,O'Keeffe, M.,Terasaki, O.,Stoddart, J. F.,Yaghi, O. M. American Association for the Advancement of Scienc 2012 Science Vol.336 No.6084
<P>We report a strategy to expand the pore aperture of metal-organic frameworks (MOFs) into a previously unattained size regime (>32 angstroms). Specifically, the systematic expansion of a well-known MOF structure, MOF-74, from its original link of one phenylene ring (I) to two, three, four, five, six, seven, nine, and eleven (II to XI, respectively), afforded an isoreticular series of MOF-74 structures (termed IRMOF-74-I to XI) with pore apertures ranging from 14 to 98 angstroms. All members of this series have noninterpenetrating structures and exhibit robust architectures, as evidenced by their permanent porosity and high thermal stability (up to 300C). The pore apertures of an oligoethylene glycol-functionalized IRMOF-74-VII and IRMOF-74-IX are large enough for natural proteins to enter the pores.</P>