Search results for "Microporous"
showing 10 items of 94 documents
A highly stable and hierarchical tetrathiafulvalene-based metal organic framework with improved performance as a solid catalyst
2018
[EN] Herein we report the synthesis of a tetrathiafulvalene (TTF)-based MOF, namely MUV-2, which shows a non-interpenetrated hierarchical crystal structure with mesoporous one-dimensional channels of ca. 3 nm and orthogonal microporous channels of ca. 1 nm. This highly stable MOF (aqueous solution with pH values ranging from 2 to 11 and different organic solvents), which possesses the well-known [Fe3(¿3-O)(COO)6] secondary building unit, has proven to be an efficient catalyst for the aerobic oxidation of dibenzothiophenes.
Inside Cover: Bidirectional Chemo-Switching of Spin State in a Microporous Framework (Angew. Chem. Int. Ed. 26/2009)
2009
Bidirectional chemo-switching of magnetism occurs in a microporous coordination polymer containing spin-crossover subunits, as described by M. Ohba, J. A. Real, S. Kitagawa, and co-workers in their Communication on page 4767 ff. In situ magnetic measurements reveal that most guest molecules transform the framework spin state from diamagnetic low spin (red) to paramagnetic high spin (yellow), whereas the guest CS2 stabilizes the low-spin state. These induced spin states are retained as a memory effect after the release of the guest.
Characterization and utilization of MFI zeolites and MCM-41 materials for gaseous pollutant adsorption
1999
Physisorption of n-hexane, trichloroethylene, tetrachloroethylene, carbon and nitrogen oxides on a microporous ZSM-5 (Si/Al=339) zeolite and an amorphous mesoporous MCM-41 (Si/Al=∞) sample was examined by isothermal thermogravimetry, manometry and calorimetry to evaluate the feasibility of using these porous materials for gaseous pollutant adsorption at room temperature. The adsorbents showed very interesting adsorption properties for hydrocarbons. ZSM-5 exhibited the strongest adsorption affinity and MCM-41 showed the largest adsorption capacity. Another main feature in this work was to observe a stepped-isotherm for the adsorption of C2Cl4 on ZSM-5. Such a substep located at very low rela…
Gravimetric and FTIR study of the interaction of tetramethylethylene on a MFI zeolite
2005
The adsorption of tetramethylethylene on a high siliceous ZSM-5 zeolite was performed by thermogravimetry, in situ FTIR spectroscopy and molecular dynamics simulation. Sorption and spectroscopic data were analysed as a function of loading and compared with molecular dynamics simulated results to characterize the adsorption process. The isotherm at 298 K does not show any deviation from the type I behaviour. The presence of admolecules in micropores does not or weakly affect zeolite framework vibration bands but induces an additional band at around 1715 cm−1 mainly due to a contribution of the microporous surface of the adsorbent. A confinement effect of the adsorbate is characterized during…
Determination of water intrusion heat in hydrophobic microporous materials by high pressure calorimetry
2010
International audience; The understanding of interactions between a solid surface and a non-wetting liquid still remains of fundamental interest in numerous research fields, from chemistry to biology. This work focuses on the mechanisms of water intrusion in hydrophobic microporous materials through the thermal analysis of the phenomenon. A specific calorimetric technique coupled to high pressure equipment has been developed to investigate equilibrium thermal effects in such thermodynamic systems from 0 to 400 MPa under isothermal conditions. First validation tests of this method were carried out by compressing degassed water in a constant volume V with successive small pressure increments …
Microporous volume and external surface of Y zeolites accessible to p-xylene and m-xylene
1997
Abstract Isothermal adsorption of p-xylene and m-xylene on NaY, KY and BaY zeolites was studied by thermogravimetry at 25°C. Adsorption isotherms showed type H4 hysteresis associated with a xylenes adsorption process activated by the pressure. Experimental data were analysed with the t-method to distinguish the amounts of xylene adsorbed in the α-cages and on the external surface of crystallites. Results were compared with those previously achieved by calorimetry. Whatever may be the isomer and the Y zeolite, the adsorption capacity of α-cages at 25 °C is equal to 3.5 molecule α−1. At saturation, the amount of xylenes adsorbed on the external surface represents 13% of the total amount adsor…
Net charge and polarizability of zeolitic Brønsted acidic sites
2007
The interacting induced-dipoles polarization model, implemented in our program POLAR, is used for the calculation of the effective polarizability of the zeolitic bridged OH group, which results much higher than that of the free silanol group. A high polarizability is also calculated for the bridged OH group with a Si4+, in the absence of Lewis-acid promotion of silanol by Al3+. The crystal polarizability is estimated from the Clausius-Mossotti relationship. Siliceous zeolites are low-permittivity isolators. The interaction of a weak base with the zeolitic OH can be considered as a local bond. Only when cations are located in the zeolite micropore, next to tetrahedra that contain trivalent c…
Pressure Effect Studies on the Spin Transition of Microporous 3D Polymer [Fe(pz)Pt(CN)4]
2018
Pressure effects on the spin transition of the three-dimensional (3D) porous coordination polymer {Fe(pz)[Pt(CN)4]} have been investigated in the interval 105 Pa–1.0 GPa through variable-temperature (10–320 K) magnetic susceptibility measurements and spectroscopic studies in the visible region at room temperature. These studies have disclosed a different behavior of the compound under pressure. In the magnetic experiments, a temperature independent paramagnetic behavior has been observed under 0.4 GPa. In contrast, at room temperature and at 0.8 GPa, a complete HS-to-LS transition has been evidenced. The differences in the magnetic behavior are strongly related with the porous structure of …
Designing conjugated microporous polymers for visible light-promoted photocatalytic carbon–carbon double bond cleavage in aqueous medium
2018
The production of valuable carbonyl compounds directly from alkenes via carbon–carbon double (CC) bond cleavage is a highly important reaction. As a promising alternative to traditional metal-catalyzed thermal reaction conditions, photocatalysis offers an environmentally friendly and sustainable synthetic strategy. However, most photocatalysts used so far were homogeneous, molecular and transition metal-based catalytic systems. Here, we report a structural design strategy of conjugated microporous polymers (CMPs) as a class of metal-free, heterogeneous, stable and reusable photocatalysts for visible light-promoted CC bond cleavage reaction. Via different electron donor and acceptor combinat…
Transport of amino acids through liquid membranes supported on novel poly(vinylidenefluoride) porous flat-sheet matrix
1997
Flat-sheet membranes from poly(vinylidenefluoride) (PVDF) were prepared by the phase inversion process. LiCl was used as a modifying agent. The porosity, maximum pore size and LEPW (liquid entry pressure of water) were determined. Three types of these membranes were tested as a support for n-decanol supported liquid membranes (SLM). Transport of eight amino acids, selected to cover a wide variety of side chains, and of phenylalanine methyl ester through n-decanol SLM were studied. The ability of amino acids to permeates through these membranes depends on the type of flat-sheet PVDF used as a support. An increase in porosity and pore size of the microporous matrix resulted in an increase of …