0000000000144411
AUTHOR
J. P. Bellat
Heptane adsorption in silicalite-1 : molecular dynamics simulation.
Molecular dynamics (MD) simulations have been used to study the adsorption process of n-heptane molecules in silicalite-1 at 300 K. MD simulated results were compared to experimental neutron diffraction (ND) and experimental self-diffusion coefficients. The analysis of MD data indicated a packing of the adsorbed molecules around 4 mol./u.c., which is not the consequence of an enthalpic effect but of an entropic effect. The role of the n-heptane chain flexibility (cis–trans conformation) in relation with the silicalite-1 channel type (straight versus sinusoidal) was outlined and enabled to understand the mobility change arising at 4 mol./u.c., according to previous experimental results. The …
New insight on the lithium hydride–water vapor reaction system
Abstract The reaction of lithium hydride (LiH) powder with pure water vapor (H2O and D2O) was studied by thermogravimetry and in situ infrared spectroscopy at 298 K over a large pressure range. The mean particle size of LiH is around 27 μm. At very low pressure, the hydrolysis starts with the formation of lithium oxide (Li2O). Then, both Li2O and lithium hydroxide (LiOH) are formed on increasing pressure, thus, creating a Li2O/LiOH bilayer. The reaction takes place through the consumption of LiH and the formation of Li2O at the LiH/Li2O interface and through the consumption of Li2O and the formation of LiOH at the Li2O/LiOH interface. Above 10 hPa, only the monohydrate LiOH·H2O is formed. T…
Gravimetric and FTIR study of the interaction of tetramethylethylene on a MFI zeolite
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…
Suivi par diffraction de rayons X “in situ” de l'évolution du paramètre de maille du ferrite nanométrique γ-Fe2O3lors de l'isotherme d'adsorption d'eau
La methode de synthese par chimie douce a ete utilisee pour synthetiser des nanoparticules de maghemite γ-Fe 2 O 3 dans une gamme de taille allant de 9 a 14 nm. Ces poudres, parfaitement cristallisees en phase spinelle, exemptes d'impuretes, avec une stoechiometrie en oxygene parfaitement controlee, ont servi de materiaux modeles pour cette etude. Le parametre de maille de ce materiau (0,8346 nm) s'avere etre non dependant de la taille. Cependant, le suivi en Diffraction de Rayons X in-situ revele des variations de ce parametre avec la modification de la surface en presence de vapeur d'eau. Les phenomenes de chimisorption et de physisorption jouent un role preponderant dans les evolutions o…
A robust viologen and Mn-based porous coordination polymer with two types of Lewis acid sites providing high affinity for H 2 O, CO 2 and NH 3
A novel porous coordination polymer [Mn(pc3)(H2O)2]·xH2O (3 < x < 4) is synthesized in water at pH = 7 using the anionic viologen-carboxylate ligand 4,4′-bipyridinium,1,1′-bis-(2,4-dicarboxyphenyl) (pc32−). Dehydration of the material results in the formation of open pores containing two types of accessible Lewis acid sites: exposed Mn2+ cations and N+ atoms of viologen units. Due to this property the PCP shows high affinity and capacity in the adsorption of H2O, CO2 and NH3. Despite the presence of strong adsorption sites this material is stable in liquid water and in gaseous NH3.
Preparation of magnetic composites of MIL-53(Fe) or MIL-100(Fe) via partial transformation of their framework into γ-Fe2O3
A novel two-step approach is proposed to obtain magnetically active composite materials consisting of MIL-53(Fe) or MIL-100(Fe) and γ-Fe2O3 particles. The first step consists in a partial transformation of the framework into a layer of γ-FeO(OH) (lepidocrocite) covering the MOF particles. We found that such a transformation can be realized under air-free conditions by hydrolysing the MOFs at pH 6.2 in the presence of FeSO4. In the second step the obtained γ-FeO(OH)/MOF composite is heated under an air flow at 250 °C in order to transform γ-FeO(OH) to γ-Fe2O3. The thus prepared composites containing 40 wt% of the magnetic phase were characterized in detail by XRD, HRTEM, FESEM, N2 adsorption…
Improved hydrophobicity of inorganic–organic hybrid mesoporous silica with cage-like pores
International audience; Hydrophobic ordered mesoporous silica particles with cage-like pores (SBA-1 type) were prepared through co-condensation of phenyltriethoxysilane (PhTES) and tetraethylorthosilicate (TEOS) at different TEOS/PhTES molar ratios. It is shown that the hydrophobic character of the particles is enhanced by increasing the phenyl loading (decreasing the TEOS/PhTES molar ratio) and that it could be further enhanced by subsequent trimethylsilyl (TMS) grafting on remaining silanol groups (TMS-PhSBA-1 sample). This increase of hydrophobicity has been evidenced on the internal surface (mesoporosity) of the particles using water adsorption and, on the external surface of the partic…
Adsorption Properties of Nax and Bax Zeolites: Correlation between Structural and Thermodynamic Results on Para- and Meta-xylene Adsorption
A comparison is made between NaX and BaX adsorption properties starting from crystallographic data and thermodynamic measurements. Adsorption isotherms and differential adsorption heats of pure para- and meta-xylenes in NaX and BaX zeolites are interpreted in the light of crystallographic results.
Characterization of a Superabsorbent Polymer.
We studied an amorphous polymer superabsorbent, able to absorb until 1000 times its weight of water. It is consisted of macromolecular chains, dependent between them by chemical bonds. The swelling of the product in the presence of water gives rise to a polyelectrolytic gel. The chemical analysis of polymer by energy dispersive spectrometry and photoelectrons spectroscopy with a microsounder X showed that the product is homogeneous. It contains carbon, oxygen, and sodium. The measurements of specific surface of the product show that the polymer is nonporous and present a weak surface of about 2.1 m2/g. The thermal study of polymer showed that, under the effect of the temperature and with at…
Characterization and utilization of MFI zeolites and MCM-41 materials for gaseous pollutant adsorption
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…
Differential calorimetric enthalpies of adsorption ofp-xylene andm-xylene on y faujasites at 25°C
The differential enthalpies of adsorption ofp-xylene andm-xylene on NaY, KY and BaY zeolites were measured by isothermal calorimetry coupled with isothermal volumetry at 25‡C. Whatever the zeolite, the enthalpies of adsorption ofp-xylene andm-xylene at low filling were of the same order of magnitude. They did not show significantly the effect of the dipolar moment ofm-xylene. Their absolute values varied in the sequence
Structural Signatures of Type IV Isotherm Steps: Sorption of Trichloroethene, Tetrachloroethene, and Benzene in Silicalite-I
We have investigated by in situ neutron diffraction the structural properties of C2HCl3, C2Cl4, and C6D6 sorbed phases in silicalite-1. Our motivation is to correlate the structure of these three confined species to the fact that their adsorption isotherms are characterized by no step, one step, and two steps, respectively. From our detailed neutron diffraction investigation, we deduce that the adsorption isotherm steps are not signatures of phase transitions but are correlated to the different adsorption stages observed during the silicalite-1 loading. For C6D6, such a loading is a three stage process (the C6D6 molecules fill successively, the intersections, then the straight channels and …
t-Curves for n-Hexane
The adsorption and desorption isotherms of n-hexane on powdered alumina and silica have been studied at 25°C over a wide range of relative pressures. Two t-curves for pore structure analysis are proposed, one for alumina (C = 12) and the second for silica (3 ≤ C ≤ 9). The statistical thickness t of the adsorbed n-hexane layer has been drawn as a function of the relative pressure assuming a maximal thickness of 0.55 nm and a mean thickness of 0.42 nm for the monolayer. The results are discussed in relation to previous published data.
Adsorption and diffusion of linear and dibranched C6 paraffins in a ZSM-5 zeolite
The adsorption of n-hexane and 2,2-dimethylbutane on a commercial ZSM-5 zeolite is studied under isothermal and isobaric conditions. ZSM-5 exhibits two different behaviours with linear and dibranched alkanes. A substep at 4 molec.uc−1 is observed on the adsorption isotherm of n-hexane at 348 K. A singular adsorption-desorption process is evidenced on the adsorption isobar at 5.5 kPa with 2,2-dimethylbutane at a temperature close to 343 K when the sample is activated at 298 K under vacuum. The diffusivities have been determined by fitting directly the uptake curves with a numerical resolution of second Fick's law based on finite difference method. Microporous diffusion seems to be rate limit…
Comportement du Gonflement d’un Polymère Superabsorbant vis-à-vis de l’Eau dans un Sol Sableux
H.Bahaj, R.Benaddi, M.Bakass,C.Bayane & J.P. Bellat a Laboratoire de Recherche sur la Reactivite des Materiaux et l’Optimisation des Procedes, REMATOP, Faculte des Sciences Semlalia, Universite Cadi Ayyad, B.P. 2390 Marrakech (Maroc). b Laboratoire de Recherche sur la Reactivite des Solides, UMR 5613 CNRS, Universite de Bourgogne, UFR ST, av. A. Savary, B.P. 47870, F-21078 Dijon cedex, France bahaj_hanane@yahoo.fr, r.benaddi@hotmail.fr, bakass@ucam.ac.ma, c.bayane@ucam.ac.ma, jean-pierre.bellat@u-bourgogne.fr
Étude thermodynamique du polymère super absorbant X10 vis–à–vis de l’eau vapeur
The organic polymers super absorbents present values of specific surface lower than 2m 2 /g. The isobars of adsorption of water vapor on studied polymer are of type III at ambient temperature with the hysterisis phenomena.For temperatures lower than ambient, the isobars become deformed because of an effect of chains. This type of polymer is characterized by a multi-layer adsorption which occurs before the full-course one is complete. During reactions of adsorption, the polymer undergoes rearrangement polymeric network which results from a co-operative diffusion of the water molecules and from a spacing of chain followed by an expansion of the polymeric network. Three types of water molecule…
The adsorption of water vapor on super absorbent product at low temperatures and low mass.
The adsorption isotherms of water vapor on super absorbent product have the same form of type III isotherm at ambient temperature with the hysteresis phenomena. For temperatures lower than ambient, the isotherms become deformed because of the chains effect. The polymer is characterized by a multilayer adsorption, which occurs before a full-course is complete. During adsorption reactions, the polymer undergoes rearrangement polymeric network, which results from a cooperative diffusion of the water molecules and from a chain spacing followed by an expansion of the polymeric network. Three types of water molecules adsorbed on polymer were identified: strongly dependent water, adsorbed water, a…
Heptane Adsorption in Silicalite-1: Neutron Scattering Investigation
International audience; Structural properties of confined deuterated n-heptane in silicalite-1 have been investigated by neutron scattering experiments during the adsorption process. At 300 K, the adsorption isotherm shows a sharp inflection at a loading near Nads ) 4 molecules per silicalite-1 unit cell. In addition, the diffusivities obtained from recent QENS data exhibit a loading dependence. Our motivation is to find structural signatures of the peculiar behavior of n-heptane in silicalite-1 and to check the numerous computer simulation findings of this behavior. Our detailed neutron diffraction investigation agrees with the MONO-ORTHO phase transition of the silicalite-1 above a Nads v…
A robust nanoporous supramolecular metal–organic framework based on ionic hydrogen bonds
International audience; Hydrogen-bond assembly of tripod-like organic cations [H3-MeTrip]3+ (1,2,3-tri(4′-pyridinium-oxyl)-2-methylpropane) and the hexa-anionic complex [Zr2(oxalate)7]6− leads to a structurally, thermally, and chemically robust porous 3D supramolecular framework showing channels of 1 nm in width. Permanent porosity has been ascertained by analyzing the material at the single-crystal level during a sorption cycle. The framework crystal structure was found to remain the same for the native compound, its activated phase, and after guest resorption. The channels exhibit affinities for polar organic molecules ranging from simple alcohols to aniline. Halogenated molecules and I2 …