[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to evaluate the efficiency of two Tunisian mineral clays to capture chromium(III) and cadmium(II) present in landfills leachate and to understand the corresponding mechanisms of sorption. Kinetic studies, adsorption isotherms, particle size distributions as well as zeta potential evolution with adsorbed amount, and pH were studied. The kinetic study revealed that a pseudo-second-order model agrees with the heavy metals adsorption experimental values for both clays. Negative zeta potential was obtained over the entire studied pH range (3–8) and no isoelectric point was found. Adsorption of Cr(III) had a significant effect on the zeta potential which goes from negative values to positive ones, indicating specific adsorption. Upon the addition of Cd(II), the clay surfaces stayed negatively charged whatever the cadmium concentration.
Full-text · Article · Jan 2016 · Desalination and water treatment
[Show abstract][Hide abstract] ABSTRACT: After examining an easy way to classify the many calorimeters described in the literature, attention is brought to the main physical quantities through which heat can be measured in a calorimeter and then to the calibration and performances of the latter. The numerous applications of calorimetry in the fields of physics, chemistry, and biology are then briefly reviewed, with adequate references.
[Show abstract][Hide abstract] ABSTRACT: Natural and manufactured disordered systems are ubiquitous and often involve hierarchical structures. This structural organization optimizes defined physical properties at several scales from molecular to representative volumes where the usual homogenization approach becomes efficient. For studying a particular physical property on these systems it is thus required to use a general method of analysis based on the joint application of complementary techniques covering the whole set of time-and length-scales. Here we review a comprehensive multiscale method presented for analyzing the three-dimensional moisture transport in hierarchical porous media such as synthesized reference silicates and cement-based materials. Several techniques (NMR spectroscopy, relaxometry, diffusometry, X-ray micro-tomography, conductivity…) have been used to evidence the interplay between the different scales involved in this transport process. This method allows answering the general opened questions concerning the scale dependence of such a moisture transport in cement-based materials. We outline the main results of the multiscale techniques applied on reference porous silicates allowing separating the impact of geometry, hydric state and wettability on the moisture transport. Based on this approach, we prove that this transport at micro- and meso-scale is determinant to modify the moisture at macro-scale during setting or for hardened cement-based materials.
No preview · Article · Jul 2015 · The European Physical Journal Special Topics
[Show abstract][Hide abstract] ABSTRACT: Nanostructured block copolymer electrolytes (BCE) are
currently attracting widespread interest for applications in rechargeable
lithium batteries. In order to investigate the influence of the composition, and
therefore that of confinement, on the conductivity, a series of triblock PS!
PEO!PS copolymers, with three linear PEO blocks of molecular weights 9,
10, or 35 kg mol!1 and with PEO weight fractions varying from 36% to 75%,
were synthesized and doped with LiTFSI. Measurements by impedance
spectroscopy of the conductivity show that it increases with PEO molecular
weight, which is quite counterintuitive. To explain this phenomenon, the
conductivity of the BCE has been modeled using three factors: (1) the
conductivity of bulk PEO, (2) the topology of the PEO percolating network,
described by the tortuosity parameter, and (3) the influence on the tortuosity
of the effective volume fraction of the PEO phase useful for the conduction, taking into account a “dead zone” excluded from ionic transport, at the PS/PEO interface. In this approach, by analogy with porous materials and in contrast with previous work, the tortuosity is not kept constant but depends on the PEO volume fraction effectively useful for charge transport. The thickness of the dead zone, 4!5 EO units (#1.6 nm), is the same as that of the exclusion zone for crystallization previously reported. This value does not depend either on the PEO molecular weight (from 9 to 35 kg mol!1) or on the EO/Li ratio (from 20 to 30). The absence of both conduction and crystallization in the excluded region could be due to the low mobility of the PEO chains in this zone. Consequently, the conductivity of BCE increases with PEO molecular weight because the proportion of the excluded zone becomes smaller as the PEO molecular weight increases. This model therefore provides a fairly precise description of the ionic conductivity of BCE used in lithium battery applications.
[Show abstract][Hide abstract] ABSTRACT: The adsorption of two pesticides (2,4-phenoxy acetic acid (2,4D) and thiabendazol) on silica, alumina, kaolin and montmorillonite is studied from adsorption isotherms and enthalpies. 2,4D is not adsorbed by silica, kaolinite and montmorillonite even in the presence of 0.01 mol l−1 divalent cations. On alumina, the energy of adsorption is comparable with that of the formation of an acid-base complex. Thiabendazol can be adsorbed on silica and clays from an ethanol solution. Most adsorption isotherms are of the Langmuir type and correspond to roughly constant adsorption enthalpies as a function of coverage except for kaolin where adsorption on both lateral and basal faces can be involved. Adsorption after introducing humic acids to the system was also studied for kaolin.
No preview · Article · Mar 2014 · Journal of Thermal Analysis and Calorimetry
[Show abstract][Hide abstract] ABSTRACT: High-energy ball-milling is proven to be an effective technique for manufacturing reactive aluminum nanopowders. The procedure of milling presented in this work allows the elaboration of aluminum powders with specific surface areas around 20 m2 /g. The particles have platelet morphology and are constituted by a nanocrystalline aluminum core surrounded by a thick amorphous alumina layer of 4.57 +-0.5 nm. The reactivity of the powders is enhanced as compared to nanopowders elaborated with techniques involving vapor phase condensation. The morphology, the microstructure and the initial thickness of the alumina layer are shown to be important parameters that influence the reactivity. The method could be extended to any other ductile metal, provided a hard surface layer is continuously formed during milling. & 2013 Elsevier B.V. All rights reserved.
Full-text · Article · Nov 2013 · Materials Letters
[Show abstract][Hide abstract] ABSTRACT: Hydration energies contribute significantly to the stability of hydrated clay minerals. However, thermodynamic data of hydration for clay minerals are still poorly known. The present study aims to improve our comprehension of the hydration processes of sodic smectite MX80, and to implement a new methodology for extracting thermodynamic data of hydration of the smectite.
[Show abstract][Hide abstract] ABSTRACT: Interaction of CO2 with mineral surfaces is of increasing importance to the activities related to CO2 sequestration and enhanced oil recovery. Adsorption/interaction of CO2 with mineral powder surfaces is addressed using microcalorimetric method coupled with gas chromatograph as a detector. Calcite powder surface is modified with stearic acid (SA) and asphaltene, while the silicate mineral powder surfaces (quartz and kaolinite) are modified with N,N-dimethyldodecylamine (NN-DMDA) and asphaltene. Unmodified calcite in presence of humidity has shown to have the highest capacity for CO2 adsorption among the tested minerals, where a reaction may occur at the calcite surface. The adsorption capacity of calcite is reduced upon modification with SA and asphaltene. Similar observation is also shown with the modified silicate minerals with asphaltene. In contrast, for the modified silicate with NN-DMDA, the adsorption capacity of CO2 increased, which may be explained by the interaction of CO2 with the amine group of NN-DMDA.
No preview · Article · Aug 2013 · Petroleum Science and Technology
[Show abstract][Hide abstract] ABSTRACT: The adsorption efficacy of 16 pharmaceuticals on six different activated carbons is correlated to the thermodynamic work of adhesion, which was derived following the surface tension component approach. Immersion calorimetry was used to determine the surface tension components of activated carbon, while contact angle measurements on compressed plates were used to determine these for solutes. We found that the acid–base surface tension components of activated carbon correlated to the activated carbon oxygen content. Solute-water interaction correlated well to their solubility, although four solutes deviated from the trend. In the interaction between solute and activated carbon, van der Waals interactions were dominant and explained 65–94% of the total interaction energy, depending on the hydrophobicity of the activated carbon and solute. A reasonable relationship (r2 > 70) was found between the calculated work of adhesion and the experimentally determined activated carbon loading.
[Show abstract][Hide abstract] ABSTRACT: Hydration properties of swelling clay minerals may be very variable depending on the chemical composition of the clay, on the nature of the interlayer cations and on the interlayer charge (Berend et al., 1995; Vieillard et al., 2011). The Wyoming smectite has been largely studied, notably for assessing its hydration behavior as a function of the interlayer cations, in connection with its structural characteristics (Ferrage et al., 2005; Salles et al., 2007). In the present work, carried out as part of a collaborative Andra/BRGM/HydrASA research program for ThermoChimie project, we propose an original experimental study, based on adsorption and desorption isotherms performed on MX80 clay samples. The goal is to determine energetic contributions to the reactions of hydration, which have been revealed to be non-negligible with respect to the stability of the clay minerals (Gailhanou et al., submitted). In particular, the present work addresses the problems of the hysteresis loop between adsorption and desorption isotherms and of the irreversibility of hydration reactions. This is directly related to the application of classical thermodynamics to the hydration reactions of clay minerals. In a first stage, an experimental study is dedicated to better understand the origin of the hysteresis loop which is systematically observed for the adsorption-desorption isotherms at 25°C. The development of the hysteresis loop has been studied by considering several kinetically related parameters: stabilization periods, temperatures (from 25°C to 60°C) and hydration steps (Figure 1). No sensible change was observed in the hysteresis loop. Therefore, the amount of adsorbed water depends on the followed reaction pathway (adsorption or desorption). The variations in microstructures and in the distribution of hydration layers (0/1/2 water layers; Ferrage et al., 2005) as a function of relative humidity (RH) could provide a possible explanation for this phenomenon.
[Show abstract][Hide abstract] ABSTRACT: The conductivity and viscosity of PEO/LiTFSI complexes are determined as a function of temperature, molecular weight (Mn) and the end group nature in view of the design of future polymer electrolytes. The results show the crucial role of the end groups on the dynamics of polymers at low Mn. A new method is proposed to estimate the glass transition temperature variation as function of Mn and end groups using conductivity data. The conductivity and viscosity plotted at constant friction factor follow a master curve which suggests that the main impact of end groups is to modify the available free volume which governs in turn the segmental dynamics. The anion and cation conductivities are separated using the cationic transport number obtained by pfg-NMR. Finally, an empirical equation based on Rouse dynamics taking into account the effect of the end groups is proposed. It reproduces with a good degree of accuracy the conductivities over the whole temperature and Mn ranges. In agreement with molecular dynamic simulations, at high Mn the limiting step is the jump of the lithium ion from one coordination site to another and is not influenced by the dynamics of the PEO chain reptation, whereas at low Mn the transport is mainly ensured by a vehicular mechanism.
Full-text · Article · Oct 2012 · Solid State Ionics
[Show abstract][Hide abstract] ABSTRACT: The thermodynamic properties of three aluminous 2:1 clay minerals were acquired at 1.013 bars and at temperatures between 5 and 500 K using various calorimetric methods. Calorimetric measurements were performed on hydrated and dehydrated <2 mu m clay fractions of smectite MX-80 (Wyoming), illite IMt-2 (Silver Hill) and beidellite SBId-1 (Black Jack Mine). After purification, the mineralogical analyses gave the following structural formulae: Na0.409K0.024Ca0.009(Si3.738Al0.262)(Al1.598Mg0.214 Fe0.1733+Fe0.0352+) O-10(OH)(2,) K0.762Na0.044(Si3.387Al0.613)(Al1.427Mg0.241Fe0.2923+Fe0.0842+)O-10(OH)(2) and Ca0.185K0.104(Si3.574Al0.426)( Al1.812Mg0.09Fe0.1123+)O-10(OH)(2) for smectite MX-80, illite IMt-2 and beidellite SBId-1, respectively. Heat capacities were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 500 K. Standard enthalpies of formation were obtained from solution-reaction calorimetry at 298.15 K. The standard Gibbs free energies of formation of the clay minerals were also calculated, together with the equilibrium constants at 25 degrees C, for anhydrous and hydrated minerals. A comparison between these experimental data and estimated values obtained from prediction models available in the literature, enabled the calculation method that appears to be the most relevant to be selected, at least for aluminous 2:1 clay minerals.
[Show abstract][Hide abstract] ABSTRACT: The removal of uremic toxins by zeolites is investigated in the context of the exploration of alternative methods to blood purification by dialysis. The case of a partially protein bound molecule, p-cresol, is studied here. High silica MFI type zeolites show a selective adsorption for p-cresol without major ion exchange with the cations present under equilibrium conditions in solution. Adsorption isotherms in different media were performed: pure water, artificial blood serum containing bovine serum albumin and human serum (HS obtained from a pool of 50 dialysis patients). p-Cresol elimination levels of 80-85% were obtained under in vitro conditions. However, in HS, p-cresol affinities for the zeolites are generally reduced as compared with pure water due to a partial obstruction of the pore system by adsorption of proteins on the external surface of zeolites particles. These results show that zeolites can be successfully employed as specific adsorbents for uremic toxins but without direct contact with serum albumin, which means only in the ultra-filtrate. (C) 2011 Elsevier Inc. All rights reserved.
No preview · Article · May 2012 · Microporous and Mesoporous Materials
[Show abstract][Hide abstract] ABSTRACT: Electromigration of ions through porous silica particles
dispersed in an electrolyte is studied by conductivity measurements. By
determining the suspension conductivity at infinite dilution of particles
where the Maxwell equation is applicable, the conductivity of the particles is
determined. At high ionic strength, this allows calculation of the tortuosity of
the particles. The tortuosity is then used to extract the pore conductivity
from the particle conductivity under low ionic strength conditions where the
surface conductivity is not negligible. Evolution of pore conductivity, which
appears to be related to pore size, is not monotonous when ionic strength
increases, showing first a decrease at very low ionic strengths, i.e., in
conditions of double layers overlap in the pores, followed by an increase to
trend toward the bulk conductivity at high ionic strength. This unexpected
behavior can be explained by the fact that the initial surface conductivity in
pores is mainly due to the protons, provided by spontaneous dissociation of surface silanol sites in water, which are subsequently exchanged by sodium.
Full-text · Article · Jan 2012 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: The aim of this study is to evaluate the capabilities of zeolites as selective sorbents for on-line dioxin monitoring. The
adsorption isotherms of 2,3-DCDD and 1,2,3,4-TCDD from isooctane on several zeolites with different pore sizes (*BEA, EMT,
FAU and MFI-type zeolites) are determined. Selective adsorption is shown for FAU and EMT-type zeolites. 2,3-DCDD is adsorbed
by FAU with the highest adsorption capacity and affinity while 1,2,3,4-TCDD is not adsorbed whatever the zeolites. The adsorption
of 2,3-DCDD inside the pores of FAU is qualitatively confirmed by diffuse reflectance UV spectrometry and thermogravimetry
KeywordsDioxin–Zeolite–Selective adsorption–Adsorption from solution
[Show abstract][Hide abstract] ABSTRACT: The paper addresses wettability alteration of calcite, quartz and kaolinite powders, with stearic acid (SA), N,N-dimethyldodecylamine (NN-DMDA) and asphaltene as oil soluble additives. It is a challenge to convert silicate based mineral surfaces from strongly water-wet to more oil-wet. Thermogravimetric analysis (TGA) of the modified powders is used to quantify the monolayer adsorption and is suggesting the possible molecular orientation on the mineral surfaces. Characterization of the mineral surface hydrophilicity/hydrophobicity due to modification is determined by the enthalpy of the water vapor adsorption isotherm. From the quantity and the affinity to water vapor adsorption, a new wettability index is suggested. The enthalpy of water adsorption relative to liquefaction enthalpy shows that stearic acid and asphaltene deeply modify the calcite toward more oil-wet for treated humidified surfaces. It is interesting to observe that although the presence of a water film on quartz and kaolinite surfaces, enhance the adsorption of N,N-dimethyldodecylamine (NN-DMDA), does not eliminate but reduces the asphaltene adsorption.Graphical abstractMicrocalorimetry set up used for water vapor adsorption enthalpy to determine hydrophilicity/hydrophobicity of modified mineral surfaces.Highlights► Investigation of wettability alteration of different minerals, with SA, NN-DMDA and asphaltene. ► Investigation of the effect of water film on adsorption of SA, NN-DMDA and asphaltene over minerals. ► Developed an approach to determine the wettability index by water vapor adsorption isotherm. ► Estimation of possible molecular orientations of organic adsorbates on the mineral surfaces, interpreted from TGA data.
No preview · Article · Jul 2011 · Colloids and Surfaces A Physicochemical and Engineering Aspects
[Show abstract][Hide abstract] ABSTRACT: The effects of SO42- and Mg2+ on the adsorption/displacement of stearic acid (SA), N,N-dimethyldodecylamine (NN-DMDA) and asphaltene, as oil soluble additives, onto or from calcite, quartz, and clay minerals are addressed in this paper. Thermal gravimetric analysis, isothermal water vapor adsorption, and contact angle methods are used to determine the extent of surface modification and evaluate the hydrophilicity/hydrophobicity of the modified powders and minerals, respectively. The experimental results of the modified mineral surfaces are analyzed using a suggested wettability index based on water vapor adsorption isotherm and contact angle. It is interesting to observe that SO42- and Mg2+ ions enhance hydrophilicity characteristic of the modified calcite surface while SO42- ions have insignificant effect on adsorption of the tested polar components on the silicate minerals. Mg2+ ions enhance the hydrophilicity of quartz and kaolinite surfaces modified by N,N-dimethyldodecylamine. On the other hand Mg2+ ions increase the hydrophobicity of silicate minerals when asphaltene is the surface modifying component. This may be due to bridging of the hydrated Mg2+ ions with asphaltene. The suggested bridging mechanism is also consistent in the case of alteration of calcite surface with asphaltene, however to lesser extent due to the more affinity toward calcite surfaces.
[Show abstract][Hide abstract] ABSTRACT: We have studied the chemical composition, the surface chemistry and the pore structure of holm-oak chars and eucalyptus chars prepared at final heating temperature in the range of 250–1000 °C from two commercial wood charcoals. Our study also includes adsorption–desorption of water vapour at 25 °C on the resulting chars. The samples were characterised by chemical analyses, Fourier transform infrared spectroscopy, adsorption (carbon dioxide, 273 K), mercury porosimetry and scanning electron microscopy. The Dubinin–Serpinsky equation (DS-2) and the Dubinin–Astakhov (DA) equation were applied to analyse the water adsorption data. The final heating temperature affects the chemical composition, the surface chemistry and the pore structure of each char series differently; the differences are of less significance at the highest temperature. The adsorption–desorption of water vapour at 25 °C reflects well the changes produced in the chars; the adsorption occurs in the micropores, and in the non-micropore structure at relative pressures higher than 0.95. The shape of the adsorption isotherms is largely dependent on the microporosity; it changes gradually from type II to type V for the chars with poorly developed microporosity (holm-oak chars), and it is more of type V for the chars with highly developed microporosity (eucalyptus chars). The DS-2 equation fails if type V is less defined, while the DA equation is always applicable and provides micropore volumes close to those determined at p/p0 = 0.95. Hysteresis is always observed; chemisorption occurs: the desorption line begins at saturation pressure and in general tends to meet near zero relative pressures.
No preview · Article · Jul 2010 · Journal of Analytical and Applied Pyrolysis