Study of physisorbed and chemisorbed carbon dioxide (CO 2 ) species was carried out on the NaX zeolite modified by cationic exchanges with bivalent cations (Ca 2+ and Ba 2+ ) by temperature-programmed desorption of CO 2 (CO 2 -TPD).Others results were obtained by infrared to complete the study.The results of this research showed, in the physisorption region (213 -473 K), that the cationic exchanges on NaX zeolite with bivalent cations increase slightly the interactions of CO 2 molecule with adsorbents and/or cationic site.Indeed, the desorption energies of physisorbed CO 2 obtained on the reference zeolite NaX (13.5 kJ•mol -1 ) are lower than that of exchanged zeolites E-CaX and E-BaX (15.77 and 15.17 kJ•mol -1 respectively).In the chemisorbed CO 2 region (573 -873 K), the desorption energies related to desorbed species (bidentate carbonates:CO -) on the exchanged zeolites E-CaX and E-BaX are about 81 kJ•mol -1 , higher than the desorbed species (bicarbonates:on the reference R-NaX (62 kJ•mol -1 ).In addition, the exchanged E-BaX zeolite develops the secondary adsorption sites corresponding to bicarbonates species with desorption energies of 35 kJ•mol -1 lower to desorption energies of bicarbonates noted on the reference zeolite NaX.

The study of the influence of operating parameters of dynamic adsorption on fixed-bed column of manganese oxoanions (MnO4-) in aqueous media on granular activated carbon (GAC), prepared from the shells palm nuts of Gabon, was carried out. The operating parameters studied were the particle size, the concentration of the initial solution (C0) of MnO4-, the flow rate (D) and the pH of the media. The results obtained on the study of the influence of operating parameters show that the best adsorption capacities at saturation (Qsat) of MnO4- ion on the CAG were obtained with particle size between 0.04 -1); with flow rate of 3 mL.min-1 (8.36 mg.g-1) and when the pH of the initial solution was equal to 3.5 (27.01 mg.g-1). Also, these results showed that the bed of prepared GAC appeared more effective when C0 was low (10 mg.L-1). The kinetic models of the different studies carried out show that the pseudo-first-order kinetic model best describes the adsorption of MnO4- ions on the GAC. The results of the intraparticle diffusion model indicate that the adsorption of MnO4- follows a multi-step process and that the intraparticle diffusion is not the limiting step. In addition, the surface adsorption plays a predominant role in the adsorption mechanism of MnO4- ions on activated carbon studied in fixed-bed column dynamics.

Pollution of surface water and groundwater by bulky molecules such as pesticides has been recognized as a major problem in many countries due to their persistence in aquatic environment and potential adverse health effects. The main purpose of this study is the development of a capable adsorbent to remove these bulky molecules from wastewater such as the pesticide Mesosulfuron-Methyl (MM) by reducing the diffusion path, to overcome the problems of diffusional limitations on microporous adsorbents. The adsorption of mesosulfuron-methyl (MM) from aqueous solution is curried out using treated acid HY zeolite. Batch sorption equilibrium and kinetic experiments are conducted to evaluate the efficiency of these materials. Parent zeolites and their derivatives have been characterized by nitrogen adsorption–desorption, pyridine chemisorption followed by infrared spectroscopy and X-ray fluorescence. The acid treatment leads to an increase in the specific surface from 691 to 853 m2 g− 1 for HY(30) and from 631 to 806 m2 g− 1 for the HY(16.6) zeolites. It also leads to a reduction in Lewis acidity from 74 to 25 µmol g− 1 and from 135 to 31 µmol g− 1 for HY(30) and HY(16.6) zeolites respectively, and increases the adsorbent-adsorbate interaction. The adsorption capacity increased from 83 to 99 % after acid treatment. The equilibrium adsorption time is decreased from 15 h to 10 min for the HY(30)_A and from 20 h to 20 min for the HY(16.6)_A for an initial concentration of 20 mg L− 1. The adsorption capacity depends on the pH solution, and the neutral form of the MM is more easily adsorbed into zeolite than the dissociated form via the framework bridged oxygen atoms. For all the samples, the pseudo-second-order kinetic model fits very well with the experimental data. In the case of the modified zeolites, the approaching equilibrium factor Rw decreases from 0.08183 to 0.00008 when the Lewis acid sites decrease; indicating that the equilibrium is reached more quickly. S-shape adsorption isotherms indicates that cooperative adsorption phenomena. Nevertheless, the shape of acid treated zeolites evolves to an L type indicating a significant enhancement of the adsorbent – adsorbate interactions inducing better adsorption efficiency. Mesosulfuron-methyl adsorption has been successfully enhanced after acid treatments of zeolites HY.

CuO nanosheets have been synthesized via the hydrothermal method at 120°C for 3 h, without using any surfactant or structure directing agent. The structural and morphological characteristics of the copper oxide have been examined with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR), scanning electron microscopy (SEM), UV-visible spectroscopy, and BET surface area analyses. The as-prepared materials have been used for the catalytic degradation of methylene blue dye (MB) in the presence of hydrogen peroxide (H 2 O 2 ). The results have demonstrated that the CuO nanosheets showed an enhanced catalytic performance with good reusability up to the fourth cycle. In addition, the effect of several parameters, including the catalyst and hydrogen peroxide quantities, the reaction temperature and the dye concentration have been also investigated for the degradation reactions of the MB. The kinetic data have revealed that the dye degradation process follows a pseudo-first order model. It should be noted that the activation energy ( E a ), enthalpy (Δ H # ), entropy (Δ S # ) and activation free energy (Δ G # ) have been calculated for the oxidation reaction. The CuO nanosheets exhibite an excellent catalytic performance for the degradation of MB. This also provides a newer route for promising dye degradation in wastewater treatment.

Study of preferential adsorption sites of H 2 O on NaX and BaX zeolites was carried out after adsorption/desorption of carbon dioxide (CO 2 ). The profiles of CO 2 desorption revealed two distinct zones. The first one, at low temperature (T < 533 K), corresponding to physisorbed CO 2 where BaX zeolite has an energy of adsorption higher than that of NaX as well as strong interactions of adsorbent/adsorbate. The second one (533–623 K) corresponds to the chemisorbed CO 2 . The presence of water influences CO 2 adsorption. The effect is more important for NaX than for BaX. For NaX, water occupies the adsorption sites of CO 2 between 373 and 483 K. In contrast, BaX preserves a majority of adsorption sites of physisorbed CO 2 in the presence of water, in particular the adsorption sites located in the interval of temperature 423–533 K.

In the present study, HY zeolite with various Si/Al ratios have been used as adsorbents for the removal of a cationic dye; methylene blue, from aqueous solution using a batch process, and a comparative study with bentonite was conducted. Characterizations of the adsorbents were carried out by nitrogen adsorption–desorption, pyridine chemisorption followed by infrared spectroscopy and X-ray fluorescence. The effects of various parameters such as contact time, initial MB concentration, adsorbent concentration and solution pH were investigated. The adsorption of methylene blue on the zeolites is directly related to the Brønsted acidity where each molecule of MB corresponds to one Brønsted acid site. This means that the adsorption mechanism occurs via a cation exchange. So, adsorption of MB can be used to determine the Brønsted acidity of HY zeolites. The highest removal efficiency (181 mg g−1) corresponding to 86% of the abatement rate has been obtained with the bentonite. At lower dye concentrations (≤ 50 mg L−1), HY (16.6) and bentonite have a close adsorption capacities, 93 mg g−1 (97%) and 96 mg g−1 (99%) respectively. For both material types, the pseudo-second-order kinetic model fits very well with the experimental data. Equilibrium data fitted well the Langmuir isotherm model in the studied concentrations range of MB.

Bulky organic pollutants such as pesticides and pharmaceutical residues are found in wastewater and are difficult to remove by microporous adsorbents because of their large size. Hierarchical zeolites as potential adsorbents for removal of heavy organic pollutants from aqueous phase are investigated. Hierarchical HMOR and HZSM-5 samples were obtained by post-synthesis desilication by alkaline treatment followed or not by acid leaching of the microporous parent zeolites. The obtained materials have been fully characterized by X-ray diffraction, N-2 physisorption, elemental analysis, pyridine adsorption followed by FTIR. Alkaline treatments lead to a framework desilication creating mesopores with the preservation of the Bronsted acidity. Material adsorption behaviors are studied in pesticide, mesosulfuron-methyl (MM), removal from aqueous phase. For all the materials, adsorption kinetics are well described by a pseudo-second order model indicating that MM molecules are chemisorbed via acido-basic interaction of the neutral form. Sorption isotherms are S-shape isotherms for the parent samples and evolve to more favorable concave isotherms for highly mesoporous samples. Thus hierarchical zeolites exhibit higher sorption rate and capacities than microporous ones. Soft acid leaching treatments carried out after alkaline one help to clean the zeolite porosity from silica debris and to enhance significantly zeolite adsorption efficiency. (C) 2015 Elsevier Inc. All rights reserved.

A thermodynamic and kinetic study was realized by competitive and non-competitive adsorption for the separation of n-hexane isomers. Two mixtures of n-C6/3MP and 3MP/23DMB were studied. For the single component adsorption the maximal adsorption capacity were close for the different isomers while the diffusivity for the 23DMB isomer was outstandingly low due to steric hindrance. For the competitive adsorption we had from an initial proportion of 50% for each sorbate an adsorption of 34% and 66% respectively for 3MP and n-C6. For the 3MP/23DMB mixture we had an adsorption of 62% and 38% for 3MP and 23DMB respectively. For the two mixtures the selectivity of the zeolite increased with the adsorption capacity and decreased after the values of 0.63 mmol/g and 1.65 mmol/g respectively for the 3MP/23DMB and n-C6/3MP mixtures. The adsorption rates were lower in the case of competitive adsorption and a kinetic separation could be envisaged for the improvement of the octane number.

The development of building materials to reduce the concentration of NO2 is growing interest in a world where the air quality in urban areas is affected by the car traffic. The main binder in concrete is the cement paste that is partly composed of calcium hydroxide. This alkaline hydrate composing the hardened cement paste shows a high BET surface area (close to 100 m2.g−1) and can absorb low-concentrations of NO2. However, the presence of CO2 in the atmosphere limits the de-polluting effect of reference cement paste, mainly due to carbonation of the alkaline hydrates (reaction leading to the formation of calcium carbonate). The results established in this paper demonstrate that the addition of activated carbon in the cement paste, because of its very high BET surface area (close to 800 m2.g−1) and its specific reactivity with NO2, can significantly improve and prolong the de-polluting effect in presence of CO2 and even after complete carbonation of the surface of the cement paste.

The Volatile Organic Compounds (VOCs) released into indoor air of confined spaces increase the risk of pulmonary diseases for numerous people. This study is a first approach to determine the adsorption of hardened cement pastes exposed to VOCs and aims to enhance this phenomenon by using activated carbon as cement additive. The entrapment of acetaldehyde by the cement-based hydrates is quantified and is confirmed by testing hardened cement paste. However, the abatement of acetaldehyde tends to decrease due to carbonation or in presence of a significant relative humidity. The adsorption of toluene by reference cement pastes is negligible but is significantly improved by the addition of a small fraction of activated carbon powder into the mix. The desorption of toluene is not detected after the heating of the hardened cement pastes until 50 degrees C, justifying the study of a new range of construction materials limiting the VOCs-based air-pollution in confined spaces. (C) 2015 Elsevier Ltd. All rights reserved.

Fundamental study of carbon dioxide (CO2) physisorption and chemisorption is investigated with the NaX zeolite modified by addition of magnesium oxide (mechanical mixtures) or by impregnation of magnesium acetate (impregnated zeolites). Defined by their textural properties, these samples are characterized using the CO2 adsorption and desorption. Complementary results are obtained with infrared experiments. This study enabled to conclude that the addition of small amounts of magnesium oxide improved the interactions of physisorbed CO2 with the materials without noticeable increase of the chemisorption. The CO2 desorption energies are increased when small magnesium amounts are added. As shown with the deconvolution of the thermal desorption curves, all the "high" temperatures physisorbed species (300-400 K) are improved at the expense of the intermediate ones when the samples are modified. (C) 2013 Elsevier Inc. All rights reserved.

The NOx pollution produced by road traffic in confined volumes, such as tunnels, is an issue for public health. This work focuses on the mechanisms of NOx removal by modified cement pastes. The samples (made of pure synthetic powders or cement paste cylinders) are continuously exposed to 220 ppbv of NO and/or 110 ppbv of NO2 gas. The ability for the main hydrates (such as Ca(OH)2 and C–S–H) to trap NO2 is then quantified. After the leaching of samples, the chromatography experiments show that the adsorbed NO2 is transformed in nitrate and nitrite ions by a disproportionate mechanism. The addition of activated carbon into cement paste enhances the NO2 abatement, which is not influenced by carbonation. The NO2 abatement by the activated carbon materials is also stable between 20 and 50 °C, revealing a competition between the disproportionate reaction and the gas adsorption.

The ability of various as-prepared and organically modified MCM-41 and HMS mesoporous silica materials to behave as efficient adsorbents for organic pollutants in aqueous solution was investigated by using different surface functionalization procedures, so as to adjust their hydrophilic/hydrophobic balance. The hydrophilic and organophilic properties of the parent silica materials and their corresponding surface functionalized counterparts were studied by using water and toluene adsorption isotherms. Their quantification was determined by the hydrophobic static index value (HI(static)), as well as by the silanol and organic group densities after the functionalization step. A clear correlation could be found between the HI(static) values and either the superficial silanol density, or the amount of organic moieties grafted or incorporated to the silica materials. For the highly organically functionalized samples, the residual superficial silanol groups (<50%) are sufficiently isolated from each other so as to prevent the water capillary condensation within the pores, thereby leading to an increased hydrophobic character of the resulting mesoporous silica. Those hydrophobic samples, for which the water liquid meniscus formation within the mesopores was minimized or avoided, exhibited a storage capacity for an organic pollutant (N,N-diethyl-m-toluamide, DEET) in aqueous solution more than 20 times higher than that of the corresponding unmodified sample, independently of the silica nature (MCM-41 or HMS). For all calcined and silylated samples, the DEET maximum adsorption capacities determined by the Langmuir model could be correlated with the silica surface coverage by trimethylsilyl groups and thus with the remaining silanol amount.

MCM-41 and non-ordered mesoporous silica were modified using hexamethyl-disilazane (HMDS). The hydrophobic and hydrophilic properties of grafted materials were studied and compared to a purely all silica BEA zeolite by using competitive and noncompetitive water toluene adsorption. A linear correlation between the silylation degree and the hydrophobicity measurements has been found for MCM-41 materials. Even if highly silylated MCM-41 material have more hydrophilic sites (silanol groups) than all silica zeolite, water molecule condensation is not observed because these sites are isolated. Thus, the highly silylated MCM-41 sample exhibits not only hydrophobicity 2.3 times higher than all silica BEA zeolite but also possesses a storage capacity for toluene and chlorobenzene 3 times higher than this zeolite. In competition with water, the organic molecule (toluene or chlorobenzene) adsorption is always favored even if water adsorption is enhanced by chlorobenzene polarity.

A thermodynamic study was realized by competitive adsorption over zeolitic adsorbents to determine the efficiency of these solids for the separation of monobranched and dibranched isomers of n-hexane. The effect of the zeolite structure was studied. The medium-pores ZSM-5-type zeolites were better than the large-pores BEA and MOR zeolites. The size and number of the extraframework cations had an important influence on the efficiency of the separation over ZSM-5 zeolites. The sodic Na(6)ZSM-5 sample was found to be the better adsorbent for the separation of the studied mixture because of steric hindrance induced by the presence of Na+ cations in the zeolite structure. The initial composition of the mixture also had an important influence on the separation. In fact, when the initial mixture was equimolar the monobranched isomer was preferentially adsorbed, whereas when the molar percentages of the isomers were different in the initial mixture the adsorption of the majority isomer was favored. The temperature of the adsorption was another important parameter influencing the separation. Indeed, when the temperature of adsorption was low the separation was more effective. At an adsorption temperature of 333 K the Na(6)ZSM-5 sample was the most efficient by adsorbing 65% of the monobranched isomer and only 35% of the dibranched isomer.

A hydrophobicity study was realized for a series of siliceous and steamed BEA, HZSM-5 and HY zeolites. The hydrophobicity was assessed according to the Weitkamp method by performing water and toluene competitive adsorption experiments. The Weitkamp hydrophobicity indexes (HI) were determined for each sample. The BEA samples were the most hydrophobic samples and there was a linear correlation between HI values and the Brønsted acidity. This was explained by a water preferential adsorption on the Brønsted acidic sites. On the contrary for the HZSM-5 and HY samples the decrease of HI with the Brønsted acidity was not linear. This was explained by a water preferential condensation in the available porous volume of the zeolites instead of water chemisorption on the Brønsted acidic sites. For the highly mesoporous samples the water adsorption was essentially localized in the mesopores so the hydrophobicity of these samples remained almost constant despite important variations of the Brønsted acidity. Due to their microporous structure, the HZSM-5 samples were more hydrophobic than the HY samples for a same value of Brønsted acidity and Si/Al ratio, despite a lower toluene adsorption for HZSM-5 samples because of steric hindrance of toluene. In the case of the competitive adsorption of water and toluene, the values of HI were essentially depending on the localization of water molecules and the global water uptake, despite a noteworthy increase of the toluene uptake.

A series of BEA samples were dealuminated from a parent sample (Cal) by steaming and acid leaching. The hydrophobicity of these samples was compared to the hydrophobicity of a purely siliceous BEA. The hydrophobicity was assessed by Weitkamp original or modified relation for water and toluene competitive and non-competitive adsorption under static or dynamic conditions. According to sample dealumination method, water adsorption sites were identified to be Brønsted acidic sites, silanols nests, extra-framework aluminum species (EFAl), microporous and mesoporous available volume. Toluene molecules were mainly physisorbed by capillary condensation in microporous and mesoporous volume. Hydrophobicity indexes achieved by non-competitive adsorption under static or dynamic conditions were not a good assessment of zeolites hydrophobicity in operating industrial conditions. On the other hand water and toluene competitive adsorption under dynamic conditions as described by Weitkamp remains an appropriate method to estimate the hydrophobicity of zeolites. According to the nature of treatment, hydrophobicity index (HI) increases when aluminum content decreases. This increase is moderate for acid leached samples and pronounced for steamed samples.

A series of HBEA dealuminated samples was prepared by treatment with HCl or steaming of a parent sample. Samples were characterized by XRD, elemental analysis, nitrogen adsorption and pyridine adsorption–desorption followed by IR spectroscopy. The hydrophobicity coefficient, determined by separated static adsorption of water and toluene was used as a quantitative measurement of the hydrophobic properties. It is shown that dealumination causes drastic increase of the hydrophobicity of the different samples. The increase of the hydrophobic character is rather higher for steamed samples than for the acid-leached ones. For the same number of Brønsted sites, the water uptake on the steamed samples corresponds to 11 molecules by unit cell whereas it is 17 for the acid-leached samples. The low hydrophobic character of acid-leached samples is attributed to the creation of hydroxyl nests during acid treatment.

The adsorption and the kinetics of diffusion of n-butane and i-butane on three HFER were studied as a function of the global Si/Al ratio from 6 to 19. The capacity of adsorption, the kinetics of diffusion and the heat of adsorption are higher for n-butane than for i-butane. N-butane is preferentially adsorbed into the micropores while i-butane is rather adsorbed into the micropores and mesopores. The sites of adsorption are energetically homogeneous for sample HFER-10 whereas they are heterogeneous for HFER-6 and HFER-19.

The acidic character of 5A zeolite as a function of the calcium content has been explored by different techniques: propylene adsorption experiments, ammonia thermodesorption followed by microgravimetry and FTIR spectroscopy. Propylene is chemisorbed and slowly transformed in carbonaceous compounds (coke) which remain trapped inside the zeolite pores. The coke quantities increase with the Ca2+ content. Olefin transformation results from an oligomerization catalytic process involving acidic adsorption sites. Ammonia thermodesorption studies as well as FTIR experiments have revealed the presence of acidic sites able to protonate NH3 molecules. This site number is also correlated to the Ca2+ ion content. As it has been observed for FAU zeolite exchanged with di- or trivalent metal cations, these sites are probably CaOH+ species whose V-as(OH) mode have a spectral signature around 3567 cm(-1).