Isabelle Batonneau-Gener

Tuning the hydrophobicity of mesoporous silica materials for the adsorption of organic pollutant in aqueous solution

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.

Tailoring the Hydrophobic Character of Mesoporous Silica by Silylation for VOC Removal

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.

Adsorptive removal of α-endosulfan from water by hydrophobic zeolites. An isothermal study.

This paper deals with the removal of α-endosulfan from water over HY and steamed HBEA zeolites. Experiments were performed to understand the adsorption mechanisms of α-endosulfan on zeolites and to determine the most efficient adsorbent for the purification of water contaminated by this pesticide. The experiments exhibit that α-endosulfan was adsorbed in the micropores. In the case of HY zeolites an adsorption of α-endosulfan molecules on BrØnsted sites was pointed out, due to a preferential water adsorption in mesopores. Moreover a physisorption of α-endosulfan occurred in micropores. For steamed HBEA zeolites physisorption in micropores was pointed out as the adsorption mode. For both types of zeolites a decrease of the adsorption capacities was noticed when the acidity of zeolites increased. There was also a linear relation between the adsorption capacities of α-endosulfan and the hydrophobicity (HI) of the samples and by determining the values of HI for a type of zeolite it was possible to deduce the uptake of α-endosulfan. The HY(40) sample was the most efficient for the removal of α-endosulfan from water because of preferential adsorption of water molecules in mesopores and lower acidity. For this sample the adsorption capacity for α-endosulfan was about 833.33 mg/g where for the most effective HBEA sample (St700(3)) the adsorption capacity was about 793.65 mg/g.

Improving of the adsorption capacity of halloysite nanotubes intercalated with dimethyl sulfoxide

Algerian halloysite intercalated with dimethyl sulfoxide (DMSO) was prepared. The starting (H) and resulting (H-DMSO) materials were characterized by X-ray powder diffraction, Fourier transformed infrared spectroscopy, thermal analysis, transmission electron microscopy, pore-size distribution analysis, and employed as crystal violet (CV+) adsorbents from aqueous solutions. Intercalation reaches a rate of 95% and increases the basal spacing to 11.2 Å. (CH3)2SO interacts with the inner surface hydroxyls of halloysite through new hydrogen bonds with the S=O groups. The release of DMSO occurs in two phases: a partial elimination at 195 °C and a second part due to the DMSO combustion at 277 °C. The TEM image of H-DMSO reveals halloysite nanotubes (HNTs) polydisperse in length and diameter. A heterogeneous distribution in the nanotube size was highlighted with pore diameters of 10–11, 20.6, 28.6, and 37.0 nm, in correlation with transmission electron microscopy. The Redlich–Peterson equation describes efficiently the CV+ adsorption onto the modified sample. H-DMSO adsorbs 93.6 against 50.9 mg g−1 for the starting material. This improving of the adsorption capacity of DMSO-intercalated HNTs, was explained via the behavior of the intercalated DMSO molecules. Intercalation constitutes a key procedure for developing new nanocomposites, attractive in technological applications, such as effective adsorbents.

Spontaneous Ionization of N‐Alkylphenothiazine Molecules Adsorbed in Channel‐Type Zeolites: Effects of Alkyl Chain Length and Confinement on Electron Transfer

The mere mixing of N-alkylphenothiazines with three channel-type acid zeolites with various structures (ferrierite, H-MFI, and mordenite) induces the spontaneous ionization of the heterocyclic molecule in high yield upon adsorption. The diffuse reflectance UV-visible absorption and Raman scattering spectra show that the accessibility of the highly polarizing acid sites is not indispensable to induce the spontaneous ionization process. Due to their particularly low ionization potential values (6.7 eV), the adsorption of the molecules on the external surface or in the inner volume is the key parameter to generate the radical cation. However, the ionization yield and charge stabilization are intimately correlated to the possibility of the zeolites accommodating molecules inside their channels. Moreover, the higher electrostatic field gradient induced by high confinement is required to favor the second ionization and dication formation. The alkyl chain length plays a decisive role by either slowing down the diffusion process or blocking the molecule at the pore entry. Therefore, the efficiency of the ionization process that depends on the number of adsorbed molecules decreases significantly from phenothiazine to the N-alkylphenothiazines. The spectral data demonstrate that deformation of the alkyl group is necessary to allow the diffusion of the molecules into the channels.

Influence of the Atmosphere on Dodecen-1 Isomerization

Abstract In industrial adsorption processes carried out in liquid phase, charges are not always degassed before being injected and so they may contain dissolved oxygen that could induce undesired reactions responsible for premature adsorbent aging. To check this, we compared the reactivity of dodecen-1 in liquid phase at 150°C under air and under argon on two differently active solids, NaY and NaHY-6.7%. It shows that the oxidant atmosphere has a significant influence on the dodecen-1 reactivity. Oxygenated compounds are formed and irreversibly adsorbed on zeolite, leading to the filling of the porosity. This effect is more marked on the less active solid.