Habiba Nouali

Synthesis of purely silica MFI-type nanosheets for molecular decontamination

Conventional syntheses of zeolites generally lead to the formation of crystals whose sizes are of the order of several microns which is not detrimental in a large number of industrial applications. However, the capacity and kinetics of pollutant adsorption which are sensitive to diffusion phenomena, surface and porous volume could potentially be improved by the use of nanocrystal or hierarchical zeolites (micro/mesoporous or micro/macroporous). Indeed, zeosil nanosheets hold great potential because of their small size and their high porous volume that promote access of pollutants and increase the adsorption capacity. Herein, silicalite-1 zeosil with a lamellar morphology was successfully synthesized under hydrothermal conditions (110 °C, 10 days) using diquaternary ammonium as structuring agent. Compared to the conventional silicalite-1 material, the porous volume of the synthesized nanosheets determined from the N2 adsorption–desorption isotherms was found to be multiplied by 3.5 (0.62 cm3 g−1) without altering the microporous volume (0.18 cm3 g−1). This result was also confirmed by the increase of the n-hexane adsorption capacity and kinetics in the silicalite-1 nanosheets compared to the conventional silicalite-1. This approach indicates a new way for obtaining zeosil materials of controlled sizes and shapes for molecular decontamination.

Water intrusion–extrusion experiments in ZIF-8: impacts of the shape and particle size on the energetic performances

The energetic performances of “ZIF-8–water” systems were evaluated using intrusion–extrusion of water under high pressure. Depending on the shape (spherical, cubic or rhombic dodecahedron) as well as the crystallite size (nanometric or micrometric scale), the energetic behaviour of the “ZIF-8–water” system can be modified.

Energetic performances of pure silica STF and MTT-type zeolites under high pressure water intrusion

Experimental water intrusion–extrusion isotherms were performed at room temperature on two pure silica MTT- and STF-type hydrophobic zeolites (zeosils) with 1D channel and cage pore systems, respectively by applying or releasing a high hydraulic pressure. These zeosils were obtained by hydrothermal synthesis in fluoride medium and characterized by structural and physicochemical methods before and after water intrusion. The system “MTT-type zeosil–water” displays a spring behavior with an intrusion pressure of 176 MPa and a stored energy of 5.3 J g−1. No influence of water intrusion on the structure of MTT-type zeosil was found. The “STF-type zeosil–water” system shows a combination of shock-absorber and bumper behavior in the first cycle with an intrusion pressure of 51 MPa. Nevertheless in the following cycles the system demonstrates a spring behavior with an intrusion pressure of 38 MPa. Such behavior can be explained by the formation of silanol groups under intrusion in some pores confirmed by NMR spectroscopy and TG data.

Effect of nanofiber diameter on water absorption properties and pore size of polyamide-6 electrospun nanoweb

Electrospinning is a common method used to produce nanofiber from almost all types of polymers. By changing effective parameters of this process, especially polymer solution concentration, it is possible to produce nanoweb that consists of nanofibers with different averages of diameter. Here, the effect of nanofibers’ diameter on textural properties (water absorption time and pore size) of polyamide-6 nanoweb has been studied. In this way, three nanowebs with nanofibers’ average diameter of 111, 151, and 318u2009nm were electrospun from three different concentrations of 15, 20, and 25u2009wt%, respectively. Contact angle measurement and mercury porosimetry were used to investigate the nanowebs’ water absorption properties and porosity (pore size). The results from the water absorption test demonstrated that the absorption time of a 2u2009µL water droplet was remarkably shorter for electrospun nanoweb with larger nanofiber diameter. Nanowebs electrospun from 15 and 20u2009wt% concentrations had roughly the same absorption regime, while for 25u2009wt% the absorption regime was totally different. Mercury porosimetry of electrospun nanowebs revealed that the pore size in the nanoweb structure decreased by decreasing average diameter of nanofibers. The results of this study showed that contact angle measurement and mercury porosimetry tests could be used as complementary methods to scanning electron microscopy and atomic force microscopy and presented as promising methods to study the textural and physical properties of electrospun nanowebs.

Influence of LiCl aqueous solution concentration on the energetic performances of pure silica chabazite

In order to study the energetic performances of different “pure silica chabazite–LiCl aqueous solution” systems, intrusion–extrusion experiments were performed under high pressure. Depending on the LiCl concentration in the aqueous medium (0 M, 5 M, 10 M, 20 M), an increase of the stored (4.4, 9.9, 13.5, 24.3 J g−1) and restored (2.6, 8.1, 11.8, 20.5 J g−1) energies are observed. Therefore, compared to the “pure silica CHA–H2O” system, the stored energy is increased by 5.5 times for the “pure silica CHA–20 M LiCl” one. The zeolite samples were characterized (XRD, TG, NMR spectroscopy, N2 adsorption and SEM) before and after the intrusion–extrusion process in order to better understand the influence of the LiCl concentration on the system behavior.

Nanocrystalline iron oxide synthesised within Hierarchical Porous Silica prepared by nanoemulsion templating

PIC (Phase Inversion Composition) O-W nanoemulsions was used as a template for the synthesis of Hierarchical Porous Silica (HPS), and the oil phase of the nanoemulsion was used as a nanoreactor for the preparation of magnetic gamma-Fe(2)O(3) nanoparticles, confined within the silica matrix.

Structure-performance relationship in CuO/SBA-15-type SOx adsorbent: evolution of copper-based species under different regenerative treatments

Sulphur oxides (SOx) represent a major air pollutant and are controlled by national and international regulations. CuO/SiO2 materials are known as SOx trap materials. However, their large-scale development is still hampered by the sintering of the active phase over multiple adsorption/regeneration cycles, leading to the progressive decrease in SOx adsorption capacities of the adsorbent. In this work, SBA-15 organised mesoporous silica was functionalized with highly dispersed Cu2+-based species. The as-obtained adsorbent was then assessed as a regenerable SOx trap material. An extended characterisation was performed along with adsorption/regeneration cycles to correlate the evolution of the copper species with the performance of the adsorbent under different regenerative treatments. Thermal regeneration at 600 °C under pure N2 leads to the formation of Cu+-based species, enabling a significant increase in SOx chemisorption efficiency, which nevertheless decreases during the subsequent cycles due to progressive sintering of the active phase, leading to bulky copper(II) oxide particles. Regeneration under reductive conditions (0.5 vol% of H2 in N2) was then investigated as a way to decrease the regeneration temperature and limit this sintering process. It was found that the general behaviour of the copper-based species was very sensitive to the regeneration temperature. At 600 °C, the active phase was completely converted into large metallic copper particles, giving rise to a fast decrease in SOx adsorption capacity of the adsorbent due to partial obstruction of the SBA-15 silica porosity. Conversely, when this regeneration was performed at 280 °C, no decrease in performances was noticed, and the copper species remained as a highly dispersed phase on the silica support.

Dioxin and 1,2-dichlorobenzene adsorption in aluminosilicate zeolite Beta

The influence of sodium cations content in zeolite Beta crystals of different sizes (between 200xa0nm and 2 μm) on the adsorption of pollutants (dioxin and polychlorobenzene) is investigated. In this study, protons which balance the negative charge of the zeolitic framework are partially replaced by sodium cations. Chemical, structural and textural analyses performed on the exchanged crystals indicate that the exchange rates reached 75–80xa0% and that the structure of zeolites is preserved. Adsorptions of pollutants in zeolite Beta samples were successfully carried out using 1,2-dichlorobenzene (gas phase) and 2,3-DiChloroDibenzo-p-Dioxin: 2,3-DCDD (liquid phase) but reveal different behaviors. Indeed, all samples adsorb the same amount (around 7 molecules) of 1,2-dichlorobenzene per unit-cell of zeolite, whereas the dioxin adsorption amounts increase with the amount of sodium cations. Compared to their protonic forms, the dioxin adsorption capacities were multiplied by a factor of 1.3 for the sodium exchanged small crystals (size between 200xa0nm and 1 μm) and by a factor of 4 for the sodium exchanged microcrystals (size between 1 and 2 μm) for an equilibrium concentration of 2,3-DCDD of 0.5xa0mmol/L in both cases.

Performance of surfactant-modified *BEA-type zeolite nanosponges for the removal of nitrate in contaminated water: Effect of the external surface

Hierarchical *BEA-type nanosponges zeolite with a high external surface area (116u2009m2.g-1) and small crystal size, synthesized in the presence of a dual-porogenic organic compound, were modified with a cationic surfactant (HDTMA+Br-: hexadecyltrimethyl ammonium bromide) in order to create a new anion exchanger system: the surfactant-modified zeolite nanosponges (SMZNS). For comparison, two other surfactant-modified *BEA-type zeolite materials, SMZMC and SMZNC, were obtained by modifying the synthesized conventional micron-size microcrytals and nanocrystals *BEA-type zeolite with HDTMA+Br-, respectively. Textural and structural properties were determined for the three prepared materials using N2 adsorption/desorption analysis, XRD, SEM, and TEM. Nitrate adsorption isotherms were drawn in a large concentration range [0.8-24.2u2009mmol.L-1] and fitted with Langmuir isotherm model. The maximum nitrate removal capacity (1338u2009mmol.Kg-1/83u2009mg.g-1) was obtained for SMZNS material. This value is the highest ever observed for nitrate removal using surfactant-modified zeolite. The nitrate removal kinetics were fitted with the pseudo second-order model for both materials SMZNS and SMZNC.

Porous sorbents for the capture of radioactive iodine compounds: a review

The number of studies on the capture of radioactive iodine compounds by porous sorbents has regained major importance in the last few years. In fact, nuclear energy is facing major issues related to operational safety and the treatment and safe disposal of generated radioactive waste. In particular during nuclear accidents, such as that in 2011 at Fukushima, gaseous radionuclides have been released in the off-gas stream. Among these, radionuclides that are highly volatile and harmful to health such as long-lived 129I, short-lived 131I and organic compounds such as methyl iodide (CH3I) have been released. Immediate and effective means of capturing and storing these radionuclides are needed. In the present review, we focus on porous sorbents for the capture and storage of radioactive iodine compounds. Concerns with, and limitations of, the existing sorbents with respect to operating conditions and their capacities for iodine capture are discussed and compared.