T. Jean Daou

Effect of Poly(ethylene glycol) Length on the in Vivo Behavior of Coated Quantum Dots

The use of nanoparticles, either for the delivery of drugs or for imaging contrast agents, or a combination of both (theranostics), is very appealing in biological and biomedical research. The design of high-quality NIR-emitting quantum dots (QDs), with outstanding optical properties in comparison to that of organic dyes, should lead to novel contrast agents with improved performance for optical and multimodal imaging. Moreover, these nanocrystals could also be used for exploring therapeutic applications, such as drug delivery or phototherapy. In this article, we report the coating of commercial ITK705-amino QDs with methoxy-terminated poly(ethylene glycol) (PEG) of different chain lengths. Homogeneous QD solutions that are stable over extended periods of time were prepared. The impact of the particle coating on their in vivo fate after tail i.v. injection was studied by fluorescence imaging. The speed of the first pass extraction of the coated QDs toward the liver decreased with the PEG length, whereas the hydrodynamic diameter of the particles was increased.

One-pot structural conversion of magadiite into MFI zeolite nanosheets using mononitrogen surfactants as structure and shape-directing agents

MFI-type materials with a lamellar morphology were successfully synthesized by using mononitrogen surfactants specifically designed by molecular modelling. The mononitrogen surfactants directed the recrystallization of a crystalline layered polysilicate formed in situ, the magadiite, into a zeolite ZSM-5. Moreover, the surfactants allow the preservation of the lamellar shape of the magadiite and inhibit a further growth into one dimension, leading to the formation of zeolite ZSM-5 nanosheets with a thickness comprised between 2 and 3 nm and a Si/Al ratio of 24. This simple approach paves a new way for obtaining zeolite materials of controlled size and shape for specific catalytic applications.

The influence of the nature of organosilane surfactants and their concentration on the formation of hierarchical FAU-type zeolite nanosheets

FAU-type zeolite (NaX) materials were synthesized in the presence of 5 organosilane surfactants [(CH3O)3SiC3H6N(CH3)2–CxH2x+1]Cl (x = 4, 8, 12, 16, 18) (denoted QASiCx) in order to introduce intracrystalline mesoporosity in the FAU-type structure. The influence of the nature of organosilane surfactants (length of the alkyl chain) and their concentrations in the synthesis medium was investigated to determine their impact on the formation of hierarchical FAU-type zeolite nanosheets. Under the basic conditions of faujasite X synthesis, (CH3O)3Si– bonds hydrolyze to –Si–OH, and yield –Si–O–Al- and –Si–O–Si-linkages that anchor to a zeolite framework. These linkages and the formation of micelles by the alkyl chains of the surfactants lead to the formation of mesopores and inhibition of the NaX crystallite growth, leading to the formation of FAU-type nanosheets depending on the alkyl chain length. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that FAU-type zeolite nanosheets were obtained only using surfactants composed of a minimum twelve carbon alkyl chain. X-ray diffraction results revealed that the optimum concentration of the organosilane to obtain a pure FAU-type material is 0.011 M. Above this concentration, the impurity phase and amorphous materials are observed. This simple approach paves a new way for obtaining hierarchical zeolite materials of controlled porosity by a direct approach for specific catalytic applications.

Adsorption kinetics and equilibrium of phenol drifts on three zeolites

In this study, the sorption of phenol drifts was studied by performing batch kinetic sorption experiments. The equilibrium kinetic data was analyzed using the pseudo-second-order kinetic model. Fowler-Guggenheim model gives a perfect fitting with the isotherm data. The influence of porous structure of a zeolite particle on phenol adsorption from aqueous solutions is analyzed and discussed. The adsorption for phenol drifts on zeolite was proved to be an exothermic process. Thus the solubility of the phenolic compound and the pH of the solution play also an important role in adsorption phenomena.The relative affinity of the phenolic compound toward the zeolite was related to the electron donor-acceptor complexes that were formed between the basic sites on the zeolite (oxygen) and hydrogens (acidic site) of the phenols. Finally zeolite seems to be an efficient adsorbent; it can be easily regenerated by methanol leaching.

Impact of extreme downsizing of *BEA-type zeolite crystals on n-hexadecane hydroisomerization

A series of *BEA-type zeolites with crystal sizes ranging from few nanometers to micrometers were synthesized. These materials were then transformed into bifunctional catalysts by platinum loading and tested in n-hexadecane isomerization. The behavior of Pt/H-*BEA catalysts depends on several parameters such as the balance between the platinum and acid functions, the metal particle size and the zeolite crystal size. In order to design an “ideal” bifunctional catalyst, the metal and acid sites must be well balanced to avoid the cracking of isomer products at low conversion, the metal must be well dispersed in order to inhibit the hydrogenolysis side reactions, and the crystal size must be as small as possible to maximize the isomer yield. But, the extreme decrease of the zeolite crystal thickness to few zeolite unit cells lowers the turnover frequency of acid sites and favors the metal sintering.

MFI-type zeolite nanosheets for gas-phase aromatics chlorination: a strategy to overcome mass transfer limitations

The continuous gas–solid (environmentally-friendly) chlorination of deactivated arenes using trichloroisocyanuric acid (TCCA, C3N3O3Cl3) as a chlorination agent was chosen to compare the catalytic performances of various MFI-type catalysts in a reaction demanding a strong acidity. Mass transfer limitations were also evaluated by reacting either chloro- or nitrobenzene through a ZSM-5 zeolite porous network having different crystal sizes and morphologies. Whereas, the reaction rate was completely controlled by internal diffusion in 10–15 μm-sized big ZSM-5 zeolite crystals (Weisz modulus, ϕbig crystals ∼ 10), the impact of internal diffusion could be ruled out for ZSM-5 nanocrystals (200–400 nm) and in stacked ZSM-5 nanosheets (thickness 2 nm). Based on reactivity differences in arene halogenation between the two nano-sized ZSM-5 zeolites, we were able to estimate the quantity of mild acidic silanol groups in ZSM-5 nanosheets to roughly 1/3 of the total amount of BrOnsted acid sites.

Hydraulic Performance Modifications of a Zeolite Membrane after an Alkaline Treatment: Contribution of Polar and Apolar Surface Tension Components

Hydraulic permeability measurements are performed on low cut-off Na-mordenite (MOR-type zeolites) membranes after a mild alkaline treatment. A decrease of the hydraulic permeability is systematically observed. Contact angle measurements are carried out (with three polar liquids) on Na-mordenite films seeded onto alumina plates (flat membranes). A decrease of the contact angles is observed after the alkaline treatment for the three liquids. According to the theory of Lifshitz-van der Waals interactions in condensated state, surface modifications are investigated and a variation of the polar component of the material surface tension is observed. After the alkaline treatment, the electron-donor contribution (mainly due to the two remaining lone electron pairs of the oxygen atoms present in the zeolite extra frameworks) decreases and an increase of the electron-receptor contribution is observed and quantified. The contribution of the polar component to the surface tension is attributed to the presence of surface defaults, which increase the surface hydrophilicity. The estimated modifications of the surface interaction energy between the solvent (water) and the Na-mordenite active layer are in good agreement with the decrease of the hydraulic permeability observed after a mild alkaline treatment.

Prediction of the mechanical properties of zeolite pellets for aerospace molecular decontamination applications

Zeolite pellets containing 5 wt % of binder (methylcellulose or sodium metasilicate) were formed with a hydraulic press. This paper describes a mathematical model to predict the mechanical properties (uniaxial and diametric compression) of these pellets for arbitrary dimensions (height and diameter) using a design of experiments (DOE) methodology. A second-degree polynomial equation including interactions was used to approximate the experimental results. This leads to an empirical model for the estimation of the mechanical properties of zeolite pellets with 5 wt % of binder. The model was verified by additional experimental tests including pellets of different dimensions created with different applied pressures. The optimum dimensions were found to be a diameter of 10–23 mm, a height of 1–3.5 mm and an applied pressure higher than 200 MPa. These pellets are promising for technological uses in molecular decontamination for aerospace-based applications.

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 (116 m2.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 [0.8-24.2 mmol.L-1] and fitted with Langmuir isotherm model. The maximum nitrate removal capacity (1338 mmol.Kg-1/83 mg.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.