Corine Gérardin

Overview and Industrial Assessment of Synthesis Strategies towards Zeolites with Mesopores

With the necessity for the refining industry to treat heavier feedstocks, there is a clear demand for improved zeolite materials displaying better accessible surface areas and higher pore volumes in order to capitalize on their effectiveness. To this end, over the last decade, there has been an intensification of research on the exploration of new routes to synthesize zeolite materials combining micropores with mesopores. Different synthesis strategies are used for their preparation (i.e., by structure breaking or so‐called ‘destructive’ pathways, or structure building or so‐called ‘constructive’ synthesis pathways). This Review discusses the variety of current synthesis strategies, while emphasizing the strengths and weaknesses of the different routes regarding material characteristics; health, safety, and environment aspects; and synthesis costs.

Al30: A Giant Aluminum Polycation

Simple hydrothermal treatment of the well-known aluminum polycation varepsilon-Al(13) produces the novel Al(30) structure (see picture), the largest polycation yet observed. Its characterization, by X-ray diffraction and NMR spectroscopy, also solved previously unassigned signals in (27)Al NMR spectra of other Al - O species.

Ecodesign of ordered mesoporous silica materials

Characterized by a regular porosity in terms of pore size and pore network arrangement, ordered mesoporous solids have attracted increasing interest in the last two decades. These materials have been identified as potential candidates for several applications. However, more environmentally friendly and economical synthesis routes of mesoporous silica materials were found to be necessary in order to develop these applications on an industrial scale. Consequently, ecodesign of ordered mesoporous silica has been considerably developed with the objective of optimizing the chemistry and the processing aspects of the material synthesis. In this review, the main strategies developed with this aim are presented and discussed.

Layered double hydroxides: precursors for multifunctional catalysts

One-pot cascade reactions which involve multifunctional catalysts possessing different functions on the surface attract a growing interest. Relevant examples of the use of this type of catalysts in one-pot syntheses involving hydrogenation/dehydrogenation and aldol condensation reactions which give rise to valuable organic compounds are reported in this paper. It is shown that the layered double hydroxides (LDH) are precursors materials particularly adapted for the preparation of catalysts exhibiting acido/basic and redox sites. The paramount importance of the nature (Lewis or Bronsted) and the strength of the basic sites, as well as the nature of the metallic function of the supported metal catalysts obtained from LDH is discussed. It is emphasized on the equilibrium between the basic and metallic functions required to reach high activities and selectivities.

Role of double-hydrophilic block copolymers in the synthesis of lanthanum-based nanoparticles

Abstract The formation of nanosized lanthanum hydroxide particles in aqueous medium was studied in the presence of double-hydrophilic block copolymers (DHBC). These copolymers contain a polyacrylic acid (PAA) block as an ionizable block, and a polyacrylamide (PAM) or a polyhydroxyethylacrylate (PHEA) block as a neutral block. The nanoparticles are synthesized by a two-step procedure. Firstly, the complexation of lanthanum ions in water by the polyacrylate blocks induced the formation of star-shaped micelles stabilized by the PAM or PHEA blocks. The micelles were characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS) and transmission electron microscopy (TEM). Secondly, the inorganic polycondensation of lanthanum ions led to the formation of organic–inorganic nanohybrids. Hairy needle-like colloids were obtained. The size of the sterically stabilized colloids was controlled by adjusting the polymer-to-metal ratio.

Molecular simulation of adsorption and transport in hierarchical porous materials.

Adsorption and transport in hierarchical porous solids with micro- (~1 nm) and mesoporosities (>2 nm) are investigated by molecular simulation. Two models of hierarchical solids are considered: microporous materials in which mesopores are carved out (model A) and mesoporous materials in which microporous nanoparticles are inserted (model B). Adsorption isotherms for model A can be described as a linear combination of the adsorption isotherms for pure mesoporous and microporous solids. In contrast, adsorption in model B departs from adsorption in pure microporous and mesoporous solids; the inserted microporous particles act as defects, which help nucleate the liquid phase within the mesopore and shift capillary condensation toward lower pressures. As far as transport under a pressure gradient is concerned, the flux in hierarchical materials consisting of microporous solids in which mesopores are carved out obeys the Navier-Stokes equation so that Darcys law is verified within the mesopore. Moreover, the flow in such materials is larger than in a single mesopore, due to the transfer between micropores and mesopores. This nonzero velocity at the mesopore surface implies that transport in such hierarchical materials involves slippage at the mesopore surface, although the adsorbate has a strong affinity for the surface. In contrast to model A, flux in model B is smaller than in a single mesopore, as the nanoparticles act as constrictions that hinder transport. By a subtle effect arising from fast transport in the mesopores, the presence of mesopores increases the number of molecules in the microporosity in hierarchical materials and, hence, decreases the flow in the micropores (due to mass conservation). As a result, we do not observe faster diffusion in the micropores of hierarchical materials upon flow but slower diffusion, which increases the contact time between the adsorbate and the surface of the microporosity.

Hydrophilic block copolymer-directed growth of lanthanum hydroxide nanoparticles

Stable hairy lanthanum hydroxide nanoparticles were synthesized in water by performing hydrolysis and condensation reactions of lanthanum cations in the presence of double hydrophilic polyacrylic acid-b-polyacrylamide block copolymers (PAA-b-PAM). In the first step, the addition of asymmetric PAA-b-PAM copolymers (Mw,PAA < Mw,PAM) to lanthanum salt solutions, both at pH = 5.5, induces the formation of monodispersed micellar aggregates, which are predominantly isotropic. The core of the hybrid aggregates is constituted of a lanthanum polyacrylate complex whose formation is due to bidentate coordination bonding between La3+ and acrylate groups, as shown by ATR-FTIR experiments and pH measurements. The size of the micellar aggregates depends on the molecular weight of the copolymer but is independent of the copolymer to metal ratio in solution. In the second step, the hydrolysis of lanthanum ions is induced by addition of a strong base such as sodium hydroxide. Either flocculated suspensions or stable anisotropic or spherical nanoparticles of lanthanum hydrolysis products were obtained depending on the metal complexation ratio [acrylate]/[La]. The variation of that parameter also enables the control of the size of the core-corona nanoparticles obtained by lanthanum hydroxylation. The asymmetry degree of the copolymer was shown to influence both the size and the shape of the particles. Elongated particles with a high aspect ratio, up to 10, were obtained with very asymmetric copolymers (Mw,PAM/Mw,PAA ≥ 10) while shorter rice grain-like particles were obtained with a less asymmetric copolymer. The asymmetry degree also influences the value of the critical metal complexation degree required to obtain stable colloidal suspensions of polymer-stabilized lanthanum hydroxide.

Ecodesign of Ordered Mesoporous Materials Obtained with Switchable Micellar Assemblies

Reduce, reuse, recycle: A new methodology allows the synthesis of ordered mesoporous materials in water at room temperature, eliminating the need for organic solvents and reducing the amount of energy consumed. It relies on the reversible formation of micelles of water-soluble block copolymers as structure-directing agents (see picture). After recovery of the mesoporous material, the reaction solution can be used again.

The control of dendritic cell maturation by pH-sensitive polyion complex micelles.

Double-hydrophilic block copolymer micelles were designed as vectors for ex vivo dendritic cell engineering to improve the delivery of therapeutic molecules in such immune cells. Polymethacrylic acid-b-polyethylene oxide (PMAA(2100)-b-POE(5000))/poly-L-lysine micelles were optimised and showed a hydrodynamic diameter of 30 nm with a peculiar core organised with hydrogen bonds as well as hydrophobic domains. The micelles proved high stability in physiological conditions (pH and ionic strength) and were also able to disassemble under acidic conditions mimicking acidic endolysosomes. The efficient endocytosis of the optimised micelles tested on bone marrow-derived dendritic cells was monitored by fluorescence-activated cell sorting and microscopy analysis. Finally, the micelle biocompatibility permitted a complete control of the dendritic cell-maturation process widening the therapeutical potential of such engineered dendritic cells for cancer vaccines as well as for immunomodulation in autoimmune diseases.

Hybrid Polyion Complex Micelles Formed from Double Hydrophilic Block Copolymers and Multivalent Metal Ions: Size Control and Nanostructure

Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al(3+), La(3+), or Al(13)(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation. Mixtures of metal cations and asymmetric block copolymers with a complexing block smaller than the stabilizing block lead to the formation of stable colloidal HPIC micelles. The hydrodynamic radius of the HPIC micelles varies with the polymer molecular weight as M(0.6). In addition, the variation of R(h) of the HPIC micelle is stronger when the complexing block length is increased than when the neutral block length is increased. R(h) is highly sensitive to the polymer asymmetry degree (block weight ratio), and this is even more true when the polymer asymmetry degree goes down to values close to 3. SANS experiments reveal that HPIC micelles exhibit a well-defined core-corona nanostructure; the core is formed by the insoluble dense poly(acrylate)/metal cation complex, and the diffuse corona is constituted of swollen neutral polymer chains. The scattering curves were modeled by an analytical function of the form factor; the fitting parameters of the Pedersens model provide information on the core size, the corona thickness, and the aggregation number of the micelles. For a given metal ion, the micelle core radius increases as the PAA block length. The radius of gyration of the micelle is very close to the value of the core radius, while it varies very weakly with the neutral block length. Nevertheless, the radius of gyration of the micelle is highly dependent on the asymmetry degree of the polymer: if the neutral block length increases in a large extent, the micelle radius of gyration decreases due to a decrease of the micelle aggregation number. The variation of the R(g)/R(h) ratio as a function of the polymer block lengths confirms the nanostructure associating a dense spherical core and a diffuse corona. Finally, the high stability of HPIC micelles with increasing concentration is the result of the nature of the coordination complex bonds in the micelle core.