Gilbert Renard

Modified SBA-15 mesoporous silica for heavy metal ions remediation

N-Propylsalicylaldimino-functionalized SBA-15 mesoporous silica was prepared, characterized and used as an adsorbent for heavy metal ions. The organic-inorganic hybrid material was obtained using successive grafting procedures of SBA-15 silica with 3-aminopropyl-triethoxysilane and salicylaldehyde, respectively. For comparison an amorphous silica gel was functionalized using the same procedure. The structure and physicochemical properties of the materials were characterized by means of elemental analysis, X-ray diffraction (XRD), nitrogen adsorption-desorption, thermogravimetric analysis and FTIR spectroscopy. The organic functional groups were successfully grafted on the SBA-15 surfaces and the ordering of the support was not affected by the chemical modification. The behavior of the grafted solids for the adsorption of heavy metals ions from aqueous solutions was investigated. The hybrid materials showed high adsorption capacity and high selectivity for copper ions. Other ions, such as nickel, zinc, and cobalt were adsorbed by the modified SBA-15 material. The adsorbent can be regenerated by acid treatment without altering its properties.

The preparation and use of novel immobilised guanidine catalysts in base-catalysed epoxidation and condensation reactions

Novel guanidine bases supported on silicas and Micelle Templated Silicas (MTS) have been prepared, and investigated in the base catalysed epoxidation of electron deficient alkenes with excellent conversions and selectivities both with respect to the alkene and the primary oxidant. They are also efficient catalysts for the condensation of malonic acid with heptanal.

Hemoglobin immobilized on mesoporous silica as effective material for the removal of polycyclic aromatic hydrocarbons pollutants from water

Free hemoglobin (Hb) in water at pH 5 is able to oxidize 11 polycyclic aromatic hydrocarbons (PAH) (300 nM each) in the presence of H2O2 amounting to 75% PAH removal. PAH are carcinogenic, mutagenic and xenobiotic pollutants found in wastewaters of oil refineries. However Hb is pH sensitive and is effective only at pH 5. In order to use Hb for real wastewater treatment (6.5 2500) and of Hb ([Hb]/[PAH] > 2) is necessary to reach an optimal PAH removal. The excess of Hb depends on the PAH physico-chemical characteristics. At pH = 7, the activity of free Hb decreased to 47% of PAH removal, whereas the Hb-immobilized silica allowed 82% of PAH removal. Immobilization of Hb in silicas leads to a protection of Hb towards pH, solvent, temperature and inactivation by H2O2. These results open the perspective for a new biotechnology process aimed at cleaning contaminated wastewaters by a reactive adsorption process followed by filtration.

Phospholipid-templated silica nanocapsules as efficient polyenzymatic biocatalysts

Solid polyenzymatic biocatalysts have been designed by combining two immobilized enzymes, the first one allowing the in situ generation of H(2)O(2) from air and the second one performing an oxidation reaction. The in situ H(2)O(2) generation system is based on the reaction of glucose with air using a glucose oxidase (GOx). The optimization of the encapsulation of GOx into phospholipids-templated silica capsules (NPS) was performed. A bienzymatic system made of GOx and horseradish peroxidase (HRP) was studied. Optimal conditions for the activity of the GOx/HRP bienzymatic system have been determined for both homogeneous and heterogeneous conditions. The encapsulation in NPS materials increases the stability of both enzymes. The performance of the encapsulated bienzymatic GOx/HRP system in the model reaction of 4-aminoantipyridine with phenol is similar when the enzymes are immobilized separately in two NPS or coencapsulated in the same NPS. An excess of peroxidase compared to GOx ([HRP]/[GOx] = 5-10) is necessary to obtain the optimal activity. To show the potentiality of bienzymatic systems in real applications, HRP has been replaced by hemoglobin, which is known for its ability to oxidize polycyclic aromatic hydrocarbons (PAH) pollutants through a pseudoperoxidase pathway. A larger excess of Hb compared to GOx ([Hb]/[GOx] = 1000) was necessary to obtain the maximum PAH removal, as Hb is not a real peroxidase as HRP but a hemoprotein with some pseudoperoxidase activity. In opposite to real enzymes, the immobilization of Hb by adsorption in mesoporous silica is preferable as its encapsulation. Therefore, the bienzymatic system made of GOx encapsulated in NPS and Hb adsorbed in mesoporous silica has been used for the removal of 11 PAH from water. This heterogeneous bienzymatic system allows 64% of PAH removal from water using simple air as oxidant.

Immobilisation of a biological chelate in porous mesostructured silica for selective metal removal from wastewater and its recovery

This study represents a preliminary stage in the development of a process aimed at the selective uptake and release of metal ions from wastewater. The process involves the immobilisation of highly selective natural chelates secreted by bacteria or other living species inside mesoporous micelle-templated silicas (MTS) that could be used as usual resins. To demonstrate the feasibility of the concept, a model system was used. It involves pyoverdin, a natural Fe(III) chelator from a Pseudomonas fluorescens strain, covalently anchored to a glycidoxypropyl linker into the large pores (13 nm) of a MTS material. The hybrid material obtained is very stable as no leaching of the pyoverdin complex was observed during repeated washings and repeated uses. The native fluorescence of the pyoverdin allows a simpler follow-up and quantification of the iron uptake and release processes. The pyoverdin-anchored MTS is very selective towards Fe(III) if a multi-metallic solution is used. MTS materials allow a higher density of pyoverdin anchoring and consequently a higher metal uptake, compared to a high-grade silica gel.

A demonstration model for a selective and recyclable uptake of metals from water: Fe(III) ions complexation and release by a supported natural fluorescent chelator

We describe here the preliminary stage of development of a process aiming at the selective uptake and release of metal ions from water. The process envisioned involves the encapsulation of highly selective natural chelates secreted by bacteria or other living species in mesoporous solids that could be used as usual resins. To demonstrate the feasibility of the concept, we use a model system involving pyoverdin, a natural Fe(III) ions chelator from a Pseudomonas fluorescens strain, encapsulated in a mesoporous templated silica. For this model study, the native fluorescence of the chelator allows a simpler follow-up and quantification of the uptake and release processes.

First simple and mild synthesis of 2-alkylbenzimidazoles involving a supported enzymatic catalyst

A new enzymatic synthesis is described for 2-alkyl-benzimidazoles a technologically important class of compounds. It is a one-step synthesis which involves a supported enzyme (Lipozyme®) and is carried out in very mild conditions in hydrocarbon solvents to give 2-alkyl-benzimidazoles in good yields, starting from the free acids. Preliminary results indicate that the reaction has a potential to produce new molecules using sensitive or conjugated acids.

Guanidine catalysts supported on silica and micelle templated silicas. New basic catalysts for organic chemistry

The preparation of guanidines covalently linked to the framework of Micelle Templated Silicas is discussed. These materials can behave as efficient catalysts in base catalysed epoxidation. Control over surface chemistry is very beneficial in enhancing selectivity and efficiency with respect to utilisation of the oxidant hydrogen peroxide. Such systems contribute to the search for cleaner manufacturing technologies. The same catalysts are active in the Linstead variation of the Knoevenagel reaction. Initial work aimed at preparing chiral guanidines attached to Micelle Templated Silica is also presented.

29-P-10-Guanidine catalysts supported on silica and micelle templated silicas: new basic catalysts for organic chemistry

Publisher Summary This chapter discusses guanidine catalysts supported on silica and micelle templated silicas. Supported guanidines are prepared through different routes, and their activity is compared in two reactions of interest. The base-catalyzed epoxidation of electron-deficient alkenes is described and proceeds with excellent conversions and selectivities when the surface is passivated by silylation. The Linstead variation of the Knoevenagel condensation is also described, which provides excellent conversions to partially decarboxylated products.

EPR Studies of New Mesostructured Silica Synthesis and Hemoglobin Encapsulation

Enzyme encapsulation in ordered porous silica has been modified by introducing a natural surfactant such as lecithin during the sol-gel process. β-lactose has been used as the enzyme protecting agent and tetraethoxysilane as the source of silica in an hydroalcoholic media. In the present study, the EPR spectroscopy of paramagnetic probes has allowed to monitor the formation of mesophases and the condensation of silica in an isotropic three-dimensional structure, named Sponge Mesoporous Silica, with a pore size of 6 nm and a specific surface area of 600 m2/g. Different techniques of characterization (nitrogen sorption, XRD, TEM, SEM) have been used to study the influence of the different reactants on the structure of the materials. Hemoglobin has been encapsulated in the different materials and its catalytic pseudo peroxydase activity has been evaluated.