Peter Hesemann

Modular thiol-ene chemistry approach towards mesoporous silica monoliths with organically modified pore walls.

The surface modification of mesoporous silica monoliths through thiol-ene chemistry is reported. First, mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol-gel hydrolysis-polycondensation reaction from tetramethyl orthosilicate (TMOS) and vinyltriethoxysilane, allyltriethoxysilane, and (3-mercaptopropyl)trimethoxysilane, respectively. By variation of the molar ratio of the comonomers TMOS and functional silane, mesoporous silica objects containing different amounts of vinyl, allyl, and thiol groups were obtained. These intermediates can subsequently be derivatized through radical photoaddition reactions either with a thiol or an olefin, depending on the initial pore wall functionality, to yield silica monoliths with different pore-wall chemistries. Nitrogen sorption, small-angle X-ray scattering, solid-state NMR spectroscopy, elemental analysis, thermogravimetric analysis, and redox titration demonstrate that the synthetic pathway influences the morphology and pore characteristics of the resulting monoliths and also plays a significant role in the efficiency of functionalization. Moreover, the different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore-wall functionalization. This report demonstrates that thiol-ene photoaddition reactions are a versatile platform for the generation of a large variety of organically modified silica monoliths with different pore surfaces.

Ionosilicas as efficient sorbents for anionic contaminants: Radiolytic stability and ion capacity

Ammonium based hybrid ionosilicas were prepared from tetrasilylated ammonium precursors. The formed material exhibited high specific surface area together with mesoporosity. Our results indicate that ionosilicas display high exchange capacity for iodide. They were submitted to 10MeV electron irradiation at a total dose of 1.7MGy. Irradiation was shown not to alter the properties of ionosilica: the morphological, textural and surface properties of the material are hardly modified. The sorption properties (sorption capacity and cumulative displacement enthalpy) are similar before and after electron irradiation. This high radiolytical stability confirms that these innovative materials have therefore high potential as anion traps for future applications in decontamination processes or long term storage of radioactive waste.

Alkylguanidinium based ionic liquids in a screening study for the removal of anionic pollutants from aqueous solution

Monoalkylguanidinium bis-trifluoromethane sulfonimides are water immiscible functional ionic liquids which appear as highly efficient phases for the sequestration of anionic pollutants from aqueous solutions. The new compounds show significantly enhanced extraction efficiency compared to conventional imidazolium based ionic liquids.

New N-guanidinium chitosan/silica ionic microhybrids as efficient adsorbent for dye removal from waste water

N-guanidinium chitosan acetate, a new chitosan derivative, was prepared via direct guanylation reaction between chitosan and cyanamide in the presence of scandium (III) triflate. Treatment of N-guanidinium chitosan acetate with 3-(trihydroxysilyl)-1-propanesulphonic acid followed by sol-gel reaction allowed accessing N-guanidinium chitosan silica hybrid material. The new ionic microhybrid was characterized using 13C and 29Si solid state NMR, IR spectroscopy, scanning electron microscopy and thermogravimetry. Further studies in the area of separation indicated very high adsorption capacity for cationic dyes such as methylene blue (MB), with capacities up to 935 mg/g. The adsorption kinetics can accurately be described by pseudo second-order model. Equilibrium adsorption data showed a better fit with Langmuir adsorption isotherm model. Recycling test showed that the ionic microhybrid can be reused in at least five adsorption-desorption cycles. These results open new perspectives and possibilities for the design of novel hybrid adsorbents for industrial and environmental applications.

New approach for immobilization of 3-aminopropyltrimethoxysilane and TiO2 nanoparticles into cellulose for BJ1 skin cells proliferation

In the present study, tosylcellulose (TC) was used as a key intermediate for the selective coupling with 3-aminopropyltrimethoxysilane (APTMS) affording amino-propylsilane-grafted tosylcellulose (TC-Si). Solid state 13C NMR and FT-IR analyses confirmed the coupling and self-condensation of APTMS along TC. The changes in the surface morphology of the functionalized cellulose were identified by SEM imaging. The thermal stability of TC-Si was significantly improved as compared to MCC and TC. A new organic/inorganic hybrid cellulosic material was fabricated by embedding TiO2 nanoparticles into TC-Si network. The new cellulose polymers were investigated for their ability to promote the proliferation of human skin fibroblast (BJ1). The cell cytotoxicity assay showed that both TC and TC-Si possessed moderate toxicity to BJ1 cells by 17% and 23.8%, respectively at 20 μM. Meanwhile, TC-Si/TiO2 hybrid enhanced the proliferation of BJ1 by 42%. Additionally TC-Si/TiO2 hybrid demonstrated promising antimicrobial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans.

Reductive mineralization of cellulose with vanadium, iron and tungsten chlorides and access to MxOy metal oxides and MxOy/C metal oxide/carbon composites

MxOy and MxOy/C composites (M=V, Fe and W) were obtained by mineralization of cellulose with several metal chlorides. Cellulose was used both as a templating agent and as an oxygen and a carbon source. Soluble chloride molecules (VOCl3 and WCl6) and a poorly soluble ionic chloride compound (FeCl3) were chosen as metal oxide precursors. In a first time, primary metal oxide/cellulose composites were obtained via a thermal treatment by reacting urea impregnated filter paper with the corresponding metal chlorides in an autoclave at 150°C after 3days. After either pyrolysis or calcination steps of these intermediate materials, interesting metal oxides with various morphologies were obtained (V2O5, V2O3, Fe3O4, WO3, H0.23WO3), composites (V2O3/C) as well as carbides (hexagonal W2C and WC, Fe3C) This result highlight the reductive role that can play cellulose during the pyrolysis step that allows to tune the composition of MxOy/C composites. The materials were characterized by FTIR, Raman, TGA, XRD and SEM. This study highlights that cellulose can be used for a convenient preparation of a variety of highly demanded MxOy and MxOy/C composites with original shapes and morphologies.