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ABSTRACT: AbstractShaped cellulosic aerogels—as the ‘young’ generation succeeding the well-established silica and synthetic polymer-based aerogels—are
intriguing materials that feature properties similar to those of their antecessors combined with the additional advantages
and characteristics of the re-growing biopolymer cellulose. Reinforced shaped cellulosic aerogels consisting of two interpenetrating
networks of cellulose and silica were prepared from shaped cellulose solutions by (1) regenerating (reprecipitating) cellulose
with ethanol, (2) subjecting the obtained shaped alcogels to sol-gel condensation with tetraethoxysilane as the principal
network-forming compound, and (3) drying the reinforced cellulose bodies with supercritical carbon dioxide. The influence
of different types of cellulose and sol-gel forming parameters on porosity, cellulose integrity, and silica content were studied
by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), gel permeation chromatography (GPC), and
nitrogen adsorption at 77K. The results of SEM and EDX confirmed the presence of silicon inside the obtained cellulosic aerogel.
GPC of the cellulosic matrix prior and after silica coating showed no alteration of the molecular weight distribution for
most of the samples, confirming a far-reaching preservation of cellulose’s chemical integrity throughout the modification
procedure. Nitrogen adsorption experiments at 77K revealed that the micro- and meso-pore characteristics were largely retained
throughout silica modification.
Graphical Abstract
KeywordsCellulose–Aerogel–Surface modification–Silica–Sol-gel–Mesoporosity
Cellulose 04/2012; 18(1):143-149. · 3.60 Impact Factor
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ABSTRACT: Metal or metal oxide nanoparticles possess unique features compared to equivalent larger-scale materials. For applications,
it is often necessary to stabilize or functionalize such nanoparticles. Thus, modification of the surface of nanoparticles
is an important chemical challenge. In this survey, various possibilities are discussed how nanoparticles can be protected
by organic ligands and how these ligands can be used to introduce functionalities. The preparative possibilities include grafting
of an already functionalized ligand on the nanoparticle surface, exchanging part or all existing ligands on the nanoparticle
surface, or grafting of a ligand on a nanoparticle followed by modification by organic chemical reactions.
Monatshefte fuer Chemie/Chemical Monthly 04/2012; 139(3):183-195. · 1.53 Impact Factor
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ABSTRACT: Titania nanoparticle networks were synthesized by the reaction between imidazole and alkyl halide functionalized anatase nanoparticles. The reaction produced imidazolium bridging units between the nanoparticles that were observed by the means of CP MAS (15)N NMR spectroscopy. The porous characteristics of the obtained nanoparticle network were investigated with nitrogen sorption experiments. From these experiments, a high surface area originating from small mesopores was observed. These results were confirmed by small-angle X-ray diffraction experiments.
Langmuir 02/2011; 27(7):4110-6. · 4.19 Impact Factor
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ABSTRACT: Recently nanoparticles ionic networks were reported in the frame of the remarkable development of new inorganic-organic hybrid materials based on nanoparticles assembly. In this article a layer-by-layer deposition method for the formation of imidazolium-based assemblies of photocatalytic titania nanoparticles is presented. This provides a new route for the controlled processing of this promising class of materials.
Chemical Communications 01/2011; 47(1):361-3. · 6.17 Impact Factor
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ABSTRACT: Recently we published the synthesis of new hybrid materials, ionic silica nanoparticles networks (ISNN), made of silica nanoparticles covalently connected by organic bridging ligands containing imidazolium units owing to a "click-chemistry-like" reaction. Among other techniques small-angle X-ray scattering (SAXS) experiments were carried out to get a better picture of the network extension. It turned out that the short-range order in ISNN materials was strongly influenced by the rigidity of the bridging ligand, while the position of the short-range order peaks confirmed the successful linking of the bridging ligands. The photoluminescence experiments reported in this communication revealed strongly enhanced emission in the hybrid material in comparison with neat imidazolium salts. Moreover the shift of the emission maximum toward longer wavelengths, obtained when varying the aromatic ring content of the bridging ligand, suggested the existence of strong π-π stacking in the hybrid material. Experiments revealed a stronger luminescence in those samples exhibiting the higher extent of short-range order in SAXS.
The Journal of Physical Chemistry C 12/2010; 114(49):21342-21347. · 4.80 Impact Factor
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ABSTRACT: Bacterial cellulose produced by the gram-negative bacterium Gluconacetobacter xylinum was found to be an excellent native starting material for preparing shaped ultra-lightweight cellulose aerogels. The procedure comprises thorough washing and sterilization of the aquogel, quantitative solvent exchange and subsequent drying with supercritical carbon dioxide at 40 degrees C and 100 bar. The average density of the obtained dry cellulose aerogels is only about 8 mg x cm(-3) which is comparable to the most lightweight silica aerogels and distinctly lower than all values for cellulosic aerogels obtained from plant cellulose so far. SEM, ESEM and nitrogen adsorption experiments at 77 K reveal an open-porous network structure that consists of a comparatively high percentage of large mesopores and smaller macropores.
Macromolecular Bioscience 02/2010; 10(4):349-52. · 3.89 Impact Factor
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ABSTRACT: Small-angle X-ray scattering (SAXS) experiments were carried out to investigate systems consisting of silica nanoparticles bridged by imidazolium-based linkers. This characterization method delivers a quantitative description of the efficiency to order nanoparticles obtained from different chemical approaches. Two packing factors were extracted from the SAXS curves, where one characterizes the stacking of the ligands and the other the order of the nanoparticles. The amount of order can be controlled by using different ligands such as mono- and diimidazolium-based ones with different flexibilities or by varying the ligand length.
04/2009;
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ABSTRACT: Ultra-lightwt. cellulose aerogels can be obtained in three steps: (1) prepn. of a cellulose soln. in molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O) at 110-120°C and casting of the viscous mass into molds; (2) extn. of the solidified castings with ethanol to initiate cellulose aggregation and to remove NMMO·H2O so that the fragile, fine-porous texture of cellulose II is largely retained; and (3) drying of the lyogel using supercrit. carbon dioxide (scCO2). According to this approach, cellulosic aerogels were prepd. from eight com. cellulosic materials and pulps and analyzed for selected chem., physicochem. and mech. parameters. The results reveal that all aerogels obtained from 3% cellulose contg. NMMO·H2O melts had a largely uniform mesoporous structure with an av. pore size of ∼9-12 nm, surface area of 190-310 m2 g-1, and specific d. of 0.046-0.069 g cm-3, but rather low mech. stability expressed as compressive yield strain of 2.9-5.5%. All samples showed viscoelastic behavior, with Young's modulus ranging from ∼5 to 10 N mm-2. Doubling the cellulose content in the NMMO·H2O melt from 3% to 6% increased Young's modulus by one order of magnitude. Shrinkage of the fragile cellulose bodies during scCO2 drying was still considerable and is subject to further investigations. Influencing parameters such as scCO2 pressure, cellulose content, regenerating solvent and the no. of regenerating baths were optimized. [on SciFinder(R)]
Holzforschung 01/2009; 63(Copyright (C) 2013 American Chemical Society (ACS). All Rights Reserved.):3-11. · 1.75 Impact Factor
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ABSTRACT: The structure of the composite material consisting of the ionic liquid 1-butyl-3-methylimidazolium nitrate (BMINO3) entrapped in a silver matrix was investigated. Entrapment is confirmed by combining thermal analysis and spectroscopic investigations and by comparing physicochemical properties of the genuine ionic liquid and the composite BMINO3@Ag. An organization of the ionic liquid molecules toward the silver surface was observed.
The Journal of Physical Chemistry B 01/2009; 112(51):16721-5. · 3.70 Impact Factor
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ABSTRACT: Complex hybrid organic-"multi inorganic" particles SiO2 PDCL-ZrO2 (Ag SiO2) (PDCL = poly(N-dicarbazolyl-lysine)) were synthesized stepwise from silica nanoparticles. First, the zirconia units were synthesized by sol-gel processing and anchored to the polyCOOH poly(dicarbazole-lysine) shell of pre-formed silica particles through metal coordination on residual COOH groups. Investigation of the particle morphology indicated a core-shell structure. A second sol-gel reaction was then carried out at the surface of the SiO2 PDCL-ZrO2 particles using a mixture of alkoxysilanes including an amino-substituted silane capable of chelating silver cations. Once the outer shell made of organically substituted silica was deposited, silver particles were generated by UV treatment, thus leading to an external layer of homogeneously dispersed silver nanoparticles in silica.
Dalton Transactions 10/2008; · 3.84 Impact Factor
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ABSTRACT: Hybrid organic–inorganic silica-based materials containing bridging ionic liquid-like entities were prepared, from 1,3-di(3-trimethoxysilylpropyl)-imidazolium
iodide and tetraethoxysilane. The final material is characterized by a high thermal stability. TEM micrographs of the obtained
hybrid material allow its comparison with silica nanoparticles bridged through ionic liquid-like links.
Monatshefte fuer Chemie/Chemical Monthly 09/2008; 139(10):1151-1156. · 1.53 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 05/2007; 2007(18):2609 - 2611. · 2.94 Impact Factor
