Marie-Alexandra Neouze

Aerogels from Unaltered Bacterial Cellulose: Application of scCO2 Drying for the Preparation of Shaped, Ultra-Lightweight Cellulosic Aerogels

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.

About the interactions between nanoparticles and imidazolium moieties: emergence of original hybrid materials

In the parallel dramatic development of both nanoparticles and ionic liquids for materials chemistry, remarkable synergy was observed when combining nanoparticles and one type of ionic liquid, namely imidazolium moieties. This feature article highlights the main steps in the use and understanding of such combinations. It starts with a presentation of the use of imidazolium based ionic liquids as synthesis media for the preparation of nanoparticles, under various classical and non-classical processes. Then, the interactions taking place between the nanoparticle surfaces and functionalized or non-functionalized imidazoliums are reviewed. A step-by-step description of the way to new hybrid materials, based on this combination of imidazolium units and nanoparticles, follows. The multiple role of the imidazolium moiety is evidenced. Finally, the main fields of application for the new hybrid materials will be presented.

Cellulosic aerogels as ultra-lightweight materials. Part 2: Synthesis and properties

Abstract Ultra-lightweight cellulose aerogels can be obtained in three steps: (1) preparation of a cellulose solution in molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O) at 110–120°C and casting of the viscous mass into moulds; (2) extraction 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 supercritical carbon dioxide (scCO2). According to this approach, cellulosic aerogels were prepared from eight commercial cellulosic materials and pulps and analysed for selected chemical, physicochemical and mechanical parameters. The results reveal that all aerogels obtained from 3% cellulose containing NMMO·H2O melts had a largely uniform mesoporous structure with an average pore size of ∼9–12 nm, surface area of 190–310 m2 g-1, and specific density of 0.046–0.069 g cm-3, but rather low mechanical stability expressed as compressive yield strain of 2.9–5.5%. All samples showed viscoelastic behaviour, with Youngs modulus ranging from ∼5 to 10 N mm-2. Doubling the cellulose content in the NMMO·H2O melt from 3% to 6% increased Youngs 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 number of regenerating baths were optimised.

Nanoparticles connected through an ionic liquid-like network

Silica nanoparticles linked through ionic liquid-like molecules are synthesized by two routes. The first approach utilized a bis(trialkoxysilyl)-substituted imidazolium iodide to link the silica nanoparticles. In the second approach, the silica nanoparticles were first modified by 3-chloropropyltrimethoxysilane and N-(3-trimethoxysilylpropyl)imidazole and then coupled through nucleophilic substitution. A comparison of both approaches shows that the second approach results in a more efficient interfacing of nanoparticles.

Confinement of 1-butyl-3-methylimidazolium nitrate in metallic silver.

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.

Nanoparticle assemblies: main synthesis pathways and brief overview on some important applications

Nanoparticle assemblies are emerging highly promising materials, which aim at making use of nanoparticles collective properties. The synthesis pathway to create nanoparticle assemblies ensures the control on the distance between the nanoparticles. Various pathways will be presented for the formation of nanoparticle assemblies: such as template-assisted or pressure-induced synthesis, layer-by-layer or evaporation-induced deposition, introduction of a molecular linker. Nanoparticle assemblies can address many cutting-edge applications like plasmonic, sensoric, or catalysis.

Photoluminescence as Complementary Evidence for Short-Range Order in Ionic Silica Nanoparticle Networks.

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.

Dispersed particle extraction--a new procedure for trace element enrichment from natural aqueous samples with subsequent ICP-OES analysis.

A novel sample pre-treatment method for multi trace element enrichment from environmental waters prior to optical emission spectrometry analysis with inductively coupled plasma (ICP-OES) is proposed, based on dispersed particle extraction (DPE). This method is based on the use of silica nanoparticles functionalized with strong cation exchange ligands. After separation from the investigated sample solution, the nanoparticles used for the extraction are directly introduced in the ICP for measurement of the adsorbed target analytes. A prerequisite for the successful application of the developed slurry approach is the use of sorbent particles with a mean size of 500 nm instead of commercially available μm sized beads. The proposed method offers the known advantages of common bead-injection (BI) techniques, and further circumvents the elution step required in conventional solid phase extraction procedures. With the use of 14.4 mL sample and addition of ammonium acetate buffer and particle slurry limits of detection (LODs) from 0.03 μg L(-1) for Be to 0.48 μg L(-1) for Fe, with relative standard deviations ranging from 1.7% for Fe and 5.5% for Cr and an average enrichment factor of 10.4 could be achieved. By implementing this method the possibility to access sorbent materials with irreversible bonding mechanisms for sample pre-treatment is established, thus improvements in the selectivity of sample pre-treatment procedures can be achieved. The presented procedure was tested for accuracy with NIST standard reference material 1643e (fresh water) and was applied to drinking water samples from the vicinity of Vienna.

Ionic nanoparticle networks: development and perspectives in the landscape of ionic liquid based materials

This feature article gives an overview of the research performed on ionic nanoparticle networks (INNs). These INNs are hybrid materials consisting of inorganic nanoparticles and ionic linkers, such as imidazolium, bisimidazolium or pyridinium. The synthesis and properties of INNs, for catalysis or sensorics, are presented. At each step INN materials are compared to other hybrid materials of similar composition such as ionogels or suspensions of imidazolium modified nanoparticles.

Shaped hemocompatible aerogels from cellulose phosphates: preparation and properties

Abstract Hemocompatible, shaped cellulose phosphate aerogels were obtained from phosphorylated cellulosic pulps of low degree of phosphorylation (DSP≤0.20) by dissolution in stabilized NMMO×H2O, shaping, reprecipitation with ethanol and subsequent scCO2 drying. The novel aerogels were found to be promising materials for cell scaffolding and bone grafting. Special features include their interconnected and spread porosity, highly porous surface and microstructure, good hemocompatibility, and suitable hydroxyl apatite-binding environment. Adsorption of Ca2+ ions to the phosphate groups did not invert the negative inflammatory response observed after phosphorylating cellulose, but increased platelet-dependent parameters of hemostasis.