Self-Confined Nucleation of Iron Oxide Nanoparticles in a Nanostructured Amorphous Precursor.

Crystallization from solution is commonly described by classical nucleation theory, although this ignores that crystals often form via disordered nanostructures. As an alternative, the classical theory remains widely used in a "multistep" variant, where the intermediate nanostructures merely introduce additional thermodynamic parameters. However, this variant still requires validation by experiments addressing indeed proper time and spatial scales (millisecond, nanometer). Here, we used in situ X-ray scattering to determine the mechanism of magnetite crystallization and, in particular, how nucleation propagates at the nanometer scale within amorphous precursors. We find that the self-confinement by an amorphous precursor slows down crystal growth by 2 orders of magnitude once the crystal size reaches the amorphous particle size (∼3 nm). Thus, not only the thermodynamic properties of transient amorphous nanostructures but also their spatial distribution determine crystal nucleation.

Toward a Chemical Control of Colloidal YVO4 Nanoparticles Microstructure.

Rare-earth-doped oxides are a class of compounds that have been largely studied in the context of the development of luminescent nanocrystals for various applications including fluorescent labels for bioimaging, MRI contrast agents, luminescent nanocomposite coatings, etc. Elaboration of colloidal suspensions is usually achieved through coprecipitation. Particles exhibit emission properties that are similar to the bulk counterparts, although altered by crystalline defects or surface quenching species. Focusing on YVO4:Eu, one of the first reported systems, the aim of this work is to revisit the elaboration of nanoparticles obtained through a simple aqueous coprecipitation route. The objective is more precisely to get a better understanding of the parameters affecting the particles' internal microstructure, a feature that is poorly controlled and characterized. We show that the hydroxyl concentration in the precursor solution has a drastic effect on the particles' microstructure. Moreover, discrepancies in the reported particle structure are shown to possibly arise from the carbonation of the strongly basic orthovanadate precursor. For this study, SAXS/WAXS is shown to be a powerful tool to characterize the multiscale structure of the particles. It could be shown that playing on the precursor composition, it may be varied between almost monocrystalline nanocrystals to particles exhibiting a hierarchical microstructure well described by a surface fractal model. This work provides a new methodology for the characterization of nanoparticles microstructure and opens new directions for its optimization in view of applications.

Aerogels from Cellulose Phosphates of Low Degree of Substitution: A TBAF·H2O/DMSO Based Approach.

Biopolymer aerogels of appropriate open-porous morphology, nanotopology, surface chemistry, and mechanical properties can be promising cell scaffolding materials. Here, we report a facile approach towards the preparation of cellulose phosphate aerogels from two types of cellulosic source materials. Since high degrees of phosphorylation would afford water-soluble products inappropriate for cell scaffolding, products of low DSP (ca. 0.2) were prepared by a heterogeneous approach. Aiming at both i) full preservation of chemical integrity of cellulose during dissolution and ii) utilization of specific phase separation mechanisms upon coagulation of cellulose, TBAF·H2O/DMSO was employed as a non-derivatizing solvent. Sequential dissolution of cellulose phosphates, casting, coagulation, solvent exchange, and scCO2 drying afforded lightweight, nano-porous aerogels. Compared to their non-derivatized counterparts, cellulose phosphate aerogels are less sensitive towards shrinking during solvent exchange. This is presumably due to electrostatic repulsion and translates into faster scCO2 drying. The low DSP values have no negative impact on pore size distribution, specific surface (SBET ≤ 310 m2 g-1), porosity (Π 95.5-97 vol.%), or stiffness (Eρ ≤ 211 MPa cm3 g-1). Considering the sterilization capabilities of scCO2, existing templating opportunities to afford dual-porous scaffolds and the good hemocompatibility of phosphorylated cellulose, TBAF·H2O/DMSO can be regarded a promising solvent system for the manufacture of cell scaffolding materials.

Tailoring photoluminescence properties in ionic nanoparticle networks.

To investigate the original and promising luminescence properties of ionic nanoparticle networks (INN), various material compositions were investigated. In this work, the linker used to network the silica nanoparticles was varied; numerous substituted or non-substituted imidazolium, pyrazolium and pyridinium linkers are presented. Photoluminescence experiments on the INN hybrid materials revealed strong emission bands over a broad range in the visible region of the light spectrum. Varying the aromatic linker between the imidazolium units induced clear shifts of the emission maxima up to 100 nm, as a consequence of π-π stacking interactions. Steric hindrance and inductive effects of the substituents, introduced on the aromatic units, also strongly influenced the luminescence properties of the materials by modifying the π-π stacking between the imidazolium rings. Small and wide-angle X-ray scattering (SAXS, WAXS) experiments revealed a clear trend between the obtained structural parameters (short-range order parameter and distance of the aromatic units within the hybrid material) and the luminescence quantum yields of the INN materials.

Exploring the molecular structure of imidazolium-silica-based nanoparticle networks by combining solid-state NMR spectroscopy and first-principles calculations.

A DFT-based molecular model for imidazolium-silica-based nanoparticle networks (INNs) is presented. The INNs were synthesized and characterized by using small-angle X-ray scattering (SAXS), NMR spectroscopy, and theoretical ab initio calculations. (11)B and (31)P HETCOR CP MAS experiments were recorded. Calculated (19)F NMR spectroscopy results, combined with the calculated anion-imidazolium (IM) distances, predicted the IM chain density in the INN, which was also confirmed from thermogravimetric analysis/mass spectrometry results. The presence of water molecules trapped between the nanoparticles is also suggested. First considerations on possible π-π stacking between the IM rings are presented. The predicted electronic properties confirm the photoluminescence emissions in the correct spectral domain.

Determination of rare earth elements in saline matrices using dispersed particle extraction and inductively coupled plasma mass spectrometry.

RATIONALE: Rare earth elements play an important role in identifying and indexing the origin of historical and geological samples. In this work, a new approach for the characterization of rare earth elements (REEs) in aqueous sample solutions with high salinity is presented. METHODS: Prior to analysis by inductively coupled plasma mass spectrometry (ICP-MS) the target analytes were separated from interfering matrix constituents by the use of surface-functionalized nanoparticles. Compared with common matrix separation techniques, such as solid-phase extraction (SPE), the strength of the method lies in the combination of an advanced extraction procedure with internal standard correction. Thus, known limitations of SPE such as column clogging or incomplete analyte elution could be completely circumvented. Furthermore, time-consuming approaches for signal quantification such as matrix-matched calibration could be avoided since the applied internal standard allows the correction of matrix-induced deviations in sample extraction and ICP-MS analysis. RESULTS: With the developed procedure detection limits <1 ng L(-1) could be achieved for all the investigated elements, with satisfactory relative standard deviations (RSDs) of 3-26% for unspiked samples and <1-2% for spiked samples. Results derived from recovery experiments with spiked oil accumulation water samples confirmed the applicability of the proposed procedure for the determination of REEs in highly saline sample solutions. The procedure was successfully applied to the study of oil accumulation water samples from different oil fields in Lower Austria. CONCLUSIONS: A sample pretreatment procedure with subsequent ICP-MS analysis for the accurate determination of REEs in aqueous sample solutions with high salinity has been developed.

Irreversible thermochromism in copper chloride Imidazolium Nanoparticle Networks.

In this work Imidazolium Nanoparticle Networks (INNs) with chloride counter-ions were used to complex copper dichloride. This complexation reaction leads to the formation of a green material. The properties of the copper INN material were compared to: first, copper imidazolium complexes, without the presence of silica nanoparticles, which are not thermochromic; second, chloride-containing INN material. The copper INN material showed irreversible thermochromic behaviour, with a clear colour change from green to yellow at 180 °C, which is due to a configuration change of the copper complex from planar to tetragonal. This structural change was studied using DSC and in situ SAXS measurements during heat treatment. The thermochromic material is stable under air up to 250 °C. This preliminary study opens the door of optical sensors for INN materials.

Porous titania ionic nanoparticle networks.

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.

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.

Combining Dispersed Particle Extraction with Dried-Droplet Laser Ablation ICP-MS for Determining Platinum in Airborne Particulate Matter.

A combination of analyte pre-concentration using dispersed particle extraction (DPE) and dried-droplet laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was developed with the aim to quantify Pt and Pd in urban particulate matter with an aerodynamic diameter ≤2.5 µm (PM2.5). The PM2.5 aerosol was collected on cellulose ester filters during a sampling period of three days, with sampling intervals of 4 h only. Each of the filters was chemically digested, and the resulting solution was pre-concentrated using DPE. Droplets taken from the pre-concentrated sample were deposited on polymeric disks and dried. These dry spots were then analyzed by means of LA-ICP-MS. This approach allowed ICP-MS analysis of solutions with high content of dissolved sorbent particles coming from the DPE procedure. Furthermore, spectral interferences arising from sample-inherent matrix elements as well as solvent-related interferences could be removed by the proposed approach. The method was validated by determining the Pt concentration in Bureau Communautaire de Référence certified reference material (BCR CRM) 723 road dust certified reference material and a good agreement with the certified value was obtained. The temporal variation of Pt during the three-day sampling period is discussed, with respect to automotive traffic. The daily average of Pt measured in the air corresponds to typical values observed in urban areas in Central Europe. Although the pre-concentration of palladium is feasible with dispersed particle extraction, the method detection limits achieved here did not allow to quantify this element in the CRM or in the PM2.5 samples. The source for these high method detection limits for palladium are blank values arising from the filter material as well as the digestion procedure of the PM2.5 samples. Instrumental sensitivity of the approach would, however, suggest that palladium quantification is possible, provided the abovementioned blank issues are controlled better.

A route to heat resistant solid membranes with performances of liquid electrolytes.

The confinement of ionic liquids within a porous silica matrix was performed by a one-step non-hydrolytic sol-gel route, leading to hybrid materials (called "ionogels") featuring both the mechanical and transparency properties of silica gels and the high ionic conductivity and thermal stability of ionic liquids.

Extraction and pre-concentration of platinum and palladium from microwave-digested road dust via ion exchanging mesoporous silica microparticles prior to their quantification by quadrupole ICP-MS.

We report on the use of mesoporous silica microparticles (µPs) functionalized with quarternary amino groups for the isolation of platinum and palladium tetrachloro complexes from aqueous road dust digests. The µPs have a size ranging from 450 to 850 nm and are suspended directly in the aqueous digests, upon which the anionic Pt and Pd complexes are retained on the cationic surface. Subsequently, the µPs are separated by centrifugation. Elements that cause spectral interferences in ICP-MS determination of Pt and Pd can be quantitatively removed by adding fresh 0.240 mol L-1 HCl to the µPs and by repeating the centrifugation step. The analyte-loaded µPs are then dissolved in 0.1 mL of 2 mol L-1 HF, diluted to 2 mL, and the solutions thus obtained are analyzed by quadrupole ICP-MS. This method avoids analyte elution from the sorbent. This "dispersed particle extraction" approach yielded a run-to-run relative standard deviation ≤ 5 % for Pt and ≤ 4 % for Pd (at 0.1 ng mL-1, n = 4 road dust digests). Method detection limits (expressed as concentrations in the dust samples) are 2 and 1 ng g-1 for Pt and Pd, respectively. The method was validated by analysis of a reference material (BCR CRM 723) and applied to the analysis of road dust samples collected in downtown Vienna. Pt and Pd concentrations in samples collected in summer and in winter were compared, with concentrations ranging from 205 to 1445 ng g-1 for Pt and from 201 to 1230 ng g-1 for Pd. Graphical AbstractMesoporous silica microparticles (µPs) functionalized with quarternary amino groups were used for isolating platinum and palladium from aqueous road dust digests. The µPs were suspended directly in the aqueous digests, and the analyte-loaded µPs were analyzed using "dispersed particle extraction".

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.

Amorphous to crystal conversion as a mechanism governing the structure of luminescent YVO4:Eu nanoparticles.

The development of functional materials by taking advantage of the physical properties of nanoparticles needs an optimal control over their size and crystal quality. In this context, the synthesis of crystalline oxide nanoparticles in water at room temperature is a versatile and industrially appealing process but lacks control especially for "large" nanoparticles (>30 nm), which commonly consist of agglomerates of smaller crystalline primary grains. Improvement of these syntheses is hampered by the lack of knowledge on possible intermediate, noncrystalline stages, although their critical importance has already been outlined in crystallization processes. Here, we show that during the synthesis of luminescent Eu-doped YVO4 nanoparticles a transient amorphous network forms with a two-level structuration. These two prestructuration scales constrain topologically the nucleation of the nanometer-sized crystalline primary grains and their aggregation in nanoparticles, respectively. This template effect not only clarifies why the crystal size is found independent of the nucleation rate, in contradiction with the classical nucleation models, but also supports the possibility to control the final nanostructure with the amorphous phase.

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 bis-nanoparticle networks.

ABSTRACT: A newly arising challenge in the field of nanoparticle research concerns the control and the understanding of the interparticle interactions and interparticle properties. This should allow the development of materials based on nanoparticle assemblies which represents a great opportunity to exploit nanoparticle collective properties. Although some nanoparticle networks have been reported, few works are addressing the highly exciting problem of forming bis-nanoparticle assemblies in which two different types of nanoparticles are present. In this article we report an original synthesis pathway for the formation of an ionic bis-nanoparticle network, silica/silver, based on the formation of an imidazolium bridging unit. The reaction used for the formation of the bridging imidazolium can be considered as click-like chemistry. The synthesis of the metal/metal oxide hybrid composite material starts from the formation of a metal oxide nanoparticle modified with an imidazole ligand. This composite formation is therefore very general and could be extended to other metal/metal oxide composites. GRAPHICAL ABSTRACT: .

Layer-by-layer assembly of titania nanoparticles based ionic networks.

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.

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.

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.

Multi-component hybrid organic-inorganic particles with highly dispersed silver nanoparticles in the external shell.

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.