20 research outputs found
Nanocrystalline and stacking-disordered ÎČ-cristobalite AlPO4: the now deciphered main constituent of a municipal sewage sludge ash from a full-scale incineration facility
This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.For the first time evidence is provided that a nanocrystalline and stacking-disordered, chemically stabilized ÎČ-cristobalite form of AlPO4 occurs in a sewage sludge ash (SSA). This proof is based on a combined X-ray powder diffraction and X-ray fluorescence investigation of an SSA produced at a large-scale fluidized bed incineration facility serving a catching area with a population of 2 million. The structural and chemical characterization was carried out on âas receivedâ SSA samples as well as on solid residues remaining after leaching this SSA in sodium hydroxide solution. Thus, it was ascertained that the observed nanocrystalline and stacking-disordered cristobalite-like component belongs to the aluminum phosphate component of this SSA, rather than to its silicon dioxide component. In addition, a direct proof is presented that the chemically stabilized ÎČ-cristobalite form of AlPO4 does crystallize from X-ray amorphous precursors under conditions that mimic the huge heating rate and short retention time (just seconds at T â 850°C), typical for fluidized bed incinerators.Peer Reviewe
Local Structure of EuropiumâDoped Luminescent Strontium Fluoride Nanoparticles: Comparative Xâray Absorption Spectroscopy and Diffraction Study
Rareâearth based luminescent materials are key functional components for the rational design of lightâconversion smart devices. Stable Eu3+âdoped strontium fluoride (SrF2) nanoparticles were prepared at room temperature in ethylene glycol. Their luminescence depends on the Eu content and changes after heat treatment. The crystallinity of heatâtreated material increases in comparison with asâsynthesized samples. Particles were investigated in solution using Xâray diffraction, smallâangle Xâray scattering, and Xâray spectroscopy. After heat treatment, the size of the disordered nanoparticles increases together with a change of their local structure. Interstitial fluoride ions can be localized near Eu3+ ions. Therefore, nonâradiative relaxation from other mechanisms is decreased. Knowledge about the cation distribution is key information for understanding the luminescence properties of any material.BAM funding program âIdeasâ (Menschen Ideen): New insights on the thermal behavior of luminescent nanoparticles from Sol-Gel synthesis by inâ
situ characterization â towards efficient upconversionPeer Reviewe
Chemical inâdepth analysis of (Ca/Sr)F2 coreâshell like nanoparticles by Xâray photoelectron spectroscopy with tunable excitation energy
The fluorolytic solâgel synthesis is applied with the intention to obtain two different types of coreâshell nanoparticles, namely, SrF2âCaF2 and CaF2âSrF2. In two separate fluorination steps for core and shell formation, the corresponding metal lactates are reacted with anhydrous HF in ethylene glycol. Scanning transmission electron microscopy (STEM) and dynamic light scattering (DLS) confirm the formation of particles with mean dimensions between 6.4 and 11.5 nm. The overall chemical composition of the particles during the different reaction steps is monitored by quantitative Al Kα excitation X-ray photoelectron spectroscopy (XPS). Here, the formation of stoichiometric metal fluorides (MF2) is confirmed, both for the core and the final coreâshell particles. Furthermore, an in-depth analysis by synchrotron radiation XPS (SR-XPS) with tunable excitation energy is performed to confirm the coreâshell character of the nanoparticles. Additionally, Ca2p/Sr3d XPS intensity ratio in-depth profiles are simulated using the software Simulation of Electron Spectra for Surface Analysis (SESSA). In principle, coreâshell like particle morphologies are formed but without a sharp interface between calcium and strontium containing phases. Surprisingly, the in-depth chemical distribution of the two types of nanoparticles is equal within the error of the experiment. Both comprise a SrF2-rich core domain and CaF2-rich shell domain with an intermixing zone between them. Consequently, the internal morphology of the final nanoparticles seems to be independent from the synthesis chronology.European Metrology Programme for Innovation and Research (EMPIR)
http://dx.doi.org/10.13039/100014132Peer Reviewe
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Chemical in-depth analysis of (Ca/Sr)F2 coreâshell like nanoparticles by X-ray photoelectron spectroscopy with tunable excitation energy
The fluorolytic solâgel synthesis is applied with the intention to obtain two different types of coreâshell nanoparticles, namely, SrF2âCaF2 and CaF2âSrF2. In two separate fluorination steps for core and shell formation, the corresponding metal lactates are reacted with anhydrous HF in ethylene glycol. Scanning transmission electron microscopy (STEM) and dynamic light scattering (DLS) confirm the formation of particles with mean dimensions between 6.4 and 11.5 nm. The overall chemical composition of the particles during the different reaction steps is monitored by quantitative Al Kα excitation X-ray photoelectron spectroscopy (XPS). Here, the formation of stoichiometric metal fluorides (MF2) is confirmed, both for the core and the final coreâshell particles. Furthermore, an in-depth analysis by synchrotron radiation XPS (SR-XPS) with tunable excitation energy is performed to confirm the coreâshell character of the nanoparticles. Additionally, Ca2p/Sr3d XPS intensity ratio in-depth profiles are simulated using the software Simulation of Electron Spectra for Surface Analysis (SESSA). In principle, coreâshell like particle morphologies are formed but without a sharp interface between calcium and strontium containing phases. Surprisingly, the in-depth chemical distribution of the two types of nanoparticles is equal within the error of the experiment. Both comprise a SrF2-rich core domain and CaF2-rich shell domain with an intermixing zone between them. Consequently, the internal morphology of the final nanoparticles seems to be independent from the synthesis chronology
Amorphes Aluminiumchlorofluorid und -bromofluorid - die stÀrksten bekannten festen Lewis-SÀuren
Die feste nichtkristalline Lewis-SĂ€ure Aluminiumchlorofluorid (ACF, AlCl(x)F(3-x), x = 0.05 .. 0.3) hat die höchste bisher bekannte Lewis-AciditĂ€t aller heterogenen Katalysatoren. Sie erreicht die StĂ€rke von Antimonpentafluorid SbF5 und ĂŒbertrifft sie in manchen FĂ€llen sogar. In dieser Arbeit wurden die Bulk-Struktur des ACF und der sehr Ă€hnlichen Verbindung Aluminiumbromofluorid (ABF) mittels IR-, ESR-, NMR- und Röntgenabsorptionsspektroskopie studiert. Die OberflĂ€che der Verbindungen wurde durch die Adsorption von Gasen bei niedrigen Temperaturen untersucht, sowie durch IR- und ESR-Spektroskopie adsorbierter SondenmolekĂŒle. Das thermische Verhalten dieser nichtkristallinen Verbindungen wurde mittels DTA verfolgt. Die Lewis-AciditĂ€t kleiner Modellverbindungen wurde NMR-spektroskopisch und mit ab initio Methoden untersucht. Alle Daten wurden mit denen der gut charakterisierten und bekannten Modifikationen des Aluminiumfluorids (AlF3) verglichen. Die kombinierten Ergebnisse der Messungen an beiden festen Phasen erlauben die Entwicklung eines Strukturmodells fĂŒr diese Verbindungen, das die meisten spektroskopischen Daten und die auĂergewöhnlich hohe Lewis-AciditĂ€t erklĂ€ren kann. Beide Phasen sind sehr Ă€hnlich zueinander. Das Vorhandensein des schwereren Halogens (Cl, Br) erzeugt eine Störung des Netzwerkes und verhindert die Ausbildung geordneter Strukturen. Der Grad der Unordnung in diesen Phasen ist höher als bei allen anderen Verbindungen des Aluminiumfluorids. Daraus resultiert eine gestörte OberflĂ€che, was wiederum zu koordinativ ungesĂ€ttigtem Aluminium an der OberflĂ€che fĂŒhrt. Die sauren Zentren in ACF und ABF sind stĂ€rker als in anderen aluminiumhaltigen Lewis-SĂ€uren.The solid non-crystalline Lewis acid aluminum chlorofluoride (ACF, AlCl(x)F(3-x), x = 0.05 .. 0.3) has the highest Lewis acidity of any heterogeneous catalyst known so far. It reaches the acidity of antimony pentafluoride (SbF5) and in some cases even exceeds it. In this work the bulk structure of ACF and of the very similar compound aluminium bromofluoride (ABF) was studied by IR, ESR, NMR, and X-ray absorption spectroscopy. The surface of the compounds was investigated by adsorption of gases at low temperatures, as well as by IR and ESR spectroscopy of adsorbed probe molecules. The thermal behavior of these non-crystalline compounds was followed by DTA. The Lewis acidity of small model compounds was studied by NMR spectroscopy and ab initio calculations. All data were compared to those of well characterized known samples of the different modifications of aluminum fluoride (AlF3). The combined results of the measurements of both solid phases allow to set up a structure model for these compounds which can explain most of the spectrocopic data and the extraordinary high Lewis acidity. Both phases are very similar to each other. The occurrence of the heavier halogen (Cl, Br) causes a perturbation of the network and prevents it from forming ordered structures. The degree of disorder of these phases is higher than for any other known compounds of aluminum fluoride. This results in an disordered surface which leads to coordinatively unsaturated aluminum at the surface. The acidic centers of ACF and ABF are stronger than in any other aluminum containing Lewis acid
Nano metal fluorides: small particles with great properties
The recently developed fluorolytic solâgel route to metal fluorides opens a very broad range of both scientific and technical applications of the accessible high surface area metal fluorides, many of which have already been applied or tested. Specific chemical properties such as high Lewis acidity and physical properties such as high surface area, mesoporosity and nanosize as well as the possibility to apply metal fluorides on surfaces via a non-aqueous sol make the fluorolytic synthesis route a very versatile one. The scope of its scientific and technical use and the state of the art are presented.Peer Reviewe
Verfahren zur Herstellung polykristalliner transparenter Formteile
Die Erfindung betrifft ein Verfahren zur Herstellung polykristalliner transparenter Formteile. Die vorliegende Erfindung legt dar, wie unter geeigneter Modifizierung der fluorolytischen Sol-Gel-Synthese spezielle CaF2-Pulver zugĂ€nglich sind, die das hĂ€ufig bei Fluoriden beobachtete Problem der Kokebildung umgehen und auĂerdem homogene CaF2-Partikel liefern, die sowohl rieselfĂ€hig als auch verpressbar sind
Toward Luminescent Composites by Phase Transfer of SrF2:Eu3+ Nanoparticles Capped with Hydrophobic Antenna Ligands
Transparent dispersions of hydrophobic SrF2â:âEu3+ nanoparticles in cyclohexane with up to 20% europium were obtained by fluorolytic solâgel synthesis followed by phase transfer into cyclohexane through capping with sodium dodecylbenzenesulfonate (SDBS). The particles were characterized by TEM, XRD and DLS as spherical objects with a diameter between 6 and 11â
nm in dry state. 1Hâ13CP MAS NMR experiments revealed the binding of the anionic sulfonate head group to the particle surface. The particles show bright red luminescence upon excitation of the aromatic capping agents, acting as antennas for an energy transfer from the benzenesulfonate unit to the Eu3+ centers in the particles. This synthesis method overcomes the current obstacle of the fluorolytic solâgel synthesis that transparent dispersions can be obtained directly only in hydrophilic solvents. To demonstrate the potential of such hydrophobized alkalineâearth fluoride particles, transparent luminescent organicâinorganic composites with 10% SrF2â:âEu3+ embedded into polyTEGDMA, polyBMA, polyBDDMA and polyD3MA, respectively, were prepared, endowing the polymers with the luminescence features of the nanoparticles.Peer Reviewe
Solid Solutions CaF<sub>2</sub>âYF<sub>3</sub> with Fluorite Structure Prepared on the SolâGel Route: Investigation by Multinuclear MAS NMR Spectroscopy
Nanoscaled
Ca<sub>1â<i>x</i></sub>Y<sub><i>x</i></sub>F<sub>2+<i>x</i></sub> (<i>x</i> = 0...0.40)
was prepared on the new fluorolytic solâgel route using organic
precursors and anhydrous HF. These nonstoichiometric fluorite-type
phases were investigated using <sup>19</sup>F MAS and <sup>19</sup>Fâ<sup>89</sup>Y CP MAS NMR. Excess fluoride ions occur as
point defects for <i>x</i> †0.01. For <i>x</i> > 0.01 excess fluoride ions start clustering. The <sup>19</sup>F spectra of these phases can be fully explained by assuming a distribution
of Ca<sup>2+</sup> and Y<sup>3+</sup> around fluoride ions. Y<sup>3+</sup> is distributed within the crystal lattice of CaF<sub>2</sub>, with higher concentrations near fluoride clusters. Two different
coordination polyhedra for Y<sup>3+</sup> are observed. The correlation
between <sup>19</sup>F and <sup>89</sup>Y signals was established
Local Structures of Solid Solutions Sr<sub>1â<i>x</i></sub>Y<sub><i>x</i></sub>F<sub>2+<i>x</i></sub> (<i>x</i> = 0...0.5) with Fluorite Structure Prepared by SolâGel and Mechanochemical Syntheses
Nanocrystalline
Sr<sub>1â<i>x</i></sub>Y<i><sub>x</sub></i>F<sub>2+<i>x</i></sub> samples (0
†<i>x</i> †0.50) were prepared by fluorolytic
solâgel and mechanochemical syntheses using anhydrous HF or
NH<sub>4</sub>F as fluorinating agents. This way, we compare the generated
nanoparticular nonstoichiometric phases synthesized by two different
routes. The obtained nonstoichiometric fluorite-type phases were studied
using <sup>19</sup>F magic-angle spinning (MAS) and <sup>19</sup>Fâ<sup>89</sup>Y CP MAS NMR techniques and applying the superposition model.
The <sup>19</sup>F spectra of these phases can be fully explained
by the distribution of Sr<sup>2+</sup> and Y<sup>3+</sup> cations
around fluoride ions. These samples can serve as model compounds for
a better structural understanding of fluorescent up- and down-converting
systems