Nanocrystalline and stacking-disordered β-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 β-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 ‘as received’ 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 β-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 ≈ 850°C), typical for fluidized bed incinerators.Peer Reviewe

Local Structure of Europium‐Doped Luminescent Strontium Fluoride Nanoparticles: Comparative X‐ray Absorption Spectroscopy and Diffraction Study

Rare‐earth based luminescent materials are key functional components for the rational design of light‐conversion smart devices. Stable Eu3+‐doped 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 heat‐treated material increases in comparison with as‐synthesized samples. Particles were investigated in solution using X‐ray diffraction, small‐angle X‐ray scattering, and X‐ray 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, non‐radiative 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 “Ideas” (Menschen Ideen): New insights on the thermal behavior of luminescent nanoparticles from Sol-Gel synthesis by in situ characterization – towards efficient upconversionPeer Reviewe

Chemical in‐depth analysis of (Ca/Sr)F2 core–shell like nanoparticles by X‐ray photoelectron spectroscopy with tunable excitation energy

The fluorolytic sol–gel synthesis is applied with the intention to obtain two different types of core–shell nanoparticles, namely, SrF2–CaF2 and CaF2–SrF2. 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 core–shell particles. Furthermore, an in-depth analysis by synchrotron radiation XPS (SR-XPS) with tunable excitation energy is performed to confirm the core–shell 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, core–shell 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

Chemical in-depth analysis of (Ca/Sr)F2 core–shell like nanoparticles by X-ray photoelectron spectroscopy with tunable excitation energy

The fluorolytic sol–gel synthesis is applied with the intention to obtain two different types of core–shell nanoparticles, namely, SrF2–CaF2 and CaF2–SrF2. 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 core–shell particles. Furthermore, an in-depth analysis by synchrotron radiation XPS (SR-XPS) with tunable excitation energy is performed to confirm the core–shell 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, core–shell 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 stärksten bekannten festen Lewis-Säuren

Die feste nichtkristalline Lewis-Säure Aluminiumchlorofluorid (ACF, AlCl(x)F(3-x), x = 0.05 .. 0.3) hat die höchste bisher bekannte Lewis-Acidität aller heterogenen Katalysatoren. Sie erreicht die Stärke von Antimonpentafluorid SbF5 und übertrifft sie in manchen Fällen sogar. In dieser Arbeit wurden die Bulk-Struktur des ACF und der sehr ähnlichen Verbindung Aluminiumbromofluorid (ABF) mittels IR-, ESR-, NMR- und Röntgenabsorptionsspektroskopie studiert. Die Oberfläche der Verbindungen wurde durch die Adsorption von Gasen bei niedrigen Temperaturen untersucht, sowie durch IR- und ESR-Spektroskopie adsorbierter Sondenmoleküle. Das thermische Verhalten dieser nichtkristallinen Verbindungen wurde mittels DTA verfolgt. Die Lewis-Acidität 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 für diese Verbindungen, das die meisten spektroskopischen Daten und die außergewöhnlich hohe Lewis-Acidität erklären kann. Beide Phasen sind sehr ähnlich 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 Oberfläche, was wiederum zu koordinativ ungesättigtem Aluminium an der Oberfläche führt. Die sauren Zentren in ACF und ABF sind stärker als in anderen aluminiumhaltigen Lewis-Säuren.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 sol–gel 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 zugänglich sind, die das häufig bei Fluoriden beobachtete Problem der Kokebildung umgehen und außerdem homogene CaF2-Partikel liefern, die sowohl rieselfähig als auch verpressbar sind

Toward Luminescent Composites by Phase Transfer of SrF2:Eu3+ Nanoparticles Capped with Hydrophobic Antenna Ligands

Transparent dispersions of hydrophobic SrF2 : Eu3+ nanoparticles in cyclohexane with up to 20% europium were obtained by fluorolytic sol‐gel 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 11 nm in dry state. 1H‐13CP 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 sol‐gel synthesis that transparent dispersions can be obtained directly only in hydrophilic solvents. To demonstrate the potential of such hydrophobized alkaline‐earth fluoride particles, transparent luminescent organic‐inorganic composites with 10% SrF2 : Eu3+ embedded into polyTEGDMA, polyBMA, polyBDDMA and polyD3MA, respectively, were prepared, endowing the polymers with the luminescence features of the nanoparticles.Peer Reviewe

Solid Solutions CaF₂–YF₃ with Fluorite Structure Prepared on the Sol–Gel Route: Investigation by Multinuclear MAS NMR Spectroscopy

Nanoscaled Ca_1–<i>x</i>Y_<i>x</i>F_2+<i>x</i> (<i>x</i> = 0...0.40) was prepared on the new fluorolytic sol–gel route using organic precursors and anhydrous HF. These nonstoichiometric fluorite-type phases were investigated using ¹⁹F MAS and ¹⁹F–⁸⁹Y 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 ¹⁹F spectra of these phases can be fully explained by assuming a distribution of Ca²⁺ and Y³⁺ around fluoride ions. Y³⁺ is distributed within the crystal lattice of CaF₂, with higher concentrations near fluoride clusters. Two different coordination polyhedra for Y³⁺ are observed. The correlation between ¹⁹F and ⁸⁹Y signals was established

Local Structures of Solid Solutions Sr_1–<i>x</i>Y_<i>x</i>F_2+<i>x</i> (<i>x</i> = 0...0.5) with Fluorite Structure Prepared by Sol–Gel and Mechanochemical Syntheses

Nanocrystalline Sr_1–<i>x</i>Y<i>_x</i>F_2+<i>x</i> samples (0 ≤ <i>x</i> ≤ 0.50) were prepared by fluorolytic sol–gel and mechanochemical syntheses using anhydrous HF or NH₄F 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 ¹⁹F magic-angle spinning (MAS) and ¹⁹F–⁸⁹Y CP MAS NMR techniques and applying the superposition model. The ¹⁹F spectra of these phases can be fully explained by the distribution of Sr²⁺ and Y³⁺ cations around fluoride ions. These samples can serve as model compounds for a better structural understanding of fluorescent up- and down-converting systems