Fluorolytic Sol Gel Research Articles

A fluorolytic sol–gel route to access an amorphous Zr fluoride catalyst: a useful tool for C–F bond activation

A route to a ZrF4 catalyst active in room temperature Friedel–Crafts and dehydrofluorination reactions was developed via a fluorolytic sol–gel route, which was followed by a postfluorination step using CHClF2.

The Correlation Between Crystal Phase and Acidity in Nickel Doped Zinc Fluoride Solid

Nickel-doped zinc fluoride (Zn 1‑x Ni x F 2 ) with x= 0; 0.025; 0.050; 0.075; 0.100 and 0.150 were synthesized from zinc acetate as precursors. Solid materials were prepared by the fluorolytic sol gel method. The resulting solid materials were characterized by XRD and FTIR. The XRD characterization of the samples showed that there were characteristic peaks of zinc fluoride, zinc oxide and zinc hydrogen fluoride. The IR characterization spectrum showed the presence of Zn-F, Zn-O and -OH bonds in the samples. Pyridine adsorbed FTIR technique explains that the material has Lewis and Brønsted acidity. The acidity site in the solid were influenced by the Zn-O and Ni-O bonds in the catalyst.

Improved Durability of Wood Treated with Nano Metal Fluorides against Brown-Rot and White-Rot Fungi

Low-water soluble metal fluorides such as magnesium fluoride (MgF2) and calcium fluoride (CaF2) were evaluated for decay protection of wood. Initially, the biocidal efficacy of nano metal fluorides (NMFs) against wood destroying fungi was assessed with an in-vitro agar test. The results from the test showed that agar medium containing MgF2 and CaF2 was more efficient in preventing fungal decay than stand-alone MgF2 or CaF2. These metal fluorides, in their nanoscopic form synthesized using fluorolytic sol-gel synthesis, were introduced into the sapwood of Scots pine and beech wood and then subjected to accelerated ageing by leaching (EN 84). MAS 19F NMR and X-ray micro CT images showed that metal fluorides were present in treated wood, unleached and leached. Decay resistance of Scots pine and beech wood treated with NMFs was tested against wood destroying fungi Rhodonia placenta and Trametes versicolor in accordance with EN 113. Results revealed that mass losses were reduced to below 3% in wood treated with the combination of MgF2 and CaF2. It is concluded that NMFs provide full protection to wood even after it has been leached and can be used as wood preservatives in outdoor environments.

Structure and properties of Er and Er/Yb-doped YF3 up-conversion phosphors compared with oxide hosts through an internal standard

YF3 has useful physico-chemical properties such as low refractive index, low phonon energies, large infrared (IR) transparency and wide band gap, making it one of the most interesting materials with optical and optoelectronic functionalities. Among different applications, YF3 appears very promising as a host matrix for lanthanide (Ln) ion doping, in particular for up-conversion photoluminescence (UCPL). In the present study, YF3 has been synthesized via a fluorolytic sol-gel (SG) route leading to a precursor solution of yttrium trifluoroacetate (Y-TFA), from which YF3 and other oxidized derivatives can be obtained by thermal decomposition. The influence of temperature on the phases obtained was investigated by Differential Scanning Calorimetry (DSC), together with an in-depth study of the crystallite sizes by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Representative NIR to visible UCPL spectra excited at 980 nm are presented for Er and Er/Yb-doped YF3 and the corresponding UC mechanisms are discussed based on 980 nm laser power dependence plots. Moreover, an internal standard method is utilized to compare YF3 with other selected oxide matrices for lanthanides, namely aluminosilicate glass (90 SiO2-10 AlO1.5), titania (TiO2) and yttria (Y2O3).

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.

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.

New 2D layered structures with direct fluorine–metal bonds: MF(CH3COO) (M: Sr, Ba, Pb)

New coordination polymers with 2D network structures with fluorine directly coordinated to the metal ion were prepared both via mechanochemical synthesis and fluorolytic sol–gel synthesis.

Effect of Calcination Temperature and Li / TFA Molar Ratio on Morphology and Phase of Lithium Fluoride Nanoparticles Produced by Fluorolytic Sol-Gel Method

Effect of Calcination Temperature and Li / TFA Molar Ratio on Morphology and Phase of Lithium Fluoride Nanoparticles Produced by Fluorolytic Sol-Gel Method

Modification of low‐molecular polylactic acid by CaF2 nanoparticles: A new approach to change its material properties

ABSTRACTDue to environmental problems and the increasing waste of resources, sustainable biodegradable plastics has become a great topic worldwide. In this communique, we present a simple low‐cost synthesis to improve one of these typically used materials, PLA (polylactic acid). CaF2 nanoparticles synthesized according the fluorolytic sol–gel synthesis in lactic acid give access to fine tune the material characteristics of LMPLA (low‐molecular polylactic acid) due to a simply to apply polycondensation reaction of lactic acid monomers. Thus, for the first time, homo dispersed CaF2 up to 15 wt % in PLA is synthesized as cubic nanomaterial improving the characteristics of a subsequently formed thermoplastic in comparison with a polycondensed PLA reference material. A detailed characterization of the synthesized material is provided by using X‐ray imaging, TEM, 19F MAS NMR, (sol) XRD, MALDI‐TOF, and nanoindentation. The results reveal a promising first step of a modification opportunity of LMPLA regarding melting point, elastic modulus, and hardness. This way it is possible to adjust material characteristics in a simple and inexpensive way, which might broaden the field of possible applications and make biodegradable plastics a more competitive alternative to conventional used ones. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47875.

Fluorolytic Sol–Gel Route and Electrochemical Properties of Polyanionic Transition‐Metal Phosphate Fluorides

Fluorine-containing polyanionic compounds have attracted much attention in the last few years as potential positive electrode materials for rechargeable batteries. With their formula Aa Mb Xc O4 Yd (A=Li, Na…; M=Ti, V, Mn, Fe, Co, Ni…; X=P or S, and Y=F, OH, O), they offer a very rich chemistry and their electrochemical properties can be tuned by carefully choosing the different constituting elements. However, synthesis approaches that allow these materials to be obtained at low temperature are almost nonexistent. In this paper, the use of a nonaqueous fluorolytic sol-gel approach is reported to synthesize a tavorite-type LiFePO4 F material and its electrochemical characterization was performed. The obtained material displays an electrochemical performance that positively compares with the literature with an excellent cycling stability (115 mA h-1 g-1 after 100 cycles at C/2 rate). A slight change in the synthesis parameters allowed Li2 CoPO4 F to be successfully obtained, demonstrating the versatility of the reported route, which can be adapted to synthesize other fluorine-containing polyanionic compounds, which are of great interest for energy storage applications.

Fluorolytic Sol–Gel Synthesis of Nanometal Fluorides: Accessing New Materials for Optical Applications

The potential of fluorolytic sol–gel synthesis for a wide variety of applications in the field of optical materials is reviewed. Based on the fluorolytic sol–gel synthesis of nanometal fluorides, sols of complex fluorometalates have become available that exhibit superior optical properties over known classical binary metal fluorides as, for instance, magnesium fluoride, calcium fluoride, or strontium fluoride, respectively. The synthesis of transparent sols of magnesium fluoroaluminates of the general composition MgxAlFy, and fluoroperovskites, [K1−xNax]MgF3, is reported. Antireflective coatings fabricated from MgF2, CaF2, MgxAlFy, and [K1−xNax]MgF3 sols and their relevant properties are comprehensively described. Especially the heavier alkaline earth metal fluorides and the fluorperovskites crystallizing in a cubic crystal structure are excellent hosts for rare earth (RE) metals. Thus, the second chapter reflects the synthesis approach and the properties of luminescent systems based on RE-doped alkaline earth metal fluorides and [K1−xNax]MgF3 phases.

Lithium fluoride/iron difluoride composite prepared by a fluorolytic sol–gel method: Its electrochemical behavior and charge–discharge mechanism as a cathode material for lithium secondary batteries

Owing to their high theoretical capacity, metal fluorides have attracted significant interest as materials for fabricating the cathode of lithium secondary batteries. In the present study, a nanocomposite of LiF and FeF2 is prepared by a fluorolytic sol–gel method in an ethanol solution, for use as the cathode material of a lithium secondary battery. The produced LiF/FeF2 composite is characterized by broad X-ray diffraction peaks attributed to the nanosized (∼10 nm) LiF and FeF2 crystals, a large Brunauer–Emmett–Teller surface area of 119 m2 g-1, and adsorption–desorption hysteresis, attributed to the presence of mesopores. The results of charge–discharge tests indicates an initial discharge capacity of 225 mAh (g-LiF/FeF2)−1 through reversal conversion at a current rate of 10 mA (g-LiF/FeF2)−1. Based on a combination of galvanostatic intermittent titration, X-ray absorption, and X-ray diffraction investigations, a new reaction mechanism is developed, namely, the conversion of the local environment of an Fe atom from a rutile-type FeF2 structure to a rhenium trioxide-type FeF3 structure during charging, with the subsequent discharge resulting in the insertion of Li+ into the rhenium trioxide-type FeF3 structure, followed by the conversion reaction to LiF and FeF2.

Aluminum oxo-fluoride clusters: A first principle investigation of stability, synthetic considerations, and the interaction with water.

The introduction of the so called fluorolytic sol-gel synthesis in 2003 gave access to previously inaccessible aluminum oxo-fluorides, thus to nanoscopic materials and, more importantly, novel catalysts. The intermediate cluster structures synthesized and stabilized by Kemnitz and coworkers have mainly been protected by iso-propoxide groups. However, since catalytic reactions take place in a large variety of media, hydrophilic analogs of those clusters would be of interest. In this manuscript, we present a computational analysis for the fluorination reaction, which represents the second part of fluorolytic sol-gel synthesis, and a theoretical study of the synthesized Al4 F4 (μ4 -O)(μ-Oi Pr)5 [H(Oi Pr)2 ] nanostructure's conversion to its hydroxylated analog Al4 F4 (μ4 -O)(μ-OH)5 [H(OH)2 ] utilizing the nudged elastic band method. Furthermore, the role of the fluorine atoms of the cluster in an aqueous medium is evaluated by studying the incremental addition of water molecules to the cluster with and without fluorine atoms. In addition, NMR shifts of clusters exhibiting different substituents are compared. It has been found that the inclusion of an explicit solvent is necessary to capture the magnetic response of the individual cluster atoms in an aqueous solvent correctly. © 2018 Wiley Periodicals, Inc.

Synthesis and Characterization of Perovskite-Type [K1−xNax]MgF3 Mixed Phases via the Fluorolytic Sol-Gel Synthesis

The focus of this article is the synthesis of perovskite-type [K1−xNax]MgF3 mixed phases via the room-temperature fluorolytic sol-gel approach. Different molar ratios of K/Na were examined and analyzed by 19F MAS NMR and X-ray powder diffraction. Starting from pure KMgF3, a systematic substitution of potassium by sodium was evidenced when replacing K by Na. As long as the amount of sodium is less than 80% as compared to potassium, spectra just show [K4−xNaxF] environments in a [K1−xNax]MgF3 mixed phase but separate structures appear when the amount of sodium is further increased. Moreover, colloidal dispersions of nanoscaled KMgF3 particles were obtained, which were used to fabricate coatings on glass slides. Thin films showed antireflective behavior and high transmittance.

Modifying the reactivity of a solid Lewis acid: niobium and antimony doped nanoscopic aluminum fluoride

A series of acid catalysts were prepared, using niobium and antimony as dopants in the fluorolytic sol–gel synthesis of high surface aluminium fluoride.

Sol-Gel-Synthesis of Nanoscopic Complex Metal Fluorides.

The fluorolytic sol-gel synthesis for binary metal fluorides (AlF3, CaF2, MgF2) has been extended to ternary and quaternary alkaline earth metal fluorides (CaAlF5, Ca2AlF7, LiMgAlF6). The formation and crystallization of nanoscopic ternary CaAlF5 and Ca2AlF7 sols in ethanol were studied by 19F liquid and solid state NMR (nuclear magnetic resonance) spectroscopy, as well as transmission electron microscopy (TEM). The crystalline phases of the annealed CaAlF5, Ca2AlF7, and LiMgAlF6 xerogels between 500 and 700 °C could be determined by X-ray powder diffraction (XRD) and 19F solid state NMR spectroscopy. The thermal behavior of un-annealed nanoscopic ternary and quaternary metal fluoride xerogels was ascertained by thermal analysis (TG/DTA). The obtained crystalline phases of CaAlF5 and Ca2AlF7 derived from non-aqueous sol-gel process were compared to crystalline phases from the literature. The corresponding nanoscopic complex metal fluoride could provide a new approach in ceramic and luminescence applications.

On the Morphology of Group II Metal Fluoride Nanocrystals at Finite Temperature and Partial Pressure of HF.

We have investigated the bulk and surface properties of the group II metal fluorides CaF, SrF and BaF using periodic density functional theory (DFT) calculations and surface thermodynamics. Our bulk results show that the best agreement with experiment is achieved with the B3LYP and PBE functionals. We determined the relative importance of the low index surfaces in vacuum and found that an fluoride microcrystal exposes only the (111) surface in which the undercoordinated cations are sevenfold coordinated. With methods of ab initio surface thermodynamics, we analyzed the stability of different surfaces under hydrogen fluoride (HF) pressure and determined the presumable shape of the crystals with respect to different HF concentrations and temperatures. In the case of CaF and SrF, the calculated shapes of the crystals agree well with TEM images of fluorolytic sol-gel synthesized nanocrystals at room temperature and high HF concentration.

Catalytic features of Nb-based nanoscopic inorganic fluorides for an efficient one-pot conversion of cellulose to lactic acid

A series of niobium-modified fluorides (denoted Nb@MgF2 and Nb@CaF2), prepared via the fluorolytic sol gel synthesis was investigated for the catalytic one-pot conversion of cellulose to lactic acid. In order to establish the main catalytic features influencing the synthesis of lactic acid, physical-chemical properties – catalytic performance correlations were made and compared with previously reported Sn@MgF2 and Nb@AlF3 catalysts. The structure of the catalysts is the result of three important parameters: the ionic radii of the guest-host cations, the fluorolysis rate of each alkoxide species and the concentration of the guest cation. As a function of these parameters samples with different catalytic performances in terms of lactic acid yields are obtained. Nb@CaF2 sample leads to similar yields to lactic acid by comparison with the previously reported Nb@AlF3 (15.4% versus 17.0%). In addition, Nb@CaF2 displays a higher hydrothermal stability.

Core–shell metal fluoride nanoparticles via fluorolytic sol–gel synthesis – a fast and efficient construction kit

An efficient, fast and easy construction kit using the fluorolytic sol–gel synthesis of rare-earth-doped alkaline earth fluoride core–shell nanoparticles at room temperature is presented, capable of synthesizing several hundred grams to kilograms of core–shell particles in one batch.

Sol–gel synthesis of Sr1−xYbxF2+x nanoparticles dispersible in acrylates

A new approach to prepare nanoparticles in SrF2-YbF3 systems via the fluorolytic sol–gel synthesis is presented.