Substitution Of Fluoride Ions Research Articles

Aniline compounds drug detection using novel gas sensor based on CuOHF-CuO/ZnOHF-ZnO nanomaterials

The novel copper hydroxyfluoride-copper oxide (CHFCO)/zinc hydroxyfluoride-zinc oxide (ZHFZO) nanomaterials were prepared by hydrothermal method and exhibited superior sensing performance for methamphetamine analogue-phenethylamine. The sensing characteristics of calcined ZHFZO rods, CHFCO flakes, and four composite nanomaterial ratios were examined. The experimental results demonstrated that the CHFCO/ZHFZO-2 sensor exhibited improved sensing performance for phenethylamine, with the optimum working temperature reduced to 200 ℃. The responses of the ZHFZO and CHFCO sensors to 10 ppm phenylethylamine were 1.9 and 3.5, respectively, while the response of the CHFCO/ZHFZO-2 sensor was enhanced to 5. With a response time (Tres) and recovery time (Trec) of 30 s for 10 ppm phenylethylamine, the sensor enables rapid detection. It has great selectivity and reproducibility for phenylethylamine and can detect concentrations as low as 125 ppb, demonstrating its potential for quantitative detection at the parts per billion (ppb) level. The prepared composites possessed unique nanostructures and large specific surface areas. The substitution of fluoride ions produces a large electronegativity and the physical adsorption of polar hydroxyl bonds combine to enhance the sensitization of phenylethylamine gas. The findings presented in this study underscore the promising potential of the synthesized nanomaterials for highly sensitive and selective detection of phenylethylamine.

Effect of High Temperatures on the Microstructure and Properties of Fluorine-Containing Hydroxyapatite-Based Materials

This paper examines the feasibility of improving the strength of hydroxyapatite prepared by precipitation from solution via partial substitution of fluoride ions for hydroxyl groups and the addition of calcium fluoride. A comparative analysis of the resultant materials is carried out using advanced physicochemical characterization techniques. Fluoride ions are shown to influence the thermal stability, sintering behavior, microstructure, and strength of ceramics produced using precipitated hydroxyapatite.

Topochemical Fluorination of n = 2 Ruddlesden-Popper Type Sr3Ti2O7 to Sr3Ti2O5F4 and Its Reductive Defluorination.

Within this study, we show that a sequence of substitutive topochemical fluorination of the n = 2 Ruddlesden-Popper type compounds Sr3Ti2O7 to Sr3Ti2O5F4 followed by reductive topochemical defluorination reactions between the oxyfluoride and the reducing agent sodium hydride allows for a substantial reduction of the oxidation state of Ti due to selective extraction and hydride substitution of fluoride ions. The oxyfluoride Sr3Ti2O5F4 has been synthesized and characterized structurally for the first time. The defluorination experiments have been conducted at temperatures as low as 300 °C, enabling also the reduction of this metastable compound. The evolution of phase fractions and unit cell volumes of various reduced phases as well as of side products has been monitored by an X-ray diffraction study as a function of the amount of sodium hydride used. Strong structural changes within the reduced phases, involving considerable decreases in the c lattice parameters partly accompanied by symmetry, lowering have been observed. To gain a deeper understanding of the structural changes, selected reduction reaction products have been further investigated by coupled analysis of X-ray and neutron powder diffraction data. Moreover, changes in the oxidation state of Ti have been studied using magnetic measurements and X-ray photoelectron spectroscopy examining differences between the bulk and the surface properties. Additionally, similarities and differences between previously published results on the topochemical defluorination of the n = 1 Ruddlesden-Popper type compound Sr2TiO3F2 are discussed.

Proton state in hydrated fluoro-substituted brownmillerites Ba2In2O5–0.5y F y ∙nН2О

Solid solutions Ba2In2O5–0.5y F y with the structure of brownmillerite are studied by IR and 1Н MAS NMR spectroscopy. During the fluorine doping, the nearest oxygen environment of indium atoms is distorted and a part of In–O bonds is shortened. It is shown that partial fluoride ion substitution for oxygen atoms results in an increase in the proton mobility in hydrated Ba2In2O5–0.5y F y ∙nН2О phases.

Hydrofluoride decomposition of natural materials including zirconium-containing minerals

Recently, interest in ammonium hydrogen difluoride (NH4HF2) as a versatile fluorinating agent for the decomposition of natural materials resumed. It is considered to be a new and more efficient than hydrofluoric acid (HF) reagent in analytical chemistry. Thermodynamically possible fluorination reactions with NH4HF2 are exothermic and proceed even at room temperature with the entropy reserve. The fluorination products are of high symmetry phases (tetragonal or cubic) with partial substitution of fluoride ion for oxide (or hydroxide). The fluorination of refractory silicate zircon (ZrSiO4) is kinetically hindered, and its complete decomposition requires the use of a Teflon autoclave at 200oC. The fluorination products are cubic (NH4)3Zr(OH)xF7-x (x ≤ 0.3) and tetragonal double salt (NH4)3SiF7, which can be separated due to incongruent sublimation of (NH4)2SiF6. The mechanism of the latter process is proposed.

Effect of F ions on physical and optical properties of fluorine substituted zinc arsenic tellurite glasses

The effect of substitution of fluoride ions for oxide ions on the physical and optical properties of glass system (20-x) ZnO-xZnF2-40As2O3-40TeO2 where x = 0, 4, 8,12,16,20 mole % were investigated. The samples prepared by melt quenching method under controlled condition. The amorphous nature of these glasses was checked by X-ray diffraction technique. The density was measured according to Archimedes principle. The room temperature absorption spectra of all glass samples were determined using UV-Vis-NIR spectrometer. The thermal behaviour, glass transition temperature and stability of glass samples were studied by a differential scanning calorimetric (DSC). The density reduction of present glasses with ZnF2 concentrations may be due to the low density of ZnF2 compared with that of ZnO. Breaking the oxide network, the cross linking degree of the glass former could be reduced which results in decrease of both Tg and Tx. In the present glass system when F ions replaced by oxygen ions UV-Vis absorption cut-off wavelength decreases. This resulted form the conversion of structural unit in the glass from TeO4 to Te(O,F)4 and then to Te(O, F)3.

Increased radiative lifetime of Tm3+:3F4 → 3H6 transition in oxyfluoride tellurite glasses

The 1.8μm emission properties of Tm3+-doped zinc tellurite glasses modified by the substitution of ZnF2 are investigated in this paper. The thermal stability, Raman and phonon sideband spectra, transmission and absorption spectra, emission spectra and decay curves are discussed. It is found that substitution of fluoride ions into the zinc tellurite matrix produces dramatic increase in the emission lifetime of Tm3+ 1.8μm emission. Absorption, Raman and phonon sideband spectra are used to estimate the local structure of Tm3+ ions. These analyses indicate structural change around Tm3+ ions caused by substitution of fluoride ions monitors the increased intrinsic radiative lifetimes. An increase in the measured radiative lifetimes of the Tm3+:3F4→3H6 transition is observed. The origin has been discussed and the reduction of OH− absorption, decrease of maximum phonon energy and phonon density are considered to be dominant in all of the nonradiative relaxations.

Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol–gel method: dissolution behaviour and biological properties after crystallisation

Hydroxyapatite (HA), fluor-hydroxyapatite (FHA) with varying levels of fluoride ion substitution and fluorapatite (FA) were synthesised by the sol–gel method as possible implant coating or bone-grafting materials. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol–water based solution. Different amounts of ammonium fluoride were incorporated for the preparation of the FHA and FA sol–gels. After heating and powdering the sol–gels, dissolution behaviour was assessed using ion chromatography to measure Ca2+ and PO4 3− ion release. Biological behaviour was assessed using cellular proliferation with human osteosarcoma cells and alamarBlue™ assay. Statistical analysis was performed with a two way analysis of variance and post hoc testing with a Bonferroni correction. Increasing fluoride substitution into an apatite structure decreased the dissolution rate. Increasing the firing temperature of the HA, FHA and FA sol–gels up to 1,000 °C decreased the dissolution rate. There was significantly higher cellular proliferation on highly substituted FHA and FA than on HA or Titanium. The properties of an implant coating or bone grafting material can be tailored to meet specific requirements by altering the amount of fluoride that is incorporated into the original apatite structure. The dissolution behaviour can further be altered by the temperature at which the sol–gel is fired.

Hydroxyapatite, fluor-hydroxyapatite and fluorapatite produced via the sol–gel method: Bonding to titanium and scanning electron microscopy

ObjectivesHydroxyapatite (HA), fluor-hydroxyapatite (FHA) with varying levels of fluoride ion substitution and fluorapatite (FA) production has been characterised and optimised by the sol–gel method and the dissolution and biological properties of these materials were investigated. It was the objective of this study to investigate the potential bond strength and interaction of these materials with titanium. MethodsHA, FHA and FA were synthesised by a sol–gel method. Calcium nitrate and triethyl phosphite were used as precursors under an ethanol–water based solution. Different amounts of ammonium fluoride (NH4F) were incorporated for the preparation of the FHA and FA sol–gels. Using a spin coating technique the sol–gels were coated onto commercially pure titanium disks and crystallised at various temperatures. Using scanning electron microscopy (SEM) and elemental analysis, the surface characteristics, coating thickness and interaction of the Ti substrate and coating were investigated. The bond strengths of the coating to the Ti were investigated using an Instron Universal Load Testing Machine. Statistical analysis was performed with a two-way analysis of variance and post hoc testing with a Bonferroni correction. Results(1) Coating speed inversely influenced the coating thickness. (2) Increasing fluoride ion substitution and heating temperature significantly increased bond strength and (3) increasing fluoride ion substitution increased the coating thickness. SignificanceFHA and FA synthesised using the sol–gel technique may offer a superior alternative to coating titanium implants with HA and plasma spraying. HA, FHA and FA materials synthesised by the sol–gel method may also have a use as bone grafting materials.

Effect of NH4F concentration in electrolyte on the fabrication of TiO2 nanotube arrays prepared by anodisation

Highly-ordered TiO2 nanotube arrays (TNTs) were prepared by anodisation in ethylene electrolytes containing 0.2–0.7 wt% NH4F. The dimension, chemical composition and optical characterisation of prepared TNTs were determined by the field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy, respectively. Both the length and inner diameter of the prepared TNTs were increased with increasing NH4F concentration of electrolyte because of the faster electrochemical dissolution rate of TiO2. However, dimension of TNTs approached stable lengths and inner diameters as the NH4F concentration was higher than 0.3 wt%. The presence of Ti3+ state was observed for TNTs prepared with increasing NH4F concentration because of the charge compensation of the substitution of fluoride ions for oxygen ions. TNTs prepared in the electrolytes containing higher NH4F concentrations exhibited superior performance on the photocatalytic decomposition of Acid Red 4 possibly because more fluorides incorporated with TNTs to inhibit the recombination of electron–hole pairs.

Improvement of lithium ion conductivity for A-site disordered lithium lanthanum titanate perovskite oxides by fluoride ion substitution

Lithium ion conducting perovskite oxides, namely La0.56−yLi0.33+3yTiO3 (y = 0, 0.01, 0.02, 0.04) with various La3+ ion concentrations and La0.56−yLi0.33TiO3−3yF3y (y = 0.01, 0.017, 0.033, 0.05) with various F− ion concentrations, were prepared. When y = 0.017, the Li-ion conductivity of La0.56−yLi0.33TiO3−3yF3y was 2.30 × 10−3 S cm−1 at 30 °C, which is one of the highest Li-ion conductivities in these systems. The F− substitution was effective for decreasing the activation energy for lithium ion migration. To understand the effect of F− ion substitution on lithium ion conduction, synchrotron X-ray absorption fine structure (XAFS) techniques were carried out. It was found with the XAFS analysis that the local distances around Ti4+ ions increased and the Debye–Waller factors decreased with F− substitution. These local structural changes were expected to expand the bottleneck for lithium ion hopping and to decrease the activation energy.

Ionic conductivity of bismuth oxofluoride BiO0.1F2.8 with tysonite-type structure (LaF3)

The complex impedance method in the temperature range of 291–660 K was used to study conductivity of oxofluoride BiO0.1F2.8 belonging to the tysonite structural type (LaF3). Bismuth oxofluoride was synthesized using a solid-phase method at 770–870 K for 1–2 h in an argon atmosphere. Heterovalent substitution of fluoride ions F− by oxygen ions O2− in the anionic BiF3 matrix sublattice results in high ionic conductivity (∼0.1 S/cm at 660 K) of BiO0.1F2.8 ceramic samples.

Optical properties of fluorine-substituted zinc bismuth phosphate glasses

The effects of the substitution of fluoride ions for oxide ions on the thermal and optical properties of ternary ZnO-Bi 2O 3-P 2O 5 glass with low-P 2O 5 content (20–25 mol%) were investigated. Fluoride ions were introduced into the glass up to about 12 mol% as ZnF 2. Raman spectra indicated that fluoride ions were substituted for oxide ions connected with bismuth ions. Deformation and glass transition temperatures decreased monotonically with fluorine concentration. The absorption edge shifted toward higher energies with increasing fluorine concentration by about 0.3 eV for 12 mol% ZnF 2 substitution. The blue shift of the absorption edge is attributable to two effects. One was a blue shift of an absorption band which was observed as a peak at 4.7 eV in the reflection spectra and was attributed to the spin forbidden 6s–6p interband transition in Bi 3+ ions. The blue shift originates from a change in electron-donating ability through anions as expected from electronegativity or optical basicity. Another is a disappearance of a shoulder at around 4.3 eV in the reflection spectra. The latter was the major reason for the large blue shift of the absorption edge energy, because the band relating to the 4.3 eV shoulder is close to the absorption edge.

Hydrolysis of antimony(III) fluoride complexes

Vibrational and 17O NMR spectroscopy in combination with quantum chemical calculations are used to investigate the hydrolysis of antimony(III) fluoride complexes. A hydrolytic decomposition of SbF3 and [SbF4]− is accompanied by oligomerization with the formation of edge-and corner-connected dimers ([Sb2O2F4]2−, [Sb2OF8]4−) and trimers ([Sb3O3F6]3−, [Sb3OF9]2−) with bridging oxygen atoms. The hydrolysis of [SbF4]− is also characterized by the presence in the solution of a discrete cation of [SbF5]2− which is least hydrolized. Only a partial isomorphic substitution of fluoride ion by hydroxide one is possible, which is reflected in the composition of K2Sb(OH)xF5−x (x = 0.3) crystals isolated from the fluoride aqueous solution.

Spectroscopic properties of Eu3+ and Tb3+ ions for local structure investigations of fluoride phosphate and phosphate glasses

Abstract The relationships between glass structure and spectroscopic properties of the doped ions Eu3+ and Tb3+ are of interest. Eu3+ and Tb3+ ions are used as structure-sensitive ions. The Ω t - parameters of Eu3+ were determined from absorption and emission spectra. The lifetime of the 5D0 state of Eu3+ was calculated from Ω t and compared with the experimentally determined lifetime. The electron-phonon coupling strength and phonon energy were obtained from phonon sideband spectroscopy. The f → d absorption transition of Tb3+ was used for determination of the nephelauxetic parameter. With increasing phosphate content the covalency between rare earth ions and surrounding ligands increases due to substitution of fluoride ions by oxygen ions having higher electron polarizability. This effect leads to increasing nephelauxetic shift, Ω 2 - parameter and electron-phonon coupling strength. In fluoride phosphate glasses, the diphosphate groups dominate the spectroscopic properties of the rare earth ions.

Relationships between glass structure and spectroscopic properties of Eu3+ and Tb3+ doped glasses

AbstractFluoride phosphate and phosphate glasses were doped with Eu3+ and Tb3+ ions. The relationships between glass structure and spectroscopic properties of the doped ions were of interest to obtain information about the local glass structure around rare earth ions.Nephelauxetic shift of Tb3+ f→d absorption band, Eu3+ fluorescence intensity ratio of 5D0→7F2 to 5D0→7F1 as well as electron‐phonon coupling strength and phonon energy determined from Eu3+ phonon sideband spectroscopy were studied in dependence on phosphate content of the host glasses. Tb3+ fluorescence intensity ratio of 5D4→7FJ to 5D3→7FJ (J= 0,1,2… 6) transitions is affected by Tb3+ concentration and OH content of the glasses.With increasing phosphate content of the glasses, the covalency between rare earth ions and surrounding ligands increases due to substitution of fluoride ions by oxygen ions having higher electron polarizability. This effect leads to increasing nephelauxetic shift, Ω2 parameter and electron‐phonon coupling strength. In fluoride phosphate glasses, the diphosphate groups dominate the spectroscopic properties of the rare earth ions. The Tb3+ fluorescence intensity ratio of 5D4→7FJ to 5D3→7FJ increases with increasing Tb3+ concentration and OH content, respectively, due to acceleration of cross‐relaxation between Tb3+ ions and due to energy transfer from Tb3+ ions to OH groups.

Synthesis of [18F]GBR 12909, a dopamine reuptake inhibitor

AbstractPreparation of no‐carrier‐added fluorine‐18 labeled GBR 12909 (1‐[2‐(bis(4‐fluorophenyl)methoxy)ethyl]‐4‐(3‐phenylpropyl)piperazine), a specific and high affinity inhibitor of dopamine reuptake, is described. 4‐Fluoro‐4′‐[18F]fluorobenzophenone was prepared by [18F]fluoride ion substitution of the corresponding trimethylammonium trifluoromethanesulfonate salt. The [18F]benzophenone was reduced to the benzhydrol, chlorinated, then used to alkylate 1‐(2‐hydroxyethyl)‐4‐(3‐phenyl‐propyl)piperazine to yield [18F]GBR 12909 in high specific activity (≥2000 Ci/mmol) and overall yields of 10–16% (corrected, 140 min synthesis).

KINETICS AND MECHANISM OF THE CHROMIUM(II)-CATALYZED SUBSTITUTION OF BROMIDE ION IN THE BROMOPENTAAQUOCHROMIUM(III) ION BY CHLORIDE AND FLUORIDE IONS

Abstract The substitution of bromide ion in the bromopentaaquochromium(III) ion by chloride and fluoride ions is catalyzed by chromium(III). The rate law for the chloride ion substitution is -d(In[CrBr2+])/dt=kCl[Cr2+] [Cl−] whereas that for fluoride ion substitution is of the form -d(In[CrBr2+])/dt=(r[HF]/[H+]) [Cr2+]/(1 + s[HF]/[H+]). At 25°C and Σ[Anions]=1.00 M the values for kCl=16.1 ± 0.7 M−2s−1 (δH#=10.8 ± 0.9 Kcal/mol; δS#=-17 ± 3 cal/deg mol), r=3.06 ± 0.18 M−1s−1 and s=2.3 ± 0.5. The results are interpreted on the basis of a mechanism which features the formation of reactive intermediates of the type CrXBr+ (X=Cl, F), but differing in the extent to which they are formed. Indirect evidence for the mechanism is adduced by the isolation of CrClBr+ and CrFBr+ from independent reactions.

Infrared spectra of calcium hydride fluoride CaF2−xHx

AbstractThe existence of solid solutions of composition CaF2−xHx (0 < x ≦ 1.24) is recently established, crystallizing in CaF2‐type cubic symmetry. There is a statistical substitution of fluoride ions by hydride ions in the CaF2 unit cell. The infrared spectroscopy gives informations on these compounds by the behaviour of the H− ions localized vibration and that of the fundamental TO mode when x varies.

Preparation de la solution solide hydrurofluoree CaF 2− xH x (0 < x ⩽ 1,24) etude structurale par diffraction des rayons X et par diffraction des neutrons

By studying the CaH 2CaF 2 system at 700°C, we associate F − and H − anions in the same ternary combination. The existence of solid solutions of composition CaF 2− x H x (0 < x ⩽ 1.24) is established, crystallizing in CaF 2-type cubic symmetry. The solid solution parameter is considered constant as the composition varies, since there is a variation of 1 100 Å between pure CaF 2 ( a = 5.463 Å) and the limit phase CaF 0.76H 1.24 ( a = 5.452(5) Å). Thus the two anions H − and F − are approximately the same size in the mixed hydride fluorides of calcium. X-ray and neutron diffraction studies indicate a structure in which there is a statistical substitution of fluoride ions by hydride ions on the 8 c sites of the CaF 2 unit cell.