Addition Of Fluoride Ions Research Articles

F − assistant synthesis of ultra-hydrothermally stable mesoporous silica by using nonionic organosilicon surfactant as templates

Mesoporous silica with thick pore wall (designated ECT) was synthesized in the presence of fluoride anions by using nonionic organosilicon surfactant (K903) as template. According to the results from XRD patterns and N 2 adsorption–desorption analysis, the addition of fluoride has a strong effect on the pore diameter and pore wall thickness of the ECT samples. 29Si MAS NMR indicates that the degree of silicate condensation is greatly enhanced by adding fluoride ions. The hydrothermal stability of the mesoporous silica (ECT) synthesized in the presence of fluoride was found to be greatly improved compared to that of the sample without addition of fluoride ions. When F/Si = 0.045, the mesostructure of the sample could still remain after refluxed in boiling water even for 20 days. The ultra hydrothermal stability could be attributed to its thick pore wall, less defects in the silica framework and high degree of polymerization of silicate. Moreover, results from SEM reveal that the addition of fluoride anions also has great effect on the morphology structure of ECT sample.

Novel side‐chain naphthalimide polyphenylacetylene as a ratiometric fluorescent chemosensor for fluoride ion

AbstractNovel polyphenylacetylene (P1) containing naphthalimides units in the side chain was designed and synthesized. The structure and properties of the polymer were characterized and evaluated by IR, NMR, UV, and PL. The measurements of sensing behavior to various halide anions, that is, F−, Cl−, Br−, and I−, reveal that the polymer is a ratiometric fluorescent chemosensors for fluoride ion. The polymer sensor shows spectral shifts and intensity changes in the presence of fluoride, in a wavelength‐ratiometric and ‐colorimetric manner, which can detect fluoride concentrations in range of 10–100 μM at visible wavelengths. The obvious colorless‐to‐yellow color change and blue‐to‐orange emission color change on the addition of fluoride ion are easily observed by naked eyes. It provides a feasible way to construct a ratiometric fluorescent chemosensors for fluoride ion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1544–1552, 2009

Electrochemical oxidation of oxalate ion in the presence of fluoride ion, and radical analysis by ESR

The problem at hand is the electrochemical oxidation of oxalate ion, which is accelerated by fluoride ion at a platinum anode. The hypothesis that fluoride ion traps incipient hydroxyl radicals as hydroxyfluoride radical anions was not supported by ESR experiments in which hydroxyl radicals were generated in the presence of the spin trap α-(4-pyridyl-1-oxide) N- tert-butyl-nitrone with and without the addition of fluoride ion. The electrochemical oxidation of oxalate at constant current followed current controlled kinetics both at a platinum anode, as observed previously, and at a boron-doped diamond anode, but the rate of the latter reaction was indifferent to the presence of fluoride ion. We propose that the competition of fluoride and hydroxide ions for the Pt/PtO n surface inhibits the dimerization reactions that lead to oxygen evolution; the displacement of oxygen evolution to more positive potentials overcomes the overpotential for the oxidation of oxalate at this anode. Fluoride ion has no influence on the oxidation of oxalate at BDD because oxygen evolution inherently occurs at more positive potentials at this anode.

Effect of Ag on the corrosion behavior of Ti–Ag alloys in artificial saliva solutions

Objectives The purpose of this study was to investigate the corrosion behavior of Ti–Ag alloys in artificial saliva solutions. Methods The corrosion behavior of experimental Ti–Ag alloys in artificial saliva was examined by means of potentiodynamic polarization measurements. The surface passive film formed was analyzed by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) methods. Results The alloys were found to develop surface passive films after immersion for 1.8 × 10 3 s. In comparison with commercially pure Ti, the Ti–Ag alloys exhibited better corrosion resistance with lower anodic current densities, larger polarization resistances, and higher open-circuit potentials. The passive film formed was predominantly composed of TiO 2, as determined by XPS. When fluoride ions were added in the solution, the TiO 2 passive film was destroyed and Na 2TiF 6 was formed. Significance Addition of Ag was found to be effective in reducing the corrosion current density and increasing the open circuit potential of titanium in artificial saliva environment. Addition of fluoride ions in the solution severely reduced the corrosion resistance of Ti–Ag alloys.

An “off–on” sensor for fluoride using luminescent CdSe/ZnS quantum dots

The fluorescence emission of CdSe/ZnS QDs was switched "off" when the native trioctylphosphine oxide ligands were exchanged for 1-(bis(eta(5)-cyclopentadienyl)iron)-methyl-3-(5,7-dimercapto-heptyl)-urea (); importantly, the emission of the resulting conjugate was switched "on" upon addition of fluoride ions.

Impact of the Linker on the Electronic and Luminescent Properties of Diboryl Compounds: Molecules with Two BMes2 Groups and the Peculiar Behavior of 1,6-(BMes2)2pyrene

To investigate the impact of the linker on the electronic and photophysical properties of diboryl compounds, three new diboryl compounds that contain two BMes2 groups (Mes = mesityl) have been synthesized, including a planar 1,6-(BMes2)2pyrene (1), a V-shaped bis(p-BMes2phenyl)diphenylsilane (4), and a U-shaped 1,8-bis(p-BMes2phenyl)naphthalene (5). For comparison, two previously known compounds, p-(BMes2)2benzene (3) and 1,8-bis(p-BMes2-biphenyl)naphthalene (6), were also investigated. The aromatic linkers in these molecules have been found to have a dramatic impact on the electron-accepting ability and Lewis acidity of the diboryl compounds through their distinct steric and electronic properties. Compound 1 has the most positive reduction potential (E1/2red1 = −1.81 V, relative to FeCp20/+), while 5 has the most negative reduction potential (E1/2red1 = −2.34 V). All compounds are blue emitters with considerable variation of emission energy and efficiencies (e.g., λem = 446, 402, 395 nm, Φ = ∼1.0, 0.17, ∼1.0 for 1, 4, and 5, respectively), and each displays a distinct and selective response toward fluoride ions. Upon addition of fluoride ions, compound 1 displays an unusual red shift and an on−off response in both absorption and fluorescent spectra. By comparing the behavior of 1 to that of the monoboryl compound 1-BMes2pyrene (2) and 3, and with TD-DFT computations on 1 and its fluoride adducts 1F and 1F2, it has been found that the peculiar response of 1 toward fluoride ions is caused by the dominance of pyrene π orbitals at the HOMO level of 1F and the relatively low-energy charge transfer from the pyrene ring to the three-coordinate boron center in 1F. The crystal structures of 2, 4, 1F2, and 5F2 were determined by X-ray diffraction analyses. The potential use of compound 1 as either a blue emitter or a bifunctional emitter in OLEDs has been demonstrated by the successful fabrication of double- and triple-layer electroluminescent devices.

Fluorescent Boron Bis(phenolate) with Association Response to Chloride and Dissociation Response to Fluoride

Addition of chloride ions to boron bis(phenolate) 5 in dichloromethane solution produces a selective fluorescence decrease. The fluorescence change is believed to be caused by associative hydrogen bonding between the chloride ion and two boronic acid groups. While addition of fluoride ions to bis(phenolate) 5 generates a purple colorimetric response, the colorimetric response is caused by fluoride induced B-O bond cleavage and air oxidation of the phenolate anion formed by this dissociation.

Structural control of mesoporous silicas with large nanopores in a mild buffer solution

In this study, a simple synthesis strategy has been developed for the systematic control of the structure and pore size of the mesoporous silicas through adjusting the ratio of tetraethoxysilane (TEOS) to tetramethoxysilane (TMOS) in a mild acidic buffer solution (acetic acid–sodium acetate pH 4.4) or the pH value using poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (EO 20PO 70EO 20) as a structure-directing agent. By varying the molar ratio of TEOS to TMOS, mesoporous silicas with 2-D hexagonal ( p6mm) pore arrangement, onion-like lamellar structure, mixed phase (vesicular hierarchical structure and cellular foam), and nanofoams with large uniform spherical cells can be obtained. Simultaneously, the pore diameter can be varied in the range of 9–50 nm. The differences in the hydrolysis and polymerization rates between TEOS and TMOS were found to play a key role in the phase transformation of the final products. When TEOS was employed as the only silica precursor, the mesostructure and pore diameter of the resultant materials could be controlled through either varying the solution pH or the addition of fluoride ion to the synthesis system. Increasing the solution pH values from 3.2 to 5.1 induces the structure transformation from uniform wormhole mesostructure to nanofoams with large uniform spherical cells, then to aggregated and collapsed vesicle-like nanofoam structure accompanied by the increase of pore diameter from 7 to 50 nm. By addition of the fluoride ion, uniform macroporous nanofoam structure (ca. 100 nm in diameter) similar to the cell wall of diatoms was obtained.

Colorimetric Fluoride‐Anion Sensor Based on Intramolecular Hydrogen Bonding and Enol–Keto Tautomerization of a Phenothiazine Derivative

AbstractA colorimetric sensor for fluoride ions based on a new sensing mechanism is reported. The colorimetric sensor contains an isomerizable enol–keto moiety as the recognition site and phenothiazine as chromogenic center. A color change visible to the naked eye is observed upon addition of fluoride ions to the solution of sensor 1 in aprotic solvents such as CHCl3 and MeCN. The sensor shows no colorimetric response for other halide ions. Enol‐keto tautomerization is proposed to be responsible for the anion sensing of 1, based on UV/VIS absorption, 1H‐NMR, and single‐crystal structure analysis.

A mesoporous silica functionalized by a covalently bound naphthalene-based receptor for selective optical detection of fluoride ion in water

The naphthalene urea fluorescent receptor 1 immobilized mesoporous silica (FMS) and the fluorescent receptor 1 immobilized silica particles (FSP) were prepared via sol–gel reaction. The sensing ability of FMS and FSP was studied by addition of the anions F –, Cl –, Br –, I – and HSO 4 - to water suspensions of the assayed solid. Of all the anions tested, addition of fluoride ion to a suspension of FMS resulted in the largest decrease in the fluorescence intensity of naphthalene of FMS. Thus, fluoride ions bind with four urea N–H protons of receptor 1 onto FMS. On the other hand, addition of Cl –, I –, Br – and HSO 4 - did not reduce the fluorescence of FMS. In case of FSP, the sensitivity for fluoride ion was 8 times lower than that of FMS due to immobilization of smaller amounts of receptor 1 in silica particles. The result implies that mesoporous silica with its large surface area is useful as a supporting material.

Selective fluoride sensing using organic–inorganic hybrid nanomaterials containing anthraquinone

Anthraquinone-based fluorescent receptor 1 was immobilized on mesoporous silica (AFMS) or on silica particles (AFSP) via a sol–gel reaction. The sensing abilities of AFMS and AFSP were studied by addition of the anions F−, Cl−, Br−, I− and HSO4− to water suspensions of the assayed solid. The addition of fluoride ions to a suspension of AFMS resulted in a large decrease in the fluorescence intensity of the anthraquinone of AFMS. Thus, fluoride ions bind to two urea N–H protons of receptor 1 in AFMS. In contrast, the addition of Cl−, Br−, I− or HSO4− did not reduce the fluorescence of AFMS. In the case of AFSP, the sensitivity for fluoride ions was 10 times lower than that of AFMS due to the immobilization of smaller amounts of receptor 1 on the silica particles. A linear response of AFMS upon the addition of fluoride ions was observed between 0.50 μM and 10.0 μM, with a detection limit of ∼0.50 μM. These results suggest that mesoporous silica with its large surface area is useful as a supporting material. Furthermore, receptor 1 was also immobilized on a glass slide surface by a sol–gel reaction. The fluorescence of 1 immobilized on a glass slide was quenched when dipped into F− solution. On the other hand, no fluorescence change was observed in Cl− solution. These results imply that 1 immobilized on a glass slide is applicable as a portable fluorescent sensor for detection of fluoride ions in the biological and environmental fields.

Synthesis and Ion Sensing Properties of New Colorimetric and Fluorimetric Chemosensors Based on Bithienyl-Imidazo-Anthraquinone Chromophores

Novel colorimetric receptors for fluoride ion sensing containing anthraquinone as a chromogenic signaling unit and imidazo-2,2'-bithiophene binding sites are reported. Well-defined color change was observed upon addition of fluoride ions to acetonitrile solutions of receptors 2. Compounds 2a-c, deprotonated after fluoride ion addition, were studied as metal ion chemosensors in the presence of Zn(II), Hg(II), and Cu(II) in acetonitrile solutions, especially compound 2a which displayed a marked change from pink to yellow-gold colors upon complexation.

Application of fluoride to enhance aluminum cementation of gold from acidic thiocyanate solution

The cementation of gold from acidic thiocyanate solution was studied using aluminum powder. The related parameters such as pH, thiocyanate concentration, gold concentration, temperature, stirring speed, aluminum/gold mass ratio, presence of iron (III) and gas atmosphere were systematically investigated. The results show that temperature and deoxygenation were determined to positively affect the gold recovery. Conversely, the presence of iron (III) inhibits significantly the cementation reaction. The addition of fluoride into leach solution could overcome the inhibitory effect of iron (III) and enhance the gold cementation rate. It was established that the rate of the reaction was first-order with respect to the gold concentration. The activation energy was found to be 41.9kJ/mol and the cementation process was considered to be chemically controlled without the presence of ferric ion and the addition of fluoride ion in solution. A possible cementation mechanism was proposed.

Nitro-Substituted Stilbeneboronate Pinacol Esters and Their Fluoro-Adducts. Fluoride Ion Induced Polarity Enhancement of Arylboronate Esters

A series of stilbeneboronate pinacol cyclic esters, containing none to three nitro groups, have been synthesized by various olefination reactions and characterized by X-ray single-crystal structure analysis. A stilbeneboronate ester bearing electron-acceptor groups experiences transition to a push-pull pi-electron system upon complexation with one fluoride ion at the boron atom. The UV-vis absorption maxima of the presented nitro-substituted stilbeneboronate esters are red-shifted upon addition of fluoride ions, indicating this binding event. The enhancement of the polarity of the investigated compounds and the changes in the electronic system were investigated by UV-vis absorption spectroscopy and solvatochromism. Additionally, studies were performed by natural bond orbital (NBO) analysis and RI-CC2 calculations of the vertical excitation energies. The synergism of fluoride ion complexation and solvation upon the UV-vis band shift is interpreted in terms of linear solvation energy relationships (LSERs) using the Kamlet-Taft solvent parameter set. It is found that the UV-vis absorption of the fluoro-boronates is strongly dependent on the solvents hydrogen-bond donating ability.

Dual chemosensing properties of new anthraquinone-based receptors toward fluoride ions

Novel colorimetric receptors 1-[(2-hydroxy-5-bromo-benzylidene)-amino]-anthraquinone, 1-[(2-hydroxy-5-methyl-benzylidene)-amino]-anthraquinone, and 1-[(2-hydroxy-5-nitro-benzylidene)-amino]-anthraquinone have been synthesized as fluoride ion sensors. A color change was observed visually (naked-eye) upon addition of fluoride ions in organic solvents to solutions of the receptors.

Three-coordinate organoboron with a BN bond: substituent effects, luminescence/electroluminescence and reactions with fluoride

Five new three-coordinate boron compounds with a B=N bond involving an indole or a substituted indole ligand including B(mesityl)2(indolyl), (1), B(mesityl)2(2-Me-indolyl), (2), B(mesityl)2(3-Me-indolyl), (3), B(mesityl)2 (7-Me-indolyl), (4), and B(mesityl)2(3-Ph-indolyl), (5) have been synthesized. The structures of these new compounds were determined by X-ray diffraction analyses. All five compounds are luminescent involving a charge transfer transition between the indolyl pi orbital and the boron p(pi) orbital. The substituent group on the indolyl ring was found to have a subtle impact on the electronic properties of compounds. NMR experiments established that the methyl group at the 7-position of indole is most effective in blocking the rotation of the mesityl group around the B-C bond. The addition of fluoride ions to this group of compounds causes luminescent quenching and an irreversible decomposition of the compounds due to the reaction of the F- adduct with water molecules. The potential use of this group of compounds as blue emitters in electroluminescent (EL) devices was demonstrated by the successful fabrication of a four-layer EL device where 1 was used as the emitter. The EL device displays a blue emission with a maximum luminescence being 1037 cd m(-2) and a maximum current efficiency about 0.7 cd A(-1) at 5 V.

Effects of inorganic additions on the performance of manganese-based conversion treatments

The electrochemical behaviour of permanganate-based no-rinse conversion coatings on AA3003-H14 aluminium alloy shows that they have promise as an alternative to toxic chromate-based coatings. A selection of inorganic additions has been made here to a simple 0.1 M KMnO 4 formulation investigated previously. The performance of the different coatings has been evaluated from potential–time and polarisation measurements in 0.5 wt % (0.085 M) NaCl solution for periods up to 3 days. The addition of fluoride ions produced no benefit, whereas Al(NO 3) 3 shows an improvement when added in small amounts. Tests with the individual ions reveal that it is Al 3+ cations, rather than NO 3 - anions, which produce the greatest benefit.

Anthracene derivatives bearing thiourea group as fluoride selective fluorescent and colorimetric chemosensors

New anthracene derivatives bearing thiourea group have been synthesized and characterized including X-ray crystallography. These chemosensors display selective ratiometric changes in their fluorescence spectra upon the addition of fluoride ion.

Contamination of silicon dioxide films by aqueous zirconium and hafnium species

Zirconium and hafnium oxides and silicates have emerged as potential replacements for SiO2 as gate dielectric material. Patterning of these materials by wet etching in fabrication areas originally designed for SiO2 gates may give rise to contamination of SiO2 by aqueous zirconium and hafnium species. This paper summarizes the work carried out to characterize the adsorption behavior of aqueous zirconium and hafnium species onto thermally grown silicon dioxide. Electrokinetic and adsorption measurements were carried out to understand the extent and nature of interaction. The adsorption of both Zr and Hf species showed a maximum at pH 5.5. Significant reduction in the adsorption of both Zr and Hf occurred upon addition of fluoride ions to the solution. Using appropriate speciation diagrams, an adsorption model has been developed to explain the experimental data.

Synthesis of Hydrothermally Stable and Long-Range Ordered Ce-MCM-48 and Fe-MCM-48 Materials

The hydrothermally stable and long-range ordered Ce-MCM-48 and Fe-MCM-48 were conveniently synthesized at 393 K for 24 h by directly adding fluoride ions to the initial gel without posttreatment and pH adjustment. The Ce-MCM-48 with a Si/Ce of 200 and 100, which were prepared by directly adding fluoride ions, could still maintain their mesoporous structures after refluxing in boiling water for 3 days. The incorporation of Ce into MCM-48 could enhance the hydrothermal stability of MCM-48 in the absence of fluoride ions; however, the incorporation of Fe into MCM-48 materials barely improved the hydrothermal stability of MCM-48 materials. The effect of adding NaF was much more efficient in enhancement of hydrothermal stability than that of the incorporation of Ce. The addition of fluoride ions mainly improves the degree of polymerization of silicates. The Ce(4+) ions in Ce-MCM-48 appear to be present partly in tetrahedral coordination in the framework and partly as CeO(2) particles on the surface of framework. The Ce positioned on the surface of pore walls and in the framework both provide the protection against water attack.