Aqueous Fluoride Solutions Research Articles

Iron (III) oxide hydroxide based novel electrode for the electrochemical detection of trace level fluoride present in water

Present article describes the development of novel electrode for the electrochemical detection of fluoride ion (F−) present in water. The electrode is prepared by growing thin iron (III) oxide hydroxide film on conducting glass substrate through simple and cost effective dip coating technique. Electrochemical sensing performances of the developed electrode through cyclic voltammetric and amperometric technique are studied within a three electrode chamber. Ag/AgCl and Pt are used as reference and counter electrodes respectively to carry out the sensing experiments. The developed working electrode shows distinguishable cyclic voltammetric and amperometric response in presence of different concentration (0.27–2.48 mM) of aqueous fluoride solution. The interference of the sensor is verified in presence of nitrate (NO3−) and chloride (Cl−) ions. In order to understand the behaviour of electrochemical interaction, the phase and morphology of the electrode material is studied prior and after sensing. A plausible mechanism is proposed for the electrochemical sensing of fluoride by iron (III) oxide hydroxide film.

Comparative study on synchronous adsorption of arsenate and fluoride in aqueous solution onto MgAlFe-LDHs with different intercalating anions.

In this study, a series of MgAlFe-LDHs (Cl−, NO3−, intercalation, and calcined products of a CO32− interlayer) was synthesized and used for adsorption of arsenate and fluoride in individual contaminants and coexisting pollutant systems. Effects of various factors such as initial pH of solution, dosage of materials, coexisting ions, contact time, and initial pollutant concentrations were evaluated. Experimental results showed that different intercalating anions had a significant effect on adsorption performance of arsenate and fluoride in water. The adsorption of arsenate and fluoride on MgAlFe-CLDH, MgAlFe–Cl-LDH or MgAlFe–NO3-LDH can be described by different adsorption isotherm equations. During the simultaneous removal process, arsenate and fluoride competed for adsorption sites of the adsorbent materials, and the fluoride ions had advantages in the competitive adsorption on MgAlFe–Cl-LDH and MgAlFe–NO3-LDH. MgAlFe–NO3-LDH was used to adsorb arsenate and fluoride in coexisting pollution systems (the concentration of each pollutant was 2 mg L−1, the adsorbent dosage was 1.5 g L−1). The remaining arsenic concentration was reduced to less than 10 μg L−1 and the remaining fluoride ion concentration to below 20 μg L−1 which meets the World Health Organization's, EPA's and China's drinking water standards for arsenic and fluoride limits. A possible mechanism is discussed with support from further XRD, SEM, and XPS analysis of the materials after their adsorption.

Orientational disorder and phase transitions in ammonium oxofluorovanadates, (NH4)3VOF5 and (NH4)3VO2F4

Single crystals of (NH4)3VOF5 and (NH4)3VO2F4 were obtained from aqueous fluoride solutions and phase transitions in these compounds were investigated using X-ray diffraction, differential scanning microcalorimetry (DSM) and vibrational spectroscopy. The room-temperature (RT) phases of these compounds belong to orthorhombic symmetry [Immm and I222, Z = 6, for (NH4)3VOF5 and (NH4)3VO2F4, respectively] with similar unit-cell parameters and two independent vanadium atoms. Above RT [at 350 and 440 K for (NH4)3VOF5 and (NH4)3VO2F4, respectively], the compounds undergo reversible phase transitions into high-symmetry dynamically disordered elpasolite-like (Fm{\bar 3}m, Z = 4) structures with six and 12 spatial orientations of the vanadium octahedron for (NH4)3VOF5 and (NH4)3VO2F4, respectively. The ligand atoms are distributed in a mixed (split) position of 24e + 96j, one of the ammonium groups is disordered on the tetrahedron 32f site, but another one forms eight spatial orientations due to disorder of its hydrogen atoms in the 96j position. DSM and spectroscopic data enable the phase transition from high temperature to room temperature to be connected with the transition from isotropic orientations of the octahedron to its two different dynamic states.

Mild and Efficient Vicinal Dibromination of Olefins Mediated by Aqueous Ammonium Fluoride

A mild and efficient vicinal dibromination of olefins has been developed by using saturated aqueous ammonium fluoride solution as the promoter. Inexpensive and commercially available N-bromosuccinimide (NBS) was used as the brominating reagent. The corresponding vicinal dibromoalkanes could be obtained in good to excellent yields.

Instantaneous and Selective Bare Eye Detection of Inorganic Fluoride Ion by Coumarin–Pyrazole‐Based Receptors

A series of rationally designed coumarin–pyrazole‐based scaffolds, equipped with N―H and C―H hydrogen bond donors (R1–R5) and containing various electron‐withdrawing groups at key positions, are synthesized and characterized in order to investigate their inorganic fluoride binding properties in highly competitive media (1:1 DMSO–water). Only one, 3‐{4‐[(2,4‐dinitrophenyl)‐hydrazonomethyl]‐1‐phenyl‐1H‐pyrazol‐3‐yl}‐chromen‐2‐one (R1), of the five compounds synthesized, is found to be capable to selectively detect inorganic fluoride via naked eye amongst other anionic species in aqueous media. Qualitative and spectroscopic studies exhibit that receptor R1 has the potential of showing instantaneous change of color from yellow to pink upon addition of sodium fluoride (0.95 ppm) in aqueous media, at concentration lower than that recommended by World Health Organization (1 ppm). Intensity of color increases with increasing fluoride concentration till 5 ppm, beyond which intensity of color change becomes saturated. This has established the applicability of this receptor for assessment of the level of fluoride in water. Anion binding studies carried out by UV–visible titration portrayed substantial bathochromic peak shift from 410 to 495 nm, upon addition of varying concentrations of aqueous sodium fluoride solution, which has validated the color change. Jobs plot data confirmed 1:1 stoichiometry between R1 and fluoride ion. 1H‐NMR investigation reveals that the deprotonation of N―H hydrogen donor group of receptor R1 and its interaction with fluoride ion is responsible for the observed color change.

Chemistry of the CARBOFTOREX process. Identification of the absorption bands of the ligands in the electronic spectra of aqueous solutions of uranyl fluoride

The electronic absorption bands of aqueous solutions of the [UO2F2(H2O) n ] complex were assigned taking into account dissociation, hydration, association, and ligand exchange. The absorption in the range of 190–400 nm was found to be related to the formation of cationic, neutral, and anionic complex species, [UO2F2(H2O) n ].

Fluorescent molecule incorporated metal-organic framework for fluoride sensing in aqueous solution

In this work, the fluorescent molecule (fluorescein sodium, FS) was successfully incorporated in the zirconium-based MOF (UiO-66) via in-situ synthesis method, which can be confirmed by FTIR spectra and fluorescence microscopic images. Based on this in-situ synthesis strategy, FS molecule can be immobilized tightly in the framework. Furthermore, the resulting FS@UiO-66 demonstrates to be a highly selective, real-time and naked-eye chemical sensor for fluoride in aqueous solution, which is mainly due to the release of FS molecule from FS@UiO-66 into the aqueous solution. Meanwhile, to the best of our knowledge, such Zr-MOF-based fluoride sensor is very rare so far. These results provide a promising approach to rationally design novel MOF-based fluorescent sensor for the target molecules.

Study about Doping Ion La3+ onto Surface of Pyrolusite Ore for Removing Simultaneously Both Fluoride and Phosphate from Wastewater

Lanthanum has been doped onto the surface of the natural Pyrolusite for simultaneous removal of phosphate and fluoride in aqueous solution. The adsorbent characterization of the materials was observed by the SEM, BET, and XRD techniques. The dynamics and isotherms models of fluoride and phosphate adsorption, with respect to pH, pHPZC, adsorbent dose, and effect of coexisting ions, were studied. The results showed that lanthanum doped Pyrolusite ore (LDPO) relatively highly adsorbed amount of phosphate and fluoride from aqueous solution. Phosphate and fluoride removal efficiencies of LDPO are approximately 97% and 95%, respectively. Pseudo-first order for kinetic studies of phosphate and fluoride removal of the LDPO was observed with high correlations for fluoride but weak correlations for phosphate. However, pseudo-second order for kinetic studies was high correlation for both phosphate and fluoride. The phosphate and fluoride adsorption capacities of the LDPO significantly decreased with the existence of coions (sulfate, chloride, and nitrate) in the aqueous solution.

New analytical method for total fluorine determination in soil samples using high-resolution continuum source graphite furnace molecular absorption spectrometry

Fluorine may be present in soil naturally, in the form of minerals (fluorite, fluorapatite and cryolite) or due to environmental pollution. Plants harvested in soils with high levels of this element might be contaminated and consequently they may present toxicological effects, such as necrosis or growth reduction. Hence, the development of reliable and appropriate methods for the accurate determination of F has become of great importance. The aim of this study was the development of an analytical method for F determination in soil samples, monitoring the rotational lines of the CaF molecule by high-resolution continuum source graphite furnace molecular absorption spectrometry using direct analysis of solid samples. All measurements were carried out using the wavelength at 606.440nm, evaluating the center pixel only, and a standard solution of 7.5gL−1 Ca was used as the molecule-forming reagent. The pyrolysis and atomization temperatures were optimized to 900°C and 2100°C, respectively; the Ca mass of 75μg was adequate to guarantee the formation of the CaF molecule in samples and standard solutions. Sample masses up to 0.25mg were weighted. Fluoride aqueous standard solutions were used for calibration, resulting in a linear working range between 1.5 and 27ngF. The characteristic mass obtained was 0.13ng and the limits of detection and quantification were 0.72 and 2.4ngmg−1, respectively, calculated for a sample mass of 0.25mg. A certified reference material of Lake Sediment (LKSD-4, Ontario, Canada) was used to confirm the trueness of the developed method. The value found for F (234±14ngmg−1) was in agreement with the certified value (260±40ngmg−1), proving that the developed method provides accurate results for F determination in soil samples. Finally, the developed method was applied for the analysis of soil samples from urban and rural areas. Considering all the investigated soil samples, the F content varied between 138 and 232ngmg−1.

Method for stepped etching of optical glass fibers

A method for stepped etching of optical glass fibers using various compositions of etching agents based on a 40% hydrofluoric acid (HF) and aqueous solutions of ammonium fluoride (NH4F) has been considered. Compositions, etching rates, the dependence of etching rate on temperature, and tyeh dependence of etching forms on composition have been determined. The potential use of the method for stepped etching of optical glass fibers in the manufacture of microelectronic devices has been demonstrated.

Controllable synthesis of mesoporous alumina with large surface area for high and fast fluoride removal

Gamma phase of mesoporous alumina (MA) with large surface area was successfully synthesized by a facile hydrothermal method followed by thermal treatment for fluoride removal. The as-synthesized MA nanoparticles with average size of 20nm–150nm have ordered wormhole-like mesoporous structure. The pore size is 5nm with a narrow distribution, and the specific surface area reaches 357m2g−1 while the bulk density is 0.45cm3g−1. Glucose as a small-molecule template plays an important role on the morphology, surface area and pore diameter of the MA. As an ionic adsorbent for fluoride removal, the maximum adsorption capacity of MA is 8.25mgg−1, and the remove efficiency reaches 90% in several minutes at pH of 3. The Langmuir equilibrium model is found to be suitable for describing the fluoride sorption on MA and the adsorption behavior follows the pseudo-second-order equation well with a correlation coefficient larger than 0.99. The larger surface area and relatively narrow pore size of MA are believed to be responsible for improving the adsorption efficiency for fluoride in aqueous solution.

Anodized Iron Oxide Nanostructures on Different Carbon Steels for Photoelectrochemical Water Splitting

AbstractIn this study, two different nanostructural iron oxide films were prepared on two kinds of carbon steels (CS) with different contents of impurities via anodization in a mixture of aqueous ammonium fluoride solution and ethylene glycol, respectively, and apply to photoelectrochemical (PEC) water splitting. After annealing, iron oxide nanotubes (NTs) was coated on surface of lower purity CS and iron oxide nanoporous (NPs) was coated on surface of higher purity CS via scanning electron microscope. X‐ray diffraction pattern shows both of samples contain a major phase of α‐Fe2O3 and a slight phase of Fe3O4. Compared with NPs, NTs behaves better absorbance ability in visible spectra range via UV‐visible absorbance spectra. From PEC response, the iron oxide NTs showed higher water splitting performance (0.10 mA/cm2 at 0.4 V vs. Ag/AgCl) than NPs (0.04 mA/cm2 at 0.4 V vs. Ag/AgCl) due to better absorbance, higher car‐ rier concentration and low charge transfer resistance.

Preparation, Corrosion and Cytocompatability <i>In Vitro</i> of Fluoride-Coated Mg-Zn-Zr Alloy

The present investigation was carried out to optimize the hydrogen fluoride (HF) aqueous solution treatment for an Mg-2.5Zn-0.5Zr alloy, in order to improve the corrosion resistance of the material for orthopaedic applications. An MgF2 coating was formed on the surface of Mg-2.5Zn-0.5Zr alloy treated with HF solution. The effect of the HF concentration and processing time on the morphology and electrochemical performance of the MgF2 coating was systematically studied. The results showed that the MgF2 coating became thick gradually with the increase of the concentration of HF solution. However, the pinhole on the surface treated with 40% HF increased significantly. The coating thickness immersed in the same concentration of HF solution increased with immersion time, and cracks formed in the surface after four hours of immersion, resulting in a decrease in the corrosion potential. When the alloy was immersed in the HF solution with a concentration 20% at 37°C for 2h, a uniform and dense fluoride coating was formed, with a thickness of MgF2 layer of about 0.5μm. The corrosion potential of the coated Mg alloy in simulated body fluid (SBF) was 0.28V higher than the uncoated one. In addition, the fluoride-coated showed a good biocompatibility.

Tuned synthesis and characterizational insight into β-cyclodextrin amended hydrous iron-zirconium hybrid oxide: a promising scavenger of fluoride in aqueous solution

Fluoride adsorption on CHIZO takes place with H-bonding inside the core, thus forming an encapsulated moiety.

Continuous treatment of boron and fluoride in aqueous solutions using a column loaded with granulated Mg–Al layered double hydroxides intercalated with nitrates

Mg–Al layered double hydroxides intercalated with NO3− (NO3·Mg–Al LDHs) were mixed with various amounts of epoxy resin to obtain granulated NO3·Mg–Al LDH samples. The granulated NO3·Mg–Al LDH samples were shown to be capable of adsorbing B from aqueous solutions and the experimental adsorption isotherm data fit well to the Langmuir model. In order to evaluate the continuous treatment of B and F− in aqueous solutions, a chromatographic column was loaded with granulated NO3·Mg–Al LDH with an LDH/epoxy resin ratio of 1:0.5 and H3BO3 and NaF solutions were passed through the columns under various conditions. The concentrations of B and F− in the elutions were found to increase with time. In addition, the concentrations of B and F− in the elutions also increased with increase in the flow rates and initial concentrations of H3BO3 and NaF, respectively, which were attributed to the flow of large amounts of B and F− into the column in a short duration. The experimental data from the column experiments were fit to the Thomas model. The relatively high R2 values under all the conditions suggest that the Thomas model adequately represents the results of the adsorption experiments. For the adsorption of both B and F−, the calculated qT from the Thomas model showed good agreement with the experimental qE values, confirming the validity of the Thomas model for the column experiments.

Study of Ion-Pairing and Thermodynamic Properties of Sodium Fluoride in Aqueous Solutions at Temperatures from 298.15 to 353.15 K

In this investigation, the water activity and osmotic coefficients of the binary solution NaF–H2O were determined using the hygrometric method, from dilution to saturation and from 298.15 to 353.15 K. The hygrometric measurement results obtained have been combined with NaF(cr) solubility data in water to construct a chemical model that calculates solute and solvent activities from 298.15 to 353.15 K and from dilute to saturated solution concentration [up to m(NaF) = 1.2 mol·kg−1 at 353.15 K], and solid–liquid equilibria in the NaF–H2O system. The solubility modelling approach, based on the fundamental Pitzer ion interaction equations, was employed. It was found, that the standard approach for 1–1 electrolytes, with three β (0) , β (1), and C ϕ single electrolyte ion interaction parameters, gives a very good agreement with osmotic coefficients data for unsaturated solutions, and with NaF(cr) equilibrium solubility data, used in parameterization. The raw experimental osmotic coefficients (ϕ) and model calculated mean activity coefficients γ(NaF) have been compared with reference experimental ϕ data, and with γ estimations made by using different calculation approaches. The comparison shows a good agreement between ϕ data at 298.15 K. There is a disagreement between γ(NaF) calculations made in this study, and calculations based on Scatchard equations, and an extended Debye–Huckel (DH) model. The Pitzer based model constructed here has been also used to calculate the thermodynamic solubility product $$ \left( {K_{\text{sp}}^{\text{o}} } \right) $$ of NaF(cr) from 298.15 to 353.15 K. The solubility isotherm m s for NaF–H2O and thermodynamic solubility product [given as ln $$ K_{\text{sp}}^{\text{o}} $$ (NaF(cr))] are presented. In the saturated solution of NaF(aq), from experimental data and Fuoss approach using the obtained parameters, the experimental and calculated association constants K ass of the ion pairs were estimated at temperatures ranging from 298.15 to 353.15 K. The results are in good agreement.

Spectroscopic and Crystal Field Consequences of Fluoride Binding by [Yb⋅DTMA]3+ in Aqueous Solution.

Yb⋅DTMA forms a ternary complex with fluoride in aqueous solution by displacement of a bound solvent molecule from the lanthanide ion. [Yb⋅DTMA⋅F]2+ and [Yb⋅DTMA⋅OH2]3+ are in slow exchange on the relevant NMR timescale (<2000 s−1), and profound differences are observed in their respective NMR and EPR spectra of these species. The observed differences can be explained by drastic modification of the ligand field states due to the fluoride binding. This changes the magnetic anisotropy of the YbIII ground state from easy‐axis to easy‐plane type, and this change is easily detected in the observed magnetic anisotropy despite thermal population of more than just the ground state. The spectroscopic consequences of such drastic changes to the ligand field represent important new opportunities in developing fluoride‐responsive complexes and contrast agents.

Spectroscopic and Crystal Field Consequences of Fluoride Binding by [Yb⋅DTMA](3+) in Aqueous Solution.

Yb⋅DTMA forms a ternary complex with fluoride in aqueous solution by displacement of a bound solvent molecule from the lanthanide ion. [Yb⋅DTMA⋅F]2+ and [Yb⋅DTMA⋅OH2]3+ are in slow exchange on the relevant NMR timescale (<2000 s−1), and profound differences are observed in their respective NMR and EPR spectra of these species. The observed differences can be explained by drastic modification of the ligand field states due to the fluoride binding. This changes the magnetic anisotropy of the YbIII ground state from easy-axis to easy-plane type, and this change is easily detected in the observed magnetic anisotropy despite thermal population of more than just the ground state. The spectroscopic consequences of such drastic changes to the ligand field represent important new opportunities in developing fluoride-responsive complexes and contrast agents.

The introduction of P–F bonds using aqueous fluoride ion and a water soluble carbodiimide: a convenient alternative synthesis of phosphorofluoridates and phosphonofluoridates

The chemistry of ribonucleotides and other phosphates is extended to include their reactions with potassium fluoride in aqueous solution in the presence of a water soluble carbodiimide. High yields (>98%) of phosphorofluoridates are formed. A combination of HPLC, mass spectrometry, and NMR confirms the identities of the products. The methodology is applied, with equally satisfactory outcomes, to the physiologically active phosphonates Adefovir® and Tenofovir®, providing new compounds. Detailed NMR studies of the new phosphonofluoridates are reported.

Kinetics and equilibrium studies on Mg–Al oxide for removal of fluoride in aqueous solution and its use in recycling

Mg–Al oxide obtained by the thermal decomposition of Mg–Al layered double hydroxide (LDH) intercalated with CO32− (CO3·Mg–Al LDH) was found to take up fluoride from aqueous solution. Fluoride was removed by rehydration of Mg–Al oxide accompanied by combination with F−. Using five times the stoichiometric quantity of Mg–Al oxide, the residual concentration of F was decreased from 100 to 6.3 mg/L in 480 min, which was below the effluent standard in Japan (8 mg/L). Removal of F− can be represented by pseudo-second-order reaction kinetics. The apparent rate constants at 10 °C, 30 °C, and 60 °C were 2.3 × 10−3, 2.2 × 10−2, and 2.5 × 10−1 g mmol−1 min−1, respectively. The apparent activation energy was 73.3 kJ mol−1. The rate-determining step for F removal by Mg–Al oxide was consistent with chemical adsorption involving intercalation of F− into the reconstructed Mg–Al LDH due to electrostatic attraction. The adsorption of F by Mg–Al oxide follows a Langmuir-type adsorption. The values of the maximum adsorption and the equilibrium adsorption constant were 3.0 mmol g−1 and 1.1 × 103, respectively, for Mg–Al oxide. The F− in the F·Mg–Al LDH thus produced was found to be anion-exchanged with CO32− in solution. The Mg–Al oxide after regeneration treatment had excellent properties for removal of F in aqueous solution. In conclusion, the results of this study indicated that Mg–Al oxide has potential for use in recycling to remove F in aqueous solution.