Neutral Phosphate Solution Research Articles

Quantitative Interpretation of Potentiodynamic Polarization Curves Obtained at High Scan Rates in Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is becoming the tool of choice for the investigation of localized metal corrosion. Typically, potentiodynamic polarization measurements in scanning electrochemical cell microscopy are performed at high potential scan rates. However, Tafel extrapolation applied to high-scan-rate potentiodynamic polarization curves would yield inaccurate corrosion kinetics due to the interference of double-layer charging current or mass transport of species in the metal oxide. Instead, the high field model was used to simulate the potentiodynamic polarization curves of pure aluminum at 25, 50, 100, and 200 mV/s in neutral and acidic phosphate solutions, thus enabling quantitative analysis of local corrosion kinetics by fitting the potentiodynamic polarization curve.

Corrosion Behavior of the AZ31 Mg Alloy in Neutral Aqueous Solutions Containing Various Anions

This work demonstrates the corrosion behavior of the AZ31 Mg alloy as a function of an immersion time of 48 h in 0.1 M HCl, H2SO4, H3PO4 and HF solutions, in which pH was adjusted to 6 to exclude the contribution of hydrogen ions (H+) and hydroxide ions (OH−). In situ observations, open circuit potential (OCP), weight changes and AC impedance measurements were performed with an immersion time of 48 h and the morphologies and chemical compositions of the surface products after 48 h of immersion were analyzed by SEM, EDS and XPS. In the chloride ion (Cl−)-containing solution, the corrosion of the AZ31 Mg alloy initiated locally and propagated discontinuously over the surface with immersion time. The OCP value of the AZ31 Mg alloy showed an initial increase from −1.51 VAg/AgCl to −1.47 VAg/AgCl after about 5 h of immersion and then a decrease to −1.51 VAg/AgCl due to corrosion initiation. In the F−-containing solution, after 48 h of immersion, the OCP showed an extremely large value of −0.6 VAg/AgCl, while the relatively lower values of −1.52 VAg/AgCl, −1.59 VAg/AgCl were seen in the solutions containing SO42− and PO43, respectively. In the sulfate ion (SO42−)-containing neutral aqueous solution, needle-like surface films were formed and there were no changes in the weight of the AZ31 Mg alloy with immersion time. In the phosphate ion (PO43−)-containing neutral aqueous solution, a vigorous gas evolution occurred, together with the formation of black surface films with cracks, and a high corrosion rate of −13.8018 × 10−3 g·cm−2·day−1 was obtained. In the fluoride ion (F−)-containing neutral aqueous solution, a surface film with crystalline grains of MgF2 was formed and the weight of the AZ31 Mg alloy increased continuously with immersion time. In conclusion, the corrosion of the AZ31 Mg alloy occurred uniformly in neutral phosphate solution but locally in chloride solution. No corrosion was observed in either the neutral sulfate or fluoride solutions.

A high-capacity nanocellulose aerogel uniformly immobilized with a high loading of nano-La(OH)3 for phosphate removal

• Q-CNF aerogel served as a porous supporter to facilitate high loading of La(OH) 3 . • L-Q aerogel exhibited state-of-the-art q m of 87.0 mg P g −1 with high La utilization. • Excellent regeneration performance was achieved by facile alkaline cleaning. • The ligand exchange and LaPO 4 formation were responsible for the adsorption process. Developing a high-performance adsorbent for scavenging phosphate from water bodies remains a huge challenge. Herein, a novel high-capacity aerogel (abbreviated as ‘L-Q aerogels’) in which macroporous surface-quaternized cellulose nanofiber (Q-CNF) aerogels served as an active adsorptive supporter to facilitate the uniform dispersion and high loading of nano-La(OH) 3 with high affinity towards phosphate was developed. Due to the abundant exposed adsorption sites, the L-Q aerogel exhibited the maximal adsorption capacity of up to 87.0 mg P g −1 , surpassing the state-of-the-art La-doped hydroxide adsorbent. The utilization efficiency of nano-La(OH) 3 was greatly enhanced after being immobilized onto the aerogel, as supported by the much higher adsorbed P amount per gram of La than the nano-La(OH) 3 adsorbent (248.5 vs. 154.0 mg P g(La) -1 ). Given the interconnected macropores, the adsorption rate constant was found to reach an extraordinarily superior value of 0.0010 g mg −1 min −1 , three times higher than that of La(OH) 3 nano-adsorbent. Besides, the hybrid aerogel possessed highly pH-dependent adsorption and showed stable adsorption capacity in both neutral and weakly acid phosphate solutions. With the assistance of good shape recovery, the L-Q aerogel was easily regenerated by convenient alkali cleaning and still maintained a high removal efficiency after 5 adsorption–desorption cycles. Impressively, the immobilization of nano-La(OH) 3 onto the Q-CNF aerogel rendered the easy-to-use implement, ease of separation from the contaminated water, and avoidable leakage into water. Both XPS and XRD results revealed that the ligand exchange between phosphate and hydroxyls together with the formation of LaPO 4 precipitates were responsible for the adsorption mechanism. All these features of extraordinary adsorption capacity, convenient regeneration and handy operation, enabled the L-Q aerogel to have a promising application in the remediation of phosphate-contaminated water.

Redox-active water-soluble carbon nanomaterials generated from graphite

The cyclic voltammetric response of the anolyte generated under strong polarization of graphite electrodes in a phosphate solution was investigated to evaluate the intrinsic electrochemical activity of water-soluble carbon-based nanomaterials contained in it. Two electroreducible oxygen-containing functional groups were identified: quinone and epoxide. Since the nanomaterial was found to be surface-bounded to the electrode, the surface coverage of quinone and epoxide groups was quantified to appraise the effect of synthesis experimental conditions on the relative amounts of the two functionalization groups. The synthesis conditions were investigated in terms of the electrolytic solution composition (ionic strength and pH) and duration of the graphite polarization under galvanostatic polarization. Most appropriate experimental conditions to generate quinone rather than epoxide moieties (Γ quin /Γ ep = 2.5) were found when the nanomaterial was generated in a 3 h-assay using a neutral pH phosphate solution with low ionic strength (I = 0.1). These results may be taken as a guideline to modulate the redox-active water-soluble carbon nanomaterial functionalization, opening new perspectives to its application in sensing, energy storage, and nanomedicine.

Efficient Solar‐Assisted O2 Reduction Using a Cofacial Iron Porphyrin Dimer Catalyst Integrated into a p‐CuBi2O4 Photocathode

A cofacial iron porphyrin heterodimer, Fe2 TPFPP-TMP showed high electrocatalytic activity, selectivity, and stability for O2 reduction to H2 O both in homogeneous non-aqueous and heterogeneous neutral aqueous solutions. When it is integrated to FTO/p-CuBi2 O4 (FTO=fluorine doped tin oxide) photocathode prepared by a simple novel method, a remarkable efficient solar-assisted O2 reduction is achieved in neutral potassium phosphate (KPi) or basic NaOH solutions saturated with O2 .

Electrodeposited Nickel-Cobalt-Sulfide Catalyst for the Hydrogen Evolution Reaction.

A novel Ni-Co-S-based material prepared by the potentiodynamic deposition from an aqueous solution containing Ni2+, Co2+, and thiourea is studied as an electrocatalyst for the hydrogen evolution reaction (HER) in a neutral phosphate solution. The composition of the catalyst and the HER activity are tuned by varying the ratio of the concentrations of Ni2+ and Co2+ ions in the electrolytes. Under optimized deposition conditions, the bimetallic Ni-Co-S exhibits higher electrocatalytic activity than its monometallic counterparts. The Ni-Co-S catalyst requires an overpotential of 150 mV for the HER onset, and 10 mA cm-2 current density is obtained at 280 mV overpotential. The catalyst exhibits two different Tafel slopes (93 and 70 mV dec-1) indicating two dissimilar mechanisms. It is proposed that the catalyst comprises two types of catalytic active sites, and they contribute selectively toward HER in different potential regions.

Fast and Simple Preparation of Iron‐Based Thin Films as Highly Efficient Water‐Oxidation Catalysts in Neutral Aqueous Solution

AbstractWater oxidation is the key step in natural and artificial photosynthesis for solar‐energy conversion. As this process is thermodynamically unfavorable and is challenging from a kinetic point of view, the development of highly efficient catalysts with low energy cost is a subject of fundamental significance. Herein, we report on iron‐based films as highly efficient water‐oxidation catalysts. The films can be quickly deposited onto electrodes from FeII ions in acetate buffer at pH 7.0 by simple cyclic voltammetry. The extremely low iron loading on the electrodes is critical for improved atom efficiency for catalysis. Our results showed that this film could catalyze water oxidation in neutral phosphate solution with a turnover frequency (TOF) of 756 h−1 at an applied overpotential of 530 mV. The significance of this approach includes the use of earth‐abundant iron, the fast and simple method for catalyst preparation, the low catalyst loading, and the large TOF for O2 evolution in neutral aqueous media.

Fast and simple preparation of iron-based thin films as highly efficient water-oxidation catalysts in neutral aqueous solution.

Water oxidation is the key step in natural and artificial photosynthesis for solar-energy conversion. As this process is thermodynamically unfavorable and is challenging from a kinetic point of view, the development of highly efficient catalysts with low energy cost is a subject of fundamental significance. Herein, we report on iron-based films as highly efficient water-oxidation catalysts. The films can be quickly deposited onto electrodes from Fe(II) ions in acetate buffer at pH 7.0 by simple cyclic voltammetry. The extremely low iron loading on the electrodes is critical for improved atom efficiency for catalysis. Our results showed that this film could catalyze water oxidation in neutral phosphate solution with a turnover frequency (TOF) of 756 h(-1) at an applied overpotential of 530 mV. The significance of this approach includes the use of earth-abundant iron, the fast and simple method for catalyst preparation, the low catalyst loading, and the large TOF for O2 evolution in neutral aqueous media.

Vertically aligned carbon nanotube-based electrodes for hydrogen production by water electrolysis

Abstract

Adsorption of 2-mercaptobenzothiazole on copper surface from phosphate solutions

Analysis of the electrochemical and XPS results has shown that adsorption of 2-mercaptobenzothiazole (MBT) on copper electrodes in neutral phosphate solutions proceeds through the formation of the chemical bonds by copper (I) cations with exo-sulfur and nitrogen atoms. A protection layer formed of Cu(I)MBT complex prevents precipitation of copper (II) phosphate on a copper surface. The thickness of the surface film consisting of a complex [Cu(I)MBT]n (having probably polymeric nature), where MBT acts as at least three-dentate ligand, increases depending on the exposure time, reaching 8–9nm after immersing for 12h in test solution. Even in a case of the preliminary formation of copper (II) phosphate on the copper electrode at the anodic potential addition of small amounts of MBT results in complete removal of copper (II) phosphate from the surface.

Electroanalytical Determination of Some Phenolic Acids by High‐Performance Liquid Chromatography at Gold Electrodes

AbstractThe electrochemical and amperometric behavior of a gold electrode was investigated towards the oxidation of several common phenolic acids in neutral phosphate solutions. Au electrodes show an appreciable stability and reproducibility of the amperometric signals by using a constant applied potential of 1.0 V vs. Ag/AgCl. Separations of selected phenolic acids using a reverse phase C18 analytical column with a mobile phase containing 10 mM NaH2PO4 plus 10 mM Na2HPO4 (pH 7) and methanol as organic modifier, are achieved isocratically in less than 30 min. The detection limits at the level of nmol/L and linear ranges of four‐five orders of magnitude are generally achieved. The proposed chromatographic strategy coupled with the electrochemical detection at the Au electrode was successful tested for the quantitative determination of phenolic acids in beer, red wine and brandy with good sensitivity and recovery.

Conversion of nacre powders to apatite in phosphate buffer solutions at low temperatures

Apatite (HAP) powders with poor crystallinity were obtained from nacre powders by treatment with phosphate buffer solutions of pH's 6.0–8.0, kept at 37 °C for 1–12 days. The effects of pH values, particle size, and reaction time on the conversion of nacre powders were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Nacre powders are converted to HAP both by treatment with the basic or neutral phosphate solutions, and by treatment with the acidic phosphate solutions without regulating pH values during the reaction using dicalcium phosphate dehydrate (DCPD) or octacalcium phosphate (OCP) as active intermediate phases. Decreasing particle size and prolonging reaction time can improve the conversion percentages of nacre powders to HAP. In addition, the dissolution–recrystallisation mechanism of HAP formation was discussed further in the present work.

Luminescence from band-gap photo-excitation of titanium anodic oxide films

Luminescence light from the anodic thin oxide films formed on titanium in neutral phosphate solution was measured by photo-excitation of ultra-violet light irradiation with 3.82 eV energy. The luminescence light is observed with a peak of about 3 eV energy that corresponds to the band-gap energy of the n-type semiconductive TiO 2 oxide. It can therefore be presumed that the luminescence is induced by de-excitation or recombination between electrons in the conduction band and holes in the valence band. The peak wavelength of the luminescence light changes with the formation potential of the oxide film from 409 nm at 1 V to 425 nm at 6 V. The shift of the peak may reflect an amorphous–crystalline transition with increase of potential.

In-situ spectroelectrochemistry (UV–visible and infrared) of anodic films on iron in neutral phosphate solutions

The composition of anodic films on iron formed at different potentials in neutral solutions has been investigated by in-situ UV–vis and IR spectroscopies in the presence of PO 4 3−, a non-contaminant inhibitor used in anticorrosive paints. Optical and electrochemical determinations were used to detect and characterize two well-defined current waves in the active region of Fe and a following passive zone at more positive potentials. The response has been associated with the presence on the surface, in the dissolution zone, of Fe 3 II[PO 4] 2 as the main species and probably some [Fe IIIPO 4]. [Fe IIIPO 4] has been detected in the passive region by in-situ IR spectroscopy. Only minor amounts of Fe 2+ and Fe 3+ species in solution have been detected optically. These phosphated overlayers are believed to provide extra protective properties to the passivating film.

インピーダンス測定によるチタン不働態皮膜の半導体的性質の評価

The dielectric and semiconductive properties of the passive film on titanium were investigated under potentiostatic polarization in neutral phosphate and borate solutions by using the impedance technique. Further topographic change of the passivated surface with potential was observed by AFM. From comparison between the film thickness and the capacitance of the space charge layer, the dielectric constant of the passive film was estimated at about 40 in the potential region lower than 3V and about 85 in the potential region higher than 3V. From the Mott-Schottky plot the donor density of the passive film was calculated, which is in the order of 1026m-3, and decreased with an increase of the film formation potential. The decrease may correspond to a change of film structure from amorphous to crystalline. At potential higher than 7.5V, breakdown of the passive film was observed, probably due to influence of very high electric field in the film. The breakdown brings about the increase of donor density, and a roughening surface due to micro-crystallization.

Effects of aluminum (III) and fluoride on the demineralization of bovine enamel: a longitudinal microradiographic study.

Longitudinal microradiography has been used to determine inhibiting effects of aluminum (III), Al, and fluoride on mineral loss from slices of bovine enamel exposed to a demineralizing solution 4 h daily for 35 days. Inhibitor treatment was 5 min four times daily. For the remaining time, the samples were immersed in a neutral calcium phosphate solution which allowed neither remineralization nor demineralization. This study indicates that a 1-mM (27 ppm) solution of Al in a 0.1-M lactate solution, pH 5, has an inhibitory effect on the in vitro demineralization of bovine enamel. Application of this solution alternating with 20 mM (380 ppm) fluoride gave the same total inhibition as treatment with 20 mM fluoride alone.

The modern understanding of the glass electrode response

Electrochemical experiments in combination with infrared spectroscopy and subsurface concentration profiling yielded information on ionic processes at the membrane surface of glass electrodes and resulted in a detailed mechanism of the glass electrode response. This “dissociation mechanism” is based on phase boundary equilibria between anionic groups at the glass surface and hydrogen or alkali ions in the solution, which control the potential of the glass and the concentrations of ions attached to the surface groups. The resulting concentration gradients between glass surface and bulk glass cause an interdiffusion of the different ions, if they are not hindered sterically to penetrate into the glass, and a diffusion potential beneath the glass surface. The interdiffusion determines the course of the glass corrosion, which thus depends on whether protons or alkali ions are attached to the surface and interdiffuse with the alkali ions of the glass, leading, respectively, to a steady-state leached layer or a continuously growing alkali-exchanged layer. pH electrodes with La2O3-containing membrane glasses show delayed interfering potential drifts in neutral and alkali phosphate and fluoride solutions caused by LaPO4 and LaF3 deposits, respectively, at the membrane surface (“phosphate” and “fluoride errors”). Equations for the phase boundary potential and phase boundary concentrations are derived on a thermodynamic and kinetic basis and are verified experimentally. Glass leaching and alkali ion interdiffusion are studied, and the diffusion potential within a leached layer is determined. The formation periods of pH and of pM glass electrodes are explained, and an indirect part of the sodium error and an irreversible sodium error are detected. Leached and alkali-exchanged layers consist of modified glass and are not “gel” layers as generally assumed. Large exchange current densities of the phase boundary equilibria explain the stability of glass electrode potentials. Migration experiments with subsequent concentration profiling showed that glasses can be alkali ion, proton, and mixed alkali ion-proton conductors and yielded concentration-dependent mobilities of lithium ions and replacing protons in a lithium silicate glass. The unchanged pH response of membranes before and after field-driven protonation, in alkali-free solutions, excludes the exchange of different ions as the origin of the glass electrode response, as assumed by the ion exchange theory, and verifies the dissociation mechanism.

Bioactive glass ceramics: properties and applications

Heat treatment of an MgO-CaO-SiO 2-P 2O 5 glass gave a glass ceramic containing crystalline apatite (Ca 10(PO 4) 6O,F 2)) and β-wollastonite (CaO.SiO 2) in an MgO-CaO-SiO 2 glassy matrix. It showed bioactivity and a fairly high mechanical strength which decreased only slowly, even under load-bearing conditions in the body. It is used clinically as artificial vertebrae, iliac bones, etc. The bioactivity of this glass ceramic was attributed to apatite formation on its surface in the body. Dissolution of calcium and silicate ions from the glass ceramic was considered to play an important role in forming the surface apatite layer. It was shown that some new kinds of bioactive materials can be developed from CaO,SiO 2-based glasses. Ceramics, metals and organic polymers coated with bone-like apatite were obtained when such materials were placed in the vicinity of a CaO,SiO 2-based glass in a simulated body fluid. A bioactive bone cement which was hardened within 4 min and bonded to living bone, forming an apatite, was obtained by mixing a CaO,SiO 2-based glass powder with a neutral ammonium phosphate solution. Its compressive strength reached 80 MPa comparable to that of poly(methyl methacrylate) within 3 d. A bioactive and ferromagnetic glass ceramic containing crystalline magnetite (Fe 3O 4) in a matrix of CaO,SiO 2-based glassy and crystalline phases was obtained by a heat treatment of a Fe 2O 3-CaO.SiO 2-B 2O 3-P 2O 5 glass. This glass ceramic was shown to be useful as thermoseeds for hyperthermia treatment of cancer.

沸騰リン酸塩溶液中におけるアルミニウムの水和酸化物皮膜の生成挙動

Aluminum foil specimens were immersed in neutral phosphate solutions with Can=10-4-10-1 M and doulbly distilled water (DDW) for 60 min at 99.5°C, and the formation behavior of hydroxide films on the surface was examined by gravimetry, chemical analysis, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and impedance measurements. In DDW, two-layer hydroxide films were observed with film formation efficiency, η, of 1.0, and in phosphate solutions, thin single-layer hydroxide films were observed with η=0.7-0.9. At Can=10-2 kmol/m3, the film thickness showed a minimum and η a maximum. The XPS results showed that phosphates are incorporated in the outer part of the films formed in phosphate solutions, and that the phosphate incorporation increases with Can. For all the films impedance measurements suggested the existence of an oxide layer with ca. 2.5 nm thickness at the interface between the hydroxide film and the metal substrate. The role of phosphate ions in the formation of hydroxide films is discussed in terms of dissolution and stabilization of the film with aluminum-phosphate complexes.

ChemInform Abstract: Passive Behavior of Iron in Alkaline Phosphate Solutions.

AbstractThe quasi‐stationary passive current of Fe is shown to be independent of the stabilization potential and the pH in neutral and alkaline phosphate solutions (polarization measurements).