Influence of F‐ doping on the microstructure,surface morphology and electrochemical properties of the lead dioxide electrode

The lead dioxide electrode (PbO₂) with Ti substrate and SnO₂‐Sb₂O₅ intermediate layer was doped by F^‐ ion through the potentiostatic anode co‐deposition method. The content of F in the coating can be controlled by adjusting deposition potential. The effect of F^‐ doping on the composition, surface morphology and electrochemical properties of the PbO₂ electrode was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy and electrochemical measurement methods. The results have confirmed that the content of β‐PbO₂ increases with increasing that of F, and the doping can make the β‐PbO₂ grains become fine and the electrode surface become smooth; the specific surface areas and conductivity increase, and the initial potential of oxygen evolution shifts toward positive direction compared with the free‐doped PbO₂ electrode; the oxygen evolution potential increases with the increasing of the F^‐content in the PbO₂ film electrode. The bulk electrolysis result demonstrated that the performances of the F‐PbO₂ electrode for anodic oxidation aniline have been improved to some extent. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation of Ce-PbO(2) modified electrode and its application in detection of anilines

The effect of Ce(III) on the morphology and structure of lead dioxide (PbO₂) modified electrode was studied in this paper. The results obtained by cyclic voltammetry (CV), X-ray diffractometion (XRD) and scanning tunneling micrograph (STM) indicated that the Ce-doped PbO₂ film consisted of a mixture of α- and β-PbO₂ crystallographic phases and the content of α-phase was higher than that in undoped PbO₂ film. PbO₂ crystal grains in nanometric size were formed on the electrode surface by doping with Ce. So that the specific surface areas and catalytic active sites of the modified electrode were increased. Hence the catalytic activity of the Ce-PbO₂ modified electrode was evidently greater than the undoped PbO₂ modified electrode. When the Ce-PbO₂ modified electrode was applied as an analytical sensor to determine aniline compounds, the linearity was in the range of 5×10⁻⁵ to 1×10⁻³ mol/l and the detection limit was 1×10⁻⁵ mol/l.     

Electrochemical Degradation of Herbicidal and Pure 2,4-Dichlorophenoxy Acetic Acid on Pb/PbO2 Modified Electrodes

Lead/lead oxide Pb/PbO₂ modified electrodes was prepared for electrocatalytic oxidation of agrochemicals including herbicidal 2,4-D (albar super) and pure 2,4-dichlorophenoxy acetic acid. The results of electrocatalytic oxidation process of the agrochemical solutions were expressed in terms of the remaining concentration and COD removal. The different operating conditions of treatment process were investigated including current density, pH, temperature, time of electrolysis, type of conductive electrolyte, and its specific conductance. This electrode gives good results for the removal of agrochemicals and COD. Also, the results showed the best conductive electrolytes is NaCl. This observation was attributed to the small size of Na⁺ and contribution of Cl^? ion in formation of OCl^?.     

Electrodeposited PbO2 thin film on Ti electrode for application in hybrid supercapacitor

PbO₂ thin films were prepared by pulse current technique on Ti substrate from Pb(NO₃)₂ plating solution. The hybrid supercapacitor was designed with PbO₂ thin film as positive electrode and activated carbon (AC) as negative electrode in the 5.3 M H₂SO₄ solution. Its electrochemical properties were determined by cyclic voltammetry (CV), charge–discharge test and electrochemical impedance spectroscopy (EIS). The results revealed that the PbO₂/AC hybrid supercapacitor exhibited large specific capacitance, high-power and stable cycle performance. In the potential range of 0.8–1.8 V, the hybrid supercapacitor can deliver a specific capacitance of 71.5 F g^?1 at a discharge current density of 200 mA g^?1(4 mA cm^?2) when the mass ratio of AC to PbO₂ was three, and after 4500 deep cycles, the specific capacitance remains at 64.4 F g^?1, or 32.2 Wh Kg^?1 in specific energy, and the capacity only fades 10% from its initial value.     

[1,1-Bis(diphenylphosphino)ferrocene]palladium(II) complexes with fluorinated benzenethiolate ligands: examination of the electronic effects in the solid state, solution and in the Pd-catalyzed Heck reaction with the catalytic system [Pd(dppf)(SRF)2]

A series of palladium thiolate complexes of the type [Pd(dppf)(SR_F)₂] have been synthesized in good yields by metathetical reactions of [Pd(dppf)Cl₂] with [Pb(SR_F)₂], (SR_F=⁻SC₆F₅, ⁻SC₆F₄-4-H, ⁻SC₆H₄-2-CF₃, ⁻SC₆H₄-4-F, ⁻SC₆H₄-3-F) and their crystal structures determined. The effect of the different thiolates in the structural properties of the complexes both in the solid state and in solution have been analyzed. Heck coupling reactions were carried out using the complexes [Pd(dppf)(SR_F)₂], SR_F=⁻SC₆F₅ (1), ⁻SC₆F₄-4-H (2), ⁻SC₆H₄-2-CF₃ (3), ⁻SC₆H₄-4-F (4), ⁻SC₆H₄-3-F (5) as catalysts in order to examine both the effect of the thiolates and the P-Pd-P bite angles in the reaction of bromobenzene and styrene. The results obtained indicate that electron-withdrawing substituents may favor higher yields in the Pd catalyzed Heck reaction using [Pd(dppf)(SR_F)₂] as catalysts.     

Direct electrocatalytic oxidation of nitric oxide and reduction of hydrogen peroxide based on α-Fe2O3 nanoparticles-chitosan composite

α-Fe₂O₃ nanoparticles prepared using a simple solution-combusting method have been dispersed in chitosan (CH) solution to fabricate nanocomposite film on glass carbon electrode (GCE). The as-prepared α-Fe₂O₃ nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The nanocomposite film exhibits high electrocatalytic oxidation for nitric oxide (NO) and reduction for hydrogen peroxide (H₂O₂). The electrocatalytic oxidation peak is observed at +0.82 V (vs. Ag/AgCl) and controlled by diffusion process. The electrocatalytic reduction peak is observed at −0.45 V (vs. Ag/AgCl) and controlled by diffusion process. This α-Fe₂O₃-CH/GCE nanocomposite bioelectrode has response time of 5 s, linearity as 5.0 × 10⁻⁷ to 15.0 × 10⁻⁶ M of NO with a detection limit of 8.0 × 10⁻⁸ M and a sensitivity of −283.6 μA/mM. This α-Fe₂O₃-CH/GCE nanocomposite bioelectrode was further utilized in detection of H₂O₂ with a detection limit of 4.0 × 10⁻⁷ M, linearity as 1.0 × 10⁻⁶ to 44.0 × 10⁻⁶ M and with a sensitivity of 21.62 μA/mM. The shelf life of this bioelectrode is about 6 weeks under room temperature conditions.     

Theoretical study of thiazole derivatives as chemosensors for fluoride anion

The interactions between chemosensor, 2-(2′-hydroxyphenyl)-4-phenylthiazole (1), and different halides (F⁻, Cl⁻, and Br⁻) and NO₃⁻ anions have been theoretically investigated at the B3LYP/6-31G(d) level with the BSSE correction. It turned out that the unique selectivity of 1 for F⁻ is ascribed to its ability of deprotonating the hydroxy group of host sensor. The intermolecular proton transfer (IPT) causes the colorimetric and fluorescent signaling of 1 for F⁻. The deprotonated complex 1⁻·HF is formed for the deprotonation process of chemosensor. The study of substituent effects suggest that the electron-donating –CH₃ and –OCH₃ substituted derivatives are expected to be promising candidates for ratiometric fluorescent F⁻ chemosensors as well as chromogenic chemosensors, while electron-donating –N(CH₃)₂ substituted derivative can serve as chromogenic F⁻ chemosensors only. Furthermore, the electron-withdrawing (–NO₂ and –Br) substituted derivatives can serve as chromogenic F⁻/CH₃COO⁻ chemosensors.     

Alignment of acentric MoO3F3 anions in a polar material: (Ag3MoO3F3)(Ag3MoO4)Cl

(Ag₃MoO₃F₃)(Ag₃MoO₄)Cl was synthesized by hydro(solvato)thermal methods and characterized by single-crystal X-ray diffraction (P3m1, No. 156, Z=1, a=7.4488(6)Å, c=5.9190(7) Å). The transparent colorless crystals are comprised of chains of distorted fac-MoO₃F₃³⁻ octahedra and MoO₄²⁻ tetrahedra anions, as suggested by the formulas Ag₃MoO₃F₃ and Ag₃MoO₄⁺, and are connected through Ag⁺ cations in a polar alignment along the c-axis. One Cl⁻ anion per formula unit serves as a charge balance and connects the two types of chains in a staggered fashion, offset by . In MoO₄²⁻, the Mo atom displaces towards a single oxide vertex, and in MoO₃F₃³⁻, the Mo displaces towards the three oxide ligands. The ordered oxide-fluoride ligands on the MoO₃F₃³⁻ anion is important to prevent local inversion centers, while the polar organization is directed by the Cl⁻ anion and interchain dipole-dipole interactions. The dipole moments of MoO₃F₃³⁻ and MoO₄²⁻ align in the negative c-axis direction, to give a polar structure with no cancellation of the individual moments. The direction and magnitude of the dipole moments for MoO₃F₃³⁻ and MoO₄²⁻ were calculated from bond valence analyses and are 6.1 and 1.9 debye (10⁻¹⁸ esu cm) respectively, compared to 4.4 debye for polar NbO₆ octahedra in LiNbO₃, and 4.5 debye for polar TiO₆ octahedra in KTiOPO₄ (KTP).     

Voltammetric behavior of copper(I)oxide modified carbon paste electrode in the presence of cysteine and ascorbic acid

The electrochemical behavior of a copper(I)oxide (Cu₂O) modified carbon paste electrode (MCPE) was investigated in different buffer solutions and in the presence of ascorbic acid (AA) and cysteine (RS). Working conditions such as pH, mineral oil, and modifier ratio were optimized. Voltammetric results revealed that RS forms rather stable complexes with Cu(I) which has a high electrocatalytic reduction peak current at −0.65 V versus SCE in borate buffer (pH 9.2). In the case of AA, a complexation occurred with Cu(II) species at the electrode surface, rather than Cu(I). The electrocatalytic reduction peak current of the Cu(II)-AA complex was observed at −0.07 V in phosphate buffer at pH 6.9. Linear responses were observed in the range 2.0×10⁻⁹ to 3.0×10⁻⁸ M with a 0.9954 correlation coefficient for RS and 1.0×10⁻⁹ to 2.0×10⁻⁸ M with a 0.9961 correlation coefficient for AA.     

Conversion of porous PbO2 layers through galvanic displacement reaction with Mn2 + ions

The galvanic exchange between Mn^2 + ions and electrodeposited porous PbO₂ was studied to produce a porous oxide whose lower conductivity prevented its direct oxygen bubble-templated anodic deposition. Immersion of PbO₂ layers in acid acetate solutions of Mn^2 + led to the formation of amorphous MnO_x shell onto PbO₂. Due to its amorphous nature, MnO_x could not be proved to be MnO₂ by XRD. However, MnO_x was cathodically stripped at the same potential as MnO₂. The deposition of the MnO_x shell onto PbO₂ enhanced the capacity of the porous electrodes.     

Macrocyclic bis(amidonaphthol)s for anion sensing: tunable selectivity by ring size in proton transfer process

The investigation on anion sensing properties for a series of macrocyclic bis(amidonaphthol)s 3a-3c reveals the significant effects of macrocyclic ring size. Among them, macrocycle 3c with the largest ring size shows F⁻ ion selectivity by causing clear red shift (24 nm) in fluorescence emission after complexation with F⁻, which results in significant color change of fluorescence from blue to green. This excellent selectivity toward F⁻ ion might be attributed to the fitness between the acidity of -OH group and the basicity of F⁻ ion. Further exploration indicates that the acidity of -OH group can be tuned by ring size to give it the capability to discriminate the subtle difference in the affinity of F⁻, CH₃COO⁻, and H₂PO₄⁻ to -OH proton.     

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

Electrochemical behavior of hexafluoroniobate (Nb(V)F₆⁻), heptafluorotungstate (W(VI)F₇⁻), and oxotetrafluorovanadate (V(V)OF₄⁻) anions has been investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F₆⁻ anion is reduced to Nb(IV)F₆²⁻ by a one-electron reversible reaction. Electrochemical reductions of W(VI)F₇⁻ and V(V)OF₄⁻ anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F₆⁻, W(VI)F₇⁻ and V(V)OF₄⁻ determined by chronoamperometry are 1.34 × 10⁻⁷, 7.45 × 10⁻⁸ and 2.49 × 10⁻⁷ cm² s⁻¹, respectively. The Stokes radii of Nb(V)F₆⁻, W(VI)F₇⁻, and V(V)OF₄⁻ in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained.     

Simple indole-based colorimetric sensors with electron-withdrawing chromophores: Tuning selectivity in anion sensing

Three simple colorimetric anion sensors (1, 2, and 3) containing anthrone, 1,3-indanedione, and malononitrile as signaling chromophores and an indole binding site have been designed and synthesized. The introduction of electron-withdrawing groups can not only provide chromogenic signal output, but also tune the sensitivity and selectivity of indole-based anion sensors by electron push–pull features. Their anion binding and sensing properties were investigated in detail by dramatic color changes, UV–vis absorption, and ¹H NMR. As results revealed, sensor 1 showed high selectivity for F⁻ over AcO⁻ and H₂PO₄⁻ with a distinct change in color due to the deprotonation of indole NH group. The excellent selectivity of 1 for F⁻ can be attributed to the fitness in the acidity of its NH-group, which is tuned to be able to distinguish the subtle difference in the affinity of F⁻, AcO⁻, and H₂PO₄⁻ to NH proton.     

Synthesis, crystal structure and optical properties of a novel sodium lead pentaborate, NaPbB5O9

A novel sodium lead pentaborate, NaPbB₅O₉, has been successfully synthesized by standard solid-state reaction. The single-crystal X-ray structural analysis showed that NaPbB₅O₉ crystallizes in the monoclinic space group P2₁/c with a=6.5324(10) Å, b=13.0234(2) Å, c=8.5838(10) Å, β=104.971(10)°, and Z=4. The crystal structure is composed of double ring [B₅O₉]³⁻ units, [PbO₇] and [NaO₇] polyhedra. [B₅O₉]³⁻ groups connect with each other forming two-dimensional infinite _∞[B₅O₉]³⁻ layers, while [PbO₇] and [NaO₇] polyhedra are located between the layers. [PbO₇] polyhedra linked together via corner-sharing O atom forming novel infinite _∞[PbO₆] chains along the c axis. The thermal behavior, IR spectrum and the optical diffuse reflectance spectrum of NaPbB₅O₉ were reported.     

Specific F binding to phenyl ring of aromatic polymers

Most of the hydrogels deswell more remarkably in F⁻ containing solutions than in other monovalent anion containing solutions. However, significant deswelling followed by abnormal reswelling of polymer gel in KF solutions with increasing F⁻ concentration was observed in a series of polymer gels consisted of phenyl rings, for instance, poly(styrene sulfonic acid) (PSSA), hydroxypropyl methylcellulose phthalate (HPMCP) and poly(4-vinyl phenol) (P4VPh) gel. Driving force of this phenomenon was studied to reveal the specific interactions involved in the aqueous systems of aromatic polymers. Elemental analysis and XPS results suggest that F⁻ is embedded to the gel by the physical adsorption of KF, as well as the interactions between phenyl ring and F⁻. Further theoretical calculations revealed that the interaction may be (phenyl)CH?F⁻(H₂O)_n interaction, which is stronger than (phenyl)CH?(H₂O)_n hydrogen bond. This kind of interaction decreases with the increasing water number and it is invalid when the surrounding water number is more than 5 for the phenol-F⁻(H₂O)_n system. Therefore, we conclude that F⁻ could bind to phenyl ring via such (phenyl)CH?F⁻(H₂O)_n interaction in solutions with low hydrophilicity. The strong polarization effect of F⁻ and (phenyl)CH?F⁻(H₂O)_n interaction are two important driving forces for the reswelling of gels.     

Boron-dipyrromethene based specific chemodosimeter for fluoride ion

3,5-Bis(trimethylsilylethynyl)-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene [BODIPY(CCTMS)₂] has been synthesized by coupling of 3,5-dibromo-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene with trimethylsilylacetylene under pd(0) coupling conditions. The BODIPY(CCTMS)₂ was used as a selective colourimetric and fluorescent chemodosimeter for fluoride ion, following the F⁻ ion induced cleavage of trimethylsilyl group, the protecting group of ethyne functionality by monitoring the changes in UV-vis and fluorescence properties. The dosimeter BODIPY(CCTMS)₂ display clear changes in colour, absorption and emission bands selectively for F⁻ ion over other anions such as Cl⁻, Br⁻, I⁻, ClO₄⁻ and HPO₄²⁻.     

Anode with the Active Layer for Electrosynthesizing Ozone in a System with Solid Polymer Electrolyte

The synthesis of catalytic coatings on porous titanium electrodes by the method of magnetron sputtering is considered. The content of dopant ions Fe³⁺ and F^– is optimized as regards the activity and stability of the PbO₂ catalyst in the reaction of ozone electrogeneration as well as the current efficiency with respect to ozone. It is shown that the best characteristics of the electrochemical ozone generator are observed on the PbO₂ catalyst doped with Fe³⁺ and F^– ions in the amount of 3–4 and 1–2 at %, respectively.     

Hydrogen production from water decomposition by redox of Fe2O3 modified with single- or double-metal additives

Iron oxide modified with single- or double-metal additives (Cr, Ni, Zr, Ag, Mo, Mo-Cr, Mo-Ni, Mo-Zr and Mo-Ag), which can store and supply pure hydrogen by reduction of iron oxide with hydrogen and subsequent oxidation of reduced iron oxide with steam (Fe₃O₄ (initial Fe₂O₃)+4H₂↔3Fe+4H₂O), were prepared by impregnation. Effects of various metal additives in the samples on hydrogen production were investigated by the above-repeated redox. All the samples with Mo additive exhibited a better redox performance than those without Mo, and the Mo-Zr additive in iron oxide was the best effective one enhancing hydrogen production from water decomposition. For Fe₂O₃-Mo-Zr, the average H₂ production temperature could be significantly decreased to 276 °C, the average H₂ formation rate could be increased to 360.9-461.1 μmol min⁻¹ Fe-g⁻¹ at operating temperature of 300 °C and the average storage capacity was up to 4.73 wt% in four cycles, an amount close to the IEA target.     

Study on the electrocatalytic degradation of 4-chlorophenol on PbO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript> composite electrode and its electrochemical property

PbO₂–ZrO₂ composite electrodes were prepared by anodic electrodeposition in the lead nitrate solution. The electrochemical property of this electrode was studied by cyclic voltammetry, polarization curves and open-circuit potential–time curves. The results show that PbO₂–ZrO₂ composite electrodes possess higher oxygen evolution overpotential and better anti-corrosion performance than traditional PbO₂ electrodes. Electrocatalytic oxidation of 4-chlorophenol (4-CPs) in aqueous solution was studied to evaluate the applications of this electrode in environmental protection. The influence of experimental parameters on the COD removal efficiency was studied on PbO₂–ZrO₂ composite electrodes as a function of the current density, initial concentration of the 4-CPs, initial pH, supporting electrolyte concentration and electrolysis time. The results show that the 4-CPs removal efficiency in 0.1 mol L^–1 Na₂SO₄ solution containing 8 mmol L^–1 4-CPs could reach 89.2% with the current density at 200 mA cm^–2 and pH value at 6.5 after 4 h. Compared with traditional PbO₂ anodes, the PbO₂–ZrO₂ composite electrodes show higher instantaneous current efficiency with degradation of 4-CPs. The experimental results demonstrate that the PbO₂–ZrO₂ composite electrodes possess the excellent electrocatalytic activity in refractory pollutants degradation.     

Simultaneous quantitative profiling of 20 isoprostanoids from omega-3 and omega-6 polyunsaturated fatty acids by LC–MS/MS in various biological samples

Isoprostanoids are a group of non-enzymatic oxygenated metabolites of polyunsaturated fatty acids. It belongs to oxylipins group, which are important lipid mediators in biological processes, such as tissue repair, blood clotting, blood vessel permeability, inflammation and immunity regulation. Recently, isoprostanoids from eicosapentaenoic, docosahexaenoic, adrenic and α-linolenic namely F₃-isoprostanes, F₄-neuroprostanes, F₂-dihomo-isoprostanes and F₁-phytoprostanes, respectively have attracted attention because of their putative contribution to health. Since isoprostanoids are derived from different substrate of PUFAs and can have similar or opposing biological consequences, a total isoprostanoids profile is essential to understand the overall effect in the testing model. However, the concentration of most isoprostanoids range from picogram to nanogram, therefore a sensitive method to quantify 20 isoprostanoids simultaneously was formulated and measured by liquid chromatography-tandem mass spectrometry (LC–MS/MS). The lipid portion from various biological samples was extracted prior to LC–MS/MS evaluation. For all the isoprostanoids LOD and LOQ, and the method was validated on plasma samples for matrix effect, yield of extraction and reproducibility were determined. The methodology was further tested for the isoprostanoids profiles in brain and liver of LDLR^−/− mice with and without docosahexaenoic acid (DHA) supplementation. Our analysis showed similar levels of total F₂-isoprostanes and F₄-neuroprostanes in the liver and brain of non-supplemented LDLR^−/− mice. The distribution of different F₂-isoprostane isomers varied between tissues but not for F₄-neuroprostanes which were predominated by the 4(RS)-4-F_4t-neuroprostane isomer. DHA supplementation to LDLR^−/− mice concomitantly increased total F₄-neuroprostanes levels compared to F₂-isoprostanes but this effect was more pronounced in the liver than brain.