Numerical simulation of electrode process in Cu/CuSO4 + H2SO4 system

In the present work, electrode process in the system Cu/CuSO₄+H₂SO₄ is considered as a sum of two single-electron electrochemical reactions that occur simultaneously on copper electrode. Numerical modelling of this process was performed taking into account diffusion, electromigration, and chemical interactions between the components of the solution. The results of calculations do not contradict the experimental facts known for this system. The behaviour in the region close to the open circuit potential can be explained by the differences in the partial currents of the reactions proceeding on the electrode. The behaviour of the surface concentrations of the components of solution in the region of the anodic overpotential points to a substantial role of electromigration processes that can be played by them in copper passivation in sulphate solutions.     

Electrosorption of tert-butyl compounds on Hg from aqueous Na2SO4 solution: tert-butylamine

The adsorption of tert-butylamine (TBUNH₂) at the Hg/0.5 M aqueous Na₂SO₄ polarized interface has been studied by means of electrocapillary measurements. Adsorption has been found to follow a Frumkin isotherm with interaction parameter corresponding to particle-particle attraction. Adsorption is congruent neither with respect to charge nor with respect to potential, but the model of two capacitors in parallel is much better approached, especially at positive rational potentials. The positive value of the interaction parameter is explained in terms of unfavourable solvent-adsorbate surface interactions, slightly dependent on the electric field. The fundamental adsorption parameter of TBUNH₂ are compared with data previously obtained for TBUOH. The behaviour of TBUNH₂ at the air-solution interface seems to exclude any specific interaction between the Hg surface and NH₂ group; the differences between TBUNH₂ and TBUOH are probably to be related to the different nature of the particle-particle interactions.     

The mechanism of the anodic formation of S2O2−8 ions on a Ti-supported IrO2 electrode in mixed aqueous solutions of H2SO4, (NH4)4SO4 and NH4F

The mechanism for the anodic formation of peroxydisulfate ion on a Ti-supported IrO₂ electrode was investigated in mixed aqueous solutions of H₂SO₄, (NH₄)SO₄ and NH₄F.Peroxydisulfate ion can be formed in higher yield at lower overpotential on the Ti-supported IrO₂ electrode, compared with smooth Pt electrode. The most probable mechanism under Langmuir conditions of intermediate adsorption was proposed as

     

Ionic conductivity of PEO9: Cu(CF3SO3)2: Al2O3 nano-composite solid polymer electrolyte

Cu⁺⁺ ion containing solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO₉:Cu(CF₃SO₃)₂ made by complexing copper triflate (CuTf₂) with PEO appears to show scientifically intriguing transport properties. Although some copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the species involved are yet to be established. In order to obtain enhanced ionic conductivities and also to contribute towards understanding the ionic transport process in Cu⁺⁺ ion containing, PEO based composite polymer electrolytes, we have studied the system PEO₉: CuTf₂: Al₂O₃ incorporating 10 wt.% of alumina filler particles of grain size 10 μm, 37 nm, 10–20 nm and also particles of pore size 5.8 nm. Thermal and electrical measurements show that the system remains amorphous down to room temperature. The composite electrolyte is predominantly an ionic conductor with electronic conductivity less than 2%. The triflate (CF₃SO₃⁻) anions appear to be the dominant carriers. The presence of alumina grains has enhanced the conductivity significantly from room temperature up to 100 °C. The nano-porous grains with 5.8 nm pore size and 150 m²/g specific surface area exhibited the maximum conductivity enhancement. This enhancement has been attributed to Lewis acid–base type surface interactions of ionic species with O²⁻ and OH⁻ groups on the filler grain surface.     

Hydrogen evolution on RuxTi1−xO2 in 0.5 M H2SO4

Hydrogen evolution from 0.5 M H₂SO₄ on Ti electrodes coated with a Ru_xTi_1−xO₂ (x=0.04-0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 °C caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe²⁺ ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from −105 mV/decade for pure titanium to about −40 mV/decade for the (RuTi)O₂ coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data, to be about 10⁻⁴ A cm⁻² after activation.     

ZrOCl_2-H_2SO_4/γ-Al_2O_3催化剂的制备及对1-丁烯齐聚反应的催化性能

以γ-Al_2O_3为载体,负载Zr OCl_2和H_2SO_4制备Zr OCl_2-H_2SO_4/γ-Al_2O_3催化剂,并用于1-丁烯齐聚反应。采用气相色谱在线分析,确定产物组成,考察制备条件对催化剂催化活性的影响,通过1-丁烯转化率和主产物选择性确定适宜的反应条件。结果表明,在Zr OCl_2和H_2SO_4负载质量分数为4.5%和焙烧温度500℃条件下制备的催化剂,在反应温度140℃、1-丁烯液时空速2 h-1和N2分压1.4 MPa条件下,表现出较好的催化活性,1-丁烯转化率96.77%,产物以二聚体(C8)为主,选择性85.99%。该催化剂失活后容易再生,且催化活性良好,1-丁烯转化率92.73%,C8选择性86.73%。     

Oxygen reduction mechanism on copper in a 0.5 M H2SO4

The mechanism of the oxygen reduction reaction (ORR) in a naturally aerated stagnant 0.5 M H₂SO₄ was studied using electrochemical methods. The cathodic polarization curve showed three different regions; electrochemical impedance spectroscopy (EIS) measurement was used accordingly. The EIS data were analyzed, and the mechanism for the ORR was proposed consequently. The three regions include a limiting current density region with the main transfer of 4e⁻ controlled by diffusion (−0.50 V < E < −0.40 V), a combined kinetic-diffusion region (−0.40 V < E < −0.20 V) with an additional 2e⁻ transfer due to the adsorption of the anions, and a hump phenomenon region (−0.20 V < E < −0.05 V), in which the chemical redox between the anodic intermediate and the cathodic intermediate , together with the electrochemical reaction, synergistically results in the acceleration of the ORR. Therefore, a coupled electrochemical/chemical process (the EC mechanism) in the hump phenomenon region was proposed, and a good agreement was found between the experimental and fitted results. The EC mechanism was confirmed by the deaerated experiments.     

Photocatalytic conversion of CH4 and CO2 to oxygenated compounds over Cu/CdS–TiO2/SiO2 catalyst

Coupled semiconductor (CS) Cu/CdS–TiO₂/SiO₂ photocatalyst was prepared using a mutli-step impregnation method. Its optical property was characterized by UV–vis spectra. BET, XRD, Raman and IR were used to study the structure of the photocatalyst. Fine CdS was found dispersed over the surface of anatase TiO₂/SiO₂ substrate. Chemisorption and IR analysis showed methane absorbed in the molecular state interacted weakly with the surface of catalyst, and the interaction of CO₂ with CS produced various forms of absorbed CO₂ species that were primarily present in the form of formate, bidentate and linear absorption species. Photocatalytic direct conversion of CH₄ and CO₂ was performed under the operation conditions: 373 K, 1:1 of CO₂/CH₄, 1 atm, space velocity of 200 h⁻¹ and UV intensity of 20.0 mW/cm². The conversion was 1.47% for CH₄ and 0.74% for CO₂ with a selectivity of acetone up to 92.3%. The reaction mechanisms were proposed based on the experimental observations.     

Electrode reaction of the Mn(II)/Mn(Hg) system in concentrated aqueous solutions of Ca(ClO4)2 at higher temperatures

The electrode reaction of the Mn(II)/Mn(Hg) system was studied in Ca(ClO₄)₂ solutions in concentrations ranging from 1 to 13.5 mole kg^?1 and temperature limits from ?5 to 160°C using chronocoulometry and cyclic voltammetry. From the analyses of formal potentials is function of water activity the hydration numbers of Mn(II) ions were estimated. The changes of rate constants and transfer coefficients with the increase of electrolyte concentration and temperature above 5 mole kg^?1 and 85°C, respectively, suggest a change in the rate-determining step from the second to the first electron. The calculated individual rate constants for both steps are presented and their changes with the increase in electrolyte concentration are discussed.     

Organically templated Np(IV) coordination polymer with in situ formed oxalate anion (ImidazoleH)[Np(C2O4)(CH3SO3)3(H2O)2]

The reaction of Np(V) methanesulfonate solution with imidazole led to the in situ formation of oxalic acid and the reduction of Np(V) to Np(IV). As a result, the novel organically templated organic polymer, (ImidazoleH)[Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂], was formed. The structure consists of infinite chains of [Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂]⁻ and imidazolium cations. The crystal structure is confirmed by IR and UV–vis spectroscopic data. This complex is the first example of structurally characterized 1:1 An(IV) oxalate.     

Transport of co-ions across ion exchange membranes in electrodialytic metathesis MgSO4 + 2KCl → K2SO4 + MgCl2

Flow rates of co-ions across membranes (Cl⁻ and SO₄²⁻ ions across Neosepta CMX cation exchange membranes, K⁺ and Mg²⁺ ions across Neosepta AMX anion exchange membranes) in the title electrodialytic metathesis have been determined. It was established that the flow of co-ions causes contamination of all solutions flowing through the electrodialyzer. For instance, Cl⁻ ions penetrate into anolyte (K₂SO₄ solution), chlorine is found among anode reaction products and deteriorates operating conditions and induces corrosive processes. A quantitative contamination assessment of two products (potassium sulphate and sodium chloride) was carried out.     

BaTi4O9（f）／0.64BaTi4O9—0.36BaPr2Ti4O12复合陶瓷的介电性研究

借助X射线衍射技术（XRD）,低频阻抗法,X射线光电子能谱（XPS）等手段对BaTi4O9(f)/0.64BaTi4O9-0.36PaPr2Ti4O12复合陶瓷新材料的相组成、介电性能和样品中Ti元素的价态变化进行了研究,研究结果表明：该复合陶瓷新材料只由BaTi4O9和BaPr2Ti4O12两相组成,加入BaTi4O9纤维后,复合陶瓷材料中Ti^3 离子和Ti^2 郭子的含理降低,氧元素的含量提高,并对该材料体系的介电性有明显的改善作用,其中含10?Ti4O9纤维的BPT10试样的性能最佳,其εr=64,tgδ=α10^-4(1MHz)。     

Solvothermal synthesis of a novel mixed valence Cu(I)/Cu(II) complex containing sulphate, malate and 4,4-bipyridine, [CuCu2(mal)(SO4)(bpy)2 · H2O]n. Unique binding mode of the malate anion

The reaction of CuSO₄ · 5H₂O with 4,4^′-bipyridine and malic acid at 140 °C under solvothermal conditions afforded a mixed valence three-dimensional coordination polymer [Cu^ICu^II₂(mal)(SO₄)(bpy)₂ · H₂O]_n, (1). The building unit consists of a Cu²⁺-dimer in which copper centers are bridged by malate and sulphate anions. SO₄²⁻ anion further connects dimeric unit with the Cu¹⁺ center. Building units are linked by 4,4^′-bipyridine ligands to form double chains, that are interconnected into 3D network through additional sulphate bridge.     

In situ corrosion monitoring of Ti–6Al–4V alloy in H2SO4/HCl mixed solution using electrochemical AFM

Electrochemical atomic force microscope (ECAFM) was employed for in situ observation of corrosion of solution annealed and furnace cooled Ti–6Al–4V titanium alloy in 0.5 mol l⁻¹ H₂SO₄ + 1 mol l⁻¹ HCl mixed solution. A scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) was also used for microstructure examination and chemical composition analysis. For solution annealed followed by furnace-cooled Ti–6Al–4V titanium alloy, selective corrosion of α phase and galvanic effect at α/β interface could be clearly observed at open circuit potential under ECAFM. A higher dissolution rate was also found in α phase than β phase on the bare Ti–6Al–4V titanium alloy. The effect of potential on the corrosion behavior was also explored. Negligible corrosion was found after potentiostatic etching at −0.5 and −0.85 V_Pt for 120 min. However, selective dissolution of α phase with respect to β phase occurred when the potential was controlled at −0.9 V_Pt. The polarity inversion during potentiostatic etching at −0.9 V_Pt was also found and discussed in this study.     

Protection of mild steel corrosion with Schiff bases in 0.5 M H2SO4 solution

Three new Schiff bases, viz., N,N′-ethylen-bis (salicylidenimine) [S₁], N,N′-isopropylien-bis (salicylidenimine) [S₂], and N-acetylacetone imine, N′-(2-hydroxybenzophenone imine) ortho-phenylen [S₃] have been investigated as corrosion inhibitors for mild steel in 0.5 M H₂SO₄ using Tafel polarization and electrochemical impedance spectroscopy (EIS). The three Schiff bases function as good inhibitors reaching inhibition efficiencies of ∼97-98% at 300 ppm concentration. The fraction <theta> of the metal surface covered by the inhibitor is found to increase with inhibitor concentration. Of the three Schiff bases, the S2 shows better efficiency than the other two Schiff bases. The adsorption of the inhibitor follows Langmuir isortherm. Thermodynamic calculations indicate the adsorption to be physical in nature.     

Photocatalytic reduction of Ag2SO4 by the Dawson anion α-[P2W18O62] and tetracobalt sandwich complexes

The photocatalytic behaviours of the Dawson salt α-K₆[P₂W₁₈O₆₂] and two isomers of the tetracobalt Dawson-derived sandwich complexes, αββα-Na₁₇[Co₄(H₂O)(OH)(P₂W₁₅O₅₆)₂]·51H₂O·2NaCl and ααβα-Na₁₆[Co₄(H₂O)₂(P₂W₁₅O₅₆)₂]·51H₂O (abbreviated ββ-{Co₄P₄W₃₀} and αβ-{Co₄P₄W₃₀}, respectively), are described and compared.The direct photochemical excitation of the polyoxometalates (POM) in the presence of propan-2-ol as electron donor leads to their reduction. With polyoxometalates as photocatalyst and propan-2-ol as sacrificial electron donor, the reduction of Ag^I₂SO₄ from aqueous solutions is observed leading to metallic Ag_n⁰ clusters and colloidal metal nanoparticles stabilized by POM.In the case of both {Co₄P₄W₃₀}, TEM experiments reveal that most of the Ag_n particles obtained with a slight excess of Ag⁺ are spherical with a quite large distribution in size between 10 and 100 nm.     

Functionalized magnetic core-shell Fe3O4@SiO2 nanoparticles as selectivity-enhanced chemosensor for Hg(II)

A colorimetric and ‘‘turn-on” fluorescent chemosensor Rho-Fe₃O₄@SiO₂ for Hg²⁺ in which N-(rhodamine-6G)lactam-ethylenediamine (Rho-en) is conjugated with the magnetic core-shell Fe₃O₄@SiO₂ NPs has been strategically designed and synthesized. The final product was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR) and UV-visible absorption and fluorescence emission. Fluorescence and UV-visible spectra results showed that the resultant multifunctional nanoparticles Rho-Fe₃O₄@SiO₂ exhibited selective ‘turn-on’ type fluorescent enhancements and distinct color changes with Hg²⁺. The selectivity of the Rho-Fe₃O₄@SiO₂ for Hg(II) ion is better than that of the Rho-en in the same conditions. In addition, the presence of magnetic Fe₃O₄ nanoparticles in the sensor Rho-Fe₃O₄@SiO₂ NPs would also facilitate the magnetic separation of the Hg(II)-Rho-Fe₃O₄@SiO₂ from the solution.     

Hexanuclear 4d–4f complexes [Ln2Ag4(ina)8(H2O)10][NO3]2 · 4H2O (Ln = Sm, Eu, Dy): Syntheses, structures and photoluminescent properties

Hexanuclear 4d–4f heterometallic complexes, [Ln₂Ag₄(ina)₈(H₂O)₁₀][NO₃] ₂ · 4H₂O [Ln = Sm (1), Eu (2), Dy (3) and Hina = isonicotinic acid], have been synthesized by the hydrothermal reaction of lanthanide oxides, Ag^I, and isonicotinic acid at a suitable temperature. Single-crystal X-ray diffraction studies indicate that these 4d–4f complexes consist of extended 1D zigzag chains structure built upon [Sm₂Ag₄(ina)₈(H₂O)₁₀] subunits connected by Ag–Ag interactions. Furthermore, the photoluminescent properties of the complex 2 were studied.     

Monolayer and bilayer conducting polymer coatings for corrosion protection of steel in 1 M H2SO4 solution

In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H₂SO₄ solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings.     

Effect of halogen ions on platinum dissolution under potential cycling in 0.5 M H2SO4 solution

The effect of ppm level of chloride and fluoride ions on the dissolution of electrochemically deposited Pt with two different thickness has been studied by using electrochemical quartz crystal microbalance (EQCM) and ICP-Mass analysis in combination with atomic force microscopy (AFM). A mass loss due to dissolution of Pt as chloride complexes was observed in as low as 10 ppm [Cl⁻] at 1.06 V versus SHE. Fluoride ion did not have any effect on the dissolution of Pt in as high as 1000 ppm [F⁻]. From the comparison of EQCM, ICP-Mass and AFM images, it was revealed that amount of platinum dissolution under potential cycling greatly depended on chloride concentration and morphology of deposited Pt layers. When Pt dissolution was induced by Cl⁻ ions, the amount of dissolved Pt did not depend on the particle size of the deposited Pt. On the other hand, in the absence of Cl⁻ induced dissolution, i.e. when oxide formation was dominant, the particle size of the deposited Pt greatly affected the amount of dissolved Pt. This was explained by considering the increase of overpotential for the reduction of chloride complex due to its high stability in chloride solution.