The photo-electrochemistry of the Rhodamine B-hydroquinone system at optically transparent bubbling gas electrodes

Use of the technique called ‘bubbling gas electrode’ yields very reproducible polarograms on solid electrodes. It is applied here to study the photoelectrochemistry of the Rhodamine B-hydroquinone system on optically transparent n-type SnO₂ and gold electrodes, in order to understand the operation of a photovoltaic cell based on due-supersensitizer couples.Rhodamine alone gives no photo-currents on gold, and weak ones on SnO₂; added hydroquinone gives rise to very intense photo-currents on both electrodes. Increasing supersensitizer concentrations lead to a plateau, allowing an estimate of the lifetime of an electro-active transient.Two mechanisms for supersensitization are envisioned: hydroquinone can donate an electron to the photo-electrogenerated oxidized rhodamine, reducing thus the cathodic tunnel-current; or the diphenol might transfer an electron to the photo-excited dye, producing thus a new oxidizable species. Taken alone, the second mechanism is unable to explain all findings.Action spectra, recorded for a large number of experimental conditions suggest a major contribution from adsorbed dye molecules; in the presence of hydroquinone, some contributions from the solution may be operative.     

Sorption of Al (III) from aqueous solution by fresh macrophyte alligator weed: Equilibrium and kinetics

The removal of Al (III) ions from aqueous solution by locally abundantly low-cost fresh macrophyte, alligator weed, was examined in batch system. Effect of initial solution pH on Al (III) adsorption was investigated and the Al (III) species present in aqueous solution were identified. The main functional groups of the alligator weed were characterized by Fourier transform infrared spectrometer (FT-IR). The equilibrium data fitted to Freundlich and Langmuir isotherms satisfactorily. The pseudo-second-order equation fitted the kinetic data very well. The intraparticle diffusion played an important role in the Al (III) sorption process. Al (III) ions were favorably adsorbed by alligator weed and the values of K_f and 1/n (Freundlich constant) at 25 °C and pH 3.5 were found as 1.9963 (mg/g)/(mg/L)^1/n and 0.7875, respectively, which are comparable to those of granular activated carbon (2.20 (mg/g)/(mg/L)^1/n and 0.8695, respectively).     

The interaction of water-soluble iron porphyrins with DNA films and the electrocatalytic properties for inorganic and organic nitro compounds

The electrochemistry of water-soluble iron porphyrins (Fe(n-TMPyP)) (where n=2 and 4) was studied as an electrochemically active film on DNA modified glassy carbon, gold, platinum, and transparent semiconductor tin oxide electrodes in solutions of various pH values. The two layers of the modified electrode containing the iron porphyrin and the DNA film were prepared by depositing the iron porphyrin on a DNA film modified electrode. The Fe(4-TMPyP)/DNA film was electrocatalytic reductive for p-nitrobenzoic acid in a weak acidic, or neutral aqueous solution through an Fe^II species, and the electrocatalytic reduction peak potential became more negative than the cathodic peak of the Fe^III/II redox couple. The electrocatalytic reduction properties by the Fe(2-TMPyP)/DNA film as catalysts for nitrite reduction have also been determined, and shown to be active through an Fe^I species and to be pH-dependent. The electrocatalytic oxidation properties of nitrite by Fe(n-TMPyP)/DNA (for n=2 and 4) film have also been determined and shown to be active through an Fe^IV species with the electrocatalytic oxidation efficiency of NO₂⁻ with Fe^IV(O)(n-TMPyP) being higher than with (HO)Fe^IV(O)(n-TMPyP). The electrocatalytic oxidation efficiency of NO₂⁻ by iron porphyrin is pH-dependent. The electrocatalytic reduction of p-nitrophenol by Fe(2-TMPyP)/DNA film are also discussed.     

Hydrous ruthenium dioxide/multi-walled carbon-nanotube/titanium electrodes for supercapacitors

Composite electrodes prepared by vertically aligned multi-walled carbon nanotubes (MWCNTs) coated with hydrous ruthenium dioxide (RuO₂·nH₂O) have previously been used in various supercapacitors. The specific capacitance when using RuO₂·nH₂O/MWCNT/Ti as electrodes in 1.0 M H₂SO₄ aqueous solution can reach up to 1652 F/g at a scan rate of 10 mV/s, which is larger than that of RuO₂·nH₂O/Ti or MWCNT/Ti. In this study, a RuO₂·nH₂O/MWCNT/Ti composite electrode was examined by X-ray photoelectron spectroscopy, which revealed the existence of hydrous ruthenium dioxide in the Ti current collector. The capacitive behavior of the electrode was analyzed by cyclic voltammetry and the galvanostatic charge–discharge method, and the morphology of the composite electrode was examined by scanning electron microscopy.     

Spectroelectrochemistry of two-layered composites of polyaniline and poly(o-aminophenol)

Electropolymerization of aniline on poly(o-aminophenol)(POAP)-coated gold and indium-doped tin oxide (ITO)-coated glass electrodes yields polyaniline(PANI)/POAP two-layer composite films, exhibiting reversible redox functions in aqueous acidic solution. The PANI deposition on the POAP-coated electrodes was monitored by cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. CV results show that PANI/POAP composite films exhibit better stability as compared to PANI films during potential cycling in aqueous acidic solutions. Characteristic UV-vis and Raman features of the composite films have been identified and their dependencies on the electrode potential are discussed. They were significantly different from the corresponding spectral characteristics of PANI and POAP films alone.     

In situ FTIR study of the decomposition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ionic liquid during cathodic polarization of lithium and graphite electrodes

In this work we analyzed the cathodic reactions of an important ionic liquid (IL) based electrolyte solution, namely lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)/N-methyl-N-methylpyrrolidinium (BMP) TFSI. In situ FTIR spectroscopy was used for the analysis of gaseous products of the electrochemical decomposition of this IL solution during cathodic polarization of lithium metal and graphite electrodes. The main volatile product of the reductive decomposition of the anion in these BMPTFSI solutions is trifluoromethane. BMP cations decompose to mixtures of tertiary amines and hydrocarbons. The composition of the products is influenced by the nature of the anode material. Graphite possesses a catalytic activity in the electroreduction process of BMP cations which occurs along with their intercalation into the graphite structure. The liquid phase after cathodic polarization of graphite electrodes was analyzed by multinuclear NMR spectroscopy coupled with FTIR spectroscopy. ¹⁵N NMR and FTIR spectra revealed an increase in the Li cations content in the electrolyte solution, as a result of BMP cations decomposition during repeated cycling of graphite electrodes.     

Microstructural evolution in MgOp/AlN composites

MgO_p/AlN composite has been fabricated by directed melt nitridation of pure Al block covered with a powder mixture of 0.5–1 mm magnesia particles and 0.075–0.15 mm chemically pure magnesium powder in flowing N₂ in the range of 900–1200 °C. The extent of Al nitridation and the depth of Al penetration into the MgO particles increases with temperature. The phase composition in the matrix from metal rich to ceramic rich can be adjusted by controlling processing temperature. A multilayer microstructure of MgO/MgAl₂O₄/AlN surrounds the MgO particles due to the interface reaction. The thickness of each layer in this structure varies with processing parameters such as the temperature and local Mg concentration, depending on the influence of these processing parameters on the interface reaction of MgAl₂O₄ formation and Al nitridation.     

Separation and concentration effect of f-MWCNTs on electrocatalytic responses of ascorbic acid, dopamine and uric acid at f-MWCNTs incorporated with poly (neutral red) composite films

A novel conductive composite film containing functionalized multi-walled carbon nanotubes (f-MWCNTs) with poly (neutral red) (PNR) was synthesized on glassy carbon electrodes (GC) by potentiostatic method. The composite film exhibited promising electrocatalytic oxidation of mixture of biochemical compounds such as ascorbic acid (AA), dopamine (DA) and uric acid (UA) in pH 4.0 aqueous solutions. It was also produced on gold electrodes by using electrochemical quartz crystal microbalance technique, which revealed that the functional properties of composite film were enhanced because of the presence of both f-MWCNTs and PNR. The surface morphology of the polymer and composite film deposited on transparent semiconductor tin oxide electrodes were studied using scanning electron microscopy and atomic force microscopy. These two techniques showed that the PNR was fibrous and incorporated on f-MWCNTs. The electrocatalytic responses of neurotransmitters at composite films were measured using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV). These experiments revealed that the difference in f-MWCNTs loading present in the composite film affected the electrocatalysis in such a way, that higher the loading showed an enhanced electrocatalytic activity. From further electrocatalysis studies, well separated voltammetric peaks were obtained at the composite film modified GC for AA, DA and UA with the peak separation of 0.17 V between AA-DA and 0.15 V between DA-UA. The sensitivity of the composite film towards AA, DA and UA in DPV technique was found to be 0.028, 0.146 and 0.084 μA μM⁻¹, respectively.     

Highly active Ni/MgO in oxidative steam pre-reforming of n-butane for fuel cell application

Oxidative steam reforming of n-butane over supported Ni catalysts at relatively low temperature, 723 K, is reported. Among all the supported 20 wt% Ni catalysts studied, only Ni/MgO was able to convert n-butane directly after O₂ oxidation. Additionally, when the Ni/MgO was prepared from an aqueous Ni(NO₃)₂ solution with pH 7, H₂ formation rate of Ni/MgO (pH 7) at a high SV (1660 l(h · g)⁻¹) was 2.3 times as high as that of conventional Ni/MgO. The higher activity of Ni/MgO (pH 7) was ascribed to stronger resistance against oxidation of Ni⁰ due to the formation of relatively large Ni⁰ particles.     

Initial surface film on magnesium metal: A characterization by X-ray photoelectron spectroscopy (XPS) and photocurrent spectroscopy (PCS)

A detailed investigation of the initial film grown on mechanically polished Mg electrodes has been carried out by ex situ X-ray Photoelectron Spectroscopy (XPS) and in situ Photocurrent Spectroscopy (PCS), allowing to reach a detailed picture of the passive layer structure. The XPS data show that the films formed soon after mechanical treatment and immersion in aqueous electrolyte have a bilayer structure, consisting of an ultra-thin MgO inner layer (∼2.5 nm) and a Mg(OH)₂ external layer. The thickness of the Mg(OH)₂ layer is a function of immersion time and solution temperature. After mechanical treatment and immersion in aqueous solution at room temperature, the MgO/Mg(OH)₂ layer in some area of electrodes is so thin to allow an electron photoemission process from the Mg Fermi level to the electrolyte conduction band. Only internal photoemission processes are evidenced for Mg electrodes aged in NaOH at 80 °C, due the formation of a thicker Mg(OH)₂ layer. From anodic photocurrent spectra an optical band gap of ∼4.25 eV has been estimated for Mg(OH)₂, lower with respect to the optical gap of the corresponding anhydrous counterpart.     

Photoelectrochemical cells with mixed polycrystalline n-type CdSPbS and CdSCdSe electrodes

The photoelectrochemical behaviour of n-type CdS (polycrystalline) containing small amount of PbS or CdSe in S^2? /S^2?_n redox system has been studied. Mixed polycrystalline n-type CdSPbS electrodes were prepared by electrodeposition and the n-type CdSCdSe electrodes were made by partial replacement of sulphide ions of CdS electrode with selenide ions from a solution of sodium selenosulphate. It has been observed that both the mixed chalcogenide electrodes exhibit better photoresponse than the simple CdS electrode.     

EXTRACTION AND SPECTROSCOPIC STUDIES OF HYDROGEN BONDING COMPLEXES OF tris(ACETYLACETONATO)ALUMINUM(III) WITH 3,5-DICHLOROPHENOL FOR A NOVEL SYNERGISM

ABSTRACT

Synergistic enhancement of the extraction of aluminium(III) with acetylacetone (Hacac) in heptane and carbon tetrachloride was observed by the addition of 3,5-dichlorophenol (DCP).This phenomenon is due to the formation of association complexes of Al(acac)₃ with DCP. From the extraction-equilibrium analysis, the association complexes were found to be Al(acac)₃·n(DCP) (n=1-3) and the overall association constants (β_ass,n) were determined. The hydrogen bonding of the hydroxyl hydrogen of DCP with Al(acac)₃ was evidenced by IR and 1H NMR spectroscopy. The β_ass,n values determined by IR were in good agreement with those’ obtained by the distribution method. The relationship between the hydrogen bond ability of tris(acetylacetonato)-metals(III) and their structure was discussed by comparison of β_ass,n for Al(acac)₃ with those for some metal(III)-acac chelates studied so far.     

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1-13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H₂O₂, and electrocatalytically oxidation active for S₂O₄²⁻ through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S₄O₆²⁻, S₂O₄²⁻, and SO₃²⁻, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.     

Homogeneous synthesis of PFSI/silica composite membranes for PEMFC operating at low humidity

A transparent and flexible composite membrane with homogeneously distributed silica was prepared by one-pot synthesis of perfluorosulfonic ionomer (PFSI) and commercial silica sol. The PFSI dissolved in N,N-dimethylformamide (DMF) was used instead of aqueous/alcohol solution to increase the co-solubility between silica sol and PFSI. The conductivity of the composite membrane was doubled than that of the host polymer membrane to a value of 0.111 S cm⁻¹. The single fuel cell testing showed that the fuel cell with homogeneous composite membrane gave much better performance under the operation conditions without external humidification compared to that of host polymer membrane and NR112 membrane. It is believed that the increase in the homogeneity of the composite membrane is benefited from the increased co-solubility between silica sol and PFSI in DMF. It can be concluded that the homogeneous distribution of the components is crucial for the better performance.     

Strategy for the syntheses of isolated fine silver nanoparticles and polypyrrole/silver nanocomposites on gold substrates

In this work, isolated fine silver nanoparticles and polypyrrole/silver nanocomposites with diameters of about 10 nm on gold substrates were first prepared by electrochemical methods. First, an Ag substrate was cycled in a deoxygenated aqueous solution containing 0.1 M HCl from −0.30 to +0.30 V versus Ag/AgCl at 5 mV/s with 30 scans. Subsequently the Ag working electrode was immediately replaced by an Au electrode and a cathodic overpotential of 0.2 V was applied under controlled sonication to synthesize Ag nanoparticles on the Au electrode. Then pyrrole monomers were encouragingly found to be polymerized on the deposited Ag nanoparticles. This polymerization is distinguishable from the known chemical or electrochemical one, due to the electrochemical activity of unreduced species of Ag_n⁺ clusters inside the nanoparticles. Also, this polymerization may be ascribed to the oxidizing agent of AuCl₄⁻, which is present on the Au electrode.     

Electrochemical behaviour of thin films of Co/Al layered double hydroxide prepared by electrodeposition

Thin films of controlled thickness of Co/Al layered double hydroxide with different Co and Al percentages have been electrosynthesized by the cathodic reduction of a 0.03 M Co and Al nitrate solution. The electrochemical behaviour of the films deposited on Pt or ITO electrodes has been deeply studied in 0.1 M NaOH solution. Our findings demonstrate that as soon as a potential is applied in the anodic direction, the films undergo an irreversible change of phase.     

Electrochemistry of terbium in the eutectic LiCl-KCl

The electrochemical behaviour of terbium at a tungsten electrode, in the eutectic LiCl-KCl molten was investigated in the temperature range 673-823 K, by means of cyclic voltammetry, chronopotentiometry and chronoamperometry. It was found that during cathodic polarization, deposition of metallic Tb from the chloride mixture onto the tungsten surface proceeds in a single step, and electrocrystallization plays an important role in the whole process. Experimental current-time transients followed the theoretical models based on instantaneous nucleation with three-dimensional growth of the nuclei whatever the applied overpotential. From chronopotentiometric measurements, the diffusion coefficient of the Tb(III) ions was determined by applying the Sand equation and modifying the immersion dept of the working electrode in stages. The validity of the Arrhenius law was also verified and the activation energy for diffusion was found to be 33.4 ± 1.5 kJ mol⁻¹.The standard apparent potential value of the Tb(III)/Tb(0) system has been determined by potentiometry at several temperatures, and the activity coefficient of Tb(III) in the molten chloride media based on a pure supercool reference state has also been calculated.     

Electropolymerization and characterization of terpyridinyl iron (II) and ruthenium (II) complexes

Electroactive 2,2′: 6,2″-terpyridinyl ligands ( 3, 5, 6 ) and their iron(II) ( 7a–9a ) and ruthenium(II) complexes ( 7b–9b ) were synthesized. Bis[3-(aminophenyl)-2,2′ :6,2″-terpyridinyl]metal(II) complexes ( 7a, 7b ) and bis[2-(hydroxyphenyl)-2,2′ :6,2″-terpyridinyl]metal(II) complexes ( 8a, 8b ) were electropolymerized on to the surface of Pt or In-SnO₂ (ITO) electrodes in acetonitrile containing Bu₄NCIO₄ by scanning the potential between O and + 1.6V (for 7a and 7b ), and ?0.8 and +1.6V (for 8a and 8b ) versus saturated calomel electrode. The electrodes obtained by electropolymerization exhibited reversible electrochromism based on Fe(II)/Fe(III) or Ru(II)/Ru(III) redox couple. Photoresponses to visible light were found in the modified electrode obtained by electropolymerization of ruthenium complex 7b in an aqueous LiClO₄ solution containing methylviologen (cation MV²⁺) under an O₂ atmosphere. The mechanism for the photoresponded cathodic current was explained in terms of an excitation of bis(terpyridinyl)ruthenium(II) complex [Ru(terpy)²₂⁺] by visible light, an electron transfer from the excited state [Ru(terpy)^2+*₂] to MV²⁺, reduction of Ru(terpy)³⁺₂ at an electrode, and oxidation of MV^+* with O₂.     

Fabrication of porous Cu supported Ni-P/CeO2 composite coatings for enhanced hydrogen evolution reaction in alkaline solution

Cost-effective electrodes with high activity for hydrogen evolution reaction (HER) and durability are required to develop clean and renewable hydrogen energy. In this work, a porous Cu supported Ni-P/CeO₂ composite coating was fabricated by a facile electrodeposition technique. Owing to the contribution from the 3D porous Cu support and the incorporating agglomeration-free and uniformly distributed CeO₂ particles into the Ni-P matrix, the optimal composite coating (porous Cu supported Ni-P/CeO₂ (20 g L^-1)) exhibits outstanding electrocatalytic performance with small overpotentials (η) of 118 and 320 mV at a cathodic current density of 10 and 100 mA cm². Moreover, the composite electrode also presents excellent electrochemical stability in the alkaline solution. This work provides a feasible option to fabricate composite electrodes that may have desirable electrochemical properties for HER.     

Fabrication and photoresponse of ZnO nanowires/CuO coaxial heterojunction

The fabrication and properties of n-ZnO nanowires/p-CuO coaxial heterojunction (CH) with a photoresist (PR) blocking layer are reported. In our study, c-plane wurtzite ZnO nanowires were grown by aqueous chemical method, and monoclinic CuO (111) was then coated on the ZnO nanowires by electrochemical deposition to form CH. To improve the device performance, a PR layer was inserted between the ZnO buffer layer and the CuO film to serve as a blocking layer to block the leakage current. Structural investigations of the CH indicate that the sample has good crystalline quality. It was found that our refined structure possesses a better rectifying ratio and smaller reverse leakage current. As there is a large on/off ratio between light on and off and the major light response is centered at around 424 nm, the experimental results suggest that the PR-inserted ZnO/CuO CH can be used as a good narrow-band blue light detector.