Comparison of polyamide nanofiltration and low-pressure reverse osmosis membranes on As(III) rejection under various operational conditions

A nanofiltration (NF) membrane and a low-pressure reverse osmosis (LPRO) membrane both with aromatic polyamide selective layer from the same manufacturer were employed for the comparison of their performances in terms of As(III) rejection and filtration flux under a variety of operational conditions. In addition to the smaller membrane pore size, the LPRO membrane possesses much more dissociable functional groups than the NF membrane. When the feed pH was below the pKa₁ value (9.22) of H₃AsO₃, for which the steric hindrance is the only rejection mechanism, the removal efficiencies by NF and LPRO were about 10% and 65%, respectively. When the feed pH was higher, for which electrostatic effect began to take effect, the removal efficiencies could reach 40% and 90% for NF and LPRO, respectively. The rejection performance of LPRO was marginally affected by the feed As(III) concentration or ionic strength, although ionic strength had a strong effect on the filtration flux. In contrast, feed As(III) concentration and ionic strength had little effect on the filtration flux but great influence on the As(III) rejection performance of NF. The filtration flux was enhanced with the increase of transmembrane pressure for either NF or LPRO. The NF model could predict the general trend of the effects of the filtration flux, the feed water chemistry and its own concentration on As(III) rejection ratio by the NF membrane, but the rejection ratios were over-predicted.     

Impact of pH on the removal of fluoride, nitrate and boron by nanofiltration/reverse osmosis

The objective of this study was to evaluate the impact of pH on boron, fluoride, and nitrate retention by comparing modelled speciation predictions with retention using six different nanofiltration (NF) and reverse osmosis (RO) membranes (BW30, ESPA4, NF90, TFC-S, UTC-60, and UTC-80A). Retention was explained with regard to speciation, membrane properties, and ion properties such as charge, hydrated size, and Gibbs energy of hydration. Flux was independent of pH, indicating that pH did not alter pore size and hence permeability for all membranes except UTC-60. Membrane charge (zeta potential) was strongly dependent on pH, as expected. Boron and fluoride retention depended on membrane type, pH, which correlated closely to contaminant speciation, and was due both to size and charge exclusion. While retention at low and neutral pH was a challenge for boron, high boron retention was achieved (> 70% above pH 11). Fluoride retention was generally > 70% above pH 7. Nitrate retention depended on membrane, and was mostly pH independent (as was the speciation). The presence of a background electrolyte matrix (20 mM NaCl and 1 mM NaHCO₃) reduced nitrate and boron retention (at high pH) due to charge shielding, and enhanced the retention of fluoride in single feed solutions, suggesting preferential transport of Cl⁻ compared to F⁻ with Na⁺.     

Use of bulk liquid membrane for the removal of chromium (VI) from aqueous acidic solution with tri-n-butyl phosphate as a carrier

Tri-n-butyl phosphate (TBP) was used as carrier for the transport of chromium (VI) through a hexane bulk liquid membrane. The transport efficiency of chromium (VI) by TBP was investigated under various experimental conditions such as pH of the feed phase (Cr (VI) solution), concentration of the receiving phase (NaOH solution), concentration of TBP in membrane, rate of stirring, effect of transport time, type of solvent, Cr (VI) concentration in feed phase, and effect of temperature. The transport efficiency increased with increasing carrier concentration from 7.5 × 10^− 2 to 2.25 × 10^− 1 mol/L. At high pH (donor phase) the transport rate of chromate ions decreased. At high stirring speed (300 rpm) the Cr (VI) transport from the feed phase to the strip phase was completed within 5 h at 27 °C. Under optimum conditions: donor phase 4.8 × 10^− 4 mol/L K₂Cr₂O₇ solution at pH 1.0 ± 0.1, acceptor phase 1.0 mol/L NaOH solution, membrane phase 2.25 × 10^− 1 mol/L, stirring speed 300 rpm, and temperature 27 °C, the flux rate was found to be 2.90 × 10^− 7 mol/m² s.     

Electrochemical degradation of 17β-estradiol (E2) at boron-doped diamond (Si/BDD) thin film electrode

Electrochemical degradation of aqueous solutions containing 17β-estradiol (E2), concentrations range of 250-750 μg dm⁻³, has been extensively studied using boron-doped diamond (BDD) anode with a working solution volume of 250 ml under galvanostatic control. Cyclic voltammetric experiments were performed to examine the redox response of E2 as a function of cycle number. The effect of operating variables such as initial concentration of E2, applied current density, supporting medium (Na₂SO₄, NaNO₃, and NaCl) and initial pH of the electrolyte (pH 2-10) were systematically examined and discussed. Electrolysis at high anodic potential causes complex oxidation of E2 that leads to form the final sole product as CO₂. A pseudo first-order kinetics for E2 decay was found against varying applied current density. Also, kinetic analysis suggests that electrooxidation reaction of E2 undergo the control of applied current density. It was observed that electrolyte pH and supporting medium have a vital role on E2 degradation. From a comparison study with other anode materials such as platinum (Pt) and glassy carbon (GC), the superiority of the BDD anode was proved. Total organic carbon results have shown that almost complete mineralization could be accomplished at higher applied current density with specific electrical charge 22.5 × 10⁻² A h dm⁻³. Mineralization current efficiency was comparatively lower with increasing applied current density.     

Bifunctional redox flow battery-1 V(III)/V(II)-glyoxal(O2) system

Bifunctional redox flow batteries (BRFB) possess functions of both electricity storage and electrochemical preparation, having the potential for increasing the electrical energy utilization. A V(III)/V(II)-glyoxal(O₂) system has been developed. Separators of the BRFB play a key role in BRFB performance. A Nafion solution was sprayed on a gas diffusion layer (GDL) at the Nafion loading of 2 mg cm⁻², and the GDL was then hot-pressed onto a Nafion115 cation exchange membrane, obtaining a modified separator. This separator not only prevents the crossover of vanadium but also has favorable conductivity, obtaining optimal charge and organic electro-synthesis performance of the BRFB. The effects of the concentrations of glyoxal and HCl on the performance of BRFB were also investigated. It is shown that the optimal concentration of glyoxal and HCl should be 1.2 and 3 M, respectively. As a result, the current efficiency of organic electro-synthesis is further increased. An acceptable discharge performance is achieved for a period exceeding 20 h at the current density of 20 mA cm⁻². The average discharge voltage of 0.73 V and the coulombic efficiency of 66% are obtained. It is demonstrated that the principle of the BRFB is feasible. However, further experiments are needed to improve the performance.     

Exploration of As(III)/As(V) Uptake from Aqueous Solution by Synthesized Calcium Sulfate Whisker

Although common calcium-containing minerals such as calcite and gypsum may fix arsenic, the interaction between modified calcic minerals and arsenic has seldom been reported. The uptake behavior of As(III)/As(V) from aqueous solutions by calcium sulfate whisker (CSW, dihydrate or anhydrite) synthesized through a cooling recrystallization method was explored. A series of batch experiments were conducted to examine the effect of pH, reaction time, whisker dosage, and initial As concentration. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the samples prepared. The results showed that pH of the aqueous solution was an important parameter for As(III)/As(V) uptake, and an excellent removal efficiency could be achieved under strongly alkaline condition. The data from batch experiments for reaction of As(V) with calcium sulfate dihydrate whisker (CSDW) and calcium sulfate anhydrous whisker (CSAW) were well described with extended Langmuir EXT1 model, from which theoretic maximum adsorption capacity of 46.57 mg As(V)·(g CSDW)^− 1 and 39.18 mg As(V)·(g CSAW)^− 1 were obtained. Some calcium arsenate solids products, such as CaAsO₃(OH) (weilite, syn), Ca₃(AsO₄)₂ (calcium arsenate), CaO–As₂O₅, Ca–As–O, Ca₅(AsO₄)₃OH·xH₂O (calcium arsenate hydroxide hydrate), and CaH(AsO₄)·2H₂O (hydrogen calcium arsenic oxide hydrate), were detected at pH = 12.5 through XRD analysis. This indicates that the interaction mechanism between As(V) and CSW is a complex adsorption process combined with surface dissolution and chemical precipitation.     

Electrochemical behavior of europium (III) in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide

N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyNTf₂) was synthesized and characterized by CHNS elemental analysis, ¹H and ¹³C NMR and IR spectroscopy. Europium tris[bis(trifluoromethylsulfonyl)imide] (Eu(NTf₂)₃) was prepared and studied for the electrochemical behavior of Eu(III) in BMPyNTf₂ at glassy carbon and stainless steel working electrodes at 298-373 K by cyclic voltammetry, chronopotentiometry and chronoamperometry. Cyclic voltammogram of Eu(III) in BMPyNTf₂ consisted of a quasi-reversible cathodic wave at −0.45 V (vs. Fc/Fc⁺, 373 K), which could be attributed to the reduction of Eu(III) to Eu(II) and an irreversible wave at −2.79 V (vs. Fc/Fc⁺) due to reduction of Eu(II) to Eu(0). The diffusion coefficient of Eu(III) in BMPyNTf₂ was determined to be in the range of ∼10⁻⁷ cm² s⁻¹ by various electrochemical methods and the charge transfer rate constant was determined to be ∼10⁻⁵ cm s⁻¹ by cyclic voltammetry.     

Separation of As(III) and As(V) by hollow fiber supported liquid membrane based on the mass transfer theory

Separation of As(III) and As(V) ions from sulphate media by hollow fiber supported liquid membrane has been examined. Cyanex 923 was diluted in toluene and used as an extractant. Water was used as a stripping solution. The extractability of As(V) was higher than As(III). When the concentration of sulphuric acid in feed solution and Cyanex 923 in liquid membrane increased, more arsenic ions were extracted into liquid membrane and recovered into the stripping solution. The mathematical model was focused on the extraction side of the liquid membrane system. The mass transfer coefficients of the aqueous phase (k _i ) and organic phase (k _m ) are 7.15×10⁻³ and 3.45×10⁻² cm/s for As(III), and 1.07×10⁻² and 1.79×10⁻² cm/s for As(V). Therefore, the rate-controlling step for As(III) and As(V) in liquid membrane process is the mass transfer in the aqueous film between the feed solution and liquid membrane. The calculated mass transfer coefficients agree with the experimental results.     

Oxygen electroreduction on Ag(1 1 1): The pH effect

The rotating ring disk method (RRDE) is applied to investigate the pH effect on oxygen reduction reaction (ORR) on Ag(1 1 1) single crystal surface in 0.1 M KOH and 0.1 M HClO₄. In 0.1 M KOH, the ORR proceeds through 4e⁻ reaction pathway with a very small (0.5-2.5%) peroxide formation in the entire potential range. In 0.1 M HClO₄ the onset potential for the ORR is shifted for ca. 400 mV toward the higher overpotentials compared to the 0.1 M KOH solution. At the low overpotentials, in 0.1 M HClO₄ the ORR proceeds entirely as a 2e⁻ process, i.e, 100% H₂O₂ formation. At higher overpotentials, the initial mixed a 2e⁻ and 4e⁻ reduction is followed by the potential region where the ORR proceeds entirely as a 4e⁻ process, with H₂O formation as a final product. The pH dependent shift in the onset of the ORR as well as the reaction pathway has been explained based on both: a thermodynamic analysis of pH independent rate determining step, and on the pH dependent change in availability of surface active sites and adsorption energies of molecular oxygen and reaction intermediates.     

Effects of specific adsorption of copper (II) ion on charge transfer reaction at the thin film LiMn2O4 electrode/aqueous electrolyte interface

This study investigated the effect of a specific adsorption ion, copper (II) ion, on the kinetics of the charge transfer reaction at a LiMn₂O₄ thin film electrode/aqueous solution (1 mol dm⁻³ LiNO₃) interface. The zeta potential of LiMn₂O₄ particles showed a negative value in 1 × 10⁻² mol dm⁻³ LiNO₃ aqueous solution, while it was measured as positive in the presence of 1 × 10⁻² mol dm⁻³ Cu(NO₃)₂ in the solution. The presence of copper (II) ions in the solution increased the charge transfer resistance, and CV measurement revealed that the lithium insertion/extraction reaction was retarded by the presence of small amount of copper (II) ions. The activation energy for the charge transfer reaction in the solution with Cu(NO₃)₂ was estimated to be 35 kJ mol⁻¹, which was ca. 10 kJ mol⁻¹ larger than that observed in the solution without Cu(NO₃)₂. These results suggest that the interaction between the lithium ion and electrode surface is a factor in the kinetics of charge transfer reaction.     

Spectroscopic study of the electrochemical behaviour of tantalum(V) chloride and oxochloride species in 1-butyl-1-methylpyrrolidinium chloride

FTIR spectroscopy was used to identify the oxochloride species of tantalum(V) in ionic liquids and to confirm the correlations between their presence in electrolytes and the changes in the route of electrochemical reduction of tantalum(V). Electrochemical behaviour of the mixtures (x)1-butyl-1-methyl-pyrrolidinium chloride-(1 − x)TaCl₅ at x = 0.80, 0.65, and 0.40 was investigated over the temperature range 90-160 °C with respect to the electrochemical deposition of tantalum and was discussed in terms of spectroscopic data. The mechanism of electrochemical reduction of tantalum(V) in the basic and acidic electrolytes depends strongly on the structure and composition of the electro active species of tantalum(V) defined by the molar composition of ionic liquids and on the competition between tantalum(V) chloride and oxochloride species. In the basic mixture at x = 0.80, with octahedral [TaCl₆]⁻ ions as the electrochemically active species only the first reduction step Ta⁵⁺ → Ta⁴⁺ at −0.31 V was observed. The competitive reduction of tantalum(V) oxochloride species occurs at more anodic potential (−0.01 V) than the reduction of the chloride complexes and can restrict the further reduction of tantalum(IV). In the basic ionic liquid at x = 0.65, the cyclic voltammograms exhibit reduction peaks at −0.31 V and −0.51 V attributed to the diffusion controlled process as [TaCl₆]⁻ + e⁻ → [TaCl₆]²⁻ and [TaCl₆]²⁻ + e⁻ → [TaCl₆]³⁻. The further irreversible reduction of tantalum(III) to metallic state may occur at −2.1 V. In the acidic ionic liquids, at x = 0.40 the electrochemical reduction of two species occurs, TaCl₆⁻ and Ta₂Cl₁₁⁻ and it is limited by two electron transfer for both of them at −0.3 V and −1.5 V, respectively.     

Electrochromic performance of a poly(3,4-ethylenedioxythiophene)-Prussian blue device encompassing a free standing proton electrolyte film

Electrochromic devices incorporating an electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film and a free standing, transparent film of a proton conducting polymer electrolyte with high ambient temperature ionic conductivity of 10⁻² S cm⁻¹ have been fabricated with and without the ion storage electrodeposited Prussian blue (PB) counter electrode layer. While coloration efficiency increases as a function of applied potential in the sole PEDOT device with largest values of CE_(max,VIS) ∼ 120 cm² C⁻¹ and CE_(max,NIR) ∼ 133 cm² C⁻¹ attained at V_c = −1.9 V, the PEDOT:PB device shows a digression from this trend. Much higher coloration efficiencies in the visible (247 cm² C⁻¹ at 570 nm) and NIR (116 cm² C⁻¹ at 1100 nm) regions are achieved for the PEDOT:PB device at a relatively lower reducing voltage of −0.8 V. The PEDOT:PB device shows fast switching redox process (t_c = 2.6 s and t_b = 1.3 s for a 50% optical contrast at 632.8 nm) and a highly reversible charge density as the ratio of Q_inserted to Q_extracted was found to vary between 0.8 and 1.0. When switched between the clear and blue states for 2000 cycles, the insignificant drop in peak current density maxima observed for the PEDOT:PB device, i.e. the good cycling stability, the facile fabrication of device assembly, the ease of scaling up the electrolyte and electrochromic coatings, indicate that this method can be adapted as a simple and inexpensive alternative to conventional electrochromic windows with high cost components.     

Electrochemical copolymerization of aniline with m-aminophenol and novel electrical properties of the copolymer in the wide pH range

A copolymer, poly(aniline-co-m-aminophenol), has been synthesized using repeated potential cycling. The monomer concentration ratio, acid concentration and applied potential strongly affect the copolymerization rate and the properties of the copolymer. The optimum conditions for the copolymerization are that the scan potential range is controlled between −0.10 and 0.95 V (vs.SCE), and a solution consists of 0.34 M aniline, 0.012 M m-aminophenol and 2 M H₂SO₄. The IR spectra of the copolymers demonstrate that the m-aminophenol units are included in the copolymer chains. The cyclic voltammograms of the copolymers in 0.3 M Na₂SO₄ solution with various pH values were performed at the potential ranges from −0.20 to 0.80 V and at a scan rate of 60 mV s⁻¹. The results indicate that the copolymer still hold 41.7% of the electrochemical activity when the copolymer electrode was transferred from a solution of pH 5.0 to a solution of pH 11.0 in the potential range of −0.20 to 0.80 V. An impedance plot of the copolymer in a solution with pH 12.0 and at 0.40 V is constructed of a semicircle and a Warburg line with a slope of 1. This means that the electrode reaction of the copolymer at pH 12.0 is also under mass transfer control. The conductivity of the copolymer prepared under the optimum conditions is 1.42 S cm⁻¹, and slightly depends on the pH value. Thus, the pH dependence of the electrical properties of the copolymer is improved compared with poly(aniline-co-o-aminophenol), and is much better than that of the parent polyaniline.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Role of surface state on the electron flow in modified TiO2 film incorporating carbon powder for a dye-sensitized solar cell

An investigation of surface-related traps in nanostructured TiO₂ films modified by the incorporation of carbon powder was conducted by the potential-step chronoamperometric method. For the modification of the morphology and surface state of the nanoporous TiO₂ electrode, the incorporation of carbon into the white TiO₂ powder was accomplished. In the chronoamperometric data, all of the transients showed an initial fast phase (<1 s) followed by a slower phase which is related to the trap filling process. The trap-filling period of the carbon incorporated TiO₂ film becomes longer, as the applied negative potential increases, due to the widely distributed traps induced by the increased surface area. Furthermore, the film capacitance was derived as a function of the applied bias by integrating the current to time curves of the chronoamperometric data. The accumulated charge of the carbon incorporated TiO₂ film increases prominently in two regions. The dominant increase shown in the positive region (−0.7 to −0.9 V vs. Ag/AgCl at pH 13) of the flat band potential implies that the electron occupancy in the surface-related traps is increased. At a more negative potential (below −1.2 V vs. Ag/AgCl), electrons from the conduction band of the TiO₂ film substantially influence the total current, thereby inducing an exponential increase in the current. Therefore, it is found that most of the traps are located in the positive region of the flat band potential, since the Fermi level of the nanostructured TiO₂ film is positioned at −1.14 V vs. Ag/AgCl at pH 13. The trap sites in the sub-bandgap region of the TiO₂ film are important in the electron transport of photoinjected electrons from dye molecules and partially charge recombination with redox electrolyte in operating dye-sensitized solar cell. The influence of charge trap formed by increased surface states on the electron transport and electron transfer was investigated by photovoltage and photocurrent transient measurements.     

Transport of cobalt(II) through a hollow fiber supported liquid membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) as the carrier

This work presents experimental, modeling and simulation studies for Co²⁺ ion extraction using hollow fiber supported liquid membrane (HFSLM) operated in a recycling mode. Extractant di-(2-ethylhexyl) phosphoric acid (D2EHPA) diluted with kerosene has been used as the membrane phase. The Co²⁺ ion concentration in the aqueous feed phase was varied in the range of 1–3 mM. Also, D2EHPA concentration was varied in the range of 10–30% (v/v). A mass transfer model has been developed considering the complexation and de-complexation reactions to be fast and at equilibrium. Equations for extractant mass balance and counter-ion (H⁺) transport have also been incorporated in the model. Extraction equilibrium constant (K_ex) for cobalt–D2EHPA system has been estimated from equilibration experiments and found to be 3.48 × 10⁻⁶. It was observed that the model results are in good agreement with the experimental data when diffusivity of metal-complex (D_m) through the membrane phase is 1.5 × 10⁻¹⁰ m²/s. Feed phase pH and strip phase acidity had negligible effect on the extraction profiles of Co²⁺ ions. An increase in D2EHPA concentration increased extraction rates of Co²⁺ ions. The membrane phase diffusion step was found to be the controlling resistance to mass transfer.     

Electrochemically synthesized nano size copolymer, poly (aniline-co-ethyl 4-aminobenzoate) and its spectroelectrochemical studies

Electroactive conducting copolymers of aniline (ANI) and ethyl 4-aminobenzoate (EAB) were prepared electrochemically. Cyclic voltammetric studies were carried out with different feed concentration of EAB on glassy carbon electrode surface. The voltammograms exhibited different behavior for different concentrations of EAB. The copolymers exhibited high solubility in many polar solvents. The scan rate exerted good influence on the polymer effect on this GCE copolymer film, revealing electroactive film’s excellent adherent properties. The effect of pH on the copolymer film showed that the polymer was electrochemically active up to pH 7.0. Spectroelectrochemical analysis of the copolymer film, carried out on an indium tin oxide (ITO) plate, showed multicolor electrochromic behavior when the applied potential was changed. The color of the copolymer was changed from neutral yellow (422 nm) to green (760 nm) and to blue (600 nm) at the concentration of 0.1 M aniline and 0.1 M EAB in 0.1 M H₂SO₄ medium. The copolymer was characterized by FT-IR spectral data. The surface morphology were studied using SEM and TEM analysis. The grain size of the copolymer was measured using XRD studies and was found to be 80 nm. The electrical conductivity of the copolymer was 3.21 × 10⁻² S cm⁻¹, as determined using a four-probe conductivity meter.     

Efficient electrochemical reduction of nitrate to nitrogen on tin cathode at very high cathodic potentials

The electrochemical reduction of nitrate on tin cathode at very high cathodic potentials was studied in 0.1 M K₂SO₄, 0.05 M KNO₃ electrolyte. A high rate of nitrate reduction (0.206 mmol min⁻¹ cm⁻²) and a high selectivity (%S) of nitrogen (92%) was obtained at −2.9 V versus Ag/AgCl. The main by-products were ammonia (8%) and nitrite (<0.02%). Small amounts of N₂O and traces of NO were also detected.As the cathodic potential increases, the %S of nitrogen increases, while that of ammonia displays a maximum at −2.2 V. The %S of nitrite decreases from 65% at −1.8 V to <0.02% at −2.4 V. The kinetic analysis indicated that the formation of nitrogen and ammonia proceeds through the intermediate nitrite.The reduction follows first order kinetics for both nitrate and nitrite at more cathodic potentials than −2.4 V, while at less negative potentials the kinetics is more complicated.The %Faradaic efficiency (%FE) of the reduction at −2.9 V was about 60% initially and decreased to 22% at 40 min.A cathodic corrosion of tin was observed, which was more intensive in the absence of nitrate. At potentials more negative than −2.4 V, small amounts of tin hydride were detected.     

A novel Electro-Fenton-Like system using PW11O39Fe(III)(H2O) as an electrocatalyst for wastewater treatment

A novel Electro-Fenton-Like (EFL) system was developed using the Keggin-type iron-substituted heteropolytungstate anion PW₁₁O₃₉Fe(III)(H₂O)⁴⁻ to substitute for Fe³⁺ in the conventional Electro-Fenton (EF) system for treatment of water polluted with organic compounds. The EFL system overcomes the drawback of low pH in conventional EF approaches and can be directly applied to neutral water treatment without any pH adjustment. Experimental results for dimethylphthalate (DMP) revealed complete degradation in <80 min in pH 6.86 solution containing 0.1 mM DMP at a potential of −0.5 V and O₂ flow rate of 60 mL min⁻¹. Total organic carbon removal of ∼56% was achieved at 120 min. Comparison with conventional EF oxidation revealed better efficiency of the present system for DMP degradation, suggesting its potential in treatment of water and wastewater with a relaxed pH requirement. The cumulative H₂O₂ concentration generated in situ at the electrode was monitored and the observed degradation rate constants k_obs were determined for different initial DMP concentrations. The ligand exchange reaction of PW₁₁O₃₉Fe(III)(H₂O)⁴⁻ with H₂O₂ and the electron transfer resulting in hydroxyl radicals were examined using HPLC and electrochemical impedance spectroscopy. An electrocatalytic model involving inner-sphere electron transfer and a reaction mechanism for PW₁₁O₃₉Fe(III)(H₂O)⁴⁻ electrocatalytic reduction of H₂O₂ are proposed.     

Preparation and characterization of thiocyanate-selective electrodes based on new complexes of copper(II) as neutral carriers

The complexes of hydroxycitronellal (o-aminobenzoic acid) copper(II) (Cu(II)-HXAB) and salicylaldehyde (o-aminobenzoic acid) copper(II) (Cu(II)-SHAB) were used as neutral carriers in PVC-based membrane ion-selective electrodes. The electrode based on Cu(II)-HXAB exhibited near-Nernstian potential response to thiocyanate (SCN⁻) in a linear range of 1.0 × 10^− 6 to 1.0 × 10^− 1 M with a detection limit of 8.5 × 10^− 7 M and a slope of − 57.3 mV/decade in 0.01 M phosphate buffer solution (pH 5.0). The electrode exhibited high selectivity to SCN⁻ over other tested anions with an anti-Hofmeister selectivity sequence. The selectivity behavior might be discussed in terms of UV-Vis spectrum and infrared spectrum. The transfer process of thiocyanate across the membrane interface was investigated by making use of the AC impedance technique. The electrode containing Cu(II)-HXAB could be applied to thiocyanate analysis in waste water with satisfactory results.