Ions In Alkaline Medium Research Articles

Automated liquid–liquid extraction procedure for the photometric determination of nanogram levels of Hg(II) in soil and sediment extracts

Herein we describe the development of an automatic liquid–liquid extraction procedure for the photometric determination of Hg(II) in soil and sediment extracts. The experimental set-up comprised a multi-commuted flow system module and homemade photometer, which used a light-emitting diode as the radiation source. The photometric method relies on the reaction of diphenylthiocarbazone (dithizone) with Hg(II) ions in alkaline medium. The obtained compound was extracted with chloroform and detected at 488 nm. In addition, the parameters that could affect the complex formation and extraction efficiency, such as, the acidity, reagent concentration, time for reaction development and extraction, and volume of extracting solvent, were studied. Under optimal conditions, a linear response that ranged from 0.25 to 10.0 μg L−1 (r2 = 0.9926) was achieved. The accuracy of the method was assessed using the sample spiking and recovery methodology. According to the results, recoveries between 90% and 116% were achieved for both the soil and sediment samples, which were appropriate for these types of samples. In addition, the samples were analyzed via cold vapor atomic absorption spectrometry. The paired t-test with nine degrees of freedom revealed that no significant differences existed between the results. Other figures of merit, namely the limit of detection of 0.018 μg L−1, coefficient of variation of 0.32% (n = 10), sampling throughput of 22 determinations per hour, dithizone, and chloroform consumptions of 0.13 µg and 0.55 mL, respectively, per determination, were achieved.

Nano‐Micro‐Structured Nickel‐Cobalt Hydroxide/Ni2P2O7 Assembly on Nickel Foam: An Outstanding Electrocatalyst for Alkaline Oxygen Evolution Reaction

AbstractThe design and development of materials for the efficient electrochemical evolution of oxygen from hydroxyl ions in alkaline media is of prime importance for reducing energy losses in water‐alkaline electrolytes. In this Communication, we report non‐noble nano‐micro‐structured Ni2P2O7 microsheets decorated with nickel‐cobalt hydroxide (Ni−Co‐hydroxide) nanoflakes for the efficient oxygen evolution reaction (OER). Remarkably, the nano‐micro‐assembled Ni−Co‐hydroxide/Ni2P2O7 structured electrode exhibits superior catalytic activity towards the OER with a relatively low overpotential of 197 mV at a current density of 10 mA/cm2 in 1.0 M KOH, coupled with excellent long‐term stability (12 h). The outstanding OER activity resulted from the nano‐micro structure of the prepared electrode with excellent redox activity in an alkaline electrolyte.

Synthesis of Iron Oxide Nanoparticles Optimized by Design of Experiments

Magnetic iron oxide nanoparticles have been widely studied for technological and biomedical applications due to its small size and the possibility of functionalizing the surface with intended molecules. Magnetite is the most used phase because of superparamagnetic characteristic, and it is synthesized by co-precipitation, starting from ferrous and ferric ions in alkaline media. However, depending on parameters of chemical reactions, such as molar ratio between iron and hydroxyl groups, stirring rate, and temperature, different iron oxide structures are formed through distinct pathways. Since several variables can affect the size, chemical composition, and crystalline structure of iron oxide nanoparticles during the synthesis, it is very important to apply experimental routines with a well-defined protocol and planning practical steps can significantly improve the quality of products. Plackett-Burman methodology from design of experiments is a filtration analysis, used in the initial stages of a process to investigate the main effects of factors over a characteristic of the final material. In this work, Plackett-Burman technique was employed in order to optimize bare iron oxide nanoparticle production by co-precipitation method, relating the different crystalline phases produced to the experimental routine. Dynamic light scattering, Fourier transform infrared spectroscopy, and X-ray diffractometry were used to characterize the samples.

PH-sensitive magnetic alginate/γ-Fe2O3 nanoparticles for adsorption/desorption of a cationic dye from water

In this study, magnetic alginate nanoparticles (AlgMNP) were synthesized using a simple and green two-step method, which can be easily developed on an industrial scale. First, coprecipitation of both ferric and ferrous ions in alkaline medium followed by oxidation of magnetite into maghemite leads to a stable colloidal dispersion called ferrofluid. A sodium alginate solution was then added to the ferrofluid in order to obtain the magnetic nanocomposite. This approach combines the advantages of a biopolymer with magnetic properties of the maghemite nanoparticles. The morphology, structure, size and composition of the magnetic nanoparticles were characterized by means of atomic absorption spectrometry, transmission electron microscopy, X-ray diffraction, Fourier-transform-infrared spectroscopy and thermogravimetric analysis. Adsorption is one of the most efficient treatments for the removal of pollutants from wastewater. But the development of efficient and environmental friendly adsorbent still remains challenging. Using AlgMNP as a magnetic adsorbent could be a suitable response to this challenge. Its adsorption efficiency was investigated by using methylene blue as pollutant. The effects of pH, contact time, and initial concentration of the dye on adsorption were investigated. The high adsorption capacity with respect to the dye in a wide pH range (273 mg/g) was explained by the way magnetic nanoparticles bind to the alginate chains. We assumed an organization with alginate strands decorated by the magnetic nanoparticles leaving the adsorption sites of the particles more accessible rather than a configuration with a complete coating of magnetic nanoparticles by alginate. The reusability was successfully demonstrated through 10 adsorption/desorption cycles.

Electrocatalytic activity of the nanostructured Au–Co catalyst deposited onto titanium towards borohydride oxidation

The nanostructured gold–cobalt catalysts were deposited onto titanium surface via galvanic displacement technique. The electrocatalytic activity of the as-prepared nanostructured Au(Co)/Ti catalysts was examined in respect to the oxidation of BH4− ions in alkaline medium by using of the cyclic voltammetry and chrono-techniques. The nanostructured catalysts were prepared via galvanic displacement reactions between hierarchical Co thin films prepared by electroless deposition and a solution of HAuCl4. The surface morphology and composition of the samples were characterized using Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and X-ray diffraction. The prepared nanostructured Au(Co)/Ti catalysts exhibit an enhanced electrochemical activity towards the electro-oxidation of H2 generated by catalytic sodium borohydride hydrolysis and oxidation of BH4− ions.

Complexation and flotation of nonferrous metal ions from alkaline solutions with N-acyl-N′-(p-toluenesulfonyl)hydrazines

Surfactant properties and complexation conditions of Cu(II), Co(II), Ni(II), Zn(II), and Cd(II) ions in alkaline media with N-acyl-N′-(p-toluenesulfonyl)hydrazines, which enable their use in ion flotation processes, were studied. The efficiency of the compounds under study as collectors in aftertreatment of alkaline wastewater to remove milligram amounts of Cu(II) and other metals by ion flotation was demonstrated.

Electrochemical oxidation of Methyl Red using Ti/Ru0.3Ti0.7O2 and Ti/Pt anodes

The present study was motivated by a report by Martínez-Huitle et al. in 2005, on the electrochemical oxidation of oxalic acid at a Pt anode in the presence of halide ions in alkaline medium. Addition of halide salts increased the mineralization rate in the order: control<NaCl<NaBr<NaF. Therefore, in this work, the direct and indirect oxidations of an organic model substrate (Methyl Red, MR) using Ti/Ru0.3Ti0.7O2 and Ti/Pt anodes were investigated. Galvanostatic electrolyses of dye solutions led to complete decoloration and total organic carbon (TOC) removal at different operating conditions (current density (j) and temperature). The influence of these parameters was examined, in order to compare the effect of active chlorine and addition of different NaCl concentrations to the dyes solutions during the mediated electrochemical oxidation of MR. Byproducts generated during the direct and indirect MR electrochemical oxidation were identified on the basis of GC–MS results. Chlorinated compounds were produced during mediated electrochemical oxidation, but these were completely eliminated in the final of the process; confirming that this treatment processes can be a suitable alternative for depuration effluents. The findings presented herein are described and discussed in the light of the existing literature data.

Effect of Cd(II) on the Ripening of Ferrihydrite in Alkaline Media

AbstractTo acquire a better understanding of the influence exerted by the presence of Cd2+ during the process of transforming ferrihydrite to goethite, the morphological and structural changes of several samples obtained by the addition of Cd2+ to a suspension of nascent goethite were explored, and their chemical reactivity in acid media assessed. The samples (series Gi) were obtained by adding, at different times during the synthesis process, Cd2+ ions to ferrihydrite (Fe5HO8.4H2O) formed in alkaline media. The suspensions were aged for 5 days at 70°C, and the amorphous materials were extracted using a HCl solution (series GHCl-i). The X-ray diffraction (XRD) patterns showed that a goethite-like phase was formed, and chemical analyses indicated that the Cd content, xCd, increased with the earlier addition of the Cd2+ ions to the Fe oxyhydroxide suspension. Lattice parameters and cell volume, obtained by the Rietveld simulation of XRD data, indicated an enlargement of the cell parameters of goethite in line with the Cd-for-Fe substitution. In order to determine the influence of oxalate ions on the non-extracted solids, a second set of samples was also prepared that was kept in contact with an ammonium oxalate solution for 4 h (series Gox-i). The dissolution behavior of two series of Cd goethites and of a third series, obtained from coprecipitation of Fe3+ and Cd2+ ions in alkaline media, was observed. Kinetics measurements in 4 M HCl showed that the initial dissolution rate of samples Gox-i decreased with aging time, while the opposite effect was observed for series GHCl-i. Dissolution–time curves were well described by the Kabai equation, and activation energies were calculated using the Arrhenius equation. The results indicate that the presence of Cd during the crystallization process of goethite leads to the formation of a Cd goethite with modified morphology, structural parameters, and chemical reactivity.

Electrocatalytic reduction of nitrite on transition and coinage metals

A systematic comparison of the electrochemical reduction of nitrite at polycrystalline metals has been carried out. In acidic media, solution-phase NO from HNO2 decomposition is converted to N2O by all noble metals in a common potential range for most metals (0.2–0.5V vs. RHE). Transition metals can also convert HNO2 directly to hydrogenated products (NH3OH+, NH4+) at lower potentials, while coinage metals (Ag, Au, Cu) feature a stepwise reduction to NO and N2O, which can be both detected by on-line mass spectrometry. The reduction of nitrite ions in alkaline media never yields gaseous products; the first electron transfer to give adsorbed NO is the rate-determining step for all noble metals. Coinage metals are largely inactive, except for Cu. The selectivity and electrocatalytic trends have been interpreted on the basis of DFT calculations of the metal–NO interaction available in the literature. In agreement with the Sabatier principle, metals with an intermediate affinity to NO are the most reactive and show the lowest tendency to poisoning. Coinage metals are a special case because of their weak NO adsorption and the formation of NO dimers.

Synthesis and Dye Adsorption Studies of Poly (N-tert -butylacrylamide-co-acrylamide/ Maleic acid) Ferrogel

The present study describes the preparation of magnetic field sensitive Ferrogel is a two step process. The first step is the synthesis of the poly(N-tert -butylacrylamide-co-acrylamide/Maleic acid), denoted as poly(NTB -co-AM/MA). In the second step magnetic Fe3O4 particle was formed in the hydrogel via co-precipitation of Fe2+ and Fe3+ ions in alkaline medium at 70°C. Ferrogel adsorbs all type of dyes. Both the concentration of magnetic particles and cross linking density of the ferrogel play an essential role in the adsorption. The adsorption rates for the dye stuffs are slow during first two minutes and it increases after 10 to 15 minutes.

Sol–gel synthesis of silica–cobalt composites by employing Co 3O 4 colloidal dispersions

Silica–cobalt composites with cobalt contents (w/w) around 10% were synthesized by employing the sol–gel method, tetraethylorthosilicate as the silica precursor and either a solution of cobalt nitrate or a colloidal dispersion of Co 3O 4 or Co(OH) 2 nanoparticles as the cobalt precursors. Cobalt oxide was obtained by the precipitation of Co 2+ ions in alkaline medium and by subsequent thermal treatment. Stable colloidal dispersions of cobalt oxide were prepared by using high power ultrasound and by covering nanoparticles with lauric acid bilayers. All materials were characterized by X-ray diffraction, infrared and Raman spectroscopy, transmission electron microscopy, and adsorption/desorption of nitrogen. Further, the reducibility of cobalt species was studied using the thermal-programmed reduction technique. All the Co 3O 4/silica composites were mesoporous (3.9–5.4 nm) with considerably high porosity (321–567 m 2 g −1). The TEM mean size of Co 3O 4 nanoparticles within the calcined composites varied from 10 to 18 nm, according to the cobalt precursor employed in the synthesis. The reducibility of cobalt species also depended on the employed cobalt precursor, as shown by the thermal programmed reduction experiments. The composites which were prepared from the Co 3O 4 colloidal dispersions were reduced at lower temperatures; 80% of the total Co amount was reduced in the range of 300–500 °C. On the other hand, only 53% of total Co in the sample prepared from cobalt nitrate solution was reduced from 200 up to 900 °C. The difference on the reducibility was attributed to morphological characteristics of the composite samples.

Nanostructured p-CuIn 3Se 5/ n-CdS heterojunction engineered using simple wet chemical approach at room temperature for photovoltaic application

Herein, we report engineering of nanostructured p-CuIn 3Se 5/ n-CdS heterojunction thin film on a glass substrate, which is prepared at room temperature using simple wet chemical approach involving ion exchange reactions between CdS and Cu +, In 3+ and Se 2− ions in alkaline medium. The uniform deposition of heterojunction thin films is achieved by optimizing the pH, temperature and molarity of the reactant bath. The as-deposited thin-films were annealed at 200 °C in air for 1 h and further characterized for structural, optical and electrical properties using UV–Vis spectrophotometer, X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), Hall effect for type of conductivity, and I– V measurement to investigate the charge conduction phenomenon. The characteristic (1 1 2) and (1 1 0) planes in XRD and the electron diffraction pattern could confirm the formation of CuIn 3Se 5. The chemical composition and the band gap energy E g = 1.4 eV of the nanostructured p-CuIn 3Se 5/ n-CdS heterojunction thin-films were confirmed using XPS and the absorbance spectra, respectively. Based on the data and energy band gap calculations of CuIn 3Se 5 and CdS thin films, the probable band alignment between the nanostructured p-CuIn 3Se 5/ n-CdS heterojunction is proposed.

Silica gel–polyethylene glycol as a new adsorbent for solid phase extraction of cobalt and nickel and determination by flame atomic absorption spectrometry

In this paper a novel solid phase extraction method to determine Co(II) and Ni(II) using silica gel-polyethylene glycol (Silica-PEG) as a new adsorbent is described. The method is based on the adsorption of cobalt and nickel ions in alkaline media on polyethylene glycol-silica gel in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The adsorption conditions such as NaOH concentration, sample volume and amount of adsorbent were optimized in order to achieve highest sensitivity. The calibration graph was linear in the range of 0.5-200.0ngmL(-1) for Co(II) and 2.0-100.0ngmL(-1) for Ni(II) in the initial solution. The limit of detection based on 3S(b) was 0.37ngmL(-1) for Co(II) and 0.71ngmL(-1) for Ni(II). The relative standard deviations (R.S.D.) for ten replicate measurements of 40ngmL(-1) of Co(II), and Ni(II) were 3.24 and 3.13%, respectively. The method was applied to determine Co(II) and Ni(II) in black tea, rice flour, sesame seeds, tap water and river water samples.

Size-modulation of thermally-annealed nanosized cobalt ferrite particles

CoFe2O4 nanoparticles were synthesized by co-precipitating Co(II) and Fe(III) ions in alkaline medium following temperature annealing, aiming to study the influence of the sintering temperature on the structure of the nanosized cubic ferrite. A group of powder samples were submitted to thermal treatment at 373, 623, 1023, 1273, and 1473 K during 30 minutes in atmospheric air. For the purpose of our investigation cobalt ferrite nanoparticles were evaluated by atomic absorption spectrophotometry, X-ray diffraction (XRD), Raman, and Mössbauer spectroscopy. The chemical composition of cobalt ferrite samples, expressed as the [Fe]/[Co] ratio, was found as 2.1. Our results reveal that the increase of the sintering temperature modifies the cation distribution profile, resulting in an improvement of the nanomaterial’s properties.

Corrosion behaviour in alkaline medium of zinc phosphate coated steel obtained by cathodic electrochemical treatment

The present work evaluated the ability of zinc phosphate coating, obtained by cathodic electrochemical treatment, to protect mild steel rebar against the localized attack generated by chloride ions in alkaline medium. The corrosion behaviour of coated steel was assessed by open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The chemical composition and the morphology of the coated surfaces were evaluated by X-ray diffraction and scanning electron microscopy. Cathodically phosphated mild steel rebar have been studied in alkaline solution with and without chloride simulating the concrete pore solution. For these conditions, the results showed that the slow dissolution of the coating generates the formation of calcium hydroxyzincate (Ca(Zn(OH) 3) 2·2H 2O). After a long immersion time in alkaline solution with and without Cl −, the coating is dense and provides an effective corrosion resistance compared to mild steel rebar.

Preparation and characterization of poly(N‐tert‐butylacrylamide‐co‐acrylamide) ferrogel

AbstractMagnetic‐field‐sensitive gel, called ferrogel, was prepared by a two‐step procedure in which first step requires synthesis of the poly(N‐tert‐butylacrylamide‐co‐acrylamide) [P(NTBA‐co‐AAm)] hydrogel and during second step magnetite (Fe3O4) particles were formed in the hydrogel via coprecipitation of Fe(II) and Fe(III) ions in alkaline medium at 70°C. The obtained ferrogel was characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy combined with energy dispersive spectroscopy, and electron spin resonance measurements. The magnetic responsive of the ferrogel was also investigated by applying magnetic field to the ferrogel. The extent of a bending degree of the ferrogel depends on the applied magnetic field strength. In addition, the magnetic responsive studies also indicated that formed magnetite content in the hydrogel is high enough to achieve considerable magnetic response to external magnetic field. As a result, the P(NTBA‐co‐AAm) ferrogel may be useful for potential applications in magnetically controlled drug release systems, magnetic‐sensitive sensors, and pseudomuscular actuators. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Oxidative dissolution of ruthenium deposits onto stainless steel by permanganate ions in alkaline medium

Abstract During spent nuclear fuel reprocessing ruthenium is liable to form black ruthenium deposits on the stainless steel walls of process equipments. These deposits promote corrosion and can eventually obstruct the off-gas lines. The results of decontamination of 304L stainless steel test specimens covered with RuO(OH)2· x H2O deposits by permanganate ions in alkaline medium are described. The ruthenium deposits were dissolved by oxidation of RuO(OH)2 to RuO4 2− ions, while the permanganate ions were reduced to MnO4 2− ions and then to manganese dioxide MnO2. The parameters affecting the kinetics of oxidative dissolution of these deposits were examined. The results indicate that the oxidative dissolution kinetics depends on the instantaneous surface area of the deposit, and that the dissolution rate increases with the concentrations of MnO4 − and OH− ions.

Effect of zinc phosphate chemical conversion coating on corrosion behaviour of mild steel in alkaline medium: protection of rebars in reinforced concrete

We outline the ability of zinc phosphate coatings, obtained by chemical conversion, to protect mild steel rebars against localized corrosion, generated by chloride ions in alkaline media. The corrosion resistance of coated steel, in comparison with uncoated rebars and coated and uncoated steel rebars embedded in mortar, were evaluated by open-circuit potential, potentiodynamic polarization, cronoamperometry and electrochemical impedance spectroscopy. The coated surfaces were characterized by x-ray diffraction and scanning electron microscopy. First, coated mild steel rebars were studied in an alkaline solution with and without chloride simulating a concrete pore solution. The results showed that the slow dissolution of the coating generates hydroxyapatite Ca10(PO4)6(OH)2. After a long immersion, the coating became dense and provided an effective corrosion resistance compared with the mild steel rebar. Secondly, the coated and uncoated steel rebars embedded in mortar and immersed in chloride solution showed no corrosion or deterioration of the coated steel. Corrosion rate is considerably lowered by this phosphate coating.

Luminescent Chemical Waves in the Cu(II)-Catalyzed Oscillatory Oxidation of SCN- Ions with Hydrogen Peroxide

The oscillatory oxidation of thiocyanate ions with hydrogen peroxide, catalyzed by Cu2+ ions in alkaline media, was so far observed as occurring simultaneously in the entire space of the batch or flow reactor. We performed this reaction for the first time in the thin-layer reactor and observed the spatiotemporal course of the above process, in the presence of luminol as the chemiluminescent indicator. A series of luminescent patterns periodically starting from the random reaction center and spreading throughout the entire solution layer was reported. For a batch-stirred system, the bursts of luminescence were found to correlate with the steep decreases of the oscillating Pt electrode potential. These novel results open possibilities for further experimental and theoretical investigations of those spatiotemporal patterns, including studies of the mechanism of this chemically complex process.

Study of molecular surface coating on the stability of maghemite nanoparticles

In this study γ-Fe 2O 3 nanoparticle, surface-coated with increasing amount of oleic acid, have been prepared while the stability against particle degradation under laser excitation intensity was investigated. Maghemite nanoparticle was obtained via oxidation of magnetite nanoparticle, the latter synthesized by co-precipitation of Fe (II) and Fe (III) ions in alkaline medium. By varying the experimental conditions of surface-coating maghemite nanoparticles with oleic acid, samples with different grafting coefficient were obtained and investigated using X-ray diffraction and different spectroscopic techniques, namely Raman, Mössbauer, and infrared. The amount of oleic acid adsorbed on the maghemite surface was estimated via the carbon content obtained from elemental analysis.