Coprecipitation/accumulation/distribution of manganese and iron, and electrochemical characteristics of Mn in calcareous seawater

A study of managanese and iron associated with particulate matter in seawaters derived from the English Channel (and North Sea). Sequential extraction procedures have been used to identify geochemical processes that govern Mn and Fe coprecipitation/accumulation/distribution in different particulate phases (carbonate; Fe-Mn(hydr)oxides; organic matter and residual phase). The oxidation states of Mn and Fe, some mechanisms of bonding and the magnetic characteristics of particles have been investigated by Mössbauer spectroscopy, electron spin resonance(ESR) spectroscopy, and mass susceptibility balance. The effect of pH and redox potential on stability of different dissolved and particulate Mn species was also examined. In the these calcareous seawaters, manganese (II) is predominantly bound to the carbonate phase (calcite) in the form of Mn_xCa_1-xCO₃. However the persistent occurrence of Mn in oxidation states > 2 in these particles has suggested the existence of manganese(III) in the polymeric FeOOH structures as an intermediate entity during Mn(II) oxidation in the sea. The activity coefficient of the entity MnOOH in FeOOH has been evaluated and p-pH diagrams of Mn have been proposed under marine conditions.     

Determination of trace levels of dissolved vanadium in seawater by use of synthetic complexing agents and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)

In the determination of traces of dissolved vanadium in complex matrices such as seawater, separation and enrichment from the matrix is of special importance. A wide variety of methods has been proposed for preconcentration, depending to the nature of samples and the methods to be used for measurement. Among these methods separation techniques based on sorption on to chelating resins seem convenient, rapid, and capable of achieving a high concentration factor. The methods proposed in this paper are based on the transformation of all dissolved vanadium species in seawater into organic complexes by use of synthetic complexing agents such as dithizone, luminol, or 8-hydroxyquinoline; the resulting vanadium-organic complexes were sorbed on to a C(18) column at a flow rate of 5 mL min(-1). The vanadium sorbed on the C(18) columns was then stripped by use of nitric acid (2 mol L(-1)) and analysed by inductively coupled plasma-atomic emission spectroscopy, ICP-AES. This method was optimised and use of other chelating resins, such as chelamine, chelex-100, and immobilised 8-hydroxyquinoline and was compared by passing seawater samples directly over the resins. The experimental conditions (pH, acid used for elution, and contact time between the liquid sample and the resin) were optimised. The results were compared for all the resins used and were indicative of excellent and coherent reproducibility.     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

Oxidation state(s) of particulate manganese in waters from the Seine river

Summary The Mn-Fe (co)precipitation process has been studied at controlled pH and constant oxygen pressure (pH8.0 and = 1 atm) by means of potentiometry (employing a platinum electrode). Taking into account previous results about the kinetics of Mn(II) oxygenation and owing to the detailed survey of the curve E vs. time, it has been possible to appraise the surface catalytic rate, k, of this process on Fe hydroxide: k=5.8×10⁺¹⁷ l⁴ mol^–4 min^–1. This rate constant has been found to be much higher than that obtained in the absence of iron: k_Mn=(4.2±1.4)×10⁺¹⁵ l⁴ mol^–4 min^–1, which is of the same order of magnitude as that reported previously for colloidal MnO₂ surface. ESR studies have shown that manganese precipitates at oxidation state IV. Qwing to the speciation of manganese, the theoretical potential of the Mn²⁺/MnO₂ couple involved can be reached using the Nernst equation. The value is comparable with that measured potentiometrically at a Pt electrode. This suggests that under our experimental conditions manganese has a significant contribution to the redox level of the medium when this does not contain oxygen. In natural media, phenomena are more complicated because particulate Mn (and Fe) may be at oxidation states 相似文献   

Facile synthesis of Cu-LDH with different Cu/Al molar ratios: application as antibacterial inhibitors

Research on Chemical Intermediates - A range of Cu-LDHs has been synthesized by co-precipitation using metal nitrate precursors and sodium carbonate under varying molar ratios Cu/Al...     

Synthesis and Characterization of Bis‐quinazolines from Linear Tetra‐amines Involving 2‐(Aminomethyl)benzenamine with Aldehydes

Three tetra‐amine compounds 2‐((2‐(2‐aminobenzylamino)ethylamino)methyl)benzenamine ( L1 ), 2‐((3‐(2‐aminobenzylamino)propylamino)methyl)benzenamine ( L2 ), and 2‐((4‐(2‐aminobenzylamino)butylamino)methyl)benzenamine ( L3 ) were synthesized and then their reaction with 2‐hydroxybenzaldehyde, 2‐nitrobenzaldehyde, and 2‐hydroxy‐3‐methoxybenzaldehyde were investigated. Treatment of L1 , L2 , and L3 with the former aldehydes gave derivatives of quinazolines in a good yield. The products have been studied with IR, ¹H NMR, ¹³C NMR, COSY, HMQC, and microanalysis.     

Enhancement of Congo red dye removal efficiency using Mg-Fe-layered double hydroxide

Research on Chemical Intermediates - In this study, Mg-Fe(II)-Al-layered double hydroxide with different molar ratios Fe/Al (Mg0.80-Fe0.14-Al0.06-LDHs and Mg0.80-Fe0.20-Al0.00-LDHs) was prepared...     

Determination of trace metal complexes by natural organic and inorganic ligands in coastal seawater.

It is well-documented that organic compounds form strong complexes with most metals in aquatic systems, and that seawater is a complex medium which contains a large variety of organic and inorganic ligands, including colloidal matter. We suggest that most trace metals are complexed in seawater and that some inorganic metals complexes are either labile or not stable. In contrast, metal-organic complexes are often stable and need various and specific treatments to be dissociated. In this paper we try to illustrate a good tendency of some trace metals to be complexed by organic ligands in seawater. A solid-phase extraction method was applied using a C18 column as a resin that is able to separate metals complexed by neutral organic ligands, and the chelamine resin to separate metal species that are present as labile inorganic complexes. The determination of total dissolved metal concentrations was achieved by formatting a metal-8-hydroxyquinoline complex, followed by adsorption on C18 columns and ICP-AES analysis.     

A percolation approach to study the high electric field effect on electrical conductivity of insulating polymer

The effect of percolation threshold on the behaviour of electrical conductivity at high electric field of insulating polymers has been briefly investigated in literature. Sometimes the dead ends links are not taken into account in the study of the electric field effect on the electrical properties. In this work, we present a theoretical framework and Monte Carlo simulation of the behaviour of the electric conductivity at high electric field based on the percolation theory using the traps energies levels which are distributed according to distribution law (uniform, Gaussian, and power-law). When a solid insulating material is subjected to a high electric field, and during trapping mechanism the dead ends of traps affect with decreasing the electric conductivity according to the traps energies levels, the correlation length of the clusters, the length of the dead ends, and the concentration of the accessible positions for the electrons. A reasonably good agreement is obtained between simulation results and the theoretical framework.