Two-metal System Research Articles

Single and combined phytoextraction of lead and cadmium on submerged plants Potamogeton pusillus L.: removal, bioaccumulation pattern, and phytotoxicity.

Under the present investigation, the submerged plant Potamogeton pusillus has been tested for the removal of lead (Pb) and cadmium (Cd). P. pusillus removal efficiency and accumulation capacity were examined in separated Pb and Cd solutions, at 0.5, 1.0, and 2mg L-1, and in solutions where both metals were present at the same concentration (0.5, 1.0, and 2mg L-1), under laboratory conditions for 3, 7, and 10days. Also, we examined the removal efficiency and accumulation capacity when a set of plants were exposed to 0.5mg L-1 of Pb (or Cd) and increasing concentrations (0.5, 1, and 2mg L-1) of Cd (or Pb) for 10days. The effect of Cd and Pb was assessed by measuring changes in the chlorophylls, carotenoids, and malondialdehyde contents. Results showed that P. pusillus could accumulate Cd and Pb from individual solutions. Roots and leaves accumulated the highest amount of Cd and Pb followed by the stems. Some phytotoxic effects were observed, especially at individual Cd exposures, but these effects were not observed in the two-metal system. The removal and accumulation of Pb by P. pusillus were significantly enhanced in the presence of Cd under certain conditions, presenting a good alternative for the removal of these metals from polluted aquifers. To the extent of our knowledge, this is the first report on both enhanced phytoextraction of Pb in the presence of Cd and bioaccumulation of these heavy metals by P. pusillus.

Competitive adsorption mechanisms of Cd(II), Cu(II) and Pb(II) on bioinspired mesoporous silica revealed by complementary adsorption/isothermal titration calorimetry studies.

This study presents the adsorption properties of a bioinspired grafted mesoporous silica material and the competitive effects between Cd(II) or Cu(II) and Pb(II) during the adsorption process. Glutathione, a natural antioxidant known for its metal binding properties, has been successfully grafted to SBA-15 mesoporous silica and the optimum adsorption parameters were determined. This original and multidisciplinary approach combines classical adsorption studies with thermodynamic investigations to understand the adsorption behavior of Cd(II), Cu(II) and Pb(II) on this material. To this end, isothermal titration calorimetry (ITC) has been used to elucidate the mechanisms of single-metal and two-metal adsorption. The results showed affinity in the order Pb(II) > Cu(II) > Cd(II) in single metal systems. Cd(II) adsorption relied mainly on physical contributions while Cu(II) and Pb(II) adsorption was shown to be chemically driven. Two-metal systems highlighted that Cd(II) and Pb(II) are adsorbed on the same coordination sites, whereas Cu(II) and Pb(II) are adsorbed on different sites. The material showed good selectivity and encouraging results were obtained on real effluents.

Magnetic Anisotropy in Heterobimetallic Complexes.

Control of spin-orbit coupling enables the targeted modulation of coherence, catalytic, and magnetic properties in metal complexes. In this Forum, we describe our approach to exerting synthetic control over spin-orbit coupling by using heavy diamagnetic main-group metals as an external source of spin-orbit coupling. By binding these elements to first-row transition metals, we can probe the manifestation of spin-orbit coupling in their properties, by breaking spin-orbit coupling into a two-atom phenomenon. Within this approach, we focus on metal-ligand covalency and the importance of covalency in spin-orbit coupling transfer. To fully understand these systems, we need to design molecules that support careful decoupling of the influences of ligand field geometry and ligand-derived spin-orbit coupling on the magnetic anisotropy of paramagnetic transition metals. These design criteria, along with the advantages of bimetallic species, are described. We anticipate this perspective will offer a fundamental model for using two-metal systems for engendering spin-orbit coupling.

Contribution of calorimetry to the understanding of competitive adsorption of calcium, strontium, barium, and cadmium onto 4A type zeolite from two-metal aqueous solutions

The contribution of isothermal titration calorimetry is discussed to elucidate the mechanism of competitive adsorption of free Ca2+, Sr2+, Ba2+, and Cd2+ cations onto 4A-type zeolite from aqueous solutions at 298 K. The individual adsorption isotherms for these cations and the related enthalpy of displacement curves were compared between single-metal and two-metal systems. Separate dilution runs carried out under the same experimental conditions provided evidence that the dilution phenomenon made no significant contribution to the total cumulative enthalpy effect. In the light of the observations made in the present study, it is postulated that divalent cations exchanged with extra-framework sodium in different crystallographic locations within the zeolite structure. The binding affinity of individual cations for the zeolite surface was established to decrease in the following order: Sr ≈ Ba > Cd > Ca, in line with the increasing endothermic character of the displacement process. The experimental ΔdplHcum values in two-metal systems were also compared with the theoretical ones obtained by summing up the individual metal contributions as measured in appropriate single-metal systems. In the case of the Sr(II) + Cd(II) system, the competition became noticeable above a total amount adsorbed of 1 mmol g−1, as indicated by great differences between the experimental and theoretical enthalpy values. For the Sr(II) + Ba(II) and Sr(II) + Ca(II) systems, the sequence of site occupation was found to be modified as a result of competition. The effect was particularly pronounced for strontium which gave more exothermic contribution to the total enthalpy of displacement.

Effect of Fe(II)/Ce(III) dosage ratio on the structure and anion adsorptive removal of hydrothermally precipitated composites: Insights from EXAFS/XANES, XRD and FTIR

In this work, we present material chemistry in the hydrothermal synthesis of new complex structure materials based on various dosage ratios of Fe and Ce (1:0, 2:1, 1:1, 1:2, 0:1), characterize them by the relevant methods that allow characterization of both crystalline and amorphous phases and correlate their structure/surface properties with the adsorptive performance of the five toxic anions. The applied synthesis conditions resulted in the formation of different compounds of Fe and Ce components. The Fe-component was dominated by various phases of Fe hydrous oxides, whereas the Ce-component was composed of various phases of Ce carbonates. The presence of two metal salts in raw materials resulted in the formation of a mesoporous structure and averaged the surface area compared to one metal-based material. The surface of all Fe-Ce composites was abundant in Fe component phases. Two-metal systems showed stronger anion removal performance than one-metal materials. The best adsorption was demonstrated by Fe-Ce based materials that had low crystallinity, that were rich in phases and that exhibited surfaces were abundant in greater number of surface functional groups. Notably, Fe extended fine structures simulated by EXAFS in these better adsorbents were rich from oscillations from both heavy and light atoms. This work provides new insights on the structure of composite inorganic materials useful to develop their applications in adsorption and catalysis. It also presents new inorganic anion exchangers with very high removal potential to fluoride and arsenate.

Two metal biosorption of chromium and copper by Ca-loaded Laminaria japonica biomass

Cu and Cr sorption capacities of Ca-loaded Laminaria japonica biomass were studied using an equilibrium methodology and evaluation of the sorption performance, and modeling in a two-metal system was carried out with a modified multi-component Langmuir isotherm. The maximum Cu and Cr uptakes calculated from the Langmuir isotherm were 1.59 mmol/g (10.1 wt.%) and 1.81 mmol/g (9.4 wt.%) at pH 4.5, respectively. The desorption efficiency of the Cr-sorbed L. japonica was approximately 5% for 8 h in the 0.1 N HNO3 solution, while that of Cu-sorbed L. japonica was more than 99% in the 0.1 N HNO3 solution. The modified Langmuir model gave the following affinity correlated coefficients: 1.12 for Cu and 7.31 for Cr at pH 4.5. The interference of Cr with Cu biosorptive uptake was assessed by ‘cutting’ the three dimensional uptake isotherm surfaces at constant second-metal final concentrations. Equimolar final equilibrium concentrations of Cu and Cr of 1 mM at pH 4.5 reduced Cu and Cr uptakes by 75.5 and 11.0%, respectively.

BIOSORPTION OF Zn2+ AND Cd2+ IN A TW0-METAL SYSTEM BY Nannochloropsis salina

Although Zn 2+ and Cd 2+ ions in waters are pollutant with a large amount due to mining and industrial activities, information relating to the use of marine microalgae Nannochloropsis salina to absorb both types of metals is still very little. A marine microalga, N . salina, was used as biosorbent for the metal ions in water. Concentration of each ion (Zn 2+ and Cd 2+ ) was 10 mg/L and the concentration ratio of Zn 2+ to Cd 2+ in the two-metal system (a combination of Zn 2+ and Cd 2+ in the culture medium) was 1:1. Experimental conditions were as follows: salinity = 25 ‰, temperature = 20 o C, and pH =7. Addition of each ion individually or the combination of ions was conducted when the optimum growth of microalgae was achieved (i.e. at the 8 th day after cultivation). The N. salina growth after the exposure of metal ions was observed daily and the metal ion concentration adsorbed was determined by using atomic absorption spectrophotometer. Results showed that N. salina can be used as biosorbent for Zn 2+ and Cd 2+ both in single metal ion and two-metal system. Biosorption of Zn 2+ by N. salina was higher than that of Cd 2+ in the single metal ion. The amount of Zn 2+ adsorbed in the two-metal system was higher than the one in the single metal ion. However, the opposite trend was observed in the case of Cd 2+ ion.

A methodological approach for dynamic modelling of membrane integrated biosorption: a case study on Sphaerotilus natans as biosorbent

This work is a review of the study performed on heavy metals biosorption by Sphaerotilus natans confined in an ultrafiltration membrane module. A methodological approach has been applied aiming at the dynamic modelling of the process: i) firstly, biosorbent was characterised according to acid-base properties of binding sites; ii) then, equilibrium studies were performed both in single metal and multimetal systems in order to evidence any competition for binding sites and to find mechanicistic models that are able to describe biosorption equilibrium; iii) finally, biosorption in membrane processes was investigated in laboratory scale, in the case of both single-metal and two-metal systems, and a dynamic model was developed accounting for binding site competition and for binding ability of cell's fragments generated by tangential flow shear stress.

Effect of aluminum in two-metal biosorption by an algal biosorbent

Heavy metal and Al sorption capacities of Ca-loaded Laminaria japonica biomass were studied using equilibrium methodology. An evaluation of sorption performance and modeling in a two-metal system was carried out using a modified multi-component Langmuir isotherm. The maximum uptakes of Cr, Pb, Cu, Cd, Zn and Al calculated from the Langmuir isotherm were 1.81, 1.68, 1.59, 1.21, 0.87, and 2.79 mmol/g at pH 4.5, respectively. The interference of Al in heavy metal biosorptive uptakes was assessed by ‘cutting’ the three-dimensional uptake isotherm surfaces at constant second-metal final concentrations. The reduction of Pb, Cu, Cd, Zn and Cr uptakes at its final equilibrium concentrations of 1 mM at pH 4.5 was 77.7%, 80.4%, 86.0%, 89.1% and 50.1% on the presence of Al ion of 1 mM, respectively. The presence of Al ion greatly affected the uptake of all heavy metals tested except for Cr.

Interference of aluminum in heavy metal biosorption by a seaweed biosorbent

Heavy metal and Al sorption capacities of Ca-loadedSargassum fluitans biomass were studied by using equilibrium methodology. An evaluation of sorption performance and modeling in a two-metal system was carried out with a modified multi-component Langmuir isotherm. The maximum uptakes of Cr, Pb, Cu, Cd, Zn and Al calculated from the Langmuir isotherm were 1.74 mmol/g, 1.65 mmol/g, 1.61 mmol/g, 1.15 mmol/g, 0.81 mmol/g, and 2.95 mmol/g at pH 4.5, respectively. The interference of Al in heavy metal biosorptive uptakes was assessed by ‘cutting’ the three-dimensional uptake isotherm surfaces at constant second-metal final concentrations. The reduction of Pb, Cu, Zn, Cd and Cr uptakes at its final equilibrium concentrations of 1 mM at pH 4.5 was 78.4%, 82.7%, 85.1%, 89.8% and 51.2% in the presence of 1mM Al ion, respectively. The presence of Al ion greatly affected the uptake of all heavy metals tested except Cr.

Biosorption of Lead(II), Nickel(II), and Copper(II) on Rhizopus arrhizus from Binary and Ternary Metal Mixtures

The biosorption of three divalent metal ions [Pb(II), Ni(II), and Cu(II)] frequently encountered together in industrial waste waters and in binary and ternary systems was studied using Rhizopus arrhizus, a filamentous fungus, in batch stirred reactors. The multimetal biosorption data were evaluated in terms of equilibrium isotherms and adsorption yields. The single-metal equilibrium data were analyzed using the Freundlich adsorption model. The individual Freundlich adsorption constants were determined and used to compare biosorptive capacity of the microorganism for different metal ions. The effects of various combinations of the metal ions on the biosorption capacity of R. arrhizus are discussed and the actions of the synergistic or antagonistic metal ion combinations were determined. For the two-metal adsorption equilibrium, competitive adsorption isotherms have been also developed. The six-parameter empirical Freundlich model, restricted to bicomponent systems, was used successfully to characterize simultaneous biosorption of Pb(II), Ni(II), and Cu(II) ions by R. arrhizus from two-metal systems. The biosorption capacity of Pb(II) in the two binary and one ternary systems, in agreement with the single-metal data, was greater than that of the Ni(II) and Cu(II) ions. The relative capacities were Pb(II) > Ni(II) > Cu(II) at pH 5.0 in single, binary, and ternary systems.

Competitive Metal Ion Adsorption in Goethite Systems Using In Situ Voltammetric Methods and Potentiometry

Competitive complexation with respect to the binary-metal ion combinations Cu(II)–Zn(II), Cu(II)–Pb(II), and Pb(II)–Zn(II) were studied at the goethite (α-FeOOH)–water interface (25°C, I = 0.1 M NaNO3). In addition to potentiometric titrations and batch adsorption experiments, an in situ voltammetric technique was utilized. Sorption studies were performed within the ranges 3.5 ≤ pH ≤ 8.5, 10−6 ≤ [M(II)]tot ≤ 10−3 M, and with solid concentrations between 0.09 and 9 g dm−3. The results obtained (metal uptake and proton release curves) were compared with corresponding predicted values, based upon previously determined thermodynamic surface complexation models for the different single-metal ion goethite systems. The surface complexation modeling was based upon the constant capacitance concept. The results showed that the Cu(II) and Zn(II) surface complexation submodels were combinatory in all two-metal systems studied, both at 10−3 M and at 10−6 M concentrations of the metals. For Pb(II) a somewhat stronger adsorption to goethite than predicted by the previously determined submodel was observed in all two-metal systems studied. These deviations could be corrected for by a moderate adjustment of the equilibrium constant for the most acidic surface complex FeOHPb2+. It can also be concluded that the in situ voltammetric technique can be applied to measure trace concentrations of at least two metal ions simultaneously occurring in goethite suspensions under varying experimental conditions with good accuracy.

Interference of Aluminum in Copper Biosorption by an Algal Biosorbent

Abstract Cu and Al sorption capacities of NaOH-treated Sargassum fluitans biomass were studied using equilibrium methodology. An evaluation of sorption performance and modeling in a two-metal system was carried out using a modified multicomponent Langmuir isotherm. The maximum Cu and Al uptakes calculated from the Langmuir isotherm were 1.54 mmol/g (9.8 weight percent) and 3.75 mmol/g (10.1 weight percent) at pH 4.5, respectively. However, these values were 1.35 mmol/g for Cu and 1.58 mmol/g for Al at pH 3.5. The modified Langmuir model gave the following affinity correlated coefficients: 0.20 for Cu and 6.82 for Al at pH 4.5, and 2.90 for Cu and 3.13 for Al at pH 3.5. The interference of Al in Cu biosorptive uptake was assessed by “cutting” the three-dimensional uptake isotherm surfaces at constant second-metal final concentrations. Equimolar final equilibrium concentrations of Cu and Al of 1 mM at pH 4.5 reduced Cu and Al uptakes by 83.4 and 5.5%, respectively. However, these reductions at pH 3.5 were 53.0 (Cu) and 29.1% (Al).

Four-Electron Reduction of Diazo Compounds at a Single Tungsten Metal Center: A Theoretical Study of the Mechanism

A possible mechanism for the unprecedented one-metal reduction of diazobenzene by the [W(OC6HPh3-η6-C6H5)(OAr)(PMe2Ph)] (OAr = 2,3,5,6-tetraphenyloxide) complex was characterized by hybrid Becke3LYP DFT calculations on the model system [W(OH)2(C6H6)(Ph3)]+ N2H2. The model reaction is shown to be strongly exothermic, and takes place via a multistep process with moderate activation energy barriers. We discuss how this specific set of ancillary ligands permits the reaction to occur on a one-metal system in place of the more usual two-metal systems.

Evaluation of the Cd, Cu, and Zn Biosorption in Two‐Metal Systems Using an Algal Biosorbent

AbstractThe equilibrium sorption capacity of the formaldehyde‐cross‐linked brown seaweed Ascophyllum nodosum biomass was studied using two‐metal systems comprising either (Cu + Zn), (Cu + Cd), or (Zn + Cd). Three‐dimensional sorption isotherm surfaces were used in the evaluation of sorption performance, replacing simple isotherm curves. While each of the metals tested can inhibit the sorption of the others, at low total residual metal concentrations the total metal sorption uptake increases. At higher total metal concentrations, the total metal sorption uptake either remains constant, or there may be a slight decrease compared to single‐metal uptakes. This is an indication of a mutual interference in the sorption uptake of the two metals tested in each system.

Glycine-nitrate synthesis of a ceramic-metal composite

A ceramic-metal composite material, consisting of NiO, NiFe 2O 4 and Cu metal, was prepared by the glycine-nitrate combustion synthesis process (GNP). The synthesized powder consisted of intimately mixed nanometer size crystallites. This GNP powder was cold-pressed and solid-state sintered, which produced a dense cermet with micron size grains. The scale of the microstructure in the GNP material was about one order of magnitude smaller (linear basis) than that for samples fabricated by mechanical mixing of single phase powders followed by sintering at a temperature above the melting point of the metal phase. The paper also discusses synthesis of powders containing a single metal, Ni, Cu, or Fe, and the two-metal system containing Ni with Cu. The phases produced by oxidizing versus reducing combustion conditions are explored.

Plasmon dispersion in two-metal systems

The hydrodynamic model incorporating spatial dispersion is used to investigate the nonretarded plasmon dispersion for a bimetallic interface and for two arbitrary metal half-spaces separated by a vacuum. For the bimetallic interface, the full curve for the well known interface plasmon, starting at omega 2=1/2( omega p12+ omega p22), is given. It is shown that a similar plasmon mode exists when the metals are cleaved and separated, but which corresponds to a different form of density fluctuation and has a dependence on the separation distance. In addition, a new 'image' plasmon omega im is predicted. This arises from the image of the denser metal 2 ( omega p2> omega p1) forming as a result of the density response of the bulk electrons in metal 1, and is independent of the parameters of the less dense metal. The generalisations of the well known symmetric ( omega +) and antisymmetric ( omega -) surface plasmons, seen for two identical metals, are also derived. The generalised upper branch omega + only appears if omega p1> omega p2/ square root 2 and forms the continuation of omega im below the bulk continuum region of the less dense metal.