Migration Of Metal Ions Research Articles

Voltage Variation of Lithium Transition Metal Oxides Caused by the Migration of Cations

In the past decade, major effort has been devoted to understanding the structure and the electrochemical benefit of lithium-rich transition metal oxides for high-energy density lithium-ion batteries because of their potentially high specific capacity of up to 250 mAh g-1 when the materials are electrochemically activated. However, a consensus has not been established yet on the local structure of this class of materials. It has been reported that the excess portion of lithium was homogeneously dissolved in the matrix of the transition metal layer (3b sites of space group 166 or R-3m), forming a solid solution. On the other hand, Thackeray and others believed that the excess lithium on 3b sites has a strong tendency to pair with manganese and segregate to form Li2MnO3 domains. Despite the discrepancy in these researchers’ findings on the local structure, both sides agreed that the excess lithium can be electrochemically activated at a potential above 4.5 V vs. Li+/Li to deliver more reversible specific capacity, offering great opportunity for use of these lithium-rich transition metal oxides as high-capacity cathode materials. However, the structural instability of the material after electrochemical activation causes a continuous decrease in its working potential, a phenomenon which we will call voltage fade, that hinders the commercial deployment of this class of high-capacity cathode materials. The migration mechanism of transition metal in the oxygen framework was investigated here to illustrate the voltage decay of lithium-rich transition metal oxides. For the first time, a voltage increase was observed during the cycling of a lithium manganese oxide spinel within a wide potential window. It was demonstrated that the voltage variation of these lithium transition metal oxides was caused by the continuous migration of transition metal ions, mostly Mn2+ and Co4+, between the octahedral and tetrahedral sites of oxygen framework, resulting in the ration change between the spinel component and layered component. Figure 1

Simulating the Sorptive Removal of Dissolved Copper by Biocarrier Beads

Biocarrier beads containing the dead biomass of Bacillus drentensis immobilized in polymer polysulfone were synthesized in order to remove heavy metals from wastewater. A series of batch experiments were carried out to identify the sorption mechanisms and the theoretical nature of the underlying processes. A mathematical model was developed to simulate the fate and transport of copper ions in a saturated fixed bed packed with biocarrier beads. Mass balance equations were established to represent the migration and distribution of metal ions in the biocarrier beads and the surrounding bulk liquid. Numerical experiments were performed using the proposed model for quantitative analysis of the temporal changes in the distribution of copper ions in and around the biocarrier beads in a fixed bed. The simulation results show that the biosorption of heavy metals by the biocarrier beads depends largely on surface adsorption. A sensitivity analysis was carried out on the major design parameters in a fixed bed. The effects of bed height, flow velocity, and influent concentration were examined by assessing a simulated breakthrough curve. The breakthrough time occurs earlier for a decreasing bed height and increasing flow velocity and influent Cu(II) concentration, whereas the slope at 50 % breakthrough becomes steeper as the flow velocity increases and the influent concentration decreases. The simulation results show that the proposed mathematical model can provide a quantitative analysis of the distribution of metal adsorbate in and around porous particulate adsorbents in a fixed bed and that it can be used as an effective predictive tool.

Effect of electro-activated brine solution on the migration of metallic ions from the cans to the product in sterilized canned sweet corn.

Tinplate cans were used to study if electro‐activated brine solution (EAS) is more corrosive than conventional one by ICP analysis. The results showed different effects of EAS on cans, alone or filled with product. Acidic EAS (pH 2–3) and Redox +900 to +1200 mV highly reacted with the cans. The concentrations of Zn, Fe, and Cu in the solution were 0.028, 28.81, and 0.022 ppm, respectively. No Sn migration was observed in this case. When neutral or acidic chlorine‐free EAS was used, no significant difference was observed in comparison with the corrosivity of standard NaCl brine. Alkaline EAS with pH>10 and negative E (≤−966 mV) did not affect Zn, Fe, and Cu migration. However, it affected tin migration. Nevertheless, it is important to mention that even if some corrosion was observed, it was in the limit of the permitted level of concentration when the cans were filled with a product.

Discovery of a surface protective layer: A new insight into countering capacity and voltage degradation for high-energy lithium-ion batteries

Capacity and voltage degradation is a crucial factor that restricts the commercialization of Li-rich layered cathode materials. Recently, it has been demonstrated that the degradation results from the structural evolution from layered to spinel-like phase, caused by the migration of transition metal (TM) ions. However, the direction and order of TM ions migration is hard to identify. In this study, a surface protective layer (SPL) is discovered for the first time at the outer edge of Li1.14Mn0.48Ni0.19Co0.19O2 nanoplate by the research on the surface condition of nanoplates after charge–discharge cycles. More importantly, by the detailed analysis for the SPL, we further reveal that the formation of SPL is active facet dependent, TM ions migrate toward the active facets, and Ni and Co ions hop more preferentially than Mn ions during the cycling. These discoveries can help to understand the fading mechanism of Li-rich layered cathode materials. In addition, electrochemical test indicates that the SPL greatly delays the corrosion of active surfaces in electrolyte and improves the cycling stability of Li-rich layered cathode materials. This insight provides a new thought for preparing long-life cathodes of high energy Li-ion batteries.

Microstructural study on degradation mechanism of layered LiNi0.6Co0.2Mn0.2O2 cathode materials by analytical transmission electron microscopy

Electrochemical performance of lithium ion batteries is associated with structural and chemical stability of electrode materials. In the case of nickel-rich layered cathode materials LiNi0.6Co0.2Mn0.2O2, cation mixing, which results from the migration of transition metal ions into vacant lithium sites, is accelerated owing to similar ionic radii between nickel and lithium. However, the inevitable lattice distortions and chemical evolution have not been investigated intensely. In this paper, we report the structural evolution localized at surface regions through electron diffraction and high resolution imaging analyses with aberration-corrected transmission electron microscopy and scanning transmission electron microscopy. Repetition of volumetric change generates cracks and voids associated with deterioration of electrochemical performance. Structural change is related with (003) intensity in electron diffraction and it can be presented by dark field transmission electron microscopy imaging at a glance. Drastic structural degradation during early cycling shows relation with rapid capacity and voltage fade. Electron energy loss spectroscopy elucidates that the structural evolution caused by the migration of Ni ions accompanies chemical modification of Mn ions and creation of hole states at the O2p level. This study provides an insight into correlating structural and chemical evolution with degradation mechanism on battery performances of LiNi0.6Co0.2Mn0.2O2 cathode materials.

Nanoscale Plasmon-Enhanced Spectroscopy in Memristive Switches.

Resistive switching memories are nonvolatile memory cells based on nano-ionic redox processes and offer prospects for high scalability, ultrafast write and read access, and low power consumption. In two-terminal cation based devices a nanoscale filament is formed in a switching material by metal ion migration from the anode to the cathode. However, the filament growth and dissolution mechanisms and the dynamics involved are still open questions, restricting device optimization. Here, a spectroscopic technique to optically characterize in situ the resistive switching effect is presented. Resistive switches arranged in a nanoparticle-on-mirror geometry are developed, exploiting the high sensitivity to morphological changes occurring in the tightly confined plasmonic hotspot within the switching material. The focus is on electrochemical metallization and the optical signatures detected over many cycles indicate incomplete removal of metal particles from the filament upon RESET and suggest that the filament can nucleate from different positions from cycle to cycle. The technique here is nondestructive and the measurements can be easily performed in tunable ambient conditions and with realistic cell geometries.

Solidification/Stabilization of Fly Ash from a Municipal Solid Waste Incineration Facility Using Portland Cement

This study investigated the solidification/stabilization of fly ash containing heavy metals using the Portland cement as a binder. It is found that both the cement/fly ash ratio and curing time have significant effects on the mechanical (i.e., compressive strength) and leaching behaviors of the stabilized fly ash mixtures. When the cement/fly ash ratio increases from 4 : 6 to 8 : 2, the increase of compressive strength ratio raises from 42.24% to 80.36%; meanwhile, the leaching amount of heavy metals decreases by 2.33% to 85.23%. When the curing time increases from 3 days to 56 days, the compressive strength ratio of mixtures raises from 240.00% to 414.29%; meanwhile, the leaching amount of heavy metals decreases by 16.49% to 88.70%. The decrease of compressive strength with the lower cement/fly ash ratios and less curing time can be attributed to the increase of fly ash loading, which hinders the formation of ettringite and destroys the structure of hydration products, thereby resulting in the pozzolanic reaction and fixation of water molecules. Furthermore, the presence of cement causes the decrease of leaching, which results from the formation of ettringite and the restriction of heavy metal ion migration in many forms, such as C-S-H gel and adsorption.

Force Field for Mg(2+), Mn(2+), Zn(2+), and Cd(2+) Ions That Have Balanced Interactions with Nucleic Acids.

Divalent metal ions are of fundamental importance to the function and folding of nucleic acids. Divalent metal ion-nucleic acid interactions are complex in nature and include both territorial and site specific binding. Commonly employed nonbonded divalent ion models, however, are often parametrized against bulk ion properties and are subsequently utilized in biomolecular simulations without considering any data related to interactions at specific nucleic acid sites. Previously, we assessed the ability of 17 different nonbonded Mg(2+) ion models to reproduce different properties of Mg(2+) in aqueous solution including radial distribution functions, solvation free energies, water exchange rates, and translational diffusion coefficients. In the present work, we depart from the recently developed 12-6-4 potential models for divalent metal ions developed by Li and Merz and tune the pairwise parameters for Mg(2+), Mn(2+), Zn(2+), and Cd(2+) binding dimethyl phosphate, adenosine, and guanosine in order to reproduce experimental site specific binding free energies derived from potentiometric pH titration data. We further apply these parameters to investigate a metal ion migration previously proposed to occur during the catalytic reaction of the hammerhead ribozyme. The new parameters are shown to be accurate and balanced for nucleic acid binding in comparison with available experimental data and provide an important tool for molecular dynamics and free energy simulations of nucleic acids where these ions may exhibit different binding modes.

Migration of ohmic heating electrode components into a food

Ohmic heating has an advantage over conventional indirect heating methods because heater (electrode) surfaces temperatures are comparatively lower as heat is generated within bulk fluid. Conventional ohmic heating under typical low frequency alternating current (50 or 60 Hz) could cause hydrogen and oxygen evolution due to electrolysis of water. This process could develop the electrodes decay or corrosion. Any decay or corrosion of electrodes shorten the life time and contaminate the food.in this study Concentrations of Fe, Cr, Ni, Mn, and Mo from the stainless steel electrode migrated into ohmically and conventionally treated soup were measured. migration of the major key metal ions from stainless steel measured by Atomic Absorbtion shows that Overall ohmic treatment yielded reduced migration residues of all metal ions, compared to the conventional retorting with similar electrodes. Concentrations of all metal ions migrated into food samples after ohmic treatment were far lower than dietary exposure levels so that this technique can ensure the safety and quality of food supplies.

Addressing the Instability of High Capacity Lithium Battery Cathodes

Layered lithium- and manganese-rich mixed metal oxides are receiving worldwide attention as cathode materials for lithium-ion batteries because, once activated above 4.5 V, they can provide the theoretical capacity of a typical LiMO2 (M=Mn, Ni, Co) electrode (250-260 mAh/g) [1-3]. These Li- and Mn-rich materials can be represented in their initial state by the two-component formula xLi2MnO3·(1-x)LiMO2 or, in normalized layered notation, Li1+xM1-xO2. Although xLi2MnO3·(1-x)LiMO2 electrodes maintain their capacity when repeatedly charged to high potetials (>4.5 V), structural changes result in voltage decay and hysteresis during repeated charge/discharge cycles, repressing their use in commercial battery products. The structural decay has been attributed to the irreversible migration of transition metal ions (predominantly Mn) into the lithium-depleted layers. This disadvantage is being addressed by slightly reducing the lithium content in parent xLi2MnO3·(1-x)LiMO2materials to introduce ‘pillaring’ transition metal ions in the lithium layers of the composite structure. This presentation will discuss the background and versatility of composite electrode structures and highlight the opportunity that these materials present for overcoming voltage fade, with a specific focus on composite ‘layered-spinel’ electrode structures. References Z. Lu and J. R. Dahn, J. Electrochem. Soc., 149,A778 (2002).J-S. Kim, C. S. Johnson, J. T. Vaughey, M. M. Thackeray, S. A. Hackney, W. Yoon and C. P. Grey, Chem Mater. 16, 1996 (2004).M. M. Thackeray, C. S. Johnson, J. T. Vaughey, N. Li and S. A. Hackney, J. Mater. Chem. 15, 2257 (2005).

Biwedge Octahedron-Shaped Li-Excess Nickel-Manganese Oxide Cathode Showing Remarkably Suppressed Potential Fade

Li-ion batteries (LIBs) are foreseen to play a very important role in energy storage for the next decade. Research for advanced Li-ion secondary batteries has been following the direction toward higher energy and power densities. Various cathode materials, such as LiCoO2, LiMn0.33Ni0.33Co0.33O2, spinel LiMn2O4,olivine LiFePO4, and Li1+x(M,Mn)1-xOy, having different or similar lattice structures have been developed. Among these materials, the class of layered Li-rich Mn-transition metal oxides (Li1+x(M,Mn)1-xOy) has lately drawn escalated attention due to their potential high capacities beyond 200 mAh/g. In these oxides, the excess Li ion gives rise to the presence of inter-grown Li2MnO3 slabs within Li(M,Mn)O2 matrix to form a layered “composite” structure. These Li2MnO3 slabs may be transformed to electrochemical active MnO2 layers by removal of Li+ upon charging above 4.5 V (versus Li/Li+) and stabilizing the layered structure under high depth of lithiation/de-lithiation during the charge/discharge cycles. During charge and discharge process, the layered composite suffers from the well known phenomena of potential fade. The potential fade has been attributable to the migration of the transition metal ions, notably manganese and nickel, into the lithium layers, causing slow transformation to a spinel-like domain within the crystal lattice. The fade results in gradual loss in energy capacity of the electrode.In this study, a biwedge octahedron-shaped Li1+x(M,Mn)1-xOy powder has been synthesized via a oxalate-based precipitation process followed by high-temperature calcination. The resulting powder shows a large aspect ratio with a width near 10 μm and a thickness of a couple of μm. The large width allows for high powder tap density, while the small thickness enables fast charging-discharging kinetics. More importantly, in either full-cell or half-cell testing, the resulting oxide electrode showed essentially no potential fade after several hundred cycles. The synthesis process and the material and electrochemical characterization results will be presented. Figure 1

Implementation of Stable Surface Structures; A Promising Key to Solve Capacity Fading Issues for the High-Voltage LiNi0.5Mn1.5O4

High-voltage spinel LiNi0.5Mn1.5O4 (LNMO) cathode materials allow three-dimensional lithium-ion diffusion in its lattice, which makes it unique among various high-voltage cathode materials. The structural changes and Mn ion dissolution of the LNMO cathode materials are some of the critical properties affecting its performance degradation, although it is considered to be a promising high-energy and high-power density cathode material for Li-ion batteries.1-3 In this study, our group extensively investigated the structural changes at the surface and bulk, where we adopted polyol process (Fig. 1) as a new method of synthesizing LNMO materials. New findings on the structural stability related to the transition metal (TM) migration are discovered for LNMO synthesized via conventional sol-gel method (SG-) versus polyol process (P-). Fig. 2a presents the relation between specific capacity and cycle number of SG- and P-LNMO. Initially, SG-LNMO has larger capacity, but the capacity of SG-LNMO degrades drastically (>50% loss of its initial capacity) even in 100cycles under high temperature 55 oC. In-depth local structural variations at the surface and bulk around Mn during cycled-aging were studied via in situ extended X-ray absorption fine structure (EXAFS) spectra. The Fourier-transformed (FT) EXAFS spectra from both transmission electron yield (TEY) and fluorescence yield (FY) mode (k3-weighted in k-space, but not phase-corrected FT, causing shorter bond lengths in the plots than for the actual bonds) at Mn K-edge are studied. For the Mn K-edge results shown in FY mode, there were negligible alterations in both the Mn-O and Mn-TM bond length from the pristine to 20th cycled state, indicating that Mn in both materials is stable and maintains its original structure within the bulk site. On the other hand, the spectral changes during cycled-aging in TEY mode, the shift of the Mn-TM bond length and the emergence of the Mn-TMtet can be observed only on the SG-LNMO. It means the migration of Mn cations (mostly Mn2+) to the surface, which is well-known phase transition phenomenon in LNMO cathode materials. Surprisingly, P-LNMO does show structural and phase stability by looking at the spectra on both at the bulk and surface even after 20th cycled. The local atomic-level crystal structures were further investigated via aberration-corrected scanning transmission electron microscopy (STEM) taken along the [110] crystallographic direction. Surface regions (~1 nm) of the cycle-aged SG-LNMO particles showed two types of local atomic-level transition metal (TM) ions migration, which is closely related to Mn ion dissolution. TM ions replace tetrahedral Li sites to form a Mn3O4-like structure, and fill the empty octahedral sites to form a rocksalt-like structure, whereas the cycle-aged P-LNMO maintained its original spinel structure. It points to a pathway toward the promising solution to prevent capacity degradation with increased structural stability against Mn dissolution. We correlated such capacity fading issues to local structural changes and more detailed results of them will be presented at the meeting. Acknowledgements H. Yoon and H. Cho acknowledge S. Khalid for technical assistance at the National Synchrotron Light Source for the use of beamline X18B. The double aberration-corrected scanning TEM (TEAM0.5) was performed with an approval of the National Center for Electron Microscopy at the Lawrence Berkeley National Laboratory (Proposal No. 3162). Reference 1. J. Song, D. W. Shin, Y. Lu, C. D. Amos, A. Manthiram and J. B. Goodenough, Chem. Mat., 2012, 24, 3101-3109. 2. N. M. Hagh, F. Cosandey, S. Rangan, R. Bartynski and G. G. Amatucci, J. Electrochem. Soc., 2010, 157, A305-A319. 3. D. Liu, W. Zhu, J. Trottier, C. Gagnon, F. Barray, A. Guerfi, A. Mauger, H. Groult, C. M. Julien, J. B. Goodenough and K. Zaghib, RSC Advances, 2014, 4, 154-167. Figure 1

Influence of Ti substitution on the structure and electrochemical properties of lithium-excess layered manganese based oxide for lithium ion batteries

A series of pure solid solution between Li2MO3 and LiNi1/2M1/2O2 (M=Ti, Mn) described as Li5/3Ni1/6Mn5/6-xTixO8/3(0≤x≤5/6) have been successfully prepared. Their hexagonal lattice parameters, a and c, change monotonously with the increase in x value. Tremendous change in their I003/I104 values indicates that Ti substitution causes cation mixing in the solid solution. The shapes in initial charge curve of solid solutions are similar to each other though charge capacities decrease for x≥4/6. On the other hand, initial discharge curve of the as synthesized solid solution are commonly composed of three plateaus which located at high voltage (>3.5V), low voltage and 2.8V plateau. Well separation of high and low voltage plateau is observed for x>4/6 and lower voltage plateau shifts dramatically to lower potential with increasing x value (3/6≤x≤5/6). Detailed analysis of initial charge/discharge and following reversible capacities indicates that peroxide type species in the solid solution play an important role in electrochemical reaction. It was found that the discharge curves of Li5/3Ni1/6Mn2/6Ti3/6O8/3 maintain its original shape after prolonged cycles, even though it is accompanied with capacity loss. Such behavior might be related with migration of metal ion into Li layer during initial charge process and result in rock salt like structure during prolonged cycling.

Correlation between transition metal ion migration and the voltage ranges of electrochemical process for lithium-rich manganese-based material

Voltage decay of Li-rich cathode material is caused by migration of transition metal (TM) ions and layered phase transformation to spinel phase. Here electrochemical studies demonstrate that charge/discharge voltage ranges have a strong impact on the voltage decay. For cells cycling in the charge/discharge condition of voltage range at 2.0–4.6 V, 3.2–4.6 V and 4.2–4.6 V, voltage decay phenomena occur to the same extent. While for the serial conditions of 2.0–4.2 V, 2.0–4.4 V, 2.0–4.6 V, 2.0–4.8 V and 2.0–4.6V + hold at 4.6 V for 5 h, voltage decay starts to occur at a typical voltage when the potential is high enough, and then phase transformation becomes severer with increased potentials, or prolonged time holding at high voltages. TM ions at high voltages have high enough energy, which can be denoted as “activation energy”, to stride across the transition state and migrate to Li vacancy, which results in spinel formation and voltage decay.

The effect of the protonic component of conduction on the electrical properties of oxide glass

A short review of works devoted to studying the effect of hydrogen-containing fragments of the structure (mainly H2O and OH−-groups) on the physicochemical (mainly electrical) properties of oxide glass has been presented. It was noted that the conduction of alkali-free oxide glass is due to the migration of protons. When introducing alkali metal oxides in their composition in the region of low Me2O concentrations, the electric current transport is due to the combined migration of protons and alkali metal ions; the conduction due to the migration of exclusively alkali ions is observed at concentrations of alkali metal ion oxides higher than 20 mol %. It was noted that in oxide glass containing ions of alkaline earth metals the conduction is also due to the migration of impurity protons. No participation of ions of alkaline earth metals in the electricity transport was observed.

The migration mechanism of transition metal ions in LiNi0.5Mn1.5O4

In situ high-energy X-ray diffraction and neutron diffraction were deployed to trace the migration of transition metal ions in LiNi0.5Mn1.5O4.

Facile synthesis of lithium-rich layered oxide Li[Li0.2Ni0.2Mn0.6]O2 as cathode of lithium-ion batteries with improved cyclic performance

Lithium-rich layered oxide has attracted much attention as a cathode of lithium-ion batteries due to its high specific capacity and relative cheapness. Although much effort has been dedicated to its development, this oxide is not used commercially because of its poor cyclic performance. In this work, we reported a facile synthesis for lithium-rich layered oxide, Li[Li0.2Ni0.2Mn0.6]O2, with improved cyclic performance, in which fast evaporation for precursor formation is introduced. The as-synthesized samples were characterized with X-ray diffraction, Raman spectroscopy and scanning electron microscope, and charge/discharge test. The results indicate that the as-synthesized samples deliver a reversible capacity of ~200 mAh g−1 and remain unchanged after 50 cycles at 0.05 C. The improved cyclic performance can be attributed to the low structural defects in lithium-rich layered oxides, which decrease the oxygen loss and manganese reduction and therefore depress the migration of transition metal ions and phase transformation.

Dopant Based Stabilization of LiCoO2: Insight from First-Principles Calculations

LiCoO2 is widely used as cathode material for Li-ion batteries (1). However, the usable specific capacity of LiCoO2 is limited to approximately half of its theoretical capacity. This limitation comes from the mechanical failure of the cathode when more than 50% of Li is deintercalated. The stability of LiCoO2 and its electrochemical performance can be improved by coating its surface with inner metal oxides (2). Such approach has been used for different cathode materials, but the origin of the stabilization effect is poorly understood. The enhanced stability of the cathodes has been rationalized invoking many effects, e.g., i) the inner metal oxides act as a physical barrier to prevent cathode-electrolyte reactions (3), and ii) the layered structure of the cathode material is stabilized by the migration of metal ions from the coating oxides (1). To have a better understanding of the stabilization mechanism, we have performed Density Functional Theory calculations of LiCoO2doped with inner metal ions (Figure 1). Such calculations allow us to study how the migration of metal ions from the coating oxides modify the structure of the cathode materials. Acknowledgments.Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division. Reference: 1. H. Li, Z. Wang, L. Chen, and X. Huang, Adv. Mater., 21, 4593–4607 (2009).2. Z. Chen, Y. Qin, K. Amine, and Y.-K. Sun, J. Mater. Chem., 20, 7606–7612 (2010).3. J.-S. Kim et al., J. Electrochem. Soc., 151, A1755–A1761 (2004). Figure 1. Schematic of some possible sites for metal dopants in LiCoO2: the left and central panels show the dopant on Li and Co sites, respectively, and the right panel shows substitution on both Li and Co sites.

A new timescale dimension for migration experiments in clay: proof of principle for the application of miniaturized clay column experiments (MCCE)

Geological clay formations are often considered as a host rock for a future nuclear waste repository. Many studies concerning sorption or desorption experiments with metal ions like radionuclides or other relevant substances (e.g. metal complexing ligands) onto/from geological clay samples are performed with the batch techniques where only small amounts of the homogenized clay is in contact with the appropriate metals diluted in high volumes of aqueous solutions. This unnatural contact of clay with water can lead to high bias or not transferable results for a risk assessment study of a future repository. Diffusion experiments as an alternative and more natural experimental tool have the lack of huge time consuming when the migration of higher valent metal ions is considered. With the herein described new miniaturized clay column setup a linker between the unnatural batch techniques and the time consuming diffusion experiments is installed. The presented miniaturized clay column experiments (MCCE) derived and modified from high performance liquid chromatography can be applied in a lot of geochemical studies. Using MCCE, migration experiments of inert tracers (iodide), natural organic matter as complexing ligands (lactate and salicylate) as well as trivalent metal ions (europium) in compacted clay can be performed within a short time span of a few minutes or hours only in contrast to several months by use of classical diffusion or column methods. As preliminary results, typical migration times through miniaturized clay columns (20 × 3.5 mm, L × ID) of iodide as inert tracer are in the range of 145 min, meanwhile increasing retention times of salicylate from about 390 min in the absence of Eu to migration times in the range of 420–470 min in the presence of different Eu concentration can be observed.

Theoretical study of “sandwich” clusters of fused magnesium porphyrin oligomers with alkali metal atoms

The structural characteristics, energies, and spectroscopic properties of two-layer and multilayer “sandwich” clusters in which rings (layers) of fused porphyrin oligomers Mg2P2 and Mg4P4 (P = C20H12N4) are separated by (Li) n metal interlayers containing from 8 to 32 lithium atoms have been calculated by the density functional theory B3LYP method. The trends in the changes in these characteristics have been scrutinized as a function of the number of introduced Li atoms and the size and number of porphyrin layers. Calculations predict the high energetic stability and possibility of the existence of these sandwiches as paramagnetic clusters with mobile intercalated lithium ions. The latter, like intercalated graphite clusters, are expected to exhibit high electronic and ionic conductivity. The most favorable (with low or zero barriers) channels of migration of metal ions between the porphyrin layers are discussed.