Enrichment Of Ions Research Articles

Electrokinetic ion enrichment in asymmetric charged nanochannels

Artificial bionic nanochannels have attracted wide attention and successfully used in various fields. In this work, a novel nanochannel with asymmetric surface charge is proposed to investigate the ion enrichment effect. The results show that the proposed nanochannel has excellent ion enrichment performance and the obtained ion enrichment ratio is up to 1500 when the ion concentration is 0.01 mM, which is much higher than precedent researches typically ranging from tens to hundreds. Besides, we found that the forward voltage bias will produce ions enrichment and the reverse voltage bias will produce ions depletion. The ion enrichment ratio is higher at the larger voltage bias, absolute surface charge density and smaller nanochannel height. In addition, the ion enrichment performance is more sensitive to the change of charged wall length and not sensitive to the change of uncharged wall length. The research report offers important information and instructions for the design and optimum on ion enrichment performance.

Scanning Ion Conductance Microscopy of Nafion-Modified Nanopores

Single nanopores in silicon nitride membranes are asymmetrically modified with Nafion and investigated with scanning ion conductance microscopy, where Nafion alters local ion concentrations at the nanopore. Effects of applied transmembrane potentials on local ion concentrations are examined, with the Nafion film providing a reservoir of cations in close proximity to the nanopore. Fluidic diodes based on ion concentration polarization are observed in the current-voltage response of the nanopore and in approach curves of SICM nanopipette in the vicinity of the nanopore. Experimental results are supported with finite element method simulations that detail ion depletion and enrichment of the nanopore/Nafion/nanopipette environment.

Durable Manganese-Based Li-Excess Electrode Material without Voltage Decay: Metastable and Nanosized Li2MnO1.5F1.5

Li-excess manganese-based oxides have been proposed as high-capacity positive electrode materials, but voltage decay associated with gradual oxygen loss hinders its use for practical applications. Herein, Li-excess manganese oxides with different fluorine contents are synthesized by high-energy mechanical milling. Although Li2MnOF2 with only divalent manganese ions cannot be synthesized, Li2MnO2F and Li2MnO1.5F1.5 are successfully synthesized. When the samples are charged to 5.0 V, both oxyfluorides deliver large reversible capacities, ∼350 mA h g–1 and ∼1000 mWh g–1. However, insufficient capacity retention is also observed because of the instability of anionic redox. In contrast, better capacity retention and higher energy density (730 mWh g–1) are obtained for Li2MnO1.5F1.5 with a 4.4 V cutoff because of the enrichment of fluoride ions and activation of Mn2+/Mn4+ cationic redox. Moreover, electrode durability is significantly improved by using a highly concentrated electrolyte, and good capacity retention without voltage decay is achieved for >180 cycles.

Salt enrichment and its deterioration in earthen sites in Emperor Qin’s Mausoleum Site Museum, China

Salt enrichment in the topsoil, owing to one-way migration of moisture from earthen sites to air environment, is an important inducement to weathering of sites and relics, such as efflorescence, recess, slice-peeling, which becomes the most important challenge to the preservation of unearthed sites and relics. Further, salt enrichments in the topsoil of undulating earthen sites are usually inhomogeneous such that it is difficult to precisely prevent the deterioration from happening of salt enrichment in the topsoil. A case study of salt enrichment at the K9901 funerary pit of Emperor Qin’s Mausoleum Site Museum was conducted by soil column experiment and numerical simulation. The water and salt transport in the earthen sites were simulated and analyzed by HYDRUS software. The simulation of the salt enrichment process at the earthen sites demonstrated that the enrichment of soluble salt ions mainly occurs on the surface of rammed earth and increases annually; the salt damage at the earthen sites can be effectively delayed by taking an environmental control measure. These results provide a reference for the prevention of salt damage at earthen sites and facilitate the daily management of earthen sites.

MgO/Molten salt interfacial thermal transport and its consequences on thermophysical property enhancement: A molecular dynamics study

The solid-liquid interface between molten salt and solid oxides is ubiquitous in the molten salt nanocomposite with enhanced heat storage and transfer properties for concentrating solar power (CSP) systems. Understanding the microscopic mechanisms of interfacial thermal transport on this solid-liquid interface have great significance for evaluating the effective thermal properties of nanocomposites. This study combines equilibrium and non-equilibrium molecular dynamics simulations to explore the thermal transport and its connection with interfacial microstructure at the solid MgO-molten Hitec salt interface. Simulation results indicate that the enhancement of thermal transport can be ascribed primarily to the highly ordered adsorption structure of molten salt ions formed at the MgO surface, and the effect medium model incorporated with the simulated interfacial thermal resistance can reproduce the thermal conductivity of nanocomposite accurately. Further investigation indicates that the stronger adsorption at the MgO (110) surface leads to smaller interfacial thermal resistance than the MgO (100) surface, while the heat transfer parallel to the slab does not show much difference in both surfaces. These findings have illustrated the enrichment of molten salt ions at the solid surface does have a strong enhancement effect on their heat transfer properties and it is also necessary to incorporate the contribution from this interfacial thermal transport enhancement when predicting the thermophysical properties of molten salt nanocomposite materials.

Luminescent CS-SiO2@TEuTTA membrane for simultaneous detection and adsorption of copper(II) ions

Detection and adsorption of excessive copper ions are essential for protecting human health and the ecosystem structure due to the toxicity of copper. Herein, relying on the unique structural properties of chitosan (CS), a CS-SiO2@TEuTTA membrane was designed and prepared for simultaneously detection and adsorption of copper ions. Lanthanide complexes were coated on the surface of SiO2 to prepare photoluminescent SiO2@TEuTTA nanospheres. Next, dual-functional CS-SiO2@TEuTTA membrane was prepared by depositing a mixing solution of CS and SiO2@TEuTTA onto a PVDF substrate. The result shows that the CS-SiO2@TEuTTA membrane has an adsorption capacity of 51.28 mg/g. Furthermore, the fluorescence of the CS-SiO2@TEuTTA membrane can be quenched by copper ions. The membrane exhibits good selectivity and sensitivity for copper ions in the range of 2–100 μM and the detection limit of the membrane is 0.18 μM. In particular, the CS-SiO2@TEuTTA membrane provides greater sensitivity to copper ions than SiO2@TEuTTA nanospheres, owing to the enrichment of copper ions in CS.

Recent Applications of Carbon Nanotubes for Separation and Enrichment of Lead Ions

Lead is one of the most toxic heavy metals released into the environment through industrial sources. Its direct determination is often a problem due to the presence of relatively complex matrices as well as low content. Thus, the additional separation and preconcentration steps are necessary in the analytical procedures. Carbon nanotubes (CNTs) continue to attract significant interest for these purposes as they exhibit a high specific surface area, exceptional porosities, and numerous adsorption sites. The modified CNTs with active groups, reagents, or materials have been widely explored using more mutual interactions that can significantly improve their sorption capacity and selectivity. This paper summarizes the recent developments from 2017 in the application of carbon nanotubes for the separation of Pb(II) and its enrichment/removal from the matrix components. Attention is given to oxidized CNTs, their modification with complexing compounds, functionalization with metal oxides and polymers, new nanocomposites, and carbon nanotube membranes.

Groundwater quality, heavy metal pollution, and health risk assessment using geospatial techniques and index methods in Eber wetland and surroundings (Afyonkarahisar/Turkey).

The continuous increase in the demand for water and the scarcity of water to be used as drinking water have made groundwater even more important. The study area, Eber wetland, is located in the Akarçay river basin, which is one of the most important river basins in Turkey. The groundwater quality and heavy metal pollution were investigated in the study using index methods. In addition, health risk assessments were performed. Ion enrichment was determined at locations E10, E11, and E21 related to water-rock interaction. In addition, nitrate pollution was observed in many samples due to agricultural activities and also fertilizer application in the areas. The water quality index (WOI) values of the groundwaters vary between 85.91 and 201.77. In general, groundwater samples located around the wetland were in the "poor water" class. According to the values for the heavy metal pollution index (HPI), all the groundwater samples are suitable for use as drinking water. They are also classified as "low pollution" according to the heavy metal evaluation index (HEI) and the value/degree of contamination (Cd). In addition, since the water is been used for drinking by the people in the area, a health risk assessment was performed to ascertain As and NO3. It was determined that the Rcancer values calculated for As were considerably higher than the tolerable/acceptable values for both adults and children. The results obtained clearly show that the groundwater should not be used as drinking water.

Detection of heavy metal ions using laser-induced breakdown spectroscopy combined with filter paper modified with PtAg bimetallic nanoparticles.

The rapid and sensitive detection of heavy metal ions is important for environment and human health. Hence, the rapid and sensitive detection of multiple heavy metals simultaneously has become a critical issue. Here, we propose a method based on laser-induced breakdown spectroscopy (LIBS) combined with filter paper modified with PtAg bimetallic nanoparticles (BNPs) (LIBS-FP-PtAgBNPs) for the ultrasensitive detection of Hg2+, Cr3+, and Pb2+. The PtAgBNPs-modified filter paper was used to efficiently and specifically adsorb Hg, Cr, and Pb, and LIBS was used to detect the Hg, Cr, and Pb simultaneously. The limits of detection for Hg, Cr, and Pb were 0.5μg/L (2.5nM), 8μg/L (0.15μM), and 2μg/L (9nM), respectively. Furthermore, this method was successfully applied to determine the concentrations of Hg, Cr, and Pb in real spiked water samples. Compared with other methods based on nanoparticle sensing, LIBS-FP-PtAgBNPs is simpler to use and can achieve highly efficient enrichment, rapid separation, and sensitive detection of heavy metal ions. The optimal detections of Hg, Cr, and Pb were achieved in the pH range of 1-6. The developed method provides a new avenue to realize the rapid and sensitive detection of trace heavy metals in the environment.

Eutectoid Transformation Kinetics of FeO under N2 and Air Atmospheres

The effect of different oxygen content on eutectoid transformation kinetics in FeO were studied in this paper. Thermogravimetric analysis was employed to investigate the eutectoid reaction in the oxide formed on pure Fe after being exposed to air at 900 °C for 10 min. The oxidized specimens were held isothermally in N2 and air from 100 s to 10,000 s in the temperature range of 350 to 550 °C, and the morphologies in FeO were observed by electron probe microanalysis. The results of the eutectoid transformation are statistically analyzed, and the dynamic model of the FeO eutectoid transformation is established based on the Johnson-Mehl-Avrami-Kolmogorov equation. Combined with the measured values and the calculation results, the time of eutectoid reaction in air is earlier than that in N2. Under the experimental conditions, the formation of Fe3O4 seams can occur at the interface of the FeO-substrate after the eutectoid reaction has begun, which means the eutectoid reaction is more determined by local ion concentration changes. At the Fe3O4-FeO interface, there is a high concentration enrichment of Fe ions, giving priority to the formation of Fe-rich FeO, which makes the eutectoid phase transition time earlier than in N2 conditions.

Biomimetic asymmetric GO/polymer nanocomposite membrane for energy harvesting

Energy harvesting based on salinity gradients between oceans and rivers can provide a clean, stable, and continuous electric output. However, it is highly dependent on the excellent performance of biomimetic ion-selective membranes. The graphene oxide (GO) membrane, as a 2D material-based layered-structure membrane, offers the possibility of efficient salinity gradient energy conversion. However, unstable stratification in aqueous solutions and the limited number of charged functional groups make practical applications difficult. A conventional symmetric structure will also reduce the effective salinity gradient owing to ion enrichment on the low-concentration side. In this study, we pre-modified GO to create an asymmetric ion-selective membrane with opposing charges. Hyperbranched polyethyleneimine (PEI) and polyacrylic acid (PAA) as surface charge donors and crosslinkers stabilise the interlayer spacing of GO and increase charge density, achieving up to 3.4 W/m2 power density under sea water and river water. Furthermore, theoretical calculations show that membranes with asymmetric structure and opposite charges can eliminate the effect of ion enrichment on the low-concentration side, thereby avoiding power consumption. This system contributes to a further step toward the application of salinity energy conversion.

Mechanistic Study of the Conductance and Enhanced Single-Molecule Detection in a Polymer-Electrolyte Nanopore.

Solid-state nanopores have been widely employed in the detection of biomolecules, but low signal-to-noise ratios still represent a major obstacle in the discrimination of nucleic acid and protein sequences substantially smaller than the nanopore diameter. The addition of 50% poly(ethylene) glycol (PEG) to the external solution is a simple way to enhance the detection of such biomolecules. Here, we demonstrate with finite-element modeling and experiments that the addition of PEG to the external solution introduces a strong imbalance in the transport properties of cations and anions, drastically affecting the current response of the nanopore. We further show that the strong asymmetric current response is due to a polarity-dependent ion distribution and transport at the nanopipette tip region, leading to either ion depletion or enrichment for few tens of nanometers across its aperture. We provide evidence that a combination of the decreased/increased diffusion coefficients of cations/anions in the bath outside the nanopore and the interaction between a translocating molecule and the nanopore-bath interface is responsible for the increase in the translocation signals. We expect this new mechanism to contribute to further developments in nanopore sensing by suggesting that tuning the diffusion coefficients of ions could enhance the sensitivity of the system.

MIL-88B(Fe)-NH2: an amine-functionalized metal-organic framework for application in a sensitive electrochemical sensor for Cd2+, Pb2+, and Cu2+ ion detection.

We propose here an electrochemical platform for multi-heavy metal ion detection in water based on MIL-88B(Fe)-NH2, an amine-functioned metal-organic framework (MOF) for modifying the surface of a glassy carbon electrode (GCE). Herein, MIL-88B(Fe)-NH2 with abundant functionalized amine groups can play the role of capture sites for the enrichment of metal ions before electrochemical oxidation sensing. MIL-88B(Fe)-NH2 was synthesized under optimized conditions through a solvothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. MIL-88B(Fe)-NH2 was then drop-casted on GCE to electrochemically determine the Cd2+, Pb2+ and Cu2+ ion concentrations by differential pulse voltammetry (DPV). The electrochemical sensor exhibits excellent electrochemical performance toward Cd2+, Pb2+ and Cu2+ ions in the large linear ranges of 0.025-1.000 μM, 0.3-10.0 μM and 0.6-10.0 μM with limits of detection that are 2.0 × 10-10 M, 1.92 × 10-7 M and 3.81 × 10-7 M, respectively. The fabricated sensor also shows high reliability and good selectivity. This MIL-88B(Fe)-NH2 application strategy is promising for the evaluation of various heavy metal ions in water.

Dual-oxidation-induced lattice disordering in a Prussian blue analog for ultrastable oxygen evolution reaction performance.

Enriching the active sites and enhancing the intrinsic activity of a single site are two basic strategies for improving the activity toward the electrocatalytic oxygen evolution reaction (OER), and designing an advanced microstructure with a boosted pre-oxidation process can further guarantee durability toward long-term catalysis. Herein, we propose a dual oxidation strategy of a Co Prussian blue analog (Co PBA), which simultaneously achieves Co3+ active site enrichment, in situ CeO2 decoration and lattice disordering with abundant undercoordinated sites, realizing highly efficient and ultrastable OER performance. The dual oxidation process can induce the enrichment of high-valence Co ions by combined chemical oxidation and d-f electron coupling compared to the singly oxidized catalysts, thereby providing more active sites with enhanced intrinsic activity for the early triggered OER process. In addition, the disordered lattice can provide abundant reactive Co sites for the pre-oxidation process, thereby leading to obvious activation of the catalysts and remarkable operational stability due to the substantially accumulated Co3+ sites. Benefitting from the structural advantages of lattice-disordered dual-oxidized Co PBA nanocages, a low overpotential of 240mV can be achieved for a 10mAcm-2 current density, and the large catalytic current density and intrinsic activity are among the best compared to those of previously reported PBA-based and PBA-derived catalysts and even RuO2 and IrO2. In addition, ultrastable OER behavior with a 263% activity enhancement in 150h can result, making the dual-oxidized catalyst a promising candidate for water electrolysis.

Detection of chromium in different valence states in water and soil using laser-induced breakdown spectroscopy combined with an ion enrichment chip

IEC–LIBS could rapidly and sensitively detect different valence states of Cr in water and soil.

SOURCE IDENTIFICATION AND VARIATION IN THE CHEMICAL COMPOSITION OF RAINWATER IN THE COASTAL AND INDUSTRIAL AREAS: A CASE STUDY OF IKOT ABASI, SOUTH-EASTERN NIGERIA

Studies on precipitation Chemistry were carried out with the aim to understand the nature and sources of rainwater at Utaewa (Location 1), a coastal village and Ikpetim, near Ibom Power Station (Location 2), all in Ikot Abasi Local Government Area, southern, Nigeria. These locations respectively represent the coastal and industrial regions. The rainwater samples, collected at these locations, were analyzed for major cations, anions, electrical conductivity and pH with the aim of identification of variation in the physiochemical compositions of the rainwater samples. The analysis of the rainwater samples gave a pH at locations 1 and 2 as 5.62 ± 0.26 and 5.77± 0.25 respectively during the wet season, while the pH of the rainwater at locations 1 and 2 during dry season were 5.41 ± 0.14 and 5.84 ± 0.21 respectively. The pH values indicated acidic water and were below the World Health Organisation (WHO) Standard of 6.5 to 8.5, but close to the World Meteorological Organisation (WMO) optimum pH value of 5.6 for rainwater from unpolluted continental areas. The predominance of 𝐶𝑙−and𝑁𝑎+ were observed in the coastal environment whereas, calcium, sulphate, nitrate and ammonium ions predominate in industrial environment where there are power generating plants, Aluminium smelting company and gas station. The total anion (37.9%) at Utaewa is less influenced by anthropogenic activities whereas total anion (72.5%) at Ikpetim, near Power Plant is influenced by pollutants emitted by anthropogenic activities. The ratio:𝐻+/(NO3- + SO42-) was observed as 0.04 and 0.008 for Utaewa and Ikpetim respectively, which are close to zero, indicating that 99 % of acidity in the rainwater is neutralized in the study area with no consequence of acidity impact on the soil, surface waters and groundwater in the study area. Ca2+ , K+ and Na+ play important roles in neutralization of acidic ions in rainwater. For source identification, correlation matrix analysis was established, which showed that at locations 1 and 2,strong correlation exists between the acidic ions SO42- and NO3-, indicating their origin from anthropogenic activities. This is viewed to be attributed to the similarity in their behaviour in precipitation and the co-emissions of their precursors, which are SO2 and NO2. The major ion enrichment factors (EF) followed the order at location 1 during the dry season;𝐶𝑎2+𝑁𝑎+⁄ (8.58) >𝐾+𝑁𝑎+⁄ (4.32) >𝑆𝑂42−𝑁𝑎+⁄ (0.68) >𝐶𝑙−𝑁𝑎+⁄ (0.11), while the enrichment factor (EF ) during the wet season at location 1 followed the order , 𝐶𝑎2+𝑁𝑎+⁄ (11.92 )>𝐾+𝑁𝑎+⁄ (3.78) >𝑆𝑂42−𝑁𝑎+⁄ (0.88) >𝐶𝑙−𝑁𝑎+⁄ (0.11).

Influence of ion exchange membrane arrangement on dual-channel flow electrode capacitive deionization: Theoretical analysis and experimentations

Flow electrode capacitive deionization (FCDI) has emerged as a viable technology for brackish water desalination. However, the mutual restriction between desalination rate and energy consumption is the current bottleneck hindering the widescale and practical application of FCDI. At this point, the relationship between the complex electrical double layer and electrodialysis mechanism is still unclear. Herein, we have constructed two kinds of dual-channel FCDI systems to investigate the influence of ion exchange membranes (IEMs) arrangement on desalination performance. The diffusion coefficient of chlorine is higher than that of sodium, resulting in the improved salt removal rate and current efficiency of dual-channel FCDI based on the NaCl electrolyte. In contrast, both systems performed identically using KCl as the majority salt in the feed stream due to the similar diffusion coefficients of both the cation and anion. The higher salt removal capability of dual-channel FCDI was achieved by (i) the thicker ion depletion layer of cation exchange membrane (CEM) enabling higher salt removal efficiency and (ii) the higher concentration of the ion enrichment layer accelerating the electro-adsorption of flow-electrodes. Both the numerical simulation and experimental results indicate that the composite mechanisms of dual-channel FCDI are beneficial to the excellent desalination performance and great energy efficiency.

Flow Electrode Capacitive Deionization System with Simultaneous Desalting of Na+ and Gathering of Na+

Oceans contain many freshwater resources and metal elements that people need, so the rational development of marine resources can solve the two major problems of shortage of freshwater resources and metal elements for people. To solve these two challenges, a system was designed to obtain freshwater resources and metallic elements simultaneously. An ion enrichment module was added to the conventional flow capacitor deionization system to collect metal elements while the seawater was deionized. A flowing electrode allows the metal elements to enter the flowing electrode through the desalination ability. It transports the metal elements to the enrichment module through the fluidity of the fluid while reducing the ion concentration at the flowing electrode, thus reducing the effect caused by the rejection of the same ion and collecting and enriching the metal elements. We purchased activated carbon to test the feasibility of the system with different mass fractions of activated carbon suspensions. The results showed that the elemental enrichment capacity of the system increased from 12.291 to 14.795 mg, and the enrichment rate increased from 13.536 to 16.294 mg cm-2 h-1 as the mass fraction of activated carbon increased. Thus, the system accomplished the goals of desalination and metal collection simultaneously.

In situ detection of Cu2+, Fe3+ and Fe2+ ions at the microbe-mineral interface during bioleaching of chalcopyrite by moderate thermophiles

Bioleaching of metal sulfides represents an interfacial process in which the spatial relationship of metal ions with microbial cells and extracellular polymeric substances (EPS) is complex. The dissolution of chalcopyrite, cell attachment, and biofilm formation patterns were assessed during bioleaching with mixed cultures at 45 °C. The analysis of confocal laser scanning microscopy (CLSM) indicated that EPS were laid flat on the surface of chalcopyrite coupons, forming monolayer biofilms, with significant amounts of Fe3+, Fe2+ and Cu2+ enriched at the cell-chalcopyrite interface. In addition, the metal ions from mineral surfaces were extracted by ultrasonication. The results showed that the mineral surface is enriched with large amounts of Fe3+ (12.07 mg/g) and Cu2+ (10.82 mg/g) during the final stage of bioleaching, and more Cu2+ ions and iron maters from bio-oxidizing maybe were enclosed in the EPS space. It was inferred that the EPS with jarosite on the surface of chalcopyrite gradually acted as a weak diffusion barrier for Cu2+, and Fe3+ ions transference during bioleaching. These results can provide important evidence to reveal the hypothesis of ''metal ions enrichment on the mineral surface'' and benefit a further understanding of the bioleaching mechanism.

Highly efficient separation and enrichment of hafnium from zirconium oxychloride solutions by advanced ion-imprinted membrane separation technology

Hafnium (Hf) is an important strategic material for the semiconductor, aerospace and nuclear industries. In this paper, an advanced ion-imprinted membranes (IIMs) separation system was prepared for the first time to achieve efficient separation and enrichment of Hf ions from zirconium oxychloride solutions. IIMs were constructed by a keyhole complex imprinting method with N, N-di-2-ethylhexyl diglycolamic acid (D2EHDGAA) as the carrier molecule, cellulose triacetate (CTA) as the base polymer and Hf ions as the template ion. In addition, amide acid driven IIMs were coupled with aspartic acid in the feed phase, which changes from preferential extraction of Zr to preferential extraction of Hf. To characterize it, we used Fourier transform infrared (FT-IR) spectroscopy and scanning election microscopy (SEM). The results showed that IIMs can increase CHf/CZr from 2.33:100 to 33.33:100 within 1 h compared with polymer inclusion membranes (PIMs) and ionic liquid supported liquid membranes (SLMs), which increased by 3.33 and 3.67 times. The selectivity and enrichment performance for the enrichment of Hf ions from Zr solution were significantly improved due to the high recognition selectivity of ion imprinting. Therefore, IIMs, as an advanced membrane separation system, may have good potential for industrial application in the field of efficient separation and enrichment of Hf ions.