Reverse Ion Research Articles

Atomic insights of electronic states engineering of GaN nanowires by Cu cation substitution for highly efficient lithium ion battery

Electronic engineering of gallium nitride (GaN) is critical for enhancement of its electrode performance. In this work, copper (Cu) cation substituted GaN (Cu-GaN) nanowires were fabricated to understand the electronically engineered electrochemical performance for Li ion storage. Cu cation substitution was revealed at atomic level by combination of X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), density functional theory (DFT) simulation, and so forth. The Cu-GaN electrode delivered high capacity of 813.2 mA h g−1 at 0.1 A g−1 after 200 cycles, increased by 66% relative to the unsubstituted GaN electrode. After 2000 cycles at 10 A g−1, the reversible capacity was still maintained at 326.7 mA h g−1. The DFT calculations revealed that Cu substitution introduced the impurity electronic states and efficient interatomic electron migration, which can enhance the charge transfer efficiency and reduce the Li ion adsorption energy on the Cu-GaN electrode. The ex-situ SEM, TEM, HRTEM, and SAED analyses demonstrated the reversible intercalation Li ion storage mechanism and good structural stability. The concept of atomic-arrangement-assisted electronic engineering strategy is anticipated to open up opportunities for advanced energy storage applications.

Groundwater fluoride concentrations in the watershed sedimentary basin of Quetta Valley, Pakistan.

Litho-geochemical characteristics of low and high fluoride (F-) groundwater along with hydrological processes were investigated to delineate its genesis and enrichment mechanism in a watershed sedimentary basin. In this study, groundwater F- concentration ranged from 0 to 20mg/L with a mean and standard deviation of 2.8 and ± 3.7mg/L, respectively. Out of N = 87, 63% of samples exceeded the World Health Organization (WHO) limit of 1.5mg/L. The order of cationic and anionic dominance in groundwater samples with mean was found in decreasing order as Na+ > Mg2+ > Ca2+ > K+ and HCO3- > SO42- > Cl- > PO43- > NO3- measured in milligrams per liter. Groundwater chemistry changed from Ca-HCO3 to Na-HCO3 type and low to high fluoride as we moved from mountain foot towards the synclinal basin. Low fluoride groundwater reflected weathering, recharge, and reverse ion exchange processes with Ca-HCO3- and Ca-Mg-Cl-type water while high fluoride groundwater revealed base ion exchange, mixing, and desorption as dominant hydrological processes with Na-HCO3 and Na-Cl types of water. Gibb's diagram showed rock weathering and mineral dissolution as the major geochemical processes controlling water chemistry with an insignificant role of evaporation in the semi-arid area. Fluoride was undersaturated with mineral fluorite, indicating fluoride in groundwater is released by secondary minerals. However, due to complex geological features, groundwater fluoride enrichment was affected by a broad-scale process across a wide area such as depth, residence time, and most important geomorphological units hosting the aquifer.

Reversible ion binding for polyelectrolytes with adaptive conformations

AbstractPolyelectrolytes may adopt rod‐ or coil‐like conformations depending on the strength of intrachain repulsion and the effective charge density. The charge density of polyelectrolytes is influenced not only by the binding of small ions, but also by the binding with oppositely charged chains. We introduce a coupled variational approach that treats reversible ion binding, adaptive chain structure, and electrostatic correlations simultaneously. This approach captures the swelling and deswelling of single polyelectrolyte chains, and the competition between interchain cross‐linking and ion binding in mixtures of polyelectrolytes. Applying our theory to study polyelectrolyte coacervation, we identify two distinct regimes. In the weak binding regime, the charge density is high and the solution properties are dependent on the conformations of polyelectrolytes. In the strong binding regime, this dependence is weakened and the solution thermodynamics are dominated by the short‐range ion‐binding equilibrium.

Superstructured mesocrystals through multiple inherent molecular interactions for highly reversible sodium ion batteries.

Soft structures in nature, such as supercoiled DNA and proteins, can organize into complex hierarchical architectures through multiple noncovalent molecular interactions. Identifying new classes of natural building blocks capable of facilitating long-range hierarchical structuring has remained an elusive goal. We report the bottom-up synthesis of a hierarchical metal-phenolic mesocrystal where self-assembly proceeds on different length scales in a spatiotemporally controlled manner. Phenolic-based coordination complexes organize into supramolecular threads that assemble into tertiary nanoscale filaments, lastly packing into quaternary mesocrystals. The hierarchically ordered structures are preserved after thermal conversion into a metal-carbon hybrid framework and can impart outstanding performance to sodium ion batteries, which affords a capability of 72.5 milliampere hours per gram at an ultrahigh rate of 200 amperes per gram and a 90% capacity retention over 15,000 cycles at a current density of 5.0 amperes per gram. This hierarchical structuring of natural polyphenols is expected to find widespread applications.

Nitrogen-doped carbon decorated TiO2/Ti3C2T MXene composites as anode material for high-performance sodium-ion batteries

Titanium oxide (TiO 2 ), which has favourable cycling stability and low preparation cost, suffers from low electrical conductivity in sodium-ion batteries (SIBs). Rational construction of nano-sized TiO 2 and conductive materials is an efficient strategy to achieve enhanced electrochemical properties . Here, nitrogen-doped carbon decorated TiO 2 /Ti 3 C 2 T x MXene (NC-TiO 2 /MXene) is synthesized by utilizing polyethyleneimine (PEI) and Ti 3 C 2 T x MXene as precursors. As a result, a crumpled NC-TiO 2 /MXene composite is fabricated, where nano-TiO 2 is dispersed on the surface of the crumpled MXene and all the elements (Ti, O, C, and N) are uniformly distributed. The large specific surface area and the stable construction of NC-TiO 2 /MXene can be beneficial for electrolyte infiltration and reversible Na ions storage. Through combining the advantages of well-dispersed TiO 2 nanoparticles, the conductive MXene network and the improved electrochemical kinetics, the NC-TiO 2 /MXene electrolyte retains excellent cycling ability (157.5 mAh g −1 at 2 A g −1 after 1900 cycles) and rate performance (100.1 mAh g −1 at 10 A g −1 ) in SIBs. This work offered a rational construction of TiO 2 -based composites with enhanced electrochemical performance . • The NC-TiO 2 /MXene is synthesized by utilizing polyethyleneimine (PEI) and Ti 3 C 2 T x MXene as precursors. • The TiO 2 content in NC-TiO 2 /MXene is 76.1 wt% because of adequate oxidation reaction in the Ti 3 C 2 T x MXene. • The NC-TiO 2 /MXene electrode delivers excellent cycling ability and rate performance in SIBs.

English

The coastal flanks of Mt Etinde is wedged between the sea and the southwestern slope of Mt Cameroon. The only fresh water resources available for multipurpose uses in this area are mountain springs and streams that drain volcanic materials. To access the sources, processes and assess the ecological risk associated with hydrochemicals and heavy metals in these mountain water resources, 18 water samples were collected in different seasons at 4 locations between may 2009 and december 2010 for major ions and heavy metals determination. The sampled waters ranged from neutral to slithly alkaline, weakly mineralized and dominated by Ca–Mg–HCO3 water type irrespective of season. The hydrochemical ratios revealed ions chemistry mostly influenced by geogenic source of silicate rock weathering and atmospheric inputs. Sampled waters had low concentration of heavy metals which are less mobile in the aqueous phase, controlled by hydraulic condition. Geochemical processes of  mineral dissolution and reverse ion exchange coupled with hydrodynamic processes of flushing at the weathering front and soil leaching are the main controls on the water chemistry in the area. Despite agricultural and other anthropogenic activities, quality indices in the study area indicate the absence of anthropogenic inputs.   Key words: Major ions, heavy metals, rocks weathering, soil leaching, water quality assessment.

Looping-in complexation and ion partitioning in nonstoichiometric polyelectrolyte mixtures.

A wide variety of intracellular membraneless compartments are formed via liquid-liquid phase separation of charged proteins and nucleic acids. Understanding the stability of these compartments, while accounting for the compositional heterogeneity intrinsic to cellular environments, poses a daunting challenge. We combined experimental and theoretical efforts to study the effects of nonstoichiometric mixing on coacervation behavior and accurately measured the concentrations of polyelectrolytes and small ions in the coacervate and supernatant phases. For synthetic polyacrylamides and polypeptides/DNA, with unequal mixing stoichiometry, we report a general "looping-in" phenomenon found around physiological salt concentrations, where the polymer concentrations in the coacervate initially increase with salt addition before subsequently decreasing. This looping-in behavior is captured by a molecular model that considers reversible ion binding and electrostatic interactions. Further analysis in the low-salt regime shows that the looping-in phenomenon originates from the translational entropy of counterions that are needed to neutralize nonstoichiometric coacervates.

Spatial variability and hydrogeochemical characterisation of groundwaters in Larkana of Sindh, Pakistan

The current study examined the groundwater quality of different sampling stations of Larkana taluka based on GIS map using the interpolation method (IDW). The IDW method was applied in ArcGIS 10.5 software. Thirty representative groundwater samples were collected, mostly used for drinking purposes and examined for 24 different parameters. The water quality index (WQI) showed that 20.0% of samples were of poor water quality. The groundwater chemistry estimated from scatter diagrams showed weathering processes occurred in the study area. The silicate, carbonate, gypsum, farward ion exchange and reverse ion exchange were major weathering processes dominated in aquifer of study area. The land use may also be affecting groundwater chemistry. The samples were examined for coefficient of correlation (r), piper hydrochemical faces, Gibbs diagram, Chadha diagram and principal components analysis. EC, TDS, Cl, TH, alkalinity, Na, SO4, Ca, K and Mg were positively correlated to each other and indicated a similar geological origin. Total dissolved solids were observed 209–1642 mg/L and 76.71% samples were within permissible limit of 1000 mg/L. The results of nitrate, nitrite, orthophosphate, and total phosphate were within limits. The results of Pb 26.67%, Cr 16.67%, Cd 23.33%, and Ni 20.0% crossed the permissible limits of WHO for drinking purposes. The groundwater was examined for suitability for irrigation and 90–100% samples were indicated suitable for irrigation.

Low-crystalline birnessite-MnO2 nanograins for high-performance supercapacitors

Crystallized transition metal oxides were widely used as the electrode materials for the electrochemical energy storage devices. However, their electrochemical performance including the capacitance and rate capability was greatly hindered due to ion penetrating long distances into the bulk regimes during the electrochemical process. Herein, low-crystalline birnessite-MnO2 nanograins are obtained, which can enhance the ion diffusion kinetics and electrochemical activity significantly due to the structural disorder and defects. The resultant electrode features a superior electrochemical performance with an areal capacitance up to 1154 mF/cm2 at 2 mA/cm2 and rate retention of 69 % when the current density increasing 10 times to 20 mA/cm2 with a commercial standard mass loading about 4.58 mg/cm2. And the cycle stability measurement shows no attenuation after 10000-cycle charge/discharge operation. Moreover, assembled asymmetric supercapacitor device (wide operation voltage of 2.3 V) delivers a maximum areal energy density of 0.36 mWh/cm2 with the areal power density of 5.57 mW/cm2. The electrochemical behavior studies and in-situ Raman reveal that the structural disorder in the low-crystalline nanograins greatly facilitate the reversible ion intercalation/deintercalation process during the electrochemical cycling process. Our results will provide an instructive route for the formulation of the design principle for the high-performance of transition metal oxides electrode material.

Phosphate Electrolyte Design for Highly Reversible Sodium Ion Batteries

Sodium ion battery (NIB) is a very promising technology for the next generation of energy storage systems because of the abundance and low cost of Na in the Earth’s crust. However, the large-scale application of NIBs is still a challenge because of limited cycle life and potential safety concerns. In this regard, electrolyte plays a critical role in both cycle life and safety of NIBs. The battery stability is directly related to the properties of the electrode-electrolyte interphase. Therefore, designing advanced electrolytes with a stable electrode-electrolyte interphase is crucial to develop stable NIBs for their practical applications in large-scale energy storage. In this work, we report a phosphate-based electrolyte for sodium ion batteries with high capacity retention and excellent coulombic efficiency (99.9 %) during long term cycling. The details together with postmortem analysis of the cycled electrode will be discussed at the presentation. The insights obtained in this work can be used to further improve cycling stability and safety of rechargeable batteries.

Review of the technologies for nitrates removal from water intended for human consumption

The goal of this paper is to review the technologies used for nitrate removal from water intended for human consumption. It also reviews the effects of nitrates on human health and the various legislative provisions in different states. The treatment technologies that will be detailed are: reverse osmosis, ion exchangers, biological denitrification and electrodialysis. For every technology, the following information will be provided: advantages, disadvantages, process performance and cost. Furthermore, there will also be examples of water treatment plants across the Globe that use these types of technologies for nitrate reduction.

Geochemical investigations of the geothermal systems from the Island of Sicily (southern Italy)

• A geochemical study on the fluids discharged in continental Sicily is presented • The models of paths circulation and fluids-rock interaction processes are depicted • The relation between the tectonic setting and the fluids geochemistry is discussed Sicily hosts many natural manifestations that include thermal waters, gas discharges and mud volcanoes. Due to the significant geodynamic and geological differences, the fluid discharges along a NE-WS–oriented transect that run from the Peloritani Mts. to the Sciacca Plain shows a large variability in water and gas chemical and isotopic compositions. The studied waters are characterized by Ca-HCO 3 , Ca(Mg)-SO 4 , Ca-Cl and Na-Cl compositions produced by distinct geochemical processes such as water-rock-gas interactions, mixing between deep and shallow aquifers and seawater and direct and reverse ion exchanges. The gas chemistry is dominated by CO 2 to the east and CO 2 -N 2 to the west of the study area, whereas the central part shows mud volcanoes discharging CH 4 -rich gases. Water isotopes suggest that the thermal waters are fed by a meteoric recharge, although isotopic exchange processes between thermal fluids and host rocks at temperature >150°C are recognized. Accordingly, liquid geothermometry suggests equilibrium temperatures up to 220°C. The carbon in CO 2 and helium isotopes of the emissions from the westernmost sector of Sicily indicate that these two gases consists of up to 40 % of a mantle component, the latter decreasing to the east down to 10% where CO 2 of thermometamorphic origin dominates. Accordingly, conceptual models of the fluid circulation for the western, central and eastern sectors are proposed. The regional geothermal reservoir, hosted in carbonates in the western sector and locally outcropping, is of low to medium temperature. Higher temperature conditions (up to 200-220°C) are suggested by geothermometry and probably related to deeper levels of the system. Sicily can be regarded as a potentially suitable area for future investigations to evaluate specific activities aimed at exploiting the geothermal resource.

Influence on Electrochemical Properties of Different Types of Manganese Oxides

Manganese oxides have been widely studied as anode materials for lithium-ion batteries because they have many advantages such as high theoretical capacity, abundant resources, low price and low environmental tox-icity. In this paper, various manganese oxide materials, i.e., MnO2, Mn3O4, MnO, (FeO)0.331(MnO)0.669 were prepared by facile methods. The above compounds were then characterized through X-ray diffraction spec-troscopy (XRD). The oxidation states of Mn in these compounds were found to be: +4, +3/+2, +2 and +2 each of them corresponding to a different crystal system, respectively: hexagonal, tetragonal cubic, cubic. The electrochemical properties of these four different manganese oxides, used as anode materials, were investigated to find the possible relationship between their valence states, crystal systems and their electrochemical properties. The results show that their electrochemical properties are influenced by their crystal system and cell parameters, while incorporating FeO into MnO has an activation effect on the reversible lithium ion in the batteries.

Temperature Sensitive and Reversible Halide Ion Exchange in Inorganic–Organic Hybrid CH3NH3PbI3−xBrx Mixed-Halide Perovskite

Ion exchange of organic-inorganic hybrid perovskite plays a significant role in controlling the performance of materials ant its devices. In this study, an interesting phenomenon was observed that the precipitate in suspension (CH3NH3PbI3−xBrx in γ-butyrolactone) brought out different colors at high and room temperature. The mechanism study appears that the phenomenon is controlled by temperature sensitive and reversible halide ion exchange in organic-inorganic hybrid CH3NH3PbI3−xBrx mixed-halide perovskite. The results of structure phase, element composition morphology and band gap illustrate that high temperature 55 °C is beneficial to the increasing of I content in MAPbI3−xBrx and room temperature or lower is advantageous to increasing of Br content in MAPbI3−xBrx. Compared with MAPbI0.76Br2.24 precipitate acquired at room temperature, MAPbI1.17Br1.83 precipitate got at high temperature illustrate wider lattice spacing, better crystallinity, better morphology and narrower band gap. The results and findings in this study will prompt the interest of readers or experts in the field of organic-inorganic hybrid perovskite materials and related optoelectronic applications.

Ultra-high gas barrier and enhanced mechanical properties of corn cellulose nanocomposite films filled with graphene oxide nanosheets

A facile and environmentally friendly route has been put forward for fabricating regenerated cellulose-based composite films (RC) with graphene oxide addition (GO). Nanocomposite films prepared through the solution blending method of cellulose solutions to a reversible ion solvent system of dimethyl sulfoxide, 1,8-diazabicyclo [5.4.0] undec-7-ene, carbon dioxide (DMSO/DBU/CO2) that contained a nano-additive of GO dispersion in DMSO. The results demonstrated that the addition of GO had a significant impact on the structural, mechanical, and gas barrier properties of the films. SEM and XRD results showed that GO was dispersed in cellulose solution uniformly. The evident red-shift of the characteristic functional groups in the Fourier transform infrared spectroscopy (FT-IR) spectra also indicated the interaction between GO and cellulose matrix. With 5 wt % GO, the oxygen permeability coefficient of corn cellulose films decreased from 1.59 × 10−12 cm3 cm cm−2 s−1 Pa−1 to 1.8 × 10−15 cm3 cm cm−2 s−1 Pa−1. Meanwhile, the thermal stability of corn cellulose film improved with the incorporation of GO.

Insight into Nickel‐Cobalt Oxysulfide Nanowires as Advanced Anode for Sodium‐Ion Capacitors

AbstractTransition metal oxides have a great potential in sodium‐ion capacitors (SICs) due to their pronouncedly higher capacity and low cost. However, their poor conductivity and fragile structure hinder their development. Herein, core‐shell‐like nickel‐cobalt oxysulfide (NCOS) nanowires are synthesized and demonstrated as an advanced SICs anode. The bimetallic oxysulfide with multiple cation valence can promote the sodium ion adsorption and redox reaction, massive defects enable accommodation of the volume change in the sodiation/desodiation process, meanwhile the core‐shell‐like structure provides abundant channels for fast transfer of sodium ions, thereby synergistically making the NCOS electrode exhibit a high reversible sodium ion storage capacity (1468.5 mAh g−1 at 0.1 A g−1) and an excellent cyclability (90.5% capacity retention after 1000 cycles). The in‐situ X‐ray diffraction analysis unravels the insertion and conversion mechanism for sodium storage in NCOS, and the enhanced capability of NCOS is further verified by the kinetic analysis and theoretical calculations. Finally, SICs consisting of the NCOS anode and a boron‐nitrogen co‐doped carbon nanotubes cathode deliver an energy density of 205.7 Wh kg−1, a power density of 22.5 kW kg−1, and an outstanding cycling lifespan. These results indicate an efficient strategy in designing a high‐performance anode for sodium storage based on bimetallic dianion compounds.

Reversible Electrochemical Energy Storage Based on Zinc-Halide Chemistry.

The development of rechargeable Zinc-ion batteries (ZIBs) has been hindered by the lack of efficient cathode materials due to the strong binding of divalent zinc ions with the host lattice. Herein, we report a strategy that eliminates the participation of Zn2+ within the cathode chemistry. The approach involves the use of composite cathode materials that contain Zn halides (ZnCl2, ZnBr2, and ZnI2) and carbon (graphite or activated carbon), where the halide ions act both as charge carriers and redox centers while using a Zn2+-conducting water-in-salt gel electrolyte. The use of graphite in the composite electrode produced batterylike behavior, where the voltage plateau was related to the standard potential of the halogen species. When activated carbon was used in the composite, however, the cell acted as a hybrid Zn-ion capacitor due to the fast, reversible halide ion electrosorption/desorption in the carbon pores. The ZnX2-activated carbon composite delivers a capacity of over 400 mAh g–1 and cell energy density of 140 Wh kg–1 while retaining over 95% of its capacity after 500 cycles. The halogen reaction mechanism has been elucidated using combinations of electrochemical and in situ spectroscopic techniques.

Na3V2O2x(PO4)2F3-2x as a stable positive electrode for potassium-ion batteries

Reversible potassium ion insertion into Na3V2O2x(PO4)2F3-2x, which is regarded as a solid solution between Na3V3+2(PO4)2F3 and Na3V4+2O2(PO4)2F is demonstrated for the first time. V3+/V4+-mixed Na3V2O2x (PO4)2F3-2x-multiwalled carbon nanotube (MWCNT) composite was prepared by a conventional hydrothermal reaction. Na3V2O2x(PO4)2F3-2x-MWCNT composite exhibiting an average electrode potential of 3.7 V in a potassium cell due to the cumulative inductive effect of phosphate fluoride oxide. The prepared composite delivers an initial discharge capacity of 118 mAh g−1 at 0.1C (13 mA g−1) rate with good cycle stability and high-rate capability performances. The electrochemical measurements, energy dispersive X-ray analysis, ex-situ, and operando X-ray diffractions provide new insights into reversible phase transformations during the subsequent cycles after an electrochemical K/Na exchange process at the initial cycle.

Increasing the Electrical Strength of the Accelerating Gap in an Electron Source with a Plasma Cathode

The stability of operation of an electron source with a plasma cathode with grid (layer) stabilization of the emission-plasma boundary and a plasma anode, whose boundary is open, is investigated. An increase in the stability of the source operation is achieved by reducing the reverse gas and ion flows, when the electron-beam trajectory changes due to the placement of the emission electrode of the electron source and a target in different planes. Calorimetric measurements of the radial distribution of the energy density of the generated electron beam were carried out under the conditions of its deflection and in the “straight” transport mode, when the collector target is on the line of sight relative to the emission electrode. It has been experimentally shown that the stability of the electron-source operation increases by several times when the beam is deflected, thus making it possible to expand the range of the beam parameters and opening up new possibilities for using such an electron source for scientific and technological purposes.

Characterization of arsenic contaminated groundwater from central Bangladesh: Irrigation feasibility and preliminary health risks assessment

To observe the current hydro-geo-chemical condition of shallow aquifers and the response from anthropogenic activities as well as to study the arsenic contents and affiliated health risks, groundwater samples from different parts of north-central Bangladesh (Tangail) were studied. In doing so, analytical parameters, including pH, total dissolved solids, electrical conductivity, dissolved oxygen, NO3−, HCO3−, Cl−, SO42-, Na, K, Ca, Mg, Fe, Cr, Mn, Ni, As, Cu, Cd, Zn, and Pb abundances were utilized. Aquifer hydrochemistry presents mainly Ca-Mg-HCO3 type water, while in some cases appreciable amount of Na+ and Cl− proclaim their presences in the formation of groundwater mineralogy. Therefore, there was significant impact from irrigation return flow to affect the groundwater hydrochemistry of this region. Source rock-water interactions in the form of dolomite and calcite weathering is the chief natural agent to provide minerals in the groundwater. The waters in the aquifer seem to be comparatively young with mostly being unsaturated in terms of carbonate minerals and having the scope of reverse ion exchange. Among the trace elements of this study average values of As, Mn, Fe, and Cd were above the guideline values, where As is the dominant contaminant in deteriorating the water quality. In terms of irrigation water indices, groundwater of the studied site is mostly suitable for agricultural usages. Although, magnesium hazard ratio and total hardness values can exert potential threats. However, As level in the studied groundwater possesses potential health hazardous for both non-carcinogenic and carcinogenic risks where children are more vulnerable than adults. The outcome this study invokes regular monitoring of groundwater quality, especially for As contamination to save the public-health.