Ion Exchange Behavior Research Articles

Sorption, kinetic and separation studies of transition and heavy metal ions using cerium amino tris-(methylene phosphonic acid)

ABSTRACT In the present study, the ion exchange behaviour of cerium (IV) amino tris-(methylenephosphonic acid) (CeATMP) towards transition and heavy metal ions has been studied by determining the values of distribution coefficient (Kd) and breakthrough capacity (BTC). Various kinetic models such as pseudo-first-order, pseudo-second-order, and intra-particle diffusion have been applied to determine ion exchange efficiency and compared with the reported works. As a result, CeATMP was found to be an efficient ion exchange material in term of a very short equilibrium time to for a metal ion to occupy an exchange site. Among the separation studies, elution behaviour of these metal ions has been executed using various acids and electrolytes media. A few binary and ternary metal ion separations also have been performed with consideration of Kd values. A study on regeneration shows that material can be reused without loss of the performance ability in term of cation exchange capacity. The present work reveals a significant use of CeATMP as an effective cation exchange material for removing and separation of inorganic contamination as environmental cleaning applications.

Correlation between Na-Cs Ion Exchange Properties in the Alkaline Form and Acid Strength in the Proton Form of Zeolite.

The ion exchange function of zeolite is useful for such a purpose as the removal of radioactive Cs species from water. In the very early days of zeolite science, the affinity of zeolites for metal cations was explained based on geometry. After the explanation presented above was proposed, many new zeolites and related materials were discovered or synthesized. Furthermore, it has become clear that the chemical nature of the ion exchange sites is strongly dependent on the framework topology. In this study, the ion exchange behavior between Na-form zeolites with different framework topologies and Cs-containing aqueous solutions was analyzed, and the equilibrium constant was calculated based on the Langmuir type equation to investigate the influence of the chemical nature of the zeolite framework on ion selectivity. The equilibrium constants at room temperature were in the order FAU < LTA < MFI < YFI < MOR. This order is the same as the order of Bro̷nsted acid strengths in the corresponding proton form zeolites. It is suggested that the delocalization of charge around the ion exchange site stabilizes a large cation whose charge is delocalized. In contrast, the equilibrium constant was not related to the pore and cavity size. This opens new insight into the influence of the chemical nature of zeolite on the affinity to cation.

Influence of MgAl–NO2-LDHs on passivation of reinforcing steel in simulated geopolymer solution

Because of ion exchange properties, the presence of layered double hydroxides (LDHs) influences passivation process of reinforcement embedded in geopolymer concrete. In this study, the ion exchange behavior of MgAl–NO2-LDHs and its effect on the characteristics of passivation film and electrochemical behavior of passive reinforcement in simulated slag-fly ash-waste ceramic powders geopolymer solution (SGP) are extensively investigated. The results indicate that LDHs with layered structure improve the protection efficiency of adsorption layer in SGP. Further, the intercalated NO2− is efficiently exchanged with OH− in SGP, thus increasing the thickness and corrosion resistance of the formed passivation film. However, because the adsorption layer halts NO2− release process, the beneficial effect is mainly observed during later immersion stage.

Anion Architecture Controls Structure and Electroresponsivity of Anhalogenous Ionic Liquids in a Sustainable Fluid.

Three nonhalogenated ionic liquids (ILs) dissolved in 2-ethylhexyl laurate (2-EHL), a biodegradable oil, are investigated in terms of their bulk and electro-interfacial nanoscale structures using small-angle neutron scattering (SANS) and neutron reflectivity (NR). The ILs share the same trihexyl(tetradecyl)phosphonium ([P6,6,6,14]+) cation paired with different anions, bis(mandelato)borate ([BMB]-), bis(oxalato)borate ([BOB]-), and bis(salicylato)borate ([BScB]-). SANS shows a high aspect ratio tubular self-assembly structure characterized by an IL core of alternating cations and anions with a 2-EHL-rich shell or corona in the bulk, the geometry of which depends upon the anion structure and concentration. NR also reveals a solvent-rich interfacial corona layer. Their electro-responsive behavior, pertaining to the structuring and composition of the interfacial layers, is also influenced by the anion identity. [P6,6,6,14][BOB] exhibits distinct electroresponsiveness to applied potentials, suggesting an ion exchange behavior from cation-dominated to anion-rich. Conversely, [P6,6,6,14][BMB] and [P6,6,6,14][BScB] demonstrate minimal electroresponses across all studied potentials, related to their different dissociative and diffusive behavior. A mixed system is dominated by the least soluble IL but exhibits an increase in disorder. This work reveals the subtlety of anion architecture in tuning bulk and electro-interfacial properties, offering valuable molecular insights for deploying nonhalogenated ILs as additives in biodegradable lubricants and supercapacitors.

Insight into ion exchange behavior of LDHs: Asynchronous chloride adsorption and intercalated ions release processes

Cl− adsorption and intercalated ions release processes during LDHs are highly intricate phenomena. In this study, ion exchange performance of LDHs with specific cation interlayers and intercalated anions (CaAl–NO3-LDHs, CaAl–NO2-LDHs, CaFeAl–NO3-LDHs and CaFeAl–NO2-LDHs) were extensively investigated. The results indicate that in the presence of low chloride concentration, the intercalated anions are prematurely released due to partial dissolution of LDHs in neutral deionized water and ion exchange with OH− in alkaline simulated concrete pore solution. Therefore, Cl− adsorption of LDHs and release process of intercalated anions in LDHs are not completely synchronized. Compared to partial LDHs dissolution, the accelerating effect of OH− exchange on intercalated anion release in simulated concrete pore solution is more pronounced. Further, higher stability of LDHs in testing solutions is mainly corresponding to higher binding energy between intercalation ions and cation interlayers, thus saturated Cl− adsorption content of NO3-LDHs with high binding energy is higher than NO2-LDHs with low binding energy, and saturated Cl− adsorption content of CaAl-LDHs with high binding energy is higher than CaFeAl-LDHs with low binding energy in testing solutions.

Synthesis, crystal structure and investigation of ion-exchange possibility for sodium tellurate NaTeO3(OH).

A new sodium tellurate has been hydrothermally synthesized and comprehensively analysed using spectroscopic and thermogravimetric techniques, resulting in the determination of its composition as NaTeO3(OH). The analysis of synchrotron X-ray and neutron diffraction data indicates that NaTeO3(OH) has a crystal structure similar to that of the previously reported tellurate, KTeO3(OH), with the space group P21/a (No. 14). NaTeO3(OH) consists of zigzag one-dimensional chains built by edge-sharing TeO6 octahedra, running parallel to the c-axis and connected to sodium and hydrogen atoms. The hydrogen atoms covalently bond to the terminal oxygen atoms on the one-dimensional chain and also form hydrogen bonds with other terminal oxygen atoms on nearby chains. The structure has been confirmed by optimization using the pseudopotential method and performing Bond Valence Sum (BVS) analysis. Although Li+ ions in LiTeO3(OH) can be exchanged reversibly with H+ ions, no ion exchange behaviour is observed in NaTeO3(OH). The difference is attributed to the size of the alkali ions and their crystal structure.

Thermodynamics of the obtained ion exchanges for the sorption of various ions in environmental wastewaters

This study focuses on investigating the thermodynamic parameters of an ion exchanger synthesized using chlorinated polypropylene with polyethylene polyamines. The ion exchanger, derived from chlorinated polypropylene, demonstrates full compliance with chemical resistance standards. The research involves the examination of isotherms governing the sorption process of Cu(II) and Ni(II) ions by the ion exchanger. These isotherms adhere to the Freundlich model, offering insights into the ion-exchange behavior of the material. Additionally, the study delves into the dynamic exchange capacity and desorption characteristics of the resulting ion exchanger in a granular state. These parameters are crucial for understanding the material's performance in practical applications, shedding light on its ability to efficiently exchange and release metal ions. By comprehensively analyzing the thermodynamic aspects and sorption behavior of the synthesized ion exchanger, this work contributes valuable knowledge to the field of ion exchange materials. The findings offer a basis for further optimization and application of such materials in various industrial processes, particularly in the removal of heavy metal ions from aqueous solutions.

Ab initio modeling of realistic tetrachloroaluminate intercalation into van der Waals electrode materials

Aluminum-ion batteries (AIBs) have recently attracted much attention due to their very fast charging and discharging speeds and excellent cycle stability. Unlike lithium-ion batteries, AIBs can be designed using a variety of ions, and the operating mechanism of ion intercalation in actual battery systems has not been fully clarified. Among them, the AIB based on tetrachloroaluminate(AlCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt;) ion has the fastest charging and discharging speed and more than 8,000 cycles of cycle stability. However, due to the large size of the AlCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; ion (∼ 5.28 Å), there has been controversy over its actual intercalation/deintercalation behavior and it is difficult to explain the characteristics of AIBs with very fast ion exchange behavior and excellent cycle stability. Theoretical studies using first-principles calculations have reported that the most stable structure when AlCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; ion is inserted into graphite is that the ion intercalation gallery of graphite should be extended to∼9 Å. However, this is in contradiction with the experimental observation results (∼5.7 Å). In this paper, we solved this discrepancy between theory and experiment, and proposed a first-principles calculation-based computational simulation model that considers more realistic ion intercalation conditions. We found that the operating mechanism of AlCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; ion intercalation can vary depending on the range of expansion of the out-of-plane lattice constant of the graphite structure. In other words, when the distance between the ion insertion galleries is physically constrained and a deformation force exists, AlCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; ion is stabilized to have a flat planar shape, which is in good agreement with the experimental observation results. We also applied the computational simulation model that considers this behavior to explain the AlCl&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;−&lt;/sup&gt; ion intercalation mechanism in 2D van der Waals electrode materials with confined out-of-plane lattice lengths, and predicted the battery performance of aluminum-ion battery electrodes in hetero-structures where different 2D materials form interfaces.

Nanoscale Ion-Exchange Materials: From Analytical Chemistry to Industrial and Biomedical Applications.

Nano-sized ion exchangers (NIEs) combine the properties of common bulk ion-exchange polymers with the unique advantages of downsizing into nanoparticulate matter. In particular, being by nature milti-charged ions exchangers, NIEs possess high reactivity and stability in suspensions. This brief review provides an introduction to the emerging landscape of various NIE materials and summarizes their actual and potential applications. Special attention is paid to the different methods of NIE fabrication and studying their ion-exchange behavior. Critically discussed are different examples of using NIEs in chemical analysis, e.g., as solid-phase extraction materials, ion chromatography separating phases, modifiers for capillary electrophoresis, etc., and in industry (fuel cells, catalysis, water softening). Also brought into focus is the potential of NIEs for controlled drug and contrast agent delivery.

A Novel Composite Hydrogel Material for Sodium Removal and Potassium Provision.

Sodium ions are commonly found in natural water sources, and their high concentrations can potentially lead to adverse effects on both the water sources and soil quality. In this study, we successfully synthesized potassium polyacrylate (KMAA) hydrogel through free radical polymerization and evaluated its capability to remove sodium ions from and supply potassium ions to aqueous solutions. To assess its performance, inductively coupled plasma emission spectroscopy (ICP) was employed to analyze the sodium ion removal capacity and potassium ion exchange capability of the KMAA hydrogel at various initial sodium ion concentrations and pH values. The results demonstrated that the KMAA hydrogel exhibited remarkable efficiency in removing sodium ions and providing potassium ions. At pH 7, the maximum adsorption capacity for sodium ions was measured at 70.7 mg·g-1. The Langmuir model, with a correlation coefficient of 0.98, was found to be more suitable for describing the adsorption process of sodium ions. Moreover, at pH 4, the maximum exchange capacity for potassium ions reached 243.7 mg·g-1. The Freundlich model, with a correlation coefficient of 0.99, was deemed more appropriate for characterizing the ion exchange behavior of potassium ions. In conclusion, the successfully synthesized KMAA hydrogel demonstrates superior performance in removing sodium ions and supplying potassium ions, providing valuable insights for addressing high sodium ion concentrations in water sources and facilitating potassium fertilizer supply.

Rapid and Selective Uptake of Radioactive Cesium from Water by a Microporous Zeolitic-like Sulfide.

The fast and efficient removal of 137Cs+ ions from water is of great significance for the further treatment and disposal of highly active nuclear waste. Hitherto, although many layered metal sulfides have been proven to be very effective in capturing aqueous cesium, three-dimensional (3D) microporous examples have rarely been explored, especially compounds that are systematically used to study cesium ion exchange behaviors. In this paper, we present detailed Cs+ ion exchange properties of a 3D, microporous, zeolitic-like sulfide, namely K@GaSnS-1, in different conditions. Isotherm studies indicate that K@GaSnS-1 has a high cesium saturation capacity of 249.3 mg/g. In addition, it exhibits rapid sorption kinetics, with an equilibrium time of only 2 min. Further studies show that K@GaSnS-1 also displays a strong preference and good selectivity for cesium, with the highest distribution coefficient Kd value up to 3.53 × 104 mL/g. Also noteworthy is that the excellent cesium ion exchange properties are well-maintained despite acidic, basic, and competitive multiple-component environments. More importantly, the Cs+-exchanged products can be easily eluted and regenerated by a low-cost and eco-friendly method. These merits demonstrated by K@GaSnS-1 render it very promising in the effective and efficient separation of radioactive cesium from nuclear waste.

Preparation of recycled poly s tyrene derivatives to remove heavy metal ions from contaminated water

In recent years, numerous researchers have concentrated on the process of turning waste into usable materials. Polystyrene and its modifications have received great attention over the past few decades due to their outstanding ion exchange behavior toward various toxic heavy metals in aqueous solutions. Therefore, this study is concerned with the preparation of three different cationic polymeric resins for the removal of Pb2+, Cd2+, and Fe3+ heavy metal ions from their contaminated water samples based on the sulfonated single-used polystyrene teacup waste (SPS), which was used to prepare sulfonated polystyrene-g-acrylamide monomer (SPS-g-Acryl) and sulfonated polystyrene-g-chitosan (SPS-g-Chit) using commercial chitosan (DD=85%) originally extracted from shrimp cortex. The concentrations of the selected heavy metal ions were measured before and after each experiment with a flame atomic absorption spectrometer (F-AAS). The analytical studies started by exploring the influence of pH (2, 4, 6, and 8) on removing the heavy metal ions Pb2+, Cd2+, and Fe3+ from their aqueous solutions. The obtained results revealed that as the pH of the analyzed ion solution is increased, the removal efficiency for ions increases. All three resins (SPS, SPS-g-Acryl, and SPS-g-Chit) had different removal efficiencies for the investigated ions, with SPS-g-Chit resin.

3D printed and stimulus responsive drug delivery systems based on synthetic polyelectrolyte hydrogels manufactured via digital light processing.

Hydrogels are three-dimensional hydrophilic polymeric networks absorbing up to and even more than 90 wt% of water. These superabsorbent polymers retain their shape during the swelling process while enlarging their volume and mass. In addition to their swelling behavior, hydrogels can possess other interesting properties, such as biocompatibility, good rheological behavior, or even antimicrobial activity. This versatility qualifies hydrogels for many medical applications, especially drug delivery systems. As recently shown, polyelectrolyte-based hydrogels offer beneficial properties for long-term and stimulus-responsive applications. However, the fabrication of complex structures and shapes can be difficult to achieve with common polymerization methods. This obstacle can be overcome by the use of additive manufacturing. 3D printing technology is gaining more and more attention as a method of producing materials for biomedical applications and medical devices. Photopolymerizing 3D printing methods offer superior resolution and high control of the photopolymerization process, allowing the fabrication of complex and customizable designs while being less wasteful. In this work, novel synthetic hydrogels, consisting of [2-(acryloyloxy) ethyl]trimethylammonium chloride (AETMA) as an electrolyte monomer and poly(ethylene glycol)-diacrylate (PEGDA) as a crosslinker, 3D printed via Digital Light Processing (DLP) using a layer height of 100 μm, are reported. The hydrogels obtained showed a high swelling degree q∞m,t ∼ 12 (24 h in PBS; pH 7; 37 °C) and adjustable mechanical properties with high stretchability (εmax ∼ 300%). Additionally, we embedded the model drug acetylsalicylic acid (ASA) and investigated its stimulus-responsive drug release behaviour in different release media. The stimulus responsiveness of the hydrogels is mirrored in their release behavior and could be exploited in triggered as well as sequential release studies, demonstrating a clear ion exchange behavior. The received 3D-printed drug depots could also be printed in complex hollow geometry, exemplarily demonstrated via an individualized frontal neo-ostium implant prototype. Consequently, a drug-releasing, flexible, and swellable material was obtained, combining the best of both worlds: the properties of hydrogels and the ability to print complex shapes.

Ion exchange behavior of astatine and bismuth

Astatine sorption by ion exchange resins from nitric acid media.

Imidazolium-Modified Silica Gel for Highly Selective Preconcentration of Ag(I) from the Nitric Acid Medium

The ion-exchange behavior of an organomineral material with an imidazolium (1-methyl-3-(prop-2-yn-1-yl)-1H-imidazol-3-ium bromide)-modified silica gel was studied for the extraction of Ag(I) from nitric acid media. The extraction from multicomponent systems containing Fe(III), Co(II), Ni(II), Cu(II), Pb(II), and Mn(II) in 100- and 1000-fold molar excesses with respect to Ag(I) was shown to occur with high selectivity. Based on the data of X-ray diffraction and X-ray fluorescence spectroscopy for samples of modified silica gel, a mixed ion exchange–adsorption mechanism for the extraction of Ag(I) was proposed. The effect of the phase contact time and the concentration of nitric acid on the distribution coefficient of Ag(I) was studied. The selectivity factors of the extraction of Ag(I) from multicomponent systems containing foreign cations in 100- and 1000-fold molar excesses under steady-state and dynamic concentration conditions were calculated.

Characterization and Optimization of Polymeric Bispicolamine Chelating Resin: Performance Evaluation via RSM Using Copper in Acid Liquors as a Model Substrate through Ion Exchange Method.

Advanced technologies of electronics industries have led to environmental contamination concerns, especially waste print circuit boards containing a very high concentration of copper (II) ions, which can be discharged in wastewater containing many contaminated metals. A low pH is a necessity for treating industrial wastewater containing heavy metals to meet engineering process design. A novel polymeric bispicolamine chelating resin, Dowex-M4195, was applied as an alternative for investigating the behavior of copper (II) in acidic solution via an ion exchange method in a batch experiment system. Characterization of physical and chemical properties before and after ion exchange were also explored through BET, SEM-EDX, FTIR and XRD. Response surface methodology was also applied for optimization of copper (II) removal capacity using design of experiment for selective chelating resin at a low pH. The results indicate that H+ Dowex-M4195 chelating resin had a high-carbon content and specific surface area of >64% and 26.5060 m2/g, respectively. It was predominantly macropore porous in nature due to the N2 gas adsorption isotherm and exhibited type IV with insignificant desorption hysteresis loop of H1-type. It was spherical and cylindrical. After the ion exchange process of copper (II)-loaded H+ Dowex-M4195, the specific surface area and total pore volume decreased by about 17.82% and 5.39%, respectively, as compared to H+ Dowex-M4195. Hysteresis loop, isotherm and pore size distribution were also similar. Regarding the functional group, the surface morphology and crystalline structures of H+ Dowex-M4195 showed copper (II) compound based on the structure of chelating resin that confirmed effective ion exchange behavior. The design of optimization indicated that copper (II) removal capacity of about 31.33 mg/g was achieved, which could be obtained at 6.96 h, pH of 2 (a desirable low pH), dose of 124.13 mg and concentration of 525.15 mg/L. The study indicated that the H+ Dowex-M4195 (which is commercially available on the market) can successfully be applied as an alternative precursor through the ion exchange method for further reuse and regeneration of the copper (II) in the electronic waste industries and other wastewater applications needed to respond the policy of biocircular green economy in Thailand.

Molecular dynamics simulation of hydration and free energy of ions in nanochannels of polyelectrolyte threaded metal organic framework and the impacts on selective ion transport

Hierarchical porous materials constructed by threading polyelectrolyte in metal organic framework (MOF) display superior ion exchange behavior. To understand the ion exchange and ion transport mechanism, we conduct molecular dynamics simulations of ions inside the nanochannel of a MOF that is threaded with a polyelectrolyte (polyelectrolyte∼MOF), specifically the poly(sodium vinyl sulfonated-co-acrylic acid)∼MIL-53(Al). We compute the free energy change and hydration number for four representative ions, Na+, K+, Cl− and Mg2+ in the absence and presence of poly(sodium vinyl sulfonated-co-acrylic acid) in a channel of MIL-53(Al). The free energy barrier to ion entry, and the interaction between ion and polyelectrolyte help to understand the selectivity in ion transport. The negative charge of polyelectrolyte can exert a repulsion to anion and attract cation in the neighboring channel of MOF, as indicated by the lower energy valley for monovalent cations Na+ and K+, and higher energy barrier for Cl−. The second hydration shell explains size-selective prohibition of the transport of divalent Mg2+ in the nanochannel of MIL-53(Al). Our results demonstrate that the ion selectivity is attributed to the synergistic effect of charge and size-exclusion of the polyelectrolyte∼MOF structure.

Ion exchange behavior of novel Pani -Ti(IV) phosphosulphosalicylate hybrid cation exchange material for the selective separation of Pb(II) in environmental remediation

ABSTRACT A new hybrid cation exchange material PANI-Ti(IV) phosphosulphosalicylate was synthesized by intercalating polyaniline (PANI) into Ti(IV) phosphosulphosalicylate (Ti(IV) PSS) using sol-gel chemical route. Then, it is renewed into H+ form and used as an adsorbent for the removal of Pb(II) from aqueous solution. The morphology and structure properties of the as prepared hybrid cation exchange material were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET), thermo gravimetric analysis (TGA-DTG), and Transmission Electron Microscopy (TEM). The sorption experiment for Pb(II) removal was performed using batch method. Dependence of adsorption on contact time, exchanger dose, Pb(II) initial concentration, pH, and temperature has been studied to achieve the optimum conditions. The adsorption isotherm, kinetics, and thermodynamics of PTPSS for Pb(II) were studied. The results of the above mentioned analyses show that the adsorption isotherm process of Pb(II) on PTPSS was closely related to Langmuir model (r2 > 0.998). The adsorption kinetic process fits well with the pseudo-second order equation. Thermodynamic studies suggested the spontaneous and exothermic nature of PTPSS system. The ion exchange adsorbent shows ion exchange capacity for Li+, Na+, and K+ ions have been found to be 1.75, 2.24, and 2.41 meq/g, respectively. Its selectivity was examined by achieving some important binary separations like Pb2+- Cd2+, Pb2+- Hg2+, Pb2+- Cu2+, Pb2+- Zn2+, Pb2+- Ni2+, and Pb2+- Fe3+ on its column. On the basis of distribution studies (Kd values), PTPSS was highly selective for Pb(II). Therefore, the hybrid cation exchange material PTPSS can be used as a potential ion exchange material for the selective separation of Pb(II) ion in environmental remediation.

Lanthanide ion exchange modulated via crystalline phase transition of a mixed-metal coordination polymer based on bis(4-nitrophenyl) phosphate

We previously reported that the CeL3 [L = bis(4-nitrophenyl) phosphate] coordination polymer (CP) exhibits exceptionally large differences in ion exchange selectivity toward neighboring ions in the lanthanide series (Ln3+). Herein we aimed to elucidate the mechanism of the unique ion-exchange behavior of CeL3 by focusing on the formation reaction of a mixed-metal CP (MM-CP) and the phase transition between two crystalline types, which occurs during the course of the ion-exchange reaction. The results of powder X-ray diffractometry of the de novo-synthesized MM-CPs indicated that the Ln3+-to-Ce3+ mixing limit, xlim, in the crystal is an important factor that determines the feasibility of the structural transition. Smaller Lu3+, Yb3+, and Tm3+ electrostatically interact with ligand molecules very strongly, which causes structural strain in MM-CP. Thus, the crystal-to-crystal structural transition tends to occur when the Ln3+ mixing ratio (x) is above xlim (∼0.2). The exchange of Ce3+ for Ln3+ (=Lu3+, Yb3+, and Tm3+) in the MM-CPs is further facilitated following structural transition because the crystalline structure formed after phase transition is known to prefer the heavy Ln3+ ions to Ce3+. In addition, the crystal lattice contracts during structural transition, and the intact CeL3 inside the particles is exposed to the solution phase, which may result in ion-exchange proceeding as a chain reaction. Hence, Ce3+-for-Ln3+ exchange is accelerated when x > xlim and disfavored when x < xlim. Consequently, large Ln3+-dependent differences in final reactivity are observed.

New insights into the arrangement pattern of layered double hydroxide nanosheets and their ion-exchange behavior with phosphate

As an ion-exchange type material, layered double hydroxides (LDH) can effectively remove phosphate from wastewater to prevent eutrophication. The exchange reaction occurs only between LDH lamellae, which is directly related to the arrangement of LDH nanosheets. Consequently, understanding the effect of LDH’s arrangement structure on ion-exchange properties is essential for its application in phosphate sequestration, which, however, is still missing. Here, we used oven-drying and freeze-drying methods to prepare two types of LDH with different arrangement patterns (O-LDH and F-LDH). A new method was established to quantitatively evaluate the ion-exchange process. Results show that the chemical functional groups of O-LDH and F-LDH were similar, but O-LDH nanosheets exhibited a bent and disordered stacking morphology, while F-LDH was arranged in parallel. The disordered structure enabled O-LDH to form pore sizes and volumes up to 6.86 and 2.96 times that of F-LDH, respectively. Besides, the phosphate capture capacity of O-LDH was 5.01 mg/g larger than that of F-LDH, and the kinetic rate was 24.0%-26.7% faster than F-LDH. The disordered stacking of O-LDH enabled it to exchange ions in all spatial direction, and its larger pore space facilitated this process. Moreover, the bending cross section of O-LDH provided additional ion-exchange channels, which reduced the ion transport distance and increased the exchange rate. This work reveals the relationship between the stacking pattern of LDH nanosheets and their ion-exchange behavior, which provides new insights and methods for solving similar ion-exchange problems.