Ion Exchange Rate Research Articles

DFT calculation and experiments for Li+/H+ ion-exchange on titanium-based lithium ion-sieves

Titanium-based lithium ion-sieves (H2TiO3) with the layered structure is an excellent adsorbent for lithium recovery from brines, since it has a high theoretical Li+ ions adsorption amount (∼142 mg/g) and a stable structure under acid regeneration. However, the formation of the strong H–O bonds in H2TiO3 leads to a greater energy barrier for re-adsorption of lithium ions, so it would be difficult to reach the theoretical lithium adsorption capacity in practical application. Moreover, the influence of H+ content in brine (pH value) on the Li+ ion adsorption amount is obvious, that limits the lithium recovery efficiency from brines. In this work, Li+/H+ ion-exchange mechanism of layered H2TiO3 (HTO) ion-sieve is investigated through DFT calculation, where the Li+ ion adsorption energies for three kinds of Li+/H+ ion-exchange pathways are calculated, and the order of priority for Li+/H+ ion-exchange is deduced and validated based on the experimental data of Li+ ions adsorption on the prepared nanometer HTO ion-sieve. Then, a quantitative relationship between Li+ ion adsorption amounts on HTO ion-sieve and pH values in Li+-containing solution is developed on the basis of the experimental data. When the nanometer HTO ion-sieve powders are formed into the millimeter PVB-HTO ion-sieve granules for industrial application, it is found that the formation of an acidic micro-environment inside of this PVB-HTO granule obviously reduces the Li+ ions adsorption rate, especially in the initial stage of Li+/H+ ion-exchange process. Finally, an improved strategy of Li+/H+ ion-exchange rate on PVB-HTO granules from a carbonate-type brine is experimentally demonstrated utilizing a batch and a fixed-bed adsorber, respectively.

Liquid bath-assisted combustion activation preparation of nitrogen/sulfur-doped porous carbon for sodium-ion battery applications

A liquid-bath-assisted salt-template combustion activation method has been developed to overcome the shortcomings of the conventional template method, including elaborate processes and environmental pollution. Herein, N/S double-doped porous carbon material (ECSK-15) with high specific surface area (1148.60 m2 g−1) is synthesized through it for sodium-ion batteries (SIBs). Benefitting from this approach, the number of ion diffusion channels and the ion exchange rate of the product are significantly increased. When using ether-based electrolyte, after 1000 cycles at a large current density of 2 A g−1, the reversible capacity could still be maintained at 135.60 mA h g−1. The assembled full cell exhibits a high reversible capacity of 480.49 mAh g−1 at a current rate of 0.5 A g−1. The energy density is calculated to be 204.11 Wh kg−1 at a power density of 160.71 W kg−1. This work provides a porous carbon anode material with good sodium-ion storage capacity and rate performance for application in SIBs.

Synthesis of Low-Silicon X-Type Zeolite from Lithium Slag and Its Fast Exchange Performance of Calcium and Magnesium Ions.

Without the addition of silicon and aluminum sources, a pure-phase KNaLSX zeolite was successfully synthesized from the residue (lithium slag), which was produced from spodumene in the production process of lithium carbonate. The KNaLSX samples were characterized by an X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), X-ray Fluorescence Spectrometer (XRF), Thermogravimetric Differential Thermal Analysis (TG-DTA), Fourier Transform Infrared Spectrometer (FT-IR), and N2 adsorption measurement. The ion exchange capacity and the ion exchange rate of calcium and magnesium ions were measured as used for a detergent builder, and the results were compared with the standard zeolites (KNaLSX and 4A). The experimental results show that the pure-phase KNaLSX synthSynthesis and characterization of co-crystalline zeolite composite of LSX/esized from lithium slag has a SiO2/Al2O3 ratio of 2.01 with a grain size of 3~4 μm, which is close to the commercial KNaLSX sample of a SiO2/Al2O3 ratio of 2.0. The BET-specific surface area of KNaLSX is 715 m2/g, which is larger than the low-silicon X-type zeolite (LSX) synthesized from waste residue reported in the literature. The ion exchange rate constant of calcium and magnesium ions in KNaLSX is 5 times and 3 times that of 4A zeolite, respectively. KNaLSX also has a high ion exchange capacity for magnesium ion of 191 mgMgCO3/g, which is 2 times than that of 4A zeolite, and a high ion exchange capacity for calcium ion of 302 mgCaCO3/g, which meets the first-grade standard of zeolite for detergent builders in China. The work provides the basis for high-value resource utilization of lithium slag and the development of a detergent builder for rapid washing.

Open-Framework Vanadate as Efficient Ion Exchanger for Uranyl Removal.

The elimination of uranium from radioactive wastewater is crucial for the safe management and operation of environmental remediation. Here, we present a layered vanadate with high acid/base stability, [Me2NH2]V3O7, as an excellent ion exchanger capturing uranyl from highly complex aqueous solutions. The material possesses an indirect band gap, ferromagnetic characteristic and a flower-like morphology comprising parallel nanosheets. The layered structure of [Me2NH2]V3O7 is predominantly upheld by the H-bond interaction between anionic framework [V3O7]nn- and intercalated [Me2NH2]+. The [Me2NH2]+ within [Me2NH2]V3O7 can be readily exchanged with UO22+. [Me2NH2]V3O7 exhibits high exchange capacity (qm = 176.19 mg/g), fast kinetics (within 15 min), high removal efficiencies (>99%), and good selectivity against an excess of interfering ions. It also displays activity for UO22+ ion exchange over a wide pH range (2.00-7.12). More importantly, [Me2NH2]V3O7 has the capability to effectively remove low-concentration uranium, yielding a residual U concentration of 13 ppb, which falls below the EPA-defined acceptable limit of 30 ppb in typical drinking water. [Me2NH2]V3O7 can also efficiently separate UO22+ from Cs+ or Sr2+ achieving the highest separation factors (SFU/Cs of 589 and SFU/Sr of 227) to date. The BOMD and DFT calculations reveal that the driving force of ion exchange is dominated by the interaction between UO22+ and [V3O7]nn-, whereas the ion exchange rate is influenced by the mobility of UO22+ and [Me2NH2]+. Our experimental findings indicate that [Me2NH2]V3O7 can be considered as a promising uranium scavenger for environmental remediation. Additionally, the simulation results provide valuable mechanistic interpretations for ion exchange and serve as a reference for designing novel ion exchangers.

RESEARCH AND MODELING KINETICS ION EXCHANGE INTERACTIONS

In detail, this study analysed the kinetics of ammonium ion adsorption under dynamic conditions in the "clinoptilolite -ammonium ion" system. The work includes constructing a mathematical model of this process, which allows us to estimate and predict its essential characteristics. Calculations of mass transfer coefficients revealed their dependence on the intensity of medium mixing. A significant result is that ion exchange occurs in externally diffusion and intradiffusion regions. Ion exchange rate constants were calculated for the regions of external and internal diffusion, contributing to a deeper understanding of the mechanisms of this complex process. The research results will expand our knowledge about ion exchange interactions in the " clinoptilolite -ammonium ion" system. In addition, they can be used to optimise the conditions of ammonium adsorption in similar systems, which is essential for practical applications related to water purification and other media from ammonium ions.

Niobium-Tungsten Bimetallic Oxide Electrodes with High Dual-Band Electrochromic Performance Prepared by Hydrothermal Method

Dual-band electrochromic (EC) smart windows, capable of selectively regulating visible (VIS) and near-infrared (NIR) light, are one of the most attractive candidates for significantly reducing the energy consumption of buildings. Niobium-tungsten bimetallic oxides exhibit a fast ion exchange rate and high cycle stability in the electrochemical field because of various structural chemistry in the pseudobinary system Nb2O5/WO3, showing excellent dual-band EC potential. Herein, we employ a facile hydrothermal technique to synthesize Nb18W16O93 (NWO) films with low temperature and facile procedure. The obtained NWO films exhibit impressive dual-band electrochromic performances, including high optical regulation (radiation blocking rates of 33.1% and 77.5% in the VIS and NIR band) and short coloring/bleaching time (12 s/2.6 s at 633 nm and 6.5 s/6.1 s at 1600 nm). These results demonstrate that NWO is a high-performance dual-band EC material and provide a practical strategy to synthesize the NWO electrodes with nanorod stacking architectures in a facile and low-cost way.

Use the hot spring’s Chloro-Alkaline Index (CAI) for the low enthalpy prospect of the Rawadanau geothermal field

The emergence of hot springs along the volcanic shelf in Indonesia is a feature of geothermal manifestations. The geothermal system is affected by heat sources, reservoir rocks, cap rocks, and meteoric water that fills and escapes as hot springs through fractures. The Rawadanau geothermal field in Serang Banten is low enthalpy prospects. Geothermal maintenance is defined by the chemical composition of the hot springs, one of which can be determined by the ion exchange rate, namely the chloro-alkaline index (CAI) method. There are 16 hot spring samples, with temperatures (31.2 - 54.6 °C), pH (6.2 – 7.3), and EC (1190 – 4460 μS/cm), respectively. The water types encountered are Na-Cl in the southern and Mg-Ca-HCO3, and Na-Mg-Ca-HCO3-Cl in the northern and western, respectively. Generally, samples taken in the rainy show negative CAI and positive CAI in the dry, while Cl-type is positive in two seasons. Based on water type and CAI show that the Na-Cl type tends to be positive in the two seasons. While the Ca-Mg-HCO3 type is positive in the dry and negative in the rainy, and the Mixed-type shows a negative CAI. The results of this study provide information for the maintenance of geothermal fields as they are developed.

Tuning the Zn2+ solvation structure in dual-salts hybrid aqueous electrolyte to stabilize the Zn metal anode

Aqueous Zn-ion battery is expected to become a substitute for Li-ion battery due to its inherent safety, low cost, and environmental friendliness. Dendrite growth and side reaction problems during electroplating lead to its low Coulombic efficiency and unsatisfactory life, which greatly limits its practical application. Here, we propose a dual-salts hybrid electrolyte, which alleviates the above issues by mixing Zn(OTf)2 to ZnSO4 solution. Extensive tests and MD simulations have shown that the dual-salts hybrid electrolyte can regulate the solvation structure of Zn2+, facilitating uniform Zn deposition, and inhibiting side reactions and dendrite growth. Hence, the dual-salts hybrid electrolyte exhibits good reversibility in Zn//Zn batteries, which can provide a lifetime of more than 880 h at 1 mA cm−2 and 1 mAh cm−2. Moreover, the average Coulombic efficiency of Zn//Cu cells in hybrid system can reach 98.2% after 520 h, much better than that of 90.7% in pure ZnSO4 electrolyte and 92.0% in pure Zn(OTf)2 electrolyte. Benefiting from the fast ion exchange rate and high ion conductivity, Zn-ion hybrid capacitor in hybrid electrolyte also displays excellent stability and capacitive performance. This effective strategy for dual-salts hybrid electrolytes provides a promising direction for designing aqueous electrolytes for Zn-ion batteries.

Toward Understanding of the Li-Ion Migration Pathways in the Lithium Aluminum Sulfides Li3AlS3 and Li4.3AlS3.3Cl0.7 via 6,7Li Solid-State Nuclear Magnetic Resonance Spectroscopy.

Li-containing materials providing fast ion transport pathways are fundamental in Li solid electrolytes and the future of all-solid-state batteries. Understanding these pathways, which usually benefit from structural disorder and cation/anion substitution, is paramount for further developments in next-generation Li solid electrolytes. Here, we exploit a range of variable temperature 6Li and 7Li nuclear magnetic resonance approaches to determine Li-ion mobility pathways, quantify Li-ion jump rates, and subsequently identify the limiting factors for Li-ion diffusion in Li3AlS3 and chlorine-doped analogue Li4.3AlS3.3Cl0.7. Static 7Li NMR line narrowing spectra of Li3AlS3 show the existence of both mobile and immobile Li ions, with the latter limiting long-range translational ion diffusion, while in Li4.3AlS3.3Cl0.7, a single type of fast-moving ion is present and responsible for the higher conductivity of this phase. 6Li-6Li exchange spectroscopy spectra of Li3AlS3 reveal that the slower moving ions hop between non-equivalent Li positions in different structural layers. The absence of the immobile ions in Li4.3AlS3.3Cl0.7, as revealed from 7Li line narrowing experiments, suggests an increased rate of ion exchange between the layers in this phase compared with Li3AlS3. Detailed analysis of spin-lattice relaxation data allows extraction of Li-ion jump rates that are significantly increased for the doped material and identify Li mobility pathways in both materials to be three-dimensional. The identification of factors limiting long-range translational Li diffusion and understanding the effects of structural modification (such as anion substitution) on Li-ion mobility provide a framework for the further development of more highly conductive Li solid electrolytes.

Dynamic ion exchange engineering BiOI-derived Bi2O2CO3 to promote CO2 electroreduction for efficient formate production

Prompt production of bismuth subcarbonate (Bi2O2CO3) intermediate is crucial for high-efficiency formate production and preservation of the bismuth-oxygen (Bi-O) structures during electrochemical CO2 reduction reaction (CO2RR) catalyzed by Bi-based catalyst. In this work, we investigate the CO2RR performance of bismuth oxyhalide (BiOX, including BiOCl, BiOBr and BiOI) catalysts with nanosheet-assembling microsphere morphology and develop an effective strategy of engineering BiOI-derived Bi2O2CO3 through dynamic ion exchange reaction to promote formate production from CO2RR. Among investigated BiOX catalysts with nanosheet-assembling microsphere morphology, BiOI exhibits the highest ion exchange rate due to the large interlayer spacing and low binding energy between [Bi2O2]2+ layer and I− ion. The produced BiOI-derived Bi2O2CO3 inherits the large interlayer spacing of BiOI and thus facilitates diffusion of HCO3– ions to promote CO2RR for formate production. By comparison with BiOCl and BiOBr, BiOI exhibits better CO2RR performance, achieving faradaic efficiency of 98 % with a current density of 42.0 mA cm−2 and excellent long-term durability. Mechanism studies demonstrate that the sufficient supply of HCO3– ions resulted from large interlayer spacing of BiOI-derived Bi2O2CO3 significantly promotes formate production and, in turn, improves the resistance of Bi-O structures to electroreduction. This work provides a deep insight into the mechanism of BiOX-catalyzed CO2RR for formate production, opening up new opportunities for developing high-performance CO2RR catalysts.

3D Printed Thick Reduced Graphene Oxide: Manganese Oxide/Carbon Nanotube Hybrid Electrode with Highly Ordered Microstructures for Supercapacitors

AbstractHigh capacitance and good rate performance supercapacitors are needed to power sensors and miniaturized electrical devices. Thick electrodes are promising to increase the mass loading of active materials in supercapacitors, but the 3D geometries and microstructures in thick electrodes still hinder the development with high electron and ion exchange rate and accessible active sites. The scaffold 3D electrodes of reduced graphene oxide:manganese oxide/carbon nanotube (rGO:MnOx/CNT) are manufactured by material extrusion 3D printing (ME3DP), where the mass ratio of rGO to MnOx/CNT composites, thickness, and mass loading per unit area are controllable. The increasing amount of MnOx/CNT composites boosts the areal capacitance. Although the rate capability decays fast with the increasing of MnOx/CNT, it remains stable at different thicknesses (1.2, 1.6, and 2 mm). 2 mm thick rGO:MnOx/CNT (weight ratio 5:3) electrode exhibits an area capacitance of 302.13 mF cm−2 at a current density of 0.5 mA cm−2, due to the highly ordered rGO networks. Compared to the casted electrodes, the microstructures in the 3D printed electrode contribute to lower resistances for the charge and ion transportation.

In situ synthesis of magnesium-doped hydroxyapatite aerogel for highly efficient U(VI) separation with ultra high adsorption capacity and excellent recyclability

Mg-doped HAP aerogel (MHAPA) was firstly in situ prepared via freeze-drying-calcination technology to capture U(VI). The U(VI) removal capacity by MHAPA even arrived 2685.6 mg g−1, which was about 2 times over purchased HAP, illustrating that the incorporation of Mg ions could greatly enhance the U(VI) removal capacity. Compared with HAP, MHAPA also showed better anti-ion interference ability and dynamic removal performances. In comparison with other HAP-based adsorbents, MHAPA possessed good recyclability and its desorption rate was up to 93.4% in the first cycle. The excellent U(VI) removal performances of MHAPA might be owing to its low crystallinity and grain size, fast ion exchange rate and partial ionization under acidic conditions, which would accelerate the process of electrostatic attraction, ion-exchange, and complexation to immobilize U(VI). To sum up, the prepared MHAPA was expected to be an environmentally friendly, recyclable and effective adsorbent to immobilize U(VI) in actual wastewater.

Effect of graphene oxide on corrosion resistance and biological activity of micro arc oxidation ceramic layer on titanium alloy

• The adhesion between ceramic layer prepared by two-step MAO and substrate is fine. • When GO content is 0.112 g/L, the adhesion between MAO layer and substrate is higher. • The corrosion resistance is improved by adding GO and it is related to GO content. • CaP-0.112GO sample has highest polarization resistance and best corrosion resistance. • GO added increases ion exchange rate and improves biological activity of MAO layer. The calcium-phosphorus ceramic layer is prepared on titanium alloy by two-step micro-arc oxidation (MAO). The effect of graphene oxide (GO) on microstructure, corrosion resistance and biological activity of MAO layer was studied. The MAO layer surface is rough and porous. When GO is added 0.112 g/L, the corrosion resistance of MAO layer and the adhesive force between MAO layer and substrate are higher. GO added improves the biological activity of MAO layer.

Influence of Mixed Na2O/K2O on Chemical Durability and Spectral Properties of P2O5-Al2O3-BaO-K2O-Na2O-Nd2O3 Phosphate Glasses.

A series of 56P2O5-7.5Al2O3-5.9BaO-(28.56-x)K2O-xNa2O-1.51Nd2O3 phosphate glasses with different Na/(Na+K) ratios, which were specially designed for high-power laser application, were prepared by a high-temperature melting method. Except for the density, refractive index, glass transition temperature, and DC conductivity, the chemical durability and spectral properties, as emphasized by high-power and high-energy laser material, were further measured and analyzed. Regarding the chemical durability, the dissolution rates of these glasses do not show an evident mixed alkali effect with increasing the Na/(Na+K) ratio, although the effect is obvious for the glass transition temperature and DC conductivity. To better understand the nature of the dissolution mechanism, the ionic release concentrations of every element are determined. Both Na and K undergo ion exchange, but the ion exchange rate of K is much larger than that of Na. In terms of the spectral properties, the J-O parameters, emission cross-section, radiation lifetime, fluorescence lifetime, effective bandwidth, fluorescence branching ratio, and quantum efficiency are determined from absorption and emission spectra. The trend of Ω2 deviating from linearity indicates that the coordination environment symmetry of Nd3+ ions and the covalence of Nd-O also present an evident mixed alkali effect. The most important finding is that the emission cross-section and fluorescence lifetime of Nd3+ ions at 1053 nm were not affected by the change in the Na/K ratio. According to the above experimental results, the optimized value of the Na/K ratio was determined, based on which the 56P2O5-7.5Al2O3-5.9BaO-(28.56-x)K2O-xNa2O-1.51Nd2O3 glass maintains a high emission cross-section with good chemical durability.

Synthesis of Anion Exchange Membranes Containing PVDF/PES and Either PEI or Fumion®.

In this work, the preparation of dense blended membranes, from blends of poly(vinylidene fluoride) (PVDF), poly(ether sulfone) (PES) and polyethyleneimine (PEI) or Fumion®, with possible applications in alkaline fuel cell (AEMFC) is reported. The blended PEI/Fumion® membranes were prepared under a controlled air atmosphere by a solvent evaporation method, and were characterized regarding water uptake, swelling ratio, thermogravimetric analysis (TGA), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), ion exchange capacity (IEC), OH− conductivity and novel hydroxide ion exchange rate (HIER), which is related to the mass transport capacity of the OH− ions through the membrane. The effect of the chemical composition on its morphological and anion exchange properties was evaluated. It was expected that the usage of a commercial ionomer Fumion®, in the blended membranes would result in better features in the electrical/ionic conductivity behaviour. However, two of the membranes containing PEI exhibited a higher HIER and OH− conductivity than Fumion® membranes, and were excellent option for potential applications in AEMFC, considering their performance and the cost of Fumion®-based membranes.

Reinforced adsorption mechanism of fluorine ions by calcium-depleted hydroxyapatite and application in the raffinate from the vanadium industry

Calcium-deficient hydroxyapatite (Ca-d HAP), an adsorbent of high defluoridation capacity with lattice defect, was prepared from vanadium industrial waste neutralization slag (NS). The adsorption performance was compared to commercially available stoichiometric HAP (S-HAP) under different solution conditions, and Ca-d HAP was superior to S-HAP. The specific surface area of Ca-d HAP was considerable (118.32 m2/g), which was 3.176 times larger than that of S-HAP (37.25 m2/g), and this was the main reason for the strong adsorption performance of Ca-d HAP. Meanwhile, due to the presence of minor impurities, such as Al and Fe, in NS, the doping of Al and Fe reduced the crystallinity after Ca-d HAP synthesis, which provided additional active sites for binding to other ions. In addition, combined with characterization analysis, it was speculated that some Ca ions in Ca-d HAP were replaced by Na ions with stronger ion-exchange properties, enhancing its adsorption performance. The adsorption mechanism of Ca-d HAP on F- ions was further investigated by discussing the surface potential, initial pH, adsorbent dosage, initial fluorine concentration, adsorption thermodynamics, and kinetics. Results showed that the Langmuir isothermal model well predicts the adsorption behavior of Ca-d HAP on F- ions at pH 3.5, with a maximum adsorption capacity of 277.78 mg/g, which is larger than most HAP adsorbents reported in the literature. In addition, the percentage adsorption of Ca-d HAP on F- ions was > 99 % in the raffinate and the NaF solution. In addition, the percentage adsorption of Ca-d HAP on F- ions was > 99 % both in the raffinate and in the NaF solution. The adsorption of F- ions by Ca-d HAP is a heat absorption process, with the ΔG° < 0 at various temperatures, demonstrating the reaction's spontaneity of the reaction. The pseudo-second-order model better described the adsorption kinetics data at 303 to 333 K, and the adsorption was regulated by chemical reactions. Overall, Ca-d HAP with lattice defects has a large ion-exchange rate and specific surface area, which is the key reason for the high adsorption performance of Ca-d HAP. Therefore, this technology provides a prospect for treating acidic wastewater with high fluorine content in the vanadium industry.

Bioactive antibacterial borate glass and glass-ceramics

This work aimed to study bioactive glass-ceramics obtained by controlled crystallization, as a function of the heat treatment time, in system 59.5B2O3-2P2O5-9.5CaO-19.5Na2O-9CaF2-0.5Ag2O (mol %). The samples were prepared by the melt-quench method, and thermally treated at 530 °C, with different times: 0, 4, 8, 12, 24 and 36 h. Results of DTA, XRD, FTIR, density and molar volume are shown. The results of XRD revealed the development of crystalline phases during the heat treatment (CaNaB5O9, Ca3(PO4)2, Na2B6O10 and Ag°). The percentage of crystallization and in the size of the crystallite show increases with the time of the heat treatment, as expected. In vitro bioactivity of the samples was analyzed by immersion in SBF for 7, 14, 21 and 28 days. XRD patterns and FTIR spectra after immersion proved HA precipitation. The pH results reveal a higher ion exchange rate for the crystallized samples. This can be associated with the microstructure changes that occur on the surface of the samples during the heat treatment and the solubility of the crystalline phases. In addition, glass and crystallized samples showed antibacterial action against E. coli, independently of the crystallization time. It is possible to conclude that glass-ceramics can potentially be used as biomaterials in the treatment of bone fractures.

Five state factors control progressive stages of freshwater salinization syndrome.

Factors driving freshwater salinization syndrome (FSS) influence the severity of impacts and chances for recovery. We hypothesize that spread of FSS across ecosystems is a function of interactions among five state factors: human activities, geology, flowpaths, climate, and time. (1) Human activities drive pulsed or chronic inputs of salt ions and mobilization of chemical contaminants. (2) Geology drives rates of erosion, weathering, ion exchange, and acidification-alkalinization. (3) Flowpaths drive salinization and contaminant mobilization along hydrologic cycles. (4) Climate drives rising water temperatures, salt stress, and evaporative concentration of ions and saltwater intrusion. (5) Time influences consequences, thresholds, and potentials for ecosystem recovery. We hypothesize that state factors advance FSS in distinct stages, which eventually contribute to failures in systems-level functions (supporting drinking water, crops, biodiversity, infrastructure, etc.). We present future research directions for protecting freshwaters at risk based on five state factors and stages from diagnosis to prognosis to cure.

How Does Ion Exchange Construct Binary Hexacyanoferrate? A Case Study.

In this work, using electrochemical active Fe as an ion-exchange element (attack side) and the NaxMnFe(CN)6 slurry with a high solid content (MnHCF) as a template (defensive side), a series of binary hexacyanoferrates are prepared via a simple Mn/Fe ion-exchange process, in which NaxFeFe(CN)6 (FeHCF) and solid solution Nax(FeMn)Fe(CN)6 are concentrated on the shell and the core, respectively. The proportions of the two structures are mainly controlled by the competition between the ion-exchange rate in the bulk material and dissolution-reprecipitation rate. Slowing down the attacking rate, such as the use of a chelating agent complexed with the attacker Fe, is advantageous to form a thermodynamically metastable state with homogeneous distribution of elements since the diffusion of Fe2+ in the solid MnHCF is relatively fast. The shell FeHCF could be adjusted by the dissolution-reprecipitation rate, which is driven by the solubility difference. Adding the chelating agent in the defensive side will promote the dissolution of MnHCF and reprecipitation of FeHCF on the surface. Meanwhile, with the increase of Fe sources, the thickness of the shell FeHCF increases, and correspondingly the content of solid solution decreased due to FeHCF is more stable than solid solutions in thermodynamics. Finally, such a design principle in this case study could also be generalized to other ion-exchange processes. Considering the difference of two components in solubility, the larger difference can make the core/shell structure more clear due to the enhancement of dissolution–reprecipitation route.

Facile and fast preparation of layered double hydroxide as a nanocarrier for ascorbic acid under ultrasonic irradiation.

Background and purpose:Layered double hydroxides (LDHs) as inorganic materials are being used in controlled release and drug delivery systems. These materials are more stable than conventional drug carriers. In this investigation, Mg/Al-ascorbic acid (ASA) LDH nanohybrid was synthesized by ultrasonic-assisted co-deposition techniques.Experimental approach:In this study, Mg/Al-LDH to adsorption of ASA anions from the alkaline solution was assembled by a facile coprecipitation technique. During this process, ultrasonic irradiation was used to increase the rate of ion exchange between LDH and ASA. The intercalated-layered structure was characterized by FT-IR spectroscopy, XRD, thermogravimetric analysis, field emission SEM, and TEM. ASA releasing from Mg/Al-ASA LDH nanohybrid was carried out in incubation sodium carbonate solution (0.5 M) at 35 °C using UV-Vis absorbance analysis at λ = 265 nmFindings/Results:The used techniques confirmed the structure of Mg/Al-LDH and indicated successful intercalation of ASA into the interlayer galleries of the LDH host. The obtained results also have shown that Mg/Al-ASA LDH nanohybrid was generated with an average diameter size of 25 nm and narrow size distribution. Analysis of the release profiles using several kinetic models suggested that the first-order rate model is the most appropriate for describing the release of ASA from Mg/Al-LDH which means the amount of drug released is proportional to the amount of remaining drug in the matrix. Thus, the amount of activity released tends to decrease in function of time.Conclusion and implications:The results showed that LDHs are good host materials to preserve the biomolecule and modify its release rate and bioavailability.