Multi-ionic Solutions Research Articles

Performance of MXene incorporated MOF-derived carbon electrode on deionization of uranium(VI)

As the key element in the nuclear industry, uranium (U) has been widely concerned for its stable acquisition and efficient recycling. Capacitive deionization (CDI), which known as a seawater desalination technology, has shown great potential for uranium-adsorption. However, the poor selectivity restricts the application of CDI in uranium extraction. In this work, a carbonized MIP-202/MXene (CMM) composite was developed for highly efficient selective electrosorption of U(VI) from multi-ionic water. The uniformly decorated MIP-202 can prevent MXene from aggregation and provide rich pore structures, large specific surface area and additional nitrogen source for the efficient electrosorption of U(VI). With the addition of MXene nanosheets, a conductive network was introduced into the CMM and improved mechanical robustness of material to facilitate rapid charge transfer at the interface. As a result, the CMM electrode exhibited a maximum adsorption capacity of 582.46 mg g−1 calculated from Langmuir model and a removal ratio of 89.1% at 1.2 V in UO22+ solution. The selectivity adsorption of CMM for UO22+ can reach 92.3% when treated with multi-ionic solution. Besides, there is an interesting fact that the decreased ratio of added MXene can got a higher adsorption capacity, which may cause by the two composite structures formed when the mixing ratio changed. Overall, the excellent conductivity, high adsorption capacity and selectivity make CMM a promising electrode in CDI for efficient extraction of uranium from water.

Enhanced selective adsorption of lead(II) from complex wastewater by DTPA functionalized chitosan-coated magnetic silica nanoparticles based on anion-synergism

Simultaneously removing heavy metal and dye from complex wastewater is of great significance to industrial wastewater treatment. Herein, a novel magnetic adsorbent, DTPA-modified chitosan-coated magnetic silica nanoparticle (FFO@Sil@Chi-DTPA), was successfully prepared and used to enhance the Pb(II) selective adsorption from multi-metal wastewater based on anion-synergism. In the competitive experiment conducted in a multi-ion solution, the type of selective adsorption of metals was changed by the adsorbents before and after amidation, in which FFO@Sil@Chi-DTPA exhibited an excellent selectively for capturing Pb(II), while FFO@Sil@Chi demonstrated highly selective adsorption of silver. More importantly, the selective adsorption of Pb(II)S by FFO@Sil@Chi-DTPA was enhanced from 111.71 to 268.01 mg g−1 when the coexisting MB concentrations ranged from 0 to 100 mg L−1 at pH 6.0. In the Pb(II)-MB binary system, Pb(II) and MB exhibited a synergistic effect, in which the presence of MB strengthened the adsorption effect of Pb(II) due to the sulfonic acid groups in MB molecules that create new specific sites for Pb(II) adsorption, while MB adsorption was also enhanced by the presence of Pb(II). This work provides a new strategy for exploring novel adsorbents that can enhance the selective removal of heavy metal in complex wastewater based on anion-synergism.

Desalination of Complex Multi-Ionic Solutions by Reverse Osmosis at Different pH Values, Temperatures, and Compositions.

For a thorough mechanistic understanding of reverse osmosis (RO), data on ion retention obtained by desalination of multi-ionic solutions are needed. In this paper, we show how to obtain such data under controlled laboratory conditions at any nonextreme pH. For that, we propose a simple method where we use N2 and CO2 gas control to set the composition of a gas phase in equilibrium with the feedwater solution. By increasing the CO2 partial pressure, the pH of the solution will decrease and vice versa. We applied this method of CO2 gas control to extend and validate an existing data set on ion retention of multi-ionic brackish water with 10 different ionic species, whereas conditions in the prior data set were slightly uncontrolled; in our new analysis, we performed experiments at precisely controlled pH and temperature. We run experiments at pH 6.73 and pH 7.11 and in a temperature range of T = 15–31 °C. Our results show that when pH is decreased, or temperature increased, the ion retention of most ions decreases. We also tested the influence of the Na+ to Ca2+ concentration ratio in this multi-ionic solution on ion retention at pH 6.73 and T ∼ 31 °C. We noticed that this ratio has a larger effect on ion retention for cations than for anions. We compare our data with the earlier reported data and describe similarities and differences. The improved data set will be an important tool for future development of accurate and validated RO ion transport models. Such RO models that describe desalination performance in detail are important for successful commercial application of the RO technology. We also discuss a relevant preparation method for water slightly oversaturated with barely soluble CaCO3 by solution preparation at high CO2 pressure, after which the solution is brought to the required pH by the N2 and CO2 gas control method.

Charge distribution in polyelectrolyte multilayer nanofiltration membranes affects ion separation and scaling propensity

Polyelectrolyte multilayer nanofiltration membranes (PEMMs) achieve tailor-made rejection and selectivity of ions for water treatment applications through a layer-by-layer coating procedure, in which a charged support membrane surface is sequentially contacted with positively and negatively charged polyelectrolytes. This results in the adsorption and formation of such selective multilayer membrane skins with defined molecular compositions. The selective properties of the PEMM depend on the intrinsic properties of the respective layers. Today’s research efforts aim to correlate the membrane’s selective characteristics, its structural parameters, and the operating conditions to a model representation of the membrane’s properties. We use our previously published pEnPEn model, which solves the pressure (p) driven transport of ions through n electrolyte layers (En) and n polyelectrolyte layers (PEn). Here, we expand the model to predict the multi-ionic pressure-induced transport through PEMMs solving one-dimensional Nernst–Planck–Poisson equations. The simulations quantify the influence of asymmetric charge distributions and individual PE layers on the ion selectivity for multi-ion solutions. These asymmetric layer properties represent the nanometer-scale membrane properties emerging from the ionic crosslinking, fixed charge compensation, and overcompensation. The model gives insight into each ion’s concentration profile for n layers of electrolyte and n layers of polyelectrolytes. Now, multi-ion compositions inside and outside of the membrane are simulated, and it is shown that the membrane charge distribution even influences the onset of scaling at the fluid membrane interface. As pEnPEn provides a detailed understanding of the rejection and selectivity characteristics as a function of membrane flux and feed concentration including feed side concentration polarization, it can now predict flux-scaling boundaries for the different membrane charge distributions, making it a powerful tool for choosing process parameters and even for designing tailored PEMMs for specific separation tasks.

Bio-Based Hydrogels With Ion Exchange Properties Applied to Remove Cu(II), Cr(VI), and As(V) Ions From Water.

Hydrogels with ion exchange properties were synthesized from compounds derived from wood biopolymer hemicellulose and from commercial vinyl monomers to be tested as active materials for the removal of Cu(II), Cr(VI), and As(V) ions. The hemicellulose O-acetyl galactoglucomannan (GGM) was used as the precursor material, and through a transesterification reaction, GGM was converted into a macromonomer GGM–glycidyl methacrylate (GGM-GMA). Subsequently, the GGM-GMA macromonomer, containing more than one methacrylate group, was used as a crosslinking agent in the synthesis of hydrogels through free-radical polymerization reactions in combination with a 2-acrylamido-2-methyl-1-propanesulfonic acid monomer to produce a cation exchange hydrogel. Also, (3-acrylamidopropyl)trimethylammonium chloride monomer was applied together with the GGM-GMA to form hydrogels that can be used as anion exchange hydrogel. The hydrogels were characterized by Fourier transform-infrared (FT-IR), 1H-NMR spectroscopy, and thermogravimetric analysis (TGA), as well as derivative thermogravimetry (DTG). The microstructure of the hydrogels was characterized by scanning electron microscopy (SEM) analysis with X-ray microanalysis energy-dispersive spectroscopy (EDS). The results obtained regarding the absorption capacity of the Cu(II), Cr(VI), and As(V) ions were studied as a function of the pH value and the initial concentration of the metal ions in the solutions. Absorption was carried out in consecutive batches, and it was found that the poly(GGM-GMA/AMPSH) hydrogel reached an absorption capacity of 90 mg g–1 for Cu(II). The poly(GGM-GMA/APTACl) hydrogel reached values of 69 and 60 mg g–1 for Cr(VI) and As(V) oxyanions, respectively. Tests with polymer blends (mixtures of anionic and cationic hydrogels) were also carried out to remove Cu(II), Cr(VI), and As(V) ions from multi-ionic solutions, obtaining satisfactory results.

Supervariate ceramics: biomineralization mechanism

Ceramics are key components of life, forming elaborate and diverse structures found in coccolith, shells, skeletons, and teeth. In materials research, however, one generally finds ceramics difficult to process because of their high hardness and melting points. How organisms effortlessly build stunning ceramic architectures, in water and at mild temperature, remains a long-standing mystery to scientists. This study discloses that biomineralization likely operates through a supervariate mechanism based on multi-ionic solutions, a mechanism that enables convenient phase and kinetic regulation through stress control. Specifically, from solutions of multiple ionic components, bioceramics with highly variable (supervariate) compositions are first produced in a gelatinous state of exceptional stability, which offers convenience in material storage, transportation, molding, and processing. Counter-intuitively, the supervariate wet gels can be solidified by simply compacting them under a mild force, whereas the formulas (e.g. carbonates or phosphates), hydration levels, and phases (amorphous or crystalline) of the resultant bioceramics can be tailored. Furthermore, we propose that the biogenic amorphous minerals (e.g. amorphous calcium carbonate) are very likely stabilized by constricting their volume at the microscale, so that they are prohibited from undergoing the prerequisite dehydration step (which requires extra volume) preceding crystallization. The new biomineralization mechanism described here answers a pivotal question on bioceramics of life.

Nanofiltration of Multi-Ion Solutions: Quantitative Control of Concentration Polarization and Interpretation by Solution-Diffusion-Electro-Migration Model.

For effective use of advanced engineering models of nanofiltration quality of experimental input is crucial, especially in electrolyte mixtures where simultaneous rejections of various ions may be very different. In particular, this concerns the quantitative control of concentration polarization (CP). This work used a rotating disklike membrane test cell with equally accessible membrane surface, so the CP extent was the same over the membrane surface. This condition, which is not satisfied in the conventional membrane test cell, made possible correcting for CP easily even in multi-ion systems. Ion rejections were studied experimentally for several dominant salts (NaCl, MgCl2, Na2SO4 and MgSO4) and trace ions (Na+, NH4+, Cl− and NO3−) using NF270 membrane. The solution–diffusion–electro–migration model was used to obtain ion permeances from the experimental measurements. The model could well fit the experimental data except in the case of NH4+. The correlations between the ion permeances and type of dominant salt are discussed in the context of the established mechanisms of NF such as Donnan and dielectric exclusion. The obtained information contributes to the systematic transport characterization of NF membranes and may be ultimately useful for computational fluid dynamics simulations of the performance of the membranes in various applications.

Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag

Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80–100% and of 98–100% in the case of the single ion and of the multi-ion solutions were obtained, respectively.

High performance functionalized UiO metal organic frameworks for the efficient and selective adsorption of Pb (II) ions in concentrated multi-ion systems

In this work, we report novel amine-functionalized zirconium-based metal organic frameworks (MOFs) for the efficient and selective removal of Pb (II) in concentrated multi-component heavy metal ions systems. Pristine UiO-66 and UiO-67 MOFs were grafted with thiourea and amidinothiourea via a facile one-step post synthetic modification. This is the first report on grafting of amidinothiourea onto MOFs. Successful grafting was confirmed by Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. A mechanism involving dehydration, ionization and coordination steps was proposed for grafting and subsequent Pb (II) binding. The microporous amidinothiourea modified UiO-66 and UiO-67 MOFs demonstrated excellent performance in their high maximum adsorption capacities of 246 and 367 mg.g−1, respectively, as well as their remarkable selectivity for Pb (II) ions in highly concentrated multi-ion solutions. This is, in addition, to their effective removal efficiencies which reached up to more than 95% at a high range of Pb (II) concentrations (25–250 ppm). Furthermore, the structural stability of the MOF crystals was maintained after adsorption and the MOF was completely regenerated for up to four cycles. The developed MOFs can thus be utilized as reliable adsorbents for Pb (II) removal from industrial wastewater effluents.

Highly effective and selective adsorption of thorium(Ⅳ) from aqueous solution using mesoporous graphite carbon nitride prepared by sol–gel template method

Selective separation of thorium resources from aqueous solutions is an ideal strategy for recovering or removing radioactive ions, as well as reducing potential human health and environmental risks. In this study, an effective adsorbent, mesoporous graphite carbon nitride (mpg-C3N4), was synthesized by a simple thermal condensation using a sacrificial LUDOX HS-40 colloidal silica as template and applied to the selective adsorption of thorium ions from the multi-ion solutions. The results of competitive experiments illustrated that mpg-C3N4/r exhibited higher selectivity and efficiency for Th(IV) over other 14 co-existing cations, with the maximum selective adsorption capacities of Th(IV) reaching to 108.18 mg g−1 for mpg-C3N4/r=1.0 which is more than g-C3N4 (36.64 mg g−1) at pH 4.0. The interaction of Th(IV) with mpg-C3N4/r=1.0 and g-C3N4 were performed using batch processing, the adsorption isotherm was well conformed to the Langmuir adsorption model, and the maximum adsorption capacity of thorium at pH 4.0 and 298 K was calculated to be 196.08 mg g−1 which is more than three times of g-C3N4 (60.60 mg g−1). Also, the results of adsorption experiments on monazite leachate showed that mpg-C3N4/r=1.0 can be successfully used as an attractive adsorbent with the high adsorption efficiency (93.53%) of thorium. This work could broaden insights into the tailored design and synthesis of mesoporous adsorbents for the selective adsorption of thorium in multi-ion solutions.

Reduced Graphene Oxide Membranes as Potential Self-Assembling Filter for Wastewater Treatment

This work focuses on the investigation of the capability of reduced graphene oxide (rGO) filters to remove metals from various wastewater. The process to produce rGO membranes is reported and discussed, as well as their ability to capture ions in complex solutions, such as tap or industrial wastewater. Multi-ion solutions, containing Cu2+, Fe3+, Ni2+, and Mn2+ to simulate mine wastewater, or Ca2+ and Mg2+ to mimic drinkable water, were used as models. In mono-ionic solutions, the best capture efficiency values were proved for Ca2+, Fe3+, and Ni2+ ions, while a matrix effect was found for multi-ion solutions. However, interesting capture efficiencies were measured in the range of 30–90%, depending on the specific ion, for both single and multi-ion solutions. An attempt is proposed to correlate ions capture efficiency with ions characteristics, such as ionic radius or charge. Combining a satisfactory capture efficiency with low costs and ease of treatment unit operations, the approach here proposed is considered promising to replace other more complex and expensive filtration techniques.

Magnetic phosphorylated chitosan composite as a novel adsorbent for highly effective and selective capture of lead from aqueous solution

Separating and recovering lead from heavy metal contaminated wastewater is crucial for the environment remediation and reutilization of lead resources. Herein, a novel adsorbent, the phosphorylated chitosan-coated magnetic silica nanoparticles (Fe3O4@SiO2@CS-P), was successfully fabricated and applied to highly selective adsorption of lead. Competitive experiments were conducted in a multi-ion solution (7 metal ions coexist) at pH 6.0, Fe3O4@SiO2@CS-P exhibited an excellent selectively for capturing lead with the distribution coefficient (0.75 L g−1) more ten times than other metal, while Fe3O4@SiO2@CS demonstrated a highly selective adsorption of silver. These implied that phosphorylation of adsorbent not only improves the sorption performance of lead, but also changes the selective adsorption of metal types. Acidity experiments can draw conclusions that Fe3O4@SiO2@CS-P exhibited better acid resistance (with barely any iron leaching) than silica-uncoated adsorbent (Fe3O4@CS-P) at pH 1.0. Furthermore, the FTIR and XPS spectra after adsorption suggested that the high adsorption performance and selective capture lead were predominantly controlled by the coordination of the phosphate groups on the surface of the adsorbent. This work shows a broad prospect of developing a series of novel, acid-resistant, good reusable and rapidly separable magnetic materials that can be used to efficiently and selectively capture lead from aqueous solutions.

Glucocorticoids are contextually pro-inflammatory in neural cells

The multimembrane hybrid system (MHS) was proposed for the separation and recovery of Zn2+ cations from a multi ionic feed phase. The composition of the aqueous solution used as the feed phase simulates qualitatively wastewater from either hydrometallurgical or electroplating processes. The effect of various physicochemical and operational parameters was investigated. It was found that Zn2+ cations can be effectively separated from multi ionic solution (according to the carrier properties) and concentrated in the stripping solution with the quasi-stationary fluxes attaining 6 × 10−10 mol/cm2 s. The sufficient selectivity and fluxes of Zn2+ ions are observed for carrier concentration in the liquid membrane varied between 0.05 and 0.1 M D2EHPA, the feed solution concentration varied between 2 × 10−3 M and 0.01 M, the striping solution concentration equals 1 M, and initial pH of the feed solution higher than 2. It was also experimentally confirmed that the cation-exchange membranes enable a long-term and continuous operation of the system.

Fabrication of soft-etched nanoporous polyimide membranes for ionic conduction and discrimination

Ionic selectivity in nanopores is usually based either on steric or charge exclusion mechanisms. By simultaneously incorporating both mechanisms into a functionalized membrane, an improved control over selectivity can be achieved. We describe the fabrication and experimental characterization of alkali metal cation-selective nanopores in heavy ion-tracked polyimide (PI) membranes using the soft-etching (SE) technique. The latent ion tracks in the PI membrane are selectively dissolved by an organic solvent to form tiny pores without affecting the bulk material. The ionic transport properties of SE-PI membranes are characterized using different electrolyte solutions containing alkali metals, divalent metals, and organic cations under symmetric and asymmetric electrolyte conditions. Under symmetric conditions, the pores exhibit ohmic behavior when exposed to alkali metal chlorides and ammonium chloride solutions while divalent cations cannot pass through the pores as evidenced from the current-voltage curves. For the case of asymmetric electrolyte conditions, current rectification suggests pore blockage from the side of membrane exposed to divalent cations and tetraalkylammonium (TAA) cations. The experimental data show that the SE-PI membranes efficiently discriminate alkali cations from divalent metal cations and ammonium cation from TAA cations. The ionic conduction of the membranes is also sensitive to the mole fraction of Ca2+ in multi-ionic solutions. The ionic transport experiments further confirm that the nanopores allow significant alkali cation fluxes while rejecting divalent cations. Based on the good stability and high selectivity, the solvent treated PI membranes constitute remarkable candidates to be employed in applications concerning a wide range of electrolyte solutions.

Design, synthesis, and study of Pd(II) ion-imprinted functionalized polymer.

Selective metal ions' extraction and recovery has various applications in the analytical field. Metal ions need to be extracted, detected, and quantified. For that purpose, ion-imprinted polymers have earned a great deal of attention during the past two decades. Pd2+ ion-imprinted hollow silica particles including an isatin Schiff base were prepared by Schiff base condensation of (3-aminopropyl)triethoxysilane and isatin. The prepared Schiff base ligand was coordinated to the target Pd2+ cations, the polymerizable Pd-complex was set aside to form gel in the company of tetraethoxysilane and the target Pd2+ cations were subsequently removed from the cross-linked silica network by means of acidified thiourea solution. All materials throughout this synthesis process were investigated utilizing mass spectrometry, elemental analysis, FTIR, and 1H-NMR. The morphological structure of both Pd2+ ion-imprinted and non-ion-imprinted silica polymer were pictured by scanning electron microscopy. Several batches were studied exploiting both Pd2+ ion-imprinted and non-ion-imprinted silica polymer to test their functionality for selective extraction of Pd2+ cations in multi-ionic solution of Ni2+, Co2+, Cu2+, Mn2+, and Pd2+.

Sorption properties of new fibrous chelate ion exchanger

The sorption properties of new iminodiacetate fibrous cation exchanger FIBAN XC-1 synthesized on a chemically resistant matrix of polypropylene fiber with a grafted copolymer of styrene and divinylbenzene, which can withstand elevated temperatures and aggressive environments, were studied. It was shown that the fibrous chelate ion exchanger FIBAN XC-1 is an effective sorbent of heavy and non-ferrous metals from multi-ionic aqueous solutions under static and dynamic conditions. It was found that the cation exchanger operates at high speeds up to 20 column volumes / min in water purification from copper and lead ions (purification from Cu2+ – 82 % and purification from Pb2+– 65 %). It was found that the fibrous chelate ion exchanger FIBAN XC-1 is easily regenerated and does not lose its sorption and mechanical properties in the sorption– regeneration cycles.

Designing and characterization of copper (II) ion-imprinted adsorbent based on isatin functionalized chitosan

An isatin functionalized chitosan derived ion-imprinted adsorbent (Cu-CIS) was designed by tailoring Cu(II) ions imprinted cavities within the modified polysaccharide network matrix that are able to capture Cu(II) ions selectively in aqueous solution. The chelating power of chitosan toward the Cu(II) ions was first enhanced via isatin functionalization, which was cross-linked using epichlorohydrin (ECH) after loading the Cu(II) ions. The selective metal ions binding sites are then formed by eluting the coordinated Cu(II) ions using EDTA to finally produce the Cu-CIS selective sorbent. The equilibrium isotherms have been utilized to anticipate the maximum capacity of the Cu-CIS sorbent and compare it with that of the blank non-imprinted sorbent NI-CIS. In addition, the significance of inserting the Cu(II) ions recognition cavities within the adsorbent matrix was pointed out by performing the adsorption in a multi-ionic solution mixture containing Co(II), Ni(II), Pb(II), Cd(II) and Cu(II) ions and the obtained selectivity coefficients in case of Cu-CIS revealed remarkable selectivity potentials toward the Cu(II) ions compared to NI-CIS. Moreover, at the consecutive performance of a Cu-CIS absorbent for five cycles, it was found that it still held 97% of its initial capacity enabling promising applications in both water treatment and Cu (II) ions recycling.

MORINGA OLEIFERA SEEDS AS A LOW-COST BIOSORBENT FOR REMOVING HEAVY METALS FROM WASTEWATER

Heavy metals are considered to be one of the major contaminants of water in recent years due to their non-biodegradable property; hence making them toxic and bioaccumulate to living organisms. Conventional methods such us chemical precipitation, physical treatment through ion exchange are used for removing heavy metal ions from water. These methods are expensive and attributed to incomplete metals removal and high cost of treatment. In recent years, researchers have found alternative low cost and effective method for removal of toxic metals through biosorption process using biological materials. Moringa oleifera seeds is one of the biological materials which has effective adsorption capacity for removal of heavy metals from water and wastewater. In this article, the seeds of Moringa oleifera seeds as a low-cost biosorbent for removal of heavy metals is presented. Moringa oleifera seeds is inexpensive material that contains amino acids. The amino acid is a major constituent of the functional groups that aids in greater ability of heavy metals removal through metal ion exchange or complexation, which is mainly affected by pH, biosorbent dosage, and contact time. Moringa oleifera seeds residues have a greater capacity to absorb heavy metals in a single solution compared to multi ion solution.

Highly selective uranium adsorption on 2-phosphonobutane-1,2,4-tricarboxylic acid-decorated chitosan-coated magnetic silica nanoparticles

The separation and recovery of uranium resources from nuclear waste solutions is important for achieving uranium reuse and environmental protection. In this study, a novel adsorbent, 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA)-decorated chitosan-coated magnetic silica nanoparticles, was fabricated and applied to the highly selective adsorption of uranium from aqueous solution. Selective sorption in a multi-ion solution (pH 4.0) containing 14 coexisting cations resulted in CoFe2O4@SiO2@CS-PBTCA showing an excellent uranium adsorption capacity of up to 83.16 mg g−1, which was much higher than that of ungrafted CoFe2O4@SiO2@CS (29.99 mg g−1). The adsorbent also exhibited higher acid resistance than uncoated silica adsorbent under pH 1.0 conditions, with CoFe2O4@SiO2@CS-PBTCA showing barely any iron and cobalt leaching, while CoFe2O4@CS-PBTCA showed iron and cobalt leaching amounts of 2.97 and 0.93 mg L−1, respectively. The desorption experiment used 0.2 M PBTCA (pH 1.0) as eluent, with the results showing that uranium ions were readily and rapidly desorbed. Furthermore, CoFe2O4@SiO2@CS-PBTCA maintained outstanding stability and adsorption performance after five reuse cycles. The mechanism for U(VI) removal was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, with the results suggesting that the adsorbent binds to uranium mainly though oxygen atoms of carboxyl groups and phosphonic groups in PBTCA. This strategy shows strong potential for developing a variety of novel, highly active, acid resistance, and reusable immobilized functional magnetic materials for effective separation of uranium from a multi-ion solution.

Simplified Prediction of Ion Removal in Capacitive Deionization of Multi-Ion Solutions

Capacitive deionization (CDI) is an upcoming desalination technology being increasingly considered to be a simple and cost-effective solution for brackish water, where electrosorption leads to the removal of charged species from water. Real-world water samples typically contain a multitude of ions that must be considered apart from sodium–chloride salt. In this work, we have developed a method to quantify the competitive adsorption of different ionic species during CDI processes. The method is straightforward, requiring a single calibrating experiment to extract a ‘periodic table’ of competitiveness scores for all ions present in the experiment. Using a dynamic Langmuir model that was developed by our group, it is shown that these scores could subsequently be used to predict the adsorption of any ion species in a multi-ion solution. Excellent agreement with data from the literature could be achieved with this model, and the method is especially well-suited for trace ions as these can be predicted directly. The derived method is simple and accurate for quantifying and predicting adsorption in multi-ion solutions and could be valuable for predicting the effect when applying CDI to real-world water samples.