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Separation of Co 2+ and Ni 2+ from Li + using an ion exchange polymer inclusion membrane.
Chromium (VI) and arsenic (V) oxoanions are major toxic heavy metal pollutants in water threatening both human health and environmental safety. Here, the development is reported of a bifunctional ionic covalent organic network (iCON) with integrated guanidinium and phenol units to simultaneously sequester chromate and arsenate in water via a synergistic ion-exchange-redox process. The guanidinium groups facilitate the ion-exchange-based adsorption of chromate and arsenate at neutral pH with fast kinetics and high uptake capacity, whereas the integrated phenol motifs mediate the Cr(VI)/Cr(III) redox process that immobilizes chromate and promotes the adsorption of arsenate via the formation of Cr(III)-As(V) cluster/complex. The synergistic ion-exchange-redox approach not only pushes high adsorption efficiency for both chromate and arsenate but also upholds a balanced Cr/As uptake ratio regardless of the change in concentration and the presence of interfering oxoanions.
The interactions between counterions and electronic carriers in electrically doped semiconducting polymers are important for delocalization of charge carriers, electronic conductivity, and thermal stability. The introduction of a dianions in semiconducting polymers leads to double doping where there is one counterion for two charge carriers. Double doping minimizes structural distortions, but changes the electrostatic interactions between the carriers and counterions. Polymeric ionic liquids (PIL) with croconate dianions are helpful to investigate the role of the counterion in p-type semiconducting polymers. PILs prevent diffusion of the cation into the semiconducting polymers during ion exchange. The redox-active croconate dianions undergo ion exchange with doped semiconducting polymers depending on their ionization energy. Croconate dianions are found to reduce doped films of poly(3-hexyl thiophene), but undergo ion exchange with a polythiophene with tetraethylene glycol side chains, P(g 4 2T-T), that has a lower ionization energy. The croconate dianion maintains crystalline order in P(g 4 2T-T) and leads to a lower activation energy for the electrical conductivity than PF 6 – counterions. The control of the doping level with croconate allows optimization of the thermoelectric performance of the semiconducting polymer. Finally, the thermal stability of the doped films of P(g 4 2T-T) is found to depend strongly on the nature of the counterion.
Astatine and bismuth sorption on several ion exchange resins from nitric acid media has been studied. This work covers commercially available resins Dowex 50 × 4, MP thiol, Dowex 1 × 8, and TEVA. One of the main advantages of using ion exchangers for astatine separation and purification is the absence of any organic media in the effluent in comparison with extraction chromatography resins. The behavior of the above-mentioned metals was investigated in up to 4 M HNO 3 solutions. The determined distribution coefficients are greater than 1 for all the resins studied, reaching 10 4 for MP thiol and TEVA resins. The interaction of nitric acid with an anion exchanger in Cl-form results in an exchange reaction, where AtO + chloro complexes can form. To understand the astatine behavior under these conditions, stability constants of AtOCl and AtOCl 2 – complexes have been reevaluated and discrepancy in the literature values has been eliminated. For each resin a thermodynamic model has been developed to suggest a possible mechanism of astatine sorption. Literature and new experimental data on bismuth sorption by studying resins in nitric acid media have been reviewed and a mathematical model to describe its behavior has been suggested. Furthermore, a ratio of corresponding fit functions of At and Bi assigned to the same resin and acidity has been used to estimate the separation factors of these elements.
Calcium-ion batteries (CIBs) have emerged as a promising alternative for electrochemical energy storage. The lack of high-performance cathode materials severely limits the development of CIBs. Vanadium oxides are particularly attractive as cathode materials for CIBs, and preinsertion chemistry is often used to improve their calcium storage performance. However, the room temperature cycling lifespan of vanadium oxides in organic electrolytes still falls short of 1000 cycles. Here, based on preinsertion chemistry, the cycling life of vanadium oxides is further improved by integrated electrode and electrolyte engineering. Utilizing a tailored Ca electrolyte, the constructed freestanding (NH 4 ) 2 V 6 O 16 ·1.35H 2 O@graphene oxide@carbon nanotube (NHVO-H@GO@CNT) composite cathode achieves a 305 mAh g -1 high capacity and 10 000 cycles record-long life. Additionally, for the first time, a Ca-ion hybrid capacitor full cell is assembled and delivers a capacity of 62.8 mAh g -1 . The calcium storage mechanism of NHVO-H@GO@CNT based on a two-phase reaction and the exchange of NH 4 + and Ca 2+ during cycling are revealed. The lattice self-regulation of V—O layers is observed and the layered vanadium oxides with Ca 2+ pillars formed by ion exchange exhibit higher capacity. This work provides novel strategies to enhance the calcium storage performance of vanadium oxides via integrated structural design of electrodes and electrolyte modification.
Defect engineering through elemental doping is an efficient way to boost the performance of semiconductor photocatalysts. For this work, transition-metal (TM) doped titanate nanowires (TNWs) were prepared via ion-exchange over the titanate precursors and demonstrated for the Rhodamine B (RhB) degradation under ultraviolet (UV) light irradiation. The ion-exchange of selective ions (V 5+ , Cr 3+ , Ni 2+ , and Zn 2+ ) with protons from pristine TNWs resulted in the hierarchical meso-porosity of nanowires with large pores of ~5–20 nm by TM doping and small pores of ~3.6–4.5 nm inherited from pristine TNWs, which facilitates the mass transfer while maintaining high surface area and active sites. Meanwhile, the TM intercalation partially reduces the Ti 4+ to Ti 3+ and narrows the optical bandgap, which, together with oxygen vacancies and superoxide radicals from pristine TNWs, enhance the adsorption and photocatalytic degradation performance of RhB. This work helps to elucidate the effects of transition-metal doping and provides a rational strategy towards high performance titanate-based photocatalysts for efficient and sustainable wastewater treatment.
Chalcogenide-based aerogels are emerging porous semiconducting nanomaterials that appeal to applications in clean energy and the environment. Here, we report a novel gel, potassium–tin–molybdenum–sulfides (KTMS), that integrates the electrostatically bound K + ions in the covalent network of Sn–Mo–S. Its gelation requires a concurrent reduction of Mo 6+ → Mo 4+/5+ and the oxidation of S 2– → Sn – (n ≈ 1) and Sn 2+ → Sn 4+ . KTMS is an amorphous semiconductor showing quantum confinement effects on band gap energies, 2.1 → 1.4 → 0.9 eV for its wet- → aero- → xerogels. Synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) revealed a complex local structure of KTMS consisting of molecular Mo 2 (S 2 ) 6 and Mo 3 S(S 2 ) 6 clusters. In addition, the Sn–S coordination is related to crystalline Na4Sn3S8 and SnS2. KTMS also demonstrated the removal of the radionuclides of Cs + , Sr 2+ , and UO 2 2+ from ppm to ppb levels with distribution constants (Kd) up to ≥104 mL/g. Notably, despite the lack of atomic periodicity in the amorphous KTMS, the K+ ion is ion-exchangeable with chemically diverse Sr 2+ , Cs + , and UO 2 2+ in aqueous solutions; especially the ion-exchange properties of Sr 2+ and UO 2 2+ ≡(O=U=O) 2+ is not known to any chalcogels known to date. The sequestration of Cs + and Sr 2+ was achieved by the exchange of K + in the amorphous KTMS, and the removal of [O=U 6+ =O] 2+ synergistically involves surface sorption via -S····U 6+ =O 2 2+ covalent interactions and ion-exchange via the hard–soft Lewis acid–base paradigm. Overall, cooperative roles played by the diverse bonding motifs, surface-exposed Lewis basic frameworks, and polarizability of the (poly)sulfides make it an exceptional adsorbent for chemically diverse radioactive species. This finding will guide the design of superior sorbents for chemically distinct metal ion separation.
Aromatic acids, such as p-coumaric acid, are valuable chemical intermediates that are used in the specialty chemical industries because they are precursors to phenylpropanoid compounds. The separation of p-coumaric acid from fermentation broths is a critical step in the biochemical production process and more broadly the circular carbon economy. Electrodeionization (EDI) has been applied toward separations of low-carbon chain acids, but purifying p-coumaric acid has been challenging due to fouling and irreversible binding with ion-exchange membranes and resins. Here, we report a new membrane wafer assembly (MWA) consisting of laminated ion exchange membranes to porous ionomer-binder resin wafers for EDI. The MWAs in an EDI stack showed a 7-fold increase in p-coumaric acid capture while also using 70% less specific energy consumption when benchmarked against state-of-the-art resin wafer EDI modules. The more efficient p-coumaric acid recovery was ascribed to (i) the 38% reduction in interfacial transport resistance between the membrane and resin wafer and (ii) using imidazolium anion exchange membranes and ionomer binders in the MWA. MD simulations revealed enhanced transport rates for p-coumarate in imidazolium ionomers through π–π interactions. As a result, adopting the new MWA significantly reduced the amount of ion-exchange membranes in EDI and may lead to drastic capital cost savings.
The membrane-based electrolysis of water is a growing topic of interest due to the advantages of employing membranes in hydrogen production efficiency and system safety over the traditional alkaline water electrolysis. Ion-exchange membranes with low gas permeability are highly desirable for stable and safe operation of membrane-based water-splitting technologies, hence gas permeability through ion-exchange membranes needs to be properly assessed with standardized methods. We addressed three methods to measure gas permeability of ion-exchange membranes, a pressure permeation cell, chronoamperometry microelectrodes, and in situ testing of the membrane electrode assembly, and provide a guideline for choosing the appropriate method for the targeted operating conditions of the water electrolyzers.
Electrodialysis (ED) desalination performance of different conventional and laboratory-scale ion exchange membranes (IEMs) has been evaluated by many researchers, but most of these studies used their own sets of experimental parameters such as feed solution compositions and concentrations, superficial velocities of the process streams (diluate, concentrate, and electrode rinse), applied electrical voltages, and types of IEMs. Thus, direct comparison of ED desalination performance of different IEMs is virtually impossible. While the use of different conventional IEMs in ED has been reported, the use of bioinspired ion exchange membrane has not been reported yet. The goal of this study was to evaluate the ED desalination performance differences between novel laboratory‑scale bioinspired IEM and conventional IEMs by determining (i) limiting current density, (ii) current density, (iii) current efficiency, (iv) salinity reduction in diluate stream, (v) normalized specific energy consumption, and (vi) water flux by osmosis as a function of (a) initial concentration of NaCl feed solution (diluate and concentrate streams), (b) superficial velocity of feed solution, and (c) applied stack voltage per cell-pair of membranes. A laboratory‑scale single stage batch-recycle electrodialysis experimental apparatus was assembled with five cell‑pairs of IEMs with an active cross-sectional area of 7.84 cm2. In this study, seven combinations of IEMs (commercial and laboratory-made) were compared: (i) Neosepta AMX/CMX, (ii) PCA PCSA/PCSK, (iii) Fujifilm Type 1 AEM/CEM, (iv) SUEZ AR204SZRA/CR67HMR, (v) Ralex AMH-PES/CMH-PES, (vi) Neosepta AMX/Bare Polycarbonate membrane (Polycarb), and (vii) Neosepta AMX/Sandia novel bioinspired cation exchange membrane (SandiaCEM). ED desalination performance with the Sandia novel bioinspired cation exchange membrane (SandiaCEM) was found to be competitive with commercial Neosepta CMX cation exchange membrane.
Extra-framework cations not only have a great impact on the structure of zeolites but also affect energetics and absorption of guest molecules. To investigate the stability and hydration of ion-exchanged zeolite ZK-5, high-temperature oxide melt solution calorimetry and direct water absorption calorimetry were used to reveal the influence of ion exchange on formation enthalpies and hydration processes. Formation enthalpies from oxides suggest that exchanging K + and Cs + with protons leads to destabilization of H-ZK-5, which is accompanied by the transition to an amorphous phase at high temperature. Water absorption and corresponding enthalpies are also affected by charge-compensating cations, for example, Na + ions in Na-ZK-5 promote the confinement of water molecules and generate higher water content and more exothermic absorption enthalpies. It is found that average ionic potentials are insufficient to explain formation enthalpies at different hydration levels, particularly for H-ZK-5 with complex cation forms. Instead, formation enthalpies from oxides generally become less exothermic as the distortion of the zeolite framework increases when replacing cations or absorbing/desorbing water molecules. Furthermore, this thermochemical study demonstrates the critical role of extra-framework cations and documents the complexity of ion exchange effects in zeolites with complicated topology and cation distribution.
Three batches of Crystalline Silicotitanate (CST) ion exchange media have been evaluated for cesium removal efficiency from a Savannah River Site (SRS) High Level Waste (HLW) supernate simulant in support of the Tank Closure Cesium Removal (TCCR) Project, which involves at-tank column waste treatment. Results will be utilized to select the CST media batch to be added to the next TCCR unit columns. Two of the CST media samples were recent production batches and the third was an archived batch studied extensively at SRS nearly two decades ago. The archived CST batch had a significantly smaller average particle diameter than more recent batches. Small-scale (∼23 mL), side-by-side column tests were conducted at 35 deg. C with each of the CST batches using the same simulant at flow rates near 1.2 mL/min (3.0-3.4 CST bed volumes/hr). The cesium ion exchange column performance results were lower than expected for all three CST batches, but the data indicated that 30% more simulant volume and 40% more equivalent CST bed volumes of solution can be processed with the older CST batch prior to reaching the 50% cesium breakthrough point than can be processed with the newer CST batches. Hydraulic evaluations of the CST columns were also conducted in simulant at 24 deg. C to determine the impact of the different particle size distributions and associated bed porosities on frictional pressure drop under dynamic flow conditions. Higher differential pressure drops were observed with the archived CST batch relative to recent production batches, due to the smaller particle size distribution and the packing characteristics of the archived batch. (authors)
The Tank Side Cesium Removal (TSCR) system, under development by Washington River Protection Solutions LLC (WRPS), will send initial low-activity Hanford waste tank supernate feeds to the Hanford Waste Treatment and Immobilization Plant (WTP) Low-Activity Waste (LAW) Facility. In addition to entrained solids removal from the supernate, the primary goal of TSCR is to remove cesium-137 ( 137 Cs) by ion exchange, allowing contact handling of the liquid effluent product at the WTP. Crystalline silicotitanate (CST) ion exchange media, manufactured by Honeywell UOP, LLC (product IONSIVTM R9140-B), was selected as the ion exchange media at TSCR. CST is a non-elutable inorganic material that has demonstrated robust chemical, physical, and radiation tolerance while maintaining functionality. However, exchange kinetics of Cs onto CST is slow, resulting in low utilization of the CST Cs load capacity before unacceptable Cs breakthrough. Two process flow designs have been tested, as follows. 1. Lead-lag column processing: The lead column was removed after the lag column effluent reached the waste acceptance criteria (WAC) limit, the lag column was moved into the lead position, and a new lag column was installed. This format used ~52% Cs load capacity on the lead column. 2. Lead-lag-polish column processing: The processing was stopped when the polish column effluent reached the WAC limit. This format resulted in 81% Cs load capacity on the lead column. Testing with diluted feed from Hanford tank AP-105 (AP-105DF) incorporated a nuanced change to the lead-lag-polish column system where the polish column was inserted when the lag column effluent reached WAC limit. A 10.9-L volume of AP-105DF (diluted to 5.6 M Na) was processed through the Direct Feed Test Platform system, established at Pacific Northwest National Laboratory to support small-scale waste qualification efforts. The columns consisted of 10-mL CST beds (CST Lot 2002009604, sieved to screen out >30-mesh particles) placed in 1.5-cm-inner-diameter columns. Feed was processed at 1.83 bed volumes (BV) per hour; the flowrate, in terms of contact time with the CST bed, matched the expected flowrate at TSCR. The <30-mesh CST sieve cut was expected to provide appropriate performance scaling to a full-height column. The installation of the polish column later in processing (after processing 523 BVs) did not appear to fundamentally change the utilization of the lead column for Cs exchange nor did it extend the total feed processing volume when compared to the previous test with AP-107 feed. Table ES.1 and Figure ES.1 summarize the measured AP-105DF Cs load performance.
The influence of dynamical ion-ion correlations and ion pairing on salt transport in ion exchange membranes remain poorly understood. In this study, we use the framework of Onsager transport coefficients within atomistic molecular dynamics sim- ulations to study the impact of ion-ion correlated motion on salt transport in hydrated polystyrene sulfonate membranes and compare with the results from aqueous salt so- lutions. At sufficiently high salt concentrations, cation-anion dynamical correlations exert a significant influence on both salt diffusivities and conductivities. Anion-anion distinct correlations, arising from the imbalance between the concentration of free (mo- bile) cations and anions, and the retarding effect of the fixed charge groups on cations, proves to be an additional important feature for polymer membranes. Furthermore, our results demonstrate that dynamical correlations should become an important consideration in experimental measurements of salt diffusivities and conductivities for non-dilute salt solutions in polymer membranes.
The Hanford Site stores an estimated 56 million gallons of mixed radioactive and chemically hazardous waste in large underground tanks. In support of the Direct Feed Low-Activity Waste (DFLAW) Program for expediting Hanford tank waste supernate treatment, laboratory-scale ion exchange processing using prototypic unit operations was conducted on AW-105 tank waste at the Pacific Northwest National Laboratory Radiochemical Processing Laboratory. This report describes the small-scale ion exchange testing with 9.2 L of diluted and filtered supernate from Tank 241-AW-105 (hereafter referred to as AW-105) at 16 °C (62 °F). One of the waste acceptance criteria (WAC) for the Waste Treatment Plant (WTP) Low-Activity Waste Facility is that the waste must contain less than 3.18×10 -5 Ci 137 Cs per mole of Na. For the AW-105 tank waste to meet this criterion, only 0.225% of the influent 137 Cs concentration may be delivered to the WTP; this requires a Cs decontamination factor of 445. Testing with AW-105 matched current Tank Side Cesium Removal (TSCR) facility prototypic operations where a lead-lag configuration was used until the lag column reached the WAC limit, then a polish column was brought online for continued processing in a lead-lag-polish column configuration. Feed was processed at 1.9 bed volumes (BVs) per hour; the flowrate, in terms of contact time with the crystalline silicotitanate (CST) bed, matched the expected flowrate at TSCR. The Cs-decontaminated product was retained for vitrification testing (to be reported separately). The lead column reached 83% Cs breakthrough after processing ~1500 BVs of feed; the 50% Cs breakthrough was interpolated from the breakthrough data and occurred at 1041 BVs. Despite the AW-105 having a significantly higher K concentration (0.55 M compared to 0.10 M), testing compared to previous AP-107 ion exchange column testing at 16 °C showed no difference in BVs processed to reach the WAC on the lead column and only an approximate ~20 BV decrease in volume processed to reach the WAC limit on the lag column. The negligible differences in capacity despite the 5x concentration differences in K was determined to be due to the significantly lower NO3 concentration in the AW-105 supernate compared to the AP-107 tank waste matrix. A comparison in breakthrough curves for the two tests also indicated slightly faster kinetic behavior in the AW-105, with the variations in feed matrices (lower NO3 concentration) likely responsible for the deviation. The Cs effluent from the lag column reached the WAC limit after processing 772 BVs. Anticipating this breakthrough point, the polish column was preemptively installed around 675 BVs. Cs breakthrough from the lag column began at 300 BVs, reaching 1.10×10 1 µCi/mL, or 14.13 % Cs breakthrough, after processing all 1500 BVs of feed. The polish column processed nominally 830 BVs and reached 2.10×10 -1 µCi/mL, or 0.27 % Cs breakthrough at the conclusion of the test. Table S.1 and Figure S.1 summarize the observed column performance and relevant Cs loading characteristics.
Selenium (Se) is an essential micronutrient but toxic at high concentrations, posing challenges for water treatment. This study investigated the removal of selenate (SeO 4 2– ) and selenite (SeO 3 2– ) using the strong-base anion-exchange resin IRA-900, particularly in the presence of competing sulfate (SO 4 2– ). The performance of the commercially available resin IRA-900 was systematically investigated. The batch equilibrium behavior was studied in both single- and binary-component systems, and the kinetic behavior was investigated in single-component systems. Results confirmed a selectivity order of SeO 4 2– > SO 4 2– > SeO 3 2– , indicating preferential SeO 4 2– removal over competing SO 4 2– but lower affinity for SeO 3 2– . The maximum total exchange capacity was determined to be 2.04 mequiv/g. Furthermore, SeO 3 2– uptake was found to be pH-dependent, whereas SeO 4 2– uptake remained stable across a broad pH range. From a modeling perspective, the Law of Mass Action model effectively described equilibrium data, and a transport–reaction modeling framework captured removal kinetics of oxyanions including film and intraparticle diffusion. Finally, X-ray photoelectron spectroscopy confirmed ion exchange between chloride and Se oxyanions as the primary removal mechanism. These findings provide fundamental insights into the removal of Se oxyanions from aqueous solutions by ion exchange.
Ion exchange membranes (IEMs) are crucial for direct fuel cells, including direct methanol and direct urea fuel cells (DUFCs). While commercially available IEMs (e.g., FAA-3-50) show decent power density in direct fuel cells, they experience considerable methanol or urea crossover, reducing device performance and motivating design of IEMs that suppress fuel crossover. Here, we prepare cross-linked IEMs with high mechanical toughness utilizing a cross-linker (methylenebis(acrylamide)), hydrophobic monomer (phenyl acrylate (PA) or phenyl methacrylate (PMA)), and charged monomer (2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) for cation exchange or methacroylcholine chloride (MACC) for anion exchange). To validate these membranes in a fuel cell application, we perform DUFC experiments utilizing a PA/MACC AEM and observe good power density compared to FAA-3-50. Furthermore, to understand the role of urea crossover in DUFC performance, permeabilities of both membranes to urea are measured by diffusion cells with in situ ATR-FTIR spectroscopy, where our PA/MACC exhibited lower urea permeability than FAA-3-50.
The influence of the copper ion exchange protocol on SCR activity of SSZ-13 is quantified. Using the same parent SSZ-13 zeolite, four exchange protocols are used to assess how exchange protocol impacts metal uptake and SCR activity. Large differences in the SCR activity, nearly 30 percentage points at 160 °C at constant copper content, are observed for different exchange protocols implying that different exchange protocols lead to different copper species. Hydrogen temperature programmed reduction on selected samples and infrared spectroscopy of CO binding corroborates this conclusion as the reactivity at 160 °C correlates with the intensity of the IR band at 2162 cm -1 . DFT-based calculations show that such an IR assignment is consistent with CO adsorbed on a Cu(I) cation within an eight-membered ring. This work shows that SCR activity can be influenced by the ion exchange process even when different protocols lead to the same metal loading. Perhaps most interesting, a protocol used to generate Cu-MOR for methane to methanol studies led to the most active catalyst both on a unit mass or unit mole copper basis. This points to a yet not recognized means to tailor catalyst activity as the open literature is silent on this issue.