Highly Selective and Rapid Uptake of Radionuclide Cesium

Article

pubs.acs.org/cm

Highly Selective and Rapid Uptake of Radionuclide Cesium Based on Robust Zeolitic Chalcogenide via Stepwise Ion-Exchange Strategy † † † † † † † Huajun Yang, Min Luo, Li Luo, Hongxiang Wang, Dandan Hu, Jian Lin, Xiang Wang, ‡ ‡ § ⊥ † Yanlong Wang, Shuao Wang, Xianhui Bu,*, Pingyun Feng,*, and Tao Wu*, † College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Jiangsu 215123, China ‡ School for Radiological and Interdisciplinary Sciences (RAD-X), Soochow University, Jiangsu 215123, China § Department of Chemistry and Biochemistry, California State University Long Beach, 1250 Bellﬂower Boulevard, Long Beach, California 90840, United States ⊥ Department of Chemistry, University of California, Riverside, Riverside, California 92521, United States

*S Supporting Information

ABSTRACT: The safe use of nuclear energy requires the development of advanced adsorbent technology to address environment damage from nuclear waste or accidental release of radionuclides. Recently developed amine-directed chalcogenide frameworks have intrinsic advantages as ion-exchange materials to capture radionuclides, because their exceptionally negative framework charge can lead to high cation-uptake capacity and their 3-D multidimensional intersecting channel promotes rapid ion diffusion and offer a unique kinetic advantage. Prior to this work, however, such advantages could not be realized because organic cations in the as-synthesized materials are sluggish during ion exchange. Here we report an ingenious approach on the activation of amine- directed zeolitic chalcogenides through a stepwise ion-exchange strategy and their use in cesium adsorption. The activated porous chalcogenide exhibits highly enhanced cesium uptake compared to the pristine form and is comparable to the best metal chalcogenide sorbents so far. Further ion-exchange experiments in the presence of competing ions confirm the high selectivity for cesium ions. Excellent removal performance has also been observed in real water samples, highlighting the importance of stepwise ion exchange strategy to activate amine-directed chalcogenide framework for 137Cs+ removal.

■ INTRODUCTION studied, but they tend to have poor performance, in addition to 17 + As an efficient and low-carbon power generation method, low chemical, radiolytic, and thermal stability. Recently, Cs − − nuclear power plays a critical role in meeting the increasing uptake in SO3H -decorated MIL-101 was reported, widening energy needs. However, nuclear wastes and reactor accidents the types of materials with potential applications in nuclear 18 could result in the leak of radionuclides into environments, energy applications. which is a key reason limiting more widespread use of nuclear Recently, Kanatzidis et al. reported the capture of radio- energy.1,2 Among various radioactive nuclides, 137Cs+ is the nuclides by metal sulfides with high selectivity and under most hazardous due to its high fission yield (6.09%), long half- variable pH.17 The selectivity by sulfides is related to the − life (∼30 years), and high solubility.3 5 When accidentally relative softness of radionuclides (e.g., Cs+,Sr2+) compared to released to the sea or ground, it must be decontaminated smaller alkali or alkaline earth ions, which is different from that 137 + immediately for public safety. The Cs ions also need to be of oxide sorbents where the hydration radius and Gibbs energy recycled effectively from nuclear waste solutions in the 137 + of dehydration of the exchanged ions play an important role in reprocessing plants. Therefore, for Cs cleanup, high 19−23 + the ion exchange process. For example, layered metal selectivity for Cs in the presence of relatively high sulfide KMS-1 has preference for Sr2+ in highly alkaline concentration of competing cations (Na+,K+,Ca2+,Mg2+), solutions and also is among the most effective sorbents for fast kinetics, and commercial availability are desired in large- 2+ 24−26 6 UO removal. Other layered metal sulfides, such as scale application. 2 Various sorbents for 137Cs+ selective uptake have been KMS-2, KTS-3, and FJSM-SnS, have also been studied for 27−29 fi fi studied. The early materials are inorganic oxides such as radionuclide capture. In addition, sul de-modi ed sorb- − − crystalline silicotitanate (CST),7 9 zeolites,10 12 silicododeca- ents, such as layered double hydroxides intercalated by molybdate,13 vanadosilicate (SGU-45),14 and clays.15 Such sorbents are inexpensive but can suffer from slow kinetics.14 Received: October 7, 2016 Furthermore, their Cs+ selectivity can decrease significantly Revised: November 13, 2016 with high salt concentrations.16 Organic resins have also been Published: November 16, 2016

fi 2− 2+ polysul des or MoS4 , have been studied for removal of UO2 ppm, H2O, Aladdin), and potassium standard solution (1000 ppm, 30 fi as well as heavy metal ions. H2O, Macklin) were used as received without any further puri cation. x− 34 Syntheses. The syntheses of UCR-20-GaGeS (GaxGe4−xS8 ), For ion-exchange applications, maximizing the concentration · 29 FJSM-SnS ((Me2NH2)4/3(Me3NH)2/3Sn3S7 1.25H2O), GaSbS-1 of exchangeable cations is of critical importance for the process · 33 ffi ([(CH3)2NH2]2Ga2Sb2S7 H2O), and KTS-3 (K2xSn4−xS8−x, x = e ciency. The concentration of cations in traditional oxide- − 28 3+ 4+ 0.65 1) are according to the literature methods. based zeolites is determined by the framework Al /Si molar Stepwise Ion-Exchange Strategy. ’ The stepwise ion-exchange ratio which has a maximum value of 1 due to the Löwenstein s strategy is composed of two steps. ̈ ’ rule (as in NaAlSiO4). Surprisingly, the Lowenstein s rule is not Step 1: The protonated amines (PA) were first exchanged out by obeyed in zeolite-type metal chalcogenides so that M3+/M4+ “soft” Cs+. Typically, 500 mg of pristine RWY is soaked in 100 mL of ratio can be significantly great than 1.31 This motivates us to CsCl aqueous solution (1 M) in glass vial, which was sealed and initiate investigating the ion-exchange applications of such subsequently put in an 85 °C oven. The CsCl solution was refreshed materials, because we expect that the large negative charge of once during treatment. After 48 h, the crystals (named as Cs@RWY) framework and the associated high concentration of exchange- were washed by deionized water and ethanol for several times, and dried in vacuum. The process can be described as follows: able cations will lead to a record-high cation exchange capacity. 85° C In addition, unlike low-dimensional materials, these zeolite-type Cs+ +⎯→ PA@RWY⎯⎯⎯ Cs@RWY + PA+ chalocgenides have 3-D multidimensional, and mutually intersecting channels that could greatly facilitate ion diffusion (PA= protonated amines) (1) and ion exchange kinetics. Step 2: 100 mg of Cs@RWY was dipped into 100 mL of KCl At the early stage of this study, we encountered a major solution (2 M) at room temperature. The solution was refreshed twice obstacle to unlock the aforementioned intrinsic advantages of with a total time of around 48 h to remove the Cs+ in the channels of zeolite-type chalcogenides. Specifically, the as-synthesized RWY completely. Subsequently, the samples (named as K@RWY) materials typically contain bulky protonated amines in the were washed by deionized water and ethanol, and dried in a vacuum channels and their ion exchange process is quite slug- oven. The ion-exchange process was according to − gish.29,32 34 + RT + Herein we designed a two-step ion-exchange strategy to K +⎯→Cs@RWY⎯+ K@RWY Cs (2) address this issue (Scheme 1). In this work, we selected a highly Ion-Exchange Experiments. Typically, 10 mg of K@RWY was added into 10 mL of aqueous solution containing different amounts of + Scheme 1. Stepwise Ion-Exchange Strategy To Prepare standard Cs solution (1000 ppm, H2O). The mixture was kept High-Performance Potassium Form of Porous Sulfide shaking for 15−18 h at room temperature. And then the polycrystal- (RWY) for Efficient Cs+ Capture line materials with darker color were isolated by filtration and washed by water and ethanol for several times. The filtrate was collected for ICP-MS or ICP-AES measurements. All the experiments were carried out by batch method. To determine the sorption isotherm, the initial concentrations Ci of Cs+ was set in the range of 1−500 ppm at room temperature with V:m = 1000 and a total contact time of 15 h. In pH−dependent experiments, the pH of the solution was adjusted either by HCl solution or NaOH solution. The pH value was measured by a PHS-3C pH meter at the beginning of the ion exchange experiments. The regeneration process is similar to the step 2 of the stepwise ion exchange strategy. For the ion-exchange experiments in potable water and seawater, generally, 10 or 40 mg of K@RWY was added into 10 mL of aqueous solution in a glass vial. The solution was intentionally contaminated by diluting the standard Cs+ solution. The weight ratios of the standard solution were smaller than 1/100 to maintain the competitive ionic stable and porous amine-directed zeolitic chalcogenide frame- concentrations of real water samples. The mixture was kept shaking at work, namely UCR-20 (zeolite type code: RWY).34,35 We room temperature for 15−18 h and then was filtered. The filtrate was demonstrated that the protonated amines located in its analyzed by ICP-MS. ffi ffi channels can be exchanged completely into “hard” alkali ions Distribution coe cient Kd, signifying the a nity and selectivity for + − through the stepwise ion-exchange strategy. Interestingly, the Cs , is calculated by the equation: Kd =[(Ci Ce)/Ce](V/m) where fi + K+-exchanged RWY (K@RWY) can rapidly capture Cs+ with Ci and Ce are the initial and nal concentrations of Cs , V is the volume of the tested solution, and m is weight of the sorbents. The high selectivity. This material also shows an excellent ability for Langmuir model of the ion exchange process is expressed as follows: Cs+ capture from real water samples including potable water and even seawater. bCe qq= m 1 + bC (3) ■ EXPERIMENTAL SECTION e where q is the maximum removal quantity of Cs+ per unit of weight Chemicals and Materials. Sulfur (S, 99.5%, powder, Sinopharm), m of sorbent, C is final concentration when the solution reaches germanium oxide (GeO , 99.99%, powder, HWRK), gallium metal f 2 equilibrium, and b is the Langmuir constant related to the affinity of (Ga, AP, bulk, Qiangshun Chemical Reagent), Antimony (Sb, 99.5%, adsorbed ions. The value of q can be calculated by metals basis, Aladdin), cesium chloride (CsCl, AR, solid, Macklin), indium (In, 99.99%, 200 mesh, HWRK), tin (Sn, 99.5%, 200 mesh, ()CCVie− Sinopharm), potassium chloride (KCl, 99.5%, solid, Macklin), q = m (4) potassium carbonate (K2CO3, 99%, solid, XiLong Chemical Reagent), tris(2-aminoethyl)amine (TAEA, 96%, liquid, Acros), sodium standard Powder X-ray Diffraction (PXRD). PXRD data were collected on ff solution (10 000 ppm, H2O, Macklin), cesium standard solution (1000 a desktop di ractometer (D2 PHASER, Bruker, Germany) using Cu

8775 DOI: 10.1021/acs.chemmater.6b04273 Chem. Mater. 2016, 28, 8774−8780 Chemistry of Materials Article

Kα (λ = 1.540 56 A) radiation operated at 30 kV and 10 mA. The from the regeneration process of KMS-1, during which the Cs+ samples were ground into fine powders for several minutes before the 2+ or UO2 -laden sample could be reused by expelling them using test. excessive K+.25,30 Elemental Analysis. Energy dispersive spectroscopy (EDS) On the basis of the above analysis, we designed a stepwise analysis was performed on scanning electron microscopy (SEM) ion-exchange strategy. First, we use “soft” alkali metal cations instrument equipped with energy dispersive spectroscopy (EDS) + detector. An accelerating voltage of 25 kV and 40 s accumulation time (nonradioactive Cs ) to exchange out organic amines under were applied. Elemental analysis of C, H, and N was performed on a conditions needed for complete exchange (e.g., heating, long VARIDEL III elemental analyzer. Each sample was analyzed for three reaction time). Then, the “soft” alkaline metal cations are times and an average value was taken. A Varian 710-ES inductively exchanged out by “hard” ones (e.g., K+) in large excess. The coupled plasma optical emission spectrometry (ICP-OES) instrument resulting K@RWY samples are used for selective radionuclide was used to determine the concentrations of Na+/K+/Ca2+/Mg2+. uptake. It should be noted that the Cs+ used for amine removal + + Because of the weak emission of Cs , the concentrations of Cs were are nonradioactive and can be recycled. determined by inductively coupled plasma mass spectrometer (ICP- Here, we choose a zeolitic chalcogenide framework RWY to MS, iCAPQ, Thermofisher Scientific). Thermogravimetric (TG) Measurement. A Shimadzu TGA-50 realize the stepwise ion-exchange strategy due to its high thermal analyzer was used to measure the TG curve by heating the porosity and stability. The structure of RWY is constructed sample from room temperature to 600 °C with heating rate of 5 °C/ from supertetrahedral T2 (GaxGe4−xS10) clusters with sodalite min under nitrogen flow. topology by treating T2 as nodes (Figure S1). Positively Fourier Transform Infrared Absorption. Fourier transform- charged amines, tris(2-dimethylaminoethyl)amine (TAEA), are Infrared spectral analysis was performed on a Thermo Nicolet Avatar disorderly located in the protonated form in the channels. 6700 FT-IR spectrometer with cesium iodide optics allowing the The PXRD measurements indicate that the structure −1 instrument to observe from 600 to 4000 cm . framework of original samples remains unchanged after ion- Gas Adsorption. N2 sorption measurement of K@RWY was exchange processes (Figure 1a). The characteristic IR peaks of carried out on a Micromeritics ASAP 2020 Physisorption Analyzer with the temperature controlled at 77 K by liquid N2. Prior to the measurement, the as-synthesized sample was dried in the vacuum oven for several hours and further dried by using the “degas” process of the surface area analyzer for 10 h at 100 °C. Ionic Conductivity. The ionic conductivity of Na@RWY was determined by ac impedance methods. The measurements were carried out with a zennium/IM6 impedance analyzer over the frequency range from 0.1 Hz to 5 MHz with an applied voltage of 50 mV. The polycrystalline powders of Na@RWY were pressed to form a cylindrical pellet (∼3 mm thickness × 5mmϕ) coated with C- pressed electrodes. The bulk conductivity was estimated by semicircle fittings of Nyquist plots. γ Radiation Resistance Experiments. A irradiation experiment Figure 1. (a) XRD patterns for pristine RWY, Cs@RWY, K@RWY, was conducted using a 60Co irradiation source (60 000 Ci). K@RWY β and the simulated RWY. (b) FT-IR spectra of pristine RWY, Cs@ was irradiated at a dose rate of 1.2 KGy/h for 100 kGy. A series of RWY, K@RWY, and TAEA. irradiation experiments were conducted using electron beams (1.2 MeV) provided by an electron accelerator. K@RWY was irradiated at a dose rate of 20 KGy/h for three different doses respectively: 80, 120, and 200 KGy. The irradiated K@RWY were further characterized by − −1 − −1 PXRD. TAEA between 2700 3000 cm and 700 1700 cm disappeared after exchange, which support the near-complete removal of TAEA (Figure 1b). The absorption peaks at 3387 RESULTS AND DISCUSSION − ■ and 1612 cm 1 of exchanged RWY correspond to the For as-synthesized amine-containing chalcogenides, the bulky characteristic vibrational absorption of H2O. TG curves of amines suffer slow exchange kinetics and a relatively high exchanged RWY exhibit a steep decrease below 120 °C(Figure temperature and a long time are required for ion S2), which further verified the existence of large amounts of − exchange.29,32 34 For efficient Cs+ capture, our strategy is to disordered water molecules in the channels of exchanged RWY. create novel metal chalcogenides in which sluggish protonated The elemental analysis of N (Table S1) shows that >96% and amines are replaced with small hard cations such as K+, which 100% of the amines were removed in Cs@RWY and K@RWY, would allow for rapid exchange with Cs+ because of the greater respectively. The complete exchange of step 2 can be further affinity of Cs+ for the chalcogenide frameworks. The challenge confirmed by SEM-EDS spectra, where Cs+ cannot be detected is that we found it difficult to replace directly the organic in K@RWY. Based on EDS and TG curves, the formula of K@ “ ” · amines with hard cations due to the weak interaction between RWY is Ga2.76Ge1.24S7.78K2.33 11.8H2O. SEM images also “hard” cations and “soft” surface sulfions. For example, for showed that the surface of the crystals remains smooth after RWY, only 61% of the organic amines can be directly ion exchange (Figure S3). exchanged out by K+ and 48% by Na+. It should be noted To determine the affinity and maximum exchange capacity of that the degree of exchange is 93% with soft Cs+ at the same K@RWY, equilibrium studies were conducted with various condition. Clearly, soft Cs+ can more effectively activate the initial concentration of Cs+ (from 1 to 500 ppm). The removal channels than hard K+ or Na+.34 Because of better mobility of capacity q plotted against the final equilibrium concentrations + + Cs compared with the organic amines, we anticipated that Cs Ce is graphed in Figure 2a. It was found that the equilibrium in the channels can be further exchanged out through data can be fitted with Langmuir model with R2 = 99.2%, which concentration difference by “hard” cations in high-enough implied that the adsorption sites in K@RWY were equivalent concentrations. The feasibility of our strategy could be seen with each site only adsorbing one Cs+ and the adsorbed Cs+ are

8776 DOI: 10.1021/acs.chemmater.6b04273 Chem. Mater. 2016, 28, 8774−8780 Chemistry of Materials Article

the regenerated K@RWY can still retain around 80% of the removal capacities (248 mg/g). To verify the improvement of ion-exchange performance by this strategy, adsorption kinetic studies of K@RWY and pristine RWY were performed at room temperature. As depicted in Figure 2c, the adsorption rate of pristine RWY was much slower than that of activated RWY. More than 3 h is needed to reach the equilibrium for pristine RWY and the removal efficiency of pristine RWY is only close to 28% even after 24 h Cs ∼ (Kd 390 mL/g). Interestingly, K@RWY can remove >97% of Cs+ in 5 min, which is comparable to KMS-1. The distribution coefficient is as large as 105 mL/g (255-fold as that of pristine form) when the solution reached equilibrium. The pristine RWY showed a maximum exchange capacity of 87 mg/ g, which is also significantly lower than that of K@RWY (316 mg/g). The enhancement of ion-exchange performance clearly demonstrated the advantage of stepwise ion-exchange strategy Figure 2. (a) Equilibrium curve for cesium uptake fitted by Langmuir for amine-directed chalcogenide frameworks. Minor fluctua- − model with Ci =1500 ppm (RT, V:m = 1000 mL/g). (b) tions of the kinetic curves in this work were often observed in Distribution coefficient and removal efficiency for cesium uptake other sorbents too, likely due to the dynamic exchange under different initial concentrations. (c) Adsorption kinetics of K@ 25,26,29 + process. RWY and Pristine RWY for Cs uptake with initial concentration Ion-exchange experiments performed under different pH around 50 ppm at room temperature (V:m = 1000 mL/g). (d) pH- values showed that the Cs+ uptake of K@RWY remained dependent cesium uptake. The initial concentrations were set to 10 ffi ppm. e cient within a wide pH range (Figure 2d). The removal efficiency can still be more than 80% even at pH = 11.8. The fi localized without transmigration. The homogeneous surface is performance is better than layered sul de sorbents (e.g., KMS- likely due to the high symmetry of RWY.34 1, KTS-3). Moreover, the stability of K@RWY is also very The maximum adsorption capacity of K@RWY was impressive. The compound could retain the crystalline structure ≤ ≤ determined to be 316 mg/g (∼2.4 mmol/g), comparable to in the condition of 1.6 pH 11.8 (Figure S4). The − the most efficient Cs+ sorbents (1.86−4.1 mmol/g).25,36 38 supernatant became turbid when K@RWY was soaked in even The capacity reached about 85% of its theoretical value. higher basic solution (pH > 11.8) but the structure of the Notably, the Langmuir constant was calculated to be 0.22 L/mg remaining solid remains unchanged. We also tested the ion exchange performance of cesium (29 L/mmol), which is only second to KTS-1, but K@RWY + + 2+ 2+ has a higher removal capacity (Table 1). Considering the high uptake in the presence of large excess of Na ,K,Ca ,Mg (Figure 3) because they were the most abundant cations in real Table 1. Comparisons of Cs+ Ion-Exchange Parameters water samples including seawater or groundwater and hence Fitted by Langmuir Model could be competing ions during cesium removal. The tolerance of cesium uptake on these competitive ions was found very a materials b (L/mmol) Kd (mL/g) qm (mg/g) impressive. The removal efficiency is more than 80% and the 3 KMS-125 9.3 ≥104 226 ± 2 distribution coefficient is more than 3 × 10 mL/g at a very n+ + 3 KMS-227 0.78 ≥103 531 ± 28 large M :Cs molar ratio (∼10 ) for any of the competitors. It KTS-139 42.6 ≥105 205 ± 6 KTS-328 12 ≥104 280 ± 11 FJSM-SnS29 0.5 ≥103 409 ± 29 (65 °C) GeSbS-240 11.3 ≥103 231 ± 15 (65 °C) 17 b ≥ 4 ± K6MS NA 10 66 4 K@RWY (this work) 29 ≥105 310 ± 4 aCalculated from the Langmuir model. bNot available. ionic strength of seawater or groundwater, the selectivity is extremely important for the real application. The large value of b indicates that K@RWY would be an excellent sorbent for selective cesium uptake. In addition, the distribution coefficient Kd values, another index of selectivity of adsorbed ions, were found very high. It was kept in the order of 105 mL/g within a wide range of initial concentrations (1−50 ppm), further proving the high selectivity. Kd increases when the initial concentration decreases (200 to 1 ppm), which makes K@ RWY highly suitable to remove 137Cs+ from contaminated seawater with very dilute concentrations. Moreover, K@RWY Figure 3. Competitive ion-exchange experiments with the initial + can remove >95% of the Cs even for the initial concentration concentration of Cs+ of 1 ppm. Variations of the distribution up to 200 ppm (Figure 2b). The regeneration process of K@ coefficient and removal efficiency with Na:Cs molar ratio (a), K:Cs RWY is similar to step 2 of stepwise ion-exchange process and molar ratio (b), Mg:Cs molar ratio (c), and Ca:Cs molar ratio (d).

8777 DOI: 10.1021/acs.chemmater.6b04273 Chem. Mater. 2016, 28, 8774−8780 Chemistry of Materials Article is interesting that K@RWY retained an efficient removal comparable to that of CST at the same condition, the best ffi × 3 ffi + 14 e ciency (Kd = 1.9 10 mL/g, and removal e ciency is commercial Cs sorbent. The kinetics of cesium capture in around 66%) even with a tremendous excess of Na+ (∼5.2 × seawater samples was also found to be very fast (Figure S11). In 104-fold). This has practical significance because the stored addition, nuclear waste remediation demands high anti- nuclear wastewater usually contains high concentrations of Na+. irradiation capability of the adsorbents. Ion exchange experi- By comparing the distribution coefficient of the ions at the ments of the irradiated materials demonstrated that the Cs+ same Mn+:Cs+ molar ratio, one can conclude that the uptake capacity of β-irradiated K@RWY retained most of the competiveness ranking of these ions follows the order of capacity of the untreated form without structural collapse or Ca2+ >Mg2+ >K+ >Na+, meaning calcium ions have the phase transformation (Figure S12), indicating excellent greatest effect on cesium removal whereas sodium ions have the radiation resistance of K@RWY. The results demonstrated least. Notably, the selectivity of K@RWY toward divalent that K@RWY is a promising ion exchanger for radionuclide cations including Ca2+ and Mg2+ is very high and is superior to 137Cs+ removal. that of FJSM-SnS and KMS-1 which have the selectivity order Besides serving as adsorbents for radionuclides removal, the 2+ 2+ + of Ca >Mg >Cs. For example, the Kd values of KMS-1 activated zeolitic chalcogenide frameworks synthesized by were found less than 102 mL/g in the presence of only 12-fold stepwise ion-exchange strategy may also find applications in 25 32,41 excess of calcium ions. In contrast, the Kd value of K@RWY gas adsorption and fast ion conductors. Our N2 adsorption was more than 104 mL/g at the same condition. One possible data confirm that K@RWY has a higher adsorption capacity of explanation is that in a flexible layered structure, more highly 298 cm3/g (Figure S13) compared with that of Cs@RWY charged cations preferentially occupy the interlayer space due (∼200 cm3/g). Complete ion exchange with Na+ can also be to the higher electrostatic interaction, whereas in a rigid 3D achieved by immersing K@RWY in highly concentrated NaCl structure monovalent cation has an advantage over more highly solution (1 M). The Na+ balanced zeolitic chalcogenide exhibits charged cations to meet the charge balance requirement and a large ionic conductivity of 6.0 × 10−4 Scm−1 under 30 °C and size match simultaneously. 55% relative humidity (Figures S14 and 15). It should be noted As mentioned above, the activated RWY exhibited excellent that ion exchange based on either pristine RWY or Cs@RWY selectivity for cesium uptake. We were then motivated to test its at the same condition is not complete due to the “harder” applicability in real water samples, in which Cs+ ions were character of the sodium ion.32,34 These results further highlight intentionally added with extremely dilute concentration the significance of a stepwise ion-exchange strategy to activate (around 1 ppm). Comparisons were also made with KTS-3, amine-directed chalcogenide frameworks. GaSbS-1, and FJSM-SnS (Figures S5−S10). In the potable water samples, the removal efficiencies were 96, 12, and 49%, ■ CONCLUSION + respectively (Figure 4). The results show that the Cs removal In conclusion, we designed and successfully realized a stepwise ion-exchange strategy based on zeolitic chalcogenide (RWY) to replace the organic amines in the channels with “hard” K+. The K@RWY could rapidly capture Cs+ with excellent selectivity, high capacity, good resistance against acid and alkali, and excellent resistance to γ- and β irradiation. High selectivity of Cs+ uptake against Na+,K+,Ca2+, and Mg2+ has been confirmed by further competitive ion exchange experiments. It should also be noted that K@RWY could capture Cs+ efficiently in real water samples including seawater with trace levels. The results indicated that K@RWY is a very promising ion exchanger for the removal of radioactive 137Cs+. Because amine-directed chalcogenide frameworks are a large family of compounds with various compositions and topologies, this strategy reported Figure 4. Comparisons of cesium uptake of different sulfides in real here could greatly extend the applications of this family of water samples (V:m ∼ 1000). The numbers above the cylinders refer materials to nuclear waste remediation and toxic metal to the removal efficiency. The initial concentrations of Cs+ were set to sequestration. be around 1 ppm. (Potable water was found to contain 40 ppm of Na+, 5 ppm K+, 25 ppm of Ca2+, and 5 ppm Mg2+. Seawater samples from ■ ASSOCIATED CONTENT Yellow Sea mainly contain 9000 ppm of Na+, 320 ppm of K+, 1100 *S Supporting Information ppm of Mg2+, and 370 ppm of Ca2+ and other ions with insignificant concentrations.) The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.6b04273. performance of K@RWY is better than these three sorbents in Structural representations, TG, EDS, etc. (PDF) potable water environment. We also evaluated the decontami- nating performance in real seawater in which the ionic strength ■ AUTHOR INFORMATION is substantially high. It was found that K@RWY still had a reasonable efficiency (54%), a little smaller than that of KTS-3 Corresponding Authors * (62%) but much higher than that of other two amine-directed X. Bu. E-mail: [email protected]. * sulfides. To enhance further the cesium uptake of K@RWY, we P. Feng. E-mail: [email protected]. * also reduced the amplitude of V:m to 250 mL/g. That is, the T. Wu. E-mail: [email protected]. adsorption sites have quadrupled. The removal efficiency was ORCID increased to a more pronounced level of ∼80%, which is Min Luo: 0000-0001-8080-0881

8778 DOI: 10.1021/acs.chemmater.6b04273 Chem. Mater. 2016, 28, 8774−8780 Chemistry of Materials Article

Shuao Wang: 0000-0002-1526-1102 (15) Sawhney, B. Potassium and cesium ion selectivity in relation to − Tao Wu: 0000-0003-4443-1227 clay mineral structure. Clays Clay Miner. 1970, 18,47 52. (16) Dyer, A.; Pillinger, M.; Harjula, R.; Amin, S. Sorption Notes characteristics of radionuclides on synthetic birnessite-type layered The authors declare no competing ﬁnancial interest. manganese oxides. J. Mater. Chem. 2000, 10, 1867−1874. (17) Manos, M. J.; Kanatzidis, M. G. Metal sulfide ion exchangers: ■ ACKNOWLEDGMENTS superior sorbents for the capture of toxic and nuclear waste-related metal ions. Chem. Sci. 2016, 7, 4804−4824. We acknowledge National Natural Science Foundation of (18) Aguila, B.; Banerjee, D.; Nie, Z.; Shin, Y.; Ma, S.; Thallapally, P. China (No. 21271135, 21671142), NSF (DMR-1506661, P.F.), K. Selective removal of cesium and strontium using porous Jiangsu Province Natural Science Fund for Distinguished frameworks from high level nuclear waste. Chem. Commun. 2016, Young Scholars (BK20160006), a start-up fund 52, 5940−5942. (Q410900712) from Soochow University, the Priority Academ- (19) Hunger, J.; Beta, I. A.; Böhlig, H.; Ling, C.; Jobic, H.; Hunger, B. Adsorption structures of water in NaX studied by DRIFT spectroscopy ic Program Development of Jiangsu Higher Education − Institutions (PAPD), and Young Thousand Talented Program. and neutron powder diffraction. J. Phys. Chem. B 2006, 110, 342 353. H.-J.Y. was supported by Jiangsu Planned Projects for (20) Nenoff, T. M.; Ockwig, N. W.; Cygan, R. T.; Alam, T. M.; Leung, K.; Pless, J. D.; Xu, H.; Hartl, M. A.; Daemen, L. L. Role of Postdoctoral Research Fund No. 1501095B. W.T. thanks Xie water in the ion selectivity of niobate-based octahedral molecular Jian for radiation and resistance measurements. sieves. J. Phys. Chem. C 2007, 111, 13212−13221. (21) Ockwig, N. W.; Greathouse, J. A.; Durkin, J. S.; Cygan, R. T.; ■ REFERENCES Daemen, L. L.; Nenoff, T. M. Nanoconfined water in magnesium-rich − (1) Brumfiel, G. Fukushima set for epic clean-up. Nature 2011, 472, 2:1 phyllosilicates. J. Am. Chem. Soc. 2009, 131, 8155 8162. 146−147. (22) Cygan, R. T.; Daemen, L. L.; Ilgen, A. G.; Krumhansl, J. L.; (2) Rivasseau, C.; Farhi, E.; Atteia, A.; Coute,́ A.; Gromova, M.; Saint Nenoff, T. M. Inelastic neutron scattering and molecular simulation of ́ the dynamics of interlayer water in smectite clay minerals. J. Phys. Cyr, D. d. G.; Boisson, A.-M.; Feret, A.-S.; Compagnon, E.; Bligny, R. − An extremely radioresistant green eukaryote for radionuclide bio- Chem. C 2015, 119, 28005 28019. decontamination in the nuclear industry. Energy Environ. Sci. 2013, 6, (23) Ockwig, N. W.; Cygan, R. T.; Criscenti, L. J.; Nenoff, T. M. − Molecular dynamics studies of nanoconfined water in clinoptilolite and 1230 1239. − (3) Romanovskiy, V. N.; Smirnov, I. V.; Babain, V. A.; Todd, T. A.; heulandite zeolites. Phys. Chem. Chem. Phys. 2008, 10, 800 807. Herbst, R. S.; Law, J. D.; Brewer, K. N. The universal solvent (24) Manos, M. J.; Ding, N.; Kanatzidis, M. G. Layered metal extraction (UNEX) process. I. Development of the UNEX process for sulfides: Exceptionally selective agents for radioactive strontium removal. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 3696−3699. the separation of cesium, strontium, and the actinides from acidic + radioactive waste. Solvent Extr. Ion Exch. 2001, 19,1−21. (25) Manos, M. J.; Kanatzidis, M. G. Highly Efficient and Rapid Cs (4) Behrens, E. A.; Sylvester, P.; Clearfield, A. Assessment of a Uptake by the Layered Metal Sulfide K2xMnxSn3−xS6 (KMS-1). J. Am. − sodium nonatitanate and pharmacosiderite-type ion exchangers for Chem. Soc. 2009, 131, 6599 6607. strontium and cesium removal from DOE waste simulants. Environ. (26) Manos, M. J.; Kanatzidis, M. G. Layered metal sulfides capture − Sci. Technol. 1998, 32, 101−107. uranium from seawater. J. Am. Chem. Soc. 2012, 134, 16441 16446. (27) Mertz, J. L.; Fard, Z. H.; Malliakas, C. D.; Manos, M. J.; (5) Awual, M. R.; Suzuki, S.; Taguchi, T.; Shiwaku, H.; Okamoto, Y.; + 2+ 2+ Yaita, T. Radioactive cesium removal from nuclear wastewater by novel Kanatzidis, M. G. Selective removal of Cs ,Sr, and Ni by − inorganic and conjugate adsorbents. Chem. Eng. J. 2014, 242, 127− K2xMgxSn3−xS6 (x= 0.5 1) (KMS-2) relevant to nuclear waste − 135. remediation. Chem. Mater. 2013, 25, 2116 2127. (6) Nenoff, T. M.; Krumhansl, J. L. Cs+ removal from seawater by (28) Sarma, D.; Malliakas, C. D.; Subrahmanyam, K. S.; Islam, S. M.; − commercially available molecular sieves. Solvent Extr. Ion Exch. 2012, Kanatzidis, M. G. K2xSn4‑xS8‑x (x = 0.65 1): a new metal sulfide for + 2+ 2+ 30,33−40. rapid and selective removal of Cs ,Sr and UO2 ions. Chem. Sci. (7) Sylvester, P.; Clearfield, A. The removal of strontium and cesium 2016, 7, 1121−1132. from simulated Hanford groundwater using inorganic ion exchange (29) Qi, X.-H.; Du, K.-Z.; Feng, M.-L.; Li, J.-R.; Du, C.-F.; Zhang, B.; materials. Solvent Extr. Ion Exch. 1998, 16, 1527−1539. Huang, X.-Y. A two-dimensionally microporous thiostannate with + 2+ (8) Celestian, A. J.; Kubicki, J. D.; Hanson, J.; Clearfield, A.; Parise, J. superior Cs and Sr ion-exchange property. J. Mater. Chem. A 2015, B. The mechanism responsible for extraordinary Cs ion selectivity in 3, 5665−5673. crystalline silicotitanate. J. Am. Chem. Soc. 2008, 130, 11689−11694. (30) Ma, S.; Huang, L.; Ma, L.; Shim, Y.; Islam, S. M.; Wang, P.; (9) Celestian, A. J.; Clearfield, A. The origin of ion exchange Zhao, L.-D.; Wang, S.; Sun, G.; Yang, X.; Kanatzidis, M. G. Efficient selectivity in a porous framework titanium silicate. J. Mater. Chem. uranium capture by polysulfide/layered double hydroxide composites. 2007, 17, 4839−4842. J. Am. Chem. Soc. 2015, 137, 3670−3677. (10) Mimura, H.; Kanno, T. Distribution and fixation of cesium and (31) Feng, P. Y.; Bu, X. H.; Zheng, N. F. The interface chemistry strontium in zeolite A and Chabazite. J. Nucl. Sci. Technol. 1985, 22, between chalcogenide clusters and open framework chalcogenides. 284−291. Acc. Chem. Res. 2005, 38, 293−303. (11) Abusafa, A.; Yücel, H. Removal of 137Cs from aqueous solutions (32) Lin, Q.; Bu, X.; Mao, C.; Zhao, X.; Sasan, K.; Feng, P. using different cationic forms of a natural zeolite: clinoptilolite. Sep. Mimicking high-silica zeolites: highly stable germanium-and tin-rich Purif. Technol. 2002, 28, 103−116. zeolite-type chalcogenides. J. Am. Chem. Soc. 2015, 137, 6184−6187. (12) Borai, E.; Harjula, R.; Paajanen, A.; Malinen, L. Efficient removal (33) Ding, N.; Kanatzidis, M. G. Selective incarceration of caesium of cesium from low-level radioactive liquid waste using natural and ions by Venus flytrap action of a flexible framework sulfide. Nat. Chem. impregnated zeolite minerals. J. Hazard. Mater. 2009, 172, 416−422. 2010, 2, 187−191. (13) Seino, S.; Kawahara, R.; Ogasawara, Y.; Mizuno, N.; Uchida, S. (34) Zheng, N.; Bu, X.; Wang, B.; Feng, P. Microporous and Reduction-induced highly selective uptake of cesium ions by an ionic photoluminescent chalcogenide zeolite analogs. Science 2002, 298, crystal based on silicododecamolybdate. Angew. Chem., Int. Ed. 2016, 2366−2369. 55, 3987−3991. (35) Baerlocher, C.; McCusker, L. Database of zeolite structures, (14) Datta, S. J.; Moon, W. K.; Choi, D. Y.; Hwang, I. C.; Yoon, K. B. 2012; http://www.iza-structure.org/databases/. A novel vanadosilicate with hexadeca-coordinated Cs+ Ions as a highly (36) Möller, T.; Harjula, R.; Pillinger, M.; Dyer, A.; Newton, J.; Tusa, effective Cs+ Remover. Angew. Chem. 2014, 126, 7331−7336. E.; Amin, S.; Webb, M.; Araya, A. Uptake of 85Sr, 134Cs and 57Co by

8779 DOI: 10.1021/acs.chemmater.6b04273 Chem. Mater. 2016, 28, 8774−8780 Chemistry of Materials Article antimony silicates doped with Ti4+,Nb5+,Mo6+ and W6+. J. Mater. Chem. 2001, 11, 1526−1532. (37) Chang, H.-L.; Shih, W.-H. A general method for the conversion of fly ash into zeolites as ion exchangers for cesium. Ind. Eng. Chem. Res. 1998, 37,71−78. (38) Bortun, A. I.; Bortun, L. N.; Poojary, D. M.; Xiang, O.; Clearfield, A. Synthesis, characterization, and ion exchange behavior of a framework potassium titanium trisilicate K2TiSi3O9 H2O and its protonated phases. Chem. Mater. 2000, 12, 294−305. (39) Kanatzidis, M. G.; Mertz, J. L.; Manos, E. Chalcogenide compounds for the remediation of nuclear and heavy metal wastes. U.S. Patent US 9056263 B2, June 16, 2015. (40) Zhang, B.; Feng, M.-L.; Cui, H.-H.; Du, C.-F.; Qi, X.-H.; Shen, N.-N.; Huang, X.-Y. Syntheses, crystal structures, ion-exchange, and photocatalytic properties of two amine-drected Ge−Sb−S compounds. Inorg. Chem. 2015, 54, 8474−8481. (41) Zheng, N.; Bu, X.; Feng, P. Synthetic design of crystalline inorganic chalcogenides exhibiting fast-ion conductivity. Nature 2003, 426, 428−432.

8780 DOI: 10.1021/acs.chemmater.6b04273 Chem. Mater. 2016, 28, 8774−8780