Efficient Functionalization of Polyethylene Fibers for the Uranium

Aug 29, 2017 - When integrated with atom transfer radical polymerization (ATRP), the grafting of acrylonitrile (AN) and hydroxyethyl acrylate (HEA) ca...
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Efficient Functionalization of Polyethylene Fibers for the Uranium Extraction from Seawater through Atom Transfer Radical Polymerization Venkata S. Neti,† Sadananda Das,† Suree Brown,‡ Christopher J. Janke,§ Li-Jung Kuo,∥ Gary A. Gill,∥ Sheng Dai,†,‡ and Richard T. Mayes*,† †

Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States Department of Chemistry, University of Tennessee, Knoxville, Tennessee, United States § Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States ∥ Marine Sciences Laboratory, Pacific Northwest National Laboratory, Sequim, Washington, United States ‡

ABSTRACT: Brush-on-brush structures are proposed as one method to overcome support effects in grafted polymers. Utilizing glycidyl methacrylate (GMA) grafted on polyethylene (PE) fibers using radiation-induced graft polymerization (RIGP) provides a hydrophilic surface on the hydrophobic PE. When integrated with atom transfer radical polymerization (ATRP), the grafting of acrylonitrile (AN) and hydroxyethyl acrylate (HEA) can be controlled and manipulated more easily than with RIGP. Poly(acrylonitrile)-co-poly(hydroxyethyl acrylate) chains were grown via ATRP on PE-GMA fibers to generate an adsorbent for the extraction of uranium from seawater. The prepared adsorbents in this study demonstrated promise (159.9 g-U/kg of adsorbent) in laboratory screening tests using a high uranium concentration brine and 1.24 g-U/kg of adsorbent in the filtered natural seawater in 21 days. The modest capacity in 21 days exceeds previous efforts to generate brushon-brush adsorbents by ATRP while manipulating the apparent surface hydrophilicity of the trunk material (PE).

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INTRODUCTION Uranium is well-known for its use in nuclear power plants and as a radioactive contaminant in industrial waste and mining waters.1,2 Great efforts have been made in recent years to develop adsorbent materials for the separation of uranium from seawater.3−8 Despite the very low concentration of uranium in seawater, 3.3 ppb, the extraction of uranium from seawater has had continued interest since the mid-1960s. More recently, researchers have focused on polyethylene (PE) fiber-based adsorbents to capture the uranium from oceans selectively due to its high strength and ease of functionalization.9−24 Covalent functionalization of uranium-coordinating organic ligands to the PE fibers provides opportunities to utilize these intriguing materials for uranium capture from seawater. Amidoximecontaining polymers and polymer fibers have received the most interest in seawater uranium extractions due to the higher selectivity in the high ionic strength media with competing ions such as iron, vanadium, zinc, copper, etc.25 Functionalization of amidoxime groups to the PE fibers involves the attachment of nitrile groups, commonly via acrylonitrile, using radiationinduced graft polymerization (RIGP) or atom transfer radical polymerization (ATRP). Adsorbents generated by RIGP suffer from low degrees of grafting, relative to ATRP-based adsorbents, and from side reactions involving radical termination limiting the number of nitrile groups available for © 2017 American Chemical Society

conversion to amidoximes. The ATRP method is chemically versatile, minimizes nitrile-based radical termination mechanisms, and is compatible with both aqueous and organic media. Moreover, it does not require the large capital expenditure involved in RIGP to generate the ionizing radiation.26−29 ATRP, however, is limited in the type of monomer that can be used, in that monomers that can coordinate copper will inhibit the polymerization. While each method has advantages and disadvantages, both still suffer from unwanted side reactions such as cyclization of adjacent nitrile groups. Furthermore, the necessary basic pretreatment of amidoxime-based adsorbents induces hydrophilicity but compromises the mechanical strength and degrades the amidoxime under prolonged reaction conditions.30 Therefore, developing an efficient method for surface engineering of amidoxime (AO) combined with other hydrophilic functional groups such as hydroxyethyl acrylate (HEA) is of crucial importance for further advancement of this class of fascinating materials for uranium uptake. Yue et al. reported the synthesis of copolymer monoliths prepared using a mesoporous ATRP initiator which were used Received: Revised: Accepted: Published: 10826

February 2, 2017 August 27, 2017 August 29, 2017 August 29, 2017 DOI: 10.1021/acs.iecr.7b00482 Ind. Eng. Chem. Res. 2017, 56, 10826−10832

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Industrial & Engineering Chemistry Research to capture uranium from seawater.27 Similarly, Saito et al. used PE fibers that possess polymeric chains of the aromatic ATRP initiator, poly(vinylbenzyl chloride), to grow poly(acrylonitrileblock-tert-butyl acrylate) as an amidoxime precursor with high grafting yields.28 Brown et al. later utilized PVC-co-CPVC fibers, sold commercially under the name Rhovyl, to produce amidoxime-based adsorbents via ATRP.29 While this is the first non-PE fiber-based adsorbent generated by ATRP, it suffers from low mechanical strength. Due to this, PE retains the distinction as the polymer support of interest. The hydrophobicity of PE presents an interesting problem. Typical PE-based adsorbents are grafted with copolymers that transform into hydrogels during the required base pretreatment. Therefore, a hydrogel is entrained within a hydrophobic matrix to extract the uranium from seawater. Grafting vinylbenzyl chloride onto PE, while an excellent ATRP initiator, does little to increase the hydrophilicity of the trunk. Therefore, a more hydrophilic ATRP initiator is needed to facilitate ion transport in the aqueous solution to the adsorbent chelation sites. Herein, we report the effort to induce hydrophilicity in the support polymer through the grafting of a hydrophilic monomer onto PE prior to ATRP polymerization of acrylonitrile and 2-hydroxyethyl acrylate.

to open the epoxide. The resulting hydroxylated GMA was then reacted with α-bromoisobutyryl bromide (BIBB) to introduce the bromide, which serves as the ATRP initiator. PE-GMABIBB fibers (75 mg), DMSO (10 mL), HEA (7.8 mL), AN (6.4 mL), and Me6TREN (0.138g) were added to a round-bottom flask equipped with a magnetic stir bar. The mixture was purged using N2, and then Cu(I)Br (10 mol %) was added to the flask under a N2 flow. The reaction was stirred slowly at 65 °C for 24 h followed by quenching with air and water. The fibers were washed with DMSO and water and subsequently dried under a vacuum at 40 °C overnight. The degree of grafting (d.g.) values were calculated from 100 times the ratio of the weight increase from grafting to the weight of PE-GMA-AN-HEA fibers. High d.g. ≥ 1900% was obtained under the studied conditions. The d.g. values presented in subsequent tables are averaged values from two repeated experiments. Amidoximation of Grafted Acrylonitrile. The PE-GMAAN-HEA fibers were treated with 5 wt % hydroxylamine hydrochloride neutralized with KOH, for conversion into amidoxime (AO) groups. The hydroxylamine solution was prepared using DMSO. Sonication was utilized to facilitate dissolution of the KOH in DMSO. The amidoximation of PEGMA-AN-HEA with hydroxylamine solution was carried out at 70 °C and for 3 h. The samples were then washed with deionized water followed by drying at 40 °C under a vacuum. NaHCO3 Conditioning. The PE-GMA-AO-HEA adsorbents were conditioned with 0.44 M NaHCO3 at 70−80 °C for 24 h before exposure to the screening brine solution as well as filtered seawater for determining the uranium uptake capacity. Characterization Methods. The scanning electron microscopy (SEM) images were collected using a JEOL JSM-6060 SEM at 4 kV. The Fourier Transform Infrared (FTIR) spectra were recorded on a PerkinElmer Frontier FTIR with a single bounce diamond attenuated total reflectance (ATR) accessory at 2 cm−1 resolution and averaged over 16 scans. The solid-state 13 C CP/MAS (cross-polarization/magic angle spinning) nuclear magnetic resonance (NMR) experiments were collected on a Varian Inova 400 MHz NMR spectrometer and referenced to an external standard (hexamethylbenzene) at 17.17 ppm. Screening with Uranyl Brine. Batch screening experiments with high uranium concentration (8 ppm) brine were conducted to identify potential candidates for true seawater investigations. The sodium-based brine solution used for screening is used to mimic the pH (∼8) sodium, chloride, and carbonate content of seawater. This is achieved by generating a brine that consists of 193 ppm sodium bicarbonate, 25 600 ppm sodium chloride, and 8 ppm uranium from uranyl nitrate hexahydrate, all of which are dissolved in deionized water (18.2 MΩ cm−1). A brine sample was collected before the addition of adsorbent to determine the initial uranium concentration. Each of the NaHCO3-conditioned PEGMA-AN-HEA adsorbents (∼15 mg) were then contacted with 750 mL of uranyl brine solution for 24 h at room temperature with constant shaking (400 rpm). After 24 h of shaking, an aliquot was taken, and the initial and final solutions were analyzed using ICP-OES (PerkinElmer Optima 2100DV ICP-OES). The uranium adsorption capacity was determined from the difference in uranium concentration in the solutions, using the following equation:

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EXPERIMENTAL SECTION Materials and Methods. All chemicals were reagent grade or higher. Acrylonitrile (AN), glycidyl methacrylate (GMA), 2hydroxyethyl acrylate (HEA), tetrahydrofuran (THF), αbromoisobutyryl bromide (BIBB), tris[2-(dimethylamino)ethyl]amine (Me6TREN), methanol, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), isopropanol (IPA), hydroxylamine hydrochloride (HA-HCl), sodium chloride (NaCl), and sodium bicarbonate (NaHCO3) were obtained from Sigma-Aldrich. Ultrapure water (18 MΩ cm−1, Thermo Scientific Nanopore) was used in the preparation of HA-HCl and KOH solutions. High-surface-area polyethylene fibers (PE, hollow-gear) were prepared by bicomponent melt-spinning at Hills, Inc. (Melbourne, FL, USA), using polylactic acid (PLA) as the sacrificial sheath polymer for the hollow-gear shaped PE. Uranyl nitrate hexahydrate (UO2(NO3)2·6H2O, B&A Quality) was used to generate the laboratory screening brine, while a 1000 ppm uranium (U) standard solution (High Purity Standards, North Charleston, USA) was used to prepare the inductively coupled plasma optical emission spectrometry (ICP-OES) standards. Radiation-Induced Graft Polymerization (RIGP). The adsorbent fibers were prepared by RIGP at the NEO Beam Electron Beam Cross-linking Facility (Mercury Plastics, Middlefield, OH, USA). Before irradiation, the PLA was removed via a THF reflux, followed by drying at 40 °C under a vacuum. Pre-weighed dry fiber samples were degassed under nitrogen and sealed inside double-layered plastic bags within a nitrogen atmosphere glovebag, and irradiated to a dose of 200 ± 10 kGy using 4.1 MeV electrons and 1.25 mA current from an RDI Dynamitron electron beam machine. The irradiated fibers were transferred to a nitrogen glovebag, stored under dry ice, and immersed in previously degassed grafting solutions consisting of GMA in DMSO and placed in an oven at 64 °C for 18 h. The grafted fibers were washed with DMF and methanol to remove unreacted monomers and homopolymers and dried at 40 °C under a vacuum. Atom Transfer Radical Polymerization (ATRP). The GMA-grafted PE fibers were contacted with dilute sulfuric acid 10827

DOI: 10.1021/acs.iecr.7b00482 Ind. Eng. Chem. Res. 2017, 56, 10826−10832

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Industrial & Engineering Chemistry Research ⎡ initial [U] mg − final [U] L ⎢ uranium capacity = ⎢ g of dry adsorbent ⎣

( )

( mgL ) ⎤⎥

monomer in the process. Finally, GMA grafts well to PE, with high degrees of grafting (up to 2000%) suggesting dense brush structures are possible. The graft process is illustrated in Scheme 1. Here, the PE is irradiated via electron beam with a

⎥ ⎦

× soln. vol. (L)

Scheme 1. Illustration of the Grafting Reactions Involved in the Brush-on-Brush Methodology (Single Oligomer Drawn for Clarity)

The ICP-OES was calibrated using a linear calibration curve comprised from six standard uranium solutions with concentrations ranging from 0 to 10 ppm, which were prepared from 1000 ppm uranium in 5 wt % nitric acid stock solution. A blank solution of 2−3 wt % nitric acid was used to monitor between samples to ensure no carryover of uranium between sample analyses. A solution of 5 ppm yttrium in 2 wt % nitric acid was used as an internal standard to correct for matrix effects, which was prepared from 1000 ppm stock solution (High-Purity Standards, North Charleston, USA). Seawater Screening with Filtered Seawater. The uranium adsorption capacities for the PE-GMA-AN-HEA adsorbents were carried out at the Marine Sciences Laboratory, Pacific Northwest National Laboratory (PNNL) in Sequim, Washington for 21 days in flow-through columns using 0.45 μm filtered ambient seawater. The PE-GMA-AN-HEA adsorbents (∼50 mg each) were conditioned with 0.44 M NaHCO3 at 70− 80 °C for 24 h prior to seawater exposure. The base conditioned adsorbents were packed while wet into columns (1″ diameter, 6″ long). Precleaned glass wool and 5 mm glass beads were used to hold the adsorbents in place within the column. Ambient seawater was pumped from Sequim Bay into holding tanks followed by successive filtration until achieving 0.45 μm filtration for the continuous-flow adsorption experiment. The temperature and flow rate were monitored using a flexible hermetically sealed RTD sensor (OMEGA Engineering, Stamford, CT, USA) and a turbine-style in-line flow sensor (Model DFS-2W, Digiflow Systems), respectively, in 10 min intervals with a data logger. The temperature of the incoming seawater was maintained at 20 ± 1 °C through the utilization of a constant temperature bath, and the velocity of seawater in each column was controlled at ∼2 cm/s using a flow rate of 250−300 mL/min. During the flow-through adsorption experiments, seawater salinity and pH were monitored daily using a hand-held salinity meter (Model 30, YSI) and pH meter (Orion 3 STAR, Thermo). After 21 days of seawater exposure, the adsorbent columns were removed from the test system and rinsed with deionized water to remove residual salt. The adsorbents were removed from the columns and weighed after drying. The adsorbents loaded with metal ions were digested with a 50% aqua regia solution at 80 °C for 3 h and diluted with deionized water to achieve the desired concentration range for IPC-OES analysis. Analysis of uranium and other trace elements in the solutions was carried out using a PerkinElmer Optima 5300DV ICP-OES, with quantification based on standard calibration curves.

200 kGy dose followed by grafting with GMA. The GMA epoxide is opened with dilute acid forming hydroxyl groups. The two hydroxyls on the GMA are reacted with the acid bromide functionality on α-bromoisobutyryl bromide (BIBB) in the presence of triethylamine in THF. Poly(acrylonitrile-co2-hydroxyethyl acrylate) is then grown under ATRP conditions with DMSO as the solvent. The choice of solvent is crucial for high degrees of grafting to ensure both the grafted polymer and monomer are soluble in the solvent. If the polymer is not soluble in the solvent, polymerization will be inhibited, and a lower d.g. will be obtained. Optimization of the ATRP polymerization resulted in grafting yields of 1900%, approximately 6 times higher than that found in RIGP-based polymerizations. FTIR spectra of the PE-GMA, PE-GMA-AN/HEA, and amidoxime-functionalized fibers are shown in Figure 1. The PEGMA in DMSO exhibited the characteristic carbonyl group stretch at 1725 cm−1, along with the epoxy stretches at 1255 and 905 cm−1 corresponding to the stretching vibration of ester groups and the bending vibration of epoxy groups, respectively. The broad peak centered at 3400 cm−1 in the spectrum of PEGMA-OH is attributed to the −OH stretching vibration, after ring opening of the epoxy groups. The new weak stretch of C− Br appeared at 668 cm−1 in PE-GMA-BIBB, suggesting the installation of ATRP initiators to the surface of PE-GMA fibers through a nucleophilic substitution reaction between the acyl bromide groups and the hydroxyl groups. A new stretch indicative of nitrile groups at 2242 cm−1 in PE-GMA-AN/HEA,

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RESULTS AND DISCUSSION Utilizing the glycidyl methacrylate (GMA) as a support for the ATRP initiator provides multiple advantages. First, grafting GMA potentially increases the hydrophilicity of the truck material, which potentially mitigates the hydrophobic nature of the PE in aqueous systems, such as seawater. This is due to the incorporation of the ester moiety from the graft polymer. Second, opening the epoxide with the dilute sulfuric acid provides multiple attachment sites for the ATRP initiators while adding two additional ester functional groups per 10828

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elimination of ammonia (NH3). The lack of a nitrile peak at ∼120 ppm indicates the complete conversion of nitrile to amidoxime. Upon grafting, the fibers became very brittle. Due to this, whole, dry fibers were unobtainable for SEM imaging. While wet, the fibers were still flexible and did not break as easily, yet, while dry, the fibers readily broke upon touch. This brittleness is attributed to the high degrees of grafting achieved. The SEM images of the RIGP-grafted and ATRP-grafted fibers are shown in Figure 3. The initial diameter of the PE-GMA fibers is 30

Figure 1. FT-IR spectra of PE-GMA, PE-GMA-OH, PE-GMA-BIBB, PE-GMA-AN/HEA, and PE-GMA-AO/HEA.

confirmed the functionalization of nitrile groups through the ATRP reaction. After amidoximation, the −CN stretch of PE-GMA-AN-HEA fibers at 2242 cm−1 disappeared and the carbonyl stretch shifted from 1719 to 1700 cm−1, which agrees with the NMR chemical shift values. The presence of CN, C−N, and N−O stretches at 1642, 1391, and 931 cm−1, respectively, confirmed the formation of amidoxime functional groups. Also, during amidoximation, some −COOH groups formed because of hydrolysis of the HEA esters (1556 cm−1) and a new band at 929 cm−1 corresponding to the N−O stretching vibration, indicative of the amidoxime formation. It is also worth mentioning that the absence of homopolymerization of nitrile groups, i.e., polyacrylonitrile, onto ATRP initiators was confirmed by the presence of −OH groups of HEA in the FT-IR spectra. Carbon-13 cross-polarization solid-state NMR (CP/MAS NMR) was used to understand the chemical constituents on the adsorbent to gain insight into the sites present. The 13C CP/MAS NMR characterization of hollow gear PE-GMA fibers (Figure 2) indicated similar signals for those shown in the AF series of adsorbents published by Das et al.25 After amidoximation, signals at ∼149 ppm and a broad peak at ∼157 ppm can be assigned to the oxime carbons in the cyclic backbone and the iminic carbons of amidoxime. This indicates similarly the cyclization of adjacent amidoxime groups with

Figure 3. Scanning electron microscope image of PE-GMA (left) and the PE-GMA-AN/HEA (right) fibers.

μm, while after grafting of AN/HEA, it increased to ∼70−80 μm. The surface of the fiber, specifically on the outer surface of the wings, appears to be rougher than the pre-ATRP grafted fiber. The surface roughness is attributed to surface grafts of the AN/HEA polymer. This is contrary to the fibers produced by RIGP where little surface roughness is observed. This difference could influence the base conditioning requirements, allowing for milder base contact to facilitate capacity enhancements. The laboratory batch prescreening of the adsorbents illustrates fundamental differences between traditional RIGP and the brush-on-brush ATRP adsorbents reported herein. In the traditional adsorbents, an aqueous 0.44 M KOH solution is utilized to pretreat, i.e., “condition,” the adsorbent prior to contacting a uranium-containing solution. The reasons for this pretreatment are currently not fully understood; however, it can be equated to hydrogel formation and stretching of the polyethylene trunk. In the case of the ATRP-based adsorbents grown from a GMA brush, a strong base pretreatment will cleave the ester, resulting in no functionality present to sequester the uranium. Indeed, this occurred when the ATRPbased adsorbents were contacted with 0.44 M KOH at 80 °C for 1 h. This led to the development of a more facile pretreatment process. No base conditioning resulted in no capacity within the high uranyl brine solution, suggesting the need still exists for a basic pretreatment. Therefore, sodium bicarbonate was chosen, representing a weak base, to pretreat the adsorbent while not cleaving the ester. Traditional times for base pretreatment were initially chosen. After 1 h of base pretreatment in 0.44 M NaHCO3 at 80 °C, the capacity was negligible (10 g-U/kg-ads) in the laboratory screening brine. Lengthening the time did not result in significant uranium capacity until 24 h at 80 °C contact time. At this point, the 400% d.g. sample exhibited 123 g-U/kg-ads capacity, and the 1900% d.g. adsorbent exhibited a capacity of 165 g-U/kg-ads. This difference illustrates the difference in the d.g. as well. The lower d.g. adsorbent is expected to exhibit a lowered uranium capacity, which was observed. The d.g. is not proportional to the uranium capacity, however, as the nearly 5-fold increase in the d.g. only resulted in a 1.3-fold increase in capacity. However, this value is in accordance with previously reported

Figure 2. 13C CP/MAS NMR spectra of PE-GMA-AO/HEA. 10829

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Figure 4. Uranium uptake properties of PE-GMA-AN-HEA fibers with a d.g. = 400% at different pH values in a brine consisting of 8 ppm U with the pH adjusted by NaHCO3 or HCl.

Figure 5. Seawater capacity (mmol-M/kg-ads) and selectivity toward uranium of the PE-GMA-AO/HEA adsorbents.

as the 70 °C pretreatment for 24 h did not result in appreciable capacity in 21 days of seawater contact. This illustrates the need for actual seawater testing and not reliance on simulated seawater brine for efficacy determinations. Repeating the experiment after pretreatment at 80 °C for 24 h resulted in an appreciable seawater capacity, 1.24 g-U/kg-ads (average of duplicate samples) after 21 days of seawater contact. This capacity is lower than the recently reported ATRP-based adsorbents from PVC-co-CPVC trunks29 where AN and HEA are copolymerized randomly via ATRP onto the chlorinated trunk. The capacity observed in 21 days is, however, comparable to that observed by Saito et al. from the block copolymer of AN-b-tert-butyl acrylate polymerized from PEgrafted with vinylbenzyl chloride after 56 days of seawater contact. Figure 5 depicts the extraction capacity and selectivity for the predominant metals extracted from seawater, i.e., iron, vanadium, uranium, zinc, and copper. Calcium (0.30 mmol-

values for the AF series of adsorbents.25 Uranium adsorption by amidoximes is pH dependent. Therefore, the 400% d.g. adsorbent was screened at various pH values to determine the extraction effectiveness. The maximum adsorption occurred at a pH of 6 with a capacity of 160 g-U/kg-ads (Figure 4). At a pH of 8, the 123 g-U/kg-ads is comparable to the 160 g-U/kgads, suggesting this would be a good candidate for seawater screening. It is interesting to note the high adsorption capacity at pH = 4, suggesting a potentially broader application for the adsorbent in acidic media. Seawater screening at a marine site ultimately determines the efficacy of an adsorbent. The Marine Sciences Laboratory of the Pacific Northwest National Laboratory determined the adsorbent capacity with 0.45 μm-filtered seawater. All initial marine testing was conducted with adsorbents that received 70 °C base pretreatment. This base conditioning was optimal in the high uranyl concentration brine and therefore was expected to translate to seawater testing. However, this was not the case, 10830

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Ca/kg-ads) and magnesium (0.68 mmol-Mg/kg-ads) are omitted from the figure for clarity, as these two metals are major ions in seawater and dominate the ions released during acid elution. In this plot, the selectivity (red squares) is defined as the millimoles of metal extracted divided by the millimoles of uranium extracted. It is important to note that while uranium is extracted at high values, vanadium, iron, and zinc are extracted in higher amounts than the uranium, resulting in uranium having a lowered selectivity relative to these metals.

REFERENCES

(1) Emsley, J. Nature’s Building Blocks: An A-Z. Guide to the Elements, 2nd ed.; Oxford University Press: New York, 2011. (2) Final Environmental Impact Statement for Standards for the Control of Byproduct Materials from Uranium Ore Processing; U.S. Environmental Protection Agency: Washington, DC, 1983; vol. 1, pp D-12− D-13. (3) Davies, R. V.; Kennedy, J.; McIlroy, R. W.; Spence, R.; Hill, K. M. Extraction of uranium from seawater. Nature 1964, 203, 1110. (4) Kanno, M. Present status of study on extraction of uranium from seawater. J. Nucl. Sci. Technol. 1984, 21, 1. (5) Kuroda, R.; Oguma, K.; Mukai, N.; Iwamoto, M. Anion-exchange enrichment and spectrophotometric determination of uranium in seawater. Talanta 1987, 34, 433. (6) Takeda, T.; Saito, K.; Uezu, K.; Furusaki, S.; Sugo, T.; Okamoto, J. Adsorption and elution in hollow-fiber-packed bed for recovery of uranium from seawater. Ind. Eng. Chem. Res. 1991, 30, 185. (7) Takahashi, A.; Ueki, Y.; Igarashi, S. Homgeneous liquid-liquid extraction of uranium(VI) from acetate aqueous solution. Anal. Chim. Acta 1999, 387, 71. (8) Zhang, A.; Asakura, T.; Uchiyama, G. The adsorption mechanism of uranium(VI) from seawater on a macroporous fibrous polymeric adsorbent containing amidoxime chelating functional group. React. Funct. Polym. 2003, 57, 67. (9) Tong, J.; Ma, Y.; Arnell, R. D.; Ren, L. Free abrasive wear behaviour of UHMWPE composites filled with wollastonite fibers. Composites, Part A 2006, 37, 38. (10) Astheimer, L.; Schenk, H. J.; Witte, E. G.; Schwochau, K. Development of sorbers for the recovery of uranium from seawater. Part 2. The accumulation of uranium from seawater by resins containing amidoxime and imidoxime functional groups. Sep. Sci. Technol. 1983, 18, 307. (11) Prasad, T. L.; Saxena, A. K.; Tewari, P. K.; Sathiyamoorthy, D. An engineering scale study on radiation grafting of polymeric adsorbents for recovery of heavy metal ions from seawater. Nucl. Eng. Technol. 2009, 41, 1101. (12) Rao, L. Recent International R&D Activities in the Extraction of Uranium from Seawater, report LBNL-4034E; Lawrence Berkeley National Laboratory: Berkeley, CA, March 15, 2010. (13) Abney, C. W.; Mayes, R. T.; Piechowicz, M.; Lin, Z.; Bryantsev, V.; Veith, G. M.; Dai, S.; Lin, W. XAFS investigation of polyamidoxime-bound uranyl contests the paradigm from small molecule studies. Energy Environ. Sci. 2016, 9, 448. (14) Pan, H.-B.; Kuo, L.-J.; Wai, C. M.; Miyamoto, N.; Joshi, R.; Wood, J. R.; Strivens, J. E.; Janke, C. J.; Das, S.; Oyola, Y.; Mayes, R. T.; Gill, G. A. Elution of uranium and transition metals from amidoxime-based polymer adsorbents for sequestering uranium from seawater. Ind. Eng. Chem. Res. 2016, 55, 4313. (15) Dietz, T. C.; Tomaszewski, C. E.; Tsinas, Z.; Poster, D.; Barkatt, A.; Adel-Hadadi, M.; Bateman, F. B.; Cumberland, L. T.; Schneider, E.; Gaskell, K.; LaVerne, J.; Al-Sheikhly, M. Uranium removal from seawater by means of polyamide 6 fibers directly grafted with diallyl oxalate through a single-step, solvent-free irradiation process. Ind. Eng. Chem. Res. 2016, 55, 4179. (16) Alexandratos, S. D.; Zhu, X.; Florent, M.; Sellin, R. Polymersupported bifunctional amidoximes for the sorption of uranium from seawater. Ind. Eng. Chem. Res. 2016, 55, 4208. (17) Piechowicz, M.; Abney, C. W.; Zhou, X.; Thacker, N. C.; Li, Z.; Lin, W. Design, synthesis, and characterization of a bifunctional chelator with ultrahigh capacity for uranium uptake from seawater simulant. Ind. Eng. Chem. Res. 2016, 55, 4170. (18) Kelley, S. P.; Barber, P. S.; Mullins, P. H.; Rogers, R. D. Structural clues to UO22+/VO2+ competition in seawater extraction using amidoxime-based extractants. Chem. Commun. 2014, 50, 12504. (19) Parker, B. F.; Knight, A. S.; Vukovic, S.; Arnold, J.; Francis, M. B. A peptoid-based combinatorial and computational approach to developing ligands for uranyl sequestration from seawater. Ind. Eng. Chem. Res. 2016, 55, 4187.

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CONCLUSION Hollow gear polyethylene fibers were irradiated and grafted with glycidyl methacrylate. The glycidyl methacrylate increases the hydrophilicity of the polyethylene while serving as a support for an ATRP initiator. Upon opening the epoxide with dilute acid, the resultant hydroxyls were reacted with αbromoisobutyryl bromide. The bromides on the surface serve as the ATRP initiators during polymerization of acrylonitrile and 2-hydroxyethyl acrylate. The glycidyl methacrylate introduces an ester that is not base-stable; therefore the basic pretreatment was modified from 0.44 M potassium hydroxide at 80 °C for 1 h to 0.44 M sodium bicarbonate at 80 °C for 24 h. Optimization of the bicarbonate pretreatment did not scale to seawater, in that adjusting the temperature to 70 °C resulted in negligible capacity. The seawater screening after pretreatment at 80 °C for 24 h resulted in a uranium capacity of 1.24 gU/kg-ads in 21 days. This value compares well to previous RIGP-ATRP hybrid brush-on-brush structures after 56 days of contact. Therefore, the adsorbent hydrophilicity, in both the trunk polymer through GMA incorporation and in the choice of 2-hydroxyethyl acrylate, results in enhanced uranium capacities from seawater.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Li-Jung Kuo: 0000-0003-1319-7394 Sheng Dai: 0000-0002-8046-3931 Richard T. Mayes: 0000-0002-7457-3261 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This invited contribution is part of the I&EC Research special issue for the 2017 Class of Influential Researchers. This research was conducted at Oak Ridge National Laboratory (ORNL) and the Marine Sciences Laboratory of Pacific Northwest National Laboratory (PNNL). The work was supported by the U.S. Department of Energy (DOE), Office of Nuclear Energy. This manuscript has been authored by UTBattelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges, that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/ downloads/doe-public-access-plan). 10831

DOI: 10.1021/acs.iecr.7b00482 Ind. Eng. Chem. Res. 2017, 56, 10826−10832

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DOI: 10.1021/acs.iecr.7b00482 Ind. Eng. Chem. Res. 2017, 56, 10826−10832