branched polymeric media: boron-chelating resins from ... · 3 versus b (oh) 4 −, is ... (kbr)...

Branched Polymeric Media Boron-Chelating Resins fromHyperbranched PolyethylenimineHimanshu Mishradagger Changjun YuDagger∥ Dennis P Chensect William A Goddard IIIdaggersect Nathan F Dalleska∥

Michael R Hoffmann∥ and Mamadou S Diallosect∥

daggerMaterials and Process Simulation Center Division of Chemistry and Chemical Engineering California Institute of TechnologyPasadena California 91125 United StatesDaggerAquaNano LLC Monrovia California United StatessectGraduate School of Energy Environment Water and Sustainability (EEWS) Korea Advanced Institute of Science and Technology(KAIST) Daejon 305-701 Republic of Korea∥Environmental Science and Engineering Division of Engineering and Applied Science California Institute of Technology PasadenaCalifornia 91125 United States

S Supporting Information

ABSTRACT Extraction of boron from aqueous solutions using selectiveresins is important in a variety of applications including desalinationultrapure water production and nuclear power generation Todayrsquoscommercial boron-selective resins are exclusively prepared by function-alization of styrene-divinylbenzene (STY-DVB) beads with N-methylgluc-amine to produce resins with boron-chelating groups However suchboron-selective resins have a limited binding capacity with a maximumfree base content of 07 eqL which corresponds to a sorption capacity of116 plusmn 003 mMolg in aqueous solutions with equilibrium boronconcentration of sim70 mM In this article we describe the synthesis andcharacterization of a new resin that can selectively extract boron fromaqueous solutions We show that branched polyethylenimine (PEI) beadsobtained from an inverse suspension process can be reacted with glucono-15-D-lactone to afford a resin consisting of spherical beads with high density of boron-chelating groups This resin has a sorptioncapacity of 193 plusmn 004 mMolg in aqueous solution with equilibrium boron concentration of sim70 mM which is 66 percentlarger than that of standard commercial STY-DVB resins Our new boron-selective resin also shows excellent regenerationefficiency using a standard acid wash with a 10 M HCl solution followed by neutralization with a 01 M NaOH solution

INTRODUCTION

Extraction of boron from aqueous solutions is important in avariety of applications including (i) desalination (ii) ultrapurewater treatment (iii) the production of high purity magnesiumoxide from brines and (iv) nuclear power generation1minus4 Boronis an essential nutrient for plants5 However it adversely affectsplant growth and damages crops (eg citrus and corn) whendesalinated water containing more than 03 mgL of boron isused in irrigation2 In semiconductor manufacturing boron isused as a p-type dopant to silicon6 To control the level ofboron in a silicon chip ultrapure water with boronconcentrations less than 1 ppb (μgL) is required In theproduction of high-purity magnesium oxides by pyrohydrolysisof magnesium chloride (MgCl2) brine excess boron (gt10 mgL) in the brine causes embrittlment of the final metal oxideproducts3 In nuclear power generation 10B-enriched mixturesof boric acid with lithium hydroxide provide inexpensive yetefficient neutron-absorbing media in the primary coolant waterof pressurized water reactors The availability of an efficient andhighly selective boric acid recovery system is the key bottleneck

for the wide-scale implementation of these neutron-absorbingmedia47

Sorption with selective and regenerable resins has emerged asan efficient and cost-effective process for extracting boron fromaqueous solutions2 The predominant boron species in aqueoussolutions H3BO3 versus B(OH)4

minus is determined by the pH ofthe solution [H3BO3(aq) pKa = 924] It is well-known thatboronborate can selectively complex with organic moietiescontaining two or more vicinal hydroxyl groups (eg diols)8

For example host functionalization with diol-bearing com-pounds has been carried out on a variety of polymeric matricesand hybrid organicminusinorganic mesoporous materials tosynthesize boron-selective ligands and sorbents79minus11 Todayrsquoscommercial boron-chelating resins are exclusively prepared byfunctionalization of cross-linked styrene-divinylbenzene (STY-

Received April 17 2012Revised July 3 2012Accepted July 24 2012Published July 24 2012

Article

pubsacsorgest

copy 2012 American Chemical Society 8998 dxdoiorg101021es301518x | Environ Sci Technol 2012 46 8998minus9004

DVB) beads with diol-bearing compounds such as N-methylglucamine However commercial STY-DVB resins withN-methylglucamine groups (eg the Amberlite IRA-743 resin)have a limited capacity with a maximum free base of 07 eqLwhich corresponds to a sorption capacity of 109 mMolg inaqueous solutions with equilibrium boron concentration ofsim100 mM12 In this article we describe the synthesis andcharacterization of a new family of resins that can selectivelyextract boron from aqueous solutions We show that cross-linked branched polyethylenimine (PEI) beads obtained froman inverse suspension process can be reacted with glucono-15-D-lactone to afford a resin consisting of spherical beads withhigh density of boron-chelating groups This regenerable resinhas a sorption capacity of 193 plusmn 004 mMolg in aqueoussolutions with equilibrium boron concentration of sim70 mMwhich is 66 percent larger than that of standard commercialSTY-DVB resins The overall results of our study suggest thatcross-linked branched PEI beads provide versatile andpromising building blocks for the preparation of regenerableboron-chelating resins with high binding capacity

EXPERIMENTAL METHODS AND PROCEDURESChemicals and Materials Reagent grade chemicals were

used to synthesize all the base PEI beads and boron-selectivePEI resins described in this study Reagent grade (gt98 wt )anhydrous potassium chloride (KCl) sodium chloride (NaCl)and sodium sulfate (Na2SO4) and ACS grade (995) boricacid were purchased from Alfa Aesar Concentrated hydro-chloric acid (12 M) was purchased from EMD The precursorpolyethylenimine macromolecules (PEI) (SP-018 (molecularweightMn = 1800) and SP-200 (Mn = 10000)) were purchasedfrom Nippon Shokubai Co Ltd Sulfonic 100 (brancheddodecyl benzene sulfonic acid 97) was purchased from theStepan Company Reagent grade (ge990) D-glucono-15-lactone 1-bromo-3-chloropropane (BCP) diisopropylethyl-amine (DIPEA) and epichlorohydrin (ECH) were purchasedfrom Sigma-Aldrich Methanol ethanol toluene sodium

bicarbonate (NaHCO3) calcium chloride dihydrate(CaCl2 middot2H2O) magnes ium chlor ide hexahydrate(MgCl2middot6H2O) and sodium hydroxide (NaOH) werepurchased from Mallinckrodt Chemicals Deionized (DI)water was obtained from a Milli-Q filtration unit (minimumresistivity 18 MΩ cmminus1) All chemicals were used as receivedThe commercial STY-DVB resin Amberlite IRA-743 which wasspecifically designed to remove boric acid and borate fromaqueous solutions was purchased from the Dow ChemicalCompany (Midland MI USA)

Resin Synthesis All base PEI beads (BPEI-1 and BPEI-2)were synthesized using an inverse suspension of water-in-toluene stabilized by a surfactant (Figure 1) The base PEIbeads were functionalized respectively with 2-oxiranylmetha-nol and glucono-15-D-lactone to produce two resins (BSR-1and BSR-2) with boron-chelating groups (Figure 1) TheSupporting Information (SI) provides a detailed description ofthe resin synthesis procedures

Resin Characterization The boron-selective PEI resins(BSR-1 and BSR-2) were characterized using a broad range ofanalytical techniquesassays including (i) FT-IR spectroscopy(ii) scanning electron microscopy (SEM) (iii) particle sizedistribution (PSD) analysis and (iv) measurements of waterand amine contents The FT-IR spectra were acquired using aBruker VERTEX 7070v FT-IR spectrometer with potassiumbromide (KBr) pellets and OPUS software for data processingAll the reported IR spectra represent averages of more than 100consecutive scans The SEM images were acquired using a Zeiss1500VP field-emission scanning electron microscope Prior toimaging each resin sample was coated with a thin andconducting graphite film The average diameter of the BSR-1beads was determined using the ImageJ software13 The meandiameter of the BSR-2 beads was measured using a MalvernHydro 2000S particle size analyzer The SEM images (Figure1S) and particle size distribution (Figure 2S) are provided inthe SI

Figure 1 Synthesis and functionalization of PEI resins with boron-chelating groups The Supporting Information (SI) provides a detailed descriptionof the resin synthesis procedures

Environmental Science amp Technology Article

dxdoiorg101021es301518x | Environ Sci Technol 2012 46 8998minus90048999

The water content of each resin was determined by drying a2 g sample of media in a desiccator at ambient temperatureunder vacuum and recording its weight until it remainedconstant The free base capacity (amine content) of each resinwas determined by performing a Mohr titration as described inASTM 2187 sections 100minus10914 In a typical titrationexperiment 4 g of resin was mixed with 10 mL of deionizedwater The resin slurry was packed in a graduated cylinder andallowed to equilibrate for 1 h The bed volume (BV) of theresin was then measured Subsequently the resin slurry waspacked in a fritted glass column and filled with 1 L of a 12 MHCl solution The acid was passed through the sample at therate of 20minus25 mLmin keeping the samples submerged in acidat all times Following this the liquid was drained to the level ofthe samples and the effluent liquid was discarded The columnwas then washed with 600minus750 mL of ethanol until a 10-mLportion of the effluent mixed with 10 mL of water achieved aconstant pH gt 40 The chloride ions bound to the protonatedamine groups of the resins were then eluted out with a 1 L of20 wt solution of sodium nitrate (NaNO3) Following thisthe concentration of chloride in the effluent was measured bytitrating 100 mL of the effluent solution with a solution of silvernitrate (AgNO3) The total amine content (TAC) (meqmL)was expressed as

= times timesV NTAC DRBV (1)

where V and N are respectively the volume (mL) andnormality (meqmL) of the AgNO3 solution BV (mL) is thevolume of the swollen resin and DR is the dilution ratio whichis equal to 10 in this caseBoron Sorption onto Pristine Resins To evaluate the

performance of our new boron-selective resins we carried outbatch studies to measure their sorption capacity in deionized(DI) water and model electrolyte solutions Batch sorptionstudies were carried out to measure the boron sorption capacityof the pristine BSR-1 and BSR-2 resins in DI water 01 M NaClsolution and a model permeate from a seawater reverseosmosis (SWRO) plant (Table 1S of the SI) To benchmarkthe performance of the BSR-1 and BSR-2 resins we alsomeasured the boron sorption capacity of a commercial STY-DVB resin with boron-chelating groups (IRA-743) in DI waterBoron sorption onto each resin was measured by mixing knownamounts of dry resin with aqueous solutions (at neutral pH)containing varying concentrations of boron Followingequilibration of the vials for 24 h the amount of boron sorbedonto each resin (Qsorbed) (millimoles of boron per g of resin)was determined using the following equation

= minusQ C C m( )sorbed bi bf (2)

where Cbi and Cbf are respectively the initial and finalconcentrations of boron (mM) in solution measured bytitration and m is the dry-mass of resin (g) per volume ofsolution (L) In a typical titration experiment 10 mL of a 05 Mmannitol solution was first added to an aliquot of 10 mL ofsupernatant solution (analyte) from each equilibrated sorptionvial Excess mannitol ensured complete binding of the dissolvedboron and release of protons (H3O

+)8 Subsequently eachanalyte was titrated against a 005 M NaOH solution (usingphenolphthalein as indicator) until it became and remainedpink for more than 30 s The concentration of boron in thesupernatant solution (Cbf) after equilibration was calculatedusing the following equation

= timesC C V V( )bf NaOH NaOH analyte (3)

where VNaOH and CNaOH are respectively the volume (mL) andconcentration (mM) of the NaOH solution and Vanalyte is thevolume of analyte (mL) Figure 3S shows that the target andmeasured boron concentrations in a series of samples in DIwater are within 05minus3 thereby confirming the accuracyprecision of the titration method in aqueous solutions withboron concentration gt2 mM8

Boron Sorption onto Regenerated Resins We alsocarried out batch studies to measure the boron sorptioncapacity of the BSR-1 and BSR-2 resins following oneregeneration cycle In a typical experiment 1 g of resin (dry-weight equivalent) was packed in a fritted glass column andeluted with a 50 mM boric acid solution until the effluentconcentration was equal to the feed concentration The resinwas regenerated by elution with a 10 M HCl solution followedby neutralization with 01 M NaOH solution Similarregeneration conditions were employed in previous studies ofboron-selective resins91012 Each regenerated resin wassubsequently washed with DI water until the pH of therinsewater remained constant (pH sim60) The neutralizedresins were collected by filtration over a Buchner funnel Batchsorption studies were subsequently carried out to measure theboron sorption capacity of the regenerated BSRs in DI waterusing the procedures described above

RESULTS AND DISCUSSIONResin Synthesis and Characterization Boron-selective

resins (BSRs) such as the commercial Amberlite IRA-743 resinare prepared by functionalization of cross-linked STY-DVBbeads using a two-step process15 In the first step chloromethylgroups are attached to the STY-DVB resins via a FriedelminusCraftsreaction involving the aromatic rings of the resin and an alkylhalide such as chloromethoxymethane in the presence of aLewis acid catalyst In the second step the chloromethyl groupsare reacted with N-methylglucamine to produce boron-chelating resins with vicinal diol groups While the aminationof chloromethylated STY-DVB beads is a facile reaction whichtakes place in high yield extensive side-reactions including thesecondary cross-linking of the aromatic rings of STY-DVBbeads via ldquomethylene bridgingrdquo occur during chlomethyla-tion1516 This reduces the number of functional sites availablefor amination and as a result STY-DVB resins with N-methylglucamine groups such as the Amberlite IRA-743 resinhave a limited capacity with a maximum free base of 07 eqLIn our efforts to develop BSRs with higher binding capacitythan those of commercial STY-DVB resins we selectedbranched polyethylenimine (PEI) as precursor both for itshigh content of reactive primarysecondary amine groups andavailability from commercial sources71718 The new BSRs wereprepared using a two-step process as illustrated in the reactionschemes shown in Figure 1 During the first step two branchedPEI macromolecules (with molar mass (Mn) of 1800 and 10000 Da) were respectively cross-linked with epichlorohydrinand a mixture of epichlorohydrin (ECH) and 1-bromo-3-chloropropane (DCP) to afford spherical beads using theinverse suspension process described by Chang et al19 In thesecond step the PEI beads (prepared using the PEI precursorswith Mn = 1800 and 10 000 Da) were functionalizedrespectively with 2-oxiranylmethanol and glucono-15-D-lactone to prepare two resins (BSR-1 and BSR-2) withboron-chelating groups The SI provides all detailed descrip-



tions of the procedures used to synthesize the BSR-1 and BSR-2 resins These new resins were characterized using a broadrange of analytical techniquesassays including (i) measure-ments of water and amine contents (ii) FT-IR spectroscopy(iii) SEM imaging and (iv) particle size distribution analysisTable 1 lists the total amine contents (TAC) of the BSR-1

and BSR-2 resins along with those of their precursor PEI beads

(BPE-1 and BPE-2) Table 1 shows that the TAC of the BPEI-1and BPEI-2 resins are both equal to 90 mMolg Howeverconsistent with the reaction schemes of Figure 1 the TAC ofthe BSR-2 resin (721 mMolg) is lower than that of the BSR-1resin (802 mMolg) Figure 2 shows the FT-IR spectra of the

BSR-2 and BPEI-2 resins The FT-IR spectrum of the BSR-2resin (Figure 2) exhibits some characteristic features ofcompounds with amide groups (eg CO stretch at 1660cmminus1) and hydroxyl groups (eg OH stretching at 3257 cmminus1)Figure 1S of the SI shows representative SEM micrographs ofthe BSR-1 and BSR-2 resin beads Using the ImageJ software13

we estimate the average diameter of the BSR-1 resin beads tobe equal to 604 μm plusmn 11 Note that the average diameter ofthe BSR-1 resin beads is significantly lower than those of STY-DVB resin beads The particle size distributions (PSD) of suchcommercial resin beads range from 300 to 1200 μm with amean diameter of 700 μm15 Figure 2S of the SI shows the PSDof the BSR-2 resin beads is comparable with that of commercial

STY-DVB resin beads In this case the PSD of the BSR-2beads which was measured using a Malvern Hydro 2000Sparticle size analyzer range from 352 to 829 μm with a volume-averaged mean diameter of 551 μm

Batch Sorption and Regeneration Studies Figure 3Ashows the sorption isotherms of boron onto the BSR-1 BSR-2

and Amberlite IRA 743 resins in DI water Figure 3B highlightsthe reproducibility of the sorption measurements Wesubsequently used the IGOR Pro 620 software to fit eachsorption isotherm to a Langmuir model as given below

=+

QK C C

K C10sorbedb max eq

b eq (4)

where Qsorbed (mMolg) is the mass of sorbed boron Cmax(mMolg) is the resin sorption capacity at saturation Kb(mMminus1) is the resin sorption constant and Ceq (mM) is theequilibrium concentration of boron in the aqueous phase Table2 lists the estimated Cmax and Kb values for the BSR-1 BSR-2and Amberlite IRA-743 resins Table 2 shows that the boronsorption capacity of the BSR-1 resin in DI water (Cmax = 121 plusmn013 mMolg) is comparable to that of the STY-DVBAmberlite IRA-743 resin which has a sorption Cmax = 116 plusmn003 mMolg Note that our estimated Cmax value for theAmberlite IRA-743 resin is very close to the measured value of109 mMolg reported by Xiao et al12 Table 2 shows that theBSR-2 resin has a boron sorption capacity of 193 plusmn 004mMolg in aqueous solution with equilibrium boronconcentration of sim70 mM This sorption capacity is 66percent larger than that of the Amberlite IRA-743 resin Notethat Figure 3A suggests the Amberlite IRA-743 resin has ahigher sorption capacity at lower boron concentration i e sim2mM However due to the limited sensitivity of our boron

Table 1 Water and Total Amine Contents of Boron-Selective and Base PEI Resins Evaluated in This Study

resin matrix functional group

watercontent()

total aminecontent

(mMolg)

BSR-1 cross-linkedPEI

cis-diol 37 802


pentahydroxyhexanamide 43 721

BPEI-1 cross-linkedPEIa

amines 68 90


amines 65 90

aThe base PEI resins contain primary secondary and tertiary amines

Figure 2 FT-IR spectra of BSR-2 and BPEI-2 resins The SI provides adetailed description of the resin synthesis procedures

Figure 3 Boron sorption onto BSR-1 BSR-2 and Amberlite IRA-743resins in deionized water at room temperature



detection method by titration (Figure 3S of the SI) additionalstudies using more sensitive boron assays are needed toquantify the performance of the BSRs in aqueous solutionscontaining boron concentrations lower than 2 mMAs a preliminary assessment of the selectivity of the BSR-1

and BSR-2 resins we measured their boron sorption isothermsin (i) a 01 M NaCl solution and (ii) a simulated permeate of aSWRO desalination plant Table 1S of the SI lists thecomposition of the SWRO permeate which was generatedusing the software IMSDesign21 Figure 4 shows a small but

consistent increase of boron uptake for the BSR-1 resin in the01 M NaCl solution compared to that in DI water For theBSR-2 resin however this increase is negligible In this casethe Cmax value of the BSR-2 resin in the simulated SWROpermeate is very close to that in DI water (Figure 4 and Table2) We speculate that the increase in boron uptake by the BSR-1 resin in 01 M NaCl is the result of two synergistic effects (i)an increase in borate [B(OH)4

minus] concentration with increasingsolution ion strength (Figure 4S of SI) and (ii) borate bindingto the protonated tertiary amine groups of the resin via ionpairing22 However additional experiments are needed tovalidate this hypothesis We also evaluated the regenerationpotential of the BSR-1 and BSR-2 resins by measuring theirboron sorption capacity in DI water after eluting the boron-laden resins with a 10 N HCl solution followed by a rinse withDI water and a wash with 01 N NaOH Similar regenerationconditions were employed in previous studies of the AmberliteIRA-743 resin91012 We found that the boron sorptioncapacities of the pristine BSR-1 and BSR-2 resins in DI waterwere not affected by regeneration (Figure 5 and Table 3)

The overall results of the sorption experiments suggest thatbranched PEI beads provide versatile building blocks for thepreparation of boron-chelating resins As shown in Table 1 thebase PEI beads have a high content of N groups (90 mMolg)including reactive primary and secondary amine groups Thusthey can be functionalized with compounds such as polyols andlactones to afford resins with high densities of boron-chelatinggroups71718 Based on the mechanisms of boron coordinationwith vicinal diol groups proposed by Yoshimura et al23 wepostulate the formation of two types of complexes in ourboron-selective PEI resins For the BSR-1 resin we hypothesizethat the mechanism of boron coordination involves theformation of a tetradentate and bischelate complex of boronborate with two hydroxyl groups from two different andcontiguous branches of the resin (Figure 6) For the BSR-2resin we postulate a mechanism of boron coordinationinvolving the formation of a tetradentate and monochelatecomplex of boronborate with four hydroxyl groups from thesame branch of a resin bead (Figure 6) Note that in bothcoordination models the tertiary amines of the BSR-1 andBSR-2 resins are not coordinated to boron (Figure 6) Wepostulate that these tertiary amine groups provide bufferingcapacity inside the BSR-1 and BSR-2 resins for favorable boronsorption at lower pH by binding the protons released by boricacid following complexation by the resin diol groups23 We alsospeculate that the protonated tertiary amines of the BSR-1 andBSR-2 resins could bind additional boron via ion-pairing withborate ions Finally we would like to mention that thesehypothetical models of boronborate coordination with thehydroxyl groups of the BSR-1 and BSR-2 resins (Figure 6) have

Table 2 Estimated Sorption Capacities (Cmax) and SorptionConstants (Kb) for BSR-1 BSR-2 and Amberlite IRA-743Resins in Deionized Water and Model Electrolytesa

resin Cmax (mMolg) Kb (mMminus1)

BSR-1 (deionized water) 121 plusmn 013 013 plusmn 005BSR-1 (01 M NaCl) 117 plusmn 008 032 plusmn 011BSR-2 (deionized water) 193 plusmn 004 026 plusmn 003BSR-2 (SWRO permeate)b 213 plusmn 010 020 plusmn 003IRA-743 (deionized water) 116 plusmn 003 660 plusmn 203

aCmax and Kb values were determined by fitting each sorption isothermto a Langmuir model bThe composition of the seawater reverseosmosis (SWRO) model permeate is listed in Table 1S of the SI

Figure 4 Boron sorption onto BSR-1 and BSR-2 resins in 01 M NaCland model seawater reverse osmosis (SWRO) permeate at roomtemperature The composition of the SWRO model permeate is listedin Table 1S of the SI

Figure 5 Boron sorption onto regenerated BSR-1 and BSR-2 resins indeionized water at room temperature The saturated BSR-1 and BSR-2resins were regenerated by elution with a 10 N HCl solution followedby neutralization with 01 N NaOH solution

Table 3 Estimated Sorption Capacities (Cmax) and SorptionConstants (Kb) for Pristine and Regenerated BSR-1 andBSR-2 Resins in Deionized Watera


BSR-1 (pristine) 121 plusmn 013 013 plusmn 005BSR-1 (regenerated)b 123 plusmn 016 013 plusmn 006BSR-2 (pristine) 193 plusmn 004 026 plusmn 003BSR-2 (regenerated)b 192 plusmn 005 026 plusmn 004

aCmax and Kb values were determined by fitting each sorption isothermto a Langmuir model bThe resins were regenerated using a standardacid wash with a 10 M HCl solution followed by neutralization with a01 NaOH solution



not been validated by independent spectroscopic and atomisticsimulation studiesEnvironmental Implications As previously stated in the

Introduction extraction of boron from solutions is important invarious environmentalindustrial processes including (i)desalination (ii) ultrapure water treatment and (iii) nuclearpower generation1minus4 In SWRO desalination plants severalstrategies have been evaluated to extract boron from aqueoussolutions water including (i) the addition of 1minus2 additional ROpasses with high pH (sim9) adjustment2425 and (ii) theutilization of enhanced membrane processes such as micellarenhanced ultrafiltration24 However due to its ease ofimplementation sorption with selective and regenerable resinshas emerged as an efficient process extracting boron fromaqueous solutions2 The overall results of our experimentssuggest that cross-linked branched polyethylenimine (PEI)beads provide versatile and promising building blocks for thepreparation of boron-selective resins with high sorptioncapacity Additional investigations are being conducted in ourlaboratory to optimize the physical properties (eg particle sizedistribution and mechanical strength) and performance (egsorption capacity and regeneration efficiency) of our PEI-basedfamily of boron-chelating resins in environmentally relevantconditions including electrolyte solutions containing lowconcentrations of boron (lt2 mM)

ASSOCIATED CONTENT

S Supporting InformationDetailed description of methods and procedures used tosynthesize the new resins and supporting tables and figuresThis material is available free of charge via the Internet athttppubsacsorg

AUTHOR INFORMATION

Corresponding AuthorE-mail mdiallokaistackr Diallowagcaltechedu phone626-395-8133

NotesThe authors declare the following competing financialinterest(s) Prof Mamadou S Diallo is the co-founder of astart-up company (AquaNano) that is scaling and commerci-alizing a new generation of high performance media based onbranched macromolecules

ACKNOWLEDGMENTS

This research was carried out at the California Institute ofTechnology and AquaNano LLC Selected materials character-ization studies (FT-IR and SEM) were carried out at the KoreaAdvanced Institute of Science and Technology (KAIST)Funding for this research was provided by the US NationalScience Foundation (NSF) (CBET Award 0506951) MSDand DPC were supported by the KAIST EEWS Initiative(NT080607C0209721) WAG III was supported partially bythe KAIST World Class University (WCU) program (NRF-31-2008-000-10055)

REFERENCES(1) Elimelech M Phillip W A The Future of seawater desalinationenergy technology and the environment Science 2011 333 712minus717(2) Xu Y Jiang J Q Technologies for boron removal Ind EngChem Res 2008 47 16minus24(3) Grinstead R R Removal of boron and calcium from magnesiumchloride brines by solvent-extraction Ind Eng Chem Prod Res Dev1972 11 454minus460(4) Ocken H An Evaluation Report of Enriched Boric Acid in EuropeanPWRs EPRI Report 1003124 Electric Power Research Institute 2001(5) Blevins D G Lukaszewski K M Boron in plant structure andfunction Annu Rev Plant Phys 1998 49 481minus500(6) Campbell S A The Science and Engineering of MicroelectronicFabrication 2nd ed Oxford University Press New York 2001(7) Smith B F Robison T W Carlson B J Labouriau A KhalsaG R K Schroeder N C Jarvinen G D Lubeck C R Folkert SL Aguino D I Boric acid recovery using polymer filtration studieswith alkyl monool diol and triol containing polyethylenimines J ApplPolym Sci 2005 97 1590minus1604(8) Vogel A I Svehla G Quantitative Inorganic Analysis Longman1987(9) Simonnot M O Castel C Nicolai M Rosin C Sardin MJauffret H Boron removal from drinking water with a boron selectiveresin Is the treatment really selective Water Res 2000 34 109minus116(10) Kaftan O Acikel M Eroglu A E Shahwan T Artok L NiC Y Synthesis characterization and application of a novel sorbentglucamine-modified MCM-41 for the removalpreconcentration ofboron from waters Anal Chim Acta 2005 547 31minus41(11) Gazi M Galli G Bicak N The rapid boron uptake by multi-hydroxyl functional hairy polymers Sep Purif Technol 2008 62 484minus488(12) Xiao Y K Liao B Y Liu W G Xiao Y Swihart G H Ionexchange extraction of boron from aqueous fluids by Amberlite IRA743 resin Chin J Chem 2003 21 1073minus1079(13) Rasband W S ImageJ U S National Institutes of HealthBethesda MD Available online at httpimagejnihgovij(14) ASTM D2187-9 Standard Test Methods for Physical and ChemicalProperties of Particulate Ion-Exchange Resins Available online at httpwwwastmorgStandardsD2187htm(15) Harland C E Ion-Exchange Theory and Practice 2nd ed RoyalSociety of Chemistry London 1994(16) Sherrington D C Preparation structure and morphology ofpolymer supports Chem Commun 1998 2275minus2286(17) Frechet J M J Boz E Chi Y Diallo M S Extraction ofAnions from Solutions and Mixtures Using Hyperbranched Macro-molecules US Patent Application 20100181257 A1 July 22 2010(18) Diallo M S Yu C J Soluble Anion Exchangers fromHyperbranched Macromolecules US Patent Application 20110315636 A1 December 29 2011(19) Chang H T Charmot D Zard S P Polyamine Polymers USPatent 7342083 B2 2008(20) WaveMetrics IGOR Pro 6 Available online at httpwwwwavemetricscom(21) Hydranautics IMSDesign Available online at httpwwwmembranescomindexphppagename=imsdesign

Figure 6 Postulated mechanisms of boron coordination with the BSR-1 and BSR-2 PEI resins in aqueous solutions These coordinationmodels have not been validated by independent spectroscopic andatomistic simulation studies



(22) Hershey J P Fernandez M Milne P J Millero F J Theionization of boric acid in NaCl Na-Ca-Cl and Na-Mg-Cl solutions at25 degC Geochim Cosmochim Acta 1986 50 143minus148(23) Yoshimura K Miyazaki Y Ota F Matsuoka S Sakashita HComplexation of boric acid with the N-methyl-D-glucamine group insolution and in crosslinked polymer J Chem Soc Faraday Trans1998 94 683minus689(24) Busch M Boron removal in sea water desalination Availableonline at httpwwwidswatercomCommonPaperPaper_58Paper_MarkusBuschpdf(25) Roh J Bartels C Wilf M Use of Dendrimers to EnhanceSelective Separation of Nanofiltration and Reverse Osmosis MembranesDesalination and Water Purification Research and DevelopmentReport No 140 2009 Available online at http wwwusbrgovpmtswaterpublicationsreportpdfsreport140pdf



DVB) beads with diol-bearing compounds such as N-methylglucamine However commercial STY-DVB resins withN-methylglucamine groups (eg the Amberlite IRA-743 resin)have a limited capacity with a maximum free base of 07 eqLwhich corresponds to a sorption capacity of 109 mMolg inaqueous solutions with equilibrium boron concentration ofsim100 mM12 In this article we describe the synthesis andcharacterization of a new family of resins that can selectivelyextract boron from aqueous solutions We show that cross-linked branched polyethylenimine (PEI) beads obtained froman inverse suspension process can be reacted with glucono-15-D-lactone to afford a resin consisting of spherical beads withhigh density of boron-chelating groups This regenerable resinhas a sorption capacity of 193 plusmn 004 mMolg in aqueoussolutions with equilibrium boron concentration of sim70 mMwhich is 66 percent larger than that of standard commercialSTY-DVB resins The overall results of our study suggest thatcross-linked branched PEI beads provide versatile andpromising building blocks for the preparation of regenerableboron-chelating resins with high binding capacity

EXPERIMENTAL METHODS AND PROCEDURESChemicals and Materials Reagent grade chemicals were

used to synthesize all the base PEI beads and boron-selectivePEI resins described in this study Reagent grade (gt98 wt )anhydrous potassium chloride (KCl) sodium chloride (NaCl)and sodium sulfate (Na2SO4) and ACS grade (995) boricacid were purchased from Alfa Aesar Concentrated hydro-chloric acid (12 M) was purchased from EMD The precursorpolyethylenimine macromolecules (PEI) (SP-018 (molecularweightMn = 1800) and SP-200 (Mn = 10000)) were purchasedfrom Nippon Shokubai Co Ltd Sulfonic 100 (brancheddodecyl benzene sulfonic acid 97) was purchased from theStepan Company Reagent grade (ge990) D-glucono-15-lactone 1-bromo-3-chloropropane (BCP) diisopropylethyl-amine (DIPEA) and epichlorohydrin (ECH) were purchasedfrom Sigma-Aldrich Methanol ethanol toluene sodium

bicarbonate (NaHCO3) calcium chloride dihydrate(CaCl2 middot2H2O) magnes ium chlor ide hexahydrate(MgCl2middot6H2O) and sodium hydroxide (NaOH) werepurchased from Mallinckrodt Chemicals Deionized (DI)water was obtained from a Milli-Q filtration unit (minimumresistivity 18 MΩ cmminus1) All chemicals were used as receivedThe commercial STY-DVB resin Amberlite IRA-743 which wasspecifically designed to remove boric acid and borate fromaqueous solutions was purchased from the Dow ChemicalCompany (Midland MI USA)

Resin Synthesis All base PEI beads (BPEI-1 and BPEI-2)were synthesized using an inverse suspension of water-in-toluene stabilized by a surfactant (Figure 1) The base PEIbeads were functionalized respectively with 2-oxiranylmetha-nol and glucono-15-D-lactone to produce two resins (BSR-1and BSR-2) with boron-chelating groups (Figure 1) TheSupporting Information (SI) provides a detailed description ofthe resin synthesis procedures

Resin Characterization The boron-selective PEI resins(BSR-1 and BSR-2) were characterized using a broad range ofanalytical techniquesassays including (i) FT-IR spectroscopy(ii) scanning electron microscopy (SEM) (iii) particle sizedistribution (PSD) analysis and (iv) measurements of waterand amine contents The FT-IR spectra were acquired using aBruker VERTEX 7070v FT-IR spectrometer with potassiumbromide (KBr) pellets and OPUS software for data processingAll the reported IR spectra represent averages of more than 100consecutive scans The SEM images were acquired using a Zeiss1500VP field-emission scanning electron microscope Prior toimaging each resin sample was coated with a thin andconducting graphite film The average diameter of the BSR-1beads was determined using the ImageJ software13 The meandiameter of the BSR-2 beads was measured using a MalvernHydro 2000S particle size analyzer The SEM images (Figure1S) and particle size distribution (Figure 2S) are provided inthe SI

Figure 1 Synthesis and functionalization of PEI resins with boron-chelating groups The Supporting Information (SI) provides a detailed descriptionof the resin synthesis procedures

























=+

QK C C

K C10sorbedb max eq

b eq (4)




watercontent()

total aminecontent

(mMolg)


cis-diol 37 802




amines 68 90


amines 65 90

























ASSOCIATED CONTENT


AUTHOR INFORMATION



ACKNOWLEDGMENTS































=+

QK C C

K C10sorbedb max eq

b eq (4)




watercontent()

total aminecontent

(mMolg)


cis-diol 37 802




amines 68 90


amines 65 90

























ASSOCIATED CONTENT


AUTHOR INFORMATION



ACKNOWLEDGMENTS




























ASSOCIATED CONTENT


AUTHOR INFORMATION



ACKNOWLEDGMENTS









branched polymeric media: boron-chelating resins from ... · 3 versus b (oh) 4 −, is ... (kbr)...

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