DTIC ADA597469: Ammonia Vapor Removal by Cu3(BTC)2 and Its Characterization by MAS NMR

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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Ammonia Vapor Removal by Cu3(BTC)2 and Its W911NF-07-1-0053
Characterization by MAS NMR
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
BD2256
6. AUTHORS 5d. PROJECT NUMBER
Gregory W. Peterson, George W. Wagner, Alex Balboa, John Mahle,
Tara Sewell, Christopher J. Karwacki 5e. TASK NUMBER
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAMES AND ADDRESSES 8. PERFORMING ORGANIZATION REPORT
NUMBER
New York Structural Biology
RRL 317B
1275 York Ave.
New York, NY 10021 -6094
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ADDRESS(ES) ARO
U.S. Army Research Office 11. SPONSOR/MONITOR'S REPORT
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The views, opinions and/or findings contained in this report are those of the author(s) and should not contrued as an official Department
of the Army position, policy or decision, unless so designated by other documentation.
14. ABSTRACT
Adsorption equilibria and NMR experiments were performed to study the adsorption and interactions of
ammonia with metal-organic framework HKUST-1, or Cu3(BTC)2 (BTC ) 1,3,5-benzenetricarboxylate).
Ammonia capacities determined from chemical breakthrough measurements show significantly higher uptake
capacities than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the
Cu3(BTC)2 framework. Indeed, 1H MAS NMR reveals that a major disruption of the relatively simple spectrum of
15. SUBJECT TERMS
metal-organic frameworks, Cu3(BTC)2, HKUST-1, 1H MAS NMR, 13C MAS NMR,
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 15. NUMBER 19a. NAME OF RESPONSIBLE PERSON
a. REPORT b. ABSTRACT c. THIS PAGE ABSTRACT OF PAGES Michael Goger
UU UU UU UU 19b. TELEPHONE NUMBER
212-939-0660
Standard Form 298 (Rev 8/98)
Prescribed by ANSI Std. Z39.18
Report Title
Ammonia Vapor Removal by Cu3(BTC)2 and Its Characterization by MAS NMR
ABSTRACT
Adsorption equilibria and NMR experiments were performed to study the adsorption and interactions of
ammonia with metal-organic framework HKUST-1, or Cu3(BTC)2 (BTC ) 1,3,5-benzenetricarboxylate).
Ammonia capacities determined from chemical breakthrough measurements show significantly higher uptake capacities
than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the Cu3(BTC)2
framework. Indeed, 1H MAS NMR reveals that a major disruption of the relatively simple spectrum of Cu3(BTC)2
occurs to generate a composite spectrum consistent with Cu(OH)2 and (NH4)3BTC species under humid conditionssthe
anticipated products of a copper(II) carboxylate reacted with limited ammonia. These species are not detected under dry
conditions; however, reaction stoichiometry combined with XRD results suggests the partial formation of an
indeterminate diammine copper(II) complex with some residual Cu3(BTC)2 structure retained. Cu(II)-induced
paramagnetic shifts exhibited by various species in 1H and 13C MAS NMR spectra are consistent with model
compounds and previous literature. Although results show extensive ammonia capacity of Cu3(BTC)2, much of the
capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.
Adsorption equilibria and NMR experiments were performed to study the adsorption and interactions of
ammonia with metal-organic framework HKUST-1, or Cu3(BTC)2 (BTC ) 1,3,5-benzenetricarboxylate).
Ammonia capacities determined from chemical breakthrough measurements show significantly higher uptake capacities
than from adsorption alone, suggesting a stronger interaction involving a potential reaction with the Cu3(BTC)2
framework. Indeed, 1H MAS NMR reveals that a major disruption of the relatively simple spectrum of Cu3(BTC)2
occurs to generate a composite spectrum consistent with Cu(OH)2 and (NH4)3BTC species under humid conditionssthe
anticipated products of a copper(II) carboxylate reacted with limited ammonia. These species are not detected under dry
conditions; however, reaction stoichiometry combined with XRD results suggests the partial formation of an
indeterminate diammine copper(II) complex with some residual Cu3(BTC)2 structure retained. Cu(II)-induced
paramagnetic shifts exhibited by various species in 1H and 13C MAS NMR spectra are consistent with model
compounds and previous literature. Although results show extensive ammonia capacity of Cu3(BTC)2, much of the
capacity is due to reaction with the structure itself, causing a permanent loss in porosity and structural integrity.
REPORT DOCUMENTATION PAGE (SF298)
(Continuation Sheet)
Continuation for Block 13
ARO Report Number 51980.5-CH
Ammonia Vapor Removal by Cu3(BTC)2 and Its ...
Block 13: Supplementary Note
© 2009 . Published in The Journal of Physical Chemistry C, Vol. 113 (31) (2009), ( (31). DoD Components reserve a
royalty-free, nonexclusive and irrevocable right to reproduce, publish, or otherwise use the work for Federal purposes, and to
authroize others to do so (DODGARS §32.36). The views, opinions and/or findings contained in this report are those of the
author(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by
other documentation.
Approved for public release; distribution is unlimited.
13906 J. Phys. Chem. C 2009, 113, 13906–13917
Ammonia Vapor Removal by Cu (BTC) and Its Characterization by MAS NMR
3 2
Gregory W. Peterson,* George W. Wagner, Alex Balboa, John Mahle, Tara Sewell, and
Christopher J. Karwacki
Edgewood Chemical Biological Center, 5183 Blackhawk Rd., APG, Maryland 21010-5424
ReceiVed: March 26, 2009; ReVised Manuscript ReceiVed: June 12, 2009
Adsorption equilibria and NMR experiments were performed to study the adsorption and interactions of
ammonia with metal-organic framework HKUST-1, or Cu (BTC) (BTC ) 1,3,5-benzenetricarboxylate).
3 2
Ammoniacapacitiesdeterminedfromchemicalbreakthroughmeasurementsshowsignificantlyhigheruptake
capacities than from adsorption alone, suggesting a stronger interaction involving a potential reaction with
the Cu (BTC) framework. Indeed, 1H MAS NMR reveals that a major disruption of the relatively simple
3 2
spectrum of Cu (BTC) occurs to generate a composite spectrum consistent with Cu(OH) and (NH ) BTC
3 2 2 4 3
species under humid conditionssthe anticipated products of a copper(II) carboxylate reacted with limited
ammonia. These species are not detected under dry conditions; however, reaction stoichiometry combined
withXRDresultssuggeststhepartialformationofanindeterminatediamminecopper(II)complexwithsome
residualCu (BTC) structureretained.Cu(II)-inducedparamagneticshiftsexhibitedbyvariousspeciesin1H
n August 24, 200910.1021/jp902736z Introduction saithnsodewlf1,3CecxatMuesnAis3niSgveNaaMpmeR2rmmsoapnneieacntrctaalpoaasrcesiticynonopsfoirsCoteusni3t(tyBwTainCthd)2msS,tCrmoudHucetcEluhMrcaoolEmfitnp1hto:eeugcGnraidetpsyna.eacrnitidcypAisrmedviudioeeutFsoolriretmearcaatttiiuoornne.wAitlhthtohuegshtrruecstuulrtes
K ooi:
Rd Highlyporousstructurespossessingfunctionalizedactivesites
W YOs.org | aorfeaemssmenotniiaalfporresreetnetnstiaonunoifqulieghcthvaallpeonrgse.Pdeuremtaoneitnsthaidgshorvpatpioonr
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aded by CITY COLLEGE d on July 1, 2009 on http:// paiearmzmeecffrffiseeotpeiursnlvccrislietettiutesiagivrselsnelfesoeysaroxrtdaboemahurdervierbnaiaaintwisrtsmlgeuaaitfabbmithfirnhlieeecmeencifeasootfionndenptuctisiepltaotgyimeuarhorablptlfleoefuctn-iwrhpognatltsatoarutsskhressruideueeidcnucehopgphc,frueeetahrhavsgstamaeehevtnneam.ec1caa,e2votmtibonvoBlemoliafeuaewton,mechndatu(ehius1maehcs0oeaoi-addfrw5dbeit)fithssnoyreooln,etrrrtslpmpcaoaottttaioiiimonoobvrndnneee- CbciassCmithnumruueaiep-3lmlai(BodolBmariigTtncrTauslCgan.yCel.tssu)C,rs2anoC,tanuiulthnde3dsf(usdoiBfei(iorSrnTdueBaCntpanotUmdo)hdx2restimthc)eicadodsgcotynao-ptnisfwnhaooaterormareemrrimonkiesxcemioetnirdrvdurogsaaec1vlb4tmtC.aiuyoLluorenee2vv+pfraaoarcalnolfhddudmeiodSamrffltOueeaecwdnSnxrocsdOhbntHeyiccxtoeaooKnilmb-omawUyrilsdpnioSetirCaryncTektuoaegp-e-tn1dnlriBasd,vay1Tate2aeeor,lC1idyydrr3
Downloublishe s(MysOteFmss).oOrfpopraorutsic-cuolaorrdninoatetioanrepomlyemtaelr-so(rPgCanPisc).frameworks ltirnickaerdbotoxyclaartbeo(xByTliCc)oxliyggaenndsa.t1o4,m15sPfrreovmiooursgsatnuidciebsenhzaevnee-s1h,o3w,5n-
P that, once formed, the copper atoms in Cu (BTC) are
3 2
MOFs represent a relatively new class of porous materials unsaturated14,15andmaythereforebeavailableforchemisorption
thatcanbetailoredtomodifysurfacearea,poresize,functional-
withammonia,whichisknowntoformcoordinationcomplexes
ity,andtopologythroughreticularchemistry,3–6amethodology with alkali and transition metals.1,16–18
advancedbyYaghiandco-workers.Reticularchemistrypermits
Thereactionofammoniawiththeindividualbuildingblocks
thesynthesisofpredeterminedstructuresbyutilizingavariety
of Cu (BTC) , i.e., Cu(II) ion and BTC, is well known. In
of inorganic and organic building blocks, thus allowing the 3 2
aqueoussolution,Cu(II)ion,inthepresenceoflimitedammonia,
developmentofhighcapacitymaterialscustomizedforspecific
is initially converted to Cu(OH) ; however, copious amounts
removalchemistries.AlthoughthemajorityofworkonMOFs ofammoniaeventuallyyield[Cu2(NH ) ]2+.19Carboxylicacids
todatehasfocusedongasstorageapplications,7–10thisclassof 3 4
initially form the ammonium salt (Scheme 1) which, with
materials shows promise for a broad range of air purification
sufficient heating, can be pyrolized to their corresponding
applications. Reticular chemistry permits the synthesis of
amides:20
predeterminedstructuresbyutilizingavarietyofinorganicand
It is further noteworthy, in particular, that copper salts of
organicbuildingblocks,thusallowingthedevelopmentofhigh
aromatic acids (i.e., Cu (BTC) ) are known to react with
capacitymaterialscustomizedforspecificremovalchemistries. 3 2
ammonia(withheating)togeneratearomaticamines,20areaction
Although MOFs have been studied for over a decade, very involving scission of the copper-carboxylate ionic bond.
limited data exist on dynamic removal of toxic gases in air
Other studies conducted on gas sorption behavior of
Cu (BTC) ,aswellasotheropen-metalsiteMOFs,concluded
*To whom correspondence should be addressed. E-mail: 3 2
thattheunsaturatedmetalsitesmaycontributesignificantlyto
[email protected]:[phone].Fax:(410)436-
5513. gas uptake.21–23 Furthermore, the relatively weak acidic coor-
10.1021/jp902736z This article not subject to U.S. Copyright. Published 2009 by the American Chemical Society
Published on Web 07/01/2009
Ammonia Vapor Removal by Cu (BTC) J. Phys. Chem. C, Vol. 113, No. 31, 2009 13907
3 2
TABLE1: MicrobreakthroughOperatingConditionsfor
EvaluationofCu(BTC)
3 2
operatingcondition value
temperature 20°C
relativehumidity -40°C(∼0%)dewpointand80%
adsorbentmass 5-10mg
adsorbentvolume 55mm3
flowrate 20mL/min
airflowvelocity 2.7cm/s
residencetime 0.16s
relative humidity), and challenged to Cu (BTC) samples at a
3 2
flowrateof20sccm(referencedto20°C).Theeffluentstream
was continuously monitored for ammonia and water break-
through to saturation with an FTIR (Nicolet 380, with DTGS
detector).
A Cu (BTC) sample was loaded into the sample tube and
3 2
Figure1. Microbreakthroughsystemschematic. driedat100°Cinanitrogenstream.Thesampletubewasthen
conditioned under dry or humid conditions. The ammonia
challengewasthenconducteduntilsaturationandfollowedby
dinationbondsofthestructuremayprovideadditionalreactive
thenpurgedwithacleanstream.Followingthepurgestep,the
centersforammoniaremoval.Inthisworkwepresentadetailed
n August 24, 200910.1021/jp902736z bNEstruxMedpaRykert.ohifmrotehunegthaamalnmSaeloycnstiiiaos,nrneimtroovgaelnpirsooptheertrimesdoaftaC,uP3X(BRTDC,)a2ntdhrMouAgSh ntoeohfnifeftcPretoeshcXa-gteemsRex.nseDpe.occ.AsooeXnndsdd-eristcaeaioyoxmnnppdssolcseoabusftrrtwteeehareekiwrntfiehogrrrusoeltpmdueagxtocthpveoorentnsdefisusratrmnewwdweiadrrisertrheietvohadebemrantsamtiibp1nole0ener0difaao°.mruCRmsmiueensnodgudnleiataasrt
K ooi: Materials.Cu(acetate)2(H2O),Cu(L-tartrate)3(H2O)3,Cu(CO3)- BrukerD8DiscoverX-raydiffractometerinthelocked-coupled
COLLEGE OF NEW YOR09 on http://pubs.acs.org | d dcsargCetairuismaolrCo(cruOCelitupvnitoH3oheg(.ynnBa)l2abttTfw,neoc1CUdnaor,mszn)3Cu2es,aas5LniSlmse-leyAtodb-iinndwe1.2twneg,h4e3zied(o,teB5Dshfnit-osrMoDeti.ruteiCpMrFtflciruc)afyoFuar3w,c(b,rrBebtoeeCheortTxehdeuxyCra3yolf(n)ipolbB2ciourctwTlara,∼aiiCcanaficsi2ne)icd2d4dsday,athfdwinNnroetoadanHhimtso.e4cnasHosAiiztzypCeleenpdmOddterhipr3bwc,eeyhnsaariinaYtzCtetrdeuarahd.grNteeeThm,bNihoi’inyesf-- (((Gossdθ41ctnieofa0.-5pfbtrt4kaθeaesVlc)riÅiztmq,nmoe)ug4mioar(0rprd1reaotatme7dzert0itrAwaea.l6tirn)oiinntodwhassnt/nha-wsmdbet(etea4hoslprc0ocine)kncaoogkokncfibrVfenholtdemra,2uo-diθnc4nmddob0e)eauedtttpmseewul0acdesAme.tid0oen)Cp2rng(.ul1mθe2aS0-oKθ1aSnhθm3Ri)ooe)°pclm.(mdhl11Aeeer°.osorn5ddams4wden(DialedÅtwiitr5moee)5i0dnti0hr0mtaa°i5ulnCdoswgXXiuiuanin--ttgKirrhttoehaaRndyyaea
Y 20 85 °C and subsequently immersed in dichloromethane for 3 characterizationtoshallowdepthtoavoidbackgroundsignals)
Downloaded by CITPublished on July 1, eodtliexnabmpyNraiospai.QsteoerrTudonaahtgtcuneoelrtenaeaaccAnorrhyefrdalsoan1stmtaod7ilvre0sapemA°twpiCmuoreet.noorsesnsEouiaarqr-becues-txii1vlrp.iaaboEntrsegaeidciadnh.guCNsnfauirdm3tor(emoBprglTe1ehCn0oig)-fa2h5Cdwtsuoveo3arra(cepBmutmTiuoaCemnxa)is2meuaqwurtueamidas- c(1asB/ln8seTd6CtaeCrupm,s)3c)d2(gaaBo(nr1foTkn8f-2eC.b3dθN)lum2Hb)eRge4s,Het0ow3aC.l0c0ueOt.2te2iion°o3µn.n(m2s2f.θo.oC4lr))mumw3e(ma5Bds.°oTa1lCaHd)nd)w2deN-diMt1Nhto2RHs01t°4ismHrprweiLCncigOttorh.fa3ADRaon2feOsattihecmcetpoimosnsnoteial.zduiCenitaiiuont(e32ng-,
pressureof1atm.Adsorbedvolumeswereinitiallyreportedat showeddissolvedBTC(8.77ppm)andDMF(8.29,3.37,and3.22
STP and subsequently converted to equivalent liquid volumes ppm),yieldinganapparentmoleratioof0.32DMFperBTC.Thus,
attheboilingpointofnitrogen.Pretreatmentconditionsforthe theCu(BTC) contained7.5wt%residualDMF.
3 2
unexposedandammonia-exposedCu (BTC) were150°Cfor BTC-NHHCO Reaction.BTC(500mg,2.4mmol)wasdry-
3 2 4 3
16 h under vacuum (∼1 × 10-9 atm). mixedwith600mgofNH HCO (7.6mmol)towhich0.5mL
4 3
Ammonia Breakthrough. A microscale breakthrough ap- of H O was added with stirring. Immediate gas evolution
2
paratus was developed to assess the adsorption and reaction indicated the desired reaction was occurring, and it subsided
behaviorofadsorbentsamplesforairpurificationapplications. afterseveralminutes.Theresultingmaterialwasallowedtodry
Thesystemwasdesignedtooperateatnearambienttemperature in air to recover the solid (NH ) BTC. 13C CP-MAS NMR
4 3
overarangeofhumidities.Aschematicofthetestapparatusis confirmedtheidentityandpurityofthetrisubstitutedmaterial.
presented in Figure 1. The test conditions are summarized in BTC-Cu(CO)Cu(OH)-NHHCO Reaction.BTC(100mg,
3 2 4 3
Table 1. Briefly, the system utilizes a small adsorbent sample 480µmol),160mgofCu(CO )Cu(OH) (720µmol),and400
3 2
size(∼5-10mg)packedintoanominal4mmi.d.frittedglass mg of NH HCO (5.1 mmol) were stirred in 1 mL of H O.
4 3 2
tube. The chemical is delivered as a dilute gas stream using a Immediategasevolutionresultedandthesolutionturneddark
gassamplingcanisterwhichhasbeenpurgedwithdryairand blue.Afterbeingstirredovernight,thedark-bluesolutionwas
sealed. A measured volume of ammonia is injected into the allowed to dry in air to yield a dark-blue solid.
canister through a septum using a gastight syringe which is NMR. 1H MAS NMR spectra were obtained using 30-45°
subsequentlypressurizedto1atm.Thecontentsweredelivered pulses and relaxation delays of 1-2 s on Varian Unityplus
byacalibratedmassflowcontrollerandverifiedwithabubble 300WB, INOVA 400WB and 600NB, and Bruker AVANCE
meter.Thedrychemicalstreamwasmixedwitheitheradryor 750WB NMR spectrometers equipped with Doty Scientific
humid air dilution stream to achieve a concentration of 1000 7-mm Super Sonic (300WB and 400WB) and 5-mm XC
mg/m3 at the either dry (-40 °C dew point) or humid (80% (600NBand750WB)VT-MASNMRprobes.13CMASNMR
13908 J. Phys. Chem. C, Vol. 113, No. 31, 2009 Peterson et al.
humid case first exposure suggests a slight discontinuity at
∼50%ofthefeedconcentration,perhapsaresultofsignificant
change in the structure of the Cu (BTC) . The humid second
3 2
exposuresampleshowsrapidbreakthroughconsistentwithloss
of porosity.
The reaction under dry conditions indicates 4 mol NH per
3
mol of Cu (BTC) are sequestered. Thus, in the absence of
3 2
water, the formation of a diammine-copper species is impli-
catedwhichwouldallowuptosixNH ifthereactionwereto
3
gotocompletionpriortoammoniabreakthrough.Suchaspecies,
Cu(NH ) CO ,isknown,25andthecompoundundergoesslow
3 2 3
decomposition upon exposure to moist air, apparently to
Cu(OH) Cu(CO ). Scheme 2 shows the formation of the
Figure2. AmmoniabreakthroughofCu(BTC) indryair. 2 3
3 2
analogouscompoundforCu (BTC) ,“Cu(NH ) BTC ”,under
3 2 3 2 2/3
dry conditions, the carboxylates of BTC serving as the coun-
terionligandsratherthancarbonatetoformthisindeterminate
species.Themoisture-promoteddecompositionofthediammine
species is also shown, forming an indeterminate copper-
hydroxide,theslightformationofwhichisdetectedby1HMAS
NMR (see below).
With ample water, ammonium salts of the BTC might be
COLLEGE OF NEW YORK on August 24, 200909 on http://pubs.acs.org | doi: 10.1021/jp902736z hFTddhhuiAgrruumyyuCmmBi//rdfisuLiieeddi3rtEc(s//yBfisot3.enr.T2ecsdx:CotpAnee)oN2dxxmsppsuHemaoorxm3sesopuunpCorrileseaaeuprbearceiatkicethasrpooaufcgiCthy6218u....(6809o3m(fBoCTl/ukC3g())B2TSCac)m2appaCaltceuis83t(y04105B%....(T0764mCor)el2/l)matiovle aoabao1hbtpwtohHcsnyurffeiioctmtFdsCNitphoMpCchioouisuosiHe1udrpcAps(nsH(Otut3(eeatcOhuSlscsdtoiMHoelesmiHfnaNernedo)stAeds)id2eraMtt2aiCedSmo.tfuiicidnnoRupotfptNT)ir(hontotltO(hhfhMeatrosnsohemusetHesirseRsseImseifd),n(xoxohc2sbrcatmpotruyreNhetihooniemntlaeoiHhsdosssrSnaieieuaawN3dsmcd.cqcfiotd)HhetTtusfprareinedasoye3hlrtmtstmeeeonieieazt.wtsu,eeprrcnacasaeciostald1triaeatopnhoes)smchladonbutwSkuacilmsubtnomcuiiimtti(htomnitylhsinioeiw,daoezeefmncjenone,soslocsrdheyatbrotnhmoNoe2(spcbeswSlp,loHppfyoiroceamenlgwe3ehcrslrshtmsooii)ehisitte.dbmrnaaposbIfbusnreunoeeeeayatScgrrdtlpicfmc2vthteoorhaohew)siarribe.nbdettmtwassimuiTamcuetoiatchesuhrneantitrtivleigidbecaooeosohn2ehlrdnneerfrtt,,,
oaded by CITY ed on July 1, 20 sir“nepCsleaPtcrx”utarmwatioeawsnntendraoeentldauo,ysbfestodaroi)n.fCe1u13dC3-BaC2tTPC1s0w2w,0ad.as6isrueMescmetHdepzxfloocroyitnetahdteitoh((nceNr(oHV9s04as)°-r3piBaponuTlalCs4rei0mzs0)aoWtaidoneBndl dpbtceauoytprsrtiaashnaicebgmitldyemtrh6yifenoNaerfinHcdrNso3thHppupee3merxrcpmi(adoInoIss)luaaiormnrefipstC(heloeuesnf3)crBl,yoaT(ms2eC4).2o0(t,1hfr)eaethnsfiepdnoecrhmco5utm.ima4vtpieiomdlleyntom,eolaafrctoeeaourdnttiadavkiloet,efirnoasinntouhdanpel/
ownlblish creolmaxpaotiuonndd(esleaey obfel2ows.)SuosliuntgionaN5MmRsspceocntrtaacwt etrimeeobatanidneda or (3) some thermal decomposition of the di- and tetraammi-
Du necopper(II) complexes during activation to release their
P on the Varian Unityplus 300WB NMR spectrometer using a
sequestered NH as shown at the bottom of Scheme 2. Note
standard5-mmsolutionNMRprobe.Allspectrawerereferenced 3
thatinthecaseofthedrysample“Cu BTC ”isnottheoriginal
to external TMS. 3 2
structure, just the indeterminate material remaining following
lossoftheNH .Forthedrysample,thepresenceofitsgreater
Results and Discussion 3
residual capacity (1.7 mol of NH per mol of Cu BTC )
3 3 2
AmmoniaBreakthroughCapacity.Ammoniabreakthrough compared to that of the humid sample (0.6) could be simply
experiments for once- and twice-exposed Cu (BTC) samples due to residual, unreacted material (detected by XRD). The
3 2
wereconducted.Inthebreakthroughcurves,Figures2-3,the ammonium carboxylate species formed in the humid sample
twice-exposedsamplesexhibitasignificantlyreducedammonia are apparently extremely stable salts, which would not be ex-
capacity relative to the once exposed samples. Ammonia is pected to release NH during activation to regenerate the free
3
known to be able to complex with either the copper atoms or carboxylate;rather,asdiscussedabove,ammoniumisretained
the carboxylates of the MOF framework. The performance of bycarboxylatesduringheating,eventuallyformingamideswhen
the once- and twice-exposed Cu (BTC) samples under both heatedtosufficientlyhightemperatures(Scheme1)sareaction
3 2
dryandhumidconditionsaresummarizedinTable2.Integration that would not regenerate NH capacity.
3
ofthebreakthroughcurvetosaturationisusedtocalculatethe The reactions depicted in Scheme 2 obviously involve the
dosage(concentration-timeproduct,Ct)andcapacity(retained structural collapse of the MOF, creating materials of indeter-
ammonia mass per mass of Cu (BTC) ). Note that substantial minatestructure.ThisissupportedbyPXRDdata,asshownin
3 2
loss in capacity is exhibited by the twice exposed samples. Figure 5, and 1H MAS NMR (see below). It should be noted
The shape of the first and second exposure breakthrough that,inthepresenceofwater,thereactionpresentedinScheme
curves under dry conditions are similar, while those at humid 2forthehumidconditioncanindeedproceedtocompletionas
conditionsdiffer.Thedrycaseindicatesthatthermalregenera- confirmed by the observation that stirring a water-suspension
tion does result in partially restored adsorption capacity. The of Cu (BTC) with excess NH HCO leads to its complete
3 2 4 3
Ammonia Vapor Removal by Cu (BTC) J. Phys. Chem. C, Vol. 113, No. 31, 2009 13909
3 2
SCHEME2
dissolutionandanimmediatedeepbluecolor,characteristicof Cu (BTC) before and after exposure to ammonia. Figure 6
3 2
the expected [Cu(NH ) (H O) ]2+ complex (see Experimental showsalinearplotofthemeasuredisothermdata,andFigure
3 4 2 2
n August 24, 200910.1021/jp902736z tfiCMShleaeeecCmrtsachipbotuiarunrtichy1d)e4.eghgteCoaroSsaumstdripumebctdruetieudrlsamrgitageeilnnCDeathdtraiyeottsanhtbpaeoaollfsCwoeFug,dm3reo(arB3njpmehTXi.Ccc-Uar)Dan2syicaunutsgadbeiitCfchsfeoresanfydcttwmreteipoamorwneseiitttpsrheuyaidctntwhCetrihIatnFhes. ehp7nxryiteshIsrhsntoisebogurFiweertisenssgsiusaaal.rdeelsAscoso6lgar,tmsbhpdseaalaindocjtoat1vrto0isoythf-ylpuo3et.mhwoMefIetsosthihalsaaeemottcttuenhrhelieaedtlrraramoatstigmaivmeewmwnuipoiltitrahnshetiisaaoaas-dnmuusssrnpoemoelrsifxbafibpelAcldeoarlsatoaaeimwodtdnsorso1euaorl0npmaf-tttipit1ovh.olneeef
K ooi: ComparingthesimulatedpowderX-raydiffractionpatternwith isotherm data on similar Cu-BTC structures indicated that
Rd
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P simulation that are difficult to explain at present.
NitrogenAdsorptionEquilibriaonAmmoniaExposedCu3- Figure6. NitrogenisothermsofCu3(BTC)2beforeandafterammonia
(BTC). Nitrogen adsorption isotherm measurements at the exposure. The dry, once-exposed sample exhibits capillary filling,
2 indicatingthepresenceofsomemacroporosity;however,thehumid,
boiling point of nitrogen, 77.34 K, were performed on
once-exposedsamplehasverylimitednitrogenadsorption,indicating
structuralcollapseand/orporeblockage.
Figure5. PXRDdataindicatethatthehumidonceammoniaexposed
(a)samplehasasignificantlydifferentXRDpatternthantheunexposed Figure 7. Log plot of nitrogen isotherms of Cu(BTC) before and
3 2
sample(c),indicatingacompletechangeintheCu(BTC) framework. after ammonia exposure. Neither the dry, once-exposed nor humid,
3 2
Thedryonce-exposed(b)samplehasapatternsomewhereinbetween once-exposedsamplesshowanylow-levelnitrogenadsorption,indicat-
theunexposedandonce-exposedhumidsamples. ingtheabsenceofmicropores.
13910 J. Phys. Chem. C, Vol. 113, No. 31, 2009 Peterson et al.
TABLE3: CalculatedPorosityandApparentSurfaceArea N /g-sorbent,indicatingcompletecollapseofthestructureand
2
ValuesfromNitrogenAdsorptionIsothermData loss of microporosity.
totalpore DRamicropore On the basis of the NH capacity, the N isotherms are in
3 2
BETcapacity volumeat volumeatSTP goodagreementforthecapacityreductionassociatedwithNH
3
Cu3(BTC)2sample (m2/g) STP(cc/g) (cc/g) adsorption and thermal regeneration.
ammoniaunexposed 1460 0.68 0.54 NMR of Paramagnetic Compounds. For MAS NMR,
dryonce-exposed 150 0.68 0.06 Cu (BTC) presents a challenge, owing to its paramagnetic
3 2
humidonce-exposed 16.2 0.49 0.003 Cu(II).Ishiietal.26havepointedoutthedifficultyofassigning
aDubinin-Radushkevichadsorptionisothermequation. peaks as a result of large paramagnetic shifts and that line-
narrowingbyhigh-powerprotondecouplingisnotaseffective
TABLE4: AmmoniaandNitrogenAdsorptionCapacityof due to the large spectral distribution of paramagnetic shifts.
Cu3(BTC)2 Moreover,McDermottetal.27notedthatwidespinningsideband
relative capacitya patternsarisewhicharereflectiveofthelargeparamagneticshift
Cu(BTC) sample adsorbate pressure (cc/g-adsorbent) dispersion, chemical shift anisotropy, and bulk susceptibility
3 2
dryunexposed ammonia 0.000145 218.0b anisotropy.
dryunexposed nitrogen 0.000145 301c Even still, McDermott et al.27 point out that well-resolved
dryonce-exposed ammonia 0.000145 106.5 MAS NMR spectra can be obtained in favorable cases where
dryonce-exposed nitrogen 0.000145 0.20 slowelectronspin-latticerelaxationandelectronspin-diffusion
aCapacity at P/P ) 0.000145, equivalent to 1000 mg/m3 (1.093 are effective at “decoupling” individual protons from the
i s
mmHg) NH, P ) 7500.0 mmHg at 298 K, V (NH) ) 24.78 L/ (normal) global proton dipolar-coupled spin system. In these
3 sat m 3
mol at 298 K. bAmmonia capacity at 298 K determined from instancescarbon-protonpairsbehaveasisolatedspinsystems.
oaded by CITY COLLEGE OF NEW YORK on August 24, 2009ed on July 1, 2009 on http://pubs.acs.org | doi: 10.1021/jp902736z abptadt8sAaSmasadhhapdndmtr1re0utoeieeemsodsc.%TrcaomsmfloirnrkoeeehnlrceordabtosrwegoabRhpctdee.snst-rodo-nHaiwoheicottcantrtuooyarievoocidgay-husn,ouermi1hplatsankrtr5senstrriasdeiaroeesiddi2ereFcmltvnnlusslrstroiiisdrebooeigzoaose,dsdaisgratunurclsrtpteadthrrdyaulsettinoteaoeetiorsiioietaoarvsnnsea6msennr2pee.,dggxid19nepnles5oohp8anitolsdx8kfinarotttarTiise0eurKtcsplmrsota%lhlstat.eeysysdntie(tadlueosisgSaciRgvdreanonteroeeeneliHereilxsvsnatnipaoa,hthetpttutScTmafeeiteaoaduooharpdumltprlpaennbelreosoplcbldeettegresfotersmssyieiiraatrtdsoetoleiutrhyotuaoipx2nsihdne.trrthnop)siehgeeid.vaFersoesmrCoumenssiIonscguneneiuahnippbcNussdfrtb3orolrgayr(sieodepowrteBttiismorsvueergdVoTsefse7reaeagaueaseiCntemsscrtwsixps0oenheu)tihpo.smg2nditsnr4othoc.,enhafsockwvasoUiyaicFoesonfinenrmsaocidlnptimcguksaradpttapturmolhhheoetneealervodeeeeeefr-rtt. dwspts1s12tCrHufaThh3Hoohppt4ilshCuteopieetroiiiaFnaulnn(nkwo-wclnatgosrdngH-Clihleie,presr1nneiageevHzHetnwacgnehiwds)idegiido)nxieohnrro,ndiupstfa,(letrfme1aeoe.v-prhTmnaHtron)ptreliFhtaaeh22intpdewhdh(nebctoues6slHhayitgelsneers19gi“seit3mlpl,2oasnihpChflOw)nirn-aI-5eeaa-n.persdgt,)pe.rrlMeTphelaa,ropws(sTmbihcenmmfFAuowpiaehooehdifil;eaoeshSurseurgvefiagttsdearcstpueCirck.Nnhlev,aaidlprailgOeeiselreitMsran.otbtir1hnaos,2isdHg82rocebi-ttsRd6,)gs)oaxil,pi,ptoMg(netlinmyosrhl-nnibnmymoplnetdAoism-1ovoetnnegeeoithceS8viseiinecrrddenstfoo3edvotnorfheieNgslbraeuretuardpepcstdfMcaptpada1oproesttb3solwirmmsedsrpCRineybbnt”eweCore;ylagvefregsMepfruiolepdenmortidsua(rhwgeresAgooaistpyssicsatldhdoSiCcohrtatt(wdfaieri,sobνnacvHaqnuaNsobnitRisheuitscaanf3auvtbhMoelaieCrwteMlnt)nle)e(dhCnRinHoe21eateeo(Atodyr-rbb7iHcb5easol1aS3iodwtnHessH2nnsusuiOepdie(atrkMed-pptreνeedlc)hHvvCyprlccRo1AioenaecmttHzon3uo)rrlurdwaC)Sngyeae-f3;lt.,
DownlPublish eaxnhdaiusssteudbsstaamntpialetesd.Tinhitshiesvinadluiceasticvaelcouflaatelodssfroofmmtihceroipsootrhoesrimty mmoagtinoent,icwacsomstpilllexv.alSiducfhorcmonaksiidnegraatsiosingsnmreegnatsrdiinngthrisespidauraa-l
dipolar interactions can similarly be employed to render 13C
data.
MAS NMR assignments for Cu (BTC) and related model
Table 3 summarizes the BET capacity (or apparent surface 3 2
compounds (Figure 8) as discussed below.
area),thetotalporevolume,andtheapparentmicroporevolume.
1H MAS NMR of Cu(BTC). The most striking feature
The fresh material exhibits 10 times greater apparent surface 3 2
present in the 1H MAS NMR spectrum of Cu (BTC) (Figure
areathanthedry,ammoniaonce-exposedsampleand100times 3 2
9) is the wide pattern of rather narrow spinning sidebands,
greater apparent surface area than the humid, ammonia once-
indicative of a rigid species unencumbered by homonuclear
exposedsample.Theapparenttotalporevolumeisnotgreatly
dipolar effects. The central peak of the sideband pattern is at
differentbetweenthethreesamplesasthisquantityiscalculated
8.1 ppm and is straightforwardly assigned to the ring protons
at a high relative pressure, where all three samples show
significantnitrogenadsorption.Theapparentmicroporevolume of the BTC constituent. There are at least two other similarly
indicatethatthemicroporouschannelsofthefreshmaterialhave sharp peaks which, lacking spinning sidebands, are obviously
been greatly widened after exposure to both dry and humid duetomotionallyaveragedspecies.Improvementinresolution
ammoniachallenges,furtherindicatingthattheporousnetwork was obtained at higher field, Figure 9, where near-baseline
has rearranged. resolution is achieved for the three major peaks at 750 MHz
Table4showsthemeasuredcapacitiesoftheCu (BTC) for (17.5 T) along with slightly better resolution of smaller,
3 2
ammonia and nitrogen at a relative pressure equivalent to the overlapping peaks (see below).
ammoniafeedconcentration(1000mg/m3,P )1.093mmHg, The anhydrous form of Cu (BTC) is purple, whereas the
i 3 2
298K)usedinthebreakthroughexperimentsdiscussedabove. hydrated form is blue.28 Exposing a nominally dry sample of
The nitrogen capacity at 0.000145 relative pressure for the Cu(BTC) toairresultedintheseriesofspectrashowninFigure
3 2
unexposedsampleishigherthantheammoniacapacityforthe 10.Itisclearfromthesespectrathatadsorbedwateryieldsthe
same sample by about 38%. Following exposure to ammonia, peakatca.12.6ppm(H O···Cu),withallthepeakstendingto
2
the nitrogen capacity decreases markedly to about 0.20 mL- shiftupfieldwithincreasedwateruptake.Furthernotethatpeaks
Ammonia Vapor Removal by Cu (BTC) J. Phys. Chem. C, Vol. 113, No. 31, 2009 13911
3 2
Figure8. SuccinctstructuralelementsofCu(BTC) andCu(II)-containingmodelcompoundsindicating13CMASNMRassignments.Assignments
3 2
maybereversedforCu(tartrate)(H2O)3(seetext).AlthoughthestructureforCu(meso-tartrate)(H2O)3isshown,Cu(D-tartrate)(H2O)3(andpresumably
the L-tartrate model compound under study) similarly possesses the two types of CO2- and HCOH groups which are differentiated by prime
notation.29ThebinuclearCu(formate) corestructureshownisstabilizedinthepresenceofamine-typeligandsbutnotwater.30ForCu(CO)Cu(OH)
2 3 2
edge-sharing Cu(II) octahedral chains (two octahedrals wide) are represented by triangles, strips of which are linked31 by the CO2- group as
3
indicated.
TABLE5: 13Cand1HMASNMRShiftsObservedforCu(BTC) andModelCompounds
3 2
compound group 13C(temp) 1H ref
CO- -183(331K) -
2
OF NEW YORK on August 24, 2009pubs.acs.org | doi: 10.1021/jp902736z CCCCCCuuuuuu(((((3(aaCfLBolc-OatreTanmt3rCai)tnaCtr)etea2eu))t·2)e(2x(2(O)H(HD(CHH22M5OO)2H2OF))5)N·3y)H2O OCCHCCCCCCCNCOHHHHHOOOOHCH′O32232322---2---2′- 1--1--5-1n-47706o82347131336528sabi97b(((g(((329a(222n(3922(3999a1892l3888Ks891KK)8KKKoK))Kb)))K)s))erveddownto173K 8-2------64-1.85411((.22144((992682(88992((88922KK899K))K88bb)K)KK))) 22t2tthhh679iiisss((11www3HCooo))rrrkkk
GE p:// dCH- 228(298K) 8.1(298K)
COLLE09 on htt HdCH2CO3<(DMF) 2-3480(,229188K(2)98K) -∼9.71,2.77.1(2(92898KK)c) thiswork
Y 20 HCdO(DMF) 165(298K) ca.12.7(298K)d
aded by CITd on July 1, H2OaCpOea2-k.assignments may be reversed. bCH assignments may be reversed. cPeak shifts upfield with increasing water adsorption. dUnderlies
oe
ownlblish assigned to residual, adsorbed DMF (see below) are observed sample(rightsideofFigure11).Ininitialspectra,abroadfeature
DPu to be easily displaced/perturbed by water as previously noted at 2.3 ppm was observed to quickly dissipate within minutes
by Chui et al.14 That adsorbed water shifts intensity from the whereas a second peak at -6.0 ppm persisted for days, and
downfield DMF peak to the upfield DMF peak is consistent thesepeaksareattributedtobulkDMFliquidandDMFsorbed
withtheassignmentofthesetwopeakstoDMF···CuandDMF onthe(exterior)surfaceofthecrystallites.Thepeaksofinterest
displaced to the channels, respectively (see below). at9.7and7.1ppmremainedunalteredwhilethesamplesatat
The identity of the remaining sharp 1H MAS NMR peak(s) room temperature. Annealing the sample at 100 °C for 23 h
was inferred from 13C MAS NMR spectra (see below) which apparentlyassistedreadsorptionofDMF;firstintothechannels
revealedthatthesampleofCu(BTC) containedaconsiderable (7.1ppm)andeventuallycomingtorestattheCu(II)sites(9.7
3 2
amount of DMF, apparently left over from its synthesis.14 ppm). Exposure to air restores the intensity of the water peak
Heating a sample of Cu (BTC) in air at 170-180 °C while at 12.7 ppm with concomitant sharpening of the DMF peaks,
3 2
intermittently observing the 1H and 13C MAS NMR spectra presumablyduetoincreasedmotionaffordedbythecoadsorbed
(Figure 11, left side) revealed immediate loss of the residual water. As further confirmation of these assignments, Soxhlet-
water peak at 12.7 ppm, slower loss of peak intensity at 7.1 extracted (MeOH) Cu (BTC) is totally devoid of both DMF
3 2
ppm, and even slower loss of peak intensity at 9.7 ppm. Loss peaks, leaving only the pristine methine spinning sideband
of intensity for the latter two peaks correlated with loss of patternandaresidualwaterpeak(seeSupportingInformation).
intensityforDMFin13CMASNMRspectra(notshown);thus, 13C MAS NMR of Cu(BTC). 13C MAS NMR spectra
3 2
thesetwopeaksareattributedtoCu(II)-boundDMF(9.7ppm) obtained for Cu (BTC) , with and without high-power proton
3 2
and “channel-DMF”14 (7.1 ppm) as a result of their relative decoupling, are shown in Figure 12 (the large peak near 115
desorptionpropensities.Also,theseassignmentsareconsistent ppm common to both spectra is due to the Kel-F rotor end-
with the water-displacement behavior noted above. caps). The difference between the two spectra is startling: In
Further confirmation of the assignments of these peaks to theabsenceofdecoupling,asharpsetofspinningsidebandsis
adsorbed DMF was obtained by observing changes in 1H and observed containing a center band at 228 ppm, whereas
13C MAS NMR spectra after adding liquid DMF to the same decoupling causes the sharp 228-ppm peak to vanish and the