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S1
Design of cost-efficient and photocatalytically activeZn-basedMOFsdecoratedwithCu2OnanoparticlesforCO2methanation
MaríaCabrero-Antonino,a,†SoniaRemiro-Buenamañana,b,†ManuelSouto,cAntonioA.
García-Valdivia,dDuaneChoquesillo-Lazarte,eSergioNavalón,aAntonioRodriguez-
Diéguez,d*GuillermoMínguezEspallargas,c*andHemenegildoGarcíaa,b,*
Supporting Information
1.Generalmethodsandmaterials2.StructuralfeaturesofMOF(Zn)3.Catalytictests4.Determinationofvalencebandenergiesandopticalgaps5.References
Electronic Supplementary Material (ESI) for ChemComm.This journal is © The Royal Society of Chemistry 2019
S2
1. Generalmethodsandmaterials
Materials and reagents. All the reagents and solvents employed in this study were of analyticalreagentorHPLCgradeandweresuppliedbySigma-Aldrich.
SynthesisofMOF(Zn)-1.3H-benzotriazole-5-carboxylate(10mg,0.06mmol)wasdissolvedin0.5mLofDMFbeforeadding0.5mLofdistilledwater.Separately16.51mg(0.09mmol)ofZn(CH3COO)2wasdissolvedin0.5mLofdistilledwaterbeforeadding0.5mLofDMF.Bothsolutionsweremixedandtheresultingsolutionwasplacedinaclosedglassvesselandintroducedinanovenat95°Cfor12h,afterwhichyellow/brownsinglecrystalswere isolated,whichwerewashedwithwater/methanol.Yield:55%basedonmetal.Heatingatdifferent temperaturesproducedifferentdegreesofbreathingasrevealedbysingle-crystaldiffraction(seebelow).
SynthesisofMOF(Zn)-2.MOF(Zn)-2isobtaineduponheatingat400°Cfor2hcrystalsofMOF(Zn)-1.
Synthesis of MOF-74(Zn). Synthesis of MOF-74(Zn) was adapted from a previously reportedprocedure.S1Amixtureof2,5-hydroxy-1,4-benzenedicarboxylicacid(H2DHBDC)(2.4g,12.1mmol)andzincnitratetetrahydrate,Zn(NO3)2·4(H20)(179mg,60.5mmol)weredissolvedinDMF(240mL)andwater(120mL),dissolvedandheatedto105°Cfor20hoursandthencooledtoroomtemperature.Yellowneedlecrystalswereobtainedinyield51%(basedonH2DHBDC)thatwerewashedwithDMFandmethanol,anddriedinair.
Synthesis of MIL-125(Ti)-NH2. MIL-125(Ti)-NH2 was prepared following previously reportedprocedures.S22-Aminoterephtalicacid(1.43g,7.9mmol)wasdissolvedin20mLofanhydrousN,N-dimethylformamide(DMF).Anhydrousmethanol(5mL)wasthenaddedtothereactionmixtureandthesystemsonicatedfor20min.ThereactionmixturewastransferredtoaTeflon-linedautoclave(50mL)andtitaniumisopropoxide(1.36g,4.8mmol)wassubsequentlyadded.Theautoclavewassealedandheatedat110°Cfor72h.AftercoolingtheTeflontoroomtemperature,theresultingprecipitatewasfiltered,washedwithDMFatroomtemperaturefor12hand,then,washedwithDMFat120°Cfor 12 h. This washing procedure was repeated usingmethanol as solvent. Finally, the solid wasrecoveredbyfiltrationanddriedintheovenat100°C.
SynthesisofCuO2@MOFsusingthephotodepositionmethod(PD).CopperNPsweredepositedinthepreviouslysynthesizedMOFs(MOF(Zn)-1,MOF(Zn)-2,MOF-74(Zn)andMIL-125(Ti)-NH2)usingthePDmethod.S3EachMOFwasdispersedbysonicationinamixtureofwater(13mL)andmethanol(5mL).Then,Cu(NO3)2·3H2Owasdissolvedinwater(2mL)anditwasaddedtotheMOFsolutionatinitial1wt%.Thesolutionwaspurgedwithargonfor20min.Finally,themixturewasirradiatedusinganUV-VisiblelightXelamp(300W)for4h.Theresultingsolidwasfiltered,washedwithwateranddriedintheovenat100°Cfor24h.
S3
2. StructuralfeaturesofMOF(Zn)
Upon heating the as-synthetised material (MOF(Zn)), the solvent molecules (DMF and H2O) areremoved from the channels causing a reversible continuous shrinkage of the structure.S4,S5 ThreedifferentMOFswithadifferentdegreeofbreathinghavebeenisolatedafter2hheatingat100°C,200 °C, and 350 °C, denoted MOF(Zn)-100, MOF(Zn)-200 (corresponding to MOF(Zn)-1), andMOF(Zn)-350.Interestingly,uponfurtherheatingat400˚C,thecrystalstructureexpandsandamuchmoreopenstructureisobtained(MOF(Zn)-2).
TheX-rayintensitydatawerecollectedonaBrukerD8Venturediffractometer(MOF(Zn),MOF(Zn)-RT, MOF(Zn)-100, MOF(Zn)-350 and MOF(Zn)-1) and on a Rigaku Oxford Diffraction Supernovadiffractometer(MOF(Zn)-1andMOF(Zn)-2),usingMo-Kαradiation.ThedataforMOF(Zn),MOF(Zn)-RT, MOF(Zn)-100, and MOF(Zn)-350were integrated with SAINTS6 and corrected for absorptioneffectswithSADABSS7.ThedataforMOF(Zn)-1andMOF(Zn)-2wereprocessedwithCrysAlisProS8,andabsorptioncorrectionsbasedonmultiple-scannedreflectionswerecarriedoutwithSCALE3ABSPACKinCrysAlisPro.AllcrystalstructuresweresolvedwithSHELXTS9andrefinedwithSHELXLS9.TheOLEX2softwarewas used as a graphical interface S10. Anisotropic atomic displacement parameterswereintroduced for all non-hydrogen atoms. Hydrogen atomswere placed at geometrically calculatedpositionsandrefinedwiththeappropriateridingmodel,withUiso(H) = 1.2Ueq(C,O)(1.5formethylgroups).
Eventhoughcrystaldatawascollectedupto0.77Angstromsresolution,crystalsstilldiffractedquiteweaklyathighangleduetotheirratherlowquality(withexceptiontoMOF(Zn)-RTandMOF(Zn)-1)and data were cut off according to intensity statistics, using restraints and constraints duringrefinement.
InMOF(Zn),itwasnotpossibletoclearlyseeelectron-densitypeaksindifferencemapswhichwouldcorrespondwithacceptablelocationsfortheHatomsbondedtoO1W.Therefore,therefinementwascompletedwithnoallowance for theseHatoms in themodel. The contributionsof thesemissingatoms(formulae,formulaweight,etc.)havebeenincludedintheCIF.
In MOF(Zn)-RT, a DMF solvent molecule was found disordered over two alternative positions(0.52:0.48 ratio), and was refined with rigid groups, partially equal anisotropic displacementparametersandrestraintsongeometryanddisplacementparameters.Inthisheavy-atomstructureitwasnotpossibletoclearlyseeelectron-densitypeaks indifferencemapswhichwouldcorrespondwithacceptablelocationsfortheHatomsofthedisorderedDMFmolecule.Therefore,therefinementwascompletedwithnoallowancefortheseHatomsinthemodel.Thecontributionsofthesemissingatoms(formulae,formulaweight,etc.)havebeenincludedintheCIF.
During the refinement ofMOF(Zn)-100, a number of ISOR restraints had to be used to obtainreasonable displacement parameters for all non-hydrogen atoms. Their Uij values were thereforerestrained to be approximately spherical. Severely disordered DMF inMOF(Zn)-100 could not bemodelledreasonably,andwerethereforeremovedfromthediffractiondata(usingtheOLEX2Masktool)butconsideredforcalculationofempiricalformula,formulaweight,density,linearabsorptioncoefficientandF(000).Asolventmaskwascalculatedand322.0electronswerefoundinavolumeof
S4
642.0Å3inonevoid.Thisisconsistentwiththepresenceof2DMFmoleculesperformulaunitwhichaccountfor320.0electrons.
AnumberofISORrestraintshadtobeusedtoobtainreasonabledisplacementparametersforallnon-hydrogen atoms inMOF(Zn)-350. Their Uij values were therefore restrained to be approximatelyspherical. In thisheavy-atomstructure itwasnotpossible to clearly seeelectron-densitypeaks indifferencemapswhichwouldcorrespondwithacceptablelocationsfortheHatomsbondedtoO1W,O2WandO3.Therefore,therefinementwascompletedwithnoallowancefortheseHatomsinthemodel.Thecontributionsofthesemissingatoms(formulae,formulaweight,etc.)havebeenincludedintheCIF.
InMOF(Zn)-1,SADI,FLAT,RIGUandEADPcommandswereusedtoobtainreasonablegeometryandanisotropic displacement parameters for the DMF solvent molecule. This molecule is disorderedacross a twofold rotation axis; bonds to symmetry equivalents were suppressed using PART -1command. Inthisheavy-atomstructure itwasnotpossibletoclearlyseeelectron-densitypeaks indifferencemapswhichwouldcorrespondwithacceptablelocationsfortheHatomsofthedisorderedDMFmolecule.Therefore,therefinementwascompletedwithnoallowancefortheseHatomsinthemodel.Thecontributionsofthesemissingatoms(formulae,formulaweight,etc.)havebeenincludedintheCIF.
WholemoleculedisorderofthebtcaligandwasmodelledinMOF(Zn)-2viaAFIX,DFIX,FLAT,EADP,andRIGUcommands.Theratiobetweenthetwocomponentswasrefinedfreelyandconvergedat0.48:0.52.ADFIXcommandwasusedtorestrainthegeometryoftheµ2-bridgingformatoligandinordertoexhibitaO-CH-OmoietybetweensymmetryrelatedZn2atoms(symmetryoperation:-x,+y,5/2-z).Figure1.d.showsa labelledORTEPplotshowingtheμ2-bridging formato ligand linkingtwosymmetry-relatedhalf-occupancyZn2atoms.CrystaldataandrefinementdetailsarelistedinTableS1.
S5
TableS1.Selectedcrystallographicdataforallcompounds.
Compound MOF(Zn)-1 MOF(Zn)-2
Activationtemperature Assynthesised 24hatRT 2hat100°C 2hat200°C 2hat350°C 2hat400°C
Spacegroup C2/c C2/c C2/c C2/c C2/c C2/c
Chemicalformula C20H24N8O9Zn3 C20H22N8O8Zn3 C20H22N8O8Zn3 C17H15N7O7Zn3 C14H16N6O10Zn3 C15H7N6O7Zn4
FormulaMass(g/mol) 716.58 698.56 698.56 625.47 624.44 644.75
a(Å) 17.7182(14) 18.037(2) 18.94(3) 19.2623(14) 19.544(2) 16.643(2)
b(Å) 13.0967(12) 12.5871(13) 10.098(16) 9.9839(6) 9.0665(12) 14.593(2)
c(Å) 11.0610(10) 11.0828(13) 10.957(17) 11.0852(7) 11.0933(13) 10.964(2)
β(°) 94.014(4) 93.046(5) 90.71(4) 90.246(8) 90.176(4) 90.296(16)
V(Å3) 2560.4(4) 2512.6(5) 2095(6) 2131.8(2) 1965.7(4) 2662.8(7)
Z 4 4 4 4 4 4
T 150K 120K 120K 120K 120K 120K
ρcalc(g·cm-3) 1.859 1.847 2.215 1.949 2.110 1.608
2qrange(°) 2.305–22.960 2.658–25.197 2.286–19.167 3.676–25.052 2.476–25.051 3.354–17.216
Data/Restraints/Parameters 1765/0/195 2238/144/226 848/90/132 1877/27/173 1588/90/150 805/263/156
Nºreflections 15414 7245 7160 16741 5727 6607
Independentreflections[I>2σ(I)]
1765 2238 848 1877 1588 805
GoF 1.106 1.072 1.664 1.126 1.060 1.165
RFactor[I>2σ(I)] R1=0.0402,wR2=0.0828
R1=0.0494,wR2=0.0831
R1=0.1798,wR2=0.4035
R1=0.0296,wR2=0.0666
R1=0.0625,wR2=0.1336
R1=0.1035,wR2=0.2575
RFactor(alldata) R1=0.0587,wR2=0.0891
R1=0.0860,wR2=0.0918
R1=0.2122,wR2=0.4232
R1=0.0349,wR2=0.0689
R1=0.1151,wR2=0.1578
R1=0.1239,wR2=0.2778
CCDCCode 1916085 1916086 1916087 1916083 1916082 1916084
S6
FigureS1. (a)Representationof thedifferent crystal structuresobtainedduring thebreathingprocessuponincreasingthetemperature.(b)DifferentviewsofthestructureofMOF(Zn)-1.(c)DifferentviewsofthestructureofMOF(Zn)-2.(d)AlabelledORTEPplotat50%probabilityleveloftheasymmetricunitofMOF(Zn)-2showingtheμ2-bridgingformatoligandlinkingtwosymmetry-relatedhalf-occupancyZn2atomsandthedisorderedbtcaligand(symmetryoperations:$1:-x,+y,5/2-z;$2:-x,-y,2-z;$3:-1/2-x,1/2+y,3/2-z;$4:1/2+x,1/2+y,+z).
S7
FigureS2.ExperimentalandsimulatedPXRDspectraoftheMOFactivatedat200˚C(MOF(Zn)-1)andat400˚C(MOF(Zn)-2).
S8
FigureS3.Thermogravimetricanalysis(TGA)profileofMOF(Zn)ataheatingrateof5ºC/minunderaconstantstreamofN2.
S9
3. CatalytictestsCatalystcharacterization
Highresolutiontransmissionelectronmicroscopyimages(HR-TEM)andscanningTEMimagesindarkfieldmode(DF-STEM)wererecordedonaJEOLJEM2100Finstrumentoperatingat200kW.AnOxforddetectorcoupledtotheSTEMinstrumentwasemployedtomeasurethecompositionofselectedMOFareas.Themetalparticlesizedistributionandstandarddeviationwereestimatedbycountingabout300nanoparticles.ThemorphologyandcompositionoftheMOFsampleswerefurthercharacterizedusingascanningelectronmicroscope(SEM,Zeissinstrument,AURIGACompact)coupledwithaEDXdetector. Isothermal nitrogen adsorption experiments were carried out using an ASAP 2010Micromeriticsdevice.X-rayphotoelectron(XP)spectrawerecollectedonaSPECSspectrometerwithaMCD-9detectorusingamonochromaticAl(Ka=1486.6eV)X-raysource.Spectradeconvolutionwasperformedwith the CASA software using the C 1s peak at 284.4 eV as binding energy reference.Inductively coupledplasmaatomic emission spectroscopy (ICP-AES) hasbeenused to confirm themetal contentof the catalystpreviouslydigested in concentratednitric acid. The contentofCu2OmetalloadedwasdeterminedbyIPC-AESbefore(0.92%wtCu)andafter(0.89%wtCu)use.
Photocatalyticmethanationtests
Forthephotoassistedmethanation,aquartzphotoreactorequippedwithaheatingmantletocontrolthedesiredtemperatureduringtheexperimentwasutilized.Thephotocatalyst(15mg)aspowderwasplacedasabedinsidethereactor,thesystemwaspurgedandchargedwithH2,andthenCO2wasadded until a ratio 4 to 1 was achieved. The photoreactor was heated up to 215 °C, once thetemperaturewasstable,thephotocatalystwasirradiatedunderUV-VislightusingaXelamp(300W)aslightsource.Thereactionwasmonitoredbytakingperiodicallygassamplesfromthereactorthatwere injected into anAgilent 490MicroGCequippedwith two channels and thermal conductivitydetectors.OnechannelallowsanalyzingH2,O2,N2andCOwithaMolSieve5Åcolumnwhiletheotherchannel shows CO2, CH4 and short chain hydrocarbons using a Pore Plot Q column. Gases werequantifiedcalibratingtheinstrumentanalyzingofgasmixtures.Thelimitofdetectionofthemicro-GCofthereactionthatisestimatedtobebelow0.1μg·cat–1·h–1.
S10
FigureS4. (a)RepresentativeDF-STEM imageofCu2O@MOF(Zn)-1. (b)EDSanalysisof twocoppernanoparticles(spectrumAandB).
FigureS5.(a,b)DF-STEMimagesofCu2O@MOF(Zn)-2.(c)Copperparticlesizedistribution
Spectrum B
Spectrum A
25nm
SpectrumA
SpectrumB
100 nm
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-1111-1212-1313-1414-1515-1616-170
5
10
15
20
25
Freq
uenc
y (%
)
Copper particle size (nm)
50 nm200 nm
a)b)
c)
S11
FigureS6.DF-STEM imagesof (a)Cu2O@MIL-125(Ti)-NH2 and (b,c)Cu2O@MOF-74(Zn). The insetsshowthecopperparticlesizedistribution, theaveragecopperparticlesizeandstandarddeviationobtainedaftercountingmorethan300particles.
Figure S7. SEM images of (a,b,c) Cu2O@MOF(Zn)-1 and (d, e, f) Cu2O@MOF(Zn)-2, revealing themorphologyofthecrystals.
0-1 1-2 2-3 3-4 4-50
10
20
30
40
50
Freq
uenc
y (%
)
Copper particle size (nm)
4.29± 0.95
2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-130
4
8
12
16
20
24
28
Freq
uenc
y (%
)
Copper particle Size (nm)
6.07± 1.52
a)b)
20µm 20µm 20µm
20µm 20µm 20µm
a)b)c)
d)e)f)
S12
FigureS8.SEMimagesof(a)Cu2O@MOF(Zn)-1and(b)Cu2O@MOF(Zn)-2.(c)ElementalanalysismappingofaselectedareaofCu2O@MOF(Zn)-1.
20µm 10µm 10µm
5µm 5µm 5µm
5µm 5µm
C O
Zn Cu
a)
b)
c)
20µm 10µm 10µm
S13
FigureS9.(a)DF-STEMand(b)BF-STEMimagesoffreshCu2O@MOF(Zn)-1photocatalyst;theinsetcorrespondstothecopperparticlesizedistributionobtainedbycountingabout300particles.(c)SEMimage of fresh SEM image and (d) XPS Cu2p spectrum of Cu2O@MOF(Zn)-1 showing the bestdeconvolutiontoindividualcomponents.
20 nm
0-1 1-2 2-30
10203040506070
Freq
uenc
y (%
)
Copper particle size (nm)
1.61± 0.46a)b)
930 940 950 960 970
36000
36500
37000
37500
38000
38500
39000
39500
CPS
Binding Energy (eV)
Cu0/Cu+
2p3/2
Cu2+
2p1/2
Cu2+
Cu2+satellite
Cu0/Cu+
10µm
c)d)
25 nm
1.6nm
S14
FigureS10.XPSspectraofCu2O@MOF(Zn)-1.(a)C1sXPS,(b)O1sXPS,(c)N1sXPS,(d)Cu2pXPS,(e)Zn2pXPS.
FigureS11.XPSspectraofCu2O@MOF(Zn)-2.(a)C1sXPS,(b)O1sXPS,(c)N1sXPS,(d)Cu2pXPS,(e)Zn2pXPS.
280 285 2904000
6000
8000
10000
12000
14000
16000
CPS
Binding Energy (eV)
930 940 950 960 970
36000
36500
37000
37500
38000
38500
39000
39500
CPS
Binding Energy (eV)
395 400 405
9000
10000
11000
12000
13000
14000
15000
CPS
Binding Energy (eV)
525 530 535 54012000
14000
16000
18000
20000
22000
24000
26000
CPS
Binding Energy (eV)
1020 1030 1040 1050
36000
38000
40000
42000
44000
46000
48000
50000
CPS
Binding Energy (eV)
a)b)c)
d)e)
C=C
O=C-O O=C-OM-O-
Cu0/Cu+
2p3/2
Cu2+
2p1/2
Cu2+
Cu2+satellite
Cu0/Cu+
Zn2p3/2
Zn2p1/2
525 530 53512000
14000
16000
18000
20000
22000
24000
CPS
Binding Energy (eV)
396 398 400 402 404 4069000
10000
11000
12000
13000
14000
15000
16000
CPS
Binding Energy (eV)
930 940 950 96025500
26000
26500
27000
27500
28000
28500
29000
CPS
Binding Energy (eV)
280 285 2904000
6000
8000
10000
12000
14000
16000
18000
CPS
Binding Energy (eV)
1020 1030 1040 1050
32000
34000
36000
38000
40000
42000
CPS
Binding Energy (eV)
a)b)c )
d)e)Cu0/Cu+
2p3/2
Cu2+
2p1/2
Cu2+
Cu2+satellite
Cu0/Cu+
Zn2p3/2
Zn2p1/2
C=C
O=C-O
O=C-O
M-O-
S15
FigureS12.PowderX-raydiffractionpatternsofthedifferentcopper-supportedMOF-basedcatalysts(MOF(Zn)-1,MOF-74(Zn)andMIL-125(Ti)-NH2)beforeandafterthephotocatalytictests.
Figure S13.DF-SEM images andEDX spectrumof selected areaof Cu2O@MOF(Zn)-1 sample after
photocatalyticmethanationofCO2.
20 nm
0-1 1-2 2-3 3-4 4-50
10
20
30
40
50
60
Freq
uenc
y (%
)
Copper particle size (nm)
1.73± 0.91
50nm 25nm
S16
-5 0 5 10 15 20 2505
101520253035404550
Light
CH
4 (µ
mol
·gca
t-1)
Time (h)
Dark
Figure S14. Reusability of Cu2O@MOF(Zn)-1 for the CH4 production at 215 °C upon 2236Wm−2
irradiationusinga300WXelamp.PH2=1.05bar,PCO2=0.25bar.LegendFirstuseCu2O@MOF(Zn)-
1(●),SeconduseCu2O@MOF(Zn)-1(♦)andthirduseofCu2O@MOF(Zn)-1(■).
S17
Figure S15. Mass spectra of the reaction products after the photocatalytic reaction using
Cu2O@MOF(Zn)-1for22hoursat215°Cusing13C18O2.
S18
4. Determinationofvalencebandenergiesandopticalgaps
FigureS16.Solid-stateCyclicVoltammetry(CV)andDifferentialPulseVoltammetry(DPV)ofMOF(Zn)-1andMOF-74(Zn)usingTBAPF60.1MinCH3CNaselectrolyteand0.05V/sscanrate.Platinumwirewasusedascounterelectrodeandsilverwireaspseudoreferenceelectrode.Ferrocenewasaddedasinternalstandard.AllpotentialsarereportedversusAg/AgCl.
S19
FigureS17.(a)UV-Visdiffusereflectanceand(b)TaucplotforMOF(Zn)-1(redline)andMOF-74(Zn)(blackline).
200 300 400 500 600 700 800
F(R)
l (nm)
1 2 3 4 5 6 70
50
100
150
200
250
300
350
400
ahn
eV
a)
b)
S20
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