Assessment of the energetic performances of various ZIFs with SOD or RHO topology using high pressure water intrusion-extrusion experiments

The energetic performances of seven SOD or RHO-topology ZIFs, with zinc or cobalt metal cation (ZIF-8, ZIF-90, Zn(dcim)2-SALE, ZIF-67, ZIF-7, ZIF-71, ZIF-11) were evaluated using water intrusion-extrusion under high pressure. The relationship between
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  DaltonTransactions PAPER Cite this:  DOI: 10.1039/c5dt03486hReceived 7th September 2015,Accepted 15th January 2016DOI: 10.1039/c5dt03486h Assessment of the energetic performances ofvarious ZIFs with SOD or RHO topology using highpressure water intrusion – extrusion experiments † Ismail Khay, Gérald Chaplais,* Habiba Nouali, Guillaume Ortiz, Claire Marichal andJoël Patarin* The energetic performances of seven SOD or RHO-topology ZIFs, with zinc or cobalt metal cation (ZIF-8,ZIF-90, Zn(dcim) 2 -SALE, ZIF-67, ZIF-7, ZIF-71, ZIF-11) were evaluated using water intrusion – extrusionunder high pressure. The relationship between the structural parameters (in particular the pore systemSOD or RHO, the type of linker, the metal cation nature) and the intrusion pressure was studied to betterunderstand the mechanism of water intrusion and the energetic behaviour for a given ZIF crystal type. “ ZIF-8 – water ” ,  “ ZIF-67 – water ”  and  “ ZIF-71 – water ”  systems display a shock-absorber behaviour. A veryimportant hysteresis for ZIF-71 and a slight di ff erence between the  󿬁 rst intrusion – extrusion cycle and thefollowing ones for ZIF-67 were observed. ZIF-8 (SOD) with zinc cation and ZIF-67 (SOD) with cobalt cationdisplay similar intrusion pressures. For ZIF-71 (RHO) material, the stored energy is more than doubled com-pared to ZIF-8 and ZIF-67 (SOD). This might be related to the topology. No water intrusion was observedafter three water intrusion – extrusion cycles, for the ZIF-90 (SOD), Zn(dcim) 2 -SALE (SOD), ZIF-7 (SOD) andZIF-11 (RHO) materials. This is explained in term of hydrophilic feature as well astopologyand linkere ff ects. 1. Introduction Crystalline porous zeolitic imidazolate frameworks (ZIFs) areassembled from tetrahedrally coordinating divalent metalcations and bridging ditopic imidazolate (or benzimidazolate)anions. 1 – 3 They possess zeolite-related frameworks with various topologies but with significantly higher pore size and volume. Furthermore, some ZIFs display both high thermaland chemical stability with a high hydrophobic character. 4 – 6 Therefore, ZIFs are involved in many potential applicationssuch as capture, storage and gas separation, 7 – 14 lumine-scence, 15 – 17 magnetism, 18 heterogenous catalysis, 11,19 – 23 anddrug delivery. 11,24 Recently, these microporous materials havebeen studied by our group for applications in the field of ener-getic, using intrusion – extrusion of water or aqueous electro-lytes solutions experiments under high pressure. 25 – 28 Theapproach is based on high pressure intrusion of liquid waterinto the pores of the hydrophobic materials. Under intrusion,the liquid water is transformed into a multitude of molecularclusters in the pores. Thus, the supplied mechanical energy during the compression step is converted to interfacial energy.By reducing the pressure, the system can induce an expulsionof the liquid out of the pores (extrusion). 29 Therefore, thesystem is able to restore, dissipate, or absorb the suppliedmechanical energy. Consequently, spring, bumper or shock-absorber behaviour can be observed, respectively. The behav-iour of the systems and the values of intrusion pressuredepend on various physicochemical and topological para-meters related to the framework such as hydrophobic/hydrophilic character, pore size and geometry and channeldimensionality. 30 The energetic performances of ZIFsmaterials, and in particular, the intrusion pressure dependalso on the shape and particle size. 28 The topology (SOD,RHO … ), the metal cation nature (zinc, cobalt, cadmium … ),and the type of linker (imidazolate or benzimidazolate … ) areexpected to possess also an influence. Consequently, in thisstudy, the energetic performances of various ZIFs (ZIF-8, ZIF-7,ZIF-90, Zn(dcim) 2 -SALE, ZIF-67, CdIF-1 with SOD topology andZIF-11 and ZIF-71 with RHO topology) are investigated using  water intrusion – extrusion experiments. The main character-istics of these materials (name, topology, linker, metal cation,cage aperture, microporous volume, BET surface area andcrystal size) are given in Table 1. † Electronic supplementary information (ESI) available: Powder XRD patterns,thermal analyses, SEM micrographs of all samples, pressure –  volume diagramsthe of   “ ZIF-7 (crude and activated) – , ZIF-90 – , Zn(dcim) 2 -SALE –  and ZIF-11 –  water ”  systems. See DOI: 10.1039/c5dt03486h Université de Strasbourg (UdS), Université de Haute Alsace (UHA), CNRS, Équipe Matériaux à Porosité Contrôlée (MPC), Institut de Science des Matériaux de Mulhouse (IS2M), UMR 7361, 3 bis rue Alfred Werner, 68093 Mulhouse Cedex, France. E-mail:,  This journal is © The Royal Societyof Chemistry 2016  Dalton Trans.    P  u   b   l   i  s   h  e   d  o  n   1   5   J  a  n  u  a  r  y   2   0   1   6 .   D  o  w  n   l  o  a   d  e   d   b  y   U  n   i  v  e  r  s   i   t  e   d  e   H  a  u   t  e   A   l  s  a  c  e  o  n   2   7   /   0   1   /   2   0   1   6   1   0  :   4   8  :   0   0 . View Article Online View Journal  2. Experimental section 2.1. Reactants, additives and solvents The following chemical compounds were used as received without any further purification,  i.e. , (i) the metal sources: zincacetate (Zn(CH 3 COO) 2 , 99%, Acros Organics), zinc acetatedihydrate (Zn(CH 3 COO) 2 ·2H 2 O, 100%, Analar Normapur), zincnitrate hexahydrate (Zn(NO 3 ) 2 ·6H 2 O, 99.9%, Sigma-Aldrich),cobalt acetate tetrahydrate (Co(CH 3 COO) 2 ·4H 2 O, 99%, Fluka),cadmium acetate dihydrate (Cd(CH 3 COO) 2 ·2H 2 O, 99%,Prolabo), (ii) the organic sources: benzimidazole (Hbim, 98%,Sigma-Aldrich), imidazole-2-carboxyaldehyde (Hica, 97%, Table 1  Representations of 2 × 2 × 2 supercells of structures adopting the SOD and RHO topologies with 4-, 6- and 8-membered facets in green,blue and magenta, respectively, and where the red spheres represent the metal cation and the black edges the linker (upper part) and the maincharacteristics of studied ZIFs (name, topology, linker, metal cation, cage aperture, microporous volume, BET surface area and crystal size) (downpart) Name Topology Linker CationCageaperture (Å)Microporous volume(cm 3 g  − 1 )BET surface area(m 2 g  − 1 ) Crystal sizeZIF-8 SOD mim Zn 2+ 3.4 a 0.66 1390 3 µmZIF-7 SOD bim Zn 2+ 2.9 a 0.207 b 405 b 200 nm – 4 µmZIF-90 SOD ica Zn 2+ 3.5 a 0.48 (0.58) c 1270 c 3 µmZn(dcim) 2 -SALE SOD dcim Zn 2+ 3.2 d  0.23 d  597 d  100 – 500 nmZIF-67 SOD mim Co 2+ 3.4 a 0.68 1452 5 – 10 µmCdIF-1 SOD mim Cd 2+ 3.9 e 0.86   f   2420  g  200 µmZIF-11 RHO bim Zn 2+ 3.0 a 0.457 b 605 b 5 – 15 µm0.582 h 1676 h ZIF-71 RHO dcim Zn 2+ 4.2  a 0.39 1050 3 µm a Data taken from ref. 2.  b Calculated value taken from ref. 31.  c Data taken from ref. 32.  d  Data taken from ref. 33.  e  Value estimated fromcrystallographic data (CCDC 743551  –  refcode GUPBUP). 34  f   Data taken from ref. 34.  g  Langmuir surface area taken from ref. 34.  h Calculated valuetaken from ref. 5. Paper Dalton Transactions Dalton Trans.  This journal is © The Royal Societyof Chemistry 2016    P  u   b   l   i  s   h  e   d  o  n   1   5   J  a  n  u  a  r  y   2   0   1   6 .   D  o  w  n   l  o  a   d  e   d   b  y   U  n   i  v  e  r  s   i   t  e   d  e   H  a  u   t  e   A   l  s  a  c  e  o  n   2   7   /   0   1   /   2   0   1   6   1   0  :   4   8  :   0   0 . View Article Online   Alfa-Aesar), 4,5-dichloroimidazole (Hdcim, 98%, Sigma- Aldrich), 2-methylimidazole (Hmim, 99%, abcr), (iii) the addi-tives: toluene (C 7 H 8 , 99.8%, Sigma-Aldrich), ammoniumhydroxide solution (NH 4 OH, 33%, Riedel-de Haën), (iv) the sol- vents:  N  ,  N  -dimethylformamide (DMF, 98%, Sigma-Aldrich),methanol (MeOH, 99.8%, Sigma-Aldrich), ethanol (EtOH,99.9%, Carlo Erba), propan-1-ol (1-PrOH, 99.5%, Sigma- Aldrich), butan-1-ol (1-BuOH, 99%, Carlo Erba), chloroform(CHCl 3 , 99.2%, Prolabo). 2.2 Syntheses of materialsZn(mim) 2  (SOD) / ZIF-8.  The micrometer-sized ZIF-8 sample was prepared from a procedure described in the litterature. 35 0.87 g (2.93 mmol) of Zn(NO 3 ) 2 ·6H 2 O was first dissolved in91.5 g of deionized water. Then, 13.62 g (165.88 mmol) of Hmim were dissolved in 30 g of deionized water. Afterwards,both solutions were mixed and stirred for 5 min at room temp-erature. The molar composition of the reactant mixture was: 1Zn:56.72 Hmim:4560 H 2 O. It was transferred into a Teflon®-lined autoclave for hydrothermal treatment at 120 °C for 6 h.The product was collected by centrifugation and washed 6times with MeOH at room temperature. The resulting ZIF-8sample was dried at room temperature overnight. Zn(bim) 2  (SOD) / ZIF-7.  The ZIF-7 sample was synthesizedaccording to the literature. 36 Separately, 0.762 g of Zn(NO 3 ) 2 ·6H 2 O (2.56 mmol) and 0.605 g of Hbim (5.12 mmol) were dissolved in 20 and 17.44 g of DMF, respectively. Then,both solutions were poured in a Teflon bottle and stirred. Thereactant mixture, with the molar composition: 1 Zn:2Hbim:200 DMF:6 H 2 O was heated without stirring at 100 °Cfor 72 h. After cooling down to room temperature, the crude white product was filtered, washed with fresh DMF, and driedunder air at room temperature. The resulting material isdenoted as  “ ZIF-7 crude ” . In order to remove the occludedDMF molecules, the sample was heated at 200 °C for 12 h. Theresulting material is denoted as  “ ZIF-7 activated ” . Zn(ica) 2  (SOD) / ZIF-90.  The ZIF-90 sample was preparedaccording to a procedure described in the literature. 37 1.743 g (18.14 mmol) of Hica was dissolved in 35.6 g of MeOH. Then,0.832 g (4.53 mmol) of Zn(CH 3 COO) 2  was dissolved in 45 g of deionized water, after that both solutions were mixed andstirred for 16 h at room temperature. The molar compositionof the final synthesis solution was: 1 Zn:4 Hica:245MeOH:550 H 2 O. After being formed, the particles were col-lected by filtration and washed 2 times with MeOH. The result-ing ZIF-90 sample was dried at room temperature overnight. Zn(dcim) 2 -SALE (SOD).  This material was synthesized using ZIF-8 as starting material in a solvent assisted ligandexchange-related process. 33 Firstly, the nanometer-sized ZIF-8 were synthesized according to a procedure similar to that described in literature. 38 44.3 g (539.4 mmol) of Hmim and1.6 g (5.4 mmol) of Zn(NO 3 ) 2 ·6H 2 O were dissolved in 150 and66.7 g of deionized water, respectively. Afterwards, zinc nitrateand Hmim solutions were quickly mixed together under stirr-ing. The final synthesis solution had the following molarcomposition 1 Zn:100 Hmim:2233 H 2 O. The mixture wasthen stirred at room temperature for 24 h. The product wascollected by centrifugation and washed 6 times with MeOH.The resulting nanometer-sized ZIF-8 sample was dried at roomtemperature overnight. Then, 200 mg (0.088 mmol) of this acti- vated nanometer-sized ZIF-8 sample were dispersed in 80 mLof 1-PrOH containing 600.2 mg (4.396 mmol) of Hdcim by sonication. The closed glass bottle was heated at 100 °C for5 d. Every 24 h the solid was centrifuged and washed with1-PrOH and redispersed in a fresh 1-propanolic Hdcim solu-tion. The final product was washed with MeOH, and thendried at room temperature in air overnight. The degree of ligand exchange was monitored by means of the liquid-state 1 H NMR. After 5 d of reaction a nearly full (about 98%) substi-tution of mim linkers by dcim moieties was observed. Co(mim) 2  (SOD) / ZIF-67.  The ZIF-67 sample was preparedaccording to a procedure described in the literature. 39 In a250 mL Teflon®-lined autoclave, 4.01 g (16.1 mmol) of Co(CH 3 COO) 2 ·4H 2 O were dissolved in 95.60 g of EtOH(2.08 mol). After stirring for 5 min, 3.96 g (48.3 mmol) of Hmim were added to give the final synthesis solution with thefollowing molar composition: 1 Co:3 Hmim:129 EtOH:4H 2 O. After stirring for 5 min, the autoclave was transferred inan oven and heated at 100 °C for 48 h. After cooling down toroom temperature, the product was collected by filtration, washed with EtOH and dried at 100 °C for 2 h. Cd(mim) 2  (SOD) / CdIF-1.  The CdIF-1 sample was syn-thesized according to a procedure described in the literature. 34 0.377 g (1.41 mmol) of Cd(CH 3 COO) 2 ·2H 2 O was placed in a42 mL Teflon®-lined autoclave and dissolved with 17.2 g of 1-BuOH. Then, 0.29 g (3.53 mmol) of Hmim was added. Afterstirring, the reactant mixture (molar composition of 1 Cd:2.5Hmim:164 1-BuOH:2 H 2 O) was heated at 120 °C for 24 h. After cooling down to room temperature, the product wascollected by filtration, washed with EtOH and dried at roomtemperature. Zn(bim) 2  (RHO) / ZIF-11.  The ZIF-11 sample was preparedaccording to a procedure described in the literature. 40 0.483 g of Hbim (4 mmol) was dissolved in 19.3 g of MeOH(602.6 mmol), followed by the addition of 18.48 g of toluene(200.6 mmol) and 4.2 g of ammonium hydroxide(44.3 mmol NH 3 ) under stirring at room temperature. Then0.444 g of Zn(CH 3 COO) 2 ·2H 2 O (2.02 mmol) was added andstirred for 3 h at room temperature to complete the crystalliza-tion. The molar composition of the final synthesis solution was: 1 Zn:2 Hbim:40 NH 3 :300 MeOH:100 C 7 H 8 :80 H 2 O.The product was collected by centrifugation and washed withMeOH, and next dried at room temperature in air overnight.Finally, the powder was heated at 200 °C under vacuum for12 h. Zn(dcim) 2  (RHO) / ZIF-71.  The ZIF-71 sample was syn-thesized according to a procedure described in the literature. 41  A solution of Zn(CH 3 COO) 2  (0.440 g, 2.39 mmol) in MeOH(70 g, 2.18 mol) and a solution of Hdcim (1.314 g, 9.59 mmol)in MeOH (70 g, 2.18 mol) were quickly poured in a glass vialand mixed, and then left without stirring at room temperaturefor 24 h. MeOH was then removed and replaced by CHCl 3 Dalton Transactions Paper This journal is © The Royal Societyof Chemistry 2016  Dalton Trans.    P  u   b   l   i  s   h  e   d  o  n   1   5   J  a  n  u  a  r  y   2   0   1   6 .   D  o  w  n   l  o  a   d  e   d   b  y   U  n   i  v  e  r  s   i   t  e   d  e   H  a  u   t  e   A   l  s  a  c  e  o  n   2   7   /   0   1   /   2   0   1   6   1   0  :   4   8  :   0   0 . View Article Online  (222 g). Right away after, the resulting suspension was centri-fuged, and the soaking centrifugation process was repeated2 more times with 22 g of CHCl 3  each time. The final product  was heated at 80 °C under vacuum for 12 h. 2.3 CharacterisationsPowder X-ray di ff  raction.  X-ray di ff  raction patterns of thedi ff  erent samples were recorded in a Debye-Scherrer geometry on a STOE STADI-P di ff  ractometer equipped with a curvedgermanium (111), primary monochromator, and a linear posi-tion-sensitive detector (6° in 2 θ  ) using Cu K α 1  radiation (  λ  =1.5406 Å). Measurements were achieved for 2 θ   angle values inthe 3 – 50 or 5 – 50 range for RHO- or SOD-topology samplesrespectively, with a step of 0.04° in 2 θ  . Scanning electron microscopy.  The morphology of the crys-tals were determined by scanning electron microscopy (SEM)using a Philips XL 30 FEG microscope. Thermogravimetric analyses.  Thermogravimetric analyses(TGA) were carried out on a TG Mettler Toledo STARe appar-atus, under air flow, with a heating rate of 2 °C min − 1 from 30to 900 °C. Nitrogen adsorption – desorption measurements.  Nitrogenadsorption – desorption isotherms were performed at 77 Kusing a Micromeritics ASAP 2420 apparatus. Prior to theadsorption measurements, the samples were outgassed at 120 °C (ZIF-67) or 200 °C overnight under vacuum. Thespecific surface areas ( S BET  and  S L ) were calculated using theBET and Langmuir methods applied in the 0.0003  ≤  p /  p °  ≤ 0.007 range. The microporous volumes ( V  µ  ) were determinedaccording to the  t  -plot method. 1 H NMR spectroscopy.  The degree of ligand exchange waschecked by   1 H NMR. About 5 mg of solid were dissolved in amixture of 85.7  μ L of DCl (7 M) and 114.3  μ L of D 2 O at roomtemperature. The suspension was mixed by sonication and500 mL of DMSO-d 6  was added for a complete dissolution of the ligand.  1 H NMR spectra were recorded on a Bruker AvanceII 400 MHz spectrometer.  Water intrusion – extrusion experiments under high pressure. The water intrusion – extrusion experiments on ZIFs samples were performed at room temperature over three cycles using amodified mercury porosimeter (Micromeritics Model AutoporeIV) as described in our previous works. 25 Typically, around100 mg of ZIFs (ZIF-8, ZIF-90, crude and activated ZIF-7,ZIF-67, Zn(dcim) 2 -SALE, ZIF-71, ZIF-11) powders were directly introduced in the cell. The values of the intrusion (  P  int  ) andextrusion (  P  ext  ) pressures correspond to that of the half volumetotal variation. The pressure is expressed in megapascal (MPa)and the volume variation in milliliter per gram of sample(mL g  − 1 ). The stored (restored) energy corresponds to the areaunder the curve when the pressure is expressed as a functionof the volume during the intrusion (extrusion) stage. Theseenergies are deduced after (i) the determination of thepressure and volume limit values during the intrusion (extru-sion) stage, (ii) the fitting of experimental data with poly-nomial model inside this interval and (iii) the estimation of the integrated value inside this interval with a standardscientific software. 3. Results and discussion 3.1 Characterisations of materials XRD.  The crystalline feature of the materials was checked by powder XRD. The experimental patterns (see Fig. S1 in theESI † ) are consistent with the simulated ones and thereby high-light the SOD topology for ZIF-8, ZIF-7, ZIF-90, Zn(dcim) 2 -SALE, ZIF-67 and CdIF-1 and the RHO topology for ZIF-11 andZIF-71. Concerning the ZIF-7 sample a drastic modification isnoted after heating (thermal activation) and corresponds tothe rhombohedral → triclinic phase transition (ZIF-7 I or ZIF-7crude → ZIF-7 II or ZIF-7 activated) evidenced recently by Zhao et al.  thank to XRD and Raman spectroscopy. 42 The release of occluded DMF molecules explains this structural change. Thermogravimetric analyses.  The thermal stability of thematerials was evaluated by thermogravimetric analyses underair with low temperature rate (2 °C min − 1 ). The TG curves aredepicted in Fig. S2 and the main mass losses are reported inTable S1 in the ESI. †  The curves reveal that all materials withthe exception of ZIF-90 are hydrophobic since no mass loss isnoticed between room temperature and the temperaturerelated to the beginning of the structural collapse. For theZIF-90 sample, a mass loss of 24.6% occurs between roomtemperature and 75 °C assigned to the release of water mole-cules entrapped in the sodalite cage. It means that this ZIF ishydrophilic as evidenced by Zhang   et al. 43 and makes it possi-ble to infer that the ZIF-90 sample formula is Zn(ica) 2 ·4.2H 2 O.Moreover, for almost all ZIF solids (by including ZIF-90sample but dismissing Zn(dcim) 2 -SALE and ZIF-71), the experi-mental mass losses, regarding the structural collapse leading to the formation of the corresponding metal oxide (ZnO,Co 3 O 4  or CdO) are in very good agreement with the theoretical values. For both Zn(dcim) 2 -based solids,  i.e. , Zn(dcim) 2 -SALEand ZIF-71, this loss is abnormally higher as observed pre- viously, 33,44  with a gap of around 10% (86% expt   vs.  76%calcd). This di ff  erence might be explained by the presence of Hdcim groups coordinated to terminal zinc atoms at thesurface of the crystal, 41 or by the escape of volatile Zn speciesin addition to the release of dcim ligand. 33 In term of thermalstability, the TG curves of both Zn(bim) 2 -based materials ( i.e. ,ZIF-7 (SOD) and ZIF-11 (RHO)) are similar with a temperatureof the starting collapse of around 475 °C, which is the highest one among the materials considered here. A comparableobservation can be realised between Zn(dcim) 2 -based solids( i.e. , Zn(dcim) 2 -SALE (SOD) and ZIF-71 (RHO)) but with a start-ing collapse temperature lower and near 350 °C. Moreover, theframework of the ZIF-8(Zn) (SOD) sample starts to collapse at almost the same temperature albeit slightly lower, that isaround 325 °C. This temperature corresponds also to the start of collapsing of its analogous CdIF-1(Cd) but is higher thanthe one assigned to ZIF-67(Co) ( ≈ 250 °C). The latter materialsare also based on mim as linker. Finally, the ZIF-90 sample Paper Dalton Transactions Dalton Trans.  This journal is © The Royal Societyof Chemistry 2016    P  u   b   l   i  s   h  e   d  o  n   1   5   J  a  n  u  a  r  y   2   0   1   6 .   D  o  w  n   l  o  a   d  e   d   b  y   U  n   i  v  e  r  s   i   t  e   d  e   H  a  u   t  e   A   l  s  a  c  e  o  n   2   7   /   0   1   /   2   0   1   6   1   0  :   4   8  :   0   0 . View Article Online  shows the lowest thermal stability for Zn-based hybrids with astarting collapse temperature near 275 °C.On the basis of these results, it can be deduced that thethermal stability: (i) increases regarding the ligand in the fol-lowing order ica < mim < dcim < bim, (ii) increases regarding the metal nature in the following order Co < Zn  ≈  Cd, (iii) isnot a ff  ected by the topology (SOD or RHO). SEM.  The crystal morphology of the samples was examinedby scanning electron microscopy. The micrographs are pre-sented in Fig. S3 in the ESI. †  The ZIF-8, ZIF-90, ZIF-11 andZIF-71 samples appear as well defined micrometer-sizedrhombic dodecahedron. The crystals of ZIF-67 sample belong to micrometric domain but their shape is more smoothed.Most of the Zn(dcim) 2 -SALE crystals are quite small(0.2 – 0.3 µm), which is consistent with the fact that this sample was prepared from a nanometer-sized ZIF-8 sample, whereasthose of the CdIF-1 sample are bigger and close to 50 to100 µm. At last, a very broad size distribution is observed forthe ZIF-7 sample. 3.2 Water stability at room temperature without pressure Prior to perform the water intrusion – extrusion experimentsunder pressure, the isomorphous samples CdIF-1 and ZIF-67 were soaked in water at room temperature for 24 h at a concen-tration similar to the one used for experiments upon highpressure. The XRD patterns of the samples recorded after fil-tration and air drying are shown in Fig. 1. It appears clearly that the soaking a ff  ects drastically the structure of CdIF-1.Indeed, the XRD pattern recorded after soaking in water doesnot correspond to the one of CdIF-1 anymore but is in very good agreement with the one of CdIF-3, a polymorph com-pound of CdIF-1 displaying the yqt1 topology, 34 denser thanthe topology SOD. For ZIF-67, both XRD pattern and nitrogenadsorption – desorption isotherm performed at 77 K (see Fig. 2)after soaking in water reveal that the structure and the porosity are preserved after such a treatment. Besides, the microporous volumes as well as the BET and Langmuir surfaces are very similar before and after soaking and consistent with the litera-ture, 39  with values of 0.68 cm 3 g  − 1 , 1452 and 1463 m 2 g  − 1 before soaking and 0.69 cm 3 g  − 1 , 1452 and 1464 m 2 g  − 1 aftersoaking.Given these results, we had to dismiss CdIF-1 as candidatefor water intrusion – extrusion experiments whereas we main-tained its Co-based analogue ZIF-67 for this purpose becauseof its high stability in water at room temperature. 3.3 Water intrusion – extrusion experiments under highpressure The pressure –  volume diagrams of the eight   “ ZIFs –  water ” systems, by removing CdIF-1 due to its instability in water (seepart 3.2 water stability at room temperature without pressure)are illustrated in Fig. 3 for  “ ZIF-8 –  water ” ,  “ ZIF-67 –  water ”  and “ ZIF-71 –  water, and in Fig. S4 in the ESI †  for the  “ ZIF-7 crude –  water ” ,  “ ZIF-7 activated –  water ” ,  “ ZIF-90 –  water ” ,  “ Zn(dcim) 2 -SALE –  water ”  and  “ ZIF-11 –  water ”  systems. The corresponding parameters are listed in Table 2. For clarity, the pressure – Fig. 2  Nitrogen sorption isotherms at 77 K expressed according to thelogarithmic scale, before (blue) and after (red) soaking in water as wellas after water intrusion – extrusion experiments (green) for ZIF-67sample. Adsorption and desorption branches are represented by  󿬁 lledand empty symbols, respectively. Fig. 1  XRD patterns of CdIF-1 and ZIF-67 recorded before (blue) andafter (red) soaking in water at room temperature for 24 h. Dalton Transactions Paper This journal is © The Royal Societyof Chemistry 2016  Dalton Trans.    P  u   b   l   i  s   h  e   d  o  n   1   5   J  a  n  u  a  r  y   2   0   1   6 .   D  o  w  n   l  o  a   d  e   d   b  y   U  n   i  v  e  r  s   i   t  e   d  e   H  a  u   t  e   A   l  s  a  c  e  o  n   2   7   /   0   1   /   2   0   1   6   1   0  :   4   8  :   0   0 . View Article Online
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