Inclusion Properties of Volatile Organic Compounds in a Calixarene

May 8, 2012 - ... di Perugia, via della Madonna Alta 138 c/d, I-06128 Perugia, Italy ... Dipartimento di Scienze della Terra, Università degli Studi ...
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Inclusion Properties of Volatile Organic Compounds in a Calixarene-Based Organic Zeolite Loredana Erra,†,⊥ Consiglia Tedesco,*,†,‡ Ivano Immediata,† Luisa Gregoli,†,# Carmine Gaeta,†,‡ Marco Merlini,§,¶ Carlo Meneghini,∥ Michela Brunelli,§,▲ Andrew N. Fitch,§ and Placido Neri†,‡ †

Dipartimento di Chimica e Biologia, Università di Salerno, via Ponte don Melillo, I-84084 Fisciano, Italy NANO_MATES, Research Centre for NANOMAterials and nanoTEchnology at Salerno University, via Ponte don Melillo, I-84084 Fisciano, Italy § European Synchrotron Radiation Facility, 8 Rue J. Horowitz, 38043 Grenoble, France ∥ Dipartimento di Fisica ‘E. Amaldi’, Università di Roma 3, Roma, Italy and CNR-TASC c/o CRG-GILDA (ESRF) Grenoble, France ‡

S Supporting Information *

ABSTRACT: The inclusion properties of a calixarene-based porous material have been studied to investigate the adsorption and the desorption of carbon tetrachloride, chloroform, and water in the zeolite-like structure. Uptake and release processes have been studied both by time-resolved powder X-ray diffraction and by thermogravimetric analysis to obtain structural and kinetic information. The selected guests are able to enter the structure with an increase in the host cell volume and with time-dependent diffusivity coefficients. Chloroform molecules act as a permanent porosity switch promoting a phase transition to non-porous triclinic form.

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Scheme 1. Proximal p-tert-Butylcalix[4]dihydroquinone 1

INTRODUCTION Adsorbents have many important applications: catalysis, gas separation and purification, and environmental protection through pollution control and abatement.1 Volatile organic compounds (VOCs) are one of the major side products of industrial productions. Adsorbents have been used principally to control the emission of VOC reducing the concentration from between 400 and 2000 ppm to under 50 ppm. Another interesting aspect is the VOCs recovery. Recovery of reusable or marketable VOCs can significantly offset the cost of emission control.2 The removal of these compounds from water or air is a stimulus for scientific research.3 Natural polymers have been used to remove pollutants from water.4 To remove VOCs from gas streams, it can be useful to contact the contaminated air with a liquid solvent: any soluble VOCs will transfer to the liquid phase. Of course, VOCs polarity leads to the choice of a suitable liquid solvent. The design of a solid-state adsorbent with the ability to adsorb both polar and nonpolar VOCs seems to be a challenge. Moreover, there is considerable interest in adsorbents with well-defined crystalline structures so it is possible to study, in an unambiguous way, the host−guest interactions.5 Proximal p-tert-butylcalix[4]dihydroquinone 1 (Scheme 1) was synthesized and structurally characterized at the Dept. of Chemistry of the University of Salerno. Cubic crystals (a = 36.412(4) Å, space group Pn-3n) were obtained by crystallization of 1 in chloroform and anhydrous ethyl acetate. © 2012 American Chemical Society

Neither chloroform molecules nor ethyl acetate molecules are present inside the cubic crystals. Instead, the crystal structure is characterized by networked channels (min and max diameter are 3.9 and 8.5 Å, respectively) filled with easily removable water (Figure 1).6 Adsorption studies showed that the BET surface area corresponds to 230 m2 g−1 (N2 at 77 K), and this material is able to adsorb CO2,7 methane,8 and acetylene.9 In the present study, we wish to explore the guest uptake and release properties of the new material, in particular, to probe the molecular affinity of the host channels. By gravimetric sorption analysis and in situ time-resolved powder X-ray diffraction, it was possible to study the uptake and release of water, CCl4, and CHCl3. Received: March 6, 2012 Revised: May 1, 2012 Published: May 8, 2012 8511

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Grenoble (France), basically for two reasons: to define the crystallite size using the Debye−Scherrer method and to verify the effect of chloroform uptake on the sample. The PXRD profile of the “as crystallized” sample was collected selecting X-rays with wavelength λ = 0.800 25(4) Å. Small amounts of compound 1 in cubic crystalline form were lightly ground with a pestle in an agate mortar and introduced into thinwalled 0.3-mm-diameter borosilicate glass capillary. The capillary was mounted on a heavy-duty goniometer head-mounted coaxial with the axis of the diffractometer and spun during measurements in order to improve randomization of the orientations of the individual crystallites. Raw data were normalized against monitor counts and detector efficiencies and rebinned into steps of 0.003° 2θ. Numerous short 1 minute scans were collected to investigate the occurrence of any radiation damage and, in that case, avoid it by translating the capillary by ∼2.0 mm in the beam (SI Figure S1). Then, a powder sample of compound 1 in the cubic crystalline form was lightly ground with a pestle in an agate mortar and introduced into thin-walled 0.5-mm-diameter borosilicate glass capillary; the capillary was immersed in liquid chloroform into a closed vial, so that the chloroform vapors could be in contact with the powder sample. Then, PXRD profiles were collected after 3 days and 10 days of exposure to chloroform vapors, selecting X-rays with wavelength λ = 0.80168(4) Å and λ = 1.25248(4) Å, respectively (SI Figure S2). Adsorption Studies. Gravimetric adsorption studies were carried out by means of a Pabisch Mettler TA4000 instrument, properly modified for this work to measure the sample weight change during the sorption and desorption processes. In particular, the sample chamber was connected to a flask containing the specific volatile compound through which a constant flow of nitrogen was allowed to pass. The flow rate was 100 cm3/min. The flow could be switched from dry N2 to vapor-saturated N2. Measurements were performed in isothermal conditions at 25 °C. Each experiment consisted of three stages: (i) the channel cleaning (to remove the channel water molecules), (ii) the adsorption stage, (iii) the desorption stage. During the cleaning, the samples were evacuated overnight by heating up to 50 °C under a purified nitrogen flow. The isothermal desorption was performed at 25 °C and followed until no detectable weight loss was observed. The evacuated sample has been characterized by high-resolution PXRD measurements to calculate the crystallite dimensions using the Scherrer equation. Instrumental contribution to line broadening can be considered negligible, as the nominal value reported in the technical description of the beamline is 0.003°.12 The value of the FWHM as obtained from Rietveld refinement, for the evacuated sample, is about 0.010°. Using the Scherrer equation13 with λ = 0.08002(4) nm, B = 0.010°, 2θ = 1.7910°, the particle dimension is 414 nm.

Figure 1. Unit cell packing for the cubic porous form of compound 1 with interconnected voids in yellow (probe radius 1.2 Å).

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EXPERIMENTAL SECTION

Time-Resolved Powder X-ray Diffraction. Time-resolved powder X-ray diffraction (PXRD) experiments have been carried out at the BM08 Gilda beamline at the ESRF (Grenoble, France). Synchrotron radiation PXRD data were collected in the Debye− Scherrer transmission geometry, with samples contained in 0.3 mm Lindemann capillary. The translating Image Plate setup10 is used to continuously monitor the crystallographic changes as a function of temperature/chemical environment. The powder samples were preliminarily heated at 50 °C under dynamic vacuum. Lindemann capillaries were filled with the anhydrous powder and mounted on a goniometer head specifically designed for the recovery of the fluxed gases or solvent vapors. The samples were first exposed to a flux of dried nitrogen at 50 °C to remove the water molecules still present in the structure channels. Diffraction patterns have also been measured during this treatment. Then, the vapors of chloroform (or carbon tetrachloride or water) were carried by the nitrogen flow into the capillary and then recovered in a liquid nitrogen trap. Powder patterns in the angular range 0−16° 2θ were continuously collected using a translating Fuji flat Image Plate (IP) detector mounted perpendicular to the incoming beam.10 The X-ray wavelength was 0.888 50 Å, the sample to detector distance 275.39 mm, the IP slit aperture 2 mm. The imaging plate translation speed was of 1 mm per minute. The experimental geometry (sample to detector distance and detector tilt) were carefully calibrated against standard LaB6 (SRM 660a) and PXRD patterns were extracted from the IP image using the Scan Zero software (available at the beamline). Corrections have been applied during data reduction: to account for (a) non-constant sample−detector distance, (b) zero-shift, (c) unequal step sizes, (d) geometric contribution to the instrumental resolution function. All the powder profiles were analyzed by Le Bail method, using the GSAS software.11 The refined parameters were the scale factor; 10 coefficients of a Chebichev polynomial curve for the background; the lattice parameters and zero shift; three profile parameter coefficients, one for the Gaussian contribution and two for the Lorentzian contribution. High-Resolution Powder X-ray Diffraction. High-resolution powder X-ray diffraction (HR-PXRD) experiments were performed at the high-resolution powder diffraction beamline ID31 at the ESRF,

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RESULTS AND DISCUSSION Influence of Humidity and Water Affinity. PXRD allows us to highlight the zeolitic behavior of the cubic organic structure. Two samples of the same batch measured at ambient conditions at different times showed a remarkable difference in the ratio between the intensity of reflections 110 and 200. A hypothesis was made that the observed behavior has to be related to ambient humidity, which could have a remarkable influence on the water content of the material. In situ PXRD experiments performed at the BM08 Gilda beamline (ESRF) allow us to prove this hypothesis. A nitrogen flow was passed into a flask with distilled water before flowing in a capillary containing the calixarene sample. PXRD patterns were registered before and after the treatment. As shown in Figure 2, the ratio between the intensities of peaks 110 and 200, I110/I200, is less than 1 at laboratory ambient conditions and is greater than 1 under saturated water vapors. 8512

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Thus, a plot of ln[Me − Mt/Me] versus time t will give a line with a slope equal to [−Dπ2/a2] from which it is possible to derive the diffusion coefficient. The adsorption and desorption isotherms, the plot of ln[Me − Mt/Me] versus t, as well as the linear fit of the data for guest adsorption and desorption are reported, respectively, in Figure 3a−f. Tables 1 and 2 report, respectively, the capacities and the diffusivity coefficients D for adsorption and desorption processes. It is evident that the diffusivity coefficients for adsorption and desorption vary with the time: in fact, it is possible to distinguish different linearity regions corresponding to changes in diffusivity during the processes.17 For CCl4 adsorption, three different trends are observed as well as for CHCl3 adsorption. In the case of water adsorption, instead, two diffusivity coefficients have been obtained. The diffusivity corresponding to the first linearity region is similar in the three cases (Mt/Me < 0.89, 0.72, 0.85 for CCl4, CHCl3, and water, respectively) as well as the values corresponding to the second region (Mt/Me < 0.99, for the three guests). Then, the CCl4 diffusivity adsorption increases by 2 orders of magnitude, while for CHCl3, it comes back to a value similar to the first region. The desorption behavior is quite different in the three cases. For CCl4, there are two linearity zones with very similar diffusivity coefficients (Mt/Me < 0.95 and Mt/Me < 0.99). CHCl3, instead, has quite complex behavior: in the first region (Mt/Me < 0.88), the diffusivity is quite low (and it becomes faster and faster with time). In spite of this, the whole amount of adsorbed chloroform is not able to be desorbed even though the desorption experiments have been prolonged, doubling the time of the measurement. In the case of chloroform, the transition to another crystalline phase could explain the different behavior (vide inf ra). For the water, two linearity regions have been detected for both adsorption and desorption experiments. The diffusivity coefficients decrease with time during the adsorption. The desorption, instead, is easier and easier as time goes on. In Situ Time-Resolved Powder X-ray Diffraction. The translating Image Plate setup available at the BM08 beamline allows us to monitor in situ the transformation induced by guest uptake and release.10 Also, in this case each experiment consisted of three stages: (i) the channel cleaning (to remove the channel water molecules), (ii) the adsorption stage, and (iii) the desorption stage. The continuous, angular, dispersed PXRD patterns were collected over a period of 90 min and integrated to obtain 36 useful powder profiles. The first observation is that after the treatments the samples remain crystalline and the powder profiles can always be indexed considering a cubic crystal system. A Le Bail fit was performed for each profile to determine the variation of the cell parameter during channel cleaning, adsorption, or desorption processes. In all cases also, significant changes in the peak intensities of low angle reflections can be observed. During the channel cleaning, PXRD patterns were collected to detect water release as evidenced by cell shrinkage. In Figure 4, the cell parameters as obtained by Le Bail fit are shown as a function of time. In Figure 5a,b, PXRD profiles are shown for CCl4 adsorption and desorption, respectively (see Supporting Information for those related to CHCl3 and water). In particular, for CCl4 during the adsorption process the 200 reflection disappears, while the intensity of the 110 reflection

Figure 2. PXRD profiles as obtained at BM08 beamline (a) in ambient conditions, (b) after 15 min exposure to water vapor.

The remarkable affinity of the cubic crystalline form of compound 1 toward water molecules is also evidenced by the presence of water guest molecules inside the structure channels in the native crystals. In spite of the crystallization conditions (slow evaporation of chloroform and ethyl acetate solution), the cubic crystalline structure, once formed, prefers to trap the environmental water inside the empty spaces. Instead, if the water is used as crystallization solvent together with chloroform, the formation of the cubic phase is prevented, and another non-porous pseudopolymorph with a triclinic unit cell (a = 11.259(3) Å, b = 17.330(4) Å, c = 9.993(3) Å, α = 92.73(2)°, β = 104.74(2)°, γ = 85.03(2)°, space group P-1) crystallizes.14 The triclinic unit cell contains two equivalent calixarene molecules, two water molecules, and two chloroform molecules. Gravimetric Adsorption Studies. Gravimetric adsorption studies were performed using a modified Pabisch Mettler TA4000 instrument to evaluate quantitatively the VOC uptake and release behavior. As for the adsorption, CCl4 uptake determines a weight percentage increase of 27%, which is equivalent to 48 CCl4 molecules per cell (guest host ratio = 1:1). CHCl3 adsorption determines a weight percentage increase of 28%, equivalent to 68 CHCl3 molecules per unit cell (guest/host ratio 1.4:1). Water adsorption determines a weight percentage increase of 9.0%, equivalent to 158 water molecules per unit cell (guest:host ratio 3.3:1). As for the desorption, a total weight loss of 25% was observed for CCl4, 15% for CHCl3, and 9% for water. In the case of CHCl3, the desorption process is markedly slower and the weight percentage loss does not correspond to the weight percentage increase during adsorption (15% vs 28%). This behavior could be explained considering that, once the powder sample is exposed to CHCl3 vapors, a vapor digestion process15 could occur leading to a structural change. To prove this hypothesis, a detailed structural analysis was performed (vide inf ra). Kinetic Analysis. The adsorption processes can be described by a type I isotherm. By assuming a Fickian behavior, it is possible to calculate the diffusivity coefficient D by the equation Me − Mt/Me = 6/π2 exp[−Dt π2/a2], where Mt is the adsorbate uptake at time t, Me the adsorbate uptake at equilibrium, and a is the crystallite size (as obtained by applying the Debye−Scherrer equation to HR-PXRD data on the same batch sample).16 8513

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Figure 3. (a) Adsorption kinetics of CCl4. (b) Desorption kinetics of CCl4. (c) Adsorption kinetics of CHCl3. (d) Desorption kinetics of CHCl3. (e) Adsorption kinetics of H2O. (f) Desorption kinetics of H2O.

Table 1. Adsorption Weight % Increase and Apparent Diffusivity Constants at Room Temperature for CCl4, CHCl3, and H2O guest

adsorption (wt %)

DA (10−13 cm2/s)

DB (10−13 cm2/s)

DC (10−13 cm2/s)

CCl4 CHCl3 H2O

27 28 9

6.3 3.3 4.2

0.8 0.5 0.6

69 4.5

Table 2. Desorption Weight % Decrease and Apparent Diffusivity Constants at Room Temperature for CCl4, CHCl3, and H2O guest

desorption (wt %)

DA (10−13 cm2/s)

DB (10−13 cm2/s)

DC (10−13 cm2/s)

CCl4 CHCl3 H2O

25 15 9

0.2 0.06 0.2

0.1 0.2 1.7

1.6

Also, the desorption behavior has been investigated by powder diffraction by calculating the cell parameters. The final cell parameter is 36.410(2) Å for CCl4, 36.252(1) Å for CHCl3,

increases; the same happens for CHCl3. During the adsorption, the cell parameter increases to a value of 36.633(2) Å for CCl4, 36.436(3) Å for CHCl3, and 36.368(3) Å for water. 8514

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the different kinetics between the gravimetric and diffraction experiments, considering that the geometry and size of the sample are different. High-Resolution Powder X-ray diffraction. To understand the results of CHCl3 vapor gravimetric sorption studies, HR-PXRD patterns were collected at the beamline ID31 at

and 36.319(2) Å for water. The cell parameter variation during guest adsorption and desorption is reported in Figure 6.18 During the desorption process (90 min), the cell parameter reaches a value similar to the one of the apohost structure (36.241(6) Å) in the case of CHCl3 and water, while for CCl4, this is not case. The complete release of CCl4 can be obtained only by prolonging the measurement for other 38 min. This highlights

Figure 7. Le Bail fit of the HR-PXRD profile for a sample of 1 exposed to CHCl3 vapors for 10 days. The observed and calculated profiles are shown, respectively, in red and green, the difference curve between the observed and calculated profiles in magenta and reflection markers as vertical bars (cubic phase in black, triclinic phase in red).

Figure 4. Cell parameter variation during channel cleaning. The line is to guide the eye.

Figure 5. PXRD profiles during CCl4 (a) adsorption and (b) desorption processes.

Figure 6. Cell parameter variation during (a) adsorption and (b) desorption for CCl4 (black squares), CHCl3 (open triangles), and water (circles). 8515

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A vapor digestion process promotes a phase change from a porous to a non-porous pseudopolymorph.15 Indeed, the possibility to control the pseudopolymorphism of 1 going from the triclinic non-porous structure to the cubic porous one, exactly in the opposite direction from the one explained here, has been already proven by us using as promoting guest CCl4.14 By exposing the triclinic non-porous form to CCl4 vapors, it is possible to transform it to the cubic porous one,14 while the cubic porous form is not altered by exposure to CCl4 vapors as demonstrated by this study.

ESRF on a time-scale comparable with the gravimetric experiment. A powder sample was loaded in a capillary and exposed for 10 days to chloroform vapors. HR-PXRD data were collected after 3 and 10 days exposure. Already after 3 days exposure, it is possible to detect the presence of another crystalline phase. A careful pattern analysis revealed that the new phase is a low-symmetry one, which corresponds to the already known triclinic pseudopolymorph containing CHCl3 (previously characterized by means of single crystal X-ray diffraction).14 The two-phase Le Bail analysis on the pattern collected after 10 days of exposure to CHCl3, considering the cubic and triclinic cells, is reported in Figure 7. For comparison also, the Le Bail analysis on the as-crystallized sample is reported in Figure 8.

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CONCLUSIONS The adsorption and desorption isotherms of CCl4, CHCl3, and water vapors on the porous organic zeolite based on proximal p-tert-butylcalix[4]dihydroquinone 1 have been studied by both gravimetric and diffraction analysis. For all three guest molecules, in situ time-resolved PXRD patterns during adsorption and desorption processes made it possible to relate the guest uptake and release to a progressive cell parameter change without the destruction of the crystalline structure, confirming both the flexibility and the strength of the purely organic zeolite. The adsorption processes can be described by a type I isotherm and, assuming a Fickian behavior, the diffusivity coefficients D have been calculated. The complex behavior of the material is evidenced by the change of diffusivity with time. In particular, during adsorption for halogenated guests three linearity regions, corresponding to three different diffusivity coefficients, can be detected, whereas for water uptake, two diffusivity coefficients have been evidenced. Probably both the chemical nature and the guest size are responsible for these differences. The desorption kinetics, instead, shows an interesting difference between CCl4 and CHCl3. In the first linearity region, in fact, the diffusivity coefficient of chloroform is smaller by 1 order of magnitude. This peculiarity leads us to investigate the structural causes of the phenomenon, discovering a vapor digestion process, which promotes a phase change from a porous to a nonporous pseudopolymorph. Thus, chloroform molecules act in this case as a permanent porosity switch.

Figure 8. Le Bail fit of the HR-PXRD profile for a sample of 1 containing only the cubic phase. The observed and calculated profiles are shown respectively in red and green, the difference curve between the observed and calculated profiles in magenta and reflection markers (vertical bars).

Indeed, CHCl3 molecules have two effects on the cubic phase: first, they enter the empty channels with an increase of the cell volume (as it has been proven by time-resolved powder diffraction on a time scale of 90 min); then, they are able to interact with the calixarene molecules by entering the molecular cavities and transforming the cubic phase to the triclinic one (Figure 9).

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ASSOCIATED CONTENT

S Supporting Information *

Experimental details and profiles of HR-PXRD and timeresolved PXRD experiments.This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; fax: (+39) 089-969603; tel: (+39) 089-969586. Present Addresses ⊥

European Synchrotron Radiation Facility, 8 Rue J. Horowitz, 38043 Grenoble, France. # Ministero delle Politiche Agricole Alimentari e Forestali, Dipartimento dell’Ispettorato Centrale della Tutela della Qualità e Repressioni Frodi dei prodotti Agroalimentari, Laboratorio di Perugia, via della Madonna Alta 138 c/d, I-06128 Perugia, Italy ¶ Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Botticelli 23, I-20133 Milano, Italy. ▲ ILL Institut Laue-Langevin BP 156, 38042 Grenoble Cedex 9, France.

Figure 9. Crystal structure of the triclinic pseudopolymorph obtained by crystallization of proximal p-tert-butylcalix[4]dihydroquinone by slow evaporation of chloroform and water.

Notes

The authors declare no competing financial interest. 8516

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(q) Soldatov, D. V.; Ripmeester, J. A. Inclusion in microporous beta-bis(1,1,1-trifluoro-5,5-dimethyl-5-methoxyacetylacetonato)copper(II), an organic zeolite mimic. Chem. Mater. 2000, 12 (7), 1827−1839. (r) Thallapally, P. K.; McGrail, P. B.; Dalgarno, S. J.; Atwood, J. L. Gas/solvent-induced transformation and expansion of a nonporous solid to 1: 1 host guest form. Cryst. Growth Des. 2008, 8 (7), 2090−2092. (6) Tedesco, C.; Immediata, I.; Gregoli, L.; Vitagliano, L.; Immirzi, A.; Neri, P. Interconnected water channels and isolated hydrophobic cavities in a calixarene-based, nanoporous supramolecular architecture. CrystEngComm 2005, 7, 449−453. (7) Thallapally, P. K.; McGrail, B. P.; Atwood, J. L.; Gaeta, C.; Tedesco, C.; Neri, P. Carbon dioxide capture in a self-assembled organic nanochannels. Chem. Mater. 2007, 19, 3355−57. (8) Tedesco, C.; Erra, L.; Brunelli, M.; Cipolletti, V. R.; Gaeta, C.; Fitch, A. N.; Atwood, J. L.; Neri, P. Methane Adsorption in a Supramolecular Organic Zeolite. Chem.Eur. J. 2010, 16 (8), 2371− 2374. (9) Erra, L.; Tedesco, C.; Cipolletti, V. R.; Annunziata, L.; Gaeta, C.; Brunelli, M.; Fitch, A. N.; Knoefel, C.; Llewellyn, P. L.; Atwood, J. L.; Neri, P. Acetylene and argon adsorption in a supramolecular organic zeolite. Phys. Chem. Chem. Phys. 2012, 14 (1), 311−317. (10) Meneghini, C.; Artioli, G.; Balerna, A.; Gualtieri, A. F.; Norby, P.; Mobilio, S. Multipurpose imaging-plate camera for in-situ powder XRD at the GILDA beamline. J. Synchrotron Rad. 2001, 8, 1162−1166. (11) Larson, A. C.; Von Dreele, R. B. GSAS - General Structure Analysis System; LANL Report LAUR 86-748; Los Alamos National Laboratory, Los Alamos, USA; available by anonymous FTP from mist.lansce.lanl.gov. (12) http://www.esrf.eu/UsersAndScience/Experiments/ StructMaterials/ID31/Technicaldescription. (13) Patterson, A. L. The Scherrer formula for X-ray particle size determination. Phys. Rev. 1939, 56, 978. (14) Tedesco, C.; Erra, L.; Immediata, I.; Gaeta, C.; Brunelli, M.; Merlini, M.; Meneghini, C.; Pattison, P.; Neri, P. Solvent Induced Pseudopolymorphism in a Calixarene-Based Porous Host Framework. Cryst. Growth Des. 2010, 10, 1527−1533. (15) Braga, D.; Giaffreda, S. L.; Grepioni, F.; Chierotti, M. R.; Gobetto, R.; Palladino, G.; Polito, M. Solvent effect in a ″solvent free″ reaction. CrystEngComm 2007, 9, 879−881. (16) Crank, J. The Mathematics of Diffusion; Oxford Press: Oxford, 1975. (17) Foley, N. J.; Thomas, K. M.; Forshaw, P. L.; Stanton, D.; Norman, P. R. Kinetics of water-vapor adsorption on activated carbon. Langmuir 1997, 13, 2083−2089. (18) Slight differences between the last adsorption value and the first desorption value are due to a time lapse related to the experimental procedure.

ACKNOWLEDGMENTS We acknowledge Mr. Olivier Grimaldi (ESRF) for technical support and Prof. Gaetano Guerra (University of Salerno) for useful discussions. We are grateful to ESRF for providing access to ID31 beamline in the context of L. E. three months stage at the ESRF and for providing access to BM08 beamline (Experiments n. 08-02-632 and n. 08-02-617). MIUR is acknowledged for financial support.

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REFERENCES

(1) (a) Fletcher, A. J.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. J.; Kepert, C. J.; Thomas, K. M. Adsorption Dynamics of Gases and Vapors on the Nanoporous Metal Organic Framework Material Ni2(4,4′-bipyridine)3(NO3)4: Guest Modification of Host Sorption Behavior. J. Am. Chem. Soc. 2001, 123, 100001. (b) Li, J.-R.; Sculley, J.; Zhou, H.-C. Metal_Organic Frameworks for Separations. Chem. Rev. 2012, 112, 869−932. (2) http://www.epa.gov/ttn/catc/dir1/fadsorb.pdf (3) Mallard Favier, I.; Baudelet, D.; Fourmentin, S. VOC trapping by new crosslinked cyclodextrin polymers. J. Inclusion Phenom. Macrocyclic Chem. 2011, 69, 433−437A. (4) Crini, G. Recent developments in polysaccharide-based materials used as adsorbents in wastewater treatment. Prog. Polym. Sci. 2005, 30 (1), 38−70. (5) (a) Massera, C.; Melegari, M.; Kalenius, E.; Ugozzoli, F.; Dalcanale, E. Supramolecular Control of Single-Crystal-to-SingleCrystal Transformation via Selective Guest Exchange. Chem.Eur. J. 2011, 17, 3064−3068. (b) Wei, W.; Wang, G.; Zhang, Y.; Jiang, F.; Wu, M.; Hong, M. A Versatile Tripodal Host with Cylindrical Conformation: Solvatomorphism, Inclusion Behavior, and Separation of Guests. Chem.Eur. J. 2011, 17, 2189−2198. (c) Wang, X. Q.; Eckert, J.; Liu, L. M.; Jacobson, A. J. Breathing and Twisting: An Investigation of Framework Deformation and Guest Packing in Single Crystals of a Microporous Vanadium Benzenedicarboxylate. Inorg. Chem. 2011, 50, 2028−2036. (d) Albunia, A.; Oliva, P.; Grassi, A. Interactions of Volatile Organic Compounds with Syndiotactic Polystyrene Crystalline Nanocavities. J. Phys. Chem. A 2011, 115, 443−452. (e) Soegiarto, A. C.; Comotti, A.; Ward, M. D. Controlled orientation of polyconjugated guest molecules in tunable host cavities. J. Am. Chem. Soc. 2010, 132 (41), 14603−14616. (f) Mckeown, N. Predictable porosity. Nat. Mater. 2011, 10, 563−564. (g) Burchell, T. J.; Enright, G. D.; Ripmeester, J. A. Guest capture, storage and removal in the TATM host framework: a single-crystal study. New J. Chem. 2008, 32, 864−871. (h) Ratcliffe, C. I.; Soldatov, D. V.; Ripmeester, J. A. Dynamics and disposition of benzene guest molecules in the micropore channels of a flexible metal-organic framework studied by 2H NMR and X-ray crystallography. Microporous Mesoporous Mater. 2004, 73, 71−79. (i) Motkuri, R. K.; Thallapally, P. K.; Nune, S. K.; Fernandez, C. A.; McGrail, B. P.; Atwood, J. L. Role of hydrocarbons in pore expansion and contraction of a flexible metal−organic framework. Chem. Commun. 2011, 47, 7077−7079. (l) Brouwer, D. H.; Moudrakovski, I. L.; Udachin, K. A.; Enright, G. D.; Ripmeester, J. A. Guest loading and multiple phases in single crystals of the van der Waals host p-tert-butylealix[4]arene. Cryst. Growth. Des. 2008, 8 (6), 1878−1885. (m) Dalgarno, S. J.; Thallapally, P. K.; Tian, J.; Atwood, J. L. Pseudo-polymorphism in the toluene solvate of p-tert-butylcalix[5] arene: structural and gas sorption investigation. New J. Chem. 2008, 32 (12), 2095−2099. (n) Manakov, A. Y.; Soldatov, D. V.; Ripmeester, J. A.; Lipkowski, J. Zeolite-like sorption of volatile organics in beta[CuL2] (L = {CF3COCHCOC(CH3)(2)OCH3}(-)). J. Phys. Chem. B 2000, 104 (51), 12111−12118. (o) Ratcliffe, C. I.; Soldatov, D. V.; Ripmeester, J. A. Dynamics and disposition of benzene guest molecules in the micropore channels of a flexible metal-organic framework studied by H-2 NMR and X-ray crystallography. Microporous Mesoporous Mater. 2004, 73 (1−2), 71−79. (p) Soldatov, D. V.; Moudrakovski, I. L.; Ratcliffe, C. I.; Dutrisac, R.; Ripmeester, J. A. Sorption of xenon, methane, and organic solvents by a flexible microporous polymer catena-bis(Dibenzoylmethanato)-(4,4′bipyridyl)nickel(II). Chem. Mater. 2003, 15 (25), 4810−4818. 8517

dx.doi.org/10.1021/la3009656 | Langmuir 2012, 28, 8511−8517