Competitive I 2 Sorption by Cu-BTC from Humid Gas Streams

Transcription

1 Supporting Information for: Competitive I 2 Sorption by Cu-BTC from Humid Gas Streams Dorina F. Sava, Karena W. Chapman, Mark A. Rodriguez, Jeffery A. Greathouse, # Paul S. Crozier,^ Haiyan Zhao, Peter J. Chupas, and Tina M. Nenoff, * Nanoscale Science Department, Sandia National Laboratories, Albuquerque, NM 87185, USA. X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA Materials Characterization and Performance Department, Sandia National Laboratories, Albuquerque, NM 87185, USA # Geochemistry Department, Sandia National Laboratories, Albuquerque, NM 87185, USA. ^ Scalable Algorithms Department, Sandia National Laboratories, Albuquerque, NM 87185, USA. S1

2 Section S1: Iodine loading Competitive I 2 /H 2 O gas sorption experiments were conducted at ambient pressure, 75 C, and 3.5% relative humidity, to form I Activated Cu-BTC was sealed with excess I 2 in an adsorption chamber (Scheme S1) and placed in a convection oven at 75 C. The iodine loaded Cu-BTC samples were recovered after different exposure times, allowed to cool in an inert environment and the mass change recorded. Different I 2 loadings were achieved on distinct individual samples (~0.28 g pristine Cu-BTC/sample) exposed in the absorption chamber for various times: 0.5 hours (~ 0.2 I/Cu), 3.5 hours (~ 1 I/Cu), 6.5 hours (~2 I/Cu), 9 hours (~ 3 I/Cu). Scheme S1. Schematic representation of the iodine loading chamber. Cu-BTC Cu-BTC Cu-BTC Cu-BTC I 2 (s) S2

3 Section S2: Micro-X-ray Fluorescence (µ-xrf) The µ-xrf analysis was performed using a Bruker M4 Tornado µ-xrf mapping system. The instrument was equipped with a micro-focused Rh source (50 kv, 600 µa) with a poly-capillary optic (~30 µm spot-size). Fluorescence spectra were collected using two silicon-drift detectors. Powder specimens were loaded in small Teflon cups (~2mm inner diameter), then secured to the xy-translation stage within the M4, and XRF spectra were collected under vacuum (~10-3 Torr). Quantification of the I/Cu ratio used the Quantitative analysis routines within the M4 software. In order to verify and ensure the accuracy of the quantitative analysis of the measured I/Cu ratio, a total of 9 samples were prepared with the following targeted I/Cu molar compositions: 10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20 and 90/10, using CuO and KI as Cu and I sources, respectively. Figure S1. The calibration function for measured vs. expected I/Cu ratios 5 4 Intercept B1 B2 Statistics Value Value Value Adj. R-S A Expected I/Cu ratios Measured I/Cu ratios S3

4 Figure S2. Micro X-ray Fluorescence (µ-xrf) data on maximally loaded sample. Table S1. The measured/raw vs. corrected I/Cu ratio I/Cu ratio Measured/raw Corrected S4

5 Section S3. Thermogravimetric-Differential Scanning Calorimetry Figure S3. TGA-DSC on maximally loaded sample (3 I/Cu). S5

6 Section S4: Temperature-programmed in situ IR spectroscopy Figure S4. Temperature programmed in situ IR (20 C C) for the ~ 3 I/Cu I BTC sample, monitoring temperature dependent event changes in the intensities of signature IR bands: (a) cm -1 and (b) cm -1. (a) (b) S6

7 Section S5: High resolution synchrotron-based powder X-ray diffraction data on incrementally loaded samples Figure S5. High resolution synchrotron-based powder X-ray diffraction data on incrementally loaded samples I at 0, 0.2, 1, 2, and 3 I/Cu. 0 I/Cu 0.2 I/Cu 1 I/Cu 2 I/Cu 3 I/Cu Intensity theta/ 0 S7

8 Section S6: Rietveld refinement of data for 0.2 I/Cu sample Figure S6. Calculated, observed and difference plots of synchrotron X-ray powder diffraction data for 0.2 I/Cu in I sample: (a) before, and (b) after modeling and refining iodine within the GSAS program. The cubic lattice parameter is: a= Å. (a) - Calculated + Observed - Difference Intensity Rp = 10.55% (b) - Calculated + Observed - Difference Intensity Rp = 5.12% S8

9 Figure S7. X-ray structural representation of 0.2 I/Cu I Ball-and-stick model; I=fuchsia, Cu=blue, C=gray, O=red; H atoms have been omitted for clarity. S9

10 Figure S8. Calculated, observed and difference patterns of synchrotron X-ray powder diffraction data of ~ 3 I/Cu in I after including I 2 in the Rietveld structure refinement within the Materials Studio v software. - Calculated + Observed - Difference Rp = 4.53 % S10

11 Section S8: Pair Distribution Function Measurements Figure S9: The area of selected peaks and the low r slope of the differential PDF. The peak area corresponds to the relative abundance of different I-framework and I-I correlations. The slope is related to the material density which increases with I 2 -loading. The low r slope of the differential PDFs and the area of low r peaks were quantified by fitting Gaussian functions and a linear baseline to the PDFs within the program fityk. The intensity of some peaks plateau at lower I 2 -loadings as the associated I 2 sorption sites become saturated Angstrom 2.96 Angstrom 3.53 Angstrom 4.03 Angstrom 4.44 Angstrom Peak Intensity weight %I 2 S11

12 Section S9. Molecular simulations Simulations were performed with the LAMMPS code. 1 The energy expression included short-range van der Waals interactions, with parameters taken from the Universal Force Field (UFF) without modification. 2 UFF parameters and fixed framework atoms have been used successfully to study the structure and dynamics of adsorbed guests. 3 Grand Canonical Monte Carlo (GCMC): The van der Waals parameters for iodine were taken from literature, 4 based on the computed viscosity data for pure I 2 gas. Insertion and deletion of iodine was controlled using the fix GCMC method in LAMMPS. A short range cutoff of 16.0 Å was applied. Iodine molecules were exchanged between Cu-BTC and an imaginary ideal gas reservoir at 298 K and a range of chemical potential values (- 14 kcal mol 1 to -11 kcal mol 1 ) corresponding to a pressure range of atm 1.46 atm. Exchanges consisted of equally-probable attempts to perform insertions or deletions of iodine molecules into or out of Cu-BTC. Insertion attempts tested random positions within the simulation domain. Deletion attempt candidates were randomly chosen from existing inserted iodine molecules. GCMC translation attempts of up to 0.2 Å were performed on existing inserted iodine molecules with an attempt frequency probability equal to that of the exchange attempts. Molecular dynamics (MD): In the explicit-atom approach, van der Waals parameters for the iodine atom were taken from UFF. Although the UFF parameters for iodine have not been optimized to reproduce the bulk properties of pure I 2, they represent a first approximation of the steric effects upon I 2 adsorption and dynamics within Cu-BTC. Simulations were performed in the canonical ensemble with a Nose-Hoover thermostat temperature of 25 C and a timestep of 1.0 fs. A short range cutoff of 16.0 Å was applied. In the explicit-atom model, the I-I bond length remained fixed at 2.66 Å using the SHAKE algorithm. 5 Simulations were run for 2.0 ns, with data from the final 1.0 ns used for averaging. S12

13 Figure S10. Incremental Radial Distribution Function (RDF) plots generated by MD simulations considering the explicit model of I 2, to highlight the population of similar binding sites at maximum iodine loading. O carb and O w refer to carboxylate and water oxygens, respectively. The simulated RDF plot indicate that the peaks between 4Å and 5Å are due to intermolecular I I as well as I framework interactions. S13

14 Figure S11. Incremental Radial Distribution Function (RDFs) plots generated by MD simulations considering the spherical model of I 2, to highlight the population of similar binding sites at maximum iodine loading. O carb and O w refer to carboxylate and water oxygen atoms, respectively. S14

15 Figure S12. Two-dimensional I 2 density contour plots from the MD simulation, using the explicit model for I 2. Primary density sites are located in the tetrahedral cavities as well as near the structural water molecules. S15

16 Figure S13. Two-dimensional I 2 density contour plots from the MD simulation, using the spherical model for I 2. Primary density sites are located in the tetrahedral cavities as well as near the structural water molecules. S16

17 References: (1) Plimpton, S. J. J. Comp. Phys. 1995, 117, 1. (2) Rappe, A. K.; Casewit, C. J.; Colwell, K. S.; Goddard, W. A.; Skiff, W. M. J. Am. Chem. Soc. 1992, 114, (3) (a) Keskin, S.; Liu, J.; Rankin, R. B.; Johnson, J. K.; Sholl, D. S. Ind. Eng. Chem. Res. 2009, 48, (b) Düren, T.; Bae, Y. S.; Snurr, R. Q. Chem. Soc. Rev. 2009, 38, (4) Hirschfelder, J. O.; Curtiss, C. F.; Bird, R. B. Molecular theory of gases and liquids (Wiley, New York, 1964). (5) Ryckaert, J. -P.; Ciccotti, G.; Berendsen, H. J. C. J. Comput. Phys. 1977, 23, 327. S17