Controlling Zeolitic Imidazolate Framework Nano- and. Microcrystal Formation: Insight into Crystal Growth by

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1 Supporting Information Controlling Zeolitic Imidazolate Framework Nano- and Microcrystal Formation: Insight into Crystal Growth by Time-Resolved In-Situ Static Light Scattering Janosch Cravillon, Roman Nayuk, Sergej Springer, Armin Feldhoff, Klaus Huber, *, and Michael Wiebcke *, Institut für Anorganische Chemie, Leibniz Universität Hannover, Callinstr. 9, Hannover Germany; Department Chemie, Universität Paderborn, Warburger Str. 100, Paderborn, Germany, Institut für Physikalische Chemie und Elektrochemie, Leibniz Universität Hannover, Callinstr. 3A, Hannover, Germany 1

2 Table of Contents Synthesis page 3 Comments on Nanocrystal Shape page 4 Time-Resolved In-Situ Static Light Scattering (SLS) pages 5-7 Small-Angle X-Ray Scattering (SAXS) pages 8-9 Powder X-Ray Diffraction (XRD) page 10 Scanning Electron Microscopy (SEM) pages Thermogravimetry / Difference Thermal Analysis (TG/DTA) page 13 Variable-Temperature X-ray Diffraction page 14 Nitrogen Physisorption pages 15 Fourier-Transform Infra-Red Spectroscopy (FT-IR) pages 16 2

3 Synthesis Materials All chemicals were purchased from Sigma-Aldrich and used as received without further purification. Chemical Purity Zn(NO 3 ) 2 6H 2 O 99.0 % 2-methylimidazole % 1-methylimidazole 99.0 % n-buthylamine % sodium formate 99.0 % methanol 99.8 % Synthesis of microcrystals with sodium formate as a modulating ligand Typically, mg (2.469 mmol) of Zn(NO 3 ) 2 6H 2 O is dissolved in 50 ml of MeOH. A second solution is prepared by dissolving mg (9.874 mmol) of Hmim and mg (9.874 mmol) of sodium formate in 50 ml of MeOH. The latter clear solution is poured into the former clear solution under stirring. After 24 h, the precipitate is recovered by filtration, washing with MeOH and drying under reduced pressure. 3

4 Comments on Nanocrystal Shape In a recent paper, Thallapally and coworkers 1 report the first shape-selective synthesis of ZIF-8 nanocrystals, claiming that their nanocrystals possess a hexagonal shape. However, it appears as if the authors have mixed up a hexagonal shape with a rhombic dodecahedral shape. For example, the nanocrystal shown on the TEM image in Fig. 1B of their paper 1 has indeed six corners but it appears with the symmetry mm2 (C 2v ) rather than with a hexagonal symmetry. When a rhombic dodecahedron is viewed directly on a {110} face the polyhedron appears exactly with mm2 (C 2v ) symmetry (compare the drawing on the left-hand side of Fig. 2b in our manuscript). Furthermore, the TEM images provided in Fig. 2 of their paper 1 display nanocrystals that clearly exhibit rhombic faces that are typical for rhombic dodecahedra. This is evidence that the authors had actually prepared ZIF-8 nanocrystals with a rhombic dodecahedral shape. [1] Nune, S. K.; Thallapally, P. K.; Dohnalkova, A.; Wang, C.; Liu, J.; Exarhos, J. Chem. Commun. 2010, 46,

5 Time-Resolved In-Situ Static Light Scattering (SLS) Experiments TR-SLS was performed with a home built multi-angle goniometer described by Becker and Schmidt. [1] Cylindrical silica glass cuvettes with a diameter of 25 mm from Hellma (Mülheim, Germany) served as scattering cells. The measuring temperature was 25 C. This goniometer was equipped with a He-Ne laser operating at a wavelength of nm and allowed simultaneous recording of the scattering intensity at 2 times 19 scattering angles. The angular regime covered a range of θ Recording of an angular dependent curve was completed after 2 ms successive recordings were added to form one measurement requiring 2 s in total. The time interval between the start of two successive measurements was 10 s. The component solutions (see syntheses) were cleaned by passing the solutions through 0.20 µm filters to remove dust particles and to combine them into the scattering cell. Addition of the second component solution determined the starting point (t = 0) of the experiment. Processing of scattering curves Scattering curves were processed as the Rayleigh ratio R θ at variable scattering angle θ. The Rayleigh ratio of the particles were calculated from the difference between the Rayleigh ratio of the particle dispersion and of the solvent. Details are given elsewhere. [2] The concentration dependence and angular dependence (i. e., dependence on q) of the Rayleigh ratios could be approximated as a linear relation [3] according to 2 Kc 1 R g = q + A2c (1) R θ M w 3 5

6 with K the contrast factor of the scattering species in solution, R θ the Rayleigh scattering of the ZIF-8 particles at the scattering angle θ, c the concentration of Zn(NO 3 ) 2 6H 2 O in g. L -1, M w the weight averaged molar mass of the ZIF-8 particles, R 2 g the z-averaged squared radius of gyration of the ZIF-8 particles and A 2 their second osmotic virial coefficient in solution. The contrast factor of the particles K = 2 2 4π n dn 4 N Aλ dc 2 (2) and the momentum transfer 4πn q = sin( θ / 2) (3) λ was calculated with Avogadro s number N A, with λ = nm the laser wavelength, with n = the refractive index of pure methanol as solvent and with dn/dc the refractive index increment of ZIF-8 in methanol. Lack of such a dn/dc forced us to apply a default value of dn/dc = 0.1 ml/g. This still reproduces correct relative values. In addition, the concentration of the constituents as well as the concentration of ZIF-8 particles depends in a complex way on the growth time. Therefore, an appropriate extrapolation of eq(1) to c = 0 was not possible. However, neglect of the concentration dependent term in eq(1) seems to be justified in the light of the very low concentrations applied in the present work. Therefore, Guinier approximation [4] of the initial part of the equation (1) was carried out 2 R g 2 θ = ln M W q (4) ln Kc R 3 6

7 in order to extract apparent particle mass values M w and size values R g of the growing ZIF-8 particles. A representative example is shown in Figure S1. Figure S1. Representative example of a scattering curve evaluated according to eq (4). [1] Becker, A.; Schmidt, M. Macromol. Chem. Macromol. Symp. 1991, 50, 249. [2] Liu, J.; Rieger, J.; Huber, K. Langmuir 2008, 24, [3] Zimm, B. J. Chem. Phys. 1948, 16, [4] Guinier, A.; Fournet, G. Small-Angle Scattering of X-Rays, Wiley: New York,

8 Small-Angle X-Ray Scattering (SAXS) Figure S2. a) Experimental SAXS pattern (black squares) taken from a methanolic disperison of the 65 nm-sized nanocrystals prepared in the absence of a modulating ligand. The fitted curve (red line) was obtained with a model of spherical particles with a Schultz size distribution (particle radius: 44 nm, polydispersity: 0.28). b) Corresponding Schultz size distribution. Figure S3. a) SAXS pattern taken from a methanolic dispersion of the 18 nm-sized nanocrystals prepared with n-butylamine as a modulating ligand. b) Corresponding PDDF curve (maximum secondary particle size: 88 nm, R g = 27 nm). In the double logarithmic representation of the SAXS pattern two regions with different slopes can be clearly identified: (i) The region at q > 0.3 (d < 21 nm) corresponds to the primary nanocrystals. The slope of ~ -4 (-3.73) suggests that the primary particles exhibit a sharp interface 8

9 to the solvent (Porod s law). (ii) The region at q < 0.3 (d > 21 nm) corresponds to the secondary particles. The slope of may be correlated with a fractal dimension of the secondary aggregates. Figure S4. a) and b) SAXS patterns of nanocrystal powders prepared with n-butylamine as a modulating ligand. The compositions of the synthesis solutions are indicated. c) and d) Inner parts of the corresponding PDDF curves. Note that for composition (6) only a shoulder (indicated by an arrow) appears in the PDDF curve, while for the other compositions the PDDF curves exhibit a clear maximum. The maxima (and shoulder) provide an estimate of the radii of the primary particles, which are assumed to be spherical and of low polydispersity. 9

10 Powder X-Ray Diffraction (XRD) Figure S5. Powder XRD patterns of nanocrystals prepared with n-butylamine as a modulating ligand. The compositions of the synthesis solutions are indicated. 10

11 Scanning Electron Microscopy (SEM) Figure S7. SEM images of intermediate particles during the formation of microcrystals in the presence of sodium formate, a) after 700 s, b) after 1000 s, c) after 1000 s, and d) after

12 Figure S8. SEM image taken during early stages of ZIF-8 microcrystal formation in the presence of sodium formate (after 600 s). Aggregates of tiny nanoparticles can be seen in the center of the SEM image. 12

13 Thermogravimetry / Difference Thermal Analysis (TG/DTA) Figure S9. TG (solid lines) and DTA curves (dotted lines), a) of 18 nm-sized nanocrystals prepared with n-butylamine as a modulating ligand, b) of 65 nm-sized nanocrystals prepared in the absence of a modulating ligand, c) of microcrystals prepared with formate as a modulating ligand, and d) of microcrystals prepared with 1-methylimidazole as a modulating ligand (air atmosphere). The total mass losses (65 %) are in agreement with the calculated ones (64 %), assuming decomposition of ZIF-8 (Zn(mim) 2 ) into solid hexagonal ZnO (as verified by XRD) and volatile products stemming from the organic ligand. 13

14 Variable-Temperature X-Ray Diffraction Figure S10. Variable-temperature XRD patterns a) of 18 nm-sized nanocrystals prepared with n-butylamine as a modulating ligand, b) of 65 nm-sized nanocrystals prepared in the absence of a modulating ligand, c) of microcrystals prepared with formate as a modulating ligand, and d) of microcrystals prepared with 1-methylimidazole as a modulating ligand. 14

15 Nitrogen Physisorption Figure S11. Mesopore size distribution of the 18 nm-sized nanocrystals prepared with n-butylamine as a modulating ligand. 15

16 Fourier-Transform Infra-Red Spectroscopy (FT-IR) Figure S13. FT-IR spectra a) of 18 nm-sized nanocrystals prepared with n-butylamine as a modulating ligand, b) of 65 nm-sized nanocrystals prepared in the absence of a modulating ligand, c) of microcrystals prepared with formate as a modulating ligand, and d) of microcrystals prepared with 1-methylimidazole as a modulating ligand. 16