Supporting Information

Transcription

1 Supporting Information MOF Channels within Porous Polymer Film: Flexible, Self-Supporting ZIF-8 Poly(ether sulfone) Composite Membrane Samuel C. Hess, Robert N. Grass, Wendelin J. Stark* *Prof. Wendelin J. Stark Institute for Chemical and Bioengineering, ETH Zürich Vladimir-Prelog-Weg 1 CH-8093 Zürich Switzerland wendelin.stark@chem.ethz.ch S1

2 XRD measurements In order to determine the proper ZIF-8 formation after synthesis, we compared XRD measurements of pure reference ZIF-8 (Basilite Z1200, BASF), ZnO particles which we expected still to be present after synthesis, and the ZIF-8/PES composite membrane. Figure S1 revealed that the final ZIF-8/PES composite membrane still contained remaining ZnO particles besides from the synthesized ZIF-8 particles. Broader peaks as observed for the ZIF-8/PES compsite membrane may refer to the nanocrystallites and heterogenous crystal sizes e.g. larger crystals on the membrane surface vs. smaller crystals wihin the membrane. 1 Figure S1: XRD pattern of ZnO, ZIF-8 crystals (Basolite Z1200) and the flexible ZIF-8/PES membrane. S2

3 Figure S2: XRD pattern of reference ZIF-8 crystals (Basolite Z1200), ZnO particles, the flexible ZIF-8/PES membrane and a PES membrane containing the ZnO seed particles. EDX Mapping Analysis The membrane samples were tested on the occurrence of sulfur being present in the poly(ether sulfone) (PES) only, oxygen being present within the PES and the zinc oxide, and zinc and nitrogen for detection of the ZIF-8. The increased oxygen occurrence within the top-layer compared to the supporting layer supported the assumption of remaining ZnO within the membrane s top layer. The EDX map is shown in Figure 5b. The occurrence of larger crystals detected by SEM analysis (Figure S3) on the upper part of the membran s cross section could not be proven by EDX. S3

4 Figure S3: SEM images of composite membrane cross section after synthesis (Step 5). Influence of pore-size on the ZIF-8 crystal island incorporation into the pores. In previous work, we developed a procedure to control the pore size of PES membranes. 2 In order to assess the influence of pore size on the incorporation of ZIF-8 crystals within the polymeric matrix we tested PES-ZnO systems of different pore sizes. Membranes with relatively small pores (average pore diameter 60 nm) were produced by casting a dispersion of ZnO/PES/glycerol (32/18/50 wt.) in DMAc (10 % wt. of PES in DMAc) using a 150 µm pitch spiral bar. Membranes with larger pores (average pore diameter 330 nm) were procuded using a dispersion of ZnO/PES/glycerol (46/25/29 wt.) in DMAc (10 % wt. of PES in DMAc) using a 90 µm pitch spiral bar. The pore size of these two different membranes (Figure 2) was determined manually by using graphic softwear tool (Photoshop) measurements. Over 90 pores per sample were measured with the Elliptical Marquee Tool. The pores average diameter was calculated from the average values of the ellipse height and width. Figure 2 revealed a much stronger incorporation of ZIF-8 islands for the membrane exhibiting bigger pores. For membranes with smaller pores it seemed as the crystals grew rather on top of the PES surface than within the porous matrix. S4

5 Influence of varying solvothermal synthesis times In order to assess the effect of different incubation times in the synthesis solution 1, the membrane was analyzed at three different timepoints during synthesis, after 5, 7 and 10 minutes (Figure S4). Apart from disappearing ZnO particles, which were still visible on the surface after 5 minutes of incubation, the ZIF-8 islands seemed to better incorporate within the polymeric structure after 10 minutes. Figure S4: Membrane (Step 3) incubated in solution 1 at 120 C for three different time periods a) incubated for 5 min, b) for 7 min, c) for 10 min. DMAc steaming optimisation In order to reach a suitable degree of membrane fusion with the ZIF-8 crystals, the membrane was incubated for different periods of time within the desiccator. For 3, 5, 7 and 10 minutes the membrane was incubated. The membrane samples after 7 and 10 minutes partially turned transparent, indicating membrane melting and pore destruction. For avoiding any DMAc condenstaion at the moment of placing the membrane within the exicator, it was preheated at 100 C for a couple of minutes. S5

6 Gas flux measurements and membrane bending Figure S5: a) Schematic illustration of the membrane bending test. Path 1 shows the bending around a 5 mm bar prior to single gas flux measurement. Alternatively unbent membranes were tested as well (path 2). An in-house built gas permeation cell combined with a soap bubble flow-meter was used for all experiments, which were conducted at room temperature (Figure S6). The membrane was fixed on an alumina plate containing a hole of 2 cm2 surface via a double sided tape (Tesa 4964 TeppichKlebeband). The trans-membrane pressure drop of 0.2 bar was confirmed by a WIKA pressure gauge CPG500. The trans-membrane gas flux was quantified using a manual bubble flowmeter (Sigma-Aldrich, 10 ml). Gas flux tests were conducted with H2, N2 and CO2. For bending the membranes, they were homogenously torn around a screw driver bar with a diameter of 5 mm, which was fixed on a laboratory stand by hand (Figure 4f). S6

7 Figure S6: Photography of the single gas flux measurement set up. S7

8 Figure S7: Hydrogen flux and H 2 /CO 2 selectivity comparison of a pure PES membrane (Nr.1 3 ), ZIF-8 containing mixed matrix membranes (Nr.2*, 4 3, ), layered ZIF-8/Polymer composite membranes (Nr.5, 7 6, 8 7, ) and the here introduced membrane containing directed ZIF-8 crystals (9, average value of samples 1-3, unbent, Table S1). The linear line represents the Robeson upper bound of polymeric membranes for H 2 /CO 2 separation. 11 *Test conducted at 35 C. Table S1: Gas flux rates of bent and unbent ZIF-8/PES composite membranes Sample Gas Flux x 10-8 [mol m -2 s -1 Pa -1 ] Selectivities H 2 CO 2 N 2 H 2 /CO 2 H 2 /N 2 1, unbent , unbent , unbent , bent , bent S8

9 Table S2: Comparison of different gas flux measurment studies for ZIF-8 membranes Support Mat. Permeance [10-7 mol m -2 s -1 Pa -1 ] Selectivity Ref. H 2 CO 2 N 2 H 2 /CO 2 H 2 /N 2 PES 3.90 ± 2.6 * 0.44 ± 0.32 * 0.34 ± 0.24 * 9.3 ± 3.1* 11.5 ± 2.1* This work Psf na 3.8 na Nylon 19.7 na 4.6 na 4.3 BPPO PVDF PES 4 na na na 9.9** * n = 3 (samples 1-3, unbent), ** Mixture gas separation factor measured at 333K References 1. Patterson, A. L., The Scherrer formula for x- ray particle size determination. Phys. Rev. 1939, 56, Hess, S. C.; Kohll, A. X.; Raso, R. A.; Schumacher, C. M.; Grass, R. N.; Stark, W. J., Template- Particle Stabilized Bicontinuous Emulsion Yielding Controlled Assembly of Hierarchical High- Flux Filtration Membranes. ACS Appl. Mater. Inter. 2015, 7, Khan, A. L.; Cano- Odena, A.; Gutierrez, B.; Minguillon, C.; Vankelecom, I. F. J., Hydrogen separation and purification using polysulfone acrylate- zeolite mixed matrix membranes. J. Membr. Sci. 2010, 350 (1-2), Yang, T.; Chung, T. S., High performance ZIF- 8/PBI nano- composite membranes for high temperature hydrogen separation consisting of carbon monoxide and water vapor. Int. J. Hydrogen Energ. 2013, 38, S9

10 5. Bushell, A. F.; Attfield, M. P.; Mason, C. R.; Budd, P. M.; Yampolskii, Y.; Starannikova, L.; Rebrov, A.; Bazzarelli, F.; Bernardo, P.; Jansen, J. C.; Lanc, M.; Friess, K.; Shantarovich, V.; Gustov, V.; Isaeva, V., Gas permeation parameters of mixed matrix membranes based on the polymer of intrinsic microporosity PIM- 1 and the zeolitic imidazolate framework ZIF- 8. J. Memb. Sci. 2013, 427, Song, Q. L.; Nataraj, S. K.; Roussenova, M. V.; Tan, J. C.; Hughes, D. J.; Li, W.; Bourgoin, P.; Alam, M. A.; Cheetham, A. K.; Al- Muhtaseb, S. A.; Sivaniah, E., Zeolitic imidazolate framework (ZIF- 8) based polymer nanocomposite membranes for gas separation. Energ. Environ. Sci. 2012, 5, Shamsaei, E.; Low, Z. X.; Lin, X. C.; Mayahi, A.; Liu, H. Y.; Zhang, X. W.; Liu, J. Z.; Wang, H. T., Rapid synthesis of ultrathin, defect- free ZIF- 8 membranes via chemical vapour modification of a polymeric support. Chem. Commun. 2015, 51, Li, W. B.; Meng, Q.; Zhang, C. Y.; Zhang, G. L., Metal- Organic Framework/PVDF Composite Membranes with High H- 2 Permselectivity Synthesized by Ammoniation. Chem- Eur J. 2015, 21, Shamsaei, E.; Lin, X. C.; Low, Z. X.; Abbasi, Z.; Hu, Y. X.; Liu, J. Z.; Wang, H. T., Aqueous Phase Synthesis of ZIF- 8 Membrane with Controllable Location on an Asymmetrically Porous Polymer Substrate. ACS Appl. Mater. Inter. 2016, 8, Nagaraju, D.; Bhagat, D. G.; Banerjee, R.; Kharul, U. K., In situ growth of metal- organic frameworks on a porous ultrafiltration membrane for gas separation. J Mater Chem A 2013, 1 (31), Robeson, L. M., The upper bound revisited. J. Memb. Sci. 2008, 320, Yao, J. F.; Dong, D. H.; Li, D.; He, L.; Xu, G. S.; Wang, H. T., Contra- diffusion synthesis of ZIF- 8 films on a polymer substrate. Chem. Commun. 2011, 47, Ge, L.; Zhou, W.; Du, A. J.; Zhu, Z. H., Porous Polyethersulfone- Supported Zeolitic Imidazolate Framework Membranes for Hydrogen Separation. J. Phys. Chem. C. 2012, 116, S10