(696e) Clustering Effects in Mixed Matrix Membranes Formed By Nano-Sized ZIF-8 and Pebax

Separation of carbon dioxide from combustion flue gases using selective membranes shows promise to be a low energy carbon capture option. [1] Polymeric membranes exhibit a trade-off between permeability and selectivity which limits their viability as an economically feasible option for use in post-combustion carbon capture. [2] A great deal of attention has been focused on mixed matrix membranes (MMMs) due to the potential improvements that can be made to the selectivity and permeability relative to pure polymer membranes as well as offering a lower cost alternative and improved handling properties relative to pure inorganic membranes. [3]

Whilst mixed matrix membranes show promise there are several challenges slowing their widespread implementation. These challenges largely revolve around minimising performance-hindering defects at the polymer-filler interface. The synthesis route and material selection are key in minimising these defects. [4] Thin membranes are also desirable for greater gas permeances and economical separation processes. Hence small particles are of particular interest but agglomeration of the particles can become an issue.

Nano-sized ZIF-8 crystals were synthesised at Deakin University. ZIF-8 is a zeolitic imidazolate framework containing cavities connected by small windows be which may allow for a molecular sieving effect to occur. [5]

Membranes composed of PEBAX MH1657 and nano-sized ZIF-8 particles were prepared and their gas transport properties tested using the constant-volume method. Significant clusters were observed using SEM at loadings of above 5 wt. %. The presence and prevalence of clusters corresponded with an increase in permeability of all gases tested (helium, nitrogen and carbon dioxide) with no appreciable loss of selectivity. A novel strategy was taken to improve the polymer-filler interface via surface modification of the ZIF-8. ZIF-8 particles were treated with ammonia gas plasma to substitute methyl groups on the surface of the particles with amine groups in order to improve the adhesion between polymer and particles and investigate the role the clusters play in the gas transport.

[1] T.C. Merkel, H. Lin, X. Wei, R. Baker, J. Memb. Sci. 359 (2010) 126.

[2] L.M. Robeson, J. Memb. Sci. 320 (2008) 390.

[3] C.M. Zimmerman, A. Singh, W.J. Koros, J. Memb. Sci. 137 (1997) 145.

[4] T.-S. Chung, L.Y. Jiang, Y. Li, S. Kulprathipanja, Prog. Polym. Sci. 32 (2007) 483.

[5] D. Fairen-Jimenez, S.A. Moggach, M.T. Wharmby, P.A. Wright, S. Parsons, T. Düren, J. Am. Chem. Soc. 133 (2011) 8900.