Incorporating Microporous Zn₃ and Zn₂Cd MOFs into Pebax/PVDF Mixed Matrix Membranes for Improved Carbon Dioxide Separation Performance

Abstract

A pair of related metal–organic frameworks (Zn 3 and Zn 2 Cd) developed in our group were incorporated into Pebax 30R51 and PVDF Kynar 761 polymers to fabricate mixed matrix membranes (MMMs). These MOFs were chosen due to the carbon dioxide molecular sieving ability of Zn 3 , and the slightly larger pore aperture of Zn 2 Cd that allows carbon dioxide and larger gases to enter the pores. For Pebax-based MMMs, this work demonstrated an over two-fold and four-and-a-half-fold increase in carbon dioxide permeability for Zn 3 - (15 wt %) and Zn 2 Cd-containing (10 wt %) MMMs over the pristine polymer. Separation selectivity (CO2:N2) of 4.21 and 7.33 were observed for Zn 3 and Zn 2 Cd (10 wt %). For PVDF-based MMMs, the incorporation of Zn 3 and Zn 2 Cd (10 wt %) increased the carbon dioxide permeability approximately two- and three-fold. The CO2/N2 selectivity of the PVDF membranes increased 73% (1.01 to 1.86) and 68% (1.01 to 1.68) when 15 wt % Zn 3 and Zn 2 Cd were incorporated into PVDF. The improved performance of Pebax over PVDF based MMMs is attributed to matching the permeability of the polymer bulk phase (Pebax over PVDF) and the dispersed phase (Zn 3 and Zn 2 Cd). The lower permeability allows the MOF, which has slow kinetics associated with molecular sieving, to participate in the permeation process better. With regards to Zn 3 vs Zn 2 Cd, while Zn 3 acts as a molecular sieve and Zn 2 Cd does not, we hypothesize that the faster diffusion of carbon dioxide gas in Zn 2 Cd can outcompete the lower nitrogen gas permeability and molecular sieving properties of Zn 3 . However, we expect that further increasing the pore aperture would increase the permeabilities of nitrogen gas such that differences in diffusion kinetics due to molecular size would be unimportant.

Methyl red based metal–organic frameworks for the selective and tuneable sensing of ammonia gas

“…With our ongoing interests in developing MOFs for environmental applications such as storage, 24 separation, 25,26 and reactivity of gases, 27 the present work focuses on sensing ammonia gas. As illustrated in Fig.…”