Abstract
Nanodiamonds (ND) have recently emerged as excellent candidates for various applications including membrane technology due to their nanoscale size, non-toxic nature, excellent mechanical and thermal properties, high surface areas and tuneable surface structures with functional groups. However, their non-porous structure and strong tendency to aggregate are hindering their potential in gas separation membrane applications. To overcome those issues, this study proposes an efficient approach by decorating the ND surface with polyethyleneimine (PEI) before embedding it into the polymer matrix to fabricate MMMs for CO2/N2 separation. Acting as both interfacial binder and gas carrier agent, the PEI layer enhances the polymer/filler interfacial interaction, minimising the agglomeration of ND in the polymer matrix, which is evidenced by the focus ion beam scanning electron microscopy (FIB-SEM). The incorporation of PEI into the membrane matrix effectively improves the CO2/N2 selectivity compared to the pristine polymer membranes. The improvement in CO2/N2 selectivity is also modelled by calculating the interfacial permeabilities with the Felske model using the gas permeabilities in the MMM. This study proposes a simple and effective modification method to address both the interface and gas selectivity in the application of nanoscale and non-porous fillers in gas separation membranes.
Highlights
Membranes are recognised as an energy-efficient and environmental-friendly separation technology for gas separation
Most of the conventional polymer membranes are restricted to a trade-off between mass transport rates and separation efficiency, while inorganic membranes face the limit of poor scalability and high cost [1,2]
Mixed matrix membranes (MMMs), which can be prepared by embedding selective filler materials into a continuous polymer matrix, offer an opportunity to overcome the drawbacks associated with pure polymer or inorganic membranes [3,4,5,6]
Summary
Membranes are recognised as an energy-efficient and environmental-friendly separation technology for gas separation. Mixed matrix membranes (MMMs), which can be prepared by embedding selective filler materials into a continuous polymer matrix, offer an opportunity to overcome the drawbacks associated with pure polymer or inorganic membranes [3,4,5,6]. With proper selection of the filler/polymer pair, mixed matrix membranes benefit from both the ease of processing of the polymer materials and superior separation properties of the filler particles. Pair-wise selection of the filler and polymer is the basis for the MMM fabrication because it is relevant to the morphology and performance of the membrane. The selection of polymer determines the minimum gas transport performance (diffusivity and solubility) of the membrane. Nano sized fillers are preferred due to their relatively good dispersion in the polymer matrix and the strong interaction with the polymer phase
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