(376bb) Gas Transport Properties of Polysulfone Mixed-Matrix Membranes Embedded with Hexamethylenetetramine Dicyanamide Cadmium Nanoparticles

Polymer membranes are used wieldy in gas separation [1,2]. A major challenge in polymer membranes is the trade-off between gas permeability and selectivity [3]. To address this challenge, mixed-matrix membranes (MMMs) have been introduced and studied. These membranes consist of organic or inorganic nanoparticles dispersed in a polymeric matrix [4]. MMMs benefit from the high flexibility and processability of polymers and the outstanding thermal resistance and gas selectivity of nanoparticles. Polysulfones (PSUs) are a class of glassy polymers with high thermal, hydrolytic, and oxidative stability. They are widely used in manufacturing gas-separation and water-purification membranes [5-6]. The polymer contains sulfonyl groups, which have high affinity for CO₂ rather than CH₄,making it suitable for manufacturing CO₂/CH₄ separation membranes. However, PSU suffers from low free volume and consequently low gas permeability. This problem can be overcome by adding nanoparticles to the PSU matrix and manufacturing a MMM [7].

This paper presents a study of embedding hexamethylenetetramine dicyanamide cadmium (HDC) nanoparticles into the matrix of PSU to fabricate a MMM using solvent evaporation. The effect of HDC nanoparticles on gas transport properties was evaluated through N₂, O₂, CH₄ and CO₂ permeation tests. It was found that membranes with 2.5 wt% of the nanoparticles have the best gas transport properties. At this nanoparticle loading level, the permeability of the membrane was lower than that of the pure PSU. However, the CO₂/CH₄, CO₂/N₂ and O₂/N₂ selectivities increased sharply. For example, at the optimum loading level, CO₂/CH₄ and CO₂/N₂ gas selectivities increased by 42.6% and 61.6%, respectively, compared with the pure PSU. The optimal membrane showed CO₂/CH₄, CO₂/N₂ and O₂/N₂ selectivities of 41.66, 20.08 and 5.09, respectively. Analyses of the chemical structures of the MMMs using SEM and FTIR spectroscopy further confirmed excellent gas sieving properties of the membranes. The results indicate that the incorporation of HDC nanoparticles into polymers allows for addressing the high free volume and poor sieving ability problems in polymer membranes.

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