Beta-cyclodextrin functionalized MWCNT: a potential nano-membrane material for mixed matrix gas separation membranes development

Abstract

In this paper, synthesized (raw) multi-walled carbon nanotubes (rMWCNTs) were functionalized with beta-cyclodextrin (bC) using Chen’s soft cutting technique. Raw multi-walled carbon nanotubes (rMWCNTs) and beta-cyclodextrin functionalized multi-walled carbon nanotubes (bCfMWCNTs) were characterized by transmission electron microscope (TEM). Neat polyimide (PI) and polyimide/bCfMWCNTs mixed matrix membranes were fabricated by immersion precipitation method. Pure methane and carbon dioxide were used as test gases to measure the permeances of membrane samples. Thermal properties of membranes and MWCNTs were characterized by differential scanning calorimetery (DSC) and thermogravimetric analysis (TGA), respectively. The TEM results showed that beta-cyclodextrin cannot only attach to the inner and outer surface of the MWCNT walls but also fill the open-ended tips of the MWCNTs. TGA thermograms showed that bCfMWCNTs are thermally less stable than rMWCNTs due to the decomposition of beta-cyclodextrin layer, which occurred before the decomposition of rMWCNTs. According to the DSC experiment, the glass transition temperature (Tg) increased as bCfMWCNTs increases in the polymer matrix. The increase in glass transition was attributed to good dispersion of the bCfMWCNTs in the polymer matrix as a result of improved attachment of bCfMWCNTs to the polymer segments. Separation properties and morphology (and distribution of bCfMWCNTs within the polymer matrix) of the fabricated membranes were analyzed by using permeation test and cross sectional FESEM micrographs respectively. Permeation test results revealed that the ideal CO2/CH4 selectivity increased considerably from neat polyimide membrane to polyimide/bCfMWCNTs mixed matrix membranes. Cross sectional FESEM results showed that well dispersed bCfMWCNTs within the polymer matrix are observable especially in case of PI/6 wt.% BFBM MMM.