Mildly oxidized SWCNT as new potential support membrane material for effective H2/CO2 separation

Abstract

We demonstrate challenging material properties of flat free-standing chemically modified single wall carbon nanotube (SWCNT) sheets potentially usable as new support materials for gas separation composite membranes. Carbon nanotube samples in bare and oxidized forms were assembled into buckypaper by a vacuum filtration from SWCNT colloidal suspension. The fundamental structure, composition and mechanical properties were examined via SEM, EDS, AFM, XPS, Raman spectroscopy and dynamical mechanical analysis. Gas permeability was determined by the fixed-volume pressure-increase permeation method at 25°C and 1bar feed overpressure. The mild SWCNT oxidation caused substantial structural rearrangement of buckypaper with significant impact on its properties. Determined partial opening of nanotubes and the introduction of oxygen-containing species decreased the initial extremely-high H2 permeability from circa 20 million (bare) to almost 5 million barrers while the ideal H2/CO2 selectivity α increased from almost non-selective 1.1 (bare) to 3.5 for the oxidized sample. Furthermore, oxidized form exhibited 2 times lower tensile strength but 2.5 times higher ductility. Such behavior indicates improved mechanical properties of oxidized samples that can undergo significant plastic deformation before the rupture. Determined features make mildly oxidized SWCNT buckypapers potentially attractive as new robust and tunable membrane support material for highly effective hydrogen separation.