Characterization of a support-free carbon nanotube-microporous membrane for water and wastewater filtration

Nonwoven carbon nanotube (CNT) laminates were characterized as support-free membranes for water filtration in terms of structural morphology, water permeability, selectivity and chemical resistance. Nominal pore rating (12–23 nm) estimated by rejection of globular proteins and fluorescence beads fall within the selectivity range of tight ultrafiltration (UF) membranes applied for wastewater treatment. The membranes displayed high permeability (120–400 LMH/bar). High selectivity regardless of high permeability seems to be due to tortuosity and pore structure of the membranes (25–50 μm thickness). The chemical stability of the membranes was tested towards common chemicals used for membrane cleaning (HCl, NaOH, NaClO) but at much severe conditions (24 h exposure at 4–10 fold higher concentrations). High resolution-X-ray photoelectron spectroscopy (XPS) was applied to evaluate chemical resistance. The relative C/O-carbon to oxygen ratio and typical deconvolution curves of C1s lines of the membranes after 24 h exposure depicted no significant changes compared to the reference samples, confirming resistance to chemical oxidation. This combination of features, added to simplicity of fabrication and post-synthesis modification and support-free configuration that enhances chemical stability, offer a worthwhile opportunity of application of these dense-array outer-walled CNT membranes in the UF range, especially at harsh conditions such as wastewater treatment.