Synthesis, characterisation and water purification properties of carbon nanotube membranes (buckypapers)

Several different series of novel, self-supporting carbon nanotube (CNT) membranes, known as buckypapers (BPs), were successfully synthesised by vacuum filtration of dispersions containing multi-walled carbon nanotubes (MWNTs), functionalised MWNTs (MWNT‒COOH and MWNT‒NH2), or single-walled carbon nanotubes (SWNTs). The formation of these dispersions was achieved by subjecting samples containing CNTs and various dispersant molecules, including a surfactant (Triton X-100 (Trix)), macrocyclic ligands (meso-tetra(4-sulfonatophenyl) porphyrin dihydrogen chloride, phthalocyanine tetrasulfonic acid or 4-Sulfonic calix[6]arene hydrate), and biopolymers (bovine serum albumin, lysozyme, chitosan, gellan gum and DNA) to ultrasonic energy. Absorption spectrophotometry and optical microscopy was used to monitor the formation of the dispersions, and determine the optimum sonication time for their formation. Microanalytical data obtained from the MWNT and SWNT BPs confirmed the retention of significant amounts of the various dispersant molecules within their structures. The electrical conductivities of the MWNT and substituted MWNT BPs varied between 24 ± 16 and 58 ± 11 S cm‒1, while the SWNT/gellan gum and SWNT/chitosan BPs exhibited the highest electrical conductivities observed (68 ± 4 and 75 ± 6 S cm‒1, respectively). All MWNT and functionalised MWNT BPs possessed hydrophilic surfaces, with contact angles ranging from 28 ± 2 to 57 ± 5°. In contrast, the SWNT BPs possessed less hydrophilic surfaces (contact angles = 63 ± 7 to 88 ± 3°). Measurement of the mechanical properties of MWNT BPs prepared using Trix or one of the macrocyclic ligand dispersants showed that their tensile strengths varied between 1.6 ± 0.7 and 13 ± 2 MPa. In contrast, tensile test measurements performed on MWNT or SWNT BPs containing biopolymers revealed that they were typically much tougher materials, as reflected in tensile strengths between 12 ± 2 and 81 ± 14 MPa