Abstract: Acid-base titrations were used to assess the covalent reactivity of carboxylic groups on single-layer graphene oxides (SLGO) or hydrazine-reduced analogues (SLGR) when treated with thionyl chloride and subsequent coupling to amines. Reflux with aggressive solvents led to size reduction and folding of individual sheets as well as loss of carboxylic groups, substantially so for SLGR. Room temperature treatment of SLGO with N-hydroxysuccinimide collapsed the sheets into star-like clusters, which exhibited poor subsequent reactivity with carbodiimides and amines. Ultimately, conventional chemical treatment of carboxylic groups on SLGO leads to morphological changes and reduced reactivity, which may potentially limit their use.
Abstract: With careful removal of acid-oxidative lattice fragments and use of acid–base titrations, the covalent reactivity of covalently bound carboxylic groups on multi-walled carbon nanotube surfaces has been directly confirmed, including intermediate states, for carbodiimide promoted amidation reactions.
Abstract: The oxidation of multi-walled carbon nanotubes (MWCNTs) with nitric acid was studied. In addition to the formation of oxygen-containing surface functional groups, the oxidative digestion of graphene caps and layers generated polycyclic aromatic substances, classified as fulvic acids (FAs). The latter remained immobilised on the MWCNT surface in acidic and neutral solutions but were released in basic pH solutions, which were subsequently separated, purified and characterised by high-performance liquid chromatography and mass spectrometry. Using acid–base titrations, the number of surface acidic functional groups was determined, which was shown to significantly decrease after FAs were removed. Depending on the length of oxidation, FAs account for up to 43% of the surface acidity of MWCNTs. The protonated solubilised fulvic acids can be readsorbed on the surface of oxidised or unfunctionalised MWCNTs, which assists the stability of carbon nanotube suspensions in the aqueous phase.
Abstract: The fabrication of buckypaper from unfunctionalised multi-walled carbon nanotubes (MWCNTs) without the aid of surfactants or surface modification techniques is accomplished through a novel and quick frit compression method. The dimensions can be controlled through the size of the syringe housing and the through the mass of carbon nanotubes added. Their thicknesses are typically much larger than surfactant-cast buckypaper, which have been synthesised from 120 μm up to 650 μm; whilst no nomenclature system exists to govern thicknesses for samples to be classified as paper, we refer to buckypaper with thicknesses greater than 500 μm as buckydiscs. Buckypaper and buckydiscs are mechanically robust to handle, flexible, stable in solvents and possess larger porosities than Triton-X100 cast buckypaper. They also exhibit a memory effect when bending wetted samples, returning to their former geometry on drying. Buckypaper and buckydiscs were studied by mercury intrusion porosimetry to reveal a distribution of mesopores and small macropores that is dependant on the surface tension of the casting solvent and therefore tuneable. Moreover, the frit compression system allows control over the 3-dimensional geometry of the buckydiscs during the casting process.
