Voltammetric and X-ray photoelectron spectroscopic fingerprinting of carboxylic acid groups on the surface of carbon nanotubes via derivatisation with arylnitro labels

4-Nitrophenol (4-NP)or 4-nitrobenzyl alc. (4-NBA) are used as voltammetric and X-ray photoelectron spectroscopic (XPS) labels for carboxylic acid groups on the surface of single-walled carbon nanotubes, "bamboo-like" and "hollow-tube" multi-walled carbon nanotubes. The surface carboxyl groups are first converted to the corresponding acyl chlorides, and coupled to the labels via the formation of an ester linkage. The voltammetric redn. of the arylnitro label allows the no. of carboxyl groups on the surface to be estd. Alternatively the percentage of the elemental surface compn. corresponding to the carboxyl groups can be measured using XPS via the emission from the N1s level of the label. The no. of electroactive quinonyl groups present on the surface relative to the no. of carboxyl groups can also be detd. voltammetrically by measuring the area under the voltammetric wave corresponding to the surface quinone groups. By combining these voltammetric and XPS results the relative percentages of the O1s spectral peak, which correspond to carboxyl and quinonyl groups, can then be detd., which also allows, by difference, an est. of the percentage elemental surface compn. of total other oxygen-contg. functionalities present such as lactones, ethers, aliph. ketones etc. The effect of std. acid pre-treatments used to introduce carboxyl groups onto the CNT surface (such as stirring in relatively concd. mixts. of nitric and sulfuric acids) on the no. of each type of oxygen functionality is compared. In all cases the no. of carboxyl groups is found to increase, but the no. of quinonyl and other oxygen-contg. functionalities is also found to increase, often to a greater extent than the carboxyl groups. [on SciFinder(R)]