Electrolysis of ammonium carbamate: a voltammetric and X-ray photoelectron spectroscopic investigation into the modification of carbon electrodes

Uchiyama et al. report that a glassy C (GC) electrode modified with surface amino groups via the electrochem. oxidn. of ammonium carbamate can react with catechol in a 1,4-Michael addn. through the surface amino groups. This was deduced from XPS data and the observation of a new reversible couple at less pos. potentials than the catechol redox couple, which was attributed to a quinone-imine-like adduct. Identical voltammetry is obsd. at an unmodified GC electrode that was oxidatively pre-treated in an identical fashion to that reported by Uchiyama et al. but in the absence of ammonium carbamate and any other sources of N. XPS characterization of a graphite electrode before and after electrolysis in ammonium carbamate soln. suggests that the N species on the C surface may not be as amino groups, but may due to adsorbed ammonium ions or the formation of amides. It is not the surface amino groups that are reacting with catechol, and alternative explanations are discussed. [on SciFinder(R)

A facile method of modifying graphite powder with aminophenyl groups in bulk quantities

A facile and rapid method of covalently modifying the surface of graphite powders with aminophenyl groups is described. This chem. modification strategy gave bulk quantities of amino-modified C powder. 4-Nitrophenyl groups are covalently attached to graphite powder via the chem. redn. of the corresponding 4-nitrobenzenediazonium tetrafluoroborate salt using aq. hypophosphorous acid. The 4-nitrophenyl groups on the C surface are then reduced to the corresponding 4-aminophenyl groups using alk. Fe(II) ammonium sulfate solns. Electrochem. and x-ray photoelectron spectroscopic characterization is carried out at each stage of the synthesis. [on SciFinder(R)

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)