Poobalasingam Abiman

Characterising chemical functionality on carbon surfaces

This feature article introduces the reader to the surface chemistry and structure of graphitic carbon materials, including carbon nanotubes. Recent work involving the development of dual labels that allow us to selectively and quantitatively label carboxyl and general carbonyl groups (such as quinones, ketones and aldehydes) and to distinguish between ortho- and para-quinone groups is reviewed. In addition, the mechanisms of covalent, chemical derivatisation of these surfaces and the reactive sites towards attack by radical and cationic intermediates are discussed, as well as the interesting effects on the pKa values of organic molecules that attachment to a carbon surface can induce. When combined, the methods described herein allow one to differentiate and explore the chemical functionality and reactive sites on graphitic carbon surfaces.

Investigating the reactive sites and the anomalously large changes in surface pKa values of chemically modified carbon nanotubes of different morphologies

“Bamboo-like” multiwalled (b-MWCNT), “hollow-tube” multiwalled (h-MWCNT) and single-walled carbon nanotubes (SWCNT), chemically modified with 1-anthraquinonyl (AQ) or 4-nitrophenyl (NP) groups, are characterized using voltammetric, electron microscopic and Raman spectroscopic techniques. The pKa values of the AQ-modified CNTs are found to be shifted by greater than three units when compared to the pKa values of anthrahydroquinone (AHQ, the reduced form of AQ) in aqueous solution to beyond pH 14. These large changes in the surface pKa values of the modified CNTs are explored further by comparing the pKa values of CNTs modified with an anthraquinonyl-2-carboxylic acid group. These groups are attached to the CNT surface via the formation of an amide bond with an aminophenyl “spacer” unit derived from the chemical reduction of NP modified CNTs. The location of reactive sites on the CNT surface is investigated and their influence on the pKa of the modified materials is discussed. Comparison with modified pyrolytic graphite electrodes exposing pure edge-plane or pure basal-plane crystal faces indicates that the modifying aryl groups are predominantly located on edge-plane like defects at the tube ends of MWCNTs. The effect of polymer formation on electron transfer kinetics of b-MWCNTs and h-MWCNTs is also discussed. In contrast SWCNTs show both significant side-wall functionalisation and fast electron transfer kinetics which is attributed to their different electronic structure.

Removal of palladium ions from aqueous systems by chemically modified cysteine carbon powder

L-Cysteine methyl ester modified graphite powder (Cyscarbon) was used as a material to remove palladium ions from aqueous media. Cheap graphite powders (2–20 μm in diameter) were surface functionalised with L-cysteine methyl ester. The removal of Pd(II) ions was studied as a function of concentration of Pd(II) ions, contact time with modified carbon and amount of modified carbon used. Determination of palladium ions was performed by adsorptive stripping voltammetry using a mercury nanodroplet array modified glassy carbon electrode. Dimethylglyoxime (DMG) was used as chelating agent for palladium. It was found that 1 g of Cyscarbon takes up 60 μM palladium ions from 25 mL of 100 μM palladium ion samples whilst the recovery experiment carried out by stirring the palladium–Cyscarbon with DMG gave a yield of 45% (optimised).