Graphite powder derivatised with poly-l-cysteine using “building-block” chemistry—a novel material for the extraction of heavy metal ions

Graphite powder derivatised with 4-nitrophenyl moieties (NPcarbon) can be used to successively attach other chemical species to the graphite surface in a controlled and selective manner. Characterisation of these novel materials was undertaken using electrochemical and X-ray photoelectron spectroscopic (XPS) techniques. We demonstrate the proof of concept of this “building-block” chemistry by first reducing the nitro groups on the NPcarbon using a Sn–HCl reduction to the corresponding aniline-like moieties, and then coupling p-nitrobenzoic acid to these via an amide-linkage. Next we demonstrate the utility of this novel derivatisation method by coupling poly-S-benzyl-L-cysteine to the reduced NPcarbon in an analogous manner. After deprotection of the thiol groups using Na in liquid ammonia, the poly-L-cysteine derivatised carbon (PCcarbon) was found to complex cadmium(II) ions. Quantitative analysis of the uptake of Cd2+ from aqueous solutions at pH 5.0 by PCcarbon was carried out using stripping-voltammetry at a boron doped diamond (BDD) electrode and revealed that PCcarbon complexed 137 ± 20 mg of Cd2+ per gram of modified PCcarbon.