Nitrogen-doped carbon nanotubes for sensitive and selective determination of heavy metals

Abstract

The present study attempts to demonstrate the potential of nitrogen-containing carbonaceous materials towards electrochemical determination of heavy metal ions. For this purpose, nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized from post treatment of oxidized carbon nanotubes (O-CNTs) in the presence of NH₃ at three different temperatures of 200, 400 and 600 °C to analyse their relevance in heavy metal ions determination. The electrocatalytic activity of these materials towards determination of Cd, Pb and Cu metal ions was examined by means of the square wave stripping voltammetry (SWSV) technique which demonstrates the suitability of all temperature variants for the desired purpose. Eventually, N-CNTs treated at 600 °C (N-CNT 600) displayed comparatively better sensitivity towards the investigated heavy metal ions (Cd, Pb and Cu) as compared to the other temperature variants of the N-CNTs (N-CNT 200 and N-CNT 400). The role of nitrogen groups was assessed in comparison with O-CNTs as it eliminates the requirement of the pre-concentration step by efficient complexation with heavy metal ions. The peak current for the Pb and Cd metal ions increased linearly in the concentration range of 0.01 μM–70 μM and 0.1 μM–100 μM respectively (individual as well as simultaneous determination). The limit of detection (LOD) was calculated to be 0.001 μM and 0.005 μM (3σ method) for the simultaneous determination of Pb and Cd metal ions respectively. Furthermore, a real time application of a N-CNT 600 modified GCE was probed by electrochemical detection of Cd and Pb metal ions in tap water and ground water.