Functionalization of amorphous nitrogenated carbon thin film electrodes for improved detection of cadmium vs. copper cations

•a-CNx modified films were obtained by functionalization through diazonium salt.•The effect of functionalization of a-CNx on Cd2+ and Cu2+ detection is carried out.•The functionalization leads to a decrease of the electrochemical reactivity.•The grafting parameters were optimized for Cd2+ and/or Cu2+ detection.•We observe a sensitive response towards Cd2+ while decreasing the Cu2+ signal.

The specificity of a sensor relative to specific cations can be modified by functionalization of amorphous nitrogenated carbon thin film (a-C:Nx) electrodes. This surface modification was performed through the reduction of diazonium salts presenting different functionalities which could interact selectively with ions in solution. Cyclic voltammetry from +0.3 to −1.0 V vs. SCE was used for the grafting process leading to the formation of covalent CC bonds onto the film surface. The precursor concentration and number of cycles were optimized and correlated to the specificity and sensitivity for copper and/or cadmium ion detection. The coverage of the electrode was checked by cyclic voltammetry measurements using the Fe(CN)63−/4− system, interface charge transfer and contact angle. It showed that the electroreduction of diazonium salt and grafting of substituted aryl groups was effective on the surface of the a-C:Nx electrodes. A greater sensitivity of the electrode to Cd2+ was observed for the highest concentrations of precursors (4-amino benzene carboxylic acid (4-ABA)) compared to the pristine electrodes. Moreover, a marked decrease of cadmium sensitivity is noted after grafting but at the same time with a decreased influence of copper on the Cd2+ signal, indicating a better specificity of these functionalized sensors.

Graphical abstractDPASV voltammograms (adjusted by removing reference curve) for Cd2+ detection with fixed Cu2+ concentration (14 ppb) obtained with a-CNx modified electrode by electrografting from 4-ABA diazonium salt (0.25 mM) in acetate buffer 0.1 M; pH = 4.9; Estep = 10 mV; Epulse = 30 mV; Edep = −1.1 V; Tdep = 120 s; Vb = 50 mV s−1.Figure optionsDownload full-size imageDownload as PowerPoint slide