Multi-Walled carbon nanotubes modified electrodes for the electroanalytical detection of highly hazardous water contaminants

Introduction Voltammetric methods, characterized by high accuracy, precision, sensitivity, specificity, reliability, easiness of use, also at very low concentrations are very interesting as valid and independent alternative to other standardized analytical methodologies to remotely monitor and register on-site and on-line the presence of contaminants of emerging concern. One of the major drawbacks of these techniques is related to significant interferences from other redox species present in the real matrix, which can undergo reactions, masking the actual signal and sometimes producing byproducts responsible of fouling phenomena. One strategy to overcome such problems is the use of modified electrodes, whose aim is the promotion or depletion of the kinetics of the target species and/or interfering species in order to perform some discrimination, or the change in the mass transport mechanism. Among different materials for the electrode modification, carbon-based nanomaterials with distinct characteristics in terms of size, surface area, strength, optical and electrical properties, represent a valid choice for the production of modified electrodes with improved performances in comparison with the conventional ones. In this context, multiwalled carbon nanotubes (MWCNT) modified electrodes have been prepared, completely characterized and employed for the electroanalytical detection in water of some contaminants of emerging concern (CEC): benzidine, o-toluidine, o-tolidine and tetramethylbenzidine, organic carcinogenic synthetic pollutants mainly used as intermediate in production of azo-dyes. Experimental After a careful investigation of the best MWCNT purification and functionalization procedures, followed by an extensive physico-chemical characterization (by BET, SEM and TEM analysis) the nanomaterials were used to prepare modified electrodes by drop-casting. The sensors were electrochemically and electroanalytically characterized by cyclic voltammetry and electrochemical impedance spectroscopy and finally used in the electroanalytical detection of the above mentioned CECs. Results and discussion [1] The extensive characterization allowed to choose MWCNTs without amorphous carbon treated in sulphonitric mixture for 24 h as the best material for electrode modification for our electroanalytical purpose. The final developed electroanalytical methodology is based on voltammetric techniques, which allow to achieve excellent results in terms of limits of detection (ppb range), sensitivity, linear correlation, precision and trueness (apparent recovery factors very close to 100 %), also minimizing problems of fouling, which strongly influence the performances of other electrodes. The use of nanomaterials further enhances the potentialities of the method, particularly with respect to conventional HPLC technique. The optimized sensors were successfully applied to monitor the disappearance of the above CECs and to compare the efficiencies of some α-, β-, γ-cyclodextrin functional nanosponges during sorption experiments. References: [1] V Pifferi et al, Electrochimica Acta 146 (2014), p. 403.