Carbon xerogel nanocomposite materials for electrochemical devicesApplication to heavy metal detection

Resumen

This Thesis describes the fabrication of both thick-film and thin-film electrodes with porous carbon nanocomposite materials and the application of these electrodes in the electrochemical analysis of heavy metals in aqueous solutions. These carbon composites were obtained from the pyrolysis of materials prepared by sol-gel chemistry approach, namely resorcinol-formaldehyde and resorcinol-formaldehyde /silica gels containing bismuth precursors. Bulk bismuth nanoparticle-carbon xerogel nanocomposite materials consist of an open porous structure of carbon with well distributed bismuth nanoparticles. These materials were ball-milled into powders of suitable size to produce conventional paste electrodes to be characterized in the lab and commercial-like screen printed thick-film electrodes. These electrodes display a superior performance in the sensitive stripping voltammetric detection of heavy metals in waters. The limit of detections for Pb(II), Cd(II) and Ni(II) obtained using these electrodes are well below the threshold concentrations established for drinking water quality by the EU and the US-EPA. The analysis of Pb(II), Cd(II), Ni(II), Zn(II) and Cu(II) have been performed in real waters of different origin and complexity, showing results in agreement with the standard mass spectroscopy method. The limitations of the developed electrodes and the interferences between different analytes were also investigated. In the case of thin film electrodes, large scale uniform and continuous carbon/silica films were deposited on 4-inch SiO2/Si wafers by spin-coating resorcinol-formaldehyde sols containing a SiO2 precursor. The interfacial adhesion between carbon films and SiO2/Si substrates is significantly enhanced by the addition of SiO2. Carbon/silica thin-film electrodes were fabricated by both photolithography and soft-lithography processes. These electrodes did not provide any cyclic voltamperometric signals in inner-sphere ferri-/ferrocyanide solutions but were successfully characterized in solutions containing outer-sphere ferrocene redox probe. The incorporation of bismuth nanoparticles into carbon/silica films during their sol-gel deposition stage is challenging due to the loss of bismuth by evaporation during pyrolysis step. Nevertheless, these electrodes were successfully applied for the detection of heavy metals by co-deposition of bismuth and heavy metals.