Glassy Carbon Electrodes Modified with Ordered Mesoporous Silica for the Electrochemical Detection of Cadmium Ions

Four different samples of ordered mesoporous silica powders (MCM-41 and SBA-15) and amino-functionalized mesoporous silica (MCM-41-NH₂ and SBA-15-NH₂) were used to prepare modified glassy carbon electrodes coated with ion-exchange polymer Nafion to be used for the electrochemical detection of Cd(II). The mesoporous silica samples were characterized through transmission electron microscopy, small-angle X-ray scattering, and N₂-adsorption/desorption isotherms. The electrodes were characterized by using square wave anodic stripping voltammetry. The effect of pH and of the silica type on the electrodes' response was investigated. The influence of amino functional groups grafted on the silica surface toward Cd(II) ion detection was also examined. The detection limits determined with the new silica-modified electrodes [between 0.36 and 1.68 μM Cd(II)] are slightly higher than those reported in the literature, but they are lower than those stipulated in the European legislation [45 μM Cd(II)] and, consequently, the electrodes could be successfully used to detect Cd(II) in aqueous solutions.