Four different samples of ordered mesoporous silica powders (MCM-41 and SBA-15) and amino-functionalized mesoporous silica (MCM-41-NH 2 and SBA-15-NH 2 ) 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 N 2 -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.
Synthetic dyes are widely used in many fields, such as textile industry, plastics, cosmetics, paper industry and many others. Due to their toxicity, they should be removed from wastes before discharging in the environment. In order to determine the efficiency of the removal process, different methods are used to detect traces of dyes in wastewaters. The most used are spectrophotometry and FIA, however the expensive equipment and complicated testing process make these methods difficult to use. On the contrary, electrochemical sensors have multiple advantages such as short response time, low price and easiness to use. In this context, several electrochemical sensors based on new carbonaceous materials were developed and characterized. Carbon nanotubes, graphene and activated carbon from Abies nordmanniana cones together with Nafion were used to modify the surface of a glassy carbon electrode by drop casting. The resulting modified electrodes were tested by SWASV and amperometry for Malachite Green detection in aqueous solutions, having low detection limits in the order of μM.
The electrochemical behavior of 10H-phenothiazine-1-carboxylic acid was investigated by square wave anodic stripping voltammetry (SWASV) at a glassy carbon electrode, which evidenced the first monoelectronic oxidation step at low potentials (around 0.25 V), slightly modulated by the nature of the solvent. The effect of three different solvents (acetonitrile, dimethyl sulfoxide and chloroform) on the strength of intramolecular hydrogen bonding associations was evidenced by DFT calculations. The computed electron density at the heterocyclic nitrogen atom appeared well correlated to the recorded oxidation potential. The possibility to use of 10H-phenothiazine-1-carboxylic acid as potential mediator for electrochemical detection of Malachite Green was explored, but the phenothiazine derivative appeared not suitable for the detection of the dye.
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