No abstract

The preparation of a carbon ceramic electrode modified with SnO 2 (CCE/SnO 2 ) using tin dibutyl diacetate as precursor was optimized by a 2 3 factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si-O-Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO 2 provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO 2 , indicating that SnO 2 when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10 −5 to 6.97×10 −4 mol L −1 with quantification and detection limits o f 3 . 8 0 × 1 0 − 5 m o l L − 1 ( 1 4 . 0 7 m g L − 1 ) a nd 1.13×10 −5 mol L −1 (4.18 mg L −1 ), respectively.

The insertion of mixed oxides into ceramic carbon electrodes (CCE) from the sol-gel process can provide materials with high purity and homogeneity without phase segregation and high stability, combining both mechanical and chemical properties of silica gel with the chemical properties of metal oxide (MxOy). This feature can provide a device with interesting properties, since the homogeneous distribution of the oxides, can minimize the resistivity provided by the silicaóxi network. In addition, the presence of acidic sites allows the immobilization of different electron mediators, which remain stable on the surface of the CCE, increasing the selectivity and sensitivity of such electrodes. Thus, the objective of this work was to incorporate the niobium oxide (V) (Nb2O5) into the structure of carbon ceramic electrode modified with tin oxide, CCE/SiO2-SnO2, in order to reduce even more the internal electrical resistance of the silica matrix, obtaining the carbon ceramic electrode, designated as CCE/SiO2-SnO2-Nb2O5. The obtained material was characterized by Fourier transform infrared spectroscopy (FTIR), which indicated that the SiO2 network is little disturbed by the incorporation of the oxides, showing evidence of Si-O-M bond formation (where M = Sn or Nb), which was corroborated by the X ray photoelectron spectroscopy technique (XPS). Raman spectra have shown an increase in the intensity ratio between the D and G bands (ID/IG), indicating that as the oxides are inserted into the SiO2 structure, an increase in the degree of system disorder occurs. From the morphological techniques, SEM (Scanning electron microscopy) and EDS (Energy dispersive X ray spectroscopy), it was shown that Sn and Nb were well distributed over the surface. ECC/SiO2-SnO2 and ECC/SiO2-SnO2-Nb2O5 presented better voltammetric responses than the systems without these oxides (ECC/SiO2), showing a diffusional mass transfer process with stable current responses after 100 voltammetric cycles, with variation of Ipa and Ipc below 5 %. These results demonstrate the potential use of these materials in the development of sensors.