An exfoliated graphite-polystyrene composite electrode was evaluated as an alternative electrode in the oxidation and the determination of oxalic acid in 0.1 M Na 2 SO 4 supporting electrolyte. Using CV, LSV, CA procedures, linear dependences I vs. C were obtained in the concentrations range of oxalic acid between 0.5 to 3 mM, with LOD =0.05 mM, and recovery degree of 98%, without need of surface renewing between successive runs. The accuracy of the methods was evaluated as excellent comparing the detection results with that obtained using conventional KMnO 4 titration method. In addition, the apparent diffusion coefficient of oxalic acid D was found to be around 2.89 · 10 -8 cm 2 ·s -1 by CA and CV.
Electrodes based on carbon, i.e., expanded graphite (20%, wt.)-epoxy composite (20EG-Epoxy) and expanded graphite (20%, wt.)-polystyrene composite (20EG-PS) have been prepared, characterized using scanning electron microscopy (SEM) and cyclic voltammetry (CV), and tested as anodic sensors. The electrodes exhibited good mechanical resistance and low electrical resistances. Scan rate dependent cyclic voltammetry responses at 20EG-Epoxy and 20EG-PS composite electrodes, which were exemplified for thiourea (TU), a toxic sulphur organic compound selected as testing target analyte in 0.1 M Na2SO4 supporting electrolyte, were investigated. The obtained voltammetric data were in accordance with those for a random array of microelectrodes. The voltammetric and chronoamperometric detection results of TU in tap water samples, without a supplementary addition of supporting electrolyte, at 20EG-Epoxy electrode proved its use for direct analysis of environmental samples.
An expanded graphite-epoxy composite electrode (EG-Epoxy) was employed for the simultaneous determination of 4-chlorophenol (4-CP) and oxalic acid (OA) by using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The results indicated that OA could be determined in the presence of the same concentrations of 4-CP within the concentration range of 0.1 mM to 0.5 mM with a relative standard deviation (RSD) smaller than 5%. Electrode fouling occurred during CA for 4-CP concentrations larger than 0.5 mM. The DPV method was used for the simultaneous determination of 4-CP and OA before and after electrochemical oxidation by chronopotentiometry under galvanostatic conditions (j ¼ 0.04 mA cm À2 , t ¼ 2 h) of a tap water sample spiked with 0.19 mM 4-CP and 0.1 M Na 2 SO 4 .
A group of carbon-based electrodes, i.e., glassy-carbon (GC), boron doped diamond (BDD), expanded graphite-polystyrene composite (EG-PS), expanded graphite-epoxy composite (EG-Epoxy) and expanded graphite-carbon nanofiberepoxy composite (EG-CNF-Epoxy) electrodes were investigated for electrochemical degradation of 4-chlorophenol (4-CP). Based on the investigated electrochemical techniques, e.g., cyclic voltammetry (CV) and chronoamperometry (CA), the operation conditions and the electrode suitable for electrochemical oxidation of 4-CP were selected. In addition, multiple pulsed amperometry (MPA) was applied for the in-situ electrochemical cleaning of the electrode surface to improve the electrode efficiency. The BDD electrode exhibited the best features related to the 4-CP electrochemical degradation efficiency.
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