Electrochemical Sensor Based on the Clay- Carbone Paste Electrode Modified by Bacteria-Polymer for Elimination of Phenol

A Cyclic voltammetry (VC), Square Wave Voltammetry and Impedance Spectroscopie methods for the determination of trace amounts of phenol at bacteria-polymer-Clay-CPE bioelectrode is proposed. The results showed that the bacteria-polymer-Clay-CPE exhibited excellent electro catalytic activity to phenol. This electrochemical biosensor shows an excellent performance for detecting phenol.


Introduction
Phenol and related compounds are widely used in industry for the manufacture of a wide variety of aromatic compounds, including rubber, fertilizers, paints, drug preparations, petroleum and agricultural industries [1,2]. Phenol is considered carcinogenic and exposure to phenol causes several symptoms such as convulsions, dizziness and irregular breathing [1,3]. Phenol is one of 129 compound chemicals considered important pollutants listed by the Environmental Protection Agency (EPA) [4,5]. Due to severe legislation, prohibit the release of toxic products into the environment. Current research has focused on the development of a simple, cost-effective, fast and reliable technology that can be used for the immediate detection of heavy metals and toxic products in the environment. In this context, a technology seems to fully correspond to the requirements necessary for sustainable development and the preservation of the ecosystem: "bio electrochemistry". This discipline can be defined as a science involving the principles of electrochemistry associated with the field of living. Here we will focus on the electrochemistry / bacteria coupling. Indeed, the conversion of the catalytic activity of a bacterium into an electric current has paved the way for the development of various and varied bioelectrodes. Their fields of application are currently numerous and particularly in fields such as energy (biopiles) and analytical applications (bacterial biosensors) [6,7].
With regard to electro-analytical techniques, procedures involving the oxidation of phenol on solid electrodes [8,9] have been reported. In addition, chemically modified carbon paste electrodes have proved very useful for analytical applications [10]. In previous work [11,12], the electrochemical oxidation of phenol has been studied. We present a simple and sensitive method of determining these compounds based on their reaction. The purpose of the work presented here was to study the electrochemical properties of phenol on the bacterial-polymer-clay modified carbon paste electrode as well as the electrochemical characterization of electrodes by the cyclic voltammetric technique, Square Wave Voltammetry and Impedance Spectroscopie.

Electrodes
Modified electrodes were prepared by mixing a carbon powder and the desired weight of clay. The body of the working electrode for voltammetric experiments was a PTFE cylinder that was tightly packed with carbon paste. The geometric area of this electrode was 0.1256cm2. Electrical contact was made at the back by means of a bare carbon.   more metals order ppm ( Figure 3). An examination of clay modified carbon paste electrode indicates some kind of agglomeration [13].      -CPE electrodes, in 0.1M NaCl medium at 100 mV / s. We find that the presence of bacteria in the mineral matrix leads to a relative increase in the current densities of the voltammogram in both anodic and cathodic scanning directions [16]. This effect appears clearly in square wave voltammetry. We find that the presence of bacteria in the mineral matrix leads to a relative increase in the current densities of the voltammogram in both anodic and cathodic scanning directions [16]. This effect appears clearly in square wave voltammetry.

Activity of the Bacteria-Polymer-CPE Electrode with respect to the Oxidation of Phenol
The oxidation of phenol on the bacteria-polymer-Clay-CPE electrode was studied by cyclic voltammetry (Figure 9)   The effect of the scanning rate on the intensities of the phenol oxidation peaks was studied by cyclic voltammetry, in 0.1M NaCl (pH=7), containing 8 mM phenol, at scanning speeds included between 40 and 120 mV.s-1 ( Figure 10). The current densities vary linearly with the scanning speed ( Figure 11), which shows that the system is in a diffusion mode. The variation of anodic peak intensity as a function of phenol concentration was followed by cyclic voltammetry (Figure 12), square wave voltammetry (Figure 13), and impedance spectroscopy.

Effect of Scanning Rate
We find that peak current densities increase with concentration, suggesting that the modified matrix has a large number of active sites. This result is confirmed by the impedance measurement, which shows a decrease in the electron transfer resistance [16].

Calibration Curves
Calibration curves were plotted from the square wave voltammetry at the surface of the polymer-Clay-CPE and bacteriapolymer-Clay-CPE electrodes ( Figure 14). These experiments are carried out in the concentration range which varies between 4 and 12 mmol l -1 . Table 1 groups together the correlation equations and the detection and quantification limits calculated for the two polymer-Clay -CPE and bacteria-polymer-CPE electrodes. We find that the presence of bacteria improves the sensitivity of the electrodes.  The Activity of the Immobilized Bacteria The activity of bacteria immobilized on the polymer-Clay-CPE electrode surface calculated for the oxidation of phenol is: