Application Study And Preparation Of Chemically Modified Electrodes In Environmental Detection

Phenol is one of the organic pollutants in the wastewater from rubber, dyes, medicine and petroleum et al. manufactures. At the present, phenol test is restricted to the total detection of volatile phenol. Therefore, it is important to establish quantitative determination methods for the specific phenol pollutant. In this dissertation, two kinds of representative phenols as model reactant: p-benzenediol and p-nitrophenol are studied by the electrochemistry examination on the carbon nanotubes modified electrodes. It is discussed that the preparation method of the electrodes and the optimal detection conditions. The electrocatalytic mechanism of the modified electrodes to phenols is studied systematically. The below conclusions are obtained:1. Using the superior physicochemical properties of the multi-walled carbon nanotubes (MWNT), the best preparation method of modified electrodes is obtained. Acid-treated MWNTs are dispersed in DMF by supersonic and then immobilized on the GC electrodes surface to form a modified electrode. In the pH 5.5-7.0 phosphate buffer solution, the electrochemistry oxidation process on the modified electrodes of p-benzenediol and p-nitrophenol can be accelerated.2. In the 0.2 mol-dm"3 pH 5.5 phosphate buffer solution, there is a keen oxidation peak of the p-benzenediol decorates on the modified electrodes. The peak potential is -0.068V. The peak current is linear to the concentration of p-benzenediol in the range of 1.6×10^-6 to2.6xlO'3 mol-dm'3. ip C/uA) = 60.0+6.2xl04c O= 0.993) . The detection limit is l.OxlCT mol-dm"3. With a 2.0xl0"4 mol-dm'3 concentration of p-benzenediol, the disturb examination (error between ±5%) is carried on. The result indicates that twenty-fold greater amount of Cu2+, Pb2+, Hg2+, Fe2+, Al3+, Zn2+, Cl", NO3" and the phenol, one-fold greater amount of o-benzenediol do not interfere with the determination of p-benzenediol. The relative standard deviation of 20 parallel determinations (RSD) is 1.5%.3. In the pH7 phosphate buffer solution, there is a pair of oxidation-reduction peak of p-nitrophenol (Eap =-0.049v; Ecp = -0.270V) between -0.6 and 0.6V on the MWNTs modified electrodes. The peak current and scanning velocity is direct ratio. The peak current is linear to the concentration of p-nitrophenol in the range of 4.0xl0"6 to 5.0xl0"4 mol-dm"3.tp (/(A) =51.0+1.29xl05c (r=0.999), The detection limit is 2.0xl0"6 mol-dm"3. With a 2.0xl0"4 mol-dm'3 concentration of p-nitrophenol, the disturb examination (error between ±5%) is carried on. The result indicates that ten-fold greater amount of Cu2+, Pb2+, Hg2+, Fe2+, Al3+. Zn2+, Cl", NO3" and the phenol, one-fold greater amount of o-nitrophenol and 2,4-dinitrophenol did not interfere with the determination of p-nitrophenol. The relative standard deviation of 5 parallel determinations (RSD) is 4.8%.4. The results indicated that under the chosen conditions, the reversibility of cyclic voltammetric response of p-nitrophenol was better, but the invertibility of p-benzenediol was worse. When the scanning speed changes between 10 210mV/s, no matter p-benzenediol or p-nitrophenol, their oxidation peak current all has the direct ratio with square root of the scanning speed. It is indicated that the oxidation-reduction processes of two phenols on the modified electrodes mainly are controlled by the proliferation.5. Taking the newly method to detect the p-benzenediol and p-nitrophenol in the simulation waste water, the recovery rate separately is 96.7%¹05% and 98%¹02%. It is concluded that the examination methods of p-benzenediol and p-nitrophenol on the MWNTs modified electrodes are two simple, fast and keen methods.