| Nitrogen heterocyclic compound is difficult to be degraded in the natural environment due to its stable structure, biological toxicity, potential teratogenicity, carcinogenicity and mutagenicity. Environmental pollution is becoming more and more serious with wide application in industry. In order to ensure the health of people, it is necessary to strengthen the determination of nitrogen heterocyclic compounds in environment and degrade them efficiently. Electrochemical oxidation could utilize the hydroxyl radicals (OH) generated on the surface of electrode to degrade the refractory pollutants even mineralization and to determine the pollutants according to the relationship between the peak current and the concentration of pollutants. The main parameter affecting the performance of electrochemical oxidation is the selection or preparation of electrode. Titanium based lead dioxide (Ti-PbO2) electrode was one kind of high performance electrodes with the characteristics of high oxygen evolution potential, strong oxidation ability, good corrosion resistance and better performance in electrochemical catalytic oxidation to cyclic compounds. However, because the electro deposition of PbO2is accompanied by formation of a nonconducting TiO2film on Ti surface which acts as a barrier for the nucleation and growth of PbO2, it is very difficult to prepare PbO2on Ti substrate directly. Changing the substrate and surface doping are the main ways to improve the performance of PbO2electrode at present. Carbon fiber can be used as the substrate to improve the performance of PbO2electrode because of its large surface area, good electrical conductivity, cost-effective price and so on.In this study, carbon fiber cloth and carbon fiber powder were selected as the substrate to support PbO2by electrodeposition. Pyridine was selected as model polltant to investigate the electrochemical oxidation behaviors on carbon fiber based PbO2modified electrodes using linear sweep voltammetry (LSV) with an electrochemical workstation (CHI660C), a saturated calomel electrode, Pt wire electrode and carbon fiber supported PbO2electrode were set as the reference, counter and working electrodes, respectively. In the study of electrochemical oxidation behavior, the effects of the components of electrodeposition bath, current density, electrodeposition time and other factors were investigated to obtain the optimum preparation conditions. Then, the surface morphology of carbon fiber supported PbO2modified electrodes were characterized by scanning electron microscope (SEM). The electrochemical oxidation behaviors of pyridine under different scan rates, pH and initial concentrations were studied detailedly on carbon fiber supported PbO2electrodes in order to obtain the optimum response conditions of pyridine and its linear response range. The electrochemical oxidation behaviors of nitrogen heterocyclic compounds with different substituent groups or double ring were also studied, such as2-aminopyridine,2-bromopyridine,3-chloropyridine, quinoline and nicotine, to provide a theoretical basis for the application of modified electrodes in electrochemical determination and degradation of these substances. The main results were as follows:(1) The PbO2/CFC modified electrode was prepared by electrodeposition method at45℃with magnetic stirring using carbon fiber cloth as the substrate. In the process of electrodeposition, the effect of the components of electrodeposition solution, current density, electrodeposition time and other factors on PbO2/CFC modified electrode were investigated. The optimum preparation conditions were obtained:150g/L of Pb(NO3)2and0.5g/L of NaF,20mA/cm2of current density and5min of electrodeposition time. Scanning electron microscope (SEM) was used to characterize the modified electrode morphology, and the result showed that PbO2was completely covered on carbon fiber cloth surface and the the crystal was uniform and dense.According to the electrochemical oxidation behaviors of pyridine on optimized PbO2/CFC electrode, it was found that the oxidation peak current was proportional to the initial concentration of pyridine with the range of0mg/L to3000mg/L at pH8.3and25mV/s scan rate. The electrochemical oxidation reaction of pyridine on PbO2/CFC electrode was controlled by diffusion and adsorption processes.(2) The PbO2/CFs/GC modified electrode was prepared by electrodepositing on glassy carbon (GC) electrode coated with carbon fiber according to the preparation condition of CFC/PbO2electrode.The electrochemical oxidation behaviors of pyridine on PbO2/CFs/GC modified electrodes was investigated, and the optimum preparation conditions were obtained:150g/L of Pb(NO3)2,0.5g/L of NaF and0.1mol/L of HNO3,20mA/cm2of current density and20min of electrodeposition time. SEM results showed that PbO2was completely covered on carbon fiber surface and the the crystal was uniform and dense.Pyridine can be readily oxidized on optimized PbO2/CFs/GC electrode, and the oxidation peak current was proportional to the initial concentration of pyridine with the range of0mg/L to1000mg/L at pH7.9and25mV/s of scan rate. The electrochemical oxidation reaction of pyridine on PbO2/CFs/GC electrode was controlled by diffusion and adsorption processes. The study found that2-aminopyridine,2-bromopyridine,3-chloropyridine, quinoline and nicotine exhibited different electrochemical oxidation behaviors on β-PbO2electrode and PbO2/CFs/GC electrode. The above-mentioned compounds were more easily oxidized on PbO2/CFs/GC electrode, implying that the application of modified electrodes in electrochemical determination and degradation of these substances is feasible.(3) On the basis of the preparation conditions of PbO2/CFs/GC electrode, doping modification of Fe3+was adopted to prepare Fe-PbO2/CFs/GC modified electrode. The electrochemical oxidation behaviors of pyridine on Fe-PbO2/CFs/GC modified electrodes under different concentration of Fe3+was investigated, and the optimum preparation conditions were obtained:3mmol/L of Fe(NO3)3,150g/L of Pb(NO3)2,0.5g/L of NaF and0.1mol/L HNO3,20mA/cm2of current density and20min of electrodeposition time. Scanning electron microscope (SEM) was used to characterize the modified electrode morphology, and the results showed that different size of particles were inlayed on the surface of Fe-PbO2/CFs/GC electrode, and the specific surface area of electrode became larger.According to the electrochemical oxidation behaviors of pyridine on optimized Fe-PbO2/CFs/GC electrode, the oxidation peak current was proportional to the initial concentration of pyridine with the range of0mg/L to1000mg/L at pH7.9and25mV/s of scan rate. The electrochemical oxidation reaction of pyridine on Fe-PbO2/CFs/GC electrode was controlled by diffusion and adsorption processes. The electrochemical oxidation behaviors showed that pyridine,2-aminopyridine,2-bromopyridine,3-chloropyridine, quinoline and nicotine could be oxidized on the the suface of Fe-PbO2/CFs/GC electrode and the oxidation potentials was1.02V,1.03V,1.20V,1.21V,0.95V and1.0V respectively. It is found that the application of modified electrodes in electrochemical determination and degradation of these substances is feasible.(4) Nafion was used as dispersive agent and binder of CFs for preparing PbO2/CFs/GC electrode. As the result of the cooperation of nafion and PbO2, PbO2/CFs/GC modified electrode exhibited better electrode performance for pyridine than that on the PbO2/CFsC modified electrode. Surface doping of Fe3+on PbO2/CFs/GC electrode increased the surface area of Fe-PbO2/CFs/GC electrode, and the oxidation current of pyridine also increased accordingly. Thus, Fe-PbO2/CFs/GC electrode may be more suitable for electrochemical determination or degradation of nitrogen heterocyclic compounds. |
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