Preparation Of Polypyrrole Nano-composite Material And Its Application To Capacitive Deionization

Capacitive deionization （CDI） desalts by adsorbing process of electrode, and the electrode materials play an important role on the desalting performance of CDI. In this work, the prepared conditions of polypyrrole/carbon nanotube nano-composite material （PPy/CNT） and polypyrrole/polyaniline （PPy/PANi） nano-composite material were optimized. Additionally, the desalting mechanism of conducting polymer as electrode material used in capacitive deionization process was also discussed and analyzed.PPy/CNT nano-composite material was obtained by chemical polymerizing pyrrole （Py） in carbon nanotube suspension using ferric chloride as oxidant. The effect of molar ratio of FeCl₃ and Py (M_FeCl3/M_Py) and mass ratio of CNT and Py （mCNT/mPy） on the specific surface area, the specific capacitance and the specific adsorption capacity of the composite material was investigated. The experimental results show that the specific surface area of PPy/CNT composite material decreases with the increase of M_FeCl3/M_Py ratio, increases with an adding mCNT/mPy ratio. But the specific surface area of composite material prepated at expermetnal conditions is much smaller than that of CNT. The specific capacity of PPy/CNT composite material gets higher with the increase of both M_FeCl3/M_Py ratio and mCNT/mPy ratio, and then gets smaller. And the highest specific capacitance can be obtained at condition of 0.50 of M_FeCl3/M_Py ratio and 0.20 of mCNT/mPy ratio. The specific capacitance of the composite material prepared at this optimal condition is 290.29 F/g which is about 20 times of that of CNT in 1.0 M KCl, and its specific adsorption capacity is 87.02 mg/g, which is 6.2 times of that of CNT electrode.PPy/PANi nano-composite material was obtained by chemical polymerizing pyrrole in polyaniline suspension using FeCl₃ as oxidant, and the polymerizing parameters were optimized. The experimental results indicate that the specific surface area of PPy/PANi nano-composite material declines with both the increase of M_FeCl3/M_Py ratio and decrease of mCNT/mPy ratio, and then increases. The specific capacity of composite material increases with a higher M_FeCl3/M_Py ratio and mCNT/mPy ratio, then decreases. And the composite material has the highest specific capacitance at 1.5 of M_FeCl3/M_Py ratio and 1.0 of mCNT/mPy ratio under the experimental conditions. The specific capacitiy of PPy/PANi composite material prepared at this optimal condition is 351.56 F/g, which is 1.9 times of that of PANi, and its specific adsorption capacity is 148.86 mg/g, which is 2.1 times of that of PANi. As compared with PPy/CNT nano-composite material, the specific capacitance and specific adsorption capacity of PPy/PANi composite material are 1.2 times and 1.7 times of that of PPy/CNT composite material, respecitively.PPy modified graphite （PPy/NG） electrode was prepared at 0.85 V vs saturated calomel electrode （SCE） by potential step at room temperature with different doped ions such as Cl-, pTS- and DBS-. Then the desalting mechanism of PPy/NG electrode used in CDI technology was investigated by adsorbing experiment. The experimetnal results indicate that when PPy/NG electrode was applied to CDI process, the desalting process operated with coaction of electrostatic adsorption and electrochemically switched ion exchange process. And the specific adsorption capacity of PPy/NG-Cl electrode under the action of electrochemically switched ion exchange performance is 76.6% of the total specific adsorption capacity, and for PPy/NG-pTS electrode, it is 83.73% of the total. It means that electrochemically switched ion exchange property plays an important role on adsorption performance. However, the specific adsorption capacity of PPy/NG-DBS electrode by electrochemically switched ion exchange performance is 43.64% of the total specific adsorption capacity, which means that the influence of electrostatic adsorption on adsorption performance is bigger than that of electrochemically switched ion exchange. Thus, PPy/NG electrode dopped with small ions has a better desalting perfoemance than that dopped with big ions in CDI technology.