Preparation And Evaluation On PPy Composite Electrode Materials For Capacitive Deionization Modules

Capacitive Deionization （CDI） technology removes ions through a Flow-throughcapacitor （FTC）. The key component of FTC is the electrodes with high capacitanceand adsorption capacity, and it is crucial to develop electrode materials with goodadsorbing performance for the development of CDI technology.In this paper, with carbon nanotube as the template, the polypyrrole/carbonnanotube （PPy/CNT） composites were prepared in ethonal solution through chemicaloxidation methode. The effects of preparation conditions on properties of PPy/CNTwere studied to obtain the optimum preparation conditions. It is found that when theFeCl3concentration is in0.210-0.270M, Py concentration in0.040-0.162M and CNTconcentration in2.000-4.000g/L, PPy/CNT composite nanofibers have uniformdiameter and steady structure; The conducitivity, specific capacitance and specificadsorption capacity of PPy/CNT firstly increase and then decrease as theconcentration of FeCl3and Py increase; The conducitivity of PPy/CNT increases withthe increasing CNT concentration, while the effects of CNT concentration on thespecific capacitance and specific adsorption capacity of PPy/CNT are not significant.The optimum preparation conditions are as follows: the concentration of FeCl3, Pyand CNT is0.210M,0.121M and3.200g/L respectively. The specific capacitance ofPPy/CNT is163.64F/g, which is tested by cyclic voltammetry under the conditions of-0.2-0.6V potential,0.005V/s scan frequency in1.0KCl solution; The desaltingexperiments were carried out in500ppm NaCl solution under the conditions of1.5Voperation potential, the distance between two electrodes of1.5cm and the adsorptiontime of900s.The adsorption capacity of the PPy/CNT is49.7mg/g.Three typical dopants （Cl-, p-TS-, DBS-） were adopted to prepare PPy withdifferent dopants. The effects of dopants on the properties of PPy were investigated.The results indicates that both PPy-Cl and PPy-DBS are in spherical morphology,while PPy-p-TS is in rectangular flakelet morphology; PPy-p-TS has larger surfacearea and better conductivity than PPy-Cl and PPy-DBS, and have the smallestelectrochemical impedance; The ion exchange capability of PPy-p-TS is285.5mg/g,which is2.70and3.44times of that of PPy-Cl and PPy-DBS respectively. The results reveal that p-TS-is better than Cl-and DBS-as the dopants of PPy, and it can enhancethe adsorbing capability of PPy.Besides, the work was also carried out to synthesize polypyrrole/polyaniline（PPy/PANI） composites in PANI dispersion. The effect of synthesis conditions （thetype and concentration of dopant acid, oxidant （Ammonium Persulfate, APS）concentration） on the properties of PPy/PANI materials were studied, obtaining theoptimum preparation parameters of PPy/PANI composites with high capacitance.Finally, the desalting performance of PPy/PANI prepared under the optimumconditions was tested in CDI process. The results indicate that the types of dopantshave significant effect on the morphology of PPy/PANI. PPy/PANI prepared inHClO₄and HCl is in nanofiber morphology, while PPy/PANI prepared in H₂SO₄is incoral-like morphology; Also, the PPy/PANI prepared in HClO₄show better propertiesin surface area, pore volume, electrochemical impedance and specific capacitance;With the increasing concentration of HClO₄and APS, both the electrochemicalimpedance and specific capacitance of PPy/PANI firstly increase and then decease.When HClO₄of1.500M as the dopant acid and the concentration of APS is0.575M,the specific capacitance of PPy/PANI is the largest,341.4F/g; The specific adsorptioncapacity in900s is46.75mg/g and the regeneration rate is95.4%.