| Development of novel electroactive materials is the key issue for watertreatment by electrochemically switched ion exchange (ESIX) method. Thehybrids of organic polymers and inorganics possessing excellent conductivity,high stability, good electroactivity and ion exchange property have receivedextensive attention. α-ZrP is a kind of inorganic layered material with excellention exchange performance but poor conductivity. Attempts of introducingconductive materials into it were made to combine the electroconductibility ofconductive materials with ion exchange performance of inorganic layeredmaterials for the removal of heavy metal ions by ESIX. In this research,polyaniline/α-zirconium phosphate and polypyrrole/α-zirconium phosphate weresynthesized respectively, the removal performance for heavy metal ions wasstudied by ESIX method.α-ZrP, as an inorganic layered material, was firstly synthesized by directprecipitation method, then it was exfoliated to nanosheets in aqueous phase.Aniline was added to the above-mentioned solution serving as the base solutionsfor electrodeposition. PANI/α-ZrP hybrid film was deposited onto porous three dimensional carbon felt (PTCF). Changes of composition and structure ofPANI/α-ZrP in reduction state and oxidation state were analyzed by FT-IR、EDS、 XPS. In addition, the adsorption and desorption mechanism wereexplained. When PANI/α-ZrP/PTCF electrode was served as working electrode,the Cd(II) ions concentration decreased from1mg·L-1to0.09mg·L-1after ionexchange for3hours with the applied potential of-0.5V (vs. SCE). While theremoval of Cd(II) ions was slower when the α-ZrP/PTCF electrode was used asworking electrode, and ions concentration just reduced to0.68mg·L-1. All theabove indicated that ion uptake ability of PANI/α-ZrP/PTCF electrode wassuperior to that of α-ZrP/PTCF. Because the PTCF did not contribute to theadsorption process, PANI/α-ZrP acted as the active component ofPANI/α-ZrP/PTCF electrode. The effects of applied potential, temperature,initial ions concentrations on the uptake of cadmium ion were examined in batchadsorption experiments. The results showed that adsorption capacity ofPANI/α-ZrP/PTCF electrode for Cd(II) increased with the increase of initial ionsconcentrations. The adsorption kinetics at different initial concentrationsfollowed pseudo-second-order model, and the lower the initial concentration offeed solution, the faster the adsorption rate of Cd(II) onto PANI/α-ZrP/PTCF.Thus, lower solution concentration is likely to reach equilibrium in a shortertime period. Moreover, temperatures had a significant impact on adsorptionprocess for Cd(II). Enhanced removal efficiency was obtained with the increaseof applied potential. The maximum adsorption capacity was determined as117.6mg·g-1by Langmuir model. Furthermore, the desorption percentage of Cd(II)can achieve98.7%in potassium ion aqueous solution with the applied potentialof0.9V.PPy/α-ZrP hybrid film was prepared on PTCF substrate by cyclicvoltammetry (CV) method. The electrochemical performance and ion exchange process was investigated by CV and EQCM. The change of composition andstructure in redox process was analyzed by FT-IR and XPS. The selectivity orderof PPy/α-ZrP/PTCF electrode followed Pb(II)>Cd(II)>Co(II)>Zn(II)>Ni(II),which implyed that this film electrode had a better selectivity for Pb(II). Theinitial ion concentration of10mg·L-1could be decreased to0.9mg·L-1by ESIX.However, it just reduced to6.6mg·L-1by IX method. The removal rate of ESIXmethod was about2.7times higher than that of IX process. The adsorptionkinetics of Pb(II) could be described properly by the pseudo-second-orderkinetic mode. A higher rate constant was obtained by ESIX. The adsorptionisothermal experiment showed that film electrode possessed a high adsorptioncapacity for Pb(II). Equilibrium adsorption data for Cd(II) are more consistentwith the Langmuir isotherm, a higher value of affinity constant for metal ionwas obtained by ESIX. |
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