Ion Exchange Behavior And Cu Modification Of Polypyrrole

Polypyrrole(PPy) is a typical conducting polymer with many advantages such as ease of preparation,special electronic and electrochemical properties,harmlessness and good environmental stability.The electrochemical property of PPy is very important because a lot of applications are based on the reversible ions insertion and ejection processes,so it is necessary to study the influence of synthesis and measurement conditions on its ions exchange behaviors.The ions exchange behaviors of PPy films doped with p-toluenesulfonate anion(pTS^-) and dodecyl sulfonate anion(DS^-)(PPy/pTS and PPy/DS) films in different solutions were investigated by means of cyclic voltammetry(CV) and electrochemical impedance(EIS),and the influence of overpotential during first reduction and Na⁺ or Cl^- insertion on the PPy films was also studied by EIS.The results showed that the PPy/pTS film can not exchange with large size ions(pTS^-) and high valence ions(Al³⁺), and its overpotential behavior was mainly due to cation insertion and can not be performed completely in solutions including only H⁺ or Al³⁺ cations.In an acidic solution,some of the electrochemical exchange especially the cation exchange process will be instead by chemical doping,and the absorption of weak acid(p-toluenesulfonate acid,HpTS) in PPy film was stronger than strong acid(hydrochloric acid,HCl).In addition,the EIS of PPy/pTS films in different condition showed that the overpotential process would improve the ionic conductivity and film capacitance and insertion with Cl^- will improve the films electronic conductivity,however,insertion with or without Na⁺ showed little difference in EIS.The reversible ion exchange behavior of PPy can be employed for electrically switched ion exchange resin.At present,the ion exchange ability was evaluated by CV method,which can not describe the exact amount of exchanged ions because that part of the CV charge was arises from other process such as the charge and discharge of electrochemical double layer.In this case,the simulation experiments of removal of ions from solution were designed,and after subtracting the same electrochemical processes,the ion exchange charge coming from ejection of the inserted ions can be obtained,which were proved by inductively coupled plasma mass spectrometry(ICPMS) and ion chromatography(IC).Based on this charge,the ion exchange ratio and the operating exchange capability of PPy films also can be counted,all of which can be used for evaluating the ion exchange ability of PPy films.And then,the ion exchange behavior of PPy doped with a variety of dopants,namely chloride,nitrate,pTS^- and DS^-,was investigated by means of CV in NaCl,NapTS and AlCl₃ aqueous solutions.Among these films,PPy/pTS(doped with the medium sized counterion pTS^-) showed the best anion exchange ability,while PPy/DS(doped with the large counterion DS^-) exhibits the best cation exchange ability.In addition,the synthesis current density and thickness of PPy films also affected its ion exchange ability.Many metals can be combined with PPy matrices to form polypyrrole-metal complexes with improved many properties and extended its application.Polypyrrole modified with Cu(PPy-Cu) complexes,showing strong chemical bonds between N and Cu, have been widely investigated because the electrical conductivity and environmental stability of PPy matrices can be improved through copper embedding.This is particularly useful because copper is relatively cheap.At present,PPy-Cu complexes are always formed by a two-step method.However,the PPy matrix synthesized in the first step is difficult to modify by Cu because the channels of the film are blocked up by the bulk of the Cu particles.As a result,available improvement in the properties of PPy-Cu materials is limited.Based on this problem,the potential pulse method was used to form a uniform composite film,by which the polymerization and modification processes can be performed simultaneously in one step.Polypyrrole/Sulfate-Copper(PPy/SO₄-Cu) complexes were synthesized by different methods,including the one-step potential pulse method and the traditional direct current two-step(TDC) method.The two methods were analyzed by scanning electron microscope(SEM),energy dispersive spectrometer(EDS),X-Ray Fluorescence(XRF),X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) to find out the influence of the different synthesis methods on the film composition and structure.Finally,the alkalescence stability and the thermal stability of these films were studied by CV,EIS and thermogravimetry(TG) measurements.The results showed that the PPy/SO₄-Cu films synthesized by different methods exhibited the same amorphous structure and Cu combination model,i.e.Cu⁺ was combined with N on the PPy chains to form the PPy/SO₄-Cu films,however,the film made by one-step pulse method has smaller PPy particles,much higher Cu content and more porous structure.And more,comparing with TDC method,one-step pulse method can generate a PPy/SO₄-Cu material with more N⁺ and lower oxidation carbon,which meant that the pulse method can obtained a PPy-Cu film with higher doping level and lower breakage of the PPy chains.The thermal stability of PPy can not be improved by Cu modified,especially the PPy/SO₄-Cu synthesized by pulse method showed the worst thermal stability.Differently,The PPy/SO₄-Cu film synthesized by the one-step pulse method exhibite improved alkalescence stability.This stability is attributed to a higher Cu content and uniform distribution in the film.And more, the specific capacitance of PPy-Cu synthesized by pulse was higher,which was mainly due to the more porous structure.