The Fabrication And Electrochemically Switched Iodide Ion Extraction Performance Of Polypyrrole And Bismuth Oxyiodide Based Iodide Ion Trap Film

Iodine has been widely used in industry,agriculture,chemical production and other fields as an indispensable raw material.Hence,iodine is an important resource for the development of national economy.However,the existing separation processes are difficult to meet the comprehensive requirements of green,economical and high efficiency due to lower concentration and high-interference ion condition of iodine resources in China.Therefore,it is essential to design an efficient and environmental-friendly process to extract and regenerate iodine resources.Electrochemically switched ion extraction(ESIE)technology is a novel film separation technology based on electroactive functional film materials,which can achieve high selectivity extraction of target ions even in low concentration.In the ESIE process,extraction and desorption of iodide ion can be achieved by adjusting the redox potential on the target ion trap film,which can not only capture target iodide ion quickly and efficiently,but also effectively recover film without secondary pollution.On the basis of liquid membrane extraction and ESIE technology,electrochemically switched ion membrane extraction(ESIME)technology was developed to extraction target ion continuously.The core of ESIE and ESIME technologies is designing electroactive extraction films/membranes with specific iodide binding sites.Hence,the research focal point of this text is the development for the good-capacity,high-selectivity and high-cycling-behavior iodide ion extraction materials to achieve efficient extraction of iodide ions.Therefore,organic iodide ion trap polypyrrole(I^--trap PPy)film,inorganic iodide ion trap bismuth oxyhalide(I^--trap BiOI)film and organic-inorganic composite PPy@BiOI(I^--trap PPy@BiOI)film are designed for extracting of iodide ion with ESIE technology.Furthermore,a triiodide ion trap PPy(I₃^--trap PPy)membrane of three-dimensional porous structure is designed for the continuous separation and extraction of iodide ions combined with ESIME technology.The specific research contents and main conclusions are as follows:(1)Iodide ion trap PPy film was fabricated on carbon cloth matrix by constant voltage method,which was used to realize efficient iodide ion extraction in the ESIE process.The effects of different preparation voltages on the structure and ESIE extraction performance of iodide ion trap PPy film were investigated,and the results displayed that the iodide ion trap PPy film prepared under a voltage of 0.9 V can extract iodine ions as high as 287 mg·g^-1 in a5 mg·L^-1 iodide solution.Besides,iodide ion trap PPy film demonstrated certain selectivity to iodide ions since ion trapping effect.Furthermore,the cycle stability of iodide ion trap PPy film was investigated.The desorption rate of iodide ion was maintained around 100%after 10cycles,indicated that iodide ion trap PPy film can be completely regenerated in the ESIE process,which provides the possibility for the industrial application of iodide ion trap PPy film.(2)Iodide ion extraction capacity by iodide ion trap PPy film was decreased significantly after 10 cycles due to the poor mechanical stability of the organic conductive polymer.In order to improve the cycling stability,inorganic film materials were developed.The inorganic iodide ion trap BiOI film was prepared by constant voltage method,and the film was used in ESIE process for the selective extraction of iodide ion.The extraction mechanism of iodide ion trap BiOI film was investigated by contrasting the morphology,structure and composition of iodide ion trap BiOI film before and after extraction of iodide ion.In addition,the effects of applied voltage,p H value and ion concentration etc.on extraction were studied.The outcome indicated that the reversible conversion between iodide ion trap BiOI(Bi₂O₃)and BiOI was realized under a voltage of-0.9 V/0.6V,and the extraction capacity of iodide ion was reached 328.3mg·g^-1.Besides,the extraction capacity of iodide ion by iodide ion trap BiOI film manifested no significantly decrease after 10 cycles stability test.Iodide ion trap BiOI film with ESIE process exhibited good electrochemical reaction reversibility,rapid adsorption kinetics,excellent thermal stability,acid resistance,outstanding selectivity and cyclic stability.(3)The large-scale iodide ion extraction is difficult to achieve since the inorganic film prepared by electrochemical method was very thin.Hence,this thesis combined iodide ion trap PPy film and iodide ion trap BiOI film to realize complementary advantages,and developed effective film materials for iodide ion extraction in the practical water system.Iodide ion trap PPy@BiOI film with core/shell structure was synthesized by constant voltage method,and the film was used in ESIE process to extract iodide ions.In the organic-inorganic composite film,the iodide ion trap PPy film plays a conductive supporting layer role to store iodide ions,while iodide ion trap BiOI acts as the selective layer to capture iodide ion.Iodide ion ESIE experiments indicated that the iodide ion trap PPy@BiOI film manifested high iodide ion extraction capacity,excellent selectivity and outstanding cycle stability;Moreover,the iodide ion trap PPy@BiOI film has environmentally friendly,simple process,low energy loss and high extraction capacity advantages.Notably,iodide ion trap PPy@BiOI film can be constantly regenerated in the ESIE process,and the film after the reaction is reusable.This work not only deepened people's understanding of iodide extraction behavior,but also provided a promising material for the efficient extraction of iodide ion from actual water systems.(4)Iodide ion trap PPy@BiOI film was used to continuous separation of iodide ion via ESIME process,however,the performance of continuous extraction was not effective,which might result from the dense film lacking porous channel.Triiodide ion trap PPy membrane with three dimensional of multi-porous structure was fabricated by constant voltage method,and the membrane was used to continuously extract iodide ions via the ESIME process.Triiodide ion trap PPy is connected each other and possesses 3D nest-network structure which is composed of unique bowl-shaped particles.Which is conducive to the penetration of iodide ions.Moreover,the iodide ion is easy to be oxidized and to cause triiodide ion,which provides an idea for high-capacity extraction of iodide ion.In the reduction process,triiodide ion will be converted into iodide ion and released to the receptor fluid,because of this,the captured triiodide ion can be quickly released.In this study,the effects of cell voltage,pulse time and different performed conditions on iodide extraction flux were investigated.The results displayed that the extraction flux of iodide ion by triiodide ion trap PPy membrane combined with ESIME technology was reached 2.87×10^-4 g·cm^-2·h^-1 under the optimized condition.Furthermore,the triiodide ion trap PPy manifested high selectivity and excellent cycle stability in the ESIME process.This work provides a novel idea for the continuous extraction of iodide ions,and the new process and membrane material were developed for the efficient extraction of iodide ion in practical water systems.