Preparation Of Polypyrrole-Based Magnetic Composites And The Adsorption For Cr(?)

Hexavalent chromium Cr(VI)is a common heavy metal ion in sewage,which has strong carcinogenicity and teratogenicity to organisms.Therefore,it is necessary to treat Cr(VI)in water.Polypyrrole(PPy)is considered as an ideal adsorption material because of its good ion exchange,redox and environmental stability,but PPy is easy to agglomerate during synthesis,which cannot give full play to its adsorption properties,and it is not easy to recover after adsorption.Hence,polypyrrole-based magnetic composites were prepared by compounding PPy with other materials and introducing magnetic particles,which can increase the dispersion of PPy,then improve its adsorption properties,and can be quickly recovered under external magnetic field.This study has high academic value and application significance.In this paper,monodisperse latex spheres(MLS),were prepared by emulsion polymerization.Magnetic latex spheres(Fe₃O₄/MLS)were prepared by coprecipitation of Fe₃O₄ on the surface of MLS,and magnetic silica microspheres(SiO₂/Fe₃O₄/MLS)were prepared by Stober method.Using Fe₃O₄/MLS and SiO₂/Fe₃O₄/MLS as carriers,pyrrole(Py)and m-phenylenediamine(mPD),were introduced to prepare polypyrrole magnetic latex spheres(PPy/Fe₃O₄/MLS),polypyrrole magnetic silica microspheres(PPy/SiO₂/Fe₃O₄/MLS)and m-phenylenediamine modified polypyrrole magnetic latex spheres(PPy-mPD/Fe₃O₄/MLS)by chemical oxidation and copolymerization.Three kinds of functional composites were used to remove Cr(?)and the adsorption mechanism was discussed.The main research work is as follows:1.PPy/Fe₃O₄/MLS was used as the adsorption material to study the adsorption of Cr(?).The effect of the ratio of Fe₃O₄ to MLS on the dispersion of the material was studied.It is found that when the ratio was 5:5,the dispersibility and magnetism of the material can be taken into account.The effects of pH value,Py content and cyclic adsorption on the removal of Cr(?)were studied.The results showed that the adsorption performance of the material was the best when the pH 2 and Py content was 50 wt%.The maximum adsorption capacity was 305.81mg/g at 298 K.After five cyclic adsorption experiments,the magnetic properties of the material decreased by about 25%,but the removal rate of Cr(?)was more than 99%in the first three times.EDS and XPS proved that Cr(VI)was removed by electrostatic interaction,ion exchange,redox and chelation.2.In the study of Cr(VI)adsorption by PPy/SiO₂/Fe₃O₄/MLS,the effect of the content of tetraethoxysilane(TEOS)on the dispersibility of the material was studied,and it was found that the dispersibility and magnetism of the material could be taken into account when its content was 60 wt%.The effects of pH value,Py content and cyclic adsorption on the removal of Cr(?)were investigated.The results showed that the adsorption performance of the material was the best at 298 K and the maximum adsorption capacity was 301.20 mg/g when the pH 2 and Py content was 50 wt%.However,after five cycles of adsorption experiments,the magnetic properties of the materials were only reduced by about 9.2%.In the first three experiments,the removal rate of Cr(VI)was more than 99%..3.PPy-mPD/Fe₃O₄/MLS was prepared by copolymerization modification of mPD and Py.The effects of the ratio of Py to mPD and the mass ratio of Py to mPD on the adsorption properties of Cr(VI)were studied.The results showed that the adsorption performance of the material was the best when the ratio of Py to mPD was 5:5 and the total content of Py and mPD was 50 wt%.Under the condition of pH 2 and 298 K,the maximum adsorption capacity was increased to 429.18 mg/g.Compared with PPy/Fe₃O₄/MLS,it was increased by about 34%.4.The adsorption processes of the three functional composites were in accordance with the pseudo-second-order kinetics and Langmuir isothermal model,indicating that the materials were mainly chemical adsorption and monolayer adsorption,and the adsorption thermodynamics showed that the adsorption process is spontaneous.EDS and XPS proved that the materials removed Cr(?)by electrostatic interaction,ion exchange,redox and chelation.