Theoretical Calculation And Iodine Extraction Performance Of Inorganic-organic Electroactive Ion Exchange Material MIL-101@PPy

As a bridge connecting experiment and theory,simulation calculation plays an important role in the fields of materials,physics,chemistry and so on.For the analysis and application of new materials,on the one hand,simulation calculation can conduct microscopic analysis of their structures from the molecular and atomic scales,which provides research ideas for material design and modification.On the other hand,the gas adsorption,catalysis,and ion separation performance of the material can be predicted,which lays the foundation for the high efficiency of the experiment.Therefore,simulation and experiment complement each other in scientific research.In this paper,combined with the practical significance of iodide ion separation,MIL-101@PPy,a novel inorganic-organic electroactive ion exchange material,is constructed.The recombination mechanism of MIL-101@PPy is explored and its separation performance for I^-is predicted.At the same time,the optimal conditions for the selective separation of I^-by the MIL-101@PPy film electrode are experimentally explained.Iodine is an essential nutrient element,and the human body needs to take in a certain amount of iodized salt every day.In industry,iodine is used in medicine,dyes,emerging LCD polarizing film materials and rocket accelerants.The demand for iodine resources in our country is large but the output is low,so its supply has long been dependent on imports.The domestic traditional iodine extraction industry is mainly based on seaweed iodine extraction and phosphate ore wet iodine extraction.In view of the limited seaweed resources and the low grade of phosphate ore,iodine extraction from saltlake brine has attracted the attention of researchers.The content of iodide ions in most saltlake brines in China is below 60 mg/L,and there are various types of interfering ions.Combined with the requirements of our country’s strategic resource development,it is of great significance to develop a technology suitable for low-concentration extraction,high selectivity to target ions,and environmentally friendly.Electronically switched ion exchange（ESIX）is a new ion separation technology based on electroadsorption,with electroactive ion exchange materials（EIXMs）as the key to selectively recognize target ions.In this paper,from the perspective of MOF-polymer,a new type of film electrode composited with metal-organic framework compound MIL-101 and organic conductive polymer PPy was constructed.The original pore of MIL-101 are reconstructed with PPy and the new pores can be used as ion transport channels,while polypyrrole can improve the conductivity of the material and act as an electron transport channel,making it suitable for ESIX systems.Simulation calculations can analyze the microstructure of EIXM and predict its ion separation performance.Firstly,the diffusion law of pyrrole monomer into MIL-101 and the recombination mechanism between the two are studied.Combining experiments and Monte Carlo simulations,MIL-101@Py models with different pyrrole contents are constructed.Molecular dynamic analysis proves that Py first distributed at the edge of the mesoporous cage when entering MIL-101 cavity,and gathers toward the center with the increase of loading capacity until it is difficult to enter.The density functional theory calculation shows that the interaction force between the Cr₃O cluster and the organic ligand in MIL-101 and the pyrrole is mainly hydrogen bonding,which is consistent with the FTIR analysis,and this process belongs to physical adsorption.Secondly,the polymerization behavior of pyrrole is explored,and the atomic charges indicated that the electronic properties of pyrrole nonamers are similar to those of polypyrrole,and the MIL-101@PPy model is constructed based on this.Finally,limited by the number of atoms in the system,the molecular dynamics method was used to roughly investigate the ion selectivity of the MIL-101@PPy system,and the reaults suggest that it showed certain advantages for I^-adsorption.During the experiment,the MIL-101 is prepared by hydrothermal method.The pyrrole monomers are filled into the MIL-101 cavity by the impregnation method.Taking advantage of the volatile property of pyrrole at room temperature,the content of pyrrole in the cavity of MIL-101 is skillfully regulated by controlling the drying time of the material.The pyrrole monomers are polymerized in situ in MIL-101 and threaed in the cage of MIL-101.The morphology and structure of the material were characterized by SEM,XRD and FTIR.Under the conditions of different voltages,different initial concentrations and different p H,the adsorption properties of the materials for iodine are investigated,and it is found that the highest adsorption capacity of iodine was 100.77 mg/g in acidic or neutral 50 mg/L KI solution with 0.6 V oxidation voltage.In the presence of interfering ions,the separation factor of I^-/SO₄^2-is up to 10.506.In conclusion,MIL-101@PPy composite film can be used for efficient extraction of I^-.