Cationic Structure Regulation Of Poly(Ionic Liquids) And Investigation Of Their Adsorption Properties For Precious Metals

The shortage of precious metals resources and outdated separation technology in China have become the bottleneck restricting the sustainable development of precious metals industry.Adsorption is currently the best method for recovering precious metals from hydrometallurgical systems due to the advantages of simple operation,high efficiency for dilute solutions,and no additional sludge,which meets the requirements of green chemistry.The ionic part of the poly（ionic liquids）could electrostatically attract precious metal chloride complexes.At the same time,it also reacts with the precious metal chloride complexes through hydrogen bonds andπ-type interactions.Therefore,it shows excellent adsorption performance.But until now,the"structure-effect"relationship between the cationic structure of polymeric ionic liquids and their adsorption properties has not been elucidated,which hinders further optimization of their properties.Therefore,the research content of this paper is as follows:（1）By changing the chain length and aromaticity of the N3 substituent,the electron and charge distribution on the imidazolium are regulated to improve the adsorption performance of the imidazolium-based poly（ionic liquids）.The changes of electrons and charges on imidazolium cations caused by different N3 substituents were studied by ¹H NMR and further DFT calculations.The interactions between different imidazolium cations and PdCl₄^2-were also studied by the crystal structure of the model adducts IM-methyl/ethyl/propyl-Pd.The effect of the N3 substituents on the adsorption performance of imidazolium-based poly（ionic liquids）was elucidated.（2）By changing the structure of the cation,including linear or cyclic,aromatic or non-aromatic,the adsorption performance of five nitrogen-containing organic cations（triethylammonium,pyrrolyl,piperidinyl,imidazolyl and pyridyl）-based polymer ionic liquids for Au（Ⅲ）were investigated.The results show that the anion-πinteraction between aromatic cations and[AuCl₄]^-enhances the interaction strength between the anions and cations.However,the surface charge delocalization of aromatic cations will lead to the decrease of the ESP on van der Waals surface of cations,which lead to worse adsorption performance of the corresponding polymer.The larger the ESP on the van der Waals surface of the aliphatic cations,the better the adsorption performance of the corresponding poly（ionic liquids）.This work clarifies that the adsorption performance of poly（ionic liquids）is mainly determined by the ESP value on the cations.The larger the cationic ESP value,the stronger the adsorption performance of the corresponding poly（ionic liquids）.Future performance optimization of poly（ionic liquids）should mainly focus on improving the ESP value on the cations.（3）We developed dicationic poly（ionic liquids）,which interacted with divalent anions(PdCl₄^2-,PtCl₄^2-,PtCl₆^2-)through charge-matched ion-pairing.The effects of contact time,initial concentration of precious metals,interfering ions and pH value on the adsorption capacity and adsoption kinetics of dicationic poly（ionic liquids）for PdCl₄^2-,PtCl₄^2-,PtCl₆^2-were studied.The effect of hydrophilic properties of the dicationic poly（ionic liquids）on adsorbing Pt（IV）was also studied.The recycling performance of dicationic poly（ionic liquids）was evaluated.The mechanism of dicationic poly（ionic liquids）adsorbing precious metal chloride complexes is believed to be through electrostatic attraction and multiple interactions,such as hydrogen bonding,anion-πinteractions,etc.