Effect of the length and aromaticity of N3-substituent on adsorption performance of imidazolium-based poly(ionic liquids) towards Pd (II)

Xin Kou; Yong Huang; Ying Yang

doi:10.1016/j.jhazmat.2021.126623

Effect of the length and aromaticity of N3-substituent on adsorption performance of imidazolium-based poly(ionic liquids) towards Pd (II)

J Hazard Mater. 2021 Oct 15:420:126623. doi: 10.1016/j.jhazmat.2021.126623. Epub 2021 Jul 9.

Authors

Xin Kou¹, Yong Huang¹, Ying Yang²

Affiliations

¹ School of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China; The Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, Lanzhou University, Lanzhou 730000, PR China.
² School of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China; The Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, Lanzhou University, Lanzhou 730000, PR China. Electronic address: yangying@lzu.edu.cn.

PMID: 34271447
DOI: 10.1016/j.jhazmat.2021.126623

Abstract

Imidazolium-based poly(ionic liquids) (PILs) have been deemed as attractive candidates in the field of precious metal adsorption. However, their further performance optimization is hampered by a lack of an inner understanding of the structure-adsorption performance relationship. In this research, electron and charge distributions of the imidazolium cations are tailored by changing the N3-substitute, and their adsorption performances for PdCl₄^2- were optimized accordingly. Furthermore, the adsorption mechanism is studied by synthesizing corresponding ionic liquid (IL) monomers and their Pd-adducts. Interestingly, longer N3 alkyl chains lead to more hydrogen bonds with PdCl₄^2-, which is beneficial for adsorption. Whereas, it is unfavorable for attracting anions due to a decrease in electrostatic potential (ESP) around cations caused by longer alkyl chains and aromatic substituents at N3 position. It is worth noting that the ESP around the cations plays a more important role in the adsorption process, which determines the adsorption performance of the imidazolium-based PILs. Thus, the performance optimization of imidazolium-based PILs should mainly focus on increasing the ESP of imidazolium cations in the future. This research highlights the potential of the cationic structure-adsorption performance relationship of PILs, which opens a new avenue to develop adsorbents for the metallurgical industry.

Keywords: Adsorption; Imidazolium-based poly(ionic liquids); N3 substituents effect; Pd (II).