Synthesis of a new ionic liquid for efficient liquid/liquid extraction of lead ions from neutral aqueous environment without the use of extractants

Abstract

This work introduces a new air and moisture stable ionic liquid which is tested for the extraction of Pb²⁺from neutral aqueous solution. Here, no chelating agents were used. Grafting coordinating functional groups on the cation of the ionic liquid was not necessary. Very small ionic liquid to aqueous phase ratio was used. The ionic liquid used for this purpose was N-hexyl-4,4-bipyridinium bis(trifluoromethylsulfonyl)imide([C₆byp][Tf₂ N]). Its synthesis is characterized by spectrometry (¹ H, ¹³ C, and ¹⁹ F NMR, ESI-MS, FTIR) as well as Carbon, Hydrogen and Nitrogen (CHN) elemental analysis. Differential scanning calorimetry (DSC) has been used to analyze in detail the thermal behavior in the temperature range of −20 to 200 °C. Interestingly, the ionic liquid demonstrated nearly complete removal of the metal ion from the aqueous phase (98.16%). Furthermore, the reusability (recyclability) investigation demonstrated that the ionic liquid can be used at least for four cycles with undiminished efficiency (98.16% for the second cycle, 97.64% for the third and fourth cycles). Its cycle ability reduces the concern arising from the high cost of ILs. This result indicates that the use of this ionic liquid for the extraction of heavy metals is very promising. The mechanism of removal of the Pb²⁺ ions is speculated to be by the formation of a complex with a formula of [Pb(C₆bpy)_n][(CF₃SO₂)₂ N]_n(NO₃), where, n = 1–6.

Keywords:

• Ionic liquid
• N-hexyl-4
• 4ʹ-bipyridinium
• liquid/liquid extraction
• recyclability
• small ionic liquid to aqueous phase ratio
• neutral aqueous phase

PUBLIC INTEREST STATEMENT

The rapid increase in the number of multidrug-resistant pathogens and cellular-based diseases is fast becoming a global concern. Thus, the discovery of novel active compounds against new targets is a matter of urgency. The conventional approach to address this impulse employing materials originating from wild growing plants and animals has shortened their life span. Apart from studying their attractive chemistry, this problem has initiated the scientific community to consider and investigate transition metal complexes as an alternative solution.

This is the first objective of our group. Furthermore, efficient and environmentally friendly applications of newly prepared materials have been the focus of attention of the global community. Thus, investigation and preparation of materials fulfilling this objective is the second objective of the group.

Competing Interests

The authors declares no competing interests.

Disclosure statement

There is no any conflict of interest among the authors.

Additional information

Funding

The authors received no direct funding for this research.

Notes on contributors

Atakilt Abebe

Dr Atakilt Abebe’s research group is consisted of some staff members of Bahir Dar University and post graduate (MSc) students. Dr. Atakilt Abebe is a full-time associate professor of Inorganic Chemistry at Bahir Dar University. He received B.Sc in Chemistry, M. Sc. and Ph. D in Inorganic Chemistry from Addis Ababa University, Ethiopia.

Atakilt Abebe’s research group works in the development of metal-based drugs employing heteroaromatic flat molecules as ligands as well as incorporation of phytochemicals with medicinally potent transition metal ions for antibacterial as well as anticancer purposes. Furthermore, the group is working in the synthesis of organic salts aiming for medicinal applications as an alternative to metal-based approaches as well as for extraction purposes. In this category, synthesis of new ionic liquids for electrochemistry and as modulators in the properties of materials isalso carried out. Atakilt Abebe has authored/coauthored more than 21 peer-reviewed originalresearch articles.