Strong and weak interactions between ionic liquids and dyes: Test to Methylene blue removal from wastewater using1-butyl-1- pyrrolidinium hexafluorophosphate

M. Mehouen, M. Kameche, B. Haddou, Z. Talbi, A. Khenifi, C. Gourdon


Abstract: Strong and weak interactions between ionic liquids and dyes have been studied. The study has been tested with the removal of methylene blue from wastewater by1-butyl-1-pyrrolidinium hexafluorophosphate. The attractive interaction between Ionic Liquid (IL) 1-butyl-1-methyl pyrrolidinium hexafluorophosphate [bmpyr] and Methylene Blue (MB) has been investigated using electric conductivity measurements. The formation of associates between the IL anion (PF6-) and cationic MB has been made in evidence by means of spectroscopic analyses namely Ultra-Violet Visible (UV-Vis), Fourier Transform Infra-Red (FTIR) and Nuclera Magnetic Resonance (NMR). The results have been compared to previous data of 1-butyl-3-methylimidazolium hexafluorophosphate [bmim]. Having the same carbon chain, this latter gives associate constants which are higher than those of the former IL[bmpyr], suggesting the induced strong interaction between both species. In effect, the envelope of electron density of ILbmim, caused by nitrogen N1 inside the cycle, increases greatly the interaction. Really, this phenomenon might be attributed to complex formation readily affected by the conjugated diene system and the presence of a low pair of electrons provided by the tertiary at N1 of [bmim] compound. Besides, the symmetrical singly charged Cl- and PF6- anions being structure breaker and borderline structure breaker respectively, determined the type of interaction that may occur between the IL and MB. The results suggest also the strongest interaction between the inorganic anion PF6- of IL and organic cation of MB leading to its reduction. At last, it has been proved through this fundamental study that IL [bmpyr] is not efficient enough to remove MB compared to other suitable ILs. It may nevertheless be good enough to detect traces of dyes in very dilute solutions.

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