Removal of toxic heavy metals, phenolic compounds and textile dyes from industrial waste water using phosphonium based ionic liquids

Abstract

This article focused on a comprehensive result of the development of three phosphonium based room temperature ionic liquids (RTILs) of same cation, trihexyltetradecylphosphonium ([PC6C6C6C14]), with different organic or inorganic anions viz. [Cl-] chloride dicyanamide [-N(CN)2−] and bis (trifluoromethyl sulfonyl) amide [-NTf2−] in extraction processes of toxic textile dyes as rhodamine B, methylene blue, methyl orange, malachite green, alizarin red S and congo red dyes from their aqueous solution, harmful heavy metals include As, Cr, Cd, Cu, Zn, Pb and Hg from their standard solutions AS(NO3)3, Cr(NO3)3, Cd(NO3)2, Hg(NO3)2, Pb(NO3)2, Zn(NO3)2 & Cu(NO3)2 respectively and phenolic compounds from rice and cashew industrial waste water. In technological front, ILs revealed a potential ability for the removal of dyes, heavy metals and phenolic compounds owing to their hydrophobic nature on investigating via liquid –liquid extraction method. The effect of contact time, solution pH and initial concentration of dyes were investigated and the result show that adsorption of dyes increases with increasing contact time and gets maximum decolourisation at acidic pH and pH 7. The extraction process of heavy metals with the ILs were investigated and were assessed using the techniques UV–Visible spectroscopy and ICP-MS (Inductive Coupled Plasma Mass Spectroscopy). The three ILs showed best extraction efficiency (approx. 100%) for all heavy metals and the dyes using proposed methodology. UV–Visible Spectroscopy quantification method was employed to analyse extracted phenolic compounds. Screening results of phenolic compounds have shown that [PC6C6C6C14][Cl] IL exhibited the capacity intake of 100% efficiency from rice and cashew industrial waste water. The ILs were characterized with thermogravimetry (TGA) and from which, the samples showed a good thermal stability up to 573 K to project them as promising one for high temperature needs in various technological fronts. Toxicity risks of the three ILs and the textile dyes used were examined by in silico OSIRIS software calculations and the ILs were found to be non-toxic.