Efficient Precipitation of Dyes from Dilute Aqueous Solutions of Ionic Liquids

Abstract

Due to their unusual properties, ionic liquids are garnering increased attention from academic and industrial research communities alike. 1 Almost every named synthesis and many more organic/inorganic/organometallic reactions have been reported in ionic liquids. 2 Novel analytical applications of ionic liquids are emerging every day; effective, and in some cases unique, utilizations of ionic liquids have been demonstrated in a variety of techniques encompassing electroanalysis, separation, extraction, spectrometry, and sensing. 1 More specifically, unique features have emerged during many investigations of extraction processes involving ionic liquids. 1,3 Some of the initial reports on the utilization of ionic liquids in extraction started to appear in the mid-to-late 1990's. 4 These reports hint towards an unexplored potential of ionic liquids in extractionbased applications.Optical dyestuff has diverse industrial applications. Unfortunately, as a consequence, they are often present in wastewater and give rise to potential hazards due to their inherent toxicity. For example, significant amounts of synthetic textile dyes that are highly water-soluble are lost into wastestreams during the manufacturing of dyestuff and other textile processing operations. 5 Since most of these dyes have high water solubility, they are generally difficult to remove by the usual waste-treatment systems. Efficient, rapid, cost-effective, and environmentally-friendly removal of dyestuff from aqueous media has always been a major issue.In this paper, we present an efficient, rapid, and remarkablyeasy way of efficiently extracting cationic dyes from their aqueous solutions using popular ionic liquids. We have demonstrated that the addition of only ∼1.7 wt% (∼0.06 M) of ionic liquids to the aqueous solutions of six popular cationic dyes resulted in almost complete precipitation of each dye from its aqueous solution. The structures of the six cationic dyes investigated are presented in Fig. 1.Aqueous solutions of the six dyes were prepared at three different concentrations of 75 μM, 750 μM, and 1.5 mM at room temperature using doubly distilled deionized water. The UV-Vis molecular absorption spectra of the dye solutions were obtained. To these dye solutions, ca. 1.7 wt% (0.06 M) ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) was directly added. The solubility of bmimPF6 in water under ambient conditions is ca. 2.1 wt%. 6Immediate precipitation of dyes was clearly evident in each case, as demonstrated in Fig. 2 for one of the dyes, pinacyanol chloride. As shown in Fig. 2, colored dye solutions became nearly clear upon the addition of bmimPF6. Solid precipitated dyes were carefully removed from the solutions. Extracted solid dyes were dried at room-temperature, after which, the 1 H NMR spectra of the dyes were collected and compared with those of dyes from the stock. The 1 H NMR spectra are found to be identical, thus confirming the identity of the precipitated dyes to be the same. Further characterization of the...

Unusual Solvatochromism within 1-Butyl-3-methylimidazolium Hexafluorophosphate + Poly(ethylene glycol) Mixtures

“…E T N in [bmim][PF 6 ] + PEG (average MW 200, 400, 600, and 1500) solutions thus obtained are listed in Table . The E T N in neat [bmim][PF 6 ] (0.67 ± 0.00 5 ) is similar to that observed in 3-methylphenol (0.67 ± 0.00 5 ) and close to that observed in tetraethylene glycol, 4-bromophenol, and 4-cyanophenol (0.66 ± 0.00 5 ). – Our [bmim][PF 6 ] E T N is in agreement with what is reported by many researchers earlier. – ,,– ,– It is observed that E T N in neat [bmim][PF 6 ] is higher than those in neat PEGs indicating higher dipolarity/polarizability and/or HBD acidity of [bmim][PF 6 ] relative to that of PEGs. As expected, E T N decreases with increasing PEG average MW.…”

“…In this context, we have earlier reported our investigations on the effects of added water, – ethanol, aqueous−ethanol, and other ionic liquids on different ILs. The miscibility of water and ethanol in the “hydrophobic” IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ]) is significantly low (∼2.1 and ∼9.7 wt %, respectively, at ambient conditions), – which, in turn, makes it difficult to modify the physicochemical properties of this common IL to any desired extent. Investigations on the addition of water and ethanol to PEGs also imply the changes in the physicochemical properties of these systems to be fairly limited …”

Preparation of a poly(acrylic acid) based hydrogel with fast adsorption rate and high adsorption capacity for the removal of cationic dyes

“…A series of physicochemical techniques, such as adsorption, 4 photocatalytic degradation, 5 electro-kinetic coagulation, 6 precipitation, 7 membrane ltration, 8 and occulation, 9 have been developed for the removal of dyes from waste water. Of these methods, adsorption emerges as a superior industrial water treatment method due to the simplicity of design, low cost, stability and reusability of the adsorbents.…”

Nano-Silica Modified with Diamine for Capturing Azo Dye from Aqueous Solutions

“…Many techniques have been applied for the removal of methyl orange such as precipitation [ 5 ], coagulation and flocculation [ 6 ], photodegradation [ 7 ], biological degradation [ 8 ], catalytic degradation [ 9 , 10 , 11 ], and adsorption [ 10 , 12 , 13 , 14 ]. Adsorption is considered among the best techniques for water treatment [ 15 , 16 ].…”