Hydrophobic D-galactose based ionic liquid for the sequestration of Pb 2+ ions from aqueous solution R. Jayachandra a , R. Lakshmipathy b , Sabbasani Rajasekhara Reddy a, ⁎ a Organic Chemistry Division, School of Advanced Sciences, VIT University, Vellore 632014, India b Centre for Material Science, KCG College of Technology, Karapakkam, Chennai 600097, India abstract article info Article history: Received 14 August 2015 Accepted 30 November 2015 Available online xxxx Herein we report the synthesis of new hydrophobic ionic liquid by simple manipulations starting from D-galac- tose. The synthesized ionic liquid 1-methyl-3-(((3aS,5S,5aR,8aR,8bS)-2,2,7,7-tetramethyltetrahydro-3aH- bis([1,3]dioxolo)[4,5-b:4′,5′-d]pyran-5-yl)methyl)-1H-imidazol-3-ium hexafluorophosphate(V) (IL 5) was completely characterized by sophisticated analytical techniques. IL 5 was investigated as adsorbent for the sequestration of Pb 2+ ions from aqueous solution and this is proved as its potential application. Batch mode stud- ies were done, by varying the batch parameters such as pH, IL dose, contact time, initial metal ion concentration and temperature. Various mathematical models such as kinetic models and isotherms were employed to under- stand the mechanism of sequestration. Thermodynamic investigations suggest that the sequestration of Pb 2+ ions is spontaneous and exothermic in nature. The maximum loading capacity of IL 5 was found to be 374.9 mg g -1 . Desorption and regeneration analysis revealed the repeated use of IL 5 in industrial processes. These results suggest that IL 5 is a potential sorbent for the elimination of Pb 2+ ions from aqueous solution. © 2015 Published by Elsevier B.V. Keywords: D-galactose N-methylimidazole Ionic liquid Lead Adsorption 1. Introduction Galactose is a simple natural carbohydrate found in two structurally similar forms (anomers), i.e., D-galactose and L-galactose. D-galactose is widespread in the living system. It is an essential component of glycoproteins, glycolipids and proteoglycans. Since the less poisonous or zero poisonous nature of carbohydrates and derivatives of carbohy- drates towards environment, they are considered as eco-friendly mate- rials. The entire present technology focuses on finding the solutions that are most economical, effective, simple, recyclable and environment friendly. The unique properties of ionic liquids (ILs) such as low or zero vapor pressure, high thermal stability, widely varying polarity, recyclability, and structural tunability [1–3], makes more convenient to satisfy the specific application requirements [4–10]. The rapid use of heavy metal ions in the current trend for various applications, lead to increased disposal of hazardous metallic substances in natural water and soil. The unusual levels of metal ions leads to severe health effects on living organisms, because most of them are toxic and persistent in nature. Before the disposal of effluents containing metal ions, proper treatment is required in order to meet the optimum accept- able levels. Lead (Pb) is one of the most hazardous metal ions and particularly a common pollutant in aquatic system [11]. A recent report from world health organization (WHO) cautioned about the health consequences of lead poisoning particularly in children. Lead poisoning can effect every organ of the body and particularly affects the central and peripheral nervous systems [12]. Adsorption of heavy metal ions onto adsorbent is found to be an economical and effective process. In continuation to this, various adsorbents ranging from low cost agricul- tural waste materials to zeolites have been studied and investigated for the sequestration of heavy metal ions from aqueous solution. Hydrophobic ionic liquids showed promising applications in extraction of heavy metal ions from aqueous solution [13–17]. Most of the imidazolium based ILs are liquids at room temperature, hence chelating agents were used for liquid–liquid extraction [18,19]. Herein we report a new, stable and hydrophobic ionic liquid by simple modifications, starting from cheap and commercially available D-galactose in good overall yields. As an application, the synthesized IL 5 (Scheme 1) was studied for its efficiency towards sequestration of Pb 2+ ions from aqueous solution. Batch parameters such as pH, contact time, dose, initial metal ion concentration and temperature were inves- tigated. The resulting data was analyzed with various mathematical models to understand the mechanism and type of adsorption process. 2. Materials and method 2.1. Synthesis of ILs Zinc chloride (ZnCl 2 ), TPP (triphenyl phosphine), iodine, imidazole, N-methyl imidazole (NMI) and sodium hexafluorophosphate (NaPF 6 ) Journal of Molecular Liquids xxx (2015) xxx–xxx ⁎ Corresponding author. E-mail addresses: sekharareddyiitm@gmail.com, sekharareddy@vit.ac.in (S.R. Reddy). MOLLIQ-05271; No of Pages 7 http://dx.doi.org/10.1016/j.molliq.2015.11.060 0167-7322/© 2015 Published by Elsevier B.V. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq Please cite this article as: R. Jayachandra, et al., Hydrophobic d-galactose based ionic liquid for the sequestration of Pb2+ ions from aqueous solution, J. Mol. Liq. (2015), http://dx.doi.org/10.1016/j.molliq.2015.11.060