1 REMOVAL OF IONIC LIQUIDS AND METHYLENE BLUE USING VARIOUS ACTIVATED CARBONS Amjad Farooq 1,2 , Laurence Reinert 2 , Jean-Marc Leveque 2 , Nicolas Papaiconomou 2 , Naseem Irfan 1 , Laurent Duclaux 2 1 Pakistan Institute of Engineering and Applied Sciences, P.O.Nilore, Islamabad, Pakistan 2 Laboratory of Molecular Chemistry & Environment, Polytech Savoie, University of Savoie, Bourget du Lac 73376, France Introduction Ionic liquids (ILs) being soluble in water pose a serious threat to the environment and their toxicity has also been reported. Only few works were focused on ILs removal through AC and a previous work based on imidazolium type ILs did not show appreciable results regarding AC [1]. A very recent detailed investigation for adsorption of imidazolium based ILs onto AC has reported the effects of cations, anions and surface chemistry on the adsorption efficiency [2]. Another issue which the environmentalists have been trying to tackle for the last many years is the removal of dyes from the waste stream of a processing/dyeing industry. The present work aims at investigating the adsorption profile and uptake of various ILs on three activated carbons coming from different origins which differ in terms of porous texture and surface chemistry. Methylene blue being a typical cationic dye was selected to compare its adsorption with the selected ILs. Experimental The three types of ionic liquids used were 1-methyl 3- octylimidazolium chloride (OMImCl), 1-butyl 3- methylimidazolium chloride (BMImCl) and octylpyridinium bromide (OPyBr). OMImCl was synthesized in our laboratory using microwave irradiation, OPyBr was also synthesized in our laboratory, whereas BMImCl and Methylene Blue (M Blue) were obtained commercially. The three activated carbons (AC) were, a microporous coal based granulated AC from China, a mesoporous AC fabric from Calgon and an AC prepared from artichokes using phosphoric acid activation (called Chinese AC, Fabric AC and Artichokes AC respectively). The adsorption experiments were all performed at 25°C by stirring stoppered 100 mL flasks containing the suspensions of AC in ILs solutions on a magnetic stirring plate. The ionic liquids and dye adsorption kinetics and isotherms on the ACs were studied using UV-Visible spectrometry. All the isotherms were obtained under controlled pH conditions in buffer solutions at pH 2, 7 and 9. A 50 mL volume of the adsorbate solution made in the buffer was stirred with weighted amounts of AC in each case (0.1 g for the Chinese AC and 0.05 g each for the Fabric AC and the Artichokes AC). The maximum absorbance was obtained at 665 nm for M Blue, 211 nm for OMImCl and BMImCl and at 260 nm for OPyBr. Results and Discussion Table 1 shows the results of the “Boehm” titrations which give the semi-quantitative value of oxygenated acidic and basic functional groups on the surfaces of the respective ACs. The Chinese AC has the least amount of acidic functional groups, whereas the Artichokes AC has the most. Table 1. Boehm titration results of three AC samples (meq.g -1 AC) Activated Carbon Carboxylic Groups (meq.g -1 ) Lactonic Groups (meq.g -1 ) Phenolic Groups (meq.g -1 ) Carbonyl Groups (meq.g -1 ) Total Basic Groups (meq.g -1 ) Chinese AC 0 0 0.07 - - Fabric AC 0 0.4 0.2 0 0.1 Artichokes AC 0.46 0.68 0.38 0.44 - The BET surface areas of the AC adsorbents, determined by using a Micromeritics ASAP2010 are shown in Table 2. The Artichokes AC has the largest surface area most of which is present as an external surface area. The Chinese AC, on the other hand is mainly microporous and the Fabric AC is mainly mesoporous. Table 2. Surface areas and pH PZC of three AC samples Activated Carbon BET Surface Area (m 2 /g) External Surface Area (m 2 /g) Micropore Area (t-plot) (m 2 /g) Micropore Volume (t-plot) (cm 3 /g) pHPZC Chinese AC 1205 632 573 0.25 9.5 Fabric AC 1769 376 - 0.25 6.8 Artichokes AC 2160 2010 156 0.043 6.0 Figure 1 shows the adsorption data at pH 2 and 9 for OPyBr onto the three AC samples. The effect of changing pH on the adsorption uptake is more pronounced in Artichokes AC. The highest sensitivity of the adsorption of this carbon to the pH variation is related to its surface chemistry which is very rich in acidic groups. At pH 2, the uptake is always less than at pH 9 due to the repulsion between the positively charged IL cation and the AC surface. Curves at pH 9 have a sharp knee as compared to the curves at pH 2 signifying a stronger interaction due to electrostatic attraction leading to a higher adsorption uptake.