Advanced Materials Research Online: 2014-01-16 ISSN: 1662-8985, Vols. 881-883, pp 1011-1014 doi:10.4028/www.scientific.net/amr.881-883.1011 2014 Trans Tech Publications, Switzerland Adsorption of Cd(II) from aqueous solution by magnetic graphene Jun Liu a, Shaowei Yuan b, Hongyan Du and Xuyao Jiang School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang 212013, China a liujun1227@mail.ujs.edu.cn, b kaoweishiwo@126.com Keywords: graphene; magnetic nanoparticles; adsorption; cadmium Abstract. In the present study, Fe 3 O 4 /graphene nanoparticles (Fe 3 O 4 /GN NPs) were obtained and modified with silane coupling agent. The effects of Cd(II) adsorption experimental parameters such as contact time and initial Cd(II) ion concentration, were investigated. The adsorption dynamics follow the laws of pseudo-second-order kinetics and the rate was controlled by chemical adsorption. The Langmuir isotherm model provided the better correlation between adsorbing capacity and equilibrium concentration. Introduction Nowadays, heavy metal ions have been common contaminants in environment, which are considered to be toxic or carcinogenic even at low concentrations. Cadmium (Cd), widely distributed in soils and water bodies, is a direct potential threat to the human health [1-3]. In the acute stage, it can damage the kidneys, liver, bone, and blood, and cause disease of anemia, emphysema, hypertension, and lung cancer [4]. Graphene (GN), a sp2, 2D-dimensional single-layer carbon sheet, has aroused great interest in the world in the last several years [5, 6]. The high specific surface area of graphene provides the potential application of high adsorption for heavy metal ions [7, 8]. Moreover, by combining fascinating merits and low costs, it suggests that GN sheets could be an ideal matrix for the growing and anchoring of a large number of functional substances [9]. Therefore, integration of magnetic nanoparticles and graphene was studied and held a great promise for removal for heavy metal ions from swage due to its magnetic separation properties under an external magnetic field [10-12]. To our kownledge, decoration with functional groups on the surface of nanoparticles was considered to improve the adsorption capacity, which had little been focused on. In the present study, 3-Methacryloxypropyl trimethoxysilane (MPTES) was used to modify the group on the surface of the nanocomposites. Materials and methods Preparation of materials. Graphite oxide (GO) was synthesized from natural graphite powder based on the modified Hummers method [13]. One-pot strategy was used to obtain well-organized Fe 3 O 4 /graphene NPs directly from GO and iron chloride (FeCl 3 6H 2 O) in the presence of hydrazine hydrate. The prepared Fe 3 O 4 /graphene NPs were added to the MPTES/ethanol mixture followed by ultrasonic dispersion. The product modified Fe 3 O 4 /graphene (M-Fe 3 O 4 /GN) was then washed several times and dried overnight under vacuum. Adsorption experiment. A 10 mg of M-Fe 3 O 4 /GN NPs were added to Cd(II) solution (100mL) of different initial cadmium ion concentration in a temperature-controlled water bath shaker, respectively. Within a certain time, the supernatant was taken out and filtered. The concentration of Cd(II) was determined by using an atomic absorption spectrophotometer. The constant qe (mg g -1 ), Cd(II) adsorption capacity at the equilibrium, was calculated as follows: where C 0 is the initial Cd(II) concentration (mg L -1 ); C e is the equilibrium Cd(II) concentration (mg L -1 ); V (L) is the volume of the solution; and w (g) is the weight of the adsorbent [14]. (1) All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-06/03/16,19:16:54)
Trancemittance 1012 Chemical, Material and Metallurgical Engineering III Adsorption kinetics often uses primary and secondary dynamics equations for simulating test data, and analyzing the change of the metal ion concentration with the adsorption time. The equation of pseudo second-order model is expressed as (2) where q e and q t (mg g -1 ) are equilibrium adsorption capacity and adsorption uptake at time t, respectively, and k 2 is the pseudo second-order rate constant. The data of cadmium adsorption were fitted with Langmuir [15] and Freundlich [16] isotherm models. The Langmuir isotherm is expressed as follows: The Freundlich isotherm is represented by the following equation: (3) (4) where C e (mg L -1 ) is the equilibrium concentration of adsorbate in solution; q e and q m (mg g -1 ) are the adsorption capacity at equilibrium (mg g -1 ) and maximum amount absorbed on the NPs. K L, K F and n are constants of equations from (3) and (4). Results and discussion Characterization study. As shown in Fig. 1(a), the peak at 1700 cm 1 was the C=O stretching vibration peaks of carboxyl and the peak at 1059 cm 1 was ascribed to the C-O stretching vibration of alkoxy [17]. The Fe-O characteristic stretching vibration peak at 568 cm 1 was observed in Fig. 1(b), which proved that Fe 3 O 4 nanoparticles were successfully anchored onto graphene sheet. In comparison with graphene oxide, Fe 3 O 4 /graphene nanocomposite showed a dramatic decrease in the intensity of the adsorption peaks of oxygen-containing functional groups, which suggested graphene oxide has been partially reduced. Peaks at 1633 and 1390 cm -1 corresponded to MPTES characteristic absorption peaks [18]. The peak at 1080 cm -1 was the Si-O stretching vibration peak, revealing the MPTES has been successfully decorated on the Fe 3 O 4 nanoparticles. (a) 1700 (b) 1059 1633 1564 1390 1080 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber/cm -1 Fig. 1 FTIR spectra of (a) GO and (b) M- Fe 3 O 4 /GN Adsorption kinetics of cadmium. The influence of agitation time on adsorption capacity (qt, mg g -1 ) of M-Fe 3 O 4 /GN NPs for cadmium ion was shown in Fig. 2. During the initial 15 min, qt for cadmium ion increased reached 106.49 mg g -1, and the adsorption proceeded slowly with contact time before reaching a plateau value after 1 h. The simulation results of kinetic parameters are presented in Table 1, which revealed the pseudo secondary dynamics equation simulated the test result very well because of the value of R 2 and a small 568
Amount of Cd(II) adsorbed(mg g -1 ) Advanced Materials Research Vols. 881-883 1013 difference between the experimental value and the theoretical value. The adsorption process follows the pseudo secondary reaction mechanism and the rate was controlled by chemical adsorption. 120 Amount of Cd(II) adsorbed(mg g -1 ) 110 100 90 15 30 45 60 75 90 contact time(min) Fig. 2 Adsorption of cadmium with time by M-Fe 3 O 4 /GN Table 1 Adsorption kinetic parameters of Cd(II) onto M-Fe 3 O 4 /GN C 0 (mg g -1 ) Experimental value of Theoretical value of k 2 (g mg -1 min -1 ) R 2 q e (mg g -1 ) q e (mg g -1 ) M-Fe 3 O 4 /GN 20 108.30 108.70 0.0385 0.999 Isotherm adsorption of cadmium. The influence of equilibrium solution concentration on adsorption capacity (q m ) of M-Fe 3 O 4 /GN NPs was illustrated in Fig. 3. The adsorption capacity increased with increasing equilibrium concentration. It could be explained to that increasing Cd(II) concentration elevated the concentration gradient between the bulk solution and the surface of the adsorbent. As presented in Table 2, Adsorption data fit Langmuir better than Freundlich isotherms. 120 110 100 90 80 70 60 50 40 30 5 10 15 20 25 Equilibrium solution concentration(mg L -1 ) Fig. 3 Adsorption of cadmium with equilibrium solution concentration by M-Fe 3 O 4 /GN Table 2 Isotherm parameters for removal of Cd(II) Langmuir Isotherm Constants Freundlich Isotherm Constants q m (mg/g) K L (L/mg) R 2 K F (L 1/n g -1 mg 1-1/n ) n R 2 M-Fe 3 O 4 /graphene 125.00 0.635 0.989 57.730 3.647 0.815
1014 Chemical, Material and Metallurgical Engineering III Conclusions (1) Fe 3 O 4 NPs were well anchored onto graphene and the product was chemically modified with MPTES successfully. (2) Cd(II) uptake onto M-Fe 3 O 4 /GN is favorable by the Pseudo secondary order kinetic model. (3) Adsorption data fit Langmuir better than Freundlich isotherms and the maximum adsorption capacity reached 125.00 mg/g. References [1] G. Tan, D. Xiao, Journal of hazardous materials, 164 (2009) 1359-1363. [2] J.O. Esalah, M.E. Weber, J.H. Vera, The Canadian Journal of Chemical Engineering, 78 (2000) 948-954. [3] M. Irani, A.R. Keshtkar, M.A. Moosavian, Chemical Engineering Journal, 200-202 (2012) 192-201. [4] S. Mustafa, M. Waseem, A. Naeem, K.H. Shah, T. Ahmad, S.Y. Hussain, Chemical Engineering Journal, 157 (2010) 18-24. [5] S. Bai, X. Shen, RSC Advances, 2 (2012) 64-98. [6] G. Zhao, L. Jiang, Y. He, J. Li, H. Dong, X. Wang, W. Hu, Advanced materials, 23 (2011) 3959-3963. [7] X. Deng, L. Lü, H. Li, F. Luo, Journal of hazardous materials, 183 (2010) 923-930. [8] X. Mi, G. Huang, W. Xie, W. Wang, Y. Liu, J. Gao, Carbon, 50 (2012) 4856-4864. [9] S. Stankovich, D.A. Dikin, G.H. Dommett, K.M. Kohlhaas, E.J. Zimney, E.A. Stach, R.D. Piner, S.T. Nguyen, R.S. Ruoff, Nature, 442 (2006) 282-286. [10] Y. Zhang, B. Chen, L. Zhang, J. Huang, F. Chen, Z. Yang, J. Yao, Z. Zhang, Nanoscale, 3 (2011) 1446-1450. [11] Y.-P. Chang, C.-L. Ren, J.-C. Qu, X.-G. Chen, Applied Surface Science, 261 (2012) 504-509. [12] J.-H. Deng, X.-R. Zhang, G.-M. Zeng, J.-L. Gong, Q.-Y. Niu, J. Liang, Chemical Engineering Journal, 226 (2013) 189-200. [13] D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z. Sun, A. Slesarev, L.B. Alemany, W. Lu, J.M. Tour, Acs Nano, 4 (2010) 4806-4814. [14] M. Arvand, M.A. Pakseresht, Journal of Chemical Technology & Biotechnology, 88 (2013) 572-578. [15] I. Langmuir, Journal of the American Chemical society, 40 (1918) 1361-1403. [16] H. Freundlich, Z. Phys. Chem, 57 (1906) 385-470. [17] V. Chandra, J. Park, Y. Chun, J.W. Lee, I.-C. Hwang, K.S. Kim, ACS nano, 4 (2010) 3979-3986. [18] X. Wang, W. Xing, L. Song, B. Yu, Y. Hu, G.H. Yeoh, Reactive and Functional Polymers, (2013).
Chemical, Material and Metallurgical Engineering III 10.4028/www.scientific.net/AMR.881-883 Adsorption of Cd(II) from Aqueous Solution by Magnetic Graphene 10.4028/www.scientific.net/AMR.881-883.1011