Kinetics of the adsorption of Pb(II) ions from aqueous solutions by graphene oxide and thiol functionalized graphene oxide Mohammad Yari a, ⁎, Mostafa Rajabi b , Omid Moradi c, ⁎, Ali Yari c , M. Asif d , Shilpi Agarwal e , Vinod Kumar Gupta e,f, ⁎⁎ a Department of Chemistry, Eslamshahr Branch, Islamic Azad University, Eslamshahr, Iran b Department of Chemistry, Arak Branch, Islamic Azad University, Arak, Iran c Department of Chemistry, Shahre-Qods Branch, Islamic Azad University, Tehran, Iran d Chemical Engineering Department, King Saud University Riyadh, Saudi Arabia e Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India f Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa abstract article info Article history: Received 11 March 2015 Received in revised form 9 May 2015 Accepted 12 May 2015 Available online xxxx Keywords: Graphene oxide Cysteamine Thiol functionalization Pb (II) Adsorption Kinetics Adsorption capacity of Pb 2+ on graphene oxide and thiol functionalized graphene oxide was well investigated and illustrated in the present work. Variable cysteamine concentrations i.e., 60, 80 and 100 mg were used as functionalizing agent for conversion of graphene oxide to thiol functionalized graphene oxide. The surface of graphene oxide (GO) was functionalized by the use of 60 mg of cysteamine (GO-SH 1 ), by 80 mg of cysteamine (GO-SH 2 ) and by 100 mg of cysteamine (GO-SH 3 ), respectively. The prepared adsorbents were characterized using Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The impact of several influential parameters such as adsorption time, pH, temperature and cysteamine concentrations on Pb 2+ adsorption was well elucidated and optimized. The optimized values of adsorbent dose, initial concentra- tion of Pb 2+ , contact time, and pH were found to be 20 mg, 25 mg/L, 60 min and 6 respectively at a temperature of 298 K. The kinetic experimental data for GO surface was well fitted and found to be in good agreement with type (II) of pseudo-second-order model, and for GO-SH 1, GO-SH 2, and GO-SH 3 the experimental data was in good agreement with pseudo first-order model, type (IV) of pseudo-second-order model and type (II) of pseudo-second-order model respectively. Results revealed that the adsorption capacity of Pb 2+ on to the devel- oped adsorbent increases with the increase in temperature, hence this process was endothermic in nature. © 2015 Published by Elsevier B.V. 1. Introduction Water pollution nowadays is a global issue due to the rapid urbani- zation and development of the industrial zone. Among the various nox- ious contaminants, heavy metals are considered as one of the most toxic ones due to their hazardous effects to aquatic organisms, plants, animals and biotic organisms of the ecosystem. One of the non-biodegradable noxious heavy metal is Pb 2+ , which is present in the effluents of many industry and factory outlets such as mining, smelting, galvaniza- tion, metal finishing and battery manufacturing [1,2]. Lead is an inor- ganic toxicant present in natural water environments; studies have shown that young children, infants and pregnant women are particular- ly susceptible to unsafe lead levels [3,4]. Many conventional methods have been used for the rapid removal of toxic metal ions from aqueous solutions including sedimentation, chemical treatment, oxidation, electrochemical methodology [5–13], bi- ological treatment, reduction, precipitation, membrane filtration, ion exchange and adsorption [14]. Among all the techniques, adsorption is a well-known equilibrium separation process and an effective method for water decontamination applications [15]. Adsorption was found to be superior over other traditional techniques for water purification and decontamination in terms of initial cost, flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants. It also does not result in the formation of any other harmful secondary pollut- ant [15]. So far, researchers have tested many different types of devel- oped adsorbents such as carbon nanotubes [16–23], MWCNTs [24,25], nanoparticles and nanocomposites [26–30], rubber tire [31,32], and other low cost adsorbents [33–38] etc. are used for the removal of nox- ious impurities from the aqueous solution. Therefore a keen attention and serious effort from researchers are required to remove these nox- ious metals from the aqueous solution, in order to do this tremendous Journal of Molecular Liquids 209 (2015) 50–57 ⁎ Corresponding authors. ⁎⁎ Correspondence to: V.K. Gupta, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India. E-mail addresses: dr.m.yari1966@gmail.com (M. Yari), o.moradi@shahryaiu.ac.ir, moradi.omid@gmail.com (O. Moradi), vinodfcy@gmail.com, vinodfcy@iitr.ac.in (V.K. Gupta). http://dx.doi.org/10.1016/j.molliq.2015.05.022 0167-7322/© 2015 Published by Elsevier B.V. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq