Mechanistic aspects of enhanced congo red adsorption over graphene oxide in presence of methylene blue Deepak Kumar Padhi a,b , K.M. Parida a,c, *, S.K. Singh a,b a Academy of Scientiﬁc and Innovative Research (AcSIR), Council of Scientiﬁc and Industrial Research, Anusandhan Bhawan, 2 Raﬁ Marg, New Delhi 110 001, India b Advanced Materials Technology Department, CSIR-Institute of Minerals and Materials Technology, Bhubaneswar, 751013 Odisha, India c Centre for Nano-Science and Nano-Technology, ITER, SOA University, Bhubaneswar, 751030 Odisha, India A R T I C L E I N F O Article history: Received 5 April 2016 Received in revised form 16 June 2016 Accepted 13 July 2016 Available online 15 July 2016 Keywords: Graphene oxide Electrostatic interaction pH Dye adsorption mechanism A B S T R A C T To elucidate the role of cationic dye for the enhanced adsorption of anionic dye over Graphene oxide(GO), we have made a novel approach to evaluate the adsorption capacity of GO for removal of Congo red (CR) from aqueous system in presence of Methylene blue (MB). Physicochemical and spectroscopic techniques have been used to assertion the interaction of dye molecules with the surface of GO. At pH = 2, GO possessed 96% adsorption capacity towards CR in presence of MB. The existing pH dependant electrostatic interaction mechanism between CR and MB dye has been explained for enhanced CR adsorption over GO surface. Fourier transform infrared spectroscopy and Raman spectrum of dye adsorbed GO also gives well support to evaluate the extent of electrostatic interaction between oxygen containing functional groups and functional moieties of dye resulting in good adsorption over GO surface. ã 2016 Elsevier Ltd. All rights reserved. 1. Introduction Graphene oxide (GO), a 2D-allotrope of carbon has stimulated signiﬁcant interest in recent years due to its extraordinary physicochemical and mechanical properties [1–4]. In fact, the structure of graphite and graphene is almost clear, but the deﬁnite structure of GO hasn’t concluded yet as its structure depends on the synthesis process and the raw materials used. Generally, it is accepted that most of oxygen atoms on GO are present in the form of hydroxyl and epoxide functional groups on its basal planes and a few in the form of carbonyl and carboxyl groups at the sheet edges [5]. The presence of these oxygen bearing functional groups on the GO surface render it as hydrophilic and high negative charge density in aqueous medium. Through dispersion or stirring, GO exists as single layer and forms stable colloid in solution phase for which it can act as weak acid cation resin and adsorbs positively charged species like organic molecules [6], metal ions [7], polymer [8] and bio-molecules [9]. As civilisation is developing, the use of several organic dyes is also increasing in various industries like cosmetics, food, textiles, paper etc. The wastes from these industries are toxic and carcinogenic in nature for which they badly inﬂuence the quality of water resulting in various undesirable consequences [10]. Hence, design of efﬁcient, novel and cost effective materials is very important for dye removal by the process of adsorption, ion exchange, coagulation, precipitation, oxidation, ﬁltration etc. [11–13]. Among all the processes, adsorption is versatile and simple, easy and cost effective. In this regard many groups have reported the adsorption capacity of GO for the removal of various organic dyes. Wang et al. has reported GO possesses 351 and 248 mg g 1 for Methylene blue (MB) and Malachite green (MG) respectively based on Langmuir isotherm which is much higher than activated carbon [14]. Sampath et al. investigated both cationic and anionic dye adsorption over GO and reduced graphene oxide (RGO) and explained all cationic dyes and anionic dyes can be efﬁciently adsorbed over GO and RGO, respectively [15]. Barkaus- kas et al. investigated the electrostatic interaction of NH 2 and SO 3 groups of Congo red (CR) dye molecule with the oxygen containing functional of GO in aqueous media [16]. Wang et al. reported the inﬂuence of temperature, pH, ionic strength, and dissolved organic matter (DOM) content on the adsorption capacity of GO for MB [17]. Das et al. have studied factors affecting the removal of MG * Corresponding author at: Academy of Scientiﬁc and Innovative Research (AcSIR), Council of Scientiﬁc and Industrial Research, Anusandhan Bhawan, 2 Raﬁ Marg, New Delhi 110 001, India. E-mail addresses: paridakulamani@yahoo.com, kmparida@immt.res.in (K.M. Parida). http://dx.doi.org/10.1016/j.jece.2016.07.011 2213-3437/ã 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Chemical Engineering 4 (2016) 3498–3511 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/je ce