Sensors and Actuators B 177 (2013) 612–619 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o me pa ge: www.elsevier.com/locate/snb Electrochemical studies of two diphenols isomers at graphene nanosheet–poly(4-vinyl pyridine) composite modified electrode Ramin M.A. Tehrani a,∗ , Hanieh Ghadimi b , Sulaiman Ab Ghani b,∗∗ a Department of Chemistry, Shahre Rey Branch, Islamic Azad University, Tehran, Iran b Pusat Pengajian Sains Kimia, Universiti Sains Malaysia, 11800 USM, Pulau Pinang, Malaysia a r t i c l e i n f o Article history: Received 27 August 2012 Received in revised form 12 November 2012 Accepted 14 November 2012 Available online 24 November 2012 Keywords: Diphenols Hydroquinone Catechol Graphene sheet Poly (4-vinyl pyridine) a b s t r a c t A voltammetric sensor for hydroquinone (HQ) and catechol (CC) was developed. This was realized by mod- ifying a glassy carbon electrode with composite film of graphene nanosheet and poly(4–vinylpyridine) (GR–P4VP/GCE). The smaller peak potential separation (E p ) of the GR-P4VP/GCE indicates the elec- trode process is very reversible as a result of increase in kinetics of electron transfer as and when P4VP was present in the modified electrode as compared to the GR/GCE and bare GCE. The pro- posed electrode has displayed a synergistic effect of P4VP and GR on the electrocatalytic oxidation of CC and HQ in sodium sulphate buffer solution (pH 2.5). The anodic peak potential, E pa , of both were clearly resolved in either cyclic voltammetry or differential pulse voltammetry which made simultaneous determination of both compounds possible. The GR–P4VP/GCE has exhibited excel- lent sensitivities in the measurement of HQ and CC with detection limits of 8.1 nM and 26 nM, respectively. The GR–P4VP/GCE developed was not interfered by traditional interferences, viz. phe- nol, nitrophenol, aminophenols, bisphenol A and chlorophenols. The GR–P4VP/GCE was successfully applied for simultaneous detection of spikes HQ and CC in tap water and lake water with encouraging results. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The simultaneous determination and isolation of phenolic com- pounds is of interest in many fields, such as medical, food and environmental controls [1–3]. Hydroquinone (HQ) and catechol (CC) are two isomers of diphenols. They are toxic to humans and difficult to degrade [3]. Furthermore, the simultaneous detection of HQ and CC is highly desirable as they usually coexist in prod- ucts due to their similarities in structures and properties [2,3]. Therefore, it is necessary to develop rapid and simple analyti- cal methods for sensitive and selective determination of HQ and CC. Graphene (GR) has been used extensively in electrochemical sensors because of its excellent conductivity, high specific surface area; high mechanical, thermal and chemical stabilities compared with graphite and carbon nanotubes [4–6]. Its unique crystal struc- ture makes it extremely attractive as a support material to promote the electrochemical reactivity of molecules on the modified elec- ∗ Corresponding author. Tel.: +98 21 55229321; fax: +98 21 55229283. ∗∗ Corresponding author. Tel.: +60 4 6534030; fax: +60 4 6574854. E-mail addresses: rmt@iausr.ac.ir (R. M.A. Tehrani), sag@usm.my (S. Ab Ghani). trode surface [7,8]. In spite of all these, functionalization and dispersion of graphene sheets are also crucial in their applica- tions. The functionalized and defective graphene sheets are more hydrophilic and can be easily dispersed in solvents with long-term stability [6,9]. In addition, appropriate chemical functionalization of graphene for example by conventional acid treatment method, for formation of–COOH and–OH groups, prevents the agglomera- tion of single layer graphene and aggregation can also be reduced by the attachment of other small molecules or polymers to the graphene sheets [6,10,11]. Meanwhile, non-covalent functional- ization, e.g., co-dispersion with polymers has proven successful in solubilizing graphene nanosheet [1]. At present, a number of methods have been developed to deter- mine CC and HQ, such as chromatography [12], spectrophotometry [13], capillary electrophoresis [14], chemiluminescence [15], pH based-flow injection analysis [16] and electrochemical methods [17–19]. The electrochemical methods have their advantages in various aspects such as excellent sensitivity, high accuracy, good reliability and low cost of instrumentation compared to the other modern techniques. Thus, they become more desirable methods for environmental and industrial analysis of CC and HQ [2,20]. How- ever, the application of conventional electrodes has its drawback in that the overpotential for oxidation of CC and HQ is high, detection 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.11.047