Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Evaluation of core-shell structured cobalt@platinum nanoparticles- decorated graphene for nitrite sensing R.M. Abdel Hameed ⁎ , Shymaa S. Medany Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt ARTICLE INFO Keywords: Platinum Cobalt Interference Nitrite Amperometry ABSTRACT A new graphene composite was fabricated with cobalt (core) and platinum (shell) nanoparticles [Co@Pt/Gr] in two-steps preparation method. This prepared electrode combined the enhanced electrocatalytic activity of platinum, increased electrical conductivity of cobalt and high surface area of graphene. Compared with Pt/Gr, Co@Pt/Gr exhibited lowered onset potential value for nitrite oxidation in 0.1 M phosphate buffer solution with increased current density. Some related kinetic parameters for nitrite oxidation at Co@Pt/Gr electrode were calculated including Tafel slope, the exchange current density, the diffusion coefficient and the heterogeneous electron transfer rate constant values. Amperometry measurements demonstrated wide linear nitrite con- centration ranges as 1 μM–2 mM and 2–15 mM with remarkably increased sensitivity values of 45.96 and 97.71 μA mM -1 cm -2 , respectively. Co@Pt/Gr electrode showed a selective response for nitrite determination in presence of common interferents. The reproducibility and stability experiments also revealed good results suggesting Co@Pt/Gr electrode for effective and valuable detection of nitrite in medicine and environmental chemistry. 1. Introduction During the nitrogen cycle, nitrites are produced from the oxidation of ammonia or reduction of nitrates [1]. Nitrite salts (sodium and po- tassium) are extensively used in food products as preservatives (E249, E250) or for fixing the clothes color. Nitrites were classified from World Health Organization (WHO) as a human health hazard. The maximum limit of nitrite in drinking water is 3 mg/L according to WHO [2]. The excessive concentration of nitrite ions in the blood leads to abnormal situations as a result of hemoglobin oxidation into methahemoglobin [3]. Formation of methahemoglobin reduces the oxygen amounts car- ried by blood resulting in blue baby syndrome or even death. The in- teraction between nitrite ions and secondary amines or amides to form N-nitrosoamines would progressively cause bladder cancer [4]. Dys- pnea, accelerated pulse, weakness, muscle tremors, vomiting and un- stable gait are observed when extensively exposed to nitrite ions. Cy- anosis and methemoglobinemia are another result for the exceeded dose of nitrite ions. This may exploit nitrite species to treat cyanide poisoning [5]. Ion chromatography, capillary electrophoresis and spectroscopy were reported as familiar techniques for the determination of nitrite ions concentration [6]. These methods have many deficiencies in- cluding time consumption, multi-step sample pretreatment and complicated protocol. Therefore, electrochemical methods have re- ceived more attention in this concern. They offered many advantages over the traditional methods such as fast response, simple operation, high sensitivity and low cost. Since nitrite is an electroactive species, it could be estimated through its oxidation or reduction processes [7,8]. Unfortunately, nitrite oxidation using bare electrodes such as platinum, glassy carbon, gold and diamond suffered from poison accumulation. The oxidation process was also observed at high potential values re- sulting in the generation of other species that affected its accuracy and sensitivity [9–11]. Accordingly, many challenges were directed to re- duce the measured overpotential values and increase the oxidation current density. Different modified electrodes were investigated for nitrite determination using metal nanoparticles [12,13], conducting polymers [14] or metal oxides [15]. Lowered nitrite oxidation peak potential value of 680 mV (SCE) was measured at metal-free nitrogen- doped reduced graphene oxide nanosheets. A linear relationship was drawn between nitrite concentration and oxidation peak current den- sity in the range of 0.5–5000 μM[16]. Nitrite oxidation was enhanced on reduced graphene/Pd nanocomposite modified glassy carbon elec- trode that was prepared by the electrochemical reduction of graphene oxide followed by electrochemical deposition of Pd nanoparticles. This modified electrode exhibited a high sensitivity value of 7.672 μA μM -1 cm -2 [17]. Kuralay et al. [18] have measured a low detection https://doi.org/10.1016/j.synthmet.2018.11.011 Received 2 August 2018; Received in revised form 7 November 2018; Accepted 14 November 2018 ⁎ Corresponding author. E-mail address: randa311eg@yahoo.com (R.M. Abdel Hameed). Synthetic Metals 247 (2019) 67–80 0379-6779/ © 2018 Elsevier B.V. All rights reserved. T