Regular Article
Electrochemical co-preparation of cobalt sulfide/reduced graphene oxide composite for electrocatalytic activity and determination of H2O2 in biological samples

https://doi.org/10.1016/j.jcis.2017.08.087Get rights and content

Abstract

In this work, we describe a simple approach for the preparation of cobalt sulfide/reduced graphene oxide (CoS/RGO) nanohybrids via single step electrochemical method. The electrocatalytic activity of the CoS/RGO nanohybrids was evaluated towards the detection hydrogen peroxide (H2O2). The physiochemical properties of the prepared composite was characterized by means of field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and X-ray powder diffraction patterns. The CoS/RGO modified electrode showed superior electrocatalytic activity towards the detection of H2O2. The amperometric (i-t) studies revealed that the CoS/RGO performed well by attaining a wide linear response range of H2O2 from 0.1 to 2542.4 μM with a lower detection limit 42 nM and the sensitivity of 2.519 μA μM−1 cm−2. Meanwhile, the CoS/RGO nanohybrids exhibited good selectivity, rapid and stable response towards H2O2. The practical applicability of the sensor was successfully evaluated in human serum and urine samples with satisfactory recoveries.

Introduction

Transition metal sulfides/oxides are act as a highly efficient and low cost material for various potential applications particularly in the field of electrocatalysis and energy storage devices [1], [2], [3], [4], [5]. Specifically, cobalt sulfide (CoS), is a phase dependent catalyst e.g., Co1−xS, CoS, CoS2, Co9S8, and Co3S4, have been widely used in different potential applications such as lithium-ion batteries [6], [7], [8], [9], [10], [11], [12], solar cells [13], [14], [15], supercapacitors [16], [17], [18], electrochemical sensor [19], [20] hydrogen evaluation and oxygen reduction reaction [21], [22], [23], [24], [25], [26], [27], [28]. Besides, cobalt sulfides have also been considered as an important material due to their distinctive magnetic, catalytic, electrical properties and their potential applications for hydrodesulfurization and hydrodearomatization in many industrial fields [6], [7], [8]. Moreover, various methods have been adapted for the synthesis of CoS nanohybrids such as hydrothermal synthesis, plasma treatment, solvothermal synthesis, pyrolysis and so on. However, these methods have some drawbacks, such as high cost, hazardous chemicals usage, doing experiments in higher temperature, time consuming and following the tedious protocol. On the other hand, the electrochemical method has tremendous advantage for material synthesis, because it is very simple and low cost method also it is less time consuming process and do not required high temperatures. Hence, in this work, we aims to use electrochemical method for the single step preparation of CoS/RGO nanohybrids [17].

Carbon based materials such as carbon aerogel [29], activated carbon [30], porous carbon [31], graphene [32], etc., offers several advantages over decades due to their specific high surface area, good conductivity, low cost and environmental friendly. Reduced graphene oxide (RGO), is a two dimensional sp2 graphitized carbon nanosheets, provides ultrahigh surface area with strong mechanical strength and good chemical stability [33]. In addition, the functionalities that present in the RGO can be used for the nucleation and anchoring the nanocrystals to achieve the covalent attachment of the hybrid nanomaterials [34], [35]. Previous studies proved that graphene supported metal oxides, hydroxides, and sulfides exhibited superior electrochemical performance for various potential applications including electrochemical sensors [26], [27], [28], [36]. Moreover, the metal sulfide based H2O2 sensor has been reported previously, but few reports are available in the literature using CoS modified electrode. Based on these, we used CoS and RGO as an active material for the effective and enhanced the electrocatalytic activity towards the detection of H2O2. Hence, in this work, we prepared the CoS/RGO nanohybrids and used it for the non-enzymatic hydrogen peroxide sensor application.

Hydrogen peroxide (H2O2) is simplest colorless peroxide and play a crucial role in biological system. Besides, it is widely applicable in pharmaceutical industries, clinical studies, environmental protection, food, and many other clinical process [37]. In addition, H2O2 is a reactive oxygen species and induced some disorders such as cancer, Alzheimer’s disease and Parkinson’s disease [33], [38]. Therefore, the detection of H2O2 in industrial and biological samples is inevitable. To date, numerous analytical methods have been utilized for the rapid and accurate detection of H2O2 including fluorescence, chemiluminescence, fluorimetry, photometry, spectrophotometry and electrochemical methods [38]. Among them, the electrochemical methods are more suitable for the low level and accurate detection of H2O2 because of their remarkable properties such as fast response, simple and low cost, higher sensitivity and user friendly. Hence, in this study, we focus to use the electrochemical method for the detection of H2O2.

In the present work, we report a facile approach for the preparation of CoS/RGO nanohybrids as an effective electrode material for non-enzymatic H2O2 sensor. The CoS/RGO nanohybrids were prepared by simple step electrochemical process, where cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and thiourea (CH4N2S) used as cobalt and sulfide precursor, respectively. To improve the electrocatalytic activity of the prepared material, we have optimized the deposition cycles and concentration of cobalt precursor. Interestingly, the optimized CoS/RGO nanohybrid exhibited an excellent electrocatalytic activity towards the H2O2 determination. In addition, the as-prepared CoS/RGO nanohybrids could be used for the detection of H2O2 in human serum and urine samples for practical applications.

Section snippets

Materials

Cobalt nitrate hexahydrate (Co(NO3)2·6H2O), thiourea (CH4N2S), monosodium phosphate (NaH2PO4) and disodium phosphate (Na2HPO4) were purchased from Aldrich. Hydrogen peroxide (H2O2) was obtained from Wako chemical industries, Taiwan. Human serum was collected from valley biomedical, Taiwan product & services, Inc and urine sample was collected from one healthy person in Taipei Tech. The supporting electrolyte, 0.05 M phosphate buffer saline (PBS) was prepared by using 0.05 M Na2HPO4 and NaH2PO4

Characterizations

The structural morphologies of as-prepared composites were characterized by field emission scanning electron microscope (FESEM) and the elemental analysis of the composite was examined by energy-dispersive X-ray spectroscopy (EDX) analysis. Fig. 1 displays the FESEM images of (A) GO, (B) RGO and (C) CoS/RGO composites. Fig. 1A depicts the FESEM image of GO, showed a crumbled like ultrafine thin layer morphology with the association of layer by layer assembly of several nanosheets. On the other

Conclusions

In summary, we demonstrated a simple and low cost method for preparation of the CoS/RGO nanohybrids based on single step electrodeposition process. The CoS/RGO nanohybrid showed superior electrocatalytic activity towards the detection of H2O2. Conversely, the CoS/RGO nanohybrids displayed a wide linear range, lower LOD and fast detection response towards H2O2 sensing. In addition, the CoS/RGO nanohybrid exhibited long term stability and good storage stability with excellent repeatability.

Acknowledgements

The financial supports for this work by the Ministry of Science and Technology (MOST), Taiwan.

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