A highly sensitive electrochemical sensor for nitrite detection based on Fe2O3 nanoparticles decorated reduced graphene oxide nanosheets
Graphical abstract
Introduction
Highly sensitive detection of nitrite (NO2−) has attracted increasing attention in the past decades due to their detrimental effect on both environment and human health. The rapid increasing pollution of ground water resources for human consumption by nitrites due to the anthropogenic activities from agriculture (by using nitrogen based fertilizer) and waste water from industry is receiving worldwide attention [1], [2], [3], [4]. The World Health Organization has fixed the maximum limit of 3 mg L−1 for nitrite in drinking water [5]. Nitrite contamination in drinking water can cause different diseases such as methemoglobinemia or “Blue Baby Syndrome” and stomach cancer by the formation of N-nitrosamines when nitrite ions interact with amines [6], [7], [8]. Therefore, it is of great importance to accurately monitor nitrite for public health, environmental and food industries. Several analytical techniques have been developed for nitrite determination including spectrophotometry [9], chemiluminescence [10], capillary electrophoresis [11] and chromatography [12]. However, these analytical methods usually have expensive equipments, tedious detection procedure and often time consuming. Compared to these methods, the electrochemical method can provide compact, relatively inexpensive, reliable, sensitive and real-time analysis [13], [14]. Moreover, the development of a rapid electrochemical method for nitrite detection without the sample pretreatment prior to analysis and also no interference from other sources (such as nitrate, sulfate, bromate ions and oxygen) is highly important. Recently, different kinds of electrochemical nitrite sensors have been fabricated based on the chemical modification of electrode [15], [16], [17], [18], [19].
Carbon nanostructures (fullerenes, carbon nanotubes and graphene) have been extensively used in electrochemistry due to the small residual current, wide potential window, excellent chemical stability in various electrolytes and easy renewable surface. It is well known that graphene (an ideal two-dimensional layered material) has been extensively used for growing and anchoring of metal oxide nanoparticles due to their unique physical and chemical properties. In this decade, metal oxide/graphene composite materials (SnO2/graphene, Cu2O/graphene, Co3O4/graphene, etc.,) have attracted a great deal of attention due to their improved electrochemical properties [20], [21], [22]. Recently, Zhang et al. [23], prepared the sensor of Cu dendrites and reduced graphene oxides, which displayed electrocatalytic activity to the detection of nitrite. Zhang et al. [24], reported the electrochemical synthesis of reduced graphene oxide/palladium nanocomposite on GC electrode, and proposed film showed good electrocatalytic activity toward oxidation of nitrite. Cui et al. [25], fabricated a composite film containing graphene nanosheets and carbon nanospheres, and then they studied its electrochemical properties, and electrocatalytic activity toward the nitrite oxidation in the presence of chitosan coated Prussian blue as redox mediator.
Hematite (Fe2O3), as an important n-type metal oxide with a narrow band gap (Eg = 2.2 eV), has received considerable attention in recent years due to its low cost, non-toxicity, easy of production and easy of storage. It has been deeply investigated because of its wide applications in catalysts, pigments, magnetic materials, gas sensors, biosensors and lithium ion batteries [26], [27], [28], [29], [30]. Several approaches have been used to synthesis metal oxide/graphene sheets hybrids; pyrolysis, thermal annealing, chemical reduction, microwave irradiation and sonochemical [31], [32], [33], [34], [35]. Further, these processes involve two steps, which involve the reduction of graphene sheets by thermal annealing or adding toxic hydrazine. Hence, these methods are obviously involving complicated experimental protocol with high energy consuming and sophisticated instrumentation techniques. Therefore, facile material preparation and electrode modification protocol with improved catalytic performance of nitrite is urgently required.
In this paper, we report the fabrication, characterization and analytical performance of a nitrite sensor based on the Fe2O3/reduced graphene oxide (rGO) composite modified glassy carbon (GC) electrode by a very simple technique. The Fe2O3/rGO composites were synthesized in ethanol by a one-step hydrothermal approach and used for the sensitive detection of nitrite for the first time. The performance of the newly fabricated nitrite sensor was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) and the results are discussed. The fabricated sensor showed high sensitivity, stability and satisfactory reproducibility.
Section snippets
Materials
Ferrous chloride and ammonia are purchased from Daejung Chemicals Ltd, South Korea. Sodium nitrite is obtained from Sisco Research Laboratories, India. The phosphate buffer solutions with different pH values were prepared using Na2HPO4 and NaH2PO4. All the reagents were of analytical grade and used without further purification.
Instrumentation
The surface morphologies of the prepared materials were characterized using a field emission-scanning electron microscope (FE-SEM) JEOL JSM-6700F. The phase purity and
Characterization of the as-prepared Fe2O3/rGO composite
The microstructure and morphology of the GO, rGO, Fe2O3/rGO composite and Fe2O3 were characterized by FE-SEM. Fig. 1 shows the FE-SEM micrographs of the GO (A) and rGO (B), in which the GO and rGO appears corrugated into a wrinkle shape. Fig. 1C shows the Fe2O3/rGO composite, it can be seen that the Fe2O3 nanoparticles were well decorated on the reduced graphene oxide sheets. These results clearly indicate the presence of strong interaction between rGO and Fe2O3 nanoparticles. The highly
Conclusion
We have demonstrated the synthesis of Fe2O3/rGO composite by an environment-friendly approach and their application in voltammetric determination of nitrite in neutral medium. The Fe2O3/rGO modified electrode provided a sheet like structure with large effective surface area, which could act as electron transfer medium and promote the charge transfer between electrode surface and nitrite. The sensitivity and detection limit for the fabricated nitrite electrochemical sensor have been found to be
Acknowledgement
This research was supported by a National Research Foundation of Korea Grant under contract 2011-0015829.
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