Semiconducting Copper Oxide Nanostructure Material and Their Modified Electrode for Electrocatalytic Oxidation of Hydrazine and Glucose

DOI: https://doi.org/10.21203/rs.3.rs-2620328/v1

Abstract

The semiconducting copper oxide (CuO) nanostructure material is synthesized by carbon sphere used as template. The copper nitrate Cu(NO3)2 used as precursor and it has converted into CuO material like a Kernel structure with diameter 350 nm. It is applied to modify the glassy carbon electrode (GCE) for electro catalytic property of glucose and hydrazine oxidation; it shows a fast response and exhibited higher electro catalyst electrocatalytic oxidation of hydrazine and glucose. The electro catalytic behavior and applications were carried out by cyclic voltammetry in 0.1 M NaOH solution. The synthesized CuO nanomaterials have been characterized by FT-IR spectrum, X-Ray Photoelectron Spectra (XPS), DRS-UV spectra, Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray pattern (EDX).

1. Introduction

Nanostructure’s materials are more attention in the recent research activities due to its potential in various applications such as electro-catalysis, drug-delivery, sensitive biological molecules, filler materials and chemical industry [1–5]. The nanostructured CuO is promising development of the non-enzymatic glucose electrocatalytic oxidation, because of its high specific surface area, good electrochemical activity, and the possibility of promoting electron transfer reactions at a lower over potential. Previous attempts to utilize the CuO nanostructures for the amperometric determination of glucose are limited. Therefore, there still remains a need for simpler processes to synthesize CuO nanostructures with superior catalytic property for fast, stable determination of glucose [6–9].

Recently research work is being carried out by various scientific communities to develop the electrode was modified with the copper oxide (CuO) at low oxidation potentials. However, the modification of the electrode surface with nano-CuO plays an important role in the analysis of glucose [10–13]. And also, hydrazine is a reactive molecule with good reducing capabilities that can participate in diverse reactions resulting in numerous applications. It is widely used as a catalyst, emulsifier, corrosion inhibitor, antioxidant, reducing agent, and oxygen scavenger. More specifically, hydrazine is used for water treatment, in agriculture, in pharmaceuticals as a chemical blowing agent, as an oxygen scavenger in boilers and hot-water heating systems to control corrosion, and in a wide variety of other applications. Therefore, the electro-oxidation of hydrazine is very important in the field of environmental and biological analysis [14–16]. This article deals with the synthesis of copper oxide nanomaterials using carbon sphere assisted solution phase growth method and its effect on the surface modification of the glassy carbon electrode. The surface modified glassy carbon electrode was further studied for the electrochemical catalysis of glucose and hydrazine.

2. Experimental

2.1. Synthesis of CuO nanomaterial

The Copper nitrate (0.02M) is dissolved in 200 ml of distilled water and stirred for 10 hours with 2.00 g of carbon sphere at room temperature [17]. The resulting reaction mixture was centrifuged at 8000 rpm to reclaim the precipitated product. The final product was filtered, washed with deionized water and ethanol several times and finally dried at 100◦C for 3 h and followed by combustion at 700oC using muffle furnace for 5 hours. It yields the copper oxide (CuO) material.


2.2. Instruments and modified electrode preparation

The CuO material structure and size of is observed and analyzed by the FESEM (HI-2108-0002- FESEM SU6600 HITACHI Ltd., Japan), and HRTEM (JEOL-3010 300 kV). The FT-IR spectrum is recorded on Bruker instruments in the range of 4000–400 cm− 1 by using KBr disks. The X-ray diffraction pattern is carried out by XRD 3003 TT instrument, which acquires 2θ range in 10°–70°. The electrochemical experiment is carried out by the CHI620A electrochemical analyzer at 25°C, with three electrode systems.

The reference and counter electrode are used as Ag/AgCl and Pt electrode respectively; all the potential is referred to Ag/AgCl reference electrode. The GCE is washed with concentrated ammonia and 1:1 ratio of concentrated nitric acid and water. Further, these GCE is polished with alumina powder (0.03 mm), and then washed with water, followed by drying, at room temperature. The CuO HNS is dispersed in 0.4% of nafion mixed with ethanol (used as binding agent), and dry at room temperature, then easily modified on the surface of GCE. The CuO material modified GCE is used as a working electrode in electrochemical oxidation. The NaOH (0.1M) solution is used as electrolyte for the electrochemical measurement; it is purged with nitrogen gas for 10 min to remove any dissolved oxygen.

3. Results And Discussion

3.1. DRS/UV analysis of CuO nanomaterial

The DRS/UV spectrum of the CuO nanomaterial was shown in Fig. 1(a). In accordance with the data published by Vicente Rives et al. [25]. The CuO peak appeared at 281 nm, correspond to the charge transfer transition between the oxygen and the metal ion (O → Cu2+). It is relatively easy to realize the corresponding band gap which is found in 4.41 eV and it is used as P-type of semiconductors. The above-mentioned band gap of the CuO materials is calculated by using Eg = hc/λ, where h = Plank’s constant, c = velocity of light, and λ = wavelength [17]. The synthesized CuO nanoparticles have nanometer scale; it is confirmed by the ban gap energy.

3.2. FT-IR analysis of CuO nanomaterial

The FT-IR spectrum of the synthesized copper oxide (CuO) material is shown peaks at two regions. In the first region appeared strong absorption band is observed at 533 cm− 1 and 1035 cm− 1, it is shown in Fig. 1(b) due to the stretching vibration of Cu-O in monoclinic phase [18]. A weak absorption peak is observed in the second region at 1386 cm− 1 and 1624 cm− 1 due to the presence of moisture in air [19, 20]. No other peak has appeared in FT-IR spectra. Finally, we can conclude the FT-IR spectrum confirms the strong characteristic peaks of Cu-O stretching vibration for the formation of CuO nanomaterial.

3.3. XRD analysis of CuO nanomaterial

The X-ray diffraction (XRD) pattern of the synthesized CuO nanomaterial is shown in Fig. 2(a). The peaks obtained and is found to be match well with the pattern of the mono clinic CuO (JCPDS No. 05-0661) with cell parameters a = 4.684 °A, b = 3.425 °A, c = 5.129 °A, and β = 99.47. The peaks are appeared at 2θ values of 32.4°, 35.4°, 38.6°, 48.7°, 53.5°, 58.2°, 61.5°, 65.75°, 66.2° and 68.0° corresponds to the crystal planes of (110), (002), (111), (200), (020), (202), (022), (310), (220), (113), respectively [21, 22]. No impurity peaks are detected in the spectrum, which indicates the complete conversion of Cu(NO3)2 precursors into CuO nanomaterial and also confirms the complete removal of CS at 700oC.

3.4. XPS analysis of the CuO nanomaterial

X-ray photoelectron spectroscopy (XPS) is a powerful technique used for the study of transition metal oxide compounds having localized valence d orbitals. The typical characterization of the XPS measurement was shown in Fig. 2(b). In CuO, the copper exists in the divalent state having mainly d9 character. The XPS data detected the Cu 2p3/2 and Cu 2p1/2 peaks appeared at 933.6 and 953.7 eV, respectively confirming the same. The Cu 2p3/2 peak showed the main peak accompanied by a series of higher binding energy peaks at 941.4, and 943.5 eV [23, 24]. The peaks are evident and indicative of an open 3d9 shell, corresponding to Cu2+ state.

3.5. FE-SEM analysis of CuO nanomaterial

The FESEM images of the synthesized CuO nanomaterial were shown in Fig. 3. It is very interesting to observe that these material are formed in different morphology, especially kernel like structures as shown in the higher magnification images (Fig. 3b,c). The size of kernels structure was found to be in the range of 350–400 nm [26, 27]. The typical size of flower was observed to be around 600 nm [28]. The corresponding EDX pattern of CuO nanomaterial was shown in Fig. 3(e) and the higher intensity peaks appeared at 1.0 keV and 8.0 keV correspond to Cu and the peak at 0.5 keV for the corresponding to O elements.

3.6. Electrochemical behavior and oxidation of glucose at CuO nanomaterial

The electrochemical behavior of synthesized CuO nanomaterial is modified on the surface of GCE, shown in Fig. 4. The studies were carried out using the deoxygenated 0.1 M NaOH as electrolyte at different scan rate like 40, 60, 80, 90, 100, 110, 120 mV/s, with the potential range from − 0.6 to 0.8 V. The results obtained were shown in Fig. 4(A). The CuO-modified GCE displayed a single irreversible reduction peak appeared at 0.303 V (vs. Ag/AgCl), while it exhibits less reduction potentials.

The electro catalytic study of the CuO nanomaterial modified GCE was carried out using deoxygenated 0.1 M NaOH solution, in the presence and absence of glucose, corresponding results shown in Fig. 4(B). A small background current was observed with the CuO nanomaterials modified GCE in the absence of glucose, which is indicated by dashed line in Fig. 4B(a). Whereas a dramatic increase of current was observed with the CuO modified GCE in the presence of glucose, due to the catalytic oxidation of glucose by CuO nanomaterial, which is indicated by solid lines in Fig. 4B(b-d). The significant oxidation of glucose at starting potential of 0.303 V (vs. Ag/AgCl), implies a strong electrocatalytic function towards glucose oxidation [29, 30]. In contrast, no obvious redox activity is observed at the bare GCE over most of the potential range. The electrochemical oxidation of glucose take place at less concentrations with less over-potential at the surface of this CuO nanomaterial modified GCE, compared with the reported by C.B Mc Auley et.al [29]. The oxidation current vs. concentration glucose is increased linearly from 0.5 to 1.5 µM of glucose (inset figure, Fig. 4B). The limit of detection was found to be 1.7×10− 7M with a correlation coefficient R2 = 0.998, intercept = 4.66 and slope = 6.8 µA/µM.

3.7. Amperometric study of glucose

The amperometric response of CuO nanomaterial modified GCE toward glucose oxidation was investigated by successively adding glucose to a continuous stirring deoxygenated 0.1 M NaOH solution. This measurement was carried out by an operation potential at 0.6 V (according to anodic peak potential ≥ 0.603 V). The typical current–time curve of the CuO nanomaterial modified GCE is shown in Fig. 5(a). There is a linear relation of the oxidation current with concentration of glucose between 0.5 µM and 2.5 µM with a correlation coefficient of 0.987, as shown in Fig. 5(b). From the slope of the calibration curve, the detection limit is calculated to be 2.38×10− 7 M. The steady-state current responses were obtained in 0.60 V applied potential, and the currents increased stepwise with successive additions of glucose [31, 32]. Such a fast response time may be attributed to fast diffusion of glucose.

In order to study the stability of the modified electrode, amperometric measurements were performed in the presence of 0.5 µM glucose periodically. When not in use, the electrode was suspended above 0.1M NaOH at 4°C in a refrigerator. The response to 0.5 µM glucose was tested intermittently. After storage for 1 week, the response of the electrode was maintained 95% of the initial values. The electrode still retained 93% of its original values after 2 weeks. The storage stability may be attributed to the stable film of CuO nanomaterial.

3.8. Electrochemical oxidation of N2H4

The electrochemical oxidation of hydrazine (N2H4) at the CuO nanomodified GCE was explored in Fig. 6, in the presence of deoxygenated 0.1 M NaOH solution containing 0.5, 1.0, and 1.5 µM of N2H4, at the scan rate of 50 mV/s. Only charging current was obtained at the bare GCE. However, presence of N2H4 exhibited an obvious anodic peak at the CuO nanomaterial modified GCE, representing that electrocatalytic function at higher concentration of N2H4, the starting oxidation potential was at 0.525 V (vs. Ag/AgCl) [33–35]. The electrochemical oxidation response was irreversible, as no cathodic current was observed during the reverse sweep. The electro oxidation of hydrazine is much sharper, which reflects a faster electron-transfer reaction and owing to less required over potential for oxidation of hydrazine.

4. Conclusion

The flower and kernel like CuO nanomaterial is synthesized by carbon sphere assisted solution phase growth method, using aqueous solutions of copper nitrate. Here the carbon sphere is used to assist in the formation of kernel-like structure material, which is exhibits an excellent non-enzymatic glucose and hydrazine electro catalytic oxidation at various concentration. The synthesized CuO nanomaterial modified GCE shows fast response, good stability to oxidation, which may be attributed to the chemical stability, preferred to the oxidation of hydrazine and glucose. These results indicate that, this CuO nanomaterial will have great potential application in electrochemical determination of glucose and hydrazine.

Declarations

Conflict of Interest: 

The authors declare that they have no conflict of interest.

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