A Facile One-Pot Synthesis of Au/Cu2O Nanocomposites for Nonenzymatic Detection of Hydrogen Peroxide
© Chen et al. 2015
Received: 10 April 2015
Accepted: 13 May 2015
Published: 3 June 2015
Au/Cu2O nanocomposites were successfully synthesized by a facile one-pot redox reaction without additional reducing agent under room temperature. The morphologies and structures of the as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The electrocatalytic performance of Au/Cu2O nanocomposites towards hydrogen peroxide was evaluated by cyclic voltammetry (CV) and chronoamperometry (CA). The prepared Au/Cu2O nanocomposite electrode showed a wide linear range from 25 to 11.2 mM (R = 0.9989) with a low detection limit of 1.05 μM (S/N = 3) and high sensitivity of 292.89 mA mM−1 cm−2. The enhanced performance for H2O2 detection can be attributed to the introduction of Au and the synergistic effect between Au and Cu2O. It is demonstrated that the Au/Cu2O nanocomposites material could be a promising candidate for H2O2 detection.
In recent years, the accurate determination of H2O2 has attracted considerable attentions because it is an important intermediate in various fields, such as food, pharmaceutical, clinical, industrial, and environmental analyses [1–4]. Up to now, a quantity of techniques including spectrometry , titrimetry , chemiluminescence , and electrochemistry  have been developed for the quantification of H2O2. Among the above-mentioned techniques, electrochemical method is attractive due to its low-expense, perfect selectivity, high-sensitivity, and straightforward manipulation [9–11]. Although the enzyme-based electrochemical H2O2 sensors exhibit obvious advantages of high selectivity, the complicated immobilization procedure, poor stability, and high cost of the enzymes still limit their extensive applications [12, 13]. Thus, the development of enzyme-free H2O2 sensors with peroxidase-like activity and enhanced performance has become a trend.
Nowadays, numerous materials have been successfully applied to construct nonenzymatic H2O2 sensors, such as Prussian blue, noble metals, transition metal oxides, carbon nanotubes, graphene, etc [1, 14–19]. It is well known that noble metals were widely used in H2O2 detection and displayed excellent performance. Particularly, Au nanomaterial exhibits good catalytic activity towards the detection of H2O2 owing to its outstanding conductivity, electroactivity, biocompatibility and nontoxicity . However, single-phase Au is too unstable to control synthesis, which suffers from difficulties such as the control of particle size, the use of stabilizing agent, and high cost. Hence, it has attracted increasing attention to Au-based nanocomposites. Up to now, Au-graphene nanosheet , Au-MnO2 , and Au-Fe3O4  have been reported to build H2O2 sensors. However, the preparation of these materials is a complicated and difficult process. Au nanoparticles were prepared by a few steps in advance and Au-based nanocomposites were obtained using various assistants under specific conditions. It is multistep, time consuming and high cost. Hence, it is essential to develop a green, environmental friendly, low-cost and efficient approach for the synthesis of Au-based nanocomposites.
Cu2O is an important semiconductor, which is widely used in solar energy conversion, catalysis, gas sensors, etc [24–26]. The value of Cu2O/Cu redox pair is 0.36 V, which is much lower than that of AuCl4 −/Au (0.93 V). Consequently, Au nanoparticles can be obtained decorating onto Cu2O through a redox reaction using Cu2O as the reducing agent. Moreover, Cu2O also has been reported as the electrocatalytic material for H2O2 detection [27, 28]. Excellent performance can be obtained by the combination of Cu2O and Au. In this paper, Au/Cu2O nanocomposites have been successfully prepared through a facile, one-pot, and green redox process using Cu2O as the reducing agent. Due to the introduction of Au and the synergistic effect between Au and Cu2O, the as-prepared product exhibited eminent performance for H2O2 detection. It is found that the Au/Cu2O nanocomposite electrode exhibits high sensitivity and low detection limit towards the reduction of H2O2. Conclusively, with the straightforward preparation and enhanced performance of Au/Cu2O nanocomposite electrode, the Au/Cu2O nanocomposite material could be a promising candidate for nonenzymatic H2O2 sensing.
Chemicals and Materials
Chloroauric acid, dopamine (DA), uric acid (UA), and Nafion solution (5.0 wt% in a mixture of low aliphatic alcohols and water) were purchased from Sigma-Aldrich (St. Louis, MO, USA). H2O2 (30 wt%), CuCl2 · 2H2O, NaH2PO4, Na2HPO4, ascorbic acid (AA), and glucose (Glu) were purchased from Chengdu Kelong Chemical Reagent (Chengdu, China). All the chemical reagents were of analytical grade and used as received without further purification. Ultrapure water (18.25 MΩ cm−1) was used for all experiments.
Synthesis of Cubic Cu2O
In order to prepare cubic Cu2O, 10 mL of 2 M NaOH aqueous solution was dropped into the transparent light green CuCl2 · 2H2O aqueous solution (100 mL, 0.01 M) under vigorous stirring at 55 °C. After stirring for 0.5 h, 10 mL of 0.6 M AA solution was added into the above dark brown turbid liquid and stirred for another 3 h. Finally, the precipitates were collected by centrifugation, followed by washing thoroughly with distilled water and ethanol before freeze drying.
Synthesis of Au/Cu2O
Au/Cu2O nanocomposites were prepared via a one-pot, straightforward, and cost-efficient approach. Typically, 15 mg Cu2O was dispersed in 10-mL distilled water by ultrasonic dispersion for 10 min, and then, 40-mg sodium citrate was added under constant stirring. About 15 min later, 0.5 mL of 5-mM chloroauric acid was added and the color of the solution turned into brown black immediately, implying the generation of Au nanoparticles. After 20 min, the resultant Au/Cu2O nanocomposites were collected by centrifugation, followed by washing carefully with distilled water and ethanol before freeze drying.
The modified electrode was prepared as follows: glassy carbon electrode (GCE, Ф 3) was polished with 0.3- and 0.05-μm alumina powder carefully and rinsed thoroughly with distilled water, followed by sonication in ethanol, nitric acid (1:1), and distilled water, respectively. The prepared nanocomposites were dispersed in 0.5 % Nafion ethanol solution (2 mg/mL) and ultrasonicated for 20 min. Then 5 μL of the suspension was dropped onto the surface of the polished GCE and dried in air.
All electrochemical measurements were performed on a μIII Autolab electrochemical workstation with a standard three-electrode cell in 0.1 M phosphate-buffered solution (PBS, pH = 7.0). Saturated calomel electrode (SCE) and platinum electrode were used as reference electrode and counter electrode, respectively. Cu2O-modified GCE (Cu2O/GCE) and Au/Cu2O-modified GCE (Au/Cu2O/GCE) were used as the working electrode. Cyclic voltammetry curves were obtained in the potential range from −0.60 to 0.20 V at different scan rates ranging from 20 to 160 mV/s. Chronoamperometric responses were measured at an applied potential of −0.3 V with the successive injection of different concentration of H2O2 per 90 s in a constant stirring system.
Morphologies and structures of the prepared products were characterized by field emission scanning electron microscopy (FESEM, Hitachi, SU-8020) equipped with energy dispersion spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) (FEI-Tecnai G2, USA), and X-ray diffraction (XRD) using Cu-Kα radiation (40 kV, 60 mA).
Results and Discussion
It is clearly found that the surfaces of the as-prepared Au/Cu2O nanocomposites were rough and uneven because of the generation of Au nanoparticles decorated on the surface of Cu2O. Figure 1c shows the XRD patterns of Cu2O nanocubes and Au/Cu2O nanocomposites. All the diffraction peaks of Cu2O crystal can be indexed to the standard cuprite structure (JCPDS 05-0667). Compared with the Cu2O diffraction pattern, two additional peaks located at about 38.2° and 44.3° were observed, which were assigned to the (111) and (200) diffraction peaks of Au (JCPDS 04-0784). In addition, the EDS spectrum (Fig. 1d) confirms the presence of Au, Cu, and O elements, which agrees with the XRD spectrum analysis. Figure 1e shows the TEM image of Au/Cu2O nanocomposites, and it is found that Au/Cu2O nanocomposites with defined cubic shapes were distinctly decorated by Au nanoparticles. Furthermore, HRTEM image (Fig. 1f) clearly shows that Au nanoparticles homogeneously distribute on the surface of Cu2O cubes and the particle size of Au is about 3 nm. It is observed that the spacing of marked adjacent lattice fringes are about 0.236 and 0.245 nm, which is consistent with the standard value of Au (111) and Cu2O (111), respectively. The result is in accordance with the XRD spectrum analysis. The formation of the Au/Cu2O heterostructures may be attributed to the similar (111) lattice spacing of Au and Cu2O, which forced Au heterogeneous nucleation on the surfaces of Cu2O cubes.
Electrochemical Performance of Au/Cu2O/GCE
Amperometric Detection of H2O2 at Au/Cu2O/GCE
Interference and Stability Study
Au/Cu2O nanocomposites were successfully synthesized by a facile one-pot green redox reaction using Cu2O as the reducing agent. The Au/Cu2O/GCE exhibited excellent performance for nonenzymatic detection of H2O2 with high selectivity, low detection limit, and strong anti-interference capability. The excellent electrocatalytic activity may be caused by the introduction of Au and the synergistic effect between Au and Cu2O. The Au/Cu2O nanocomposite material is promising for practical applications in nonenzymatic detection of H2O2.
This study is supported by the National Natural Science Foundation of China (21403020, 21401015), the Basic and Frontier Research Program of Chongqing Municipality (cstc2014jcyjA50012), and the Foundation of Chongqing University of Arts and Sciences (Z2011XC15).
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