CuO nanocrystals were prepared with hydrothermal synthesis method. The morphology of the nano-CuO was characterized by scanning electron microscopy. The prepared shuttlelike CuO nanocrystals were modified to glass carbon electrode (GCE) to form nano-CuO/GCE modified electrode. The obtained modified electrode showed an excellent electrocatalytic property towards hydrogen peroxide in 0.01 M NaOH containing 0.09 M KCl electrolyte. Under the optimal experiment conditions, the electrocatalytic response current of this sensor was proportional to the H2O2 concentration in the range of 0.02
Among numerous biological, chemical, environmental, pharmaceutical, and clinical studies, hydrogen peroxide plays a fundamental role as an oxidizing, bleaching and sterilizing agent [
Nanoparticles as modification materials have been extensively employed in various fields owing to the small size, large surface area, and some other especial properties. Numerous nanometal oxides, such as manganese dioxide [
In the paper, a shuttle-like CuO nanocrystals were prepared according to the reported method [
Hydrogen peroxide (30% (v/v) aqueous solution) was purchased from Sinopharm Chemical Reagent Co., Ltd. The stock solutions were prepared fresh with doubly distilled water. All other reagents were purchased from Shanghai Chemical Reagent Company and were of analytical grade and used without further purification. Doubly distilled water was used throughout the experiments. The supporting electrolyte we used in this experiment was 0.01 M NaOH solution containing 0.09 M KCl.
All the electrochemical measurements including cyclic voltammetry (CV) and amperometric response (i-t) were carried out with CHI660A electrochemical workstation (Chenhua Instruments Co., Shanghai, China). A conventional three-electrode system was employed. A bare glass carbon electrode (GCE, Ø3.0 mm) or nano-CuO-modified GCE was used as the working electrode, and an Ag/AgCl (KCl, 3.0 M) electrode and a platinum wire electrode were used as the reference electrode and the counter electrode, respectively. A magnetic stirrer provided the convective transport during the amperometric measurements. All experiments were performed at room temperature. Scanning electron microscopy (SEM) was obtained on S-4800 field emission scanning electron microanalyser (Hitachi, Japan).
The preparation of the nano-CuO was performed as follows: in the first place, 0.25 g Cu(CH3COO)2 · H2O and 0.77 g cetyltrimethylammonium bromide (CTAB) were put in a 60 mL teflon-lined stainless steel autoclave, then 40 mL doubly distilled water was poured into the autoclave with stirring. Afterward, 4 mL, 0.5 M NaOH was tardily added into the above solution under stirring. Completing all the above steps, it was necessary to make sure that the autoclave was tightly sealed. Meanwhile, the temperature of autoclave was maintained at 120°C for 12 h and then cooled to room temperature naturally. The precipitate was centrifuged and washed with doubly distilled water and absolute ethanol several times over and over, then dried in vacuum at 70°C for several hours.
Prior to the modification, the GCE was mechanically polished with alumina powder (Al2O3, 0.05
Via scanning electron microscopy (SEM), the morphologies and structures of the surface film of the modified electrode was characterized. Figure
SEM image of shuttlelike CuO nanocrystal film.
A Nyquist diagram of electrochemical impedance spectrum was an effective way to measure the electron-transfer resistance. Figure
Electrochemical impedance spectra of bare GCE (a) and nano-CuO/GCE (b) in 1 mM [Fe(CN)6]3−/4− + 1 M KCl.
The electrochemical behaviors of H2O2 on nano-CuO/GCE were explored. As shown in Figure
Cyclic voltammograms of bare GCE (a) and nano-CuO/GCE (b) in 0.01 M NaOH + 0.09 M KCl solution containing 0.1 mM H2O2. Scan rate: 0.10 Vs−1.
The dependence of H2O2 anodic peak current on scan rates was examined. Figure
Cyclic voltammetric curves of nano-CuO/GCE in 0.01 M NaOH + 0.09 M KCl solution containing 0.1 mM H2O2 at different scan rates. Scan rates:
In order to optimize the electrocatalytic response to H2O2 on the nano-CuO/GCE, the effect of NaOH concentration and the nano-CuO film thickness on anodic peak current was explored. Maintaining system ion concentration 0.1 M, the concentrations were changed from 0.001 to 0.1 M for NaOH and from 0.099 to 0 for KCl. With increment of NaOH concentration, anodic peak current of H2O2 increased. When NaOH concentration was improved to be 0.01 M, the peak current achieved the best value. Subsequently, it came to a gradual decrease with increasing NaOH concentration. Accordingly, during this experiment we chose 0.01 M NaOH containing 0.09 M KCl as the supporting electrolyte.
In preparing the sensor, the amount of modifying material on the surface of electrode influences the sensor response to detecting target. Hence, the influence of nano-CuO film thickness on electrode on sensor response to H2O2 was examined in this paper. The amount of nano-CuO on the GCE was controlled to be 0.028, 0.056, 0.085, 0.113, 0.142, and 0.212 mg (cm2)−1, respectively, and the anodic peak currents of 0.1 mM H2O2 were measured. The experimental results showed that anodic peak current of H2O2 increased with the increment of the nano-CuO amount. When the amount of nano-CuO was improved to be 0.113 mg (cm2)−1, the peak current achieved the best value. Subsequently, it came to a gradual decrease with increasing the nano-CuO amount (shown in Figure
Current response of nano-CuO/GCE for 0.1 mM H2O2 inside the electrochemical reactor at various modification amounts of nano-CuO on the electrode, electrolyte: 0.01 M NaOH + 0.09 M KCl solution.
The amperometric response of nano-CuO/GCE upon adding H2O2 little by little every 50 s was tested at the applied potential 0.19 V in 0.01 M NaOH containing 0.09 M KCl electrolyte solution with continuous stirring under the optimal conditions. As shown in Figure
Performance comparison of the H2O2 sensors based on different-materials-modified electrodes.
Material | Linear range ( | Detection limit (nM) | Sensitivity | Reference |
---|---|---|---|---|
MWCNT/Ag nanohybrids | 50~17000 | 500 | 1.42 | [ |
Nano-TiO2/DNA/thionin nanocomposite | 50~22300 | 50000 | — | [ |
Nafion and copper oxide nanoparticles | 0.15~9000 | 60 | — | [ |
CuO flower-like nanomaterials | 42.5~4000 | 167 | 88.4 | [ |
CuO shuttlelike nanocrystals | 0.02~250 | 7 | 227 | This study |
Amperometric current-time curves for H2O2 oxidation on the nano-CuO/GCE, at applied potential 0.19 V (versus Ag/AgCl) in 0.01 M NaOH + 0.09 M KCl solution. Concentrations were used in the range between 0.02
The stability and reproducibility of this sensor were also examined. The prepared electrochemical sensor possessed long-term stability because the nano-CuO material could strongly be adsorbed on surface of glassy carbon electrode. We used this electrochemical sensor to detect H2O2 several times every day intermittently and also studied the storage stability of the sensor by storing it in air at ambient conditions when not in use. Three days later the response of the sensor maintained 99.2% and after three weeks the response retained 93.6% of the original value. This study indicated that nano-CuO/GCE have good stability and it can be used repeatedly.
In real samples, some coexisting electroactive species might affect the sensor response. And so three kinds of potential interferences 100
Effects of UA, AA, and AP interferences on the amperometric response to H2O2 in 5 mL 0.01 M NaOH + 0.09 M KCl solution.
For verifying the applicability of the nano-CuO-modified GCE for analysis application, recovery experiment was carried out using the modified electrode. Under the optimal conditions, we added H2O2 into the samples with the concentration of 50, 100, and 200
The detection results of H2O2 concentration in test samples.
Sample | Added (10−4 M) | Found (10−4 M) | Recovery % | |
Tap water | 1 | 0.5 | 0.49 | 98% |
2 | 1 | 0.99 | 99% | |
3 | 2 | 1.95 | 97.5% |
We have successfully fabricated a high-sensitivity, fast-response, and highly selective amperometric H2O2 sensor based on CuO nanoshuttles. The shuttlelike CuO nanoparticles were immobilized onto surface of electrode by absorption and can greatly increase the electrocatalytic active area and also obviously promote electron transfer abilities between H2O2 molecules and electrode. The nano-CuO/GCE exhibited the prominent activity for redox of H2O2, and the fabricated sensor gave a good stability and reproducibility, which could be used as an amperometric sensor for determination of low-concentration H2O2 in samples.
The authors thank the National Natural Science Foundation of China (Grant no. 20775002) for financial support. The paper was supported by Program for Innovative Research Team in Anhui Normal University.