Ultrasonics Sonochemistry xxx (2014) xxx–xxx
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Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection Guo-Hai Yang, Abulikemu Abulizi, Jun-Jie Zhu ⇑ State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
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Article history: Received 29 November 2013 Received in revised form 31 December 2013 Accepted 7 January 2014 Available online xxxx Keywords: Boron nitride sheets Sonochemical route Gold nanoparticles Electrochemical sensor Hydrogen peroxide
a b s t r a c t A simple sonochemical route was developed for the preparation of gold nanoparticles/boron nitride sheets (AuNPs/BNS) nanocomposites without using reducing or stabilizing agents. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and UV–vis absorption spectra were used to characterize the structure and morphology of the nanocomposites. The experimental results showed that AuNPs with approximately 20 nm were uniformly attached onto the BNS surface. It was found that the AuNPs/BNS nanocomposites exhibited good catalytic activity for the reduction of H2O2. The modified electrochemical sensor showed a linear range from 0.04 to 50 mM with a detection limit of 8.3 lM at a signal-to-noise ratio of 3. The findings provide a low-cost approach to the production of stable aqueous dispersions of nanoparticles/BNS nanocomposites. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Graphene, a monolayer of carbon atoms closely packed into honeycomb two-dimensional (2D) carbon material, has attracted enormous interest from both the experimental and theoretical science communities [1–3]. Due to their 2D layer structure analogous to graphene, boron nitride sheets (BNS) have received a great deal of attention for potential applications [4–6], because of their many attractive properties, such as high mechanical strength, high temperature stability, large thermal conductivity, and large surface area [7–9]. In addition, the impact of BNS in association with other nanomaterials to produce nanocomposites with promising potential applications such as sensors, energy storage, and catalysis has captured the interest of some researchers [10–13]. However, most of the reported work on the preparation of BNS-based nanocomposites required a surfactant or reductant [10,12,14]. Surfactants were commonly used for the exfoliation and dispersion of BNS; while reductants were used to reduce metal ions to nanoparticles. Thus, it is crucial to explore alternative environmentally sustainable and rapid methods for the synthesis of BNS-based nanocompsites. Sonication is a simple, multi-purpose technique used in the preparation of nanomaterials, which is based on acoustic cavitation, namely the formation, growth and implosive collapse of bubbles in a liquid. It permits access to a range of chemical reactions which are normally inaccessible [15,16]. Therefore it is worth not⇑ Corresponding author. Tel./fax: +86 25 83597204. E-mail address: [email protected] (J.-J. Zhu).
ing that the sonochemical method embodies the principles of green chemistry [17]. As one of the most extensively studied nanomaterials, gold nanoparticles (AuNPs) have received increasing attention due to their distinctive physical and chemical properties and their wide application in optics, electronics, catalysis, biology and sensors [18–20]. It is expected that a hybrid composed of BNS and AuNPs can be a novel functional material for application in electrochemistry. What is more, to the best of our knowledge, no report addressed the synthesis of AuNPs/BNS nanocomposites using a sonochemical strategy. Herein, we report the simple sonochemical fabrication of AuNPs/BNS nanocomposites without using reducing or stabilizing agents. The as-prepared AuNPs/BNS nanocomposites were found to be well-dispersed with AuNPs uniformly distributed on BNS. The possible growth and formation mechanism are discussed. We also demonstrate the fabrication of a nonenzymatic H2O2 sensor using the resulting nanocomposites. The electrochemical sensor showed high stability and excellent electrocatalytic activity toward H2O2 with a linear range from 0.04 to 50 mM and a detection limit of 8.3 lM. 2. Experimental 2.1. Materials BN powder (size 1–2 lm, 99.99%), NaH2PO4, Na2HPO4, and H2O2 (30 wt%) were purchased from Aladdin Chemistry Co. Ltd.
http://dx.doi.org/10.1016/j.ultsonch.2014.01.020 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
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G.-H. Yang et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
Chloroauric acid (HAuCl44H2O) was from Shanghai Chemical Reagent Co. (China). Phosphate buffer saline (PBS, 0.01 M, pH 7.4) contained 136.7 mM NaCl, 2.7 mM KCl, 8.7 mM Na2HPO4 and 1.4 mM KH2PO4. All other reagents were of analytical grade. All aqueous solutions were prepared using ultra-pure water (Milli-Q, Millipore). 2.2. Apparatus Atomic force microscopy (AFM) image was obtained in tapping mode on an Agilent 5500 (Agilent Technologies, Inc., USA). Scanning electron microscopy (SEM) images were obtained on a Hitachi S4800 scanning electron microscope at an accelerating voltage of 5 kV. Transmission electron microscopy (TEM) images and Highresolution TEM images were taken using a JEOL JEM-2010 transmission electron microscope at an accelerating voltage of 200 kV. X-ray diffraction (XRD) measurements were performed on a Japan Shimadzu XRD-6000 diffractometer (Cu-Ka, k = 1.5418 Å) at a scanning rate of 5°/min in the 2h range from 10° to 80°. UV–vis absorption spectra of the samples were taken periodically on a Shimadzu UV-3600 spectrophotometer. Raman spectra were recorded on a Renishaw RM-1000 with excitation from the 514 nm line of an Ar-ion laser with a power of approximately 5 mW. Electrochemical measurements were performed on a CHI 660D workstation (Shanghai Chenhua, China) electrode system comprised of a platinum wire auxiliary, a saturated calomel reference and the modified glass carbon (GCE) working electrode. 2.3. Synthesis of the AuNPs/BNS nanocomposites BNS were exfoliated according to the literature with minor modification [21]. Briefly, 100 mg BN powder was dispersed in 50 ml deionized water using a bath sonicator (Branson 2510, 40 kHz) for 8 h. The dispersion was then allowed for 24 h. Then the dispersion was centrifuged at 2000 rpm for 20 min, after which decantation was carried out by pippetting off the top half of the dispersion into a glass pot. The concentration of the obtained BNS in water was 0.05 mg mL1. To obtain AuNPs/BNS, an aliquot of a HAuCl4 aqueous solution (10 mM, 2.5 mL) was then added to
the as-prepared BNS dispersion (0.05 mg mL1, 10 mL). Afterward, the reaction system in a beaker of 25 mL was exposed to highintensity ultrasonic irradiation (Sonics VCX-750 ultrasonic processor with flat head tip, 750 W at 30% amplitude, 20 kHz) for 30 min at 25 °C. After centrifugation, the nanocomposites were obtained, and further washed with deionized water three times. For comparison, the AuNPs/BNS sample was also prepared under the same conditions by a mild stirring method instead of ultrasonic irradiation at 25 °C. 2.4. Preparation of the modified electrode Glassy carbon electrode (GCE) was polished with 1.0 and 0.3 lm alumina powders, respectively, and then ultrasonically cleaned in ethanol and double-distilled water for about 1 min, respectively. The suspension of AuNPs/BNS nanocomposite (0.5 mg mL1, 5 lL) was dropped onto the GCE. Finally the modified AuNPs/BNS/GCE was used to follow the electrochemical experiments. For comparison, the other modified electrodes were prepared with the similar procedure. The electrolyte solutions were deoxygenated with N2 for 30 min and kept under N2 atmosphere during electrochemical examinations. 3. Results and discussion 3.1. Characterization of AuNPs/BNS nanocomposites The aqueous BNS dispersions were obtained using a previously described procedure. Decoration of BNS with AuNPs was achieved by a simple sonochemical method without reducing or stabilizing agents. In the reaction, 0.025 mmol HAuCl4 was used, and the gold content in the product was determined to be 0.017 mmol, using inductively coupled plasma atomic emission spectroscopy (ICPAES). Finally, the product yield was about 68.0% (HAuCl4 as reference). Fig. 1A and B show the SEM and TEM images of as-prepared BNS with the size of hundreds of nanometers. The sheets were well-ordered 2D shaped. A HRTEM image (inset of Fig. 1B) shows that the BNS have a few layers. The structure of BNS was also revealed using typical AFM images. Fig. 1C shows that the thickness
Fig. 1. (A) SEM image of BNS, (B) TEM image of BNS, inset: a HRTEM image of BNS, (C) AFM image and (D) Raman spectrum of BNS.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
G.-H. Yang et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
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Fig. 2. (A) SEM image of AuNPs/BNS nanocomposites. (B) TEM image of AuNPs/BNS nanocomposites, inset: a HRTEM image of one single nanoparticle on BNS. (C) EDX spectrum of AuNPs/BNS nanocomposites. (D) Histogram of AuNPs size distribution.
of the BNS was approximately 1.2–1.4 nm, corresponding to around 3–4 layers [22]. The micrograph also reveals that the BNS seems to be exfoliated into homogeneous sheets. Fig. 1D displays the typical Raman spectra for BNS. The peaks at around 1365 cm1 corresponded to the high-frequency E2g vibrating mode of BN [14,23]. The as-prepared BNS with high surface area can be used as efficient templates for loading various nanoparticles. In the case of AuNPs/BNS nanocomposites, it was found that AuNPs with high-density were attached to the BNS surface and scattered well on the sheets (Fig. 2A and B). The inset of Fig. 2B shows a HRTEM image of a boron nitride sheet in the vicinity of a gold nanoparticle, which revealed well-defined nanocrystalline gold on BNS. The chemical composition of the obtained AuNPs/BNS nanocomposites was determined by EDX analysis. The results showed the presence of Au besides B and N, with the existence of a Cu signal due to the TEM sample grid (Fig. 2C). The average size of AuNPs was approximately 20 nm (Fig. 2D). The relative standard deviation (RSD) for the content of Au in the AuNPs/BNS nanocomposites was 3.56%.
Fig. 3. UV–vis spectra of BNS and AuNPs/BNS nanocomposites. Inset: photographs of aqueous dispersions of BNS (a) and AuNPs/BNS nanocomposites (b).
Fig. 3 shows the UV–vis spectra of the aqueous dispersion of BNS and the resulting AuNPs/BNS nanocomposites. BNS exhibited a strong band centered at 203.5 nm, which was consistent with previous observations [24]. The UV–vis absorption peak of AuNPs/BNS nanocomposites at 523 nm showed that the AuNPs had been formed on the surface of BNS. The inset of Fig. 3 shows photographs of the aqueous dispersion of BNS (left) and AuNPs/ BNS (right), revealing a distinct color change from white to pink after sonochemical treatment. Such an observation provides another piece of evidence to support the formation of AuNPs [25]. The formation of products was also showed by the corresponding XRD patterns. As shown in Fig. 4, the strong diffraction peaks at the Bragg angles of 26.2° and 54.8° corresponded to the (0 0 2) and (0 0 4) planes of the BNS, respectively [26]. With regard to the AuNPs/BNS nanocomposites, Bragg angles of 38.0°, 44.2°, 64.5° and 77.4° were clearly observed, which corresponded to the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes of the AuNPs [27]. The typical diffraction peaks for BNS were also observed. These results confirmed that the AuNPs anchored on BNS were well crystallized. The AuNPs/BNS nanocomposites were successfully prepared.
Fig. 4. XRD spectrum of BNS and AuNPs/BNS nanocomposites.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
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Fig. 5. Illustration of the synthesis of AuNPs/BNS nanocomposites via sonication.
It was demonstrated that clean and well-dispersed AuNPs could be prepared by strongly anchoring the AuNPs on BNS surface. Fig. 5 illustrates the uniform distribution of AuNPs on BNS achieved using the sonochemical method. A possible mechanism for the formation of AuNPs/BNS nanocomposites is as follows: hydroxyl groups and defect sites were generated on the sheet surface during the synthesis of BNS from BN powder, and the in situ formed BNS had a negative zeta potential [28]. X-ray photoelectron spectroscopy confirmed the existence of O and H. When metal ions are added to the BNS solution, the BNS exhibit high absorption capacity toward positively-charged Au(III) ions through physisorption, electrostatic binding, or charge-transfer interaction, which act as the initial nucleation site for AuNPs [29]. The reduction of gold metal ions was realized under the combined effect of BNS and sonication. With increasing reaction time, the gold seeds grew to approximately 20 nm. Moreover, the homogenous AuNPs should be attached onto the surface of BNS without aggregation under sonication. Previous reports have explored that both MoS2 and graphene oxide sheets could, respectively, reduce AuCl43 and PdCl42 to generate AuNPs and PdNPs without any additional reductant [30,31], and the underlying mechanism was likely due to the redox reaction between supports and metal ions. Control experiments showed that AuNPs could not grow well on BNS using a conventional stirring method (Fig. 6). In addition, the uniform dispersion of the AuNPs takes place in situ without any surface functionalization. We considered that the sonolysis of water at ambient atmosphere led to the generation of various radicals, such as H, O2 and OH radicals, and the formed reducing species such as H, H2 and H2O2 played an important role in the synthesis of the AuNPs/BNS nanocomposites [16]. It was proposed that the following possible sequence of reactions occurred:
H2 O ! H þ OH
ð1Þ
BNS þ OH ðH Þ ! M þ H2 O
ð2Þ
AuCl4 þ M ! AuNPs=BNS þ 4Cl
ð3Þ
where M corresponded to reducing species and pyrolysis radicals. Moreover, the physical effect of the extreme temperature, pressure and high cooling rates of ultrasonication may promote the reduction reaction in a shorter time. Furthermore, the presence of AuNPs on exfoliated BNS not only improved their dispersion, but also would modify charge transport between the sheets and enhance their catalytic efficiency.
Fig. 6. TEM image of the sample prepared using a conventional stirring method.
Fig. 7. CVs of a bare GCE (a), BNS/GCE (b), and AuNPs/BNS/GCE (c), in N2 saturated 0.1 MPBS at pH 7.4 in the presence of 10.0 mM H2O2 (scan rate: 0.05 V s1). Inset: the CV of AuNPs/BNS/GCE E in 0.1 MPBS (pH 7.4) without H2O2.
bare GCE and BNS/GCE. In contrast, AuNPs/BNS/GCE exhibited a marked catalytic current peak about 28 lA in intensity at 0.53 V (curve c). This improved electrocatalytic ability was
3.2. Electrochemical performance of the AuNPs/BNS/GCE towards H2O2 As a demonstration of the application of such nanocomposites, we constructed an enzymeless H2O2 sensor by direct deposition of the aqueous dispersion of AuNPs/BNS nanocomposites on a GCE surface. Fig. 7 shows cyclic voltammetric (CV) responses of 5.0 mM H2O2 in 0.1 M N2-saturated PBS (pH = 7.4) at different electrodes. No redox peaks were observed in the absence of H2O2 for AuNPs/BNS/GCE (inset of Fig. 7), indicating that the modified electrode was non-electroactive in the selected potential region. When 5.0 mM of H2O2 was added into the N2-saturated PBS, no reduction peak was observed on the bare GCE (curve a) and BNS/GCE (curve b), which indicated that H2O2 reduction was not achieved at the
Fig. 8. Typical steady-state response of the AuNPs/BNS/GCE to successive injection of H2O2 into the N2 saturated PBS under stirring. The inset was the calibration curve. Applied potential: 0.40 V; supporting electrolyte: 0.1 MPBS of pH 7.4.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
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G.-H. Yang et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx Table 1 Summary of the analytical performances of reported H2O2 detection systems. Electrode materials
Detection limit (lM)
Linear range (mM)
Reference
AgNP/rGO HRP–Au–chitosan–clay Nafion/HRP/GNSs–TiO2 Poly-brilliant cresyl blue/AuNPs Cytc/Nanoporous Au AuNPs/BNS
28 9 5.9 23 6.3 8.3
0.1–40 0.039–31 0.041–0.63 0.06–10 0.01–12 0.04–50
38 39 40 41 42 This work
attributed to the synergistic effect of AuNPs and BNS, in which AuNPs had electrocatalytic ability towards H2O2 and the BNS provided a large specific surface area to increase the loading amount of H2O2. Importantly, by altering the band structure, AuNPS/BNS nanocomposites promoted the efficient interfacial charge transfer for electrochemical sensing [26,32].
Furthermore, the reproducibility of the AuNPs/BNS/GCE fabrication was also investigated. The RSD of the current signal for 0.5 mM H2O2 at six modified electrodes prepared under the same conditions was 4.56%, suggesting good reproducibility and precision. After the modified electrode was stored in the refrigerator at 4 °C for 2 weeks, the current response to 0.5 mM H2O2 remained 94.37% of its original response. These results demonstrate that the sensor exhibited excellent long-term stability.
3.3. Amperometric response and calibration curve for H2O2 detection 4. Conclusion Fig. 8 shows the typical amperometric response of the AuNPs/ BNS/GCE with successive additions of different concentrations of H2O2 into 0.1 M N2-saturated PBS (pH 7.4) at an applied potential of 0.4 V. It can be seen that AuNPs/BNS/GCE responded quickly to the change in H2O2 concentration and achieved 95% of the maximum steady-state current within 2 s after the addition of H2O2, indicating a fast diffusion of the substrate in the hybrid film modified electrode. The inset shows the calibration curve of the sensor. The linear detection range was estimated to be from 0.04 to 50 mM (r = 0.997), and the detection limit was estimated to be 8.3 lM at a signal-to-noise ratio of 3. A comparison of the linear range and detection limit of the sensor with other previously reported H2O2 sensors is shown in Table 1 [33–37]. It can be seen that the performance of the sensor was comparable and even better than those obtained with several recently reported electrodes. To evaluate the selectivity of the AuNPs/BNS/GCE, the effects of some possible interferents on the amperometric detection of H2O2 were investigated. Fig. 9 shows the amperometric response obtained following successive additions of 1.0 mM H2O2 and possible interferents in 0.1 M N2saturated PBS (pH 7.4) at an applied potential of 0.4 V. As shown in Fig. 9, the response current of ascorbic acid (AA), dopamine (DA), and glucose did not cause any observable interference in the detection of H2O2. This suggested that these species had no obvious interference in the reduction of H2O2. The selectivity for H2O2 amperometric detection was very good on the AuNPs/BNS modified GCE.
Fig. 9. Current–time curves for the AuNPs/BNS/GCE exposed to DA (1.0 mM), AA (1.0 mM), glucose (1.0 mM) and H2O2 (1.0 mM) each.
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Contents lists available at ScienceDirect
Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection Guo-Hai Yang, Abulikemu Abulizi, Jun-Jie Zhu ⇑ State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
a r t i c l e
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Article history: Received 29 November 2013 Received in revised form 31 December 2013 Accepted 7 January 2014 Available online xxxx Keywords: Boron nitride sheets Sonochemical route Gold nanoparticles Electrochemical sensor Hydrogen peroxide
a b s t r a c t A simple sonochemical route was developed for the preparation of gold nanoparticles/boron nitride sheets (AuNPs/BNS) nanocomposites without using reducing or stabilizing agents. Transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and UV–vis absorption spectra were used to characterize the structure and morphology of the nanocomposites. The experimental results showed that AuNPs with approximately 20 nm were uniformly attached onto the BNS surface. It was found that the AuNPs/BNS nanocomposites exhibited good catalytic activity for the reduction of H2O2. The modified electrochemical sensor showed a linear range from 0.04 to 50 mM with a detection limit of 8.3 lM at a signal-to-noise ratio of 3. The findings provide a low-cost approach to the production of stable aqueous dispersions of nanoparticles/BNS nanocomposites. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Graphene, a monolayer of carbon atoms closely packed into honeycomb two-dimensional (2D) carbon material, has attracted enormous interest from both the experimental and theoretical science communities [1–3]. Due to their 2D layer structure analogous to graphene, boron nitride sheets (BNS) have received a great deal of attention for potential applications [4–6], because of their many attractive properties, such as high mechanical strength, high temperature stability, large thermal conductivity, and large surface area [7–9]. In addition, the impact of BNS in association with other nanomaterials to produce nanocomposites with promising potential applications such as sensors, energy storage, and catalysis has captured the interest of some researchers [10–13]. However, most of the reported work on the preparation of BNS-based nanocomposites required a surfactant or reductant [10,12,14]. Surfactants were commonly used for the exfoliation and dispersion of BNS; while reductants were used to reduce metal ions to nanoparticles. Thus, it is crucial to explore alternative environmentally sustainable and rapid methods for the synthesis of BNS-based nanocompsites. Sonication is a simple, multi-purpose technique used in the preparation of nanomaterials, which is based on acoustic cavitation, namely the formation, growth and implosive collapse of bubbles in a liquid. It permits access to a range of chemical reactions which are normally inaccessible [15,16]. Therefore it is worth not⇑ Corresponding author. Tel./fax: +86 25 83597204. E-mail address: [email protected] (J.-J. Zhu).
ing that the sonochemical method embodies the principles of green chemistry [17]. As one of the most extensively studied nanomaterials, gold nanoparticles (AuNPs) have received increasing attention due to their distinctive physical and chemical properties and their wide application in optics, electronics, catalysis, biology and sensors [18–20]. It is expected that a hybrid composed of BNS and AuNPs can be a novel functional material for application in electrochemistry. What is more, to the best of our knowledge, no report addressed the synthesis of AuNPs/BNS nanocomposites using a sonochemical strategy. Herein, we report the simple sonochemical fabrication of AuNPs/BNS nanocomposites without using reducing or stabilizing agents. The as-prepared AuNPs/BNS nanocomposites were found to be well-dispersed with AuNPs uniformly distributed on BNS. The possible growth and formation mechanism are discussed. We also demonstrate the fabrication of a nonenzymatic H2O2 sensor using the resulting nanocomposites. The electrochemical sensor showed high stability and excellent electrocatalytic activity toward H2O2 with a linear range from 0.04 to 50 mM and a detection limit of 8.3 lM. 2. Experimental 2.1. Materials BN powder (size 1–2 lm, 99.99%), NaH2PO4, Na2HPO4, and H2O2 (30 wt%) were purchased from Aladdin Chemistry Co. Ltd.
http://dx.doi.org/10.1016/j.ultsonch.2014.01.020 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
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Chloroauric acid (HAuCl44H2O) was from Shanghai Chemical Reagent Co. (China). Phosphate buffer saline (PBS, 0.01 M, pH 7.4) contained 136.7 mM NaCl, 2.7 mM KCl, 8.7 mM Na2HPO4 and 1.4 mM KH2PO4. All other reagents were of analytical grade. All aqueous solutions were prepared using ultra-pure water (Milli-Q, Millipore). 2.2. Apparatus Atomic force microscopy (AFM) image was obtained in tapping mode on an Agilent 5500 (Agilent Technologies, Inc., USA). Scanning electron microscopy (SEM) images were obtained on a Hitachi S4800 scanning electron microscope at an accelerating voltage of 5 kV. Transmission electron microscopy (TEM) images and Highresolution TEM images were taken using a JEOL JEM-2010 transmission electron microscope at an accelerating voltage of 200 kV. X-ray diffraction (XRD) measurements were performed on a Japan Shimadzu XRD-6000 diffractometer (Cu-Ka, k = 1.5418 Å) at a scanning rate of 5°/min in the 2h range from 10° to 80°. UV–vis absorption spectra of the samples were taken periodically on a Shimadzu UV-3600 spectrophotometer. Raman spectra were recorded on a Renishaw RM-1000 with excitation from the 514 nm line of an Ar-ion laser with a power of approximately 5 mW. Electrochemical measurements were performed on a CHI 660D workstation (Shanghai Chenhua, China) electrode system comprised of a platinum wire auxiliary, a saturated calomel reference and the modified glass carbon (GCE) working electrode. 2.3. Synthesis of the AuNPs/BNS nanocomposites BNS were exfoliated according to the literature with minor modification [21]. Briefly, 100 mg BN powder was dispersed in 50 ml deionized water using a bath sonicator (Branson 2510, 40 kHz) for 8 h. The dispersion was then allowed for 24 h. Then the dispersion was centrifuged at 2000 rpm for 20 min, after which decantation was carried out by pippetting off the top half of the dispersion into a glass pot. The concentration of the obtained BNS in water was 0.05 mg mL1. To obtain AuNPs/BNS, an aliquot of a HAuCl4 aqueous solution (10 mM, 2.5 mL) was then added to
the as-prepared BNS dispersion (0.05 mg mL1, 10 mL). Afterward, the reaction system in a beaker of 25 mL was exposed to highintensity ultrasonic irradiation (Sonics VCX-750 ultrasonic processor with flat head tip, 750 W at 30% amplitude, 20 kHz) for 30 min at 25 °C. After centrifugation, the nanocomposites were obtained, and further washed with deionized water three times. For comparison, the AuNPs/BNS sample was also prepared under the same conditions by a mild stirring method instead of ultrasonic irradiation at 25 °C. 2.4. Preparation of the modified electrode Glassy carbon electrode (GCE) was polished with 1.0 and 0.3 lm alumina powders, respectively, and then ultrasonically cleaned in ethanol and double-distilled water for about 1 min, respectively. The suspension of AuNPs/BNS nanocomposite (0.5 mg mL1, 5 lL) was dropped onto the GCE. Finally the modified AuNPs/BNS/GCE was used to follow the electrochemical experiments. For comparison, the other modified electrodes were prepared with the similar procedure. The electrolyte solutions were deoxygenated with N2 for 30 min and kept under N2 atmosphere during electrochemical examinations. 3. Results and discussion 3.1. Characterization of AuNPs/BNS nanocomposites The aqueous BNS dispersions were obtained using a previously described procedure. Decoration of BNS with AuNPs was achieved by a simple sonochemical method without reducing or stabilizing agents. In the reaction, 0.025 mmol HAuCl4 was used, and the gold content in the product was determined to be 0.017 mmol, using inductively coupled plasma atomic emission spectroscopy (ICPAES). Finally, the product yield was about 68.0% (HAuCl4 as reference). Fig. 1A and B show the SEM and TEM images of as-prepared BNS with the size of hundreds of nanometers. The sheets were well-ordered 2D shaped. A HRTEM image (inset of Fig. 1B) shows that the BNS have a few layers. The structure of BNS was also revealed using typical AFM images. Fig. 1C shows that the thickness
Fig. 1. (A) SEM image of BNS, (B) TEM image of BNS, inset: a HRTEM image of BNS, (C) AFM image and (D) Raman spectrum of BNS.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
G.-H. Yang et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx
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Fig. 2. (A) SEM image of AuNPs/BNS nanocomposites. (B) TEM image of AuNPs/BNS nanocomposites, inset: a HRTEM image of one single nanoparticle on BNS. (C) EDX spectrum of AuNPs/BNS nanocomposites. (D) Histogram of AuNPs size distribution.
of the BNS was approximately 1.2–1.4 nm, corresponding to around 3–4 layers [22]. The micrograph also reveals that the BNS seems to be exfoliated into homogeneous sheets. Fig. 1D displays the typical Raman spectra for BNS. The peaks at around 1365 cm1 corresponded to the high-frequency E2g vibrating mode of BN [14,23]. The as-prepared BNS with high surface area can be used as efficient templates for loading various nanoparticles. In the case of AuNPs/BNS nanocomposites, it was found that AuNPs with high-density were attached to the BNS surface and scattered well on the sheets (Fig. 2A and B). The inset of Fig. 2B shows a HRTEM image of a boron nitride sheet in the vicinity of a gold nanoparticle, which revealed well-defined nanocrystalline gold on BNS. The chemical composition of the obtained AuNPs/BNS nanocomposites was determined by EDX analysis. The results showed the presence of Au besides B and N, with the existence of a Cu signal due to the TEM sample grid (Fig. 2C). The average size of AuNPs was approximately 20 nm (Fig. 2D). The relative standard deviation (RSD) for the content of Au in the AuNPs/BNS nanocomposites was 3.56%.
Fig. 3. UV–vis spectra of BNS and AuNPs/BNS nanocomposites. Inset: photographs of aqueous dispersions of BNS (a) and AuNPs/BNS nanocomposites (b).
Fig. 3 shows the UV–vis spectra of the aqueous dispersion of BNS and the resulting AuNPs/BNS nanocomposites. BNS exhibited a strong band centered at 203.5 nm, which was consistent with previous observations [24]. The UV–vis absorption peak of AuNPs/BNS nanocomposites at 523 nm showed that the AuNPs had been formed on the surface of BNS. The inset of Fig. 3 shows photographs of the aqueous dispersion of BNS (left) and AuNPs/ BNS (right), revealing a distinct color change from white to pink after sonochemical treatment. Such an observation provides another piece of evidence to support the formation of AuNPs [25]. The formation of products was also showed by the corresponding XRD patterns. As shown in Fig. 4, the strong diffraction peaks at the Bragg angles of 26.2° and 54.8° corresponded to the (0 0 2) and (0 0 4) planes of the BNS, respectively [26]. With regard to the AuNPs/BNS nanocomposites, Bragg angles of 38.0°, 44.2°, 64.5° and 77.4° were clearly observed, which corresponded to the (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes of the AuNPs [27]. The typical diffraction peaks for BNS were also observed. These results confirmed that the AuNPs anchored on BNS were well crystallized. The AuNPs/BNS nanocomposites were successfully prepared.
Fig. 4. XRD spectrum of BNS and AuNPs/BNS nanocomposites.
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Fig. 5. Illustration of the synthesis of AuNPs/BNS nanocomposites via sonication.
It was demonstrated that clean and well-dispersed AuNPs could be prepared by strongly anchoring the AuNPs on BNS surface. Fig. 5 illustrates the uniform distribution of AuNPs on BNS achieved using the sonochemical method. A possible mechanism for the formation of AuNPs/BNS nanocomposites is as follows: hydroxyl groups and defect sites were generated on the sheet surface during the synthesis of BNS from BN powder, and the in situ formed BNS had a negative zeta potential [28]. X-ray photoelectron spectroscopy confirmed the existence of O and H. When metal ions are added to the BNS solution, the BNS exhibit high absorption capacity toward positively-charged Au(III) ions through physisorption, electrostatic binding, or charge-transfer interaction, which act as the initial nucleation site for AuNPs [29]. The reduction of gold metal ions was realized under the combined effect of BNS and sonication. With increasing reaction time, the gold seeds grew to approximately 20 nm. Moreover, the homogenous AuNPs should be attached onto the surface of BNS without aggregation under sonication. Previous reports have explored that both MoS2 and graphene oxide sheets could, respectively, reduce AuCl43 and PdCl42 to generate AuNPs and PdNPs without any additional reductant [30,31], and the underlying mechanism was likely due to the redox reaction between supports and metal ions. Control experiments showed that AuNPs could not grow well on BNS using a conventional stirring method (Fig. 6). In addition, the uniform dispersion of the AuNPs takes place in situ without any surface functionalization. We considered that the sonolysis of water at ambient atmosphere led to the generation of various radicals, such as H, O2 and OH radicals, and the formed reducing species such as H, H2 and H2O2 played an important role in the synthesis of the AuNPs/BNS nanocomposites [16]. It was proposed that the following possible sequence of reactions occurred:
H2 O ! H þ OH
ð1Þ
BNS þ OH ðH Þ ! M þ H2 O
ð2Þ
AuCl4 þ M ! AuNPs=BNS þ 4Cl
ð3Þ
where M corresponded to reducing species and pyrolysis radicals. Moreover, the physical effect of the extreme temperature, pressure and high cooling rates of ultrasonication may promote the reduction reaction in a shorter time. Furthermore, the presence of AuNPs on exfoliated BNS not only improved their dispersion, but also would modify charge transport between the sheets and enhance their catalytic efficiency.
Fig. 6. TEM image of the sample prepared using a conventional stirring method.
Fig. 7. CVs of a bare GCE (a), BNS/GCE (b), and AuNPs/BNS/GCE (c), in N2 saturated 0.1 MPBS at pH 7.4 in the presence of 10.0 mM H2O2 (scan rate: 0.05 V s1). Inset: the CV of AuNPs/BNS/GCE E in 0.1 MPBS (pH 7.4) without H2O2.
bare GCE and BNS/GCE. In contrast, AuNPs/BNS/GCE exhibited a marked catalytic current peak about 28 lA in intensity at 0.53 V (curve c). This improved electrocatalytic ability was
3.2. Electrochemical performance of the AuNPs/BNS/GCE towards H2O2 As a demonstration of the application of such nanocomposites, we constructed an enzymeless H2O2 sensor by direct deposition of the aqueous dispersion of AuNPs/BNS nanocomposites on a GCE surface. Fig. 7 shows cyclic voltammetric (CV) responses of 5.0 mM H2O2 in 0.1 M N2-saturated PBS (pH = 7.4) at different electrodes. No redox peaks were observed in the absence of H2O2 for AuNPs/BNS/GCE (inset of Fig. 7), indicating that the modified electrode was non-electroactive in the selected potential region. When 5.0 mM of H2O2 was added into the N2-saturated PBS, no reduction peak was observed on the bare GCE (curve a) and BNS/GCE (curve b), which indicated that H2O2 reduction was not achieved at the
Fig. 8. Typical steady-state response of the AuNPs/BNS/GCE to successive injection of H2O2 into the N2 saturated PBS under stirring. The inset was the calibration curve. Applied potential: 0.40 V; supporting electrolyte: 0.1 MPBS of pH 7.4.
Please cite this article in press as: G.-H. Yang et al., Sonochemical fabrication of gold nanoparticles–boron nitride sheets nanocomposites for enzymeless hydrogen peroxide detection, Ultrason. Sonochem. (2014), http://dx.doi.org/10.1016/j.ultsonch.2014.01.020
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G.-H. Yang et al. / Ultrasonics Sonochemistry xxx (2014) xxx–xxx Table 1 Summary of the analytical performances of reported H2O2 detection systems. Electrode materials
Detection limit (lM)
Linear range (mM)
Reference
AgNP/rGO HRP–Au–chitosan–clay Nafion/HRP/GNSs–TiO2 Poly-brilliant cresyl blue/AuNPs Cytc/Nanoporous Au AuNPs/BNS
28 9 5.9 23 6.3 8.3
0.1–40 0.039–31 0.041–0.63 0.06–10 0.01–12 0.04–50
38 39 40 41 42 This work
attributed to the synergistic effect of AuNPs and BNS, in which AuNPs had electrocatalytic ability towards H2O2 and the BNS provided a large specific surface area to increase the loading amount of H2O2. Importantly, by altering the band structure, AuNPS/BNS nanocomposites promoted the efficient interfacial charge transfer for electrochemical sensing [26,32].
Furthermore, the reproducibility of the AuNPs/BNS/GCE fabrication was also investigated. The RSD of the current signal for 0.5 mM H2O2 at six modified electrodes prepared under the same conditions was 4.56%, suggesting good reproducibility and precision. After the modified electrode was stored in the refrigerator at 4 °C for 2 weeks, the current response to 0.5 mM H2O2 remained 94.37% of its original response. These results demonstrate that the sensor exhibited excellent long-term stability.
3.3. Amperometric response and calibration curve for H2O2 detection 4. Conclusion Fig. 8 shows the typical amperometric response of the AuNPs/ BNS/GCE with successive additions of different concentrations of H2O2 into 0.1 M N2-saturated PBS (pH 7.4) at an applied potential of 0.4 V. It can be seen that AuNPs/BNS/GCE responded quickly to the change in H2O2 concentration and achieved 95% of the maximum steady-state current within 2 s after the addition of H2O2, indicating a fast diffusion of the substrate in the hybrid film modified electrode. The inset shows the calibration curve of the sensor. The linear detection range was estimated to be from 0.04 to 50 mM (r = 0.997), and the detection limit was estimated to be 8.3 lM at a signal-to-noise ratio of 3. A comparison of the linear range and detection limit of the sensor with other previously reported H2O2 sensors is shown in Table 1 [33–37]. It can be seen that the performance of the sensor was comparable and even better than those obtained with several recently reported electrodes. To evaluate the selectivity of the AuNPs/BNS/GCE, the effects of some possible interferents on the amperometric detection of H2O2 were investigated. Fig. 9 shows the amperometric response obtained following successive additions of 1.0 mM H2O2 and possible interferents in 0.1 M N2saturated PBS (pH 7.4) at an applied potential of 0.4 V. As shown in Fig. 9, the response current of ascorbic acid (AA), dopamine (DA), and glucose did not cause any observable interference in the detection of H2O2. This suggested that these species had no obvious interference in the reduction of H2O2. The selectivity for H2O2 amperometric detection was very good on the AuNPs/BNS modified GCE.
Fig. 9. Current–time curves for the AuNPs/BNS/GCE exposed to DA (1.0 mM), AA (1.0 mM), glucose (1.0 mM) and H2O2 (1.0 mM) each.
AuNPs/BNS nanocomposites were successfully synthesized using a simple sonochemical route without reducing or stabilizing agents. It was shown that AuNPs of approximately 20 nm were uniformly attached to BNS. The detection of H2O2 without an enzyme in the electrode modified by AuNPs/BNS nanocomposites was also demonstrated and revealed that the nanocomposites showed excellent catalytic activity for the reduction of H2O2. This work could open the door for the fabrication of various types of metal BNS-based nanocomposites which will have wide application in the fields of catalysis, the environment, and new energy. Acknowledgments This research was financially supported by National Basic Research Program of China (2011CB933502), and the National Natural Science Foundation of China (21305120, and 21121091). References [1] M. Pumera, Graphene-based nanomaterials and their electrochemistry, Chem. Soc. Rev. 39 (2010) 4146–4157. [2] V. Berry, Impermeability of graphene and its applications, Carbon 62 (2013) 1– 10. [3] M. Shun, H.H. Pua, J.H. Chen, Graphene oxide and its reduction: modeling and experimental progress, RSC Adv. 2 (2012) 2643–2662. [4] Y. Kubota, K. Watanabe, O. Tsuda, T. Taniguchi, Deep ultraviolet light-emitting hexagonal boron nitride synthesized at atmospheric pressure, Science 317 (2007) 932–934. [5] Y. Lin, J.W. Connell, Advances in 2D boron nitride nanostructures: nanosheets, nanoribbons, nanomeshes, and hybrids with graphene, Nanoscale 4 (2012) 6908–6939. [6] H. Zeng, C.Y. Zhi, Z. Zhang, X. Wei, X. Wang, W. Guo, Y. Bando, D. Golberg, ‘‘White graphenes’’: boron nitride nanoribbons via boron nitride nanotube unwrapping, Nano. Lett. 10 (2010) 5049–5055. [7] T. Ainsbury, A. Satti, P. May, Z. Wang, I. Mcgovern, Y.K. Gun’ko, J. Coleman, Oxygen radical functionalization of boron nitride nanosheets, J. Am. Chem. Soc. 134 (2012) 18758–18771. [8] K. Watanabe, T. Taniguchi, T. Niiyama, K. Miya, M. Taniguchi, Far-ultraviolet plane-emission handheld device based on hexagonal boron nitride, Nat. Photonics 3 (2009) 591–594. [9] A. Lyalin, A. Nakayama, K. Uosaki, T. Taketsugu, Functionalization of monolayer h-BN by a metal support for the oxygen reduction reaction, J. Phys. Chem. C 117 (2013) 21359–21370. [10] Y.T. Liu, Z.Q. Duan, X.M. Xie, X.Y. Ye, A universal strategy for the hierarchical assembly of functional 0/2D nanohybrid, Chem. Commun. 49 (2013) 1642– 1644. [11] L. Ci, L. Song, C.H. Jin, D. Jariwala, D.X. Wu, Y.J. Li, A. Srivastava, Z.F. Wang, K. Storr, L. Balicas, F. Liu, P.M. Ajayan, Atomic layers of hybridized boron nitride and graphene domains, Nature Mater. 9 (2010) 430–435. [12] X.J. Chen, W.Z. Zang, K. Vimalanathan, K. Raston, A versatile approach for decorating 2D nanomaterials with Pd or Pt nanoparticles, Chem. Commun. 49 (2013) 1160–1162.
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