A sonoelectrochemical preparation of graphene nanosheets with graphene quantum dots for their use as a hydrogen peroxide sensor

Accepted Manuscript A sonoelectrochemical preparation of graphene nanosheets with graphene quantum dots for their use as a hydrogen peroxide sensor Zhe-Ting Liu, Jyun-Sian Ye, Su-Yang Hsu, Chien-Liang Lee PII:

S0013-4686(17)32752-4

DOI:

10.1016/j.electacta.2017.12.178

Reference:

EA 30966

To appear in:

Electrochimica Acta

Received Date: 2 June 2017 Revised Date:

22 September 2017

Accepted Date: 30 December 2017

Please cite this article as: Z.-T. Liu, J.-S. Ye, S.-Y. Hsu, C.-L. Lee, A sonoelectrochemical preparation of graphene nanosheets with graphene quantum dots for their use as a hydrogen peroxide sensor, Electrochimica Acta (2018), doi: 10.1016/j.electacta.2017.12.178. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical Abstract

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A sonoelectrochemical preparation of graphene nanosheets with graphene quantum dots for their use

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as a hydrogen peroxide sensor

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Zhe-Ting Liu, Jyun-Sian Ye, Su-Yang Hsu, Chien-Liang Lee*

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Abstract:

A sonoelectrochemical method has been successfully developed for the preparation of graphene nanosheet (GN)-supported graphene quantum dots (GN/GQDs) whereby sodium n-octyl sulfate intercalates into the interlayer spaces of a graphite working electrode under the combined effect of an

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applied potential and acoustic vibration power (640 W). GNs containing only pores can be prepared by lengthening the carbon chain of sodium n-alkyl sulfate (SCxS, x = 10, 12, and 14). Raman and X-ray photoelectron spectroscopic analyses and electrochemical analysis show that the densities of the

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structural defects on the GN/GQDs and different GNs and their responding activities for H2O2 reduction are dependent on the carbon chain length of SCxS. These GN/GQDs have been used as non-enzymatic

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sensors for the determination of H2O2.

*

Corresponding author. Tel/ Fax: 886-7-3814526-5131, [email protected]; [email protected]; [email protected]

886-7-3830674.

E-mail

address:

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ACCEPTED MANUSCRIPT 1. Introduction The electrochemical method for the preparation of graphene nanosheets (GNs) involves a layerby-layer intercalation of an ionic compound into a graphite electrode and a sequential exfoliation of the GNs in an electrolyte under an applied electric field [1, 2]. This simple preparative method for

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GNs provides an alternative to the classical chemical method [3, 4] which involves the reduction of graphene oxide typically prepared following the Hummers method [5]. However, theoretically, there is a diffusion layer at the interface of the electrode and the electrolyte in an electrochemical system.

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The slow mass transport kinetics can be attributed to a thick diffusion layer. Therefore, the production

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efficiency for GNs may be limited by the slow mass transport.

Sonoelectrochemistry involves the modification of electrochemical systems with ultrasonic radiation [6]. With the assistance of acoustic radiation, the diffusion layer can be effectively disrupted and the mass transport of ions across the electrical double layer can be improved. This method has been predominantly employed for the rapid production of nanoparticles (NPs) based on Pt [7, 8], Ag

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[9], and Cu [10].

Hydrogen peroxide sensors are a rapidly growing set of methods and techniques that have found

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applications in diverse fields such as food additives [11], clinical applications [12], and environmental analyses [13]. High concentrations of H2O2 in the body can result in its reaction with

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life-essential elements such as Cu and Fe, leading to a Fenton reaction in living cells and the accumulation of these metal ions [14]. With ageing, accumulation of Cu and Fe in brain can cause neurodegenerative diseases [14]. Therefore, it is very important to be able to detect H2O2 for maintaining good health. Many enzymatic biosensors have been developed for measuring H2O2 [1517]. Recently, due to the intrinsic nature of enzymes in enzymatic biosensors, non-enzymatic electrochemical sensors composed of Pt [18-20], Ag [21], and Au nanomaterials [22] have been developed. However, these noble metal catalysts are expensive, which restricts their commercialization as sensors. 2

ACCEPTED MANUSCRIPT Previously, we have reported a sonoelectrochemical method for the preparation of GNs having more physical defects [23]. A graphite working electrode was rapidly intercalated by sodium ndodecyl sulfate (SC12S) and the GNs were then exfoliated under the combined application of ultrasonic power (240 W) and fixed potentials. In this study, GNs were bonded with graphene

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quantum dots (GN/GQDs) using sodium n-octyl sulfate (SC8S) as an intercalating agent and high acoustic power (640 W). By lengthening the carbon chain of sodium n-alkyl sulfate (SCxS, x = 10, 12, 14), GNs that have only vacancy holes can be prepared. The extent of defects present on these GNs is

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dependent on the carbon chain length of SCxS. Thus, GN/GQDs and various GNs have been applied as catalysts for the hydrogen peroxide reduction reaction (HPRR) and as non-enzymatic sensors in the

2. Experimental

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2.1 Chemicals and Materials

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determination of H2O2.

The chemicals and working electrodes required in the sonoelectrochemical preparation of GN/GQDs or GNs with vacancy holes were SC8S (Alfa Aesar, 99%), sodium n-decyl sulfate (SC10S, Alfa Aesar,

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99%), SC12S (J. T. Baker, 100%), sodium n-tetradecyl sulfate (SC14S, J. T. Baker, 100%), and graphite plate (Anatech, 99.99%, 1 cm × 1 cm × 2 mm). The chemicals used for electrochemical measurements

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include H2O2 (Sigma Aldrich, 35%), Na2H2PO4 (SHOWA, 98%), Na2HPO4 (SHOWA, 99%), Lascorbic acid (AA, Sigma Aldrich, 99.7%), uric acid (UA, Panreac, 98%), Nafion (Dupont, 5 wt%), and milk (Wei Chuan).

2.2 Preparation and materials analyses of GN/GQDs and porous GNs The GN/GQDs were prepared by a sonoelectrochemical method using 20 mL of a 0.05 M SC8S aqueous solution as the electrolyte under ultrasonic radiation and an applied potential (2.9776 V vs.

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ACCEPTED MANUSCRIPT Ag/AgCl/3 M KCl). The power and frequency of the ultrasonic oscillator (Elma, P60H) were 640 W and 37 kHz, respectively. A three-electrode cell consisting of a graphite plate (1 cm × 1 cm × 0.3 cm) as the working electrode, a Pt counter electrode (1 cm × 1 cm × 0.05 cm), and a Ag/AgCl (3 M KCl) reference electrode, was used. These three electrodes were connected to a potentiostat (PGSTAT 302N,

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Autolab). The working and counter electrodes were fixed in place using a Teflon spacer and the spacing between them was ca. 0.5 cm. After six hours, solutions containing dispersed powders of GN/GQDs were obtained.

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Following the same procedure with 20 mL of 0.05 M solution of SC10S, SC12S, or SC14S, GNs with vacancy holes were prepared (GNSC10S, GNSC12S, or GNSC14S, respectively)). The GNs were precipitated

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from the as-prepared solutions to remove impurities using a centrifugal force of 9720 g in a centrifuge (Hettich, MIKRO 22R). Subsequently, in order to remove free SCxS, the solution was precipitated using high-speed centrifugation at 16,430 g. The centrifugal force to dislodge impurities for the GN/GQDs was 6220 g.

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The morphology of the synthesized GNs was examined using transmission electron microscopy (TEM, JEOL JEM-2100) and spherical-aberration corrected field TEM (80 kV, JEOL JEM –ARM200FTH). The crystalline structures of GNs were detected by X-ray diffraction spectroscopy (XRD, Bruker D8,

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Cu anode). Raman (Horiba HR800) and X-ray photoelectron spectroscopies (XPS, VersaProbe PHI

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5000) were used to confirm the sp3/sp2 ratios and O-containing groups, respectively. 2.3 Electrocatalysis and sensing of H2O2 The catalytic properties of GN/GQDs were compared with that of porous GNs in the hydrogen peroxide reduction reaction (HPRR) by electrochemical measurements on a computer-controlled potentiostat (PGSTAT 302N, Autolab) using a catalyst-coated glassy carbon electrode (GCE, 0.07 cm2). An aqueous solution containing 14 µg of the carbon catalyst and a Nafion solution (5.36 µL, 0.05 wt%) were sequentially drop-casted onto the GCE surface and dried to obtain a homogeneous layer at 60 °C in an oven. The measurements were performed in a N2-saturated 0.01 M phosphate 4

ACCEPTED MANUSCRIPT buffered saline (PBS) solution (100 mL, pH = 7.4), with or without 5 mM H2O2, using a threeelectrode cell with the catalyst-covered electrode serving as the working electrode, Pt foil as the counter electrode, and an Ag/AgCl (3 M KCl) reference electrode. The PBS solution was prepared by mixing 158.3 mL of a 0.02 M Na2H2PO4 aqueous solution and 341.7 mL of a 0.02 M Na2HPO4

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aqueous solution. The mixed solution was sequentially diluted with 500 mL of deionized water. In order to remove potential interference from impurities on the catalyst during sensing of H2O2, the working electrode was scanned from −0.6 V to 0.6 V using cyclic voltammetry (CV) for 20 cycles at

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a rate of 150 mV s−1 and for 10 cycles at a rate of 50 mV s−1. For electrochemically sensing H2O2, the sensitivity and interference studies were performed by using transient HPRR experiments, whereby a

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potential of −0.4 V (vs. Ag/AgCl) was applied continuously. In the interference study, the times for the addition of 2 mM H2O2, 0.4 mM AA, 0.4 mM UA, and 2 mM H2O2 were 40, 80, 120, and 160 s after triggering the measurement, respectively. Real sample analysis was conducted by using different concentrations of the H2O2 solutions mixed with milk (1 mL) added to the PBS solution (5 mL, 0.01

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3. Results and Discussion

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The weights of the GNs produced using SCxS as intercalating agents at a fixed potential (2.977 V)

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with or without ultrasonic radiation are given in Table 1. The amount of the GN exfoliated by the intercalation of SC8S under the electric field was only 0.13 mg. When coupled with acoustic radiation, the weight increased to 2.84 mg, an increase of 21.8 times. Therefore it may be concluded that the amount of GN produced had improved by using the sonoelectrochemical method. It is noteworthy that the yield of GNs increased with decreasing molecular weight of the intercalating agent. The weights of the GNs prepared by using SC10S, SC12S, and SC14S were 2.52, 2.46, and 2.33 mg, respectively. The data obtained from XRD spectra (Fig. S1) is summarized in Table S1 (Supporting Information, SI) and shows that three layers of GNs are prepared by the sonoelectrochemical method in all cases. Therefore, 5

ACCEPTED MANUSCRIPT the number of layers of GNs and their weight can be increased by increasing the carbon chain-length of SCxS. Figure 1 reveals the amperometric currents for the electrochemical behaviour of various SCxS under ultrasonic radiation at 37kHZ and 640 W. The order of the responding limiting current was determined to be SC8S > SC10S > SC12S > SC14S. Thus, the limiting current was found to be inversely

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proportional to the molecular weight of the GNs. The mass transport increased considerably, as evidenced by the greater limiting current required for SC8S in comparison with the limiting current in the silent condition (or an electrochemical medium only), as shown in the inset of Fig. 1. The improved

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mass transport could be attributed to a decreasing thickness of the diffusion layer.

Furthermore, it is noteworthy that the density of defects of the prepared GNs is also dependent on

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the length of the carbon chain of the employed intercalating compound. Figure 2 shows the TEM images of the exfoliated GNs after various SCxS were intercalated into the graphite electrodes under sonoelectrochemical condition. In the case of SC8S, the GN bonded with small black GQDs (Fig. 2a) having a mean diameter of 4.8 nm (Fig. S2). The high-resolution image (Fig. 2b) measured using

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spherical-aberration corrected field TEM clearly reveals the crystalline nature of GQDs and their lattice spacing of 0.21 nm. This observation is consistent with the (100) lattice spacing of the GQDs prepared by hydrothermal treatment of polythiophene [24] and glucose [25]. In contrast, the vacancy

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holes were observed in the case of GNSC10S, GNSC12S, and GNSC14S, as shown in Fig. 2c, 2d, and 2e, respectively. In the electrochemically prepared GNs [1, 26] such large holes were absent. In addition,

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the aberration-corrected high-resolution TEM image (Fig. S3) of the GNSC14S showed various structural defects (5-7-7-5 defect, 5-8-5 defect, and the 5-9 vacancy defect) and A-B-A stacking, as labelled in yellow. Typically, the contribution to the defect density from the both structural defects and O-containing groups can be expressed by the ratio of the intensity of the D band to that of G band (ID/IG) in the Raman spectrum [27]. The Raman spectra (Fig. 3) The ID/IG value for the GN/GQDs can be determined from their Raman spectra (Fig. 3) and was found to be 0.99. The ID/IG for GNSC10S, GNSC12S, and GNSC14S were found to be 0.91, 0.74, and 0.49, respectively. Thus, the decreasing order

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ACCEPTED MANUSCRIPT of ID/IG values is GN/GQDs > GNSC10S > GNSC12S > GNSC14S. Similar results were obtained by XPS. High resolution narrow scans from the C region (Fig. S4) of all four GNs were obtained and it was concluded that the changes in the ID/IG ratio caused by chemical defects could be eliminated. Therefore, the defects on GNSC10S, GNSC12S, and GNSC14S might simply be a result of the vacancy holes that are

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plausibly created by the strike of acoustic microjets. For the GN/GQDs, defects may originate from the many edges and steps of the GQDs on the GN, as observed in Fig. 2b. The significant number of the steps and edges further induced the increase in the intensity of D band.

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The prepared GNs with various defect densities were tested as catalysts for the HPRR and sensing H2O2. Figure 4 and its inset show the cyclic voltammogram obtained by measuring the electrochemical

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response of the different GN-covered GCEs in a 0.01 M aqueous solution of PBS, with and without 5 mM H2O2 under an inert N2 atmosphere, respectively. The CV curves (inset in Fig. 4) of all GNs show a paired redox peak at ~ 0 V and −0.2 V in the PBS solution which is similar to that of carbon nanotubes bonded with a carboxylic acid group [28]. The CV curves after the addition of 5 mM H2O2

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showed steep reducing currents but for GN/GQDs, the curve started at an earlier potential of 0.1 V, indicating a smaller overpotential toward HPRR. At −0.4 V, the catalytic current using GN/GQDs was found to be 1.06 × 10−1 mA, which was significantly greater than the catalytic currents of 9 × 10−2 mA

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and 6.5 × 10−2 mA obtained using GNSC10S and GNSC12S, respectively. The GN/GQDs also showed a

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current that was 2.07 times higher than that of GNSC14S for which the current was 4 × 10−2 mA. Based on the unique catalytic power of GN/GQDs, the feasibility of using these materials and GNSC10S, GNSC12S, and GNSC14S as potential H2O2 sensors was also investigated. Figure 5a depicts the current-time response of GN/GQDs compared to other GNs in PBS solutions with successive injections of different concentrations of H2O2 at an applied potential of −0.4 V. After sequential addition of the aliquots of H2O2 to the PBS solution under stirring, the reduction current on the GN/GQDs increased more quickly compared to the other GN catalysts and reached a steady-state

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ACCEPTED MANUSCRIPT current within 30 s. The reposing current (the inset) using GN/GQDs was sensible for the low H2O2 concentration. The calibration curves in Fig. 5b show the linear relationship between current response and H2O2 concentration for different GNs. Thus, the sensitivity of the sensor material can be estimated from the

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slope (Fig. 5b) over the geometric surface area (0.07 cm2 ) of a GCE [29]. The comparative results are summarized in Table 2, which shows that better sensitivities are achieved by using GN/GQDs in different linear ranges. Interestingly, the range of limiting concentrations in linear analysis is

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dependent on the types of GNs. The GN/GQDs can effectively detect concentrations of H2O2 as low as 0.02 mM, which is still lower than the concentrations of 0.1 mM and 0.2 mM that were determined for

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GNSC10S and GNSC12S, respectively. For GNSC14S, the initial concentration (0.4 mM) in the linear range means less sensible for the present of H2O2. The limit of detection (LOD) refers to the lowest concentration of H2O2 that can be measured with reasonable statistical certainty [30]. Based on the calibration curves (Fig. 5b) and the formula for calculating LOD [31], the GN/GQDs were found to

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have a lower LOD (0.252 µM) at a signal-to-noise ratio of 3.

Table 3 shows that the sensitivity of GN/GQDs is much higher than those using a rGO/Ag NPs [32], rGO/polyaniline/Pt NP [33] , and graphene-supported Au/Pd nanoalloy/indium tin oxide [34] under a

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linear range of 0.02-0.4 mM, which almost covers the concentration range (0.05–0.25%) of H2O2 in

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milk, as a preservative in commercial production [35, 36]. Typically, the electrochemically active surface area (ECSA) is also a factor that influences the activity of the catalysts. In order to precisely determine the ECSA of these GNs, CV experiments were performed at different scan rates for measuring the double-layer capacitance (Cdl) [37]. Figure S5 shows the CV curves and the corresponding Cdl values (at 0.1 V vs. reversible hydrogen electrode, RHE) at different scan rates for the different GNs tested in the range of 0.05 V to 0.15 V (vs. RHE) in 0.1 M KOH solution. A comparison clearly shows that the non-faradaic current densities of GN/GQDs are more significant than that of the three GNs. The ECSA value, calculated as the mean of ‫ ݈݀ܥ‬over Cs, 8

ACCEPTED MANUSCRIPT was determined to be 225.75 cm2 for the GN/GQDs. Here, Cs is the specific capacitance of a flat electrode and has the value of 40 µF cm−2. The ECSA of GN/GQDs was thus found to be greater than that for GNSC10S, GNSC12S, and GNSC14S (165.88 cm2, 108.38 cm2, and 50.13 cm2, respectively. Among these tested materials, the GN/GQDs showed the largest ECSA value, which could be attributed to the

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step edges, as seen in Fig. 1a. Therefore, the appearance of steps on the GNs increases their ECSA and improves their activity toward the HPRR. In addition, the GN/GQDs showed a remarkable resistance toward foreign substances in the determination of H2O2. Figure 6 illustrates comparable current-time

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curves for these four GNs at an applied potential of −0.4 V in a PBS solution with sequentially added 2 mM H2O2, 0.4 mM AA, 0.4 mM UA, and 2 mM H2O2. Clearly, with the help of GQDs, the active sites

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available to H2O2 become greater in number, which results in a significant signal-to-noise ratio for the HPRR but is ineffective for AA and UA sensing.

The feasibility of GN/GQDs for their use as sensors was evaluated by performing real sample analyses. The sensing of H2O2 using GN/GQDs as catalysts was performed by using the calibration

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curve (Fig. 5b) to determine the recovery of the different concentrations of H2O2 in commercially available milk. The analyses samples were prepared by adding different concentrations of H2O2 to 5.9 mL of milk solutions, which contained 0.9 mL commercially available milk and 5 mL of a 0.01 M PBS

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solution. The final H2O2 concentrations in the samples were 0.05 mM, 0.1 mM, and 0.15 mM. A high recovery and low relative standard deviation (RSD) were determined for the three measurements,

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summarized in Table 4, which clearly demonstrated that the methodology presented in this work can be applied for the detection of H2O2 in a milk sample.

4. Conclusions Several porous GNs (GNSC10S, GNSC12S, and GNSC14S) and GN/GQDs were selectively prepared by modifying the carbon chain length of SCxS intercalated into a graphite working electrode under a sonoelectrochemical medium. It was found that the extent of structural defects and the ECSA of these 9

ACCEPTED MANUSCRIPT materials follow the order GN/GQDs > GNSC10S > GNSC12S > GNSC14S. Furthermore, among these nanomaterials, the GN/GQDs showed a greater catalytic activity in the HPRR and could be used as a non-enzymatic sensor for the determination of H2O2.

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Acknowledgements The authors thank the Ministry of Science and Technology, Taiwan, for financially supporting this research under Contract No. MOST 103-2221-E-151-054-MY3 as well as Miss Yin-Mei Chang at

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Yat-Sen University for their help in TEM experiments.

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National Tsing Hua University and Mr. Hsien-Tsan Lin of Regional Instruments Center at National Sun

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[35] S. Ohgiyal, T. Hoshino, H. Okuyama, S. Tanakal, K. Ishizakil, Biotechnology of enzymes from cold-adapted microorganisms, 1 ed., Speringer Heidelberg, German, 1999.

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[36] X. Zhu, X.H. Niu, H.L. Zhao, M.B. Lan, Doping ionic liquid into Prussian blue-multiwalled carbon nanotubes modified screen-printed electrode to enhance the nonenzymatic H2O2 sensing performance, Sens. Actuator B-Chem. 195 (2014) 274-280.

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[37] Y. Jia, L.Z. Zhang, A.J. Du, G.P. Gao, J. Chen, X.C. Yan, C.L. Brown, X.D. Yao, Defect graphene as a trifunctional catalyst for electrochemical reactions, Adv. Mater. 28 (2016) 9532-9538.

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[38] H. Mei, W. Wu, B. Yu, H. Wu, S. Wang, Q. Xia, Nonenzymatic electrochemical sensor based on Fe@Pt core–shell nanoparticles for hydrogen peroxide, glucose and formaldehyde, Sens. Actuator BChem. 223 (2016) 68-75.

[39] O.G. Sahin, Microwave-assisted synthesis of PtAu@C based bimetallic nanocatalysts for nonenzymatic H2O2 sensor, Electrochim. Acta, 180 (2015) 873-878. [40] B. Patella, R. Inguanta, S. Piazza, C. Sunseri, A nanostructured sensor of hydrogen peroxide, Sens. Actuator B-Chem. 245 (2017) 44-54.

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ACCEPTED MANUSCRIPT [41] Z. Li, X. Zheng, J. Zheng, A non-enzymatic sensor based on Au@Ag nanoparticles with good

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stability for sensitive detection of H2O2, New J. Chem. 40 (2016) 2115-2120.

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ACCEPTED MANUSCRIPT Figure captions Figure 1 Amperometric currents for the electrochemical behaviour of various SCxS intercalating into graphite electrodes under ultrasonic radiation at 40 kHz with 640 W. Applied potential = 2.977 V.

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Inset: Amperometric current responses using SC8S at the applied potential only. Figure 2 TEM images (a, c−e) and high-resolution TEM image (b) of GN/GQDs (a, b), GNSC10S (c), GNSC12S (d), and GNSC14S (e).

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Figure 3 Raman spectra of GN/GQDs, GNSC10S, GNSC12S, and GNSC14S.

Figure 4 CV curves of GN/GQDs, GNSC10S, GNSC12S, and GNSC14S for the catalytic reaction of HPRR in

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PBS solutions. Inset: CV curves in the PBS solution without H2O2.

Figure 5 Performance of GN/GQDs, GNSC10S, GNSC12S, and GNSC14S as non-enzymatic H2O2 sensors. (a) Amperometric current-time response and (b) corresponding calibration curves in PBS (0.01 M) solution after successive injections of different concentrations of H2O2 at an applied potential of −0.4 V (Inset: calibration curves in the range of 0−10 mM).

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Figure 6 Effect of interference on GN/GQDs, GNSC10S, GNSC12S, and GNSC14: current vs. time curves of H2O2 sensing at an applied potential of −0.4 V in 0.01 M PBS solution with the order of addition as 2

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mM H2O2, 0.4 mM AA, 0.4 mM UA, and 2 mM H2O2.

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Table 1. A comparison of the amounts of GNs prepared by sonoelectrochemical and electrochemical methods.

Electrochemical methoda Sonoelectrochemical method

GNSC14S (mg) 0.14 2.33

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This method involved using a fixed potential (2.977 V).

GNSC12S (mg) 0.14 2.46

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a

GNSC10S (mg) 0.12 2.52

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GN/GQD (mg) 0.13 2.84

Preparative method

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ACCEPTED MANUSCRIPT Table 2. A summary of the linear range, sensitivity, correlation coefficient, and LOD of GN/GQD,

Sensitivity (mA mM-1 cm-2)

Correlation coefficient

LOD (µM)

GN/GQD

0.02-0.4 0.7-7.6 9.6-39.6

0.897 0.0958 0.013

0.9954 0.9836 0.9618

0.252

GNSC10S

0.1-0.4 0.7-5.6 9.6-27.6

0.674 0.0828 0.0139

0.9843 0.9783 0.9787

0.405

GNSC12S

0.2-0.7 1.1-5.6 7.6-21.6

0.41 0.0571 0.0133

GNSC14S

0.4-2.9 3.7-9.6 11.6-39.6

SC

0.9967 0.9802 0.9666

1.36

0.9945 0.9865 0.9868

5.58

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0.0728 0.0357 0.0141

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Linear range (mM)

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GNSC10S, GNSC12S, and GNSC14S-covered GCEs used as H2O2 sensors.

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ACCEPTED MANUSCRIPT Table 3. Figures of merit of recently reported non-enzymatic methods for amperometric determination of H2O2 in PBS solutions. Applied potential (V/ vs. Ag/AgCl)

Linear range (mM)

Sensitivity (mA mM-1 cm-2)

LOD (µM)

Ref.

3D-rGO/Ag NPa/GCE

-0.3 V

0.016-27

0.4197

6.8

[32]

Fe@Pt/GCE

0.4 V

0.0025-41.61

0.219

0.75

[38]

Pt0.5Au0.5@C

0.3 V

0.007–6.5

0.2103

2.4

[39]

-0.2 V

0.053 - 4.4

rGO/PANI /Pt NPa/GCE

0V

0.02 - 8

Graphene-supported Au/Pd nanoalloy/ITOd

-0.6 V

0.005 - 11.5

Au@Ag NPa/GCE

-0.2 V

0.005 - 10

-0.4 V

0.02-0.4 0.7-7.6 9.6-39.6

Pd NWs /Au layer

GN/GQD/GCE c

[40]

0.257

1.1

[33]

0.1869

1

[34]

0.1162

1.3

[41]

0.897 0.0958 0.013

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This work

Polyaniline, and

d

Indium tin oxide electrode.

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Nanoparticle, b Nanowires,

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0.368

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c

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b

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Electrode

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Table 4. Real sample assays using GN/GQDs for the detection of H2O2 mixed with a commercial milk/PBS solution.

Found (mM)

R.S.D (%)

Recovery (%)

0.05

0.05058

2.78

101.1

0.1

0.09847

1.15

98.6

0.15

0.14375

1.83

95.83

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Add (mM)

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Fig. 1

60

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40 30 20

35

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SC8S

30

10

current / mA

25

0

SC10S

20

SC12S

15 10

-10 0

60

60

120 180 240 300 Intercalating time / min

120

360

180

SC14S

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0

240

300

360

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Intercalating time / min

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Current / mA

50

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Fig. 2

(d)

(b)

(e)

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(a)

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Fig. 3

Intensity / a.u.

GNSC10S

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GN/GQDs

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1200

1400

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GNSC14S

1600

1800

2000

-1

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Raman shift / cm

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0.04

GN/GQDs GNSC10S

0.00

GNSC14S 0.06

Without 5mM H2O2

-0.04

0.04

I / mA

0.02

-0.08

SC

0.00

-0.02 -0.04

-0.12

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GNSC12S

-0.06

-0.6

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-0.08 -0.4

-0.2

0.0

0.2

0.4

0.6

E vs Ag / AgCl / V

-0.16 -0.6 -0.4 -0.2

0.0

0.2

0.4

0.6

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E vs Ag / AgCl / V

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I / mA

0.08

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(b) GN/GQDs

GNSC12S

GNSC10S

GNSC14S

0.16

GNSC12S

0.12

I / mA

0.3 mM

-0.10

0.4 mM 0.6 mM 0.8 mM 1 mM 0.5 mM 0.7 mM 0.9 mM

0.00

-0.15

-0.02 -0.03

0.10

0.04

4 mM

-0.04 0.05 mM

t/s

200

80

100

0.00

120

0

2

4

6

8

10

0.00 -5 0 5 10 15 20 25 30 35 40 45 50 C / mM

400 Time / s

600

800

C / mM

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0

60

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-0.20

40

0.06

0.02

-0.06 20

0.08

0.04

0.02 mM 0.03 mM

0

GNSC14S

0.12

3 mM

-0.05

0.08

2 mM

-0.01

I / mA

I / mA

-0.05 0.1 mM 0.2 mM

GN/GQDs GNSC10S

I / mA

0.00

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(a)

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0.04

2 mM H2O2 0.4 mM AA 2 mM H2O2 0.4 mM UA

0.00

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-0.12

GN/GQD GNSC10S

-0.16

GNSC12S GNSC14S

0

40

80

120

200

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Time / s

160

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-0.20

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-0.08

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I / mA

-0.04

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ACCEPTED MANUSCRIPT A sonoelectrochemical method is developed for preparing GN/GQDs. SC8S intercalates into graphite electrode under 640 W of acoustic vibration





power. The various sodium n-alkyl sulfate for preparing GN/GQDs and GNs is studied. GN/GQDs have been used as electrochemical H2O2 sensor.

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