Facile Synthesis of Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets

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Facile Synthesis of Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets with Enhanced Electrocatalytic Activity for Glucose Oxidation Yun Shu, Bing Li, Jingyuan Chen, Qin Xu, Huan Pang, and Xiaoya Hu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17005 • Publication Date (Web): 02 Jan 2018 Downloaded from http://pubs.acs.org on January 2, 2018

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ACS Applied Materials & Interfaces

Facile Synthesis of Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets with Enhanced Electrocatalytic

Activity

for

Glucose

Oxidation Yun Shu, Bing Li, Jingyuan Chen, Qin Xu, Huan Pang,* Xiaoya Hu* School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China *

Corresponding author. Email: [email protected], [email protected]

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ABSTRACT: Two-dimensional (2D) ultrathin nickel-cobalt phosphate nanosheets were synthesized using a simple one-step hydrothermal method. The morphology and structure of nanomaterials synthesized under different Ni/Co ratios were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). And the influence of nanomaterials’ structure on the electrochemical performance for glucose oxidation was investigated. It’s found that the thinnest nickel-cobalt phosphate nanosheets synthesized with a Ni/Co ratio of 2:5 showed the best electrocatalytic activity for glucose oxidation. And the ultrathin nickel-cobalt phosphate nanosheet was used as an electrode material to construct a non-enzymatic electrochemical glucose sensor. The sensor showed a wide linear range (2 µM~4470 µM) and a low detection limit (0.4 µM) with a high sensitivity of 302.99 µA•mM−1•cm−2. Furthermore, the application of the as-prepared sensor in detection of glucose in human serum was successfully demonstrated. These superior performances prove that the ultrathin 2D nickel-cobalt phosphate nanosheet is promising material in the field of electrochemical sensing.

KEYWORDS: Nickel-cobalt phosphate; nanosheets; electrocatalytic activity; glucose; human serum

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INTRODUCTION So far, various 2D nanomaterials such as graphene, transition metal dichalcogenides, metal organic-framework (MOF), metal oxides and hydroxides have been widely explored.1-7 In particular, 2D ultrathin nanosheets have received great attentions in recent years. Their 2D morphology and ultrathin thickness make them possess unique chemical and physical properties, such as many highly accessible active sites on their surface, ultrahigh specific surface area, and maximum mechanical flexibility.4 These characteristics make them extensively used in the fields of electrochemical energy storage, catalytic, sensing and optoelectronic devices.8-11 To date, various chemical methods have been developed to synthesis 2D nanosheets, however, it still remains great challenge to synthesize uniform ultrathin 2D nanosheets with highly accessible surface active sites. Especially for synthesis of multi-component compounds with ultrathin nanosheets morphologies and significant functionalities. Transition metal (Co, Ni) phosphates have received great interest for decades and extensively applied in the areas of electrochemical energy storage and electrocatalysts for splitting water due to their high electrochemical activities.12-14 Manickam et al. reported the synthesis of porous sodium nickel phosphate nanosheets at diff erent temperatures and its performance evaluated for supercapacitor applications.15 In our previous work, ultrathin cobalt phosphate nanosheets are successfully synthesized and applied as an electroactive material for supercapacitors.16 However, the applications of multi-component transition metal phosphates nanosheets in the field of sensors have been rarely reported.

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Accurate detection of glucose is important in clinical diagnostics, food industry, and the biotechnology. Over the past few decades, various techniques have been developed to detect glucose. Electrochemical method has drawn great attention attribute to its unique advantages, such as easy operation process, simple instrumentation, low cost, and excellent sensitivity. Conventional electrochemical glucose biosensors are based on glucose oxidase (GOD), which show high selectivity and high sensitivity. However, the high cost and poor stability of the enzyme limit the wide applications of these enzymatic glucose biosensors. Therefore, great attention has been employed to the establishment of non-enzymatic glucose sensors. Previous research shows that due to the novel physical and chemical properties of nanomaterials,

nanomaterials

exhibit

electrocatalytic

activity

that

can

be

electrocatalytic oxidation of glucose. While the electrode material is considered as a very important factor affecting the performances of non-enzymatic electrochemical glucose sensors. Herein, in this work, the ultrathin nickel-cobalt phosphate nanosheets were prepared using a simple and mild hydrothermal method. Furthermore, we investigated the effect of Ni/Co ratio on the growth of nanomaterials. The morphology and structure of as-prepared nanomaterials were characterized by TEM, SEM, XRD, and XPS respectively. The nanosheets synthesized under different conditions were used to electrocatalytic oxidation of glucose (Scheme 1). The thinnest nickel-cobalt phosphate nanosheets showed the best electrochemical performance for glucose oxidation. The high electrocatalytic activities of nickel-cobalt phosphate nanosheets could be attributed to their ultrathin thickness (~4.5 nm) that endows them with sufficient electroactive sites. It demonstrates that the nickel-cobalt phosphate nanosheets could be expect to be applied in practical glucose detection. 4


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Scheme 1. (A) Illustration of the Morphological Changes for Products Synthesized under Different Ni/Co Ratios. (B) Schematic of Nickel-cobalt Phosphate Modified GCE for Electrocatalytic Oxidation of Glucose.

EXPERIMENTAL SECTION Reagents and Apparatus. Nafion solution was bought from DuPont. All other reagents were purchased from Sinopharm Chemical Reagent Shanghai Co., Ltd., 0.1 M NaOH solution was used as the supporting electrolyte. Synthesis of nickel-cobalt phosphate nanosheet. The nanomaterials were synthesized using a simple hydrothermal method according to the method we previous reported with some variations.17 0.2 g nickel acetate, 0.5 g cobalt acetate and 0.5 g sodium pyrophosphate were mixed in 10 mL of distilled water, after stirring the mixture for 30 min, then the mixture was heated to 160°C and reacted for 8 h. Finally, the product was washed by distilled water and ethanol for three times respectively.

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The sample was denoted as P2. Synthesis of other nickel-cobalt phosphate samples were similar to the above procedures except the variation of the amounts of nickel acetate. The detailed synthesis parameters were shown in Table S1. The product synthesized without addition of nickel acetate was denoted as P1, and the product synthesized with addition of 0.4 g nickel acetate was denoted as P3. Materials characterization. The morphology of nanomaterials was observed on the JEM-2100 transmission electron microscopy and the field-emission scanning electron microscopy (FESEM, Supra 55, Zeiss). High resolution transmission electron microscopy images, scanning transmission electron microscopy (STEM) and EDS mapping images were obtained on the Tecnai G2 F30 transmission electron microscopy (at an acceleration voltage of 300 kV). Atomic force microscope (AFM) images were captured with a MFP-3D-SA (Asylum Research, USA). XRD characterization was performed on Bruker AXS D8 Advance diffractometer. XPS analysis was obtained on Thermo Scientific ESCALAB 250Xi X-ray photoelectron spectrometer. Preparation of the Modified Electrodes. At first, glassy carbon electrode (GCE, diameter 3 mm) was carefully polished with 0.3 µm Al2O3 slurry, and cleaned by brief ultrasonication with deionized water, and then dried with highly purity nitrogen. For surface modification, 3 mg nickel-cobalt phosphate nanosheets were dispersed in 100 µL 1% Nafion solution (1 wt% in ethanol), then ultrasound the suspension for 20 min. A certain volume (5 µL) of suspension was added onto the surface of precleaned GCE and dried in air as the working electrode. All experiments were used in a three-electrode cell system for saturated calomel electrode (SCE) acting as reference electrode, where platinum (Pt) wire act as a counter electrode by using the electrochemical workstation (CHI760D, CHI Incorporation, Shanghai). The glucose 7



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sensing measurements were investigated by the cyclic voltammetry (CV) and amperometry (i-t) techniques, respectively. Detection of glucose in human serum samples. Human whole blood samples were obtained from the hospital of Yangzhou university. Blood samples were centrifuged at 3000 g for 5 min to remove cells and cellular debris from serum. Then glucose, serum, glucose and the mixture of serum with glucose were successively spiked into 10 mL N2-saturated 0.1 M NaOH solution. The current responses were recorded. The glucose levels in serum samples and recovered ratios of glucose were calculated.

RESULTS ANG DISCUSSION Characterization of the

Synthesized

Materials.

Nanomaterials

were

synthesized by a simple hydrothermal method using cobalt acetate, nickel acetate (absence for sample P1), and sodium pyrophosphate as reactants. Figure 1A-C shows the SEM images of as-prepared nanomaterials. Rectangular nanosheet-like nanomaterials were synthesized without Ni(CH3COO)2 (Figure 1A). When Ni(CH3COO)2 is added, and as the amount of Ni(CH3COO)2 increases, the morphology of nanomaterials changes from rounded rectangular nanosheets (Figure 1B) to elliptical nanosheets (Figure 1C). XRD (Figure 1D) is used to identify the crystal structure of the nanomaterials. In the XRD pattern, the reaction product is Co2P2O7 (JCPDS No. 79-0825) when there is no Ni(CH3COO)2 as reactant. With the continuous increase of Ni(CH3COO)2, the diffraction peaks of Co2P2O7 gradually disappeared and diffraction peaks of Co3(PO4)2 (JCPDS No. 80-1997) are gradually stronger. Major diffraction peaks at 17.9°, 26.1°, 26.9°, and 27.5°can be indexed to the (111), (112), (202), and (021) facet and other weak diffraction peaks at 13.4°, 8


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34.1°, 38.5°, 48.5°, and 53.7° can be indexed to (101), (121), (031), (402), and (224) facet of the Co3(PO4)2 phases. Meanwhile, diffraction peaks of the Ni3(PO4)2 phases (JCPDS No. 70-1796) can also be observed. Thus the reaction products P2 and P3 are nickel-cobalt phosphate nanosheets.

Figure 1. The SEM images of synthesized cobalt pyrophosphate (A) and nickel-cobalt phosphate sample (B-C, B-sample P2, C-sample P3). (D) (a) XRD pattern of the cobalt pyrophosphate (sample P1 without addition of Ni(CH3COO)2). (b, c) XRD patterns of the nickel-cobalt phosphate (sample P2-P3).

The TEM, HRTEM, and AFM images further identify the synthesized products (sample P2) are uniform 2D nanosheets (Figure 2A-2C). The length and width of a nanosheet is about 200~400 nm and 80 nm. The AFM analysis was conducted in tapping mode to collect phase and height data of the as-prepared nickel-cobalt phosphate nanosheets simultaneously (Figure 2C). The AFM height image indicates that the average thickness of the nickel-cobalt phosphate nanosheets is about 4.5 nm, 9



suggesting ultrathin nickel-cobalt phosphate nanosheets are synthesized. Figure S1 shows the AFM image and TEM image of sample P3 which were synthesized while continuing to increase the amount of Ni(CH3COO)2. The morphology makes some changes, while changing from rounded rectangular nanosheets to elliptical nanosheets. However, it is still nanosheets with the thickness of about 20 nm. Elemental mapping of nickel-cobalt phosphate demonstrates Co, Ni, P and O elements are homogeneous distributed within the nickel-cobalt phosphate (Figure 2D). XPS analysis is used to identify the valence state of the Co, Ni, P, O elements. According to the XPS analysis (Figure 2E, 2F, 2G, 2H), the binding energies for Ni 2p3/2 and Ni 2p1/2 are centered at around 856.6 and 874.2 eV with two shake-up satellite peaks (861.2 and 880.3 eV), which verifies the presence of Ni(II) (Figure 2F). The Co 2p spectrum can be best fitted by Co 2p3/2 and Co 2p1/2 peaks located at around 781.4 and 797.8 eV, yielding characteristics of the Co(II) state (Figure 2G). The peaks located at 133.4 and 134.3 eV correspond to the characteristic P 2p3/2 peaks of P(V). The XPS results further show that the as-synthesized product is nickel-cobalt phosphate. Figure S2-S3 shows the XPS spectra of sample P1 and P3. Co(II) and P(V) were existed in the sample P1, further suggests the product is cobalt pyrophosphate. Simultaneously the exist of Ni(Ⅱ), Co(II) and P(V) in sample P3 further exhibits the products are nickel-cobalt phosphate.

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Figure 2. (A) TEM image of nickel-cobalt phosphate (sample P2). (B) HRTEM image of nickel-cobalt phosphate (sample P2). (C) AFM image of nickel-cobalt phosphate (sample P2). Inset: the height profile of nickel-cobalt phosphate. (D) Elemental mapping images of nickel-cobalt phosphate. (E) XPS spectra of the as-prepared nickel-cobalt phosphate (sample P2). (F), (G), (H) XPS spectra of Ni 2p, Co 2p, and P 2p for nickel-cobalt phosphate.

Electrochemistry Behavior of Nanomaterials. The electrochemical behavior was performed in 0.1 M NaOH electrolyte with cyclic voltammetry (CV) technique. Nickel-cobalt phosphate (sample P2) based GCE exhibits a pair of redox peaks 11



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(Figure 3A inset and 3B). The anodic peak and cathodic peak locate at +0.56 V and +0.38 V respectively. Also the nickel-cobalt phosphate (sample P3) based GCE possesses a pair of redox peaks with the anodic peak and cathodic peak locate at +0.52 V and +0.43 V respectively (Figure 3A inset and S4). The appearance of redox peaks could be attributed to the redox reactions of the nickel and cobalt-based composites in NaOH electrolyte and its corresponding mechanisms are given by:18 NiCo2O4 + OH− + H2O → NiO(OH) + 2CoO(OH) + e− CoO(OH) + OH− → CoO2 + H2O + e−

(1) (2)

While the cobalt pyrophosphate (sample P1) have no redox peaks (Figure 3A inset). The reason may be that high amount of pyrophosphate blocks the electrochemical activities of cobalt ions. Figure 3B displays the peak current and potential change as scan rates increase. The anodic and cathodic peak currents of the nickel-cobalt phosphate/GCE increase linearly with the scan rates range from 10~100 mV•s-1, suggesting a surface-controlled electrochemical process of nickel-cobalt phosphate.19 Figure 3A shows the electrochemical behavior of different samples in a 1.6 mM glucose solution. It illustrates that the oxidation and reduction peaks of sample P2 and P3 modified GCEs are much higher than bare GCE and sample P1 modified GCE at the same condition. Furthermore, it can be observed that oxidation current responses increase with the concentration of glucose on the sample P2 and P3 modified GCEs (Figure 3C and 3D), demonstrating that glucose can be easily oxidized on the surface of nickel-cobalt phosphate (sample P2 and P3) over a wide concentration window. It indicates that sample P2-P3 on the surface of electrode show better electrochemical behavior because of high conductivity and high capacitive current. The enhancement of anodic current can be ascribed to the glucose oxidation to gluconolactone. The 12


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irreversible glucose catalytic oxidation process is accompanied by the conversion of Ni(III) to Ni(II) and Co(IV) to Co(III): Co(Ⅳ) + Ni(Ⅲ) + glucose → Co(Ⅲ) + Ni(Ⅱ) + gluconolactone CVs of the nickel-cobalt phosphate GCE in presence of glucose at different scan rates were performed to further study the electrocatalytic activities of the nickel-cobalt phosphate for glucose oxidation (Figure S5). A good linearity is obtained by plotting the peak currents vs square root of scan rates, suggesting that the oxidation of glucose is confined by diff usion of glucose molecules to the electrolyte/electrode interface.20-21

Figure 3. (A) CV curves of cobalt phosphate (sample P1), nickel-cobalt phosphate (sample P2-P3) modified GCEs and bare GCE in N2-saturated 0.1 M NaOH with 1.6 mM glucose and without glucose (inset) at a scan rate of 100 mV•s-1. (B) CV curves of nickel-cobalt phosphate modified GCEs in 0.1 M NaOH at different scan rates (sample P2). Scan rates (a–j): 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 mV•s−1. Inset: the plot of cathodic and anodic peak currents versus scan rates. 13



(C) and (D) are the typical CV curves of nickel-cobalt phosphate modified GCEs (sample P2 and P3) in the presence of different concentrations of glucose in 0.1 M NaOH at a scan rate of 100 mV•s-1.

Amperometric Detection of Glucose at the Nickel-cobalt Phosphate GCE. The detection sensitivity on the relevant modified electrodes is further explored through amperometric study. Figure S6 displays the influence of the applied potential on the current response of nickel-cobalt phosphate modified GCE towards 15 µM glucose. It can be seen that the maximum current response is obtained when the potential is 0.55 V. So the potential is chosen as 0.55 V in the following experiments. The typical i-t curves of different samples modified GCEs for the gradual injection of different amounts of glucose at 0.55 V are displayed in Figure S7A. Comparing with sample P1 and P3 modified GCEs, P2 modified GCE exhibits the maximum current response when adding the same concentration of glucose. The corresponding current vs concentration calibration plots clearly show that the P2 modified GCE displays the highest sensitivity (Figure S7B). Therefore, the analytical performance of non-enzymatic glucose electrochemical sensor based on nickel-cobalt phosphate (sample P2) is investigated in detail. Figure 4A further shows the current response of nickel-cobalt phosphate (sample P2) modified GCEs with successive addition of glucose concentration (a wider concentration window) in 0.1 M NaOH solution. With the addition of glucose, the current increases rapidly, indicating its excellent glucose detection performance. The corresponding calibration curve for glucose detection is plotted in Figure 4B. The sensor exhibits a linear range from 2 µM to 4470 µM glucose with a correlation coefficient (R2) of 0.9925. The sensitivity is calculated to be 302.99 µA•mM−1•cm−2. When the concentration of glucose increases to 5.67 mM, it is found that the current response reaches saturation gradually, indicating that all active sites of the electrode 14


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are covered with reaction intermediates at high concentration of glucose. The detection limit for the sensor is estimated to be 0.4 µM (signal-to-noise ratio S/N = 3). Therefore, the nickel-cobalt phosphate is excellent as the promising candidate for glucose sensing with a low detection limit, wide linear range, and high sensitivity. The analytical performance is compared with reported glucose non-enzymatic and enzymatic electrochemical sensors (Table 1), showing our analytical parameters are satisfactory and even better than those previous sensors. The high electrocatalytic performance is due to its high electrical conductivity and many electroactive sites, eff ciently accelerating the electron transfer rate between the electrode and electrolyte during the glucose oxidation. Also the amperometric i-t and corresponding current vs concentration calibration curves for sample P3 modified GCEs are displayed in Figure S8. A linear range from 1 µM to 3000 µM is established. And the detection limit is estimated to be 0.5 µM. The sensitivity is calculated to be 142.35 µA•mM−1•cm−2.

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Figure 4. (A) Amperometric i-t curve of the response of nickel-cobalt phosphate (sample P2) modified GCE to glucose with successive additions of glucose in the N2-saturated 0.1 M NaOH at 0.55 V. Inset: i-t curve of the response of modified GCE to glucose with successive additions of 4, 8, 16, 20, 40 µM glucose. (B) Corresponding calibration curve of current versus glucose concentration for modified GCE. Error bars are the standard error of the mean (5 parallel electrodes). (C) Amperometric i-t response of nickel-cobalt phosphate (sample P2) modified GCE at 0.55 V in N2-saturated 0.1 M NaOH with the successive addition of 65 µM glucose, 0.1 mM KCl, 0.1 mM AA, 0.1 mM DA, 0.1 mM UA and a second addition of 65 µM glucose. (D) Amperometric responses recorded at the nickel-cobalt phosphate (sample P2) GCE on the successive addition of glucose, serum, glucose and the mixture of serum with glucose.

Anti-Interference, Reproducibility, Stability Studies of the Sensor. The selectivity of the sensor is tested with various electroactive species such as KCl, ascorbic acid (AA), dopamine (DA). Figure 4C displays there is no obvious current changes except the addition of glucose. Results indicate the sensor possesses good anti-interference. For reproducibility test, five different nickel-cobalt phosphate modified GCEs were tested with 50 µM glucose and the relative standard deviation (RSD) is 2.3%. Long-time stability is performed by measuring the current response of 1 mM glucose for a month, reveling the modified GCE maintained 97% of its original value (Figure S9). The above results demonstrate the nickel-cobalt phosphate based sensor has good reproducibility and long-time stability.

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Table 1. A comparison with previously reported non-enzymatic and enzymatic electrochemical sensors. Electrode materials

Morphology

Detection limit (µM)

NixCo3-x(PO4)213

2.5

Ni3(PO4)222

Linear range

Sensitivity

(µM)

(mA•M−1•cm−2)

2.5-320

Up to 20000

Ni3(PO4)2 VSB-523

0.04

0.1-21 µM

200

0.5-10.0 mM

NiO/Foam Ni4

6.15

18-1200

395

Co3O424

0.97

up to 2040

36.25

NiCo2O425

1.49

5-15000

91.34 mV/decade

NiCo2O4/3D graphane19

0.38

0.5-590

2524

Ni0.3Co2.7O426

1

1-2550

206500

Ni−Co NSs/RGO27

3.79

10-2650

1773.61

17



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Cu/Cu2O28

1.6

Up to 40000

1434.12

Pd85Cu9Pt6 TNCs29

1.29

1000-10000

553

Pt/Au30

7.7

10-7500

IL/GOx/Ag@Zn-TSA31

0.8

2-1022

PDA/ZIF-8@rGO/GCE32

0.33

1–1200,

1.27 (µA•mM−1)

1200–3600

Nickel-cobalt phosphate

0.4

2-3000

302.99

(This work)

Detection of Glucose in Human Serum. Furthermore, the nickel-cobalt phosphate modified electrode is utilized to test the glucose levels in human blood serum samples using standard addition method, two additions of standard glucose samples, two additions of serum samples, two additions of standard glucose samples, and one addition of mixed (serum and glucose) samples were performed respectively. And the results are shown in Figure 4D. It indicates an acceptable recovery ranging from 98.3% to 101.6% in human serum samples (Table 2). The glucose levels are determined to be 5.08 mM and 4.96 mM for two human serum samples respectively, which are close to the values of 5.02 and 5.35 mM obtained by enzyme catalytic spectrophotometry. Table 2. Analytical results for the determination of glucose in human serum samples. 18


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Added (µM) Sample 1

Sample 2

Found (µM)

Mean Recovery (%)

RSD (%, n=3) 0

0

33.02

0

25

57.95

99.7

1.5

50

83.32

100.6

2.3

75

108.25

100.3

1.8

0

32.24

0

0

25

57.65

101.6

1.6

50

82.15

98.3

2.1

75

107.63

100.5

2.5

CONCLUSION 2D nickel-cobalt phosphate nanosheets were synthesized using a simple, low cost and efficient hydrothermal method. By controlling diff erent nickel acetate concentrations, the morphology of nanosheet has changed from rectangular nanosheets to elliptical nanosheets. AFM results indicated the thickness of nickel-cobalt phosphate nanosheet synthesized with a Ni/Co ratio of 2:5 was only about 4.5 nm. The electrochemical behaviors of different products were compared, results indicated the thinnest nanosheets exhibited the highest electrocatalytic activity for glucose oxidation, mainly attributed to its high specific surface area and multiple electroactive sites. The as-fabricated nickel-cobalt phosphate nanosheets based non-enzymatic electrochemical sensor exhibited high performance, such as a low detection limit, a high sensitivity, a wide linear range, long-term stability and good reproducibility. Furthermore, the glucose levels in human serum samples were determined within the fabricated sensor and achieved satisfactory results, which

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suggesting that the 2D nickel-cobalt phosphate nanosheets are promising materials in clinical diagnosis, food and environmental chemistry fields.

ASSOCIATED CONTENT

Supporting Information The AFM and TEM images of nickel-cobalt phosphate (sample P3), XPS spectra of the cobalt pyrophosphate (sample P1), XPS spectra of the sample P3, CV curve of sample P3 modified GCEs in NaOH solution without glucose, CV curves of P2 and P3 modified GCEs in NaOH with glucose at different scan rates, influence of the applied potential on the current response of sample P2 modified GCE, amperometric i-t curves of the responses of sample P1, P2, P3 modified GCEs with successive additions of glucose and corresponding calibration curves of current versus glucose concentrations, amperometric i-t curve of the response of sample P3 modified GCE with successive additions of glucose and corresponding calibration curve of current versus glucose concentrations for P3 modified GCE, and variation of the current response to glucose for nickel-cobalt phosphate modified GCE versus storage time are described in detail. The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * Email: [email protected] * Email: [email protected]

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Notes The authors declare no competing financial interest

ACKNOWLEDGMENTS We gratefully acknowledge the financial support from the NSFC (Nos. 21705141, 21275124, 21275125, 21575124, 21675140, 21201010, and 21671170), Jiangsu Planned Projects for Postdoctoral Research Funds (1601075C), Postdoctoral Science Foundation of China (2016M601897), the Program for New Century Excellent Talents in University (grant no. NCET-13-0645), PAPD and TAPP of Jiangsu Higher Education Institutions, Graduate Innovation Project Foundation of Jiangsu province (KYLX 1333 and KYLX 1334) and Natural Science Research Projects of Jiangsu Higher Education (16KJB150044). Yangzhou University Innovation and Cultivation Fund (2016CXJ014).

REFERENCES (1) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A., Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306 (5696), 666-669. (2) Gopalakrishnan, K.; Sultan, S.; Govindaraj, A.; Rao, C. N. R., Supercapacitors Based on Composites of PANI with Nanosheets of Nitrogen-doped RGO, BC1.5N, MoS2 and WS2. Nano Energy 2015, 12, 52-58. (3) Shu, Y.; Chen, J.; Xu, Q.; Wei, Z.; Liu, F.; Lu, R.; Xu, S.; Hu, X., MoS2 Nanosheet-Au Nanorod Hybrids for Highly Sensitive Amperometric Detection of H2O2 in Living Cells. J. Mater. Chem. B 2017, 5 (7), 1446-1453.

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(4) Zhao, M.; Wang, Y.; Ma, Q.; Huang, Y.; Zhang, X.; Ping, J.; Zhang, Z.; Lu, Q.; Yu, Y.; Xu, H.; Zhao, Y.; Zhang, H., Ultrathin 2D Metal-Organic Framework Nanosheets. Adv. Mater. 2015, 27 (45), 7372-7378. (5) Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S., Electronics and Optoelectronics of Two-dimensional Transition Metal Dichalcogenides. Nat. Nanotech. 2012, 7 (11), 699-712. (6) Shu, Y.; Xu, J.; Chen, J.; Xu, Q.; Xiao, X.; Jin, D.; Pang, H.; Hu, X., Ultrasensitive Electrochemical Detection of H2O2 in Living cells Based on Ultrathin MnO2 Nanosheets. Sens. Actuators, B 2017, 252, 72-78. (7) Wang, L.; Lin, C.; Zhang, F.; Jin, J., Phase Transformation Guided Single-Layer beta-Co(OH)(2) Nanosheets for Pseudocapacitive Electrodes. Acs Nano 2014, 8 (4), 3724-3734. (8) Wang, T.; Chen, S.; Pang, H.; Xue, H.; Yu, Y., MoS2‐ Based Nanocomposites for Electrochemical Energy Storage. Adv. Sci. 2017, 4 (2), 1600289. (9) McAteer, D.; Gholamvand, Z.; McEvoy, N.; Harvey, A.; O'Malley, E.; Duesberg, G. S.; Coleman, J. N., Thickness Dependence and Percolation Scaling of Hydrogen Production Rate in MoS2 Nanosheet and Nanosheet-Carbon Nanotube Composite Catalytic Electrodes. Acs Nano 2016, 10 (1), 672-683. (10) Su, F.; Zhang, S.; Ji, H.; Zhao, H.; Tian, J. Y.; Liu, C. S.; Zhang, Z.; Fang, S.; Zhu, X.; Du, M., Two-Dimensional Zirconium-Based Metal-Organic Framework Nanosheet Composites Embedded with Au Nanoclusters: A Highly Sensitive Electrochemical Aptasensor toward Detecting Cocaine. Acs Sensors 2017, 2 (7), 998. (11) Yin, Z.; Li, H.; Li, H.; Jiang, L.; Shi, Y.; Sun, Y.; Lu, G.; Zhang, Q.; Chen, X.; Zhang, H., Single-Layer MoS2 Phototransistors. Acs Nano 2012, 6 (1), 74-80. (12) Yeo, P. S. E.; Ng, M.-F., Gismondine cobalt phosphate (CoPO4) as A Monovalent-ion Battery Cathode Material: A First-principles Study. J. Mater. Chem. A 2017, 5 (19), 9287-9292.

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Page 22 of 26

Page 23 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13) Zhang, J.; Yang, Y.; Zhang, Z.; Xu, X.; Wang, X., Rapid Synthesis of Mesoporous NixCo3-x(PO4)2 Hollow Shells Showing Enhanced Electrocatalytic and Supercapacitor Performance. J. Mater. Chem. A 2014, 2 (47), 20182-20188. (14) Kim, H.; Park, J.; Park, I.; Jin, K.; Jerng, S. E.; Kim, S. H.; Nam, K. T.; Kang, K., Coordination Tuning of Cobalt Phosphates Towards Efficient Water Oxidation Catalyst. Nat. Commun. 2015, 6, 8253. (15) Minakshi, M.; Mitchell, D.; Jones, R.; Alenazey, F.; Watcharatharapong, T.; Chakraborty, S.; Ahuja, R., Synthesis, Structural and Electrochemical Properties of Sodium Nickel Phosphate for Energy Storage Devices. Nanoscale 2016, 8 (21), 11291. (16) Pang, H.; Liu, Y.; Li, J.; Ma, Y.; Li, G.; Ai, Y.; Chen, J.; Zhang, J.; Zheng, H., Cobalt Phosphite Microarchitectures Assembled by Ultralong Nanoribbons and Their Application as Effective Electrochemical Capacitor Electrode Materials. Nanoscale 2013, 5 (2), 503. (17) Li, B.; Gu, P.; Feng, Y.; Zhang, G.; Huang, K.; Xue, H.; Pang, H., Ultrathin Nickel–Cobalt Phosphate 2D Nanosheets for Electrochemical Energy Storage under Aqueous/Solid‐ State Electrolyte. Adv. Funct. Mater. 2017, 27 (12), 1605784. (18) Liu, X.; Shi, S.; Xiong, Q.; Li, L.; Zhang, Y.; Tang, H.; Gu, C.; Wang, X.; Tu, J., Hierarchical NiCo2O4@NiCo2O4 Core/Shell Nanoflake Arrays as High-Performance Supercapacitor Materials. ACS Appl. Mater. Interfaces 2013, 5 (17), 8790-8795. (19) Wu, M.; Meng, S.; Wang, Q.; Si, W.; Huang, W.; Dong, X., Nickel-Cobalt Oxide Decorated Three-Dimensional Graphene as an Enzyme Mimic for Glucose and Calcium Detection. ACS Appl. Mater. Interfaces 2015, 7 (38), 21089-21094. (20) Sivakumar, M.; Madhu, R.; Chen, S. M.; Veeramani, V.; Manikandan, A.; Hung, W. H.; Miyamoto, N.; Chueh, Y. L., Low Temperature Chemical Synthesis of CoWO4 Nanospheres for Sensitive Non-Enzymatic Glucose Sensor. J. Phys. Chem. C 2016, 120, 17024-17028. (21) Shu, Y.; Yan, Y.; Chen, J.; Xu, Q.; Pang, H.; Hu, X., Ni and NiO Nanoparticles Decorated Metal-Organic

Framework

Nanosheets:

Facile

Synthesis

and

High-Performance

Non-enzymatic Glucose Detection in Human Serum. ACS Appl. Mater. Interfaces 2017, 9, 22342-22349. 23



(22) Al-Omair, M. A.; Touny, A. H.; Al-Odail, F. A.; Saleh, M. M., Electrocatalytic Oxidation of Glucose at Nickel Phosphate Nano/Micro Particles Modified Electrode. Electrocatalysis 2017, 8 (4), 340-350. (23) Hassaninejad-Darzi, S. K.; Gholami-Esfidvajani, M., Preparation of Nanoporous Nickel Phosphate VSB-5 Nanorods Carbon Paste Electrode as Glucose Non-enzymatic Sensor. J. Porous Mater. 2017, 24 (1), 85-95. (24) Ding, Y.; Wang, Y.; Su, L.; Bellagamba, M.; Zhang, H.; Lei, Y., Electrospun Co3O4 Nanofibers for Sensitive and Selective Glucose Detection. Biosens. Bioelectron. 2010, 26 (2), 542-548. (25) Hussain, M.; Ibupoto, Z. H.; Abbasi, M. A.; Liu, X.; Nur, O.; Willander, M., Synthesis of Three Dimensional Nickel Cobalt Oxide Nanoneedles on Nickel Foam, Their Characterization and Glucose Sensing Application. Sensors 2014, 14 (3), 5415-5425. (26) Liu, Y.; Zhang, Y.; Wang, T.; Qin, P.; Guo, Q.; Pang, H., Mesoporous Ni0.3Co2.7O4 Hierarchical Structures for Effective Non-enzymatic Glucose Detection. Rsc Adv. 2014, 4 (63), 33514-33519. (27) Wang, L.; Lu, X.; Ye, Y.; Sun, L.; Song, Y., Nickel-cobalt Nanostructures Coated Reduced Graphene Oxide Nanocomposite Electrode for Non-enzymatic Glucose Biosensing. Electrochim. Acta 2013, 114 (Supplement C), 484-493. (28) Cheng, X.; Zhang, J.; Chang, H.; Luo, L.; Nie, F.; Feng, X., High performance Cu/Cu2O nanohybrid electrocatalyst for non-enzymatic glucose detection. J. Mater. Chem. B 2016, 4 (27), 4652-4656. (29) Fu, S.; Zhu, C.; Song, J.; Engelhard, M.; Xia, H.; Du, D.; Lin, Y., PdCuPt Nanocrystals

with Multibranches for Enzyme-Free Glucose Detection. ACS Appl. Mater. Interfaces 2016, 8 (34), 22196-22200. (30) Nantaphol, S.; Watanabe, T.; Nomura, N.; Siangproh, W.; Chailapakul, O.; Einaga, Y., Bimetallic Pt–Au nanocatalysts electrochemically deposited on boron-doped diamond electrodes for nonenzymatic glucose detection. Biosens. Bioelectron. 2017, 98, 76-82.

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(31) Dong, S.; Zhang, D.; Suo, G.; Wei, W.; Huang, T., Exploiting multi-function Metal-Organic Framework nanocomposite Ag@Zn-TSA as highly efficient immobilization matrixes for sensitive electrochemical biosensing. Anal. Chim. Acta 2016, 934, 203. (32) Yang, W.; Chen, H.; Yun, Z.; Fu, H.; Liu, M.; Li, X., Preparation of graphene nano-sheet bonded PDA/MOF microcapsules with immobilized glucose oxidase as a mimetic multi-enzyme system for electrochemical sensing of glucose. J. Mater. Chem. B 2016, 4 (21), 3695-3702.

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2D ultrathin nickel-cobalt phosphate nanosheets were synthesized using a simple hydrothermal method and used for construction of electrochemical glucose sensor. 205x138mm (300 x 300 DPI)


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Facile Synthesis of Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets

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