In situ electrodeposition of mesoporous aligned α-Fe2O3 nanoflakes for highly sensitive nonenzymatic H2O2 sensor

Accepted Manuscript Full Length Article In situ electrodeposition of mesoporous aligned α-Fe2O3 nanoflakes for highly sensitive nonenzymatic H2O2 sensor Jiajia Cai, Shilei Ding, Guang Chen, Yunlan Sun, Qian Xie PII: DOI: Reference:

S0169-4332(18)31675-1 https://doi.org/10.1016/j.apsusc.2018.06.108 APSUSC 39616

To appear in:

Applied Surface Science

Received Date: Revised Date: Accepted Date:

16 March 2018 7 June 2018 13 June 2018

Please cite this article as: J. Cai, S. Ding, G. Chen, Y. Sun, Q. Xie, In situ electrodeposition of mesoporous aligned α-Fe2O3 nanoflakes for highly sensitive nonenzymatic H2O2 sensor, Applied Surface Science (2018), doi: https:// doi.org/10.1016/j.apsusc.2018.06.108

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.

In situ electrodeposition of mesoporous aligned α-Fe2O3 nanoflakes for highly sensitive nonenzymatic H2O2 sensor Jiajia Cai1, Shilei Ding1, Guang Chen1, Yunlan Sun1, Qian Xie2* 1 2

School of Energy and Environment, Anhui University of Technology, Ma’anshan, 243002, China School of Metallurgic Engineering, Anhui University of Technology, Ma’anshan, 243032, China

*Qian Xie, E-mail: [email protected]

Abstract: Mesoporous

aligned

hematite

nanoflakes

(MA-α-Fe2O3)

were

in

situ

electrochemically synthesized on the fluorine-doped tin oxide coated glass (FTO) substrate and studied for electrocatalytic reduction and sensing H2O2. Morphology and crystallinity of films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The vertical aligned MA-α-Fe2O3 mesostructured films showed (110) preferential growth, offering both the fast electron transfer path and diffusion of reactants and products. Thus the sensing performance of MA-α-Fe2O3 displayed an unprecedented sensitivity of 422.5 μA/(mMcm2), a wide linear range up to 3.145 mM and an excellent detection limit of 22 μM. Furthermore, the sensor also exhibited good anti-interference, reproducibility, stability, feasibility for real sample detection. These results indicated that MA-α-Fe2O3 could be a promising electrochemical material as nonenzymatic H2O2 sensor.

Keywords: mesoporous α-Fe2O3 nanoflakes; H2O2 sensor; crystal orientation; high sensitivity; electrochemical catalysts. 1 / 25

1. Introduction Hydrogen peroxide(H2O2) is a critical intermediate that plays an essential role in clinical diagnosis, food, environmental field, industrial field and energy reactions, which include oxygen evolution reaction(OER), oxygen reduction reaction(ORR) etc.[1] Owing to the importance, multiple methods have been developed for the detection

of

H2O2,

such

as

spectrophotometry[2],

fluorescence[3],

chemiluminescence[4], enzymatic methods[5]. However, these methods are complex, expensive, time consuming and poor long-term stability. Electrochemical approach for H2O2 detection has attracted tremendous attention for its practical merits, such as time saving, simplicity, low-cost and suitable for real-time application.[6,7] Till now, many excellent electrochemical sensors have been developed, the enzyme or protein based sensor exhibited high sensitivity and specificity[8,9], but they are instable, high cost, time consuming and affected by the working conditions(temperature, pH, toxic chemicals)[10,11]. Comparing with the enzymatic electrodes, the nonenzymatic electrodes are implemented, such as noble metals, noble metal alloys. However, these electrodes have serious drawbacks of low sensitivity and high cost[12,13]. Therefore, the development electrocatalysts with low cost, high sensitivity and stability for nonenzymatic H2O2 detection are urgent. α-Fe2O3 is the promising metal oxide for the active electrode material of nonenzymatic electrochemical sensors. Due to the low cost, environmental friendly, chemical stable over a broad range of pH, and abundant[14], α-Fe2O3 has been widely used as sensors[15–17]. Its performance not only depends on the instinct properties, 2 / 25

but also relies on its microstructure. Especially, the α-Fe2O3 with microstructure in nanoscale shows unique physical, electronic properties[18]. Considering the agglomeration of nanoparticles, large size particles always appear during the preparation, therefore tuning the size and morphology of α-Fe2O3 have attracted tremendous attention. Until now, α-Fe2O3 with unique microstructures and excellent properties of H2O2 sensing have been synthesized with the assist of surfactants. The α-Fe2O3 nanorings were found effective in sensing H2O2 with the sensitivity of 310.0 μA mM -1 cm-2[19]. H. Chen et al.[10]prepared crumpled α-Fe2O3 particles by the liquid phase-based ultrasonic-assisted method, and it displayed a sensitivity of 385.59 μA mM-1 cm-2. S. Majumder et al.[15]synthesized the α-Fe2O3 with 3D microsnowflakes architecture, and its sensitivity reached 7.16 μA mM-1 cm-2. In spite of this, these nanoparticles were also prone to aggregating when they were integrated on the electrode, reducing the efficient diffusion of reactants and products, and the preparations were tedious[11]. Furthermore, the sensitivity and stability of sensor also suffered from the weak mechanical interaction between the catalysts and substrates[20], and prevented these nanomaterial sensors from being widely used in practical application[21]. Herein, we prepared free-standing, mesoporous aligned hematite nanoflakes (MA-α-Fe2O3) for electrochemical enzyme-free sensing of H2O2 via in situ electrodeposition method (Scheme S1), which kept the sensors from agglomeration and displayed the strong mechanical strength with the substrate. Such an in-situ prepared nanoflakes not only showed good mechanical robustness, well electrical 3 / 25

contact, and fast electron transfer, but supplied the suitable paths for mass transport, which would further improve the sensitivity of the sensors. Cyclic voltammetry (CV) and chronoamperometry were used to detect the electrochemical performance of the sensor. The MA-α-Fe2O3 exhibited high catalytic activity towards H2O2. The wide linear range changed from 0.05 to 3.145 mM, a low detection limit of 22 μM and a sensitivity of 422.5 μA/(mMcm2). To the best of our knowledge, this was the highest sensitivity ever achieved with hematite. Moreover, the sample also exhibited a satisfactory anti-interference performance, real sample detection, reproducibility and stability. Such an efficient H2O2 sensor possessed excellent potential for practical applications. 2. Experimental 2.1 Material synthesis The free-standing, vertical aligned MA-α-Fe2O3 film was prepared by electrodeposition

method.

Initially,

the

fluorine

doped

tin

oxide

(FTO)

substrates[22,23] were cleaned by washing with the acetone (once), ethanol(twice), for 30 min in an ultrasonic bath, respectively. The electrolyte contained 0.3 M NH4Cl, 0.2 M FeCl2·4H2O, and pH was adjusted by adding a small amount of 1 M NaOH and was monitored by the Fisher Scientific Accumet pH meter[24]. Then the electrodeposition were carried out in a three-electrode system using Bipotentiostat (Model AFCBP1) with FTO as working electrode(WE), a platinum plate (1.0 cm ×1.0 cm) as counter electrode(CE), Ag/AgCl electrode (saturated KCl) as reference electrode(RE), as shown in the Scheme S1. Nitrogen was purged before and during 4 / 25

the electrodeposition. The as-prepared electrodes were further calcined in the oven at 500 °C for 2 h, and then furnace cooling. 2.2 Characterization The morphology of electrodes was characterized by FE-SEM (Field Emission Scanning Electron Microscope, JEM-7001F) and HR-TEM (High Resolution Transmission Electron Microscope, JEM-2100F). The X-ray Diffraction (XRD) patterns of the samples were taken on a PANnalytical-X’Pert diffract meter with a Cu Kα radiation. 2.3 Electrochemical measurement Electrochemical experiments were performed in a three-electrode system using Bipotentiostat (Model AFCBP1) with MA-α-Fe2O3 as WE, the active area was 1 cm2, a platinum plate (1.0 cm ×1.0 cm) as CE, Ag/AgCl electrode (saturated KCl) as RE. The electrolyte was 0.01 M phosphate-buffered saline (PBS), which pH was 7.4. All the reagents which were purchased from the Sinopharm chemical regents Co.,Ltd. were of analytical regent grade and used without further purification. And all solutions throughout experiments were prepared with deionized water. 3. Results and discussion 3.1 Structure and morphology of the MA-α-Fe2O3 The crystalline structures of electrodes are shown in Figure 1. The as-deposited electrode only shows the diffraction peaks from the FTO substrate (SnO2, PDF#41-1445), as shown in Figure 1(a), indicating the amorphous nature of Fe species on the electrode during the electrodeposition. Figure 1(b) shows the XRD 5 / 25

pattern of film calcined at 500°C for 2 h in air, the distinguishable diffraction peaks at 2θ=24.1°, 33.2°, 35.6°, 40.9°, 49.5°, 54.1°, 62.4°, 64.0° can be indexed to the rhombohedral α-Fe2O3 (PDF#33-0664). No characteristic peaks are observed for impurities, such as β-FeOOH, Fe3O4. In addition, the MA-α-Fe2O3 shows (110) orientation preference, indicating more (001) planes lie perpendicular to the FTO. α-Fe2O3 shows great anisotropic conductivity due to the crystal structure, in which the electron mobility in (001) basal plane is 104 faster than in its orthogonal planes. This behavior is similar to graphite and MoS2[25,26], which also show divergent electrode kinetics between basal plane and edge plane. As for graphite, the edge plane provides the active sites and electron transport, while for the MoS 2, edge plane shows much faster electron transfer kinetics. These phenomena indicate that the MA α-Fe2O3 electrode may show excellent responsive of H2O2 for the fast electron transport ability in (001) planes[27,28]. The morphology of MA-α-Fe2O3 before and after calcination was characterized by FE-SEM, as shown in Figure 2. Figure 2(a), (b) shows the as-deposited film that consists of nanoflakes roughly 50 nm in thickness, 0.5-3 μm in length, about 2.5μm in height (from the cross-section view of nanoflakes in Figure 2(b)). These nanoflakes are vertically oriented, random distributed on the FTO and formed macro pores with a diameter of about 500 nm. The film morphology after calcination is shown in Figure 2(c). With the top edge changes from straight to curved, the macro pores between nanoflakes grow larger to about 750 nm. Meanwhile, mesoporous pores can be seen clearly on the lateral surface of the nanoflakes. The obvious changes can be attributed 6 / 25

to the volumetric shrinkage of the nanoflakes during the calcination for the loss of hydroxyl groups and water molecules. However, the height of nanoflakes changes little, as shown in Figure 2(d). In addition, from the cross section in Figure 2(d), the free-standing MA-α-Fe2O3 displays strong mechanical interaction between the catalysts and substrate, further indicating the qualification for practical application. To further investigate the mesoporous structure on the nanoflakes, they were starched from the MA-α-Fe2O3 film with a blade and diffused into the ethanol, then transferred to the Cu grid. The TEM image of a piece of nanoflake (Figure 3(a)) displays mesoporous structure, which is composed of nanoparticles with a size of 20-40 nm, as shown in Figure 3(c), and it is consistent with the SEM observation. Such a mesoporous structure is beneficial for the diffusion of reactants and products during the electrochemical reaction. The selected area electron diffraction(SAED) pattern in Figure 3(b) demonstrates polycrystalline nature of the nanoflakes. Moreover, the detailed conditions optimization, such as the influence of electrolyte pH and electrodeposition time on morphology and H2O2 sensoring were investigated, as shown in supporting information Figure S1-S4, Table S1-S2. 3.2 The sensing performance of MA-α-Fe2O3 The mechanism of H2O2 reduction is illustrated in Scheme S1, Fe(III) was firstly reduced to Fe(II), which then reduced the H2O2 into H2O, and corresponding with the Fe(II) oxidizing to Fe(III).[29] The electrocatalytic behavior of MA-α-Fe2O3 towards H2O2 reducing was characterized by the CVs in 0.01 M PBS buffer with the scan rate of 10 mV/s in the 7 / 25

potential range of -0.6 ~ 0.2 V at room temperature, as shown in Figure 4. In the presence of H2O2, MA-α-Fe2O3 shows a cathodic peak near -0.17 V, which can be assigned to a typical electrocatalytic reduction process towards H 2O2. The H2O2 reduction peak current intensity increases as a function of H2O2 concentration, demonstrating the potential capability of the prepared hematite electrode to be utilized in amperometric current-time application for the precisely detection of H2O2. To evaluate the reaction kinetics, Figure 5(a) displays CVs of the MA-α-Fe2O3 electrode measured at different scan rates in 0.01 M PBS electrolyte. The cathodic peak current increases with the scan rate. The linear relationship of peak current versus the square root of scan rate is shown in Figure 5(b), suggesting that the process is diffusion-controlled. Such a relationship confirms the fast charge transport in the MA-α-Fe2O3 matrix. The MA-α-Fe2O3 electrodes were further investigated with amperometry method to characterize the H2O2 sensing performance, including sensitivity, detection limit, and linear range. The H2O2 stock solution was added into the 0.01 M PBS solution (pH=7.4) at an applied potential of -0.17 V vs Ag/AgCl successively with constant stirring. Figure 6(a) shows the current response curve of the electrode. Obviously, the H2O2 sensor shows a fast response within 4.5 s, which is comparable to the other excellent sensors[20]. Meanwhile, its current density increases with the H2O2 concentration. When the concentration is over 3.145 mM, the current response deviates the linear, then reaches the plateau slowly (Figure 6(b)). And the linear equation

curve

for

H2O2 8 / 25

sensing

is

expressed

as:

in the

linear range of 0.05~3.145 mM (R2=0.996). The detection limit is calculated to be as low as 22 μM at the signal to noise of 3. Meanwhile, the sensitivity achieves 422.5 μA/(mMcm2) by the slope of linear curve. To the best of our knowledge, this is the highest sensitivity ever achieved with hematite, which is even higher than some precise

metal

sensors

and

graphene

based

sensors,

enzymatic

H2O2

biosensors[8,20,30]. The performance of the electrode with other sensors are compared both in Table 1 and Table S3. The excellent sensitivity can be attributed to two reasons, on the one hand, the fast electron transport in the film with preferred (110) orientation, for which the electron mobility in (001) is 104 higher than in its orthogonal planes, as reported in our previous works[27,28]. On the other hand, the porous MA structure would facilitate the diffusion of reactants and products during the electrochemical reaction. The selectivity is the essential core of electrochemical sensors. Herein, the anti-interference investigation of the MA-α-Fe2O3 sensor was tested by adding the ascorbic acid(AA) and uric acid(UA), glucose, nitrite, and methanol. The experiments were carried out in 0.01 M PBS of pH 7.4. At the applied potential of -0.17 V vs Ag/AgCl, the effects of AA, UA, glucose, nitrite, and methanol with 0.1 mM for the detection of 0.5 mM H2O2 can be totally negligible, as shown in Figure 7. Obviously, the test data shows that sensor features high capability of anti-interference, as well as the good stability. The reproducibility of the prepared hematite electrode was studied by preparing 9 / 25

3 electrodes separately under the same conditions. The anodic currents of these 3 electrodes towards 50 M H2O2 yielded a relative standard deviation (RSD) of 4.1%, which indicated an acceptable reproducibility. For one electrode, it was stored in room temperature for three months and the cathodic current of 50 M H2O2 was retained 92.7% of its initial value. In order to demonstrate the feasibility of using the prepared electrode for practical analysis, the electrode was applied to detect the H 2O2 in diluted disinfectant (labeled 2-3% H2O2). In comparison with the potassium permanganate titration method, the results determined by the H2O2 sensor were in satisfactory agreement, as shown in Table 2. The result proved that the sensor had potential to apply in determination of H2O2 in real samples.

4. Conclusions In summary, we have represented a simple method to prepare the mesoporous hematite nanoflakes originally, which are vertically aligned on the FTO. The (110) preferential orientation of the nanoflakes provides the fast charge transport path, and the mesoporous structure formed by α-Fe2O3 particles presents the ideal sites for the diffusion of products and reactants. The results demonstrate that the sensor made of the MA-α-Fe2O3 exhibits an unprecedented sensitivity of 422.5 μA/(mMcm2), a wide linear range up to 3.145 mM and an excellent detection limit of 22 μM. And the electrode also showed the significant anti-interference stability, and feasibility for real sample detection. Therefore, the MA-α-Fe2O3 is the promising H2O2 sensor for the

potential application in the field of energy reactions, catalysis, diagnosis, etc. 10 / 25

Acknowledgements We acknowledge the Research Foundation of Young Teachers in Anhui University of Technology (Nos.QZ201720 and QZ201605), the Open Foundation of State Key Laboratory

of

Rolling

Technology

and

Automatic

Rolling,

Northeastern

University(No.2016006), and National Natural Science Foundation of China (Nos.51674004 and 51676001) for financial support.

11 / 25

References

[1] Y. Jiao, Y. Zheng, M. Jaroniec, S.Z. Qiao, Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions, Chem. Soc. Rev. 44 (2015) 2060–2086. [2]

E.M.

Elnemma,

Spectrophotometric

determination

of

hydrogen

peroxide

by

a

hydroquinone-aniline system catalyzed by molybdate, Bull. Korean Chem. Soc. 25 (2004) 127–129. [3]

E. Ito, S. Watabe, M. Morikawa, H. Kodama, R. Okada, T. Miura, Detection of H2O2 by Fluorescence Correlation Spectroscopy, in: Methods Enzymol., Elsevier, 2013: pp. 135–143.

[4]

S. Hanaoka, J.-M. Lin, M. Yamada, Chemiluminescent flow sensor for H2O2 based on the decomposition of H2O2 catalyzed by cobalt(II)-ethanolamine complex immobilized on resin, Anal. Chim. Acta. 426 (2001) 57–64.

[5]

A.K.M. Kafi, G. Wu, A. Chen, A novel hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase onto Au-modified titanium dioxide nanotube arrays, Biosens. Bioelectron. 24 (2008) 566–571.

[6]

K. Fang, Y. Yang, L. Fu, H. Zheng, J. Yuan, L. Niu, Highly selective H2O2 sensor based on 1-D nanoporous Pt@C hybrids with core-shell structure, Sens. Actuators B Chem. 191 (2014) 401–407.

[7]

Y. Xue, G. Maduraiveeran, M. Wang, S. Zheng, Y. Zhang, W. Jin, Hierarchical oxygen-implanted MoS2 nanoparticle decorated graphene for the non-enzymatic electrochemical sensing of hydrogen peroxide in alkaline media, Talanta. 176 (2018) 397–405.

[8]

G. Fusco, P. Bollella, F. Mazzei, G. Favero, R. Antiochia, C. Tortolini, Catalase-based modified graphite electrode for hydrogen peroxide detection in different beverages, J. Anal. Methods Chem. 2016 (2016) 1–12.

[9]

J. Hong, Y.X. Zhao, B.L. Xiao, A. Moosavi-Movahedi, H. Ghourchian, N. Sheibani, Direct electrochemistry of hemoglobin immobilized on a functionalized multi-walled carbon nanotubes and gold nanoparticles nanocomplex-modified glassy carbon electrode, Sensors. 13 (2013) 8595–8611.

[10] C. Hao, F. Feng, X. Wang, M. Zhou, Y. Zhao, C. Ge, K. Wang, The preparation of Fe 2O3 nanoparticles by liquid phase-based ultrasonic-assisted method and its application as enzyme-free sensor for the detection of H2O2, RSC Adv. 5 (2015) 21161–21169. [11] L. Li, Z. Du, S. Liu, Q. Hao, Y. Wang, Q. Li, T. Wang, A novel nonenzymatic hydrogen peroxide sensor based on MnO2/graphene oxide nanocomposite, Talanta. 82 (2010) 1637–1641. [12] P. M. Nia, F. Lorestani, W.P. Meng, Y. Alias, A novel non-enzymatic H2O2 sensor based on polypyrrole nanofibers–silver nanoparticles decorated reduced graphene oxide nano composites, Appl. Surf. Sci. 332 (2015) 648–656. [13] D. Suazo. Dávila, J. R. Meléndez, J. Koehne, M. Meyyappan, C.R. Cabrera, Surface analysis and electrochemistry of a robust carbon-nanofiber-based electrode platform H2O2 sensor, Appl. Surf. Sci. 384 (2016) 251–257. [14] G.S. Cao, P. Wang, X. Li, Y. Wang, G. Wang, J. Li, A sensitive nonenzymatic hydrogen peroxide sensor based on Fe3O4–Fe2O3 nanocomposites, Bull. Mater. Sci. 38 (2015) 163–167. [15] S. Majumder, B. Saha, S. Dey, R. Mondal, S. Kumar, S. Banerjee, A highly sensitive non-enzymatic hydrogen peroxide and hydrazine electrochemical sensor based on 3D 12 / 25

micro-snowflake architectures of α-Fe2O3, RSC Adv. 6 (2016) 59907–59918. [16] C.V.Gopal Reddy, O.K. Tan, W. Cao, W. Zhu, Preparation of Fe2O3(0.9)-SnO2(0.1) by hydrazine method application as an alcohol sensor, Sens. Actuator B. 81 (2002) 170–175. [17] P. Karthick Kannan, R. Saraswathi, An impedimetric ammonia sensor based on nanostructured α-Fe2O3, J. Mater. Chem. A. 2 (2014) 394–394. [18] W. Chen, S. Cai, Q.Q. Ren, W. Wen, Y.D. Zhao, Recent advances in electrochemical sensing for hydrogen peroxide: a review, The Analyst. 137 (2012) 49–58. [19] X. Hu, J.C. Yu, J. Gong, Q. Li, G. Li, α-Fe2O3 nanorings prepared by a microwave-assisted hydrothermal process and their sensing properties, Adv. Mater. 19 (2007) 2324–2329. [20] S. Du, Z. Ren, J. Wu, W. Xi, H. Fu, Vertical α-FeOOH nanowires grown on the carbon fiber paper as a free-standing electrode for sensitive H2O2 detection, Nano Res. 9 (2016) 2260–2269. [21] J. Jiang, Y. Li, J. Liu, X. Huang, C. Yuan, X.W.D. Lou, Recent advances in metal oxide-based electrode architecture design for electrochemical Energy storage, Adv. Mater. 24 (2012) 5166–5180. [22] K.T. Lee, D.M. Liu, Y.Y. Liang, N. Matsushita, T. Ikoma, S.Y. Lu, Porous fluorine-doped tin oxide as a promising substrate for electrochemical biosensors—demonstration in hydrogen peroxide sensing, J. Mater. Chem. B. 2 (2014) 7779–7784. [23] C.Y. Lin, Y.H. Lai, A. Balamurugan, R. Vittal, C.W. Lin, K.C. Ho, Electrode modified with a composite film of ZnO nanorods and Ag nanoparticles as a sensor for hydrogen peroxide, Talanta. 82 (2010) 340–347. [24] S.H. Tamboli, G. Rahman, O.S. Joo, Influence of potential, deposition time and annealing temperature on photoelectrochemical properties of electrodeposited iron oxide thin films, J. Alloys Compd. 520 (2012) 232–237. [25] C.E. Banks, R.G. Compton, Edge plane pyrolytic graphite electrodes in electroanalysis: An [26]

[27]

[28]

[29]

[30] [31]

[32]

overview, Anal. Sci. 21 (2005) 1263–1268. S.M. Tan, A. Ambrosi, Z. Sofer, Š. Huber, D. Sedmidubský, M. Pumera, Pristine basal- and edge-plane-oriented molybdenite MoS2 exhibiting highly anisotropic properties, Chem. Eur. J. 21 (2015) 7170–7178. J. Cai, S. Li, Y. Liu, M. Gao, D. Wang, G. Qin, Orientation modulated charge transport in hematite for photoelectrochemical water splitting, Funct. Mater. Lett. 9 (2016) 1650047–1650047. S. Li, J. Cai, Y. Liu, M. Gao, F. Cao, G. Qin, Tuning orientation of doped hematite photoanodes for enhanced photoelectrochemical water oxidation, Sol. Energy Mater. Sol. Cells. 179(2018). 328–333. C. Hao, Y. Shen, Z. Wang, X. Wang, F. Feng, C. Ge, Y. Zhao, K. Wang, Preparation and characterization of Fe2O3 nanoparticles by solid-phase method and its hydrogen peroxide sensing properties, ACS Sustain. Chem. Eng. 4 (2016) 1069–1077. R. Zhang, W. Chen, Recent advances in graphene-based nanomaterials for fabricating electrochemical hydrogen peroxide sensors, Biosens. Bioelectron. 89 (2017) 249–268. A.K. Dutta, S.K. Maji, D.N. Srivastava, A. Mondal, P. Biswas, P. Paul, B. Adhikary, Peroxidase-like activity and amperometric sensing of hydrogen peroxide by Fe2O3 and Prussian Blue-modified Fe2O3 nanoparticles, J. Mol. Catal. Chem. 360 (2012) 71–77. X. Liu, J. Liu, Z. Chang, L. Luo, X. Lei, X. Sun, α-Fe2O3 nanorod arrays for bioanalytical applications: Nitrite and hydrogen peroxide detection, RSC Adv. 3 (2013) 8489–8489. 13 / 25

Table 1 Table 1 Comparison of linear range (LR), sensitivity and detection limit (DL) of various H2O2 sensors. Electrode materials

LR(mM)

Sensitivity

DL(μM)

Reference

Fe2O3/GC

0.01-0.15

2.40 μA/mM

11

[31]

3D micro-snowflake structure α-Fe2O3

0.1-5.5

7.2 μA/(mMcm2)

10

[15]

α-Fe2O3 nanorod arrays

0.0005-3

77.3 μA/(mMcm2)

0.2

[32]

G-Fe2O3-CS/GC

0.01-6

84.3 μA/(mMcm2)

1.1

[29]

Vertical α-FeOOH

0-6.5

194.0 μA/(mMcm2)

18

[20]

α-Fe2O3 nanorings

0.0005-0.11

310.0 μA mM-1 cm-2

N/A

[18]

MA-α-Fe2O3 nanoflakes

0.05-3.145

422.5 μA/(mMcm2)

22

This work

14 / 25

Table 2 Table2 Results of H2O2 analysis in disinfectant sample determined by the proposed amperometric sensor and the titration method. Sample

Present method(μM)

RSD(%)

Titration method(μM)

RSD(%)

Disinfectant

878.6

0.58

882.0

0.65

15 / 25

Figure captions Figure 1 XRD patterns of the films electrodeposited in 0.2 M FeCl2, at -0.2 V vs Ag/AgCl, for 5 min, (a) as-deposited and (b) after calcination at 500 °C for 2 h in air. Figure 2 SEM of the surface and cross-section of films, (a)-(b) as-deposited, and (c)-(d) after annealing in air at 500°C for 2 h. Figure 3 (a) Low magnification TEM image, (b) the SAED pattern, and (c) high magnification TEM image of a piece of nanoflake from MA α-Fe2O3. The sample was prepared in 0.2 M FeCl2 at -0.2 V Ag/AgCl for 5 min, and followed by annealing in air at 500°C for 2 h. Figure 4 CV response of MA-α-Fe2O3 to H2O2 with different concentration at a scan rate of 10 mV/s in 0.01 M PBS electrolyte (pH 7.4) at room temperature. Figure 5 (a) CV of MA-α-Fe2O3 electrode in the 0.01 M PBS, 0.2 mM H2O2 electrolyte at different scan rate (20, 30, 40, 50, 60, 70, 80, 90 mV/s), (b) regression plot, equation, factor of peak current with the square root of scan rate. Figure 6 (a) Amperometric response obtained under the increasing H2O2 concentration at -0.17 V vs Ag/AgCl for MA-α-Fe2O3 electrode, (i), (ii) are the magnified view of amperometric response when the H2O2 concentration is 0.05 mM and 0.1 mM (b) corresponding linear fit plot of current vs concentration of H2O2. Figure 7 Amperometric response of the 0.5 mM H2O2 of MA-α-Fe2O3 electrode upon subsequent additions of 0.1 mM AA, UA, glucose, nitrite, and methanol at -0.17 V vs Ag/AgCl in 0.01 M PBS of pH 7.4.

16 / 25

Figure 1

17 / 25

Figure 2

18 / 25

Figure 3

19 / 25

Figure 4

20 / 25

Figure 5

21 / 25

Figure 6

22 / 25

Figure 7

23 / 25

Graphical

Abstract

Free-standing, mesoporous aligned hematite nanoflakes(MA-α-Fe2O3) have been successfully prepared on a substrate by the simple electrodeposition method. The MA-α-Fe2O3 exhibits high catalytic activity towards H2O2. It displays an unprecedented sensitivity of 422.5 μA/(mM cm2), a wide linear range up to 3.145 mM and an excellent detection limit of 22 μM.

24 / 25

Research Highlights Mesoporous, vertical aligned nanoflakes film is prepared by in situ electrodeposition. Film provides high active sites, facilitates the diffusion of reactants and products. The (110) preferred film is provided with the fast electron transport path. As H2O2 sensor, the hematite film exhibits remarkable sensitivity.

25 / 25