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Hydrothermalsynthesizedurchin-likenickel-cobaltcarbonatehollowspheresforsensitiveamperometricdetectionofnitrite

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DOI:10.1016/j.jallcom.2017.03.059

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Journal of Alloys and Compounds 708 (2017) 780e786

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Journal of Alloys and Compounds

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Hydrothermal synthesized urchin-like nickel-cobalt carbonate hollowspheres for sensitive amperometric detection of nitrite

Shun Lu a, b, Chi Yang a, *, Ming Nie b, **

a Yale-NUIST Center on Atmospheric Environment, Nanjing University of Information Science and Technology, Nanjing 210044, Chinab Faculty of Materials and Energy, Southwest University, Chongqing 400715, China

a r t i c l e i n f o

Article history:Received 6 February 2017Received in revised form1 March 2017Accepted 6 March 2017Available online 8 March 2017

Keywords:Urchin-likeNickel-cobalt carbonateElectrochemical sensorNitrite

* Corresponding author.** Corresponding author.

E-mail addresses: yangchi@seu.edu.cn (C. Yang), ni

http://dx.doi.org/10.1016/j.jallcom.2017.03.0590925-8388/© 2017 Elsevier B.V. All rights reserved.

a b s t r a c t

In this article, we present a facile and low-cost method to prepare urchin-like nickel-cobalt carbonatehollow spheres that display excellent electrooxidation of nitrite. The as-fabricated samples are charac-terized by XRD, SEM, TGA, and BET. The results confirm that the successful formation of nickel carbonateand cobalt carbonate at ratio of 1/2, and their entirely uniform hollow microspherical structure with anaverage pore size of 4 nm and a pore volume of 0.15 cm3 g�1. Moreover, the as-prepared nitrite sensor hasa good electrochemical response with the linear range of 5e4000 mM and the detection limit of 0.002 mMunder optimum conditions, respectively with the correlation coefficient of 0.999. The fabricated nitritesensor also exhibited high sensitivity and good stability.

© 2017 Elsevier B.V. All rights reserved.

1. Introduction

Growing concernworldwide about environmental pollution andits effect on the air quality, food safety and human health, envi-ronment problems had attracted much attention in the past de-cades [1,2]. Unlike several other global problems such asgreenhouse effect and soil erosion, ubiquitous urban smog (PM 2.5,particulate matter less than 2.5 mM) has rapidly ascended to hottopic mostly due to soaring public outcries and extensive mediacoverages while related research discourse clearly lags behind. Onaverage, PM 2.5 is majorly composed of organic matters, sulfate,nitrate and ammonium in Beijing [3], Although the detailed effectsof each type of PM on health have not yet been established, recentstudies have identified a strong exposureeresponse relationshipbetween PM and both short-term and long-term health effects [4].Therefore, monitoring air, soil and water for hazardous pollutants isimportant and based on the need to protect the environment andpublic health from potential pollutants.

Nitrite, an intermediate product in the nitrogen cycle, is also oneof the most common pollutants in aquatic environment [5]. Theimportance of nitrite stems from its effects on human health, and

emingcqu@126.com (M. Nie).

nitrite can become poisonous at high concentrations to animals andhuman beings because it probably results in generation of carci-nogenic nitrosamines [6]. Nitrous acidmay dissociate in to OH� andNOþ. The latter radical oxidizes the Fe2þ of the hemoglobin to Fe3þ,which in oxidized form is unable to adsorb O2 [7]. Therefore, thedetection of nitrite (NO2

�) is of great importance. Additionally, ni-trite is widely used as a preservative, dyeing agent, fertilizer andfood additive [8,9]. Nitrite is also important in biochemistry as asource of the potent vasodilator nitric oxide [10]. Therefore, a va-riety of techniques have been developed for the detection andmonitoring of nitrite, such as chromatography, chemiluminescence,capillary electrophoresis, spectrophotometry and electrochemicalmethods [11e15]. Among them, electrochemical techniques arepreferred because of their rapid response, relatively low cost, highsensitivity, time saving, and good selectivity [15,16].

Generally, the electrochemical methods for detection of nitrite,can be divided into two distinct types: (1) oxidation, and (2)reduction, of nitrite on different electrodes [10]. Anodic oxidation ofnitrite is preferred with the final product of nitrate (NO3

�), due toseveral by-products depending on electrode condition and prop-erty of catalysts affecting reduction of nitrite on cathode [17,18].However, the electrooxidation of nitrite has some drawbacks,sluggish electron transfer kinetics included. Additionally, theoxidation of nitrite on these conventional solid electrodes, stillsuffers large overpotentials, causes surface oxide formation as wellas fouling effects, and decreases the selectivity and accuracy by

S. Lu et al. / Journal of Alloys and Compounds 708 (2017) 780e786 781

other electroactive interferences [18]. In order to circumvent theseinherent difficulties, the surface of bare electrodes is being modi-fied with suitable catalysts to increase interfacial electron transferand decrease the oxidation potential [9].

Recently, nano/micro devices fabricated by nanometer-sizedbuilding blocks have been regarded as promising electrocatalyststoward energy storage and conversion, such as oxygen reductionreaction (ORR), oxygen evolution reaction (OER), and electro-chemical capacitors (ECs) due to their nano/micro-scale secondblocks and large active sites density [19e22]. Particularly, spinelnickel cobaltite (NiCo2O4), as one of mixed metal compounds, hasrecently attracted growing interests, because of its different mor-phologies and electrochemical applications [23]. Generally, thespinel NiCo2O4 is made up of Ni2þ, Co2þ, and urea via hydrothermaltreatment and thermal decomposition [24,25]. Among those pro-cedures, we accidently discovered its intermediate product, nickel-cobalt carbonate, which possesses novel structures and morphol-ogies [26,27]. To the best of our knowledge, nickel and cobalt-basedoxides, layered double hydroxides, and metal-organic frameworkshave attracted much attention because of their potentially highactivity and relatively easy operation, however, nickel-cobalt car-bonate (here, denoted as NC) with novel properties has been rarelystudied in electrochemical detection [24,26,28,29]. Previous liter-ature, which based on their nano/micro-structure and character-ized via microscopy techniques, were reported to detect nitrite,especially for porous materials. Mesopores are supposed to facili-tate the diffusion of reactants in the electrocatalytic process andincrease the number of available active sites [23]. Therefore, BETtest was applied to analysis its structure information.

Herein, we present a facile and low-cost method to prepareurchin-like NC hollow spheres that display excellent electro-oxidation of nitrite. The as-obtained hollow spheres have entirelyuniformmicrospherical structure with an average pore size of 4 nmand a pore volume of 0.15 cm3 g�1, which would facilitate reactanttransport inside the pores, assuring better contact the catalyst andbetter stability. The as-synthesized sensor shows good electro-chemical response to nitrite and offers a new platform fordesigning sensors to detect nitrite sensitively and selectively.

2. Experimental

2.1. Materials

Ni(NO3)2$6H2O and Co(NO3)2$6H2O were bought from Sigma-eAldrich (China) Co., Ltd. Sodium nitrite (NaNO2) was purchasedfrom Sinopharm Chemical Reagent Co., Ltd. Phosphate bufferedsolution (PBS, 0.1 M) containing 0.15 M NaCl was prepared bymixing different proportions of NaH2PO4 and Na2HPO4, and thenthe pH adjusted with 0.1 M NaOH and H3PO4. Deionized water wasused for preparation of aqueous solution, and all the chemicalsused in this study were analytical grade and were used withoutfurther purification.

2.2. Preparation of NiCo2CO3(OH)2 hollow spheres

In a typical synthesis, 40.0 g CO(NH2)2 was dissolved in 75 mLdeionizedwater with assistance of ultrasonic vibration, followed byrapid addition of 25 mL 1.46 g Ni(NO3)2$6H2O and 2.91 g Co(N-O3)2$6H2O aqueous solution. The mixturewas dealt with ultrasonicfor 30 min at room temperature, then the solution was transferredto a Teflon-lined stainless steel autoclave and heated in an oven at90 �C for 6 h. The precipitates were dried at 65 �C for 6 h in avacuum oven, then collected by centrifugal filtration, washed withdeionized water and absolute ethanol to obtain the NiCo2CO3(OH)2materials.

2.3. Characterization

To evaluate the crystalline structure of the as-obtained NC, X-raydiffraction measurements were carried out on a D/Max-III (XRD,Rigaku Co. Ltd., Japan) using Cu Ka radiation l ¼ 0.15406 nm at ascanning rate of 5�/min and operated at 34 kV and 26 mA. Themorphologies were observed by field emission scanning electronmicroscopy (FESEM, Hitachi S4800, Japan) and constituent contentwas analyzed by energy-dispersive X-ray spectroscopy (EDS, Ox-ford Co. Ltd., England). Transmission electron microscopy in-vestigations were carried out on TEM JEM-2010HR at 200 kV (TEM,JEOL, Japan), the corresponding selected area electron diffraction(SAED) and high resolution TEM (HRTEM) were used to charac-terize the morphology and structure. Thermogravimetric analysis(TGA) was conducted by an integrated thermal analyzer (STA 449C)with a heating speed of 10 �C/min in air. The Bru-nauereEmmetteTeller specific surface area (BET) of the samplewas characterized by analysis of the N2 adsorptionedesorptionisotherms, performed at 77 K with Micromeritics ASAP 2020sorption analyzer in a relative pressure (P/P0) range from 10�6 to 1after degassing the samples at 200 �C for 3 h.

2.4. Electrochemical characterization

Electrochemical studies were carried out in a standard three-electrode system controlled by electrochemical workstation (CHI630D, Chenhua Ltd, Co. China). A glassy carbon electrode (GCE,4 mm in diameter) was polished carefully on felt pads with 1.0, 0.3and 0.05 mm alumina slurry in turn and cleaned by brief sonicationin ethanol and water until a mirror-like surface was formed. Adefined amount of NC (2.0 mg) were suspended in 2 mL ethanoland ultrasonicated for 30 min. Then a drop of the suspension(1.0 mg/mL, 4.0 mL) was coated on the surface of freshly polishedGCE, then casted with nafion (wt. 5.0%, 4.0 mL) and dried in aninverted beaker at room temperature. The mass loading of activematerials was about 0.03 mg cm�2. The as-prepared NC spheresmodified on GCE (denoted as NCE), a platinum foil, and a saturatedcalomel electrode (SCE) were used as the working electrode,counter electrode, and reference electrode, respectively. The elec-trochemical performances were examined by cyclic voltammetry(CV) and amperometric response (i-t). The electrolytes for testswere 0.1 M PBS. All the tests were carried out at room temperature(about 25 �C).

3. Results and discussion

NC hollow spheres, which are mixedmetal carbonate salts, werefabricated by reacting metal cations (Ni2þ and Co2þ) with CO3

2� andOH� anions slowly released from the hydrolysis of urea during thehydrothermal process, as illustrated in Scheme 1.

X-ray diffraction is employed to characterize the crystal struc-ture of sample. Fig.1a depicts the typical Powder XRD pattern of theNC sample. By comparing the peak positions with the standard PDFcards, it is easy to found that this compound is composed of twophase: NiCO3(OH)2$2H2O (PDF #29-0868) andCo(CO3)0.5(OH)2$0.11H2O (PDF #48-0083), rather not NiCo2O4 (PDF#20-0781). Fig. 1bed demonstrates the FESEM images withdifferent magnifications for NC hollow spheres.

Urchin-like microspheres with a size of ~3.5 mm can be foundclearly in Fig. 1b, and the surface of these spherical structures isfixed with many nanowires (NWs) with sharp tips in a radial form,they take on an urchin-like appearance as a whole. Hollow struc-tures also can be confirmed (Fig. 1c). The as-obtained NC hollowsphere also entirely consists of uniform micro spherical structurewithout the size change, but spheres aggression in part area may

Scheme 1. Preparation of urchin-like NC hollow sphere and its modified electrode (NCE).

Fig. 1. Powder XRD patterns (a), different magnification SEM images (b, c) and thermogravimetric curve (d) of NC hollow spheres.

S. Lu et al. / Journal of Alloys and Compounds 708 (2017) 780e786782

result of decreasing the amount of active sites. Fig. 1d displays TGAcurves of NC hollow spheres in the temperature range of20e700 �C, which depict three different decomposition modes forthe various carbonate species produced from NC hollow spheres.The TGA curve showed a total weight loss of ~60% in the giventemperature range. Water loss of around 8% was observed until200 �C and the sum of CO2 weight loss arrived ~50% until 600 �C,which can be ascribed the decomposition of carbonates that cobaltand nickel carbonate included.

Fig. 2a describes the element mapping results for the distribu-tions of Ni and Co homogeneously based on an individual NC

hollow sphere. To further confirm the composition of the NCproduct, EDS was conducted. Ni, Co, C, and O elements weredetected (Fig. 2b), and the contents of Ni and Co were determinedto be 6.51 and 13.34%, respectively. The atom ratio of Ni to Co isclose to 1: 2, in good agreement with the stoichiometric ratio of Ni/Co in NiCo2CO3(OH)2 hollow spheres.

The NC hollow spheres have a large surface area of~101.54 m2 g�1 with a type-IV isotherm measured by the BETmethod [30]. The distinct hysteresis loop at a relative pressure ofabove 0.5e0.8 reflects the capillary condensation of mesopores, aspresented in Fig. 3a. The mesoporous structure has an average pore

Fig. 2. Element mapping (a) and EDS (b) of urchin-like NC hollow spheres.

Fig. 3. Nitrogen adsorption and desorption isotherm (a) and the corresponding BJH pore size distribution curve (b) of the urchin-like NC hollow spheres.

S. Lu et al. / Journal of Alloys and Compounds 708 (2017) 780e786 783

size of 4 nm and a pore volume of 0.15 cm3 g�1, as verified by theBarrett-Joyner-Halenda (BJH) method (inset of Fig. 3b). The meso-porous structure can be ascribed to the successive release and lossof CO2 and H2O during the hydrothermal treatment of the NiC-o2(OH)3y(CO3)1.5(2-y)$nH2O precursor [31].

TEM analysis was performed to examine the crystal orientationsand growth directions of urchin-like NC hollow spheres. It is foundthat NC hollow spheres are assembled by many nanospikes (Fig. 4aand b). HRTEM analysis provides more detailed structural infor-mation about the fine crystal structures (Fig. 4c). The clear latticefringes of NC, revealing their good crystallization. The distance ofthe interplanar distance between adjacent lattice spacing is ca.0.23 nm, which is consistent with the (1 1 1) planes of the face-centered-cubic (fcc) NC hollow spheres. This observation in-dicates that NC hollow spheres preferentially grow along the (111)directions in the present synthesis, although different orientationsof the lattice fringes are detected from other nanospikes. Addi-tionally, their polycrystalline structures are clearly demonstratedby the respective SAED pattern taken from urchin-like NC hollowspheres (Fig. 4d).

In order to evaluate the potential application of NC hollowspheres, electrochemical sensors for nitrite detection are fabricatedby dropping the dispersion solution with NC hollow spheres onsurface of GCE. Fig. 5a is the typical CV curves, showing the CVs ofbare GCE (dark cyan line) and NCE (red line) towards the oxidationof 5.0 mM nitrite, meanwhile, bare GCE (black line) and NCE (blueline) also are observed in the absence of nitrite. In the potentialrange of 0.2e1.2 V, bare GCE (black line) does not show any redoxpeak. In contrast, a dramatic change in the CV curve is observed

with the NCE (red line), especially around 0.9 V, which is corre-sponded to the oxidation of nitrite.

The plot of Fig. 5b demonstrates the influence of pH (in therange of 5.4e8.0) on the anodic peak current response. The resultsshow that the peak current increases rapidly with increasing pHand reaches a maximum at pH 7.0. Further increasing pH to 8.0decreases the current response. This result is well in accordancewith previous reports [9,32]. The cause of relatively low currentresponse at acidic mediummay be due to the disporportionation ofNO2

� to NO and NO3�. On the other hand, the lack of proton at higher

pH conditions will also affect the current response because theoxidation of nitrite is a proton dependent process. Moreover, someoxidation products formed at the electrode surface under high pHconditions would also inhibit the oxidation process. Therefore, pH7.0 was selected as the optimal pH. The charge transfer propertiesof NCE were characterized by the electrochemical method. Asdepicted in Fig. 5c, the obtained CVs at the bare GCE (black line) andNCE (red line) in the 5 mM K3[Fe(CN)6] and 0.1 M KCl solution at50 mV s�1. A pair of redox peaks was observed in each CV, whichwas ascribed to the redox of [Fe(CN)6]3þ. After being modified withNC, the anodic peak and cathodic peak (red line) both increasedbecause of the good electrical conductivity and large specific sur-face area of NC [26,33].

The effect of scan rate (n) on the oxidation of nitrite has beenperformed at NCE from 20 to 200 mV s�1 in PBS (0.1 M, pH 7.0)containing 5.0 mM nitrite. Fig. 6a depicts the relationship betweenscan rate and anodic current response of nitrite oxidation. It isnoted that the oxidation potential of nitrite gradually shifts to thepositive potential when the scan rate increases. The results show

Fig. 4. TEM (a and b) and HRTEM image (c), SAED pattern (d) of NC hollow spheres.

Fig. 5. (a) CVs on the bare GCE (black line), NCE (blue line) in 0.1 M PBS (pH 7.0) and bare GCE (dark cyan line), NCE (red line) in 0.1 M PBS (pH 7.0) with 5.0 mM nitrite solution, (b)The effect of pH on the current response of 5.0 mM nitrite at NCE, (c) CVs of the bare GCE (black line), and NCE (red line) in the 5 mM K3[Fe(CN)6]/0.1 M KCl solution. Scan rate:50 mV s�1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6. (a) CVs of nitrite (5.0 mM) on NCE in PBS (0.1 M, pH 7.0) at different scan rates (20e200 mV s�1), inset: the plot of peak current vs. square root of scan rates, (b) Amperometricresponse of NCE in 0.1 M PBS (pH 7.0) with 0.1 mM of nitrite solution at potential of 0.90 V, inset: the plot of I vs. t�1/2 derived from the amperometric i-t curve.

S. Lu et al. / Journal of Alloys and Compounds 708 (2017) 780e786784

Fig. 7. (a) Amperometric responses of nitrite on NCE upon successive addition of nitrite to 0.1 M PBS (pH 7.0) by applying a constant potential of 0.9 V. (b) the plot of current vs.nitrite concentration.

Table 1Comparison of NCE with other sensors for nitrite detection.

Electrode materials Methods Linear range/mM LOD/mM Ref.

Au aNPs/bCh cDPV 0.4e750 0.1 [35]Fe2O3 NPs/rGO DPV 0.05e780 0.015 [16]b-MnO2 Amperometric 0.29e26090 0.29 [36]AuePd/rGO Amperometric 0.05e1000 0.02 [37]Au NPs/dMWCPE eSWV 0.05e250 0.01 [38]Ag nanoplates Amperometric 10e1000 1.2 [39]NC Amperometric 5e4000 0.002 This work

a Nanoparticles.b Choline chloride (Ch).c Differential Pulse Voltammetry.d Multi-walled carbon nanotube/carbon paste electrode.e Square Wave Voltammograms.

S. Lu et al. / Journal of Alloys and Compounds 708 (2017) 780e786 785

that the oxidation current of nitrite is proportional to the squareroot of scan rate (the inset of Fig. 6a). The linear regression equationfor the anodic peak current is y ¼ 10.565 þ 1.36241*n1/2;R2 ¼ 0.99295. Good linear relationship obtained between n1/2 andIpa confirmed that the oxidation process is diffusion-controlled.Remarkably, the nitrite oxidation is a second-order homogeneousdisporportionation process and the mechanism of the oxidationcan be expressed as Eq. (1) [34].

NO2� þ H2O / NO3

� þ 2Hþ þ 2e� (1)

Fig. 8. (a) Amperometric response for the detection of 0.5 mM nitrite solution containing diffconstant potential of 0.9 V. Each addition increases 0.5 mM nitrite. (b) Stability tests for NC

Fig. 6b depicts the amperometric response of NCE in 0.1 mM ofnitrite solutionwhen a potential of 0.9 Vwas applied. A straight lineplot of the current against minus square root of time was deduced,as depicts in the inset of Fig. 6b, further confirming that theoxidation of nitrite is a typical diffusion controlled process.

Fig. 7a shows the amperometric iet curve obtained at NCE uponsuccessive addition of nitrite at the applied potential of 0.9 V. Thelinear response range of the biosensor was from 5 to 4000 mMwitha regression coefficient of 0.999 (n ¼ 19) and a sensitivity of1.21 � 10�4 mA mM�1 cm�2, and the detection limit (LOD) wasestimated to be 0.002 mM (a signal to noise ratio of 3) (Fig. 7b).Performances of various nitrite biosensors are listed in Table 1. It isclear that the performance of NCE was significantly improved. Theimportant analytical parameters such as test technique, linearrange, and LOD of the sensor were compared with previous reports(Table 1).

Interference experiments were performed to investigate theselectivity of the proposed sensor towards detection of NO2

� inpresence of common ions such as urea acid (UA), ascorbic acid (AA)and glucose (Fig. 8a), NCE exhibited well defined amperometricresponse towards detection of 0.5 mM of nitrite, whereas no note-worthy amperometric responses were observed for the addition of100, 40, and 100-fold excess of UA, AA, and glucose, respectively.But quick and stable response was observed again for the additionof 0.5 mM nitrite into the same PBS coexisting with the above said

erent interfering chemicals: 50 mM UA, 20 mM AA, 50 mM Glucose on NCE by applying aE in 0.1 M PBS (pH 7.0) containing 10 mM nitrite.

S. Lu et al. / Journal of Alloys and Compounds 708 (2017) 780e786786

interferences.The stability of the NCE was also studied. The CV currents could

be remained at constant values upon 100 continuous CV cycles atthe potential range from 0.2 to 1.2 V in 0.1 M PBS (pH 7.0) with thescan rate of 50 mV s�1. Fig. 8b shows that the current assigned tonitrite oxidation is 92.4% of the initial value after 100 cycles, thussuggesting good electrode stability owing to an efficient protectionof Nafion on the NCE.

4. Conclusions

In summary, we fabricated a simple, urchin-like electrocatalystwith the utilization of the nickel and cobalt carbonate compound,which offers this novel nanomaterial promising application forsensitive detection of nitrite. The as-prepared electrode made up ofNC and Nafion displayed good electrochemical response to nitritewith the linear range of 5e4000 mM and the detection limit of0.002 mM. All of these results further confirmed that the NCE playeda significant role in detection of nitrite. The successful applicationof nickel and cobalt carbonate compound indicates that modifiedelectrode provide a new platform for designing sensors to deter-mine nitrite sensitively and selectively. The fabricated nitritebiosensor also exhibited high sensitivity and good stability.

Acknowledgements

The financial supports from National Natural Science Founda-tion of China (61404075), China Postdoctoral Science Foundation(No.2016M601694) and Postdoctoral Science Foundation of JiangsuProvince (No.1601090B) are greatly acknowledged. S. Lu alsothanked the Center of Analysis and Testing of Southeast Universityfor its help in FESEM observation (Ying Zhang), BET operation(Zeming Wang).

References

[1] S. Peng, G. Jin, L. Li, K. Li, M. Srinivasan, S. Ramakrishna, J. Chen, Multi-func-tional electrospun nanofibres for advances in tissue regeneration, energyconversion & storage, and water treatment, Chem. Soc. Rev. 45 (2016)1225e1241.

[2] C.A. Martínez-Huitle, M.A. Rodrigo, I. Sir�es, O. Scialdone, Single and coupledelectrochemical processes and reactors for the abatement of organic waterpollutants: a critical review, Chem. Rev. 115 (2015) 13362e13407.

[3] Q. He, G. Zhou, F. Geng, W. Gao, W. Yu, Spatial distribution of aerosol hy-groscopicity and its effect on PM 2.5 retrieval in East China, Atmos. Res. 170(2016) 161e167.

[4] Q. Yin, J. Wang, M. Hu, H. Wong, Estimation of daily PM 2.5 concentration andits relationship with meteorological conditions in Beijing, J. Environ. Sci. 48(2016) 161e168.

[5] Y. Wang, S. Hu, Applications of carbon nanotubes and graphene for electro-chemical sensing of environmental pollutants, J. Nanosci. Nanotechnol. 16(2016) 7852e7872.

[6] W. Lijinsky, E. Conrad, R. Van de Bogart, Carcinogenic nitrosamines formed bydrug/nitrite interactions, Nature 239 (1972) 165e167.

[7] J.H. Seinfeld, S.N. Pandis, Atmospheric Chemistry and Physics: from AirPollution to Climate Change, Wiley-Interscience, New York, 2006, pp.761e818.

[8] K. Calfum�an, M.J. Aguirre, P. Canete-Rosales, S. Bollo, R. Llusar, M. Isaacs,Electrocatalytic reduction of nitrite on tetraruthenated metalloporphyrins/Nafion glassy carbon modified electrode, Electrochimica Acta 56 (2011)8484e8491.

[9] L. Fu, S. Yu, L. Thompson, A. Yu, Development of a novel nitrite electrochemicalsensor by stepwise in situ formation of palladium and reduced grapheneoxide nanocomposites, RSC Adv. 5 (2015) 40111e40116.

[10] J.O. Lundberg, E. Weitzberg, M.T. Gladwin, The nitrateenitriteenitric oxidepathway in physiology and therapeutics, Nat. Rev. Drug Discov. 7 (2008)156e167.

[11] C. Lopez-Moreno, I.V. Perez, A.M. Urbano, Development and validation of anionic chromatography method for the determination of nitrate, nitrite andchloride in meat, Food Chem. 194 (2016) 687e694.

[12] J. Wu, X. Wang, Y. Lin, Y. Zheng, J.-M. Lin, Peroxynitrous-acid-inducedchemiluminescence detection of nitrite based on microfluidic chip, Talanta154 (2016) 73e79.

View publication statsView publication stats

[13] Z. Kalaycıo�glu, F.B. Erim, Simultaneous determination of nitrate and nitrite infish products with improved sensitivity by sample stacking-capillary elec-trophoresis, Food Anal. Methods 9 (2016) 706e711.

[14] K.M. Miranda, M.G. Espey, D.A. Wink, A rapid, simple spectrophotometricmethod for simultaneous detection of nitrate and nitrite, Nitric Oxide 5 (2001)62e71.

[15] J. Davis, M.J. Moorcroft, S.J. Wilkins, R.G. Compton, M.F. Cardosi, Electro-chemical detection of nitrate and nitrite at a copper modified electrode, An-alyst 125 (2000) 737e742.

[16] S. Radhakrishnan, K. Krishnamoorthy, C. Sekar, J. Wilson, S.J. Kim, A highlysensitive electrochemical sensor for nitrite detection based on Fe2O3 nano-particles decorated reduced graphene oxide nanosheets, Appl. Catal. B Envi-ron. 148 (2014) 22e28.

[17] H. Wu, S. Fan, W. Zhu, Z. Dai, X. Zou, Investigation of electrocatalytic pathwayfor hemoglobin toward nitric oxide by electrochemical approach based onprotein controllable unfolding and in-situ reaction, Biosens. Bioelectron. 41(2013) 589e594.

[18] J. Jiang, W. Fan, X. Du, Nitrite electrochemical biosensing based on coupledgraphene and gold nanoparticles, Biosens. Bioelectron. 51 (2014) 343e348.

[19] Y.G. Guo, J.S. Hu, L.J. Wan, Nanostructured materials for electrochemical en-ergy conversion and storage devices, Adv. Mater. 20 (2008) 2878e2887.

[20] J. Wang, Y. Fu, Y. Xu, J. Wu, J.-H. Tian, R. Yang, Hierarchical NiCo2O4 hollownanospheres as high efficient bi-functional catalysts for oxygen reduction andevolution reactions, Int. J. Hydrog. Energy 41 (2016) 8847e8854.

[21] X. Lv, Y. Zhu, H. Jiang, X. Yang, Y. Liu, Y. Su, J. Huang, Y. Yao, C. Li, Hollowmesoporous NiCo2O4 nanocages as efficient electrocatalysts for oxygen evo-lution reaction, Dalton Trans. 44 (2015) 4148e4154.

[22] G. Gao, H.B. Wu, S. Ding, L.M. Liu, X.W. Lou, Hierarchical NiCo2O4 nanosheetsgrown on Ni nanofoam as high-performance electrodes for supercapacitors,Small 11 (2015) 804e808.

[23] X. Tong, S. Chen, C. Guo, X. Xia, X.Y. Guo, Mesoporous NiCo2O4 nanoplates onthree-dimensional graphene foam as an efficient electrocatalyst for the oxy-gen reduction reaction, ACS Appl. Mater. Interfaces 8 (42) (2016)28274e28282.

[24] G. Zhang, B.Y. Xia, X. Wang, Strongly coupled NiCo2O4-rGO hybrid nanosheetsas a methanol-tolerant electrocatalyst for the oxygen reduction reaction, Adv.Mater. 26 (2014) 2408e2412.

[25] Y. Xiao, C. Hu, L. Qu, C. Hu, M. Cao, Three-dimensional macroporous NiCo2O4sheets as a non-noble catalyst for efficient oxygen reduction reactions, Chem.A Eur. J. 19 (2013) 14271e14278.

[26] H.-P. Cong, S.-H. Yu, Shape control of cobalt carbonate particles by a hydro-thermal process in a mixed solvent: an efficient precursor to nanoporouscobalt oxide architectures and their sensing property, Cryst. Growth Des. 9(2008) 210e217.

[27] J. Xiao, S. Yang, Sequential crystallization of sea urchin-like bimetallic (Ni, Co)carbonate hydroxide and its morphology conserved conversion to porousNiCo2O4 spinel for pseudocapacitors, RSC Adv. 1 (2011) 588e595.

[28] C. Shang, S. Dong, S. Wang, D. Xiao, P. Han, X. Wang, L. Gu, G. Cui, Coaxial Ni(x)Co(2x)(OH)(6x)/TiN nanotube arrays as supercapacitor electrodes, ACS Nano 7(2013) 5430e5436.

[29] Q. Shi, Z. Chen, Z. Song, J. Li, J. Dong, Synthesis of ZIF-8 and ZIF-67 by steam-assisted conversion and an investigation of their tribological behaviors,Angew. Chem. Int. Ed. 50 (2011) 672e675.

[30] S. Brunauer, P.H. Emmett, E. Teller, Adsorption of gases in multimolecularlayers, J. Am. Chem. Soc. 60 (1938) 309e319.

[31] J. Wu, R. Mi, S. Li, P. Guo, J. Mei, H. Liu, W.-M. Lau, L.-M. Liu, Hierarchical three-dimensional NiCo2O4 nanoneedle arrays supported on Ni foam for high-performance supercapacitors, RSC Adv. 5 (2015) 25304e25311.

[32] O. Brylev, M. Sarrazin, L. Rou�e, D. B�elanger, Nitrate and nitrite electrocatalyticreduction on Rh-modified pyrolytic graphite electrodes, Electrochimica Acta52 (2007) 6237e6247.

[33] T. Wu, J. Li, L. Hou, C. Yuan, L. Yang, X. Zhang, Uniform urchin-like nickelcobaltite microspherical superstructures constructed by one-dimensionnanowires and their application for electrochemical capacitors, Electro-chimica Acta 81 (2012) 172e178.

[34] R. Guidelli, F. Pergola, G. Raspi, Voltammetric behavior of nitrite ion on plat-inum in neutral and weakly acidic media, Anal. Chem. 44 (1972) 745e755.

[35] P. Wang, Z. Mai, Z. Dai, Y. Li, X. Zou, Construction of Au nanoparticles oncholine chloride modified glassy carbon electrode for sensitive detection ofnitrite, Biosens. Bioelectron. 24 (2009) 3242e3247.

[36] J.-J. Feng, P.-P. Zhang, A.-J. Wang, Y. Zhang, W.-J. Dong, J.-R. Chen, One-pothydrothermal synthesis of uniform b-MnO 2 nanorods for nitrite sensing,J. Colloid Interface Sci. 359 (2011) 1e8.

[37] S.-S. Li, Y.-Y. Hu, A.-J. Wang, X. Weng, J.-R. Chen, J.-J. Feng, Simple synthesis ofworm-like Au-Pd nanostructures supported on reduced graphene oxide forhighly sensitive detection of nitrite, Sens. Actuators B Chem. 208 (2015)468e474.

[38] A. Afkhami, F. Soltani-Felehgari, T. Madrakian, H. Ghaedi, Surface decorationof multi-walled carbon nanotubes modified carbon paste electrode with goldnanoparticles for electro-oxidation and sensitive determination of nitrite,Biosens. Bioelectron. 51 (2014) 379e385.

[39] Z. Wang, F. Liao, T. Guo, S. Yang, C. Zeng, Synthesis of crystalline silvernanoplates and their application for detection of nitrite in foods, J. Electroanal.Chem. 664 (2012) 135e138.