Supporting Information

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1 Supporting Information NiFe-Layered Double Hydroxide Nanosheet Arrays Supported on Carbon Cloth for Highly Sensitive Detection of Nitrite Yue Ma,, Yongchuang Wang,, Donghua Xie,, Yue Gu,, Haimin Zhang, Guozhong Wang, Yunxia Zhang, 1, Huijun Zhao, and Po Keung Wong & Key Laboratory of Materials Physics, Centre for Environmental and Energy Nanomaterials, Anhui Key Laboratory of Nanomaterials and Nanotechnology, CAS Centre for Excellence in Nanoscience, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei , China. University of Science and Technology of China, Hefei , P. R. China Centre for Clean Environment and Energy, Griffith University, Gold Coast Campus, Queensland 4222, Australia. & School of Life Sciences, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China. * Correspondence Author. yxzhang@issp.ac.cn Fax: ; Tel: S-1

2 EXPERIMENTAL SECTION Chemicals. Carbon cloth was purchased from Shanghai Hesen Electric Co. Ltd. Iron(III) nitrate nonahydrate (Fe(NO 3 ) 3 9H 2 O), nickel nitrate hexahydrate (Ni(NO 3 ) 2 6H 2 O), urea (CO(NH 2 ) 2 ), ammonium fluoride (NH 4 F), sodium nitrite (NaNO 2 ), sodium nitrate (NaNO 3 ), sodium chloride (NaCl), sodium acetate (NaAc), sodium carbonate (Na 2 CO 3 ), disodium hydrogen phosphate dodecahydrate (Na 2 HPO 4 12H 2 O), sodium dihydrogen phosphate dihydrate (NaH 2 PO 4 2H 2 O), zinc sulfate heptahydrate (ZnSO 4 7H 2 O), potassium chloride (KCl), magnesium sulfate heptahydrate (MgSO 4 7H 2 O), calcium chloride (CaCl 2 ), sodium bromate (NaBrO 3 ), sodium iodate (NaIO 3 ) and hydrogen peroxide (H 2 O 2 ) were purchased from Sinopharm Chemical Reagent Co. Ltd. Stock solution of NaNO 2 was freshly prepared before experiments. Phosphate buffer solution (PBS, 0.1 M, ph 7.0) was prepared by mixing standard stock solutions of Na 2 HPO 4 and NaH 2 PO 4. Deionized (DI) water with a resistivity of above 18.2 MΩ cm was obtained using a JL-RO100 Millipore-Q Plus water purifier and used throughout the experiments. All chemicals were of analytical grade and used directly without any further purification during the experiments. Characterization. The phase and crystalline structure of the obtained samples was characterized by X-ray diffraction (XRD, X Pert Pro Super, Philips Co., the Netherlands) with Cu Kα radiation ( Å). The morphology and microstructural observations were carried out on field emission scanning electron microscope (FESEM, SU 8020) at an acceleration voltage of 5 kv and transmission electron microscopy (TEM) on a JEOL-2010 microscope operating at an accelerating voltage of 200 kv. The compositions of resulting products were examined by energy-dispersive X-ray spectroscopy (EDS) attached to SEM. S-2

3 Raman spectra were measured on a Renishaw Micro-Raman Spectroscopy (Renishaw invia Reflex) using 532 nm laser excitation. The molar ratio between Fe and Ni in the resultant products was determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, ICP-6300, Thermo Fisher Scientific). Fourier transform infrared spectra (FT-IR) were recorded on a Thermo Nicolet NEXUS FT-IR spectrophotometer in the wave number range of cm -1 at a resolution of 4 cm -1 using the KBr pellet method. X-ray photoelectron spectroscopy (XPS) analyses were conducted on a Thermo Scientific ESCALAB 250 equipped with a focused monochromatic Al Kα X-ray source, in which all of the binding energies were calibrated with reference to the C 1s peak (284.8 ev). Electrochemical Measurements. A CHI 760E electrochemical workstation (Shanghai Chenhua Instrument Co., China) was employed for all electrochemical measurements at ambient temperature. A conventional three electrode system was employed for electrochemical determination of nitrite, in which the as-synthesized NiFe-LDH NSAs/CC was directly used as the binder-free working electrode with the effective size of 1 1cm, a platinum wire as auxiliary electrode and a Ag/AgCl electrode as reference electrode. Cyclic voltammogram (CV) and chronoamperometric (I-T) experiments were performed to evaluate the electrochemical response for detection of nitrite ions. The CVs were tested in a voltage window between 0.2 and 1.1 V at a wide range of scan rates, ranging from 10 to 100 mv s -1. The chronoamperometric (I-T) curves were measured at an applied potential of 0.90 V. 0.1 M of PBS (PH=7.0) was used as the supporting electrolyte solution, purged with high purity N 2 for 30 min before each measurement in order to remove the dissolved oxygen. Furthermore, a nitrogen atmosphere was maintained during the whole measurements. S-3

4 Figure S1. EDS spectrum of the as-prepared NiFe-LDH NSAs/CC composite. Figure S2. SEM images of NiFe-LDH/CC with different Ni/Fe molar ratios under different magnifications: (a) and (b) 5:1; (c) and (d) 1:1; (e) and (f) 1:3. S-4

5 Figure S3. SEM images of (a) and (b) Ni(OH)2/CC, (c) and (d) FeOOH/CC composites at different magnifications. Figure S4. XRD patterns of Ni(OH)2/CC (a) and FeOOH/CC (b). S-5

6 Figure S5. FT-IR spectrum of NiFe-LDH NSAs/CC. Figure S6. Cyclic voltammograms of (a) Ni(OH) 2 /CC and (c) FeOOH/CC electrodes in the solution containing 5.0 mm [Fe(CN) 6 ] 3-/4- (1:1 molar ratio) and 0.1 M KCl at different scan rates; (b) and (d) the linear relationship between the anodic peak currents and the square root of the scan rate. S-6

7 Figure S7. Cyclic voltammograms of NiFe-LDH/CC electrodes with different Ni/Fe molar ratios in the solution containing 5.0 mm [Fe(CN) 6 ] 3-/4- (1:1 molar ratio) and 0.1 M KCl at different scan rates: (a) 5:1, (c) 1:1 and (e) 1:3; (b), (d) and (f) the corresponding linear relationship between the anodic peak currents and the square root of the scan rate. S-7

8 Figure S8. (a) CVs of the fabricated NiFe-LDH/CC electrodes with different Ni/Fe molar ratios in the presence of 1.0 mm NaNO 2 in N 2 -saturated 0.1 M PBS at a scan rate of 50 mv s -1. Figure S9. Cyclic voltammograms of six different NiFe-LDH NSAs/CC electrodes in the presence of 1 mm NaNO 2 in N 2 -saturated 0.1 M PBS at a scan rate of 50 mv/s. S-8

9 Figure S10. Cyclic voltammograms of a NiFe-LDH NSAs/CC electrode before and after 30 days of storage in the presence of 1 mm NaNO 2 in N 2 -saturated 0.1 M PBS at a scan rate of 50 mv/s. S-9