Abstract Of Cyclic Voltammograms

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Fig. 3. Cyclic voltammograms (A) and Nyquist plots (B) recorded at bare GCE (a), β-Ni(OH)2/GCE (b) and β-Ni(OH)2@CDs/GCE (c) in a 0.1 M KCl solution containing 5 mM Fe(CN)63-/4-. Inset of Fig. 3B: Equivalent circuit applied to fit impedance measurements, where: Rs is the resistance of electrolyte solution; Rct is the charge transfer resistance, W is warburg impedance and CPE is constant phase element.

3.5. Electrocatalytic oxidation of nitrite on the modified electrode
The electrocatalytic activity of the β-Ni(OH)2@CDs/GCE toward nitrite was studied by recording cyclic voltammograms from the range of potential 0.3 to 1.1 V in the absence (a) and presence (d) of 100 μM nitrite, and compared with other different electrodes such as β-Ni(OH)2/GCE and bare GCE. As can be seen from Fig. 4, there is no well defined peak on bare GCE, which may be due to the sluggish electron transfer process in GCE. At β-Ni(OH)2/GCE, the weak peak appears at 0.96 V related to oxidation process of NO2− to NO3− according to the following reaction:
NO2− + H2O NO3− + 2H+ + 2e− (8)
In addition, no evidence of peaks was found at β-Ni(OH)2@CDs/GCE in the absence of nitrite, while after adding 100 µM nitrite into the phosphate buffer solution (pH 7.0), an obvious irreversible oxidation peak at about 0.82 V is observed (curve d), which is 140 mV negatively shifted compared with β-Ni(OH)2/GCE. Furthermore, the oxidation peak current on β-Ni(OH)2@CDs/GCE is larger than that on β-Ni(OH)2/GCE. This indicated that the large effective area of electrode resulting from high conductivity and high surface area of CDs, as well as the synergistic effects of β-Ni(OH)2 and CDs improve the catalytic behavior toward the oxidation of nitrite.Fig. 4. cyclic voltammograms (CVs) of the bare GCE (b), β-Ni(OH)2/GCE (c), and β-Ni(OH)2/CDs/GCE (a, d) in the absence (a) and presence of 100 μM nitrite (b, c, d) recorded in 0.1 M phosphate buffer solution (pH 7.0) at the scan rate of 50 mV s−1.

Effect of pH solution
The effects of the solution pH on the peak current and potential for nitrite oxidation using β-Ni(OH)2/CDs/GC electrode were investigated by 0.1 mol l−1 phosphate buffer in the pH range of 1-10. As shown in Fig. S2, the current responses
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