Electronic Supplementary Material for the manuscript entitled “A nanomaterial composed of cobalt nanoparticles, poly(3,4-ethylenedioxythiophene) and graphene with high electrocatalytic activity for nitrite oxidation”

Qi Wanga, b,, Yanbin Yunc

Fig.S1indicates that the current response ofnitrite decreased as thedeposition cycle number was greater than2. Therefore, the amount of PEDOT obtained at 2cycles was found to be optimal number for electrocatalytic oxidationof nitrite.

Fig.S1The effect of the cycle number for the electro-deposition of PEDOT film on thecurrent responseofnitrite.

Fig.S2 displayed the effect ofthe electrodeposition circles of Co nanoparticles on electrocatalytic currents of 0.5 mM nitrite on the CoNPs-PEDOT-GE/GCE. Asshown in Fig. S2, the maximum response current was observed when theelectrodepositioncircles reached 10.It which might due to the followingreasons: first, the amount of Co nanoparticles entrapped in thePEDOT-GE film increased when the electrodeposition circles increased, but after too many electrodeposition circles, there would be someparticles that suffered from marked diffusion interference and thenformed large-sized Co nanoclusters, which could affect the highlyelectrocatalytic oxidation of nitrite ions. Therefore, 10 circles electrodepositionwas chosen in our experiments.

Fig.S2The effect of electrodeposition circles on current response of CoNPs-PEDOT-GE/GCE to addition of 0.5 mM NaNO2.

Fig.S3displayed the effect of the solution pH on the electrochemical response of the nitrite using 0.1M phosphate buffer solution at pH 4-9 were studied. The peak current changed with pH in the range from 4 up to 6.5. At pH 6.5 the peak current reached its maximum. A decrease in the current was observed when the solution pH was higher than 6.5. Thus, the optimum pH for further studies was set in 6.5.

Fig.S3Influence of the pH on the sensor response obtained by cyclic voltammetry in 0.5 mMNO2−. Measurements carried out in 0.1 Mphosphate buffer solution. Scan rate: 0.025 Vs−1.

Table S1The influence of some inorganic ions on the peak current of 10 μMNO2−.

Foreign ions / Concentration (μM) / Signal change (%) / Foreign ions / Concentration (μM) / Signal change (%)
Mg2+ / 1 mM / 4.36 / Cl- / 1 mM / 0.75
Na+ / 1 mM / 3.05 / Br- / 0.2 mM / 3.64
Ca2+ / 1 mM / 2.12 / H2O2 / 0.2 mM / 4.23
Ni2+, / 1 mM / -4.15 / SCN- / 0.2 mM / 3.88
K+ / 1 mM / -3.56 / ascorbic acid / 0.2 mM / 5.56
SO42- / 1 mM / -3.34 / I- / 0.1 mM / 7.97
NO3- / 1 mM / -1.22 / SO32- / 0.1 mM / 7.52
PO43- / 1 mM / 3.35 / S2O32- / 0.1 mM / 6.62

Further, to understand the fast electron transfer reaction of nitriteat the CoNPs- PEDOT-GE/GCE quantitatively, we have calculatedthe standard heterogeneous rate constant (ko) for nitrite at the CoNPs-PEDOT -GE/GCE using Velasco equation [1]. In orderto determine the koit is necessary to find the diffusion coefficientfor the oxidation of nitrite. The apparent diffusion coefficient(Dapp) value was determined by a single potential chronoamperometrytechnique based on the Cottrell slope obtained by plottingcurrent versus 1/√time. The Dappof 4.08×10-5cm2s-1wasobtained for nitrite at the CoNPs-PEDOT-GE/GCE. The value of kowas calculated to be 6.2×10-3cms-1.This value was higher than those of 5.4×10-3cms-1for SiO2/SnO2/Phosphate/CoPmodified electrode[2] and 6.06×10-3cms-1for p-ATT modified electrode[3].Theenhancement in the electron transfer rate constant could beattributed to the synergetic effect of the high conductivity of PEDOT-GE composite and catalytic effects of Co NPs.

References

[1] Velasco JG (1997) Determination of standard rate constants for electrochemical irreversible processes from linear sweep voltammograms. Electroanalysis 9: 880

[2] Cardoso WS, Gushikem Y (2005)Electrocatalytic oxidation of nitrite on a carbon pasteelectrode modified with Co(II) porphyrin adsorbed onSiO2/SnO2/Phosphate prepared by the sol-gel method. Journal Electroanal Chem 583: 300

[3]Kalimuthu P, John SA (2009)Highly sensitive and selective amperometric determination of nitriteusing electropolymerized film of functionalized thiadiazolemodified glassy carbon electrode. Electrochem Commun 11: 1065

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