Electronic Supplementary Material
A sensitive nitrite sensor using an electrode consisting of reduced graphene oxide functionalized with ferrocene
Amal Rabtia, Sami Ben Aounb* and Noureddine Raouafia*
a University of Tunis El Manar, Faculty of Science, Department of Chemistry, Laboratory of Analytical Chemistry and Electrochemistry (LR99ES15), Campus universitaire de Tunis El Manar 2092, Tunis, Tunisia
b Taibah University, Faculty of Science, Department of Chemistry, PO. Box 30002 Al-Madinah Al-Munawarah, Saudi Arabia
*Corresponding author: Sami Ben Aoun,
*Corresponding author: Noureddine Raouafi,
Preparation of reduced graphene oxide
In order to reduce graphene oxide, 10 mL of GO solution (1 mg.mL-1) were prepared. Then 0.5 g of NaOH was added and the mixture was refluxed for 1h, cooled to RT and centrifuged for 30 min. The supernatant was removed and a 12 % HCl solution was added and the mixture was further refluxed for 1h. After being cooled to RT, the product was isolated by repeated centrifugation then subsequently washed with water and acetone. The rGO powder was dried at 60 °C overnight.
Preparation of the ferrocene derivative
Scheme S1. Steps for the preparation of amFc compound: the tosylation of ferrocenemethanol and then its azidation
Ferrocenylmethanol (500.0 mg, 2.31 mmol), 1.1 equivalent of tosyl chloride (485.3 mg, 2.54 mmol) and 1.1 equivalent of pyridine (205 µL, 2.54 mmol) were mixed together in 5 mL of acetonitrile (ACN) then sonicated for 30 min to yield the ferrocenylmethyltosylate in 84.7 % of yield.
Ferrocenylmethyltosylate (700 mg, 1.9 mmol) was mixed with sodium azide (615 mg, 9.45 mmol) in 15 mL dimethylformamide (DMF). The solution was stirred for 1 hour at 60 °C to give the ferrocenylmethylazide (amFc) in 85.0 % of yield. The amFc was purified by silica column chromatography eluted by 20 % of ethyl acetate in cyclohexane. 1H NMR δH (300.13 MHz, CDCl3, Me4Si): 4.12 (bs, 2H, CH2N3), 4.17 (bs, 5H, CH(Cp)), 4.19 (m, 4H, 2CH(CP)), 4.23 (m, 4H, 2CH(CP)); 13C NMR δC (75.1 MHz, CDCl3, TMS): 51.03, 68.0, 68.83, 82.25.
Figure S1. Wide scan survey XPS spectrum of the amFc–rGO nanomaterial.
Figure S2. EDX analysis shows the presence of Fe in amFc-rGO
Figure S3. Plot of nitrite anodic peak potential vs. the logarithm of scan rates.
Figure S4. Response dependence pH of the electrode in presence of 1 mM NaNO2 with CV (error bars represent the standard deviation of 3 independent experiments).
In order to study the pH dependence of the nitrite electrochemical response on amFc-rGO electrode, CV of 1 mM nitrite was recorded in the pH range of 5.8 – 8.0 in a 0.1 M PBS. As shown in Fig. S4, the oxidation peak current of nitrite increased with pH in the range of 5.8 –7.0 while it decreased when solution pH was higher than 7.0. In fact, the instability of nitrite in strong acidic conditions, due to its decomposition into NO and NO3- [1], may explain the small peak current at lower pH (<7.0). At higher pH, the shortage of protons makes the electrocatalytic oxidation of nitrite more difficult which explains the nitrite peak current decrease [2]. Therefore, PBS with pH 7.0 was chosen for the rest of the electrochemical sensing of nitrite in our experiments.
Figure S5. Dependence of the electrode response on the applied potential in presence of 1 mM NaNO2 at pH 7.4. Error bars represent the standard deviation of 3 independent experiments.
The influence of applied potential on the amperometric response of amFc-rGO electrode to nitrite was then investigated by varying the potential from 500 mV to 900 mV. Higher peak currents were obtained for potentials starting from 700 mV to 900 mV. Knowing that at higher potential, the detection of nitrite can suffer from interference by other oxidized compounds such as Cl− or Br− in real sample analysis, a potential of 700 mV was chosen for the chronoamperometric nitrite detection.
Figure S6. The responses of 3 independently prepared amFc–rGO electrodes using DPV in a 0.1 M PBS containing 50 µM NaNO2 at scan rate of 50 mV.s–1.
Figure S7. Stability of the amFc-rGO electrode assessment using cyclic voltammograms in 1 mM nitrite (A) for 100 cycles; (B) The first cycle before (a) and after (b) 100 scans.
Figure S8. Stability of the amFc-rGO electrode assessment using cyclic voltammograms in 1 mM nitrite before (a) and after (b) 4 weeks of storage.
References
[1] Guidelli R, Pergola F, Raspi G (1972) Voltammetric behavior of nitrite ion on platinum in neutral and weakly acidic media, Anal Chem 44:745.
[2] Wang Y, Laborda E, Compton RG (2012) Electrochemical oxidation of nitrite: Kinetic, mechanistic and analytical study by square wave voltammetry, J Electroanal Chem 670:56.
Table S1. Comparison of the prepared sensor performances with other electrochemical sensors reported in literaturea
Thionine-ACNTs/GCE / 1.12 / 3-500 / 0.900 V / [6]
PEDOT/(CNCC/PDDA)4/GCE / 0.057 / 0.2-1730 / 0.800 V c / [10]
PEDOT/AuNP/GCE / 0.06 / 0.2-1400 / 0.800 V / [11]
np-PdFe/GCE / 0.8 / 500-25500 / 1.200 V d / [12]
AuCu NCNs/GCEb / 0.2 / 10-4000 / - / [13]
PTB-MWCNTs/GCE / 0.019 / 0.039-1100 / 0.730 V c / [14]
GNs/GCE / 0.22 / 0.5-105 / 0.900 V / [15]
CR-GO/GCE / 1 / 8.9–167 / 0.800 V / [16]
CS/FEPA-GO/GCE / 0.1 / 0.3-3100 / 0.756 V c / [17]
K-doped graphene/GCEb / 0.2 / 0.5-3900 / - / [18]
graphene/polypyrrole/CS/GCE / 0.1 / 0.5-722 / 0.900 V c / [19]
PDDA-rGO/GCE / 0.2 / 0.5-2000 / 0.750 V c / [20]
f-ZnO@rFGO/GCE / 41 / 10-5000 / 0.900 V / [21]
CeOrGo/GCE / 0.18 / 0.7-385 / 1.000 V / [22]
Fc-rGO / 0.35 / 2.5-14950 / 0.700 V / This work
a ACNTs: Aligned carbon nanotubes; CNCC: Carboxylated nanocrystalline cellulose, PDDA: Poly(diallyldimethyl ammonium chloride); PTB: Poly(toluidine blue); GNs: Graphene nanoribbons; CR-GO: Chemically reduced graphene oxide; FEPA: (4-ferrocenylethyne)phenylamine; PDDA: Poly(diallyldimethylammonium chloride); b DPV was used; c Reference electrode: Saturated calomel electrode; d Reference electrode: Reversible hydrogen electrode.
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