Full Article: https://doi.org/10.1016/j.jtice.2018.09.021

1. ELECTROOXIDATION OF
NITRITE BASED ON GREEN
SYNTHESIS OF GOLD
NANOPARTICLES USING
HIBISCUS SABDARIFFA LEAVES
SITI HUSNAA MOHD TAIB, KAMYAR SHAMELI, POORIA
MOOZARM NIA, MOHAMMAD ETESAMI, MIKIO MIYAKE,
ROSHAFIMA RASIT ALI, EBRAHIM ABOUZARI-LOTF, ZAHRA
IZADIYAN

2. INTRODUCTION
Nitrite (NO2
-)
chromatograp
hy
spectroscopy
polarography
electrochemic
al methods
Simple, time-saving
sample preparation
procedures
Cause carcinogenic
effect
3 mg/L
Electrooxidatio
n (anodic
oxidation):
oxidation at
cathode in an
electrolytic cell

3. INTRODUCTION
• The electrooxidation of NO2
- at the traditional electrodes suffers large
overpotentials and the electrode tend to be poisoned by the products
generated during the electrochemical process [8].
• To resolve the problems and enhance the sensitivity for detection of NO2
-,
the usage of metal NPs must be immobilized on the surfaces of electrode.
• Au-NPs on the surface electrodes would enable rapid electron-transfer
kinetics and reduce overpotentials [10].
• The application of Au-NPs modified electrode present larger surface area
and more active sites for the electrooxidation process compared to
unmodified electrodes and subsequently improve the detection limit,
sensitivity and response potential window in electrochemical studies [11].

4. INTRODUCTION
• Commonly known as roselle.
• A type of herbs plant that belongs to the Malvaceae
family.
• Commonly, used in meals as vegetables [12].
• Contain polyphenols of the flavonoids type in simple or
polymerised form.
• Flavonoid: hibiscitrin (hibiscetin-3-glucoside),
quercetin, luteolin, chlorogenic acid, protocatechuic
acid, pelargonidic acid, eugenol, and ergosterol [13].
Hibiscus sabdariffa leaves

5. METHODOLOGY

6. RESULTS AND DISCUSSION
Fig. 2. UV–vis spectrum for H. sabdariffa L. extract and
biosynthesized Au-NPs at different stirring time intervals.
Synthesis of Au-NPs
Fig. 1. The colour change of (a) H. sabdariffa L. extract and
the synthesized Au-NPs with increasing stirring time from (b)
10, (c) 20, (d) 40, (e) 60, (f) 80, (g) 100 and (h) 120 min.
(323
nm)

7. RESULTS AND DISCUSSION
Fig. 4. TEM image and particle size distribution of Au-NPs obtained
by reduction with H. sabdariffa L. at (a) 40, (b) 80 and (c) 120 min.
Synthesis of Au-NPs
Fig. 3. XRD pattern of (a) H. sabdariffa L. extract and
(b) synthesized Au-NPs at 80 min.

8. RESULTS AND DISCUSSION
Table 1: Comparative study – Zeta potential
versus pH.
Synthesis of Au-NPs
Fig. 5. (a) FESEM image and (b) EDX spectrum of Au-NPs
obtained by reduction with H. sabdariffa L. at 80 min..
Sample Zeta potential (mV) pH
H. sabdariffa L. extract -13.76 3.1
Au-NPs at 40 min -10.32 2.6
Au-NPs at 80 min -9.40 2.5
Au-NPs at 120 min -8.37 2.4

9. RESULTS AND DISCUSSION
Synthesis of Au-NPs
Fig. 6. FTIR spectra for (a) H. sabdariffa L. extract and (b)
synthesized Au-NPs at 80 min.
Fig. 7. Structural characteristics of chlorogenic acid
compound present in the H. sabdariffa L.

10. RESULTS AND DISCUSSION
Synthesis of Au-NPs
Fig. 8. Chromatogram of compounds in the H. sabdariffa L. aqueous extract and proposed structures for the identified compounds.
• Thermally unstable of
chlorogenic acid and it is
readily decomposed to
quinic acid and caffeic
acid [14].
• Furthermore, chlorogenic
acid can be cleaved into
these two natural
compounds, by the
hydrolysis of an ester
bond [15].
3.56 min

11. RESULTS AND DISCUSSION
Synthesis of Au-NPs
Fig. 9. Mechanism of the formation of Au-NPs by chlorogenic acid
compound present in H. sabdariffa L. extract.

12. RESULTS AND DISCUSSION
Fig. 10. (a) Cyclic voltammograms obtained for different stirring time of Au-NPs in 1 mM NO2
− + 0.1 M KCl solution, (b) The
effect of pH of electrolyte on the current response for 0.1 mM nitrite ions at Au-NPs electrode.
Electrocatalytic studies

13. RESULTS AND DISCUSSION
Fig. 11. (a) Steady-state response of Au-NPs/GCE to successive injections of NO2
− in 0.1 M KCl solution with an applied potential
of 0.8 V. The inset is the steady-state current vs. NO2- concentration, (b) Amperometric response of Au-NPs to successive addition
of NaNO2, NaCl, KCl, KNO3, CuCl2, and Na2SO4 at pH 7.
Amperometric detection of nitrite ion

14. RESULTS AND DISCUSSION
Sample
Number
Added
(mM)
RSD%
Measured by
biosensor (mM)
Recovery
%
1 0.1 3.33 0.0984 98.4
2 0.5 3.299 0.498 99.6
3 5 3.23 4.952 99.04
4 10 3.44 10.112 101.12
Table 2: Nitrite determination in real samples
Fig. 12. Stability of Au-NPs/GCE over 3
weeks in 0.1 M KCl with addition of 1 mM
NO2
- at 0.8 V vs. SCE.
Real SampleStability

15. CONCLUSION
• The Au-NPs have an average size of 7 ± 2 nm, with a spherical
shape was successfully obtained by a simple green synthesis
method using H. sabdariffa L. extract which act as reductant and
stabilizer.
• The Au-NPs modified electrodes has acceptable stability,
repeatability and reproducibility towards determination of nitrite
with a low LOD of 0.11 μM and the linear range up to 10 mM.
• The Au-NPs modified electrode holds possible applications for
evaluating specific concentration range of nitrite ions in water.

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17. THANK YOU
FOR YOUR ATTENTIONS