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 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 60, 2017 

A publication of 

 
The Italian Association 

of Chemical Engineering 
Online at www.aidic.it/cet 

Guest Editors: Luca Di Palma, Elisabetta Petrucci, Marco Stoller
Copyright © 2017, AIDIC Servizi S.r.l. 
ISBN 978-88-95608- 50-1; ISSN 2283-9216 

Graphene Oxide as a Novel Nanoplatform for Electrochemical 
Detection of Arsenic (III)  

Maria Sarnoa,b, Carmela Scudieria*, Andrea Longoa, Paolo Ciambellia,b 

a 
Department of Industrial Engineering, University of Salerno, via Giovanni Paolo II, 132 - 84084 Fisciano (SA), Italy 

2
 NANO_MATES Research Centre, University of Salerno, via Giovanni Paolo II, 132 - 84084 Fisciano (SA), Italy 

cscudieri@unisa.it 

In this paper, we present a novel and stable electrochemical sensor made of a magnetite/graphene oxide 
(Fe3O4/rGO) nanocomposite. It was deposited on a glassy carbon electrode for electroanalytical detection of 
As3+, via cyclic voltammetry and square wave anodic stripping voltammetry in phosphate buffer solutions. The 
electrode shows a very good relation between current response and amount of arsenic in a concentration of 
pollutants ranging from micromolar to nanomolar. Our sensor is easy to use, inexpensive and has allowed 
sensitive detection of As in non-acidic media (pH=7). 

1. Introduction  
Arsenic exists in many different chemical forms in nature, particularly, in groundwater they are found almost 
exclusively as arsenite (AsO2

−, As3+) and arsenate (HAsO4
2−, As5+). Arsenic compounds are known to be toxic 

and the exposure of humans, animals and ecosystems remains an international concern (Majid et al., 2006). 
Furthermore, the toxicity of arsenic is greatly dependent on As3+ that is 50 times more toxic than arsenate 
(Mandal et al., 2002). The maximum permissible arsenic contaminant level for the World Health Organization’s 
(WHO) in drinking water is 10 μg L-1 (World Health Organization, 2004). Therefore, arsenic poisoning is an 
urgent problem requiring easy and efficient detection strategies. To date, a variety of analytical methods have 
been applied to detect arsenic including inductively coupled plasma mass spectrometry (ICP) (Alvarez-Llamas 
et al., 2005) atomic fluorescence spectrometry (Cai et al., 2000), and graphite furnace atomic adsorption 
spectrometry (Zhang et al., 2011). These methods require the use of expensive instrumentation and high 
operating costs for arsenic detection (Story et al., 1992). However, electrochemical methods are the most 
promising techniques, because they are cheap and can provide very accurate measurements with a rapid 
analysis time (Vandehecke et al., 2007). As reported in the recent studies, electrochemical detection of As3+, 
has been achieved using the hanging mercury drop electrode (Vandehecke et al., 2007) and the mercury film 
electrode (Sun et al., 1997). Moreover, due to the potential toxicity of mercury together with operational 
limitations, portable sensors utilizing mercury electrodes were subsequently replaced by other solid metal 
substrates, such as platinum (Hignett et al., 2004), gold (Simm et al., 2004), and silver (Ivandini et al., 2007). 
Among these, gold was found to be the superior substrate for the working electrode (Sun et al.,1997). 
However, gold is not cost-effective for commercial products. Furthermore, the gold-based electrodes need to 
be operated in strongly acid media which could cause the problems of producing toxic arsine gas, generating 
interface from H2 evolution and causing unsafety for transport. In addition, surface fouling is a common 
problem which needs to be resolved (Ivandini et al., 2007). 
On the other hand, from these results emerged that some problems can be associated with arsenic 
voltammetry at solid electrodes, such as: limited sensitivity, low electron transfer kinetics, high overpotential at 
which electron transfer process occurs, low stability over a wide range of solution composition, and no 
reproducibility of the electrode surfaces between each measurements. In an effort to overcomes these 
limitations, it was found the higher sensitivity of the anodic stripping potentiometric or voltammetric detection 
of arsenic (Sun et al., 1997). On the other hand, nanometer size materials (Welch et al., 2006; Yang et al., 
2006), have been used successfully for electroanalytical detection of As3+ using cyclic voltammetry (CV) or 
anodic stripping voltammetry techniques. In particular, glassy carbon electrode (GCE) modified with 

                               
 
 

 

 
   

                                                  
DOI: 10.3303/CET1760003

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Please cite this article as: Sarno M., Scudieri C., Longo A., Ciambelli P., 2017, Graphene oxide as a novel nanoplatform for electrochemical 
detection of arsenic (iii), Chemical Engineering Transactions, 60, 13-18  DOI: 10.3303/CET1760003 

13



nanoparticles (NPs) of gold (Au), platinum nanoparticles (Pt) and boron (B) doped diamond electrode modified 
with nanoparticles of platinum, have been tested. Although modified electrodes have shown interesting ability 
toward arsenic detection, they also display many problems related to the immobilization of the mediator, its 
toxicity and cost. Considering these limitations, developing a cheap and easily constructed modified electrode 
with outstanding arsenic detection performance is an urgent and important research effort. 
Ferroferric oxide (Fe3O4) NPs is a low-cost, environmentally friendly and easy-prepared material, which has 
received much attention for arsenic removal because of their excellent adsorption ability (Gao et al., 2013; Wei 
et al., 2016). However, a conduction pathways for electrons below NPs can amplify current signal further 
enhancing sensitivity (Kumar et al., 2016). Nanocarbons based electrochemical sensors have improved 
performance due to their catalytic properties coupled with better conductivity, high loading capability and 
stability. Among them, graphene oxide (GO) is considered an excellent nanoplatform to develop 
electrochemical sensors, due to the nature of the atoms on its surface (Kumar et al., 2016). 
In this paper, we present a novel electrochemical sensor made of Fe3O4/rGO deposited on a GCE for 
electroanalytical detection of arsenic via cyclic voltammetry (CV) and square wave anodic stripping 
voltammetry (SWASV) in phosphate buffer solutions. Fe3O4/rGO shows a very good relation between current 
response and amount of arsenic in a wide range of pollutants concentration, due to the electrocatalytic ability 
of rGO and the high adsorption ability of Fe3O4 towards As(III). Our sensor is easy to use, inexpensive and 
has allowed fast and sensitive detection of arsenic in non-acidic media (pH=7).  

2. Experimental Section 
2.1 Preparation of GO nanosheets 

In a typical experiment (Sarno et al., 2016a; Sarno et al., 2016b), pure graphite powder was treated with 
H2SO4, then, KMnO4 was added at a temperature below 10°C. After 1 h, the system was heated up to 40°C 
for 30 min; during oxidation and intercalation, the volume of graphite expands and leaded to increased system 
viscosity. Then, the mixture was diluted with 100 mL of distilled water and 20 mL of H2O2 were added to the 
mixture to reduce residual KMnO4. After centrifugation, the resulting dispersion was dried and solid graphite 
oxide (GrO) was obtained. Further exfoliation was obtained by sonication and, after a suitable centrifugation, 
the supernatant phase (GO) was collected. 

2.2 Preparation of Fe3O4/rGO  

Fe3O4/GO nanocomposite was prepared by thermolysis of Iron(III) acetylacetonate [Fe(acac)3] in the presence 
of GO, 1,2-hexadecanediol, oleic acid, oleylamine and benzyl ether (Sarno et al., 2015). The mixture was 
magnetically stirred and heated to 200°C for 2 h under nitrogen flow. Then, under a blanket of nitrogen, it was 
heated to reflux (~ 300°C) for 1 h and cooled to room temperature. A black material was obtained after intense 
washing and centrifugation. 

2.3 Materials characterization.  

The characterization of materials was obtained by the combined use of different techniques. TEM images 
were obtained with a FEI Tecnai electron microscope operating at 200 kV with a LaB6 filament as the source 
of electrons. The preparation of samples for TEM analysis involved sonication in ethanol for 2–5 min and 
deposition on a carbon grid. XRD measurements were performed with a Bruker D8 X-ray diffractometer using 
CuKα radiation. Powder samples were outgassed in He flow at 523K for 12h before measurements. FT-IR 
spectra were acquired by a Vertex 70 Apparatus (Bruker Corporation). For the electrochemical measurements 
4 mg of the samples were dispersed in 80 μl of 5 wt.% Nafion solution to form a homogeneous ink. Then, the 
ink was dip casted onto a glassy carbon electrode, 3 mm in diameter, to give a thin film. Cyclic voltammetry 
(CV) curves were obtained using a PGSTAT302N Autolab Instruments Metrohm, using saturated calomel as e 
reference electrode, graphite as counter electrode and loadable glassy carbon as working electrode. The 
measurements were performed in phosphate buffer solution (pbs) at pH 7, 0.1M and for the arsenic detection 
tests in a 1 mg/L solution of sodium (meta) arsenite (NaAsO2, Sigma-Aldrich, ≥90%). 

3. Results and discussion  
The morphological and internal structural of Fe3O4/rGO nanocomposite were determined TEM analysis. The 
TEM images are showed in Figure 1, at increasing magnifications. They give a clear evidence that the as 
synthesized Fe3O4/rGO nanocomposite consists of Fe3O4 NPs, mean diameter ~25 nm, dispersed on GO 
nanosheets. The TEM images reveal that the Fe3O4 nanoparticles are attached to the graphene sheets, even 
after the ultrasonication used to disperse the nanocomposites for TEM characterization.  
 

14



 

Figure 1: TEM images of as prepared of Fe3O4/rGO. 

Figure 2 illustrates the detection strategy of As3+ based on the good adsorption ability of Fe3O4 NPs on the GO 
carpet. The As3+ is first adsorbed and reduced, after the redox to As3+ occurs producing a stripping arsenic 
peak (Davies et al., 2005).   

   

Figure 2: Scheme of detection strategy of As3+ based on adsorption ability of Fe3O4 NPs and electrocatalytic 
properties of rGO. 
 
The diffraction peaks of GO was shown in Figure 3a. The peaks at around 2ϑ = 10.4° and 42.7° correspond to 
the (001) and (100) reflections of GO. The interlayer spacing calculated from the (001) reflection is 8.5 Å. The 
XRD pattern of GO indicates that the original graphite powders had almost been completely oxidized (Sarno et 
al., 2016b). The XRD profile of Fe3O4 NPs is shown in Figure 3b. The typical peak at 2θ = 30.4° (220), 35.4° 
(311), 43.2° (400), 53.7° (422), 57.4° (511) and 62.7° (440) of magnetite can be observed (Gao et al., 2011). 
In the XRD profile shown in Figure 3c for Fe3O4/rGO the peaks of nanoparticles are clearly visible. On the 
other hand, the absence of the typical peaks of GO and the appearance of a weak peak at about 26° evidence 
the GO reduction. This occurred during the nanoparticles synthesis for both thermal and chemical 
phenomenon, leading to a reduced graphene oxide (rGO) with a good level of exfoliation (Yang et al.; 2015). 
The infrared spectrum of GO (Figure 4) shows a complex pattern due to the presence of oxygen containing 
species formed by graphite oxidation (Eigler et al., 2012). The signals between 3600 and 3200 cm-1 are due to 
the O–H stretching vibration of free water, hydroxyl groups and adsorbed water molecules. Peak from 
carboxyl groups at about 1724 cm-1 is also present. The signal at 1615 cm-1 is related to the skeletal vibration 
of C=C bond, while the signal at 1403 cm-1 corresponds to O–H deformation vibrations from carboxylic groups 
(Stankovich et al., 2006). C–O vibrations of different species, mainly epoxy and hydroxyl groups, are present 

Fe3O4/rGO

15



in the range from 1300 to 800 cm-1 (Alhwaige et al., 2013). In particular, we assign the band at 1221 cm-1 to 
epoxy vibration group (Acik et al., 2010). The peak at 1059 cm-1 might also originate from skeletal C–C 
vibrational modes (Tamás Szabó et al., 2005). In the spectrum of Fe3O4 bands from the inorganic core and 
organic NPs coating can be observed (Sarno et al., 2016c). The Fe3O4/rGO spectrum shows a lower number 
of peaks due unreduced oxygenated groups of the carbonaceous carpet. In particular, the peaks related to 
C=O bonds, epoxy groups and carboxyl groups disappeared, while the peak generated by skeletal vibration 
(1615 cm-1) is still present.   

 
Figure 3: XRD spectrum of GO (a), Fe3O4 (b) and Fe3O4/rGO (c). 

 

Figure 4: FT-IR spectra of GO, Fe3O4 and Fe3O4/rGO. 
 
In order to verify the electrocatalytic activity of GO, Fe3O4 and Fe3O4/GO on glassy carbon electrodes (GCE), 
electrochemical measurements in the presence of arsenite were carried out. In particular, the electrochemical 
behaviour of electrodes modified were further studied by cyclic voltammetry (CV) curves using 0,1M PBS at 
pH 7 in presence of arsenite. In particular, Figure 5a shows CV curves of the modified electrodes, for bare 
GCE (not shown here) no redox response to As3+ can be seen in the potential range from -1 V to 1 V. Fe3O4 
NPs shows the anodic and cathodic peaks current  which could be attributed to redox process of Fe

2+/Fe3+ 
species. GO also shows a non-perfect rectangular shape during the scan between -1V until to 1 V. On the 
other hand, in the CV curve of Fe3O4/GO two well defined peaks at about -0.18 V due to oxidation to As

3+ , 
and in the reverse scan the peak around -0.44 V due to conversion of As3+ to Aso (Kumar et al., 2016), can be 
seen. In Figure 5b some cyclic voltammograms of the Fe3O4/GO in the presence of different concentrations of 
arsenite  were shown. In particular, with increasing As3+ concentration the anodic peak currents increased and 
cathodic peaks disappeared. The catalytic peak currents are proportional to the concentration of arsenic in the 
wide range from 0.1 μM to 1 μM and from 10 μM to 150 μM. The linear correlation between the peaks current 
and the arsenic concentrations in solution are shown in Figure 5d and Figure 5e. To further examine the 
analytical performance of Fe3O4/rGO on GCE towards arsenic, SWASV was employed because of its high 

10 20 30 40 50 60 70

In
te

n
si

ty
  

a
.u

.

2 θ°
10 20 30 40 50 60 70 80

GO

100
002

 

In
te

ns
ity

  a
.u

.

2 θ°

001

30 40 50 60 70

 

In
te

ns
ity

  a
.u

.

2 θ°

Fe3O4

440
511

422

400

311

220

Fe3O4/rGO

10 30 50 70

a b c

4000 3500 3000 2500 2000 1500 1000 500

 GO
 Fe

3
O

4

 Fe
3
O

4
/GO T

ra
ns

m
itt

an
ce

 (%
)

 

Wavelenght  (cm-1)

rGO

16



sensitivity in comparison to CV curves. Figure 5c presents the SWASV analytical characteristics for 
Fe3O4/rGO at different concentrations of the analyte: deposition time 120 s, 12 mV step potential, 20 mV 
amplitude and 92 Hz frequency. The deposition step involved pre-concentration of As(III) species form the 
solution onto Fe3O4/rGO electrode surface by reduction of As

3+ to As(0) at -0.35 V. On the other hand, a 
significant peak at -0.18 V is observed in the stripping scan form -0.5 to 0.8 V attributed to the oxidation of 
deposited As(0) to As3+ species in stripping step. As(III) was detected with a sensitivity of 2.6 μA ppb-1 and  a 
theoretical limit of detection (LOD) of 0.38 ppb. 

 
Figure 5: Comparison of cyclic voltammograms of GO, Fe3O4 and Fe3O4/rGO on GCE in PBS at pH 7 in the 
potential range of (-1–1) V at a scan rate of 2 mV/s in the presence of 50 μM of arsenite; (a). Cyclic 
voltammograms of Fe3O4/rGO on GCE in pbs in pH 7 at a scan rate of 20 mV/s at increasing arsenic 
concentration: 1, 10, 50 and 150 μM; (b). SWASV  with Fe3O4/rGO on GCE in PBS at pH 7 at increasing 
arsenic concentration: 0.01, 0.05, 0.06, 0.07 and 0.1 μM; (c). Relation between arsenite concentration with 
peak current from cycling voltammetry as in (b); (d, e). Relation between arsenite concentration with peak 
current from SWASV as in (c); (f).  

4. Conclusion 

In this work, we have present a novel and stable electrochemical sensor made of Fe3O4/rGO deposited on a 
glassy carbon electrode (GCE) for electroanalytical detection of As3+, via cyclic voltammetry and square wave 
anodic stripping voltammetry in phosphate buffer solutions. The electrode made of Fe3O4 nanoparticles (25 
nm mean diameter) on rGO shows a very good relation between current response and amount of analyte in a 
wide range of pollutant concentration, due to the electrocatalytic ability of rGO and the high adsorption ability 
of Fe3O4 towards As(III). Our sensor is easy to use, inexpensive and has allowed fast and sensitive detection 
of As (LOD=0.38 ppb and  sensitivity=2.6 μA ppb-1) in a non-acidic media. 

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-1,2 -1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2
-2,0x10-4

-1,5x10-4

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Cu
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C
ur

re
nt

 (A
)

Potential (V)

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