Epoxy/Graphite Composite Electrode Modified with Recycled Silver Nanoparticles: An Eco-Friendly Strategy to Improve Lead Detection

Abstract

In this work, silver nanoparticles (AgNPs) obtained from photographic waste were synthesized and electrodeposited via cyclic voltammetry using epoxy-graphite composite as an electrochemical substrate. Both electrodes, unmodified (Epoxy/C) and modified (Epoxy/C/AgNPs), were characterized electrochemically by electrochemical impedance spectroscopy (EIS), charge transfer constant (K 0), and electroactive area. The modified electrode provided lower charge transfer resistance (275 Ω), more kinetically favored electron transfer (K 0 = 1.15 × 10-3 cm s-1), and a 1.7-fold increase in the active area compared to the unmodified electrode. Additional characterizations by scanning electron microscopy (SEM) and Raman spectroscopy confirmed the presence of AgNPs structures on the carbonaceous surface. As a proof of concept, Pb 2+ was used as a model analyte, and a square wave anodic stripping voltammetry (SWASV) method was developed to evaluate the analytical performance of both electrodes. A wider linear range (4.0 to 40.0 µg L-1), the appropriate limit of detection (1.2 µg L-1), and a 6-fold increase in sensitivity were found using the modified electrode, suggesting that the AgNPs significantly contributed to the performance of the electrode. The proposed method was applied to three real water samples, where the Pb 2+ levels varied from 11.3 to 19.5 µg L-1. The proposed protocol (reuse of silver waste) has proven to be a powerful tool for improving the detection of Pb 2+ , which can be helpful for other electrochemical sensing applications in locations with minimal infrastructure.

Full text

Article J. Braz. Chem. Soc., Vol. 00, No. 00, 1-8, 2023
©2023 Sociedade Brasileira de Química
https://dx.doi.org/10.21577/0103-5053.20230071
*e-mail: rafaeldornellas@id.uff.br
Editor handled this article: Rodrigo A. A. Muñoz (Associate)
This manuscript is part of a series of publications in the Journal of the
Brazilian Chemical Society by young researchers who work in Brazil or
have a solid scientic connection with our country. The JBCS welcomes
these young investigators who brighten the future of chemical sciences.
Epoxy/Graphite Composite Electrode Modied with Recycled Silver Nanoparticles:
An Eco-Friendly Strategy to Improve Lead Detection
Taíssa S. Cabral,a Suéllen F. L. do Nascimento,a Lucas V. de Faria,a Thalles P. Lisboa,b
Pedro H. S. Borges,c Edson Nossol, c Felipe S. Semaan, a Rafael M. Dornellas *,a and
Wagner F. Pachecoa
aDepartamento de Química Analítica, Instituto de Química, Universidade Federal Fluminense,
24020‑141 Niterói‑RJ, Brazil
bDepartamento de Química, Instituto de Ciências Exatas, Universidade Federal de Juiz de Fora,
36036‑900 Juiz de Fora‑MG, Brazil
cInstituto de Química, Universidade Federal de Uberlândia, 38400‑902 Uberlândia‑MG, Brazil
In this work, silver nanoparticles (AgNPs) obtained from photographic waste were synthesized
and electrodeposited via cyclic voltammetry using epoxy-graphite composite as an electrochemical
substrate. Both electrodes, unmodified (Epoxy/C) and modified (Epoxy/C/AgNPs), were
characterized electrochemically by electrochemical impedance spectroscopy (EIS), charge transfer
constant (K0), and electroactive area. The modied electrode provided lower charge transfer
resistance (275 Ω), more kinetically favored electron transfer (K0 = 1.15 × 10-3 cm s-1), and a 1.7-
fold increase in the active area compared to the unmodied electrode. Additional characterizations
by scanning electron microscopy (SEM) and Raman spectroscopy conrmed the presence of
AgNPs structures on the carbonaceous surface. As a proof of concept, Pb2+ was used as a model
analyte, and a square wave anodic stripping voltammetry (SWASV) method was developed to
evaluate the analytical performance of both electrodes. A wider linear range (4.0 to 40.0 µg L-1),
the appropriate limit of detection (1.2 µg L-1), and a 6-fold increase in sensitivity were found using
the modied electrode, suggesting that the AgNPs signicantly contributed to the performance of
the electrode. The proposed method was applied to three real water samples, where the Pb2+ levels
varied from 11.3 to 19.5 µg L-1. The proposed protocol (reuse of silver waste) has proven to be a
powerful tool for improving the detection of Pb2+, which can be helpful for other electrochemical
sensing applications in locations with minimal infrastructure.
Keywords: large-scale production, electrochemistry, conductive materials, recycling, metals
Introduction
Composite electrodes are dened as the combination of
two or more materials that gives rise to a hybrid material
with physicochemical and mechanical characteristics
of both substances or new characteristics resulting from
the mixture between them.1 Generally, a composite
electrode is prepared from a mixture of conductive and
insulating phases. The most commonly used conductive
phase is graphite, while the insulating phases can be oils,
waxes, polymers, and resins, which are responsible for
agglomerating the graphite powder and giving the electrode
stability and mechanical properties.2-4 The properties of this
material depend on the nature, quantity, and distribution of
each component. These electrodes can be used in several
electrochemical applications and present advantages of
the low cost, simplicity, and versatility of preparation,
mechanical resistance, durability, surface regeneration
through simple procedures, good conductivity, and the
possibility of surface modication.5-8
Many strategies to produce composite electrodes are
found in the literature.9 The ease of preparation of these
materials allows the construction of sensors of different
shapes and sizes, besides the possibility of incorporating
modiers, bringing innite possibilities and applications.
Some of the most common examples of these electrodes

Epoxy/Graphite Composite Electrode Modied with Recycled Silver Nanoparticles J. Braz. Chem. Soc.2
are graphite composites with epoxy resin,10 parafn,11
polyurethane,12 and polypyrrole,13 among others. Such
electrodes have been used to determine different analytes
(organic and inorganic species) in various matrices,
demonstrating their versatility.14-16
Surface modication of composite electrodes has been
an approach used in many studies due to providing improved
sensitivity and selectivity. Currently, several nanostructured
materials are used temporarily or permanently for this
purpose through electrodeposition and/or adsorption by
covalent and/or ionic interactions. Among the various
nanomaterials available for surface modication, silver
nanoparticles (AgNPs) can be highlighted.17,18 Some
advantages associated with these particles are improved
conductivity and signal-to-noise ratio of measurements,
more favorable mass and charge transport, increased
electroactive area, and control at the electrode/solution
interface.19 Moreover, in some cases, it avoids the formation
of fouling on the electrode surface by adsorption and/or
polymerization of reaction intermediates.20 Although
digital image processing has become popular in the last
two decades, some sectors still employ chemical image
processing on paper, especially photographic studios,
generating a large amount of silver waste, which is an
environmental concern. The process of recycling this silver
for electrode surface modication is an environmentally
feasible strategy following green chemistry protocols.21
Thus, in this work, we developed a composite electrode
composed of epoxy resin and graphite, and its surface was
modied with silver nanoparticles, obtained by recycling
photographic waste. The produced electrochemical
sensor (namely Epoxy/C/AgNPs) was characterized
electrochemically, morphologically, and structurally.
Subsequently, the sensor was applied to determine lead in
environmental samples by square wave anodic stripping
voltammetry (SWASV) as a proof of concept.
Experimental
Reagents
All reagents were of analytical grade and used without
any prior purification steps. Deionized water with a
resistivity of 18.2 MΩ cm obtained by a pro system
(Sartorius Arium®, Göttingen, Germany) was used to
prepare the solutions. The Pb2+, Cu2+, Cd2+, and Zn2+
standard solutions were purchased from Qhemis High
Purity (São Paulo, Brazil). Graphite powder (particle
diameter < 20 µm) was purchased from Sigma-Aldrich,
(St. Louis, USA) and epoxy resin was purchased from
Avipol (Santo André, Brazil). Potassium chloride and
potassium ferricyanide were obtained from Vetec (Rio
de Janeiro, Brazil). Ammonium sulde from Dinâmica
(Indaiatuba, Brazil), perchloric acid from Hexis (São Paulo,
Brazil), nitric acid from Vetec (Rio de Janeiro, Brazil) and
sulfuric acid from Nuclear (São Paulo, Brazil). Potassium
thiocyanate and ammoniacal ferric sulfate were purchased
from Synth (Diadema, Brazil) and used as titrants and
indicators in the volumetric titration of silver extracted
from photographic waste, respectively.
Instrumentation
A 797 VA Computrace potentiostat (Metrohm, Utrecht,
Netherlands) controlled by software version 1.3.1 was used
for all electrochemical measurements. Epoxy/C/AgNPs,
Ag|AgCl|KCl(sat.), and stainless-steel wire electrodes were
used as working, reference, and auxiliary electrodes,
respectively. The scanning electron microscopy (SEM)
images were obtained with a Vega 3 microscope (Tescan,
Brno-Kohoutovice, Czech Republic) located in the
Multipurpose Laboratory of the Institute of Chemistry,
Federal University of Uberlândia (LMIQ-UFU). The
instrument was operated at 5 kV using a secondary electron
detector. Energy dispersive X-ray spectra were obtained
from images acquired from the SEM using the INCA X-Act
detector (Oxford Instruments, Abingdon, UK) coupled to
the microscope. The equipment used to obtain the Raman
spectra was the LabRAM HR Evolution microscope
(HORIBA, Kyoto, Japan), located in the Laboratory of New
Insulating and Semiconductor Materials (LNMIS) of the
Physics Institute of the Federal University of Uberlândia.
The incidence power was 50%, and the laser wavelength
was 785 nm.
Production of the epoxy resin/graphite electrode
The composite electrodes were produced according
to studies previously reported in the literature.22,23 Briey,
the electrode was prepared by mixing graphite powder
with epoxy resin (65:35 m/m, respectively), already
containing an appropriate amount of the catalyst agent.
The homogenized carbon paste obtained was added to a
polyethylene syringe (internal volume of 1.0 mL, diameter
of 4 mm) containing a copper wire (to make electrical
contact with the potentiostat) and then kept under pressure
for 24 h. For this purpose, a bench lathe was used, where
both extremities of the syringe were pressed to compact
the composite material. After this period, the electrode
surface was polished on sandpaper of different sizes (600
to 1500grit), followed by paper to obtain a homogeneous
surface.

Cabral et al. 3Vol. 00, No. 00, 2023
Extraction of silver from photographic industry effluent
After the last stage of traditional photo processing,
the residual silver is solubilized in sodium thiosulfate.
The residue used here was supplied by the Institute of
Art and Communication photographic laboratory of at
the Fluminense Federal University. The collection was
performed using plastic bottles, and the material was
subsequently stored at room temperature. The procedure
adopted in this work was to extract silver from the
complex formed with thiosulfate24 through its precipitation
with sulde and the subsequent elimination in the acid
medium under heating at 70 °C for 4 h. Initially, 100 mL
of ammonium sulde (3.0 mol L-1) were added to 200mL
of the solution from photo processing. This solution
was ltered, and the solid dissolved in 80 mL of HNO3
(8.0mol L-1), and the resulting solution was heated on
a hotplate using a closed system.25 The quantication of
silver in this solution was performed by volumetry, and a
concentration of 0.0067 ± 0.0003 mol L-1 was found. This
solution was stored at room temperature.
Modification of the epoxy resin/graphite composite electrode
with AgNPs
The procedure for electrodeposition of the AgNPs
(0.0067 mol L-1) film onto the composite electrode
surface was properly optimized using scan rates between
50 to 200mV s-1, scan numbers from 1 to 6, with range
potential of -0.9 to 0.6 V, step potential of 10 mV and
HNO3 remaining from the extraction process of silver
as supporting electrolyte. The selected conditions
were 50mV s-1 and 4scans, which provided a better
electrochemical response for Pb2+.
Electrochemical measurements
Electrochemical impedance spectroscopy (EIS)
analyses were performed using 1.0 mmol L-1 [Fe(CN)6]3-/4-
in 0.1mol L-1 KCl solution. For this, a frequency range
of 50 kHz to 0.1 Hz with an amplitude of 10 mV and
10 data points per decade of frequency and a half-wave
potential of +0.24 V were used. The equivalent Randles
circuit was applied to determine the charge transfer
resistance (Rct) related to the [Fe(CN)6]3-/4- redox probe.
The determinations of Pb2+ were conducted by SWASV,
whose instrumental parameters were properly optimized.
Sample collection and preparation
Natural water samples were collected from three
lagoons, Araruama, Saquarema, and Rio Vargem in Itaboraí,
all located in the state of Rio de Janeiro, Brazil. Sampling
was performed by a surface collection of approximately
1.5 L in plastic bottles previously decontaminated in HNO3
(10% v/v) for 24 h. All samples were acidied using HNO3
(5% v/v) and ltered in a membrane lter (pore size 0.2μm)
to eliminate suspended particles. After ltration, 5 mL of
samples were diluted in 20 mL of supporting electrolyte
and immediately analyzed by SWASV.
Analysis by graphite furnace atomic absorption spectrometry
All samples were also analyzed by graphite furnace
atomic absorption spectrometry (GF AAS) using a
spectrometer model SOLAAR Series M5, (Thermo
Scientic, Waltham, USA) equipped with a hollow lead
cathode lamp (Photron Lamps, Narre Warren, Australian)
operating at a maximum current of 4 mA and equipped with
a background corrector (deuterium lamp) and pyrolytically
coated graphite tubes. The equipment was used with the
following instrumental analysis conditions: wavelength
217 nm, bandpass 0.5 nm, and manual injection mode with
25 µL of solution. An analytical curve was constructed
from 5 to 30 µg L-1, and the water samples were also
ltered and diluted 2-fold in HNO3 solution (2% v/v). The
heating program used for GF AAS analysis followed the
recommendations provided by the equipment software and
are shown in Table 1.
Results and Discussion
Characterization of the electrode surfaces
Firstly, EIS measurements were performed to investigate
the Rct of both Epoxy/C and Epoxy/C/AgNPs electrodes.
From the Nyquist plots (Figure 1), it was possible to
estimate Rct values of 350 and 275 Ω for unmodied and
modied electrodes, respectively, indicating faster electron
transfer after the modication process. Subsequently, the
electroactive areas of the three independent electrodes were
also estimated by Randles-Sevcik’s theory.26 The values were
estimated as 0.141 ± 0.002 and 0.249 ± 0.011 cm2 for the bare
Table 1. Heating program used for Pb2+ analysis by GF AAS
Step Temperature/
°C time / s Heating
ramp / (°C s-1)
Air ow /
(L min-1)
Drying 100 30 10 0.2
Pyrolysis 800 20 150 0.2
Atomization 1200 3 0 off
Cleaning 2500 3 0 0.2

Epoxy/Graphite Composite Electrode Modied with Recycled Silver Nanoparticles J. Braz. Chem. Soc.4
and modied electrode, respectively, suggesting that AgNPs
structures caused a 1.7-fold increase in the area. Such a result
corroborates those obtained by EIS, with the favoring of
charge transfer. A relative standard deviation (RSD) of 4.4%
indicates adequate manufacturing reproducibility even after
surface modication with AgNPs. Moreover, values of the
heterogeneous electron transfer constant (K0) achieved were
higher for the modied electrode (1.15 × 10-3 cm s-1) when
compared to the unmodied electrode (9.23×10-4cms-1).
This demonstrated that in fact, the modication of the
electrode surface was responsible for favoring the redox
reactions kinetically.
SEM images were obtained under a magnication
of 10,000 times for morphological analysis, as shown in
Figure 2. On the unmodied surface (Figure 2a), it was
noted compact sheets typical of graphite27 with small
deformations possibly generated during the manufacturing
steps of the electrode. Already on the modied surface
(Figure 2b), the contrast between the electrode surface
and the electrodeposited silver nanoparticles can be
observed, which have a spherical shape and particle size
frequency of 121 ± 4 nm (see Figure 2c), indicating that
the modification was successfully performed. Energy
dispersive X-ray spectroscopy (EDS) spectra was also
recorded for the unmodied and modied surfaces. As
can be seen, on the Epoxy/C electrode (Figure 2d), there
is a predominant peak referring to the carbon present in
the graphitic material. In contrast, the Epoxy/C/AgNPs
electrode (Figure 2e), besides this peak, there is also a
peak related to silver. This result conrms the presence of
AgNPs electrodeposited on the electrode surface. In the
spectrum shown in Figure 2e, there is also a low-intensity
peak related to oxygen that can be justied by the use of
HNO3 in the step of obtaining silver from the residue of the
photo revelation process.28 This oxidizing agent is capable
of breaking part of the graphitic structure (sp2 hybridized
carbons) by the insertion of oxygenated functional groups
forming structural defects, which may have occurred on
the surface of the carbon material.
The Raman spectra were normalized as a function
of the G-band (at around 1580 cm-1) of the unmodied
material due to the surface-enhanced Raman scattering
(SERS) effect, which is a phenomenon occasioned by
the presence of nanoparticles, which intensies the light
scattering, signicantly increasing the acquired signal.29
In fact, the presence of nanoparticles affects the structure
of the material used as a substrate, which can be seen by
the difference in intensity of the bands characteristic of
graphitic materials (D and G) in both spectra (Figure 3).
The spectra of Epoxy/C/AgNPs (Figure 3, line blue)
exhibit a vibrational band around 248 cm-1 related to
Figure 1. EIS spectra obtained on Epoxy/C (red ball) and Epoxy/C/AgNPs
(black square) using 1.0 mmol L-1 [Fe(CN)6]3-/4- as redox probe and
0.1mol L-1 KCl as supporting electrolyte. The inserted graph represents
the magnication of the EIS spectrum. Instrumental conditions: frequency
range 0.1 Hz to 50 KHz and amplitude 10 mV.
Figure 2. SEM images obtained from (a) Epoxy/C and (b) Epoxy/C/
AgNPs electrodes, (c) relative frequency histograms of particle sizes
Epoxy/C/AgNPs (n = 200), and EDS spectra recorded from (d) Epoxy/C
and (e) Epoxy/C/AgNPs surfaces.

Cabral et al. 5Vol. 00, No. 00, 2023
the Ag-O bond present in the nanoparticle network.30
The intensity of this band is directly associated with the
morphology presented by these nanostructures.31 When
modifying the surface with AgNPs, a higher ID/IG ratio is
observed than the unmodied electrode.27 This factor is
related to the electrode modication procedures since the
insertion of nanoparticles breaks the network ordering of
sp2 carbon atoms.32
Analytical performance of the proposed electrode for Pb2+
determination
The influence of SWASV parameters on the
electrochemical prole of Pb2+ were appropriately studied.
Special attention was devoted to the deposition potential
and deposition time, which are directly associated with the
accumulation of Pb2+ species on the electrode surface, and,
consequently, the method’s detectability. It was noted that at
potentials more negative than -0.6 occurred a considerable
decrease in analytical response probably due to the evolution
of hydrogen gas (blocking the active sites) on the electrode
surface. On the other hand, at deposition times greater than
150 s, there was no signicant increase in current, owing to
the saturation of the active sites. Therefore -0.6 V and 150s
were selected for the accumulation step. In experiments
using SWASV, conditioning steps are usually used to clean
the electrode surface between measurements, but under the
proposed platform this additional step was not required, as no
memory effects and/or surface fouling were observed between
successive measurements. The other SWASV parameters
were selected considering the compromise between
peak resolution and current intensity (Table 2), and the
supporting electrolyte was adapted from the previous work.33
Under the previously optimized instrumental parameters,
electrochemical measurements were performed using the
non-modified and modified electrodes with 40 µg L-1
Pb2+ (Figure 4a). An approximately 7-fold increase in
the peak current of Pb2+ was achieved when the modied
electrode (Figure 4a, red line) was used, indicating that
the AgNPs caused an improvement in the Pb2+ response.
Subsequently, calibration curves were prepared using both
electrodes, Epoxy/C (Figure 4b) and Epoxy/C/AgNPs
(Figure 4c), with Pb2+ concentrations ranging from 4.0
to 48.0µgL-1 (n = 3). Linear ranges between 28.0 and
48.0µg L-1 (Ip=-1.04 + 0.08 [Pb2+] / µg L-1, Pearson’s
correlation coefcient (r2) = 0.982) and 4.0 and 40.0 µg L-1
(Ip=1.74+0.47 [Pb2+] / µg L-1, r2 = 0.996) were attained
for the unmodied (Figure 4d, black line) and modied
electrode (Figure 4d, red line), respectively. The limit of
detection (LOD) and quantication (LOQ) values were
calculated following the principles of the International
Union of Pure and Applied Chemistry (IUPAC),34 where
LOD = 3sB/S and LOQ = 10sB/S (sB is the standard
deviation of ten measurements with the lower concentration
level of Pb2+ and S is the slope of the calibration curve).
The analytical parameters, such as linear range, LOD, LOQ,
and sensitivity are shown in Table 3.
It is observed that lower LOD (1.2 µg L-1), and higher
sensitivity (ca.6-fold increase) were attained using the
Epoxy/C/AgNPs electrode. In addition, the surface
modication process provided a wider linear working
range for Pb2+ monitoring. These results agree with the
electrochemical characterizations discussed earlier, which
showed that after modication with AgNPs, there was an
increase in charge transfer and active sites, allowing the
detection of low levels of Pb2+, which is mandatory when
environmental samples are analyzed. It is important to
highlight that solutions obtained from the silver residues
of the photographic process were stable for 4 years for
Epoxy/C surface modication. This stability was evaluated
by monitoring the peak current intensity of 28 µmol L-1
Pb2+ solution (relative standard deviation (RSD) = 7.1%)
after different surface modications using the same silver
residue solution.
The selectivity of the proposed method was evaluated
in the presence of other metallic species, such as Cd2+,
Zn2+, and Cu2+, using two ratios (1:1 and 1:2) between
Pb2+ and each interfering agent, respectively (Figure 5).
These studies were performed using 20 µg L-1 Pb2+ and 20
Table 2. SWASV conditions used for the determination of Pb2+
Parameter Studied range Selected values
Deposition potential / V -0.3 - -0.8 -0.6
Deposition time / s 30-180 150
Step potential / mV 5-30 5
Amplitude / mV 10-100 20
Frequency / Hz 10-100 50
Scan rate / (mV s-1) 50-500 250
Supporting electrolyte -0.1 mol L-1 HClO4
Figure 3. Raman spectra obtained from Epoxy/C (black line) and
Epoxy/C/AgNPs (blue line) electrode surfaces.

Epoxy/Graphite Composite Electrode Modied with Recycled Silver Nanoparticles J. Braz. Chem. Soc.6
and 40 µg L-1 of the other metals. Considering both ratios
investigated, there were no variations greater than 10% on
the electrochemical response of Pb2+, indicating adequate
selectivity in the presence of these metals.
Real water samples (collected from three lakes) were
submitted for analysis to demonstrate the developed sensor’s
applicability. Only one sample presented Pb2+ levels lower
than LOD (1.2 µg L-1) and consequently in agreement
with the maximum limit allowed (10.0µgL-1) by Brazilian
regulatory agencies (CONAMA No. 347 of 2005),35 which
can be seen in Table 4. On the other hand, the other samples
showed Pb2+ levels above the limit allowed by the same
legislation. These results were statistically compared to
those obtained by GF AAS at a 95% condence level using
the paired student t-test (tcalculated< tcritical), which conrmed
the accuracy of the SWASV analysis.
The analytical performance of the proposed electrode
was compared to other silver-modied electrodes for the
sensing of Pb2+ in environmental water (Table 5). As can
Table 3. Analytical parameters obtained for the detection of Pb2+ using
unmodied and modied electrodes
Analytical parameter Electrode
Epoxy/C Epoxy/C/AgNPs
Linear range / (µg L-1) 28.0-48.0 4.0-40.0
LOD / (µg L-1) 8.9 1.2
LOQ / (µg L-1) 29.6 4.0
Sensitivity / (µA L µg-1) 0.08 0.47
LOD: limit of detection; LOQ: limit of quantication.
Figure 4. (a) SWASV recordings of 40 µg L-1 Pb2+ solution using the Epoxy/C (black line) and Epoxy/C/AgNPs (red line) electrodes. SWASV voltammograms
achieved using Pb2+ concentration ranging from 4.0 to 48.0 µg L-1 on Epoxy/C (b) and Epoxy/C/AgNPs (c) surfaces and the respective calibration curves
(d) using unmodied (black line) and modied (red line) electrodes. The dashed lines indicate the corresponding blanks. SWASV conditions: see Table 2.
Figure 5. Inuence of possible interfering species (Cd2+, Zn2+, and Cu2+) on the electrochemical response of 20 µg L-1 Pb2+ using 1:1 (a) and 1:2 (b) ratios.

Cabral et al. 7Vol. 00, No. 00, 2023
be seen, all works show better analytical performance in
terms of LOD, linear range and deposition time when
compared to the sensor developed here. Even using shorter
deposition times, the other works achieved a lower LOD.
Thus, probably the substrate and material used for surface
modication, as well as other instrumental parameters, are
also relevant in affecting the detectability of the method.
However, it is worth noting that the estimated LOD is
lower than that recommended by the Brazilian regulation
agency, and therefore perfectly suited for the proposed
application. On the other hand, it is important to note that
such sensors use expensive materials as substrate (glassy
carbon electrode), and the surface modication procedures
are time-consuming. Opposite to this, we use an affordable
epoxy/graphite composite as an electrochemical platform
which is easily produced on a large scale in laboratories
with minimal infrastructure. Moreover, we demonstrate
a user-friendly approach following green chemistry
principles by reusing residual silver from photo-developing
processes. It is also worth mentioning that the modication
step via electrodeposition is very fast (120 s); only four
consecutive scans are required.
Conclusions
A new strategy to produce silver-modied electrodes
was demonstrated based on the reuse of silver residue from
photographic processes. The residual silver was properly
extracted and electrodeposited using epoxy-graphite
composite as substrate. Morphological (SEM images) and
structural characterizations conrmed that the modication
was carried out successfully. As a proof of concept, Pb2+
was selected as a model analyte and a SWASV method
was developed. Better detectability and sensitivity were
obtained on the modied surface, suggesting that recycled
AgNPs are good candidates for improved Pb2+ detection. In
fact, the modied electrode provided sufcient LOQ value
(4.0 µg L-1) to detect Pb2+ levels as required by regulatory
agencies (10.0 µg L-1). The approach proposed here is
extremely feasible for low-income locations and can be
extended to the sensing of other metallic species as well
as organic analytes.
Acknowledgments
The authors would like to thank the support from
FINEP, CAPES, Brazilian Institute of Science and
Technology (INCT) in Carbon Nanomaterials FAPEMIG,
FAPEMIG (APQ-01207-17). Rafael M. Dornellas and
Lucas V. de Faria would like to thank the support from
FAPERJ (E-26/211.465/2019, E-33/201.429/2022,
E-26/205.806/2022 and 205.807/2022). The authors
would also like to acknowledge the Multiuser Laboratory
of Chemistry Institute at the University of Uberlândia for
support involving SEM experiments and the Multiuser
Laboratory- LM-INFIS at the University of Uberlândia for
the acquisition of Raman spectra.
Author Contributions
Taíssa S. Cabral was responsible for conceptualization, data curation,
investigation, and validation; Suéllen F. L. do Nascimento for data
curation, investigation, visualization, writing original draft, writing-
review and editing; Lucas V. de Faria for data curation, investigation,
validation, visualization, writing original draft, writing-review and
editing; Thalles P. Lisboa validation, visualization, writing-review and
editing; Pedro H. S. Borges for data curation, investigation, validation;
Edson Nossol for investigation, visualization, writing-review and
Table 4. Concentration values of Pb2+ found in the analyzed water samples
Sample [Pb2+] / (µg L-1)
SWASV GF AAS
A 19.5 ± 1.7 20.5 ± 0.9
B 11.3 ± 1.8 9.1 ± 0.5
C < LODa< LODb
Samples from the Araruama (A), Saquarema (B), and Itaborai (C) lagoons.
All analyzes were performed in triplicate (n = 3); Student’s t-test: tcalculated =
0.37 tcritical = 12.71, condence level: 95%. a1.2 µg L-1; b1.3 µg L-1. SWASV:
square wave anodic stripping voltammetry; GF AAS: graphite furnace
atomic absorption spectrometry; LOD: limit of detection.
Table 5. Comparison of the proposed electrode with other electrochemical sensors reported in the literature for Pb2+ determination
Electrode Technique Deposition time / s LOD / (µg L-1) Linear range / (µg L-1) Reference
GCE/poly(1,8DAF)/AgNPs SWASV 120 0.03 0.005-0.058 36
GCE/AgNPs SWASV 50 0.010 0.010-0.062 37
GCE/Ibu-AgNPs DPASV n.m. 0.01 0.1-1500 38
Epoxy/C/AgNPs SWASV 150 1.2 4.0-40.0 this work
GCE/poly(1,8DAF)/AgNPs: glassy carbon electrode modied with silver nanoparticles deposited on poly(1,8-diaminonaphthalene); GCE/AgNPs: glassy
carbon electrode modied with silver nanoparticles; GCE/Ibu-AgNPs: glassy carbon electrode modied with ibuprofen and silver nanoparticles; Epoxy/C/
AgNPs: epoxy-graphite composite modied with recycled silver nanoparticles; SWASV: square wave anodic stripping voltammetry; DPASV: differential
pulse anodic stripping voltammetry; LOD: limit of detection; n.m: not mentioned.

Epoxy/Graphite Composite Electrode Modied with Recycled Silver Nanoparticles J. Braz. Chem. Soc.8
editing; Felipe S. Semaan for visualization, writing original draft,
writing-review and editing; Rafael M. Dornellas for formal analysis
funding acquisition, project administration, resources, writing original
draft, writing-review and editing; Wagner F. Pacheco for formal analysis
funding acquisition, project administration, resources, writing original
draft, writing-review and editing.
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Submitted: February 23, 2023
Published online: May 11, 2023
This is an open-access article distributed under the terms of the Creative Commons Attribution License.