Microchimica Acta (2023) 190:273

https://doi.org/10.1007/s00604-023-05858-0

ORIGINAL PAPER

Electrochemically reduced graphene oxide films from Zn‑C battery

waste for the electrochemical determination of paracetamol
and hydroquinone
Rafael Matias Silva1 · Gabriel Henrique Sperandio1 · Alexsandra Dias da Silva1 · Leonardo Luiz Okumura1 ·
Renê Chagas da Silva2 · Renata Pereira Lopes Moreira1 · Tiago Almeida Silva1

Received: 27 March 2023 / Accepted: 3 June 2023 / Published online: 23 June 2023
© The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2023

Abstract
Contributing to the development of sustainable electroanalytical chemistry, electrochemically reduced graphene oxide (ERGO)
films obtained from residual graphite of discharged Zn-C batteries are proposed in this work. Graphite from the cathode of
discarded Zn-C batteries was recovered and used in the synthesis of graphene oxide (GO) by the modified Hummer’s method.
The quality of the synthesized GO was verified using different characterization methods (FT-IR, XRD, SEM, and TEM). GO
films were deposited on a glassy carbon electrode (GCE) by the drop coating method and then electrochemically reduced by
cathodic potential scanning using cyclic voltammetry. The electrochemical features of the ERGO films were investigated using
the ferricyanide redox probe, as well as paracetamol (PAR) and hydroquinone (HQ) molecules as model analytes. From the
cyclic voltammetry assays, enhanced heterogeneous electron transfer rate constants (k0) were observed for all redox systems
studied. In analytical terms, the ERGO-based electrode showed higher analytical sensitivity than the bare and GO-modified
GCE. Using differential pulse voltammetry, wide linear response ranges and limits of detection of 0.14 μmol ­L−1 and 0.65 μmol
­L−1 were achieved for PAR and HQ, respectively. Furthermore, the proposed sensor was successfully applied to the determi-
nation of PAR and HQ in synthetic urine and tap water samples (recoveries close to 100%). The outstanding electrochemical
and analytical properties of the proposed ERGO films are added to the very low cost of the raw material, being presented as a
green-based alternative for the development of electrochemical (bio)sensors with unsophisticated resources.

Keywords Sustainable electroanalysis · Recycling material · Electronic waste · Carbonaceous materials · Voltammetry ·
Sensors

Introduction health, and they also contain high value-added materials such
as nickel, copper, and carbon, with a wide range of applica-
The advance in battery production has brought worldwide ben- tions. The batteries have a graphite rod inside [1]. Obtaining
efits such as the development of new energy storage devices and pure graphite is costly and natural reserves are limited. Similarly,
electrical and electronic devices [1]. However, it is estimated graphite synthesis in the laboratory is a complex, costly, and
that this expansion generates nearly 2 million tons of battery time-consuming procedure [3]. Graphene and its derivatives can
waste annually, of which less than half is recycled [2]. Some be obtained from graphite, whose diverse characteristics, such as
batteries contain toxic metals such as mercury, lead, and cad- large surface area, high number of charge carriers, ionic mobil-
mium, which can contaminate water resources and harm human ity, mechanical strength, conductivity, flexibility, and versatil-
ity, make these materials very appealing to the market [4]. The
graphene obtained from the reuse of this graphite is a possibility
* Tiago Almeida Silva to give an application to this material, reusing and minimizing
tiago.a.silva@ufv.br the discarded waste, following part of the principles of green
1
Department of Chemistry, Federal University of Viçosa, chemistry, favoring economic sectors and society.
Viçosa, MG 36570‑900, Brazil One of the applications would be the use of graphite elec-
2
Department of Physics, Federal University of Viçosa, Viçosa, trodes in the development of electrochemical sensors, because
MG 36570‑900, Brazil these sensors achieve low limit of detection (LOD) values, high

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sensitivity, high stability, and short response time, appreciable of electrochemical and analytical features of ERGO-based
parameters in analysis and monitoring systems [5]. As pro- films obtained from waste Zn-C batteries is presented for
posed by Kumar et al. [2] who synthesized graphene quantum the first time in this work.
dots (GQDs) with electrochemical and luminescent properties
from used alkaline batteries. The exfoliation of graphite was
performed by the electrophoretic exfoliation method, where
graphite was taken from two alkaline batteries, and the elec- Experimental
trolyte was prepared with citric acid and NaOH. The graph-
ites were used as anode and cathode electrodes. By applying Reagents, materials, and solutions
a potential difference (ddp) for a period of time, the solution
had its color changed to dark brown, indicative of the graphite Sodium nitrate and sulfuric acid were purchased from Neon.
exfoliation process. In the studies that evaluated the electro- Potassium permanganate, hydrogen peroxide (30% w/v), sodium
chemical activity of the GQDs, it was observed the significant borohydride, nickel sulfate heptahydrate, and cobalt nitrate hexa-
increase of the anodic (Ipa) and cathodic (Ipc) peak current hydrate were purchased from Vetec. The hydrochloric acid (37%
intensities of a glassy carbon electrode (GCE) modified by the w/v) was obtained from Alphatec. Sodium hydrogen phosphate,
GQDs. Impedimetric measurements revealed values of charge sodium dihydrogen phosphate, potassium chloride, potassium
transfer resistance (Rct) for GCE and GCE/GQDs electrodes ferricyanide, paracetamol, and hydroquinone were purchased
of 39.66 × ­102 Ω and 3.50 × ­102 Ω, respectively, evidenc- from Sigma-Aldrich. All solutions were prepared with ultrapure
ing the application of GQDs in electrochemical (bio)sensors. water (ρ > 18.2 MΩ cm) supplied by a Milli-Q® purification
Obtaining regenerative graphene oxide (Re-GO) from used dry system. All reagents were used as received, without going
battery carbon rods by freeze-drying post-processing method through further purification processes.
at −55 °C and 20 Pa was proposed by Zhang et al. [6]. Elec-
trochemical studies have demonstrated that the incorporation
of Re-GO into the studied composite resulted in an increase in Synthesis of GO from discarded Zn‑C batteries
Ipa and Ipc intensities, the effective improvement of conductiv-
ity coming from the incorporation of Re-GO into the system, Zn-C batteries were acquired from battery collection center
and the good stability of the material. The production of GO in the Viçosa city of Minas Gerais state, Brazil. The bat-
from dry cell graphite electrodes was studied by Azam et al. teries were opened with pliers to remove the external zinc
[3]. To obtain a fine graphite powder, the authors first sanded cup. Then, the rod-shaped carbon cathode was removed
and washed the electrodes to remove the outer adherent paste. with pliers and crushed to obtain a fine powder. Finally, the
Once dry, the electrodes were ground into powder and treated material was sieved (80-mesh). The GO was synthesized
with aqua regia to remove impurities, and again washed and according to adapted Hummer’s method [8]. The processed
dried for use. FT-IR spectra, Raman spectra, and X-ray diffrac- graphite from spent Zn-C batteries (1.00 g), sodium nitrate
tion patterns showed bands, and peaks, characteristic of GO, (1.00 g), and 50.00 mL of concentrated sulfuric acid were
which confirm that graphene was obtained from waste batter- added to a round-bottomed flask. The system was added in
ies. Aiming to obtain GO in a cheaper and environmentally an ultrasound device (frequency of 40 kHz) containing an
friendly way, Band et al. [7] extracted graphite from used dry ice bath (0 °C) by 15 min and kept in an exhaust hood. Then,
batteries. The exfoliation process by electrochemical means potassium permanganate (6.00 g) was added slowly in the
used initially voltage polarization of 2V for 2 min, and then system and kept in ultrasound device for another 1 h. After
10V for 1.5–2h, and a GO yield of 88% was obtained. After this time, 100 mL of ultrapure water was slowly added to
physicochemical and electrochemical characterizations, it was the system and sonicated for another 2 h. The temperature
observed that a GO with few layers and with morphological was controlled to not exceed 80 °C. Then, another 400 mL
and electrochemical characteristics suitable for application in of ultrapure water was added, followed by the addition of
sensors was obtained. 12 mL of hydrogen peroxide (30% m/v). The system was
Given the discussions presented, this work aims to centrifuged (6000 rpm by 7 min), followed by three wash
reduce the waste generated by the disposal of used Zn-C steps with HCl solution at 3% (v/v). The solid GO was dried
batteries by reusing graphite as a starting material to at 35 °C for 12 h and stored at room temperature.
obtain an electrochemically reduced GO film (ERGO)
and study its efficiency in the development of electro- Preparation of modified electrodes
chemical sensors. As proof of concept, the electrochemi- from electrochemical reduction of GO
cal responses to paracetamol (PAR) and hydroquinone
(HQ) molecules were investigated on the modified sen- The glassy carbon electrode (GCE) was first polished in alu-
sors. To the best of our knowledge, the systematic study mina (1 μm, Buehler) and rinsed in ultrapure water. Then,

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Microchim Acta (2023) 190:273 Page 3 of 16 273

it was taken to the ultrasonic bath for cleaning with 70% voltammetry (CV) using the Fe(CN)63−/4− redox probe. For
(v/v) ethanol and subsequently with ultrapure water. The this, the CV measurements were taken at different scan rates
synthesized GO was applied as a modifier of the GCE sub- (10 to 300 mV s­ −1) in 0.1 mol L ­ −1 KCl solution containing
−4 −1
strate. For this, the drop coating method was used to obtain 9.9 × 1­ 0 mol L ­ ­K3Fe(CN)6. From these datasets, the
the films, which used 8 μL of a 2 mg m ­ L−1 GO dispersion respective heterogeneous electron transfer rate constants (k0)
prepared in dimethylformamide (DMF) and overnight dry- were determined.
ing. The cyclic voltammetry (CV) technique was applied to The electrochemical sensing performance of the work-
obtain the electrochemically reduced GO films (ERGO) in ing electrodes was assessed through the model molecules
which the measurements were performed in the potential paracetamol (PAR) and hydroquinone (HQ) by cyclic vol-
range of 0.0 V to −1.5 V in a 0.1 mol ­L−1 phosphate buffer tammetry (CV) and linear sweep voltammetry (LSV). In
solution (pH 5.0) [9]. this evaluation, the electrochemical behavior of the com-
pounds was explored, and their analytical parameters were
Characterization of materials determined from analysis of the respective analytical curves.
The CV and LSV experiments with the model molecules
The GO was characterized by X-ray diffraction. The analy- were conducted in 0.1 mol ­L−1 phosphate buffer solution
ses were carried in a Bruker D8-Discovery diffractor using at pH 7.0. For construction of the respective analytical
copper metal as a target, wavelength of 1.54 Å, voltage of curves, LSV voltammograms were collected with the ana-
45 kV, sweep speed of 0.05° 2.5 ­s−1 in a range of 5 to 40°. lyte concentration ranging of 0.13 mmol ­L−1 to 1.0 mmol
The GO was also characterized by Raman spectroscopy, ­L−1. By doing these, it was possible to evaluate the effect of
using a MicroRaman - InVia Renishaw equipment. The GCE modification with GO and ERGO in terms of analyti-
conditions used were laser with a wavelength of 633 nm, cal sensitivity (slope of the analytical curve). Additionally,
potency of 3 mW, co-additions equal to 5, and an integra- differential pulse voltammetry (DPV) was adopted for the
tion time of 30 s. determination of PAR and HQ with the ERGO-GCE sen-
For the analysis by transmission electron microscopy sor for recording the analytical performance parameters for
(TEM) was used a Tecnai equipment, G2-20 Supertwin FEI each analyte (linear range, detection limit, and analytical
– 200 kV equipped with X-ray energy-dispersive spectros- sensitivity). Synthetic urine and tap water were analyzed
copy (EDS) and the scanning electron microscopy (SEM) by the proposed voltammetric methods in terms of recovery
was carried out using a FEI Quanta and model 200 FEG percentage. Synthetic urine was prepared according to the
device. procedure of Parham and Zargar [10]. Thus, 0.73 g of NaCl,
The surface area of GO was determined using a Quan- 0.40 g of KCl, 0.28 g of ­CaCl2.2H2O, 0.56 g of ­Na2SO4,
tachrome Instruments, model Nova 1200e. The samples 0.35 g of K ­ H2PO4, 0.25 g of N ­ H4Cl, and 6.25 g of urea
were weighed and previously degassed at 250°C for 5 h and were dissolved in 0.1 mol ­L−1 phosphate buffer solution (pH
subsequently analyzed. The specific surface area was deter- = 7.0) in a 250-mL volumetric flask and stored at 4 °C in
mined by the DFT method. the refrigerator. Both samples were fortified by the support-
The characterization of oxygenated functional groups pre- ing electrolyte and analyzed directly without any dilution
sent in the material was characterized by Fourier transform or extra sample preparation step. For the case of working
infrared spectroscopy. A VARIAN 660-IR instrument with a with real urine samples, a step-by-step protocol is following
PIKE GladiATR attenuated total reflectance accessory with proposed for preparing the collected sample and perform-
diamond crystal was used. Transmittance was evaluated in ing the voltammetric analysis. In this sense, the volume of
the wave number range from 200 to 4000 ­cm−1. sample to be collected in the clinic will depend on the vol-
ume of the available electrochemical cell, in the case of the
Electrochemical assays apparatus of this work, 30 mL. Next, the collected sample
needs to be enriched with the constituent salts of the 0.1 mol
A potentiostat/galvanostat PGSTAT128 N (Metrohm) con- ­L−1 phosphate buffer to correct the pH to 7.0 (optimal pH
trolled with NOVA software (version 2.1.5) was employed for the voltammetric measurement). The calculated mass of
for the electrochemical measurements. The electrochemi- salt for 30 mL of sample is as follows: m(NaH2PO4) = 198.7
cal assays were conducted in a conventional three-electrode mg and m(Na2HPO4) = 239.2 mg. Check the pH of the urine
cell, using an Ag/AgCl (3.0 mol L ­ −1 KCl) as the reference sample with a calibrated pH meter. Subsequently, the sample
electrode, a platinum (Pt) foil as auxiliary electrode, and needs to be transferred to the electrochemical cell, and this
GCE (d = 3.0 mm), GO-GCE, or ERGO-GCE as the work- assembled with the three electrodes, including the ERGO-
ing electrodes. GCE as a working electrode. Next, set the parameters of the
The previous electrochemical characterization of the DPV technique as indicated: amplitude (a) = 60 mV, modu-
different electrode materials was performed by cyclic lation time (tm) = 50 ms, and scan rate (v) = 20 mV ­s−1.

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Fig. 1  Diffractogram of (a)

graphite obtained from spent
Zn-C batteries and (b) synthe-
sized GO

Then, perform the anodic potential scan of +0.2V to +0.6V

registering the respective differential pulse voltammogram.
With the registered differential pulse voltammogram, apply
the baseline to the voltammograms through the moving aver-
age and start the peak search to collect the PAR anodic peak
current at +0.38V (vs. Ag/AgCl (3.0 mol L ­ −1 KCl)). With
this anodic peak current value, the PAR concentration can
be obtained by interpolation on the analytical curve.
Finally, the voltammetric measurements were carried out
in duplicate, and the experiment was conducted with three
replications. The baseline of the voltammograms was cor-
rected through the moving average, using the tool available
in the NOVA software system, version 2.5.1.
For the analysis of the samples of tap water and synthetic
urine by the comparative method, UV-Vis spectrophotom-
etry was performed in an Agilent 8453 UV-visible Spec-
troscopy instrument, equipped with 1-cm quartz cuvettes.
Fig. 2  FT-IR of graphite and GO from Zn-C batteries

Results and discussions ­cm−1, attributed to the stretching of hydroxyl groups (νOH)
bonds, probably due to the water. Another common band
Materials characterization occurs at 1600 ­cm−1, attributed to the stretching of the C=C
bond. The band observed at 1730 ­cm−1 can be attributed
The XRD obtained of graphite from Zn-C batteries and to the stretching of carbonyl (νC=O) of carboxylic acids,
synthesized GO are shown in Fig. 1 (a) and (b), respec- esters, and ketones. The bands at 1226 and 1051 c­ m−1 can
tively. The characteristic graphite peaks are observed at 2θ = be related to the C–O stretching vibrations. Similar results
26.4°, attributed to the basal plane (002) of the graphite; 2θ were observed by Jankovský et al. [16].
= 42.4°, attributed to the (100) plane; and 2θ = 54.5°, attrib- GO images obtained by transmission and scanning elec-
uted to the (004) plane. Similar results were obtained by tron microscopy are shown in Fig. 3 (a) and (b), respectively.
other authors [11–13]. In the case of XRD pattern obtained The GO sheets can be seen from the TEM images of Fig. 3
for the GO (Fig. 1 (b)), it can be observed a residual peak (a). In Fig. 3 (b), it is observed that the material is porous.
of graphite at 2θ = 26.4° and 42.4°, besides the appearance The specific surface area (31.048 ­m2 ­g−1) was determined
of the peak in 2θ = 9.2° which is in agreement with the by nitrogen adsorption analysis. Very similar morphologies
results found by Marcano et al. [14]. According to Rabia of GO were observed by Jankovský and coworkers [16]. The
and coworkers [15], this new peak confirms that graphite EDS data recorded for the synthesized GO is provided in
was exfoliated to obtain GO sheets. Figure S1 (a) (please see “Electronic Supplementary Mate-
The FT-IR results are shown in Fig. 2. It can be observed rial”). From the obtained EDS spectrum, the GO elemental
the formation of new bands in the GO due to the oxida- composition consisted mainly of carbon (40.7%) and oxygen
tion of graphite. Both materials presented bands at 3435 (12.7%). Some elements were detected in low percentages

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Microchim Acta (2023) 190:273 Page 5 of 16 273

Fig. 3  (a) TEM and (b) SEM

images recorded of GO obtained
from Zn-C batteries

(e.g., sodium, aluminum, silicon, sulfur, potassium, and

manganese), which is understandable considering the rea-
gents involved in the adopted chemical synthesis route. Zn
and other metallic impurities from the discharged Zn-C bat-
tery were not observed. The presence of copper is due to the
grid used in the TEM-EDS analysis.
Raman spectroscopy was applied to characterize the syn-
thesized GO, allowing to reveal possible structural defects.
The Raman spectrum recorded for GO is shown in Figure S1
(b). Thus, it was verified peaks located at 1350 c­ m−1 and 1579
­cm−1, which are related to the D and G bands, respectively.
The G band corresponds to the first-order scattering of the
­E2g phonon, in the center of the Brillouin zone [17, 18]. The
D band is attributed to the collective respiration modes of the
rings within the graphene lattice, and it is usually attributed to
the disorder and imperfection of the carbon crystallites. The
G′ band at 2704 ­cm−1 was also observed, being this the second Fig. 4  Cyclic voltammogram recorded in 0.1 mol ­ L−1 phosphate
order of the zone boundary phonons [19]. Moreover, the D + buffer solution (pH 5.0) using GO-GCE. v = 50 mV ­s−1
D′ band was recorded at 2941 c­ m−1, suggesting the presence
of structural defects caused by the strong oxidation of graph-
ite to provide GO sheets [20]. The presence of defects in the to the reduction of oxygenated functional groups present
graphene structure is known to enhance the electrochemical throughout the graphene sheets, such as epoxy, peroxy,
properties of the material [21]. and aldehyde groups [22], represented by the following
redox half-reaction proposed by Raj and John [23], Eq. 1:
Electrochemical characterization of ERGO‑based
electrode GO(s) + aH+ (aq) + be− → ERGO(s) + cH2 O(l) (1)

From the electrochemical reduction of GO (Eq. 1), the

The electrochemical reduction of the GO film deposited
­sp2 backbone of graphene sheets is regenerating, reestab-
on the GCE surface was carried out by cyclic voltamme-
lishing the high electrical conductivity of graphene [22].
try at the cathodic potential region (potential window of
It is also possible to observe that in subsequent cycles, the
0.0 V to −1.5 V). The successive cyclic voltammograms
cathodic peak is no longer detectable, tending to obtain a
recorded within this potential window are provided in
stable baseline (capacitive current). This indicates that the
Fig. 4. Observing the CV profile, a well-defined and pro-
reduction of GO sheets occurred quickly and extensively
nounced cathodic peak was observed in the first poten-
by the electrochemical route, according to the results
tial cycle at −1.2 V, without the occurrence of anodic
reported by Zhang et al. [22] and Guo et al. [9].
peaks after the inversion of the potential scanning direc-
To examine the electrochemical features of the produced
tion, demonstrating the irreversible nature of the verified
GO and ERGO films on GCE surface, cyclic voltammetry
reduction process. This cathodic peak has been attributed

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273 Page 6 of 16 Microchim Acta (2023) 190:273

Fig. 5  Cyclic voltammograms

recorded in 0.1 mol L ­ −1 KCl in
the absence (dotted lines) and
presence (full lines) of 9.9 ×
­10−4 mol ­L−1 ­K3Fe(CN)6 using
(a) bare GCE, (b) GO-GCE,
and (c) ERGO-GCE. v = 50
mV ­s−1. (d) Comparison of the
cyclic voltammograms recorded
towards the ­K3Fe(CN)6 redox
probe using bare GCE, GO-
GCE, and ERGO-GCE

tests were conducted with the Fe(CN)63−/4− redox probe. The the presence of the redox probe, anodic and cathodic peaks
Fe(CN)63−/4− redox couple is classified as an inner sphere were verified in all cases, referring to the reversible redox
redox probe and, therefore, it is sensitive to the electrode process of metallic center (­ Fe3+/2+). However, compara-
surface or the influence of surface oxygen functionalities as tively, it is noted in Fig. 5 (d) that from the modification with
described by Chen and McCreery [24]. When focusing on ERGO, the voltammetric profile was significantly altered,
modified glassy carbon electrodes with electrochemically with the obtaining of higher peak current intensities. In addi-
reduced GO films, the works provided by Pumera and col- tion, the peak-to-peak potential separation (ΔEp) was lower
laborators [25–28] show that this inner sphere redox probe for the ERGO-based electrode, showing a better reversibil-
becomes very sensitive to the degree of electrochemical ity of the redox process. Table 1 gathers electrochemical
reduction of the GO films, making it a good choice when parameters collected from the CVs of Fig. 5 (d). Therefore,
dealing with the examination of the effective electrochemical the value of ΔEp decreased by about 66% from the use of the
reduction of GO films. Therefore, considering the objective electrode modified with ERGO. Moreover, the Ipa/Ipc ratio
of evaluating the electrochemical quality of ERGO films obtained in the case of ERGO-GCE was closer to the unit
obtained from residual graphite of discharged Zn-C batter- (Ipa/Ipc = 1.0), which corroborates with the higher degree of
ies, the use of the Fe(CN)63−/4− redox probe provided a refer- reversibility for the redox probe.
ence condition based on the previous literature working with In order to investigate in more detail the electrochemical
ERGO films synthesized from analytical grade reagents. behavior of the electrodes, CV assays at different scan rates
Figure 5 (a–c) provide the CV profiles recorded with the were conducted with the same redox probe. In Figures S2
different electrodes (bare GCE, GO-GCE, and ERGO-GCE)
in the presence and absence of the Fe(CN)63−/4− redox probe. Table 1  Electrochemical parameters obtained from CV assays for the
As expected, no redox peaks were noticed in the blank solu- different working electrodes
tion (i.e., only supporting electrolyte), solely the typical Electrode ΔEp (mV)* Ipa/Ipc ratio* k0 (cm ­s−1)
capacitive behavior. Indeed, a cathodic peak around −0.3
GCE 224 ± 72 0.6 ± 0.1 (1.00 ± 0.06) × 1­ 0−3
V was observed in the case of ERGO-GCE, which can be
GO-GCE 222 ± 10 0.73 ± 0.02 (7.2 ± 0.6) × ­10−4
related to the dissolved oxygen in the supporting electrolyte
ERGO-GCE 78 ± 3 0.83 ± 0.03 (6.2 ± 0.7) × ­10−3
solution, since this peak was undetected when the solution
was purged with ­N2 gas (data not shown). As can be seen, in *Data recorded at v = 50 mV ­s−1

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Microchim Acta (2023) 190:273 Page 7 of 16 273

(a-c) are shown the cyclic voltammograms recorded in the decrease in oxygenated functionalities, the electronic/elec-
scan rate range of 10 to 300 mV s­ −1. From these voltam- trostatic repulsion effects between the surface oxygenated
mograms, the curves of anodic (Ipa) and cathodic (Ipc) peak groups and negatively charged ferro/ferricyanide complex
current versus the square root of the scan rate (v1/2) for all are minimized, promoting a faster heterogeneous electron
electrodes were constructed, and they can be visualized in transfer. Thus, the formation of ERGO provides enhanced
Figures S2 (d-f). Linear relationships between Ipa vs. v1/2 and electronic mobility, appreciable electrocatalysis, and good
Ipc vs. v1/2 were observed, indicating that the redox process electrical conductivity, which are desirable characteristics
was controlled by diffusional mass transport [29]. Thus, the in the development of sensitive sensors and rapid detection
data obtained from the CV scan rate study were explored the species of interest [33]. Huang et al. [34] investigated
for the calculation of the respective heterogeneous electron the ultrasensitive detection of metronidazole, where RGO
transfer rate constants (k0). In this case, the proposed Nichol- was used as one of the modifiers on the GCE surface. The
son-Shain method [30] (Eq. 2) for quasi-reversible redox hydrothermal reduction process of GO allowed a decrease
systems controlled by diffusion was applied: in the oxygenated groups present in its structure, resulting
in a material with high electrical conductivity and excellent
𝛹 = k0 (𝜋DnvF∕RT)−1∕2 (2) catalytic activity. The charge transfer resistance, determined
by electrochemical impedance spectroscopy, of bare GCE
where Ψ is a kinetic parameter and the other terms have
that was initially recorded to be around 125 Ω, decreased to
their usual meanings. The Ψ values can be easily obtained
60 Ω in the RGO/GCE film.
using Eqs. 3 and 4 proposed by Lavagnini et al. [31], which
It is noteworthy, however, that the ERGO material pro-
relate Ψ and the ΔEp value for each scan rate:
posed in this work was obtained sustainably, in this case, dis-
(3) charged batteries from disposal, a source of zero cost tending
( ) ( )
𝛹 = −0.6288 + 0.0021𝛥Ep ∕ 1 − 0.017𝛥Ep
raw material. Moreover, still on the electrochemical quality
of electrodes modified with ERGO films, the susceptibility
𝛹 = 2.18 (𝛽∕𝜋)1∕2 exp − 𝛽 2 F∕RT nΔEp (4)
[ ( ) ]
of the employed method of synthesis and fabrication of films
was tested by comparing the voltammetric profile of GCEs
being β the transfer coefficient in Eq. 4, and the other
modified from GO synthesized in three different batches and
terms have already been defined. Equations 3 and 4 are
different brands of discarded battery. Figure S3 shows the
applied depending on the value of n×ΔEp at each scan rate;
CVs obtained in this case towards the Fe(CN)63−/4− redox
Eq. 3 is used when n×ΔEp < 200 mV and Eq. 4 in those
probe. As expected, variations of the voltammetric profile
cases with n×ΔEp ≥ 200 [31, 32]. Considering n = 1 for
were observed, including the background current. How-
the used redox probe, n×ΔEp values greater and less than
ever, comparing the background-subtracted peak currents,
200 mV were obtained (bare GCE and GO-GCE, specifi-
relative standard deviation (RSD) values of 7.7% and 11.1%
cally) and, thus, each equation was applied to predict Ψ in
were obtained for Ipa and Ipc, respectively. In the case of
their respective validity ranges. From the calculated Ψ val-
ΔEp parameter, this displayed an RSD of 13.9%. Taking
ues, curves of Ψ vs. 32.79 v−1/2 were constructed for all the
into account the inevitable variability of the residual bat-
studied electrodes. The constant parameter 32.79 represents
tery sources used, these variations in the electrochemical
the constant terms of the Nicholson-Shain equation (i.e.,
behavior of the modified electrodes are considered quite
(πDnF/RT)−1/2 in Eq. 2). From that, the k0 constant is directly
satisfactory.
obtained as the slope of the Ψ vs. 32.79 v−1/2 linear regres-
sions. The obtained values of k0 are displayed in Table 1.
Electrochemical response of paracetamol
Again, a better behavior of the GCE modified with ERGO
and hydroquinone on ERGO‑based electrode
was verified, with a k0 constant 6.2 times higher than the one
obtained for bare GCE. This set of results is in agreement
The electrochemical response of the ERGO-modified elec-
with what has been observed by different authors for the
trodes was evaluated against PAR and HQ model molecules
characterization of ERGO films using the Fe(CN)63−/4− inner
as proof of concept. Both molecules were selected consider-
sphere probe. As discussed by Moo et al. [27], the change
ing their well-established electrochemical behavior, allowing
in the voltammetric profile of this redox couple after the
to evaluate the quality of the prepared ERGO comparing
electrochemical GO reduction step can be explained by two
with the literature. Through the cyclic voltammograms of
factors. Firstly, the presence of oxygenated functional groups
Figs. 6 (a–c) and 7 (a–c), it was observed that bare GCE and
in the GO sheets disrupts the s­ p2 carbon network resulting
graphene films-modified GCEs were able to record the redox
in lower conductivity and, consequently, the electrochemi-
reactions of PAR and HQ, being observed the presence of
cal reduction reconstitutes the electrical conductivity by
the expected anodic and cathodic peaks. The previous lit-
reestablishing the π-conjugated system. Secondly, with the
erature reports that both molecules undergo reversible redox

13
273 Page 8 of 16 Microchim Acta (2023) 190:273

Fig. 6  Cyclic voltammograms

recorded in 0.1 mol L­ −1 phos-
phate buffer solution (pH = 7.0)
in the absence (dotted lines)
and presence (full lines) of 5.0
× ­10−4 mol ­L−1 PAR using (a)
bare GCE, (b) GO-GCE, and
(c) ERGO-GCE. v = 50 mV
­s−1. (d) Comparison of the
cyclic voltammograms recorded
towards the PAR analyte using
bare GCE, GO-GCE, and
ERGO-GCE

Fig. 7  Cyclic voltammo-

grams recorded in 0.1 mol L ­ −1
phosphate buffer solution (pH
= 7.0) in the absence (dotted
lines) and presence (full lines)
of 5.0 × 1­ 0−4 mol ­L−1 HQ using
(a) bare GCE, (b) GO-GCE,
and (c) ERGO-GCE. v = 50
mV ­s−1. (d) Comparison of the
cyclic voltammograms recorded
towards the HQ analyte using
bare GCE, GO-GCE, and
ERGO-GCE

13
Microchim Acta (2023) 190:273 Page 9 of 16 273

Table 2  Electrochemical parameters obtained from CV assays for the factors 10.37 and 13.45 correspond to the constant terms
different working electrodes towards PAR and HQ of the Nicholson-Shain equation (Eq. 2) corrected by the
Analyte Electrode ΔEp (mV)* Ipa/Ipc ratio* k0 (cm ­s−1) respective diffusion coefficients of the studied molecules as
well as considering n = 2. The k0 values calculated for each
PAR GCE 539 ± 134 1.04 ± 0.07 (2.0 ± 0.3) × ­10−6
analyte and electrode are organized in Table 2. Reinforcing
GO-GCE 502 ± 58 0.92 ± 0.3 (1.8 ± 0.2) × ­10−6
the previous finding in terms of ΔEp, the k0 constants for the
ERGO-GCE 78 ± 3 1.12 ± 0.06 (5.0 ± 0.1) × ­10−3
electrodes modified with the ERGO film were significantly
HQ GCE 333 ± 53 0.75 ± 0.01 (3.4 ± 0.1) × ­10−5
higher than those obtained with bare GCE and GO-GCE.
GO-GCE 316 ± 29 0.78 ± 0.01 (5.1 ± 0.3) × ­10−5
This evidence reinforces the findings with the redox probe,
ERGO-GCE 61 ± 10 0.93 ± 0.09 (1.0 ± 0.05) ×
making clear the possibility of obtaining ERGO with excel-
­10−2
lent electrochemical activity from residual graphite.
*Data recorded at v = 50 mV s­ −1 Additionally, regarding the redox behavior of PAR and
HQ molecules on ERGO-GCE, the influence of pH was stud-
ied by monitoring the voltammetric profile of both analytes
reactions at pH 7.0, involving two protons and two electrons in 0.1 mol ­L−1 phosphate buffer solutions with pH ranging
(n = 2) [35–39]. Figures 6 (d) and 7 (d) allow a clear com- of 2.0 to 8.0. The cyclic voltammograms obtained as well
parison of the respective Ipa and Ipc currents recorded on the as the plots of Ipa and Epa vs. pH recorded in both cases can
different electrodes, where greater intensities are noted by be seen in Figure S6 (a-d). Thus, with the pH change from
using the ERGO-GCE. This result is promising because it 2.0 to 8.0, an enhanced analytical signal was increasingly
can lead to high analytical sensitivities. obtained, until reaching an optimal working condition at pH
Table 2 provides the respective values of ΔEp and Ipa/Ipc 7.0, that is, with the highest possible peak current intensity.
ratio extracted from the cyclic voltammograms of Figs. 6 (d) Thus, the 0.1 mol ­L−1 phosphate buffer solution with pH =
and 7 (d). The reversibility of the respective redox processes 7.0 was chosen for the further experiments, and this finding
can be inferred initially by the Ipa/Ipc ratios, being close to was also very interesting, considering that the target matrice
unity for PAR in all cases; however, this only happened samples (urine and water) usually present pH close to 7.0.
using the ERGO-GCE in the case of the HQ molecule. The Furthermore, linear relationships between Epa and pH were
most enthusiastic result, however, concerns the ΔEp values, achieved, with experimental slopes of −(0.061 ± 0.002)
which were significantly lower using the ERGO-GCE. This V ­pH−1 and (−0.0587 ± 0.009) V ­pH−1 for PAR and HQ,
parameter decreased by factors between approximately 6–7 respectively. These experimental slopes were close to the
times after electrochemical reduction of the GO film, sug- theoretical Nernstian slope for redox processes involving the
gesting faster charge transfer kinetics on the ERGO-GCE. same number of protons and electrons (−0.0592 V p­ H−1).
To provide more accurate information about the charge This verification is in agreement with the possible redox
transfer kinetics of PAR and HQ redox processes, the previ- mechanisms proposed for PAR and HQ with the transfer of
ously described procedure for the determination of k0 kinetic two electrons and two protons [40, 41].
constants was again pursued. In this way, CV measurements
at different scan rates were taken, and the cyclic voltammo- Sensitivity towards paracetamol and hydroquinone
grams recorded in the scan rate range of 10 to 300 mV s­ −1
using the different electrodes for PAR and HQ are shown in To access the potentialities of the proposed ERGO-modi-
Figures S4 (a-c) and S5 (a-c), respectively. From the peak fied electrode from an analytical point of view, the analyti-
currents collected at different scan rates, the Ipa vs. v1/2 and cal sensitivity of the electrodes was accessed towards the
Ipc vs. v1/2 curves were constructed, which are presented in determination of PAR and HQ. For this comparative evalu-
Figures S4 (d-f) and S5 (d-f). Linear relationships were con- ation, the anodic peak of both analytes was monitored by
ferred in all cases, indicating the predominant control of the linear sweep voltammetry (LSV). Figure 8 provides the
redox responses by diffusional mass transport. Referring to linear sweep voltammograms recorded at different concen-
quasi-reversible and diffusion-controlled redox processes, trations of PAR and HQ using bare GCE, GO-GCE, and
the Lavagnini et al. [31] and Nicholson-Shain [30] equations ERGO-GCE. From this set of voltammograms, the respec-
were again adopted for the prediction of Ψ and k0 values. tive analytical curves were constructed (shown in Fig. 8
However, it should be noted that other diffusion coefficients (d) and (h)). The analytical curves were constructed in
had to be used in these cases. Using apparent diffusion coef- the same concentration range, for an appropriate compari-
ficients from literature for PAR (DPAR = 3.8 × ­10−5 ­cm2 son of the analytical sensitivities. Thus, well-fitted linear
­s−1) [40] and HQ (DHQ = 2.26 × 1­ 0−5 ­cm2 ­s−1) [41], the k0 regressions were obtained in all cases (correlation coef-
constants were recorded as the slope of the Ψ vs. 10.37 v−1/2 ficients not less than 0.990, Table 3) in the concentration
(PAR) and Ψ vs. 13.45 v−1/2 (HQ) curves. In these cases, the range of 0.13 to 1.0 mmol ­L−1. The analytical sensitivities

13
273 Page 10 of 16 Microchim Acta (2023) 190:273

Fig. 8  Linear sweep voltammograms recorded in 0.1 mol L ­ −1 phos- 0.21; 4: 0.37; 5: 0.54; 6: 0.70; 7: 0.86; and 8: 1.0 mmol ­L−1) using
phate buffer solution (pH = 7.0) containing (a–c) different PAR con- bare GCE, GO-GCE, and ERGO-GCE. Analytical curves obtained
centrations (1: 0.0; 2: 0.13; 3: 0.21; 4: 0.37; 5: 0.54; 6: 0.70; 7: 0.86; for (d) PAR (Ip vs. c(PAR)) and (h) HQ (Ip vs. c(HQ)) using the dif-
and 8: 1.0 mmol ­L−1) or (e–g) HQ concentrations (1: 0.0; 2: 0.13; 3: ferent working electrodes (bare GCE, GO-GCE, and ERGO-GCE)

Table 3  Analytical sensitivity of the different working electrodes pulse voltammetry (DPV) technique was chosen for further
towards PAR and HQ determination by LSV exploration of ERGO-GCE as an electrochemical sensor in
Analyte Electrode Sensitivity (μA L r the determination of PAR and HQ. Regarding the techni-
­mmol−1) cal parameters (scan rate, amplitude, and modulation time)
applied in the DPV measurements, these were selected con-
PAR GCE 17.9 0.999
sidering the obtainment of well-defined and high-intensity
GO-GCE 11.3 0.994
analytical signals (i.e., anodic peak current). Thus, Fig. 9
ERGO-GCE 32.2 0.990
(a) and (b) provide the differential pulse voltammograms
HQ GCE 12.7 0.998
collected against different concentrations of both analytes
GO-GCE 11.3 0.998
for the construction of the respective analytical curves. The
ERGO-GCE 43.3 0.996
analytical curves obtained for PAR and HQ are included in
the insets of Fig. 9 (a) and (b), being both linear in the con-
centration ranges of 4.2 to 69.8 μmol ­L−1, respectively, obey-
(slope of the analytical curves) are provided in Table 3. ing the following linear regression equations, Eqs. 5 and 6:
Thus, the electrode modified with ERGO was the one with
Ip∕μA = −(0.15 ± 0.06) μA + (0.421 ± 0.003) μA L μmol−1 c(PAR)∕μmol L−1 , r = 0.999
the highest analytical sensitivities, being 1.8 and 3.4 times (5)
greater than those obtained with the bare CGE for PAR −1 −1
Ip∕μA = (0.56 ± 0.07) μA + (0.351 ± 0.002) μA L μmol c(HQ)∕μmol L , r = 0.994
and HQ determination, respectively. These results demon- (6)
strate the potentiality of the proposed modified electrode to
carry out electroanalytical determinations with enhanced Therefore, analytical sensitivities of 0.421 μA L μmol−1
analytical sensitivity. In this sense, in the sequence, a set (or 5.955 μA c­ m−2 L μmol−1) and 0.351 μA L μmol−1 (or
of results is provided to complement this first evaluation 4.965 μA ­cm−2 L μmol−1) were obtained respectively for the
regarding the determination of PAR and HQ using the determination of PAR and HQ. The limits of detection (LOD)
ERGO-based GCE as the voltammetric sensor. were determined using the relation 3 × (sb/m), where sb is the
standard deviation of ten blank measurements (n = 10) and m
DPV determination of paracetamol is the analytical sensitivity. Thus, LODs equal to 0.14 μmol
and hydroquinone using ERGO‑based electrode ­L−1 and 0.65 μmol ­L−1 were determined for PAR and HQ.
Table 4 provides a summary of the analytical parameters from
From the previous results involving the comparison of ana- the most recent work for electrochemical detection of PAR
lytical sensitivity of the different electrodes, the differential and HQ. As can be seen, the proposed ERGO-GCE sensor

13
Microchim Acta (2023) 190:273 Page 11 of 16 273

Fig. 9  Differential pulse voltammograms recorded in 0.1 mol ­ L−1 ­ −1) using ERGO-GCE.
4: 20.7; 5: 37.2; 6: 53.6; and 7: 69.8 μmol L
phosphate buffer solution (pH = 7.0) containing different (a) PAR Insets: Analytical curves obtained for PAR (Ip vs. c(PAR)) and HQ
concentrations (1: 0.0; 2: 4.2; 3: 12.5; 4: 20.7; 5: 37.2; 6: 53.6; and (Ip vs. c(HQ)). DPV parameters: a = 60 mV, tm = 50 ms, and, v = 20
7: 69.8 μmol L ­ −1) or (b) HQ concentrations (1: 0.0; 2: 4.2; 3: 12.5; mV ­s−1

achieved linearity in the same linear range and/or in lower case of PAR and water in the case of HQ) on the ERGO-
concentration ranges for the analytes. Table 4 brings several GCE response was evaluated by comparing the analytical
works using electrodes modified with reduced graphene oxide signal of PAR and HQ in the presence and absence of the
films synthesized using P.A. graphite power from commercial concomitants. Table S1 gathers the percentage error values
sources. Interestingly, the proposed ERGO-modified electrode obtained by comparing the peak currents recorded in the
was able to generate satisfactory analytical parameters in the absence and presence of each of the concomitants evalu-
face of these works, such as the one reported by Rocha et al. ated at two analyte:possible interfering concentration ratios:
[67], who carried out the voltammetric determination of HQ 1:1 and 1:10. Thus, from data of Table S1 the ERGO-GCE
with a ERGO-modified GCE within a very similar linear sensor did not suffer significant interference from the evalu-
range. The advantage of ERGO-GCE over other systems is ated concomitants, with errors ranging from −14.26% to
that this system is easy to construct, with a single modifier +7.43%, respectively.
material, but with good analysis performance. Mainly, it Then, PAR and HQ were determined in samples of inter-
reuses graphite from spent batteries, decreasing the amount est in each case. Thus, PAR being configured as a drug and
of waste that could be incorrectly disposed of in the envi- HQ a recurrent phenolic pollutant, the determinations were
ronment. Evaluating possible disadvantages or drawbacks of carried out in synthetic urine and tap water samples. Table 5
the developed voltammetric methods for the determination brings together the recovery results obtained for the analysis
of PAR and HQ, these are those inherent to electrodes modi- of spiked samples at two concentration levels. The recovery
fied with nanostructured films. In this sense, the analytical percentages ranged of 87.6 to 106%, proving the satisfac-
frequency is still low, and, for a commercially viable use, the tory accuracy of the sensor based on ERGO film obtained
mechanization/automation of the manufacturing process of from residual graphite. In addition, the samples were also
the electrochemical sensor based on ERGO films needs to be analyzed by UV-Vis spectrophotometry as a comparative
implemented to scale up the technology. method. The calibration curves obtained for PAR and HQ
The response stability of the modified electrode was inves- in this case can be seen in Figures S7 (a) and (b). Thus,
tigated from DPV measurements (n = 10) carried out succes- Table 5 also shows the concentrations found by the compara-
sively at two concentration levels within the obtained linear tive method and the respective relative errors. Therefore, the
ranges: 16.6 μmol L ­ −1 and 49.5 μmol L
­ −1. Thus, relative stand- results provided by both methods (spectrophotometric and
ard deviations (RSD) of only 3.8% and 1.8% for PAR and 4.0% voltammetric) were quite consistent, with relative errors of
and 1.6% for HQ were obtained, demonstrating the excellent less than ±14.3%. This set of results supports the verification
response stability of the proposed modified electrode. that the developed voltammetric methods based on ERGO-
The possible interference of concomitant substances GCE as the modified electrode present appropriate accuracy
typically found in the target matrice samples (urine in the for analyzing samples for the presence of PAR and HQ.

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273 Page 12 of 16 Microchim Acta (2023) 190:273

Table 4  Voltammetric methods reported for determination of PAR or HQ

Analyte Electrode Voltammetric technique Linear range LOD (μmol ­L−1) Ref.
(μmol ­L−1)

PAR Cu-MOF/HNTs/rGO DPV 0.5–250 0.15 [42]

Pd@α-MnO2/G DPV 0.1–375 0.059 [43]
α-Fe2O3/graphene-GCE DPV 0.3–1800 0.095 [44]
ZnO/ZnNi2O4@porous carbon@COFTM DPV 0.048–130 0.012 [45]
ILC-CPE DPV 0–120 2.8 [36]
Poly (L-leucine)/MCPE DPV 20–90 0.44 [35]
CeO2NP’s CV 1000–5000 1000 [46]
(NCS-NDG)-SDS DPV 0.01–90 0.0015 [47]
ERGO-SbNPs-PGE AdsDPV 0.1–1.0 0.057 [48]
GCPE/RGO SWV 4–220 0.307 [49]
rGFP-1 DPV 1−1000 0.013 [50]
MnCo-P/S-RGO/GCE Amperometry 0.05–1.94 0.00139 [51]
MoS2-TiO2/rGO/SPE DPV 0.1–0.125 0.046 [52]
ERGO-GCE DPV 4.2–69.8 0.14 This work
HQ Poly(neutral red)/P-Gr/GCE AdSDPV 0.005–0.10 0.0017 [53]
0.10–10
rGO@Au/PNVCL/m-BiVO4/GCE LSV 2–152 0.6 [54]
OGO-GCE DPV 0–35 0.114 [55]
rGO/L-Cys DPV 2–160 1.5 [56]
G-PBAT DPV 100–1400 1.01 [39]
GSEC SWV 0.5–200 0.1 [57]
NFG-BAC/GCE DPV 2–1000 0.4 [38]
PC/LLSP800 DPV 19.9–318.3 0.16 [58]
Zn@ZnO CV 10–90 0.10443 [59]
COFs/MWCNT/GCE DPV 4–450 0.38 [37]
Poly (direct yellow 11)/MPGE CV 10–70 0.16 [60]
N-rGO/CuO-ILCPE DPV 1–600 0.25 [61]
NCB/rGO DPV 0.05–20.0 0.0165 [62]
NiO/rGO/ f MWCNTs DPV 10–300 0.040 [63]
RGO–PDA–cMWCNT DPV 0.5–5000 0.066 [64]
Pt-Co/RGO DPV 0.005–0.1 0.00009 [65]
Ni/N-GO/GCE DPV 1.0–800 0.16 [66]
ERGO/GCE DPV 10–100 0.004 [67]
ERGO-GCE DPV 4.2–69.8 0.65 This work

α-Fe2O3/graphene-GCE, hematite and graphene nanocomposite immobilized on glassy carbon electrode; AdSDPV, adsorptive stripping differential pulse
voltammetry; CeO2NP’s, cerium oxide nanoparticles, graphite powder, and silicon oil immobilized on carbon paste electrode; COFs/MWCNT/GCE,
imine bond-linked covalent organic framework with multi-walled carbon nanotubes to glassy carbon electrode; CRGO/GCE, glassy carbon electrode
modified with chemically reduced graphene oxide; Cu-MOF/HNTs/rGO, nanocomposite of copper metal-organic frameworks, halloysite nanotubes, and
reduced graphene oxide; CV, cyclic voltammetry; DPV, differential pulse voltammetry; ERGO-SbNPs-PGE, disposable pencil graphite electrode modi-
fied with reduced graphene oxide-antimony nanocomposite; GCPE/RGO, glassy carbon paste electrode modified with reduced graphene oxide; G-PBAT,
graphite and the polymer poly (butylene adipate-co-terephthalate) immobilized in glassy carbon electrode; GSEC, graphene sheets embedded carbon
film; ILC-CPE, ionic liquid crystal in carbon paste electrode; LSV, linear sweep voltammetry; MnCo-P/S-RGO, glassy carbon electrode modified with
manganese phosphide and cobalt on reduced sulfur-doped graphene oxide composite; MoS2-TiO2/rGO/SPE, screen-printed electrode modified by reduced
molybdenum disulfide-titanium dioxide/graphene oxide nanocomposite; NCB/rGO, glassy carbon electrode modified with reduced nitrogen-doped car-
bon black/graphene oxide nanohybrid; (NCS-NDG)-SDS, hybrid porous nanocomposite of carboxylated nanocellulose, nitrogen-doped graphene, and an
anionic surfactant sodium dodecyl sulfate immobilized in glassy carbon electrode; NFG-BAC/GCE, nano-flake graphite and bamboo activated carbon
composites onto a glassy carbon electrode; Ni/N-GO/GCE, glassy carbon electrode modified with Ni/N-doped graphene oxide composite; NiO/rGO/ f
MWCNTs, modified platinum fused electrode sequentially doped with functionalized multi-walled carbon nanotubes decorated by reduced graphene oxide
and nickel oxide nanoparticles; N-rGO/CuO-ILCPE, copper oxide nanoparticles on nitrogen-doped reduced graphene oxide nanocomposite ionic liquid
modified carbon paste electrode; OGO-GCE, oxidative graphene oxide fabricated onto a glassy carbon electrode; PC/LLSP800, porous carbons derived
from Longquan lignite with microporous and mesoporous structure were fabricated by pyrolysis, carbonization, and activation under activation tempera-
ture by 800 °C; Pd@α-MnO2/G, palladium atom on the surface of α-MnO2 nanorods supported graphene; Poly (direct yellow 11)/MPGE, poly (direct
yellow 11) modified pencil graphite electrode; Poly (L-leucine)/MCPE, poly (L-leucine) immobilized on carbon paste electrode; Poly(neutral red)/P-Gr/
GCE, conductive poly(neutral red), porous graphene immobilized in glassy carbon electrode; Pt-Co/RGO, screen-printed electrode modified with plat-
inum-cobalt nanoparticles supported by reduced graphene oxide; rGFP-1, glassy carbon electrode modified with ferrocene-based nanocomposites cou-

13
Microchim Acta (2023) 190:273 Page 13 of 16 273

Table 4  (continued)
pled to polyoxometalates and reduced graphene oxide; rGO@Au/PNVCL/m-BiVO4/GCE, reduced graphene oxide nanomaterial with gold nanoparticles,
temperature sensitive polymer film (N-vinylcaprolactam), and bismuth monoclinic metavanadate immobilized in glassy carbon electrode; rGO/L-Cys,
reduced graphene oxide cross-linked L-cysteine modified glassy carbon electrode; RGO-PDA-cMWCNT, glassy carbon electrode modified with reduced
graphene-polydopamine-carboxylated multi-walled carbon oxide nanocomposite; SWV, square-wave voltammetry; Zn@ZnO, core-shell nanostructures of
zinc oxide@zinc; ZnO/ZnNi2O4@porous carbon@COFTM, zeolitic imidazolate framework-8 (ZIF-8) composed of 2-methylimidazole and ­Zn2+, porous
carbon, and covalent organic structures

Table 5  Determination of Analyte Sample Concentration (μmol ­L−1) Recovery* Error** (%)
PAR and HQ in different
matrice samples by the Added Found (voltam- Found (comparative
proposed voltammetric method metric method) UV-Vis method)
and comparative UV-Vis
spectrophotometric method PAR Urine 8.3 (8.1 ± 0.1) (8.3 ± 0.1) 97.6 −2.4
33.1 (32 ± 2) (35.1 ± 0.0) 96.7 −8.8
HQ Tap water 8.3 (8.8 ± 0.9) (7.7 ± 0.5) 106 +14.3
33.1 (29 ± 2) (32.7 ± 0.1) 87.6 −11.3

*Recovery = c(Added)/c(Found), voltammetric method × 100%

**Error = [c(Voltammetric method) − c(Comparative UV-Vis method)] / c(Comparative UV-Vis method)]
× 100%

Conclusions around the world. The sensor architecture proposed here can be
widely exploited for the development of electrochemical sensors
GO was synthesized starting from graphite obtained of carbon with scarce resources for diverse applications, some of which
cathodes of discharged and discarded Zn-C batteries. From the are under development in our laboratories.
set of characterizations carried out, it was possible to success-
Supplementary Information The online version contains supplemen-
fully confirm the synthesis of GO sheets. Then, GO films were tary material available at https://d​ oi.o​ rg/1​ 0.1​ 007/s​ 00604-0​ 23-0​ 5858-0.
deposited on GCE, and electrochemically reduced by cyclic vol-
tammetry. Through this, the π-conjugate system of graphene was Acknowledgements The authors are grateful to UFV/DEQ for the
reconstituted, reestablishing the high electrical conductivity in infrastructure.
the ERGO films. This was supported by the significantly lower Funding This work received financial support from CAPES, CNPq,
ΔEp values recorded for the ferricyanide redox probe as well and FAPEMIG (Grant Numbers: RED-00144-22, APQ-0008321, and
as for the paracetamol and hydroquinone model molecules. By APQ-03113-22).
studies of cyclic voltammetry at different scan rates, the k0 con-
stants for all electrodes and electroactive species studied were Declarations
systematically determined, and it was noted that ERGO-GCE Conflict of interest The authors declare that they have no competing
provided higher k0 in the order of approximately 10–1000 times. of interests.
Aiming at its application in the development of electrochemical
sensors, the analytical sensitivities of the different electrodes
(bare GCE, GO-GCE, and ERGO-GCE) were recorded by
LSV towards the determination of PAR and HQ, from which References
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bimetallic Pt-Co nanoparticles for the ultra-sensitive detection jurisdictional claims in published maps and institutional affiliations.
of tert-butyl hydroquinone. Inorg Chem Commun 151:110627.
https://​doi.​org/​10.​1016/j.​inoche.​2023.​110627 Springer Nature or its licensor (e.g. a society or other partner) holds
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based on Ni/N-doped graphene oxide for the determination author(s) or other rightsholder(s); author self-archiving of the accepted
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