Graphene oxide modified H4L-ion imprinting electrochemical sensor for the detection of uranyl ions

Article abstract of DOI:10.1002/zaac.202100182

The rapid development of the nuclear industry has gradually aroused people′s attention to the problem of nuclear pollution. Due to the biological toxicity of uranium and its aqueous solution, simple and rapid detection of uranium in the water environment is quite important. An ion imprinted carbon nanomaterial (graphene oxide) electrochemical sensor for the detection of trace uranyl ions was prepared by using the synthesized bipolar tetradentate macrocyclic uranyl ligand cyclo-bis-phenylenediamine-bis-(phenylmethyl-diphyrrolecarbaldehyde) (H₄L) as functional monomer. The sol-gel polymer was prepared by hydrolysis and polymerization of H₄L ligand, 3-aminopropyltrimethoxysilane and tetraethoxysilane. H₄L-ion imprinted polymer (U-IIP) was prepared by adding 1 mM uranyl ion as template ions. Then the polymer was bonded to graphene oxide modified carbon paste electrode, and the template ions were eluted to obtain H₄L-ion imprinted-graphene oxide modified carbon paste electrode (U-IIP/GO/CPE). Differential pulse voltammetry was used to detect trace uranyl ions. The results showed that the U-IIP/GO/CPE sensor system can detect uranyl ions with high sensitivity and specificity, and the peak current appeared around ?0.26v. In the range of 0.01 μM～3.0 μM, the detection current had a good linear relationship with the molar concentration of uranyl ions, and the method detection limit was 1.32 nM (S/N=3). Through the detection of actual samples, it had a good acceptable recovery rate (95.45 %～106.25 %), and the relative standard deviation was less than 3.25 %.

Full text of DOI:10.1002/zaac.202100182

Journal of Inorganic and General Chemistry
doi.org/10.1002/zaac.202100182
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Graphene oxide modified H4L-ion imprinting
electrochemical sensor for the detection of uranyl ions
Yujie Li+,[a] Zhimei Wang+,[a] Chen Liu,[b] Di Zhang,[b] Lifu Liao,[b] and Xilin Xiao*[a, b, c]
The rapid development of the nuclear industry has gradually
aroused people’s attention to the problem of nuclear pollution.
Due to the biological toxicity of uranium and its aqueous
solution, simple and rapid detection of uranium in the water
environment is quite important. An ion imprinted carbon
nanomaterial (graphene oxide) electrochemical sensor for the
detection of trace uranyl ions was prepared by using the
synthesized bipolar tetradentate macrocyclic uranyl ligand
cyclo-bis-phenylenediamine-bis-(phenylmethyl-diphyrrolecar-
baldehyde) (H4L) as functional monomer. The sol-gel polymer
was prepared by hydrolysis and polymerization of H4L ligand, 3-
aminopropyltrimethoxysilane and tetraethoxysilane. H4L-ion
imprinted polymer (U-IIP) was prepared by adding 1 mM uranyl
ion as template ions. Then the polymer was bonded to
graphene oxide modified carbon paste electrode, and the
template ions were eluted to obtain H4L-ion imprinted-
graphene oxide modified carbon paste electrode (U-IIP/GO/
CPE). Differential pulse voltammetry was used to detect trace
uranyl ions. The results showed that the U-IIP/GO/CPE sensor
system can detect uranyl ions with high sensitivity and
specificity, and the peak current appeared around À 0.26v. In
the range of 0.01 μM~3.0 μM, the detection current had a good
linear relationship with the molar concentration of uranyl ions,
and the method detection limit was 1.32 nM (S/N=3). Through
the detection of actual samples, it had a good acceptable
recovery rate (95.45%~106.25%), and the relative standard
deviation was less than 3.25%.
Introduction
and reproductive tissues.[5] Therefore, timely and accurate detec-
tion of trace amounts of uranium in the environment is essential
for both healthy life and environmental protection.[6] There are
many methods for the detection of uranium, such as capillary
zone electrophoresis,[7] inductively coupled plasma emission
spectroscopy,[8] ion chromatography,[9] inductively coupled plasma
mass spectrometry,[10] graphite furnace atomic absorption
spectrometry,[11] spectrophotometry,[12] fluorescence[13] and neu-
tron activation analysis.[14] Although these schemes offer the
advantages of high sensitivity and low detection limits, they
require expensive equipment as well as higher operating costs. In
contrast, electrochemical sensors prepared using chemically
modified electrodes are effective detection techniques that require
low cost equipment, rapid analysis,[15] ease of operation and high
detection sensitivity.[16] Moreover, among the conventional meth-
ods for the detection of uranyl ions in solution,[17] adsorption
solvation voltammetry (AdSV)[18] is one of the most commonly
used methods. When uranium forms complexes with surface
active ligands and is deposited adsorptively on the electrode
surface, it makes the sensitivity of the sensor further improved.[19]
Although suspended mercury droplets and mercury film electro-
des have been used for AdSV determination of uranium, the
biological toxicity of mercury has increased people’s interest in
non-mercury sensors.[20] For this purpose, new electrode materials
and methods for measurement of uranium have been developed,
such as modified carbon paste electrodes,[21] self-assembled
monolayer gold-based electrodes,[22] carbon nanotube modified
Uranium is a radioactive and biotoxic metallic element that
commonly causes environmental contamination through a variety
of nuclear processes, including nuclear power generation, nuclear
waste disposal, nuclear accidents,[1] and the burning of fossil
fuels.[2] Humans may come into contact with uranium through
inhalation of contaminated airborne dust or ingestion of contami-
nated food.[3] While soluble uranium compounds can be excreted
from the body to some extent, insoluble uranium compounds,
especially in the form of dust, can be inhaled by the body and
cause great harm when they adhere to the lungs.[4] In addition,
uranium that enters the body becomes uranyl ions (UO22+), which
can accumulate and cause fatal damage to bones, liver, kidneys,
[a] Y. Li,+ Z. Wang,+ Prof. Dr. X. Xiao
College of Resource & Environment and Safety Engineering,
University of South China,
Hengyang City 421001, P.R. China
E-mail: xiaoxl2001@163.com
[b] C. Liu, D. Zhang, Prof. L. Liao, Prof. Dr. X. Xiao
College of Chemistry and Chemical Engineering,
Hunan Province Key Laboratory of Typical Environmental
Pollution and Health Hazards,
University of South China,
Hengyang City 421001, P.R. China
[c] Prof. Dr. X. Xiao
State Key Laboratory of Chemo & Biosensing and Chemometrics,
Hunan University,
electrodes,[23]
screen-printed
electrodes,[24]
carbon
fiber
electrodes,[25] and graphite electrodes.[26]
Changsha City 410082, Hunan Province, P.R. China
[+] Yujie Li and Zhimei Wang contributed equally to this work.
Graphene, as a two-dimensional carbon nanomaterial, has
received much attention due to its specific properties such as high
surface area, excellent electrical conductivity and mechanical
Supporting information for this article is available on the WWW
under https://doi.org/10.1002/zaac.202100182
Z. Anorg. Allg. Chem. 2021, 647, 1–8
1
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
resonance spectrometer (Brooker), pHs-10 C digital acidity meter
strength. It has been shown that the chemical activity, electronic
(Shanghai Lei Magnetic Scientific Instrument Factory). All the
chemicals involved in the experiment were analytically pure. N,N-
and optical properties of carbon materials can be tuned by adding
suitable functional groups.[27] Graphene oxide (GO) contains a
monoatomic layer of functionalized (oxidized) graphene and has
been used as an electrode modification material due to its special
performance.[28] GO has a high specific surface area, excellent
electrochemical properties, and can be chemically coupled with
nanoparticles,[29] organic compounds,[30] and biomolecules.[31]
Currently, ion-imprinted polymers (IIPs)[32] are widely used for
the detection of trace metal ions due to its stability[33] low cost[34]
and ease of preparation.[35] Usually, we synthesize IIPs by mixing
functional monomers, target ions (templates)[36] and excess cross-
linking agent. After polymerization, the template ions are eluted
from the polymer to form a binding point[37] that is completely
complementary to the size, shape and function of the measured
element, which is beneficial to the combination with the target
element.[38] At present, this technology is combined with various
methods such as spectrophotometry and electrochemistry, and
has been successfully used for trace detection of metal ions such
as chromium,[39] copper,[40] silver,[41] lead,[42] and cadmium.[43] Since
the cavity of the imprinted polymer can coordinate with related
metal ions, and the coordination between the metal and the
ligand is relatively stable to the non-covalent bond, at the same
time, the binding and breaking speed of the coordination bond
can be controlled by changing the environmental conditions,[44] so
the method has excellent selectivity and stability. Even under
harsh chemical conditions, IIPs have excellent stability and
durability. At present, IIPs modified electrodes based on electro-
chemical detection have also been successfully applied to a variety
of metal ions.[45]
dimethylformamide
(DMF),
3-aminopropyltrimethoxysilane
(APTMS), GO, tetraethoxysilane (TEOS), phosphorus oxychloride
(POCl3), benzaldehyde, pyrrole, ortho-phenylenediamine and tri-
fluoroacetic acid (TFA) were purchased from Aladdin Reagents Co.,
Ltd (Shanghai, P.R. China). Uranyl nitrate hexahydrate was pur-
chased from Hubei Chushengwei Chemical Co., Ltd (Wuhan, P.R.
China). Redistilled water was used throughout the experiment, and
all solutions were prepared according to the conventional method.
Synthesis of H4L
According to the preparation method of reference,[46] we optimized
and successfully synthesized H4L. For the specific steps, please refer
to the supporting information.
Preparation of carbon paste electrode modified by GO
First, pure graphite powder (4 g) and paraffin oil (1 mL) were added
into a 25 mL beaker, and ethanol was used as the solvent. The
mixture was stirred with a glass rod until a uniform paste was
formed, and ultrasonic treatment lasted for 20 min. The mixture
°
was then dried in an oven at 60 C for 6 h to remove the solvent.
Blocks of graphite were ground into powder using glass rods, and
the powder was filled into a polyethylene plastic tube with a
diameter of 3.5 mm and a length of 5 cm. Pressure was applied to
the tube and the electrode was polished to achieve a smooth
electrode surface. The other end was connected with a pencil lead.
Finally, GO (5 mg) was dissolved in DMF (5 mL) and treated with
ultrasound for 90 min. Drops of 30 μL of the above solution were
added to the surface of the carbon paste electrode and the solvent
°
was dried and evaporated at 35 C. Thus the GO modified carbon
paste electrode (GO/CPE) was fabricated.
In this paper, we report a carbon paste electrode electro-
chemical sensor based on ion-imprinted sol-gel modification.
For the first time, a carbon paste electrode modified with a
bipolar tetradentate macrocyclic ligand H4L ion imprinted
polymer was prepared for the highly sensitive and selective
detection of UO22+. The U-IIP and blank control non-imprinted
polymer (N-IIP) were synthesized separately. In addition, the
Synthesis of U-IIP/GO/CPE and N-IIP/GO/CPE
2+
We took H4L (functional monomer) (1 mL, 1 mM) and UO2
(template ion) (1.5 mL, 1 mM) and mixed them with ethanol at
°
35 C for 30 min. Then, APTMS (stabilizer) (500 μL), TEOS (cross-
linker) (100 μL) and NaOH (100 μL 1 M) were added and stirred at
2+
design, synthesis, characterization and combination with UO2
room temperature for 1.5 h to prepare a gel solution containing
uranium ion template (U-IIP). The gel solution (N-IIP) as a blank
of these ion-imprinted sol-gel materials are also introduced in
detail. The introduction of GO has also enhanced the sensor’s
response to template ions. The constructed electrochemical
sensor is cheap, stable, sensitive and has rapid response. It has
been successfully applied to the analysis of water samples of
Xiangjiang river and soil samples around uranium tailings.
2+
control was prepared by replacing UO2
(template ion) with
1.5 mL redistilled water. Finally, GO/CPE was immersed in the
prepared U-IIP and N-IIP, respectively, so that the surface of the
electrode was completely covered by the solution. Then, the
electrode was placed at room temperature to evaporate and dry, so
that midU-IIP/GO/CPE containing template ions and the blank
control electrode N-IIP/GO/CPE were obtained. After that, 1.0 M HCl
was prepared in a large beaker, and the beaker was placed in a dry
magnetic stirrer. After adding magnets, stir the HCI slightly to make
the surface of the HCl solution flow slowly, and the electrode
surface was immersed in it to elute about 15 min. When the surface
of the electrode changed from yellow to white, it indicated that the
template ions on the midU-IIP/GO/CPE had been eluted, thereby U-
IIP/GO/CPE was prepared. Then connected U-IIP/GO/CPE and N-IIP/
GO/CPE to the electrochemical workstation for comparison experi-
Experimental Section
Instruments and reagents
All electrochemical tests were completed by CHI-660 C electro-
chemical workstation (Shanghai Chenhua Instrument Co., Ltd.). The
standard three-electrode system includes: U-IIP/GO/CPE as the
working electrode, saturated calomel electrode (SCE) as the
reference electrode and platinum electrode as the counter
electrode. Energy dispersive spectroscopy (EDS) analysis was
performed on JSM-6700F scanning electron microscope (SEM), and
the other equipment includes: Bruker 400-MHz nuclear magnetic
2+
ments (Figure 1A). The combination of UO2 and H4L is shown in
Figure 1B.
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
2
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Figure 2. SEM images the surface of electrodes (A) GO/CPE; (B) N-
IIP/GO/CPE; (C) midU-IIP/GO/CPE; (D) U-IIP/GO/CPE.
Figure 1. (A) Preparation schematic diagram of U-IIP/GO/CPE; (B)
Combination of UO2 and H4L.
2+
that of midU-IIP/GO/CPE (Figure 2C), because the surface of N-
IIP/GO/CPE does not form an imprinting cavity, while the
surface of midU-IIP/GO/CPE is flatter, because the high concen-
2+
tration of UO2 solution combines with the surface to form a
Electrochemical determination
gel-like film. However, the surface of the electrode after elution
(U-IIP/GO/CPE) is relatively rough, which just indicates the
successful formation of ion imprinting binding sites and cavities
on the electrode surface (Figure 2D)
An electrochemical workstation was connected to construct a
standard three-electrode system: platinum as the counter electrode,
saturated glycerin as the reference electrode, and U-IIP/GO/CPE as
2+
the working electrode. First, U-IIP/GO/CPE was put into 5 ml UO2
solution for testing, and the open-circuit adsorption was conducted
for 20 min. The electrode was then immersed in a buffer solution
containing KCl (0.1 M) and Tris-HCl (0.1 M, pH=7.3) for the DPV
test. The potential scanning range was À 0.5 V to 0 V, the potential
increment was 20 mV, the scanning rate was 120 mVsÀ 1, the pulse
width was 120 ms, and the pulse amplitude was 50 mV.
2.3. Electrochemical characterization of U-IIP/GO/CPE
sensor
2.3.1. Template elution and rebinding experiment
DPV was used to explore the elution and recombination of
templates on different sensors under the same conditions. The
peak current of midU-IIP/GO/CPE occurs at À 0.26 V (Fig-
ure 3Ab), while the peak current is very weak after removal of
template ions by HCl (1 M) elution, indicating that template
ions have been effectively removed (Figure 3Ae). After immers-
2. Results and Discussion
2.1. Study of the spectral properties of H4L
The spectral properties of H4L are shown in supporting informa-
tion.
2+
ing U-IIP/GO/CPE in UO2 solution (2.8 μM) for 20 min, it can
be seen from Figure 3Aa that the detected peak current is
significantly higher than that of the N-IIP/GO/CPE (Figure 3Ac)
control group, which is about 3 times the peak current detected
in GO/CPE (Figure 3Ad). The reason may be that N-IIP/GO/CPE
2.2. Characterization of sensors
2+
The GO/CPE, midU-IIP/GO/CPE, N-IIP/GO/CPE and U-IIP/GO/CPE
were scanned by scanning electron microscope (SEM) to
investigate their nanoscale surface properties and character-
istics. As expected, the surface of GO/CPE (Figure 2A) has many
scattered filamentous stripes, indicating that GO can be well
absorbed and dispersed on the bare carbon paste electrode. In
addition, the surface of N-IIP/GO/CPE (Figure 2B) is tighter than
does not contain an ion-imprinted cavity, and UO2 cannot
undergo redox reactions on the electrode surface, resulting in a
weak voltammetric signal. Therefore, it can be concluded that
the ion imprinted cavities on U-IIP/GO/CPE greatly enhance the
2+
coordination with UO2 and improve the sensor sensitivity.
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
3
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
occupied after the sensor is combined with UO22+, resulting in
an increase in the Rct value.
2.4. Optimization of experimental conditions
2.4.1. Optimization of sol-gel conditions
In the whole process of preparing gel, the ligand H4L
complexed with uranyl ions to form the complex. The amount
of APTMS, TEOS, NaOH added and the reaction time of forming
sol-gel film are very important in the experimental process. The
single variable method was used in the experiment. When the
amount of cross-linking agent (TEOS) was too small, the
template ion could not be cross-linked with the polymer well,
which affected the determination of the experiment. When
TEOS was excessive, it was difficult for the template ions to
elute from the imprinted cavity, which affected the elution-
recombination experiment. Finally, we found that the optimal
reaction conditions were APTMS (500 μL), TEOS (300 μL), NaOH
(50 μL, 1 M), and the reaction time was 1.5 h.
Figure 3. (A) Schematic diagram of response current DPV: (a) Detect
2+
2+
2.8 μM UO2 with U-IIP/GO/CPE ; (b) Detect 2.8 μM UO2 with
2+
midU-IIP/GO/CPE; (c) Detect 2.8 μM UO2 with N-IIP/GO/CPE; (d)
2+
Detect 2.8 μM UO2 with GO/CPE; (e) DPV Signals of U-IIP/GO/CPE
2.4.2. Optimization of the eluent and elution time
in buffer solution; (B) Impedance spectrum at 2 mM K3Fe(CN)6/
K4Fe(CN)6: (a) N-IIP/GO/CPE; (b) GO/CPE; (c) midU-IIP/GO/CPE; (d) U-
IIP/GO/CPE (added 2.8 μM UO22+); (e) U-IIP/GO/CPE; (C) Effect of
inorganic acid eluent on the detection of uranyl ions by U-IIP/GO/
CPE.
The elution of template ions from midU-IIP/GO/CPE is a key step
for subsequent ion recombination and electrochemical detection.
The eluted electrode has a stronger electrical signal in the
detection solution. The experiment used sulfuric acid, acetic acid,
nitric acid and hydrochloric acid at different concentrations to
select the best eluent for the elution rate of UO22+. It can be seen
from Figure 3C that the elution efficiency of 1 M HCl is the highest,
and a strong electrical signal is displayed on the electrode surface.
At the same concentration, the elution rate of hydrochloric acid is
higher than that of other inorganic acids, which may be attributed
to the increase of heteroatoms in the ligands by protonation. In
addition, the influence of time on the elution effect was studied,
and HCL (1 M) was used as the eluent. We found that 15 min is
the best time for elution efficiency.
2.3.2. Electrochemical impedance diagram
Electrochemical Impedance Spectroscopy (EIS) was used to
analyze the electrochemical properties of different sensor
surfaces. The mixed solution of K3Fe(CN)6/K4Fe(CN)6 (2.0 mM)
and potassium chloride (0.2 M) was used for electrochemical
study at a frequency ranging from 0.1 Hz to 100000 Hz, signal
amplitude of 5 mV and potential of 0.25 V. ZView software was
used to fit the electrochemical impedance data, and the
resistance values (Rct) of different sensors were obtained (Fig-
ure 3B). It can be seen from the figure that the GO/CPE
impedance is 1987 Ω (Figure 3Bb), and when the GO/CPE is
covered with the ion-imprinted polymer, Rct drops to 1625 Ω
(Figure 3Bc), indicating that the polymer layer has been
successfully constructed, and the ion-imprinted polymer layer
can accelerate charge transfer. The impedance value of N-IIP/
GO/CPE is 2512 Ω (Figure 3Ba), which is much larger than the
Rct of midU-IIP/GO/CPE (Figure 3Bc), mainly due to the lack of
probe channels on the N-IIP/GO/CPE surface. However, the Rct
of U-IIP/GO/CPE decreases to 389 Ω (Figure 3Be), indicating that
the probe channel has been successfully constructed and
imprinted holes formed on the surface of the sensor, thus
promoting the passage of probe molecules. It can be seen from
Figure 3Bd that when the U-IIP/GO/CPE is immersed in 2.8 μM
2.4.3. Effect of pH
After exploring the influence of HAc-NaAc, citric acid-sodium
citrate, Tris-HCl, phosphoric acid-sodium phosphate and other
buffer solutions on the current intensity of the sensor, Tris-HCl was
finally selected as the best buffer solution. In addition, the pH of
the buffer solution is also very important for the detection current
of the sensor. We detected the influence of the pH value on the
sensor in the range of 4.0 to 9.0, and the results are shown in
Figure 4A. The data shows that the electrode response drops
sharply when the pH value is lower than 7.3. This is due to the
protonation of the nitrogen atom of the H4L functional group on
U-IIP/GO/CPE, which weakens the interaction between UO22+ and
the electron pair on the nitrogen atom of the H4L functional
group. On the other hand, at a pH higher than 7.3, metal ions may
be hydrolyzed, and the formation of negatively charged salts and
2+
UO2 solution for 20 min, the Rct value of the sensor increases
to 876 Ω, which indicates that the imprinting holes are
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
4
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
0.01 μM to 3.0 μM. The fitted linear equation is Ip(μA)=5.455c
(μmolLÀ 1)+13.46, and the correlation coefficient R=0.998. On
this basis, according to the formula S/N=3 and S/N=10, the
method detection limit (MDL) and the limit of quantification
(LOQ)[47] can be obtained respectively. Therefore, the MDL and
LOQ of the method based on this range are about 1.32 nM and
4.4 nM. Where “S” is the standard deviation of the intercept and
“N” is the slope.
2.5.2. Experimental study of interference and selectivity of
ion imprinting sensors
In order to test the specificity of the sensor for UO22+ recognition,
after adding 2.8 μM UO22+ to the detection solution, a solution
containing 10 times the concentration of Co2+, Zn2+, Cu2+, Ni2+
and other metal ions was added. The experimental results show
that when Fe2+, Cd2+, Mn2+, Fe3+, Ag+, Co2+, Cr3+, Al3+ and Pb2+
are interfering cations, the voltammetric signal of the modified
electrode is not affected, which indicates that the electrode has
good selectivity for UO22+. As shown in Figure 5Aa, when the Hg2+
/UO22+ concentration ratio is 10, the influence of Hg2+ on the DPV
signal is also negligible; and when the concentration ratio is
greater than 10, Hg2+ will partially affect the electrode signal
(Figure 5Ab), but the masking agent can be added to reduce
interference. In addition, Figure 5B shows that N-IIP/GO/CPE has
no obvious response signal to UO22+ at À 0.26 V, and the
interference is very obvious when only Hg2+ is present in the
solution. Therefore, comparing the two figures shows that the U-
Figure 4. (A) Effect of pH on the sensor when detecting uranyl ions;
(B) Effect of enrichment time on detection of UO2 by U-IIP/GO/
CPE; (C) Current and calibration curve of U-IIP/GO/CPE at different
concentrations of uranyl ions (concentrations from top to bottom:
3.0, 2.25, 1.5, 0.8, 0.3, 0.15, 0.05, 0.01 μM).
2+
hydroxyl complexes may prevent the interaction of UO22+ with
H4L in the sol-gel polymer. As a result, the volt-ampere response is
reduced. Therefore, the Tris-Hcl buffer solution with pH=7.3 was
selected as the best condition for this experiment.
IIP/GO/CPE sensor has a good recognition performance for UO22+
.
2.4.4. Optimization of enrichment time
2.5.3. Stability and reproducibility of U-IIP/GO/CPE
Under optimal experimental conditions, the other experimental
conditions were kept unchanged, and the influence of the
enrichment time on the sensitivity of the sensor in the 5~25 min
period was studied. The results are shown in Figure 4B. It can be
seen that before 20 min, with the increase of the enrichment time,
the voltammetric signal intensity increases significantly, until the
adsorption equilibrium is reached at 20 min. This phenomenon
can be attributed to the adsorption saturation of the electrode
surface. However, with the further increase of the enrichment
time, the voltammetry signal weakly attenuate. Thus, 20 min was
chosen as the best adsorption time in this experiment.
The experiment also studied the repeatability and stability of
the U-IIP/GO/CPE sensing system. Using the same experimental
conditions on the same modified electrode, the concentration
2+
of 2.8 μM UO2 solution was determined 6 times, and the
relative standard deviation (RSD) was 4.60%. The repeatability
of the electrode was evaluated with five different electrodes
(built using the same procedure), and the RSD was 3.90%. In
2.5. Performance of U-IIP/GO/CPE sensors
2.5.1. U-IIP/GO/CPE sensor calibration curves and detection
limits
Under the optimal experimental conditions, the U-IIP/GO/CPE
2+
Figure 5. (A) The response of U-IIP/GO/CPE in 2.8 μM UO22+and
Hg2+: (a) 2.8 μM UO22+and Hg2+;(b) 2.8 μM UO22+and 28 μM
Hg2+;(c) 2.8 μM Hg2+ in 0.1 M KCl and Tris-Hcl buffer at pH=7.3; (B)
the same experiment with N-IIP/GO/CPE.
sensor system was placed in different concentrations of UO2
solution, and the DPV detection data was used to draw
Figure 4C. It can be seen from the figure that the peak current
is proportional to the concentration of UO2 in the range of
2+
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
5
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
2+
Table 1. U-IIP/GO/CPE sensors for UO2 analysis in actual samples (n=6).
Sample
This method
Added UO2
(μM)
ICP-MS
Found
(μM)
2+
Found
(μM)
Relative
recovery (%)
RSD
(%)
Relative
recovery (%)
RSD
(%)
t-test[a]
Soil sample 1
Soil sample 2
Soil sample 3
Water sample 1
Water sample 2
0.25
0.25
0.25
0.50
0.50
0.239
0.266
0.241
0.486
0.511
95.45
106.25
96.55
97.22
102.22
2.51
3.25
2.92
3.05
2.23
0.240
0.257
0.245
0.483
0.519
95.83
102.86
97.91
96.55
103.85
1.52
2.36
1.95
1.21
2.20
0.352
1.967
0.960
0.515
1.273
[a] Tabulated t-value for four degrees of freedom at 95% confidence level is 2.228.
addition, after one month of storage under dry conditions at
room temperature, the long-term stability of the prepared
sensor was tested. For the same uranyl ion solution, the current
response value reached 95% of the original response value,
which indicates that the modified electrode has good stability.
the statistical difference between this method and ICP-MS, and
the results show that the detection precision of the two
methods is not significantly different. This shows that the
prepared U-IIP/GO/CPE is suitable for the determination of trace
uranium ions in real samples and has good stability.
2.5.4. Test the performance of real samples
2.6. Comparison of the sensor reported in this article with
other electrochemical sensors in the literatures for UO2
2+
In order to test the performance of the sensor in real samples,
we collected soil samples from uranium tailings around
Hengyang City and water samples from the Xiangjiang River for
analysis. The soil sample was prepared into a solution using a
specific method (see supporting information), and the samples
were added to the test container to be tested according to the
above-mentioned best experimental method. Each sample was
added, detected, and recovered using the standard addition
Comparing this work with other electrochemical sensors, it can be
seen intuitively from Table 2 that the U-IIP/GO/CPE electrochem-
ical sensor has a wider linear relationship and a lower detection
limit. Moreover, the electrode is easy to prepare and low in cost,
and each modified electrode is about 0.8 dollars. Therefore, this
sensor has potential value for the detection of trace UO22+
.
method, and six parallel determinations were performed on
2+
each sample. UO2 solutions with a concentration of 0.25 μM 3. Conclusions
and 0.50 μM were added to the soil and water samples to be
tested respectively. The experimental data in Table 1 shows
that the sample recovery rate is between 95.45% and 106.25%,
and the relative standard deviation is 2.23% to 3.25%. In
addition, the method was compared with the inductively
coupled plasma mass spectrometry (ICP-MS) method, and the
results were within 95% confidence level and acceptable error
range. At the same time, we used the standard addition method
to perform repeated experiments on three sets of samples, and
analyzed the precision of the method. The intra-day precision (6
parallel experiments were performed in each group in one day)
was 4.60% or less, and the inter-day precision (the electrode
was placed for about a month and the experiments were
carried out on 3 different days, each group performs 6 parallel
experiments) was 5.16% or less. The t-test was used to evaluate
In this work, a new type of electrochemical sensor for the
determination of trace uranyl ions was prepared for the first
time in a carbon paste electrode modified by ion imprinting
combined with bipolar tetradentate functional monomer H4L.
Compared with U-IIP/GO/CPE and N-IIP/GO/CPE, the electrode
modified with ion imprinting made the sensor’s specific
recognition of uranium ions enhanced significantly. In addition,
the addition of GO increased the specific surface area of the
sensor and optimized the conductivity of the electrode, thereby
obtaining an ideal electrochemical response. It also had
excellent selectivity in the presence of high concentrations of
interfering ions. At the same time, the use of ICP-MS technology
as a comparative verification for the detection of uranium
concentration indicates that this electrochemical sensing
Table 2. Comparison of electrochemical sensor performance between U-IIP/GO/CPE and other literatures.
Electrode
Method
Linear range
(μM)
Detection limit
(μM)
References
Pt1Ru2-PCs/GCE
MMIP/MCPE
Au/NPCsÀ GCE
GRA-SPEs
DPV
DPV
DPV
DPV
DPV
0.168–3.528
0.06–50
0.12–95.1
0.005–0.1
0.01–3.0
0.024
[18]
[44]
[48]
[49]
0.0173
0.0494
0.0045
0.00132
U-IIP/GO/CPE
This work
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
6
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
[22] U. Pinaeva, T. C. Dietz, M. Al Sheikhly, E. Balanzat, M. Castellino,
system has the advantages of sensitivity, high precision, good
T. L. Wade, M. C. Clochard, Reactive and Functional Polymers
2019, 142, 77–86.
[23] X. Wu, Q. Huang, Y. Mao, X. Wang, Y. Wang, Q. Hu, H. Wang, X.
Wang, TrAC Trends Anal. Chem. 2019, 118, 89–111.
[24] Z. F. Akl, T. A. Ali, J. Radioanal. Nucl. Chem. 2017, 314, 1865–
1875.
[25] Y. Liao, M. Wang, D. Chen, Appl. Surf. Sci. 2019, 484, 83–96.
[26] A. Özcan, M. Gürbüz, A. A. Özcan, Talanta 2018, 187, 125–132.
[27] H. Lee, T. K. Choi, Y. B. Lee, H. R. Cho, R. Ghaffari, L. Wang, H. J.
Choi, T. D. Chung, N. Lu, T. Hyeon, Nat. Nanotechnol. 2016, 11,
566–572.
reproducibility, low method detection limit, and system
stability. Moreover, the cost of each modified electrode is very
low, which is conducive to further promotion as a probe for
detecting UO22+. Therefore, the U-IIP/GO/CPE sensing system
may be able to provide a reference for the further preparation
of electrochemical sensors for the detection of uranyl ions.
Acknowledgements
[28] P. Reanpang, J. Upan, J. Jakmunee, Talanta 2021, 122493.
[29] Z. Zhang, F. Ahmad, W. Zhao, W. Yan, W. Zhang, H. Huang, C.
Ma, J. Zeng, Nano Lett. 2019, 19, 4029–4034.
[30] H. Yan, Y. Xie, Y. Jiao, A. Wu, C. Tian, X. Zhang, L. Wang, H. Fu,
Adv. Mater. 2018, 30, 1704156.
[31] P. Chen, K. Xu, T. Zhou, Y. Tong, J. Wu, H. Cheng, X. Lu, H. Ding,
C. Wu, Y. Xie, Angew. Chem. Int. Ed. 2016, 55, 2488–2492;
Angew. Chem. 2016, 128, 2534–2538.
[32] C. Lin, H. Wang, Y. Wang, L. Zhou, J. Liang, Int. J. Environ. Anal.
Chem. 2011, 91, 1050–1061.
This work was financially supported by the National Natural
Science Foundation of China (11475079), the Natural Science
Foundation of Hunan Province (No. 2019JJ40244), Hengyang
science and technology planning project (No. 202010031546)
and Open Fund Project of State Key Laboratory of Chemo-
Biosensing and Metrology (Hunan University) (2018014). The
authors declare that they have no competing interests.
[33] M. M. Yusoff, N. R. N. Mostapa, M. S. Sarkar, T. K. Biswas, M. L.
Rahman, S. E. Arshad, M. S. Sarjadi, A. D. Kulkarni, Journal of
Rare Earths 2017, 35, 177–186.
Keywords: Electrochemistry · Trace analysis · Uranyl ions · Ion-
imprinting · Graphene oxide
[34] J. Muñoz, R. Montes, J. Bastos-Arrieta, M. Guardingo, F. Busqué,
D. Ruíz-Molina, C. Palet, J. García-Orellana, M. Baeza, Sens.
Actuators B 2018, 273, 1807–1815.
[35] M. Yolcu, N. Dere, Electroanalysis 2018, 30, 1147–1154.
[36] P. Yáñez-Sedeño, S. Campuzano, J. M. Pingarrón, Anal. Chim.
Acta 2017, 960, 1–17.
[37] F. An, B. Gao, X. Feng, J. Appl. Polym. Sci. 2009, 112, 2241–2246.
[38] P. Peng, L. Liao, Z. Yu, M. Jiang, J. Deng, X. Xiao, Int. J. Environ.
Anal. Chem. 2019, 99, 1495–1514.
[1] T. Kim, T. H. Tran, S. Y. Hwang, J. Park, D. X. Oh, B.-S. Kim, ACS
Nano 2019, 13, 3796–3805.
[2] K. Vohra, A. Vodonos, J. Schwartz, E. A. Marais, M. P. Sulprizio,
L. J. Mickley, Environ. Res. 2021, 195, 110754.
[3] S. A. Sarkodie, S. Adams, Sci. Total Environ. 2018, 643, 1590–
1601.
[4] D. Dewar, in Nuclear Non-Proliferation in International Law-
Volume IV, Springer, 2019, pp. 229–235.
[5] S. Wang, Y. Ran, B. Lu, J. Li, H. Kuang, L. Gong, Y. Hao, Biol.
Trace Elem. Res. 2019, 1–10.
[6] H. Takahashi, Y. Izumoto, T. Matsuyama, H. Yoshii, X-Ray
Spectrom. 2019, 48, 366–374.
[7] Z. Gao, W. Zhong, Anal. Bioanal. Chem. 2021, 1–16.
[8] H. Ahmad, U. Haseen, K. Umar, M. S. Ansari, M. N. M. Ibrahim,
Microchim. Acta 2019, 186, 649.
[9] S. Wang, H. Chen, B. Sun, Food Chem. 2020, 315, 126158.
[10] S. V. Jovanovic, T. Kell, J. El-Haddad, C. Cochrane, C. Drum-
mond, A. El-Jaby, J. Radioanal. Nucl. Chem. 2020, 323, 831–838.
[11] M. Schneider, H. R. Cadorim, B. Welz, E. Carasek, J. Feldmann,
Talanta 2018, 188, 722–728.
[12] K. Danchana, C. T. de Souza, E. Palacio, V. Cerdà, Microchem. J.
2019, 150, 104148.
[13] S. Zheng, H. Wang, Q. Hu, Y. Wang, J. Hu, F. Zhou, P. Liu, Sens.
Actuators B 2017, 253, 766–772.
[14] B. Ozden, C. Brennan, S. Landsberger, Environmental Earth
Sciences 2019, 78, 114.
[15] B. Zheng, J. Li, Z. Zheng, C. Zhang, C. Huang, J. Hong, Y. Li, J.
Wang, Opt. Laser Technol. 2021, 133, 106522.
[16] T. Liu, J. Yuan, B. Zhang, W. Liu, L. Lin, Y. Meng, S. Yin, C. Liu, F.
Luan, Environ. Sci. Technol. 2019, 53, 14612–14619.
[17] Z. Zhou, Y. Zhou, X. Liang, F. Xie, S. Liu, J. Ma, J. Radioanal.
Nucl. Chem. 2019, 322, 2049–2056.
[39] S. Parvizi, M. Behbahani, A. Esrafili, New J. Chem. 2018, 42,
10357–10365.
[40] S. Di Masi, A. Pennetta, A. Guerreiro, F. Canfarotta, G. E.
De Benedetto, C. Malitesta, Sens. Actuators
B 2020, 307,
127648.
[41] M. Behbahani, F. Omidi, M. G. Kakavandi, G. Hesam, Appl.
Organomet. Chem. 2017, 31, e3758.
[42] H. Ebrahimzadeh, M. Behbahani, Arab. J. Chem. 2017, 10,
S2499-S2508.
[43] V. Zarezade, M. Behbahani, F. Omidi, H. S. Abandansari, G.
Hesam, RSC Adv. 2016, 6, 103499–103507.
[44] C. Su, Z. Li, D. Zhang, Z. Wang, X. Zhou, L. Liao, X. Xiao, Biosens.
Bioelectron. 2020, 148, 111819.
[45] H. Wang, D. Qian, X. Xiao, S. Gao, J. Cheng, B. He, L. Liao, J.
Deng, Biosens. Bioelectron. 2017, 94, 663–670.
[46] J. Wang, J. Xue, X. Xiao, L. Xu, M. Jiang, P. Peng, L. Liao,
Spectrochim. Acta Part A 2017, 187, 104–109.
[47] W. Zhang, Y. Hua, Q. Lu, W. Qiu, Y. Li, Journal of Hygiene
Research 2021, 50, 625–632.
[48] F. Li, R. Li, Y. Feng, T. Gong, M. Zhang, L. Wang, T. Meng, H. Jia,
H. Wang, Y. Zhang, Mater. Sci. Eng. C 2019, 95, 78–85.
[49] V. T. Kostaki, A. B. Florou, M. I. Prodromidis, Electrochim. Acta
2011, 56, 8857–8860.
[18] X. Cao, Y. Sun, Y. Wang, Z. Zhang, Y. Dai, Y. Liu, Y. Wang, Y. Liu,
J. Solid State Electrochem. 2021, 25, 425–433.
[19] I. Gęca, M. Ochab, M. Korolczuk, Talanta 2020, 207, 120309.
[20] S. Güney, O. Güney, Sens. Actuators B 2016, 231, 45–53.
[21] L. A. Romero-Cano, A. I. Zárate-Guzmán, F. Carrasco-Marín, L. V.
González-Gutiérrez, J. Electroanal. Chem. 2019, 837, 22–29.
Manuscript received: May 23, 2021
Revised manuscript received: August 10, 2021
Accepted manuscript online: August 20, 2021
Z. Anorg. Allg. Chem. 2021, 1–8
www.zaac.wiley-vch.de
7
© 2021 Wiley-VCH GmbH
��
These are not the final page numbers!

ARTICLE
Y. Li, Z. Wang, C. Liu, D. Zhang,
Prof. L. Liao, Prof. Dr. X. Xiao*
1 – 8
Graphene oxide modified H4L-ion
imprinting electrochemical sensor
for the detection of uranyl ions