Three-template ion imprinting electrochemical sensor for synchronous detection of As (III), Cd (II) and Pb (II) and application

Abstract

The invention discloses an electrochemical sensor based on a three-template ion imprinting technology. The electrochemical sensor is used for synchronously detecting As (III), Cd (II) and Pb (II). The sensor takes a glassy carbon electrode as a substrate, an NH2-UiO-66 (Hf) (at) rGO composite material and electrodeposited Bi nanoparticles are sequentially modified, and an imprinted polymer film taking As, Cd and Pb as template ions and MAA and PAR as functional monomers is introduced on the basis. The prepared AsCdPb-IIM / NH2-UiO-66 (Hf) (at) rGO (at) Bi / GCE sensor has the high specific surface area of MOF, the excellent electro-catalytic performance of rGO and Bi-NPs and the high selective recognition capability of ion imprinting, shows good response potential, ultralow detection limit (reaching 10 <-10 > mol.L <-1 >) and wide linear range, is high in recovery rate in a surface water sample, and has good stability and anti-interference capability. The method is easy and convenient to operate, low in cost, high in sensitivity and suitable for rapid detection of trace heavy metal ions in the environment.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensing, particularly to a method for detecting heavy metal pollution in the chemical analysis of water pollutants. Specifically, it relates to a three-template ion-imprinted electrochemical sensor for the simultaneous detection of As(III), Cd(II), and Pb(II), enabling the simultaneous detection of As(III), Cd(II), and Pb(II) in environmental water samples. Background Technology

[0002] Arsenic, cadmium, and lead are long-standing pollutants affecting water bodies. These pollutants, entering water bodies through leaching, surface runoff, industrial emissions, and groundwater infiltration, cause a series of ecological, environmental, and drinking water safety problems due to their environmental persistence and cumulative toxicity. Arsenic, in particular, is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) and is closely associated with skin, bladder, and lung cancer. After being absorbed by the human body, its physiological activity primarily disrupts cell metabolism through interference with enzyme function and oxidative phosphorylation, leading to skin lesions, cardiovascular diseases, and nerve damage. Cadmium, due to its strong cellular interference (manifested in interfering with cellular calcium metabolism) and its tendency to accumulate in the kidneys and bones, is a major cause of kidney damage, osteoporosis, and lung diseases. Lead exposure has a clear link to damage to the nervous system, especially posing a significant threat to children. It not only replaces calcium absorption in bones but also interferes with hemoglobin synthesis, leading to diseases including, but not limited to, cognitive impairment, developmental delays, kidney failure, and cardiovascular diseases. It is worth noting that although the World Health Organization (WHO) and local environmental agencies have set toxicity thresholds for arsenic, cadmium, and lead in water at 10 µg / L, 3 µg / L, and 10 µg / L, respectively, the bioaccumulation effects of arsenic, cadmium, and lead, as well as the trace synergistic effects of simultaneous exposure, can amplify their toxic effects on organisms. Therefore, simultaneous monitoring of these pollutants, especially the accurate determination of co-pollutant levels of arsenic, cadmium, and lead in water bodies, is of great significance for environmental water quality supervision, food safety, and public health exposure prevention. However, existing detection methods (AAS, ICP-MS, GFAAS, XRF, HPLC-ICP) have many limitations in accurately detecting these co-pollutants simultaneously, including reliance on imported equipment, specialized operation, high cost, time-consuming nature, and large scale. Electrochemical analysis strategies, due to their high sensitivity, rapid response, low cost, and wide applicability, have become one of the most promising alternative analytical methods in the field of modern environmental safety monitoring. However, the electrochemical detection of As(III), Cd(II), and Pb(II) still faces many challenges. There are three main reasons: ① Arsenic has extremely low electrochemical response activity; ② It has weak anti-interference ability in complex environmental matrices; ③ Cadmium and lead are more likely to adsorb onto the electrode surface and form a passivation layer, inhibiting the detection of arsenic. Furthermore, existing electrochemical sensors have not yet been able to simultaneously and selectively detect arsenic, cadmium, and lead, resulting in this significant technological gap in electrochemical sensing technology.

[0003] To overcome these limitations, using ion-imprinted nanomaterials (IIMs) to modify electrodes is an effective approach to enhance the anti-interference capability and avoid competitive adsorption of coexisting ions when detecting multiple metal ions (two or more). IIMs work by binding the target analyte (template) to a functional monomer via covalent or non-covalent interactions, followed by the formation of a rigid polymer matrix around the template-monomer complex under the action of crosslinking agents and initiators. After template extraction, cavities complementary to the template in shape, size, and functional group orientation remain. These non-biological nanomaterials, mimicking antigen-antibody behavior, not only possess enzyme-like functionality but also offer advantages such as lower cost and higher stability. However, the immaturity of functional monomer screening methods leads to low recognition efficiency, limiting the further development of IIMs in the sensor field. Computational chemistry methods, by simulating the interaction between the template and functional monomer, can predict the optimal monomer and monomer-template complex, reducing the need for experimental screening and thus further optimizing IIM design, improving its recognition efficiency and sensor performance. Furthermore, selecting suitable electrochemically active supporting materials is crucial for improving sensor performance. Materials such as graphene and UIO-66 metal-organic frameworks (MOFs) have proven to be ideal candidates for enhancing sensor sensitivity and selectivity due to their excellent conductivity, large specific surface area, and ability to tune porosity. Notably, some metal nanoparticles, such as the pale pink-lustered late-transition metal bismuth (Bismuth, Bi), possess unique electrochemical catalytic behavior due to the lone pair electron effect of its 6s² electronic configuration, making them a non-toxic alternative to mercury-based electrodes for electrochemical analysis.

[0004] Against this backdrop, the present invention provides a novel As(III), Cd(II), and Pb(II) heavy metal sensor. This sensor combines ion imprinting technology with electroactive support materials (such as NH2-UiO-66(Hf)@rGO@Bi) to prepare a biomimetic sensing probe via in-situ photoinduced self-polymerization. Specifically, a pre-prepared NH2-Hf-MOF composite material and graphene redox (rGO) are fixed on the surface of a glassy carbon electrode (GCE) using a drop-casting method. Subsequently, electropolymerized bismuth nanoparticles (Bi-NPs) are embedded in the NH2-Hf-MOF@rGO, and an imprinting polymerization solution is added dropwise. Under the action of infrared light, the self-polymerization of the monomers is initiated to form a surface-imprinted polymer layer. NH2-Hf-MOF@rGO acts as a synergistic effect of a conductive and electrochemically active substrate, while the Bi nanoparticles (Bi-NPs) enhance the sensitivity, and the molecularly imprinted polymers (MIPs) provide high selectivity. Simultaneously, computational simulations further support the design and optimization of the molecular imprinting process, ensuring the accuracy of recognition sites for As(III), Cd(II), and Pb(II) ions. The electrochemical response, selectivity, sensitivity, and repeatability of the proposed sensor were systematically studied and characterized using voltammetry. Furthermore, this invention validates the sensor's applicability in real samples and evaluates its ability to detect trace heavy metals in complex matrices. Computational simulations further confirm the binding interaction between sensor design and the molecular level. Through a combination of experimental and theoretical methods, this study provides a reliable platform for the selective and efficient detection of heavy metals, paving the way for sensor development in environmental monitoring and public health fields. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that existing electrochemical sensors cannot achieve simultaneous high-sensitivity selective detection of multiple heavy metal ions such as As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ), and traditional ion-imprinted membranes have problems such as uneven distribution of recognition sites, difficulty in eluting template ions, and poor membrane conductivity.

[0006] Therefore, this invention provides a tritemplate ion-imprinted electrochemical sensor for the simultaneous detection of As(III), Cd(II), and Pb(II) and its application. The sensor uses a glassy carbon electrode as a substrate, with the surface sequentially modified from the inside out by: a composite functional layer composed of an amino-modified metal-organic framework material UiO-66-NH2(Hf) and rGO; an electrodeposited Bi nanoparticle catalytic layer; and a tritemplate ion-imprinted polymer recognition layer formed by polymerization of As(III), Cd(II), and Pb(II) as template ions, and MAA and PAR as functional monomers, initiated by infrared light.

[0007] The present invention also relates to the fabrication process of the sensor, including GCE pretreatment, drop-coating of composite material, electrodeposition of Bi, imprinted film polymerization and template elution steps; and provides a method for simultaneous quantitative detection of heavy metals based on DPASV.

[0008] This invention discloses a three-template ion-imprinted electrochemical sensor for the simultaneous detection of As(III), Cd(II), and Pb(II), the sensor comprising:

[0009] The modified glassy carbon electrode (GCE) has the following surface modifications: a graphene composite metal-organic framework material layer based on NH2-UiO-66(Hf)@rGO; an electrodeposited Bi nanoparticle (Bi-NPs) layer; and a three-template ion-imprinted polymer film layer formed by infrared-initiated polymerization using As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) as template ions and methacrylic acid (MAA) and 4-(2-pyridinium azo)resorcinol (PAR) as functional monomers.

[0010] This invention discloses a three-template ion-imprinted electrochemical sensor for the simultaneous detection of As(III), Cd(II), and Pb(II). The preparation method of the modified electrode includes the following specific steps:

[0011] 1) Pretreatment of glassy carbon electrode: The polished glassy carbon electrode was placed in buffer solution A and cyclic voltammetry was performed until a stable voltammogram was obtained;

[0012] 2) The pretreated glassy carbon electrode is placed in solution B and activated by cyclic voltammetry under stirring until a stable voltammogram is obtained. The glassy carbon electrode is then removed, washed with ultrapure water, and dried with nitrogen to obtain the activated glassy carbon electrode.

[0013] 3) A suspension of amino-modified hafnium-based metal-organic framework material composite reduced graphene oxide (NH2-UiO-66(Hf)@rGO) was dropped onto an activated glassy carbon electrode and allowed to air dry to obtain an NH2-UiO-66(Hf)@rGO / GCE electrode.

[0014] 4) The NH2-UiO-66(Hf)@rGO / GCE electrode was placed in buffer solution C and bismuth nanoparticles (Bi-NPs) were loaded onto the NH2-UiO-66(Hf)@rGO nanomaterial by constant potential electrochemical deposition to obtain the NH2-UiO-66(Hf)@rGO@Bi / GCE electrode;

[0015] 5) The imprinted polymerization solution containing As(III), Cd(II), and Pb(II) templates was drop-coated onto NH4+. 2-The UiO-66(Hf)@rGO@Bi / GCE electrode surface was then quickly covered with a coverslip to assist in film formation, and photopolymerization was carried out under infrared light. After the reaction was completed, the electrode was naturally cooled to room temperature, and then suspended in ultrapure water at 2-5 cm for more than 6 hours. After the coverslip was removed, the electrode was eluted with a mixed solution of EDTA (ethylenediaminetetraacetic acid) and HCl to remove the imprinted ions As(III), Cd(II), and Pb(II). The electrode was then washed with ultrapure water to obtain a glassy carbon electrode (AsCdPb-IIM / NH2-UiO-66(Hf)@rGO@Bi / GCE) modified with a surface molecular imprinted composite film. When not in use, the electrode was stored in the refrigerator's crisper drawer.

[0016] In industrial applications, the pretreatment of glassy carbon electrodes may specifically include: placing the polished glassy carbon electrode in buffer solution A and performing cyclic voltammetry scanning until a stable voltammogram is obtained; the polishing method involves placing a 6 mm diameter glassy carbon electrode (GCE) on a chamois polishing cloth and polishing it with alumina (Al2O3) powder of 0.5, 0.3, and 0.05 μm, respectively, followed by ultrasonic cleaning with ultrapure water, anhydrous ethanol, and ultrapure water for 2 min in sequence, and then purging with nitrogen and drying; the buffer solution A has a pH of 6 and contains 0.1 mol / L potassium chloride and 5 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6], and the voltage range of the cyclic voltammetry is -0.2 to 0.6 V, the scan rate is 20 to 120 mV / s, and the equilibration time is 10 s.

[0017] Preferably, buffer solution A has a pH of 6, contains 0.1 mol / L potassium chloride, 5 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6], and the voltage range of cyclic voltammetry is -0.2 to 0.6 V, the scan rate is 20 to 120 mV / s, and the equilibration time is 10 s.

[0018] In industrial applications, a pretreated glassy carbon electrode is placed in a sulfuric acid solution and activated by cyclic voltammetry under stirring until a stable voltammogram is obtained. The glassy carbon electrode is then removed, washed with ultrapure water, and dried with nitrogen to obtain the activated glassy carbon electrode. The concentration of the sulfuric acid solution is 0.05~0.5 mol / L, the voltage range of the cyclic voltammetry is -0.3~1.3V, and the scan rate is 50~100mV / s. Preferably, solution B is a sulfuric acid solution with a concentration of 0.05~0.5 mol / L, the voltage range of the cyclic voltammetry is -0.3~1.3V, and the scan rate is 50~100mV / s.

[0019] Preferably, NH2-UiO-66(Hf)@rGO is prepared by the following process:

[0020] Under continuous stirring, 0.1–1.0 g HfCl4, 0.5–1.5 g aminoterephthalic acid (NH2-BDC), and 0.05–1.50 g reduced graphene oxide (rGO) were dissolved in 10–50 mL DMF in proportion, and 0.5–3 mL acetic acid was added as a regulator. The mixture was then sonicated for 5–30 min. The mixture was then transferred to a 100 mL high-pressure reactor and reacted at 120–180 °C for 12–36 h. The mixture was washed three times with DMF and further washed with ethanol. The product was collected by centrifugation and dried under vacuum at 60–120 °C for 18–28 h, preferably 24 h, to obtain UiO-66-NH2(Hf)@rGO.

[0021] Preferably, the solvent for the UiO-66-NH2(Hf)@rGO suspension is anhydrous ethanol, and the amount of solute is 0.5~5.0 mg (solute concentration is 0.5~5.0 mg / mL). The suspension is ultrasonically treated for 5~30 min, wherein 2.0~15.0 μL of the suspension is dropped onto the surface of the activated GCE to obtain the UiO-66-NH2(Hf)@rGO / GCE modified electrode. In industrial applications, the UiO-66-NH2(Hf)@rGO composite suspension is dropped onto the activated glassy carbon electrode and allowed to air dry to obtain the UiO-66-NH2(Hf)@rGO / GCE modified electrode; the suspension is obtained by ultrasonically mixing equal volumes of a UiO-66-NH2(Hf) solution with a concentration of 1~5 mg / mL and an rGO solution with a concentration of 2~6 mg / mL for 2~4 h.

[0022] Preferably, the buffer solution C is a PBS electrolyte solution of 0.1~3.0 mM, more preferably 0.5 mM Bi(NO3)3·5H2O; the concentration of the PBS electrolyte solution is 0.05~0.3 M, more preferably 0.1 M.

[0023] Preferably, Bi-NPs are prepared by the following process:

[0024] The UiO-66-NH2(Hf)@rGO / GCE modified electrode was immersed in a PBS electrolyte solution containing 0.1~3.0 mM, preferably 0.1~1 mM Bi(NO3)3·5H2O; under magnetic stirring, deposition was carried out at a constant potential of -0.8~-1.2 V for 60~300 s, preferably 80s~300s, by a potentiostatic method; the electrode was gently washed with pure water and air-dried to obtain the UiO-66-NH2(Hf)@rGO@Bi / GCE modified electrode; the concentration of the PBS electrolyte solution was 0.05~0.3 M.

[0025] In this invention, the imprinted polymerization solution containing As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) as three templates in step 5) is prepared by the following scheme:

[0026] An imprinting polymerization solution containing As(III), Cd(II), and Pb(II) was prepared using acetonitrile as a solvent. The imprinting polymerization solution containing As(III), Cd(II), and Pb(II) contained sodium arsenite 0.0015~0.05 mmol / L, cadmium acetate 0.0015~0.05 mmol / L, lead nitrate 0.0015~0.05 mmol / L, methacrylic acid 0.05~0.2 mmol / L, 4-(2-pyridinium azo)resorcinol 0.05~0.2 mmol / L, ethylene glycol dimethacrylate 0.5~2 mmol / L, and azobisisobutyronitrile 0.0275~0.11 mmol / L.

[0027] Preferably, the photopolymerization time in step 5) is 120~360min, preferably 180min.

[0028] In industrial applications, an imprinted polymerization solution containing As(III), Cd(II), and Pb(II) is drop-coated onto the surface of NH2-Hf-MOF@rGO@Bi / GCE, and then a coverslip is quickly placed on top to assist film formation. The film is then subjected to photopolymerization under infrared light for 180 min. After the reaction, the film is allowed to cool naturally to room temperature, and then the electrode is suspended in ultrapure water at a depth of 2-5 cm overnight. After the coverslip is removed, the AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE sensing electrode is obtained. The sensing electrode is eluted with a mixed solution of 0.05 M EDTA (ethylenediaminetetraacetic acid) and 0.1 M HCl to remove the template ions As(III), Cd(II), and Pb(II). The electrode is then washed with ultrapure water to obtain a template-free AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE modified electrode, which is then stored in the refrigerator's crisper drawer.

[0029] In industrial applications, the preparation of the imprinted polymerization solution of the three templates As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) can be optimized by simulation using Gaussian software, which can be used to optimize the template ions As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) with the optimal functional monomers MAA and PAR and their molar ratios.

[0030] This invention discloses an application of a three-template ion-imprinted electrochemical sensor for the simultaneous detection of As(III), Cd(II), and Pb(II), comprising the following steps:

[0031] Step 1

[0032] The sensor is used as the working electrode, and together with the Ag / AgCl reference electrode and the platinum counter electrode, a three-electrode system is formed.

[0033] Step Two

[0034] The three-electrode system was placed in buffer solutions D containing different concentrations of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ). Differential pulsed cathodic stripping voltammetry was used to measure the concentrations of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) in buffer solutions D. DPASV pulse curves of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were plotted. Standard curves of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were obtained based on the relationship between the peak value of the differential pulse current and the concentrations of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ).

[0035] The buffer solution D is a phosphate buffer solution, wherein the concentration of sodium hydrogen phosphate is 0.05~0.3 mol / L, the concentration of sodium dihydrogen phosphate is 0.05~0.3 mol / L, the concentration of KCl electrolyte is 0.01~1.0 mol / L, and the concentration of As(III) is 1.0×10⁻⁶. -10 ~5.1×10 -5 mol / L, Cd(II) concentration is 1.0×10 -10 ~5.1×10 -5 mol / L, Pb(II) concentration is 1.0×10 -10 ~5.1×10 -5 mol / L; its pH value is 5~10;

[0036] Step 3

[0037] The DPASV method was used to determine the heavy metal sample solution of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) under the same conditions as in step 2). The corresponding DPASV pulse curves were plotted and the peak currents of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were obtained. The peak currents of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were substituted into the standard curve corresponding to step 2) to obtain the concentration of heavy metals As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) in the sample solution, thus realizing the simultaneous quantitative detection of heavy metal ions.

[0038] As a preferred embodiment, this invention provides an application of a three-template ion-imprinted electrochemical sensor for the simultaneous detection of As(III), Cd(II), and Pb(II). A glassy carbon electrode modified with a surface-imprinted composite film is used as the working electrode, an Ag / AgCl electrode as the reference electrode, and a platinum column electrode as the counter electrode. The DPASV method is used to measure buffer solutions D with different concentrations of As(III), Cd(II), and Pb(II), and differential pulse curves of As(III), Cd(II), and Pb(II) are plotted. Standard curves of As(III), Cd(II), and Pb(II) are obtained by plotting the relationship between peak current and the concentrations of As(III), Cd(II), and Pb(II). The surface-imprinted composite film modified glassy carbon electrode is AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE; the surface-imprinted polymer film modified glassy carbon electrode is a glassy carbon electrode modified with a three-template molecularly imprinted polymer film of As(III), Cd(II), and Pb(II).

[0039] Buffer solution D is a phosphate buffer solution (PBS) with a concentration of 0.1 mol / L and a pH of 5–10. The concentrations of As(III), Cd(II), and Pb(II) in buffer solution D are 1.0 × 10⁻⁶. -10 ~5.1×10 -5 mol / L;

[0040] The deposition potential of the DPASV method is -0.8 V to -1.2 V, the deposition time is 80 s to 600 s, and the settling time is 10–20 s; the dissolution initiation potential is -1.2 V, the dissolution termination potential is 1.0 V, the pulse amplitude is 0.05 s, the pulse period is 0.5 s, the amplitude is 0.05 V, and the equilibrium time is 5 to 10 s.

[0041] In step two (please consider whether this parameter is from step two or step three), while stirring the buffer solution D, a deposition potential of -0.8 V to -1.2 V is applied to the working electrode to reduce all target metals As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) to the electrode surface; the deposition time is 80s to 600s, then stirring is stopped, and the solution is allowed to stand for 10 to 20 seconds to stabilize the metal deposits on the electrode surface.

[0042] Preferably, in step two, the starting potential of the differential pulse voltammetry is -1.4 to -1.1V, the ending potential is 0.9 to 1.2V, the pulse amplitude is 0.01 to 0.1s, the pulse period is 0.1 to 1.0s, the amplitude is 0.01 to 1.00V, and the equilibrium time is 5 to 10s.

[0043] In this invention, the MIM / NH2-Hf-MOF@rGO@Bi / GCE electrode, reference electrode, and counter electrode are placed in a measuring cell containing a sample solution of heavy metals As(III), Cd(II), and Pb(II) to be tested. The DPASV method is used to measure the sample solution of heavy metals As(III), Cd(II), and Pb(II) under the same conditions as in step (1). Differential pulse curves are plotted to obtain the peak currents of As(III), Cd(II), and Pb(II). The peak currents of As(III), Cd(II), and Pb(II) are substituted into the standard curve corresponding to step (1) to obtain the concentrations of heavy metals As(III), Cd(II), and Pb(II) in the sample solution of heavy metals As(III), Cd(II), and Pb(II) to be tested.

[0044] The principle of simultaneous electrochemical detection of heavy metal ions As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ):

[0045] The principle of simultaneous electrochemical detection of heavy metal ions As(III), Cd(II), and Pb(II) consists of two steps. The first step is pre-enrichment, which involves enriching Cd(II) and Pb(II) on a modified electrode in 10 mL of 0.1 M PBS (pH=6) electrolyte solution containing a certain concentration of As(III), Cd(II), and Pb(II) heavy metal ions at a potential of -0.8 to -1.2 V. The reactions that occur in this process are as follows:

[0046] As 3+ +3e － As 0

[0047] Cd 2+ +2e － Cd 0

[0048] Pb 2+ +2e － Pb 0

[0049] The second step is dissolution. After As(III), Cd(II), and Pb(II) are enriched on the working electrode, the potential is scanned at a constant rate using the DPV method (differential pulse voltammetry). The metals deposited on the modified electrode will be oxidized back to their ionic form under a specific voltage, exhibiting a unique oxidation peak and generating a measurable anodic current. The corresponding oxidation reaction for this process is:

[0050] As 0 -3e － As 3+

[0051] Cd0 -2e － Cd 2+

[0052] Pb 0 -2e － Pb 2+

[0053] The peak current is proportional to the measured ion. The current is measured and the corresponding potential is recorded to calculate the metal ion concentration.

[0054] Under optimized conditions, this sensor exhibits excellent electrochemical responses to As(III), Cd(II), and Pb(II) at approximately 0.75, -0.65, and -0.85 V (relative to an Ag / AgCl reference electrode), respectively, with detection limits reaching 1.0 × 10⁻⁶ V. -10 mol·L -1 (S / N=3), and also has 1.1×10 -9 ~1.2×10 -6 mol L -1 It has a wide linear range and good repeatability and anti-interference ability. In surface water analysis, Cd 2+ The average recovery rate was 109%, As 3+ The average recovery rate was 93%, Pb 2+ The average recovery rate was 92%.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) For the first time, simultaneous electrochemical detection of three highly toxic heavy metal ions was achieved, with detection limits below 1.0 × 10⁻⁶. -10 mol·L -1 It has a wide linear range (0.0002~32.3 μmol·L⁻¹). -1 );

[0057] (2) The use of MOF@rGO@Bi composite material enhances the reactivity of the electrode interface and improves the electron transfer rate; (3) The three-template ion imprinting strategy enhances the molecular recognition ability of multi-metal ions and improves the selectivity and anti-interference ability; (4) The detection method is simple to operate and has good stability. It is suitable for rapid on-site analysis of trace heavy metal ions in environmental water samples and has good application prospects in the fields of water quality safety monitoring and public health protection. Attached Figure Description

[0058] Figure 1The images shown are SEM images of UiO-66-NH2(Hf) (a), UiO-66-NH2(Hf)@rGO (b), UiO-66-NH2(Hf)@rGO@Bi (c), and IIM / UiO-66-NH2(Hf)@rGO@Bi before (d) and after (e) template removal, as well as XRD (f) images of c, d, e, and NIP in Example 1.

[0059] Figure 2 The FTIR spectra of UiO-66-NH2(Hf) (curve d), IIM / UiO-66-NH2(Hf)@rGO@Bi before template removal (curve a), after template removal (curve b), and without imprint (curve c) in Example 2, as well as their EDS plots before (B) and after (C) elution;

[0060] Figure 3 In Example 3, at 5.0 mmol L -1 K3Fe(CN)6 and 0.1 mol L -1 In KCl, (a) bare GCE, (b) UiO-66-NH2(Hf)@rGO / GCE, (c) UiO-66-NH2(Hf)@rGO@Bi / GCE, (d) CV plot (A) and EIS plot (B) of IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE before (d) and after (e) washing AsCdPb;

[0061] Figure 4 The current response intensity of AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE at different enrichment times in Example 4 (containing 1.0 μmol L... -1 0.1 mol L of AsCdPb -1 (in PBS test solution)

[0062] Figure 5 0.1 mol L in Example 5 -1 In PBS buffer solution (pH 6.0), the peak current (A), magnified view (B), and linear relationship (C) between the DPV oxidation of AsCdPb by IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE and its concentration logarithm were observed. The reaction was carried out with continuous addition of 0.0005–35.0 μmol / L PBS. -1 Linear relationship between the DPV response current and its concentration logarithm for Cd(D), Pb(E), and As(F); a: 0; b: 5.0 × 10⁻⁶ -10 c: 1.1×10 -9 ; d: 2.5×10 -9e: 4.8×10 -9 ;f: 1.5×10 -8 g: 7.5×10 - 8 h: 5.5×10 -7 i: 3.5×10 -6 ; Detailed Implementation

[0063] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0064] This invention, based on Molecular Imprinting Technology (MIT), constructs a molecularly imprinted membrane (MIM) that simultaneously recognizes three metal ions: As(III), Cd(II), and Pb(II), achieving highly selective and sensitive recognition of these ions in environmental water samples. The MIM is obtained by polymerizing a complex of functional monomers methacrylic acid (MAA) and 4-(2-pyridinium azo)resorcinol (PAR) with template ions As(III), Cd(II), and Pb(II) under infrared irradiation, followed by the addition of crosslinking agent ethylene glycol dimethacrylate (EGDMA) and initiator AIBN. To enhance the sensor's conductivity and enrichment capacity, a MOF-based interface material is formed by combining UiO-66-NH2(Hf) with reduced graphene oxide (rGO). Bismuth nanoparticles (Bi-NPs) are then introduced onto the surface of this MOF via electrochemical deposition, forming a UiO-66-NH2(Hf)@rGO@Bi / GCE composite electrode, providing a suitable carrier platform for subsequent MIM polymerization. Furthermore, the selection of functional monomer types and molar ratios, template elution methods, deposition potentials, and detection parameters were all obtained through simulation calculations and experimental optimization. The final sensor was used for the simultaneous detection of As(III), Cd(II), and Pb(II) in actual water samples, exhibiting low detection limits, a wide linear range, and advantages such as simple operation, rapid response, and no need for large analytical instruments. The technical implementation process of this invention is illustrated below through specific embodiments.

[0065] Example 1: Construction of AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE sensing electrode

[0066] (1) Synthesis of UiO-66-NH2(Hf)@Bi composite material

[0067] Under continuous stirring, 0.5 g HfCl4, 1.0 g aminoterephthalic acid (NH2-BDC), and 0.1 g reduced graphene oxide (rGO) were dissolved in 30 mL N,N-dimethylformamide (DMF), with 1.5 mL acetic acid added as a modifier. To improve the dispersibility of rGO, the mixture was sonicated for 15 minutes. The mixture was then transferred to a 100 mL high-pressure reactor and reacted at 180°C for 24 h to promote the formation of UiO-66-NH2(Hf)@rGO. After cooling to room temperature, the product was washed three times with DMF to remove unreacted raw materials and impurities, and further washed with ethanol to improve purity. Finally, the product was collected by centrifugation and dried under vacuum for 24 h (60°C) to obtain a black powder, yielding UiO-66-NH2(Hf)@rGO.

[0068] (2) Electrodeposition preparation of Bi nanoparticles

[0069] The above-mentioned UiO-66-NH2(Hf)@rGO composite material was ultrasonically dispersed in ethanol (mass concentration 1.0 mg / mL). 10 μL of this dispersion was drop-coated onto the surface of a pretreated glassy carbon electrode (GCE) and dried under an infrared lamp to obtain the UiO-66-NH2(Hf)@rGO / GCE electrode. This electrode was then immersed in a 0.1 M PBS buffer solution containing 0.5 mM Bi(NO3)3·5H2O and deposited at a constant potential of –1.0 V for 170 seconds. After removal, it was gently washed with deionized water and air-dried to obtain the UiO-66-NH2(Hf)@rGO@Bi / GCE electrode.

[0070] (3) Construction of AsCdPb three-template imprinted polymeric membrane

[0071] 0.0015 mmol sodium arsenite (As source) was dissolved in 100 μL of ultrapure water and added together with 0.0015 mmol cadmium acetate, 0.0015 mmol lead nitrate, 0.1 mmol MAA, and 0.1 mmol PAR into 480 μL of acetonitrile. The mixture was sonicated for 10 minutes and allowed to stand overnight. Then, 1.0 mmol of crosslinking agent EGDMA was added, and the mixture was sonicated for 5 minutes. Finally, 0.03 mmol AIBN was added, and the mixture was sonicated for 10 minutes. The mixture was then stored in a refrigerator for later use. 20 μL of the above prepolymer solution was dropped onto the surface of the UiO-66-NH2(Hf)@rGO@Bi / GCE electrode, covered with a coverslip, and polymerized under infrared lamp irradiation for 4 hours. After cooling, the electrode was immersed in an EDTA-HCl mixture to elute the template ions, finally obtaining the AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE modified electrode.

[0072] The morphology and structural characteristics of the obtained laminated materials and imprinted films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) for the imprinted films on the surfaces of UiO-66-NH2(Hf), UiO-66-NH2(Hf)@rGO, UiO-66-NH2(Hf)@rGO@Bi, and IIM / UiO-66-NH2(Hf)@rGO@Bi before and after template removal. The results are as follows: Figure 1 As shown. Figure 1 The SEM image in (a) shows that the initially synthesized UiO-66-NH2(Hf) nanoparticles are uniformly distributed and have a consistent morphology, exhibiting a regular octahedral crystal structure with an average particle size of approximately 22 ± 2 nm (as shown in the magnified inset). Figure 1 In (f), the corresponding XRD test results (curve c) show a significant diffraction peak at 2θ ≈ 9.4°, corresponding to the (001) crystal plane, indicating that the MOF material has good crystallinity and stable lattice arrangement. After being combined with reduced graphene oxide (rGO) ( Figure 1 (b) The surface morphology of the material changed significantly, with a large-area wrinkled layered structure, exhibiting typical rGO sheet-like stacking characteristics, verifying the formation of a flexible conductive framework. Simultaneously, some UiO-66-NH2(Hf) nanoparticles were embedded in the rGO wrinkled structure, forming a "point-surface" composite system. The characteristic peak appearing at 2θ ≈ 21.2° in the XRD curve belongs to the (002) crystal plane of rGO, further verifying the successful construction of the UiO-66-NH2(Hf)@rGO material. Subsequently, Bi nanoparticles were deposited on the surface of UiO-66-NH2(Hf)@rGO using a constant potential electrodeposition method. The SEM image of the resulting material (Fig. 1(c)) shows that the surface is further covered with a layer of uniformly sized, densely distributed, rough spherical particles, exhibiting a typical polycrystalline particle aggregation state. In the XRD pattern, the diffraction peaks at 2θ ≈ 26.5° and 28.6° are attributed to the (012) and (104) hexagonal crystal planes of metallic Bi, respectively, indicating that Bi-NPs have good nucleation and crystallization, regular structure, and ideal composite effect. Figure 1 (d) shows the surface morphology of the composite material after the AsCdPb multi-metal ion imprinted membrane (IIM) polymerization is completed. It can be observed that the UiO-66-NH2(Hf)@rGO@Bi support is coated with a highly cross-linked polymeric membrane layer. The membrane layer is dense and continuous with a rough surface, forming a three-dimensional porous network structure. After elution ( Figure 1 (e) The material surface becomes smoother, the particle structure is smaller and more dispersed, and the surface pores increase, indicating that the imprinted cavities have been effectively activated and the template ions have been successfully removed. Figure 1 XRD curves c, d, and e in (f) correspond to the crystal structure evolution of IIM / UiO-66-NH2(Hf)@rGO@Bi before, after, and in NIP, respectively. The main peak positions in all sample spectra remain similar, indicating that the UiO-66-NH2(Hf)@rGO@Bi framework structure was not destroyed during imprinted polymerization and elution, demonstrating good crystal stability. However, in the post-elution sample (curve e), the Bi diffraction peak intensity is enhanced, which is speculated to be related to the increased exposure of the Bi surface after the removal of the polymer film or its surface reconstruction after interaction with template ions. Overall, this composite material exhibits good controllability and stability during structure construction, with each component synergistically constructed at multiple scales, providing a structural basis and material guarantee for subsequent highly selective electrochemical recognition.

[0073] Example 2: Material composition of AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi

[0074] The introduction and removal process of template ions in the imprinted film was systematically characterized by Fourier transform infrared spectroscopy (FT-IR) and energy dispersive spectroscopy (EDS) of the UiO-66-NH2(Hf) support and its imprinted composite material. Figure 2 In the FTIR spectrum of UiO-66-NH2(Hf) (curve d), at approximately 3400 cm⁻¹... -1 The broad peak at 1650 cm⁻¹ can be attributed to the stretching vibration of –NH₂ or –OH. -1 The strong peaks nearby are attributed to the C=O stretching vibration of the carboxyl group in the ligand, indicating the successful synthesis of the MOF framework structure. In the uneluted template-free IIM / UiO-66-NH2(Hf)@rGO@Bi material (curve a), the peaks at 2959 cm⁻¹ are also observed. -1 1700 cm -1 With 1560 cm -1 Characteristic vibrational peaks of methylene C–H (from initiator AIBN), carboxyl C=O (from MAA), and azo N=N (from PAR) were observed at 830 cm⁻¹, confirming the successful polymerization of the functional monomers on the material surface. Furthermore, at 830 cm⁻¹... -1 The As–O vibration peak at 512 cm⁻¹ appeared. -1The M–O (metal–oxygen) coordination vibration peaks at the location correspond to the binding sites of As(Ⅲ) and Cd / Pb(Ⅱ), respectively, further confirming that the template ions are effectively embedded in the imprinted membrane. After elution (curve b), the intensity of the characteristic peaks related to the template ions is significantly reduced or disappears, especially the signal in the M–O region, indicating that the template ions are successfully removed; at the same time, the spectrum gradually tends to be consistent with the non-imprinted polymer (NIM, curve c) without the introduction of template molecules, indicating that the imprinted sites are successfully released and the composite structure is stable and intact. Furthermore, the EDS surface scan ( Figure 2 B) shows that As, Cd, and Pb are uniformly distributed in the blot membrane before elution, but after elution ( Figure 2 C) The wt% contents of the three components decreased significantly from 8.59%, 8.51%, and 0.59% to 0%, 0.05%, and 0.05%, respectively, verifying the complete removal of template ions. Combined with the analysis results of FT-IR and EDS, the successful insertion and controllable release of metal ions in the imprinted film were confirmed, which is the structural guarantee for constructing a highly selective electrochemical recognition interface.

[0075] Example 3: Electrochemical performance testing of AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE

[0076] At 5 mM [Fe(CN)6] 3- / 4- (containing 0.1 mol L) -1 Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed in KCl to evaluate the electrochemical performance of the modified electrode. Figure 3 As shown in Figure A, compared to the unmodified GCE (curve a), the redox peak current of the UiO-66-NH2(Hf)@rGO modified electrode is significantly increased (curve b). This indicates that the effective surface area of ​​the electrode is increased, thus improving the electron transfer efficiency. After further modification with bismuth nanoparticles (curve c), UiO-66-NH2(Hf)@rGO@Bi / GCE exhibits a larger specific surface area. After imprinting As, Cd, and Pb films (curve d), [Fe(CN)6] 3- / 4- The disappearance of the probe redox current is attributed to the formation of a dense, weakly conductive AsCdPb imprinted film. After removing As, Cd, and Pb from the imprinted film (curve e), a pair of redox peaks higher than those of the bare electrode (curve a) reappear, suggesting that the imprinted cavity generated after elution can promote [Fe(CN)6]. 3− / 4− Redox reaction of ion pairs on the sensor surface. Figure 3 B shows the Nyquist plots corresponding to different modified electrodes in A. Typically, a semi-circular pattern and R are observed in the high-frequency region. ctRelated; exhibits a linear response in the low-frequency region, related to the diffusion process. After modification, the EIS behavior of the electrode is similar to the voltammetric response. Compared to the bare electrode (R... ct = 100Ω), the UiO-66-NH2(Hf)@rGO@Bi / GCE electrode has the smallest semicircular diameter (R ct = 15Ω), with minimal charge transfer resistance, the maximum R obtained by IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE ct (350Ω) is significantly reduced (R) after the imprinted AsCdPb is removed. ct = 30Ω). The EIS results further demonstrate the successful construction of the imprint sensor and its integration capability.

[0077] Example 4: Optimization of detection conditions for AsCdPb-IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE

[0078] To investigate the effect of the detection electrolyte solution on the detection of IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE, at (1) 0.1 mol L -1 KNO3 (pH 5.0) (2) 5.0 mmol L -1 KCl; (3) 0.1 mol L -1 NaAc-HAc (pH 5.2); (4) 0.1 mol L -1 The response current of the fabricated sensor to AsCdPb was measured using DPASV technology in PBS (pH 6.0) electrolyte solution. Compared to baselines obtained from all supporting electrolytes, the response current at 0.1 mol L⁻¹ was [data missing]. -1 PBS showed the widest electrochemical window, from -1.2 to +1.0 V, with the lowest background noise. Therefore, 0.1 mol L⁻¹ was chosen due to its large electrochemical window, low background noise, and relatively low operational risk. -1 PBS was used as the electrolyte for subsequent detection experiments.

[0079] Furthermore, for DPASV technology, the pre-enrichment time is also one of the important factors affecting the sensor's response to the target ion AsCdPb. At different enrichment times, the electrode was immersed in a solution containing 1.0 μmol L... -1 0.1 mol L of AsCdPb -1 The DPV response of the electrode was measured in PBS solution. Figure 4As shown, the peak current reaches its maximum value within a 70-second enrichment period. After a longer period, an overpotential arises due to enrichment equilibrium, affecting the sensor's sensitivity. Furthermore, when the pre-enrichment deposition potential is too high (greater than -0.9 V), significant hydrogen evolution occurs during the pre-enrichment process. However, excessively low deposition potentials reduce the effectiveness of the pre-enrichment step, thus decreasing the detection sensitivity of DPAVS.

[0080] Example 5: Electrochemical simultaneous detection of As(III), Cd(II), and Pb(II)

[0081] The aforementioned imprinted electrode was used as the working electrode, forming a three-electrode system with an Ag / AgCl reference electrode and a platinum counter electrode. The system was placed in PBS buffer (pH 6.5, containing 0.1 mol / L KCl). After deposition at –1.1 V for 120 s and a resting time of 10 s, differential pulsed cathode stripping voltammetry (DPASV) was used to scan the voltage range from –1.2 V to 1.0 V, acquiring the reduction peak current signals of As(III), Cd(II), and Pb(II). Standard curves were plotted and used for the simultaneous quantitative detection of the three heavy metal ions in the water sample. The As(III) concentration in the PBS buffer solution was 1.0 × 10⁻⁶. -10 mol / L ~5.0×10 -5 mol / L, Cd(II) concentration is 1.0×10 -10 mol / L ~5.0×10 -5 mol / L, Pb(II) concentration is 1.0 × 10⁻⁶ mol / L. -10 mol / L ~5.0×10 -5 mol / L;

[0082] The response curves of differential pulse anodic stripping voltammetry (DPASV) for simultaneous detection of three heavy metal ions (As, Cd, Pb) are shown below. Figure 5 As shown in Figure A, the dissolution peaks of the three target ions are observed at -0.88 V (Cd), -0.65 V (Pb), and 0.77 V (As) (vs. Ag / AgCl). Within the same electrochemical window, the dissolution peaks of Cd and As are located at the far end of the window, while the dissolution peak of Pb is located in between, demonstrating good separation and avoiding signal overlap. This provides a good potential-based basis for simultaneous ternary detection. Figure 5 Image B is a magnified view of its local area, clearly showing the symmetry of the peak shape and the stability of the signal response. Figure 5 In C, as the concentrations of Cd, Pb, and As gradually increase (0.0005~3.5 μmol L), -1 The peak currents of all samples showed a linear increase with the logarithm of the concentration. In the lower concentration range (0.0005~0.0048 μmol / L), the peak currents were... -1) and higher concentration range (0.015~3.5 μmol L) -1 Two linear equations were obtained by fitting the data, which reflects that the sensor has good response sensitivity in different concentration ranges.

[0083] Specifically, the linear regression equation for Cd(Ⅱ) is I(μA) = 2.88 + 13.38logC Cd (μmol L) -1 (R) 2 =0.978) and I(μA) = 7.89 + 23.69logC Cd (μmol L) -1 (R) 2 = 0.999), demonstrating extremely high sensitivity and linear response to Cd(II). For Pb(II), the linear relationships are I(μA) = 7.07 + 1.35logC Pb (μmol L) -1 (R) 2 = 0.999) and I(μA) = 18.06 + 6.08logC Pb (μmol L) -1 (R) 2 = 0.999); while the fitting equation corresponding to As(Ⅲ) is I(μA) = 6.98 + 1.49logC As (μmol L) -1 (R) 2 = 0.994) and I(μA) = 9.13 + 2.15logC As (μmol L) -1 (R) 2 = 0.999), and the limit of detection (LOD) is 0.1 nmol L. -1 The above data demonstrate that the sensor exhibits excellent linear response to all three metal ions across a wide concentration range. Notably, in the AsCdPb ternary coexistence system, the dissolution peak current response of As is more significant, with a markedly enhanced peak height, indicating that the sensor retains excellent recognition capability for As even in complex systems. Furthermore, the ternary detection exhibits a bilinear response, possibly due to sufficient adsorption sites in the low concentration range, which gradually saturate in the high concentration range, resulting in different current response rates. In summary, the IIM / UiO-66-NH2(Hf)@rGO@Bi / GCE sensor demonstrates good potential resolution, linear response, and an extremely low detection limit in the simultaneous detection of multiple metal ions, showcasing the application potential of the IIM / UiO-66-NH2(Hf)@rGO@Bi composite film in the precise monitoring of multiple targets in real-world complex environments.

[0084] To verify the reliability of the experimental results, the prepared electrode was used to determine AsCdPb in real water bodies (tap water and Fuxian Lake). A specific concentration of metal ions was added using the standard addition method, and the corresponding results are shown in Table 1. It can be seen that after four parallel determinations, the average AsCdPb detection values ​​in both tap water and Fuxian Lake water were less than 0.24 nmol / L. -1 and 1.28 nmol L -1 and 1.48 nmol L -1 The levels are all far below the World Health Organization standards and national standards (5 μg / L). -1 0.015 mg L -1 and 0.015 mg L -1 The RSD values ​​of the determination results using standard AsCdPb were all within 4.5%, and the recoveries were between 95.0% and 110.0%, which preliminarily indicates that the determination results are accurate and reliable.

[0085]

[0086] The embodiments described above are merely specific implementations of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A three-template ion-imprinted electrochemical sensor for simultaneous detection of As(III), Cd(II) and Pb(II), characterized in that, The sensor includes: The modified glassy carbon electrode has the following components on its surface from the inside out: a graphene composite metal-organic framework material layer based on NH2-UiO-66(Hf)@rGO; an electrodeposited Bi nanoparticle layer; and a three-template ion-imprinted polymer film layer formed by infrared-initiated polymerization using As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) as template ions and methacrylic acid and 4-(2-pyridinium azo)resorcinol as functional monomers.

2. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(III), Cd(II), and Pb(II) according to claim 1, characterized in that: The specific steps for preparing the modified electrode are as follows: 1) Pretreatment of glassy carbon electrode: The polished glassy carbon electrode was placed in buffer solution A and cyclic voltammetry was performed until a stable voltammogram was obtained; 2) The pretreated glassy carbon electrode is placed in solution B and activated by cyclic voltammetry under stirring until a stable voltammogram is obtained. The glassy carbon electrode is then removed, washed with ultrapure water, and dried with nitrogen to obtain the activated glassy carbon electrode. 3) A suspension of amino-modified hafnium-based metal-organic framework material composite reduced graphene oxide, namely NH2-UiO-66(Hf)@rGO, was dropped onto an activated glassy carbon electrode and allowed to air dry to obtain an NH2-UiO-66(Hf)@rGO / GCE electrode. 4) The NH2-UiO-66(Hf)@rGO / GCE electrode was placed in buffer solution C and bismuth nanoparticles were loaded onto the NH2-UiO-66(Hf)@rGO nanomaterial by electrochemical deposition to obtain the NH2-UiO-66(Hf)@rGO@Bi / GCE electrode; 5) The imprinted polymerization solution containing As(III), Cd(II), and Pb(II) templates was drop-coated onto the surface of the NH2-UiO-66(Hf)@rGO@Bi / GCE electrode. Then, a coverslip was placed on the electrode to assist in film formation, and the electrode was subjected to photopolymerization under infrared light. After the reaction was completed, the electrode was cooled to room temperature and then suspended in ultrapure water at a depth of 2-5 cm for more than 6 hours. After the coverslip was removed, the electrode was washed with a mixed solution of EDTA-HCl to remove the imprinted ions As(III), Cd(II), and Pb(II). The electrode was then washed with ultrapure water to obtain a glassy carbon electrode modified with a surface molecular imprinted composite film, namely AsCdPb-IIM / NH2-UiO-66(Hf)@rGO@Bi / GCE. When not in use, the electrode was stored in the refrigerator's crisper drawer.

3. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) according to claim 2, characterized in that: The pH of buffer solution A is 6. Buffer solution A contains 0.1 mol / L potassium chloride and 5 mmol / L K3[Fe(CN)6] / K4[Fe(CN)6]. The voltage range of cyclic voltammetry is -0.2 to 0.6 V, the scan rate is 20 to 120 mV / s, and the equilibration time is 10 s.

4. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) according to claim 2, characterized in that: The solution B is a sulfuric acid solution with a concentration of 0.05~0.5mol / L. The voltage range of the cyclic voltammetry is -0.3~1.3V, and the scan rate is 50~100mV / s.

5. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) according to claim 2, characterized in that: NH2-UiO-66(Hf)@rGO is prepared by the following process: Under continuous stirring, 0.1–1.0 g HfCl4, 0.5–1.5 g aminoterephthalic acid, and 0.05–1.50 g reduced graphene oxide were dissolved in 10–50 mL DMF in proportion, and 0.5–3 mL acetic acid was added as a regulator. The mixture was then sonicated for 5–30 min. The mixture was then transferred to a 100 mL high-pressure reactor and reacted at 120–180°C for 12–36 h. The mixture was washed three times with DMF and further washed with ethanol. The product was collected by centrifugation and dried under vacuum at 60–120°C for 18–28 h, preferably 24 h, to obtain UiO-66-NH2(Hf)@rGO.

6. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) according to claim 2, characterized in that: The solvent for the UiO-66-NH2(Hf)@rGO suspension is anhydrous ethanol, the amount of solute is 0.5~5.0 mg, and the concentration of solute is 0.5~5.0 mg / mL. The suspension is sonicated for 5~30 min. 2.0~15.0 μL of the suspension is dropped onto the surface of the activated GCE to obtain the UiO-66-NH2(Hf)@rGO / GCE modified electrode.

7. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) according to claim 2, characterized in that: The buffer solution C is a PBS electrolyte solution of 0.1~3.0 mM, preferably 0.5 mM Bi(NO3)3·5H2O; the concentration of the PBS electrolyte solution is 0.05~0.3 M, preferably 0.1 M; Bi-NPs are prepared by the following process: The UiO-66-NH2(Hf)@rGO / GCE modified electrode was immersed in a PBS electrolyte solution containing 0.1~3.0 mM Bi(NO3)3·5H2O; under magnetic stirring, deposition was carried out at a constant potential of -0.8 ~ -1.2V for 60~300 s by a potentiostatic method, and the electrode was gently washed with pure water and air-dried to obtain the UiO-66-NH2(Hf)@rGO@Bi / GCE modified electrode; the concentration of the PBS electrolyte solution was 0.05~0.3 M.

8. The three-template ion-imprinted electrochemical sensor for simultaneous detection of As(Ⅲ), Cd(Ⅱ) and Pb(Ⅱ) according to claim 2, characterized in that: The imprinted polymerization solution containing As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) as three templates in step 5) is prepared by the following scheme: An imprinting polymerization solution containing As(III), Cd(II), and Pb(II) was prepared using acetonitrile as a solvent. The imprinting polymerization solution containing As(III), Cd(II), and Pb(II) contained sodium arsenite 0.0015~0.05 mmol / L, cadmium acetate 0.0015~0.05 mmol / L, lead nitrate 0.0015~0.05 mmol / L, methacrylic acid 0.05~0.2 mmol / L, 4-(2-pyridinium azo)resorcinol 0.05~0.2 mmol / L, ethylene glycol dimethacrylate 0.5~2 mmol / L, and azobisisobutyronitrile 0.0275~0.11 mmol / L. In step 5), the photopolymerization time is 120~360 min.

9. An application of the three-template ion-imprinted electrochemical sensor for simultaneous detection of As(III), Cd(II) and Pb(II) as described in any one of claims 1-8, characterized in that... Includes the following steps: Step 1 The sensor is used as the working electrode, and together with the Ag / AgCl reference electrode and the platinum counter electrode, a three-electrode system is formed. Step Two The three-electrode system was placed in buffer solutions D containing different concentrations of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ). Differential pulsed cathodic stripping voltammetry was used to measure the concentrations of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) in buffer solutions D. DPASV pulse curves of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were plotted. Standard curves of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were obtained based on the relationship between the peak value of the differential pulse current and the concentrations of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ). The buffer solution D is a phosphate buffer solution, wherein the concentration of sodium hydrogen phosphate is 0.05~0.3 mol / L, the concentration of sodium dihydrogen phosphate is 0.05~0.3 mol / L, the concentration of KCl electrolyte is 0.01~1.0 mol / L, and the concentration of As(III) is 1.0×10⁻⁶. -10 ~5.1×10 -5 mol / L, Cd(II) concentration is 1.0×10 -10 ~5.1×10 -5 mol / L, Pb(II) concentration is 1.0×10 -10 ~5.1×10 -5 mol / L; its pH value is 5~10; Step 3 The DPASV method was used to determine the heavy metal sample solution of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) under the same conditions as in step 2). The corresponding DPASV pulse curves were plotted and the peak currents of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were obtained. The peak currents of As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) were substituted into the standard curve corresponding to step 2) to obtain the concentration of heavy metals As(Ⅲ), Cd(Ⅱ), and Pb(Ⅱ) in the sample solution, thus realizing the simultaneous quantitative detection of heavy metal ions. In step two, while stirring the buffer solution D, a deposition potential of -0.8 V to -1.2 V is applied to the working electrode to reduce all target metals As(III), Cd(II), and Pb(II) to the electrode surface; the deposition time is 80 s to 600 s, stirring is stopped, and the solution is allowed to stand for 10 to 20 seconds to stabilize the metal deposits on the electrode surface.

10. The application of the three-template ion-imprinted electrochemical sensor for simultaneous detection of As(III), Cd(II) and Pb(II) according to claim 9, characterized in that: In step two, the starting potential of the differential pulse voltammetry is -1.4 to -1.1V, the ending potential is 0.9 to 1.2V, the pulse amplitude is 0.01 to 0.1s, the pulse period is 0.1 to 1.0s, the amplitude is 0.01 to 1.00V, and the equilibrium time is 5 to 10s.

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