Method for detecting heavy metals in water

Abstract

The invention provides a water quality heavy metal detection method, and belongs to the technical field of heavy metal detection. Preparing a gold / titanium dioxide nano composite material; preparing a gold / titanium dioxide / carboxymethyl chitosan / glassy carbon electrode; establishing a standard curve, preparing a Pb < 2 + > and Cd < 2 + > mixed standard solution, recording a dissolution peak current, drawing a peak current-concentration calibration curve, and calculating a linear equation and a detection limit; carrying out a labeling recovery experiment; titanium dioxide and a high-conductivity nano material are compounded, and the photocatalytic characteristic of titanium dioxide, the conductivity of gold nanoparticles and the adsorption capacity of carboxymethyl chitosan are combined, so that the efficient enrichment capacity is reserved, and meanwhile, the electron transmission efficiency of an electrode interface is remarkably improved; therefore, high-sensitivity and high-selectivity detection of trace Cd < 2 + > and Pb < 2 + > in a water body is realized, and the industrial problem that sensitivity and portability of a traditional method are difficult to consider at the same time is effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal detection, and particularly relates to a method for detecting heavy metals in water quality. Background Art

[0002] Heavy metal pollution can damage the aquatic ecosystem and threaten biodiversity through bioaccumulation and food chain magnification effects. For aquatic organisms, heavy metals can inhibit the photosynthesis of algae and the reproductive ability of fish, and even lead to population extinction. In addition, after the polluted water is used for irrigating farmland, heavy metals will accumulate in the soil, reducing the yield and safety of crops. Heavy metals (such as lead, cadmium, mercury, arsenic, etc.) can cause chronic or acute toxicity to the human body even at extremely low concentrations, and accumulate through drinking water or the food chain, causing various diseases. Lead binds to enzymes containing sulfhydryl (-SH) in the body, such as δ-aminolevulinic acid dehydratase, interfering with enzyme activity and disrupting heme synthesis, resulting in anemia; cadmium competes with zinc (Zn) and copper (Cu) for binding to metallothionein (MT), leading to disorders in the metabolism of essential trace elements and inhibiting the activity of superoxide dismutase (SOD), exacerbating the damage of free radicals to cells.

[0003] Currently, the detection of Cd 2+ and Pb 2+ in water mainly relies on traditional methods such as colorimetry, enzyme-linked immunosorbent assay, and atomic absorption spectrometry. Although these techniques can achieve quantitative analysis, they generally have limitations such as insufficient sensitivity, high detection cost, and poor portability of equipment. In contrast, electrochemical analysis provides a more practical solution for heavy metal detection due to its advantages such as miniaturization of equipment, high sensitivity, and rapid response. In the field of electrochemical sensing materials, titanium dioxide (TiO 2 ) nanomaterials have attracted much attention due to their excellent electrochemical stability, strong adsorption ability, and catalytic activity, especially outstanding performance in the preconcentration of heavy metal ions. However, compared with conductive matrices such as gold, platinum nanomaterials, or graphene, the intrinsic conductivity of titanium dioxide is relatively weak, resulting in insufficient conversion efficiency of the recognition signal for heavy metal ions and limiting the further improvement of detection performance. Water-soluble carboxymethyl chitosan (CMCS) has significant advantages as a cross-linking agent. The abundant carboxyl groups (-COOH) on the CMCS molecular chain dissociate into -COO - under neutral conditions, forming stable coordination bonds with Cd 2+ and Pb 2+ , enabling the preconcentration of target ions on the electrode surface to improve the preconcentration efficiency. Moreover, CMCS has higher selectivity for Cd 2+ / Pb 2+ than common interfering ions (such as Ca 2+ and Mg 2+), and still maintains a recovery rate of >90% in the presence of interfering ions at 100-fold concentration.

[0004] In view of the above problems, the present invention proposes a method for detecting heavy metals in water quality. Summary of the Invention

[0005] The object of the present invention is to address the above problems existing in the prior art and propose a method for detecting heavy metals in water quality.

[0006] The object of the present invention can be achieved by the following technical solutions: A method for detecting heavy metals in water quality, comprising: S1. Pretreat the glassy carbon electrode; S2. Prepare gold / titanium dioxide (Au / TiO 2 ) nanocomposite. Weigh 20 mL of titanium dioxide dispersion, add 250 μL of HAuCl 4 solution and 150 μL of K 2 CO 3 solution under stirring conditions, and then quickly add 100 mL of NaBH 4 solution. Dropwise add it repeatedly 5 times to make it react completely, wash the mixed solution 3 - 5 times, and perform vacuum drying; S3. Prepare gold / titanium dioxide / carboxymethyl chitosan / glassy carbon electrode (Au / TiO 2 / CMCS / GCE). Pipette 10 - 15 μL of gold / titanium dioxide (Au / TiO 2 ) dispersion and 0 - 5 μL of carboxymethyl chitosan (CMCS) solution and mix them, perform ultrasonic dispersion. After mixing evenly, pipette the mixed solution and evenly drop - coat it on the surface of the glassy carbon electrode, and dry it at room temperature; S4. Establish a standard curve. Prepare a mixed standard solution of Pb 2+ and Cd 2+ , record the stripping peak current, plot the peak current - concentration calibration curve, and calculate the linear equation and detection limit; S5. Pretreat the water sample. Use tap water as the detection sample. The sample is filtered through a 0.45 μm filter membrane, and PBS is added to adjust the pH to 5.0; S6. Conduct a standard addition recovery experiment. Add known concentrations of Pb 2+ and Cd 2+ , detect according to the above steps, and calculate the recovery rate.

[0007] Verify the reliability of the method through the standard addition recovery experiment to ensure the accuracy of actual water sample detection.

[0008] Preferably, in step S1, the pretreatment of the glassy carbon electrode includes polishing, activation, and electrochemical activation, using 0.3 μm and 0.05 μm of Al 2 O 3The electrode surface was polished to a mirror surface on suede with the suspension, rinsed with ultrapure water, ultrasonically cleaned in ethanol and ultrapure water for 5 minutes, dried with nitrogen, and then heated in 0.5 MH 2 SO 4 The solution was scanned cyclically in the potential window of -1.5~1.5V until it stabilized.

[0009] Glassy carbon electrode (GCE), made of high-purity carbon material, has the characteristics of wide potential window, low background current and easy modification. It is a commonly used substrate electrode for electrochemical analysis. Cyclic scanning in acidic solution can remove surface adsorbed impurities and generate oxygen-containing functional groups (such as -COOH, -OH), which promotes the fixation of nanomaterials. 2 O 3 Polishing and electrochemical activation remove the oxide layer and impurities on the electrode surface, improve the uniformity of the electrode surface, reduce background noise, and scan cyclic voltammetry to a stable state to ensure that the active sites on the electrode surface are fully exposed and enhance the loading effect of subsequent modified materials.

[0010] Preferably, in step S2, the step of preparing titanium dioxide includes: respectively taking 6.0 mL of anhydrous ethanol and 6.0 mL of glacial acetic acid, adding 5.0 mL of ultrapure water, stirring evenly, and recording as solution A; weighing 15.0 g of ultrapure water, 100 g of n-butyl titanate, 2.0 mL of glacial acetic acid and 2.0 mL of dimethyl sulfoxide, stirring for 30 minutes, and recording as solution B; after solution B is heated to 30°C, solution A is added dropwise to the mixed solution under vigorous stirring conditions, stirred for 30 minutes, and after the solution becomes gel-like, stirring is continued for 1 hour, and it is allowed to stand at room temperature for 48 hours to be completely aged; the aged product is dried at 100°C, the dried product is ground into powder, and calcined at a high temperature of 450°C for 1.5 hours.

[0011] Synthesis of high-purity anatase TiO by sol-gel method 2 The calcination temperature (450°C) is used to precisely control the crystal form and ensure photocatalytic activity. Dimethyl sulfoxide (DMSO) is added as a structure-directing agent to inhibit excessive grain growth and obtain nanoparticles with uniform particle size. A three-dimensional network structure is formed through hydrolysis-condensation reaction, and finally calcination is performed to remove organic matter and obtain the target oxide.

[0012] Preferably, in step S2, the concentration of the titanium dioxide dispersion is 1 mg / mL, and the concentration of HAuCl 4 The concentration of the solution is 1%, K 2 CO 3 The concentration of the solution is 0.1 mol / L, NaBH 4 The concentration of the solution is 0.01 mol / L, NaBH 4 The solution is ready for use, which prevents it from oxidative failure and ensures the high efficiency of the reduction reaction.

[0013] Sodium borohydride releases active hydrogen (H - ), reducing Au 3+ to Au 0 and forming gold nanoparticles. The carrier (such as TiO 2 ) can disperse the active component (AuNPs), prevent their agglomeration and inactivation, and at the same time provide an electron transport channel.

[0014] Preferably, in step S2, during washing, the reacted mixed solution is stirred at 12000 r / min, washed 3 - 5 times with ultrapure water and absolute ethanol, and dried in vacuum at 60 °C.

[0015] The centrifugation speed and time need to be optimized according to the particle size and density. Too low will result in incomplete washing, and too high may damage the material structure. High-speed centrifugation (12000 r / min) is used to thoroughly remove unreacted HAuCl 4 and by-products, avoiding impurity interference in subsequent detections. Ethanol washing is convenient for removing organic residues, and vacuum drying is used to prevent the oxidation or structural collapse of the nanomaterials. Moisture is removed under reduced pressure at a low temperature (60 °C) to avoid sintering of the nanoparticles or crystal form transformation at high temperatures.

[0016] Preferably, in step S3, the volume ratio of the added gold / titanium dioxide dispersion to the carboxymethyl chitosan solution is 6:1; Among them, the concentration of the gold / titanium dioxide (Au / TiO 2 ) dispersion is 1 mg / mL, and the concentration of the carboxymethyl chitosan (CMCS) solution is 1%.

[0017] Preferably, in step S3, 10 - 15 μL of the gold / titanium dioxide dispersion (Au / TiO 2 ) (with a concentration of 1 mg / mL) is taken, 0 - 5 μL of glutaraldehyde solution (Gd) (with a concentration of 1%) is added, ultrasonically dispersed, and after mixing evenly, 7 μL of the mixed solution is evenly dropped on the surface of the glassy carbon electrode and dried at room temperature to prepare the gold / titanium dioxide / glutaraldehyde / glassy carbon electrode (Au / TiO 2 / Gd / GCE) as a control group; 10 - 15 μL of the gold / titanium dioxide dispersion (Au / TiO 2 ) (with a concentration of 1 mg / mL) is taken, 0 - 5 μL of pure water is added, ultrasonically dispersed, and after mixing evenly, 7 μL of the mixed solution is evenly dropped on the surface of the glassy carbon electrode and dried at room temperature to prepare the gold / titanium dioxide / glassy carbon electrode (Au / TiO 2 / GCE) as a control group.

[0018] Glutaraldehyde forms covalent bonds through the reaction of aldehyde groups with amino groups and is commonly used to fix biomolecules (such as enzymes). However, it may block the pores of the electrode. A glutaraldehyde cross-linking control group is set up to verify the adsorption effect of carboxymethyl chitosan, exclude the interference of other factors, and clarify the specific roles of each component in the detection by comparing and excluding variable interference.

[0019] Preferably, in step S5, a 0.1 mol / L sodium acetate solution and acetic acid solution are respectively prepared with tap water as the solvent. Acetic acid solution is added to the sodium acetate solution, and the pH of the mixed solution is adjusted to 5.0 to prepare an acetic acid buffer solution with pH = 5.0.

[0020] Preferably, in step S4, when preparing the mixed standard solution of Pb 2+ and Cd 2+ , the concentration ranges of Pb 2+ and Cd 2+ are 0.01 - 10.00 μmoL / L.

[0021] Compared with the prior art, the present water quality heavy metal detection method has the following beneficial effects: 1. A water quality heavy metal detection method provided by the present invention uniformly loads gold nanoparticles on the surface of titanium dioxide to form Au / TiO 2 , and carboxymethyl chitosan (CMCS) is introduced as a three-dimensional cross-linking agent, thereby realizing the highly sensitive and highly selective detection of trace Cd 2+ and Pb 2+ in water.

[0022] 2. A water quality heavy metal detection method provided by the present invention can effectively reduce the impedance of the electrode and improve the detection sensitivity by electrochemically characterizing the gold / titanium dioxide modified glassy carbon electrode (Au / TiO 2 / GCE).

[0023] 3. A water quality heavy metal detection method provided by the present invention, based on differential pulse voltammetry (DPV) analysis, compares the response characteristics of the bare GCE and Au / TiO 2 / CMCS / GCE to the Cd 2+ / Pb 2+ mixed solution, and proves that the two ions have independent electrochemical oxidation paths on the surface of the modified electrode, meeting the potential resolution requirements for synchronous detection.

[0024] 4. A water quality heavy metal detection method provided by the present invention systematically evaluates the effects of two types of cross-linking agents, glutaraldehyde (Gd) and carboxymethyl chitosan (CMCS), on the sensing performance, and verifies that the addition of CMCS can significantly improve the Ip and mechanical stability of the system.

[0025] 5. A water quality heavy metal detection method provided by the present invention verifies the accuracy of this method through a standard addition recovery test.

[0026] In summary, the present invention provides a water quality heavy metal detection method. By compounding titanium dioxide with highly conductive nanomaterials, combining the photocatalytic properties of titanium dioxide, the conductivity of gold nanoparticles, and the adsorption ability of carboxymethyl chitosan, while retaining its high-efficiency enrichment ability, the electron transfer efficiency at the electrode interface is significantly improved, thereby realizing the highly sensitive and highly selective detection of trace Cd 2+ and Pb 2+ in water, effectively solving the industry problem that it is difficult to balance the sensitivity and portability of traditional methods. Description of the Drawings

[0027] Figure 1 It is a comparison result diagram of the electrochemical impedance spectra (EIS) of different sensors in Specific Example 2.

[0028] Figure 2 It is a comparison diagram of the differential pulse voltammetry (DPV) response characteristics of different sensors for the Cd 2+ and Pb 2+ mixed solution in Specific Example 3.

[0029] Figure 3 It is a diagram of the influence of different crosslinking agents on the sensor in Specific Example 4. Detailed Embodiments

[0030] The following are specific examples of the present invention in combination with the drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these examples. Specific Example 1:

[0031] A water quality heavy metal detection method includes: S1. Pretreat the glassy carbon electrode; S2. Prepare gold / titanium dioxide (Au / TiO 2 ) nanocomposite materials. Weigh 20 mL of titanium dioxide dispersion, add 250 μL of HAuCl 4 solution and 150 μL of K 2 CO 3 solution under stirring conditions, then quickly add 100 mL of NaBH 4 solution, and repeatedly drip it 5 times to make it react completely. Wash the mixed solution 3 - 5 times and perform vacuum drying; S3. Prepare a gold / titanium dioxide / carboxymethyl chitosan / glassy carbon electrode (Au / TiO 2 / (CMCS / GCE), aspirate 10 - 15 μL of gold / titanium dioxide dispersion and 0 - 5 μL of carboxymethyl chitosan solution, mix them, perform ultrasonic dispersion. After mixing evenly, aspirate the mixed solution and evenly drop - coat it on the surface of the glassy carbon electrode, and dry it at room temperature; S4. Establish a standard curve, prepare a mixed standard solution of Cd 2+ and Pb 2+ Record the stripping peak current, plot the peak current - concentration calibration curve, and calculate the linear equation and detection limit; S5. Pretreat the water sample. Use tap water as the test sample. The sample is filtered through a 0.45 - μm filter membrane, and PBS is added to adjust the pH to 5.0; S6. Conduct a standard addition recovery experiment. Add known concentrations of Cd 2+ and Pb 2+ , detect according to the above steps, and calculate the recovery rate.

[0032] Verify the reliability of the method through the standard addition recovery experiment to ensure the accuracy of the actual water sample detection.

[0033] In step S1, the pretreatment of the glassy carbon electrode includes polishing, activation, and electrochemical activation. Use 0.3 - μm and 0.05 - μm Al 2 O 3 suspension to polish the electrode surface to a mirror on suede, rinse with ultrapure water, ultrasonically clean in ethanol and ultrapure water for 5 minutes in sequence, dry with nitrogen, and perform cyclic voltammetry scanning in 0.5 M H 2 SO 4 solution in the potential window of - 1.5 - 1.5 V until stable.

[0034] The glassy carbon electrode (GCE), made of high - purity carbon material, has the characteristics of a wide potential window, low background current, and easy modification. It is a commonly used substrate electrode for electrochemical analysis. Cyclic scanning in an acidic solution can remove surface - adsorbed impurities and generate oxygen - containing functional groups (such as - COOH, - OH), which promotes the fixation of nanomaterials. Through Al 2 O 3 polishing and electrochemical activation, remove the oxide layer and impurities on the electrode surface, improve the surface uniformity of the electrode, reduce background noise, perform cyclic voltammetry scanning until the stable state to ensure that the active sites on the electrode surface are fully exposed and enhance the loading effect of the subsequent modified materials.

[0035] In step S2, the steps for preparing titanium dioxide include: separately sucking 6.0 mL of absolute ethanol and 6.0 mL of glacial acetic acid, adding 5.0 mL of ultrapure water, and stirring evenly to obtain solution A; weighing 15.0 g of ultrapure water, 100 g of tetrabutyl titanate, 2.0 mL of glacial acetic acid, and 2.0 mL of dimethyl sulfoxide, stirring for 30 min to obtain solution B; when solution B is heated to 30 °C, under vigorous stirring conditions, solution A is added dropwise to the mixed solution, stirred for 30 min, and after the solution becomes gel-like, continue stirring for 1 h, and let it stand at room temperature for 48 h to complete aging; dry the aged product at 100 °C, grind the dried product into powder, and calcine it at 450 °C for 1.5 h.

[0036] High-purity anatase TiO is synthesized by the sol-gel method 2 , the calcination temperature (450 °C) precisely controls the crystal form to ensure photocatalytic activity. Dimethyl sulfoxide (DMSO) is added as a structure-directing agent to inhibit excessive grain growth, obtain nanoparticles with uniform particle size, form a three-dimensional network structure through hydrolysis-polycondensation reaction, and finally calcine to remove organic matter to obtain the target oxide.

[0037] In step S2, the concentration of the titanium dioxide dispersion is 1 mg / mL, and the concentration of the HAuCl 4 solution is 1%, and the concentration of the K 2 CO 3 solution is 0.1 mol / L, and the concentration of the NaBH 4 solution is 0.01 mol / L. The NaBH 4 solution is prepared and used immediately to prevent its oxidation and inactivation and ensure the efficiency of the reduction reaction.

[0038] Sodium borohydride releases active hydrogen (H - ) under alkaline conditions, reducing Au 3+ to Au 0 , forming gold nanoparticles. The carrier (such as TiO 2 ) can disperse the active component (AuNPs), prevent its agglomeration and inactivation, and at the same time provide an electron transport channel.

[0039] In step S2, during washing, stir the reaction mixture at 12000 r / min, wash it 3 - 5 times with ultrapure water and absolute ethanol, and dry it under vacuum at 60 °C.

[0040] The centrifugation speed and time need to be optimized according to the particle size and density. Too low will result in incomplete washing, and too high may damage the material structure. High-speed centrifugation (12000 r / min) is used to thoroughly remove the unreacted HAuCl 4By-products are removed to avoid interference from impurities in subsequent detections. Ethanol washing facilitates the removal of organic residues, and vacuum drying is used to prevent the oxidation or structural collapse of the nanomaterials. Moisture is removed under reduced pressure at a low temperature (60 °C) to avoid sintering of the nanoparticles or crystal form transformation caused by high temperatures.

[0041] In step S3, the volume ratio of the added gold / titanium dioxide dispersion to the carboxymethyl chitosan solution is 6:1. Among them, the concentration of the gold / titanium dioxide dispersion is 1 mg / mL, and the concentration of the carboxymethyl chitosan solution is 1%.

[0042] In step S3, 10 - 15 μL of the gold / titanium dioxide dispersion with a concentration of 1 mg / mL is aspirated, 0 - 5 μL of a glutaraldehyde solution with a concentration of 1% is added, and ultrasonic dispersion is carried out. After mixing evenly, 7 μL of the mixed solution is evenly dropped on the surface of the glassy carbon electrode and dried at room temperature to prepare a gold / titanium dioxide / glutaraldehyde / glassy carbon electrode as a control group. Glutaraldehyde forms covalent bonds through the reaction of aldehyde groups with amino groups and is often used to fix biomolecules (such as enzymes), but it may block the pores of the electrode. A glutaraldehyde cross-linking control group is set up to verify the adsorption effect of carboxymethyl chitosan, exclude interference from other factors, and clarify the specific roles of each component in the detection by comparing and excluding variable interference.

[0043] Aspirate 10 - 15 μL of the gold / titanium dioxide dispersion (with a concentration of 1 mg / mL), add 0 - 5 μL of pure water, carry out ultrasonic dispersion, and after mixing evenly, aspirate 7 μL of the mixed solution and evenly drop it on the surface of the glassy carbon electrode and dry at room temperature to prepare a gold / titanium dioxide / glassy carbon electrode as a control group.

[0044] In step S5, a 0.1 mol / L sodium acetate solution and acetic acid solution are respectively prepared with tap water as the solvent. Acetic acid solution is added to the sodium acetate solution, and the pH of the mixed solution is adjusted to 5.0 to prepare an acetic acid buffer solution with pH = 5.0.

[0045] In step S4, when preparing the Pb 2+ and Cd 2+ mixed standard solution, the concentration ranges of Pb 2+ and Cd 2+ are 0.01 - 10.00 μmoL / l. Specific Example 2:

[0046] To clarify the influence of the addition of gold nanoparticles on titanium dioxide nanoparticles, Specific Example 2 is the electrochemical performance detection of the Au / TiO 2 composite material mentioned in Specific Example 1. The content of Specific Example 2 is as follows: 1. Preparation of the Au / TiO 2 composite material 6.0 mL of absolute ethanol and 6.0 mL of glacial acetic acid were respectively pipetted into a conical flask, 5.0 mL of ultrapure water was added, and the mixture was stirred evenly and denoted as solution A. 15.0 g of ultrapure water, 100 g of tetrabutyl titanate, 2.0 mL of glacial acetic acid and 2.0 mL of dimethyl sulfoxide were weighed into a conical flask and stirred with a magnetic stirrer for 30 min, denoted as solution B. Solution B was heated to 30 °C, and solution A was added dropwise to the mixed solution under vigorous stirring, and stirred with a magnetic stirrer for 30 min. After the solution became gel-like, stirring was continued for 1 h, and then it was left standing at room temperature for 48 h to complete aging. The aged product was dried at 100 °C, the dried product was ground into powder, and calcined at 450 °C for 1.5 h to obtain TiO 2 . Au / TiO was prepared by the sodium borohydride reduction method 2 . 20 mL of TiO 2 dispersion (1 mg / mL) was weighed into a conical flask, and 250 μL of HAuCl 4 solution (1%) and 150 μL of K 2 CO 3 solution (0.1 mol / L) were added under magnetic stirring. Then, 100 mL of freshly prepared NaBH 4 solution (0.01 mol / L) was quickly added, and it was repeatedly added dropwise 5 times to complete the reaction. Then, the reaction mixture was washed 3 - 5 times with ultrapure water and absolute ethanol at 12000 r / min, and finally the product was dried in vacuum at 60 °C to obtain Au / TiO 2 .

[0047] 2. Coating the electrode 12 μL of Au / TiO 2 dispersion was pipetted and 2 μL of pure water was added, ultrasonically dispersed, and after mixing evenly, 7 μL of the mixed solution was evenly dropped on the surface of the glassy carbon electrode. The glassy carbon electrode (GCE) without coated material was used as the control group

[0048] 3. Electrochemical characterization of the Au / TiO 2 composite material 10 mmol / L of [Fe(CN)6] 3+ solution was used to perform electrochemical impedance spectroscopy (ElS) on GCE and Au / TiO 2 / GCE respectively

[0049] 3. Results Figure 1 showed the glassy carbon electrode (GCE) and the gold / titanium dioxide modified glassy carbon electrode (Au / TiO 2The comparison results of the electrochemical impedance spectroscopy (EIS) of (GCE). Among them, curve A corresponds to the bare GCE, and curve B corresponds to Au / TiO 2 / GCE. Through the analysis of the spectra, it can be obtained that compared with using GCE alone, after the surface of GCE is modified with Au / TiO 2 , the impedance decreases. Gold nanoparticles (AuNPs), as highly conductive components, effectively reduce the charge transfer impedance at the electrode / electrolyte interface by constructing a three-dimensional electron transport network. Titanium dioxide (TiO 2 ) has relatively weak intrinsic conductivity, but its heterojunction interface with AuNPs can induce the local surface plasmon resonance effect (LSPR), which further promotes the electron transition process. In summary, Au / TiO 2 has good conductivity, can effectively reduce the impedance of the electrode, and improve its sensitivity. Specific Example 3:

[0050] Specific Example 3 is for the electrochemical performance detection of Pb 2+ and Cd 2+ in different sensors. The content of Specific Example 3 is as follows: 1. Preparation of Au / TiO 2 composite material Respectively suck 6.0 mL of absolute ethanol and 6.0 mL of glacial acetic acid into a conical flask, add 5.0 mL of ultrapure water, and stir evenly, denoted as solution A. Weigh 15.0 g of ultrapure water, 100 g of tetrabutyl titanate, 2.0 mL of glacial acetic acid and 2.0 mL of dimethyl sulfoxide into a conical flask, and stir with a magnetic stirrer for 30 min, denoted as solution B. Heat solution B to 30 °C, and drop solution A into the mixed solution under vigorous stirring, stir with a magnetic stirrer for 30 min, continue to stir for 1 h after the solution becomes gel-like, and then let it stand at room temperature for 48 h to completely age. Dry the aged product at 100 °C, grind the dried product into powder, and calcine it at 450 °C for 1.5 h to obtain TiO 2 . Prepare Au / TiO 2 by the sodium borohydride reduction method. Weigh 20 mL of TiO 2 dispersion (1 mg / mL) into a conical flask, add 250 μL of HAuCl 4 solution (1%) and 150 μL of K 2 CO 3 solution (0.1 mol / L) under magnetic stirring, and then quickly add 100 mL of freshly prepared NaBH 4Solution (0.01 mol / L), dropwise added repeatedly 5 times to make it react completely, and then the reaction mixture solution was washed 3 - 5 times with ultrapure water and absolute ethanol under the condition of 12000 r / min. Finally, the product was dried in vacuum at 60 °C to obtain Au / TiO 2 .

[0051] 2. Preparation of Au / TiO 2 / CMCS / GCE Absorb 12 μL of the Au / TiO 2 dispersion solution, add 2 μL of the solution, ultrasonically disperse it, and after mixing evenly, absorb 7 μL of the mixed solution and evenly drop - coat it on the surface of the glassy carbon electrode. The glassy carbon electrode without coated material was used as the control group.

[0052] 3. Electrochemical performance detection of Pb 2+ and Cd 2+ in different sensors Using the pH = 5.0 ABS buffer solution as the electrolyte solution, the prepared GCE and Au / TiO 2 / CMCS / GCE sensors were used to simultaneously perform differential pulse (Differential Pulse Voltammetry, DPV) scans on the mixed solution of 2.0 μmol / L Pb 2+ and Cd 2+ .

[0053] 4. Results Figure 2 Shows the comparison of the differential pulse voltammetry (DPV) response characteristics of the bare glassy carbon electrode (GCE) and the gold / titanium dioxide / carboxymethyl chitosan composite modified electrode (Au / TiO 2 / CMCS / GCE) to the mixed solution of Cd 2+ and Pb 2+ . Among them, curve a corresponds to Au / TiO 2 / CMCS / GCE, and curve b corresponds to the bare GCE. Figure 2 There are two characteristic oxidation peaks of Cd 2+ and Pb 2+ in (curve a), and its peak shape is sharp and completely separated, proving that the two ions have independent electrochemical oxidation paths on the surface of the modified electrode, meeting the potential resolution requirements for synchronous detection. In contrast, the response current of the bare GCE (curve b) is significantly reduced, and the peak position shifts significantly, indicating that the unmodified electrode has insufficient enrichment ability and electron transfer efficiency for heavy metal ions. Specific Example 4:

[0054] Specific Example 4 is about the influence of different cross - linkers on Au / TiO 2The influence of / CMCS / GCE, and the content of Specific Example 4 is as follows: 1. Preparation of Au / TiO 2 Composite material Respectively suck 6.0 mL of absolute ethanol and 6.0 mL of glacial acetic acid into a conical flask, add 5.0 mL of ultrapure water, stir evenly, and record it as Solution A. Weigh 15.0 g of ultrapure water, 100 g of tetrabutyl titanate, 2.0 mL of glacial acetic acid and 2.0 mL of dimethyl sulfoxide into a conical flask, and use a magnetic stirrer to stir for 30 min, and record it as Solution B. Heat Solution B to 30 °C, and under vigorous stirring conditions, add Solution A dropwise to the mixed solution, use a magnetic stirrer to stir for 30 min. After the solution becomes gel-like, continue to stir for 1 h, and then let it stand at room temperature for 48 h to make it fully age. Dry the aged product at 100 °C, grind the dried product into powder, and calcine it at 450 °C for 1.5 h to obtain TiO 2 . Prepare Au / TiO 2 by using sodium borohydride reduction method. Weigh 20 mL of TiO 2 dispersion (1 mg / mL) into a conical flask, and add 250 μL of HAuCl 4 solution (1%) and 150 μL of K 2 CO 3 solution (0.1 mol / L) under magnetic stirring conditions, and then quickly add 100 mL of freshly prepared NaBH 4 solution (0.01 mol / L), and add it dropwise repeatedly 5 times to make it fully react. Then wash the reacted mixed solution with ultrapure water and absolute ethanol 3 - 5 times under the condition of 12000 r / min, and finally vacuum dry the product at 60 °C to obtain Au / TiO 2 .

[0055] 2. Preparation of Au / TiO 2 / CMCS / GCE Respectively use 1.0% glutaric dialdehyde (Gd) and CMCS as crosslinking agents. Suck 12 μL of Au / TiO 2 dispersion and add 2 μL of CMCS solution, and record it as Group A (Au / TiO 2 / CMCS / GCE). Suck 12 μL of Au / TiO 2 dispersion (concentration is 1 mg / mL), add 2 μL of Gd solution, as Control Group 1, and record it as Group B (Au / TiO 2 / Gd / GCE). Suck 12 μL of Au / TiO 2 dispersion (concentration is 1 mg / mL), add 2 μL of pure water, as Control Group 2, and record it as Group C (Au / TiO 2 / (GCE) was ultrasonically dispersed. After mixing evenly, 7 μL of the mixed solution was aspirated and evenly drop-coated on the surface of the glassy carbon electrode to prepare a sensor for simultaneous DPV scanning of a mixed solution of 2.0 μmol / L Pb 2+ and Cd 2+ .

[0056] 3. Results As can be seen from Figure 3 , in the control group without the introduction of a cross-linking agent (Au / TiO 2 / GCE), the oxidation peak currents (Ip) for 2.0 μmol / L Cd 2+ and Pb 2+ were relatively low. When constructing Au / TiO 2 / Gd / GCE with Gd as the cross-linking agent, the Ips of Cd 2+ and Pb 2+ at the same concentration were significantly increased respectively. This phenomenon is attributed to the cross-linking effect of Gd 3+ : It binds to the surface hydroxyl groups (-OH) of TiO 2 and the defect sites of Au nanoparticles through coordination bonds to form a stable three-dimensional anchoring network, effectively inhibiting the aggregation of nanomaterials, and enabling the high specific surface area (138 m² / g) of TiO 2 and the conductivity of Au (conductivity 4.1×10 7 S / m) to be fully exerted, thereby enhancing the adsorption-electron transfer synergistic effect on heavy metal ions.

[0057] When further using carboxymethyl chitosan (CMCS) as the cross-linking agent (Au / TiO 2 / CMCS / GCE), the Ips of Cd 2+ and Pb 2+ jumped further, showing a significant improvement compared to the Gd cross-linking system. This significant performance optimization stems from the dual functions of CMCS: First, the amino groups (-NH 2 ) and carboxyl groups (-COO - ) on its molecular chain form a hydrogen bond cross-linking network with the Au / TiO 2 complex through electrostatic interaction, greatly improving the mechanical stability of the modified layer; Second, the film-forming property of CMCS enables the Au / TiO 2 nanoparticles to be evenly dispersed on the electrode surface, exposing more active sites, and realizing enhanced selective adsorption through the specific coordination of carboxyl groups with Pb 2+ . Based on the above results, 1.0% CMCS was finally selected as the optimized cross-linking agent. Specific Example Five:

[0058] Under the optimal test conditions, the prepared Au / TiO 2 / CMCS / GCE for Cd in the range of 0.01 - 10.00 μmol / L 2+ and Pb 2+ were simultaneously scanned by DPV. The concentrations of Cd 2+ and Pb 2+ showed linear relationships with their peak currents within certain ranges, and their linear equations were Ip1 = 5.8802C 1 + 0.9113 (C 1 represents the concentration of Cd 2+ ), r 2 = 0.9997 and lp2 = 13.2617C 2 + 0.2125 (C 2 represents the concentration of Pb 2+ ), r 2 = 0.9991; the detection limits (S / N = 3) were 0.0238 and 0.0055 μmol / L respectively, meeting the test requirements. Specific Example Six:

[0059] Under the optimal test conditions, tap water was used as the detection object for detection and analysis. The results showed that neither Ca 2+ nor Pb 2+ was detected. To verify the accuracy of the method, Cd 2+ with gradient concentrations (0.5, 1.0, 2.0 μg / L) and Pb 2+ with gradient concentrations (0.3, 0.6, 1.2 μg / L) standard solutions were added to the water samples respectively, and a standard addition recovery experiment (n = 3) was carried out using the Au / TiO 2 / CMCS / GCE sensor.

[0060]

[0061] As shown in Table 1, the spiked recovery rates of Cd 2+ were 92.51% - 96.37% (RSD = 1.8% - 2.6%), and the recovery rates of Pb 2+ were 93.12% - 97.12% (RSD = 1.2% - 2.1%), all meeting the requirements of the "Technical Guidelines for the Revision of Environmental Monitoring Analysis Method Standards HJ168 - 2020" for the recovery rate (80% - 120%) and precision (RSD ≤ 10%) of trace analysis.

[0062] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for detecting heavy metals in water, characterized in that: include: S1. Pre-treating the glassy carbon electrode; S2. Prepare gold / titanium dioxide nanocomposite materials, weigh 20 mL of titanium dioxide dispersion, add 250 μL of HAuCl4 solution and 150 μL of K2CO3 solution under stirring, then quickly add 100 mL of NaBH4 solution, repeatedly add dropwise 5 times to make it react completely, wash the mixed solution 3 to 5 times, and vacuum dry; S3, prepare gold / titanium dioxide / carboxymethyl chitosan / glassy carbon electrode, take 10~15μL gold / titanium dioxide dispersion and 0~5μL carboxymethyl chitosan solution, mix, perform ultrasonic dispersion, mix evenly, take the mixture and evenly drop it on the surface of glassy carbon electrode, and dry at room temperature; S4. Establish standard curve and prepare Pb 2+ and Cd 2+ Mix the standard solution, record the dissolution peak current, draw the peak current-concentration calibration curve, and calculate the linear equation and detection limit; S5. Water sample pretreatment: tap water was used as the test sample. The sample was filtered through a 0.45 μm filter membrane and PBS was added to adjust the pH to 5.

0. S6. Perform spike recovery experiment and add known concentration of Pb 2+ and Cd 2+ , detect according to the above steps and calculate the recovery rate.

2. A method for detecting heavy metals in water according to claim 1, characterized in that: In step S1, the glassy carbon electrode is pretreated including polishing, activation and electrochemical activation. The electrode surface is polished to a mirror surface on suede using 0.3 μm and 0.05 μm Al2O3 suspensions, rinsed with ultrapure water, ultrasonically cleaned in ethanol and ultrapure water for 5 minutes, dried with nitrogen, and cyclically scanned in a 0.5MH2SO4 solution with a potential window of -1.5~1.5V until stable.

3. A method for detecting heavy metals in water according to claim 1, characterized in that: In step S2, the step of preparing titanium dioxide includes: taking 6.0 mL of anhydrous ethanol and 6.0 mL of glacial acetic acid respectively, adding 5.0 mL of ultrapure water, stirring evenly, and recording as solution A; weighing 15.0 g of ultrapure water, 100 g of n-butyl titanate, 2.0 mL of glacial acetic acid and 2.0 mL of dimethyl sulfoxide, stirring for 30 minutes, and recording as solution B; heating solution B to 30°C, adding solution A dropwise to the mixed solution under vigorous stirring conditions, stirring for 30 minutes, and continuing to stir for 1 hour after the solution becomes gel-like, and standing at room temperature for 48 hours to fully age it; drying the aged product at 100°C, grinding the dried product into powder, and calcining at 450°C for 1.5 hours.

4. A method for detecting heavy metals in water according to claim 3, characterized in that: In step S2, the concentration of the titanium dioxide dispersion is 1 mg / mL, the concentration of the HAuCl4 solution is 1%, the concentration of the K2CO3 solution is 0.1 mol / L, the concentration of the NaBH4 solution is 0.01 mol / L, and the NaBH4 solution is ready for use.

5. A method for detecting heavy metals in water according to claim 4, characterized in that: In step S2, during washing, the mixed solution after the reaction is stirred at 12000 r / min, washed 3 to 5 times with ultrapure water and anhydrous ethanol, and dried in vacuum at 60°C.

6. A method for detecting heavy metals in water according to claim 1, characterized in that: In step S3, the volume ratio of the added gold / titanium dioxide dispersion and carboxymethyl chitosan solution is 6:1; The concentration of the gold / titanium dioxide dispersion was 1 mg / mL, and the concentration of the carboxymethyl chitosan solution was 1%.

7. A method for detecting heavy metals in water according to claim 6, characterized in that: In step S3, 10-15 μL of a gold / titanium dioxide dispersion with a concentration of 1 mg / mL was drawn, 0-5 μL of a 1% glutaraldehyde solution was added, ultrasonic dispersion was performed, and after mixing evenly, 7 μL of the mixture was drawn and evenly dropped on the surface of the glassy carbon electrode, and dried at room temperature to prepare a gold / titanium dioxide / glutaraldehyde / glassy carbon electrode as a control group; 10~15μL of 1mg / mL gold / titanium dioxide dispersion was taken, 0~5μL of pure water was added, ultrasonic dispersion was performed, and after mixing evenly, 7μL of the mixture was taken and evenly dropped on the surface of the glassy carbon electrode, and dried at room temperature to prepare a gold / titanium dioxide / glassy carbon electrode as a control group.

8. A method for detecting heavy metals in water according to claim 1, characterized in that: In step S5, 0.1 mol / L sodium acetate solution and acetic acid solution are prepared respectively with tap water as solvent, the acetic acid solution is added to the sodium acetate solution, and the pH of the mixed solution is adjusted to 5.0 to prepare an acetate buffer solution with a pH of 5.

0.

9. A method for detecting heavy metals in water according to claim 1, characterized in that: In step S4, Pb 2+ and Cd 2+ When mixing standard solutions, Pb 2+ and Cd 2+ The concentration range is 0.01~10.00μmoL / L.

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