A schiff base-based coordination polymer, an electrochemical sensor and a preparation method and application thereof

Abstract

The application relates to the technical field of electroanalytical chemistry, and particularly discloses a Schiff base coordination polymer, an electrochemical sensor and a preparation method and application thereof. The chemical formula of the Schiff base coordination polymer is [Cu3(L1)2H2O] * 7DMF * 16H2O. The [Cu3(L1)2H2O] * 7DMF * 16H2O provided by the application has a conjugate structure, a unique channel structure and multiple functional groups, is beneficial to electron transmission, can be widely applied to the fields of electrocatalysis and electrochemical sensors, can be applied to trace detection of Cr(VI) and Hg(II), has the advantages of low detection limit, high sensitivity, good electrochemical stability and strong anti-interference capability, and has a wide application prospect in the field of trace detection of Cr(VI) and Hg(II) in industrial wastewater, domestic water and the like.

Description

Technical Field

[0001] This invention relates to the field of electroanalytical chemistry, and in particular to a Schiff base coordination polymer, an electrochemical sensor, its preparation method, and its application. Background Technology

[0002] Chromium (Cr) and mercury (Hg) are common heavy metal pollutants. Cr(VI) mainly originates from industrial wastewater from electroplating, leather tanning, and dyeing industries. It possesses strong oxidizing properties and high toxicity, and can accumulate in organisms through the food chain, causing serious damage to the human respiratory, digestive, and skin systems. Hg(II) mainly comes from waste emissions from industries such as chemical, electronics, and mining. In nature, it transforms into organomercury compounds such as methylmercury. These compounds have even higher biotoxicity, capable of crossing the blood-brain barrier and placental barrier, causing irreversible damage to the central nervous system and fetal development. In environmental and biological samples, Cr(VI) and Hg(II) are usually present at trace levels. However, even very low concentrations of these heavy metal ions can pose potential risks to ecosystems and human health. Therefore, trace detection of Cr(VI) and Hg(II) is of paramount importance.

[0003] Traditional detection methods such as atomic absorption spectrometry (AAS) and inductively coupled plasma mass spectrometry (ICP-MS), while possessing high sensitivity, typically require complex sample pretreatment and expensive equipment. Electrochemical sensing methods have attracted widespread attention due to their advantages of simple operation, high sensitivity, and short analysis time. However, current electrochemical sensors for detecting Cr(VI) and Hg(II) still suffer from drawbacks such as high fabrication costs, poor selectivity and stability, and low sensitivity. Therefore, finding a novel electrode material that is inexpensive and has excellent performance is of significant practical importance. Summary of the Invention

[0004] To address the problems of high preparation cost, poor selectivity and stability, and low sensitivity in existing electrochemical sensors for detecting Cr(VI) and Hg(II), this invention provides a Schiff base coordination polymer, an electrochemical sensor, its preparation method, and its application.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the embodiments of the present invention is as follows:

[0006] In a first aspect, the present invention provides a Schiff base coordination polymer with the chemical formula: [Cu3(L1)2H2O]·7DMF·16H2O, wherein the structure of L1 is as shown in formula (Ⅰ), and DMF is N,N-dimethylformamide;

[0007]

[0008] Compared to existing technologies, the Schiff base coordination polymer provided by this invention contains azo, amino, and imine groups. The nitrogen atom can act as a Lewis base, interacting with metal ions through various mechanisms such as hydrogen bonding, acid-base interactions, and coordination reactions. Furthermore, its high porosity and large specific surface area make its adsorption sites readily interact with metal ions, significantly improving its adsorption rate. Simultaneously, the coordination polymer contains an azo conjugated structure, which helps shorten the electron transport path and increase the electron transport rate. Moreover, the coordination polymer formed by ligand L1 has a three-dimensional framework structure with multi-angle channels, effectively promoting the transport and migration of reaction substrates and products. The largest channel is... This channel can accommodate the detected Cr(VI) and Hg(II) into its internal space, while preventing some larger or mismatched ions from entering the pores or active sites of the coordination polymer, thereby reducing interference from other ions. In solutions containing multiple metal ions, this coordination polymer can more accurately identify and detect Cr(VI) and Hg(II), improving the selectivity and accuracy of detection. In addition, Cu has unpaired d-orbital electrons that can move freely. The coordination polymer formed with the L1 precursor has high conductivity and stability, maintaining stable performance during electrochemical detection. This effectively reduces background signal fluctuations caused by structural changes, improving the reliability and repeatability of the detection signal. It has broad application prospects in the field of Cr(VI) and Hg(II) detection.

[0009] Secondly, the present invention also provides a method for preparing a Schiff base coordination polymer, comprising the following steps:

[0010] In a strong acid solution, 5-aminoisophthalic acid and sodium nitrite undergo a diazotization reaction to yield a diazonium salt solution.

[0011] The diazonium salt solution was added to an alkaline solution of 3-tert-butyl-2-hydroxybenzaldehyde to carry out a coupling reaction, yielding the coupled reactant.

[0012] The coupled reactant was subjected to an aldehyde-amine condensation reaction with trans-1,2-cyclohexanediamine to obtain the L1 precursor shown in formula (II);

[0013]

[0014] The L1 precursor and copper salt were subjected to a coordination reaction to obtain a Schiff base coordination polymer.

[0015] The method for preparing Schiff base coordination polymers provided by this invention first involves preparing an L1 precursor with a specific structure through a diazotization reaction, a coupling reaction, and an aldehyde-amine condensation reaction of 5-aminoisophthalic acid, sodium nitrite, 3-tert-butyl-2-hydroxybenzaldehyde, and trans-1,2-cyclohexanediamine. Then, the L1 precursor is coordinated with a Cu salt to form a Schiff base coordination polymer. The L1 precursor with its special structure contains various functional groups, such as carboxyl, hydroxyl, and azo groups. These functional groups and the coordination structure formed with Cu provide abundant electrochemical active sites. Furthermore, this coordination polymer maintains stable electrochemical performance over a wide potential range, showing broad application prospects in the field of electrochemical sensing.

[0016] Specifically, the preparation method of the Schiff base coordination polymer includes the following steps:

[0017] Step a: Add 5-aminoisophthalic acid to a strong acid solution, mix well, and add sodium nitrite solution dropwise at -5℃ to 5℃ to carry out a diazotization reaction to obtain a diazonium salt solution.

[0018] Step b: Add 3-tert-butyl-2-hydroxybenzaldehyde to a strong alkaline solution, mix well, add the above diazonium salt solution, carry out the coupling reaction, adjust the pH to 3-4 after the reaction is completed, separate the solid and liquid, and obtain the coupled reaction product;

[0019] Step c: The coupled reactant and trans-1,2-cyclohexanediamine are subjected to an aldehyde-amine condensation reaction in an alcohol solvent. After the reaction is completed, the mixture is cooled to crystallize, the solid and liquid are separated, and the mixture is dried to obtain the L1 precursor.

[0020] Step d: The copper salt and the L1 precursor are added to an aqueous solution of N,N-dimethylformamide and reacted at 80°C to 90°C to obtain the Schiff base coordination polymer.

[0021] Further, the molar ratio of 5-aminoisophthalic acid, 3-tert-butyl-2-hydroxybenzaldehyde and trans-1,2-cyclohexanediamine is 2:(1-1.4):(0.08-0.1).

[0022] Furthermore, the molar ratio of Cu to L1 precursor in the copper salt is (1.8–2.5):1.

[0023] Furthermore, the concentration of the 5-aminoisophthalic acid in the strong acid solution is 1.5 mol / L to 2.5 mol / L.

[0024] Furthermore, the concentration of the trans-1,2-cyclohexanediamine in the alcohol solvent is 0.07 mol / L to 0.15 mol / L.

[0025] Furthermore, the concentration of 3-tert-butyl-2-hydroxybenzaldehyde in a strong alkaline solution is 0.3 mol / L to 1.5 mol / L.

[0026] Further, the volume ratio of the strong acid solution to the sodium nitrite solution is (3.5-4.5):(2-3), wherein the strong acid solution is a mixture of concentrated hydrochloric acid and water with a volume ratio of 1:(2.5-3.5), and the concentration of the sodium nitrite solution is 3mol / L-4mol / L.

[0027] It should be noted that the concentrated hydrochloric acid used in this invention refers to commercially available concentrated hydrochloric acid with a concentration of 10 mol / L to 12 mol / L, preferably 12 mol / L.

[0028] Furthermore, the concentration of the copper salt in the N,N-dimethylformamide aqueous solution is 8 mmol / L to 9 mmol / L.

[0029] Further, in step b, the strong alkaline solution is a 2 mol / L to 3 mol / L sodium hydroxide solution.

[0030] Further, in step c, the alcohol solvent is methanol.

[0031] Furthermore, in step c, the cooling and crystallization temperature is 0℃~4℃, and the cooling and crystallization time is 10h~14h.

[0032] Furthermore, in step d, the reaction is carried out in a high-pressure hydrothermal reactor for 68-72 hours. During the high-pressure reaction, the C=N double bond of the L1 precursor breaks, forming the structure shown in formula (Ⅰ). This structure contains more functional groups and also contains a conjugated structure, which is beneficial for electron transport.

[0033] Further, in step d, the volume ratio of N,N-dimethylformamide to water in the N,N-dimethylformamide aqueous solution is 4:(1-2).

[0034] The preparation method of the Schiff base coordination polymer provided by this invention is simple, the raw materials are readily available, the reaction conditions are mild, the product preparation cost is low, and it can be mass-produced industrially, thus having high application value.

[0035] Thirdly, the present invention also provides the application of the above-mentioned Schiff base coordination polymer in the detection of Cr(VI) and Hg(II) in water.

[0036] This invention selects L1 with a specific structure as a ligand, which can provide suitable binding sites and spatial environments for Cr(VI) and Hg(II), enabling the coordination polymer to selectively adsorb and detect target ions in complex environments, reducing interference from other ions. At the same time, the coordination polymer has good chemical stability and can maintain structural and performance stability under various conditions, ensuring the accuracy and reliability of detection. It has high application prospects in the detection of Cr(VI) and Hg(II) in water.

[0037] Fourthly, the present invention provides an electrochemical sensor comprising the above-described Schiff base coordination polymer.

[0038] The Schiff base coordination polymer provided by this invention contains a large number of functional groups, such as carboxyl, hydroxyl, and azo groups, which can provide abundant electrochemical active sites. During electrochemical detection, these active sites can undergo effective electron transfer with the target analyte, thereby generating obvious electrochemical signals and significantly improving the detection performance of electrochemical sensing. Furthermore, this Schiff base coordination polymer has good chemical and thermal stability. During electrochemical detection, it may come into contact with various electrolyte solutions, organic solvents, and different temperature conditions. The polymer can maintain structural and performance stability under these environments, ensuring the reliability and repeatability of the detection results. Therefore, it has broad application prospects in the field of electrochemical sensing.

[0039] Furthermore, the method for preparing the electrochemical sensor includes the following steps:

[0040] Step a: Weigh the Schiff base coordination polymer and the toner separately, and ultrasonically disperse them evenly in Nafion solution to obtain a dispersion.

[0041] Step b: Drop the dispersion onto the surface of the GCE electrode and let it dry to obtain the electrochemical sensor.

[0042] The electrode material prepared by the above method is directly drop-coated onto the surface of a glassy carbon electrode and dried at room temperature. The resulting film does not crack and adheres firmly to the electrode surface, which is beneficial to improving the sensitivity and stability of the electrochemical sensor.

[0043] Furthermore, the mass ratio of the Schiff base coordination polymer to the toner is 1:1 to 1:5, preferably 1:2.

[0044] Furthermore, the concentration of the dispersion is 60 mg / mL.

[0045] For example, the Nafion solution mentioned above is a 0.5% Nafion solution.

[0046] Optionally, the amount of dispersion applied to the GCE electrode is 12 μL.

[0047] Optimal concentration and drop volume allow for a more uniform distribution of Schiff base coordination polymers and toner on the GCE electrode surface, thereby improving the electrode's sensing performance.

[0048] It should be noted that before preparing the electrochemical sensor, the GCE electrode was polished on a polishing pad with 0.05 μm alumina powder, then dried and cleaned with nitrogen gas before being drop-coated with the above dispersion.

[0049] The present invention also provides the application of the above-mentioned electrochemical sensor in the detection of Cr(VI) and Hg(II) in water.

[0050] The Schiff base coordination polymer provided by this invention has a high affinity for Cr(VI) and Hg(II), which is beneficial for the selective adsorption of Cr(VI) and Hg(II) and avoids interference from other metal cations in the detection. When prepared as an electrochemical sensor, it can achieve rapid detection of Cr(VI) and Hg(II) with high sensitivity and low detection limit. The detection limit for Cr(VI) is 0.173 μM, and the sensitivity is 0.11 μA·μM. -1 The detection limit for Hg(II) was 0.194 μM, and the sensitivity was 0.095 μA·μM. -1 It is simple to operate and has good cycle stability, providing an efficient, sensitive and convenient method for detecting Cr(VI) and Hg(II) in water systems in practical environments. Attached Figure Description

[0051] Figure 1 A schematic diagram of the coordination structure of the compound [Cu3(L1)2H2O]·7DMF·16H2O prepared in Example 1;

[0052] Figure 2 This is a schematic diagram of the structure of the compound [Cu3(L1)2H2O]·7DMF·16H2O prepared in Example 1, wherein, Figure 2 (a) is a schematic diagram of the one-dimensional straight-chain structure of the above compound; Figure 2 (b) is a schematic diagram of the two-dimensional layered structure of the above compound;

[0053] Figure 3 A schematic diagram of the three-dimensional supramolecular structure of the compound [Cu3(L1)2H2O]·7DMF·16H2O prepared in Example 1;

[0054] Figure 4 EIS images of electrodes prepared in Example 1 from Schiff base coordination polymers and carbon powder in different mass ratios;

[0055] Figure 5The it response curves and linear fitting curves of the 1-GCE electrode prepared in Example 1 in Cr(VI) solutions of different concentrations are shown, where (a) is the it response curve and (b) is the linear fitting curve of Cr(VI) concentration and response current.

[0056] Figure 6 The it response curves and linear fitting curves of the 1-GCE electrode prepared in Example 1 in Hg(II) solutions of different concentrations are shown, where (a) is the it response curve and (b) is the linear fitting curve of Hg(II) concentration and response current.

[0057] Figure 7 The interference resistance test results of the 1-GCE electrode prepared in Example 1 for different ions;

[0058] Figure 8 The results show the stability test results of the 1-GCE electrode prepared in Example 1. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0060] To better illustrate the present invention, further examples are provided below.

[0061] Example 1

[0062] Preparation of Schiff base coordination polymers:

[0063] Step 1: Preparation of Schiff base ligands:

[0064] Weigh 6.6211 g of 5-aminoisophthalic acid, add 5 mL of concentrated hydrochloric acid and 15 mL of water, stir under ice-water bath conditions, and add 12 mL of 3.3 mol / L sodium nitrite solution dropwise to obtain a yellow viscous liquid; weigh 4.4309 g of 3-tert-butyl-2-hydroxybenzaldehyde, add it to 50 mL of 2.2 mol / L sodium hydroxide solution, and slowly add the above yellow viscous liquid dropwise under stirring conditions at 0–5 °C to obtain a dark red liquid. Continue stirring for 2 hours, let stand, slowly add acetic acid to adjust the pH to 3–4, filter, and obtain a yellow solid;

[0065] Weigh 1.1120 g of a yellow solid and 0.1713 g of trans-1,2-cyclohexanediamine, add to 10 mL of methanol, stir to dissolve, recrystallize at 0–4 °C for 12 h, filter, and dry to obtain an orange-yellow ligand H6L, with the following structural formula:

[0066]

[0067] Step 2: Preparation of Schiff base coordination polymerization:

[0068] Weigh 0.0097 g Cu(NO3)2·2.5H2O and 0.0160 g of the H6L ligand prepared above, add 4 mL N,N-dimethylformamide and 1 mL water, then add the mixture to a high-pressure reactor and react at 80 °C for 72 h. Filter, wash and dry to obtain Schiff base coordination polymer [Cu3(L1)2H2O]·7DMF·16H2O, hereinafter referred to as compound 1.

[0069] The crystal structure of the [Cu3(L1)2H2O]·7DMF·16H2O compound prepared in this embodiment was determined, and the results are shown in Tables 1 and 2.

[0070] Table 1 Bond lengths of compound 1 and bond angle (°)

[0071]

[0072]

[0073] Note: #1 -x, -y-1, -z; #2 -x-1 / 2,y-1 / 2,-z+1 / 2; #3 -x-1 / 2,y+1 / 2,-z+1 / 2; #4 x, y+1, z; # 5 x, y-1, z; #6 x-1 / 2, -y-3 / 2, z+1 / 2; #7 -x-1 / 2,y-1 / 2,-z+1 / 2.

[0074] Table 2 Crystal data of compound 1

[0075]

[0076]

[0077] Note: a R1=Σ||F o |-|F c || / Σ|F o | b wR2={Σ[w(F o 2 -F c 2 ) 2 ] / Σw(F o 2 )2 ]} 1 / 2

[0078] Single-crystal diffraction indicates that the compound belongs to the monoclinic P21 / n space group, such as Figure 1 As shown, the structural unit of the complex includes one coordinated water molecule, two ligand units, and three Cu molecules. 2+ Ions. Cu1 forms a five-coordinate system by coordinating with four carboxyl oxygen atoms on four ligands and one water molecule. Cu1 is also bridged with Cu1 from another asymmetric unit and four carboxyl groups from four different ligands to form a paddlewheel-shaped secondary building unit, [Cu2(COO)4]. Cu2 forms a four-coordinate system by coordinating with two nitrogen atoms and one hydroxyl oxygen atom from the same ligand, and one carboxylate oxygen atom from another ligand. Cu3 also adopts a tetrahedral coordination geometry, coordinated by one hydroxyl oxygen atom, two nitrogen atoms from the same ligand, and one carboxylate oxygen atom from another ligand. Figure 2 As shown, the ligands utilize nitrogen and hydroxyl oxygen atoms as coordination sites, while the external carboxylate groups are coordinated in a monodentate manner. Subsequently, Cu1 ions interconnect these chains to form a two-dimensional layered structure. Furthermore, from... Figure 2 As can be seen in (a), the channel size of a single structure is close to This facilitates electron transport and increases the electron transfer rate, thereby improving the electrical properties of the compound. The three dimensions of compound 1 are as follows: Figure 3 As shown.

[0079] Preparation of [Cu3(L1)2H2O]·7DMF·16H2O modified electrode:

[0080] The glassy carbon electrode was polished on a polishing plate with alumina powder of 1.0 μm, 0.5 μm and 0.05 μm respectively. After each polishing, it was ultrasonically cleaned in distilled water, anhydrous ethanol and distilled water respectively, and then dried with nitrogen gas for later use.

[0081] The [Cu3(L1)2H2O]·7DMF·16H2O compound and carbon powder prepared above were weighed at ratios of 1:1, 1:2, 1:3, and 1:5, respectively, with a total mass of 12 mg. The mixtures of different ratios were added to 0.2 mL of 0.5% Nafion solution and ultrasonically dispersed for 30 min to ensure uniform dispersion. 12 μL of the suspension was pipetted onto the pretreated glassy carbon electrode and placed vertically under an infrared lamp until the film was completely fixed on the surface of the glassy carbon electrode to obtain the modified electrode.

[0082] Using the modified electrode prepared above as the working electrode, a graphite rod as the counter electrode, and Ag / AgCl as the reference electrode, a three-electrode method testing system was assembled. Electrochemical impedance spectroscopy was first performed in a mixed solution containing 5 mM K3Fe(CN)6 and 0.1 M KCl, and the results are as follows: Figure 4 As shown, when the mass ratio of [Cu3(L1)2H2O]·7DMF·16H2O compound to carbon powder is 1:1, 1:2, 1:3, and 1:5, the corresponding resistance values ​​are 38.1Ω, 16.7Ω, 19.8Ω, and 24.9Ω, respectively. Therefore, the mass ratio of [Cu3(L1)2H2O]·7DMF·16H2O compound to carbon powder is 1:2, which has the lowest electrochemical impedance. Therefore, the modified electrode (abbreviated as 1-GCE) prepared in this ratio was used for the following tests.

[0083] Electrochemical detection of Cr(VI):

[0084] Electrochemical detection of Cr(VI) was performed using the modified 1-GCE electrode prepared above via the amperometric method. The test parameters were: applied potential -0.08 V, sampling interval of 2 s, current equilibration at the start of the test, followed by continuously increasing the concentration of K₂Cr₂O₇ in 0.5 M H₂SO₄ solution to obtain the response current for different concentrations of Cr(VI). The concentration range of Cr(VI) was 5 μM to 510 μM. The results are as follows. Figure 5 As shown.

[0085] The results showed that the modified electrode exhibited a good linear response in the range of 5 μM to 510 μM, and the linear regression equation was: I R (μA)=-0.11C (μM)–15.49 (R=0.999, I R (The average response current). Based on S / N = 3, the detection limit and sensitivity of compound 1 for Cr(VI) were calculated. The detection limit was 0.173 μM (17.99 ppb), and the sensitivity was 0.11 μA·μM. -1 .

[0086] Electrochemical detection of Hg(II)

[0087] Electrochemical detection of Hg(II) was performed using the modified electrode 1-GCE prepared above via the amperometric method. The test parameters were: applied potential -0.06 V, sampling interval of 2 s, current equilibration at the start of the test, followed by continuously increasing the concentration of HgCl2 in a 0.5 M H₂SO₄ solution to obtain the response current for different concentrations of Hg(II). The concentration range of Hg(II) was 5 μM to 510 μM. The results are as follows: Figure 6 As shown.

[0088] The results showed that the modified electrode exhibited a good linear response in the range of 5 μM to 510 μM, and the linear regression equation was: I R (μA)=-0.095C(μM)–0.99(R=0.999, I R (The average response current). Based on S / N = 3, the detection limit and sensitivity of compound 1 for Hg(II) were calculated. The detection limit was 0.194 μM, and the sensitivity was 0.095 μA·μM. -1 .

[0089] Electrochemical selectivity test

[0090] Electrochemical selectivity was studied using the modified electrode prepared above via the amperometric method. The test parameters were: applied potential -0.08 V, sampling interval of 2 s, current equilibration at the start of the test, and after the blank current stabilized, 50 μM Cr(VI) was added to a 0.5 M H₂SO₄ solution. After observing a significant current response, 500 μM Na₂ was added sequentially every 40 s. + K + Ca 2+ Co 2+ Cd 2+ Cr 3+ Mg 2+ Mn 2+ Ni 2+ Zn 2+ The result is as follows Figure 7 As shown.

[0091] The results showed that, except for Cr(VI), the modified electrode 1-GCE did not exhibit a significant response signal to other metal ions, proving that these metal ions did not interfere with the detection of Cr(VI). Finally, the addition of 50 μM Cr(VI) to the system again resulted in a significant current response, indicating that the prepared electrochemical sensor has good selectivity and anti-interference ability.

[0092] Electrochemical stability test:

[0093] The electrochemical stability of the modified electrode prepared above was studied using the amperometric method. The test parameters were: applied potential -0.08V, chronoamperometric testing in 0.5M H₂SO₄ solution containing 50μM Cr(VI) for 8 hours. The results are as follows: Figure 8 As shown.

[0094] The results showed that during the continuous 8-hour chronoamperometric test, only a small change was observed initially, indicating that compound 1 can remain stable over a long period of time, demonstrating that 1-GCE has excellent electrochemical stability.

[0095] Example 2

[0096] Preparation of Schiff base coordination polymers:

[0097] Step 1: Preparation of Schiff base ligands:

[0098] Weigh 6.6211 g of 5-aminoisophthalic acid, add 4.5 mL of concentrated hydrochloric acid and 11.5 mL of water, stir under ice-water bath conditions, and add 10 mL of 3.3 mol / L sodium nitrite solution dropwise to obtain a yellow viscous liquid; weigh 3.4077 g of 3-tert-butyl-2-hydroxybenzaldehyde, add 20 mL of 2.2 mol / L sodium hydroxide solution, and slowly add the above yellow viscous liquid dropwise under stirring conditions at 0–5 °C to obtain a dark red liquid. Continue stirring for 2 h, let stand, slowly add acetic acid to adjust the pH to 3–4, filter, and obtain a yellow solid;

[0099] Weigh 1.1120 g of the yellow solid and 0.1927 g of trans-1,2-cyclohexanediamine, add them to 20 mL of methanol, stir to dissolve, recrystallize at 0–4 °C for 12 h, filter, and dry to obtain the orange-yellow ligand H6L, with the following structural formula:

[0100]

[0101] Step 2: Preparation of Schiff base coordination polymerization:

[0102] Weigh 0.0097 g Cu(NO3)2·2.5H2O and 0.0180 g of the H6L ligand prepared above, add 4 mL N,N-dimethylformamide and 1 mL water, then add the mixture to a high-pressure reactor and react at 85 °C for 70 h. Filter, wash and dry to obtain Schiff base coordination polymer [Cu3(L1)2H2O]·7DMF·16H2O, hereinafter referred to as compound 1.

[0103] Fabrication of electrochemical sensors:

[0104] The glassy carbon electrode was polished on a polishing plate with alumina powder of 1.0 μm, 0.5 μm and 0.05 μm respectively. After each polishing, it was ultrasonically cleaned in distilled water, anhydrous ethanol and distilled water respectively, and then dried with nitrogen gas for later use.

[0105] Weigh the prepared [Cu3(L1)2H2O]·7DMF·16H2O compound and carbon powder at a ratio of 1:2, with a total mass of 12 mg. Add the mixtures of different proportions to 0.2 mL of 0.5% Nafion solution and sonicate for 30 min to ensure uniform dispersion. Use a pipette to take 12 μL of the suspension and drop it onto the pretreated glassy carbon electrode. Place it vertically under an infrared lamp until the film is completely fixed on the surface of the glassy carbon electrode to obtain the electrochemical sensor.

[0106] Example 3

[0107] Preparation of Schiff base coordination polymers:

[0108] Step 1: Preparation of Schiff base ligands:

[0109] Weigh 6.6211 g of 5-aminoisophthalic acid, add 5 mL of concentrated hydrochloric acid and 17 mL of water, stir under ice-water bath conditions, and add 15 mL of 3.3 mol / L sodium nitrite solution dropwise to obtain a yellow viscous liquid; weigh 4.6108 g of 3-tert-butyl-2-hydroxybenzaldehyde, add it to 50 mL of 2.2 mol / L sodium hydroxide solution, and slowly add the above yellow viscous liquid dropwise under stirring conditions at 0–5 °C to obtain a dark red liquid. Continue stirring for 2 hours, let stand, slowly add acetic acid to adjust the pH to 3–4, filter, and obtain a yellow solid;

[0110] Weigh 1.1120 g of a yellow solid and 0.2129 g of trans-1,2-cyclohexanediamine, add them to 15 mL of methanol, stir to dissolve, recrystallize at 0–4 °C for 12 h, filter, and dry to obtain the orange-yellow ligand H6L, with the following structural formula:

[0111]

[0112] Step 2: Preparation of Schiff base coordination polymerization:

[0113] Weigh 0.0097 g Cu(NO3)2·2.5H2O and 0.0140 g of the H6L ligand prepared above, add 4 mL N,N-dimethylformamide and 1 mL water, then add the mixture to a high-pressure reactor and react at 90 °C for 68 h. Filter, wash and dry to obtain Schiff base coordination polymer [Cu3(L1)2H2O]·7DMF·16H2O, hereinafter referred to as compound 1.

[0114] Fabrication of electrochemical sensors:

[0115] The glassy carbon electrode was polished on a polishing plate with alumina powder of 1.0 μm, 0.5 μm and 0.05 μm respectively. After each polishing, it was ultrasonically cleaned in distilled water, anhydrous ethanol and distilled water respectively, and then dried with nitrogen gas for later use.

[0116] Weigh the prepared [Cu3(L1)2H2O]·7DMF·16H2O compound and carbon powder at a ratio of 1:2, with a total mass of 12 mg. Add the mixtures of different proportions to 0.2 mL of 0.5% Nafion solution and sonicate for 30 min to ensure uniform dispersion. Use a pipette to take 12 μL of the suspension and drop it onto the pretreated glassy carbon electrode. Place it vertically under an infrared lamp until the film is completely fixed on the surface of the glassy carbon electrode to obtain the electrochemical sensor.

[0117] Tests showed that Examples 2 and 3 could achieve technical effects that were basically equivalent to those of Example 1.

[0118] In summary, the Schiff base coordination polymer [Cu3(L1)2H2O]·7DMF·16H2O prepared in the embodiments of the present invention has a conjugated structure, a unique pore structure, and multiple functional groups, which are beneficial to electron transport. It can be widely used in electrocatalysis and electrochemical sensors. When applied to the trace detection of Cr(VI) and Hg(II), it has the advantages of low detection limit, high sensitivity, good electrochemical stability, and strong anti-interference ability. It has broad application prospects in the trace detection of Cr(VI) and Hg(II) in industrial wastewater, domestic water, and other water quality.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Schiff base coordination polymer, characterized in that, Its chemical formula is: [Cu3(L1)2H2O]·7DMF·16H2O, wherein the structure of L1 is as shown in formula (Ⅰ), and DMF is N,N-dimethylformamide; 2. The method for preparing the Schiff base coordination polymer according to claim 1, characterized in that, Includes the following steps: In a strong acid solution, 5-aminoisophthalic acid and sodium nitrite undergo a diazotization reaction to yield a diazonium salt solution. The diazonium salt solution was added to an alkaline solution of 3-tert-butyl-2-hydroxybenzaldehyde to carry out a coupling reaction, yielding the coupled reactant. The coupled reactant was subjected to an aldehyde-amine condensation reaction with trans-1,2-cyclohexanediamine to obtain the L1 precursor shown in formula (II); The L1 precursor and copper salt were subjected to a coordination reaction to obtain a Schiff base coordination polymer.

3. The method for preparing the Schiff base coordination polymer as described in claim 2, characterized in that, Specifically, the steps include the following: Step a: Add 5-aminoisophthalic acid to a strong acid solution, mix well, and add sodium nitrite solution dropwise at -5℃ to 5℃ to carry out a diazotization reaction to obtain a diazonium salt solution. Step b: Add 3-tert-butyl-2-hydroxybenzaldehyde to a strong alkaline solution, mix well, add the above diazonium salt solution, carry out the coupling reaction, adjust the pH to 3-4 after the reaction is completed, separate the solid and liquid, and obtain the coupled reaction product; Step c: The coupled reactant and trans-1,2-cyclohexanediamine are subjected to an aldehyde-amine condensation reaction in an alcohol solvent. After the reaction is completed, the mixture is cooled to crystallize, the solid and liquid are separated, and the mixture is dried to obtain the L1 precursor. In step d, the copper salt and the L1 precursor are added to an aqueous solution of N,N-dimethylformamide and reacted at 80°C to 90°C to obtain a Schiff base coordination polymer.

4. The method for preparing the Schiff base coordination polymer as described in claim 2 or 3, characterized in that, The molar ratio of 5-aminoisophthalic acid, 3-tert-butyl-2-hydroxybenzaldehyde, and trans-1,2-cyclohexanediamine is 2:(1–1.4):(0.08–0.1); and / or The molar ratio of Cu to L1 precursor in the copper salt is (1.8–2.5):

1.

5. The method for preparing the Schiff base coordination polymer as described in claim 3, characterized in that, The concentration of the 5-aminoisophthalic acid in the strong acid solution is 1.5 mol / L to 2.5 mol / L; and / or The concentration of the trans-1,2-cyclohexanediamine in the alcohol solvent is 0.07 mol / L to 0.15 mol / L; and / or The concentration of 3-tert-butyl-2-hydroxybenzaldehyde in a strong alkaline solution is 0.3 mol / L to 1.5 mol / L.

6. The method for preparing the Schiff base coordination polymer as described in claim 4, characterized in that, The volume ratio of the strong acid solution to the sodium nitrite solution is (3.5–4.5):(2–3), wherein the strong acid solution is a mixture of concentrated hydrochloric acid and water with a volume ratio of 1:(2.5–3.5), and the concentration of the sodium nitrite solution is 3 mol / L–4 mol / L; and / or The concentration of the copper salt in the aqueous solution of N,N-dimethylformamide is 8 mmol / L to 9 mmol / L.

7. The application of the Schiff base coordination polymer of claim 1 in the detection of Cr(VI) and Hg(II) in water.

8. An electrochemical sensor, characterized in that, Includes the Schiff base coordination polymer as described in claim 1.

9. The electrochemical sensor according to claim 8, characterized in that, Its preparation method includes the following steps: Step a: Weigh the Schiff base coordination polymer and the toner separately, and ultrasonically disperse them evenly in Nafion solution to obtain a dispersion. Step b: Drop the dispersion onto the surface of the GCE electrode and let it dry to obtain the electrochemical sensor.

10. The application of the electrochemical sensor according to claim 8 in the detection of Cr(VI) and Hg(II) in water.

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