Schiff base coordination polymer, electrochemical sensor as well as preparation method and application of electrochemical sensor

Abstract

The invention 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 of the Schiff base coordination polymer. The chemical formula of the Schiff base coordination polymer is [Cu3 (L1) 2H2O]. 7DMF. 16H2O. The invention further discloses a preparation method of the Schiff base coordination polymer. The [Cu3 (L1) 2H2O]. 7DMF. 16H2O provided by the invention has a conjugated structure, a unique pore structure and multiple functional groups, is beneficial to electron transport, can be widely applied to the fields of electro-catalysis, electrochemical sensors and the like, is applied to trace detection of Cr (VI) and Hg (II), has the advantages of low detection limit, high sensitivity, good electrochemical stability, strong anti-interference capability and the like, and can be widely applied to the fields of electrocatalysis, electrochemical sensors and the like. The method has a wide application prospect in the field of trace detection of Cr (VI) and Hg (II) in water such as industrial wastewater and domestic water.

Description

Technical Field

[0001] The present invention relates to the technical field of electroanalytical chemistry, and in particular to a Schiff base coordination polymer, an electrochemical sensor, and a preparation method and application thereof. Background Art

[0002] Chromium (Cr) and mercury (Hg) are common heavy metal pollutants. Cr (VI) mainly comes from industrial wastewater such as electroplating, leather making, printing and dyeing. It is highly oxidizing and highly toxic. It can be enriched in organisms through the food chain, causing serious damage to the human respiratory system, digestive system and skin. Hg (II) mainly comes from waste emissions from chemical, electronic, mining and other industries. It will be converted into organic mercury compounds such as methylmercury in nature. These compounds have higher biological toxicity. They can penetrate the blood-brain barrier and placental barrier, causing irreversible damage to the central nervous system and fetal development. Cr (VI) and Hg (II) are usually present at trace levels in environmental and biological samples. However, even very low concentrations of these heavy metal ions may pose potential risks to ecosystems and human health. Therefore, trace detection of Cr (VI) and Hg (II) is of great significance.

[0003] Although traditional detection methods such as atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS) have high sensitivity, these methods usually require complex sample pretreatment and expensive instruments and equipment. Electrochemical sensing methods have received widespread attention due to their advantages such as simple operation, high sensitivity, and short analysis time. However, the current electrochemical sensors for detecting Cr(VI) and Hg(II) still have disadvantages such as high preparation cost, poor selectivity and stability, and low sensitivity. Therefore, it is of great practical significance to find a new electrode material with low price and excellent performance. Summary of the invention

[0004] In view of the fact that existing electrochemical sensors for detecting Cr(VI) and Hg(II) still have the problems of high preparation cost, poor selectivity and stability, and low sensitivity, the present invention provides a Schiff base coordination polymer, an electrochemical sensor, and a preparation method and application thereof.

[0005] To solve the above technical problems, the technical solution provided by the embodiment of the present invention is:

[0006] In a first aspect, the present invention provides a Schiff base coordination polymer, the chemical formula of which is: [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 with the prior art, the Schiff base coordination polymer provided by the present invention contains azo groups, amino groups and imino groups, wherein the nitrogen atom can act as a Lewis base, interacting with metal ions in various forms such as hydrogen bonds, acid-base and coordination reactions, and its high porosity and large specific surface area make it easy for its adsorption sites to interact with metal ions, thereby significantly improving its adsorption rate for metal ions; at the same time, the coordination polymer contains an azo conjugated structure, which is beneficial to shorten the electron transmission path and improve the electron transmission rate, and the coordination polymer formed by the ligand L1 is a three-dimensional framework structure with multi-angle channels, which can effectively promote the transmission and migration of reaction substrates and products, wherein the largest channel is This channel can accommodate the detected Cr(VI) and Hg(Ⅱ) into its internal space, and prevent some ions with larger size or mismatched shape from entering the pores or active sites of the coordination polymer, thereby reducing the interference of other ions. In a solution containing multiple metal ions, the 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 by it and the L1 precursor has high conductivity and stability, and can maintain stable performance during electrochemical detection, thereby effectively reducing background signal fluctuations caused by structural changes, improving the reliability and repeatability of detection signals, and has broad application prospects in the field of Cr(VI) and Hg(Ⅱ) detection.

[0009] In a second aspect, the present invention further 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 obtain a diazonium salt solution;

[0011] adding the diazonium salt solution to an alkaline solution of 3-tert-butyl-2-hydroxybenzaldehyde to carry out a coupling reaction to obtain a coupling reactant;

[0012] The coupling reactant is subjected to an aldehyde amine condensation reaction with trans-1,2-cyclohexanediamine to obtain a L1 precursor represented by formula (II);

[0013]

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

[0015] The preparation method of the Schiff base coordination polymer provided by the present invention comprises the following steps: firstly, 5-aminoisophthalic acid, sodium nitrite, 3-tert-butyl-2-hydroxybenzaldehyde and trans-1,2-cyclohexanediamine are sequentially subjected to diazotization reaction, coupling reaction and aldehyde-amine condensation reaction to prepare an L1 precursor with a specific structure, and then the L1 precursor is coordinated with a Cu salt to form a Schiff base coordination polymer. The L1 precursor with a specific structure contains a variety of functional groups, such as carboxyl, hydroxyl, azo, etc. These functional groups and the coordination structure formed with Cu can provide abundant electrochemical active sites. At the same time, the coordination polymer can maintain stable electrochemical performance in a wide potential range, and has broad application prospects in the field of electrochemical sensing.

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

[0017] Step a, adding 5-aminoisophthalic acid to a strong acid solution, mixing evenly, and adding dropwise a sodium nitrite solution at -5°C to 5°C to carry out a diazotization reaction to obtain a diazonium salt solution;

[0018] Step b, adding 3-tert-butyl-2-hydroxybenzaldehyde to a strong base solution, mixing evenly, adding the above-mentioned diazonium salt solution, and performing a coupling reaction. After the reaction is completed, adjusting the pH to 3-4, and performing solid-liquid separation to obtain a coupling reactant;

[0019] Step c, subjecting the coupling reactant and trans-1,2-cyclohexanediamine to an aldehyde-amine condensation reaction in an alcohol solvent, cooling and crystallizing after the reaction, separating the solid from the liquid, and drying to obtain an L1 precursor;

[0020] Step d, adding the copper salt and the L1 precursor into an N,N-dimethylformamide aqueous solution, reacting at 80° C. to 90° C. to obtain a Schiff base coordination polymer.

[0021] Furthermore, the molar ratio of the 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 in the copper salt to the L1 precursor 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 the 3-tert-butyl-2-hydroxybenzaldehyde in the strong alkaline solution is 0.3 mol / L to 1.5 mol / L.

[0026] Furthermore, 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 mixed solution of concentrated hydrochloric acid and water in a volume ratio of 1:(2.5-3.5), and the concentration of the sodium nitrite solution is 3 mol / L-4 mol / L.

[0027] It should be noted that the concentrated hydrochloric acid used in the present 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] Furthermore, in step b, the strong alkaline solution is a 2 mol / L to 3 mol / L sodium hydroxide solution.

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

[0031] Furthermore, in step c, the temperature of the cooling and crystallization is 0°C to 4°C, and the time of the cooling and crystallization is 10h to 14h.

[0032] Furthermore, in step d, the reaction is carried out in a high pressure hydrothermal autoclave for 68 hours to 72 hours. During the high pressure reaction, the C=N double bond of the L1 precursor is broken to form a structure shown in formula (I), which contains more functional groups and a conjugated structure, which is conducive to the transmission of electrons.

[0033] Furthermore, 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 the 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, and has high promotion and application value.

[0035] In a third aspect, the present invention also provides the use of the above-mentioned Schiff base coordination polymer in detecting Cr(VI) and Hg(II) in water.

[0036] The present 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), so that the coordination polymer can selectively adsorb and detect target ions in a complex environment and reduce the interference of other ions. At the same time, the coordination polymer has good chemical stability and can maintain the stability of structure and performance under various conditions, ensuring the accuracy and reliability of detection. It has a high application prospect in detecting Cr(VI) and Hg(II) in water bodies.

[0037] In a fourth aspect, the present invention provides an electrochemical sensor: comprising the above-mentioned Schiff base coordination polymer.

[0038] The Schiff base coordination polymer provided by the present invention contains a large number of functional groups, such as carboxyl, hydroxyl, azo groups, etc., which can provide abundant electrochemical active sites. In the process of electrochemical detection, these active sites can effectively transfer electrons with the target analyte, thereby generating obvious electrochemical signals, which can significantly improve the detection performance of electrochemical sensing. In addition, the Schiff base coordination polymer has good chemical stability and thermal stability. In the process of electrochemical detection, it may be exposed to various electrolyte solutions, organic solvents and different temperature conditions. The polymer can maintain the stability of structure and performance under these environments, ensuring the reliability and repeatability of the detection results. Therefore, it has broad application prospects in the field of electrochemical sensing detection.

[0039] Furthermore, the preparation method of the electrochemical sensor comprises the following steps:

[0040] Step a, weighing the Schiff base coordination polymer and carbon powder respectively, and uniformly dispersing them in a Nafion solution by ultrasonication to obtain a dispersion;

[0041] Step b, applying the dispersion droplets to the surface of the GCE electrode and drying the dispersion droplets to obtain the electrochemical sensor.

[0042] The electrode material prepared by the above preparation method is directly drop-coated onto the surface of the glassy carbon electrode and dried at room temperature. The obtained film does not crack and is firmly adhered 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 carbon powder is 1:1 to 1:5, preferably 1:2.

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

[0045] Illustratively, the Nafion solution is a 0.5% Nafion solution.

[0046] Optionally, the amount of dispersion solution dropped onto the GCE electrode is 12 μL.

[0047] The optimal concentration and drop coating amount can make the Schiff base coordination polymer and carbon powder more evenly distributed on the surface of the GCE electrode, thereby improving the sensing performance of the electrode.

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

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

[0050] The Schiff base coordination polymer provided by the present invention has a high affinity for Cr(VI) and Hg(II), is conducive to the selective adsorption of Cr(VI) and Hg(II), avoids the interference of other metal cations on the detection, and is prepared into an electrochemical sensor to realize the rapid detection of Cr(VI) and Hg(II), with high sensitivity and low detection limit. The detection limit of Cr(VI) is 0.173μM and the sensitivity is 0.11μA·μM -1 The detection limit for Hg(Ⅱ) is 0.194μM and the sensitivity is 0.095μA·μM -1 The method is simple to operate and has good cyclic stability, which provides an efficient, sensitive and simple method for detecting Cr(VI) and Hg(Ⅱ) in water systems in actual environments. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0052] Figure 2 This is a schematic diagram of the structure of the [Cu3(L1)2H2O]·7DMF·16H2O compound prepared in Example 1, wherein: Figure 2 (a) is a schematic diagram of the one-dimensional linear 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 Schematic diagram of the three-dimensional supramolecular structure of the [Cu3(L1)2H2O]·7DMF·16H2O compound prepared in Example 1;

[0054] Figure 4 1 is an EIS graph of the electrode prepared from the Schiff base coordination polymer and the carbon powder in different mass ratios in Example 1;

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

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

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

[0058] Figure 8 The stability test results of the 1-GCE electrode prepared in Example 1. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0060] In order to better illustrate the present invention, further examples are given below.

[0061] Example 1

[0062] Preparation of Schiff base coordination polymers:

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

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

[0065] Weigh 1.1120 g of yellow solid and 0.1713 g of trans-1,2-cyclohexanediamine, add them into 10 mL of methanol, stir and dissolve, recrystallize at 0-4°C for 12 h, filter and dry to obtain orange-yellow ligand H6L, the structural formula of which is as follows:

[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 mixed solution into a high-pressure reactor, react at 80°C for 72 h, filter, wash, and dry to obtain a 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 example 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 showed that the compound was monoclinic P21 / n space group, such as Figure 1 As shown, the structural unit of the complex includes a coordinated water molecule, two ligand units and three Cu 2+ ions. Cu1 forms a penta-coordinate structure by coordinating with the carboxyl oxygen atoms on four ligands and a water molecule. Cu1 is bridged with Cu1 from another asymmetric unit and four carboxyl groups from four different ligands to form a [Cu2(COO)4] paddle-wheel-shaped secondary building unit. Cu2 forms a tetra-coordinate structure 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 a 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 atoms and hydroxyl oxygen atoms as coordination sites, while the external carboxylate groups coordinate in a monodentate manner, and then the Cu1 ions interconnect these chains together to form a two-dimensional layer structure. Figure 2 As can be seen in (a), the channel size of a single structure is close to It is beneficial to the transmission of electrons and increases the transfer speed of electrons, thereby improving the electrical properties of the compound. Figure 3 shown.

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

[0080] The glassy carbon electrode was polished on a polishing plate with 1.0 μm, 0.5 μm and 0.05 μm alumina powder respectively, and ultrasonically cleaned in distilled water, anhydrous ethanol and distilled water respectively after each polishing, and dried with nitrogen for standby use;

[0081] The [Cu3(L1)2H2O]·7DMF·16H2O compound and carbon powder prepared above were weighed in the ratio of 1:1, 1:2, 1:3 and 1:5 respectively, with a total mass of 12 mg. The mixtures in different proportions were added with 0.2 mL of 0.5% nafion solution respectively, and ultrasonically dispersed for 30 min to make them evenly dispersed. 12 μL of the suspension was aspirated with a pipette, and drop-coated on 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 a modified electrode.

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

[0083] Electrochemical detection of Cr(VI):

[0084] The modified electrode 1-GCE prepared above was used for electrochemical detection of Cr(VI) by amperometric method. The test parameters were: applied potential -0.08V, sampling test interval of 2s, current balance at the beginning of the test, and then the concentration of K2Cr2O7 in the solution was continuously increased in 0.5M H2SO4 solution to obtain the response current of different concentrations of Cr(VI). The concentration range of Cr(VI) was 5μM to 510μM. The results are shown in Figure 2. Figure 5 shown.

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

[0086] Electrochemical Detection of Hg(Ⅱ)

[0087] The modified electrode 1-GCE prepared above was used for electrochemical detection of Hg(Ⅱ) by amperometric method. The test parameters were: applied potential -0.06V, sampling test interval of 2s, current balance at the beginning of the test, and then the concentration of HgCl2 in the solution was continuously increased in 0.5M H2SO4 solution to obtain the response current of different concentrations of Hg(Ⅱ). The concentration range of Hg(Ⅱ) was 5μM to 510μM. The results are shown in Figure 2. Figure 6 shown.

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

[0089] Electrochemical selectivity test

[0090] The modified electrode prepared above was used for electrochemical selectivity study by amperometry. The test parameters were: applied potential -0.08V, sampling test interval of 2s, current balance at the beginning of the test, after the blank current stabilized, 50μM Cr(VI) was added to the 0.5MH2SO4 solution, and after an obvious current response was seen, 500μM Na + , K + , Ca 2+ 、Co 2+ 、Cd 2+ Cr 3+ Mg 2+ , Mn 2+ 、Ni 2+ 、Zn 2+ , the results are as follows Figure 7 shown.

[0091] The results showed that, except for Cr(VI), the modified electrode 1-GCE showed no obvious response signals to other metal ions, proving that these metal ions did not interfere with the detection of Cr(VI). Finally, when 50 μM Cr(VI) was added to the system, it showed an obvious current response, indicating that the prepared electrochemical sensor has good selectivity and anti-interference ability.

[0092] Electrochemical stability test:

[0093] The modified electrode prepared above was used for electrochemical stability study by amperometric method. The test parameters were: applied potential -0.08V, chronoamperometric test for 8h in 0.5M H2SO4 solution containing 50μM Cr(VI). Figure 8 shown.

[0094] The results showed that during the 8-hour continuous chronoamperometric test, only a slight change was shown at the beginning, indicating that compound 1 can remain stable for a long time, indicating that 1-GCE has excellent electrochemical stability.

[0095] Example 2

[0096] Preparation of Schiff base coordination polymers:

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

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

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

[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 mixed solution into a high-pressure reactor, react at 85°C for 70 h, filter, wash, and dry to obtain a Schiff base coordination polymer [Cu3(L1)2H2O]·7DMF·16H2O, hereinafter referred to as compound 1.

[0103] Preparation of electrochemical sensor:

[0104] The glassy carbon electrode was polished on a polishing plate with 1.0 μm, 0.5 μm and 0.05 μm alumina powder respectively, and ultrasonically cleaned in distilled water, anhydrous ethanol and distilled water respectively after each polishing, and dried with nitrogen for standby use;

[0105] The [Cu3(L1)2H2O]·7DMF·16H2O compound and carbon powder prepared above were weighed in a ratio of 1:2 with a total mass of 12 mg. The mixtures in different ratios were respectively added with 0.2 mL of 0.5% nafion solution and ultrasonically dispersed for 30 min to make them evenly dispersed. 12 μL of the suspension was taken with a pipette and drop-coated on the pretreated glassy carbon electrode. The electrode was placed vertically under an infrared lamp until the film was completely fixed on the surface of the glassy carbon electrode to obtain an electrochemical sensor.

[0106] Example 3

[0107] Preparation of Schiff base coordination polymers:

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

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

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

[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 mixed solution into a high-pressure reactor, react at 90°C for 68 h, filter, wash, and dry to obtain a Schiff base coordination polymer [Cu3(L1)2H2O]·7DMF·16H2O, hereinafter referred to as compound 1.

[0114] Preparation of electrochemical sensor:

[0115] The glassy carbon electrode was polished on a polishing plate with 1.0 μm, 0.5 μm and 0.05 μm alumina powder respectively, and ultrasonically cleaned in distilled water, anhydrous ethanol and distilled water respectively after each polishing, and dried with nitrogen for standby use;

[0116] The [Cu3(L1)2H2O]·7DMF·16H2O compound and carbon powder prepared above were weighed in a ratio of 1:2 with a total mass of 12 mg. The mixtures in different ratios were respectively added with 0.2 mL of 0.5% nafion solution and ultrasonically dispersed for 30 min to make them evenly dispersed. 12 μL of the suspension was taken with a pipette and drop-coated on the pretreated glassy carbon electrode. The electrode was placed vertically under an infrared lamp until the film was completely fixed on the surface of the glassy carbon electrode to obtain an electrochemical sensor.

[0117] After testing, embodiments 2 to 3 can achieve technical effects basically equivalent to embodiment 1.

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

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in 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: The following steps are involved: In a strong acid solution, 5-aminoisophthalic acid and sodium nitrite undergo a diazotization reaction to obtain a diazonium salt solution; adding the diazonium salt solution to an alkaline solution of 3-tert-butyl-2-hydroxybenzaldehyde to carry out a coupling reaction to obtain a coupling reactant; The coupling reactant is subjected to an aldehyde amine condensation reaction with trans-1,2-cyclohexanediamine to obtain a L1 precursor represented by formula (II); The L1 precursor and copper salt are subjected to coordination reaction to obtain a Schiff base coordination polymer.

3. The method for preparing a Schiff base coordination polymer according to claim 2, characterized in that: The specific steps include: Step a, adding 5-aminoisophthalic acid to a strong acid solution, mixing evenly, and adding dropwise a sodium nitrite solution at -5°C to 5°C to carry out a diazotization reaction to obtain a diazonium salt solution; Step b, adding 3-tert-butyl-2-hydroxybenzaldehyde to a strong base solution, mixing evenly, adding the above-mentioned diazonium salt solution, and performing a coupling reaction. After the reaction is completed, adjusting the pH to 3-4, and performing solid-liquid separation to obtain a coupling reactant; Step c, subjecting the coupling reactant and trans-1,2-cyclohexanediamine to an aldehyde-amine condensation reaction in an alcohol solvent, cooling and crystallizing after the reaction, separating the solid from the liquid, and drying to obtain an L1 precursor; Step d: adding the copper salt and the L1 precursor to an aqueous solution of N,N-dimethylformamide and reacting them at 80° C. to 90° C. to obtain a Schiff base coordination polymer.

4. The method for preparing a Schiff base coordination polymer according to 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 a Schiff base coordination polymer according to 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 the 3-tert-butyl-2-hydroxybenzaldehyde in the strong alkaline solution is 0.3 mol / L to 1.5 mol / L.

6. The method for preparing a Schiff base coordination polymer according to 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 mixed solution of concentrated hydrochloric acid and water in 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 N,N-dimethylformamide aqueous solution is 8 mmol / L to 9 mmol / L.

7. Use of the Schiff base coordination polymer described in claim 1 in detecting Cr(VI) and Hg(II) in water.

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

9. The electrochemical sensor according to claim 8, characterized in that The preparation method thereof comprises the following steps: Step a, weighing the Schiff base coordination polymer and carbon powder respectively, and uniformly dispersing them in a Nafion solution by ultrasonication to obtain a dispersion; Step b, applying the dispersion droplets to the surface of the GCE electrode and drying the dispersion droplets to obtain the electrochemical sensor.

10. Use of the electrochemical sensor according to claim 8 in detecting Cr(VI) and Hg(II) in water.

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