An all-solid-state calcium ion selective electrode suitable for concrete

Abstract

This invention discloses an all-solid-state calcium ion selective electrode suitable for concrete. The all-solid-state calcium ion selective electrode of this invention comprises a wire, an electronic conductor, an Fe3O4@CNTs transconducting layer, a calcium ion selective membrane, a shell, and a fixing material. The wire, electronic conductor, Fe3O4@CNTs transconducting layer, and calcium ion selective membrane are sequentially connected from top to bottom into a single unit placed inside the shell, with the upper section of the wire located outside the shell. The upper and lower sections of the electronic conductor are encapsulated with the shell using a fixing material. The all-solid-state calcium ion selective electrode of this invention exhibits high conductivity, stable electrode potential, and strong working performance, adapting to the complex internal environment of concrete, including high alkalinity and multiple ions. This electrode can monitor the calcium ion concentration at different depths in the concrete structure in real time using potential changes, providing a basis for evaluating the degree of concrete corrosion, assessing the risk of steel corrosion, and evaluating structural safety.

Description

Technical Field

[0001] This invention relates to the field of building sensors, and particularly to hydraulic engineering, and is a fully solid-state calcium ion selective electrode suitable for use in concrete erosion environments. Background Technology

[0002] Concrete is the most widely used and consumed building material in the world today. It is formed by cementitious materials binding block and granular materials into a whole through their own physicochemical processes, giving it a certain strength. Concrete structures such as dams, sluice gates, bridge piers, and tunnel linings, which are in long-term contact with water, undergo leaching erosion (dissolution) under the influence of water. This means that the solid phase of the hardened cement paste gradually dissolves, leading to the destruction of the concrete's integrity. Among the hardened cement paste, calcium hydroxide, a cement hydration product, has the highest solubility. Under the action of flowing water, calcium hydroxide gradually dissolves, increasing the porosity of the cement paste and reducing the alkalinity inside the concrete. High-calcium cement hydration products decompose to compensate for the reduced alkalinity, ultimately leading to a decrease in strength and structural damage. Therefore, changes in the calcium oxide content in the liquid phase of concrete are an important indicator for assessing the degree of concrete erosion.

[0003] In reinforced concrete structures, a dense passivation film forms on the surface of the reinforcing bars in highly alkaline concrete, protecting them. When the alkalinity of the concrete decreases to a certain level, the passivation film on the surface of the reinforcing bars cannot remain stable, increasing the risk of corrosion. Therefore, changes in the calcium oxide content in the liquid phase of concrete are an important indicator for assessing the risk of reinforcing bar corrosion and structural safety.

[0004] Currently, most methods for determining the degree of concrete corrosion use EDTA titration or colorimetric methods that involve observing color changes in the cross-section of a sample with an indicator. Other methods include using mass loss rate, calcium ion dissolution, and microscopic detection to assess the degree of concrete corrosion. These methods are typically time-consuming, lack precision, and cannot provide in-situ monitoring of concrete corrosion.

[0005] Calcium ion sensors can quickly, simply, accurately, and economically detect calcium ions in liquid samples. Currently available calcium ion sensors are mainly used in biological, ecological, and industrial fields, such as detecting changes in intracellular calcium ion concentration, calcium ion concentration in blood, and calcium ion concentration in milk. These sensors typically require the pH value of the sample to be within the range of 4–10 and also have operating temperature requirements. However, cement concrete is a highly alkaline material, usually with a pH value above 12.5, and its liquid phase contains various ions. Especially in complex environmental media, in addition to the various ions inherent in the concrete itself, ions from the environmental medium can migrate into the concrete, interfering with the detection results. Summary of the Invention

[0006] To address the challenge that existing calcium ion sensors cannot be directly used for the detection of calcium ions in concrete, this invention provides an all-solid-state calcium ion selective electrode suitable for testing the concentration of calcium ions in concrete.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A solid-state calcium ion selective electrode suitable for concrete includes a wire, an electronic conductor, an Fe3O4@CNTs transconducting layer, a calcium ion selective membrane, a shell, and a fixing material. The wire, electronic conductor, Fe3O4@CNTs transconducting layer, and calcium ion selective membrane are connected in sequence from top to bottom to form a whole and placed inside the shell. The upper part of the wire is located outside the shell, and the upper part of the electronic conductor and the lower part of the wire are encapsulated with the shell by a fixing material.

[0009] The lower end of the wire is connected to the upper end of the electronic conductor. The lower end of the electronic conductor is coated with Fe3O4@CNTs to form a Fe3O4@CNTs transconducting layer. The calcium ion selective membrane is loaded below the Fe3O4@CNTs transconducting layer.

[0010] The preparation method of the Fe3O4@CNTs includes the following steps:

[0011] (1) After dispersing CNTs in acid with ultrasonication, pour them into a reaction vessel, keep them at 55-65℃ for 1-2 hours, and let them cool naturally to room temperature to obtain mixture I;

[0012] The acid mentioned in step (1) is nitric acid or a mixed solution of nitric acid and sulfuric acid, wherein the concentration of the acid is 0.45 to 0.55 mol / L;

[0013] The ultrasonic dispersion time mentioned in step (1) is 3 to 5 hours;

[0014] (2) After treating the mixture I obtained in step (1) with an ultrasonic generator for 1 hour, it is diluted and filtered multiple times with deionized water. When the pH value of the solution is between 6.5 and 7.5, it is centrifuged to separate the solid matter from the deionized water and then vacuum dried to obtain CNT.

[0015] The centrifugation speed mentioned in step (2) is 7000-9000 r / min;

[0016] The vacuum drying temperature in step (2) is 55-65℃;

[0017] (3) Dissolve FeCl2·4H2O and SnCl4·5H2O in deionized water, then add the CNTs obtained in step (2), disperse ultrasonically for at least 10 min, and add NaOH solution dropwise under vigorous stirring to obtain mixture II;

[0018] The concentration of the NaOH solution mentioned in step (3) is 2 mol / L;

[0019] The mass fractions of each raw material component in step (3) are as follows:

[0020]

[0021] The above-mentioned NaOH mass fractions refer to the solute mass in the NaOH solution.

[0022] Furthermore, the Fe / Sn molar ratio must be 2:1;

[0023] (4) Transfer the mixture II obtained in step (3) into a reaction vessel to react and obtain mixture III;

[0024] In step (4), the reaction temperature is 230–245℃ and the reaction time is 18–30 h.

[0025] (5) Centrifuge the mixture III obtained in step (4) using a centrifuge, collect the solid material, wash it multiple times with deionized water and vacuum dry it to obtain Fe3O4@CNT;

[0026] In step (5), the centrifugation speed is 7000-9000 r / min and the centrifugation time is 10-15 min.

[0027] The calcium ion selective membrane is prepared by adding calcium ion carrier ETH5234, ion exchanger NaTFPB, polymer PVC matrix and plasticizer o-NPOE into a container, then adding redistilled THF, and stirring at room temperature to obtain a calcium ion selective membrane with uniform concentration.

[0028] The mass fractions of each raw material component are as follows:

[0029]

[0030] Furthermore, the connection between the lower end of the wire and the upper end of the electronic conductor in this invention is achieved by high-temperature welding or bonding with conductive adhesive.

[0031] Furthermore, the fixing material described in this invention is epoxy resin.

[0032] Furthermore, the thickness of the calcium ion selective membrane described in this invention is 30–50 μm.

[0033] Furthermore, the Fe3O4@CNTs transduction layer of the present invention has a thickness of 50–100 μm.

[0034] Furthermore, the conductor described in this invention is preferably a copper wire.

[0035] Furthermore, the electronic conductor described in this invention is a copper rod electronic conductor, a pretreated copper rod electronic conductor, or metals such as platinum and gold, or glassy carbon electrodes, etc., as materials for the electronic conductor.

[0036] Furthermore, the electronic conductor described in this invention is preferably a pretreated copper rod electronic conductor. The pretreatment method for the copper rod electronic conductor includes: first, ultrasonically cleaning the copper rod electronic conductor with acetone for 10-15 minutes, then ultrasonically cleaning it with 0.1 mol / L dilute hydrochloric acid solution for 10-15 minutes, then ultrasonically cleaning it with deionized water for 10-15 minutes, and finally drying it.

[0037] Furthermore, the outer shell of the present invention is preferably made of PC material, and its shape is preferably tubular.

[0038] The preparation method of the all-solid-state calcium ion selective electrode of the present invention specifically includes the following steps:

[0039] (1) Connect the upper end of the electronic conductor to the lower end of the wire;

[0040] (2) Add Fe3O4@CNTs to an organic solvent and disperse it ultrasonically to obtain a uniform mixture; then coat the mixture onto the lower end of the electronic conductor. After the organic solvent has completely evaporated, coat it again; repeat this process 2-3 times to obtain the Fe3O4@CNTs transconducting layer.

[0041] The organic solvent mentioned in step (2) is a mixture of DOP and a 0.1% ethanol solution;

[0042] The amounts of each component in step (2) are as follows: 20 parts by mass of Fe3O4@CNTs, and 1 part by mass of organic solvent;

[0043] The ultrasonic dispersion time in step (2) is 30-40 min;

[0044] (3) Load the calcium ion selective membrane onto the Fe3O4@CNTs transduction layer obtained in step (2);

[0045] (4) Finally, the wires, electronic conductors, Fe3O4@CNTs transconducting layer and calcium ion selective film connected as a whole are placed into the shell. The upper part of the electronic conductor and the upper part of the shell are fixed to the inner wall of the shell with a fixing material, and the upper part of the wire is exposed outside the shell, thus obtaining the all-solid calcium ion selective electrode of the present invention.

[0046] The method of using the all-solid-state calcium ion selective electrode described in this invention is as follows:

[0047] For existing concrete structures, a hole is pre-drilled in the concrete to be tested, with the hole depth being the depth to be tested. The aforementioned all-solid-state calcium ion selective electrode is placed in the tube and fixed in a detachable manner, with the bottom of the electrode shell in contact with the bottom of the hole. In addition, a solid reference electrode is inserted to form a dual-electrode system, which can then be used to detect and monitor the calcium ion concentration in the concrete.

[0048] For new buildings, before pouring concrete, a certain length of tube, made of materials such as stainless steel or PC, with a diameter slightly larger than the maximum diameter of the electrode, is pre-installed at the location to be tested, with the bottom ends of each tube being equidistant from each other. This serves as a mold. The bottom of the tube is then plugged with an easily removable, non-absorbent rod before pouring concrete. After construction is completed, the non-absorbent rod is removed from the tube, and the aforementioned all-solid-state calcium ion selective electrode is placed inside. The electrode is fixed in a detachable manner, with the bottom of the electrode in contact with the bottom of the hole, allowing for the detection and monitoring of calcium ion concentration in the concrete.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The all-solid-state calcium ion selective electrode described in this invention has high calcium ion conductivity and selectivity, high conductivity, stable electrode potential, and strong working performance.

[0051] (2) The all-solid-state calcium ion selective electrode of the present invention is adapted to the complex internal environment of concrete, such as high alkalinity and multiple ions, and is not affected by the service environment of concrete. The electrode potential fluctuates little and the accuracy is high. For example, the high alkalinity of concrete, the presence of other ions, and pressure will not interfere with the test results.

[0052] (3) The all-solid-state calcium ion selective electrode of the present invention can monitor the calcium ion concentration at different depths in concrete structures in real time by using potential changes, providing a basis for evaluating the degree of concrete corrosion, the risk of steel corrosion and structural safety assessment.

[0053] (4) The all-solid-state calcium ion selective electrode structure and process described in this invention are simple and inexpensive. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the all-solid-state calcium ion selective electrode structure described in this invention.

[0055] Figure 2 This is a graph showing the relationship between the open-circuit potential of the all-solid-state calcium ion selective electrode and the negative logarithm of the calcium ion concentration when the thickness of the calcium ion selective film is 50 μm.

[0056] Figure 3This is a graph showing the relationship between the open-circuit potential of the all-solid-state calcium ion selective electrode and the negative logarithm of the calcium ion concentration when the thickness of the calcium ion selective film is 40 μm, as described in Embodiment 2 of the present invention.

[0057] Figure 4 This is a graph showing the relationship between the open-circuit potential of the all-solid-state calcium ion selective electrode and the negative logarithm of the calcium ion concentration when the thickness of the calcium ion selective film is 30 μm, as described in Embodiment 1 of the present invention.

[0058] Figure 5 This is the chronopotential spectrum of the all-solid-state calcium ion selective electrode described in Embodiment 3 of the present invention.

[0059] Figure 1 The components are labeled as follows: 1. Wire, 2. Electron conductor, 3. Fe3O4@CNTs transconducting layer, 4. Calcium ion selective membrane, 5. Shell, 6. Fixing material. Detailed Implementation

[0060] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. For clarity, the various parts in the drawings are not drawn to scale. Furthermore, some well-known parts may not be shown in the drawings.

[0061] The all-solid-state calcium ion selective electrode for concrete described in this invention includes a wire 1, an electronic conductor 2, an Fe3O4@CNTs transconducting layer 3, a calcium ion selective membrane 4, and a shell 5. The upper section and above of the electronic conductor 2 are connected to the inner wall of the shell 5 by a fixing material (epoxy resin) 6, which also serves as an encapsulation. The lower end of the wire 1 is connected to the upper end of the electronic conductor 2. The Fe3O4@CNTs transconducting layer 3 is loaded on the lower end face of the electronic conductor 2, and the calcium ion selective membrane 4 is loaded on the end face of the Fe3O4@CNTs transconducting layer 3. The electrode is then placed inside the shell 5, and the upper section and above of the electronic conductor 2 are connected to and encapsulated by the fixing material 6.

[0062] The conductor 1 is a copper wire, the electronic conductor 2 is a pre-treated copper rod electronic conductor, and the outer shell 5 is a PC tube.

[0063] Example 1

[0064] The conductor is made of copper.

[0065] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0066] The preparation of Fe3O4@CNTs includes the following steps:

[0067] (1) CNTs were dispersed by ultrasonication in 0.45 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0068] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 55°C to obtain CNT.

[0069] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0070] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0071] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0072] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0073] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0074] (1) Connect the upper end of the copper rod to the wire;

[0075] (2) Add 100mg Fe3O4@CNTs and 5mg DOP to 1mL of 1.0% ethanol solution and disperse ultrasonically for 30min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain a Fe3O4@CNTs transduction layer with a thickness of 50μm;

[0076] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 30 μm;

[0077] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0078] Example 2

[0079] The conductor is made of copper.

[0080] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 12 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 12 min, and finally ultrasonically clean with deionized water for 12 min, then dry for later use.

[0081] The preparation of Fe3O4@CNTs includes the following steps:

[0082] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1.5 h. After natural cooling to room temperature, mixture I was obtained.

[0083] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0084] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0085] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0086] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0087] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0088] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0089] (1) Connect the upper end of the copper rod to the wire;

[0090] (2) Add 100mg Fe3O4@CNTs and 5mg DOP to 1mL of 1.0% ethanol solution and disperse ultrasonically for 30min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain a Fe3O4@CNTs transduction layer with a thickness of 50μm;

[0091] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 40 μm;

[0092] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0093] Example 3

[0094] The conductor is made of copper.

[0095] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 15 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 15 min, and finally ultrasonically clean with deionized water for 15 min, then dry for later use.

[0096] The preparation of Fe3O4@CNTs includes the following steps:

[0097] (1) CNTs were dispersed by ultrasonication in 0.55 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 65 °C for 2 h. After natural cooling to room temperature, mixture I was obtained.

[0098] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0099] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0100] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0101] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0102] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0103] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0104] (1) Connect the upper end of the copper rod to the wire;

[0105] (2) Add 100mg Fe3O4@CNTs and 5mg DOP to 1mL of 1.0% ethanol solution and disperse ultrasonically for 30min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain a Fe3O4@CNTs transduction layer with a thickness of 50μm;

[0106] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0107] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0108] Example 4

[0109] The conductor is made of copper.

[0110] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0111] The preparation of Fe3O4@CNTs includes the following steps:

[0112] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0113] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0114] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0115] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0116] (5) The mixture III was centrifuged at 7000 r / min for 10 min, the solid material was collected, washed with deionized water multiple times and vacuum dried to obtain Fe3O4@CNT.

[0117] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0118] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0119] (1) Connect the upper end of the copper rod to the wire;

[0120] (2) 100 mg Fe3O4@CNTs and 5 mg DOP were added to 1 mL of 1.0% ethanol solution and ultrasonically dispersed for 30 min to obtain a homogeneous mixture. The mixture was coated onto the lower cross-section of a copper rod. After the organic solvent had completely evaporated, the coating was repeated. After repeating this process several times, Fe3O4@CNTs transduction layers with a thickness of 60 μm were obtained.

[0121] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0122] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0123] Example 5

[0124] The conductor is made of copper.

[0125] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0126] The preparation of Fe3O4@CNTs includes the following steps:

[0127] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 4 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0128] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0129] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0130] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0131] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0132] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0133] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0134] (1) Connect the upper end of the copper rod to the wire;

[0135] (2) 100 mg Fe3O4@CNTs and 5 mg DOP were added to 1 mL of 1.0% ethanol solution and ultrasonically dispersed for 30 min to obtain a homogeneous mixture. The mixture was coated onto the lower cross-section of a copper rod. After the organic solvent had completely evaporated, the coating was repeated. After repeating this process several times, Fe3O4@CNTs transduction layers with a thickness of 70 μm were obtained.

[0136] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0137] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0138] Example 6

[0139] The conductor is made of copper.

[0140] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0141] The preparation of Fe3O4@CNTs includes the following steps:

[0142] (1) CNTs were dispersed in 0.5 mol / L nitric acid by ultrasonication for 5 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0143] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 9000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0144] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0145] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0146] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0147] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0148] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0149] (1) Connect the upper end of the copper rod to the wire;

[0150] (2) Add 100 mg Fe3O4@CNTs and 5 mg DOP to 1 mL of 1.0% ethanol solution and ultrasonically disperse for 30 min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain Fe3O4@CNTs transduction layers with a thickness of 80 μm.

[0151] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0152] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0153] Example 7

[0154] The conductor is made of copper.

[0155] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0156] The preparation of Fe3O4@CNTs includes the following steps:

[0157] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0158] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0159] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0160] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0161] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0162] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0163] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0164] (1) Connect the upper end of the copper rod to the wire;

[0165] (2) Add 100mg Fe3O4@CNTs and 5mg DOP to 1mL of 1.0% ethanol solution and disperse ultrasonically for 30min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain a Fe3O4@CNTs transduction layer with a thickness of 90μm;

[0166] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0167] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0168] Example 8

[0169] The conductor is made of copper.

[0170] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0171] The preparation of Fe3O4@CNTs includes the following steps:

[0172] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0173] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0174] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0175] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0176] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0177] Preparation of calcium ion selective membrane: 1.656 mg of calcium ion carrier ETH 5234, 1.728 mg of ion exchanger NaTFPB, 118.872 mg of polymer PVC matrix, and 237.744 mg of plasticizer o-NPOE were added to a container, followed by the addition of 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0178] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0179] (1) Connect the upper end of the copper rod to the wire;

[0180] (2) Add 100 mg Fe3O4@CNTs and 5 mg DOP to 1 mL of 1.0% ethanol solution and ultrasonically disperse for 30 min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain a Fe3O4@CNTs transduction layer with a thickness of 100 μm;

[0181] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0182] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0183] Example 9

[0184] The conductor is made of copper.

[0185] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0186] The preparation of Fe3O4@CNTs includes the following steps:

[0187] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0188] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0189] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0190] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0191] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0192] Preparation of calcium ion selective membrane: 1.6 mg calcium ion carrier ETH 5234, 1.728 mg ion exchanger NaTFPB, 118.872 mg polymer PVC matrix, and 237.744 mg plasticizer o-NPOE were added to a container, followed by 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0193] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0194] (1) Connect the upper end of the copper rod to the wire;

[0195] (2) Add 100mg Fe3O4@CNTs and 5mg DOP to 1mL of 1.0% ethanol solution and disperse ultrasonically for 30min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain Fe3O4@CNTs transduction layers with a thickness of 50μm.

[0196] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0197] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0198] Example 10

[0199] The conductor is made of copper.

[0200] Pretreatment of electronic conductor copper rods: First, ultrasonically clean with acetone for 10 min, then ultrasonically clean with 0.1 mol / L dilute hydrochloric acid solution for 10 min, and finally ultrasonically clean with deionized water for 10 min, then dry for later use.

[0201] The preparation of Fe3O4@CNTs includes the following steps:

[0202] (1) CNTs were dispersed by ultrasonication in 0.5 mol / L nitric acid for 3 h, then poured into a reaction vessel and kept at 60 °C for 1 h. After natural cooling to room temperature, mixture I was obtained.

[0203] (2) After treating mixture I with an ultrasonic generator for 1 hour, it was diluted and filtered multiple times with deionized water. When the pH of the solution was 7, it was centrifuged at 8000 r / min to separate the solid matter from the deionized water and then vacuum dried at 60°C to obtain CNTs.

[0204] (3) Dissolve 0.80g FeCl2·4H2O and 0.70g SnCl4·5H2O (Fe / Sn molar ratio of 2:1) in 40mL of deionized water, then add 0.07g CNT, disperse by ultrasonication for 10min, and add 2.4g NaOH (2M) dropwise under vigorous stirring to obtain mixture II;

[0205] (4) Transfer mixture II to a reaction vessel and keep it at 240℃ for 24 hours to obtain mixture III;

[0206] (5) Centrifuge the mixture Ⅲ at 8000r / min for 10min, collect the solid material, wash it with deionized water several times and vacuum dry it to obtain Fe3O4@CNT.

[0207] Preparation of calcium ion selective membrane: 1.7 mg calcium ion carrier ETH 5234, 1.728 mg ion exchanger NaTFPB, 118.872 mg polymer PVC matrix, and 237.744 mg plasticizer o-NPOE were added to a container, followed by 1.8 mL of redistilled THF. The mixture was stirred at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

[0208] The preparation of an all-solid-state calcium ion selective electrode suitable for concrete includes the following steps:

[0209] (1) Connect the upper end of the copper rod to the wire;

[0210] (2) Add 100mg Fe3O4@CNTs and 5mg DOP to 1mL of 1.0% ethanol solution and disperse ultrasonically for 30min to obtain a homogeneous mixture; coat the mixture onto the lower cross-section of a copper rod, and after the organic solvent has completely evaporated, coat again; repeat this process several times to obtain Fe3O4@CNTs transduction layers with a thickness of 50μm.

[0211] (3) A calcium ion selective membrane was loaded onto the Fe3O4@CNTs transduction layer with a thickness of approximately 50 μm;

[0212] (4) The wires, copper rod, Fe3O4@CNTs transconducting layer and calcium ion selective membrane connected as a whole are placed into the shell. The upper part of the copper rod and above are fixed to the inner wall of the shell by fixing material, thus obtaining an all-solid calcium ion selective electrode suitable for concrete.

[0213] Performance testing

[0214] Using a saturated calomel electrode as a reference electrode, sodium hydroxide solutions of different concentrations were prepared, and the open-circuit potential of the all-solid-state calcium ion selective electrode applicable to concrete of this invention was tested at different pH values.

[0215] The different selective electrodes from Examples 1, 2, 3, 4, 5, 6, 7, and 8 were respectively added to 10 liters of deionized water. 0 -10 -6 A calcium ion selective electrode and a saturated calomel electrode were placed in a solution containing mol of CaCl2 to measure their open-circuit potential and to calculate the slope of their response curves.

[0216] Prepare NaOH solutions with pH values ​​of 7, 8, 9, 10, 11, and 12 respectively, and then add 10 mg / L of NaOH to each solution. 3 mol of CaCl2 was used to immerse the calcium ion selective electrode and the saturated calomel electrode from Example 3 in the solution for 3 hours, and their open circuit potential was continuously measured and the offset was recorded.

[0217] Figure 2 To illustrate the relationship between the electrode open-circuit potential and the logarithm of the negative calcium ion concentration at pH 7 in Example 3 (calcium ion selective membrane thickness is 50 μm), the fitting equation is y = 46.4x - 439.2, R0 2 = 0.98448, where y is the open-circuit potential and x is the negative logarithm of the calcium ion concentration. Fitted curve R 2 The value of 0.98448 indicates that the fitted curve has a very high goodness of fit and the fitted equation is reliable.

[0218] Figure 3 To test the relationship between the electrode open-circuit potential and the logarithm of the negative calcium ion concentration at pH 7 in Example 2 (selective membrane thickness 40 μm), the fitting equation is y = 42.1x - 423.5, R0 2 = 0.9549, where y is the open-circuit potential and x is the negative logarithm of the calcium ion concentration. Fitted curve R 2 The value of 0.9549 indicates that the fitted curve has a high goodness of fit and the fitted equation is reliable.

[0219] Figure 4The graph showing the relationship between the electrode open-circuit potential and the logarithm of the negative calcium ion concentration at pH 7 in Example 1 (selective membrane thickness 30 μm) is fitted with the equation y = 40.9x - 166.1, R0 2 = 0.98356, where y is the open-circuit potential and x is the negative logarithm of the calcium ion concentration. Fitting curve R 2 The value of 0.98356 indicates that the fitting curve has a high goodness of fit within the range shown in the figure, and the fitting equation is reliable. This demonstrates that the all-solid-state calcium ion selective electrode described in this invention is relatively reliable, has good ion conductivity, and good workability.

[0220] The all-solid-state calcium ion selective electrode from Example 3 was used as the working electrode, the saturated calomel electrode as the reference electrode, and the platinum electrode as the auxiliary electrode. These electrodes were immersed in 0.1 mol / L CaCl₂ solution and then connected to an electrochemical workstation. Chronopotential testing was performed at ±1 nA. The test results... Figure 5 As shown, the potential difference is small, indicating that its stability is good.

[0221] Table 1 shows the slope of the potential response curves and the reliability R obtained from tests of different transduction layer film thicknesses in Examples 3, 4, 5, 6, 7, and 8. 2 The table (with a selective film thickness of 50 μm) shows that the sensor has the best responsiveness when the transconductance layer thickness is 100 μm, but the difference in responsiveness is not significant. Considering cost, an electrode with a transconductance layer thickness of 50 μm was selected for other experiments.

[0222] Table 1 shows the slope and reliability of the different transduction layer film thicknesses and potential response curves obtained in Examples 3, 4, 5, 6, 7, and 8.

[0223]

[0224] Table 2 shows the potential shift after immersion in solutions of different pH values ​​for 1 hour using the selective electrode from Example 3. The table shows that the potential shift is low. While the potential shift gradually increases with pH, ​​it remains at a low level. This indicates good alkali resistance and suitability for concrete applications.

[0225] Table 2. Relationship between potential shifts after immersion in solutions of different pH values ​​for 1 hour, obtained from selective electrode testing in Example 3.

[0226]

[0227] Table 3 shows the slopes of the response curves of the selective electrodes prepared with different ratios of selective membranes described in Examples 3, 9, and 10 in solution, as well as the slopes of the response curves obtained using the separate solution method, i.e., soaking in a 0.001 mol / L magnesium chloride solution for one day and then sequentially placing them in a 10% magnesium chloride solution. -1 10 -2 10 -3 The selectivity coefficients for each cation prepared in mol / L MgCl2, KCl, NaCl and CaCl2 solutions are shown in the table. It can be seen from the table that the electrode has good selectivity and good working performance.

[0228] Table 3. Slopes of the response curves of the selective electrodes described in Examples 3, 9, and 10 in solution and their selectivity coefficients for each cation.

[0229] Example 9 Example 3 Example 10 Calcium ion carrier amount (g) 1.6 1.656 1.7 slope 43.7 46.4 38.9 <![CDATA[Mg 2+ Selectivity coefficient 4.9 5.3 5.5 <![CDATA[Na 2+ Selectivity coefficient 3.72 4.36 4.4 <![CDATA[K 2+ Selectivity coefficient 3.95 4.6 4.8

Claims

1. A fully solid-state calcium ion selective electrode suitable for concrete, characterized in that, The device includes a wire (1), an electronic conductor (2), a Fe3O4@CNTs transconducting layer (3), a calcium ion selective membrane (4), a shell (5), and a fixing material (6). The wire (1), electronic conductor (2), Fe3O4@CNTs transconducting layer (3), and calcium ion selective membrane (4) are connected from top to bottom to form a whole and placed inside the shell (5). The upper part of the wire is located outside the shell. The upper part of the electronic conductor and the lower part of the wire are encapsulated with the shell using the fixing material (6). The lower end of the wire is connected to the upper end of the electronic conductor. The lower end of the electronic conductor is coated with Fe3O4@CNTs to form a Fe3O4@CNTs transconducting layer. The calcium ion selective membrane is loaded below the Fe3O4@CNTs transconducting layer. The calcium ion selective membrane is prepared by adding calcium ion carrier ETH5234, ion exchanger NaTFPB, polymer PVC matrix and plasticizer o-NPOE into a container, followed by adding redistilled THF, and stirring at room temperature until homogeneous to obtain a calcium ion selective membrane with uniform concentration.

2. The all-solid-state calcium ion selective electrode suitable for concrete according to claim 1, characterized in that, The preparation method of the Fe3O4@CNTs includes the following steps: (1) After dispersing CNTs in acid with ultrasonication, pour them into a reaction vessel, keep them at 55-65℃ for 1-2 hours, and let them cool naturally to room temperature to obtain mixture I; (2) After treating the mixture I obtained in step (1) with an ultrasonic generator for 1 hour, it is diluted and filtered multiple times with deionized water. When the pH value of the solution is between 6.5 and 7.5, it is centrifuged to separate the solid matter from the deionized water and then vacuum dried to obtain CNT. (3) Dissolve FeCl2·4H2O and SnCl4·5H2O in deionized water, then add the CNTs obtained in step (2), disperse ultrasonically for at least 10 min, and add NaOH solution dropwise under vigorous stirring to obtain mixture II; (4) Transfer the mixture II obtained in step (3) into a reaction vessel to react and obtain mixture III; (5) Centrifuge the mixture III obtained in step (4) using a centrifuge, collect the solid material, wash it multiple times with deionized water and vacuum dry it to obtain Fe3O4@CNT.

3. The all-solid-state calcium ion selective electrode suitable for concrete according to claim 2, characterized in that, The acid mentioned in step (1) is nitric acid or a mixed solution of nitric acid and sulfuric acid, wherein the concentration of the acid is 0.45 to 0.55 mol / L; the ultrasonic dispersion time is 3 to 5 hours. The centrifugation speed in step (2) is 7000-9000 r / min, and the vacuum drying temperature is 55-65℃; The concentration of the NaOH solution in step (3) is 2 mol / L, and the mass fractions of each raw material component are as follows: The above-mentioned NaOH mass fractions refer to the solute mass in the NaOH solution. Furthermore, the Fe / Sn molar ratio must be 2:1; In step (4), the reaction temperature is 230–245℃ and the reaction time is 18–30 h. In step (5), the centrifugation speed is 7000-9000 r / min and the centrifugation time is 10-15 min.

4. The all-solid-state calcium ion selective electrode suitable for concrete according to claim 1, characterized in that, The method for preparing the calcium ion selective membrane involves the following mass fractions of each raw material component:

5. A fully solid-state calcium ion selective electrode suitable for concrete according to any one of claims 1 to 4, characterized in that, The lower end of the wire is connected to the upper end of the electronic conductor by high-temperature welding or bonding with conductive adhesive, and the wire is a copper wire. The fixing material is epoxy resin; The electronic conductor is a copper rod electronic conductor, a pretreated copper rod electronic conductor, or a metal or glassy carbon electrode as the material of the electronic conductor. The outer shell is made of PC material and is tubular in shape.

6. A fully solid-state calcium ion selective electrode suitable for concrete according to any one of claims 1 to 4, characterized in that, The thickness of the calcium ion selective membrane is 30–50 μm; The Fe3O4@CNTs transduction layer has a thickness of 50–100 μm.

7. A fully solid-state calcium ion selective electrode suitable for concrete according to claim 5, characterized in that, The pretreated copper rod electronic conductor is pretreated by ultrasonic cleaning with acetone for 10-15 min, followed by ultrasonic cleaning with 0.1 mol / L dilute hydrochloric acid solution for 10-15 min, then ultrasonic cleaning with deionized water for 10-15 min, and finally drying.

8. A method for preparing an all-solid-state calcium ion selective electrode suitable for concrete according to any one of claims 1 to 7, characterized in that, Specifically, the following steps are included: (1) Connect the upper end of the electronic conductor to the lower end of the wire; (2) Add Fe3O4@CNTs to an organic solvent and disperse it ultrasonically to obtain a uniform mixture; then coat the mixture onto the lower end of the electronic conductor. After the organic solvent has completely evaporated, coat it again; repeat this process 2-3 times to obtain the Fe3O4@CNTs transconducting layer. The organic solvent mentioned in step (2) is a mixture of DOP and a 0.1% ethanol solution; The amounts of each component in step (2) are as follows: 20 parts by mass of Fe3O4@CNTs, and 1 part by mass of organic solvent; The ultrasonic dispersion time in step (2) is 30-40 min; (3) Load the calcium ion selective membrane onto the Fe3O4@CNTs transduction layer obtained in step (2); (4) Finally, the wires, electronic conductors, Fe3O4@CNTs transconducting layer and calcium ion selective film connected as a whole are placed into the shell. The upper part of the electronic conductor and above is fixed to the inner wall of the shell with a fixing material, and the upper part of the wire is exposed outside the shell, thus obtaining the all-solid calcium ion selective electrode.

9. A method for applying the all-solid-state calcium ion selective electrode for concrete as described in any one of claims 1 to 7, characterized in that, The all-solid-state calcium ion selective electrode is suitable for use in existing concrete buildings and new buildings.

10. The application method according to claim 9, characterized in that, When the all-solid-state calcium ion selective electrode is applied to existing concrete buildings, a hole is pre-drilled in the concrete to be tested, with the depth of the hole being the depth of the concrete to be tested. The all-solid-state calcium ion selective electrode is placed in the tube and fixed in a detachable manner. The bottom of the electrode shell is in contact with the bottom of the hole. In addition, a solid reference electrode is inserted to form a dual-electrode system, which can then be used to detect and monitor the calcium ion concentration in the concrete. When the all-solid-state calcium ion selective electrode is applied to new buildings, before concrete pouring, a tube of a certain length, made of materials such as stainless steel or PC, with a diameter slightly larger than the maximum diameter of the electrode, is pre-installed at the location to be tested, with the bottom ends of each tube being equidistant from each other, serving as a mold. The bottom of the tube is then plugged with an easily removable non-absorbent rod before concrete is poured. After construction is completed, the non-absorbent rod is removed from the tube, and the all-solid-state calcium ion selective electrode is placed inside the tube. The electrode is fixed in a detachable manner, with the bottom of the electrode in contact with the bottom of the hole, allowing for the detection and monitoring of calcium ion concentration in the concrete.

Images