A device and method for detecting metal ions in solution based on ice-water liquid-solid phase transition

Abstract

The present invention discloses a device and method for detecting metal ions in a solution based on an ice-water liquid-solid phase transition. The droplet shaping unit of the metal ion detection device is made of a transparent, low-temperature-resistant material and has a droplet-shaped cavity with an open bottom end. A refrigeration unit is detachably and sealedly connected to the bottom end of the droplet shaping unit and is used to cool the solution to be tested to produce a two-dimensional droplet-shaped slice of the solution to be tested. An image acquisition system is arranged horizontally relative to the droplet shaping unit and focuses on the droplet-shaped solution to be tested to record the ice-water liquid-solid phase transition process of the solution to be tested. An image analysis system is used to analyze the ice-water liquid-solid phase transition process of the solution to be tested obtained by the image acquisition system, obtain the ice-water liquid-solid phase transition characteristics, and infer the ion type or concentration of the solution to be tested based on the ice-water liquid-solid phase transition characteristics. The above-mentioned detection device has the characteristics of high detection efficiency, low cost, no pollution, strong environmental adaptability, and simple structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion detection in solution, and in particular relates to a device and method for detecting metal ions in solution based on ice-water liquid-solid phase transition. Background Art

[0002] Solutions generated by industrial wastewater discharge, mining, agricultural pollution, electronic waste dismantling, and domestic sewage may contain metal ions such as calcium, magnesium, lead, and cadmium. These ions, due to their difficulty in degradation and easy accumulation, have had a significant impact on the ecological environment, human health, industrial production, and other fields. In terms of the ecological environment, heavy metals such as lead and cadmium can cause soil degradation, acute poisoning of aquatic organisms, and loss of biodiversity; in terms of human health, long-term exposure to water containing mercury and arsenic can cause cancer, damage to the nervous system, and liver and kidney disease; in industrial production, metal ions can cause product defects, equipment corrosion, and even safety accidents, and incomplete industrial wastewater treatment is more likely to cause secondary pollution. Rapid detection and precise quantification of metal ions in solutions has become a core technical challenge in pollution control, disease prevention, and resource recycling.

[0003] Currently, metal ion detection primarily relies on atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), electrochemical analysis, and spectrophotometry. For example, Chinese invention patent application number 201510495087.9, entitled "Determination of Trace Copper, Zinc, and Iron in Mineral Water by Ion Pair-Cloud Point Extraction-Flame Atomic Absorption Spectrometry," utilizes the absorption of light of characteristic wavelengths by specific elements to detect metal ions. This method relies on large, precision instruments and suffers from high equipment costs, complex operational procedures, and long detection cycles. Chinese invention patent application number 201510076553.X, entitled "A Method for Detecting Trace Metal Particle Morphology in Flue Gas Based on Plasma Inductively Coupled Atomic Absorption Spectrometry," utilizes high-frequency inductive coupling to generate a high-temperature plasma to ionize the sample, followed by mass-to-charge ratio separation and detection by a mass spectrometer for qualitative and quantitative analysis of metal ions. However, this method also suffers from high equipment costs, complex maintenance, limited sample pretreatment and applicability, and limited portability. Chinese invention patent application number 202010389232.6, entitled "A composite electrode for heavy metal ion detection and its preparation method," prepares a composite electrode that can be used for electrochemical detection of heavy metal lead and cadmium ions and solutions containing heavy metal ions. However, this method has disadvantages such as sensitivity to the solution matrix and electrode contamination or passivation, resulting in insufficient stability. Chinese invention patent application number 202111611159.3, entitled "A method for detecting ferrous ions in water," uses spectrophotometry for ferrous ion detection. This method has relatively low accuracy and is susceptible to interference from coexisting substances. It also suffers from limited detection sensitivity and insufficient result stability.

[0004] The shortcomings of existing methods for detecting metal ions in solutions can be summarized as follows: (1) Existing atomic absorption spectrometry requires frequent replacement of element-specific light sources, making it impossible to achieve simultaneous detection of multiple elements. In addition, the detection sensitivity is significantly affected by matrix effects, and trace analysis relies on complex sample pretreatment. (2) The purchase and maintenance costs of inductively coupled plasma mass spectrometry equipment are high, and high-salt or highly soluble solid samples can easily lead to cone clogging. Isotope interference and memory effects require additional correction techniques to eliminate. (3) Electrochemical analysis is susceptible to interference from coexisting ions, and the electrode surface modification process is complex, resulting in poor long-term stability and insufficient repeatability. (4) The detection sensitivity of spectrophotometry is limited by the specificity of the color developer, and turbidity or coexisting coloring substances can easily introduce errors, and complex pretreatment steps are required. The above shortcomings have led to significant limitations in the detection efficiency, cost control, and field adaptability of existing methods. Summary of the Invention

[0005] In order to overcome the limitations of existing metal ion detection technology in solutions, the present invention provides a device and method for detecting metal ions in solutions based on ice-water liquid-solid phase transition. The detection device and method have the characteristics of high detection efficiency, low cost, pollution-free, strong environmental adaptability and simple structure. They effectively solve the problems of existing technologies in terms of efficiency, portability and economy, and provide a pollution-free and highly universal innovative solution for the detection of metal ions in solutions.

[0006] In order to achieve the above object, the present invention adopts the following specific technical solutions:

[0007] The present invention provides a device for detecting metal ions in a solution based on the liquid-solid phase transition of ice water. The device comprises a droplet shaping unit, a refrigeration unit, an image acquisition system, and an image analysis system. The droplet shaping unit is made of a transparent, low-temperature-resistant material and has a droplet-shaped cavity with an open bottom. The droplet-shaped cavity is used to accommodate a solution to be tested. The solution to be tested is a metal ion solution of unknown type and concentration.

[0008] The refrigeration unit is detachably and sealedly connected to the bottom end of the droplet shaping unit, and is used to cool the solution to be tested to produce a two-dimensional droplet-shaped slice of the solution to be tested;

[0009] The image acquisition system is arranged horizontally opposite to the droplet shaping unit and focuses on the droplet-shaped test solution to record the ice-water liquid-solid phase transition process of the test solution;

[0010] The image analysis system is connected to the image acquisition system signal, and is used to analyze the ice-water liquid-solid phase transition process of the test solution obtained by the image acquisition system, obtain the ice-water liquid-solid phase transition characteristics, and infer the ion type or concentration of the test solution based on the ice-water liquid-solid phase transition characteristics.

[0011] Furthermore, the image acquisition system is used to record in real time the growth process of dendrites in the recalescence stage and ice in the freezing stage during the ice-water liquid-solid phase transition process of the test solution.

[0012] Furthermore, the image analysis system calculates the average dendrite growth rate based on the final height of the dendrite and the dendrite growth time, and calculates the average freezing rate based on the final height of the ice and the time required for the test solution to completely solidify, and then infers the ion type or concentration of the test solution based on the average dendrite growth rate and the average freezing rate of the test solution.

[0013] Furthermore, the droplet shaping unit is composed of a first transparent acrylic plate, a polydimethylsiloxane interlayer and a second transparent acrylic plate which are sealed and connected in sequence;

[0014] The droplet-shaped cavity is provided in the polydimethylsiloxane interlayer;

[0015] The polydimethylsiloxane interlayer is provided with a communicating liquid injection channel at the top of the droplet-shaped cavity.

[0016] Furthermore, the refrigeration unit is a compression refrigeration device, an absorption refrigeration device or a semiconductor refrigeration device;

[0017] When the refrigeration unit is a semiconductor refrigeration device, it includes a semiconductor refrigeration sheet, a heat exchanger, a copper plate, a low-temperature constant temperature tank, a heat insulation material and a control unit;

[0018] The hot end of the semiconductor refrigeration chip is attached to the heat exchanger, and the cold end is attached to the copper plate for transferring heat; a refrigerant circulates between the heat exchanger and the low-temperature constant temperature bath; the control unit is connected to the semiconductor refrigeration chip and is used to control the temperature of the semiconductor refrigeration chip;

[0019] The top of the copper plate is inserted into the gap between the first transparent acrylic plate and the second transparent acrylic plate, and is in close contact with the polydimethylsiloxane interlayer to ensure that the solution to be tested does not leak; the outer side of the copper plate is affixed with the thermal insulation material to reduce cold loss.

[0020] Furthermore, it also includes a liquid injection system;

[0021] The liquid injection system is used to inject the solution to be tested into the droplet-shaped cavity of the droplet shaping unit through the liquid injection channel.

[0022] Furthermore, the injection system is a micro-syringe or a micro-injection pump;

[0023] The control unit is a digital thermostat;

[0024] The image acquisition system is a high-speed camera;

[0025] The image analysis system is a computer.

[0026] In addition, the present invention also provides a detection method using the above-mentioned metal ion detection device, which comprises the following steps:

[0027] The first step is to tightly connect the droplet shaping unit with the refrigeration unit;

[0028] The second step is to inject the test solution into the droplet shaping unit;

[0029] The third step is to adjust the image acquisition system so that it focuses on the droplet-shaped solution to be tested;

[0030] Step 4: Regulate the temperature of the refrigeration unit T n The temperature is lowered below the freezing point of the solution to be tested, causing the solution to undergo an ice-water liquid-solid phase transition;

[0031] Step 5: Calculate the dendrite growth model coefficients related to the type and concentration of metal ions x The specific value of is determined by the dendrite growth model coefficient under the condition of known ion species. x Estimate the concentration of the solution to be tested or calculate the dendrite growth model coefficient under the condition of known ion concentration. x Infer the ion species of the solution to be tested;

[0032] Step 6: Calculate the freezing model coefficients related to the type and concentration of metal ions g The specific value of is determined by the frozen model coefficient under the condition that the ion species are known. g Estimate the ion concentration of the solution to be tested or calculate the frozen model coefficient under the condition of known ion concentration g Infer the ion species of the solution to be tested;

[0033] The seventh step is to achieve mutual verification of the test results through collaborative analysis of the average dendrite growth rate and the average freezing rate.

[0034] Furthermore, in the second step, the solution to be tested is injected into the droplet shaping unit using a liquid injection system;

[0035] In the fifth step, the dendrite growth model coefficients are calculated x The specific process is:

[0036] The final height of the dendrites in the recalescence stage of the test solution was measured using an image analysis system. H d and dendrite growth time t d , the actual average growth rate of dendrites v d The calculation formula is:

[0037] v d = H d / t d (1);

[0038] Theoretical average dendrite growth rate The calculation formula is:

[0039] (2);

[0040] In the above formula, k i is the thermal conductivity of ice, r i is the density of ice, L is the latent heat of solidification phase change of the solution, u is the kinematic viscosity of the solution, c is the ice-water interfacial energy, A is the temperature gradient constant at the ice-water interface, T f is the solution solidification phase transition temperature, v is the solution flow rate;

[0041] Simplified theoretical average dendrite growth rate The calculation formula is:

[0042] (3);

[0043] In the above formula, x is the dendrite growth model coefficient, which is related to the ion species and concentration;

[0044] The actual average dendrite growth rate calculated by formula (1) is substituted into formula (3), and the dendrite growth model coefficient is obtained by fitting the actual average dendrite growth rate calculated using formula (3): x The specific value of .

[0045] Furthermore, in the sixth step, the frozen model coefficients are calculated g The specific process is:

[0046] Use the image analysis system to measure the final height of ice after the test solution is completely solidified H f and time required for complete solidification t f Calculate the average freezing rate and the actual average freezing rate v f The calculation formula is:

[0047] v f = H f / t f (4);

[0048] Theoretical average freezing rate The calculation formula is:

[0049] (5);

[0050] In the above formula, L w is the latent heat of solidification of water, C p is the specific heat capacity of water at constant pressure, g is the freezing model coefficient associated with ion species and concentration;

[0051] The actual average freezing rate calculated by formula (4) is substituted into formula (5), and the freezing model coefficient is obtained by fitting the calculated actual average freezing rate using formula (5): g The specific value of .

[0052] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0053] The above-described metal ion detection device and method is based on the liquid-solid phase transition of ice-water. It exploits the physical phenomenon of differences in the liquid-solid phase transition characteristics of different metal ion solutions to detect metal ions in the test solution. By controlling the temperature of a refrigeration unit to solidify the test solution, a droplet shaping unit, an image acquisition system, and an image analysis system are used to visualize the liquid-solid phase transition characteristics of the test solution and detect the metal ions. Compared with existing methods for detecting metal ions in solutions, this method, which utilizes the liquid-solid phase transition characteristics of ice-water solutions, offers simplicity, a wide range of applicability, high detection efficiency, low cost, no pollution, and strong environmental adaptability.

[0054] The material of the droplet shaping unit and the shape and volume of the droplet-shaped cavity inside it can be adjusted to obtain higher metal ion detection accuracy; the refrigeration temperature provided by the refrigeration unit can be adjusted to obtain higher metal ion detection efficiency; the droplet shaping unit and the refrigeration unit can be flexibly disassembled to achieve efficient and continuous detection of metal ions in multiple test solutions; the test solution has multiple ice-water liquid-solid phase transition characteristic parameters that can be used for ion detection, and the test results can be mutually verified through multi-parameter collaborative analysis, significantly improving the detection accuracy and reliability of the results. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Schematic diagram of the principle of the metal ion detection device of the present invention;

[0056] Figure 2 Schematic diagram of the liquid-solid phase transition process of a metal ion solution droplet into ice water;

[0057] Figure 3 is the relationship between the type and concentration of metal ions and the dendrite growth rate;

[0058] Figure 4 This is a graph showing the relationship between the type and concentration of metal ions and the freezing rate;

[0059] Figure 5 Schematic diagram of the specific structure of the metal ion detection device in Example 1 of the present invention;

[0060] Figure 6 Experimental photos of the final morphology of dendrites during the recalescence stage in MgCl2 solutions with different concentrations;

[0061] Figure 7is the relationship between the concentration of MgCl2 solution and the dendrite growth rate;

[0062] Figure 8 is the relationship between ion type and concentration and the mathematical model coefficient.

[0063] Among them, 1-test solution, 2-droplet shaping unit, 3-refrigeration unit, 4-liquid injection system, 5-image acquisition system, 6-image analysis system, 101-dendrite, 102-ice, 201-first layer of transparent acrylic plate, 202-second layer of transparent acrylic plate, 203-polydimethylsiloxane interlayer, 301-copper plate, 302-semiconductor refrigeration sheet, 303-control unit, 304-heat exchanger, 305-low-temperature constant temperature bath, 306-insulation material. DETAILED DESCRIPTION

[0064] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0065] The present invention aims to exploit the differences in the liquid-solid phase transition characteristics of different metal ion solutions, such as ice crystal growth rate and freezing rate, by inducing the phase transition using temperature-controlled equipment and monitoring the characteristic parameters. This allows for the detection of metal ions in solution based on a quantitative correlation model between the ion species and concentration and the phase transition characteristic parameters. Based on the liquid-solid phase transition characteristics of the target metal ion solution, the ion species and concentration are detected, achieving an integrated "sampling-detection-analysis" process.

[0066] Example 1

[0067] This embodiment provides a device for detecting metal ions in solution based on liquid-solid phase transition of ice water. Figure 1 This is a schematic diagram of the principle of the metal ion detection device. Figure 2 Schematic diagram of the liquid-solid phase transition process of a metal ion solution droplet into ice water. Figure 2 The figure shows the initial state, reheating stage, freezing stage and final state of the melt; the metal ion detection device includes a droplet shaping unit 2, a refrigeration unit 3, an image acquisition system 5 and an image analysis system 6; wherein:

[0068] The droplet shaping unit 2 is made of a transparent low-temperature resistant material and has a droplet-shaped cavity with an open bottom inside. The droplet-shaped cavity is used to accommodate the test solution 1; the test solution 1 is a metal ion solution of unknown type and concentration;

[0069] The refrigeration unit 3 is detachably and hermetically connected to the bottom end of the droplet shaping unit 2, so that the solution to be tested 1 in the droplet shaping device can be directly and closely contacted with the refrigeration unit 3, and is used to cool the solution to be tested 1 to produce a two-dimensional droplet-shaped slice of the solution to be tested 1; the refrigeration unit 3 is a compression refrigeration device, an absorption refrigeration device or a semiconductor refrigeration device.

[0070] Image acquisition system 5 is positioned horizontally opposite droplet shaping unit 2 and focuses on the droplet-shaped test solution 1 to record the ice-water liquid-to-solid phase transition of the test solution 1 in real time. Image acquisition system 5 also records the growth of dendrites 101 during the recalescence phase and ice 102 during the freezing phase of the test solution 1 during the ice-water liquid-to-solid phase transition. Image acquisition system 5 is a high-speed camera.

[0071] Image analysis system 6 is signal-connected to image acquisition system 5 and is used to analyze the ice-water liquid-to-solid phase transition process of test solution 1 obtained by image acquisition system 5, obtain the ice-water liquid-to-solid phase transition characteristics, and infer the ion species or concentration of test solution 1 based on the ice-water liquid-to-solid phase transition characteristics. Image analysis system 6 calculates the average dendrite growth rate based on the final height of dendrite 101 and the dendrite growth time, and calculates the average freezing rate based on the final height of ice 102 and the time required for complete solidification of test solution 1. Based on the average dendrite growth rate and average freezing rate of test solution 1, the ion species or concentration of test solution 1 are inferred. Image analysis system 6 is a computer.

[0072] In the above metal ion detection device, if Figure 5 As shown, the droplet shaping unit 2 is composed of a first transparent acrylic plate 201, a polydimethylsiloxane interlayer 203, and a second transparent acrylic plate 202, which are sealed and connected in sequence; a droplet-shaped cavity is provided in the polydimethylsiloxane interlayer 203; and a connected liquid injection channel is provided at the top of the droplet-shaped cavity in the polydimethylsiloxane interlayer 203.

[0073] like Figure 5 As shown, when the refrigeration unit 3 is a semiconductor refrigeration device, it includes a copper plate 301, a semiconductor refrigeration sheet 302, a control unit 303, a heat exchanger 304, a low-temperature constant temperature bath 305 and a thermal insulation material 306; the hot end of the semiconductor refrigeration sheet 302 is attached to the heat exchanger 304, and the cold end is attached to the copper plate 301 for transferring heat; a refrigerant circulates between the heat exchanger 304 and the low-temperature constant temperature bath 305; the control unit 303 is connected to the semiconductor refrigeration sheet 302 and is used to control the temperature of the semiconductor refrigeration sheet 302. The control unit 303 is a digital thermostat; the top end of the copper plate 301 is inserted into the gap between the first layer of transparent acrylic plate 201 and the second layer of transparent acrylic plate 202, and is in close contact with the polydimethylsiloxane interlayer 203 to ensure that the solution 1 to be tested will not leak; the outer side of the copper plate 301 is attached with a thermal insulation material 306 to reduce the loss of cooling capacity.

[0074] The metal ion detection device further includes a liquid injection system 4, which is used to inject a predetermined volume of the test solution 1 into the droplet-shaped cavity of the droplet shaping unit 2 through the liquid injection channel. The liquid injection system 4 is a micro-syringe or a micro-injection pump.

[0075] Example 2

[0076] This embodiment provides a detection method using a metal ion detection device according to the above embodiment, the detection method comprising the following steps:

[0077] The first step is to tightly connect the droplet shaping unit 2 with the refrigeration unit 3;

[0078] In the second step, a predetermined volume of the test solution 1 is injected into the droplet shaping unit 2 using the injection system 4;

[0079] The third step is to adjust the image acquisition system 5 so that it focuses on the droplet-shaped test solution 1;

[0080] Step 4: Regulate the temperature of refrigeration unit 3 T n The temperature is lowered below the freezing point of the test solution 1, so that the test solution 1 undergoes an ice-water liquid-solid phase transition;

[0081] Step 5: Use the image analysis system 6 to measure the final height of the dendrite 101 of the solution 1 under test during the recalescence stage. H d and dendrite growth time t d , the actual average growth rate of dendrites v d The calculation formula is:

[0082] v d = H d / t d (1);

[0083] Theoretical average dendrite growth rate The calculation formula is:

[0084] (2);

[0085] In the above formula, k i is the thermal conductivity of ice 102, r i is the density of ice 102, L is the latent heat of solidification phase change of the solution, u is the kinematic viscosity of the solution, c is the ice-water interfacial energy,A is the temperature gradient constant at the ice-water interface, T f is the solution solidification phase transition temperature, v is the solution flow rate;

[0086] Simplified theoretical average dendrite growth rate The calculation formula is:

[0087] (3);

[0088] In the above formula, x is the dendrite growth model coefficient, which is related to the ion species and concentration; Figure 3 is the relationship between the type and concentration of metal ions and the average growth rate of dendrites, where v d,0 is the ion concentration C The average growth rate of dendrites when 0 is 0. Solutions with different metal ion types and concentrations each correspond to a x value, and thus can be established x The relationship between the type and concentration of metal ions and the average growth rate of dendrites can be obtained through experiments.

[0089] The actual average dendrite growth rate calculated by formula (1) is substituted into formula (3), and the dendrite growth model coefficient is obtained by fitting the actual average dendrite growth rate calculated using formula (3): x The specific value of is determined by the dendrite growth model coefficient under the condition of known ion species. x Estimate the concentration of the solution 1 to be tested or calculate the dendrite growth model coefficient under the condition of known ion concentration. x Infer the ion species of the test solution 1;

[0090] Step 6: Use the image analysis system 6 to measure the final height of the ice 102 after the test solution 1 is completely solidified. H f and time required for complete solidification t f The average freezing rate is calculated and the actual average freezing rate is calculated as follows:

[0091] v f = H f / t f (4);

[0092] Theoretical average freezing rate The calculation formula is:

[0093] (5);

[0094] In the above formula, L w is the latent heat of solidification of water, C p is the specific heat capacity of water at constant pressure, g is the freezing model coefficient associated with ion species and concentration;

[0095] The actual average freezing rate calculated by formula (4) is substituted into formula (5), and the freezing model coefficient is obtained by fitting the calculated actual average freezing rate using formula (5): g The specific value of is determined by the frozen model coefficient under the condition that the ion species are known. g Estimate the ion concentration of the test solution 1 or calculate the frozen model coefficient under the condition of known ion concentration. g Infer the ion species of the test solution 1; Figure 4 is the relationship between the type and concentration of metal ions and the average freezing rate, where v f,0 is the ion concentration C The average freezing rate when 0 is 0. Solutions with different metal ion types and concentrations each correspond to a g value, and thus can be established g The relationship between the type and concentration of metal ions and the average freezing rate can be obtained through experiments.

[0096] The seventh step is to achieve mutual verification of the test results through collaborative analysis of the average dendrite growth rate and the average freezing rate.

[0097] Example 3

[0098] This embodiment provides a device for detecting metal ions in solution based on liquid-solid phase transition of ice water. Figure 5As shown, the solution to be tested 1 in the device is a MgCl2 ion solution of unknown concentration; the droplet shaping unit 2 is composed of a 5mm thick first transparent acrylic plate 201, a 5mm thick second transparent acrylic plate 202 and a 0.3mm thick polydimethylsiloxane interlayer 203 fixedly connected, and the first transparent acrylic plate 201, the second transparent acrylic plate 202 and the polydimethylsiloxane interlayer 203 can be fixedly connected by bonding or bolts and nuts; the polydimethylsiloxane interlayer 203 03 is provided with a liquid injection channel and a droplet-shaped cavity with a diameter of 2mm and a contact angle of 90°; the refrigeration unit 3 adopts a semiconductor refrigeration device, which includes a copper plate 301, a semiconductor refrigeration sheet 302, a control unit 303, a heat exchanger 304, and a low-temperature constant temperature bath 305; the specifications of the semiconductor refrigeration sheet 302 are 40mm×40mm×10mm, and the hot end of the semiconductor refrigeration sheet 302 is attached to the heat exchanger 304 with a specification of 40mm×40mm×20mm; the heat exchanger 304 A refrigerant circulates between the low-temperature constant temperature bath 305, and the heat exchanger 304 is cooled by the refrigerant. The semiconductor refrigeration sheet 302 is connected to the control unit 303. The control unit 303 is a digital thermostat for controlling the temperature of the semiconductor refrigeration sheet 302. The cold end of the semiconductor refrigeration sheet 302 is attached to a 0.3 mm thick copper plate 301 for heat transfer. The top of the copper plate 301 is inserted into the gap between the first layer of transparent acrylic plate 201 and the second layer of transparent acrylic plate 202 and is connected to the polydimethylsiloxane. The interlayer 203 is in close contact to ensure that the test solution 1 does not leak; the outer side of the copper plate 301 is affixed with an insulating material 306 to reduce the cold loss of the copper plate 301; the injection system 4 is a micro-injection system that injects 2 μL of the test solution 1 into the droplet-shaped cavity through the injection channel at the top of the polydimethylsiloxane interlayer 203; the image acquisition system 5 is a high-speed camera for capturing the ice-water phase transition process of the test solution 1; the image acquisition system 5 is connected to the image analysis system 6, which is a computer.

[0099] Example 4

[0100] The method for detecting metal ions using the metal ion detection device in the third embodiment includes the following steps:

[0101] In the first step, the copper plate 301 is inserted into the gap between the first transparent acrylic plate 201 and the second transparent acrylic plate 202 and is in close contact with the bottom end of the polydimethylsiloxane interlayer 203;

[0102] In the second step, 2 μL of the test solution 1 is injected into the droplet-shaped cavity in the polydimethylsiloxane interlayer 203 by the injection system 4;

[0103] The third step is to adjust the image acquisition system 5 so that it focuses on the droplet-shaped test solution 1;

[0104] Step 4: The control unit 303 is used to adjust the temperature of the semiconductor refrigeration chip 302 to -10°C, causing the solution to undergo a liquid-to-solid phase transition.

[0105] Step 5: Use the image analysis system 6 to measure the final height of the dendrites of the solution 1 under test during the recalescence stage. H d and dendrite growth time t d ;

[0106] The sixth step is to use the formula v d = H d / t d The calculated actual average dendrite growth rate is substituted into the formula In the paper, the actual average growth rate of dendrites is used instead of the theoretical average growth rate of dendrites. , calculate the coefficients related to ion concentration and type x , under the condition of known ion species, according to the coefficient x Estimate the concentration of test solution 1.

[0107] Figure 6 The final morphology of dendrites in the recalescence stage of MgCl2 solutions with different concentrations is shown in the experimental photos. The height and growth time of dendrite 101 are different under different ion concentrations. 2+ The relationship between ion concentration and dendrite growth rate is as follows Figure 7 As shown, Mg can be established 2+ Ion concentration and dendrite growth rate v d The relationship between them is:

[0108] (6);

[0109] In the above formula, C is the ion concentration in ppm; based on the actual average growth rate of dendrites, the Mg content in the test solution 1 can be detected according to the above formula. 2+ The concentration of ions.

[0110] Based on the dendrite growth rate results under multiple different metal ion types and concentrations, the coefficient related to the metal ion type and concentration can be obtained. x , and the relationship is:

[0111] (7);

[0112] like Figure 8 As shown, the dendrite growth rate under the coupling effect of ion species and concentration can be established.v d The relationship is:

[0113] (8);

[0114] In the above formula, C is the ion concentration in ppm; R is the ion radius, and its unit is pm (picometer). According to the above formula, the metal ion concentration in a solution with known metal ion type can be detected, and the metal ion type in a solution with known metal ion concentration can also be detected.

[0115] The above-described metal ion detection device and method is based on the liquid-solid phase transition of ice water. It utilizes the physical phenomenon of differences in the liquid-solid phase transition characteristics of different metal ion solutions to detect metal ions in a test solution 1. The test solution 1 is solidified by controlling the temperature of a refrigeration unit 3. The droplet shaping unit 2, image acquisition system 5, and image analysis system 6 enable visualization of the liquid-solid phase transition characteristics of the test solution 1 and detection of metal ions. Compared to existing methods for detecting metal ions in solutions, such as spectroscopy, electrochemistry, and chemical colorimetry, detecting metal ions using the liquid-solid phase transition characteristics of ice water offers simplicity, a wide range of applicability for ion types and concentrations, high detection efficiency, low cost, no pollution, and strong environmental adaptability.

[0116] The material of the droplet shaping unit 2 and the shape and volume of the droplet-shaped cavity inside it can be adjusted to obtain higher metal ion detection accuracy; the refrigeration temperature provided by the refrigeration unit 3 can be adjusted to obtain higher metal ion detection efficiency; the droplet shaping unit 2 and the refrigeration unit 3 can be flexibly disassembled to achieve efficient and continuous detection of metal ions in multiple test solutions 1; the test solution 1 has multiple ice-water liquid-solid phase transition characteristic parameters that can be used for ion detection, and the mutual verification of the test results is achieved through multi-parameter collaborative analysis, which significantly improves the detection accuracy and reliability of the results.

[0117] Obviously, those skilled in the art may make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A device for detecting metal ions in solution based on liquid-solid phase transition of ice water, characterized in that: It includes a droplet shaping unit, a refrigeration unit, an image acquisition system, and an image analysis system; The droplet shaping unit is made of a transparent low-temperature resistant material and has a droplet-shaped cavity with an open bottom inside. The droplet-shaped cavity is used to accommodate a solution to be tested. The solution to be tested is a metal ion solution of unknown type and concentration. The refrigeration unit is detachably and sealedly connected to the bottom end of the droplet shaping unit, and is used to cool the solution to be tested to produce a two-dimensional droplet-shaped slice of the solution to be tested; The image acquisition system is arranged horizontally opposite to the droplet shaping unit and focuses on the droplet-shaped test solution to record the ice-water liquid-solid phase transition process of the test solution; The image analysis system is connected to the image acquisition system signal, and is used to analyze the ice-water liquid-solid phase transition process of the test solution obtained by the image acquisition system, obtain the ice-water liquid-solid phase transition characteristics, and infer the ion type or concentration of the test solution based on the ice-water liquid-solid phase transition characteristics.

2. The metal ion detection device according to claim 1, wherein The image acquisition system is used to record in real time the growth process of dendrites in the recalescence stage and ice in the freezing stage during the ice-water liquid-solid phase transition process of the solution to be tested.

3. The metal ion detection device according to claim 2, wherein: The image analysis system calculates the average dendrite growth rate based on the final height of the dendrite and the dendrite growth time, and calculates the average freezing rate based on the final height of the ice and the time required for the test solution to completely solidify. The ion type or concentration of the test solution is then inferred based on the average dendrite growth rate and average freezing rate of the test solution.

4. The metal ion detection device according to claim 1, wherein The droplet shaping unit is composed of a first transparent acrylic plate, a polydimethylsiloxane interlayer and a second transparent acrylic plate which are sealed and connected in sequence; The droplet-shaped cavity is provided in the polydimethylsiloxane interlayer; The polydimethylsiloxane interlayer is provided with a communicating liquid injection channel at the top of the droplet-shaped cavity.

5. The metal ion detection device according to claim 4, wherein: The refrigeration unit is a compression refrigeration device, an absorption refrigeration device or a semiconductor refrigeration device; When the refrigeration unit is a semiconductor refrigeration device, it includes a semiconductor refrigeration sheet, a heat exchanger, a copper plate, a low-temperature constant temperature tank, a heat insulation material and a control unit; The hot end of the semiconductor refrigeration chip is attached to the heat exchanger, and the cold end is attached to the copper plate for transferring heat; a refrigerant circulates between the heat exchanger and the low-temperature constant temperature bath; the control unit is connected to the semiconductor refrigeration chip and is used to control the temperature of the semiconductor refrigeration chip; The top of the copper plate is inserted into the gap between the first transparent acrylic plate and the second transparent acrylic plate, and is in close contact with the polydimethylsiloxane interlayer to ensure that the solution to be tested does not leak; the outer side of the copper plate is affixed with the thermal insulation material to reduce cold loss.

6. The metal ion detection device according to claim 5, characterized in that: Also included is a fluid injection system; The liquid injection system is used to inject the solution to be tested into the droplet-shaped cavity of the droplet shaping unit through the liquid injection channel.

7. The metal ion detection device according to claim 6, wherein: The injection system is a micro syringe or a micro injection pump; The control unit is a digital thermostat; The image acquisition system is a high-speed camera; The image analysis system is a computer.

8. A detection method using the metal ion detection device according to any one of claims 1 to 7, characterized in that: The following steps are involved: The first step is to tightly connect the droplet shaping unit with the refrigeration unit; The second step is to inject the test solution into the droplet shaping unit; The third step is to adjust the image acquisition system so that it focuses on the droplet-shaped solution to be tested; Step 4: Regulate the temperature of the refrigeration unit T n The temperature is lowered below the freezing point of the solution to be tested, causing the solution to undergo an ice-water liquid-solid phase transition; Step 5: Calculate the dendrite growth model coefficients related to the type and concentration of metal ions ξ The specific value of is determined by the dendrite growth model coefficient under the condition of known ion species. ξ Estimate the concentration of the solution to be tested or calculate the dendrite growth model coefficient under the condition of known ion concentration. ξ Infer the ion species of the solution to be tested; Step 6: Calculate the freezing model coefficients related to the type and concentration of metal ions ζ The specific value of is determined by the frozen model coefficient under the condition that the ion species are known. ζ Estimate the ion concentration of the solution to be tested or calculate the frozen model coefficient under the condition of known ion concentration ζ Infer the ion species of the solution to be tested; The seventh step is to achieve mutual verification of the test results through collaborative analysis of the average dendrite growth rate and the average freezing rate.

9. The detection method according to claim 8, wherein In the second step, the solution to be tested is injected into the droplet shaping unit using a liquid injection system; In the fifth step, the dendrite growth model coefficients are calculated ξ The specific process is: The final height of the dendrites in the recalescence stage of the test solution was measured using an image analysis system. H d and dendrite growth time t d , the actual average growth rate of dendrites v d The calculation formula is: v d = H d / t d （1）； Theoretical average dendrite growth rate The calculation formula is: （2）； In the above formula, k i is the thermal conductivity of ice, ρ i is the density of ice, L is the latent heat of solidification phase change of the solution, υ is the kinematic viscosity of the solution, γ is the ice-water interfacial energy, A is the temperature gradient constant at the ice-water interface, T f is the solution solidification phase transition temperature, v is the solution flow rate; Simplified theoretical average dendrite growth rate The calculation formula is: （3）； In the above formula, ξ is the dendrite growth model coefficient, which is related to the ion species and concentration; The actual average dendrite growth rate calculated by formula (1) is substituted into formula (3), and the dendrite growth model coefficient is obtained by fitting the actual average dendrite growth rate calculated using formula (3): ξ The specific value of .

10. The detection method according to claim 9, wherein In the sixth step, the frozen model coefficients are calculated ζ The specific process is: Use the image analysis system to measure the final height of ice after the test solution is completely solidified H f and time required for complete solidification t f Calculate the average freezing rate and the actual average freezing rate v f The calculation formula is: v f = H f / t f （4）； Theoretical average freezing rate The calculation formula is: （5）； In the above formula, L w is the latent heat of solidification of water, C p is the specific heat capacity of water at constant pressure, ζ is the frozen model coefficient associated with ion species and concentration; The actual average freezing rate calculated by formula (4) is substituted into formula (5), and the freezing model coefficient is obtained by fitting the calculated actual average freezing rate using formula (5): ζ The specific value of .

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