Method and system for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH

Abstract

This application belongs to the technical field of water environment monitoring, and specifically discloses a method and system for integrally detecting total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH. The method for integrally detecting total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH includes: (1) sending the water sample to be detected into the digestion module, where cobalt-aluminum layered double hydroxide is provided; (2) sequentially adding a digestion solution and a buffer solution into the digestion module, mixing, and heating for digestion; (3) sending the digested solution to the total nitrogen colorimetric module for color development and testing the total nitrogen concentration value; meanwhile, sending the digested solution to the total phosphorus colorimetric module for color development and testing the total phosphorus concentration value. This application can significantly reduce the high energy consumption and strong corrosiveness defects of the traditional digestion process by constructing an adsorption-catalysis synergistic mechanism mediated by CoAl-LDH, realize the efficient integrated detection of total phosphorus and total nitrogen in water samples, and at the same time solve the problem of low conversion efficiency of nitrogen and phosphorus substances under medium-temperature conditions.

Description

Technical Field

[0001] This application belongs to the technical field of water environment monitoring, and particularly relates to a method and system for integrally detecting total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH. Background Art

[0002] Water environment monitoring is a core link in environmental protection and ecological governance. Among them, total nitrogen (TN) and total phosphorus (TP), as key indicators of water eutrophication, their accurate detection is of great significance for evaluating water quality, warning ecological risks, and formulating treatment strategies. Currently, TN / TP detection technologies are mainly divided into four categories: chemical digestion-spectrophotometry, chromatography, spectrometry, and electrochemistry. Among them, spectrophotometry based on chemical digestion is widely adopted by Chinese national standards (GB 11893-89-1989, HJ 636-2012) and international mainstream methods (such as EPA methods) due to its low cost and strong universality. However, traditional technologies face the following common challenges:

[0003] 1) High energy consumption: The national standard method relies on high-temperature and high-pressure digestion at 120°C - 150°C, with high energy consumption and high instrument operation risks.

[0004] 2) Risk of secondary pollution: The large use of strong acids (concentrated sulfuric acid, nitric acid) leads to high waste liquid treatment costs, and high-temperature digestion is prone to generate toxic gases such as nitrogen oxides.

[0005] 3) Interference from complex matrices: High-turbidity and high-chromaticity water samples require additional pretreatment, and the detection sensitivity (the TP detection limit is 0.02 mg / L) is difficult to meet the monitoring requirements of surface water Class I standard (TP ≤ 0.01 mg / L).

[0006] 4) Barriers to multi-target detection: TN / TP requires independent digestion processes, with low reuse rates of instruments and reagents and high comprehensive costs. Summary of the Invention

[0007] This application aims to solve at least one of the technical problems in the related technologies to some extent. For this purpose, the objective of this application is to propose a method and system for integrally detecting total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH. By constructing an adsorption-catalysis synergy mechanism mediated by CoAl-LDH, this application can significantly reduce the high energy consumption and strong corrosiveness defects of traditional digestion processes, realize the efficient integrated detection of total phosphorus and total nitrogen in water samples, and at the same time, this application has successfully overcome the technical bottleneck of low conversion efficiency of nitrogen and phosphorus substances under medium-temperature conditions.

[0008] In one aspect of this application, a method for integrally detecting total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH is proposed. According to the embodiments of this application, the method includes:

[0009] (1) sending a water sample to be tested to a digestion module, wherein the digestion module is provided with a cobalt-aluminum layered double hydroxide;

[0010] (2) adding digestion solution and buffer solution to the digestion module in sequence, mixing, and heating for digestion;

[0011] (3) The solution after decomposition is transferred to the total nitrogen colorimetric module for color development and the total nitrogen concentration is tested. At the same time, the solution after decomposition is transferred to the total phosphorus colorimetric module for color development and the total phosphorus concentration is tested.

[0012] The method for integrated detection of total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH according to the embodiment of the present application has the following advantages: 1) High-efficiency digestion at medium temperature: The traditional national standard method (HJ 636-2012, GB 11893-89-1989) requires digestion at 120°C high temperature and high pressure for 30 minutes, while the catalytic digestion method based on CoAl-LDH catalytic material in the present application only requires digestion at 60°C~70°C for 2min~30min to achieve complete mineralization of organic nitrogen and phosphorus substances, breaking through the bottleneck of high energy consumption and safety hazards of traditional high-temperature digestion, and significantly reducing detection energy consumption. 2) Improved digestion rate: The present application can accelerate the digestion process of pollutants through the synergistic catalytic system of LDH catalyst and buffer, and the catalytic efficiency is 2.3 times higher than that of traditional Fe-based catalysts. This synergistic mechanism can make the mineralization rate (i.e., digestion rate) of organic nitrogen and phosphorus reach more than 98% at 70°C. Taking sodium glycerophosphate as an example, the digestion rate of total phosphorus can reach 99.2%~100%, and taking glycine as an example, the digestion efficiency of total nitrogen can reach 98.7%~100%. 3) Green chemical process: This application uses a synergistic catalytic system of LDH catalyst and buffer to reduce the amount of acid and alkali in the buffer, while avoiding secondary pollution problems such as nitrogen oxide escape, significantly improving the safety and environmental protection of the operation. In addition, the life of the digestion module is extended, greatly reducing the overall equipment cost and operation and maintenance cost. Specifically, the alkalinity in the total nitrogen reaction system can be reduced, the service life of the digestion module can be extended, and the life of the digestion component can be extended from 6 months to 1-3 years. 4) Integrated detection of total phosphorus and total nitrogen: The traditional method requires the digestion of TN / TP samples separately (each requires an independent process), while this application uses the adsorption-catalytic synergistic effect of LDH to achieve integrated digestion of total phosphorus and total nitrogen, synchronously release nitrate and phosphate, and achieve integrated detection of total phosphorus and total nitrogen.

[0013] In some embodiments of the present application, in step (1), the Co in the cobalt-aluminum layered double hydroxide 2+ With Al 3 + The atomic ratio is (2~3):1, and the interlayer Cl - intercalation; and / or, the digestion module is coated with a membrane layer comprising the cobalt aluminum layered double hydroxide.

[0014] In some embodiments of the present application, in step (1), the method for preparing the cobalt-aluminum layered double hydroxide includes: dissolving aluminum chloride and cobalt chloride in a hydrochloric acid solution, where the atomic ratio of Co 2+ to Al 3+ is (2-3):1 to obtain solution A; mixing an ammonia water solution and a saturated ammonium chloride solution, adjusting the pH value to 11.8-12.2 to obtain solution B; while stirring solution B, dropping solution A into solution B and adjusting the pH value of the reaction system to remain at 11.8-12.2 with ammonia water; aging the reaction system; washing and drying the precipitate formed in the reaction system to obtain the cobalt-aluminum layered double hydroxide.

[0015] In some embodiments of the present application, in step (1), based on 10 mL of the water sample to be detected, the mass of the cobalt-aluminum layered double hydroxide in the digestion module is 0.006 g to 0.1 g.

[0016] In some embodiments of the present application, in step (2), the digestion solution is a persulfate solution with a concentration of 40 g / L to 50 g / L; and / or, the buffer solution is an aqueous solution containing sulfuric acid and sulfate, the pH value of the buffer solution is 2.4-2.6, and the concentration of the sulfate in the buffer solution is 0.09 mol / L to 0.11 mol / L.

[0017] In some embodiments of the present application, in step (2), based on 10 mL of the water sample to be detected, the dosage of the digestion solution is 1.5 mL to 2.5 mL, and the dosage of the buffer solution is 0.8 mL to 1.2 mL.

[0018] In some embodiments of the present application, in step (2), the temperature of the heating digestion is 60°C to 70°C, and the time of the heating digestion is 2 min to 30 min.

[0019] In some embodiments of the present application, in step (3), transfer the solution after digestion to the total phosphorus colorimetric module, add a total phosphorus color reagent and a total phosphorus reducing agent for color development, and test the total phosphorus concentration value.

[0020] In some embodiments of the present application, the total phosphorus color reagent is an aqueous solution containing sulfuric acid, ammonium molybdate, and potassium antimonyl tartrate. The concentration of sulfuric acid in the total phosphorus color reagent is 0.45 mol / L to 0.55 mol / L, the mass fraction of ammonium molybdate in the total phosphorus color reagent is 1% to 3%, and the mass fraction of potassium antimonyl tartrate in the total phosphorus color reagent is 0.25% to 0.4%; and / or, the total phosphorus reducing agent is an ascorbic acid solution with a concentration of 10 g / L to 100 g / L.

[0021] In the second aspect of the present application, the present application proposes a system for implementing the above-described method for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH. According to an embodiment of the present application, the above system includes: a digestion module, a metering module, a total nitrogen colorimetric module, a total phosphorus colorimetric module, and a multi-way drain valve. A cobalt-aluminum layered double hydroxide is provided in the digestion module, and a plurality of valves are provided on the multi-way drain valve; the digestion module is connected to the metering module through the valves on the multi-way drain valve, the total nitrogen colorimetric module is connected to the metering module through the valves on the multi-way drain valve, and the total phosphorus colorimetric module is connected to the metering module through the valves on the multi-way drain valve.

[0022] The system for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH according to an embodiment of the present application has the following advantages: 1) Medium-temperature and high-efficiency digestion: The traditional national standard methods (HJ 636-2012, GB 11893-89-1989) need to carry out digestion for 30 minutes under high temperature and high pressure conditions of 120 °C, while the catalytic digestion system of the present application based on CoAl-LDH catalytic material only needs to carry out digestion for 2 minutes to 30 minutes under medium temperature conditions of 60 °C to 70 °C to achieve complete mineralization of organic nitrogen and phosphorus substances, breaking through the bottleneck of high energy consumption and safety hazards of traditional high-temperature digestion, and significantly reducing the detection energy consumption. 2) Improved digestion rate: The system of the present application can accelerate the digestion process of pollutants through the synergistic catalytic system of LDH catalyst and buffer solution, and the catalytic efficiency is 2.3 times higher than that of traditional Fe-based catalysts. This synergistic mechanism can make the mineralization rate (i.e., digestion rate) of organic nitrogen and phosphorus reach more than 98% at 70 °C. Taking sodium glycerophosphate as an example for total phosphorus, its digestion rate can reach 99.2% to 100%, and taking glycine as an example for total nitrogen, its digestion efficiency can reach 98.7% to 100%. 3) Green chemical process: The system of the present application can reduce the usage of acids and alkalis in the buffer solution through the synergistic catalytic system of LDH catalyst and buffer solution, and at the same time avoid secondary pollution problems such as the escape of nitrogen oxides, significantly improving the safety and environmental protection of operation. In addition, the service life of the digestion module is extended, and the overall equipment cost and operation and maintenance cost are greatly reduced. Specifically, the alkalinity in the total nitrogen reaction system can be reduced, and the service life of the digestion module can be extended. The service life of the digestion component is extended from 6 months to 1 to 3 years. 4) Integrated detection of total phosphorus and total nitrogen: The traditional method needs to digest TN / TP samples separately (each requires an independent process), while the system of the present application utilizes the adsorption-catalytic synergistic effect of LDH to achieve integrated digestion of total phosphorus and total nitrogen, synchronously release nitrate and phosphate, and at the same time can achieve integrated detection of total phosphorus and total nitrogen.

[0023] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Description of the Drawings

[0024] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:

[0025] Figure 1 is a schematic flow chart of a method for integrated catalytic digestion and detection of total nitrogen and total phosphorus based on CoAl-LDH in some embodiments of the present application;

[0026] Figure 2 is a schematic structural diagram of a system for integrated catalytic digestion and detection of total nitrogen and total phosphorus based on CoAl-LDH in some embodiments of the present application;

[0027] Figure 3 is a scanning electron microscope (SEM) image of the CoAl-LDH material in Embodiment 1 of the present application, where Figure 3 a in is the scanning electron microscope (SEM) image at a magnification of 10,000, Figure 3 b in is the scanning electron microscope (SEM) image at a magnification of 50,000, Figure 3 c in is the scanning electron microscope (SEM) image at a magnification of 100,000;

[0028] Figure 4 is a transmission electron microscope (TEM) image of the CoAl-LDH material in Embodiment 1 of the present application, where Figure 4 a in is the transmission electron microscope (TEM) image at a magnification of 200,000, Figure 4 b in is the transmission electron microscope (TEM) image at a magnification of 500,000.

[0029] Reference numerals:

[0030] 100 - digestion module, 200 - metering module, 300 - total phosphorus colorimetric module, 400 - total nitrogen colorimetric module, 500 - multi-way drain valve, 501 - first valve, 502 - second valve, 503 - third valve, 504 - fourth valve, 505 - fifth valve, 506 - sixth valve, 507 - seventh valve, 508 - eighth valve, 509 - ninth valve, 510 - tenth valve, 511 - eleventh valve, 512 - twelfth valve, 600 - liquid stop valve. Detailed Description of the Embodiments

[0031] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and should not be construed as limiting the present application.

[0032] The present application was proposed by the inventors based on the following problems:

[0033] The inventors have found through research that layered double hydroxide (LDH) materials have adjustable lamellar composition, high specific surface area, and adsorption-catalysis synergistic effects. LDH materials can enrich pollutants through interlayer anion exchange and activate oxidants (such as persulfate) using surface active sites to achieve efficient mineralization of organic matter under low-temperature conditions.

[0034] Existing research mostly focuses on the catalytic mechanisms of single pollutants (TN or TP), lacking a systematic solution for multi-target synchronous detection, and industrialization issues such as material stability and cost controllability have not been fully resolved.

[0035] In response to the above industry pain points, this application innovatively develops a medium-temperature catalytic digestion method based on CoAl-LDH, achieving integrated and efficient detection of total phosphorus and total nitrogen through material design, process optimization, and integration of detection methods.

[0036] In view of this, in one aspect of this application, this application proposes a method for integrated detection of total nitrogen and total phosphorus by medium-temperature catalytic digestion based on CoAl-LDH. According to the embodiments of this application, with reference to the attached Figure 1 , the method includes: S100: Sending the water sample to be detected to the digestion module, where cobalt-aluminum layered double hydroxide is provided; S200: Sequentially adding a digestion solution and a buffer solution to the digestion module, mixing, and heating for digestion; S300: Taking the digested solution to the total nitrogen colorimetric module for color development and testing the total nitrogen concentration value; at the same time, taking the digested solution to the total phosphorus colorimetric module for color development and testing the total phosphorus concentration value.

[0037] The method for integrated detection of total nitrogen and total phosphorus by medium-temperature catalytic digestion based on CoAl-LDH according to the embodiments of this application constructs an adsorption-catalysis synergistic mechanism mediated by CoAl-LDH, significantly reducing the high energy consumption and strong corrosiveness defects of traditional digestion processes, and can achieve integrated and efficient detection of total phosphorus and total nitrogen in water samples. This technical solution successfully overcomes the technical bottleneck of low conversion efficiency of nitrogen and phosphorus substances under medium-temperature conditions, providing a new solution for field water quality monitoring.

[0038] Specifically, this application is based on the lamellar metal coordination regulation technology, and precisely designs a two-dimensional hexagonal sheet-like structure CoAl-LDH material with a Co / Al atomic ratio of (2~3):1 through the coprecipitation method. The Cl - intercalation between its layers and surface hydroxyl groups form Brønsted acid active sites, which can break through the bottleneck of insufficient medium-temperature catalytic activity. This material realizes the adsorption-catalysis synergistic effect through the charge balance of Co 2+ / Al 3+ and anion regulation: The Cl -Enrich nitrogen / phosphorus-containing organic matter through electrostatic action, and activate persulfate with surface hydroxyl groups to generate high-concentration SO4 - · and ·OH free radicals (the concentration of which can be increased by about 4.8 times). At the same time, Co 2+ / Co 3+ promotes the cleavage of chemical bonds and dehydrogenation reactions in pollutant molecules, thus accelerating the pollutant digestion process, and the catalytic efficiency is increased by 2.3 times compared with traditional Fe-based catalysts. This synergistic mechanism can achieve an organic nitrogen and phosphorus mineralization rate (i.e., digestion rate) of over 98% at 70°C (traditionally ≥120°C), significantly reducing energy consumption.

[0039] Compared with the prior art, this method has the following advantages:

[0040] 1) Medium-temperature and high-efficiency digestion: The traditional national standard methods (HJ 636-2012, GB 11893-89-1989) need to carry out digestion for 30 minutes under high temperature and high pressure conditions of 120°C. However, the catalytic digestion method based on CoAl-LDH catalytic material in this application only needs to be digested for 2-30 minutes under medium temperature conditions of 60°C - 70°C to achieve complete mineralization of organic nitrogen and phosphorus substances, breaking through the bottleneck of high energy consumption and safety hazards of traditional high-temperature digestion, and significantly reducing the detection energy consumption.

[0041] 2) Improved digestion rate: Through the synergistic catalytic system of LDH catalyst and buffer solution in this application, the pollutant digestion process can be accelerated, and the catalytic efficiency is increased by 2.3 times compared with traditional Fe-based catalysts. This synergistic mechanism can make the organic nitrogen and phosphorus mineralization rate (i.e., digestion rate) reach over 98% at 70°C. Taking sodium glycerophosphate as an example for total phosphorus, its digestion rate can reach 99.2% - 100%, and taking glycine as an example for total nitrogen, its digestion efficiency can reach 98.7% - 100%.

[0042] 3) Green chemical process: Through the synergistic catalytic system of LDH catalyst and buffer solution in this application, the usage of acids and bases in the buffer solution can be reduced, and at the same time, secondary pollution problems such as the escape of nitrogen oxides can be avoided, significantly improving the safety and environmental protection of the operation. In addition, the service life of the digestion module is extended, greatly reducing the overall equipment cost and operation and maintenance cost. Specifically, the alkalinity in the total nitrogen reaction system can be reduced, and the service life of the digestion module can be extended. The service life of the digestion component is extended from 6 months to 1 - 3 years.

[0043] 4) Integrated detection of total phosphorus and total nitrogen: Traditional methods need to digest TN / TP samples separately (each requires an independent process), while this application utilizes the adsorption-catalytic synergistic effect of LDH to achieve integrated digestion of total phosphorus and total nitrogen, synchronously releasing nitrate and phosphate, and at the same time can achieve integrated detection of total phosphorus and total nitrogen.

[0044] The following is a detailed description of the method for integrated detection of total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH proposed in this application:

[0045] Specifically, referring to the attached Figure 1 , the method for integrated catalytic digestion and detection of total nitrogen and total phosphorus based on CoAl-LDH includes the following steps:

[0046] S100: Send the water sample to be detected into the digestion module, and cobalt-aluminum layered double hydroxide is provided in the digestion module;

[0047] In this step, the water sample to be detected is sent into the digestion module, and cobalt-aluminum layered double hydroxide is provided in the digestion module. The water sample to be detected may contain phosphorus-containing substances (such as sodium glycerophosphate) and nitrogen-containing substances (such as glycine).

[0048] According to some specific embodiments of the present application, the Co in the above cobalt-aluminum layered double hydroxide 2+ and Al 3+ have an atomic ratio of (2-3):1, for example, it can be 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, etc., and Cl is intercalated between layers - .

[0049] According to still some specific embodiments of the present application, the preparation method of the above cobalt-aluminum layered double hydroxide includes:

[0050] Dissolve aluminum chloride (AlCl3) and cobalt chloride (CoCl2) in dilute hydrochloric acid solution, where the atomic ratio of Co 2+ and Al 3+ is (2-3):1 (for example, it can be 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, etc.) to obtain solution A;

[0051] Mix ammonia water (NH4OH) solution and saturated ammonium chloride (NH4Cl) solution, and adjust the pH value to 11.8-12.2 (for example, it can be 11.8, 11.9, 12, 12.1, 12.2) to obtain solution B;

[0052] While vigorously stirring solution B, slowly drop solution A into solution B through a peristaltic pump, and adjust the pH value of the reaction system with ammonia water to maintain it at 11.8-12.2 (for example, it can be 11.8, 11.9, 12, 12.1, 12.2);

[0053] After all of solution A is added, age the above reaction system. As some specific embodiments, it can be aged at 65°C-75°C (for example, it can be 65°C, 68°C, 70°C, 72°C, 75°C, etc.) for 24±1 h;

[0054] The precipitate formed in the reaction system was washed and dried to obtain cobalt-aluminum layered double hydroxide. As some specific embodiments, the precipitate formed in the reaction system was washed with deionized water 3 to 5 times, then washed with ethanol 1 to 2 times, and finally, the washed precipitate was dried in a vacuum drying oven at 65 °C to 75 °C.

[0055] Characterized by scanning electron microscopy SEM (as shown in the appendix Figure 3 shown) and transmission electron microscopy TEM (as shown in the appendix Figure 4 shown), the above cobalt-aluminum layered double hydroxide exhibits a typical layered stacking morphology, and the layer spacing is about 0.76 nm. When it is applied to the total phosphorus and total nitrogen digestion reaction, during the digestion process, LDH improves the mineralization efficiency through three paths: ① Cl in the interlayer domain - adsorbs and enriches nitrogen / phosphorus-containing organic matter through electrostatic interaction; ② surface hydroxyl groups activate persulfate to generate high-concentration SO4 - · and ·OH free radicals (EPR confirmed that the free radical concentration increased by 4.8 times); ③ Co 2+ / Co 3+ redox pair promotes electron transfer, which can accelerate the dehydrogenation and bond-breaking processes of pollutant molecules, and the catalytic efficiency is 2.3 times higher than that of traditional Fe-based catalysts.

[0056] According to some other specific embodiments of the present application, a film layer containing cobalt-aluminum layered double hydroxide is coated in the digestion module. Thus, the water sample to be detected can be effectively digested under the catalytic action of the above cobalt-aluminum layered double hydroxide in cooperation with the digestion solution and the buffer solution.

[0057] According to some other specific embodiments of the present application, based on 10 mL of the water sample to be detected, the mass of cobalt-aluminum layered double hydroxide in the digestion module is 0.006 g to 0.1 g, for example, it can be 0.006 g, 0.01 g, 0.02 g, 0.05 g, 0.08 g, 0.1 g, etc. Thus, it can ensure the complete digestion of nitrogen and phosphorus substances.

[0058] S200: Add the digestion solution and the buffer solution to the digestion module in sequence, mix, and heat for digestion;

[0059] In this step, add the digestion solution and the buffer solution to the digestion module in sequence, mix evenly, and heat for digestion.

[0060] According to some other specific embodiments of the present application, the above digestion solution is a persulfate (such as K2S2O8) solution with a concentration of 40 g / L to 50 g / L, for example, it can be 40 g / L, 42 g / L, 44 g / L, 46 g / L, 48 g / L, 50 g / L, etc. Thus, the above digestion solution can effectively achieve the digestion of nitrogen and phosphorus substances.

[0061] According to some further specific embodiments of the present application, the buffer solution is an aqueous solution containing sulfuric acid and sulfate. The pH value of the buffer solution is 2.4 - 2.6, for example, it can be 2.4, 2.5, 2.6, etc. The concentration of sulfate (such as K2SO4) in the buffer solution is 0.09 mol / L - 0.11 mol / L, for example, it can be 0.09 mol / L, 0.1 mol / L, 0.11 mol / L, etc. Through the synergistic catalytic system of the LDH catalyst and the above buffer solution, the present application can reduce the usage of acids and bases in the buffer solution, and at the same time avoid secondary pollution problems such as the escape of nitrogen oxides, significantly improving the safety and environmental protection of the operation.

[0062] According to some further specific embodiments of the present application, based on 10 mL of the water sample to be detected, the dosage of the digestion solution is 1.5 mL - 2.5 mL (for example, it can be 1.5 mL, 1.8 mL, 2 mL, 2.2 mL, 2.5 mL, etc.), and the dosage of the buffer solution is 0.8 mL - 1.2 mL (for example, it can be 0.8 mL, 0.9 mL, 1.0 mL, 1.1 mL, 1.2 mL, etc.). Thus, the complete digestion of nitrogen and phosphorus substances can be effectively achieved.

[0063] According to some further specific embodiments of the present application, the temperature of the above heating digestion is 60°C - 70°C, for example, it can be 60°C, 62°C, 64°C, 65°C, 66°C, 68°C, 70°C, etc., and the heating digestion time is 2 min - 30 min, for example, it can be 2 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, etc. Thus, by limiting the temperature and time of the above heating digestion within the above range, the complete digestion of nitrogen and phosphorus substances in the water sample to be detected can be achieved. The traditional national standard methods (HJ636 - 2012, GB 11893 - 89 - 1989) need to carry out digestion for 30 min under high temperature and high pressure conditions of 120°C, while the catalytic digestion method based on the CoAl - LDH catalytic material of the present application only needs to carry out digestion for 2 min - 30 min under medium temperature conditions of 60°C - 70°C to achieve the complete mineralization of organic nitrogen and phosphorus substances, breaking through the bottleneck of high energy consumption and safety hazards of traditional high - temperature digestion, and significantly reducing the detection energy consumption.

[0064] S300: Transfer the digested solution to the total nitrogen colorimetric module for color development and test the total nitrogen concentration value; at the same time, transfer the digested solution to the total phosphorus colorimetric module for color development and test the total phosphorus concentration value.

[0065] In this step, transfer the digested solution to the total nitrogen colorimetric module for color development and test the total nitrogen concentration value; at the same time, transfer the digested solution to the total phosphorus colorimetric module, add the total phosphorus color - developing agent and the total phosphorus reducing agent, carry out color development for 30 s - 5 min, and test the total phosphorus concentration value.

[0066] According to some further specific embodiments of the present application, the total phosphorus chromogenic reagent is an aqueous solution containing sulfuric acid, ammonium molybdate and potassium antimonyl tartrate. The concentration of sulfuric acid in the total phosphorus chromogenic reagent is 0.45 mol / L to 0.55 mol / L (for example, it can be 0.45 mol / L, 0.47 mol / L, 0.5 mol / L, 0.52 mol / L, 0.55 mol / L, etc.), the mass fraction of ammonium molybdate in the total phosphorus chromogenic reagent is 1% to 3% (for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, etc.), and the mass fraction of potassium antimonyl tartrate in the total phosphorus chromogenic reagent is 0.25% to 0.4% (for example, it can be 0.25%, 0.3%, 0.35%, 0.4%, etc.). The present application adopts the molybdenum-antimony-ascorbic acid chromogenic system of H2SO4 + ammonium molybdate + potassium antimonyl tartrate, which can improve the detection sensitivity of total phosphorus to 0.01 mg / L (RSD < 1.5%), and can achieve accurate detection of class I water in lakes and reservoirs.

[0067] As a specific embodiment, the preparation method of the above total phosphorus chromogenic reagent includes: ① Measure about 500 mL of deionized water and pour it into a 1 L beaker; slowly pour 27.2 mL of concentrated sulfuric acid along the wall of the beaker; stir and cool to room temperature, transfer it to a 1 L volumetric flask, make up the volume to the calibration line, and shake well for standby. ② Weigh 10 g of ammonium molybdate in a beaker; add about 500 mL of 0.5 mol / L H2SO4, stir until completely dissolved (if the dissolution is slow, it can be slightly heated to 60 °C), and then add 2.7 g of potassium antimonyl tartrate and stir until completely dissolved; ③ Transfer the mixed solution to a 1 L volumetric flask, and make up the volume to the calibration line with 0.5 mol / L H2SO4, and shake well.

[0068] According to some further specific embodiments of the present application, the total phosphorus reducing agent is an ascorbic acid solution with a concentration of 10 g / L to 100 g / L (for example, it can be 10 g / L, 20 g / L, 40 g / L, 60 g / L, 80 g / L, 100 g / L, etc.).

[0069] In the second aspect of the present application, the present application proposes a system for implementing the method for catalytic digestion and integrated detection of total nitrogen and total phosphorus based on CoAl-LDH in the above embodiments. According to the embodiments of the present application, referring to the attached Figure 2 , the above system includes: a digestion module 100, a metering module 200, a total nitrogen colorimetric module 400, a total phosphorus colorimetric module 300 and a multi-way discharge valve 500. A cobalt-aluminum layered double hydroxide is provided in the digestion module 100, and a plurality of valves are provided on the multi-way discharge valve 500; the digestion module 100 is connected to the metering module 200 through the valves on the multi-way discharge valve 500, the total nitrogen colorimetric module 400 is connected to the metering module 200 through the valves on the multi-way discharge valve 500, and the total phosphorus colorimetric module 300 is connected to the metering module 200 through the valves on the multi-way discharge valve 500.

[0070] Specifically, referring to the attached Figure 2 As shown in Figure 2 , the multi-way drain valve 500 includes a first valve 501 communicating with the digestion module 100, a second valve 502 communicating with the total phosphorus colorimetric module 300, a third valve 503 communicating with the total nitrogen colorimetric module 400, a fourth valve 504 communicating with the digestion solution, a fifth valve 505 communicating with the regenerant, a sixth valve 506 communicating with the buffer solution, a seventh valve 507 communicating with the total phosphorus chromogenic agent, an eighth valve 508 communicating with the total phosphorus reducing agent, a ninth valve 509 communicating with the total phosphorus and total nitrogen mixed standard solution, a tenth valve 510 communicating with the water sample to be tested, an eleventh valve 511 communicating with pure water, and a twelfth valve 512 for backup. Each valve is connected to a different liquid or module. By rotating the multi-way drain valve 500, different channels can be selected for operation.

[0071] The specific operation process is as follows:

[0072] 1) Take the water sample to be tested: Open the tenth valve 510, and the metering module 200 accurately takes a preset volume of the water sample to be tested. Close the tenth valve 510, open the first valve 501, transfer the water sample to be tested to the digestion module 100 (coated with an LDH film and containing CoAl-LDH material), and close the first valve 501.

[0073] 2) Take the digestion solution: Open the fourth valve 504, and the metering module 200 accurately takes a preset volume of the digestion solution. Close the fourth valve 504, open the first valve 501, transfer the digestion solution to the digestion module 100, and close the first valve 501.

[0074] 3) Take the buffer solution: Open the sixth valve 506, and the metering module 200 accurately takes a preset volume of the buffer solution. Close the sixth valve 506, open the first valve 501, transfer the buffer solution to the digestion module 100, and close the first valve 501.

[0075] 4) Heat digestion: Heat the digestion module 100 to 60°C - 70°C for digestion for 2 min - 30 min, and then cool down.

[0076] 5) Total nitrogen test: Open the first valve 501, and the metering module 200 accurately takes a preset volume of the digested solution. Close the first valve 501; open the third valve 503, transfer the digested solution to the total nitrogen colorimetric module 400, and close the third valve 503; develop color and test the total nitrogen concentration value.

[0077] 6) Total phosphorus test: Open the first valve 501, and the metering module 200 accurately takes a preset volume of the digested solution. Close the first valve 501, open the second valve 502, transfer the digested solution to the total phosphorus colorimetric module 300, and close the second valve 502; Open the seventh valve 507, and the metering module 200 accurately takes a preset volume of the total phosphorus color developing agent. Close the seventh valve 507, open the second valve 502, transfer the total phosphorus color developing agent to the total phosphorus colorimetric module 300, and close the second valve 502; Open the eighth valve 508, and the metering module 200 accurately takes a preset volume of the total phosphorus reducing agent. Close the eighth valve 508, open the second valve 502, transfer the total phosphorus reducing agent to the total phosphorus colorimetric module 300, and close the second valve 502; Conduct color development and test the total phosphorus concentration value.

[0078] 7) Drain the waste liquid from the digestion module 100 (this step can be carried out simultaneously with step 6) total phosphorus color development step): Open the first valve 501, the metering module 200 sucks the waste liquid remaining in the digestion module 100, close the first valve 501, open the stop valve 600, and drain the waste liquid in the digestion module 100.

[0079] 8) Catalyst activation and regeneration: Open the fifth valve 505, and the metering module 200 accurately takes a preset volume of the regenerant (for example, it can be a 4 - 15 g / L NaOH solution). Close the fifth valve 505, open the first valve 501, transfer the regenerant to the digestion module 100, and close the first valve 501; Open the eleventh valve 511, and the metering module 200 accurately takes a preset volume of pure water. Close the eleventh valve 511, open the first valve 501, transfer the pure water to the digestion module 100, and close the first valve 501 for activation and regeneration. The catalyst CoAl-LDH material can be regenerated by alkali activation, so as to realize the long-term stability detection of total phosphorus and total nitrogen.

[0080] 9) Drain the waste liquid from the total nitrogen and total phosphorus colorimetric modules (this step can be carried out simultaneously with step 8) activation and regeneration step): Open the third valve 503, the metering module 200 sucks the waste liquid remaining in the total nitrogen colorimetric module 400, close the third valve 503, open the stop valve 600, and drain the waste liquid in the total nitrogen colorimetric module 400; Open the second valve 502, the metering module 200 sucks the waste liquid remaining in the total phosphorus colorimetric module 300, close the second valve 502, open the stop valve 600, and drain the waste liquid in the total phosphorus colorimetric module.

[0081] 10) Drain the waste liquid from the digestion module 100: Open the first valve 501, the metering module 200 sucks the waste liquid remaining in the digestion module 100, close the first valve 501, open the stop valve 600, and drain the waste liquid in the digestion module 100.

[0082] 11) Clean the entire system: Open the eleventh valve 511. The metering module 200 takes a preset volume of pure water, closes the eleventh valve 511, opens the first valve 501, and transfers the pure water to the digestion module 100; Open the first valve 501, the metering module 200 takes a preset volume of pure water, closes the first valve 501, opens the third valve 503, and transfers the pure water to the total nitrogen colorimetric module 400, then closes the third valve 503; Open the first valve 501, the metering module 200 takes a preset volume of pure water, closes the first valve 501, opens the second valve 502, and transfers the pure water to the total phosphorus colorimetric module 300, then closes the second valve 502.

[0083] 12) Drain the cleaning wastewater in the system: Open the third valve 503. The metering module 200 sucks the wastewater remaining in the total nitrogen colorimetric module 400, closes the third valve 503, opens the stop valve 600, and drains the wastewater in the total nitrogen colorimetric module 400; Open the second valve 502. The metering module 200 sucks the wastewater remaining in the total phosphorus colorimetric module 300, closes the second valve 502, opens the stop valve 600, and drains the wastewater in the total phosphorus colorimetric module.

[0084] 13) Repeat steps 11) and 12) to ensure that the system is completely cleaned.

[0085] In the embodiment of the present application, the main function of the stop valve 600 is to prevent liquid backflow and leakage, ensuring the normal operation and operational safety of the system. During the above operation process, the specific functions of the stop valve 600 are as follows:

[0086] Prevent waste liquid backflow: In the steps of draining waste liquid (such as steps 7, 9, 10, 12), after the metering module 200 sucks the waste liquid and closes the corresponding valve, the stop valve 600 is opened to ensure that the waste liquid can be smoothly drained from the system, while preventing the waste liquid from flowing back into the system during the drainage process, avoiding contaminating other modules or affecting subsequent operations. Prevent liquid leakage: During the operation of the system, the stop valve 600 can play a sealing role to prevent liquid from leaking during non-draining stages, ensuring the tightness of the system and operational safety. Control waste liquid discharge: By controlling the opening and closing of the stop valve 600, the waste liquid discharge process can be precisely controlled to ensure that the waste liquid can be completely drained from the system.

[0087] It should be noted that after the total phosphorus and total nitrogen mixed standard solution connected to the ninth valve 509 is processed by the digestion module 100 and the colorimetric module, corresponding signal values will be generated. Through these signal values, a test curve can be drawn for calculating the concentration during the subsequent testing of the water sample to be tested. During the testing process, after the water sample to be tested undergoes the same processing steps, its signal value is measured and substituted into the previously established test curve, thereby calculating the concentration value of the water sample. This process ensures the accuracy of the measurement and the effectiveness of the system calibration. The above content belongs to the conventional technical means in this field and will not be elaborated here.

[0088] The system for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH according to the embodiments of the present application has the following advantages: 1) Medium-temperature and high-efficiency digestion: The traditional national standard methods (HJ 636-2012, GB 11893-89-1989) require digestion at 120°C under high temperature and high pressure conditions for 30 minutes, while the catalytic digestion system of the present application based on CoAl-LDH catalytic material only needs to be digested at 60°C - 70°C for 2 minutes - 30 minutes to achieve the complete mineralization of organic nitrogen and phosphorus substances, breaking through the bottleneck of high energy consumption and safety hazards of traditional high-temperature digestion, and significantly reducing the detection energy consumption. 2) Improved digestion rate: The system of the present application can accelerate the digestion process of pollutants through the synergistic catalytic system of LDH catalyst and buffer solution, and the catalytic efficiency is 2.3 times higher than that of traditional Fe-based catalysts. This synergistic mechanism can make the mineralization rate (i.e., digestion rate) of organic nitrogen and phosphorus reach more than 98% at 70°C. Taking sodium glycerophosphate as an example for total phosphorus, its digestion rate can reach 99.2% - 100%, and taking glycine as an example for total nitrogen, its digestion efficiency can reach 98.7% - 100%. 3) Green chemical process: The system of the present application can reduce the usage of acids and alkalis in the buffer solution through the synergistic catalytic system of LDH catalyst and buffer solution, and at the same time avoid secondary pollution problems such as the escape of nitrogen oxides, significantly improving the safety and environmental protection of the operation. In addition, it prolongs the service life of the digestion module, greatly reducing the overall equipment cost and operation and maintenance cost. Specifically, it can reduce the alkalinity in the total nitrogen reaction system and extend the service life of the digestion module. The service life of the digestion component is extended from 6 months to 1 - 3 years. 4) Integrated detection of total phosphorus and total nitrogen: The traditional method requires separate digestion of TN / TP samples (each requires an independent process), while the system of the present application utilizes the adsorption-catalytic synergistic effect of LDH to achieve integrated digestion of total phosphorus and total nitrogen, synchronously releasing nitrate and phosphate, and at the same time can achieve integrated detection of total phosphorus and total nitrogen.

[0089] Embodiments of the present application will be described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation of the present application. Additionally, if not explicitly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. Reaction conditions not listed are also easily obtainable by those skilled in the art.

[0090] Example 1

[0091] This example provides a method for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH, which uses the attached Figure 2 system shown, and includes the following steps:

[0092] 1) Take the water sample to be tested: Open the tenth valve 510, and the metering module 200 accurately takes 10 mL of the water sample to be tested (including sodium glycerophosphate and glycine), close the tenth valve 510, open the first valve 501, transfer the water sample to be tested into the digestion module 100 (coated with LDH film, including 0.006 g of CoAl-LDH material), and close the first valve 501.

[0093] 2) Take the digestion solution: Open the fourth valve 504, and the metering module 200 accurately takes 2 mL of the digestion solution (50 g / L K2S2O8 solution), close the fourth valve 504, open the first valve 501, transfer the digestion solution to the digestion module 100, and close the first valve 501.

[0094] 3) Take the buffer solution: Open the sixth valve 506, and the metering module 200 accurately takes 1 mL of the buffer solution, close the sixth valve 506, open the first valve 501, transfer the buffer solution to the digestion module 100, and close the first valve 501. The buffer solution is prepared by mixing 0.1 mol / L H2SO4 solution and 0.2 mol / L K2SO4 solution in a volume ratio of 1:1, with a pH of 2.5.

[0095] 4) Heat and digest: Heat the digestion module 100 to 70 °C and digest for 10 min, then cool to 50 °C.

[0096] 5) Total nitrogen test: Open the first valve 501, and the metering module 200 accurately takes 5 mL of the digested solution, close the first valve 501; open the third valve 503, transfer the digested solution to the total nitrogen colorimetric module 400, and close the third valve 503; develop color for 1 min and test the total nitrogen concentration value.

[0097] 6) Total phosphorus test: Open the first valve 501, and the metering module 200 accurately takes 5 mL of the digested solution. Close the first valve 501, open the second valve 502, transfer the digested solution to the total phosphorus colorimetric module 300, and close the second valve 502; Open the seventh valve 507, and the metering module 200 accurately takes 1 mL of total phosphorus color reagent (a mixed solution containing 0.5 mol / L H2SO4 + 1% ammonium molybdate + 0.27% potassium antimonyl tartrate). Close the seventh valve 507, open the second valve 502, transfer the total phosphorus color reagent to the total phosphorus colorimetric module 300, and close the second valve 502; Open the eighth valve 508, and the metering module 200 accurately takes 1 mL of total phosphorus reducing agent (50 g / L ascorbic acid solution). Close the eighth valve 508, open the second valve 502, transfer the total phosphorus reducing agent to the total phosphorus colorimetric module 300, and close the second valve 502; Color for 3 min, and test the total phosphorus concentration value.

[0098] 7) Drain the waste liquid from the digestion module 100 (this step can be carried out simultaneously with step 6) total phosphorus color development step): Open the first valve 501, the metering module 200 sucks the waste liquid remaining in the digestion module 100, close the first valve 501, open the stop valve 600, and drain the waste liquid in the digestion module 100.

[0099] 8) Catalyst activation and regeneration: Open the fifth valve 505, and the metering module 200 accurately takes 3 mL of regenerant (10 g / L NaOH solution). Close the fifth valve 505, open the first valve 501, transfer the regenerant to the digestion module 100, and close the first valve 501; Open the eleventh valve 511, and the metering module 200 accurately takes a preset volume of pure water. Close the eleventh valve 511, open the first valve 501, transfer the pure water to the digestion module 100, and close the first valve 501, and activate and regenerate for 3 min.

[0100] 9) Drain the waste liquid from the total nitrogen and total phosphorus colorimetric modules (this step can be carried out simultaneously with step 8) activate and regenerate for 3 min step): Open the third valve 503, the metering module 200 sucks the waste liquid remaining in the total nitrogen colorimetric module 400, close the third valve 503, open the stop valve 600, and drain the waste liquid in the total nitrogen colorimetric module 400; Open the second valve 502, the metering module 200 sucks the waste liquid remaining in the total phosphorus colorimetric module 300, close the second valve 502, open the stop valve 600, and drain the waste liquid in the total phosphorus colorimetric module.

[0101] 10) Drain the waste liquid from the digestion module 100: Open the first valve 501, the metering module 200 sucks the waste liquid remaining in the digestion module 100, close the first valve 501, open the stop valve 600, and drain the waste liquid in the digestion module 100.

[0102] 11) Clean the entire system: Open the eleventh valve 511, the metering module 200 takes about 13 mL of pure water, close the eleventh valve 511, open the first valve 501, and transfer the pure water to the digestion module 100; Open the first valve 501, the metering module 200 takes about 5.5 mL of pure water, close the first valve 501, open the third valve 503, and transfer the pure water to the total nitrogen colorimetric module 400, close the third valve 503; Open the first valve 501, the metering module 200 takes about 7.5 mL of pure water, close the first valve 501, open the second valve 502, and transfer the pure water to the total phosphorus colorimetric module 300, close the second valve 502.

[0103] 12) Drain the cleaning wastewater in the system: Open the third valve 503, the metering module 200 sucks the wastewater remaining in the total nitrogen colorimetric module 400, close the third valve 503, open the stop valve 600, and drain the wastewater in the total nitrogen colorimetric module 400; Open the second valve 502, the metering module 200 sucks the wastewater remaining in the total phosphorus colorimetric module 300, close the second valve 502, open the stop valve 600, and drain the wastewater in the total phosphorus colorimetric module.

[0104] 13) Repeat steps 11) and 12) to ensure that the system is completely cleaned.

[0105] The preparation process of the above CoAl-LDH material is as follows:

[0106] First, prepare two solutions, labeled as solution A and solution B respectively. The preparation method of solution A is: Dissolve 1.81 g of aluminum chloride (AlCl3) and 5.35 g of cobalt chloride (CoCl2) in 200 mL of dilute hydrochloric acid solution, where the atomic ratio of Co 2+ to Al 3+ is (3:1). Solution B is an ammonia water (NH4OH) solution, and its pH value is adjusted to 12 with saturated ammonium chloride (NH4Cl) solution. While vigorously stirring solution B, solution A is slowly added dropwise to solution B through a peristaltic pump, and the pH value of the reaction system is continuously maintained at about 12 with ammonia water. After all 200 mL of solution A is added, the mixture is aged at 70 °C for 24 h. Subsequently, the generated precipitate is washed 5 times with deionized water and then 2 times with ethanol. Finally, the washed precipitate is dried in a vacuum drying oven at 70 °C to obtain the CoAl-LDH material.

[0107] Perform SEM testing on the above-prepared CoAl-LDH material, and the test results are as Figure 3 shown. Perform TEM testing on the above-prepared CoAl-LDH material, and the test results are as Figure 4 shown. From Figure 3 and Figure 4It can be seen that the CoAl-LDH material exhibits a typical layered stacking morphology, and the interlayer spacing is about 0.76 nm.

[0108] After calculation, the digestion rate of sodium glycerophosphate in the water sample to be measured in this example is about 99.6%, and the digestion rate of glycine is about 99.4%.

[0109] Example 2

[0110] The method of this example is basically the same as that of Example 1, except that:

[0111] 4) Heating and digestion: After heating the digestion module to 60 °C and digesting for 30 min, it is cooled to 50 °C.

[0112] After calculation, the digestion rate of sodium glycerophosphate in the water sample to be measured in this example is about 98.7%, and the digestion rate of glycine is about 98.3%.

[0113] Example 3

[0114] The method of this example is basically the same as that of Example 1, except that:

[0115] 4) Heating and digestion: After heating the digestion module to 65 °C and digesting for 20 min, it is cooled to 50 °C.

[0116] After calculation, the digestion rate of sodium glycerophosphate in the water sample to be measured in this example is about 99.3%, and the digestion rate of glycine is about 99.0%.

[0117] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0118] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. A method for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl layered double hydroxide, characterized in that, Comprising: (1) Sending the water sample to be detected into a digestion module, wherein a cobalt-aluminum layered double hydroxide is provided in the digestion module; (2) Sequentially adding a digestion solution and a buffer solution into the digestion module, mixing, and heating for digestion; (3) Sending the digested solution to a total nitrogen colorimetric module for color development and testing the total nitrogen concentration value; meanwhile, sending the digested solution to a total phosphorus colorimetric module for color development and testing the total phosphorus concentration value. In step (1), Co in the cobalt-aluminum layered double hydroxide 2+ and Al 3+ have an atomic ratio of (2-3):1, and Cl - is intercalated between the layers. In step (2), the digestion solution is a persulfate solution with a concentration of 40 g / L to 50 g / L; The buffer solution is an aqueous solution containing sulfuric acid and sulfate, the pH value of the buffer solution is 2.4 to 2.6, and the concentration of the sulfate in the buffer solution is 0.09 mol / L to 0.11 mol / L.

2. The method according to claim 1, wherein A film layer containing the cobalt-aluminum layered double hydroxide is coated in the digestion module.

3. The method according to claim 1, characterized in that In step (1), the preparation method of the cobalt-aluminum layered double hydroxide includes: Dissolve aluminum chloride and cobalt chloride in hydrochloric acid solution, where the atomic ratio of Co 2+ to Al 3+ is (2 - 3):1 to obtain solution A; Mixing an ammonia water solution and a saturated ammonium chloride solution, and adjusting the pH value to 11.8 to 12.2 to obtain solution B; While stirring solution B, dropping solution A into solution B and adjusting the pH value of the reaction system to be maintained at 11.8 to 12.2 with ammonia water; Aging the reaction system; Washing and drying the precipitate generated in the reaction system to obtain the cobalt-aluminum layered double hydroxide.

4. The method according to claim 1, wherein In step (1), based on 10 mL of the water sample to be detected, the mass of the cobalt-aluminum layered double hydroxide in the digestion module is 0.006 g to 0.1 g.

5. The method according to claim 1, characterized in that, In step (2), based on 10 mL of the water sample to be detected, the dosage of the digestion solution is 1.5 mL to 2.5 mL, and the dosage of the buffer solution is 0.8 mL to 1.2 mL.

6. The method according to claim 1, characterized in that, In step (2), the temperature of the heating digestion is 60 °C to 70 °C, and the time of the heating digestion is 2 min to 30 min.

7. The method according to any one of claims 1-6, characterized in that, In step (3), sending the digested solution to the total phosphorus colorimetric module, adding a total phosphorus color developer and a total phosphorus reducing agent for color development and testing the total phosphorus concentration value.

8. The method according to claim 7, wherein The total phosphorus color developer is an aqueous solution containing sulfuric acid, ammonium molybdate and potassium antimonyl tartrate, the concentration of the sulfuric acid in the total phosphorus color developer is 0.45 mol / L to 0.55 mol / L, the mass fraction of the ammonium molybdate in the total phosphorus color developer is 1% to 3%, and the mass fraction of the potassium antimonyl tartrate in the total phosphorus color developer is 0.25% to 0.4%; And / or, the total phosphorus reducing agent is an ascorbic acid solution with a concentration of 10 g / L to 100 g / L.

9. A system for implementing the method for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl layered double hydroxide according to any one of claims 1-8, characterized in that, Comprising: A digestion module, a metering module, a total nitrogen colorimetric module, a total phosphorus colorimetric module and a multi-way discharge valve, wherein a cobalt-aluminum layered double hydroxide is provided in the digestion module, and multiple valves are provided on the multi-way discharge valve; The digestion module is connected to the metering module through the valve on the multi-way discharge valve, the total nitrogen colorimetric module is connected to the metering module through the valve on the multi-way discharge valve, and the total phosphorus colorimetric module is connected to the metering module through the valve on the multi-way discharge valve.

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