CoAl-LDH-based catalytic digestion integrated total nitrogen and total phosphorus detection method and system

Abstract

The invention belongs to the technical field of water environment monitoring, and particularly discloses a CoAl-LDH-based catalytic digestion integrated total nitrogen and total phosphorus detection method and system.The CoAl-LDH-based catalytic digestion integrated total nitrogen and total phosphorus detection method comprises the steps that 1, a water sample to be detected is conveyed into a digestion module, and cobalt-aluminum layered double hydroxides are arranged in the digestion module; (2) sequentially adding a digestion solution and a buffer solution into a digestion module, mixing, heating and digesting; (3) transferring the dissolved solution to a total nitrogen colorimetric module, carrying out color development, and testing a total nitrogen concentration value; meanwhile, the dissolved solution is delivered to a total phosphorus colorimetric module for color development, and the total phosphorus concentration value is tested. By constructing a CoAl-LDH mediated adsorption-catalysis synergistic mechanism, the defects of high energy consumption and strong corrosivity in the traditional digestion process can be remarkably reduced, integrated efficient detection of total phosphorus and total nitrogen in a water sample is realized, and meanwhile, the problem of low conversion efficiency of nitrogen and phosphorus substances under a medium-temperature condition is solved.

Description

Technical Field

[0001] This application belongs to the technical field of water environment monitoring, and particularly relates to a method and system for integrated detection of 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) are key indicators of water eutrophication. Their accurate detection is of great significance for evaluating water quality, warning of ecological risks, and formulating treatment strategies. Currently, TN / TP detection technologies are mainly divided into four categories: chemical digestion-spectrophotometry, chromatography, spectroscopy, 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: 1) High energy consumption: National standard methods rely on high-temperature and high-pressure digestion at 120°C to 150°C, which consumes a large amount of energy and poses great risks in instrument operation.

[0003] 2) Risk of secondary pollution: The extensive use of strong acids (concentrated sulfuric acid, nitric acid) leads to high costs for waste liquid treatment, and high-temperature digestion is prone to generating toxic gases such as nitrogen oxides.

[0004] 3) Interference from complex matrices: Water samples with high turbidity and high chromaticity require additional pretreatment, and the detection sensitivity (the detection limit of TP is 0.02 mg / L) is difficult to meet the monitoring requirements of surface water class I standards (TP ≤ 0.01 mg / L).

[0005] 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

[0006] 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 integrated detection of 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 integrated and efficient 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.

[0007] In one aspect of this application, a method for integrated detection of total nitrogen and total phosphorus by catalytic digestion based on CoAl-LDH is proposed. According to the embodiments of this application, the method includes: (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; (2) adding digestion solution and buffer solution to the digestion module in sequence, mixing, and heating for digestion; (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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] In some embodiments of the present application, in step (3), the solution after digestion is transferred to the total phosphorus colorimetric module, and a total phosphorus color reagent and a total phosphorus reducing agent are added for color development to test the total phosphorus concentration value.

[0016] 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.

[0017] In the second aspect of the present application, the present application proposes a system for implementing the method for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH in the above embodiments. According to the embodiments 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 discharge valve. A cobalt-aluminum layered double hydroxide is provided in the digestion module, and a plurality of valves are provided on the multi-way discharge valve; the digestion module is connected to the metering module through a valve on the multi-way discharge valve, the total nitrogen colorimetric module is connected to the metering module through a valve on the multi-way discharge valve, and the total phosphorus colorimetric module is connected to the metering module through a valve on the multi-way discharge valve.

[0018] 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) need to carry out digestion for 30 min under high temperature and high pressure conditions of 120 °C, while the catalytic digestion system based on CoAl-LDH catalytic material in the present application only needs to carry out digestion for 2 min to 30 min 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 can achieve integrated digestion of total phosphorus and total nitrogen by using the adsorption-catalytic synergistic effect of LDH, synchronously release nitrate and phosphate, and at the same time can achieve integrated detection of total phosphorus and total nitrogen.

[0019] 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

[0020] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description of embodiments in conjunction with the accompanying drawings, where: Figure 1 It is a schematic flowchart 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; Figure 2 It 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; Figure 3 It is a scanning electron microscope (SEM) image of the CoAl-LDH material in Example 1 of the present application, where Figure 3 a in it is a scanning electron microscope (SEM) image at a magnification of 10,000, Figure 3 b in it is a scanning electron microscope (SEM) image at a magnification of 50,000, Figure 3 c in it is a scanning electron microscope (SEM) image at a magnification of 100,000; Figure 4 It is a transmission electron microscope (TEM) image of the CoAl-LDH material in Example 1 of the present application, where Figure 4 a in it is a transmission electron microscope (TEM) image at a magnification of 200,000, Figure 4 b in it is a transmission electron microscope (TEM) image at a magnification of 500,000.

[0021] Reference numerals: 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

[0022] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying 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 accompanying drawings are exemplary and are intended to explain the present application and should not be construed as limiting the present application.

[0023] The present application was proposed by the inventors based on the following problems: The inventors have found through research that layered double hydroxide (LDH) materials have adjustable lamellar compositions, high specific surface areas, 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.

[0024] Existing research has mostly focused on the catalytic mechanisms of single pollutants (TN or TP), lacking systematic solutions for multi-target synchronous detection, and industrialization issues such as material stability and cost controllability have not been fully resolved.

[0025] 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.

[0026] 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 a digestion module, in which 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 a total nitrogen colorimetric module for color development and testing the total nitrogen concentration value; at the same time, taking the digested solution to a total phosphorus colorimetric module for color development and testing the total phosphorus concentration value.

[0027] 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, by constructing an adsorption-catalysis synergistic mechanism mediated by CoAl-LDH, significantly reduces 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.

[0028] 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 can achieve adsorption-catalysis synergistic effects through charge balance and anion regulation of Co 2+ / Al 3+ : Cl - between the LDH layers enriches nitrogen / phosphorus-containing organic matter through electrostatic interaction, and surface hydroxyl groups activate persulfate to generate a high concentration of SO 4- · and ·OH free radicals (the free radical concentration can be increased by about 4.8 times), and at the same time Co 2+ / Co 3+ promotes the breaking of chemical bonds and dehydrogenation reactions in pollutant molecules, thus accelerating the decomposition process of pollutants. The catalytic efficiency is 2.3 times higher than that of traditional Fe-based catalysts. This synergistic mechanism can achieve an organic nitrogen and phosphorus mineralization rate (i.e., decomposition rate) of over 98% at 70°C (traditionally ≥120°C), significantly reducing energy consumption.

[0029] Compared with the prior art, this method has the following advantages: 1) Medium-temperature and high-efficiency decomposition: The traditional national standard methods (HJ 636-2012, GB 11893-89-1989) need to decompose for 30 minutes under high temperature and high pressure conditions of 120°C, while the catalytic decomposition method based on CoAl-LDH catalytic material in this application only needs to decompose 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 bottlenecks of high energy consumption and safety hazards in traditional high-temperature decomposition, and significantly reducing the detection energy consumption.

[0030] 2) Improved decomposition rate: Through the synergistic catalytic system of the LDH catalyst and the buffer solution in this application, the decomposition process of pollutants can be accelerated, and the catalytic efficiency is 2.3 times higher than that of traditional Fe-based catalysts. This synergistic mechanism can make the organic nitrogen and phosphorus mineralization rate (i.e., decomposition rate) reach over 98% at 70°C. Taking sodium glycerophosphate as an example for total phosphorus, its decomposition rate can reach 99.2% - 100%, and taking glycine as an example for total nitrogen, its decomposition efficiency can reach 98.7% - 100%.

[0031] 3) Green chemical process: Through the synergistic catalytic system of the LDH catalyst and the buffer solution in this application, the usage of acids and bases in the buffer solution can be reduced, and at the same time, problems such as secondary pollution caused by 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 decomposition 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 decomposition module can be extended. The service life of the decomposition component is extended from 6 months to 1 - 3 years.

[0032] 4) Integrated detection of total phosphorus and total nitrogen: Traditional methods need to decompose TN / TP samples separately (each requires an independent process), while this application utilizes the adsorption-catalytic synergistic effect of LDH to achieve integrated decomposition of total phosphorus and total nitrogen, synchronously releasing nitrates and phosphates, and at the same time enabling integrated detection of total phosphorus and total nitrogen.

[0033] The following details the method for integrated detection of total nitrogen and total phosphorus by catalytic decomposition based on CoAl-LDH proposed in this application: Specifically, refer to the attached Figure 1, The above method for integrated catalytic digestion and detection of total nitrogen and total phosphorus based on CoAl-LDH comprises the following steps: S100: Send the water sample to be detected into the digestion module, where cobalt-aluminum layered double hydroxide is provided; In this step, send the water sample to be detected into the digestion module, where cobalt-aluminum layered double hydroxide is provided. The water sample to be detected may contain phosphorus-containing substances (such as sodium glycerophosphate) and nitrogen-containing substances (such as glycine).

[0034] According to some specific embodiments of the present application, Co in the above cobalt-aluminum layered double hydroxide 2+ and Al 3+ have an atomic ratio of (2-3):1, such as 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, etc., and Cl - is intercalated between layers.

[0035] According to some other specific embodiments of the present application, the preparation method of the above cobalt-aluminum layered double hydroxide includes: Dissolve aluminum chloride (AlCl 3 ) and cobalt chloride (CoCl 2 ) in dilute hydrochloric acid solution, where the atomic ratio of Co 2+ and Al 3+ is (2-3):1 (such as 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, 3:1, etc.) to obtain solution A; Mix ammonia water (NH 4 OH) solution and saturated ammonium chloride (NH 4 Cl) solution, and adjust the pH value to 11.8-12.2 (such as 11.8, 11.9, 12, 12.1, 12.2) to obtain solution B; While vigorously stirring solution B, slowly drip solution A into solution B through a peristaltic pump, and adjust the pH value of the reaction system to be maintained at 11.8-12.2 (such as 11.8, 11.9, 12, 12.1, 12.2) with ammonia water; 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 (such as 65°C, 68°C, 70°C, 72°C, 75°C, etc.) for 24±1 h; Wash and dry the precipitate formed in the reaction system to obtain cobalt-aluminum layered double hydroxide. As some specific embodiments, wash the precipitate formed in the reaction system 3-5 times with deionized water, then wash it 1-2 times with ethanol, and finally dry the washed precipitate in a vacuum drying oven at 65°C-75°C.

[0036] Characterized by scanning electron microscopy (SEM) (as shown in the appendix Figure 3 ), and transmission electron microscopy (TEM) (as shown in the appendix Figure 4 ), the above cobalt-aluminum layered double hydroxide presents a typical layered stacking morphology, and the interlayer 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 SO 4 - · and ·OH free radicals (EPR confirms that the free radical concentration increases 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.

[0037] 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.

[0038] According to some other specific embodiments of the present application, 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, 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, the complete digestion of nitrogen and phosphorus substances can be ensured.

[0039] S200: Add the digestion solution and the buffer solution to the digestion module in sequence, mix, and heat for digestion; In this step, add the digestion solution and the buffer solution to the digestion module in sequence, mix evenly, and heat for digestion.

[0040] According to some other specific embodiments of the present application, the above digestion solution is a persulfate solution with a concentration of 40 g / L to 50 g / L (such as K 2 S 2 O 8 ), 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.

[0041] According to some other 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 to 2.6, for example, it can be 2.4, 2.5, 2.6, etc., and the sulfate (such as K 2 SO 4)(The concentration) in the buffer solution is 0.09 mol / L to 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 amount of acid and alkali 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.

[0042] According to some other 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 to 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 to 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.

[0043] According to some other specific embodiments of the present application, the temperature of the above heating digestion is 60°C to 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 to 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 to 30 min under medium temperature conditions of 60°C to 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.

[0044] 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.

[0045] 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 developer and the total phosphorus reducing agent, carry out color development for 30 s to 5 min, and test the total phosphorus concentration value.

[0046] 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 H 2 SO 4 + 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.

[0047] 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 inner wall of the beaker; stir and cool to room temperature, transfer it to a 1 L volumetric flask, and make up to the scale line, shake well and set aside. ② Weigh 10 g of ammonium molybdate in a beaker; add about 500 mL of 0.5 mol / L H 2 SO 4 , 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 to the scale line with 0.5 mol / L H 2 SO 4 , shake well.

[0048] 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.).

[0049] In the second aspect of the present application, the present application proposes a system for implementing the above embodiments of the method for catalytic digestion integrated detection of total nitrogen and total phosphorus based on CoAl-LDH. According to the embodiments of the present application, refer 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 drain valve 500. A cobalt-aluminum layered double hydroxide is provided in the digestion module 100, and multiple valves are provided on the multi-way drain valve 500. The digestion module 100 is connected to the metering module 200 through a valve on the multi-way drain valve 500. The total nitrogen colorimetric module 400 is connected to the metering module 200 through a valve on the multi-way drain valve 500. The total phosphorus colorimetric module 300 is connected to the metering module 200 through a valve on the multi-way drain valve 500.

[0050] Specifically, referring to the appendix Figure 2 , the above multi-way drain valve 500 includes a first valve 501 connecting to the digestion module 100, a second valve 502 connecting to the total phosphorus colorimetric module 300, a third valve 503 connecting to the total nitrogen colorimetric module 400, a fourth valve 504 connecting to the digestion solution, a fifth valve 505 connecting to the regenerant, a sixth valve 506 connecting to the buffer solution, a seventh valve 507 connecting to the total phosphorus chromogenic agent, an eighth valve 508 connecting to the total phosphorus reducing agent, a ninth valve 509 connecting to the total phosphorus and total nitrogen mixed standard solution, a tenth valve 510 connecting to the water sample to be tested, an eleventh valve 511 connecting to 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.

[0051] The specific operation process is as follows: 1) Take the water sample to be tested: Open the tenth valve 510. 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 and transfer the water sample to be tested into the digestion module 100 (coated with an LDH film and containing CoAl-LDH material). Close the first valve 501.

[0052] 2) Take the digestion solution: Open the fourth valve 504. The metering module 200 accurately takes a preset volume of the digestion solution. Close the fourth valve 504. Open the first valve 501 and transfer the digestion solution into the digestion module 100. Close the first valve 501.

[0053] 3) Take the buffer solution: Open the sixth valve 506. The metering module 200 accurately takes a preset volume of the buffer solution. Close the sixth valve 506. Open the first valve 501 and transfer the buffer solution into the digestion module 100. Close the first valve 501.

[0054] 4) Heat digestion: Heat the digestion module 100 to 60°C - 70°C for digestion for 2 min - 30 min, and then cool down.

[0055] 5) Total nitrogen test: Open the first valve 501, and the metering module 200 accurately takes a preset volume of the digested solution, then close the first valve 501; Open the third valve 503, transfer the digested solution to the total nitrogen colorimetric module 400, and then close the third valve 503; Conduct color development and test the total nitrogen concentration value.

[0056] 6) Total phosphorus test: Open the first valve 501, and the metering module 200 accurately takes a preset volume of the digested solution, then close the first valve 501. Open the second valve 502, transfer the digested solution to the total phosphorus colorimetric module 300, and then 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, then 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 then 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, then close the eighth valve 508. Open the second valve 502, transfer the total phosphorus reducing agent to the total phosphorus colorimetric module 300, and then close the second valve 502; Conduct color development and test the total phosphorus concentration value.

[0057] 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, and the metering module 200 sucks the waste liquid remaining in the digestion module 100, then close the first valve 501. Open the stop valve 600 to drain the waste liquid from the digestion module 100.

[0058] 8) Catalyst activation and regeneration: Open the fifth valve 505, and the metering module 200 accurately takes a preset volume of the regeneration agent (for example, it can be a 4 - 15 g / L NaOH solution), then close the fifth valve 505. Open the first valve 501, transfer the regeneration agent to the digestion module 100, and then close the first valve 501; Open the eleventh valve 511, and the metering module 200 accurately takes a preset volume of pure water, then close the eleventh valve 511. Open the first valve 501, transfer the pure water to the digestion module 100, and then 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.

[0059] 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, and the metering module 200 sucks the waste liquid remaining in the total nitrogen colorimetric module 400, then close the third valve 503. Open the stop valve 600 to drain the waste liquid from the total nitrogen colorimetric module 400; Open the second valve 502, and the metering module 200 sucks the waste liquid remaining in the total phosphorus colorimetric module 300, then close the second valve 502. Open the stop valve 600 to drain the waste liquid from the total phosphorus colorimetric module.

[0060] 10) Drain the waste liquid of 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 liquid stop valve 600, and drain the waste liquid in the digestion module 100.

[0061] 11) Clean the entire system: Open the eleventh valve 511, the metering module 200 takes a preset volume 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 a preset volume 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 a preset volume 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.

[0062] 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 liquid 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 liquid stop valve 600, and drain the wastewater in the total phosphorus colorimetric module.

[0063] 13) Repeat steps 11) and 12) to ensure that the system is completely cleaned.

[0064] In the embodiments of the present application, the main function of the liquid 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 liquid stop valve 600 are as follows: Prevent waste liquid backflow: In the steps of draining waste liquid (such as steps 7, 9, 10, 12), when the metering module 200 sucks the waste liquid and closes the corresponding valve, the liquid 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 liquid stop valve 600 can play a sealing role to prevent liquid leakage during non-drainage stages, ensuring the sealing performance of the system and operational safety. Control waste liquid discharge: By controlling the opening and closing of the liquid 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.

[0065] 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 plotted 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 to calculate 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.

[0066] 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. However, the catalytic digestion system based on CoAl-LDH catalytic material in the present application only needs to digest 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 in 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.

[0067] 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 to the present application. Additionally, if not specified otherwise, all reagents used in the following embodiments can be purchased on the market or synthesized according to methods described herein or known methods. Reaction conditions not listed are also easily obtainable by those skilled in the art.

[0068] Example 1 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: 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 an LDH film, including 0.006 g of CoAl-LDH material), and close the first valve 501.

[0069] 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 K 2 S 2 O 8 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.

[0070] 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 H 2 SO 4 solution and 0.2 mol / L K 2 SO 4 solution in a volume ratio of 1:1, with a pH of 2.5.

[0071] 4) Heat and digest: Heat the digestion module 100 to 70 °C for digestion for 10 min, and then cool it to 50 °C.

[0072] 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.

[0073] 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 developing agent (a mixed solution containing 0.5 mol / L H 2 SO 4 + 1% ammonium molybdate + 0.27% potassium antimonyl tartrate), 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 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 for total phosphorus colorimetry, and close the second valve 502; Develop color for 3 min and test the total phosphorus concentration value.

[0074] 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.

[0075] 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, close the first valve 501, and activate and regenerate for 3 min.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 13) Repeat steps 11) and 12) to ensure that the system is completely cleaned.

[0081] The preparation process of the above CoAl-LDH material is as follows: 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 (AlCl 3 ) and 5.35 g of cobalt chloride (CoCl 2 ) 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 (NH 4 OH) solution, and its pH value is adjusted to 12 with saturated ammonium chloride (NH 4 Cl) solution. While vigorously stirring solution B, slowly drip solution A into solution B through a peristaltic pump, and continuously maintain the pH value of the reaction system at about 12 with ammonia water. After all 200 mL of solution A is added, age the mixture at 70 °C for 24 h. Subsequently, wash the generated precipitate 5 times with deionized water and then 2 times with ethanol. Finally, dry the washed precipitate in a vacuum drying oven at 70 °C to obtain the CoAl-LDH material.

[0082] Perform SEM testing on the prepared CoAl-LDH material above, and the test results are as Figure 3 shown. Perform TEM testing on the prepared CoAl-LDH material above, and the test results are asFigure 4 As shown. From Figure 3 and Figure 4 it can be seen that the CoAl-LDH material presents a typical layered stacked morphology, and the interlayer spacing is about 0.76 nm.

[0083] 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%.

[0084] Example 2 The method of this example is basically the same as that of Example 1, except that: 4) Heating and digestion: After heating the digestion module to 60 °C and digesting for 30 min, it is cooled to 50 °C.

[0085] 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%.

[0086] Example 3 The method of this example is basically the same as that of Example 1, except that: 4) Heating and digestion: After heating the digestion module to 65 °C and digesting for 20 min, it is cooled to 50 °C.

[0087] 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%.

[0088] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means 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 a suitable manner in any one or more embodiments or examples. 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.

[0089] 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 detecting total nitrogen and total phosphorus by integrated catalytic digestion based on CoAl-LDH, characterized in that: include: (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; (2) adding digestion solution and buffer solution to the digestion module in sequence, mixing, and heating for digestion; (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.

2. The method according to claim 1, characterized in that 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 containing the cobalt-aluminum layered double hydroxide.

3. The method according to claim 1, characterized in that In step (1), the method for preparing the cobalt-aluminum layered double hydroxide comprises: Aluminum chloride and cobalt chloride are dissolved in hydrochloric acid solution, where Co 2+ With Al 3+ The atomic ratio is (2~3):1, and solution A is obtained; Mix the aqueous ammonia solution and the saturated ammonium chloride solution, and adjust the pH value to 11.8-12.2 to obtain solution B; While stirring the solution B, adding the solution A dropwise into the solution B, and adjusting the pH value of the reaction system with aqueous ammonia to maintain at 11.8-12.2; Aging the reaction system; The precipitate generated in the reaction system is washed and dried to obtain the cobalt aluminum layered double hydroxide.

4. The method according to claim 1, characterized in that: In step (1), based on 10 mL of the water sample to be tested, 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), 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 comprising 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-0.11 mol / L.

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

7. 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.

8. The method according to any one of claims 1 to 7, characterized in that In step (3), the undissolved solution is added to the total phosphorus colorimetric module, a total phosphorus colorimetric agent and a total phosphorus reducing agent are added to develop color, and the total phosphorus concentration value is tested.

9. The method according to claim 8, characterized in that The total phosphorus color developer is an aqueous solution containing sulfuric acid, ammonium molybdate and potassium antimony tartrate, wherein the concentration of sulfuric acid in the total phosphorus color developer is 0.45 mol / L to 0.55 mol / L, the mass fraction of ammonium molybdate in the total phosphorus color developer is 1% to 3%, and the mass fraction of potassium antimony 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.

10. A system for implementing the method for detecting total nitrogen and total phosphorus by catalytic digestion integrated with CoAl-LDH according to any one of claims 1 to 9, characterized in that: include: A digestion module, a metering module, a total nitrogen colorimetric module, a total phosphorus colorimetric module and a multi-way exhaust valve, wherein the digestion module is provided with cobalt-aluminum layered double hydroxide, and the multi-way exhaust valve is provided with a plurality of valves; The digestion module is connected to the metering module through the valve on the multi-way exhaust valve, the total nitrogen colorimetric module is connected to the metering module through the valve on the multi-way exhaust valve, and the total phosphorus colorimetric module is connected to the metering module through the valve on the multi-way exhaust valve.

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