A zeolite and S110MH mixed adsorption membrane, its preparation method and application

Abstract

This invention belongs to the field of in-situ analysis technology of ammonia nitrogen and nitrate nitrogen at the aquatic environment interface, specifically relating to a zeolite and S110MH mixed adsorption membrane, its preparation method, and its application. The zeolite and S110MH mixed adsorption membrane provided by this invention comprises an agar hydrogel and adsorbent particles dispersed in the agar hydrogel. The adsorbent particles include zeolite particles and anion exchange resin particles. This invention provides a method for preparing the zeolite and S110MH mixed adsorption membrane, the functional parameters of the mixed adsorption membrane and its installed DGT device, and the testing method of DGT in various environmental media. Experiments show that the DGT device installed on the zeolite and S110MH mixed adsorption membrane provided by this invention can accurately measure the time-averaged concentration or diffusion flux of ammonia nitrogen and nitrate nitrogen in water, sediment, or rhizosphere of aquatic plants, reflecting the bioavailability, geochemical processes, and mobility of inorganic nitrogen.

Description

Technical Field

[0001] This invention belongs to the field of in-situ analysis technology of ammonia nitrogen and nitrate nitrogen at the interface of aquatic environment, specifically involving a zeolite and S110MH mixed adsorption membrane, its preparation method and application. Background Technology

[0002] High concentrations of inorganic nitrogen in water bodies (lakes, estuaries, rivers, and oceans) can lead to eutrophication and algal blooms. Geochemical processes in the sub-oxidative / reduced layer of sediments exacerbate the risk of inorganic nitrogen release into water bodies. The main components of inorganic nitrogen in water are nitrate nitrogen and ammonia nitrogen, primarily sourced from domestic sewage, surface runoff, industrial and agricultural wastewater, and endogenous nitrogen release from sediments. Aquatic plants can absorb and fix nitrogen from sediments in their rhizosphere, reducing endogenous nitrogen release. Therefore, it is necessary to accurately test ammonia nitrogen and nitrate nitrogen in water bodies, sediments, or the rhizosphere of aquatic plants.

[0003] Conventional sampling methods alter nitrogen speciation during sample collection, transportation, and pretreatment, and only provide the inorganic nitrogen concentration at a single sampling point, failing to accurately reflect the daily average inorganic nitrogen level. Passive sampling technology—DGT (Differentiation Gradient Diffusion Membrane)—provides the time-averaged concentration of inorganic nitrogen over a sampling period and allows for in-situ collection of the active components of inorganic nitrogen, accurately reflecting the bioavailability and speciation of solutes. The DGT device consists of a base and a cap. An adsorption membrane (containing bonding reagents), a diffusion membrane, and a filter membrane are placed sequentially on the base, and then the cap is used to seal and fix the three membranes. The cap's window can contact water, sediment, or the rhizosphere of aquatic plants. After diffusing through the diffusion membrane, the solute is bonded and fixed on the surface of the adsorption membrane. By analyzing the mass of solute absorbed by the adsorption membrane, and then applying Fick's first law, the solute flux or concentration in the surrounding medium at the DGT surface can be calculated.

[0004] The main components of inorganic nitrogen in water are ammonia nitrogen and nitrate nitrogen. Currently, mixed adsorption membranes that can simultaneously test ammonia nitrogen and nitrate nitrogen include: A520E+Prch (using two ion exchange resins, Prch and A520E) or ZrO-AT (using ZrO to measure inorganic phosphorus; A-62MP to measure nitrate nitrogen; and T-42H to measure ammonia nitrogen). However, the above-mentioned mixed adsorption membranes have problems with low adsorption capacity, test accuracy, and test precision when testing ammonia nitrogen and nitrate nitrogen in water, sediments, or the rhizosphere of aquatic plants. Summary of the Invention

[0005] The purpose of this invention is to provide a novel zeolite and S110MH mixed adsorption membrane, its preparation method and application. The zeolite and S110MH mixed adsorption membrane provided by this invention has the advantages of high adsorption capacity, high testing accuracy and precision, and high elution efficiency.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a zeolite and S110MH mixed adsorption membrane, comprising an agar hydrogel and adsorbent particles dispersed in the agar hydrogel, wherein the adsorbent particles comprise zeolite particles and anion exchange resin particles; the particle size of the adsorbent particles is ≤20μm, and the anion exchange resin particles are S110MH anion exchange resin particles.

[0008] Preferably, the zeolite particles have a silicon-to-aluminum ratio of 4.25 to 5.25 and a pore size of 16 to 24 nm.

[0009] Preferably, the mass ratio of the zeolite particles to the anion exchange resin particles is (2.2-4):(2.8-4).

[0010] Preferably, the mass ratio of the zeolite particles to the volume of the zeolite and S110MH mixed adsorption membrane is (2.2-4) g: 2.88 cm³. 3 .

[0011] Preferably, the thickness of the zeolite and S110MH mixed adsorption membrane is 0.01 cm or 0.04 cm.

[0012] This invention provides a method for preparing the zeolite and S110MH mixed adsorption membrane described in the above technical solution, comprising the following steps:

[0013] The adsorbent particles and hot agar aqueous solution are mixed and dispersed to obtain a hot mixed solution;

[0014] The hot mixed solution is poured into a mold, then cooled, and after demolding, the zeolite and S110MH mixed adsorption membrane is obtained.

[0015] Preferably, the agar content in the hot agar aqueous solution is 2.0% (m / v), and the temperature of the hot agar aqueous solution is 75-80℃;

[0016] During the injection process, the temperature of the mold is 75–80°C.

[0017] Preferably, the initial gel membrane obtained after demolding further includes: immersing and washing the initial gel membrane with ultrapure water at least four times to obtain the zeolite and S110MH mixed adsorption membrane.

[0018] The present invention relates to the application of the zeolite and S110MH mixed adsorption membrane provided by the present invention or the zeolite and S110MH mixed adsorption membrane prepared by the preparation method described above in the detection of inorganic nitrogen in environmental media, wherein the inorganic nitrogen includes ammonia nitrogen and nitrate nitrogen.

[0019] Preferably, the environmental medium includes water, sediment, or the rhizosphere of aquatic plants.

[0020] This invention provides a zeolite and S110MH hybrid adsorption membrane, comprising an agar hydrogel and adsorbent particles dispersed in the agar hydrogel. The adsorbent particles include zeolite particles and anion exchange resin particles; the particle size of the adsorbent particles is ≤20 μm, and the anion exchange resin particles are S110MH anion exchange resin particles. Studying the speciation, bioavailability, migration and transformation processes, sediment passivation mechanisms, and rhizosphere nitrogen migration-absorption processes of inorganic nitrogen in water, sediments, or aquatic plants requires simultaneous testing of both ammonia nitrogen and nitrate nitrogen. This invention provides a zeolite and S110MH hybrid adsorption membrane capable of simultaneously testing ammonia nitrogen and nitrate nitrogen, used for assembling an in-situ testing device—DGT. The zeolite and S110MH hybrid adsorption membrane provided by this invention uses zeolite particles as the adsorbent for ammonia nitrogen, S110MH anion exchange resin as the adsorbent for nitrate nitrogen, and agar hydrogel as the matrix. This invention provides the DGT functional parameters of the zeolite and S110MH hybrid adsorption membrane and testing methods in various environmental media. Experiments show that the DGT device installed with the zeolite and S110MH mixed adsorption membrane provided by this invention can accurately test the time-averaged concentration or diffusion flux of ammonia nitrogen and nitrate nitrogen in water, sediment or rhizosphere of aquatic plants, reflecting the bioavailability, geochemical processes and mobility of inorganic nitrogen.

[0021] In summary, compared with existing single adsorption membranes, the zeolite and S110MH hybrid adsorption membrane provided by this invention can save the amount of agar reagent required for adsorption membrane preparation, reduce the number of operations in the environmental medium, and only require one elution for ammonia nitrogen and nitrate nitrogen analysis. Compared with existing adsorption membranes, such as single adsorption membranes (zeolite) or hybrid adsorption membranes (A520E+Prch and ZrO-AT), the zeolite and S110MH hybrid adsorption membrane provided by this invention has the following advantages: the agar-based adsorption membrane preparation method is simple, efficient, and effective; agar, zeolite, and S110MH are inexpensive and readily available; the prepared hybrid adsorption membrane can meet the measurement requirements of most ammonia nitrogen and nitrate nitrogen in water bodies; and it has high test accuracy and precision, and high elution efficiency. In conclusion, the adsorption membrane provided by this invention is a novel zeolite and S110MH hybrid adsorption membrane, which can be used to install an in-situ testing device—DGT—for simultaneous and accurate testing of ammonia nitrogen and nitrate nitrogen in water bodies, sediments, and rhizosphere of aquatic plants. Attached Figure Description

[0022] Figure 1 A schematic diagram of the mold structure for preparing a zeolite and S110MH mixed adsorption membrane and an agar diffusion membrane, as well as the two types of gels.

[0023] Figure 2 A top view of the mold opening and a schematic diagram of the hot adhesive solution being poured into the opening;

[0024] Figure 3This is a schematic diagram of a circular DGT structure;

[0025] Figure 4 This is a schematic diagram of the absorption of solute by a circular DGT in aqueous solution.

[0026] Figure 5 A simple DGT dosing device for on-site testing of ammonia nitrogen / nitrate nitrogen in water bodies;

[0027] Figure 6 A schematic diagram of DGT probe testing in natural sediments and overlying sediments;

[0028] Figure 7 This is a schematic diagram of the DGT probe structure;

[0029] Figure 8 A schematic diagram of the root box, aquatic plants, and sensor structure;

[0030] Figure 9 This is a schematic diagram of the experimental water tank and its auxiliary devices;

[0031] Figure 10 The operating time corresponding to the mass (M) of ammonia nitrogen or nitrate nitrogen accumulated in the DGT of the zeolite and S110MH mixed adsorption membrane.

[0032] Figure 11 The mass curves of ammonia nitrogen or nitrate nitrogen absorption by zeolite and S110MH DGT within the corresponding time (T=64h);

[0033] Figure 12 The curve showing the reciprocal (1 / M)(1 / μg) of the mass of ammonia nitrogen or nitrate nitrogen accumulated by zeolite and S110MH DGT corresponding to the thickness of the diffusion layer (Δg, cm);

[0034] Figure 13 DGT concentration profiles of ammonia nitrogen and nitrate nitrogen in control sediments and covered sediment columns;

[0035] Figure 14 This is a diffusion flux profile of oxygen concentration, ammonia nitrogen, and nitrate nitrogen in rhizosphere sediments.

[0036] In the diagram: 1: Mold; 2: Tempered glass plate; 3: U-shaped polytetrafluoroethylene (PTFE) gasket; 4: Plastic clamp; 5: Slit of mold opening; 6: Zeolite and S110MH mixed adsorption membrane; 7: Agar; 8: Zeolite particles; 9: S110MH particles; 10: Agar diffusion membrane; 11: Hot mixed solution; 12: Dropper; 13: PVDF filter membrane; 14: Circular DGT; 15: DGT base; 16: Cap with a window in the center; 17: Plastic frame; 18: Plastic liquid tank; 19: Solution; 20: Stirring magnet; 21: Magnetic stirrer; 22: Simple DGT dispensing device; 23: Float; 24: Plumb bob; 25: Main frame; 26: Overlying water; 27: Sediment; 28: Control sediment column; 29: Covering sediment column; 30: DGT probe; 31: Covering agent; 32: DGT plastic base plate; 33: DGT plastic cover plate; 34: Root box; 35: Aquatic plants; 36: Removable wall; 37: Roots; 38: Fluorescent sensing membrane; 39: Sediment / water interface; 40: Sensing membrane; 41: Inlet pipe; 42: Outlet pipe; 43: Fluorescent tube; 44: Plastic cover plate; 45: Experimental water tank; 46: Multifunctional water environment index testing probe; 47: Aeration head. Detailed Implementation

[0037] This invention provides a zeolite and S110MH mixed adsorption membrane, comprising an agar hydrogel and adsorbent particles dispersed in the agar hydrogel, wherein the adsorbent particles comprise zeolite particles and anion exchange resin particles; the particle size of the adsorbent particles is ≤20μm, and the anion exchange resin particles are S110MH anion exchange resin particles.

[0038] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well-known to those skilled in the art. In this invention, the SIR-110-MP-HP anion exchange resin particles are abbreviated as: S110MH.

[0039] The zeolite and S110MH mixed adsorption membrane provided by this invention comprises agar hydrogel. In this invention, the agar hydrogel serves as the matrix of the zeolite and S110MH mixed adsorption membrane.

[0040] The zeolite and S110MH mixed adsorption membrane provided by this invention comprises adsorbent particles. In this invention, the adsorbent particles include zeolite particles and anion exchange resin particles. Preferably, the adsorbent particles are ground zeolite particles and ground anion exchange resin particles. The particle size of the adsorbent particles is ≤20 μm, and in the examples, it can be 12 μm.

[0041] In this invention, the silicon-to-aluminum ratio of the zeolite particles is preferably 4.25 to 5.25, and the pore size is preferably 16 to 24 nm.

[0042] In this invention, the anion exchange resin particles are preferably SIR-110-MP-HP anion exchange resin particles (abbreviated as S110MH in this invention). In this invention, the S110MH anion exchange resin particles selectively adsorb nitrates while significantly reducing sulfate ion interference.

[0043] In this invention, the preferred mass ratio of the zeolite particles to the anion exchange resin particles is (2.2-4):(2.8-4), and in the embodiments it can be 3.5:3.

[0044] In this invention, the preferred mass ratio of the zeolite particles to the volume of the zeolite and S110MH mixed adsorption membrane is (2.2–4) g: 2.88 cm³. 3 In the example, the ratio can be 3.5g: 2.88cm. 3 .

[0045] In this invention, the thickness of the zeolite and S110MH mixed adsorption membrane is preferably 0.01 cm or 0.04 cm. An agar diffusion membrane (control group) was prepared using a 1.5% agar hot solution with thicknesses of 0.04 cm, 0.08 cm, or 0.12 cm. In embodiments of this invention, the dimensions of the zeolite and S110MH mixed adsorption membrane are preferably 18 × 4 × 0.01 cm. 3 Or 18×4×0.04cm 3 .

[0046] This invention provides a method for preparing the zeolite and S110MH mixed adsorption membrane described in the above technical solution, comprising the following steps:

[0047] The adsorbent particles and hot agar aqueous solution are mixed and dispersed to obtain a hot mixed solution;

[0048] The hot mixed solution is poured into a mold and then cooled. After demolding, the zeolite and S110MH mixed adsorption membrane is obtained.

[0049] This invention involves mixing and dispersing adsorbent particles with a hot agar aqueous solution to obtain a hot mixed solution. The preferred method for preparing the adsorbent particles includes: mixing the zeolite powder and S110MH to obtain an initial mixed powder; and grinding the initial mixed powder to obtain the adsorbent particles. In this invention, the zeolite powder is an aluminosilicate mineral with high cation exchange and physical adsorption capacity. The pore size is preferably 16–24 nm; the maximum thermal stability temperature is preferably 750 °C; the cation exchange capacity is preferably 50 Meq / g; the preferred mass content of the main components of the zeolite powder is: SiO2 69.58%, Al2O3 12.20%; the Si / Al ratio of the zeolite powder is preferably 4.25–5.25. The particle size of the zeolite powder is preferably ~20 μm. S110MH is a selective macroporous strong basic anion exchange resin. The polymer matrix of S110MH is styrene crosslinked DVB. This improves the selectivity for nitrates while significantly reducing the interference of sulfate ions. S110MH exhibits faster adsorption kinetics. The unprocessed S110MH particles have a particle size of 30 μm; the total exchange capacity is preferably 0.6 meq / mL, and the maximum thermal stability temperature is preferably 121℃. The adsorbent particles are ground using a grinder. The particle size of the ground adsorbent particles is preferably ≤20 μm, but in the examples it can be 12 μm.

[0050] In this invention, the agar content in the hot agar aqueous solution is preferably 2.0% (m / v). The temperature of the hot agar aqueous solution is preferably 75-80°C. The preparation method of the hot agar aqueous solution preferably includes: first heating the water and then mixing it with agar to obtain a premixed solution; second heating the premixed solution to boiling to obtain a clear agar solution. The temperature of the first heating is preferably 75-80°C.

[0051] In this invention, the adsorbent particles and the hot agar aqueous solution are preferably mixed and dispersed in an ultrasonic disperser, and the mixing and dispersion is preferably ultrasonic dispersion. This invention does not have special requirements for the specific implementation of the ultrasonic dispersion, as long as the adsorbent particles are uniformly dispersed in the hot agar aqueous solution.

[0052] After obtaining the hot mixed solution, the present invention injects the hot mixed solution into a mold and then cools it. After demolding, the zeolite and S110MH mixed adsorption membrane is obtained.

[0053] In this invention, the temperature of the mold during injection is preferably 75–80°C. A schematic diagram of the mold structure is shown below. Figure 1As shown. The mold includes: two strips of tempered glass, each strip preferably measuring 20cm × 5cm × 0.5cm (length × width × thickness); a U-shaped polytetrafluoroethylene (PTFE) gasket, one end of which is open, and its length and width are the same as the tempered glass plate; the width of each of the three edges of the U-shaped PTFE gasket is 1cm; the thickness of the U-shaped PTFE gasket is preferably 0.4mm. In this invention, when the mold is used, the two strips of tempered glass are placed face to face, and the U-shaped plastic gasket is placed between the two strips of tempered glass; plastic clips fix the two strips of tempered glass and the U-shaped plastic gasket; a narrow slit is formed in the middle of the mold. In this invention, before the pouring, the mold is preferably preheated to 80°C in an oven. The cooling is preferably performed by placing the mold filled with the hot mixed solution in a room temperature environment. The cooling time is preferably 1 hour.

[0054] In this invention, after demolding, an initial gel membrane is obtained. Preferably, the invention further includes: immersing and washing the initial gel membrane with ultrapure water at least four times to obtain the zeolite and S110MH mixed adsorption membrane. The immersion and washing time with ultrapure water is preferably 4 hours each time. This invention preferably uses ultrapure water for immersion and washing to remove impurities and any possible color from the initial gel membrane. This invention preferably places the zeolite adsorption membrane in ultrapure water for long-term storage.

[0055] The present invention relates to the application of the zeolite and S110MH mixed adsorption membrane provided by the present invention or the zeolite and S110MH mixed adsorption membrane prepared by the preparation method described above in the detection of inorganic nitrogen in environmental media, wherein the inorganic nitrogen includes ammonia nitrogen and nitrate nitrogen.

[0056] In this invention, the environmental medium preferably includes water, sediment, or the rhizosphere of aquatic plants.

[0057] In this invention, the preferred method for testing the function of the zeolite and S110MH mixed adsorption membrane includes:

[0058] (i) Determination of adsorption and elution efficiency: Prepare a mixed standard solution (500 mL) of ammonia nitrogen and nitrate nitrogen, both with a concentration of 5.0 mg / L. -1pH = 7.0 ± 0.2, 0.001 M NaCl. 10 mL of the above mixed reaction solution was used for the absorption experiment of a circular zeolite and S110MH mixed adsorption membrane (diameter: 2.5 cm; thickness: 0.04 cm); in addition, the circular adsorption membrane after reaction was eluted with 0.5, 1.0 and 2.0 M NaCl solutions, 1.0 M HCl, NaOH and KCl solutions; the concentrations of ammonia nitrogen and nitrate nitrogen in the mixed standard reaction solution after the experiment and the elution solution of the zeolite and S110MH mixed adsorption membrane were determined, the absorption efficiency and elution efficiency were calculated, and the appropriate elution solution and concentration were selected. The experimental results showed that the absorption efficiency of the zeolite and S110MH mixed adsorption membrane for nitrogen in the reaction solution was 94.3% (NH4-N) and 97.9% (NO3-N); the elution efficiency with 1 M NaCl was the best, which was 101% (NH4-N) and 95.1% (NO3-N).

[0059] (ii) Kinetic absorption experiments and determination of diffusion coefficient: such as Figure 3 As shown, a zeolite and S110MH mixed adsorption membrane 6 with a diameter of 2.5 cm, an agar diffusion membrane 10, and a PVDF filter membrane 13 are sequentially placed on the plastic base 15 of the circular DGT, and then a cap 16 with a window is attached to form a circular DGT 14. Figure 4 As shown, prepare 8L of standard solution 19 (10.0mg / L) -1 NO3-N, 3.0 mg / L -1 NH4-N and 0.001M NaCl (pH = 7.0 ± 0.2) were stored in a plastic liquid tank 18. Fifteen circular DGT14s were mounted on a plastic frame 17 and placed in a standard solution 19 in the plastic liquid tank 18. The liquid tank was placed on a magnetic stirrer 21, and the solution was stirred by a stirring magnet 20. The circular DGT14s were placed in the solution for 4, 8, 12, 16, and 24 hours. Three circular DGT14s were taken out, and the corresponding standard solution samples (5 mL) were taken out at the same time. The mass of ammonia nitrogen and nitrate nitrogen adsorbed and accumulated by DGT and the nitrogen concentration of the water sample were analyzed. Based on the curve of the mass of ammonia nitrogen or nitrate nitrogen accumulated by the adsorption membrane corresponding to the operation time and the univariate linear regression equation, the diffusion coefficient of nitrogen nitrogen or nitrate nitrogen in the agar diffusion layer at 25℃ can be obtained according to formula (1).

[0060]

[0061] Where 'a' is the slope of the linear regression equation of the solute mass M (ng) adsorbed by the DGT adsorption membrane corresponding to time T (s); Δg is the thickness of the diffusion layer (diffusion membrane + filter membrane) (cm); and A is the area of ​​the diffusion layer (cm²). 2 C is the concentration of the solute in the solution (ng / mL). -1 ).

[0062] The correlation coefficients of the univariate linear regression equations for the curves of inorganic nitrogen mass accumulated on the adsorption membrane versus operating time obtained from the experimental results were 0.998 (NH4-N) and 0.993 (NO3-N), respectively; at a water temperature of 25℃, the diffusion coefficients of NH4-N and NO3-N in the agar diffusion layer were 14.3 × 10⁻⁶, respectively. -6 and 8.4×10 -6 cm 2 s -1 .

[0063] (iii) Determination of adsorption capacity: such as Figure 4 As shown, prepare 8L of standard reaction solution (20mg / L). -1 NH4-N, 15mg L - 1 NO3-N, pH=7.0±0.2; 0.001mol L -1 NaCl was used to adsorb nitrogen by placing 27 circular DGTs in standard reaction solution 19. At reaction times of 4, 8, 12, 16, 24, 32, 44, 56, and 72 hours, the three sets of circular DGTs were removed, along with water samples. The adsorption mass of the DGTs and the concentration of ammonia or nitrate nitrogen in the water samples were analyzed. Absorption curves of the accumulated ammonia or nitrate nitrogen mass of the DGT adsorption membrane at different reaction times were plotted to evaluate the nitrogen absorption characteristics and adsorption capacity of the zeolite and S110MH mixed adsorption membrane.

[0064] Based on the above experiments, the adsorption capacities of the zeolite and S110MH mixed adsorption membranes were obtained as follows: 605±24 μg / circular DGT(NH4-N) and 359±20 μg / circular DGT(NO3-N).

[0065] (iv) Effects of pH and interfering ions: (1) Prepare a series of mixed standard solutions (nitrate nitrogen + ammonia nitrogen) with pH values ​​(3.5-9.0); place the corresponding n sets of circular DGT in Figure 4 (1) In the standard reaction solution 19, react for 24 hours; (2) Prepare a series of NaCl (0.0001-0.1 mol L) with different concentrations of interfering ions. -1 A mixed standard solution (nitrate nitrogen + ammonia nitrogen; pH = 7.0 ± 0.2) was prepared, and the corresponding n sets of circular DGT were placed in the plastic container of the above solution and allowed to react for 24 hours. After the above two solutions reacted, the circular DGT and water samples were taken out, and the mass accumulated by the zeolite and S110MH mixed adsorption membrane was analyzed. Then, according to formula (5), it was converted into DGT - ammonia nitrogen [C DGT (NH4-N)] or DGT-nitrate[C DGT [NO3-N] concentration. C DGT (NH4-N) or C DGT(NO3-N) and the concentration of the reacting solution (C) solui The ratio is used to measure the effect of pH or interfering ions on the determination.

[0066] Based on the above experiments, under most normal aquatic environmental conditions, the pH (3.5-8.5); or ionic strength: nitrate nitrogen (0.0001-0.014M NaCl; ammonia nitrogen (0.0001-0.008M NaCl), the ratio of ammonia nitrogen or nitrate nitrogen to the concentration of the reacting solution determined by DGT (C DGT / C solu A value between 0.90 and 1.10 is sufficient to achieve the required accuracy and precision for the test. In water bodies with high ionic strength, a thicker diffusion membrane and a shorter test time should be used to improve the accuracy and precision of the test.

[0067] (3) Testing and subsequent analysis methods for zeolite and S110MH DGT in environmental media

[0068] DGT installed with zeolite and S110MH adsorption membranes can be used for testing in water bodies, natural sediments, passivated sediments, and the rhizosphere of aquatic plants. Specific testing methods:

[0069] (i) Test method for circular DGT in water: such as Figure 3 As shown, three types of agar diffusion membranes 10 (thicknesses of different thicknesses), a 0.01 cm PVDF filter membrane 13, and a zeolite and S110MH mixed adsorption membrane 6 are assembled into a circular DGT 14. The circular DGT housing consists of a base 15 and a cap 16 with a window. Figure 5 As shown, three circular DGTs are installed in a simple delivery device 22, which includes a float 23, a cuboid main frame 25, and a plumb bob 24. The simple delivery device 22 is placed in the water and tested for 24 hours. Water samples are taken multiple times within 24 hours. Then, spectrophotometric analysis of DGT-ammonia nitrogen or DGT-nitrate nitrogen eluent or nitrogen in the collected water samples is performed. According to the univariate linear curve of 1 / M vs. Δg in formula (2), the slope and intercept of the linear regression equation are obtained, and then the thickness (δ) of the diffusion boundary layer (DBL) is calculated. Based on formula (5), δ, and the diffusion layer thickness Δg (Δg = 0.09 cm calculated with a diffusion membrane thickness of 0.08 cm + a PVDF filter membrane thickness of 0.01 cm), the time-averaged concentration (C) of DGT in the water is calculated. DGT By comparing the time-averaged concentration with the instantaneous water sample concentration, the causes can be identified, revealing the eutrophication characteristics of the water body.

[0070]

[0071] Where M is the mass (ng) of soluble NH4-N or NO3-N accumulated on the adsorption membrane; t is the DGT operating time (s); Δg is the diffusion layer thickness (cm); A is the exposed area of ​​the DGT window (cm2); and D is the diffusion coefficient of the solute in the diffusion layer (cm). 2 s -1 C represents the concentration of the solute in the water (ng / mL). -1 The thickness δ of the diffusion confinement layer can be obtained by dividing the intercept by the slope.

[0072] The mass of solute (M) accumulated on the DGT adsorption membrane can be calculated according to formula (3); the diffusion flux (F) of DGT can be obtained according to formula (4) or (5). DGT ) or the time-averaged concentration of DGT as measured (C DGT ):

[0073] M = C e (V gel +V acid ) / f e Formula (3);

[0074]

[0075] Among them, C DGT It is the DGT concentration (μg mL) -1 M is the mass of solute accumulated in the mixed adsorption film of zeolite and S110MH (μg); Δg is the thickness of the diffusion layer (cm); δ is the thickness of the diffusion boundary layer (DBL) (cm); D is the diffusion coefficient of the solute in the diffusion layer (cm). 2 s -1 ); t is the DGT operation time (s); A is the DGT window exposure area (cm²). 2 ).

[0076] (ii) DGT testing methods for ammonia and nitrate nitrogen in natural sediments and covered sediments: such as Figure 6 As shown, columnar sediments were collected from the water body using a columnar sediment sampler (PVC pipe height: 50cm; inner diameter: 8cm). The heights of sediment 27 and the overlying water layer 26 were 40cm and 10cm, respectively, and then transported back to the laboratory. Figure 6 This demonstrates the effectiveness of the DGT probe at the interface between the control sediment column 28 and the overburden sediment column 29. A layer of covering agent 31, composed of fine sand, is applied to the surface of the columnar sediments to form an overburden sediment; the overburden layer 31 is 2.0 cm thick and the overburden is maintained for at least 3 months. After the experiment, as... Figure 7As shown, the DGT probe 30 is installed as follows: zeolite and S110MH mixed adsorption membrane 6, agar diffusion membrane 10 and PVDF filter membrane 13 are placed sequentially on the DGT plastic base plate 32, and the DGT plastic cover plate 33 is fastened to assemble the DGT probe 30. After 24 hours of deoxygenation treatment with the DGT probes, two DGT probes using a mixed zeolite and S110MH membrane were immediately tested at the sediment / water interface of the control and cover columns for 24 hours. After testing, the probes and the mixed zeolite and S110MH membranes were removed. The mixed zeolite and S110MH membranes were cut into strips with a vertical resolution of 2 or 5 mm using a ceramic cutter. After elution with 1M NaCl solution, ammonia nitrogen was determined by Nessler spectrophotometry and nitrate nitrogen was determined by ultraviolet dual-wavelength spectrophotometry according to the "National Environmental Protection Standards of the People's Republic of China (HJ535-2009; HJ / T346-2007)". The DGT concentration profiles of ammonia nitrogen and nitrate nitrogen at the sediment / water interface were calculated. The DGT-ammonia nitrogen and nitrate nitrogen concentration profiles of the covered sediment / water interface can be compared with the DGT profiles of control sediments (peak, low, and average values). Combined with the changes in nitrogen speciation and environmental parameters (pH and dissolved oxygen) in the stratified samples of covered or control sediments, the control effect of cover on the endogenous release of nitrogen from sediments can be studied.

[0077] (iii) Membrane-sensor measurements of inorganic nitrogen or environmental parameters (dissolved oxygen or pH) in the rhizosphere of aquatic plants: such as Figure 8 As shown, after the aquatic plant 35 is successfully cultivated in the root box 34 and the experimental water tank 45, the sensing membrane 40 is installed close to the detachable wall 36 of the root box. The sensing membrane 40 includes two types: (1) PVDF filter membrane + zeolite and S110MH mixed adsorption membrane 6 or (2) PVDF filter membrane + zeolite and S110MH mixed adsorption membrane + fluorescence sensing membrane. Sensing membrane installation method: (1) a rectangular zeolite and S110MH mixed adsorption membrane 6 (thickness: 0.01cm) or (2) a fluorescence sensing membrane 38 of the same shape (thickness: 20μm) + zeolite and S110MH mixed adsorption membrane 6 is pasted on the detachable wall 36 of the root box 34; then a PVDF filter membrane 13 is pasted; the detachable wall is reinstalled on the side of the root box, with the uppermost part of the window slightly lower than the sediment / water interface 39, to ensure that the root 37 of the selected aquatic plant 35 is in close contact with the PVDF filter membrane 13. like Figure 9As shown, the root box 34 is placed in the center of the experimental water tank 45. The experimental water tank 45 is a rectangular plastic water tank with an inlet pipe 41 and an outlet pipe 42 connected to its two sides to ensure water circulation and exchange within the tank. Two aeration heads 47 are installed on the left and right sides of the experimental water tank 45 to introduce air or argon gas into the water to control dissolved oxygen levels. Above the opening of the experimental water tank 45 is a plastic cover 44 of the same diameter. When argon gas is introduced into the water, this cover is placed on top to ensure airtightness and stable dissolved oxygen levels. A multi-functional water environment index testing probe 46 is placed in the water covering the root box 34 to measure the dissolved oxygen concentration in the water covering the root box online. A fluorescent lamp 43 is located above the experimental water tank 45 to simulate natural light changes over 24 hours. After culturing for 8 hours under defined environmental conditions (light / dark or aeration), the root box 34 was removed and placed in a planar photoelectric testing device to test the 2D distribution of dissolved oxygen or pH, and the 1D profile of dissolved oxygen concentration or pH was calculated. The root box was opened, and the zeolite and S110MH mixed adsorption membrane was removed. The adsorption membrane was cut with a ceramic cutter at a vertical spatial resolution of 2 or 5 mm. After elution with 1M NaCl solution, ammonia nitrogen was determined by Nessler spectrophotometry and nitrate nitrogen by ultraviolet dual-wavelength spectrophotometry according to the "National Environmental Protection Standards of the People's Republic of China (HJ535-2009; HJ / T346-2007)," obtaining the DGT diffusion flux profile of ammonia nitrogen or nitrate nitrogen. For sensors only equipped with a PVDF filter membrane + zeolite and S110MH mixed adsorption membrane, the fluorescence membrane test was not required; the adsorption membrane was directly removed from the root box, cut and eluted, and ammonia nitrogen and nitrate nitrogen were measured to calculate the DGT diffusion flux profile. Based on rhizosphere nitrogen / nitrate ratio and / or environmental conditions (pH or dissolved oxygen) profiles, combined with the physicochemical properties of roots, sediments and overlying water, this study reveals the mechanisms of nitrogen migration and absorption in the rhizosphere of aquatic plants and how these mechanisms are influenced by environmental conditions.

[0078] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0079] Example 1

[0080] This embodiment provides a method for preparing a mixed adsorption membrane of zeolite and S110MH, including the following steps:

[0081] (i) Pretreatment of the adsorbent: Prepare 3.5 g of zeolite particles (Beijing Huaye Huanyu Chemical Co., Ltd., Beijing, China) and 3.0 g of S110MH (hereinafter referred to as S110-MH) anion exchange resin (Beijing Chunda Technology Co., Ltd., Beijing, China). Zeolite particles: particle size: ~20 μm; pore size: 16–24 nm; thermal stability: 750 °C; cation exchange capacity: 50 Meq / g; main component mass content: SiO2 69.58%; Al2O3 12.20%; Si / Al 4.25–5.25. S110MH anion exchange resin: total exchange capacity 0.60 meq / mL; particle size: 30 μm. Grind the above two adsorbent particles using a grinder, and measure the particle size using a laser particle size analyzer until the particle size after grinding is ~12 μm. Thoroughly mix the ground adsorbent particles, store in brown test bottles at 4 °C.

[0082] (ii) Installing and heating the mold: A schematic diagram of the structure of the mold 1 used in this embodiment is shown below. Figure 1 As shown, mold 1 consists of two flat strips of tempered glass 2 (length × width × thickness = 20 × 5 × 0.5 cm) and a U-shaped polytetrafluoroethylene (PTFE) gasket 3 placed in the middle. Four thicknesses of the U-shaped PTFE gasket 3 (thicknesses of 0.01, 0.04, 0.08, and 0.12 cm) can be used to prepare: (i) a zeolite + S110MH mixed adsorption membrane with a thickness of 0.01 or 0.04 mm, or (ii) an agar adsorption membrane with a thickness of 0.04, 0.08, or 0.12 cm. Each frame of the U-shaped PTFE gasket 3 is 1 cm wide; the two short frames on the left and right are 5 cm high, and the bottom long frame is 20 cm long. In the middle of the mold is a rectangular slit 5 (the dimensions of the rectangular slit 5 are length × width × thickness = 18 × 4 × 0.01, 0.04, 0.08, or 0.12 cm). Five plastic clips 4 are used to fix two tempered glass pieces 2 and one U-shaped PTFE gasket 3; then the mold 1 is placed in an oven and heated to 80°C.

[0083] (iii) Preparation of hot agar aqueous solution (2.0%, m / v): Place 25 mL of deionized water in a 50 mL beaker, place the beaker in a sterile glove box, and heat it to 80 °C using an electric furnace; accurately weigh 0.5 g of agar powder (Thermo Fisher Scientific, Beijing, China), and slowly pour it into the hot water in the beaker, stirring thoroughly with a glass rod. After it has basically dissolved, reheat the beaker until the agar solution boils, and use an ultrasonic disperser to evenly disperse the agar in the water until the agar is completely dissolved and the solution is clear, thus obtaining the hot agar aqueous solution.

[0084] (iv) Preparation of the zeolite and S110MH mixed adsorption membrane: The pretreated adsorbent (zeolite and S110MH; see step (i)) was poured into a hot agar solution (see step (iii)), and the adsorbent was uniformly dispersed using an ultrasonic disperser. The mold was immediately removed from the oven (80°C), and then... Figure 2 As shown, the adsorbent particles + agar hot solution, i.e., hot mixed solution 11, in the beaker is drawn up with dropper 12 and dropped into the narrow slit 5 of mold 1, so that the solution evenly fills the entire narrow slit 5; after mold 1 has cooled at room temperature for 2 hours, the mold glass plate is opened and the zeolite and S110MH mixed adsorption membrane (length × width × thickness = 18 × 4 × 0.01 or 18 × 4 × 0.04 cm) is carefully removed. 3 Place the mixture in 0.5L of deionized water and change the water every 4 hours for a total of 5 times to remove impurities and any possible color from the zeolite and S110MH mixed adsorption membrane. Then, store the zeolite + S110-MH zeolite and S110MH mixed adsorption membrane in deionized water.

[0085] (v) Preparation of agar diffusion membrane (1.5%, m / v): Weigh 0.325 g of agar powder and prepare a hot agar aqueous solution according to the method described in step (iii). Immediately remove the mold (80°C) from the oven, use a dropper to draw the agar solution from the beaker, and drop the solution into the narrow slit 5 of the mold 1, so that the solution evenly fills the entire narrow slit 5; after the mold cools at room temperature for 2 hours, open the tempered glass plate 2 of the mold and carefully remove the zeolite adsorption membrane (length × width × thickness = 18 × 4 × 0.04, 0.08, or 0.12 cm). 3 Place the agar diffusion membrane in 0.5L of deionized water and change the water every 4 hours for a total of 5 times to remove impurities and any possible color from the membrane. Then, store the agar diffusion membrane 10 (1.5%, m / v) in 0.001M NaCl solution.

[0086] (2) DGT Function Test of Zeolite and S110MH Mixed Adsorption Membrane

[0087] (i) Determination of adsorption and elution efficiency: Prepare a mixed standard solution of NH4-N + NO3-N (5.0 + 5.0 mg / L) -1200 mL. Adjust the pH to 7.0 ± 0.2 with HCl or NaOH solution, then add NaCl reagent to achieve a NaCl molar concentration of 0.001 M in the mixed standard solution. Prepare 18 centrifuge tubes (20 mL each), placing 10 mL of the mixed standard solution and one circular zeolite and S110MH mixed adsorption membrane (diameter = 2.5 cm, thickness = 0.04 cm) in each tube. Place them on a constant temperature shaker at 500 rpm / min and room temperature for 24 h. Then, remove the zeolite and S110MH mixed adsorption membrane and place it in a 5 mL plastic centrifuge tube. Soak every 3 membranes in a specific concentration (volume: 4 mL) of an eluent for 24 h. The eluents to be tested include concentrations of 0.5, 1.0, and 2.0 mol·L⁻¹. -1 NaCl solution; concentration 1.0 mol·L⁻¹ -1 HCl, NaOH, and KCl solutions were used. The concentrations of ammonia nitrogen or nitrate nitrogen after the eluent or mixed standard solution were analyzed using a spectrophotometer. The absorption efficiency or elution efficiency was calculated using formula (6) or (7).

[0088]

[0089] Among them, C 标1 and C 标2 These are the concentrations (μg / mL) of the mixed standard solution before and after reaction. -1 );C solu The concentration of the elution buffer (μg mL) -1 ); 4 is the volume of the eluent (mL); 0.1964 is the volume of the zeolite and S110MH mixed adsorption membrane (mL); 10 is the volume of the mixed standard reaction solution (mL).

[0090] The absorption efficiency of the above (1) zeolite and S110MH mixed adsorption membrane for inorganic nitrogen in solution and (2) the elution efficiency and elution coefficient corresponding to different concentrations of eluent are shown in Table 1. Absorption efficiency: 94.3% (NH4-N) and 98.4% (NO3-N). A 1 mol L... -1 NaCl solution was used as the eluent; the corresponding elution efficiencies were 101.0 ± 3.1% (NH4-N) or 95.1 ± 2.9% (NO3-N).

[0091] Table 1. Absorption efficiency of zeolite and S110MH mixed adsorption membrane for inorganic nitrogen in solution, and elution efficiency and elution coefficient for eluents of different concentrations.

[0092]

[0093] (ii) Kinetic absorption experiment and determination of diffusion coefficient: Prepare 8 L of ammonia nitrogen and nitrate nitrogen mixed standard solution in a plastic liquid tank, wherein: C(NO3-N) = 10.0 mg / L -1 C(NH4-N) = 3.0 mg / L -1 NaCl concentration = 0.001 mol / L -1 Adjust the solution pH to 7.0 ± 0.2 using NaOH or HCl. Place the above liquid container on a magnetic stirrer. Prepare 5 sets of 15 circular zeolite and S110MH mixed adsorption membranes DGT (diffusion membrane thickness: 0.08 cm), such as... Figure 4 As shown, they were installed on the plastic frame 17, and the plastic frame 17 was immediately placed into the liquid cylinder. The magnetic stirrer was started, and the time was recorded. At the 4th, 8th, 12th, 16th, and 24th hour of action, one set of three DGTs was removed, along with the corresponding mixed standard solution sample. The mass of ammonia nitrogen and nitrate nitrogen accumulated on the DGT adsorption membrane and the nitrogen concentration of the water sample were analyzed. The curves based on the mass of ammonia nitrogen or nitrate nitrogen accumulated on the adsorption membrane corresponding to the operating time were presented. Figure 10 The diffusion coefficients of ammonia nitrogen or nitrate nitrogen in the agar diffusion layer at the actual temperature of the working liquid can be calculated using the univariate linear regression equation and calculation formula (1). Then, the diffusion coefficients of the two inorganic nitrogens in the agar diffusion layer at 25℃ can be obtained according to the calculation formula (8).

[0094]

[0095] Where: T is the actual temperature of the working fluid; D T It is the diffusion coefficient of ammonia nitrogen or nitrate nitrogen in the agar diffusion layer at the actual temperature of the working solution; D 25 It is the diffusion coefficient of ammonia nitrogen or nitrate nitrogen in the agar diffusion layer at 25℃.

[0096] Based on the above experiments and calculations, the absorption curves of DGT for ammonia nitrogen or nitrate nitrogen are as follows: Figure 10 As shown. Figure 10 ammonia nitrogen accumulated by zeolite and S110MH DGT ( Figure 10 (as shown in the image above) or nitrate ( Figure 10 The figure below shows the kinetic absorption curves, linear regression equations, and correlation coefficients for mass (M) corresponding to operating time (T = 24 h). The accumulated mass at each time point is expressed as the average of three measurements, M ± SD (standard deviation) (n = 3); Experimental conditions: Initial concentration of the reaction solution: NH₄⁻N = 3.2 mg / L -1 NO3-N = 10.4 mg / L -1 Final concentration of the reaction solution: NH4-N = 3.1 mg / L -1 NO3-N = 10.2 mg / L -1NaCl concentration: 0.001M; water temperature: 18.0±0.3℃. Based on the linear regression equation, formulas (1) and (8) can be used to calculate the diffusion coefficients of NH4-N and NO3-N in the agar diffusion layer at 25℃, which are 14.3×10⁻⁶ respectively. -6 and 8.40×10 -6 cm 2 s -1 .

[0097] (ii) Adsorption capacity of the zeolite and S110MH mixed adsorption membrane: A standard mixed solution of ammonia nitrogen and nitrate nitrogen (8L) was placed in a plastic liquid tank 18, wherein: C(NO3-N) = 10.0 mg / L -1 C(NH4-N) = 20.0 mg / L -1 NaCl concentration = 0.001 mol / L -1 The pH of the solution was adjusted to 7.0 ± 0.2 using NaOH or HCl. The plastic liquid container 18 was placed on a magnetic stirrer. Then, 27 circular zeolite and S110MH mixed adsorption membranes (DGT) were installed in a plastic frame and immediately placed in... Figure 4 The plastic liquid tank 18 was filled with the liquid, and the magnetic stirrer was activated. At each of the following reaction times (4, 8, 16, 24, 32, 40, 48, 56, and 64 hours), each set of circular DGT was removed, along with a water sample. The mass of ammonia or nitrate nitrogen adsorbed by the DGT and the concentration of ammonia or nitrate nitrogen in the water sample were analyzed using a spectrophotometer. Absorption curves corresponding to the mass of ammonia or nitrate nitrogen accumulated on the DGT adsorption membrane at different times can be obtained. Figure 11 ), Figure 11 The triangular or rhomboid dots in the diagram represent the mass of ammonia nitrogen or nitrate nitrogen, respectively, which is the mass of ammonia nitrogen or nitrate nitrogen accumulated in the mixed adsorption membrane at different action times within T=64h. Figure 11 The two dashed lines represent the theoretically predicted mass curves of ammonia nitrogen or nitrate nitrogen accumulated on the mixed adsorption membrane within 64 hours. Experimental conditions: Initial concentration of the reaction solution: NH4-N = 20 mg / L -1 NO3-N = 15 mg / L -1 Final concentration of the reaction solution: NH4-N = 19.5 mg / L -1 NO3-N = 14.8 mg / L -1 (pH = 7.22 ± 0.2; NaCl concentration: 0.001 M; water temperature: 18.0 ± 0.3 °C) shape. Based on Figure 11 The shape of the mass curves of ammonia nitrogen or nitrate nitrogen accumulated in the zeolite and S110MH mixed adsorption membrane at different time points can be used to evaluate the adsorption characteristics and maximum adsorption capacity of the mixed adsorption membrane. Figure 11It was observed that the maximum accumulation of NH4-N was observed at 32 h (765±24 μg / DGT), followed by a slow decline in the absorption curve from 40 h to 64 h; the maximum accumulation of NO3-N was observed at 48 h (501±20 μg / DGT), followed by a slow decline in the absorption curve from 56 h to 64 h. The slow decline in the latter half of the curve is due to competition for zeolite bonding sites with other cations (e.g., Na+). + Or the S110MH bonding site is competed for by other anions (e.g., Cl). - The adsorption capacity of ammonia nitrogen or nitrate nitrogen in the zeolite and S110MH mixed adsorption membrane is less than that of the adsorption membrane prepared with a single adsorbent. This is because the amount of zeolite or S110MH used in the mixed adsorption membrane is less than that used in the corresponding single adsorbent membrane. In fact, the concentration of ammonia nitrogen or nitrate nitrogen in natural water bodies is much lower than the concentration of the standard mixed adsorption solution. The DGT installed with the zeolite and S110MH mixed adsorption membrane prepared by this patented method can fully guarantee the accurate measurement of ammonia nitrogen or nitrate nitrogen in natural water bodies for at least 2 days.

[0098] (iii) Effects of pH and ionic strength on the test: (1) In Figure 4 The 10 plastic liquid tanks shown contain 2L of ammonia nitrogen and nitrate nitrogen mixed standard solution, wherein: C(NO3-N) = 10.0mg / L. -1 C(NH4-N) = 3.0 mg / L -1 NaCl concentration = 0.001 mol / L -1 The pH of the solution was adjusted to 3.0, 3.5, 4.0, 5.0, 6.0, 7.0, 8.5, 9.0 and 9.5 using 0.01M NaOH or 0.01M HCl. Thirty circular DGTs were assembled, with three installed on each frame, and placed in the corresponding liquid tanks for each pH. All liquid tanks were placed on a magnetic stirrer. The magnetic stirrer was started, and after 24 hours, the DGTs and water samples from each liquid tank were removed; (2) In Figure 4 The seven plastic liquid cylinders shown contain 2L of ammonia nitrogen and nitrate nitrogen mixed standard solution, wherein C(NO3-N) = 10.0 mg / L. -1 C(NH4-N) = 3.0 mg / L -1 pH = 7.0 ± 0.2 mol L -1 Then, a series of solutions with varying ionic strengths were prepared using NaCl: 0.0001, 0.0001, 0.001, 0.005, 0.01, 0.05, and 0.1 mol / L. -1Assemble 21 circular DGTs, with 3 mounted on each frame and placed in the corresponding liquid tanks for each ion strength. Place all liquid tanks on a magnetic stirrer. Start the magnetic stirrer and after 24 hours, remove the DGTs and water samples from each tank. Determine the ammonia nitrogen or nitrate nitrogen concentration (CL) of the DGT eluent and water samples obtained in steps (1) and (2) above using spectrophotometry. solu (NH4-N) or C solu (NO3-N); calculate the DGT concentration of ammonia nitrogen or nitrate nitrogen, which is C. DGT (NH4-N) or C DGT (NO3-N). Using C DGT (NH4-N) / C solu (NH4-N) or C DGT (NO3-N) / C solu The (NO3-N) ratio is used to measure the influence of pH or interfering ions on the determination.

[0099] The results showed that within the pH range (3.5–8.5), C solu (NH4-N) / C solu (NH4-N)(0.91-1.09) or C solu (NO3-N) / C solu (NO3-N) (0.92-1.10) (Table 2) meets the standard for accurate determination (0.90-1.10); that is, within the pH range of most water bodies, zeolite and S110MH DGT can be used to accurately determine ammonia nitrogen and nitrate nitrogen in water. When the NaCl concentration range is 0.0001-0.01M, C solu (NO3-N) / C solu (NO3-N)(0.94-1.05)(Table 3). When the NaCl concentration range is 0.0001-0.005M, C solu (NH4-N) / C solu(NH4-N)(0.94-1.04)(Table 3). To obtain the upper limit of ionic strength for ammonia nitrogen or nitrate nitrogen testing, (1) the DGT concentration of ammonia nitrogen standard solutions was tested using 0.002, 0.004, 0.008, and 0.01 M NaCl solutions; and (2) the DGT concentration of nitrate nitrogen standard solutions was determined using 0.012, 0.014, 0.018, 0.02, and 0.04 M NaCl solutions. The results showed that the upper limit of ionic strength (NaCl concentration) for achieving the standard was 0.008 M (NH4-N) and 0.014 M (NO3-N), respectively. The upper limit of ionic strength for the above NH4-Ni test was slightly lower than that of 0.012 M NaCl for Prch DGT and higher than that of 0.01 M NaCl solution for A520E DGT. The zeolite and S110MH mixed adsorption membrane DGT can accurately determine ammonia nitrogen and nitrate nitrogen for most water bodies with a certain ionic strength. In water bodies with high ionic strength, a thicker agar diffusion membrane (thickness: 0.80, 1.00 or 1.20 mm) and a shorter test time (e.g., 12–16 h) should be used to improve the accuracy and precision of the test.

[0100] Table 2. Ratios of ammonia or nitrate nitrogen concentrations measured by DGT in aqueous solutions at different pH levels to those measured by conventional methods.

[0101]

[0102]

[0103] Table 3. Ratios of ammonia nitrogen or nitrate nitrogen concentrations in aqueous solutions measured by DGT to those measured by conventional methods under different ionic strengths.

[0104]

[0105] (3) Testing of ammonia nitrogen and nitrate nitrogen in water, sediment or rhizosphere of aquatic plants using zeolite and S110MH mixed adsorption membrane DGT

[0106] (i) Testing of circular zeolite and S110MH mixed adsorption membrane DGT in water: Three types of circular DGT with agar diffusion membranes of varying thicknesses (0.4, 0.8, and 1.2 mm) were prepared for 24-hour testing at three sampling points in a river in a city of a certain province. The PVDF filter membrane thickness was 0.1 mm. The two sampling points (1, 2, and 3) were located in the river water below a bridge, with horizontal distances from the bridge's vertical projection of 0, 20, and 50 m, respectively. The distances from the edge of each of the three sampling points were 2 m, with water depths of 1.5, 1.8, and 1.4 m, respectively. Three DGT dispensers were used to test ammonia nitrogen and nitrate nitrogen at the above sampling points. Specifically: (1) Prepare 3 DGT samples for each of the above 3 thickness diffusion membranes, for a total of 9 samples. Install 1 DGT dispenser and place it at a sampling point 20m away from the bridge for testing; (2) Prepare 6 DGT samples with a diffusion membrane of 0.8mm. Install 3 samples in each of the other 2 dispensers and place them at sampling points 0m and 50m away from the bridge for testing. The water depth for DGT testing is the surface water (water depth: 0.3m) for ammonia nitrogen and nitrate nitrogen. At 0, 8, 16 and 24h of DGT measurement, collect 50mL of water sample from the same depth at each sampling point and store it in a refrigerator at 4℃. After 24 hours of DGT testing, the feeder was removed, the DGT was disassembled, and the zeolite and S110MH mixed adsorption membrane was taken out. It was eluted with 1M NaCl solution (4 mL) for 24 hours. The concentration of ammonia nitrogen or nitrate nitrogen in the eluent was determined by Nessler's colorimetry or UV dual-wavelength spectrophotometry. The mass (M; μg) of ammonia nitrogen or nitrate nitrogen accumulated on each DGT adsorption membrane was calculated. A curve was plotted showing the reciprocal of M (1 / M)(1 / μg) corresponding to the thicknesses Δg of the three diffusion layers (0.05, 0.09, and 0.13 cm). Figure 12 ), Figure 12 The curve representing the reciprocal (1 / M) (1 / μg) of the mass of ammonia nitrogen or nitrate nitrogen accumulated in the zeolite and S110MH mixed adsorption membrane with DGT corresponds to the diffusion layer thickness (Δg, cm); the thickness (δ) (cm) of the diffusion confinement layer (DBL) is used to calculate the mass of DGT accumulated at the diffusion layer thickness Δg (0.05, 0.09, or 0.13 cm); the mass is expressed as the average of three measurements, M ± SD (standard deviation) (n = 3); experimental conditions: pH = 7.80 ± 0.14; ionic strength = 0.165 ± 0.006 mS cm. -1 (Water temperature = 18.0 ± 0.1℃), based on the regression equation of the curve and the intercept of formula (2) and slope The ratio of the diffusion confinement layer thickness (δ) was calculated to be 0.026 cm (ammonia nitrogen) and 0.030 cm (nitrate nitrogen). Substituting the correction parameter δ into formula (5) can accurately calculate the DGT concentrations of nitrate nitrogen and ammonia nitrogen in the three sample points. The DGT concentrations of ammonia nitrogen and nitrate nitrogen obtained from this test and the instantaneous water sample concentrations at four time points for each sample point are shown in Table 4. As can be seen from Table 4, the instantaneous water sample concentration and the time-averaged concentration (C DGT The differences are significant because water quality changes considerably within 24 hours. Instantaneous water samples can only represent the concentration of ammonia or nitrate nitrogen at the sampling time point, and cannot represent the average concentration of nitrate and ammonia nitrogen at the sampling point within 24 hours. DGT tests the time-averaged concentration, which can more accurately reflect the pollution level of inorganic nitrogen in the water sample at the sampling point.

[0107] Table 4 shows the DGT test concentrations of ammonia nitrogen and nitrate nitrogen in the surface water of a river in a certain city of a certain province, and the routine test concentrations of four samples taken from the same point within 24 hours.

[0108]

[0109] (ii) Testing of ammonia and nitrate nitrogen in sediments using a zeolite and S110MH mixed adsorption membrane DGT probe, and evaluation of sediment cover effect: Two sediment samples were collected from one sampling point in a lake in a city of a certain province using a Petersen column sediment sampler; the PVC sampling tube used was 50 cm long and 8 cm in inner diameter; the collected column sediment layer was 35 cm thick, with an overlying water thickness of 15 cm. After being transported back to the laboratory, the samples were incubated in an incubator. The endogenous release of nitrogen from the sediments was controlled using a natural cover material—fine sand (particle size ≈ 100 μm). The overlying water above one of the column sediment samples was slowly extracted using a peristaltic pump and a plastic hose, and the aforementioned cover material—fine sand (49.98 g)—was used to cover the top layer of the sediment, with a cover thickness of 2 cm. The overlying water was then slowly poured back into the top layer of the column sediment. Zeolite and S110MH adsorption membranes (15 cm long and 1.8 cm wide), agar diffusion membranes, and PVDF filter membranes were sequentially overlapped and installed within a DGT probe plastic frame. The previously installed DGT probes were placed in a plastic container filled with ultrapure water and purged with argon gas for 24 hours to remove oxygen. Two DGT probes were then inserted into the covered sediment column and control sediment column, respectively, with a DGT probe window depth of 15 cm, including 2 cm of overlying water and 13 cm of covered sediment. At 0, 7, 30, 50, and 100 days after covering the top of a columnar sediment column with a cover agent (fine sand), the DGT probes were used to measure the control and passivated sediment layers for 24 hours, for a total of 5 measurements. Simultaneously, 20 mL of overlying water was collected, and the original overlying water was added to the PVC tube to the previous level. After the DGT test, the probes were removed, and the adsorption membranes were cut at the DGT window with a cutting tool. Then, using a ceramic cutting tool, the adsorption membrane was cut into strips with a vertical resolution of 5 mm. The strips were eluted with 2 mL of NaCl (1 M) solution for 24 h. Then, the mass of ammonia nitrogen and nitrate nitrogen accumulated in each strip was analyzed on a micro spectrophotometer using Nessler's colorimetry or ultraviolet dual-wavelength spectrophotometry, and the DGT concentration profile of ammonia nitrogen and nitrate nitrogen at the sediment / water interface was calculated according to formula (5). Figure 13 Based on the above profile and formulas (9) and (10), the diffusion flux (F) at the sediment / water interface was calculated. The ammonia nitrogen F values ​​for the control sediment and the passivated sediment (100 d) were 170 and -115 μg m³, respectively. -2 d -1 The F values ​​for nitrate and nitrogen were 618 and -219 μg m, respectively. -2 d -1 .

[0110]

[0111] Where: F is the cross-interfacial diffusion flux of ammonia nitrogen or nitrate nitrogen between sediments and the water boundary (μg m³). -2 d or mg m -2d); Fs and Fw are the diffusion fluxes (μg m³) in sediment and overlying water, respectively. -2 d or mg m -2 d); or These are the concentration gradients of ammonia nitrogen or nitrate nitrogen in the sediment or overlying water, respectively; Ds and Dw (cm³). 2 s -1 ) are the sediment diffusion coefficient and the water diffusion coefficient, respectively; φ is the sediment porosity.

[0112] Simultaneously, the concentrations of various nitrogen forms in the overlying water samples collected each time were analyzed using the aforementioned method. After the final DGT test at 100 days, the overlying water was extracted, and two sediment columns were cut at a vertical resolution of 1 cm to analyze the nitrogen forms and organic matter content of each sediment layer. The peak values ​​of DGT profiles for ammonia nitrogen and nitrate nitrogen in the overlying sediments and control sediments, as well as the interfacial diffusion flux, the concentrations of total nitrogen, inorganic nitrogen, organic nitrogen, ammonia nitrogen, and nitrate nitrogen in the overlying water, and the nitrogen forms and content distribution in the sediment stratification samples were compared to evaluate the control effect on the endogenous inorganic nitrogen load of the natural material—fine sand overlying sediments.

[0113] (iii) Testing of zeolite and S110MH mixed adsorption membrane in the rhizosphere of aquatic plants; seedlings of aquatic plants (e.g., Vallisneria natans) (length: 12 cm; weight: 2.2 g) were planted in root boxes; the root boxes were cuboids made of transparent PVC glass plates; one side was a removable glass plate; the root boxes were placed in an experimental water tank, which used a reflux pump for water circulation; a light simulation system was installed on the upper part of the experimental water tank to simulate daily light / dark changes; the experimental water tank was also connected to an aeration system that could aerate air or argon into the water to control the oxygen content in the root boxes. After adjusting the light / dark and anaerobic / aerobic conditions of the root box and stabilizing the environment for 8 hours, remove the root box, open the removable wall, and attach two types of sensors to the wall according to two schemes: (1) PVDF filter membrane (thickness: 0.1mm) and zeolite and S110MH mixed adsorption membrane (thickness: 0.01cm); (2) PVDF filter membrane (thickness: 0.1mm) and zeolite and S110MH mixed adsorption membrane (thickness: 0.01cm) + dissolved oxygen fluorescence sensing membrane (20μm). The size of each membrane of the above two types of sensors is 2×5cm (width×length). The two-layer membrane (first sensor) or three-layer membrane (second sensor) of the above sensors are placed tightly attached in sequence from the rhizosphere to the removable wall. Wrap the root box with the dissolved oxygen fluorescence sensing membrane installed on the wall with black plastic sheeting, leaving only the opening at the top aquatic plant end to communicate with the outside. Then place the root boxes (the first root box corresponding to the first sensor and the second root box corresponding to the second sensor) into the experimental water tank, keep the environmental conditions stable, and cultivate for 4-8 hours. Then, take out the first root box or the second root box, and immediately place the second root box in the box-type planar optical electrode equipment to take a fluorescence image, save it on the computer, analyze the fluorescence signal, and obtain a one-dimensional profile of the rhizosphere dissolved oxygen concentration. Then, take out the zeolite and S110MH mixed adsorption membrane of the second root box or the first root box, cut it with a ceramic cutter with a vertical resolution of 1 mm, and then elute each strip with 1M NaCl (2 mL) solution. Use a micro spectrophotometer to determine the concentration of ammonia nitrogen and nitrate nitrogen in the eluent; calculate the DGT profile diffusion flux (F) of the two inorganic nitrogens in the rhizosphere according to formula (4). DGT Rhizosphere sediments and roots were collected for subsequent analysis of sediment nitrogen and organic matter, as well as root nitrogen analysis. The one-dimensional DGT diffusion fluxes of ammonia nitrogen and nitrate nitrogen in rhizosphere sediments and the rhizosphere dissolved oxygen concentration profiles under the above aerobic-light conditions are shown below. Figure 14 As shown. Based on the 1D DGT diffusion flux profiles of rhizosphere ammonia nitrogen and nitrate nitrogen or the rhizosphere dissolved oxygen concentration profiles, combined with the physicochemical properties of rhizosphere sedimentation and the nitrogen content in Vallisneria natans roots, this study investigates the mechanisms by which rhizosphere dissolved oxygen affects the migration and transformation of ammonia nitrogen and nitrate nitrogen, as well as the mechanisms by which light or dissolved oxygen in water affects rhizosphere oxygen secretion.

[0114] As can be seen from the above embodiments, the zeolite and S110MH mixed adsorption membrane provided by the present invention, compared with existing single adsorption membranes, can save the amount of reagents required for adsorption membrane preparation, reduce the number of operations in the environmental medium, and only requires one elution for ammonia nitrogen and nitrate nitrogen analysis. Compared with existing zeolite and S110MH mixed adsorption membranes, the zeolite and S110MH mixed adsorption membrane provided by the present invention has the advantages of higher adsorption capacity, higher testing accuracy and precision, and higher elution efficiency. In summary, the Huhe adsorption membrane provided by the present invention is a novel DGT zeolite and S110MH mixed adsorption membrane, which can be used for simultaneous and accurate testing of ammonia nitrogen and nitrate nitrogen in water bodies, sediments, and rhizosphere of aquatic plants.

[0115] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. The application of a zeolite and S110MH mixed adsorption membrane in the detection of inorganic nitrogen in environmental media, characterized in that, The inorganic nitrogen includes ammonia nitrogen and nitrate nitrogen; the zeolite and S110MH mixed adsorption membrane includes agar hydrogel and adsorbent particles dispersed in the agar hydrogel, the adsorbent particles include zeolite particles and anion exchange resin particles; the particle size of the adsorbent particles is 12~20 μm, the silica-alumina ratio of the zeolite particles is 4.25~5.25, the pore size is 16~24 nm, and the anion exchange resin particles are S110MH anion exchange resin particles; the mass ratio of the zeolite particles to the anion exchange resin particles is (2.2~4):(2.8~4).

2. The application of the zeolite and S110MH mixed adsorption membrane according to claim 1 in the detection of inorganic nitrogen in environmental media, characterized in that, The mass ratio of the zeolite particles to the volume of the zeolite and S110MH mixed adsorption membrane is (2.2~4) g : 2.88 cm³. 3 .

3. The application of the zeolite and S110MH mixed adsorption membrane according to claim 1 in the detection of inorganic nitrogen in environmental media, characterized in that, The thickness of the zeolite and S110MH mixed adsorption membrane is 0.01 cm or 0.04 cm.

4. The application of the zeolite and S110MH mixed adsorption membrane according to claim 1 in the detection of inorganic nitrogen in environmental media, characterized in that, The preparation method of the zeolite and S110MH mixed adsorption membrane includes the following steps: The adsorbent particles and hot agar aqueous solution are mixed and dispersed to obtain a hot mixed solution; The hot mixed solution is poured into a mold, then cooled, and after demolding, the zeolite and S110MH mixed adsorption membrane is obtained.

5. The application of the zeolite and S110MH mixed adsorption membrane according to claim 4 in the detection of inorganic nitrogen in environmental media, characterized in that, The temperature of the hot agar aqueous solution is 75~80℃; During the injection process, the temperature of the mold is 75~80℃.

6. The application of the zeolite and S110MH mixed adsorption membrane according to claim 4 in the detection of inorganic nitrogen in environmental media, characterized in that, The process of obtaining the initial gel membrane after demolding further includes: immersing and washing the initial gel membrane with ultrapure water at least four times to obtain the zeolite and S110MH mixed adsorption membrane.

7. The application of the zeolite and S110MH mixed adsorption membrane according to claim 1 in the detection of inorganic nitrogen in environmental media, characterized in that, The environmental medium includes water bodies, sediments, or the rhizosphere of aquatic plants.

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