Method for determining the electron transfer rate of dissolved organic matter in soil

Abstract

The application discloses a method for measuring the electron transfer speed of dissolved organic matter in soil, and comprises the following steps: taking soil samples from wetland shallow soil, one layer every 2 cm, and taking more than three soil samples in total; adding the soil samples into ultrapure water to configure a suspension liquid; extracting dissolved organic matter in the soil suspension liquid by means of a shaking table oscillation, centrifugation and membrane filtration; obtaining an organic matter solution; using a three-electrode system and connecting an electrochemical workstation at room temperature; obtaining parameters such as peak current and peak potential by means of a cyclic voltammetry method; combining the concentration of the dissolved organic matter and the average molecular weight of the dissolved organic matter; and calculating the electron transfer rate constant k of the soil sample according to a Butler-Volmer equation. 0 The arithmetic mean of more than three electron transfer rate constants k 0 is calculated to represent and quantify the electron transfer speed of the dissolved organic matter in the surface layer of the wetland. The application has the advantages of simple process, convenient operation and specific quantification of the electron transfer speed of the dissolved organic matter in the shallow soil of the wetland.

Description

Technical Field

[0001] This invention relates to a method for determining the electron transfer rate of dissolved organic matter in soil, belonging to the field of electrochemical technology. Background Technology

[0002] In recent years, greenhouse gas emissions have been rising year by year, posing a huge threat to human living environment and global health. Wetland soils, as an important source of greenhouse gases, have attracted attention. In addition, wetlands such as marshes, tidal flats, and lakeshores are important natural ecosystems and natural resources, with multiple environmental functions such as flood control, climate regulation, water conservation, water purification, and biodiversity maintenance. However, wetland pollution has become increasingly serious recently. It is worth noting that both types of environmental problems involve electron transfer in biogeochemical cycles, but the extent to which dissolved organic matter in shallow wetland soils participates in these processes remains unclear, which has already sparked widespread discussion.

[0003] It is currently known that dissolved organic matter in soil participates in electron transfer processes as an electron shuttle through its active components. Quinones, humic acids, cysteine, and other sulfur-containing molecules are well-known as typical exogenous shuttles. However, there is a lack of experimental methods to characterize and quantify the electron transfer capacity of dissolved organic matter in soil. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a simple and direct calculation method for determining the electron transfer rate of dissolved organic matter in soil.

[0005] The technical solution of this invention is as follows:

[0006] A method for determining the electron transfer rate of dissolved organic matter in soil, the specific steps of which are as follows:

[0007] (1) Soil sample collection: Using a syringe soil sampler, at least 3 soil samples were collected in the shallow soil layer of the wetland, with each layer being 2 cm thick.

[0008] (2) Preparation of dissolved organic matter solution in soil: Soil sample was prepared by adding ultrapure water at a certain water-soil ratio to form a suspension. The dissolved organic matter in the soil suspension was extracted by shaking, centrifugation and membrane filtration to obtain organic matter solution.

[0009] (3) Using Ag / AgCl electrode, platinum wire, and glassy carbon electrode as the reference electrode, counter electrode, and working electrode, respectively, as a three-electrode system, and connecting it to an electrochemical workstation, the organic matter solution from step (2) was used as the electrolyte. Cyclic voltammetry was performed with the scanning voltage window, scanning speed, number of scan cycles, scanning time interval, and rest time set to obtain cyclic voltammetry curves. Based on the peak current, peak potential, working electrode surface area, number of electrons transferred, Faraday constant, and concentration of dissolved organic matter in the organic matter solution, the electron transfer rate constant k of dissolved organic matter in the soil sample was calculated using the Butler-Volmer equation. 0 :

[0010]

[0011] In the formula: Intercept is the natural logarithm of the absolute value of the peak current at different scan rates and the intercept of the linear fit of the overpotential; overpotential is the difference between the peak potential and the formal potential; and formal potential is the average of the oxidation peak potential and the reduction peak potential.

[0012] n is the number of electrons transferred; in this invention, n is taken as 2.

[0013] F is Faraday's constant;

[0014] A represents the surface area of ​​the working electrode, in m². 2 ;

[0015] C represents the concentration of the dissolved organic matter in the solution, expressed in mol / L.

[0016] e is a natural constant, and the same applies throughout the text;

[0017] Calculate k for samples with 3 or more layers 0 The arithmetic mean represents the rate of electron transfer in dissolved organic matter in shallow wetland soil.

[0018] When extracting dissolved organic matter from the soil in step (2), the ratio of soil to water is 1:3 to 1:10 g / mL.

[0019] Step (2) The temperature of the shaker is 25-30℃, the shaking speed is 100-200rpm, the time is 12-48h, and the centrifuge tubes in the shaker are placed horizontally.

[0020] Step (2) The centrifugation speed is 2000-4000 r / min and the centrifugation time is 15-30 min.

[0021] In step (2), the pore size of the filter membrane is 0.45 μm.

[0022] Step (3) The voltage window is -2 to 2V, the scanning speed is 10 to 160mV / s, the number of scanning circles is 2 to 6, the time interval is 0.001 to 0.1s, and the rest time is 1 to 30s.

[0023] The advantages of this invention are:

[0024] 1. The soil sample collection of this invention is flexible and simple, and the experimental process is green and environmentally friendly.

[0025] 2. The process of this invention is simple and easy to operate, and it can specifically quantify the electron transfer rate of dissolved organic matter in shallow wetland soil. Attached Figure Description

[0026] Figure 1 The electron transfer rate constant k in Example 1 0 ;

[0027] Figure 2 The electron transfer rate constant k in Example 2 0 ;

[0028] Figure 3 The electron transfer rate constant k in Example 3 0 . Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0030] Example 1

[0031] A method for determining the electron transfer rate of dissolved organic matter in shallow wetland soil, the specific steps of which are as follows:

[0032] (1) Obtaining shallow soil samples from wetlands: Using a syringe soil sampler, three soil samples were taken from the shallow soil layer of wetlands under woody vegetation cover, within 0-6 cm, in layers of 2 cm each; three samples were taken from each layer.

[0033] (2) Preparation of dissolved organic matter solution in soil: ultrapure water was added to shallow soil samples of wetland at a soil:water ratio of 1:3 g / mL. The samples were shaken at 100 rpm for 12 h at 25 ℃ and then taken out. The soil suspension was centrifuged at 2000 r / min for 15 min and then filtered through a 0.45 μm filter membrane to obtain organic matter solution, which was then stored at 4 ℃ for a short period of time.

[0034] (3) The total organic carbon content of the dissolved organic matter solution was determined using a total organic carbon analyzer; the average relative molecular mass of the dissolved organic matter was determined using Fourier transform ion cyclotron resonance mass spectrometry, and then the concentration of dissolved organic matter in the organic matter solution was calculated; (4) A three-electrode system (Ag / AgCl reference electrode, platinum wire and glassy carbon electrode as reference electrode, counter electrode and working electrode respectively) was used and connected to an electrochemical workstation. For each depth scan, 8 mL of soil dissolved organic matter solution was added to a small glass cup. The scanning voltage window was set to -2 to 2V, the scanning speed was 10, 20, 40, 60, 80, 100, 120, 140 and 160 mV / s, the number of scans was 2, the scanning time interval was 0.001s, and the rest time was 1s. Cyclic voltammetry curves were obtained. The peak current, peak potential, working electrode surface area, electron transfer number, Faraday constant and dissolved organic matter concentration were combined to calculate the k in the depth of 0 to 6 cm. 0 The electron transfer rate constant k of dissolved organic matter in soil samples was calculated using the Butler-Volmer equation. 0 :

[0035]

[0036] In the formula: Intercept is the natural logarithm of the absolute value of the peak current at different scan rates and the intercept of the linear fit of the overpotential; overpotential is the difference between the peak potential and the formal potential; and formal potential is the average of the oxidation peak potential and the reduction peak potential.

[0037] n is the number of electrons transferred, and n is 2.

[0038] F is Faraday's constant;

[0039] A represents the surface area of ​​the working electrode, in m². 2 ;

[0040] C represents the concentration of the dissolved organic matter in the solution, expressed in mol / L.

[0041] Calculate k for 3-layer sample 0 The arithmetic mean represents the rate of electron transfer in dissolved organic matter in shallow wetland soil.

[0042] Example 2

[0043] A method for determining the electron transfer rate of dissolved organic matter in shallow wetland soil, the specific steps of which are as follows:

[0044] (1) Obtaining shallow soil samples from wetlands: Using a syringe soil sampler, collect soil samples from the shallow soil layer of wetlands under woody vegetation cover, within 0-8 cm, in layers of 2 cm, for a total of four layers, and collect four soil samples; three samples are collected from each layer.

[0045] (2) Preparation of dissolved organic matter solution in soil: ultrapure water was added to the shallow soil sample of wetland at a soil:water ratio of 1:5 g / mL. The sample was shaken at 160 rpm for 24 h at 26 ℃. The soil suspension was centrifuged at 3000 r / min for 20 min and then filtered through a 0.45 μm filter membrane to obtain the dissolved organic matter solution in soil. The solution was then stored at 4 ℃ for a short period of time.

[0046] (3) The total organic carbon content of the dissolved organic matter solution was determined using a total organic carbon analyzer; the average relative molecular mass of the dissolved organic matter was determined using Fourier transform ion cyclotron resonance mass spectrometry, and then the concentration of dissolved organic matter in the organic matter solution was calculated; (4) A three-electrode system (Ag / AgCl reference electrode, platinum wire and glassy carbon electrode as reference electrode, counter electrode and working electrode respectively) was used and connected to an electrochemical workstation. For each depth scan, 8 mL of soil dissolved organic matter solution was added to a small glass cup. The scanning voltage window was set to -2 to 2V, the scanning speed was 10, 20, 40, 60, 80, 100, 120, 140 and 160 mV / s, the number of scans was 4, the scanning time interval was 0.01s, and the rest time was 15s. Cyclic voltammetry curves were obtained. The peak current, peak potential, working electrode surface area, electron transfer number, Faraday constant and dissolved organic matter concentration were combined to calculate the k within the depth of 0 to 8 cm. 0 The electron transfer rate constant k of dissolved organic matter in soil samples was calculated using the Butler-Volmer equation. 0 :

[0047]

[0048] In the formula: Intercept is the natural logarithm of the absolute value of the peak current at different scan rates and the intercept of the linear fit of the overpotential; overpotential is the difference between the peak potential and the formal potential; and formal potential is the average of the oxidation peak potential and the reduction peak potential.

[0049] n is the number of electrons transferred, and n is 2.

[0050] F is Faraday's constant;

[0051] A represents the surface area of ​​the working electrode, in m². 2 ;

[0052] C represents the concentration of the dissolved organic matter in the solution, expressed in mol / L.

[0053] Calculate k for 4-layer sample 0 The arithmetic mean represents the rate of electron transfer in dissolved organic matter in shallow wetland soil.

[0054] Example 3

[0055] A method for determining the electron transfer rate of dissolved organic matter in shallow wetland soil, the specific steps of which are as follows:

[0056] (1) Obtaining shallow soil samples from wetlands: Using a syringe soil sampler, five soil samples were taken from the shallow soil layer of wetlands under woody vegetation cover, within 0-10cm, in layers of 2cm each, for a total of five layers; three samples were taken from each layer.

[0057] (2) Preparation of dissolved organic matter solution in soil: ultrapure water was added to the shallow soil sample of wetland at a soil:water ratio of 1:10 g / mL. The sample was shaken at 200 rpm for 48 h at 30 ℃. The soil suspension was centrifuged at 4000 r / min for 30 min and then filtered through a 0.45 μm filter membrane to obtain organic matter solution, which was then stored at 4 ℃ for a short period of time.

[0058] (3) The total organic carbon content of the dissolved organic matter solution was determined using a total organic carbon analyzer; the average relative molecular mass of the dissolved organic matter was determined using Fourier transform ion cyclotron resonance mass spectrometry, and then the concentration of dissolved organic matter in the organic matter solution was calculated; (4) A three-electrode system (Ag / AgCl reference electrode, platinum wire and glassy carbon electrode as reference electrode, counter electrode and working electrode respectively) was used and connected to an electrochemical workstation. For each depth scan, 8 mL of soil dissolved organic matter solution was added to a small glass cup. The scanning voltage window was set to -1.5 to 1.5 V, the scanning speed was 10, 20, 40, 60, 80, 100, 120, 140 and 160 mV / s, the number of scans was 6, the scanning time interval was 0.1 s, and the resting time was 30 s. Cyclic voltammetry curves were obtained. The peak current, peak potential, working electrode surface area, electron transfer number, Faraday constant and dissolved organic matter concentration were combined to calculate the k in the depth of 0 to 10 cm. 0 The electron transfer rate constant k of dissolved organic matter in soil samples was calculated using the Butler-Volmer equation. 0 :

[0059]

[0060] In the formula: Intercept is the natural logarithm of the absolute value of the peak current at different scan rates and the intercept of the linear fit of the overpotential; overpotential is the difference between the peak potential and the formal potential; and formal potential is the average of the oxidation peak potential and the reduction peak potential.

[0061] n is the number of electrons transferred, and n is 2.

[0062] F is Faraday's constant;

[0063] A represents the surface area of ​​the working electrode, in m². 2 ;

[0064] C represents the concentration of the dissolved organic matter in the solution, expressed in mol / L.

[0065] Calculate k for 5-layer sample 0 The arithmetic mean represents the rate of electron transfer in dissolved organic matter in shallow wetland soil.

[0066] Figure 1 The electron transfer rate constant k in Example 1 0 The value shows that k ranges from 0 to 6 cm. 0 It is 0.13 cm / s. Figure 2 The electron transfer rate constant k in Example 2 0 The value shows that k is within the range of 0-8cm. 0 It is 0.13 cm / s. Figure 3 The electron transfer rate constant k in Example 3 0 The value shows that k0 is 0.12 cm / s within the range of 0 to 10 cm.

[0067] The above embodiments also illustrate that there are differences in the electron transfer rate of dissolved organic matter at different depths in different regions of shallow wetland soil, providing a new perspective for those in the art to use k0 to estimate greenhouse gas emissions and soil pollution remediation.

Claims

1. A method for determining the electron transfer rate of dissolved organic matter in soil, characterized in that, The specific steps are as follows: (1) Take soil samples from the shallow soil layer of the wetland, with each layer being 2cm thick, and take at least 3 soil samples in total. (2) Soil samples were added to ultrapure water to prepare a suspension. The dissolved organic matter in the soil suspension was extracted by shaking, centrifugation and membrane filtration to obtain an organic matter solution. (3) Using Ag / AgCl electrode, platinum wire and glassy carbon electrode as reference electrode, counter electrode and working electrode respectively as three electrode system, and connected to an electrochemical workstation, the organic matter solution in step (2) is used as electrolyte. The scanning voltage window, scanning speed, number of scan cycles, scanning time interval and rest time are set to obtain cyclic voltammetry curves. Combined with peak current, peak potential, working electrode surface area, electron transfer number, Faraday constant and organic matter solution concentration, the electron transfer rate constant k of dissolved organic matter in soil sample is calculated according to the Butler-Volmer equation. 0 : In the formula: Intercept is the natural logarithm of the absolute value of the peak current at different scan rates and the intercept of the linear fit of the overpotential; overpotential is the difference between the peak potential and the formal potential; and formal potential is the average of the oxidation peak potential and the reduction peak potential. n is the number of electrons transferred, n = 2; F is Faraday's constant; A represents the surface area of ​​the working electrode, in m². 2 ; C represents the concentration of the organic matter solution, in mol / L. Calculate k for soil samples with more than 3 layers 0 The arithmetic mean of the values ​​is used to quantify the electron transfer rate of dissolved organic matter in shallow wetland soil.

2. The method for determining the electron transfer rate of dissolved organic matter in soil according to claim 1, characterized in that, Step (2) The mixing ratio of soil and ultrapure water is 1:3 to 1:10 g / mL.

3. The method for determining the electron transfer rate of dissolved organic matter in soil according to claim 1, characterized in that, Step (2) The temperature of the shaker is 25-30℃, the shaking speed is 100-200rpm, and the time is 12-48h.

4. The method for determining the electron transfer rate of dissolved organic matter in soil according to claim 1, characterized in that, Step (2) The centrifugation speed is 2000-4000 r / min and the centrifugation time is 15-30 min; the filter membrane pore size is 0.45 μm when passing through the membrane.

5. The method for determining the electron transfer rate of dissolved organic matter in soil according to claim 1, characterized in that, Step (3) The voltage window is -2 to 2V, the scanning speed is 10 to 160mV / s, the number of scanning circles is 2 to 6, the time interval is 0.001 to 0.1s, and the rest time is 1 to 30s.

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