A quantitative determination method for vacancy defect concentration in metastable iron oxides

Abstract

The present invention provides a method for quantitatively determining the vacancy defect concentration of metastable iron oxides, comprising: adding FeCl2 solutions with different concentrations into a buffer solution containing KCl to obtain mixed solutions with different #imgabs0# concentrations; taking the mixed solutions with different #imgabs1# concentrations, respectively adding metastable iron oxides, fully mixing them, adding a mediator substance to carry out a reaction, after the reaction ends, filtering, and respectively measuring the #imgabs2# concentration and redox potential of the binary heterogeneous system; fitting the #imgabs3# concentration values of the binary heterogeneous system and their corresponding redox potential values E H to obtain the vacancy defect concentration through the fitted function and the thermodynamic reaction equation. The present invention effectively solves the accurate determination of the redox potential value (E H ) of the heterogeneous system, and can also in-situ measure the metastable structure of redox-active nanoparticles, which has important guiding significance for predicting the abiotic attenuation rate of site pollutants.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental earth sciences, and in particular relates to a method for quantitatively determining the concentration of vacancy defects in metastable iron oxides. Background Art

[0002] Soil and sediments are usually rich in iron oxides, which profoundly affect the migration and transformation of pollutants. Affected by factors such as natural environmental temperature, redox conditions, and impurity ions, iron oxides have poor crystallinity and commonly have vacancy defect structures. The presence of defects will greatly affect the redox, adsorption, electron transfer, mineral microbial transformation and other reaction processes at the mineral interface.

[0003] There are two main types of common characterization methods: transmission electron microscopy (TEM) and spectroscopy. The resolution of TEM is generally at the nanometer level, and the atomic structure can be observed. Generally, the atomic image can be observed after filtering the surface lattice image, so defects can be seen through high-resolution TEM images. Spectroscopic characterization mainly includes Raman, fluorescence spectroscopy and electron paramagnetic resonance spectroscopy. For example, when using Raman spectroscopy to identify graphene, the defects in graphene cause two new vibration modes to appear in the Raman spectrum, namely the D peak (1350cm -1 ) and D' peak (1620cm -1 ). For fluorescence spectroscopy, defects can cause fluorescence peaks in two-dimensional materials, and the defects can be analyzed based on the location of the fluorescence peaks.

[0004] The biggest problem with these characterization techniques is that the strength of the spectral signal cannot directly reflect the absolute content of the number of vacancy defects. In essence, it is still a qualitative and semi-quantitative analysis method. Once the experimental conditions in the literature are different, the experimental results under the same system may be significantly different, which may lead to deviations in the understanding of the surface properties of iron oxide. It is of great significance to achieve defect quantification, focus on the key factor of the systematic changes in the characteristics and number of vacancy defects in iron minerals, combine conventional analytical methods with thermodynamic techniques, reveal the microscopic mechanism of the influence of iron mineral substructure on its reaction activity, and clearly answer the scientific question of the correspondence between the structure of iron minerals and their properties.

[0005] Therefore, the applicant considers providing a method for quantitatively calculating the vacancy defects in metastable iron oxides. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for quantitatively determining the concentration of vacancy defects in metastable iron oxides, which has the advantages of in-situ measurement and low cost, and fills the gap in the quantitative calculation of defect structures in active nano-oxide particles.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for quantitatively determining the concentration of vacancy defects in metastable iron oxides comprises the following steps:

[0009] 1) Add different concentrations of FeCl2 solution to the buffer solution containing KCl to obtain different Concentration of mixed solution;

[0010] 2) Take the different concentrations, respectively adding metastable iron oxides, and after fully mixing, respectively adding mediating substances to the reaction system for reaction, and filtering after the reaction to obtain multiple binary heterogeneous systems; respectively determining the binary heterogeneous systems concentration; the plurality is at least four;

[0011] 3) respectively measuring the redox potential of the binary heterogeneous system;

[0012] 4) For the binary heterogeneous system Concentration value and its corresponding redox potential value E H The fitting is performed and the vacancy defect concentration is obtained through the fitted function and the thermodynamic reaction equation.

[0013] Preferably, in the determination method, the entire determination process is carried out at room temperature, and the environment in which the determination process is carried out is an anaerobic environment with an oxygen content of <5ppm; in the determination method, the pH value is kept constant throughout the determination process by a pH adjuster, and the pH value is 5.0~8.0.

[0014] Preferably, the pH value is 6.0.

[0015] Preferably, in step 1), the buffer substance of the buffer solution is any one of diethylpiperazine, morpholineethanesulfonic acid monohydrate, and 3-morpholinepropanesulfonic acid; and the pH adjuster is KOH and / or HCl.

[0016] Preferably, in the mixed solution of step 1), Concentration range: 0.1mmol·L -1 ~10mmol·L -1 , the concentration of the buffer solution is 20~50mM, and the concentration of KCl is 20~30mmol·L -1 .

[0017] Preferably, in the mixed solution of step 1), the concentration of KCl is 25 mmol·L -1 .

[0018] Preferably, in step 2), after the metastable iron oxide is added to the mixed solution, the concentration of the metastable iron oxide in the mixed solution is 1 g / L.

[0019] Preferably, in step 2), the metastable iron oxide is any one or more of hematite, lepidocrocite, ferrihydrite, and magnetite; the mediating substance is any one of cyanomethyl viologen, hexaamineruthenium chloride, ethyl viologen, and diquat; and the concentration of the mediating substance in the reaction system is 10-20 μmol·L -1 .

[0020] Preferably, in step 3), the redox potential is measured using a potentiometric titrator combined with a platinum ring redox composite electrode, comprising the following steps:

[0021] 3.1) Electrode pretreatment: soaking the platinum ring redox composite electrode in HCl and KCl solutions successively;

[0022] 3.2) Determination of redox potential: insert the pretreated platinum ring redox composite electrode into the binary heterogeneous system, and continuously measure the potential using a potentiometric titrator under magnetic stirring conditions, and record the redox potential value after equilibrium. E H .

[0023] Preferably, in step 4), the fitted function is y=a+bx, where y is E H , x is , a is the intercept, b is the slope; when the metastable iron oxide structure contains oxygen vacancies, the thermodynamic reaction equation is:

[0024] ;

[0025] The oxygen vacancy concentration is calculated by the following formula:

[0026] ;

[0027] Alternatively, when the metastable iron oxide structure contains iron vacancies, the thermodynamic reaction equation is:

[0028]

[0029] The iron vacancy concentration is calculated by the following formula:

[0030]

[0031] In the formula, E H is the redox potential value of the binary heterogeneous system; is the standard reduction potential, In a binary heterogeneous system Fe 2+ concentration, m is oxygen vacancy, and n is iron vacancy.

[0032] Compared with the existing methods, the technical solution provided by the present invention has the following advantages and beneficial effects:

[0033] With the advancement of electrochemical technology, it is possible to measure and calculate the mineral-bound Fe 2+ The reduction potential ( E H ) is possible, considering that the defect structure may affect its thermodynamic properties, the defective iron oxide is used to react with hematite-Fe 2+ The redox potential value of binary heterogeneous system ( E H ) is associated with quantitative calculation of the defect structure of iron oxide, which not only effectively solves the redox potential value of heterogeneous system ( E H ) can also be accurately determined and the metastable structure of redox-active nanoparticles can be measured in situ, which is of great significance for predicting the abiotic decay rate of site pollutants.

[0034] The present invention is based on a novel technique of thermodynamic method and establishes a mediated potential method, which can measure the redox potential ( E H ) value, and combined with the actual measured E H A thermodynamic relationship is established with the concentration of Fe(II) in the solution and a reaction formula is derived to reversely calculate the size of the defect concentration in the iron oxide mineral. The present invention is aimed at iron oxide-hematite, which is ubiquitous in nature, widely used in engineering systems, and does not undergo phase change under the experimental conditions of the present invention. The verification of the slope in the thermodynamic relationship reaction formula established according to the scheme of the present invention and the theoretical slope further proves that the method established by the scheme of the present invention is accurate and reliable. The mediated potential method established by the scheme of the present invention has the advantages of in-situ measurement and low cost, which makes up for the quantitative calculation problem of defect structures in measuring active nano-oxide particles in the prior art. At the same time, the relevant results are of great significance for correctly understanding the iron-mediated biogeochemical cycle in complex systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a data fitting result diagram in the embodiments and comparative examples of the present invention, wherein: Figure 1 a is the fitting result diagram of control example 1 and control example 2, Figure 1 b is the fitting result diagram of Example 1 and Example 2, Figure 1c is the fitting result diagram of Example 3 and Example 4. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the preferred implementation scheme of the present invention is described below in conjunction with specific embodiments, but it should not be understood as limiting the present invention and is only used as an example.

[0037] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0038] The present invention provides a method for quantitatively determining the concentration of vacancy defects in metastable iron oxides, comprising the following steps:

[0039] 1) Add KCl and buffer solution to a 25 mL brown glass bottle, and add different concentrations of FeCl2 stock solution. Use KOH and HCl to control the required pH value to 5.0-8.0. After fully mixing, take a sample to measure the mixed solution. concentration. is the Fe in solution 2+ In the mixed solution, the concentration of KCl is 25mmol·L -1 The concentration of the buffer solution is 25 mmol·L -1 , The concentration is 0.1mmol·L -1 ~10mmol·L -1 within the range.

[0040] The buffer substance is any one of the following: diethylpiperazine [DEPP], morpholineethanesulfonic acid monohydrate [MES], 3-morpholinepropanesulfonic acid [MOPS].

[0041] Determination of mixed solution by o-phenanthroline spectrophotometry Initial concentration.

[0042] 2) Metastable iron oxide was then added to the mixed solution and mixed thoroughly for 1 hour. Then, a mediator was added to the reaction system and mixed for 24 hours to obtain a binary heterogeneous system. The sample was filtered through a 0.22 μm filter and the binary heterogeneous system was determined by o-phenanthroline spectrophotometry. Concentration. Three parallel samples were set for all samples to ensure the accuracy of the test. After the metastable iron oxide was added to the mixed solution, the concentration of the metastable iron oxide in the mixed solution was 1g / L. The metastable iron oxide is any one of hematite, lepidocrocite, ferrihydrite, and magnetite. The mediating substance is any one of cyanomethyl viologen, hexaammineruthenium chloride, ethyl viologen and diquat, and the concentration of the mediating substance in the reaction system is 10~20μmol·L -1 .

[0043] 3) Determining the equilibrium redox potential of a binary heterogeneous system, specifically comprising the following steps:

[0044] 3.1) Electrode pretreatment: The platinum ring redox composite electrode was pretreated by soaking in HCl (0.1~1M) and KCl (3M) for several hours.

[0045] 3.2) Determination of redox potential: Insert the pretreated platinum ring redox composite electrode into the experimental sample, and continuously measure the potential using a potentiometric titrator under magnetic stirring conditions, record the value every 2 seconds, and record the redox potential value after equilibrium. E H .

[0046] Platinum ring was used as the working electrode, Ag / AgCļ was used as the reference electrode, and 3 mol·L -1 KCl was used as the reference solution.

[0047] All the above-mentioned protocols were carried out in an anaerobic glove box.

[0048] For multiple different The mixed solutions of different concentrations were subjected to steps 1) to 3 in sequence to obtain multiple sets of binary heterogeneous systems. Concentration values ​​and their corresponding redox values E H . Wherein, a plurality is at least four.

[0049] 4) For at least four binary heterogeneous systems Concentration and redox value E H The fitting is performed and the vacancy defect concentration is obtained through the fitted function and the thermodynamic reaction equation.

[0050] According to the following thermodynamic reaction equation:

[0051] Defect-free hematite-Fe 2+ The redox half-reactions of the binary heterogeneous system are as follows:

[0052] ; (Formula 1)

[0053] The Nernst equation corresponding to the above redox half reaction is as follows:

[0054] ; (Formula 2)

[0055] in is the redox potential value of the binary heterogeneous system, is the standard reduction potential, In a binary heterogeneous system Fe 2+ concentration,[ H + ] is the solution H + concentration, R is the ideal gas constant, T is the temperature, and F is the Faraday constant. At room temperature (298K), Equation 2 is simplified to:

[0056] ; (Formula 3)

[0057] Where V is volt-ampere (unit of voltage).

[0058] When the iron oxide structure contains oxygen vacancies or iron vacancies, the iron oxide can be expressed as and , the corresponding redox half reactions are as follows:

[0059] ; (Formula 4)

[0060] ; (Formula 5)

[0061] The Nernst equations corresponding to the half reactions shown in Equation 4 and Equation 5 are as follows:

[0062] ; (Formula 6)

[0063] ; (Formula 7)

[0064] The above Nernst equation simplifies to:

[0065] When the metastable iron oxide structure contains oxygen vacancies, the thermodynamic reaction equation is:

[0066] ; (Formula 8)

[0067] Alternatively, when the metastable iron oxide structure contains iron vacancies, the thermodynamic reaction equation is:

[0068] ; (Formula 9)

[0069] Obtaining binary heterogeneous systems Concentration and redox potential E H The relationship between them can be obtained by fitting the test data.

[0070] The fitted function is y=a+bx, where y is E H , x is ;

[0071] The slope is b. In actual situations, b is always negative, and m and n are both positive. For ease of calculation, the following directly uses Perform calculations.

[0072] When the metastable iron oxide structure contains oxygen vacancies, , oxygen vacancy defect ; When the metastable iron oxide structure contains iron vacancies, , iron vacancy defect .

[0073] The entire measurement process is carried out at room temperature, and the measurement process is carried out in an anaerobic environment with an oxygen content of <5ppm; the pH value remains unchanged during the entire measurement process, and KOH and / or HCl are used as pH adjusters with a pH value of 5.0~8.0.

[0074] The present invention is further described below by reference examples and embodiments.

[0075] Some of the instruments and reagents used in the control examples and embodiments are as follows:

[0076] Instruments and equipment: Metrohm 836 Titrando automatic potentiometric titrator, equipped with 6.0451.100 platinum ring redox composite electrode (Metrohm, Switzerland); anaerobic glove box (M3RAUN, W15392-4, operating condition: oxygen <0.5ppm).

[0077] Reagent raw materials: ferrous chloride (FeCl2·6H2O, Sigma-Aldrich, USA);

[0078] Potassium chloride (KCl, Sinopharm Chemical Reagent Co., Ltd.);

[0079] Ferric nitrate (FeNO3, Sinopharm Chemical Reagent Co., Ltd.);

[0080] Sodium borohydride (NaBH4, Tianjin Fengchuan Chemical Reagent Technology Co., Ltd.);

[0081] Potassium hydroxide (KOH, Sinopharm Chemical Reagent Co., Ltd.);

[0082] Hydrochloric acid (HCl, Sinopharm Chemical Reagent Co., Ltd.).

[0083] Buffer substances: diethylpiperazine [DEPP], pKa 4.7, 98%; morpholineethanesulfonic acid monohydrate [MES], pKa 6.1, ≥99.0%; 3-morpholinepropanesulfonic acid [MOPS], pKa 7.2, ≥99.0%.

[0084] All reagents were of analytical grade or above, and all aqueous solutions were prepared with ultrapure water.

[0085] The implementation environment of the scheme of the present invention is an anaerobic glove box, in which the oxygen content in the box is less than 5ppm and the temperature is room temperature (298K). To eliminate oxygen interference, all solutions must be purged with inert gases such as nitrogen or argon for several hours or days, or prepared with oxygen-free water.

[0086] The anaerobic chamber provides a relatively anaerobic and dry environment, which can avoid the influence of oxygen in the system on Fe(II).

[0087] The pH value remained constant throughout the assay.

[0088] Buffer reagents: morpholineethanesulfonic acid monohydrate [MES], pH 5.0, aladdin Chemicals Inc., ≥99.0%; 3-morpholinepropanesulfonic acid [MOPS], pH 7.0, aladdin Chemicals Inc., ≥99.0%). If the concentration is too high or too low, the pH of the system will be unstable. However, the type of buffer has its own pH buffer range, and the appropriate type and concentration of buffer should be selected according to the required system pH.

[0089] Mediator: Hexaammineruthenium chloride ([Ru(NH3)6]Cl2, ≥99.9%, Sigma-Aldrich, St. Louis, MO, USA).

[0090] Iron oxide 1# is defect-free hematite and is prepared by the following method: Take 500mL of 0.1mol·L -1 Fe(NO3)3 solution, 300mL 1mol·L -1 KOH, 50mL 1mol·L -1 NaHCO3, after mixing, aged at 90℃ for 4 days, washed the sample with ultrapure water, freeze-dried, and ground through a 100-mesh sieve. The sieved product was calcined in a muffle furnace at 600℃ for 5h to obtain defect-free hematite;

[0091] Iron oxide 2# is hematite containing oxygen vacancies, and is prepared by the following method: iron oxide 1# is immersed in a 1.5M NaBH4 solution for reaction for several hours, and then washed with water and ethanol for multiple times and dried in an oven at 40°C to prepare hematite containing oxygen vacancies;

[0092] Iron oxide 3# is hematite containing iron vacancies, which is prepared by the following method: a portion of iron oxide 1# is placed in a ball mill for mechanical ball milling for 12 hours to prepare hematite containing iron vacancies. Example 1

[0093] The test sample in this embodiment is iron oxide 2# (hematite containing oxygen vacancies). The pH value remains unchanged during the entire measurement process and is 5.0.

[0094] A method for quantitatively determining the concentration of vacancy defects in metastable iron oxides comprises the following steps:

[0095] 1) Prepare mixed solution: add KCl and MES solution to a 25 mL brown glass bottle, add FeCl2 stock solution of different concentrations, use 1 M KOH and HCl to control the pH value to 5.0, and obtain mixed solution; there are five mixed solutions, and The concentrations are 0.2mM, 0.4mM, 1.0mM, 3.0mM, and 5.0mM respectively; the concentration of KCl in the mixed solution is 25mmol·L -1 The concentration of the buffer substance is 25 mmol·L -1 The initial concentration of the mixed solution was determined by o-phenanthroline spectrophotometry.

[0096] 2) Add 0.015g of iron oxide 2# to the mixed solution, and the concentration after addition is 1g·L -1 , react for 1 hour; after the reaction, add 10mM [Ru(NH3)6]Cl2 as a mediator to the reaction system, and the concentration of the mediator after addition is 10μM. Stir in the dark for 24 hours to obtain a binary heterogeneous system. 1M KOH and HCl are used again to control the pH value of the reaction system to 5.0. Samples are taken through a 0.22μm filter, and the o-phenanthroline spectrophotometry is used to determine the five binary heterogeneous systems. concentration.

[0097] 3) Use a platinum ring composite redox electrode (Ag / AgCl as reference electrode) to measure the suspension in a glove box E H The value is monitored over time until no significant change is observed, which is the value of the iron oxide 2-Fe(II) binary heterogeneous system at pH = 5.0. E H value.

[0098] 3.1) Electrode pretreatment: The platinum ring redox composite electrode was pretreated by soaking in HCl (0.1~1M) and KCl (3M) for several hours.

[0099] 3.2) Determination of redox potential: Insert the pretreated platinum ring redox composite electrode into the experimental sample. Under magnetic stirring conditions, use a potentiometric titrator to continuously measure the potential, record the value every 2 seconds, and record the redox potential value after equilibrium.

[0100] Platinum ring was used as the working electrode, Ag / AgCl was used as the reference electrode, and 3 mol·L -1 KCl was used as the reference solution. All the above schemes were carried out in an anaerobic glove box.

[0101] 4) Concentration and redox value of five binary heterogeneous systems E H The fitting is performed and the vacancy defect concentration is obtained through the fitted function and the thermodynamic reaction equation. Example 2

[0102] The difference between this embodiment and embodiment 1 is that the pH value during the whole determination process is kept at 6.0; and the buffer solution is MOPS solution. Example 3

[0103] The difference between this embodiment and embodiment 2 is that the test sample is iron oxide 3# (hematite containing iron vacancies). Example 4

[0104] The difference between this embodiment and embodiment 3 is that the pH value is maintained at 7.0 during the entire measurement process.

[0105] Comparative Example 1

[0106] The difference between this control example and Example 1 is that the test sample is iron oxide 1# (defect-free hematite).

[0107] Comparative Example 2

[0108] The difference between this comparative example and Example 1 is that the test sample is iron oxide 1# (defect-free hematite). The pH value is kept at 6.0 during the whole measurement process. MOPS solution is used as the buffer solution.

[0109] The experimental results of Examples 1-4 are shown in Table 1, and the experimental results of Comparative Examples 1-2 are shown in Table 2.

[0110] Table 1: Fe(II) concentration and pH value of hematite-Fe(II) binary heterogeneous system containing vacancy defects under different pH conditions E h value

[0111]

[0112] Table 2: Fe(II) concentration and pH value of defect-free hematite-Fe(II) binary heterogeneous system under different pH conditions E h value

[0113]

[0114] From Table 2 and Figure 1 a It can be seen that with the defect-free hematite-Fe(II) binary heterogeneous system As the concentration increases, the redox potential value E H The lower the pH, the higher the redox potential value E H The actual measured value of the embodiment is E H The data and the Nernst equation are fitted by the least squares multivariate linear fitting method to obtain the following formula:

[0115] ;

[0116] That is, defect-free hematite system The slopes of the term are -56mV and -57mV at pH 5.0 and 6.0, respectively. The slopes are very similar and close to the theoretical value of ‒59mV. At pH 5.0 and 6.0, the errors of both are very small. This shows that the reaction of the defect-free hematite-Fe(II) binary heterogeneous system is a transfer process of 1 electron and 3 protons, which conforms to the Nernst equation. According to the fitting, further calculations can be obtained for defect-free hematite. The values ​​are 675mV and 680mV respectively, which is comparable to the defect-free hematite in the prior art. The values ​​are close, especially when the pH is 6.0. The value error is smaller, which proves the accuracy of the fitting model.

[0117] As shown in Table 1, Table 2 and Figure 1 As shown in b, with the binary system As the concentration increases, the redox potential values ​​in Examples 1-2 and Comparative Examples 1-2 E H The actual measured E H The data and the Nernst equation are fitted by the least squares multivariate linear fitting method to obtain the following formula:

[0118] ;

[0119] That is, the hematite system containing oxygen vacancy defects The slopes of the term are -133 mV and -118 mV at pH 5.0 and 6.0, respectively. The slope of , which can be calculated middle , b is the slope ， The unit is V , and 0.56 and 0.50 were calculated, thus the oxygen vacancies were quantitatively calculated, preferably the oxygen vacancy defect concentration at pH 6.0.

[0120] As shown in Table 1, Table 2 and Figure 1 As shown in c, with the binary system As the concentration increases, the redox potential values ​​of Examples 3-4 and Comparative Examples 1-2 E H There is also a big difference compared with the actual measured E H The data and the Nernst equation are fitted by the least squares multivariate linear fitting method to obtain the following formula:

[0121]

[0122] That is, the hematite system containing iron vacancy defects The slopes of the term are -48 mV and -49 mV at pH 6.0 and 7.0, respectively. The slope of , which can be calculated middle , b The unit is V , and calculated to be 0.142 and 0.127, thus the iron vacancy concentration was quantitatively calculated.

[0123] The invention discloses a quantitative calculation method for constructing metastable structures in iron oxide minerals by thermodynamic method, belonging to the field of soil and materials. The invention measures the redox potential ( E H ) value, and combined with the actual measured E H Thermodynamic relationships and reaction equations are established with the Fe(II) concentration in the solution, and the defect concentration in the iron oxide mineral is reversely calculated. The quantitative calculation method for constructing the metastable structure in the iron oxide mineral using thermodynamic methods provided by the present invention can establish a quantitative method for vacancy defects in iron oxide, quantify the number of vacancy defects on the surface of iron oxide, and provide useful clues for the development of nano-defect engineering strategies. At the same time, the redox ability of the heterogeneous system can also be analyzed, which is of great significance for predicting the reduction of pollutants by the system.

[0124] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for quantitatively determining the concentration of vacancy defects in metastable iron oxides, characterized in that: The following steps are involved: 1) Add different concentrations of FeCl2 solution to the buffer solution containing KCl to obtain different Concentration of mixed solution; 2) Take the different concentrations, respectively adding metastable iron oxides, and after fully mixing, respectively adding mediating substances to the reaction system for reaction, and filtering after the reaction is completed to obtain multiple binary heterogeneous systems; The binary heterogeneous system was determined concentration; the plurality is at least four; 3) respectively measuring the redox potential of the binary heterogeneous system; 4) For the binary heterogeneous system Concentration value and its corresponding redox potential value E H Fitting is performed to obtain the vacancy defect concentration through the fitted function and the thermodynamic reaction equation; the fitted function is y=a+bx, y is E H , x is , a is the intercept, b is the slope; when the metastable iron oxide structure contains oxygen vacancies, the thermodynamic reaction equation is: ； The oxygen vacancy defect concentration is calculated by the following formula: ； Alternatively, when the metastable iron oxide structure contains iron vacancies, the thermodynamic reaction equation is: ； The iron vacancy defect concentration is calculated by the following formula: ； In the formula, E H is the redox potential value of the binary heterogeneous system; is the standard reduction potential, In a binary heterogeneous system Fe 2+ concentration, m is the oxygen vacancy defect concentration, and n is the iron vacancy defect concentration.

2. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 1, characterized in that: In the determination method, the entire determination process is carried out at room temperature, and the environment in which the determination process is carried out is an anaerobic environment with an oxygen content of <5ppm; in the determination method, the pH value is kept constant throughout the determination process by a pH adjuster, and the pH value is 5.0~8.

0.

3. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 2, characterized in that: The pH value is 6.

0.

4. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 2, characterized in that: In the step 1), the buffer substance of the buffer solution is any one of diethylpiperazine, morpholineethanesulfonic acid monohydrate, and 3-morpholinepropanesulfonic acid; and the pH regulator is KOH and / or HCl.

5. The method for quantitatively determining the vacancy defect concentration of metastable iron oxide according to claim 1, characterized in that: In the mixed solution of step 1), Concentration range: 0.1mmol·L -1 ~10mmol·L -1 , the concentration of the buffer solution is 20~50mM, and the concentration of KCl is 20~30mmol·L -1 .

6. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 5, characterized in that: In the mixed solution of step 1), the concentration of KCl is 25 mmol·L -1 .

7. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 1, characterized in that: In the step 2), after the metastable iron oxide is added to the mixed solution, the concentration of the metastable iron oxide in the mixed solution is 1 g / L.

8. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 1, characterized in that: In the step 2), the metastable iron oxide is any one or more of hematite, lepidocrocite, ferrihydrite, and magnetite; the mediating substance is any one of cyanomethyl viologen, hexaammineruthenium chloride, ethyl viologen, and diquat; the concentration of the mediating substance in the reaction system is 10-20 μmol·L -1 .

9. The method for quantitatively determining the concentration of vacancy defects in metastable iron oxides according to claim 1, characterized in that: In the step 3), the redox potential is measured using a potentiometric titrator combined with a platinum ring redox composite electrode, comprising the following steps: 3.1) Electrode pretreatment: soaking the platinum ring redox composite electrode in HCl and KCl solutions successively; 3.2) Determination of redox potential: insert the pretreated platinum ring redox composite electrode into the binary heterogeneous system, and continuously measure the potential using a potentiometric titrator under magnetic stirring conditions, and record the redox potential value after equilibrium. E H .

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