A method for rapid detection of redox capacity of heterogeneous aquifer media

Abstract

The present invention provides a method for rapidly detecting the redox capacity of a heterogeneous aquifer medium, and belongs to the technical field of redox analysis of aquifer medium. The method provided by selecting ethyl viologen and 2,2-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) as chemical probes has higher reaction activity and more accurate test results than traditional chemical probes, and the reaction rate between the probe and the aquifer medium is faster, thereby realizing accurate and efficient testing of the redox capacity of the aquifer medium. The method provided by the present invention can be applied to the rapid and convenient testing of the redox capacity of the actual aquifer medium, and the test accuracy reaches mmol e ‑ / kg, the reaction and test time does not exceed 20min, which realizes low-cost, efficient, convenient and accurate testing of the redox capacity of heterogeneous aquifer media (such as sand, silt, and clay loam).

Description

Technical Field

[0001] The invention relates to the technical field of redox analysis of aquifer media, and in particular to a method for rapidly detecting the redox capacity of heterogeneous aquifer media. Background Art

[0002] In-situ chemical / biological remediation and enhanced natural attenuation are common technologies for remediating groundwater pollution. However, due to the redox heterogeneity of aquifers, it is difficult to accurately assess the dosage and remediation cycle of aquifer remediation agents. Insufficient dosage of remediation agents will lead to incomplete pollution remediation, while excessive dosage will bring the risk of secondary pollution to the aquifer. To effectively solve the above problems, it is necessary to accurately characterize the redox heterogeneity of aquifers in order to accurately assess the dosage of remediation agents, so as to achieve the goal of green, economical and efficient remediation of contaminated aquifers.

[0003] At present, the main method for analyzing the redox capacity of aquifer media is the chemical probe method. The testing principle of the chemical probe method is to calculate the redox capacity of the aquifer media based on the change in the concentration of the chemical probe before and after the reaction. The existing reducing chemical probes mainly include chromium chloride, Ti(III)-ligand, H2S / Zn(0), and dithionite hydrochloric acid, and the oxidizing chemical probes mainly include Fe(III)-ligand complex and potassium dichromate. For details, please refer to references 1-3. However, existing studies have confirmed that there is an inaccuracy problem when using the above-mentioned redox components as chemical probes. For example, when chromium chloride is used as a chemical probe to test the oxidation capacity of aquifer media, the test results are dozens of times higher than the theoretical value, as shown in reference 2; when Fe(III)-ligand complex is used as a chemical probe to test the reduction capacity of aquifer media, it often takes dozens of hours or even days to reach reaction equilibrium, but the actual test time is often only a few hours, which leads to low test results.

[0004] Compared with the above-mentioned chemical probes, ethyl viologen (EV) and 2,2-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) have the advantages of moderate reactivity and stability, and the standard redox potentials of EV and ABTS are -0.45V vs.SHE and 0.7V vs.SHE, respectively, which are close to the redox range under natural conditions. Therefore, thermodynamically, EV and ABTS can be used as chemical probes to determine the redox capacity of aquifer media. However, the purchased EV and ABTS are in the ground state, so they need to be activated into free radical form before they can be used as chemical probes to test the redox capacity of aquifer media. Therefore, establishing appropriate activation, purification and testing methods is the key to applying EV and ABTS as chemical probes to test the redox capacity of aquifer media. At present, studies have reported the use of NaClO as an oxidant to activate ABTS into a free radical form of ABTS. ·-The reduction capacity of dissolved organic matter can be tested later, see references 4-6 for details. However, the above studies did not remove the residual NaClO, that is, did not remove ABTS ·- Compared with dissolved organic matter, the actual aquifer medium reduction capacity is lower, so residual chemicals may interfere with the test of the actual aquifer medium reduction capacity. In addition, no research has reported the activation, purification and testing methods of EVs.

[0005] Therefore, it is urgent for scientific researchers to develop activation, purification and testing methods for EV and ABTS, so as to establish a method that can accurately analyze the redox capacity of actual aquifer media and provide better technical guidance for real-time adjustment of remediation agent dosage in in situ groundwater pollutant remediation. Summary of the invention

[0006] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art, provide a new chemical probe method using EV and ABTS as chemical probes, establish a chemical method for activating and purifying EV and ABTS, and use spectrophotometry to test the changes in EV and ABTS free radical concentrations before and after the chemical probes are mixed with aquifer media. This method can quickly and conveniently test the redox capacity of heterogeneous aqueous media, and provide technical guidance for real-time adjustment of the dosing of remediation agents in in-situ groundwater contaminant remediation.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The first object of the present invention is to provide a method for rapidly detecting the redox capacity of a heterogeneous aquifer medium, comprising the following steps:

[0009] Step S1: Activation and purification of chemical probes

[0010] S11. Activation and purification of EV chemical probe solution

[0011] Preparation of oxidation capacity standard stock solution: Prepare EV standard stock solution using ultrapure water as diluent;

[0012] Preparation of oxidation capacity standard solution: The above oxidized EV was reduced to EV free radical (EV) using palladium-catalyzed H2 reduction technology under alkaline and anaerobic conditions. ·+ ), to obtain an active EV chemical probe solution;

[0013] In some embodiments, palladium-H2 is used to catalyze the reduction of EVs in the EV standard stock solution under alkaline anaerobic conditions. 2+ EV free radical form (EV ·+ ), to obtain an active EV chemical probe solution;

[0014] Purification of the oxidation capacity standard active solution: the palladium catalyst particles were removed from the active EV chemical probe solution, and the introduction of the H2-N2 mixed gas (gas composition: 4% H2, 96% N2) was stopped to terminate the reaction, and the pH was further adjusted to neutral to obtain a purified active EV chemical probe solution;

[0015] S12. Activation and purification of ABTS chemical probe solution

[0016] Preparation of reduction capacity standard stock solution: Prepare ABTS standard stock solution using ultrapure water as diluent;

[0017] Preparation of reduction capacity standard solution: using thermally activated S2O8 2- The reduced ABTS is oxidized to ABTS free radicals to obtain active ABTS (i.e., ABTS ·- ) chemical probe solution;

[0018] In some embodiments, persulfate is used to oxidize ABTS in the ABTS standard stock solution under heating conditions in a water bath. 2- ABTS free radical form (ABTS ·- ), to obtain an active ABTS chemical probe solution;

[0019] Reduction capacity standard active solution purification: Adding dissolved Fe(II) to remove residual S2O8 in the active ABTS chemical probe solution 2- , and adjusting the pH to neutral to precipitate the Fe(III) produced in the system, and filtering to obtain a purified active ABTS chemical probe solution;

[0020] In some embodiments, dissolved Fe(II) is added to the active ABTS solution to remove residual S2O8 2- , taking advantage of the fact that dissolved Fe(II) can be removed by precipitation under neutral conditions, the pH is adjusted to 6.5-6.9, and the purified active ABTS chemical probe solution is obtained by filtration;

[0021] Step S2: Standard curves of active EV chemical probe solution and ABTS chemical probe solution

[0022] S21. Standard curve of active EV chemical probe solution

[0023] Take fully activated (100%) active EV (i.e. EV ·+ ) Chemical probe solution, diluted with oxygen-free water to obtain different concentrations of EV ·+ Chemical probe solution was prepared and the pH was adjusted to 7.0. UV-visible spectrophotometry was used to measure different concentrations of EV at 603 nm. ·+ The absorbance value of EV ·+The linear relationship between millimolar concentration and absorbance value is shown in Equation 1;

[0024] S22, Standard curve of active ABTS chemical probe solution

[0025] Take fully activated (100%) active ABTS (i.e. ABTS ·- ) Chemical probe solution, diluted with oxygen-free water to obtain different concentrations of ABTS ·- Chemical probe solution was prepared and the pH was adjusted to 7.0. UV-visible spectrophotometry was used to measure different concentrations of ABTS at 734 nm. ·- The absorbance value of ABTS ·- The linear relationship between millimolar concentration and absorbance value is shown in Equation 1;

[0026] A=ε·C·L Formula 1;

[0027] Among them, A represents the absorbance of active EV or active ABTS under certain concentration conditions;

[0028] C is the millimolar concentration of active EVs or the millimolar concentration of active ABTS, in mmol / L;

[0029] ε is the millimolar extinction coefficient of active EV or active ABTS, in mM -1 cm -1 The millimolar extinction coefficient of active EV is 12.44±0.27mM at pH=7.0-7.5 and wavelength 603nm. -1 cm -1 The millimolar extinction coefficient of active ABTS is 14.25±0.01mM at pH=6.5-6.9 and wavelength 734nm. -1 cm -1 ;

[0030] L is the optical path of the cuvette, in cm;

[0031] Step S3: Determine the sample

[0032] Preparation of oxidation capacity sample solution: Take an appropriate amount of heterogeneous aquifer medium and add it to the pre-diluted active EV chemical probe solution, and react in the dark to obtain oxidation capacity sample solution;

[0033] Preparation of reduced capacity sample solution: Take an appropriate amount of heterogeneous aquifer medium and add it to the pre-diluted active ABTS chemical probe solution, and react in the dark to obtain the reduced capacity sample solution;

[0034] By using spectrophotometry to test the absorbance changes before and after the reaction between the active EV chemical probe and the sample, and the absorbance changes before and after the reaction between the active ABTS chemical probe and the sample, the electron transfer amount of the sample can be obtained, as shown in Formula 2.

[0035]

[0036] Among them, E 样品 The oxidation capacity or reduction capacity of the sample is measured in mmol e - / kg;

[0037] C0 is the concentration of the active EV chemical probe before mixing with the sample or the concentration of the active ABTS chemical probe before mixing with the sample;

[0038] C1 is the concentration of the active EV chemical probe after the reaction with the sample or the concentration of the active ABTS chemical probe after the reaction with the sample;

[0039] is the number of electrons before and after the unit chemical probe reaction, where both active EV and active ABTS are 1;

[0040] V is the volume of the probe and sample reaction system, in L;

[0041] m 样品 It is the dry weight of sample and probe added for reaction, in g.

[0042] Furthermore, the concentration of the oxidation or reduction capacity standard stock solution is 0.1-5 mM.

[0043] Furthermore, the palladium-H2 catalytically reduces EV in the EV standard stock solution under alkaline oxygen-free conditions. 2+ EV is a free radical form of EV ·+ The process is: use alkali solution to 2+ The pH of the solution was adjusted to 13, and after nitrogen was passed to deoxygenate the solution, the solution was transferred into an anaerobic glove box, and the gauze-wrapped palladium-alumina particles were added to the EV 2+ The solution was added with H2-N2 mixed gas for activation for 3 days. After activation, the palladium particles were taken out and the pH was adjusted to 7.0-7.5 for standby use.

[0044] Further, the persulfate heat activated ABTS 2- ABTS is the free radical form of ABTS ·- The process is: according to ABTS 2- With S2O8 2- The theoretically safe molar concentration ratio is 2:1 and thermally activated in a 50°C water bath for 2 hours in the dark.

[0045] Furthermore, in the process of adding dissolved Fe(II) to remove residual persulfate, the amount of FeSO4 added is calculated according to Formula 3:

[0046] V1=V2·(C 0h -C 1h ) / 10 Formula 3;

[0047] Wherein, V1 is the volume of 10mM FeSO4 added, in mL; V2 is the volume of ABTS standard stock solution, in mL; C 0h is the concentration of ABTS standard stock solution before activation, in mM; C 1h ABTS standard stock solution activated for 1 hour ·- 10 is the maximum concentration of FeSO4 at pH 1, in mM; 10 is the molar concentration of FeSO4 at pH 1, in mM.

[0048] In some embodiments, the pH is adjusted to 6.5-6.9 to precipitate excess FeSO4, and the active ABTS filtrate is collected by filtering with a 0.45 μm filter membrane for later use.

[0049] Furthermore, the millimolar extinction coefficient ε of the active EV chemical probe is 12.44±0.27 mM at a pH of 7.0 to 7.5 and a wavelength of 603 nm. -1 cm -1 The millimolar extinction coefficient ε of the active ABTS chemical probe is 14.25±0.10 mM at a pH of 6.5-6.9 and a wavelength of 734 nm. -1 cm -1 .

[0050] Furthermore, the dosage of the heterogeneous aquifer medium is 0.1 to 1 g.

[0051] It should be noted that the heterogeneous aqueous medium samples include sandy samples (sand content>55%) and silty / clay samples (sand content<55%). In order to avoid large sampling heterogeneity errors, the sample dosage of the sandy sample is 0.2~1g, and the sample dosage of the clay sample is 0.1~1g.

[0052] Furthermore, the probe concentration prepared by the oxidation or reduction capacity sample solution needs to dilute the active probe concentration to a range of 0.1 to 1 mM.

[0053] Furthermore, during the oxidation capacity determination process, the dosage volume of the active EV chemical probe was determined based on the color change of the probe, and the blue active EVs turned into light blue.

[0054] Furthermore, during the reduction capacity determination process, the dosage of the active ABTS chemical probe was determined based on the color change of the probe, and the green active ABTS turned into light green.

[0055] Furthermore, in the preparation of the oxidation or reduction capacity sample solution, the mixing reaction time of the active probe EV or ABTS and the sample is 10 to 15 minutes.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) The present invention provides a method for rapidly detecting the redox capacity of a heterogeneous aquifer medium, so as to realize rapid testing of the redox capacity of a heterogeneous aquifer in a field. Ethyl viologen (EV, -0.45V vs. SHE) and 2,2-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS, 0.7V vs. SHE) are selected as chemical probes for testing oxidation capacity and reduction capacity, respectively. The chemical probes are activated and purified into free radical form by chemical methods, and the change in free radical concentration before and after the mixing reaction of the chemical probes and the aquifer medium is tested by spectrophotometry to rapidly determine the redox capacity of the aquifer medium, so as to provide guidance for the addition of agents in site remediation.

[0058] (2) The present invention is to efficiently activate EV to EV free radicals (EV ·+ ), proposed to use palladium to catalyze H2 to produce atomic hydrogen for efficient reduction of EV 2+ The conception of EV free radicals. Since H2 has a low solubility in the aqueous phase and the palladium catalyst is easily separated from the solution phase, it is easy to remove the palladium catalyst and H2 from the aqueous solution to obtain EV free radicals with higher purity. At the same time, a method of removing residual persulfate by exogenous addition of dissolved Fe(II) is proposed. Dissolved Fe(II) can effectively reduce and remove residual persulfate, and the generated Fe(III) is easy to precipitate and remove under neutral conditions. Therefore, the method of sequential Fe(II) reduction and Fe(III) precipitation can effectively remove residual persulfate, thereby improving the activity purity of the chemical probe and avoiding the interference of residual activation agents on the reduction capacity test of aquifer media.

[0059] (3) Compared with traditional chemical probes, the method provided by the present invention has higher reaction activity, higher test result accuracy, and faster reaction rate between the probe and the aquifer medium, thereby achieving accurate and efficient testing of the redox capacity of the aquifer medium.

[0060] (4) The method provided by the present invention can be applied to the rapid and convenient testing of the redox capacity of actual aquifer media, with a test accuracy of mmol e - / kg, the reaction and test time does not exceed 20min, achieving low-cost, efficient, convenient and accurate testing of the redox capacity of heterogeneous aquifer media. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 A schematic diagram of a method for rapidly detecting the redox capacity of a heterogeneous aquifer medium provided by the present invention;

[0062] Figure 2 The color change and characteristic spectrum of the chemical probe provided by the present invention before and after activation;

[0063] Figure 3a is the concentration standard curve of active EVs;

[0064] Figure 3b is the concentration standard curve of active ABTS;

[0065] Figure 4 The graph shows the EDC / EAC and spike recovery results of actual aquifer medium samples tested using active ABTS and EV as chemical probes;

[0066] Figure 5 Compose a three-line diagram for soil machinery. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solution and advantages of the present invention clearer, embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0068] Terminology Note:

[0069] Heterogeneous aquifer: refers to an aquifer whose permeability varies spatially;

[0070] Redox capacity: The total concentration of redox-related components, or the total amount of electrons that can be transferred (released or accepted).

[0071] The transformation process between EV and EV free radicals:

[0072]

[0073] ABTS and ABTS free radical transformation process:

[0074]

[0075] The test process for rapid detection of the redox capacity of heterogeneous aquifer media provided by the present invention is mainly divided into three steps. The first step is to prepare and purify the active chemical probe; the second step is to mix the active chemical probe with the aquifer medium sample for reaction; the third step is to measure the concentration difference of the chemical probe by spectrophotometry, and then convert it into the oxidation / reduction capacity of the aquifer medium under the corresponding probe potential.

[0076] refer to Figure 1 , the implementation schemes of EV test of aquifer medium oxidation capacity (EAC) and ABTS test of aquifer medium reduction capacity (EDC) are described below:

[0077] 1. EV test of EAC of aquifer media

[0078] Palladium-H2 is used to catalyze the reduction of EV to EV free radical form under alkaline anaerobic conditions. The ground state EV is prepared into a solution, and the pH of EV is adjusted to 13 with NaOH. After nitrogen is passed to deoxygenate, the EV solution (pH = 13) is transferred to an anaerobic glove box (96% N2 + 4% H2) for light-protected activation, and a N2-H2 (96% N2 + 4% H2) mixed gas is passed and a palladium-alumina catalyst is added. H2 generates atomic hydrogen under palladium catalysis and then reduces EV 2+ For EV ·+ After activation for 1 to 3 days, a high concentration of alkaline EV activity chemical probe can be obtained.

[0079] Before testing the sample, take a certain amount of active EV mother solution, add oxygen-free MOPS buffer (pH = 7.0 ~ 7.5) and H2SO4 in turn, adjust the pH to 7.0 ~ 7.5, and obtain the active EV chemical probe to be used. During the activation and purification process of this active EV chemical probe, the previously added H2 and palladium-alumina catalyst can be directly physically separated, and only acid and base reagents are added later, without the introduction of other chemical agents from the outside, so a high-purity active EV chemical probe is obtained. The entire EV preparation process is carried out in an anaerobic glove box, and the solutions used are all deoxygenated by nitrogen in advance.

[0080] The prepared active EVs were mixed with 0.1-1 g (wet weight) of aquifer medium sample in the dark for 15 min to test the active EVs before mixing with the sample. ·+ Absorbance, and supernatant EV after mixing with sample for 15 min ·+ The absorbance of EV ·+ The concentration difference is used to convert the EAC of the aquifer medium sample.

[0081] It should be noted that the reaction and testing of active EVs with samples must be carried out under anaerobic conditions.

[0082] 2. ABTS test of EDC of aquifer media

[0083] Use persulfate to heat activate ABTS to form ABTS free radical. 2- With S2O8 2- The reaction molar concentration ratio was 2:1 and the activation was carried out in a 50°C water bath in the dark for 2 h. During the activation process, ABTS 2- Oxidized to ABTS ·- , S2O8 2- Reduced to SO4 2- , that is, active ABTS free radicals are obtained.

[0084] Removal of residual S2O8 by exogenous addition of dissolved Fe(II) to the active ABTS probe 2- To improve the purity of active ABTS. Before each test sample, take out a certain volume V of active ABTS mother solution and follow the ABTS ·- The maximum activation concentration is added with an appropriate amount of FeSO4 to remove residual Na2S2O8, and the pH is adjusted to 6.5-6.9 with MOPS buffer and NaOH solution to precipitate the generated dissolved Fe(III). Finally, the Fe(III) precipitate in the active ABTS probe is removed by filtration with a 0.45μm filter head, and the filtrate is the high-purity active ABTS chemical probe.

[0085] The purified active ABTS was mixed with 0.2-1 g (wet weight) of the aquifer medium sample in the dark for 15 min, and the active ABTS was tested by spectrophotometry. ·- Absorbance, and ABTS in the supernatant after mixing with the sample for 15 minutes ·- The absorbance of ABTS ·- The concentration difference is used to convert the EDC of the aquifer medium sample.

[0086] In some embodiments, the solid-to-liquid ratio after the aquifer medium sample is mixed with the active chemical probe needs to be controlled to be less than 10 g / L to avoid test errors caused by adsorption of the probe and the sample.

[0087] In some embodiments, if the aquifer medium sample is viscous, it can be pre-dispersed evenly with an appropriate amount of oxygen-free water to prevent the sample from being unable to fully contact the probe during the reaction.

[0088] Example 1

[0089] This example is about preparing, purifying and testing active chemical probes.

[0090] (1) Preparation of 200 mL 5 mM EV activity probe:

[0091] ① Preparation of EV active mother solution: weigh 0.37g EV, dissolve in 200mL ultrapure water, adjust pH to 13 with 5M NaOH, pass nitrogen to deoxygenate for 15min and transfer to an anaerobic glove box (96% N2 + 4% H2) to stand in the dark, add 2-5g palladium-alumina particles and pass N2-H2 mixed gas (96% N2 + 4% H2), and use the principle of palladium-catalyzed H2 reduction to activate EV ·+ After the third day of activation, the EV activity concentration reached a stable state (activation rate > 90%) and was ready for use. The EV activity mother solution was stored in an anaerobic glove box away from light.

[0092] ② Preparation of EV active stock solution: Take a certain amount of EV active mother solution before testing, first add 0.1M 3-(N-morpholine) propanesulfonic acid (MOPS), pH = 7.0 ~ 7.5, add the amount to control the final MOPS concentration in the EV stock solution ≤ 10mM), then add oxygen-free 1MH2SO4 to adjust the pH to 7.0 ~ 7.5 (strictly control the pH value, pH < 7.0 will accelerate EV ·+ Decay rate, pH>7.5 will slow down EV ·+ The active EV chemical probe solution is obtained by the electron transfer rate of the sample. This preparation process needs to be carried out in an anaerobic glove box.

[0093] (2) Preparation of 200 mL 5 mM ABTS active probe:

[0094] ① Preparation of active ABTS mother solution: According to the molecular weight of chemical reagents ABTS and Na2S2O8, weigh 0.55g ABTS and 0.12g Na2S2O8 respectively, dissolve ABTS and Na2S2O8 solids in a glass bottle filled with 200mL ultrapure water, and after complete dissolution, quickly transfer the glass bottle to a 50℃ water bath in a dark water bath for 2h to obtain 5mM active ABTS mother solution. Place the activated ABTS active mother solution in a dark place at 4℃ for later use, and the validity period of this mother solution is about 5d.

[0095] ② Purify the ABTS active stock solution (remove the remaining Na2S2O8 from the reaction): Before each sample test, take out a certain volume V2 of ABTS active mother solution, add V1 volume of 10mM FeSO4 (pH=1) to remove the residual Na2S2O8, V1 is calculated according to formula (3), then add an appropriate volume of 0.1M MOPS buffer salt (pH=6.7~6.9, control the MOPS buffer salt concentration in the stock solution ≤10mM), and adjust the pH to 6.7~6.9 with 1M NaOH to remove the residual FeSO4 and the generated dissolved Fe(III), mix well and filter with a 0.45μm filter head, collect the filtrate as the high-purity active ABTS chemical probe solution, protect from light and deoxygenate with nitrogen for later use.

[0096] V1=V2·(C 0h -C 1h ) / 10 Formula 3;

[0097] Wherein, V1 is the volume of 10mM FeSO4 added, in mL; V2 is the volume of ABTS standard stock solution, in mL; C 0h is the concentration of ABTS standard stock solution before activation, in mM; C 1h ABTS is activated for 1 hour by ABTS standard stock solution. ·- 10 is the maximum concentration of FeSO4 at pH 1, in mM; 10 is the molar concentration of FeSO4 at pH 1, in mM.

[0098] (3) UV-Vis spectrophotometry to measure the molar concentration of chemical probes

[0099] 1 mM EV was catalytically reduced to complete reduction (~99.99%) using palladium hydrogen at pH = 13 under anaerobic conditions. The absorbance was tested using a UV spectrophotometer in an anaerobic glove box. The initial EV was colorless. After activation, the EV ·+ Blue, EV ·+ The corresponding characteristic absorption peak is at a wavelength of 603 nm. After 5 days of reduction, the completely reduced EVs were diluted 10 to 50 times, and different concentrations of EVs were measured at 603 nm. ·+ The absorbance of EV ·+ The linear relationship between concentration C and absorbance A (Equation 1), the millimolar extinction coefficient ε is 12.44±0.27mM -1 cm -1 .

[0100] 1 mM ABTS was oxidized with excess persulfate to completely activate ABTS (~99.99% ABTS 2- Convert to ABTS ·- ). First, use UV spectroscopy to scan the changes in the absorption spectrum of ABTS before and after oxidation. The initial ABTS is colorless, and the activated ABTS ·- Green, ABTS ·- The corresponding characteristic absorption peak is at a wavelength of 734 nm. The completely oxidized ABTS is then diluted 10-100 times and different concentrations of ABTS are measured at 734 nm using a UV spectrophotometer. ·- The absorbance of ABTS ·- The linear relationship between concentration C and absorbance A (Equation 1), millimolar extinction coefficient ε is 14.25±0.10mM -1 cm -1 .

[0101] A=ε·C·L Formula 1;

[0102] (4) Active chemical probe test samples

[0103] Taking advantage of the fact that ABTS and EV have two different colors in the oxidized and reduced states, and the oxidized / reduced state of the probe is reversible, the absorbance change before and after the reaction of the chemical probe with the sample can be tested by spectrophotometry to obtain the electron transfer amount of the sample (Formula 2). The active chemical probe and the sample are mixed and reacted for 15 minutes to reach equilibrium, and the active ABTS (ABTS ·- / ABTS>40%) and EV(EV ·+ / EV>90%), the attenuation is less than 5% within 1 h, that is, the self-attenuation of the chemical probe during the sample testing process can be ignored.

[0104]

[0105] refer to Figure 2 , are the color changes and spectrophotometric test results of the active chemical probe established in this embodiment before and after activation. The photometric method tests the absorbance of EV at a wavelength of 603nm, and the absorbance of ABTS at a wavelength of 734nm.

[0106] The results of ultraviolet full spectrum scanning showed that EV free radicals had a characteristic absorption peak at a wavelength of 603nm, and the absorbance of EV free radicals at a wavelength of 603nm increased with the increase of free radical concentration, while the ground state EV had no characteristic peak at this wavelength, so 603nm was selected as the characteristic wavelength of EV free radicals; ABTS free radicals had significant characteristic absorption peaks at wavelengths of 645nm and 734nm, among which ABTS free radicals of different concentrations at a wavelength of 734nm had higher absorbance than 645nm, and the absorption peak at 734nm increased with the increase of ABTS free radical concentration, and the ground state ABTS had no characteristic absorption peak at a wavelength of 734nm, so 734nm was selected as the characteristic wavelength of ABTS free radicals.

[0107] refer to Figure 3a and Figure 3b , is the concentration curve of the active chemical probe tested by the spectrophotometric method in this embodiment, and the millimolar extinction coefficient ε of EV is 12.44±0.27mM -1 cm -1 (0~0.07mM), the millimolar extinction coefficient ε of ABTS is 14.25±0.10mM -1 cm -1 (0~0.06mM).

[0108] Example 2

[0109] This example is a test of the detection limit and precision of a standard sample using an active chemical probe.

[0110] Standard sample detection limit test method: Test the linear curve of the standard sample concentration, take the minimum concentration within the 99% confidence interval of the linear fit, test 7 times, and the detection limit is 3.143 times the standard deviation of the 7 results (detection limit = 3.143 × STDEV)

[0111] Sample precision % test method: N times repeated test results deviate from each other, test sample at a suitable concentration 3-4 times, precision = STDEV / AVE×100%, wherein the probe method takes 0.2~1g of sample for testing respectively.

[0112] Note 1: The traditional chemical probe used to test the sample oxidation capacity (EAC) is the reducing agent trivalent titanium-ethylenediaminetetraacetic acid complex (Ti(III)-EDTA). The test process is to react 0.5g of aquifer medium sample with 10mL of reducing agent 0.008M Ti(III)-0.05M EDTA under anaerobic conditions at pH 6.0 in the dark for 12-24h. The concentration change of Ti(III) is tested at 550nm using an ultraviolet photometer, which is the EAC of the sample. The entire sample reaction and test are carried out under anaerobic conditions. For details, refer to Reference 1.

[0113] Note 2: The traditional chemical probe used to test the reduction capacity (EDC) of the sample is the oxidant acidic potassium dichromate (K2Cr2O7-H2SO4). The test process is to react 0.5g of the aquifer medium sample with 10mL of the oxidant 0.02M K2Cr2O7-60% (w / w) H2SO4 at 150°C for 3h. The DPC colorimetric method (diphenylcarbohydrazide complexes with Cr(VI) to produce purple) is used to test the concentration change of Cr(VI) at 540nm on a UV photometer, which is the EDC of the sample. For the specific test process, refer to Reference 2.

[0114] As shown in Table 1, the detection method provided by the present invention has lower precision than the existing traditional chemical probe method, higher stability and shorter detection time.

[0115] Table 1.

[0116]

[0117] Example 3

[0118] This example uses an active chemical probe to test the redox capacity of actual aquifer media.

[0119] This example uses a novel chemical probe method to test the EAC / EDC results of aquifer medium samples of different textures and redox states, and adds standard components to test the results of spiked recovery of aquifer medium.

[0120] (1) First, the oxidation / reduction capacity of the aquifer medium was tested using a new chemical probe method. 0.2-0.5 g (wet weight) of the aquifer medium was weighed into a 50 mL centrifuge tube. The aquifer medium was mixed with an appropriate amount of oxygen-free water in advance to fully disperse the aquifer medium and avoid insufficient contact between the aquifer medium and the probe. For clay samples, 20-50 mL of oxygen-free water was added in advance to control the solid-liquid ratio of the aquifer medium and the EV / ABTS probe to be <10 g / L after mixing to avoid test errors caused by adsorption of the probe and the sample. The active EV / ABTS and the aquifer medium sample were shaken in the dark for 15 minutes to achieve stability. After the reaction, the probe absorbance of the supernatant was tested by centrifugation and converted to the EAC / EDC of the aquifer medium.

[0121] (2) Based on the test results of each aquifer medium, the standard substance is added at a molar electron mass ratio of 0.5 to 1.5 between the actual sample and the standard substance. - / g of aquifer medium sample, the dosage of the standard substance is consistent with the dosage of the standard substance when tested alone. The oxidation / reduction capacity of the aquifer medium and the standard substance sample was tested again using the new chemical probe method. The recovery concentration of the standard substance was obtained by subtracting the results of the two tests, and the spike recovery rate was obtained by comparing it with the concentration when the standard substance was tested alone. Among them, the external standard sample selected in the EV test was ferrihydrite, and the external standard sample selected in the ABTS test was siderite. The test results showed that the spike recovery rate of the aquifer medium was between 90% and 110%. In addition, three representative textures of aquifer media were selected, namely oxidized and reduced sandy soil and reduced silt loam. The external standard samples in the EV test were replaced with oxidized nontronite and β-MnO2, and the external standard sample in the ABTS test was replaced with reduced nontronite. The spike recovery rate of EAC / EDC in the aquifer medium was tested again to avoid the selectivity of the standard sample. The spiked recovery of the EV test aquifer medium was 106.32±7.8%, and the spiked recovery of the ABTS test aquifer medium was 94.49±8.45%, indicating that this method is suitable for testing heterogeneous aquifer medium samples.

[0122] See Table 2 for the basic properties of the aquifer medium samples used in the new chemical probe method test in this embodiment. Samples S1, S2, and S3 are sandy soils, S4, S5, and S6 are loamy sandy soils, S7 and S8 are silt soils, S9 is silty clay loam, and S10, S11, S12, and S13 are silty loam. The classification of soil texture is based on the reference soil mechanical composition three-line diagram (such as Figure 5 Specifically, the soil particle size is divided into three categories, namely clay particles <2μm, silt particles of 2-50μm and sand particles of 50-2000μm. The texture is divided according to the mass percentage composition of the three particle sizes.

[0123] refer to Figure 4 , are the results of the EAC / EDC and spike recovery rates of the aquifer medium tested using the new chemical probe method with EV and ABTS as probes according to this embodiment. The spike recovery rate of the oxidation capacity of the aquifer medium tested by EV is 106.32±7.8%, and the spike recovery rate of the reduction capacity of the aquifer medium tested by ABTS is 94.49±8.45%.

[0124] Table 2

[0125]

[0126] References:

[0127] 1.Heron, G., Christensen, TH, Tjell, JC, Oxidation capacity of aquifersediments. Environmental Science & Technology. 1994, 28, 153-158.

[0128] 2.Barcelona, ​​MJ, Holm, TR, Oxidation-reduction capacities of aquifersolids. Environmental Science & Technology. 1991, 25, 1565-1572.

[0129] 3.Bauer,M.,Heitmann,T.,Macalady,DL,Blodau,C.,Electron transfercapacities and reaction kinetics of peat dissolved organic matter,Environmental Science&Technology.2007,41,139-145.

[0130] 4. Walpen, N., Schroth, MH, Sander, M., Quantification of phenolicantioxidant moieties in dissolved organic matter by flow-injection analysis with electrochemical detection. Environmental Science & Technology. 2016, 50, 6423-6432.

[0131] 5.Yuan,Y.,Zhang,H.,We,Y.,Si,Y.,Li,G.,Zhang,F.,Onsite quantifyingelectron donating capacity of dissolved organic matter.Science of the TotalEnvironment.2019,662,57-64.

[0132] 6. Walpen, N., Houska, J., Salhi, E., Sander, M., Gunten, U., Quantification of the electron donating capacity and UV absorbance of dissolved organic matter during ozonation of secondary wastewater effluent by an assay and an automated analyzer. Water Research. 2020, 185, 116235.

[0133] For matters not mentioned above, the prior art applies.

[0134] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for rapidly detecting the redox capacity of a heterogeneous aquifer medium, characterized in that: The following steps are involved: S1. Activation and purification of chemical probes S11. Activation and purification of EV chemical probe solution Preparation of oxidation capacity standard stock solution: Prepare EV standard stock solution using ultrapure water as diluent; Preparation of oxidation capacity standard solution: Using palladium-catalyzed H2 reduction technology under alkaline and anaerobic conditions, the oxidized EVs in the EV standard stock solution were reduced to EV free radicals to obtain an active EV chemical probe solution; Purification of the oxidation capacity standard active solution: the palladium catalyst particles are taken out from the active EV chemical probe solution, and the introduction of the H2-N2 mixed gas is stopped to terminate the reaction, and the pH is further adjusted to neutral to obtain a purified active EV chemical probe solution; S12. Activation and purification of ABTS chemical probe solution Preparation of reduction capacity standard stock solution: Prepare ABTS standard stock solution using ultrapure water as diluent; Preparation of reduction capacity standard solution: using thermally activated S2O8 2− The technology oxidizes the reduced ABTS in the ABTS standard stock solution into ABTS free radicals to obtain an active ABTS chemical probe solution; Reduction capacity standard active solution purification: Adding dissolved Fe(II) to remove residual S2O8 in the active ABTS chemical probe solution 2− , and adjusting the pH to neutral to precipitate the Fe(III) produced in the system, and filtering to obtain a purified active ABTS chemical probe solution; S2. Standard curves of active EV chemical probe solution and ABTS chemical probe solution S21. Standard curve of active EV chemical probe solution Take the fully activated active EV chemical probe solution and dilute it with oxygen-free water to obtain different concentrations of EV ·+ Chemical probe solution was prepared and the pH was adjusted to 7.

0. UV-visible spectrophotometry was used to measure different concentrations of EV at 603 nm. ·+ The absorbance value of EV ·+ The linear relationship between millimolar concentration and absorbance value is shown in Equation 1; S22, Standard curve of active ABTS chemical probe solution Take the fully activated active ABTS chemical probe solution and dilute it with oxygen-free water to obtain different concentrations of ABTS ·− Chemical probe solution was prepared and the pH was adjusted to 7.

0. The ABTS concentrations were measured at 734 nm using UV-visible spectrophotometry. ·− The absorbance value of ABTS ·− The linear relationship between millimolar concentration and absorbance value is shown in Equation 1; Formula 1; in, A Represents the absorbance of active EV or active ABTS under certain concentration conditions; is the millimolar concentration of active EVs or active ABTS, in mmol / L; is the millimolar extinction coefficient of active EV or active ABTS, in mM -1 · cm -1 The millimolar extinction coefficient of active EV is 12.44±0.27 mM at pH=7.0~7.5 and wavelength 603 nm. -1 cm -1 The millimolar extinction coefficient of active ABTS is 14.25±0.01 mM at pH=6.5~6.9 and wavelength 734 nm. -1 · cm -1 ; L is the optical path of the cuvette, in cm; S3. Determination of samples Preparation of oxidation capacity sample solution: Take an appropriate amount of heterogeneous aquifer medium and add it to the pre-diluted active EV chemical probe solution, and react in the dark to obtain oxidation capacity sample solution; Preparation of reduced capacity sample solution: Take an appropriate amount of heterogeneous aquifer medium and add it to the pre-diluted active ABTS chemical probe solution, and react in the dark to obtain the reduced capacity sample solution; By using spectrophotometry to test the absorbance changes before and after the reaction between the active EV chemical probe and the sample, and the absorbance changes before and after the reaction between the active ABTS chemical probe and the sample, the electron transfer amount of the sample can be obtained, as shown in Formula 2. Formula 2 Among them, E 样品 The oxidation capacity or reduction capacity of the sample is measured in mmol e - / kg; is the concentration of the active EV chemical probe before mixing with the sample or is the concentration of the active ABTS chemical probe before mixing with the sample; is the concentration of the active EV chemical probe after the reaction with the sample or is the concentration of the active ABTS chemical probe after the reaction with the sample; is the number of electrons before and after the unit chemical probe reaction, where both active EV and active ABTS are 1; V is the volume of the probe and sample reaction system, in L; m 样品 It is the dry weight of sample and probe added for reaction, in g.

2. The method according to claim 1, characterized in that The concentration of the oxidation or reduction capacity standard stock solution is 0.1-5 mM.

3. The method according to claim 1, characterized in that In step S11, the process of palladium-catalyzed H2 reduction technology is to catalytically reduce EV in the EV standard stock solution under alkaline anaerobic conditions. 2+ EV is a free radical form of EV ·+ The process is: use alkali solution to 2+ The pH of the solution was adjusted to 13, and after nitrogen was passed to deoxygenate the solution, the solution was transferred into an anaerobic glove box, and the gauze-wrapped palladium-alumina particles were added to the EV 2+ The solution was activated by introducing H2-N2 mixed gas for 3 days.

4. The method according to claim 1, characterized in that In step S12, the process of oxidizing reduced ABTS to ABTS free radicals is as follows: thermal activation of ABTS by persulfate 2− ABTS is the free radical form of ABTS ·− According to ABTS 2− With S2O8 2− The theoretical molar concentration ratio for complete reaction is 2:1 and thermal activation is carried out in a water bath at 50°C for 2 h in the dark.

5. The method according to claim 1, characterized in that Using FeSO4 as dissolved Fe(II), the amount of added FeSO4 is calculated according to formula 3: Formula 3; in, is the volume of 10 mM FeSO4 added, in mL; is the volume of ABTS standard stock solution, in mL; is the concentration of ABTS standard stock solution before activation, in mM; ABTS standard stock solution was activated for 1 h. ·− 10 is the maximum concentration of FeSO4 at pH 1, in mM; 10 is the molar concentration of FeSO4 at pH 1, in mM.

6. The method according to claim 2, characterized in that Millimolar extinction coefficients of the active EV chemical probes 12.44±0.27 mM at pH 7.0-7.5 and wavelength 603 nm -1 · cm -1 , the millimolar extinction coefficient of the active ABTS chemical probe 14.25±0.10 mM at pH 6.5-6.9 and wavelength 734 nm -1 · cm -1 .

7. The method according to claim 3, characterized in that The dosage of the heterogeneous aquifer medium is 0.1~1 g.

8. The method according to claim 3, characterized in that The probe concentration prepared by the oxidation or reduction capacity sample solution needs to dilute the active probe concentration to a range of 0.1-1 mM.

9. The method according to claim 3, characterized in that During the oxidation capacity measurement, the dosage of the active EV chemical probe was determined based on the color change of the probe, and the blue active EV turned into light blue. During the reduction capacity measurement, the dosage of the active ABTS chemical probe was determined based on the color change of the probe, and the green active ABTS turned into light green.

10. The method according to claim 3, characterized in that In the preparation of the oxidation or reduction capacity sample solution, the mixing reaction time of the active probe EV or ABTS and the sample is 10 to 15 minutes.

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