Recoverable surface active material responsive to redox switch and methods of making and using the same

Abstract

This invention discloses a recyclable surfactant material with a redox switch response for remediating tetrachloroethylene contamination in aquifers, as well as its preparation and application methods, belonging to the field of environmental engineering technology. The recyclable surfactant material of this invention is sodium selenide dialkylcarboxylate, whose preparation method is simple, the synthesis conditions are mild, and no special equipment is required. The resulting recyclable surfactant material has solubilizing properties and good water solubility. Upon addition of an oxidant (30wt% H2O2), the recyclable surfactant material of this invention transforms into a non-surface-active material that loses its surface activity and solubilizing ability. The water solubility of the non-surface-active material decreases, allowing for material recovery through filtration and solution separation. Adding a reducing agent, sodium sulfite, to the non-surface-active material will transform it back into the original recyclable surfactant material. This invention's method is simple and can easily achieve the interconversion between surfactant and non-surface-active materials using a redox response, making the surfactant material recyclable and reusable. This provides a reference for the solubilization and remediation of tetrachloroethylene contamination in aquifers using SEAR technology.

Description

Technical Field

[0001] This invention specifically relates to a recyclable selenium-containing surfactant material with a redox switch response for remediating tetrachloroethylene contamination in aquifers, as well as its preparation and application methods, belonging to the field of environmental engineering technology. Background Technology

[0002] Tetrachloroethylene (PCE) is widely used as a dry cleaning agent and pesticide. After leakage, it gradually seeps into aquifers. Due to its large usage, slow biodegradability, harmful effects on humans, and wide-ranging pollution, it has become a common groundwater contaminant. Furthermore, PCE has low water solubility and strong hydrophobicity, coupled with its high O / W interfacial tension, making it prone to retention in the pores of the medium and difficult to remove. This results in time-consuming and inefficient remediation of chlorinated hydrocarbon contamination in aquifers. Surfactant-enhanced aquifer remediation (SEAR) technology can effectively shorten the extraction-treatment time. It mainly utilizes surfactants, i.e., solubilizing materials, to increase the solubility and flowability of tetrachloroethylene in water, allowing the contaminant to be extracted with the aqueous phase. Therefore, SEAR technology is an effective and practical technique for remediating tetrachloroethylene-contaminated sites.

[0003] In recent years, conventional surfactant-enhanced remediation has faced the challenge of separating pollutants from surfactants after mixing with them. This makes it impossible to reuse surfactants, requiring large quantities in practical applications and resulting in excessively high environmental remediation costs. Furthermore, directly discharging conventional surfactants into wastewater treatment plants increases the load on treatment equipment, leading to significant resource waste. Separating surfactants avoids these problems and allows them to be reused for solubilization remediation, achieving resource recycling. Therefore, considering both economic and environmental factors, the final stage of SEAR technology needs to address the effective separation of surfactants and organic pollutants, as well as the recycling of surfactants. Switchable surfactants can effectively solve this problem. Therefore, to achieve the recycling of surfactants, developing switchable surfactants with both solubilization capabilities and recyclability is crucial for advancing SEAR technology for the solubilization remediation of chlorinated hydrocarbon-contaminated aquifers. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a recyclable surfactant material that possesses both solubilizing properties and redox switching response, offering a reference for separating surfactant materials from pollutants and for the recycling of surfactant materials.

[0005] This invention provides a selenium-containing surfactant material, wherein the surfactant material is sodium dialkylcarboxylate selenide, and its structural features are represented by the following general formula:

[0006] M +- OOC(CH2) n Se(CH2) n COO - M +

[0007] In the formula, n can be 8, 10, or 11, and M... + Sodium ions

[0008] A method for preparing sodium dialkylcarboxylate selenide, a recyclable surfactant material with redox switch response, characterized in that the preparation method includes the following steps:

[0009] A mixture of selenium powder and ultrapure water was stirred at room temperature for 10 minutes and then cooled in an ice-water bath. A sodium borohydride solution dissolved in ice water was added dropwise to the mixture, and the mixture was stirred continuously at room temperature for 10 minutes to obtain a colorless Na2Se solution. The Na2Se solution was stirred at 50°C for 20 minutes, and then a bromoalkyl acid dissolved in tetrahydrofuran was added to it. The mixture was stirred for 18 hours to obtain a yellow mixture. The yellow mixture was extracted three times with dichloromethane, dried with anhydrous sodium sulfate, allowed to stand overnight, and evaporated under reduced pressure to obtain dialkyl selenide. The dialkyl selenide was dissolved in ethanol and added to a saturated NaOH ethanol / water solution (ethanol to water volume ratio of 9:1). The solution was filtered to obtain yellow crystals, which are the recyclable surfactant material with the target redox switch response.

[0010] Furthermore, the mass ratio of selenium powder to water is 1.4836:20.

[0011] Furthermore, the mass ratio of sodium borohydride to water is 1.7047:15.

[0012] Furthermore, the molar ratio of the tetrahydrofuran to the bromoalkyl acid is 24:1.

[0013] The beneficial effects of this invention are as follows:

[0014] 1. The redox-switching responsive recyclable surfactant prepared by this invention is a reusable surfactant. During use, by alternately adding oxidant and reducing agent, the interconversion between surfactant and non-surface active materials can be easily achieved. In this way, the separation of surfactant after use becomes relatively easy, making the surfactant reusable.

[0015] 2. The redox-responsive recyclable surfactant material prepared by this invention has the ability to solubilize tetrachloroethylene compared with general redox-responsive surfactant materials, and can be used to remediate tetrachloroethylene in underground aquifers.

[0016] 3. The preparation method of the selenium-containing redox switching surfactant material prepared by the present invention is simple, the preparation conditions are mild, and no special equipment is required. Attached Figure Description

[0017] Figure 1 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 Mass spectra of the corresponding oxidation states;

[0018] Figure 2 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 And the corresponding nuclear magnetic resonance selenium spectra for the oxidized and reduced states;

[0019] Figure 3 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 And the corresponding zeta potential diagrams for the oxidized and reduced states;

[0020] Figure 4 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 And the viscosity diagrams for the corresponding oxidized and reduced states;

[0021] Figure 5 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 And the surface tension changes of the corresponding oxidized and reduced aqueous solutions;

[0022] Figure 6 Recyclable surfactants, sodium diheptylcarboxylate C8-Se-C8 and sodium didecylcarboxylate C8, are used to demonstrate the redox switch response of different ratios of oxidant (30wt% H2O2) and reductant (Na2SO3). 11 -Se-C 11 Influence diagram of switching conversion rate;

[0023] Figure 7 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 A diagram illustrating the redox cycle of an aqueous solution;

[0024] Figure 8 Recyclable surfactants, sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8), for redox switching responses at different concentrations. 11 -Se-C 11 and its corresponding oxidation state C8-Se-C8-O x and C 11 -Se-C 11 -O x Solubilization of tetrachloroethylene by aqueous solution;

[0025] Figure 9 Recyclable surfactants for redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 Diagram showing precipitation under alternating redox conditions. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific implementation schemes:

[0027] Example 1

[0028] Sodium selenide diheptylcarboxylate C8-Se-C8, a recyclable surfactant material with a redox switch response, was prepared. A mixture of 1.4836 g selenium powder and 25 mL ultrapure water was stirred at room temperature for 10 min, then cooled in an ice-water bath. A solution of sodium borohydride (1.7047 g) dissolved in 15 mL ice water was added dropwise to the mixture, and stirring was continued at room temperature for 10 min, yielding a colorless Na2Se solution. The Na2Se solution was stirred continuously at 50 °C for 20 min, and then 8.4 g of 8-bromooctanoic acid dissolved in 75 mL tetrahydrofuran was added, with stirring continued for 18 h. The yellow mixture was extracted three times with dichloromethane, dried over anhydrous sodium sulfate, allowed to stand overnight, and evaporated under reduced pressure to obtain selenium diheptylcarboxylate. The selenium diheptylcarboxylate was dissolved in ethanol and added to a saturated NaOH ethanol / water solution (ethanol to water volume ratio 9:1). After filtration, yellow crystals were obtained, which were the target redox switch-responsive recyclable surfactant material C8-Se-C8.

[0029] Example 2

[0030] Sodium didecylcarboxylate C, a recyclable surfactant material with redox switching response. 11 -Se-C 11 A mixture of 1.4836 g selenium powder and 25 mL ultrapure water was stirred at room temperature for 10 min, then cooled in an ice-water bath. A solution of sodium borohydride (1.7047 g) dissolved in 15 mL ice water was added dropwise to the mixture, and stirring was continued at room temperature for 10 min, yielding a colorless Na₂Se solution. The Na₂Se solution was stirred continuously at 50 °C for 20 min, then 10 g of 11-bromoundecanoic acid dissolved in 75 mL tetrahydrofuran was added, and stirring was continued for 18 h. The yellow mixture was extracted three times with dichloromethane, dried over anhydrous sodium sulfate, allowed to stand overnight, and evaporated under reduced pressure to obtain selenium didecylcarboxylate. Selenium didecylcarboxylate was dissolved in ethanol, added to a saturated NaOH ethanol / water solution (ethanol to water volume ratio 9:1), filtered, and yellow crystals were obtained, which is the recyclable surfactant C of the target redox switch response. 11 -Se-C 11 .

[0031] Example 3

[0032] The redox-switched recyclable surfactants C8-Se-C8 and C from Examples 1 and 2 are used. 11 -Se-C 11 Mass spectrometry measurements were performed, such as... Figure 1 (A) Figure 1 As shown in (C), the spectrum obtained from ESI-MS is... - OOC(CH2)7Se(CH2)7COO - (m / z = 362.84) - OOC(CH2) 10 Se(CH2) 10 COO - (m / z = 446.84) is in perfect agreement with the theoretical calculation, proving that the selenium-containing switching surfactants C8-Se-C8 and C 11 -Se-C 11 Synthesis; such as Figure 1 (B) Figure 1 As shown in (D), the oxidation product of C8-Se-C8 is C8-Se-C8-O. x In negative ion mode, the molecular ion peak is m / z = 378.84, C 11 -Se-C 11 Oxidation product C 11 -Se-C 11 -O x In negative ion mode, the molecular ion peak is m / z = 462.84, which is exactly one higher than before oxidation.16 The amount of O proves the properties of the surface-active materials C8-Se-C8 and C. 11 -Se-C 11 The synthesis also proved that it was oxidized to NaOOC(CH2)7SeO(CH2)7COONa and NaOOC(CH2). 10 SeO(CH2) 10 COONa.

[0033] Example 4

[0034] The redox-switched recyclable surfactants C8-Se-C8 and C from Examples 1 and 2 are used. 11 -Se-C 11 And the corresponding oxidation products C8-Se-C8-Ox and C 11 -Se-C 11 -Ox and its corresponding reduced state were measured using NMR selenium spectra. For example... Figure 2 As shown, the chemical shift of Se shifted from 300 to 1200 after oxidation, and returned to 300 after reduction, proving the effectiveness of the surface-active materials C8-Se-C8 and C... 11 -Se-C 11 The synthesis also proved that it was oxidized to NaOOC(CH2)7SeO(CH2)7COONa and NaOOC(CH2). 10 SeO(CH2) 10 COONa.

[0035] Example 5

[0036] Zeta potential determination. Recyclable reactive surfactants C8-Se-C8 and C from Examples 1 and 2, exhibiting redox switching response, were used. 11 -Se-C 11 Prepare the corresponding aqueous solution and measure the Zeta potential using a Zeta potential meter, such as... Figure 3 As shown. C8-Se-C8 and C 11 -Se-C 11 The zeta potential of aqueous solutions is always negative. The negative potential of surfactants causes them to generate electrostatic repulsion with negatively charged aqueous media, making them less susceptible to adsorption and thus minimizing adsorption loss. C8-Se-C8 and C 11 -Se-C 11 The oxidation products showed a significant difference in zeta potential compared to the initial state of the surface active material. After reduction, the zeta potential returned to the initial state, indicating the occurrence of a redox response process.

[0037] Example 6

[0038] Viscosity determination. Recyclable surfactants C8-Se-C8 and C from Examples 1 and 2, exhibiting redox switching response, were used. 11 -Se-C 11 Prepare the corresponding aqueous solution and measure its viscosity using a viscometer, such as... Figure 4 As shown. The viscosity of the C8-Se-C8 aqueous solution is 1 cP, the same as that of water. It requires low injection pressure during groundwater flushing and exhibits good migration properties within aquifers; C 11 -Se-C 11 The viscosity of the aqueous solution is 4.39 cP. After oxidation, the viscosity of the aqueous solution is the same as that of water. After reduction, due to the addition of sodium sulfite as a reducing agent to form sodium sulfate, the viscosity of the aqueous solution is still higher than that of water but lower than that of the initial state (cP). 11 -Se-C 11 The viscosity of the aqueous solution. The migration performance of C8-Se-C8 aqueous solution in the aquifer is greater than that of C. 11 -Se-C 11 Aqueous solution.

[0039] Example 7

[0040] Surface tension and CMC were measured. Recyclable reactive surfactants C8-Se-C8 and C from Examples 1 and 2 with redox switching response were used. 11 -Se-C 11 Aqueous solutions with mass concentrations ranging from 1 g / L to 10 g / L were prepared. The surface tension of these solutions, along with their oxidized and reduced aqueous solutions, was measured at room temperature using a QBZY fully automated surface tension meter. A graph was plotted with solution concentration on the x-axis and surface tension on the y-axis. The solution concentration corresponding to the inflection point of the decrease in surface tension is the critical micelle concentration (CMC). When the solution concentration is higher than the CMC, micelles with solubilizing ability are formed. Results are as follows: Figure 5 As shown, C 11 -Se-C 11 The CMC of the aqueous solution is 4.06 g / L, and the CMC of the C8-Se-C8 aqueous solution is 5.48 g / L. The CMC of the C8-Se-C8 aqueous solution is higher than that of the C8-Se-C8 aqueous solution. 11 -Se-C 11 The aqueous solution indicates that C8-Se-C8 is more water-soluble than C8-Se-C8. 11 -Se-C 11 .

[0041] Example 8

[0042] Recyclable surfactants C8-Se-C8 and C with different ratios of oxidant and reductant responding to redox switching. 11 -Se-C 11An investigation into the effect of switching conversion rate. This investigation aimed to explore the oxidation of the surface-active material C8-Se-C8 to the non-surface-active material C8-Se-C8-Ox, and the effect of the surface-active material C... 11 -Se-C 11 Oxidation to non-surface-active material C 11 -Se-C 11 -Ox conversion rate, i.e., the amount of hydrogen peroxide required to achieve the highest conversion rate, was determined by preparing 100 mL of a 30 g / L surfactant solution and dividing it into 10 equal portions of 10 mL each. Different volumes of 30 wt% H₂O₂ aqueous solution (n(oxidant):n(surfactant) = 0.5:1-5:1) were added to each portion. Then, 5 mL of the sample solution was taken and 0.5 mL of buffer solution and 5.0 mL of KSCN solution were added. After shaking and standing for 20 min, 3.0 mL of Rhodamine B solution and 0.8 mL of L-Wein-80 solution were added, diluted with water to 15 mL, shaken, and stood for 20 min. The absorbance was then measured at 606 nm using a corresponding reagent blank as a reference. The conversion rate results are shown below. Figure 6 As shown in (A), when the ratio of n(oxidant) to n(surfactant) is 3.5 to 1, the conversion rate of the oxidant is the highest and can reach over 90%.

[0043] To investigate the reduction of the non-surface-active material C8-Se-C8-Ox to the surface-active material C8-Se-C8-Re and the non-surface-active material C 11 -Se-C 11 -Ox is reduced to the surface-active material C. 11 -Se-C 11 -Re conversion rate, i.e., the amount of sodium sulfite required to achieve the highest conversion rate, is determined by preparing 100 mL of a 30 g / L surfactant solution and oxidizing it with the optimal amount of hydrogen peroxide determined above. The solution is then divided into 10 equal portions, each 10 mL, and different amounts of sodium sulfite are added to each portion to ensure that the sodium sulfite reacts with C8-Se-C8-Ox and C8-Ox in the system. 11 -Se-C 11 -Ox is formed in different molar ratios (n(reducing agent):n(surfactant) = 1:1-10:1). Then, 0.5 mL of buffer solution and 5.0 mL of KSCN solution are added to 5 mL of sample solution. After shaking and standing for 20 min, 3.0 mL of Rhodamine B solution and 0.8 mL of L-Wein-80 solution are added. The solution is diluted with water to 15 mL, shaken, and stood for 20 min. The absorbance is measured at a wavelength of 606 nm using the corresponding reagent blank as a reference. The conversion results are as follows: Figure 6 As shown in (B), when the ratio of n (reducing agent) to n (surfactant) is 3:1, the conversion rate can reach over 95%.

[0044] Example 9

[0045] Determination of redox response cycling performance. Recyclable surfactants C8-Se-C8 and C from Examples 1 and 2 with redox switching response were used. 11 -Se-C 11 The surfactant was prepared as an aqueous solution using sodium sulfite as a reducing agent and H₂O₂ (30 wt% aqueous solution) as an oxidizing agent. The C₈-Se-C₈ and C₈-Se-C₈ reactions were observed. 11 -Se-C 11 The redox response performance was investigated. Hydrogen peroxide was added at a ratio of n(surfactant):n(H₂O₂, 30wt% aqueous solution) = 3:1, and the mixture was ultrasonically mixed and kept at a constant temperature of 30℃ for 12 hours to ensure complete oxidation. After oxidation, sodium sulfite was added to the oxidized sample, and the sample was reduced within 30 minutes. The surface tension of the surfactant in its initial, oxidized, and reduced states was measured to explore its redox response cycle performance. Figure 7 As shown, C8-Se-C8 and C 11 -Se-C 11 All of them can be cycled at least 4 times and have stable properties.

[0046] Example 10

[0047] C8-Se-C8 and C 11 -Se-C 11 Solubilization experiments of PCE with the corresponding oxidation products were conducted. Recyclable surfactants C8-Se-C8 and C from Examples 1 and 2, exhibiting redox switching response, were used. 11 -Se-C 11 C8-Se-C8 and C were prepared at different concentrations (5, 10, 20, 30, 40 g / L). 11 -Se-C 11 Solutions and C8-Se-C8-Ox, C 11 -Se-C 11 -Ox solution, 10 mL was transferred in parallel to a sealed glass bottle, 125 μL of NAPL-phase PCE was added, and the bottle was placed in a water bath shaker at 150 rpm and 25 °C for 48 h. After centrifugation at 5000 rpm for 20 min, the supernatant was collected and the PCE concentration was determined by HPLC. Results are as follows: Figure 8 As shown, the optimal solubilizing concentration for C8-Se-C8 is 30 g / L, and the solubilizing ability of C8-Se-C8 for PCE is significantly better than that of C8-Se-C8-Ox; C 11 -Se-C 11 The optimal solubilizing concentration is 40 g / L, and C 11 -Se-C 11The solubilizing ability for PCE is significantly better than that for C. 11 -Se-C 11 -Ox.

[0048] Example 11

[0049] Recyclable surfactants with redox switching response: sodium diheptylcarboxylate selenide (C8-Se-C8) and sodium didecylcarboxylate selenide (C8-Se-C8). 11 -Se-C 11 Precipitation under alternating redox conditions is as follows: Figure 9 As shown, with the alternating addition of oxidizing and reducing agents, C8-Se-C8-Ox and C8-Ox reacted within four cycles. 11 -Se-C 11 -Ox can be stably precipitated in large quantities, facilitating subsequent separation and reuse.

Claims

1. A recyclable surfactant material with a redox-switching response, characterized in that, The surface-active material is sodium dialkylcarboxylate selenide, and its structural characteristics are represented by the following general formula. M + -OOC(CH2) n Se(CH2) n COO - M + (1) In the formula, n is 8 or 11, and M is... + It is a sodium ion.

2. The method for preparing a redox-responsive recyclable surfactant material as described in claim 1, characterized in that, The preparation method includes the following steps: stirring a mixture of selenium powder and ultrapure water at room temperature for 10 minutes, and then cooling it in an ice-water bath; adding a sodium borohydride solution dissolved in ice water dropwise to the above mixture, and stirring continuously at room temperature for 10 minutes to obtain a colorless Na2Se solution within 10 minutes; stirring the Na2Se solution at 50°C for 20 minutes, then adding a bromoalkyl acid dissolved in tetrahydrofuran, and continuing to stir for 18 hours to obtain a yellow mixture; extracting the yellow mixture three times with dichloromethane, then drying it with anhydrous sodium sulfate, letting it stand overnight, and evaporating it under reduced pressure to obtain dialkyl selenide; dissolving the dialkyl selenide in ethanol, adding it to a saturated NaOH ethanol aqueous solution, filtering, and obtaining yellow crystals, which are the recyclable surfactant material with the target redox switch response.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the tetrahydrofuran to the bromoalkyl acid is 24:

1.

4. The preparation method according to claim 2, characterized in that, The specific method for recycling the surface-active material after solubilizing tetrachloroethylene is as follows: an oxidant is added to the solution to convert the surface-active material into a non-surface-active material and to precipitate the non-surface-active material for recycling. After recycling, a reducing agent, sodium sulfite, is added to convert the non-surface-active material back into a surface-active material for reuse.

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