Biochar-loaded nano zero-valent iron repair material as well as preparation method and application thereof

Abstract

The invention relates to a biochar-loaded nano zero-valent iron repair material as well as a preparation method and application thereof. The biochar loaded nano zero-valent iron repair material is prepared from a persulfate-biochar carrier and metal sulfide modified composite acid stabilized nano zero-valent iron sol, the composite acid is composed of gallic acid and humic acid / fulvic acid; the preparation method comprises the following steps: S1, preparing a persulfate-biochar carrier; and S2, preparing the biochar loaded nano zero-valent iron repair material. The method is applied to groundwater chlorohydrocarbon pollution remediation. According to the method, in the reductive dechlorination process of the nano zero-valent reduced iron, released Fe < 2 + > can strengthen persulfate, Fe < 2 + > is regenerated by utilizing the reduction effect of gallic acid on reacted Fe < 3 + >, and catalytic circulation of iron is maintained; humic acid / fulvic acid is used for efficiently driving the degradation process; and metal sulfide is utilized to catalyze reduction of organic chlorine chemicals, so that the reductive dechlorination performance of the nano-iron material is improved, and the repairing effect of chlorinated hydrocarbon is optimized.

Description

Technical Field

[0001] This invention relates to the field of chlorinated hydrocarbon pollution remediation technology, specifically to biochar-supported nano-zero-valent iron remediation materials, their preparation methods, and applications. Background Technology

[0002] Chlorinated solvents are widely used in various industrial processes (pharmaceuticals, degreasing, leather, electronics, dry cleaning, and pesticides, etc.). Due to problems such as irregular management and disposal, chlorinated hydrocarbon pollutants have entered the groundwater environment, causing widespread groundwater pollution by chlorinated organic solvents, posing serious health risks to the public and ecosystems. As a result, scholars both domestically and internationally have conducted extensive research on groundwater pollution by chlorinated organic solvents. Biochar-loaded nano-zero-valent iron (nZVI / BC) composites, prepared using biochar (BC) as a carrier, have shown good performance in many areas (such as heavy metals in soil and groundwater), attracting widespread attention from researchers. The nZVI / BC composite material possesses both the reducing activity of nZVI and the adsorption properties of biochar, making it a novel composite environmental functional material suitable for extensive research.

[0003] Traditional biochar-supported nano-zero-valent iron has the following drawbacks: 1. nZVI is easily passivated and deactivated, resulting in a short reaction life: When nZVI is directly loaded onto biochar, it will oxidize rapidly when exposed to air or water, forming a dense iron oxide (FeO, Fe2O3, Fe3O4) passivation layer on the surface. This shell will severely hinder the electron transfer between the core zero-valent iron and pollutants, leading to a rapid decline in material activity, i.e., a "disposable" material that cannot function effectively for a sustained period; 2. Low electron utilization efficiency and poor selectivity for the reduction and degradation of target pollutants: nZVI has strong reducing properties, but it is non-specific. It will react indiscriminately with water, dissolved oxygen in water, and other non-target pollutants, resulting in a large waste of electrons. It is not efficient for pollutants that need to be reduced and degraded (such as chlorinated organics). Summary of the Invention

[0004] To address the aforementioned problems, this invention provides biochar-supported nano-zero-valent iron repair materials, their preparation methods, and applications.

[0005] The technical solution of the present invention is: a biochar-supported nano-zero-valent iron remediation material, which is composed of a persulfate-biochar carrier and a composite acid-stabilized nano-zero-valent iron sol modified by metal sulfides loaded on the surface of the persulfate-biochar carrier; The preparation method of the metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol is as follows: Under nitrogen protection, the compound acid is dissolved in deoxygenated ultrapure water at a ratio of 1-2g:100mL and stirred until completely dissolved to obtain the compound acid solution; the compound acid is composed of gallic acid and humic acid / fulvic acid in a mass ratio of 1:1-3. Then press Fe 2+ Soluble ferrous salts were added to the composite acid solution at a ratio of 0.4-0.6 g: 100 mL to react and generate an aqueous solution of the soluble ferric salt-composite acid complex. Then, with continuous stirring, an aqueous solution of alkali metal borohydride was added dropwise to the aqueous solution of the soluble ferric salt-composite acid complex at a dropping rate of 1-2 drops / second, according to a molar ratio of alkali metal borohydride to ferrous ions of 2.5-3.5:1. After the reaction was completed, stirring and aging were continued for 25-35 min to obtain nano-zero ferric sol. Finally, a mixed suspension containing metal sulfides at a concentration of 1-5 mg / mL was added dropwise to the above-mentioned nano-zero-valent iron sol. After stirring for 1-2 hours, the mixture was vacuum filtered, and then the product was washed 3-5 times alternately with deoxygenated anhydrous ethanol and ultrapure water. Finally, the product was dispersed in deoxygenated water at a concentration ratio of 1-5 g / L to obtain a metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol. The volume ratio of the nano-zero-valent iron sol to the mixed suspension containing metal sulfides was 4-8:1.

[0006] Explanation: To address the short lifespan issue of existing biochar-supported nano-zero-valent iron (ZCE) technologies, a composite acid stabilizer is introduced. Gallic acid, rich in phenolic hydroxyl groups, efficiently reduces Fe(III) on the surface of the ZCE nano-zero-valent iron to Fe(II), maintaining the catalytic cycle of the Fenton / Fenton-like reaction and significantly preserving the activity of the ZCE nano-zero-valent iron. It is highly efficient, water-soluble, and reasonably priced. Humic acid / fulvic acid, containing quinone and phenolic hydroxyl groups, can accept electrons from metal borohydrides and then transfer them to pollutants or Fe(III), efficiently driving the degradation process. This further solves the problems of low electron utilization efficiency and poor selectivity in the reduction and degradation of target pollutants in existing technologies. Furthermore, the sulfur atoms in metal sulfides can regulate the electronic structure, and S... 2- It can directly transfer electrons to pollutants for reduction and dechlorination, thereby increasing the reduction and dechlorination rate of organochlorine compounds and effectively improving the electron utilization efficiency of zero-valent iron. And S 2- It can form coordination bonds with functional groups in complex acids (especially humic acids), enhancing their fixation and dispersion in materials; the layered structure of MoS2 can adsorb complex acids, forming a more stable complex interface, enhancing the overall structural stability, making the load more robust, and further improving the remediation effect on chlorinated hydrocarbon pollution. Mixing nano-zero-valent iron sol with a mixed suspension containing metal sulfides in the above proportions allows each nano-zero-valent iron sol to be effectively modified by the metal sulfides, resulting in well-dispersed and uniformly modified composite nanomaterials. This significantly improves the reduction and dechlorination rate and electron utilization efficiency of chlorinated organic pollutants.

[0007] Furthermore, the metal sulfide is one or more of FeS, MoS2, NiS, and CoS; Note: These metal sulfides have variable valence states and can catalyze the reduction of organochlorines, greatly improving the reductive dechlorination performance of nano-iron materials. Furthermore, the soluble iron salt is one of ferrous sulfate and ferrous chloride, or two of them in any proportion; the alkali metal borohydride is potassium borohydride or sodium borohydride. Note: The above-mentioned iron salts are readily soluble in water and can rapidly provide the Fe required for the preparation of nano-zero valent iron. 2+ Potassium borohydride or sodium borohydride can provide strongly reducing hydrogen anions, which can efficiently and controllably reduce Fe. 2+ It is reduced to nano-zero valent iron.

[0008] Further, the metal sulfide is pre-exfoliated: the metal sulfide powder is dispersed in ultrapure water at a concentration of 0.1-0.5 mg / mL, and pulsed ultrasonic treatment is performed at a power of 300-600 W for 1-4 hours under ice-water bath conditions of 2-8℃ to obtain a metal sulfide nanosheet suspension after exfoliation. Note: This exposes more edge active sites, resulting in higher catalytic activity and further enhancing the reductive dechlorination catalytic performance of the metal sulfide-modified nano-zero-valent iron composite material.

[0009] This invention also provides a method for preparing biochar-supported nano-zero-valent iron remediation materials, comprising the following steps: S1. Preparation of persulfate-biochar carrier Peanut shells are cleaned and dried at 65-75℃ for 20-28 hours. Then, the peanut shells and persulfate powder are ball-milled together at a weight ratio of 5-10:1. The mixture is then placed in a muffle furnace and pyrolyzed at 300-600℃ under controlled oxygen conditions for 1.5-2.5 hours. Finally, the mixture is impregnated with a 28-32% nitric acid solution for 1.5-2.5 hours, washed 3-5 times with deionized water, and dried at 65-75℃ for 1.5-2.5 hours to obtain the persulfate-biochar carrier. S2. Preparation of biochar-supported nano-zero-valent iron remediation materials S2-1. Under nitrogen protection, weigh the persulfate-biochar carrier prepared in S1 and add it to a three-necked flask containing ultrapure water to obtain a carrier suspension with a concentration of 5-10 wt%. S2-2, Stir at 100-200 rpm and add the metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol dropwise at a rate of 1-2 mL / min to the carrier suspension obtained in S2-1 at a mass ratio of nano-zero-valent iron to biochar carrier of 1:1-3, and react for 2-4 h; During this process, the nano-zero-valent iron sol will gradually be adsorbed and fixed in the huge specific surface area and abundant pores of biochar; S2-3: Finally, vacuum filtration is performed, and the filter cake is washed 3-5 times with anhydrous ethanol and ultrapure water alternately to remove unsupported nanoparticles and impurities. Finally, it is dried in a vacuum drying oven at 60-70℃ for 12-24 hours. The dried block product is then ground through a 60-100 mesh sieve in an oxygen-free environment to obtain biochar-supported nano-zero-valent iron repair material. Explanation: The persulfate loaded on the surface of biochar can fully utilize nano-zero ferric iron, which can not only reduce chlorinated hydrocarbons but also activate persulfate to generate highly oxidizing sulfate free radicals. This further degrades chlorinated hydrocarbons through two pathways: reductive dechlorination and free radical oxidative decomposition, significantly improving degradation efficiency and treatment range. The combined action of composite acid and metal sulfide on nano-zero ferric iron can significantly improve the dechlorination rate and the electron utilization efficiency of nano-zero ferric iron, making the consumption of nano-zero ferric iron more controllable and effective, avoiding instantaneous deactivation, and thus endowing the material with long-lasting performance, making it suitable for long-term remediation of groundwater.

[0010] Furthermore, in S1, the ball milling method is to alternate between forward and reverse ball milling, with a ball milling speed of 200-300 rpm, a frequency of once every 20-30 minutes, and a ball milling time of 5-30 hours; Note: Unidirectional long-term ball milling causes the material to stratify due to centrifugal force. Alternating forward and reverse directions enables efficient mixing of the material in the ball mill jar, thereby generating a persulfate-biochar carrier with a stable structure and uniform distribution of active sites.

[0011] Furthermore, in S1 and S2-3, the parameters for vacuum filtration are: vacuum pressure -0.06 - -0.08 MPa, filter membrane using 0.22-0.45 μm hydrophilic mixed cellulose ester or polyvinylidene fluoride microporous filter membrane, and filtration time of 10-30 min. Note: Under the above parameters, the filter cake can remain intact, moist, and without cracks, thus achieving the best loading and purification effect.

[0012] This invention also provides an application of a biochar-supported nano-zero-valent iron remediation material. Based on the above-mentioned remediation material, it is applied to groundwater contaminated with chlorinated hydrocarbons. The application method is as follows: using 0.1 mol·L⁻¹ -1 Hydrochloric acid or 0.1 mol·L -1 Sodium hydroxide was used to adjust the pH of the aqueous solution containing chlorinated hydrocarbons to 4.4-9.9. 0.5-4 g / L of biochar-supported nano-zero-valent iron remediation material was added to the aqueous solution containing chlorinated hydrocarbons, and the mixture was stirred to react. The reaction temperature was 15-40℃ and the reaction time was 10-300 min.

[0013] Furthermore, the chlorinated hydrocarbon is any one or more of trichloroethylene, chloroform, and chlorobenzene.

[0014] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention addresses the problems of short lifespan, low electron utilization efficiency, and poor selectivity in the reduction and degradation of target pollutants by supporting nano-zero valent iron on biochar in existing technologies. It utilizes nano-zero valent iron stabilized by a composite acid to support persulfate-biochar, so that the nano-zero valent iron can release Fe during the reduction and dechlorination process. 2+ Strengthening persulfate, and simultaneously reacting with Fe after the reaction 3+ The reaction causes Fe 2+ Concentration can be effectively controlled; gallic acid can effectively regenerate Fe. 2+ This maintains the catalytic cycle of iron; humic acid / fulvic acid acts as an electron shuttle, efficiently enhancing electron transfer efficiency and driving the degradation process; the modification of composite acid-stabilized nano-zero-valent iron sol with metal sulfides achieves sulfur atom-controlled electronic structure regulation, and utilizes S... 2 - It can directly act as an electron donor to participate in reduction and dechlorination, greatly improving the electron utilization efficiency and reaction rate of zero-valent iron.

[0015] (2) The metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol prepared in this invention ensures the full dissolution of the stabilizer by first preparing a composite acid solution, and then adding Fe. 2+ This allows it to preferentially coordinate with the phenolic hydroxyl and carboxyl functional groups on the complex acid molecule, forming a soluble iron salt-complex acid complex. This effectively prevents the aggregation of nano-zero valent iron. Then, under the protection of the complex acid, borohydride is used to bind the Fe... 2+ The reduced iron is reduced to zero-valent iron. The presence of the complex acid further stabilizes the newly generated nano-zero-valent iron crystal nuclei, preventing agglomeration. Finally, stirring on the surface of the nano-zero-valent iron sol allows metal sulfides to be more efficiently modified on its surface or in the gaps, ensuring that the sulfides can expose their active sites to the maximum extent, thereby improving the reduction and dechlorination performance of the composite material. Attached Figure Description

[0016] Figure 1 This is a comparison chart of the degradation efficiency of chlorobenzene by the composite materials prepared in Examples 1-14 and Comparative Examples 1-3 of the present invention after 90 minutes of repair. Figure 2 This is a comparison chart of the degradation efficiency of chlorobenzene by the composite materials prepared in Examples 1 / 2, Examples 15-26 and Comparative Examples 4-5 of the present invention after 90 min of repair. Figure 3 This is a comparison chart showing the degradation efficiency of chlorobenzene by the composite materials prepared in Examples 1 / 2 and Examples 27-29 of this invention after 90 minutes of repair. Detailed Implementation

[0017] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0018] Example 1: A biochar-supported nano-zero-valent iron remediation material, consisting of a persulfate-biochar carrier and a composite acid-stabilized nano-zero-valent iron sol modified with metal sulfides loaded on the surface of the persulfate-biochar carrier; The preparation method of metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol is as follows: Under nitrogen protection, the compound acid was dissolved in deoxygenated ultrapure water at a ratio of 1.5g:100mL and stirred until completely dissolved to obtain the compound acid solution; the compound acid was composed of gallic acid and humic acid in a mass ratio of 1:2. According to Fe 2+ A soluble ferrous salt was added to the composite acid solution at a ratio of 0.5 g: 100 mL, reacting to form an aqueous solution of the soluble ferrous salt-composite acid complex. Then, with continuous stirring, an aqueous solution of alkali metal borohydride was added dropwise to the aqueous solution of the soluble ferrous salt-composite acid complex at a dropping rate of 1 drop / second, according to a molar ratio of alkali metal borohydride to ferrous ions of 3:1. After the reaction was completed, stirring and aging continued for 30 min to obtain nano-zero-valent iron sol. The soluble ferrous salt was ferrous sulfate; the alkali metal borohydride was sodium borohydride. Finally, a mixed suspension containing metal sulfides at a concentration of 3 mg / mL was added dropwise to the above-mentioned nano-zero-valent iron sol. After stirring for 1.5 h, the mixture was vacuum filtered for 20 min under a vacuum pressure of -0.07 MPa. The product was then washed four times alternately with deoxygenated anhydrous ethanol and ultrapure water. Finally, the product was dispersed in deoxygenated water at a concentration ratio of 3 g / L to obtain a metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol. The volume ratio of the nano-zero-valent iron sol to the mixed suspension containing metal sulfides was 6:1. The metal sulfide was MoS2. The filter membrane was a 0.22 μm hydrophilic mixed cellulose ester. The above-mentioned biochar-supported nano-zero-valent iron remediation material was applied to groundwater contaminated with chlorinated hydrocarbons. The application method was as follows: using 0.1 mol·L⁻¹... -1 The pH of the aqueous solution containing chlorinated hydrocarbons was adjusted to 5.7 with hydrochloric acid. 2 g / L of biochar-supported nano-zero-valent iron remediation material was added to the aqueous solution containing chlorinated hydrocarbons, and the mixture was stirred to react. The reaction temperature was 22℃ and the reaction time was 90 min. The chlorinated hydrocarbon was chlorobenzene.

[0019] Example 2: A method for preparing a biochar-supported nano-zero-valent iron remediation material based on Example 1, comprising the following steps: S1. Preparation of persulfate-biochar carrier Peanut shells were cleaned and dried at 70℃ for 24 hours. Then, the peanut shells and persulfate powder were ball-milled together at a weight ratio of 7:1. The mixture was then placed in a muffle furnace and pyrolyzed at 450℃ with limited oxygen for 2 hours. Finally, the mixture was impregnated with a 30% nitric acid solution for 2 hours, washed four times with deionized water, and dried at 70℃ for 2 hours to obtain the persulfate-biochar carrier. In S1, the ball milling method was alternating forward and reverse operation, with a ball milling speed of 250 rpm and a frequency of one rotation every 25 minutes for 20 hours. S2. Preparation of biochar-supported nano-zero-valent iron remediation materials S2-1. Under nitrogen protection, weigh the persulfate-biochar carrier prepared in S1 and add it to a three-necked flask containing ultrapure water to obtain a carrier suspension with a concentration of 8 wt%. S2-2, Stir at 150 rpm and add the metal sulfide modified composite acid-stabilized nano-zero-valent iron sol dropwise at a rate of 1.5 mL / min to the carrier suspension obtained in S2-1 at a mass ratio of nano-zero-valent iron to biochar carrier of 1:2, and react for 3 h. S2-3: Finally, vacuum filtration was carried out for 20 min under a vacuum pressure of -0.07 MPa and a 0.22 μm hydrophilic mixed cellulose ester filter membrane. The filter cake was washed 5 times alternately with anhydrous ethanol and ultrapure water. Finally, it was dried in a vacuum drying oven at 65℃ for 18 h. The dried block product was ground through a 60-100 mesh sieve under an oxygen-free environment to obtain biochar-supported nano-zero-valent iron remediation material.

[0020] Example 3: Unlike Example 1, the composite acid is composed of gallic acid and humic acid in a mass ratio of 1:1.

[0021] Example 4: Unlike Example 1, the composite acid is composed of gallic acid and fulvic acid in a mass ratio of 1:3.

[0022] Example 5: Unlike Example 1, under nitrogen protection, the composite acid was dissolved in deoxygenated ultrapure water at a ratio of 1g:100mL and stirred until completely dissolved to obtain the composite acid solution.

[0023] Example 6: Unlike Example 1, under nitrogen protection, the composite acid was dissolved in deoxygenated ultrapure water at a ratio of 2g:100mL and stirred until completely dissolved to obtain the composite acid solution.

[0024] Example 7: Unlike Example 1, according to Fe 2+ Soluble ferrous salt was added to the composite acid solution at a ratio of 0.4 g: 100 mL to react and generate an aqueous solution of soluble ferric salt-composite acid complex. Then, the mixture was stirred continuously, and an aqueous solution of alkali metal borohydride was added dropwise to the aqueous solution of soluble ferric salt-composite acid complex at a dropping rate of 1 drop / second according to a molar ratio of alkali metal borohydride to ferrous ions of 2.5:1. After the reaction was completed, the mixture was stirred and aged for 25 min to obtain nano-zero ferric sol.

[0025] Example 8: Unlike Example 1, according to Fe 2+ Soluble ferrous salt was added to the composite acid solution at a ratio of 0.6 g: 100 mL to react and generate an aqueous solution of soluble ferric salt-composite acid complex. Then, the mixture was stirred continuously, and an aqueous solution of alkali metal borohydride was added dropwise to the aqueous solution of soluble ferric salt-composite acid complex at a dropping rate of 2 drops / second, according to a molar ratio of alkali metal borohydride to ferrous ions of 3.5:1. After the reaction was completed, the mixture was stirred and aged for 35 min to obtain nano-zero ferric sol.

[0026] Example 9: Unlike Example 1, the soluble iron salt is ferrous chloride.

[0027] Example 10: Unlike Example 1, the alkali metal borohydride is potassium borohydride.

[0028] Example 11: Unlike Example 1, a mixed suspension containing metal sulfides with a concentration of 1 mg / mL was added dropwise to the above-mentioned nano-zero-valent iron sol. After stirring for 1 h, the mixture was vacuum filtered for 10 min under a vacuum pressure of -0.06 MPa. The product was then washed three times alternately with deoxygenated anhydrous ethanol and ultrapure water. Finally, the product was dispersed in deoxygenated water at a concentration ratio of 1 g / L to obtain a metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol.

[0029] Example 12: Unlike Example 1, a mixed suspension containing metal sulfides at a concentration of 5 mg / mL was added dropwise to the above-mentioned nano-zero-valent iron sol. After stirring for 2 hours, the mixture was vacuum filtered for 10-30 minutes under a vacuum pressure of -0.08 MPa. The product was then washed 5 times alternately with deoxygenated anhydrous ethanol and ultrapure water. Finally, the product was dispersed in deoxygenated water at a concentration ratio of 5 g / L to obtain a metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol.

[0030] Example 13: Unlike Example 1, the metal sulfide is FeS.

[0031] Example 14: Unlike Example 1, the metal sulfide is NiS.

[0032] Example 15: Unlike Example 1, the application method is as follows: using 0.1 mol·L⁻¹ -1 The pH of the aqueous solution containing chlorinated hydrocarbons was adjusted to 4.4 with hydrochloric acid. 0.5 g / L of biochar-supported nano-zero-valent iron remediation material was added to the aqueous solution containing chlorinated hydrocarbons, and the mixture was stirred to react. The reaction temperature was 15℃ and the reaction time was 30 min.

[0033] Example 16: Unlike Example 1, the application method is as follows: using 0.1 mol·L -1 The pH of the aqueous solution containing chlorinated hydrocarbons was adjusted to 9.9 with sodium hydroxide. 4 g / L of biochar-supported nano-zero-valent iron remediation material was added to the aqueous solution containing chlorinated hydrocarbons, and the mixture was stirred to react. The reaction temperature was 40℃ and the reaction time was 300 min.

[0034] Example 17: Unlike Example 2, in S1, peanut shell raw material was cleaned and dried at 65°C for 20 hours. Then, peanut shell raw material and persulfate powder were ball-milled together at a weight ratio of 5:1. The mixture was then placed in a muffle furnace and pyrolyzed at 300°C with limited oxygen for 1.5 hours. Finally, it was impregnated with a 32% nitric acid solution for 1.5 hours, washed three times with deionized water, and dried at 65°C for 1.5 hours to obtain persulfate-biochar carrier.

[0035] Example 18: Unlike Example 2, in S1, peanut shell raw material was cleaned and dried at 75°C for 28 hours. Then, peanut shell raw material and persulfate powder were ball-milled together at a weight ratio of 10:1. The mixture was then placed in a muffle furnace and pyrolyzed at 600°C with limited oxygen for 2.5 hours. Finally, it was impregnated with a 28% nitric acid solution for 2.5 hours, washed 5 times with deionized water, and dried at 75°C for 2.5 hours to obtain persulfate-biochar carrier.

[0036] Example 19: Unlike Example 2, in S1, the ball milling method is alternating forward and reverse ball milling, the ball milling speed is 200 rpm, the frequency is once every 20 minutes, and the ball milling time is 5 hours.

[0037] Example 20: Unlike Example 2, in S1, the ball milling method is alternating forward and reverse ball milling, the ball milling speed is 300 rpm, the frequency is once every 30 minutes, and the ball milling time is 30 hours.

[0038] Example 21: Unlike Example 2, in S2-1, under nitrogen protection, the persulfate-biochar carrier prepared in S1 was weighed and added to a three-necked flask containing ultrapure water to obtain a carrier suspension with a concentration of 10 wt%.

[0039] Example 22: Unlike Example 2, in S2-1, under nitrogen protection, the persulfate-biochar carrier prepared in S1 was weighed and added to a three-necked flask containing ultrapure water to obtain a carrier suspension with a concentration of 5 wt%.

[0040] Example 23: Unlike Example 2, in S2-2, the composite acid-stabilized nano-zero-valent iron sol modified with metal sulfide was added dropwise at a rate of 1 mL / min to the carrier suspension obtained in S2-1 while stirring at a rate of 100 rpm and according to the mass ratio of nano-zero-valent iron to biochar carrier of 1:1. The reaction was carried out for 2 h.

[0041] Example 24: Unlike Example 2, in S2-2, the composite acid-stabilized nano-zero-valent iron sol modified with metal sulfide was added dropwise at a rate of 2 mL / min to the carrier suspension obtained in S2-1, with stirring at a rate of 200 rpm and a mass ratio of nano-zero-valent iron to biochar carrier of 1:3. The reaction was carried out for 4 h.

[0042] Example 25: Unlike Example 2, S2-3: Finally, vacuum filtration was carried out for 10 min under vacuum pressure of -0.06 MPa and the filter membrane was a 0.22 μm hydrophilic mixed cellulose ester. The filter cake was washed three times alternately with anhydrous ethanol and ultrapure water. Finally, it was dried in a vacuum drying oven at 60°C for 12 h.

[0043] Example 26: Unlike Example 2, S2-3: Finally, vacuum filtration was carried out for 30 min under the conditions of vacuum pressure -0.08 MPa and 0.22 μm hydrophilic mixed cellulose ester filter membrane, and the filter cake was washed 5 times alternately with anhydrous ethanol and ultrapure water, and finally dried in a vacuum drying oven at 70°C for 24 h.

[0044] Example 27: Unlike Example 1, the metal sulfide was pre-exfoliated: the metal sulfide powder was dispersed in ultrapure water at a concentration of 0.3 mg / mL, and pulsed sonication was performed at 450 W for 3 h under ice-water bath conditions at 5°C to obtain a metal sulfide nanosheet suspension after exfoliation.

[0045] Example 28: Unlike Example 27, metal sulfide powder was dispersed in ultrapure water at a concentration of 0.1 mg / mL and subjected to pulsed ultrasonic treatment at 300 W for 1 h under ice-water bath conditions at 2°C to obtain a suspended metal sulfide nanosheet after exfoliation.

[0046] Example 29: Unlike Example 27, metal sulfide powder was dispersed in ultrapure water at a concentration of 0.5 mg / mL and subjected to pulsed ultrasonic treatment at 600 W for 4 hours under ice-water bath conditions at 8°C to obtain a suspended metal sulfide nanosheet after exfoliation.

[0047] Experimental Example: This experimental example is based on the scheme described in Examples 1 / 2, and aims to illustrate the practical application effect of the present invention. The concentration of chlorobenzene in the water sample before the reaction was 79.63 mg / L. The concentration of chlorobenzene in the obtained sample after 90 min of reaction was determined using headspace gas chromatography-mass spectrometry, and the degradation efficiency was calculated. 1. To investigate the effects of metal sulfide-modified composite acid-stabilized nano-zero-valent iron sol and its preparation method on the remediation effect of biochar-supported nano-zero-valent iron remediation materials on chlorinated hydrocarbons. Comparative Example 1: Unlike Example 1, gallic acid was replaced with tannic acid.

[0048] Comparative Example 2: Unlike Example 1, the metal sulfide-modified composite acid-stabilized nano-zero-valent iron is not in a sol state.

[0049] Comparative Example 3: Unlike Example 1, no metal sulfide modification was performed on the composite acid-stabilized nano-zero-valent iron.

[0050] Conclusion: A comparison of Examples 1, 3-4, and Control Example 1 shows that replacing gallic acid with tannic acid has a negative impact on the degradation efficiency of chlorobenzene. This is because the zero-valent iron stabilized by tannic acid can effectively overcome the easy aggregation and oxidation characteristics of zero-valent iron, prolong the reaction activity of zero-valent iron, and enhance the strengthening effect of sodium persulfate. Compared with the degradation effect of iron-palladium nanoparticles on chlorobenzene, the degradation efficiency can reach 90.42% in 90 minutes. However, under the same reaction conditions, using the system of Example 1 of this invention, the degradation rate of chlorobenzene can reach 96.08% in 90 minutes. This is because gallic acid is rich in phenolic hydroxyl structures, which can efficiently reduce Fe(III) on the surface of nano-zero-valent iron to Fe(II), maintain the catalytic cycle of Fenton / Fenton-like reaction, and greatly maintain the activity of nano-zero-valent iron. Therefore, it can be concluded that gallic acid selected in this application is more advantageous. The comparison of Examples 1, 5-10 and Comparative Example 2 shows that the non-sol state of metal sulfide-modified composite acid-stabilized nano-zero-valent iron also has an adverse effect on the degradation efficiency of chlorobenzene. This is because the sol state can effectively penetrate into the internal pores of the biochar carrier, achieving uniform loading from the outside to the inside, ensuring that the nano-zero-valent iron and persulfate are in full and close contact. When groundwater flows through, pollutants will enter the interior of the biochar and be effectively degraded. Other forms of particles are prone to irreversible aggregation, which reduces the specific surface area and thus reduces the number of active sites, affecting its dispersion and initial activity, thereby reducing the ability to repair chlorinated hydrocarbons. A comparison of Examples 1, 11-14, and Comparative Example 3 shows that not modifying the composite acid-stabilized nano-zero-valent iron with metal sulfides also negatively impacts the degradation efficiency of chlorobenzene. This is because the benzene ring structure of chlorobenzene is very stable, and the C-Cl bond energy is high, making it difficult to be directly reduced and degraded, resulting in a slow reaction. In Comparative Example 3, relying solely on the reducing properties of nano-zero-valent iron resulted in a very slow degradation rate of chlorobenzene and an incomplete reaction. Metal sulfides, on the other hand, have variable valence states and can catalyze the reduction of organochlorines, greatly improving the reductive dechlorination performance of the nano-iron material. Therefore, considering all factors, Examples 1 and 2 are the optimal solutions.

[0051] 2. Investigating the effect of the preparation method of biochar-supported nano-zero-valent iron remediation material on the remediation effect of biochar-supported nano-zero-valent iron remediation material on chlorinated hydrocarbons. Comparative Example 4: Unlike Example 2, the pyrolysis temperature in the muffle furnace is 800°C.

[0052] Comparative Example 5: Unlike Example 2, the ball milling method does not involve alternating forward and reverse milling.

[0053] Comparative Example 6: Unlike Example 2, the mass ratio of nano-zero valent iron to biochar carrier is 1:4.

[0054] Conclusion: The comparison between Examples 2 and Examples 17-18 shows that biochar prepared at different temperatures has little effect on the removal of chlorobenzene. 300℃, 500℃ and 700℃ all have good removal effects on chlorobenzene. In terms of the removal rate trend, the overall removal effect at 300℃ is better and the fluctuation is smaller. However, in Control Example 4, further increase in pyrolysis temperature will cause a significant decrease in the chlorobenzene removal rate. This is because excessively high pyrolysis temperature has an adverse effect on the biochar carrier. A large amount of surface functional groups are burned off, which weakens its binding ability with active components. As the pyrolysis temperature increases, the amorphous carbon structure of biochar will transform into highly ordered graphitized carbon, which is more chemically inert and has lower reactivity. A comparison of Examples 2, 19-20 and Comparative Example 5 shows that the lack of alternating forward and reverse ball milling weakens the chlorobenzene removal effect. This is because the unidirectional long-term ball milling used in Comparative Example 5 causes the material to separate due to centrifugal force, thereby reducing the mixing capacity. In contrast, the alternating forward and reverse ball milling of this application enables efficient mixing of the material in the ball mill jar, which is beneficial for generating a persulfate-biochar carrier with a stable structure and uniform distribution of active sites, thereby optimizing the remediation capacity for chlorinated hydrocarbons. The comparison of Examples 2 and 23-24 shows that a carbon-to-iron ratio of 2:1 yields the best removal effect for mixed pollutants, achieving a chlorobenzene removal rate of 96.08%. The removal rate decreases with increasing carbon-to-iron ratio. The removal rate of mixed pollutants at a carbon-to-iron ratio of 1:1 is slightly lower than at 2:1 and 3:1, possibly because a large amount of nZVI is distributed on the surface of the biochar, occupying adsorption sites for the mixed pollutants. The slightly lower carbon-to-iron ratio of 4:1 in Comparative Example 6 compared to 2:1 may be due to excessive biochar covering the active sites of nZVI, potentially limiting the reaction between nZVI and the mixed pollutants. Alternatively, as the carbon-to-iron ratio increases, more loading material has a porous structure, allowing more nZVI to exist within the pore structure of the biochar. In summary, the remediation material of this application achieves the best remediation effect at a carbon-to-iron ratio of 2:1.

[0055] 3. To investigate the effect of metal sulfide pre-exfoliation treatment on the remediation effect of biochar-supported nano-zero-valent iron remediation materials on chlorinated hydrocarbons. Conclusion: The comparison between Examples 1 / 2 and Examples 27-29 shows that pre-exfoliation treatment of metal sulfides can further improve the degradation efficiency of chlorobenzene. This is because the morphology of the exfoliated nanosheets is more conducive to the exposure of active sites, thereby enhancing the catalytic ability. Therefore, considering all factors, Example 27 is the optimal solution, which can achieve a degradation efficiency of 98.26% for chlorobenzene within 90 min.

Claims

1. A biochar supported nano zero-valent iron remediation material, characterized in that, A metal sulfide modified composite acid stabilized nano zero-valent iron sol is prepared by a persulfate-biochar carrier and the metal sulfide modified composite acid stabilized nano zero-valent iron sol loaded on the surface of the persulfate-biochar carrier. The preparation method of the metal sulfide modified composite acid stabilized nano zero-valent iron sol is as follows: Under the protection of nitrogen, 1-2 g of composite acid is dissolved in deoxygenated ultrapure water at the ratio of 1-2 g: 100 mL, and stirred until completely dissolved to obtain a composite acid solution; the composite acid is composed of gallic acid and humic acid / fulvic acid at the mass ratio of 1:1-3; Then press Fe 2+ Soluble ferrous salts were added to the composite acid solution at a ratio of 0.4-0.6 g: 100 mL to react and generate an aqueous solution of the soluble ferric salt-composite acid complex. Then, with continuous stirring, an aqueous solution of alkali metal borohydride was added dropwise to the aqueous solution of the soluble ferric salt-composite acid complex at a dropping rate of 1-2 drops / second, according to a molar ratio of alkali metal borohydride to ferrous ions of 2.5-3.5:

1. After the reaction was completed, stirring and aging were continued for 25-35 min to obtain nano-zero ferric sol. Finally, a mixed suspension containing metal sulfide with a concentration of 1-5 mg / mL is added dropwise to the above nano zero-valent iron sol, stirred for 1-2 h, vacuum filtered, and then the product is washed with deoxygenated anhydrous ethanol and ultrapure water alternately for 3-5 times; finally, the product is dispersed in deoxygenated water at a concentration of 1-5 g / L to obtain the metal sulfide modified composite acid stabilized nano zero-valent iron sol; the volume ratio of the nano zero-valent iron sol to the mixed suspension containing metal sulfide is 4-8:

1.

2. The biochar-supported nano-zero-valent iron remediation material as described in claim 1, characterized in that, The metal sulfide is one or more of FeS, MoS2, NiS, and CoS.

3. The biochar-supported nano-zero-valent iron remediation material as described in claim 1, characterized in that, The soluble iron salt is one or any proportion of two of ferrous sulfate and ferrous chloride; the alkali metal borohydride is potassium borohydride or sodium borohydride.

4. The preparation method of the biochar supported nano zero-valent iron remediation material according to any one of claims 1-3, characterized in that, The method comprises the following steps: S1, preparation of a persulfate-biochar carrier The peanut shell raw material is cleaned, dried at 65-75°C for 20-28 h, then the peanut shell raw material and persulfate powder are jointly ball-milled and mixed at a weight ratio of 5-10:1, then put into a muffle furnace and pyrolyzed at a temperature of 300-600°C for 1.5-2.5 h under limited oxygen control, finally immersed in a 28-32% mass concentration nitric acid solution for 1.5-2.5 h, washed with deionized water for 3-5 times, and dried at 65-75°C for 1.5-2.5 h to obtain the persulfate-biochar carrier; S2, preparation of a biochar loaded nano zero-valent iron remediation material S2-1, under the protection of nitrogen, the persulfate-biochar carrier prepared in S1 is weighed and added to a three-necked flask containing ultrapure water to obtain a carrier suspension with a concentration of 5-10 wt%; S2-2, stirring at a speed of 100-200 rpm, and adding the metal sulfide modified composite acid stabilized nano zero-valent iron sol to the carrier suspension obtained in S2-1 at a rate of 1-2 mL / min at a mass ratio of nano zero-valent iron to biochar carrier of 1:1-3, and reacting for 2-4 h; S2-3: finally, vacuum filtration is performed, and the filter cake is washed with anhydrous ethanol and ultrapure water alternately for 3-5 times, and finally dried in a vacuum drying oven at 60-70°C for 12-24 h, the dried block-shaped product is ground to pass through a 60-100 mesh sieve in an anaerobic environment to obtain the biochar loaded nano zero-valent iron remediation material.

5. The method of claim 4, wherein the biochar-supported nano zero-valent iron remediation material is prepared by the steps of: a) mixing the biochar and the nano zero-valent iron to form a mixture; b) adding the mixture to the water; and c) stirring the mixture in the water. In S1, the ball-milling method is positive and negative alternating ball-milling, the ball-milling speed is 200-300 rpm, the frequency is 20-30 min per turn, and the ball-milling time is 5-30 h.

6. The method of claim 4, wherein the biochar-supported nano zero-valent iron remediation material is prepared by the steps of: mixing a biochar with a nano zero-valent iron to form a mixture; and heating the mixture to a temperature of 200-400 °C for 1-3 hours. In S1 and S2-3, the parameters of vacuum filtration are as follows: vacuum pressure -0.06 - -0.08 MPa, filter membrane is 0.22-0.45 μm hydrophilic mixed cellulose ester or polyvinylidene fluoride microporous filter membrane, and the filtration time is 10-30 min.

7. Use of a biochar-supported nano zero-valent iron remediation material, based on the remediation material according to any one of claims 1 to 3 or the remediation material prepared according to the method of any one of claims 4 to 6, characterized in that, It is applied to groundwater chlorinated hydrocarbon pollution, and the application method is: using 0.1mol·L -1 Hydrochloric acid or 0.1mol·L -1 Sodium hydroxide adjusts the pH of the water solution containing chlorinated hydrocarbon pollution to 4.4-9.9, adds 0.5-4g / L of biochar loaded nano zero-valent iron remediation material to the water solution containing chlorinated hydrocarbon pollution, and stirs and reacts; wherein, the reaction temperature is 15-40℃, and the reaction time is 10-300min.

8. The use of a biochar-supported nano zero-valent iron remediation material according to claim 7, characterized in that, The chlorinated hydrocarbon is any one or two or more of trichloroethylene, trichloromethane and chlorobenzene.

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