Sulfidized nano zero-valent iron composite material, and preparation method and application thereof

Abstract

The application belongs to the technical field of environmental functional materials, and particularly relates to a sulfidized nano zero-valent iron composite material, a preparation method and application thereof. The sulfidized nano zero-valent iron composite material comprises biochar and sulfidized nano zero-valent iron loaded thereon. The application provides a preparation method of the sulfidized nano zero-valent iron composite material, which comprises the following steps: dispersing biochar in a ferrous salt solution to form a mixed solution under the protection of an inert atmosphere; dissolving a reducing agent and a sulfidizing agent in an alkaline solution to obtain a mixed reaction solution; and adding the mixed reaction solution into the mixed solution to obtain the sulfidized nano zero-valent iron composite material through reduction and sulfidization reaction. The sulfidization modification technology is combined with biochar loading, the biochar effectively prevents nano particle agglomeration, improves material stability and dispersity, the adsorption function and the catalytic degradation function of the sulfidized zero-valent iron are synergistic, and the removal efficiency of the composite material on persistent organic pollutants such as perfluorinated compounds is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, specifically relating to a sulfurized nano-zero valent iron composite material, its preparation method and application, particularly a biochar-supported sulfurized nano-zero valent iron composite material, its preparation method and its application in removing pollutants such as perfluorinated compounds (PFAS) from water. Background Technology

[0002] Nano-zero valent iron (NZVI) has been widely studied for the remediation of heavy metals and chlorinated organic compounds in groundwater and wastewater due to its strong reducing properties and high reactivity. However, traditional NZVI particles have high surface energy, making them prone to aggregation and surface oxidation passivation, leading to a rapid decrease in reactivity and low electron utilization efficiency. Furthermore, its removal effect on some highly chemically stable pollutants such as perfluorinated compounds (PFAS) is limited. The CF bond energy in PFAS molecules is extremely high, making it difficult to effectively break through conventional reduction or oxidation processes.

[0003] To improve the properties of NZVI, sulfidation modification to form sulfidated nano-zero-valent iron (S-NZVI) has become an effective strategy. Sulfidation can form FeS with good electrical conductivity on the iron surface. x The layer not only inhibits passivation of the iron matrix but also improves the material's selectivity for target pollutants and electron transport efficiency. However, S-NZVI particles themselves still face the problem of easy aggregation, and their reactive sites are easily consumed rapidly during treatment. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a sulfurized nano-zero valent iron composite material, its preparation method and application, so as to solve the problems of easy agglomeration, poor stability and low removal efficiency of persistent pollutants such as perfluorinated compounds (PFAS) in existing nano-zero valent iron materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The present invention provides a sulfidated nano-zero valent iron composite material, comprising biochar and sulfidated nano-zero valent iron supported on the biochar.

[0006] By loading sulfide-containing zero-valent iron nanoparticles onto biochar, agglomeration due to high surface energy can be effectively prevented, significantly improving the material's dispersibility and stability. Simultaneously, the abundant pore structure and surface functional groups of biochar can adsorb and enrich pollutants in water, increasing their local concentration on the material surface. This, combined with the active sites provided by the sulfide-containing zero-valent iron, creates a synergistic "adsorption-degradation" effect. This effectively solves the problems of easy agglomeration and deactivation of active sites associated with traditional nano-zero-valent iron and its sulfide products, and significantly enhances the removal capacity for stubborn pollutants such as perfluorinated compounds.

[0007] Biochar (BC) is a carbon-rich porous material produced by the pyrolysis of biomass under oxygen-deficient or inert atmosphere-deficient conditions. It has abundant pore structure, large specific surface area and diverse surface functional groups, making it an ideal carrier for nanomaterials and an adsorbent for pollutants.

[0008] Preferably, the molar ratio (S / Fe) of sulfur to iron in the sulfidated nano-zero valent iron is 0.01 to 0.5.

[0009] This specific S / Fe ratio range was optimized. Within this range, sufficient amounts of FeS with good electrical conductivity can be formed. x (where x is 1 or 2) layers to promote electron transfer and inhibit iron nucleus passivation, while avoiding excessive sulfur covering too many zero-valent iron active sites, thereby improving the material's reaction selectivity and stability while maintaining high intrinsic reactivity.

[0010] Preferably, the biochar is obtained by pyrolysis of biomass under an inert atmosphere.

[0011] By controlling the pyrolysis atmosphere, biochar can be guaranteed to have stable chemical properties and a rich pore structure, laying the foundation for its loading function and adsorption performance.

[0012] This invention provides a method for preparing the aforementioned sulfurized nano-zero-valent iron composite material, comprising the following steps: S1. Under an inert atmosphere, biochar powder is dispersed in a ferrous salt solution to obtain a mixture; S2. Under an inert atmosphere, the reducing agent and the sulfiding agent are dissolved together in an alkaline solution to obtain a reduction-sulfidation mixed solution; S3. Add the reduction-sulfurization mixture to the mixture to carry out the reduction and sulfidation reaction; S4. After the reaction is complete, the obtained solid product is separated, washed and dried to obtain the sulfurized nano-zero valent iron composite material.

[0013] Based on the aforementioned technical means, this method employs a "one-step co-reduction sulfidation" process, directly reducing ferrous ions to zero-valent iron in the presence of biochar and simultaneously carrying out sulfidation. This method is concise, easy to operate, and the reaction is conducted under an inert atmosphere, effectively preventing the oxidation of nano-zero-valent iron during the formation process. Biochar is uniformly dispersed in the system from the initial stage of the reaction, serving as nucleation sites to guide the formation and loading of sulfidated nano-zero-valent iron on its surface, which is beneficial for forming a well-dispersed and firmly bonded composite material.

[0014] Preferably, the ferrous salt is selected from one or both of FeSO4·7H2O and FeSO4.

[0015] Preferably, the reducing agent is NaBH4.

[0016] Preferably, the vulcanizing agent is selected from Na2S2O4, Na2S2O3 or Na2S·9H2O.

[0017] These reagents are all common chemical raw materials, with low cost and high reaction efficiency, which is conducive to industrial application.

[0018] Preferably, the alkaline solution is an aqueous solution of NaOH, and the concentration of NaOH is 0.05%~0.2% (w / v).

[0019] This concentration range provides a suitable alkaline environment, ensuring the stability and reduction efficiency of the reducing agent NaBH4, while avoiding unnecessary side reactions or changes in the material structure due to excessive alkalinity.

[0020] Preferably, the molar ratio of the ferrous salt to NaBH4 is 1:4~6.

[0021] Preferably, the mass ratio of the biochar to the zero-valent iron in the composite material is 1:1~3.

[0022] These optimized material ratios ensure that the reduction reaction proceeds fully, while achieving the best loading ratio between the biochar carrier and the active components, thus balancing the activity and stability of the material.

[0023] Preferably, the reduction-sulfurization mixture is added to the mixture by a dripping method, and the dripping is completed at a uniform rate within 5 to 10 minutes. After the dripping is completed, the reaction continues for 20 to 40 minutes.

[0024] Controlling the dropping rate and reaction time is beneficial for controlling the nucleation and growth process of nanoparticles, obtaining uniformly sized and evenly distributed sulfide nano-zero valent iron, and fully loading it onto biochar.

[0025] Preferably, the method for preparing the biochar powder includes: The biomass raw material is pretreated, then placed in an inert atmosphere for constant-temperature pyrolysis, washed, and dried to obtain the biochar powder.

[0026] This preparation method can effectively utilize biomass resources such as agricultural waste. The preparation process is simple, and the resulting biochar has stable and adjustable properties.

[0027] Preferably, the biomass raw material is at least one selected from rice straw, corn straw, and wheat straw; More preferably, the biomass raw material is rice straw.

[0028] Preferably, the isothermal pyrolysis is performed by programming the temperature to 550-800 ℃ at a rate of 2-10 ℃ / min, and then maintaining the temperature at that temperature for 1-4 hours.

[0029] Preferably, the inert atmosphere is nitrogen or argon.

[0030] Rice straw is an abundant renewable resource. Using programmed temperature pyrolysis is beneficial for forming a well-developed multi-level porous structure. The temperature and time range mentioned are the preferred conditions for obtaining high specific surface area and high-performance biochar.

[0031] The present invention also provides the application of the aforementioned sulfide nano-zero valent iron composite material or the aforementioned sulfide nano-zero valent iron in the removal of perfluorinated compounds from water.

[0032] The sulfide nano-zero-valent iron composite material of this invention combines the adsorption and enrichment capacity of biochar with the reducing / catalytic activity of sulfide nano-zero-valent iron, making it particularly suitable for treating chemically stable and difficult-to-degrade perfluorinated compounds (PFAS). Its application in water purification can achieve highly efficient removal of pollutants.

[0033] Preferably, the method of application includes: The sulfurized nano-zero-valent iron composite material was added to a water body with a pH of 3-5 and containing 50-100 µg / L of perfluorinated compounds at a dosage of 0.5-2 g / L. 5-15 minutes after the start of the reaction, hydrogen peroxide solution was added as an oxidant to continue the reaction, thereby removing the perfluorinated compounds from the water body.

[0034] Based on the above application method, acidic conditions are conducive to the corrosion and electron release of zero-valent iron and promote hydrogen peroxide activation. Adding the material at the initial stage of the reaction and then introducing hydrogen peroxide later can construct a highly efficient Fenton / advanced oxidation synergistic system. Both the sulfide-containing zero-valent iron and biochar in the composite material can promote the decomposition of hydrogen peroxide to generate strong oxidizing free radicals, thereby attacking and degrading the adsorbed and enriched perfluorinated compound molecules. This method is simple to operate, operates under mild conditions, and exhibits high removal efficiency for low concentrations of PFAS, showing promising prospects for practical applications.

[0035] The beneficial effects of this invention: The sulfide nano-zero-valent iron composite material of the present invention effectively solves the problems of easy agglomeration and poor stability of nanoparticles by loading sulfide nano-zero-valent iron onto biochar. The porous structure of biochar not only immobilizes the nanoparticles but also enriches pollutants, and synergistically interacts with the reducing / oxidizing active sites of sulfide zero-valent iron, significantly improving the overall removal efficiency of pollutants.

[0036] The preparation method of the sulfidated nano-zero-valent iron composite material of the present invention provides a clear and optimized range for key parameters in various preparation methods, such as the S / Fe molar ratio, material ratio, reaction temperature, and time. The process exhibits good repeatability and is easy to implement and scale up. By comparing the effects of different sulfiding agents (Na2S2O4, Na2S2O3, Na2S·9H2O) and different S / Fe ratios, it is clarified that when Na2S2O4 is used as the sulfiding agent and the S / Fe ratio is approximately 0.1, the material exhibits superior catalytic activity, providing clear guidance for optimizing material performance.

[0037] The sulfurized nano-zero-valent iron composite material of this invention, when used in conjunction with hydrogen peroxide to degrade extremely difficult-to-degrade perfluorinated compounds in water, can construct a highly efficient Fenton / reduction-like system under mild conditions. Experiments show that this sulfurized nano-zero-valent iron composite material achieves a removal rate of 87.386% for low-concentration perfluorooctanoic acid (PFOA, 100 µg / L) after 20 minutes of reaction, demonstrating excellent degradation performance and practical application potential. It has significant application value in the field of environmental functional materials technology. Attached Figure Description

[0038] Figure 1 X-ray diffraction (XRD) spectra and related comparison results of sulfidated nano-zero valent iron with an S / Fe ratio of 0.1 prepared by different sulfiding agents used in Examples 1-6 and nano-zero valent iron prepared in Comparative Example 1; Figure 2 The image shows a comparison of the specific surface area of ​​sulfided nano-zero valent iron with an S / Fe ratio of 0.1 prepared using different sulfiding agents in Examples 1-6, and nano-zero valent iron prepared in Comparative Example 1. Figure 3 The image shows a comparison of the water contact angles of sulfided nano-zero valent iron with an S / Fe ratio of 0.1 prepared using different sulfiding agents in Examples 1-6, and nano-zero valent iron prepared in Comparative Example 1. Figure 4 XPS Fe 2p plot of the nano-zero valent iron prepared in Comparative Example 1; Figure 5 XPS Fe 2p plot of the SNZVI-1 / Na2S2O4 material with an S / Fe ratio of 0.1 prepared in Example 1; Figure 6 XPS Fe 2p plot of the SNZVI-2 / Na2S2O4 material with an S / Fe ratio of 0.1 prepared in Example 4; Figure 7 XPS Fe 2p plot of the SNZVI-1 / Na2S2O3 material with an S / Fe ratio of 0.1 prepared in Example 2; Figure 8XPS Fe 2p plot of the SNZVI-2 / Na2S2O3 material with an S / Fe ratio of 0.1 prepared in Example 5; Figure 9 XPS Fe 2p plot of the SNZVI-1 / Na2S·9H2O material with an S / Fe ratio of 0.1 prepared in Example 3; Figure 10 XPS Fe 2p plot of the SNZVI-2 / Na2S·9H2O material with an S / Fe ratio of 0.1 prepared in Example 6; Figure 11 XPS S 2p plot of the SNZVI-1 / Na2S2O4 material with an S / Fe ratio of 0.1 prepared in Example 1; Figure 12 XPS S 2p plot of the SNZVI-2 / Na2S2O4 material with an S / Fe ratio of 0.1 prepared in Example 4; Figure 13 XPS S 2p plot of the SNZVI-1 / Na2S2O3 material with an S / Fe ratio of 0.1 prepared in Example 2; Figure 14 XPS S 2p plot of the SNZVI-2 / Na2S2O3 material with an S / Fe ratio of 0.1 prepared in Example 5; Figure 15 XPS S 2p plot of the SNZVI-1 / Na2S·9H2O material with an S / Fe ratio of 0.1 prepared in Example 3; Figure 16 XPS S 2p plot of the SNZVI-2 / Na2S·9H2O material with an S / Fe ratio of 0.1 prepared in Example 6; Figure 17 This is a scanning electron microscope (SEM) image of the biochar (BC-600) prepared in Example 7 of this invention; Figure 18 This is a scanning electron microscope (SEM) image of the biochar-supported sulfurized nano-zero-valent iron composite material (S-NZVI / BC) prepared in Example 8 of this invention; Figure 19 The energy dispersive spectroscopy (EDS) surface scan of the biochar (BC-600) prepared in Example 7 of this invention; Figure 20 The energy dispersive spectroscopy (EDS) surface scan of the biochar-supported sulfurized nano-zero-valent iron composite material (S-NZVI / BC) prepared in Example 8 of this invention; Figure 21This is a comparison of the PFOA removal rates over time for SNZVI-1 / Na2S2O4 materials and NZVI with different S / Fe ratios in Example 9. Figure 22 This is a comparison of the PFOA removal rates over time for SNZVI-2 / Na2S2O4 materials and NZVI with different S / Fe ratios in Example 9. Figure 23 This is a comparison of the PFOA removal rates over time for SNZVI-1 / Na2S2O3 materials and NZVI with different S / Fe ratios in Example 9. Figure 24 This is a comparison of the PFOA removal rates over time for SNZVI-2 / Na2S2O3 materials and NZVI with different S / Fe ratios in Example 9. Figure 25 This is a comparison of the PFOA removal rates over time for SNZVI-1 / Na2S·9H2O materials and NZVI with different S / Fe ratios in Example 9. Figure 26 This is a comparison of the PFOA removal rates over time for SNZVI-2 / Na2S·9H2O materials and NZVI with different S / Fe ratios in Example 9. Figure 27 The graph shows a comparison of the PFOA removal rate over time of the biochar-supported sulfidated nano-zero-valent iron composite material (S-NZVI / BC) prepared in Example 8. Detailed Implementation

[0039] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0040] This invention aims to provide a sulfurized nano-zero valent iron composite material, its preparation method, and its application, in order to solve the problem of low degradation efficiency of nano-zero valent iron, as well as the problem of nano-zero valent iron agglomeration, and to improve the stability of nano-zero valent iron and enhance its ability to degrade perfluorooctanoic acid.

[0041] To make the technical problems, solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description of the sulfurized nano-zero-valent iron composite material, its preparation method, and its application, in conjunction with specific embodiments and accompanying drawings. Obviously, the described specific embodiments are merely some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the specific embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0042] Unless otherwise specified in the specific embodiments, the techniques or conditions described in the literature in this field or in accordance with the product instructions shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0043] All the liquid-phase synthesis experiments described below used deoxygenated deionized water that had been purged with nitrogen for more than 30 minutes; all experiments were conducted in a room-temperature reaction system under constant nitrogen protection.

[0044] Example 1 The one-step preparation of sulfide nano-zero valent iron (using Na2S2O4 as the sulfiding agent) includes the following steps: S1. Accurately weigh four portions of 9.925 g FeSO4·7H2O and place them in 1 L three-necked flasks respectively. Then add 200 mL of deoxygenated deionized water to each flask and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain four ferrous salt solutions. S2. Accurately weigh four 6.8 g portions of NaBH4, and then add different masses of Na2S2O4 (0.0311 g, 0.3109 g, 0.9327 g, and 1.5547 g, respectively). Mix the two together and dissolve them in four 200 mL portions of pre-prepared 0.1% (w / v) NaOH aqueous solution until completely dissolved, to obtain four reduction-sulfidation mixtures with different masses of Na2S2O4. S3. Place four three-necked flasks containing ferrous salt solutions on a magnetic stirrer. While stirring, slowly and uniformly add the four portions of the reduction-sulfurization mixture prepared in S2 into the ferrous salt solution over 10 minutes through a polytetrafluoroethylene constant pressure funnel. S4. After the addition was complete, the reaction was carried out at room temperature (about 25 °C) for 30 minutes. After the reaction was completed, the mixture was vacuum filtered using a Buchner funnel to remove the supernatant. The solid was washed three times with ethanol / water. The washed wet material was dried in a vacuum drying oven at 60 °C for 20 hours to obtain four types of one-step sulfidated nano-zero valent iron (SNZVI-1 / Na2S2O4) with different S / Fe ratios (0.01, 0.1, 0.3, and 0.5, respectively).

[0045] Example 2 The one-step preparation of nano-zero valent iron sulfide (using Na2S2O3 as the sulfiding agent) includes the following steps: S1. Accurately weigh four portions of 9.925 g FeSO4·7H2O and place them in 1 L three-necked flasks respectively. Then add 200 mL of deoxygenated deionized water to each flask and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain four ferrous salt solutions. S2. Accurately weigh four 6.8 g portions of NaBH4, and then add different masses of Na2S2O3 (0.0282 g, 0.2822 g, 0.8466 g, and 1.411 g, respectively). Mix the two together and dissolve them in four 200 mL portions of pre-prepared 0.1% (w / v) NaOH aqueous solution until completely dissolved, to obtain four reduction-sulfidation mixtures with different masses of Na2S2O3. S3. Place four three-necked flasks containing ferrous salt solutions on a magnetic stirrer. While stirring, slowly and uniformly add the four portions of the reduction-sulfurization mixture prepared in S2 into the ferrous salt solution over 10 minutes through a polytetrafluoroethylene constant pressure funnel. S4. After the addition was complete, the reaction was carried out at room temperature (about 25 °C) for 30 minutes. After the reaction was completed, the mixture was vacuum filtered using a Buchner funnel to remove the supernatant. The solid was washed three times with ethanol / water. The washed wet material was dried in a vacuum drying oven at 60 °C for 20 hours to obtain four types of one-step sulfidated nano-zero valent iron (SNZVI-1 / Na2S2O3) with different S / Fe ratios (0.01, 0.1, 0.3, and 0.5, respectively).

[0046] Example 3 The one-step preparation of nano-zero valent iron sulfide (using Na2S·9H2O as the sulfiding agent) includes the following steps: S1. Accurately weigh four portions of 9.925 g FeSO4·7H2O and place them in 1 L three-necked flasks respectively. Then add 200 mL of deoxygenated deionized water to each flask and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain four ferrous salt solutions. S2. Accurately weigh four 6.8 g portions of NaBH4, and then add different masses of Na2S·9H2O (0.0858 g, 0.8575 g, 2.5723 g, and 4.2872 g, respectively). Mix the two together and dissolve them in four 200 mL portions of pre-prepared 0.1% (w / v) NaOH aqueous solution until completely dissolved, to obtain four reduction-sulfidation mixtures with different masses of Na2S·9H2O. S3. Place four three-necked flasks containing ferrous salt solutions on a magnetic stirrer. While stirring, slowly and uniformly add the four portions of the reduction-sulfurization mixture prepared in S2 into the ferrous salt solution over 10 minutes through a polytetrafluoroethylene constant pressure funnel. S4. After the addition was complete, the reaction was carried out at room temperature (about 25 °C) for 30 minutes. After the reaction was completed, the mixture was vacuum filtered using a Buchner funnel to remove the supernatant. The solid was washed three times with ethanol / water. The washed wet material was dried in a vacuum drying oven at 60 °C for 20 hours to obtain four types of one-step sulfidated nano-zero valent iron (SNZVI-1 / Na2S·9H2O) with different S / Fe ratios (0.01, 0.1, 0.3, and 0.5, respectively).

[0047] Example 4 The two-step method for preparing sulfide nano-zero-valent iron (using Na2S2O4 as the sulfiding agent) includes the following steps: S1. Accurately weigh four portions of 9.925 g FeSO4·7H2O and place them in 1 L three-necked flasks respectively. Then add 200 mL of deoxygenated deionized water to each flask and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain four ferrous salt solutions. S2. Accurately weigh four 6.8 g portions of NaBH4 and dissolve each portion in 200 mL of a pre-prepared 0.1% (w / v) NaOH aqueous solution until completely dissolved, to obtain four reducing solutions; S3. Place four three-necked flasks containing ferrous salt solutions on a magnetic stirrer. While stirring, slowly and uniformly add the four portions of reducing solution prepared in S2 to the ferrous salt solution over 10 minutes using a polytetrafluoroethylene constant pressure funnel; thus obtaining four NZVI suspensions. S4. Different masses of Na2S2O4 (0.0311 g, 0.3109 g, 0.9327 g, and 1.5547 g respectively) were dissolved in 100 mL of aqueous solution to obtain four vulcanizing agent solutions. Then, the four vulcanizing agent solutions were added dropwise to the four NZVI suspensions prepared in S3 at a uniform and slow rate over 10 minutes. S5. After the addition was complete, the reaction was carried out at room temperature (about 25 °C) for 30 minutes. After the reaction was completed, the mixture was vacuum filtered using a Buchner funnel to remove the supernatant. The solid was washed three times with ethanol / water. The washed wet material was dried in a vacuum drying oven at 60 °C for 20 hours to obtain four types of two-step sulfidation nano-zero valent iron (SNZVI-2 / Na2S2O4) with different S / Fe ratios (0.01, 0.1, 0.3, and 0.5, respectively).

[0048] Example 5 The two-step method for preparing nano-zero-valent iron sulfide (using Na2S2O3 as the sulfiding agent) includes the following steps: S1. Accurately weigh four portions of 9.925 g FeSO4·7H2O and place them in 1 L three-necked flasks respectively. Then add 200 mL of deoxygenated deionized water to each flask and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain four ferrous salt solutions. S2. Accurately weigh four 6.8 g portions of NaBH4 and dissolve each portion in 200 mL of a pre-prepared 0.1% (w / v) NaOH aqueous solution until completely dissolved, to obtain four reducing solutions; S3. Place four three-necked flasks containing ferrous salt solutions on a magnetic stirrer. While stirring, slowly and uniformly add the four portions of reducing solution prepared in S2 to the ferrous salt solution over 10 minutes using a polytetrafluoroethylene constant pressure funnel; thus obtaining four NZVI suspensions. S4. Dissolve different masses of Na2S2O3 (0.0282 g, 0.2822 g, 0.8466 g, and 1.411 g, respectively) in 100 mL of aqueous solution to obtain four vulcanizing agent solutions. Then, add the four vulcanizing agent solutions dropwise to the four NZVI suspensions prepared in S3 at a uniform and slow rate over 10 minutes. S5. After the addition was complete, the reaction was carried out at room temperature (about 25 °C) for 30 minutes. After the reaction was completed, the mixture was vacuum filtered using a Buchner funnel to remove the supernatant. The solid was washed three times with ethanol / water. The washed wet material was dried in a vacuum drying oven at 60 °C for 20 hours to obtain four types of two-step sulfidation nano-zero valent iron (SNZVI-2 / Na2S2O3) with different S / Fe ratios (0.01, 0.1, 0.3, and 0.5, respectively).

[0049] Example 6 The two-step method for preparing nano-zero-valent iron sulfide (using Na2S·9H2O as the sulfiding agent) includes the following steps: S1. Accurately weigh four portions of 9.925 g FeSO4·7H2O and place them in 1 L three-necked flasks respectively. Then add 200 mL of deoxygenated deionized water to each flask and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain four ferrous salt solutions. S2. Accurately weigh four 6.8 g portions of NaBH4 and dissolve each portion in 200 mL of a pre-prepared 0.1% (w / v) NaOH aqueous solution until completely dissolved, to obtain four reducing solutions; S3. Place four three-necked flasks containing ferrous salt solutions on a magnetic stirrer. While stirring, slowly and uniformly add the four portions of reducing solution prepared in S2 to the ferrous salt solution over 10 minutes using a polytetrafluoroethylene constant pressure funnel; thus obtaining four NZVI suspensions. S4. Dissolve different masses of Na2S·9H2O (0.0858 g, 0.8575 g, 2.5723 g, and 4.2872 g, respectively) in 100 mL of aqueous solution to obtain four vulcanizing agent solutions. Then, add the four vulcanizing agent solutions dropwise to the four NZVI suspensions prepared in S3 at a uniform and slow rate over 10 minutes. S5. After the addition was complete, the reaction was carried out at room temperature (about 25 °C) for 30 minutes. After the reaction was completed, the mixture was vacuum filtered using a Buchner funnel to remove the supernatant. The solid was washed three times with ethanol / water. The washed wet material was dried in a vacuum drying oven at 60 °C for 20 hours to obtain four types of two-step sulfidation nano-zero valent iron (SNZVI-2 / Na2S·9H2O) with different S / Fe ratios (0.01, 0.1, 0.3, and 0.5, respectively).

[0050] Example 7 The preparation method of biochar (BC-600) includes the following steps: S1. Collect rice straw, rinse it with tap water, place it in a ventilated place to air dry naturally for 48 hours, and then put it in a vacuum drying oven at 60 ℃ for 24 hours; S2. Use a pulverizer to pulverize the dried straw from S1, and pass it through a 100-mesh standard sieve to obtain straw powder; S3. Weigh the straw powder from S2 and spread it evenly in a quartz boat. Place the quartz boat in the isothermal zone of the tubular furnace quartz tube. Before pyrolysis, purge with high-purity nitrogen (99.9%) at a flow rate of 100 mL / min for 1 hour to completely remove air from the furnace tube. Subsequently, under the protective condition of continuous nitrogen flow, raise the temperature to 600 ℃ at a rate of 5 ℃ / min and maintain this temperature for pyrolysis for 2 hours. After pyrolysis, stop heating and allow the furnace to cool naturally to room temperature under continuous nitrogen purging. S4. Take out the pyrolyzed biochar, place it in a beaker, add enough deionized water to thoroughly wash away water-soluble substances, and then put it in a vacuum drying oven at 60 ℃ for 48 hours to obtain the final biochar, labeled as BC-600.

[0051] Example 8 The preparation method of the sulfurized nano-zero valent iron composite material (S-NZVI / BC, using Na2S2O4 as the sulfurizing agent, S / Fe=0.3, where the addition of sulfide is to slow down agglomeration and oxidation, compensate for the uneven distribution of sulfur phase in the one-step preparation, offset the sulfur loss and sulfur oxidation during the preparation / transfer process, and enhance the resistance to environmental interference in practical applications, so S / Fe=0.3 is adopted here) includes the following steps: S1. Under constant nitrogen protection at room temperature, accurately weigh 9.925 g of FeSO4·7H2O into a 1 L three-necked flask, add 200 mL of deoxygenated deionized water and stir to dissolve, obtaining a ferrous acid salt solution. After dissolving, add 1 g of biochar powder and stir for 30 min until fully mixed to obtain a mixed solution. The mass ratio of biochar to zero-valent iron was 1:2 (W / W); the deoxygenated deionized water was obtained by purging deionized water with N2 for 30 minutes. S2. Under constant nitrogen protection at room temperature, accurately weigh 6.8 g NaBH4 and 0.9327 g Na2S2O4 (corresponding to a target S / Fe molar ratio of 0.3), and dissolve them together in 200 mL of 0.1% (w / v) NaOH aqueous solution to obtain a reduction-sulfidation mixed solution. The molar ratio of ferrous salt to NaBH4 is 1:5. The one-step reduction and sulfidation process offers advantages such as extremely simple operation, significantly reduced time, avoidance of secondary pollution, higher raw material utilization, reduced overall cost by more than 50%, and higher batch stability. Therefore, the one-step method is chosen.

[0052] S3. Using a polytetrafluoroethylene constant pressure funnel, add the reduction-vulcanization mixed solution from S2 dropwise to the mixture in S1 at a uniform rate over 10 minutes. After the addition is complete, react at room temperature (approximately 25 °C) for 30 minutes. S4. After the reaction is complete, the mixture is allowed to stand and precipitate under nitrogen atmosphere, and washed three times with pure water. The supernatant is removed by filtration using a Buchner funnel and dried in a vacuum drying oven at 60 ℃ for 20 hours to obtain biochar-supported sulfide nano-zero-valent iron particles (S-NZVI / BC), i.e., sulfide nano-zero-valent iron composite material. Subsequently, the biochar-supported sulfide nano-zero-valent iron particles are washed three times with ethanol / water and separated by a magnet (magnetic separation is more effective and consumes less energy than other separation methods). Then, they are vacuum dried at a vacuum degree of -0.1 MPa and a temperature of 60 ℃ for 20 hours. The obtained particles are ground and stored in sealed vials before use.

[0053] Example 9 A method for evaluating the performance of biochar-supported sulfide nano-zero-valent iron composites and sulfide nano-zero-valent iron materials in degrading perfluorooctanoic acid (PFOA) includes the following steps: 500 mL of perfluorooctanoic acid (PFOA) solution (100 µg / L) was added to a three-necked flask. The pH was adjusted to 4 using a 1 mol / L hydrochloric acid aqueous solution. The reaction temperature was 25 °C. Then, the materials prepared in Examples 1-8 and Comparative Example 1 (1 g / L) were added respectively. After 10 min of reaction, hydrogen peroxide aqueous solution was added, with a mass ratio of hydrogen peroxide to iron of 1:3. At 5, 10, 20, 40, 60, 90, and 120 min of reaction, 1 mL of sample was taken from each beaker, filtered through a 0.22 µm filter, and measured. The PFOA concentration was determined by high performance liquid chromatography-tandem mass spectrometry (LC-MS).

[0054] Comparative Example 1 The preparation of nano-zero valent iron (NZVI) includes the following steps: S1. Accurately weigh 9.925 g FeSO4·7H2O and place it in a 1 L three-necked flask. Then add 200 mL of deoxygenated deionized water and stir magnetically at 300 rpm at room temperature until the solid is completely dissolved to obtain a ferrous salt solution. S2. Accurately weigh 6.8 g of NaBH4 and dissolve it in 200 mL of a pre-prepared 0.1% (w / v) NaOH aqueous solution until it is completely dissolved to obtain a reducing solution; S3. Place the three-necked flask containing the ferrous salt solution on a magnetic stirrer. While stirring, slowly and uniformly add the reducing solution from S2 to the ferrous salt solution from S1 through a polytetrafluoroethylene constant pressure funnel over 10 minutes. After the addition is complete, react at room temperature (approximately 25 °C) for 30 minutes. S4. After the reaction is complete, vacuum filtration is performed using a Buchner funnel to remove the supernatant. The solid is washed three times with ethanol / water. The washed wet material is then dried in a vacuum drying oven at 60 °C for 20 hours to obtain nano-zero valent iron (NZVI).

[0055] Detection and Analysis 1) Characterization of materials The crystal structure, specific surface area, water contact angle, and surface elements of S-NZVI-1, S-NZVI-2 with an S / Fe ratio of 0.1 prepared in Examples 1-6 and NZVI prepared in Comparative Example 1 were characterized and analyzed.

[0056] The effect of sulfidation on the crystal structure was studied by X-ray diffraction (XRD); the chemical state of the material surface elements, especially the Fe 2p and S 2p spectra, was analyzed by X-ray photoelectron spectroscopy (XPS); the specific surface area of ​​the material was analyzed by nitrogen adsorption-desorption isotherms; and the water contact angle of the material was measured using a water droplet angle meter. The results are as follows: Figures 1 to 16 As shown.

[0057] The morphology, elemental distribution, and content of BC-600 prepared in Example 7 and S-NZVI / BC prepared in Example 8 were characterized and analyzed. The morphology of the materials was observed using a scanning electron microscope (SEM), and the elemental distribution and content were detected using an energy dispersive spectroscopy (EDS) instrument. The results are as follows: Figures 17 to 20 As shown in Tables 1 and 2.

[0058] Table 1 shows the elemental content analyzed by BC-600 energy dispersive spectroscopy. Table 2 shows the elemental content analyzed by S-NZVI / BC energy dispersive spectroscopy. Table 1 shows the energy dispersive spectroscopy (EDS) analysis results of BC-600 obtained in Example 7, and Table 2 shows the EDS analysis results of S-NZVI / BC obtained in Example 8. Table 1 shows that the main elements contained in BC-600 are C and O, with C atoms accounting for 83.96% and O atoms accounting for 12.47%, and no sulfur was detected. Table 2 shows that the main elements contained in S-NZVI / BC are C, O, and Fe, with atomic percentages of 61.27%, 11.63%, and 24.86%, respectively, and S atoms accounting for 1.53%, indicating that iron and sulfur atoms were successfully loaded onto the biochar.

[0059] Figure 1 (a) shows the X-ray diffraction (XRD) spectra of sulfided nano-zero valent iron with an S / Fe ratio of 0.1 prepared using different sulfiding agents in Examples 1-6, and nano-zero valent iron prepared in Comparative Example 1. Figure 1As shown in (b), the lattice constant of NZVI is 0.2865 nm; the lattice constants of the three sulfided nano-zero-valent iron materials synthesized by the two-step method are: SNZVI-2 / Na2S2O4 (0.2891 nm) > SNZVI-2 / Na2S2O3 (0.2869 nm) > SNZVI-2 / Na2S (0.2868 nm); the lattice constants of the three sulfided nano-zero-valent iron materials synthesized by the one-step method are: SNZVI-1 / Na2S2O4 (0.2874 nm) > SNZVI-1 / Na2S (0.2867 nm) > SNZVI-1 / Na2S2O3 (0.2866 nm). Therefore, regardless of whether it is a one-step or two-step sulfidation method, the lattice constant of the material obtained when Na2S2O4 is used as the sulfiding agent is higher than that of the materials synthesized by the other two sulfiding agents. Figure 1 As shown in (c), the lattice spacing of the six sulfide materials exhibits the following pattern: SNZVI-2 / Na2S2O4 (0.2045 nm) > SNZVI-2 / Na2S2O3 (0.2029 nm) > SNZVI-2 / Na2S (0.2028 nm); SNZVI-1 / Na2S2O4 (0.2033 nm) > SNZVI-1 / Na2S (0.2028 nm) > SNZVI-1 / Na2S2O3 (0.2027 nm). From Figure 1 As shown in (d), the grain sizes of the six vulcanizing materials also exhibit a pattern consistent with the lattice constant, as follows: SNZVI-2 / Na2S2O4 (11.6208 nm) > SNZVI-2 / Na2S2O3 (11.1024 nm) > SNZVI-2 / Na2S (11.0058 nm); SNZVI-1 / Na2S2O4 (11.1941 nm) > SNZVI-1 / Na2S (10.8517 nm) > SNZVI-1 / Na2S2O3 (10.8426 nm). The results indicate that the material synthesized using Na2S2O4 as the vulcanizing agent has the largest grain size.

[0060] Figure 2 This is a comparison of the specific surface area of ​​sulfided nano-zero valent iron (NZVI) with an S / Fe ratio of 0.1 prepared using different sulfiding agents in Examples 1-6, and that of nano-zero valent iron prepared in Comparative Example 1. The results show that NZVI has a lower specific surface area (13.03 m²). 2The specific surface area of ​​NZVI (25.78 m² / g) may be due to its self-aggregation. Sulfidation can significantly increase the specific surface area of ​​NZVI because it can alleviate the aggregation of NZVI to some extent. Under the same sulfidation method, the specific surface area of ​​the material obtained using Na₂S₂O₄ as the sulfiding agent is larger than that of the material obtained using other sulfiding agents, as shown below: SNZVI₂ / Na₂S₂O₄ (25.78 m² / g). 2 / g)>SNZVI-2 / Na2S (18.54 m 2 / g)>SNZVI-2 / Na2S2O3 (17.89 m 2 / g);SNZVI-1 / Na2S2O4 (19.82 m 2 / g)>SNZVI-1 / Na2S2O3 (12.17 m 2 / g)>SNZVI-1 / Na2S (7.61 m 2 / g). This may be because when Na2S2O4 is used as a vulcanizing agent to prepare materials, the distribution between the resulting particles is more uniform compared to when other vulcanizing agents are used.

[0061] Figure 3 The image shows a comparison of the water contact angles of sulfided nano-zero-valent iron with an S / Fe ratio of 0.1 prepared using different sulfiding agents in Examples 1-6, and nano-zero-valent iron prepared in Comparative Example 1. Figure 3 As shown, the contact angle trends of the materials are as follows: SNZVI-2 / Na2S2O4 > SNZVI-1 / Na2S2O3 > SNZVI-1 / Na2S2O4 > NZVI > SNZVI-1 / Na2S > SNZVI-2 / Na2S2O3 > SNZVI-1 / Na2S. The contact angle reflects the hydrophilic / hydrophobic properties of the materials. The results show that all prepared materials exhibit hydrophobicity, with SNZVI-2 / Na2S2O4 exhibiting the greatest relative hydrophobicity.

[0062] Figure 4 The image shows the XPS Fe 2p plot of the nano-zero-valent iron prepared in Comparative Example 1. Figure 4 As shown, for NZVI, Fe 0 Fe II and Fe III The contents were 17.56%, 42.52% and 39.92% respectively, indicating that the surface chemical state of Fe in NZVI was in a mixed valence state, and some NZVI was inevitably oxidized when exposed to air during preparation and storage.

[0063] Figure 5-10XPS Fe 2p spectra of the materials with S / Fe ratio of 0.1 prepared in Examples 1-6. The results show that the contents of Fe 0 、Fe II and Fe III in SNZVI-2 / Na2S2O4 are 11.21%, 59.49% and 29.3% respectively; the contents of Fe 0 、Fe II and Fe III in SNZVI-2 / Na2S2O3 are 10.43%, 54.49% and 35.08% respectively; the contents of Fe 0 、Fe II and Fe III in SNZVI-2 / Na2S are 12.33%, 50.91% and 36.76% respectively. This indicates that when synthesizing sulfurized nano zero-valent iron materials by the two-step method, the content of reduced Fe in the materials obtained with different sulfurizing agents all increases, and the trend of the content of reduced Fe is: SNZVI-2 / Na2S2O4 > SNZVI-2 / Na2S2O3 > SNZVI-2 / Na2S; the trend of the content of oxidized Fe (Fe III ) is: SNZVI-2 / Na2S2O4 (29.3%) < SNZVI-2 / Na2S2O3 (35.08%) < SNZVI-2 / Na2S (36.76%). In addition, there is also the following rule for the content of oxidized Fe in the sulfurized nano zero-valent iron materials synthesized by the one-step method: SNZVI-1 / Na2S2O4 (32.88%) < SNZVI-1 / Na2S2O3 (36.57%) < SNZVI-1 / Na2S (40.07%). This shows that when using sodium dithionite (Na2S2O4) as the sulfurizing agent, the content of reduced Fe in the material is the highest, so the effect of improving the antioxidant ability of NZVI is more significant.

[0064] Figure 11-16 XPS S 2p spectra of the materials with S / Fe ratio of 0.1 prepared in Examples 1-6. The results show that the oxidized sulfur (SO3 2- and SO4 2-) The total content of [substance] is 32.01%. The total content of sulfur in the oxidized state in SNZVI-2 / Na2S2O3 is 49.25%. The total content of sulfur in the oxidized state in SNZVI-2 / Na2S is 36.52%. This indicates that when synthesizing sulfurized nano-zero-valent iron materials by the two-step method, the content of sulfur in the oxidized state in the materials obtained with different sulfurizing agents all decreases, and the trend of the content of sulfur in the oxidized state is: SNZVI-2 / Na2S2O4 < SNZVI-2 / Na2S < SNZVI-2 / Na2S2O3. Among them, when using Na2S2O4 as the sulfurizing agent, the content of sulfur in the oxidized state is the lowest. The content of S in the reduced sulfur in the materials with an S / Fe ratio of 0.1 prepared in Examples 1-6 n 2- are respectively: SNZVI-2 / Na2S2O4 (21.54%) < SNZVI-2 / Na2S2O3 (35.28%) < SNZVI-2 / Na2S(40.7%); SNZVI-1 / Na2S2O4 (33.72%) < SNZVI-1 / Na2S2O3 (45.37%) < SNZVI-1 / Na2S(52.71%). Since the reducing ability of S n 2- in the reduced sulfur is weak, when the content of S n 2- in the material decreases, the reducing ability of the material can be improved to a certain extent.

[0065] In summary, through the analysis of the chemical states of Fe and S elements in the material, it is strongly confirmed that sulfurization can improve the antioxidant performance of NZVI. When using sodium dithionite (Na2S2O4) as the sulfurizing agent, the effect of improving the antioxidant ability of NZVI is the most significant, followed by sodium thiosulfate (Na2S2O3), and the weakest in improving the antioxidant ability of the material is using sodium sulfide (Na2S) as the sulfurizing agent.

[0066] Figure 17 This is the scanning electron microscope (SEM) image of the biochar (BC-600) prepared in Example 7 of the present invention. Figure 18 This is the scanning electron microscope (SEM) image of the biochar-supported sulfurized nano-zero-valent iron composite material (S-NZVI / BC) prepared in Example 8 of the present invention. As Figure 17-18 shown, it can be seen from the SEM images at 5000 times and 20000 times that the surface of the biochar is relatively flat. After loading sulfurized nano-zero-valent iron particles, there are many flocculent aggregates on the surface of the obtained S-NZVI / BC material, and some are embedded in the pores. This indicates that after the sulfurized nano-zero-valent iron particles are compounded with the biochar, it is beneficial to the dispersion of the sulfurized nano-zero-valent iron particles, thereby improving the degradation efficiency of the material.

[0067] Figure 19The image shown is an energy dispersive spectroscopy (EDS) surface scan of the biochar (BC-600) prepared in Example 7 of this invention. Figure 20 This is an energy dispersive spectroscopy (EDS) surface scan of the biochar-supported sulfurized nano-zero-valent iron composite material (S-NZVI / BC) prepared in Example 8 of this invention. Figure 19 As shown, the surface of BC-600 is composed of C and O atoms; as Figure 20 As shown, the surface of S-NZVI / BC is composed of C, O, Fe, and S atoms. These results indicate that sulfide nano-zero valent iron was successfully dispersed on the surface of biochar.

[0068] 2) Degradation analysis of perfluorooctanoic acid in water The materials prepared in Examples 1-8 and Comparative Example 1 were subjected to PFOA degradation experiments according to the method described in Example 9. The effects of different sulfiding agents, different S / Fe ratios, different synthesis methods (one-step method, two-step method), and loading onto biochar on PFOA degradation were compared. Performance results are presented as a curve of PFOA removal rate versus time, as shown below. Figures 21-27 As shown in the figure. The results show that when Na2S2O4 is used as the sulfiding agent and the S / Fe ratio is 0.1, the materials generally exhibit superior activity. The composite material (S-NZVI / BC) loaded with biochar showed almost no removal effect after 5 minutes of reaction. After adding hydrogen peroxide after 10 minutes of reaction, the removal rate reached 87.386% after 20 minutes, 85.877% after 40 minutes, and 85.801% after 60 minutes. This indicates that after adding hydrogen peroxide, the composite material (S-NZVI / BC) loaded with biochar exhibited the fastest removal rate and the highest removal rate (removal rate >85% after 20 minutes), significantly better than the single NZVI material and the S-NZVI material without biochar, proving the synergistic effect of sulfidation and loading in this invention.

[0069] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a sulfide nano-zero-valent iron composite material, characterized in that, The sulfidated nano-zero valent iron composite material includes biochar and sulfidated nano-zero valent iron supported on the biochar. The biochar is obtained by pyrolysis of biomass under an inert atmosphere; The preparation of the sulfurized nano-zero-valent iron composite material includes the following steps: Under an inert atmosphere, biochar powder was dispersed in a ferrous salt solution to obtain a mixture; Under an inert atmosphere, the reducing agent and the sulfiding agent are dissolved together in an alkaline solution to obtain a reduction-sulfidation mixed solution; The reduction-sulfidation mixture is added to the mixture to carry out reduction and sulfidation reactions, thereby obtaining a sulfidated nano-zero-valent iron composite material. The ferrous salt is selected from one or both of FeSO4·7H2O and FeSO4; And / or, the reducing agent is NaBH4; And / or, the vulcanizing agent is selected from at least one of Na2S2O4, Na2S2O3 and Na2S·9H2O; And / or, the alkaline solution is an aqueous solution of NaOH, wherein the concentration of NaOH in the aqueous solution is 0.05%~0.2%; And / or, the molar ratio of the ferrous salt to NaBH4 is 1:4~6; And / or, the mass ratio of the biochar to zero-valent iron is 1:1~3.

2. The sulfide nano-zero-valent iron composite material prepared by the preparation method according to claim 1, characterized in that, The molar ratio (S / Fe) of sulfur to iron in the sulfidated nano-zero valent iron is 0.01~0.

5.

3. The method for preparing the sulfide nano-zero-valent iron composite material according to claim 1, characterized in that, The method for preparing the biochar powder includes the following steps: The biomass raw material is pretreated, then placed in an inert atmosphere for constant-temperature pyrolysis, washed, and dried to obtain the biochar powder.

4. The method for preparing the sulfide nano-zero-valent iron composite material according to claim 3, characterized in that, The biomass raw material is at least one of rice straw, corn straw, and wheat straw; And / or, the isothermal pyrolysis is performed by programming the temperature to 550-800 °C at a rate of 2-10 °C / min, and then maintaining the temperature at that temperature for 1-4 hours; And / or, the washing is to clean the biochar after constant-temperature pyrolysis with water; And / or, the drying is performed at a temperature of 60 °C for 48 h to obtain the biochar powder.

5. The method for preparing the sulfide nano-zero-valent iron composite material according to claim 1, characterized in that, The reduction-sulfurization mixture is added to the mixture by dripping. The dripping is completed at a uniform rate within 5 to 10 minutes. After the dripping is completed, the reaction continues for 20 to 40 minutes. And / or, the inert atmosphere is nitrogen or argon.

6. The application of the sulfurized nano-zero-valent iron composite material as described in claim 2 in the removal of perfluorinated compounds from water.

7. The application according to claim 6, characterized in that, The method of application includes: adding the sulfurized nano-zero valent iron composite material at a dosage of 0.5~2 g / L to a water body with a pH of 3~5 and containing 50~100 μg / L of perfluorinated compounds; adding hydrogen peroxide solution as an oxidant 5~15 minutes after the start of the reaction, and continuing the reaction to remove perfluorinated compounds from the water body.

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