Modified zero-valent iron / biochar composite material rich in oxygen vacancies and application of modified zero-valent iron / biochar composite material

Abstract

The invention relates to an oxygen vacancy-rich modified zero-valent iron / biochar composite material and application thereof. The modified zero-valent iron / biochar composite material comprises a biochar carrier and zero-valent iron loaded on the biochar carrier, the surface of the zero-valent iron is coated with sulfur-containing ferrides and / or boron-containing ferrides, and the surface of the zero-valent iron contains rich oxygen vacancies; the modified zero-valent iron / biochar composite material is specifically prepared by the following steps: dispersing a biochar carrier and zero-valent iron in oxygen-free water, and grinding; adding a sulfur source or a boron source into the ground suspension, fully stirring and grinding, and drying; and soaking in a reducing solution, calcining at high temperature, and cooling to obtain the modified zero-valent iron / biochar composite material. Compared with the prior art, the modified zero-valent iron / biochar composite material prepared by the invention can be synergistically used with a compound oxidant to realize effective remediation of organic contaminated soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation composite materials, and in particular relates to a modified zero-valent iron / biochar composite material rich in oxygen vacancies and applications thereof. Background Art

[0002] Organic pollutants such as petroleum hydrocarbons, plastic additives, antibiotics, and organic pesticides are firmly adsorbed on the soil surface due to their high hydrophobicity, thus changing the structure and properties of the soil, resulting in a series of adverse effects such as reduced enzyme activity, changes in microbial communities and vegetation. Effective reduction and elimination of soil organic pollution is a difficult problem that needs to be solved urgently in the current field of soil remediation. At present, chemical oxidation technology is widely used to treat organically contaminated soil. Among them, persulfate is widely used as an oxidant in chemical oxidation remediation technology due to its good stability, high solubility, easy mass transfer, and strong oxidizing ability of sulfate radicals produced after activation.

[0003] Zero-valent iron activated persulfate can produce strong oxidizing free radicals (such as sulfate radicals (SO4 · -) and hydroxyl radicals (·OH)) have been widely used to repair organic contaminated soils, but there are problems such as easy passivation of zero-valent iron and the high price of persulfate compared to hydrogen peroxide. In addition, the residual concentration of organic pollutants in the repaired soil is still likely to exceed the limit values ​​of soil organic pollutants in the "Agricultural Land Soil Environmental Quality Standards" and "Soil Environmental Quality Standards". The main reason for this is that organic pollutants are stubbornly adsorbed in aged soils, resulting in very low effective state concentrations. It is difficult for oxidants to effectively degrade organic pollutants adsorbed in the soil. Even if the amount of oxidant is increased, the degradation effect of organic pollutants will not increase significantly.

[0004] Therefore, the treatment effect of existing technologies on organic pollutants in soil still does not meet people's expectations. It is necessary to overcome the problems of zero-valent iron passivation, high cost of persulfate, and difficulty in desorbing organic pollutants from aged soil in the existing zero-valent iron activated persulfate technology, and to seek more economical, environmentally friendly and efficient remediation technology for removing soil organic pollutants.

[0005] Superoxide free radicals (O2 ·- ) can play a role similar to that of surfactants in "eluting and desorbing" soil organic pollutants. Superoxide radicals are a type of free radical with nucleophilicity and reducing properties. Similar to active oxygen species such as strong oxidizing hydroxyl radicals and sulfate radicals, they are widely present in nature and are one of the most commonly designed active oxygen species in the fields of chemistry, environment, and medicine. Studies have shown that superoxide radicals have a solvation effect on the soil surface and can promote the desorption of organic pollutants from the soil by competing for adsorption sites. After desorption, organic pollutants are more easily degraded by strong oxidizing free radicals (such as hydroxyl radicals and sulfate radicals).

[0006] Compared with the desorption of organic pollutants by the micellar action of surfactants, the method of desorption of organic pollution in soil based on superoxide radicals has no toxic byproducts, high efficiency, and is a green environmental protection technology. At present, the most classic way to generate superoxide radicals for the remediation of organic polluted soil is to catalyze the hydrogen peroxide propagation reaction, in which superoxide radicals are generated by the reaction of high-concentration hydrogen peroxide (>0.3M) and hydroxyl radicals (Formula 1). This method has two disadvantages. First, high-concentration hydrogen peroxide applied to the soil will quickly decompose and release heat, causing soil burning, microbial "vacuum" and other soil degradation problems; secondly, the generation of superoxide radicals consumes hydrogen peroxide and hydroxyl radicals, reducing the utilization rate of oxidants and the oxidation efficiency of pollutants. Therefore, improving the generation technology of superoxide radicals and applying it to the remediation of petroleum hydrocarbon contaminated soil is of great significance to the remediation and management of contaminated sites.

[0007] OH + H2O2 → O2 - + H2O+ H + (1)

[0008] Chinese patent CN108675430A discloses a method for using transition metal oxyhydroxide as a catalyst to catalyze monopersulfate or monopersulfate to produce sulfate radicals, hydroxyl radicals, superoxide radicals and singlet oxygen non-radicals. However, the preparation process of transition metal oxyhydroxide is cumbersome and energy-intensive.

[0009] Chinese patent CN108380661A discloses a method for ex situ remediation of organic contaminated soil by a persulfate and hydrogen peroxide compound system, which introduces natural organic small molecules and activates the persulfate and hydrogen peroxide compound system through iron-containing minerals to ex situ remediate organic contaminated soil. However, when sodium persulfate, hydrogen peroxide and natural small molecule acid are added at the same time, the temperature of the soil system can reach as high as 51°C, and the insulation zone above 40°C reaches about 50 minutes. There are still soil degradation problems such as soil "burns" and microbial vacuum caused by the large-scale use of hydrogen peroxide.

[0010] Chinese patent CN108658211A discloses a method for treating sewage by coupling Fenton oxidation with zero-valent iron activated persulfate. The method first adds nano-zero-valent iron and persulfate to the sewage to be treated, maintains the ratio of nano-zero-valent iron and persulfate so that the pH of the reaction solution is maintained between 3-4, and then adds hydrogen peroxide to initiate Fenton oxidation. This method mainly targets pollutants in water and has not yet involved how to enhance the generation of superoxide radicals to remove organic pollutants stubbornly adsorbed in the soil.

[0011] Therefore, a soil remediation material and a soil remediation method that can synergistically reduce organic pollutants in the soil based on superoxide radical-promoted desorption and strong oxidative free radicals (hydroxyl radicals and sulfate radicals) oxidative degradation are still to be developed. Summary of the invention

[0012] The purpose of the present invention is to effectively reduce the content of organic pollutants in organically contaminated soil and to provide a modified zero-valent iron / biochar composite material rich in oxygen vacancies and its application.

[0013] The purpose of the present invention can be achieved by the following technical solutions:

[0014] The present invention provides a modified zero-valent iron / biochar composite material rich in oxygen vacancies, which comprises a biochar carrier and zero-valent iron loaded on the biochar carrier, wherein the surface of the zero-valent iron is coated with a sulfur-containing iron compound and / or a boron-containing iron compound, and the surface of the zero-valent iron contains abundant oxygen vacancies;

[0015] The modified zero-valent iron / biochar composite material rich in oxygen vacancies is specifically prepared by the following method:

[0016] S1: Dispersing the biochar carrier and zero-valent iron in oxygen-free water for grinding;

[0017] S2: adding a sulfur source or a boron source to the ground suspension, stirring and grinding the suspension, and drying the suspension to obtain a composite material of biochar loaded with sulfur-containing iron compounds and / or boron-containing iron compounds;

[0018] S3: soaking the composite material in a reducing solution, calcining at high temperature, and cooling to obtain the modified zero-valent iron / biochar composite material rich in oxygen vacancies.

[0019] Furthermore, the biochar carrier includes one or more of plant- or animal-derived biochars such as rice husk biochar, straw biochar, camphor tree branch biochar, animal manure biochar or sludge biochar.

[0020] Furthermore, the zero-valent iron is selected from commercially available iron powder or scrap iron.

[0021] Furthermore, the particle size of the zero-valent iron / biochar composite material is 0.1-30 μm.

[0022] Furthermore, the mass ratio of the biochar carrier to the zero-valent iron is 1:(1-10), preferably 1:(1.6-5).

[0023] Furthermore, the molar ratio of the zero-valent iron (calculated as iron) to the sulfur source (calculated as sulfur) is 100:(1-2).

[0024] Furthermore, the molar ratio of the zero-valent iron (calculated as iron) to the boron source (calculated as boron) is 100:(0.5-4).

[0025] Furthermore, in step S1, the grinding temperature is 20-80°C, and the grinding time is 1-5h.

[0026] Furthermore, the grinding is performed by using a sand mill, and the rotation speed of the sand mill is 250-700 rpm.

[0027] Furthermore, in step S2, the sulfur source is sulfur powder or a sulfur-containing compound.

[0028] Furthermore, the particle size of the sulfur powder is 50-250 meshes.

[0029] Furthermore, the sulfur-containing compound includes one or more of FeS, NaS2, KS2, Na2S2O3 or Na2S2O4.

[0030] Furthermore, in step S2, the boron source is boron powder or a boron-containing compound.

[0031] Furthermore, the particle size of the boron powder is 50-250 mesh.

[0032] Furthermore, the boron-containing compound includes one or more of B2O3, H3BO3 or BN.

[0033] Furthermore, in step S3, the reducing solution is selected from a strongly reducing sodium borohydride solution, the solution concentration is 0.1-4 mol / L, and the soaking time is 2-5 h.

[0034] Furthermore, the high-temperature calcination is carried out in a muffle furnace, the calcination temperature is 400-900° C., and the calcination time is 1-3 hours.

[0035] The present invention also provides an application of a modified zero-valent iron / biochar composite material rich in oxygen vacancies, wherein the modified zero-valent iron / biochar composite material rich in oxygen vacancies is used for soil remediation of organic polluted soil to reduce the content of organic pollutants in the soil;

[0036] The soil remediation specifically includes the following processes:

[0037] (1) Tillage treatment: Add modified zero-valent iron / biochar composite material rich in oxygen vacancies to organically contaminated soil at a ratio of 0.1-3% of soil mass and till evenly;

[0038] (2) Sprinkler irrigation treatment: the compound oxidant is sprayed into the above soil to form soil slurry, and the active substance in the compound oxidant is added at a ratio of 0.1-3% of the soil mass;

[0039] Wherein, the active substance in the composite oxidant includes persulfate and an auxiliary oxidant, and the auxiliary oxidant is selected from hydrogen peroxide or chlorine dioxide;

[0040] (3) Aging maintenance: Aging maintenance takes 24-72 hours, during which time the soil should be plowed and watered regularly.

[0041] Furthermore, the pollutants in the organically contaminated soil include one or more of petroleum hydrocarbons, polycyclic aromatic hydrocarbons, plastic additives, organophosphorus pesticides, organochlorine pesticides, antibiotics or hormones.

[0042] Furthermore, the persulfate is selected from one of sodium persulfate, potassium persulfate or ammonium persulfate.

[0043] Furthermore, the mass ratio of the persulfate to the active component in the auxiliary oxidant is (0.5-15):1.

[0044] The present invention integrates the interaction of persistent free radicals in the biochar environment, zero-valent iron, ferrous sulfide, iron boride, and surface oxygen vacancies to promote the generation of superoxide free radicals. On the basis of using superoxide free radicals to promote the desorption of petroleum hydrocarbons in the soil, a composite oxidant is added simultaneously, and modified zero-valent iron rich in oxygen vacancies is used to simultaneously activate the generation of strong oxidizing sulfate free radicals and hydroxyl free radicals to further oxidize and degrade the desorbed petroleum hydrocarbons. Among them, the addition of biochar makes up for the defect of insufficient specific surface area of ​​micron zero-valent iron. Crystalline ferrous sulfide or iron boride is coated on the surface of zero-valent iron to replace the passivation film (iron oxide) that may be formed, which can effectively prevent the passivation of zero-valent iron. The oxygen vacancies on the surface of zero-valent iron are conducive to the activation of oxidants to reduce the excessive ferrous iron to SO4 · -Ineffective consumption. The use of compound oxidants improves the removal efficiency of soil organic pollutants while reducing the use of persulfate and saving costs.

[0045] The modified zero-valent iron / biochar composite material and the compound oxidant of the present invention are used to synergistically reduce organic pollutants in soil as follows: the persistent free electrons on the surface of biochar and the active energy of the zero-valent iron surface rich in oxygen vacancies activate the oxidant (O2, persulfate, chlorine dioxide or hydrogen peroxide) to produce superoxide radicals, strong oxidizing hydroxyl radicals and sulfate radicals; superoxide radicals have a site "desorption" effect on soil organic pollutants, can promote the dissolution of hydrophobic petroleum hydrocarbons into the water phase, and increase the interaction between pollutants and strong oxidizing free radicals (·OH, SO4 · -), thereby improving the degradation efficiency of pollutants.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The present invention activates oxidants (O2, persulfate, chlorine dioxide or hydrogen peroxide) under the synergistic effect of persistent free radicals in the biochar environment, zero-valent iron, surface sulfur compounds (boron compounds), and surface oxygen vacancies to produce superoxide radicals, strong oxidizing hydroxyl radicals (·OH) and sulfate radicals (SO4 · -), and on the basis of using superoxide radicals to promote the desorption of organic pollutants in the soil, the strong oxidizing (·OH) and sulfate radicals (SO4 · -) Further oxidative degradation of desorbed organic pollutants to reduce organic pollutants in the soil.

[0048] (2) The present invention makes up for the defect of insufficient specific surface area of ​​zero-valent iron through the composite preparation of biochar and zero-valent iron, and constructs abundant oxygen vacancies on the surface of the material through coating the surface of zero-valent iron with sulfur-containing iron compound / boron-containing iron compound to prevent the passivation of iron, and then undergoes strong reduction and high-temperature calcination treatment, thereby successfully preparing a modified zero-valent iron / biochar composite material rich in oxygen vacancies that can be used as a soil remediation material.

[0049] (3) The soil remediation method of the present invention has strong universality and no strict requirements on the initial pH conditions of the contaminated soil. It can efficiently degrade organic matter in the soil within a wide pH range. The process is simple and easy to operate, and it has the value of large-scale promotion and application.

[0050] (4) The materials required by the present invention are widely available and inexpensive, and the driving force for degrading pollutants is strong, fast, and the reagent utilization efficiency is high.

[0051] (5) The present invention uses a composite oxidant mainly composed of persulfate and supplemented by hydrogen peroxide or chlorine dioxide, which improves the removal efficiency of soil organic pollutants while reducing the amount of persulfate used, thereby saving economic costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a transmission electron microscope (TEM) image of the sulfur-modified zero-valent iron / biochar composite material prepared in Example 1 of the present invention.

[0053] Figure 2 These are the XRD and XPS spectra of the sulfur-modified zero-valent iron / biochar composite material prepared in Example 1 of the present invention.

[0054] Figure 3 This is a diagram of the electronic paramagnetic spectrum signal of superoxide radicals generated by the sulfur-modified zero-valent iron / biochar composite material activated oxidant prepared in Example 1 of the present invention.

[0055] Figure 4 This is a diagram of the surface oxygen vacancy electron paramagnetic signal of the sulfur-modified zero-valent iron / biochar composite material prepared in Example 1 of the present invention.

[0056] Figure 5 The sulfur-modified zero-valent iron / biochar composite material prepared in Example 1 of the present invention activates the dual oxidant (H2O2, PDS) to produce strong oxidative free radicals (·OH, SO4 · -)'s electron paramagnetic signal diagram.

[0057] Figure 6 This is a scanning electron microscope (SEM) image of the boron-modified zero-valent iron / biochar composite material prepared in Example 6 of the present invention. DETAILED DESCRIPTION

[0058] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0059] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0060] The zero-valent iron in the following embodiments is commercially available micron-sized zero-valent iron powder, and the biochar is commercially available rice husk biochar.

[0061] Embodiment 1:

[0062] This embodiment provides a sulfur-modified zero-valent iron / biochar composite material rich in oxygen vacancies, and the specific preparation process is as follows:

[0063] (1) Biochar and iron powder were added into oxygen-free water at a mass ratio of 1:1.6, and continuously ground with a sand mill. The sand milling temperature was 55°C, the sand milling time was 3 hours, and the sand milling speed was 450 rpm, to obtain a biochar-loaded zero-valent iron composite material.

[0064] (2) adding sulfur powder of about 150 mesh to the suspension after grinding in step (1), and continuing grinding for 3 hours; wherein the molar ratio of zero-valent iron (calculated as iron) to sulfur powder (calculated as sulfur) is 100:1.

[0065] (3) The suspended matter was filtered, washed three times, and then immersed in a 1 mol / L NaHB4 solution for 3 h. The suspended matter was then calcined at 500 °C in a muffle furnace for 2 h. The mixture was cooled to obtain a sulfur-modified zero-valent iron / biochar composite material rich in oxygen vacancies.

[0066] The sulfur-modified zero-valent iron / biochar composite material finally obtained in this example was characterized as follows:

[0067] (1) Morphological characterization: The prepared sulfur-modified zero-valent iron / biochar composite material was sampled and characterized by transmission electron microscopy, such as Figure 1 As shown in the figure, it can be observed that the particle size of the sulfur-modified zero-valent iron / biochar composite material is about 100nm, that is, 0.1μm, and it appears as a thin layer or sphere.

[0068] (2) Component characterization: The components of the prepared sulfur-modified zero-valent iron / biochar composite material were characterized by XRD and XPS. Figure 2 As shown in Figure 2, the XRD pattern of the sulfur-modified zero-valent iron / biochar composite shows two diffraction peaks at 44.7° and 65.1°, corresponding to the (110) and (200) planes of α-zero-valent iron (JCPDS 06–0696). x ) did not appear in the XRD pattern of sulfur-modified zero-valent iron / biochar composites, which may be due to their low content or amorphous structure, but XPS analysis showed that S 2– (161.4 and 162.6 eV) and S n 2– (163.5 and 164.7 eV).

[0069] (3) Identification of superoxide radicals: When the prepared sulfur-modified zero-valent iron / biochar composite material was used to activate different oxidants, there were obvious signal peaks of superoxide radicals in the EPR detection system, such as Figure 3 As shown, when persulfate (PDS) or dual oxidants (Bi-ox, H2O2 and PDS) were activated, the electron paramagnetic spectroscopy signal of superoxide radicals was observed to be 2.84 times stronger than that of H2O2 alone.

[0070] (4) The surface oxygen vacancy electron paramagnetic signal of sulfur-modified zero-valent iron / biochar composites is shown in Figure 2. Figure 4 The strong electron paramagnetic signal of the characteristic signal peak of oxygen vacancies (g factor is 2.003) was identified as oxygen vacancies.

[0071] (5) Strong oxidizing free radicals (hydroxyl radical (·OH) and sulfate radical (SO4 · -)) Identification: The prepared sulfur-modified zero-valent iron / biochar composite was used to activate the dual oxidants (H2O2, PDS), and it was found that strong oxidative free radicals (·OH, SO4 · -) of the electron paramagnetic signal, such as Figure 5 As shown, it is shown that the sulfur-modified zero-valent iron / biochar composite material has a strong oxidation ability when used in conjunction with a composite oxidant.

[0072] Embodiment 2:

[0073] This embodiment provides a sulfur-modified zero-valent iron / biochar composite material rich in oxygen vacancies. The difference from Embodiment 1 is that in step (2) of this embodiment, the molar ratio of zero-valent iron (calculated as iron) to sulfur powder (calculated as sulfur) is 100:1.5.

[0074] Embodiment 3:

[0075] This embodiment provides a sulfur-modified zero-valent iron / biochar composite material rich in oxygen vacancies. The difference from Embodiment 1 is that in step (2) of this embodiment, the molar ratio of zero-valent iron (calculated as iron) to sulfur powder (calculated as sulfur) is 100:1.8.

[0076] Embodiment 4:

[0077] This embodiment provides a sulfur-modified zero-valent iron / biochar composite material rich in oxygen vacancies. The difference from Example 1 is that in step (2) of this embodiment, NaS2 is added to the suspension, and the molar ratio of zero-valent iron (in terms of iron) to NaS2 (in terms of sulfur) is 10:1. The other steps refer to Example 1.

[0078] Embodiment 5:

[0079] This embodiment provides a sulfur-modified zero-valent iron / biochar composite material rich in oxygen vacancies. The difference from Example 1 is that in step (2) of this embodiment, Na2S2O4 is added to the suspension, and the molar ratio of zero-valent iron (in terms of iron) to Na2S2O4 (in terms of sulfur) is 100:1. The other steps refer to Example 1.

[0080] Embodiment 6:

[0081] This embodiment provides a boron-modified zero-valent iron / biochar composite material rich in oxygen vacancies. The difference from Example 1 is that in step (2) of this embodiment, boron powder is added to the suspension, and the molar ratio of zero-valent iron (in terms of iron) to boron powder (in terms of boron) is 100:4. The other steps refer to Example 1.

[0082] The surface morphology of the boron-modified zero-valent iron / biochar composite material prepared in this example is as follows: Figure 6 As shown, scanning electron microscopy was used to detect the zero-valent iron particles before and after modification, and it was found that the average particle size of the zero-valent iron particles before modification was 100 μm, while the average particle size of the boron-modified zero-valent iron material was 25 μm, indicating that boron modification can reduce the particle size of the zero-valent iron particles and increase the specific surface area.

[0083] Embodiment 7:

[0084] This embodiment provides a boron-modified zero-valent iron / biochar composite material rich in oxygen vacancies. The difference from Example 1 is that in step (2) of this embodiment, B2O3 is added to the suspension, and the molar ratio of zero-valent iron (in terms of iron) to boron powder (in terms of boron) is 100:2. The other steps refer to Example 1.

[0085] Comparative Example 1:

[0086] This embodiment provides a sulfur-modified zero-valent iron material without a biochar carrier. The difference from Embodiment 1 is that in this embodiment, only iron powder is added in step (1), and no biochar is added.

[0087] Comparative Example 2:

[0088] This embodiment provides an unmodified zero-valent iron biochar composite material. The difference from Embodiment 1 is that in this embodiment, iron powder is used instead of sulfur powder in step (2) and no sulfur element is introduced.

[0089] Comparative Example 3:

[0090] This embodiment provides a sulfur-modified zero-valent iron / biochar composite material that does not contain oxygen vacancies. The difference from Embodiment 1 is that in this embodiment, the material is directly dried after filtration in step (3) and is not subjected to subsequent sodium borohydride soaking and muffle furnace high-temperature calcination processes.

[0091] In addition, hydrophobic organic pollutants (such as petroleum hydrocarbons, plastic additives, etc.) are firmly adsorbed on the soil surface and have extremely low water solubility, which limits the pollutants from contacting the strong oxidizing free radicals in the solution and results in a low pollutant removal rate. The classic method based on catalyzing the propagation of hydrogen peroxide to produce superoxide radicals to promote the desorption of organic pollutants from the soil has the problem of "burning" the soil and low oxidant utilization efficiency.

[0092] Based on this, the present invention uses the modified zero-valent iron / biochar composite material rich in oxygen vacancies to remediate organic contaminated soil. The specific process is as follows:

[0093] (1) Tillage treatment: Add the prepared oxygen vacancy-rich zero-valent iron / biochar composite material to the organically contaminated soil at a ratio of 0.1-3% of the soil mass and till the soil evenly.

[0094] (2) Spray irrigation treatment: spray the compound oxidant into the soil to form soil slurry. Spray the compound oxidant into the soil to form soil slurry, and the active substance in the compound oxidant is added at a ratio of 0.1-3% of the soil mass.

[0095] The active substances in the composite oxidant include persulfate and auxiliary oxidant, and the mass ratio of active components in persulfate and auxiliary oxidant is (0.5-5): 1. The auxiliary oxidant is selected from hydrogen peroxide or chlorine dioxide, and the persulfate can be selected from one of sodium persulfate, potassium persulfate or ammonium persulfate.

[0096] (3) Curing and aging: Curing and aging takes 24-72 hours. During the curing period, the soil is plowed 2-3 times and water is sprayed 1-3 times according to the soil to water mass ratio (1-2):20.

[0097] The present invention refers to the zero-valent iron / biochar composite material and soil remediation method prepared above, and formulates soil remediation methods with different parameters, and uses petroleum hydrocarbons as an example to test the residual rate of organic pollutants. The test steps of the residual rate of petroleum hydrocarbons are as follows:

[0098] (1) Obtaining petroleum hydrocarbon contaminated soil: Take an appropriate amount of soil 10-20 cm below the surface near the gas station pipeline, remove impurities such as rubble, place the sample in a 60°C oven for 48 h to dry, then grind it through a 400-mesh sieve and place it in a desiccator for later use.

[0099] (2) The specific operation of removing petroleum hydrocarbons from soil by oxidation and degradation is as follows: 5 g of petroleum hydrocarbon-contaminated soil is placed in a 40 mL transparent glass bottle with a rubber gasket cap, 0.005 g of oxygen vacancy-rich zero-valent iron / biochar composite material is added, and a composite oxidant water solution is added. Then, the glass bottle is covered with a lid and placed in a floor shaker to mix evenly and age for several days.

[0100] (3) After aging, remove the lid of the glass bottle containing the soil and place it in a -20°C refrigerator for at least 2 hours, then transfer it to a freeze dryer and dry it for at least 48 hours. After drying, take out the glass bottle and add 10 mL of n-hexane. Quickly tighten the cap and shake to mix the n-hexane and soil evenly. Then, perform ultrasonic extraction at 100 W for 30 minutes, filter the supernatant, and detect it with a gas chromatograph (GC).

[0101] The test results of different soil remediation methods and petroleum hydrocarbon residual rates are shown in the following table:

[0102] Table 1 Test results of petroleum hydrocarbon residual rate

[0103]

[0104]

[0105] According to the above table:

[0106] (1) Comparison of soil treatment methods 1-3 shows that when the molar ratio of zero-valent iron (in terms of iron) to sulfur powder (in terms of sulfur) is in the range of 100:1-2, the removal rate of soil petroleum hydrocarbons by the modified zero-valent iron / biochar composite material with rich oxygen vacancies activated the dual oxidant is above 70%, which is much higher than the removal rate of control 3 (only dual oxidant without activator) (15%). Among them, when the molar ratio of zero-valent iron (in terms of iron) to sulfur powder (in terms of sulfur) is increased from 100:1 to 100:1.5, it is found that the residual rate of petroleum hydrocarbons is reduced from 26.1% to 19.4%. When the molar ratio is further increased to 100:1.8, it is found that the residual rate of petroleum hydrocarbons increases to 29.1%, indicating that the molar ratio of zero-valent iron (in terms of iron) to sulfur powder (in terms of sulfur) has a greater impact on the removal of soil petroleum hydrocarbons.

[0107] (2) Influence of modified raw materials (comparison between Example 1 and Examples 4-5): Under the same dosage of compound oxidant, the removal rate of petroleum hydrocarbons by the materials prepared using NaS2, Na2S2O4 or sulfur powder as the sulfur source in the dual oxidant system is above 70%, which is much higher than the removal rate of control 3 (only dual oxidant without activator) (15%); the removal rate of petroleum hydrocarbons by the materials prepared using different sulfur sources differs by 13.7%.

[0108] (3) Effect of modified raw materials (soil remediation methods 6-7): The modified zero-valent iron biochar activated dual oxidant with oxygen vacancies prepared using boron powder and B2O3 as boron sources had a removal rate of more than 70% for soil petroleum hydrocarbons, which was much higher than the removal rate of control 3 (only dual oxidant without activator) (15%). Among them, the removal rate of soil petroleum hydrocarbons by the composite material activated dual oxidant prepared with B2O3 as the boron source was 7.5% higher than that of the material prepared with boron powder.

[0109] (4) Comparison between soil remediation method 1 and soil remediation method 7 shows that different compositions of dual oxidants: H2O2 / persulfate or chlorine dioxide / persulfate, can be activated by the modified zero-valent iron biochar composite material rich in oxygen vacancies to remove soil petroleum hydrocarbons (removal rate > 70%), which is 72.5%-22% higher than the removal rate of soil petroleum hydrocarbons by the oxidation system using a single oxidant (control 4-6). Among them, the removal effect of the dual oxidant of chlorine dioxide / persulfate on soil petroleum hydrocarbons is 10.6% higher than that of the dual oxidant of H2O2 / persulfate.

[0110] (5) Soil remediation method 1. Comparison of controls 7-9 shows that the removal rate of soil petroleum hydrocarbons by activated dual oxidants of sulfide zero-valent iron without biochar loading (control 7) is less than 30%, the removal rate of soil petroleum hydrocarbons by activated dual oxidants of unmodified zero-valent iron biochar composite material (control 8) is 24.4%, and the removal rate of soil petroleum hydrocarbons by activated dual oxidants of sulfur-modified zero-valent iron / biochar composite material without oxygen vacancies (control 9) is 31.2%. The above control experiments show that oxygen vacancies, modification and biochar in the modified zero-valent iron biochar composite material with oxygen vacancies referred to in the present invention all play an irreplaceable role in activating dual oxidants to degrade soil organic pollutants.

[0111] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A modified zero-valent iron / biochar composite material rich in oxygen vacancies, characterized in that: It includes a biochar carrier and zero-valent iron loaded on the biochar carrier, wherein the surface of the zero-valent iron is coated with sulfur-containing iron compounds and / or boron-containing iron compounds, and the surface of the zero-valent iron contains abundant oxygen vacancies; The modified zero-valent iron / biochar composite material rich in oxygen vacancies is specifically prepared by the following method: S1: Dispersing the biochar carrier and zero-valent iron in oxygen-free water for grinding; S2: adding a sulfur source or a boron source to the ground suspension, stirring and grinding the suspension, and drying the suspension to obtain a composite material of biochar loaded with sulfur-containing iron compounds and / or boron-containing iron compounds; S3: soaking the composite material in a reducing solution, calcining at high temperature, and cooling to obtain the modified zero-valent iron / biochar composite material rich in oxygen vacancies.

2. The modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 1, characterized in that: The biochar carrier includes one or more of rice husk biochar, straw biochar, camphor tree branch biochar, animal manure biochar or biogas residue biochar; The zero-valent iron is selected from commercially available iron powder or waste iron filings.

3. The modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 1, characterized in that: The particle size of the zero-valent iron / biochar composite material is 0.1-30 μm.

4. The modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 1, characterized in that: The mass ratio of the biochar carrier to the zero-valent iron is 1:(1-10); The molar ratio of the zero-valent iron (calculated as iron) to the sulfur source (calculated as sulfur) is 100:(1-2); The molar ratio of the zero-valent iron (calculated as iron) to the boron source (calculated as boron) is 100:(0.5-4).

5. The modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 1, characterized in that: In step S1, the grinding temperature is 20-80°C and the grinding time is 1-5h; The grinding is performed by using a sand mill, and the rotation speed of the sand mill is 250-700 rpm.

6. The modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 1, characterized in that: In step S2, the sulfur source is sulfur powder or a sulfur-containing compound; the particle size of the sulfur powder is 50-250 mesh, and the sulfur-containing compound includes one or more of FeS, NaS2, KS2, Na2S2O3 or Na2S2O4; The boron source is boron powder or a boron-containing compound; the particle size of the boron powder is 50-250 meshes, and the boron-containing compound includes one or more of B2O3, H3BO3 or BN.

7. The modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 1, characterized in that: In step S3, the reducing solution is selected from a sodium borohydride solution, the solution concentration is 0.1-4 mol / L, and the soaking time is 2-5 h; The high-temperature calcination is carried out in a muffle furnace, the calcination temperature is 400-900° C., and the calcination time is 1-3 hours.

8. An application of the modified zero-valent iron / biochar composite material rich in oxygen vacancies according to any one of claims 1 to 7, characterized in that: The modified zero-valent iron / biochar composite material rich in oxygen vacancies is used for soil remediation of organic polluted soil to reduce the content of organic pollutants in the soil; The soil remediation specifically includes the following processes: (1) Tillage treatment: Add modified zero-valent iron / biochar composite material rich in oxygen vacancies to organically contaminated soil at a ratio of 0.1-3% of soil mass and till evenly; (2) Sprinkler irrigation treatment: the compound oxidant is sprayed into the above soil to form soil slurry, and the active substance in the compound oxidant is added at a ratio of 0.1-3% of the soil mass; Wherein, the active substance in the composite oxidant includes persulfate and an auxiliary oxidant, and the auxiliary oxidant is selected from hydrogen peroxide or chlorine dioxide; (3) Aging maintenance: Aging maintenance takes 24-72 hours, during which time the soil should be plowed and watered regularly.

9. The use of a modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 8, characterized in that: The pollutants in the organically contaminated soil include one or more of petroleum hydrocarbons, polycyclic aromatic hydrocarbons, plastic additives, organophosphorus pesticides, organochlorine pesticides, antibiotics or hormones.

10. The use of a modified zero-valent iron / biochar composite material rich in oxygen vacancies according to claim 8, characterized in that: The persulfate is selected from one of sodium persulfate, potassium persulfate or ammonium persulfate; The mass ratio of the persulfate to the active component in the auxiliary oxidant is (0.5-15):1.

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