Ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, preparation method and application thereof

Abstract

The present invention belongs to the technical field of heavy metal pollution remediation, and in particular relates to a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, its preparation method and application. The present invention combines a solvent-free synthesis process with a low-temperature one-step pyrolysis method, and utilizes pyrolysis gas byproducts to prepare a composite material in situ under carrier gas-free and oxygen-limited conditions. Compared with the existing technology, the preparation process of the present invention is green, environmentally friendly and pollution-free, with low preparation costs, and realizes efficient utilization of precursor materials; the solvent-free synthesis process adopted can be easily expanded by amplifying the raw materials; at the same time, the obtained material does not require mechanical ball milling, solvent impregnation, drying and other pre-treatment processes, and solid-phase one-step pyrolysis has the advantages of simple preparation method, low reaction temperature, short time, etc., excellent Cr(VI) removal performance, and can selectively remove Cr(VI) in the presence of high salt concentrations.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal pollution remediation, and in particular relates to a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, a preparation method thereof, and applications thereof. Background Art

[0002] Chromium (Cr) is an important raw material in the leather making, electroplating, pigment and other industrial fields. Its large-scale application has led to an increasingly prominent problem of environmental Cr pollution. Among the various chemical forms of Cr, hexavalent Cr (Cr(VI)) is listed as a priority pollutant due to its strong oxidizing properties, high mobility and carcinogenic and teratogenic properties. By reducing the highly toxic Cr(VI) to the less toxic Cr(III) and converting it into stable Cr(OH)3 or Cr x Fe 1-x (OH)3 precipitation effectively reduces the mobility and bioavailability of Cr(VI) and is the core strategy for Cr(VI) pollution control.

[0003] Natural and synthetic ferrous sulfide (FeS) is widely used in the field of wastewater and soil heavy metal pollution remediation due to its unique physical and chemical properties, especially for the treatment of Cr (VI) pollution. FeS has a high specific surface area, multiple active sites (Fe 2+ 、S 2- ) and magnetic response properties, which can achieve efficient removal of Cr(VI) through an adsorption-redox coupling mechanism. However, traditional FeS is prone to agglomeration and inactivation, has low permeability, and poses a risk of secondary contamination.

[0004] The use of porous carrier loading strategies can significantly improve the dispersibility and stability of FeS. Currently developed carrier systems include natural silicate minerals, high molecular polymers and biochar. Among them, biochar, as a carbon-rich porous material prepared by biomass pyrolysis, has the following significant advantages in loading FeS: (1) The three-dimensional network pore structure can provide ideal FeS loading sites; (2) The rich oxygen-containing functional groups (-COOH, -OH, etc.) on the surface give it excellent metal coordination ability; (3) Active sites can be constructed through nitrogen and sulfur co-doping modification, significantly enhancing the chemical adsorption capacity of Cr(VI). In addition, biochar as a carrier can not only improve the dispersion of FeS particles, but its surface nitrogen and sulfur species can also serve as electron transport media to accelerate the adsorption of FeS. 2+ / S 2- The electron transfer process to Cr(VI) significantly improves the Cr(VI) removal efficiency. Therefore, the preparation of FeS-loaded nitrogen-sulfur co-doped biochar composites and their use in Cr(VI) removal is expected to become one of the effective means of efficiently controlling Cr pollution in the environment.

[0005] Current FeS-biochar composite preparation techniques primarily rely on traditional processes such as hydrothermal synthesis, impregnation pyrolysis, and carboxymethyl cellulose (CMC) stabilization. However, these methods generally employ multi-step processes, resulting in complex workflows and high energy costs. Furthermore, the solvent systems used in the preparation process can easily oxidize and inactivate the synthesized FeS, and waste acid disposal can increase the environmental burden. Therefore, developing simple, environmentally friendly preparation methods is of great scientific and engineering significance for promoting the practical application of high-performance Cr(VI) contamination remediation materials. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a ferrous sulfide loaded nitrogen-sulfur co-doped biochar composite material, its preparation method and application. The preparation method is simple and has low cost, and the prepared ferrous sulfide loaded nitrogen-sulfur co-doped biochar composite material can achieve efficient control of Cr(VI) pollution.

[0007] The present invention provides a method for preparing a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, comprising the following steps:

[0008] S1) mixing a biomass raw material, thiourea and an iron salt to obtain a mixture;

[0009] S2) pyrolyzing the mixture at high temperature under oxygen-limited conditions to obtain a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material.

[0010] Preferably, the mass of the biomass raw material is 20% to 50% of the total mass of the biomass raw material, thiourea and iron salt; and the molar ratio of thiourea to iron salt is 1:(0.5 to 2).

[0011] Preferably, the biomass raw material is selected from one or more of tea leaves, corn stalks and dichotoma; the iron salt is selected from one or more of anhydrous ferrous sulfate, anhydrous ferric citrate and anhydrous ferric nitrate.

[0012] Preferably, the biomass raw material is pretreated and then mixed with thiourea and iron salt; the pretreatment specifically comprises: washing, drying, crushing and sieving the biomass raw material; the mesh size of the sieving is 50-100 meshes.

[0013] Preferably, the oxygen-limited condition is that there is no carrier gas, the mixture is placed in a sealed container, or the mixture is wrapped with metal foil.

[0014] Preferably, the temperature of the high-temperature pyrolysis is 500° C. to 700° C.; the duration after reaching the high-temperature pyrolysis temperature is 60 to 180 min; and the heating rate of the high-temperature pyrolysis is 7 to 10° C. / min.

[0015] Preferably, after the high-temperature pyrolysis is completed, the product is naturally cooled to room temperature and ground through a 50-100 mesh sieve to obtain a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material.

[0016] The present invention also provides a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material prepared by the above preparation method, comprising nitrogen-sulfur co-doped biochar and FeS particles loaded on the nitrogen-sulfur co-doped biochar.

[0017] Preferably, the FeS particles are a single FeS phase, and the particle size thereof is 50-200 nm.

[0018] Preferably, the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material has a sulfur content of 22% to 26% and an iron content of 30% to 40%.

[0019] The present invention also provides a method for repairing Cr(VI) pollution, comprising the following steps:

[0020] The Cr(VI)-containing solution is mixed with the above-mentioned ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material to remove Cr(VI); the Cr(VI)-containing solution includes a Cr(VI)-containing solution with a high salt concentration.

[0021] The present invention provides a method for preparing a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, comprising the following steps: S1) mixing a biomass feedstock, thiourea, and an iron salt to obtain a mixture; S2) pyrolyzing the mixture at high temperature under oxygen-limited conditions to obtain the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material. Compared to existing technologies, the present invention combines a solvent-free synthesis process with a low-temperature, one-step pyrolysis method. Under carrier-gas-free, oxygen-limited conditions, the composite material is prepared in situ using pyrolysis gas byproducts, achieving efficient utilization of the precursor materials. Furthermore, the solvent-free synthesis process can be easily scaled up based on the raw materials, facilitating large-scale production and potential industrial applications. Furthermore, the pyrolysis gas byproducts are used in situ in the material synthesis, making it both environmentally friendly and pollution-free, while also significantly reducing costs. Furthermore, the obtained material eliminates the need for pretreatment processes such as mechanical ball milling, solvent impregnation, and drying, and is prepared by solid-phase one-step pyrolysis. This method is simple, low-cost, and has low reaction temperatures and short reaction times, making it suitable for large-scale production. It exhibits excellent Cr(VI) removal performance and can selectively remove Cr(VI) in the presence of high salt concentrations.

[0022] Experiments show that the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material prepared by the present invention can effectively remove Cr(VI) from water through adsorption and reduction, and the removal effect is relatively good. The Cr(VI) removal rate in electroplating wastewater can reach more than 99.8% within 24 hours. The hexavalent chromium concentration in the wastewater after repair (less than 0.027 mg / L) is much lower than the emission limit of 0.2 mg / L in the "Electroplating Pollutant Emission Standard" (GB21900-2008). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the SEM image of FeS@NSBC-A prepared in Example 1;

[0024] Figure 2 XRD spectra of different FeS-loaded nitrogen-sulfur co-doped biochar composite materials prepared in Examples 1 to 5;

[0025] Figure 3 Graph showing the removal performance of Cr(VI) by different FeS-loaded nitrogen-sulfur co-doped biochar composite materials prepared in Examples 1 to 5;

[0026] Figure 4 This is the effect of pyrolysis temperature on the Cr(VI) removal performance of FeS-loaded nitrogen-sulfur co-doped biochar composite material;

[0027] Figure 5 The FeS@NSBC-A prepared in Example 1 reacts with Cr(VI) and Cl at different concentrations. - 、SO4 2- Cr(VI) removal efficiency diagram when coexisting;

[0028] Figure 6 This is a diagram showing the remediation effect of FeS@NSBC-A prepared in Example 1 on electroplating wastewater containing Cr(VI);

[0029] Figure 7 XRD spectra of FeS@NSBC-A prepared in Example 1 and different comparative materials prepared in Comparative Example 1 and Comparative Example 2;

[0030] Figure 8 This is a performance comparison chart of FeS@NSBC-A prepared in Example 1, commercial FeS, and different comparative materials prepared in Comparative Examples 1 to 6. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] The present invention provides a preparation method of a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, comprising the following steps: S1) mixing a biomass raw material, thiourea and an iron salt to obtain a mixture; S2) pyrolyzing the mixture at a high temperature under oxygen-limited conditions to obtain a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material.

[0033] The present invention has no particular limitation on the sources of all raw materials, and any commercially available raw materials may be used.

[0034] According to the present invention, the biomass raw material is any biomass raw material familiar to those skilled in the art and is not particularly limited. In the present invention, waste biomass raw material is preferably used, more preferably one or more of tea leaves, corn stalks, and dichotoma, and even more preferably one or more of expired tea leaves, corn stalks, and dichotoma. The present invention utilizes waste materials as a resource by producing biochar through pyrolysis of biomass.

[0035] According to the present invention, the biomass raw material is pretreated and then mixed with thiourea and iron salt; the pretreatment is preferably specifically: washing, drying, crushing and sieving the biomass raw material; the mesh size of the sieving is preferably 50-100 mesh.

[0036] According to the present invention, the iron salt is any iron salt known to those skilled in the art without any particular limitation. In the present invention, it is preferably one or more of anhydrous ferrous sulfate, anhydrous ferric citrate and anhydrous ferric nitrate.

[0037] The biomass raw material, thiourea and iron salt are mixed to obtain a mixture; preferably, the pretreated biomass raw material, thiourea and iron salt are mixed to obtain a mixture; wherein thiourea can be used as a nitrogen source and a sulfur source at the same time, not only participating in the generation of FeS, but also realizing nitrogen and sulfur co-doping of biochar, and also generating reducing substances to provide a reducing environment for pyrolysis; the mass of the biomass raw material is preferably 20% to 50% of the total mass of the biomass raw material, thiourea and iron salt; optionally, the mass of the biomass raw material is 20% to 50% of the total mass of the biomass raw material, thiourea and iron salt. 25%, 30%, 35%, 40%, 45%, 50% or a range between any two of the above values; the molar ratio of thiourea to iron salt is preferably 1: (0.5~2); optionally, the molar ratio of thiourea to iron salt is 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2 or a range between any two of the above ratios; the mixing method is a method well known to those skilled in the art and has no special limitations, including but not limited to shaking mixing and / or grinding mixing.

[0038] The mixture is subjected to high-temperature pyrolysis under oxygen-limited conditions; the oxygen-limited conditions are preferably no carrier gas, the mixture is placed in a sealed container or the mixture is wrapped with metal foil; the sealed container is preferably a corundum boat with a cover or a quartz boat with a cover; the metal foil is preferably aluminum foil; the high-temperature pyrolysis is preferably carried out in a high-temperature furnace, more preferably in a muffle furnace or a tube furnace; the temperature of the high-temperature pyrolysis is preferably 500°C to 700°C; optionally, the temperature of the high-temperature pyrolysis is 500°C, 550°C, 600°C, 650°C, 700°C or a range between any two of the above values; the time after reaching the high-temperature pyrolysis temperature is preferably 60 to 180 min; optionally, the time after reaching the high-temperature pyrolysis temperature is 60 min, 80 min, 100 min, 120 min, 150 min, 180 min min or a range between any two of the above values; the heating rate of the high-temperature pyrolysis is preferably 7~10°C / min; optionally, the heating rate of the high-temperature pyrolysis is 7°C / min, 8°C / min, 9°C / min, 10°C / min or a range between any two of the above values.

[0039] After the high-temperature pyrolysis is completed, it is preferably cooled naturally to room temperature and ground through a 50-100 mesh sieve to obtain a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material; optionally, the mesh number of the sieve is 50 mesh, 60 mesh, 70 mesh, 80 mesh, 90 mesh, 100 mesh or a range between any two of the above values.

[0040] The present invention combines a solvent-free synthesis process with a low-temperature one-step pyrolysis method. Under carrier gas-free and oxygen-limited conditions, the pyrolysis gas byproducts are used to in-situ prepare a composite material, thereby achieving efficient utilization of precursor materials. At the same time, the solvent-free synthesis process can be easily expanded in scale by amplifying the raw materials, which is conducive to large-scale production and potential industrial applications. In addition, the pyrolysis gas byproducts are used to participate in the material synthesis in situ, which is both environmentally friendly and pollution-free, and can effectively save costs. In addition, the obtained material does not require pre-treatment processes such as mechanical ball milling, solvent impregnation, and drying. The material is prepared by solid-phase one-step pyrolysis, which has a simple preparation method, low cost, low reaction temperature, short reaction time, can be produced on a large scale, and has excellent Cr(VI) removal performance.

[0041] The present invention also provides a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material prepared by the above preparation method, comprising nitrogen-sulfur co-doped biochar and FeS particles loaded on the nitrogen-sulfur co-doped biochar.

[0042] In a specific embodiment provided by the present invention, the FeS is a single pure phase, and the particle size of the FeS particles is preferably 50-200 nm; optionally, the particle size of the FeS particles is 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or a range between any two of the above values.

[0043] In a specific embodiment provided by the present invention, the mass content of carbon element in the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material is preferably 22%~26%, more preferably 23%~26%, more preferably 24%~25.5%, more preferably 24.5%~25%, and most preferably 24.9%.

[0044] In a specific embodiment provided by the present invention, the mass content of nitrogen in the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material is preferably 4% to 8%, more preferably 5% to 7%, further preferably 5.5% to 6.5%, and most preferably 5.9% to 6%.

[0045] In a specific embodiment provided by the present invention, the mass content of sulfur element in the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material is preferably 22% to 26%, more preferably 22.5% to 25.5%, further preferably 23% to 25%, further preferably 23.5% to 24.5%, and most preferably 24%.

[0046] In a specific embodiment provided by the present invention, the mass content of iron element in the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material is preferably 30%~40%, more preferably 32%~38%, more preferably 33%~36%, more preferably 34%~35%, and most preferably 34.3%~34.5%.

[0047] The present invention also provides an application of the above-mentioned ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material in the remediation of Cr(VI) pollution.

[0048] The present invention also provides a method for remediating Cr(VI) pollution, comprising the following steps: mixing a Cr(VI)-containing solution with the above-mentioned ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material to remove Cr(VI).

[0049] In a specific embodiment provided by the present invention, the concentration of Cr(VI) in the Cr(VI)-containing solution is preferably 5~50 mg / L; the addition amount of the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material is preferably 0.5~2 g / L; the mixing temperature is preferably 20℃~50℃; the mixing method is preferably shaking; the mixing speed is preferably 150~200 rpm; and the mixing time is preferably 20~52 h.

[0050] In a specific embodiment provided by the present invention, the Cr(VI)-containing solution is preferably Cr(VI)-containing electroplating wastewater.

[0051] In a specific embodiment provided by the present invention, the Cr(VI)-containing solution comprises a Cr(VI)-containing solution with a high salt concentration.

[0052] To further illustrate the present invention, a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material, a preparation method thereof, and applications thereof provided by the present invention are described in detail below with reference to examples.

[0053] The reagents used in the following examples are all commercially available.

[0054] Example 1

[0055] 1.1 Wash, dry, crush and pass the discarded expired tea leaves through a 50-mesh sieve to obtain expired tea powder;

[0056] 1.2 Weigh 1 g of expired tea powder, 1 g of thiourea, and 2 g of anhydrous ferrous sulfate into a centrifuge tube and shake to mix evenly.

[0057] 1.3 Place the mixture from step 1.2 in a covered corundum-quartz boat in a high-temperature tube furnace and pyrolyze it for 120 min at 500°C and a heating rate of 10°C / min under oxygen-limited conditions (no gas flow). Cool naturally to room temperature and grind through a 100-mesh sieve to obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite, designated FeS@NSBC-A.

[0058] The surface morphology of FeS@NSBC-A prepared in Example 1 was observed using a scanning electron microscope (SEM). Figure 1 As shown. Figure 1 It can be seen that Fe particles are evenly distributed on the surface of biochar, and surface FeS is successfully loaded on biochar; the particle size of the prepared FeS particles is about 50~200 nm.

[0059] Example 2

[0060] 2.1 Wash, dry, crush and pass the discarded expired tea leaves through a 50-mesh sieve to obtain expired tea powder;

[0061] 2.2 Weigh 1 g of expired tea powder, 1 g of thiourea, and 1 g of anhydrous ferrous sulfate in a mortar, grind them thoroughly, and mix them evenly.

[0062] 2.3 The mixture obtained in step 2.2 was placed in a covered corundum quartz boat, wrapped in aluminum foil, and placed in a muffle furnace. Pyrolysis was performed under oxygen-limited conditions at 500°C for 120 min at a heating rate of 7°C / min. After cooling naturally to room temperature, the mixture was ground through an 80-mesh sieve to obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite, designated FeS@NSBC-B.

[0063] Example 3

[0064] 3.1 Wash, dry, crush and pass the waste corn straw raw materials through a 50-mesh sieve to obtain corn straw powder;

[0065] 3.2 Weigh 1 g corn straw powder, 2 g thiourea, and 3.22 g anhydrous ferric citrate into a 50 mL centrifuge tube, mix, and shake for 5 min to mix evenly.

[0066] 3.3 Place the solid mixture obtained in step 3.2 in a covered corundum-quartz boat in a high-temperature tube furnace and pyrolyze it for 180 min at 700°C and a heating rate of 8°C / min under oxygen-limited conditions. After cooling, grind the mixture through a 100-mesh sieve to obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite, designated FeS@NSBC-C.

[0067] Example 4

[0068] 4.1 Wash, dry, crush and pass through a 50-mesh sieve to obtain Dicranopteris dichotoma powder;

[0069] 4.2 Weigh 1 g of Dicranopteris dichotoma powder, 1 g of thiourea, and 3.18 g of anhydrous ferric nitrate into a 50 mL centrifuge tube and shake to mix thoroughly.

[0070] 4.3 Place the mixture obtained in step 4.2 in a covered corundum quartz boat, wrap it with aluminum foil, and place it in a muffle furnace. Pyrolysis is carried out under oxygen-limited conditions at 600°C for 120 min at a heating rate of 10°C / min. After cooling, grind it through an 80-mesh sieve to obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite, designated FeS@NSBC-D.

[0071] Example 5

[0072] 5.1 Wash, dry, crush and pass through a 50-mesh sieve to obtain Dicranopteris dichotoma powder;

[0073] 5.2 Weigh 1 g of Dicranopteris dichotoma powder, 2 g of thiourea, and 3.18 g of anhydrous ferric nitrate into a 50 mL centrifuge tube, mix, and shake for 5 min to mix evenly.

[0074] 5.3 Place the mixture obtained in step 5.2 in a covered corundum quartz boat, wrap it with aluminum foil, and place it in a muffle furnace. Pyrolysis is carried out under oxygen-limited conditions at 500°C for 60 min at a heating rate of 9°C / min. After cooling, grind it through a 100-mesh sieve to obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite, designated FeS@NSBC-E.

[0075] The phase composition of the different FeS-loaded nitrogen-sulfur co-doped biochar composite materials prepared in Examples 1 to 5 was analyzed using X-ray diffractometer (XRD). The results are as follows: Figure 2 As shown. Figure 2 It can be seen that the physical phase of the materials prepared under different precursor ratios, different pyrolysis temperatures and other conditions is all single FeS, indicating that the FeS-loaded nitrogen-sulfur co-doped biochar composite was successfully prepared.

[0076] Example 6

[0077] 6.1 Wash, dry, crush and pass the discarded expired tea leaves through a 50-mesh sieve to obtain expired tea powder;

[0078] 6.2 Weigh 1 g of expired tea powder, 1 g of thiourea, and 2 g of anhydrous ferrous sulfate into a centrifuge tube and shake to mix evenly.

[0079] 6.3 Place the mixture obtained in step 6.2 in a covered corundum quartz boat in a high-temperature tube furnace and pyrolyze it for 120 min at 600°C under oxygen-limited conditions at a heating rate of 10°C / min. Cool naturally to room temperature and grind through a 100-mesh sieve to obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite material, designated FeS@NSBC-F.

[0080] Example 7

[0081] 7.1 Wash, dry, crush and pass the discarded expired tea leaves through a 50-mesh sieve to obtain expired tea powder;

[0082] 7.2 Weigh 1 g of expired tea powder, 1 g of thiourea, and 2 g of anhydrous ferrous sulfate into a centrifuge tube and shake to mix evenly.

[0083] 7.3 Place the mixture obtained in step 7.2 in a covered corundum quartz boat in a high-temperature tube furnace and pyrolyze it for 120 min at 700°C and a heating rate of 10°C / min under oxygen-limited conditions (no gas flow). Cool naturally to room temperature, grind through a 100-mesh sieve, and obtain the FeS-loaded nitrogen-sulfur co-doped biochar composite, designated FeS@NSBC-G.

[0084] Application Example 1

[0085] This application example provides a test of the removal effect of Cr(VI) in water by different FeS-loaded nitrogen-sulfur co-doped biochar composite materials prepared in Examples 1 to 5.

[0086] The specific process is as follows:

[0087] 200 mg of FeS@NSBC was added to 100 mL of Cr(VI) solution with a Cr(VI) concentration of 10 mg / L and a pH of 5.6. The mixture was shaken at 30°C for 52 h at a speed of 200 rpm. Sampling times were set at 0, 1, 3, 7, 12, 24, 36, and 52 h. The samples were filtered and the Cr(VI) concentration was determined using the diphenylcarbazide colorimetric method.

[0088] The results are as follows Figure 3 As shown. Figure 3 It can be seen that different FeS-loaded nitrogen-sulfur co-doped biochar composites have a good removal effect on Cr(VI), and the optimal removal rate can reach more than 99.9%.

[0089] Application Example 2

[0090] This application example tests the Cr(VI) removal performance of different FeS-loaded, nitrogen-sulfur co-doped biochar composites prepared in Examples 1, 6, and 7. This study investigates the effect of pyrolysis temperature on the Cr(VI) removal performance of these FeS-loaded, nitrogen-sulfur co-doped biochar composites. The detailed process is the same as in Application Example 1.

[0091] The results are as follows Figure 4 As shown. Figure 4 It can be seen that with the increase of temperature, the removal effect of FeS-loaded nitrogen-sulfur co-doped biochar composite material on Cr(VI) gradually decreases. The FeS-loaded nitrogen-sulfur co-doped biochar composite material prepared at 500℃ has the best removal effect on Cr(VI).

[0092] Application Example 3

[0093] This application example provides different concentrations of coexisting anions (Cl - 、SO4 2- ) The Cr(VI) removal effect of FeS@NSBC-A prepared in Example 1 was tested.

[0094] The specific process is as follows:

[0095] Accurately weigh 400 mg of FeS@NSBC-A and place it in a 250 mL conical flask. Add Cr(VI) and Cl - and SO4 2- The solution mixture was 200 mL, the pH of the solution was 5.6, and it was placed on a shaker at room temperature for 24 h. The concentration of Cr(VI) was 5 mg / L, and the concentration of Cl - and SO4 2- The concentration gradient was set to 5, 50, and 500 mg / L. After sampling, the sample was filtered and the concentration of Cr(VI) in the solution was determined by diphenylcarbazide spectrophotometry.

[0096] The results are as follows Figure 5 As shown. Figure 5 It can be seen that Cl - and SO4 2- The effect on Cr(VI) removal of FeS@NSBC-A was weak, while FeS@NSBC-A had a significant effect on Cr(VI) removal.

[0097] Application Example 4

[0098] This application example tests the effectiveness of FeS@NSBC-A prepared in Example 1 in removing Cr(VI) from electroplating wastewater. The electroplating wastewater has a pH of 3.28, indicating acidic Cr(VI)-containing wastewater. The Cr(VI) concentration is approximately 13.5 mg / L, the organic carbon content is 0.118 mg / L, and the concentrations of sodium, potassium, cadmium, rubidium, strontium, zirconium, nickel, and zinc are 0.280, 4.523, 0.133, 0.0800, 0.0880, 0.115, 2.84, and 0.500 mg / L, respectively.

[0099] The specific process is as follows:

[0100] 400 mg of FeS@NSBC-A was added to 200 mL of Cr(VI)-containing electroplating wastewater and incubated at 30°C for 36 hours at a controlled shaking speed of 200 rpm. Sampling was performed at 0, 1, 3, 7, 12, 24, and 36 hours. The samples were filtered and Cr(VI) concentrations were determined using the diphenylcarbazide colorimetric method.

[0101] The results are as follows Figure 6 As shown. Figure 6 It can be seen that FeS@NSBC-A has a significant effect on the removal of Cr(VI), with a removal rate of more than 90% within 12 h and an optimal removal rate of more than 99.8%.

[0102] Comparative Example 1

[0103] This comparative example is the same as Example 1 except that thiourea in step (2) is replaced with ammonium sulfate containing the same amount of sulfur and nitrogen. The prepared material is named comparative material 1.

[0104] Comparative Example 2

[0105] In this comparative example, an iron sulfide / carbon comparative material was prepared according to the method in Chinese Patent Publication No. CN112700968A. The synthesis method is as follows:

[0106] 2.1 Weigh 2 g of ferrous sulfate, 1 g of thiourea, and 1 g of sucrose respectively and place them in a ball mill using ethanol as the milling medium at 300 rpm for 3 h to obtain the iron sulfide precursor.

[0107] 2.2 The iron sulfide precursor was placed in a corundum ark and calcined at 500 °C for 4 h in an argon flow at a flow rate of 100 mL / min, and then slowly cooled to room temperature as the furnace cooled.

[0108] 2.3 The calcined product was centrifuged and washed at 7500 r / min, three times with deionized water and two times with ethanol. After five centrifugal washes, the resulting powder was dried at 80°C for 12 h to obtain the target product, designated Comparative Material 2.

[0109] The phase composition of the comparative materials prepared in Comparative Examples 1 and 2 was analyzed using an X-ray diffractometer (XRD). Figure 7 As shown. Figure 7 It can be seen that the material phases prepared in Comparative Examples 1 and 2 are Fe3O4 and FeS, while the material phase prepared in the embodiment of the present invention is FeS, which proves that under the preparation conditions of the present invention, the sulfur-containing gas generated by the decomposition of thiourea at high temperature participates in the synthesis of FeS in the FeS-loaded nitrogen-sulfur co-doped biochar material, so that the prepared iron phase is a single FeS, showing one of the unique advantages of the present invention.

[0110] Comparative Example 3

[0111] This comparative example is the same as comparative example 2 except that sucrose is replaced by expired tea leaves. The prepared material is named comparative material 3.

[0112] Comparative Example 4

[0113] In this comparative example, nitrogen-doped biochar loaded with ferrous sulfide was prepared according to the method in Chinese Patent Publication No. CN114160100A. The synthesis method is as follows:

[0114] 4.1 After washing the expired tea leaves five times, they were dried in an oven at 80°C for 12 h, crushed, and passed through a 100-mesh sieve to obtain tea powder. The tea powder was added to a tube furnace, heated to 300°C under a nitrogen atmosphere, and kept at 300°C for 120 min. After the end of the heat preservation, it was naturally cooled, soaked in 0.1 M hydrochloric acid, rinsed to neutrality, and dried overnight to obtain raw biochar. The raw biochar was ball-milled with ammonia water at a mass-to-volume ratio of 1 g:15 mL. The ball milling jar was made of agate jar and agate balls. The size and number of agate balls were 10 mm:6 mm:2 mm = 2:20:22. The ball milling was carried out at 300 r / min for 12 h. After ball milling, it was washed with distilled water to neutrality and dried to obtain nitrogen-doped biochar.

[0115] 4.2 FeSO4·7H2O was added to deionized water, and Na2S solution was added under a nitrogen atmosphere. The mixture was magnetically stirred for 1 hour to obtain ferrous sulfide. The ratio of the mass of the nitrogen-doped biochar to the mass of the ferrous sulfide was 1 g:0.5 g for ball milling. The selected ball milling jar was made of zirconia jar and zirconia balls. The size and ratio of the zirconia balls were 10 mm:6 mm:2 mm = 1:10:11. The ball milling was carried out continuously at 300 r / min for 12 hours. After ball milling, the mixture was sieved through a 100-mesh sieve. The prepared material was named comparative material 4.

[0116] Comparative Example 5

[0117] This comparative example is the same as Example 1 except that the pyrolysis under oxygen-limited conditions was changed to pyrolysis in a carbon dioxide atmosphere with a gas flow rate of 50 mL / min. The prepared material is named Comparative Material 5.

[0118] Comparative Example 6

[0119] This comparative example was the same as Example 1 except that the pyrolysis under oxygen-limited conditions was changed to pyrolysis in a nitrogen atmosphere with a gas flow rate of 50 mL / min. The prepared material was named Comparative Material 6.

[0120] An elemental analyzer was used to determine the percentages of C, H, N, and S in the FeS@NSBC-A prepared in Example 1 and the comparative materials prepared in Comparative Examples 2, 5, and 6. Microwave digestion and inductively coupled plasma optical emission spectrometry were also used to determine the percentage of Fe in the different materials. The results are shown in Table 1. Table 1 shows that the FeS@NSBC-A material has a high N content, and the S content (24.0%) is higher than the theoretical value (the S content of FeS in the material calculated based on the Fe content is 19.6%), indicating that co-doping of N and S elements was achieved in the material during the preparation process. Furthermore, compared to the three comparative materials, FeS@NSBC-A has the highest sulfur content, indicating that under the preparation method provided by the present invention, the sulfur-containing gas product produced by the precursor material can participate to a greater extent in the material synthesis process.

[0121] Table 1 Elemental composition analysis of different materials

[0122]

[0123] Application Example 5

[0124] This application example provides a performance comparison test of the FeS@NSBC-A prepared in Example 1, different comparison materials prepared in Comparative Examples 1 to 6, and common commercially available FeS (passed through a 100-mesh sieve).

[0125] The specific process is as follows:

[0126] 200 mg of the material was added to 200 mL of a solution containing 10 mg / L Cr(VI) at a pH of 5.6. The mixture was shaken at 30°C for 24 hours at a controlled speed of 200 rpm. After the reaction was complete, the sample was filtered and the Cr(VI) concentration in the filtrate was determined using the diphenylcarbazide colorimetric method.

[0127] The results are as follows Figure 8 Show. Depend on Figure 8 Compared to commercially available FeS and six comparative materials, FeS@NSBC-A prepared in Example 1 achieved the best Cr(VI) removal performance after 24 hours of reaction, reaching 97.9%. This performance is 3.49, 2.35, 1.36, 2.46, 1.37, 1.56, and 2.37 times that of commercially available FeS and comparative materials 1–6, respectively. The presence of Fe₃O₄ as an impurity in comparative materials 1 and 2 reduced their Cr(VI) removal efficiency. Furthermore, comparative material 3, prepared using sucrose as the carbon source, exhibited lower Cr(VI) removal efficiency, likely due to the low surface oxygen and nitrogen functional groups on the biochar produced after sucrose carbonization.

[0128] In summary, the new FeS-loaded nitrogen-sulfur co-doped biochar prepared by the present invention, especially FeS@NSBC-A, has excellent Cr(VI) removal performance, and its advantages in preparation method are more obvious. It does not require complex pretreatment process, the preparation process is simple, and has the advantages of being environmentally friendly, low cost, and can be prepared in batches.

[0129] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. Application of a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material in Cr(VI) pollution remediation, characterized in that: The preparation method of the ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material comprises the following steps: S1) mixing a biomass raw material, thiourea and an iron salt without a solvent to obtain a mixture; S2) pyrolyzing the mixture at high temperature under oxygen-limited conditions to obtain a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material; The mass of the biomass raw material is 20% to 50% of the total mass of the biomass raw material, thiourea and iron salt; the molar ratio of thiourea to iron salt is 1:1; The biomass raw material is selected from one or more of tea leaves, corn stalks and dichotoma; the iron salt is selected from one or more of anhydrous ferrous sulfate, anhydrous ferric citrate and anhydrous ferric nitrate; The oxygen-limited condition is that there is no carrier gas and the mixture is placed in a sealed container; the high-temperature pyrolysis is carried out in a tube furnace; The high-temperature pyrolysis temperature is 500°C; the duration after reaching the high-temperature pyrolysis temperature is 120-180 min; the high-temperature pyrolysis heating rate is 7-10°C / min; The ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material has a sulfur content of 22% to 26% by mass and an iron content of 30% to 40% by mass.

2. The use according to claim 1, characterized in that The mixing in step S1) is shaking mixing and / or grinding mixing.

3. The use according to claim 1, characterized in that The biomass raw material is pretreated and then mixed with thiourea and iron salt; the pretreatment specifically includes: washing, drying, crushing and sieving the biomass raw material; the mesh size of the sieving is 50-100 meshes.

4. The use according to claim 1, characterized in that After the high-temperature pyrolysis is completed, the product is naturally cooled to room temperature and ground through a 50-100 mesh sieve to obtain a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material.

5. The use according to any one of claims 1 to 4, characterized in that The ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material comprises nitrogen-sulfur co-doped biochar and FeS particles loaded on the nitrogen-sulfur co-doped biochar.

6. The use according to claim 5, characterized in that The FeS particles are single FeS phase, and the particle size thereof is 50-200 nm.

7. The use according to claim 1, characterized in that The following steps are involved: A Cr(VI)-containing solution is mixed with a ferrous sulfide-loaded nitrogen-sulfur co-doped biochar composite material to remove Cr(VI); the Cr(VI)-containing solution includes Cr(VI)-containing electroplating wastewater.

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