A sulfur-doped birch charcoal-based material, a synthesis method and application thereof

Abstract

This invention discloses a sulfur-doped birch charcoal-based material, its synthesis method, and its application, belonging to the technical field of water pollution control and solid waste resource utilization. The invention involves high-temperature pyrolysis of birch powder under a nitrogen atmosphere to obtain birch-based biochar. The birch-based biochar is then mixed with sodium thiosulfate and ball-milled. The ball-milled product is subsequently separated, washed, and dried to obtain the sulfur-doped birch charcoal-based material. This material exhibits excellent adsorption capacity and extremely fast kinetics for Cr(VI) in water. In particular, the composite material with a sulfur doping content of 15 wt% shows a removal rate exceeding 94% within 6 minutes, with a maximum adsorption capacity of 71.4 mg / g. The sulfur-doped birch charcoal-based material prepared by this invention has good stability and excellent recyclability (efficiency > 83% after 5 cycles), demonstrating potential for practical application.

Description

Technical Field

[0001] This invention belongs to the technical field of water pollution control and solid waste resource utilization, and particularly relates to a sulfur-doped birch charcoal-based material, its synthesis method and application. Background Technology

[0002] Chromium (Cr) is a heavy metal widely used in industries such as electroplating and dye manufacturing. Its hexavalent state (Cr(VI)) poses a serious threat to aquatic ecosystems and human health due to its high toxicity, carcinogenicity, and strong migration. Therefore, developing efficient and environmentally friendly technologies to remove Cr(VI) from water bodies is of paramount importance.

[0003] Currently, adsorption is widely used for Cr(VI) removal due to its low cost and ease of operation. Biochar, a porous material with a large specific surface area obtained from biomass pyrolysis, is an ideal adsorbent matrix. However, the adsorption capacity of raw biochar is limited, and modification is usually required to improve its remediation capacity in complex water bodies. Physical modification methods such as ball milling, ultrasonication, and steam activation offer relatively limited improvements and do not significantly increase the number of chemisorption sites. Chemical modification methods such as acid / alkali treatment and organic compound grafting (e.g., PEI (polyethyleneimine)) can introduce specific functional groups to enhance electrostatic attraction or complexation, but the use of highly corrosive reagents during the modification process introduces the risk of secondary pollution, and some modification processes are complex. Metal-loading modification methods (such as loading zero-valent iron, iron oxides, zinc, etc.) carry the risk of metal leaching, which may cause secondary pollution. Biological modification methods suffer from slow processes, the activity of microorganisms is greatly affected by environmental conditions, and the application in engineering is difficult. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a sulfur-doped birch charcoal-based material, its synthesis method, and its applications. This method utilizes physical ball milling technology to composite sulfur species with biochar, aiming to significantly enhance its adsorption capacity and removal rate of Cr(VI) in water by controlling the surface chemical properties and pore structure of the material. Simultaneously, its tolerance and recyclability in actual aquatic environments are investigated, providing a new material and method for the efficient treatment of chromium-containing wastewater.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for synthesizing sulfur-doped birch charcoal-based materials, comprising the following steps: Birch wood powder was pyrolyzed at high temperature under a nitrogen atmosphere to obtain birch-based biochar (WFB); the birch-based biochar was mixed with sodium thiosulfate (Na2S2O3·5H2O) and ball-milled; the ball-milled product was then separated, washed and dried to obtain the sulfur-doped birch char-based material (WFB@SX, where X represents the mass percentage of sodium thiosulfate loading, and X is 5%-20%).

[0006] Atomic doping is an effective strategy for optimizing the performance of biochar. Sulfur (S) doping can introduce acidic active sites and redox-active functional groups, enhancing its binding capacity for heavy metal ions and improving its pore structure. Ball milling, as a green and efficient physical modification method, has the advantages of being environmentally friendly and easy to operate. It can achieve the breaking and reconstruction of chemical bonds in the carbon framework through mechanical energy transfer, promoting the uniform dispersion of sulfur species in biochar. Compared with traditional chemical modification that requires high-temperature pyrolysis, ball milling allows for precise control of the sulfur doping amount through precise control of the feed ratio, providing a new approach for preparing high-performance, recyclable adsorbent materials. Based on the inherent advantages of biochar, this invention combines sulfur doping chemical modification with the physical activation of ball milling to develop an adsorbent (i.e., sulfur-doped birch charcoal-based material) that can rapidly and efficiently remove Cr(VI) from water, possessing significant research value and application prospects.

[0007] Further, the sodium thiosulfate in the sulfur-doped birch charcoal-based material accounts for 5%-20% by mass; preferably, the sodium thiosulfate in the sulfur-doped birch charcoal-based material accounts for 10%-20% by mass; more preferably, the sodium thiosulfate in the sulfur-doped birch charcoal-based material accounts for 10%-15% by mass, and most preferably 15%.

[0008] Furthermore, the high-temperature pyrolysis is performed by heating to 900 °C at a heating rate of 5 °C / min and maintaining that temperature for 3 h.

[0009] Furthermore, the ball milling speed is 300-500 rpm, and the ball milling time is 4 hours. During this process, the mechanical energy causes the biochar particles to be fully broken and refined, while simultaneously promoting the physical mixing and possible mechanochemical reactions between sodium thiosulfate and the biochar surface, thereby achieving effective doping and dispersion of sulfur species in the carbon matrix.

[0010] Furthermore, the ball-to-material ratio during ball milling is 10:1.

[0011] The present invention also provides a sulfur-doped birch charcoal-based material synthesized according to the above method.

[0012] The present invention also provides the application of the above-mentioned sulfur-doped birch charcoal-based material in the removal of hexavalent chromium (Cr(VI)) from water.

[0013] Furthermore, the dosage of the sulfur-doped birch charcoal-based material is 1.0 g / L.

[0014] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The preparation process of this invention is green and simple: it adopts physical ball milling method, without the need for high temperature calcination load or the use of toxic chemical reagents such as strong acid and strong alkali. The process is simple, energy consumption is low, environmentally friendly and has no secondary pollution.

[0015] (2) The adsorption performance of this invention is highly efficient and rapid: The sulfur-doped birch charcoal-based material prepared by this invention exhibits excellent adsorption capacity and extremely fast kinetics for Cr(VI) in water. In particular, the WFB@S-15% composite material with a sulfur doping content of 15wt% shows a removal rate of over 94% within 6 minutes, with a maximum adsorption capacity of 71.4 mg / g. The sulfur-doped birch charcoal-based material prepared by this invention has good stability and good recycling performance (efficiency >83% after 5 cycles), and has potential for practical application.

[0016] (3) This invention uses waste birch wood as raw material to realize the high-value utilization of biomass waste, which is in line with the concept of green and sustainable development. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 Raman spectra of WFB synthesized in Comparative Example 1, WFB@S-10% synthesized in Example 3, WFB@S-15% synthesized in Example 1, and WFB@S-20% synthesized in Example 4.

[0018] Figure 2 The curves showing the removal rate of Cr(VI) by the materials synthesized in Examples 1-4 and Comparative Examples 1-2 over time are shown under the conditions of pH = 2, dosage of 1.0 g / L, and 25 ℃.

[0019] Figure 3 The cycling performance of WFB@S-15% synthesized in Example 3 is shown.

[0020] Figure 4 The images show scanning electron microscope (SEM) images of WFB synthesized in Comparative Example 1 and WFB@S-15% synthesized in Example 1, where a is WFB and b is WFB@S-15%. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] Embodiments of the present invention provide a method for synthesizing sulfur-doped birch charcoal-based materials, comprising the following steps: Birch wood powder was pyrolyzed at high temperature under a nitrogen atmosphere to obtain birch wood-based biochar (WFB); the birch wood-based biochar was mixed with sodium thiosulfate (Na2S2O3·5H2O) and ball-milled; the ball-milled product was then separated, washed and dried to obtain sulfur-doped birch wood-based material (WFB@SX, where X represents the mass percentage of sodium thiosulfate loading, and X is 5%-20%).

[0027] In a preferred embodiment of the present invention, sodium thiosulfate accounts for 5%-20% of the adsorbent in the sulfur-doped birch charcoal-based material; more preferably, the mass percentage of sodium thiosulfate in the sulfur-doped birch charcoal-based material is 10%-20%; more preferably, the mass percentage of sodium thiosulfate in the adsorbent in the sulfur-doped birch charcoal-based material is 10%-15%, and most preferably 15%. The sulfur-doped birch charcoal-based material prepared by the present invention uses porous, high-specific-surface-area birch-based biochar as a framework, and sulfur species (derived from sodium thiosulfate) exist in the material in the form of physical doping and surface modification through ball milling. When the sodium thiosulfate loading is 15% (mass percentage), the resulting material (WFB@S-15%) has superior overall performance.

[0028] In a preferred embodiment of the present invention, high-temperature pyrolysis is performed by heating to 900 °C at a heating rate of 5 °C / min and maintaining that temperature for 3 h.

[0029] In a preferred embodiment of the present invention, the ball milling speed is 300-500 rpm and the ball milling time is 4 h; preferably, the ball milling speed is 400 rpm.

[0030] In a preferred embodiment of the present invention, the ball-to-material ratio during ball milling is 10:1.

[0031] In a preferred embodiment of the present invention, after ball milling, the resulting mixture is transferred to a container, deionized water is added, and the mixture is magnetically stirred at room temperature for 30 minutes to disperse the unbound components in the water; then solid-liquid separation is performed, and the filter cake is washed multiple times with deionized water to remove possible soluble impurities.

[0032] In a preferred embodiment of the present invention, the method for synthesizing sulfur-doped birch charcoal-based materials includes the following steps: Preparation of birch-based biochar (WFB): Sufficient birch powder was spread evenly on a tray and placed in a 60 ℃ forced-air drying oven for 24 h to completely remove moisture. The dried wood powder was weighed and placed in a corundum boat, which was then placed in a tube furnace. After the furnace was closed, high-purity nitrogen (N2) was introduced for atmosphere replacement for at least 20 min. Subsequently, under continuous nitrogen protection, the temperature was heated to 900 ℃ at a programmed heating rate of 5 ℃ / min and maintained at this temperature for pyrolysis for 3 h. After pyrolysis, the heating was turned off, and the furnace temperature was allowed to drop naturally to room temperature. The product was then removed, yielding black birch-based biochar, which was ground, sieved, collected, and labeled as WFB.

[0033] Accurately weigh sodium thiosulfate (Na2S2O3·5H2O) according to a sodium thiosulfate loading of 15% (by mass) (WFB@SX, where X represents the mass percentage of sodium thiosulfate loading, X being 5%-20%). Place both (Na2S2O3·5H2O and WFB) into a zirconia ball mill jar, and add zirconia grinding balls (ball-to-material ratio of 10:1). Seal the ball mill jar and fix it on a planetary ball mill. Set the ball mill speed to 400 rpm, start the machine, and continuously ball mill for 4 hours.

[0034] After ball milling, open the mill jar and transfer all the solid mixture into a 250 mL beaker. Add 100 mL of deionized water to the beaker and stir at a medium speed (450 rpm) for 30 minutes at room temperature using a magnetic stirrer to ensure thorough dispersion. Then, perform solid-liquid separation using suction filtration or centrifugation. Wash the filter cake repeatedly with deionized water until the filtrate is clear (if the mill jar and grinding balls are clean, this step mainly removes any remaining soluble salts—sodium thiosulfate). Transfer the washed wet filter cake to a petri dish, spread it out, and place it in an 80°C forced-air drying oven for 24 hours. After drying, grind the solid block product to obtain sulfur-doped birch charcoal-based material.

[0035] Birch wood undergoes pyrolysis at 900℃, forming a carbon skeleton (WFB) with a high specific surface area and abundant porosity. This provides a vast carrying capacity for subsequent doping and contaminant adsorption. Ball milling not only achieves a uniform physical mixture of sodium thiosulfate and biochar, but its mechanical energy is also more likely to break the chemical bonds of the carbon skeleton, creating new defects and edge sites. These defects typically provide highly active adsorption or reaction centers. During ball milling, sulfur species in sodium thiosulfate (such as S₂O₃) are... 2 ⁻) Through mechanochemical action to produce -SO x Sulfur-containing functional groups are doped into the carbon matrix in the form of -CSC-, etc. These sulfur-containing functional groups have two key roles: 1. Providing acidic sites and positive charges: In acidic adsorption environments (especially pH=2), sulfur-containing groups can be protonated, making the material surface positively charged, which interacts with negatively charged chromate ions (HCrO4⁻, Cr2O7). 2 ⁻) Strong electrostatic attraction is generated, which is the main driving force for rapid initial adsorption. As redox active sites: intermediate valence states of sulfur (e.g., +2, +4) endow it with redox activity, allowing it to directly participate in electron transfer. Low-valence sulfur species in the material (such as the potentially formed sulfite SO3) 2(⁻) It can act as an electron donor to directly reduce highly toxic and highly mobile Cr(VI) to less toxic and easily precipitated Cr(III). This process is rapid and thorough, and is the core of achieving rapid removal. The highly graphitized biochar substrate (obtained by pyrolysis at 900℃) is itself a good electronic conductor. Defects generated by sulfur doping and ball milling further optimize the electron transport path, promote the transfer of electrons from the interior of the material to the Cr(VI) adsorbed on the surface, and accelerate the reduction reaction.

[0036] Embodiments of the present invention also provide a sulfur-doped birch charcoal-based material synthesized according to the above method.

[0037] Embodiments of the present invention also provide the application of the above-mentioned sulfur-doped birch charcoal-based material in the removal of hexavalent chromium (Cr(VI)) from water.

[0038] In a preferred embodiment of the present invention, the amount of sulfur-doped birch charcoal-based material added is 1.0 g / L.

[0039] In a preferred embodiment of the invention, the removal of hexavalent chromium (Cr(VI)) from water is carried out at room temperature.

[0040] In a preferred embodiment of the present invention, the pH value of the water is 2. If the pH value of the water is not 2, the pH value of the water is first adjusted to 2 with hydrochloric acid or sodium hydroxide solution, and then sulfur-doped birch charcoal-based material is added.

[0041] The sulfur-doped birch charcoal-based material of the present invention can effectively remove Cr(VI) from water. When the concentration of Cr(VI) in the water is 10-100 mg / L, the sulfur-doped birch charcoal-based material of the present invention has a good Cr(VI) removal rate, and can achieve a Cr(VI) removal rate of 71.4% in 14 minutes, which can quickly remove Cr(VI) from water.

[0042] In this invention, high-purity nitrogen refers to nitrogen with a purity of 99.99% or higher.

[0043] Existing research (such as Du et al., Sulfur-Modified Biochar Efficiently Removes Cr(VI) from Water by Sorption and Reduction, 2023) has reported the preparation of sulfur-modified biochar for the removal of Cr(VI) from water via a two-step pyrolysis method. This method relies on high-temperature two-step pyrolysis (>400℃) to achieve sulfur doping, and under optimal conditions, the Cr(VI) removal rate is 92%, with an adsorption capacity of approximately 40 mg / g. However, this method has the following limitations: 1. The preparation process is complex, requiring two-step pyrolysis, resulting in high energy consumption; 2. The adsorption rate is slow, making rapid removal difficult.

[0044] This invention is the first to propose using a ball milling method to dope sodium thiosulfate into birch-based biochar to prepare sulfur-doped carbon-based materials (WFB@SX), which has the following differences: 1. Traditional view holds that sulfur doping requires high-temperature pyrolysis to introduce sulfur functional groups (e.g., the method reported by Du et al. requires temperatures above 444℃ to facilitate the formation of active sulfur species). However, this invention achieves effective sulfur doping at room temperature through the mechanochemical action of ball milling, breaking the prejudice that high-temperature pyrolysis is necessary, significantly reducing energy consumption, and simplifying the process.

[0045] 2. Ultra-fast removal kinetics: WFB@S-15% achieves a Cr(VI) removal rate of over 94% within 6 minutes, far exceeding the adsorption rate of existing sulfur-modified biochar (92% removal rate in 60 minutes). 3. High adsorption capacity: The maximum adsorption capacity of the material of this invention reaches 71.4 mg / g, which is nearly 80% higher than the 40 mg / g reported in the literature; 4. Excellent cycle stability: The removal rate of the material of this invention remains above 83% after 5 cycles, indicating that the material has a stable structure and excellent regeneration performance; 5. Green preparation process: The composite of biochar and sulfur can be completed at room temperature, without the need for high temperatures, strong acids or alkalis, and without the risk of secondary pollution, which conforms to the concepts of green environmental protection and sustainable development. In contrast, the literature requires the introduction of nitrogen gas and a temperature of 300-600℃, making the operation conditions cumbersome.

[0046] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0047] All raw materials used in the embodiments of the present invention were obtained through commercial purchase.

[0048] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0049] The technical solution of the present invention will be further illustrated by the following embodiments.

[0050] Example 1 A method for synthesizing sulfur-doped birch charcoal-based materials, comprising the following steps: Preparation of birch-based biochar (WFB): Sufficient birch powder was spread evenly on a tray and placed in a 60 ℃ forced-air drying oven for 24 h to completely remove moisture. The dried wood powder was weighed and placed in a corundum boat, which was then placed in a tube furnace. After the furnace was closed, high-purity nitrogen (N2) was introduced for atmosphere replacement for 20 min. Subsequently, under continuous nitrogen protection, the temperature was raised to 900 ℃ at a programmed heating rate of 5 ℃ / min and maintained at this temperature for pyrolysis for 3 h. After pyrolysis, the heating was turned off, and the furnace temperature was allowed to drop naturally to room temperature. The product was then removed, yielding black birch-based biochar, which was ground, sieved, collected, and labeled as WFB.

[0051] Accurately weigh 1.00 g of the prepared WFB. Accurately weigh 0.17 g of sodium thiosulfate (Na₂S₂O₃·5H₂O) according to a sodium thiosulfate loading of 15% (mass percentage). (The calculation method for sodium thiosulfate loading is as follows: Sodium thiosulfate loading = (m...) 硫代硫酸钠 / (m WFB + m 硫代硫酸钠 Add 100% (x100%) of the mixture to a zirconia ball mill jar, along with zirconia grinding balls (ball-to-material ratio 10:1). Seal the jar and secure it to a planetary ball mill. Set the mill speed to 400 rpm, start the machine, and continuously mill for 4 hours.

[0052] After ball milling, the mill jar was opened, and all the solid mixture inside was completely transferred to a 250 mL beaker. 100 mL of deionized water was added to the beaker, and the mixture was stirred at a medium speed (450 rpm) for 30 minutes at room temperature using a magnetic stirrer to ensure thorough dispersion. Subsequently, solid-liquid separation was performed using vacuum filtration. The filter cake was repeatedly washed with deionized water until the filtrate was clear. The washed wet filter cake was transferred to a petri dish, spread out, and placed in an 80°C forced-air drying oven for 24 hours. After drying, the solid block product was ground to obtain sulfur-doped birch charcoal-based material, denoted as WFB@S-15%.

[0053] Example 2 This embodiment provides a method for synthesizing sulfur-doped birch charcoal-based material. The steps are the same as in Embodiment 1, except that the mass of sodium thiosulfate weighed is 0.05 g, and the resulting sulfur-doped birch charcoal-based material is denoted as WFB@S-5%.

[0054] Example 3 This embodiment provides a method for synthesizing sulfur-doped birch charcoal-based material. The steps are the same as in Example 1. 0.11 g of sodium thiosulfate is weighed, and the resulting sulfur-doped birch charcoal-based material is denoted as WFB@S-10%.

[0055] Example 4 This embodiment provides a method for synthesizing sulfur-doped birch charcoal-based materials. The steps are the same as in Embodiment 1, except that the mass of sodium thiosulfate weighed is 0.25 g, and the resulting sulfur-doped birch charcoal-based material is denoted as WFB@S-20%.

[0056] Example 5 This embodiment provides a method for synthesizing sulfur-doped birch charcoal-based materials. The steps are the same as in Embodiment 1, except that the ball mill speed is set to 300 rpm.

[0057] Example 6 This embodiment provides a method for synthesizing sulfur-doped birch charcoal-based materials. The steps are the same as in Embodiment 1, except that the ball mill speed is set to 500 rpm.

[0058] Comparative Example 1 Raw biochar (WFB) was prepared by performing only the first step in Example 1 without any modification, and the product was the control sample WFB.

[0059] Comparative Example 2 To compare the key role of the ball milling process, a stirred-mix control sample (WFB@S-stir) was prepared. The specific steps were as follows: 1.00 g of WFB and 0.17 g of sodium thiosulfate from Example 1 were weighed and placed in a 250 mL beaker, and 100 mL of deionized water was added. The mixture was continuously stirred at a constant speed (450 rpm) for 4 h at room temperature using a magnetic stirrer (simulating a processing time similar to ball milling, but without mechanical impact). After stirring, the same filtration, washing, and drying operations were performed as in Example 1, and the resulting product was designated WFB@S-stir.

[0060] Comparative Example 3 The operation steps are exactly the same as in Example 1, except that the sulfur source is replaced with thiourea, and the resulting product is denoted as WFB@thiourea-15%.

[0061] Comparative Example 4 The operation steps are exactly the same as in Example 1, except that birch charcoal is replaced with pine charcoal, and the resulting product is denoted as Pine@S-15%.

[0062] Figure 1Raman spectra of WFB synthesized in Comparative Example 1, WFB@S-10% synthesized in Example 3, WFB@S-15% synthesized in Example 1, and WFB@S-20% synthesized in Example 4 are shown. Raman spectroscopy can be used to reveal the degree of graphitization / defects in birch-derived carbon materials. The intensity ratio of the D peak to the G peak (ID / IG) represents the disorder in carbonaceous materials. A higher ID / IG generally indicates an increased abundance of defects and disorder, suggesting more adsorption and catalytic active sites. With increasing S content, the ID / IG value increases from 1.12 for WFB to 1.15 for WFB@S-20%, indicating that S incorporation produces more defects and higher disorder. This may be because the radius of sulfur atoms is larger than that of carbon atoms, causing local lattice distortion and preventing the crystal from maintaining a planar structure. Therefore, the gradual increase in the ID / IG ratio indicates a corresponding increase in sulfur doping.

[0063] Figure 4 The images show scanning electron microscope (SEM) images of the WFB synthesized in Comparative Example 1 and the WFB@S-15% synthesized in Example 1, where a is WFB and b is WFB@S-15%. Figure 4 It can be clearly seen that WFB has a smooth surface and exhibits a lamellar structure composed of wood fibers. In contrast, WFB@S-15% is a rough, densely packed block agglomerate, possibly because the amorphous regions formed during ball milling have more surface energy, leading to the aggregation of carbon particles after ball milling.

[0064] The sulfur content of the sulfur-doped birch carbon-based materials prepared in Examples 1, 3-4, and Comparative Example 2 was analyzed by a high-frequency infrared carbon-sulfur analyzer according to GB / T6730.61-2005. The results are shown in Table 1.

[0065] Table 1 Table 1 shows that the actual sulfur content in the material gradually increases with the increase of the sulfur precursor loading ratio. However, the sulfur content of WFB@S-stir prepared by the conventional stirring method (Comparative Example 2) is significantly lower than that of the sample prepared by the ball milling method. This difference indicates that the stirring method has limited effectiveness in achieving effective composite of sulfur and birch carbon matrix, possibly due to its lower mechanical force, resulting in a lower sulfur loading rate.

[0066] Application Example 1 Take a series of 100 mL Erlenmeyer flasks and add 20 mL of Cr(VI) solution (initial concentration 20.0 mg / L) to each. Adjust the initial pH of the solution to 2.0 with dilute HCl (concentration as above). Then, add accurately weighed WFB@S-15% to each Erlenmeyer flask to make the dosage 1.0 g / L. Place the Erlenmeyer flasks in a constant temperature water bath at 25 ℃ and start shaking at 150 rpm. At preset time points (0.5 min, 1 min, 2 min, 3 min, 4 min, 6 min, 8 min, 10 min, 14 min), remove the Erlenmeyer flasks, quickly filter them through a 0.22 μm filter, and immediately measure the remaining Cr(VI) concentration in the filtrate. Calculate the removal rate at different time points based on the concentration difference before and after adsorption. The results are shown in Table 2.

[0067] Table 2 Application Example 2 First, potassium dichromate (K₂Cr₂O₇) was weighed, dissolved in deionized water, and diluted to volume to prepare a series of Cr(VI) solutions with different concentrations (10 mg / L, 20 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, 100 mg / L). The initial pH of the Cr(VI) solutions was adjusted to 2.0 using dilute HCl (0.1 M) or NaOH solution (0.1 M). Then, accurately weighed WFB@S-15% was added to the conical flask containing the Cr(VI) solution with an initial pH of 2.0, making the dosage 1.0 g / L. The process was carried out in a constant temperature water bath at 25 ℃, with shaking started at 150 rpm. At the preset time point (14 min), the conical flask was removed, and the sample was quickly filtered through a 0.22 μm filter. The concentration of the remaining Cr(VI) in the filtrate was immediately measured. The removal rate was calculated based on the concentration difference before and after adsorption, and the results are shown in Table 3.

[0068] Table 3 Application Example 3 Using the above method, the removal rate of Cr(VI) from a 20.0 mg / L Cr(VI) solution was tested using the materials synthesized in Examples 1-4 and Comparative Examples 1-2 at pH = 2, dosage 1.0 g / L, and 25 ℃. The curves showing the change in Cr(VI) removal rate over time are shown in the figure. Figure 2 The removal rates of Cr(VI) at 6 min are shown in Table 4. The results indicate that WFB@S-15% achieved a removal rate of 94.6% for 20 mg / L Cr(VI) at 6 min, demonstrating the best performance.

[0069] Table 4 Application Example 4 The WFB@S-15% material after one adsorption experiment was recovered by filtration. Specifically, the adsorbent containing Cr(VI) was immersed in 50 mL of 2 mol / L NaOH solution and shaken at room temperature for 2 h to desorb. After desorption, the material was separated by filtration, washed with deionized water until neutral, and dried again at 80 °C. This "adsorption-desorption-drying" process was repeated 5 times. Each cycle involved a new batch of Cr(VI) adsorption experiments under the same conditions, and the removal rate was calculated. The results are shown in Table 5. The results indicate that after 5 cycles, the removal rate of Cr(VI) by WFB@S-15% remained at 83.8%. Figure 3 This demonstrates its excellent reusability.

[0070] Table 5 Application Example 5 Take a series of 100 mL Erlenmeyer flasks and add 20 mL of Cr(VI) solution (initial concentration 20.0 mg / L) to each flask. Adjust the initial pH of the solution to 2.0 with dilute HCl (concentration as above). Then, add accurately weighed WFB@thiourea-15% synthesized in Comparative Example 3 to each Erlenmeyer flask, making the dosage 1.0 g / L. Place the Erlenmeyer flasks in a constant temperature water bath at 25 ℃ and start shaking at 150 rpm. At preset time points (0.5 min, 1 min, 2 min, 3 min, 4 min, 6 min, 8 min, 10 min, 14 min), remove the Erlenmeyer flasks, quickly filter them through a 0.22 μm filter, and immediately measure the concentration of the remaining Cr(VI) in the filtrate. Calculate the removal rate at different time points based on the concentration difference before and after adsorption. The results are shown in Table 6.

[0071] Table 6 After replacing the sulfur source (replacing sodium thiosulfate with thiourea), the removal rate of the obtained material after 8 minutes was 50.7%, which is significantly lower than the removal rate of the material prepared with sodium thiosulfate as the sulfur source.

[0072] This is because sodium thiosulfate has reducing properties, which facilitates the reduction of active functional groups and the removal of chromium. Furthermore, sodium thiosulfate has low acute toxicity, classifying it as a low-toxicity or practically non-toxic substance, and has minimal impact on microorganisms and ecosystem functions.

[0073] Application Example 6 Take a series of 100 mL Erlenmeyer flasks and add 20 mL of Cr(VI) solution (initial concentration 20.0 mg / L) to each. Adjust the initial pH of the solution to 2.0 with dilute HCl (concentration as above). Then, add accurately weighed pine wood@S-15% synthesized in Comparative Example 4 to each Erlenmeyer flask, making the dosage 1.0 g / L. Place the Erlenmeyer flasks in a constant temperature water bath at 25 ℃ and start shaking at 150 rpm. At preset time points (0.5 min, 1 min, 2 min, 3 min, 4 min, 6 min, 8 min, 10 min, 14 min), remove the Erlenmeyer flasks, quickly filter them through a 0.22 μm filter, and immediately measure the remaining Cr(VI) concentration in the filtrate. Calculate the removal rate at different time points based on the concentration difference before and after adsorption. The results are shown in Table 7.

[0074] Table 7 The removal rate of sulfur-doped pine carbon-based material was 78.9% after 10 minutes, which was lower than that of sulfur-doped birch carbon-based material. This demonstrates that birch, as a hardwood precursor, has a porous fibrous structure that facilitates the formation of high specific surface area channels, low ash content that reduces pore blockage and exposes more active sites, and is widely available and renewable, making it a superior choice for preparing the material of this invention.

[0075] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing sulfur-doped birch charcoal-based materials, characterized in that, Includes the following steps: Birch wood powder was pyrolyzed at high temperature under a nitrogen atmosphere to obtain birch-based biochar; the birch-based biochar was mixed with sodium thiosulfate and ball-milled; the ball-milled product was then separated, washed and dried to obtain the sulfur-doped birch char-based material.

2. The method for synthesizing sulfur-doped birch charcoal-based materials according to claim 1, characterized in that, The sodium thiosulfate in the sulfur-doped birch charcoal-based material accounts for 5%-20% by mass.

3. The method for synthesizing sulfur-doped birch charcoal-based materials according to claim 2, characterized in that, The sodium thiosulfate in the sulfur-doped birch charcoal-based material accounts for 10%-20% by mass.

4. The method for synthesizing sulfur-doped birch charcoal-based materials according to claim 3, characterized in that, The sodium thiosulfate in the sulfur-doped birch charcoal-based material accounts for 10%-15% by mass.

5. The method for synthesizing sulfur-doped birch charcoal-based materials according to claim 1, characterized in that, The high-temperature pyrolysis is performed by heating the temperature to 900°C at a rate of 5°C / min and maintaining that temperature for 3 hours.

6. The method for synthesizing sulfur-doped birch charcoal-based materials according to claim 1, characterized in that, The ball mill rotates at 300-500 rpm for 4 hours.

7. The method for synthesizing sulfur-doped birch charcoal-based materials according to claim 1, characterized in that, The ball-to-material ratio during ball milling is 10:

1.

8. A sulfur-doped birch charcoal-based material, characterized in that, It is synthesized according to the synthesis method according to any one of claims 1-7.

9. The application of a sulfur-doped birch charcoal-based material as described in claim 8 in the removal of hexavalent chromium from water.

10. The application according to claim 9, characterized in that, The dosage of the sulfur-doped birch charcoal-based material is 1.0 g / L.

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