A sulfur-doped biocarbon / modified carbon nitride composite material, a preparation method and applications thereof

Abstract

This invention discloses a sulfur-doped biomass carbon / modified carbon nitride composite material, its preparation method, and its application. It belongs to the field of selective recovery of precious metals and simultaneous degradation of persistent organic pollutants. This invention is the first to utilize a sulfur-doped biomass carbon / modified carbon nitride composite material to selectively recover precious metals and simultaneously degrade organic pollutants in industrial wastewater containing precious metals. This composite material has strong versatility, eliminating the need for pretreatment of wastewater such as pH adjustment and pollutant removal, greatly reducing the cumbersome procedures in traditional adsorption and recovery processes, saving energy, and offering both environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of selective recovery of precious metals and simultaneous degradation of persistent organic pollutants, and specifically relates to a sulfur-doped biocarbon / modified carbon nitride composite material, its preparation method and its application. Background Technology

[0002] Among the wide range of water pollution sources, industrial wastewater discharge not only exacerbates environmental pollution but also causes serious harm to human health. These harmful effects stem from the large amounts of metals and persistent organic pollutants present in wastewater. In recent years, wastewater generated by industries related to the mining, extraction, purification, and processing of various precious metals (gold, silver, ruthenium, rhodium, palladium, osmium, iridium, and platinum) has attracted global attention. This industrial wastewater contains large amounts of high-value metals, and failure to effectively utilize these resources will not only lead to resource waste but also environmental pollution. Therefore, developing effective methods for extracting precious metals from secondary sources is crucial not only for mitigating environmental problems but also for addressing the challenges of resource scarcity.

[0003] In secondary sources such as industrial wastewater or leachates, precious metals mainly exist in the form of anions, such as AuCl. 4− PtCl6 2− and PdCl4 2− Traditional methods for extracting precious metals from secondary sources include solvent extraction, electrodeposition, membrane separation, adsorption, displacement, and catalytic reduction. Among these methods, adsorption involves immobilizing ions on the surface or within the structure of the adsorbent by utilizing the interaction between the adsorbent and the target ions. It is commonly used for the adsorption and recovery of precious metals from wastewater due to its advantages such as simple operation, high recovery efficiency, and minimal environmental impact. Currently, various adsorbents have been used for precious metal recovery, including activated carbon, metal oxides, silica-based materials, and metal-organic frameworks (MOFs). Among these, traditional materials such as activated carbon, zeolites, metal oxides, and silica are widely studied as stable adsorbents for precious metal recovery due to their low preparation cost and large specific surface area. However, these materials lack specific functional sites with strong affinity for precious metals, resulting in limited adsorption selectivity and capacity. Other emerging adsorbent materials, such as MOFs, exhibit high specific surface area and high porosity, providing abundant active sites for precious metal recovery and thus demonstrating excellent adsorption efficiency. However, most MOFs are unstable in water, increasing the risk of secondary pollution caused by metal ion leakage. In addition, persistent organic pollutants in industrial wastewater tend to adhere to the active sites of adsorption materials, further reducing the adsorption efficiency of precious metals.

[0004] Therefore, there is an urgent need in this field to develop a method that can simultaneously achieve efficient, stable, and highly selective recovery of precious metal resources and effective removal of persistent organic pollutants in real-world complex wastewater environments, thereby realizing synergistic resource utilization and pollution reduction in the industrial wastewater treatment industry. Summary of the Invention

[0005] To address the above problems, this invention provides a sulfur-doped bio-carbon / modified carbon nitride composite material, its preparation method, and its applications.

[0006] One of the technical solutions provided by this invention: A method for preparing a sulfur-doped biochar / modified carbon nitride composite material includes the following steps: mixing a biochar precursor, a sulfur source, and inorganic matter, and calcining the mixture once under an inert gas atmosphere to obtain sulfur-doped biochar; dispersing the sulfur-doped biochar, carbon nitride precursor, and organic modifier in a solvent and performing a solvothermal reaction to obtain a mixture; and calcining the mixture a second time under an inert gas atmosphere to prepare the sulfur-doped biochar / modified carbon nitride composite material.

[0007] Optionally, the preparation method of the biochar precursor includes the following steps: using green beans as raw material, after washing, drying, grinding and sieving, the beans are stirred and mixed with sulfuric acid to carry out a hydrothermal reaction to obtain the biochar precursor.

[0008] The green beans are washed with deionized water and dried at 40-100℃. After drying, the green beans are ground and passed through a 50-150 mesh sieve. The concentration of sulfuric acid is 1-10 mol / L, the mass ratio of green beans to sulfuric acid is (1-10):(100-500), the hydrothermal reaction temperature is 120-200℃, and the time is 1-15 h.

[0009] A strong π-π interaction force is formed between sulfur-doped biochar and modified carbon nitride, resulting in good interfacial contact. After being combined with highly conductive sulfur-doped biochar, the photocatalytic activity of modified carbon nitride is effectively enhanced. The sulfur-doped biochar / modified carbon nitride composite material prepared in this invention has specific adsorption sites with strong affinity for noble metals, enabling selective adsorption of noble metals. Based on the synergistic adsorption and photocatalytic capabilities of the materials, this sulfur-doped biochar / modified carbon nitride composite material can efficiently recover noble metals and remove persistent organic pollutants from wastewater.

[0010] Furthermore, the mass ratio of the biochar precursor, sulfur source and inorganic matter is (0.4-0.5):1:(0.1-0.6).

[0011] Furthermore, the sulfur source includes one or both of sublimed sulfur and thiourea; and / or the inorganic substance includes one or both of potassium hydroxide, sodium hydroxide, potassium bicarbonate, and sodium bicarbonate.

[0012] Furthermore, the temperature of the first calcination is 450-700℃, the heating rate is 1-5℃ / min, and the time is 0.5-6h.

[0013] Furthermore, the mass ratio of the sulfur-doped biochar, carbon nitride precursor, and organic modifier is 1:(20-100):(10-20).

[0014] Further, the carbon nitride precursor includes at least one of thiourea, dicyandiamide, melamine, and urea; and / or, the organic modifier includes at least one of pyromellitic dianhydride, perylene diimide, nicotinic acid, L-cysteine, and trithiocyanate.

[0015] Furthermore, the temperature of the solvothermal reaction is 50-200℃, and the time is 1-20h.

[0016] Furthermore, the temperature of the secondary calcination is 400-700℃, the heating rate is 1-5℃ / min, and the reaction time is 1-10h.

[0017] The second technical solution provided by this invention: A sulfur-doped bio-carbon / modified carbon nitride composite material prepared by the above preparation method.

[0018] The third technical solution provided by this invention: Application of the above-mentioned sulfur-doped biocarbon / modified carbon nitride composite material in the selective recovery of precious metals and simultaneous catalytic degradation of persistent organic pollutants in industrial wastewater.

[0019] The application includes the following steps: dispersing the sulfur-doped biocarbon / modified carbon nitride composite material in industrial wastewater containing precious metals, stirring under ultraviolet light irradiation, recovering precious metals and simultaneously degrading organic pollutants.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects: This invention is the first to utilize a sulfur-doped biochar / modified carbon nitride composite material to selectively recover precious metals and simultaneously degrade organic pollutants in industrial wastewater containing precious metals. A strong π-π interaction force forms between the sulfur-doped biochar and the modified carbon nitride in the composite material, resulting in excellent interfacial contact, a high specific surface area, and enhanced photocatalytic activity. This leads to a high adsorption capacity for precious metal ions and a strong mineralization capacity for organic pollutants. Simultaneously, the composite material possesses specific adsorption sites with strong affinity for precious metals, exhibiting excellent selectivity and recovery rate. Furthermore, this composite material is highly versatile, eliminating the need for pretreatment such as pH adjustment and pollutant removal, significantly reducing the cumbersome procedures of traditional adsorption and recovery processes, saving energy, and offering both environmental and economic benefits.

[0021] The sulfur-doped biomass carbon / modified carbon nitride composite material provided by this invention has a high specific surface area, reaching 434.15 m². 2 / g, selectively recovers gold, silver, ruthenium, rhodium, palladium, osmium, iridium and platinum in real complex wastewater, with a precious metal recovery rate of over 99%.

[0022] The high specific surface area carbon-based composite material for efficient and selective recovery of precious metals provided by this invention has a simple preparation process, low production cost, is suitable for large-scale production, and has a short precious metal recovery process, thus having potential industrial application value. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The XRD patterns are of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride sample obtained in Comparative Example 2. Figure 2 XPS images of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride sample obtained in Comparative Example 2 are shown. (a) is the C 1s spectrum, (b) is the N 1s spectrum, and (c) is the S 2p spectrum. Figure 3 The BET plots are of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride sample obtained in Comparative Example 2, where (a) is the N2 adsorption / desorption isotherm plot; and (b) is the specific surface area bar chart. Figure 4 This is a SEM image of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1; Figure 5 The elemental distribution diagram of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1 is shown. Figure 6 The TOC change curves over time during the treatment of industrial wastewater by the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride obtained in Comparative Example 2 are shown. Figure 7The adsorption curves of different metal ions in industrial wastewater at different pH values ​​are shown for the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride obtained in Comparative Example 2. Among them, (a) is Au(III) at pH 1.2; (b) is Cu(II), Cd(II), and Co(II) at pH 1.2; (c) is Au(III) at pH 12.7; and (d) is Cu(II), Cd(II), and Co(II) at pH 12.7.

[0025] Figure 8 The images show the adsorption curves of different precious metal ions in industrial wastewater at different pH values ​​obtained from the sulfur-doped biomass carbon / modified carbon nitride composite material in Example 1. (a) represents silver, ruthenium, palladium, rhodium, osmium, iridium and platinum at pH 1.2; (b) represents silver, ruthenium, palladium, rhodium, osmium, iridium and platinum at pH 12.7. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] 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.

[0031] This invention provides a method for preparing a sulfur-doped biochar / modified carbon nitride composite material, comprising the following steps: using green beans as raw material, washing, drying, grinding, and sieving the beans, then mixing them with sulfuric acid for a hydrothermal reaction to obtain a biochar precursor; adding a sulfur source and inorganic matter to the biochar precursor, and calcining it under an inert gas atmosphere to obtain sulfur-doped biochar; dispersing the sulfur-doped biochar, carbon nitride precursor, and organic modifier in a solvent, and reacting them with a solvothermal agent to obtain a mixture; and calcining the mixture in a tube furnace to obtain the sulfur-doped biochar / modified carbon nitride composite material.

[0032] This invention utilizes an in-situ thermal polymerization method to prepare a sulfur-doped biomass carbon / modified carbon nitride composite material. A strong π-π interaction force forms between the sulfur-doped biomass carbon and the modified carbon nitride, resulting in excellent interfacial contact and a high specific surface area. Furthermore, the photocatalytic activity of the modified carbon nitride is effectively enhanced after compositing with highly conductive sulfur-doped biomass carbon. Based on the synergistic adsorption and photocatalytic capabilities of the materials, the sulfur-doped biomass carbon / modified carbon nitride composite material can efficiently recover precious metals and remove persistent organic pollutants from wastewater. Simultaneously, the addition of organic modifiers endows the composite material with specific adsorption sites, effectively improving its selectivity and recovery rate for precious metals.

[0033] Example 1: A method for preparing a sulfur-doped biochar / modified carbon nitride composite material (1) Using green beans as raw material, wash with deionized water and dry at 60°C. After drying, grind the green beans and pass them through a 100-mesh sieve to obtain green bean powder. Mix 1g of green bean powder with 60mL of 3mol / L H2SO4 evenly, then put it into a polytetrafluoroethylene reactor liner and keep it at 160°C for 10h. After the reaction is completed, filter it, wash it with deionized water and ethanol respectively, and vacuum dry it (60°C, 6h) to obtain biochar precursor. (2) Take 1g of the biochar precursor obtained in step (1), grind and mix it with 2g of thiourea and 1g of potassium hydroxide, heat it to 600℃ (heating rate is 3℃ / min) under nitrogen atmosphere, and calcine it for 3h to obtain sulfur-doped biochar. (3) Disperse the sulfur-doped biochar obtained in step (2) with melamine and L-cysteine ​​in deionized water at a mass ratio of 0.5:10:10, place it in the liner of a polytetrafluoroethylene reactor, keep it at 160℃ for 12h, filter after the reaction, wash with deionized water and ethanol respectively, and vacuum dry (60℃, 6h) to obtain a mixture; (4) The mixture obtained in step (3) is placed in a tube furnace and heated to 550°C (heating rate is 3°C / min). The mixture is calcined under nitrogen atmosphere for 5 h to prepare sulfur-doped biocarbon / modified carbon nitride composite material.

[0034] Example 2: A method for preparing a sulfur-doped biochar / modified carbon nitride composite material (1) Using green beans as raw material, wash with deionized water and dry at 40 °C. After drying, grind the green beans and pass through a 50-mesh sieve to obtain green bean powder. Mix 1g of green bean powder with 5.5mL of 10mol / L H2SO4 and then place it in a polytetrafluoroethylene reactor liner. Keep it at 120 °C for 15h. After the reaction is completed, filter it and wash it with deionized water and ethanol respectively. Then, vacuum dry it (60 °C, 6h) to obtain biochar precursor. (2) Take 0.5g of the biochar precursor obtained in step (1), grind and mix it with 1g of thiourea and 0.1g of potassium hydroxide, heat it to 700℃ (heating rate is 5℃ / min) under nitrogen atmosphere, and calcine it for 0.5h to obtain sulfur-doped biochar. (3) Disperse the sulfur-doped biochar obtained in step (2) with melamine and L-cysteine ​​in deionized water at a mass ratio of 0.01:1:0.1, place it in the liner of a polytetrafluoroethylene reactor, keep it at 50°C for 20 h, filter after the reaction, wash with deionized water and ethanol respectively, and vacuum dry (60°C, 6 h) to obtain a mixture; (4) The mixture obtained in step (3) is placed in a tube furnace and heated to 400℃ (heating rate is 1℃ / min). The mixture is calcined under nitrogen atmosphere for 10h to prepare sulfur-doped biocarbon / modified carbon nitride composite material.

[0035] Example 3: A method for preparing a sulfur-doped biochar / modified carbon nitride composite material (1) Using green beans as raw material, wash with deionized water and dry at 100℃. After drying, grind the green beans and pass through a 150-mesh sieve to obtain green bean powder. Mix 1g of green bean powder with 272mL of 1mol / L H2SO4 evenly. Then, put it into the liner of a polytetrafluoroethylene reactor and keep it at 200℃ for 1h. After the reaction is completed, filter it, wash it with deionized water and ethanol respectively, and vacuum dry it (60℃, 6h) to obtain biochar precursor. (2) Take 2g of the biochar precursor obtained in step (1), grind and mix it with 5g of thiourea and 3g of potassium hydroxide, heat it to 450℃ (heating rate is 1℃ / min) under nitrogen atmosphere, and calcine it for 6h to obtain sulfur-doped biochar. (3) Disperse the sulfur-doped biochar obtained in step (2) with melamine and L-cysteine ​​in deionized water at a mass ratio of 1:20:20, place it in a polytetrafluoroethylene reactor liner, keep it at 200℃ for 1h, filter after the reaction, wash with deionized water and ethanol respectively, and vacuum dry (60℃, 6h) to obtain a mixture. (4) The mixture obtained in step (3) is placed in a tube furnace and heated to 700°C (heating rate is 5°C / min). The mixture is calcined under nitrogen atmosphere for 1 hour to prepare sulfur-doped biocarbon / modified carbon nitride composite material.

[0036] Comparative Example 1 (1) Using green beans as raw material, wash with deionized water and dry at 60℃. After drying, grind the green beans and pass through a 100-mesh sieve to obtain green bean powder. Mix 1g of green bean powder with 60mL of 3mol / L H2SO4 evenly, then put it into a polytetrafluoroethylene reactor liner and keep it at 160℃ for 10h. After the reaction is completed, filter, wash with deionized water and ethanol respectively, and vacuum dry (60℃, 6h) to obtain biochar precursor. (3) Take 1g of the biochar precursor obtained in step (1), grind and mix it with 2g of thiourea and 1g of potassium hydroxide, heat it to 600 ℃ (heating rate of 3℃ / min) under nitrogen atmosphere, and calcine it for 3h to obtain sulfur-doped biochar.

[0037] Comparative Example 2 (1) Melamine and L-cysteine ​​were dispersed in deionized water at a mass ratio of 1:1, placed in a polytetrafluoroethylene reactor liner, and kept at 160°C for 12 h. After the reaction was completed, the mixture was filtered, washed with deionized water and ethanol respectively, and dried under vacuum (60°C, 6 h) to obtain a mixture. (2) The mixture obtained in step (1) is placed in a tube furnace and heated to 550°C (heating rate is 3°C / min). The mixture is calcined under a nitrogen atmosphere for 5 hours to prepare modified carbon nitride.

[0038] Performance testing In order to determine the selectivity and recovery rate of precious metals and the catalytic degradation performance of persistent organic pollutants by the materials prepared in Examples 1-3, Comparative Examples 1 and 2, this invention applies the materials prepared in Examples 1-3, Comparative Examples 1 and 2 to actual industrial wastewater to conduct selective recovery of precious metals and simultaneous catalytic degradation of persistent organic pollutants.

[0039] This invention selects organic wastewater containing gold, copper, cadmium and cobalt from a certain factory, adds the materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 at a feed ratio of 30 mg / L, stirs for 10-80 min under 40W ultraviolet lamp irradiation, collects the filtrate after filtration, and detects the concentration of residual metal ions and total organic carbon (TOC) in the filtrate.

[0040] Figure 1 The XRD patterns are of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride sample obtained in Comparative Example 2. The XRD pattern of the sulfur-doped biomass carbon / modified carbon nitride composite material has four characteristic peaks at 12.8°, 24.0°, 27.2°, and 43.5°, which correspond to the (100) crystal plane of carbon nitride, the (002) crystal plane of amorphous carbon, the (002) crystal plane of carbon nitride, and the (002) crystal plane of crystalline carbon, respectively. This indicates that the molecular structure of biomass carbon and carbon nitride was not destroyed after compositing. This proves that the present invention successfully synthesized the sulfur-doped biomass carbon / modified carbon nitride composite material.

[0041] Figure 2 XPS spectra of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride sample obtained in Comparative Example 2, where (a) is the C 1s spectrum, (b) is the N 1s spectrum, and (c) is the S 2p spectrum. Figure 2 As can be seen from the data, compared with sulfur-doped biomass carbon and modified carbon nitride, the C 1s spectrum of the sulfur-doped biomass carbon / modified carbon nitride composite material shows a new π-π pattern. The peaks indicate that the modified carbon nitride is bonded to the sulfur-doped biomass carbon through π-π interactions. Furthermore, compared to sulfur-doped biomass carbon and modified carbon nitride alone, the larger CSC and C-OH peak areas of the sulfur-doped biomass carbon / modified carbon nitride composite indicate that the introduction of L-cysteine ​​and sulfur-doped biomass carbon increases the CSC bonds and hydroxyl groups in the composite, which is beneficial for the adsorption of noble metal ions. These results demonstrate that the sulfur-doped biomass carbon / modified carbon nitride composite possesses good interfacial contact and abundant CSC bonds and hydroxyl groups.

[0042] Figure 3 The BET plots are shown for the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride sample obtained in Comparative Example 2, where (a) is the N2 adsorption / desorption isotherm plot; (b) is the specific surface area histogram; from Figure 3 As can be seen, compared with sulfur-doped biomass carbon and modified carbon nitride, the sulfur-doped biomass carbon / modified carbon nitride composite material has the highest specific surface area, at 434.15 m². 2 / g, the above results indicate that the sulfur-doped biomass carbon / modified carbon nitride composite material prepared in this invention has a high specific surface area.

[0043] Figure 4 This is a SEM image of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1. Figure 4 The sulfur-doped biomass carbon / modified carbon nitride composite material is shown to be porous and blocky.

[0044] Figure 5 This is the elemental distribution diagram of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1. Figure 5 This indicates that C, N, and S elements are uniformly distributed in the composite material.

[0045] Figure 6 The figures show the TOC (Total Volatile Organic Compound) versus time curves of the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride obtained in Comparative Example 2 during the treatment of industrial wastewater. Figure 6 As can be seen, compared with sulfur-doped biomass carbon and modified carbon nitride, the TOC of industrial wastewater treated with the sulfur-doped biomass carbon / modified carbon nitride composite material was significantly reduced, with a 95% reduction in TOC after 80 minutes. This indicates that the photocatalytic activity of modified carbon nitride was effectively enhanced after being combined with highly conductive sulfur-doped biomass carbon. These results demonstrate that the sulfur-doped biomass carbon / modified carbon nitride composite material prepared in this invention can effectively remove organic pollutants from industrial wastewater containing precious metals.

[0046] Figure 7 The adsorption curves of different metal ions in industrial wastewater at different pH values ​​are shown for the sulfur-doped biomass carbon / modified carbon nitride composite material obtained in Example 1, the sulfur-doped biomass carbon obtained in Comparative Example 1, and the modified carbon nitride obtained in Comparative Example 2. Among them, (a) is Au(III) at pH 1.2; (b) is Cu(II), Cd(II), and Co(II) at pH 1.2; (c) is Au(III) at pH 12.7; and (d) is Cu(II), Cd(II), and Co(II) at pH 12.7. Figure 7The results show that the sulfur-doped biomass carbon / modified carbon nitride composite material exhibits higher gold ion recovery efficiency compared to sulfur-doped biomass carbon and modified carbon nitride, achieving recovery rates of 99.7% and 99.1% in acidic (pH=1.2) and alkaline (pH=12.7) wastewater, respectively. Furthermore, the sulfur-doped biomass carbon / modified carbon nitride composite material shows virtually no adsorption of copper, cadmium, and cobalt ions, indicating that the increase in CSC bonds and hydroxyl groups enhances the selectivity and recovery rate of the composite material for noble metal ions. These results demonstrate that the sulfur-doped biomass carbon / modified carbon nitride composite material prepared in this invention can efficiently and selectively recover noble metal ions from complex industrial wastewater.

[0047] Figure 8 The images show the adsorption curves of different precious metal ions in industrial wastewater at different pH values ​​obtained from the sulfur-doped biomass carbon / modified carbon nitride composite material in Example 1. (a) represents silver, ruthenium, palladium, rhodium, osmium, iridium and platinum at pH 1.2; (b) represents silver, ruthenium, palladium, rhodium, osmium, iridium and platinum at pH 12.7.

[0048] Figure 8 The results showed that the recoveries of silver, ruthenium, palladium, rhodium, osmium, iridium, and platinum in acidic (pH=1.2) wastewater were 99.2%, 99.7%, 99.8%, 99.5%, 99.1%, 99.3%, and 99.5%, respectively, while the recoveries in alkaline (pH=12.7) wastewater were 99.2%, 99.1%, 99.3%, 99.5%, 99.4%, 99.6%, and 99.1%, respectively. These results indicate that the sulfur-doped biomass carbon / modified carbon nitride composite material prepared in this invention can effectively recover the aforementioned precious metals from wastewater.

[0049] The specific surface area of ​​the sulfur-doped biomass carbon / modified carbon nitride composite material prepared in Example 2 was 407.58 m². 2 / g; the TOC of the wastewater can be reduced by 90% after 80 min; the recoveries of gold, silver, ruthenium, palladium, rhodium, osmium, iridium and platinum in acidic wastewater are 99.1%, 99.0%, 99.2%, 99.1%, 99.0%, 99.0%, 99.1% and 99.3%, respectively, and the recoveries of gold, silver, ruthenium, palladium, rhodium, osmium, iridium and platinum in alkaline wastewater are 99.0%, 99.0%, 99.1%, 99.2%, 99.3%, 99.1%, 99.2% and 99.0%, respectively.

[0050] The specific surface area of ​​the sulfur-doped biomass carbon / modified carbon nitride composite material prepared in Example 3 was 423.79 m². 2 / g; the TOC of the wastewater can be reduced by 92% after 80 min; the recoveries of gold, silver, ruthenium, palladium, rhodium, osmium, iridium and platinum in acidic wastewater are 99.5%, 99.1%, 99.5%, 99.6%, 99.4%, 99.2%, 99.2% and 99.6% respectively, and the recoveries of gold, silver, ruthenium, palladium, rhodium, osmium, iridium and platinum in alkaline wastewater are 99.3%, 99.0%, 99.2%, 99.2%, 99.6%, 99.3%, 99.4% and 99.3% respectively.

[0051] In summary, this invention utilizes an in-situ thermal polymerization method to prepare a sulfur-doped biomass carbon / modified carbon nitride composite material. A strong π-π interaction force is formed between the sulfur-doped biomass carbon and the modified carbon nitride, resulting in excellent interfacial contact and a high specific surface area. Based on the synergistic adsorption effect, enhanced photocatalytic ability, and abundant CSC bonds and hydroxyl groups, the sulfur-doped biomass carbon / modified carbon nitride composite material can efficiently and selectively recover precious metals and simultaneously remove persistent organic pollutants from complex wastewater.

[0052] 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. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a sulfur-doped bio-carbon / modified carbon nitride composite material, characterized in that, Includes the following steps: A mixture of biochar precursor, sulfur source, and inorganic matter is calcined once under an inert gas atmosphere to obtain sulfur-doped biochar. The sulfur-doped biochar, carbon nitride precursor, and organic modifier are dispersed in a solvent and subjected to a solvothermal reaction to obtain a mixture. The mixture is then calcined a second time under an inert gas atmosphere to prepare the sulfur-doped biochar / modified carbon nitride composite material.

2. The method for preparing the sulfur-doped bio-carbon / modified carbon nitride composite material according to claim 1, characterized in that, The mass ratio of the biochar precursor, sulfur source and inorganic matter is (0.4-0.5):1:(0.1-0.6).

3. The method for preparing the sulfur-doped biochar / modified carbon nitride composite material according to claim 1, characterized in that, The sulfur source includes one or both of sublimed sulfur and thiourea; and / or, the inorganic substance includes one or both of potassium hydroxide, sodium hydroxide, potassium bicarbonate, and sodium bicarbonate.

4. The method for preparing the sulfur-doped bio-carbon / modified carbon nitride composite material according to claim 1, characterized in that, The temperature of the first calcination is 450-700℃, the heating rate is 1-5℃ / min, and the time is 0.5-6h.

5. The method for preparing the sulfur-doped bio-carbon / modified carbon nitride composite material according to claim 1, characterized in that, The mass ratio of the sulfur-doped biochar, carbon nitride precursor and organic modifier is 1:(20-100):(10-20).

6. The method for preparing the sulfur-doped bio-carbon / modified carbon nitride composite material according to claim 1, characterized in that, The carbon nitride precursor includes at least one of thiourea, dicyandiamide, melamine, and urea; and / or, the organic modifier includes at least one of pyromellitic dianhydride, perylene diimide, nicotinic acid, L-cysteine, and trithiocyanate.

7. The method for preparing the sulfur-doped biochar / modified carbon nitride composite material according to claim 1, characterized in that, The solvothermal reaction is carried out at a temperature of 50-200℃ for 1-20 hours.

8. The method for preparing the sulfur-doped bio-carbon / modified carbon nitride composite material according to claim 1, characterized in that, The secondary calcination temperature is 400-700℃, the heating rate is 1-5℃ / min, and the reaction time is 1-10h.

9. A sulfur-doped biochar / modified carbon nitride composite material prepared by the preparation method according to any one of claims 1-8.

10. The application of the sulfur-doped biochar / modified carbon nitride composite material of claim 9 in the selective recovery of precious metals and simultaneous catalytic degradation of persistent organic pollutants in industrial wastewater.

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