Sulfate ion intercalated zinc-manganese LDH supported biochar composite material, and preparation method and application thereof

Abstract

The application provides a preparation method of a sulfur ion intercalation zinc-manganese LDH supported biochar composite material, which comprises the following steps: washing and drying rice straw, crushing and sieving the rice straw to obtain rice straw powder; taking the rice straw powder, adding zinc chloride and manganese chloride tetrahydrate, and dispersing the mixture in deionized water to obtain a mixed solution; adjusting the pH of the mixed solution to alkaline, continuing to stir, centrifuging and washing, and drying to obtain a precursor powder; pyrolyzing the precursor powder in an inert atmosphere to obtain a zinc-manganese layered double hydroxide supported biochar composite material; and performing sulfur ion intercalation treatment on the composite material, centrifuging and washing, and drying to obtain a target material. The application also provides the composite material prepared by the above method and application. The zinc-manganese layered double hydroxide is supported on the biochar and modified by sulfur ion intercalation, so that the defects of single biochar, i.e. weak adsorption capacity for heavy metal anions, are compensated, and the synchronous and efficient adsorption and removal of heavy metal ions in water are realized.

Description

Technical Field

[0001] This invention relates to the field of adsorption materials and water treatment technology, and in particular to a sulfur ion intercalated zinc-manganese layered double hydroxide (LDH) supported biochar composite material, its preparation method and application. Background Technology

[0002] Heavy metals are difficult to biodegrade and can accumulate in organisms through the food chain, posing a long-term potential risk to the ecological environment and human health. Polluted water bodies commonly exhibit complex pollution from heavy metal cations and anions, with common cations including copper and lead ions, and anions including tetravalent chromium and pentavalent arsenic ions. Faced with severe water pollution problems, there is an urgent need to find low-cost water treatment technologies. Among numerous wastewater treatment technologies, adsorption is the preferred method due to its high efficiency, low cost, and ease of operation. Biochar (BC), with its superior properties such as being environmentally friendly, rich in functional groups, and having a rich pore structure, has emerged as a novel adsorbent.

[0003] Biochar, as a novel adsorbent, exhibits adsorption of heavy metals through various mechanisms including electrostatic attraction, ion exchange, precipitation, and physical adsorption, displaying different adsorption behaviors for different heavy metal ions. The surface of biochar is rich in functional groups, enabling strong interactions with heavy metals such as electrostatic attraction, ion exchange, and surface complexation. Most biochar surfaces are highly electronegative, exhibiting strong electrostatic adsorption of positively charged heavy metal cations; simultaneously, they possess excellent cation exchange capacity, further enhancing the adsorption effect on heavy metal cations through ion exchange.

[0004] However, due to the overall negative charge on the surface of biochar, its adsorption effect on heavy metal anions existing in the form of oxygen anions is poor, which severely limits its application in the treatment of complex heavy metal wastewater. For example, arsenic in water mainly exists in the form of oxygen anions, which are more easily adsorbed through electrostatic interactions and complexation with metal cations. Biochar alone has low removal efficiency and poor treatment effect for arsenic ions.

[0005] Therefore, to achieve simultaneous and efficient removal of multiple ions, further technological innovation and modification optimization are still needed when using biochar to treat wastewater containing both anionic and cationic heavy metal ions. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a sulfur ion intercalated zinc-manganese LDH-supported biochar composite material, its preparation method and application. By loading zinc-manganese layered double hydroxide onto biochar and modifying it with sulfur ion intercalation, the invention overcomes the deficiency of single biochar in adsorbing heavy metal anions, and achieves simultaneous and efficient adsorption and removal of anions and cations of heavy metals in water, providing strong support for environmental remediation.

[0007] The present invention solves the above-mentioned technical problems by adopting the following technical solutions: A method for preparing a sulfur ion intercalated zinc-manganese LDH-supported biochar composite material includes the following steps: (1) Wash and dry the rice straw to constant weight, then crush and sieve it to obtain rice straw powder; (2) Take the rice straw powder, add zinc chloride and manganese chloride tetrahydrate, disperse them together in deionized water and stir evenly to obtain a mixed solution; (3) Adjust the pH of the mixed solution to alkaline, continue stirring, and after centrifugation, washing, and drying, obtain the precursor powder; (4) The precursor powder was pyrolyzed under an inert atmosphere to obtain a zinc-manganese layered double hydroxide supported biochar composite material. (5) The obtained composite material is placed in a sodium sulfide solution for sulfur ion intercalation treatment, and after centrifugation, washing and drying, the sulfur ion intercalated zinc manganese LDH supported biochar composite material is obtained.

[0008] As one of the preferred embodiments of the present invention, in step (1), the drying temperature is 70~90℃, and the powder is passed through an 80~120 mesh sieve.

[0009] As one of the preferred embodiments of the present invention, in step (2), the molar ratio of zinc chloride to manganese chloride tetrahydrate is 1:1, and the stirring time is 3~5h.

[0010] As one of the preferred embodiments of the present invention, in step (3), an alkaline reagent is used to adjust the pH value of the mixed solution to 9-11, and the stirring time is 20-26 hours.

[0011] As one of the preferred embodiments of the present invention, in step (3), the drying temperature is 60~80℃ and the drying time is 20~26h.

[0012] As one of the preferred embodiments of the present invention, in step (4), the inert atmosphere is a nitrogen atmosphere. Before pyrolysis, nitrogen is introduced to purge the air in the device. During the pyrolysis process, the nitrogen flow rate is 180~220mL / min, the heating rate is 12~18℃ / min, the pyrolysis temperature is 450~550℃, and the pyrolysis time is 1~3h.

[0013] As one of the preferred embodiments of the present invention, in step (5), the concentration of sodium sulfide solution is 0.01~0.03mol / L, and the stirring time for intercalation treatment is 5~7h.

[0014] As one of the preferred embodiments of the present invention, in step (5), the drying temperature is 40~60℃, and the product is dried to constant weight.

[0015] A sulfur ion intercalated zinc-manganese LDH supported biochar composite material is prepared by the above-described preparation method.

[0016] An application of the above-mentioned sulfur ion intercalated zinc-manganese LDH supported biochar composite material is to use the sulfur ion intercalated zinc-manganese LDH supported biochar composite material as an adsorbent to simultaneously adsorb anionic and cationic heavy metal ions in wastewater.

[0017] The advantages of this invention compared to the prior art are: (1) In this invention, zinc-manganese layered double hydroxides are uniformly loaded onto the surface and micropores of biochar. The biochar carrier provides a large adhesion area, effectively inhibiting the aggregation and accumulation of LDHs particles, so that the active components are uniformly dispersed, and the adsorption performance of the composite material is synergistically enhanced, thereby improving the removal capacity of various pollutants. (2) The present invention uses sulfur ion intercalation modification to regulate the surface electrical properties and interlayer structure of the material, making up for the defect of poor adsorption capacity of single biochar for heavy metal anions, and realizing the simultaneous and efficient adsorption of heavy metal anions and cations in wastewater. (3) The raw materials of this invention are widely available. It uses rice straw, an agricultural waste, as raw material, which is inexpensive and environmentally friendly, and can realize the resource utilization of solid waste. (4) The composite material preparation method of the present invention is simple and reliable, the process conditions are controllable, the preparation process is simple, the material has good stability, and it has good application prospects in the field of composite heavy metal wastewater treatment. Attached Figure Description

[0018] Figure 1 These are microstructure test images of the composite material of the present invention in Experimental Example 1; Figure 2 This is a comparison diagram of the heavy metal adsorption performance of the modified composite material of the present invention and the original rice straw biochar material in Experiment Example 1; Figure 3 These are the X-ray diffraction patterns of the composite material of the present invention before and after adsorption of heavy metals in Experimental Example 1; Figure 4 This is a test diagram of the cyclic regeneration performance of the composite material of the present invention in Experimental Example 1. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Furthermore, the raw materials, reagents, or devices used in the following embodiments, unless otherwise specified, can be obtained from conventional commercial channels or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0020] Example 1 The preparation method of the sulfur ion intercalated zinc-manganese LDH supported biochar composite material in this embodiment is as follows: (1) Wash the rice straw, dry it at 80°C to constant weight, then grind the dried rice straw into powder and pass it through a 100-mesh sieve to obtain rice straw powder.

[0021] (2) Take 10g of rice straw powder obtained in the above steps, add zinc chloride and manganese chloride tetrahydrate in a molar ratio of 1:1, and disperse them together in deionized water. After stirring magnetically for 4 hours, a mixed solution is obtained.

[0022] (3) Adjust the pH of the mixed solution to 10 using sodium hydroxide solution, continue magnetic stirring for 24 hours, centrifuge and wash until the supernatant is clear, and then dry in an oven at 70°C for 24 hours.

[0023] (4) The precursor powder was placed in a tube furnace and pyrolyzed at 500°C for 2 hours. Before heating, N2 was introduced to purge the air in the device. During the pyrolysis process, a gas flow rate of 200 mL / min was used to raise the temperature from room temperature to the specified temperature at a rate of 15°C / min. The temperature was then naturally cooled to room temperature in an N2 atmosphere to obtain a zinc-manganese layered double hydroxide supported biochar composite material.

[0024] (5) The obtained composite material was immersed in a 0.02 mol / L sodium sulfide solution, magnetically stirred for 6 h, centrifuged and washed several times until the supernatant was clear, and then dried in an oven at 50 °C to constant weight to obtain the sulfur ion intercalated zinc manganese LDH supported biochar composite material.

[0025] Example 2 The preparation method of the sulfur ion intercalated zinc-manganese LDH supported biochar composite material in this embodiment is as follows: (1) Wash the rice straw, dry it at 70°C to constant weight, then grind the dried rice straw into powder and pass it through an 80-mesh sieve to obtain rice straw powder.

[0026] (2) Take 10g of rice straw powder obtained in the above steps, add zinc chloride and manganese chloride tetrahydrate in a molar ratio of 1:1, and disperse them together in deionized water. After stirring magnetically for 3 hours, a mixed solution is obtained.

[0027] (3) Adjust the pH of the mixed solution to 9 using sodium hydroxide solution, continue magnetic stirring for 20 hours, centrifuge and wash until the supernatant is clear, and then dry in an oven at 60°C for 26 hours.

[0028] (4) The precursor powder was placed in a tube furnace and pyrolyzed at 450°C for 3 hours. Before heating, N2 was introduced to purge the air in the device. During the pyrolysis process, a gas flow rate of 180 mL / min was used to raise the temperature from room temperature to the specified temperature at a heating rate of 12°C / min. The temperature was then naturally cooled to room temperature in an N2 atmosphere to obtain a zinc-manganese layered double hydroxide supported biochar composite material.

[0029] (5) The obtained composite material was immersed in a 0.01 mol / L sodium sulfide solution, magnetically stirred for 5 h, centrifuged and washed several times until the supernatant was clear, and then dried in an oven at 40 °C to constant weight to obtain the sulfur ion intercalated zinc manganese LDH supported biochar composite material.

[0030] Example 3 The preparation method of the sulfur ion intercalated zinc-manganese LDH supported biochar composite material in this embodiment is as follows: (1) Wash the rice straw, dry it at 90°C to constant weight, then grind the dried rice straw into powder and pass it through a 120-mesh sieve to obtain rice straw powder.

[0031] (2) Take 10g of rice straw powder obtained in the above steps, add zinc chloride and manganese chloride tetrahydrate in a molar ratio of 1:1, and disperse them together in deionized water. Stir magnetically for 5 hours to obtain a mixed solution.

[0032] (3) Adjust the pH of the mixed solution to 11 using sodium hydroxide solution, continue magnetic stirring for 26 hours, centrifuge and wash until the supernatant is clear, and then dry in an oven at 80°C for 20 hours.

[0033] (4) The precursor powder was placed in a tube furnace and pyrolyzed at 550°C for 1 hour. Before heating, N2 was introduced to purge the air in the device. During the pyrolysis process, a gas flow rate of 220 mL / min was used to raise the temperature from room temperature to the specified temperature at a heating rate of 18°C / min. The temperature was then naturally cooled to room temperature in an N2 atmosphere to obtain a zinc-manganese layered double hydroxide supported biochar composite material.

[0034] (5) The obtained composite material was immersed in a 0.03 mol / L sodium sulfide solution, magnetically stirred for 7 h, centrifuged and washed several times until the supernatant was clear, and then dried in an oven at 60 °C to constant weight to obtain the sulfur ion intercalated zinc manganese LDH supported biochar composite material.

[0035] Experimental Example 1 Structural characterization and adsorption performance testing of the composite material of this invention: The sulfur ion intercalated zinc-manganese LDH supported biochar composite material of the present invention (taking the composite material prepared in Example 1 as an example) was used to carry out structural characterization, heavy metal adsorption performance testing, phase change analysis before and after adsorption, and recycling performance testing.

[0036] I. Material Structure Characterization The microstructure of the composite material was observed using scanning electron microscopy (SEM).

[0037] II. Adsorption Performance Test Solutions of As(III) and Cu(II) with different concentration gradients were prepared, and the pH of the system was adjusted to 7.0. Raw rice straw biochar (raw BC, as a control) and the sulfur ion intercalated zinc manganese LDH supported biochar composite material of the present invention (modified BC) were weighed and placed in conical flasks and magnetically stirred. Adsorption experiments were carried out in three systems: single arsenic solution, single copper solution, and arsenic-copper mixed solution. The mixture was magnetically stirred until the adsorption reached equilibrium. Then the mixed solution was filtered, and the concentrations of As(III) and Cu(II) in the filtered solution were measured.

[0038] III. Analysis of Phase Structure Before and After Adsorption Composite material samples were collected separately after adsorbing no heavy metals, after adsorbing copper ions (Cu(II)), and after adsorbing arsenic ions (As(III)). The crystal structure of the three samples was tested by X-ray diffraction to analyze the phase changes and mechanisms of action during the adsorption process.

[0039] IV. Recycling Experiment The composite material that had completed adsorption in the adsorption performance test was desorbed and regenerated using an alkaline sodium hydroxide solution. The regenerated composite material was then used again to adsorb mixed heavy metals As(III) and Cu(II). The adsorption-desorption process was repeated five times, and the concentrations of As(III) and Cu(II) in the filtered solution were measured.

[0040] V. Test Results The results of the micromorphology test are shown below Figure 1 This indicates that the composite material of the present invention has a uniformly distributed sheet-like structure on its surface, and the sheet-like structure is tightly attached to the surface of the biochar matrix to form a coating layer. The layered double hydroxide exhibits a standard regular hexagonal crystal morphology, proving that the zinc-manganese layered double hydroxide was successfully loaded on the surface of biochar and completed crystal growth.

[0041] Adsorption test results are shown in Figure 2The results showed that in a single arsenic solution, the original biochar (BC) removed only about 5% of arsenic ions, while the modified BC removed about 67%. In a single copper solution, the original BC removed about 7% of copper ions, while the modified BC removed nearly 100%. In a mixed arsenic and copper solution, the original BC removed about 20% of arsenic ions and about 25% of copper ions, while the modified BC improved the removal rate of arsenic ions to about 73% and still maintained a near 100% removal rate of copper ions. Overall, the unmodified original biochar (original BC) exhibited extremely poor adsorption performance for arsenic and copper. The sulfur ion intercalation modified composite material (modified BC) of this invention significantly improved the adsorption capacity of arsenic ions, achieving simultaneous and efficient removal of both heavy metals, arsenic and copper.

[0042] The X-ray diffraction test results are shown in Figure 3 The black curve represents the XRD pattern of the composite material of the present invention without adsorbed heavy metals. Characteristic diffraction peaks (labeled α) corresponding to the (006), (009), (012), and (018) crystal planes appear at 2θ of 23.1°, 34.3°, 38.2°, and 45.2°, respectively, which are typical characteristic peaks of layered double hydroxides. Characteristic peaks of ZnO (β) and MnO2 (χ) also appear, indicating that zinc-manganese LDH has been successfully loaded and pyrolyzed to form the target composite structure. The blue curve represents the XRD pattern of the composite material after adsorbing copper ions. Obvious characteristic diffraction peaks of CuS (labeled δ) appear in the pattern, indicating that copper ions have undergone a sulfidation precipitation reaction on the material surface. At the same time, the intensity of some LDH characteristic peaks is weakened, indicating that ion exchange occurs during the adsorption process. The orange curve represents the XRD pattern of the composite material after adsorbing arsenic ions. The position of its characteristic peaks is not significantly shifted compared with the unadsorbed sample, but the peak shape is slightly broadened, indicating that arsenic ions are mainly fixed by complexing with hydroxyl groups on the material surface without destroying the layered structure of the material.

[0043] The results of the recycling experiment are shown below Figure 4 This indicates that the composite material of the present invention can achieve a removal rate of 76.5% for As(III) on the first use, and the removal rate is still above 60% when it is recycled for the third time; the material has excellent adsorption stability for Cu(II), and after five cycles of adsorption and desorption, the removal rate of Cu(II) can still reach 80.72%, which has good reuse value.

[0044] Experiment Example 2 Comparative test of adsorption properties of composite materials at different modification stages: This experimental example uses unintercalated zinc-manganese LDH-supported biochar (Zn / Mn-LDH@BC) as the test object, and compares it with the sulfur ion intercalation modified composite material of the present invention to verify the key role of sulfur ion intercalation modification in improving the adsorption performance of heavy metals.

[0045] I. Preparation of Test Materials Zinc-manganese LDH-supported biochar semi-finished product was prepared according to steps (1) to (4) of Example 1, omitting the sulfur ion intercalation modification process in step (5), and unmodified Zn / Mn-LDH@BC sample was obtained.

[0046] II. Adsorption Performance Test Prepare As(III) and Cu(II) solutions with the same concentration gradient as in Experimental Example 1, adjust the pH of the system to 7.0, weigh the above unmodified Zn / Mn-LDH@BC into an Erlenmeyer flask and stir magnetically until adsorption reaches equilibrium. Then filter the mixture and measure the concentrations of As(III) and Cu(II) in the filtered solution. The tests were conducted in three systems: a single arsenic solution, a single copper solution, and a mixed arsenic-copper solution.

[0047] III. Test Results The test results are shown in Table 1 below.

[0048] Table 1. Heavy metal removal rate test results of unmodified Zn / Mn-LDH@BC Testing System Single arsenic removal rate Single copper removal rate Mixed arsenic removal rate Mixed copper removal rate Zn / Mn-LDH@BC 51.49% 99.79% 71.88% 99.57% The results showed that the unmodified Zn / Mn-LDH@BC exhibited excellent removal efficiency for the heavy metal cation copper, achieving a removal rate of 99.79% in the single copper system and maintaining a high removal rate of 99.57% in the mixed system. However, its removal capacity for the heavy metal anion arsenic was significantly insufficient, with a removal rate of only 51.49% in the single system and a slight increase to 71.88% in the mixed system, still far below the 73.0% removal rate of the sulfide-intercalated modified composite material of this invention. Therefore, it was impossible to achieve simultaneous and efficient removal of both arsenic and copper. This comparison demonstrates that sulfide-intercalation modification is a key technical means to improve the adsorption capacity of the composite material for arsenic ions and achieve synergistic removal of cations and anions.

[0049] In summary, this invention uses rice straw-based biochar as a matrix, loads it with zinc-manganese layered double hydroxides, and modifies it with sulfur ion intercalation to obtain a composite adsorbent material. This material possesses a rich porous structure and multiple adsorption active sites, and can be stably formed by controlling the preparation process. Compared to original biochar and unmodified composite materials, the material of this invention significantly improves the adsorption capacity for As(III) while maintaining excellent adsorption performance for Cu(II), enabling simultaneous and efficient removal of arsenic and copper heavy metals in weakly acidic aquatic environments. Furthermore, the raw materials of this invention are readily available, the process is simple, the cost is low, and it exhibits good recyclability, showing promising application prospects in the field of heavy metal wastewater treatment.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sulfur ion intercalated zinc-manganese LDH-supported biochar composite material, characterized in that, Includes the following steps: (1) Wash and dry the rice straw to constant weight, then crush and sieve it to obtain rice straw powder; (2) Take the rice straw powder, add zinc chloride and manganese chloride tetrahydrate, disperse them together in deionized water and stir evenly to obtain a mixed solution; (3) Adjust the pH of the mixed solution to alkaline, continue stirring, and after centrifugation, washing, and drying, obtain the precursor powder; (4) The precursor powder was pyrolyzed under an inert atmosphere to obtain a zinc-manganese layered double hydroxide supported biochar composite material. (5) The obtained composite material is placed in a sodium sulfide solution for sulfur ion intercalation treatment, and after centrifugation, washing and drying, the sulfur ion intercalated zinc manganese LDH supported biochar composite material is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the drying temperature is 70~90℃, and the powder is passed through an 80~120 mesh sieve.

3. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of zinc chloride to manganese chloride tetrahydrate is 1:1, and the stirring time is 3~5h.

4. The preparation method according to claim 1, characterized in that, In step (3), the pH value of the mixed solution is adjusted to 9-11 using an alkaline reagent, and the stirring time is 20-26 hours.

5. The preparation method according to claim 1, characterized in that, In step (3), the drying temperature is 60~80℃ and the drying time is 20~26h.

6. The preparation method according to claim 1, characterized in that, In step (4), the inert atmosphere is a nitrogen atmosphere. Before pyrolysis, nitrogen is introduced to purge the air in the device. During pyrolysis, the nitrogen flow rate is 180~220mL / min, the heating rate is 12~18℃ / min, the pyrolysis temperature is 450~550℃, and the pyrolysis time is 1~3h.

7. The preparation method according to claim 1, characterized in that, In step (5), the concentration of sodium sulfide solution is 0.01~0.03 mol / L, and the stirring time for intercalation treatment is 5~7 h.

8. The preparation method according to claim 1, characterized in that, In step (5), the drying temperature is 40~60℃, and the product is dried to constant weight.

9. A sulfur ion-intercalated zinc-manganese LDH-supported biochar composite material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the sulfur ion intercalated zinc-manganese LDH supported biochar composite material as described in claim 9, characterized in that, The sulfur ion intercalated zinc-manganese LDH supported biochar composite material is used as an adsorbent to simultaneously adsorb anionic and cation-heavy metal ions in wastewater.

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