Biochar-based magnetic photocatalytic composite material and efficient photocatalytic water treatment device and method suitable for the material

Abstract

This invention discloses a biochar-based magnetic photocatalytic composite material and a highly efficient photocatalytic water treatment device and method adapted to the material; the biochar-based magnetic photocatalytic composite material is a biochar composite material co-doped with ZnFe2O4 and nitrogen, which has visible light photocatalytic activity and magnetic separation characteristics; the highly efficient photocatalytic water treatment device adapted to the biochar-based magnetic photocatalytic composite material includes a cyclone dispersion and photocatalytic reaction unit, a magnetically enhanced cyclone separation unit, and a closed-loop automatic circulation unit, which are sequentially connected by pipelines to form a circulation loop.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering and water treatment technology, specifically relating to a biochar-based magnetic photocatalytic composite material and a highly efficient photocatalytic water treatment device and method adapted to the material. Background Technology

[0002] With the acceleration of industrialization, various organic pollutants, especially antibiotic wastewater, pose a serious threat to the aquatic environment. Traditional water treatment methods suffer from low efficiency, high cost, and the potential for secondary pollution. Biochar-based composite materials have attracted widespread attention in the fields of adsorption and catalysis due to their wide availability, tunable structure, and environmental friendliness. However, the narrow photoresponse range and difficulty in recycling of ordinary biochar materials limit their practical application.

[0003] Magnetic photocatalytic materials combine the advantages of magnetic separation and photocatalytic degradation, but existing materials still suffer from problems such as low visible light utilization, high carrier recombination rate, and poor cycle stability. In addition, traditional photocatalytic reaction devices often struggle to achieve efficient material dispersion, sufficient illumination, in-situ separation, and recycling, especially for weakly magnetic materials, which are easily lost in dynamic water flow, resulting in low recovery rates.

[0004] Therefore, developing a biochar-based composite material with high visible light photocatalytic activity, easy magnetic recovery, and stable structure, and designing a matching high-efficiency water treatment device that can synergistically enhance its adsorption, photocatalytic separation, and cycle process, is of great significance for promoting the application of this type of material from the laboratory to practical engineering applications. Summary of the Invention

[0005] One objective of this invention is to provide a biochar-based magnetic photocatalytic composite material and its preparation method. This material has abundant mesoporous structure, high magnetic responsiveness, and an expanded visible light absorption range, and combines adsorption and photocatalysis synergistic effects, making it suitable for the efficient degradation of organic pollutants.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a biochar-based magnetic photocatalytic composite material includes the following steps: (1) Wash, dry, crush and sieve the biomass raw materials to obtain biomass powder, soak in phosphoric acid solution at 60-80℃ for 2 hours for pre-activation, wash and dry; (2) Dissolve FeSO4·7H2O and ZnSO4·7H2O in deionized water at a Fe to Zn molar ratio of 1.8:1 to prepare a mixed solution with a total metal ion concentration of 0.1 mol / L. Add urea and ascorbic acid while stirring, wherein the mass of urea is 80% of the dry weight of biomass and the molar amount of ascorbic acid is 1 times the total number of metal ions. (3) Add the biomass powder treated in step (1) to the mixed solution in step (2), impregnate it with ultrasound at 40-60℃ for 1 hour, let it stand for 12 hours, and then dry it at 80℃ until the moisture is completely evaporated. (4) Place the dried mixture in a crucible, heat it to 200°C in a muffle furnace at 5°C / min and hold for 1 hour, then heat it to 600°C at the same rate and hold for 4 hours, and then let it cool naturally. (5) Grind and sieve the pyrolysis product, wash it alternately with deionized water and anhydrous ethanol until neutral, and dry it to obtain ZnFe2O4-N co-doped biochar-based magnetic photocatalytic composite material.

[0007] As a preferred technical solution, the biomass raw material is selected from at least one of ginkgo leaves, corn cobs, and walnut shells.

[0008] A biochar-based magnetic photocatalytic composite material prepared by the above preparation method is a biochar composite material co-doped with ZnFe2O4 and nitrogen, which has visible light photocatalytic activity and magnetic separation characteristics.

[0009] The second objective of this invention is to provide a highly efficient photocatalytic water treatment device and method adapted to the above-mentioned biochar-based magnetic photocatalytic composite material, which can simultaneously optimize material dispersion, photocatalytic reaction, in-situ separation and automatic circulation.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-efficiency photocatalytic water treatment device adapted to the aforementioned biochar-based magnetic photocatalytic composite material includes the following units connected sequentially through pipelines to form a circulation loop: The cyclone dispersion and photocatalytic reaction unit includes a cylindrical light-transmitting reaction chamber with a water inlet pipe tangentially arranged on the side wall, a feed port at the top, and a visible light source inside; The magnetically enhanced cyclone separation unit includes a cylindrical cyclone section and a conical material-gathering section, with electromagnets arranged in layers around the outer periphery of the conical material-gathering section; The closed-loop automatic circulation unit includes a return pipe and a delivery pump located at the bottom of the separation unit, which are used to transport the catalyst slurry captured by the separation unit back to the reaction unit.

[0011] As a preferred technical solution, the light source in the swirling dispersion and photocatalytic reaction unit is a visible light source, and a power adjustment device is provided.

[0012] As a preferred technical solution, the electromagnet assembly is arranged in layers along the outer wall of the conical aggregate section, and the magnetic field strength gradually increases from top to bottom, forming a gradient magnetic field from weak to strong.

[0013] A method for water treatment using the aforementioned high-efficiency photocatalytic water treatment device includes: (a) The biochar-based magnetic photocatalytic composite material is fed into the swirling dispersion and photocatalytic reaction unit, dispersed in the swirling flow formed by tangential water inlet, and the light source is turned on to carry out the photocatalytic reaction; (b) After the reaction, the mixture enters the magnetically enhanced cyclone separation unit, where the photocatalytic composite material is separated and enriched under the coupling effect of centrifugation and gradient magnetic field. (c) The separated water is discharged from the top of the separation unit, captured by the magnetic field and enriched in the photocatalytic composite material at the bottom of the separation unit to form a high-concentration slurry, which is then pumped back to the reaction unit for recycling via the return pipe.

[0014] As a preferred technical solution, in step (a), the organic pollutants in the water include tetracycline antibiotics.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Material level: By co-doping ZnFe2O4 with N, the visible light response range of biochar is effectively broadened, and the separation efficiency of photogenerated carriers is improved; the material has both adsorption properties and magnetism, making it easy to separate and recover from water.

[0016] 2. Device level: Through the integrated design of swirling flow-magnetic field-reflux, the pain points of weak magnetic materials being difficult to disperse, separate and circulate in the flow system are solved, realizing the online regeneration and continuous use of catalytic materials.

[0017] 3. System Synergy: The materials and equipment are highly matched, and the entire process of "adsorption-catalysis-separation-reflux" can be optimized in dynamic water treatment, improving treatment efficiency and economy. Attached Figure Description

[0018] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 The N2 adsorption-desorption isotherms of BC, NBC, MBC, and MNBC prepared in the examples and comparative examples are shown. Figure 2 FTIR spectra of GLP, MBC, and MNBC prepared in the examples and comparative examples; Figure 3 This is a schematic diagram of the structure of the high-efficiency photocatalytic water treatment device of the present invention; Figure 4 This is a comparison chart of the effects of different photocatalytic materials on the degradation of tetracycline. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0020] I. Preparation of Biochar-Based Magnetic Photocatalytic Composite Materials Example 1

[0021] (1) Take dried ginkgo leaves, pulverize them and sieve them to obtain 10-30 mesh powder. Soak them in phosphoric acid solution at 70℃ for 2 hours, wash them with deionized water and dry them. (2) Weigh FeSO4·7H2O and ZnSO4·7H2O, and prepare a mixed solution with a total metal ion concentration of 0.1 mol / L according to Fe:Zn=1.8:1 (molar ratio). Add urea (equivalent to 80% of the dry weight of biomass) and ascorbic acid (molar ratio of 1:1 with the total metal ion) while stirring. (3) Add the pretreated biomass powder to the above solution, ultrasonically impregnate at 50°C for 1 hour, let stand for 12 hours, and dry at 80°C; (4) Transfer the dried sample into a crucible, heat it to 200°C in a muffle furnace at 5°C / min and hold for 1 hour, then heat it to 600°C at the same rate and hold for 4 hours, and then let it cool naturally. (5) After grinding the product, it is passed through a 100-200 mesh sieve, washed with deionized water and ethanol alternately until neutral, and dried at 80°C to obtain ZnFe2O4-N co-doped biochar-based composite material (denoted as MNBC).

[0022] Comparative Example 1 (1) Take dried ginkgo leaves, pulverize them and sieve them to obtain 10-30 mesh powder. Soak them in phosphoric acid solution at 70℃ for 2 hours, wash them with deionized water and dry them. (2) Weigh FeSO4·7H2O and ZnSO4·7H2O, and prepare a mixed solution with a total metal ion concentration of 0.1 mol / L according to Fe:Zn=1.8:1 (molar ratio). Add ascorbic acid (molar ratio of 1:1 with total metal ions) while stirring. (3) Add the pretreated biomass powder to the above solution, ultrasonically impregnate at 50°C for 1 hour, let stand for 12 hours, and dry at 80°C; (4) Transfer the dried sample into a crucible, heat it to 200°C in a muffle furnace at 5°C / min and hold for 1 hour, then heat it to 600°C at the same rate and hold for 4 hours, and then let it cool naturally. (5) After grinding the product, it is passed through a 100-200 mesh sieve, washed with deionized water and ethanol alternately until neutral, and dried at 80°C to obtain ZnFe2O4 doped biochar-based material without nitrogen source (denoted as MBC).

[0023] Comparative Example 2 (1) Take dried ginkgo leaves, pulverize them and sieve them to obtain 10-30 mesh powder. Soak them in phosphoric acid solution at 70℃ for 2 hours, wash them with deionized water and dry them. (2) Prepare a urea solution (equivalent to 80% of the dry weight of biomass); (3) Add the pretreated biomass powder to the above solution, ultrasonically impregnate at 50°C for 1 hour, let stand for 12 hours, and dry at 80°C; (4) Transfer the dried sample into a crucible, heat it to 200°C in a muffle furnace at 5°C / min and hold for 1 hour, then heat it to 600°C at the same rate and hold for 4 hours, and then let it cool naturally. (5) After grinding the product, it is passed through a 100-200 mesh sieve, washed with deionized water and ethanol alternately until neutral, and dried at 80°C to obtain N-doped biochar-based material without iron salt or zinc salt (denoted as NBC).

[0024] Comparative Example 3 (1) Take dried ginkgo leaves, pulverize them and sieve them to obtain 10-30 mesh powder. Soak them in phosphoric acid solution at 70℃ for 2 hours, wash them with deionized water and dry them. (2) Transfer the pretreated biomass powder into a crucible, heat it to 200°C in a muffle furnace at 5°C / min and hold for 1 hour, then heat it to 600°C at the same rate and hold for 4 hours, and then cool it naturally. (3) After grinding the product, it is passed through a 100-200 mesh sieve, washed with deionized water and ethanol alternately until neutral, and dried at 80°C to obtain biochar-based material (denoted as BC) without iron salt, zinc salt and nitrogen source.

[0025] The surface area (BET) of MNBC prepared in Example 1, MBC prepared in Comparative Example 1, NBC prepared in Comparative Example 2, BC prepared in Comparative Example 3, and GLP (short for Ginkgo biloba leaf) was analyzed, and the results are shown in Table 1.

[0026] Table 1. BET Results for BC, NBC, MBC, and MNBC As shown in Table 1, the original biochar BC possesses a high specific surface area and microporous characteristics. After nitrogen doping (NBC), the specific surface area decreased to 118.1 m². 2 The average pore size increased significantly to 10.02 nm, indicating that the doping process strongly modified the carbon framework, introducing nitrogen-containing functional groups and generating a significant pore-expanding effect. After loading with ZnFe2O4, the specific surface area of ​​MBC recovered to 154.7 m² / g. 2 / g, forming a mesoporous system of 6.52 nm. Ultimately, the co-doped material MNBC possesses a 32.8 nm... 2 With a specific surface area of ​​ / g and an average pore size of 9.54 nm, it exhibits an optimized structure dominated by mesopores.

[0027] Figure 1The isotherms for N2 adsorption and desorption at 77 K for BC, NBC, MBC, and MNBC prepared in the examples and comparative examples are shown. The isotherms for BC and NBC show a rapid increase in adsorption capacity in the low-pressure region, exhibiting typical Type I isotherms. However, the isotherms for MBC and MNBC transform into Type IV isotherms with a distinct hysteresis loop, demonstrating that the functionalized modification of the materials successfully constructed a pore structure dominated by slit-like mesopores formed by the accumulation of plate-like particles. This textural evolution from micropores to mesopores is consistent with the data in Table 1, indicating that the prepared MNBC material possesses mesoporous channels conducive to reactant transport, laying the structural foundation for its adsorption-photocatalytic synergistic performance.

[0028] Figure 2 The FTIR spectra of BC, NBC, MBC, and MNBC prepared in the examples and comparative examples were used to identify the surface functional groups of the materials. 2345 cm⁻¹ -1 Attributable to the antisymmetric stretching vibration of CO2 in the air, 2216 cm -1 Corresponding to the stretching vibrations of unsaturated bonds such as C≡N or C≡C, 610 cm -1 Originating from the vibration of the aromatic C=C skeleton, 1215 cm -1 The confirmation of CN bond formation is a signal of successful nitrogen doping, 886 cm⁻¹. -1 These vibrations belong to the out-of-plane bending vibrations of the aromatic ring CH. Data show that, except for the enhanced and stable CN bond characteristic peak after nitrogen doping, the intensities of the other vibrational peaks attributed to the carbon framework all exhibit a regular decrease from BC, NBC, MBC to MNBC. This systematic attenuation confirms that ZnFe2O4 loading significantly alters the surface chemical environment of biochar, while the stable existence of CN bonds in MNBC and the synergistic weakening of the carbon framework signal reveal a strong interaction between nitrogen doping and metal loading.

[0029] II. High-efficiency photocatalytic water treatment equipment and its operation The high-efficiency photocatalytic water treatment device of the present invention, such as Figure 3 As shown, the following units are connected sequentially via pipelines to form a loop: The swirling dispersion and photocatalytic reaction unit includes a cylindrical light-transmitting reaction chamber 1, a water inlet pipe 2 tangentially provided on the side wall, a feeding port 3 at the top, a visible light source 4 inside and a power adjustment device; The magnetically enhanced cyclone separation unit includes a cylindrical cyclone section 5 and a conical material-gathering section 6. The outer circumferential layer of the conical material-gathering section 6 has an electromagnet group 7, and the magnetic field strength gradually increases from top to bottom, forming a gradient magnetic field from weak to strong. The closed-loop automatic circulation unit includes a return pipe and a delivery pump 8 located at the bottom of the separation unit, which are used to transport the catalyst slurry captured by the separation unit back to the reaction unit.

[0030] The operation process of the high-efficiency photocatalytic water treatment device of the present invention is as follows: (a) The photocatalytic material is put into the swirling dispersion and photocatalytic reaction unit, dispersed in the swirling flow formed by tangential water inlet, and the light source is turned on to carry out the photocatalytic reaction; (b) After the reaction, the mixture enters the magnetically enhanced cyclone separation unit. The mixture forms a stable centrifugal flow field in the cylindrical cyclone section, which pre-enriches the low-density weak magnetic catalyst material to the wall of the separation chamber. The fluid enters the conical material accumulation section, and the cavity diameter shrinks to further enhance the centripetal effect, causing the catalyst material to accumulate to the bottom. At this time, the electromagnet group arranged in layers along the outer wall of the conical section is activated according to the preset program to form a gradient magnetic field that gradually increases in strength. The upper magnetic field initially captures the dispersed catalyst material, while the lower strong magnetic field performs secondary capture and retention of the catalyst material slurry enriched at the bottom. (c) The separated water is discharged from the top of the separation unit, captured by the magnetic field and enriched in the photocatalytic material at the bottom of the separation unit to form a high-concentration slurry, which is then pumped back to the reaction unit for recycling via the return pipe.

[0031] Using a 50 mg / L tetracycline solution as simulated wastewater, various photocatalytic materials were added and continuously operated in a high-efficiency photocatalytic water treatment device for 12 hours to test the adsorption and photocatalytic performance of various photocatalytic materials.

[0032] Figure 4 The diagram compares the photocatalytic effects of different materials on tetracycline degradation. The results show that BC and NBC hardly adsorbed tetracycline within 100 minutes, while MBC and MNBC showed adsorption efficiencies of only 18.4% and 20.5% for TC, respectively. Furthermore, the degradation efficiencies of Vis, BC / Vis, NBC / Vis, and MBC / Vis systems for tetracycline were also not significant. However, the MNBC / Vis system achieved a tetracycline removal rate close to 60%. This indicates that MNBC exhibits stronger photocatalytic performance than NBC and MBC, suggesting that co-doping with ZnFe2O4 and N is beneficial for improving the visible light response performance of the material and can effectively enhance the visible light photocatalytic performance of BC.

[0033] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a biochar-based magnetic photocatalytic composite material, characterized in that, Includes the following steps: (1) Wash, dry, crush and sieve the biomass raw materials to obtain biomass powder, soak in phosphoric acid solution at 60-80℃ for 2 hours for pre-activation, wash and dry; (2) Dissolve FeSO4·7H2O and ZnSO4·7H2O in deionized water at a Fe to Zn molar ratio of 1.8:1 to prepare a mixed solution with a total metal ion concentration of 0.1 mol / L. Add urea and ascorbic acid while stirring, wherein the mass of urea is 80% of the dry weight of biomass and the molar amount of ascorbic acid is 1 times the total number of metal ions. (3) Add the biomass powder treated in step (1) to the mixed solution in step (2), impregnate it with ultrasound at 40-60℃ for 1 hour, let it stand for 12 hours, and then dry it at 80℃ until the moisture is completely evaporated. (4) Place the dried mixture in a crucible, heat it to 200°C in a muffle furnace at 5°C / min and hold for 1 hour, then heat it to 600°C at the same rate and hold for 4 hours, and then let it cool naturally. (5) Grind and sieve the pyrolysis product, wash it alternately with deionized water and anhydrous ethanol until neutral, and dry it to obtain ZnFe2O4-N co-doped biochar-based magnetic photocatalytic composite material.

2. The preparation method according to claim 1, characterized in that, The biomass raw material is selected from at least one of ginkgo leaves, corn cobs, and walnut shells.

3. A biochar-based magnetic photocatalytic composite material prepared according to the preparation method of claim 1 or 2, characterized in that, It is a biochar composite material co-doped with ZnFe2O4 and nitrogen, which has visible light photocatalytic activity and magnetic separation characteristics.

4. A high-efficiency photocatalytic water treatment device adapted to the biochar-based magnetic photocatalytic composite material of claim 3, characterized in that, This includes the following units that are connected sequentially via pipelines to form a circulation loop: The cyclone dispersion and photocatalytic reaction unit includes a cylindrical light-transmitting reaction chamber with a water inlet pipe tangentially arranged on the side wall, a feed port at the top, and a visible light source inside; The magnetically enhanced cyclone separation unit includes a cylindrical cyclone section and a conical material-gathering section, with electromagnets arranged in layers around the outer periphery of the conical material-gathering section; The closed-loop automatic circulation unit includes a return pipe and a delivery pump located at the bottom of the separation unit, which are used to transport the catalyst slurry captured by the separation unit back to the reaction unit.

5. The high-efficiency photocatalytic water treatment device according to claim 4, characterized in that, The light source in the swirling dispersion and photocatalytic reaction unit is a visible light source, and it is equipped with a power adjustment device.

6. The high-efficiency photocatalytic water treatment device according to claim 4, characterized in that, The electromagnets are arranged in layers along the outer wall of the conical aggregate section, and the magnetic field strength gradually increases from top to bottom, forming a gradient magnetic field from weak to strong.

7. A method for water treatment using the high-efficiency photocatalytic water treatment device according to any one of claims 4-6, characterized in that, include: (a) The biochar-based magnetic photocatalytic composite material of claim 3 is fed into the swirling dispersion and photocatalytic reaction unit, dispersed in the swirling flow formed by tangential water inlet, and the light source is turned on to carry out the photocatalytic reaction; (b) After the reaction, the mixture enters the magnetically enhanced cyclone separation unit, where the photocatalytic composite material is separated and enriched under the coupling effect of centrifugation and gradient magnetic field. (c) The separated water is discharged from the top of the separation unit, captured by the magnetic field and enriched in the photocatalytic composite material at the bottom of the separation unit to form a high-concentration slurry, which is then pumped back to the reaction unit for recycling via the return pipe.

8. The method according to claim 7, characterized in that, In step (a), the organic pollutants in the water include tetracycline antibiotics.

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