Bismuth oxyhalide / biochar composite material as well as preparation method and application thereof

Abstract

The invention discloses a bismuth oxyhalide / biochar composite material as well as a preparation method and application thereof, and belongs to the technical field of inorganic materials. The preparation method of the bismuth oxyhalide / biochar composite material comprises the following steps: uniformly mixing biochar and an organic solvent, adding a bismuth source and halide salt, and carrying out microwave heating coprecipitation to obtain the bismuth oxyhalide / biochar composite material. The bismuth oxyhalide / biochar composite material prepared by the invention has a good catalytic degradation effect on printing and dyeing wastewater, the degradation balance is basically achieved within 30 minutes, and the degradation rate is up to 96% or above.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inorganic materials, in particular to a bismuth oxyhalide / biochar composite material and a preparation method and application thereof. BACKGROUND

[0002] The bismuth oxyhalide / biochar composite material has strong adsorption performance on organic pollutants, can promote the photocatalytic degradation of the organic pollutants on the surface of the bismuth oxyhalide, and thus can improve the photocatalytic performance of the bismuth oxyhalide. At present, the bismuth oxyhalide / biochar composite material is mostly prepared by a hydrothermal method, specifically, bismuth salt, halide salt and solvent are mixed to form a solution, and the solution is loaded on a MOFs-derived lignocarbon material by a hydrothermal method. However, this method has problems such as high reaction temperature and long reaction time. SUMMARY

[0003] The present application aims to provide a bismuth oxyhalide / biochar composite material and a preparation method and application thereof to solve the problems in the prior art.

[0004] To achieve the above-mentioned purpose, the present application provides the following solutions.

[0005] One of the technical solutions of the present application is a preparation method of a bismuth oxyhalide / biochar composite material, comprising the following steps:

[0006] The bismuth source and the halide salt are added after the biochar and the organic solvent are uniformly mixed, and then microwave heating co-precipitation is performed to obtain the bismuth oxyhalide / biochar composite material.

[0007] Preferably, the preparation method of the biochar comprises the following steps:

[0008] The biomass raw material is pyrolyzed under an inert atmosphere to obtain the biochar.

[0009] Preferably, the biomass raw material comprises corn straw.

[0010] Preferably, the pyrolysis comprises: first, heating at a heating rate of 5-10℃ / min to 300-350℃, and then maintaining the temperature for 0.5-1.0h; and then, heating at a heating rate of 10-20℃ / min to 550-700℃, and then maintaining the temperature for 2.0-4.0h.

[0011] Preferably, the molar ratio of the bismuth source to the halide salt is 1:(1-1.5).

[0012] Preferably, the organic solvent comprises ethylene glycol methyl ether, glycerol, ethylene glycol or ethanol.

[0013] The halide salt comprises sodium halide, potassium halide or hexadecyl trimethyl ammonium halide.

[0014] The halogen in the halogenated salt includes Cl, Br or I;

[0015] The bismuth source includes bismuth sulfide, bismuth oxide, bismuth chloride or bismuth nitrate, and is more preferably bismuth nitrate;

[0016] Preferably, the theoretical mass of the bismuth oxyhalide is calculated based on the molar amount of bismuth in the bismuth source, and the mass ratio of the theoretical mass of the bismuth oxyhalide to the mass of the biochar is controlled to be 1:(0.1-1.5).

[0017] Preferably, the parameter condition of the microwave heating co-precipitation includes: a working frequency of 20MHz-300GHz, an output power of 500-1000W, a reaction temperature of 60-80℃, and a reaction time of 0.5-2h.

[0018] The second technical solution of the present application is a bismuth oxyhalide / biochar composite material prepared by the above preparation method.

[0019] The third technical solution of the present application is an application of the above bismuth oxyhalide / biochar composite material in treatment of printing and dyeing wastewater.

[0020] Preferably, the printing and dyeing wastewater includes methylene blue wastewater.

[0021] Preferably, the application method includes: adding the bismuth oxyhalide / biochar composite material into the printing and dyeing wastewater, and performing a catalytic degradation reaction with a 500W xenon lamp as a light source.

[0022] Preferably, the concentration of pollutants in the printing and dyeing wastewater is 10-50mg / L, the pH value of the printing and dyeing wastewater is 7.0-10.0, and the addition amount of the bismuth oxyhalide / biochar composite material is 0.05-0.5g / L.

[0023] Preferably, the concentration of pollutants in the printing and dyeing wastewater is 20mg / L, the pH value of the printing and dyeing wastewater is 8.0, and the addition amount of the bismuth oxyhalide / biochar composite material is 0.15g / L.

[0024] The present application discloses the following technical effects:

[0025] The method of the present application can reduce the preparation temperature and time of the bismuth oxyhalide / biochar composite material, and realize rapid and efficient preparation of the bismuth oxyhalide / biochar composite material.

[0026] The bismuth oxyhalide / biochar composite material prepared by the present application has good catalytic degradation effect on printing and dyeing wastewater, and basically reaches degradation equilibrium in 30min, with a degradation rate of 96% or above; and the raw materials used in the preparation process of the present application are cheap and easy to obtain, the preparation method is simple, and the present application is convenient for popularization and use. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0028] Figure 1 XRD patterns of the BiOCl / BC composite prepared in Example 1, the BiOBr / BC composite prepared in Example 2, the BiOI / BC composite prepared in Example 3 and the biochar (BC) prepared in Comparative Example 1;

[0029] Figure 2 SEM pattern of the biochar (BC) prepared in Comparative Example 1;

[0030] Figure 3 SEM pattern of the BiOCl / BC composite prepared in Example 1;

[0031] Figure 4 SEM pattern of the BiOBr / BC composite prepared in Example 2;

[0032] Figure 5 SEM pattern of the BiOI / BC composite prepared in Example 3;

[0033] Figure 6 Nitrogen adsorption-desorption curves of the BiOCl / BC composite prepared in Example 1, the BiOBr / BC composite prepared in Example 2, the BiOI / BC composite prepared in Example 3 and the biochar (BC) prepared in Comparative Example 1, wherein (A) is Comparative Example 1, (B) is Example 1, (C) is Example 2 and (D) is Example 3;

[0034] Figure 7 UV-Vis diffuse reflectance spectra of the BiOCl / BC composite prepared in Example 1, the BiOBr / BC composite prepared in Example 2 and the BiOI / BC composite prepared in Example 3;

[0035] Figure 8 Degradation rates of methylene blue of BiOCl prepared in Comparative Example 2, BiOBr prepared in Comparative Example 3 and BiOI prepared in Comparative Example 4;

[0036] Figure 9 Degradation rates of methylene blue of the BiOCl / BC composite prepared in Example 1, the BiOBr / BC composite prepared in Example 2 and the BiOI / BC composite prepared in Example 3. DETAILED DESCRIPTION

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In a first aspect, the present invention provides a method for preparing a bismuth halide / biochar composite material, comprising the following steps:

[0044] (1) Collected corn stalks, take the stem part, wash, cut, crush and soak in potassium hydroxide with a concentration of 1.0-4.0 mol / L for 12.0 h, filter, wash and dry to obtain pretreated corn stalks;

[0045] A certain amount of pretreated corn stalks is weighed in a crucible and placed in a tube furnace under nitrogen protection, first heated to 300-350℃ at a heating rate of 5-10℃ / min, and then heated to 550-700℃ at a heating rate of 10-20℃ / min, and kept for 2.0-4.0h, and then cooled to obtain crude carbon;

[0046] The crude carbon is ground and passed through a 100 mesh sieve to obtain a biochar powder (BC);

[0047] (2) The biochar powder (BC) is mixed with an organic solvent, and then a bismuth source and a halide salt (the halogen in the halide salt is Cl, Br or I) are added and mixed uniformly, and then microwave heating co-precipitation is carried out, and then cooling, filtration, washing and drying are carried out to obtain a bismuth oxyhalide / biochar composite material (BiOX / BC composite material, X=Cl, Br or I).

[0048] Preferably, the molar ratio of the bismuth source to the halide salt is 1:(1-1.5).

[0049] Preferably, the organic solvent includes ethylene glycol methyl ether, glycerol, ethylene glycol or ethanol.

[0050] The halide salt includes sodium halide, potassium halide or cetyltrimethylammonium halide.

[0051] The bismuth source includes bismuth sulfide, bismuth oxide, bismuth chloride or bismuth nitrate, and more preferably bismuth nitrate.

[0052] Preferably, the theoretical mass of bismuth oxyhalide is calculated based on the molar amount of bismuth in the bismuth source, and the mass ratio of the theoretical mass of bismuth oxyhalide to the mass of biochar is controlled to be 1:(0.1-1.5).

[0053] Preferably, the parameter conditions of microwave heating co-precipitation include a working frequency of 20MHz-300GHz, an output power of 500-1000W, a reaction temperature of 60-80℃, and a reaction time of 0.5-2h.

[0054] In a second aspect of the present application, a bismuth oxyhalide / biochar composite material prepared by the above preparation method is provided.

[0055] In a third aspect of the present application, the bismuth oxyhalide / biochar composite material is applied in the treatment of printing and dyeing wastewater.

[0056] Preferably, the printing and dyeing wastewater includes methylene blue wastewater.

[0057] Preferably, the application method includes adding the bismuth oxyhalide / biochar composite material into the printing and dyeing wastewater, and carrying out a catalytic degradation reaction with a 500W xenon lamp as a light source.

[0058] Preferably, the concentration of pollutants in the printing and dyeing wastewater is 10-50 mg / L, the pH value of the printing and dyeing wastewater is 7.0-10.0, and the addition amount of the bismuth oxyhalide / biochar composite material is 0.05-0.5 g / L.

[0059] Preferably, the concentration of pollutants in the printing and dyeing wastewater is 20 mg / L, the pH value of the printing and dyeing wastewater is 8.0, and the addition amount of the bismuth oxyhalide / biochar composite material is 0.15 g / L.

[0060] Example 1

[0061] A preparation method of a bismuth oxyhalide / biochar composite material:

[0062] (1) The collected corn stalks were washed, cut, broken, and then soaked in 2.0 mol / L potassium hydroxide for 12.0 h, filtered, washed, and dried to obtain pretreated corn stalks;

[0063] The pretreated corn stalks were weighed and placed in a crucible, which was then placed in a tube furnace under nitrogen protection. The temperature was first raised to 350℃ at a rate of 5℃ / min, and then raised to 550℃ at a rate of 10℃ / min. After 2.0 h of heat preservation, the crude carbon was obtained after cooling.

[0064] The crude carbon was ground and passed through a 100-mesh sieve to obtain biochar powder (BC).

[0065] (2) 5.20 g of biochar powder (BC) was added to 40 mL of ethylene glycol methyl ether and magnetically stirred until uniform. Then, 9.70 g (0.02 mol) of bismuth nitrate (Bi(NO3)3·5H2O) and 1.49 g of potassium chloride (0.02 mol) were added respectively (the molar ratio of bismuth nitrate to potassium chloride was 1:1, and the mass ratio of biochar to bismuth oxyhalide was 1:1). The mixture was uniformly mixed and co-precipitated by microwave heating. After cooling, filtering, washing (using deionized water and ethanol), and drying, the BiOCl / BC composite material was obtained by grinding into powder.

[0066] The parameters for microwave heating co-precipitation were as follows: working frequency of 1000 MHz, output power of 800 W, reaction temperature of 80℃, and reaction time of 1.0 h.

[0067] Example 2

[0068] A preparation method of a bismuth oxyhalide / biochar composite material:

[0069] (1) The collected corn stalks were washed, cut, broken, and then soaked in 2.0 mol / L potassium hydroxide for 12.0 h, filtered, washed, and dried to obtain pretreated corn stalks;

[0070] The pretreated corn stalks were weighed into a crucible and placed in a tube furnace under nitrogen protection. The temperature was first raised to 350℃ at a rate of 5℃ / min, and then maintained for 0.5h. The temperature was then raised to 550℃ at a rate of 10℃ / min, and then maintained for 2.0h. After cooling, the crude carbon was obtained;

[0071] The crude carbon was ground and passed through a 100 mesh sieve to obtain a biochar powder (BC).

[0072] (2) 6.10g of the biochar powder (BC) was added to 40mL of ethylene glycol methyl ether and magnetically stirred until uniform. Then, 9.70g (0.02mol) of bismuth nitrate (Bi(NO3)3·5H2O) and 2.38g of potassium bromide (0.02mol) were added (the molar ratio of bismuth nitrate to potassium bromide was 1:1, and the mass ratio of biochar to bismuth oxybromide was 1:1). The mixture was uniformly mixed and co-precipitated by microwave heating. After cooling, filtering, washing, and drying, the powder was obtained by grinding. A BiOBr / BC composite material was obtained.

[0073] The parameters for microwave heating co-precipitation were as follows: the working frequency was 1000MHz, the output power was adjusted to 800W, the reaction temperature was controlled at 80℃, and the reaction time was 1.0h.

[0074] Example 3

[0075] A method for preparing a bismuth oxyiodide / biochar composite material:

[0076] (1) The corn stalks were collected, washed, cut, and crushed. The stem part was soaked in a 2.0mol / L potassium hydroxide solution for 12.0h. After filtering, washing, and drying, pretreated corn stalks were obtained.

[0077] The pretreated corn stalks were weighed into a crucible and placed in a tube furnace under nitrogen protection. The temperature was first raised to 350℃ at a rate of 5℃ / min, and then maintained for 0.5h. The temperature was then raised to 550℃ at a rate of 10℃ / min, and then maintained for 2.0h. After cooling, the crude carbon was obtained;

[0078] The crude carbon was ground and passed through a 100 mesh sieve to obtain a biochar powder (BC).

[0079] (2) 7.04 g of biochar powder (BC) was added to 40 mL of ethylene glycol methyl ether and stirred magnetically until uniform, then 9.70 g (0.02 mol) of bismuth nitrate (Bi(NO3)3·5H2O) and 3.32 g of potassium iodide (0.02 mol) were added respectively (the molar ratio of bismuth nitrate to potassium iodide was 1:1, and the mass ratio of biochar to bismuth oxyiodide was 1:1), mixed uniformly, and then microwave heating co-precipitation was performed, followed by cooling, filtration, washing, drying, and grinding into powder to obtain a BiOI / BC composite material.

[0080] The parameter conditions for microwave heating co-precipitation were as follows: the working frequency was 1000 MHz, the output power was adjusted to 800 W, the reaction temperature was controlled at 80°C, and the reaction time was 1.0 h.

[0081] Comparative Example 1

[0082] A method for preparing biochar (BC) comprises the following steps:

[0083] The collected corn stalks were washed, cut, and crushed, and then soaked in 2.0 mol / L potassium hydroxide solution for 12.0 h. After filtration, washing, and drying, pretreated corn stalks were obtained.

[0084] An appropriate amount of pretreated corn stalks was weighed into a crucible and placed in a tube furnace under nitrogen protection. First, the temperature was raised to 350°C at a rate of 5°C / min, and then the temperature was raised to 550°C at a rate of 10°C / min. After 2.0 h of heat preservation, the crude carbon was obtained after cooling.

[0085] The crude carbon was ground and passed through a 100-mesh sieve to obtain biochar powder (BC).

[0086] Comparative Example 2

[0087] A method for preparing BiOCl comprises the following steps:

[0088] 9.70 g (0.02 mol) of Bi(NO3) 3· 5H2O and 1.49 g (0.02 mol) of potassium chloride were added to 40 mL of ethylene glycol methyl ether, and then placed in a microwave oven for microwave heating reaction. After the reaction was completed, the mixture was cooled, filtered, washed, and dried, and then ground into powder to obtain BiOCl powder.

[0089] The parameter conditions for microwave heating reaction were as follows: the working frequency was 1000 MHz, the output power was adjusted to 800 W, the reaction temperature was controlled at 80°C, and the reaction time was 1.0 h.

[0090] Comparative Example 3

[0091] A method for preparing BiOBr comprises the following steps:

[0092] Take 9.70 g (0.02 mol) Bi (NO3) 3· 5H2O and 2.38 g (0.02 mol) potassium bromide, add 40 mL of ethylene glycol methyl ether, make it fully dissolved, then put it into the microwave oven for microwave heating reaction, after the reaction is completed, cool, filter, wash and dry, take out and grind into powder to obtain BiOBr powder.

[0093] Among them, the parameter conditions of microwave heating reaction are: working frequency is 1000 MHz, adjusting output power is 800 W, control reaction temperature is 80℃, and reaction time is 1.0 h.

[0094] Comparative example 4

[0095] A method for preparing BiOI:

[0096] Take 9.70 g (0.02 mol) Bi (NO3) 3· 5H2O and 3.32 g (0.02 mol) potassium iodide, add 40 mL of ethylene glycol methyl ether, make it fully dissolved, then put it into the microwave oven for microwave heating reaction, after the reaction is completed, cool, filter, wash and dry, take out and grind into powder to obtain BiOI powder.

[0097] Among them, the parameter conditions of microwave heating reaction are: working frequency is 1000 MHz, adjusting output power is 800 W, control reaction temperature is 80℃, and reaction time is 1.0 h.

[0098] Example 1

[0099] The XRD patterns of the BiOCl / BC composite material prepared in Example 1, the BiOBr / BC composite material prepared in Example 2, the BiOI / BC composite material prepared in Example 3 and the biochar (BC) prepared in Comparative Example 1 are shown in Figure 1 .

[0100] From Figure 1 It can be seen that the biochar (BC) has no obvious diffraction peak intensity, indicating that the biochar has poor crystallinity and is an amorphous structure, and there is a SiO2 diffraction peak (impurity peak) at 2θ = 26.5°; BiOCl / BC is a typical tetragonal BiOCl (JCPDS 06-0249), BiOBr / BC is a typical tetragonal BiOBr (JCPDS 78-0348) diffraction peak, and BiOI / BC is a typical tetragonal BiOI (JCPDS 73-2062); There is no SiO2 and amorphous carbon peak in the diffraction peak, indicating that the carbon peak is covered by the BiOX peak.

[0101] The SEM pattern of the biochar (BC) prepared in Comparative Example 1 is shown inFigure 2 The SEM image of the BiOCl / BC composite material prepared in Example 1 is shown in Figure 3 The SEM image of the BiOBr / BC composite material prepared in Example 2 is shown in Figure 4 The SEM image of the BiOI / BC composite material prepared in Example 3 is shown in Figure 5 .

[0102] As can be seen from Figures 2 to 5 , the biochar (BC) is amorphous, the BiOCl / BC and BiOBr / BC composite material samples are sheet-like BiOCl and BiOBr entraining biochar, and the biochar is attached to the sheet, and the size of the sheet is about 2-3 μm; the BiOI / BC composite material sample is a flower-like structure assembled by nanosheets, and the diameter is about 5-10 μm.

[0103] The nitrogen adsorption-desorption curves of the BiOCl / BC composite material prepared in Example 1, the BiOBr / BC composite material prepared in Example 2, the BiOI / BC composite material prepared in Example 3, and the biochar (BC) prepared in Comparative Example 1 are shown in Figure 6 , wherein (A) is Comparative Example 1, (B) is Example 1, (C) is Example 2, and (D) is Example 3.

[0104] As can be seen from Figure 6 , the adsorption-desorption value of the biochar is as high as about 500 cm 3 / g, and the adsorption-desorption value of the BiOX / BC is significantly reduced, but in general, the adsorption value of the composite material is maintained at about 100 cm 3 / g.

[0105] The UV-Vis diffuse reflectance spectra of the BiOCl / BC composite material prepared in Example 1, the BiOBr / BC composite material prepared in Example 2, and the BiOI / BC composite material prepared in Example 3 are shown in Figure 7 .

[0106] As can be seen from Figure 7 , the intersection wavelength of the BiOX / BC composite material absorbance curve and the abscissa gradually increases, and the intersection coordinates of the BiOCl / BC and BiOBr / BC absorbance curves are about 350 nm and 620 nm, and the corresponding photon energy is 3.54 ev and 2.0 ev, respectively. After the combination of BiOX and BC, they all move in the direction of increasing wavelength, and the visible excitation light wavelength of BiOI / BC is the largest, and the lower the excitation energy required, the better the visible light catalytic performance.

[0107] Application Example 1

[0108] (1) Take 200 mL methylene blue solution with concentration of 20 mg / L and pH value of 8.0, add BiOCl catalyst prepared in Comparative Example 2 to make the concentration of catalyst 0.15 g / L, then carry out photocatalytic degradation reaction in special photocatalytic reaction instrument (reaction test tube is special quartz material glass tube) with light source of 500 W xenon lamp, take sample at different reaction time, measure and calculate the degradation rate of methylene blue (η = (A0- At) / A0 x 100%, A0 is the initial concentration of methylene blue original solution, mg / L; A is the concentration of methylene blue solution at t, mg / L), draw the curve of degradation rate changing with degradation time, the results are shown in Figure 8 .

[0109] (2) Synchronize with step (1), the difference is only that BiOCl catalyst prepared in Comparative Example 2 is replaced by equal mass of BiOBr prepared in Comparative Example 3, the results are shown in Figure 8 .

[0110] (3) Synchronize with step (1), the difference is only that BiOCl catalyst prepared in Comparative Example 2 is replaced by equal mass of BiOI prepared in Comparative Example 4, the results are shown in Figure 8 .

[0111] (4) Synchronize with step (1), the difference is only that BiOCl catalyst prepared in Comparative Example 2 is replaced by equal mass of BiOCl / BC composite material prepared in Example 1, the results are shown in Figure 9 .

[0112] (5) Synchronize with step (1), the difference is only that BiOCl catalyst prepared in Comparative Example 2 is replaced by equal mass of BiOBr / BC composite material prepared in Example 2, the results are shown in Figure 9 .

[0113] (6) Synchronize with step (1), the difference is only that BiOCl catalyst prepared in Comparative Example 2 is replaced by equal mass of BiOI / BC composite material prepared in Example 3, the results are shown in Figure 9 .

[0114] It can be seen from Figure 8 that when the degradation time is 200 min, the degradation rate of methylene blue by BiOCl is 61.7%, the degradation rate of methylene blue by BiOBr is 94.4%, and the degradation rate of methylene blue by BiOI is 70.3%;

[0115] It can be seen from Figure 9 that when the degradation time is 30 min, the degradation rate of methylene blue by BiOCl / BC composite material is 97.3%, the degradation rate of methylene blue by BiOBr / BC composite material is 96.8%, and the degradation rate of methylene blue by BiOI / BC composite material is 97.5%.

[0116] The above-described embodiments are merely intended to describe the preferred modes of the present application, and are not intended to limit the scope of the present application. Various modifications and improvements of the present application made by those skilled in the art based on the above-described embodiments should fall within the scope of the present application defined by the claims.

Claims

1. A method for preparing a bismuth oxyhalide / biochar composite material, characterized by, The method comprises the following steps: The bismuth oxyhalide / biochar composite material is prepared by mixing the biochar and the organic solvent, adding a bismuth source and a halide salt, and then performing microwave heating co-precipitation.

2. The production method according to claim 1, characterized by, The method for preparing the biochar comprises the following steps: The biochar is prepared by pyrolyzing a biomass raw material in an inert atmosphere.

3. The production method according to claim 2, characterized by, The biomass raw material comprises corn stalks.

4. The production method according to claim 2, characterized by, The pyrolysis comprises the following steps: first, heating at a temperature increasing rate of 5-10℃ / min to 300-350℃, and then maintaining the temperature for 0.5-1.0h; and then, heating at a temperature increasing rate of 10-20℃ / min to 550-700℃, and then maintaining the temperature for 2.0-4.0h.

5. The preparation method according to claim 1, characterized in that, The molar ratio of the bismuth source to the halide salt is 1:(1-1.5).

6. The method of claim 1, wherein, The organic solvent comprises ethylene glycol methyl ether, glycerol, ethylene glycol or ethanol. The halide salt comprises sodium halide, potassium halide or cetyltrimethylammonium halide. The halogen in the halide salt comprises Cl, Br or I. The bismuth source comprises bismuth sulfide, bismuth oxide, bismuth chloride or bismuth nitrate.

7. The production method according to claim 6, wherein The theoretical mass of the bismuth oxyhalide is calculated based on the molar amount of bismuth in the bismuth source, and the mass ratio of the theoretical mass of the bismuth oxyhalide to the mass of the biochar is controlled to be 1:(0.1-1.5).

8. The method of claim 1, wherein, The parameter conditions of the microwave heating co-precipitation comprise the following: a working frequency of 20MHz-300GHz, an output power of 500-1000W, a reaction temperature of 60-80℃, and a reaction time of 0.5-2h. 9.A bismuth oxyhalide / biochar composite material prepared by the method according to any one of claims 1-8. 10.Use of the bismuth oxyhalide / biochar composite material according to claim 9 in the treatment of printing and dyeing wastewater.

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