Preparation method of bismuth single element / bismuth oxide / carbon nitride composite material and application thereof as chlorine removal agent

Abstract

The application discloses a preparation method of a bismuth single element / bismuth oxide / carbon nitride composite material and application of the bismuth single element / bismuth oxide / carbon nitride composite material as a chlorine removal agent, and the bismuth single element / bismuth oxide / carbon nitride composite chlorine removal agent is prepared by taking bismuth nitrate pentahydrate as raw material and introducing melamine precursor. In the process of calcination, the melamine generates elemental carbon and carbon monoxide, and plays a regulating role in the morphology of the chlorine removal agent; the reducing property generated in the forming process can convert Bi 3+ into Bi single element, and the surface plasmon resonance effect of the Bi single element is utilized to improve the photocatalytic chlorine removal performance of the composite chlorine removal agent.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of materials, and particularly relates to preparation of a bismuth element / bismuth oxide / carbon nitride composite chlorine removal agent. BACKGROUND

[0002] As an important part of wastewater, chloride ions (Cl - ) are difficult to be fully removed due to their characteristics of not being directly degraded by other microorganisms. There are a large number of chloride ions in domestic water, industrial wastewater and ecological environment. Chloride ions in water not only result from human activities, but also are released from nature into human society due to evaporation, water flow, crustal movement and the like. Due to the toxicity and corrosiveness of chloride ions, they cause serious harm to water bodies, vegetation and microorganisms and the like. Industrial circulating cooling water is a typical water body for chloride ion removal technology research. In the “Design Specification for Industrial Circulating Cooling Water Treatment” (GB 50050-2007) issued by China, the Cl - concentration in water in stainless steel equipment, water pipelines and the like is specified to be ≤1000 mg / L. Because of the strong activation performance of chloride ions, they can damage the passivation film of stainless steel, corrode metal equipment and cause safety hazards. In the natural environment, the accumulation of chloride ions in soil can have different effects on different crops. When the concentration of chloride ions in soil is higher than the chlorine tolerance concentration of crops, the crops will show different degrees of poisoning.

[0003] Currently, the principle of removing chloride ions mainly includes two kinds, anion substitution principle and combination with corresponding cations for removal. The commonly used methods for removing chloride ions mainly include bismuth oxide chlorine removal method, chemical precipitation method and ion exchange method and the like. The ion exchange method has a high removal rate, but the concentration of chloride ions to be treated cannot be too high, and it has not been widely used in industrial production. The chemical precipitation method is widely used. The silver chloride precipitation method is the earliest chlorine removal method, which removes chloride ions by generating water-insoluble silver chloride through the reaction of chloride ions and silver ions. However, the price of silver salt is high, and it cannot be widely used. The ultra-high lime aluminum method removes chloride ions in wastewater by the co-precipitation reaction of calcium hydroxide and sodium metaaluminate to form Fred salt. Although the chlorine removal effect is good, a large amount of solid waste is generated in the reaction, which is difficult to handle.

[0004] In recent years, bismuth oxide as a kind of efficient chlorine removal agent is more and more valued by people. Bismuth oxide is dissolved in acid, not dissolved in water and alkali monoclinic crystal. Because of its unique physical and chemical properties, it is widely used in various fields. Because the bismuth oxide of delta crystal form has a cubic prasiolite structure, 1 / 4 of the oxygen ion position in the crystal lattice is vacant, so it has very high oxygen ion conductivity, and is a very potential electrolyte material for solid oxide fuel cell or oxygen sensor. Although the price of bismuth oxide is high, it is still an excellent chlorine removal agent with great market potential because it can be recycled.

[0005] As a new type of two-dimensional material, oxygen-functionalized carbon nitride nanosheet is rich in various active groups such as amino, hydroxyl and carboxyl groups on its surface. These active groups not only provide good adsorption sites for heavy metal ions in wastewater, but also provide active sites for chemical modification. In terms of cost, oxygen-functionalized graphite phase carbon nitride nanosheet has the advantages of easy preparation of raw materials and low price compared with carbon nanotubes and fullerene. Therefore, oxygen-functionalized carbon nitride nanosheet is expected to become an industrialized adsorbent. SUMMARY

[0006] The application discloses preparation of bismuth single element / bismuth oxide / carbon nitride composite chlorine removal agent, and further discloses that the bismuth single element / bismuth oxide / carbon nitride composite material is used as an adsorbent for chlorine ions in wastewater. Bismuth single element / bismuth oxide / carbon nitride composite chlorine removal agent is prepared by using bismuth nitrate pentahydrate as raw material and introducing melamine precursor. 3+ During calcination, elemental carbon and carbon monoxide are generated, which can control the morphology of the chlorine removal agent. The reducing property generated during the formation of the chlorine removal agent can convert Bi into Bi single element, so that the surface plasmon resonance effect of the Bi single element is utilized to improve the photocatalytic chlorine removal performance of the composite chlorine removal agent.

[0007] The technical scheme adopted by the application is as follows:

[0008] The preparation method of the bismuth single element / bismuth oxide / carbon nitride composite material comprises the following steps:

[0009] S1, melamine is added to deionized water and stirred to obtain an A solution;

[0010] S2, bismuth nitrate pentahydrate is dissolved with concentrated nitric acid and heated and stirred until completely dissolved to obtain a B solution;

[0011] S3, the A solution is poured into the completely dissolved B solution, and the pH is adjusted to 8-10 with sodium hydroxide; ultrasonic treatment is performed for 5-10 min; and magnetic stirring is performed for 20-60 min;

[0012] S4, aging: water bath heating at 70-90 DEG C for 6-8 h; centrifugation with anhydrous ethanol three times to remove deionized water and alkali;

[0013] S5, the solid collected after centrifugation is placed in an oven for drying;

[0014] S6, after the sample is dried, it is ground with a mortar and pestle, moved to a crucible and placed in a muffle furnace, and heated at a rate of 5-15℃ / min to 400-600℃ for 2-9h.

[0015] The concentration of the A solution is 10-60g / L.

[0016] The amount of bismuth nitrate pentahydrate added to the B solution is calculated according to the molar ratio of C in the melamine of the A solution to Bi in the B solution of 1:0.3-1.

[0017] The ratio of melamine to bismuth nitrate pentahydrate is added according to the molar ratio C:Bi = 1:0.3-1.

[0018] In S3, the pH is preferably adjusted to 9, ultrasonicated for 5min, and magnetically stirred for 20min.

[0019] In S4, the aging is preferably performed by water bath heating at 80℃ for 8h.

[0020] In S6, the calcination is preferably performed at a rate of 10℃ / min to 550℃ for 6h.

[0021] The bismuth single element / bismuth oxide / carbon nitride composite material prepared by any one of the above preparation methods.

[0022] The bismuth single element / bismuth oxide / carbon nitride composite material, wherein the material is a micron irregular particle, the molar ratio of C:Bi is 0.1:0.03-0.1, and as the relative content of bismuth increases, the irregular particles increase, and prismatic particles begin to appear and have a stacking trend.

[0023] The bismuth single element / bismuth oxide / carbon nitride composite material, wherein the molar ratio of C:Bi is preferably 0.1:0.05.

[0024] The bismuth single element / bismuth oxide / carbon nitride composite material is used as a chlorine removal agent.

[0025] The composite material is added to wastewater for reaction, and a 1000W mercury lamp is used for irradiation during the reaction for 30-60min.

[0026] The composite material is added to wastewater containing chlorine according to the molar ratio Bi 3+ :Cl - =0.5-2:1.

[0027] The S3 step of the application can simultaneously prepare bismuth oxide and carbon nitride oxide.

[0028] The application studies the influence of different molar ratios of C and Bi in melamine and bismuth nitrate pentahydrate on the photocatalytic dechlorination performance; the dechlorination efficiency is determined by comparing the concentration before and after dechlorination, and the best sample is obtained. The results show that under light, the photocatalytic dechlorination efficiency of the composite dechlorination agent (C / Bi-0.05) obtained by the molar ratio of C:Bi of 0.1:0.05 is the most obvious, which is 12.56%, and the overall removal efficiency of chloride ions is 81.35%; while the composite dechlorination agent (C / Bi-0.03) obtained by the molar ratio of C:Bi of 0.1:0.03 has the highest dark reaction and photocatalytic dechlorination efficiency, which are 44.02% and 52.17% respectively. The composite material is characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy spectrum (EDS), transmission electron microscope (TEM) and energy spectrum, X-ray photoelectron spectrometer (XPS), specific surface area (BET) and photoluminescence spectrum (PL). The results show that the bismuth single element / bismuth oxide / carbon nitride composite material of the application is micron irregular particles, and the particle dispersity is relatively good, melamine plays an important role in the morphology of the dechlorination agent in the process of forming g-C3N4, and the g-C3N4 alone shows a wrinkled sheet shape. With the increase of the relative content of bismuth, more irregular particles appear, and prismatic particles begin to appear, and have a stacking trend. Under light conditions, the diffraction peak of BiOCl is sharper, and the purity of the generated BiOCl is higher. The BiOCl nanosheet forms a three-dimensional hierarchical structure between the layers, increases the specific surface area and active centers, and enables the light reflection process to improve the photon utilization rate, further enabling the photocatalyst to generate more photoelectron-hole pairs, thereby improving the photocatalytic activity.

[0029] Advantages:

[0030] Firstly, the application synthesizes a dechlorination agent with the best ratio of bismuth single element / bismuth oxide / carbon nitride composite material, which can separate the photoelectron-hole pairs through the oxidation-reduction reaction of light energy under the photocatalytic effect, and then convert it into chemical energy to form photoelectron-hole pairs, thereby improving the utilization efficiency of photoelectron-hole pairs.

[0031] Secondly, carbon nitride provides many oxygen-containing functional groups and increases the specific surface area of the material, thereby providing more active sites for the determination of chloride ions. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 XRD patterns of different samples, (a) pure g-C3N4; (b) pure Bi2O3; (c) C / Bi-0.1,; (d) C / Bi-0.07; (e) C / Bi-0.05; (f) C / Bi-0.03;

[0033] Figure 2XRD patterns of samples before and after chlorine removal, (a) C / Bi-0.05 chlorine removal under light for 1h, (b) C / Bi-0.05 chlorine removal under dark, (c) C / Bi-0.05.

[0034] Figure 3 SEM observation of the morphology of the prepared product is a 2μm level image, a pure Bi2O3; b C / Bi-0.03; c C / Bi-0.05; d C / Bi-0.07; e C / Bi-0.1; f pure g-C3N4; pure Bi2O3(a) shape is relatively smooth, with the increase of the relative content of bismuth, more irregular particles, starting to appear prismatic particles, and there is a tendency to stack; C / Bi-0.05(c) particles have relatively good dispersion; C / Bi-0.1(e) appears relatively regular rod. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0036] Unless otherwise specifically indicated, the numerical values set forth in these embodiments do not limit the scope of the present application. Techniques, methods, which are known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered as part of the specification where appropriate. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0037] The experimental methods in the following embodiments without specific conditions are generally determined according to national standards; if there is no corresponding national standard, the international standard or the standard requirement proposed by the relevant enterprise is followed. Unless otherwise specified, all parts are weight parts, and all percentages are weight percentages.

[0038] Example 1

[0039] I. Synthesis steps of composite material:

[0040] (1) A solution: 4 parts of 4.20g melamine were weighed into a beaker, 80mL of deionized water was added and stirred;

[0041] (2), B solution: the mass of bismuth nitrate pentahydrate (Bi(NO3)3.5H2O) is respectively: 14.5521g (C: Bi = 0.1:0.03, marked as C / Bi-0.03), 24.2535g (C: Bi = 0.1:0.05, marked as C / Bi-0.05), 33.9549g (C: Bi = 0.1:0.07, marked as C / Bi-0.07), 48.507g (C: Bi = 0.1:0.1, marked as C / Bi-0.1) are placed in a beaker, dissolved with concentrated nitric acid, heated to 25 DEG C, and stirred until completely dissolved;

[0042] (3), C solution: pour the A solution into the completely dissolved B solution, and adjust the pH to 9 with sodium hydroxide (NaOH);

[0043] (4), cover with plastic wrap, and place in an ultrasonic cleaner for 5 min;

[0044] (5), magnetic stirring instrument stirring for 20 min;

[0045] (6), aging: water bath heating at 80 DEG C for 8h;

[0046] (7), anhydrous ethanol centrifugation three times, and remove the deionized water and alkali;

[0047] (8), the collected solid after centrifugation is placed in an oven at 80 DEG C and dried for 8h;

[0048] (9), after the sample is dried, it is ground with a mortar, moved to a crucible, and placed in a muffle furnace, and calcined at a temperature increasing rate of 10 DEG C / min for 6h at 550 DEG C to prepare the bismuth single element / bismuth oxide / carbon nitride composite material.

[0049] The composite material is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy spectrum (EDS), transmission electron microscopy (TEM) and energy spectrum, X-ray photoelectron spectrometer (XPS), specific surface area (BET) and photoluminescence spectrum (PL). The results show that the bismuth single element / bismuth oxide / carbon nitride composite material of the application is micron irregular particles, and the particle dispersity is relatively good.

[0050] The morphology of the prepared sample is observed by SEM, as shown in Figure 3 , which are all 2μm level images, and it can be seen that the composite chlorine removal agent is micron irregular particles, and the g-C3N4 alone shows a wrinkled sheet shape. Figure 3 a) the shape is relatively smooth, with the increase of the relative content of bismuth, more irregular particles appear, and the beginning of the prismatic particles, and there is a stacking trend. C / Bi-0.05 Figure 3 c) the particle dispersity is relatively good; in C / Bi-0.1 Figure 3e) The appearance of more regular rods. By comparing the images of different proportions, it can be seen that melamine plays an important role in regulating the morphology of the chlorine removal agent in the process of forming g-C3N4.

[0051] Example 2 Chlorine removal effect of composite materials with different C:Bi ratios

[0052] (1) C / Bi-0.03Cl - Treatment with a concentration of 600 mg / L:

[0053] Melamine and bismuth nitrate pentahydrate were weighed according to the molar ratio of C:Bi as 0.1:0.03 (denoted as C / Bi-0.03), dissolved and mixed together, and then subjected to ultrasonic treatment, stirring, aging, washing, drying, grinding, and calcination at 450°C for 4h to obtain the composite chlorine removal agent.

[0054] For 25ml Cl - Wastewater with a concentration of 600 mg / L, the chlorine removal agent was added to the wastewater according to the molar ratio Bi 3+ :Cl - = 0.5:1 and reacted for 30 min. After the reaction, solid-liquid separation was performed, and the Cl - concentration of the liquid part was determined. The chlorine removal efficiency of this embodiment under dark conditions was 64.02%.

[0055] Light reaction was based on dark reaction, and a 1000W mercury lamp was turned on during the reaction to irradiate for 30 min. After the reaction, solid-liquid separation was performed, and the Cl - concentration of the liquid part was determined. The chlorine removal efficiency of this embodiment under light conditions was 72.17%.

[0056] (2) C / Bi-0.05Cl - Treatment with a concentration of 3000 mg / L:

[0057] Melamine and bismuth nitrate pentahydrate were weighed according to the molar ratio of C:Bi as 0.1:0.05 (denoted as C / Bi-0.05), dissolved and mixed together, and then subjected to ultrasonic treatment, stirring, aging, washing, drying, grinding, and calcination at 550°C for 6h to obtain the Bi2O3 / g-C3N4 composite chlorine removal agent. For 25ml Cl - Wastewater with a concentration of 3000 mg / L, the chlorine removal agent was added to the wastewater according to the molar ratio Bi 3+ :Cl - = 1:1 and reacted for 1h. After the reaction, solid-liquid separation was performed, and the Cl - concentration of the liquid part was determined. The chlorine removal efficiency of this embodiment under dark conditions was 74.02%.

[0058] The light reaction is based on the dark reaction. A 1000W mercury lamp is turned on during the reaction. After 1h of reaction, solid-liquid separation is performed after the reaction is completed. The Cl - concentration is determined. The dechlorination efficiency of this embodiment under light conditions is 80.7%.

[0059] (3) C / Bi-0.07 Cl - treatment with a concentration of 5000mg / L:

[0060] Melamine and bismuth nitrate pentahydrate are weighed according to the molar ratio of C:Bi as 0.1:0.07 (denoted as C / Bi-0.07), dissolved and mixed together, and then subjected to ultrasonic treatment, stirring, aging, washing, drying, grinding, and calcination at 550°C for 5h to obtain a Bi2O3 / g-C3N4 composite dechlorination agent. The dechlorination agent is added to 25ml of wastewater with a Cl - concentration of 5000mg / L according to the molar ratio Bi 3+ :Cl - =1.5:1, and the reaction is allowed to proceed for 90min. After the reaction is completed, solid-liquid separation is performed, and the Cl - concentration of the liquid part is determined. The dechlorination efficiency of this embodiment under dark conditions is 68.79%.

[0061] The light reaction is based on the dark reaction. A 1000W mercury lamp is turned on during the reaction. After 90min of reaction, solid-liquid separation is performed after the reaction is completed, and the Cl - concentration of the liquid part is determined. The dechlorination efficiency of this embodiment under light conditions is 81.35%.

[0062] (4) C / Bi-0.1 Cl - treatment with a concentration of 10000mg / L:

[0063] Melamine and bismuth nitrate pentahydrate are weighed according to the molar ratio of C:Bi as 0.1:0.1 (denoted as C / Bi-0.1), dissolved and mixed together, and then subjected to ultrasonic treatment, stirring, aging, washing, drying, grinding, and calcination at 600°C for 9h to obtain a Bi2O3 / g-C3N4 composite dechlorination agent. The dechlorination agent is added to 25ml of wastewater with a Cl - concentration of 10000mg / L according to the molar ratio Bi 3+ :Cl - =2:1, and the reaction is allowed to proceed for 120min. After the reaction is completed, solid-liquid separation is performed, and the Cl - concentration of the liquid part is determined. The dechlorination efficiency of this embodiment under dark conditions is 76.48%.

[0064] The light reaction is based on the dark reaction, and a 1000W mercury lamp is turned on during the reaction. After 120 minutes of reaction, solid-liquid separation is performed after the reaction is completed, and the Cl - concentration is measured. The dechlorination efficiency under light conditions in this embodiment is 85.84%.

[0065] A comparative experiment is set up: pure g-C3N4 and pure Bi2O3.

[0066] 600mg / L of NaCl is selected as the simulated wastewater for photocatalytic degradation. The corresponding dark condition is used as a control group. The photocatalytic activity of the composite dechlorination agent is evaluated. In the dark condition: 600ppm of Cl - solution is prepared, the solution is adjusted to pH 1, and the dosage is according to the molar ratio Bi2O3:Cl - =0.5:1, 25mL of the prepared NaCl solution is taken with a pipette and placed in five 50ml glass bottles; 0.1147g (C / Bi-0.03 dechlorination agent), 0.1078g (C / Bi-0.05 dechlorination agent), 0.1023g (C / Bi-0.07 dechlorination agent), 0.0998g (C / Bi-0.1 dechlorination agent), and 0.0985g (Bi2O3 alone) are weighed and added to the five volumetric flasks. Dechlorination is carried out in the dark. 2-3mL of the supernatant is taken at 0min, 10min, 20min, 30min, and 60min. After dechlorination, dilution and filtration are performed to analyze the concentration of Cl in the supernatant by chromatography. In the light condition: the operation steps are the same as in the dark reaction, and light is added, a rotor is added, and a 1000W mercury lamp is turned on. 2-3mL of the supernatant is taken at 0min, 10min, 20min, 30min, and 60min. After dechlorination, dilution and filtration are performed to analyze the concentration of Cl in the supernatant by chromatography. It is found that under both dark and light conditions, the dechlorination effect of the dechlorination agent with different proportions is improved compared with pure Bi2O3. In the dark, the dechlorination effect of C / Bi-0.03 is the best, reaching 44.02%; the dechlorination efficiency of C / Bi-0.05 is 38.79%; when light is introduced, the efficiency of the C / Bi-0.05 sample is improved by 12.56% compared with the dark condition, reaching 51.35%

[0067] Under the condition of no light, part of Bi2O3 generates BiOCl in acidic Cl - solution, and the reaction equation is as follows:

[0068] Bi2O3+6H + →3H2O+2Bi 3+

[0069] 2Bi 3+ +Cl- + H2O → BiOCl↓ + 2H +

[0070] When UV light was introduced, Bi produced surface plasmon resonance effect, electrons overflowed the metal surface to the conduction band of BiOCl, and enhanced the built-in electric field of BiOCl. The generated BiOCl and Bi2O3 / g-C3N4 formed a heterojunction, reacted again, and generated more BiOCl (h + ) holes and Bi2O3 (e - ), the reaction equation is:

[0071] BiOCl / Bi2O3 → BiOCl (h + ) / Bi2O3 (e _ )

[0072] Addition: Figure 1 XRD was used to characterize the phase purity and crystal structure of the prepared samples. The g-C3N4 prepared in the blank sample Figure 1 (a) had a strong peak at 27.5°, which was attributed to the (110) diffraction plane of g-C3N4. The diffraction peaks of Bi2O3 alone belonged to the monoclinic phase (JCPDS 41-1449), and the main peaks at 2θ were 27.5°, 33.3° and 46.4°, corresponding to the (120), (121) and (041) crystal planes. In particular, the peak at 27.5° was very sharp, indicating that the prepared sample had very high crystallinity. In Figure 1 (d-f) new peaks at 24.1°, 30.3° and 32.9° were also observed, which could be attributed to the (200), (212) and (130) crystal planes of the triclinic phase ω-Bi2O3 (JCPDS 50-1088). The formation of ω-Bi2O3 was attributed to the immobilization effect of g-C3N4. During the reduction of Bi2O3, metallic Bi was formed and attached to the surface of g-C3N4, and when exposed to air, Bi was oxidized by O2 in the air, at which time ω-Bi2O3 was formed in preference to α-Bi2O3. The characteristic diffraction peak position of Bi corresponded to Bi (JCPDS 85-1330) at 2θ of 39.7°, 44.7°, 48.8°, corresponding to the (110), (015) and (202) crystal planes. Careful observation of the diffraction peak intensity of Bi showed that the diffraction peak intensity gradually weakened with the decrease of the proportion of C in C / Bi-0.05, C / Bi-0.03 Figure 1 (e, f). This was because the generated C and CO were not enough to reduce a large amount of Bi2O3. The peak intensity of g-C3N4 doped in the synthesized materials at different ratios seemed to be slightly different. The diffraction pattern and peak intensity of C / Bi-0.05 were similar to those of the original Bi2O3, and no significant g-C3N4 peaks were observed.

[0073] Figure 2 BiOCl (JCPDS 73-2060) was observed in the sample after chlorine removal under dark and light conditions, with diffraction peaks at 2θ of 25.9°, 33.5°, 36.665°, 41.005°, corresponding to (011), (012), (003) and (112) crystal planes, respectively. The diffraction peak intensity of Bi2O3 (2θ = 27.392°, (-121) plane) was significantly weakened after chlorine removal, because part of the surface Bi2O3 reacted to form BiOCl, which had a certain impact on the structure. In Figure 3 In (a, b), it can be observed that the diffraction peak of BiOCl under light is sharper, indicating that the purity of BiOCl generated under light is higher.

Claims

1. A method for preparing a bismuth element / bismuth oxide / carbon nitride composite material, characterized in that, The steps include: S1, adding melamine to deionized water and stirring to obtain solution A; S2. Dissolve bismuth nitrate pentahydrate in concentrated nitric acid, heat and stir until completely dissolved to obtain solution B; S3. Pour solution A into solution B that has been completely dissolved, adjust the pH to 8-10 with alkali; sonicate for 5-10 min; stir magnetically for 20-60 min. S4. Aging: Heating in a water bath at 70~90℃ for 6~8 hours; Centrifuge three times with anhydrous ethanol to remove deionized water and alkali; S5. Place the solid collected after centrifugation into an oven to dry; S6. After drying the sample, grind it in a mortar and pestle, transfer it to a crucible and place it in a muffle furnace. Heat the sample to 400-600℃ at a heating rate of 5-15℃ / min and calcine for 2-9 hours.

2. The method for preparing the bismuth element / bismuth oxide / carbon nitride composite material according to claim 1, characterized in that, The concentration of solution A is 10~60g / L.

3. The method for preparing the bismuth element / bismuth oxide / carbon nitride composite material according to claim 1, characterized in that, The mass of bismuth nitrate pentahydrate added to solution B is based on a molar ratio of C in melamine in solution A to Bi in solution B of 1:0.3~1.

4. The method for preparing the bismuth element / bismuth oxide / carbon nitride composite material according to claim 1, characterized in that, In step 6), the temperature is increased to 550 ℃ at a rate of 10 ℃ / min and calcined for 6 h.

5. The bismuth element / bismuth oxide / carbon nitride composite material prepared by any one of the preparation methods of claims 1 to 4.

6. The bismuth element / bismuth oxide / carbon nitride composite material according to claim 5, characterized in that, The material consists of micron-sized irregular particles. As the relative content of bismuth increases, the number of irregular particles increases, and prismatic particles begin to appear, with a tendency to stack.

7. The application of the bismuth element / bismuth oxide / carbon nitride composite material according to claim 5 as a dechlorination agent.

8. The application according to claim 7, characterized in that, The composite material was added to the wastewater for reaction, and the reaction was carried out under the illumination of a 1000 W mercury lamp for 30-60 minutes.

9. The application according to claim 8, characterized in that, The composite material is prepared according to the molar ratio Bi 3+ :Cl - = 0.5~2:1 added to chlorine-containing wastewater.

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