Preparation method and application of magnetic modified three-dimensional flower-shaped n-bi2o2co3 / g-c3n4 photocatalytic material

Abstract

The application provides a preparation method and application of a magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material and belongs to the technical field of inorganic-organic composite nanomaterial preparation. 2+ and Fe 3+ The magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is obtained through filtering, washing and drying after reaction after the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material prepared in S2 is dispersed into a mixed solution of Fe and Fe, aging under N2 protection, and adjusting the pH to 8-9. The method uses g-C3N4 nanosheets as a sacrifice template, part of the g-C3N4 is peeled off to provide C and N sources under high-temperature alkaline conditions, N-Bi2O2CO3 is in-situ grown on the surface of the g-C3N4 that is not peeled off, a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 binary heterojunction composite material is self-assembled, a template removal process is not needed, and the method has the characteristics of environmental protection, low cost, simple and controllable operation, etc.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of inorganic-organic composite nanomaterials, and particularly relates to a preparation method and application of a magnetic modified three-dimensional flower-shaped N-Bi2O2CO3 / g-C3N4 photocatalytic material. BACKGROUND

[0002] Due to the unique Aurigillius-type layered structure, Bi2O2CO3 is formed by the alternately stacked (Bi2O2) 2+ layer and CO3 2- layer. The layered crystal structure endows Bi2O2CO3 with internal electric field and non-centrosymmetric polarization effect, thereby promoting the separation of photo-induced charges. In addition, the anisotropy of the layered structure will promote the migration of photo-generated carriers along the surface of the material. However, pure Bi2O2CO3 has a relatively wide band gap and only responds to ultraviolet light. Studies have shown that the construction of Bi2O2CO3-based heterojunction composite materials can establish an electric field at the interface, thereby improving the separation and transmission efficiency of photo-generated charges, so it has become one of the classic methods to solve the bottleneck of photocatalysis. From the perspective of charge transfer, interface and material design or synthesis, the traditional Z-type heterojunction has low redox ability for photo-generated electrons and holes, and has obvious limitations. However, the S-type heterojunction system is mainly composed of n-n type semiconductors of oxidizing type photocatalyst and reducing type photocatalyst. In the S-type heterojunction, strong photo-generated electrons and holes are respectively retained in the high reduction CB and strong oxidation VB, and the meaningless photo-generated charge carriers are recombined, introducing a strong oxidation-reduction potential.

[0003] As a metal-free, visible light responsive, covalent binary CN polymer organic semiconductor photocatalyst, g-C3N4 has a 2D layered structure similar to graphene, and has attracted great interest and research enthusiasm in the field of photocatalysis due to its narrow band gap (about 2.7 eV), large specific surface area, unique chemical and optical properties, adjustable structure, excellent thermal and chemical stability, and non-toxicity. At present, various methods have been reported to prepare Bi2O2CO3 / g-C3N4 heterojunction, such as ultrasonic-solvothermal method (CN109261193A), chemical precipitation method and hydrothermal method, etc. These methods usually synthesize two pure substances separately, and then assemble them together to form a heterojunction. This post-synthesis technique leads to poor control between g-C3N4 and Bi2O2CO3. This poor contact control inevitably amplifies the internal resistance, hinders the charge migration, and even seriously limits the photocatalytic stability.

[0004] In recent years, in order to expand the light absorption region of the photocatalyst, improve the utilization rate of sunlight, and enhance the photocatalytic activity, researchers have carried out a lot of work in constructing novel two-dimensional or three-dimensional structures. However, the particle size of the powder photocatalyst is too small during use, which is not conducive to recycling and reuse, hindering its practical application. SUMMARY

[0005] Therefore, the application provides a preparation method and application of a magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material. The method uses g-C3N4 nanosheets as a sacrificial template, and under high-temperature alkaline conditions, part of the g-C3N4 is peeled off to provide C and N sources, and N-Bi2O2CO3 is in-situ grown on the surface of the other g-C3N4 that has not been peeled off to form a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 binary heterojunction composite material. The method does not require a template removal process and has the characteristics of environmental protection, low cost, simple and controllable operation.

[0006] The technical scheme of the application is as follows:

[0007] The application provides a preparation method of a magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material, which comprises the following steps:

[0008] S1, preparing g-C3N4 nanosheets: melamine is calcined at low temperature to obtain g-C3N4 powder, then the g-C3N4 powder is added to anhydrous ethanol, ultrasonic dispersion is performed to make it uniformly dispersed, the upper suspension is taken, and after filtration, washing and freeze-drying, g-C3N4 nanosheets are obtained;

[0009] S2, preparing a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material: g-C3N4 nanosheets prepared in S1 are added to a bismuth nitrate solution to obtain a uniform suspension solution, after adjusting the pH to alkaline, hydrothermal reaction is performed, and then the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is obtained after filtration, washing and drying, which is used as a precursor;

[0010] S3, preparing a magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material: the precursor prepared in S2 is dispersed into a Fe 2+ and Fe 3+ solution, and is aged under inert gas protection, then the pH is adjusted to 9-10, and the magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is obtained after reaction, filtration, washing and drying.

[0011] In an embodiment of the present application, the low-temperature calcination in step S1 is heated to 540-550 °C at a heating rate of 4.0-5.0 °C / min and maintained for 4-5 h.

[0012] In an embodiment of the present application, the bismuth nitrate solution in step S2 is preferably obtained by dissolving bismuth nitrate pentahydrate in a nitric acid solution, wherein the volume ratio of nitric acid in the nitric acid solution is 1 / 9-1 / 10.

[0013] In an embodiment of the present application, the mass ratio of the bismuth nitrate pentahydrate and the g-C3N4 powder in step S2 is less than 5:1.

[0014] In an embodiment of the present application, the hydrothermal reaction in step S2 is carried out at 140-180 °C for 4-16 h.

[0015] In an embodiment of the present application, the aging time in step S3 is 30-60 min.

[0016] In an embodiment of the present application, the mass ratio of Fe3O4 to the N-Bi2O2CO3 / g-C3N4 photocatalytic material in the magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material prepared in step S3 is 0.05:1-0.4:1.

[0017] In an embodiment of the present application, the mass ratio of N-Bi2O2CO3 to g-C3N4 in the magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is preferably 1:10-2:5.

[0018] The present application also provides the use of the above magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material in degrading organic pollutants, wherein the organic pollutants include at least one of printing and dyeing wastewater, pharmaceutical wastewater, and mine wastewater.

[0019] In an embodiment of the present application, the magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is added to the organic pollutants and catalytically decomposed under visible light.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] 1.The method of the present application uses g-C3N4 nanosheets as a sacrificial template, and during the reaction process, part of the g-C3N4 is peeled off under high-temperature alkaline conditions to provide C and N sources, and N-Bi2O2CO3 is in-situ grown on the surface of the other g-C3N4 that has not been peeled off to form a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 binary heterojunction composite material without a template removal process, and the method has the characteristics of environmental protection, low cost, simple and controllable operation, etc.

[0022] 2.The magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material obtained by the present application has the advantages of visible light response, good treatment effect, easy recovery, etc. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 XRD, FTIR, TEM and BET characterization results of g-C3N4 nanosheets prepared in Example 1 of the present application are shown in the following figures:

[0024] Figure 2 XRD characterization results of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials obtained at different pH values in Example 2 of the present application are shown in the following figure:

[0025] Figure 3 XRD and FTIR characterization results of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials obtained at different heat treatment temperatures in Example 3 of the present application are shown in the following figures:

[0026] Figure 4 XRD, FTIR and SEM characterization results of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials obtained at different heat treatment times in Example 4 of the present application are shown in the following figures:

[0027] Figure 5 XRD and FTIR characterization results of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials obtained at different g-C3N4 addition amounts in Example 5 of the present application are shown in the following figures:

[0028] Figure 6 SEM characterization results of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials obtained at different g-C3N4 addition amounts in Example 5 of the present application are shown in the following figure:

[0029] Figure 7XRD, FTIR and SEM characterization results of the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material with different proportions of N-Bi2O2CO3 and g-C3N4 in the embodiment 6 of the present application are shown in the following figures;

[0030] Figure 8 XPS characterization results of g-C3N4, Bi2O2CO3, N-Bi2O2CO3 and NBOC / CN-2 in the embodiment 6 of the present application are shown in the following figures;

[0031] Figure 9 Degradation efficiency of butyl xanthate by g-C3N4, N-Bi2O2CO3, NBOC / CN-1, NBOC / CN-2, NBOC / CN-3, NBOC / CN-4 and Bi2O2CO3 / g-C3N4-2 and degradation effect of butyl xanthate by NBOC / CN-2 in the present application are shown in the following figures;

[0032] Figure 10 XRD and FTIR characterization results of the magnetic modified N-Bi2O2CO3 / g-C3N4 composite material obtained in the embodiment 7 of the present application are shown in the following figures;

[0033] Figure 11 SEM characterization results and S3 element distribution of the magnetic modified N-Bi2O2CO3 / g-C3N4 composite material obtained in the embodiment 7 of the present application are shown in the following figures;

[0034] Figure 12 Magnetic separation and recovery effect of the magnetic modified N-Bi2O2CO3 / g-C3N4 composite material obtained in the embodiment 7 of the present application are shown in the following figures;

[0035] Figure 13 Degradation effect of butyl xanthate by the magnetic modified N-Bi2O2CO3 / g-C3N4 composite material obtained in the embodiment 7 of the present application are shown in the following figures;

[0036] Figure 14 Degradation effect of butyl xanthate by the magnetic modified N-Bi2O2CO3 / g-C3N4 composite material obtained in the embodiment 8 of the present application are shown in the following figures. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0038] Embodiment 1

[0039] Preparation of g-C3N4 nanosheet

[0040] The preparation method is as follows:

[0041] Put 10 g melamine into a clean ceramic crucible, place it in a muffle furnace, heat to 550 °C at a rate of 5 °C / min and keep for 4 h, cool to room temperature, get yellow powder, take out and grind thoroughly with agate mortar, add to a suitable amount of anhydrous ethanol, ultrasonic dispersion, remove the bottom particles and filter the upper suspension, freeze-drying to obtain g-C3N4 nanosheets.

[0042] (B) Test results:

[0043] XRD detection of g-C3N4 nanosheets is shown in (a) of Figure 1 , which shows that g-C3N4 has a strong characteristic peak at 2θ = 27.5 ° and a weak characteristic peak at 13.1 °, corresponding to the (002) and (100) crystal faces of g-C3N4 (JCPDS 87-1526), respectively, the former is caused by the interlayer stacking of aromatic segments, and the latter is caused by the three-S-triazine unit; no other diffraction peaks are found, indicating that g-C3N4 has high purity and crystallinity.

[0044] FTIR detection of g-C3N4 nanosheets is shown in (b) of Figure 1 , which shows that the infrared spectrum of g-C3N4 is divided into two relatively wide absorption bands and one sharp absorption peak: 3000-3400 cm -1 , 1200-1700 cm -1 and 808 cm -1 . The wide absorption peak at 3000-3400 cm -1 is caused by the stretching mode of NH2 or NH groups at the end of aromatic ring defect sites; in addition, the several strong absorption peaks between 1200-1700 cm -1 belong to the stretching vibration peaks of C-N heterocycle (C6N7), and the absorption peak at 808 cm -1 belongs to the typical 3-S-triazine structural unit of g-C3N4; the absorption peak at 890 cm -1 belongs to the N-H deformation mode.

[0045] TEM detection of g-C3N4 nanosheets is shown in (c) of Figure 1 , which shows that the g-C3N4 after ultrasonic exfoliation and freeze-drying is in the form of nanosheets.

[0046] BET detection of g-C3N4 nanosheets is shown in (d) of Figure 1 , which shows that the specific surface area of g-C3N4 is 63.24 m 2Figure 6 shows the N2adsorption-desorption isotherms of the as-prepared N- Bi2O2CO3 / g-C3N4 photocatalytic materials. The isotherms exhibit a typical type IV isotherm with a H1 hysteresis loop, indicating the presence of mesoporous structure. The inset is the pore size distribution based on the Barrett-Joyner-Halenda (BJH) method, and it is observed that the pore size of the as-prepared N-Bi2O2CO3 / g-C3N4 photocatalytic material is mainly concentrated in 3.7 nm, and it is speculated that these small mesopores are derived from the gap between the nanosheets.

[0047] Example 2

[0048] Influence of pH on the preparation of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials

[0049] Three clean beakers were prepared, and 0.5 g of Bi(NO3)3·5H2O and 20 mL of dilute nitric acid solution (volume ratio 1:10) were added, respectively, and ultrasonic dispersion was performed for 30 min to make it completely dissolved, then 1 g of g-C3N4 nanosheet was added, respectively, and NaOH (1 M) was used to adjust the pH value to 1, 8, and 13, respectively, and then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel reaction kettle, and then constant volume was performed to 70 %, and then placed in a constant temperature drying box and reacted at 180 °C for 10 h, and then cooled to room temperature, and then the obtained product was filtered, washed, and dried to obtain a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material, and the XRD characterization results thereof are shown in Figure 2 .

[0050] As can be seen from Figure 2 : when no sodium hydroxide solution is added to adjust the pH value, the pH value of the system is 1, and the obtained product has X-ray diffraction peaks at 10.23°, 31.38°, and 42.15°, which correspond to the (002), (114), and (008) crystal planes of Bi2O2(OH)NO3 (JCPDS No. 74-9823), respectively. When the sodium hydroxide solution is added dropwise to control the pH value of the system to 8, the XRD characterization results of the obtained product show that obvious X-ray diffraction peaks are observed at 2θ = 12.93°, 23.90°, 26.03°, 30.25°, 32.72°, 35.31°, 42.29°, 46.96°, 52.22°, and 56.89°, which correspond to the (002), (011), (004), (013), (110), (112), (114), (020), (116), and (123) crystal planes of Bi2O2CO3 (JCPSD No. 41-1488, a = 3.865 Å, b = 3.865 Å, c = 13.675 Å), respectively. When the pH value is further increased to 13, no new characteristic peaks are observed, indicating that the obtained product has high purity; in addition, it is observed that the intensity of the (004) crystal plane is enhanced with the increase of the pH value, indicating that the increase of the pH value of the system is beneficial to the growth of the (004) crystal plane of the product.

[0051] Example 3

[0052] Influence of heat treatment temperature on preparation of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material

[0053] Five clean beakers were prepared, 0.5 g of Bi(NO3)3·5H2O and 20 mL of dilute nitric acid solution (volume ratio 1:9) were added respectively, and ultrasonic dispersion was carried out for 30 min to make it completely dissolved, then 1 g of g-C3N4 nanosheet was added respectively, NaOH (1M) was used to adjust the pH value to 8, then it was transferred to a 100 mL polytetrafluoroethylene lined stainless steel reactor, and the volume was adjusted to 70 %, and then it was put into a constant temperature drying oven and reacted at 100 °C, 120 °C, 140 °C, 160 °C and 180 °C respectively for 10 h, after cooling to room temperature, the obtained product was filtered, washed and dried to obtain three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material, and the XRD and FTIR characterization results are shown as (a) and (b) in Figure 3

[0054] It can be seen from Figure 3 that the X-ray diffraction peaks of the product obtained at 100 °C at 10.31 °, 20.71 °, 23.88 °, 25.54 °, 28.11 °, 31.37 ° and 33.58 ° correspond to the (002), (004), (111), (112), (113), (114) and (021) crystal faces of Bi2O2(OH)NO3 (JCPDS No. 74-9823) respectively. As the temperature rises to 140 °C, the characteristic peak intensity of g-C3N4 at 27.5° decreases, and new characteristic peaks appear at 2θ = 12.93 °, 23.90 °, 26.03 °, 30.25 °, 32.72 °, 35.31 °, 42.29°, 46.96 °, 52.22 ° and 56.89 °, which correspond to the (002), (011), (004), (013), (110), (112), (114), (020), (116) and (123) crystal faces of tetragonal Bi2O2CO3 (JCPSD No. 41-1488, a = 3.865 Å, b = 3.865 Å, c = 13.675 Å) respectively, indicating that part of g-C3N4 as a sacrificial template is hydrolyzed to generate CO3 2- under alkaline hydrothermal conditions, and through ion exchange, replaces NO3 - ​N-Bi2O2CO3 / g-C3N4 heterojunction was obtained by in-situ growth of Bi2O2CO3 on the surface of g-C3N4. When the temperature continued to rise to 160 °C, the peak intensity gradually increased, and the peak position did not change, indicating that the crystallinity of the generated N-Bi2O2CO3 increased and no impurities were generated. The FTIR of g-C3N4 was divided into two relatively wide absorption bands and one sharp absorption peak: 3000-3400 cm -1 , 1200-1700 cm -1 , and 808 cm -1 . The wide absorption peak at 3000-3400 cm -1 was caused by the stretching mode of the terminal NH2 or NH group of the aromatic ring defect site; in addition, the dense absorption band region between 1200-1700 cm -1 belongs to the stretching vibration of C-N heterocyclic (C6N7) units, and the absorption peak at 808 cm -1 belongs to the typical 3-S-triazine structure unit of g-C3N4; the absorption peak at 890 cm -1 belongs to the N-H deformation mode. For Bi2O2CO3, the absorption band at 846 cm -1 corresponds to the out-of-plane bending mode of CO3 2- , the absorption peaks at 1391 cm -1 and 1468 cm -1 belong to the anti-symmetric vibration mode of CO3 2- , 1068 cm -1 belongs to the symmetric stretching vibration mode of CO3 2- , and the relatively wide absorption in the range of 3000 cm -1 to 3500 cm -1 is attributed to the -OH functional group and physically adsorbed water.

[0055] Example 4

[0056] Influence of heat treatment time on the preparation of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials

[0057] Five clean beakers were prepared, 0.5 g Bi(NO3)3·5H2O and 20 mL dilute nitric acid solution (volume ratio 1:9) were added respectively, and ultrasonic dispersion was carried out for 30 min to make it completely dissolved, then 1 g of g-C3N4 nanosheet was added respectively, NaOH (1M) was used to adjust the pH value to 8, then it was transferred to a 100 mL polytetrafluoroethylene lined stainless steel reactor, and the volume was adjusted to 70%, and then it was put into a constant temperature drying oven and reacted at 160 °C for 1 h, 4 h, 8 h, 12 h and 16 h respectively. After cooling to room temperature, the obtained product was filtered, washed and dried to obtain a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material, and the XRD and FTIR characterization results are shown in Figure 4 Fig. 1.

[0058] The SEM characterization results of the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material are shown in Figure 4 Fig. 2, wherein Fig. 2(c) is the thermal reaction time of 1 h, Fig. 2(d) is the thermal reaction time of 4 h, Fig. 2(e) is the thermal reaction time of 8 h, Fig. 2(f) is the thermal reaction time of 12 h, and Fig. 2(g) is the thermal reaction time of 16 h.

[0059] From Figure 4 It can be seen that: the product obtained by hydrothermal reaction for 1 h is located at 10.31 °, 20.71 °, 23.88 °, 25.54 °, 28.11 °, 31.37 ° and 33.58 °, which corresponds to (002), (004), (111), (112), (113), (114) and (021) crystal faces of Bi2O2(OH)NO3 (JCPDS No. 74-9823) respectively. As the hydrothermal reaction time is prolonged to 4 h, 2θ=12.93°, 23.90°, 26.03°, 30.25°, 32.72°, 35.31°, 42.29°, 46.96°, 52.22° and 56.89°, which corresponds to (002), (011), (004), (013), (110), (112), (114), (020), (116) and (123) crystal faces of tetragonal Bi2O2CO3 (JCPSD No. 41-1488, a=3.865 Å, b=3.865 Å, c=13.675 Å) crystal respectively. When the reaction time is further prolonged to 12 h, a weak small peak appears at 2θ=6.27°, which corresponds to (001) crystal face, indicating that the crystallinity of g-C3N4 nanorod is higher than that of g-C3N4 nanosheet. Figure 4b is the infrared spectrum of the product obtained at different temperatures, the FTIR of g-C3N4 is divided into two relatively wide absorption bands and one sharp absorption peak: 3000-3400 cm -1 , 1200-1700 cm -1 and 808 cm -1 . The wide absorption peak at 3000-3400 cm -1 is caused by the stretching mode of the terminal NH2 or NH group of the aromatic ring defect site; in addition, several strong absorption peaks between 1200-1700 cm -1 belong to the stretching vibration peaks of C-N heterocycle (C6N7), and the absorption peak at 808 cm -1 belongs to the typical 3-S-triazine structural unit of g-C3N4; the absorption peak at 890 cm -1 belongs to the N-H deformation mode. For Bi2O2CO3, the absorption peaks at 1391 cm -1 and 1468 cm -1 belong to the anti-symmetric vibration V3 mode of CO3 2- , 1068 cm -1 and 846 cm -1 belong to the symmetric stretching vibration V1 mode and the out-of-plane bending V2 mode of CO3 2- , and the relatively wide absorption in the range of 3000 cm -1 to 3500 cm -1 is attributed to the -OH functional group and physically adsorbed water. Figure 4 (c-g) are the morphology diagrams of the materials prepared at different hydrothermal treatment times, and it is observed that with the extension of the hydrothermal treatment time, three-dimensional flower-like structures assembled by nanosheets are gradually formed.

[0060] Example 5

[0061] Influence of g-C3N4 Nanosheet Addition Amount on the Preparation of Three-dimensional Flower-like N-Bi2O2CO3 / g-C3N4 Photocatalytic Materials

[0062] Four clean beakers were prepared, and 0.5 g of Bi(NO3)3·5H2O and 20 mL of dilute nitric acid solution (volume ratio 1:9) were added to each beaker respectively. The mixtures were ultrasonically dispersed for 30 min to ensure complete dissolution. The amount of g-C3N4 nanosheets added was then controlled to be 0.1 g, 0.2 g, 0.3 g, and 0.5 g, respectively. The pH was adjusted to 8 using NaOH (1 M). The mixtures were then transferred to a 100 mL stainless steel reactor lined with polytetrafluoroethylene, and the volume was brought to 70%. The reactor was placed in a constant temperature drying oven and reacted at 160 °C for 8 h. After cooling to room temperature, the resulting product was filtered, washed, and dried to obtain a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material. The XRD and FTIR characterization results are shown in the figures below. Figure 5 (a) and (b) in the figure. Their SEM characterization results are shown in [reference needed]. Figure 6 As shown in (a), (b), (c), and (d) of the figure, the amount of g-C3N4 nanosheets added in Figure (a) is 0.1 g, the amount of g-C3N4 nanosheets added in Figure (b) is 0.2 g, the amount of g-C3N4 nanosheets added in Figure (c) is 0.3 g, and the amount of g-C3N4 nanosheets added in Figure (d) is 0.5 g.

[0063] Depend on Figure 5 and Figure 6 It can be seen that when the amount of g-C3N4 added is 0.1 g, the diffraction peaks of the product at 2θ=12.93 °, 23.90 °, 26.03 °, 30.25 °, 32.72 °, 35.31 °, 42.29 °, 46.96 °, 52.22 ° and 56.89 ° are observed, which correspond one-to-one with the (002), (011), (004), (013), (110), (112), (114), (020), (116) and (123) crystal planes of tetragonal Bi2O2CO3 (JCPSD No.41-1488) crystal. The diffraction peaks are sharp and no other diffraction peaks are detected, indicating that the obtained product has high purity and good crystallinity. It is noteworthy that when the amount of g-C3N4 added increased to 0.2 g, other diffraction peaks were gradually observed to form. Furthermore, as the amount of g-C3N4 added further increased, the positions of the diffraction peaks remained unchanged, but their intensities increased. (See details...) Figure 5 a. Figure 5b is the FT-IR characterization result of the product obtained at different g-C3N4 addition amounts, it can be found that when the addition amount of g-C3N4 is 0.1 g, the functional groups of the obtained product correspond well to the characteristic functional groups of Bi2O2CO3; with the increase of the addition amount of g-C3N4, the characteristic absorption peak of g-C3N4 is gradually detected. To further prove the above analysis, a certain amount of g-C3N4 can be completely decomposed under alkaline hydrothermal conditions to provide carbon source for the generation of Bi2O2CO3; in addition, after reaching the dissolution equilibrium, nanorod-shaped g-C3N4 is obtained by recrystallization. Figure 6 a clearly shows that N-Bi2O2CO3 is in the form of nanosheet with a thickness of about 35.6 nm. With the increase of the addition amount of g-C3N4, the nanosheets gradually gather together, and when the addition amount of g-C3N4 reaches 0.5 g, three-dimensional flower-shaped product can be observed. It is shown that under strong alkaline hydrothermal conditions, part of g-C3N4 can be completely peeled off to generate nanosheet-shaped N-Bi2O2CO3. With the increase of the addition amount of g-C3N4, a part of g-C3N4 which is not peeled off provides growth points for in-situ growth of N-Bi2O2CO3, and then three-dimensional flower-shaped structure is obtained.

[0064] Example 6

[0065] Preparation of three-dimensional flower-shaped N-Bi2O2CO3 / g-C3N4 photocatalytic material

[0066] Four clean beakers were prepared, different amounts of Bi(NO3)3·5H2O and 20 mL dilute nitric acid solution (volume ratio 1:9) were added respectively, and ultrasonic dispersion was carried out for 30 min to make it completely dissolved, then 1 g of g-C3N4 nanosheet was added, NaOH (1 M) was used to adjust the acid-base degree of the solution to control pH=8, then it was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel reaction kettle, and the volume was adjusted to 70%, and then it was put into a constant temperature drying box and reacted at 160 °C for 8 h. After cooling to room temperature, the obtained product was filtered, washed and dried, and named as NBOC / CN-1, NBOC / CN-2, NBOC / CN-3 and NBOC / CN-4, respectively, corresponding to the mass ratio of N-Bi2O2CO3:g-C3N4 in the product being 10%, 20%, 30% and 40%, respectively. The XRD and FTIR characterization results of the product and the control are shown in (a) and (b) of Figure 7 , the SEM characterization structure is shown in (c), (d), (e), (f) of Figure 7 , wherein (c) corresponds to NBOC / CN-1, (d) corresponds to NBOC / CN-2, (e) corresponds to NBOC / CN-3, and (f) corresponds to NBOC / CN-4.

[0067] In this example, g-C3N 4、 N-Bi2O2CO3、 Bi₂O₂CO₃ was used as a control, and g-C₃N₄ was derived from Example 1. N-Bi₂O₂CO₃ 3、 The preparation method of Bi2O2CO3 is as follows:

[0068] Preparation of pure N-Bi2O2CO3

[0069] The experiment on the effect of the amount of g-C3N4 nanosheets added in Example 5 shows that when the amount of g-C3N4 added is controlled within 0.1 g and other conditions remain unchanged, pure N-Bi2O2CO3 can be obtained. The specific preparation method of pure N-Bi2O2CO3 in this example is as follows:

[0070] Add 0.5 g Bi(NO3)3·5H2O and 20 mL dilute nitric acid solution (volume ratio 1:9), and ultrasonically disperse for 30 min to completely dissolve. Then control the amount of g-C3N4 nanosheets added to 0.1 g, and adjust the pH of the solution with NaOH (1 M) to control pH=8. Then transfer to a 100 mL polytetrafluoroethylene-lined stainless steel reactor, make up to 70% volume, and place in a constant temperature drying oven to react at 160°C for 8 h. After cooling to room temperature, the obtained product is filtered, washed, and dried to obtain pure N-Bi2O2CO3.

[0071] Preparation of pure Bi2O2CO3

[0072] Add 0.5 g Bi(NO3)3·5H2O and 20 mL dilute nitric acid solution (volume ratio 1:9), and ultrasonically disperse for 30 min to completely dissolve. Then add 0.1 g sodium carbonate, and adjust the pH to 8 with NaOH (1 M). Transfer to a 100 mL polytetrafluoroethylene-lined stainless steel reactor, bring the volume to 70%, and place in a constant temperature drying oven at 160 °C for 8 h. After cooling to room temperature, filter, wash, and dry the product to obtain pure Bi2O2CO3.

[0073] Depend on Figure 7It can be seen that for Bi2O2CO3, all the diffraction peaks match with pure tetragonal Bi2O2CO3 (JCPDS No. 41-1488); and for g-C3N4, the diffraction peaks match with g-C3N4 (JCPDS 87-1526). By comparing the XRD patterns of N-Bi2O2CO3 and Bi2O2CO3, it can be seen that the diffraction peak of N-Bi2O2CO3 at (110) is enhanced, indicating that N-Bi2O2CO3 grows preferentially along the (110) crystal plane. The XRD pattern of NBOC / CN-1 can simultaneously retrieve the two typical diffraction peaks of Bi2O2CO3 and g-C3N4; however, with the increase of the mass ratio of Bi2O2CO3, the characteristic peaks of g-C3N4 cannot be observed in the XRD patterns of NBOC / CN-3 and NBOC / CN-4. In order to further prove that NBOC / CN-3 and NBOC / CN-4 contain both Bi2O2CO3 and g-C3N4, the functional groups of the series of products were characterized by FTIR, and the results are shown in FIG. 6b. The results show that N-Bi2O2CO3 / g-C3N4 has several strong absorption peaks between 1000-1700 cm-1, which belong to the stretching vibration peaks of C-N heterocyclic (C6N7); the absorption peak at 808 cm-1 belongs to the typical 3-S-triazine structure unit of g-C3N4; the absorption peak at 890 cm-1 belongs to the N-H deformation mode; and the absorption peaks between 3100-3400 cm-1 belong to the N-H and C-OH groups. In addition, with the increase of the mass ratio of Bi2O2CO3, the Bi-O absorption peak is gradually observed. Figure 7 -1 -1 -1 -1 Figure 7 (c-f) are the morphology diagrams of the series of N-Bi2O2CO3 / g-C3N4, and with the increase of the mass ratio of Bi2O2CO3, the product gradually assembles from nanosheet to three-dimensional flower-like structure, and further grows to form microspheres with a diameter of about 4.5 um. Based on the above experimental results, it is proved that a part of g-C3N4 is destroyed by strong alkali during the hydrothermal treatment process, providing carbon source for the formation of CO3 2-

[0074] Figure 8 ​​​​​​a are the XPS survey spectra of g-C3N4, Bi2O2CO3, N-Bi2O2CO3 and NBOC / CN-2, where the XPS survey spectrum of Bi2O2CO3 only shows the characteristic peaks of Bi, C and O. While for NBOC / CN-2, the characteristic peaks of Bi, C, N and O elements are observed at 162.2 eV, 286.3 eV, 398.5 eV and 531.4 eV, respectively, and no other element signal is detected, indicating that only these four elements are contained in NBOC / CN-2. It is worth noting that by comparing the survey spectra of Bi2O2CO3 and N-Bi2O2CO3, it can be found that a weak N 1s characteristic peak appears near 400 eV for N-Bi2O2CO3, while there is no such peak for pure Bi2O2CO3, which is more obvious by comparing the local enlarged figures, indicating that N is doped in-situ into N-Bi2O2CO3 during the hydrothermal treatment process, and the doped N will replace the oxygen atoms in the Bi2O2CO3 lattice, which will change the band structure of Bi2O2CO3. The surface atomic concentration of doped nitrogen is 1.08% determined by XPS, and the existence of N in N-Bi2O2CO3 is further confirmed by elemental analysis, and the determined concentration is 0.82%, which is slightly lower than the calculated value by XPS, which can be attributed to the fact that XPS is a measurement technique mainly used for surface characterization. Since the doped nitrogen element comes from the sacrificial template g-C3N4, the concentration of doped nitrogen can be adjusted by controlling the amount of g-C3N4 added. In addition, the XPS survey spectrum of g-C3N4 shows a weak O 1s characteristic peak near 531.4 eV in addition to the characteristic peaks of C and N, which is attributed to the adsorbed water or oxygen molecules on the surface of the material. Figure 8 (b-e) are high-resolution spectra of different elements, wherein Figure 8 b is the Bi 4f high-resolution XPS spectrum, the two strong peaks centered at 159.3 eV and 164.6 eV are attributed to Bi 4f 7 / 2 and Bi 4f 5 / 2 , respectively, corresponding to the characteristic peaks of Bi 3+ in Bi2O2CO3. The binding energy drifts to different degrees are observed in N-Bi2O2CO3 and NBOC / CN-2, which can be attributed to the change of internal electron density caused by N doping and heterojunction formation. In addition, compared with N-Bi2O2CO3, the Bi 4f 7 / 2 and Bi4f 5 / 2 peaks of the sample of NBOC / CN-2 have a positive shift to high binding energy, indicating that the electron density around the Bi element in the NBOC / CN-2 sample is lower, which is caused by the interaction between g-C3N4 and N-Bi2O2CO3, which is consistent with the FT-IR spectrum in which the peak at 554 cm -1The red shift of the Bi-O bond is consistent. The C 1s high-resolution XPS spectra (8c) show that the C1s peak around 284.8 eV in all samples is attributed to adventitious carbon species in the XPS measurement. The peak at 288.2 eV in g-C3N4 is identified as sp2 hybridized carbon (N-C=N) in the g-C3N4 matrix, while the C 1s peaks centered at 288.7 eV and 288.8 eV in N-Bi2O2CO3 and NBOC / CN-2 samples can be attributed to the carbonate ion in the samples. Compared with pure g-C3N4 and N-Bi2O2CO3, the C 1s binding energy of NBOC / CN-2 sample shows a positive shift, further confirming the change of CO3 2 bond during the in-situ preparation of N-Bi2O2CO3 / g-C3N4 using g-C3N4 as a sacrificial template. 2- Figure 8 d The N 1s high-resolution XPS spectra show that the N 1s peak around 398.7 eV can be attributed to sp2 hybridized aromatic nitrogen (C=N-C) bonded to carbon atoms, while the N 1s peak around 400 eV can be attributed to tertiary nitrogen N-(C)3 group or H-N-(C)2 group, respectively, and the weak peak around 405 eV can be attributed to the excitation charge effect (Long et al. 2014; Wang et al. 2016). Compared with pure g-C3N4, the N 1s peak corresponding to sp2 hybridized aromatic N bonded to carbon atoms (C-N=C) has a positive shift to high binding energy, which can be attributed to the interaction between the N atom of C-N=C and the C atom of CO3 2- in the N-Bi2O2CO3 / g-C3N4 sample. Figure 8 e The O 1s high-resolution XPS spectra of Bi2O2CO3 can be fitted into two peaks at 530.0 eV and 531.0 eV, where the peak at 530.0 eV can be attributed to the Bi-O bond of Bi2O2CO3, and the peak at 531.0 eV is caused by the carbonate species, adsorbed H2O on the surface or surface hydroxyl groups. It is noted that N-Bi2O2CO3 and NBOC / CN-2 can be fitted into three peaks at 529 eV, 530 eV and 531 eV, which can be attributed to the fact that the doped N replaces the oxygen atom in the Bi2O2CO3 lattice, which is beneficial to promote photocatalytic activity. It is noted that the O 1s binding energy in NBOC / CN-2 has a positive shift compared with N-Bi2O2CO3, indicating that the density of the electron cloud around the O atom is reduced, which is due to the electron-withdrawing effect of the -C≡N triple bond of g-C3N4, and the interface formed in the heterojunction is beneficial to the effective separation and transfer of carriers, resulting in the reduction of the electron cloud around the O atom. The DOS of the valence band (VB) is shown in Fig. 8f. Figure 8 ​f, it is interesting to observe an additional diffused electronic state above the valence band maximum (VBM) on the VB edge for N-Bi2O2CO3 compared to Bi2O2CO3, which indicates the presence of a midgap above the VB. The formation of the midgap can be attributed to the in-situ nitrogen doping, which changes the band structure of Bi2O2CO3. The newly formed midgap between the VB and the conduction band (CB) can shift the light absorption spectrum of the nitrogen-doped three-dimensional flower-like N-Bi2O2CO3 microspheres towards the visible light.

[0075] Comparative Example 1

[0076] Referring to the preferred embodiment of the preparation of Bi2O2CO3 / g-C3N4-2 flower-like composite photocatalyst in Chinese patent CN109261193A, the preparation method is as follows:

[0077] 1. Put 6 g of melamine into a 50 mL corundum crucible, heat to 550 °C in a muffle furnace at a heating rate of 5 °C / min, and calcine for 4 h to obtain a light yellow powder of g-C3N4 with amorphous nanoparticles.

[0078] 2. Weigh 0.485 g of bismuth nitrate pentahydrate and dissolve it in a mixed solution of 24 mL of ethylene glycol and 6 mL of deionized water. Stir at room temperature until clear to obtain a bismuth carbonate precursor solution.

[0079] 3. Add 0.5 g of g-C3N4 nano powder prepared in step 1 to the bismuth carbonate precursor solution obtained in step 2, and ultrasonic for 1 h to obtain a uniformly mixed suspension.

[0080] 4. Transfer the suspension obtained in step 3 to a 100 mL polytetrafluoroethylene-lined stainless steel reaction kettle, place it in a constant temperature drying oven at 180 °C for 12 h. After the reaction is completed, naturally cool to room temperature, and the precipitate is washed with water and anhydrous ethanol for 3 times each, then dried at 80 °C for 12 h. The obtained product is named as Bi2O2CO3 / g-C3N4-2.

[0081] Respectively, 50 mg of g-C3N4 (preparation method of Example 1), N-Bi2O2CO3 (preparation method of Example 6), Bi2O2CO3 / g-C3N4-2 (preparation method of Comparative Example 1), NBOC / CN-1, NBOC / CN-2, NBOC / CN-3, NBOC / CN-4 (preparation method of Example 6) were added to 50 mL of butyl xanthate solution (30 mg / L), respectively, and the degradation effect was investigated in a photoreactor, and the results are as follows Figure 9As shown in the figure, it can be seen that the degradation efficiency of butyl xanthate under the action of NBOC / CN-2 is the highest. The degradation rate of butyl xanthate under the action of NBOC / CN-2 is 82.14% after visible light irradiation for 60 minutes, and the degradation rate of butyl xanthate under the action of Bi2O2CO3 / g-C3N4-2 is 66.34%. Figure 9 b shows the change of the ultraviolet-visible absorption intensity of butyl xanthate at 301 nm under the action of NBOC / CN-2 with the light irradiation time, indicating that NBOC / CN-2 has good photocatalytic degradation performance on butyl xanthate under visible light irradiation.

[0082] Example 7

[0083] Preparation of magnetic modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material

[0084] Different masses of FeCl3·6H2O were dissolved in deionized water, and the volume was made to 1 L to obtain solution A; different masses of FeCl2·4H2O were dissolved in deionized water, and the volume was made to 1 L to obtain solution B; a clean two-necked flask was taken, 1 g of NBOC / CN-2 prepared in Example 6 was added, 50 mL of solution A and 50 mL of solution B were added in turn, N2 was introduced and the air was continuously stirred to exhaust, the whole system was aged for 30 min under N2 protection, so that Fe 3+ and Fe 2+ ions were fully adsorbed on the surface of NBOC / CN-2, then NaOH (2 M) solution was added dropwise to the mixed solution under stirring to adjust pH=10, the obtained product was filtered, washed and dried, and according to the Fe3O4 material ratio of 5%, 10%, 20%, 30% and 40%, the corresponding products were named as S1, S2, S3, S4 and S5, and the XRD and FTIR characterization results are shown in Figure 10 , the SEM characterization results are shown in Figure 11 , wherein, Fig. (a), Fig. (b), Fig. (c), Fig. (d), Fig. (e) and Fig. (f) respectively represent the morphology of NBOC / CN-2 (prepared in Example 6), S1, S2, S3, S4 and S5, Fig. (g) is an element distribution diagram, and Fig. (h), Fig. (i), Fig. (j), Fig. (k) and Fig. (l) respectively represent the distribution of elements Bi, C, N, O and Fe in sample S3, and the magnetic separation of different products is shown in Figure 12 , wherein, the right sample bottles in Fig. (a), Fig. (b), Fig. (c), Fig. (d), Fig. (e) respectively represent the magnetic separation of S1, S2, S3, S4 and S5, and the left sample bottles represent the magnetic separation of NBOC / CN-2.

[0085] Weigh out 50 mg each of g-C3N4 (prepared by Example 1), N-Bi2O2CO3 (prepared by Example 6), and NBOC / CN-2 (prepared by Example 6, N-Bi2O2CO3). 3 / g-C3N4), S1, S2, S3, S4, and S5 were added to 50 mL of butyl xanthate solution (30 mg / L), and the degradation effect was investigated in a photoreactor. The results are as follows: Figure 13 As shown, Figure (a) is a degradation rate graph of butyl xanthate, and Figure (b) is a degradation kinetic curve.

[0086] Depend on Figure 11 It can be seen that the magnetically modified three-dimensional flower-like N-Bi₂O₂CO₃ / g-C₃N₄ photocatalyst exhibits a three-dimensional flower-like structure. Compared with the unmodified (NBOC / CN-2) material, the magnetic modification did not adversely affect the structure of the N-Bi₂O₂CO₃ / g-C₃N₄ photocatalyst. Sample S3 contains five elements: Bi, C, N, O, and Fe.

[0087] Depend on Figure 12 It can be seen that as the Fe3O4 content increases, the magnetic separation effect of S1, S2, S3, S4 and S5 becomes better and better.

[0088] Depend on Figure 13 It can be seen that the degradation rate of S3, the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material prepared in this embodiment, is as high as 97.44%.

[0089] In summary, the degradation efficiency of butyl xanthate by the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is further improved after magnetic modification.

[0090] Example 8

[0091] A method for preparing magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic materials includes the following steps:

[0092] Step 1: Preparation of g-C3N4 nanosheets: Place 10 g of melamine in a clean ceramic crucible, place it in a muffle furnace, heat it to 540 °C at a heating rate of 5 °C / min and maintain it for 5 h, cool it to room temperature to obtain a yellow powder, take it out and grind it thoroughly with an agate mortar, mix it evenly with an appropriate amount of anhydrous ethanol, sonicate it for 2 h, remove the bottom particles, filter the upper suspension, and freeze-dry to obtain g-C3N4 nanosheets.

[0093] Step 2, preparation of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material: 0.5 g of Bi(NO3)3·5H2O was dissolved in 20 mL of dilute nitric acid solution (volume ratio 1:10) and ultrasonically dispersed for 30 min to completely dissolve, then 1 g of g-C3N4 nanosheet was added, and the pH was adjusted to 8 using NaOH (1 M), then transferred to a 100 mL polytetrafluoroethylene-lined stainless steel reaction kettle, and then the volume was adjusted to 70%, and then placed in a constant temperature drying oven and reacted at 160 °C for 8 h. After cooling to room temperature, the obtained product was filtered, washed and dried to obtain a three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material.

[0094] Step 3, preparation of magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material: 3.82 g of FeCl3·6H2O was dissolved in deionized water to obtain solution A; 10.39 g of FeCl2·4H2O was dissolved in deionized water to obtain solution B; a clean two-necked flask was taken and the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material prepared in step 2 was added, then 50 mL of solution A and 50 mL of solution B were added in sequence, N2 was introduced and the air was continuously stirred to exhaust, the whole system was aged for 60 min under N2 protection, so that Fe 3+ and Fe 2+ ions were fully adsorbed on the surface of N-Bi2O2CO3 / g-C3N4, then NaOH (2 M) solution was added dropwise under stirring to adjust the pH to 10, and the obtained product was filtered, washed and dried to obtain a magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material.

[0095] Under the action of the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material prepared in the example, the absorbance of butyl xanthate at 301 nm changed with the light irradiation time as shown in Figure 14 The degradation rate was 97.05% after 60 min of light irradiation.

[0096] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material, characterized in that, Includes the following steps: S1. Preparation of g-C3N4 nanosheets: Melamine was calcined at low temperature to obtain g-C3N4 powder. Then, the g-C3N4 powder was added to anhydrous ethanol and ultrasonically dispersed to make it uniform. The upper suspension was taken, filtered, washed and freeze-dried to obtain g-C3N4 nanosheets. S2. Preparation of three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material: g-C3N4 nanosheets prepared in S1 were added to bismuth nitrate solution and dispersed to obtain a uniform suspension. After adjusting the pH to alkaline, a hydrothermal reaction was carried out. Then, after filtration, washing and drying, the three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material was obtained as a precursor. S3. Preparation of magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material: The precursor prepared in S2 is dispersed into Fe... 2+ and Fe 3+ The material was aged in solution under inert gas protection, and then the pH was adjusted to 9-10. After the reaction, it was filtered, washed and dried to obtain magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material.

2. The preparation method of the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 1, characterized in that, The low-temperature calcination in step S1 involves heating to 540-550℃ at a heating rate of 4.0-5.0℃ / min and holding for 4-5 hours.

3. The preparation method of the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 1, characterized in that, The bismuth nitrate solution in step S2 is preferably obtained by dissolving bismuth nitrate pentahydrate in nitric acid solution, wherein the volume ratio of nitric acid in the nitric acid solution is 1 / 9-1 / 10.

4. The preparation method of the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 3, characterized in that, The mass ratio of bismuth pentahydrate nitrate and g-C3N4 powder in step S2 is less than 5:

1.

5. The preparation method of a magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 1, characterized in that, The hydrothermal reaction described in step S2 is carried out at 140-180℃ for 4-16 hours.

6. The preparation method of a magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 1, characterized in that, The aging time in step S3 is 30-60 minutes.

7. The preparation method of the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 1, characterized in that, In the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material prepared in step S3, the mass ratio of Fe3O4 to N-Bi2O2CO3 / g-C3N4 photocatalytic material is 0.05:1-0.4:

1.

8. The preparation method of a magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material according to claim 1, characterized in that, In the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material, the preferred mass ratio of N-Bi2O2CO3 to g-C3N4 is 1:10-2:

5.

9. The application of the magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material synthesized by the method according to any one of claims 1-8 in the degradation of organic pollutants, wherein the organic pollutants include at least one of dyeing and printing wastewater, pharmaceutical wastewater and mining wastewater.

10. The application according to claim 9, characterized in that, The steps are as follows: The magnetically modified three-dimensional flower-like N-Bi2O2CO3 / g-C3N4 photocatalytic material is added to the organic pollutants and catalytically decomposed under visible light.

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