Self-supporting Bi-doped cobalt-based semiconductor photocatalyst as well as preparation method and application thereof

Abstract

The invention discloses a self-supporting Bi-doped cobalt-based semiconductor photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of catalytic materials. The preparation method of the self-supporting Bi-doped cobalt-based semiconductor photocatalyst comprises the following steps: sequentially dissolving a cobalt source, urea (CO (NH2) 2) and a bismuth source in water to obtain a precursor solution; and putting foamed nickel into the precursor solution, reacting, and calcining to obtain the self-supporting Bi-doped cobalt-based semiconductor photocatalyst. According to the method, Bi ions are introduced into Co3O4 crystals through ion doping, and an energy band structure and an electronic structure of the Co3O4 crystals are regulated and controlled, so that the utilization rate of photo-induced electrons is increased, toluene mineralization is facilitated to form non-toxic carbon dioxide, toluene is efficiently and rapidly removed under visible light, and efficient degradation of VOCs is realized. In addition, gram-negative bacteria and gram-positive bacteria can be inhibited in the degradation process at the same time, and wide application prospects are achieved in the aspect of environmental protection.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic materials, and in particular to a self-supporting Bi-doped cobalt-based semiconductor photocatalyst and a preparation method and application thereof. Background Art

[0002] With the rapid development of social economy, the problem of indoor air quality has become increasingly prominent. In modern office environments, office automation equipment such as computers, printers and copiers have become an important source of indoor volatile organic compounds (VOCs). Among them, toluene, as a typical toxic and harmful gas pollutant that is prevalent in indoor environments, has a significantly higher indoor concentration than the original traditional environment, posing a major threat to human health. The current mainstream toluene purification technologies mainly include adsorption, photocatalytic oxidation and thermal catalytic oxidation (including high-temperature catalysis and room-temperature catalysis). Among them, photocatalytic oxidation technology has significant advantages such as high efficiency and environmental friendliness, and is more worthy of research. Therefore, there is an urgent need to develop new photocatalysts with both high catalytic activity and long-term stability to degrade VOCs with long-term stability, thereby achieving efficient control of VOCs.

[0003] Cobalt-based oxides (such as Co3O4, CoO) have attracted much attention due to their unique physicochemical properties. Among them, Co3O4, as a typical transition metal oxide, has low cost, excellent water resistance, high chemical stability, large specific surface area and unique electronic structure, showing important application potential in many fields such as catalysis, energy storage and environmental governance. However, undoped Co3O4 materials are wide bandgap semiconductors, and their photogenerated carriers are easy to recombine, resulting in limited photocatalytic performance. Therefore, improving the photocatalytic activity of cobalt-based oxides through material design optimization so that they can be better applied to toluene removal is of great significance for achieving efficient degradation of VOCs. Summary of the Invention

[0004] The present invention aims to provide a self-supporting Bi-doped cobalt-based semiconductor photocatalyst, its preparation method, and its application, to address the aforementioned problems in the background art. By introducing Bi ions into Co3O4 crystals through ion doping, the present invention modulates its energy band structure and electronic structure, thereby improving the utilization rate of photogenerated electrons, facilitating the mineralization of toluene to form non-toxic carbon dioxide, and achieving efficient and rapid removal of toluene under visible light, thereby achieving efficient degradation of VOCs. Furthermore, the photocatalyst can simultaneously inhibit both Gram-negative and Gram-positive bacteria during the degradation process, thus possessing broad application prospects in environmental protection.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a method for preparing a self-supporting Bi-doped cobalt-based semiconductor photocatalyst, comprising the following steps:

[0007] A cobalt source, urea (CO(NH2)2) and a bismuth source are sequentially dissolved in water to obtain a precursor solution;

[0008] The nickel foam is placed in the precursor solution, reacted, and calcined to obtain the self-supporting Bi-doped cobalt-based semiconductor photocatalyst.

[0009] Preferably, the nickel foam has a size of 3cm×4cm×1.0mm and a surface density of 350g / m 2 , pore density 110ppi, porosity 98%.

[0010] Preferably, the nickel foam further comprises a pretreatment step before use, specifically: washing the nickel foam with acetone, ethanol and deionized water in sequence for 30 to 40 minutes to remove impurities and grease on the surface of the nickel foam, and then drying it for use.

[0011] Preferably, the cobalt source is cobalt nitrate (Co(NO3)2·6H2O); the bismuth source is bismuth nitrate (Bi(NO3)3·5H2O).

[0012] Preferably, the mass ratio of the cobalt source, urea and bismuth source is (2.0-2.2) g: (0.72-0.75) g: (0.48-0.5) g.

[0013] Preferably, the reaction temperature is 90-100° C. and the reaction time is 8-9 h.

[0014] Preferably, the calcination comprises the following steps: heating to 350-400° C. at a heating rate of 3-5° C. / min, and then keeping the temperature for 3-4 hours.

[0015] The second technical solution of the present invention is to provide a self-supporting Bi-doped cobalt-based semiconductor photocatalyst obtained according to the above preparation method.

[0016] The third technical solution of the present invention is to provide an application of the above-mentioned self-supporting Bi-doped cobalt-based semiconductor photocatalyst in the photocatalytic degradation of VOCs.

[0017] Preferably, the VOCs is toluene.

[0018] The fourth technical solution of the present invention is to provide an application of the above-mentioned self-supporting Bi-doped cobalt-based semiconductor photocatalyst in the field of photocatalytic sterilization.

[0019] Preferably, the sterilized bacteria include Escherichia coli and / or Staphylococcus aureus.

[0020] The present invention uses nickel foam as a catalyst to provide a growth substrate, cobalt nitrate as a cobalt source, urea as a structure-directing agent, and then adds a bismuth dopant. By controlling the reaction temperature and time of the hydrothermal method, Bi doping is achieved.

[0021] The beneficial technical effects of the present invention are as follows:

[0022] This invention introduces Bi ions into Co₃O₄ crystals through ion doping, modulating their energy band and electronic structures. This improves the utilization rate of photogenerated electrons, facilitates the mineralization of toluene into non-toxic carbon dioxide, and enables efficient and rapid removal of toluene under visible light, effectively degrading VOCs. Furthermore, the degradation process can simultaneously inhibit both Gram-negative and Gram-positive bacteria, offering broad application prospects in environmental protection.

[0023] This invention provides a self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst (Bi-Co₃O₄ photocatalyst), which can be quickly and easily prepared through a simple hydrothermal reaction combined with calcination. Furthermore, the Bi-doped Co₃O₄ nanomaterial exhibits excellent sterilization efficacy against bacteria such as Staphylococcus aureus and Escherichia coli, demonstrating the broad potential of this photocatalyst in environmental protection applications.

[0024] This invention uses nickel foam as a substrate, effectively circumventing the problems of traditional powdered catalysts, such as difficulty in recycling and easy solidification, as well as the potential for traditional polymer binders to impair electron conduction and cover active sites. Furthermore, the Bi-Co₃O₄ photocatalyst, in its nanowire form, provides more active sites for the reaction, facilitating the adsorption and activation of toluene, thereby achieving rapid and efficient toluene removal. Test results demonstrate that the product of this invention exhibits superior photocatalytic performance, achieving 100% toluene degradation efficiency within 30 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 The XRD patterns of the products of Example 1 and Comparative Example 1 are shown.

[0027] Figure 2 1 is an SEM image of the product of Example 1; wherein (a), (b), (c), and (d) are SEM images at different magnifications, respectively.

[0028] Figure 3 This is the EDS diagram of the product in Example 1.

[0029] Figure 4 It is the full XPS spectrum of the products of Example 1 and Comparative Example 1.

[0030] Figure 5 This is a physical picture of the quartz reactor used in the present invention.

[0031] Figure 6 The degradation rate curves of the products of Example 1 and Comparative Examples 1-4 for toluene are shown.

[0032] Figure 7 The toluene mineralization rate curves of the products of Example 1 and Comparative Examples 1-4 are shown.

[0033] Figure 8 This is the cyclic stability diagram of the product in Example 1.

[0034] Figure 9 The bacterial growth diagrams are of the original bacterial sample and the bacterial sample after 24 hours of culture on the plate of the product of Example 1.

[0035] Among them, (a) is the original bacterial sample, and (b) is the bacterial sample after the product of Example 1 was plated and cultured for 24 hours.

[0036] Figure 10 The following are SEM images of the original bacterial sample and the bacterial sample after 24 hours of culture on the plate with the product of Example 1. Among them, (a)-(b) are the original bacterial samples, and (c)-(d) are the bacterial samples with the addition of Example 1. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0038] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0039] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention pertains. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. It should be noted that any details not described herein are conventional procedures in the art and are not the focus of the present invention.

[0040] The terms “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0041] The present invention provides a method for preparing a self-supporting Bi-doped cobalt-based semiconductor photocatalyst, comprising the following steps:

[0042] A cobalt source, urea (CO(NH2)2) and a bismuth source are sequentially dissolved in water to obtain a precursor solution;

[0043] The nickel foam is placed in the precursor solution, reacted, and calcined to obtain the self-supporting Bi-doped cobalt-based semiconductor photocatalyst.

[0044] Preferably, the nickel foam has a size of 3cm×4cm×1.0mm and a surface density of 350g / m 2 , pore density 110ppi, porosity 98%.

[0045] Preferably, the nickel foam further comprises a pretreatment step before use, specifically: washing the nickel foam with acetone, ethanol and deionized water in sequence for 30 to 40 minutes to remove impurities and grease on the surface of the nickel foam, and then drying it for use.

[0046] More preferably, the cleaning is ultrasonic cleaning, and a clean nickel foam substrate is obtained by ultrasonic cleaning; the frequency of the ultrasonic cleaning is 35 to 55 kHz.

[0047] Preferably, the cobalt source is cobalt nitrate (Co(NO3)2·6H2O); the bismuth source is bismuth nitrate (Bi(NO3)3·5H2O).

[0048] Preferably, the mass ratio of the cobalt source, urea and bismuth source is (2.0-2.2) g:(0.72-0.75) g:(0.48-0.5) g, more preferably 2.184 g:0.721 g:0.485 g.

[0049] Preferably, the reaction temperature is 90-100° C. and the reaction time is 8-9 h.

[0050] More preferably, the reaction temperature is 100° C. and the reaction time is 8 h.

[0051] By controlling the temperature and time, it is possible to both in-situ grow Co3O4 on nickel foam and achieve Bi doping. If the reaction temperature is too low, in-situ growth of Co3O4 and ion doping cannot be achieved; if the temperature is too high, the purity of Co3O4 will be affected, Bi doping will be unfavorable, and energy consumption will be too high.

[0052] Preferably, the calcination comprises the following steps: heating to 400° C. at a heating rate of 5° C. / min, and then keeping the temperature for 4 hours.

[0053] The present invention also provides a self-supporting Bi-doped cobalt-based semiconductor photocatalyst obtained according to the above preparation method.

[0054] The self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst (Bi-Co3O4 photocatalyst) prepared by the present invention not only broadens the light response range of Co3O4, improves the electron utilization rate, avoids the rapid recombination of electrons and holes, is beneficial to the catalytic degradation of toluene, but also effectively solves the problems of difficult recovery and easy solidification of traditional powder catalysts.

[0055] The present invention also provides an application of the above-mentioned self-supporting Bi-doped cobalt-based semiconductor photocatalyst in photocatalytic degradation of VOCs.

[0056] Preferably, the VOCs is toluene.

[0057] The present invention also provides an application of the above-mentioned self-supporting Bi-doped cobalt-based semiconductor photocatalyst in the field of photocatalytic sterilization.

[0058] Preferably, the sterilized bacteria include Escherichia coli and / or Staphylococcus aureus.

[0059] The nickel foam used in the following examples and comparative examples of the present invention has the following specifications: surface density 350g / m 2 The pore density is 110 ppi and the porosity is 98%. In the present invention, there is no particular limitation on the source of the nickel foam, and commercial products known to those skilled in the art can be used.

[0060] The washing reagents in the present invention are acetone, ethanol and deionized water, and there is no particular limitation on their sources.

[0061] The sources of Co(NO3)2·6H2O, CO(NH2)2, and Bi(NO3)3·5H2O in the present invention are not particularly limited, and commercially available products known to those skilled in the art may be used.

[0062] In the present invention, there is no special limitation on the operation method of mixing foamed nickel, Co(NO3)2·6H2O, CO(NH2)2, Bi(NO3)3·5H2O and deionized water. A mixing method familiar to those skilled in the art can be adopted to ensure that the foamed nickel is completely immersed in the uniformly mixed solution.

[0063] The present invention does not specifically limit the method for using the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst in the photocatalytic degradation of toluene, and the catalyst application method well known to those skilled in the art can be used. In the present invention, the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst is used in the process of photocatalytic degradation of toluene in a self-made quartz reactor. The actual picture of the quartz reactor is as follows: Figure 5 shown.

[0064] The present invention does not specifically limit the method for testing the degradation rate of toluene by the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst, and catalyst testing methods familiar to those skilled in the art can be used. In the present invention, gas chromatography is used to test the degradation effect of the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst on toluene. The gas chromatography measurement operation of the present invention is not specifically limited, and catalyst testing methods familiar to those skilled in the art can be used.

[0065] The raw materials used in the following examples and comparative examples of the present invention are all commercially available products.

[0066] Example 1

[0067] A method for preparing a self-supporting Bi-doped cobalt-based semiconductor photocatalyst comprises the following steps:

[0068] (1) The specifications are 3cm×4cm×1.0mm and the surface density is 350g / m 2 Nickel foam with a pore density of 110 ppi and a porosity of 98% was cleaned with acetone, ethanol, and water in sequence by ultrasonic cleaning (frequency of 55 kHz) for 30 min and then air-dried.

[0069] (2) In a 100 mL beaker, 2.184 g Co(NO3)2·6H2O, 0.721 g CO(NH2)2, 0.485 g Bi(NO3)3·5H2O, and 60 mL deionized water were added in sequence and ultrasonicated for 30 min to obtain a precursor solution;

[0070] (3) mixing the nickel foam in step (1) with the precursor solution in step (2), and then performing a hydrothermal reaction at 100° C. for 8 h;

[0071] (4) After the reaction is completed, the material is cooled to room temperature, washed, and dried. The dried material is heated to 400°C in a muffle furnace at a heating rate of 5°C / min and then kept warm for 4 h to obtain a self-supporting Bi-doped cobalt-based semiconductor photocatalyst (denoted as Bi-Co3O4).

[0072] Comparative Example 1

[0073] The only difference from Example 1 is that the addition of Bi(NO3)3·5H2O in step (2) is omitted, and an undoped self-supporting Co3O4 catalyst (denoted as Co3O4) is obtained.

[0074] Figure 1 The XRD patterns of the products of Example 1 and Comparative Example 1 are shown.

[0075] Depend on Figure 1 It can be seen that the diffraction peaks of the Bi-doped catalyst of Example 1 are almost identical to those of the original Co3O4 catalyst. However, compared with the original Co3O4, a larger negative shift can be observed at the (311) crystal plane of Bi-Co3O4, indicating that the lattice constant along (311) increases. Therefore, it can be seen that the present invention successfully prepared a self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst.

[0076] Figure 2 1 is an SEM image of the product of Example 1; wherein (a), (b), (c), and (d) are SEM images at different magnifications, respectively.

[0077] Depend on Figure 2 It can be seen that the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst prepared by the present invention has a nanowire structure.

[0078] Figure 3 This is the EDS diagram of the product in Example 1.

[0079] Depend on Figure 3 It can be seen that the Bi element in the product was successfully doped.

[0080] Figure 4 It is the full XPS spectrum of the products of Example 1 and Comparative Example 1.

[0081] Depend on Figure 4 It can be seen that the product of Example 1 has a corresponding spectrum peak of Bi element, indicating that a self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst has been successfully prepared.

[0082] Comparative Example 2

[0083] The only difference from Example 1 is that the amount of Bi(NO3)3·5H2O added in step (2) is changed from 0.485 g to 0.243 g, and the obtained catalyst is recorded as 0.5Bi-Co3O4.

[0084] Comparative Example 3

[0085] The only difference from Example 1 is that the amount of Bi(NO3)3·5H2O added in step (2) is changed from 0.485 g to 0.364 g, and the obtained catalyst is recorded as 0.75Bi-Co3O4.

[0086] Comparative Example 4

[0087] The only difference from Example 1 is that the amount of Bi(NO3)3·5H2O added in step (2) is changed from 0.485 g to 0.606 g, and the obtained catalyst is recorded as 1.25Bi-Co3O4.

[0088] Effect verification

[0089] (1) The elemental composition of the loaded products of Example 1 and Comparative Example 1 was tested by ICP-OES / MS (the test method was: the Bi-Co3O4 powder loaded on the nickel foam substrate was gently scraped off, and then the elemental composition test was performed). The test results are shown in Table 1.

[0090] Table 1 Element composition test

[0091]

[0092] (2) In order to verify the degradation efficiency of the product obtained by the present invention on toluene, the following tests were carried out on Example 1 and Comparative Examples 1-4: The degradation efficiency of the catalyst on toluene was tested by gas chromatograph, and a xenon lamp was used to simulate sunlight conditions (with a 420 nm filter added). Two catalysts were placed on a glass fiber filter membrane and then placed in a 450 mL homemade quartz glass reactor (such as Figure 5 As shown in the figure, the initial toluene concentration is set to 50 ppm and the actual contact area of the catalyst is 24 cm 2 , and then connect the reactor to a gas chromatograph (GC); during the test reaction process, samples were taken every 5 minutes to detect the toluene concentration in the reactor and calculate the toluene mineralization rate. The test results are as follows Figure 6-7 shown.

[0093] Figure 6 The degradation rate curves of the products of Example 1 and Comparative Examples 1-4 for toluene are shown.

[0094] Bi-Co3O4 material has the ability to darkly adsorb toluene without adding light; Figure 6 The period from -20 to 0 min on the horizontal axis represents the adsorption of toluene by the material before irradiation, and the period from 0 to 30 min represents the data of the photocatalytic reaction after the xenon lamp is turned on.

[0095] from Figure 6 It can be seen that the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst prepared in Example 1 of the present invention can degrade 100% of 50 ppm toluene within 30 minutes, and its photocatalytic performance also has better advantages compared with Comparative Examples 1-4.

[0096] Figure 7 The toluene mineralization rate curves of the products of Example 1 and Comparative Examples 1-4 are shown.

[0097] from Figure 7 As can be seen, the catalyst prepared in Example 1 significantly converted toluene into carbon dioxide, demonstrating its excellent catalytic performance. However, under the same degradation conditions, the mineralization rate of the product in Comparative Example 1 was less than 80%, indicating poor performance. Therefore, the cyclic stability of the product in Comparative Example 1 was not tested.

[0098] (3) The product of Example 1 was subjected to a cycle performance test using a gas chromatography detection method, using a photocatalytic xenon lamp as the light source (with a 420 nm filter added), and a homemade quartz reactor (such as Figure 5 The photocatalytic toluene experiment was carried out as shown in Figure 1. The initial toluene concentration was 50 ppm and the actual contact reaction area of the catalyst was 24 cm 2 (i.e. the area of two 3cm×4cm nickel foams), use a gas chromatograph to test the toluene concentration during the reaction, take samples every 5 minutes to test the toluene concentration in the reactor, and calculate the toluene degradation efficiency to obtain a toluene degradation efficiency curve. Then repeat the above operation 11 times, and calculate the toluene concentration and toluene mineralization rate respectively. The test results are as follows Figure 8 shown.

[0099] Figure 8 This is the cyclic stability diagram of the product in Example 1.

[0100] from Figure 8 It can be seen that after 11 consecutive experiments of toluene degradation, the catalytic performance of the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst decreased slightly, indicating that the catalyst has excellent cycle stability.

[0101] (4) The sterilization performance test of the product of Example 1 was carried out by the following test method: the original bacterial sample (a mixed bacterial flora of Escherichia coli and Staphylococcus aureus, with the inoculation ratio of the two bacteria being 0.3%:0.3%) was inoculated on a clean bench, 50 μL of bacterial solution was added to the solid agar medium to coat the plate, and then the catalyst was placed in the culture medium, sealed with a biofilm, and placed under a xenon lamp (with a 420 nm filter) for 60 minutes. The culture medium was then placed in an oven at 35°C for 24 hours. The test results are as follows: Figure 9-10 shown.

[0102] Figure 9 The bacterial growth diagrams are of the original bacterial sample and the bacterial sample after 24 hours of culture on the plate of the product of Example 1.

[0103] Among them, (a) is the original bacterial sample, and (b) is the bacterial sample after the product of Example 1 was plated and cultured for 24 hours.

[0104] from Figure 9It can be seen that no bacteria grow around the catalyst of Example 1, which intuitively illustrates the sterilization effect of the catalyst.

[0105] Figure 10 The following are SEM images of the original bacterial sample and the bacterial sample after 24 hours of culture on the plate with the product of Example 1. Among them, (a)-(b) are the original bacterial samples, and (c)-(d) are the bacterial samples with the addition of Example 1.

[0106] from Figure 10 It can be seen that after the catalyst is added, the surfaces of Escherichia coli and Staphylococcus aureus are damaged, indicating that the self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst prepared in Example 1 can kill Escherichia coli and Staphylococcus aureus at the same time, and has a good sterilization effect.

[0107] It should be noted that, from Figure 10 It can be seen from the SEM image that the number of E. coli is greater than that of Staphylococcus aureus, which is due to the shorter generation time of E. coli.

[0108] The self-supporting Bi-doped p-type cobalt-based semiconductor photocatalyst synthesized in the present invention solves the problems of traditional Co3O4's wide band gap, difficulty in excitation, and low electron utilization. By doping, the light response range is broadened, an electron channel is provided, which is conducive to the generation of active substances, thereby achieving efficient oxidative degradation of toluene.

[0109] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a self-supporting Bi-doped cobalt-based semiconductor photocatalyst, characterized in that: The following steps are involved: dissolving a cobalt source, urea, and a bismuth dopant in water in sequence to obtain a precursor solution; The nickel foam is placed in the precursor solution, reacted, and calcined to obtain the self-supporting Bi-doped cobalt-based semiconductor photocatalyst.

2. The preparation method according to claim 1, characterized in that The cobalt source is cobalt nitrate; and the bismuth dopant is bismuth nitrate.

3. The preparation method according to claim 1, characterized in that The mass ratio of the cobalt source, urea and bismuth dopant is (2.0-2.2) g: (0.7-0.75) g: (0.2-0.6) g.

4. The preparation method according to claim 1, characterized in that The reaction temperature is 90-100° C. and the reaction time is 8-9 hours.

5. The preparation method according to claim 1, characterized in that The calcination comprises the following steps: heating to 350-400° C. at a heating rate of 3-5° C. / min, and then keeping the temperature for 3-4 hours.

6. A self-supporting Bi-doped cobalt-based semiconductor photocatalyst obtained according to the preparation method according to any one of claims 1 to 5.

7. Use of the self-supporting Bi-doped cobalt-based semiconductor photocatalyst according to claim 6 in photocatalytic degradation of VOCs.

8. The use according to claim 7, characterized in that The VOCs is toluene.

9. Use of the self-supporting Bi-doped cobalt-based semiconductor photocatalyst according to claim 6 in the field of photocatalytic sterilization.

10. The use according to claim 9, characterized in that The sterilized bacteria include Escherichia coli and / or Staphylococcus aureus.

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