A catalyst for degrading COD in wastewater and its preparation method

Abstract

The present invention relates to a catalyst for degrading COD in wastewater and a preparation method thereof, comprising the following steps: a first step of preparing niobium pentoxide; a second step of preparing a pre-reaction solution: weighing octadecyltrimethylammonium chloride, thioacetamide, and distilled water, mixing them, stirring them uniformly, adding niobium pentoxide powder, and stirring them again until uniform to obtain a mixed solution A; weighing hafnium oxychloride octahydrate and distilled water, mixing them, stirring them thoroughly to obtain a mixed solution B; mixing the mixed solution B with the mixed solution A to obtain a mixed solution C; a third step of performing a hydrothermal reaction: pouring the mixed solution C into a reactor and heating it for reaction to obtain a product D; and a fourth step of high-temperature sintering to obtain niobium pentoxide / carbon-doped hafnium disulfide. The photocatalyst of the present invention is a composite product of carbon-doped hafnium disulfide and niobium pentoxide. It not only has good catalytic degradation efficiency for organic pollutants in wastewater, but is also not easily deactivated, has excellent reusability, and has a long service life.

Description

Technical Field

[0001] The present invention relates to the field of wastewater degradation, and in particular to a catalyst for degrading COD in wastewater and a preparation method thereof. Background Art

[0002] After biochemical treatment of industrial and municipal wastewater, the effluent still contains a certain concentration of organic matter. These organic compounds are generally difficult to biodegrade, and constitute the main chemical oxygen demand (COD) in the biochemical treatment effluent. With the continuous improvement of industrial and municipal wastewater discharge standards, the effluent COD of biochemical treatment systems often fails to meet discharge standards. Furthermore, the demand for reclaimed water reuse is also increasing, objectively requiring the addition of advanced treatment units after biochemical treatment of industrial and municipal wastewater. Advanced wastewater and sewage treatment technologies mainly include adsorption, membrane separation, and advanced oxidation technologies.

[0003] Adsorption technology is a relatively mature deep treatment technology that can economically and effectively remove odors, decolorize, and separate heavy metals and organic pollutants. However, adsorbents (such as granular activated carbon, activated carbon fiber, and resins) are expensive and difficult to regenerate. The solid waste that is inevitably produced is a difficult secondary pollution, and it does not essentially eliminate pollutants. Membrane separation technology is divided into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis according to the pore size of the membrane. Its characteristics are a wide range of separation targets and good effluent quality, but investment and operating costs are relatively high, the membrane life is short, and it inevitably produces "concentrated water" with high organic and salt concentrations. The treatment and disposal of "concentrated water" is a difficult problem. This technology essentially concentrates pollutants into "concentrated water". The most commonly used advanced oxidation technology is photocatalytic oxidation, which not only has a fast reaction speed but also generally does not produce secondary pollution. It is particularly suitable for treating difficult-to-biodegrade organic matter.

[0004] Currently, the most commonly used catalyst for photocatalytic oxidation is nanometal oxide. Although nanometal oxide photocatalytic materials can catalytically degrade organic pollutants in wastewater to a certain extent, they still have problems such as being not resistant to pollution, easy to deactivate and having a short service life, making it difficult to meet industrial application requirements. Summary of the Invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a catalyst for degrading COD in wastewater and a preparation method thereof.

[0006] The purpose of the present invention is achieved by adopting the following technical solutions:

[0007] In a first aspect, the present invention discloses a method for preparing a catalyst for degrading COD in wastewater, comprising the following steps:

[0008] The first step is to prepare niobium pentoxide:

[0009] Weighing niobium pentoxide, grinding it, sieving it, collecting it into a crucible, and then placing it in a muffle furnace for heating treatment. After cooling in the furnace, niobium pentoxide powder is obtained;

[0010] The second step is to prepare the pre-reaction solution:

[0011] Weigh octadecyltrimethylammonium chloride, thioacetamide, and distilled water, mix them, stir them evenly, add niobium pentoxide powder, and stir them again until they are evenly mixed to obtain a mixed solution A; weigh hafnium oxychloride octahydrate and distilled water, mix them, and stir them thoroughly to obtain a mixed solution B; gradually add the mixed solution B dropwise to the continuously stirred mixed solution A, and stir them evenly after the addition is complete to obtain a mixed solution C;

[0012] The third step is hydrothermal reaction:

[0013] Pour the mixed solution C into the reactor and heat it for reaction. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it to obtain product D.

[0014] Step 4: High temperature sintering:

[0015] The product D is placed in a muffle furnace and subjected to a temperature-raising treatment under the protection of a rare gas. After the reaction is completed, the product is ground and sieved to obtain niobium pentoxide / carbon-doped hafnium disulfide.

[0016] Preferably, in the first step, the purity of niobium hydrogen pentoxide is higher than 99.9%, and after grinding, it is sieved through a 250-300 mesh screen.

[0017] Preferably, in the first step, the conditions in the muffle furnace are: firstly heating to 350-550°C under air, keeping the temperature for 1-2 hours, then heating to 600-800°C, keeping the temperature for 2-4 hours.

[0018] Preferably, in the mixed solution A of the second step, the mass volume ratio of niobium pentoxide powder, octadecyltrimethylammonium chloride, thioacetamide and distilled water is 1g:(0.1-0.3)g:(0.8-1.6)g:(50-100)mL.

[0019] Preferably, in the mixed solution B of the second step, the mass volume ratio of hafnium oxychloride octahydrate to distilled water is (0.4-0.8) g: (50-100) mL.

[0020] Preferably, the dropwise addition rate of the mixed solution C in the second step is 40-80 drops / minute, and stirring is continued for 1-2 hours after the dropwise addition is completed.

[0021] Preferably, in the third step, the temperature in the reactor is set to 180-260° C., and the reaction time is set to 15-30 h.

[0022] Preferably, in the fourth step, the sintering temperature is 750-850° C., and the sintering time is 1.5-3.5 hours.

[0023] Preferably, in the fourth step, the rare gas is one of helium, neon, argon, krypton and xenon.

[0024] Preferably, in the fourth step, the product is ground and then passed through a 100-150 mesh sieve.

[0025] In a second aspect, the present invention discloses a catalyst for degrading COD in wastewater, which is prepared by the above method.

[0026] In a third aspect, the present invention discloses the use of a catalyst for degrading COD in wastewater in organic wastewater.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention prepares a catalyst capable of degrading COD in wastewater. The catalyst is a photocatalyst material, and the material body is a composite product of carbon-doped hafnium disulfide and niobium pentoxide. It not only has good catalytic degradation efficiency for ammonia nitrogen and COD in wastewater, but also is not easy to deactivate, has very good reusability, and has a long service life.

[0029] 2. The catalyst prepared in this invention uses niobium pentoxide as a matrix, in situ-generated and carbon-doped hafnium disulfide as a composite. Compared to traditional metal oxides, this composite product has a higher specific surface area, is more active, is easier to post-process, and can be used for a longer period of time.

[0030] 3. In the present invention, carbon-doped hafnium disulfide is prepared by adding octadecyltrimethylammonium chloride during the preparation of hafnium disulfide. On the one hand, it acts as a surfactant to enhance the dispersibility, and on the other hand, it can introduce long-chain carbon polymers, thereby carbonizing to form carbon intercalations during the subsequent sintering process, thereby obtaining carbon-doped hafnium disulfide. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the presence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships, without substantially changing the technical content, should also be regarded as the scope of the present invention.

[0032] In order to better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0033] The present invention will be further described below with reference to the following examples.

[0034] Example 1

[0035] A method for preparing a catalyst for degrading COD in wastewater comprises the following steps:

[0036] The first step is to prepare niobium pentoxide:

[0037] Weigh niobium pentoxide H5Nb3O 10 After grinding (purity higher than 99.9%), pass through a 300-mesh sieve, collect into a crucible, and then place in a muffle furnace. Under air conditions, first heat to 350-550°C, keep warm for 1-2 hours, then heat to 600-800°C, keep warm for 2-4 hours, and cool in the furnace to obtain niobium pentoxide Nb2O5 powder;

[0038] The second step is to prepare the pre-reaction solution:

[0039] Weigh octadecyltrimethylammonium chloride (STAC), thioacetamide (TAA), and distilled water, mix them, stir them evenly, add niobium pentoxide (Nb2O5) powder, the mass volume ratio of niobium pentoxide powder, octadecyltrimethylammonium chloride, thioacetamide, and distilled water being 1 g:0.2 g:1.2 g:80 mL, and stir them again until they are evenly mixed to obtain a mixed solution A; weigh hafnium oxychloride octahydrate (Cl2HfO·8H2O) and distilled water, the mass volume ratio of hafnium oxychloride octahydrate to distilled water being 0.6 g:80 mL, and stir them thoroughly to obtain a mixed solution B; gradually add the mixed solution B dropwise to the continuously stirred mixed solution A at a dropping rate of 60 drops / minute. After the addition is complete, continue stirring for 1.5 hours to obtain a mixed solution C;

[0040] The third step is hydrothermal reaction:

[0041] Pour the mixed solution C into the reactor and keep it at 220℃ for 24 hours. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it at 100℃ to obtain product D.

[0042] Step 4: High temperature sintering:

[0043] The product D was placed in a muffle furnace, heated to 800°C under the protection of rare gas, and kept warm for 2.5 hours. After the reaction was completed, it was ground into powder and passed through a 100-mesh sieve to obtain niobium pentoxide / carbon-doped hafnium disulfide Nb2O5 / C-HfS2.

[0044] Example 2

[0045] A method for preparing a catalyst for degrading COD in wastewater comprises the following steps:

[0046] The first step is to prepare niobium pentoxide:

[0047] Weighing niobium pentoxide (purity greater than 99.9%), grinding it, passing it through a 250-mesh sieve, collecting it into a crucible, and then placing it in a muffle furnace. Under air conditions, heating it to 350° C., keeping it warm for 4 hours, and cooling it in the furnace to obtain niobium pentoxide powder.

[0048] The second step is to prepare the pre-reaction solution:

[0049] Weigh octadecyltrimethylammonium chloride, thioacetamide, and distilled water, mix them, and stir them evenly. Then, add niobium pentoxide powder in a mass-to-volume ratio of 1 g:0.1 g:0.8 g:50 mL of niobium pentoxide powder, octadecyltrimethylammonium chloride, thioacetamide, and distilled water. Stir again until uniform to obtain a mixed solution A. Weigh hafnium oxychloride octahydrate and distilled water, mix them in a mass-to-volume ratio of 0.4 g:50 mL of hafnium oxychloride octahydrate and distilled water. After thorough stirring, obtain a mixed solution B. Gradually add the mixed solution B dropwise to the continuously stirred mixed solution A at a dropping rate of 40 drops / minute. After the addition is complete, continue stirring for 1 hour to obtain a mixed solution C.

[0050] The third step is hydrothermal reaction:

[0051] Pour the mixed solution C into the reactor and heat it at 180°C for 30 hours. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it at 80°C to obtain product D.

[0052] Step 4: High temperature sintering:

[0053] The product D was placed in a muffle furnace, heated to 750°C under the protection of a rare gas, and kept warm for 3.5 hours. After the reaction was completed, it was ground into powder and passed through a 100-mesh sieve to obtain niobium pentoxide / carbon-doped hafnium disulfide.

[0054] Example 3

[0055] A method for preparing a catalyst for degrading COD in wastewater comprises the following steps:

[0056] The first step is to prepare niobium pentoxide:

[0057] Weighing niobium pentoxide (purity greater than 99.9%), grinding it, passing it through a 300-mesh sieve, collecting it into a crucible, and then placing it in a muffle furnace. Under air conditions, heating it to 500°C, keeping it at that temperature for 3 hours, and cooling it in the furnace to obtain niobium pentoxide powder.

[0058] The second step is to prepare the pre-reaction solution:

[0059] Weigh octadecyltrimethylammonium chloride, thioacetamide, and distilled water, mix them, stir them evenly, add niobium pentoxide powder, the mass volume ratio of niobium pentoxide powder, octadecyltrimethylammonium chloride, thioacetamide, and distilled water is 1g:0.2g:1g:60mL, and stir again until uniform to obtain a mixed solution A; weigh hafnium oxychloride octahydrate and distilled water, mix them, the mass volume ratio of hafnium oxychloride octahydrate and distilled water is 0.5g:60mL, and stir thoroughly to obtain a mixed solution B; gradually add the mixed solution B dropwise to the continuously stirred mixed solution A at a dropwise addition rate of 70 drops / minute. After the dropwise addition is complete, continue stirring for 1-2 hours to obtain a mixed solution C;

[0060] The third step is hydrothermal reaction:

[0061] Pour the mixed solution C into the reactor and keep it at 200℃ for 28h. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it at 120℃ to obtain product D.

[0062] Step 4: High temperature sintering:

[0063] The product D was placed in a muffle furnace, heated to 800°C under the protection of a rare gas, and kept warm for 2 hours. After the reaction was completed, it was ground into powder and passed through a 150-mesh sieve to obtain niobium pentoxide / carbon-doped hafnium disulfide.

[0064] Example 4

[0065] A method for preparing a catalyst for degrading COD in wastewater comprises the following steps:

[0066] The first step is to prepare niobium pentoxide:

[0067] Weighing niobium pentoxide (purity greater than 99.9%), grinding it, passing it through a 300-mesh sieve, collecting it into a crucible, and then placing it in a muffle furnace. Under air conditions, heating it to 550°C, keeping it at this temperature for 2 hours, and cooling it in the furnace to obtain niobium pentoxide powder.

[0068] The second step is to prepare the pre-reaction solution:

[0069] Weigh octadecyltrimethylammonium chloride, thioacetamide, and distilled water, mix them, stir them evenly, add niobium pentoxide powder, the mass volume ratio of niobium pentoxide powder, octadecyltrimethylammonium chloride, thioacetamide, and distilled water is 1g:0.3g:1.6g:100mL, and stir again until uniform to obtain a mixed solution A; weigh hafnium oxychloride octahydrate and distilled water, mix them, the mass volume ratio of hafnium oxychloride octahydrate and distilled water is 0.8g:100mL, and stir thoroughly to obtain a mixed solution B; gradually add the mixed solution B dropwise to the continuously stirred mixed solution A at a dropwise addition rate of 80 drops / minute. After the dropwise addition is complete, continue stirring for 2 hours to obtain a mixed solution C;

[0070] The third step is hydrothermal reaction:

[0071] Pour the mixed solution C into the reactor and heat it at 260°C for 30 hours. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it at 120°C to obtain product D.

[0072] Step 4: High temperature sintering:

[0073] The product D was placed in a muffle furnace, heated to 850°C under the protection of a rare gas, and kept warm for 1.5 hours. After the reaction was completed, it was ground into powder and passed through a 150-mesh sieve to obtain niobium pentoxide / carbon-doped hafnium disulfide.

[0074] Comparative Example 1

[0075] A catalyst for degrading COD in wastewater is niobium pentoxide Nb2O5 powder, and the specific preparation process is the same as that of Example 1.

[0076] Comparative Example 2

[0077] A catalyst for degrading COD in wastewater is carbon-doped hafnium disulfide (C-HfS2). The specific preparation process includes:

[0078] The first step is to prepare the pre-reaction solution:

[0079] Weigh octadecyltrimethylammonium chloride (STAC), thioacetamide (TAA), and distilled water, mix them, stir them evenly, and obtain a mixture A in a mass-volume ratio of 0.2 g:1.2 g:80 mL. Stir them again until they are evenly distributed to obtain a mixture A. Weigh hafnium oxychloride octahydrate (Cl2HfO·8H2O) and distilled water, mix them in a mass-volume ratio of 0.6 g:80 mL. Stir them thoroughly to obtain a mixture B. Gradually add the mixture B dropwise to the continuously stirred mixture A at a rate of 60 drops / minute. After the addition is complete, continue stirring for 1.5 hours to obtain a mixture C.

[0080] The second step is hydrothermal reaction:

[0081] Pour the mixed solution C into the reactor and keep it at 220℃ for 24 hours. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it at 100℃ to obtain product D.

[0082] The third step is high temperature sintering:

[0083] The product D was placed in a muffle furnace, heated to 800°C under the protection of a rare gas, and kept warm for 2.5 hours. After the reaction was completed, it was ground into powder and passed through a 100-mesh sieve to obtain carbon-doped hafnium disulfide C-HfS2.

[0084] Comparative Example 3

[0085] A catalyst for degrading COD in wastewater is niobium pentoxide / hafnium disulfide Nb2O5 / HfS2. The preparation process differs from that of Example 1 only in that octadecyltrimethylammonium chloride is not added. The specific preparation process includes:

[0086] The first step is to prepare niobium pentoxide, which is the same as in Example 1.

[0087] The second step is to prepare the pre-reaction solution:

[0088] Weighing thioacetamide TAA and distilled water, mixing them, stirring them evenly, adding niobium pentoxide Nb2O5 powder, with the mass volume ratio of niobium pentoxide powder, thioacetamide, and distilled water being 1 g:1.2 g:80 mL, and stirring again until uniform to obtain a mixed solution A; weighing hafnium oxychloride octahydrate Cl2HfO·8H2O and distilled water, mixing them, with the mass volume ratio of hafnium oxychloride octahydrate to distilled water being 0.6 g:80 mL, and stirring thoroughly to obtain a mixed solution B; gradually adding the mixed solution B dropwise to the continuously stirred mixed solution A at a dropping rate of 60 drops / minute, and continuing stirring for 1.5 hours after the addition is complete, to obtain a mixed solution C;

[0089] The third step is hydrothermal reaction:

[0090] Pour the mixed solution C into the reactor and keep it at 220℃ for 24 hours. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it at 100℃ to obtain product D.

[0091] Step 4: High temperature sintering:

[0092] The product D was placed in a muffle furnace, heated to 800°C under the protection of a rare gas, and kept warm for 2.5 hours. After the reaction was completed, it was ground into powder and passed through a 100-mesh sieve to obtain niobium pentoxide / hafnium disulfide Nb2O5 / HfS2.

[0093] In order to more clearly illustrate the present invention, corresponding tests were performed on the catalysts of Example 1 of the present invention and Comparative Examples 1-3.

[0094] The detection process is as follows:

[0095] (1) Chemical industrial wastewater was used as the experimental wastewater source. The initial concentration of ammonia nitrogen in the wastewater was detected to be 227 mg / L, and the initial concentration of COD was 623 mg / L.

[0096] (2) The experimental wastewater source was divided into four equal parts, and the catalysts prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were added respectively, and then stirred evenly. The mass concentration of the catalyst was 80 mg / L, and then each wastewater source was marked respectively.

[0097] (3) Place each wastewater source under ultraviolet irradiation at an irradiation dose of 120mW / cm 2 The distance between the light source and the water source was 30 cm, the temperature was set to 35°C, and the degradation treatment was carried out under stirring conditions.

[0098] (4) Start the degradation treatment and measure the ammonia nitrogen concentration and COD concentration in the wastewater source at 30 minutes and 60 minutes of treatment, respectively. Record them as the ammonia nitrogen degradation concentration and COD degradation concentration, respectively. Then calculate the degradation percentage according to the formula:

[0099] Ammonia nitrogen degradation rate (%) = (initial ammonia nitrogen concentration - ammonia nitrogen degradation concentration) / initial ammonia nitrogen concentration × 100%;

[0100] COD degradation rate (%) = (COD initial concentration - COD degradation concentration) / COD initial concentration × 100%.

[0101] The test results are shown in Table 1:

[0102] Table 1 Efficiency of catalyst in degrading wastewater

[0103]

[0104] (5) After the wastewater treatment, the catalyst was filtered and collected, and then soaked in acetone and ultrasonicated for 0.5 h, and then dried and put back into use. After being reused 10 times in the manner of step (2), the ammonia nitrogen and COD degradation efficiency of the wastewater were tested again after 60 min. The test results are shown in Table 2:

[0105] Table 2 Degradation efficiency of the catalyst after repeated use 10 times

[0106] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Ammonia nitrogen degradation rate 98.1％ 92.0％ 92.8％ 95.8％ COD degradation rate 92.7％ 84.9％ 87.1％ 89.2％

[0107] Result analysis:

[0108] As can be seen from Table 1, the degradation rate of ammonia nitrogen by the catalyst prepared in Example 1 of the present invention reached 93.8% at 30 minutes and 98.9% at 60 minutes; the degradation rate of COD reached 87.3% at 30 minutes and 93.5% at 60 minutes. This shows that the catalyst prepared in Example 1 of the present invention has very good photocatalytic efficiency and is superior to the performance of other comparative examples. As can be seen from Table 2, the catalyst prepared in Example 1 of the present invention can still maintain a high ammonia nitrogen degradation rate and COD degradation rate after ten repeated uses, indicating that it is highly reusable, not easy to deactivate, and has a long service life.

[0109] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0110] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a catalyst for degrading COD in wastewater, characterized in that: The following steps are involved: The first step is to prepare niobium pentoxide: Weighing niobium pentoxide, grinding it, sieving it, collecting it into a crucible, and then placing it in a muffle furnace for heating treatment. After cooling in the furnace, niobium pentoxide powder is obtained; The second step is to prepare the pre-reaction solution: Weigh octadecyltrimethylammonium chloride, thioacetamide, and distilled water, mix them, stir them evenly, add niobium pentoxide powder, and stir them again until they are evenly mixed to obtain a mixed solution A; weigh hafnium oxychloride octahydrate and distilled water, mix them, and stir them thoroughly to obtain a mixed solution B; gradually add the mixed solution B dropwise to the continuously stirred mixed solution A, and stir them evenly after the addition is complete to obtain a mixed solution C; The third step is hydrothermal reaction: Pour the mixed solution C into the reactor and heat it for reaction. After the reaction is completed, filter the reaction solution in the reactor, wash it with water three times, and dry it to obtain product D. Step 4: High temperature sintering: The product D is placed in a muffle furnace and subjected to a temperature-raising treatment under the protection of a rare gas. After the reaction is completed, the product is ground and sieved to obtain niobium pentoxide / carbon-doped hafnium disulfide.

2. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein In the first step, the purity of niobium hydrogen pentoxide is higher than 99.9%, and after grinding, it is passed through a 250-300 mesh sieve.

3. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein In the first step, the conditions in the muffle furnace are: firstly heating to 350-550°C under air, keeping the temperature for 1-2 hours, then heating to 600-800°C, keeping the temperature for 2-4 hours.

4. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein In the mixed solution A of the second step, the mass volume ratio of niobium pentoxide powder, octadecyltrimethylammonium chloride, thioacetamide and distilled water is 1g:(0.1-0.3)g:(0.8-1.6)g:(50-100)mL.

5. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein In the mixed solution B of the second step, the mass volume ratio of hafnium oxychloride octahydrate and distilled water is (0.4-0.8) g: (50-100) mL.

6. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein: In the mixed solution C of the second step, the dropping speed is 40-80 drops / minute, and stirring is continued for 1-2 hours after the dropping is completed.

7. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein: In the third step, the temperature in the reactor is set to 180-260° C., and the reaction time is set to 15-30 h.

8. The method for preparing a catalyst for degrading COD in wastewater according to claim 1, wherein: In the fourth step, the sintering temperature is 750-850° C., and the sintering time is 1.5-3.5 hours.

9. A catalyst for degrading COD in wastewater, characterized in that: The preparation method according to claim 1 is used for preparation.

10. Use of the catalyst for degrading COD in wastewater according to claim 9 in organic wastewater.

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