Preparation of photocatalytic carbon dots based on dye wastewater and method for degrading dye wastewater

Abstract

The present application relates to the field of sewage treatment, and specifically discloses a kind of photocatalytic carbon dots based on dye wastewater preparation, and a kind of method based on the photocatalytic carbon dots catalytic degradation dye wastewater.The treatment method comprises the following steps: rhodamine B dye wastewater preparation photocatalyst carbon dots, carbon dots separation and purification, photocatalytic degradation of dye wastewater.The present application uses dye wastewater containing rhodamine B in printing and dyeing mill as raw material, and prepares carbon dot material with photocatalytic activity by one-step hydrothermal method;The carbon dots can effectively treat the actual dye wastewater under acidic conditions and light conditions, meet the standard of pipe discharge;The prepared carbon dots have high catalytic efficiency, low dosage, fast wastewater degradation speed;And can be recycled, the photocatalytic performance of the recovered carbon dots is stable, and the degradation performance still maintains more than 85% degradation effect after four cycles;It provides a new way for resource utilization of waste, and also provides a method for treatment of printing and dyeing wastewater.It has good practical applicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, and specifically discloses a kind of photocatalytic carbon dots based on dye wastewater preparation, and a kind of photocatalytic carbon dots based on the method for catalytic degradation of dye wastewater. BACKGROUND

[0002] With the rapid development of textile printing and dyeing industry, the problems of printing and dyeing wastewater are increasingly prominent. Printing and dyeing wastewater often has high concentration, high colority, poor biodegradability, and contains toxic and harmful ingredients, which belongs to typical refractory wastewater. At present, the commonly used treatment technologies include Fenton method, ozone oxidation method, photocatalytic method, adsorption method, membrane separation method and biological method, etc. Among them, the photocatalytic degradation method uses the photogenerated carriers (electrons and holes) generated by the excitation of semiconductor materials by light to degrade organic pollutants through oxidation-reduction reaction. Unlike the process of transferring pollutants (such as adsorption method, membrane separation method, etc.), photocatalytic method does not use potentially dangerous oxidants (such as ozone, hydrogen peroxide, etc.), and can completely convert pollutants into carbon dioxide and water, so it is an environmentally friendly and efficient water treatment process.

[0003] The wastewater generated by printing and dyeing enterprises often contains dye compounds such as rhodamine B, methyl orange, methyl red, methylene blue, phenol, phenolphthalein, methyl green, ketamine yellow, and methylene orange. These dye compounds are widely used in the printing and dyeing process and exist in wastewater. They have strong colority and chemical stability, and need to be treated properly to reduce pollution to the environment. Rhodamine B is a common organic dye, which is widely used in the textile industry due to its high chemical stability, strong coloring performance, and color fastness. However, rhodamine B is confirmed to have potential toxicity, carcinogenicity and mutagenicity, and once discharged into water bodies, it will have great harm to humans and the ecological environment. The wastewater containing rhodamine B has high colority, poor biodegradability and is difficult to degrade, and the ordinary biological treatment method and physicochemical method have poor degradation effect. S.J. Tong et al. disclosed a photocatalyst in Preparation of carbon quantum dots / TiO2 composite and application for enhanced photodegradation of rhodamine B, which achieved a degradation rate of 85% at a catalyst concentration of 1 g / L. However, the existing technology of photocatalyst degrading rhodamine B still has problems such as high catalyst dosage and slow degradation rate.

[0004] Developing low-cost and high-performance semiconductor photocatalytic materials is the key to the practical application of photocatalytic degradation technology. Metal oxides (such as TiO2 and ZnO), metal sulfides (such as CdS and MoS2) and non-metal catalysts (C3N4, C3N5 and carbon dots) are photocatalytic materials reported at present. The first two have high photocatalytic activity, but low visible light utilization rate, poor stability and easy photo corrosion; and non-metal photocatalysts have the advantages of wide raw material sources, simple synthesis method, low toxicity and visible light response, and become the substitute for metal-based photocatalytic materials. As a new type of carbon-based material with good water solubility, strong chemical stability, good biocompatibility and anti-photobleaching, carbon dots have been widely used as photocatalytic materials for wastewater treatment. However, in the conventional carbon dot catalytic water treatment system, carbon dots need to be purchased separately, which brings great economic pressure.

[0005] Therefore, it is of great practical significance to provide a catalyst prepared from wastewater containing rhodamine B as raw material source and used for degrading dye wastewater. SUMMARY

[0006] In order to solve the problems existing in the prior art, the present application is based on the concept of "waste treatment with waste", and aims to provide a fluorescent carbon dot prepared from dye wastewater containing rhodamine B as raw material, and a method and system for degrading dye wastewater by using the same as a photocatalyst.

[0007] The present application is realized by the following technical solutions:

[0008] In a first aspect, the present application first provides a method for photocatalytic degradation of dye wastewater, comprising the following steps:

[0009] Step S1, preparing photocatalyst carbon dots: adding concentrated sulfuric acid to dye wastewater containing rhodamine B, and reacting under heating conditions to obtain a crude product containing photocatalyst carbon dots;

[0010] Step S2, separation and purification of photocatalyst carbon dots: mixing the carbon dot crude product prepared in step S1 with silica gel uniformly, eluting with eluent, purifying and separating by column chromatography, collecting the first component, and drying to obtain photocatalyst carbon dots;

[0011] Step S3, degradation of dye wastewater: adding the photocatalyst carbon dots prepared in step S2 to the dye wastewater, and treating the dye wastewater under acidic conditions and light conditions.

[0012] Further, the concentration of sulfuric acid in the reaction system of step S1 is 0.8-1.2 mol / L.

[0013] Further, the reaction temperature in step S1 is 140-200 DEG C, and the reaction time is 6-9 h.

[0014] Further, in step S2, the ratio of crude product to silica gel is 1:1.2-1:2;

[0015] In some embodiments, the elution solvent is selected from methanol and ethyl acetate at a volume ratio of 1:5, methanol and dichloromethane at a volume ratio of 1:6, and methanol and petroleum ether at a volume ratio of 1:8.

[0016] In a preferred embodiment, methanol and ethyl acetate at a volume ratio of 1:5 are selected as the eluent.

[0017] In some embodiments, in step S2, the drying conditions are rotary evaporation followed by freeze-drying or vacuum drying.

[0018] Further, in step S3, the dye wastewater includes but is not limited to dye wastewater containing one or a combination of rhodamine B, China blue, methyl orange, methylene blue, and indigo carmine.

[0019] Further, in step S3, the pH of the dye wastewater degradation system is 0-4.

[0020] In some embodiments, the pH of the dye wastewater degradation system is 0-2.

[0021] Further, in step S3, the light conditions are sunlight or a xenon lamp.

[0022] In a preferred embodiment, in step S3, the light conditions are sunlight. In the method for photocatalytic degradation of dye wastewater provided in the present application, after adding the photocatalytic carbon dots to the dye wastewater, the reaction can be carried out under sunlight, which can save a large amount of energy in industrial applications.

[0023] Further, in step S3, the concentration of carbon dots in the dye wastewater degradation system is 0.08-0.44 g / L. The photocatalytic carbon dots provided in the present application have high catalytic efficiency and can effectively catalyze the degradation of dye wastewater at a low content.

[0024] As a preferred, the aforementioned method for photocatalytic degradation of dye wastewater further comprises step S4, photocatalyst carbon dot recovery: using column chromatography to recover, pouring the used carbon dot solution into a chromatography column, after the solution flows out of the chromatography column, adding ethanol to the chromatography column for elution, until there is no fluorescent substance in the effluent; collecting the carbon dot ethanol solution by rotary evaporation and drying to obtain recovered photocatalytic carbon dot powder.

[0025] In a second aspect, the present application provides a photocatalyst for degrading dye wastewater, which is prepared by steps S1 and S2 in the aforementioned method for photocatalytic degradation of dye wastewater.

[0026] In a third aspect, the application provides a rhodamine B-containing dye wastewater degradation system, which adopts the method for photocatalytic degradation of dye wastewater described above; in the rhodamine B-containing dye wastewater degradation system, the wastewater to be treated is divided into two parts, the first part is used to prepare the photocatalyst carbon dots, and the prepared photocatalyst carbon dots are added into the second part of the wastewater to be treated, so as to realize wastewater treatment under light irradiation.

[0027] The system can realize efficient photocatalytic degradation of the rhodamine B-containing dye wastewater without external photocatalyst.

[0028] Beneficial effects:

[0029] (1) The application is based on the concept of "waste treatment with waste", and the dye wastewater containing rhodamine B from a printing and dyeing plant is used as raw material to prepare carbon dot materials with photocatalytic activity by one-step hydrothermal method, and the carbon dot materials are used as photocatalysts to degrade the dye wastewater by using various active oxygen generated under light stimulation, which has excellent degradation effect; the actual dye wastewater can be effectively treated under acidic conditions and light conditions, and the discharge standard is met;

[0030] (2) The photocatalyst for degrading dye wastewater provided by the application has the characteristics of high catalytic efficiency and low catalyst dosage, and the catalyst concentration is as low as 0.08 g / L; and the degradation speed is fast, and 97% of rhodamine B can be degraded in 25 minutes;

[0031] (3) The photocatalyst carbon dots prepared by the application can be recycled by cation exchange resin, and the photocatalytic performance of the recycled carbon dots is stable, and the degradation performance still remains more than 85% after four cycles;

[0032] (4) The dye wastewater degradation method of the application can catalyze the reaction under natural light without additional energy, so as to realize efficient catalytic degradation of dye wastewater;

[0033] (5) The application provides a new way for resource utilization of waste, and also provides a method for treatment of printing and dyeing wastewater, which has good practical applicability. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 1;

[0035] Figure 2 UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 2;

[0036] Figure 3 UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 3;

[0037] Figure 4UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 4;

[0038] Figure 5 UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 5;

[0039] Figure 6 UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 6;

[0040] Figure 7 UV absorption spectrum of rhodamine B degraded by carbon dots prepared in Example 7;

[0041] Figure 8 Degradation rate of rhodamine B at different pH under light;

[0042] Figure 9 Degradation rate of rhodamine B at different carbon dot concentrations under light;

[0043] Figure 10 Photocatalytic degradation of different dyes by carbon dots prepared in Example 4.a.Chinese orchid;b.methyl orange;c.methylene blue;d.indigo carmine;

[0044] Figure 11 Degradation of actual printing and dyeing wastewater.a.degradation of printing and dyeing wastewater by carbon dots under xenon lamp;b.degradation of printing and dyeing wastewater by carbon dots under sunlight;c.diagram of device for degrading printing and dyeing wastewater by carbon dots under sunlight;

[0045] Figure 12 a.diagram of device for recycling carbon dots;b.circulation test experiment. DETAILED DESCRIPTION

[0046] In order to make the above-mentioned objects, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below in combination with the description of the embodiments.

[0047] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0048] (1) Degradation performance evaluation: the absorbance ratio (C / C0) of the maximum characteristic absorption peak of the dye in the ultraviolet-visible spectrum before and after degradation is used to evaluate the photocatalytic performance of the carbon dots, wherein C is the concentration of the dye solution at a certain time, C0 is the concentration of the dye solution at the initial time, and the degradation rate is (C0-C) / C0, which is used to evaluate the performance of the carbon dots in degrading the dye.

[0049] (2) The dye wastewater in the example is from a dyeing factory in Wuxi. The COD value of the wastewater is 5000-7000. According to the working condition, the concentration fluctuates. The main component is rhodamine B, and there are also some methylene blue, China blue and methyl orange. The total content of methylene blue, China blue and methyl orange in the water body is about 10%-15%.

[0050] Example 1

[0051] 300 mL of dye wastewater was measured in a beaker, 13 mL of concentrated sulfuric acid (0.8 mol / L) was added, and the solution was transferred to a 1 L polytetrafluoroethylene reactor after mixing. The solution was reacted at 180°C for 8h. After the reaction was completed, it was cooled to room temperature, and the crude product was collected. The crude product was mixed with silica gel, and methanol and ethyl acetate (1:5, v / v) were used as eluent to purify and separate by column chromatography. According to the luminescence of the substances in the column chromatography, there are two main components in the chromatographic column. The first component was collected, and after rotary evaporation and freeze-drying, a solid powder was obtained, which was a photocatalyst carbon dot.

[0052] 5mg / L rhodamine B was used as a pollutant, and 0.2g / L carbon dots were used as a photocatalyst. The pH was adjusted to 2, as shown in Figure 1 The absorbance ratio of rhodamine B at 554nm before and after degradation showed that the carbon dots could remove 79% of rhodamine B in 50s.

[0053] Example 2

[0054] 300 mL of dye wastewater was measured in a beaker, 19.6 mL of concentrated sulfuric acid (1.2 mol / L) was added, and the solution was transferred to a 1 L polytetrafluoroethylene reactor after mixing. The solution was reacted at 180°C for 8h. After the reaction was completed, it was cooled to room temperature, and the crude product was collected. The crude product was mixed with silica gel, and methanol and ethyl acetate (1:5, v / v) were used as eluent to purify and separate by column chromatography. According to the luminescence of the substances in the column chromatography, there are two main components in the chromatographic column. The first component was collected, and after rotary evaporation and freeze-drying, a solid powder was obtained, which was a photocatalyst carbon dot.

[0055] 5mg / L rhodamine B was used as a pollutant, and 0.2g / L carbon dots were used as a photocatalyst. The pH was adjusted to 2, as shown in Figure 2 The absorbance ratio of rhodamine B at 554nm before and after degradation showed that the carbon dots could remove 79% of rhodamine B in 50s.

[0056] Example 3

[0057] Take 300 mL of dye wastewater in a beaker, add 16.4 mL of concentrated sulfuric acid (1 mol / L) to it, mix well, and then transfer the solution to a 1 L polytetrafluoroethylene reactor, and react at 180°C for 9h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, and after rotary evaporation and freeze-drying, the solid powder is obtained, which is the photocatalyst carbon dots.

[0058] Take 300 mL of dye wastewater in a beaker, add 16.4 mL of concentrated sulfuric acid (1 mol / L) to it, mix well, and then transfer the solution to a 1 L polytetrafluoroethylene reactor, and react at 180°C for 9h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, and after rotary evaporation and freeze-drying, the solid powder is obtained, which is the photocatalyst carbon dots. Figure 3

[0059] Example 4:

[0060] Take 300 mL of dye wastewater in a beaker, add 16.4 mL of concentrated sulfuric acid (1 mol / L) to it, mix well, and then transfer the solution to a 1 L polytetrafluoroethylene reactor, and react at 180°C for 9h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, and after rotary evaporation and freeze-drying, the solid powder is obtained, which is the photocatalyst carbon dots.

[0061] Take 300 mL of dye wastewater in a beaker, add 16.4 mL of concentrated sulfuric acid (1 mol / L) to it, mix well, and then transfer the solution to a 1 L polytetrafluoroethylene reactor, and react at 180°C for 9h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, and after rotary evaporation and freeze-drying, the solid powder is obtained, which is the photocatalyst carbon dots. Figure 4

[0062] Example 5:

[0063] Take 300 mL of dye wastewater in a beaker, add 16.4 mL of concentrated sulfuric acid (1 mol / L) to it, mix well, and then transfer the solution to a 1 L polytetrafluoroethylene reactor, and react at 180°C for 9h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, and after rotary evaporation and freeze-drying, the solid powder is obtained, which is the photocatalyst carbon dots.

[0064] ​​With 5mg / L rhodamine B as pollutant, 0.2g / L carbon dots as photocatalyst, adjusting pH to 2, as shown in Figure 5 The absorbance ratio of rhodamine B at 554nm before and after degradation shows that the carbon dots can remove 71% of rhodamine B within 50s.

[0065] Example 6:

[0066] Take 300mL dye wastewater in a beaker, add 16.4mL concentrated sulfuric acid (1mol / L) to it, mix well, then transfer the solution to a 1L polytetrafluoroethylene reactor, and react at 140℃ for 8h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel evenly, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, rotary evaporate, freeze-dry to obtain the solid powder, which is the photocatalyst carbon dots.

[0067] With 5mg / L rhodamine B as pollutant, 0.2g / L carbon dots as photocatalyst, adjusting pH to 2, as shown in Figure 6 The absorbance ratio of rhodamine B at 554nm before and after degradation shows that the carbon dots can remove 78% of rhodamine B within 50s.

[0068] Example 7:

[0069] Take 300mL dye wastewater in a beaker, add 16.4mL concentrated sulfuric acid (1mol / L) to it, mix well, then transfer the solution to a 1L polytetrafluoroethylene reactor, and react at 200℃ for 8h. After the reaction is completed, cool to room temperature, and collect the crude product. Mix the crude product with silica gel evenly, and use methanol and ethyl acetate (1:5, v / v) as eluent, and use column chromatography for purification and separation. According to the luminescence of the substances in the column chromatography, there are two main components in the column, collect the first component, rotary evaporate, freeze-dry to obtain the solid powder, which is the photocatalyst carbon dots.

[0070] With 5mg / L rhodamine B as pollutant, 0.2g / L carbon dots as photocatalyst, adjusting pH to 2, as shown in Figure 6 The absorbance ratio of rhodamine B at 554nm before and after degradation shows that the carbon dots can remove 85% of rhodamine B within 50s.

[0071] Example 8:

[0072] Rhodamine B as the pollutant, the carbon dots prepared in Example 3 were selected as the photocatalyst, and the concentration of the carbon dots was 0.2 g / L. The degradation of Rhodamine B under different pH (pH was 0, 1, 2, 4, 6, and 8, respectively) test conditions was investigated. As shown in Figure 8 at pH 1, Rhodamine B could hardly be degraded under no light conditions, and under light conditions, the removal rate of Rhodamine B was 96% within 30 min. When pH was 2, the degradation rate of Rhodamine B could still reach more than 50%. The degradation rate decreased as the pH continued to increase.

[0073] Example 9:

[0074] Rhodamine B as the pollutant, the carbon dots prepared in Example 3 were selected as the photocatalyst, and the concentration of the carbon dots was 0.2 g / L. The degradation of Rhodamine B under different pH (pH was 0, 1, 2, 4, 6, and 8, respectively) test conditions was investigated. As shown in Figure 9 under no light conditions, Rhodamine B could hardly be degraded, and under light conditions, the degradation efficiency of Rhodamine B could all reach more than 90% within 25 min when the concentration of the carbon dots was in the range of 0.08-0.44 g / L.

[0075] Example 10: Degradation of simulated dye wastewater

[0076] 25 mL of 50 mg / L Chinese orchid, methyl orange, methylene blue, and indigo carmine solutions were respectively prepared, the pH of the solutions was adjusted to 1, 0.17 g / L of the carbon dots prepared in Example 3 was added, and the ultraviolet-visible spectrum of the dye solution was recorded every certain time under the irradiation of a xenon lamp (300 W). The maximum absorption peak position of different dyes was different, the characteristic peak of methyl orange was at 505 nm, the characteristic peak of methylene blue was at 665 nm, and the characteristic peak of Chinese orchid was at 600 nm.

[0077] Under the conditions of adding the carbon dots and light irradiation, the experimental results are shown in Figure 10 As shown in the figure, the characteristic peak intensity of all dyes gradually weakened, indicating that the concentration of the dyes gradually decreased. Indigo carmine could be completely degraded within 4 min, and Chinese orchid, methyl orange, and methylene blue were degraded within 6 min, 12 min, and 20 min, respectively, and the degradation rate was all more than 90%.

[0078] Example 11: Degradation of actual printing and dyeing wastewater

[0079] Two 1.5L of actual printing and dyeing wastewater were measured respectively, one was used to study the photocatalytic performance of carbon dots under xenon lamp, and the other was placed outdoors to investigate the actual photocatalytic effect of carbon dots under sunlight. The initial pH of the system was controlled to be about 1, and the concentration of carbon dots in the system was 0.17g / L. After a certain period of time, a certain volume of water sample was removed, and the COD value of the water sample was measured according to the national standard method (GB11914-8) as 5050mg / L. The photocatalytic degradation performance of carbon dots under xenon lamp and sunlight was evaluated by the COD ratio (COD / COD0) before and after degradation. It can be seen from Figure 11 that under the condition of xenon lamp irradiation, 92% of COD can be removed within 60min, and under the condition of sunlight irradiation, 91% of COD can be removed within 90min.

[0080] Example 12: Recovery of carbon dots

[0081] As shown in Figure 12 , 100g of cationic resin was weighed and loaded into a chromatographic column, and the carbon dot solution after use in Example 3 was poured into the chromatographic column. After the solution in the chromatographic column was completely drained, ethanol was used to elute the cationic resin after adsorbing the carbon dots, and the elution was stopped until no green fluorescence appeared in the elution. The collected ethanol solution of carbon dots was evaporated by rotary evaporation and vacuum dried to obtain carbon dot powder for standby. After four cycles of recovery by cationic resin, the photocatalytic degradation performance of carbon dots on printing and dyeing wastewater still maintained more than 85%.

[0082] In summary, the printing and dyeing wastewater containing rhodamine B from a dyeing factory was used as raw material to prepare carbon dot materials with photocatalytic activity by one-step hydrothermal method. The carbon dots can effectively treat actual dye wastewater under acidic conditions and light conditions. The prepared carbon dots have the characteristics of high catalytic efficiency, low catalyst dosage, fast wastewater degradation speed, and can be recycled and reused. The photocatalytic performance of the recovered carbon dots is stable, and the degradation performance still maintains more than 85% degradation effect after four cycles.

[0083] The above examples are only for illustrating the technical concept and characteristics of the present application, the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and it cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for photocatalytic degradation of dye wastewater, characterized in that, The method comprises the following steps: Step S1, preparing photocatalyst carbon dots: adding sulfuric acid to dye wastewater containing rhodamine B, and reacting under heating conditions to prepare a crude product containing photocatalyst carbon dots; Step S2, separating and purifying the photocatalyst carbon dots: mixing the carbon dot crude product prepared in step S1 with silica gel uniformly, purifying and separating by column chromatography, eluting with an eluent, collecting the first component, and drying to obtain the photocatalyst carbon dots; Step S3, degrading dye wastewater: adding the photocatalyst carbon dots prepared in step S2 to the dye wastewater, and treating the dye wastewater under acidic conditions and light conditions; In step S1, the reaction temperature is 140-200°C, and the reaction time is 6-9h; In step S3, the pH of the dye wastewater degradation system is 0-4.

2. A method of photocatalytic degradation of dye wastewater as claimed in claim 1, wherein, In the reaction system of step S1, the concentration of sulfuric acid is 0.8-1.2mol / L.

3. A method of photocatalytic degradation of dye wastewater as claimed in claim 1, wherein, In step S2, the eluent is selected from methanol and ethyl acetate in a volume ratio of 1:5, methanol and dichloromethane in a volume ratio of 1:6, or methanol and petroleum ether in a volume ratio of 1:8; and the drying conditions are rotary evaporation followed by freeze-drying or vacuum drying.

4. A method of photocatalytic degradation of dye wastewater as claimed in claim 1, wherein, the photocatalyst is Ti02. In step S3, the dye wastewater includes dye wastewater containing one or a combination of rhodamine B, Chinese blue, methyl orange, methylene blue, and indigo carmine.

5. A method of photocatalytic degradation of dye wastewater as claimed in claim 1, wherein, In step S3, the light conditions are sunlight or a xenon lamp.

6. A method of photocatalytic degradation of dye wastewater as claimed in claim 1, wherein, In step S3, the concentration of the carbon dots in the dye wastewater degradation system is 0.08-0.44g / L.

7. A method of photocatalytic degradation of dye wastewater as claimed in claim 1, wherein, It also comprises step S4, recovering the photocatalyst carbon dots: recovering by column chromatography, pouring the used carbon dot solution into a chromatography column, adding ethanol to the chromatography column for elution after the solution flows out of the chromatography column, and stopping when there is no fluorescent substance in the effluent; and obtaining carbon dot powder by rotary evaporation and drying of the collected carbon dot ethanol solution.

8. A photocatalyst for degrading dye wastewater, characterized by, The photocatalyst carbon dots are prepared by steps S1 and S2 in the method for photocatalytic degradation of dye wastewater according to any one of claims 1-6.

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