High-efficiency cds / ag3po4 composite photocatalyst and preparation method and application thereof

Abstract

The application discloses a kind of efficient CDs / Ag3PO4 Composite photocatalyst and its preparation method and application, the O-CDs is prepared with citric acid as carbon source to CDs / Ag3PO4 Composite photocatalyst, then the surface chemical structure of O-CDs is regulated using different reagents, then further in-situ precipitation Ag3PO4, and the CDs / Ag3PO4 Composite photocatalyst with different band structure is prepared.Meanwhile, the application of the prepared CDs / Ag3PO4 Composite photocatalyst is applied to photocatalytic degradation reaction to degrade organic dye, compared with the CDs / Ag3PO4 Composite photocatalyst prepared by O-CDs without regulation, the catalytic degradation effect is better.Compared with prior art, the efficient CDs / Ag3PO4 Composite photocatalyst prepared by the application has higher photocatalytic activity.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a high-efficiency CDs / Ag3PO4 composite photocatalyst, its preparation method, and its application. Background Technology

[0002] With economic development, more and more water resources are severely polluted, and the number of organic pollutants that are difficult to decompose in water bodies is increasing, which has a significant negative impact on human survival and the sustainable development of the environment. Currently, the main technology for treating organic matter in water is biotechnology, but its effectiveness in treating highly toxic synthetic organic compounds is not ideal. Semiconductor photocatalysis technology can degrade organic matter in water that is difficult to treat biologically, offering advantages such as high removal rates, no secondary pollution, fast degradation rates, and mild reaction conditions, making it a promising research and application area in pollution treatment. Silver phosphate (Ag3PO4) has a suitable band gap and can effectively photocatalytically degrade organic pollutants such as dyes and antibiotics in water using visible light, achieving water purification and making it an ideal catalytic material in the field of photocatalysis. However, Ag3PO4 suffers from drawbacks such as low aqueous solubility, poor adsorption performance, photocorrosion, and poor stability, limiting its application prospects.

[0003] Carbon nanodots (CDs) are a novel type of zero-dimensional carbon-based nanomaterial. Their surfaces are coated with various oxygen-containing groups such as hydroxyl, carbonyl, and carboxyl groups, exhibiting numerous excellent properties including low toxicity, photostability, broad absorption, tunable fluorescence emission, upconversion luminescence, and good water solubility. They have been explored for use in composites with Ag3PO4 to enhance the photocatalytic activity of Ag3PO4 for the degradation of environmental pollutants. However, the photocatalytic efficiency of this composite photocatalyst is significantly affected by the surface structure of the carbon dots.

[0004] Therefore, how to provide a highly efficient CDs / Ag3PO4 composite photocatalyst with improved photocatalytic activity to achieve the technical effect of effectively degrading organic pollutants in water is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a highly efficient CDs / Ag3PO4 composite photocatalyst. O-CDs (initial carbon dots) are prepared, and then the surface chemical structure of O-CDs is adjusted by directional oxidation / reduction technology, thereby effectively improving and regulating the photocatalytic activity of CDs / Ag3PO4 composite photocatalyst and improving its photocatalytic degradation efficiency.

[0006] To achieve the above objectives, this invention provides a method for preparing a high-efficiency CDs / Ag3PO4 composite photocatalyst, the preparation method comprising:

[0007] S1. O-CDs were synthesized via a hydrothermal method using citric acid as a precursor.

[0008] S2. The surface chemical structure of the obtained O-CDs is controlled to obtain the controlled O-CDs;

[0009] S3. Dissolve silver acetate, polyvinylpyrrolidone, and the obtained regulated O-CDs in water, and add 0.05-0.1 mol / L sodium hydrogen phosphate aqueous solution dropwise to obtain a suspension. Stir the suspension at 300-500 rpm for 3-5 hours in the dark at 15-30℃, then filter and collect the solid. Wash the collected solid with water 3-4 times, and then dry it in the dark at 45-60℃ for 10-14 hours to obtain the CDs / Ag3PO4 composite photocatalyst.

[0010] In the first aspect, the mass ratio of silver acetate, polyvinylpyrrolidone, and the obtained regulated O-CDs is (150–350):(200–700):(1.5–4); the mass and volume ratio of the obtained regulated O-CDs to water is (1.5–4) mg:(15–40) mL; the mass and volume ratio of the obtained regulated O-CDs to the aqueous solution of disodium hydrogen phosphate is (1.5–4) mg:(10–30) mL; and the pore size of the filter membrane used for filtration is 0.22–0.8 μm.

[0011] In the first aspect, the synthesis of O-CDs using citric acid as a precursor via a hydrothermal method specifically includes: placing citric acid in a reaction vessel, then heating it to 180–220°C at a heating rate of 5–15°C / min and holding it at that temperature for 2–5 hours; then removing it and allowing it to cool naturally to 15–30°C to obtain crude O-CDs; adjusting the pH of the crude O-CDs to 6.9–7.1 with a 0.5–1.5 mol / L sodium hydroxide aqueous solution, then dialyzing it in a dialysis bag with a molecular weight cutoff of 500 Da for 2–5 days; then collecting the substance in the dialysis bag and freeze-drying it for 12–24 hours to obtain O-CDs.

[0012] In the first aspect, the process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with NaBH4 to obtain carbon dots labeled as NaBH4-CDs.

[0013] In the first aspect, the surface hydroxylation treatment of the obtained O-CDs to obtain carbon dots labeled NaBH4-CDs specifically includes: adding O-CDs to an aqueous solution of sodium borohydride with a concentration of 1-3 mol / L, and stirring at 300-500 rpm for 22-26 hours at 15-30°C to obtain a mixed solution; then adjusting the pH of the obtained mixed solution to 6.9-7.1 using an aqueous solution of hydrochloric acid with a concentration of 0.1-1 mol / L, and then dialyzing it in a dialysis bag with a molecular weight cutoff of 500 Da for 2-5 days; then collecting the material in the dialysis bag and freeze-drying it for 12-24 hours to obtain carbon dots labeled NaBH4-CDs; the mass-to-volume ratio of O-CDs to the aqueous solution of sodium borohydride is (15-30) mg:(3.75-7.5) mL.

[0014] In the first aspect, the process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with Des Martin reagent (DMP) to obtain carbon dots labeled as DMP-CDs.

[0015] In the first aspect, the treatment of the obtained O-CDs with Dys-Martin reagent (DMP) to obtain carbon dots labeled as DMP-CDs specifically includes: dissolving the O-CDs in water to obtain an aqueous solution of O-CDs; then dispersing DMP in dichloromethane, and then adding it to the obtained aqueous solution of O-CDs; stirring at 300-500 rpm for 22-26 hours at 15-30°C; then adding an aqueous solution of sodium bicarbonate with a concentration of 0.5-1.5 g / mL at a titration rate of 5-20 mL / min until no bubbles are generated during the titration; then separating the aqueous phase and the organic phase using a separatory funnel and collecting the aqueous phase to obtain an aqueous carbon dot solution. The pH of the aqueous carbon dot solution was adjusted to 6.9–7.1 using a 0.5–1.5 mol / L hydrochloric acid aqueous solution and a 0.5–1.5 mol / L sodium hydroxide aqueous solution. The solution was then dialyzed for 2–5 days in a dialysis bag with a molecular weight cutoff of 500 Da. The contents of the dialysis bag were collected and freeze-dried for 12–24 hours to obtain carbon dots labeled DMP-CDs. The mass-to-volume ratio of O-CDs to water was (12–30) mg:(150–300) μL; the mass-to-volume ratio of DMP to dichloromethane was (0.075–0.115) g:(1.5–3) mL.

[0016] In the first aspect, the process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with HNO3 to obtain carbon dots labeled as HNO3-CDs.

[0017] In the first aspect, the process of treating the obtained O-CDs with HNO3 to obtain carbon dots labeled as HNO3-CDs specifically includes: adding O-CDs to a nitric acid solution with a concentration of 1.5–2.5 mol / L, stirring at 300–500 rpm for 10–14 hours at 15–30°C, adjusting the pH to 6.9–7.1 using a sodium hydroxide aqueous solution with a concentration of 0.5–1.5 mol / L, and then dialyzing for 2–5 days using a dialysis bag with a molecular weight cutoff of 500 Da. After dialysis, the material in the dialysis bag is collected, and the collected material is freeze-dried for 12–24 hours to obtain carbon dots labeled as HNO3-CDs; the mass and volume ratio of O-CDs to nitric acid solution is (15–30) mg:(4–7) mL.

[0018] This invention also provides an application of a highly efficient CDs / Ag3PO4 composite photocatalyst, which uses the prepared highly efficient CDs / Ag3PO4 composite photocatalyst as a catalyst to photocatalytically degrade organic dyes.

[0019] Beneficial effects:

[0020] Due to the adoption of the above technical solution, compared with the prior art, the present invention has the following advantages: 1) The present invention uses citric acid as a carbon source, prepares O-CDs (initial carbon dots) by hydrothermal method, and uses different reagents to directionally oxidize or reduce the functional groups on the surface of the carbon dots to change the surface chemical structure of the carbon dots. Then, after further in-situ precipitation of Ag3PO4, composite photocatalysts CDs / Ag3PO4 with different band structures are prepared. In the present invention, the carbon dots are reduced by NaBH4, oxidized by Dysmann reagent (DMP), or oxidized by nitric acid (HNO3) to change the surface chemical structure of the carbon dots. After the carbon dots are reduced by NaBH4, oxidized by Dysmann reagent (DMP), or oxidized by nitric acid (HNO3), the carbon-carbon double bond content in the carbon dots is increased; 2) After the carbon dots are oxidized by Dysmann reagent (DMP), the carbon-carbon double bond content in the carbon dots is increased, and the carbonyl content in the carbon dots is also increased, which further improves the CDs / Ag3PO4 prepared using the oxidized carbon dots. 3) After oxidizing carbon dots with nitric acid (HNO3), the carbon double bond content in the carbon dots is increased, which further improves the photocatalytic activity and photocatalytic degradation efficiency of the CDs / Ag3PO4 composite photocatalyst prepared using the oxidized carbon dots; 4) After reducing carbon dots with NaBH4, the carbonyl content of the carbon dots decreases, but the carbon double bond content increases. Based on the competitive effect of the increase in carbon double bond content and the decrease in carbonyl content, the catalytic efficiency of the CDs / Ag3PO4 composite photocatalyst prepared using the carbon dots is higher than that of the CDs / Ag3PO4 composite photocatalyst prepared without reducing carbon dots with NaBH4; 5) In the prepared CDs / Ag3PO4 composite photocatalyst, the carbon material and the Ag3PO4 composite photocatalyst follow a Z-type catalyst structure. Electrons located on the conduction band of Ag3PO4 are transferred to the carbon dots, which promotes the separation of electrons and holes on the surface of Ag3PO4. An increase in the content of carbonyl groups and carbon-carbon double bonds in carbon dots can alter their electronic structure. Increased carbonyl content leads to a narrowing of the band gap, while an increase in carbon-carbon double bonds indicates π-wavelength variation. - Increased delocalization of the electronic system leads to a narrower band gap (the conduction band of carbon dots gradually decreases, while the valence band gradually increases), which is more conducive to the transfer of conduction band electrons to carbon dots in silver phosphate catalysts. This reduces the probability of electron-hole recombination in silver phosphate catalysts, thereby improving the catalytic efficiency of composite photocatalysts. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the preparation process of the CDs-Ag3PO4 composite photocatalyst in Example 1 of the present invention;

[0023] Figure 2 These are the kinetic curves of the CDs / Ag3PO4 composite photocatalysts prepared in Examples 1 to 4 of this invention, and the fitting curves of the corresponding kinetic constants of the catalysts, for the photocatalytic degradation of methyl orange at room temperature and atmospheric pressure.

[0024] Figure 3 This is a transmission electron microscope characterization image of the CDs / Ag3PO4 composite photocatalyst prepared in Example 1 of this invention;

[0025] Figure 4 This is a transmission electron microscope characterization image of the CDs / Ag3PO4 composite photocatalyst prepared in Example 2 of this invention;

[0026] Figure 5 This is a transmission electron microscope characterization image of the CDs / Ag3PO4 composite photocatalyst prepared in Example 3 of this invention;

[0027] Figure 6 This is a transmission electron microscope characterization image of the CDs / Ag3PO4 composite photocatalyst prepared in Example 4 of this invention;

[0028] Figure 7 These are the infrared spectra of the carbon dots prepared in Examples 1 to 4 of this invention;

[0029] Figure 8 These are high-resolution X-ray photoelectron spectra of the carbon dots prepared in Examples 1 to 4 of this invention;

[0030] Figure 9 This invention describes the effect of different capture agents on the photocatalytic rate of the CDs / Ag3PO4 composite photocatalyst prepared in Example 1. Detailed Implementation

[0031] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this specification are within the scope of protection of this invention.

[0032] Example 1

[0033] like Figure 1 As shown, this embodiment provides a method for preparing a high-efficiency CDs / Ag3PO4 composite photocatalyst, specifically including: S1, synthesizing O-CDs via a hydrothermal method using citric acid as a precursor; S2, regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs; S3, dissolving silver acetate, polyvinylpyrrolidone, and the obtained regulated O-CDs in water, and adding dropwise a 0.05-0.1 mol / L sodium hydrogen phosphate aqueous solution to obtain a suspension; stirring the obtained suspension at 300-500 rpm for 3-5 hours in a light-protected state at 15-30℃, then filtering and collecting the solid. The obtained solid was washed with water 3-4 times, and then dried at 45-60℃ in the dark for 10-14 hours to obtain the CDs / Ag3PO4 composite photocatalyst; the mass ratio of silver acetate, polyvinylpyrrolidone and the obtained regulated O-CDs was (150-350):(200-700):(1.5-4); the mass and volume ratio of the obtained regulated O-CDs to water was (1.5-4) mg:(15-40) mL; the mass and volume ratio of the obtained regulated O-CDs to disodium hydrogen phosphate aqueous solution was (1.5-4) mg:(10-30) mL; the pore size of the filter membrane used for filtration was 0.22-0.8 μm.

[0034] Compared with the prior art, the preparation method of the high-efficiency CDs / Ag3PO4 composite photocatalyst provided in Embodiment 1 of the present invention has the following advantages: 1) The present invention uses citric acid as a carbon source, prepares O-CDs (initial carbon dots) by hydrothermal method, and uses different reagents to directionally oxidize or reduce the functional groups on the surface of the carbon dots to change the surface chemical structure of the carbon dots. Then, after further in-situ precipitation of Ag3PO4, composite photocatalysts CDs / Ag3PO4 composite photocatalysts with different band structures are prepared. In the present invention, Na is used... NaBH4 reduction treatment, DMP oxidation, or nitric acid (HNO3) oxidation of carbon dots alters their surface chemical structure. NaBH4 reduction treatment, DMP oxidation, or HNO3 oxidation all increase the carbon-carbon double bond content of the carbon dots. 2) DMP oxidation of carbon dots not only increases the carbon-carbon double bond content but also the carbonyl group content, further enhancing the chemical composition of the oxidized carbon dots. The photocatalytic activity and photocatalytic degradation efficiency of the CDs / Ag3PO4 composite photocatalyst prepared by carbon dots were improved; 3) After oxidation of carbon dots with nitric acid (HNO3), the carbon-carbon double bond content in the carbon dots was increased, which further improved the photocatalytic activity and photocatalytic degradation efficiency of the CDs / Ag3PO4 composite photocatalyst prepared by the oxidized carbon dots; 4) After reduction treatment of carbon dots with NaBH4, the carbonyl content of the carbon dots decreased, but the carbon-carbon double bond content increased. The competitive effect of increased carbonyl content and decreased carbonyl content leads to a higher catalytic efficiency of the CDs / Ag3PO4 composite photocatalyst prepared via this carbon dot compared to the CDs / Ag3PO4 composite photocatalyst prepared without NaBH4 reduction treatment of the carbon dot; 5) In the prepared CDs / Ag3PO4 composite photocatalyst, the carbon material and Ag3PO4 composite photocatalyst follow a Z-type catalyst structure, with electrons located on the conduction band of Ag3PO4 transferred to the carbon dot, promoting the separation of electrons and holes on the Ag3PO4 surface. The increased carbonyl and carbon-carbon double bond content in the carbon dot can change its electronic structure. The increase in carbonyl content causes a narrowing of the band gap, and the increase in carbon-carbon double bond indicates π - Increased delocalization of the electronic system leads to a narrower band gap (the conduction band of carbon dots gradually decreases, while the valence band gradually increases), which is more conducive to the transfer of conduction band electrons to carbon dots in silver phosphate catalysts. This reduces the probability of electron-hole recombination in silver phosphate catalysts, thereby improving the catalytic efficiency of composite photocatalysts.

[0035] In some possible implementations, the synthesis of O-CDs using citric acid as a precursor via a hydrothermal method specifically includes: placing citric acid in a reaction vessel, then heating it to 180–220°C at a heating rate of 5–15°C / min and holding it at that temperature for 2–5 hours; then removing it and allowing it to cool naturally to 15–30°C to obtain crude O-CDs; adjusting the pH of the crude O-CDs to 6.9–7.1 with a 0.5–1.5 mol / L sodium hydroxide aqueous solution, then dialyzing it in a dialysis bag with a molecular weight cutoff of 500 Da for 2–5 days; then collecting the substance in the dialysis bag and freeze-drying it for 12–24 hours to obtain O-CDs.

[0036] Specifically, the process of hydrothermal synthesis of O-CDs using citric acid as a carbon source at 180–220℃ is simple and convenient. Citric acid is widely available, making it easy to prepare on a large scale and thus economically beneficial.

[0037] In some possible implementations, the process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with NaBH4 to obtain carbon dots labeled as NaBH4-CDs; the process of treating the obtained O-CDs with NaBH4 to obtain carbon dots labeled as NaBH4-CDs specifically includes: adding the O-CDs to an aqueous solution of sodium borohydride with a concentration of 1-3 mol / L, and stirring at 300-500 rpm at 15-30°C. The mixture was stirred at a stirring speed for 22–26 hours to obtain a mixed solution. The pH of the mixed solution was then adjusted to 6.9–7.1 using a 0.1–1 mol / L hydrochloric acid aqueous solution. The solution was then placed in a dialysis bag with a molecular weight cutoff of 500 Da and dialyzed for 2–5 days. The contents of the dialysis bag were then collected and freeze-dried for 12–24 hours to obtain carbon dots labeled NaBH4-CDs. The mass-to-volume ratio of the O-CDs to the sodium borohydride aqueous solution was (15–30) mg:(3.75–7.5) mL.

[0038] Specifically, surface hydroxylation treatment of O-CDs with sodium borohydride can increase the hydroxyl content on the surface of O-CDs. The increase in hydroxyl content is formed by the reduction of carbonyl groups, which will reduce the carbonyl content. However, the increased carbon-carbon double bond content of O-CDs after sodium borohydride treatment will improve the catalytic efficiency of the CDs / Ag3PO4 composite photocatalyst prepared from O-CDs treated with sodium borohydride through the competitive effect of the increased carbon-carbon double bond content and the decreased carbonyl content.

[0039] In some possible implementations, the process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with Dys-Martin reagent (DMP) to obtain carbon dots labeled as DMP-CDs; the process of treating the obtained O-CDs with DMP to obtain carbon dots labeled as DMP-CDs specifically includes: dissolving the O-CDs in water to obtain an aqueous solution of O-CDs; then dispersing DMP in dichloromethane, then adding it to the obtained aqueous solution of O-CDs, stirring at 300-500 rpm for 22-26 hours at 15-30°C, and then adding a 0.5-1.5 mol / L sodium bicarbonate aqueous solution at a titration rate of 5-20 mL / min until... No bubbles were generated during the titration. The aqueous and organic phases were then separated using a separatory funnel, and the aqueous phase was collected to obtain an aqueous carbon dot solution. The pH of the aqueous carbon dot solution was adjusted to 6.9–7.1 using a 0.5–1.5 mol / L hydrochloric acid aqueous solution and a 0.5–1.5 mol / L sodium hydroxide aqueous solution. The solution was then dialyzed in a dialysis bag with a molecular weight cutoff of 500 Da for 2–5 days. The contents of the dialysis bag were then collected and freeze-dried for 12–24 hours to obtain carbon dots labeled DMP-CDs. The mass-to-volume ratio of O-CDs to water was (12–30) mg:(150–300) μL. The mass-to-volume ratio of DMP to dichloromethane was (0.075–0.115) g:(1.5–3) mL.

[0040] Specifically, in the process of surface treatment of O-CDs using DMP, the purpose of adding sodium bicarbonate aqueous solution is to neutralize the acetic acid and excess DMP generated during the reaction by adding excess sodium bicarbonate. Surface carbonylation treatment of O-CDs using DMP increases the carbon-carbon double bond and carbonyl group content on the O-CDs surface. Since carbon-carbon double bonds and carbonyl groups have a significant impact on the band gap, this further improves the catalytic degradation efficiency of the CDs / Ag3PO4 composite photocatalyst prepared after treatment of O-CDs using DMP.

[0041] In some possible implementations, the process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with HNO3 to obtain carbon dots labeled as HNO3-CDs; the process of treating the obtained O-CDs with HNO3 to obtain carbon dots labeled as HNO3-CDs specifically includes: adding the O-CDs to a nitric acid solution with a concentration of 1.5–2.5 mol / L, and heating at 15–30°C at 300–500 rpm. The mixture is stirred at a stirring speed of 1 / min for 10–14 hours, and then the pH is adjusted to 6.9–7.1 using a sodium hydroxide aqueous solution with a concentration of 0.5–1.5 mol / L. Then, the mixture is dialyzed for 2–5 days using a dialysis bag with a molecular weight cutoff of 500 Da. After dialysis, the contents of the dialysis bag are collected and freeze-dried for 12–24 hours to obtain carbon dots labeled HNO3-CDs. The mass and volume ratio of the O-CDs to the nitric acid solution is (15–30) mg:(4–7) mL.

[0042] Specifically, surface treatment of O-CDs with nitric acid increases the carbon-carbon double bond content on the surface of O-CDs, thereby further improving the catalytic degradation efficiency of the CDs / Ag3PO4 composite photocatalyst prepared after O-CDs treatment with nitric acid.

[0043] Example 2

[0044] Example 2 of this invention provides a high-efficiency CDs / Ag3PO4 composite photocatalyst, prepared by the preparation method described in Example 1 above. Those skilled in the art will understand that this high-efficiency CDs / Ag3PO4 composite photocatalyst is prepared by hydrothermal synthesis of O-CDs (initial carbon points) using citric acid as a carbon source. Then, the surface chemical structure of the synthesized O-CDs is regulated using reagents, followed by in-situ precipitation of Ag3PO4 to prepare CDs / Ag3PO4 composite photocatalysts with different band structures. The reagents used for treatment include any one of NaBH4, Dess-Martin reagent (DMP), and nitric acid. The CDs / Ag3PO4 composite photocatalyst prepared from O-CDs treated with these reagents exhibits better photocatalytic activity compared to the CDs / Ag3PO4 composite photocatalyst prepared from untreated O-CDs. It should be noted that the high-efficiency CDs / Ag3PO4 composite photocatalyst in Example 2 was prepared according to the preparation method described in Example 1. Therefore, the performance principle of the high-efficiency CDs / Ag3PO4 composite photocatalyst in Example 2 will not be repeated here. For the parts not described in detail, please refer to Example 1.

[0045] Example 3

[0046] Example 3 of this invention provides an application of a highly efficient CDs / Ag3PO4 composite photocatalyst. The highly efficient CDs / Ag3PO4 composite photocatalyst of Example 2 is applied to the photocatalytic degradation of organic dyes, using methyl orange as the organic dye to be degraded. The CDs / Ag3PO4 composite photocatalyst prepared by this invention exhibits good photocatalytic degradation activity for methyl orange. It should be noted that the CDs / Ag3PO4 composite photocatalyst is the same as that described in Example 2. The CDs / Ag3PO4 composite photocatalyst in Example 2 was prepared according to the preparation method described in Example 1.

[0047] To further illustrate the technical solution of this application and support the technical problem to be solved by this application, specific examples of the preparation method are given below, such as Examples 1 to 4.

[0048] DMP: Des Martin reagent, CAS No.: 87413-09-0.

[0049] Example 1

[0050] 2g of citric acid was placed in a high-pressure polytetrafluoroethylene reaction vessel, then heated in a muffle furnace to 200℃ at a heating rate of 10℃ / min and held for 3 hours. After that, it was taken out and naturally cooled to 25℃ to obtain crude O-CDs product. The pH of the crude O-CDs product was adjusted to 7 with a 1mol / L sodium hydroxide aqueous solution. Then, it was placed in a dialysis bag with a molecular weight cutoff of 500Da and dialyzed for 3 days. The substance in the dialysis bag was then collected and freeze-dried for 16 hours to obtain O-CDs.

[0051] 0.25 g silver acetate, 0.5 g polyvinylpyrrolidone, and 2.5 mg of the obtained O-CDs were dissolved in 25 mL of water. 20 mL of 0.075 mol / L disodium hydrogen phosphate aqueous solution was added dropwise to obtain a suspension. The suspension was stirred at 400 rpm for 4 hours at 25 °C in the dark. The mixture was then filtered through a 0.45 μm filter membrane, and the solid was collected. The collected solid was washed three times with water and then dried in an oven at 50 °C in the dark for 12 hours to obtain the CDs / Ag3PO4 composite photocatalyst.

[0052] Example 2

[0053] 2g of citric acid was placed in a high-pressure polytetrafluoroethylene reaction vessel, then heated in a muffle furnace to 200℃ at a heating rate of 10℃ / min and held for 3 hours. After that, it was taken out and naturally cooled to 25℃ to obtain crude O-CDs product. The pH of the crude O-CDs product was adjusted to 7 with a 1mol / L sodium hydroxide aqueous solution. Then, it was placed in a dialysis bag with a molecular weight cutoff of 500Da and dialyzed for 3 days. The substance in the dialysis bag was then collected and freeze-dried for 16 hours to obtain O-CDs.

[0054] 20 mg of the obtained O-CDs were added to 5 mL of a 2 mol / L sodium borohydride aqueous solution and stirred at 400 rpm for 24 hours at 25 °C to obtain a mixed solution. The pH of the mixed solution was then adjusted to 7 using a 1 mol / L hydrochloric acid aqueous solution. The solution was then placed in a dialysis bag with a molecular weight cutoff of 500 Da and dialyzed for 3 days. The contents of the dialysis bag were then collected and freeze-dried for 18 hours to obtain carbon dots labeled NaBH4-CDs.

[0055] 0.25 g of silver acetate, 0.5 g of polyvinylpyrrolidone, and 2.5 mg of carbon dots labeled NaBH4-CDs were dissolved in 25 mL of water. 20 mL of 0.075 mol / L disodium hydrogen phosphate aqueous solution was added dropwise to obtain a suspension. The suspension was stirred at 400 rpm for 4 hours at 25 °C in the dark. The mixture was then filtered through a 0.45 μm filter membrane, and the solid was collected. The collected solid was washed three times with water and then dried in an oven at 50 °C in the dark for 12 hours to obtain the CDs / Ag3PO4 composite photocatalyst.

[0056] Example 3

[0057] 2g of citric acid was placed in a high-pressure polytetrafluoroethylene reaction vessel, then heated in a muffle furnace to 200℃ at a heating rate of 10℃ / min and held for 3 hours. After that, it was taken out and naturally cooled to 25℃ to obtain crude O-CDs product. The pH of the crude O-CDs product was adjusted to 7 with a 1mol / L sodium hydroxide aqueous solution. Then, it was placed in a dialysis bag with a molecular weight cutoff of 500Da and dialyzed for 3 days. The substance in the dialysis bag was then collected and freeze-dried for 16 hours to obtain O-CDs.

[0058] 20 mg of O-CDs were dissolved in 200 μL of water to obtain an aqueous solution of O-CDs. Then, 0.088 g of DMP was dispersed in 2 mL of dichloromethane and added to the O-CDs aqueous solution. The mixture was stirred at 400 rpm for 24 hours at 25 °C. Then, a 1 mol / L sodium bicarbonate aqueous solution was added dropwise at 15 mL / min until no bubbles were generated during the titration. The aqueous and organic phases were then separated using a separatory funnel and the aqueous phase was collected to obtain an aqueous carbon dot solution. The pH of the aqueous carbon dot solution was adjusted to 7 using a 1 mol / L hydrochloric acid aqueous solution and a 1 mol / L sodium hydroxide aqueous solution. The solution was then dialyzed in a dialysis bag with a molecular weight cutoff of 500 Da for 3 days. The contents of the dialysis bag were then collected and freeze-dried for 18 hours to obtain carbon dots labeled as DMP-CDs.

[0059] 0.25 g of silver acetate, 0.5 g of polyvinylpyrrolidone, and 2.5 mg of carbon dots labeled DMP-CDs were dissolved in 25 mL of water. 20 mL of 0.075 mol / L disodium hydrogen phosphate aqueous solution was added dropwise to obtain a suspension. The suspension was stirred at 400 rpm for 4 hours at 25 °C in the dark. The mixture was then filtered through a 0.45 μm pore size filter and the solid was collected. The collected solid was washed three times with water and then dried in an oven at 50 °C in the dark for 12 hours to obtain the CDs / Ag3PO4 composite photocatalyst.

[0060] Example 4

[0061] 2g of citric acid was placed in a high-pressure polytetrafluoroethylene reaction vessel, then heated in a muffle furnace to 200℃ at a heating rate of 10℃ / min and held for 3 hours. After that, it was taken out and naturally cooled to 25℃ to obtain crude O-CDs product. The pH of the crude O-CDs product was adjusted to 7 with a 1mol / L sodium hydroxide aqueous solution. Then, it was placed in a dialysis bag with a molecular weight cutoff of 500Da and dialyzed for 3 days. The substance in the dialysis bag was then collected and freeze-dried for 16 hours to obtain O-CDs.

[0062] 20 mg of the obtained O-CDs were added to 5 mL of 2 mol / L nitric acid solution and stirred at 400 rpm for 12 hours at 25 °C. The pH was then adjusted to 7 using 1 mol / L sodium hydroxide aqueous solution. The mixture was then dialyzed for 3 days using a dialysis bag with a molecular weight cutoff of 500 Da. After dialysis, the contents of the dialysis bag were collected and freeze-dried for 18 hours to obtain carbon dots labeled HNO3-CDs.

[0063] 0.25 g of silver acetate, 0.5 g of polyvinylpyrrolidone, and 2.5 mg of carbon dots labeled HNO3-CDs were dissolved in 25 mL of water. 20 mL of 0.075 mol / L disodium hydrogen phosphate aqueous solution was added dropwise to obtain a suspension. The suspension was stirred at 400 rpm for 4 hours at 25 °C in the dark. The mixture was then filtered through a 0.45 μm filter membrane, and the solid was collected. The collected solid was washed three times with water and then dried in an oven at 50 °C in the dark for 12 hours to obtain the CDs / Ag3PO4 composite photocatalyst.

[0064] The applications and performance tests of the CDs / Ag3PO4 composite photocatalysts prepared in Examples 1-4 are as follows:

[0065] Application in photocatalytic degradation of organic dyes: The CDs / Ag3PO4 composite photocatalyst prepared in this invention is used for photocatalytic degradation of organic dyes. The photocatalytic degradation method for organic dyes is as follows:

[0066] Preliminary preparation: Weigh 0.03g of the CDs / Ag3PO4 composite photocatalyst prepared in Examples 1-4 above into a 100mL quartz beaker, add 13.3mL of ultrapure water, and sonicate at 300W for 5 seconds to uniformly disperse the catalyst in the ultrapure water to obtain a composite catalyst dispersion; using methyl orange as the organic dye to be degraded, add 26.6mL of methyl orange solution with a concentration of 60mg / L to the composite catalyst dispersion to make the initial concentration of methyl orange 40mg / L to obtain the reaction system, and then place it on a magnetic stirrer;

[0067] Photocatalytic reaction: The photocatalytic reaction was carried out at 25℃. Based on the previous preparation, the system was first stirred at 100 rpm for 60 minutes in the dark at 25℃ to allow the reaction system to reach adsorption-desorption equilibrium. During this period, samples were taken every 20 minutes. The samples were centrifuged at 10,000 rpm and the supernatant was collected and stored in the dark for later analysis. Then, the reaction system was irradiated with a xenon lamp with a filter (λ>420nm) as the light source, and the system was stirred at 100 rpm. Samples were taken at regular intervals. When the solution color hardly changed over time, sampling was stopped. The samples were centrifuged at 10,000 rpm and the supernatant was collected and stored in the dark for later analysis.

[0068] Detection: The absorbance of methyl orange in the supernatant sample taken from the photocatalytic reaction was measured at a wavelength of 463 nm using a UV-Vis spectrophotometer. The concentration of methyl orange in the supernatant was calculated based on the initial concentration of methyl orange. Kinetic curves of the photocatalytic degradation of methyl orange by the CDs / Ag3PO4 composite photocatalyst and fitting curves of the corresponding kinetic constants of the CDs / Ag3PO4 composite photocatalyst were plotted. The results are shown in […]. Figure 2 .

[0069] Transmission electron microscopy characterization: The CDs / Ag3PO4 composite photocatalysts prepared in Examples 1–4 were characterized using transmission electron microscopy. The characterization results are shown in the figure. Figures 3-6 .

[0070] Infrared spectroscopy characterization: The carbon dots prepared in Examples 1-4 were characterized by infrared spectroscopy using an infrared spectrometer. The characterization results are shown in the figure. Figure 7 .

[0071] XPS characterization: The carbon dots prepared in Examples 1–4 were characterized using X-ray photoelectron spectroscopy. The characterization results are shown in [Figure 1]. Figure 8 By calculating the peak area after XPS peak fitting based on the characterization results, the relative contents of various photogroups on each carbon point in Examples 1 to 4 were obtained, and the results are shown in Table 1.

[0072] Table 1. Relative content of various photogroups on carbon dots

[0073] Example C = C CO C=O -OC=O Example 1 0.62758 0.10513 0.16997 0.09731 Example 2 0.65922 0.16047 0.13897 0.04134 Example 3 0.70226 0.09351 0.18112 0.0231 Example 4 0.67589 0.09162 0.16056 0.07192

[0074] The effect of the scavenger on the photocatalytic rate of the CDs / Ag3PO4 composite photocatalyst was tested: The catalyst was divided into four groups: no scavenger group, scavenger group 1, scavenger group 2, and scavenger group 3, based on whether a scavenger was added or not. For the no-scavenger group: 0.03 g of the CDs / Ag3PO4 composite photocatalyst prepared in Example 1 was weighed into a 100 mL quartz beaker, and 13.3 mL of ultrapure water was added. The catalyst was ultrasonically dispersed uniformly in the ultrapure water at 300 W for 5 seconds to obtain a composite catalyst dispersion. Methyl orange was used as the organic dye to be degraded, and 26.6 mL of a 60 mg / L methyl orange solution was added to the composite catalyst dispersion to make the initial concentration of methyl orange 40 mg / L, thus obtaining a reaction system without a scavenger. The scavenger for scavenger group 1 was disodium ethylenediaminetetraacetate (EDTA). Specifically, 0.03 g of the CDs / Ag3PO4 composite photocatalyst prepared in Example 1 was weighed... The g3PO4 composite photocatalyst was placed in a 100mL quartz beaker, and 11.3mL of ultrapure water was added. The mixture was ultrasonically dispersed in the ultrapure water at 300W for 5 seconds to obtain a composite catalyst dispersion. Using methyl orange as the organic dye to be degraded, 26.6mL of a 60mg / L methyl orange solution was added to the composite catalyst dispersion, followed by 2mL of a 0.26mol / L ethylenediaminetetraacetic acid disodium salt aqueous solution to bring the initial methyl orange concentration to 40mg / L, thus obtaining the first group of scavenger reaction systems. The scavenger for the second group was isopropanol (IPA), specifically: 0.03g of the CDs / Ag3PO4 photocatalyst prepared in Example 1 was weighed... 4. The composite photocatalyst was placed in a 100 mL quartz beaker, and 11.3 mL of ultrapure water was added. The mixture was ultrasonically dispersed in the ultrapure water at 300 W for 5 seconds to obtain a composite photocatalyst dispersion. Using methyl orange as the organic dye to be degraded, 26.6 mL of a 60 mg / L methyl orange solution was added to the composite photocatalyst dispersion, followed by 2 mL of a 1 mg / mL isopropanol aqueous solution to bring the initial concentration of methyl orange to 40 mg / L, thus obtaining the second group of scavenger reaction systems. The scavenger for the third group was p-benzoquinone (PBQ), specifically: 0.03 g of the CDs / Ag3PO4 composite photocatalyst prepared in Example 1 was weighed and placed in a 100 mL quartz beaker. In a quartz beaker, 12.3 mL of ultrapure water was added, and the catalyst was sonicated at 300 W for 5 seconds to uniformly disperse the catalyst in the ultrapure water, obtaining a composite catalyst dispersion. Using methyl orange as the organic dye to be degraded, 26.6 mL of a 60 mg / L methyl orange solution was added to the composite catalyst dispersion, followed by 1 mL of a 0.6 mg / mL p-benzoquinone aqueous solution to bring the initial concentration of methyl orange to 40 mg / L, resulting in three reaction systems for the scavenging agent. The methyl orange was then degraded using the aforementioned photocatalytic reaction method applying the CDs / Ag3PO4 composite photocatalyst to the photocatalytic degradation of organic dyes. The degradation results are expressed as degradation rate, and the degradation results are shown in [Figure number missing]. Figure 9 .

[0075] Through the Figure 2 Analysis shows that the photocatalytic rates of the CDs / Ag3PO4 composite photocatalysts prepared in Examples 2-4 are all higher than those of the CDs / Ag3PO4 composite photocatalyst synthesized from untreated O-CDs in Example 1, and the photocatalytic rates are: Example 3 > Example 4 > Example 2 > Example 1. To further investigate the photocatalytic process, kinetic analysis was performed on the photocatalytic reaction. The photocatalytic reaction of this invention follows a first-order kinetic equation (ln(C0 / C) = kt), where k is the rate constant. In the photocatalytic reaction, the value of k in Example 3 is 0.085 min. -1 Secondly, the k value in Example 4 is 0.062 min. -1 The second lowest k value is 0.023min in Example 2. -1 In Example 1, the minimum value of k is 0.014min. -1 .

[0076] Through the Figures 3-6 Analysis shows that, through transmission electron microscopy imaging, the CDs / Ag3PO4 composite photocatalysts prepared in Examples 1-4 have basically the same particle size, and the morphology of the CDs / Ag3PO4 composite photocatalysts is nearly face-centered cubic with small carbon dots attached to the surface. Further analysis shows that the particle size of the CDs / Ag3PO4 composite photocatalyst in Example 1 is 306.25±64.23 nm, the particle size of the CDs / Ag3PO4 composite photocatalyst in Example 2 is 306.67±64.24 nm, the particle size of the CDs / Ag3PO4 composite photocatalyst in Example 3 is 316.47±45.31 nm, and the particle size of the CDs / Ag3PO4 composite photocatalyst in Example 4 is 314.33±61.11 nm.

[0077] Through the Figure 7 Analysis shows that, Figure 7 The characterization refers to the surface chemical groups on the sample surface. The carbon dots prepared in Examples 1-4 are at 3431 cm⁻¹. -1 Absorption peaks are present at all locations, which are caused by the stretching vibration of OH. In infrared spectroscopy analysis, the peak at 1685 cm⁻¹ is [missing value]. -1 1584cm -1 Corresponding to the C=O stretching vibrations in the carboxyl and carbonyl groups, respectively, 1346 cm⁻¹ -1 The absorption peak at that point corresponds to the CO stretching vibration. Figure 7In the comparison of the carbon dots of Example 3 (DMP-CDs) and Example 4 (HNO3-CDs) with the O-CDs of Example 1, the carbon dots showed increased intensity of both the carbonyl C=O stretching vibration peak and the C=O vibration peak of the carboxyl group, while the CO stretching vibration was weakened, indicating that some hydroxyl groups on the carbon dot surface were directionally oxidized to carbonyl groups; the carbon dots of Example 2 (NaBH4-CDs) showed an increased intensity at 1346 cm⁻¹. -1 The CO stretching vibration absorption peak at the O-CDs in Example 2 is enhanced compared to that of the O-CDs in Example 1, indicating that the NaBH4 reduction treatment in Example 2 mainly increased the hydroxyl content on the surface of the O-CDs. This increase in hydroxyl content is due to the reduction of carbonyl groups, thus reducing the carbonyl content. Combined with the above... Figure 2 Analysis shows that the higher the carbonyl content of the carbon dots on the surface of the CDs / Ag3PO4 composite photocatalyst, the higher the photocatalytic efficiency of the composite catalyst. This may be because the carbonyl content in the carbon dots has a significant impact on the band gap of the carbon dots. When the carbonyl content is increased, the band gap of the carbon dots becomes smaller, which is conducive to the transfer of conduction band electrons from Ag3PO4 to the carbon dots, thereby reducing the probability of electron-hole recombination and improving the photocatalytic efficiency of the CDs / Ag3PO4 composite photocatalyst.

[0078] Through the Figure 8 As can be seen from the analysis in Table 1, Figure 8 Table 1 shows the carbon element binding on the carbon dots prepared in Examples 1-4. After high-resolution XPS peak fitting of the C1s of the carbon dots, four peaks were fitted for the carbon dots in Examples 1-4: graphite carbon at 284.5 eV, alcohol carbon at 286.0 eV, carbonyl carbon at 287.9 ​​eV, and carboxyl carbon at 289.0 eV. Table 1 and the above-mentioned peak fitting... Figure 2 Combined with the analysis, it can be seen that the DMP-CDs carbon dots in Example 3 have the highest content of carbon-carbon double bonds and carbonyl groups, and the CDs / Ag3PO4 composite photocatalyst in Example 3 has the highest catalytic rate. The carbon-carbon double bond content in the HNO3-CDs carbon dots in Example 4 increased by 4.8% compared with the O-CDs in Example 1, while the carbonyl content remained basically unchanged. The CDs / Ag3PO4 composite photocatalyst in Example 4 had the second highest catalytic rate, indicating that the increase in the carbon-carbon double bond content in the carbon dots is beneficial to improving the catalytic rate of the composite catalyst. The carbon-carbon double bond content in the NaBH4-CDs carbon dots in Example 2 increased by 3.6% compared with the O-CDs in Example 1, but the carbonyl content decreased by 3%. The CDs / Ag3PO4 composite photocatalyst in Example 2 had a higher catalytic rate than the CDs / Ag3PO4 composite photocatalyst in Example 1, indicating that the carbon-carbon double bonds in the surface carbon dots have a greater impact on the composite catalyst.

[0079] Through the Figure 9 Analysis shows that, Figure 9To investigate the effect of adding and not adding a scavenging agent on the degradation rate of methyl orange in the photocatalytic degradation reaction, the main active substance in the photocatalytic process is usually photogenerated holes (h). + ), superoxide radicals (·O) 2- ) and hydroxyl radicals (·OH), EDTA, IPA, and PBQ can respectively capture h + ·OH and ·O 2- If the photocatalytic rate is significantly lower after adding the scavenger compared to the group without the scavenger, it indicates that the free radicals captured by the scavenger are the main active substances playing a role in the photocatalytic process; Figure 9 In the study, methyl orange was completely degraded without the addition of a scavenging agent, while its degradation was significantly inhibited with the addition of a scavenging agent. Specifically, the degradation rate was 24.1% after the addition of disodium ethylenediaminetetraacetate (EDTA), 48.5% after the addition of isopropanol (IPA), and 44.2% after the addition of p-benzoquinone (PBQ). This indicates that h + ·OH and ·O 2- All play a role in the degradation process, among which h + It plays a major role in the photocatalytic degradation reaction of CDs / Ag3PO4 composite photocatalyst. This is likely because in the CDs / Ag3PO4 composite photocatalyst, part of the Ag3PO4 surface is covered with carbon dots, forming a Z-type CDs / Ag3PO4 photocatalytic system. Under light radiation, both Ag3PO4 and CDs are excited to generate electron-hole pairs (e-hole pairs). - -h + h produced in Ag3PO4 + The e remains in the valence band, while the e in the conduction band remains in the valence band. - This is then transferred to CDs, realizing the photogenerated e in Ag3PO4. - -h + Effective separation. The h-value left after the valence band electron transition of Ag3PO4. + Its potential is generally around +2.85 eV, and it has strong oxidizing properties. When it migrates to the Ag3PO4 surface, it can degrade adsorbed organic matter. The electrons enriched in the CDs conduction band... - Beneficial for O2 ·- The generation of [something] can also degrade organic matter.

[0080] In summary, the particle size of carbon dots in the CDs / Ag3PO4 composite photocatalyst has a certain influence on its photocatalytic activity. Furthermore, the increase in the content of carbon-carbon double bonds and carbonyl groups on the carbon dot surface is more conducive to electron transfer, thereby enabling the generation of more h groups in the Ag3PO4 valence band. + A large number of h +The transfer to the Ag3PO4 surface promotes the degradation of organic matter and enhances the photocatalytic rate of the CDs / Ag3PO4 composite photocatalyst. In this invention, the surface chemical structure of O-CD (initial carbon dots) is regulated to prepare the CDs / Ag3PO4 composite photocatalyst, which effectively improves the photocatalytic rate of the CDs / Ag3PO4 composite photocatalyst.

[0081] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing a high-efficiency CDs / Ag3PO4 composite photocatalyst, characterized in that, The preparation method includes: S1. O-CDs were synthesized via a hydrothermal method using citric acid as a precursor. S2. The surface chemical structure of the obtained O-CDs is controlled to obtain the controlled O-CDs; S3. Dissolve silver acetate, polyvinylpyrrolidone, and the obtained regulated O-CDs in water, and add dropwise a 0.05-0.1 mol / L disodium hydrogen phosphate aqueous solution to obtain a suspension. Stir the suspension at 300-500 rpm for 3-5 hours in the dark at 15-30℃, then filter and collect the solid. Wash the collected solid with water 3-4 times, and then dry it in the dark at 45-60℃ for 10-14 hours to obtain the CDs / Ag3PO4 composite photocatalyst. The mass ratio of silver acetate, polyvinylpyrrolidone, and the obtained regulated O-CDs is (150-350):(200-700):(1.5-4); the mass and volume ratio of the obtained regulated O-CDs to water is (1.5-4) mg:(15-40) mL; and the mass and volume ratio of the obtained regulated O-CDs to the disodium hydrogen phosphate aqueous solution is (1.5-4). mg: (10~30) mL; the pore size of the filter membrane used for filtration is 0.22~0.8 μm; The process of regulating the surface chemical structure of the obtained O-CDs to obtain regulated O-CDs specifically includes: treating the obtained O-CDs with a Desmond-Martin reagent to obtain carbon dots labeled as DMP-CDs; The specific steps for treating the obtained O-CDs with the Dys-Martin reagent to obtain carbon dots labeled DMP-CDs include: dissolving the O-CDs in water to obtain an aqueous solution of O-CDs; then dispersing the Dys-Martin reagent in dichloromethane, and then adding it to the obtained O-CDs aqueous solution; stirring at 300-500 rpm for 22-26 hours at 15-30°C; then adding a 0.5-1.5 mol / L sodium bicarbonate aqueous solution at a titration rate of 5-20 mL / min until no bubbles are generated during the titration; then separating the aqueous and organic phases using a separatory funnel and collecting the aqueous phase to obtain an aqueous carbon dot solution; adjusting the pH of the obtained aqueous carbon dot solution to 6.9-7.1 using a 0.5-1.5 mol / L hydrochloric acid aqueous solution and a 0.5-1.5 mol / L sodium hydroxide aqueous solution; and then adding a molecular weight cutoff of 500... Dialyze in a dialysis bag for 2-5 days, then collect the contents of the dialysis bag and freeze-dry the collected contents for 12-24 hours to obtain carbon dots labeled DMP-CDs; the mass-to-volume ratio of the O-CDs to water is (12-30) mg:(150-300) μL; the mass-to-volume ratio of the Dys-Martin reagent to dichloromethane is (0.075-0.115) g:(1.5-3) mL.

2. The preparation method of the high-efficiency CDs / Ag3PO4 composite photocatalyst as described in claim 1, characterized in that, The process of synthesizing O-CDs using citric acid as a precursor via a hydrothermal method specifically includes: placing citric acid in a reaction vessel, heating it to 180-220°C at a heating rate of 5-15°C / min and holding it at that temperature for 2-5 hours; then removing it and allowing it to cool naturally to 15-30°C to obtain crude O-CDs; adjusting the pH of the crude O-CDs to 6.9-7.1 with a 0.5-1.5 mol / L sodium hydroxide aqueous solution, then dialyzing it in a dialysis bag with a molecular weight cutoff of 500 Da for 2-5 days; then collecting the substance from the dialysis bag and freeze-drying it for 12-24 hours to obtain O-CDs.

3. A high-efficiency CDs / Ag3PO4 composite photocatalyst, characterized in that: It was prepared using the method described in any one of claims 1 to 2 for the preparation of a high-efficiency CDs / Ag3PO4 composite photocatalyst.

4. An application of a high-efficiency CDs / Ag3PO4 composite photocatalyst, characterized in that: The high-efficiency CDs / Ag3PO4 composite photocatalyst described in claim 3 is used as a catalyst for the photocatalytic degradation of organic dyes.

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