A two-dimensional layered nitrogen-doped carbon quantum dot modified graphitic carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst and its preparation method

Abstract

A two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst and a preparation method thereof according to the present invention relate to the technical field of water treatment materials. In order to solve the problem that the existing spinel-type calcium ferrite catalyst has a small number of surface oxygen vacancies, the number of anions and cations that can be accommodated is limited, and it cannot more effectively promote the decomposition of ozone to generate active free radicals, resulting in low catalytic activity of the catalyst. The present invention combines the sol-gel method and the hydrothermal method to prepare a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst. The chemical formula of the catalyst is Cl-CaFe2O4 / g-C3N4 / NCQDs. Compared with CaFe2O4, the catalytic activity is significantly enhanced, it has a larger surface area, provides more active sites and oxygen vacancies, and can promote ozone to generate more active free radicals.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment materials, and in particular, to a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst and a preparation method thereof. Background Art

[0002] Antibiotics are widely used in the treatment of diseases of humans and livestock. After a large amount of antibiotics enter the environment, due to their inherent antibacterial properties, it is difficult to remove them through traditional wastewater treatment processes. Norfloxacin (NOR) belongs to fluoroquinolone antibiotics. Trace levels of norfloxacin have potential adverse effects on aquatic wildlife, ecosystems, and human health, and may lead to the generation of antibiotic-resistant bacteria.

[0003] The catalytic ozonation technology uses a catalyst to accelerate the generation of active free radicals by ozone, and mineralizes refractory organic pollutants into H2O and CO2. Heterogeneous catalysts mainly include noble metal catalysts, transition metal catalysts, alkaline earth metal catalysts, and non-metal catalysts. Among them, noble metal catalysts have strong catalytic performance, good stability, and long service life, but their high price, difficult recovery, and the dissolution of heavy metal ions into the solution will also cause secondary pollution, which limits their application and development in the catalytic ozonation degradation of organic pollutants. Transition metal oxides mainly include oxides of iron, cobalt, nickel, etc. Because the d electron layer of their metal cations is easy to gain and lose electrons, they have strong redox performance. Most transition metal oxides have good stability, low preparation cost, and convenient recovery. However, compared with transition metal oxides, spinel-type oxides have stronger stability. Among them, the spinel-type CaFe2O4 catalyst is mainly concentrated in the fields of photocatalysis, electrocatalysis, etc., and there are few application studies in catalytic ozonation. The main reason is that the number of surface oxygen vacancies is small, and the number of anions and cations that can be accommodated is limited, and it cannot more effectively promote the decomposition of ozone to generate active free radicals. Therefore, the degradation efficiency of organic wastewater is low. In order to improve the efficiency of the CaFe2O4 catalyst in catalytic ozonation of organic wastewater, more oxygen vacancies and active sites need to be provided on its surface to receive more anions and cations and promote the decomposition of ozone to generate more active free radicals.

[0004] Therefore, the existing technology needs to be further improved and perfected. Summary of the Invention

[0005] The technical problem to be solved by the present invention is:

[0006] The existing spinel-type calcium ferrite catalyst has a small number of surface oxygen vacancies, and the number of anions and cations that can be accommodated is limited, which cannot more effectively promote the decomposition of ozone to generate active free radicals, resulting in low catalytic activity of the catalyst.

[0007] The technical solution adopted by the present invention to solve the above technical problem:

[0008] The present invention provides a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst, and the catalyst is a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst, and the chemical formula of the catalyst is Cl-CaFe2O4 / g-C3N4 / NCQDs.

[0009] The present invention provides a preparation method of a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst, comprising the following steps:

[0010] I. Preparing a precursor solution A: Dissolving calcium nitrate and iron nitrate in deionized water, stirring until completely dissolved, and then adding citric acid and calcium chloride, and stirring evenly to obtain the precursor solution A;

[0011] II. Preparing a sol B: Heating and stirring the precursor solution A to prepare the sol B;

[0012] III. Preparing a gel C: Drying the sol B to obtain the gel C;

[0013] IV. Preparing carbon nitride (g-C3N4): Calcining melamine to obtain g-C3N4 powder;

[0014] V. Preparing N-doped carbon quantum dots (NCQDs): Adding citric acid and urea to deionized water, performing a hydrothermal reaction to obtain NCQDs;

[0015] VI. Preparing Cl-CaFe2O4 / g-C3N4 (CCG): Mixing the gel C and g-C3N4 powder thoroughly in an agate mortar to obtain a mixture, and calcining the mixture to obtain Cl-CaFe2O4 / g-C3N4 (CCG);

[0016] VII. Preparing a ternary composite material Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD): Adding CCG and NCQDs to deionized water in proportion, stirring and mixing, and performing a hydrothermal reaction, filtering the precipitate, washing the precipitate with ethanol and deionized water, and drying to obtain a Cl-CaFe2O4 / g-C3N4 / NGQDs (CCGD) catalyst.

[0017] Furthermore, the molar ratio of calcium nitrate, iron nitrate, citric acid and calcium chloride in step I is (0.5-1):(1-3):(3-6):(0.1-0.5).

[0018] Furthermore, the calcination temperature of melamine in step IV is not lower than 500 °C.

[0019] Further, the molar ratio of citric acid to urea in step five is (1-3):1.

[0020] Further, the conditions of the hydrothermal reaction in step five are to react at 160-200 °C for 6-10 h.

[0021] Further, the mass ratio of gel C to g-C3N4 in step six is (1-4):1.

[0022] Further, the calcination temperature of the mixture in step six is not lower than 800 °C.

[0023] Further, the conditions of the hydrothermal reaction in step seven are to react at 160-200 °C for 6-10 h.

[0024] Further, the conditions of the drying in step seven are to dry at 60-120 °C for 6-10 h.

[0025] Further, the ratio of CCG to NCQDs in step seven is 1 g:(3-6) mL.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The present invention uses the sol-gel method and the hydrothermal method in combination to prepare a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst. Compared with CaFe2O4, the catalytic activity is significantly enhanced, it has a larger surface area, provides more active sites and oxygen vacancies, and can promote ozone to generate more active free radicals.

[0028] The present invention uses citric acid with strong reducibility as a complexing agent. After the solvent evaporates, the solution becomes viscous, and the complex molecules approach each other and are linked by hydrogen bonds to form a gel. Through the induction of anionic chlorine, without changing the spatial structure, the anionic component is enhanced, and the structural stability and conductivity of the catalyst are improved. During the coupling process of carbon nitride and calcium ferrite, electron-hole pairs are separated by inhibiting the heterojunction. A large number of holes in the valence band of carbon nitride are enriched and react with ozone to generate more active free radicals to enhance the catalytic activity of the catalyst. The addition of carbon quantum dots affects the shape and conductivity of calcium ferrite, induces intrinsic defects in the crystal, provides more active sites and oxygen vacancies, which is beneficial to electron transfer during the catalytic reaction process and generates a large amount of surface active oxygen. Due to the nitrogen-induced charge redistribution, nitrogen-doped carbon quantum dots have higher catalytic activity in redox reactions, are extremely easy to disperse and aggregate in water, and they can form an effective and stable catalyst with calcium ferrite. Description of the Drawings

[0029] Figure 1Schematic diagram of the electron transfer process of the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst in the embodiment of the present invention;

[0030] Figure 2 Scanning electron micrograph of the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst in the embodiment of the present invention;

[0031] Figure 3 XRD pattern of the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst in the embodiment of the present invention;

[0032] Figure 4 XPS spectrum of the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst in the embodiment of the present invention. Detailed implementation manners

[0033] In order to enable those skilled in the art to better understand the solution of the present invention, the exemplary embodiments or examples of the present invention will be described below in conjunction with the accompanying drawings. Obviously, the described embodiments or examples are only part of the embodiments or examples of the present invention, rather than all of them. All other embodiments or examples obtained by those of ordinary skill in the art based on the embodiments or examples of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0034] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] The present invention provides a preparation method of a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst, which includes the following steps:

[0036] I. Preparation of precursor solution A: Dissolve calcium nitrate and iron nitrate in deionized water, stir until completely dissolved, then add citric acid and calcium chloride, and stir evenly to obtain precursor solution A;

[0037] II. Preparation of sol B: Heat and stir precursor solution A to prepare sol B;

[0038] III. Preparation of gel C: Dry sol B to obtain gel C;

[0039] IV. Preparation of carbon nitride (g-C3N4): Calcinate melamine to obtain g-C3N4 powder;

[0040] V. Preparation of N-doped carbon quantum dots (NCQDs): Citric acid and urea are added to deionized water, and a hydrothermal reaction is carried out to obtain NCQDs;

[0041] VI. Preparation of Cl-CaFe2O4 / g-C3N4 (CCG): Gel C and g-C3N4 powder are thoroughly mixed in an agate mortar to obtain a mixture, and the mixture is calcined to obtain Cl-CaFe2O4 / g-C3N4 (CCG);

[0042] VII. Preparation of ternary composite Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD): CCG and NCQDs are added to deionized water in proportion, stirred and mixed, and a hydrothermal reaction is carried out. The precipitate is filtered, washed with ethanol and deionized water, and dried to obtain a Cl-CaFe2O4 / g-C3N4 / NGQDs (CCGD) catalyst, and the chemical formula of the catalyst is Cl-CaFe2O4 / g-C3N4 / NCQDs.

[0043] In an embodiment of the present invention, in Step I, the preferred molar ratio of calcium nitrate, iron nitrate, citric acid and calcium chloride is (0.5 - 1):(1 - 3):(3 - 6):(0.1 - 0.5).

[0044] To make melamine fully react to form g-C3N4, the calcination temperature of melamine in the above Step IV is preferably not lower than 500 °C.

[0045] In an embodiment of the present invention, in Step V, the preferred molar ratio of citric acid to urea is (1 - 3):1.

[0046] To make citric acid and urea fully react, the conditions for the hydrothermal reaction in Step V are to react at 160 - 200 °C for 6 - 10 h.

[0047] In an embodiment of the present invention, in Step VI, the preferred mass ratio of gel C to g-C3N4 is (1 - 4):1.

[0048] In an embodiment of the present invention, in Step VI, the preferred calcination temperature of the mixture is not lower than 800 °C.

[0049] To make CCG and NCQDs fully react, the conditions for the hydrothermal reaction in Step VII are to react at 160 - 200 °C for 6 - 10 h.

[0050] In an embodiment of the present invention, in Step VII, the preferred ratio of CCG to NCQDs is 1 g:(3 - 6) mL.

[0051] Hereinafter, specific examples and comparative examples will be combined to illustrate the beneficial effects of the present invention.

[0052] Example 1: A preparation method of a two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst is specifically completed according to the following steps:

[0053] I. Preparation of precursor solution A: Dissolve 0.005 mol of calcium nitrate and 0.02 mol of iron nitrate in 100 ml of deionized water, stir at a temperature of 40 °C until the solids are completely dissolved, then add 0.04 mol of citric acid and 0.005 mol of calcium chloride, and stir evenly until completely dissolved to obtain precursor solution A;

[0054] II. Preparation of sol B: Place solution A in a constant temperature water bath at 85 °C and stir for 2 h to obtain sol B;

[0055] III. Preparation of gel C: Dry sol B in a constant temperature drying oven at 120 °C to obtain gel C;

[0056] IV. Preparation of carbon nitride (g-C3N4): Calcinate 10 g of melamine in a muffle furnace at 550 °C in a closed state for 4 h to obtain yellow powder g-C3N4;

[0057] V. Preparation of N-doped carbon quantum dots (NCQDs): Dissolve 0.02 mol of citric acid and 0.01 mol of urea in 100 ml of deionized water, and carry out a hydrothermal reaction at 180 °C for 6 h to obtain NCQDs;

[0058] VI. Preparation of Cl-CaFe2O4 / g-C3N4 (CCG): Thoroughly mix 2 g of gel C and 0.5 g of g-C3N4 in an agate mortar for 15 min; Calcinate the obtained mixture at 850 °C for 4 h to form Cl-CaFe2O4 / g-C3N4 (CCG);

[0059] VII. Preparation of ternary composite material Cl-CaFe2O4 / g-C3N4 / NCQDs: Add 1 g of CCG and 5 mL of NCQDs solution to 50 mL of deionized water, stir for 2 h, and keep it at 180 °C in a polytetrafluoroethylene-lined autoclave for 6 h, filter to obtain a precipitate, wash it alternately with ethanol and deionized water 3 times, and dry it at 90 °C for 8 h to obtain a red-brown magnetic powder Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst.

[0060] Perform scanning electron microscopy on the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst obtained in Example 1, as Figure 2 shown, it can be seen that the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst obtained in Example 1 has a two-dimensional layered structure.

[0061] The two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst obtained in Example 1 was characterized by XRD, as Figure 3 shown, it can be seen that the catalyst retains the original spinel structure basis.

[0062] The Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst obtained in Example 1 was detected by XPS spectrum, as Figure 4 shown, the Ca element in the Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst obtained in Example 1 is all Ca 2+ , the Fe element is Fe 3+ and Fe 2 + , indicating that electron transfer occurs on the surface of the Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst, and at the same time oxygen vacancies are generated, which is beneficial to improving the catalytic performance; the peak value of chlorine can be detected in the XPS spectrum of the Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst, indicating that chlorine has been successfully doped into the calcium ferrite crystal.

[0063] Example 2: The difference between this example and Example 1 is that

[0064] I. Prepare precursor solution A: Dissolve 0.01 mol of calcium nitrate and 0.03 mol of iron nitrate in 100 ml of deionized water, stir at a temperature of 40 °C until the solid is completely dissolved, then add 0.05 mol of citric acid and 0.001 mol of calcium chloride, and stir evenly until completely dissolved to obtain precursor solution A.

[0065] Example 3: The difference between this example and Example 1 is that

[0066] I. Prepare precursor solution A: Dissolve 0.01 mol of calcium nitrate and 0.01 mol of iron nitrate in 100 ml of deionized water, stir at a temperature of 40 °C until the solid is completely dissolved, then add 0.03 mol of citric acid and 0.001 mol of calcium chloride, and stir evenly until completely dissolved to obtain precursor solution A.

[0067] Example 4: The difference between this example and Example 1 is that

[0068] V. Prepare N-doped carbon quantum dots (NCQDs): Dissolve 0.01 mol of citric acid and 0.01 mol of urea in 100 ml of deionized water, and carry out hydrothermal reaction at 180 °C for 6 h to obtain NCQDs.

[0069] Example 5: The difference between this example and Example 1 is that

[0070] V. Preparation of N-doped carbon quantum dots (NCQDs): 0.03 mol of citric acid and 0.01 mol of urea were dissolved in 100 ml of deionized water, and hydrothermal reaction was carried out at 180 °C for 6 h to obtain NCQDs.

[0071] Example 5: The difference between this example and Example 1 is that

[0072] VI. Preparation of Cl-CaFe2O4 / g-C3N4 (CCG): 1 g of gel C and 0.5 g of g-C3N4 were thoroughly mixed in an agate mortar for 15 min, and the obtained mixture was calcined at 850 °C for 4 h to form Cl-CaFe2O4 / g-C3N4 (CCG).

[0073] Example 6: The difference between this example and Example 1 is that

[0074] VI. Preparation of Cl-CaFe2O4 / g-C3N4 (CCG): 1.5 g of gel C and 0.5 g of g-C3N4 were thoroughly mixed in an agate mortar for 15 min. The obtained mixture was calcined at 850 °C for 4 h to form Cl-CaFe2O4 / g-C3N4 (CCG).

[0075] Example 7: The difference between this example and Example 1 is that

[0076] VI. During the preparation of Cl-CaFe2O4 / g-C3N4 (CCG), 0.5 g of gel C and 0.5 g of g-C3N4 were thoroughly mixed in an agate mortar for 15 min. The obtained mixture was calcined at 850 °C for 4 h to form Cl-CaFe2O4 / g-C3N4 (CCG).

[0077] Example 8: The difference between this example and Example 1 is that

[0078] VII. Preparation of ternary composite Cl-CaFe2O4 / g-C3N4 / NCQDs: 1 g of CCG and 3 mL of NCQDs solution were added to 50 mL of deionized water, stirred for 2 h, and kept at 180 °C in a Teflon-lined autoclave for 6 h. The precipitate was filtered, washed alternately with ethanol and deionized water 3 times, and dried at 90 °C for 8 h to obtain a red-brown magnetic powder Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst.

[0079] Example 9: The difference between this example and Example 1 is that

[0080] VII. Preparation of ternary composite material Cl-CaFe2O4 / g-C3N4 / NCQDs: Add 1 g of CCG and 6 mL of NCQDs solution into 50 mL of deionized water, stir for 2 h, and keep it at 180 °C for 6 h in a high-pressure reactor lined with polytetrafluoroethylene. Filter to obtain the precipitate, wash it alternately with ethanol and deionized water three times, and dry it at 90 °C for 8 h to obtain the red-brown magnetic powder Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst.

[0081] Example 10: The difference between this example and Example 1 is that

[0082] III. Preparation of gel C: Dry the sol B in a constant-temperature drying oven at 80 °C to obtain gel C;

[0083] Example 11: The difference between this example and Example 1 is that

[0084] The conditions for the hydrothermal reaction in Step VII are to react at 160 °C for 10 h.

[0085] Example 12: The difference between this example and Example 1 is that

[0086] The conditions for the hydrothermal reaction in Step VII are to react at 200 °C for 6 h.

[0087] Example 13: The difference between this example and Example 1 is that

[0088] The conditions for drying in Step VII are to dry at 60 °C for 10 h.

[0089] Example 14: The difference between this example and Example 1 is that

[0090] The conditions for drying in Step VII are to dry at 120 °C for 8 h.

[0091] Comparative Example 1: Preparation method of Cl-CaFe2O4 (CCF) catalyst, which is specifically prepared according to the following steps:

[0092] I. Preparation of precursor solution A. Dissolve 0.005 mol of calcium nitrate and 0.02 mol of iron nitrate in 100 ml of deionized water, stir at 40 °C for 30 min (the solid is completely dissolved), then add 0.04 mol of citric acid and 0.005 mol of calcium chloride, and stir evenly until completely dissolved to obtain precursor solution A;

[0093] II. Preparation of sol B. Stir the solution A in a constant-temperature water bath at 85 °C for 2 h to obtain sol B;

[0094] III. Preparation of gel C: Dry the obtained sol B in a constant-temperature drying oven at 120 °C to obtain gel C;

[0095] IV. Preparation of Cl-CaFe2O4 (CCF). The gel C was calcined at 850 °C for 4 h to form the Cl-CaFe2O4 (CCF) catalyst.

[0096] Comparative Example 2: Preparation method of the Cl-CaFe2O4 / g-C3N4 (CCG) catalyst, which was specifically completed according to the following steps:

[0097] I. Preparation of the precursor solution A. 0.005 mol of calcium nitrate and 0.02 mol of iron nitrate were dissolved in 100 ml of deionized water, stirred at 40 °C for 30 min (the solid was completely dissolved), then 0.04 mol of citric acid and 0.005 mol of calcium chloride were added, and then stirred evenly until completely dissolved to obtain the precursor solution A;

[0098] II. Preparation of the sol B. The solution A was placed in an 85 °C constant temperature water bath and stirred for 2 h to obtain the sol B;

[0099] III. Preparation of the gel C. The obtained sol B was dried in a constant temperature drying oven at 120 °C to obtain the gel C;

[0100] IV. Preparation of carbon nitride (g-C3N4). 10 g of melamine was calcined in a muffle furnace at 550 °C in a closed state for 4 h to obtain the yellow powder g-C3N4;

[0101] V. Preparation of Cl-CaFe2O4 / g-C3N4 (CCG). 2 g of the gel C and 0.5 g of g-C3N4 were fully mixed in an agate mortar for 15 min. The obtained mixture was calcined at 850 °C for 4 h to obtain the Cl-CaFe2O4 / g-C3N4 (CCG) catalyst.

[0102] Comparative Example 3

[0103] 1 L of norfloxacin wastewater with a concentration of 20 mg / L was placed in a glass reactor, and ozone with a concentration of 1.24 mg / L and a flow rate of 1000 mg / min was introduced for 2 min; the ozonation treatment alone was carried out for 60 min. Every 10 min, 10 mL of the sample was taken by a peristaltic pump, filtered through a 0.22 μm filter membrane, and the remaining norfloxacin concentration in the wastewater was detected by ultraviolet spectrophotometry at 278 nm. The degradation curve of the norfloxacin wastewater was drawn according to the detected data, and the removal rate was calculated.

[0104] Example 15

[0105] 1. Place 1 L of norfloxacin wastewater with a concentration of 20 mg / L into a glass reactor, and introduce ozone with a concentration of 1.24 mg / L and a flow rate of 1000 mg / min for 2 min; add 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 1.

[0106] 2. Continuously carry out catalytic ozonation treatment for 60 min. Every 10 min, sample 10 mL using a peristaltic pump. After filtering through a 0.22 μm filter membrane, detect the remaining norfloxacin concentration in the wastewater by ultraviolet spectrophotometry at 278 nm. Draw the degradation curve of the norfloxacin wastewater based on the detected data, and calculate the removal rate. After the catalytic ozonation treatment of the catalyst is completed, perform magnetic recovery.

[0107] Example 16: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 2 is added.

[0108] Example 17: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 3 is added.

[0109] Example 18: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 4 is added.

[0110] Example 19: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 5 is added.

[0111] Example 20: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 6 is added.

[0112] Example 21: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 7 is added.

[0113] Example 22: The difference between this example and Example 15 is that in step 1, 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 8 is added.

[0114] Example 23: The difference between this example and Example 15 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 9 was added in Step 1.

[0115] Example 24: The difference between this example and Example 15 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 10 was added in Step 1.

[0116] Example 25: The difference between this example and Example 15 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 11 was added in Step 1.

[0117] Example 26: The difference between this example and Example 15 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 12 was added in Step 1.

[0118] Example 27: The difference between this example and Example 15 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 13 was added in Step 1.

[0119] Example 28: The difference between this example and Example 15 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 / NCQDs (CCGD) catalyst prepared in Example 14 was added in Step 1.

[0120] Comparative Example 4: The difference between this example and Example 5 is that 0.1 g of the Cl-CaFe2O4 (CF) catalyst prepared in Comparative Example 1 was added in Step 1.

[0121] Comparative Example 5: The difference between this example and Example 5 is that 0.1 g of the Cl-CaFe2O4 / g-C3N4 (CCG) catalyst prepared in Comparative Example 2 was added in Step 1.

[0122] The norfloxacin removal rate (%) results obtained by summarizing Examples 15 - 28 and Comparative Examples 3 - 5 are shown in Table 1. It can be seen that the norfloxacin removal rate in Example 15 reached 70.04% after 60 min of catalytic ozonation treatment, which was 31.66% higher than the removal rate of ozone alone in Comparative Example 3, and was significantly improved compared with Cl-CaFe2O4 in Comparative Example 4 and Cl-CaFe2O4 / g-C3N4 in Comparative Example 5, indicating that the induction of chloride ions, the coupling of carbon nitride and spinel calcium ferrite, and the composite of nitrogen-doped carbon quantum dots in the catalyst are beneficial to improving the catalytic performance.

[0123] Table 1

[0124] 10 (min) 20 (min) 30 (min) 40 (min) 50 (min) 60 (min) Example 15 17.15 30.17 44.35 52.43 62.92 70.04 Example 16 13.92 23.45 34.48 42.01 53.64 58.54 Example 17 13.98 23.12 33.75 41.87 52.32 57.43 Example 18 14.35 24.55 39.01 50.55 60.12 67.68 Example 19 14.2 24.27 38.37 49.55 59.53 67.59 Example 20 14.81 26.07 36.66 45.38 57.37 63.04 Example 21 14.07 24.02 36.94 47.37 55.02 60.95 Example 22 14.41 24.67 39.33 50.98 60.34 67.77 Example 23 14.31 24.45 38.56 50.01 59.92 67.54 Example 24 16.92 29.76 42.98 51.12 62.03 69.53 Example 25 14.52 24.71 40.01 50.03 60.42 68.02 Example 26 14.61 24.82 40.13 50.12 60.51 68.21 Example 27 15.11 26.04 41.76 50.54 61.24 68.98 Example 28 16.05 27.43 42.23 50.98 61.67 69.01 Comparative Example 3 9.3 14.5 21.51 28.45 33.24 38.38 Comparative Example 4 12.55 17.88 30.08 36.4 41.73 50.49 Comparative Example 5 13.84 22.99 33.45 41.69 49.29 53.77

[0125] Although the present invention is disclosed as above, the protection scope of the present invention disclosure is not limited thereto. Those skilled in the art of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

[0126] Working principle:

[0127] As Figure 1 shown, the present invention reduces the oxidation of calcium and chlorine leaching in calcium ferrite by in-situ doping of chloride ions, enhances the anion component without changing the spatial structure of calcium ferrite, and improves its structural stability and conductivity. The electronegativity of halogen chlorine is lower than that of oxygen. After doping, the metal-oxygen covalent bond can be enhanced, which is beneficial to electron transfer in the catalytic process; by chlorine substitution, the electrochemical potential of the original catalyst is reduced, forming an in-situ doped metal oxide (hydroxide) phase, and the catalytic reaction is easier to carry out, and the catalyst activity is higher.

[0128] During the coupling process of carbon nitride and calcium ferrite, electron-hole pairs are separated by suppressing the heterojunction, a large number of holes in the valence band of carbon nitride are enriched, and react with ozone to generate more active free radicals, enhancing the catalytic activity of the catalyst. The addition of carbon quantum dots affects the shape and conductivity of calcium ferrite, induces intrinsic defects in the crystal, provides more active sites and oxygen vacancies, which is beneficial to electron transfer in the catalytic reaction process and generates a large amount of surface active oxygen. Due to the nitrogen-induced charge redistribution, nitrogen-doped carbon quantum dots have higher catalytic activity in redox reactions, are extremely easy to disperse and aggregate in water, and their doping with calcium ferrite can form a stable catalyst to effectively remove norfloxacin in aqueous solution.

Claims

1. A two-dimensional layered nitrogen-doped carbon quantum dot modified graphitic carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment, characterized in that, The chemical formula of the catalyst is Cl-CaFe2O4 / g-C3N4 / NCQDs; The preparation method of the two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst comprises the following steps: I. Prepare precursor solution A: Dissolve calcium nitrate and iron nitrate in deionized water, stir until completely dissolved, then add citric acid and calcium chloride, and stir evenly to obtain precursor solution A; II. Prepare sol B: Heat and stir precursor solution A to prepare sol B; III. Prepare gel C: Dry sol B to obtain gel C; IV. Prepare g-C3N4: Calcinate melamine to obtain g-C3N4 powder; V. Prepare NCQDs: Add citric acid and urea to deionized water, carry out hydrothermal reaction to obtain NCQDs; VI. Prepare Cl-CaFe2O4 / g-C3N4: Thoroughly mix gel C and g-C3N4 powder in an agate mortar to obtain a mixture, and calcinate the mixture to obtain Cl-CaFe2O4 / g-C3N4; VII. Prepare the ternary composite material Cl-CaFe2O4 / g-C3N4 / NCQDs: Add Cl-CaFe2O4 / g-C3N4 and NCQDs to deionized water in proportion, stir and mix, and carry out hydrothermal reaction. Filter the precipitate, wash the precipitate with ethanol and deionized water, and dry to obtain the Cl-CaFe2O4 / g-C3N4 / NCQDs catalyst.

2. The two-dimensional layered nitrogen-doped carbon quantum dot modified graphitic carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 1, wherein, In step I, the molar ratio of calcium nitrate, iron nitrate, citric acid and calcium chloride is (0.5~1):(1~3):(3~6):(0.1~0.5).

3. The two-dimensional layered nitrogen-doped carbon quantum dot modified graphitic carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 2, characterized in that, In step IV, the calcination temperature of melamine is not lower than 500 °C.

4. The two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 3, characterized in that, In step V, the molar ratio of citric acid to urea is (1~3):

1.

5. The two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 4, wherein, In step V, the conditions of the hydrothermal reaction are to react at 160~200 °C for 6 h~10 h.

6. The two-dimensional layered nitrogen-doped carbon quantum dot modified graphitic carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 5, wherein, In step VI, the mass ratio of gel C to g-C3N4 is (1~4):

1.

7. The two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 6, characterized in that, In step VI, the calcination temperature of the mixture is not lower than 800 °C.

8. The two-dimensional layered nitrogen-doped carbon quantum dot modified carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 7, characterized in that, In step VII, the conditions of the hydrothermal reaction are to react at 160~200 °C for 6 h~10 h.

9. The two-dimensional layered nitrogen-doped carbon quantum dot modified graphitic carbon nitride supported in-situ chlorine-doped calcium ferrite nano-magnetic composite catalyst for water treatment according to claim 8, wherein, In step VII, the ratio of Cl-CaFe2O4 / g-C3N4 to NCQDs is 1 g:(3~6) mL.

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