Preparation methods and applications of chlorine-doped carbon dot-modified carbon nitride materials

Abstract

This invention discloses a chlorine-doped carbon dot-modified carbon nitride material, its preparation method, and its applications, belonging to the field of photocatalyst materials technology. The invention uses mulberry twig powder as raw material, disperses it in water, adds thionyl chloride, mixes it, and heats it to 180-200℃ for 10-12 hours to prepare chlorine-doped carbon dots. After filtration and purification, chlorine-doped carbon quantum dot materials, denoted as Cl-CQDs, are obtained. A certain amount of urea and Cl-CQDs powder are dissolved, mixed, dried to remove moisture, and the dried powder is calcined in a tube furnace to obtain chlorine-doped carbon dot-modified carbon nitride material, labeled Cl-CTCN. The preparation method of this invention is simple, convenient to operate, has mild reaction conditions, and low raw material cost, making it suitable for large-scale industrial production. The Cl-CTCN of this invention has good photocatalytic performance, good recyclability, and can be applied to the photocatalytic degradation of organic pollutants such as tetracycline, rhodamine B, and methyl orange, as well as photocatalytic water splitting for hydrogen production, demonstrating broad applicability.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials technology, specifically relating to a chlorine-doped carbon dot modified carbon nitride material, its preparation method, and its application. Background Technology

[0002] The narrow absorption range of visible light, limited active sites, and high recombination rate of photogenerated carriers in graphitic carbon nitride (g-C3N4) limit its practical application in photocatalysis. To address this limitation, carbon quantum dots (CQDs) can be used to modify g-C3N4, leveraging their excellent photosensitivity, strong upconversion ability, and superior electronic mediator properties to further enhance their photocatalytic activity. However, the hydrophilic CQDs and hydrophobic carbon nitride (g-C3N4) struggle to establish a tight interfacial bond, significantly impacting the charge transfer rate and leading to the recombination of photogenerated electrons and holes, thus limiting the photocatalytic activity of CQDs / g-C3N4 composites. Studies have demonstrated that common non-metallic elements such as N, S, and B can be used as dopant elements to modify CQDs, significantly promoting interfacial interactions and electron transfer efficiency between CQDs and g-C3N4. Wang et al. synthesized S-CQDs by adding L-cysteine ​​as a sulfur source, and the degradation rate of tetracycline reached 82.67% after being combined with hollow tube g-C3N4. Recent studies have shown that due to the significant differences in atomic size and electronegativity between C and Cl, the introduction of Cl can greatly alter the structure and chemical properties of CQDs. However, the preparation of common Cl-CQDs generally requires multiple substitution steps, making the preparation method complex, and the photocatalytic activity of Cl-CQDs alone is limited. Therefore, it is essential to propose a simple and economical method for preparing high-performance Cl-CQDs / g-C3N4 (Cl-CTCN) materials. Summary of the Invention

[0003] To address the above problems, this invention provides a chlorine-doped carbon dot-modified carbon nitride material, its preparation method, and its applications. A one-step hydrothermal method is employed, using thionyl chloride as an external chlorine source and mulberry twig powder as a carbon source to prepare chlorine-modified CQDs (Cl-CQDs). A simple in-situ composite strategy is adopted: while urea is calcined at high temperature in a tube furnace under a nitrogen atmosphere to convert it into g-C3N4, the prepared Cl-CQDs are simultaneously composited with g-C3N4, successfully preparing a Cl-CTCN photocatalyst with high photocatalytic activity.

[0004] This invention is achieved through the following technical solution:

[0005] A method for preparing chlorine-doped carbon dot-modified carbon nitride material, characterized by comprising the following steps:

[0006] (1) Preparation of chlorine-doped carbon quantum dot materials: Weigh mulberry twig powder, disperse it in water, and slowly add thionyl chloride to it. Sonicate until mixed, then transfer the suspension to a reaction vessel and heat it to 180-200℃ for 10-12 hours. After the reaction vessel cools to room temperature, heat the resulting brown suspension in an oven to remove unreacted thionyl chloride and then centrifuge it. Finally, filter and purify the supernatant after centrifugation, and freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot materials, denoted as Cl-CQDs.

[0007] (2) Preparation of chlorine-doped carbon dot modified carbon nitride material: Take a certain amount of urea and the Cl-CQDs powder obtained in step (1) and dissolve them in water. Stir with ultrasound to make them fully dissolved and mixed. Then put the mixed solution into an oven to dry and remove moisture. Grind the dried solid to obtain a light brown powder. Then place the mixed light brown powder in a tube furnace for calcination. The resulting brown powder is the chlorine-doped carbon dot modified carbon nitride material, labeled as Cl-CTCN.

[0008] As a preferred technical solution, in step (1), the mass-to-volume ratio (g / mL) of the mulberry twig powder and thionyl chloride is 1:0.5 to 1.0.

[0009] As a preferred technical solution, in step (1), the oven temperature is 100-120℃ for 40-60 minutes to remove unreacted thionyl chloride.

[0010] As a preferred technical solution, in step (1), the continuous stirring time is 25-32 min.

[0011] As a preferred technical solution, in step (1), the supernatant is filtered through a 0.22μm filter membrane to obtain a Cl-CQDs solution, and then purified by dialysis using a 1000Da dialysis bag for 20-24 hours.

[0012] As a preferred technical solution, in step (2), the mass ratio of urea to Cl-CQDs powder is 1000:0.5-2.5.

[0013] As a preferred technical solution, in step (2), the ultrasonic immersion time is 3 hours and the ultrasonic power is 40 kHz.

[0014] As a preferred technical solution, in step (2), the calcination temperature in the tubular furnace is 500-600℃ for 1.5-2h, the heating rate is 5-10℃ / min, and the nitrogen flow rate is 40-50mL / min.

[0015] This invention relates to the application of chlorine-doped carbon dot-modified carbon nitride materials in photocatalysis. The materials of this invention can be used for the photocatalytic degradation of pollutants such as tetracycline (TC), rhodamine B (RhB), and methyl orange (MO), achieving a degradation rate of over 90%. They can also be used for photocatalytic water splitting to produce hydrogen.

[0016] The principle of this invention: Chlorine-doped CQDs (Cl-CQDs) are prepared using a one-step hydrothermal method with thionyl chloride as the external chlorine source and mulberry twig powder as the carbon source. A simple in-situ recombination strategy is then employed: while urea is calcined at high temperature in a tube furnace under a nitrogen atmosphere to obtain g-C3N4, the prepared Cl-CQDs are recombinated with g-C3N4 to successfully prepare a Cl-CTCN photocatalyst with high photocatalytic activity. Under the same conditions, the photocatalytic effects of g-C3N4 (TCN) prepared without CQDs and CQDs / g-C3N4 (CTCN) prepared with CQDs are compared.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0018] 1. This invention utilizes a single hydrothermal method, employing thionyl chloride as an external chlorine source and mulberry twigs as raw material to prepare chlorine-doped CQDs (Cl-CQDs). Then, using an in-situ recombination strategy, while calcining urea at high temperature in a tube furnace under a nitrogen atmosphere to obtain g-C3N4, the Cl-CQDs are simultaneously recombinated with g-C3N4 to prepare a Cl-CTCN photocatalyst. This invention features a simple method, mild reaction conditions, and low raw material costs, making it suitable for large-scale industrial production.

[0019] 2. In the photocatalytic degradation of tetracycline (TC) by the chlorine-doped carbon dot-modified carbon nitride material of the present invention, Cl-CTCN-5 achieved a TC degradation rate of 91.7%, which is 3.89 times and 2.07 times that of TCN (23.6%) and CTCN (44.3%), respectively. Moreover, the photocatalytic activity of Cl-CTCN reached its optimal level when the amount of Cl-CQDs added was 5 mg.

[0020] 3. In the preparation process of this invention, the calcination temperature is crucial to the preparation of the catalyst material. The photocatalytic degradation effect of Cl-CTCN on TC reaches its optimal level of 91.7% at 550℃. This is because lower temperatures cannot completely convert the precursor into g-C3N4, while excessively high temperatures can easily cause carbonization of the material, affecting its formation.

[0021] 4. In the photocatalytic experiment of TC by the chlorine-doped carbon dot modified carbon nitride material of the present invention, the photocatalytic degradation rate decreased by 10.4% after five cycles of experiment, indicating that the chlorine-doped carbon dot modified carbon nitride material of the present invention can maintain good stability during the photocatalytic process.

[0022] 5. The chlorine-doped carbon dot-modified carbon nitride material of the present invention exhibits catalytic degradation rates of 96.7% and 99.6% for Rhodamine B (RhB) and methyl orange (MO), respectively. This demonstrates the good applicability of the product Cl-CTCN of the present invention, which can be applied to the photocatalytic degradation process of various substances, thus having a wider range of applications.

[0023] 6. The material of this invention exhibits stable efficiency in the photocatalytic water splitting process for hydrogen production, with the hydrogen production rate remaining essentially unchanged within 4 hours. The sample demonstrates the best photocatalytic hydrogen evolution performance when the Cl-CQDs content is 5 mg (i.e., Cl-CTCN-5), with an average hydrogen production rate reaching 1397.5 μmol g. -1 h -1 The activity was 2.76 times that of TCN and 1.72 times that of CTCN, respectively. Furthermore, after five cycles and 20 hours of illumination, Cl-CTCN maintained similar photocatalytic hydrogen evolution activity, indicating good photostability. The structural composition and crystal structure did not change significantly after use. This demonstrates that the Cl-CTCN of this invention maintains good activity and stability during repeated cycles. Attached Figure Description

[0024] Figure 1 This is a flowchart of the preparation process of the present invention.

[0025] Figure 2 Characterization diagrams of TCN (comparative example) and Cl-CTCN (Example 1) are shown; where (a) is the SEM image of TCN, (bc) is the SEM image of Cl-CTCN, (dg) is the elemental distribution diagram of Cl-CTCN, and (h) is the EDS image of Cl-CTCN.

[0026] Figure 3 The images shown are TEM, HRTEM, and EDS images of Cl-CTCN from Example 1; where (ab) is the TEM image of Cl-CTCN, (c) is the HRTEM image of Cl-CTCN, and (d) is the EDS image of Cl-CQDs.

[0027] Figure 4 The images show the FT-IR and XRD patterns of three materials: TCN, CTCN, and Cl-CTCN. (a) is the FT-IR spectrum, and (b) is the XRD pattern.

[0028] Figure 5 The N2 adsorption-desorption curves and pore size distribution diagrams are shown for three materials: TCN, CTCN, and Cl-CTCN. (a) shows the N2 adsorption-desorption curves, and (b) shows the pore size distribution diagram.

[0029] Figure 6The figures show the photocatalytic degradation of tetracycline (TC) by three different catalysts: TCN, CTCN, and Cl-CTCN. (a) Degradation curves; (b) Pseudo-first-order kinetics; (c) Adsorption curves; (d) Effect of calcination temperature; and (e) Cyclic experiment of TC degradation by Cl-CTCN.

[0030] Figure 7 The process of Cl-CTCN degrading tetracycline TC is shown; (a) represents the effect of pH; (b) represents the effect of inorganic anions; and (c) represents the effect of different pollutants.

[0031] Figure 8 The photocatalytic reduction performance of three different catalysts, TCN, CTCN, and Cl-CTCN, was analyzed. (a) shows the hydrogen production curve; (b) shows the effect of Cl-CQDs content; (c) shows the hydrogen production rate and apparent quantum efficiency; (d) shows the hydrogen production cycle test of Cl-CTCN; (e) shows the FT-IR comparison before and after use; and (f) shows the XRD comparison before and after use. Detailed Implementation

[0032] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing chlorine-doped carbon dot-modified carbon nitride materials includes the following steps:

[0035] (1) Preparation of chlorine-doped carbon quantum dot material: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and slowly add 2 mL of thionyl chloride (SOCl2) to it, and sonicate thoroughly until mixed. Then transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 200 °C for 12 h. After the reactor cools to room temperature, heat the resulting brown suspension in an oven at 100 °C for 1 h to remove unreacted SOCl2, and then centrifuge. Filter the supernatant after centrifugation through a 0.22 μm filter membrane to obtain Cl-CQDs solution, and dialyze it using a 1000 Da dialysis bag for 24 h. Freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs;

[0036] (2) Preparation of chlorine-doped carbon dot-modified carbon nitride material: 6g of urea and 5mg of Cl-CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at a power of 40kHz to ensure complete dissolution and mixing. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground to obtain a light brown powder. Finally, the mixed light brown powder was placed in a tube furnace and calcined at 550℃ for 2h at a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The resulting brown powder is the chlorine-doped carbon dot-modified carbon nitride material, labeled Cl-CTCN-5.

[0037] Example 2

[0038] A method for preparing chlorine-doped carbon dot-modified carbon nitride materials includes the following steps:

[0039] (1) Preparation of chlorine-doped carbon quantum dot material: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and slowly add 2 mL of thionyl chloride (SOCl2) to it, and sonicate thoroughly until mixed. Then transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 200 °C for 12 h. After the reactor cools to room temperature, heat the resulting brown suspension in an oven at 100 °C for 1 h to remove unreacted SOCl2, and then centrifuge. Filter the supernatant after centrifugation through a 0.22 μm filter membrane to obtain Cl-CQDs solution, and dialyze it using a 1000 Da dialysis bag for 24 h. Freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs;

[0040] (2) Preparation of chlorine-doped carbon dot-modified carbon nitride material: 6g of urea and 3mg of Cl-CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at a power of 40kHz to ensure complete dissolution and mixing. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground to obtain a light brown powder. Finally, the mixed light brown powder was placed in a tube furnace and calcined at 550℃ for 2h at a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The resulting brown powder was the chlorine-doped carbon dot-modified carbon nitride material, labeled Cl-CTCN-3.

[0041] Example 3

[0042] A method for preparing chlorine-doped carbon dot-modified carbon nitride materials includes the following steps:

[0043] (1) Preparation of chlorine-doped carbon quantum dot material: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and slowly add 2 mL of thionyl chloride (SOCl2) to it, and sonicate thoroughly until mixed. Then transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 200 °C for 12 h. After the reactor cools to room temperature, heat the resulting brown suspension in an oven at 100 °C for 1 h to remove unreacted SOCl2, and then centrifuge. Filter the supernatant after centrifugation through a 0.22 μm filter membrane to obtain Cl-CQDs solution, and dialyze it using a 1000 Da dialysis bag for 24 h. Freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs;

[0044] (2) Preparation of chlorine-doped carbon dot-modified carbon nitride material: 6g of urea and 10mg of Cl-CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at a power of 40kHz to ensure complete dissolution and mixing. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground to obtain a light brown powder. Finally, the mixed light brown powder was placed in a tube furnace and calcined at 550℃ for 2h at a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The resulting brown powder was the chlorine-doped carbon dot-modified carbon nitride material, labeled Cl-CTCN-10.

[0045] Example 4

[0046] A method for preparing chlorine-doped carbon dot-modified carbon nitride materials includes the following steps:

[0047] (1) Preparation of chlorine-doped carbon quantum dot material: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and slowly add 2 mL of thionyl chloride (SOCl2) to it, and sonicate thoroughly until mixed. Then transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 200 °C for 12 h. After the reactor cools to room temperature, heat the resulting brown suspension in an oven at 100 °C for 1 h to remove unreacted SOCl2, and then centrifuge. Filter the supernatant after centrifugation through a 0.22 μm filter membrane to obtain Cl-CQDs solution, and dialyze it using a 1000 Da dialysis bag for 24 h. Freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs;

[0048] (2) Preparation of chlorine-doped carbon dot-modified carbon nitride material: 6g of urea and 15mg of Cl-CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at a power of 40kHz to ensure complete dissolution and mixing. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground to obtain a light brown powder. Finally, the mixed light brown powder was placed in a tube furnace and calcined at 550℃ for 2h at a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The resulting brown powder is the chlorine-doped carbon dot-modified carbon nitride material, labeled Cl-CTCN-15.

[0049] Example 5

[0050] A method for preparing chlorine-doped carbon dot-modified carbon nitride materials includes the following steps:

[0051] (1) Preparation of chlorine-doped carbon quantum dot material: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and slowly add 4 mL of thionyl chloride (SOCl2) to it, and sonicate thoroughly until mixed. Then transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 200 °C for 12 h. After the reactor cools to room temperature, heat the resulting brown solution in an oven at 100 °C for 1 h to remove unreacted SOCl2, and then centrifuge. Filter the supernatant after centrifugation through a 0.22 μm filter membrane to obtain Cl-CQDs solution, and dialyze it using a 1000 Da dialysis bag for 24 h. Freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs;

[0052] (2) Preparation of chlorine-doped carbon dot modified carbon nitride material: 6g of urea and 5mg of Cl-CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at a power of 40kHz to ensure complete dissolution and impregnation. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground to obtain a light brown powder. Finally, the mixed light brown powder was placed in a tube furnace and calcined at 600℃ for 1.5h at a heating rate of 10℃ / min and a nitrogen flow rate of 50mL / min. The resulting brown powder is the chlorine-doped carbon dot modified carbon nitride material, labeled Cl-CTCN.

[0053] Example 6

[0054] A method for preparing chlorine-doped carbon dot-modified carbon nitride materials includes the following steps:

[0055] (1) Preparation of chlorine-doped carbon quantum dot material: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and slowly add 2 mL of thionyl chloride (SOCl2) solution, and sonicate thoroughly until mixed. Then transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 180 °C for 10 h. After the reactor cools to room temperature, heat the resulting brown solution in an oven at 120 °C for 40 min to remove unreacted SOCl2. Finally, filter the supernatant after centrifugation through a 0.22 μm filter membrane to obtain Cl-CQDs solution, and dialyze it using a 1000 Da dialysis bag for 20 h. Freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs;

[0056] (2) Preparation of chlorine-doped carbon dot-modified carbon nitride material: 6g of urea and 5mg of Cl-CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at a power of 40kHz to ensure complete dissolution and impregnation. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground to obtain a light brown powder. Finally, the mixed light brown powder was placed in a tube furnace and calcined at 500℃ for 2h at a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The resulting brown powder is the chlorine-doped carbon dot-modified carbon nitride material, labeled Cl-CTCN.

[0057] Comparative Example 1

[0058] Dissolve 6g of urea in 10mL of deionized water and stir and sonicate for 3 hours. Place in an oven to dry and remove moisture, and grind the dried solid thoroughly. Place the ground powder in a tube furnace and calcine at 550℃ for 2 hours, with a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The obtained powder is labeled as TCN (pure g-C3N4 material).

[0059] Comparative Example 2

[0060] The preparation of carbon dot-modified carbon nitride materials includes the following steps:

[0061] (1) Preparation of carbon quantum dot materials: Weigh 4.0 g of mulberry twig powder, disperse it in 50 mL of deionized water, and sonicate thoroughly until well mixed. Transfer the suspension to a 100 mL polytetrafluoroethylene reactor and heat it to 200 °C for 12 h. After the reactor cools to room temperature, centrifuge and filter the supernatant through a 0.22 μm filter membrane to obtain a CQDs solution, which is then purified by dialysis using a 1000 Da dialysis bag for 24 h. Freeze-dry the purified solution to obtain carbon quantum dot materials, denoted as CQDs;

[0062] (2) Preparation of carbon dot modified carbon nitride material: 6g of urea and 5mg of CQDs powder were dissolved in 10mL of deionized water and stirred and sonicated for 3h at an ultrasonic power of 40kHz to ensure complete dissolution and mixing. The mixed solution was placed in an oven to dry and remove moisture, and the dried solid was thoroughly ground. Finally, the ground powder was placed in a tube furnace and calcined at 550℃ for 2h at a heating rate of 5℃ / min and a nitrogen flow rate of 40mL / min. The resulting powder is carbon dot modified carbon nitride material, labeled CTCN.

[0063] Material property analysis

[0064] To further illustrate the characteristics of the chlorine-doped carbon dot-modified carbon nitride material (Cl-CTCN) prepared in this invention and its role in photocatalytic reactions, the following experiments are conducted:

[0065] (a) Electron microscopy test:

[0066] The surface morphology of the Cl-CTCN material prepared in Example 1 and the TCN material prepared in Comparative Example 1 was characterized using a scanning electron microscope (TESCAN MIRA LMS, Czech Republic), and elemental composition analysis was performed using energy-dispersive X-ray spectroscopy (EDS) to obtain... Figure 2 .

[0067] Depend on Figure 2 The comparison shows that, from Figure 2 As can be seen from (a) and (b), g-C3N4 exhibits a multi-layered, graphite-like nanosheet stacked structure with curled edges, while the introduction of Cl-CQDs did not change the microstructure of g-C3N4. Figure 2 (dh) is the elemental mapping and EDS diagram of Cl-CTCN, which shows that the catalyst contains four elements: carbon (58.08%), nitrogen (37.53%), oxygen (3.62%) and chlorine (0.77%), further illustrating the composite of Cl-CQDs and g-C3N4.

[0068] Due to the small size of Cl-CQDs, they could not be observed in SEM. Therefore, the catalyst Cl-CTCN was further observed in TEM, and the results are as follows. Figure 3 As shown. Among them, Figure 3 (a) indicates that the g-C3N4 support has a porous sheet-like structure because urea, as a precursor, generates ammonia gas at high temperature. The thermal etching effect of ammonia gas forms a mesoporous structure on the TCN surface, thereby increasing the specific surface area of ​​the material and providing more active sites. Figure 3 (bc) marks Cl-CQDs, indicating that Cl-CQDs were successfully and uniformly composited onto the surface of g-C3N4. Figure 3(c) clearly shows the lattice fringes formed by the (100) crystal plane in Cl-CQDs, with a lattice spacing of 0.22 m. The EDS results of Cl-CQDs are shown in [reference needed]. Figure 3 (d) shows a chlorine content of 3.84%, demonstrating the successful introduction of chlorine. Because SOCl2 is readily soluble in water, reacting to produce HCl and SO2, it is difficult to completely introduce chlorine atoms into the CQDs, thus affecting the chlorine content in Cl-CQDs. The oxygen content of 16.72% further indicates the presence of a large number of oxygen-containing groups in the Cl-CQDs.

[0069] (II) Analysis of Crystal Structure and Phase Composition of Materials by FT-IR and XRD Analysis

[0070] The composition and crystal structure of different catalysts (Cl-CTCN, TCN, CTCN) were determined by FT-IR and XRD, and the results are as follows: Figure 4 As shown. Figure 4 (a) It can be seen that Cl-CTCN, CTCN, and TCN have similar FT-IR spectra, and none of the characteristic vibrational peaks have changed significantly, indicating that the addition of Cl-CQDs and CQDs does not change the structure of TCN, especially the 3000-3500 cm⁻¹ peak. –1 The broad peak at 1200-1650 cm⁻¹ is due to the presence of NH and OH bonds, while the peak at 1200-1650 cm⁻¹ is due to the presence of NH and OH bonds. –1 The presence of multiple peaks at 813 cm⁻¹ is attributed to the tensile vibrations of the g-C₃N₄ heterocycle. –1 The peak at that location represents a typical heptaazine unit of g-C3N4.

[0071] XRD pattern as follows Figure 4 As shown in (b), TCN, CTCN, and Cl-CTCN all exhibit diffraction peaks at 13.1° and 27.4°, corresponding to the (100) and (002) crystal planes of g-C3N4. With the introduction of Cl-CQDs and CQDs, the characteristic peaks of g-C3N4 are slightly weakened and exhibit a slight blue shift. This is because the introduction of carbon quantum dots hinders the stacking between layers of g-C3N4 and the crystallinity of the heptaazine units.

[0072] (III) Material Specific Surface Area Analysis

[0073] The surface area and pore size distribution of three material samples—TCN, CTCN, and Cl-CTCN—were measured using a nitrogen adsorption / desorption analyzer (ASAP 2020). The results are shown in Table 1. Figure 5 From Table 1 and Figure 5 (a) It can be seen that the specific surface area of ​​Cl-CTCN is 55.2636 m². 2 / g, compared to TCN (44.1725m 2 / g) and CTCN (52.0345m 2 The increase in pore size (g) is due to the introduction of Cl-CQDs, which increases the specific surface area of ​​the catalyst, shortening the mass transfer path and providing more active sites. This is likely because Cl-CQDs insert into the interlayer of g-C3N4, increasing the interlayer distance and thus the specific surface area. The pore size distribution is shown below. Figure 5 (b) Cl-CTCN exhibits the largest pore volume (0.1828 cm³). 3 / g), which is beneficial for adsorption and catalytic reactions.

[0074] Table 1. Specific surface area and pore structure parameters of TCN, CTCN, and Cl-CTCN

[0075]

[0076] (iv) Photocatalytic degradation of tetracycline (TC) experiment

[0077] 1. Photocatalytic degradation of tetracycline

[0078] Using tetracycline (TC) as the target pollutant, photocatalytic activity experiments were conducted using Example 1 (Cl-CTCN-5), Comparative Example 1 (TCN), and Comparative Example 2 (CTCN) as catalysts.

[0079] A 300W xenon lamp with an ultraviolet filter (λ>420nm) was selected as the light source. 40mg of different catalysts were added to 40mL of a 20mg / L TC solution, respectively. The solution was first stirred in the dark for 30min to ensure adsorption-desorption equilibrium before the photocatalytic experiment. During the reaction, 3mL of suspension was extracted from the photocatalytic tube every 30min, filtered through a 0.22μm filter membrane, and the absorbance of TC was measured at λ=357nm using a UV-Vis spectrophotometer. All reactions were performed three times, and the average value was used for calculation to reduce error.

[0080] The solution concentration is directly proportional to the absorbance of the characteristic absorption peak of the solution, and the removal rate (η) of TC can be calculated according to formula (1-1). First-order reaction kinetics were used to fit the experimental data, and the apparent rate constant was calculated according to formula (1-2).

[0081] η=(c0-C t ) / C0×100%=(A0-A t ) / A0×100% (1-1)

[0082] ln(C0 / C t )=kt (1-2)

[0083] Where t(min) is the reaction time; C0 is the initial concentration of TC; C t At represents the concentration of TC after time t; A0 represents the initial absorbance of TC. t k is the absorbance of TC after time t; -1 ) is the apparent rate constant.

[0084] 2. Cyclic Experiment:

[0085] To evaluate the recyclability of the photocatalyst CCN, the degraded suspension was filtered and washed with water and ethanol, respectively. After drying, the recovered photocatalyst was reused for the degradation of TC. The process was repeated five times under the same conditions to determine the recyclability of the photocatalyst CCN.

[0086] Experimental results of photocatalytic degradation of TC are as follows Figure 6 As shown. From Figure 6 (a) It can be seen that after 120 min of light exposure, Cl-CTCN-5 achieved a TC degradation rate of 91.7%, which is 3.89 times and 2.07 times that of TCN (23.6%) and CTCN (44.3%), respectively.

[0087] At the same time from Figure 6 As shown in (a), when the amount of Cl-CQDs added is 5 mg, the photocatalytic activity of C1-CTCN-5 reaches its optimum (91.7%), which is 1.09 times, 1.18 times, and 1.54 times higher than that of C1-CTCN-3 (84.3%), Cl-CTCN-10 (77.8%), and Cl-CTCN-15 (59.6%), respectively. An appropriate amount of Cl-CQDs can act as an electron transfer medium, promoting the separation of photogenerated carriers, while excessive Cl-CQDs will compete with g-C3N4 for photons, thus affecting the photocatalytic activity.

[0088] The catalytic results within 1 hour after the light-on were simulated using a pseudo-first-order kinetic model. Figure 6 (b) It can be seen that TCN, CTCN, and C1-CTCN-x all exhibit pseudo-first-order reaction kinetics. The calculated maximum apparent kinetic rate constant k for C1-CTCN is 0.0269 min. -1 The values ​​are TCN (0.0018min). -1 ) and CTCN (0.0042min -1 The C1-CTCN showed superior performance, with a 14.9-fold and 6.40-fold increase in efficacy compared to the C1-CTCN.

[0089] The adsorption of TC by different materials in the dark, as follows: Figure 6As shown in (c), C1-CTCN exhibits better adsorption performance for TC than TCN and CTCN. This demonstrates that the larger specific surface area of ​​C1-CTCN provides more adsorption sites, thereby increasing the amount of TC adsorbed by the catalyst.

[0090] Calcination temperature is crucial to the catalyst preparation process. The activity of the catalyst was investigated by setting different calcination temperatures, and the results are as follows: Figure 6 As shown in (d), the photocatalytic degradation of TC by C1-CTCN reaches its optimal effect at 550℃. This is because lower temperatures cannot completely convert the precursor into g-C3N4, while excessively high temperatures can easily cause the material to carbonize, affecting the formation of the material.

[0091] Depend on Figure 6 (e) shows that the photocatalytic degradation rate of Cl-CTCN decreased by only 10.4% after five cycles of the experiment, indicating that it can maintain stability during the photocatalytic process.

[0092] (V) Analysis of the Influence of pH Value

[0093] To investigate the effect of pH on the degradation process in real water bodies, pH was used as the evaluation factor, and the degradation results of tetracycline (TC) at different pH values ​​were measured. The photocatalytic degradation of TC by Cl-CTCN under different pH conditions is shown below. Figure 7 As shown in (a), the degradation rate of TC gradually increases with increasing pH, reaching its maximum at pH = 9.

[0094] (vi) Stability analysis of Cl-CTCN

[0095] Inorganic anions are abundant in real water bodies, therefore this study investigated and analyzed the effects of common anions in water on the photocatalytic process. At the initial stage of the reaction, 5 mM NaCl, Na₂SO₄, NaNO₃, NaHCO₃, and Na₂HPO₄ were added respectively, while keeping other conditions constant, and the effects of different anions on the photocatalytic degradation of TC were measured.

[0096] The results are as follows Figure 7 As shown in (b). HCO3 - and HPO4 - It exhibits a slight promoting effect, because HCO3 - and HPO4 - The addition of [a substance] affected the pH of the reaction, making the reaction system weakly alkaline, thereby promoting the degradation process. Cl [a substance]... - and SO4 2- Because it can act as a free radical scavenger and compete with TC molecules for adsorption, it exhibits a significant inhibitory effect on photocatalytic degradation efficiency, and the higher the charge, the stronger the inhibitory effect. -The addition of [a specific compound] will, on the one hand, inhibit light absorption and reduce the catalytic effect, and on the other hand, it can generate other free radicals under light to promote the catalytic process. Therefore, it has little impact on the degradation results. In general, Cl-CTCN can remain stable in water.

[0097] (VII) Applicability Analysis of Cl-CTCN:

[0098] To explore the applicability of the material of this invention, Cl-CTCN was used to photocatalytically degrade different organic pollutants. Tetracycline (TC) was replaced with 10 mg / L methyl orange (MO) and rhodamine B (RhB), respectively, while keeping other conditions the same, and the effects of different organic pollutants on the photocatalytic degradation of Cl-CTCN were determined.

[0099] Experimental results are as follows Figure 7 As shown in (c), at an initial concentration of 10 mg / L, after 30 min of dark adsorption and 120 min of light irradiation, Cl-CTCN exhibited photocatalytic degradation rates of 96.7% and 99.6% for Rhodamine B (RhB) and methyl orange (MO), respectively, both demonstrating excellent photocatalytic degradation effects. This indicates that the Cl-CTCN material of the present invention has good applicability.

[0100] (VIII) Photocatalytic Reduction Performance Analysis of Cl-CTCN

[0101] The photocatalytic reduction capabilities of three materials—TCN, CTCN, and Cl-CTCN—as different catalysts were determined using the hydrogen production rate from water splitting under visible light irradiation as an indicator.

[0102] The photocatalytic hydrogen evolution experiment used a 300W xenon lamp with an ultraviolet filter (λ>420nm) as the light source. The initial pH of the solution was maintained at 7±0.1, and the reaction temperature at 6±1℃. First, 50mg of different catalysts were added to a quartz reaction vessel containing 90mL of deionized water, along with 10mL of sacrificial agent triethanolamine (TEAO). The mixture was sonicated for 30min to ensure homogeneity. Then, 3% chloroplatinic acid was added, and the mixture was irradiated for 30min to deposit nano-Pt. Before the reaction began, air was removed from the reactor using a vacuum pump to maintain an oxygen-free, sealed environment. During the reaction, the suspension was continuously stirred at 600rpm to ensure a more uniform reaction. H2 gas generated by the reaction system was collected hourly using an automatic sampler. Hydrogen concentration was detected using gas chromatography.

[0103] Figure 8 The effects of different catalysts on photocatalytic water splitting for hydrogen production are shown. Figure 8As shown in (a), TCN, CTCN, and Cl-CTCN all exhibit stable photocatalytic water splitting for hydrogen production efficiency, with the hydrogen production rate remaining essentially unchanged within 4 hours. This is related to the good chemical stability of g-C3N4 itself. Figure 8 (b) It can be seen that the sample exhibits the best photocatalytic hydrogen evolution performance when the Cl-CQDs content is 5 mg (i.e., Cl-CTCN-5), which is consistent with the degradation experiments. This is because the presence of an appropriate amount of carbon dots broadens the light absorption range of the photocatalyst and improves its light absorption capacity, while excessive carbon dots compete with g-C3N4 for photons, leading to a decrease in hydrogen evolution efficiency. Figure 8 As can be seen from (a) and (c), the hydrogen production rate of the pure g-C3N4 catalyst TCN is relatively low, only 507.1 μmol g. -1 h -1 With the introduction of carbon dots, the hydrogen production rates of both the prepared CTCN and Cl-CTCN increased, with Cl-CTCN showing a greater increase, achieving an average hydrogen production rate of 1397.5 μmol g. -1 h -1 These figures are 2.76 and 1.72 times higher than those of TCN and CTCN, respectively. This is because the introduction of chlorine can further increase the absorption of visible light by the material, thereby increasing the hydrogen evolution rate. Furthermore, Figure 8 (c) shows the apparent quantum efficiency (AQE) of different catalysts, of which the AQE of Cl-CTCN (1.44%) is approximately 2.88 times that of TCN (0.50%).

[0104] To determine the material's recyclability, five cycles were performed, and the results are shown below. Figure 8 (d) Cl-CTCN maintained similar photocatalytic hydrogen evolution activity after 20 h of illumination, indicating that the photocatalyst has good photostability. FT-IR and XRD measurements were performed on the used samples, and the results are as follows: Figure 8 As shown in (e) and (f), the structural composition and crystal structure of Cl-CTCN did not change significantly after use. These results indicate that Cl-CTCN can maintain its activity and stability during repetition.

Claims

1. A method for preparing a chlorine-doped carbon dot-modified carbon nitride material, characterized in that, Includes the following steps: (1) Preparation of chlorine-doped carbon quantum dot material: Weigh mulberry twig powder, disperse it in water, and slowly add thionyl chloride to it. Sonicate until mixed, then transfer the suspension to a reaction vessel and heat it to 180-200 ℃ for 10-12 h. After the reaction vessel cools to room temperature, heat the resulting brown suspension in an oven to remove unreacted thionyl chloride and centrifuge. Finally, filter and purify the supernatant after centrifugation, and freeze-dry the purified solution to obtain chlorine-doped carbon quantum dot material, denoted as Cl-CQDs; The mass-volume ratio of mulberry twig powder to thionyl chloride is 1:0.5~1.0; (2) Preparation of chlorine-doped carbon dot modified carbon nitride material: Take a certain amount of urea and the Cl-CQDs powder obtained in step (1) and dissolve them in water. Stir with ultrasound to make them fully dissolved and mixed. Then put the mixed solution into an oven to dry and remove moisture. Grind the dried solid to obtain a light brown powder. Then place the mixed light brown powder in a tube furnace for calcination. The resulting brown powder is the chlorine-doped carbon dot modified carbon nitride material, labeled as Cl-CTCN. The mass ratio of urea to Cl-CQDs powder is 1000: 0.5-2.

5.

2. The method for preparing chlorine-doped carbon dot-modified carbon nitride material according to claim 1, characterized in that, In step (1), the oven temperature is 100-120 °C for 40-60 min to remove unreacted thionyl chloride.

3. The method for preparing chlorine-doped carbon dot-modified carbon nitride material according to claim 1, characterized in that, In step (1), the supernatant is filtered through a 0.22 μm filter membrane to obtain a Cl-CQDs solution, and then purified by dialysis using a 1000 Da dialysis bag for 20-24 h.

4. The method for preparing chlorine-doped carbon dot-modified carbon nitride material according to claim 1, characterized in that, In step (2), the ultrasonic stirring time is 3 h and the ultrasonic power is 40 kHz.

5. The method for preparing chlorine-doped carbon dot-modified carbon nitride material according to claim 1, characterized in that, In step (2), the calcination temperature in the tubular furnace is 500-600 ℃ for 1.5-2 h, the heating rate is 5-10 ℃ / min, and the nitrogen flow rate is 40-50 mL / min.

6. The application of a chlorine-doped carbon dot-modified carbon nitride material obtained by the preparation method as described in any one of claims 1 or 5 in photocatalysis.

7. The application of the chlorine-doped carbon dot-modified carbon nitride material according to claim 6 in photocatalysis, characterized in that, Its applications include photocatalytic degradation of tetracycline, rhodamine B, and methyl orange, as well as photocatalytic water splitting for hydrogen production.

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