Preparation method and application of a composite photocatalytic material based on graphite-phase carbon nitride and in-situ grown TiO2 heterojunction
By growing TiO2 heterojunction composite materials with controllable crystal phase ratios in situ on graphitic carbon nitride, the problem of low efficiency caused by charge-carrying recombination in graphitic carbon nitride photocatalytic materials is solved, and a highly efficient photocatalytic water purification effect is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF METAL RESEARCH - CHINESE ACAD OF SCI
- Filing Date
- 2022-12-31
- Publication Date
- 2026-06-09
AI Technical Summary
Existing graphitic carbon nitride (g-C3N4) photocatalytic materials suffer from severe charge recombination, resulting in low photocatalytic efficiency and limiting their effectiveness in practical applications.
By in-situ growing TiO2 heterojunction composite materials with controllable crystal phase ratios on graphitic carbon nitride, TiO2/g-C3N4 ternary composite photocatalyst materials were prepared in one step using the molten salt method, realizing the separation and interfacial migration of charge carriers between heterojunctions.
This improved the photocatalytic water purification capability of photocatalytic materials, achieved efficient separation of photogenerated electrons and holes, and significantly improved the degradation efficiency of organic pollutants in water.
Smart Images
Figure HDA0004032979060000011 
Figure HDA0004032979060000021 
Figure HDA0004032979060000022
Abstract
Description
Technical Field
[0001] This invention relates to the fields of functional nanomaterial preparation, solar energy utilization and environmental protection, specifically to a method for preparing and applying a TiO2 heterojunction composite photocatalytic material based on in-situ growth of TiO2 on graphitic carbon nitride. Background Technology
[0002] In recent years, the non-metallic polymer photocatalytic material g-C3N4 has attracted widespread attention in the field of photocatalytic water purification due to its abundant raw material sources, ease of synthesis, and environmental friendliness. However, the low photocatalytic efficiency of single-phase g-C3N4 prepared by direct thermal polymerization of nitrogen-rich precursors still poses a significant challenge to its practical application. The main reason for this is the severe charge recombination problem, which greatly limits its photocatalytic performance. To address this issue, a highly effective strategy is to construct g-C3N4-based heterojunction photocatalytic composite material systems. By combining semiconductor photocatalytic materials with suitable band structures, a built-in electric field is formed at the two-phase interface, thereby promoting the efficient separation of photogenerated carriers. TiO2 is one of the most widely studied materials in the field of photocatalysis, and numerous studies have demonstrated that constructing TiO2 / g-C3N4 composite photocatalytic materials can significantly improve the photocatalytic efficiency of single-phase materials. For example, Li et al. directly prepared g-C3N4 by calcining a mixture of bulk g-C3N4 and titanate nanotubes. 4 / TiO2 (anatase) Z-mechanism photocatalyst material: Experimental results show that the Z-mechanism system is beneficial for carrier separation and its photocatalytic efficiency in degrading propylene is 25 times higher than that of single-phase g-C3N4 {Applied Surface Science 391(2017)184–193}. Zhang et al. prepared a g-C3N4 / TiO2 heterogeneous photocatalyst with high specific surface area using an in-situ hydrothermal method combined with secondary calcination. The synthesized material exhibited high efficiency in degrading rhodamine B {Journal of Hazardous Materials 394(2020)122529}. On the other hand, the molten salt method has also been applied to the preparation of g-C3N4 / TiO2 heterogeneous photocatalysts due to its advantages such as fine particle size, high purity, controllable structure, simple reaction process, and ease of control. For example, Zhang et al. used P25(TiO2) and melamine as reaction precursors to prepare g-C3N4 / TiO2 composite photocatalysts with high adsorption capacity and efficient photocatalytic activity {Journal of Photochemistry & Photobiology A: Chemistry 362(2018)1–13}. However, to our knowledge, there are few reports on the in-situ growth of TiO2 heterojunction composite photocatalysts on g-C3N4, and there are almost no reports on the in-situ growth of TiO2 heterojunction photocatalyst composites with controllable crystal phase ratios on g-C3N4. Summary of the Invention
[0003] The purpose of this invention is to provide a method for preparing and applying a TiO2 heterojunction composite photocatalytic material with controllable phase ratio grown in situ on graphitic carbon nitride. By preparing a TiO2 (rutile) / TiO2 (anatase) / g-C3N4 ternary composite photocatalytic material with controllable phase ratio, the separation of charge carriers between the TiO2 heterojunctions and the migration at the interface between TiO2 and g-C3N4 heterojunctions can be simultaneously achieved, thereby fundamentally improving the photocatalytic water purification capability of the photocatalytic material system.
[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0005] A method for preparing TiO2 heterojunction composite photocatalyst material with controllable crystal phase ratio grown in situ on graphitic carbon nitride is disclosed. The method utilizes direct thermal polymerization of nitrogen-rich precursor to prepare graphitic carbon nitride (g-C3N4) material, uses rutile TiO2 as titanium source, and employs molten salt method to prepare TiO2 heterojunction / g-C3N4 composite photocatalyst material on g-C3N4 in one step.
[0006] The nitrogen-rich precursors are urea, cyanamide, dinitrile diamine, or melamine.
[0007] The rutile TiO2 is commercially available rutile TiO2 or laboratory-prepared and synthesized rutile TiO2.
[0008] The method for preparing TiO2 heterojunction / g-C3N4 composite photocatalyst material using molten salt-assisted one-step preparation includes the following steps:
[0009] (1) Add nitrogen-rich precursor solid powder into a covered corundum crucible and calcine it in a muffle furnace at 500-650°C for 1-6 hours in an air atmosphere to obtain the graphite phase carbon nitride (g-C3N4) material.
[0010] (2) Transfer the clear solution obtained in step (1) to an 80℃ drying oven and dry for 12 hours to obtain a white solid powder. Mix g-C3N4, rutile TiO2 and metal halide salt obtained in step (1) in a certain mass ratio and grind in a mortar for a certain time to obtain a uniform solid powder;
[0011] (3) The white solid powder obtained in step (2) is added to an alumina crucible and calcined in a muffle furnace at 500–650°C for 1–6 hours in an air atmosphere to obtain the ultrathin carbon nitride (UCN) material. The white solid powder obtained in step (2) is added to a covered alumina crucible and calcined in a muffle furnace at 500–650°C for 0.5–6 hours in an air atmosphere. After the temperature drops to room temperature, the sample is washed three times with boiling water to remove the salt in the sample. Finally, the sample is dried in an oven at 60°C to obtain the TiO2 (rutile) / TiO2 (anatase) / g-C3N4 composite material.
[0012] The grinding time in the mortar during step (2) is 10-60 minutes.
[0013] In step (3), the metal halide salt is LiCl, KCl, or a mixture of both, and may also be LiBr, KBr, or a mixture of both. The mass ratio of the metal halide salt mixture LiX (Cl or Br):KX (Cl or Br) is (50-55)%:(50-45)%.
[0014] The ratio of g-C3N4, rutile TiO2 and metal halide added in step (3) is (0.1-1.0) g: (0.1-1.0) g: (10-50) g.
[0015] The in-situ grown TiO2 heterojunction composite photocatalytic material on g-C3N4 can be directly applied to the photocatalytic purification of organic pollutants in water.
[0016] The design principle of this invention is as follows:
[0017] The fundamental starting point of this invention is that the main bottleneck restricting the practical application of semiconductor photocatalytic materials is the easy recombination of photogenerated carriers, leading to low photocatalytic efficiency. To solve this problem, we chose to construct a TiO2 / g-C3N4 heterojunction material as a model. Through a molten salt-assisted preparation method, we synthesized a TiO2 heterojunction composite photocatalytic material with controllable crystal phase ratio on g-C3N4 in one step. This simultaneously achieves carrier separation between the TiO2 heterojunction and interface migration between TiO2 and g-C3N4, thereby fundamentally improving the photocatalytic water purification capability of the photocatalytic material system. The ultimate goal is to obtain a photocatalytic material system with potential practical and commercial value through material design.
[0018] The advantages of this invention are:
[0019] 1. This invention employs molten salt assistance and, under the synergistic effect of g-C3N4, for the first time discovers the transformation of rutile TiO2 to anatase TiO2, and can controllably prepare it by means of heterogeneous titanium dioxide with an effective crystal phase ratio.
[0020] 2. This invention employs a molten salt-assisted method to construct a heterogeneous catalyst on g-C3N4. The in-situ prepared ternary catalyst can effectively solve the carrier recombination problem and extend the carrier lifetime, providing a new approach for the future design and synthesis of highly efficient photocatalytic water purification materials.
[0021] 3. The process of this invention is simple, easy to operate, and has low energy consumption, making it suitable for mass production.
[0022] 4. The in-situ grown TiO2 heterojunction composite photocatalytic material on g-C3N4 of the present invention achieves efficient separation of photogenerated electrons and holes, has high photocatalytic activity and can be directly used to remove organic pollutants in water, and has potential practical application value. Attached Figure Description
[0023] Figure 1 The images show XRD and SEM morphology of the crystal structure of the material prepared in Example 1; where: (a) XRD; (b) SEM.
[0024] Figure 2 The images show the XRD patterns of the TiO2 / g-C3N4 heterojunction materials prepared in Example 2 with different calcination times.
[0025] Figure 3 The images show the XRD patterns of TiO2 / g-C3N4 heterojunction materials prepared at different calcination temperatures in Example 3.
[0026] Figure 4The image shows the XRD pattern of TiO2 / g-C3N4 three-phase heterojunction materials prepared under the single-component salt KCl conditions of Example 4, with the addition of different BCN and rutile TiO2.
[0027] Figure 5 The results of the visible light photocatalytic degradation of tetracycline in water by the photocatalytic material prepared in Example 1 are shown.
[0028] Figure 6 The results are from the visible light photocatalytic degradation of Rhodamine B in water using the photocatalytic material prepared in Example 2. Detailed Implementation
[0029] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0030] Example 1:
[0031] (1) Weigh 5 grams of melamine and place it in a covered crucible. Heat it to 550°C in a muffle furnace at a heating rate of 2.3°C / min and calcine for 4 hours to obtain blocky carbon nitride (BCN).
[0032] (2) A certain proportion of bulk carbon nitride, commercial rutile, and KCl-LiCl eutectic salt (59.2 mol% LiCl + 40.8 mol% KCl) were mixed evenly in a mortar, with a mass ratio of bulk carbon nitride: rutile: eutectic salt = 1:0.25:10. The evenly mixed powder was transferred to a covered crucible and heated to 550℃ in a muffle furnace at a heating rate of 5℃ / min for 2 hours. After the temperature dropped to room temperature, the sample was washed three times with boiling water to remove the salt. Finally, the sample was dried in an oven at 60℃ to obtain TiO2 / g-C3N4 heterojunction photocatalytic material.
[0033] (3) As a control, molten salt rutile without carbon nitride (denoted as TiO2-MS) and molten salt carbon nitride without rutile (denoted as BCN-MS) were synthesized under the same conditions.
[0034] (4) Figure 1(a) shows the XRD pattern of the synthesized material. As shown in the figure, the crystal structure of rutile TiO2 remained basically unchanged before and after molten salt treatment. The (100) crystal plane of bulk carbon nitride shifted from 13.4° to 8°, and the (002) crystal plane shifted from 27.2° to 29.1°, proving that the molten salt process improved the crystallinity of BCN. The experimental results are consistent with the literature report {ACS Catalysis 6 (2016), 3921-3931}. The synthesized material has good crystallinity. The material obtained after 2 hours of molten salt treatment showed obvious diffraction peaks of TiO2 (rutile), TiO2 (anatase), and g-C3N4, proving that the crystal structure of TiO2 (rutile) changed under molten salt conditions, generating a TiO2 / g-C3N4 three-phase heterojunction photocatalytic material. Figure 1 (b) shows the SEM image of the synthesized TiO2 / g-C3N4 three-phase heterojunction material, in which the octahedral morphology is typical anatase TiO2, and TiO2 (rutile) and g-C3N4 are nanoparticles and nanosheets, respectively.
[0035] Example 2:
[0036] (1) Weigh 0.338 g of BCN and 0.085 g of rutile TiO2 prepared in Example 1 and place them into a mortar containing 2.7 g of KCl and 3.3 g of LiCl. Grind vigorously for 15 minutes until uniformly mixed. Then, transfer the uniformly mixed powder to a covered crucible and heat it to 550 °C in a muffle furnace at a heating rate of 5 °C / min. Calcination was carried out for a certain time, and five groups of experiments were investigated, with calcination times controlled at 0.5, 1, 2, 4, and 6 hours, respectively. After the temperature dropped to room temperature, the sample was washed three times with boiling water to remove the salt in the sample. Finally, the sample was dried in an oven at 60 °C to obtain TiO2 / g-C3N4 heterojunction photocatalytic materials with different calcination times.
[0037] (2) Figure 2 The figure shows the XRD pattern of the prepared material as a function of calcination time. It is clear from the figure that the rutile TiO2 content gradually decreases while the anatase TiO2 content gradually increases with increasing calcination time, further demonstrating that the crystal structure of TiO2 (rutile) undergoes a transformation under molten salt conditions.
[0038] Example 3:
[0039] (1) The difference from Example 2 is that the calcination time was controlled to be 4 hours and the calcination temperature was adjusted during the synthesis process in step (1). There were five groups of experiments: Group 1: calcination temperature 500℃; Group 2: calcination temperature 525℃; Group 3: calcination temperature 550℃; Group 4: calcination temperature 600℃; Group 5: calcination temperature 650℃.
[0040] (2) Figure 3The figure shows the XRD pattern of the prepared material as a function of calcination temperature. It is clearly visible that as the calcination temperature increases, the rutile TiO2 content gradually decreases while the anatase TiO2 content gradually increases, further demonstrating that the crystal structure of TiO2 (rutile) undergoes a transformation under molten salt conditions.
[0041] Example 4:
[0042] (1) Weigh 5 grams of melamine and place it in a covered crucible. Heat it to 550°C in a muffle furnace at a heating rate of 2.3°C / min and calcine for 4 hours to obtain blocky carbon nitride (BCN).
[0043] (2) Weigh 3g of BCN prepared in step (1), 0.5g of rutile, and 20g of KCl, mix and grind them. Transfer the uniformly mixed powder to a covered crucible and heat it in a muffle furnace to 600℃ at a heating rate of 10℃ / min for 2 hours. After the temperature drops to room temperature, wash the sample three times with boiling water to remove the salt in the sample. Finally, dry the sample in an oven at 60℃ to obtain TiO2 / g-C3N4 heterojunction photocatalytic material.
[0044] (3) As a control, under the same conditions, the ratio of BCN to rutile was changed to 1:1, 3:1, 4:1 and 6:1 respectively, and three other groups of samples were obtained in the same way.
[0045] (4) By Figure 4 It can be seen that when the ratio of BCN to rutile is 1:1, only the rutile phase is present in the XRD. However, when the amount of rutile is reduced, and the ratio of CN to rutile is 3:1, 4:1, and 6:1, peaks representing the anatase phase appear at 25.36° and 48.021°, corresponding to the (101) and (004) crystal planes of anatase, respectively. Furthermore, as the amount of rutile decreases, the content of the anatase phase gradually increases. The rutile content of samples with different ratios is as follows: when BCN:rutile = 1:1, 3:1, 4:1, and 6:1, W... 金红石 = 98.14%, 90.03%, 98.14%, and 78.34%. This shows that the greater the amount of CN compared to rutile, the easier it is for the rutile phase to reverse into the anatase phase.
[0046] Example 5:
[0047] This example demonstrates the application of the photocatalytic material prepared in Example 1 to the photocatalytic degradation of the antibiotic tetracycline. The process is as follows:
[0048] 1) Add 20 mg of the powder obtained in Example 1 to a 50 ppm tetracycline aqueous solution and stir magnetically for 30 minutes in the dark. Then place the suspension under a 300W xenon lamp light source with a wavelength of 400-700 nm visible light and an intensity of 45 mW / cm². 2 Expose to light for 30 minutes.
[0049] 2) At regular intervals, take 10 mL of the suspension and centrifuge to separate the nanoparticles. Take the supernatant and determine the concentration of the remaining tetracycline in the solution.
[0050] Example 6:
[0051] This example demonstrates the application of TiO2 / g-C3N4 heterojunction photocatalytic materials prepared in Example 2 with different calcination times in the degradation of colored organic pollutants. The process is as follows:
[0052] 1) Add 20 mg of the powder obtained in Example 2 to a 10 ppm Rhodamine B aqueous solution and stir magnetically for 30 minutes in the dark. Then place the suspension under a 300W xenon lamp light source with a wavelength of visible light (400-700 nm) and an intensity of 45 mW / cm². 2 Expose to light for 120 minutes.
[0053] 2) At regular intervals, take 10 mL of the suspension and centrifuge to separate the nanopowder. Take the supernatant and determine the concentration of Rhodamine B remaining in the solution.
[0054] The experimental results of the above embodiments and application examples are as follows:
[0055] Figure 5 The results shown are from the visible light photocatalytic degradation experiments of tetracycline in water using the BCN, rutile TiO2, and TiO2 / g-C3N4 photocatalyst materials prepared in Example 1. Figure 4 It can be seen that: ① Under visible light irradiation for 30 minutes, the synthesized BCN and rutile TiO2 photocatalysts degrade 10% and 30% of tetracycline, respectively; ② Compared with single-phase BCN and rutile TiO2 photocatalysts, 10 ppm of tetracycline can be degraded by 80% of TiO2 / g-C3N4 photocatalysts within 30 minutes.
[0056] Figure 6 The image shows the visible light photocatalytic degradation results of Rhodamine B in water using TiO2 / g-C3N4 photocatalyst materials prepared in Example 2 with different calcination times. From... Figure 6 It can be seen that under visible light irradiation, as the calcination time increases, the anatase content gradually increases, and the photocatalytic activity of the generated TiO2 (rutile) / TiO2 (anatase) / g-C3N4 three-phase composite material is significantly increased. 10 ppm of tetracycline can be completely degraded within 15 minutes.
[0057] The results of the embodiments show that the present invention, combining the molten salt method and rutile TiO2, successfully achieved the controllable preparation of TiO2 heterojunction composite photocatalytic materials with controllable crystal phase ratios grown in situ on g-C3N4. Through the in-situ construction of a ternary catalyst design, efficient separation of photogenerated electron-hole pairs was achieved. This photocatalytic material, after being excited by visible light, can be directly applied to the purification of colored pollutants (Rhodamine B) and colorless organic antibiotic pollutants (tetracycline) in water, solving the problem of low photocatalytic efficiency in traditional photocatalytic materials.
Claims
1. A method for preparing a TiO2 heterojunction composite photocatalytic material with controllable phase ratio grown in situ on graphitic carbon nitride, characterized in that: This method utilizes direct thermal polymerization of nitrogen-rich precursors to prepare graphitic carbon nitride (g-C3N4) materials, employs rutile TiO2 as a titanium source, and utilizes the molten salt method to prepare TiO2 heterojunction / g-C3N4 composite photocatalytic materials in a single step on g-C3N4. The aforementioned TiO2 heterogeneous phase is a TiO2 heterogeneous phase consisting of rutile and anatase phases; The molten salt method involves directly mixing g-C3N4 and TiO2 powders into a low-temperature eutectic salt and calcining it at 500–650 °C for 0.5–6 hours in an air atmosphere.
2. The preparation method of TiO2 heterojunction composite photocatalytic material with controllable crystal phase ratio based on in-situ growth on graphitic carbon nitride according to claim 1, characterized in that: The nitrogen-rich precursor is urea, cyanamide, dinitrile diamine, or melamine.
3. The preparation method of TiO2 heterojunction composite photocatalytic material with controllable crystal phase ratio based on in-situ growth on graphitic carbon nitride according to claim 1, characterized in that: The rutile TiO2 mentioned is commercially available rutile TiO2 or laboratory-prepared and synthesized rutile TiO2.
4. The preparation method of TiO2 heterojunction composite photocatalytic material based on in-situ growth of controllable phase ratio on graphitic carbon nitride according to any one of claims 1-3, characterized in that: The method specifically includes the following steps: Nitrogen-rich precursor solid powder was added to a covered corundum crucible and calcined in a muffle furnace at 500–650°C for 1–6 hours in an air atmosphere to obtain the graphitic carbon nitride (g-C3N4) material. The g-C3N4 obtained in step (1), rutile TiO2, and metal halide salts are mixed in a certain mass ratio and ground in a mortar for a certain time to obtain a uniform solid powder. The white solid powder obtained in step (2) was added to a covered corundum crucible and calcined in a muffle furnace. After the temperature dropped to room temperature, the sample was washed three times with boiling water to remove the salt in the sample. Finally, the sample was dried in an oven at 60°C to obtain the TiO2 heterojunction / g-C3N4 composite photocatalytic material.
5. The preparation method of TiO2 heterojunction composite photocatalytic material based on in-situ growth of controllable phase ratio on graphitic carbon nitride according to claim 4, characterized in that: In step (2), the grinding time in the mortar is 10-60 minutes; in step (3), the metal halide salt is LiX, KX or a mixture of the two; the mass ratio of LiX:KX in the mixture is (50-55)%:(50-45)%; X is Cl or Br.
6. The preparation method of TiO2 heterojunction composite photocatalytic material with controllable crystal phase ratio based on in-situ growth on graphitic carbon nitride according to claim 4, characterized in that: In step (3), the ratio of g-C3N4, rutile TiO2 and metal halide added is (0.1-1.0) g: (0.1-1.0) g: (10-50) g.
7. A TiO2 heterojunction / g-C3N4 composite photocatalytic material with controllable phase ratio grown in situ on graphitic carbon nitride using the method described in claim 1.
8. The application of the TiO2 heterojunction composite photocatalytic material with controllable phase ratio grown in situ on graphitic carbon nitride according to claim 7, characterized in that: This photocatalytic material is directly applied to the photocatalytic purification of organic pollutants in water.