Process for preparing a highly crystalline polyheptazine imide
By using rare earth oxides and metal salts for heat treatment, the problems of low crystallinity and insufficient photocatalytic activity of graphitic carbon nitride were solved, and highly crystalline polyheptamethrin imide was prepared, which improved the photocatalytic performance and is suitable for photocatalytic degradation of organic pollutants, synthesis of hydrogen peroxide and photocatalytic hydrogen production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHEASTERN UNIV CHINA
- Filing Date
- 2024-02-05
- Publication Date
- 2026-06-16
AI Technical Summary
Existing graphitic carbon nitride materials have low crystallinity, many internal defects, difficulty in carrier migration, and insufficient photocatalytic activity. Existing methods for crystallinity control are complex and not suitable for commercialization.
A rare earth oxide and metal salt heat treatment method was adopted. After uniformly grinding and mixing nitrogen-rich precursors, metal salts and rare earth oxides, the mixture was calcined under a specific atmosphere, washed and dried to obtain highly crystalline polyheptamethrin imide. Rare earth oxides were used to promote the transformation of the graphitic carbon nitride crystal structure.
It improves the crystallinity and carrier separation and migration ability of the material, significantly enhances photocatalytic performance, and is suitable for commercial production.
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Figure CN118002179B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of photocatalytic materials, specifically a method for preparing highly crystalline polyheptamethrin imide by heat treatment of rare earth oxides and metal salts. Background Technology
[0002] Carbon nitride is a non-crystalline nitrogen-carbon compound with a two-dimensional planar network structure, including α-phase, β-phase, cubic phase, quasi-cubic phase, and graphitic phase (Teter DM et al, Low-compressibility carbon nitrides, Science, 1996, 271, 53-55). Among them, graphitic carbon nitride is the most stable soft phase under normal temperature and pressure, possessing good visible light absorption, high physicochemical stability, and low preparation cost, making it a promising photocatalyst. Thermal polycondensation is a commonly used method in the laboratory to prepare graphitic carbon nitride, which involves heating and calcining one or more carbon-nitrogen compound precursors such as cyanamide, urea, melamine, and thiourea. However, the graphitic carbon nitride synthesized in this way has an amorphous melon structure (Wang XC et al, A metal-free polymeric photocatalyst for hydrogen production from water under visible light, Nature Materials, 2009, 8, 76-80). This amorphous melon-structured graphitic carbon nitride consists of a zigzag chain structure composed of in-plane triazine or heptaazine basic units connected by bridging nitrogen atoms, with the chains linked by hydrogen bonds. However, due to incomplete condensation and the presence of numerous amino groups, the crystallinity is low. Furthermore, the increased defects enhance the recombination rate of photogenerated electrons and holes, hindering the migration of photogenerated charge carriers to the material surface to participate in photocatalytic redox reactions, thus limiting the material's photocatalytic efficiency.
[0003] To address the aforementioned drawbacks of graphitic carbon nitride, methods such as morphology control, elemental doping, construction of heterojunction composites, and crystallinity regulation have been developed to improve its photocatalytic performance. Ionothermal methods are an important means of regulating the crystallinity of graphitic carbon nitride. LiCl / KCl mixtures (45:55wt%, Tm = 352℃) exhibit high stability, non-corrosiveness, non-toxicity, and good precursor solubility. They are molten at 550℃, a commonly used calcination temperature for nitrogen-containing precursors and their derivatives, and are therefore used as heat conductors to promote more complete polycondensation of graphitic carbon nitride, forming polyheptaazineimide (PHI) and polytriazineimide (PTI) structures (XCWang et al, Tri s triazine-Based Crystalline Graphitic Carbon Nitrides for Highly Efficient Hydrogen Evolution Photocatalysis, ACSCatalysis, 2016, 6, 3921-3931). Compared to melon-based graphitic carbon nitride, polyheptaazine imide (PHI) and polytriazine imide (PTI) possess long-range ordered structures and more extended conjugated planes, and exhibit more complete polymerization, implying better crystallinity and fewer defects. This effectively reduces recombination centers for photogenerated electrons and holes, promoting carrier separation. Furthermore, compared to the PTI structure, the PHI heptaazine structure has a larger π-conjugated system, which is beneficial for light trapping and the migration of photogenerated carriers. Sealing and calcining nitrogen-containing precursors in ampoules or using microwave-assisted heating can enhance the crystallinity of graphitic carbon nitride, but these methods are complex and require sophisticated equipment, making them unsuitable for widespread application or commercialization. Meanwhile, there are few reports on the control of the crystallinity of polyheptaazine imide (PHI). Therefore, developing a simple and low-cost method for controlling the crystallinity of graphitic carbon nitride and polyheptaazine imide (PHI) structures has significant application value. Summary of the Invention
[0004] The purpose of this invention is to provide a method for preparing highly crystalline polyheptamethrin imide (PHI), which utilizes a rare earth oxide and metal salt heat treatment process to achieve control over the crystal structure of graphitic carbon nitride, thereby solving the problems faced by graphitic carbon nitride as a functional material, such as low crystallinity, numerous internal defects, difficulty in carrier migration, and insufficient photocatalytic activity.
[0005] The technical solution of this invention is:
[0006] A method for preparing highly crystalline polyheptamethrin imide involves uniformly grinding and mixing a nitrogen-rich precursor, a metal salt, and rare earth oxides, followed by calcination under a specific atmosphere. The residue after calcination is then washed and dried to remove the metal salt, yielding highly crystalline polyheptamethrin imide (PHI). The rare earth oxides and metal salts, at high temperatures, influence the polycondensation process of the nitrogen-rich precursor and alter the crystal structure of graphitic carbon nitride, resulting in highly crystalline polyheptamethrin imide (PHI) with improved crystallinity, charge carrier behavior, and photocatalytic performance.
[0007] The method for preparing highly crystalline polyheptamethrin imide (PHI) uses a nitrogen-rich precursor that is one or a mixture of dicyandiamide, melamine, and urea.
[0008] The method for preparing highly crystalline polyheptamethrin imide (PHI) uses a single salt of potassium chloride, a single salt of sodium chloride, or a binary salt of sodium chloride and potassium chloride. Preferably, in the binary salt, the mass ratio of sodium chloride to potassium chloride is 0.5–0.9.
[0009] In the method for preparing highly crystalline polyheptamethrin imide (PHI), the rare earth oxide is ytterbium oxide.
[0010] In the method for preparing highly crystalline polyheptamethrinimide (PHI), the mass ratio of nitrogen-rich precursor to metal salt is 1:1 to 1:10. The mass ratio of rare earth oxide to nitrogen-rich precursor is 0.01% to 1%.
[0011] In the method for preparing highly crystalline polyheptamethrin imide (PHI), the nitrogen-rich precursor, rare earth oxide, and metal salt need to be ground evenly in a mortar.
[0012] The method for preparing highly crystalline polyheptamethrin imide (PHI) involves calcination in an atmosphere at a temperature of 500–600 °C, a heating rate of 2–10 °C / min, and a calcination time of 2–6 h.
[0013] The method for preparing highly crystalline polyheptamethrin imide (PHI) uses air, nitrogen, or argon as the calcination atmosphere.
[0014] The method for preparing highly crystalline polyheptamethrin imide (PHI) involves repeatedly washing the obtained solid sample with deionized water at a temperature of 20–80°C after the calcination reaction to remove the remaining metal salts from the reaction, and then drying the washed sample in an oven at 50–80°C.
[0015] The method for preparing highly crystalline polyheptamethrin imide (PHI) utilizes a rare earth oxide and metal salt heat treatment process to alter the crystal structure of graphitic carbon nitride, thereby further improving carrier behavior and photocatalytic activity.
[0016] The advantages and beneficial effects of this invention are as follows:
[0017] This invention provides a method for preparing highly crystalline polyheptamethrin imide (PHI). Using a metal salt as a template, it catalyzes the calcination polycondensation of the precursor, transforming graphitic carbon nitride from a melon structure to a PHI structure, thus achieving structural control of graphitic carbon nitride. The addition of rare earth oxides promotes deamination of the precursor during calcination, enhancing the orderliness of the in-plane and interlayer atomic arrangement of PHI and improving its crystallinity. This invention further improves the crystallinity of the material based on the PHI structure, filling the gap in PHI structure crystallinity control. This invention is the first to utilize rare earth oxides to achieve crystallinity control of PHI. Adding a small amount of rare earth oxides during calcination avoids the introduction of large amounts of impurity elements that could affect the PHI structure. This invention does not use expensive or toxic raw materials, embodying a green and environmentally friendly research philosophy. The material synthesis process is simple and conducive to large-scale commercial production. The method for preparing highly crystalline polyheptamethrin imide (PHI) provided by this invention can achieve crystal structure regulation of polyheptamethrin imide (PHI), improve the low crystallinity of graphitic carbon nitride, reduce internal defects, and promote the separation and migration of photogenerated carriers. It can be applied to photocatalytic degradation of organic pollutants, synthesis of hydrogen peroxide, photocatalytic hydrogen production, or total water splitting. Attached Figure Description
[0018] Figure 1 The X-ray diffraction patterns of the samples are shown below. The horizontal axis 2Theta represents the diffraction angle (degree), and the vertical axis Intensity represents the diffraction peak intensity (au). (a) represents PHI, and (b) represents PHI-Yb.
[0019] Figure 2 The graph shows a comparison of the photocatalytic performance of the samples; where the horizontal axis Time represents time (min) and the vertical axis In (C0 / C), (a) represents PHI and (b) represents PHI-Yb. Detailed Implementation
[0020] The present invention will now be further described in detail with reference to embodiments and accompanying drawings.
[0021] Example 1
[0022] (1) Commercially available melamine, KCl, NaCl and Yb2O3 were selected as raw materials.
[0023] (2) Grind 5g melamine, 5.6g KCl, 4.4g NaCl and 5mg Yb2O3 for 30min to achieve uniform mixing.
[0024] (3) Add the sample collected in (2) into the crucible, place it in the center of the muffle furnace, heat and calcine it in air atmosphere, increase the temperature by 5℃ / min, set the target temperature of the muffle furnace to 550℃, hold for 4h, and cool it to room temperature with the furnace.
[0025] (4) The sample collected in (3) was repeatedly washed and precipitated with deionized water at 60°C to remove metal salts from the sample until no white precipitate was produced when the supernatant was titrated with silver nitrate. The precipitate was then dried in an oven at 70°C.
[0026] Example 2
[0027] (1) Commercially available melamine, KCl, NaCl and Yb2O3 were selected as raw materials.
[0028] (2) Grind 1g of melamine, 5.6g of KCl, 4.4g of NaCl and 10mg of Yb2O3 for 30min to achieve uniform mixing.
[0029] (3) Add the sample collected in (2) into the crucible, place it in the center of the muffle furnace, heat and calcine it under a nitrogen atmosphere, raise the temperature by 2.5℃ / min, set the target temperature of the muffle furnace to 500℃, hold for 6 hours, and cool it to room temperature with the furnace.
[0030] (4) The sample collected in (3) was repeatedly washed and precipitated with deionized water at 20°C to remove metal salts from the sample until no white precipitate was produced when the supernatant was titrated with silver nitrate. The precipitate was then dried in an oven at 75°C.
[0031] Example 3
[0032] (1) Commercially available melamine, KCl and Yb2O3 were selected as raw materials.
[0033] (2) Grind 10g of melamine, 10g of KCl and 1mg of Yb2O3 for 30min to achieve uniform mixing.
[0034] (3) Add the sample collected in (2) into the crucible, place it in the center of the muffle furnace, and heat it in air atmosphere. The temperature rises by 10℃ / min, the target temperature of the muffle furnace is set to 600℃, the holding time is 2.5h, and the furnace is cooled to room temperature.
[0035] (4) The sample collected in (3) was repeatedly washed and precipitated with deionized water at 20°C to remove metal salts from the sample until no white precipitate was produced when the supernatant was titrated with silver nitrate. The precipitate was then dried in an oven at 80°C.
[0036] Structural characterization:
[0037] Figure 1 The PHI-Yb shown is the X-ray diffraction pattern characterization of the PHI-Yb obtained in Example 1. It was obtained by calcining a mixture of a nitrogen-containing precursor and a metal salt. Figure 1 (a) The three diffraction peaks at 8°, 10° and 28° correspond to the (100), (110) and (002) crystal planes of the polyheptamethrin imide (PHI) structure, respectively. Figure 1 (b) is PHI-Yb obtained by treating a nitrogen-containing precursor with both metal salts and rare earth oxides, retaining the (100), (110), and (002) crystal planes of polyheptaazine imide (PHI). Compared to PHI, the (002) crystal plane of PHI-Yb migrates at a large angle, indicating that the rare earth oxides promote the close stacking of adjacent heptaazine layers. Simultaneously, the full width at half maximum (FWHM) of the (002) crystal plane of PHI-Yb is significantly reduced compared to the PHI structure, indicating improved crystallinity. Reduced interlayer spacing and higher crystallinity can promote the migration of photogenerated carriers in the stacked structure, reduce non-radiative recombination at recombination centers such as defect sites, and improve the photocatalytic performance of the catalyst.
[0038] Photocatalytic testing
[0039] The photocatalytic performance of the photocatalyst was evaluated using Rhodamine B (RhB) degradation as an example: 25 mg of the photocatalyst from Example 1 was added to 80 mL of a 20 mg / L RhB solution. After adsorption in the dark for 30 minutes, the solution was irradiated with a Xe lamp (power: 300 W) equipped with a UV cutoff filter (λ > 420 nm). At fixed time intervals, 5 mL of the suspension was collected and centrifuged. The absorbance of the supernatant was measured using a UV-Vis spectrophotometer at the maximum absorbance peak (λ = 554 nm) to evaluate the RhB degradation performance of the photocatalyst. Figure 2 A comparison of the photocatalytic degradation performance of Rhodamine B in the samples shows that the photocatalytic performance of PHI-Yb is 2.29 times that of the PHI structure.
[0040] The results show that this invention is the first to utilize rare earth oxides to regulate the crystallinity of polyheptamethrinimide (PHI). By adding a small amount of rare earth oxides, the orderliness of the in-plane and interlayer atomic arrangement of PHI is significantly improved, further enhancing the crystallinity of the PHI structure and filling the gap in PHI structure crystallinity regulation. This provides a method for regulating the crystallinity of graphitic carbon nitride, which can be applied to photocatalytic degradation of organic pollutants, synthesis of hydrogen peroxide, photocatalytic hydrogen production, or total water splitting.
Claims
1. A method for preparing highly crystalline polyheptamethrin imide, characterized in that, A nitrogen-rich precursor, a metal salt, and rare earth oxides are uniformly ground and mixed, and then calcined under an atmosphere of air, nitrogen, or argon. After calcination, the residue is washed and dried to remove the metal salt, yielding highly crystalline polyheptamethrin imide (PHI). The nitrogen-rich precursor is one or a mixture of several of dicyandiamide, melamine, and urea. The metal salt is a single salt of potassium chloride, a single salt of sodium chloride, or a binary salt of potassium chloride and sodium chloride. The mass ratio of rare earth oxides to nitrogen-rich precursors is 0.01%–1%. The calcination temperature is 500–600℃, the heating rate is 2–10℃ / min, and the calcination time is 2–6 h.
2. The method for preparing highly crystalline polyheptamethrin imide (PHI) according to claim 1, characterized in that, The mass ratio of potassium chloride to sodium chloride in a binary salt is 0.5 to 0.
9.
3. The method for preparing highly crystalline polyheptamethrin imide (PHI) according to claim 1, characterized in that, The rare earth oxide is ytterbium oxide.
4. The method for preparing highly crystalline polyheptamethrin imide (PHI) according to claim 1, characterized in that, The mass ratio of nitrogen-rich precursor to metal salt is 1:1 to 1:
10.
5. In the method for preparing highly crystalline polyheptamethrin imide (PHI) according to claim 1, 2, 3 or 4, the nitrogen-rich precursor, rare earth oxide and metal salt mixture needs to be ground evenly in a mortar.
6. The method for preparing highly crystalline polyheptamethrin imide (PHI) according to claim 1, 2, 3 or 4, wherein after the calcination reaction is completed, the obtained solid sample is repeatedly washed with deionized water at a temperature of 20~80℃ to remove the metal salt remaining in the reaction, and the washed sample is placed in an oven at 50~80℃ to dry.
7. Highly crystalline polyheptaazine imide (PHI), characterized in that, It is prepared by any one of the preparation methods described in claims 1-6.