A method for preparing carbon nitride-bismuth oxide composite nanosheets by molten salt one-pot method

Abstract

The application provides a method for preparing carbon nitride-carbonate bismuth oxide composite nanosheets by a molten salt one-pot method, sodium bismuthate, melamine and sodium nitrate are mixed and uniformly ground to obtain a solid mixture; the solid mixture is heated at 350 DEG C, sodium nitrate is molten to form an ionic molten salt medium, and a one-pot reaction is simultaneously carried out in the medium: sodium bismuthate and melamine are converted into carbonate bismuth oxide through an oxidation-reduction reaction, melamine is simultaneously converted into graphite phase carbon nitride through a polymerization reaction, and the synergistically generated carbonate bismuth oxide and graphite phase carbon nitride are in-situ compounded to form g-C3N4-Bi2O2CO3 composite nanosheets. The application is based on a synthesis strategy of realizing multiple chemical reactions in a single molten salt environment, in-situ compounding to form a heterojunction, and simultaneously generating g-C3N4 and Bi2O2CO3 in one step and in-situ bonding, and the preparation steps are simple, the operation is convenient, the reaction conditions are mild, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and photocatalysis, and in particular to a method for preparing carbon nitride-bismuth oxycarbonate (g-C3N4-Bi2O2CO3) composite nanosheets by a one-pot molten salt process. Background Technology

[0002] Graphitic carbon nitride (g-C3N4) and bismuth oxycarbonate (Bi2O2CO3) are both semiconductor materials with excellent photocatalytic performance. When used alone, g-C3N4 responds well to ultraviolet and visible light, but its utilization rate in near-infrared light is relatively low. Bi2O2CO3 has a regular morphology and strong photochemical stability, but it suffers from high recombination rates of photogenerated electron-hole pairs and a narrow photoresponse range. Therefore, g-C3N4 and Bi2O2CO3 have some limitations when used alone. Researchers have therefore focused on combining them to form heterojunctions, which can effectively promote the separation of photogenerated carriers, broaden the photoresponse range, and improve their photocatalytic efficiency and performance.

[0003] However, existing methods for preparing g-C3N4 and Bi2O2CO3 composite materials often employ a step-by-step approach: first, Bi2O2CO3 and g-C3N4 are synthesized separately, and then they are composited again through physical or chemical means. For example, Hua Yingjie et al. first synthesized Bi2O2CO3 via a hydrothermal method, and then used an electrostatic adsorption method to physically composite g-C3N4 and Bi2O2CO3 through condensation and reflux, thereby synthesizing a Bi2O2CO3 composite g-C3N4 material. Such methods are cumbersome and lengthy, and the two semiconductor components cannot form an in-situ chemically bonded heterojunction, which limits the material's performance and large-scale application.

[0004] Based on this, the present invention proposes a method for preparing g-C3N4-Bi2O2CO3 composite nanosheets by molten salt-assisted one-pot method. This method achieves multiple chemical reactions in a single molten salt environment at a relatively low temperature, and simultaneously generates two semiconductor components and forms a heterojunction in situ. It has the advantages of low synthesis temperature, simple process and easy industrialization. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing g-C3N4-Bi2O2CO3 composite nanosheets by a one-pot molten salt method. The method is based on a synthesis strategy that enables multiple chemical reactions to be completed synergistically in a single molten salt environment and to form heterojunctions in situ. It simultaneously generates g-C3N4 and Bi2O2CO3 in one step and bonds them in situ. The preparation steps are simple, the operation is convenient, and the reaction conditions are mild, making it suitable for industrial production.

[0006] The present invention solves the above-mentioned technical problems by adopting the following technical solutions: A method for preparing g-C3N4-Bi2O2CO3 composite nanosheets using a one-pot molten salt process involves mixing sodium bismuthate, melamine, and sodium nitrate as solid raw materials, grinding them evenly to obtain a solid mixture; heating the solid mixture at 350°C to melt sodium nitrate and form an ionic molten salt medium, in which a simultaneous one-pot reaction is carried out: sodium bismuthate and melamine undergo a redox reaction to convert into bismuth oxycarbonate, while melamine simultaneously undergoes a polymerization reaction to convert into graphitic carbon nitride; the synergistically generated bismuth oxycarbonate and graphitic carbon nitride then combine in situ to form g-C3N4-Bi2O2CO3 composite nanosheets.

[0007] As one of the preferred embodiments of the present invention, the molar ratio of sodium bismuthate, melamine and sodium nitrate is 1:6:40.

[0008] As one of the preferred embodiments of the present invention, the heating is carried out in a high-temperature furnace, and the heating reaction time is 2 to 6 hours.

[0009] As one of the preferred embodiments of the present invention, the overall reaction process is as follows: .

[0010] As one of the preferred embodiments of the present invention, after the reaction is completed, the product is washed with deionized water and then dried at 120°C for 2 hours to obtain the g-C3N4-Bi2O2CO3 composite nanosheets.

[0011] As one of the preferred embodiments of the present invention, the thickness of the g-C3N4-Bi2O2CO3 composite nanosheet is 8~11nm.

[0012] As one of the preferred embodiments of the present invention, the average grain size of Bi2O2CO3 in the prepared g-C3N4-Bi2O2CO3 composite nanosheets is 86.3~97.9nm.

[0013] Reaction principle: In an ionic molten salt medium formed by sodium nitrate, melamine on the surface of sodium bismuthate undergoes a redox reaction with sodium bismuthate, converting sodium bismuthate into bismuth oxycarbonate. Simultaneously, melamine polymerizes within the molten salt system, generating graphitic carbon nitride. These two processes synergistically generate and recombine in situ, ultimately forming g-C3N4-Bi2O2CO3 composite nanosheets. In this reaction system, the molten salt exhibits ionic liquid properties, effectively dissolving melamine. Furthermore, the molten salt's low viscosity and high ion mobility enable the construction of efficient mass transfer channels, enhancing reaction efficiency and ensuring the full bonding of bismuth oxycarbonate and graphitic carbon nitride, ultimately leading to the stable preparation of g-C3N4-Bi2O2CO3 composite nanosheets.

[0014] The advantages of this invention compared to the prior art are: This invention employs a one-pot molten salt synthesis process, utilizing an ionic molten salt medium formed by melting sodium nitrate to simultaneously complete redox and polymerization reactions, achieving in-situ composite of bismuth oxycarbonate and graphitic carbon nitride in one step. This avoids the cumbersome steps of traditional stepwise preparation and secondary composite processes. Furthermore, the reaction conditions are mild, the synthesis temperature is moderate, the preparation process is simple, and the operation is efficient. At the same time, the unique physicochemical properties of the molten salt medium of this invention can optimize the reaction mass transfer process, promote the tight bonding of the two components and the formation of a stable heterostructure, effectively improve the photocatalytic performance of the material, and have low preparation costs and controllable production processes, thus possessing good industrial application value. Attached Figure Description

[0015] Figure 1 The image shows a scanning electron microscope (SEM) image of the product prepared in Example 2 of the present invention (the scale bar is 500 nm). Figure 2 The XRD patterns of the products prepared in Examples 1, 2, and 3 of this invention are shown (with reference to the XRD standard cards of g-C3N4 and Bi2O2CO3). Figure 3 The XRD patterns of the products prepared in Example 2 and the comparative example of the present invention are shown (with reference to the XRD standard cards of g-C3N4 and Bi2O2CO3). Detailed Implementation

[0016] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Furthermore, unless otherwise specified, the reagents and experimental methods used in the following embodiments, comparative examples, and experimental examples are all conventional reagents or methods in the art and will not be described again.

[0017] Example 1 This embodiment describes a method for preparing g-C3N4-Bi2O2CO3 composite nanosheets using a one-pot molten salt method. (1) Mix 0.01 mol sodium bismuthate, 0.06 mol melamine and 0.4 mol sodium nitrate solid raw materials, grind them evenly, and obtain a solid mixture.

[0018] (2) The solid mixture obtained in step (1) is added to a 50ml alumina crucible with a lid and placed in a high-temperature furnace and heated at 350℃ for 2 hours. During the heating process, sodium nitrate melts to form an ionic molten salt medium, and the following concerted reaction occurs in this molten salt medium: sodium bismuthate reacts with melamine in a redox reaction to convert it into bismuth oxycarbonate, and melamine simultaneously undergoes a polymerization reaction to convert it into graphitic carbon nitride. The synergistically generated bismuth oxycarbonate and graphitic carbon nitride recombine in situ to form g-C3N4-Bi2O2CO3. The overall reaction process is as follows: .

[0019] (3) The product obtained in step (2) is washed with deionized water and dried at 120°C for 2 hours to obtain the target product g-C3N4-Bi2O2CO3 composite nanosheets.

[0020] Example 2 This embodiment describes a method for preparing g-C3N4-Bi2O2CO3 composite nanosheets using a one-pot molten salt method. (1) Mix 0.01 mol sodium bismuthate, 0.06 mol melamine and 0.4 mol sodium nitrate solid raw materials, grind them evenly, and obtain a solid mixture.

[0021] (2) The solid mixture obtained in step (1) is added to a 50ml alumina crucible with a lid and placed in a high-temperature furnace and heated at 350℃ for 4 hours. During the heating process, sodium nitrate melts to form an ionic molten salt medium, and the following concerted reaction occurs in this molten salt medium: sodium bismuthate reacts with melamine in a redox reaction to convert it into bismuth oxycarbonate, while melamine undergoes a polymerization reaction to convert it into graphitic carbon nitride. The synergistically generated bismuth oxycarbonate and graphitic carbon nitride recombine in situ to form g-C3N4-Bi2O2CO3. The overall reaction process is as follows: .

[0022] (3) The product obtained in step (2) is washed with deionized water and dried at 120°C for 2 hours to obtain the target product g-C3N4-Bi2O2CO3 composite nanosheets.

[0023] Example 3 This embodiment describes a method for preparing g-C3N4-Bi2O2CO3 composite nanosheets using a one-pot molten salt method. (1) Mix 0.01 mol sodium bismuthate, 0.06 mol melamine and 0.4 mol sodium nitrate solid raw materials, grind them evenly, and obtain a solid mixture.

[0024] (2) The solid mixture obtained in step (1) was added to a 50 ml alumina crucible with a lid and placed in a high-temperature furnace and heated at 350 °C for 6 h. During the heating process, sodium nitrate melted to form an ionic molten salt medium, and the following concerted reaction occurred in the molten salt medium: sodium bismuthate reacted with melamine in a redox reaction to convert it into bismuth oxycarbonate, and melamine simultaneously underwent a polymerization reaction to convert it into graphitic carbon nitride. The synergistically generated bismuth oxycarbonate and graphitic carbon nitride were combined in situ to form g-C3N4-Bi2O2CO3. The overall reaction process is as follows: .

[0025] (3) The product obtained in step (2) is washed with deionized water and dried at 120°C for 2 hours to obtain the target product g-C3N4-Bi2O2CO3 composite nanosheets.

[0026] Comparative Example The preparation method of g-C3N4-Bi2O2CO3 composite nanosheets in this comparative example is basically the same as that in Example 2. The main difference is that NaNO3 is not added. The other raw material types, molar ratios, and process steps (heating temperature, time, washing, and drying conditions) are completely consistent with those in Example 2.

[0027] Experimental Example 1 The product obtained in the above embodiments (taking Example 2 as an example) was observed under a scanning electron microscope (SEM), and the results are as follows. Figure 1 As shown. From Figure 1 It can be seen that the prepared g-C3N4-Bi2O2CO3 composite material exhibits a three-dimensional flower-like hierarchical structure formed by the self-assembly of ultrathin nanosheets. The sheet thickness is uniform, about 8~11nm, and the sheets are interspersed and there is no obvious agglomeration.

[0028] The results show that the molten salt one-pot method of the present invention achieves uniform and effective composite of g-C3N4 and Bi2O2CO3. The two components grow in situ and are tightly bonded to form composite nanosheets with a thickness of about 8~11 nm, constructing a structurally stable heterojunction. At the same time, it retains the high specific surface area characteristics of the nanosheet material, which is beneficial to providing abundant active sites for photocatalytic reactions.

[0029] Experiment Example 2 X-ray diffraction (XRD) analysis was performed on the products obtained in the above examples and comparative examples, and the results are as follows: Figure 2 , Figure 3 As shown.

[0030] Figure 2 The XRD patterns of the products prepared in Examples 1, 2, and 3 of this invention are shown below. Figure 3 The XRD patterns of the products prepared in Example 2 and the comparative example of this invention are shown, with reference to the X-ray diffraction standard cards for Bi2O2CO3 (PDF#25-1464) and g-C3N4 (PDF#87-1526). Figure 2 It can be seen that the XRD patterns of the products in each embodiment show obvious characteristic diffraction peaks of Bi2O2CO3 and relatively weak characteristic diffraction peaks of g-C3N4, and no diffraction peaks of other substances, indicating that the products in each embodiment are composed only of Bi2O2CO3 and g-C3N4 crystals, and are pure g-C3N4-Bi2O2CO3 composite nanosheets. Figure 3It can be seen that, compared to Example 2, the diffraction peak intensity of the comparative sample is significantly reduced. Besides the weak Bi₂O₂CO₃ diffraction peak, there are also numerous diffraction peaks of other substances, indicating incomplete reaction, poor crystal integrity, and failure to obtain a pure target product. This suggests that without the NaNO₃ molten salt medium, the redox and polymerization reactions cannot proceed sufficiently, making it difficult to form a fully crystalline composite structure.

[0031] Furthermore, based on the XRD patterns of the products from Examples 1, 2, and 3, and using the Scherrer formula, the average grain sizes of Bi₂O₂CO₃ in the products from Examples 1, 2, and 3 were calculated to be 86.3 nm, 91.5 nm, and 97.9 nm, respectively. This indicates that the average grain size of Bi₂O₂CO₃ in the products increases slowly with increasing reaction time.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing carbon nitride-bismuth oxycarbonate composite nanosheets using a one-pot molten salt process, characterized in that, Sodium bismuthate, melamine, and sodium nitrate solid raw materials are mixed and ground evenly to obtain a solid mixture. The solid mixture is heated at 350°C to melt sodium nitrate and form an ionic molten salt medium. The reaction is carried out simultaneously in the molten salt medium using a one-pot method: sodium bismuthate and melamine undergo a redox reaction to convert into bismuth oxycarbonate, while melamine undergoes a polymerization reaction to convert into graphitic carbon nitride. The synergistically generated bismuth oxycarbonate and graphitic carbon nitride are in-situ composited to form g-C3N4-Bi2O2CO3 composite nanosheets.

2. The method according to claim 1, characterized in that, The molar ratio of sodium bismuthate, melamine, and sodium nitrate is 1:6:

40.

3. The method according to claim 1, characterized in that, The heating is carried out in a high-temperature furnace, and the heating reaction time is 2-6 hours.

4. The method according to claim 1, characterized in that, The overall reaction process is as follows: 。 5. The method according to claim 1, characterized in that, After the reaction was completed, the product was washed with deionized water and then dried at 120°C for 2 hours to obtain the g-C3N4-Bi2O2CO3 composite nanosheets.

6. The method according to claim 1, characterized in that, The thickness of the g-C3N4-Bi2O2CO3 composite nanosheets is 8~11 nm.

7. The method according to any one of claims 1 to 6, characterized in that, In the prepared g-C3N4-Bi2O2CO3 composite nanosheets, the average grain size of Bi2O2CO3 is 86.3~97.9 nm.

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