Method for preparing hydrogen peroxide using modified carbon nitride

Abstract

The application discloses a method for preparing hydrogen peroxide by using modified carbon nitride, and the method is a photocatalytic reaction of water by using the modified carbon nitride, wherein the modified carbon nitride is prepared by using cyanamide precursor as raw material, natural sea salt and iodine-containing inorganic salt as modifiers after calcination. In the application, the natural sea salt and the iodine-containing inorganic salt are used as the modifiers to modify the carbon nitride, so that multi-element doping can be realized, and the defect structure can be enriched, the modified carbon nitride has the dual advantages of multi-element doping and rich cyan group structure defects, the modified carbon nitride prepared by the method has the advantages of strong light absorption capacity, high photo-generated carrier separation efficiency, high selectivity, high photocatalytic activity and the like, and exhibits very excellent photocatalytic performance, can efficiently reduce oxygen to generate hydrogen peroxide under visible light, has the advantages of low cost, high yield and the like, can realize low-cost and large-scale preparation of hydrogen peroxide, has high use value and good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of graphitic carbon nitride photocatalyst technology, and relates to a method for preparing hydrogen peroxide, specifically a method for preparing hydrogen peroxide using modified carbon nitride. Background Technology

[0002] Hydrogen peroxide, as a clean energy source and an important oxidant, has been widely used due to its high energy density and environmental friendliness. Currently, the main methods for preparing hydrogen peroxide include the anthraquinone method, electrochemical synthesis, and noble metal catalysis. However, these methods inevitably involve drawbacks such as cumbersome synthesis processes, high energy consumption, and environmental pollution. Compared with traditional methods, the method of preparing hydrogen peroxide using semiconductor photocatalysts uses water and oxygen as raw materials, requiring only solar energy for synthesis without other energy input. It offers advantages such as safety, environmental friendliness, and low cost, attracting widespread attention.

[0003] Graphitic carbon nitride (CNO) possesses advantages such as abundant raw material sources, simple preparation methods, excellent photoelectric properties, stable structural properties, and environmental friendliness, making it an ideal photocatalyst for hydrogen peroxide production. However, existing CNO is mainly synthesized by direct thermally induced polymerization of cyanamide precursors. This type of CNO has limited visible light absorption and low photogenerated carrier separation efficiency, resulting in low photocatalytic activity. Furthermore, its low selectivity for molecular oxygen reduction hinders the efficient generation of hydrogen peroxide. Consequently, the efficiency of CNO photocatalytic hydrogen peroxide production is too low to meet practical application requirements. To address the aforementioned issues, researchers have proposed a strategy for doping and modifying graphitic carbon nitride, primarily through single-element doping, such as single-metal doping (K, Na, Fe, Mg, Pt, Au, etc.) or single-non-metal doping (O, S, B, P, Cl, etc.). However, single-element doping has some limitations, such as: (a1) single-metal doping has limited ability to adjust the electronic structure of carbon nitride and fails to significantly improve light absorption; (a2) metal elements incorporated into the carbon nitride framework through coordination bonds or electrostatic interactions have poor stability and are easily dissolved; (a3) ​​single-non-metal doping cannot effectively reduce the charge transport resistance of carbon nitride, has limited effect on increasing active sites, and still exhibits poor selectivity for molecular oxygen reduction, which is not conducive to improving the effect. In addition, some researchers have proposed a strategy of multi-element doping modification of graphitic carbon nitride, but the following drawbacks still exist: (b1) Multi-element doping tends to form more photogenerated carrier recombination centers, which is not conducive to improving the photocatalytic performance of carbon nitride, and thus not conducive to improving the generation efficiency of hydrogen peroxide by modified carbon nitride. For example, although the light absorption performance of multi-element co-doped carbon nitride synthesized by calcination using only sea salt and dicyandiamide as raw materials is enhanced, the photogenerated carrier separation efficiency is very low. Therefore, when it is used to synthesize hydrogen peroxide, the highest generation rate is only 0.294 mmol·g. -1 ·h -1 (b2) The modification process is complex. For example, in the existing methods for preparing potassium and iodine co-doped carbon nitride, potassium iodide needs to be prepared into photo-oxidized potassium iodide first, and then the photo-oxidized potassium iodide is used as a raw material to be mixed with melamine and calcined. It can be seen that the preparation process of this method is complex and not conducive to the large-scale preparation of graphitic carbon nitride, which in turn is not conducive to the practical industrial application of graphitic carbon nitride in the preparation of hydrogen peroxide. (b3) The raw material cost is high. For example, potassium iodide is used in large quantities and is expensive, which is not conducive to reducing the preparation cost of modified carbon nitride, resulting in the production cost of hydrogen peroxide remaining high. Therefore, obtaining a modified carbon nitride with a simple preparation process, low cost, strong light absorption capacity, high photogenerated carrier separation efficiency, and high selectivity for molecular oxygen reduction is of great significance for the efficient synthesis of hydrogen peroxide and the promotion of the widespread application of hydrogen peroxide. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing hydrogen peroxide using modified carbon nitride with low cost and high yield.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing hydrogen peroxide using modified carbon nitride, wherein the method utilizes modified carbon nitride to perform a photocatalytic reaction on water; the modified carbon nitride is prepared by calcination using cyanamide precursors as raw materials and natural sea salt and iodine-containing inorganic salts as modifiers.

[0007] In a further improvement to the above-described method for preparing hydrogen peroxide using modified carbon nitride, the mass ratio of natural sea salt to cyanamide precursor is 0.2–0.6:1; the mass ratio of iodine-containing inorganic salt to cyanamide precursor is 0.2–0.6:1; the cyanamide precursor is at least one of cyanamide, dicyandiamide, and melamine; and the iodine-containing inorganic salt is at least one of potassium iodide and sodium iodide.

[0008] The above-described method for preparing hydrogen peroxide using modified carbon nitride is further improved by comprising the following steps:

[0009] S1. A precursor mixture is prepared by mixing cyanamide precursors, natural sea salt, and iodine-containing inorganic salts.

[0010] S2. The precursor mixture is calcined to obtain modified carbon nitride.

[0011] The above-mentioned method for preparing hydrogen peroxide using modified carbon nitride is further improved by step S1, which is: preparing a solution of natural sea salt, adding a cyanamide precursor and an iodine-containing inorganic salt, and drying to obtain a precursor mixture; the drying temperature is 60℃~90℃.

[0012] The above-mentioned method for preparing hydrogen peroxide using modified carbon nitride is further improved in step S1, in which the natural sea salt is further subjected to the following treatment before use: the natural sea salt is heated to 400℃~600℃ at a heating rate of 2℃ / min~10℃ / min and kept at that temperature for 2h~6h to complete the pretreatment of the natural sea salt.

[0013] The above-described method for preparing hydrogen peroxide using modified carbon nitride is further improved in step S2, wherein the calcination heating rate is 2℃ / min to 10℃ / min; the calcination temperature is 400℃ to 600℃; the calcination time is 2h to 6h; and after calcination, the method further includes the following steps: grinding the calcined product, washing the ground product with water and ethanol in sequence, and drying it to obtain modified carbon nitride.

[0014] The above-mentioned method for preparing hydrogen peroxide using modified carbon nitride is further improved by using modified carbon nitride to perform a photocatalytic reaction on water, including the following steps: mixing modified carbon nitride with water to perform a photocatalytic reaction to obtain hydrogen peroxide; wherein the amount of modified carbon nitride added is 0.1g to 1g per liter of water.

[0015] In a further improvement to the above-described method for preparing hydrogen peroxide using modified carbon nitride, a sacrificial agent is added to the water; the volume fraction of the sacrificial agent in the water is 5% to 20%; and the sacrificial agent is at least one of isopropanol, methanol, and ethanol.

[0016] In a further improvement to the above-described method for preparing hydrogen peroxide using modified carbon nitride, the photocatalytic reaction is carried out under the illumination of a light source; the wavelength of the light source is greater than 420 nm; and the light source is a xenon lamp.

[0017] In a further improvement to the above-described method for preparing hydrogen peroxide using modified carbon nitride, the photocatalytic reaction is carried out at a temperature of 20°C to 30°C, and the reaction time is 0.5 h to 4 h.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] (1) To address the shortcomings of existing modified carbon nitrides, such as poor light absorption, low photogenerated carrier separation efficiency, low selectivity for molecular oxygen reduction, complex preparation process, and high preparation cost, resulting in high production cost and low yield of hydrogen peroxide, this invention creatively provides a method for preparing hydrogen peroxide using modified carbon nitride. The modified carbon nitride is used to perform a photocatalytic reaction on water, wherein the modified carbon nitride is prepared from cyanamide precursors, natural sea salt, and iodine-containing inorganic salts (containing I...). - This invention prepares carbon nitride by calcination using iodine-containing inorganic salts as modifiers. Compared with conventional modified carbon nitride, this invention uses natural sea salt and iodine-containing inorganic salts as modifiers, and performs multi-element doping on carbon nitride during calcination. On the one hand, the natural sea salt used contains various metal and non-metal elements, such as Na, Ca, Mg, K, and Cl, thus enabling multi-element modification of carbon nitride and combining the advantages of non-metallic and metallic doping. This allows for the introduction of more active sites and energy levels, thereby enhancing the adsorption capacity, light absorption capacity, and photocatalytic activity of the photocatalyst, and ultimately improving the conversion efficiency of the target reactants. Simultaneously, the sodium and potassium cations present in natural sea salt have a structural tailoring effect on carbon nitride, forming a large number of cyano defect structures. These defect structures will facilitate the adsorption of molecular oxygen, giving it higher oxygen reduction selectivity and promoting the generation of H2O2. On the other hand, by introducing iodine-containing inorganic salts (such as potassium iodide) into the preparation of modified carbon nitride, I-type ions are formed between the carbon nitride layers. - / I3 - Circulation center, I - / I3 - The presence of a cycle can promote the migration of photogenerated carriers, thereby effectively suppressing their recombination. Therefore, in this invention, by using natural sea salt and iodine-containing inorganic salts as modifiers to modify carbon nitride, the combined effect of these two agents not only achieves multi-element doping but also enriches the defect structure. This gives the modified carbon nitride the dual advantages of multi-element doping and abundant cyano structural defects. Multi-element doping helps to regulate the electronic band structure of carbon nitride, improves light absorption performance, reduces charge transfer resistance, and promotes the separation of photogenerated carriers. Meanwhile, the abundant cyano structural defects facilitate the adsorption of molecular oxygen, improving oxygen reduction selectivity. Thus, the modified carbon nitride of this invention exhibits advantages such as strong light absorption, high photogenerated carrier separation efficiency, high selectivity for molecular oxygen reduction, and high photocatalytic activity, demonstrating excellent photocatalytic performance. Under visible light, it can efficiently reduce oxygen to hydrogen peroxide, with a hydrogen peroxide generation rate as high as 38 mmol·g⁻¹. -1 ·h -1 This far exceeds the 0.3–15 mmol·g of similar catalysts (carbon nitride defective catalysts, carbon nitride-based heteroatom-doped catalysts, carbon nitride crystalline catalysts, etc.). -1 ·h -1 The yield is 200-300 times that of unmodified carbon nitride. Furthermore, in this invention, modified carbon nitride is prepared via a one-pot co-heating method using cyanamide precursors as raw materials and natural sea salt and iodine-containing inorganic salts as modifiers. This method is simple, efficient, and scalable, suitable for industrial application. In addition, the natural sea salt used is a natural resource with high availability, sustainability, and environmental friendliness. Compared to synthetic chemicals, it is cheaper, and using natural sea salt for modification can effectively reduce the cost of catalyst preparation. Therefore, the method for preparing hydrogen peroxide using modified carbon nitride in this invention has the advantages of low cost and high hydrogen peroxide yield, enabling low-cost, large-scale preparation of hydrogen peroxide and providing a promising solution for the practical production of hydrogen peroxide.

[0020] (2) In this invention, by optimizing the mass ratio of natural sea salt to cyanamide precursor to 0.2–0.6:1 and the mass ratio of iodine-containing inorganic salt to cyanamide precursor to 0.2–0.6:1, more active sites and I-containing inorganic salts can be formed in the modified carbon nitride during calcination. - / I3 - The circulating center can significantly improve the utilization rate of sunlight, generate more electrons and holes, and promote the migration and separation of photogenerated carriers, exhibiting higher photogenerated carrier separation efficiency and better photocatalytic performance. When used to prepare hydrogen peroxide, it can significantly increase the yield of hydrogen peroxide. Attached Figure Description

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0022] Figure 1 Scanning electron microscope (SEM) images of g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI prepared in Example 1 of this invention.

[0023] Figure 2 X-ray diffraction patterns of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0024] Figure 3 Fourier transform infrared spectra of g-C3N4, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0025] Figure 4 The X-ray photoelectron spectra of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0026] Figure 5 The light absorption spectra of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0027] Figure 6 The image shows the Kubelka-Munk transform function curves of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0028] Figure 7 The Mott-Schottky curves are shown for g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0029] Figure 8 The above are the band structure diagrams of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0030] Figure 9 The photocurrent curves of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0031] Figure 10 The photoluminescence spectra of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0032] Figure 11 Electrochemical impedance spectroscopy diagrams of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention.

[0033] Figure 12 The figures show the performance and yield of hydrogen peroxide produced by photocatalysis using g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI in Example 1 of this invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0035] The materials and instruments used in the following examples are all commercially available.

[0036] Example

[0037] A method for preparing hydrogen peroxide using modified carbon nitride involves photocatalytic reaction of water with modified carbon nitride, wherein the modified carbon nitride is prepared by calcination using cyanamide precursors as raw materials and natural sea salt and iodine-containing inorganic salts as modifiers.

[0038] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the mass ratio of natural sea salt to cyanamide precursor is 0.2 to 0.6:1, more preferably, the mass ratio of natural sea salt to cyanamide precursor is 0.3 to 0.4:1, and even more preferably, the mass ratio of natural sea salt to cyanamide precursor is 0.33:1, wherein the cyanamide precursor is at least one of cyanamide, dicyandiamide, and melamine.

[0039] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the mass ratio of iodine-containing inorganic salt to cyanamide precursor is 0.2 to 0.6:1. More preferably, the mass ratio of iodine-containing inorganic salt to cyanamide precursor is 0.4 to 0.6:1. Even more preferably, the mass ratio of iodine-containing inorganic salt to cyanamide precursor is 0.5:1. The iodine-containing inorganic salt is at least one of potassium iodide and sodium iodide.

[0040] The method for preparing hydrogen peroxide using modified carbon nitride in this invention includes the following steps:

[0041] S1. A precursor mixture is prepared by mixing cyanamide precursors, natural sea salt, and iodine-containing inorganic salts.

[0042] S2. The precursor mixture is calcined to obtain modified carbon nitride.

[0043] In the method for preparing hydrogen peroxide using modified carbon nitride of this invention, step S1 is as follows: Natural sea salt is prepared into a solution, a cyanamide precursor and an iodine-containing inorganic salt are added, and the solution is dried at a temperature of 60℃~90℃ until the water evaporates completely, yielding a precursor mixture, wherein the cyanamide precursor is dicyandiamide. Preparing the natural sea salt solution includes the following steps: dissolving the natural sea salt in water, filtering out insoluble matter using a 0.22-micron filter head, and obtaining a natural sea salt solution.

[0044] In the preparation process of the precursor mixture of the present invention, the drying method is water bath evaporation, and the drying temperature is further preferably 65-80°C, and even more preferably 70°C.

[0045] In this invention, the method for preparing hydrogen peroxide using modified carbon nitride utilizes commercially available natural sea salt. This commercially available natural sea salt can be used directly as a modifier, or it can be pretreated before being mixed with cyanamide precursors and iodine-containing inorganic salts to form a precursor mixture. The pretreatment of the natural sea salt before use includes the following steps: heating the natural sea salt to 400℃-600℃ at a heating rate of 2℃ / min-10℃ / min and holding at that temperature for 2h-6h to complete the pretreatment. The benefits of pretreating the natural sea salt in this invention include: allowing excess calcium and magnesium ions in the natural sea salt to form metal oxides during calcination, which can then be removed during the subsequent dissolution and filtration process. This prevents excessive metal oxides from adhering to the carbon nitride surface during the preparation of modified carbon nitride, which could hinder light absorption and potentially become recombination centers for photogenerated carriers, adversely affecting the photocatalytic process.

[0046] In the pretreatment process of natural sea salt in this invention, the pretreatment heating rate of natural sea salt is more preferably 4 to 7 °C / min, and even more preferably 5 °C / min.

[0047] In the pretreatment process of natural sea salt in this invention, the pretreatment calcination temperature of natural sea salt is further preferably 450-550°C, and even more preferably 500°C.

[0048] In the pretreatment process of natural sea salt in this invention, the pretreatment calcination time of natural sea salt is preferably 3 to 5 hours, and even more preferably 4 hours.

[0049] In the preparation method of modified carbon nitride of the present invention, in step S2, the heating rate of calcination is 2℃ / min to 10℃ / min, more preferably, the heating rate is 4℃ / min to 6℃ / min, and even more preferably, the heating rate is 5℃ / min.

[0050] In the preparation method of modified carbon nitride of the present invention, in step S2, the calcination temperature is 400℃~600℃, more preferably 450~600℃, and even more preferably 500~580℃, especially 550℃.

[0051] In the method for preparing modified carbon nitride of the present invention, in step S2, the calcination time is 2h to 6h, more preferably 3h to 3h, and even more preferably 4h.

[0052] In the preparation method of modified carbon nitride of the present invention, step S2, after calcination, further includes the following steps: grinding the calcined product, washing the ground product sequentially with water and ethanol, and drying to obtain modified carbon nitride. In this invention, grinding the calcined product can prepare uniform and fine powders, which are easier to disperse during catalysis and have a larger specific surface area, exposing more catalytic sites, thus facilitating the catalytic reaction. Simultaneously, washing the ground product with water and ethanol can remove excess molten salt that has not been incorporated into the carbon nitride.

[0053] In the preparation method of modified carbon nitride of the present invention, the modified carbon nitride obtained has a structure co-doped with multiple ions such as Na, K, I, Cl, Mg, and Ca, and has abundant cyano structural defects.

[0054] The present invention provides a method for preparing hydrogen peroxide using modified carbon nitride, which involves photocatalytic reaction of water with modified carbon nitride, comprising the following steps: mixing modified carbon nitride with water to carry out a photocatalytic reaction to obtain hydrogen peroxide.

[0055] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the amount of modified carbon nitride added is 0.1g to 1g per liter of water, more preferably 0.3g to 0.7g per liter of water, and even more preferably 0.4g to 0.6g per liter of water.

[0056] In the method for preparing hydrogen peroxide using modified carbon nitride of this invention, a sacrificial agent is also added to the water.

[0057] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the volume fraction of the sacrificial agent in water is 5% to 20%, and more preferably, the volume fraction of the sacrificial agent in water is 8% to 12%.

[0058] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the sacrificial agent is at least one of isopropanol, methanol and ethanol, and more preferably, the sacrificial agent is one of isopropanol, methanol and ethanol.

[0059] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the photocatalytic reaction is carried out under the irradiation of a light source; the wavelength of the light source is greater than 420 nm.

[0060] In the method for preparing hydrogen peroxide using modified carbon nitride in this invention, a xenon lamp is used as the light source, and the light intensity of the xenon lamp is preferably 60–450 mW / cm². 2 More preferably, it is 150–350 mW / cm 2 .

[0061] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the photocatalytic reaction is carried out at a temperature of 20°C to 30°C, and the photocatalytic reaction temperature is further preferably 22°C to 28°C, and even more preferably 24°C to 26°C.

[0062] In the method for preparing hydrogen peroxide using modified carbon nitride of the present invention, the photocatalytic reaction time is 0.5h to 4h, and more preferably 1 to 3h, and even more preferably 1.5 to 2h.

[0063] To further illustrate the present invention, the following embodiments provide a detailed description of a modified carbon nitride and its preparation method, as well as a method for photocatalytic preparation of hydrogen peroxide. However, it should be understood that these embodiments are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating procedures. They are only for further illustrating the features and advantages of the present invention, and are not intended to limit the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0064] Example 1

[0065] A method for preparing hydrogen peroxide using modified carbon nitride, specifically involving the photocatalytic reaction of modified carbon nitride with water to prepare hydrogen peroxide, includes the following steps:

[0066] Pour 45 mL of ultrapure water into a 150 mL beaker, add 50 mL of isopropanol as a sacrificial agent, and then add 10 mg of modified carbon nitride (g-C3N4-HI). Stir magnetically and react in the dark for 20 min. Then turn on the light source. The light source system uses a 300 W xenon lamp equipped with an ultraviolet cutoff filter (the cutoff filter transmits light with a wavelength greater than 420 nm) to irradiate the ultrapure water. Use modified carbon nitride as a catalyst to carry out a photocatalytic reaction on the water, converting the water into hydrogen peroxide.

[0067] Control group: Carbon nitride (g-C3N4-HI) was replaced by carbon nitride modified with natural sea salt (g-C3N4-H) and carbon nitride modified with potassium iodide (g-C3N4-I), while other conditions were the same.

[0068] In this embodiment, the modified carbon nitride (g-C3N4-HI) used is prepared by calcination using dicyandiamide as a raw material, natural sea salt and potassium iodide as modifiers, including the following steps:

[0069] S1. Weigh 5g of natural sea salt and place it in a 50ml covered crucible. Place the crucible in a muffle furnace and heat it to 500℃ at a rate of 5℃ / min. Maintain the temperature for 4 hours. After it cools naturally to room temperature, grind it to obtain the pretreated natural sea salt.

[0070] S2. Weigh 1g of pretreated natural sea salt, add ultrapure water, and sonicate for 30 minutes. Remove the filter head of the solution using a syringe to obtain a natural sea salt solution. Add the natural sea salt solution to a 100mL beaker containing a solid mixture of 3g dicyandiamide and 1.5g potassium iodide. Then, evaporate the mixture to dryness in a water bath at 70℃, and after careful grinding, obtain a white powder, which is the precursor mixture.

[0071] S3: Place the white powder in a 50mL covered crucible, place it in a muffle furnace, heat it to 550℃ at a rate of 5℃ / min, maintain it for 4h, and after it cools naturally to room temperature, grind it, wash it several times with ultrapure water and ethanol, dry it in an oven at 60℃, and grind it again to obtain a light yellow modified carbon nitride powder, denoted as g-C3N4-HI.

[0072] In this embodiment, the preparation method of carbon nitride (g-C3N4) is basically the same as that of modified carbon nitride (g-C3N4-HI), except that in the preparation method of carbon nitride (g-C3N4), natural sea salt and potassium iodide are not added, and dicyandiamide is directly calcined.

[0073] In this embodiment, the preparation method of natural sea salt modified carbon nitride (g-C3N4-H) is basically the same as that of modified carbon nitride (g-C3N4-HI), except that potassium iodide is not added in the preparation method of natural sea salt modified carbon nitride (g-C3N4-H), and carbon nitride is synthesized by heating natural sea salt with dicyandiamide.

[0074] In this embodiment, the preparation method of potassium iodide modified carbon nitride (g-C3N4-I) is basically the same as that of modified carbon nitride (g-C3N4-HI), except that: in the preparation method of potassium iodide modified carbon nitride (g-C3N4-I), natural sea salt is not added, and carbon nitride is synthesized by heating potassium iodide and dicyandiamide together.

[0075] The morphology of g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI prepared in Example 1 of this invention was characterized by scanning electron microscopy. The results are shown in [reference needed]. Figure 2 .

[0076] Figure 1 Scanning electron microscope (SEM) images of g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI prepared in Example 1 of this invention. Figure 1 In the above, (a) is g-C3N4; (b) is g-C3N4-H; (c) is g-C3N4-I; and (d) is g-C3N4-HI.

[0077] Depend on Figure 1 It can be seen that all catalysts exhibit a layered, stacked, blocky morphology. The difference lies in the structure: g-C3N4-H has a more fragmented layered structure with more pores, while g-C3N4-HI has a more compact stacked structure, forming a smoother block. Furthermore, SEM-EDS-Mapping analysis of g-C3N4-HI revealed the presence of elements such as Na, K, I, Cl, Mg, and Ca. Figure 1 e) indicates the presence of these ion dopants in the modified carbon nitride.

[0078] The crystal structures of g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI prepared in Example 1 of this invention were characterized by X-ray diffraction. The results are shown in [reference needed]. Figure 2 .

[0079] Figure 2 X-ray diffraction patterns of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0080] Depend on Figure 2 It can be seen that g-C3N4 exhibits two diffraction peaks at 13.0° and 27.4°. The stronger peak at 27.3° is called the (002) diffraction plane, which is related to the periodic stacking pattern of the interface in the conjugated aromatic hydrocarbon system. The weaker peak at 13.0° corresponds to the (100) diffraction plane, which is attributed to the in-plane ordered repetition of the tris-s-triazine unit, an indicator of g-C3N4 formation. In g-C3N4-H, g-C3N4-I, and g-C3N4-HI, the (100) diffraction peak almost disappears, and the (002) diffraction peak is also significantly weakened, indicating that the ordered structure of the salt ion doping pair is interfered with in the salt ion co-thermal assisted synthesis.

[0081] The chemical structures of g-C3N4, g-C3N4-I, and g-C3N4-HI prepared in Example 1 of this invention were characterized using Fourier transform infrared spectroscopy. The results are shown in [reference needed]. Figure 3 .

[0082] Figure 3Fourier transform infrared spectra of g-C3N4, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0083] Depend on Figure 3 It can be seen that the Fourier transform infrared spectra of g-C3N4-I and g-C3N4-HI are roughly the same as those of g-C3N4, indicating that the salt ion-assisted synthesized g-C3N4-I and g-C3N4-HI have similar chemical structures to g-C3N4, with both exhibiting characteristic stretching vibration absorption peaks of g-C3N4. However, some new absorption peaks also appeared in g-C3N4-I and g-C3N4-HI, indicating that the salt ion co-heating synthesis process has some influence on the basic framework of g-C3N4. Specifically, the 3100–3500 cm⁻¹ peaks... -1 The broad absorption band between them corresponds to the stretching vibrations of the terminal amino group (-NH) and the hydroxyl group (-OH) in the adsorbed water, located at 808 cm⁻¹. -1 The absorption peak at 1100 to 1700 cm⁻¹ is attributed to the out-of-plane bending vibration of the triazine ring. -1 The series of characteristic peaks belong to the tensile vibrations of the CN heterocycle in the heptaazine ring. In g-C3N4-I and g-C3N4-HI, the peak at 993 cm⁻¹... -1 There is a distinct new absorption peak nearby, which may be attributed to the formation of a covalent bond between the salt ion and the carbon atom in the triazine ring structure during the cothermal synthesis process, at 2174 cm⁻¹. -1 A new peak was also observed, corresponding to the stretching vibration of the asymmetric cyano group (-C≡N). These indicate that salt ions such as K and Na form chemical bonds with the nitrogen and carbon atoms in g-C3N4, introducing the -C≡N group. These results confirm the successful introduction of ion doping into the modified carbon nitride g-C3N4-HI, resulting in abundant cyano defects.

[0084] The g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention were characterized by X-ray photoelectron spectroscopy, and the results are shown in [reference needed]. Figure 4 .

[0085] Figure 4 The X-ray photoelectron spectra of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention are shown. Figure 4 In the above, (a) is g-C3N4; (b) is g-C3N4-HI.

[0086] Depend on Figure 4 It can be seen that for g-C3N4 ( Figure 4a) Its C1s spectrum has three peaks at 288.13, 286.29, and 284.80 eV, which belong to the heterocyclic carbon (N=CN) and peripheral C-NHx species of the heptaazine unit, as well as graphitic carbon (CC and C=C). Furthermore, the peak intensities of C-NHx species are significantly increased in g-C3N4-HI, mainly because g-C3N4-HI has abundant cyano (-C≡N) structures, and the binding energy of -C≡N is similar to that of C-NHx species. N1s( Figure 4 (b) The spectrum shows three peaks at 401.07, 399.56, and 398.61 eV, which originate from the N atoms of the N-Hx, N-(C)3, and CN=C groups, respectively. Compared with g-C3N4, g-C3N4-HI exhibits significant chemical shifts in the C1s and N1s main peaks, which may be due to the strong interaction between the C or N atoms of the heptaazine ring and the co-heated salt atoms resulting from the co-thermal synthesis with sea salt and potassium iodide.

[0087] The optical absorption properties of g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI prepared in Example 1 of this invention were characterized using X-ray absorption spectroscopy. The results are shown in [reference needed]. Figure 5 .

[0088] Figure 5 The light absorption spectra of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0089] Depend on Figure 5 As can be seen, compared with g-C3N4, the light absorption edges of the other catalysts all show a significant redshift, indicating enhanced visible light harvesting ability. g-C3N4-HI exhibits strong absorption in the 500-800 nm wavelength range. Their Fourier transform infrared spectra reveal the presence of cyano groups in the doped samples, indicating the introduction of defects. These defects can introduce new energy levels into the semiconductor band structure, thereby enhancing light absorption.

[0090] Figure 6 The image shows the Kubelka-Munk transform function curves of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0091] Depend on Figure 6 It can be seen that the band gap energy (E) of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI is... g The values ​​are 2.78, 2.70, 2.69, and 2.66 eV, respectively.

[0092] Figure 7The Mott-Schottky curves are shown for g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0093] Depend on Figure 7 It can be seen that g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI are all n-type semiconductors, and their flat-band potentials (E0) for Ag / AgCl are... fb The values ​​are -1.21, -1.30, -0.92 and -1.12V respectively, corresponding to reversible hydrogen electrode (RHE) potentials of -1.01, -1.10, -0.72 and -0.92V respectively.

[0094] Figure 8 The above are the band structure diagrams of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI prepared in Example 1 of this invention.

[0095] Depend on Figure 8 It can be seen that for the conduction band potential (E) of an n-type semiconductor CB Position ratio E fb The voltage is 0.1V higher, therefore the E of g-C3N4, g-C3N4-H, g-C3N4-I and g-C3N4-HI is higher. CB They are -1.11, -1.20, -0.82, and -1.02 V, respectively. Based on the valence band potential (E... VB )Formula E VB =E CB +E g Their E VB The values ​​are 1.67, 1.50, 1.87 and 1.64V respectively.

[0096] Figure 9 The photocurrent curves of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0097] Depend on Figure 9 It can be seen that the photocurrent density of g-C3N4-HI is much higher than that of g-C3N4, confirming that g-C3N4-HI has a higher photogenerated carrier separation efficiency.

[0098] Figure 10 The photoluminescence spectra of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention are shown.

[0099] Depend on Figure 10 It can be seen that the photoluminescence peak intensity of g-C3N4-HI is lower than that of g-C3N4, indicating a higher separation efficiency of photogenerated electrons and holes.

[0100] Figure 11Electrochemical impedance spectroscopy diagrams of g-C3N4 and g-C3N4-HI prepared in Example 1 of this invention.

[0101] Depend on Figure 11 It can be seen that the semi-circular radius of g-C3N4-HI is smaller than that of g-C3N4, indicating that g-C3N4-HI has lower internal resistance, which is beneficial to electron conduction.

[0102] During the photocatalytic reaction, samples were taken at reaction times of 10 min, 20 min, 30 min, and 40 min. The catalyst was removed by filtration through a 0.22 μm nylon filter. 0.5 mL of 0.5 M sulfuric acid solution and 0.5 mL of 0.05 M potassium titanium oxalate solution were added to 1 mL of the filtrate. After 30 min of sufficient color development, the UV absorption intensity at 400 nm was measured using a UV-Vis spectrophotometer to determine the hydrogen peroxide concentration. The effect of different types of modified carbon nitride on the hydrogen peroxide yield was calculated, and the results are as follows: Figure 12 As shown.

[0103] Figure 12 The figures show the performance and yield of hydrogen peroxide produced by photocatalysis using g-C3N4, g-C3N4-H, g-C3N4-I, and g-C3N4-HI in Example 1 of this invention.

[0104] like Figure 12 As shown, the hydrogen peroxide production performance of g-C3N4-H, g-C3N4-I, and g-C3N4-HI was significantly higher than that of g-C3N4. g-C3N4-HI exhibited the best hydrogen peroxide production performance, with a hydrogen peroxide concentration reaching 4.835 mM within only 40 min, corresponding to a yield as high as 36.260 mmol·g⁻¹. -1 ·h -1 It is g-C3N4 (0.148 mmol·g -1 ·h -1 The H2O2 production rate of g-C3N4 modified with sea salt and potassium iodide alone was 245 times higher than that of g-C3N4-HI, indicating that simple modification with sea salt and potassium iodide can significantly enhance the photocatalytic hydrogen peroxide production performance of g-C3N4. However, the H2O2 production rates of g-C3N4-H and g-C3N4-I modified with only sea salt and only potassium iodide were significantly lower than those of g-C3N4-HI, suggesting that the modified g-C3N4 exhibits the best performance when both sea salt and potassium iodide are present, and that both sea salt and potassium iodide play important roles in the modification of carbon nitride.

[0105] As can be seen from the above, the modified carbon nitride prepared by co-modification with natural sea salt and potassium iodide in this invention has enhanced light absorption capacity, enabling better utilization of sunlight. It also exhibits higher photogenerated carrier separation efficiency and stronger photogenerated electron conduction capacity, thus significantly enhancing photocatalytic performance. More importantly, the abundant cyano structural defects promote the adsorption of molecular oxygen, enhancing the selectivity for oxygen reduction and thereby promoting the generation of hydrogen peroxide. Therefore, in the method for preparing hydrogen peroxide using modified carbon nitride in this invention, the modified carbon nitride, with its strong light absorption capacity, high photogenerated carrier separation efficiency, high selectivity for molecular oxygen reduction, and high photocatalytic activity, can efficiently reduce oxygen and generate hydrogen peroxide under visible light, with a hydrogen peroxide generation rate as high as 38 mmol·g⁻¹. -1 ·h -1 This far exceeds the 0.3–15 mmol·g of similar catalysts (carbon nitride defective catalysts, carbon nitride-based heteroatom-doped catalysts, carbon nitride crystalline catalysts, etc.). -1 ·h -1 It is 200 to 300 times more potent than unmodified carbon nitride, and has the advantages of low cost and high hydrogen peroxide yield. It can realize the low-cost and large-scale preparation of hydrogen peroxide, and is suitable for industrial promotion and application. It has good application prospects and can provide a potential solution for the actual production of hydrogen peroxide.

[0106] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing hydrogen peroxide using modified carbon nitride, characterized in that, The method utilizes modified carbon nitride to perform a photocatalytic reaction on water; the modified carbon nitride is prepared by calcining cyanamide precursors, natural sea salt, and iodine-containing inorganic salts as modifiers; the natural sea salt is further subjected to the following treatment before use: the natural sea salt is heated to 400℃~600℃ at a heating rate of 2℃ / min~10℃ / min and held at that temperature for 2 h~6 h to complete the pretreatment of the natural sea salt.

2. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 1, characterized in that, The mass ratio of the natural sea salt to the cyanamide precursor is 0.2–0.6:1; the mass ratio of the iodine-containing inorganic salt to the cyanamide precursor is 0.2–0.6:1; the cyanamide precursor is at least one of cyanamide, dicyandiamide, and melamine; and the iodine-containing inorganic salt is at least one of potassium iodide and sodium iodide.

3. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 2, characterized in that, The method for preparing the modified carbon nitride includes the following steps: S1. A precursor mixture is prepared by mixing cyanamide precursors, natural sea salt, and iodine-containing inorganic salts. S2. The precursor mixture is calcined to obtain modified carbon nitride.

4. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 3, characterized in that, Step S1 is as follows: Natural sea salt is made into a solution, cyanamide precursor and iodine-containing inorganic salt are added, and dried to obtain a precursor mixture; the drying temperature is 60℃~90℃.

5. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 4, characterized in that, In step S2, the heating rate of calcination is 2℃ / min to 10℃ / min; the calcination temperature is 400℃ to 600℃; the calcination time is 2 h to 6 h; after the calcination is completed, the following steps are also included: grinding the calcined product, washing the ground product with water and ethanol in sequence, and drying it to obtain modified carbon nitride.

6. The method for preparing hydrogen peroxide using modified carbon nitride according to any one of claims 1 to 5, characterized in that, The photocatalytic reaction of water using modified carbon nitride includes the following steps: mixing modified carbon nitride with water to carry out a photocatalytic reaction to obtain hydrogen peroxide; the amount of modified carbon nitride added is 0.1g to 1g per liter of water.

7. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 6, characterized in that, The water also contains a sacrificial agent; the volume fraction of the sacrificial agent in the water is 5% to 20%; the sacrificial agent is at least one of isopropanol, methanol and ethanol.

8. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 7, characterized in that, The photocatalytic reaction is carried out under the illumination of a light source; the wavelength of the light source is greater than 420 nm; the light source is a xenon lamp.

9. The method for preparing hydrogen peroxide using modified carbon nitride according to claim 8, characterized in that, The photocatalytic reaction is carried out at a temperature of 20℃ to 30℃; the photocatalytic reaction time is 0.5h to 4h.

Images