Preparation method of carbon nitride homojunction photocatalyst

Abstract

The application discloses a preparation method of carbon nitride homojunction photocatalyst and belongs to the technical field of photocatalysis. m 尿素1 Urea with a mass of 0.5g is calcined in a muffle furnace at 400-500 DEG C for 1h to obtain a precursor; then, the precursor, urea, NaCl and KCl are uniformly mixed in a mass ratio of 5:7.5:3-5:12.5:3, and are placed in the muffle furnace again and calcined at 550 DEG C for 3h; the product is fully washed with water, centrifuged and dried to obtain the carbon nitride homojunction photocatalyst. m 尿素1 : m 尿素2 : m （NaCl+KCl） = 5:7.5:3-5:12.5:3, m NaCl : m KCl = 5:2, and the product is fully washed with water, centrifuged and dried to obtain the carbon nitride homojunction photocatalyst. −1 −1 −1 −1 The hydrogen production rate of the prepared photocatalyst in deionized water can reach 8193 µmol·g −1 ·h −1 , and the hydrogen production rates in simulated seawater and real seawater can reach 5694 and 6318 µmol·g −1 ·h −1 , respectively.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a method for preparing a carbon nitride homojunction photocatalyst. Background Technology

[0002] According to the source of hydrogen, hydrogen is divided into gray hydrogen, blue hydrogen and green hydrogen. Green hydrogen refers to hydrogen produced using renewable energy. Undoubtedly, the ability to develop efficient green hydrogen production technology is the key to determining whether green hydrogen can become a substitute for fossil energy. In 1972, researchers Fujishima and Honda of the University of Tokyo discovered that TiO2 single crystal electrodes can decompose water and release hydrogen under ultraviolet light irradiation, thus opening the prelude to the research of photocatalytic water splitting hydrogen production technology. The photocatalytic water splitting hydrogen production reaction includes the following four processes: (1) light absorption: the photocatalyst absorbs photon energy to generate photogenerated carriers; (2) photogenerated carrier separation: photogenerated electrons jump from the valence band to the conduction band, leaving photogenerated holes in the valence band; (3) photogenerated carrier migration: photogenerated electrons and holes migrate to the reactive sites on the surface of the photocatalyst; (4) surface reaction: photogenerated electrons undergo reduction reaction, and photogenerated holes undergo oxidation reaction. From the reaction process of photocatalytic water splitting hydrogen production, it can be seen that the photocatalyst is the core of the photocatalytic water splitting hydrogen production reaction, which can determine the efficiency of the photocatalytic water splitting hydrogen production reaction. Therefore, developing efficient photocatalysts is key to achieving efficient photocatalytic water splitting for hydrogen production, and this is also a current research hotspot in the field of photocatalysis.

[0003] Carbon nitride is an ancient synthetic polymer with five allotropes: α-carbon nitride, β-carbon nitride, cubic carbon nitride, quasi-cubic carbon nitride, and graphitic carbon nitride. Among these, graphitic carbon nitride's band structure meets the thermodynamic potential requirements for photocatalytic water splitting, and it boasts advantages such as inexpensive and readily available raw materials, simple preparation methods, visible light responsiveness, and non-toxicity to the environment and organisms, making it highly favored by researchers in the field of photocatalytic water splitting for hydrogen production. Nevertheless, due to slow photogenerated carrier migration and severe photogenerated carrier recombination, intrinsic graphitic carbon nitride photocatalysts exhibit relatively low performance in water splitting for hydrogen production, and in most cases, rely on the noble metal Pt as a co-catalyst. To further improve the photocatalytic performance of carbon nitride in water splitting for hydrogen production, numerous modification methods have been attempted, such as morphology and structure control, heteroatom doping, defect introduction, and heterostructure construction. In addition to these common modification methods, in recent years, researchers have also begun research on constructing homojunctions to optimize the photocatalytic performance of carbon nitride. For example, Deng et al. prepared a homojunction photocatalyst composed of nitrogen-deficient carbon nitride and intact carbon nitride by calcining dicyandiamide-supported carbon nitride, thereby improving the photocatalytic performance and achieving a photocatalytic water splitting hydrogen production rate of 5.01 mmol·g. − 1·h −1(Deng QH, Li HP, Ba GM, Huo TT, and Hou WG, Journal of Colloid and Interface Science 586 (2021) 748–757). Chen et al. obtained a carbon nitride homojunction photocatalyst by growing hydroxyl-deficient carbon nitride on a hydroxyl-rich carbon nitride surface, which can perform efficient photocatalytic water oxidation to hydrogen peroxide (Chen QC, Lu CJ, Ping BY, Li GY, Chen JY, Sun ZM, Zhang YJ, Ruan QS, and Tao L, Applied Catalysis B : Environmental324 (2023) 122216). The above studies show that homojunction construction can improve the photocatalytic activity of carbon nitride by promoting the transfer and separation of interfacial charge carriers. However, the construction of efficient homojunction photocatalysts is not easy. The difficulty lies in how to achieve differentiated electronic structures on both sides of the junction to obtain the driving force for interfacial charge transfer, and how to obtain a tight interfacial structure to ensure the smooth flow of charge transfer channels. Currently, there are few related reports. Therefore, developing practical carbon nitride homojunction photocatalyst preparation technology is of great significance.

[0004] Based on the above analysis, this invention uses urea as a precursor and employs a novel ionothermal-assisted two-step thermal polymerization strategy to prepare a carbon nitride homojunction photocatalyst with high and low crystallinity properties. It exhibits highly efficient photocatalytic water splitting to produce hydrogen and shows promising prospects for practical application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a carbon nitride homojunction photocatalyst. The raw materials are inexpensive and readily available, the method is simple, the process is highly controllable, and it is easy to scale up. The prepared photocatalyst can perform a highly efficient photocatalytic water splitting reaction to produce hydrogen, showing great research value and practical application prospects.

[0006] The objective of this invention is achieved through the following technical solution: (1) Take the mass as m 尿素1 Urea was calcined in a muffle furnace at 400-500°C for 1 hour to obtain the precursor; (2) According to m 尿素1 : m 尿素2 : m （NaCl+KCl） = 5:7.5:3~5:12.5:3, mNaCl : m KCl = The precursor, urea, NaCl and KCl were mixed in a mass ratio of 5:2 and placed in a muffle furnace again. The mixture was calcined at 550°C for 3 hours and thoroughly washed. The product was then separated by centrifugation and dried to obtain the carbon nitride homojunction photocatalyst.

[0007] The carbon nitride homojunction photocatalyst disclosed in this invention has the following advantages compared with existing photocatalysts: (1) This invention uses urea as a single raw material and applies an ionothermal assisted two-step thermal polymerization strategy to prepare carbon nitride homojunction photocatalyst. The raw material is cheap and readily available, the preparation method is simple, the time is short, the process is controllable, and it is easy to achieve large-scale production.

[0008] (2) The carbon nitride homojunction photocatalyst prepared in this invention is composed of highly crystalline carbon nitride and low-crystalline carbon nitride. First, the difference in crystallinity causes the carbon nitrides to exhibit different band structures, forming a strong built-in electric field at the homojunction interface, providing a driving force for charge transfer. Second, thanks to the special preparation process, a tight interfacial bond is formed between the highly crystalline and low-crystalline carbon nitrides, providing a short and smooth channel for charge transfer between them. These two factors ensure that the prepared carbon nitride homojunction photocatalyst exhibits highly efficient photocatalytic water splitting to produce hydrogen.

[0009] (3) The carbon nitride homojunction photocatalyst prepared in this invention can achieve a high photocatalytic water splitting hydrogen production rate in the photocatalytic water splitting reaction without the participation of noble metal Pt. The hydrogen production rate in deionized water can reach 8193 µmol·g −1 ·h −1 The hydrogen production rates in simulated seawater and real seawater can reach 5694 and 6318 µmol·g, respectively. −1 ·h −1 . Attached Figure Description

[0010] Figure 1 This is a scanning electron microscope image of the carbon nitride homojunction photocatalyst prepared in Example 1; Figure 2 The infrared spectrum of the carbon nitride homojunction photocatalyst prepared in Example 1; Figure 3 These are transmission and high-resolution transmission electron microscopy images of the carbon nitride homojunction photocatalyst prepared in Example 1. Figure 4 The graph shows the water splitting hydrogen production performance of the carbon nitride homojunction photocatalyst prepared in Example 1. Figure 5 The graph shows the water splitting hydrogen production performance of the carbon nitride homojunction photocatalyst prepared in Example 2. Figure 6 The graph shows the water splitting hydrogen production performance of the carbon nitride homojunction photocatalyst prepared in Example 3. Figure 7 The graph shows the hydrogen production performance of simulated seawater decomposition of the carbon nitride homojunction photocatalyst prepared in Example 4. Figure 8 The graph shows the performance of the carbon nitride homojunction photocatalyst prepared in Example 5 in the decomposition of seawater to produce hydrogen. Detailed Implementation

[0011] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the accompanying drawings and specific embodiments are merely examples and do not limit the scope of the present invention in any way.

[0012] Example 1 (1) Preparation of carbon nitride homojunction photocatalyst An alumina crucible containing 6.00 g of urea was placed in a muffle furnace and calcined at 450 °C for 1 hour to obtain a precursor. Then, the precursor was mixed with 12.00 g of urea, 2.57 g of NaCl, and 1.03 g of KCl, and placed back into the muffle furnace for calcination at 550 °C for 3 hours. Finally, the product was thoroughly washed with water, centrifuged, and dried; this product is the carbon nitride homojunction photocatalyst. Its scanning electron microscope image is attached to the instruction manual. Figure 1 From the appendix Figure 1 As can be seen, the photocatalyst exhibits a flower-like morphology composed of ultrathin nanosheets. Its infrared spectrum is shown in the attached instruction manual. Figure 2 810 cm in the picture −1 The peak at 1100–1700 cm⁻¹ corresponds to the characteristic vibrational mode of the triazine unit in carbon nitride. −1 The peaks in the wavenumber range correspond to the bending and stretching vibration modes of the heptaazine ring in carbon nitride, at 2170 cm⁻¹. −1 The peak at 3300 cm⁻¹ is related to the stretching of the cyano (−C≡N) group in carbon nitride. −1 The broad wavenumber peaks correspond to bridging or terminal amino groups and intermolecular hydrogen bonds in carbon nitride, confirming that the prepared photocatalyst is carbon nitride. Its transmission and high-resolution transmission electron microscopy images are attached to the instruction manual. Figure 3 From the appendix Figure 3 (a) The transmission electron microscope image presented further reveals the nanosheet structure of the photocatalyst, from the attached... Figure 3(b) The high-resolution transmission electron microscopy image shows clear and complete lattice fringes with interplanar spacings of 0.81 and 1.07 nm, corresponding to the (002) and (100) crystal planes of highly crystalline carbon nitride, respectively. In addition, surrounding these clear lattice fringes, some areas show very blurred lattice fringes, indicating that some carbon nitride in the photocatalyst is in a low-crystallinity state. The above characterization results demonstrate that the prepared carbon nitride homojunction photocatalyst is composed of highly crystalline carbon nitride and low-crystallinity carbon nitride.

[0013] (2) Performance test of photocatalytic water splitting for hydrogen production Using ammonium tetrathiomolybdate as a raw material, molybdenum disulfide co-catalyst was deposited on the surface of the prepared carbon nitride homojunction using ultraviolet light reduction. The product was then centrifuged, washed, and dried. Next, the obtained product was ultrasonically dispersed in 100 mL of deionized water with a lactic acid content of 20 vol.%, and the dispersion was transferred to a borosilicate glass reactor connected to a Labsolar-6A gas analyzer. The reactor was sealed, and the reaction solution was evacuated while condensation was applied to maintain the reaction solution temperature at 5°C. Finally, a 300 W xenon lamp light source was moved to the top of the reactor to initiate the photocatalytic reaction. Samples were automatically taken from the reaction system every 30 minutes and injected into a gas chromatograph for gas content analysis. The water splitting and hydrogen production performance of this carbon nitride homojunction photocatalyst is described in the appendix of the instruction manual. Figure 4 .from Figure 4 It can be seen that the amount of hydrogen produced increases almost linearly with the extension of illumination time, and the average hydrogen production rate reaches 8193 µmol·g over 2 hours. −1 ·h −1 .

[0014] Example 2 (1) Preparation of carbon nitride homojunction photocatalyst An alumina crucible containing 6.00 g of urea was placed in a muffle furnace and calcined at 500 °C for 1 hour to obtain a precursor. The precursor was then mixed with 12 g of urea, 2.57 g of NaCl and 1.03 g of KCl and placed back into the muffle furnace, where it was calcined at 550 °C for 3 hours. Finally, the product was thoroughly washed with water, centrifuged, and dried to obtain a carbon nitride homojunction photocatalyst.

[0015] (2) Performance test of photocatalytic water splitting for hydrogen production The photocatalytic water splitting hydrogen production performance was tested according to step (2) in Example 1. The results are shown in the appendix of the instruction manual. Figure 5 .from Figure 5 As can be seen, the average hydrogen production rate of this photocatalyst reaches 6654 µmol·g over 2 hours. −1 ·h −1 .

[0016] Example 3 (1) Preparation of carbon nitride homojunction photocatalyst An alumina crucible containing 6.00 g of urea was placed in a muffle furnace and calcined at 450 °C for 1 hour to obtain a precursor. Then, the obtained precursor was mixed with 15 g of urea, 2.57 g of NaCl and 1.03 g of KCl and placed back into the muffle furnace, and calcined at 550 °C for 3 hours. Finally, the product was thoroughly washed with water, centrifuged, and dried to obtain a carbon nitride homojunction photocatalyst.

[0017] (2) Performance test of photocatalytic water splitting for hydrogen production The photocatalytic water splitting hydrogen production performance was tested according to step (2) in Example 1. The results are shown in the appendix of the instruction manual. Figure 6 .from Figure 6 As can be seen, the average hydrogen production rate of this photocatalyst reaches 5979 µmol·g over 2 hours. −1 ·h −1 .

[0018] Example 4 (1) Preparation of carbon nitride homojunction photocatalyst The carbon nitride homojunction photocatalyst was prepared according to step (1) in Example 1.

[0019] (2) Performance test of photocatalytic decomposition of simulated seawater to produce hydrogen Using 100 mL of simulated seawater (3.5 wt.% sodium chloride solution) with a lactic acid content of 20 vol.% instead of 100 mL of deionized water with a lactic acid content of 20 vol.%, the photocatalytic decomposition of simulated seawater to produce hydrogen was tested according to Example 1 (2). The results are shown in the appendix to the instruction manual. Figure 7 .from Figure 7 It can be seen that the average hydrogen production rate of the prepared carbon nitride homojunction photocatalyst is 5694 µmol·g over 2 hours. −1 ·h −1 .

[0020] Example 5 (1) Preparation of carbon nitride homojunction photocatalyst The carbon nitride homojunction photocatalyst was prepared according to step (1) in Example 1.

[0021] (2) Performance test of photocatalytic seawater decomposition for hydrogen production 100 mL of seawater with a lactic acid content of 20 vol.% (taken from the Third Bathing Beach of Qingdao) was used instead of 100 mL of deionized water with a lactic acid content of 20 vol.%, and the photocatalytic decomposition of seawater to produce hydrogen was tested according to Example 1 (2). The results are shown in the appendix to the instruction manual. Figure 8.from Figure 8 It can be seen that the average hydrogen production rate of the prepared carbon nitride homojunction photocatalyst is 6318 µmol·g over 2 hours. −1 ·h −1 .

[0022] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a carbon nitride homojunction photocatalyst, characterized in that... This photocatalyst was prepared by the following method: (1) Take the mass as m 尿素1 Urea was calcined in a muffle furnace at 450°C for 1 hour to obtain the precursor; (2) The obtained precursor and mass are... m 尿素2 After mixing urea, NaCl and KCl, the mixture was calcined twice in a muffle furnace at 550°C for 3 hours and thoroughly washed. The product was then separated by centrifugation and dried to obtain the carbon nitride homojunction photocatalyst.

2. The method for preparing a carbon nitride homojunction photocatalyst as described in claim 1, characterized in that, In step (2) m 尿素1 : m 尿素2 : m （NaCl+KCl） = 5:7.5:3~5:12.5:3, m NaCl : m KCl = 5:

2.

3. The application of the photocatalyst prepared by the method described in claim 1 in photocatalytic water splitting for hydrogen production.

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