Photocatalytic material based on nitrogen carbide network structure as well as preparation method and application of photocatalytic material

Abstract

The invention discloses a photocatalytic material based on a nitrogen carbide network structure as well as a preparation method and application of the photocatalytic material. Relates to the field of photocatalytic materials. The photocatalytic material comprises a nitrogen carbide network structure, and structural oxygen is introduced into the structure; the photocatalytic material is in a nanorod shape, the length of the nanorod shape is 250-500 nm, and the width of the nanorod shape is 50-100 nm; oxygen in the structure is a-C-O-C-group. The catalytic material of the present invention is visible light ([lambda] gt; according to the present invention, the optical absorption within the wavelength range (420 nm) and the long wavelength range is significantly enhanced, the structure defect during the synthesis process is less, the excellent performance is represented in the hydrogen production reaction, and the hydrogen production activity can achieve 6420 [mu] mol h <-1 > g <-1 >.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic materials, and in particular to a photocatalytic material based on a carbonitride network structure, and a preparation method and application thereof. Background Art

[0002] As people's concerns about energy shortages and environmental pollution grow, photocatalytic technology has been widely used in hydrogen production, environmental remediation, and carbon dioxide (CO2) reduction due to its potential applicability.

[0003] Photocatalysis is a technology that uses light energy to promote chemical reactions. Its core principle is to absorb light energy through a specific catalyst, stimulating electrons on its surface, thereby accelerating or driving a series of chemical reactions. The widespread application of this technology has not only transformed traditional catalytic reaction mechanisms but also provided new solutions for environmental protection, energy conversion, pollution control, and other fields. With its advantages of being environmentally friendly, highly efficient, and sustainable, photocatalysis has become a hot topic in scientific research and industrial applications in recent years.

[0004] The working principle of photocatalysis relies on the absorption and utilization of light by the catalyst material. Generally speaking, photocatalytic materials need to have a spectral range that can absorb sufficient energy and be able to effectively convert the absorbed light energy into chemical energy. These materials can generate electron-hole pairs under the irradiation of light, where the electrons and holes carry negative and positive charges respectively, and can further participate in the reaction. The surface properties of the catalyst determine the selectivity and efficiency of the reaction. Therefore, the selection of appropriate photocatalytic materials is a key factor affecting the effectiveness of photocatalytic reactions.

[0005] Photocatalytic materials generally need to meet several basic requirements. First, the photocatalyst must be able to absorb sufficient light energy under appropriate lighting conditions, usually ultraviolet light or visible light. Second, the photocatalyst must have a suitable energy band structure that can effectively separate photogenerated electrons and holes and prevent electron-hole recombination, thereby improving the efficiency of the photocatalytic reaction. Third, the surface of the photocatalyst must have sufficient active sites to effectively contact the reactants and promote the occurrence of the reaction. Finally, the photocatalytic material should also have good stability and recyclability to meet long-term use requirements.

[0006] In the development of photocatalytic technology, various types of photocatalytic materials have emerged, the most typical of which include semiconductor materials, metal nanoparticles, metal oxides, carbon-based materials, etc.

[0007] Carbon-based materials, including graphene, carbon nanotubes, and carbon quantum dots, have also attracted widespread attention in recent years. Their excellent electrical conductivity and large surface area make them excellent candidates for photocatalytic reactions. Another major advantage of carbon-based materials is their broad absorption range, enabling them to respond to a wider range of visible light. Furthermore, the surface of carbon-based materials can be functionalized to introduce more active sites, thereby improving the efficiency of photocatalysis.

[0008] Polymeric carbon nitride (PCN) is a typical photocatalytic polymer, characterized by simple synthesis, low cost, high stability, and suitable band structure. However, traditional thermal polymerization methods often result in numerous defects and low surface area, which reduces the utilization efficiency of visible light and increases the recombination of photogenerated charges. These problems seriously hinder the practical application of PCN. Therefore, it is necessary to manipulate the molecular structure of the original PCN to address these issues.

[0009] In recent years, ionothermal methods have attracted widespread attention as a simple and efficient method to optimize the molecular structure of PCN. Non-toxic and non-corrosive molten salts can serve not only as templates but also as solvents, improving the crystallinity and mass transfer efficiency of PCN. For example, with the assistance of LiCl, highly crystalline polytriazine imides (PTIs) with different aspect ratios were successfully prepared, showing excellent photocatalytic activity in the overall water splitting process. The improvement in crystallinity, coupled with the reduction of defects and trapping centers, effectively suppressed charge recombination and promoted charge transfer. Studies have reported the successful preparation of high-specific surface area and high-crystalline PTI by melamine thermal polymerization in an inert liquid environment of KCl-LiCl eutectic salt. However, due to the presence of Li salt, the s-triazine motif generated in PTI usually exhibits low delocalization, which limits its photocatalytic activity under visible light irradiation.

[0010] Previous studies have also reported schemes for regulating the molecular structure of PCN by ionothermal methods. However, the apparent quantum yields (AQYs) of the photocatalysts prepared in these reports were unsatisfactory. The AQYs at 400 nm were only about 3.26%, at 450 nm were only 0.32-18.8%, at 500 nm were only 0.18-2.0%, at 550 nm were only 0.10-3.69%, and at 600 nm were only about 0.003%. This may be due to defective recombination centers caused by copolymerization or doping. Therefore, an effective strategy is urgently needed to improve the utilization of visible light photons and simultaneously achieve excellent charge separation performance.

[0011] In many previous reports, O-doped PCNs showed a significant expansion of the optical absorption range. +The injected g-C3N4 activates more n→π* transitions, thereby enhancing visible light harvesting and exhibiting excellent photocatalytic performance. Using hydrochloric acid semicarbazide as a raw material, O-doped PCN (ONLH), in which O atoms and N groups are simultaneously connected to heptazine chains, was prepared by thermal polymerization. The synthesized polymer can be excited by wavelengths ranging from ultraviolet to near-infrared. Unlike the strategy of doping, which leads to structural destruction and reduced crystallinity, the structural oxygen generated by the special precursor itself is introduced into the C3N4 framework, forming a highly crystalline structure. However, the low specific surface area and high carrier recombination of ONLH still limit its photocatalytic performance.

[0012] Based on this, there is an urgent need to develop a photocatalytic material with broad-spectrum light response, efficient charge separation and high specific surface area. Summary of the Invention

[0013] The purpose of the present invention is to develop a photocatalytic material with broad spectrum light response, efficient charge separation and high specific surface area.

[0014] A first aspect of the present invention is:

[0015] Provided is a photocatalytic material.

[0016] The second aspect of the present invention is:

[0017] Provided is a method for preparing a photocatalytic material.

[0018] The third aspect of the present invention is:

[0019] Application of the photocatalytic material.

[0020] Specifically, the technical solution adopted according to the first aspect of the present invention is:

[0021] A photocatalytic material comprises a carbonized nitrogen network structure, wherein structural oxygen is introduced into the structure;

[0022] The photocatalytic material is in the form of nanorods, and the length of the nanorods is 250-500 nm and the width is 50-100 nm;

[0023] The structural oxygen is a -COC- group.

[0024] According to the embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0025] The present invention introduces structural oxygen-COC-groups into the structure of the photocatalytic material, thereby expanding the long-wavelength optical absorption of the photocatalytic material, thereby significantly enhancing the light absorption capacity of the photocatalytic material within 300 to 800 nm. The photocatalytic material of the present invention has a nanorod morphology, and the size of the nanorods is regulated to optimize the light absorption range, thereby achieving a higher capture efficiency of visible light. The quantum size effect is optimized, further enhancing the light absorption capacity and increasing the density of active sites, thereby solving the problems of the narrow light absorption range and high charge recombination rate of traditional carbon nitride materials.

[0026] Through oxygen doping and nanorod structure (MOCN x ) significantly improves the specific surface area and carrier separation efficiency, successfully solving the problems of narrow light absorption range and high charge recombination rate of traditional carbon nitride materials. The catalytic material of the present invention optimizes the quantum size effect by regulating the size of the nanorods, enhances the light absorption capacity and increases the density of active sites. In addition, the catalytic material of the present invention has significantly enhanced optical absorption in the visible light (λ>420nm) and long wavelength ranges, has fewer structural defects during the synthesis process, and exhibits excellent performance in the hydrogen production reaction, with a hydrogen production activity of up to 6420μmolh -1 g -1 .

[0027] According to one embodiment of the present invention, the structural formula of the photocatalytic material contains a -C≡N group and Na ions and / or K ions. This improves the in-plane crystallinity of the catalytic material, provides abundant active sites, and significantly enhances the efficiency of carrier separation and migration.

[0028] According to one embodiment of the present invention, the structural formula of the photocatalytic material contains sp substituted by O atoms. 2 N structure. The nanorod structure of the present invention (MOCN x ) part of sp 2 The N of the bond is replaced by O, which promotes the separation of photogenerated carriers.

[0029] According to one embodiment of the present invention, the sp 2 The N structure and the O atoms are derived from the raw material of the photocatalytic material of the present invention: semicarbazide hydrochloride.

[0030] According to one embodiment of the present invention, the specific surface area of ​​the photocatalytic material is 5.2 m 2 g -1 -73.2m 2 g -1 .

[0031] According to one embodiment of the present invention, the specific surface area of ​​the photocatalytic material is 69.7 m 2 g-1 -73.2m 2 g -1 .

[0032] According to one embodiment of the present invention, the structural formula of the photocatalytic material is:

[0033]

[0034] Specifically, the technical solution adopted according to the second aspect of the present invention is:

[0035] A method for preparing the photocatalytic material comprises the following steps:

[0036] S1 was pre-calcined using semicarbazide hydrochloride as a precursor;

[0037] S2 calcines the material obtained in S1 under a protective atmosphere and a molten salt environment to obtain the photocatalytic material.

[0038] According to the embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0039] The present invention uses hydrochloric acid semicarbazide as a raw material and calcines it to produce a heptazine chain nanorod structure with O atoms and N groups connected simultaneously through thermal polymerization. The precursor is then calcined in a molten salt environment to introduce molten salt ions through a molten salt ion thermal method, which acts as a template to induce the formation of the nanorod structure. The present invention combines the above-mentioned heptazine chain nanorod structure control with the molten salt ion thermal method, resulting in a photocatalytic material with fewer structural defects and excellent hydrogen production performance, with a hydrogen production activity of up to 6420 μmol h -1 g -1 .

[0040] In addition, unlike conventional doping strategies that lead to structural destruction and reduced crystallinity, the present invention introduces structural oxygen generated by the special precursor semicarbazide hydrochloride itself into the structure, which can form a highly crystalline nanorod structure.

[0041] According to one embodiment of the present invention, the calcination temperature in step S1 is 400-470° C., and the calcination temperature in step S2 is 550-650° C. The two different reaction stages use different temperatures. By optimizing the calcination temperature range, the precursor is fully polymerized while avoiding structural damage, and a balance is achieved between crystallinity and defect control.

[0042] According to one embodiment of the present invention, the calcination time of step S1 is consistent with the calcination time of step S2. Preferably, the calcination time of steps S1 and S2 is both 2-2.5 hours.

[0043] According to one embodiment of the present invention, the molten salt is a mixture of NaCl and KCl in a molar ratio of 76-80:24-25. When different masses of hydrochloric acid semicarbazide are polymerized with the NaCl-KCl molten salt, photocatalysts with similar structural formulas are generated, but their morphologies vary, and this morphological difference significantly affects the performance of the photocatalyst. Preferably, the molten salt is a mixture of NaCl and KCl in a molar ratio of 76:24.

[0044] According to one embodiment of the present invention, the mass ratio of the semicarbazide hydrochloride to the molten salt is 80-110: 6. The amount of the raw material components of the photocatalytic material will affect the morphology of the photocatalytic material, such as the specific surface area and pore volume.

[0045] According to one embodiment of the present invention, the mass ratio of the semicarbazide hydrochloride to the molten salt is 80-90:6-6.5.

[0046] According to one embodiment of the present invention, the mass ratio of the semicarbazide hydrochloride to the molten salt is 80-100:6-6.5.

[0047] According to one embodiment of the present invention, the mass ratio of the semicarbazide hydrochloride to the molten salt is 80-90:6.

[0048] According to one embodiment of the present invention, the mass ratio of the semicarbazide hydrochloride to the molten salt is 100-110:6.

[0049] Generally speaking, the greater the dosage ratio of semicarbazide hydrochloride, the larger the specific surface area and pore volume of the prepared photocatalyst will be, thereby providing more active sites and improving the photocatalytic activity. However, the present invention has found through creative experiments that when the mass ratio of semicarbazide hydrochloride to molten salt is 80-90:6, the photocatalytic activity of the prepared photocatalyst is extremely high, while when the mass ratio of semicarbazide hydrochloride to molten salt is 100-110:6, the specific surface area and pore volume of the prepared photocatalyst will decrease sharply, resulting in a weakening of the photocatalytic activity of the prepared photocatalyst; when the mass ratio of semicarbazide hydrochloride to molten salt is greater than 100-110:6, the photocatalytic activity of the prepared photocatalyst is even worse.

[0050] According to one embodiment of the present invention, step S2 further comprises the following step: washing the calcined product with hot water to remove impurities and increase the specific surface area and surface active site exposure of the material.

[0051] Another aspect of the present invention relates to the use of the photocatalytic material for hydrogen production by water decomposition under visible light. This includes the photocatalytic material described in the embodiment of the first aspect. Because this application utilizes all of the technical solutions of the above-mentioned photocatalytic material, it at least has all the beneficial effects brought about by the technical solutions of the above-mentioned embodiments. The present invention utilizes the wide spectral response characteristics of the photocatalytic material to significantly increase the hydrogen production rate, solving the problem of low light energy utilization efficiency of traditional catalysts.

[0052] Another aspect of the present invention relates to the use of the photocatalytic material for the degradation of bisphenol A. This includes the photocatalytic material described in the embodiment of the first aspect. Because this application utilizes all of the technical solutions of the above-mentioned photocatalytic material, it possesses at least all of the beneficial effects of the technical solutions of the above-mentioned embodiments. By leveraging the enhanced redox capacity and adsorption properties of the photocatalytic material, the present invention achieves efficient pollutant degradation and expands its application scenarios in environmental remediation.

[0053] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0055] Figure 1 Flowchart for preparing photocatalytic materials for Examples 1-4.

[0056] Figure 2 These are SEM images of the photocatalytic materials prepared in Examples 1-4.

[0057] Figure 3 The UV-visible diffuse reflectance spectra of the photocatalytic materials obtained in Examples 1-4 and Comparative Example 1 are shown.

[0058] Figure 4 Graph showing the photocatalytic hydrogen production rates of the photocatalytic materials obtained in Examples 1-4 and Comparative Example 1.

[0059] Figure 5 Graph showing the photocatalytic hydrogen production rates of the photocatalytic materials obtained in Example 2 and Comparative Examples 2-5.

[0060] Figure 6 These are the photocatalytic degradation test diagrams of the photocatalytic materials obtained in Examples 1-4 and Comparative Example 1.

[0061] Figure 7 The photocurrent and EIS Nyquist test graphs of the photocatalytic materials obtained in Example 2 and Comparative Example 1 are shown.

[0062] Figure 8This is a photocatalytic stability test chart of the photocatalytic material obtained in Example 2. DETAILED DESCRIPTION

[0063] The terms "preferred," "more preferred," and the like, used herein refer to embodiments of the present invention that may provide certain benefits under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the present invention.

[0064] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are understood to include any and all subranges subsumed therein.

[0065] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of the present invention.

[0066] Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0067] Example 1

[0068] A photocatalytic material comprising a carbonized nitrogen network structure and having a nanorod morphology, wherein the nanorods are approximately 250 nm in length and 50 nm in width;

[0069] The structural formula of the above-mentioned photocatalyst is:

[0070]

[0071] A method for preparing the above-mentioned photocatalytic material, the flow chart is as follows Figure 1 As shown, Figure 1 HCl and NH3 are gases volatilized from the material itself during the high-temperature thermal polymerization process. Specifically, the process includes the following steps:

[0072] S1 Weigh 80 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 450 °C in a muffle furnace for 2 h to obtain a precursor;

[0073] S2: After the precursor is cooled to room temperature, it is mixed with 6.0g of metal salt (4.28g NaCl and 1.72g KCl) and ground for 20min. The mixture is calcined at 600℃ for 2h in a nitrogen-filled tube furnace and cooled naturally to room temperature. The mixture is thoroughly washed with deionized water and dried in a vacuum oven to obtain the photocatalytic material, which is named MOCN. 80 sample.

[0074] Example 2

[0075] A photocatalytic material comprising a carbonized nitrogen network structure and having a nanorod morphology, wherein the nanorods are approximately 300 nm in length and 60 nm in width;

[0076] The structural formula of the above-mentioned photocatalyst is:

[0077]

[0078] A method for preparing the above-mentioned photocatalytic material, the flow chart is as follows Figure 1 As shown, the following steps are included:

[0079] S1 Weigh 90 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 450 °C in a muffle furnace for 2 h to obtain a precursor;

[0080] S2: After the precursor is cooled to room temperature, it is mixed with 6.0g of metal salt (4.28g NaCl and 1.72g KCl) and ground for 20min. The mixture is calcined at 600℃ for 2h in a nitrogen-filled tube furnace and cooled naturally to room temperature. The mixture is thoroughly washed with deionized water and dried in a vacuum oven to obtain the photocatalytic material, which is named MOCN. 90 sample.

[0081] Example 3

[0082] A photocatalytic material comprising a carbonized nitrogen network structure and having a nanorod morphology, wherein the nanorods are approximately 400 nm in length and 75 nm in width;

[0083] The structural formula of the above-mentioned photocatalyst is:

[0084]

[0085] A method for preparing the above-mentioned photocatalytic material, the flow chart is as follows Figure 1 As shown, the following steps are included:

[0086] S1: Weigh 100 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid. Calcined in a muffle furnace at 450 °C for 2 h to obtain a precursor.

[0087] S2: After the precursor is cooled to room temperature, it is mixed with 6.0g of metal salt (4.28g NaCl and 1.72g KCl) and ground for 20min. The mixture is calcined at 600℃ for 2h in a nitrogen-filled tube furnace and cooled naturally to room temperature. The mixture is thoroughly washed with deionized water and dried in a vacuum oven to obtain the photocatalytic material, which is named MOCN. 100 sample.

[0088] Example 4

[0089] A photocatalytic material comprising a carbonized nitrogen network structure and having a nanorod morphology, wherein the nanorods are approximately 500 nm in length and 100 nm in width;

[0090] The structural formula of the above-mentioned photocatalyst is:

[0091]

[0092] A method for preparing the above-mentioned photocatalytic material, the flow chart is as follows Figure 1 As shown, the following steps are included:

[0093] S1 Weigh 110 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 450 °C in a muffle furnace for 2 h to obtain a precursor;

[0094] S2: After the precursor is cooled to room temperature, it is mixed with 6.0g of metal salt (4.28g NaCl and 1.72g KCl) and ground for 20min. The mixture is calcined at 600℃ for 2h in a nitrogen-filled tube furnace and cooled naturally to room temperature. The mixture is thoroughly washed with deionized water and dried in a vacuum oven to obtain the photocatalytic material, which is named MOCN. 110 sample.

[0095] Comparative Example 1

[0096] Comparative Example 1 differs from Example 2 only in that 6.0 g of metal salt (4.28 g NaCl and 1.72 g KCl) is not added. Since no metal salt is added, step S2 does not require water washing to remove excess metal salt. Therefore, step S2 of Comparative Example 1 does not include a water washing and drying step. The sample prepared in Comparative Example 1 is named OCN.

[0097] Compared with Example 1, since no sodium potassium salt is added in Comparative Example 1, neither the strong electron-withdrawing group -C≡N nor Na and K ions are introduced into the structure of the photocatalytic material.

[0098] Specifically:

[0099] A method for preparing an oxygen self-doped g-C3N4 photocatalyst comprises the following steps:

[0100] S1 Weigh 90 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 450 °C in a muffle furnace for 2 h to obtain a precursor;

[0101] S2: The obtained precursor is cooled to room temperature and then ground for 20 minutes, then calcined at 600°C for 2 hours in a nitrogen-filled tubular furnace, naturally cooled to room temperature, and ground and collected for treatment.

[0102] The photocatalyst material was prepared through the above steps, and the sample was named OCN.

[0103] Comparative Example 2

[0104] The only difference between Comparative Example 2 and Example 2 is that semicarbazide hydrochloride is replaced with urea in Comparative Example 2, and the sample prepared in Comparative Example 2 is named MUCN.

[0105] Specifically:

[0106] A method for preparing a g-C3N4 photocatalyst using urea as a precursor comprises the following steps:

[0107] S1: Weigh 90 g of urea and transfer it to a 150 mL alumina crucible with a lid. Calcined in a muffle furnace at 450 °C for 2 h to obtain a precursor.

[0108] After the above precursor S2 is cooled to room temperature, it is mixed with 6.0g of metal salt (4.28g NaCl and 1.72g KCl) and ground for 20min, then calcined at 600℃ in a nitrogen-filled tube furnace for 2h, naturally cooled to room temperature, thoroughly washed with deionized water, dried in a vacuum oven, and ground and collected.

[0109] The photocatalyst material was prepared through the above steps, and the sample was named MUCN.

[0110] Comparative Example 3

[0111] The only difference between Comparative Example 3 and Example 2 is that the muffle furnace calcination temperature in S1 of Comparative Example 3 is 400° C., and the prepared sample is named MOCN-400.

[0112] Specifically:

[0113] A method for preparing a temperature-controlled g-C3N4 photocatalyst comprises the following steps:

[0114] S1 Weigh 90 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 400 °C in a muffle furnace for 2 h to obtain a precursor;

[0115] S2 The obtained precursor was cooled to room temperature and ground with 6.0 g of metal salt (4.28 g NaCl and 1.72 g KCl) for 20 min, then calcined at 600 °C in a nitrogen-filled tube furnace for 2 h. The mixture was naturally cooled to room temperature, and the mixture was thoroughly washed with deionized water and dried in a vacuum oven.

[0116] A photocatalytic composite material was prepared through the above steps, and the sample was named MOCN-400.

[0117] Comparative Example 4

[0118] The only difference between Comparative Example 4 and Example 2 is that the muffle furnace calcination temperature in step S1 of Comparative Example 4 is 430° C., and the prepared sample is named MOCN-430.

[0119] Specifically:

[0120] A method for preparing a temperature-controlled g-C3N4 photocatalyst comprises the following steps:

[0121] S1 Weigh 90 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 430 °C in a muffle furnace for 2 h to obtain a precursor;

[0122] S2 The obtained precursor was cooled to room temperature and ground with 6.0 g of metal salt (4.28 g NaCl and 1.72 g KCl) for 20 min, and then calcined at 600 ° C for 2 h in a nitrogen-filled tube furnace; naturally cooled to room temperature, the mixture was thoroughly washed with deionized water, and dried in a vacuum oven.

[0123] A photocatalytic composite material was prepared through the above steps, and the sample was named MOCN-430.

[0124] Comparative Example 5

[0125] The only difference between Comparative Example 5 and Example 2 is that the muffle furnace calcination temperature in step S1 of Comparative Example 5 is 470° C., and the prepared sample is named MOCN-470.

[0126] Specifically:

[0127] A method for preparing a temperature-controlled g-C3N4 photocatalyst comprises the following steps:

[0128] S1 Weigh 90 g of semicarbazide hydrochloride and transfer it to a 150 mL alumina crucible with a lid, and calcine it at 470 °C in a muffle furnace for 2 h to obtain a precursor;

[0129] S2 The obtained precursor was cooled to room temperature and ground with 6.0 g of metal salt (4.28 g NaCl and 1.72 g KCl) for 20 min, then calcined at 600 °C in a nitrogen-filled tube furnace for 2 h. The mixture was naturally cooled to room temperature, and the mixture was thoroughly washed with deionized water and dried in a vacuum oven.

[0130] A photocatalytic composite material was prepared through the above steps, and the sample was named MOCN-470.

[0131] Performance testing:

[0132] The photocatalytic materials prepared in Examples 1-4 were characterized by SEM to observe their surface morphology. The test results are as follows: Figure 2 shown.

[0133] Figure 2 a in the figure is the SEM image of the sample of Example 1; Figure 2 b is the SEM image of the sample of Example 2; Figure 2 c is the SEM image of the sample of Example 3; Figure 2 d in FIG is the SEM image of the sample of Example 4.

[0134] Depend on Figure 2 It can be seen that the samples of Examples 1-4 all exhibited uniform nanorod structures, and as the content of semicarbazide further increased during the thermal polymerization process, MOCN 80 to MOCN 110 The length of the nanorods increases from 250 nm to 500 nm, and the width increases from 50 nm to 100 nm. The catalytic material of the present invention optimizes the quantum size effect, enhances the light absorption capacity and increases the density of active sites by regulating the size of the nanorods.

[0135] The photocatalytic materials obtained in Examples 1-4 and Comparative Example 1 were subjected to elemental composition and BET specific surface area analysis to characterize the element content and specific surface area changes of the samples. The test results are shown in Table 1.

[0136] As can be seen from Table 1, the sample MOCN of Example 1 80 (69.7m 2 g -1 ) and Example 2 sample MOCN 90 (73.2m 2 g -1 ) BET The value is much higher than that of the sample OCN (4.4m 2 g -1 ), the larger the S BET The pore volume of the photocatalyst will provide more active sites, thereby improving the photocatalytic activity. 100(36.1m 2 g -1 ) and MOCN 110 (5.2m 2 g -1 ) BET With MOCN x The further increase of the amount of semicarbazide hydrochloride added significantly reduced the pore volume, resulting in a sharp decrease in the photocatalytic activity.

[0137] Table 1 OCN and MOCN x Elemental composition and BET specific surface area

[0138]

[0139]

[0140] The photocatalytic materials obtained in Examples 1-4 and Comparative Example 1 were subjected to UV-visible diffuse reflectance spectroscopy testing (Hitachi U-3010 UV-vis spectrometer, using BaSO4 as a reference) to characterize the light absorption range and ability of the samples. The test results are as follows: Figure 3 As shown, Figure 3 In the figure, Wavelength is the wavelength and Absorbance is the absorbance.

[0141] Depend on Figure 3 It can be seen that compared with the photocatalytic material OCN prepared in Comparative Example 1, the photocatalytic material MOCN prepared in Examples 1-4 is x The absorption in the range of 300-440 nm is significantly enhanced, which may be due to the formation of cyanide groups and the increase of introduced O elements caused by the ionothermal method. 80 and MOCN 90 The quantum size effect caused by the formation of one-dimensional nanorods with smaller particle size weakens the light absorption intensity in the range of 440-800nm. Correspondingly, the color of OCN changes from reddish brown to MOCN. 80 With the further increase of semicarbazide content during thermal polymerization, MOCN 100 and MOCN 110 The particle size of the nanorods gradually increased, and their light absorption capacity in the range of 440-800nm ​​was significantly enhanced.

[0142] Will Figure 3 By analyzing Table 1, we can know that MOCN 80 and MOCN 90 With a large S BETThe pore volume of the photocatalyst can provide more active sites for the photocatalytic material, thereby improving the photocatalytic activity; MOCN 100 and MOCN 110 The further increase of the amount of semicarbazide added in hydrochloric acid makes MOCN 100 and MOCN 110 The nanorods have larger particle size and stronger light absorption ability.

[0143] The photocatalytic hydrogen production rate test was carried out on the photocatalytic materials obtained in Examples 1-4 and Comparative Example 1. The test results are as follows: Figure 4 As shown, Figure 4 The vertical axis is the hydrogen production rate.

[0144] The instrument used for the test is: Labsolar-6A photocatalytic online analysis system from Beijing Perfect Light Technology Co., Ltd.;

[0145] The reaction solution used in the test was prepared by adding 50 mg of the photocatalytic material to 100 mL of an aqueous solution containing 10 mL of a sacrificial agent, triethanolamine, and 3 wt% of Pt as a co-catalyst.

[0146] The light source used in the test is PLS-SXE 300 / 300UV, and the light intensity is: 100mW / cm 2 ,λ>420nm.

[0147] Depend on Figure 4 It can be seen that compared with the sample OCN in comparative example 1, almost all the photocatalytic materials obtained by repolymerizing hydrochloric acid semicarbazide under NaCl-KCl molten salt (photocatalytic materials of Examples 1-4) have obvious improvement in photocatalytic hydrogen production performance.

[0148] In detail, the hydrogen production rate of the sample OCN prepared in Comparative Example 1 is 200 μmol h -1 g -1 .

[0149] MOCN prepared in Example 1 80 The hydrogen production rate is 4820 μmol h -1 g -1 , which is higher than the hydrogen production rate of the sample OCN prepared in Comparative Example 1;

[0150] MOCN prepared in Example 2 90 The hydrogen production rate is 6420 μmol h -1 g -1 , higher than the MOCN prepared in Example 1 80 hydrogen production rate.

[0151] MOCN prepared in Example 3100 The hydrogen production rate is 3560 μmol h -1 g -1 , lower than the MOCN prepared in Example 2 90 hydrogen production rate.

[0152] MOCN prepared in Example 4 110 The hydrogen production rate is 2020 μmol h -1 g -1 , which is lower than the MOCN prepared in Example 3 100 hydrogen production rate.

[0153] In summary, for the hydrogen production rate: MOCN prepared in Example 2 90 >MOCN prepared in Example 1 80 >MOCN prepared in Example 3 100 >MOCN prepared in Example 4 110 >Comparative Example: OCN sample prepared.

[0154] The photocatalytic hydrogen production rate test was carried out on the photocatalytic materials obtained in Example 2 and Comparative Examples 2-5. The test results are as follows: Figure 5 As shown, Figure 5 The vertical axis is the hydrogen production rate.

[0155] In detail, the hydrogen production rate of the sample MUCN prepared in Comparative Example 2 was 3012 μmol h -1 g -1 , MOCN prepared in Example 2 90 The hydrogen production rate is 6420 μmol h -1 g -1 , indicating that the presence of oxygen doping not only improves the hydrophilicity of the material, but also expands the visible light absorption, effectively improving the photocatalytic performance of the material;

[0156] MOCN prepared in Example 2 90 The hydrogen production rate is 6420 μmol h -1 g -1 The hydrogen production rate of the sample MOCN-400 prepared in comparative example 3 is 3400 μmol h -1 g -1 The hydrogen production rate of the sample MOCN-430 prepared in Comparative Example 4 was 4260 μmol h -1 g -1 The hydrogen production rate of the sample MOCN-430 prepared in comparative example 5 was 4460 μmol h -1 g -1, indicating that when the calcination temperature in step S1 increases from 400 °C to 450 °C, the hydrogen production performance of the product catalyst is further improved. However, when the calcination temperature is further increased to 470 °C, the performance gradually decreases, which may be because the CN structure is destroyed due to the high temperature.

[0157] In summary, the sample MOCN was obtained by thermal polymerization of an appropriate amount of hydrochloric acid semicarbazide with the assistance of NaCl-KCl molten salt. 90 The photocatalytic hydrogen production rate of the photocatalytic composite material prepared in Example 2 is the highest. However, as the amount of hydrochloric acid semicarbazide is further increased, the hydrogen production performance of the prepared photocatalytic composite material sample will gradually decrease. This may be due to the excessive amount of precursor, which will change some properties of the semiconductor and affect the photocatalytic performance of the material. In addition, it can be seen from Table 2 that MOCN 90 The hydrogen production efficiency exceeds that of most previously reported PCN-based photocatalysts. This significantly improved performance indicates that the 90 In the photocatalytic reaction, the photon utilization efficiency is higher, especially in the longer wavelength range.

[0158] The samples obtained in Examples 1-4 and Comparative Example 1 were subjected to photocatalytic degradation tests. The test results are shown in FIG. Figure 6 As shown, Figure 6 Irradiation time is the irradiation time, C t / C0 is the ratio of the reactant concentration to time.

[0159] The instruments used for the test were: high performance liquid chromatography system (HPLC) and fluorescence detector (Waterse2695 Alliance, USA), and analysis was performed at 245 nm;

[0160] The preparation method and test method of the reaction solution used in the test are as follows: 50 mg of the photocatalytic material is dispersed in 100 mL of BPA (bisphenol A) aqueous solution (20 mg L -1 ) and stirred continuously for 60 min to conduct a dark pre-adsorption experiment. The system was then exposed to irradiation from a 300 W xenon lamp (PLS-SXE300D, Beijing Perfectlight Technology Co., Ltd.) equipped with a 420 nm cutoff filter, and 3 mL of the reaction solution (filtrate) was periodically extracted using a 0.45 μm membrane.

[0161] from Figure 6 It is known that compared with the OCN sample in comparative example 1, the photodegradation rate of BPA in the samples of examples 1-4 is also significantly improved, showing the same performance as the nanorod structure MOCN. x The HER showed a similar trend.

[0162] Specifically, due to S BET The difference is that the adsorption rate of OCN in comparative example 1 is 15.7%, and the adsorption rate of MOCN in example 2 is 90 The adsorption rate of OCN to BPA was 24.9%. In 90 minutes, the degradation rate of OCN to BPA was only 34.9%, while MOCN 90 The removal rate of bisphenol A was 100%. In addition, the photodegradation kinetics of bisphenol A conformed to the pseudo-first-order model, which fitted well with the experimental data. More importantly, compared with the comparative example, in the samples of Examples 1-4, S BET , hydrophilicity, in-plane crystallinity, redox ability, and C≡N and O substituted sp 2 The formation of N together contributes to the abundance of active sites. These improvements promote the dispersion of the catalyst material of the present invention in aqueous solution, promote the effective separation and migration of photogenerated carriers, and significantly improve the photocatalytic activity of the catalyst material of the present invention.

[0163] In summary, in the process of preparing the catalyst material, the present invention uses NaCl-KCl molten salt as an auxiliary, and in the presence of an appropriate amount of hydrochloric acid semicarbazide and NaCl-KCl salt, a sample MOCN obtained by thermal polymerization is obtained. 90 The photocatalytic degradation performance of BPA is the highest, that is, the photocatalytic composite material prepared in Example 2 has the best photocatalytic degradation performance of BPA. As the amount of hydrochloric acid semicarbazide is further increased, the degradation performance of BPA of the photocatalytic material samples prepared in Examples 3-4 will gradually decrease compared with Example 2, which further shows that the effective control of the amount of precursor will make the sample MOCN obtained by CN network structure 90 Possesses the highest photocatalytic degradation efficiency.

[0164] The sample MOCN obtained in Example 2 90 The photocurrent and EIS Nyquist tests were performed on the OCN sample of comparative example 1. The test results are as follows: Figure 7 shown.

[0165] Depend on Figure 7 It can be seen that the sample MOCN of Example 2 90 The electrochemical impedance spectroscopy (EIS) semicircle of MOCN is significantly smaller than that of OCN in comparative example 1, indicating that 90 The charge transfer rate is faster, which is because the metal salt NaCl-KCl is added in Example 2 compared with Comparative Example 1, which can serve as a template to induce the formation of nanorod structure.

[0166] Under visible light irradiation (λ≥420nm), MOCN 90 The transient photocurrent response intensity of MOCN is about 3.5 times that of OCN, which further proves that 90The reason is that, compared with Comparative Example 1, the S BET Increased, and introduced -C≡N (comparative example 1 does not add sodium potassium salt, in the structure of its photocatalytic material, will not introduce strong electron-withdrawing group -C≡N, nor will it introduce Na and K ions). In addition, the O-substituted sp 2 N and Na / K ions contribute to the formation of a large number of catalytic active sites and efficient charge transfer channels, thereby promoting photocatalytic activity.

[0167] The sample MOCN obtained in Example 2 90 The photocatalytic stability test was carried out, and the test results were as follows Figure 8 As shown, Figure 8 Where Time is time and H2 evolution is hydrogen production activity.

[0168] Depend on Figure 8 It can be seen that after 4 cycles of continuous illumination for 16 hours (the generated hydrogen is vacuumed out every 4 hours, which is counted as one cycle), the sample MOCN 90 The hydrogen production activity of the catalyst has basically not decayed, which proves that the catalyst has good stability. The reason is that the hydrochloric acid semicarbazide and the metal salt in a specific dosage ratio form a more stable polymeric carbon nitride framework during thermal polymerization, making its structure less likely to be destroyed during the reaction. Therefore, the catalyst of the present invention has good application prospects in practical applications.

[0169] The sample MOCN obtained in Example 2 90 The apparent quantum yield (AQY) test was performed, and the test results are shown in Table 2.

[0170] The AQY test method is: using Perfect Light Labsolar-6A all-glass automatic online gas analysis system and Fuli GC9790SD gas chromatograph for testing. Specifically, 0.05g of the sample MOCN obtained in Example 2 90 The mixture was then mixed with 10 mL of triethanolamine (TEOA), 5 mL of a 3 wt% Pt solution in H2PtCl6·6H2O, and 85 mL of deionized water to obtain a mixture. The mixture was then transferred to a reactor. Prior to irradiation, the reaction system was closed to create a sealed environment and completely degassed for 30 minutes. During irradiation, the optical densities of incident light at 450 nm, 500 nm, 550 nm, 600 nm, and 650 nm were 2.3445, 2.33325, 2.382, 2.115, and 2.026, respectively. The reactor was maintained at 5°C and cooled by circulating water.

[0171] The calculation method of AQY (%) is:

[0172] 2 × the number of hydrogen molecules generated in the reaction ÷ the number of incident photons irradiating the reaction system × 100%.

[0173] Table 2

[0174]

[0175] The above are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A photocatalytic material, characterized in that: comprising a carbonized nitrogen network structure, wherein structural oxygen is introduced into the structure; The photocatalytic material is in the form of nanorods, and the length of the nanorods is 250-500 nm and the width is 50-100 nm; The structural oxygen is a -COC- group.

2. A photocatalytic material according to claim 1, characterized in that: The structural formula of the photocatalytic material contains a -C≡N group, and Na ions and / or K ions.

3. The photocatalytic material according to claim 1, characterized in that: The structural formula of the photocatalytic material contains sp 2 N structure.

4. A photocatalytic material according to any one of claims 1 to 3, characterized in that: The structural formula of the photocatalytic material is:

5. A method for preparing a photocatalytic material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1 was pre-calcined using semicarbazide hydrochloride as a precursor; S2 calcines the material obtained in S1 under a protective atmosphere and a molten salt environment to obtain the photocatalytic material.

6. The method according to claim 5, characterized in that: The calcination temperature of step S1 is 400-470°C, and the calcination temperature of step S2 is 550-650°C.

7. The method according to claim 5, characterized in that: The molten salt is a mixture of NaCl and KCl, with a molar ratio of 76-80:24-25.

8. The method according to claim 5, characterized in that: The mass ratio of the semicarbazide hydrochloride to the molten salt is 80-110:

6.

9. The method according to claim 8, characterized in that: The mass ratio of the semicarbazide hydrochloride to the molten salt is 80-90:

6.

10. Use of the photocatalytic material according to any one of claims 1 to 3 in decomposing water to produce hydrogen under visible light.

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