Semi-crystalline carbon nitride-based composite photocatalyst and preparation method thereof
By optimizing the mass ratio of melamine to thiourea and layering the molten salt through a one-pot molten salt in-situ doping process, the problems of incomplete structure and uneven doping of semi-crystalline carbon nitride-based composite photocatalysts were solved, achieving high efficiency in photocatalytic activity and stability, especially in the removal of imidacloprid in pesticide wastewater treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-03-13
AI Technical Summary
Existing semi-crystalline carbon nitride-based composite photocatalysts suffer from incomplete semi-crystalline structures, reduced light absorption efficiency and carrier migration performance due to deviations in feed ratio and mixing uniformity, as well as inaccurate temperature control during preparation. Furthermore, uneven potassium thiocyanate doping affects process reproducibility and performance consistency.
A one-pot molten salt in-situ doping process was adopted. By controlling the mass ratio of melamine to thiourea and layering the molten salt, sulfur, potassium elements and cyano groups were introduced simultaneously to form a stable liquid reaction environment, optimize the semi-crystalline structure and hollow tubular morphology, and enhance the migration efficiency and light absorption capacity of photogenerated carriers.
This improved the photocatalytic activity and stability of the catalyst, solved the crystal structure defect problem caused by uneven element distribution in traditional methods, ensured the batch stability and process reproducibility of the catalyst, and promoted the efficient degradation performance of the photocatalyst in the visible light region.
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Figure CN121648951A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of composite semiconductor photocatalyst technology, specifically to a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method. Background Technology
[0002] Composite semiconductor photocatalysts are functional materials formed by combining different semiconductor materials. Their core feature is the construction of heterojunction structures to improve photocatalytic efficiency.
[0003] Currently, the preparation of this semi-crystalline carbon nitride-based composite photocatalyst relies on a specific ratio of melamine and thiourea precursors, as well as a molten salt system of potassium chloride and lithium chloride monohydrate. If the feeding ratio and mixing uniformity deviate, it is impossible to form uniform co-doping of sulfur, potassium elements and cyano groups, resulting in incomplete development of the semi-crystalline structure of the catalyst and a decrease in the regularity of the hollow tubular morphology, which in turn affects its light absorption efficiency and carrier migration performance. At the same time, in the thermal polycondensation reaction stage, if the temperature control precision is insufficient and the heating rate fluctuates, it is easy to cause instability in the molten salt liquid environment, making it difficult to ensure the full generation and doping consistency of potassium thiocyanate, which will cause performance differences between batches of catalysts, reduce process reproducibility, and face quality control challenges in actual large-scale production.
[0004] Therefore, a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method are proposed to solve the above problems. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method, which solves the problems mentioned in the background art, such as the incomplete development of the semi-crystalline structure of the catalyst and the difficulty in ensuring the sufficient generation and consistency of potassium thiocyanate doping.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method, wherein the catalyst is specifically used for photocatalytic degradation of environmental pollutants, particularly for the removal of imidacloprid in pesticide wastewater treatment; The catalyst is synthesized using a one-pot molten salt in-situ doping process. This process provides a stable liquid reaction environment during the thermal polycondensation of the precursor by the molten salt mixture, thereby enabling the simultaneous introduction of sulfur, potassium and cyano groups and enhancing the formation of the semi-crystalline structure. Specifically, the catalyst is composed of cyano-containing polymeric carbon nitride nanorods, wherein sulfur atoms are doped by replacing nitrogen atoms in the CNC bond of the backbone, and potassium ions are modified between the nanorod chains to jointly enhance the migration efficiency and light absorption capacity of photogenerated carriers. The catalyst has a hollow tubular microstructure with a rough surface, which increases the contact area between the catalyst and the pollutants and promotes multiple reflections and refractions of light within the material, thereby improving light utilization efficiency. In terms of performance, the catalyst exhibits high photocatalytic activity in the visible light region.
[0007] Furthermore, in the catalyst, the polymerized carbon nitride nanorods are derived from melamine and thiourea precursors, wherein the mass ratio of melamine to thiourea is 8:0.5-2. This optimized mass ratio ensures uniform doping of sulfur and potassium elements, as well as the introduction of cyano groups, thereby improving the crystallinity and photocatalytic performance of the catalyst.
[0008] Furthermore, the rough-surfaced hollow tubular structure has porous features and a high specific surface area, which can promote the diffusion of reactant molecules and the separation of photogenerated electron-hole pairs. The structure is observed to be a uniform rod-shaped morphology by transmission electron microscopy. Compared with traditional bulk carbon nitride, it has improved light absorption efficiency and enhanced charge separation ability. This is because the unique tubular design reduces the exciton Coulomb force binding and improves the exciton energy transfer efficiency, especially by accelerating pollutant degradation by generating singlet oxygen.
[0009] Furthermore, the method for preparing the catalyst includes the following steps: (1) Melamine, thiourea and a partially molten salt mixture are mixed and ground to obtain a precursor mixture. The molten salt mixture is composed of potassium chloride and lithium chloride monohydrate, with a fixed mass of 3.3g of potassium chloride and 2.7g of lithium chloride monohydrate, and the partially molten salt is 1 / 2 of the total molten salt mass. (2) The remaining molten salt, which is also 1 / 2 of the total molten salt mass, is mixed and ground, and then evenly covered on the precursor mixture to form a layered structure; (3) The mixture obtained in step (2) is subjected to thermal polycondensation reaction. After the reaction, the molten salt is removed by washing with water and dried to obtain the photocatalyst. The preparation method utilizes in-situ molten salt doping technology to control the doping process at different melting point stages, simplifying the traditional multi-step synthesis and improving production efficiency and product uniformity.
[0010] Furthermore, the grinding process employs both mechanical and manual methods, with a grinding time of 5-20 minutes, to ensure thorough mixing of the precursors and optimization of the crystal structure. The thermal polycondensation reaction is carried out at 450-550℃ for 3-5 hours, with a heating rate of 6-10℃ / min. These conditions optimize the formation of the semi-crystalline structure and avoid performance degradation caused by over-polymerization.
[0011] Furthermore, in the molten salt mixture, the mass ratio of potassium chloride to lithium chloride monohydrate is fixed at approximately 1.22:1, i.e., 3.3g:2.7g. This ratio ensures the stability of the liquid environment and prevents deammoniation of carbon nitride during the thermal polycondensation process by releasing hydrogen chloride, while promoting the formation of potassium thiocyanate, thereby achieving co-doping of cyano groups and sulfur and potassium elements. The one-pot design of the method reduces costs and avoids additional doping steps, giving the catalyst high uniformity and repeatability.
[0012] Furthermore, a method for treating pesticide wastewater includes the following steps: (1) Under light-protected conditions, the photocatalyst is mixed with wastewater containing pesticides and subjected to adsorption treatment to obtain a mixed solution; (2) Under visible light conditions, the mixture obtained in step (1) is subjected to photocatalytic reaction to degrade pollutants in wastewater.
[0013] Furthermore, the pesticide in the pesticide wastewater is imidacloprid, with an initial concentration of 2-10 mg / L, preferably 5-10 mg / L. The mass ratio of the photocatalyst to the pesticide is 20-80:1, preferably 40-60:1. This ratio ensures sufficient catalytic active sites while avoiding catalyst waste. The adsorption treatment time is 15-25 minutes to achieve a synergistic effect of adsorption-photocatalysis.
[0014] Furthermore, the visible light wavelength is greater than 420nm, and the light source is a xenon lamp; the conditions for the photocatalytic reaction include: temperature of 5-40℃, pH of 3-9, rotation speed of 500-700rpm, and time of 1-2 hours. These conditions optimize the photocatalytic efficiency and ensure the stability and repeatability of the reaction system, so that the removal rate remains at a high level during recycling.
[0015] Furthermore, in the recycling performance test, after five repeated experiments, the removal rate of imidacloprid by the catalyst remained above 75%, and the photocatalytic activity did not decrease. This performance is attributed to the semi-crystalline structure of the catalyst and the stability of the doping elements, which gives it long-term application potential in the field of environmental photocatalysis.
[0016] Compared with the prior art, the present invention provides a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method, which has the following beneficial effects: 1. In this invention, by employing a one-pot molten salt in-situ doping process and controlling a specific mass ratio of melamine to thiourea, it is possible to ensure uniform co-doping of sulfur, potassium, and cyano groups during the precursor thermal polycondensation process. This promotes the formation of a semi-crystalline structure and the construction of a hollow tubular morphology with a rough surface. This preparation method improves the catalyst's absorption capacity for visible light and the migration efficiency of photogenerated carriers, and solves the problem of crystal structure defects caused by uneven element distribution in traditional doping methods.
[0017] 2. In this invention, a stable liquid reaction environment is formed during the thermal polycondensation stage by adding molten salt in a layered manner and controlling the heating process. This promotes the formation of potassium thiocyanate and the consistency of element doping. This innovative process ensures that the catalyst has excellent batch stability and process reproducibility, and solves the problem of performance differences caused by temperature fluctuations in traditional methods.
[0018] 3. In this invention, the semi-crystalline polymerized carbon nitride nanorod composite photocatalyst has a unique surface rough hollow tubular structure and optimized chemical composition, which enables it to maintain efficient adsorption-photocatalytic synergy under a wide range of environmental conditions. The catalyst exhibits excellent structural stability and active site retention during recycling, solving the technical problem of easy deactivation of traditional catalysts under complex water quality conditions. Attached Figure Description
[0019] Figure 1 This is a flowchart illustrating the preparation steps of a semi-crystalline carbon nitride-based composite photocatalyst according to the present invention. Figure 2 The images are transmission electron microscope (TEM) images of the carbon nitride composite photocatalyst prepared in Example 1 and the carbon nitride nanorod catalyst prepared in Comparative Example 1, where a is a TEM image of the carbon nitride composite photocatalyst and b is a TEM image of the carbon nitride nanorod catalyst. Figure 3 The XRD patterns are of the carbon nitride composite photocatalyst prepared in Example 1 and the carbon nitride nanorod catalyst prepared in Comparative Example 1 of the present invention. Figure 4 Fourier transform infrared spectra of the carbon nitride composite photocatalyst prepared in Example 1 and the carbon nitride nanorod catalyst prepared in Comparative Example 1, respectively, according to the present invention. Figure 5 XPS image of the carbon nitride-based composite photocatalyst prepared in Example 1 of the present invention, a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method; Figure 6This is a schematic diagram showing the relationship between the concentration of imidacloprid and photocatalytic time during photocatalytic degradation in the visible light region of the carbon nitride composite photocatalyst prepared in Example 1 and the carbon nitride nanorod catalyst prepared in Comparative Example 1, which is a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method according to the present invention. Figure 7 This image shows the removal rate of the carbon nitride-based composite photocatalyst prepared in Example 1 of the present invention when it is used to treat imidacloprid wastewater. Detailed Implementation
[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0021] Please see Figure 1-7 The specific implementation of a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method is as follows: Example 1: A semi-crystalline carbon nitride-based composite photocatalyst and its preparation method. The catalyst is specifically designed for photocatalytic degradation of environmental pollutants, particularly for the removal of imidacloprid in pesticide wastewater treatment. The catalyst is synthesized using a one-pot molten salt in-situ doping process. This process provides a stable liquid reaction environment during the thermal polycondensation of the precursor by the molten salt mixture, enabling the simultaneous introduction of sulfur, potassium and cyano groups, and enhancing the formation of the semi-crystalline structure. Specifically, the catalyst is composed of cyano-containing polymeric carbon nitride nanorods, in which sulfur atoms are doped by replacing nitrogen atoms in the CNC bond of the backbone, and potassium ions are modified between the nanorod chains to jointly enhance the migration efficiency and light absorption capacity of photogenerated carriers. The catalyst has a hollow tubular microstructure with a rough surface. This structure can increase the contact area between the catalyst and the pollutants and promote multiple reflections and refractions of light inside the material, thereby improving light utilization efficiency. In terms of performance, the catalyst exhibits high photocatalytic activity in the visible light region.
[0022] In the catalyst, the polymerized carbon nitride nanorods are derived from melamine and thiourea precursors, with a mass ratio of melamine to thiourea of 8:0.5. This optimized mass ratio ensures uniform doping of sulfur and potassium elements, as well as the introduction of cyano groups, thereby improving the crystallinity and photocatalytic performance of the catalyst.
[0023] The rough-surfaced hollow tubular structure has porous features and a high specific surface area, which can promote the diffusion of reactant molecules and the separation of photogenerated electron-hole pairs. The structure is observed to be a uniform rod-shaped structure by transmission electron microscopy. Compared with traditional bulk carbon nitride, it has improved light absorption efficiency and enhanced charge separation ability. This is because the unique tubular design reduces the exciton Coulomb force binding and improves the exciton energy transfer efficiency, especially by generating singlet oxygen to accelerate pollutant degradation.
[0024] The catalyst preparation method includes the following steps: (1) Melamine, thiourea and partially molten salt mixture are mixed and ground to obtain precursor mixture. The molten salt mixture is composed of potassium chloride and lithium chloride monohydrate, with a fixed mass of 3.3g potassium chloride and 2.7g lithium chloride monohydrate, and the partially molten salt is 1 / 2 of the total molten salt mass. (2) The remaining molten salt, which is also 1 / 2 of the total molten salt mass, is mixed and ground, and then evenly coated on the precursor mixture to form a layered structure; (3) The mixture obtained in step (2) is subjected to thermal polycondensation reaction. After the reaction, the molten salt is removed by washing with water and dried to obtain the photocatalyst. The preparation method utilizes in-situ molten salt doping technology to control the doping process at different melting point stages, simplifying the traditional multi-step synthesis and improving production efficiency and product uniformity.
[0025] The grinding process employs both mechanical and manual methods, with a grinding time of 5 minutes, to ensure thorough mixing of the precursors and optimization of the crystal structure. The thermal polycondensation reaction is carried out at 450℃ for 3 hours with a heating rate of 6℃ / min. These conditions optimize the formation of the semi-crystalline structure and avoid performance degradation caused by over-polymerization.
[0026] In the molten salt mixture, the mass ratio of potassium chloride to lithium chloride monohydrate is fixed at approximately 1.22:1, i.e., 3.3g:2.7g. This ratio ensures the stability of the liquid environment and prevents deammoniation of carbon nitride during the thermal polycondensation process by releasing hydrogen chloride, while promoting the formation of potassium thiocyanate, thereby achieving co-doping of cyano groups and sulfur and potassium elements. The one-pot design of the method reduces costs and avoids additional doping steps, giving the catalyst high uniformity and reproducibility.
[0027] A method for treating pesticide wastewater includes the following steps: (1) Under light-protected conditions, the photocatalyst was mixed with wastewater containing pesticides and subjected to adsorption treatment to obtain a mixed solution; (2) Under visible light conditions, the mixture obtained in step (1) is subjected to photocatalytic reaction to degrade pollutants in wastewater.
[0028] The pesticide in the pesticide wastewater is imidacloprid, with an initial concentration of 2 mg / L, preferably 5 mg / L. The mass ratio of photocatalyst to pesticide is 20:1, preferably 40:1. This ratio ensures sufficient catalytic active sites while avoiding catalyst waste. The adsorption treatment time is 15 minutes to achieve the synergistic effect of adsorption-photocatalysis.
[0029] The visible light wavelength is greater than 420nm, and the light source is a xenon lamp. The photocatalytic reaction conditions include a temperature of 5℃, a pH of 3, a rotation speed of 500rpm, and a time of 1 hour. These conditions optimize the photocatalytic efficiency and ensure the stability and repeatability of the reaction system, so that the removal rate remains at a high level during recycling.
[0030] In the recycling performance test, after five repeated experiments, the removal rate of imidacloprid remained above 75%, and the photocatalytic activity did not decrease. This performance is attributed to the semi-crystalline structure of the catalyst and the stability of the doped elements, which makes it have long-term application potential in the field of environmental photocatalysis.
[0031] Example 2: A semi-crystalline carbon nitride-based composite photocatalyst and its preparation method. The catalyst is specifically designed for photocatalytic degradation of environmental pollutants, particularly for the removal of imidacloprid in pesticide wastewater treatment. The catalyst is synthesized using a one-pot molten salt in-situ doping process. This process provides a stable liquid reaction environment during the thermal polycondensation of the precursor by the molten salt mixture, enabling the simultaneous introduction of sulfur, potassium and cyano groups, and enhancing the formation of the semi-crystalline structure. Specifically, the catalyst is composed of cyano-containing polymeric carbon nitride nanorods, in which sulfur atoms are doped by replacing nitrogen atoms in the CNC bond of the backbone, and potassium ions are modified between the nanorod chains to jointly enhance the migration efficiency and light absorption capacity of photogenerated carriers. The catalyst has a hollow tubular microstructure with a rough surface. This structure can increase the contact area between the catalyst and the pollutants and promote multiple reflections and refractions of light inside the material, thereby improving light utilization efficiency. In terms of performance, the catalyst exhibits high photocatalytic activity in the visible light region.
[0032] In the catalyst, the polymerized carbon nitride nanorods are derived from melamine and thiourea precursors, with a mass ratio of melamine to thiourea of 8:0.95. This optimized mass ratio ensures uniform doping of sulfur and potassium elements, as well as the introduction of cyano groups, thereby improving the crystallinity and photocatalytic performance of the catalyst.
[0033] The rough-surfaced hollow tubular structure has porous features and a high specific surface area, which can promote the diffusion of reactant molecules and the separation of photogenerated electron-hole pairs. The structure is observed to be a uniform rod-shaped structure by transmission electron microscopy. Compared with traditional bulk carbon nitride, it has improved light absorption efficiency and enhanced charge separation ability. This is because the unique tubular design reduces the exciton Coulomb force binding and improves the exciton energy transfer efficiency, especially by generating singlet oxygen to accelerate pollutant degradation.
[0034] The catalyst preparation method includes the following steps: (1) Melamine, thiourea and partially molten salt mixture are mixed and ground to obtain precursor mixture. The molten salt mixture is composed of potassium chloride and lithium chloride monohydrate, with a fixed mass of 3.3g potassium chloride and 2.7g lithium chloride monohydrate, and the partially molten salt is 1 / 2 of the total molten salt mass. (2) The remaining molten salt, which is also 1 / 2 of the total molten salt mass, is mixed and ground, and then evenly coated on the precursor mixture to form a layered structure; (3) The mixture obtained in step (2) is subjected to thermal polycondensation reaction. After the reaction, the molten salt is removed by washing with water and dried to obtain the photocatalyst. The preparation method utilizes in-situ molten salt doping technology to control the doping process at different melting point stages, simplifying the traditional multi-step synthesis and improving production efficiency and product uniformity.
[0035] The grinding process employs both mechanical and manual methods, with a grinding time of 12.5 minutes, to ensure thorough mixing of the precursors and optimization of the crystal structure. The thermal polycondensation reaction is carried out at 500℃ for 4 hours with a heating rate of 8℃ / min. These conditions optimize the formation of the semi-crystalline structure and avoid performance degradation caused by over-polymerization.
[0036] In the molten salt mixture, the mass ratio of potassium chloride to lithium chloride monohydrate is fixed at approximately 1.22:1, i.e., 3.3g:2.7g. This ratio ensures the stability of the liquid environment and prevents deammoniation of carbon nitride during the thermal polycondensation process by releasing hydrogen chloride, while promoting the formation of potassium thiocyanate, thereby achieving co-doping of cyano groups and sulfur and potassium elements. The one-pot design of the method reduces costs and avoids additional doping steps, giving the catalyst high uniformity and reproducibility.
[0037] A method for treating pesticide wastewater includes the following steps: (1) Under light-protected conditions, the photocatalyst was mixed with wastewater containing pesticides and subjected to adsorption treatment to obtain a mixed solution; (2) Under visible light conditions, the mixture obtained in step (1) is subjected to photocatalytic reaction to degrade pollutants in wastewater.
[0038] The pesticide in the pesticide wastewater is imidacloprid, with an initial concentration of 6 mg / L, preferably 7.5 mg / L. The mass ratio of photocatalyst to pesticide is 50:1, preferably 50:1. This ratio ensures sufficient catalytic active sites while avoiding catalyst waste. The adsorption treatment time is 20 minutes to achieve the synergistic effect of adsorption-photocatalysis.
[0039] The visible light wavelength is greater than 420nm, and the light source is a xenon lamp. The photocatalytic reaction conditions include a temperature of 22.5℃, a pH of 6, a rotation speed of 600rpm, and a time of 1.5 hours. These conditions optimize the photocatalytic efficiency and ensure the stability and repeatability of the reaction system, so that the removal rate remains at a high level during recycling.
[0040] In the recycling performance test, after five repeated experiments, the removal rate of imidacloprid remained above 75%, and the photocatalytic activity did not decrease. This performance is attributed to the semi-crystalline structure of the catalyst and the stability of the doped elements, which makes it have long-term application potential in the field of environmental photocatalysis.
[0041] Example 3: A semi-crystalline carbon nitride-based composite photocatalyst and its preparation method. The catalyst is specifically designed for photocatalytic degradation of environmental pollutants, particularly for the removal of imidacloprid in pesticide wastewater treatment. The catalyst is synthesized using a one-pot molten salt in-situ doping process. This process provides a stable liquid reaction environment during the thermal polycondensation of the precursor by the molten salt mixture, enabling the simultaneous introduction of sulfur, potassium and cyano groups, and enhancing the formation of the semi-crystalline structure. Specifically, the catalyst is composed of cyano-containing polymeric carbon nitride nanorods, in which sulfur atoms are doped by replacing nitrogen atoms in the CNC bond of the backbone, and potassium ions are modified between the nanorod chains to jointly enhance the migration efficiency and light absorption capacity of photogenerated carriers. The catalyst has a hollow tubular microstructure with a rough surface. This structure can increase the contact area between the catalyst and the pollutants and promote multiple reflections and refractions of light inside the material, thereby improving light utilization efficiency. In terms of performance, the catalyst exhibits high photocatalytic activity in the visible light region.
[0042] In the catalyst, the polymerized carbon nitride nanorods are derived from melamine and thiourea precursors, with a mass ratio of melamine to thiourea of 8:2. This optimized mass ratio ensures uniform doping of sulfur and potassium elements, as well as the introduction of cyano groups, thereby improving the crystallinity and photocatalytic performance of the catalyst.
[0043] The rough-surfaced hollow tubular structure has porous features and a high specific surface area, which can promote the diffusion of reactant molecules and the separation of photogenerated electron-hole pairs. The structure is observed to be a uniform rod-shaped structure by transmission electron microscopy. Compared with traditional bulk carbon nitride, it has improved light absorption efficiency and enhanced charge separation ability. This is because the unique tubular design reduces the exciton Coulomb force binding and improves the exciton energy transfer efficiency, especially by generating singlet oxygen to accelerate pollutant degradation.
[0044] The catalyst preparation method includes the following steps: (1) Melamine, thiourea and partially molten salt mixture are mixed and ground to obtain precursor mixture. The molten salt mixture is composed of potassium chloride and lithium chloride monohydrate, with a fixed mass of 3.3g potassium chloride and 2.7g lithium chloride monohydrate, and the partially molten salt is 1 / 2 of the total molten salt mass. (2) The remaining molten salt, which is also 1 / 2 of the total molten salt mass, is mixed and ground, and then evenly coated on the precursor mixture to form a layered structure; (3) The mixture obtained in step (2) is subjected to thermal polycondensation reaction. After the reaction, the molten salt is removed by washing with water and dried to obtain the photocatalyst. The preparation method utilizes in-situ molten salt doping technology to control the doping process at different melting point stages, simplifying the traditional multi-step synthesis and improving production efficiency and product uniformity.
[0045] The grinding process employs both mechanical and manual methods, with a grinding time of 20 minutes, to ensure thorough mixing of the precursors and optimization of the crystal structure. The thermal polycondensation reaction is carried out at 550℃ for 5 hours with a heating rate of 10℃ / min. These conditions optimize the formation of the semi-crystalline structure and avoid performance degradation caused by over-polymerization.
[0046] In the molten salt mixture, the mass ratio of potassium chloride to lithium chloride monohydrate is fixed at approximately 1.22:1, i.e., 3.3g:2.7g. This ratio ensures the stability of the liquid environment and prevents deammoniation of carbon nitride during the thermal polycondensation process by releasing hydrogen chloride, while promoting the formation of potassium thiocyanate, thereby achieving co-doping of cyano groups and sulfur and potassium elements. The one-pot design of the method reduces costs and avoids additional doping steps, giving the catalyst high uniformity and reproducibility.
[0047] A method for treating pesticide wastewater includes the following steps: (1) Under light-protected conditions, the photocatalyst was mixed with wastewater containing pesticides and subjected to adsorption treatment to obtain a mixed solution; (2) Under visible light conditions, the mixture obtained in step (1) is subjected to photocatalytic reaction to degrade pollutants in wastewater.
[0048] The pesticide in the pesticide wastewater is imidacloprid, with an initial concentration of 10 mg / L, preferably 10 mg / L. The mass ratio of photocatalyst to pesticide is 80:1, preferably 60:1. This ratio ensures sufficient catalytic active sites while avoiding catalyst waste. The adsorption treatment time is 25 minutes to achieve the synergistic effect of adsorption-photocatalysis.
[0049] The visible light wavelength is greater than 420nm, and the light source is a xenon lamp. The photocatalytic reaction conditions include: a temperature of 40℃, a pH of 9, a rotation speed of 700rpm, and a time of 2 hours. These conditions optimize the photocatalytic efficiency and ensure the stability and repeatability of the reaction system, so that the removal rate remains at a high level during recycling.
[0050] In the recycling performance test, after five repeated experiments, the removal rate of imidacloprid remained above 75%, and the photocatalytic activity did not decrease. This performance is attributed to the semi-crystalline structure of the catalyst and the stability of the doped elements, which makes it have long-term application potential in the field of environmental photocatalysis.
[0051] Comparative Example 1 differs from Example 1 in that: in preparing the semi-crystalline polymerized carbon nitride nanorod composite photocatalyst, this comparative example did not use thiourea as a precursor, but only used melamine for thermal polycondensation. Specifically, the preparation method included: mixing and grinding 0.8g of melamine with a partially molten salt mixture, namely 1.65g of potassium chloride and 1.35g of lithium chloride monohydrate, for 5 minutes to obtain a precursor mixture, then covering it with the remaining molten salt, and thermally polycondensing it at 500°C for 4 hours, and finally washing and drying it with water to obtain the catalyst. This comparative example lacks the doping of sulfur and cyano groups, resulting in a blocky structure of the catalyst, a narrow light absorption range, and the inability to form a rough, hollow tubular feature, thereby reducing the photocatalytic activity and stability.
[0052] Comparative Example 2 differs from Example 2 in that: in this comparative example, lithium chloride monohydrate was not used in the molten salt mixture; only potassium chloride was used as the molten salt component. Specifically, the preparation method included: mixing and grinding 0.8g of melamine and 0.1g of thiourea with a portion of the molten salt, namely 3.3g of potassium chloride, without lithium chloride monohydrate, for 12.5 minutes, followed by thermal polycondensation under a covering. Other conditions were the same as in Example 2. Because this comparative example lacked lithium chloride monohydrate, it could not prevent the deammoniation of carbon nitride through the release of hydrogen chloride during the thermal polycondensation process, resulting in insufficient potassium thiocyanate formation, uneven doping of cyano and potassium elements, poor catalyst crystallinity, and low photogenerated carrier migration efficiency.
[0053] Comparative Example 3 differs from Example 3 in that: in this comparative example, a low-temperature short-time process is used in the thermal polycondensation reaction, specifically, the thermal polycondensation temperature is reduced to 400°C and the time is shortened to 2 hours, with the heating rate maintained at 10°C / min. This condition cannot provide a stable liquid environment, resulting in insufficient in-situ doping of the molten salt, failure of sulfur and potassium elements to be introduced into the carbon nitride framework, hindering the formation of the catalyst's semi-crystalline structure, and causing the surface to be rough and the hollow tubular features to be indistinct, thus reducing the photocatalytic performance.
[0054] Comparative Example 4 differs from Example 3 in that: this comparative example did not use a molten salt covering step in the preparation process, but simply mixed the precursor with the molten salt and then directly thermally polycondensed it. This comparative example lacks a layered covering structure, resulting in an uneven reaction environment, making it impossible to achieve in-situ doping. The catalyst structure is dense, with a small specific surface area and low light reflection and refraction efficiency, thus affecting the degradation effect of pollutants.
[0055] The performance of a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and methods are as follows: Transmission electron microscopy analysis: The morphology of the catalyst was observed using a JEOL JEM-F200 transmission electron microscope to evaluate the uniformity and pore characteristics of the surface rough hollow tubular structure, in order to verify the enhancing effect of the structure on light absorption.
[0056] X-ray diffraction analysis: The crystal structure and semi-crystalline properties of the catalyst were detected using a Bruker D8 Advance XRD analyzer. The degree of reduction in interlayer hydrogen bonds was assessed by the changes in diffraction peak intensity to ensure structural stability.
[0057] Fourier transform infrared spectroscopy analysis: using a Shimadzu IRTracer-100 spectrometer, at 2170 cm⁻¹ -1 The characteristic peak of cyano group was detected to confirm the effect of the dopant element introduction and to analyze the changes in chemical bonds.
[0058] Photocatalytic degradation test: Under visible light conditions greater than 420 nm, the catalyst was mixed with imidacloprid wastewater, and the removal rate within 60 minutes was determined by high performance liquid chromatography to evaluate the photocatalytic activity.
[0059] Cyclic stability test: Five repeated photocatalytic experiments were conducted, and the removal rate after each cycle was calculated to verify the reusability and durability of the catalyst.
[0060] X-ray photoelectron spectroscopy analysis: Thermo Fisher Scientific ESCALAB Xi+ XPS instrument was used to detect the 2p peaks of sulfur and potassium, analyze the elemental doping state and chemical environment, and confirm the effect of sulfur and potassium modification.
[0061] The test data of a semi-crystalline carbon nitride-based composite photocatalyst and its preparation method in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: By comparing and analyzing the data in the table, it can be seen that the semi-crystalline carbon nitride-based composite photocatalyst and its preparation method in Examples 1-3 exhibit superior performance compared to the semi-crystalline carbon nitride-based composite photocatalyst and its preparation method in Comparative Examples 1-4. This indicates that by employing a one-pot molten salt in-situ doping process and controlling the specific mass ratio of melamine to thiourea, uniform co-doping of sulfur, potassium, and cyano groups can be ensured during the precursor thermal polycondensation process, promoting the formation of a semi-crystalline structure and the construction of a rough-surfaced hollow tubular morphology. This preparation method improves the catalyst's absorption capacity for visible light and the migration efficiency of photogenerated carriers, and solves the crystal structure defect problem caused by uneven element distribution in traditional doping methods through layering. The covered molten salt addition method and controlled temperature rise program create a stable liquid reaction environment during the thermal polycondensation stage, promoting the formation of potassium thiocyanate and the consistency of elemental doping. This innovative process ensures excellent batch stability and process reproducibility of the catalyst, solving the performance difference problem caused by temperature fluctuations in traditional methods. The semi-crystalline polymerized carbon nitride nanorod composite photocatalyst prepared has a unique surface rough hollow tubular structure and optimized chemical composition, enabling it to maintain efficient adsorption-photocatalytic synergy under a wide range of environmental conditions. The catalyst exhibits excellent structural stability and active site retention during recycling, solving the technical problem of easy deactivation of traditional catalysts under complex water quality conditions.
[0062] By comparing and analyzing the relevant data in the table, it can be seen that the semi-crystalline carbon nitride-based composite photocatalyst and its preparation method of the present invention have superior comprehensive performance.
[0063] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0064] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A semi-crystalline carbon nitride-based composite photocatalyst, characterized in that: The catalyst is specifically designed for the photocatalytic degradation of environmental pollutants, particularly for the removal of imidacloprid in pesticide wastewater treatment. The catalyst is synthesized using a one-pot molten salt in-situ doping process. This process provides a stable liquid reaction environment during the thermal polycondensation of the precursor by the molten salt mixture, thereby enabling the simultaneous introduction of sulfur, potassium and cyano groups and enhancing the formation of the semi-crystalline structure. Specifically, the catalyst is composed of cyano-containing polymeric carbon nitride nanorods, wherein sulfur atoms are doped by replacing nitrogen atoms in the CNC bond of the backbone, and potassium ions are modified between the nanorod chains to jointly enhance the migration efficiency and light absorption capacity of photogenerated carriers. The catalyst has a hollow tubular microstructure with a rough surface, which increases the contact area between the catalyst and the pollutants and promotes multiple reflections and refractions of light within the material, thereby improving light utilization efficiency. In terms of performance, the catalyst exhibits high photocatalytic activity in the visible light region.
2. The semi-crystalline carbon nitride-based composite photocatalyst according to claim 1, characterized in that: In the catalyst, the polymerized carbon nitride nanorods are derived from melamine and thiourea precursors, wherein the mass ratio of melamine to thiourea is 8:0.5-2. This optimized mass ratio ensures uniform doping of sulfur and potassium elements, as well as the introduction of cyano groups, thereby improving the crystallinity and photocatalytic performance of the catalyst.
3. The semi-crystalline carbon nitride-based composite photocatalyst according to claim 1, characterized in that: The rough-surfaced hollow tubular structure has porous features and a high specific surface area, which can promote the diffusion of reactant molecules and the separation of photogenerated electron-hole pairs. The structure is observed to be a uniform rod-shaped structure by transmission electron microscopy. Compared with traditional bulk carbon nitride, it has improved light absorption efficiency and enhanced charge separation ability. This is because the unique tubular design reduces the exciton Coulomb force binding and improves the exciton energy transfer efficiency, especially by generating singlet oxygen to accelerate pollutant degradation.
4. The method for preparing a semi-crystalline carbon nitride-based composite photocatalyst according to claims 1-3, characterized in that: Includes the following steps: (1) Melamine, thiourea and a partially molten salt mixture are mixed and ground to obtain a precursor mixture. The molten salt mixture is composed of potassium chloride and lithium chloride monohydrate, with a fixed mass of 3.3g of potassium chloride and 2.7g of lithium chloride monohydrate, and the partially molten salt is 1 / 2 of the total molten salt mass. (2) The remaining molten salt, which is also 1 / 2 of the total molten salt mass, is mixed and ground, and then evenly covered on the precursor mixture to form a layered structure; (3) The mixture obtained in step (2) is subjected to thermal polycondensation reaction. After the reaction, the molten salt is removed by washing with water and dried to obtain the photocatalyst. The preparation method utilizes in-situ molten salt doping technology to control the doping process at different melting point stages, simplifying the traditional multi-step synthesis and improving production efficiency and product uniformity.
5. The method for preparing a semi-crystalline carbon nitride-based composite photocatalyst according to claim 4, characterized in that: The grinding process employs both mechanical and manual methods, with a grinding time of 5-20 minutes, to ensure thorough mixing of the precursors and optimization of the crystal structure. The thermal polycondensation reaction is carried out at 450-550℃ for 3-5 hours, with a heating rate of 6-10℃ / min. These conditions optimize the formation of the semi-crystalline structure and avoid performance degradation caused by over-polymerization.
6. The method for preparing a semi-crystalline carbon nitride-based composite photocatalyst according to claim 4, characterized in that: In the molten salt mixture, the mass ratio of potassium chloride to lithium chloride monohydrate is fixed at approximately 1.22:1, i.e., 3.3g:2.7g. This ratio ensures the stability of the liquid environment and prevents deammoniation of carbon nitride during the thermal polycondensation process by releasing hydrogen chloride, while promoting the formation of potassium thiocyanate, thereby achieving co-doping of cyano groups and sulfur and potassium elements. The one-pot design of the method reduces costs and avoids additional doping steps, giving the catalyst high uniformity and reproducibility.
7. A method for treating pesticide wastewater using the semi-crystalline polymerized carbon nitride nanorod composite photocatalyst according to any one of claims 1-3, characterized in that: Includes the following steps: (1) Under light-protected conditions, the photocatalyst is mixed with wastewater containing pesticides and subjected to adsorption treatment to obtain a mixed solution; (2) Under visible light conditions, the mixture obtained in step (1) is subjected to photocatalytic reaction to degrade pollutants in wastewater.
8. The semi-crystalline carbon nitride-based composite photocatalyst and its preparation method according to claim 7, characterized in that: The pesticide in the pesticide wastewater is imidacloprid, with an initial concentration of 2-10 mg / L, preferably 5-10 mg / L. The mass ratio of the photocatalyst to the pesticide is 20-80:1, preferably 40-60:
1. This ratio ensures sufficient catalytic active sites while avoiding catalyst waste. The adsorption treatment time is 15-25 minutes to achieve a synergistic effect of adsorption and photocatalysis.
9. The semi-crystalline carbon nitride-based composite photocatalyst and its preparation method according to claim 7, characterized in that: The visible light wavelength is greater than 420nm, and the light source is a xenon lamp. The conditions for the photocatalytic reaction include: temperature of 5-40℃, pH of 3-9, rotation speed of 500-700rpm, and time of 1-2 hours. These conditions optimize the photocatalytic efficiency and ensure the stability and repeatability of the reaction system, so that the removal rate remains at a high level during recycling.
10. The semi-crystalline carbon nitride-based composite photocatalyst according to claim 1, characterized in that: In the performance test of recycling, the catalyst maintained a removal rate of over 75% for imidacloprid after five repeated experiments, and its photocatalytic activity did not decrease. This performance is attributed to the semi-crystalline structure of the catalyst and the stability of the doped elements, giving it long-term application potential in the field of environmental photocatalysis.