Preparation method of thiourea functionalized covalent triazine framework material

Abstract

The invention relates to a preparation method of a thiourea functionalized covalent triazine framework material, and belongs to the technical field of catalysts. According to the method, the thiourea functionalized covalent triazine framework material with high photocatalytic efficiency and good stability is successfully prepared from a cyano monomer containing a thiourea group through a self-polymerization method, the preparation process is simple, complex equipment is not needed, the cost is controllable, and application in large-scale production is facilitated.

Description

Technical Field

[0001] The invention relates to a preparation method of a thiourea functionalized covalent triazine framework material, belonging to the technical field of catalysts. Background Art

[0002] The development of renewable and sustainable energy has become a global focus. Among them, the use of solar energy to drive photocatalysis to reduce oxygen to hydrogen peroxide is considered to be an energy-saving, efficient, safe and environmentally friendly strategy. Traditional semiconductor photocatalysts generally have problems such as insufficient light absorption capacity and low charge separation efficiency in the process of solar energy utilization, which leads to limited photocatalytic performance and makes it difficult to meet the needs of industrial applications. In contrast, organic semiconductor photocatalysts have attracted widespread attention due to their excellent visible light absorption capacity, adjustable energy level structure and simple synthesis method. Among them, covalent triazine organic frameworks (CTFs) have shown great potential in the field of solar-driven chemical transformation due to their good visible light response and excellent chemical and thermal stability. However, the CTFs materials prepared by the traditional cyano self-polymerization method mainly exist in a block form, which not only leads to a low specific surface area, making it difficult to fully expose the catalytic active sites, thereby limiting the progress of the catalytic reaction, but also aggravates the recombination of photogenerated carriers, reduces the separation efficiency of electron-hole pairs, and significantly reduces the utilization efficiency of solar energy. These defects greatly restrict the application of CTFs materials in energy and environmental fields such as photocatalytic synthesis of hydrogen peroxide.

[0003] In recent years, in order to overcome the structural limitations of bulk CTFs materials, researchers have proposed a series of morphology control strategies, such as preparing CTFs materials into nanosheets, nanotubes or ultra-thin layered structures to increase the specific surface area, improve the utilization of catalytic active sites, and promote the separation and migration of photogenerated carriers. In addition, supercritical fluid-assisted synthesis technology has also been widely used to prepare highly ordered nanoscale CTFs materials, such as Chinese patent CN109354697B, a method for preparing covalent organic framework materials in supercritical fluids. The method in this patent uses supercritical fluids (such as supercritical CO2 or ethanol) as reaction media. By precisely controlling the solubility, diffusion rate and chemical reaction conditions, the uniform nano-sizing of CTFs materials is achieved, and a porous structure is constructed at the same time, thereby significantly improving the photocatalytic performance. However, supercritical fluid-assisted synthesis technology has problems such as complex preparation process (precise control of parameters such as temperature and pressure in the synthesis process), strict equipment requirements (the equipment needs to operate under high temperature and high pressure conditions), and high cost (high equipment investment and maintenance costs), which limit its application in large-scale production. Therefore, exploring simpler, more efficient and low-cost preparation strategies to improve the photocatalytic performance of CTFs materials and promote their industrial application in the field of solar chemical utilization remains a key direction of current research. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing a thiourea-functionalized covalent triazine framework material. By self-polymerizing a cyano monomer containing a thiourea group, a thiourea-functionalized covalent triazine framework material with high photocatalytic efficiency and good stability is successfully prepared. The method has a simple preparation process, does not require complex equipment, has controllable costs, and is conducive to application in large-scale production.

[0005] To achieve the purpose of the present invention, the following technical solutions are provided.

[0006] A method for preparing a thiourea-functionalized covalent triazine framework material, wherein the material is prepared by self-polymerizing a cyano monomer containing a thiourea group; the specific steps are as follows:

[0007] (1) Mixing the cyano precursor 1,3-bis(4-cyanophenyl)thiourea and zinc chloride in an anhydrous and oxygen-free environment to obtain a solid powder;

[0008] The mass ratio of 1,3-bis(4-cyanophenyl)thiourea to zinc chloride is 1:2 to 1:6.

[0009] Preferably, grinding is used to mix uniformly.

[0010] The anhydrous and oxygen-free environment may adopt a glove box in the prior art in the field.

[0011] (2) The solid powder obtained in step (1) is placed in a vacuum environment and heated to 200° C. to 400° C., and calcined at a constant temperature for 4 h to 8 h, and then cooled to ambient temperature. The calcined solid product is ground into powder, washed with water to remove unpolymerized impurities, and the washed precipitate is dried to obtain a yellow powder, which is a thiourea-functionalized covalent triazine framework material.

[0012] Specifically, the solid powder obtained in step (1) is placed in a vacuum environment and heated by the following method:

[0013] Solid powder is added into a Pyrex glass tube, which is evacuated through a double-row tube and flame-sealed using a high-temperature torch. The Pyrex glass tube containing the solid powder is heated in a tube furnace.

[0014] The preferred heating rate is 3°C min -1 ~5℃min -1 .

[0015] Trifluoroethanesulfonic acid is preferably added during grinding so that the solid product is broken down into a powder.

[0016] The unpolymerized impurities are preferably removed by washing with water and washed to neutrality. The washed precipitate is dried to obtain a yellow powder, which is a thiourea-functionalized covalent triazine framework material.

[0017] Furthermore, a thiourea-functionalized covalent triazine framework material is added to water and mixed evenly, and then rapidly frozen with liquid nitrogen to crystallize the material, followed by freeze-drying to sublime the water molecules, thereby obtaining a yellow product, which is a thiourea-functionalized covalent triazine framework material with a nanoribbon structure.

[0018] The ratio of the mass (mg) of the thiourea functionalized covalent triazine framework material to the volume (mL) of water is 1:1-5.

[0019] Ultrasonic mixing is preferably used.

[0020] An application of the thiourea-functionalized covalent triazine framework nanomaterial of the present invention is to use it as a photocatalyst for photocatalytic production of hydrogen peroxide, and the material has high photocatalytic activity and stability.

[0021] Beneficial effects

[0022] (1) The present invention provides a method for preparing a thiourea-functionalized covalent triazine framework material. The method successfully prepares a thiourea-functionalized covalent triazine framework material with high photocatalytic efficiency and good stability by self-polymerizing a cyano monomer containing a thiourea group. The method has a simple preparation process, does not require complex equipment, has controllable costs, and is conducive to application in large-scale production.

[0023] (2) The present invention provides a method for preparing a thiourea-functionalized covalent triazine framework material. In step (1) of the method, the mass ratio of 1,3-bis(4-cyanophenyl)thiourea to zinc chloride is limited to 1-2:1-6. This is mainly because in the cyano group self-polymerization reaction, zinc chloride acts as a Lewis acid catalyst, coordinates with the cyano group, induces cyano group activation, and improves the reaction activity of the triazine reaction; at the same time, an appropriate amount of zinc chloride can effectively promote the cross-linking polymerization of the monomer, thereby improving the material to maintain a complete conjugated triazine skeleton, and improving the crystallinity and stability of the material. In addition, zinc chloride plays a role similar to a "sacrificial template", so that the material obtains a higher specific surface area and a porous structure.

[0024] Zinc chloride is a Lewis acid catalyst. If there is too much zinc chloride, it will lead to excessive cross-linking during the polymerization process, forming a dense structure, reducing the specific surface area, and reducing the catalytic and adsorption capacity of the material; if there is too little, the cyano group will be insufficiently activated, resulting in incomplete triazine reaction, low skeleton cross-linking degree, and reduced mechanical strength and stability of the material; too much 1,3-bis(4-cyanophenyl)thiourea will cause monomers that do not participate in the reaction to affect the purity of the material and even form by-products; too little 1,3-bis(4-cyanophenyl)thiourea will lead to insufficient introduction of thiourea groups, resulting in a weakening of the built-in electric field strength of the CTFs material, thereby inducing a decrease in the utilization efficiency of photogenerated electrons and holes.

[0025] (3) The present invention provides a method for preparing a thiourea-functionalized covalent triazine framework material. In step (2) of the method, the solid powder obtained in step (1) is placed in a vacuum environment and heated to 200°C to 400°C, and calcined at a constant temperature for 4h to 8h. This is not an adjustment of conventional technical means in this field. The inventors have found that appropriate temperature reaction helps zinc chloride activate the cyano group (-CN), inducing the ring closure reaction of the triazine ring, thereby forming a highly stable covalent triazine framework; at the same time, the vacuum environment helps to inhibit side reactions, improve the volatilization efficiency of zinc chloride, and avoid the formation of impurities such as zinc oxide; in addition, the appropriate time range can fully solidify the CTFs structure, improve its thermal stability, avoid structural collapse during subsequent use, and prevent excessive carbonization from causing a decrease in material conductivity or an increase in brittleness.

[0026] When the temperature is too high, the triazine skeleton will decompose, reducing the stability of the material; the thiourea group will thermally decompose, reducing the catalytic activity and selectivity; excessive carbonization will reduce the specific surface area and adsorption catalytic performance of the material; when the temperature is too low, the cyanide self-polymerization reaction is incomplete, resulting in an incomplete CTFs structure, low crosslinking, and poor mechanical strength and thermal stability of the material; the thiourea group is unevenly distributed, affecting the functionalization of the material and leading to poor catalytic activity; zinc chloride cannot be completely melted, resulting in excessive template residue, affecting the catalyst pore structure. When the calcination time is too long, it will cause local collapse of the skeleton, reducing the specific surface area of the material; the thiourea group will degrade, affecting the catalytic selectivity and stability; when the calcination time is too short, the structure is not fully solidified, and the zinc chloride may not be completely removed, affecting the pore structure; the thiourea group fails to fully bind to the CTFs framework, affecting the degree of functionalization.

[0027] (4) The present invention provides a method for preparing a thiourea functionalized covalent triazine framework material. In step (2), the heating rate is preferably 3°C min -1 ~5℃min -1This adjustment is not a conventional technical approach in the field. The inventors have discovered that controlling the heating rate can optimize and ensure a smooth material synthesis process, avoiding unnecessary side reactions. A slower heating rate ensures uniform reaction performance, preventing thermal stress or excessive temperature differences during heating, thereby ensuring the stability of the entire reaction system. By optimizing the heating rate, while controlling the heating rate, the effects of this thermal expansion can be effectively reduced, thereby maintaining a stable material structure.

[0028] When the heating rate is too high, various parts of the reaction system may be affected by uneven temperature, resulting in local high temperature, which may cause the reaction process to run away and even cause undesirable side reactions such as thermal decomposition, sintering or excessive carbonization. It may also cause catalysts such as zinc chloride (if not completely removed) to remain and affect the formation of the material's pore structure, resulting in a decrease in specific surface area or pore blockage, affecting the performance of the final material. The material may expand unevenly due to excessive temperature gradients, resulting in excessive internal stress, which in turn affects the structural integrity of the material. When the heating rate is too low, the heating process will be too long. Although it can ensure the uniformity of the reaction, it may cause the reaction time to be too long, resulting in energy waste and reduced efficiency. At the same time, too slow a heating time may cause some reactions to be incomplete or over-react under the action of too long, affecting the performance of the final material. In addition, too long a heating time may also reduce the stability of the material, affecting its performance in subsequent processing.

[0029] (5) The present invention provides a method for preparing a thiourea-functionalized covalent triazine framework material, wherein the method prepares a thiourea-functionalized covalent triazine framework material with a nano-belt structure by utilizing a freezing self-assembly technique, wherein the ratio of the mass (mg) of the thiourea-functionalized covalent triazine framework material to the volume (mL) of water is controlled to be 1:1 to 5, which is not an adjustment by conventional technical means in this field. The inventors have found that the freezing self-assembly technique is a method of spontaneously arranging the material molecules into a specific structure by freezing a solution or suspension. The solvent (water) in the solution will crystallize at low temperatures, causing the solute in the solution, i.e., the thiourea-functionalized covalent triazine framework precursor, to form a self-organized structure; the change in the volume of the ice crystals during the freezing process will promote the directional arrangement of the solid molecules, thereby precisely regulating the formation of the nanostructure, and controlling the morphology and pore structure of the material through the freezing and thawing process.

[0030] Within the appropriate dosage ratio, the material successfully self-assembles into a nanoribbon structure. This structure is primarily formed through water crystallization and the aggregation and alignment of precursor molecules during the freeze-self-assembly process. The nanoribbon structure helps increase the material's specific surface area and porosity, enhancing its activity and selectivity in catalytic reactions. Furthermore, the nanoribbon structure offers increased surface exposure, providing more reactive sites, particularly in catalytic reactions, and thus enhancing the material's catalytic ability. The material's structure also enhances the diffusivity of reactants and products during catalytic reactions, increasing reaction rate and efficiency. Furthermore, by adjusting the dosage ratio, the material's pore structure can be manipulated to achieve microporous / mesoporous structures suitable for catalytic reactions and adsorption. The nanoribbon structure's inherently high specific surface area significantly enhances adsorption and electrochemical energy storage performance. Finally, the presence of thiourea groups imparts a strong hydrophilicity and polarity to the material, enhancing its adsorption capacity for specific reactants in aqueous solutions. This helps evenly distribute the thiourea groups across the triazine framework, further enhancing the material's functionalization.

[0031] When the concentration of the thiourea-functionalized covalent triazine framework material is too low, the precursor molecules are unevenly distributed during freezing, resulting in incomplete self-assembly or the formation of irregular structures. Meanwhile, excessive water can cause ice crystals to grow too quickly, inhibiting the orderly arrangement of the precursor molecules and forming larger particles or uneven pore structures. Furthermore, nanoribbon structures may be difficult to form, and instead, more dispersed particles or other undesirable morphologies may be produced.

[0032] When the concentration of the thiourea-functionalized covalent triazine framework material is too high, the precursor cannot be effectively dispersed during freezing, and may instead form aggregates, resulting in an uneven structure. Excessively high mass ratios can cause the solvent (water) to crystallize too slowly, thereby affecting the material's self-assembly process, resulting in structural instability or the inability to form the desired nanoribbon morphology.

[0033] (6) The present invention provides a method for preparing a thiourea-functionalized covalent triazine framework material. The thiourea-functionalized covalent triazine framework material prepared by the method is modified with a thiourea functional group to increase the dipole moment of the material and promote the separation and migration of photogenerated charges. A strongly polar thiourea group is introduced into the CTFs structure, and its polar effect is utilized to induce the formation of a built-in electric field within the material surface, prompting photogenerated electrons to migrate to low-energy regions and photogenerated holes to move to high-energy regions, thereby effectively suppressing the rapid recombination of electron-hole pairs and significantly improving photocatalytic activity.

[0034] The introduction of thiourea groups enables the carbonyl (C=O) and sulfur (S) atoms in the molecular structure to act as additional electron acceptors or donors, thereby optimizing the electron cloud distribution of CTFs materials, reducing the band gap width, improving the absorption capacity of visible light, and further enhancing the photocatalytic performance.

[0035] The hydrophilic characteristics of the thiourea group enhance the interfacial wettability of the material, enabling it to exhibit better dispersibility and reactivity in the photocatalytic aqueous reaction system, providing a more favorable microenvironment for efficient photocatalytic processes.

[0036] (7) The invention provides a method for preparing a thiourea-functionalized covalent triazine framework material. The method can be further optimized to prepare the material with a nanoribbon structure, optimize the micromorphology, increase hydrophilicity, and promote the red shift of the light absorption edge to the visible light region, effectively enhance its light absorption capacity, and increase the H2O2 generation rate. The maximum catalytic activity of photocatalytic oxygen reduction to synthesize hydrogen peroxide can reach 3462.4 μmol h -1 g -1 , and the nanobelt structure can significantly improve the stability of the catalyst. After 16 hours of testing, the photosynthetic H2O2 catalytic performance did not show obvious attenuation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 These are the scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the bulk S-CTF and S-CTF nanobelts in Example 1.

[0038] Figure 2 These are the water contact angle test results of the bulk S-CTF and S-CTF nanobelts in Example 1.

[0039] Figure 3 This is the UV-visible spectra of the bulk S-CTF and S-CTF nanobelts in Example 1.

[0040] Figure 4 The electrochemical impedance curves of the bulk S-CTF and S-CTF nanobelts in Example 1 and CTF-1 in Comparative Example 1 are shown in FIG. Figure 4 a) and transient photocurrent spectrum ( Figure 4 b).

[0041] Figure 5 The photoluminescence spectra of the S-CTF nanobelts in Example 1 and the CTF-1 in Comparative Example 1 are shown in FIG. Figure 5 a) and steady-state surface photovoltage test results ( Figure 5 b).

[0042] Figure 6This is a graph showing the catalytic performance test results of the bulk S-CTF, S-CTF nanobelts in Example 1 and CTF-1 in Comparative Example 1 as photocatalysts.

[0043] Figure 7 The cyclic stability test diagram of the S-CTF nanobelt photocatalyst in Example 1 ( Figure 7 a) and long time test chart ( Figure 7 b). DETAILED DESCRIPTION

[0044] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but this does not limit the present invention.

[0045] Example 1

[0046] A method for preparing a thiourea-functionalized covalent triazine framework material, comprising the following steps:

[0047] (1) Add 170 mg of 1,3-bis(4-cyanophenyl)thiourea to 1020 mg of zinc chloride and grind rapidly for 30 min in an anhydrous and oxygen-free environment provided by a glove box to obtain a solid powder.

[0048] (2) The solid powder prepared in step (1) was added to a Pyrex glass tube, the Pyrex glass tube was evacuated through a double-row tube, and flame-sealed with a high-temperature torch. The Pyrex glass tube containing the solid powder was heated in a tube furnace at 5°C min -1 The mixture was heated to 300°C at a heating rate of 1000 °C, calcined at a constant temperature for 6 h, and then cooled to ambient temperature. The calcined solid product was ground into powder. Trifluoroethanesulfonic acid was added during grinding to decompose the solid product into powder. The product was washed 6 times with 3 L of deionized water to remove unpolymerized impurities and washed until neutral. The washed precipitate was dried to obtain a yellow powder product, which was recorded as bulk S-CTF.

[0049] (3) 50 mg of the yellow powder product prepared in step (2) was added to 150 mL of water and ultrasonically mixed, and then rapidly frozen with liquid nitrogen to crystallize the powder. The powder was then dried at -52 °C in a freeze dryer for 72 h to sublime the water molecules. The final product was a yellow nanomaterial, which was recorded as S-CTF nanobelt.

[0050] Example 2

[0051] (1) Add 170 mg of 1,3-bis(4-cyanophenyl)thiourea to 340 mg of zinc chloride and grind rapidly for 30 min in an anhydrous and oxygen-free environment provided by a glove box to obtain a solid powder.

[0052] (2) The solid powder prepared in step (1) was added to a Pyrex glass tube, the Pyrex glass tube was evacuated through a double-row tube, and flame-sealed with a high-temperature torch. The Pyrex glass tube containing the solid powder was heated in a tube furnace at 3°C min -1 The mixture was heated to 200°C at a heating rate of 1000 °C, calcined at a constant temperature for 4 hours, and then cooled to ambient temperature. The calcined solid product was ground into powder. Trifluoroethanesulfonic acid was added during grinding to decompose the solid product into powder. The product was washed 6 times with 3 L of deionized water to remove unpolymerized impurities and washed until neutral. The washed precipitate was dried to obtain a yellow powder product, which was recorded as bulk S-CTF.

[0053] (3) 50 mg of the yellow powder product prepared in step (2) was added to 50 mL of water and ultrasonically mixed uniformly. The product was rapidly frozen with liquid nitrogen to crystallize the powder, and then dried at -52 ° C. in a freeze dryer for 72 h to sublime the water molecules. The final product was a yellow nanomaterial, recorded as S-CTF nanobelt.

[0054] Example 3

[0055] A method for preparing a thiourea-functionalized covalent triazine framework material, comprising the following steps:

[0056] (1) Add 170 mg of 1,3-bis(4-cyanophenyl)thiourea to 1020 mg of zinc chloride and grind rapidly for 30 min in an anhydrous and oxygen-free environment provided by a glove box to obtain a solid powder.

[0057] (2) The solid powder prepared in step (1) was added to a Pyrex glass tube, the Pyrex glass tube was evacuated through a double-row tube, and flame-sealed with a high-temperature torch. The Pyrex glass tube containing the solid powder was heated in a tube furnace at 5°C min -1 The mixture was heated to 400°C at a heating rate of 1000 °C, calcined at a constant temperature for 8 h, and then cooled to ambient temperature. The calcined solid product was ground into powder. Trifluoroethanesulfonic acid was added during grinding to decompose the solid product into powder. The product was washed 6 times with 3 L of deionized water to remove unpolymerized impurities and washed until neutral. The washed precipitate was dried to obtain a yellow powder product, which was recorded as bulk S-CTF.

[0058] (3) 50 mg of the yellow powder product prepared in step (2) was added to 150 mL of water and ultrasonically mixed, and then rapidly frozen with liquid nitrogen to crystallize the powder. The powder was then dried at -52 °C in a freeze dryer for 72 h to sublime the water molecules. The final product was a yellow nanomaterial, which was recorded as S-CTF nanobelt.

[0059] Comparative Example 1 - Reference: Energy Environ. Sci., 2018, 11, 1617-1624

[0060] (1) 340 mg of 1,4-dicyanobenzene precursor was added to 720 mg of zinc chloride and rapidly ground for 30 min in an anhydrous and oxygen-free environment provided by a glove box to obtain a solid powder.

[0061] (2) The solid powder prepared in step (1) was added to a Pyrex glass tube, the Pyrex glass tube was evacuated through a double-row tube, and flame-sealed with a high-temperature torch. The Pyrex glass tube containing the solid powder was heated in a tube furnace at 5°C min -1 The mixture was heated to 300°C at a heating rate of 1000 °C, calcined at a constant temperature for 6 hours, and then cooled to ambient temperature. The calcined solid product was ground into powder. Trifluoroethanesulfonic acid was added during grinding to decompose the solid product into powder. The solid product was washed 6 times with 3 L of deionized water to remove unpolymerized impurities and washed until neutral. The washed precipitate was dried to obtain a final product as a yellow powder product, recorded as CTF-1.

[0062] Test Analysis

[0063] The products in Examples 1 to 3 and Comparative Example 1 were tested and analyzed as follows:

[0064] (1) Molecular structure characterization

[0065] The X-ray diffraction (Bruker D8 Advance, Germany, wavelength 0.154 nm, X-ray source Cu Kα), X-ray photoelectron spectroscopy (ULVAC-PHI 5000 Versaprobe III, Japan) and solid-state 13 C nuclear magnetic resonance spectrometer (Bruker AvanceⅢHD 700MHz, Germany, 13 CNMR) and other instruments to characterize the molecular structure of the test substance. First, XRD is used to determine the crystalline structure of the test substance, and XPS is used to analyze the elemental composition, element valence analysis and element semi-quantitative analysis of the binding energy of each element in the test substance. 13 C NMR obtains the chemical shift information of the C element of the desired test substance to determine the molecular structure and elemental composition of the material.

[0066] The yellow powder product prepared in step (2) of Examples 1 to 3, i.e., bulk S-CTF, and the final yellow nanomaterial prepared in step (3), i.e., S-CTF nanobelts, were tested. The results showed that a unit structure in the material is shown in the following formula (I):

[0067]

[0068] The material is composed of a plurality of repeated unit structures, wherein the broken bond of the N atom in the unit structure represents the connection position between one unit structure and the next unit structure. Therefore, it can be seen that the products prepared in steps (2) and (3) are both a thiourea-functionalized covalent triazine framework material.

[0069] The final yellow powder product prepared in Comparative Example 1, namely CTF-1, was tested. The results showed that a unit structure in the material was as shown in the following formula (II):

[0070]

[0071] The material is composed of a plurality of repeated unit structures, and the broken bonds in the unit structures represent the connection positions between one unit structure and the next unit structure.

[0072] (2) Microscopic morphology observation

[0073] Scanning electron microscope (Zeiss Supra 55, SEM, Japan), transmission electron microscope (HT7700, TEM, Japan High-Tech, Japan) and high-resolution transmission electron microscope (HT7700, HRTEM, Japan High-Tech, Japan) can be used to observe the nanomorphology, microstructure, micro-region composition and elemental composition of the desired test substance.

[0074] The bulk S-CTF and S-CTF nanobelts in Examples 1 to 3 were observed. The microscopic morphology of Example 1 is as follows: Figure 1 The SEM image of the bulk S-CTF shows a bulk structure, as shown in Figure 1 As shown in a, it has obvious agglomeration phenomenon, which is not very conducive to its dispersion and catalytic process in the aqueous reaction system. On the contrary, the covalent triazine framework material functionalized with thiourea after freezing self-assembly, namely S-CTF nanobelt, presents a nanobelt structure, as shown in Figure 1 (b) The nanoribbons have a width of 30 nm to 70 nm, which facilitates the adsorption of organic molecular dyes and the migration of photogenerated carriers during photocatalysis. Furthermore, the nanoribbons are dispersed in the aqueous reaction system, increasing the contact area between the catalyst and the reaction system.

[0075] Comparing the TEM images of bulk S-CTF and S-CTF nanoribbons, it can be seen that Figure 1 c and Figure 1d. S-CTF nanobelts exhibit a nanobelt structure, which is attributed to the fact that during the freezing self-assembly process, the bulk S-CTF is dispersed in an aqueous solution, and the water molecules act as a soft template to disperse the bulk. The S-CTF is then fixed through a rapid freezing process. As the ice crystals sublime, the S-CTF maintains its dispersed nanobelt structure, indicating that the bulk structure can change the microscopic morphology of the final S-CTF photocatalyst after nanosizing, thereby affecting its catalytic performance.

[0076] High-magnification TEM images, ambient dark-field TEM images, and TEM-Mapping images of S-CTF nanobelts are shown in the figure. Figure 1 As shown in Figure e, analysis shows that the S-CTF nanobelts are composed of C, N, and O, and are evenly distributed. Since the content of S in the precursor is extremely low, this may cause it to not be displayed in the mapping.

[0077] The results of bulk S-CTF and S-CTF nanobelts in Examples 2 and 3 are similar to those of the corresponding materials in Example 1.

[0078] (3) Water contact angle test

[0079] The water contact angle of the bulk S-CTF and S-CTF nanobelts in Examples 1 to 3 was tested using an Excellence Optical Contact Angle and Interfacial Tension Meter 602. The test conditions were as follows: 50 mg of powder sample was pressed into a tablet, placed on the test platform, 0.2 μL of water droplets were added, and the tablets were photographed with a high-speed camera to determine the water contact angle.

[0080] The test results of Example 1 are as follows Figure 2 As shown in the figure, the S-CTF nanobelts exhibit a smaller water contact angle, indicating that they have better water molecule adsorption ability in the aqueous reaction system. This may be attributed to the fact that during the frozen self-assembly process, O or OH in the water molecules are adsorbed on the surface of the material, and the smaller water contact angle will promote the catalytic process in the aqueous reaction system.

[0081] The results of bulk S-CTF and S-CTF nanobelts in Examples 2 and 3 are similar to those of the corresponding materials in Example 1.

[0082] (4) UV diffuse reflection test

[0083] The bulk S-CTF and S-CTF nanobelts in Examples 1 to 3 were subjected to UV diffuse reflectance tests using a Shimadzu UV-2600i instrument. The test conditions were as follows: 30 mg of powder sample was placed in a reactor with a quartz light window. The instrument test parameters were as follows: wavelength range: 300-800 nm, spectral band width: 0.5 nm, and scanning speed: 2000 nm / min.

[0084] The test results of Example 1 are as follows Figure 3 As shown in the figure, the absorption edge of S-CTF nanoribbons red-shifts to the visible light region, and the absorption edge can reach 600nm. This may be attributed to the fact that the nanoribbon structure causes a large number of defects and multiple scattering, resulting in a significant enhancement of its light absorption intensity in the entire spectral range.

[0085] The results of bulk S-CTF and S-CTF nanobelts in Examples 2 and 3 are similar to those of the corresponding materials in Example 1.

[0086] (5) Electrochemical impedance spectroscopy (EIS) and transient photocurrent testing

[0087] The bulk S-CTF and S-CTF nanobelts in Example 1 and the CTF-1 in Comparative Example 1 were tested using electrochemical impedance spectroscopy (EIS) and transient photocurrent. The EIS test instrument was Shanghai Chenhua 660+. The test conditions were as follows: a three-electrode system consisting of a reference electrode Ag / AgCl electrode, a counter electrode Pt sheet electrode, and a working electrode coated with a catalyst-containing FTO glass was tested. The working electrode was prepared as follows: 5 mg of the catalyst was dispersed in 1 mL of ethanol, 10 μL of a 5% mass fraction of Nafion solution was added, and ultrasonicated for 30 minutes to form a uniform slurry, which was then applied to the conductive surface of the FTO glass and dried naturally for later use. 0.5 M Na2SO4 solution was used as the electrolyte solution, and the air was removed with N2. Cyclic voltammetry (CV) was performed before the test to stabilize the working electrode. The test instrument parameter settings were as follows: the frequency was set to 0.1 Hz to 10,000 Hz, and the amplitude was set to 0.005 V.

[0088] The transient photocurrent test instrument is the Shanghai Chenhua 660e+Pfle IPCE 1000 photoelectrochemical test system. Test conditions: The test is carried out by a three-electrode system consisting of a reference electrode Ag / AgCl electrode, a counter electrode Pt sheet electrode, and a working electrode coated with a catalyst FTO glass. The preparation method of the working electrode is as follows: 5 mg of the catalyst is dispersed in 1 mL of ethanol, and then 10 μL of a 5% mass fraction Nafion solution is added, ultrasonicated for 30 minutes to form a uniform slurry, and applied to the conductive surface of the FTO glass. It is naturally dried and used for later use. 0.5M Na2SO4 solution is used as the electrolyte solution, and N2 is used to exclude air. Cyclic voltammetry (CV) is performed to scan before the test to stabilize the working electrode. Test instrument parameter settings: frequency is set to 0.1Hz~10000Hz, and amplitude is set to 0.005v. Test instrument parameter settings: voltage is set to 0.5V (relative to Ag / AgCl), and the scan rate is set to 5mV s -1 The illumination time window was 10 s. The photogenerated electron-hole migration efficiency in each material was tested.

[0089] Comparing the Nengquist radius of S-CTF nanoribbons and CTF-1, Figure 4 As shown in Figure a, S-CTF nanoribbons have a lower electrochemical impedance, which is attributed to the thiourea group as a polar unit, which promotes the separation and migration of photogenerated charges. In addition, compared with bulk S-CTF, S-CTF nanoribbons have a smaller curve radius, indicating that S-CTF nanoribbons have a lower electrochemical impedance. This is attributed to the lower resistance of photogenerated carrier transfer at the interface between the nanostructure and the electrolyte, which facilitates the transfer of photogenerated carriers between the interfaces.

[0090] In the transient photocurrent spectrum, Figure 4 As shown in Figure 2 (b), the photocurrent of S-CTF nanoribbons is significantly enhanced compared to that of bulk S-CTF and CTF-1. The larger photocurrent of S-CTF nanoribbons indicates that during light irradiation, more photogenerated charges migrate and separate, resulting in a larger current. The smaller electrochemical impedance and larger photocurrent intensity of S-CTF nanoribbons help improve the utilization efficiency of photogenerated electrons in the photocatalytic process and further promote the enhancement of photocatalytic activity.

[0091] The results of bulk S-CTF and S-CTF nanobelts in Examples 2 and 3 are similar to those of the corresponding materials in Example 1.

[0092] (6) Photoluminescence spectrum and steady-state surface photovoltage analysis

[0093] To investigate the efficient separation and migration of photogenerated carriers in S-CTF nanoribbons, photoluminescence spectroscopy and steady-state surface photovoltage analysis were performed on bulk S-CTF and S-CTF nanoribbons from Example 1, as well as CTF-1 from Comparative Example 1. The photoluminescence spectroscopy instrument was a Hitachi F-7000. Test conditions: 30 mg of powder sample was placed in a reactor equipped with a quartz window. Instrument parameters: wavelength range: 380 nm to 700 nm, spectral bandwidth: 0.5 nm, emission wavelength: 337 nm, scan speed: 1000 nm / min.

[0094] The steady-state surface photovoltage test instrument is a CEL-SPS1000 surface photovoltage spectrometer; test conditions: 80 mg of powder sample is pressed into a 1 cm × 2 cm sheet material and placed on the test bench; instrument test parameters: spectral wavelength range: 300 nm to 600 nm, spectral resolution: 2 nm.

[0095] After the photogenerated carriers jump, they will further undergo radiative transitions. When the carriers jump again, some of them will recombine and produce fluorescence. Therefore, the fluorescence intensity can measure the efficiency of photogenerated carrier separation. Comparing the photoluminescence intensity of S-CTF nanobelts and CTF-1, as shown in the figure, Figure 5As shown in Figure a, with the introduction of polar thiourea groups, the fluorescence of S-CTF nanobelts is rapidly quenched during the recombination of photogenerated carriers, resulting in a rapid decrease in fluorescence intensity. Therefore, S-CTF nanobelts have a high efficiency in photogenerated electron-hole separation.

[0096] The steady-state surface photovoltage test results are as follows: Figure 5 As shown in (b), the S-CTF nanobelts exhibited a strong photovoltage signal in the wavelength range of 350 nm to 450 nm, indicating that rapid charge transfer occurred on the surface of the S-CTF nanobelts under light conditions, indicating that the polar groups and frozen self-assembly synergistically optimized the photogenerated charge migration rate between S-CTF nanobelt molecules and promoted the orderly separation of photogenerated charges.

[0097] The results of bulk S-CTF and S-CTF nanobelts in Examples 2 and 3 are similar to those of the corresponding materials in Example 1.

[0098] (7) Photocatalyst photosynthetic hydrogen peroxide test

[0099] The test system for photocatalytic O2 reduction is based on a pure water system under saturated O2 conditions, without adding additional sacrificial agents and co-catalysts. The bulk S-CTF, S-CTF nanobelts in Example 1 and CTF-1 in Comparative Example 1 are used as photocatalysts, respectively.

[0100] In the test of photosynthetic hydrogen peroxide by photocatalyst, 10mg of photocatalyst was placed in a closed reactor, and oxygen was introduced. It was irradiated with a xenon lamp. Every 10 minutes, 2mL of liquid was taken and the solid catalyst was filtered with a filter membrane. Then, 2mL of Ce(SO4)2) solution with a concentration of 1mM was extracted and mixed. The H2O2 concentration was measured by UV-visible spectrometer. 4+ The light yellow solution undergoes a reduction reaction with H2O2 to generate Ce 3+ Colorless solution, the reaction chemical equation is: 2Ce 4+ +H2O2→2Ce 3+ +2H + +O2. Therefore, the Ce before and after the reaction can be measured by UV-visible spectrophotometer 4+ The concentration change can be used to indirectly calculate the generated H2O2 concentration: C(H2O2)=1 / 2×C(Ce 4+ ). Ce 4+ The ultraviolet absorption wavelength of the light yellow solution is 316nm. Figure 6 a is Ce 4+ UV-visible absorption spectrum after the reaction with S-CTF nanobelt photocatalyst to produce H2O2. Figure 6 As shown in a, as the photocatalytic reaction proceeds, the H2O2 concentration gradually increases and 4+A redox reaction occurs to generate colorless Ce 3+ solution, resulting in a decrease in its absorbance, and the performance of photosynthesis of H2O2 was calculated through the linear relationship between absorbance and H2O2 concentration.

[0101] Figure 6 b is the relationship between illumination time and photocatalytic performance when CTF-1, bulk S-CTF and S-CTF nanobelts are used as photocatalysts respectively. Figure 6 As shown in (b), the H2O2 concentration of the photocatalyst gradually increased with the increase of illumination time, indicating the reliability of the H2O2 concentration test method.

[0102] Figure 6 c shows the photocatalytic H2O2 synthesis performance of CTF-1, bulk S-CTF, and S-CTF nanobelts as photocatalysts, respectively, showing the H2O2 generation rate of the photocatalysts. The H2O2 generation rate of CTF-1 is 367.1 μmol h -1 g -1 After the introduction of polar thiourea groups, the H2O2 generation rate of bulk S-CTF reached 1374.8 μmol h -1 g -1 Compared with CTF-1, the performance is improved by 3.75 times. The excellent photocatalytic ability of bulk S-CTF is attributed to the efficient utilization of photoexcited charge carriers. After freeze self-assembly treatment, the photocatalytic performance of S-CTF nanobelts is improved to 3462.4 μmol h -1 g -1 , indicating that the frozen self-assembled optimized nanostructure promotes the improvement of light absorption capacity and the enhanced efficiency of photogenerated carrier utilization.

[0103] The results of bulk S-CTF and S-CTF nanobelts in Examples 2 and 3 are similar to those of the corresponding materials in Example 1.

[0104] (8) Cyclic stability test and long-term stability test

[0105] Material stability is an important parameter for determining photocatalytic performance. Cyclic stability and long-term stability tests were performed on the S-CTF nanobelts used as photocatalysts in Example 1. The test equipment and test conditions were the same as those used in the (7) test of the photocatalyst for photosynthesis of hydrogen peroxide.

[0106] Figure 7 a is a cyclic stability test diagram of S-CTF nanobelts as photocatalysts. The results show that after 4 cycle tests, the photocatalytic H2O2 production performance of S-CTF nanobelts did not show obvious attenuation, indicating that S-CTF nanobelts have good photochemical stability.

[0107] Figure 7b is a long-term test diagram of S-CTF nanobelts as a photocatalyst. The results show that S-CTF nanobelts exhibit a regular increase in H2O2 performance within 16 hours, further demonstrating that the material has good photocatalytic stability.

[0108] The results of the S-CTF nanobelts in Examples 2 and 3 were similar to those of the corresponding materials in Example 1.

Claims

1. A method for preparing a thiourea-functionalized covalent triazine framework material, characterized in that: (1) mixing a cyano precursor 1,3-bis(4-cyanophenyl)thiourea and zinc chloride at a mass ratio of 1:2 to 1:6 in an anhydrous and oxygen-free environment to obtain a solid powder; (2) The solid powder is placed in a vacuum environment and heated to 200°C to 400°C for constant calcination for 4h to 8h, then cooled to ambient temperature, the calcined solid product is ground into powder, washed with water, and the precipitate obtained by washing is dried to obtain a thiourea-functionalized covalent triazine framework material.

2. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 1, characterized in that: In step (1), grinding and mixing are performed uniformly.

3. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 1, characterized in that: In step (2), the specific method of placing the solid powder in a vacuum environment for heating is as follows: adding the solid powder to a Pyrex glass tube, evacuating the Pyrex glass tube through a double-row tube, flame-sealing the Pyrex glass tube with a high-temperature torch, and heating the Pyrex glass tube containing the solid powder in a tube furnace.

4. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 1, characterized in that: In step (2), the heating rate is 3°C min -1 ~5℃min -1 .

5. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 1, characterized in that: In step (2), trifluoroethanesulfonic acid is added during grinding.

6. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 1, characterized in that: In step (2), the unpolymerized impurities are removed by washing with water and the mixture is washed to neutrality.

7. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 1, characterized in that: In step (2), the specific method of placing the solid powder in a vacuum environment for heating is as follows: adding the solid powder to a Pyrex glass tube, evacuating the Pyrex glass tube through a double-row tube, flame-sealing the Pyrex glass tube with a high-temperature torch, and heating the Pyrex glass tube containing the solid powder in a tube furnace; The heating rate is 3℃min -1 ~5℃min -1 ; Add trifluoroethanesulfonic acid during grinding; The unpolymerized impurities were removed by washing with water and the mixture was washed to neutrality.

8. The method for preparing a thiourea functionalized covalent triazine framework material according to any one of claims 1 to 7, characterized in that: A thiourea-functionalized covalent triazine framework material is added to water and mixed evenly, and then rapidly frozen by liquid nitrogen and freeze-dried to obtain a thiourea-functionalized covalent triazine framework material with a nanoribbon structure; The ratio of the mass mg of the thiourea functionalized covalent triazine framework material to the volume mL of water is 1:1 to 5.

9. The method for preparing a thiourea functionalized covalent triazine framework material according to claim 8, characterized in that: Ultrasonic mixing was used to mix evenly.

10. Use of a thiourea-functionalized covalent triazine framework nanomaterial according to any one of claims 1 to 9, characterized in that: The application is to use the photocatalyst to produce hydrogen peroxide through photocatalysis.

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