Triazinyl conjugated polymer containing benzodithiazole unit as well as preparation method and application of triazinyl conjugated polymer

Abstract

The invention relates to a triazinyl conjugated polymer of a benzodithiazole unit, which is characterized in that the triazinyl conjugated polymer has the following structure: # imgabs0 #, and in different structural units of the triazinyl conjugated polymer, R groups are independently-CN or-CO-NH2. A benzodithiazole unit is adopted to replace traditional aryl to serve as a conjugated link unit of a covalent triazine framework (CTFs), and the CTFs with high photocatalytic hydrogen production activity can be obtained by means of the better photoelectric property of benzodithiazole; furthermore, the unreacted cyano group in the polymer is hydrolyzed to be converted into the acylamino group, so that the effect of remarkably improving the photocatalytic hydrogen production rate of the CTFs is achieved. The scheme provided by the invention has a good application prospect in photocatalytic water desorption of hydrogen.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic hydrogen evolution, and particularly relates to a triazine-based conjugated polymer with photocatalytic hydrogen evolution function and a preparation method thereof. Background Art

[0002] Hydrogen energy is a new energy source with abundant sources, clean products, high calorific value, and large production capacity. Photocatalytic hydrogen evolution reaction is a technology that can produce high-purity hydrogen and has broad application prospects. Organic conjugated polymers can change their photocatalytic properties by adjusting their structure. Therefore, the development of organic conjugated polymer photocatalysts with high catalytic performance will promote the hydrogen energy industry and reduce environmental pollution. Traditional photoelectrocatalytic hydrogen evolution catalysts include inorganic semiconductor nanomaterials such as TiO2 and CdS. However, traditional photocatalytic hydrogen evolution catalysts have the problem that the larger the band width and the larger the transition energy, the less likely electrons are to be excited. Providing a new photocatalytic water hydrogen production material with a low band gap width and continuously adjustable optical properties will help solve this problem.

[0003] Organic conjugated polymers have attracted considerable attention due to their tunable structure and function, low cost, and excellent optical stability. Research has shown that constructing electron push-pull effects is also an effective method for improving photocatalytic performance. For example, Cheng et al. prepared a series of donor-acceptor photocatalysts incorporating strong electron-withdrawing fluorine atoms, such as the linear conjugated polymers B-FOBT-1,4-E and B-FOBT-1,3,5-E. Their design strategy involved the simultaneous introduction of electron-donating methoxy groups and electron-withdrawing fluorine atoms into the benzodithiophene (BT) backbone. The results showed that the hydrogen production was 3.1 and 28.8 times greater than that of the fluorine-free polymers, respectively. In 2014, Lotsch et al. reported a covalent triazine framework compound (CTF) with photocatalytic water splitting activity. This marked the first application of triazine ring-containing COFs in photocatalytic hydrogen production. Covalent triazine frameworks (CTFs) are nitrogen-rich covalent organic frameworks with aromatic triazine rings as the basic linking units. Due to its π-conjugated structure, CTFs can effectively improve the charge transfer efficiency in the conjugated system. At the same time, the triazine ring structure of CTFs is rich in nitrogen, which provides CTFs with more active sites and is also beneficial to improving its photocatalytic hydrogen evolution activity.

[0004] The conjugated linking units of existing covalent triazine framework (CTFs) polymers are mainly benzene rings or other aromatic groups. Although the aromatic groups themselves have a conjugated π-electron system, their electronic structure may not be flexible enough, resulting in their wide bandgap limiting visible light absorption and failing to effectively promote charge separation and transfer. Therefore, the photocatalytic hydrogen evolution activity of the existing covalent triazine framework polymers still needs to be improved. Summary of the Invention

[0005] (1) Technical issues to be solved

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a triazine-based conjugated polymer containing benzodithiazole units, a preparation method and application thereof, which uses benzodithiazole units to replace traditional aromatic groups as conjugated linking units of covalent triazine framework polymers, and utilizes the excellent photoelectric properties of benzodithiazole to obtain triazine-based conjugated polymers with high photocatalytic hydrogen production activity; furthermore, the present invention also hydrolyzes the unreacted cyano groups in the polymer to convert them into amide groups, thereby significantly improving the photocatalytic hydrogen production rate of the product.

[0007] The invention also relates to a preparation method and application of the triazine-based conjugated polymer.

[0008] (2) Technical solution

[0009] In a first aspect, the present invention provides a triazine-based conjugated polymer of benzodithiazole units having the following structure:

[0010]

[0011] Wherein, in different structural units of the triazine-based conjugated polymer, the R group is independently -CN or -CO-NH2.

[0012] All R groups in the triazine-based conjugated polymer are -CN, or all R groups are -CO-NH2, or the R groups in some structural units of the triazine-based conjugated polymer are -CN, while the R groups in another part of the structural units are -CO-NH2; preferably, the proportion of R groups in the triazine-based conjugated polymer that are -CO-NH2 accounts for more than 30% of the total number of R groups, preferably more than 50%.

[0013] In a second aspect, the present invention provides a method for preparing a triazine-based conjugated polymer containing a benzodithiazole unit, the preparation method comprising: synthesizing a monomer A using 4-cyanobenzaldehyde and 2,5-diamino-1,4-benzenedithiol dihydrochloride as raw materials; and subjecting the monomer A to condensation polymerization to obtain a triazine conjugated polymer Th-CTF. The reaction scheme is shown as follows:

[0014]

[0015] During the above reaction process, the -CN at the A-terminal ends of the three monomers are condensed to form a triazine group, but the -CN at the A-terminal ends of some monomers do not participate in the condensation reaction and are retained.

[0016] According to a preferred embodiment of the present invention, during the synthesis of monomer A, the solvent is anhydrous ethanol. After heating and reflux reaction for a period of time under stirring, hydrogen peroxide is added to continue the reaction. After the reaction is completed, the reaction liquid is cooled, the product is centrifuged and separated, and the product is washed with anhydrous ethanol and dried to obtain monomer A.

[0017] Preferably, during the synthesis of monomer A, the molar ratio of 4-cyanobenzaldehyde to 2,5-diamino-1,4-benzenedithiol dihydrochloride is 2:1, the concentration of 4-cyanobenzaldehyde in the reaction system is 30-40 mM; and the amount of hydrogen peroxide added is 6-8 times the molar amount of 2,5-diamino-1,4-benzenedithiol dihydrochloride.

[0018] Preferably, during the synthesis of monomer A, the reaction temperature is 75°C-80°C, first stirred and heated under reflux at this temperature for 1-2 hours, then hydrogen peroxide is added and the reaction is continued at this temperature for 0.5-1 hour, and then naturally cooled to room temperature. The product is centrifuged and separated, and the product is washed with anhydrous ethanol and dried at 50-80°C to obtain monomer A.

[0019] According to a preferred embodiment of the present invention, the reaction conditions of the condensation polymerization are as follows: monomer A and trifluoromethanesulfonic acid are placed in a sealed reactor and sealed, and placed at 115-125°C for a constant temperature reaction for 6-12 hours. After the reaction is completed, the reaction system is cooled to room temperature, the reaction solution is neutralized with alkali to neutrality, the product is centrifuged, washed with distilled water and anhydrous ethanol in sequence, and dried to obtain a triazine-based conjugated polymer containing benzodithiazole units, which is recorded as Th-CTF.

[0020] Preferably, 5 mL of trifluoromethanesulfonic acid is used for every 100 mg of monomer A. The reaction temperature is preferably 120°C, and the reaction time is preferably 8 hours. Trifluoromethanesulfonic acid catalyzes the polymerization of the cyano groups of three adjacent monomers A, producing a triazine polymer. Preferably, the drying temperature is 60-80°C, such as 65°C, and the drying time is 8-16 hours, preferably 12 hours. Anhydrous potassium carbonate or sodium carbonate is preferably used as the base.

[0021] According to a preferred embodiment of the present invention, the preparation method further comprises: hydrolyzing the residual -CN at the terminal of the triazine conjugated polymer Th-CTF to convert it into an amide group.

[0022] Preferably, the method for hydrolyzing the terminal residual -CN in the triazine conjugated polymer Th-CTF to convert it into an amide group is as follows: dispersing the triazine conjugated polymer Th-CTF in a reaction vessel containing 10-15M concentrated hydrochloric acid, sealing the reaction vessel, and ultrasonically treating at 28-35 ° C for 30-40 min. After adding deionized water, the reaction is continued at 28-35 ° C for 15-30 min, and then transferred to 0-4 ° C for 30-40 min; thereafter, the reaction solution is neutralized with an alkali (anhydrous sodium carbonate or anhydrous potassium carbonate) to neutrality, the product is separated by high-speed centrifugation, and the product is washed with water and anhydrous ethanol for more than 4 times, and then dried to obtain a modified material Th-CTF-amide in which the residual cyano group in the triazine conjugated polymer Th-CTF is completely or partially converted into an amide group.

[0023] Preferably, the method for hydrolyzing the terminal residual -CN in the triazine conjugated polymer Th-CTF to convert it into an amide group is as follows: the triazine conjugated polymer Th-CTF is dispersed in a reaction vessel containing 12M concentrated hydrochloric acid, the reaction vessel is sealed, and ultrasonically treated at 60HZ for 30 minutes in a 30 ° C water bath, and deionized water 3-5 times the volume of concentrated hydrochloric acid is added, and the reaction is continued in a 30 ° C water bath for 20 minutes, and then transferred to an ice-water mixed bath for 30 minutes; thereafter, in an ice-water mixed bath, the reaction solution is neutralized with anhydrous potassium carbonate to neutrality, the product is centrifuged at 6000 rpm, and the product is washed 6 times with water and anhydrous ethanol, and then dried in an oven at 65 ° C for 8 hours to obtain a modified material Th-CTF-amide in which the residual cyano group in the triazine conjugated polymer Th-CTF is completely or partially converted into an amide group.

[0024] Preferably, the conversion rate of the residual cyano groups in the triazine conjugated polymer Th-CTF into amide groups reaches above 30%, preferably 100%.

[0025] In traditional methods, after triazine polymers are prepared through trifluoromethanesulfonic acid-catalyzed cyano polymerization, the unreacted residual cyano groups in the material are not treated. In the present invention, the residual cyano groups in the triazine conjugated polymer Th-CTF are converted into amide groups, which can achieve unexpected technical effects. The photocatalytic hydrogen evolution rate of the product after conversion to amide groups is more than four times that of the unconverted polymer.

[0026] In a third aspect, the present invention provides the use of the triazine-based conjugated polymer containing benzodithiazole units as a photocatalytic hydrogen evolution catalyst.

[0027] (3) Beneficial effects

[0028] (1) The triazine conjugated polymer Th-CTF provided by the present invention is a covalent triazine framework polymer with benzodithiazole units as conjugated linking units. It is a special organic framework material. It uses benzodithiazole groups as linking units, which enriches the types of linking units in structure. In addition, the benzodithiazole groups have excellent photoelectric properties, so that the photocatalytic hydrogen production rate of the triazine conjugated polymer Th-CTF before hydrolysis cyanide modification can reach 4.80mmol / g·h, which is better than most of the currently reported photocatalytic hydrogen evolution catalysts, such as graphite phase carbon nitride (g-C3N4) and traditional covalent triazine framework materials with aromatic groups as conjugated linking units.

[0029] (2) After obtaining the covalent triazine framework polymer Th-CTF with benzodithiazole units as conjugated linking units, the present invention further hydrolyzes the terminal residual -CN in the covalent triazine framework polymer under high concentration acid to convert it into an amide group, thereby obtaining an amide group-modified covalent triazine framework polymer Th-CTF-amide, the photocatalytic hydrogen production rate of which increases to 19.21 mmol / g·h, which is more than 4 times that of the amide group-modified covalent triazine framework polymer. In addition, the absorption range of Th-CTF-amide is extended to 641 nm (wider than the 600 nm absorption range of the covalent triazine framework polymer Th-CTF before modification). The AC impedance of Th-CTF-amide is much smaller than that of Th-CTF, and it has higher charge separation efficiency, higher HOMO and lower LUMO. It can be seen that the introduction of amide groups significantly enhances the hydrogen evolution performance of Th-CTF-amide. This discovery provides a new idea for improving the photocatalytic hydrogen evolution activity of covalent triazine framework materials.

[0030] In summary, the two covalent triazine framework polymers Th-CTF and covalent triazine framework polymer Th-CTF-amide provided by the present invention have good application potential in photocatalytic water splitting to produce hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The infrared spectra of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0032] Figure 2 XRD patterns of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0033] Figure 3 SEM images of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0034] Figure 4UV-visible diffuse reflectance spectra (A) and bandgap width diagram (B) of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0035] Figure 5 The cyclic voltammetry curves of the covalent triazine framework polymer Th-CTF (A) and Th-CTF-amide (B) are shown.

[0036] Figure 6 Energy level diagram of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0037] Figure 7 Transient photocurrent response diagram of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0038] Figure 8 EIS spectra of covalent triazine framework polymers Th-CTF and Th-CTF-amide.

[0039] Figure 9 The photocatalytic water decomposition hydrogen production-time curves of covalent triazine framework polymers Th-CTF and Th-CTF-amide. DETAILED DESCRIPTION

[0040] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0041] Example 1

[0042] This example synthesizes a covalent triazine framework polymer material with benzodithiazole units as conjugated linking units. The preparation process includes: synthesizing monomer A using 4-cyanobenzaldehyde and 2,5-diamino-1,4-benzenedithiol dihydrochloride as raw materials, condensing and polymerizing monomer A to obtain a triazine conjugated polymer Th-CTF, and characterizing the structure and properties of the polymer. The preparation method is as follows:

[0043] (1) Synthesis of Monomer A

[0044] 103.36 mg of 4-cyanobenzaldehyde, 96.64 mg of 2,5-diamino-1,4-benzenedithiol dihydrochloride, and 25 mL of anhydrous ethanol were placed in a 100 mL three-necked flask to prepare a mixed reaction system. The mixed reaction system was heated to reflux at 75-80°C while stirring for 1.5 hours. Five drops of 30% hydrogen peroxide were then added and the reaction was continued for 0.5 hours before terminating. The product was cooled naturally to room temperature, centrifuged, washed with anhydrous ethanol, and dried in an oven at 65°C for 4 hours to obtain monomer A. The reaction process is shown below:

[0045]

[0046] (2) Preparation of covalent triazine framework polymers

[0047] 100 mg of monomer A and 5 mL of trifluoromethanesulfonic acid were added to a 15 mL pressure-resistant bottle, the bottle mouth of the pressure-resistant bottle was sealed with raw tape, and the reaction was carried out in a 120°C oil bath for 8 hours. After the reaction, the system was cooled to room temperature and neutralized with anhydrous potassium carbonate to a pH value of 7. The product was centrifuged and washed with distilled water and anhydrous ethanol. After drying in a 65°C oven for 10 hours, a covalent triazine framework polymer was obtained, which was recorded as Th-CTF. Among them, trifluoromethanesulfonic acid can catalyze the polymerization of the cyano groups of three adjacent monomers A to produce a triazine polymer. The reaction process is shown as follows:

[0048]

[0049] Example 2

[0050] In this example, the covalent triazine framework polymer Th-CTF prepared in Example 1 was further hydrolyzed in a high-concentration acid solution to convert the residual -CN therein into amide groups, thereby obtaining an amide-modified covalent triazine framework polymer, designated as Th-CTF-amide.

[0051] The synthesis method of the polymer Th-CTF-amide is as follows: 100 mg of the covalent triazine framework polymer Th-CTF is placed in a 100 mL round-bottom flask, 25 mL of 12 M concentrated hydrochloric acid is added, the round-bottom flask is sealed with a sealing film, and the system is placed in a 30°C water bath and sonicated at 60 Hz for 0.5 h. After adding 100 mL of deionized water, the system is reacted in the water bath for 20 min, and finally the system is placed in an ice-water mixed bath for 30 min. In the ice-water mixed bath, the reaction solution is neutralized with anhydrous potassium carbonate until neutral, centrifuged at 6000 rpm, and the product is isolated. The precipitate is washed six times with water and anhydrous ethanol, and finally, the product is dried in a 65°C oven for 8 h to obtain the amide-modified covalent triazine framework polymer Th-CTF-amide. The reaction process is expressed as follows:

[0052]

[0053] After the hydrolysis treatment, at least 30% of the residual -CN in the covalent triazine framework polymer Th-CTF is converted into amide groups. Because -CN is a relatively stable group under neutral and weakly acidic conditions, only a very small amount of -CN in the covalent triazine framework polymer Th-CTF is likely to undergo hydrolysis and conversion to amides during conventional photoelectrocatalytic water desorption and hydrogenation reactions. The present invention utilizes conditions such as high-concentration hydrochloric acid, water bath sonication, and an ice-water mixed bath reaction to convert 30%-100% of the residual -CN in the covalent triazine framework polymer Th-CTF into amide groups.

[0054] The covalent triazine framework polymer Th-CTF prepared in Example 1 and the amide-modified covalent triazine framework polymer Th-CTF-amide prepared in Example 2 were subjected to infrared detection, X-ray diffraction detection, electron microscopy, UV-visible diffuse reflectance detection, cyclic voltammetry, energy level analysis, photoelectric detection, AC impedance analysis, and photocatalytic hydrogen production rate testing. The results of the aforementioned tests and analyses are as follows:

[0055] (1) Infrared detection

[0056] Depend on Figure 1 The infrared spectrum shows that at 1550cm -1 and 1400cm -1 Both Th-CTF and Th-CTF-amide showed strong absorption peaks, corresponding to the stretching vibrations of C=N and CN, respectively. This indicates that the cyano group in the monomer underwent cyclotrimerization. -1 ~1700cm -1 The strong absorption peak corresponds to the thiazole ring. It can also be seen from the figure that at 2200 cm -1 There is an inconspicuous small peak at 900°, which is the stretching vibration absorption peak of C=N bond. This shows that there is still a small amount of unreacted -C=N (cyano group) in the material Th-CTF. The Th-CTF-amide material obtained after concentrated hydrochloric acid treatment in Example 2 still has a weak characteristic peak in this range, indicating that the C=N in the material Th-CTF-amide is not completely hydrolyzed, and 900° -1 ~1600cm -1 The characteristic peaks of triazine ring and phenylene in the range of 3000 cm-1 and 3000 cm-2 have almost no change, indicating that the triazine skeleton of Th-CTF-amide material remains stable in acid. -1 There is a characteristic peak around 1600 cm, which is attributed to NH. Because C=O is combined with the thiazole ring, it -1 ~1700cm -1 The absorption peak intensity of Th-CTF is higher than that of Th-CTF.

[0057] (2) X-ray diffraction detection

[0058] Depend on Figure 2 As can be seen, the polymer Th-CTF prepared in Example 1 and the polymer Th-CTF-amide prepared in Example 2 exhibit broad peaks at 15° to 35°, indicating that both polymers are amorphous. Data analysis indicates that ultrasonication in a strong acid environment does not alter the material's crystalline form.

[0059] (3) Electron microscopy observation

[0060] Depend on Figure 3 As can be seen from the electron microscope image a, the material Th-CTF presents an irregular block-shaped particle accumulation morphology, while Figure 3 As can be seen from b, the polymer Th-CTF-amide can be clearly seen to have protrusions on the surface of the material, indicating that the material Th-CTF-amide has a certain crystal morphology.

[0061] (4) UV-visible diffuse reflectance detection

[0062] Depend on Figure 4 As can be seen from Figure A, which is a UV-visible diffuse reflectance graph, the absorption curve of the polymer material Th-CTF shows some absorption across the entire visible light range, with a particularly pronounced absorption peak between 400 and 600 nm. The absorption curve of the polymer Th-CTF-amide also covers the entire visible light range, with significant absorption between approximately 400 and 641 nm. This indicates that the polymer Th-CTF-amide is more efficient in utilizing sunlight than the polymer Th-CTF. Therefore, the hydrolysis of the cyanide group to an amide group increases the wavelength range of sunlight available for photocatalysis. Figure 4 Figure B is the bandgap width diagram of the polymers Th-CTF and Th-CTF-amide. According to the figure, it can be observed that the curve of the material Th-CTF intersects the horizontal axis at approximately 2.36eV, and the curve of the material Th-CTF-amide intersects the horizontal axis at approximately 2.16eV. These intersections correspond to the optical band gaps (bandgap widths) of the two materials. Among them, the bandgap width of the material Th-CTF is approximately 2.36eV. The bandgap width of the material Th-CTF-amide is approximately 2.16eV. This means that Th-CTF-amide has a smaller bandgap width than Th-CTF, and electrons are more easily excited.

[0063] (5) Cyclic voltammetry test

[0064] Figure 5Figures A and B show the current responses of the polymeric materials Th-CTF and Th-CTF-amide at different potentials, respectively. Cyclic voltammetry analysis shows that the band gap of the Th-CTF material is 1.295 eV. The band gap of the Th-CTF-amide material is 1.088 eV. This indicates that the Th-CTF-amide material has a smaller band gap, which means that it may undergo electronic transitions at lower energies, thereby exhibiting better light absorption performance or a wider spectral response range. Within the same potential range, the current response of the Th-CTF material is relatively small, especially during the forward scan, where the current increases more slowly. Within the same potential range, the current response of the Th-CTF-amide material is significantly larger, especially during the forward scan, where the current increases rapidly. This indicates that the current response of Th-CTF-amide is stronger at the same potential, suggesting that its charge transport ability and conductivity may be superior to those of Th-CTF. The CV curve of the Th-CTF material shows a relatively gentle upward trend. The CV curve of Th-CTF-amide also shows an upward trend, but with a steeper slope and a more pronounced current increase at higher potentials, potentially suggesting stronger redox activity. This suggests that Th-CTF-amide exhibits more active redox behavior, likely related to the amide groups in its molecular structure, which can provide additional electron donor or acceptor capabilities.

[0065] (6) Energy level analysis

[0066] The HOMO and LUMO values of a material determine its oxidation and reduction abilities. The higher the LUMO energy value, the better its reducing ability, and the lower the HOMO energy value, the better its oxidizing ability.

[0067] Depend on Figure 6 The energy level diagram analysis shows that the LUMO value of the material Th-CTF is 0.29 lower than the reduction potential of H*. At the same time, the HOMO value of Th-CTF is 0.29 lower than that of O 2- The oxidation potential of Th-CTF-amide is 2.62 higher. The LUMO value of Th-CTF-amide is 1.06 lower than the reduction potential of H*. At the same time, the HOMO value of Th-CTF is 2- The oxidation potential of Th-CTF-amide is higher. Therefore, the HOMO and LUMO of Th-CTF-amide are higher than those of Th-CTF. Therefore, the driving force for water decomposition of Th-CTF-amide is stronger than that of Th-CTF.

[0068] The LUMO value of Th-CTF-amide (1.3 eV) is indeed lower than that of Th-CTF (1.51 eV), and the HOMO value of Th-CTF-amide (-0.86 eV) is indeed slightly lower than that of Th-CTF (-0.85 eV), rather than higher.

[0069] (7) Photoelectric detection

[0070] like Figure 7 As shown in Figure 1, the transient photocurrent response diagram of the polymer materials Th-CTF and Th-CTF-amide. Figure 7 The photocurrent graph shows that the photocurrent response of the polymer material Th-CTF-amide is greater than that of the polymer Th-CTF. The photocurrent value of the polymer material Th-CTF-amide is calculated to be 6.63 μA.cm -2 , while the photocurrent value of the polymer material Th-CTF is 1.65μA.cm -2 ; It is only 1 / 4 of the polymer material Th-CTF-amide.

[0071] (8) AC impedance analysis

[0072] See also Figure 8 Figure 2 shows the electrochemical impedance spectroscopy (EIS) curves of the polymer materials Th-CTF and Th-CTF-amide. Analysis of the curves reveals that the arc radius of the electrochemical impedance of the polymer material Th-CTF-amide is much smaller than that of Th-CTF. This suggests that hydrolyzing the cyano groups into amide groups significantly reduces the charge transfer barrier at the reaction interface of the material itself, resulting in a higher electron transfer rate for the amide-modified polymer material Th-CTF-amide, thereby enhancing the photocatalytic hydrogen evolution performance of the polymer Th-CTF-amide.

[0073] (9) Photocatalytic water decomposition hydrogen production test

[0074] like Figure 9 The graph shows the relationship between the amount of hydrogen produced by photocatalytic water decomposition of polymer materials Th-CTF and Th-CTF-amide and time. Figure 9As shown, the calculated average hydrogen evolution rate of Th-CTF-amide is 19.21 mmol / g·h, while the average hydrogen evolution rate of Th-CTF is 4.8 mmol / g·h, which is only 1 / 4 of the average hydrogen evolution rate of Th-CTF-amide. It can be seen that the hydrogen evolution performance of the polymer material Th-CTF-amide is much better than that of the polymer material Th-CTF. This shows that after the residual cyano group in the polymer is hydrolyzed into an amide group, the photocatalytic water hydrogen production performance of the polymer will be increased. Furthermore, the two materials were tested under the same conditions for four photocatalytic hydrogen evolution experiments to verify the stability of the materials. It can be found that both polymer materials have high stability during the photocatalytic hydrogen evolution reaction process.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements, or when the technical features in the above embodiments do not conflict with each other, can be combined in the manner described in the embodiments, and these modifications, replacements or combinations do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A triazine-based conjugated polymer of benzodithiazole units, characterized in that: It has the following structure: Wherein, in different structural units of the triazine-based conjugated polymer, the R group is independently -CN or -CO-NH2.

2. A method for preparing a triazine-based conjugated polymer containing a benzodithiazole unit, characterized in that: The preparation method comprises: synthesizing a monomer A using 4-cyanobenzaldehyde and 2,5-diamino-1,4-benzenedithiol dihydrochloride as raw materials; and subjecting the monomer A to condensation polymerization to obtain a triazine conjugated polymer Th-CTF. The reaction scheme is shown as follows:

3. The preparation method according to claim 2, characterized in that During the synthesis of monomer A, the solvent is anhydrous ethanol. After heating and reflux reaction for a period of time under stirring, hydrogen peroxide is added to continue the reaction. After the reaction is completed, the reaction solution is cooled, the product is centrifuged and separated, and the product is washed with anhydrous ethanol and dried to obtain monomer A.

4. The preparation method according to claim 3, characterized in that During the synthesis of monomer A, the molar ratio of 4-cyanobenzaldehyde to 2,5-diamino-1,4-benzenedithiol dihydrochloride is 2:1, the concentration of 4-cyanobenzaldehyde in the reaction system is 30-40 mM; and the amount of hydrogen peroxide added is 6-8 times the molar amount of 2,5-diamino-1,4-benzenedithiol dihydrochloride.

5. The preparation method according to claim 3, characterized in that During the synthesis of monomer A, the reaction temperature is 75°C to 80°C, and the mixture is first stirred and refluxed at this temperature for 1-2 hours. After hydrogen peroxide is added, the reaction is continued at this temperature for 0.5-1 hour, and the mixture is naturally cooled to room temperature. The product is centrifuged and separated, and the product is washed with anhydrous ethanol and dried at 50-80°C to obtain monomer A.

6. The preparation method according to claim 2, characterized in that The reaction conditions of the condensation polymerization are as follows: monomer A and trifluoromethanesulfonic acid are placed in a sealed reactor and sealed, and the reaction is carried out at a constant temperature of 115-125°C for 6-12 hours. After the reaction is completed, the reaction system is cooled to room temperature, the reaction solution is neutralized with alkali to neutrality, the product is centrifuged, washed with distilled water and anhydrous ethanol in sequence, and dried to obtain a triazine-based conjugated polymer containing benzodithiazole units, which is recorded as Th-CTF.

7. The preparation method according to claim 6, characterized in that The reaction conditions of the condensation polymerization are as follows: 5 mL of trifluoromethanesulfonic acid is used for every 100 mg of monomer A; the reaction temperature is 120° C.; the reaction time is 8 h; and the base is anhydrous potassium carbonate or sodium carbonate.

8. The preparation method according to claim 2, characterized in that The preparation method further comprises: hydrolyzing the -CN residues remaining at the end of the triazine conjugated polymer Th-CTF to convert them into amide groups.

9. The preparation method according to claim 8, characterized in that The method for hydrolyzing the terminal residual -CN in the triazine conjugated polymer Th-CTF to convert it into an amide group comprises: dispersing the triazine conjugated polymer Th-CTF in a reaction vessel containing 10-15M concentrated hydrochloric acid, sealing the reaction vessel, ultrasonically treating at 28-35°C for 30-40 minutes, adding deionized water, continuing the reaction at 28-35°C for 15-30 minutes, and then transferring the reaction to 0-4°C for 30-40 minutes; then neutralizing the reaction solution with alkali to neutrality, separating the product by high-speed centrifugation, washing the product with water and anhydrous ethanol for more than four times, and drying to obtain a modified material Th-CTF-amide in which the residual cyano groups in the triazine conjugated polymer Th-CTF are fully or partially converted into amide groups.

10. Use of the triazine-based conjugated polymer containing benzodithiazole units according to claim 1 as a photocatalytic hydrogen evolution catalyst.

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