Preparation of TpHz-TFHz composite material and application of TpHz-TFHz composite material in photocatalytic full water splitting performance

Abstract

The invention relates to preparation of a TpHz-TFHz composite material and application of the TpHz-TFHz composite material in photocatalytic full water splitting performance. In order to solve the problems of low light utilization rate and low total water splitting efficiency of the existing single COF materials, namely TpHz and TFHz photocatalytic total water splitting materials, the invention provides a preparation method of a novel TpHz-TFHz composite material, which comprises the following steps: firstly, mixing 1, 3, 5-trialdehyde phloroglucinol, hydrazine hydrate, 2, 4, 6-tri (4-aldehyde phenyl)-1, 3, 5-trialdehyde phloroglucinol, hydrazine hydrate and 2, 4, 6-tri (4-aldehyde phenyl)-1, 3, 5-tri (4-aldehyde phenyl)-1, 3, 5-tri (4-aldehyde phenyl)-1, 3, 5-tri (4-aldehyde phenyl)-1, 3, 5-tri (4-aldehyde phenyl) The preparation method comprises the following steps: uniformly stirring 1, 3, 5-triazine and hydrazine hydrate in a mixed solution of DMSO, ethanol and acetic acid to prepare TpHz COF and a TFHz COF precursor; and heating the two obtained COF precursors at 120 DEG C for 72 hours by a solvothermal method, and reacting to obtain the TpHz-TFHz composite material. The preparation process is simple and effective, the reagent consumption is low, and the yield is high; the photocatalyst provided by the invention can effectively solve the problem of low photocatalytic complete water splitting efficiency, experiments show that the composite material has excellent photocatalytic complete water splitting performance, the rate of hydrogen production by complete water splitting under visible light irradiation can reach 70.71 [mu] mol.h <-1 >. G <-1 >, and the rate of oxygen production can reach 35.35 [mu] mol.h <-1 >. G <-1 >.

Description

Technical Field

[0001] The invention belongs to the field of photocatalytic materials, and specifically relates to the preparation of a TpHz-TFHz composite material and the application of its photocatalytic water splitting performance. Background Art

[0002] With the rapid economic development and the increasing population, human society is increasingly dependent on energy. The rapid consumption of traditional fossil energy has triggered a severe energy crisis and led to serious environmental pollution and ecological damage. The development of clean and renewable energy is particularly important for solving contemporary energy and environmental problems. Among many energy sources, hydrogen energy has the advantages of being renewable, high in energy density, and zero pollution. It is considered to be one of the most promising energy sources for solving the energy crisis. Photocatalytic water splitting using inexhaustible solar energy as the driving force to produce hydrogen and oxygen is the cleanest and most effective way. However, due to the problem of easy recombination of electrons and holes in photocatalysts, the efficiency of water splitting is extremely low. Therefore, the development of efficient catalysts, maximizing the use of visible light, and improving the efficiency of electron-hole separation are still the key in this field.

[0003] Covalent organic frameworks (COFs) are porous crystalline materials formed by covalently connecting elements such as C, O, N, and H. They have the advantages of light weight, low density, high specific surface area, regular structure, uniform pores, relatively stable structure, and easy functional modification. COFs have great potential for application in many fields such as gas storage and separation, catalysis, sensing, energy storage, and photoelectric conversion. However, single-component COFs photocatalysts have serious photogenerated electron-hole recombination problems, which limits the further improvement of the COFs photocatalyst's overall water splitting activity. Therefore, the development of a composite material with high photocatalytic overall water splitting efficiency has become a research hotspot.

[0004] Compared with the previously reported heterojunctions formed by inorganic-organic substances, the heterojunctions formed by COFs and COFs are more tightly bound and more effectively promote the effective separation of charges. The recombination rate of photogenerated charges will be greatly reduced, and the charge carriers have a longer lifespan, thereby effectively improving the activity of the photocatalyst and the effectiveness of charge transfer, which is more conducive to the photocatalytic functional application of the material. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that electron holes in photocatalysts are easy to recombine and the water decomposition efficiency is low, thereby providing a preparation method of a TpHz-TFHz composite material and the application of photocatalytic water decomposition performance.

[0006] The preparation method of a TpHz-TFHz composite material of the present invention is completed by the following steps: Step 1: Add 1,3,5-trialdehyde phloroglucinol and hydrazine hydrate into a test tube, then add a mixed solution of DMSO, ethanol and acetic acid, and perform ultrasonic treatment at an ultrasonic frequency of 40 KHz for 30 to 35 minutes to obtain a TpHzCOF precursor; The mass of 1,3,5-trialdehyde phloroglucinol described in step 1 is 10.5 mg; The volume of hydrazine hydrate in step 1 is 3.6 μL; The molar ratio of 1,3,5-trialdehyde phloroglucinol and hydrazine hydrate in step 1 is 2:3; The volume ratio of DMSO, ethanol and acetic acid in step 1 is 5:5:1; The concentration of acetic acid used in step 1 is 12 mol·L -1 ; Step 2: Add 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and hydrazine hydrate to a test tube, then add a mixed solution of DMSO, ethanol and acetic acid, and perform ultrasonic treatment at an ultrasonic frequency of 40 KHz for 30 to 35 minutes to obtain a TFHz COF precursor; The mass of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine described in step 2 is 19.6 mg; The volume of hydrazine hydrate in step 2 is 3.6 μL; The molar ratio of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and hydrazine hydrate in step 2 is 2:3; The volume ratio of DMSO, ethanol and acetic acid in step 2 is 5:5:1; The concentration of acetic acid used in step 2 is 12 mol·L -1 ; Step 3: Add the COF precursors of TpHz and TFHz obtained in steps 1 and 2 into a heat-resistant glass tube, perform ultrasonic treatment for 30 to 35 minutes at an ultrasonic frequency of 40 kHz, perform three freeze-thaw cycles for degassing in a liquid nitrogen bath, seal and heat at 120°C for 72 hours, filter and wash with tetrahydrofuran several times, and dry to obtain a TpHz-TFHz composite material; In step 3, the yields of COF of TpHz and TFHz under the same reaction conditions are both about 80%. By controlling the dosage of different raw materials, the molar ratios of TpHz and TFHz COF in the composite material are 7:3; 6:4; 5:5; 4:6; 3:7.

[0007] Application of the TpHz-TFHz composite material provided by the present invention in photocatalytic water splitting: In order to investigate the photocatalytic water splitting effect of TpHz-TFHz material, its visible light photocatalytic water splitting performance was tested according to the following method; the test process is as follows: TpHz-TFHz (10 mg) is used as the photocatalyst, deionized water (50 mL) is used as the reaction liquid, ultrasound is applied for 30 minutes to form a uniform suspension, and a xenon lamp (λ>420 nm) is used as the light source for testing.

[0008] Beneficial effects of the present invention: The present invention adopts a solvothermal method, and uses 2,4,6-tris(4-formylphenyl)-1,3,5-triazine, 1,3,5-triformylphloroglucinol and hydrazine hydrate as raw materials respectively, and successfully synthesizes TpHz COF and TFHz COF. However, the two materials have poor visible light absorption capacity and cannot photolyze water into hydrogen and oxygen. Therefore, the present invention composites TpHz and TFHz in a precursor state to synthesize a new composite material TpHz-TFHz, which effectively improves the photocatalytic water splitting performance. The photocatalytic water splitting hydrogen production rate of the TpHz-TFHz composite material (4:6) can reach 70.71 μmol·h -1 ·g -1 , the oxygen production rate can reach 35.35μmol·h -1 ·g -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is the X-ray powder diffraction pattern of TpHz-TFHz material;

[0010] Figure 2 It is the infrared spectrum of TpHz-TFHz material;

[0011] Figure 3 This is the Mott-Schottky test diagram of TFHz material;

[0012] Figure 4 This is the Mott-Schottky test diagram of TpHz material;

[0013] Figure 5 This is the Mott-Schottky test diagram of TpHz-TFHz material;

[0014] Figure 6 This is the UV-vis DRS test chart of TpHz-TFHz material;

[0015] Figure 7 The energy band structure diagram of TpHz-TFHz material;

[0016] Figure 8 This is the photocatalytic water splitting performance diagram of TpHz-TFHz materials; DETAILED DESCRIPTION

[0017] The present invention is further described below with reference to examples. These examples are only used to illustrate the method of the present invention and have no limitation on the scope of application of the present invention.

[0018] Example 1: The preparation of a TpHz-TFHz composite material of this embodiment is completed according to the following steps: Step 1: 10.5 mg (0.05 mmol) of 1,3,5-trialdehyde phloroglucinol and 3.6 μL (0.075 mmol) of hydrazine hydrate were added to a test tube, followed by a mixed solution of DMSO, ethanol and acetic acid, and ultrasonically treated at an ultrasonic frequency of 40 KHz for 30 to 35 min to obtain a TpHz COF precursor; Step 2: 19.6 mg (0.05 mmol) of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 3.6 μL (0.075 mmol) of hydrazine hydrate were added to a test tube, followed by a mixed solution of DMSO, ethanol and acetic acid, and ultrasonic treatment was performed at an ultrasonic frequency of 40 KHz for 30 to 35 min to obtain a TFHz COF precursor; Step 3: Add the TpHz and TFHz COF precursors obtained in steps 1 and 2 into a heat-resistant glass tube, perform ultrasonic treatment for 30 to 35 minutes at an ultrasonic frequency of 40 kHz, perform three freeze-thaw cycles for degassing in a liquid nitrogen bath, seal and heat at 120°C for 72 hours, filter and wash with tetrahydrofuran several times, and dry to obtain a TpHz-TFHz (molar mass ratio of 5:5) composite material.

[0019] Example 2: This embodiment is different from Example 1 in that the masses of 1,3,5-trialdehyde pyrogallol and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine described in the steps are 14.7 mg and 11.8 mg respectively, and the other steps and parameters are the same as those in Example 1; a TpHz-TFHz (molar mass ratio of 7:3) composite material is obtained.

[0020] Example 3: This embodiment is different from Example 1 in that the masses of 1,3,5-trialdehyde pyrogallol and 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine described in the steps are 12.6 mg and 15.7 mg respectively, and the other steps and parameters are the same as those in Example 1; a TpHz-TFHz (molar mass ratio of 6:4) composite material is obtained.

[0021] Example 4: This embodiment is different from Example 1 in that the masses of 1,3,5-trialdehyde pyrogallol and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine described in the steps are 8.4 mg and 23.6 mg respectively, and the other steps and parameters are the same as those in Example 1; a TpHz-TFHz (molar mass ratio of 4:6) composite material is obtained.

[0022] Example 5: This embodiment is different from Example 1 in that the masses of 1,3,5-trialdehyde hydroquinone and 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine described in the steps are 6.3 mg and 27.5 mg respectively, and the other steps and parameters are the same as those in Example 1; a TpHz-TFHz (molar mass ratio of 3:7) composite material is obtained.

[0023] To verify the beneficial effects of the present invention, the following tests were performed: 1. X-ray diffraction (XRD) analysis: Use X-rays of sufficient energy to irradiate the sample. The substances in the sample are excited and produce secondary fluorescent X-rays. The position (peak position) of the diffraction angle is used to perform qualitative analysis of the compound. It has been determined that the crystal form of the TpHz-TFHz composite material provided by the present invention is consistent with the single crystal diffraction simulation and has the characteristic peaks of the monomer. 2. Infrared spectrum test: Determine the molecular structure of the compound through infrared spectroscopy, compare the spectrum of the standard, determine the characteristic functional groups, and assist XRD test to determine that the product has been successfully synthesized; 3. Mott-Schottky test: Use an electrochemical workstation to test the conductive glass coated with the semiconductor sample to determine the flat band potential of the semiconductor, and then calculate the conduction band position of the semiconductor, and combine with UV-vis DRS test to calculate the valence band position of the semiconductor; 4. UV-vis DRS test: Use the reflection of light on the surface of the material to obtain the information of the material; UV-vis DRS test is performed on semiconductors. Under light excitation, charge transfer occurs, electrons absorb energy, photons are transferred from the donor to the acceptor, and an absorption spectrum is generated in the ultraviolet region; the diffuse reflection spectrum can be obtained by simultaneously detecting the mirror reflection light and diffuse reflection light of the solid powder sample, and the band gap width of the semiconductor can be obtained by calculating the diffuse reflection spectrum, and the band structure of the semiconductor can be obtained by combining with the Mott-Schottky test.

Claims

1. A method for preparing a TpHz-TFHz composite material is carried out according to the following steps: Step 1: 10.5 mg (0.05 mmol) of 1,3,5-trialdehyde phloroglucinol and 3.6 μL (0.075 mmol) of hydrazine hydrate were added to a test tube, followed by a mixed solution of DMSO, ethanol and acetic acid, and ultrasonically treated at an ultrasonic frequency of 40 KHz for 30 to 35 min to obtain a TpHz COF precursor; Step 2: 19.6 mg (0.05 mmol) of 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and 3.6 μL (0.075 mmol) of hydrazine hydrate were added to a test tube, followed by a mixed solution of DMSO, ethanol and acetic acid, and ultrasonic treatment was performed at an ultrasonic frequency of 40 KHz for 30 to 35 min to obtain a TFHz COF precursor; Step 3: Add the TpHz and TFHz COF precursors obtained in steps 1 and 2 into a heat-resistant glass tube, perform ultrasonic treatment for 30 to 35 minutes at an ultrasonic frequency of 40 kHz, perform three freeze-thaw cycles for degassing in a liquid nitrogen bath, seal and heat at 120°C for 72 hours, filter and wash with tetrahydrofuran several times, and dry to obtain a TpHz-TFHz (molar mass ratio of 5:5) composite material.

2. According to claim 1, the molar ratio of 1,3,5-trialdehyde phloroglucinol and hydrazine hydrate is 3:

2.

3. According to claim 1, the molar ratio of 2,4,6-tris(4-formaldehydephenyl)-1,3,5-triazine and hydrazine hydrate is 3:

2.

4. According to claim 1, the volume ratio of DMSO, ethanol and acetic acid in step 1 and step 2 is 5:5:

1.

5. The concentration of acetic acid used in step 1 and step 2 according to claim 1 is 12 mol·L -1。 6. The preparation of a TpHz-TFHz composite material according to claim 1, characterized in that The optimal ratio of TpHz-TFHz in step 3 is 4:6.

Images