Photocatalyst for hydrogen production and oxygen production through visible light catalytic complete water splitting, preparation method and application

Abstract

The invention belongs to the technical field of visible light catalysis full water splitting, and particularly relates to a photocatalyst for hydrogen production and oxygen production through visible light catalysis full water splitting, a preparation method and application. The photocatalyst provided by the invention comprises a covalent organic framework material TTA-Bp, and the covalent organic framework material is formed by carrying out condensation reaction on 2, 4, 6-tri (4-aminophenyl)-1, 3, 5-triazine and 2, 2 '-bipyridine-5, 5'-diformaldehyde; the covalent organic framework material is loaded with the bipyridine functional group, the Ni nano-particles are loaded on the covalent organic framework material, Ni atoms in the Ni nano-particles and the bipyridine functional group in the covalent organic framework material form a coordination effect, and the Ni nano-particles have a Ni hydroxide crystal phase. The photocatalyst prepared by the invention successfully realizes efficient catalysis and full water splitting hydrogen production and oxygen production reactions under the visible light condition, and the catalyst has excellent stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of visible light catalytic complete water splitting, and specifically relates to a photocatalyst for producing hydrogen and oxygen by visible light catalytic complete water splitting, a preparation method and an application thereof. Background Art

[0002] Hydrogen (H2), as a clean, carbon-free fuel, has a high gravimetric energy density and is considered an important option to replace non-renewable fossil resources. Converting solar energy into renewable hydrogen through photocatalytic technology can not only alleviate the energy crisis, but also reduce environmental pollution. It is an economical and environmentally friendly sustainable development route. The photocatalytic water splitting reaction uses solar energy to decompose water into hydrogen and oxygen, which is expected to achieve efficient conversion of solar energy to chemical energy. Among them, visible light catalytic water splitting has important application potential because it can maximize the use of solar energy reaching the earth's surface. Therefore, the development of efficient and stable photocatalysts for visible light catalytic water splitting is of great significance to promote the development of clean energy technology.

[0003] The photocatalytic water splitting reaction involves multiple steps such as light absorption, charge separation and transport, and surface reaction. Due to the extremely fast relaxation of the photoexcited state, the lifetime of the photogenerated electron-hole pairs is usually only a few picoseconds, and they are easily lost through recombination, while the surface proton reduction reaction (hydrogen evolution reaction, HER) and the water oxidation reaction (oxygen evolution reaction, OER) require longer time (several milliseconds or even longer). In particular, the hydrogen evolution reaction, as a two-electron interface reaction, is usually much slower than the generation rate of photogenerated charges, resulting in limited overall reaction efficiency. Therefore, how to effectively separate the photogenerated charges and quickly transfer them to the reaction site, as well as how to accelerate the surface reaction kinetics, are major challenges faced in improving the efficiency of photocatalysis.

[0004] At present, efficient photocatalytic water splitting reactions usually rely on precious metals (such as platinum) as co-catalysts to improve reaction activity. However, the high cost and limited resources of precious metals restrict their large-scale application. Developing low-cost photocatalysts that do not require the participation of precious metals and achieving efficient photocatalytic degradation of water is also a practical problem that needs to be solved urgently.

[0005] High-performance photocatalysts are often highly active, but are more susceptible to photocorrosion or structural degradation under long-term illumination and reaction environments, resulting in decreased activity. How to design photocatalysts with high stability and durability to cope with complex photocatalytic reaction conditions is also an important challenge in achieving their practical application.

[0006] The photocatalytic water splitting reaction requires efficient catalysis of both hydrogen and oxygen evolution reactions, which places higher demands on the performance of the catalyst. Currently, most reported high-performance photocatalysts are mainly targeted at a single reaction, while non-precious metal catalysts that can efficiently catalyze both hydrogen and oxygen evolution reactions are still relatively rare.

[0007] In summary, although visible light photocatalytic water splitting technology has important potential value, its practical application still faces many challenges such as low charge separation efficiency, slow surface reaction kinetics, dependence on precious metal co-catalysts, insufficient catalyst stability and complexity of overall water splitting reaction. Therefore, the development of efficient, stable and low-cost photocatalysts is of great significance to promote the practical application of visible light photocatalytic water splitting technology. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention provides a photocatalyst for producing hydrogen and oxygen by completely splitting water under visible light catalysis, a preparation method and an application thereof.

[0009] The first aspect of the present invention is to provide a photocatalyst for producing hydrogen and oxygen by completely splitting water under visible light catalysis, comprising a covalent organic framework material TTA-Bp, wherein the covalent organic framework material is formed by a condensation reaction of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,2'-bipyridine-5,5'-dicarboxaldehyde; and further comprising Ni species nanoparticles supported on the covalent organic framework material, wherein a coordination effect is formed between the Ni atoms in the Ni species nanoparticles and the bipyridine functional groups in the covalent organic framework material, and the Ni species nanoparticles have a crystal phase of Ni hydroxide.

[0010] As a further optimization scheme of the above-mentioned photocatalyst, the loading amount of Ni is 3% to 10% of the mass of the covalent organic framework material.

[0011] As a further optimization scheme of the above-mentioned photocatalyst, Ni species nanoparticles loaded on the covalent organic framework material are formed from Ni salt precursors in a weak alkaline solution environment.

[0012] As a further optimization scheme of the above-mentioned photocatalyst, the Ni salt precursor is nickel sulfate hexahydrate, hexamethylenetetramine is used to form a weak alkaline solution, and sodium citrate is added to form a complex with nickel ions to slow down the ion precipitation rate.

[0013] The second aspect of the present invention is to provide a method for preparing a photocatalyst for producing hydrogen and oxygen by catalytically splitting water under visible light, comprising the following steps:

[0014] Step S1: 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,2'-bipyridine-5,5'-dicarbaldehyde are reacted in a solvent to form a covalent organic framework material TTA-Bp;

[0015] Step S2: dispersing the covalent organic framework material TTA-Bp in an aqueous solution containing a Ni salt precursor, wherein the Ni salt precursor is nickel sulfate hexahydrate;

[0016] Step S3: mixing the dispersion obtained in step S2 with an aqueous solution containing hexamethylenetetramine;

[0017] Step S4: subjecting the mixed solution obtained in step S3 to hydrothermal treatment and drying to obtain a photocatalyst for producing hydrogen and oxygen by completely splitting water under visible light catalysis.

[0018] As a further optimization scheme of the above-mentioned photocatalyst preparation method, in step S1, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,2'-bipyridine-5,5'-dicarboxaldehyde are added to a mixed solution of mesitylene and acetic acid in a molar ratio of 2:3, and the mixture is encapsulated in a pyrrolidine glass tube and evacuated, heated to react to obtain a solid, and impurities are removed and dried to obtain the covalent organic framework material TTA-Bp.

[0019] As a further optimization scheme of the above-mentioned photocatalyst preparation method, in step S2, the covalent organic framework material TTA-Bp is first mixed with water, dispersed by ultrasonic treatment, and then nickel sulfate hexahydrate is added and stirred to mix.

[0020] As a further optimization scheme of the above-mentioned photocatalyst preparation method, in step S3, an aqueous solution containing sodium citrate and hexamethylenetetramine is added to the dispersion prepared in step S2, and the mixture is mixed evenly.

[0021] As a further optimization scheme of the above-mentioned photocatalyst preparation method, in step S4, the mixed solution prepared in step S3 is transferred to a stainless steel autoclave lined with polytetrafluoroethylene, and reacted at 90-150°C for 6-18h. The solid is taken out and freeze-dried to obtain a photocatalyst for visible light catalytic complete water splitting to produce hydrogen and oxygen.

[0022] The third aspect of the present invention is to provide the use of the above-mentioned photocatalyst in the preparation of clean energy, that is, the photocatalyst is used in the reaction of preparing hydrogen and oxygen by photocatalytic water splitting driven by solar energy.

[0023] Beneficial Effects

[0024] The present invention prepares a series of Ni@TTA-Bp photocatalysts, and successfully realizes the highly efficient catalytic reaction of hydrogen and oxygen production by water splitting under visible light conditions. Among them, the 5% Ni@TTA-Bp catalyst exhibits the best photocatalytic performance, with an H2 generation rate of 0.52mmol g-1h-1 and an O2 generation rate of 0.26mmol g-1h-1, and the generation of hydrogen and oxygen strictly follows the stoichiometric ratio of 2:1. In the prepared photocatalyst, Ni species form uniformly dispersed nanoparticles on the surface of TTA-Bp, providing abundant highly active sites and significantly improving the activity of the catalyst. The TTA-Bp framework not only serves as a stable carrier of Ni species, but also promotes the migration of electrons and holes through its long-range ordered structure. The bipyridine functional group releases oxygen as an oxidation site of water, greatly improving the kinetics of the water splitting reaction. In addition, the catalyst exhibits good stability in 5 rounds of cycle experiments, and the crystal structure does not change significantly, showing excellent durability. The present invention does not require the use of precious metals, thus reducing costs. At the same time, comparative experiments verify the key importance of the synergistic effect of Ni and TTA-Bp to photocatalytic activity, providing a new solution for efficient, stable and low-cost photocatalytic water splitting to produce hydrogen and oxygen. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD spectra of photocatalyst and Ni(OH)2.

[0026] Figure 2 Transmission electron microscopy (TEM) characterization of the photocatalyst.

[0027] Figure 3 XRD spectrum of the photocatalyst after the cycling experiment.

[0028] Figure 4 This is the time-dependent complete water splitting activity curve of the photocatalyst under visible light irradiation.

[0029] Figure 5 This is the UV spectrum of the photocatalyst.

[0030] Figure 6 Tauc plot of the photocatalyst.

[0031] Figure 7 Mott-Schottky diagram of the photocatalyst. DETAILED DESCRIPTION

[0032] The present invention is further illustrated by specific examples below. These examples are exemplary and are intended to illustrate the problem and explain the present invention, but are not intended to be limiting.

[0033] Embodiment 1

[0034] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0035] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.0284 g) was then added to the suspension and stirred for 0.5 h.

[0036] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (HMTA) (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0037] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 5% Ni@TTA-Bp was obtained after freeze drying for 12 hours.

[0038] Embodiment 2

[0039] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0040] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.017 g) was then added to the suspension and stirred for 0.5 h.

[0041] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step, and continue stirring for 1 h.

[0042] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 3% Ni@TTA-Bp was obtained after freeze drying for 12 hours.

[0043] Embodiment 3

[0044] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0045] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.05617 g) was then added to the suspension and stirred for 0.5 h.

[0046] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0047] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 10% Ni@TTA-Bp was obtained after freeze drying for 12 hours.

[0048] Embodiment 4

[0049] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0050] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.0284 g) was then added to the suspension and stirred for 0.5 h.

[0051] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step, and continue stirring for 1 h.

[0052] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 120°C for 10 hours. Finally, 5% Ni@TTA-Bp(120) was obtained by freeze drying for 12 hours.

[0053] Embodiment 5

[0054] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0055] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.0284 g) was then added to the suspension and stirred for 0.5 h.

[0056] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step, and continue stirring for 1 h.

[0057] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 150°C for 10 hours. Finally, 5% Ni@TTA-Bp(150) was obtained by freeze drying for 12 hours.

[0058] Embodiment 6

[0059] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0060] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.0284 g) was then added to the suspension and stirred for 0.5 h.

[0061] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0062] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 18 hours. Finally, 5% Ni@TTA-Bp (18h) was obtained by freeze drying for 12 hours.

[0063] Embodiment 7

[0064] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0065] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.0284 g) was then added to the suspension and stirred for 0.5 h.

[0066] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0067] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 6 hours. Finally, 5% Ni@TTA-Bp (6h) was obtained after freeze drying for 12 hours.

[0068] Comparative Example 1

[0069] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), benzidine (BD) (0.00039 mol, 0.072 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube and vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-BD.

[0070] (2) First, TTA-BD (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Then, nickel sulfate hexahydrate (0.0284 g) was added to the above suspension and stirred for 0.5 h.

[0071] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0072] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 5% Ni@TTA-BD was obtained after freeze drying for 12 hours.

[0073] Comparative Example 2

[0074] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0075] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Copper sulfate (0.0163 g) was then added to the suspension and stirred for 0.5 h.

[0076] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (HMTA) (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0077] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 5% Cu@TTA-Bp was obtained after freeze drying for 12 hours.

[0078] Comparative Example 3

[0079] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0080] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Zinc sulfate (0.0163 g) was then added to the suspension and stirred for 0.5 h.

[0081] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and hexamethylenetetramine (HMTA) (0.03 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0082] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 5% Zn@TTA-Bp was obtained after freeze drying for 12 hours.

[0083] Comparative Example 4

[0084] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarbaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube and vacuumed in liquid nitrogen for 3 cycles.

[0085] (2) The reaction tube was reacted at 120° C. for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90° C. for 24 h, and finally dried at 60° C. for 12 h to obtain TTA-Bp.

[0086] Comparative Example 5

[0087] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), benzidine (BD) (0.00039 mol, 0.072 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube and vacuumed in liquid nitrogen for 3 cycles.

[0088] (2) The reaction tube was reacted at 120° C. for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90° C. for 24 h, and finally dried at 60° C. for 12 h to obtain TTA-BD.

[0089] Comparative Example 6

[0090] (1) 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA) (0.00026 mol, 0.092 g), 2,2'-bipyridine-5,5'-dicarboxaldehyde (Bp) (0.00039 mol, 0.0827 g), 1,4-dioxane (0.9 mL), mesitylene (5.1 mL) and 6 mol / L acetic acid solution (0.2 mL) were added to a pyrrolidine glass tube, and the mixture was vacuumed in liquid nitrogen for 3 cycles. The reaction tube was reacted at 120°C for 3 days. After the reaction was completed, the solid product was collected by filtration, extracted at 90°C for 24 h, and finally dried at 60°C for 12 h to obtain TTA-Bp.

[0091] (2) TTA-Bp (0.2 g) was mixed with 15 mL of water and ultrasonically treated for 1 hour. Nickel sulfate hexahydrate (0.0284 g) was then added to the suspension and stirred for 0.5 h.

[0092] (3) Add an aqueous solution prepared by dissolving sodium citrate (0.006344 g) and sodium hydroxide (0.008 g) in 15 mL of deionized water, mix with the solution obtained in the second step and continue stirring for 1 h.

[0093] (4) The mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and stirred at 90°C for 10 hours. Finally, 5% Bulk Ni@TTA-Bp was obtained by freeze drying for 12 hours.

[0094] Performance Testing

[0095] Test Example 1

[0096] Test object: The catalysts prepared in Examples 1 to 7 and Comparative Examples 1 to 5 were applied to the photocatalytic water splitting reaction to produce hydrogen, and their hydrogen evolution rates and oxygen evolution rates were tested.

[0097] Test conditions: In a typical photocatalytic water splitting experiment, 20 mg of catalyst was added to 50 mL of aqueous solution, and the air was evacuated from the container and replaced with argon. A 300 W xenon lamp (PLSXE300D) was used as the light source with a UV cutoff filter (λ>420 nm), and the reaction was carried out at room temperature, illuminated and stirred. After 5 hours of illumination, the gas was taken by an automatic sampling system and the generated hydrogen and oxygen were detected by gas chromatography (Agilent 7890B).

[0098] Test results: as shown in Table 1.

[0099] Table 1: The rates of hydrogen and oxygen production from water splitting catalyzed by visible light

[0100]

[0101] The present invention successfully prepared a series of Ni@TTA-Bp photocatalysts and applied them to visible light catalytic water splitting to produce hydrogen and oxygen. The results showed that under visible light conditions and without the use of any precious metals, all embodiments achieved excellent hydrogen evolution rates and oxygen evolution rates, and the two gases were generated in a strict ratio of 2:1. This challenging result reflects the feasibility and potential value of these new catalysts in the application of efficient photocatalytic water splitting to produce hydrogen and oxygen. In particular, Example 1 (5% Ni@TTA-Bp) exhibited the best photocatalytic performance, with an H2 generation rate of 0.52mmol g-1h-1 and an O2 generation rate of 0.26mmol g-1h-1.

[0102] Comparative Example 1 uses another COF material with a similar structure while keeping the Ni loading amount and loading method unchanged. The activity of the obtained photocatalyst (5% Ni@TTA-BD) in the visible light catalytic complete water splitting to produce hydrogen and oxygen is significantly reduced compared with Example 1. The H2 generation rate is 0.16mmol g-1h-1, and the O2 generation rate is 0.08mmol g-1h-1, which is less than one-third of the reaction rate of Example 1. Comparative Examples 4 and 5 use two COF materials (TTA-Bp and TTA-BD) alone to carry out photocatalytic complete water splitting reactions, and it is found that neither can produce hydrogen and oxygen. The above results show that the excellent photocatalytic activity of the Ni@TTA-BD series catalysts of the present invention comes from the joint action of Ni and TTA-BD. Although TTA-BD itself does not show obvious photocatalytic activity, it plays a vital role in the construction of the overall photocatalytic activity.

[0103] Comparative Examples 2 and 3, while keeping the COF material (TTA-Bp) unchanged, used the same loading amount and loading method to load Cu and Zn respectively, and the activity of the obtained photocatalysts in the visible light catalytic complete water splitting to produce hydrogen and oxygen was significantly reduced compared with Example 1. Among them, the H2 generation rate of 5% Cu@TTA-Bp was 0.15mmol g-1h-1, and the O2 generation rate was 0.074mmol g-1h-1, which was less than one-third of the reaction rate of Example 1; the H2 generation rate of 5% Zn@TTA-Bp was 0.05mmol g-1h-1, and the O2 generation rate was 0.022mmol g-1h-1, which was less than one-tenth of the reaction rate of Example 1. It was verified again that the coordination of nickel (Ni) and the TTA-Bp framework is crucial to the activity of the visible light catalytic complete water splitting reaction.

[0104] Comparative Example 6 adopts a different loading method compared to Example 1. A block Ni photocatalyst loaded on the surface of TTA-Bp is prepared under sodium hydroxide solution conditions for a complete water splitting reaction. Both the hydrogen evolution rate and the oxygen evolution rate are not ideal, indicating that the distribution of metal Ni on the TTA-Bp framework also plays an important role in the reaction activity.

[0105] Test Example 2

[0106] The photocatalyst 5% Ni@TTA-Bp prepared in Example 1 was characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). Figure 1Curve a in the middle is the XRD spectrum of the 5% Ni@TTA-Bp catalyst, and curve b is the XRD spectrum of Ni(OH)2. By comparative analysis, it can be seen that there are Ni species in the Ni(OH)2 crystal phase in the photocatalyst. In addition, the Ni species in the photocatalyst is formed by slow loading under the regulation of organic amines, and the Ni metal salt precursor is gradually hydrolyzed on the surface of the covalent organic framework to generate Ni nanoparticles. Unlike precipitation using strong bases such as sodium hydroxide, this method controls the slow release of hydroxide to coordinate Ni with the nitrogen atoms in the bipyridine group to form Ni-N bonds, rather than Ni-O or Ni-Ni bonds, which is conducive to the formation of uniformly dispersed nanoparticle Ni species on the surface of TTA-Bp. Figure 2 TEM characterization results further confirmed that the Ni species in the form of nanoparticles were uniformly distributed on the catalyst surface.

[0107] Test Example 3

[0108] Test object: the photocatalyst prepared in Example 1.

[0109] Test method: The stability of the catalyst was evaluated by photocatalytic water splitting cycle experiment. Under the same experimental conditions as in Example 1, the photocatalyst 5% Ni@TTA-Bp was subjected to 5 cycles of test, and the hydrogen and oxygen production rates of each cycle were measured. The results are shown in Table 2. In order to characterize the structural stability of the catalyst, the 5% Ni@TTA-Bp sample after the cycle experiment was subjected to X-ray diffraction (XRD) analysis. The results are shown in Table 2. Figure 3 shown.

[0110] Table 2: Stability test results of Example 1

[0111] Cycle times <![CDATA[H2 rate (mmol g -1 h -1 )]]> 1 0.52 2 0.51 3 0.51 4 0.50 5 0.51

[0112] The results show that after 5 rounds of photocatalytic TC degradation cycle experiments, 5% Ni@TTA-Bp still maintains stable photocatalytic activity. The catalyst recovered after the cycle test was tested, and the results showed that its crystal structure remained unchanged after a long time. The XRD curve of the 5% Ni@TTA-Bp sample after the cycle experiment was not significantly different from the XRD curve before use, indicating that the crystal phase structure of the catalyst did not change significantly during the reaction, further confirming its good structural stability and durability in photocatalytic reactions.

[0113] Test Example 4

[0114] Figure 4The time-dependent complete water splitting activity curve of 5% Ni@TTA-Bp catalyst under visible light irradiation is shown. The catalyst prepared in Example 1 was tested for 5 hours of photocatalytic complete water splitting, and the results showed that the production of hydrogen and oxygen strictly followed the stoichiometric ratio of 2:1. This result verifies the mechanism of complete water splitting, and water molecules are completely decomposed into hydrogen and oxygen during the photocatalytic process.

[0115] Test Example 5

[0116] The catalyst prepared in Example 1 was tested by UV spectrum and Mott-Schottky curve. Figure 5 As shown, it shows that the light absorption edge of TTA-Bp is above 500nm. Figure 5 The Tauc diagram was drawn using the Kubelka-Munk theory (KM) theory, such as Figure 6 The band gap of TTA-Bp is calculated to be 2.4 eV. The Mott-Schottky plot is measured, as shown in Figure 7 As shown, the conduction band bottom (CBM) is determined to be -0.8 V vs. NHE. Combined with the band gap width, the valence band top of TTA-Bp is finally determined to be 1.4 V vs. NHE. Therefore, the conduction band minimum (CBM) potential of TTA-Bp can show sufficient reduction and oxidation potential for protons and H2O, respectively.

[0117] In summary, the present invention successfully prepared a series of Ni@TTA-Bp photocatalysts, which can quickly and efficiently decompose water into hydrogen and oxygen under visible light, and show good stability and cyclic reusability. TTA-Bp and Ni species play an important role in the photocatalytic activity. The uniformly dispersed specific Ni species provide abundant high-activity sites. The long-range ordered structure of TTA-Bp itself promotes the migration of electrons and holes. The TTA-Bp framework allows a strong host-guest interaction to form stably loaded Ni species nanoparticles, in which the bipyridine fragment acts as a stable carrier of Ni species on the one hand, and as an oxidation site of water to precipitate oxygen on the other hand, greatly improving the kinetics of the water decomposition reaction.

[0118] The above embodiments are exemplary, and their purpose is to illustrate the technical concept and features of the present invention so that people familiar with the technology in this field can understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A photocatalyst for producing hydrogen and oxygen by completely splitting water under visible light catalysis, characterized in that: The invention comprises a covalent organic framework material TTA-Bp, wherein the covalent organic framework material is formed by a condensation reaction of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,2'-bipyridine-5,5'-dicarboxaldehyde; and further comprises Ni species nanoparticles supported on the covalent organic framework material, wherein a coordination effect is formed between Ni atoms in the Ni species nanoparticles and bipyridine functional groups in the covalent organic framework material, and the Ni species nanoparticles have a crystal phase of Ni hydroxide.

2. The photocatalyst for producing hydrogen and oxygen by visible light catalytic water splitting according to claim 1, characterized in that: The loading amount of Ni is 3% to 10% of the mass of the covalent organic framework material.

3. The photocatalyst for producing hydrogen and oxygen by visible light catalytic water splitting according to claim 1, characterized in that: The Ni species nanoparticles supported on the covalent organic framework material are formed from a Ni salt precursor in a weak alkaline solution environment.

4. The photocatalyst for producing hydrogen and oxygen by visible light catalytic water splitting according to claim 3, characterized in that: The Ni salt precursor is nickel sulfate hexahydrate, hexamethylenetetramine is used to form the weak alkaline solution, and sodium citrate is added to form a complex with nickel ions to slow down the ion precipitation rate.

5. A method for preparing a photocatalyst for producing hydrogen and oxygen by catalytically splitting water under visible light, characterized in that: The following steps are involved: Step S1: 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,2'-bipyridine-5,5'-dicarbaldehyde are reacted in a solvent to form a covalent organic framework material TTA-Bp; Step S2: dispersing the covalent organic framework material TTA-Bp in an aqueous solution containing a Ni salt precursor, wherein the Ni salt precursor is nickel sulfate hexahydrate; Step S3: mixing the dispersion obtained in step S2 with an aqueous solution containing hexamethylenetetramine; Step S4: subjecting the mixed solution obtained in step S3 to hydrothermal treatment and drying to obtain a photocatalyst for producing hydrogen and oxygen by completely splitting water under visible light catalysis.

6. The method for preparing a photocatalyst for producing hydrogen and oxygen by catalytically splitting water under visible light according to claim 5, characterized in that: In step S1, 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,2'-bipyridine-5,5'-dicarboxaldehyde are added to a mixed solution of mesitylene and acetic acid at a molar ratio of 2:3, encapsulated in a pyrrolidine glass tube and evacuated, heated to react to obtain a solid, impurities are removed and dried to obtain a covalent organic framework material TTA-Bp.

7. The method for preparing a photocatalyst for producing hydrogen and oxygen by catalytically splitting water under visible light according to claim 5, characterized in that: In step S2, the covalent organic framework material TTA-Bp is first mixed with water, dispersed by ultrasonic treatment, and then nickel sulfate hexahydrate is added and stirred for mixing.

8. The method for preparing a photocatalyst for producing hydrogen and oxygen by catalytically splitting water under visible light according to claim 5, characterized in that: In step S3, an aqueous solution containing sodium citrate and hexamethylenetetramine is added to the dispersion obtained in step S2 and mixed evenly.

9. The method for preparing a photocatalyst for producing hydrogen and oxygen by catalytically splitting water under visible light according to claim 5, characterized in that: In step S4, the mixed solution obtained in step S3 is transferred to a stainless steel autoclave lined with polytetrafluoroethylene, and reacted at 90-150° C. for 6-18 hours. The solid is taken out and freeze-dried to obtain a photocatalyst for producing hydrogen and oxygen by fully splitting water under visible light.

10. Use of the photocatalyst according to any one of claims 1 to 4 in preparing clean energy, characterized in that: The photocatalyst is used in the reaction of preparing hydrogen and oxygen by photocatalytic water decomposition driven by solar energy.

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