A method for photocatalytic hydrogen evolution of a carbon nitride supported copper-based MOF catalyst

Abstract

This invention discloses a photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst, belonging to the field of photocatalytic hydrogen production technology. This invention solves the technical problems of low activity, unsuitable reaction conditions, and poor hydrogen production efficiency of existing photocatalytic hydrogen production methods using carbon nitride-based catalysts. The key points of the technical solution are: using C3N4-C-MOF2.0 prepared by a molar ratio of C3N4-C and Cu(NO3)2·3H2O of 1:2.0 as the photocatalyst, eosin Y as the photosensitizer, and triethanolamine as the electron donor, an aqueous reaction system with pH 8.0-9.0 is prepared according to the specified ratio. After degassing, the reaction is carried out at 6℃ under visible light above 420 nm for 3 h. The hydrogen production is detected by gas chromatography, and the catalyst can be recycled. This method has high hydrogen production efficiency, with a hydrogen evolution rate of 12.7 mmol·g. ‑1 ·h ‑1 The catalyst exhibits good stability, the process is simple and controllable, and it is environmentally friendly, making it suitable for large-scale green hydrogen production driven by visible light.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic hydrogen production technology, specifically to a photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst. It is particularly suitable for a highly efficient photocatalytic water splitting process driven by visible light, and belongs to the field of green energy production technology. Background Technology

[0002] With the increasing severity of the global energy crisis and environmental problems, the development of clean and renewable hydrogen energy has become a research hotspot in the energy field. Photocatalytic water splitting for hydrogen production, which can directly convert solar energy into hydrogen energy, has advantages such as zero carbon emissions and strong sustainability, and is considered one of the most promising methods for green hydrogen production.

[0003] Graphitic carbon nitride (g-C3N4), as a non-metallic polymer semiconductor photocatalyst, has attracted widespread attention in the field of photocatalytic hydrogen production due to its suitable band structure, good chemical stability, low cost, and ease of preparation. However, pure g-C3N4 suffers from defects such as limited specific surface area, fast recombination rate of photogenerated electron-hole pairs, and narrow visible light absorption range, resulting in low photocatalytic hydrogen production activity.

[0004] Metal-organic framework (MOF) materials, especially copper-based MOFs (Cu-MOFs), possess ultra-high specific surface area, tunable pore structure, and abundant active sites. Furthermore, the redox properties of Cu²⁺ / Cu⁺ endow them with excellent photocatalytic response. Constructing heterojunctions by combining Cu-MOFs with g-C₃N₄ is an effective strategy to improve the photocatalytic performance of g-C₃N₄. However, traditional composite methods often involve physical mixing or disordered loading, which can lead to problems such as masking of Cu-MOF active sites, weak interfacial contact in the heterojunction, and low charge transport efficiency, thus limiting the photocatalytic hydrogen production performance of the composite material.

[0005] Meanwhile, in existing photocatalytic water splitting hydrogen production processes, reaction conditions have not been systematically optimized, and the efficiency of catalysts, the stability and reproducibility of the hydrogen production reaction all need to be improved. Furthermore, there is a lack of specific photocatalytic hydrogen production process parameters for carbon nitride-copper-based MOF composite catalysts, making it difficult to fully utilize the synergistic catalytic advantages of the composite material. Therefore, developing a photocatalytic water splitting hydrogen production method adapted to carbon nitride-supported copper-based MOF composite catalysts, with controllable reaction conditions, high hydrogen production efficiency, and good stability, has significant practical application value. Summary of the Invention

[0006] Purpose of the invention This invention aims to overcome the shortcomings of existing technologies and provide a photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst. This method optimizes the reaction system and process parameters for photocatalytic hydrogen production by taking into account the structural and performance characteristics of the carboxyl-functionalized carbon nitride-supported copper-based MOF (C3N4-C-MOF) composite catalyst. This achieves efficient and stable water splitting for hydrogen production under visible light. Furthermore, the optimal reaction conditions were determined using response surface methodology, significantly improving hydrogen production efficiency and catalyst recyclability.

[0007] Technical solution To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst, comprising a carboxyl-functionalized carbon nitride-supported copper-based MOF (C3N4-C-MOF) as the photocatalyst, eosin Y as the photosensitizer, and triethanolamine as the electron donor, to construct an aqueous photocatalytic reaction system, and to achieve hydrogen production through water splitting under visible light irradiation, specifically including the following steps: 1. Catalyst pretreatment: C3N4-C-MOF2.0 with a molar ratio of C3N4-C to Cu(NO3)2・3H2O of 1:2.0 was selected as the photocatalyst. It was ground to a particle size of 100-200 mesh, vacuum dried and placed in a desiccator for later use. The C3N4-C-MOF2.0 is a mesoporous material with an average pore size of 4-5 nm and a specific surface area of ​​more than 20.37 m² / g.

[0008] 2. Preparation of photocatalytic reaction system: In the photocatalytic reactor, deionized water, triethanolamine, the C3N4-C-MOF2.0 photocatalyst pretreated in step 1, and eosin Y were added sequentially. The mixture was ultrasonically dispersed for 20-30 min to form a uniform suspension reaction system. The volume ratio of triethanolamine to deionized water was 1:24, the amount of photocatalyst added was 0.005 g / 50 mL of the reaction system, and the amount of eosin Y added was 0.0075 g / 50 mL of the reaction system. The pH value of the reaction system was adjusted to 8.0-9.0.

[0009] 3. Degassing of the reaction system: Seal the photocatalytic reactor containing the suspended reaction system, turn on the vacuum pump to evacuate the air in the reaction system, maintain the vacuum environment in the reactor, and prevent oxygen from interfering with the photocatalytic hydrogen production reaction.

[0010] 4. Visible light photocatalytic hydrogen production reaction: The degassed reactor was placed in the photocatalytic activity evaluation system, and the cooling circulation device was turned on to control the temperature of the reaction system at 6℃. A 300W xenon lamp equipped with a 420nm long-pass filter was used as the visible light source to irradiate the reaction system. The distance between the light source and the reactor was 10-15cm. The photocatalytic hydrolysis hydrogen production reaction was carried out under stirring conditions for 3 hours.

[0011] 5. Hydrogen production detection: An online gas chromatograph with nitrogen as the carrier gas is used to detect the hydrogen generated during the photocatalytic reaction in real time, and the hydrogen generation rate and cumulative hydrogen production are recorded.

[0012] 6. Catalyst recycling: After the reaction is completed, the reaction system is centrifuged to separate the solid C3N4-C-MOF2.0 catalyst. The catalyst is then washed with ethanol and deionized water 3-5 times in sequence, dried under vacuum, and the above steps 2-5 are repeated to achieve catalyst recycling.

[0013] Furthermore, in step 2, the pH value of the reaction system is adjusted using dilute hydrochloric acid or dilute sodium hydroxide solution, preferably to 9.0.

[0014] Furthermore, in step 4, the stirring rate is 300-500 r / min to ensure that the catalyst is uniformly dispersed in the reaction system and fully exposed to visible light.

[0015] Furthermore, the preparation method of the C3N4-C-MOF2.0 includes the following steps: a. Preparation of carboxyl-functionalized carbon nitride (C3N4-C): Dicyandiamide, cyanuric chloride and 4-cyanobenzoic acid were dissolved in acetonitrile in a molar ratio of 1:2:2. After mixing and stirring for 1 h, the mixture was transferred to a high-pressure reactor lined with polytetrafluoroethylene and reacted at 180 °C for 24 h using a solvothermal method. After cooling, the mixture was centrifuged, washed, dried and ground to obtain C3N4-C powder. Preparation of bbC3N4-C-MOF2.0: Cu(NO3)2・3H2O was dissolved in deionized water, and C3N4-C powder was added. The molar ratio of C3N4-C to Cu(NO3)2・3H2O was 1:2.0. After sonication for 0.5 h, the mixture was dried at 90 °C for 6 h. Unadsorbed Cu²⁺ was removed by washing. Then, a mixed solution of 1,3,5-benzoic acid and ethanol-DMF (volume ratio 1:1) was added. After stirring for 30 min, the mixture was transferred to a high-pressure reactor and reacted at 100 °C for 10 h. After centrifugation, washing, and drying at 60 °C, the C3N4-C-MOF2.0 composite catalyst was obtained.

[0016] Beneficial effects Compared with the prior art, the present invention has the following significant advantages: 1. High hydrogen production efficiency: This invention selects the best-performing C3N4-C-MOF2.0 as the photocatalyst, and combined with optimized reaction system and process parameters, the photocatalytic hydrogen evolution rate can reach 12.68 mmol·g under visible light irradiation. -1 ·h -1 It is far superior to the hydrogen production efficiency of pure g-C3N4, uncarboxylated C3N4-MOF and single Cu-MOF, and is 1.68 times the hydrogen production efficiency of unmodified C3N4-MOF.

[0017] 2. Controllable and adaptable reaction conditions: Based on the structural characteristics of the C3N4-C-MOF composite catalyst, the dosage of photosensitizer and electron donor, as well as parameters such as reaction pH, temperature, and light conditions, were systematically optimized. The optimal reaction conditions (reaction time 3h, pH 9.0, Cu content 0.2g / 50mL system) were determined by response surface methodology, which fully leveraged the heterojunction synergistic catalytic advantages of the composite material, effectively suppressed the recombination of photogenerated electron-hole pairs, and improved charge separation and transport efficiency.

[0018] 3. The catalyst has good stability and can be recycled: The hydrogen production method of the present invention does not damage the catalyst. After the reaction, the C3N4-C-MOF2.0 catalyst recovered can be recycled 5 times after simple washing and drying, and the hydrogen production only decreases slightly. Moreover, the crystal structure and chemical functional groups of the catalyst do not change significantly. It has good structural stability and recycling performance, which reduces the cost of hydrogen production.

[0019] 4. Simple process operation and easy to scale up production: The photocatalytic hydrogen production method of the present invention does not require complicated equipment, the reaction conditions are mild, the visible light source is readily available, the process steps are clear and highly controllable, and the reaction system is an aqueous system, which is environmentally friendly and suitable for large-scale industrial production, providing a feasible technical solution for green hydrogen production.

[0020] 5. Good synergy of the reaction system: With eosin Y as a photosensitizer and triethanolamine as an electron donor, a highly efficient photocatalytic synergistic system is formed with the C3N4-C-MOF2.0 catalyst. Eosin Y can expand the visible light absorption range, and triethanolamine can capture photogenerated holes in time, further inhibiting charge recombination and improving the continuous ability of hydrogen production reaction. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 is a transmission electron microscope image of the C3N4-C-MOF2.0 catalyst used in the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The scope of protection of the present invention is not limited to the following embodiments, and all equivalent transformations made based on the technical solution of the present invention fall within the scope of protection of the present invention. The C3N4-C-MOF2.0 composite catalyst used in the present invention was prepared according to the aforementioned preparation method. The photocatalytic activity evaluation system adopted was a CEL-PAEM-D8Pro model (Beijing Zhongjiao Jinyuan), the gas chromatograph adopted was a GC-2014C model (Shimadzu), and the xenon lamp was 300W equipped with a 420nm long-pass filter.

[0023] Example 1 A photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst, comprising the following steps: 1. Catalyst pretreatment: C3N4-C-MOF2.0 with a molar ratio of C3N4-C to Cu(NO3)2・3H2O of 1:2.0 was selected as the photocatalyst. It was ground to 150 mesh, vacuum dried at 60℃ for 12h, and then placed in a desiccator for later use.

[0024] 2. Preparation of photocatalytic reaction system: In a 50mL photocatalytic reactor, add 48mL of deionized water and 2mL of triethanolamine, then add 0.005g of pretreated C3N4-C-MOF2.0 photocatalyst and 0.0075g of eosin Y, and ultrasonically disperse for 25min to form a uniform suspension system; adjust the pH of the system to 9.0 with dilute sodium hydroxide solution.

[0025] 3. Degassing of the reaction system: Seal the reaction vessel, turn on the vacuum pump to evacuate for 10 minutes to remove the air inside the vessel and maintain a vacuum environment.

[0026] 4. Visible light photocatalytic hydrogen production reaction: Place the reactor in the photocatalytic activity evaluation system, turn on the cooling circulation device, and control the reaction system temperature to 6℃; turn on the 300W xenon lamp (420nm long-pass filter), with the distance between the light source and the reactor 12cm, adjust the stirring rate to 400r / min, and irradiate the reaction for 3h.

[0027] 5. Hydrogen production detection: The amount of hydrogen produced was detected in real time using an online gas chromatograph (nitrogen as carrier gas), and the hydrogen evolution rate was measured to be 12.68 mmol·g. -1 ·h -1 .

[0028] 6. Catalyst recycling: After the reaction, the catalyst was collected by centrifugation, washed four times each with ethanol and deionized water, dried under vacuum at 60°C, and then steps 2-5 were repeated. After five recycling cycles, the hydrogen evolution rate remained at 10.5 mmol·g. -1 ·h -1 The catalyst structure remained largely unchanged.

[0029] Example 2 A photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst, comprising the following steps: 1. Catalyst pretreatment: Same as in Example 1.

[0030] 2. Preparation of photocatalytic reaction system: In a 50mL photocatalytic reaction vessel, add 48mL of deionized water and 2mL of triethanolamine, then add 0.005g of C3N4-C-MOF2.0 photocatalyst and 0.0075g of eosin Y, sonicate for 20min, and adjust the pH of the system to 8.5 with dilute hydrochloric acid.

[0031] 3. Degassing of the reaction system: Same as in Example 1.

[0032] 4. Visible light catalytic hydrogen production reaction: control the reaction temperature at 6℃, the distance between the xenon lamp source and the reaction vessel at 10cm, the stirring rate at 300r / min, and irradiate the reaction for 3h.

[0033] 5. Hydrogen production detection: The hydrogen evolution rate was measured to be 11.25 mmol·g. -1 ·h -1 .

[0034] 6. Catalyst recycling: Same as in Example 1, after 5 cycles, the hydrogen evolution rate remained at 9.8 mmol·g. -1 ·h -1 above.

[0035] Comparative Example 1 Using pure g-C3N4 as the photocatalyst, and with all other reaction conditions identical to those in Example 1, the hydrogen evolution rate was measured to be only 0.53 mmol·g. -1 ·h -1 The efficiency is far lower than that of the hydrogen production method of this invention.

[0036] Comparative Example 2 Using uncarboxylated C3N4-MOF2.0 as the photocatalyst, and with all other reaction conditions identical to those in Example 1, the hydrogen evolution rate was measured to be 7.54 mmol·g. -1 ·h -1 It is approximately 59% of the hydrogen production efficiency of the method of the present invention.

[0037] Comparative Example 3 The reaction time was changed to 2 hours, and all other reaction conditions were exactly the same as in Example 1. The hydrogen evolution rate was measured to be 9.38 mmol·g. -1 ·h -1 Due to insufficient reaction time, the catalytic performance of the catalyst was not fully utilized, resulting in a significant decrease in hydrogen production efficiency.

[0038] Comparative Example 4 The pH of the reaction system was adjusted to 7.0, and all other reaction conditions were exactly the same as in Example 1. The hydrogen evolution rate was measured to be 6.22 mmol·g. -1 ·h -1 A slightly acidic reaction environment is not conducive to the photocatalytic hydrogen production reaction, and the charge separation efficiency is reduced.

[0039] The results of the above examples and comparative examples show that the photocatalytic water splitting hydrogen production method of the present invention using carbon nitride-supported copper-based MOF catalyst can significantly improve the efficiency of water splitting hydrogen production under visible light by selecting the optimal C3N4-C-MOF2.0 catalyst and optimizing process parameters such as reaction pH, time, and temperature. Moreover, the catalyst has good cycle stability and has obvious technical advantages compared with the prior art.

[0040] This invention is not limited to the specific embodiments described above. Those skilled in the art can make various modifications or variations within the scope of the essence of this invention, and these modifications or variations should also be considered within the scope of protection of this invention.

Claims

1. A method for photocatalytic water splitting to produce hydrogen using a carbon nitride-supported copper-based MOF catalyst, characterized in that, A photocatalytic reaction system was constructed using carboxyl-functionalized carbon nitride supported copper-based MOF as a photocatalyst, eosin Y as a photosensitizer, and triethanolamine as an electron donor to achieve hydrogen production by water electrolysis under visible light irradiation. The photocatalyst was C3N4-C-MOF2.0, which was prepared by mixing C3N4-C and Cu(NO3)2·3H2O in a molar ratio of 1:2.

0.

2. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to claim 1, characterized in that, Includes the following steps: (1) Catalyst pretreatment: C3N4-C-MOF2.0 is ground to 100-200 mesh, vacuum dried and placed in a desiccator for later use; (2) Preparation of photocatalytic reaction system: Deionized water, triethanolamine, pretreated C3N4-C-MOF2.0 and eosin Y are added to the photocatalytic reaction vessel, ultrasonically dispersed for 20-30 min, and the pH value of the reaction system is adjusted to 8.0-9.0; (3) Degassing of the reaction system: Seal the photocatalytic reactor, evacuate the reactor to remove air and maintain a vacuum environment; (4) Visible light catalytic hydrogen production reaction: The reaction vessel was placed in the photocatalytic activity evaluation system, the reaction system temperature was controlled at 6℃, and a 300W xenon lamp equipped with a 420nm long-pass filter was used as the visible light source for irradiation, and the reaction was carried out under stirring conditions; (5) Hydrogen production detection: The amount of hydrogen produced during the photocatalytic reaction was detected using an online gas chromatograph with nitrogen as the carrier gas.

3. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to claim 2, characterized in that, In step (2), the volume ratio of triethanolamine to deionized water is 1:24, the amount of C3N4-C-MOF2.0 added is 0.005g / 50mL of the reaction system, and the amount of eosin Y added is 0.0075g / 50mL of the reaction system.

4. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to claim 2, characterized in that, In step (2), the pH value of the reaction system is adjusted by dilute hydrochloric acid or dilute sodium hydroxide solution, preferably to 9.

0.

5. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to claim 2, characterized in that, In step (4), the distance between the visible light source and the reaction vessel is 10-15 cm, the stirring rate is 300-500 r / min, and the photocatalytic reaction time is 3 h.

6. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to any one of claims 1-5, characterized in that, The C3N4-C-MOF2.0 is a mesoporous material with an average pore size of 4-5 nm, and its preparation method includes the following steps: (1) Preparation of carboxyl-functionalized carbon nitride C3N4-C: Dicyandiamide, cyanuric chloride and 4-cyanobenzoic acid were dissolved in acetonitrile in a molar ratio of 1:2:

2. After mixing and stirring for 1 h, the mixture was subjected to a solvothermal reaction at 180 °C for 24 h. After cooling, the mixture was centrifuged, washed, dried and ground to obtain C3N4-C powder. (2) Preparation of C3N4-C-MOF2.0: Cu(NO3)2·3H2O was dissolved in deionized water, C3N4-C powder was added and ultrasonicated for 0.5 h, dried at 90℃ for 6 h, and then washed to remove unadsorbed Cu²+; then 1,3,5-benzotriic acid and ethanol-DMF mixed solution with a volume ratio of 1:1 were added, stirred for 30 min, and then subjected to a solvothermal reaction at 100℃ for 10 h. After centrifugation, washing, and drying at 60℃, C3N4-C-MOF2.0 was obtained.

7. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to claim 2, characterized in that, It also includes a catalyst recycling step: centrifuge the system after the reaction in step (5), collect the solid phase C3N4-C-MOF2.0, wash it with ethanol and deionized water, vacuum dry it, and repeat the operation of steps (2)-(5) in claim 2.

8. The photocatalytic water splitting method for hydrogen production using a carbon nitride-supported copper-based MOF catalyst according to claim 1, characterized in that, The C3N4-C and Cu-MOF form a type II heterojunction, enabling a hydrogen evolution rate of up to 12.7 mmol·g⁻¹ in photocatalytic hydrolysis for hydrogen production. -1 ·h -1 .

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