Preparation method and hydrogen production application of ultrathin oxygen-doped graphite carbon nitride nanosheet loaded amorphous mesoporous nickel hydroxide photocatalyst

Abstract

The application provides a preparation method and hydrogen production application of an ultrathin oxygen-doped graphite carbon nitride nanosheet loaded amorphous mesoporous nickel hydroxide photocatalyst. First, the ultrathin oxygen-doped graphite carbon nitride nanosheet loaded amorphous mesoporous nickel hydroxide photocatalyst is prepared by a co-heating method and an in-situ method. The application has a higher hydrogen production capacity of 4764.9 mu mol h under the following conditions: a temperature condition of 25 DEG C, a solvent condition of 90 mL of water and 10 mL of triethanolamine, and a condition of 150 uL of 1 g / 100 mL of chloroplatinic acid aqueous solution. ‑1 ·g ‑1 The catalyst has a higher specific surface area and better cycle stability.

Description

Technical Field

[0001] This invention relates to a method for preparing an ultrathin oxygen-doped graphitic carbon nitride nanosheet-supported amorphous mesoporous nickel hydroxide photocatalyst for hydrogen production and its application in water splitting for hydrogen production. Background Technology

[0002] Currently, the world is striving to address numerous challenges and issues related to the environment and energy sector. On the one hand, the use of traditional energy sources such as coal and oil has led to substantial greenhouse gas emissions, exacerbating the impacts of global warming and climate change. On the other hand, the development and use of renewable energy also face various technological obstacles and limitations. In this context, photocatalytic hydrogen evolution has emerged as a promising environmentally friendly energy production technology, characterized by its high efficiency, sustainability, and ease of storage and transportation. It will play an increasingly important role in the future of the environment and energy sector. However, most photocatalysts have certain limitations, including a narrow absorption range of sunlight and low charge separation efficiency, which restricts their industrial applications. Therefore, there is an urgent need to develop photocatalysts with broad absorption spectra and high charge separation efficiency.

[0003] Graphitized carbon nitride (g-C3N4 or CN) is a photocatalyst with a sheet-like structure, excellent thermal stability, visible light responsiveness, and a large specific surface area, providing numerous catalytic active sites. It is a non-toxic, metal-free photocatalyst and has been extensively studied due to its potential application in hydrogen production and water splitting. Despite its advantages, CN has limitations such as a narrow absorption spectrum and low electron transfer efficiency. To overcome these limitations, researchers have explored elemental doping and heterojunction engineering methods to improve photocatalytic activity. Non-metallic atoms, such as phosphorus, oxygen, sulfur, and boron, can be introduced through doping, creating additional energy levels in the valence band and increasing the maximum position of the valence band. This improves the electron-hole pair separation efficiency and increases the rate of the photocatalytic reaction. In particular, oxygen doping has proven to be an effective method for extending the photoreaction due to its excellent electronic modulation effect. It is worth noting that doping with non-metallic elements can have complex effects on the electronic structure, configuration, and chemical properties of the photocatalyst. Therefore, a comprehensive consideration is needed in practical applications to achieve optimal catalytic performance. The formation of heterojunction structures can further improve the carrier separation and transport rates. Compared with single catalysts, heterojunctions of semiconductor materials can promote the direct transfer of electrons and holes within the heterojunction, thereby reducing electron-hole pair recombination and achieving higher photocatalytic activity. Furthermore, heterojunctions formed from semiconductor materials with broad-spectrum responses enable them to absorb more solar energy. Ni(OH)₂ possesses excellent light absorption properties, high photocatalytic hydrogen evolution efficiency, convenient synthesis and processing, and high stability. Therefore, it has been widely used in the field of photocatalytic water splitting. In addition, amorphous materials generally exhibit a higher specific surface area than crystalline materials, mainly due to the lack of long-range ordered structures. These surfaces provide more reaction sites; however, research on amorphous Ni(OH)₂ (a-Ni(OH)₂) is still relatively limited.

[0004] An ultrathin porous CN nanosheet with oxygen-doped defects, denoted as OCN, was prepared using a simple co-thermal method. Subsequently, a heterojunction with α-Ni(OH)₂, denoted as a-Ni(OH)₂ / OCN, was prepared in situ through a stirring process. The porous ultrathin OCN nanosheet and the mesoporous amorphous structure of α-Ni(OH)₂ increased the specific surface area and active sites, improved the proton transport rate, and maximized the bonding between the two catalysts. Furthermore, oxygen doping altered the band structure of CN, improved the position of the band gap (VB), shortened the band gap, and broadened the absorption of sunlight. In addition, the heterojunction structure formed between OCN and α-Ni(OH)₂ promoted electron separation and improved charge separation efficiency. This novel heterojunction assembly exhibits excellent photocatalytic hydrogen production performance, providing new insights for the preparation of high-performance CN-based photocatalysts and the development of novel environmental energy sources. The implementation of this project was supported by the National Natural Science Foundation of China (No. 21277008; 20777005), the Beijing Natural Science Foundation (No. 8082008), and the National Key Research and Development Program of China (No. 2017YFC0209905), and is also the research content of these projects. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an ultrathin oxygen-doped carbon nitride nanosheet-supported amorphous mesoporous nickel hydroxide photocatalyst and its application in photocatalytic hydrogen production. An ultrathin porous CN nanosheet with oxygen-doped defects, denoted as OCN, was prepared using a simple co-thermal method. Subsequently, an amorphous Ni(OH)₂ heterojunction, denoted as a-Ni(OH)₂ / OCN, was prepared in situ through stirring. The resulting a-Ni(OH)₂ / OCN heterojunction photocatalyst exhibits a high specific surface area, broad spectral absorption, and excellent charge separation, demonstrating superior photocatalytic hydrogen production performance and cycle stability. The composite material has a high specific surface area of ​​30.66 m². 2 / g, a-Ni(OH)2 / OCN exhibits the highest photocatalytic hydrogen production rate: 4764.9 μmol·h⁻¹. -1 ·g -1 It is 4.7 times that of CN. The results show that the key factor for the improved hydrogen production performance of the a-Ni(OH)2 / OCN heterojunction photocatalyst is the synergistic effect of oxygen doping and heterojunction.

[0006] This invention provides a method for preparing an a-Ni(OH)2 / OCN heterojunction catalyst for photocatalytic hydrogen production:

[0007] (1) Mix and grind 20g of urea and 2g of oxalic acid, then calcine them in a muffle furnace at 520℃ for 2h at a heating rate of 3℃ per minute to obtain OCN. CN is obtained without adding oxalic acid. Then, disperse 0.1g of CN or OCN and 0.01g of Ni(NO3)2·6H2O in 50mL of ethanol, then add 0.02g of KHCO3, stir for 2h, then centrifuge several times with water and ethanol, and dry to obtain a-Ni(OH)2 / CN or a-Ni(OH)2 / OCN.

[0008] (2) 50 mg of the catalyst prepared above was placed in a reaction apparatus, 90 mL of water and 10 mL of triethanolamine were added, and then 150 μL of a chloroplatinic acid aqueous solution with a concentration of 1 g / 100 mL was added. The reaction temperature was 25 °C and the reaction time was 3 h. The final photocatalytic hydrogen production rate of a-Ni(OH)2 / OCN was 4764.9 μmol·h. -1 ·g -1 . Attached Figure Description

[0009] Figure 1 The XRD patterns of the CN, OCN, CN / a-Ni(OH)2, and OCN / a-Ni(OH)2 catalysts prepared in this invention are shown.

[0010] Figure 2 Figure 1 shows the N2- adsorption / desorption of the CN, OCN, CN / a-Ni(OH)2, and OCN / a-Ni(OH)2 catalysts prepared in this invention.

[0011] Figure 3 The hydrogen production performance of the CN, OCN, CN / a-Ni(OH)2, and OCN / a-Ni(OH)2 catalysts prepared in this invention is shown in the figure.

[0012] Figure 4 The diagram shows the hydrogen production cycle of the OCN / a-Ni(OH)2 catalyst prepared in this invention. Detailed Implementation

[0013] 50 mg of adsorbent was used in the experiment.

[0014] Example 1

[0015] (1) 20g of urea was calcined in a muffle furnace at 520℃ for 2h at a heating rate of 3℃ per minute to obtain CN.

[0016] (2) 50 mg of the catalyst prepared above was placed in the reaction apparatus, 90 mL of water and 10 mL of triethanolamine were added, and then 150 μL of chloroplatinic acid aqueous solution with a concentration of 1 g / 100 mL was added. Finally, the apparatus was evacuated, the reaction temperature was 25 °C, and the reaction time was 3 h. The final CN photocatalytic hydrogen production rate was 1024.2 μmol·h. -1 ·g -1 .

[0017] Example 2

[0018] (1) Mix and grind 20g of urea and 2g of oxalic acid, then calcine them in a muffle furnace at 520℃ for 2h at a heating rate of 3℃ per minute to obtain OCN.

[0019] (2) 50 mg of the catalyst prepared above was placed in the reaction apparatus, 90 mL of water and 10 mL of triethanolamine were added, and then 150 μL of a 1 g / 100 mL aqueous solution of chloroplatinic acid was added. Finally, the apparatus was evacuated, the reaction temperature was 25 °C, and the reaction time was 3 h. The final OCN photocatalytic hydrogen production rate was 2645.2 μmol·h. -1 ·g -1 .

[0020] Example 3

[0021] (1) 20g of urea was calcined in a muffle furnace at 520℃ for 2h at a heating rate of 3℃ per minute to obtain CN. Then, 0.1g of CN and 0.01g of Ni(NO3)2·6H2O were dispersed in 50mL of ethanol, and then 0.02g of KHCO3 was added. The mixture was stirred for 2h, then centrifuged several times with water and ethanol, and dried to obtain a-Ni(OH)2 / CN.

[0022] (2) 50 mg of the catalyst prepared above was placed in the reaction apparatus, 90 mL of water and 10 mL of triethanolamine were added, and then 150 μL of chloroplatinic acid aqueous solution with a concentration of 1 g / 100 mL was added. Finally, the apparatus was evacuated, the reaction temperature was 25 °C, and the reaction time was 3 h. The final a-Ni(OH)2 / CN photocatalytic hydrogen production rate was 2327.4 μmol·h. -1 ·g -1 .

[0023] Example 4

[0024] (1) 20g of urea and 2g of oxalic acid were mixed and ground, and then calcined in a muffle furnace at 520℃ for 2h at a heating rate of 3℃ per minute to obtain OCN. Then, 0.1g of OCN and 0.01g of Ni(NO3)2·6H2O were dispersed in 50mL of ethanol, and then 0.02g of KHCO3 was added. The mixture was stirred for 2h, and then centrifuged several times with water and ethanol and dried to obtain α-Ni(OH)2 / OCN.

[0025] (2) 50 mg of the catalyst prepared above was placed in the reaction apparatus, 90 mL of water and 10 mL of triethanolamine were added, and then 150 μL of chloroplatinic acid aqueous solution with a concentration of 1 g / 100 mL was added. Finally, the apparatus was evacuated, the reaction temperature was 25 °C, and the reaction time was 3 h. The final a-Ni(OH)2 / OCN photocatalytic hydrogen production rate was 4764.9 μmol·h. -1 ·g -1 .

Claims

1. A method for preparing an ultrathin oxygen-doped graphitic carbon nitride nanosheet supported amorphous mesoporous nickel hydroxide photocatalyst for photocatalytic hydrogen production, characterized in that, Comprising the following steps: (1) Preparation of oxygen-doped defect ultrathin porous CN nanosheets Preparation of oxygen-doped defect ultrathin porous CN nanosheets by co-thermal method: 20 g of urea and 2 g of oxalic acid were mixed and ground, then calcined at 520℃ for 2h in a muffle furnace with a heating rate of 3℃ per minute, to obtain oxygen-doped defect ultrathin porous CN nanosheets, denoted as OCN; (2) In-situ preparation of amorphous Ni(OH)2 / OCN heterojunction catalyst Preparation of amorphous Ni(OH)2 / OCN heterojunction catalyst by in-situ method: 0.1 g of OCN and 0.01 g of Ni(NO3)2·6H2O were dispersed in 50 mL of ethanol, then 0.02 g of KHCO3 was added, stirred for 2h, then centrifuged with water and ethanol several times, and dried to obtain amorphous Ni(OH)2 / OCN heterojunction catalyst, denoted as a-Ni(OH)2 / OCN.

2. Use of the catalyst prepared according to the method of claim 1 in the photocatalytic production of hydrogen, characterized in that: Take 50 mg of the above prepared catalyst and place it in a reaction device, add 90 mL of water and 10 mL of triethanolamine, then add 150 μL of chloroplatinic acid aqueous solution with a concentration of 1 g / 100 mL, finally vacuum the device, the reaction temperature is 25℃, and the reaction time is 3h.

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