Bromine / cobalt co-doped hollow rod-like carbon nitride photocatalyst and preparation method thereof

Abstract

This invention discloses a bromine / cobalt co-doped hollow rod-shaped carbon nitride photocatalyst and its preparation method, belonging to the technical field of photocatalytic materials and CO2 resource utilization. The invention involves the self-assembly of melamine and cyanuric acid to form a supramolecular rod-shaped precursor, followed by thermal polymerization to obtain hollow rod-shaped carbon nitride (RCN). Using RCN as a support and cobalt nitrate and hexadecyltrimethylammonium bromide as doping sources, a hydrothermal reaction is then performed to prepare the bromine / cobalt co-doped hollow rod-shaped carbon nitride Br / Co-RCN photocatalyst. This catalyst exhibits a hollow rod morphology, a large specific surface area, and uniform doping of bromine and cobalt within the carbon nitride framework. The catalyst of this invention demonstrates excellent photocatalytic CO2 reduction performance under simulated sunlight, achieving a CO yield of 130.06 μmol·g. ‑1 ·h ‑1 Furthermore, the preparation process is simple, the conditions are mild, and the reproducibility is good, showing promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst and CO2 resource utilization technology, specifically relating to a bromine / cobalt co-doped hollow rod-shaped carbon nitride photocatalyst for photocatalytic reduction of CO2 and its preparation method. Background Technology

[0002] With the massive consumption of fossil fuels, CO2 emissions continue to increase, leading to increasingly prominent greenhouse effect and energy crisis issues. Photocatalytic reduction technology, which uses solar energy to drive the conversion of CO2 into fuels or chemical feedstocks such as CO and CH4, has attracted widespread attention due to its mild reaction conditions and environmental friendliness.

[0003] Graphitic carbon nitride (g-C3N4), as a non-metallic semiconductor photocatalytic material, possesses advantages such as visible light response, good chemical stability, and low preparation cost, and shows promising application prospects in the field of photocatalytic CO2 reduction. However, existing g-C3N4 materials generally suffer from problems such as small specific surface area, severe recombination of photogenerated carriers, and insufficient CO2 adsorption and activation capabilities, which limit further improvement of their photocatalytic performance.

[0004] To address the aforementioned issues, existing technologies typically modify g-C3N4 through morphology control or elemental doping. For example, constructing nanosheets, porous, or hollow structures to increase specific surface area, or introducing metallic or non-metallic elements to modulate band structure and carrier behavior. However, single modification methods often fail to simultaneously achieve optimal light absorption, carrier separation, and surface reactivity, thus still falling short of the requirements for highly efficient CO2 photocatalytic reduction. Therefore, how to improve the separation efficiency of photogenerated carriers and CO2 reduction performance while maintaining the structural stability of g-C3N4 through rational structural design and synergistic elemental doping is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a bromine / cobalt co-doped hollow rod-shaped carbon nitride photocatalyst and its preparation method. By constructing a hollow rod-shaped structure and combining it with synergistic doping of bromine and cobalt, the separation and migration efficiency of photogenerated carriers in the catalyst is improved, thereby enhancing the photocatalytic reduction performance of CO2. To achieve the above objective, this invention constructs a bromine / cobalt co-doped hollow rod-shaped carbon nitride photocatalyst, and the preparation method is as follows:

[0006] (1) First, hollow rod-shaped carbon nitride (RCN) was prepared. The steps were as follows: 3.20 g of melamine and 3.22 g of cyanuric acid were added to 250 mL of deionized water and stirred at 80 °C until completely dissolved to obtain melamine solution and cyanuric acid solution. Then, the cyanuric acid solution was poured into the melamine solution and stirred at 500 rpm for 4 h. The white precipitate was collected and washed three times with deionized water at 80 °C. The precipitate was dried at 100 °C for 12 h and then heated to 520 °C at a heating rate of 2 °C / min and kept at that temperature for 4 h. The precipitate was then naturally cooled to room temperature to obtain RCN.

[0007] (2) Then, bromine / cobalt co-doped hollow rod-shaped carbon nitride (Br / Co-RCN) was prepared. The steps were as follows: 90 mg RCN was stirred and dispersed in 15 mL of deionized water, 10 mg Co(NO3)2·6H2O was dispersed in 15 mL of ethylene glycol, and 100 mg hexadecyltrimethylammonium bromide (CTAB) was dispersed in 5 mL of ethylene glycol to obtain the reaction precursor solutions respectively; 15 mL of Co(NO3)2·6H2O ethylene glycol solution and 5 mL of CTAB ethylene glycol solution were mixed and added dropwise to 15 mL of RCN aqueous dispersion, and then stirred continuously at 500 rpm for 2 h. The mixture was then placed in a 100 mL high-pressure reactor and kept at 180 ℃ for 2 h to obtain a white precipitate. The precipitate was then washed twice with deionized water and ethanol respectively; finally, the precipitate was dried in a vacuum oven at 80 ℃ for 12 h to obtain Br / Co-RCN.

[0008] This invention has the following characteristics: By combining bromine / cobalt co-doping with hollow rod-shaped structure design, a Br / Co-RCN photocatalyst with a unique three-dimensional porous framework is prepared. Its advantages are: (1) The hollow rod-shaped morphology gives the catalyst a larger specific surface area and abundant internal and external surface active sites. The specific surface area of ​​Br / Co-RCN reaches 5.8 times that of ordinary carbon nitride (CN), while providing excellent light capture and reactant diffusion channels; (2) The synergistic effect of bromine and cobalt co-doping with the hollow structure not only optimizes the band structure of the material, but also significantly inhibits the recombination of photogenerated carriers and promotes efficient charge separation and migration; (3) The entire preparation process uses common chemicals as raw materials and is achieved through controllable self-assembly and hydrothermal reaction. The process does not require complex templates, the conditions are mild and reproducible, and it has the potential for large-scale production. Finally, the CO yield of this catalyst reached 130.06 μmol·g under simulated sunlight. -1 ·h -1 It exhibits photocatalytic CO2 reduction performance that is significantly superior to that of traditional carbon nitride materials. Attached Figure Description

[0009] Figure 1 This is a flowchart illustrating the preparation method of Br / Co-RCN photocatalysts.

[0010] Figure 2 Scanning electron microscope (SEM) image of Br / Co-RCN prepared for this invention.

[0011] Figure 3 X-ray diffraction (XRD) patterns of CN, RCN, Br-doped hollow rod carbon nitride (Br-RCN), Co-doped hollow rod carbon nitride (Co-RCN), and Br / Co-RCN. Figure 3 a), Fourier transform infrared (FTIR) spectrum ( Figure 3 b), and X-ray photoelectron spectroscopy (XPS) plot ( Figure 3 c C 1s, Figure 3 d N 1s, Figure 3 e Br 3d, Figure 3 f Co 2p).

[0012] Figure 4 The UV-Vis DRS spectra of CN, RCN, Br-RCN, Co-RCN, and Br / Co-RCN are shown. Figure 4 a) and transient photocurrent response (TPR) diagram ( Figure 4 b).

[0013] Figure 5 Photocatalytic CO2 reduction of CO using CN, RCN, Br-RCN, Co-RCN, and Br / Co-RCN. Figure 5 a) and CH4 ( Figure 5 b) Production comparison chart. Detailed Implementation

[0014] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0015] The preparation method of Br / Co-RCN in this invention is as follows: Figure 1As shown, the following steps are included: (1) First, hollow rod-shaped carbon nitride (RCN) is prepared. The steps are as follows: 3.20 g of melamine and 3.22 g of cyanuric acid are added to 250 mL of deionized water and stirred at 80 °C until completely dissolved to obtain melamine solution and cyanuric acid solution; then, the cyanuric acid solution is poured into the melamine solution and stirred at 500 rpm for 4 h. The white precipitate is collected and washed 3 times with deionized water at 80 °C; the precipitate is dried at 100 °C for 12 h, and then heated to 520 °C at a heating rate of 2 °C / min, kept at the temperature for 4 h, and naturally cooled to room temperature to obtain RCN. (2) Then, bromine / cobalt co-doped hollow rod-shaped carbon nitride (Br / Co-RCN) was prepared. The steps were as follows: 90 mg RCN was stirred and dispersed in 15 mL of deionized water, 10 mg Co(NO3)2·6H2O was dispersed in 15 mL of ethylene glycol, and 100 mg hexadecyltrimethylammonium bromide (CTAB) was dispersed in 5 mL of ethylene glycol to obtain the reaction precursor solutions respectively; 15 mL of Co(NO3)2·6H2O ethylene glycol solution and 5 mL of CTAB ethylene glycol solution were mixed and added dropwise to 15 mL of RCN aqueous dispersion, and then stirred continuously at 500 rpm for 2 h. The mixture was then placed in a 100 mL high-pressure reactor and kept at 180 ℃ for 2 h to obtain a white precipitate. The precipitate was then washed twice with deionized water and ethanol respectively; finally, the precipitate was dried in a vacuum oven at 80 ℃ for 12 h to obtain Br / Co-RCN.

[0016] The principle of hollow rod-shaped structure formation is as follows: During the pre-assembly process, melamine and cyanuric acid self-assemble through hydrogen bonds and van der Waals forces to form a rod-shaped precursor with an ordered supramolecular structure. During the subsequent thermal polymerization process, the surface of the precursor preferentially undergoes polycondensation and cross-linking to form a dense carbon nitride shell. Meanwhile, due to limited mass transfer and a relatively slow thermal polymerization rate, the internal region undergoes melting and decomposition at high temperatures, generating gas that diffuses outwards, accompanied by volume shrinkage. Ultimately, an internal cavity structure is formed while maintaining the rod-shaped morphology.

[0017] The mass contents of Br and Co in Br / Co-RCN were determined to be 2.93 wt.% and 4.14 wt.% by ion chromatography (IC) and inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0018] SEM images of Br / Co-RCN show that it has a hollow rod-like structure, such as Figure 2 As shown. The advantage of this structure lies in its large specific surface area. The specific surface area of ​​the catalyst, measured using a nitrogen adsorption analyzer, is 14.64 m² for CN. 2 g -1 The RCN is 51.24 m.2 g -1 The Br / Co-RCN ratio is 85.18 m. 2 g -1 This demonstrates that the large specific surface area of ​​the Br / Co-RCN hollow rod structure exposes more reactive sites, which is beneficial for the diffusion of CO2 within the catalyst and its adsorption on the surface. On the other hand, the hollow rod structure facilitates multiple reflections and absorptions of light within the catalyst, thereby improving light absorption efficiency.

[0019] In contrast, the preparation method of ordinary carbon nitride (CN) is as follows: 5 g of melamine is placed in a 100 mL covered crucible, and the temperature is increased from room temperature to 550 °C at a heating rate of 5 °C / min. The temperature is maintained for 4 hours. The product is washed twice with deionized water and ethanol, respectively, and then dried under vacuum at 60 °C for 12 hours to obtain CN.

[0020] In contrast, the preparation method of Br-doped hollow rod-shaped carbon nitride (Br-RCN) is as follows: 90 mg RCN is dispersed in 15 mL of deionized water with stirring, and 100 mg of hexadecyltrimethylammonium bromide (CTAB) is dispersed in 5 mL of ethylene glycol to prepare a reaction precursor solution; 5 mL of CTAB ethylene glycol solution is added dropwise to 15 mL of RCN aqueous dispersion, and then stirred continuously at 500 rpm for 2 h. The mixture is then placed in a 100 mL high-pressure reactor and kept at 180 ℃ for 2 h. The precipitate is then washed twice with deionized water and ethanol, respectively. Finally, the precipitate is dried in a vacuum oven at 80 ℃ for 12 h to obtain Br-RCN.

[0021] In contrast, the preparation method of Co-doped hollow rod-shaped carbon nitride (Co-RCN) is as follows: 90 mg RCN is dispersed in 15 mL of deionized water, and 10 mg Co(NO3)2·6H2O is dispersed in 15 mL of ethylene glycol to prepare a reaction precursor solution; 15 mL of Co(NO3)2·6H2O ethylene glycol solution is added dropwise to 15 mL of RCN aqueous dispersion, and then stirred continuously at 500 rpm for 2 h. The mixture is then placed in a 100 mL high-pressure reactor and kept at 180 ℃ for 2 h. The precipitate is then washed twice with deionized water and ethanol, respectively. Finally, the precipitate is dried in a vacuum oven at 80 ℃ for 12 h to obtain Co-RCN.

[0022] The X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) spectra of CN, RCN, Br-RCN, Co-RCN, and Br / Co-RCN are shown below. Figure 3 As shown in (a), (b) and (c)-(f). Figure 3(a) XRD pattern and (b) FTIR pattern show that Br / Co-RCN maintains the same crystal structure and functional group structure as ordinary CN, indicating the successful synthesis of Br / Co-RCN; Figure 3 (c)-(f) demonstrate that Br and Co elements were successfully doped into the crystal structure of carbon nitride and bonded to the carbon or nitrogen atoms of carbon nitride itself, which also shows the successful synthesis of Br / Co-RCN.

[0023] The UV-Vis absorption spectra (UV-vis DRS) and transient photocurrent response (TPR) plots of CN, RCN, Br-RCN, Co-RCN, and Br / Co-RCN are shown below. Figure 4 As shown in (a) and (b), Figure 4 (a) shows that Br / Co-RCN has a larger visible light absorption range and intensity than CN, RCN, Br-RCN, and Co-RCN. Figure 4 (b) shows that Br / Co-RCN has a larger photocurrent intensity than CN, RCN, Br-RCN and Co-RCN, which proves the effectiveness of Br / Co-RCN in broadening the visible light absorption of carbon nitride and enhancing carrier migration and separation.

[0024] A 300 W xenon lamp without a filter was used to provide broad-spectrum illumination conditions simulating sunlight. A photocatalytic reactor with a transparent quartz window at the top was used as the reaction apparatus. 10 mL of deionized water was placed in the reactor. 20 mg of the aforementioned CN, RCN, Br-RCN, Co-RCN, and Br / Co-RCN catalysts were ground into fine powder and dispersed in the deionized water within the reactor. After evacuating the reactor, high-purity CO2 gas was introduced to atmospheric pressure. The photocatalytic CO2 reduction reaction was tested by stirring at 500 rpm. The reduction products were detected using a gas chromatograph (FULI GC9790II). Figure 5 As shown, compared with the catalytic abilities of CN, RCN, Br-RCN, and Co-RCN, the prepared Br / Co-RCN catalyst exhibited the highest CO yield, reaching 130.06 μmol·g. -1 ·h -1 The performance is 36 times that of the original CN and 18 times that of RCN, and also far exceeds the yield of Br-RCN and Co-RCN, proving that the Br / Co-RCN catalyst provided by this invention has excellent photocatalytic CO2 reduction performance.

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a bromine / cobalt co-doped hollow rod-shaped carbon nitride photocatalyst, characterized in that, The preparation steps include the following: (1) The hollow rod-shaped carbon nitride (RCN) was prepared by adding 3.20 g of melamine and 3.22 g of cyanuric acid to 250 mL of deionized water and stirring at 80 °C until completely dissolved to obtain melamine solution and cyanuric acid solution; the cyanuric acid solution was poured into the melamine solution and stirred for 4 h, the white precipitate was collected and washed 3 times with deionized water at 80 °C; the precipitate was dried at 100 °C for 12 h, heated to 520 °C at a heating rate of 2 °C / min, kept at the temperature for 4 h, and naturally cooled to room temperature to obtain RCN; (2) Preparation of bromine / cobalt co-doped hollow rod-shaped carbon nitride Br / Co-RCN: 90 mg RCN was stirred and dispersed in 15 mL of deionized water, 10 mg Co(NO3)2·6H2O was dispersed in 15 mL of ethylene glycol, and 100 mg hexadecyltrimethylammonium bromide (CTAB) was dispersed in 5 mL of ethylene glycol to obtain the reaction precursor solutions respectively; 15 mL of Co(NO3)2·6H2O ethylene glycol solution and 5 mL of CTAB ethylene glycol solution were mixed and added dropwise to 15 mL of RCN aqueous dispersion, stirred continuously for 2 h, and then transferred to a 100 mL high-pressure reactor and kept at 180 ℃ for 2 h to obtain a white precipitate. The precipitate was washed twice with deionized water and ethanol respectively; finally, the precipitate was dried in a vacuum oven at 80 ℃ for 12 h to obtain Br / Co-RCN.

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