A method for preparing porous carbon nitride / carbon composite photocatalyst and its application.

Abstract

This invention belongs to the field of photocatalytic hydrogen production technology and discloses a method for preparing a porous carbon nitride / carbon composite photocatalyst. The method employs a coaxial electrospray method, using an acetic acid aqueous solution of graphitic carbon nitride and chitosan as the shell solution, a zinc salt solution as the core solution, and a sodium hydroxide solution as the receiving liquid to prepare carbon nitride / chitosan / zinc salt composite particles. The composite particles are centrifuged, washed with water, and freeze-dried to obtain a precursor. The precursor is then heat-treated, followed by acid washing, water washing, and freeze-drying to obtain the porous carbon nitride / carbon composite catalyst. This method uses zinc salt as a pore-forming agent and chitosan as a carbon source, employs a coaxial electrospray method to prepare the precursor, and then heat-treats to obtain the porous carbon nitride / carbon composite catalyst. This catalyst has a large specific surface area and can achieve full-spectrum absorption, exhibiting high visible light photocatalytic hydrogen production performance when used for photocatalytic hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic hydrogen production technology, and relates to a method for preparing a porous carbon nitride / carbon composite photocatalyst and its application. Background Technology

[0002] Traditional fossil fuels, due to their limited reserves and the numerous environmental problems caused by their combustion, can no longer meet human needs. Against the backdrop of carbon peaking and carbon neutrality, green hydrogen energy has become an important direction for future energy. Photocatalysis driven by sunlight can convert low-energy-density solar energy into high-energy-density chemical energy. Utilizing photocatalysis for efficient hydrogen production is a strategically significant endeavor that will provide new insights into solving the energy crisis and environmental pollution problems.

[0003] The principle of photocatalytic hydrogen production is as follows: a semiconductor photocatalyst is excited to generate electron-hole pairs under a certain light source. When electrons migrate to the catalyst surface, they reduce water to hydrogen, while the holes are consumed by the added sacrificial agent. Therefore, the key to realizing photocatalytic water splitting for hydrogen production is to find a photocatalyst with suitable energy band, stability, high efficiency, and low cost and availability.

[0004] Graphitic carbon nitride (CN, g-C3N4) has attracted much attention due to its excellent visible light response, superior thermal stability, and chemical stability, and has been widely used in various photocatalyst research and development fields. However, CN has disadvantages such as low photogenerated charge mobility, difficulty in separation, low conductivity, and narrow spectral absorption range, which limit its development. Currently, there is an urgent need to develop a method for preparing carbon nitride with a large specific surface area, capable of achieving full-spectrum absorption, and exhibiting good photocatalytic hydrogen production performance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing and applying a porous carbon nitride / carbon composite photocatalyst. The method uses zinc salt as a pore-forming agent and chitosan as a carbon source, employing a coaxial electrospray method to prepare the precursor. The precursor is then heat-treated to obtain the porous carbon nitride / carbon composite catalyst, which exhibits a large specific surface area and full-spectrum absorption. When used for photocatalytic hydrogen production, it demonstrates high visible light photocatalytic hydrogen production performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a porous carbon nitride / carbon composite photocatalyst. The method employs a coaxial electrospray method, using an aqueous acetic acid solution of graphitic carbon nitride and chitosan as the shell solution, a zinc salt solution as the core solution, and a sodium hydroxide solution as the receiving liquid to prepare carbon nitride / chitosan / zinc salt composite particles. The composite particles are centrifuged, washed with water, and freeze-dried to obtain a precursor. The precursor is then heat-treated and subsequently acid-washed, washed with water, and freeze-dried to obtain the porous carbon nitride / carbon composite catalyst.

[0008] The preparation method of a porous carbon nitride / carbon composite photocatalyst of the present invention specifically includes the following steps:

[0009] Step 1): Heat-treating urea in a muffle furnace to obtain graphitic carbon nitride;

[0010] Step 2): Disperse the graphitic carbon nitride obtained in Step 1 into water, add acetic acid and chitosan, and stir to form a gel to obtain the shell solution of coaxial electrospraying.

[0011] Step 3): Prepare a zinc salt solution as the core layer solution for the coaxial electro-spraying method;

[0012] Step 4): Prepare a sodium hydroxide solution as the receiving liquid for the coaxial electrospray method;

[0013] Step 5): Control the electrostatic voltage, shell flow rate and core flow rate of the coaxial electro-injection device to obtain carbon nitride-chitosan-zinc salt composite particles;

[0014] Step 6): The composite particles obtained in Step 5 are centrifuged, washed with water, and freeze-dried to obtain a precursor. The precursor is placed in a tube furnace for heat treatment, and then acid-washed, washed with water, and freeze-dried to obtain a porous carbon nitride / carbon composite catalyst.

[0015] In step 2) of the technical solution of the present invention, the amount of carbon nitride dispersed is 0.3 g, the amount of acetic acid added is 0.3~0.9 mL, and the amount of chitosan added is 0.1~0.5 g.

[0016] The zinc source of the zinc salt solution described in this invention is selected from zinc acetate, zinc nitrate, zinc chloride, or zinc sulfate, and the concentration of the zinc salt solution is 40~60 g / L.

[0017] The concentration of the sodium hydroxide solution in the technical solution of the present invention is 10~30 g / L.

[0018] The coaxial electro-injection device described in the present invention has an applied voltage of 20 kV, a shell flow rate of 0.4 mL / h, and a core flow rate of 0.2 mL / h.

[0019] The heat treatment conditions described in the technical solution of this invention are as follows: nitrogen atmosphere, temperature of 450~600 ℃, and holding time of 2~6 h.

[0020] This invention uses an acetic acid aqueous solution of graphitic carbon nitride and chitosan as the shell solution, a zinc salt solution as the core solution, and a sodium hydroxide solution as the receiving solution to prepare carbon nitride / chitosan / zinc salt composite particles via a coaxial electrospray method. In this process, droplets of carbon nitride / chitosan gel coated with zinc salt are coaxially electrosprayed. Upon entering the sodium hydroxide solution, due to the presence of hydroxyl groups, the chitosan polymer chains containing carbon nitride and zinc salt rapidly break down, causing the droplets to condense into spheres. After centrifugation and washing with water until neutral, the carbon nitride / chitosan / zinc salt precursor is obtained. In the subsequent heat treatment, the chitosan is carbonized, and the zinc salt is converted into zinc oxide, with some volatilization. The zinc oxide is then removed by acid washing. Throughout the process, the zinc salt acts as a pore-forming agent, and the chitosan acts as a carbon source providing the structural framework, resulting in a porous carbon nitride / carbon composite catalyst with a porous structure. Furthermore, the presence of carbon enables the catalyst to achieve full-spectrum absorption, showing promising application prospects in the field of photocatalytic hydrogen production.

[0021] Secondly, the present invention provides the application of the porous carbon nitride / carbon composite photocatalyst prepared by the above-mentioned method in visible light catalytic hydrogen production.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention features an ingenious design, using zinc salt as a pore-forming agent and chitosan as a carbon source. A precursor is prepared using a coaxial electrospray method, and then heat-treated to obtain a porous carbon nitride / carbon composite catalyst. This catalyst has a large specific surface area and can achieve full-spectrum absorption, exhibiting high visible light photocatalytic hydrogen production performance when used for photocatalytic hydrogen production. Attached Figure Description

[0024] Figure 1 A schematic diagram of the preparation of porous carbon nitride / carbon composite catalyst precursors by coaxial electroinjection method.

[0025] Figure 2 The XRD patterns are those of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4.

[0026] Figure 3 The images show SEM images of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4.

[0027] Figure 4 The figures show the nitrogen adsorption-desorption isotherms and pore size distribution diagrams of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4.

[0028] Figure 5 The UV-Vis diffuse reflectance spectra of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 are shown.

[0029] Figure 6The graphs show the visible light catalytic hydrogen evolution performance of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4.

[0030] Figure 7 The image shows the it curves of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4. Detailed Implementation

[0031] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0032] In the following embodiments:

[0033] Photocatalytic detection system: Beijing Pofila Photocatalytic 6A Photocatalytic System.

[0034] Light source model: Beijing Pofila 300W Xe lamp, used with a 420 nm filter.

[0035] Gas chromatograph (GC): Shanghai Tianmei GC-7900.

[0036] In the visible light photocatalytic hydrogen evolution solution, triethanolamine is used as a sacrificial reagent.

[0037] Pt was selected as a co-catalyst for the visible light photocatalytic hydrogen evolution test.

[0038] This invention employs a coaxial electro-injection method to prepare the precursor, as illustrated in the schematic diagram of the preparation process. Figure 1 As shown.

[0039] Example 1

[0040] (1) Place 10g of urea in a muffle furnace, raise the temperature to 550℃ at a rate of 5℃ / min and hold for 4h, and then allow it to cool naturally to room temperature to obtain porous carbon nitride, denoted as CN.

[0041] (2) Take 0.3 g CN and disperse it in 10 mL of deionized water, then add 0.6 mL of acetic acid and 0.3 g of chitosan and stir until it becomes gel-like, as the shell solution for coaxial electrospraying.

[0042] (3) Prepare a zinc acetate solution with a concentration of 50 g / L as the core layer solution for the coaxial electrospray method.

[0043] (4) Prepare a sodium hydroxide solution with a concentration of 20 g / L as the receiving solution for the coaxial electrospray method.

[0044] (5) Apply a 20 kV electrostatic voltage to the coaxial electric nozzle, set the shell flow rate to 0.4 mL / h, and the core flow rate to 0.2 mL / h.

[0045] (6) The carbon nitride / chitosan / zinc salt composite particles prepared by coaxial electro-injection were centrifuged, washed with water and freeze-dried to obtain a precursor. The precursor was placed in a tube furnace under a nitrogen atmosphere and heat-treated at 600℃ for 4 hours. Then, after acid washing, water washing and freeze-drying again, a porous carbon nitride / carbon composite catalyst was obtained, denoted as CN-Zn(AC)2.

[0046] Example 2

[0047] This embodiment is the same as that in embodiment 1, except that the zinc source in step (3) is changed to zinc nitrate, and the resulting porous carbon nitride / carbon composite catalyst is denoted as CN-Zn(NO3)2.

[0048] Example 3

[0049] This embodiment is the same as that in embodiment 1, except that the zinc source in step (3) is changed to zinc chloride, and the resulting porous carbon nitride / carbon composite catalyst is denoted as CN-ZnCl2.

[0050] Example 4

[0051] This embodiment is the same as that in embodiment 1, except that the zinc source in step (3) is changed to zinc sulfate, and the resulting porous carbon nitride / carbon composite catalyst is denoted as CN-ZnSO4.

[0052] The XRD patterns of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 are as follows: Figure 2 As shown, the XRD pattern of the prepared porous carbon nitride / carbon composite catalyst has diffraction peaks at 2θ = 13.1° and 27.7°, corresponding to the (100) and (002) crystal planes of carbon nitride, respectively; and diffraction peaks at 2θ = 25° and 44°, corresponding to the (002) and (100) crystal planes of carbon, respectively, indicating the successful preparation of the porous carbon nitride / carbon composite catalyst.

[0053] SEM images of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 are shown below. Figure 3 As shown, where Figure 3 a-3d correspond to the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4, respectively. It can be seen that all samples exhibit a porous structure.

[0054] The nitrogen adsorption-desorption isotherms and pore size distribution diagrams of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 are shown below. Figure 4 As shown, the specific surface areas of CN-Zn(AC)2, CN-Zn(NO3)2, CN-ZnCl2, and CN-ZnSO4 are 115.84, 103.62, 110.02, and 78.92 m², respectively. 2 / g ( Figure 4 -a), with average pore sizes of 6.7, 7.32, 5.55, and 3.46 nm, respectively. Figure 4 -b) A larger specific surface area can provide more catalytic reaction active sites for photocatalytic reactions, which is beneficial to the improvement of performance. This is mainly due to the addition of zinc salt as a pore-forming agent. Moreover, zinc acetate has a greater effect on improving performance than zinc nitrate, zinc chloride and zinc sulfate.

[0055] The UV-Vis diffuse reflectance spectra of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 are shown below. Figure 5 As shown, it can be seen that, compared with the photocatalyst CN prepared by conventional methods (step 1 of Example 1), the samples prepared in Examples 1 to 4 all exhibited full-spectrum absorption performance. The wider spectral absorption is beneficial to improving the photocatalytic hydrogen production performance.

[0056] The CN-Zn(AC)2 prepared in this example was subjected to electrochemical and visible light photocatalytic hydrogen evolution performance tests. The visible light photocatalytic hydrogen evolution performance of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 is shown in the figure below. Figure 6 As shown, the visible light photocatalytic hydrogen production rates of the prepared CN-Zn(AC)2, CN-Zn(NO3)2, CN-ZnCl2, and CN-ZnSO4 are 316.3, 229.1, 235.6, and 184.4 μmol / g / h, respectively. The it curves of the porous carbon nitride / carbon composite catalysts prepared in Examples 1-4 are shown in the figure. Figure 7 As shown, CN-Zn(AC)2 exhibits the best photocurrent response compared to other zinc salt-assisted preparations of porous carbon nitride / carbon composite catalysts, which is mainly attributed to the more significant pore-forming effect of zinc acetate.

[0057] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for preparing a porous carbon nitride / carbon composite photocatalyst, characterized in that, Carbon nitride / chitosan / zinc salt composite particles were prepared by coaxial electro-spraying method, using an acetic acid aqueous solution of graphitic carbon nitride and chitosan as the shell solution, a zinc salt solution as the core solution, and a sodium hydroxide solution as the receiving liquid. The composite particles were centrifuged, washed with water, and freeze-dried to obtain a precursor. The precursor was then heat-treated, acid-washed, washed with water, and freeze-dried to obtain a porous carbon nitride / carbon composite catalyst.

2. The preparation method according to claim 1, characterized in that, Specifically, the following steps are included: Step 1): Heat-treating urea in a muffle furnace to obtain graphitic carbon nitride; Step 2): Disperse the graphitic carbon nitride obtained in Step 1 into water, add acetic acid and chitosan, and stir to form a gel to obtain the shell solution of coaxial electrospraying. Step 3): Prepare a zinc salt solution as the core layer solution for the coaxial electro-spraying method; Step 4): Prepare a sodium hydroxide solution as the receiving liquid for the coaxial electrospray method; Step 5): Control the electrostatic voltage, shell flow rate and core flow rate of the coaxial electro-injection device to obtain carbon nitride-chitosan-zinc salt composite particles; Step 6): The composite particles obtained in Step 5 are centrifuged, washed with water, and freeze-dried to obtain a precursor. The precursor is placed in a tube furnace for heat treatment, and then acid-washed, washed with water, and freeze-dried to obtain a porous carbon nitride / carbon composite catalyst.

3. The preparation method according to claim 2, characterized in that, In step 2), the amount of carbon nitride dispersed is 0.3 g, the amount of acetic acid added is 0.3~0.9 mL, and the amount of chitosan added is 0.1~0.5 g.

4. The preparation method according to claim 1 or 2, characterized in that, The zinc source of the zinc salt solution is selected from zinc acetate, zinc nitrate, zinc chloride or zinc sulfate, and the concentration of the zinc salt solution is 40~60 g / L.

5. The preparation method according to claim 1 or 2, characterized in that, The concentration of the sodium hydroxide solution is 10~30g / L.

6. The preparation method according to claim 2, characterized in that, The applied voltage of the coaxial electro-injection device is 20kV, the shell flow rate is set to 0.4 mL / h, and the core flow rate is set to 0.2 mL / h.

7. The preparation method according to claim 1 or 2, characterized in that, The heat treatment conditions are as follows: nitrogen atmosphere, temperature of 450~600 ℃, and holding time of 2~6 h.

8. The application of the porous carbon nitride / carbon composite photocatalyst prepared by the preparation method according to any one of claims 1 to 7 in visible light photocatalytic hydrogen production.

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