CoFe hydrotalcite / sulfonated C3N4 catalyst and its synthesis method and application

Abstract

The present invention provides a CoFe hydrotalcite / sulfonated C3N4 catalyst and its synthesis method and application. The method comprises dissolving equimolar amounts of cobalt nitrate and ferric nitrate in deionized water, adding a sodium hydroxide solution and stirring to obtain a solid, and then centrifuging, washing, and drying the obtained solid to obtain the CoFe hydrotalcite; calcining urea in a muffle furnace to obtain C3N4, and heating and soaking the C3N4 in a dilute sulfuric acid solution, centrifuging, washing, and drying to obtain the sulfonated C3N4; and dispersing the CoFe hydrotalcite and the sulfonated C3N4 in an aqueous solution, allowing the solution to stand, and self-assembling through electrostatic adsorption to obtain the CoFe hydrotalcite / sulfonated C3N4 catalyst. The CoFe hydrotalcite / sulfonated C3N4 catalyst prepared in the present application has good photocatalytic nitrogen fixation performance and improves the photocatalytic nitrogen fixation efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst synthesis, and in particular to a CoFe hydrotalcite / sulfonated C3N4 catalyst and a synthesis method and application thereof. Background Art

[0002] As an important chemical product, NH3 has important applications in agriculture and industry. The traditional method of preparing NH3 is to convert N2 and H2 into NH3 under high temperature and high pressure under the action of catalyst. This process consumes a lot of energy and is prone to produce SO2 and NO due to the combustion of fossil fuels during the preparation process. x It also requires hazardous hydrogen as a raw material, which carries certain risks. Photocatalytic nitrogen fixation uses light energy to convert nitrogen in the air into NH3. This technology is a mild reaction process that directly utilizes light energy without causing the pollution caused by fossil fuel combustion, making it a promising technology for synthesizing NH3.

[0003] However, due to the high bond energy of the nitrogen-nitrogen triple bond in the N2 molecule, it is difficult to activate the N2 molecule by conventional means. In addition, due to factors such as the high recombination rate of photogenerated electrons and holes, the photocatalytic nitrogen fixation catalysts in the existing technology have poor photocatalytic performance, and the nitrogen fixation efficiency is usually on the order of tens of micromoles per gram per hour, which also indirectly leads to the high energy consumption of the current NH3 synthesis process. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a CoFe hydrotalcite / sulfonated C3N4 catalyst and a synthesis method thereof, which are used to solve the technical problem of poor photocatalytic performance of photocatalytic nitrogen fixation catalysts in the prior art.

[0005] In one aspect, the present invention provides a method for synthesizing a CoFe hydrotalcite / sulfonated C3N4 catalyst, comprising:

[0006] Equal moles of cobalt nitrate and ferric nitrate are dissolved in deionized water, sodium hydroxide solution is added and stirred to obtain a solid, and the obtained solid is separated by centrifugation, washed and dried to obtain CoFe hydrotalcite;

[0007] Calcining urea in a muffle furnace to obtain C3N4, and then heating and soaking the C3N4 in a dilute sulfuric acid solution, centrifugally washing, and drying to obtain sulfonated C3N4;

[0008] The CoFe hydrotalcite and the sulfonated C3N4 are dispersed in an aqueous solution, allowed to stand, and a CoFe hydrotalcite / sulfonated C3N4 catalyst is obtained by electrostatic adsorption self-assembly.

[0009] In addition, the above-mentioned CoFe hydrotalcite / sulfonated C3N4 catalyst synthesis method according to the present invention may also have the following additional technical features:

[0010] Furthermore, in the step of adding sodium hydroxide solution and stirring to obtain a solid, the stirring method includes:

[0011] The cells were stirred under strong ultrasound in a cell disruptor for 30 minutes.

[0012] Further, in the step of obtaining C3N4 by calcining urea in a muffle furnace:

[0013] In an air atmosphere, the calcination temperature of urea is 500° C.-600° C., and the calcination time is 1.5 h-2.5 h.

[0014] Furthermore, the C3N4 is placed in a dilute sulfuric acid solution for heating and soaking:

[0015] The heating soaking time is 1.5h-2.5h.

[0016] Furthermore, in the step of dispersing the CoFe hydrotalcite and the sulfonated C3N4 in an aqueous solution, allowing the solution to stand, and obtaining the CoFe hydrotalcite / sulfonated C3N4 catalyst by electrostatic adsorption self-assembly:

[0017] The standing time is 1.5h-2.5h.

[0018] In one aspect, the present invention further provides a CoFe hydrotalcite / sulfonated C3N4 catalyst, which is prepared by the above-mentioned CoFe hydrotalcite / sulfonated C3N4 catalyst synthesis method.

[0019] Another aspect of the present invention provides an application of a CoFe hydrotalcite / sulfonated C3N4 catalyst in photocatalytic nitrogen fixation.

[0020] The above-mentioned CoFe hydrotalcite / sulfonated C3N4 catalyst and its synthesis method and application provide a new synthesis method of CoFe hydrotalcite / sulfonated C3N4 catalyst to prepare a new catalyst, which replaces the catalyst in the existing technology and improves the photocatalytic nitrogen fixation efficiency of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The photocatalytic nitrogen fixation performance and cycle life of the catalysts with different ratios of CoFe hydrotalcite / sulfonated C3N4 are shown;

[0022] Figure 2 XRD results of CoFe hydrotalcite / sulfonated C3N4 catalyst;

[0023] Figure 3UV-visible diffuse reflectance spectra, Schottky curves and band structure diagrams of CoFe hydrotalcite, C3N4 and sulfonated C3N4.

[0024] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0027] To address the technical problem of poor photocatalytic performance of existing photocatalytic nitrogen fixation catalysts, this application provides a CoFe hydrotalcite / sulfonated C3N4 catalyst, its synthesis method, and application. The CoFe hydrotalcite / sulfonated C3N4 catalyst exhibits excellent photocatalytic nitrogen fixation performance (212 μmol / g / h) and a long cycle life (after four cycles, it still retains over 85% of the activity of a fresh sample). Compared with a reference sample, the presence of the electron-withdrawing sulfonic acid group lowers the conduction band energy level of C3N4, causing photogenerated electrons generated on the CoFe hydrotalcite surface to flow toward the C3N4 surface, thereby promoting the separation of photogenerated electrons and holes on the CoFe hydrotalcite surface and improving the catalyst's photocatalytic nitrogen fixation efficiency.

[0028] Specifically, the synthesis method of CoFe hydrotalcite / sulfonated C3N4 catalyst includes steps S101-S103:

[0029] S101. Dissolve equimolar amounts of cobalt nitrate and ferric nitrate in deionized water, add sodium hydroxide solution and stir to obtain a solid, and separate the obtained solid by centrifugation, wash and dry to obtain CoFe hydrotalcite.

[0030] In some optional embodiments, equimolar amounts of cobalt nitrate and ferric nitrate are dissolved in deionized water, sodium hydroxide solution is added, and the mixture is stirred under strong ultrasound of a cell disruptor for 30 minutes to obtain a solid.

[0031] S102, calcining urea in a muffle furnace to obtain C3N4, and placing the C3N4 in a dilute sulfuric acid solution for heating and soaking, centrifugation washing, and drying to obtain sulfonated C3N4.

[0032] In some optional embodiments, the urea is calcined at a temperature of 500°C to 600°C for a time of 1.5 to 2.5 hours. Preferably, the urea is calcined at a temperature of 550°C for 2 hours in an air atmosphere, with a heating rate of 20°C / min. Furthermore, the C3N4 is heated and soaked in a dilute sulfuric acid solution for 1.5 to 2.5 hours, preferably for 2 hours.

[0033] S103, dispersing CoFe hydrotalcite and sulfonated C3N4 in an aqueous solution, allowing it to stand, and obtaining a CoFe hydrotalcite / sulfonated C3N4 catalyst through electrostatic adsorption self-assembly.

[0034] In some optional embodiments, the standing time is 1.5 h to 2.5 h, preferably 2 h. Specifically, the sulfonation treatment has the advantage of modifying C3N4 by electron-withdrawing groups, lowering the conduction band energy level of C3N4, causing photogenerated electrons to tend to gather at the C3N4 end, extending the lifetime of photogenerated electrons, and thus improving the photocatalytic nitrogen fixation efficiency of the CoFe hydrotalcite / sulfonated C3N4 catalyst.

[0035] In this scheme, CoFe hydrotalcite is a single crystal phase of hydrotalcite, and C3N4 is grafted with sulfonic acid groups; sulfonated C3N4 forms a type II heterojunction with CoFe hydrotalcite; the sulfonic acid group acts as an electron-withdrawing group to promote the transfer of photogenerated charges to C3N4, thereby improving the photogenerated electron-hole separation efficiency and photocatalytic nitrogen fixation life of the catalyst.

[0036] The present invention designs a CoFe hydrotalcite / C3N4 catalyst based on the concept of constructing a Type II heterojunction. This catalyst exhibits a Type II heterojunction, enabling photogenerated electrons to migrate from the higher-energy conduction band of the CoFe hydrotalcite to the lower-energy conduction band of the C3N4. Furthermore, the present invention introduces electron-withdrawing groups to sulfonate the C3N4, further lowering its conduction band energy level. This enhances the charge transfer process from the CoFe hydrotalcite conduction band to the C3N4 conduction band, effectively strengthening the separation of photogenerated electrons and holes in the catalyst, thereby improving the catalyst's photocatalytic nitrogen fixation performance.

[0037] The present invention also provides a CoFe hydrotalcite / sulfonated C3N4 catalyst for photocatalytic nitrogen fixation. The catalyst is prepared by irradiating the reactor with simulated sunlight using a 300W xenon lamp. 0.1g of the catalyst is dissolved in 100mL of water and placed in a quartz reactor. The reactor is separated from the center of the light source by 15cm, and the reaction is carried out under nitrogen protection. The generated hydrogen is detected by chromatography, and the generated ammonia is developed with Nessler's reagent and then detected by spectrophotometry. The catalyst exhibits an ammonia production activity of 212 μmol / g / h and an N2 selectivity of 89%, 23 times that of the CoFe hydrotalcite catalyst. The catalyst also exhibits stable catalytic performance, maintaining over 85% of the activity of a fresh sample after four cycles of performance testing.

[0038] To facilitate understanding of the present invention, several embodiments of the present invention are provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive disclosure of the present invention.

[0039] Example 1

[0040] The synthesis method of the CoFe hydrotalcite / sulfonated C3N4 catalyst in the embodiment of the present invention comprises:

[0041] First, CoFe hydrotalcite was prepared by dissolving 0.5 mol / L cobalt nitrate and 0.5 mol / L ferric nitrate in 100 mL of deionized water. A 2.5 mol / L sodium hydroxide solution (100 mL) was added and stirred under strong ultrasound in a cell disruptor for 30 minutes. The resulting solid was centrifuged, washed five times with water, and dried to obtain CoFe hydrotalcite.

[0042] Secondly, urea is calcined in a muffle furnace to obtain C3N4. Specifically, in this embodiment, the calcination temperature is 550°C in an air atmosphere, the heating rate is 20°C / min, and C3N4 is obtained after calcination for 2 hours;

[0043] Next, sulfonated C3N4 was prepared by placing 0.1 g of C3N4 in a dilute sulfuric acid solution (1 mol / L, 100 mL), heating it (60°C) and soaking it for 2 hours. The solution was then centrifuged, washed with water 5 times, and dried to obtain sulfonated C3N4.

[0044] Finally, a CoFe hydrotalcite / sulfonated C3N4 catalyst was prepared. 0.1 g of CoFe hydrotalcite and 0.1 g of sulfonated C3N4 were dispersed in an aqueous solution and allowed to stand for 2 hours. The resulting solid was separated by centrifugation, washed five times with water, and dried. The CoFe hydrotalcite / sulfonated C3N4 catalyst was self-assembled via electrostatic adsorption.

[0045] For details, see Figure 1 , Figure 1The following graph shows the photocatalytic nitrogen fixation performance and cycle life of catalysts with different CoFe hydrotalcite / sulfonated C3N4 ratios. In this example, the mass ratios of CoFe hydrotalcite and sulfonated C3N4 used during the electrostatic self-assembly process were 1:9, 1:1, and 9:1. As shown in the graph, all three CoFe hydrotalcite / sulfonated C3N4 ratios exhibited excellent nitrogen fixation performance, with the 1:1 CoFe hydrotalcite / sulfonated C3N4 catalyst exhibiting the best nitrogen fixation performance, reaching 212 μmol / g / h. Furthermore, the cycle life of the catalysts with these three ratios was excellent, maintaining over 85% of the catalytic activity of the fresh sample after four photocatalytic nitrogen fixation cycles, demonstrating the excellent photocatalytic stability of the CoFe hydrotalcite / sulfonated C3N4 catalysts.

[0046] In order to further understand the performance of the CoFe hydrotalcite / sulfonated C3N4 catalyst obtained by the synthesis method in this example, the phase analysis and band structure analysis of the CoFe hydrotalcite / sulfonated C3N4 catalyst were performed in this example. Specifically:

[0047] 【1】The phase information of CoFe hydrotalcite / sulfonated C3N4 catalyst is as follows:

[0048] like Figure 2 As shown, Figure 2 The XRD results of CoFe hydrotalcite / sulfonated C3N4 catalyst are shown in Figure 1. Figure 1 The XRD curve of the CoFe hydrotalcite sample showed diffraction peaks at 24.9°, 32.4°, 38.6°, 42.7°, 46.5°, 53.5°, 61.8°, and 65.9°, which are attributed to the hydrotalcite crystalline phase. No diffraction peaks attributable to other impurities were detected, indicating that the CoFe hydrotalcite sample is a single hydrotalcite crystal form. When sulfonated C3N4 is composited with CoFe hydrotalcite, the diffraction peaks attributable to CoFe hydrotalcite in the catalyst XRD curve do not disappear. Instead, a new diffraction peak at 27.4° appears, which is attributed to C3N4. This indicates that the sulfonated C3N4 maintains the C3N4 structure and that its composite with CoFe hydrotalcite does not affect the crystal form of the CoFe hydrotalcite.

[0049] 【2】Band structure analysis of CoFe hydrotalcite / sulfonated C3N4 catalyst

[0050] The band gaps of CoFe hydrotalcite and sulfonic acid modified C3N4 were determined by UV-visible diffuse reflectance. Figure 3As shown in the figure, the intersection points of the epitaxial tangent of the UV-visible diffuse reflectance curves of CoFe hydrotalcite, C3N4, and sulfonated C3N4 with the X-axis are 430nm, 437nm, and 448nm, respectively; corresponding to the band gap widths of 2.88eV, 2.83eV, and 2.76eV. The flat band potentials of C3N4 and CoFe hydrotalcite were determined by Mott-Schottky plots. Figure 3 As shown, the intersection points of the epitaxial tangent lines of the Mott-Schottky curves with the x-axis for the CoFe hydrotalcite, C3N4, and sulfonated C3N4 samples are -1.10V, -1.04V, and -1.01V, respectively, corresponding to the flat band potentials of these samples. Since the conduction band position of semiconductor catalysts typically differs from the flat band potential by 0.1V, we can derive the conduction band positions of the CoFe hydrotalcite, C3N4, and sulfonated C3N4 samples to be -1.20V, -1.14V, and -1.11V, respectively. According to the notion EVB = ECB - EBG, based on the conduction band position and band gap, we can calculate the valence band positions of the CoFe hydrotalcite, C3N4, and sulfonated C3N4 samples to be 1.68V, 1.69V, and 1.65V, respectively. This provides a complete band structure. The conduction and valence band energies of CoFe hydrotalcite are smaller than those of C3N4 and sulfonated C3N4. This suggests that the CoFe hydrotalcite / C3N4 catalyst series possesses a type II heterojunction. Photoexcited electrons on the CoFe hydrotalcite surface possess higher energy, potentially allowing them to spontaneously migrate toward the lower-energy conduction band of C3N4, thereby achieving photogenerated electron-hole separation. This is consistent with the catalyst's nitrogen fixation efficiency: sulfonated C3N4, modified with strongly electron-withdrawing groups, has the lowest conduction band energy level, leading to the greatest tendency for photogenerated electrons on CoFe hydrotalcite to migrate toward it. Consequently, the catalyst exhibits the best photogenerated electron-hole separation efficiency and, consequently, the best nitrogen fixation activity.

[0051] Based on the above results, the CoFe hydrotalcite / sulfonated C3N4 catalyst exhibits excellent photocatalytic nitrogen fixation performance (212 μmol / g / h) and a long cycle life (after four cycles, it still retains over 85% of the activity of a fresh sample). Compared to a reference sample, the presence of the electron-withdrawing sulfonic acid group lowers the conduction band energy level of C3N4, causing photogenerated electrons on the CoFe hydrotalcite surface to flow toward the C3N4 surface, thereby promoting the separation of photogenerated electrons and holes on the CoFe hydrotalcite surface and improving the catalyst's photocatalytic nitrogen fixation efficiency.

[0052] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0053] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for synthesizing a CoFe hydrotalcite / sulfonated C3N4 catalyst, characterized in that: include: Equimolar amounts of cobalt nitrate and ferric nitrate were dissolved in deionized water, sodium hydroxide solution was added, and the mixture was stirred under strong ultrasound in a cell crusher to obtain a solid, and the obtained solid was separated by centrifugation, washed, and dried to obtain CoFe hydrotalcite; Calcining urea in a muffle furnace to obtain C3N4, and then heating and soaking the C3N4 in a dilute sulfuric acid solution, centrifugally washing, and drying to obtain sulfonated C3N4; The CoFe hydrotalcite and the sulfonated C3N4 are dispersed in an aqueous solution and allowed to stand to obtain a CoFe hydrotalcite / sulfonated C3N4 catalyst by electrostatic adsorption self-assembly, wherein the sulfonated C3N4 and the CoFe hydrotalcite form a type II heterojunction, the energy of the CoFe hydrotalcite is higher than the energy of the conduction band of the C3N4, and the photogenerated electrons migrate from the conduction band of the CoFe hydrotalcite to the conduction band of the C3N4 to improve the photocatalytic nitrogen fixation performance of the catalyst; In the step of obtaining the CoFe hydrotalcite / sulfonated C3N4 catalyst by electrostatic adsorption self-assembly, the mass ratios of the CoFe hydrotalcite and sulfonated C3N4 included 1:9, 1:1 and 9:

1.

2. The method for synthesizing the CoFe hydrotalcite / sulfonated C3N4 catalyst according to claim 1, wherein: In the step of adding sodium hydroxide solution and stirring to obtain a solid, the stirring method includes: The cells were stirred under strong ultrasound in a cell disruptor for 30 minutes.

3. The method for synthesizing the CoFe hydrotalcite / sulfonated C3N4 catalyst according to claim 1, characterized in that: In the step of obtaining C3N4 by calcining urea in a muffle furnace: In an air atmosphere, the calcination temperature of urea is 500° C.-600° C., and the calcination time is 1.5 h-2.5 h.

4. The method for synthesizing the CoFe hydrotalcite / sulfonated C3N4 catalyst according to claim 1, characterized in that: The C3N4 is placed in a dilute sulfuric acid solution and heated and soaked in the step: The heating soaking time is 1.5h-2.5h.

5. The method for synthesizing the CoFe hydrotalcite / sulfonated C3N4 catalyst according to claim 1, characterized in that: In the step of dispersing the CoFe hydrotalcite and the sulfonated C3N4 in an aqueous solution, allowing the aqueous solution to stand, and obtaining the CoFe hydrotalcite / sulfonated C3N4 catalyst by electrostatic adsorption self-assembly: The standing time is 1.5h-2.5h.

6. A CoFe hydrotalcite / sulfonated C3N4 catalyst, characterized in that The catalyst is prepared by the synthesis method of CoFe hydrotalcite / sulfonated C3N4 catalyst described in any one of claims 1 to 5.

7. Use of the CoFe hydrotalcite / sulfonated C3N4 catalyst according to claim 6 in photocatalytic nitrogen fixation.

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