A g-C3N4-N 3C NiS photocatalysts, their methods and applications

Abstract

This application belongs to the field of photocatalytic nitrogen fixation material preparation technology, specifically relating to a g-C3N4-N3C / NiS photocatalyst, its method, and its application. This method involves preparing N... 3C The vacant g-C3N4 was dissolved in water, sonicated, and then nickel nitrate hexahydrate solution was added to obtain a mixed solution. Thiourea was then dissolved in water and mixed thoroughly with the mixed solution, placed in a reaction vessel, and heated to react. After the reaction was completed, the mixture was cooled to room temperature, separated, washed, and dried to obtain the g-C3N4-N3C / NiS photocatalyst. This invention prepares a N-containing photocatalyst via in-situ thermal decomposition. 3C The vacant CN nanosheets were then used to modify NiS nanosheets onto CN-N nanosheets via in-situ growth. 3C A photocatalyst containing a type II heterojunction structure was successfully prepared at -0.5 μm by introducing N2. 3C Vacancies and NiS can effectively enhance the photocatalytic nitrogen fixation performance of CN.

Description

Technical Field

[0001] This application belongs to the field of photocatalytic nitrogen fixation material preparation technology, specifically relating to a g-C3N4-N 3C / NiS photocatalysts, their methods, and applications. Background Technology

[0002] Ammonia (NH3), an essential substance in human production and daily life, is not only a basic chemical substance in biosynthetic fertilizers but also serves as a fuel and clean energy carrier. Currently, the main industrial synthesis method is the Haber-Bosch process, which produces ammonia by reacting nitrogen and hydrogen under high temperature (500 ℃), high pressure (20~50 MPa) and catalytic conditions. This method is energy-intensive and generates large amounts of greenhouse gases, causing significant environmental pollution. Therefore, finding a low-energy, green, and sustainable production method is urgently needed. Photocatalytic nitrogen fixation has emerged as a solution. Photocatalytic nitrogen fixation refers to a catalyst driven by sunlight, causing electrons to jump from the valence band to the conduction band, forming electron-hole pairs, which then react with N2 adsorbed on the catalyst, reducing it to NH3. This method was first proposed in 1977 by Schrauzer and Guth, who successfully reduced N2 to NH3 by irradiating TiO2 with ultraviolet-visible light at room temperature. Since then, numerous researchers have experimentally verified the feasibility of this method.

[0003] g-C3N4, as a classic photocatalyst, possesses a suitable band gap (2.72 eV), good thermal stability, and low cost, making it widely used in the field of photocatalysis. However, the excessively high photogenerated carrier recombination efficiency and relatively few active sites of pure g-C3N4 limit its photocatalytic activity to some extent. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a g-C3N4-N 3C NiS photocatalysts, their methods, and applications, specifically employing the following technical solutions: In a first aspect, the present invention provides a g-C3N4-N 3C The preparation method of / NiS photocatalyst includes the following steps: Will contain N 3C The vacant g-C3N4 was dissolved in water, sonicated, and then nickel nitrate hexahydrate solution was added to obtain a mixed solution; Thiourea was dissolved in water and mixed thoroughly with the solution. The mixture was then placed in a reaction vessel and heated to react. After the reaction was completed, the mixture was cooled to room temperature, separated, washed, and dried to obtain the g-C3N4-N. 3C / NiS photocatalyst.

[0005] As a further preferred embodiment, the one containing N 3C The preparation process of vacant g-C3N4 is as follows: Ammonium acetate and urea were dissolved in water, mixed thoroughly, and then placed in a crucible. The mixture was heated to 550 °C at a heating rate of 5 °C / min and calcined for 2 hours to obtain the product containing N. 3C Vacant g-C3N4.

[0006] This invention utilizes an in-situ pyrolysis method to synthesize N-containing... 3C Empty CN-N 3C -0.5% of the nitrate, nickel nitrate hexahydrate, and thiourea were hydrothermally synthesized at 180 °C using the original growth method to form CN-N with a type II heterojunction structure. 3C -0.5 / NiS hybrid material. Transient photocurrent and photoluminescence results showed that the highest photogenerated carrier separation rate was achieved when the NiS content was 0.002 mol. In a photocatalytic nitrogen fixation experiment under simulated sunlight irradiation conditions, after four hours of irradiation, when the amount of NiS added was 0.002 mol, CN-N... 3C The ammonia yield of -0.5 / NiS was the highest (285.87 μmol / L), which is 8.1 times that of pure carbon nitride (35.23 μmol / L). Compared with CN-N... 3C In comparison, CN-N 3C The visible light photocatalytic performance of the -0.5 / NiS hybrid material is significantly improved.

[0007] As a further preferred embodiment, the mass ratio of ammonium acetate to urea is 1:2.

[0008] As a further preferred embodiment, the nickel nitrate hexahydrate solution contains nickel nitrate hexahydrate and N... 3C The ratio of vacant g-C3N4 is 0.0015 mol - 0.003 mol : 0.15 g.

[0009] As a further preferred embodiment, nickel nitrate hexahydrate and containing N 3C The ratio of vacant g-C3N4 to vacant cells was 0.002 mol: 0.15 g. When the amount of NiS added was 0.002 mol, CN-N 3C The ammonia yield was highest with -0.5 / NiS (285.87 μmol / L), which is 8.1 times that of pure carbon nitride (35.23 μmol / L). Compared to nitrogen-free... 3CCompared to the vacant 0.002CN / NiS complex (111.08 μmol / L), its photocatalytic nitrogen fixation performance was improved by 2.54 times. Furthermore, compared to pure CN, the 0.002CN / NiS complex exhibited a 3.15-fold improvement in photocatalytic nitrogen fixation performance.

[0010] As a further preferred embodiment, the molar ratio of nickel nitrate hexahydrate to thiourea is 1:3.

[0011] As a further preferred embodiment, the specific process of the heating reaction is as follows: Heat to 180 °C at a heating rate of 5 °C / min and hold for 6 h.

[0012] As a further preferred embodiment, the ultrasound is performed using an ultrasonic cell disruptor for a duration of 25-40 minutes.

[0013] Secondly, the present invention provides a g-C3N4-N 3C / NiS photocatalyst was prepared by the above preparation method.

[0014] Thirdly, the present invention provides the above-mentioned g-C3N4-N 3C Application of NiS photocatalyst in photocatalytic nitrogen fixation and ammonia production.

[0015] The beneficial effects of this invention are as follows: This invention prepares N-containing materials through in-situ thermal decomposition. 3C Vacancies in CN nanosheets were then used to modify NiS nanosheets onto CN-N nanosheets via in-situ growth. 3C A photocatalyst containing a type II heterojunction structure was successfully prepared at -0.5. On the one hand, N... 3C The introduction of vacancies provides more active sites for photocatalytic nitrogen fixation, reduces the band gap of CN, and thus has a positive impact on photocatalytic nitrogen fixation activity. On the other hand, NiS and CN-N... 3C The type II heterojunction formed at the -0.5 contact interface can improve the separation efficiency of photogenerated electron-hole pairs. Therefore, by introducing N... 3C Vacancies and NiS can effectively enhance the photocatalytic nitrogen fixation performance of CN, providing a new approach to improving the photocatalytic nitrogen fixation efficiency of CN. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying 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.

[0017] Figure 1 The figures shown are CN(a) and CN-N. 3C- SEM image at 0.5 (b); Figure 2 The image shows CN-N. 3C TEM image (a), HRTEM image (b), HAADF image, and CN-N at -0.5 3C EDX elemental spectra (ce) of C and N in -0.5; Figure 3 The image shows CN and CN-N at different ratios. 3C X-ray diffraction pattern; Figure 4 The diagram shows CN and CN-N. 3C- X-ray photoelectron spectra of C1s (a) and N1s (b) at 0.5; Figure 5 The diagram shows CN and CN-N. 3C- Electron paramagnetic spectrum at 0.5; Figure 6 The image shows CN-N. 3C -0.5 (a), NiS (b) and CN-N 3C SEM image of -0.5 / NiS(c); Figure 7 The image shows CN-N. 3C TEM (a) and HRTEM (b) images of -0.5 / NiS; Figure 8 The image shows CN-N. 3C Elemental distribution map of -0.5 / NiS; Figure 9 The image shows CN-N. 3C -0.5, NiS, and CN-N 3C X-ray diffraction spectrum of -0.5 / NiS; Figure 10 The image shows CN-N. 3C -0.5 and CN-N 3C High-resolution XPS spectra of C1s (a), N1s (b), S2p (c) and Ni2p (d) of -0.5 / NiS; Figure 11 The image shows CN-N. 3C -0.5, NiS and CN-N 3C TPR (a), EIS (b), and PL (c) spectra of -0.5 / NiS; Figure 12 The image shows CN-N. 3C -0.5, NiS and CN-N 3CThe ultraviolet diffuse reflectance of -0.5 / NiS (a) and the correspondence between the converted Kubelka-Munk function and photon energy (b, c); Figure 13 The image shows CN-N. 3C Mott-Schottky plots of -0.5 (a) and NiS (b); Figure 14 The image shows CN-N. 3C -0.5, NiS and CN-N 3C -0.5 / NiS of DMPO-·O2 - (a) and EPR spectra of DMPO-·OH (b); Figure 15 The diagram shows CN and CN-N. 3C -0.5, NiS, 0.002CN / NiS and CN-N 3C Photocatalytic nitrogen fixation performance of -0.5 / NiS; Figure 16 The figure shown is 0.002CN-N 3C Photocatalytic nitrogen fixation cycle performance diagram of -0.5 / NiS; Figure 17 The image shows CN-N. 3C Catalytic mechanism diagram of the -0.5 / NiS complex; Figure 18 The image shows ammonia (NH4+). 4+ Standard curve. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The g-C3N4 used in this invention is prepared by the following steps: Weigh 10 g of urea into a beaker, add 30 mL of deionized water, stir with a magnetic stirrer for 15 minutes, then pour the solution into a crucible, place it in a muffle furnace, heat to 550 °C for 2 hours at a heating rate of 5 °C / min, and obtain g-C3N4 (denoted as CN).

[0020] In addition, the ammonium ion standard curve used in the following examples is as follows: Figure 18 As shown, the specific process for plotting its standard curve is as follows: Configure 0 mol / L, 6×10 5mol / L, 8×10 5 mol / L, 10×10 5 mol / L, 12×10 5 mol / L, 14×10 5 A standard solution of ammonium ions (mol / L) was poured into 10 mL colorimetric tubes and diluted to 5 mL. Then, 100 μL of potassium sodium tartrate solution (500 mg / L) and 100 μL of Nessler's reagent were added, and the solutions were shaken well and allowed to stand for 15 minutes. The absorbance at 420 nm was then measured using a UV spectrophotometer. After correcting the absorbance with a blank control, a standard curve was plotted with the solution concentration on the x-axis and absorbance on the y-axis.

[0021] Example 1 A g-C3N4-N 3C The preparation method of / NiS photocatalyst includes the following steps (1) Place 0.0015 mol nickel nitrate hexahydrate and 0.0045 mol thiourea (molar ratio of nickel nitrate hexahydrate to thiourea = 1:3) into beakers respectively, add 10 mL of deionized water to each and dissolve completely to obtain nickel nitrate hexahydrate and thiourea solutions respectively; (2) Add 30 mL of deionized water to a mixture of 0.5 g ammonium acetate and 10 g urea, stir with a magnetic stirrer for 15 minutes to mix evenly, then pour the solution into a crucible, place it in a muffle furnace, and calcine at 550 °C with a heating rate of 5 °C / min for 2 hours to obtain g-C3N4-N 3C -0.5 (denoted as CN-N) 3C -0.5).

[0022] (3) Weigh 0.15 g of CN-N 3C -0.5% of the solution was added to 30 mL of deionized water and then sonicated for 30 minutes using an ultrasonic cell disruptor. Then, nickel nitrate hexahydrate solution was added dropwise to CN-N. 3C The mixed solution was obtained by stirring the solution in a -0.5 solution for 30 min. (4) Thiourea solution was gradually added dropwise to the above mixed solution and stirred until homogeneous. The mixture was then poured into a 100 mL high-temperature and high-pressure reactor and heated to 180 °C at a rate of 5 °C / min, and kept there for 6 hours. After cooling to room temperature, the solid-liquid mixture was separated by vacuum filtration and thoroughly washed with deionized water and ethanol. The mixture was then dried overnight in a vacuum oven at 60 °C to obtain g-C3N4-N. 3C / NiS (denoted as 0.002-CN-N) 3C -0.5 / NiS).

[0023] Example 2 A g-C3N4-N3C The preparation method of the / NiS photocatalyst is similar to that in Example 1, except that "0.0015 mol nickel nitrate hexahydrate" in step (1) of Example 1 is changed to "0.002 mol nickel nitrate hexahydrate". The molar ratio of nickel nitrate hexahydrate to thiourea remains unchanged at 1:3, resulting in 0.002-CN-N 3C -0.5 / NiS.

[0024] Example 3 A g-C3N4-N 3C The preparation method of the / NiS photocatalyst is similar to that in Example 1, except that "0.0015 mol nickel nitrate hexahydrate" in step (1) of Example 1 is changed to "0.0025 mol nickel nitrate hexahydrate". The molar ratio of nickel nitrate hexahydrate to thiourea remains unchanged at 1:3, resulting in 0.0025-CN-N 3C -0.5 / NiS.

[0025] Example 4 A g-C3N4-N 3C The preparation method of the / NiS photocatalyst is similar to that in Example 1, except that "0.0015 mol nickel nitrate hexahydrate" in step (1) of Example 1 is changed to "0.003 mol nickel nitrate hexahydrate". The molar ratio of nickel nitrate hexahydrate to thiourea remains unchanged at 1:3, resulting in 0.003-CN-N 3C -0.5 / NiS.

[0026] Comparative Example 1 The preparation of NiS nanosheets specifically includes the following steps: 0.01 mol of Ni(NO3)2·6H2O and 0.03 mol of thiourea were weighed and placed in separate beakers. 25 mL of deionized water was added to each beaker. Thiourea solution was added dropwise to nickel nitrate hexahydrate solution. After stirring evenly, the mixture was poured into a 100 mL high-temperature and high-pressure reactor and heated to 180 °C at a heating rate of 5 °C / min and held for 6 hours. After cooling to room temperature, the solid-liquid mixture was separated by a vacuum filtration device and thoroughly washed with deionized water and ethanol. The mixture was then dried overnight in a vacuum oven at 60 °C to obtain nickel sulfide nanosheets (NiS).

[0027] Comparative Example 2 A method for preparing a g-C3N4 / NiS photocatalyst, the specific preparation process of which is similar to that of Example 2, the only difference being that the "CN-N" in step (3) of Example 2 is not used. 3C "-0.5" should be changed to "excluding N". 3CThe vacant g-C3N4” remains unchanged, and the process remains the same, resulting in 0.002CN / NiS.

[0028] Example 5 In this embodiment, step 2 of Example 1 is modified by replacing "0.5 g ammonium acetate" with "0.3 g ammonium acetate, 0.4 g ammonium acetate, 0.5 g ammonium acetate, 0.6 g ammonium acetate, and 0.7 g ammonium acetate" to prepare different proportions of N-containing compounds. 3C Vacant g-C3N4-N 3C Materials, and N prepared in the examples 3C Vacant g-C3N4-N 3C Material characterization tests (1) SEM, TEM, X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis and electron paramagnetic spectroscopy analysis The result is as follows Figures 1-5 As shown: from Figure 1 SEM images showed CN and CN-N 3C -0.5 has a similar porous layered structure, but CN-N can be easily seen. 3C The micropores at -0.5 μm are denser, and the overall structure is looser. This may be due to the CO2 and NH3 generated during the reaction of urea and ammonium acetate. To more clearly observe the morphology and structure of the catalyst, TEM tests were performed. from Figure 2 CN-N can be clearly observed 3C -0.5 exhibits a distinct layered porous morphology. This is due to the CN-N... 3C -0.5 has low crystallinity; its lattice fringes were not observed in the figure. Figure 2 CN-N can be observed in (d) and (e). 3C C and N elements at -0.5 are uniformly distributed in the selected region.

[0029] from Figure 3 It can be seen that CN exhibits two distinct characteristic peaks near 13.0 nm and 27.4 nm, corresponding to the (100) and (002) crystal planes of g-C3N4, respectively, which match the standard pattern of g-C3N4 (JCPDS 87-1526). Compared with pure CN, N is introduced... 3C The diffraction peak of the (002) plane of the vacant CN is slightly shifted to the right, which may be due to the N 3C The introduction of vacancies causes distortion in the crystal structure, which in turn affects the interplanar spacing. When the interplanar spacing decreases, the diffraction angle increases, which leads to a rightward shift of the XRD peak.

[0030] Figure 4 (a) and (b) show CN and CN-N.3C High-resolution XPS spectra of C1s and N1s at -0.5 eV. In the C1s spectrum, we can observe three peaks at 288.2 eV, 286.8 eV, and 284.8 eV, corresponding to C-(N)3 and C-NH3 of CN, respectively. X And foreign hydrocarbons (C=C / CC). The three peaks at 403.3 eV, 400.1 eV, and 398.1 eV in the N1s spectrum are amino hydrocarbons (C-NH4+). X The peaks are composed of three-coordinate nitrogen (N-(C)3) and two-coordinate nitrogen (C=NC) in carbon nitride. Further observation of the positions of these peaks reveals an interesting phenomenon: CN-N... 3C Compared to pure CN, the N1s peak of -0.5 is significantly shifted to a higher angle. This phenomenon occurs because nitrogen vacancies, as defects, generate a local electric field within carbon nitride. This local electric field alters the energy state of electrons, making them more tightly bound and requiring higher energy to be excited, thus causing the XPS peak to shift towards higher binding energies.

[0031] To further prove N 3C The existence of vacancies was verified by combining XPS peak area, elemental analysis, and EPR testing. CN and CN-N were obtained by calculating the XPS peak area. 3C The C / N ratios of -0.5 are 0.744 and 1.102 respectively, proving that CN-N 3C Nitrogen vacancies exist on the surface at -0.5. Elemental analysis results show that CN and CN-N are present. 3C The C / N ratios for -0.5 are 0.657 and 0.674, respectively. This result indicates that CN-N 3C Nitrogen vacancies also exist within the -0.5 range. Furthermore, to demonstrate that nitrogen vacancies are distributed in N... 3C For the site, N was calculated for CN and CN-0.5, respectively. 3C / N 2C and N 3C / C-NH x The peak area ratio indicates that CN-N 3C -0.5 (0.524) of N 3C / N 2C Significantly lower than CN (0.598), while CN and CN-N 3C -0.5 of N 3C / C-NH x The ratio remained essentially unchanged at approximately 1.84, indicating that nitrogen vacancies were mainly distributed in the N2 region. 3C The EPR results also confirmed the presence of nitrogen vacancies. Figure 5 ). For CN-N 3CVacancy tests of EPR at -0.5 revealed a single Lorentz curve with a g value of 2.004, while pure CN did not show a response signal, indicating the successful introduction of nitrogen vacancies.

[0032] Example 6 This embodiment describes the CN-N prepared in the above embodiments. 3C Characterization tests were performed on -0.5 / NiS, as follows: (1) Scanning electron microscopy and transmission electron microscopy analysis The morphology of the catalyst was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Figure 6 The SEM image in (a) shows that NiS nanosheets are largely stacked in bulk, while from CN-N 3C SEM image of -0.5 / NiS ( Figure 6 (b) CN-N can be observed 3C -0.5 nanosheets are tightly attached to bulk NiS. To further verify CN-N... 3C The -0.5 / NiS composite was successfully prepared and characterized by TEM. The results are as follows: Figure 7 As shown. From Figure 7 (a) CN-N can be clearly seen 3C -0.5 nanosheets were attached to NiS nanosheets, consistent with SEM results. Further verification of CN-N... 3C Whether there is a tight contact between -0.5 and NiS, HRTEM images were obtained at the contact area ( Figure 7 (b)). Therefore, CN-N 3C The 0.5 nm nanosheets were in close contact with the NiS crystal, indicating that the heterojunction was successfully prepared. Furthermore, lattice fringes with a spacing of 0.2251 nm were observed, which correspond to the (211) crystal plane of NiS. Figure 8 CN-N was displayed. 3C From the HAADF and mapping images of -0.5 / NiS, it is easy to see that C, N, S, and Ni elements are evenly distributed and cross-linked with each other.

[0033] (2) X-ray diffraction analysis The crystal structure and composition of the product were analyzed by XRD, and the results are as follows: Figure 9As shown. In the diffraction pattern of NiS, the diffraction peaks at 18.43°, 30.19°, 32.15°, 35.75°, 37.36°, 40.5°, 48.86°, 50.23°, 52.66°, 56.35°, 57.52°, and 59.75° match well with the hexagonal NiS crystal phase (PDF#86-2281), corresponding to the (110), (101), (300), (021), (220), (211), (131), (410), (401), (321), (330), and (012) crystal planes, respectively. In CN-N 3C In the -0.5 diffraction pattern, the two characteristic peaks at 12.9° and 27.41° correspond to the (100) and (002) crystal planes of CN, respectively, and match the standard pattern of CN (JCPDS 87-1526). In the 0.002CN-N... 3C The diffraction peaks of NiS are clearly visible in the -0.5 / NiS diffraction pattern, and there is a distinct characteristic peak at 27.22° corresponding to CN-N. 3C The (002) crystal plane at -0.5°C showed no other impurity peaks, indicating that high-purity 0.002CN-N was successfully prepared via the original growth method. 3C -0.5 / NiS complex.

[0034] (3) X-ray photoelectron spectroscopy analysis To further investigate the surface elemental states and electron flow directions of the material, CN-N 3C -0.5, NiS and CN-N 3C X-ray photoelectron spectroscopy (XPS) analysis was performed on -0.5 / NiS. The results are as follows: Figure 10 As shown, Figure 10 (a) shows the high-resolution XPS spectrum of C1s, with the three peaks at 288.1, 286.1, and 284.8 eV attributed to C-(N)3 and C-NH compounds of CN, respectively. x (x=1, 2) and foreign hydrocarbons (CC / C=C). Interestingly, with CN-N 3C A comparison of -0.5 revealed that CN-N 3C The three C1s peaks of -0.5 / NiS all shift towards higher binding energies, indicating that electrons in the composite material originate from the CN-N junction. 3C -0.5 flows to NiS. In the high-resolution XPS spectrum of N1s ( Figure 10 (b) The three peaks at 404.3, 400.0 and 398.4 eV are C-NH x The amino and heptaazine unit skeletons in (x=1, 2) have three coordination (N) groups. 3C ) and two coordinations (N2C Nitrogen atom. Same as C1s, CN-N 3C The three N1s peaks of -0.5 / NiS all shift towards higher binding energies. In S2p ( Figure 10 In the high-resolution XPS spectrum of (c), the two peaks at 169.1 and 163.8 eV correspond to S2p. 1 / 2 and S2p 3 / 2 This indicates that S is based on S 2- NiS and CN-N exist in the form of 3C -0.5 / NiS. But compared to NiS, CN-N 3C Both peaks of the S2p of -0.5 / NiS shift towards lower binding energies. Similar to S2p, the Ni2p binding energy of the composite material also shifts towards lower binding energies. Figure 10 (d) Ni2p in NiS 1 / 2 Peaks and Ni2p 3 / 2 The electron energies of the peaks are 874.7 eV and 856.8 eV, respectively. The peaks at 880.4 and 861.7 eV can be attributed to satellite peaks, indicating that Ni is produced by Ni... 2+ It exists in the form of.

[0035] (4) Photoelectrochemical testing and steady-state fluorescence spectroscopy analysis To further study N 3C The effects of vacancies and NiS co-catalyst introduction on photogenerated charge separation efficiency were investigated, and the concentrations of CN and CN-N were measured. 3C -0.5, NiS and CN-N 3C Transient photocurrent response and electrochemical impedance spectroscopy (EIS) of -0.5 / NiS. Figure 11 (a) It can be seen that CN and CN-N 3C -0.5, NiS and CN-N 3C After five cycles of on / off lamp irradiation, the current intensity of the -0.5 / NiS catalysts did not decrease significantly. This result indicates that the stability of the above catalysts is excellent. Furthermore, due to defect effects, CN-N 3C The current intensity of -0.5 is much higher than that of CN. This result indicates that CN-N 3C The electron-hole separation efficiency is higher at -0.5. And 0.002CN-N 3C The strongest photocurrent response of -0.5 / NiS indicates its highest electron-hole separation efficiency. Furthermore, from the EIS spectrum ( Figure 11 (b) It can be seen that 0.002CN-N 3C The arc radius of -0.5 / NiS is greater than that of CN-N. 3C -0.5 > CN, indicating 0.002CN-N 3C-0.5 / NiS has a lower surface resistance and a faster interface charge transfer rate, a result consistent with the conclusions obtained from the TPR spectrum. Therefore, N 3C The introduction of vacancies and NiS significantly promotes the transport of photogenerated electrons from the interior to the surface. Furthermore, we tested the PL spectrum of the catalyst to investigate its photovoltaic properties. Figure 11 (c) Displays CN, CN-N 3C -0.5, NiS and CN-N 3C Photoluminescence (PL) spectrum of -0.5 / NiS at an excitation wavelength of 325 nm. The photoluminescence intensities, from smallest to largest, are 0.002 CN-N. 3C -0.5 / NiS>CN-N 3C -0.5 > CN. It is well known that the lower the intensity of PL, the lower the recombination rate of photogenerated charges. The above results indicate that N 3C The introduction of vacancies and NiS can effectively suppress the recombination of photogenerated carriers and improve the transport and utilization of photogenerated carriers.

[0036] (5) Analysis of ultraviolet diffuse reflectance spectrum and Mott-Schottky curve Analysis of NiS composites with CN-N by UV-Vis diffuse reflectance absorption spectroscopy 3C The influence of -0.5 electron band structure and optical properties. From... Figure 12 (a) It can be seen that CN exhibits classic semiconductor absorption in the ultraviolet and part of the visible light region. Its absorption edge is approximately 460 nm. Compared to pure CN, CN-N... 3C -0.5 and CN-N 3C The absorption edge of -0.5 / NiS showed a significant red shift, and the light absorption intensity in the 400–800 nm region also increased. This is likely due to the introduction of nitrogen vacancies and the addition of NiS. The introduction of nitrogen vacancies can alter the band gap of CN, while NiS and CN-N... 3C Electron transfer occurs between the -0.5 contact surfaces, thereby enhancing their light absorption intensity and charge transfer efficiency. Figure 12 (b) and (c) demonstrate the transformation of the Kubel Replika-Munk function with CN and CN-N. 3C -0.5, NiS and 0.002CN-N 3C Corresponding curves for photon energies of -0.5 / NiS. CN, CN-N 3C -0.5, NiS and 0.002CN-N 3C -0.5 / NiS band gap (E g The values ​​were estimated to be 2.57, 2.48, 1.21, and 2.34 eV, respectively. Further determination of CN and CN-N... 3C-0.5, the band structure of NiS, we measured their Mott-Schottky curves, as shown... Figure 13 As shown, according to formula E NHE =E Ag / AgCl +0.197 indicates that CN-N 3C -0.5 and flat band potential of NiS (E fb The values ​​are -1.23 and 1.07 eV (vs Ag / AgCl), equivalent to -1.03 and 1.27 eV (vs NHE). CN-N 3C The -0.5 curve has a positive slope, indicating that it is an n-type semiconductor. It is well known that the E0.5 of an n-type semiconductor... CB Compared to its E fb The value is 0.1 V lower, therefore CN-N 3C -0.5 of E CB The value is -1.13 eV (vs NHE). The Mott-Schottky plot of NiS has a negative slope, indicating it is a p-type semiconductor. Considering that the Fermi level of a p-type semiconductor is approximately 0.1 eV negative compared to the top of its valence band, the valence band potential of NiS is 1.37 eV. According to formula E... g =E VB E CB E obtained from ultraviolet diffuse reflectance g It can be known that CN-N 3C -0.5 of E VB The E of NiS is 1.35 eV (vs NHE). CB The value is -0.16 eV (vs NHE). This result is consistent with the interleaved band structure of a type II heterojunction.

[0037] (6) Electron paramagnetic spectrum analysis To further understand the electron transfer pathways in the photocatalytic nitrogen fixation reaction, electron paramagnetic spectroscopy was used for analysis. Figure 14 CN-N 3C -0.5, NiS and CN-N 3C -0.5 / NiS complex·O2 - The capture experiment of ·OH, Figure 14 The experimental results in (a) show that CN-N 3C -0.5 and CN-N 3C -0.5 / NiS composites all exhibit ·O2 - The EPR signal peak, and CN-N 3C The signal peak intensity at -0.5 is higher than that of CN-N. 3C The peak intensity of the -0.5 / NiS composite was observed, while NiS did not show O2. -The signal peak indicates that electrons originate from CN-N 3C The conduction band at -0.5 flows to the conduction band of NiS. And... Figure 14 (b) The CN-N signal in the ·OH capture EPR signal diagram 3C -0.5, NiS and CN-N 3C The -0.5 / NiS composites all exhibited EPR signal peaks for ·OH, but the peak intensity of NiS was significantly higher than that of CN-N. 3C -0.5 / NiS and CN-N 3C -0.5, while CN-N 3C The ·OH signal peak of -0.5 / NiS is slightly higher than that of CN-N. 3C The signal peak at -0.5 indicates a flow from the NiS valence band to CN-N. 3C Hole flow in the -0.5 valence band. Combined NiS and CN-N. 3C The electron-hole transfer paths between -0.5 and the previously obtained band structure results confirm that NiS and CN-N 3C A type II heterojunction was formed between the -0.5 contact surfaces. The formation of this structure promoted the separation of photogenerated carriers and greatly improved the separation and utilization rate of photogenerated electron and hole pairs.

[0038] Example 7 This embodiment describes the CN-N prepared above. 3C Photocatalytic nitrogen fixation activity of the -0.5 / NiS composite was studied. (1) CN-N 3C Photocatalytic nitrogen fixation performance analysis of the -0.5 / NiS composite The photocatalytic nitrogen fixation performance test was conducted in a sealed quartz glass reactor under a N2 atmosphere, using a 300 W xenon lamp to simulate sunlight. The specific operating procedure was as follows: First, 50 mg of the test substance was ultrasonically dispersed in 100 mL of a methanol-water mixture (methanol to water volume ratio 1:9) for 15 minutes. The mixed solution was then poured into the reaction apparatus, and the quartz glass plate was covered and clamped. Cooling water was then introduced. Next, N2 / Ar (99.999%) was introduced into the reactor for 30 minutes in darkness. Then, the light source was turned on 2 cm away from the reactor, and the supernatant was sampled every hour using a disposable syringe sampler. The supernatant was filtered through a disposable polyethersulfone filter membrane. The filtered supernatant was then poured into a 10 mL cuvette and brought to a final volume of 5 mL. 100 μL of potassium sodium tartrate solution (500 mg / L) and 100 μL of Nessler's reagent were added and shaken well. After standing for 15 minutes, the absorbance at a wavelength of 420 nm was measured using a UV spectrophotometer.

[0039] By substituting the obtained absorbance into the ammonium ion standard curve, the specific concentration of ammonium ions in the solution can be obtained. The experimental results are as follows: Figure 15 As shown. After four hours of illumination, compared to pure CN (35.23 μmol / L), 0.002CN-N 3C The photocatalytic nitrogen fixation performance of the -0.5 / NiS composite (285.87 μmol / L) was improved by 8.1 times, while that of the N-free composite was significantly improved. 3C The photocatalytic nitrogen fixation performance of the 0.002CN / NiS complex (111.08 μmol / L) with vacant sites was improved by 2.54 times. Furthermore, the photocatalytic nitrogen fixation performance of the 0.002CN / NiS complex was improved by 3.15 times compared to pure CN. These results indicate that N... 3C The introduction of vacancies and NiS promoted the photocatalytic nitrogen fixation of CN. Furthermore, when the amount of NiS added was greater than 0.002 mol, CN-N... 3C The performance of the -0.5 / NiS composite decreased instead of increased. This is because excessive NiS content disrupts the synergistic effect between carbon nitride and nickel sulfide, affecting charge transfer and energy transfer efficiency among the components of the composite, thus inhibiting the overall activity of the photocatalyst. Furthermore, excessive nickel sulfide content may occupy active sites of other effective components or alter the surface properties of the composite, hindering reactant adsorption and reaction, ultimately leading to a decrease in photocatalytic activity.

[0040] (2) CN-N 3C Photocatalytic stability analysis of the -0.5 / NiS complex To investigate CN-N 3C For stability of -0.5 / NiS, we selected 0.002CN-N, which has the best performance. 3C -0.5 / NiS was used to conduct photocatalytic nitrogen fixation cycle experiments. 0.002CN-N 3C The performance of -0.5 / NiS was tested following the above photocatalytic nitrogen fixation experimental procedure, with five sets of experiments repeated, each group irradiated for four hours. The results are as follows: Figure 16 As shown, after five repeated experiments, 0.002 CN-N 3C The photocatalytic nitrogen fixation performance of the -0.5 / NiS composite decreased by 20.19%, indicating that the catalytic material has good stability.

[0041] In addition, this invention also provides CN-N 3C The photocatalytic nitrogen fixation mechanism of the -0.5 / NiS complex (e.g.) Figure 17 As shown), specifically: when a beam of energy is greater than or equal to NiS and CN-N 3C When light with a band gap of -0.5 is irradiated onto the catalyst, NiS and CN-N3C -0.5 When excited by light, NiS generates electrons and holes. Electrons move to their respective conduction bands, while holes remain in the valence band. This is because NiS reacts with CN-N. 3C The role of type II heterojunction formed by -0.5 contact, CN-N 3C Electrons in the -0.5 conduction band migrate to the conduction band of NiS, while holes in the NiS valence band migrate to the CN-N junction. 3C A valence band shift of -0.5 occurs. Subsequently, the strongly reducing electrons in the NiS conduction band undergo a reduction reaction with the N2 adsorbed on the catalyst, while CN-N... 3C Holes with a strong oxidizing property in the -0.5 valence band react with water to produce O2.

[0042] The embodiments of this application have been described above with reference to the accompanying drawings. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the core ideas of this application. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. g containing type II heterojunction C3N4 N 3C The application of NiS photocatalyst in photocatalytic nitrogen fixation and ammonia production is characterized by... The g containing type II heterojunction C3N4 N 3C The preparation method of / NiS photocatalyst includes the following steps: Ammonium acetate and urea were dissolved in water, mixed thoroughly, and then placed in a crucible. The mixture was heated to 550°C at a heating rate of 5°C / min and calcined for 2 hours to obtain a product containing N. 3C empty g C3N4; Will contain N 3C empty g C3N4 is dissolved in water, sonicated, and then nickel nitrate hexahydrate solution is added to obtain a mixed solution; Thiourea was dissolved in water and mixed thoroughly with the mixture, then placed in a reaction vessel and heated to react. After the reaction was completed, the mixture was cooled to room temperature, separated, washed, and dried to obtain the g containing the type II heterostructure. C3N4 N 3C / NiS photocatalyst; Among them, the nickel nitrate hexahydrate solution contains nickel nitrate hexahydrate and N 3C empty g The dosage of C3N4 is 0.0015 mol. 0.003 mol: 0.15 g; The specific process of the heating reaction is as follows: heat to 180°C at a heating rate of 5°C / min and maintain for 6 h.

2. The application according to claim 1, characterized in that, The mass ratio of ammonium acetate to urea is 1:

2.

3. The application according to claim 1, characterized in that, Nickel nitrate hexahydrate and containing N 3C empty g The ratio of C3N4 used is 0.002 mol: 0.15 g.

4. The application according to claim 1, characterized in that, The molar ratio of nickel nitrate hexahydrate to thiourea is 1:

3.

5. The application according to claim 1, characterized in that, The ultrasound was performed using an ultrasonic cell disruptor for 25 minutes. 40 min.

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