阅读说明：本技术 一种空心环状氮化碳光催化剂及其制备方法 (Hollow annular carbon nitride photocatalyst and preparation method thereof ) 是由 孙娜 周春宇 张松 于 2021-01-04 设计创作，主要内容包括：本发明公开了一种空心环状氮化碳光催化剂及其制备方法,该空心环状氮化碳光催化剂,包含由三聚氰胺与氰尿酸为前驱体形成超分子,将所述超分子在H-2/N-2混合气体的气氛中锻烧获得空心环状氮化碳。所述H-2/N-2混合气体,H-2占2-10％,N-2占90-98％。该氮化碳光催化剂具有较大的比表面积和更高的催化活性。(The invention discloses a hollow annular carbon nitride photocatalyst and a preparation method thereof, wherein the hollow annular carbon nitride photocatalyst comprises supermolecules formed by melamine and cyanuric acid as precursors, and the supermolecules are put in H 2 /N 2 Calcining in the atmosphere of mixed gas to obtain the hollow annular carbon nitride. Said H 2 /N 2 Mixed gas of H 2 2-10% of N 2 Accounting for 90 to 98 percent. The carbon nitride photocatalyst has a large specific surfaceArea and higher catalytic activity.)

1. The hollow annular carbon nitride photocatalyst comprises supermolecules formed by melamine and cyanuric acid serving as precursors, and is characterized in that: the supramolecule is represented by the formula H₂/N₂Calcining in the atmosphere of mixed gas to obtain the hollow annular carbon nitride.

2. A carbon nitride photocatalyst in accordance with claim 1, said H₂/N₂Mixed gas of H₂2-10% of N₂90-98%, preferably H₂5% of N₂Accounting for 95 percent.

3. The carbon nitride photocatalyst according to claim 1, wherein the molar ratio of the precursor, melamine and cyanuric acid is 1: 1.

4. a preparation method of a hollow annular carbon nitride photocatalyst comprises the following steps:

1) dissolving melamine in DMSO to form a melamine solution;

2) dissolving cyanuric acid in DMSO to form a cyanuric acid solution;

3) mixing the melamine solution obtained in the step 1) with the cyanuric acid solution obtained in the step 2), heating and stirring, and filtering to obtain a supermolecular solid;

4) placing the supermolecule solid into a non-sealed calcining device, and placing the supermolecule solid into H₂/N₂Heating and calcining in the atmosphere of mixed gas;

5) and after the calcination is finished, naturally cooling to room temperature to obtain the hollow annular carbon nitride photocatalyst.

5. The method of claim 4, wherein: in step 4), the H₂/N₂Mixed gas of which H₂2-10% of N₂90-98%, preferably H₂The content of the active ingredients accounts for 5 percent,N₂accounting for 95 percent.

6. The process according to claim 4, wherein in step 4), the calcination temperature is 500-600 ℃, preferably 550 ℃, and the calcination time is 3-5h, preferably 4 h.

7. The method according to claim 6, wherein the heating is carried out at a heating rate of 2.3 ℃ for min^-1。

8. The method according to claim 4, wherein in step 3), the molar ratio of melamine to cyanuric acid is 1: 1.

9. the preparation method according to claim 4, wherein in the step 3), the heating and stirring are carried out at a temperature of 110 ℃ and 130 ℃, preferably at a temperature of 120 ℃, and the stirring time is 15-30min, preferably at a time of 20 min.

10. The method according to claim 4, wherein the melamine solution or the cyanuric acid solution is used in a concentration of 0.05 to 0.5mol/L, preferably 0.3 to 0.4mol/L in steps 1) and 2).

11. The method of claim 4, wherein the step 3) further comprises washing the supramolecular solid with ethanol, drying to obtain solid powder, and performing a next calcination process.

Technical Field

The invention belongs to the field of catalysts, and particularly relates to a hollow annular carbon nitride photocatalyst and a preparation method thereof.

Background

Photocatalysts driven in the visible light region have attracted great attention in terms of environmental pollution and consumption of fossil resources. Among various photocatalytic semiconductors, graphite-like phase carbon nitride (g-C)₃N₄) Has the characteristics of wide source, low price, good thermal stability, unique electronic structure and the like. However, the device is not suitable for use in a kitchenThe graphite-like carbon nitride has the defects of low specific surface area, low sunlight absorption efficiency, rapid recombination of photo-generated electron-hole pairs and the like. The reaction atmosphere has a great influence on the chemical composition, structure and performance of the graphite-like phase carbon nitride. Meanwhile, the preparation method in the prior art needs to synthesize graphite-like phase carbon nitride by a two-step calcination method: firstly, synthesizing blocky graphite-like phase carbon nitride by utilizing a thermal polymerization method, and then introducing another gas to treat the graphite-like phase carbon nitride during secondary calcination.

CN106622326 discloses a method for preparing a carbon nitride material, which comprises the following steps: firstly, mixing a dimethyl sulfoxide solution of cyanuric acid and a dimethyl sulfoxide solution of melamine to form a white emulsion; secondly, oscillating the white emulsion obtained in the first step, centrifuging, and removing the solvent dimethyl sulfoxide to obtain a white precipitate; thirdly, adding a polar solvent into the white precipitate, continuing to oscillate for 20min, and then centrifuging to remove the redundant solvent, wherein the polar solvent adopts methanol, ethanol or acetone, and the volume of the polar solvent adopted in the third step is the same as the total volume of the dimethyl sulfoxide adopted in the first step; and fourthly, drying the solid obtained in the third step to obtain powder, and continuously performing heat treatment for 4.0-5.0 hours at 550 +/-10 ℃ in a nitrogen atmosphere to obtain the core-shell carbon nitride heterojunction.

The inventor of the invention unexpectedly finds that in the process of photocatalyst-like, in the process of supermolecule calcination technology, a proper amount of gas H is added into nitrogen in the atmosphere gas₂When the catalyst is used, the photocatalytic activity of the graphite-like phase carbon nitride can be obviously improved. Thus, the present invention has been completed.

Disclosure of Invention

The invention aims to provide a hollow annular carbon nitride photocatalyst and a preparation method thereof. Compared with the traditional method, the preparation method is simpler to operate and more economical.

In one embodiment, the hollow ring-shaped carbon nitride photocatalyst of the present invention comprises a supermolecule formed by melamine and cyanuric acid as precursors, and the supermolecule is H₂/N₂Calcining in mixed gas atmosphere.

Preferably, the hollow cyclic carbon nitride photocatalyst of the present invention, said H₂/N₂Mixed gas of H₂2-10% of N₂90-98%, more preferably, H₂5% of N₂Accounting for 95 percent. The molar ratio of melamine to cyanuric acid of the precursor is 1: 1.

in another embodiment, the present invention provides a method for preparing a hollow annular carbon nitride photocatalyst, comprising the steps of:

1) dissolving melamine in DMSO to form a melamine solution;

2) dissolving cyanuric acid in DMSO to form a cyanuric acid solution;

3) mixing the melamine solution obtained in the step 1) with the cyanuric acid solution obtained in the step 2), heating and stirring, and filtering to obtain a supramolecular solid;

4) placing the supermolecule solid into a non-completely sealed calcining device, and placing the device in H₂/N₂Heating and calcining in the atmosphere of mixed gas;

5) and after the calcination is finished, naturally cooling to room temperature to obtain the hollow annular carbon nitride photocatalyst.

Preferably, the preparation method of the invention is characterized in that: in step 4), the H₂/N₂Mixed gas of which H₂2-10% of N₂90-98%, more preferably H₂5% of N₂Accounting for 95 percent.

In the preparation method of the invention, in the step 4), the calcination temperature is 500-600 ℃, preferably 550 ℃, the calcination time is 3-5h, preferably 4h, the heating and calcination are carried out, and the heating rate is 2.3 ℃ for min^-1。

In the preparation method of the invention, in the step 3), the molar ratio of the melamine to the cyanuric acid is 1: 1, the heating and stirring are carried out, wherein the heating temperature is 110-130 ℃, the preferred temperature is 120 ℃, and the stirring time is 15-30min, the preferred time is 20 min.

In the step 3), the preparation method of the present invention further includes washing the supramolecular solid obtained by filtering with ethanol, drying to obtain supramolecular powder solid, and performing the next calcination process, wherein the drying temperature is 50-70 ℃, preferably 60 ℃, and the drying time is 3-5 hours, preferably 4 hours.

The solution of the above-mentioned process of the present invention, step 1) or 2), has a solute concentration of 0.05 to 0.5mol/L, preferably 0.3 to 0.4 mol/L.

The preparation method of the invention is a simple and economic method. Melamine and cyanuric acid are used as precursors, and supermolecule formed by the melamine and the cyanuric acid generates NH in the pyrolysis process₃(g) And H₂O (g). The interlayer distance of the original graphite-like phase carbon nitride is 0.320nm and is greater than H₂O (g) (0.25 nm). Thus, H₂O (g) can enter into the graphite-like phase carbon nitride layer to react with carbon atoms [ H ]₂O(g)+C(s)→CO(g)+H₂(g)]. At the same time, gas NH is generated₃(g) CO (g) and H₂(g) The method fully utilizes the one-time calcination work of the micromolecule gas generated in the pyrolysis process to prepare the hollow annular graphite-like carbon nitride with high porosity, high specific surface area and nitrogen defect, thereby improving the catalytic activity of hydrogen production.

Drawings

FIG. 1 is a flow chart of the preparation of CN-H, CN-N carbon nitride of example 1 and comparative example 1;

FIG. 2 is an XRD and IR patterns of samples of CN-H, CN-N carbon nitride of example 1 and comparative example 1;

FIG. 3 is an X-ray photoelectron spectroscopy full spectrum XPS summary of CN-H, CN-N carbon nitride samples of example 1 and comparative example 1;

FIG. 4 is an X-ray photoelectron spectrum of CN-H, CN-N carbon nitride samples of example 1 and comparative example 1;

FIG. 5 is a Scanning Electron Micrograph (SEM) of CN-N and CN-H carbon nitride samples;

FIG. 6 is a Transmission Electron Micrograph (TEM) of CN-N and CN-H carbon nitride samples;

FIG. 7 is a nitrogen adsorption and desorption curve and a material pore size distribution diagram of CN-N and CN-H carbon nitride samples;

FIG. 8 is a graph of the UV-VIS diffuse reflectance spectra of CN-N and CN-H carbon nitride samples;

FIG. 9 is a graph of decay curves and fitted parameters for transient fluorescence spectra for CN-N and CN-H carbon nitride samples;

FIG. 10 is a graph of electrochemical impedance spectra and photocurrent response in visible light for CN-N and CN-H carbon nitride samples;

FIG. 11 is a graph of the cycling stability of photocatalytic hydrogen production and AQE and CN-H photocatalytic hydrogen production under visible light illumination for CN-N and CN-H carbon nitride samples;

Detailed Description

The following examples are merely representative to aid in a further understanding of the spirit of the invention, and are not intended to limit the scope of the invention in any way.

Example 1 preparation of hollow ring-like graphite-like phase carbon nitride photocatalyst

Melamine/cyanuric acid supramolecules are used as precursors, and hydrogen is introduced: the defective ring-like graphite-like carbon nitride is prepared in a nitrogen (5%: 95%) atmosphere.

The preparation process comprises the following steps:

1) preparation of supramolecular solids

3.96mmol of melamine was dissolved in 20mL of DMSO. While 3.96mmol of cyanuric acid was dissolved in 10mL of DMSO. Mixing the above two solutions, stirring at 120 deg.C for 20min, filtering to obtain white supermolecular solid, washing with ethanol, and drying at 60 deg.C for 4 hr to obtain supermolecular powder.

2) Pyrolysis reaction

The supermolecule powder obtained in the previous step is put into a 30mL alumina porcelain boat, and the porcelain boat with the same size is covered on the supermolecule powder to retain the self-generated micromolecule gas. Leave the gap between upper and lower porcelain boat, outside hydrogen: introducing nitrogen (5%: 95%) mixed gas atmosphere, heating to 550 deg.C, maintaining for 4 hr at heating rate of 2.3 deg.C for min^-1. After the calcination process is finished, the obtained product is naturally cooled to room temperature, and the obtained product is a hollow annular graphite-like phase carbon nitride photocatalyst which is marked as CN-H. The preparation flow chart of the CN-H carbon nitride is shown in figure 1.

In the above process, the self-generated NH is utilized in the thermal polymerization process₃、H₂O、CO and introduced N₂/H₂The structure and the morphology of the graphite-like phase carbon nitride are regulated and controlled by the mixed gas atmosphere, the hollow annular porous carbon nitride containing structural defects is prepared, and the photocatalytic activity, particularly the hydrogen production performance, of the carbon nitride material is improved.

Comparative example 1

Following the procedure of example 1, only N₂/H₂Replacement of mixed gas atmosphere by N₂An atmosphere. The graphite-like phase carbon nitride photocatalyst is prepared and is marked as CN-N. The preparation flow chart is shown in figure 1. FIG. 1 is a schematic view showing the preparation flow of CN-H and CN-N in example 1 and comparative example 1, and the carbon nitride in example 1 has a hollow ring shape, while the carbon nitride in comparative example 1 has a spherical shape.

Experimental example 1 characterization of the materials

XRPD patterns and IR testing

The CN-H and CN-N carbon nitride samples obtained in example 1 and comparative example 1 were subjected to XRD spectrum (Cu target source) and IR spectrum tests, respectively.

The results are shown in FIG. 2, in which (a) is an X-ray diffraction pattern and (b) is a Fourier transform infrared spectrum. FIG. 2a is an X-ray diffraction pattern (XRD) with a diffraction peak at 12.9 ° corresponding to the (100) plane, which is a characteristic diffraction peak formed by the in-layer structure of the triazine unit; the diffraction peak at 27.8 ° corresponds to the (002) plane, which is formed by stacking of aromatic ring interlamination structures. The distance between aromatic rings of CN-H is about 0.323 nm. As can be seen from FIG. 2a, the intensity of the characteristic diffraction peak of CN-H at 12.9 ℃ becomes weaker, indicating that the in-layer structure of the triazine ring unit is destroyed. The peak at 27.83 ° shifts to the left, from 27.83 ° to 27.59 °, reflecting the increased interlayer spacing of CN-H, and this structural change is also confirmed by the following morphological analysis, pore volume and BET specific surface area tests.

FIG. 2b is a Fourier transform infrared (FT-IR) spectrum of CN-N and CN-H. As can be seen from XRPD and FT-IR spectra, all characteristic peaks of CN-H are very similar to CN-N, indicating that CN-H after mixed gas modification still maintains the original chemical framework. In FIG. 2b, at 812cm^-1The strong absorption peak corresponds to the breathing vibration mode of the triazine ring unit; the center is positioned at 1200-1600cm^-1Pair of absorption bands ofCorresponding to the aromatic type g-C₃N₄N (-C) of middle C-N heterocycle₃And C-NH-C; and is positioned at 3000-3500cm^-1The inner broad absorption band is mainly non-condensed amino-NH₂and-NH-stretching vibration and surface bonding H₂the-OH stretching of the O molecule vibrates.

XPS spectra testing

X-ray photoelectron spectroscopy (ThermoFisher Escalab 250 XI) was used, and the specific parameters tested were: al K alpha rays of 1486.6eV were used, and the transmitted energy was 150W and 30 eV.

The XPS summary of carbon nitride of CN-N and CN-H of example 1 and comparative example 1 was tested and the results are shown in FIG. 3, FIG. 3 is the XPS summary, with CN-N and CN-H having three peaks at 288, 398 and 531eV, which are C, N and the O element, respectively.

Two g-C of CN-N and CN-H₃N₄The relative contents of the sample element species are shown in table 1.

TABLE 1 CN-N and CN-H sample element species and relative content

FIG. 3 shows: the peak area ratio of C-NHx in CN-H is less than that of CN-N, which indicates that in hydrogen: under the condition of nitrogen (5%: 95%) atmosphere, the carbon element in C-NHx is reduced.

The X-ray photoelectron spectra of the carbon nitrides of CN-N and CN-H of example 1 and comparative example 1 were measured, and the results are shown in fig. 4, in which (a) is a spectrum of C1s of the CN-N sample, (b) is a spectrum of N1s of the CN-N sample, (C) is a spectrum of C1s of the CN-H sample, and (d) is a spectrum of N1s of the CN-H sample.

The carbon nitrides of CN-N and CN-H of example 1 and comparative example 1 were analyzed for their relative contents of elements by X-ray photoelectron spectroscopy, and the results are shown in Table 2.

TABLE 2 analysis of relative contents of elements in X-ray photoelectron spectroscopy

As a result of the elemental analysis, the C/N atomic ratio of CN-N was 0.580 in comparison with the C/N atomic ratio of CN-H was 0.577 in Table 1. Hydrogen gas: g-C prepared under the mixed gas condition of nitrogen (5%: 95%)₃N₄The relative carbon content decreases. Taking into account g-C₃N₄There are many different types of carbon species in it, and further studies are necessary to verify this conclusion.

FIG. 3 is an X-ray photoelectron spectroscopy total spectrum (XPS) with CN-N and CN-H having three peaks at 288, 398 and 531eV 3, C, N and O elements, respectively. The results of X-ray photoelectron spectroscopy (XPS) are shown in FIGS. 3 and 4. FIGS. 4a and 4C show the C1S spectra, with four peaks at 284.5, 286.2, 287.9 and 293.3eV corresponding to surface carbon contamination, C-NH respectively_x，g-C₃N₄N-C-N of aromatic rings and pi excitation of oxazine rings pi → pi. Table 2 shows two g-C₃N₄Relative content of sample element species. C-NH in CN-H_xThe peak area ratio is less than CN-N, which is indicated in the hydrogen: C-NH under the atmosphere of nitrogen (5%: 95%)_xThe carbon element in (2) is reduced. Fig. 4b and 4d show the N1S pattern for the sample, with four peaks at 398.5, 399.9, 400.8 and 404.1eV corresponding to C ═ N-C, N- (C), respectively₃，NH_xAnd pi excitation of the oxazine ring pi → pi. NH of CN-H_x/(C＝N-C+N(-C)₃) The peak area ratio was less than CN-N, indicating a decrease in amino groups at the boundary of the CN-H sample. From the above, it is inferred that after carbon atoms are consumed by water molecules, nitrogen atoms occupy the original carbon positions, and the structure thus formed is called a nitrogen defect. The defect CN-H can improve the delocalization capability of electrons, enhance the electrical conductivity and the mobility of photogenerated electrons and holes, effectively promote the separation of photogenerated electron and hole pairs and further improve the photocatalytic performance.

Experimental example 2 morphological analysis

The structures and the morphologies of the CN-N and CN-H carbon nitrides of example 1 and comparative example 1 were observed by scanning with an electron microscope and by a transmission electron microscope. The structure is shown in fig. 5 and 6.

FIG. 5 is a Scanning Electron Micrograph (SEM) of CN-N and CN-H samples. The results of A and B in FIG. 5 show that CN-N is a spherical structure having an average diameter of about 3 to 5 μm, the spherical structure of CN-N is formed by aggregation of nano-platelets by molecular self-assembly, and CN-H in FIG. 5 is a hollow ring-like graphite-like phase carbon nitride having a smaller particle size than CN-N. Indicating that in the presence of hydrogen: the surface appearance of the synthesized carbon nitride is obviously changed under the mixed atmosphere of nitrogen (5%: 95%).

FIG. 6 is a Transmission Electron Micrograph (TEM) of CN-N and CN-H. In FIG. 6, a, b and c are CN-N samples, and d, e and f are CN-H samples. It can be obviously observed from the transmission diagram that the CN-H sample has fewer stacked layers, large specific surface area and small lamella thickness, and the hollow annular structure is beneficial to improving the photocatalytic hydrogen production performance.

Experimental example 3 texture characteristics analysis

Specific surface area analyzer (MICROMERITICS ASAP 2020HD88) was used, and the specific parameters tested were: the nitrogen sorption/desorption isotherm curves of the powdered graphite-like phase carbon nitride samples were tested at a temperature of 77.4K. The carbon nitrides of CN-N and CN-H of example 1 and comparative example 1 were subjected to a nitrogen adsorption and desorption test and a pore size distribution test, and the results are shown in fig. 7. FIG. 7 is a nitrogen adsorption and desorption curve of CN-N and CN-H samples, wherein the inset is a pore size distribution diagram of the CN-N and CN-H materials.

FIG. 7 shows the results for Brunauer-Deming-Deming-Teller species, two g-Cs for CN-N and CN-H₃N₄The samples are all isotherms of type IV, indicating the presence of mesopores (2-10 nm). And two g-C₃N₄The hysteresis loop of the sample was of the type H3, indicating that the holes were slit-shaped. The CN-H sample had a specific surface area of 133.16m² g ^-1Pore volume of 0.4710cm³ g^-1(ii) a The specific surface area of CN-N is 102.82m² g^-1The pore volume was 0.4710cm³ g^-1. The interpolation in FIG. 7 investigated the pore size distribution of CN-N and CN-H in the 2-10nm range using the BJH method. The peak at 3nm of CN-H is strongly reduced, indicating that the pore volume around 3nm is less than that of CN-N. However, CN-H has a larger pore volume at 100 nm. The increase of the specific surface area of CN-H indicates that the hydrogen in the supermolecular thermal polymerization process: the mixed atmosphere of nitrogen (5%: 95%) can effectively inhibit g-C₃N₄The interlayer accumulation of the material provides more reactions for the photocatalysis reaction processThe site of activity.

Experimental example 4 optical Property analysis

The CN-N and CN-H samples of example 1 and comparative example 1 were tested for UV-visible diffuse reflectance spectra and the results are shown in FIG. 8. FIG. 8 is a graph of the UV-visible diffuse reflectance spectra of CN-N and CN-H samples, with the inset being (α H upsilon)^1/2Graph with (h upsilon).

FIG. 8 shows g-C₃N₄The absorption edge of the material is red-shifted from CN-N to CN-H. Furthermore, the absorption capacity of the CN-H sample for visible light is reduced compared to CN-N. This result is consistent with the pale yellow color of CN-H, the darker color of the CN-N sample, and the better light absorption. In the inset of FIG. 8 (α h upsilon)^1/2Plotting (h upsilon) can obtain the forbidden band width. The forbidden band widths of CN-N and CN-H are respectively 2.76eV and 2.74 eV. Compared with CN-N, the forbidden band width of CN-H is slightly reduced.

The CN-N and CN-H samples of example 1 and comparative example 1 were tested for transient fluorescence spectra. The results are shown in FIG. 9 and Table 3.

TABLE 3 kinetic parameters of transient fluorescence Spectroscopy

In order to further and further examine the recombination behavior of the photon-generated carriers, the carrier lifetime of CN-N and CN-H is researched by using transient fluorescence spectrum. Transient fluorescence spectroscopy was excited at 400nm and detected at 450 nm. The curve was fitted with the third order exponential decay kinetics equation (1). Herein, equation (2) is used to calculate the average lifetime τ_avg。

The attenuation curves and fitting parameters are shown in FIG. 9 and Table 3, respectively. The average lifetime of CN-H was 4.36ns, which was longer than CN-N (3.45 ns). During irradiation, (τ)₂) A recombination process corresponding to photo-generated electrons and holes; (τ)₁) Corresponding to non-radiative processes; (τ)₃) Corresponding to the energy transfer process. In contrast, CN-H differs from CN-N in the non-radiative and energy transfer processes, indicating that the two samples have different emission pathways. In the process of compounding photoproduction electrons and holes, the proportion of CN-H is 31.2 percent and is higher than that of CN-N (18.9 percent). The CN-H service life is prolonged because the nitrogen defect enhances the delocalized electron capability of the sample, thereby improving the separation efficiency and the transmission efficiency of the photon-generated carriers.

Experimental example 5 photoelectrochemical Property test

The photo-generated current density and electrochemical impedance spectra were measured by the CHI660D electrochemical workstation. 0.1mg of the photocatalyst was dispersed in a mixed solution composed of 300. mu.L of water, 100. mu.L of isopropyl alcohol and 10. mu.L of Nafion solution (5 wt%). After 3h of sonication, the resulting catalyst slurry was dispersed at about 2cm²Area fluorine doped tin oxide (FTO) glass. After drying, the mixture was washed with 0.5M Na₂SO₄A three-electrode system was assembled in aqueous solution, including a photocatalyst electrode, an electrode (Pt) and a reference electrode (Ag/AgCl). Both tests were performed using xenon lamp illumination at a wavelength of 420 nm.

The CN-N and CN-H samples of example 1 and comparative example 1 were tested for electrochemical impedance spectroscopy and photocurrent response under visible light. The results are shown in FIG. 10.

FIG. 10 shows (a) the electrochemical impedance spectra of CN-N and CN-H samples, and (b) the photocurrent response curves of CN-N and CN-H samples under visible light

Fig. 10a, b show electrochemical impedance spectra and transient photocurrent response spectra (EIS). In FIG. 10b, CN-H shows a higher photocurrent signal than CN-N, indicating an improved separation efficiency of electron-hole pairs. Electrochemical resistance spectra As shown in FIG. 10a, the larger the arc radius, the higher the charge transfer resistance, and the better the charge transfer efficiency of CN-H over CN-N, indicating that nitrogen defects facilitate the separation and transfer of electron-hole pairs. By combining the above analysis, it is found that the structural defects have important significance for improving the photocatalytic activity.

Experimental example 6 photocatalytic Performance test

In order to examine the catalytic performance of the samples under visible light, the CN-N and CN-H samples of the example 1 and the comparative example 1 are studied on the hydrogen production activity of photocatalytic water decomposition.

The photocatalytic water splitting hydrogen production experiment and test process are as follows:

100mg of photocatalyst was added to a quartz reactor containing 90mL of deionized water, ultrasonically dispersed, then 10mL of triethanolamine (TEOA, 10 vol%) was added to the solution, and finally a quantitative solution of the co-catalyst (H) was added₂PtCl₆). After the reagents are added, the reactor is quickly covered by quartz glass, and then nitrogen is introduced into the quartz reactor to ensure that a reaction system is in an anaerobic state and is sealed by a rubber plug. Mounting a filter (lambda) on the xenon lamp>420nm) and the fixed light-liquid distance is 10 cm. Starting condensed water, irradiating with 300W xenon lamp for 1H, and discharging H₂PtCl₆After reduction to Pt helper catalyst, the vessel was sealed. And introducing nitrogen for 10min, discharging other gases, then extracting 1mL of gases by using a 10mL needle tube at an interval of 1h, reading and recording the peak area generated by hydrogen in the gas curve of the sample, and determining the composition of the mixed atmosphere in the photocatalytic hydrogen production system by means of a gas chromatograph. The amount of hydrogen species n is calculated as follows: from the ideal gas law PV — nRT, the amount of hydrogen species can be calculated. In the formula, R is a constant 8.314 J.mol^-1·K^-1T is the temperature of the cooling water in the quartz reactor, V is the volume of hydrogen and P is the atmospheric pressure. The sealed container is purged by nitrogen after 4 hours, four cycles are carried out in the reaction process, and the nitrogen is used for testing the cycle stability of the photocatalyst sample

The results are shown in FIG. 11. In FIG. 11, (a) shows the photocatalytic hydrogen production and AQE of CN-N and CN-H samples under visible light illumination, and (b) shows the cycling stability of the photocatalytic hydrogen production by CN-H.

As shown in FIG. 11a, the apparent rate of CN-H was 1096. mu. molg^-1h^-1Much higher than CN-N477 mu mol g^-1h^-1The apparent rate of CN-H was increased by 2.3 times. Furthermore, the AQE at 420nm of CN-H is about 0.69%,above CN-N (0.30%), indicating hydrogen: nitrogen defects generated in a mixed atmosphere of nitrogen (5%: 95%) effectively increase g-C₃N₄Photocatalytic activity of (1). As shown in FIG. 11b, in order to examine the photocatalytic stability of CN-H, the test was continuously cycled for 16H. In the continuous hydrogen evolution process, the total hydrogen yield of 4h is 4.357 mmoleg^-1And the catalytic activity is not obviously reduced, which shows that CN-H has excellent photocatalytic stability.

In summary, supramolecules formed by melamine and cyanuric acid are selected as precursors, and hydrogen is used: the defective annular graphite-like phase carbon nitride is prepared by a thermal polymerization method by using a nitrogen (5%: 95%) mixed gas as an atmosphere. Various characterizations and photocatalytic performance researches are carried out on the prepared graphite-like phase carbon nitride material, and the following conclusion is obtained:

(1) the results of structural characterization and analysis of the annular graphite-like carbon nitride show that, compared with CN-N, the chemical structure, crystal structure and other aspects of the CN-H sample are not obviously changed, and hydrogen is introduced: CN-H still keeps the original structure of the carbon nitride in the atmosphere of nitrogen (5%: 95%). The interlayer spacing of CN-H is increased, which is beneficial to improving the specific surface area (133.16 m) of the CN-H sample² g^-1) And adsorption performance to water molecules. Hydrogen in supramolecular thermal polymerization: the mixed atmosphere of nitrogen (5%: 95%) can effectively inhibit g-C₃N₄Interlaminar stacking of materials. The CN-H sample has thin lamella thickness and few stacked layers, and provides more reactive sites for the photocatalytic reaction process.

(2) The average lifetime of CN-H was 4.36ns longer than CN-N (3.45ns) due to the formation of nitrogen defect structure in the sample. The defect can improve the delocalization capability of electrons, enhance the conductivity and the mobility of photo-generated electron-hole pairs, and effectively promote the separation of the photo-generated electron-hole pairs, thereby improving the performance of photocatalytic hydrogen production.

(3) CN-H has a lower light absorption capacity and a slightly smaller forbidden band width (2.74eV) than CN-N. In the research of photocatalytic water splitting hydrogen production, the hydrogen production rate of CN-H under the condition of visible light is 1096 mu mol g^-1h^-1Is 2.3 times of CN-N under the same test conditions. The total hydrogen yield in 4h in the photocatalysis circulation experiment is 4.357mmol g^-1The prepared CN-H has good photocatalytic stability and shows certain applicability.