Three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of photocatalysts, and relates to a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, mixing a phosphorus source, SiO2 nanospheres and melamine, and calcining in a nitrogen atmosphere to obtain a calcined product; s2, soaking the calcined product in a sodium hydroxide solution, and then washing and drying to obtain the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst. Based on the technical advantages of phosphorus-doped and three-dimensional ordered macroporous materials, the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst is successfully prepared, and the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst has rich active sites, enhances migration and separation of photon-generated carriers and improves the light absorption capacity, so that the catalytic activity of photocatalytic production of H2O2 is improved, and the generation rate of H2O2 is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysts and relates to a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst and a preparation method and application thereof. Background Art

[0002] Hydrogen peroxide (H2O2), an environmentally friendly strong oxidant, has been widely used in fields such as papermaking, healthcare, and wastewater treatment. However, the traditional synthesis method, the anthraquinone method, requires multiple hydrogen oxidation steps, resulting in high energy consumption and the production of toxic byproducts. Direct synthesis using H2 and O2 requires precious metal catalysts, which is costly and hazardous. Therefore, it is necessary to find a green and efficient production process.

[0003] Photocatalysis is considered a promising method because it uses only H2O and O2 as raw materials and sunlight as energy. It can be carried out at room temperature and pressure, which is consistent with the concept of sustainable green development. The preparation of efficient photocatalysts is a key step in the photocatalytic production of H2O2. Ideal photocatalysts must possess excellent light absorption, rapid carrier separation, and suitable energy band positions. Among the previously published photocatalysts, graphitic carbon nitride (g-C3N4) has attracted widespread attention due to its unique two-dimensional conjugated structure, suitable energy band position, and simple synthesis process. However, due to the limited exposed surface active sites of g-C3N4, poor light absorption capacity, high recombination efficiency of photogenerated carriers, and inability to effectively activate reactants during adsorption, the catalytic activity for photocatalytic H2O2 production is relatively poor. Summary of the Invention

[0004] In response to the technical problems that the existing photocatalyst g-C3N4 has limited exposed surface active sites, poor light absorption capacity, high photogenerated carrier recombination efficiency, and cannot effectively activate reactants during the adsorption process, resulting in poor catalytic activity for photocatalytic H2O2 production, the present invention provides a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst, its preparation method and application.

[0005] Leveraging the technological advantages of phosphorus doping and three-dimensionally ordered macroporous materials, this study successfully prepared a three-dimensionally ordered macroporous phosphorus-doped carbon nitride photocatalyst with abundant active sites. The phosphorus doping and the three-dimensionally ordered macroporous (3DOM) structure synergistically enhance the migration and separation of photogenerated charge carriers, improving light absorption capacity and thereby boosting the catalytic activity and rate of photocatalytic H2O2 production.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst comprises the following steps:

[0008] S1, mixing a phosphorus source, SiO2 nanospheres and melamine, and calcining them under a nitrogen atmosphere to obtain a calcined product;

[0009] S2. Soaking the calcined product in a sodium hydroxide solution, and then washing and drying it to obtain a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst.

[0010] It is further defined that in step S1, the mass ratio of the phosphorus source, SiO2 nanospheres and melamine is 1:(10-200):(10-200).

[0011] It is further defined that in step S1, the phosphorus source is hexachlorotricyanamide, dicyanammonium phosphate or 2-aminoethylphosphonic acid.

[0012] It is further defined that the calcination process in step S1 is: first heating to 500°C-520°C at a heating rate of 2°C / min and calcining for 2h-4h; then heating to 520°C-550°C at a heating rate of 4°C / min and calcining for 2h-4h.

[0013] It is further defined that in step S2, the concentration of the sodium hydroxide solution is 1 mol / L-6 mol / L, and the soaking time is 6 h-12 h.

[0014] The three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst is prepared by the preparation method of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst.

[0015] It is further defined that the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst presents an ordered skeleton structure with a pore size of 400 nm; the average specific surface area is 16.1 m 2 / g; the band gap value is 2.54eV; the apparent quantum yield at 420nm is 1.84%.

[0016] The three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst is used to improve the efficiency of photocatalytic H2O2 production.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Leveraging the technological advantages of phosphorus doping and three-dimensional ordered macroporous materials, this invention successfully fabricated a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst with abundant active sites. While constructing the 3DOM structure, cyanide (CN) groups were also introduced. The phosphorus doping replaced the carbon atoms in the CN structure and introduced impurity energy levels, thereby adjusting the material's energy band structure. The synergistic effect of the cyanide and phosphorus groups enhanced the catalyst's light absorption capacity, which is beneficial for boosting the photocatalyst's catalytic activity for H2O2 production.

[0019] 2. Research has shown that the introduction of phosphorus and cyanide groups into a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst synergistically regulates the material's electronic structure, resulting in localized distribution of the HOMO and LUMO regions, creating new electron-rich regions, adjusting the catalyst's charge distribution, and jointly promoting carrier separation. The prepared three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst exhibits a smaller work function, which facilitates electron escape from the material surface. It also exhibits lower adsorption energy for O2, resulting in efficient H2O2 production.

[0020] 3. The present invention utilizes the synergistic effect of phosphorus doping and three-dimensional ordered macroporous materials to prepare a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst with high photocatalytic activity, making the H2O2 yield as high as 1734.90 μmol / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the preparation method of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst of the present invention;

[0022] Figure 2 is the XRD pattern of different catalysts;

[0023] Figure 3 FTIR spectra of different catalysts;

[0024] Figure 4 The SEM images of the catalysts prepared in Example 1 and the comparative example; wherein: (a) is CN, (b) is PCN, (cd) is 3DOM-CN, and (ef) is 3DOM-PCN;

[0025] Figure 5 is the SEM image of SiO2 nanospheres;

[0026] Figure 6 The microstructure of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst; (ad) are EDS mapping images, (e) is HRTEM, and (f) is SAED spectrum;

[0027] Figure 7 is the EDS spectrum of the 3DOM-PCN photocatalyst of Example 1;

[0028] Figure 8 N2 adsorption-desorption curves of CN of Comparative Example 1 and 3DOM-PCN of Example 1;

[0029] Figure 9 XPS spectra of CN and 3DOM-PCN photocatalysts; (a) is the full spectrum, (b) is the C1s spectrum, (c) is the N1s spectrum, and (d) is the P 2p spectrum;

[0030] Figure 10 Results of the light absorption performance of CN and 3DOM-PCN photocatalysts; (a) UV-vis DRS spectrum, (b) band gap energy spectrum, (c) Mott-Schottky curve of CN, (d) Mott-Schottky curve of 3DOM-CN;

[0031] Figure 11 VB-XPS results of CN and 3DOM-PCN photocatalysts; (a) is the VB-XPS spectrum of CN, (b) is the VB-XPS spectrum of 3DOM-PCN, and (c) is the energy band diagram;

[0032] Figure 12 The electronic structures of CN and 3DOM-PCN photocatalysts; where: (a) is the DOS of CN, (b) is the total electron integral number of CN, (c) is the DOS of 3DOM-PCN, and (d) is the total electron integral number of 3DOM-PCN;

[0033] Figure 13 PDOS of CN prepared in Comparative Example 1;

[0034] Figure 14 PDOS of 3DOM-PCN prepared in Example 1;

[0035] Figure 15 Electrostatic potential results of CN and 3DOM-PCN; where: (a) is the ESP diagram of CN, (b) is the ESP diagram of 3DOM-PCN, (c) is the work function of CN, and (d) is the work function of 3DOM-PCN;

[0036] Figure 16 The photocurrent test results of the catalysts prepared in Example 1 and the comparative examples are shown in FIG. 1 , wherein: (a) is the photocurrent spectrum, and (b) is the EIS graph;

[0037] Figure 17 PL spectra of different catalysts prepared in Example 1 and comparative examples;

[0038] Figure 18 The carrier dynamics of the catalysts corresponding to Example 1 and the comparative example; wherein: (ab) are the HOMO and LUMO of CN, (cd) are the HOMO and LUMO of PCN, and (ef) are the HOMO and LUMO of 3DOM-PCN;

[0039] Figure 19 The photocatalytic H2O2 production performance diagram of different photocatalysts;

[0040] Figure 20 are the rate constants for the generation and decomposition of H2O2 by different photocatalysts;

[0041] Figure 21 The decomposition diagram of H2O2 with different catalysts;

[0042] Figure 22 ESP result for O2;

[0043] Figure 23 is the adsorption energy of CN and three-dimensional ordered macroporous phosphorus-doped carbon nitride for O2; where: (a) is the adsorption model and adsorption energy of CN for O2, (b) and (c) are the adsorption models and adsorption energies of 3DOM-PCN for O2 at different sites;

[0044] Figure 24 Three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst; (a) free radical capture experiment, (b)·O2 - ESR detection spectrum;

[0045] Figure 25 Diagram of the H2O2 production mechanism of three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst. DETAILED DESCRIPTION

[0046] The present invention will be described in further detail below with reference to the accompanying drawings and examples, but the embodiments of the present invention are not limited thereto. Other methods for preparing the compounds of the present invention are considered to be within the scope of the present invention by making some conventional modifications to the reaction conditions of the present invention.

[0047] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0048] Technologies, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies, methods, and equipment should be considered part of the specification.

[0049] It should also be understood that the specific embodiments described above are only used to explain the present invention, and the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, which should be covered by the scope of protection of the present invention / invention.

[0050] The technical idea of ​​the present invention is: using phosphorus source, SiO2 nanospheres and melamine as raw materials to prepare a phosphorus-doped carbon nitride photocatalyst with a three-dimensional ordered macroporous structure, for the first time introducing a surface strong electron-withdrawing group - a cyano functional group on the surface of the phosphorus-doped carbon nitride photocatalyst, and phosphorus doping replaces the C atoms in the CN structure, introducing an impurity energy level; and through theoretical calculations, in-depth analysis of the effect of the cyano functional group on the energy band modification and charge separation of phosphorus-doped carbon nitride is carried out, indicating that the cyano group can change the electron distribution of carbon nitride through the inductive effect, narrow its band gap, and enhance its visible light absorption capacity; in addition, the polarization effect of the cyano group can promote the separation of photogenerated electron-hole pairs, significantly improving the efficiency of photocatalytic hydrogen peroxide production.

[0051] The present invention provides a method for preparing a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst, comprising the following steps:

[0052] S1, mixing a phosphorus source, SiO2 nanospheres and melamine, and calcining them under a nitrogen atmosphere to obtain a calcined product;

[0053] In step S1, the mass ratio of the phosphorus source, SiO2 nanospheres and melamine is 1:(10-200):(10-200).

[0054] Exemplarily, in step S1, the mass ratio of the phosphorus source, SiO2 nanospheres and melamine is 1:10:10, 1:20:20, 1:50:50, 1:100:100, 1:150:150, 1:200:200, 1:10:200, or 1:200:10.

[0055] In step S1, the phosphorus source is hexachlorotricyanophosphate, dicyanammonium phosphate or 2-aminoethylphosphonic acid.

[0056] The calcination process in step S1 is: firstly heating the temperature to 500°C-520°C at a heating rate of 2°C / min and calcining for 2h-4h; then heating the temperature to 520°C-550°C at a heating rate of 4°C / min and calcining for 2h-4h.

[0057] S2. Soaking the calcined product in a sodium hydroxide solution, and then washing and drying it to obtain a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst.

[0058] In step S2, the concentration of the sodium hydroxide solution is 1 mol / L-6 mol / L, and the soaking time is 6 h-12 h.

[0059] The three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst prepared by the preparation method of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst of the present invention exhibits an ordered skeleton structure and a pore size of 400nm; the average specific surface area is 16.1m 2 / g; a band gap of 2.54eV; and an apparent quantum yield of 1.84% at 420nm. The material possesses abundant active sites, with P doping replacing C atoms in the CN lattice and introducing impurity energy levels, thereby adjusting the material's band structure. While constructing the 3DOM structure, cyanide groups are also introduced. The synergistic effect of cyanide and phosphorus enhances the migration and separation of photogenerated carriers and improves light absorption, resulting in an advantage in increasing the efficiency of photocatalytic H2O2 production.

[0060] The above technical solution of the present invention is described in detail below with reference to specific embodiments.

[0061] It should be noted that, in the following examples, unless otherwise specified, the chemical reagents, drugs, etc. used are all commercially available products in the art.

[0062] In the following examples, unless otherwise specified, all operations employed are routine operations in the art.

[0063] Example 1

[0064] See also Figure 1 The method for preparing the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst provided in this embodiment comprises the following steps:

[0065] S1. 1 g of melamine, 1 g of SiO2 nanospheres, and 0.1 g of a phosphorus source (hexachlorocyanophosphate (HCCP)) were thoroughly ground and mixed until uniform; then, the mixture was transferred to a porcelain boat, and under a nitrogen atmosphere, the temperature was first increased to 520°C at a heating rate of 2°C / min and calcined for 2 h; then the temperature was increased to 550°C at a heating rate of 4°C / min and calcined for 2 h to obtain a calcined product;

[0066] S2. The calcined product was placed in a 6 mol / L NaOH solution and soaked for 6 h to remove SiO2; the obtained product was then cross-washed with water and anhydrous ethanol several times, and after drying, a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst was obtained, which was recorded as 3DOM-PCN.

[0067] In this embodiment, the SiO2 nanospheres were prepared using conventional techniques. Specifically, ethyl silicate was added to a mixture of ethanol and aqueous ammonia, stirred at room temperature for 1 hour, centrifuged with ethanol and water, and dried to obtain the SiO2 nanospheres. The ratios of the raw materials used are conventional and are not limited here.

[0068] Example 2

[0069] The preparation method of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst provided in this embodiment includes the following steps:

[0070] S1. 1 g of melamine, 1 g of SiO2 nanospheres, and 0.01 g of a phosphorus source (hexachlorocyanophosphate (HCCP)) were thoroughly ground and mixed until uniform; then, the mixture was transferred to a porcelain boat, and under a nitrogen atmosphere, the temperature was first increased to 520°C at a heating rate of 2°C / min and calcined for 2 h; then the temperature was increased to 550°C at a heating rate of 4°C / min and calcined for 2 h to obtain a calcined product;

[0071] S2. The calcined product was placed in a 6 mol / L NaOH solution and soaked for 6 h to remove SiO2; the obtained product was then cross-washed with water and anhydrous ethanol several times, and after drying, a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst was obtained, which was recorded as 3DOM-PCN.

[0072] Example 3

[0073] The preparation method of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst provided in this embodiment includes the following steps:

[0074] S1. Thoroughly grind and mix 10 g of melamine, 10 g of SiO2 nanospheres, and 0.05 g of a phosphorus source (hexachlorocyanophosphate (HCCP)) until uniform. Subsequently, transfer the mixture to a porcelain boat and, under a nitrogen atmosphere, heat the mixture to 520°C at a heating rate of 2°C / min and calcine for 2 h; then heat the mixture to 550°C at a heating rate of 4°C / min and calcine for 2 h to obtain a calcined product.

[0075] S2. The calcined product was placed in a 6 mol / L NaOH solution and soaked for 6 h to remove SiO2; the obtained product was then cross-washed with water and anhydrous ethanol several times, and after drying, a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst was obtained, which was recorded as 3DOM-PCN.

[0076] In the above embodiment, the phosphorus source can be replaced with hexachlorocyanophosphate. The mass ratio of the phosphorus source, SiO2 nanospheres, and melamine can be arbitrarily selected and replaced within the range of 1:(10-200):(10-200); the calcination temperature can be arbitrarily selected and replaced within the range of 500℃~520℃ and 520℃~550℃; the calcination time can be arbitrarily selected and replaced within the range of 2h~4h; the concentration of the sodium hydroxide solution can be arbitrarily selected and replaced within the range of 1mol / L-6mol / L, and the immersion time can be arbitrarily selected and replaced within the range of 6h-12h. After these replacements and referring to the method of Example 1, a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst can be prepared.

[0077] Furthermore, the performance of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst prepared in the above embodiment was studied. In order to demonstrate the technical advantages of the photocatalyst prepared by the present invention, the following comparative examples were designed.

[0078] Comparative Example 1

[0079] 1g of melamine was placed in an alumina crucible, covered, and calcined at 550°C for 4 hours in a muffle furnace at a heating rate of 5°C / min. After the crucible cooled to room temperature, the carbon nitride catalyst g-C3N4 (denoted as CN) was obtained.

[0080] Comparative Example 2

[0081] Phosphorus-doped catalyst g-C3N4 was synthesized by thermal polymerization method.

[0082] 1g of melamine and 0.1g of a phosphorus source (hexachlorocyanophosphate (HCCP)) were uniformly mixed and placed in an alumina crucible. The mixture was covered and calcined in a muffle furnace at 550°C for 4 hours at a heating rate of 5°C / min. After cooling to room temperature, the product was ground to obtain the phosphorus-doped catalyst g-C3N4, designated PCN.

[0083] Comparative Example 3

[0084] 1g of melamine and 1g of SiO2 nanospheres were thoroughly ground and mixed until homogeneous. The mixture was then transferred to a porcelain boat and calcined at 520°C for 2h at a heating rate of 2°C / min under a nitrogen atmosphere. Subsequently, the mixture was calcined at 550°C for 2h at a heating rate of 4°C / min to obtain a calcined product. The calcined product was then soaked in a 6mol / L sodium hydroxide solution for 6h to remove the SiO2. The resulting product was then cross-washed several times with water and anhydrous ethanol and dried to obtain a phosphorus-free, three-dimensional ordered macroporous catalyst, g-C3N4, designated as 3DOM-CN.

[0085] Specifically, TEM and XPS were used to characterize the morphology and elemental states of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst (3DOM-PCN) prepared in the above examples. Furthermore, the photocatalytic H₂O₂ production mechanism was further investigated through quenching experiments, EPR and other testing methods, and density functional theory (DFT) calculations.

[0086] Test 1

[0087] The 3DOM-PCN of Example 1, the CN of Comparative Example 1, the PCN of Comparative Example 2 and the 3DOM-CN of Comparative Example 3 were taken as test samples, and the crystal structures of the test samples were investigated by XRD characterization. The results are as follows: Figure 2 shown.

[0088] See also Figure 2Two characteristic peaks of CN were observed at 13.1 and 27.7°, corresponding to the (100) and (002) crystal planes, respectively, representing the in-plane arrangement and interlayer stacking of CN. Compared with CN, the characteristic peak positions of PCN did not change, indicating that P doping has little effect on the in-plane skeleton structure of CN. In addition, after structural engineering, the peak of the (002) crystal plane shifted at a high angle and became wider, indicating that the interlayer spacing was reduced and the stacking of the aromatic system was suppressed, which is beneficial to charge transport and thus improves the H2O2 generation activity.

[0089] Test 2

[0090] The 3DOM-PCN of Example 1, the CN of Comparative Example 1, the PCN of Comparative Example 2 and the 3DOM-CN of Comparative Example 3 were characterized by FTIR to determine their chemical structures. The results are as follows: Figure 3 shown.

[0091] See also Figure 3 All samples showed similar FTIR spectra, 807 cm -1 Attributed to the out-of-plane bending vibration of the heptazine ring. 1200-1600cm -1 Represents the stretching vibration mode of the heptazine ring and the CN heterocyclic ring within the basic unit layer. 3000-3500cm -1 The broad peaks near 2170 cm-1 are related to the vibration of OH and NH bonds, which may be caused by the amino groups at the edge of CN and adsorbed water molecules. -1 There is an obvious characteristic peak at the end, which is attributed to the characteristic peak of the cyanide formed by the -C-NH2 at the end. The presence of the cyanide is conducive to capturing more photons and improving the light absorption ability.

[0092] Test 3

[0093] The 3DOM-PCN of Example 1, the CN of Comparative Example 1, the PCN of Comparative Example 2 and the 3DOM-CN of Comparative Example 3 were taken as test samples, and the morphology of the test samples was investigated by SEM. The results are shown in FIG. Figure 4 shown.

[0094] See also Figure 4 , CN exhibits a blocky structure with a rough surface ( Figure 4 (a)); PCN shows a similar morphology to CN ( Figure 4 (b)), which indicates that the introduction of P atoms does not change the CN skeleton structure. To construct three-dimensional ordered CN, SiO2 nanospheres were used as templates. SiO2 nanospheres showed a highly uniform and tightly packed arrangement structure with an average size of about 400 nm (e.g. Figure 5 ).like Figure 4 (c)- Figure 4As shown in (f), both 3DOM-CN and 3DOM-PCN exhibit an ordered skeletal structure and a pore size of 400 nm, which is consistent with the size of SiO2 nanospheres. Therefore, the mass transfer channels of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst (3DOM-PCN) prepared by this invention are not hindered, facilitating the transport and diffusion of reactants, which is of great significance for improving photocatalytic activity.

[0095] Test 4

[0096] The 3DOM-PCN of Example 1 was used as a test sample, and the microstructure of 3DOM-PCN was investigated using HAADF. The results are as follows: Figure 6 and Figure 7 shown.

[0097] Figure 6 (a)- Figure 6 (d) and Figure 7 It shows that C, N, and P elements are evenly distributed in 3DOM-PCN; Figure 6 (e) No obvious lattice fringes were observed for 3DOM-PCN, showing a typical amorphous structure. Figure 6 (f) is the selected area electron diffraction (SAED) image of 3DOM-PCN. It can be clearly observed that 3DOM-PCN shows relatively unclear diffraction rings; the result is consistent with the XRD result of 3DOM-PCN.

[0098] Furthermore, the 3DOM-PCN of Example 1 and the CN of Comparative Example 1 were used as test samples, and the specific surface area and pore size distribution of the test samples were investigated by N2 adsorption-desorption. Figure 8 and as shown in Table 1.

[0099] Table 1 Specific surface area and pore size parameters of CN and 3DOM-PCN

[0100] Test samples <![CDATA[Specific surface area (m 2 / g)]]> Pore ​​diameter (nm) CN 15.7 21.4 3DOM-PCN 16.1 23.1

[0101] See also Figure 8 From Table 1, we can see that both CN and 3DOM-PCN exhibit type-Ⅳ isotherms with H3 hysteresis loops. The specific surface area of ​​3DOM-PCN (16.1m 2 / g) is larger than the specific surface area of ​​CN (15.7m 2 / g). At the same time, 3DOM-PCN has a larger pore size, which is conducive to the mass transfer of dissolved oxygen and H2O2, thereby accelerating the reaction kinetics and improving the catalytic activity.

[0102] Test 5

[0103] The surface elements and chemical states of 3DOM-PCN prepared in Example 1 and CN prepared in Comparative Example 1 were investigated by XPS. The results are as follows: Figure 9 shown.

[0104] from Figure 9 As shown in (a), C and N elements are observed in the full spectra of CN and 3DOM-PCN. Furthermore, the Na element detected in 3DOM-PCN likely originates from the residual NaOH etching of the SiO2 nanosphere template. Notably, weak but non-negligible P 2s and P 2p signals were detected in 3DOM-PCN, demonstrating the successful incorporation of the P element. Figure 9 As shown in the C1s XPS spectrum of (b), three peaks appeared at 284.8eV, 286.4eV and 288.3eV, representing the chemical bond of CC / C=C in the adventitious carbon, the sp bond connected to -NHx and cyano groups, respectively. 2 carbon, and sp in the seven nitrogen ring units 2 In addition, compared with CN, the increase in the peak area of ​​3DOM-PCN at 286.4 eV may be due to the introduction of -C≡N, because its binding energy is similar to that of C-NH x Similar; NC=N moves toward the direction of high binding energy, indicating that the electron density around the C atom decreases, which may be due to the substitution of P doping for the C atom. Figure 9 In the N1s XPS spectrum of (c), 398.6 eV, 400.2 eV, and 401.3 eV are attributed to N1 (C=NC), N2 (N-C3), and terminal -NH x The peak position of 3DOM-PCN slightly changes, which indicates that the structural engineering and phosphorus doping do not change the basic CN heterocyclic structure of CN. Figure 9 The P 2p spectrum of (d) is divided into two characteristic peaks, namely 132.8 eV (PN) and 133.8 eV (P=N), which indicates that P replaces C atoms instead of N atoms because the binding energy of PC is at 131 eV.

[0105] Test 6

[0106] The 3DOM-PCN of Example 1, the CN of Comparative Example 1, the PCN of Comparative Example 2 and the 3DOM-CN of Comparative Example 3 were taken as test samples, and the light absorption properties of the test samples were studied respectively. The results are as follows: Figure 10 shown.

[0107] Figure 10(a) UV-vis DRS was used to explore the light absorption capacity of the test samples. It can be seen that the original CN showed an absorption edge at about 471nm. After P doping, the absorption edge of PCN was slightly red-shifted (483nm). After constructing 3DOM, the light absorption capacity of 3DOM-CN and 3DOM-PCN was enhanced. This is because the cyano group is a chromogenic group, and CN itself also contains a chromogenic group (such as C=C). When the two are connected through a conjugated structure, the electron delocalization range is expanded, and its light absorption wavelength will undergo a red-shift phenomenon, thereby increasing the light absorption capacity of 3DOM-PCN. In addition, the band gap (E g ).from Figure 10 (b) It can be seen that the E of CN, PCN, 3DOM-CN, and 3DOM-PCN g They are 2.51eV, 2.46eV, 2.41eV and 2.54eV respectively. Figure 10 (c)- Figure 10 (d) shows the Mott-Schottky curves of CN and 3DOM-PCN at 500 Hz, 1000 Hz, and 1500 Hz; all curves show positive slopes, indicating that both CN and 3DOM-PCN are n-type semiconductors.

[0108] In addition, the valence band (VB) positions of CN and 3DOM-PCN were calculated based on VB-XPS, as shown in Figure 2. Figure 11 As shown. Figure 11 (a) and Figure 11 (b) shows that the VB of CN and 3DOM-PCN are 2.02 eV and 1.78 eV, respectively. g The calculated CB positions of CN and the conduction band (CB) positions of 3DOM-PCN were -0.49 eV and -0.76 eV, respectively. This indicates that 3DOM-PCN modifies the CB and VB positions of CN, making the 3DOM-PCN prepared in Example 1 more conducive to oxygen reduction and water oxidation, thereby improving catalytic activity.

[0109] Based on the above results, the energy band positions of CN and 3DOM-PCN were plotted, see Figure 11 (c). It can be seen that the introduction of -C≡N and P can adjust the band structure, broaden the light absorption range of the material, adjust the band structure of CN, shift the CB position negatively, enhance the reduction ability of electrons, and be more favorable for 2e - ORR, thereby improving the photocatalytic performance of the catalyst.

[0110] The electronic structures of CN and 3DOM-PCN were further investigated and the total electron integrals were calculated, e.g. Figure 12 、 Figure 13 and Figure 14shown.

[0111] from Figure 12 (a) and Figure 12 (c) It can be seen that the main process of CN light absorption is the excitation of electrons from N 2p state to C 2p state. The VB of CN is mainly occupied by N 2p orbital, while the CB is mainly occupied by C 2p orbital. According to PDOS analysis, sp 2 The contribution of hybrid orbitals to DOS is relatively large, indicating that the electronic structure of CN is similar to that of sp 2 Hybrid orbitals are closely related (see Figure 13 ). The main process of light absorption in 3DOM-PCN is the excitation of electrons from N 2p states to C 2p states. VB is mainly occupied by N 2p orbitals, while CB is mainly occupied by C 2p and P3p orbitals (see Figure 14 ).from Figure 12 (b) and Figure 12 (d) It can be seen that the total electron integral curves of CN and 3DOM-PCN show the same trend. The total electron integral number of the two systems is mainly occupied by s orbitals and p orbitals. In the 3DOM-PCN system, the total electron integral number increases; this is because the total energy of the band is significantly improved after P doping and the introduction of cyanide.

[0112] Figure 15 is the electrostatic potential diagram of CN and 3DOM-PCN. Figure 15 (a) and Figure 15 (b) It can be seen that the electron cloud of CN is mainly distributed in the center of the ring; while the electron cloud of 3DOM-PCN is concentrated in the center of the ring near the cyanide and P doping, thereby generating a new electron-rich region, which is conducive to the migration and separation of photogenerated carriers, thereby increasing the generation rate of H2O2. Compared with CN, the electrostatic potential of 3DOM-PCN is reduced, which indicates that P doping and structural engineering can enhance the electron donating ability of CN. The work function (Φ) was calculated to explore the effect of the catalyst on e - The strength of the constraint, such as Figure 15 (c) and Figure 15 As shown in (d), the work function of 3DOM-PCN is much smaller than that of CN, which is mainly due to the synergistic effect of P doping and cyanide. Its presence greatly reduces the surface sensitivity of the material to e - The binding force promotes e - Escape from the surface of the material and then participate in the catalytic reaction.

[0113] Test 7

[0114] The 3DOM-PCN of Example 1, the CN of Comparative Example 1, the PCN of Comparative Example 2, and the 3DOM-CN of Comparative Example 3 were taken as test samples to explore the carrier separation ability of the test samples.

[0115] First, the photocurrent test was carried out on the test samples, and the results were as follows: Figure 16 shown.

[0116] from Figure 16 (a) shows that the photocurrent intensity of PCN is increased compared with CN. In addition, after constructing 3DOM, the photocurrent intensity is further increased. The photocurrent intensity of 3DOM-PCN is the largest, indicating that its electron-hole separation efficiency is the highest. This shows that P doping and cyanide enhance the electronic structure of the material, resulting in more efficient carrier dynamics. Electrochemical impedance spectroscopy (EIS) is used to further explore the photogenerated carrier separation process of the material. The smaller the arc radius, the smaller the impedance and the more efficient the carrier separation efficiency. See Figure 16 (b) 3DOM-PCN has the smallest impedance radius, which means that its charge transfer resistance is the smallest and the separation efficiency of photogenerated carriers is the highest.

[0117] In addition, the charge transfer properties of the material were verified by PL, and the results were as follows Figure 17 As shown in the figure, 3DOM-PCN has the highest PL intensity, indicating a faster recombination rate of photogenerated carriers. This is because the P and cyanide groups modify the electronic structure, thereby promoting more efficient charge transfer. The presence of cyanide groups may contribute to the localized electronic state, promoting enhanced carrier dynamics and improving overall recombination efficiency.

[0118] Secondly, the carrier dynamics of the test samples were further explored by DFT calculations, and the results are as follows Figure 18 shown.

[0119] Figure 18 (a) and Figure 18 (b) shows the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of CN. HOMO is concentrated on the N atom, and LUMO is concentrated on the C atom. Due to the highly symmetrical structure of CN, the HOMO and LUMO are evenly distributed, resulting in a high e- / h+ recombination rate, which limits its photocatalytic activity. Figure 18 (c) and Figure 18 (d) Compared with CN, the HOMO and LUMO distributions of PCN show significant spatial separation characteristics, which shows that the introduction of P doping destroys the symmetry of the original structure; Figure 18 (e) and Figure 18 (f) The HOMO of 3DOM-PCN is primarily localized around the P-doped cyano group, while the LUMO is primarily concentrated on the P-doped heptazine unit. This indicates that the introduction of the cyano group leads to a more localized spatial separation of the HOMO and LUMO in 3DOM-PCN compared to PCN, which facilitates carrier separation and significantly enhances the redox activity of the photocatalyst.

[0120] Test 8

[0121] The 3DOM-PCN of Example 1, the CN of Comparative Example 1, the PCN of Comparative Example 2 and the 3DOM-CN of Comparative Example 3 were used as test samples, and the photocatalytic activity of the test samples was investigated under simulated sunlight. The results are as follows: Figure 19 shown.

[0122] from Figure 19 It can be seen that within 1 hour, the H2O2 production of the original CN was only 286.50 μmol / L. After P doping, the activity of PCN was 1.89 times that of CN (542.77 μmol / L). In contrast, the catalytic activities of 3DOM-CN and 3DOM-PCN were significantly improved, 5.23 times and 6.12 times that of CN, respectively. This shows that the 3DOM structure plays an important role in the activity of the catalyst. The H2O2 production of 3DOM-CN was 1484.61 μmol / L, which was due to the strong light harvesting ability and carrier separation ability of the terminal cyano group. It is worth noting that the H2O2 production of 3DOM-PCN was 1734.90 μmol / L, which shows that the dual strategy of P doping and constructing 3DOM can synergistically promote the generation of H2O2.

[0123] As we all know, the generation of H2O2 is usually accompanied by decomposition. Therefore, the decomposition rate of H2O2 of different test samples was explored, and the generation rate of H2O2 (K) was calculated based on zero-order kinetics and first-order kinetics. f ) and decomposition rate (K d ); the result is as follows Figure 20 and Figure 21 shown.

[0124] Figure 20 It can be seen that 3DOM-PCN has the lowest K d value and the highest K f Value, from Figure 21 3DOM-PCN exhibits the lowest H2O2 decomposition activity, demonstrating excellent H2O2 production efficiency. Furthermore, 3DOM-PCN exhibits an apparent quantum yield (AQY) of 1.84% at 420 nm, demonstrating excellent light utilization efficiency.

[0125] In the entire reaction system, O2 is first adsorbed, which is the first step in producing H2O2. To this end, the ESP of O2 ( Figure 22 ) to determine the adsorption sites of O2; then, the adsorption energies of CN and 3DOM-PCN for O2 were calculated by DFT ( Figure 23 ).

[0126] According to the principle of "like repels like, opposites attract," regions on the surfaces of CN and 3DOM-PCN with suitable electrostatic potential can generate favorable electrostatic interactions with the charge distribution of O2, thereby promoting adsorption. Combining the ESPs of CN and 3DOM-PCN, the adsorption energies of O2 on CN and 3DOM-PCN were calculated by placing regions with negative electrostatic potential of O2 in contact with regions with positive electrostatic potential of CN and 3DOM-PCN.

[0127] from Figure 23 As can be seen from the figure, the adsorption energy of O2 on 3DOM-PCN at different sites is greater than that of CN. Among them, the adsorption energy of O2 around the P element is 26.21 times that of CN, which indicates that cyanide and P doping can effectively improve the yield of H2O2. This shows that the strong adsorption of O2 by the catalyst can promote the occurrence of ORR reaction, thereby achieving efficient H2O2 generation.

[0128] The differences in H2O2 generation performance were evaluated by comparing the 3DOM-PCN catalyst system prepared in Example 1 with reported CN-based catalyst systems. It can be seen that the 3DOM-PCN prepared in Example 1 has a much better H2O2 generation efficiency than the reported CN-based catalyst system, indicating that the 3DOM structure and P doping have great application prospects in the CN regulation mechanism.

[0129] Table 2 Comparison of H2O2 production performance of CN-based photocatalysts

[0130]

[0131] It should be noted that the sacrificial agent is added to the photocatalytic reaction in order to capture holes (h + ), as a hole trapping agent, thereby increasing the H2O2 production; wherein EtOH represents ethanol and IPA represents isopropyl alcohol.

[0132] The references in Table 2 are as follows. The performance of the CN-based catalyst system reported in each reference is compared with the 3DOM-PCN catalyst prepared in the present invention.

[0133] [1]Zhou J,Shan T,Zhang F,et al.A Novel Dual-Channel Carbon NitrideHomojunction with Nanofibrous Carbon for Significantly BoostingPhotocatalytic Hydrogen Peroxide Production[J].Advanced Fiber Materials,2024,6(2):387-400.

[0134] [52Mahvelati-Shamsabadi T,Fattahimoghaddam H,Lee B-K,et al.Caesiumsites coordinated in Boron-doped porous and wrinkled graphitic carbon nitridenanosheets for efficient charge carrier separation and Transfer:Photocatalytic H2 and H2O2 production[J].Chemical Engineering Journal,2021,423:130067.

[0135] [3]Zhu Y,Sun Y,Khan J,et al.NaClO-induced sodium-doped cyano-richgraphitic carbon nitride nanosheets with nitrogen vacancies to boostphotocatalytic hydrogen peroxide production[J].Chemical Engineering Journal,2022,443:136501.

[0136] [4]Li Z, Zhou Y, Zhou Y, et al. Dipole field in nitrogen-enriched carbonnitride with external forces to boost the artificial photosynthesis ofhydrogen peroxide[J]. Nature Communications, 2023, 14(1):5742.

[0137] [5]Zeng S, Li L, Yang Z, et al. Polymeric Carbon Nitride from Inorganic Precursor in Eutectic Salts: Enhanced Exciton Dissociation and PhotocatalyticH2O2 Production[J]. The Journal of Physical Chemistry C, 2022, 126(47): 20028-20035.

[0138] Test 9

[0139] In order to explore the mechanism of photocatalytic H2O2 production by 3DOM-PCN, a certain amount of capture agent was added to the 3DOM-PCN of Example 1 during the photocatalytic reaction, wherein AgNO3 captured e - , C6H8O6 captures O2 - , EDTA-2Na captures holes h + , CH3OH captures OH, and the result is as follows Figure 24 shown.

[0140] from Figure 24 (a) It can be seen that when AgNO3 and C6H8O6 are added to the reaction system, the content of H2O2 decreases linearly, which indicates that e - and O2 - is the main active species. In addition, when EDTA-2Na is added, the H2O2 content also decreases, indicating that + It also participates in the H2O2 reaction, but is not the main active species. On the contrary, after adding CH3OH, the H2O2 content did not decrease, indicating that ·OH is not an intermediate in the production of H2O2, which is consistent with the band gap results, because the VB potential of 3DOM-PCN (1.78eV) is more negative than E0(·OH / H2O)=2.73eV. Therefore, ESR further proves that ·O2 - existence. Figure 24(b) shows that no obvious signal peak appears in the dark. When there is a light source, DMPO-·O2 is detected. - signal, which proves that O2 - It is the main active group for the generation of H2O2. In summary, the photocatalytic production of H2O2 is mainly carried out through a two-step single-electron oxygen reduction (O2→·O2 - →H2O2), and the one-step two-electron water oxidation plays an auxiliary role (H2O→H2O2).

[0141] Based on the above conclusions, the photocatalytic mechanism of 3DOM-PCN was proposed ( Figure 25 ): Under light, the e - It is excited to jump to CB and leave h on VB + Due to the introduction of cyanide and P element doping, the charge distribution is uneven, which accelerates the e - / h + Separated and migrated to the catalyst surface. The O2 adsorbed around the catalyst was e - Reduced to O2 - And the h on VB + Oxidation of isopropanol to form protons (H + ), O2 - Combined H + and an e - Thus, H2O2 is generated. In addition, h + It can also directly oxidize H2O to H2O2. In this system, e - and h + They all participate in the generation of H2O2, greatly improving the utilization efficiency of photogenerated carriers.

[0142] In summary, this paper successfully constructed a three-dimensional ordered macroporous phosphorus-doped carbon nitride (3DOM-PCN) via thermal polymerization, leveraging the synergistic effects of phosphorus doping and a three-dimensional ordered macroporous structure (3DOM structure). On the one hand, phosphorus doping replaces carbon atoms in the CN lattice and introduces impurity energy levels, thereby adjusting the material's band structure. On the other hand, the 3DOM structure's abundant active sites and large mass transfer channels improve light utilization efficiency and successfully introduces cyanide groups, whose presence further facilitates light absorption. Therefore, phosphorus doping and the introduction of cyanide groups synergistically modulate the material's electronic structure, resulting in localized distribution of the HOMO and LUMO regions, the creation of new electron-rich regions, a reduction in the electrostatic potential of CN, and enhanced O₂ adsorption, endowing 3DOM-PCN with highly efficient photocatalytic activity. Photocatalytic H₂O₂ production is achieved via two pathways: a two-step one-electron oxygen reduction and a one-step two-electron water oxidation, with a high H₂O₂ yield of 1734.90 μmol / L. This paper systematically illustrates the synergistic mechanism of phosphorus doping and 3DOM structure construction, providing new insights for the design of efficient carbon nitride-based catalysts.

[0143] It should be noted that the above experimental tests are all based on the three-dimensional ordered macroporous phosphorus-doped carbon nitride 3DOM-PCN prepared in Example 1. When the three-dimensional ordered macroporous phosphorus-doped carbon nitride prepared in Example 2, Example 3 and other alternative examples are tested, they show similar or similar performance to Example 1, enhance the migration and separation of photogenerated carriers, improve the light absorption capacity, thereby enhancing the catalytic activity of photocatalytic H2O2 production and increasing the H2O2 generation rate.

[0144] The above are several relatively preferred implementation methods of the preparation method of the present invention, but they cannot be used as limitations on the technical solutions protected by the present invention. Any replacement solutions obtained by ordinary technicians in this field without making creative work based on the technical ideas of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst, characterized in that: The following steps are involved: S1, mixing a phosphorus source, SiO2 nanospheres and melamine, and calcining them under a nitrogen atmosphere to obtain a calcined product; S2. Soaking the calcined product in a sodium hydroxide solution, and then washing and drying it to obtain a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst.

2. The method for preparing the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 1, characterized in that: In the step S1, the mass ratio of the phosphorus source, SiO2 nanospheres and melamine is 1:(10-200):(10-200).

3. The method for preparing the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 1, characterized in that: In step S1, the phosphorus source is hexachlorotricyanophosphate, dicyanammonium phosphate or 2-aminoethylphosphonic acid.

4. The method for preparing the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 1, characterized in that: The calcination process in step S1 is: firstly heating the temperature to 500-520°C at a heating rate of 2°C / min and calcining for 2-4 hours; then heating the temperature to 520-550°C at a heating rate of 4°C / min and calcining for 2-4 hours.

5. The method for preparing the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 1, characterized in that: In step S2, the concentration of the sodium hydroxide solution is 1 mol / L-6 mol / L, and the soaking time is 6 h-12 h.

6. A three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst prepared by the method for preparing a three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 1.

7. The three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 6, characterized in that: The three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst exhibits an ordered skeleton structure with a pore size of 400 nm and an average specific surface area of ​​16.1 m 2 / g; the band gap value is 2.54eV; the apparent quantum yield at 420nm is 1.84%.

8. Use of the three-dimensional ordered macroporous phosphorus-doped carbon nitride photocatalyst according to claim 6 in improving the efficiency of photocatalytic H2O2 production.

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