Graphite-phase carbon nitride photocatalyst based on nitrogen-defect sulfur-doped coupled S-type homojunction as well as preparation method and application of graphite-phase carbon nitride photocatalyst

Abstract

The invention belongs to the technical field of photocatalysis, and particularly relates to a graphite-phase carbon nitride photocatalyst based on a nitrogen-defect sulfur-doped coupled S-type homojunction as well as a preparation method and application of the graphite-phase carbon nitride photocatalyst. N-defect g-C3N4 (NA-DCN) and S-doped g-C3N4 (NA-SCN) are respectively constructed through nitric acid assisted treatment, and directed migration of photon-generated carriers is realized by using an S-type homojunction interface so as to inhibit recombination; stable interface bonding is formed through component proportion optimization, and the specific surface area and the number of active sites of the material are synchronously increased. Finally, through multi-dimensional structure regulation and control, the problems that the g-C3N4 is limited in photoresponse range, fast in carrier recombination and difficult in consideration of catalytic activity and stability are synchronously solved, the photocatalytic hydrogen production performance of the g-C3N4 is remarkably enhanced, and a reliable technical scheme is provided for large-scale application of an efficient carbon nitride-based photocatalytic material.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis technology, specifically relating to a graphitic carbon nitride photocatalyst based on nitrogen-defect sulfur doping coupled S-type homojunction, its preparation method, and its application. Background Technology

[0002] With the continued growth of global energy demand and the increasingly serious problem of greenhouse gas emissions from fossil fuel use, the development of clean and renewable energy technologies has become an urgent priority. Among the many solutions, photocatalysis technology can directly convert solar energy into chemical energy, providing an effective way to achieve sustainable development. This technology is particularly promising in two applications: first, photocatalytic water splitting to produce clean hydrogen; and second, reducing carbon dioxide into high-value-added fuels. To realize these applications, the key lies in preparing non-toxic, inexpensive, efficient, and stable visible light photocatalysts.

[0003] Among existing photocatalytic materials, graphitic carbon nitride (g-C3N4) has become a research hotspot due to its unique performance advantages. This material possesses a suitable band gap (approximately 2.7 eV), exhibiting good visible light absorption, excellent acid and alkali tolerance, and thermal stability. Furthermore, its precursors (such as melamine, dicyandiamine, and urea) are widely available, inexpensive, and simple to synthesize, thus demonstrating great application potential in photocatalytic water splitting for hydrogen production and carbon dioxide reduction. However, pristine g-C3N4 prepared by direct polymerization often suffers from high recombination rates of photogenerated carriers, leading to low photocatalytic efficiency. This rapid recombination mainly stems from the strong localization of photogenerated carriers within the heptaazine unit and the spatial overlap between their lowest unoccupied and highest occupied molecular orbitals.

[0004] To overcome this limitation, researchers have explored various strategies to enhance photocatalytic performance by altering the intrinsic structure of g-C3N4, including morphology design through precursor pre-organization and electronic structure modulation through nonmetallic doping and defect introduction. However, due to issues such as carrier localization, rapid recombination of photogenerated carriers within g-C3N4 remains a major challenge.

[0005] By designing heterojunction / homogeneous structures, the directional spatial migration of photogenerated carriers between different photocatalysts can be achieved, effectively suppressing their recombination. Among various heterojunction / homogeneous junction types, the S-scheme system is a superior alternative to traditional type II and Z-scheme systems due to its unique charge transfer mechanism. Unlike type II and Z-scheme systems, the S-scheme system selectively recombines low-energy electrons and holes while retaining high-energy carriers to maintain strong photocatalytic redox capabilities. Summary of the Invention

[0006] To overcome the shortcomings of existing g-C3N4 photocatalysts, such as narrow light absorption range, low carrier separation efficiency, and insufficient cycle stability, this invention aims to provide an S-type homojunction g-C3N4 photocatalyst with synergistic regulation of N defects and S doping, along with its preparation method and applications. N-defective g-C3N4 (NA-DCN) and S-doped g-C3N4 (NA-SCN) are constructed through nitric acid-assisted treatment, respectively. The S-type homojunction interface enables directional migration of photogenerated carriers to suppress recombination. Further optimization of the component ratios forms a stable interface, simultaneously increasing the material's specific surface area and the number of active sites. Ultimately, through multi-dimensional structural regulation, the limitations of g-C3N4's limited light response range, rapid carrier recombination, and the difficulty in balancing catalytic activity and stability are simultaneously addressed, significantly enhancing its photocatalytic hydrogen production performance and providing a reliable technical solution for the large-scale application of highly efficient carbon nitride-based photocatalytic materials.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a graphitic carbon nitride photocatalyst based on a nitrogen-deficient sulfur-doped coupled S-type homojunction, comprising the following steps: S1. Preparation of NA-DCN: Dicyandiamide and cyanuric acid were blended to prepare the first supramolecular composite solid, which was then calcined to obtain nitrogen-defect graphitic carbon nitride, i.e., NA-DCN; S2. Preparation of NA-SCN: After preparing a second supramolecular composite solid by blending urea and trithiocyanate, the solid was calcined to obtain sulfur-doped graphitic carbon nitride, i.e., NA-SCN; S3. Preparation of graphitic carbon nitride photocatalyst: NA-DCN and NA-SCN were mixed and calcined to obtain graphitic carbon nitride photocatalyst.

[0008] In some preferred embodiments, the mass ratio of dicyandiamide to cyanuric acid is (5~7):(2~4), and / or the mass ratio of urea to cyanuric acid is (5~7):(2~4).

[0009] In some preferred embodiments, the first supramolecular composite solid is prepared by: mixing dicyandiamide and cyanuric acid, adding deionized water and concentrated nitric acid, stirring continuously, and heating to remove the solvent, thereby obtaining the product; and / or, the second supramolecular composite solid is prepared by: mixing urea and thiocyanate, adding deionized water and concentrated nitric acid, stirring continuously, and heating to remove the solvent, thereby obtaining the product.

[0010] In some preferred embodiments, the calcination conditions are: under inert gas protection, at 5~10℃·min -1 The temperature is increased to 500~550℃ at a certain rate, and then calcined for 4~5 hours.

[0011] In some preferred embodiments, the mass ratio of NA-DCN to NA-SCN is (1~2):(1~2).

[0012] In some preferred embodiments, the specific method of S3 is as follows: NA-DCN and NA-SCN are dissolved separately in deionized water to prepare dispersions, then mixed; concentrated nitric acid is added; the mixture is stirred continuously and heated to remove the solvent; the solid is washed and dried; and then, under inert gas protection, it is heated at 5~10℃·min. -1 The temperature was increased to 500~550℃ at a certain rate and calcined for 4~5 hours to obtain a graphitic carbon nitride photocatalyst.

[0013] The second aspect of this invention provides a graphitic carbon nitride photocatalyst based on a nitrogen-defect sulfur-doped coupled S-type homojunction, which is obtained by the above preparation method.

[0014] The third aspect of this invention provides the application of a graphitic carbon nitride photocatalyst based on a nitrogen-deficient sulfur-doped coupled S-type homojunction, which is used in photocatalytic reactions.

[0015] A fourth aspect of the present invention provides a method for photocatalytic water splitting to produce hydrogen, using the above-mentioned graphitic carbon nitride photocatalyst for catalysis.

[0016] This invention does not impose any specific limitations on the method of photocatalytic water splitting to produce hydrogen. Based on the above-mentioned graphitic carbon nitride photocatalyst, conventional methods in the art can be used.

[0017] The fifth aspect of the present invention provides a method for reducing carbon dioxide using a photocatalyst, wherein the above-mentioned graphitic carbon nitride photocatalyst is used for catalysis.

[0018] This invention does not impose any specific limitations on the method of carbon dioxide reduction using photocatalysts. Based on the above-mentioned graphitic carbon nitride photocatalyst, conventional methods in the art can be used.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention proposes for the first time an innovative process combining nitric acid-assisted self-assembly copolymerization with stepwise calcination, successfully preparing an S-type homojunction photocatalyst composed of N-defective graphitic carbon nitride and S-doped graphitic carbon nitride. This technology, through the synergistic regulation of N defects and S doping, simultaneously optimizes bulk carrier separation and directional interfacial charge migration in g-C3N4, and, combined with the construction of mesoporous nanosheet morphology, significantly improves the visible light utilization efficiency and photocatalytic capability of the material, providing a novel technical pathway for efficient photocatalytic hydrogen production and carbon dioxide reduction.

[0020] 2. This invention uses readily available and inexpensive dicyandiamide, cyanuric acid, urea, and trithiocyanuric acid as raw materials to obtain a 1NA-DCN / 1NA-SCNS homojunction photocatalyst with a mesoporous nanosheet structure. Systematic characterization results confirm that this homojunction catalyst exhibits comprehensive performance breakthroughs compared to the single g-C3N4 component: Firstly, the light absorption and electronic structure are significantly optimized, with the light absorption edge of NA-SCN extended to 480 nm and that of NA-DCN reaching 467 nm. The composite of the two retains a broad spectral response capability and maintains a high redox potential through an S-type charge transfer mechanism; secondly, the surface structure and active sites are greatly improved, with the specific surface area of ​​1NA-DCN / 1NA-SCN reaching 118.3 m². 2 ·g -1 , respectively NA-SCN (44.1m) 2 ·g -1 2.7 times that of NA-DCN (65.7m) 2 · / g -1 The S-type homojunction catalyst exhibits 1.8 times the activity of its predecessor, with a mesoporous structure and uniform elemental distribution (C, N, S) providing ample active sites for the reaction. Photocatalytic performance tests show that this catalyst demonstrates superior activity in energy conversion, achieving a hydrogen production rate of 7607.4 μmol·h⁻¹ using the 1NA-DCN / 1NA-SCN method. -1 ·g -1 They are NA-SCN (553.2 μmol·h⁻¹) -1 ·g -1 13.7 times that of NA-DCN (781.2 μmol·h⁻¹) -1 ·g -1 The efficiency is 9.7 times that of other methods; in the photocatalytic reduction of carbon dioxide in pure water, no sacrificial agent or additional co-catalyst is required, and the CH4 generation rate reaches 82.3 μmol·h⁻¹. -1 ·g -1 The CO production rate was 14.5 μmol·h⁻¹. -1 ·g -1 It has a CH4 electron selectivity of up to 95.8%, combining high activity with product selectivity.

[0021] In summary, this invention successfully developed a g-C3N4-based S-type homojunction photocatalyst with high efficiency in charge separation, broad spectral response, and high structural stability through a simple nitric acid-assisted self-assembly and stepwise calcination method. The preparation process exhibits good reproducibility, low-cost and readily available raw materials, and the resulting product demonstrates significant advantages in photocatalytic water splitting for hydrogen production and carbon dioxide reduction, providing novel materials and process solutions for the practical application of clean energy conversion and carbon cycle technologies. Attached Figure Description

[0022] Figure 1(AC) are transmission electron microscope (TEM) images of the photocatalysts of Example 1 and Comparative Examples 2 and 3, respectively.

[0023] Figure 2 The UV-Vis absorption spectra of the photocatalysts of Example 1 and Comparative Examples 2 and 3 are shown (with actual photos).

[0024] Figure 3 The above are bar charts showing the apparent zeta potential of the photocatalysts in Example 1 and Comparative Examples 2 and 3.

[0025] Figure 4 The graph shows a comparison of the hydrogen production rate curves of the photocatalysts in Examples 1-3 and Comparative Examples 2 and 3.

[0026] Figure 5 The bar chart shows the hydrogen production activity of the photocatalysts in Examples 1-3 and Comparative Examples 2 and 3.

[0027] Figure 6 (A) Full X-ray photoelectron spectroscopy (XPS) spectra of 1NA-DCN / 1NA-SCN in Example 1, NA-SCN in Comparative Example 2, and NA-DCN in Comparative Example 3. Figure 6 The XPS high-resolution spectra of C1s, N1s, and S2p of 1NA-DCN / 1NA-SCN in Example 1, NA-SCN in Comparative Example 2, and NA-DCN in Comparative Example 3 are shown in (B)-(D) respectively.

[0028] Figure 7 The figures show the N2 adsorption-desorption isotherms and specific surface area data of the photocatalysts of Example 1 and Comparative Examples 2 and 3.

[0029] Figure 8 The images show the electron paramagnetic resonance (EPR) spectra of the photocatalysts in Example 1 and Comparative Examples 2 and 3.

[0030] Figure 9 The bar chart shows the product formation rate of photocatalytic reduction of carbon dioxide using the photocatalysts of Example 1 and Comparative Examples 2 and 3.

[0031] Figure 10 The image shows the electron selectivity of the products from the photocatalytic reduction of carbon dioxide using the photocatalysts of Example 1 and Comparative Examples 2 and 3. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1 This embodiment provides a graphitic carbon nitride photocatalyst based on a nitrogen-deficient sulfur-doped coupled S-type homojunction. The preparation method includes the following steps: S1. Take 6.00 g of dicyandiamide and 3.00 g of cyanuric acid, and grind and mix them in a mortar for 30 min. Transfer the mixed powder to a beaker, add 40 mL of deionized water, and stir until dissolved. Then, accurately measure 5.00 mL of concentrated nitric acid using a pipette, and slowly add it dropwise to the above solution while continuously stirring. After the addition is complete, continue stirring at room temperature for 1 h. Next, transfer the mixed solution to an 80 °C oil bath and heat for 5 h to completely evaporate the solvent, obtaining a dicyandiamide-cyanuric acid supramolecular composite solid. Grind the solid into a fine powder and transfer it to a covered alumina crucible. Place the crucible in a tube furnace and purge with high-purity argon as a protective atmosphere. Heat at 5 °C / min. -1 The temperature was programmed to rise to 500℃ and held at that temperature for 4 hours. After the calcination process was completed, the furnace was allowed to cool naturally to room temperature. The product was then removed, ground, and a nitrogen-defective graphitic carbon nitride (NA-DCN) powder sample was obtained.

[0034] S2. Take 6.00 g of urea and 3.00 g of trithiocyanate and place them in a 250 mL beaker. Add 40 mL of deionized water and stir at 60 °C until completely dissolved. Then, accurately measure 5.00 mL of concentrated nitric acid using a pipette and slowly add it dropwise to the above solution while continuously stirring. After the addition is complete, continue stirring at room temperature for 1 h. Next, transfer the mixed solution to an 80 °C oil bath and heat for 5 h to completely evaporate the solvent, obtaining a urea-trithiocyanate supramolecular composite solid. Grind the solid into a fine powder and transfer it to a covered alumina crucible. Place the crucible in a tube furnace and purge with high-purity argon as a protective atmosphere. Heat at 5 °C / min. -1 The temperature was programmed to rise to 500℃ and held at that temperature for 4 hours. After the calcination process was completed, the furnace was allowed to cool naturally to room temperature. The product was then removed, ground, and a sulfur-doped graphitic carbon nitride (NA-SCN) powder sample was obtained.

[0035] S3. Weigh 0.15g of NA-DCN and 0.15g of NA-SCN powder, disperse them separately in 10mL of deionized water, and sonicate for 30min to form a uniform suspension. Under magnetic stirring, slowly pour the NA-DCN suspension into the NA-SCN suspension and continue stirring for 30min. Then, add 5.00mL of concentrated nitric acid dropwise to the mixed suspension, stirring for 5min after the addition is complete. Transfer the mixture to a round-bottom flask and reflux in a 130℃ oil bath for 3h. After the reaction is complete, cool to room temperature, filter, and wash with deionized water and anhydrous ethanol. Dry the filter cake in a 70℃ vacuum drying oven for 12h. Grind the dried sample, spread it evenly in an alumina crucible, and heat under argon protection at 5℃·min. -1 The temperature was raised to 500℃ and calcined for 4 hours. After natural cooling, the final S-type homojunction photocatalyst was obtained, denoted as 1NA-DCN / 1NA-SCN.

[0036] Example 2 The specific implementation method of this embodiment is the same as that of embodiment 1, except that in S3, NA-DCN is 0.10g and NA-SCN is 0.20g, and the resulting S-type homojunction photocatalyst is denoted as 1NA-DCN / 2NA-SCN.

[0037] Example 3 The specific implementation method of this embodiment is the same as that of embodiment 1, except that in S3, NA-DCN is 0.20g and NA-SCN is 0.10g, and the resulting S-type homojunction photocatalyst is denoted as 2NA-DCN / 1NA-SCN.

[0038] Example 4 The specific implementation method of this embodiment is the same as that of embodiment 1, except that concentrated nitric acid is not added to the mixed suspension in S3.

[0039] S3. Weigh 0.15g of NA-DCN and 0.15g of NA-SCN powder, disperse them separately in 10mL of deionized water, and sonicate for 30min to form a uniform suspension. Under magnetic stirring, slowly pour the NA-DCN suspension into the NA-SCN suspension and continue stirring for 30min. Then, add 25.00mL of deionized water dropwise to the mixed suspension, stirring for 5min after the addition is complete. Transfer the mixture to a round-bottom flask and reflux in a 130℃ oil bath for 3h. After the reaction is complete, cool to room temperature, filter, and wash with deionized water and anhydrous ethanol. Dry the filter cake in a 70℃ vacuum drying oven for 12h. Grind the dried sample, spread it evenly in an alumina crucible, and heat under argon protection at 5℃·min. -1The temperature was raised to 500℃ and calcined for 4 hours. After natural cooling, the final S-type homojunction photocatalyst was obtained, denoted as 1NA-DCN / 1NA-SCN(W).

[0040] Example 5 The specific implementation method of this embodiment is the same as that of embodiment 1, except that concentrated nitric acid and deionized water are added to the mixed suspension in S3.

[0041] S3. Weigh 0.15g of NA-DCN and 0.15g of NA-SCN powder, disperse them separately in 10mL of deionized water, and sonicate for 30min to form a uniform suspension. Under magnetic stirring, slowly pour the NA-DCN suspension into the NA-SCN suspension and continue stirring for 30min. Then, add 20.00mL of deionized water to the mixed suspension, followed by dropwise addition of 5.00mL of concentrated nitric acid. After the addition is complete, continue stirring for 5min. Transfer the mixture to a round-bottom flask and reflux in a 130℃ oil bath for 3h. After the reaction is complete, cool to room temperature, filter, and wash with deionized water and anhydrous ethanol. Dry the filter cake in a 70℃ vacuum drying oven for 12h. Grind the dried sample, spread it evenly in an alumina crucible, and heat under argon protection at 5℃·min. -1 The temperature was raised to 500℃ and calcined for 4 hours. After natural cooling, the final S-type homojunction photocatalyst was obtained, denoted as 1NA-DCN / 1NA-SCN(NA).

[0042] Comparative Example 1 At room temperature, 2.00 g of melamine was weighed and placed in a covered crucible. The crucible was then placed in a muffle furnace for calcination, with a heating program of 5 °C / min. -1 The temperature was raised to 520℃ and held for 4 hours, and then naturally cooled to obtain a graphitic carbon nitride photocatalyst, abbreviated as CN.

[0043] Characterization results show that the absorption edge of CN is 460 nm, and the specific surface area of ​​CN is 5.7 m². 2 ·g -1 Photocatalytic performance tests showed that the photocatalytic hydrogen production rate of CN was 78.0 μmol·h⁻¹. -1 ·g -1 In the photocatalytic reduction of carbon dioxide in pure water, no sacrificial agent or additional co-catalyst is required, and the CH4 formation rate is 1.63 μmol·h⁻¹. -1 ·g -1 The CO production rate is 0.32 μmol·h⁻¹. -1 ·g -1 The electron selectivity of CH4 is 95.3%.

[0044] Comparative Example 2 Take 6.00 g of urea and 3.00 g of trithiocyanate and place them in a 250 mL beaker. Add 40 mL of deionized water and stir at 60 °C until completely dissolved. Then, accurately measure 5.00 mL of concentrated nitric acid using a pipette and slowly add it dropwise to the above solution while continuously stirring. After the addition is complete, continue stirring at room temperature for 1 h. Next, transfer the mixed solution to an 80 °C oil bath and heat for 5 h to completely evaporate the solvent, obtaining a urea-trithiocyanate supramolecular composite solid. Grind the solid into a fine powder and transfer it to a covered alumina crucible. Place the crucible in a tube furnace and purge with high-purity argon as a protective atmosphere. Heat at 5 °C·min -1 The temperature was programmed to rise to 500℃ and held at that temperature for 4 hours. After the calcination process was completed, the furnace was allowed to cool naturally to room temperature. The product was then removed, ground, and a sulfur-doped graphitic carbon nitride (NA-SCN) powder sample was obtained.

[0045] Characterization results show that the absorption edge of NA-SCN is 480 nm, and the specific surface area of ​​NA-SCN is 44.1 m². 2 ·g -1 The photocatalytic performance test results show that the photocatalytic hydrogen production rate of NA-SCN is 553.2 μmol·h⁻¹. -1 ·g -1 In the photocatalytic reduction of carbon dioxide in pure water, no sacrificial agent or additional co-catalyst is required, and the CH4 formation rate is 18.4 μmol·h⁻¹. -1 ·g -1 The CO production rate was 40.8 μmol·h⁻¹. -1 ·g -1 The electron selectivity of CH4 is 64.3%.

[0046] Comparative Example 3 Take 6.00 g of dicyandiamide and 3.00 g of cyanuric acid, and grind and mix them in a mortar for 30 min. Transfer the mixed powder to a beaker, add 40 mL of deionized water, and stir until dissolved. Then, accurately measure 5.00 mL of concentrated nitric acid using a pipette and slowly add it dropwise to the above solution while continuously stirring. After the addition is complete, continue stirring at room temperature for 1 h. Next, transfer the mixed solution to an 80 °C oil bath and heat for 5 h to completely evaporate the solvent, obtaining a dicyandiamide-cyanuric acid supramolecular composite solid. Grind the solid into a fine powder and transfer it to a covered alumina crucible. Place the crucible in a tube furnace and purge with high-purity argon as a protective atmosphere. Heat at 5 °C·min -1 The temperature was programmed to rise to 500℃ and held at that temperature for 4 hours. After the calcination process was completed, the furnace was allowed to cool naturally to room temperature. The product was then removed, ground, and a nitrogen-defective graphitic carbon nitride (NA-DCN) powder sample was obtained.

[0047] Characterization results show that the absorption edge of NA-DCN is 467 nm, and the specific surface area of ​​NA-DCN is 65.7 m². 2 ·g -1 The photocatalytic performance test results show that the photocatalytic hydrogen production rate of NA-DCN is 781.2 μmol·h⁻¹. -1 ·g -1 In the photocatalytic reduction of carbon dioxide in pure water, no sacrificial agent or additional co-catalyst is required, and the CH4 formation rate is 63.0 μmol·h⁻¹. -1 ·g -1 The CO production rate was 10.1 μmol·h⁻¹ -1 ·g -1 The electron selectivity of CH4 is 96.1%.

[0048] Comparative Example 4 S1. Weigh 10 mmol of lanthanum nitrate hexahydrate and 10 mmol of titanium sulfate into 60 mL of ultrapure water, and gradually dissolve them under magnetic stirring. Then add 20 mL of 5 mol / L sodium hydroxide solution and continue stirring for 2 hours to obtain a white suspension. Transfer the system obtained from the above reaction to a hydrothermal reactor, heat the reactor to 200 °C in an oven, and perform a hydrothermal reaction at 200 °C for 72 h. After the reactor is cooled to room temperature, filter and wash the obtained solid, and finally transfer it to an oven and maintain it at 60 °C for 24 h to obtain a white powder solid.

[0049] S2. Take 187 mg of the white powder solid obtained from the above steps, mix and grind it evenly with 10 g of urea, 6.2 g of potassium chloride and 7.2 g of lithium chloride monohydrate, transfer it to an oven and keep it at 120°C for 10 h, then transfer it to a muffle furnace and heat it to 500°C at a rate of 5°C / min, and keep it at 500°C for 5 h, and finally let it cool naturally to room temperature.

[0050] S3. After the above reaction is completed, the solid obtained is dissolved, filtered, and washed to remove potassium chloride and lithium chloride. Then, it is transferred to an oven and kept at 60°C for 24 h to obtain the heterojunction material g-C3N4 / La2Ti2O7.

[0051] The photocatalytic performance test results show that the photocatalytic hydrogen production rate of g-C3N4 / La2Ti2O7 is 109.2 μmol·h. -1 ·g -1 In the photocatalytic reduction of carbon dioxide in pure water, no sacrificial agent or additional co-catalyst is required, and the CH4 formation rate is 1.6 μmol·h⁻¹. -1 ·g -1 The CO production rate is 2.3 μmol·h⁻¹. -1 ·g -1The electron selectivity of CH4 is 73.1%.

[0052] Application Example 1-1 This application example provides a method for photocatalytic water splitting to produce hydrogen, the specific steps of which are as follows: 0.04 g of the 1NA-DCN / 1NA-SCN photocatalyst from Example 1 was added to a 105 mL sealed heat-resistant glass side-window reactor, along with 10 mL of triethanolamine aqueous solution as a sacrificial agent; and 0.1 mL of chloroplatinic acid hexahydrate aqueous solution (0.001 g / mL) was added as a co-catalyst. Platinum metal was photodeposited onto the 1NA-DCN / 1NA-SCN catalyst under a xenon lamp. The reactor was purged with argon gas for 15 min to remove oxygen. The reactor was maintained at 35 °C using circulating water. A magnetic stirrer was turned on, and a 300 W xenon lamp equipped with a cutoff filter (λ=420 nm) was used for illumination. Hydrogen was quantitatively detected using gas chromatography.

[0053] Application Example 1-2 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 1NA-DCN / 2NA-SCN as in example 2.

[0054] Application Examples 1-3 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 2NA-DCN / 1NA-SCN as in example 3.

[0055] Application Examples 1-4 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 1NA-DCN / 1NA-SCN(W) from example 4.

[0056] Application Examples 1-5 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 1NA-DCN / 1NA-SCN (NA) in example 5.

[0057] Application Example 2-1 This application example provides a method for the photocatalytic reduction of carbon dioxide, with the following specific steps: In a 250 mL quartz reactor, 0.01 g of the 1NA-DCN / 1NA-SCN photocatalyst from Example 1 was added and dispersed in 10 mL of deionized water. The reactor was purged with carbon dioxide gas for 30 min to remove air. The reactor was maintained at 35 °C using circulating water. A magnetic stirrer was turned on, and a 300 W xenon lamp equipped with a cutoff filter (λ=420 nm) was used for illumination. The product was detected by gas chromatography and a flame ionization detector.

[0058] Application Example 2-2 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 1NA-DCN / 2NA-SCN as in example 2.

[0059] Application Example 2-3 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 2NA-DCN / 1NA-SCN as in example 3.

[0060] Application Example 2-4 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 1NA-DCN / 1NA-SCN(W) from example 4.

[0061] Application Example 2-5 The specific implementation method of this application example is the same as that of application example 1-1, except that the photocatalyst is 1NA-DCN / 1NA-SCN (NA) in example 5.

[0062] Performance testing The products obtained in the above embodiments were characterized, and the results of the characterization diagrams and application examples are shown in the figure. Figure 1-10 .

[0063] Figure 1 (A) and (C) are transmission electron microscopy (TEM) images of the photocatalysts of Example 1 and Comparative Examples 2 and 3, respectively. Figure 1 As can be seen, NA-DCN exhibits a sheet-like stacked nanostructure, while NA-SCN has a more dense particle agglomeration morphology. The 1NA-DCN / 1NA-SCN structure clearly distinguishes the sheet-like region of NA-DCN from the particle region of NA-SCN, intuitively demonstrating the interfacial composite structure formed by the two in the homojunction sample.

[0064] Figure 2 The UV-Vis absorption spectra of the photocatalysts in Example 1 and Comparative Examples 2 and 3 are shown (with photographs of the actual products). Figure 2 As can be seen from the curves, the light absorption capabilities of the three samples are clearly demonstrated: the absorption edge of NA-DCN is 467.6 nm, NA-SCN is red-shifted to 480.1 nm, and 1NA-DCN / 1NA-SCN is further red-shifted to 491.5 nm, indicating that the homojunction sample has a wider light absorption range; the physical photograph on the right shows that all three are light-colored powders, which also indirectly reflects the differences in the optical properties of the materials.

[0065] Figure 3 The above are bar charts showing the apparent zeta potentials of the photocatalysts in Example 1 and Comparative Examples 2 and 3. Figure 3As can be seen, the zeta potential of NA-SCN is -17.1mV, that of NA-DCN is -14.8mV, while the zeta potential of 1NA-DCN / 1NA-SCN is only -4.6mV. This difference indicates that the interfacial charge distribution of the homojunction sample is more balanced, reflecting the change in the surface charge characteristics after NA-DCN and NA-SCN are combined.

[0066] Figure 4 This is a comparison of the hydrogen production rate curves of the photocatalysts in Examples 1-3 and Comparative Examples 2 and 3. From... Figure 4 As can be seen, the hydrogen production of Comparative Examples 2 and 3 increased slowly, while the hydrogen production of Examples 1, 2, and 3 was significantly higher. Among them, the hydrogen production of Example 1 increased the fastest, which shows that the photocatalytic hydrogen production activity of the homojunction sample formed by NA-DCN and NA-SCN is far superior to that of a single component, and the homojunction with a 1:1 mass ratio has the best performance.

[0067] Figure 5 Bar charts showing the hydrogen production activity of the photocatalysts in Examples 1-3 and Comparative Examples 2 and 3. From... Figure 5 As can be seen, the samples obtained by calcining the mixture of NA-DCN and NA-SCN exhibit higher photocatalytic hydrogen production activities than those of Comparative Example 2 and Comparative Example 3. This indicates that the present invention successfully improved the photocatalytic performance by constructing N-defective g-C3N4 (NA-DCN) and S-doped g-C3N4 (NA-SCN) through nitric acid-assisted treatment, and then optimizing the component ratio.

[0068] Figure 6 (A) Full X-ray photoelectron spectroscopy (XPS) spectra of 1NA-DCN / 1NA-SCN in Example 1, NA-SCN in Comparative Example 2, and NA-DCN in Comparative Example 3. Figure 6Images (B) through (D) show the XPS high-resolution spectra of C1s, N1s, and S2p of the 1NA-DCN / 1NA-SCN from Example 1, the NA-SCN from Comparative Example 2, and the NA-DCN from Comparative Example 3, respectively. The full spectra show that the NA-SCN exhibits an S2p peak in addition to C, N, and O, confirming successful S doping; the NA-DCN contains only C, N, and O elements and has no S signal; the 1NA-DCN / 1NA-SCN simultaneously possesses characteristic peaks of C, N, O, and S, directly proving that this homojunction sample is a composite of NA-DCN and NA-SCN. As can be seen from the high-resolution images, characteristic peaks such as CN and C=N appear in 1NA-DCN / 1NA-SCN, NA-DCN, and NA-SCN. The C=C peak of 1NA-DCN / 1NA-SCN is consistent with that of the single component, indicating that the carbon bond structure remains unchanged. The binding energies of the NC and NH peaks of 1NA-DCN / 1NA-SCN are between those of NA-DCN and NA-SCN, reflecting the interfacial charge regulation of the homojunction. The difference between the S2p peak of 1NA-DCN / 1NA-SCN and that of NA-SCN also confirms the presence of S doping in the homojunction.

[0069] Figure 7 The figures show the N2 adsorption-desorption isotherms and specific surface area data of the photocatalysts of Example 1 and Comparative Examples 2 and 3. Figure 7 As can be seen, the N2 adsorption-desorption isotherms of the photocatalysts in Example 1, Comparative Examples 2, and 3 all exhibit type IV curves with significant hysteresis loops, indicating that the synthesized photocatalysts are all mesoporous adsorbent materials. Furthermore, compared to the specific surface areas of the photocatalysts in Comparative Examples 2 and 3 (44.1 m², respectively), the N2 adsorption-desorption isotherms are significantly different. 2 g -1 65.7m 2 g -1 The specific surface area of ​​1NA-DCN / 1NA-SCN in Example 1 is 118.3 m². 2 g -1 The specific surface area of ​​the material is much higher than that of a single component, indicating that the etching and thermal stripping effects of nitric acid during the preparation of the S-type homojunction can generate more hollow and macropores, further increasing the specific surface area of ​​the material and providing more reaction sites for photocatalytic reactions.

[0070] Figure 8 The images show the electron paramagnetic resonance (EPR) spectra of the photocatalysts in Example 1 and Comparative Examples 2 and 3. Figure 8 As can be seen, the signal at g=2.004 corresponds to unpaired electrons in the material. The signal intensity of 1NA-DCN / 1NA-SCN at this position is significantly higher than that of NA-SCN and NA-DCN, indicating that the nitrogen defect concentration is higher in the homojunction sample. This result confirms the regulatory effect of nitric acid treatment on the defect structure.

[0071] Figure 9 The bar chart shows the product formation rates of the photocatalytic reduction of carbon dioxide using the photocatalysts of Example 1 and Comparative Examples 2 and 3. From... Figure 9 As can be seen from the data, the CO generation rate of NA-SCN in a single component is 19.4 μmol·h⁻¹. -1 ·g -1 CH4 content was 57.3 μmol·h⁻¹ -1 ·g -1 The CO content of NA-DCN is 10.1 μmol·h⁻¹. -1 ·g -1 The CH4 generation rate was 63 μmol·h⁻¹·g⁻¹ for 1NA-DCN / 1NA-SCN, while the CH4 generation rate was significantly increased to 82.3 μmol·h⁻¹. -1 ·g -1 The CO production rate is 14.5 μmol·h⁻¹. -1 ·g -1 This indicates that the homojunction sample exhibits significantly better selectivity and generation activity for CH4 than the single component, demonstrating the synergistic effect of N defects and S doping on enhancing the photocatalytic carbon dioxide reduction performance.

[0072] Figure 10 The bar chart shows the electron selectivity of the products from the photocatalytic reduction of carbon dioxide using the photocatalysts of Example 1 and Comparative Examples 2 and 3. NA-DCN exhibits extremely high CH4 electron selectivity (96.1%), while NA-SCN shows very low CH4 electron selectivity (64.3%). This is because NA-DCN and NA-SCN have different titanium dioxide reduction active sites on their surfaces. Similarly, 1NA-DCN / 1NA-SCN also exhibits extremely high CH4 electron selectivity (95.8%). Considering the formed S-shaped homojunction structure, the similar CH4 electron selectivity of 1NA-DCN / 1NA-SCN to NA-DCN should be attributed to the photocatalytic reduction reaction sites being located on the NA-DCN surface, further indicating the formation of an S-shaped homojunction between NA-DCN and NA-SCN.

[0073] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a graphitic carbon nitride photocatalyst based on a nitrogen-defect sulfur-doped coupled S-type homojunction, characterized in that, Includes the following steps: S1. Preparation of NA-DCN: Dicyandiamide and cyanuric acid were blended to prepare the first supramolecular composite solid, which was then calcined to obtain nitrogen-defect graphitic carbon nitride, i.e., NA-DCN; S2. Preparation of NA-SCN: After preparing a second supramolecular composite solid by blending urea and trithiocyanate, the solid was calcined to obtain sulfur-doped graphitic carbon nitride, i.e., NA-SCN; S3. Preparation of graphitic carbon nitride photocatalyst: NA-DCN and NA-SCN were mixed and calcined to obtain graphitic carbon nitride photocatalyst.

2. The preparation method according to claim 1, characterized in that, The mass ratio of dicyandiamide to cyanuric acid is (5~7):(2~4), and / or the mass ratio of urea to cyanuric acid is (5~7):(2~4).

3. The preparation method according to claim 2, characterized in that, The preparation method of the first supramolecular composite solid is as follows: dicyandiamide and cyanuric acid are mixed, deionized water and concentrated nitric acid are added, the mixture is stirred continuously and then heated to remove the solvent, and / or the preparation method of the second supramolecular composite solid is as follows: urea and thiocyanate are mixed, deionized water and concentrated nitric acid are added, the mixture is stirred continuously and then heated to remove the solvent, and the mixture is obtained.

4. The preparation method according to claim 3, characterized in that, The calcination conditions were all: under inert gas protection, at 5~10℃·min. -1 The temperature is increased to 500~550℃ at a certain rate, and then calcined for 4~5 hours.

5. The preparation method according to claim 4, characterized in that, The mass ratio of NA-DCN to NA-SCN is (1~2):(1~2).

6. The preparation method according to claim 5, characterized in that, The specific method of S3 is as follows: NA-DCN and NA-SCN are dissolved separately in deionized water to prepare dispersions, then mixed together. Concentrated nitric acid is added, and the mixture is stirred continuously and heated to remove the solvent. After washing and drying the solid, it is heated at 5~10℃·min under inert gas protection. -1 The temperature was increased to 500~550℃ at a certain rate and calcined for 4~5 hours to obtain a graphitic carbon nitride photocatalyst.

7. A graphitic carbon nitride photocatalyst based on a nitrogen-defect sulfur-doped coupled S-type homojunction, characterized in that, The preparation method according to any one of claims 1-6 is obtained.

8. The application of the graphitic carbon nitride photocatalyst based on nitrogen-defect sulfur-doped coupled S-type homojunction as described in claim 7, characterized in that, It is applied to photocatalytic reactions.

9. A method for photocatalytic water splitting to produce hydrogen, characterized in that, Catalysis was performed using the graphitic carbon nitride photocatalyst as described in claim 7.

10. A method for reducing carbon dioxide using a photocatalyst, characterized in that, Catalysis was performed using the graphitic carbon nitride photocatalyst as described in claim 7.

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