A cyanide-modified single-site carbon nitride catalyst and a method for photocatalytic hydrogen production

Abstract

This invention discloses a cyanide-modified single-site carbon nitride photocatalyst and a method for photocatalytic hydrogen production. The catalyst uses carbon nitride as a support and is obtained through photochemical synthesis, where metal and carbon nitride are irradiated with visible light in a cyanide solution. During the catalytic process, a local coordination environment regulation strategy is employed. Pretreatment of the single-site carbon nitride with cyanide adjusts the electronic and geometric structure of the central metal atom, thereby adjusting the binding energy between the metal center and reactant molecules and intermediates, thus regulating its photocatalytic hydrogen production activity. The catalyst preparation method of this invention is simple, environmentally friendly, and low-cost. Cyanide can act as a good ligand to precisely regulate the electronic structure of the catalyst metal sites (e.g., Ni, Co, Pd), thereby improving the photocatalytic hydrogen production activity of single-site carbon nitride. The catalyst of this invention has universality, and the metal coordination environment regulation strategy provides a new approach to regulating photocatalytic hydrogen production activity.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic hydrogen production technology, specifically relating to a cyanide-modified single-site carbon nitride catalyst and a method for photocatalytic hydrogen production using the catalyst. Background Technology

[0002] Photocatalytic hydrogen production is a promising green technology for converting solar energy into chemical energy and an effective way to utilize renewable energy. Catalysts with atomically dispersed sites, characterized by maximized atom utilization and tunable coordination configurations, typically exhibit excellent catalytic activity and have attracted widespread attention in the field of photocatalytic hydrogen production. However, developing efficient and inexpensive transition metal catalysts is very challenging. Precise design and control of the electronic states and coordination structures of active sites on the catalyst surface are key to promoting the adsorption and activation of hydrogen protons. Therefore, there is an urgent need to develop new catalyst design strategies to precisely control the electronic structure of catalysts, thereby effectively improving the activity of transition metal catalysts.

[0003] Typically, the state of the d-orbital electronic structure of transition metal compounds directly influences the adsorption and activation of hydrogen protons and their reduction reaction intermediates. By utilizing the d-band center of transition metals, the adsorption energy of adsorbed molecules on the metal surface can be correlated, and catalytic activity can be predicted in a simple way. Theoretically, the binding energy of reactant molecules and intermediates can be controlled by adjusting the position of the d-band center of the transition metal in the catalyst, thereby regulating the catalytic reaction efficiency. Currently, researchers mostly optimize the position of the d-band center of transition metals by constructing structural defects. Common strategies include: doping, vacancy construction, single-atom dispersion, stress engineering, alloying, amorphization, crystal phase adjustment, and construction of heterojunction interfaces. However, the synthesis methods are generally complex and lack universality. Among these, the coordinating atoms surrounding the central metal atom play a crucial role in its catalytic activity, selectivity, and stability. Coordination environment modification strategies can adjust the electronic and geometric structures of the central metal atom by adjusting the coordination environment, thereby changing the adsorption activity of the metal atom for reactants and thus affecting catalytic performance. The coordination environment of the metal atom is the core of designing high-performance single-point catalysts, as it provides appropriate metal-support interactions. Therefore, catalytic performance is typically enhanced by modulating the electronic and geometric structure of the central metal atom through local coordination regulation of single-site catalysts. The coordination environment of a single-site catalyst can be regulated by altering the coordinating species, adjusting the coordination number, introducing heteroatoms, or introducing other metals. Among these, the ability to utilize the coordination microenvironment to allow different catalytic sites to combine with different coordination environments, thereby achieving unique electronic structures and maximizing catalytic efficiency, has attracted widespread research interest. Acetonitrile and other cyanides are commonly used as polar aprotic solvents or reactants. Studies have shown that acetonitrile can serve as a good solvent to better promote photocatalytic hydrogen evolution in the photocatalytic hydrogen evolution reaction. Meanwhile, as early as 1914, research reported MX2·RCN compounds formed from metal halides and cyanides such as acetonitrile or benzonitrile. Therefore, acetonitrile molecules can not only act as solvents but also as excellent ligands to locally regulate the coordination of the metal sites on catalysts, enabling modification of the coordination environment of metal sites in single-site carbon nitride catalysts, thereby affecting catalytic activity. Summary of the Invention

[0004] The purpose of this invention is to provide a universally applicable cyanide-modified single-site carbon nitride catalyst and a method for photocatalytic hydrogen production.

[0005] To achieve the above objectives, the cyanide-modified single-site carbon nitride catalyst provided by the present invention is prepared by the following method:

[0006] Step 1: Melamine is stirred in concentrated hydrochloric acid for 30-60 minutes, then centrifuged and dried. The resulting solid is calcined at 400-600°C for 3-5 hours in air. The ground powder product is mixed and ground evenly with potassium chloride and lithium chloride in an anhydrous and oxygen-free environment. It is then calcined at 500-600°C for 4-6 hours in an inert atmosphere. The resulting product is washed with water and dried to obtain carbon nitride.

[0007] Step 2: Carbon nitride is uniformly dispersed into cyanide, then an aqueous solution of a metal salt is added. The mixture is stirred at 70–90°C for 6–10 hours. The resulting product is centrifuged and then dispersed back into cyanide. The mixture is irradiated under visible light for 2–3 hours, washed with water, and dried to obtain a cyanide-modified single-site carbon nitride catalyst. The metal salt is a chloride or nitrate salt of any one of Ni, Co, or Pd. The cyanide is any one of acetonitrile or phenylacetonitrile. The mass content of the metal in the cyanide-modified single-site carbon nitride catalyst is 0.25%–3%.

[0008] In step 1 above, melamine is preferably stirred in concentrated hydrochloric acid for 40 minutes, centrifuged and dried. The resulting solid is heated to 500°C in air at a heating rate of 8-12°C / min and calcined at a constant temperature for 4 hours. The ground powder product is mixed and ground evenly with potassium chloride and lithium chloride in an anhydrous and oxygen-free environment. It is then heated to 550°C in an inert atmosphere at a heating rate of 4-6°C / min and calcined at a constant temperature for 4 hours. The resulting product is washed with water and dried to obtain carbon nitride.

[0009] In step 1 above, it is further preferred that the mass ratio of the powdered product to potassium chloride and lithium chloride is 1:5 to 7:4 to 5.

[0010] In step 2 above, it is preferable to uniformly disperse carbon nitride in cyanide, then add an aqueous solution of metal salt, stir at 80°C for 8 hours, centrifuge the resulting product and then disperse it in cyanide, irradiate it under visible light with λ>420nm for 2.5 hours, wash with water and dry to obtain a cyanide-modified single-site carbon nitride catalyst.

[0011] In addition, the present invention provides two methods for photocatalytic hydrogen production. One method involves placing the cyanide-modified single-point carbon nitride catalyst described above into a reaction tube, adding triethanolamine and deionized water, and irradiating with visible light under an inert atmosphere for 4–6 hours. Preferably, the mass ratio of the cyanide-modified single-point carbon nitride catalyst to triethanolamine and deionized water is 1:10–15:15–20.

[0012] Another photocatalytic hydrogen production method provided by the present invention includes the following steps:

[0013] Step 1: Melamine is stirred in concentrated hydrochloric acid for 30-60 minutes, then centrifuged and dried. The resulting solid is calcined at 400-600°C for 3-5 hours in air. The ground powder product is mixed and ground evenly with potassium chloride and lithium chloride in an anhydrous and oxygen-free environment. It is then calcined at 500-600°C for 4-6 hours in an inert atmosphere. The resulting product is washed with water and dried to obtain carbon nitride.

[0014] Step 2: Disperse carbon nitride uniformly in deionized water, then add an aqueous solution of a metal salt, stir at 70-90°C for 6-10 hours, centrifuge the resulting product, then disperse it in deionized water again, irradiate under visible light for 2-3 hours, wash with water, and dry to obtain single-point carbon nitride; the metal salt is any chloride or nitrate salt of Ni, Co, or Pd; the mass content of the metal in the single-point carbon nitride is 0.25%-3%.

[0015] Step 3: Add single-point carbon nitride to the reaction tube, add cyanide, triethanolamine, and deionized water, and irradiate with visible light for 4 to 6 hours under an inert atmosphere; the cyanide is either acetonitrile or phenylacetonitrile.

[0016] In the above-mentioned photocatalytic hydrogen production method, step 1 preferably involves stirring melamine in concentrated hydrochloric acid for 40 minutes, centrifuging and drying it, then heating the resulting solid to 500°C in air at a heating rate of 8-12°C / min and calcining it at a constant temperature for 4 hours. The ground powder product is then mixed and ground evenly with potassium chloride and lithium chloride in an anhydrous and oxygen-free environment, and heated to 550°C in an inert atmosphere at a heating rate of 4-6°C / min and calcined at a constant temperature for 4 hours. The resulting product is then washed with water and dried to obtain carbon nitride. The mass ratio of the powder product to potassium chloride and lithium chloride is 1:5-7:4-5.

[0017] In the above-mentioned photocatalytic hydrogen production method, step 2 preferably involves uniformly dispersing carbon nitride in deionized water, then adding an aqueous solution of a metal salt, stirring at 80°C for 8 hours, centrifuging the resulting product, then dispersing it in deionized water, irradiating it under visible light with λ>420nm for 2.5 hours, washing the resulting product with water, then dispersing it in deionized water, washing it with water, and drying it to obtain single-point carbon nitride.

[0018] In the above-mentioned photocatalytic hydrogen production method, the preferred mass ratio of the single-point carbon nitride, triethanolamine, deionized water, and cyanide in step 3 is 1:10-15:15-20:6-8.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention utilizes a photochemical synthesis method to obtain a cyanide-modified single-site carbon nitride catalyst by irradiating a metal and carbon nitride in cyanide with visible light. During catalytic hydrogen production, by employing a local coordination environment control strategy, treating the single-site carbon nitride with cyanide can adjust the electronic and geometric structure of the central metal atom, thereby adjusting the binding energy between the metal center and reactant molecules and intermediates, thus regulating its photocatalytic hydrogen production activity. The catalyst preparation method of this invention is simple, environmentally friendly, and low-cost. Cyanide can act as a good ligand to precisely control the electronic structure of the catalyst metal sites (e.g., Ni, Co, Pd, etc.), thereby improving the activity of the single-site catalyst for photocatalytic hydrogen production.

[0021] 2. This invention uses carbon nitride as a support to obtain single-site carbon nitride under visible light irradiation with a metal salt. Then, using this single-site carbon nitride as a pre-catalyst, a carbon nitride photocatalyst with acetonitrile-modified single-site coordination is prepared in the photocatalytic hydrogen evolution reaction (HER). During the catalytic process, after acetonitrile modification, the catalyst possesses moderate adsorption capacity. Because its active sites can still adsorb hydrogen intermediates even after adsorbing cyanide, the adsorption barrier of HER is lowered compared to the unregulated single-site catalyst, accelerating hydrogen production. The catalyst of this invention has universality; the cyanide regulation strategy can be applied to metal catalysts formed from different transition metals. The metal coordination environment regulation strategy provides a new approach to regulating the photocatalytic hydrogen production activity. Attached Figure Description

[0022] Figure 1 The XRD patterns are of CCN in Comparative Example 1, Ni1-CCN in Example 1, Co1-CCN in Example 2, and Pd1-CCN in Example 3.

[0023] Figure 2 This is a spherical aberration corrected electron microscope (HAADF-STEM) image of Ni1-CCN in Example 1.

[0024] Figure 3 CCN in Comparative Example 1, Ni1-CCN in Example 1, Co1-CCN in Example 2, Pd1-CCN in Example 3, and CCN in Comparative Example 2 (ACN) In Example 4, Ni1-CCN (ACN) Co1-CCN in Example 5 (ACN) Pd1-CCN in Example 6 (ACN) The ultraviolet-visible diffuse reflectance spectrum.

[0025] Figure 4 The Ni1-CCN in Example 1, the Co1-CCN in Example 2, the Pd1-CCN in Example 3, and the Ni1-CCN in Example 4 are all examples of this type of CNC. (ACN)Co1-CCN in Example 5 (ACN) Pd1-CCN in Example 6 (ACN) HER diagram.

[0026] Figure 5 Comparative Example 1 (CCN), Example 1 (Ni1-CCN), and Example 4 (Ni1-CCN) (ACN) XPS graph.

[0027] Figure 6 The images show the EPR diagrams of CCN in Comparative Example 1 and Ni1-CCN in Example 1.

[0028] Figure 7 CCN in Comparative Example 1, Ni1-CCN in Example 1, Co1-CCN in Example 2, Pd1-CCN in Example 3, and CCN in Comparative Example 2 (ACN) In Example 4, Ni1-CCN (ACN) Co1-CCN in Example 5 (ACN) And Pd1-CCN in Example 6 (ACN) Activity test diagram.

[0029] Figure 8 This is an activity test diagram of Ni1-CCN in systems with different acetonitrile contents in Example 1. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0031] Example 1

[0032] Step 1: Stir 10g of melamine in 300mL of concentrated hydrochloric acid for 40min, centrifuge, and dry in an 80℃ oven. The resulting solid powder is heated to 500℃ in air at a heating rate of 10℃ / min and calcined at a constant temperature for 4h. After grinding, take 600mg of the ground powder product, 3.3g of potassium chloride, and 2.7g of lithium chloride, mix and grind them evenly in an anhydrous and oxygen-free environment, heat to 550℃ in argon atmosphere at a heating rate of 5℃ / min, and calcine at a constant temperature for 4h. The resulting product is washed with water and dried at 60℃ to obtain carbon nitride (CCN).

[0033] Step 2: Disperse 100 mg CCN evenly in 30 mL of deionized water, and add 400 μL of 2.5 mg / mL NiCl2 aqueous solution. Stir at 80 °C for 8 h. After centrifugation, disperse the resulting product in 15 mL of deionized water and irradiate it under a 450 nm LED lamp for 2.5 h. After washing with water and drying at 60 °C, obtain single-point carbon nitride (denoted as Ni1-CCN).

[0034] Step 3: Add 30 mg Ni1-CCN to the reaction tube, along with 0.3 mL acetonitrile, 0.3 mL triethanolamine, and 0.5 mL deionized water. Seal the reaction tube with a rubber stopper. While vigorously stirring, purge the reaction tube with argon gas to expel any air inside. After sealing, irradiate the tube under a 450 nm LED lamp for 6 hours to perform the photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0035] Example 2

[0036] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0037] Step 2: Disperse 100 mg CCN evenly in 30 mL of deionized water, and add 400 μL of 2.5 mg / mL CoCl2 aqueous solution. Stir at 80 °C for 8 h. After centrifugation, disperse the resulting product in 15 mL of deionized water and irradiate it under a 450 nm LED lamp for 2.5 h. After washing with water and drying at 60 °C, obtain single-point carbon nitride (denoted as Co1-CCN).

[0038] Step 3: Add 30 mg Co1-CCN to the reaction tube, along with 0.3 mL acetonitrile, 0.3 mL triethanolamine, and 0.5 mL deionized water. Seal the reaction tube with a rubber stopper. While stirring vigorously, purge the reaction tube with argon gas to expel the air inside. After sealing, irradiate under a 450 nm LED lamp for 6 hours to carry out the photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0039] Example 3

[0040] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0041] Step 2: Disperse 100 mg CCN evenly in 30 mL of deionized water, and add 400 μL of 2.5 mg / mL PdCl2 aqueous solution. Stir at 80 °C for 8 h. After centrifugation, disperse the resulting product in 15 mL of deionized water and irradiate it under a 450 nm LED lamp for 2.5 h. After washing with water and drying at 60 °C, obtain single-point carbon nitride (denoted as Pd1-CCN).

[0042] Step 3: Add 30 mg of Pd1-CCN to the reaction tube, along with 0.3 mL of acetonitrile, 0.3 mL of triethanolamine, and 0.5 mL of deionized water. Seal the reaction tube with a rubber stopper. While stirring vigorously, purge the reaction tube with argon gas to expel the air inside. After sealing, irradiate under a 450 nm LED lamp for 6 hours to carry out the photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the gas produced using a syringe and test the gas yield using a gas chromatograph.

[0043] Comparative Example 1

[0044] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0045] Step 2: Add 30 mg CCN to the reaction tube, along with 0.3 mL acetonitrile, 0.3 mL triethanolamine, and 0.5 mL deionized water. Seal the reaction tube with a rubber stopper. While stirring vigorously, purge the reaction tube with argon gas to expel any air inside. After sealing, irradiate the tube under a 450 nm LED lamp for 6 hours to perform the photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0046] Example 4

[0047] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0048] Step 2: 100 mg CCN was uniformly dispersed in 30 mL of acetonitrile, and 400 μL of 2.5 mg / mL NiCl2 aqueous solution was added. The mixture was stirred at 80 °C for 8 h. After centrifugation, the resulting product was dispersed in 15 mL of acetonitrile and irradiated under a 450 nm LED lamp for 2.5 h. The resulting product was washed with water and dried at 60 °C to obtain acetonitrile-modified single-site carbon nitride (denoted as Ni1-CCN). (ACN) ).

[0049] Step 3: Add 30mg Ni1-CCN (ACN) Add 0.3 mL of triethanolamine and 0.5 mL of deionized water to a reaction tube, seal the tube with a rubber stopper, and purge the tube with argon gas while stirring vigorously to expel any air inside. After sealing, irradiate the tube under a 450 nm LED lamp for 6 hours to perform a photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0050] Example 5

[0051] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0052] Step 2: 100 mg CCN was uniformly dispersed in 30 mL of acetonitrile, and 400 μL of 2.5 mg / mL CoCl2 aqueous solution was added. The mixture was stirred at 80 °C for 8 h. After centrifugation, the resulting product was dispersed in 15 mL of acetonitrile and irradiated under a 450 nm LED lamp for 2.5 h. The resulting product was washed with water and dried at 60 °C to obtain acetonitrile-modified single-site carbon nitride (denoted as Co1-CCN). (ACN) ).

[0053] Step 3: Add 30mg Co1-CCN (ACN) Add 0.3 mL of triethanolamine and 0.5 mL of deionized water to a reaction tube, seal the tube with a rubber stopper, and purge the tube with argon gas while stirring vigorously to expel any air inside. After sealing, irradiate the tube under a 450 nm LED lamp for 6 hours to perform a photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0054] Example 6

[0055] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0056] Step 2: 100 mg CCN was uniformly dispersed in 30 mL of acetonitrile, and 400 μL of 2.5 mg / mL PdCl2 aqueous solution was added. The mixture was stirred at 80 °C for 8 h. After centrifugation, the resulting product was dispersed in 15 mL of acetonitrile and irradiated under a 450 nm LED lamp for 2.5 h. The resulting product was washed with water and dried at 60 °C to obtain acetonitrile-modified single-site carbon nitride (denoted as Pd1-CCN). (ACN) ).

[0057] Step 3: Add 30mg Pd1-CCN (ACN) Add 0.3 mL of triethanolamine and 0.5 mL of deionized water to a reaction tube, seal the tube with a rubber stopper, and purge the tube with argon gas while stirring vigorously to expel any air inside. After sealing, irradiate the tube under a 450 nm LED lamp for 6 hours to perform a photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0058] Comparative Example 2

[0059] Step 1: Prepare carbon nitride (CCN) according to the method in Step 1 of Example 1.

[0060] Step 2: 100 mg CCN was uniformly dispersed in 30 mL of acetonitrile and stirred at 80 °C for 8 h. The resulting product was centrifuged and then dispersed in 15 mL of acetonitrile. The product was irradiated under a 450 nm LED lamp for 2.5 h. The resulting product was washed with water and dried at 60 °C to obtain acetonitrile-modified carbon nitride (denoted as CCN). (ACN) ).

[0061] Step 3: Add 30mg CCN (ACN) Add 0.3 mL of triethanolamine and 0.5 mL of deionized water to a reaction tube, seal the tube with a rubber stopper, and purge the tube with argon gas while stirring vigorously to expel any air inside. After sealing, irradiate the tube under a 450 nm LED lamp for 6 hours to perform a photocatalytic hydrogen production reaction. After the reaction is complete, extract 500 μL of the generated gas using a syringe and test the gas yield using a gas chromatograph.

[0062] The structures of the carbon nitride, single-site carbon nitride, and acetonitrile-modified single-site carbon nitride prepared above were characterized, and the results are shown in the figure. Figures 1-5 .

[0063] Depend on Figure 1 It can be seen that the diffraction peaks of pure CCN and all single-point carbon nitride only exhibit the two characteristic peaks of carbon nitride. Samples containing Ni, Co, and Pd do not show metal-related diffraction peaks. Therefore, it can be preliminarily concluded that single-point catalysts can be easily synthesized using photochemical synthesis methods, and that this method has a certain degree of universality. Figure 2 The aberration-corrected electron microscopy (HAADF-STEM) results of Ni1-CCN further confirm that Ni exists in the catalyst as single-point particles. The circles in the figure mark the locations of these single-point Ni particles, all of which are atomic-sized bright spots. It can be clearly seen that the single-point Ni particles are uniformly dispersed on the CCN support in the Ni1-CCN sample. These characterization results further indicate that the metal does not exhibit obvious clusters, but is mainly loaded onto the CCN in a single-point form.

[0064] In addition, we also through Figure 3 The ultraviolet-visible diffuse reflectance spectroscopy further verified the coordination properties between acetonitrile and the metal. Treatment of carbon nitride with acetonitrile revealed that acetonitrile has a certain influence on the molecular structure of carbon nitride, altering its optical properties. Furthermore, in CCN... (ACN)Two absorption states, π-π* and n-π* electronic transitions, can be observed in the spectrum, with absorption shoulders between 400–450 nm and 450–800 nm. The shoulder intensity between 400–450 nm is higher than that of CCN, indicating enhanced structural order in CCN, while the newly formed shoulder between 450–800 nm is attributed to doping in the carbon nitride framework. Metal loading of the catalyst revealed changes in the optical properties of the metal catalysts supported in acetonitrile and aqueous systems. These results preliminarily suggest that acetonitrile has a certain degree of control over the structure of carbon nitride itself. After metal loading, the acetonitrile loading on the catalyst shifts from the support to the metal center. The changes in the catalyst at a single point verify that acetonitrile mainly modulates the electronic and geometric structure of the central metal atom. From the above conclusions, the changes in the absorption spectrum and other spectral properties of acetonitrile-modified carbon nitride further verify that acetonitrile, as a ligand, alters the position of the d-orbital energy level of the metal center, affecting the D-band center.

[0065] The D-band center determines the energy level of charge transfer transitions in the complex, which can be used to predict catalytic performance and can be reflected in HER through the binding energies of reactant molecules and intermediates. Figure 4 Theoretical analysis of the HER reaction mechanism reveals that the binding energies of HER reactant molecules and intermediates change before and after acetonitrile coordination modification of metal carbon nitride. Specifically, after acetonitrile modification, the intermediates of Ni1-CCN, Co1-CCN, and Pd1-CCN exhibit very low adsorption energies in the catalyst, lower than those before acetonitrile modification. This indicates that acetonitrile coordination regulation leads to faster HER reaction kinetics on these three catalysts. These results demonstrate that acetonitrile successfully modulates and enhances the photocatalytic hydrogen evolution activity of metal carbon nitride, enabling simple prediction and regulation of photocatalytic activity.

[0066] Depend on Figure 5 XPS analysis showed that acetonitrile modification did indeed affect the molecular structure of the catalyst. Comparison with CCN, Ni1-CCN, and Ni1-CCN further confirmed this effect. (ACN) The Ni2p, C1s, and N1s spectra show that after modification with acetonitrile, Ni1-CCN... (ACN) The Ni, C, and N components were all shifted, verifying the effect of acetonitrile modification on the catalyst structure.

[0067] The photocatalytic hydrogen production test results in Examples 1-6 and Comparative Examples 1-2 are shown below. Figures 6-8 .

[0068] pass Figure 6 EPR testing revealed that the intensity of free radicals was higher in the presence of acetonitrile, demonstrating that the presence of acetonitrile better promotes the oxidation reaction and further facilitates the separation of photogenerated carriers. Figure 7 Photocatalytic activity tests showed that the activities of Ni1-CCN, Co1-CCN, and Pd1-CCN were significantly improved after acetonitrile modulation, which is completely consistent with the theoretical analysis results of HER. The predicted HER activity perfectly matches the actual experimental results. Furthermore, the improved catalytic activity is due to the modification of the metal on carbon nitride by acetonitrile, rather than carbon nitride itself. Figure 8 It can be seen that the amount of acetonitrile adsorbed has a certain impact on the catalytic activity. This is because after acetonitrile is adsorbed on the catalyst, it can modify the metal. However, if the amount of acetonitrile adsorbed is too large, it will occupy the active sites, which will reduce the photocatalytic hydrogen evolution activity. If the amount of adsorption is too small, the impact on the catalytic activity will be very small.

Claims

1. A cyanide-modified single-site carbon nitride catalyst, characterized in that... The cyanide-modified single-site carbon nitride catalyst was prepared by the following steps: Step 1: Melamine is stirred in concentrated hydrochloric acid for 30-60 minutes, then centrifuged and dried. The resulting solid is calcined at 400-600 °C for 3-5 hours in air. The ground powder product is mixed and ground evenly with potassium chloride and lithium chloride in an anhydrous and oxygen-free environment. It is then calcined at 500-600 °C for 4-6 hours in an inert atmosphere. The resulting product is washed with water and dried to obtain carbon nitride. Step 2: Carbon nitride is uniformly dispersed into cyanide, and then an aqueous solution of a metal salt is added. The mixture is stirred at 70–90 °C for 6–10 hours. The resulting product is centrifuged and then dispersed back into cyanide. The product is irradiated under visible light for 2–3 hours, washed with water, and dried to obtain a cyanide-modified single-site carbon nitride catalyst. The metal salt is a chloride or nitrate salt of any one of Ni, Co, or Pd. The cyanide is any one of acetonitrile or phenylacetonitrile. The mass content of the metal in the cyanide-modified single-site carbon nitride catalyst is 0.25%–3%.

2. The cyanide-modified single-site carbon nitride catalyst according to claim 1, characterized in that: In step 1, melamine is stirred in concentrated hydrochloric acid for 40 minutes, then centrifuged and dried. The resulting solid is heated to 500 °C in air at a heating rate of 8–12 °C / min and calcined at a constant temperature for 4 hours. The ground powder product is mixed and ground evenly with potassium chloride and lithium chloride in an anhydrous and oxygen-free environment. It is then heated to 550 °C in an inert atmosphere at a heating rate of 4–6 °C / min and calcined at a constant temperature for 4 hours. The resulting product is washed with water and dried to obtain carbon nitride.

3. The cyanide-modified single-site carbon nitride catalyst according to claim 1 or 2, characterized in that: In step 1, the mass ratio of the powdered product to potassium chloride and lithium chloride is 1:5 to 7:4 to 5.

4. The cyanide-modified single-site carbon nitride catalyst according to claim 1, characterized in that: In step 2, carbon nitride is uniformly dispersed into cyanide, and then an aqueous solution of metal salt is added. The mixture is stirred at 80°C for 8 hours. The resulting product is centrifuged and then dispersed back into cyanide. The product is then irradiated under visible light with a wavelength of λ > 420 nm for 2.5 hours, washed with water, and dried to obtain a cyanide-modified single-site carbon nitride catalyst.

5. A method for photocatalytic hydrogen production, characterized in that, The cyanide-modified single-point carbon nitride catalyst of claim 1 is placed in a reaction tube, and triethanolamine and deionized water are added. The mixture is then irradiated with visible light for 4 to 6 hours under an inert atmosphere.

6. The method for photocatalytic hydrogen production according to claim 5, characterized in that, The mass ratio of the cyanide-modified single-site carbon nitride catalyst to triethanolamine and deionized water is 1:10-15:15-20.

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