Preparation method of Cu / Ni dual-promoter based on g-C3N4

Abstract

The invention discloses a preparation method of a Cu / Ni dual-promoter based on g-C3N4, and belongs to the technical field of photocatalysts.The preparation method comprises the steps that 1, bulk phase g-C3N4 is prepared, specifically, the bulk phase g-C3N4 is prepared through direct condensation polymerization of dicyandiamide through heat treatment under the atmospheric pressure condition; step 2, preparation of Ni-Cu-C3N4: firstly, stripping a bulk phase g-C3N4 into a sheet structure; the preparation method comprises the following steps: adding CuSO4. 5H2O and Ni (NO3) 2.6 H2O, dropwise adding a NaBH4 alkaline solution into a g-C3N4 suspension containing Cu < 2 + > and Ni < 2 + >, and carrying out mixing treatment to obtain Ni-Cu-C3N4; according to the preparation method of the Cu / Ni double co-catalyst based on g-C3N4, the efficient hydrogen production of g-C3N4 is realized through the synergistic effect between the Cu co-catalyst and the Ni co-catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and in particular to a method for preparing a Cu / Ni dual-promoter catalyst based on g-C3N4. Background Art

[0002] The overexploitation and consumption of traditional fossil fuels have led to a serious energy crisis in human society, prompting the world to pay close attention to the development of renewable energy. Hydrogen (H2) has high calorific value and is a clean product, making it an ideal alternative energy carrier to fossil fuels. Using renewable solar energy to split water to generate H2, thereby converting solar energy into high calorific value hydrogen, has broad application potential. Since Fujishima Akira and Honda Kenichi first reported TiO2-catalyzed water splitting to generate H2 in 1972, the development of new and efficient photocatalysts has become the primary task of photocatalytic hydrogen production.

[0003] Among the many semiconductor photocatalysts, g-C3N4 has attracted much attention due to its excellent sunlight-driven hydrogen production performance since its pioneering research as a photocatalytic hydrogen production material in 2009. The polymerized g-C3N4 has a suitable band structure to drive water splitting to produce H2, but its photocatalytic activity is still limited by the limited light absorption range, insufficient catalytic sites, and serious photogenerated carrier recombination. Fortunately, g-C3N4 modified with cocatalysts can significantly improve the carrier utilization efficiency and reduce the surface reaction overpotential of g-C3N4. At the same time, the cocatalyst can serve as a proton reduction site to accelerate the generation of H2. Common noble metal cocatalysts such as Pd, Pt, and Au have been shown to have a strong ability to promote H2 release, but their high cost limits large-scale application. Therefore, it is imperative to develop new non-noble metal cocatalysts with excellent photocatalytic hydrogen production performance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a Cu / Ni dual-promoter based on g-C3N4 to solve the above problems.

[0005] To achieve the above object, the present invention provides a method for preparing a Cu / Ni dual-promoter catalyst based on g-C3N4, comprising the following steps:

[0006] Step 1, preparation of bulk g-C3N4: bulk g-C3N4 is prepared by direct polycondensation of dicyandiamide by heat treatment under atmospheric pressure;

[0007] Step 2, preparation of Ni-Cu-C3N4: First, the bulk phase g-C3N4 is peeled off into a thin sheet structure; after the treatment, CuSO4·5H2O and Ni(NO3)2·6H2O are added to the suspension respectively; then, NaBH4 alkaline solution is prepared, and the NaBH4 alkaline solution is added dropwise to the Cu-containing2+ and Ni 2+ The mixed solution was stirred continuously for 30 minutes to ensure complete reduction of metal ions. Finally, the precipitate was washed with distilled water and alcohol several times and dried. The obtained sample was named 3%Ni-3%Cu-C3N4.

[0008] Preferably, in the above-mentioned preparation method of the Cu / Ni dual-cocatalyst based on g-C3N4, the specific process of preparing the bulk g-C3N4 in the step one is as follows: 14 g of dicyandiamide is placed in an alumina crucible with a lid, heated to 550°C in a muffle furnace at a heating rate of 5°C / min, and maintained for 3 hours, and after natural cooling, a yellow bulk g-C3N4 is obtained for subsequent experiments.

[0009] Preferably, in the above-mentioned preparation method of the Cu / Ni dual-cocatalyst based on g-C3N4, the specific treatment process of exfoliating the bulk phase g-C3N4 into a thin flake structure in the step 2 is as follows: 200 mg of bulk phase g-C3N4 is dispersed in 60 mL of deionized water and magnetically stirred for 1 hour; then the suspension is ultrasonically treated for 2 hours to exfoliate the bulk phase g-C3N4 into a thin flake structure at room temperature.

[0010] Preferably, in the above-mentioned method for preparing a Cu / Ni dual-promoter based on g-C3N4, 16.3 mg CuSO4·5H5O and 18.9 mg Ni(NO3)2·6H2O are added in step 2.

[0011] Preferably, in the above-mentioned method for preparing a Cu / Ni dual-cocatalyst based on g-C3N4, the method for preparing the NaBH4 alkaline solution in step 2 is to dissolve 1 g of NaOH in 20 mL of distilled water, and then add 0.14 g of NaBH4 to prepare an alkaline solution.

[0012] Preferably, in the above-mentioned method for preparing a Cu / Ni dual-promoter based on g-C3N4, the condition for complete reduction in step 2 is that obvious bubbles are generated and the color of the solution changes from blue to light yellow.

[0013] Preferably, in the above-mentioned method for preparing a Cu / Ni dual-cocatalyst based on g-C3N4, the drying condition in the step 2 is drying in a vacuum oven at 50°C for 3 hours.

[0014] Therefore, the present invention adopts a method for preparing a Cu / Ni dual-promoter based on g-C3N4 of the above structure, wherein nickel (Ni) is used as an electron pool and the outermost electron configuration is 3d 8 4s 2, which can effectively collect photogenerated electrons for further use in the generation of H2. The outermost electron configuration of copper (Cu) is 3d 10 4s 1 , exhibiting local surface plasmon resonance (LSPR) under sunlight irradiation, which can generate additional high-energy hot electrons to participate in the photocatalytic release of H2. In the present invention, Cu with LSPR effect and Ni as electron pool are co-modified on g-C3N4 through an in-situ reduction process to improve the photocatalytic hydrogen production performance of g-C3N4. Performance evaluation shows that the dual Cu / Ni co-catalyst significantly improves the photocatalytic hydrogen production activity of g-C3N4 (1017μmolg -1 h -1 ), which is 63.5 times that of bulk g-C3N4. Experimental results combined with theoretical calculations show that Cu can not only generate hot electrons and promote the transfer of electrons to Ni, but also push the d-band center upward and optimize the *H adsorption / desorption energy of Ni sites. The study revealed that the synergistic effect between Cu and Ni co-catalysts is the key factor in achieving efficient hydrogen production from g-C3N4.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 (a) Schematic diagram of the preparation of a 3% Ni-3% Cu-C3N4 photocatalyst according to an embodiment of a method for preparing a Cu / Ni dual-promoter based on g-C3N4 of the present invention; (b, c) XRD spectra of g-C3N4, 6% Ni-C3N4, 6% Cu-C3N4 and 3% Ni-3% Cu-C3N4; (d) FT-IR spectra of g-C3N4, 6% Ni-C3N4, 6% Cu-C3N4 and 3% Ni-3% Cu-C3N4;

[0017] Figure 2 (ab) TEM images of 3% Ni-3% Cu-C3N4 according to an embodiment of a method for preparing a Cu / Ni dual-promoter based on g-C3N4 of the present invention; (c) HRTEM image of 3% Ni-3% Cu-C3N4; (d) HAADF-STEM element distribution map of 3% Ni-3% Cu-C3N4;

[0018] Figure 3 High-resolution XPS spectra of the photocatalysts C1s (a), N1s (b), Ni2p (c) and Cu2p (d) in an embodiment of a method for preparing a Cu / Ni dual-promoter based on g-C3N4 of the present invention;

[0019] Figure 4(a) and (b) the hydrogen generation rate of the obtained photocatalyst of the embodiment of the preparation method of the Cu / Ni dual-promoter based on g-C3N4 of the present invention; (c) the comparison with the most advanced g-C3N4-based photocatalyst reported; (d) the hydrogen generation cycle test of 3% Ni-3% Cu-C3N4;

[0020] Figure 5 The ultraviolet-visible diffuse reflectance spectra (UV-VisDRS) of 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and bulk g-C3N4 in an embodiment of a method for preparing a Cu / Ni dual-promoter based on g-C3N4 of the present invention and the corresponding band gap diagram (a), Mott-Schottky diagram (b), photocurrent-time response curve (c), steady-state photoluminescence (PL) spectrum (d), electrochemical impedance spectrum (EIS) (e) and time-resolved photoluminescence (TRPL) decay spectrum (f);

[0021] Figure 6 This is an embodiment of the preparation method of a Cu / Ni dual-cocatalyst based on g-C3N4 of the present invention: (a) charge density difference diagram of Ni-Cu-C3N4; (b) partial density of states (PDOS) diagram of Ni-C3N4 and Ni-Cu-C3N4; (c) hydrogen adsorption-desorption Gibbs free energy spectrum; (d) photocatalytic hydrogen evolution mechanism on 3% Ni-3% Cu-C3N4. DETAILED DESCRIPTION

[0022] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings, and "multiple" generally includes at least two.

[0024] It should also be noted that the term "includes", "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, so that a commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the commodity or device including the elements.

[0025] Example 1

[0026] A method for preparing a Cu / Ni dual-promoter catalyst based on g-C3N4 comprises the following steps:

[0027] Step 1, preparation of bulk g-C3N4: Bulk g-C3N4 is prepared by direct polycondensation of dicyandiamide by heat treatment under atmospheric pressure; 14 g of dicyandiamide is placed in an alumina crucible with a lid, heated to 550°C in a muffle furnace at a heating rate of 5°C / min, and maintained for 3 hours, and after natural cooling, yellow bulk g-C3N4 is obtained for subsequent experiments.

[0028] Step 2, preparation of Ni-Cu-C3N4: First, 200 mg of bulk g-C3N4 was dispersed in 60 mL of deionized water and magnetically stirred for 1 hour; then the suspension was ultrasonically treated for 2 hours to peel the bulk g-C3N4 into a thin sheet structure at room temperature; after the treatment, 16.3 mg of CuSO4·5H5O and 18.9 mg of Ni(NO3)2·6H2O were added to the suspension respectively; then, 1 g of NaOH was dissolved in 20 mL of distilled water, and 0.14 g of NaBH4 was added to prepare an alkaline solution, and the NaBH4 alkaline solution was added dropwise to the Cu-containing 2+ and Ni 2+ The mixed solution was stirred continuously for 30 min to ensure complete reduction of metal ions. During this process, obvious bubbles were generated and the color of the solution changed from blue to light yellow. Finally, the obtained precipitate was washed with distilled water and alcohol several times and dried in a vacuum oven at 50 °C for 3 h. The obtained sample was named 3%Ni-3%Cu-C3N4.

[0029] Comparative Example 1

[0030] Preparation of 6% Ni-C3N4: First, 200 mg of bulk g-C3N4 was dispersed in 60 mL of deionized water and magnetically stirred for 1 hour; then the suspension was ultrasonically treated for 2 hours to exfoliate the bulk g-C3N4 into a thin sheet structure at room temperature; after the treatment, 18.9 mg of Ni(NO3)2·6H2O was added to the suspension; then, 1 g of NaOH was dissolved in 20 mL of distilled water, and 0.14 g of NaBH4 was added to prepare an alkaline solution, and the NaBH4 alkaline solution was added dropwise to the Ni-containing 2+ The mixed solution was stirred continuously for 30 minutes to ensure complete reduction of metal ions. Finally, the obtained precipitate was washed with distilled water and alcohol several times and dried in a vacuum oven at 50°C for 3 hours. 6% Ni-C3N4 was obtained.

[0031] Comparative Example 2

[0032] Preparation of 6% Cu-C3N4: First, 200 mg of bulk g-C3N4 was dispersed in 60 mL of deionized water and magnetically stirred for 1 hour. Then, the suspension was ultrasonically treated for 2 hours to exfoliate the bulk g-C3N4 into a thin sheet structure at room temperature. After the treatment, 16.3 mg of CuSO4·5H5O was added to the suspension. Then, 1 g of NaOH was dissolved in 20 mL of distilled water, and 0.14 g of NaBH4 was added to prepare an alkaline solution. The NaBH4 alkaline solution was added dropwise to the Cu-containing 2+ The mixed solution was stirred continuously for 30 min to ensure complete reduction of metal ions. Finally, the obtained precipitate was washed with distilled water and alcohol several times and dried in a vacuum oven at 50 °C for 3 h. 6% Cu-C3N4 was obtained.

[0033] The preparation strategy of Ni-Cu-C3N4 is as follows Figure 1 a. First, the bulk g-C3N4 was exfoliated into nanosheets in water by ultrasonic treatment. Subsequently, Ni 2+ and Cu 2+ ions, which can be easily adsorbed by the abundant anchoring sites of g-C3N4 nanosheets. Finally, the adsorbed Ni 2+ and Cu 2+ The Ni and Cu nanoparticles were in situ reduced to the surface of g-C3N4 nanosheets. The control samples 6% Ni-C3N4 and 6% Cu-C3N4 were also prepared by the same strategy.

[0034] X-ray diffraction (XRD) tests were performed on bulk g-C3N4, 6% Ni-C3N4, 6% Cu-C3N4 and 3% Ni-3% Cu-C3N4 to study the crystal structure of the photocatalyst. Figure 1As shown in Figure b, the bulk g-C3N4 exhibits characteristic peaks at 12.8° and 27.6°, corresponding to the (100) and (002) crystal planes of the g-C3N4 graphite structure, respectively (JCPDS 87-1526). The results show that dicyandiamide can be successfully converted into yellow g-C3N4 by thermal polycondensation. It is worth noting that compared with the bulk g-C3N4, 6% Ni-C3N4, 6% Cu-C3N4 and 3% Ni-3% Cu-C3N4 appear at similar diffraction peak positions, but with weaker intensities, indicating that the bulk g-C3N4 has been exfoliated into nanosheets and the metal co-catalyst is attached to the g-C3N4 nanosheets. In particular, the (002) peaks of 6%Ni-C3N4, 6%Cu-C3N4, and 3%Ni-3%Cu-C3N4 shift slightly to lower angles compared to that of bulk g-C3N4, which indicates that there is a strong interaction between the metal co-catalyst and g-C3N4, e.g. Figure 1 As shown in c.

[0035] Meanwhile, Fourier transform infrared spectroscopy (FT-IR) was used to further analyze the microstructure of bulk g-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and 3%Ni-3%Cu-C3N4, as shown in Figure 2. Figure 1 d. The bulk g-C3N4 has the following wavelengths at 810, 1200-1750 and 2400 cm -1 The absorption peaks at 2400 cm-1 and 2400 cm-2 are shown, corresponding to the breathing mode of the triazine unit, the stretching vibration mode of the N-heterocyclic ring and the NH stretching vibration mode of the edge amino group. It is worth noting that compared with the bulk phase g-C3N4, 6% Ni-C3N4, 6% Cu-C3N4 and 3% Ni-3% Cu-C3N4 have a peak at 2400 cm-1. -1 The NH stretching mode at 810 cm -1 The triazine ring peak at is enhanced, which further indicates that the strong interaction between the metal co-catalyst and g-C3N4 leads to the disorder of the planar structure of g-C3N4 nanosheets.

[0036] In order to directly observe the morphology and structural composition of 3%Ni-3%Cu-C3N4, transmission electron microscopy (TEM) analysis was carried out. Figure 2 As shown in a, the metal nanoparticles are highly dispersed on the g-C3N4 nanosheets. Further enlarged images show that most of the nanoparticles are evenly distributed on the g-C3N4, and a small number of nanoparticles are slightly aggregated, as shown in Figure 2 b. In addition, in the high-resolution transmission electron microscopy (HRTEM) image, Figure 2c, two groups of clear lattice fringes can be observed at the same time, where the lattice spacing is 0.126nm and 0.18nm, corresponding to the (220) crystal plane of face-centered cubic Ni and the (200) crystal plane of face-centered cubic Cu, respectively. At the same time, the amorphous structure around the lattice fringes of Ni-Cu nanoparticles can be attributed to g-C3N4 nanosheets. In addition, the element distribution map of 3%Ni-3%Cu-C3N4 by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows that, as shown in Figure 2 d, Ni and Cu elements are uniformly distributed on g-C3N4 nanosheets. These results further demonstrate that the Ni-Cu co-catalysts are firmly anchored on g-C3N4 nanosheets.

[0037] X-ray photoelectron spectroscopy (XPS) was used to further study the chemical states of bulk g-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and 3%Ni-3%Cu-C3N4. Figure 3 As shown in a, the C1s spectra of the four photocatalysts are divided into three peaks, located at 284.8, 286.3 and 288.1 eV, which are respectively attributed to the CC bond, the sp bonded to the amino group (C-NH2), and the 2 Hybridized C and sp bonded to N in the triazine ring 2 Hybrid C (NCN). At the same time, the N1s spectrum of bulk g-C3N4 ( Figure 3 b) is divided into three peaks, located at 398.7, 399.4 and 401.1 eV. The peak at 398.7 eV comes from the CN network with three sp 2 The peak at 401.1eV corresponds to the bridging nitrogen atom (N-(C)3) bonded to the C atom, while the peak at 401.1eV corresponds to the hydrogen-containing amino group (NH or NH2 bond). These features are similar in 6%Ni-C3N4, 6%Cu-C3N4 and 3%Ni-3%Cu-C3N4. However, the binding energy of the 399.4eV peak attributed to N-C2 in the bulk g-C3N4 is increased compared with that of 6%Ni-C3N4, 6%Cu-C3N4 and 3%Ni-3%Cu-C3N4. This may be caused by the coordination synergy between the metal and the nitrogen atom in N-C2 in g-C3N4, that is, the metal nanoparticles are tightly coordinated with the g-C3N4 nanosheets, resulting in a change in the potential of the nitrogen atom. This further indicates that there is a strong interaction between the Cu / Ni dual co-catalyst and the g-C3N4 nanosheets. In addition, the high-resolution XPS spectrum of Ni 2p ( Figure 3 c) shows that the Ni element is mainly in the form of metallic Ni at 852.3 eV. 0 and 856.4 eV of Ni oxide 3+ This may be the result of partial oxidation of Ni nanoparticles exposed to air. Similarly, the Cu 2p spectrum is dominated by metallic Cu at 932.5 eV.0 composition, corresponding to Cu 2p 3 / 2 and Cu 2p 1 / 2 ( Figure 3 d). Based on XPS analysis, it is shown that the metal Cu and Ni nanoparticles have been successfully coordinated with the g-C3N4 nanosheets, which is beneficial to the further separation and transmission of photogenerated carriers.

[0038] The photocatalytic hydrogen generation performance was evaluated by using triethanolamine (TEOA) as a sacrificial agent and simulated sunlight as a light source. The specific method is as follows: 10 mg of photocatalyst was dispersed in 10 mL of triethanolamine solution (10% volume fraction) and placed in a 25 mL sealed quartz reactor. Before illumination, the reactor was completely evacuated to remove residual air in the solution. Subsequently, the reactor was illuminated using a 300W xenon lamp equipped with an AM1.5G cutoff filter. The production of hydrogen was analyzed by gas chromatograph (Shimadzu GC-2014, with argon as carrier gas). The hydrogen production was recorded every 1 hour, and the total test time was 5 hours. In addition, the cyclic stability of 3% Ni-3% Cu-C3N4 was evaluated with the same steps. It is worth noting that after the first round of experiments, the reaction system was evacuated again for 30 minutes, followed by the second, third and fourth rounds of tests, and no new samples, solvents or sacrificial agents were used during the entire cycle. The results showed that the amount of hydrogen produced by 3%Ni-3%Cu-C3N4 reached 5085.6 μmol g -1 , significantly higher than 6%Cu-C3N4, 6%Ni-C3N4 and bulk g-C3N4, such as Figure 4 In addition, Figure 4 As shown in b, 3%Ni-3%Cu-C3N4 exhibits the best hydrogen generation rate of 1017 μmol g -1 h -1 , is 6% Ni-C3N4 (257 μmol g -1 h -1 ) is 3.9 times that of 6% Cu-C3N4 (175 μmol g -1 h -1 ) and bulk g-C3N4 (16 μmol g -1 h -1 ). This enhanced hydrogen generation activity can be attributed to the synergistic effect between the Cu and Ni co-catalysts. The photocatalytic hydrogen generation activity of 3%Ni-3%Cu-C3N4 is comparable to that of the most advanced g-C3N4-based photocatalysts reported, such as Figure 4 c. In addition, the photocatalytic hydrogen generation performance of 3%Ni-3%Cu-C3N4 was maintained after at least four cycles, as shown in Figure 4 d.

[0039] Light absorption is the first step of the photocatalytic reaction, and g-C3N4, 6%Ni-C3N4, 6%Cu-C3N4, and 3%Ni-3%Cu-C3N4 were evaluated by UV-Vis diffuse reflectance spectroscopy (UV-VisDRS). Figure 5 As shown in a. All samples showed typical absorption edges in the 400-420nm region, and metal Cu and Ni significantly enhanced the light absorption range and intensity of g-C3N4. In particular, the absorption of 3%Ni-3%Cu-C3N4 in the range of 420nm to 800nm ​​was significantly enhanced compared with 6%Cu-C3N4, 6%Ni-C3N4 and bulk g-C3N4. In addition, 6%Cu-C3N4 and 3%Ni-3%Cu-C3N4 showed additional broad absorption bands in the range of 600-750nm, which can be attributed to the local surface plasmon resonance (LSPR) of metal Cu. In addition, the UV-Vis DRS results were converted by the Kubelka-Munk function, and the corresponding band gaps were calculated to be 2.23, 2.41, 2.55, and 2.71 eV, corresponding to 3% Ni-3% Cu-C3N4, 6% Ni-C3N4, 6% Cu-C3N4, and bulk g-C3N4, respectively.

[0040] In order to clarify the band structures of g-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and 3%Ni-3%Cu-C3N4, the flat band potentials were evaluated by Mott-Schottky plots. Figure 5 As shown in Figure 2b, the flat band potentials (Efb) of 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and bulk g-C3N4 are -0.80, -0.75, -0.63 and -0.59V, respectively. Generally, Efb is 0.1-0.2eV higher than the conduction band (CB) potential of n-type semiconductors. Here, it is assumed that the potential difference between the conduction band and Efb is 0.2eV, which is used to estimate the conduction band potential of the above photocatalysts. Therefore, the conduction band potentials of 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and bulk g-C3N4 are calculated to be -1.00, -0.95, -0.83 and -0.79V, respectively. At the same time, the corresponding valence band (VB) potentials were derived using the band gap and conduction band potential, which were 1.23, 1.45, 1.72, and 1.92 eV, respectively. It is worth noting that the conduction band potential of 3% Ni-3% Cu-C3N4 is significantly lower than that of 6% Ni-C3N4, 6% Cu-C3N4, and bulk g-C3N4, which may enhance its reduction ability and thus significantly promote the photocatalytic hydrogen evolution reaction. The band structure shows that these photocatalysts can thermodynamically catalyze the water decomposition reaction to generate hydrogen, and have catalytic potential under the condition of using TEOA as a sacrificial reagent.

[0041] To further investigate the photogenerated carrier dynamics in 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and bulk g-C3N4, transient photocurrent response, steady-state photoluminescence (PL) test, electrochemical impedance spectroscopy (EIS) measurement and time-resolved photoluminescence (TRPL) decay spectrum experiments were performed. Figure 5 As shown in c, the photocurrent density of 3%Ni-3%Cu-C3N4 (0.79 μA cm -2 ) is significantly higher than that of bulk g-C3N4 (0.42 μA cm -2 )、6%Cu-C3N4(0.46μA cm -2 ) and 6% Ni-C3N4 (0.65μA cm -2 ). This indicates that g-C3N4 modified with Ni / Cu dual co-catalyst has the highest number of carriers. PL results show that Cu and Ni co-catalysts help to suppress the recombination of photogenerated carriers, such as Figure 5 d, and the Ni / Cu dual co-catalyst in 3%Ni-3%Cu-C3N4 has the most significant inhibition on the recombination rate of photogenerated carriers. In addition, the EIS results show that 3%Ni-3%Cu-C3N4 exhibits the smallest semicircle radius in the Nyquist plot, indicating that the Ni / Cu dual co-catalyst effectively reduces the charge transfer resistance, such as Figure 5 e.

[0042] TRPL results were further used to study the lifetime of photogenerated carriers in 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and bulk g-C3N4, as shown in Figure 5 f and Table 1. The results show that the metal co-catalysts (Cu and Ni) effectively shortened the carrier lifetime, indicating that a new carrier transfer channel was formed from g-C3N4 to the co-catalyst. The average lifetimes of 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and bulk g-C3N4 were 5.073ns, 5.101ns, 5.807ns and 6.168ns, respectively. Compared with the control sample, the carrier lifetime of 3%Ni-3%Cu-C3N4 was significantly shortened, which may be due to the formation of a dual carrier transfer channel between g-C3N4 and Ni / Cu nanoparticles. This shows that the dual carrier transfer channel in 3%Ni-3%Cu-C3N4 contributes to the spatial separation of photogenerated carriers and accelerates the charge transfer rate.

[0043] Table 1 Exponential decay fitting parameters of fluorescence lifetime of 3%Ni-3%Cu-C3N4, 6%Ni-C3N4, 6%Cu-C3N4 and pure g-C3N4

[0044] Samples <![CDATA[τ1(ns)]]> <![CDATA[τ2(ns)]]> <![CDATA[τ3(ns)]]> <![CDATA[τ n (ns)]]> <![CDATA[3%Ni-3%Cu-C3N4]]> 0.626 2.504 11.917 5.073 <![CDATA[6%Ni-C3N4]]> 0.683 2.55 12.770 5.101 <![CDATA[6%Cu-C3N4]]> 1.020 3.847 18.453 5.807 <![CDATA[C3N4]]> 1.080 3.900 18.580 6.168

[0045] The charge dynamics and migration kinetics were analyzed using time-resolved photoluminescence (TRPL). The average lifetime was determined by applying a third-order exponential equation:

[0046]

[0047] To further elucidate the synergistic mechanism between Ni and Cu co-catalysts, the differential charge density in the Ni-Cu-C3N4 system was analyzed using Bader charge calculation based on density functional theory (DFT). Figure 6 As shown in Figure a, in the Ni-Cu-C3N4 system, a significant charge density redistribution occurs between the components. It is observed that Cu tends to lose charge, while Ni accumulates charge, which is beneficial to the spatial separation of carriers within g-C3N4. This indicates that the hot electrons generated on the Cu site first flow to g-C3N4, while the photogenerated electrons in g-C3N4 are effectively transferred to the Ni active site under simulated sunlight irradiation. Therefore, the hot electrons generated by the localized surface plasmon resonance (LSPR) effect of Cu and the photogenerated electrons generated by g-C3N4 will eventually transfer to the Ni active site through the synergistic effect of Cu and Ni.

[0048] To further investigate the effect of Cu on Ni active sites, the electronic structures of Ni alone and coexisting Ni / Cu dual co-catalysts on g-C3N4 were analyzed using partial density of states (PDOS) calculations. Figure 6 The calculation results show that the d-band center of Ni in Ni-Cu-C3N4 (-1.38 eV) is closer to the Fermi level than that of Ni-C3N4 (-1.42 eV). The upward shift of the d-band center in Ni-Cu-C3N4 reduces the antibonding state, resulting in a stronger interaction between the Ni active site and the adsorbed species (H).

[0049] Generally speaking, the Gibbs free energy of H adsorption (|ΔG *H |) is related to the hydrogen generation performance, (|ΔG *H |ΔG) values ​​close to 0 indicate an ideal binding strength for H, which is beneficial for the adsorption and subsequent desorption of hydrogen on the active sites. Then, DFT was used to calculate the Gibbs free energy of hydrogen adsorption-desorption on Ni active sites (|ΔG *H |). The calculation models include Ni-C3N4, Cu-C3N4, pure g-C3N4 and Ni-Cu-C3N4. Figure 6 As shown in c, the (|ΔG *H|) is lower than that of Ni-C3N4, Cu-C3N4 or pure g-C3N4, indicating that the presence of Cu significantly optimizes the adsorption / desorption process of H on Ni active sites and ultimately improves the H2 generation efficiency.

[0050] Figure 6 d shows a proposed mechanism of Cu / Ni synergistic enhancement of photocatalytic H2 generation. The charge-deficient Cu and charge-rich Ni co-catalysts can strengthen the electron transfer direction. Under simulated sunlight irradiation, metallic Cu generates hot electrons through the localized surface plasmon resonance (LSPR) effect, while g-C3N4 simultaneously generates photogenerated electrons. These hot electrons generated on the Cu site are first transferred to g-C3N4 and transferred to the active Ni site together with the electrons generated by g-C3N4 under light irradiation. The upward shift of the d-band center of Ni in Ni-Cu-C3N4 reduces the antibonding state, resulting in a stronger interaction between the Ni active site and the adsorbed H, allowing the accumulated electrons to further reduce H. The lowest |ΔGH| value promotes the adsorption of H and the subsequent hydrogen desorption, thereby improving the photocatalytic H2 generation performance.

[0051] Therefore, the present invention adopts a method for preparing a Cu / Ni dual-promoter based on g-C3N4 of the above structure, wherein nickel (Ni) is used as an electron pool and the outermost electron configuration is 3d 8 4s 2 , which can effectively collect photogenerated electrons for further use in the generation of H2. The outermost electron configuration of copper (Cu) is 3d 10 4s 1 , exhibiting local surface plasmon resonance (LSPR) under sunlight irradiation, which can generate additional high-energy hot electrons to participate in the photocatalytic release of H2. In the present invention, Cu with LSPR effect and Ni as an electron pool are co-modified on g-C3N4 through an in-situ reduction process to improve the photocatalytic hydrogen production performance of g-C3N4. The band structure shows that this Cu / Ni co-modified g-C3N4 can thermodynamically catalyze the photocatalytic water decomposition reaction to produce hydrogen, and uses TEOA as a sacrificial reagent. Performance studies have shown that the dual Cu / Ni co-catalyst enables g-C3N4 to achieve an impressive photocatalytic H2 evolution rate of 1017μmol g -1 h -1, which is 63.5 times that of bulk g-C3N4. Carrier dynamics studies show that Cu / Ni co-modified g-C3N4 exhibits the largest number of photogenerated electrons, the lowest carrier recombination rate, the lowest charge transfer resistance, and the fastest charge transfer speed. The unique Cu co-catalyst not only provides hot electrons, but also creates an electron-deficient state, which helps to transfer charges to electron-rich Ni active sites through g-C3N4. In addition, the presence of Cu causes the d-band center of the Ni active site to shift upward, resulting in a stronger interaction between Ni and adsorbed H species. The Cu co-catalyst also optimizes the adsorption / desorption energy of H on the Ni active site, significantly improving hydrogen generation. The excellent H2 generation performance is attributed to the synergistic effect between Cu and Ni co-catalysts, highlighting their optimal synergistic effect as key factors. The study reveals that the synergistic effect between Cu and Ni co-catalysts is a key factor in achieving efficient hydrogen production from g-C3N4.

[0052] It should be noted that all calculations in the present invention are performed using the CASTEP module. The spin-polarized density functional theory (DFT) is calculated using the Perdew-Burke-Ernzerh of (PEB) function under the generalized gradient approximation (GGA). The plane wave cutoff energy is set to 400 eV. The valence electron configurations of the atoms involved are 4s3d (Cu), 4s 2 3d 8 (Ni), 2s 2 2p 2 (C), 2s 2 2p 3 (N) and 1s 1 (H). The vacuum layer height is set to To eliminate the interaction between adjacent layers. For geometry optimization and energy calculations, a 1×2×1 Fine-point center k-point grid in the Brillouin zone is used. During geometry optimization, the top atoms are allowed to fully relax, while the bottom 2 layers of atoms remain fixed. The G value is defined as follows: G = EA-B–(EA+EB), where EA-B is the total energy calculated by DFT, EA is the energy of individual A, and EB is the energy of individual B.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a Cu / Ni dual-promoter based on g-C3N4, characterized in that: The steps include: Step 1, preparation of bulk g-C3N4: bulk g-C3N4 is prepared by direct polycondensation of dicyandiamide by heat treatment under atmospheric pressure; Step 2, preparation of Ni-Cu-C3N4: First, the bulk phase g-C3N4 is peeled off into a thin sheet structure; after the treatment, CuSO4·5H2O and Ni(NO3)2·6H2O are added to the suspension respectively; then, NaBH4 alkaline solution is prepared, and the NaBH4 alkaline solution is added dropwise to the Cu-containing 2+ and Ni 2+ The mixed solution was stirred continuously for 30 minutes to ensure complete reduction of metal ions. Finally, the precipitate was washed with distilled water and alcohol several times and dried. The obtained sample was named 3%Ni-3%Cu-C3N4.

2. The method for preparing a Cu / Ni dual promoter based on g-C3N4 according to claim 1, characterized in that: The specific process of preparing bulk g-C3N4 in step 1 is as follows: 14 g of dicyandiamide is placed in an alumina crucible with a lid, heated to 550°C in a muffle furnace at a heating rate of 5°C / min, and maintained for 3 hours. After natural cooling, yellow bulk g-C3N4 is obtained for subsequent experiments.

3. The method for preparing a Cu / Ni dual promoter based on g-C3N4 according to claim 2, characterized in that: The specific processing process of exfoliating the bulk phase g-C3N4 into a thin flake structure in the step 2 is as follows: 200 mg of bulk phase g-C3N4 is dispersed in 60 mL of deionized water and magnetically stirred for 1 hour; then the suspension is ultrasonically treated for 2 hours to exfoliate the bulk phase g-C3N4 into a thin flake structure at room temperature.

4. The method for preparing a Cu / Ni dual-promoter based on g-C3N4 according to claim 3, characterized in that: In the step 2, 16.3 mg CuSO4·5H5O and 18.9 mg Ni(NO3)2·6H2O were added.

5. The method for preparing a Cu / Ni dual promoter based on g-C3N4 according to claim 4, characterized in that: The method for preparing the NaBH4 alkaline solution in step 2 is to dissolve 1 g of NaOH in 20 mL of distilled water, and then add 0.14 g of NaBH4 to prepare the alkaline solution.

6. The method for preparing a Cu / Ni dual-promoter based on g-C3N4 according to claim 5, characterized in that: The condition for complete reduction in step 2 is that obvious bubbles are generated and the color of the solution changes from blue to light yellow.

7. The method for preparing a Cu / Ni dual promoter based on g-C3N4 according to claim 6, characterized in that: The drying condition in the step 2 is drying in a vacuum oven at 50° C. for 3 hours.

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