Pd / L-BCN photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a Pd / L-BCN photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalysts. The preparation method of the Pd / L-BCN photocatalyst comprises the following steps: preparing a boron nitride precursor by taking melamine and boric acid as raw materials, uniformly mixing lithium chloride serving as a template agent with the boron nitride precursor, and calcining to obtain an L-BCN nanosheet; and dipping the L-BCN nanosheet in a palladium salt solution, and then reacting under the action of a reducing agent to obtain the Pd / L-BCN photocatalyst. The preparation method provided by the invention is simple and easy to implement, and the prepared Pd / L-BCN catalyst can efficiently catalyze formic acid to produce hydrogen and has excellent cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalysts, and particularly to a Pd / L-BCN photocatalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Carbon dioxide is one of the main greenhouse gases released by industries, power plants, fuel combustion, and other human activities, and it is closely related to environmental problems. Hydrogen has become a widely recognized and promising clean energy source. Formic acid has characteristics such as high hydrogen content (4.4 wt%), high volume capacity (53 g / L), stability, low toxicity, and wide availability, and is considered to be one of the most promising hydrogen carriers, playing an important role in the overall realization of a hydrogen economy. However, the production of hydrogen from formic acid requires highly selective and efficient catalysts.

[0003] In recent years, palladium catalysts have shown particular potential. However, the performance of such catalysts depends to a large extent on the nature of their supports, and the support itself can regulate the metal-support interaction. Therefore, choosing the appropriate modification technology and appropriate support material is crucial for maximizing catalytic performance. Summary of the Invention

[0004] Based on the above, the object of the present invention is to provide a Pd / L-BCN photocatalyst, a preparation method thereof, and an application thereof.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is a preparation method of a Pd / L-BCN photocatalyst, comprising the following steps:

[0007] Using melamine (C3H6N6) and boric acid (H3BO3) as raw materials to prepare a boron nitride precursor, and then using lithium chloride (LiCl) as a template agent to mix evenly with the boron nitride precursor and calcine to obtain L-BCN nanosheets;

[0008] Immersing the L-BCN nanosheets in a palladium salt solution, and then reacting under the action of a reducing agent to obtain the Pd / L-BCN photocatalyst.

[0009] In the present invention, the preparation of the boron nitride precursor using melamine and boric acid as raw materials is specifically: mixing melamine, boric acid, and a solvent evenly and reacting at 90 °C for 30 min. The solvent in the present invention is water; the present invention does not make special limitations on the amount of water used, and the amount used can satisfy the reaction of melamine and boric acid. After the reaction, the step of drying the obtained product is further included; the drying temperature is 60 °C and the time is 12 h.

[0010] In the present invention, the mass ratio of melamine to boric acid is 4:(1 - 4) (preferably 4:1, 4:2, 4:3 or 4:4); the mass ratio of the boron nitride precursor to lithium chloride is 1:5.

[0011] In the present invention, there is no special limitation on the way of uniformly mixing lithium chloride and the boron nitride precursor, and the well-known technical means in the art can be selected, for example: grinding.

[0012] In the present invention, the calcination procedure is as follows: heating to 380°C at a rate of 6.8°C / min, holding for 120 min, and then heating to 550°C at a heating rate of 6.8°C / min and holding for 240 min. After the calcination, the steps of washing and drying the obtained product are further included.

[0013] In the present invention, the ratio of the L-BCN nanosheets to Pd in the palladium salt solution is 0.2 g:(0.1 - 0.4) mmol (preferably 0.2 g:0.1 mmol, 0.2 g:0.2 mmol, 0.2 g:0.3 mmol or 0.2 g:0.4 mmol).

[0014] In the present invention, the palladium salt solution is a K2PdCl4 solution.

[0015] In the present invention, the impregnation time is 24 h and the temperature is room temperature.

[0016] In the present invention, the reducing agent is sodium borohydride; the mass ratio of sodium borohydride to L-BCN nanosheets is 0.16:0.2.

[0017] In the present invention, when the reaction is carried out under the action of the reducing agent, the reaction temperature is -3°C and the time is 5 h; after the reaction, the steps of collecting the product and washing and drying the obtained product are further included.

[0018] The second technical solution of the present invention is a Pd / L-BCN photocatalyst prepared by the above preparation method.

[0019] The third technical solution of the present invention is an application of the above Pd / L-BCN photocatalyst in catalyzing hydrogen production from formic acid (FA).

[0020] In the method for catalyzing hydrogen production from formic acid by the Pd / L-BCN photocatalyst, under light irradiation, when the temperature of the reaction system is 25°C - 45°C, the concentration of sodium formate (SF) is 0.5 - 1.5 mmol, and the catalyst dosage is 25 - 100 mg, hydrogen production from formic acid is catalyzed.

[0021] The present invention discloses the following technical effects:

[0022] In the present invention, melamine and boric acid are used as precursors, lithium chloride is used as a templating agent, and BCN nanosheets are synthesized by a template method. Then, metal Pd is loaded by an impregnation reduction method to prepare a Pd / L-BCN catalyst with a layered structure. The preparation method is simple and easy to implement.

[0023] The Pd / L-BCN catalyst prepared in the present invention can efficiently catalyze hydrogen production from formic acid and has excellent cyclic stability. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 Among them, (a), (b), and (c) are SEM images of the Pd / L-BCN catalyst in Example 1 at different magnification factors, (d), (e), and (f) are TEM images of the Pd / L-BCN catalyst in Example 1 at different magnification factors, (g) is a lattice fringe calculation diagram, and (h) is the HADDF-STEM image of the Pd / L-BCN catalyst and the corresponding mapping diagrams of elements B, C, N, and Pd.

[0026] Figure 2 XRD patterns (a) and FT-IR spectra (b) of Pd / L-BCN, Pd / BCN, and L-BCN in Example 1.

[0027] Figure 3 XPS full spectra of Pd / L-BCN and Pd / BCN in Example 1.

[0028] Figure 4 XPS spectra of the (a) B 1s region, (b) C 1s region, (c) N 1s region, and (d) Pd 3d region of Pd / L-BCN and Pd / BCN in Example 1.

[0029] Figure 5 Ultraviolet-visible light absorption spectra (a), band gap energies (b), and XPS valence band spectra (c) of Pd / L-BCN and Pd / BCN in Example 1, and (d) band structure schematic diagram.

[0030] Figure 6 Mott-Schottky diagrams of Pd / L-BCN (a) and Pd / BCN (b) in Example 1.

[0031] Figure 7Photoluminescence spectra (a), time-resolved PL decay spectra (b), EIS Nyquist plots (c), and transient photocurrent response spectra (d) of Pd / L-BCN and Pd / BCN in Example 1.

[0032] Figure 8 For effect verification, (a) Relationship between time and volume of hydrogen production from formic acid decomposition catalyzed by different amounts of boric acid doping under visible light irradiation, and (b) corresponding TOF values of formic acid decomposition.

[0033] Figure 9 For effect verification, (a) Relationship between time and volume of hydrogen production from FA decomposition catalyzed by different amounts of metals under visible light irradiation, and (b) corresponding TOF values of FA decomposition.

[0034] Figure 10 For effect verification, (a) Relationship between time and volume of hydrogen production from FA decomposition catalyzed by different salt templates (LiCl, KCl, NaCl, LiF) under visible light conditions, and (b) comparison of corresponding TOF values of the catalysts.

[0035] Figure 11 For effect verification, (a) Relationship between time and volume of hydrogen production from FA decomposition catalyzed by Pd / L-BCN and Pd / BCN under light and dark conditions, and (b) corresponding TOF values of FA decomposition.

[0036] Figure 12 For effect verification, (a) Pd / L-BCN under light, (c) Pd / L-BCN under dark, relationship between hydrogen production amount and reaction time of FA decomposition reaction at different temperatures, and (b) and (d) corresponding Arrhenius plots of lnk vs 1000 / T.

[0037] Figure 13 For effect verification, (a) Relationship between gas volume and time of hydrogen production from formic acid decomposition catalyzed by different amounts of Pd / L-BCN under light conditions, and (b) logarithmic relationship between gas generation rate and catalyst dosage.

[0038] Figure 14 For effect verification, rate curves of hydrogen production from formic acid decomposition catalyzed by Pd / L-BCN with different concentrations of SF solution at 30℃ under light conditions.

[0039] Figure 15 For effect verification, isotope labeling experiment of hydrogen production from formic acid on Pd / L-BCN catalyst: (a) Curve of gas volume change with time generated using different isotope-labeled reagents, and (b) kinetic isotope effect (KIE) data.

[0040] Figure 16For performance verification, (a) cyclic performance diagram of the FA hydrogen production reaction catalyzed by Pd / L-BCN under light conditions, (b) Pd / L-BCN under dark conditions, and (c) Pd / BCN under light conditions.

[0041] Figure 17 For performance verification, (a) comparison of the catalyst XRD before and after cycling of Pd / L-BCN, and (b), (c), (d), (e), (f) XPS comparison spectra of Pd / L-BCN after the cycling reaction. Detailed implementation manners

[0042] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0043] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0045] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0046] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0047] The relevant experiments and methods involved in the present invention are as follows:

[0048] 1. Characterization methods:

[0049] (1) Transmission Electron Microscope (TEM): The microscopic morphology analysis of the sample was completed with the JEM-2100F field emission transmission electron microscope of JEOL.

[0050] (2) Scanning Electron Microscope (SEM): The catalyst sample was characterized by a TESCAN MIRA LMS field emission scanning electron microscope (SEM) from the Czech Republic. In the sample pretreatment stage, the powder sample was fixed on the sample stage by conductive adhesive, effectively ensuring the conductivity of the sample and the stability of observation.

[0051] (3) Powder X-ray Diffraction Pattern (XRD): A Rigaku SmartLab SE powder diffractometer was used for phase identification, equipped with a copper target (CuKα, ), and the scanning rate was 1°·min -1 .

[0052] (4) X-ray Photoelectron Spectroscopy (XPS): The chemical state of surface elements of the sample was analyzed by a Thermo Fisher K-Alpha small area electron spectrometer.

[0053] (5) Ultraviolet-Visible Diffuse Reflectance Absorption Spectroscopy (UV-vis DRS): The light absorption characteristics of the sample were measured using a Shimadzu UV-3600 spectrophotometer, and data were collected in diffuse reflection mode.

[0054] (6) Photoluminescence Spectroscopy (PL): Carrier recombination information was obtained with an Edinburgh FLS1000 fluorescence spectrometer, and the tests included time-resolved fluorescence decay curves and steady-state emission spectra.

[0055] (7) Photoelectric Performance Test: The photoelectrochemical properties were tested using a CHI660E electrochemical workstation. For the transient photocurrent response, the test light source was a xenon lamp > 400 nm, and the light illumination time interval was 20 s (20 s of light on, 20 s of light off), and more than 4 cycles of tests were carried out; the test frequency range of electrochemical impedance (EIS) was 0.1 Hz - 100 KHz, and the electrolyte was 2.5 mmol·L -1 potassium ferricyanide solution; for the Mott-Schottky test, 0.5 M Na2SO4 solution was used as the base solution, the potential range was -1 to 1 V, and multi-frequency scanning was carried out at 1000 - 3000 Hz.

[0056] 2. Hydrogen production experiment by formic acid decomposition:

[0057] The dosage of the catalyst used in the catalytic reaction of the present invention is as follows: Pd / L-BCN: 100 mg; the reactor is a specially designed photocatalytic reactor, and the reaction temperature is controlled by a low-temperature constant temperature bath. The mixed solution of HCOOH and HCOONa is injected into the photoreactor with a medical syringe, and the photocatalytic decomposition reaction of formic acid starts. The reaction rate of hydrogen production by formic acid decomposition is calculated based on the recorded gas volume and reaction time. In this experiment, the influence of a single variable on the hydrogen production rate by formic acid decomposition was explored by the method of controlling variables.

[0058] 3. Catalyst recycling stability test

[0059] Based on the experimental data, catalysts with better performance were selected and subjected to a recycling stability test of the catalytic reaction. Under the same reaction conditions, after a catalytic reaction was completed, the reacted catalyst was centrifuged, washed with water, dried, and ground to obtain the recycled catalyst. The first experimental operation was repeated, and the recycling stability of the catalyst was tested by comparing the reaction rate of the recycled catalyst for hydrogen production by formic acid decomposition.

[0060] 4. Catalyst performance evaluation parameters

[0061] (1) Activation energy (E a )

[0062] The activation energy reflects the minimum energy threshold required for reactant molecules to transform into the activated state, and its value directly reflects the difficulty of the chemical reaction. The E a in this article is calculated from the Arrhenius equation (1):

[0063]

[0064] This equation reveals the internal relationship between the rate constant k and temperature. A is the pre-exponential factor, R is the molar gas constant, and T is the thermodynamic temperature. From the formula, when the activation energy decreases, the reaction energy barrier decreases, and molecules are more likely to cross the energy barrier, thus significantly enhancing the reaction kinetic rate.

[0065] (2) Turnover frequency (TOF)

[0066] TOF is a key parameter characterizing the amount of product converted per unit mass or mole of the catalyst per unit time, and its value can directly reflect the catalytic performance of the catalyst. The TOF value in this article is calculated according to Equation (2):

[0067]

[0068] In the formula, n H2 is the total number of moles of H2 released. n metal corresponds to the total number of moles of the metal component in the catalyst, and t is the reaction time.

[0069] The technical solutions described in the present invention are conventional solutions in the art unless otherwise specified. The reagents or raw materials used are commercially available or publicly disclosed unless otherwise specified.

[0070] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments. However, the content of the present invention is not limited to the following embodiments.

[0071] Example 1

[0072] (1) Preparation of L-BCN: Weigh 0.62 g of H3BO3 and place it in a 50 mL beaker. Add a rotor, then add 3 mL of distilled water to it. Place it in a water bath at 90 °C and stir until the boric acid is completely dissolved. Immediately add a mixed solution of 1.26 g of C3H6N6 and 4 mL of distilled water and stir evenly. Keep it at 90 °C for 30 min, then place it in a blast drying oven at 60 °C and dry for 12 h. Grind and weigh to obtain the precursor.

[0073] Weigh 2.00 g of the precursor and 10.00 g of LiCl in a mortar, quickly grind until they are evenly mixed, then spread them evenly in a quartz boat and put it into a muffle furnace for roasting. Heat it to 380 °C at a rate of 6.8 °C / min in static air, keep it warm for 120 min, then heat it to 550 °C at the same heating rate and keep it warm for 240 min. The program ends. After cooling to room temperature, collect the yellow flaky solid, put it into a 500 mL beaker, add 500 mL of deionized water, place it on a magnetic stirrer and stir vigorously for 24 h. After that, perform suction filtration, then put the solid product into a 500 mL beaker for secondary water washing for 24 h. After that, perform suction filtration again. The obtained solid product is put into a blast drying oven to dry, ground and weighed, and then sealed and stored for later use.

[0074] The preparation method of BCN is the same as the above steps, except that the addition of LiCl and the water washing with deionized water are omitted. The yellow product (BCN) obtained by roasting is directly ground and weighed, and then sealed and stored.

[0075] (2) Preparation of Pd / L-BCN: Weigh 0.20 g of the support and place it at the bottom of the nested cup. Then add the K2PdCl4 solution (in the added K2PdCl4 solution, the molar amount of K2PdCl4 is 0.40 mmol), add a magnetic stir bar, seal it with plastic wrap, and place the nested cup on a magnetic stirrer and stir at room temperature for 24 h. Then connect a low-temperature constant temperature bath, and add a reducing agent (0.16 g of sodium borohydride dissolved in 4 mL of deionized water) at -3 °C, and stir and reduce at a constant temperature for 5 h. After the reduction is completed, centrifuge the mixture in the nested cup in a high-speed centrifuge, remove the supernatant, and place the obtained solid product in a blast drying oven to dry for 12 h. After sufficient grinding, a black powdery catalyst is obtained (when the support is L-BCN, the obtained catalyst is Pd / L-BCN; when the support is BCN, the obtained catalyst is Pd / BCN).

[0076] Example 2

[0077] The only difference from Example 1 is that 0.62 g of H3BO3 and 1.26 g of C3H6N6 are adjusted to 0 g of H3BO3 and 1.26 g of C3H6N6, 0.31 g of H3BO3 and 1.26 g of C3H6N6, 0.93 g of H3BO3 and 1.26 g of C3H6N6, 1.24 g of H3BO3 and 1.26 g of C3H6N6, and other steps and parameters are the same as those in Example 1 (that is, the mass ratio of boric acid to melamine is adjusted from 2:4 to 0:4, 1:4, 3:4, 4:4). The obtained Pd / L-BCN is denoted as Pd / L-BCN(x), where x represents the mass ratio of boric acid to melamine.

[0078] Example 3

[0079] The only difference from Example 1 is that in the added K2PdCl4 solution, the molar amount of K2PdCl4 is adjusted from 0.4 mmol to 0.1 mmol, 0.2 mmol, 0.3 mmol, and other steps and parameters are the same as those in Example 1. The obtained Pd / L-BCN is denoted as Pd / L-BCN-y, where y represents the molar amount of K2PdCl4.

[0080] Example 4

[0081] The only difference from Example 1 is that LiCl is adjusted to KCl, NaCl, and LiF, and other steps and parameters are the same as those in Example 1. The obtained Pd / L-BCN are respectively denoted as Pd / L-BCN-KCl, Pd / L-BCN-NaCl, and Pd / L-BCN-LiF.

[0082] Characterization:

[0083] The morphologies, XRD, etc. of the catalysts obtained with different raw material ratios are similar. Taking the catalyst obtained in Example 1 as an example, it was characterized.

[0084] As Figure 1 In (a)-(c), the morphologies of the catalyst Pd / L-BCN at different magnifications of the scanning electron microscope are shown. It can be seen that the catalyst exhibits an obvious layered structure with different degrees of wrinkles, which exposes more edge active sites of the catalyst and is beneficial to the adsorption of reactant molecules and charge transfer. Figure 1 In (d)-(f), the images of the catalyst Pd / L-BCN at different magnifications of the transmission electron microscope are shown. It can be further seen that the catalyst is a wrinkled layered structure. At the same time, Figure 1 In (g), the lattice fringe spacing of Pd measured by the high-resolution TEM characterization diagram is 0.224 nm, corresponding to the (111) crystal plane of Pd, further confirming the successful loading of Pd nanoparticles in the catalyst. Figure 1 In (h), it is the high-angle annular dark field-transmission electron microscope image (HAADF-STEM) of Pd / L-BCN and the elemental mapping diagrams of B, C, N, and Pd. It can be seen from the figure that the four elements are evenly distributed, indicating that boric acid has been successfully incorporated into the carbon nitride framework, and the Pd nanoparticles are evenly loaded on the carrier and there is no agglomeration on the surface, verifying the successful synthesis of the catalyst Pd / L-BCN.

[0085] Figure 2 In (a), it is the XRD pattern of the catalysts Pd / L-BCN, Pd / BCN, and the carrier L-BCN. It can be observed from the figure that a relatively broad diffraction peak can be detected at 2θ = 27° for all three samples, indicating a structure similar to graphene. By observing the patterns of the two samples Pd / L-BCN and Pd / BCN, diffraction peaks appear at 2θ = 40.12°, 46.67°, and 68.12°, which correspond to the (111), (200), and (220) crystal planes of Pd (PDF#46-1043). Combining the analysis of TEM, it can be known that the metal Pd nanoparticles are successfully loaded on the carrier. Fourier transform infrared (FT-IR) spectroscopy was used to test the chemical structure of the samples. Figure 2 In (b), it is the FT-IR spectrum of the catalysts Pd / L-BCN, Pd / BCN, and the carrier L-BCN. It can be observed from the figure that peaks only appear at 640 cm -1 for the carrier L-BCN and the catalyst Pd / L-BCN, which may be related to LiCl; the peaks appearing at 801 cm -1 and 1389 cm -1 correspond to the out-of-plane B-N-B bending vibration and the in-plane B-N stretching vibration, respectively; the peak appearing at 1634 cm -1 is attributed to the stretching vibration of C-N; in the range of 3200 - 3450 cm-1 The broad peak observed at [location] corresponds to the stretching vibration of N-H.

[0086] X-ray photoelectron spectroscopy (XPS) was used to analyze the surface chemical composition, chemical state, and electronic structure of the catalyst. Figure 3 Figures [X] are the full XPS spectra of Pd / L-BCN and Pd / BCN, in which the signals of B, C, N, O, and Pd can be clearly detected. B, C, N, and Pd mainly originate from the catalyst, and O may come from the carrier and the oxidation of the metal surface. In the high-resolution B1s spectrum of the Pd / L-BCN catalyst ( Figure 4 in (a)), the fitting peaks at 190.9 eV and 191.9 eV are attributed to B-N and B-O bonds, indicating that boron atoms form covalent bonds with nitrogen and oxygen, which helps to enhance the structural stability of the carrier. In the C1s spectra of the Pd / L-BCN and Pd / BCN catalysts ( Figure 4 in (b)), the peaks at 284.8 eV, 285.8 eV, and 288.0 eV correspond to C-C, C-NH, and N-C=N bonds respectively. The existence of these peaks confirms the synergistic effect of the sp 2 hybrid structure of the carbon material and nitrogen doping. In the N1s spectra of the Pd / L-BCN and Pd / BCN catalysts ( Figure 4 in (c)), the peak at 398.6 eV is attributed to the B-N bond, and the peak at 400.2 eV corresponds to the -NH2 bond, which is consistent with the FT-IR characterization results of the catalyst. According to previous studies, the -NH2 group can act as a proton scavenger to promote the cleavage of the O-H bond, thus improving the catalytic performance of FA hydrogen production. Figure 4 Figure (d) is the Pd 3d XPS spectrum of the Pd / L-BCN and Pd / BCN catalysts. By observing the Pd 3d fitting peaks of these two catalysts, they can be divided into Pd 0 and Pd 2+ , Pd 0 helps to break the C-H bond, while Pd 2 + promotes the adsorption of FA ions. The coexistence of these two states plays a key role in the catalytic ability of Pd-based catalysts in FA hydrogen production. In the Pd peaks of Pd / L-BCN, they can be divided into Pd 0 (335.8 eV and 340.8 eV) and Pd 2+ (337.9 eV and 343.0 eV), while for Pd / BCN, its Pd peaks can be divided into Pd 0 (335.2 eV and 340.5 eV) and Pd 2+ (337.2 eV and 342.3 eV). Comparing the two catalysts, the binding energy (BE) of Pd 2+ shifts to a higher binding energy value by 0.3 - 0.6 eV, Pd0 The BE shifts towards higher binding energy values by 0.7 - 0.8 eV, indicating that the addition of LiCl induces charge transfer from Pd to the support (L-BCN), and indirectly suggesting the presence of strong metal-support interactions in the catalyst, which affects the activity of Pd. In addition, the positive shift of the binding energy is usually associated with a decrease in electron density, implying that the electron interaction between Pd and the electron-rich support may optimize the adsorption / desorption behavior of the active sites. This finding provides a theoretical basis for regulating the electronic structure of Pd through support modification and then designing highly efficient hydrogen production catalysts for FA.

[0087] As Figure 5 shown in (a) below, both Pd / L-BCN and Pd / BCN exhibit significant light absorption capabilities in the visible light range of 400 - 800 nm. To deeply reveal the optical bandgap characteristics of the materials, the Kubelka-Munk function was used to process the data, and the bandgaps of Pd / L-BCN and Pd / BCN were calculated to be 2.63 eV and 2.76 eV respectively ( Figure 5 in (b) below), and the bandgap energy decreased significantly (ΔEg = 0.13 eV), confirming that the synergistic effect of the d-orbital electrons of metallic Pd and the support may form sub-energy levels in the forbidden band, reducing the bandgap and thus expanding the visible light response range of the materials. Further, through valence band spectrum analysis of X-ray photoelectron spectroscopy (XPS), the positions of the valence band spectra of the two samples of Pd / L-BCN and Pd / BCN were measured to be 1.55 eV and 1.57 eV respectively ( Figure 5 in (c) below). Combining the ultraviolet bandgap data to draw a band structure schematic diagram, as Figure 5 shown in (d) below, the bottom of the conduction band of Pd / L-BCN shifts negatively compared to Pd / BCN, indicating that Pd / L-BCN has stronger photo-generated electron reduction ability, which is beneficial to the photocatalytic reduction reaction. This can be attributed to the introduction of the salt template to improve the utilization rate of carriers, effectively suppressing electron-hole recombination, and thus promoting the improvement of the photothermal catalytic reaction efficiency.

[0088] In the Mott-Schottky (M-S) test, the slopes of the curves at different frequencies were used to calculate the carrier concentration, and the intercept of the curve with the potential axis corresponds to the flat band potential (E fb ) of the catalyst under specific conditions, as Figure 6 shown below. The slopes of the curves of the catalysts Pd / L-BCN and Pd / BCN are both positive, indicating that both catalysts exhibit n-type semiconductor characteristics. During the experiment, the reference electrode selected was the Ag / AgCl electrode, and the obtained conduction band potentials were -1.28 V (Pd / L-BCN) and -1.39 V (Pd / BCN). According to the Nernst equation E fb = E Ag / AgCl + E 0Ag / AgCl The value of E can be calculated fb with respect to the position of the normal hydrogen electrode (NHE), where at room temperature, the value of E 0 Ag / AgCl is approximately 0.197 V. Through calculation, it can be known that the E of Pd / L-BCN fb is -1.08 V vs NHE, and the E of Pd / BCN fb is -1.19 V vs NHE. For an n-type semiconductor, E fb is close to the position of the bottom of the conduction band. Therefore, the conduction band edge of Pd / L-BCN is approximately 0.11 V higher than that of Pd / BCN, indicating that it has stronger thermodynamic reduction ability. This result is consistent with the data obtained from ultraviolet-visible absorption spectroscopy and valence band spectroscopy. From the calculation results, it can also be seen that the flat band potential of Pd / L-BCN is more positive than that of Pd / BCN, indicating that the introduction of LiCl may make the catalyst bandgap smaller, which is more conducive to electron transport. In photocatalysis, a more positive flat band potential may mean a higher conduction band edge, inhibiting the carrier recombination of the passivation layer on the catalyst surface and improving the utilization rate of photogenerated electrons, thereby enhancing the catalyst activity in the photocatalytic decomposition of formic acid to produce hydrogen.

[0089] As shown in Figure 7 (a) in is the photoluminescence (PL) spectra of two catalysts, Pd / L-BCN and Pd / BCN. The PL intensity is usually related to the recombination efficiency of photogenerated electron-hole pairs in the material. By comparing Pd / L-BCN and Pd / BCN, it can be found that the PL intensity of Pd / L-BCN is the weakest, indicating that the radiative recombination efficiency of photogenerated electron-hole pairs decreases, which reflects the improvement of the separation efficiency of photogenerated carriers and the inhibition of the recombination process. This phenomenon can be attributed to the directional charge separation effect induced by the layered structure of L-BCN and the promotion of interfacial charge transfer by Pd single atoms as electron capture centers. The time-resolved PL decay spectra Figure 7 ((b) in) reflect the survival time of photogenerated electron-hole pairs. The average lifetime of Pd / L-BCN is 0.69 ns, and the average lifetime of Pd / BCN is 0.73 ns. Compared with each other, the average lifetime of Pd / L-BCN is slightly shorter. Combining the PL intensity analysis, this shortening of the lifetime is not due to accelerated recombination, but because the carriers are consumed faster through non-radiative pathways (such as surface catalytic reactions). This synergistic effect indicates that the catalyst Pd / L-BCN has better charge separation-migration-reaction coupling kinetics. The arc radius in the electrochemical impedance spectroscopy (EIS) is usually related to the charge transfer impedance (Rct), as shown in Figure 7As shown in Fig. (c), compared with Pd / BCN, the former has the smallest arc radius of Pd / L-BCN, indicating that the charge transfer impedance is smaller, and the migration and transfer frequency of charges in the catalyst is higher. This may be related to the layered structure of Pd / BCN, which may provide a continuous charge transport channel and reduce the interfacial barrier. The transient photocurrent response spectrum is usually directly related to the generation, separation, and migration efficiency of photo-generated carriers. As Figure 7 shown in Fig. (d), Pd / L-BCN has a larger and stable transient photocurrent response, indicating that Pd / L-BCN can effectively accelerate charge separation and transfer.

[0090] Effect verification:

[0091] Weigh 100 mg of the catalyst and pour it obliquely into the bottom of the photocatalytic reactor. Add a magnetic stir bar, seal the reactor top cover by the liquid seal method, then place the reactor on a magnetic stirrer, connect a low-temperature constant temperature bath, set the reaction temperature. After the temperature is stable, turn on the xenon lamp to focus the light source center on the exact center of the photoreactor. Check the airtightness of the reactor. Inject a 2 mL mixed solution of HCOOH (3 mmol) and HCOONa (1 mmol) preheated at the same temperature into the reactor with a syringe, and the photocatalytic formic acid decomposition reaction starts. Record the reaction time from the discharge of the first bubble. Record the time every time 5 mL of gas is generated until no bubbles are generated and stop timing.

[0092] In this experiment, the influence of a single variable on the hydrogen production rate of ammonia borane decomposition was explored by the method of controlling variables. By changing the amount of Pd metal loaded on the catalyst (0.10 mmol, 0.20 mmol, 0.30 mmol, 0.40 mmol), the concentration of sodium formate (0.00 mmol, 0.50 mmol, 1.00 mmol, 1.50 mmol), the amount of catalyst (25 mg, 50 mg, 75 mg, 100 mg), the reaction temperature (25 °C, 30 °C, 35 °C, 40 °C, 45 °C), the boron doping ratio (0:4, 1:4, 2:4, 3:4, 4:4), different salt templates (LiCl, KCl, NaCl, LiF), different solvents (HCOOD, DCOOH, D2O), and the presence or absence of light, the influence of each factor on the hydrogen production rate of the catalyst for formic acid decomposition was explored.

[0093] 1. Influence of boric acid doping amount on the performance of the catalyst

[0094] Taking the formic acid decomposition to produce hydrogen as the reaction model, the action rules of different ratios of boric acid and melamine (Example 1 and Example 2) on the catalytic performance of the catalyst were systematically investigated. The experiment was carried out under the constant temperature condition of 30 °C, and a photocatalytic system was constructed with a xenon lamp light source. Comparative studies were carried out by controlling a single variable. As Figure 8(As shown in (a) of Fig. 0:4, 1:4, 2:4, 3:4, 4:4 in the figure respectively represent Pd / L-BCN(0:4), Pd / L-BCN(1:4), Pd / L-BCN, Pd / L-BCN(3:4), Pd / L-BCN(4:4)). The experimental results show that when the mass ratio of boric acid to melamine increases from 0:4 to 2:4, the formic acid decomposition activity of the catalyst is significantly improved. According to XPS characterization, this is attributed to the synergistic effect of boric acid and melamine. The B-O sites in boric acid can optimize the position of the metal d-band center, while the nitrogen-doped carbon skeleton formed by the pyrolysis of melamine effectively improves the electron transport ability. When the ratio increases to 3:4 and 4:4, the catalytic performance shows a similar level, indicating that the active sites tend to be saturated. As Figure 8 shown in (b) of Fig., it is found through TOF value analysis that the catalytic activity of the catalyst is optimal at a ratio of 2:4, and the corresponding TOF value is 1339.29 h -1 . Based on the above experimental results, the subsequent research will use a mass ratio of 2:4 of boric acid to melamine as the optimization condition for in-depth exploration.

[0095] 2. Influence of different Pd loadings on the performance of the catalyst

[0096] Explore the influence of different metal loadings (0.1 mmol, 0.2 mmol, 0.3 mmol, 0.4 mmol, i.e., Example 1 and Example 3) of the catalyst on the performance of hydrogen production by catalytic decomposition of formic acid. Under the condition that the reaction temperature is 30 °C, a xenon lamp is used as the light source to test the ability of a series of catalysts with different metal loadings synthesized to catalyze the decomposition of formic acid to produce hydrogen. Figure 9 (In the figure, n metal = 0.1 mmol, n metal = 0.2 mmol, n metal = 0.3 mmol, n metal = 0.4 mmol respectively represent Pd / L-BCN-0.1, Pd / L-BCN-0.2, Pd / L-BCN-0.3, Pd / L-BCN). (a) in the figure shows the reaction rate of different catalysts for catalytic decomposition of formic acid to produce hydrogen, Figure 9 and (b) in the figure is a graph of the TOF values of the catalytic reactions corresponding to the catalysts with different metal loadings. It can be seen from the figure that the catalytic activity of the catalyst shows a significant dependence on the loading. When the metal loading is low, the number of active sites on the catalyst is insufficient, and the hydrogen production effect is poor. While when the metal loading is too high, it is easy to cause agglomeration of metal particles, reducing the specific surface area and the exposure of effective active sites. In this article, when the catalyst is loaded with 0.4 mmol of Pd metal, the catalytic activity of the catalyst is optimal, and the corresponding TOF value also reaches the maximum value, which is 1339.29 h -1 .

[0097] 3. Influence of Different Salt Template Agents on Catalyst Performance

[0098] Under the condition that the experimental conditions remain unchanged, LiCl was replaced with KCl, NaCl, and LiF as templates for comparison (Example 1 and Example 4). As Figure 10 (In the figure, LiCl, KCl, NaCl, and LiF represent Pd / L-BCN, Pd / L-BCN-KCl, Pd / L-BCN-NaCl, and Pd / L-BCN-LiF respectively), the catalyst with LiCl as the template showed the highest catalytic efficiency, and its turnover frequency (TOF) reached 1339.29 min-1, significantly better than other template systems. The catalytic performance of NaCl was at a medium level, with a reaction time of 7.2 min, followed by KCl with a time of 11.6 min. It is worth noting that the catalytic activity of LiF was the worst, and it took 21.6 min to generate 45 mL of gas. These results highlight the important role of salt templates in optimizing catalytic performance, and LiCl showed the best effect under the test conditions. These results may be related to the ionic radius of the cations. The difference in ionic radius gradient (Li + <Na + <K + ) led to changes in the pore structure of the template, thus affecting the exposure degree of active sites in the catalyst. LiCl was beneficial to the formation of highly dispersed nanoparticles due to its smaller ionic size; among the anions, Cl - had a weaker coordination ability than F - and was more likely to fall off during the chemical reduction process, which was beneficial to the formation of highly active metal catalytic centers. The strong coordination effect of F- in the LiF system might cause the aggregation of Pd species and reduce the number of effective active sites, resulting in the worst effect.

[0099] 4. Influence of Light on the Catalytic Activity of Catalysts for Hydrogen Production by Formic Acid Decomposition

[0100] Under the constant temperature condition of 30 °C, the influence of light on the catalytic activity of Pd / L-BCN and Pd / BCN for hydrogen production by formic acid decomposition was investigated. During the experiment, a xenon lamp was used to simulate visible light as the light source, and the xenon lamp was turned off under dark conditions. As Figure 11 shown in (a), the hydrogen production efficiency of both catalysts under light conditions was significantly better than that under dark conditions, indicating that xenon lamp illumination might promote the activation of formic acid molecules through the photothermal effect and cooperate with the d electron band of Pd to reduce the reaction activation energy, confirming that the photoinduced effect could effectively improve the catalytic activity. It can also be observed from Figure 11 (b) that the TOF value of Pd / L-BCN under light conditions (1339.29 h -1 ) was that under dark conditions (618.13 h -1) 2.2 times that of (). This indicates that the generation of photo-generated carriers may optimize the electron transfer path on the catalyst surface, thereby enhancing the kinetic process of formic acid decomposition reaction. Combining with the optoelectronic characterization test ( Figure 5 ) It can be seen that the relatively narrow bandgap (Eg) enables electrons to be quickly excited from the valence band (VB) to the conduction band (CB), forming an efficient charge migration channel; and the separation efficiency of electron-hole pairs generated under light illumination is significantly improved, effectively suppressing the recombination process, prolonging the carrier lifetime, and thus enhancing the charge diffusion ability.

[0101] 5. Activation energy of the catalyst for hydrogen production by formic acid decomposition

[0102] To calculate the activation energy of Pd / L-BCN and Pd / BCN for hydrogen production by formic acid decomposition, temperature gradient experiments were carried out under light and dark conditions respectively, and the test temperature range was 25 °C - 45 °C (interval of 5 °C). As Figure 12 shown in (a) below, under light illumination, the increase in reaction temperature significantly enhances the hydrogen production efficiency of the catalyst for formic acid, which is mainly attributed to the fact that increasing the temperature not only accelerates the Brownian motion of reactant molecules, but also increases the effective collision probability by increasing the molecular kinetic energy. When the reaction temperature is 45 °C, the reaction time for hydrogen production by formic acid decomposition is the shortest (1.13 min), and when the reaction temperature is 25 °C, the reaction completion time is the longest (3.82 min). According to the Arrhenius equation, with the reciprocal of time as the abscissa and the slope of the hydrogen production rate curve of the catalyst at different temperatures as the ordinate, the activation energy of Pd / L-BCN catalyst for hydrogen production by formic acid decomposition under light illumination is calculated to be 49.8 kJ·mol -1 ( Figure 12 shown in (b) below). A series of catalytic reactions with the same temperature gradient were carried out on the Pd / L-BCN catalyst under non-light conditions ( Figure 12 shown in (c), (d) below). As the reaction temperature increases, the catalytic reaction rate increases, significantly shortening from 7.82 min (25 °C) for the reaction to complete to 1.53 min (45 °C). After calculation, the activation energy of the catalytic reaction under non-light conditions is 61.0 kJ·mol -1It can be seen from this that within the same temperature range, the catalyst exhibits similar temperature response characteristics, and the hydrogen production rate of formic acid decomposition increases with the increase of the reaction temperature. This indicates that increasing the reaction temperature provides additional energy for the catalytic reaction to occur, promoting the acceleration of the formic acid decomposition process. It also shows that the light illumination conditions have a significant promoting effect on the performance of the single-metal catalyst. This is mainly attributed to the photosensitive characteristics of the L-BCN support material: when irradiated by light, electrons in the semiconductor material undergo a transition from the valence band to the conduction band, forming electron-hole pairs. In addition, the presence of metal nanoparticles effectively inhibits the recombination of electron-hole pairs, thereby improving the catalytic efficiency. This discovery provides important theoretical support for the development of efficient photocatalysts.

[0103] 6. Influence of Catalyst Dosage on the Reaction Rate of Formic Acid Decomposition for Hydrogen Production

[0104] To investigate the influence of the dosage of the Pd / L-BCN catalyst on the reaction rate of formic acid decomposition for hydrogen production, by the single-variable method, the reaction conditions were controlled to be consistent, and the regulatory effect of the dosage of the Pd / L-BCN catalyst (25 mg, 50 mg, 75 mg, 100 mg) on the reaction kinetics was investigated. As Figure 13 shown in (a) below, with the increase of the catalyst dosage, the gas generation rate of the reaction system shows a significant increasing trend, indicating that the increase in the number of active sites of the catalyst effectively promotes the formic acid decomposition process. To further reveal the kinetic relationship between the catalyst dosage and the catalytic reaction rate, the logarithms of the two were taken for linear fitting to obtain Figure 13 shown in (b) below. The slope of the obtained fitting curve is 1.34, indicating that the dosage of the catalyst for formic acid decomposition to produce hydrogen can be approximately regarded as first-order reaction kinetics.

[0105] 7. Catalytic Performance of the Catalyst for Formic Acid Decomposition to Produce Hydrogen at Different SF Concentrations

[0106] At a reaction temperature of 30 °C and under light conditions, the catalytic performance of 100 mg of the Pd / L-BCN catalyst for formic acid decomposition to produce hydrogen at different SF concentrations (0 mmol, 0.50 mmol, 1.00 mmol, 1.50 mmol) was investigated. The experimental results are as Figure 14 shown below. It can be observed that SF solutions with different concentrations have a certain influence on the catalytic activity of formic acid decomposition to produce hydrogen. When no SF is added, it takes 8.4 min to complete the hydrogen evolution process. However, this does not mean that the greater the SF concentration, the better the reaction effect. The gas evolution time of the 1.0 mmol SF solution (2.93 min) is 1.2 min shorter than that of the 1.5 mmol SF solution (4.13 min), indicating that there is a threshold effect between the SF concentration and the catalytic activity.

[0107] 8. Influence of Different Substrates and Solvents on the Hydrogen Production Rate of the Catalyst for Formic Acid Decomposition

[0108] To study the reaction mechanism of the formic acid hydrogen production reaction, the kinetic isotope effect (KIE) of the formic acid hydrogen production reaction on the catalyst was explored in the experiment. For formic acid, the hydrogen atom can exchange with heavy water (D2O) at room temperature, while the hydrogen atom in the methyl group can hardly exchange with heavy water under the reaction conditions. Therefore, to study KIE, we used different substrates (including HCOOH, formic acid-d acid (DCOOH), formic acid-d (HCOOD), formic acid-d2 (DCOOD)) and solvents (including H2O and D2O) to carry out the formic acid decomposition reaction on the Pd / L-BCN catalyst. As Figure 15 shown in (a) below, when the solvent for the catalytic reaction is HCOOD + D2O, the reaction rate of Pd / L-BCN catalyzing formic acid decomposition to produce hydrogen is better than that of DCOOH + D2O and DCOOD + D2O. Since the rate of the formic acid hydrogen production reaction usually remains constant in the initial stage of the reaction, in the KIE study, we used the initial rate to characterize the formic acid hydrogen production reaction. In this article, the and values were calculated to be 13.17, 7.18, 6.08, 1.83 ( Figure 15 in (b) below), and these data can reflect that the reaction rate of the reaction containing hydrogen isotope (H) is faster. By comparing the KIE values, it is found that the cleavage of α-H in the formic acid molecule is the rate-determining step of the reaction.

[0109] 9. Recycling stability of the catalyst

[0110] To test the recycling stability of the Pd / L-BCN catalyst, under the condition of keeping all experimental conditions the same, the formic acid decomposition hydrogen production reaction was carried out multiple times under light conditions and dark conditions respectively, and the data were recorded, as Figure 16 shown in (a) and (b) below. Under light conditions, after 50 catalytic reactions, the reaction time of the Pd / L-BCN catalyst for catalyzing formic acid decomposition to produce hydrogen was accelerated, shortening from 2.93 min to 2.30 min; under non-light conditions, it shortened from 5.33 min to 4.47 min after 5 cycles. By comparison, it can be seen that whether under light or non-light conditions, the reaction time of formic acid hydrogen production has been improved. As Figure 16 shown in (c) below is the recycling data graph of the Pd / BCN catalyst for catalyzing formic acid decomposition to produce hydrogen under light conditions. After 5 cycles, the time for the catalyst to complete the catalytic reaction shortened from 4.52 min to 2.47 min. The above results show that both the Pd / L-BCN catalyst and the Pd / BCN catalyst have excellent recycling stability, which indicates that as the main component of the Pd-based catalyst support, there is a metal-support interaction between the two, effectively inhibiting the migration and aggregation of metal nanoparticles, which provides a new support design strategy for the development of highly efficient formic acid hydrogen production catalysts.

[0111] The Pd / L-BCN catalyst after cyclic testing was characterized by XRD, and the characterization results were compared with those of the catalyst that did not participate in the reaction to determine whether the crystal structure of the catalyst changed before and after the reaction. The characterization results are as Figure 17 shown in (a) below. It can be observed that whether before or after cycling, the peak positions of the catalyst on the Pd(111), Pd(220), and Pd(200) crystal planes did not shift, indicating that there was no obvious lattice distortion or phase change in the catalyst before and after cycling. By comparing the intensities of the diffraction peaks of the catalyst before and after cycling, it was found that the diffraction peaks of both the support and the metal were significantly enhanced after cycling. This may be due to the structural reorganization of the interfacial reaction between the support and the metal during cycling, which is one of the reasons for the excellent cyclic stability of the catalyst. The Pd / L-BCN catalyst after cyclic testing was characterized by XPS, and the characterization results were compared with those of the catalyst that did not participate in the reaction. The results are as Figure 17 shown in (b)-(f) below. In the XPS spectra before and after cycling, obvious characteristic signals of each element are still present, and the characteristic peaks corresponding to each element have basically not shifted significantly. This indicates that the surface chemical composition, chemical state, and electronic structure of the catalyst after catalytic cyclic testing have hardly changed, which also indirectly explains one of the reasons why the Pd / L-BCN catalyst still maintains good catalytic performance after multiple cyclic tests.

[0112] In summary, (1) The Pd / L-BCN catalyst obtained by the template method and the impregnation reduction method has a stable layered structure, and its catalytic activity for hydrogen production by formic acid decomposition is better than that of the Pd / BCN catalyst. Under the conditions of 30 °C and light, the catalyst prepared by using the support obtained by calcining with H3BO3:C3H6N6 at 2:4 and adding LiCl and loading 0.4 mmol Pd has the best catalytic performance, and the corresponding TOF is 1339.29 h -1 , which is twice that in the case of no light (618.13 h -1 ).

[0113] (2) The reaction rate curves of the Pd / L-BCN catalyst for hydrogen production by formic acid decomposition at different temperatures show that the reaction rate increases with the increase of the reaction temperature, and the activation energy of the reaction is 49.8 kJ / mol.

[0114] (3) The catalytic mechanism of Pd / L-BCN for hydrogen production from formic acid was explored by kinetic isotope effect (KIE). Deuterated formic acid (DCOOH, HCOOD, DCOOD) was combined with H2O and D2O. The experimental results show that the cleavage of α-H in the formic acid molecule is the rate-determining step of the reaction.

[0115] (4) From the cyclic tests of hydrogen production by formic acid decomposition, it can be seen that after 50 cycles, the reaction time of Pd / L-BCN after 50 cycles under light and after 5 cycles without light has increased; the reaction time of Pd / BCN after 5 cycles under light has also increased. This indicates that both catalysts possess excellent stability, which is attributed to the fact that the metal-support interaction between the BCN support and Pd nanoparticles effectively inhibits particle agglomeration. This provides a new carrier design strategy for constructing highly efficient and stable supported metal catalysts and expands the research idea of improving the durability of the catalytic system based on interface regulation.

[0116] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of Pd / L-BCN photocatalyst, characterized in that, It includes the following steps: Prepare a boron nitride precursor using melamine and boric acid as raw materials. Then, use lithium chloride as a template agent, mix it evenly with the boron nitride precursor, and calcine to obtain L-BCN nanosheets; Immerse the L-BCN nanosheets in a palladium salt solution, and then react under the action of a reducing agent to obtain the Pd / L-BCN photocatalyst.

2. The preparation method according to claim 1, characterized in that, The specific method for preparing the boron nitride precursor using melamine and boric acid as raw materials is: mix melamine, boric acid, and a solvent evenly and react at 90 °C for 30 min.

3. The preparation method according to claim 1, characterized in that, The mass ratio of melamine to boric acid is 4:(1 - 4); the mass ratio of the boron nitride precursor to lithium chloride is 1:

5.

4. The preparation method according to claim 1, characterized in that, The calcination procedure is: heat up to 380 °C at a rate of 6.8 °C / min, hold for 120 min, then heat up to 550 °C at a heating rate of 6.8 °C / min, and hold for 240 min.

5. The preparation method according to claim 1, characterized in that The ratio of the L-BCN nanosheets to Pd in the palladium salt solution is 0.2 g:(0.1 - 0.4) mmol.

6. The preparation method according to claim 1, characterized in that, The impregnation time is 24 h, and the temperature is room temperature.

7. The preparation method according to claim 1, characterized in that, The reducing agent is sodium borohydride; the mass ratio of sodium borohydride to L-BCN nanosheets is 0.16:0.

2.

8. The preparation method according to claim 1, wherein When reacting under the action of a reducing agent, the reaction temperature is -3 °C, and the time is 5 h.

9. A Pd / L-BCN photocatalyst prepared by the preparation method according to any one of claims 1 - 8.

10. An application of the Pd / L-BCN photocatalyst according to claim 9 in catalyzing hydrogen production from formic acid.

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