Method for piezoelectric photocatalytic synthesis of hydrogen peroxide

Abstract

The application provides a piezoelectric photocatalytic method for synthesizing hydrogen peroxide, comprising the following steps: S1, mixing water and a composite catalyst in a dark environment to obtain a pretreated solution; the composite catalyst comprises cyanogroup carbon nitride and iron-nickel layered double hydroxide; S2, performing piezoelectric photocatalytic treatment on the pretreated solution to obtain hydrogen peroxide; the piezoelectric photocatalytic treatment comprises: under the joint driving of ultrasonic waves and visible light, using dissolved oxygen in water as raw material, catalyzing oxygen reduction reaction to generate hydrogen peroxide; the ultrasonic waves excite the piezoelectric effect of the composite catalyst; and the visible light excites the photocatalytic effect of the composite catalyst. The application overcomes the technical bottlenecks in the conventional photocatalytic technology, such as low hydrogen peroxide yield and selectivity, strong dependence on noble metal cocatalyst, limited conversion efficiency of single light energy input and the like, promotes the two-electron oxygen reduction path, and improves the hydrogen peroxide yield.

Description

Technical Field

[0001] This invention relates to the field of hydrogen peroxide synthesis, and more particularly to a method for synthesizing hydrogen peroxide by piezoelectric photocatalysis. Background Technology

[0002] Hydrogen peroxide (H2O2), as an important green oxidant, has wide applications in chemical synthesis, environmental remediation, and energy. Currently, large-scale industrial production of hydrogen peroxide mainly relies on the anthraquinone process, which suffers from problems such as complex processes, high energy consumption, the use of precious metal catalysts, and the generation of organic waste. Therefore, developing a new green, safe, and low-energy-consumption route for hydrogen peroxide synthesis is of great significance. Photocatalytic oxygen reduction synthesis of hydrogen peroxide, with its mild reaction conditions, is considered a highly promising alternative. Among these, polymer semiconductor catalysts based on carbon nitride (g-C3N4) have attracted widespread attention due to their low cost and good stability. However, traditional g-C3N4 catalysts suffer from limited visible light absorption and low photogenerated carrier separation efficiency, resulting in low catalytic activity.

[0003] More importantly, the process of reducing O2 to H2O2 involves two electrons (O2 → ·O2). - → H2O2) and a single electron (O2→ ·O2) - There are two competing pathways for hydrogen peroxide, the latter generating reactive oxygen species that lead to selective decomposition. Therefore, precisely controlling and promoting the two-electron oxygen reduction pathway is the core challenge for improving the yield and selectivity of hydrogen peroxide. To improve performance, existing technologies mostly seek breakthroughs in material modification, such as introducing noble metals (e.g., Pt, Au) as co-catalysts to promote charge separation and provide highly active sites; however, the use of noble metals significantly increases costs, limiting their large-scale application; in addition, relying solely on light energy input often encounters bottlenecks in improving catalytic efficiency.

[0004] Therefore, it is necessary to provide a method for the piezoelectric photocatalytic synthesis of hydrogen peroxide to solve the technical problem of how to promote the two-electron oxygen reduction pathway and improve the yield of hydrogen peroxide. Summary of the Invention

[0005] The main objective of this invention is to provide a method for the piezoelectric photocatalytic synthesis of hydrogen peroxide, aiming to solve the technical problem of how to promote the two-electron oxygen reduction pathway and improve the yield of hydrogen peroxide.

[0006] To achieve the above objectives, the present invention provides a method for the piezoelectric photocatalytic synthesis of hydrogen peroxide, comprising the following steps:

[0007] S1, mix water and composite catalyst in the dark to obtain pretreatment solution;

[0008] The composite catalyst comprises carbon cyanonitride and iron-nickel layered double hydroxide, wherein the carbon cyanonitride and the iron-nickel layered double hydroxide form an interfacial contact; the composite catalyst has a heterojunction structure capable of promoting electron-hole pair separation and activating molecular oxygen; the carbon cyanonitride has a heptaazine unit structure and contains a cyano group;

[0009] S2, perform piezoelectric photocatalytic treatment on the pretreatment solution to obtain hydrogen peroxide;

[0010] The piezoelectric photocatalytic treatment includes: using dissolved oxygen in water as a raw material, catalyzing the reduction of oxygen to generate hydrogen peroxide under the combined drive of ultrasound and visible light; the ultrasound excites the piezoelectric effect of the composite catalyst; and the visible light excites the photocatalytic effect of the composite catalyst.

[0011] Further, in step S1, the mass-to-volume ratio of the composite catalyst to water is 0.2-1.0 mg / mL.

[0012] Furthermore, in step S1, the mixing time is 30-60 minutes.

[0013] Furthermore, during the piezoelectric photocatalytic treatment, the power of the ultrasonic wave is 80-400W.

[0014] Furthermore, during the piezoelectric photocatalytic treatment, the wavelength of the visible light is not less than 420 nm.

[0015] Furthermore, the visible light source is a xenon lamp with a 420 nm cutoff filter; the power of the xenon lamp is 200-500W.

[0016] Furthermore, the piezoelectric photocatalytic treatment is carried out under stirring conditions.

[0017] Furthermore, the duration of the piezoelectric photocatalytic treatment is 60-150 min.

[0018] Furthermore, the method for obtaining the cyano nitride includes: dissolving urea and potassium hydroxide in anhydrous ethanol, drying to obtain a precursor; and calcining the precursor to obtain the cyano nitride.

[0019] The mass ratio of urea to potassium hydroxide is 1000-2000:1; the calcination temperature is 500-600℃; and the calcination time is 3-6 hours.

[0020] Furthermore, the composite catalyst is obtained by mixing the carbon cyanide, ferric nitrate nonahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride in water to obtain a suspension; and then subjecting the suspension to hydrothermal treatment followed by solid-liquid separation to obtain the composite catalyst.

[0021] The mass ratio of carbon cyanonitride to ferric nitrate nonahydrate is 0.2-1:1, and the mass ratio of ferric nitrate nonahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride is 1:1.4-1.5:1.4-1.6:0.5-0.6; the hydrothermal treatment temperature is 110-130℃, and the hydrothermal treatment duration is 5-8 hours.

[0022] The main principle of piezoelectric photocatalytic synthesis of H2O2 in this invention is as follows: The composite catalyst used in this invention comprises carbon cyanide (CCN) and iron-nickel layered double hydroxide (Fe-Ni LDH), with the CCN and Fe-Ni LDH forming an interfacial contact. Under the synergistic effect of ultrasound and visible light, the CCN component, due to its cyano modification breaking structural symmetry, generates a significant piezoelectric effect. The generated piezoelectric field couples with the photogenerated built-in electric field at the Fe-Ni LDH / CCN heterojunction interface, synergistically driving the efficient separation and directional migration of photogenerated carriers. This synergistic field effect precisely regulates the reduction pathway of molecular oxygen, preferentially promoting its reduction through a two-step single-electron process (O2 → ·O2). - → The conversion is carried out by OOH, and the key intermediate is strengthened. The generation and stabilization of OOH ultimately achieves the efficient and highly selective synthesis of H2O2. The entire process can be efficiently completed under non-precious metal catalytic systems and mild conditions.

[0023] Compared with the prior art, the present invention has at least the following advantages:

[0024] 1. This invention achieves simultaneous improvement in catalytic efficiency and selectivity: Based on a composite catalyst comprising layered double hydroxides of cyanocarbon nitride and iron-nickel forming an interfacial contact, the synergistic effect of piezoelectricity and photocatalysis effectively promotes the separation and migration of photogenerated carriers, while precisely controlling the two-step single-electron oxygen reduction reaction pathway. Using the composite catalyst of this invention for piezoelectric photocatalysis not only yields 2.4 times the H2O2 produced by photocatalysis alone, but also far exceeds the combined yield of piezoelectric photocatalysis by CCN and Fe-NiLDH alone.

[0025] 2. This invention constructs a non-precious metal high-efficiency catalytic system: a heterojunction catalyst is constructed using Fe-Ni LDH and CCN, which completely avoids the use of precious metals and significantly reduces material costs while ensuring excellent catalytic performance.

[0026] 3. This invention breaks through the efficiency limitation of a single energy field: by synergistic input of ultrasound and visible light, the coupling utilization of mechanical energy and light energy is realized, overcoming the technical bottleneck of low utilization efficiency of single light energy and significantly improving energy utilization efficiency.

[0027] 4. This invention provides a green synthesis route under mild conditions: the method can be carried out efficiently at room temperature and pressure without the need for high temperature and high pressure equipment, and the reaction process is clean and pollution-free, providing a new route for the green synthesis of H2O2.

[0028] In summary, this invention promotes the two-electron oxygen reduction pathway and improves hydrogen peroxide yield. It overcomes the technical bottlenecks of traditional photocatalysis, such as low H2O2 yield and selectivity, strong dependence on noble metal co-catalysts, and limited conversion efficiency of single light energy input. Thus, it achieves the regulation of the intermediate in a two-step single-electron process under mild conditions using a non-noble metal catalyst through the synergistic effect of piezoelectricity and photocatalysis. The generation of OOH enables the efficient and selective synthesis of H2O2. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0030] Figure 1 The above figures show the H2O2 synthesis performance under illumination in Comparative Examples 7-12 of this invention.

[0031] Figure 2 The above are the H2O2 synthesis performance diagrams under ultrasonic driving (ultrasound) in Comparative Examples 13-18 of this invention;

[0032] Figure 3 The above figures show the H2O2 synthesis performance under the combined drive of ultrasound (sonication) and light in Examples 1-4 and Comparative Examples 1-2 of this invention.

[0033] Figure 4 The above figures show the H2O2 synthesis performance under combined ultrasonic (sonic) and light irradiation in Example 1 and Comparative Examples 3-6 of this invention.

[0034] Figure 5 The diagram shows the piezoelectric photocatalytic synthesis performance of the 3CCN / Fe-Ni LDH composite catalyst in the presence of different scavengers in Example 2 of this invention.

[0035] Figure 6 The image shows the ESR spectrum of the 3CCN / Fe-Ni LDH composite catalyst during the piezoelectric photocatalytic reaction in Example 2 of this invention; where (a) is the DMPO-·O2 spectrum. - Spectrum (b) is the DMPO-·OH spectrum;

[0036] Figure 7 The in-situ infrared spectrum of molecular oxygen activated by the 3CCN / Fe-Ni LDH composite catalyst in Example 3 of this invention is shown; wherein, (a) is 800-1700 cm⁻¹ -1 Infrared spectra at wavenumbers, (b) 2800-3700 cm⁻¹ -1 Infrared spectrum at wavenumber;

[0037] Figure 8 In Example 3 of this invention, the ESR spectrum of the 3CCN / Fe-Ni LDH composite catalyst DMPO-·OOH was detected.

[0038] Figure 9 In Example 4 of this invention, the generation rate constant (K) of H2O2 generated by CNN, Fe-Ni LDH, and 3CCN / Fe-Ni LDH piezoelectric photocatalysis was analyzed. f ) and decomposition rate constant (K d );

[0039] Figure 10 The graph shows the performance of the piezoelectric photocatalytic decomposition of H2O2 by the CNN, Fe-Ni LDH, and 3CCN / Fe-Ni LDH composite catalysts in Example 4 of this invention.

[0040] Figure 11 In Example 5 of this invention, the photoluminescence spectra (PL) and electrochemical impedance spectroscopy (EIS) of CNN and each CCN / Fe-Ni LDH are analyzed; where (a) is the photoluminescence spectrum (PL) and (b) is the electrochemical impedance spectroscopy (EIS).

[0041] Figure 12 In Example 5 of this invention, the LSV curves measured on the RDE at different rotational speeds of the CCN are analyzed.

[0042] Figure 13 In Example 5 of this invention, the LSV curves of 3CCN / Fe-Ni LDH measured on RDE at different rotational speeds are analyzed.

[0043] Figure 14 Koutecky-Levich plots of CCN and 3CCN / Fe-Ni LDH in Example 5 of this invention;

[0044] Figure 15 This invention analyzes the reaction energies of oxygen reduction to H2O2 on CNN and 3CCN / Fe-Ni LDH under different conditions in Example 5.

[0045] Figure 16The X-ray diffraction patterns and infrared absorption spectra of CCN, Fe-Ni LDH, and each CCN / Fe-Ni LDH are shown in Example 6 of this invention; where (a) is the X-ray diffraction pattern and (b) is the infrared absorption spectrum.

[0046] Figure 17 For example 6 of this invention, the ultraviolet-visible absorption spectra of CCN, Fe-Ni LDH, and each CCN / Fe-Ni LDH are analyzed.

[0047] Figure 18 The N2 adsorption-desorption curves of CCN, Fe-Ni LDH, and 3CCN / Fe-Ni LDH in Example 6 of this invention are analyzed.

[0048] Figure 19 The following are transmission electron microscope (TEM) images of CCN, Fe-Ni LDH, and 3CCN / Fe-Ni LDH in Analytical Example 6 of this invention; wherein, (a) is the TEM image of CCN; (b) is the TEM image of Fe-Ni LDH; (c) is the TEM image of 3CCN / Fe-Ni LDH; (d) is the lattice analysis of 3CCN / Fe-Ni LDH; and (e) is the elemental mapping analysis of 3CCN / Fe-Ni LDH.

[0049] Figure 20 The images shown are piezoelectric force microscopy (PFM) and Kelvin probe force microscopy (KPFM) images of 3CCN / Fe-Ni LDH in Analysis Example 6 of this invention; where (a) is the butterfly amplitude ring and phase reversal curve of 3CCN / Fe-Ni LDH, (b) is the KPFM potential image of 3CCN / Fe-Ni LDH in the dark, (c) is the KPFM potential image of 3CCN / Fe-Ni LDH under illumination, and (d) is the corresponding surface potential of 3CCN / Fe-Ni LDH.

[0050] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0053] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0054] It is important to understand that piezoelectric catalysis, as a novel strategy utilizing mechanical energy to drive chemical reactions, exhibits great potential for coupling with photocatalysis. Theoretically, the built-in electric field generated by piezoelectric materials under ultrasonic waves can effectively promote the separation and migration of photogenerated electron-hole pairs. However, designing a non-noble metal synergistic catalytic system that can simultaneously and efficiently respond to both light and mechanical vibrations and precisely control the oxygen reduction pathway remains a pressing technical challenge in this field. Developing a non-noble metal catalytic method that can fully utilize the photo-piezoelectric synergistic effect to achieve efficient and highly selective synthesis of H2O2 under mild conditions is not only of significant scientific importance but also has broad application prospects.

[0055] This invention provides a method for synthesizing hydrogen peroxide via piezoelectric photocatalysis, comprising the following steps:

[0056] S1, mix water and composite catalyst in the dark to obtain pretreatment solution.

[0057] As a specific explanation of step S1, in step S1, the mass-to-volume ratio of the composite catalyst to water is 0.2-1.0 mg / mL, and more specifically 0.5-0.7 mg / mL; the water contains dissolved oxygen; in specific experiments, the volume of water can be 50-100 mL.

[0058] In step S1, the mixing time is 30-60 min, or more specifically 30-40 min; the mixing method is stirring; this invention ensures that the catalyst is dispersed in water and that its adsorption-desorption of the reactants reaches an equilibrium state by mixing.

[0059] In this invention, during the process of obtaining the pretreatment solution, water, the composite catalyst, and EDTA-2Na can be mixed together, and the concentration of EDTA-2Na in the pretreatment solution is 0.4-0.6 mmol / L; or, water, the composite catalyst, and isopropanol can be mixed together, and the concentration of isopropanol in the pretreatment solution is 0.8-1.2 mmol / L.

[0060] In this invention, the composite catalyst comprises carbon cyanonitride and iron-nickel layered double hydroxide, wherein the carbon cyanonitride and the iron-nickel layered double hydroxide form an interfacial contact; the carbon cyanonitride exhibits an ultrathin nanosheet morphology, and the iron-nickel layered double hydroxide exhibits a multi-level nanoflower structure; in some embodiments, the mass ratio of the carbon cyanonitride to the iron-nickel layered double hydroxide is 1-4:1, more preferably 2.9-3.1:1, and more preferably 3:1.

[0061] In this invention, the composite catalyst has a heterojunction structure that can promote electron-hole pair separation and activate molecular oxygen; specifically, the composite catalyst is composed of piezoelectric carbon cyanide and photoelectric iron-nickel layered double hydroxide, forming a heterojunction structure that can promote electron-hole pair separation and activate molecular oxygen.

[0062] In this invention, the cyanocarbon nitride has a heptaazine unit structure and contains a cyano group; the method for obtaining the cyanocarbon nitride includes: dissolving urea and potassium hydroxide in anhydrous ethanol, drying to obtain a precursor at a temperature of 70-90°C; calcining the precursor to obtain the cyanocarbon nitride; wherein the mass ratio of urea to potassium hydroxide is 1000-2000:1, more preferably 1400-1600:1; the calcination temperature is 500-600°C, and the calcination time is 3-6 hours, more preferably 3-5 hours; the calcination is carried out in an air atmosphere; after calcination, the carbon is washed with water and ethanol, and then dried.

[0063] In this invention, the composite catalyst is obtained by: mixing carbon cyanide, ferric nitrate nonahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride in water to obtain a suspension; subjecting the suspension to hydrothermal treatment and separating the solid and liquid to obtain the composite catalyst; wherein, after solid-liquid separation, the solid is washed with water and ethanol and then dried. The mass ratio of carbon cyanonitride to ferric nitrate nonahydrate is 0.2-1:1, more preferably 0.7-0.8:1, more preferably 0.73-0.75:1; the mass ratio of ferric nitrate nonahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride is 1:1.4-1.5:1.4-1.6:0.5-0.6; the mass-to-volume ratio of ferric nitrate nonahydrate to water is 5-10 mg / mL, more preferably 5-8 mg / mL, more preferably 6-7 mg / mL; the hydrothermal treatment temperature is 110-130℃; and the hydrothermal treatment duration is 5-8 h, more preferably 5-7 h.

[0064] S2, the pretreatment solution is subjected to piezoelectric photocatalytic treatment to obtain hydrogen peroxide.

[0065] The piezoelectric photocatalytic treatment includes: catalyzing the reduction of dissolved oxygen in water to generate hydrogen peroxide under the combined drive of ultrasound and visible light; the ultrasound excites the piezoelectric effect of the composite catalyst; and the visible light excites the photocatalytic effect of the composite catalyst. Specifically, this invention uses a cyanocarbon nitride composite catalyst (CCN / Fe-Ni LDH) modified with iron-nickel layered double hydroxides to catalyze the reduction of molecular oxygen to hydrogen peroxide under the synergistic effect of ultrasound and visible light.

[0066] In this invention, the oxygen reduction reaction follows a two-step single-electron reaction pathway, sequentially generating... O2 and The OOH intermediate is ultimately converted into H2O2. The ultrasound is used to excite the piezoelectric effect of the cyano-carbon nitride component in the composite catalyst, generating a polarized electric field; the visible light is used to excite the photocatalytic effect of the composite catalyst; the polarized electric field and the photogenerated electric field work synergistically to directionally drive the separation of photogenerated carriers and reduce... O2→ The Gibbs free energy barrier of the OOH reaction step.

[0067] As an explanation of the piezoelectric photocatalysis, the power of the ultrasound is 80-400W, further 80-360W or 350-370W; the wavelength of the visible light is not less than 420nm. The light source for the visible light is a xenon lamp with a 420nm cutoff filter; the power of the xenon lamp is 200-500W, further 300-500W or 250-350W. Specifically, a 300W xenon lamp light source is used to simulate visible light irradiation, and simultaneously a 360W ultrasound device is used to provide ultrasonic radiation.

[0068] In this invention, the piezoelectric photocatalytic treatment is carried out under stirring conditions; the duration of the piezoelectric photocatalytic treatment is 60-150 min, further 60-80 min, further 70-80 min, and further 75-80 min.

[0069] It should be noted that this invention uses a CCN / Fe-Ni LDH heterojunction composite material formed by supporting iron-nickel layered double hydroxides on cyano-functionalized carbon nitride nanosheets as a catalyst to achieve highly selective reduction of oxygen to hydrogen peroxide under the synergistic effect of ultrasound and visible light. The introduction of cyano groups breaks the structural symmetry of the triazine unit, enhances the material's dipole moment and spontaneous polarization field, and significantly improves its piezoelectric response performance. The piezoelectric field generated by ultrasound excitation further synergizes with the photogenerated electric field to jointly promote the conversion of molecular oxygen to hydrogen peroxide via a two-step single-electron reduction pathway. The OOH intermediate significantly improves the generation rate and selectivity of H2O2. This invention enables the green synthesis of hydrogen peroxide under ambient temperature and pressure conditions, featuring mild reaction conditions, high energy efficiency, good selectivity, and no need for precious metal co-catalysts, thus showing promising application prospects in the field of green hydrogen peroxide manufacturing.

[0070] It should also be noted that the present invention can also inhibit the decomposition of hydrogen peroxide; in the present invention, the Fenton-like reactivity of the iron-nickel layered double hydroxide is inhibited, so that the increase in the generation rate constant of the composite catalyst during the catalytic generation of hydrogen peroxide is much greater than the increase in the decomposition rate constant, thereby achieving efficient accumulation of hydrogen peroxide.

[0071] The following are specific examples of the present invention:

[0072] Example 1

[0073] A method for synthesizing hydrogen peroxide, comprising the following steps:

[0074] (1) Measure 50 mL of deionized water and place it in the reactor, and add 30 mg of the pre-prepared catalyst to it; in the dark environment, stir continuously at a constant speed for 30 min to ensure that the catalyst is dispersed in the water and that its adsorption-desorption of the reactants reaches equilibrium, and obtain the pretreated solution.

[0075] In this embodiment, the catalyst is a CCN / Fe-Ni LDH composite catalyst, which is a composite catalyst modified with iron-nickel layered double hydroxides to modify carbon cyanonitride.

[0076] In this embodiment, the CCN / Fe-Ni LDH composite catalyst is obtained as follows:

[0077] 15 g of urea and 0.01 g of potassium hydroxide were dissolved in 30 mL of anhydrous ethanol and stirred until completely dissolved to obtain a mixed solution. The solution was dried at 80 °C to obtain a solid precursor. The precursor was placed in a muffle furnace and calcined at 550 °C for 4 h in air at a heating rate of 5 °C / min. After natural cooling, a crude product was obtained. The crude product was washed and dried alternately with deionized water and ethanol to obtain carbon cyanonitride nanosheets, which are uniformly referred to as CCN nanosheets in this invention.

[0078] 300 mg of the obtained CCN nanosheets were added to 60 mL of deionized water along with 404 mg of ferric nitrate nonahydrate, 581.6 mg of nickel nitrate hexahydrate, 600.6 mg of urea, and 222.2 mg of ammonium fluoride. The mixture was stirred for 2 h to form a uniform suspension. The suspension was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 120 °C for 6 h. After the reaction was completed, the solid product was collected, washed with deionized water and ethanol, and dried to obtain the target product, the CCN / Fe-Ni LDH composite catalyst. The CCN / Fe-NiLDH composite catalyst in this embodiment is uniformly referred to as the 3CCN / Fe-Ni LDH composite catalyst in this invention.

[0079] (2) Simultaneously turn on the ultrasonic generator with a power of 360 W and the xenon lamp light source with a 420 nm cutoff filter, and apply ultrasonic (ultrasound) and visible light irradiation (light) to the pretreatment liquid under continuous stirring to start the piezoelectric-photocatalytic reaction and catalyze the reduction of oxygen to generate hydrogen peroxide.

[0080] At 0, 15, 30, 45, 60 and 75 min after the start of the reaction, 2 mL of the reaction solution was taken and filtered through a 0.45 μm microporous membrane to remove catalyst particles. The H2O2 concentration was then determined by iodometric titration.

[0081] Example 2

[0082] Compared to Example 1, the only difference in this embodiment is that the amount of CCN nanosheets added is adjusted to 100 mg during the process of obtaining the CCN / Fe-Ni LDH composite catalyst, while other conditions remain unchanged. The CCN / Fe-Ni LDH composite catalyst in this embodiment is uniformly referred to as 1CCN / Fe-Ni LDH composite catalyst in this invention.

[0083] Example 3

[0084] Compared to Example 1, the only difference in this embodiment is that the amount of CCN nanosheets added is adjusted to 200 mg during the process of obtaining the CCN / Fe-Ni LDH composite catalyst, while other conditions remain unchanged. The CCN / Fe-Ni LDH composite catalyst in this embodiment is uniformly referred to as 2CCN / Fe-Ni LDH composite catalyst in this invention.

[0085] Example 4

[0086] Compared to Example 1, the only difference in this embodiment is that the amount of CCN nanosheets added is adjusted to 400 mg during the process of obtaining the CCN / Fe-Ni LDH composite catalyst, while other conditions remain unchanged. The CCN / Fe-Ni LDH composite catalyst in this embodiment is uniformly referred to as the 4CCN / Fe-Ni LDH composite catalyst in this invention.

[0087] Comparative Example 1

[0088] Compared to Example 1, this comparative example only changed the catalyst to CCN nanosheets (same as Example 1), while keeping other conditions unchanged.

[0089] Comparative Example 2

[0090] Compared to Example 1, this comparative example only changed the catalyst to Fe-Ni LDH, while keeping other conditions unchanged.

[0091] The Fe-Ni LDH was obtained as follows: 404 mg of ferric nitrate nonahydrate, 581.6 mg of nickel nitrate hexahydrate, 600.6 mg of urea and 222.2 mg of ammonium fluoride were added to 60 mL of deionized water and stirred for 2 h. The mixture was then transferred to a 100 mL high-pressure reactor lined with polytetrafluoroethylene and subjected to hydrothermal reaction at 120 °C for 6 h. After the reaction was completed, the solid was washed with deionized water and ethanol and dried. The resulting product is uniformly referred to as Fe-Ni LDH in this invention.

[0092] Comparative Example 3

[0093] Compared to Example 1, this comparative example only changed the catalyst to a 3CN / Fe-Ni LDH catalyst, while keeping all other conditions unchanged.

[0094] The 3CN / Fe-Ni LDH catalyst was obtained by placing 15 g of urea in a muffle furnace and heating it to 550 °C at a heating rate of 5 °C / min under an air atmosphere. After calcination for 4 h, the crude product was obtained after natural cooling. The crude product was washed and dried alternately with deionized water and ethanol to obtain carbon nitride nanosheets (CN).

[0095] Take 300 mg of the obtained CN nanosheets, and add them together with 404 mg of ferric nitrate nonahydrate, 581.6 mg of nickel nitrate hexahydrate, 600.6 mg of urea and 222.2 mg of ammonium fluoride into 60 mL of deionized water. Stir for 2 h to form a uniform suspension. Transfer the suspension to a 100 mL high-pressure reactor and hydrothermally react at 120 °C for 6 h. After the reaction is completed, collect the solid product, wash it with deionized water and ethanol, and dry it to obtain the target product, which is uniformly referred to as 3CN / Fe-Ni LDH in this invention.

[0096] Comparative Example 4

[0097] Compared to Example 1, this comparative example only changed the catalyst to a 3CNCOOH / Fe-Ni LDH catalyst, while keeping all other conditions unchanged.

[0098] The 3CNCOOH / Fe-Ni LDH catalyst was obtained by placing 15 g of urea in a muffle furnace and heating it to 550 °C at a heating rate of 5 °C / min under an air atmosphere. After calcination for 4 h, the crude product was obtained after natural cooling. The crude product was washed and dried alternately with deionized water and ethanol to obtain carbon nitride nanosheets (CN).

[0099] 1 g of the obtained CN was added to a flask containing 50 mL of HNO3 solution (5 M), and the suspension was refluxed at 125 °C. After the reaction was completed, the product was washed with a large amount of deionized water and freeze-dried to obtain carboxyl-functionalized carbon nitride nanosheets (CNCOOH).

[0100] Take 300 mg of the obtained CNCOOH nanosheets, and add them together with 404 mg of ferric nitrate nonahydrate, 581.6 mg of nickel nitrate hexahydrate, 600.6 mg of urea and 222.2 mg of ammonium fluoride into 60 mL of deionized water. Stir for 2 h to form a uniform suspension. Transfer the suspension to a 100 mL high-pressure reactor and hydrothermally react at 120 °C for 6 h. After the reaction is completed, collect the solid product. The product obtained by washing with deionized water and ethanol and drying is uniformly referred to as 3CNCOOH / Fe-Ni LDH in this invention.

[0101] Comparative Example 5

[0102] Compared to Example 1, this comparative example only changed the catalyst to a 3CCN / Fe-Co LDH catalyst, while keeping other conditions unchanged.

[0103] The 3CCN / Fe-Co LDH catalyst was obtained as follows: CCN nanosheets were obtained in the same manner as in Example 1; 300 mg of the obtained CCN nanosheets were added to 60 mL of deionized water along with 404 mg of ferric nitrate nonahydrate, 582.1 mg of cobalt nitrate hexahydrate, 600.6 mg of urea, and 222.2 mg of ammonium fluoride, and stirred for 2 h to form a uniform suspension; the suspension was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 120 °C for 6 h; after the reaction was completed, the solid product was collected, and the product obtained by washing with deionized water and ethanol and drying was uniformly referred to as 3CCN / Fe-Co LDH in this invention.

[0104] Comparative Example 6

[0105] Compared to Example 1, this comparative example only changed the catalyst to a 3CCN / CuFe2O4 catalyst, while keeping other conditions unchanged.

[0106] The 3CCN / CuFe2O4 catalyst was obtained as follows: CCN nanosheets were obtained in the same manner as in Example 1; 300 mg of the obtained CCN nanosheets were added to 60 mL of ethylene glycol along with 808 mg of ferric nitrate nonahydrate, 241.6 mg of copper nitrate trihydrate, and 246.9 mg of anhydrous sodium acetate, and stirred for 2 h to form a uniform suspension; the suspension was transferred to a 100 mL high-pressure reactor and hydrothermally reacted at 180 °C for 12 h; after the reaction was completed, the solid product was collected, washed with deionized water and ethanol to obtain the precursor; in a muffle furnace, the precursor was heated to 400 °C at a rate of 5 °C / min and held at 400 °C for 2 h, and the resulting product was uniformly referred to as 3CCN / CuFe2O4 in this invention.

[0107] Comparative Example 7

[0108] Compared to Example 1, this comparative example omits the application of ultrasound.

[0109] In this comparative example, a method for synthesizing hydrogen peroxide includes the following steps:

[0110] (1) Measure 50 mL of deionized water and place it in the reactor, and add 30 mg of the pre-prepared catalyst (same as in Example 1); in the dark environment, stir continuously at a constant speed for 30 min to ensure that the catalyst is dispersed in the water and that its adsorption-desorption of the reactants reaches equilibrium, and obtain the pretreated solution.

[0111] (2) Turn on a 300 W xenon lamp light source with a 420 nm cutoff filter and apply visible light irradiation (lighting) to the pretreatment liquid under continuous stirring to carry out photocatalytic reaction.

[0112] At 0, 15, 30, 45, 60 and 75 min after the start of the reaction, 2 mL of the reaction solution was taken and filtered through a 0.45 μm microporous membrane to remove catalyst particles. The H2O2 concentration was then determined by iodometric titration.

[0113] Comparative Example 8

[0114] Compared to Comparative Example 7, this comparative example only adjusts the method of obtaining the catalyst, while other conditions are the same as in Comparative Example 7; in this comparative example, the method of obtaining the catalyst is the same as in Example 2.

[0115] Comparative Example 9

[0116] Compared to Comparative Example 7, this comparative example only adjusts the method of obtaining the catalyst, while other conditions remain the same as in Comparative Example 7; in this comparative example, the method of obtaining the catalyst is the same as in Example 3.

[0117] Comparative Example 10

[0118] Compared to Comparative Example 7, this comparative example only adjusts the method of obtaining the catalyst, while other conditions remain the same as in Comparative Example 7; in this comparative example, the method of obtaining the catalyst is the same as in Example 4.

[0119] Comparative Example 11

[0120] Compared to Comparative Example 7, this comparative example only changed the method of obtaining the catalyst, while other conditions remained the same as in Comparative Example 7; in this comparative example, the method of obtaining the catalyst was the same as in Comparative Example 1.

[0121] Comparative Example 12

[0122] Compared to Comparative Example 7, this comparative example only changed the method of obtaining the catalyst, while other conditions remained the same as in Comparative Example 7; in this comparative example, the method of obtaining the catalyst was the same as in Comparative Example 2.

[0123] Comparative Example 13

[0124] Compared to Example 1, this comparative example omits only the visible light irradiation from a 300 W xenon lamp light source.

[0125] In this comparative example, a method for synthesizing hydrogen peroxide includes the following steps:

[0126] (1) Measure 50 mL of deionized water and place it in the reactor, and add 30 mg of the pre-prepared catalyst (same as in Example 1); in the dark environment, stir continuously at a constant speed for 30 min to ensure that the catalyst is dispersed in the water and that its adsorption-desorption of the reactants reaches equilibrium, and obtain the pretreated solution.

[0127] (2) Turn on the ultrasonic generator with a power of 360 W and carry out the piezoelectric catalytic reaction under ultrasonic and continuous stirring conditions.

[0128] At 0, 15, 30, 45, 60 and 75 min after the start of the reaction, 2 mL of the reaction solution was taken and filtered through a 0.45 μm microporous membrane to remove catalyst particles. The H2O2 concentration was then determined by iodometric titration.

[0129] Comparative Example 14

[0130] Compared to Comparative Example 13, this comparative example only adjusts the method of obtaining the catalyst, while other conditions are the same as in Comparative Example 13; in this comparative example, the method of obtaining the catalyst is the same as in Example 2.

[0131] Comparative Example 15

[0132] Compared to Comparative Example 13, this comparative example only adjusts the method of obtaining the catalyst, while other conditions are the same as in Comparative Example 13; in this comparative example, the method of obtaining the catalyst is the same as in Example 3.

[0133] Comparative Example 16

[0134] Compared to Comparative Example 13, this comparative example only adjusts the method of obtaining the catalyst, while other conditions are the same as in Comparative Example 13; in this comparative example, the method of obtaining the catalyst is the same as in Example 4.

[0135] Comparative Example 17

[0136] Compared to Comparative Example 13, this comparative example only changed the method of obtaining the catalyst, while other conditions remained the same as in Comparative Example 13; in this comparative example, the method of obtaining the catalyst was the same as in Comparative Example 1.

[0137] Comparative Example 18

[0138] Compared to Comparative Example 13, this comparative example only changed the method of obtaining the catalyst, while other conditions remained the same as in Comparative Example 13; in this comparative example, the method of obtaining the catalyst was the same as in Comparative Example 2.

[0139] Analysis example 1

[0140] 1. Performance testing of H2O2 synthesis catalyzed by CNN, Fe-Ni LDH, and various CCN / Fe-Ni LDH methods:

[0141] For the H2O2 synthesis performance under illumination in Comparative Examples 7-12, please refer to [reference needed]. Figure 1 As shown in Table 1; for comparative examples 13-18, the H2O2 synthesis performance under ultrasonic (sonic) driving is shown in [reference needed]. Figure 2 As shown in Table 2; for the H2O2 synthesis performance under combined ultrasonic and light irradiation in Examples 1-4 and Comparative Examples 1-2, please refer to Table 2. Figure 3 As shown in Table 3, the catalytic activity of the prepared samples was evaluated by generating H2O2 under visible light irradiation (L), ultrasound (U), and ultrasound and visible light irradiation (U+L). Figure 1-3The catalyst symbols and catalytic conditions in the text correspond to the relevant case studies.

[0142] Table 1 Performance test of synthesized H2O2 in Comparative Examples 7-12

[0143]

[0144]

[0145] Table 3 Performance tests of synthesized H2O2 in Examples 1-4 and Comparative Examples 1-2

[0146]

[0147] The H2O2 yields of CCN and Fe-Ni LDH were low, reaching only 123.2 μM and 12.4 μM respectively after 75 min of reaction under illumination. This low performance is mainly attributed to the limited photogenerated electrons and holes in the bulk phase. Compared to CCN and Fe-Ni LDH, the H2O2 yield of the CCN / Fe-Ni LDH composite catalyst was improved, indicating that the formation of the heterojunction contributes to the photocatalytic performance.

[0148] Notably, the synergistic effect of ultrasonic vibration and light irradiation significantly improved the piezoelectric photocatalytic performance of the CCN / Fe-Ni LDH composite catalyst. Specifically, the H2O2 yield in the 3CCN / Fe-Ni LDH / U+L system (Example 1) reached 663.6 μM after 75 min of reaction, significantly higher than that of CCN and Fe-Ni LDH under the same conditions, and 2.4 times that of the 3CCN / Fe-Ni LDH / L system (Comparative Example 7) and 3.28 times that of the 3CCN / Fe-Ni LDH / U system (Comparative Example 13). This significant enhancement can be attributed to the establishment of an effective polarization electric field in the CCN / Fe-Ni LDH heterojunction under the action of ultrasound. This electric field generates a piezoelectric potential in response to deformation energy. Due to its well-matched band structure and polarization-induced piezoelectric potential, photogenerated electrons and holes bind and undergo directional transfer and migration within CCN and Fe-Ni LDH, thereby enhancing the activation of molecular oxygen.

[0149] 2. Performance testing of H2O2 synthesis catalyzed by 3CN / Fe-Ni LDH, 3CNCOOH / Fe-Ni LDH, 3CCN / Fe-Co LDH, and 3CCN / CuFe2O4:

[0150] For the H2O2 synthesis performance under combined ultrasonic (sonic) and light irradiation in Comparative Examples 3-6, please refer to [link to relevant documentation]. Figure 4 As shown in Table 4, the catalytic activity of the prepared samples was evaluated by generating H2O2 under ultrasonic and visible light irradiation (U+L). Figure 4The catalyst symbols and catalytic conditions in the text correspond to the relevant case studies.

[0151] Table 4 Performance tests of synthesized H2O2 in Comparative Examples 3-6

[0152]

[0153] Under ultrasonic and visible light irradiation (U+L), 3CCN / Fe-Ni LDH can synthesize 663.6 μM H2O2 within 75 min, significantly higher than that of 3CN / Fe-Ni LDH and 3CNCOOH / Fe-Ni LDH in Comparative Examples 3-4. This indicates that introducing cyano groups into carbon nitride can effectively enhance its piezoelectric response performance, thereby increasing the piezoelectric photocatalytic H2O2 yield. Furthermore, compared to 3CCN / Fe-Co LDH and 3CCN / CuFe2O4 in Comparative Examples 5-6, the H2O2 generation rate of 3CCN / Fe-Ni LDH is also higher, suggesting that the interfacial electronic structure between CCN and Fe-Ni LDH is more conducive to the migration and separation of photogenerated carriers.

[0154] Analysis example 2

[0155] Mechanism study of 3CCN / Fe-Ni LDH composite catalyst in piezoelectric photocatalytic synthesis of hydrogen peroxide:

[0156] 1. Performance analysis of piezoelectric photocatalytic synthesis of H2O2 by 3CCN / Fe-Ni LDH composite catalyst in the presence of different scavengers.

[0157] (1) Blank group: The method of synthesizing hydrogen peroxide was carried out in the same way as in Example 1.

[0158] (2) N2 group: The same method for synthesizing hydrogen peroxide as in Example 1 was implemented, and nitrogen aeration (10 mL / min) was continuously carried out during the process of obtaining the pretreatment liquid and the catalytic reaction.

[0159] (3) EDTA-2Na group: The method for synthesizing hydrogen peroxide was carried out in the same way as in Example 1. During the process of obtaining the pretreatment solution, deionized water, catalyst, and EDTA-2Na (used to capture photogenerated holes) were stirred together. The concentration of EDTA-2Na in the pretreatment solution was 0.5 mmol / L.

[0160] (4) p-BQ group: The method for synthesizing hydrogen peroxide was carried out in the same way as in Example 1, and in the process of obtaining the pretreatment solution, deionized water, catalyst, and p-benzoquinone (p-BQ, used to capture ·O2) were added. - The mixture was stirred together, and the concentration of p-benzoquinone in the pretreatment solution was 1 mmol / L.

[0161] (5) AgNO3 group: The method for synthesizing hydrogen peroxide was carried out in the same way as in Example 1. During the process of obtaining the pretreatment solution, deionized water, catalyst and AgNO3 (used to capture photogenerated electrons) were stirred together. The concentration of AgNO3 in the pretreatment solution was 1 mmol / L.

[0162] (6) IPA group: The method for synthesizing hydrogen peroxide was carried out in the same way as in Example 1. During the process of obtaining the pretreatment solution, deionized water, catalyst and isopropanol (IPA, used to capture ·OH) were stirred together. The concentration of isopropanol in the pretreatment solution was 1 mmol / L.

[0163] like Figure 5 As shown, after introducing N2 to remove dissolved oxygen, the yield of H2O2 decreased sharply, indicating that O2 is an important source of H2O2 for the piezoelectric-photocatalytic synthesis of 3CCN / Fe-Ni LDH.

[0164] Since the generation of H2O2 mainly originates from the electron-induced oxygen reduction reaction (ORR), the photogenerated electrons and possible ·O2 were investigated. - The effects of adding AgNO3 and p-BQ are evident. It can be seen that the formation of H2O2 is significantly suppressed after adding AgNO3 and p-BQ, indicating that photogenerated electrons and ·O2 are affected. - It plays an irreplaceable role in the synthesis of H2O2, which also indicates that the synthesis of H2O2 is caused by a two-step single-electron O2 reduction pathway.

[0165] Conversely, the addition of EDTA-2Na and IPA to the 3CCN / Fe-Ni LDH piezoelectric photocatalytic system promoted the generation of H2O2, indicating that water oxidation and ·OH are not the sources of H2O2 generation. The increase in H2O2 generation is attributed to EDTA-2Na acting as a hole trapping agent, accelerating the O2-induced ORR process.

[0166] 2. DMPO-·O2 in the piezoelectric photocatalytic reaction of the 3CCN / Fe-Ni LDH composite catalyst - ESR spectral analysis of DMPO-·OH.

[0167] 1 mg of 3CCN / Fe-Ni LDH composite catalyst (same as in Example 1) was added to 5 mL of deionized water to prepare a catalyst solution. 50 μL of the scavenging agent 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO) was dissolved in 5 mL of water to prepare a DMPO scavenging agent solution. Superoxide radicals (·O2) -In the capture experiments of hydroxyl radicals (·OH), 0.5 mL of catalyst solution was added to a centrifuge tube containing 1 mL of DMPO capture agent solution. At the same time, a 360 W ultrasonic generator and a 300 W xenon lamp with a 420 nm cutoff filter were turned on. After reacting for 6 min, the reaction was placed in an ESR instrument (JEOL JES-FA200) for detection.

[0168] like Figure 6 As shown, DMPO-·O2 in ratios of 1:1:1:1 and 1:2:2:1 were captured during ESR detection. - The peak of the DMPO-·OH adduct indicates that ·O2 is generated simultaneously during the reaction. - And ·OH. Furthermore, scavenging agent experiments showed that the addition of p-BQ inhibited the production of H2O2, indicating that ·O2... - It participates in the formation of H2O2 as an intermediate. Since the capture of ·OH does not inhibit the formation of H2O2, it indicates that the detected ·OH mainly originates from the decomposition of H2O2.

[0169] Analysis example 3

[0170] Tests on intermediate products of hydrogen peroxide synthesis using 3CCN / Fe-Ni LDH composite catalyst:

[0171] In-situ infrared spectroscopy analysis of molecular oxygen activation by the 3CCN / Fe-Ni LDH composite catalyst and ESR spectroscopy analysis of DMPO-·OOH were performed. In-situ infrared spectroscopy was conducted on a Nicolet iS50 diffuse reflectance infrared Fourier transform spectrometer. 5 mg of 3CCN / Fe-Ni-LDH was placed in the sample chamber of the in-situ infrared reaction cell, and high-purity argon gas (flow rate: 50 mL / min) was introduced for continuous degassing at 393 K for 2 hours. Subsequently, 5 μL of ultrapure water was injected into the reactor, and a certain amount of O2 was injected into the sealed reaction chamber. The reaction was initiated using a 300 W xenon lamp with a 420 nm cutoff filter, and samples were taken every 15 min for in-situ infrared spectroscopy detection.

[0172] like Figure 7 As shown in part (a), at 1159 cm -1 and 1284 cm -1 The different absorption peaks appear at the O2 position, which is attributed to O2. - And the stretching vibrations of OO; where O2 - The formation originates from molecular oxygen being converted into ·O2 through a single-electron reduction process. - , while OO comes from the ·OOH species.

[0173] The detection process for DMPO-·OOH is the same as that for DMPO-·O2. -And DMPO-·OH. See also Figure 8 As shown, ESR measurements also confirmed the presence of ·OOH, as a DMPO-·OOH adduct peak was detected; these results indicate that molecular oxygen forms ·O2 through a two-step single-electron reaction. - And the ·OOH intermediate, thereby promoting the formation of H2O2. Furthermore, such as Figure 7 As shown in part (b), 3000–3500 cm⁻¹ was detected in the in-situ FTIR spectrum. -1 The OH vibration peak at the point indicates that ·OH is also an important intermediate in the 3CCN / Fe-Ni LDH reaction process.

[0174] Analysis example 4

[0175] Performance testing of 3CCN / Fe-Ni LDH composite catalyst for piezoelectric photocatalytic decomposition of hydrogen peroxide:

[0176] 1. The formation rate constant (Kf) and decomposition rate constant (Kd) of H2O2 generated by the piezoelectric photocatalysis of the 3CCN / Fe-Ni LDH composite catalyst were analyzed. Since the accumulation of H2O2 is the result of a dynamic equilibrium between its formation and decomposition, the Kf / Kd value of H2O2 was investigated. f and K d Among them, K f and K d Following the zeroth-order and first-order dynamic assumptions respectively, through the analysis of... Figure 3 The performance curves of H2O2 were obtained by fitting.

[0177] like Figure 9 As shown, K f K d From CCN at 7.763 μM min -1 and 0.023 min -1 Increased to 24.259 μM min for 3CCN / Fe-Ni LDH. -1 and 0.035 min -1 Although K f and K d The values ​​all increased, but the K of 3CCN / Fe-Ni LDH... f It is 3.12 times that of CCN, while K d The increase was only 52.2%, indicating that the introduction of Fe-Ni LDH into CCN is more conducive to the generation of H2O2.

[0178] 2. Study on the piezoelectric photocatalytic decomposition of hydrogen peroxide using 3CCN / Fe-Ni LDH composite catalyst:

[0179] (1) Measure 50 mL of H2O2 aqueous solution with a concentration of 1 mmol / L and place it in a reactor. Add 30 mg of 3CCN / Fe-Ni LDH composite catalyst (same as Example 1) or 30 mg of CCN (same as Comparative Example 1) or 30 mg of Fe-Ni LDH (same as Comparative Example 2). In a dark environment, stir continuously at a constant speed for 30 min to ensure that the catalyst is dispersed in the H2O2 aqueous solution and that its adsorption-desorption of the reactants reaches equilibrium, and obtain the pretreated solution.

[0180] (2) Simultaneously turn on the ultrasonic generator with a power of 360 W and the xenon lamp light source with a 420 nm cutoff filter, and apply ultrasonic and visible light irradiation to the pretreatment liquid under continuous stirring to start the piezoelectric-photosynergistic catalytic decomposition of hydrogen peroxide reaction.

[0181] Samples were taken at 75 minutes after the start of the reaction for testing. Specifically, the catalyst particles were removed by filtration through a 0.45 μm microporous membrane, and the H2O2 concentration was then determined by iodometric titration.

[0182] Figure 10 The image shows the performance of the 3CCN / Fe-Ni LDH composite catalyst in piezoelectric photocatalytic decomposition of H2O2. Figure 10 As shown, after 75 min of reaction, 3CCN / Fe-Ni LDH can decompose approximately 21.4% of H2O2, while Fe-Ni LDH exhibits higher reactivity, with approximately 42.5% of H2O2 being decomposed. This indicates that the introduction of CCN can suppress the Fenton-like activity of Fe-Ni LDH, making it easier for H2O2 generated by the piezoelectric photocatalysis of 3CCN / Fe-NiLDH to accumulate.

[0183] Analysis example 5

[0184] Characterization of the piezoelectric / photoelectric properties of the CCN / Fe-Ni LDH composite catalyst:

[0185] 1. CNN analysis of photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) of various CCN / Fe-Ni LDH composite catalysts.

[0186] Add 5 mg of CNN or each CCN / Fe-Ni LDH composite catalyst to 2 mL of deionized water and sonicate for 30 min to obtain a suspension; place the suspension on a Fluromax-4 fluorescence spectrometer to detect PL, with an excitation wavelength of 320 nm.

[0187] like Figure 11As shown in section (a), a distinct emission peak was detected at 500 nm, which is due to the rapid recombination of photogenerated electron-hole pairs in CCN. Compared to CCN, the PL signal of the CCN / Fe-Ni LDH composite catalyst was significantly weakened, indicating that the interface structure restricted the recombination of photogenerated electrons and holes.

[0188] The photoelectric properties were detected using a CHI 760E electrochemical workstation in conjunction with a standard three-electrode system. In this system, platinum wire, a saturated Ag / AgCl electrode, and fluorine-doped SnO2 (FTO) conductive glass coated with catalyst were used as the counter electrode, reference electrode, and working electrode, respectively. The working electrode was prepared as follows: CNN or various CCN / Fe-Ni LDH composite catalysts were added to 400 μL of PVA solution (0.25 wt%, W / V), sonicated for 30 min, and then 200 μL of the mixture was uniformly coated onto an effective working area of ​​1 cm². 2 The working electrode was obtained by drying FTO at 60 °C in an oven. EIS was applied at 10... 5 -10 2 Measured at open-circuit potential within the Hz frequency range.

[0189] like Figure 11 As shown in section (b), the EIS spectrum shows that the CCN / Fe-Ni LDH composite catalyst has a smaller semi-circular radius, indicating that the introduction of Fe-Ni LDH can effectively reduce the electron transfer resistance of CCN and promote the separation and migration of photogenerated carriers.

[0190] 2. Analysis of LSV curves of CCN and 3CCN / Fe-Ni LDH measured on RDE at different rotational speeds; and Koutecky-Levich analysis of CCN and 3CCN / Fe-Ni LDH.

[0191] Rotating electrode (RDE) assays were performed on a CHI 760E electrochemical workstation using O2-saturated phosphate buffer (pH 7, 0.1 M). In linear sweep voltammetry (LSV) assays, the scan rate was set to 10 mV / s, and the rotation speeds were 400, 900, 1600, and 2500 rpm. The average number of electrons transferred (n) in the oxygen reduction reaction was calculated using the Koutecky-Levich equation.

[0192] like Figure 12-13As shown, the current density increases with increasing rotational speed, which is due to the shortening of the diffusion layer caused by the increased rotational speed. Compared to CCN, 3CCN / Fe-Ni LDH exhibits a larger current intensity, indicating stronger electron reduction performance. To determine the electron transfer number (n), Koutecky-Levich curve fitting was performed using RDE data at a potential of -0.8 V (vs. Ag / AgCl); from Figure 14 It can be seen that the electron transfer number of the initial CCN is 1.37, while that of 3CCN / Fe-Ni LDH is 1.68. This indicates that the coupling of CCN and Fe-Ni LDH selectively enhances the two-step single-electron O2 reduction pathway.

[0193] 3. Analysis of the reaction energy of oxygen reduction to H2O2 on 3CCN / Fe-Ni LDH under different conditions.

[0194] The reaction energy was calculated using CASTEP. The Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation and projected augmented wave (PAW) were employed in the calculations. To eliminate the effects of periodic interactions, a vacuum layer with a thickness of 15 Å was added; the energy cutoff for plane waves was set to 400 eV, and a 3×3×1 k-point grid was used. The relevant calculation parameters are as follows: the convergence criterion for interatomic forces was set to 0.01 eV / Au, the maximum stress was 0.1 GPa, and the convergence criterion for total energy was set to 1×10⁻⁶. -5 eV / atom, with a maximum displacement of 0.002 Å.

[0195] Since the main step in ORR to generate H2O2 is an intermediate... OOH ( O2→ OOH → The formation of H2O2 was investigated, and therefore the Gibbs free energy (ΔG) for H2O2 formation was calculated. See [link to relevant documentation] for details. Figure 15 The original CCN exhibited high performance. OOH ( O2→ The OOH energy barrier, with a ΔG value of 0.28 eV, is unfavorable for H2O2 formation. Conversely, the 3CCN / Fe-Ni LDH composite catalyst can effectively regulate the energy barrier. O2 and The binding energy of the OOH intermediate will O2→ The energy of OOH decreased to 0.19 eV. Furthermore, with an increased pressure of 100 MPa (simulating bubble explosion), both the ORR pathways of CCN and 3CCN / Fe-Ni LDH exhibited low energy barriers. These results indicate that, under the piezoelectric effect, the heterojunction formed by CCN and Fe-Ni LDH can effectively generate H2O2 from dissolved oxygen as a direct feedstock.

[0196] Analysis example 6

[0197] The CCN / Fe-Ni LDH composite catalyst in this invention was analyzed by X-ray diffraction, infrared absorption spectroscopy, piezoelectric force microscopy, and Kelvin probe force microscopy, and the following test spectra were obtained.

[0198] from Figure 16 As can be seen in part (a), two peaks at 13.0° and 27.4° were detected in CCN, which can be attributed to the in-plane repetition (100) and interlayer stacking (002) of the heptaazine units. For the Fe-Ni LDH sample, the characteristic peaks appearing at 2θ = 11.6°, 23.2°, 33.7°, 34.4°, 39.0°, 46.4°, 59.8° and 61.3° correspond to its (003), (006), (101), (012), (015), (018), (110) and (113) crystal planes, respectively (JCPDS No. 40-0215). In the CCN / Fe-NiLDH composite catalyst, diffraction peaks of CCN and Fe-Ni LDH can be observed, and the (002) peak gradually strengthens with the increase of CCN content.

[0199] from Figure 16 As can be seen from part (b), for CCN, 3000~3500 cm -1 The absorption peak originates from the stretching vibrations of the NH and OH bonds, 1200~1600 cm⁻¹. -1 The absorption peak is related to the stretching vibration of the CN heterocycle, 810 cm⁻¹ -1 The peak at that point represents the out-of-plane bending vibration of the heptaazine unit. Simultaneously, at 2180 cm⁻¹... -1 A weak absorption peak was detected, which originated from the asymmetric stretching vibration of the cyano group (C≡N). Furthermore, the spectrum of the CCN / Fe-Ni LDH composite catalyst was similar to that of CCN, and no obvious vibrational signal was observed in Fe-Ni LDH, which can be attributed to its inorganic semiconductor properties.

[0200] from Figure 17It can be seen that CCN exhibits a sharp absorption edge at 480 nm, while Fe-Ni LDH shows obvious absorption throughout the visible light region; after being combined with Fe-Ni LDH, the light absorption capacity of the CCN / Fe-Ni LDH composite catalyst is significantly enhanced.

[0201] from Figure 18 It can be seen that all samples exhibit typical Type IV isotherms with an H3 hysteresis loop, indicating the presence of mesopores (2-50 nm). Furthermore, the BET surface areas of CCN, 3CCN / Fe-Ni LDH, and Fe-Ni LDH are 62.0 m², respectively. 2 g -1 58.9 m 2 g -1 and 39.8 m 2 g -1 The average pore sizes were 33.1 nm, 29.7 nm and 26.3 nm, respectively, indicating that these samples could provide sufficient adsorption and reaction sites.

[0202] from Figure 19 It can be seen that CCN exhibits an ultrathin nanosheet morphology, while Fe-Ni LDH exhibits a hierarchical nanoflower structure. In the 3CCN / Fe-Ni LDH composite catalyst, close bonding between CCN and Fe-Ni LDH is observed, forming a good interfacial contact. Specifically, the 0.26 nm lattice fringes correspond to the (012) plane of Fe-Ni LDH, while the alattice structure belongs to CCN. Elemental mapping also shows that C, N, O, Fe, and Ni are uniformly distributed in the 3CCN / Fe-Ni LDH composite catalyst.

[0203] from Figure 20 As shown in section (a), a distinct amplitude-voltage butterfly loop and a clear phase reversal curve were detected within the applied voltage range of -10 to 10 V, indicating that the 3CCN / Fe-Ni LDH possesses excellent piezoelectric properties. The maximum effective piezoelectric coefficient (d) of the 3CCN / Fe-Ni LDH was determined by calculating the slope of the amplitude loop. 33 ) is 213 pmV -1 Furthermore, the piezoelectric response of 3CCN / Fe-Ni LDH was further investigated using Kelvin probe force microscopy (KPFM). Figure 20 As can be seen from sections (b) to (d), the surface potential of 3CCN / Fe-Ni LDH under illumination is approximately 17.1 mV, which is 4.1 mV lower than the 21.2 mV in darkness. The decrease in surface potential is attributed to the presence of a dipole field and strong electron-withdrawing groups (cyano groups), which can enhance the spontaneous polarization of 3CCN / Fe-Ni LDH and drive the directional transfer of electrons under illumination.

[0204] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for synthesizing hydrogen peroxide via piezoelectric photocatalysis, characterized in that, Including the following steps: S1, mix water and composite catalyst in the dark to obtain pretreatment solution; The composite catalyst comprises carbon cyanonitride and iron-nickel layered double hydroxide, wherein the carbon cyanonitride and the iron-nickel layered double hydroxide form an interfacial contact; the composite catalyst has a heterojunction structure capable of promoting electron-hole pair separation and activating molecular oxygen; the carbon cyanonitride has a heptaazine unit structure and contains a cyano group; The method for obtaining the cyanocarbon nitride includes: dissolving urea and potassium hydroxide in anhydrous ethanol, drying to obtain a precursor; calcining the precursor to obtain the cyanocarbon nitride; the mass ratio of urea to potassium hydroxide is 1000-2000:1; the calcination temperature is 500-600℃, and the calcination time is 3-6h. The composite catalyst is obtained by mixing carbon cyanide, ferric nitrate nonahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride in water to obtain a suspension; subjecting the suspension to hydrothermal treatment, followed by solid-liquid separation to obtain the composite catalyst; the mass ratio of carbon cyanide to ferric nitrate nonahydrate is 0.7-0.8:1, and the mass ratio of ferric nitrate nonahydrate, nickel nitrate hexahydrate, urea, and ammonium fluoride is 1:1.4-1.5:1.4-1.6:0.5-0.6; the hydrothermal treatment temperature is 110-130℃, and the hydrothermal treatment duration is 5-8 hours. S2, perform piezoelectric photocatalytic treatment on the pretreatment solution to obtain hydrogen peroxide; The piezoelectric photocatalytic treatment includes: using dissolved oxygen in water as a raw material, catalyzing the reduction of oxygen to generate hydrogen peroxide under the combined drive of ultrasound and visible light; the ultrasound excites the piezoelectric effect of the composite catalyst; and the visible light excites the photocatalytic effect of the composite catalyst.

2. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 1, characterized in that, In step S1, the mass-to-volume ratio of the composite catalyst to water is 0.2-1.0 mg / mL.

3. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 1, characterized in that, In step S1, the mixing time is 30-60 minutes.

4. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 1, characterized in that, During the piezoelectric photocatalytic treatment, the power of the ultrasonic waves is 80-400W.

5. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 1, characterized in that, During the piezoelectric photocatalytic treatment, the wavelength of the visible light is not less than 420 nm.

6. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 5, characterized in that, The visible light source is a xenon lamp with a 420 nm cutoff filter; the power of the xenon lamp is 200-500W.

7. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 1, characterized in that, The piezoelectric photocatalytic treatment is carried out under stirring conditions.

8. The method for synthesizing hydrogen peroxide by piezoelectric photocatalysis according to claim 1, characterized in that, The duration of the piezoelectric photocatalytic treatment is 60-150 min.

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