Biomass carbon-based composite catalyst heterostructure, preparation method and application thereof

Abstract

This invention provides a heterostructure construction, preparation method, and application of a biomass carbon-based composite catalyst, as well as the field of photocatalytic materials, including a composite catalyst of x%-g-C3N4 / BC. C -X or x%-g-C3N4 / BC H -X, where x has a value of 0.5~5; the composite catalyst is a 2D / 1D type II heterostructure; cattail biomass carbon is used as a support, and carbon nitride is attached to the surface of the cattail biomass carbon, with a mass ratio of carbon nitride to cattail biomass carbon of (0.1~10):1. This invention employs the above-mentioned heterostructure construction, preparation method, and application of a biomass carbon-based composite catalyst, significantly reducing the recombination probability of electron-hole pairs. The electrons enriched in the conduction band of biomass carbon have sufficient reduction potential to convert H+ in water... + The cells are reduced to H2, while the holes enriched in the g-C3N4 valence band are consumed by the sacrificial agent, thus continuously driving the photocatalytic reaction.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials, and in particular to the construction, preparation method and application of a heterostructure of a biomass carbon-based composite catalyst. Background Technology

[0002] To mitigate the severe recombination of electron-hole pairs and broaden the light absorption range of photocatalysts while increasing the number of active sites on their surface, various modification strategies have been employed. However, current semiconductor photocatalysts suffer from inherent defects such as small specific surface area, severe recombination of photogenerated electron-hole pairs, and limited visible light absorption range. These inherent defects lead to lower migration efficiency of photogenerated carriers, reducing the overall reaction rate, while the limited number of active sites hinders reactant adsorption and catalytic reactions. Summary of the Invention

[0003] The purpose of this invention is to provide a heterostructure construction, preparation method and application of a biomass carbon-based composite catalyst. By utilizing the difference in band structure between biomass carbon and carbon nitride (g-C3N4), the separation of electron-hole pairs is promoted, thereby improving the reaction efficiency, enabling more electrons to participate stably in the reaction, and at the same time broadening the light absorption range of carbon nitride.

[0004] To achieve the above objectives, this invention provides a heterostructured biomass carbon-based composite catalyst, wherein the composite catalyst is x%-g-C3N4 / BC C -X or x%- g-C3N4 / BC H -X, where the value of x is 0.5, 1, 2, or 5; the composite catalyst is a 2D / 1DII type heterostructure. Using cattail biomass carbon as a carrier, carbon nitride is attached to the surface of the cattail biomass carbon, and the mass ratio of carbon nitride to cattail biomass carbon is (0.1~10):1.

[0005] Preferably, the composite catalyst is x%- g-C3N4 / BC C At -X, the biomass carbon of cattail has a one-dimensional transparent tubular structure; The composite catalyst is x%- g-C3N4 / BC H At -X, the biomass carbon of cattail is in a broken state; Carbon nitride has a layered structure.

[0006] A method for preparing a heterostructured biomass carbon-based composite catalyst includes the following steps: Carbonization of biomass to produce biomass carbon BC C -X; Biomass carbon and carbon nitride were combined using a hydrothermal method. After the reaction was completed, the mixture was filtered, washed, and dried to obtain x%- g-C3N4 / BC. C-X, where x has a value of 0.5 to 5.

[0007] Preferably, it includes the following steps: Carbonization of biomass to produce biomass carbon BC C -X; Biomass carbon is activated using a hydrothermal method, and the activated biomass carbon BC is then processed. H -X recombines with carbon nitride, and after the reaction is complete, the mixture is filtered, washed, and dried to obtain x%- g-C3N4 / BC. H -X, where the value of x is 0.5 to 5.

[0008] Preferably, the temperature for carbonization of biomass is 600~900℃, and the holding time is 2~5h.

[0009] Preferably, during biomass carbon activation treatment, the mass ratio of biomass carbon to activator is 1:3, and the biomass includes cattail, cotton, or pulp residue.

[0010] Preferably, during biomass carbon activation, the biomass carbon and activator are mixed, ground, and then calcined at high temperature. The high temperature calcination temperature is 800~900℃, and the holding time is 2~5h. Activators include potassium hydroxide or potassium carbonate.

[0011] Preferably, the composite ratio of biomass carbon to nitrogen oxides is (95~99.5):(0.5~5); The composite ratio of activated biomass carbon to nitrogen oxides is (95~99.5):(0.5~5).

[0012] Preferably, during hydrothermal treatment, the hydrothermal temperature is 160~180℃ and the hydrothermal time is 10~16h.

[0013] Application of a heterostructured biomass carbon-based composite catalyst in photocatalysis.

[0014] Therefore, the present invention employs the above-mentioned heterostructure construction, preparation method, and application of a biomass carbon-based composite catalyst, and the technical effects are as follows: A type II heterojunction with band matching based on biomass carbon was realized; The charge separation direction is clear, and the driving force is strong; To broaden the absorption range of visible light; Cattail is a precursor to biomass carbon, with extremely low cost and readily available raw materials; After carbonization, cattails have a one-dimensional tubular carbon structure, which facilitates electron transport. Using cattail biomass carbon as the main catalyst is green and environmentally friendly, enabling the recycling of waste. Attached Figure Description

[0015] Figure 1 Here is a SEM image of the composite catalyst; Figure 1 (a) is a SEM image of the composite catalyst at 50 μm; Figure 1 (b) is a SEM image of the composite catalyst at 30 μm; Figure 1 (c) is a SEM image of the composite catalyst at 10 μm; Figure 2 The XRD patterns are those of Examples 1-8; Figure 2 (a) XRD patterns of Examples 1-4; Figure 2 (b) are the XRD patterns of Examples 5-8; Figure 3 XPS spectra of Examples 1-8; Figure 3 (a) XPS spectra of Examples 1-4; Figure 3 (b) XPS spectra of Examples 5-8; Figure 4 g-C3N4 / BC C XPS C1s and N1s spectra of -X; Figure 4 (a) is BC C -X、g-C3N4 / BC C XPS C1s spectra of -X and g-C3N4; Figure 4 (b) is g-C3N4 / BC C N1s spectra of -X and g-C3N4; Figure 5 The Raman spectra of Examples 1-8; Figure 5 (a) Raman spectra of Examples 1-4; Figure 5 (b) Raman spectra of Examples 5-8; Figure 6 The ultraviolet absorption spectra of Examples 1-8 are shown below. Figure 6 (a) shows the ultraviolet absorption spectra of Examples 1-4; Figure 6 (b) shows the ultraviolet absorption spectra of Examples 5-8; Figure 7 The graphs show the photocatalytic hydrogen production rates of Examples 1-8; Figure 7 (a) is a graph showing the photocatalytic hydrogen production rate of Examples 1-4; Figure 7 (b) is a graph showing the photocatalytic hydrogen production rate of Examples 5-8; Figure 8 Electrochemical impedance spectroscopy of Examples 1-8; Figure 8 (a) Electrochemical impedance spectroscopy for Examples 1-4; Figure 8 (b) Transient photocurrent response spectra of Examples 1-4; Figure 8 (c) Fluorescence spectra of Examples 1-4; Figure 8(d) shows the electrochemical impedance spectroscopy spectra of Examples 5-8; Figure 8 (e) shows the transient photocurrent response spectra of Examples 5-8; Figure 8 (f) shows the fluorescence spectra of Examples 5-8; Figure 9 EPR spectra of Examples 1-8; Figure 9 (a) EPR spectra of superoxide anions captured in Examples 1-4; Figure 9 (b) EPR spectra of hydroxyl radicals captured in Examples 1-4; Figure 9 (c) EPR spectra of superoxide anions captured in Examples 5-8; Figure 9 (d) EPR spectra of hydroxyl radicals captured in Examples 5-8; Figure 10 MS curves and XPS (valence band spectra) for Examples 1-4; Figure 10 (a) is the bandgap spectrum of g-C3N4 calculated using the Tauc method; Figure 10 (b) is the MS curve of g-C3N4; Figure 10 (c) is the XPS valence band spectrum of cattail biomass after carbonization in Example 3; Figure 10 (d) is the MS curve of cattail biomass carbonization in Example 3; Figure 11 This is a diagram of the reaction mechanism of heterojunctions. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0018] Biomass carbon, as the main body of the photocatalyst, has a clearly measurable conduction band bottom potential and valence band top potential. Biomass carbon and carbon nitride form a type II heterostructure with band matching, satisfying the following: the conduction band bottom potential of carbon nitride is more negative, and the valence band top potential of biomass carbon is more positive. Thus, under photoexcitation, photogenerated electrons migrate directionally from the conduction band of carbon nitride to the conduction band of biomass carbon, and photogenerated holes migrate directionally from the valence band of biomass carbon to the valence band of carbon nitride, achieving efficient spatial separation of electrons and holes.

[0019] Under visible light irradiation, both photocatalysts in the composite sample were excited to generate photogenerated electron-hole pairs. Due to the staggered arrangement of their band positions, the photogenerated carriers underwent directional migration: electrons from the conduction band of g-C3N4 spontaneously transferred to the conduction band of biomass carbon, while holes from the valence band of biomass carbon transferred to the valence band of g-C3N4. Ultimately, electrons were enriched on the conduction band surface of biomass carbon, and holes were enriched on the valence band surface of g-C3N4, achieving effective spatial separation and significantly reducing the recombination probability of electron-hole pairs. The electrons enriched in the conduction band of biomass carbon possessed sufficient reduction potential to convert H+ in the water... + The cells are reduced to H2, while the holes enriched in the g-C3N4 valence band are consumed by the sacrificial agent, thus continuously driving the photocatalytic reaction.

[0020] Example 1 A method for preparing a heterostructured biomass carbon-based composite catalyst includes the following steps: Cattail was carbonized to obtain cattail-based biomass carbon BC. C -X, carbonization temperature is 900℃, and holding time is 2h.

[0021] Cattail biomass carbon BC C -X and carbon nitride were mixed evenly at a mass ratio of 99.5:0.5, then deionized water was added. After ultrasonication and stirring, the mixture was transferred to a reaction vessel for hydrothermal treatment at 180℃ for 12 hours. After the hydrothermal reaction was completed, the mixture was filtered, washed, and dried to obtain 0.5%-g-C3N4 / BC. C -X.

[0022] Example 2 The difference from Example 1 is that the mass ratio of cattail-based biomass carbon to carbon nitride is 99:1, yielding 1%-g-C3N4 / BC. C -X.

[0023] Example 3 The difference from Example 1 is that the mass ratio of cattail-based biomass carbon to carbon nitride is 98:2, yielding 2%-g-C3N4 / BC. C -X.

[0024] Example 4 The difference from Example 1 is that the mass ratio of cattail-based biomass carbon to carbon nitride is 95:5, yielding 5%-g-C3N4 / BC. C -X.

[0025] Example 5 A method for preparing a heterostructured composite catalyst includes the following steps: Cattail was carbonized to obtain cattail-based biomass carbon BC. C-X, carbonization temperature is 900℃, and holding time is 2h.

[0026] Cattail biomass carbon BC C -X and potassium hydroxide were mixed at a mass ratio of 1:3 and then ground. The ground sample was placed in a porcelain boat and treated at high temperature to obtain activated cattail-based biomass carbon (BC). H -X), the high-temperature treatment temperature is set to 900℃, and the holding time is 2h.

[0027] Cattail biomass carbon BC H -X and carbon nitride were mixed evenly at a mass ratio of 99.5:0.5, then deionized water was added. After ultrasonication and stirring, the mixture was transferred to a reaction vessel for hydrothermal treatment at 180℃ for 12 hours. After the hydrothermal reaction was completed, the mixture was filtered, washed, and dried to obtain 0.5%-g-C3N4 / BC. H -X.

[0028] Example 6 The difference from Example 5 is that the mass ratio of cattail-based biomass carbon to carbon nitride is 99:1, yielding 1%-g-C3N4 / BC. H -X.

[0029] Example 7 The difference from Example 5 is that the mass ratio of cattail-based biomass carbon to carbon nitride is 98:2, resulting in 2%-g-C3N4 / BC. H -X.

[0030] Example 8 The difference from Example 5 is that the mass ratio of cattail-based biomass carbon to carbon nitride is 95:5, yielding 5%-g-C3N4 / BC. H -X.

[0031] Example 9 The difference from Example 1 is that cattail is replaced with cotton, otherwise it is the same as Example 1.

[0032] Example 10 The difference from Example 1 is that cattail is replaced with pulp residue, otherwise it is the same as Example 1.

[0033] Example 11 The difference from Example 1 is that potassium hydroxide is replaced with potassium carbonate, otherwise it is the same as Example 1.

[0034] like Figure 1 As shown, the biomass carbon of cattail is a one-dimensional transparent tubular structure. After being combined with carbon nitride, it becomes a one-dimensional transparent tubular structure with a large number of lamellar structures attached, confirming the combination of the two.

[0035] like Figure 2As shown, two broad peaks are generated near 23° and 45°, corresponding to the (002) and (100) crystal planes of the carbon material, respectively. The absence of obvious carbon nitride XRD peaks is due to the combined effects of the broad carbon peak coverage, low carbon nitride loading, and decreased crystallinity.

[0036] like Figure 3 As shown, as the carbon nitride loading increases from 0.5% to 5%, the nitrogen content in the composite material also increases, confirming the composite nature of the two.

[0037] like Figure 4 As shown, in the C1s spectrum, compared with carbon nitride, the composite material's C1s spectrum shifts towards higher binding energies, indicating that the electron density around the carbon atoms from carbon nitride in the composite material is reduced (due to the loss of some electrons). The composite material and BC... C Compared to -X, its C1s spectrum shifts towards lower binding energy, indicating that the composite material originates from BC. C The electron density around the carbon atoms of -X increases (because they gain some electrons). The above electron movement process indicates that the direction of electron flow in the composite material is from carbon nitride to BC. C -X. The N1s spectrum of the composite material also shifts towards higher binding energies compared to carbon nitride. As a whole, carbon nitride loses electrons. To compensate for the lost electrons, electrons are rearranged inside carbon nitride, resulting in a decrease in the electron density around nitrogen atoms, which confirms the electron transfer path in the composite material.

[0038] like Figure 5 As shown, with the increase of carbon nitride loading, Figure 5 (a) and Figure 5 (b) I of the composite material D / I G The ratios all showed a trend of first decreasing and then increasing, reaching their minimum value at 2% load. D / I G A smaller value indicates fewer harmful deep-level defects on the surface of the composite material at that loading level, resulting in lower electron transport resistance and more electrons available for hydrogen production. The results show that an appropriate amount of carbon nitride loading can effectively passivate harmful deep-level defects on the carbon nanotube surface, improving the graphitization degree and conductivity of the carbon matrix. When the loading exceeds 2%, the agglomeration of carbon nitride leads to the introduction of a large number of new defects, causing I... D / I G The ratio increased.

[0039] like Figure 6 As shown, the composite sample with a 2% load has the highest absorbance, indicating that the composite sample with a 2% load is more conducive to absorbing light. At the same time, the composite material has a certain light absorption capacity in the whole spectrum. Compared with the narrow absorption range of semiconductors for visible light, carbon materials have a wider light absorption range.

[0040] like Figure 7 As shown, 2-g-C3N4 / BC C -X and 2-g-C3N4 / BC H Compared to composite samples with other loading levels, the -X sample exhibits a higher hydrogen production rate. The hydrogen production rate at 1 h is lower than that at 0.5 h. The first most likely reason is the consumption of the sacrificial agent. The initial sacrificial agent concentration is low, and over time, it is gradually consumed, increasing the number of holes and intensifying electron-hole recombination. This reduces the number of electrons available for hydrogen production, thus decreasing efficiency. The second possible reason is the oxidation of the carbon material. Oxygen-containing functional groups on the carbon surface may oxidize upon contact with holes, producing carbon dioxide, which reduces the electron transport capacity of the carbon material and hinders effective electron transfer from the nitrided carbon surface. The third reason is catalyst agglomeration or sedimentation. Catalyst particles may agglomerate under stirring, light heating, and bubble disturbance. Agglomerated catalyst particles settle to the bottom of the reactor, unable to receive sufficient light. Furthermore, some catalyst particles are blocked by upper particles during stirring, preventing adequate light absorption and reducing hydrogen production performance.

[0041] like Figure 8 (a) and Figure 8 As shown in (d), 2-g-C3N4 / BC C -X and 2-g-C3N4 / BC H -X corresponds to a smaller radius, indicating a lower surface charge transfer impedance and a faster electron transport rate; for example Figure 8 (b) and Figure 8 As shown in (e), 2-g-C3N4 / BC C -X and 2-g-C3N4 / BC H The higher photocurrent intensity of -X indicates that it can generate more photogenerated carriers; such as Figure 8 (c) and Figure 8 As shown in (f), 2-g-C3N4 / BC C -X and 2-g-C3N4 / BC H The -X fluorescence intensity is the lowest, indicating that its electron-hole pair recombination degree is the lowest. These factors combined also confirm the existence of 2-g-C3N4 / BC. C -X and 2-g-C3N4 / BC H The hydrogen production rate of -X is higher than that of composite samples with other loadings.

[0042] like Figure 9 As shown in (a), BC C -X and 2-g-C3N4 / BC C -X does not produce superoxide anions under dark conditions. After exposure to light, BC...C -X and 2-g-C3N4 / BC C -X all produce superoxide anions and BC C -X produces a larger number of superoxide anions, indicating that under the same light conditions, for 2-g-C3N4 / BC... C -X produces a low concentration of superoxide anions under light conditions, with only a few electrons participating in the reduction process to generate superoxide anions. More electrons can participate in the reduction to produce hydrogen, thus improving hydrogen production efficiency. For Figure 9 (b) shows that regardless of whether it is dark or lit, BC C -X and 2-g-C3N4 / BC C -X does not produce hydroxyl radicals, indicating that hydroxyl radicals are not oxidation products of the reaction in the whole system. Figure 9 In (c), BC H -X and 2-g-C3N4 / BC H Compared to -X, more superoxide anions are produced, indicating that the composite sample can improve the utilization rate of electron reduction. Figure 9 (d) indicates that regardless of whether it is dark or lit, BC H -X and 2-g-C3N4 / BC H -X does not produce hydroxyl radicals, indicating that hydroxyl radicals are not oxidation products of the reaction in the whole system.

[0043] according to Figure 10 The MS curve and XPS valence band spectrum can be plotted. Figure 11 Heterojunction reaction mechanism diagram: g-C3N4 has a more negative conduction band potential, and electrons will spontaneously migrate from higher energy levels to lower energy levels: the direction of electron movement is: g-C3N4 flows towards BC. C -X, in BC C A reduction reaction occurs at the conduction band of -X; BC C -X has a more positive valence band potential, and holes will migrate from lower energy levels to higher energy levels: the direction of hole migration is: BC C -X flows to g-C3N4, where oxidation occurs at the top of the valence band. For example... Figure 11 As shown, the electron and hole transfer process described above promotes the separation of electron-hole pairs, allowing electrons and holes to react separately and reducing the recombination of electron-hole pairs.

[0044] Therefore, the present invention adopts the above-mentioned construction, preparation method and application of a heterostructure of biomass carbon-based composite catalyst, which utilizes the difference in band structure between biomass carbon and carbon nitride (g-C3N4) to promote the separation of electron-hole pairs, thereby improving the reaction efficiency, enabling more electrons to participate in the reaction stably, and at the same time broadening the light absorption range of carbon nitride.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A heterogeneous structure for a biomass carbon-based composite catalyst, characterized in that, The composite catalyst is x%- g-C3N4 / BC C -X or x%- g-C3N4 / BC H -X, where the value of x is 0.5, 1, 2, or 5; the composite catalyst is a 2D / 1D type II heterostructure. Using cattail biomass carbon as a carrier, carbon nitride is attached to the surface of the cattail biomass carbon, and the mass ratio of carbon nitride to cattail biomass carbon is (0.1~10):

1.

2. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 1, characterized in that, The composite catalyst is x%- g-C3N4 / BC C At -X, the biomass carbon of cattail has a one-dimensional transparent tubular structure; The composite catalyst is x%- g-C3N4 / BC H At -X, the biomass carbon of cattail is in a broken state; Carbon nitride has a layered structure.

3. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 1, characterized in that, Includes the following steps: Carbonization of biomass to produce biomass carbon BC C -X; Biomass carbon and carbon nitride were combined using a hydrothermal method. After the reaction was completed, the mixture was filtered, washed, and dried to obtain x%- g-C3N4 / BC. C -X, where x has a value of 0.5 to 5.

4. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 1, characterized in that, Includes the following steps: Carbonization of biomass to produce biomass carbon BC C -X; Biomass carbon is activated using a hydrothermal method, and the activated biomass carbon BC is then processed. H -X recombines with carbon nitride, and after the reaction is complete, the mixture is filtered, washed, and dried to obtain x%- g-C3N4 / BC. H -X, where x has a value of 0.5 to 5.

5. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 3 or 4, characterized in that, The temperature for carbonization of biomass is 600~900℃, and the holding time is 2~5h.

6. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 4, characterized in that, During biomass carbon activation treatment, the mass ratio of biomass carbon to activator is 1:3, and the biomass includes cattails, cotton, or pulp residue.

7. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 4, characterized in that, During biomass carbon activation, the biomass carbon is mixed and ground with an activator and then calcined at high temperature. The high temperature calcination temperature is 800~900℃, and the holding time is 2~5h. Activators include potassium hydroxide or potassium carbonate.

8. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 3 or 4, characterized in that, The composite ratio of biomass carbon to nitrogen oxides is (95~99.5):(0.5~5); The composite ratio of activated biomass carbon to nitrogen oxides is (95~99.5):(0.5~5).

9. The method for preparing a heterostructured biomass carbon-based composite catalyst according to claim 3 or 4, characterized in that, During hydrothermal treatment, the hydrothermal temperature is 160~180℃ and the hydrothermal time is 10~16h.

10. The application of the heterostructured biomass carbon-based composite catalyst according to claim 1, and the heterostructured biomass carbon-based composite catalyst prepared according to claim 3 or 4, in photocatalysis.

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