A quercetin-based methyl blue photocatalyst, its preparation method, and its application.

Abstract

This invention discloses a quercetin-methylene blue composite photocatalyst, its preparation method, and its application, relating to the field of photocatalyst preparation technology. The method includes the following steps: S1: Quercetin and methylene blue are placed in a beaker, deionized water is added, followed by H2SO4 and anhydrous ethanol, and the mixture is stirred to obtain a mixed solution; S2: The mixed solution is transferred to a hydrothermal reactor with a polytetrafluoroethylene liner for a isothermal reaction; S3: After the isothermal reaction, the mixture is cooled to room temperature, the reaction product is washed with deionized water, and then dried and ground into powder to obtain the final product. The photocatalyst of this invention utilizes the double hydrogen bond between the hydroxyl groups of quercetin and the sulfonic acid and amino groups of methylene blue to construct a stable composite structure, significantly enhancing its photocatalytic activity. Under visible light irradiation, the prepared photocatalyst exhibits excellent depolymerization performance in lignite, efficiently generating humic acid and fulvic acid rich in hydroxyl and amino groups.

Description

Technical Field

[0001] This invention relates to the field of photocatalyst preparation technology, specifically to a quercetin-methyl blue photocatalyst, its preparation method, and its application. Background Technology

[0002] Lignite, a low-rank coal rich in humic substances, still possesses significant development potential in resource conversion due to its low degree of coalification and abundance of oxygen-containing functional groups. Its unique molecular structure allows it to be converted into fuels and basic organic intermediates during depolymerization, while also yielding high-value-added humic acid and fulvic acid. Humic acid, composed of various aromatic and aliphatic structural units and rich in active functional groups such as carboxyl and hydroxyl groups, exhibits excellent complexing ability and electron transport properties, making it widely used in agriculture, environmental remediation, and catalysis. Fulvic acid, as a mixture of natural organic weak acids with a smaller molecular weight and more porous structure, possesses excellent water solubility and metal chelating properties, demonstrating significant effects in improving plant nutrient absorption and regulating soil structure. Therefore, constructing efficient and green lignite depolymerization strategies to achieve targeted release of humic substances can not only improve the comprehensive utilization efficiency of resources but also align with the current energy transition needs for low-carbon and sustainable development.

[0003] Traditional depolymerization methods, such as high-temperature pyrolysis, oxidative extraction, and biological treatment, often suffer from high energy consumption, poor reaction selectivity, and environmental pollution, necessitating cleaner alternative technologies. Photocatalytic advanced oxidation processes are an effective way to convert solar energy into chemical energy, capable of generating •OH and O2• under light-driven conditions. - Highly reactive species can be used to selectively break down complex organic macromolecules, demonstrating great potential for coal-based resource conversion and high-value utilization. By constructing heterojunction interfaces, optimizing band structure, and regulating charge migration behavior, photocatalytic performance can be significantly improved, providing key material support for the directional depolymerization of lignite.

[0004] Therefore, developing a photocatalytic composite material that is easy to prepare and has excellent performance is a technical problem that urgently needs to be solved by people in this field. Summary of the Invention

[0005] To address the above-mentioned problems, this invention provides a quercetin-based methyl blue photocatalyst, its preparation method, and its applications.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a method for preparing a quercetin-based methyl blue photocatalyst, specifically comprising the following steps:

[0008] S1: Place quercetin and methylene blue in a beaker, add deionized water, then add H2SO4 and anhydrous ethanol and stir to obtain a mixed solution;

[0009] S2: Transfer the mixed solution to a hydrothermal reactor with a polytetrafluoroethylene liner for constant temperature reaction;

[0010] S3: After the isothermal reaction is completed, cool to room temperature, wash the reaction product with deionized water, then dry and grind it into powder to obtain the quercetin composite methyl blue photocatalyst.

[0011] Further, in step S1, the mass ratio of quercetin to methylene blue is 0.2~0.6:0.1; the concentration of H2SO4 is 1M; the volume ratio of deionized water, H2SO4 and anhydrous ethanol is 4:1:1; and the solid-liquid ratio of methylene blue to deionized water is 0.1g:4mL.

[0012] Furthermore, in step S1, the stirring time is 30 minutes.

[0013] Furthermore, in step S2, the volume of the polytetrafluoroethylene liner is 100 mL; the temperature of the isothermal reaction is 200 °C; and the reaction time is 15 h.

[0014] Furthermore, in step S3, the drying temperature is 80°C.

[0015] The present invention also provides a quercetin composite methyl blue photocatalyst prepared by the above preparation method.

[0016] Furthermore, the photocatalyst is composed of quercetin and methylene blue through a double hydrogen bond interaction, forming an S-type heterojunction structure; the double hydrogen bond interaction is a hydrogen bond formed between the hydroxyl group of quercetin and the sulfonic acid group and amino group of methylene blue.

[0017] The present invention also provides an application of the above-mentioned quercetin composite methyl blue photocatalyst in the depolymerization of lignite. The application is to use the quercetin composite methyl blue photocatalyst to perform photocatalytic depolymerization of lignite under sodium hydroxide solution and visible light irradiation conditions to generate humic acid and fulvic acid.

[0018] Furthermore, the mass ratio of the quercetin composite methyl blue photocatalyst to lignite is 1:5; and the concentration of the sodium hydroxide solution is 1 mol / L.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This invention, for the first time, constructs a composite photocatalyst with an S-shaped heterojunction structure through the double hydrogen bond interaction between quercetin and methylene blue, significantly improving the catalytic efficiency of the photocatalyst. The hydrogen bond interaction between the polyhydroxyl groups of quercetin and the sulfonic acid and amino groups of methylene blue stabilizes the structure of the composite material and effectively promotes the separation of photogenerated electrons and holes, extending their lifetime and reducing carrier recombination, thereby improving photocatalytic performance. Compared with existing technologies, the composite catalyst of this invention, by constructing a multiphase composite structure, facilitates the effective separation and transport of photogenerated electrons and holes, reduces the carrier recombination rate, and thus improves the efficiency of the photocatalytic reaction to a certain extent, showing good application prospects. Furthermore, the prepared catalyst can efficiently depolymerize lignite, especially in generating high-value-added humic acid and fulvic acid. The entire preparation process is simple, uses inexpensive raw materials, is pollution-free, and has a short preparation time and low energy consumption, exhibiting excellent green environmental protection characteristics and broad industrial application prospects. Attached Figure Description

[0021] Figure 1 The images show the photocatalytic depolymerization effects of different catalysts prepared in Examples 1-5 on lignite under visible light.

[0022] Figure 2 The images show the photocatalytic depolymerization of lignite by pure quercetin and pure methylene blue under visible light, as used in Comparative Examples 1-2.

[0023] Figure 3 The following are the Fourier Transform Infrared (FTIR) spectra of quercetin, methylene blue and their composite photocatalyst (MBQ4), where (A) are the FTIR spectra of quercetin, methylene blue and MBQ4; and (B) are the magnified FTIR spectra of quercetin, methylene blue and MBQ4 in the characteristic wavenumber range.

[0024] Figure 4 X-ray photoelectron spectroscopy (XPS) of quercetin, methylene blue and their composite photocatalyst (MBQ4) are shown, where (A) is the C 1s XPS spectrum; (B) is the O 1s XPS spectrum; (C) is the N 1s XPS spectrum; and (D) is the S 2p XPS spectrum.

[0025] Figure 5The work function and interfacial charge distribution characteristics of quercetin, methylene blue, and their composite photocatalyst (MBQ4) are shown. (A) Work function and Fermi level distribution of quercetin; (B) Work function and Fermi level distribution of methylene blue; (C) Work function variation of the MBQ4 composite system; (D) Three-dimensional spatial distribution characteristics of the differential charge density at the interface of the MBQ4 composite system (Perspective 1), where yellow and blue areas represent electron-rich and electron-depleted regions, respectively; (E) Three-dimensional spatial distribution characteristics of the differential charge density at the interface of the MBQ4 composite system (Perspective 2); (F) Three-dimensional spatial distribution characteristics of the differential charge density at the interface of the MBQ4 composite system (Perspective 3); (G) Interfacial structural model of the MBQ4 composite system (Configuration 1); (H) Interfacial structural model of the MBQ4 composite system (Configuration 2); (I) Interfacial structural model of the MBQ4 composite system (Configuration 3). Detailed Implementation

[0026] To make the objectives and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0027] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0028] Example 1

[0029] A method for preparing a quercetin-based methyl blue photocatalyst includes the following steps:

[0030] S1: Place 0.20g quercetin and 0.10g methylene blue in a 10mL beaker, add 4mL deionized water, then add 1mL 1M H2SO4 and 1mL anhydrous ethanol and stir for 30min to obtain a mixed solution;

[0031] S2: Transfer the mixed solution to a hydrothermal reactor with a 100mL polytetrafluoroethylene liner and react at a constant temperature of 200℃ for 15h.

[0032] S3: After the isothermal reaction is completed, cool to room temperature, wash the reaction product with deionized water, then dry at 80°C and grind into powder to obtain quercetin composite methyl blue photocatalyst (MBQ), denoted as MBQ1.

[0033] The catalyst was used for lignite depolymerization: under 1 mol / L sodium hydroxide solution and visible light irradiation, MBQ1 was used to photocatalytically depolymerize lignite (the mass ratio of photocatalyst to lignite was 1:5) to generate humic acid and fulvic acid.

[0034] Example 2

[0035] The difference from Example 1 is that in step S1, the mass of quercetin is 0.30g, and a quercetin composite methyl blue photocatalyst material, denoted as MBQ2, is prepared.

[0036] Example 3

[0037] The difference from Example 1 is that in step S1, the mass of quercetin is 0.40g, and a quercetin composite methyl blue photocatalyst material, denoted as MBQ3, is prepared.

[0038] Example 4

[0039] The difference from Example 1 is that in step S1, the mass of quercetin is 0.50g, and a quercetin composite methyl blue photocatalyst material, denoted as MBQ4, is prepared.

[0040] The photocatalyst in this embodiment is not a simple physical mixture of quercetin and methylene blue, but rather a stable composite structure constructed through interfacial coupling at the molecular level, on which an S-type heterojunction with distinct electronic structure characteristics is formed.

[0041] First, by Figure 3 Through infrared spectroscopy (FTIR) and Figure 4 X-ray photoelectron spectroscopy (XPS) analysis revealed that the hydroxyl group (-OH) in the quercetin molecule and the sulfonic acid group (-SO3) in the methylene blue molecule... - Formed between ) Hydrogen bonds are formed, and simultaneously, the amino group (-NH-) in methylene blue forms a bond with the carbonyl group (C=O) of quercetin. Hydrogen bonds. Among them, such as... Figure 3 The broadening and redshift of the hydroxyl stretching vibration peak in (A)-3 (B) FTIR spectra, as well as the changes in the characteristic peaks related to sulfonic acid and carbonyl groups, indicate a change in the chemical environment of the relevant functional groups; simultaneously, such as Figure 4 The binding energies of characteristic peaks such as O 1s, N 1s, and S 2p in (A)-4(D) XPS show an overall shift, reflecting a redistribution of electron cloud density at the interface. This "double hydrogen bond" significantly enhances the interfacial bonding strength between the two components, shortens the interfacial electron transport distance, and provides a stable structural basis for subsequent heterojunction interfacial electron coupling.

[0042] Based on this, work function tests and electronic structure analyses were performed on quercetin, methylene blue, and their composite photocatalysts, and the results are as follows: Figure 5 As shown in (A)-5(C), the work function test results indicate that the work function of methylene blue is 3.524 eV, significantly lower than that of quercetin (4.699 eV). When the two materials form a composite interface, due to the difference in Fermi levels, electrons spontaneously migrate from the methylene blue side (with the lower work function) to the quercetin side (with the higher work function) until the Fermi levels of the system reach equilibrium, thus forming a stable built-in electric field at the interface. The work function of the composite material is adjusted to 3.850 eV, falling between that of the two individual components, further indicating a significant electron redistribution behavior at the interface.

[0043] To visually reveal the direction of interfacial charge migration, density functional theory (DFT) differential charge density calculations were further performed on the composite system, and the results were similar. Figure 5 As shown in (D)-5(I), the results show that a significant electron depletion region appears on the methylene blue side of the interface region, while a significant electron enrichment region is observed on the quercetin side, clearly indicating that electrons migrate directionally from methylene blue to quercetin.

[0044] The electron migration behavior driven by the work function difference and the differential charge density distribution results corroborate each other, proving that a directional carrier migration channel dominated by the built-in electric field is formed at the recombination interface. This is consistent with the typical characteristics of S-type heterojunctions, where low-energy carriers preferentially recombine at the interface, while high-energy carriers are retained in different components.

[0045] In summary, the stable composite structure formed by the double hydrogen bond interface coupling, and the interfacial electron migration behavior revealed by work function regulation and differential charge density analysis, confirm that the photocatalyst has successfully constructed an S-type heterojunction structure with distinct electronic structure characteristics between quercetin and methylene blue, and is not a simple physical mixture system.

[0046] Example 5

[0047] The difference from Example 1 is that in step S1, the mass of quercetin is 0.60g, and a quercetin composite methyl blue photocatalyst material, denoted as MBQ5, is prepared.

[0048] Comparative Example 1

[0049] Pure quercetin photocatalyst, purchased from Shanghai Maclean Biochemical Technology Co., Ltd., CAS: 117-39-5.

[0050] Comparative Example 2

[0051] Pure methyl blue photocatalyst, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS: 28983-56-4.

[0052] Experimental Example 1

[0053] The photocatalysts prepared in Examples 1-5 and Comparative Examples 1-2 were used to depolymerize lignite under visible light. The specific steps are as follows: 0.05 g of photocatalyst sample and 0.25 g of lignite (lignite to photocatalyst mass ratio of 5:1) were added to 5 mL of 1 mol / L sodium hydroxide solution, sonicated for 3 min, and a magnetic stirrer was added. The photocatalytic instrument was started, and the rotation and stirring were activated. The reaction system was placed in the photocatalytic instrument, and the mixture was irradiated and stirred under visible light for 3 hours. After the irradiation, the mixture was filtered and washed several times with distilled water to obtain a lignite depolymerization solution. 98% H2SO4 (1M) was added to the depolymerization solution to make the pH less than 1, and the solution was allowed to stand for 8-10 hours. The depolymerization solution that formed a brown precipitate was centrifuged, dried, and weighed to calculate the yield of humic acid. The supernatant obtained by centrifugation contained depolymerized fulvic acid. The supernatant was extracted with ethyl acetate, then rotary evaporated, dried, and weighed to calculate the yield of fulvic acid. The formulas for calculating the yields of humic acid and fulvic acid are shown in Formula 1 and Formula 2.

[0054]

[0055]

[0056] From the appendix Figure 1 As can be seen, the MBQ1 photocatalyst of Example 1, under visible light irradiation, yielded 75.76% humic acid and 8.66% fulvic acid in 3 hours. The MBQ2 photocatalyst of Example 2, under visible light irradiation, yielded 78.57% humic acid and 10.00% fulvic acid in 3 hours. The MBQ3 photocatalyst of Example 3, under visible light irradiation, yielded 80.01% humic acid and 10.06% fulvic acid in 3 hours. The MBQ4 photocatalyst of Example 4, under visible light irradiation, yielded 82.63% humic acid and 12.13% fulvic acid in 3 hours. The MBQ5 photocatalyst of Example 5, under visible light irradiation, yielded 56.11% humic acid and 7.46% fulvic acid in 3 hours.

[0057] From the appendix Figure 2 It can be seen that, under visible light irradiation, the pure quercetin photocatalyst of Comparative Example 1 can achieve a humic acid yield of 49.76% and a fulvic acid yield of 13.2% after 3 hours. Under visible light irradiation, the pure methyl blue photocatalyst of Comparative Example 2 can achieve a humic acid yield of 10.92% and a fulvic acid yield of 4.40% after 3 hours.

[0058] Therefore, it can be seen that the quercetin-methyl blue photocatalysts prepared in Examples 1-5 have a good depolymerization effect on lignite. Among them, the MBQ4 photocatalyst has the highest yield of humic acid and fulvic acid obtained from the depolymerization of lignite, indicating that the MBQ4 photocatalyst has the best depolymerization effect on lignite.

[0059] In this embodiment, the quercetin and methylene blue composite photocatalyst, under photoexcitation, interacts through the double hydrogen bond interaction between quercetin and methylene blue. and A stable composite structure is formed. This composite structure enhances the coupling of interfacial charges and the structural stability of the material. In the composite catalyst, a built-in electric field is formed between quercetin and methylene blue, effectively promoting the spatial separation of photogenerated electrons and holes and suppressing the recombination of electron-hole pairs. In addition, the photocatalyst exhibits excellent •OH and O2• - The ability to generate free radicals significantly promotes the breakage of aromatic and aliphatic structures in lignite, thereby improving the yield and quality of humic substances.

[0060] In summary, the photocatalyst composite material prepared in this embodiment exhibits stable performance, good depolymerization effect on lignite, and uses inexpensive and pollution-free raw materials. The preparation time is short and energy consumption is low, showing promising application prospects in addressing the energy crisis and in the field of photocatalysis. It can be produced on a large scale.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of a quercetin-based methyl blue photocatalyst, characterized in that: The application involves using the quercetin-methyl blue photocatalyst to photocatalytically depolymerize lignite under sodium hydroxide solution and visible light irradiation conditions to generate humic acid and fulvic acid. The preparation method of the quercetin-methyl blue photocatalyst specifically includes the following steps: S1: Place quercetin and methylene blue in a beaker, add deionized water, then add H2SO4 and anhydrous ethanol and stir to obtain a mixed solution; wherein, the mass ratio of quercetin to methylene blue is 0.2~0.6:0.1; the concentration of H2SO4 is 1M; the volume ratio of deionized water, H2SO4 and anhydrous ethanol is 4:1:1; the solid-liquid ratio of methylene blue to deionized water is 0.1g:4mL; S2: Transfer the mixed solution to a hydrothermal reactor with a polytetrafluoroethylene liner for constant temperature reaction; S3: After the isothermal reaction is completed, cool to room temperature, wash the reaction product with deionized water, then dry and grind it into powder to obtain the quercetin composite methyl blue photocatalyst. In the photocatalyst, quercetin and methylene blue are combined through double hydrogen bond interactions to form an S-type heterojunction structure; the double hydrogen bond interaction is a hydrogen bond formed between the hydroxyl group of quercetin and the sulfonic acid group and amino group of methylene blue.

2. The application according to claim 1, characterized in that: The mass ratio of the quercetin-methyl blue photocatalyst to lignite is 1:5; the concentration of the sodium hydroxide solution is 1 mol / L.

3. The application according to claim 1, characterized in that: In step S1, the stirring time is 30 minutes.

4. The application according to claim 1, characterized in that: In step S2, the volume of the polytetrafluoroethylene liner is 100 mL; the constant temperature reaction temperature is 200 °C; and the reaction time is 15 h.

5. The application according to claim 1, characterized in that: In step S3, the drying temperature is 80°C.

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