Titanium oxide core-shell structure photocatalyst loaded with metal particles, and preparation method and application thereof

Abstract

This invention discloses a titanium dioxide core-shell structured photocatalyst supported on metal particles. The catalyst is obtained by calcining titanium-based metal-organic framework material MIL-125(Ti) as a precursor, after introducing metal components, tannic acid, and metal coordination. Titanium oxide forms the core structure, and a carbon layer coating the surface forms the shell structure, supporting metal particles. During preparation, the preparation conditions can be optimized by controlling the concentration of metal ions, the concentration of tannic acid, and the pH of the tannic acid coordination system. This photocatalyst exhibits high catalytic activity, target product selectivity, and cycle stability in the photocatalytic oxidation conversion of biomass derivatives. It is suitable for the selective oxidation of biomass platform compounds such as 5-hydroxymethylfurfural to prepare high-value-added products. Furthermore, the preparation method is simple, the raw materials are widely available, and it is suitable for catalytic conversion applications under visible light conditions, demonstrating good application prospects and promotional value.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic conversion technology of biomass derivatives, specifically to a titanium dioxide core-shell structured photocatalyst supported on metal particles and its preparation method. Background Technology

[0002] Biomass, as an important renewable carbon resource, is characterized by high oxygen content and complex structure. Its efficient conversion into high-value-added chemicals is a crucial pathway to promoting green and sustainable development. In recent years, the targeted conversion and high-value utilization of biomass derivatives have received widespread attention. 5-Hydroxymethylfurfural (HMF), as a typical biomass-derived platform compound, can be selectively oxidized to prepare high-value-added products such as 2,5-dicarboxyfuran (DFF), 5-formyl-2-furancarboxylic acid (FFCA), and 2,5-furandicarboxylic acid (FDCA). This conversion process has become a research hotspot for the high-value utilization of biomass.

[0003] Titanium oxide (TiO2) semiconductor materials possess advantages such as high chemical stability, wide availability, low cost, and environmental friendliness, leading to their widespread application in photocatalysis. However, TiO2 still faces significant limitations in the photocatalytic oxidation of biomass derivatives. On one hand, its ability to utilize visible light is limited, and photogenerated electrons and holes readily recombine, resulting in low efficiency in the formation of active species during the catalytic process. On the other hand, the oxidation process of biomass derivatives such as HMF typically involves multiple steps, and the electron transport capability, active site distribution, and structural stability of the catalyst surface all significantly influence reaction activity and target product selectivity. Existing TiO2 catalytic systems struggle to simultaneously achieve both high substrate conversion rates and high target product selectivity. Therefore, developing photocatalysts with rapid charge transfer rates, high catalytic activity, and excellent selectivity has become an urgent need to overcome current technological bottlenecks. Summary of the Invention

[0004] This invention provides a titanium dioxide core-shell structured photocatalyst supported on metal particles. Comparative results show that introducing a carbon shell reduces the size of the metal particles in the catalyst, which is beneficial for improving the catalyst's structural characteristics and enhancing its photocatalytic activity and target product selectivity. Through gradient control and optimization of relevant parameters, the prepared photocatalyst exhibits high reactivity and target product selectivity in the catalytic conversion of biomass derivatives.

[0005] To address the aforementioned technical problems, this invention proposes a titanium oxide core-shell structured photocatalyst loaded with metal particles. The catalyst is obtained by introducing metal, coordinating tannic acid with metal, and calcining the titanium-based metal-organic framework material MIL-125(Ti) as a precursor. In this process, titanium oxide forms the core structure, and the carbon layer covering the surface of the core structure forms the shell structure. The catalyst is loaded with metal particles.

[0006] The metal is selected from one or more of Fe, Co, Ni, and Cu.

[0007] Meanwhile, this invention also provides a method for preparing the above-mentioned titanium dioxide core-shell structured photocatalyst supported on metal particles, the method comprising the following steps:

[0008] Step 1) Grind the titanium-based metal-organic framework MIL-125(Ti) thoroughly in an agate mortar for 30-60 min to obtain a relatively uniform powder; then, mix the powder at a concentration of 10 mg / mL. -1 The concentration of the metal ion was dispersed in a near-neutral phosphate buffer solution with a pH of 6.5–7.5 and then ultrasonically dispersed; subsequently, a metal solution and a tannic acid solution were added to obtain a mixture in which the metal ion concentration was 1.2–4.8 mmol / mL. -1 The molar ratio of tannic acid to metal ions is 1:1 to 4:1; the mixture is stirred thoroughly to obtain an intermediate product.

[0009] Step 2) After washing and drying the intermediate product with deionized water, it is evenly spread in a container and calcined in a muffle furnace; the calcination process conditions are: a heating rate of 4~5℃ / min from room temperature. -1 The temperature was raised to 450~550℃ and held for 4 h; after calcination, it was naturally cooled to room temperature to obtain a titanium oxide core-shell structured photocatalyst loaded with metal particles, denoted as photocatalyst TiO2@CM.

[0010] Furthermore, in the preparation method described in this invention, wherein:

[0011] In step 1), the preparation steps of the titanium-based metal-organic framework MIL-125(Ti) are as follows: terephthalic acid is dissolved in a mixed solution of N,N-dimethylformamide and anhydrous methanol, and then tetrabutoxytitanium is added. After forming a transparent solution under stirring conditions, the solution is reacted at 160°C for 20 h. After washing and drying, the solution is thoroughly ground and ready for use.

[0012] In step 1), the phosphate buffer is prepared by mixing NaH2PO4 and Na2HPO4 in a molar ratio of 2:1 and adding deionized water to a concentration of 20 mmol / L. -1 .

[0013] In step 1), the concentration of the metal solution is 30 mmol / L. -1 The concentration of the tannic acid solution is 30 mmol / L. -1 .

[0014] The titanium dioxide core-shell structure photocatalyst with metal particles supported by this invention was used for photocatalytic conversion of biomass derivatives. During the reaction, the photocatalyst was added to the biomass derivative solution, wherein the molar ratio of the added photocatalyst to the biomass derivative was 200 mg: 1 mmol. After ultrasonic dispersion, the solution was stirred in the dark for 30-60 min, and then reacted at 25°C for 6-12 h under visible light irradiation.

[0015] The biomass derivative includes 5-hydroxymethylfurfural. The conversion reaction system is carried out under visible light irradiation at 25°C for 6-12 h. The photocatalyst is used to catalyze the oxidation of 5-hydroxymethylfurfural to 2,5-dicarboxyfuran, 5-formyl-2-furancarboxylic acid, and 2,5-furandicarboxylic acid. The conversion rate of 5-hydroxymethylfurfural is 56.1%-86.1%; the selectivity of the target product is 58.32%-75.40%; the yield of 2,5-dicarboxyfuran is 31.97%-46.51%; the yield of 5-formyl-2-furancarboxylic acid is 3.71%-14.76%; and the yield of 2,5-furandicarboxylic acid is 0.37%-7.09%.

[0016] Furthermore, the conversion reaction system was subjected to visible light irradiation at 25°C for 8 h, and the conversion rate of 5-hydroxymethylfurfural was 75.31%~82.25%; the selectivity of the target product was 67.95%~75.40%; the yield of 2,5-dicarboxyfuran was 40.94%~48.37%; the yield of 5-formyl-2-furancarboxylic acid was 7.68%~9.30%; and the yield of 2,5-furandicarboxylic acid was 1.54%~4.34%.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] The photocatalyst of this invention uses MIL-125(Ti) as a precursor, which is prepared by introducing metal particles and further modifying it with tannic acid followed by calcination. The TiO2 semiconductor substrate forms the core, and the tannic acid-derived carbon layer forms the shell, supporting the metal particles. During the preparation process, MIL-125(Ti) is dispersed in a buffer system and the metal is introduced. Simultaneously, tannic acid is added for surface coordination modification, resulting in a tannic acid-modified precursor. After calcination, a titanium dioxide core-shell structure photocatalyst TiO2@CM with metal particles is formed. During the preparation process, the metal ion concentration, the molar ratio of tannic acid to metal ions, and the pH of the polyphenol coordination system are controlled to optimize the metal dispersion state, carbon layer coating structure, and interfacial electron transport performance of the photocatalyst. This catalyst can be used for the photocatalytic oxidation conversion of biomass derivatives. Compared with existing catalytic systems, the catalytic system constructed in this invention effectively improves the photocatalytic reaction activity and enhances the selectivity and yield of the target product, exhibiting excellent catalytic performance. Attached Figure Description

[0019] Figure 1 TEM image of the MIL-125(Ti) precursor prepared in Example 1;

[0020] Figure 2 a), b), and c) are TEM images of TiO2, TiO2 / Cu, and TiO2@C-Cu, respectively; d), e), and f) are HRTEM images of the corresponding samples, showing the lattice fringes of TiO2, TiO2 / Cu, and TiO2@C-Cu.

[0021] Figure 3 The XRD patterns of the MIL-125(Ti), TiO2, TiO2@C-Fe, TiO2@C-Co, TiO2@C-Ni and TiO2@C-Cu catalysts in Example 3 are shown below.

[0022] Figure 4 This is a comparison chart of the conversion rates and selectivity of MIL-125, TiO2, TiO2 / Cu, TiO2@C, and TiO2@C-Cu catalysts in the HMF photocatalytic oxidation reaction in Example 8.

[0023] Figure 5 The conversion rate and target product selectivity of TiO2@CM catalysts obtained under different metal ion concentrations in HMF photocatalytic oxidation reaction were determined after 8 h of illumination.

[0024] Figure 6 The conversion rate and target product selectivity of TiO2@CM catalysts obtained under different tannic acid concentrations in HMF photocatalytic oxidation reaction were determined after 8 h of illumination.

[0025] Figure 7The conversion rate and target product selectivity of TiO2@CM catalysts obtained under different pH conditions of tannic acid coordination reaction systems after 8 h of light irradiation were compared in the HMF photocatalytic oxidation reaction. Detailed Implementation

[0026] This invention provides a titanium dioxide core-shell structured photocatalyst with supported metal particles suitable for the photocatalytic conversion of biomass derivatives, and its construction method. The catalyst uses MIL-125(Ti) as a precursor, and by introducing metal and further constructing a carbon layer on the material surface, a TiO2@CM composite structure is formed after calcination. In this composite structure, TiO2 acts as the semiconductor host, providing a photoresponsive framework; the metal component acts as an active site, promoting substrate activation and electron transfer; and the carbon layer acts as a conductive interface layer, improving the separation and transport of photogenerated carriers, thereby enhancing the activity, selectivity, and stability in the photocatalytic conversion reaction of biomass derivatives. The TiO2@C-Cu catalyst exhibits the best catalytic performance in the HMF photocatalytic oxidation reaction.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] Example 1:

[0029] Preparation of the MIL-125(Ti) precursor used in the photocatalyst of this invention: 3 g of terephthalic acid was weighed and added to a mixed solvent containing 54 mL of N,N-dimethylformamide (DMF) and 6 mL of anhydrous methanol, and stirred until dissolved; then 1.1 mL of tetrabutoxytitanium was added, and stirring continued to form a transparent solution. The resulting solution was transferred to a reaction vessel and heated at 160 °C for 20 h. After the reaction was completed, it was naturally cooled to room temperature, filtered to obtain a white solid, and thoroughly washed with DMF and anhydrous methanol, respectively. Finally, the washed solid was dried at 70 °C for 10 h to obtain the MIL-125(Ti) precursor. It was then thoroughly ground in an agate mortar for 30 min to obtain a relatively uniform powder for later use.

[0030] Figure 1 TEM images of the MIL-125(Ti) precursor prepared in Example 1 are shown, indicating that the MIL-125(Ti) precursor has a relatively regular and complete particle morphology, providing a good structural basis for subsequent calcination conversion and metal loading.

[0031] Example 2:

[0032] Preparation of phosphate buffer used in this invention: Using deionized water as solvent, a solution of NaH₂PO₄ and Na₂HPO₄ in a molar ratio of 2:1 was prepared to achieve a concentration of 20 mmol / L. -1Phosphate buffer solution with a pH of 7.26.

[0033] Comparative Example 1:

[0034] Preparation of TiO2 / Cu photocatalyst: 150 mg of MIL-125(Ti) prepared in Example 1 was weighed and ultrasonically dispersed in the phosphate buffer prepared in Example 2. Then, 600 μL of a 30 mmol / L solution was added under stirring. -1 A copper chloride solution was prepared. The system was further diluted with phosphate buffer to a total volume of 15 mL and stirred at room temperature for 12 h. After the reaction was complete, the mixture was repeatedly washed with deionized water until the supernatant was clear. The solid was collected by centrifugation and dried under vacuum at 70 °C to obtain the MIL-125 / Cu precursor. The precursor was then placed in a muffle furnace and heated at 5 °C for 1 min. -1 The temperature was increased to 500℃ at a certain rate and then calcined for 4 h to obtain TiO2 / Cu photocatalyst.

[0035] Preparation of pure TiO2 material: Pure TiO2 material can be obtained by directly calcining MIL-125(Ti) under the same calcination conditions as described above.

[0036] Comparative Example 2:

[0037] Preparation of TiO2@C photocatalyst: 150 mg of MIL-125(Ti) prepared in Example 1 was weighed and dispersed in 15 mL of phosphate buffer prepared in Example 2. Then, 300 μL of 30 mmol / L solution was added to the system. -1 A tannic acid solution was prepared. The resulting suspension was stirred at room temperature for 12 h, and the solid was collected by centrifugation, washed three times with deionized water, and vacuum dried at 70 °C. The product was then placed in a muffle furnace and heated at 5 °C for 1 min. -1 The temperature was increased to 500℃ and calcined at that temperature for 4 hours. After calcination, the temperature was naturally cooled to room temperature, and the product obtained was TiO2@C photocatalyst.

[0038] Example 3:

[0039] Preparation of TiO2@C-Cu photocatalyst: 150 mg of MIL-125(Ti) prepared in Example 1 was weighed and dispersed in 15 mL of phosphate buffer prepared in Example 2. Then, 300 μL of 30 mmol / L solution was added to the system. -1 Tannic acid solution and 600 μL of 30 mmol L -1A copper chloride solution was used. The resulting suspension was stirred at room temperature for 12 h, and the solid was collected by centrifugation, washed three times with deionized water, and vacuum dried at 70 °C to obtain the intermediate product, denoted as TA-MIL-125 / Cu precursor. The above precursor TA-MIL-125 / Cu was placed in a muffle furnace and heated at 5 °C for 1 min. -1 The temperature was increased to 500℃ and calcined at that temperature for 4 hours. After calcination, the temperature was naturally cooled to room temperature, and the product obtained was the photocatalyst TiO2@C-Cu.

[0040] Following the above method and steps, copper chloride was replaced with ferric chloride, cobalt chloride, or nickel chloride, while keeping other conditions unchanged, to prepare photocatalysts TiO2@C-Fe, TiO2@C-Co, and TiO2@C-Ni, respectively.

[0041] like Figure 2 As shown, a)–c) are TEM images of TiO2 and Cu / TiO2 prepared in Comparative Example 1 and TiO2@C-Cu prepared in Example 3, respectively, and d)–f) are HRTEM images of the corresponding samples. The TEM images show that TiO2@C-Cu exhibits a more pronounced coating structure compared to TiO2 and Cu / TiO2, indicating that the carbon layer has been successfully constructed on the material surface. The HRTEM images reveal clear lattice fringes, with an interplanar spacing of approximately 0.358 nm corresponding to the (101) plane of TiO2, and interplanar spacings of approximately 0.200 nm or 0.181 nm belonging to the (111) plane of Cu, indicating that the obtained catalyst has good crystallinity and that Cu has been successfully introduced into the TiO2 matrix. Simultaneously, a clear interface is observed between the TiO2 and Cu-related lattice regions, indicating that a close contact has been formed between them, which is beneficial for interfacial electron transport. Compared with TiO2 / Cu, the Cu-related lattice features in TiO2@C-Cu are finer and more uniformly distributed, indicating that the introduction of the carbon layer has a certain confinement and dispersion effect on Cu, which is beneficial to improving the dispersion uniformity of metal particles.

[0042] Figure 3 The XRD patterns are shown for the MIL-125(Ti) catalyst prepared in Example 1, the TiO2 catalyst prepared in Comparative Example 1, and the TiO2@C-Fe, TiO2@C-Co, TiO2@C-Ni, and TiO2@C-Cu catalysts prepared in Example 3. It can be seen that the MIL-125(Ti) precursor transforms into the TiO2 crystalline phase after calcination. Compared with TiO2, the photocatalysts still retain the characteristic diffraction peaks of TiO2, indicating that the main crystalline phase structure of TiO2 was not destroyed after the introduction of the carbon layer and metal particles, and the material still maintains good crystal structure stability.

[0043] Example 4:

[0044] Construction of the photocatalytic reaction system: 20 mg of the photocatalyst TiO2@C-Cu prepared in Example 3 was added to a 30 mL photochemical reactor containing 10 mL of HMF aqueous solution with a concentration of 10 mmol / L. -1 The reaction mixture was sonicated for 5 min to ensure thorough dispersion of the catalyst and substrate, and then stirred in the dark for 30 min to reach adsorption-desorption equilibrium. A 300 W xenon lamp was used as the light source, and the photocatalytic reaction was carried out after filtering out ultraviolet light with a 420 nm cutoff filter. The reaction temperature was controlled at 25℃. 0.2 mL samples were taken every 1 h during the reaction and analyzed by high-performance liquid chromatography (HPLC) to determine the HMF conversion, target product yield, and selectivity.

[0045] The high-performance liquid chromatograph is equipped with an HPX-87H column, using 5 mmol / L... -1 Sulfuric acid aqueous solution was used as the mobile phase at a flow rate of 0.6 mL / min. -1 The column temperature was 40℃, the detection wavelength was 265 nm, and the runtime for each detection was 60 min. The HMF conversion, selectivity, and target product yield were calculated based on the HMF concentrations before and after the reaction, as well as the product concentrations. The calculation formulas are as follows:

[0046]

[0047]

[0048]

[0049] To investigate the cyclic stability of the catalyst, a repeated reuse experiment was conducted on TiO2@C-Cu under the same reaction conditions. After each reaction, the catalyst was recovered by centrifugation, washed several times with deionized water and ethanol, and dried at 60°C before being used in the next reaction. After 5 cycles, the HMF conversion remained above 90% of the initial value, and the DFF yield remained above 90% of the initial value.

[0050] Following the same method described above, TiO2@C-Fe, TiO2@C-Co, or TiO2@C-Ni photocatalysts were used instead of TiO2@C-Cu for photocatalytic reactions. The reaction solutions were sampled and analyzed to determine the HMF conversion rate, target product yield, and selectivity corresponding to each photocatalyst.

[0051] like Figure 4As shown, under the same reaction conditions, MIL-125(Ti) prepared in Example 1, TiO2 and TiO2 / Cu prepared in Comparative Example 1, TiO2@C prepared in Comparative Example 2, and TiO2@C-Cu prepared in Example 3 were used as catalysts for HMF photocatalytic oxidation. After a reaction time of 8 h, the HMF conversion rate of MIL-125 was 55.32%, with a target product selectivity of 5.78%; the HMF conversion rate of TiO2 was 69.27%, with a target product selectivity of 3.1%; the HMF conversion rate of TiO2 / Cu was 62.79%, with a target product selectivity of approximately 40%; the HMF conversion rate of TiO2@C was 65.37%, with a target product selectivity of 3.1%; and the HMF conversion rate of TiO2@C-Cu was 82.25%, with a target product selectivity of 75.4%.

[0052] The results show that the MIL-125(Ti) precursor itself possesses certain photocatalytic activity, but its HMF conversion and target product selectivity are both low. After calcination to form TiO2, the HMF conversion improved, but the target product selectivity remained low, indicating that while TiO2 alone can promote substrate conversion, its ability to direct the formation of the target product is weak. Compared to TiO2, TiO2 / Cu showed significantly improved target product selectivity, indicating that the introduction of Cu metal components is beneficial for improving the reaction pathway regulation and promoting target product formation, but its HMF conversion did not significantly improve. On the other hand, the improvement in HMF conversion and target product selectivity of TiO2@C compared to TiO2 was limited, indicating that the introduction of carbon coating alone did not significantly improve catalytic performance.

[0053] In comparison, TiO2@C-Cu exhibits both higher HMF conversion and target product selectivity, significantly outperforming MIL-125(Ti), TiO2, TiO2 / Cu, and TiO2@C. This result indicates a synergistic promoting effect between the introduction of metal particles and carbon layer coating: the metal particles enhance the selectivity for target product formation, while the carbon layer coating helps regulate the dispersion state and interfacial structure of metal species, further improving the overall photocatalytic oxidation performance of the catalyst. Therefore, the core-shell structured metal-supported TiO2-based photocatalyst described in this invention demonstrates excellent performance and promising application potential in HMF photocatalytic oxidation reactions.

[0054] Tables 1, 2, 3, and 4 show the conversion rates of 5-hydroxymethylfurfural, the selectivity of the target product, and the yields of DFF, FFCA, and FDCA when the photocatalysts TiO2@C-Cu, TiO2@C-Fe, TiO2@C-Co, and TiO2@C-Ni prepared in Example 3 were used to catalyze the oxidation of 5-hydroxymethylfurfural to 2,5-dicarboxyfuran, with the reaction system subjected to visible light irradiation at 25°C for 6–12 h. Table 5 summarizes the conversion rates of 5-hydroxymethylfurfural, the selectivity of the target product, and the yields of DFF, FFCA, and FDCA when the photocatalysts TiO2@C-Cu, TiO2@C-Fe, TiO2@C-Co, and TiO2@C-Ni prepared in Example 3 were used to catalyze the oxidation of 5-hydroxymethylfurfural to 2,5-dicarboxyfuran, with the reaction system subjected to visible light irradiation at 25°C for 8 h.

[0055] Table 1

[0056]

[0057] Table 2

[0058]

[0059] Table 3

[0060]

[0061] Table 4

[0062]

[0063] Table 5

[0064]

[0065] Example 5:

[0066] Optimization of metal ion concentration in the preparation method of this invention.

[0067] Based on Example 3, all conditions remained unchanged except for the metal ion concentration. That is, the tannic acid concentration was kept constant at 0.3 mmol / L. -1 Under the given conditions, the molar ratios of tannic acid to metal ions were 1:2, 1:4, 1:8, 1:16, and 1:32, respectively. These ratios were adjusted by controlling the concentration of the metal salt solution to 0.6 mmol / L. -1 1.2 mmol / L -1 2.4 mmol L -1 4.8 mmol / L -1 and 9.6 mmol L -1TA-MIL-125 / M precursors with different metal incorporation ratios were prepared and further calcined to obtain the corresponding TiO2@CM catalysts. The catalytic performance of the catalysts obtained under different metal solution concentrations was compared to investigate the effect of metal ion concentration on catalyst performance.

[0068] like Figure 5 As shown, with the metal ion concentration increasing from 0.6 mmol / L... -1 Increased to 2.4 mmol L -1 The catalyst showed an increasing trend in both HMF conversion and target product selectivity. When the metal ion concentration was further increased to 4.8 mmol L⁻¹, the conversion rate was higher than that of the target product. -1 and 9.6 mmol L -1 At this point, the catalytic performance decreased. The results indicate that the metal ion concentration has a significant impact on catalyst performance; when the metal ion concentration is controlled within the range of 1.2–4.8 mmol / L... -1 When the catalyst was obtained, it exhibited good catalytic performance; among which 2.4 mmol L -1 The overall catalytic performance is optimal at this time.

[0069] Example 6:

[0070] The optimization of the molar ratio of tannic acid to metal ions in the preparation method of this invention.

[0071] Based on Example 3, all conditions remained unchanged except for the tannic acid concentration. Specifically, the metal ion concentration was fixed at 0.6 mmol / L. -1 Under these conditions, the concentration of tannic acid solution was adjusted to 0.3 mmol / L. -1 0.6 mmol L -1 1.2 mmol / L -1 2.4 mmol L -1 and 4.8 mmol L -1 TA-MIL-125 / M precursors with different tannic acid concentrations were prepared by setting the molar ratio of tannic acid to metal ions to 1:2, 1:1, 2:1, 4:1, and 8:1, respectively. These precursors were then further calcined to obtain the corresponding TiO2@CM catalysts. The catalytic performance of the catalysts obtained under different tannic acid concentrations was compared to investigate the effect of the molar ratio of tannic acid to metal ions on catalyst performance.

[0072] like Figure 6As shown, the conversion rate of tannic acid to metal ions and the selectivity of the target product of the catalyst gradually increased with the increase of the molar ratio of tannic acid to metal ions from 1:2 to 2:1. When the molar ratio of tannic acid to metal ions continued to increase to 4:1 and 8:1, the catalytic performance decreased. The results indicate that the molar ratio of tannic acid to metal ions has a significant impact on the catalytic performance of the catalyst. When the molar ratio of tannic acid to metal ions is 1:1 to 4:1, the obtained catalyst has better catalytic performance, among which the catalyst with a molar ratio of tannic acid to metal ions of 2:1 has the best overall catalytic performance.

[0073] Example 7:

[0074] Optimization of pH in tannic acid coordination reaction system.

[0075] Based on Example 6, all conditions remained unchanged except for the pH of the reaction system during tannic acid coordination. The tannic acid coordination reaction was carried out at pH 5, 6, 7, 8, and 9 by adjusting the pH of the reaction system. TA-MIL-125 / Cu precursors were prepared under different pH conditions and further calcined to obtain the corresponding TiO2@C-Cu catalysts. The catalytic performance of the catalysts obtained under different pH conditions was compared to investigate the effect of the reaction system pH on the catalyst preparation effect and catalytic performance.

[0076] like Figure 7 As shown, the pH of the reaction system is a crucial factor affecting the catalytic performance of the obtained catalyst. Within the scope of this example, the catalyst exhibits superior catalytic performance when the pH of the reaction system is 6.5–7.5, with the catalyst prepared at a pH of 7 showing the best catalytic performance. When the pH of the reaction system is below 6.5 or above 7.5, the catalytic performance of the obtained catalyst decreases.

[0077] In the preparation method of this invention, the preparation process of the photocatalyst can be controlled by adjusting the concentration of metal ions, the molar ratio of tannic acid to metal ions, and the pH of the tannic acid coordination system, thereby affecting the composition and catalytic performance of the resulting photocatalyst. The main influence mechanisms are as follows:

[0078] (1) The effect of metal ion concentration. The metal ion concentration has a significant impact on the catalytic performance of the obtained catalyst. When the metal ion concentration is 1.2~4.8 mmol L... -1 At this time, the obtained catalyst exhibited good catalytic performance, with a metal ion concentration of 2.4 mmol / L. -1 The catalytic performance is optimal when the metal ion concentration is below 1.2 mmol / L. -1 or higher than 4.8 mmol / L -1When the concentration of metal ions decreases, the catalytic performance of the resulting catalyst declines. This indicates that there is an optimal range for the concentration of metal ions, and controlling it within this range is beneficial for obtaining better catalytic effects.

[0079] (2) Effect of the molar ratio of tannic acid to metal ions. The concentration of tannic acid has a significant impact on the catalytic performance of the obtained catalyst. As the molar ratio of tannic acid to metal ions increases from 1:2 to 2:1, the catalytic performance of the obtained catalyst gradually improves; when the molar ratio continues to increase to 4:1 and 8:1, the catalytic performance decreases. Among them, when the molar ratio of tannic acid to metal ions is 1:1 to 4:1, the obtained catalyst exhibits better catalytic performance, with 2:1 being the best, indicating that controlling the molar ratio of tannic acid to metal ions within a suitable range is beneficial to improving catalytic performance.

[0080] (3) Effect of pH on the tannic acid coordination system. The pH of the tannic acid coordination system has a significant impact on the catalytic performance of the obtained catalyst. Within the scope of this invention, when the pH of the reaction system is close to neutral, the obtained catalyst exhibits better catalytic performance, with pH 7 showing relatively superior catalytic performance; when the reaction system is acidic or alkaline, the catalytic performance of the obtained catalyst decreases. This indicates that controlling the pH of the tannic acid coordination system near neutral is beneficial to improving catalytic performance.

[0081] (4) Synergistic Regulation. The concentration of metal ions, the molar ratio of tannic acid to metal ions, and the pH of the tannic acid coordination system all have a significant impact on the catalytic performance of the obtained catalyst, and there is a synergistic effect among the three. By matching and regulating the above parameters, the catalytic performance of the obtained catalyst can be further improved.

[0082] In summary, in the preparation method of this invention, the concentration of the metal ion is controlled to be 1.2~4.8 mmol L. -1 The resulting catalyst exhibited good catalytic performance, preferably 2.4 mmol / L. -1 When the molar ratio of tannic acid to metal ions is 1:1 to 4:1, 2:1 is preferred; when the pH of the tannic acid coordination reaction system is controlled at 6.5 to 7.5, 7 is preferred. Under the above preferred conditions, the obtained catalyst exhibits superior photocatalytic activity and selectivity.

[0083] This invention prepares a TiO2@CM composite catalyst by using MIL-125(Ti) as a precursor, introducing a metal, and further constructing a tannic acid-derived carbon layer. The catalyst combines the synergistic advantages of the TiO2 semiconductor framework, metal active sites, and the conductive interface of the carbon layer, significantly improving the photocatalytic oxidation efficiency and target product selectivity of biomass derivatives, especially HMF. Among them, the TiO2@C-Cu catalyst exhibits the best performance, indicating that this structural design has promising application prospects in the visible light photocatalytic conversion of biomass-derived platform molecules.

[0084] It should be noted that the above embodiments are only preferred embodiments of the present invention. Equivalent substitutions or changes made by those skilled in the art to the types of raw materials, types of metals, carbon layer control methods, reaction conditions and detection methods without departing from the spirit and substance of the present invention shall fall within the protection scope of the present invention.

Claims

1. A titanium dioxide core-shell structured photocatalyst supported on metal particles, characterized in that, The catalyst is obtained by introducing metal, coordinating tannic acid with metal, and calcining the titanium-based metal-organic framework material MIL-125(Ti) as a precursor. The catalyst has titanium oxide as the core structure and a carbon layer covering the surface of the core structure as the shell structure. Metal particles are loaded in the catalyst.

2. The titanium dioxide core-shell structured photocatalyst with supported metal particles according to claim 1, characterized in that, The metal is selected from one or more of Fe, Co, Ni, and Cu.

3. A method for preparing a titanium dioxide core-shell structured photocatalyst with supported metal particles as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1) Grind the titanium-based metal-organic framework MIL-125(Ti) thoroughly in an agate mortar for 30–60 min to obtain a relatively uniform powder; then, mix the powder at a concentration of 10 mg / mL. -1 The concentration of the metal ion was dispersed in a phosphate buffer solution with a pH of 6.5–7.5 and then ultrasonically dispersed; subsequently, a metal solution and a tannic acid solution were added to obtain a mixture in which the metal ion concentration was 1.2–4.8 mmol / L. -1 The molar ratio of tannic acid to metal ions is 1:1 to 4:1; the mixture is stirred thoroughly to obtain an intermediate product. Step 2) After washing and drying the intermediate product with deionized water, it is evenly spread in a container and calcined in a muffle furnace; the calcination process conditions are: a heating rate of 4~5℃ / min from room temperature. -1 The temperature was raised to 450~550℃ and held for 4 hours; after calcination, it was naturally cooled to room temperature to obtain a titanium oxide core-shell structured photocatalyst loaded with metal species.

4. The preparation method according to claim 3, characterized in that, In step 1), the preparation steps of the titanium-based metal-organic framework MIL-125(Ti) are as follows: terephthalic acid is dissolved in a mixed solution of N,N-dimethylformamide and anhydrous methanol, and then tetrabutoxytitanium is added. After forming a transparent solution under stirring conditions, the solution is reacted at 160°C for 20 h. After washing and drying, the solution is thoroughly ground to obtain powder.

5. The preparation method according to claim 3, characterized in that, In step 1), the phosphate buffer is prepared by mixing NaH2PO4 and Na2HPO4 in a molar ratio of 2:1 and adding deionized water to a concentration of 20 mmol / L. -1 .

6. The preparation method according to claim 3, characterized in that, In step 1), the concentration of the metal solution is 30 mmol / L. -1 The concentration of the tannic acid solution is 30 mmol / L. -1 .

7. The application of a titanium dioxide core-shell structured photocatalyst supported on metal particles, characterized in that, The photocatalyst prepared by any one of the preparation methods of claims 3 to 6 is used in the photocatalytic conversion reaction of biomass derivatives. During the reaction, the photocatalyst is added to the biomass derivative solution, wherein the molar ratio of the added amount of the photocatalyst to the molar amount of the biomass derivative is 200 mg: 1 mmol. After ultrasonic dispersion, the solution is stirred in the dark for 30 to 60 min, and then reacted at 25°C for 6 to 12 h under visible light irradiation.

8. The application of the photocatalyst according to claim 7, characterized in that, The biomass derivative includes 5-hydroxymethylfurfural. The conversion reaction system is subjected to visible light irradiation at 25°C for 6–12 h. The photocatalyst is used to catalyze the oxidation of 5-hydroxymethylfurfural to generate the target products 2,5-dicarboxyfuran, 5-formyl-2-furancarboxylic acid, and 2,5-furandicarboxylic acid. The conversion rate of 5-hydroxymethylfurfural is 56.10%–86.10%; the selectivity of the target products is 58.32%–75.40%; the yield of 2,5-dicarboxyfuran is 31.97%–46.51%; the yield of 5-formyl-2-furancarboxylic acid is 3.71%–14.76%; and the yield of 2,5-furandicarboxylic acid is 0.37%–7.09%.

9. The application of the photocatalyst according to claim 8, characterized in that, The conversion reaction system was subjected to visible light irradiation at 25°C for 8 h. The conversion rate of 5-hydroxymethylfurfural was 75.31%–82.25%; the selectivity of the target product was 67.95%–75.40%; the yield of 2,5-dicarboxyfuran was 40.94%–48.37%; the yield of 5-formyl-2-furancarboxylic acid was 7.68%–9.30%; and the yield of 2,5-furandicarboxylic acid was 1.54%–4.34%.

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