Photocatalytic material, preparation method thereof and application of photocatalytic material in preparation of biodiesel

Abstract

The invention relates to the technical field of photocatalytic synthesis of biofuels, in particular to a photocatalytic material, a preparation method of the photocatalytic material and application of the photocatalytic material in preparation of biodiesel. According to the specific technical scheme, the preparation method comprises the following steps: (1) dissolving ZrCl4 and Zn (NO3) 2.6 H2O in DMF, then adding H2BDC and concentrated HCl, carrying out ultrasonic treatment and stirring, then carrying out a high-temperature reaction, then cooling to room temperature, centrifuging, washing and drying to obtain ZnUiO-66; and (2) stirring ZnUiO-66 in HCl, filtering, washing to be neutral, soaking in CH3OH overnight, and drying to obtain the A / ZnUiO-66-x photocatalytic material. According to the method, the clean visible light energy is utilized to drive the esterification reaction to efficiently convert into the high-quality biodiesel under extremely mild conditions. The defects that a traditional homogeneous acid catalyst is high in corrosivity and difficult to recycle, and the biodiesel technology is high in energy consumption are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic synthesis of biofuels, and specifically to a photocatalytic material, a preparation method thereof, and an application thereof in the preparation of biodiesel, and more particularly to a preparation method of a cluster-defective metal-organic framework (MOF) material A / ZnUiO-66-x with excellent photocatalytic activity and an application thereof in the efficient preparation of biodiesel under visible light drive. Background Art

[0002] Developing green, renewable alternative energy sources has become a key path to resolving energy crises and environmental issues. Biodiesel, a typical biomass-derived fuel, is considered one of the clean energy alternatives with the greatest industrial potential due to its excellent renewability, biodegradability, and combustion properties similar to petrochemical diesel. Based on the core concept of efficient utilization of biomass resources, an innovative process for producing biodiesel using liquid biomass as a raw material has been proposed. This technical solution not only significantly reduces production costs but also maximizes the value of biomass resources, providing a new technological breakthrough for the biodiesel industry to expand into high-value-added bio-based chemicals.

[0003] In the existing technology, traditional heterogeneous catalysts have technical bottlenecks such as insufficient pore structure control and uneven distribution of active sites, which seriously restrict the improvement of catalytic efficiency. In response to this technical problem, the present invention adopts the UiO-66 series metal-organic framework materials with adjustable pore structure, ultra-high specific surface area and easy functional modification as catalyst carriers. The unique structural characteristics of this material provide a new material basis for solving the technical defects of existing catalytic systems, showing outstanding technical advantages and broad application prospects in the field of biodiesel preparation. Although a variety of defect construction methods have been developed, further improving the photocatalytic efficiency of MOFs still faces challenges, and the effective use of electrons has become the key to breaking through this dilemma. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a photocatalytic material, a preparation method thereof, and an application in the preparation of biodiesel. The present invention introduces Zn clusters to change the electronic structure of the photocatalytic material, provide a more efficient charge transfer path, create more accessible active sites, and at the same time improve the photogenerated charge transfer rate.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] The present invention discloses a method for preparing a photocatalytic material, comprising the following steps:

[0007] (1) ZrCl4 and Zn(NO3)2·6H2O were dissolved in DMF, and then H2BDC and concentrated HCl were added. The mixture was ultrasonically treated and stirred, and then cooled to room temperature after high temperature reaction. After centrifugation, washing, and drying, ZnUiO-66 was obtained.

[0008] (2) ZnUiO-66 was stirred in HCl, filtered, washed until neutral, and then soaked in CH3OH overnight. After drying, A / ZnUiO-66-x photocatalytic material was obtained.

[0009] Preferably, in step (1), the molar ratio of ZrCl4 to Zn(NO3)2·6H2O is 1:0.1-0.4.

[0010] Preferably, in step (1), the volume-to-mass ratio of DMF, HCl, and H2BDC is 40-56:1-2.5:1.35-4.05.

[0011] Preferably, in step (1), the temperature of the high temperature reaction is 110-130° C., and the reaction time is 20-28 h.

[0012] Preferably, in step (2), the stirring speed is 400-600 r / min, and the stirring time is 5-15 min.

[0013] Preferably, in step (2), the drying temperature is 60-100° C., and the drying time is 8-16 hours.

[0014] Correspondingly, an A / ZnUiO-66 photocatalytic material is prepared by the preparation method.

[0015] Preferably, the A / ZnUiO-66 photocatalytic material prepared by the preparation method is used in the photocatalytic preparation of biodiesel.

[0016] Preferably, the application process is: A / ZnUiO-66 photocatalytic material, methanol and oleic acid are added to a quartz photoreactor, which is sealed and then irradiated with visible light using a 300W xenon lamp as a light source, and the mixture is stirred at room temperature for 3-5 hours; after the reaction is completed, methanol and water are removed by rotary evaporation to obtain a biodiesel product.

[0017] Preferably, the amount of the A / ZnUiO-66 photocatalytic material is 1-5 wt %, and the molar ratio of methanol to oleic acid is 6:1-12:1.

[0018] The present invention has the following beneficial effects:

[0019] 1. The present invention uses Zn, which is abundant, low-cost and low-toxic, as the doping metal. At the same time, the introduction of Zn can change the electronic structure and provide a more efficient charge transfer path. It is introduced into the catalytic material for modification. The method is simple and cost-effective.

[0020] 2. The A / ZnUiO-66-x photocatalytic material synthesized in the present invention has a simple process flow, mild conditions, a pollution-free and environmentally friendly preparation process, and has the advantages of being fast and efficient.

[0021] 3. The A / ZnUiO-66-x photocatalytic material synthesized in the present invention achieves a biodiesel yield of 97.58% under the optimal reaction conditions of a reaction time of 4 h, a catalyst dosage of 4 wt%, and an alcohol-to-oil molar ratio of 12:1 by precisely controlling the ratio of Zn to Zr and selectively removing Zn partially through acid etching. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a transmission electron microscope image of A / ZnUiO-66-0.2 prepared in Example 1;

[0023] Figure 2 These are infrared test images of different samples in Example 1 and Example 2;

[0024] Figure 3 These are Raman test images of different samples in Example 1 and Example 2;

[0025] Figure 4 Thermogravimetric analysis diagrams of different samples in Example 1 and Example 2;

[0026] Figure 5 The UV-visible diffuse reflectance spectra of different samples in Example 1 and Example 2 are shown;

[0027] Figure 6 1 and 2 are photoluminescence spectra of different samples in Example 1 and Example 2;

[0028] Figure 7 These are the experimental results of using A / ZnUiO-66-x (x = 0.1, 0.2, 0.3, 0.4) as a photocatalytic material for the photocatalytic preparation of biodiesel in Example 3; wherein: a) biodiesel yield of different catalytic materials; b) effect of reaction time, c catalyst dosage, and d methanol / oleic acid molar ratio on biodiesel yield. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0031] The present invention discloses a method for preparing a cluster defect type A / ZnUiO-66 photocatalytic material, comprising the following steps:

[0032] (1) ZrCl4 and different masses of Zn(NO3)2·6H2O were dissolved in DMF (dimethylformamide), and then H2BDC (terephthalic acid) and concentrated HCl were added thereto. The mixture was ultrasonically treated (the ultrasonic treatment time was preferably 20 min, the ultrasonic frequency was 40 kHz, and the power was 240 W), stirred (stirred at a speed of 500 rpm for 1 h), and then transferred to a polytetrafluoroethylene-lined stainless steel reactor. After high-temperature reaction at 110-130°C for 20-28 h, it was cooled to room temperature, centrifuged, and then washed three times with DMF and CH3OH respectively. After drying, ZnUiO-66 with different Zn:Zr molar ratios was obtained. As a preferred embodiment, the high-temperature reaction temperature was 120°C for 24 h; the drying temperature was 60°C for 12 h.

[0033] The molar ratio of ZrCl4 to Zn(NO3)2·6H2O is 1:0.1-0.4; and the volume-to-mass ratio of DMF, HCl, and H2BDC is 40-56:1-2.5:1.35-4.05.

[0034] (2) The dried ZnUiO-66 with different Zn:Zr molar ratios is stirred and filtered in HCl (excess) at pH = 1, with a stirring speed of 400-600 r / min and a stirring time of 5-15 min (preferably 10 min). Wash with deionized water until neutral, and finally wash with CH3OH. The obtained material is then soaked in CH3OH overnight and dried at 60-100°C for 8-16 h to obtain the final A / ZnUiO-66-x photocatalytic material. As a preferred solution, the drying temperature is 80°C and the time is 12 h.

[0035] The present invention also provides a cluster defect type A / ZnUiO-66-x photocatalytic material prepared by the above preparation method.

[0036] The present invention also provides the use of the cluster defect type A / ZnUiO-66-x photocatalytic material prepared by the above preparation method in the photocatalytic preparation of biodiesel.

[0037] The application includes the following steps: 1-5 wt% of a photocatalyst, methanol, and oleic acid are added to a quartz photoreactor with a total volume of 10 mL. After sealing, the mixture is stirred at room temperature for a predetermined period of time under visible light irradiation using a 300W xenon lamp (λ>420nm) as a light source. After the reaction is complete, CH3OH and water are removed by rotary evaporation (75°C, 20 minutes, 0.1 MPa vacuum) to obtain a biodiesel product. The molar ratio of methanol to oleic acid is 6:1-12:1.

[0038] The present invention will be further described below with reference to specific embodiments.

[0039] Example 1

[0040] A cluster defect type A / ZnUiO-66 photocatalytic material is prepared by the following steps:

[0041] (1) 1.89 g ZrCl₄ and 0.48 g Zn(NO₃)₂·6H₂O were dissolved in 48.70 mL DMF, and then 2.70 g H₂BDC and 1.43 mL HCl were added. The mixture was ultrasonicated for 20 min and stirred for 1 h. It was then transferred to a hydrothermal reactor and reacted at 120°C for 24 h. After cooling to room temperature, the product was centrifuged and washed three times with DMF and three times with CH₃OH. The resulting material was named ZnUiO-66.

[0042] (2) The obtained ZnUiO-66 was stirred in HCl for 10 minutes, filtered, washed with deionized water until neutral, and finally washed with CH3OH. The obtained material was then soaked in CH3OH overnight and dried at 80°C for 12 hours to finally obtain catalyst A / ZnUiO-66-0.2. Its transmission electron microscope image is shown as follows Figure 1 As shown by Figure 1 It can be seen that the cluster loss can be clearly observed, which can be attributed to the local structural changes caused by the removal of part of the Zn by acid etching.

[0043] Example 2

[0044] The preparation method was the same as in Example 1, except that the amount of Zn(NO₃)₂·6H₂O added was replaced with 0.24 g, 0.72 g, and 0.96 g, respectively, to prepare A / ZnUiO-66 photocatalytic materials with different Zn source contents. The products were labeled A / ZnUiO-66-0.1, A / ZnUiO-66-0.3, and A / ZnUiO-66-0.4, respectively, based on the different ratios. Without the addition of Zn(NO₃)₂·6H₂O, the resulting catalyst was labeled UiO-66-0.

[0045] Characterization of the prepared photocatalyst:

[0046] 1. The UiO-66-0 and A / ZnUiO-66-x (x = 0.1, 0.2, 0.3, 0.4) obtained in Example 1 and Example 2 were characterized by Fourier transform infrared (FT-IR). Figure 2 As shown, all samples showed similar peak patterns. -1 The characteristic peak at 668cm is due to the interaction between Zr and H2BDC ligands, which is specifically manifested as the stretching vibration of Zr-(OC) bond, indicating the existence of UiO-66 framework structure and providing key evidence for the successful preparation of photocatalytic materials. -1 The nearby peaks correspond to the vibration of the Zn-O bond, confirming that the Zn element was successfully introduced into the material framework.

[0047] 2. Raman spectroscopy was performed on UiO-66-0 and A / ZnUiO-66-x (x = 0.1, 0.2, 0.3, 0.4) obtained in Example 1 and Example 2. Figure 3 It can be seen that the above characteristic peak intensities of the A / ZnUiO-66 sample are lower than those of UiO-66-0, which is attributed to the cluster defects produced in the material. These defects are likely to cause changes in the electron cloud distribution of the material, thereby affecting the chemical bond environment.

[0048] 3. Thermogravimetric analysis (TGA) was performed on UiO-66-0 and A / ZnUiO-66-x (x = 0.1, 0.2, 0.3, 0.4) obtained in Example 1 and Example 2. Figure 4 It can be seen that the results show that all samples exhibit three significant weight loss stages.

[0049] 4. The UiO-66-0 and A / ZnUiO-66-x (x = 0.1, 0.2, 0.3, 0.4) obtained in Example 1 and Example 2 were subjected to UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) test. Figure 5It can be seen that UiO-66-0 exhibits an absorption band in the ultraviolet region and no obvious absorption peak in the visible light region, indicating limited light absorption performance. In contrast, A / ZnUiO-66 with cluster defects not only exhibits improved light response around 252nm, but also exhibits extended light absorption in the visible light region with a significantly increased absorption intensity. This indicates that cluster defects broaden the material's light absorption range, improving light energy utilization.

[0050] 5. Photoluminescence (PL) spectra of UiO-66-0 and A / ZnUiO-66-x (x=0.1, 0.2, 0.3, 0.4) obtained in Example 1 and Example 2 were tested. Figure 6 It can be seen that the recombination probability of photogenerated carriers in UiO-66-0 is relatively high, while the photoluminescence spectrum peak intensity of A / ZnUiO-66-x, obtained after acid washing, is significantly weakened compared to UiO-66-0, which proves that the presence of cluster defects can improve the transfer efficiency of electrons and holes. Among them, A / ZnUiO-66-0.2 has the lowest peak intensity, indicating that its carrier recombination is most suppressed.

[0051] Example 3

[0052] This embodiment provides a method for preparing biodiesel by photocatalysis, which is carried out according to the following steps:

[0053] The photocatalytic production of biodiesel using free fatty acids as raw materials proceeds as follows: A predetermined amount of photocatalyst, 2.5 mL of methanol, and 1 g of oleic acid are added to a 10 mL quartz photoreactor. After sealing, the mixture is stirred at room temperature for a predetermined period of time (3-5 hours) under visible light irradiation using a 300 W xenon lamp (λ > 420 nm). After completion of the reaction, the catalyst is recovered by centrifugation. The CH3OH and water are removed by rotary evaporation (75°C, 20 minutes, 0.1 MPa vacuum) to obtain the biodiesel product.

[0054] The corresponding yield was calculated using a gas chromatograph. The specific operating information is as follows: injection port temperature 523K, detector temperature 523K, separation ratio 20:1, column box temperature program set to 453K, and 15K min -1 The heating rate was raised to 513 K and maintained at 513 K for 8 min. In addition, the injection volume was 1 μL, the nitrogen carrier gas flow rate was 45 mL / min, the air flow rate was 45 mL / min, and the hydrogen flow rate was 40 mL / min.

[0055] Using methyl heptadecanoate (C17:0) as the internal standard, the mass of the generated fatty acid methyl ester and the yield of biodiesel were calculated according to the formula:

[0056]

[0057] Wherein, ∑A represents the total peak area of ​​biodiesel; A C17:0 and m C17:0 represent the peak area and mass of the internal standard, respectively.

[0058] The photocatalytic activity of oleyl esterification of different catalytic materials was tested (e.g. Figure 7 a) Blank experiments indicate that the reaction does not occur spontaneously, suggesting that a photocatalyst is essential for the efficient conversion of oleic acid. A / ZnUiO-66-0.2 exhibits excellent catalytic performance, achieving a high biodiesel yield.

[0059] from Figure 7 The experimental data shown in Figure b shows that as the reaction time increases, the biodiesel yield initially increases and then decreases. By the time the reaction time reaches 4 hours, the reaction has reached dynamic equilibrium, and further increases in reaction time do not improve the yield. Therefore, 4 hours is determined to be the optimal reaction time.

[0060] exist Figure 7 In section c, the relationship between catalyst dosage and biodiesel yield was investigated. Within a certain range, increasing the catalyst dosage provides more active sites, effectively accelerating the reaction. However, excessive catalyst increases the system complexity and can also cause catalyst agglomeration, reducing the utilization of effective active sites. Therefore, a 4 wt% catalyst dosage was selected for subsequent experiments.

[0061] The effects of different methanol / oleic acid molar ratios on yield were investigated ( Figure 7 d). When the methanol / oleic acid molar ratio is gradually increased from 6:1 to 12:1, the biodiesel yield shows a linear growth trend and eventually reaches 97.58%. However, as the methanol / oleic acid molar ratio increases, the yield decreases instead of increasing. This is attributed to excessive adsorption of excess methanol on the catalyst surface, thereby shielding the active sites of the catalyst, severely limiting the effective mutual contact between oleic acid and the catalyst, and thus adversely affecting the performance of the catalyst. In addition, if the amount of methanol in the reaction system is too much, it will increase the difficulty in the subsequent product separation process and also increase production costs. Therefore, taking various factors into consideration, it is determined that the appropriate methanol / oleic acid molar ratio is 12:1.

[0062] Therefore, under the optimal reaction conditions: 4h, 4wt%, 12:1, the yield of biodiesel can reach up to 97.58%.

[0063] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a photocatalytic material, characterized in that: The following steps are involved: (1) ZrCl4 and Zn(NO3)2·6H2O were dissolved in DMF, and then H2BDC and concentrated HCl were added. The mixture was ultrasonically treated and stirred, and then cooled to room temperature after high temperature reaction. After centrifugation, washing, and drying, ZnUiO-66 was obtained. (2) ZnUiO-66 was stirred in HCl, filtered, washed until neutral, and then soaked in CH3OH overnight. After drying, A / ZnUiO-66-x photocatalytic material was obtained.

2. The preparation method according to claim 1, wherein: In step (1), the molar ratio of ZrCl4 to Zn(NO3)2·6H2O is 1:0.1-0.

4.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the volume mass ratio of DMF, HCl and H2BDC is 40-56:1-2.5:1.35-4.

05.

4. The preparation method according to claim 3, wherein: In step (1), the temperature of the high temperature reaction is 110-130° C., and the reaction time is 20-28 h.

5. The preparation method according to claim 1, wherein: In step (2), the stirring speed is 400-600 r / min, and the stirring time is 5-15 min.

6. The preparation method according to claim 1, wherein: In step (2), the drying temperature is 60-100° C., and the drying time is 8-16 hours.

7. An A / ZnUiO-66 photocatalytic material prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the A / ZnUiO-66 photocatalytic material prepared by the preparation method according to any one of claims 1 to 6 in the photocatalytic preparation of biodiesel.

9. The use according to claim 8, characterized in that: The application process is as follows: A / ZnUiO-66 photocatalytic material, methanol and oleic acid are added to a quartz photoreactor, which is sealed and then irradiated with visible light using a 300W xenon lamp as a light source. The mixture is stirred at room temperature for 3-5 hours. After the reaction is completed, methanol and water are removed by rotary evaporation to obtain a biodiesel product.

10. The use according to claim 9, characterized in that: The amount of the A / ZnUiO-66 photocatalytic material is 1-5 wt %, and the molar ratio of methanol to oleic acid is 6:1-12:1.

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