Preparation and application of a bifunctional catalyst for photocatalytic oxidation of styrene

Abstract

The application discloses a preparation method of a heterojunction bifunctional photocatalytic material Cu-BTC-TiO2 and application of the material in photocatalytic oxidation of phenylethylene, and relates to the following steps: under mild conditions, a MOF material Cu-BTC is compounded with a semiconductor TiO2 to obtain a bifunctional catalyst, and the catalyst successfully realizes the oxidation of aryl ethylene under the condition that oxygen is used as an oxygen source, and a series of aromatic aldehydes are synthesized by the method. The method has the advantages of recyclable catalyst, mild conditions, large-scale synthesis and the like. The application provides a new path of high efficiency, mildness and greenness for the preparation of aromatic aldehydes through the oxidation of aryl ethylene.

Description

Technical Field

[0001] This invention relates to the field of composite photocatalysts, and in particular to a bifunctional catalyst for the photocatalytic oxidation of styrene, its preparation method, and its application. Background Technology

[0002] The selective oxidation of styrene, a downstream petroleum product, into high-value-added carbonyl compounds is a fundamental chemical transformation in fine chemicals and organic synthetic chemistry. (C. Ayed, J. Yin, K. Landfester, KAI Zhang, Angew. Chem. Int. Ed. 2023, 62, e2022 16159. BNR Winayu, W.-C. Weng, H. Chu, J. Photochem. Photobio. AChem. 2023, 439, 114613.) The selective oxidation of styrene to benzaldehyde is particularly challenging because the over-oxidation of benzaldehyde to benzoic acid and other side reactions lead to the formation of numerous byproducts, which greatly limits their applications. (X.Guan, CDDuan, HXWang, B.Lu, JXZhao, QHCai, New J.Chem. 2021, 45, 18192. P.Cancino, V.Paredes-García, P.Aguirre, E.Spodine, Catal.Sci.Technol. 2014, 4, 2599.) Therefore, it is urgent to develop an efficient and green method for the selective oxidation of styrene to benzaldehyde. In recent years, various heterogeneous and homogeneous catalysts have been studied for the thermal cracking of C=C to aldehydes. (P. Cancino, V. Paredes-García, P. Aguirre, E. Spodine, Catal. Sci. Technol. 2014, 4, 2599. YHFu, L. Xu, HMShen, H. Yang, FM Zhang, WD Zhu, MHFan, Chem. Eng. J. 2016, 299, 135–141. VAGhadge, K .Ravi,DRNaikwadi,PBShinde,AVBiradar,GreenChem.2023,25,2863.DXMa,YWZhang,HHZhao,K.Liu,L.Wang,Appl .Surf.Sci.2022,571,151363.S.Ayadi,N.Moussa,D.Cherni,I.Jaouali,A.Guesmi,NBHamadi,A.Houas,J.Porous Mater.2023,30,183-192.JSChai,HBChong,SXWang,S.Yang,MZWu,MZZhu,RSC Adv.2016,6,111399.ZYZhang,WDChen,JFLuo,TetrahedronLett.2020, 61, 152527. G. Urgoitia, R. San Martin, M. T. Herrero, E. Domínguez, Adv. Synth. Catal. 2016, 358, 1150–1156.) However, most of these methods suffer from long reaction times, harsh reaction conditions, poor chemoselectivity and regioselectivity, and other drawbacks. The use of volatile organic solvents and other issues (ZY Zhang, WDChen, JFLuo, Tetrahedron Lett. 2020, 61, 152527.) limits their application and is inconsistent with the principles of green chemistry. In recent years, photocatalysis has been considered one of the most promising technologies due to its mild conditions and sustainable energy, and has been widely applied in organic synthesis, pollutant degradation, and chemical engineering (X. Yang, SY Zhang, PX Li, SY Gao, R. Cao, J. Mater. Chem. A. 2020, 8, 20897. WQ Guo, T. Guo, YZ Zhang, LF Yin, YRDai, Chemosphere 2023, 339, 139486.). In particular, the photocatalytic selective oxidation of styrene to styrene oxides, alcohols, ketones, aldehydes, and organic acids has attracted the interest of chemists. Therefore, the photocatalytic oxidation of styrene has been successfully carried out in both heterogeneous and homogeneous catalytic systems. (LLLiu,L.Zhang,F.Wang,K.Qi,HYZhang,XQCui,WTZheng,Nanoscale 2019,11,7554.YCDeng,X.-J.Wei,H.Wang,YHSun,T. X.Wang,Angew.Chem.Int.Ed.2017,56,832–836.)Synthesis of a scaffold with a high-density scaffold, a scaffold MOF(P.Canc ino,V.Pares-Garcia,P.Aguirre,E.Spodine,Catal.Sci.Technol.2014,4,2599.Y HFu, L. Xu, HMShen, H. Yang, FMZhang, WDZhu, MHFan, J. Chem.Eng.2016, 299, 135–141 State Chem.2021,298,122151.PHGuo,SHZhang,HCCheng,XYZeng,HLWang,RAFischer,M.Muhler,Catal.Sci.Technol.2023,13,2728.YWXiao,WXGuo,HH Chen, HFLi, XJXu, P. Wu, Y. Shen, B. Zheng, FWHuo, WDWei, Mater.Chem.Front Appl.Nano Mater.2018,1,5289-5296.)Inorganic TiO2(BNRWinayu,W.-C.Weng,H.Chu,J.Photochem.Photobio.AChem. 2023, 439, 114613. S. Ayadi, N. Moussa, D. Cherni, I. Jaouali, A. Guesmi, NB Hamadi, A. Houas, J. Porous Mater.2023,30,183-192.XYQiao,ZSXiong,YWang,RWWang,ZTHang,SLQiu,J.Colloid InterfaceSci.2023,651,235–242.L.Nie,KKXin,WSLi,XPZh ou,Catal.Commun.2007,8,488-492.)Observation of a smooth-running skeletal muscle.MOFs possess high surface area, ordered pore size, and metallic active sites, exhibiting complementary physicochemical properties to TiO2, and offer advantages such as low cost and non-toxicity. However, drawbacks such as large band gaps, high electron-hole recombination rates, agglomeration in suspended systems, and weak photogenerated carrier separation efficiency make semiconductor photocatalysis challenging. These limitations of TiO2 semiconductor catalysts can be addressed by integrating TiO2 into metal and / or non-metallic supports, thereby improving the photocatalytic efficiency of TiO2 and hindering electron-hole recombination. For example, Guo and Zhang prepared a series of bimetallic porous CuRu-BTC (HPCuRu-BTC) MOFs and porous defect-engineered MOFs (HP-DEMOFs) for styrene oxidation. (PH Guo, SH Zhang, HCCheng, XY Zeng, HL Wang, RA Fischer, M. Muhler, Catal. Sci. Technol. 2023, 13, 2728.) Wang's group developed a bishell TiO2@mesoporous organosilica nanotube as an amphiphilic photoactive nanoreactor for the efficient photocatalytic oxidation of styrene (XY Qiao, ZSXiong, Y. Wang, RWWang, ZT Zhang, SLQiu, J. Colloid Interface Sci. 2023, 651, 235–242.). Compared with microporous Cu-BTC with a single metal component, the styrene conversion of HPCuRu-BTC and HP-DEMOFs was increased by 2-fold and 20-fold, respectively, after 7 h of reaction under the same conditions. However, the low selectivity and participation of tert-butyl hydroperoxide (TBHP) as an initiator hinders its application in fine chemical synthesis. Therefore, MOFs represent a multifunctional heterogeneous photocatalytic platform that allows for the design of semiconductor catalysts with readily available Lewis acids and the construction of heterojunction structures. MOF-supported TiO2 combines the advantages of both unit types, promoting substrate diffusion and improving the selectivity and efficiency of photocatalytic conversion. Among various MOF materials, Cu-BTC is a mature MOF material with high specific surface area and pore volume, providing active sites for semiconductor materials and accelerating charge transfer. For example, Lei's team synthesized a core-shell Cu-BTC@TiO2 catalyst for the photocatalytic oxidation of thio compounds (J. Liu, X.-M. Li, J. He, L.-Y. Wang, J.-D. Lei, Materials 2018, 11, 2209.). The team synthesized a supported nanocomposite material by loading a TiO2 photocatalyst onto a Cu-BTC surface for the degradation of organic dyes (AN). D. Karamanis, E. Chalkia, D. Tuncel, Mater. Chem. Phys. 2017, 187, 5-10.) Huo's team developed a CuO / TiO2 catalyst by growing Cu-BTC composite materials and then pyrolyzing CO oxidation. (H. Liu, SY Zhang, YY Liu, ZHYang, X. Feng, XH Lu, FW Huo, Small 2015, 11, 3130–3134.) Umar and Kansal synthesized Cu-BTC-derived Cu-doped TiO2 nanoparticles for photoinduced decomposition of the antibiotic ofloxacin (OFX). (R. Kaur, A. Kaur, R. Kaur, S. Singh, MS Bhatti, A. Umar, S. Baskoutas, SK Kansal, Adv. Powder Technol. 2021, 32, 1350–1361.) To our knowledge, there is very little research to date on the photocatalytic selective oxidation of styrene using Cu-BTC and TiO2 composites. Here, we propose that the selectiveness and efficiency of the photocatalytic oxidation of styrene can be improved by installing TiO2 in Cu-BTC to form a heterojunction. Summary of the Invention

[0003] This invention provides a method for preparing and applying a bifunctional catalyst for the photocatalytic oxidation of styrene, thereby solving the problems existing in the prior art. By developing a bifunctional catalyst, this invention combines MOF materials with semiconductors, creating a new, efficient, mild, and green pathway for styrene oxidation. It is a novel green route that can achieve highly selective styrene oxidation.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] This invention provides a method for preparing a bifunctional catalyst for the photocatalytic oxidation of styrene and the application of the catalyst, comprising the following steps:

[0006] First, copper nitrate trihydrate (0.435 g, 1.8 mmol) was dissolved in anhydrous ethanol, and then pyromellitic acid (0.210 g, 1 mmol) was added. The mixture formed the MOF material Cu-BTC. This was then uniformly mixed with anhydrous ethanol solution containing titanium dioxide (0.072 g, 0.9 mmol), and stirred at room temperature for 1 hour. After the reaction was complete, the mixture was allowed to stand for 6 hours. Finally, the blue precipitate was centrifuged (7000 rpm, 4 min), washed with ethanol (30 mL x 3), and dried under vacuum at 60 °C overnight. This yielded a bifunctional catalyst for the photocatalytic oxidation of styrene.

[0007] Under mild reaction conditions, using Cu-BTC-TiO2 as a catalyst and water as a reaction solvent, and irradiated with blue light for 4 hours in an oxygen atmosphere, the selective oxidation of styrene to benzaldehyde was completed.

[0008] Further, the homogeneous mixture is characterized in that the molar ratio of copper nitrate trihydrate to titanium dioxide is (1-3):(1-3), preferably 1.8-2.5:1. The volume ratio of the Cu-BTC solution to the TiO2 solution is 1-4:1-4, preferably 1-2:0.5-1; the concentration ratio is 2-8:1, preferably 5-7:1. The molar concentration of titanium dioxide in the anhydrous ethanol solution containing dissolved titanium dioxide is 0.01-0.20 mmol / mL, preferably 0.02-0.06 mmol / mL.

[0009] Furthermore, the synthesis method uses a single green solvent, anhydrous ethanol, and the synthesis reaction conditions are: stirring at room temperature for 1 hour, followed by standing for 6 hours after the reaction is completed.

[0010] Furthermore, the bifunctional photocatalyst Cu-BTC-TiO2 exhibits mild and efficient catalytic oxidation of styrene, with high conversion (99%) and high chemoselectivity (82%). Moreover, the catalyst can still achieve a product yield of 76% after being reused 7 times, demonstrating good recycling performance.

[0011] This invention provides a method for preparing a bifunctional catalyst as described above for preparing a bifunctional catalyst for the photocatalytic oxidation of styrene.

[0012] The present invention discloses the following technical effects:

[0013] To obtain Cu-BTC-TiO2 materials with nanoscale dimensions, this invention uses anhydrous ethanol as the reaction solvent to prepare photocatalytic materials. First, copper nitrate trihydrate is fully dissolved in anhydrous ethanol, then trimesic acid is added to ensure complete dissolution, and then the solution is mixed into titanium dioxide that has been uniformly dispersed in anhydrous ethanol and stirred for 1 hour. After standing for 6 hours, the solution is washed, centrifuged, and vacuum dried.

[0014] This invention presents a bifunctional catalyst obtained by combining the MOF material Cu-BTC with the semiconductor TiO2 phase under mild conditions. This catalyst successfully oxidizes aryl ethylene under oxygen-source conditions, and a series of aromatic aldehydes were synthesized through this method. This method has advantages such as catalyst recyclability, mild conditions, and the ability to be synthesized on a large scale. This invention provides a new, efficient, mild, and green route for the oxidation of aryl ethylene to aromatic aldehydes.

[0015] This invention simultaneously solves the problems of harsh conditions such as high temperature and high pressure in traditional organic catalysis and the use of organic reagents, as well as the problem of recyclable photocatalysts, avoiding resource waste and environmental pollution. Furthermore, the universality of the substrates was studied, and it was found that the catalyst has good catalytic activity for a variety of different organic compounds based on styrene, providing valuable reference for future industrial development. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the synthesis process of the catalyst synthesized in Example 1;

[0018] Figure 2 SEM images of (a): Cu-BTC, (b): TiO2 and (c): Cu-BTC-TiO2 synthesized in Example 1; TEM image of (d): Cu-BTC-TiO2; elemental mapping of (ef): Cu-BTC-TiO2;

[0019] Figure 3 This is a schematic diagram of the photocatalytic system reaction device;

[0020] Figure 4 The image shows the hydrogen NMR spectrum obtained from the substrate universality study in Example 4. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] Example 1

[0027] like Figure 1 As shown, the synthesis method of the catalyst Cu-BTC-TiO2 is as follows:

[0028] First, copper nitrate trihydrate (0.435 g, 1.8 mmol) was dissolved in 20 mL of anhydrous ethanol, and then pyromellitic acid (0.210 g, 1 mmol) was added. The mixture formed the MOF material Cu-BTC. This was then thoroughly mixed with 20 mL of anhydrous ethanol containing titanium dioxide (0.072 g, 0.9 mmol) and stirred at room temperature for 1 hour. After the reaction was complete, the mixture was allowed to stand for 6 hours. Finally, the blue precipitate was centrifuged (7000 rpm, 4 minutes), washed with ethanol (30 mL three times), and dried under vacuum at 60 °C overnight. The target catalyst Cu-BTC-TiO2 was obtained.

[0029] Example 2

[0030]

[0031] like Figure 2 As shown, the method for catalytic oxidation of styrene to benzaldehyde using the catalyst Cu-BTC-TiO2 is as follows:

[0032] A mixture of styrene (0.012 mL, 0.1 mmol) and the catalyst Cu-BTC-TiO2 (15 mg, prepared in Example 1) was dispersed in 20 mL of water in a quartz tube (20 mL). The quartz tube was equipped with a magnetic stir bar, and the tube opening was sealed. The internal chamber of the quartz tube was connected to a balloon (natural latex balloon) containing 1 L of oxygen through a tubing, allowing the reaction to proceed under an oxygen atmosphere. The reaction mixture was then irradiated at room temperature for 4 hours under an 18 W blue LED (wavelength 465-470 nm). The reaction was completed under GC (GC-Agilent 2014C) monitoring. The catalyst was recovered by centrifugation and vacuum dried for use in the next experiment. The crude product, after removing the catalyst, was extracted with ethyl acetate (5 mL each time, 3 times). The combined ethyl acetate phases were dried over anhydrous sodium sulfate, and the residue obtained by vacuum concentration was purified by silica gel column chromatography (petroleum ether / ethyl acetate = 3:1, v / v) to obtain the desired product, benzaldehyde. The product's characteristics were confirmed by 1H NMR (Bruker Avance NEO 600). The product parameters obtained using NMR spectroscopy are as follows:

[0033] Benzaldehyde Colorless liquid(82%isolated yield,0.16mmol,17.0mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,5 / 1). 1 H NMR (600MHz, CDCl3) δ: 10.00 (s, 1H), 7.88-7.86 (m, 2H), 7.63-7.60 (m, 1H), 7.53-7.51 (m, 2H); MS m / z: 106.

[0034] Example 3

[0035] Styrene (1a) was selected for initial optimization of the photocatalytic aerobic oxidation reaction. Various semiconductor and supported semiconductor catalysts were screened using water as the solvent and molecular oxygen as the oxidant.

[0036] To our delight, the Cu-BTC-TiO2 catalyzed reaction yielded the desired product benzaldehyde (2a) in 82% yield. As expected, conventional semiconductors and MOFs exhibited poor reaction results. The process and conditions were the same as in Example 2, except that, for example, titanium dioxide (TiO2), cadmium sulfide (CdS), and graphitic carbon nitride (g-C3N4) were used as catalysts in equivalent quantities to replace Cu-BTC-TiO2, resulting in low yields of 26%, 20%, and 22%, respectively.

[0037] The process and conditions were the same as in Example 2, except that the single-metal component Cu-BTC (copper nitrate trihydrate (0.435 g, 1.8 mmol) was dissolved in 20 mL of anhydrous ethanol, then pyromellitic acid (0.210 g, 1 mmol) was added, the mixture was stirred for 1 h, and allowed to stand for 6 h. The blue precipitate was washed (30 mL each time, three times), centrifuged, and dried to form the MOF material Cu-BTC) was used to replace Cu-BTC-TiO2 as the catalyst. GC only detected trace amounts of the product (result: Trace).

[0038] For other M-BTC supported semiconductor catalysts, the process and conditions were the same as in Example 2, except that a different catalyst was used, such as bulk Cu-BTC-TiO2. First, copper nitrate trihydrate (0.435 g, 1.8 mmol) was dissolved in 10 mL of anhydrous ethanol, then trimesic acid (0.210 g, 1 mmol) was added, and the two were mixed to form the MOF material Cu-BTC. This was then uniformly mixed with 20 mL of anhydrous ethanol solution containing titanium dioxide (0.072 g, 0.9 mmol) and stirred at room temperature for 0.5 hours. Subsequently, the mixture was transferred to a 100 mL polytetrafluoroethylene reactor and heated to 150°C in a drying oven. After 12 hours of continuous cooling to room temperature, the blue precipitate was centrifuged (7000 rpm, 4 minutes), washed with ethanol (30 mL each time, three times), and dried under vacuum at 60°C overnight. The target catalysts, blocky Cu-BTC-TiO2 and nano-Cu-BTC-g-C3N4, were obtained. (First, copper nitrate trihydrate (0.435 g, 1.8 mmol) was dissolved in 20 mL of anhydrous ethanol, then trimellitic acid (0.210 g, 1 mmol) was added, and the mixture formed the MOF material Cu-BTC. This was then uniformly mixed with 20 mL of anhydrous ethanol solution containing graphitic carbon nitride (0.059 g, 1.8 mmol), and stirred at room temperature for 1 hour. After the reaction was complete...) After standing for 6 hours, the pale blue precipitate was centrifuged (7000 rpm, 4 minutes), washed with ethanol (30 mL each time, three times), and dried under vacuum at 60°C overnight. The target catalyst Cu-BTC-g-C3N4 and nano-Cu-BTC-CdS were obtained. First, copper nitrate trihydrate (0.435 g, 1.8 mmol) was dissolved in 20 mL of anhydrous ethanol, then trimellitic acid (0.210 g, 1 mmol) was added, and the two were mixed to form the MOF material Cu-BTC. This was then uniformly mixed with 20 mL of anhydrous ethanol solution containing cadmium sulfide (0.144 g, 1.0 mmol), and stirred at room temperature for 1 hour. After the reaction was complete, it was allowed to stand for 6 hours, and finally... The green precipitate was centrifuged (7000 rpm, 4 minutes), washed with ethanol (30 mL each time, three times), and dried under vacuum at 60 °C overnight. The target catalysts Cu-BTC-CdS and Co-BTC-TiO2 were obtained. (First, cobalt nitrate hexahydrate (0.215 g, 0.74 mmol) was dissolved in 30 mL of a mixed solvent of DMF:CH3CH2OH:H2O (1:1:1), then pyromellitic acid (0.150 g, 0.71 mmol) was added, and the two were mixed to form the MOF material Cu-BTC; then, it was uniformly mixed with 20 mL of anhydrous ethanol solution containing titanium dioxide (0.183 g, 2.3 mmol), and stirred at room temperature for 0.5 hours.)The mixture was then transferred to a 100 mL polytetrafluoroethylene reactor and heated to 150 °C in a drying oven for 12 hours. After naturally cooling to room temperature, the precipitate was centrifuged (7000 rpm, 4 minutes), washed with ethanol (30 mL each time, three times), and dried under vacuum at 60 °C overnight. The target catalysts Co-BTC-TiO2 and Ni-BTC-TiO2 were obtained. First, nickel nitrate hexahydrate (0.290 g, 1.0 mmol) was dissolved in 20 mL of anhydrous ethanol, then trimesic acid (0.210 g, 1 mmol) was added, and the two were mixed to form the MOF material Cu-BTC. This was then uniformly mixed with 20 mL of anhydrous ethanol solution containing titanium dioxide (0.072 g, 0.9 mmol), and stirred at room temperature for 1 hour. After the reaction was complete, the mixture was allowed to stand for 6 hours. Finally, the precipitate was centrifuged (7000 rpm, 4 minutes), washed with ethanol (30 mL each time, three times), and dried under vacuum at 60 °C overnight. Using Ni-BTC-TiO2 as a mass substitute for Cu-BTC-TiO2 yielded catalytic effects of 33%, 33%, trace, trace, and trace, respectively, all of which were inferior to the catalytic effects of nano-Cu-BTC-TiO2 (82%).

[0039] The above results confirm the key roles of TiO2 and Cu-BTC in photocatalytic conversion.

[0040] Furthermore, the nanostructure of the catalyst is also essential for this reaction. Subsequently, we screened different molar ratios of Cu-BTC and TiO2, using the same process and conditions as in Example 1, except that the content of titanium dioxide in the anhydrous ethanol solution containing dissolved titanium dioxide was changed. Catalysts with different molar ratios of Cu-BTC and TiO2 (1:1, 1:2, 2:1, 3:1) were prepared. When the catalysts with Cu-BTC and TiO2 molar ratios of 1:1, 1:2, 2:1, and 3:1 were applied (using the same process and conditions as in Example 2), the yields were 27%, 40%, 82%, and 47%, respectively. The results indicate that the optimal ratio of MOF to semiconductor TiO2 is 2:1.

[0041] We then investigated the effect of the solvent, using the same procedures and conditions as in Example 2, except that the reaction did not occur when the solvent was an organic solvent, ethanol or acetonitrile, which replaced water by an equal volume. Furthermore, the reaction yield was 60% with a mixed solvent of ethanol:water (1:1, volume ratio, equal volume replacement of water) and 73% with acetonitrile:water (1:1, volume ratio, equal volume replacement of water), which did not improve the reaction yield when water was used as the solvent.

[0042] Inspired by the above results, the catalyst dosage was investigated, with the same process and conditions as in Example 2, except that 5.0, 10.0, 15.0, and 20 mg of catalyst were used to obtain the desired product in yields of 33%, 40%, 82%, and 40%, respectively (2a). Decreasing or increasing the catalyst dosage did not improve the product yield.

[0043] Finally, the reaction time was optimized. Different reaction times were tested within the range of 2-10 hours. The process and conditions were the same as in Example 2, except that the yields at reaction times of 2h, 4h, 6h, 8h, and 10h were 47%, 82%, 79%, 80%, and 81%, respectively, with the highest yield observed at 4h. The optimal reaction conditions were: Cu-BTC-TiO2 (15mg) and styrene (0.1mmol) dissolved in water (2mL), stirred at room temperature for 4 hours under an oxygen atmosphere and irradiation by an 18W blue LED.

[0044] Example 4

[0045]

[0046] A mixture of 1a (0.1 mmol) and Cu-BTC-TiO2 (15 mg) was dispersed in 2 mL of water in a 20 mL quartz tube equipped with a magnetic stir bar and an oxygen bulb. The quartz tube was sealed with a magnetic stir bar, and the internal chamber of the quartz tube was connected to a balloon (natural latex balloon) containing 1 L of oxygen through a tubing to allow the reaction to proceed under an oxygen atmosphere. The reaction mixture was irradiated with an 18 W blue LED at room temperature for 4 hours. After the reaction was complete, the mixture was extracted with ethyl acetate (5 mL × 3 times, 5 mL each time), the ethyl acetate phases were combined, dried over anhydrous Na2SO4, and concentrated under vacuum. The residue was purified by silica gel column chromatography (elution: petroleum ether / ethyl acetate = 3:1, v / v) to obtain the corresponding product.

[0047] A variety of substrates for substituted styrene 1a were screened, with substituents R including: para-methyl, para-methoxy, para-acetoxy, para-tert-butyl, para-oxytert-butyl, para-fluorine, para-chlorine, para-bromine, para-nitro, para-hydroxymethyl, meta-methyl, meta-chlorine, meta-nitro, ortho-chlorine, etc.

[0048] The substrate range of substituted styrene 1a has been expanded, including:

[0049]

[0050] First, electron-donating substituents at the para-position of the benzene ring in styrene were tested. Substituents such as para-methyl, para-methoxy, para-methoxy, para-tert-butyl, and para-tert-butyl all showed good tolerance, with corresponding product yields of 50-60% under both standard and modified conditions. In contrast, electron-withdrawing aromatics also showed good tolerance under standard conditions, providing the desired product in yields of 64-80%. Notably, halogen substitutions at different positions on the benzene ring also performed well, indicating significant potential for further conversion. Second, the substrate range for meta-substituted styrene was evaluated. 1-Methyl-3-vinylbenzene, 1-chloro-3-vinylbenzene, and 1-nitro-3-vinylbenzene successfully produced the target product in yields of 57-81%. Furthermore, the sterically hindered 1-chloro-2-vinylbenzene was also compatible with the reaction; extending the reaction time to 6 hours resulted in an expected product yield of 70%.

[0051] Typical compound characterization data

[0052] Benzaldehyde Colorless liquid(82%isolated yield,0.16mmol,17.0mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,5 / 1). 1 HNMR (600MHz, CDCl3) δ: 10.00 (s, 1H), 7.88-7.86 (m, 2H), 7.63-7.60 (m, 1H), 7.53-7.51 (m, 2H); MS m / z: 106.

[0053] 4-MethylbenzaldehydePale yellow liquid(65%isolated yield,0.13mmol,15.6mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,3 / 1). 1 H NMR (600MHz, CDCl3) δ: 9.96 (s, 1H), 7.77 (d, J = 12.0Hz, 2H), 7.32 (d, J = 6.0Hz, 2H), 2.43 (s, 3H); MS m / z: 120.

[0054] 4-MethoxybenzaldehydeColorless liquid(53%isolated yield,0.11mmol,15.0mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,3 / 1). 1 H NMR(600MHz,CDCl3)δ:9.87(s,1H),7.82(d,J=8.8Hz,2H),7.00(d,J=8.7Hz,2H),3.87(s,3H);MS m / z:136.

[0055] 4-Formylphenyl acetateColorless liquid(60%isolated yield,0.12mmol,19.7mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,5 / 1). 1 H NMR(600MHz,CDCl3)δ:9.99(s,1H),7.92(dt,J=8.9,2.4Hz,2H),7.28(dt,J=7.7,2.0Hz,2H),2.33(s,3H);MS m / z:164.The spectrum data are consistent with thosereported in the reference literature.

[0056] 4-(tert-Butyl)benzaldehyde Colorless liquid(51%isolated yield,0.10mmol,16.2mg).Purification by flash chromatography(Petroleum ether). 1 HNMR(600MHz,CDCl3)δ:9.99(s,1H),7.82(d,J=8.5Hz,2H),7.56(d,J=8.4Hz,2H),1.36(s,9H);MS m / z:162.

[0057] 4-(tert-Butoxy)benzaldehyde Yellow liquid(50%isolated yield,0.10mmol,17.8mg).Purification by flash chromatography(Petroleum ether / Ethylacetate,10 / 1). 1 H NMR(600MHz,CDCl3)δ:9.91(s,1H),7.80(dt,J=8.6,2.6Hz,2H),7.09(dt,J=8.6,2.5Hz,2H),1.44(s,9H);MS m / z:178.

[0058] 4-Fluorobenzaldehyde Colorless liquid(64%isolated yield,0.13mmol,16.1mg).Purification by flash chromatography(Petroleum ether). 1 H NMR(600MHz,CDCl3)δ:9.96(s,1H),7.91-7.88(m,2H),7.22-7.19(m,2H);MS m / z:124.

[0059] 4-Chlorobenzaldehyde White solid(67%isolated yield,0.13mmol,18.2mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,10 / 1). 1 HNMR(600MHz,CDCl3)δ:9.98(s,1H),7.82(dt,J=8.6,2.2Hz,2H),7.51(dt,J=8.3,2.2Hz,2H);MS m / z:140.

[0060] 4-BromobenzaldehydeWhite solid(70%isolated yield,0.14mmol,25.6mg).Purification by flash chromatography(Petroleum ether). 1H NMR(600MHz,CDCl3)δ:9.96(s,1H),7.73(dt,J=8.5,2.1Hz,2H),7.67(dt,J=8.4,1.9Hz,2H);MS m / z:183.

[0061] 4-Nitrobenzaldehyde Yellow solid(72%isolated yield,0.14mmol,21.1mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,10 / 1). 1 HNMR(600MHz,CDCl3)δ:10.16(s,1H),8.39(dt,J=8.6,2.0Hz,2H),8.07(dt,J=8.8,2.1Hz,2H);MS m / z:151.

[0062] 4-(hydroxymethyl)benzaldehydeColorless liquid(80%isolated yield,0.16mmol,21.8mg).Purification by flash chromatography(Petroleum ether / Ethylacetate,2 / 1). 1 H NMR(600MHz,CDCl3)δ:10.00(s,1H),7.87(d,J=8.2Hz,2H),7.53(d,J=8.0Hz,2H),4.80(s,2H),2.01(s,1H);MS m / z:136.

[0063] 3-Methylbenzaldehyde Colorless liquid(57%isolated yield,0.11mmol,13.2mg).Purification by flash chromatography(Petroleum ether). 1 H NMR(600MHz,CDCl3)δ:9.98(s,1H),7.68-7.66(m,2H),7.44-7.40(m,2H),2.42(s,3H);MS m / z:120.

[0064] 3-Chlorobenzaldehyde Colorless liquid(81%isolated yield,0.16mmol,22.4mg).Purification by flash chromatography(Petroleum ether). 1 H NMR(600MHz,CDCl3)δ:9.97(s,1H),7.84(t,J=1.7Hz,1H),7.75(dt,J=7.6,1.3Hz,1H),7.59(dq,J=7.9,1.1Hz,1H),7.47(t,J=7.7Hz,1H);MS m / z:140.

[0065] 3-Nitrobenzaldehyde White solid(70%isolated yield,0.14mmol,21.1mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,20 / 1). 1 HNMR(600MHz,CDCl3)δ:10.12(s,1H),8.71(t,J=1.9Hz,1H),8.48(dq,J=8.2,1.1Hz,1H),8.23(dt,J=7.6,1.3Hz,1H),7.77(t,J=7.9Hz,1H);MS m / z:151.

[0066] 2-Chlorobenzaldehyde Colorless solid(70%isolated yield,0.14mmol,19.6mg).Purification by flash chromatography(Petroleum ether / Ethyl acetate,20 / 1). 1 H NMR(600MHz,CDCl3)δ:10.47(s,1H),7.90(dd,J=7.7,1.7Hz,1H),7.53-7.50(m,1H),7.44(dd,J=8.0,0.9Hz,1H),7.38-7.36(m,1H);MS m / z:140.

[0067] [1,1'-Biphenyl]-4-carbaldehyde White solid(69%isolated yield,0.14mmol,25.5mg).Purification by flash chromatography(Petroleum ether / Ethylacetate,60 / 1). 1 H NMR (600MHz, CDCl3) δ: 10.06 (s, 1H), 7.96 (dd, J = 6.6, 1.8Hz, 2H), 7.76 (d, J = 8.2Hz, 2H), 7.65-7.63 (m, 2H), 7.50-7.48 (m, 2H), 7.44-7.41 (m, 1H); MS m / z:182.

[0068] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a bifunctional photocatalyst for the photocatalytic oxidation of styrene, characterized by the following steps: First, copper nitrate trihydrate was dissolved in anhydrous ethanol, and then trimellitic acid was added to form a solution containing MOF material Cu-BTC. This solution was then mixed with anhydrous ethanol solution containing titanium dioxide to form a homogeneous mixture. After stirring at room temperature, the mixture was allowed to stand for 4-12 hours. Finally, solid-liquid separation was performed, and the solid precipitate was washed with anhydrous ethanol and dried. This yielded a bifunctional catalyst for the photocatalytic oxidation of styrene. The molar ratio of copper nitrate trihydrate to trimellitic acid was 0.5-4:0.5-4, the molar concentration of copper nitrate in the MOF material Cu-BTC solution was 0.01-0.20 mmol / mL, and the molar concentration of titanium dioxide in the anhydrous ethanol solution was 0.01-0.20 mmol / mL. In the homogeneous mixture, the molar ratio of copper nitrate trihydrate to titanium dioxide was (1-3):(1-3), and the reaction time was 0.5-2 hours.

2. The preparation method according to claim 1, characterized in that, The molar ratio of copper nitrate trihydrate to pyromellitic acid is 0.8-2.5:0.8-1.0; The molar concentration of copper nitrate in the solution of the MOF material Cu-BTC is 0.08-0.15 mmol / mL; The molar concentration of titanium dioxide in anhydrous ethanol solutions containing dissolved titanium dioxide is 0.02-0.06 mmol / mL; In the homogeneous mixture, the molar ratio of copper nitrate trihydrate to titanium dioxide is 1.8-2.5:

1.

3. The preparation method according to claim 1, characterized in that, The reaction time is 0.8-1.2 hours; allow it to stand for 5-8 hours. The synthesis method used a single green solvent, anhydrous ethanol, and the synthesis reaction was carried out under room temperature stirring conditions, resulting in the rapid production of the nano-photocatalytic material Cu-BTC-TiO2.

4. A bifunctional catalyst for photocatalytic oxidation of styrene, prepared by any one of the preparation methods described in claims 1-3.

5. The use of the bifunctional catalyst of claim 4 in the process of photocatalytic oxidation of styrene or substituted styrene to prepare benzaldehyde or substituted benzaldehyde.

6. The application according to claim 5, characterized in that, Using water as a reaction solvent, photocatalytic oxidation of styrene or one or more substituted styrene compounds is achieved to synthesize benzaldehyde or one or more substituted benzaldehyde compounds.

7. The application according to claim 6, characterized in that, In the photocatalytic system, the ratio of the bifunctional catalyst, water, and styrene is (5-20 mg): (1-6 mL): (11.0-24.0 µL).

8. The application according to claim 7, characterized in that, In the photocatalytic system, the ratio of the bifunctional catalyst, water, and styrene is 14-16 mg : 2-4 mL : 11.5-12.0 µL.

9. The application according to claim 5 or 6, characterized in that, In the photocatalytic system, the light wavelength is 465-470 nm, and the irradiation reaction time is 2-10 hours.

10. The application according to claim 9, characterized in that, The irradiation reaction time is 4-6 hours.

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