Hollow photoactive Cu / Zn-MOFs catalyst as well as preparation method and application thereof

Abstract

The invention provides a hollow photoactive Cu / Zn-MOFs catalyst as well as a preparation method and application thereof, and relates to the technical field of photocatalytic materials. According to the invention, through an improved Ostwald ripening method, copper metal particles are anchored on the surface of Zn-TPBD, and the Cu / Zn-MOFs composite material with a clear structure and a hollow structure is successfully prepared. Cu / Zn-MOFs have the advantages of wide absorption range, high charge separation efficiency, strong O2 adsorption / activation capability, good recycling property, light / heat stability, low cost, easy obtaining and the like, and the Cu / Zn-MOFs prepared by the method can be used as a catalyst in photocatalytic aerobic dehydrogenation reaction to realize 99% conversion rate of quinoline; meanwhile, the photocatalyst shows high-efficiency photocatalytic activity on oxidative dehydrogenation reaction of polysubstituted quinoline derivatives, and the stability of the structure and the catalytic efficiency can still be kept after multiple times of cyclic catalytic use. The Cu / Zn-MOFs catalyst prepared by the preparation method disclosed by the invention provides favorable conditions for realizing efficient and green synthesis of quinoline derivatives.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic materials technology, specifically to a hollow photoactive Cu / Zn-MOFs catalyst, its preparation method, and its applications. Background Technology

[0002] In recent years, with the continuous improvement of global economic development and industrialization, human consumption of fossil fuels such as coal, oil, and natural gas has increased dramatically, leading to increasingly serious problems such as energy shortages, environmental pollution, and sustainable development. To address the energy shortages and environmental pollution caused by fossil fuel consumption, scientists have successively devoted themselves to research on new alternative clean energy sources. Solar energy, as a renewable and clean energy source, has received continuous and widespread attention from scientists. Based on this, visible light-excited photocatalytic oxidation-reduction technology can achieve efficient conversion of solar energy into chemical energy, while simultaneously converting inexpensive organic substrates into high-value-added pharmaceutical intermediates or fine chemicals. Furthermore, visible light-excited photocatalytic oxidation-reduction technology has advantages such as mild reaction conditions, low cost, few byproducts, and low energy consumption, and therefore has been widely applied in materials science, biochemistry, and drug synthesis.

[0003] Quinolines and their derivatives are an important class of aromatic nitrogen-containing heterocyclic compounds with a wide range of physiological and pharmacological activities, such as antiarrhythmic, antimalarial, anticancer, antibacterial, and antiviral effects. Traditional methods for preparing quinoline derivatives include coal tar extraction, Friedlander condensation, and Povarov synthesis; however, these methods face challenges such as complex operation, cumbersome steps, poor selectivity, and significant environmental hazards. In recent years, visible light-mediated photocatalytic aerobic dehydrogenation reactions for the preparation of quinoline derivatives have attracted attention. This method utilizes visible light to excite the electron cloud on the surface of a photocatalyst, generating photogenerated electrons that oxidize adsorbed molecular oxygen (O2) into reactive oxygen species (ROS), such as superoxide radicals (•O2). — Singlet oxygen ( 1 O2 and other substances have the advantages of being mild, green, and sustainable.

[0004] The photocatalytic redox process excited by visible light is affected by three factors: light source, photocatalyst, and substrate activity. Among them, the photocatalyst is crucial for the efficient conduction of the photocatalytic reaction. Currently, commonly used photocatalyst materials mainly include inorganic semiconductors (TiO2), noble metal complexes (ruthenium terpyridine, iridium terpyridine), organic molecular dyes (fluorescein), metal sulfides, metal nitrides, molecular sieves, etc. These photocatalysts all have excellent photophysical properties, but they also have the following disadvantages: (1) narrow light absorption range, which cannot make full use of visible light; (2) low charge separation efficiency, and photogenerated electron-hole pairs are easy to recombine; (3) insufficient O2 adsorption / activation capacity, which affects the generation of reactive oxygen species (ROS); (4) poor photochemical stability, and catalytic activity is difficult to maintain; (5) the catalysts prepared by traditional methods have a single structure and lack synergistic effect, which cannot simultaneously solve the problems of light absorption, charge separation and O2 activation; thus causing a significant decrease in photocatalytic efficiency.

[0005] Based on the above background, there is an urgent need to construct a photocatalyst that simultaneously possesses a wide absorption range, high charge separation efficiency, and strong O2 adsorption / activation ability. In addition, it should also have good recyclability, light / thermal stability, and be inexpensive and readily available, so as to achieve efficient and green synthesis of quinoline derivatives. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a hollow photoactive Zn-MOFs-supported electron-deficient Cu nanoparticles (Cu / Zn-MOFs) photocatalyst obtained by an improved Ostwald ripening method.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] First, this invention provides a hollow photoactive Cu / Zn-MOFs catalyst, which is prepared from N,N,N',N'-tetratetra(4-(4'-carboxy)biphenyl)-1,4-phenylenediamine (H4TPBD), zinc salt, and copper salt in a mass ratio of 1-3:5-7:0.8-1.2 using a solvothermal method and the Ostwald ripening method.

[0011] The preferred mass ratio of N,N,N',N'-tetratetra(4-(4'-carboxy)biphenyl)-1,4-phenylenediamine (H4TPBD), zinc salt, and copper salt is 2:6:1.

[0012] The zinc salt is a soluble zinc salt, specifically any one of zinc sulfate, zinc chloride, and zinc nitrate.

[0013] The copper salt is a soluble copper salt, specifically any one of copper sulfate, copper chloride, and copper nitrate.

[0014] The N,N,N',N'-tetratetra(4-(4'-carboxy)biphenyl)-1,4-phenylenediamine (H4TPBD) was prepared according to the method described in the reference. The reference is: Leixin Hou, Xu Jing,* Huilin Huang, and Chunying Duan, Merging Charge Transfer into Metal−Organic Frameworks to Achieve HighReduction Potentials via Multiphoton Excitation, ACS Appl. Mater. Interfaces 2022, 14, 15307−15316. DOI: 10.1021 / acsami.2c01595.

[0015] Furthermore, this invention also provides a method for preparing a hollow, photoactive Cu / Zn-MOFs catalyst, wherein the Cu / Zn-MOFs catalyst is prepared according to the following steps:

[0016] (1) Mix zinc salt and H4TPBD in N,N-dimethylamide (DMF) and react in a solvothermal reactor at 120-140℃ for more than 24 hours, then cool to room temperature to obtain Zn-TPBD;

[0017] (2) Disperse Zn-TPBD in a cosolvent of DMF / ethylene glycol v / v=1:1-1.2, then add copper salt, and then heat at 150-160℃ for more than 48h. After cooling to room temperature, take out the reactants, centrifuge to obtain solid, wash with deionized water, and then vacuum dry to obtain orange solid, which is the Cu / Zn-MOFs catalyst.

[0018] Furthermore, this invention also provides the application of hollow photoactive Cu / Zn-MOFs prepared by the above method as catalysts in the photocatalytic aerobic dehydrogenation reaction to prepare quinoline derivatives.

[0019] (III) Beneficial Effects

[0020] This invention utilizes an improved Ostwald ripening method to anchor copper metal particles onto the surface of Zn-TPBD, successfully preparing a well-defined hollow Cu / Zn-MOF composite material. Benefiting from its unique non-covalently bonded DA structure, the Cu / Zn-MOFs retain excellent crystallinity, while exhibiting improved chemical stability, thermal stability, and photoelectric properties compared to the parent Zn-MOFs. Furthermore, the synergistic effect of electron-donating and electron-accepting units in the hollow Cu / Zn-MOFs promotes the separation of photogenerated carriers and the generation of reactive oxygen species. This provides a structural and theoretical basis for using Cu / Zn-MOFs as photocatalysts. It is worth emphasizing that the DA structure of Cu / Zn-MOFs significantly enhances catalytic efficiency. Using the Cu / Zn-MOFs prepared by this invention as a catalyst, a 99% conversion rate of quinoline can be achieved in the photocatalytic aerobic dehydrogenation reaction. Importantly, the Cu / Zn-MOFs prepared by this invention maintain structural and catalytic efficiency stability even after multiple catalytic cycles. Furthermore, unlike traditional inorganic catalysts, the Cu / Zn-MOFs prepared in this invention exhibit highly efficient photocatalytic activity for the oxidative dehydrogenation of polysubstituted quinoline derivatives under relatively mild conditions. The Cu / Zn-MOFs catalysts prepared in this invention provide favorable conditions for the efficient and green synthesis of quinoline derivatives. Attached Figure Description

[0021] Figure 1 This is a synthetic route diagram for Cu / Zn-TPBD.

[0022] Figure 2 PXRD (a), thermogravimetric analysis results (b), PXRD spectra of Cu / Zn-TPBD before and after solvent treatment (c), FTIR spectrum of Cu / Zn-TPBD (d), and Raman spectrum of Cu / Zn-TPBD (e) are shown.

[0023] Figure 3 SEM images of Zn-TPBD (a) and Cu / Zn-TPBD (bc), EDX elemental mapping image of Cu / Zn-TPBD (d), and HRTEM image of Cu / Zn-TPBD (e).

[0024] Figure 4 XPS spectra of Zn-TPBD (a), C 1s XPS spectra (b), N 1s XPS spectra (c) and O 1s XPS spectra (d) are shown.

[0025] Figure 5The Cu 2p XPS spectrum of Cu / Zn-TPBD (a), the XANES K edge spectrum of Cu / Zn-TPBD (b), and the EXAFS spectrum of Cu / Zn-TPBD (c) are shown.

[0026] Figure 6 The optical and optoelectronic properties of Cu / Zn-TPBD are characterized as follows: UV / visDRS analysis of Zn-TPBD and Cu / Zn-TPBD (a), Tauc plot (b), Mott-Schottky plot of Cu / Zn-TPBD (c) and Zn-TPBD (d), band alignment of Zn-TPBD and Cu / Zn-TPBD (e), transient photocurrent response of Zn-TPBD and Cu / Zn-TPBD (f), EIS Nyquist plot of Zn-TPBD and Cu / Zn-TPBD (g), and solid-state emission spectra of Zn-TPBD and Cu / Zn-TPBD (h).

[0027] Figure 7 This refers to the photocatalytic reaction of THQ oxidizing to quinoline under different conditions.

[0028] Figure 8 The results of the four-cycle catalytic reaction efficiency of Cu / Zn-TPBD are shown in (a), and the PXRD (b) and infrared spectra of Cu / Zn-TPBD before and after four cycles are shown in (c).

[0029] Figure 9 This is a general formula for the oxidative dehydrogenation reaction of polysubstituted quinoline derivatives using Cu / Zn-TPBD as a photocatalyst. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] I. Preparation of Hollow Photoactive Cu / Zn-MOF Catalysts

[0033] (1) Mix 1.5g zinc nitrate and 0.5g H4TPBD in 100mL N,N-dimethylamide (DMF) and react in a solvothermal reactor at 120℃ for 24h. Then cool to room temperature to obtain yellow solid Zn-TPBD.

[0034] (2) The acetone-activated Zn-TPBD was dispersed in 50 mL of DMF / ethylene glycol (v / v=1:1) co-solvent, and then 0.25 g of copper nitrate was added. The mixture was then heated at 150 °C for 48 h. After cooling to room temperature, the reactants were removed, centrifuged to obtain a solid, washed with deionized water, and then dried under vacuum to obtain an orange solid, which is the Cu / Zn-MOFs catalyst, hereinafter referred to as Cu / Zn-TPBD.

[0035] The synthetic route of Cu / Zn-TPBD is as follows: Figure 1 As shown.

[0036] The N,N,N',N'-tetratetra(4-(4'-carboxy)biphenyl)-1,4-phenylenediamine (H4TPBD) was prepared according to the method described in the reference. The reference is: Leixin Hou, Xu Jing,* Huilin Huang, and Chunying Duan, Merging Charge Transfer into Metal−Organic Frameworks to Achieve HighReduction Potentials via Multiphoton Excitation, ACS Appl. Mater. Interfaces 2022, 14, 15307−15316. DOI: 10.1021 / acsami.2c01595.

[0037] II. Structural Characterization of Cu / Zn-TPBD

[0038] Powder X-ray diffraction results showed that Cu / Zn-TPBD exhibited characteristic PXRD patterns corresponding to the original Zn-TPBD, confirming that its phase purity and crystal structure were preserved. Figure 1 b). Furthermore, Cu / Zn-TPBD exhibits characteristic PXRD peaks corresponding to the face-centered cubic copper (111) crystal plane, confirming that metallic copper species were successfully anchored on the Zn-TPBD surface (results are shown in Figure 1). Figure 2 As shown in a). The thermal stability of the prepared Cu / Zn-TPBD was evaluated by thermogravimetric analysis (TGA), and the results showed that it had good thermal stability and could maintain structural integrity even at temperatures up to 400℃. Figure 2 (b) Excellent thermal stability is crucial for sustained photocatalytic applications. Furthermore, its chemical stability was evaluated by immersing Cu / Zn-TPBD samples in various solvents at room temperature. Figure 2 c). The PXRD patterns of Cu / Zn-TPBD remained almost unchanged before and after solvent treatment, indicating that it has excellent structural integrity and stability.

[0039] The FTIR spectrum of Cu / Zn-TPBD is highly similar to that of Zn-TPBD, at 1720 cm⁻¹. -1 (C=O stretching vibration), 1190cm -1 (CO stretching vibration), 1316 cm -1 A characteristic absorption peak appears at (CN stretching vibration), at 1598 cm⁻¹. -1 and 1278 cm -1 The presence of two distinct peaks at this location is attributed to the vibrations of the aromatic C=C skeleton. Figure 2 d). Furthermore, the Raman characteristic peaks corresponding to Cu / Zn-TPBD remain consistent with those of the original Zn-TPBD, confirming that the framework structure remains intact after loading with metallic copper. Figure 2 e)

[0040] SEM results show that Zn-TPBD has a two-dimensional lamellar structure, while Cu / Zn-TPBD exhibits a regular spherical morphology with an average diameter of approximately 5 μm. Figure 3 ab); SEM images of the broken spheres confirmed the formation of hollow cavities, and the shell structure of the hollow spheres consisted of thick nanosheets (3c). EDX elemental mapping showed that Cu, Zn, C, O, and N were uniformly distributed in Cu / Zn-TPBD, further confirming the uniform dispersion of metallic copper within the framework ( Figure 3 d). Furthermore, TEM analysis showed that the copper nanoparticles in Cu / Zn-TPBD were uniformly dispersed, with an average diameter of approximately 14.8 nm ( ). Figure 3 e)

[0041] X-ray photoelectron spectroscopy (XPS) characterization further confirmed the presence of C, O, N, Zn, and Cu elements in Cu / Zn-TPBD. Figure 4 a), consistent with EDX analysis results. Compared to the original Zn-TPBD, the binding energies of Cu / Zn-TPBD, specifically C 1s (288.3, ​​285.2, and 284.1 eV), N 1s (399.3 eV), and O 1s (531.6 eV), all show significant positive shifts, indicating that the electron density of the H4TPBD chromophore is reduced due to the introduction of copper. Figure 4 Furthermore, the Cu 2p XPS spectrum of Cu / Zn-TPBD shows two peaks at 932.8 eV and 953.6 eV, corresponding to Cu 2p and 953.6 eV, respectively. 0 Or Cu⁺’s 2p³ / 2 and 2p¹ / 2 ( Figure 5a). Subsequently, XANES analysis of the electronic structure and local coordination environment of Cu showed that the pre-edge characteristic position at 8981 eV in Cu / Zn-TPBD clearly indicates that Cu in Cu / Zn-TPBD is in the form of metallic Cu. 0 The existence of valence states may be attributed to the presence of ultra-small Cu. Figure 5 b). Consistent with XANES data, EXAFS analysis showed a strong characteristic peak in Cu / Zn-TPBD at approximately 2.2 Å, corresponding to the Cu-Cu interatomic spacing ( Figure 5 c).

[0042] III. Optical and photoelectric properties characterization of Cu / Zn-TPBD

[0043] UV-Vis DRS results showed that Cu / Zn-TPBD exhibited a broad absorption band in the 500-700 nm range compared to Zn-TPBD. This is attributed to the synergistic effect of Zn-TPBD and copper doping, which enhanced light absorption and promoted efficient charge carrier generation. Figure 6 a). Tautogram obtained by UV-vis DRS shows that the optical band gaps of Zn-TPBD and Cu / Zn-TPBD are 2.53 eV and 2.48 eV, respectively. Figure 6 (b) The decrease in bandgap value further indicates the successful introduction of electron-deficient copper. Mott-Schottky plots confirm that both zinc-based metal-organic frameworks are n-type semiconductors, with conduction band potentials of -0.76 V and -0.89 V (relative to the standard hydrogen electrode, NHE), respectively. Figure 6 cd), both are lower than O2 / •O2 — Its redox potential (-0.33 V) can effectively activate O2 to generate •O2. — (Key intermediate in photocatalytic reaction) Figure 6 e). Furthermore, compared to Zn-TPBD, Cu / Zn-TPBD exhibits a higher photocurrent response and a lower charge transfer resistance (e). Figure 6 The result (fg) indicates that it is more efficient in the generation, separation, and transfer of charge carriers. Under 420 nm excitation, the photoluminescence intensity of Cu / Zn-TPBD at 570 nm is significantly lower than that of the original Zn-TPBD (fg). Figure 6 This also demonstrates the efficient separation and migration of photogenerated electron-hole pairs (h), which also indicates the efficient separation and migration of photogenerated electron-hole pairs.

[0044] In summary, this invention successfully prepared a well-defined hollow Cu / Zn-TPBD composite material by anchoring copper metal particles onto the surface of Zn-TPBD using an improved Ostwald ripening method. Benefiting from the unique non-covalently bonded DA structure, Cu / Zn-TPBD retains excellent crystallinity, and its chemical stability, thermal stability, and photoelectric properties are all improved compared to the parent Zn-TPBD. Furthermore, the synergistic effect of electron-donating and electron-accepting units in the hollow Cu / Zn-TPBD promotes the separation of photogenerated carriers and the generation of reactive oxygen species. This provides a structural and theoretical basis for Cu / Zn-TPBD as a photocatalyst.

[0045] Example 2

[0046] Photocatalytic performance testing of Cu / Zn-TPBD

[0047] In 5 mL of O2-saturated acetonitrile solvent, 0.5 mmol of 1,2,3,4-tetrahydroquinoline (THQ) and 10 mg of Cu / Zn-TPBD were added, followed by irradiation with a 450 nm LED for 12 hours (condition 1). The product was then collected and analyzed by HPLC. Other reaction systems with different conditions were also established, and the conversion rate of THQ to quinoline under different conditions was calculated. The results are as follows: Figure 7 As shown.

[0048] Comparing the results under conditions 1-4, it is evident that light, Cu / Zn-TPBD, and oxygen play decisive roles in the aforementioned catalytic reactions. Comparing conditions 1 and 5-8, it is clear that Zn-TPBD, H4TPBD, Cu(NO3)2, or their physical mixtures exhibit low catalytic activity, while the DA structure of Cu / Zn-TPBD significantly enhances catalytic efficiency. Using the Cu / Zn-TPBD prepared in this invention as a catalyst, a 99% conversion rate of quinoline can be achieved in the photocatalytic aerobic dehydrogenation reaction.

[0049] Example 3

[0050] Catalytic stability test of Cu / Zn-TPBD

[0051] In 5 mL of O2-saturated acetonitrile solvent, 0.5 mmol of 1,2,3,4-tetrahydroquinoline (THQ) and 10 mg of Cu / Zn-TPBD were added, followed by irradiation with a 450 nm LED for 12 hours. The product was then collected and analyzed by HPLC to calculate the quinoline conversion. The catalyst was recovered by centrifugation, washing, and drying after the reaction, and reused in the same reaction system. This cycle was repeated four times. After the cycle, the structure of the recovered Cu / Zn-TPBD sample was analyzed by XRD and FTIR.

[0052] Cyclic results showed that Cu / Zn-TPBD maintained over 95% catalytic activity after four cycles. XRD and FTIR results indicated that Cu / Zn-TPBD retained its intact structure after multiple catalytic reactions, demonstrating excellent catalytic stability. Figure 8 ac).

[0053] Furthermore, unlike traditional inorganic catalysts, the Cu / Zn-TPBD prepared in this invention exhibits highly efficient photocatalytic activity for the oxidative dehydrogenation of polysubstituted quinoline derivatives under relatively mild conditions, as shown in Table 1. (The general reaction route formula is as follows...) Figure 9 (As shown).

[0054] Reactants Reaction products Conversion 1a 2a 99% 1b 2b 90% 1c 2c 94% 1d 2d 86% 1e 2e 78% 1f 2f 92% 1g 2d 85%

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hollow photoactive Cu / Zn-MOFs catalyst, characterized in that, The Cu / Zn-MOFs catalyst was prepared from N, N, N', N'-tetratetra(4-(4'-carboxy)biphenyl)-1,4-phenylenediamine (H4TPBD), zinc salt, and copper salt in a mass ratio of 1-3:5-7:0.8-1.2 using a solvothermal method and an Oswald ripening method.

2. The hollow photoactive Cu / Zn-MOFs catalyst according to claim 1, characterized in that, The zinc salt is a soluble zinc salt, specifically any one of zinc sulfate, zinc chloride, and zinc nitrate.

3. The hollow photoactive Cu / Zn-MOFs catalyst according to claim 1, characterized in that, The copper salt is a soluble copper salt, specifically any one of copper sulfate, copper chloride, and copper nitrate.

4. A method for preparing a hollow photoactive Cu / Zn-MOFs catalyst as described in claim 1, characterized in that... The Cu / Zn-MOFs catalyst was prepared according to the following steps: (1) Mix zinc salt and H4TPBD in N,N-dimethylamide (DMF) and react in a solvothermal reactor at 120-140℃ for more than 24 hours, then cool to room temperature to obtain Zn-TPBD; (2) Disperse Zn-TPBD in a cosolvent of DMF / ethylene glycol v / v=1:1-1.2, then add copper salt, and then heat at 150-160℃ for more than 48h. After cooling to room temperature, take out the reactants, centrifuge to obtain solid, wash with deionized water, and then vacuum dry to obtain orange solid, which is the Cu / Zn-MOFs catalyst.

5. The application of the hollow photoactive Cu / Zn-MOFs catalyst as described in claim 1 in the photocatalytic aerobic dehydrogenation reaction to prepare quinoline derivatives.

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