Cu4 cluster MOF polyacid hybrid material and application thereof in photocatalytic hydrogen evolution

Abstract

The application relates to the field of photocatalytic hydrogen evolution, and specifically discloses a Cu4 cluster MOF polyacid hybrid material and application thereof in photocatalytic hydrogen evolution. In view of the three core problems of high cost caused by noble metal dependence, low activity and poor stability caused by high electron-hole recombination rate and narrow light absorption range of existing photocatalytic hydrogen evolution catalysts, the application describes a preparation method of a polyacid metal organic framework hybrid material (Cu4-PW 12 ) prepared by one-step hydrothermal method. The application realizes photocatalytic hydrogen evolution without noble metal dependence by innovatively combining the synergistic advantages of the proton conduction capacity of a polyoxometalate (POM) and the three-dimensional porous structure of a metal organic framework (MOF). The material has simple preparation process, cheap and easily available raw materials and excellent performance, can be widely applied to the fields of solar photocatalytic water splitting for hydrogen production, new energy storage and the like, provides key technical support for promoting the industrialization of clean hydrogen energy, and has remarkable economic value and environmental protection significance.

Description

Technical Field

[0001] This invention relates to the field of photocatalytic hydrogen evolution, and particularly to a Cu4 cluster MOF multi-acid hybrid material (Cu4-PW). 12 Preparation of ) Background Technology

[0002] Faced with the dual pressures of a escalating global energy crisis and excessive fossil fuel consumption, developing clean and renewable alternative energy sources has become crucial for solving energy and environmental problems. Hydrogen energy, with its combustion product being only water, high energy density, and renewability, is considered one of the most promising clean energy sources. In particular, solar-driven photocatalytic water splitting for hydrogen production directly converts solar energy into chemical energy, making it an ideal pathway for large-scale hydrogen production. However, traditional photocatalysts generally suffer from three key problems: low catalytic efficiency, poor stability, and high cost. Therefore, developing efficient, stable, low-cost, and precious metal-free hydrogen evolution photocatalysts has become a core challenge urgently needing breakthroughs in the field of photocatalysis. Polyoxometalates (POMs), as a class of nanoscale metal-oxygen cluster compounds formed by oxygen atom bridging of former transition metals such as vanadium, molybdenum, and tungsten, exhibit broad application potential in photoelectrocatalysis and new energy fields due to their defined nanostructure, excellent proton conductivity, and tunable redox properties, providing ideal inorganic cluster building blocks for designing novel photocatalysts. However, pure POMs have significant drawbacks: on the one hand, their low LUMO energy level and wide HOMO-LUMO band gap result in insufficient photogenerated electron reduction capacity, making it difficult to meet the thermodynamic requirements for hydrogen desorption from water; on the other hand, the light absorption range of pure POMs is limited to the ultraviolet region, resulting in low solar energy utilization, and noble metal co-catalysts are required to improve catalytic activity, further increasing costs. Metal-organic frameworks (MOFs), due to their high specific surface area, tunable pore structure, and abundant metal active sites, have become ideal building blocks for constructing highly efficient photocatalytic systems. Based on the aforementioned research status and technological needs, hybrid design of POMs (or their reduced form HPB) with MOFs can achieve complementary advantages. Summary of the Invention

[0003] This invention aims to design and prepare a novel hybrid photocatalytic material (Cu4-PW) based on POM and MOF. 12 ), through transition metal (copper) complexes to phosphotungstic acid (H3PW) 12 O 40 PW (abbreviated as PW) 12A three-dimensional network structure of POM-MOF hybrid system was constructed by modifying POM with metal orbitals. This design effectively solves the problems of low efficiency, poor stability, and high cost of traditional catalysts; it enhances the LUMO energy level of POM through metal orbital hybridization to meet the thermodynamic requirements of hydrogen desorption from water; and it improves the stability and recyclability of the material through the three-dimensional hybrid structure, ultimately achieving efficient, stable, and low-cost solar-driven photocatalytic hydrogen desorption from water.

[0004] A Cu4-PW for photocatalytic hydrogen evolution 12 The chemical formula is (PMo) 12 O 40 [Cu4(C6H4N5)6], wherein the ligand is 5-pyridine-2-tetrazazole (HL); the crystal system is triclinic; the space group is Pī; the unit cell parameters are α=99.5880(10), β=94.6680(10), γ=111.1370(10), a=11.4282(9) Å, b=12.4480(10) Å, c=15.2890(13) Å, z=1.

[0005] A method for preparing Cu4 cluster MOF multi-acid hybrid materials for photocatalytic hydrogen evolution is carried out according to the following steps:

[0006] (1) Take 0.34 g of H3PW 12 O 40 ·xH2O, 0.19 g CuCl2 and 0.05 g HL were dissolved sequentially in 30 mL of deionized water, and the pH of the solution was adjusted to 4.6 with 1 mol / L HCl solution. The solution was stirred at room temperature for 0.5 h.

[0007] (2) Divide the above solution into three equal portions and transfer them into 15 mL reaction vessels. Place them in an oven at 140 °C for 48 h, and then gradually cool them down to 80 °C at a rate of 10 °C / h.

[0008] (3) Finally, after natural cooling to room temperature, the lake blue rhombic blocky crystals were washed to obtain Cu4 cluster MOF multi-acid hybrid material, with a yield of 75%;

[0009] The chemical formula of the Cu4 cluster MOF multi-acid hybrid material mentioned in step (3) is (PMo 12 O 40 [Cu4(C6H4N5)6], wherein the ligand is 5-pyridine-2-tetrazazole; the crystal system is triclinic; the space group is Pī; the unit cell parameters are α=99.5880(10), β=94.6680(10), γ=111.1370(10), a=11.4282(9) Å, b=12.4480(10) Å, c=15.2890(13) Å, z=1.

[0010] The above Cu4-PW 12 Hybrid materials and their preparation and application are mainly in the field of photocatalytic water splitting for hydrogen production.

[0011] The above application method is as follows: 5 mg of photocatalyst was added to the reaction system, and water / acetone (1 / 2) was used as the photocatalytic reaction solution. Photocatalytic hydrogen production was conducted under 500 W xenon lamp irradiation, with triethanolamine selected as the electron sacrificial agent. After 6 h of photocatalytic hydrogen evolution reaction, Cu4-PW 12 The total hydrogen evolution was 16.95 mmol g. -1 The catalytic rate is 2825 μmol g. -1 h -1 .

[0012] Compared with the prior art, the present invention has the following characteristics:

[0013] Novel Cu4-PW 12 As a POM-MOF hybrid system, the photocatalytic material exhibits multi-dimensional advantages compared to existing technologies. Its preparation method is relatively simple, requiring stirring at room temperature for 0.5 h followed by holding at 140 ℃ for 48 h in a reactor. The yield is high, reaching 75%. In terms of performance, it overcomes the efficiency bottleneck of traditional catalysts, solves the light absorption limitation problem of pure polyoxometalates (POMs), and the three-dimensional MOF structure provides a stable support for HPB, ensuring sustained broad-spectrum response; simultaneously, it utilizes Cu⁺ / Cu 2⁺ The hybridization of the dual-valent active sites with the metal orbitals of POM significantly improves the photogenerated electron-hole separation efficiency, and electrochemical impedance spectroscopy confirms that its electronic conductivity is superior to that of pure PW. 12 The hydrogen evolution rate reached 2825 μmol g. -1 h -1 This material achieves highly efficient catalysis without the need for precious metal co-catalysts. Regarding stability, the hydrothermally synthesized material exhibits multiphase characteristics, is insoluble in water and common organic solvents, and its three-dimensional POM-MOF hybrid structure resists corrosion and oxidation. Single-crystal X-ray diffraction and X-ray powder diffraction confirm its regular structure and high purity, facilitating recycling and extending its service life. In terms of cost, the abundant metal Cu replaces precious metal co-catalysts, reducing raw material costs. The synthesis process is simple, requiring only pH adjustment and a 140℃ reaction time of 48 hours to prepare high-purity crystals; the preparation process has low energy consumption and is easily scaled up industrially. Structurally, a three-dimensional "POM-MOF-HPB" network is constructed, where Cu ions and HL form the MOF framework, and PW... 12 (and HPB) are embedded in it to achieve synergistic effects of adsorption, light absorption, charge separation and catalysis. Attached Figure Description

[0014] Figure 1 This is an X-ray powder diffraction pattern of a Cu4 cluster MOF polyacid hybrid material prepared in Example 1 of the present invention.

[0015] Figure 2 This is an X-ray photoelectron spectrum of a Cu4 cluster MOF polyacid hybrid material prepared in Example 1 of the present invention.

[0016] Figure 3 The fluorescence spectrum (PL) of a Cu4 cluster MOF polyacid hybrid material prepared in Example 1 of this invention.

[0017] Figure 4 The images show the liquid UV-Vis absorption spectra of the HBP state of a Cu4 cluster MOF polyacid hybrid material prepared in Example 1 of this invention, and the liquid UV-Vis absorption spectra of the HBP state after exposure to O2.

[0018] Figure 5 Motter-Schottky assay (MS) was performed on a Cu4 cluster MOF multiacid hybrid material prepared in Example 1 of this invention.

[0019] Figure 6 The electrochemical impedance spectroscopy (EIS) is shown for a Cu4 cluster MOF polyacid hybrid material prepared in Example 1 of this invention.

[0020] Figure 7 The total amount and rate of photocatalytic hydrogen evolution of a Cu4 cluster MOF polyacid hybrid material prepared in Example 1 of this invention under different conditions.

[0021] Figure 8 This is a schematic diagram of the structure of a Cu4 cluster MOF multi-acid hybrid material prepared in Example 1 of the present invention. Detailed Implementation

[0022] The present invention will be described in detail below with reference to the accompanying drawings and embodiments: Embodiment 1, a Cu4 cluster MOF multi-acid hybrid material, comprising the following preparation steps:

[0023] (1) Take 0.34 g of H3PW 12 O 40 ·xH2O, 0.19 g CuCl2 and 0.05 g HL were dissolved sequentially in 30 mL of deionized water, and the pH of the solution was adjusted to 4.6 with 1 mol / L HCl solution. The solution was stirred at room temperature for 0.5 h.

[0024] (2) Divide the above solution into three equal portions and transfer them into 15 mL reaction vessels. Place them in an oven at 140 °C for 48 h, and then gradually cool them down to 80 °C at a rate of 10 °C / h.

[0025] (3) Finally, the product was naturally cooled to room temperature and washed to obtain lake blue rhomboid block crystals as the target product, with a yield of 75%.

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments: Attached Figure Description

[0027] (a) X-single crystal diffraction structure analysis data of a Cu4 cluster MOF multi-acid hybrid material in Example 1 are shown in Table 1.

[0028] Table 1

[0029] Material 1 <![CDATA[Molecular weight of compound, Crystal system, Space group, a, Å, b, Å, c, Å, α, deg, β, deg, γ, deg, V, Å 3 ZD calcd / g·cm -3 T / K, F(000), R int GOF on F 2 R1 / wR2 [I≥2σ(I)], R1, a wR2 b (alldata)]]> <![CDATA[Cu4-PW 12 4108.21 Three oblique Pī11.4282(9)12.4480(10)15.2890(13)99.5880(10)94.6680(10)111.1370(10))1976.5(3)13.451296.151841.00.03411.1180.0837 / 0.21690.0926 / 0.2277]]>

[0030] a R1 = ∑║F o │─│F c ║ / ∑│F o │, b wR2= {∑[w(F o 2 —F c 2 ) 2 ] / ∑[w(F o 2 ) 2 ]} 1 / 2

[0031] As shown in Table 1, the chemical formula of a Cu4 cluster MOF multi-acid hybrid material in Example 1 is (PMo 12 O 40 [Cu4(C6H4N5)6], Example: A polyacid cluster PMo in a Cu4 cluster MOF polyacid hybrid structure 12 The polyacid molecule is linked to the organometallic complex via Mo-O-Cu coordination bonds. Each group of six organic ligands is coordinated with nitrogen and copper atoms, forming a unit cell structure where a metal-organic complex and a polyacid molecule are linked by coordination bonds. The polyacid-organic complex extends spatially to form a one-dimensional chain structure, which then forms a three-dimensional supramolecular structure through intermolecular forces. This spatial structure facilitates rapid electron transfer between the polyacid and the metal-organic complex. This stable connection method can improve the catalytic efficiency of photocatalytic water splitting for hydrogen production.

[0032] Furthermore, by X-ray powder diffraction analysis and comparison with known structures, Cu4-PW can be confirmed. 12 The purity of the synthesis.

[0033] Figure 1 This is an X-ray powder diffraction pattern of a Cu4 cluster MOF multiacid hybrid material.

[0034] (ii) X-ray photoelectron spectroscopy (XPS) was performed on a Cu4 cluster MOF multiacid hybrid material from Example 1 to determine the oxidation states of Cu and W and the presence of impurities. XPS analysis showed that in the Cu 2p spectrum, Cu²⁺ was affected by [Ar] 3d. 9 The electronic configuration contains unpaired electrons in Cu 2p 3 / 2 The main peak of Cu 2p1 / 2 (954.28 eV) appears on the high binding energy side (e.g., at 942.68, 944.88, and 963.68 eV), indicating that Cu⁺ is [Ar] 3d¹. 0 Full-shell structure, no satellite peaks, its Cu 2p 3 / 2 (931.38 eV), Cu 2p 1 / 2 The (951.28 eV) peak lacks satellite peak characteristics. In the W 4f spectrum, the characteristic peaks at 35.88 and 37.88 eV correspond to W 4f7 / 2 and W 4f5 / 2, respectively, indicating that W is W 6 The oxidation states are Cu²⁺ and Cu⁺. In summary, it can be determined that Cu exists in two oxidation states: Cu²⁺ and Cu⁺, and W is W. 6 ⁺, and without any impurity characteristics.

[0035] Figure 2 The image shows an X-ray photoelectron spectrum of a Cu4 cluster MOF multiacid hybrid material.

[0036] (III) The fluorescence spectrum (PL) of a Cu4 cluster MOF multi-acid hybrid material in Example 1 was analyzed. Characterization of photogenerated electron-hole separation using fluorescence spectroscopy revealed that weaker fluorescence intensity correlated with higher separation efficiency. At an excitation wavelength of 290 nm, PW... 12 The fluorescence is strong at 400 nm, while Cu4-PW 12 The near absence of fluorescence indicates that Cu4-PW 12 The high separation rate of photogenerated electrons and holes, the effective transfer of photogenerated electrons, and the enhanced photocatalytic reaction activity are all achieved.

[0037] Figure 3 The image shows the fluorescence spectrum (PL) of a Cu4 cluster MOF multiacid hybrid material.

[0038] (iv) Liquid UV-Vis absorption spectra of the HBP state of a Cu4 cluster MOF polyacid hybrid material in Example 1 and its liquid UV-Vis absorption spectra after exposure to O2. Liquid UV-Vis absorption spectroscopy of the irradiated suspension revealed that the suspension gradually deepened in color to a darker blue with increasing irradiation time, and the intensity of the absorption band at 580 nm increased accordingly, indicating that the amount of heteropolyblue species increased with increasing irradiation time. When the reaction suspension was exposed to air and came into contact with O2, the HPB visible absorption band gradually weakened and eventually disappeared, and the solution returned to colorless, confirming the reversibility of polyanion reduction. Therefore, the HPB concentration is one of the important factors for polyacids to participate as photocatalysts in the photocatalytic hydrogen evolution reaction.

[0039] Figure 4 The image shows the liquid UV-Vis absorption spectrum of the HBP state of a Cu4 cluster MOF multiacid hybrid material and the liquid UV-Vis absorption spectrum of the HBP state after exposure to O2.

[0040] (v) A Motter-Schottky test (MS) was performed on a Cu4 cluster MOF multi-acid hybrid material from Example 1. Electrochemical flat-band potential measurements showed that Cu4-PW 12 The tangent slope is positive, classifying it as an n-type semiconductor. Its flat-band potential is -0.24 V vs. Ag / AgCl, which translates to -0.043 V vs. NHE standard conduction band potential. Parent PW 12 The conduction band potential of 0.24 V vs. NHE does not meet the conditions for photocatalytic hydrogen production, while Cu4-PW 12 Due to the introduction of transition metals and hybridization with multiple acid orbitals, the conduction band potential is increased to meet the conditions for hydrogen production; moreover, its three-dimensional layered structure improves the band gap and conduction band position, resulting in better synergistic efficiency and expected better photocatalytic activity.

[0041] Figure 5 This is a Motterschottky (MS) spectra of a Cu4 cluster MOF multiacid hybrid material.

[0042] (vi) Electrochemical impedance spectroscopy (EIS) was performed on a Cu4 cluster MOF multi-acid hybrid material from Example 1 to characterize the charge transfer resistance of the photocatalyst. Since no obvious semi-circular shape was observed in the high-frequency region, the ohmic impedance of the crystalline material, represented by the intersection of the curve and the X-axis, can also be used to represent the electron conduction capability. As shown in the figure, the order of the intersection points of the curve and the X-axis is PW. 12 Cu4-PW 12 This indicates that the introduction of organometallic complexes results in lower ohmic impedance and stronger electronic conductivity in the material, thus successfully improving the ease of recombination of photogenerated electrons and holes in the parent polyacid.

[0043] Figure 6 The image shows the electrochemical impedance spectroscopy (EIS) diagram of a Cu4 cluster MOF multiacid hybrid material.

[0044] (VII) The total amount and rate of hydrogen evolution in the Cu4 cluster MOF polyacid hybrid material of Example 1 were tested under different conditions. In the photocatalytic hydrogen production experiment, the effects of three sacrificial agents—triethylamine (TEA), Na2S / Na2SO3, and triethanolamine (TEOA)—were investigated using water / acetone (1 / 2) as the reaction solution and 5 mg of photocatalyst under 500W xenon lamp irradiation. The results showed that when TEA and Na2S / Na2SO3 were used as sacrificial agents, the hydrogen production was low, while when TEOA was used as a sacrificial agent, the Cu4-PW... 12 After 6 hours of photocatalytic hydrogen evolution, the total hydrogen evolution amount reached 16.95 mmol / g, and the catalytic rate was 2825 μmol / g. -1 h -1 TEOA was chosen because of its strong reducing ability, which can reduce tungsten-based heteropolyacids to heteropolyblue species to promote electron transfer. In addition, it is often used as a reducing agent in material preparation to reduce the valence state of metals, which is beneficial to photocatalytic reactions.

[0045] Figure 7 The figure shows the total amount and rate of hydrogen evolution in a Cu4 cluster MOF multi-acid hybrid material under different conditions.

[0046] (viii) Based on single-crystal X-ray diffraction data, a schematic diagram of the Cu4 cluster MOF multi-acid hybrid material structure in Example 1 is presented, illustrating Cu4-PW. 12 Atomic arrangement: Cu ions and organic ligands (HL) construct metal-organic frameworks (MOFs), polyacids [PW] 12 O 40 [³⁻] anions are embedded as building blocks to form a three-dimensional (3D) hybrid network structure. Each unit cell contains one [PW] ion. 12 O 40 The POM and MOF hybrid structure consists of 3⁻, 4 Cu atoms (including monovalent and divalent atoms with different coordination modes) connected to 6 organic ligands. This hybrid structure promotes electron transfer and light absorption through the synergistic effect of the two, which helps to improve the stability and photocatalytic activity of the material.

[0047] Figure 8 The diagram shows a schematic of a Cu4 cluster MOF multi-acid hybrid material.

[0048] In summary, this experiment employed a hydrothermal synthesis method, utilizing H3PW 12 O 40 Using xH2O (phosphotungstic acid), CuCl2 (copper chloride), and HL as precursors, a stable Cu4-PW catalyst with excellent photocatalytic hydrogen evolution performance was successfully prepared. 12 catalyst.

Claims

1. A Cu4 cluster MOF multi-acid hybrid material (Cu4-PW) 12 The preparation of phosphotungstic acid (H3PW) was carried out by hydrothermal synthesis. 12 O 40 Using xH₂O (phosphotungstic acid), CuCl₂ (copper chloride), and HL (5-pyridine-2-tetrazazole) as precursors, a lake-blue rhombic blocky crystal with the chemical formula (PMo) was obtained. 12 O 40 [Cu4(C6H4N5)6], where, The ligand is 5-pyridine-2-tetrazazole; the crystal system is triclinic; the space group is Pī; the unit cell parameters are α=99.5880(10), β=94.6680(10), γ=111.1370(10), a=11.4282(9) Å, b=12.4480(10) Å, c=15.2890(13) Å, z=1. This hybrid material is used for photocatalytic hydrogen evolution.

2. A Cu4-PW as described in claim 1 12 The preparation method of [the substance] is as follows: (1) Take 0.34 g of H3PW 12 O 40 ·xH2O, 0.19 g CuCl2 and 0.05 g HL were dissolved sequentially in 30 mL of deionized water, and the pH of the solution was adjusted to 4.6 with 1 mol / L HCl solution. The solution was stirred at room temperature for 0.5 h. (2) Divide the above solution into three equal portions and transfer them into 15 mL reaction vessels. Place them in an oven at 140 °C for 48 h, and then gradually cool them down to 80 °C at a rate of 10 °C / h. (3) Finally, after naturally cooling to room temperature and washing, lake-blue rhombic blocky crystals were obtained as Cu4-PW. 12 The yield was 75%. The Cu4-PW described in step (3) 12 The chemical formula is (PMo) 12 O 40 [Cu4(C6H4N5)6], where, The ligand is 5-pyridine-2-tetrazazole; the crystal system is triclinic; the space group is Pī; the unit cell parameters are α=99.5880(10), β=94.6680(10), γ=111.1370(10), a=11.4282(9) Å, b=12.4480(10) Å, c=15.2890(13) Å, z=1.

3. A Cu4-PW as described in claim 2 12 Its characteristics The material's single-cell structure contains one polyacid (PW) 12 O 40 ) 3- The anion contains 4 Cu atoms and 6 organic ligands (5-pyridin-2-tetrazazole). Of the 4 Cu atoms, 2 are five-coordinated (Cu... ＋ ), 2 Cu atoms with hexacoordinate 2+ Furthermore, Cu ions and organic ligands construct metal-organic frameworks (MOFs), (PW 12 O 40 ) 3- Anions are embedded within it to form a three-dimensional (3D) hybrid network structure.

4. The preparation method according to claim 2 prepares a Cu4-PW 12 Its characteristics Utilizing phosphotungstic acid H3PW 12 O 40 • xH2O (phosphotungstic acid), CuCl2 (copper chloride) and HL (5-pyridine-2-tetrazazole) are used as precursors for hydrothermal synthesis and are applied in the field of photocatalytic water splitting to produce hydrogen.

5. A Cu4-PW prepared by the method described in claim 2 12 Its characteristics are, This material is an n-type semiconductor with a flat band potential of -0.24 V vs. Ag / AgCl (equivalent to -0.043 V vs. NHE standard conduction band potential). Cu is present in the material. + and Cu 2+ Two oxidation states, W element is W 6+ It is insoluble in water and common organic solvents and has a three-dimensional POM-MOF hybrid structure.

6. A Cu4-PW according to claim 2 12 Its application in photocatalytic hydrogen evolution is characterized by, The application method is as follows: 5 mg of photocatalyst was added to the reaction system, and water / acetone (1 / 2) was used as the photocatalytic reaction solution. Photocatalytic hydrogen production was carried out under 500 W xenon lamp irradiation. Triethanolamine was selected as the electron sacrificial agent. After 6 h of photocatalytic hydrogen evolution reaction, Cu4-PW 12 The total hydrogen evolution was 16.95 mmol / g. -1 The catalytic rate is 2825 μmol g. -1 h -1 .

7. The Cu4-PW according to claim 2 12 The material's distinctive feature lies in the construction method of its three-dimensional hybrid network structure, revealing the differentiated role of Cu ions in constructing the MOF framework and explaining the basis for the formation of the hybrid structure.

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