Preparation and photocatalytic application of a hexanuclear Ni cluster-modified germanium tungstate material

Abstract

A hexanuclear Ni cluster-modified germanotungstic acid material and its application. The purpose of this invention is to develop a hexanuclear Ni cluster-modified germanotungstic acid material and its photocatalytic application, which can effectively overcome the shortcomings of traditional multi-acid materials, such as easy solubility, poor stability, and the need for noble metals as co-catalysts. The chemical formula of the hexanuclear Ni cluster-modified germanotungstic acid material is (GeW... 12 O 40 )[Ni II The reaction mixture is 6(pzta)6(H2O)4(OH)2, where pzta is 3-(pyridin-4-yl)pyrazole. Preparation method: Germanium tungstate, cobalt chloride, ammonium metavanadate, and 3-(pyridin-4-yl)pyrazole are dissolved in deionized water to obtain a reaction solution. The pH is adjusted, and the solution is then placed in a polytetrafluoroethylene reactor at 180°C for 72 hours. The temperature is then programmed to decrease to 80°C, and the oven is directly closed to obtain brownish-green rhombic blocky crystals. This invention provides a hexanuclear Ni cluster-modified germanium tungstate material.

Description

Technical Field

[0001] This invention relates to a hexanuclear Ni cluster-modified germanium tungstate material and its photocatalytic application. Background Technology

[0002] Hydrogen energy is considered a promising clean energy source. Due to its advantages such as high efficiency, ubiquity, recyclability, and high energy density, photocatalytic water splitting to produce hydrogen is an effective way to alleviate environmental and energy pressures.

[0003] Polyacids are inorganic metal-oxygen clusters formed from transition metals, possessing excellent photosensitivity, capable of rapid and reversible multi-electron transfer, and maintaining structural stability. Therefore, polyacids are considered ideal photocatalysts. However, in the field of photocatalysis, traditional polyacid catalysts typically exhibit photocatalytic activity only under ultraviolet light irradiation, and their activity is relatively low. To overcome the shortcomings of traditional polyacid catalysts, a feasible approach is to combine polyacids with appropriate organometallic complexes to prepare novel photocatalysts, thereby improving their utilization of visible light.

[0004] Polyacids are composed of transition metal-oxygen anion clusters of d 0 The electronic structure of polyacids exhibits diversity in composition and structure, allowing for molecular-level regulation. Most classical polyacids are only active under ultraviolet light irradiation when heteropolyblue is not produced, and few exhibit activity under visible light irradiation, with relatively poor activity. Modification with transition metals can yield reduced polyacids, thereby enhancing photocatalytic activity. However, due to the differences in the electronic structures of different metals, the catalytic activity of metal ions varies. Among them, high-dimensional crystalline materials modified with high-nuclear polymetallic metals exhibit better catalytic activity while also possessing good stability.

[0005] Such materials typically have the following advantages:

[0006] 1. High-dimensional polyacid-based metal-organic frameworks provide organic ligands with regular porous structures, increasing the overall structural stability while possessing high porosity. This allows H+ in water to pass through. + It enters and achieves direct contact with the metal active sites inside the framework, thereby promoting the photocatalytic reaction.

[0007] 2. High-core metal clusters possess unique synergistic catalytic effects. Multiple metal atoms within a cluster can work together, exhibiting unique catalytic properties that a single metal atom cannot achieve. The synergistic effect between different metal atoms can enhance the rate and selectivity of catalytic reactions.

[0008] 3. Germanium tungstic acid (GTA) is a wide-bandgap semiconductor, typically around 3.5 eV. This gives it excellent light absorption performance in the ultraviolet region, enabling it to effectively utilize high-energy ultraviolet light for photocatalytic reactions. GTA exhibits good catalytic activity in the photocatalytic degradation of organic pollutants. Its unique crystal structure and electronic properties allow it to effectively separate photogenerated electron-hole pairs, improving photocatalytic efficiency. However, research on GTA photocatalysts remains limited, indicating significant potential for future development.

[0009] In summary, designing and preparing germanium tungstate materials modified with high-nuclear-metal clusters and applying them to photocatalytic water splitting for hydrogen production is a meaningful endeavor. Summary of the Invention

[0010] The purpose of this invention is to provide a hexanuclear Ni-modified germanium tungstate-based crystal material and its photocatalytic application, overcoming the shortcomings of traditional polyacids, such as easy solubility, poor stability, and the need for noble metals as co-catalysts.

[0011] The chemical formula of a hexanuclear Ni cluster-modified germanium tungstate material is (GeW 12 O 40 )[Ni II [6(pzta)6(H2O)4(OH)2], where pzta is 3-(pyridin-4-yl)pyrazole; the crystal system is trigonal triclinic; the space group is R-3; and the unit cell parameters are α = 90°, β = 90°, and γ = 120°. z = 3.

[0012] A method for preparing a hexanuclear Ni cluster-modified germanic tungstate material is carried out according to the following steps:

[0013] (1) Preparation of reaction solution with pH value of 2.0: Weigh 0.33g of K4 (GeW) containing germanotungstic acid. 12 O 40 0.16 g of cobalt chloride CoCl2·4H2O, 0.35 g of ammonium metavanadate NH4VO3 and 0.45 g of pzta were dissolved in 36 mL of deionized water. The pH of the solution was adjusted to 6.6 with 1 M HCl / NaOH solution and stirred at room temperature for 2 h.

[0014] (2) The above solution was divided into three equal portions and transferred to 20 mL polytetrafluoroethylene reaction vessels. The mixture was kept at 180 °C for 72 h, then the temperature was programmed to decrease to 80 °C and the oven was directly shut off, yielding brownish-green rhombic block crystals. The product was separated by water washing and dried to obtain a hexanuclear Ni cluster-modified germanium tungstate material (GeW). 12 O 40 )[Ni II[6(pzta)6(H2O)4(OH)2], abbreviated as Ni6-GeW 12 .

[0015] Compared with the prior art, the present invention has the following characteristics:

[0016] Using germanotungstic acid, transition metal elements Ni and PzTa as raw materials, a novel polyacid-based metal-organic framework crystalline material with the same structure was successfully prepared via a one-pot hydrothermal synthesis method. This method overcomes the drawbacks of traditional polyacids, which are readily soluble in water and require noble metals as co-catalysts. The conduction band potential was improved by UV-Vis diffuse reflectance.

[0017] Photocatalytic water splitting for hydrogen production experiments show that Ni6-GeW 12 The catalytic hydrogen production rate is 842 μmol·g -1 h -1 It is 14 times the rate of hydrogen production catalyzed by the parent polyacid germanium tungstate. Ni6-GeW 12 The photocurrent intensity is greater than that of the parent polyacid germanium tungstate, indicating that the recombination rate of photogenerated electrons and holes is significantly improved after the introduction of hexanuclear transition metal elements.

[0018] This invention provides a hexanuclear Ni cluster-modified germanium tungstate material. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a hexanuclear Ni cluster modified germanium tungstate material prepared in Example 1.

[0020] Figure 2 The image shows the X-ray powder diffraction pattern of a hexanuclear Ni cluster-modified germanium tungstate material prepared in Example 1.

[0021] Figure 3 The X-ray photoelectron spectroscopy of a hexanuclear Ni cluster modified germanium tungstate material prepared in Example 1 is shown.

[0022] Figure 4 This is a schematic diagram illustrating the temperature-dependent magnetic susceptibility of a hexanuclear Ni cluster-modified germanium tungstate material prepared in Example 1.

[0023] Figure 5 The photocatalytic cycle stability diagram and X-ray diffraction patterns before and after illumination are shown for a hexanuclear Ni cluster modified germanium tungstate material prepared in Example 1.

[0024] Figure 6 The cyclic voltammogram of a hexanuclear Ni cluster-modified germanium tungstate material prepared in Example 1 was recorded in a 0.5 mol / L H2SO4 solution at a scan rate of 0.1 V / s. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Example 1: A hexanuclear Ni cluster modified germanic tungstate material, comprising the following preparation steps:

[0027] (1) Preparation of reaction solution with pH value of 2.0: Weigh 0.33g of K4 (GeW) containing germanotungstic acid. 12 O 40 0.16 g of cobalt chloride CoCl2·4H2O, 0.35 g of ammonium metavanadate NH4VO3 and 0.45 g of pzta were dissolved in 36 mL of deionized water. The pH of the solution was adjusted to 6.6 with 1 M HCl / NaOH solution and stirred at room temperature for 2 h.

[0028] (2) The above solution was divided into three equal portions and transferred to 20 mL polytetrafluoroethylene reaction vessels. The mixture was kept at 180 °C for 72 h, then the temperature was programmed to decrease to 80 °C and the oven was directly shut off, yielding brownish-green rhombic block crystals. The product was separated by water washing and dried to obtain a hexanuclear Ni cluster-modified germanium tungstate material (GeW). 12 O 40 )[Ni II [6(pzta)6(H2O)4(OH)2], abbreviated as Ni6-GeW 12 .

[0029] The X-ray single-crystal diffraction structure analysis data of the hexanuclear Ni cluster modified germanium tungstate material prepared in Example 1 are shown in Table 1.

[0030] Table 1: Ni6-GeW 12 Crystallographic Data Sheet

[0031]

[0032] 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

[0033] X-ray single-crystal diffraction analysis showed that the chemical formula of the hexanuclear Ni cluster modified germanate tungstate material prepared in Example 1 (GeW 12 O 40 )[NiII [6(pzta)6(H2O)4(OH)2], with the molecular formula C 36 H 34 GeN 30 Ni6O 46 W 12 .

[0034] The present invention will be further described below with reference to the accompanying drawings and Embodiment 1:

[0035] Figure 1 This is a schematic diagram of the structure of a hexanuclear Ni cluster-modified germanium tungstate material prepared in Example 1. The basic structural unit consists of a multi-acid anion GeW 12 It consists of 6 Ni ions and 6 pzta organic ligands. The structure contains a polyacid anion cluster, GeW. 12 By coordinating terminal oxygen with hexanuclear metal ions, photogenerated electrons can be rapidly transferred through chemical bonds, which is beneficial for photocatalytic water splitting to produce hydrogen.

[0036] Figure 2 The image shows the X-ray powder diffraction pattern of a hexanuclear Ni cluster-modified germanitic tungstate material prepared in Example 1. The powder XRD diffraction peak positions of the compounds match well with the simulated XRD diffraction peak positions obtained from single-crystal analysis, indicating that the compounds all have high purity.

[0037] Figure 3 The X-ray photoelectron spectroscopy (XPS) of a hexanuclear Ni cluster-modified germanitic tungstate material prepared in Example 1 is shown. All Ge atoms in the crystal are +4 valence, and all W atoms are +6 valence, forming a Ni6-GeW... 12 Ni in the compound has a single oxidation state of +2. X-ray photoelectron spectroscopy was used to further determine the elemental composition and oxidation state of the compound. Ni6-GeW 12 The XPS spectrum is shown in the figure. (High-resolution XPS spectrum of Ni 2p) Figure 3 The characteristic peaks at 855.34 eV and 872.92 eV shown in -a) belong to Ni. 2+ The characteristic peaks at 861.22 eV and 878.84 eV are for Ni. 2+ The satellite peak. Ni 2+ The electron configuration is t 2g 6 e g 2 ,π(t 2g There are no single electrons in the orbital σ(e) g The orbital contains two unpaired electrons, therefore electrons cannot be transferred through the π bond of O. The XPS high-resolution spectrum of W4f is compared with that of Ni6-GeW. 12Similar to W 4f, the characteristic peaks at 34.33 eV and 36.47 eV are W 6+ Characteristic peaks ( Figure 3 -b).

[0038] Figure 4 This is a schematic diagram illustrating the temperature-dependent magnetic susceptibility of a hexanuclear Ni cluster-modified germanitic tungstate material prepared in Example 1. (Ni6-GeW) 12 χ at room temperature m The T value is 6.6 cm. 3 K mol -1 This is six Ni with g≈2.2. II Expected values ​​for ions. Due to Ni II The ion-formed dimers possess double-NN-bridges and are further connected via pyrazine bridges, resulting in very weak antiferromagnetic coupling. As the temperature decreases, χ... m T decreases steadily, with a larger decrease below 50K. This phenomenon indicates that Ni... II There is antiferromagnetic coupling between the ions. A good fit can be obtained using the following parameters: g = 2.188(2), Jdim = -5.25(2)cm -1 j = -0.28(1)cm -1 |D|=6.2(1)cm -1 .

[0039] Figure 5 The image shows the photocatalytic cycling stability of a hexanuclear Ni-cluster modified germanotungstate material prepared in Example 1, along with its X-ray diffraction patterns before and after illumination. Under typical photocatalytic hydrogen evolution test conditions, after 30 hours of illumination (5 cycles), the photocatalytic hydrogen evolution activity of the crystalline material was close to its initial value, indicating good photocatalytic cycling stability. Subsequently, the photocatalyst after the photocatalytic reaction was collected by centrifugation, and X-ray powder diffraction was used to verify the structural stability. X-ray powder diffraction showed that the peak positions of the compound did not change, indicating that the compound's structure was not destroyed and it possesses good structural stability.

[0040] Figure 6 Cyclic voltammetry of a hexanuclear Ni-cluster modified germanotungstate material prepared in Example 1, recorded in 0.5 mol / L H₂SO₄ solution at a scan rate of 0.1 V / s. Ni₆-GeW 12 Six pairs of redox peaks were observed (I-I', II-II', III-III', IV-IV', V-V', and VI-VI'), with half-wave potentials of -0.632V (I-I'), -0.540V (II-II'), -0.418V (III-III'), 0.08V (IV-IV'), and 0.237V (V-V') assigned to W.VI / W V The redox process, with a half-wave potential of +0.464V (VI-VI'), is attributed to Ni. 2+ The redox process at the W center. The curves show that the reduction potential difference between the W center and the metal ions allows photogenerated electrons to transfer from the W center to the metal ions. More importantly, Ni6-GeW 12 The reduction peaks are sufficiently negative, especially I-I', which allows H2 generation to be driven.

[0041] In summary, the hexanuclear Ni-cluster modified germanium-tungstate material prepared in Example 1 overcomes the drawbacks of traditional multi-acids, which are readily soluble in water and require noble metals as co-catalysts. This work can provide a reference for the design and preparation of high-performance water splitting photocatalysts for hydrogen production.

Claims

1. A hexanuclear Ni cluster-modified germanium tungstate material, characterized in that... The chemical formula of a hexanuclear Ni cluster-modified germanium tungstate material is (GeW 12 O 40 )[Ni II 6(pzta)6(H2O)4(OH)2], where pzta is 3-(pyridin-4-yl)pyrazole; the crystal system is trigonal triclinic; the space group is R-3; the unit cell parameters are α=90°, β=90°, γ=120°, a=18.1118(8) Å, b=18.1118(8) Å, c=20.8280(17) Å, z=3.

2. The application of the hexanuclear Ni cluster-modified germanium tungstate material according to claim 1, characterized in that... A hexanuclear Ni cluster-modified germanium tungstate material can be used for photocatalytic water splitting to produce hydrogen; experiments on photocatalytic water splitting to produce hydrogen show that Ni6-GeW 12 The catalytic hydrogen production rate is 842 μmol·g -1 h -1 It is 14 times the rate of hydrogen production catalyzed by the parent polyacid germanium tungstate.

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