Pt-loaded MOF photocatalyst with bimetallic uiO-66-nh2 as support

Abstract

The application discloses a MOF photocatalyst with a bimetallic UiO-66-NH2 as a carrier loaded with Pt, and the photocatalyst is prepared by a solvothermal method, a modification carrier of UiO-66-NH2 (Zr:Ce=2:1), and a sodium borohydride reduction method for loading Pt. The obtained Pt@UiO-66-NH2 (Zr:Ce=2:1) photocatalyst has a high degradation rate, a high mineralization rate and high stability in a photocatalytic degradation process of toluene, and the preparation method is simple and easy to implement, so that the photocatalyst has a good application prospect in a terminal treatment process of photocatalytic VOCs oxidative degradation.

Description

Technical Field

[0001] This invention belongs to the field of air pollution control, the field of treatment of organized VOC emissions, and the field of treatment of unorganized VOC emissions. Specifically, it relates to a MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 carrier, its preparation method, and its application. This catalyst can achieve photocatalytic degradation of VOCs and has good degradation rate, mineralization rate, and stability, providing a new approach for the photocatalytic oxidation and degradation of VOCs. Background Technology

[0002] In recent years, rapid global population growth and industrial development have triggered energy crises and environmental pollution, seriously impacting human health and sustainable environmental development. Therefore, environmental protection and pollutant degradation technologies have become paramount topics. Volatile organic compounds (VOCs), particularly those contributing to photochemical smog and fine particulate matter (PM2.5), are among the most critical pollutants. 2.5 The important precursors of secondary pollutants such as VOCs (volatile organic compounds) and ozone (O3) have become a focus of attention for researchers both domestically and internationally. Some VOCs are ozone precursors, which can enhance the greenhouse effect and are irritating and toxic to humans, irritating the eyes and respiratory tract, damaging the central nervous system, and harming the liver, kidneys, brain, and nervous system. In some cases, they can even be carcinogenic, teratogenic, and toxic to the reproductive system. In addition to source control, VOCs treatment technologies should be strengthened, including adsorption, combustion, photocatalysis, and biocatalysis. Adsorption technologies require regular replacement and regeneration of adsorbents and cannot completely decompose VOCs; combustion technologies consume large amounts of fuel and pose a risk of secondary pollution; biocatalysis technologies have high requirements for environmental conditions such as temperature and humidity, are complex to operate, and their treatment effect is affected by microbial activity. Photocatalysis technology has significant advantages including high efficiency in degrading VOCs, no secondary pollution, simple operation, compact equipment, no need for additional energy consumption, and broad spectrum applicability. These advantages make photocatalysis one of the most studied and applied technologies in the field of VOCs exhaust gas treatment.

[0003] Metal-organic frameworks (MOFs), as a novel class of porous materials, possess high specific surface area, tunable pore size and chemical composition, and abundant functional modification sites, and have been widely studied and applied in the adsorption and catalytic degradation of VOCs. Currently, research on MOFs in VOCs degradation mainly focuses on the following aspects:

[0004] Adsorption performance of MOFs: MOFs possess high specific surface area and tunable pore size, allowing for optimization of adsorption performance by adjusting their structure and composition, thereby enhancing their adsorption capacity and selectivity for VOCs. For example, introducing different functionalized groups or metal ions can enhance the affinity and adsorption capacity of MOFs for specific VOCs. Several studies have reported the adsorption performance of different MOFs for various VOCs. For instance, MOFs such as UiO-66 and MIL-101 exhibit good adsorption capacity for VOCs such as benzene, toluene, and xylene.

[0005] Catalytic performance of MOFs: MOFs can serve as catalyst supports, loading active components onto their channels or surfaces to achieve the catalytic degradation of VOCs. By adjusting the structure and composition of MOFs, the activity and stability of the catalyst can be controlled, thereby improving the catalytic degradation efficiency. For example, introducing metal ions or functionalized groups can enhance the catalytic activity and selectivity of MOFs. Summary of the Invention

[0006] To address the issues of low degradation and mineralization rates and poor stability in existing VOCs photocatalytic oxidation degradation applications, this invention provides a method for preparing and applying a MOF photocatalyst supported on Pt using a bimetallic UiO-66-NH2 carrier. This method is simple and rapid, and the resulting catalyst exhibits high photocatalytic VOCs oxidation degradation rate, mineralization rate, and stability, providing a new approach for subsequent catalyst design.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A certain amount of Ce was introduced onto the basic support UiO-66-NH2(Zr) to form UiO-66-NH2 (Zr:Ce = 2:1 molar ratio). The introduction of Ce into the metal-oxygen cluster improves the visible light absorption and photoresponse of the catalyst, reduces impedance, and promotes carrier separation, thereby enhancing activity and catalytic degradation efficiency. Pt, as a co-catalyst, combined with the support, can further improve the visible light absorption and photoresponse of the catalyst, reduce impedance, and promote carrier separation.

[0009] As described above, the photocatalyst was evaluated using a 300W xenon lamp with the light wavelength (λ) controlled within the range of 320–780 nm. The reaction temperature was controlled at 170℃, and the light intensity was 610 mW·cm. -2 Capable of producing 200 ppm toluene gas at a space velocity of 30,000 mL·g −1 ·h −1 Under these conditions, the degradation rate is 100%, the mineralization rate is close to 100%, and the catalytic activity remains stable for 5 hours.

[0010] A MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 support, wherein the photocatalyst is a highly dispersed catalyst modified with bimetallic MOF material UiO-66-NH2 as the support, Zr and Ce as the central metals, and Pt as a co-catalyst.

[0011] Preferably, the Pt content in the photocatalyst accounts for 1.0 wt% of the total catalyst, and the molar ratio of metal centers Zr:Ce in the UiO-66-NH2 support is 2:1.

[0012] Preferably, the method for preparing the MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 support is as follows: using zirconium chloride and cerium chloride as metal precursors, 2-aminoterephthalic acid is added to synthesize a bimetallic UiO-66-NH2 support, and the co-catalyst Pt is supported on the obtained bimetallic UiO-66-NH2 support by loading a sodium chloroplatinate solution, and then reducing Pt with sodium borohydride.

[0013] Specifically, the preparation steps include the following:

[0014] (1) The UiO-66-NH2(Zr) and UiO-66-NH2(Zr:Ce=2:1) ​​samples were synthesized by a solvothermal method: First, zirconium chloride, cerium chloride and 2-aminoterephthalic acid were added to N,N-dimethylformamide (DMF) under vigorous magnetic stirring. The amounts of zirconium chloride and cerium chloride added were (0.24 g, 0 g) or (0.18 g, 0.12 g), corresponding to UiO-66-NH2(Zr) and UiO-66-NH2(Zr:Ce=2:1), respectively. Then, glacial acetic acid was added dropwise, with the amount of DMF being 60 g. mL, the amount of glacial acetic acid is 6 mL, then sonicated for 30 min until a clear solution is obtained, transferred to 100 mL Teflon liner, and reacted in an oven at 120 °C for 24 h. After the reaction vessel cools naturally, the residue is washed with DMF and methanol, centrifuged and filtered, and the resulting yellow solid is vacuum dried at 60 °C for 12 h.

[0015] (2) UiO-66-NH2(Zr) and UiO-66-NH2(Zr:Ce=2:1) ​​were activated at 150℃ for 3h to remove the solvent from the cavity. 30mL of anhydrous n-hexane was added to 200mg of UiO-66-NH2(Zr) or UiO-66-NH2(Zr:Ce=2:1) ​​carrier, and the mixture was sonicated for 1h to form a homogeneous suspension. Sodium chloroplatinate solution (4.2mg·mL⁻¹) was added dropwise over 10min. -1Add 0.48 mL of 0.3 M NaBH4 solution, continue stirring for 3 h, the suspension becomes clear, the solid adheres to the cup wall, remove n-hexane, wash with ethanol, centrifuge, and dry the obtained solid under vacuum at 60 °C for 12 h; then add 10 mL of 0.3 M NaBH4 solution, continue stirring for 15 min, centrifuge, wash with deionized water to obtain precipitate, and dry under vacuum at 80 °C for 12 h to obtain 1 wt% Pt@UiO-66-NH2(Zr) and 1 wt% Pt@UiO-66-NH2(Zr:Ce=2:1).

[0016] Applications: MOF photocatalysts supported on Pt using bimetallic UiO-66-NH2 are applied to end-of-pipe treatment systems for VOCs oxidation and degradation under ultraviolet-visible light photocatalysis, ultraviolet photocatalysis, ultraviolet-visible light photothermal catalysis, or ultraviolet photothermal catalysis.

[0017] The significant advantages of this invention are:

[0018] This invention modifies UiO-66-NH2(Zr) by introducing appropriate proportions of Ce and Pt metals. Introducing Ce into the metal center of UiO-66-NH2 reduces the lowest unoccupied molecular orbital (LUMO), increasing the likelihood of ligand excitation during light absorption and facilitating ligand-to-metal charge transfer (LMCT). This results in more efficient separation of photogenerated charges and extends the lifetime of the photoexcited state. The modified catalyst Pt@UiO-66-NH2 (Zr:Ce = 2:1 molar ratio) exhibits excellent photogenerated carrier transport efficiency and a lower photogenerated carrier recombination rate, demonstrating good photocatalytic activity in photothermal catalytic oxidation reactions. During LMCT, electrons generated by photoexcitation must ultimately flow to the unoccupied Zr 4d or Ce 4f orbitals, with Zr 4d having a higher energy level than Ce 4f. Only by introducing Ce into the metal center can the LUMO be reduced, thus benefiting LMCT. Simply loading Ce onto UiO-66-NH2 does not achieve these effects.

[0019] The generated photogenerated electrons are transferred to Pt, which further promotes the separation of photogenerated charge carriers. The electron-rich Pt is more conducive to the adsorption and activation of molecular oxygen. On the other hand, Pt promotes the adsorption and ring-opening oxidation reaction of toluene, and the adsorption and mineralization reaction of intermediate species are carried out in a cycle, thus maintaining stability and a high mineralization rate during the oxidation and degradation of toluene. Attached Figure Description

[0020] Figure 1 The XRD patterns of UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​obtained in Example 1 are shown below.

[0021] Figure 2 The UV-diffuse reflectance spectra of UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​obtained in Example 1 are shown.

[0022] Figure 3 The TEM image of 1wt% Pt@UiO-66-NH2 (Zr:Ce=2:1) ​​obtained in Example 1;

[0023] Figure 4 Impedance diagrams of UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​obtained in Example 1;

[0024] Figure 5 The PL plots are for UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​obtained in Example 1;

[0025] Figure 6 The evaluation diagram shows the photocatalytic oxidation degradation of toluene by 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​obtained in Example 1. Detailed Implementation

[0026] To make the above features and advantages of the present invention more apparent and understandable, specific embodiments are described below in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0027] Example 1

[0028] Preparation of 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​catalysts:

[0029] (1) The UiO-66-NH2(Zr) and UiO-66-NH2(Zr:Ce=2:1) ​​samples were synthesized by a solvothermal method: First, zirconium chloride, cerium chloride and 2-aminoterephthalic acid were added to N,N-dimethylformamide (DMF) under vigorous magnetic stirring. The amounts of zirconium chloride and cerium chloride added were (0.24 g, 0 g) or (0.18 g, 0.12 g), corresponding to UiO-66-NH2(Zr) and UiO-66-NH2(Zr:Ce=2:1), respectively. Then, glacial acetic acid was added dropwise, with the amount of DMF being 60 g. mL, the amount of glacial acetic acid is 6 mL, then sonicated for 30 min until a clear solution is obtained, transferred to 100 mL Teflon liner, and reacted in an oven at 120 °C for 24 h. After the reaction vessel cools naturally, the residue is washed with DMF and methanol, centrifuged and filtered, and the resulting yellow solid is vacuum dried at 60 °C for 12 h.

[0030] (2) UiO-66-NH2(Zr) and UiO-66-NH2(Zr:Ce=2:1) ​​were activated at 150℃ for 3h to remove the solvent from the cavity. 30mL of anhydrous n-hexane was added to 200mg of UiO-66-NH2(Zr) or UiO-66-NH2(Zr:Ce=2:1) ​​carrier, and the mixture was sonicated for 1h to form a homogeneous suspension. Sodium chloroplatinate solution (4.2mg·mL⁻¹) was added dropwise over 10min. -1 Add 0.48 mL of 0.3 M NaBH4 solution, continue stirring for 3 h, the suspension becomes clear, the solid adheres to the cup wall, remove n-hexane, wash with ethanol, centrifuge, and dry the obtained solid under vacuum at 80 °C for 12 h; then add 10 mL of 0.3 M NaBH4 solution, continue stirring for 15 min, centrifuge, wash with deionized water to obtain precipitate, dry at 60 °C for 12 h to obtain 1 wt% Pt@UiO-66-NH2(Zr) and 1 wt% Pt@UiO-66-NH2(Zr:Ce=2:1).

[0031] Example 2

[0032] Catalyst performance evaluation

[0033] In the evaluation of the photothermal catalytic toluene degradation catalyst, a toluene mixture of 200 ppm with an oxygen content of 20% was used at atmospheric pressure, with a flow rate of 50 mL·min. -1 The catalyst was 100 mg packed into a quartz reactor at a space velocity of 30,000 mL⋅g. −1 ⋅h −1 The photocatalytic degradation catalyst was evaluated by controlling the light wavelength (λ) range of 320–780 nm using a 300 W xenon lamp, with the reaction temperature controlled at 170 °C and the light intensity at 610 mW·cm². -2The concentrations of toluene and CO2 were detected by gas chromatography with an FID detector. The formulas (1) and (2) for calculating the toluene degradation rate and mineralization rate are as follows.

[0034] Toluene degradation rate (%) = ([C7H8]) in - [C7H8] out ) / [C7H8] in ×100% (1)

[0035] Toluene mineralization rate (%) = [CO2] out / ([C7H8] in (2) ×7)×100%

[0036] Figure 1 The XRD patterns are shown for the obtained UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr), and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​catalysts. From... Figure 1 As can be seen, the introduction of Ce did not disrupt the inherent crystal structure of UiO-66-NH2, and no X-ray diffraction peaks of Pt metal or metal oxide were detected, indicating that the amount of Pt introduced was small and uniformly distributed in the support.

[0037] Figure 2 The UV-Vis diffuse reflectance spectra of the obtained UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr), and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1) ​​catalysts are shown. Figure 2 As can be seen, the introduction of Ce and Pt significantly enhances the visible light trapping capability, reduces the bandgap, and significantly improves the transmission efficiency of photogenerated carriers.

[0038] Figure 3 Transmission electron microscopy (TEM) image of the obtained 1 wt% Pt@UiO-66-NH2 (Zr:Ce=2:1) ​​catalyst. Figure 3 It can be seen that the Pt metal nanoparticles are uniformly distributed and tightly bonded to the catalyst support.

[0039] Figure 4 Impedance plots for the obtained UiO-66-NH2(Zr), UiO-66-NH2(Zr:Ce=2:1), 1wt% Pt@UiO-66-NH2(Zr), and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1). From Figure 4It can be seen that a smaller impedance radius indicates better electron transfer capability, which will accelerate electron transfer and suppress the recombination of photogenerated electron-hole pairs. Figure 5 It can be seen that the decrease in photoluminescence intensity indicates a reduction in the recombination degree of photogenerated carriers. The introduction of Ce facilitates ligand-metal-oxygen cluster charge transfer (LMCT), while the introduction of Pt facilitates the separation of photogenerated carriers.

[0040] Figure 6 Evaluation graphs of the photocatalytic oxidation degradation of toluene by 1wt% Pt@UiO-66-NH2(Zr) and 1wt% Pt@UiO-66-NH2(Zr:Ce=2:1). Figure 5 It can be seen that 1 wt% Pt@UiO-66-NH2 (Zr:Ce=2:1) ​​can produce 200 ppm toluene gas at a space velocity of 30000 mL⋅g. −1 ⋅h −1 At a temperature of 170℃, the degradation rate was 100%, the mineralization rate was close to 100%, and the catalytic activity remained stable for 5 hours. In contrast, in the same 5-hour catalytic degradation evaluation, 1wt% Pt@UiO-66-NH2(Zr) required 200℃ to achieve the same activity.

[0041] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. An application of a MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 support in VOCs degradation, characterized in that: The MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 support is applied to an end-of-pipe treatment system for VOCs oxidation and degradation under ultraviolet-visible light photothermal catalysis or ultraviolet-photothermal catalysis, with a degradation temperature of 170℃. The photocatalyst is a highly dispersed catalyst modified with Pt as a co-catalyst, using the bimetallic MOF material UiO-66-NH2 as the support. The Pt content in the photocatalyst accounts for 1.0 wt% of the total catalyst, and the molar ratio of metal centers Zr:Ce in the UiO-66-NH2 support is 2:

1. The method for preparing the MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 support specifically includes the following steps: (1) The UiO-66-NH2 sample was synthesized by a solvothermal method: First, zirconium chloride, cerium chloride and 2-aminoterephthalic acid were added to DMF under vigorous magnetic stirring, and glacial acetic acid was added dropwise. The volume ratio of DMF to glacial acetic acid was 10:

1. Then, the mixture was sonicated for 30 min until a clear solution was obtained. The solution was transferred to a Teflon liner and reacted in an oven at 120℃ for 24 h. After cooling, the mixture was centrifuged and filtered. The resulting yellow solid was vacuum dried for 12 h to obtain the UiO-66-NH2 support. (2) The UiO-66-NH2 support obtained in step (1) was activated at 150℃ for 3h, cooled and anhydrous n-hexane was added, and sonicated for 1h to form a uniform suspension. Sodium chloroplatinate solution was added dropwise and stirred for 3h. Ethanol was added for washing and centrifugation was performed. The resulting solid was vacuum dried at 60℃ for 12h. Then NaBH4 solution was added and stirred for 15min. After centrifugation, deionized water was washed to obtain a precipitate. The precipitate was vacuum dried at 80℃ to obtain a MOF photocatalyst with Pt supported on a bimetallic UiO-66-NH2 support. In step (1), the amount of DMF used is 60 mL, the amount of glacial acetic acid used is 6 mL, and the amounts of zirconium chloride and cerium chloride used are 0.18 g and 0.12 g, respectively; In step (2), the concentration of sodium chloroplatinate solution is 4.2 mg·mL. -1 The amount added was 0.48 mL per 200 mg UiO-66-NH2 carrier.

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