Method for degrading PFOA (perfluorooctanoic acid) through cooperation of MOF (metal organic framework) / persulfate and photocatalysis

Abstract

The invention discloses a method for photocatalytic degradation of PFOA (perfluorooctanoic acid) by cooperation of MOF (metal organic framework) / persulfate, which comprises the following steps: dissolving zirconium chloride and 2-aminoterephthalic acid in DMF (dimethyl formamide) according to a certain proportion, and preparing a UiO-66 photocatalyst by a solvothermal method; dispersing a proper amount of prepared UiO-66 in a PFOA solution, adding sodium persulfate, and adjusting the pH value to be acidic; stirring is performed under a dark condition to ensure that adsorption-desorption balance is achieved, then a xenon lamp is used for simulating sunlight irradiation, sodium persulfate is activated to generate free radicals, a photocatalyst adsorbs and oxidizes PFOA, and the two components cooperate to efficiently degrade the PFOA. The operation and preparation method is simple and high in controllability, and a low-cost and efficient green catalysis technology is provided for complete mineralization of PFOA.

Description

Technical Field

[0001] This invention belongs to the field of catalysis technology, specifically relating to a method for the efficient catalytic degradation of PFOA under sunlight irradiation, using MOF material as a photocatalyst and persulfate as an oxidant. Background Technology

[0002] Perfluorooctanoic acid (PFOA) is a newly emerging synthetic fluorinated organic acid. Due to the high energy of the CF bond (631.5 kJ mol / L) and the strong electronegativity of the F atom, PFOA exhibits high persistence and bioaccumulation in the environment, and is widely present in aquatic environments. Its outstanding surface activity, hydrophobicity, oleophobicity, high temperature resistance, and chemical resistance make it widely used in waterproof and stain-resistant materials, cosmetics, leather textiles, industrial additives, and food packaging. Numerous studies have shown that its presence can cause damage to the immune system, endocrine disorders, developmental delays, and even cancer, posing a significant threat to ecosystems and human health, necessitating effective measures to address PFOA pollution.

[0003] Existing PFOA removal technologies mainly include activated carbon adsorption, cometabolite biotransformation, and chemical degradation. Compared to physical methods, which are easily affected by reaction conditions and cause secondary pollution, and biological treatment methods, which have low degradation efficiency and long reaction cycles, chemical methods have higher removal efficiency. Chemical degradation methods mainly include electrochemical oxidation, photocatalytic degradation, and persulfate activation. Photocatalysis stands out due to its environmental benefits, low cost, and high energy efficiency. Photochemical methods use sunlight to excite photocatalytic materials, generating strong oxidizing holes and active free radicals (such as •OH). Compared to the advanced oxidation process of hydroxyl radicals, the advanced oxidation process of persulfate has a higher oxidation potential, a longer half-life, and lower pH sensitivity. However, the pure persulfate system is less effective when used alone, and its effect on PFOA degradation is limited.

[0004] Traditional semiconductor photocatalysts suffer from poor photocatalytic efficiency due to the easy recombination of photogenerated electron-hole pairs, limited light-harvesting ability, and low charge utilization. Metal-organic frameworks (MOFs), on the other hand, are crystalline materials with two- or three-dimensional porous structures possessing specialized periodic network units. These MOFs consist of metal ions / clusters linked to organic ligands via coordination covalent bonds, resulting in a controllable porous structure and adjustable specific surface area. It has been widely used in adsorption, separation, catalysis and other fields. As a MOF material, UiO-66 has disadvantages such as limited photoresponse range, difficulty in effectively exciting electron-hole pairs under visible light, low adsorption capacity, insufficient active sites and poor photocatalytic performance, and is not suitable for use alone for efficient degradation of PFOA.

[0005] To address the issues of low quantum efficiency of pure photocatalyst (UiO-66) and the difficulty in achieving efficient mineralization using a single persulfate process, we have developed a synergistic system of UiO-66 and persulfate, providing a new approach for water pollution control and environmental protection. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing UiO-66 photocatalyst using a solvothermal method, with sodium persulfate as the oxidant. The two work synergistically to promote interfacial adsorption and electron transfer processes on the photocatalyst surface, thereby activating sodium persulfate and achieving efficient degradation of PFOA. This addresses the problems mentioned in the background section regarding the low quantum efficiency of UiO-66 alone and the difficulty in achieving efficient mineralization using a single persulfate process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for MOF / persulfate synergistic photocatalytic degradation of PFOA, comprising the following steps: Step 1): Preparation of UiO-66 photocatalyst using a solvothermal method: Zirconium tetrachloride, 2-aminoterephthalic acid, and DMF were mixed and stirred until homogeneous. The mixture was poured into a stainless steel reactor and reacted in an oven. Step 2): Add the prepared UiO-66 photocatalyst to the PFOA solution, and simultaneously add the oxidant sodium persulfate to adjust the pH. Step 3): After stirring in the dark to ensure adsorption-desorption equilibrium, use a xenon lamp to simulate sunlight. UiO-66 and sodium persulfate work together to efficiently degrade PFOA.

[0008] Preferably, in step 1, the zirconium tetrachloride is 200-250 mg, the 2-aminoterephthalic acid is 180-200 mg, and the DMF is 40-80 mL.

[0009] Pour the mixture into a stainless steel reactor and react it in an oven at 150-200 ℃ for 45-50 hours.

[0010] Preferably, in step 2, the UiO-66 photocatalyst is 0.3-30 mg, sodium persulfate is 10-200 mg, the PFOA solution concentration is 1-10 ppm, and the volume is 40-80 mL. The pH of the degradation system should be >3.

[0011] Preferably, in step 3, after stirring in the dark for 55-65 minutes to ensure adsorption-desorption equilibrium is reached, the material is irradiated with a xenon lamp to simulate sunlight for 3.5-4.5 hours for degradation.

[0012] The UiO-66 photocatalyst selected in this invention possesses a large specific surface area and adjustable pore size, enabling efficient adsorption of PFOA molecules and providing reactive sites. Sodium persulfate activation generates sulfate radicals; the two work synergistically to efficiently disrupt the PFOA structure. Bonds, degrading them into and A novel photocatalytic-oxidative synergistic degradation system was constructed, providing a low-cost, green, and efficient catalytic technology for the degradation of PFOA. Attached Figure Description

[0013] Figure 1 The X-ray diffraction (XRD) pattern of the UiO-66 photocatalyst obtained in Example 1; Figure 2 The image shows the transmission electron microscope (TEM) pattern of the UiO-66 photocatalyst obtained in Example 1. Figure 3 The figure shows the photocatalytic degradation of PFOA by the UiO-66 / persulfate system obtained in Example 1 under xenon lamp irradiation. Figure 4 The image shows the ESR signal of the UiO-66 / persulfate system obtained in Example 1. Detailed Implementation The following examples further illustrate the above-described content of the present invention, but it should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0014] Example 1 This invention provides a method for the synergistic photocatalytic degradation of PFOA by UiO-66 / persulfate, specifically including the following steps: Step 1: Preparation of UiO-66 photocatalyst: Pour 50 mL of DMF into a beaker, add 232 mg of zirconium tetrachloride and 181 mg of 2-aminoterephthalic acid in a 1:1 ratio to the beaker, and mix thoroughly. Pour the mixture into a stainless steel autoclave and react at 120°C for 48 h in an oven. After the reaction solution cools naturally to room temperature, centrifuge, collect the lower precipitate, and wash it 7 times with methanol to remove residual N,N-dimethylformamide (DMF) molecules. Dry under vacuum at 80°C for 12 h.

[0015] Step 2: Disperse 2.5 mg of UiO-66 in 50 mL of 5 ppm PFOA solution, add 119 mg of sodium persulfate, and adjust the pH to 5.

[0016] Step 3: Stir in the dark for 60 min to ensure adsorption-desorption equilibrium is reached. Simulate sunlight irradiation with a xenon lamp and degrade for 4 h to achieve synergistic degradation of PFOA by UiO-66 and sodium persulfate.

[0017] An X-ray diffractometer with a Cu Ka radiation source (λ=0.1541 nm) was used. Phase analysis was performed on the diffraction pattern of the sample powder. The obtained UiO-66 diffraction pattern is shown below. Figure 1 As shown, the most prominent diffraction peaks appear in the low 2θ region: sharp peaks at 7.25°, 8.44°, and 25.67° correspond to the (111), (002), and (006) crystal planes, respectively. Among them, the dominant (111) diffraction peak has the highest intensity and the narrowest peak width, indicating that the UiO-66 framework has a highly ordered atomic arrangement and excellent crystallinity.

[0018] Transmission electron microscopy (TEM) images at different magnifications, as shown in 2a-d, reveal that UiO-66 exhibits a highly ordered and spatially uniform three-dimensional octahedral nanocrystal array. This unique morphology offers significant advantages in photon capture, reactant activation, and adsorption.

[0019] Example 2 The difference between this embodiment and Embodiment 1 is that only pure UiO-66 is used as a photocatalyst to degrade PFOA, and sodium persulfate is not added.

[0020] Step 1: Same as in Example 1.

[0021] Step 2: Disperse 2.5 mg of UiO-66 in 50 mL of 5 ppm PFOA solution.

[0022] Step 3: Stir in the dark for 60 min to ensure adsorption-desorption equilibrium is reached. Use a xenon lamp to simulate sunlight irradiation for 4 h to test the adsorption and degradation effect of pure UiO-66 on PFOA under conditions without oxidant.

[0023] Figure 3 The photocatalytic performance was shown, with the pure UiO-66 system achieving only 11.7% PFOA degradation rate within 4 hours, which is far lower than the UiO-66 / persulfate synergistic system in Example 1.

[0024] Example 3 The difference between this embodiment and Embodiment 1 is that only sodium persulfate is used as an oxidant to degrade PFOA, and UiO-66 is not added.

[0025] Step 1: Disperse 119 mg of sodium persulfate in 50 mL of 5 ppm PFOA solution.

[0026] Step 2: Stir in the dark for 60 min to ensure adsorption-desorption equilibrium is reached. Simulate sunlight irradiation with a xenon lamp and degrade for 4 h to examine the degradation effect of sodium persulfate on PFOA in the absence of a photocatalyst.

[0027] The degradation rate of the sodium persulfate system alone was 35.4%, which was much lower than that of the UiO-66 / persulfate system in Example 1. When the photocatalyst and oxidant worked together, the degradation rate reached 90.5%, which was 7.7 times that of pure UiO-66 and 2.6 times that of sodium persulfate alone.

[0028] Using DMPO as a trapping agent, electron paramagnetic resonance (ESR) was employed to verify the presence of active species in the UiO-66 / persulfate reaction system under illumination. Figure 4 As shown, in the UiO-66 / persulfate system, no characteristic peaks appeared under dark conditions, but after 10 min of light irradiation, characteristic peaks appeared. The intensity peak. The intensities of the four characteristic peaks are 1:2:2:1, The characteristic peaks correspond to a ratio of 1:1:1:1:1. However, The signal is much lower This is because DMPO... Secondary capture rate constant Comparison of More than 4 times higher, under the same competitive conditions, It is more easily captured and forms a stable spin adduct.

[0029] This invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by this invention.

Claims

1. A method for the synergistic photocatalytic degradation of PFOA by MOF / persulfate, characterized in that: Includes the following steps: Step 1): Preparation of UiO-66 photocatalyst using a solvothermal method: Zirconium tetrachloride, 2-aminoterephthalic acid, and DMF were mixed and stirred until homogeneous. The mixture was poured into a stainless steel reactor and reacted in an oven. Step 2): Add the prepared UiO-66 photocatalyst to the PFOA solution, and simultaneously add the oxidant sodium persulfate to adjust the pH. Step 3): After stirring in the dark to ensure adsorption-desorption equilibrium, use a xenon lamp to simulate sunlight. UiO-66 and sodium persulfate work together to efficiently degrade PFOA.

2. The method for synergistic photocatalytic degradation of PFOA by MOF / persulfate according to claim 1, characterized in that: In step 1, zirconium tetrachloride is 200-250 mg, 2-aminoterephthalic acid is 180-230 mg, and DMF is 40-80 mL.

3. The method for synergistic photocatalytic degradation of PFOA by MOF / persulfate according to claim 1, characterized in that: In step 1, the mixture is poured into a stainless steel reactor and reacted in an oven at a temperature of 150-200 ℃ for 45-50 hours.

4. The method for MOF / persulfate synergistic photocatalytic degradation of PFOA according to claim 1, characterized in that: In step 2, the UiO-66 photocatalyst is 0.2-30 mg, sodium persulfate is 10-200 mg, the PFOA solution concentration is 1-10 ppm, and the volume is 40-80 mL.

5. The method for MOF / persulfate synergistic photocatalytic degradation of PFOA according to claim 1, characterized in that: In step 2, the pH of the degradation system should be greater than 3.

6. The method for MOF / persulfate synergistic photocatalytic degradation of PFOA according to claim 1, characterized in that: In step 3, the mixture is stirred in the dark for 55-65 minutes to ensure that the adsorption-desorption equilibrium is reached. Then, it is irradiated with a xenon lamp to simulate sunlight for 3.5-4.5 hours to degrade the material.

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