Defect-state low-temperature plasma catalyst and preparation method and application thereof

Abstract

This invention relates to the field of water treatment technology, and more particularly to a defect-state low-temperature plasma catalyst, its preparation method, and its application. This invention utilizes the pre-coordination effect and steric hindrance effect of amino acids to synthesize coordinate-unsaturated Mn-MOFs, and subsequently synthesizes oxygen-vacancy-rich MnO through a thermochemical reaction. 2‑x The catalyst exhibited extremely strong catalytic performance in the coupled NTP degradation of sulfamethoxazole, achieving a degradation efficiency of up to 81% for the sulfamethoxazole pollutant. MnO 2‑x The porous structure of the catalyst enhances its adsorption capacity for polluting substrates. The oxygen vacancies on the catalyst surface can act as active sites for activating ozone molecules, thereby activating and decomposing the harmful gas O3 molecules generated by NTP to produce highly oxidizing ·OH free radicals. This improves the degradation capacity of NTP for polluting substrates without causing secondary pollution.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a defect-state low-temperature plasma catalyst, its preparation method, and its application. Background Technology

[0002] Sulfonamides are commonly used in aquaculture to prevent and treat bacterial infections in aquatic products, such as hemorrhagic septicemia, gill rot, enteritis, and red spot disease. With the development of nearshore aquaculture, antibiotic pollution, represented by sulfonamides, inevitably appears in the ocean. The residues and long-term presence of sulfonamides in the environment can force microorganisms to develop drug resistance, which can then be transmitted to humans through the food chain, causing bacterial resistance and threatening human life. Traditional organic wastewater purification technologies include physical, biological, chemical, and advanced oxidation technologies, but these have drawbacks such as high cost, large sludge production, unstable post-treatment water quality, and secondary pollution to the environment.

[0003] Plasma is the fourth state of matter besides solid, liquid, and gas, in which the total amount of positive and negative charges is equal, thus exhibiting electrical neutrality. Based on the temperature differences among its internal components, plasma can be classified into high-temperature plasma and low-temperature plasma. Compared to high-temperature plasma, low-temperature plasma (Non-Thermal Plasma, NTP) is considered a more promising technology for remediating organic pollution in the atmosphere and water. The apparent temperature of low-temperature plasma can be as low as 300K, while the electron temperature can be greater than 104K. This means that in low-temperature plasma, most of the energy is used to generate highly reactive species such as electrons, free radicals, and ions to participate in chemical reactions, rather than dissipating heat by heating the gas. With the participation of highly reactive free radicals, the rate of plasma chemical reactions is accelerated. Therefore, low-temperature plasma has high energy efficiency, and even chemical reactions that require high temperatures can be achieved at sufficiently high rates at room temperature, making it particularly suitable for treating low concentrations of organic pollutants.

[0004] When treating organic wastewater, under normal temperature and pressure, high-energy electrons in low-temperature plasma can ionize and activate oxygen and water molecules at the gas-liquid interface into highly oxidizing HO· radicals. Simultaneously, other highly oxidizing substances such as O3, ·O, and ·H are generated, thus oxidizing the organic matter in the water. Due to the complex variety of active species within NTPs and the diversity of organic pollutant reaction pathways, NTPs often suffer from poor organic matter conversion selectivity, low energy utilization efficiency, and numerous harmful byproducts in practical industrial applications. Furthermore, high-power NTP reactors can also produce high concentrations of O3 and NO. x Harmful gases, etc. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing technologies in the degradation of organic pollutants by low-temperature plasma, such as poor selectivity of organic matter conversion, low energy utilization efficiency, and a large number of harmful byproducts. It provides a defective state low-temperature plasma catalyst and its preparation method, and applies it to the treatment of organic pollutants in water under low-temperature plasma drive to overcome the above-mentioned defects.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a defect-state low-temperature plasma catalyst, comprising the following steps:

[0008] (1) Disperse MnCl2 into a mixed solution of water and N,N-dimethylformamide to obtain a MnCl2 dispersion. Add glycine to the MnCl2 dispersion and stir to obtain solution A.

[0009] (2) Add terephthalic acid to N,N-dimethylformamide and stir to obtain solution B;

[0010] (3) Mix solution A and solution B and stir to obtain mixed solution C;

[0011] (4) The mixed solution C was transferred to a hydrothermal reactor, and after the reaction was completed, it was centrifuged, washed and dried to obtain Mn-BTC-glycine material;

[0012] (5) The Mn-BTC-glycine material obtained in step (4) is calcined under an inert atmosphere to obtain defective MnO. 2-x This refers to the low-temperature plasma catalyst.

[0013] To address the limitations of NTPs, scientists have proposed a technique that combines catalysts with NTPs. This technique leverages the synergistic effect between NTPs and catalysts to achieve high treatment efficiency at low discharge power. Furthermore, it reduces the energy required to apply the NTP, thus avoiding the toxic byproducts generated during high-power NTP operation. Coupled with low-temperature plasma technology and catalytic oxidation technology, the removal rate and energy efficiency of organic pollutants can be further improved. Therefore, the performance of the catalyst is crucial for the degradation of organic pollutants using low-temperature plasma (NTP) coupled catalytic technology.

[0014] This invention provides a novel method for preparing a defect-state low-temperature plasma catalyst by constructing oxygen vacancies in transition metal oxides. First, coordinate-unsaturated Mn-MOFs are synthesized in an aqueous solution system using the pre-coordination effect and steric hindrance effect of amino acids. Subsequently, oxygen-vacancy-rich MnO is synthesized via a thermochemical reaction.2-x The catalyst is the defect-state low-temperature plasma catalyst. This preparation method has a fast reaction rate, high crystal quality of MOF, and produces MnO. 2-x Exhibiting an irregular spherical shape with numerous grooves and pores, it greatly increases the catalyst's adsorption efficiency for polluting substrates. Furthermore, the defective MnO... 2-x The catalyst is rich in oxygen vacancies, which activate and decompose ozone molecules generated by NTP activation to produce highly oxidizing ·OH radicals, further enhancing the coupling effect between the catalyst and NTP, thereby greatly improving catalytic efficiency. This catalyst exhibits extremely strong catalytic performance in the application of NTP-coupled degradation of sulfamethoxazole pollutants, achieving a degradation efficiency of up to 81%. MnO 2-x The porous structure of the catalyst enhances its adsorption capacity for polluting substrates. Oxygen vacancies on the catalyst surface can act as active sites for activating ozone molecules, decomposing the harmful O3 molecules generated by NTP into highly oxidizing ·OH radicals. This improves the degradation capacity of NTP for polluting substrates without causing secondary pollution. This is also demonstrated by active species quenching experiments, showing that in the NTP and MnO2-x catalytic system, the dominant active species is the ·OH radicals generated after the activation and decomposition of ozone molecules.

[0015] Preferably, in step (1), water and N,N-dimethylformamide are mixed in a volume ratio of (1:5) to (1:10) to form a mixed solution, the concentration of MnCl2 in the MnCl2 dispersion is 0.02 to 0.05 mol / L, and the molar ratio of glycine to MnCl2 in solution A is (1:2) to (1:3).

[0016] Further preferably, in step (1), water and N,N-dimethylformamide form a mixed solution in a volume ratio of 1:10, the concentration of MnCl2 in the MnCl2 dispersion is 0.05 mol / L, and the molar ratio of glycine to MnCl2 in solution A is 1:2.

[0017] Preferably, the concentration of terephthalic acid in solution B is 0.05–0.08 mol / L.

[0018] The amount of terephthalic acid (BTC) used needs to be lower than the coordination saturation number of Mn-BTC. At the same time, if the amount is too low, it will affect the structural stability of Mn-BTC.

[0019] Further preferably, the molar ratio of MnCl2 in solution A to terephthalic acid in solution B is 12:5.

[0020] Preferably, the heating reaction temperature in step (4) is 120-180°C and the time is 8-15 hours.

[0021] Excessively high hydrothermal temperature or excessively long hydrothermal time will result in excessively large MOF crystals with a smaller specific surface area, which is detrimental to the catalytic reaction process. Conversely, excessively low hydrothermal temperature or excessively short hydrothermal time will hinder the growth of MOF crystals.

[0022] Further preferably, the heating reaction temperature in step (4) is 120°C and the time is 8 hours.

[0023] Preferably, the centrifugation speed in step (4) is 8000-10000 r / min and the centrifugation time is 5-10 min.

[0024] Further preferred, in step (4), the washing is performed three times with ethanol and deionized water, and the centrifugation speed is 8000 r / min.

[0025] Preferably, the drying temperature in step (4) is 60-80°C and the drying time is 24-48h.

[0026] Further preferred, the drying temperature in step (4) is 60°C and the time is 24h.

[0027] Preferably, the calcination temperature in step (5) is 550–700°C and the time is 3–5 h.

[0028] Calcination temperatures above 700℃ will cause the catalyst structure to collapse, while calcination temperatures that are too low will cause MOF crystals to crystallize into MnO. 2-x The catalyst conversion process is incomplete, so the temperature is set at 550–700°C.

[0029] Further preferred, the calcination temperature in step (5) is 550°C and the time is 4 hours.

[0030] Secondly, the present invention provides a defect-state low-temperature plasma catalyst, which is prepared by the aforementioned preparation method.

[0031] Thirdly, the present invention provides a low-temperature plasma catalyst prepared by the preparation method described above, or the application of the low-temperature plasma catalyst in the treatment of organic pollutants in water under low-temperature plasma driving.

[0032] Preferably, the organic pollutant is a sulfamethoxazole pollutant.

[0033] The present invention has the following beneficial effects:

[0034] (1) This invention provides a novel method for preparing a defect-state low-temperature plasma catalyst by constructing oxygen vacancies in transition metal oxides. First, coordination-unsaturated Mn-MOFs are synthesized by utilizing the pre-coordination effect and steric hindrance effect of amino acids. Then, oxygen-vacancy-rich MnO is synthesized through a thermochemical reaction. 2-x The catalyst is the defect-state low-temperature plasma catalyst, and this preparation method has a fast reaction rate and high crystal quality of MOF;

[0035] (2) The defective MnO prepared in this invention 2-x The catalyst is rich in oxygen vacancies, which activate and decompose ozone molecules generated by NTP activation to produce highly oxidizing ·OH free radicals, further enhancing the coupling effect between the catalyst and NTP, thereby greatly improving the catalytic efficiency. This catalyst has shown extremely strong catalytic performance in the application of NTP coupling for the degradation of sulfamethoxazole pollutants, and the degradation efficiency of sulfamethoxazole pollutants can reach 81%, which can achieve efficient and rapid removal of sulfamethoxazole pollutants in aqueous solution; (3) defective MnO 2-x The porous structure of the catalyst enhances its adsorption capacity for polluting substrates. The oxygen vacancies on the catalyst surface can act as active sites for activating ozone molecules, thereby activating and decomposing the harmful gas O3 molecules generated by NTP to produce highly oxidizing ·OH free radicals. This improves the degradation capacity of NTP for polluting substrates without causing secondary pollution. Attached Figure Description

[0036] Figure 1 MnO 2-x Low-magnification scanning electron microscope image of the material.

[0037] Figure 2 MnO 2-x XRD pattern of the catalyst.

[0038] Figure 3 MnO 2-x EPR spectra of the catalyst and MnO2.

[0039] Figure 4 MnO with defect state 2-x Time curve of catalyst-driven descent solution of succinylamine under low-temperature plasma.

[0040] Figure 5 The results of the catalytic degradation experiments of each component after the addition of three free radical quenchers are shown in a dot-line graph. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0042] Example 1: Preparation of defective MnO 2-x catalyst

[0043] (1) Dissolve 0.6 mmol of MnCl2 in a mixed solution consisting of 5 mL H2O and 25 mL N,N-dimethylformamide (DMF), stir for 20 min to dissolve and disperse evenly, add 0.3 mmol of glycine to the above solution, stir again to disperse evenly to obtain mixed solution A;

[0044] (2) Dissolve 0.25 mmol of terephthalic acid (BTC) in 5 ml of DMF to obtain solution B. Add solution B to solution A and stir again for 30 min to disperse evenly, to obtain mixed solution C.

[0045] (3) The above mixed solution C was transferred to a 50mL hydrothermal reactor and kept at 120℃ for 8 hours. It was then reacted in a 70℃ forced-air drying oven for 26 hours. After the reaction was completed, Mn-BTC-glycine material was obtained.

[0046] (4) The Mn-BTC-glycine material obtained after the reaction was placed in a quartz boat and calcined at a set temperature of 550℃ for 4 hours in a tube furnace under a nitrogen atmosphere to obtain defective MnO. 2-x catalyst.

[0047] Comparative Example 1: Preparation of MnO2 catalyst

[0048] The difference between this comparative example and Example 1 is that step (1) is omitted from the step of adding glycine in Example 1. The rest of the synthesis steps are exactly the same as in Example 1, and the MnO2 catalyst is prepared experimentally.

[0049] For the synthesized MnO 2-x The morphology and surface structure of the catalyst were characterized by SEM, such as... Figure 1 As shown, from Figure 1 The sample exhibits an irregular spherical shape, which significantly increases its specific surface area, thereby increasing the number of catalytically active sites. Further high-magnification scanning electron microscopy revealed numerous grooves and micropores on the surface of the spherical material; the presence of these channels significantly enhances the mass transport of contaminants at the material interface.

[0050] For the synthesized MnO 2-x Catalysts are used for characterizing crystal structures, such as Figure 2 As shown, from Figure 2 The diffraction peaks at 3.25°, 4.784°, 19.188°, 31.59°, 37.024°, 45.006°, 59.514°, and 65.468° closely match the characteristic diffraction peaks of the standard MnO2 spectrum (PDF#30-0820). This indicates that the MOF generated after the hydrothermal reaction following the high-temperature and high-pressure reaction... s The material has been heat-treated to become MnO 2-x The peaks in the XRD pattern all show a sharp peak shape, indicating that MnO was synthesized in a relatively stable manner. 2-x The material crystallizes well, and the synthesized material exhibits a good crystal form and has good structural stability.

[0051] Characterizing the oxygen vacancy concentration in the synthesized materials, such as... Figure 3 As shown, from Figure 3 It can be seen that the unpaired electron signal peak of pure MnO2 in Comparative Example 1 is weaker, while that of MnO2 synthesized in Example 1 is weaker. 2-x The presence of strong unpaired electron signal peaks indicates that the synthesized MnO2-x material has an abundant oxygen vacancy concentration.

[0052] Example 2: Preparation of defective MnO 2-x catalyst

[0053] (1) Take 1.1 mmol of MnCl2 and dissolve it in a mixed solution consisting of 4 mL H2O and 32 mL N,N-dimethylformamide (DMF). Stir for 20 min to dissolve and disperse evenly. Add 0.4 mmol of glycine to the above solution and stir again to disperse evenly to obtain mixed solution A.

[0054] (2) Dissolve 0.3 mmol of terephthalic acid (BTC) in 5 ml of DMF to obtain solution B. Add solution B to solution A and stir again for 30 min to disperse evenly, to obtain mixed solution C.

[0055] (3) The above mixed solution C was transferred to a 50mL hydrothermal reactor and kept at 120℃ for 8 hours. It was then reacted in a 70℃ forced-air drying oven for 26 hours. After the reaction was completed, Mn-BTC-glycine material was obtained.

[0056] (4) The Mn-BTC-glycine material obtained after the reaction was placed in a quartz boat and calcined at a set temperature of 620℃ for 5 hours under a nitrogen atmosphere in a tube furnace to obtain defective MnO. 2-x catalyst.

[0057] Example 3: Preparation of defective MnO 2-x catalyst

[0058] (1) Take 1.6 mmol of MnCl2 and dissolve it in a mixed solution consisting of 3 mL H2O and 30 mL N,N-dimethylformamide (DMF). Stir for 20 min to dissolve and disperse evenly. Add 0.53 mmol of glycine to the above solution and stir again to disperse evenly to obtain mixed solution A.

[0059] (2) Dissolve 0.4 mmol of terephthalic acid (BTC) in 5 ml of DMF to obtain solution B. Add solution B to solution A and stir again for 30 min to disperse evenly, to obtain mixed solution C.

[0060] (3) The above mixed solution C was transferred to a 50mL hydrothermal reactor and kept at 120℃ for 8 hours. It was then reacted in a 70℃ forced-air drying oven for 26 hours. After the reaction was completed, Mn-BTC-glycine material was obtained.

[0061] (4) The Mn-BTC-glycine material obtained after the reaction was placed in a quartz boat and calcined at a set temperature of 700℃ for 3 hours in a tube furnace under a nitrogen atmosphere to obtain defective MnO. 2-x catalyst.

[0062] Example 4: Application of defect-state low-temperature plasma catalysts in the treatment of organic pollutants in water.

[0063] Application of defective MnO 2-x The method for treating organic matter in water by catalyst-coupled NTP is as follows:

[0064] (1) Mix 50 ml of sulfamethoxazole contaminant solution (10 mg / L) with defective MnO 2-x Catalyst mixing, catalyst MnO 2-x The dosage is 2 g / L, and the mixture is stirred at room temperature for 30 min until the catalyst is saturated.

[0065] (2) Start the NTP reactor. The operating power of the NTP reactor is 20-. The distance between the NTP and the liquid surface is 10. After reacting for 10 min, take out a certain amount of the mixed solution and filter it through a 0.22 μm filter membrane. Analyze the concentration change of sulfamethoxazole in the solution using high performance liquid chromatography. Plot the degradation effect versus time curve to evaluate MnO. 2-x The ability of catalysts to degrade pollutants under NTP-driven conditions.

[0066] Comparative Example 2: This comparative example differs from Example 4 in that the MnO in Example 4 is used in this example. 2-xThe catalyst was removed, and the catalytic degradation ability of NTP alone for sulfamethoxazole was evaluated. The remaining steps were basically the same as in Example 4.

[0067] Comparative Example 3: This comparative example differs from Example 4 in that the MnO in Example 4 is used in this example. 2-x The catalyst was replaced with a MnO2 catalyst, and the degradation ability of the MnO2 catalyst for pollutants under NTP-driven conditions was evaluated. The remaining operating steps were the same as in Example 4.

[0068] like Figure 4 As shown, the degradation curves of sulfamethoxazole differ significantly depending on the presence of different catalysts. In the NTP system without a catalyst, the degradation trend of sulfamethoxazole is not obvious; after 60 minutes of reaction, only 13% of sulfamethoxazole is degraded. However, with the addition of MnO2 catalyst, the degradation efficiency of sulfamethoxazole can reach 60% under the synergistic reaction of the catalyst and NTP. The defective MnO2 catalyst... 2-x After the catalyst is coupled with NTP, the degradation efficiency of sulfamethoxazole can reach 81%; this indicates that the defective state of MnO 2-x The catalyst exhibited stronger catalytic degradation ability when coupled with NTP.

[0069] Investigating NTPs and Defect-State MnO 2-x Coupling mechanism of catalysts:

[0070] Research Content 1: (1) Mix 50 ml of sulfamethoxazole contaminant solution (10 mg / L) with defective MnO 2-x Catalyst mixing, catalyst MnO 2-x The dosage was 2 g / L. The mixture was stirred at room temperature for 30 min until the catalyst adsorption was saturated. Then, 20 mg of tert-butanol was added as a sacrificial agent to quench the ·OH free radicals in the system.

[0071] (2) Start the NTP reactor. The operating power of the NTP reactor is 20-. The distance between the NTP and the liquid surface is 10. After reacting for 10 min, take out a certain amount of the mixed solution and filter it through a 0.22 μm filter membrane. Analyze the concentration change of sulfamethoxazole in the solution using high performance liquid chromatography. Plot the degradation effect versus time curve to evaluate MnO. 2-x The ability of catalysts to degrade pollutants under NTP-driven conditions;

[0072] Research Content 2: Replace tert-butanol in Research Content 1 with furfural to quench the substances produced in the system. 1 O2, the remaining operating steps are the same as those in the first exploration content;

[0073] Investigation 3: Replace tert-butanol in Investigation 1 with p-benzoquinone to quench the ·O2 generated in the system. 2-The remaining operational steps are the same as those in Investigation 1;

[0074] The experimental section has already mentioned p-benzoquinone (C6H4O2) and tert-butanol (C4H... 10 O) and furfuryl alcohol (C5H6O2) can quench the ·O2- and ·OH- in NTPs, respectively. 1 O2, experimental results are as follows Figure 5 As shown. (Through) Figure 5 It can be seen that the images of the group with added furfuryl alcohol are similar to those of the control group, indicating that its degradation rate and degradation percentage hardly decreased, proving that... 1 O2 plays a relatively minor role in the degradation of sulfamethoxazole, and inhibiting its formation does not significantly affect the degradation process. The addition of tert-butanol resulted in a substantial decrease in both the degradation rate and degradation percentage, indicating that ·OH plays a major role in the degradation of sulfamethoxazole. The reduction in the degradation rate and degradation percentage of the benzoquinone component was less pronounced, suggesting that ·O2- played a role in the degradation experiment.

Claims

1. The application of a defect-state low-temperature plasma catalyst in the treatment of organic pollutants in water under low-temperature plasma driving, characterized in that, The method for preparing the defect-state low-temperature plasma catalyst includes the following steps: (1) Disperse MnCl2 into a mixed solution of water and N,N-dimethylformamide to obtain a MnCl2 dispersion. Add glycine to the MnCl2 dispersion and stir to obtain solution A. (2) Terephthalic acid was added to N,N-dimethylformamide and stirred to obtain solution B; (3) Mix solution A and solution B and stir to obtain mixed solution C; (4) The mixed solution C was transferred to a hydrothermal reactor, and after the reaction was completed, it was centrifuged, washed and dried to obtain Mn-BTC-glycine material; (5) The Mn-BTC-glycine material obtained in step (4) is calcined under an inert atmosphere to obtain defect-state MnO. 2-x This is the low-temperature plasma catalyst; In step (1), water and N,N-dimethylformamide are mixed in a volume ratio of (1:5) to (1:10) to form a mixed solution. The concentration of MnCl2 in the MnCl2 dispersion is 0.02 to 0.05 mol / L. The molar ratio of glycine to MnCl2 in solution A is (1:2) to (1:3). The heating reaction temperature in step (4) is 120-180℃, and the time is 8-15h; The calcination temperature in step (5) is 550-700℃ and the time is 3-5h.

2. The application as described in claim 1, characterized in that, The concentration of terephthalic acid in solution B is 0.05–0.08 mol / L.

3. The use according to claim 1, wherein The centrifugation speed in step (4) is 8000-10000 r / min, and the centrifugation time is 5-10 min.

4. The use according to claim 1, wherein The drying temperature in step (4) is 60-80℃ and the time is 24-48h.

5. The application as described in claim 1, characterized in that, The organic pollutant is a new sulfamethoxazole pollutant.

Images