A method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the MOF channels.

Abstract

This invention discloses a method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the channels of a metal-organic framework (MOF). It belongs to the technical fields of catalytic degradation of organic pollutants and metal-organic framework materials. This invention enhances the built-in electric field of the MOF material by introducing counterions within the MOF channels and working in conjunction with donor and acceptor units on the framework. When the MOF material with the enhanced built-in electric field is added to a methylene blue aqueous solution, under xenon lamp irradiation in sunlight, the methylene blue removal rate can reach 90% after 35 minutes. Furthermore, the MOF material in this method has a wide light absorption window (200-1000 nm) and strong absorbance, enabling highly efficient degradation of organic matter; the material is easy to recycle and produces no secondary pollution; the synthesis method is simple, and the crystal structure is well-defined, which is beneficial for the practical application of metal-organic framework materials in the purification of dye wastewater.

Description

Technical Field

[0001] This invention belongs to the field of catalytic degradation of organic pollutants and metal-organic framework technology, specifically relating to a method for photocatalytic degradation of methylene blue by utilizing a built-in electric field enhanced by counterions within the pores of a MOF. Background Technology

[0002] Methylene blue, a thiazide dye, is frequently used industrially for dyeing cotton, silk, and paper. It is also used for coloring bamboo and wood, and in the manufacture of inks and lakes. While relatively stable in air, it is readily soluble in water, ethanol, and chloroform. It is a representative pollutant in dye wastewater. Direct discharge without treatment makes it difficult for the natural environment to purify the wastewater, causing the dye to circulate and accumulate. Excessive concentrations of methylene blue can damage the gastrointestinal tract, kidneys, cardiovascular system, and central nervous system in humans, and high concentrations can cause poisoning and death in animals. Therefore, there is an urgent need to develop effective methods for removing organic pollutants from wastewater. Currently, the treatment of organic dyes in wastewater mainly includes physical, chemical, and biological methods. Representative processes include ozone oxidation, biodegradation, adsorption, coagulation, membrane separation, and photocatalysis. Photocatalysis is widely considered a promising technology that can provide a safe and green approach to wastewater treatment.

[0003] Photocatalysis is an advanced technology that utilizes photon energy through catalysts to transform many chemical reactions that require harsh conditions into reactions that can occur under milder environments. A suitable photocatalyst is crucial for improving the catalytic efficiency and selectivity of the catalytic system. Previously reported photocatalysts for pollutant degradation are mostly inorganic semiconductor materials, such as oxides (TiO2, Fe2O3, and ZnO) and sulfides (ZnS and CdS). While these materials possess advantages such as suitable band positions, non-toxicity, low cost, and strong light absorption, leading to widespread attention and application in photocatalysis, electrocatalysis, and energy storage, they still suffer from high recombination rates of photogenerated carriers, severely impacting their photocatalytic activity. In contrast, some novel photocatalysts, such as graphitized carbon nitride (g-C3N4), metal-organic frameworks (MOFs), and covalent organic polymers, exhibit excellent properties such as visible light response and high light utilization.

[0004] MOFs (Metal-Organic Facility-Containing Elements) are a class of porous crystalline materials assembled from metal salts and organic ligands via coordination bonds. They possess diverse and easily tunable structures, and their porous structure provides MOFs with more exposed active sites and substrate / product transport channels, facilitating rapid transfer and utilization of photogenerated charges. Furthermore, the perfectly ordered crystalline structure of MOFs helps reduce the recombination of photogenerated electrons and holes. These structural characteristics make them excellent new platforms for photocatalysis. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the pores of a MOF (Metal-Oxygen Foil) catalyst. Under xenon lamp irradiation in sunlight, the Cu-MOF catalyst achieves a 90% removal rate of methylene blue after 35 minutes, exhibiting excellent cycle stability and enabling highly efficient organic matter degradation. The material is easily recyclable, producing no secondary pollution. The synthesis method is simple, and the crystal structure is well-defined, making it a promising candidate for practical applications in dye wastewater purification.

[0006] To achieve the above-mentioned objective, this invention provides a method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the pores of a MOF, comprising the following steps:

[0007] S1. The built-in electric field of Cu-MOF material is enhanced by the synergistic effect of counter ions in the pores and donor-acceptor units on the framework.

[0008] S2. The Cu-MOF catalyst was added to a methylene blue aqueous solution, stirred in the dark for a period of time, and then subjected to degradation reaction under xenon lamp irradiation.

[0009] As a preferred embodiment of the present invention, the enhanced electric field of the Cu-MOF is achieved by the counter anions in the pores and the donor-acceptor units on the framework. The framework structure of the material is composed of rigid π-conjugated molecules 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole and monovalent / divalent copper. The planar structure is connected by monovalent / divalent copper and formate ions.

[0010] As a preferred embodiment of the present invention, the method for enhancing the built-in electric field of Cu-MOF materials by utilizing counterion-resistant ion synergistic framework donor-acceptor units, wherein the counterion-resistant anions within the channels include, but are not limited to, BF4. - PF6 - F - Cl - ,Br - or NO2 - One of the anions in it.

[0011] As a preferred embodiment of the present invention, the preparation method of Cu-MOF material reinforced by donor and acceptor units on the counterion synergistic framework is as follows: 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole, copper tetrafluoroborate, and a reaction solvent are added to a reaction vessel. After the reactants are mixed evenly, the sealed vessel is placed in an oven and reacted for a period of time. After cooling, the mixture is filtered, washed, and dried to obtain the single-crystal MOF material. The molar ratio of 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole to copper tetrafluoroborate is (0.5–1.5):1; the reaction solvent is DMF (N,N-dimethylformamide) and methanol, with a volume ratio of (1.5–2.5):1.

[0012] As a preferred technical solution of the present invention, in the preparation process of Cu-MOF material reinforced by donor and acceptor units on the counter ion synergistic framework, the reaction container includes, but is not limited to, a 10ml glass bottle, a 20ml glass bottle, a round-bottom flask or a pressure-resistant bottle; the mixing method is ultrasonic dispersion, the ultrasonic power is (100-200)W, and the ultrasonic time is (15-30)min.

[0013] As a preferred technical solution of the present invention, the Cu-MOF material with built-in electric field enhancement is applied to the photocatalytic degradation of organic pollutants. Specifically, the mass-volume ratio of Cu-MOF material to methylene blue solution is (5-15) mg: (60-100) mL.

[0014] As a preferred technical solution of the present invention, the Cu-MOF material with built-in electric field enhancement is applied to the photocatalytic degradation of organic pollutants, and the stirring time in the dark is (15-20) min, and the stirring table speed is (200-800) r / min.

[0015] As a preferred embodiment of the present invention, the Cu-MOF material with built-in electric field enhancement is applied to the photocatalytic degradation of organic pollutants, with a xenon lamp power density of (100-200) mW / cm². 2 .

[0016] As a preferred embodiment of the present invention, the Cu-MOF material with built-in electric field enhancement is applied to the photocatalytic degradation of organic pollutants, wherein the Cu-MOF catalyst reacts with methylene blue at (20-30)℃.

[0017] The technical effects of this invention are:

[0018] This invention enhances the built-in electric field of MOF materials by introducing counterions within the MOF channels and working in conjunction with donor and acceptor units on the framework. When the MOF material with the enhanced built-in electric field is immersed in a methylene blue aqueous solution, under xenon lamp irradiation in sunlight, the methylene blue removal rate reaches 90% after 35 minutes. Furthermore, the MOF material in this method possesses a broad light absorption window (200-1000 nm) and strong absorbance, enabling efficient degradation of other organic compounds besides methylene blue. The MOF material is easy to recycle and produces no secondary pollution. The synthesis method is simple, and the crystal structure is well-defined, which is beneficial for the practical application of metal-organic framework materials in dye wastewater purification. Attached Figure Description

[0019] Figure 1 It is the standard curve of methylene blue solution;

[0020] Figure 2 This is the kinetic curve of the methylene blue solution;

[0021] Figure 3 This is a diagram showing the water stability of the Cu-MOF catalyst;

[0022] Figure 4 This is the UV-Vis absorption spectrum of the Cu-MOF catalyst;

[0023] Figure 5 The graphs show the process curves of photocatalytic degradation of methylene blue (MB) by Cu-MOF catalysts of different concentrations.

[0024] Figure 6 This is a graph showing the cycle performance of the Cu-MOF catalyst;

[0025] Figure 7 This is the degradation curve of methylene blue under catalyst-free light conditions. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0027] Example 1

[0028] A method for photocatalytic degradation of methylene blue utilizing a built-in electric field enhanced by counterions within the channels of a MOF includes the following steps:

[0029] Step 1: Material preparation. 2.93 mg (0.01 mmol) of 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole, 5.27 mg (0.01 mmol) of copper tetrafluoroborate (L), 3 ml of DMF, and 1.5 ml of methanol were added to a 10 ml glass bottle. The bottle was sealed and sonicated for 20 min. The sealed glass bottle was then placed in an 80 °C oven for 72 h. The resulting product was filtered, washed, and dried to obtain the Cu-MOF material.

[0030] Step 2: The prepared Cu-MOF catalyst was dried in a vacuum drying oven at 70℃ for 72 hours. 10 mg of the catalyst was then placed in a quartz beaker containing 50 mL of 10 mg / L methylene blue solution. This means that the concentration of the Cu-MOF catalyst in the dye solution was 0.2 g / L.

[0031] Step 3: Use a 300W xenon lamp (>420nm) at 100mW / cm². 2 The reaction is irradiated with high power density light, and a cooling system is connected to ensure that the entire reaction process is carried out at 25°C.

[0032] Step 4: Take 4 mL of suspension every 5 min, centrifuge at 5000 rad / min for 5 min to remove Cu-MOF photocatalyst particles, and obtain a clear methylene blue solution.

[0033] Step 5: Prepare five standard methylene blue solutions of different concentrations: 2 mg / L, 4 mg / L, 6 mg / L, and 8 mg / L. Measure the absorbance at λ = 664 nm using a UV-2600 UV-Vis spectrophotometer, and plot the standard curve. (See attached image) Figure 1 The relationship between the absorbance and concentration of the methylene blue solution can be obtained as: y = 0.02638*x + 0.00151.

[0034] Step Six: Use a UV-2600 UV-Vis spectrophotometer to measure the absorbance of the methylene blue solution (MB) taken at different times at λ = 664 nm. Calculate the concentration of the methylene blue solution (MB) at the corresponding time based on the standard curve from Step Five.

[0035] Step 7: Calculate the degradation rate of methylene blue solution under the action of 10 mg Cu-MOF catalyst according to Lambert-Beer's law. The formula is as follows: η%=(1-C t / C0)×100%. See details of the degradation process. Figure 2 .Depend on Figure 2 It can be seen that the degradation rate increases continuously over time until it reaches saturation at 35 minutes and then stops increasing.

[0036] Figure 3The image shows the water stability diagram corresponding to the Cu-MOF catalyst in Example 1. Figure 3 It can be seen that the Cu-MOF catalyst can maintain its crystallinity after being soaked in water for two days, and the Cu-MOF catalyst can exist stably in solution.

[0037] Figure 4 The image shows the UV-Vis absorption curve of the Cu-MOF catalyst in Example 1. As can be seen from the figure, the Cu-MOF catalyst has good light absorption behavior, can better utilize visible light, and has higher catalytic efficiency.

[0038] Example 2

[0039] To achieve the large-scale synthesis of Cu-MOF obtained in Example 1, 177.82 mg (0.6 mmol) of 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole, 316.19 mg (0.6 mmol) of copper tetrafluoroborate (L), 180 ml of DMF, and 90 ml of methanol were added to a 350 ml pressure-resistant bottle, sealed, and sonicated for 20 min. The sealed glass bottle was then placed in an 80 °C oven for 72 h. The resulting product was filtered, washed, and dried to obtain the product MOF. Figure 7 This is the PXRD pattern of Cu-MOF catalysts prepared by the batch method. As can be seen from the figure, the crystalline structure of the material prepared by the batch method is maintained.

[0040] Example 3

[0041] The difference from Example 3 is that the concentration of Cu-MOF catalyst in the dye solution is 0.5 g / L.

[0042] Example 4

[0043] The difference from Example 3 is that the concentration of Cu-MOF catalyst in the dye solution is 1 g / L.

[0044] Example 5

[0045] The difference from Example 3 is that the concentration of Cu-MOF catalyst in the dye solution is 1.5 g / L.

[0046] Example 6

[0047] The difference from Example 3 is that the concentration of Cu-MOF catalyst in the dye solution is 2 g / L.

[0048] Figure 5 This is a graph showing the photocatalytic degradation process of methylene blue (MB) using Cu-MOF catalysts of different concentrations. Figure 5We can see that the degradation rate of methylene blue increases with the increase of Cu-MOF photocatalyst concentration, but decreases with further increases in concentration after the catalyst concentration reaches 1 g / L. This is because when the photocatalyst concentration reaches saturation, excessive photocatalyst tends to aggregate, reducing light penetration and the number of surface active sites for photon absorption, thus leading to a decrease in its degradation efficiency for methylene blue (MB).

[0049] Example 7

[0050] The Cu-MOF catalyst prepared in Example 1 was added to a quartz beaker containing 50 mL of a 10 mg / L methylene blue solution, making the catalyst concentration in the dye solution 1 g / L. After photocatalytic degradation of the methylene blue solution for 35 minutes according to the steps in Example 1, the Cu-MOF powder was collected by centrifugation, dried, and the operation was repeated. Figure 6 The cycling performance of the Cu-MOF catalyst was recorded. As shown in the figure, the Cu-MOF catalyst still maintains good catalytic performance after three cycles.

[0051] Comparative Example 1

[0052] Without adding a catalyst, the methylene blue solution was directly subjected to a light-induced reaction.

[0053] Step 1: Prepare 50 ml of a 10 mg / L methylene blue solution in a quartz glass.

[0054] Step 2: Irradiate with a 300W xenon lamp (>420nm) at a light power density of 100mW / cm2. The reaction is connected to a cooling system to ensure that the entire reaction process is carried out at 25℃.

[0055] Step 3: Take 4 mL of solution every 5 minutes and centrifuge at 5000 rad / min for 5 minutes to obtain a clear methylene blue solution.

[0056] Step 4: Use a UV-2600 UV-Vis spectrophotometer to measure the absorbance of the methylene blue solution (MB) taken at different times at λ = 664 nm. Calculate the concentration of the methylene blue solution (MB) at the corresponding time based on the standard curve from Step 5 of Example 1.

[0057] Step 5: Calculate the self-degradation rate of the methylene blue solution according to the Lambert-Beer Law. The degradation process curve is shown in [reference needed]. Figure 7 .

[0058] contrast Figure 2 Figure 7 It can be seen that the self-degradation rate of methylene blue solution is very small. Figure 2 The degradation rate is due to the role of the Cu-MOF catalyst.

[0059] This invention develops a method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the channels of a MOF (Metal-Oxide-Fuel). The method is simple to operate, highly efficient, and produces no secondary pollution. The catalyst is easy to synthesize, can be mass-produced, exhibits strong thermal and chemical stability, high catalytic yield, and good recyclability. This material can be mass-produced using pressure-resistant bottles, enabling batch preparation and laying the foundation for its practical industrial application.

[0060] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to these embodiments, including but not limited to modifying the type of contaminant, reaction temperature, light intensity, catalyst concentration, etc., and applying the general principle of enhancing the built-in electric field within the pore synergistic framework unit described herein to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the channels of a MOF, characterized in that, Includes the following steps: S1. The built-in electric field of Cu-MOF material is enhanced by the synergistic effect of counter ions in the pores and donor-acceptor units on the framework. S2. The Cu-MOF catalyst was added to a methylene blue aqueous solution and stirred in the dark for a period of time before being subjected to degradation reaction under xenon lamp irradiation. The enhanced electric field of the Cu-MOF is achieved by the counter anions in the pores and the donor-acceptor units on the framework. The framework structure of the Cu-MOF material is composed of rigid π-conjugated molecules 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazolyl and monovalent / divalent copper. The planar structure is connected by monovalent / divalent copper and formate ions. The counteracting anions within the channels include BF4. - PF6 - F - Cl - ,Br - or NO2 - One of the anions in; The preparation method of Cu-MOF material is as follows: 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole, copper tetrafluoroborate and reaction solvent are added to the reaction vessel. After the reactants are mixed evenly, the sealed container is placed in an oven and reacted for a period of time. After cooling, the material is filtered, washed and dried to obtain single crystal MOF material. In the preparation of Cu-MOF materials, the molar ratio of 2,5-bis(4-pyridyl)thiazo[5,4-d]thiazole to copper tetrafluoroborate is (0.5~1.5):1; the reaction solvent is DMF (N,N-dimethylformamide) and methanol, with a volume ratio of (1.5~2.5):

1. In the degradation reaction, the mass-to-volume ratio of Cu-MOF material to methylene blue solution is 5~15 mg: 60~100 mL.

2. The method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within MOF channels according to claim 1, characterized in that... During the preparation of Cu-MOF materials, the reaction vessel includes a 10ml glass bottle, a 20ml glass bottle, or a pressure-resistant bottle; the mixing method is ultrasonic dispersion, with an ultrasonic power of 100~200W and an ultrasonic time of 15~30min.

3. The method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the MOF channels according to claim 1, characterized in that, Stirring time in the dark is 15-20 minutes, and the stirring speed is 200-800 r / min.

4. The method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the MOF channels according to claim 1, characterized in that, The xenon lamp power density is 100~200 mW / cm². 2 .

5. The method for photocatalytic degradation of methylene blue using a built-in electric field enhanced by counterions within the MOF channels according to claim 1, characterized in that, The Cu-MOF catalyst reacts with methylene blue at 20-30°C.

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