Microdroplet-photofenton-photocatalysis synergistic organic dye degradation method

Abstract

The application discloses a micro-droplet-light Fenton-light catalysis synergistic organic dye degradation method, and belongs to the field of organic dye degradation. The degradation method comprises the following steps: constructing a micro-droplet generating device based on gas-assisted spraying; mixing an organic dye solution with a light Fenton reagent and a light catalyst, and forming micro-droplets with a diameter of less than or equal to 70 microns through the micro-droplet generating device; applying an excitation light source to the generated micro-droplets to activate a light reaction, and generating a light Fenton-light catalysis synergistic reaction to degrade the organic dye; collecting the droplets after the reaction through ice bath to form a degradation product solution; taking the micro-droplets as micro-reactors, and based on the special gas-liquid interface effect and the strong electric field effect of the gas-liquid interface, water molecules are ionized to form free radicals ·OH; under the condition of light irradiation, g-C3N4 nanosheets generate electron migration to produce photo-generated electrons and photo-generated holes, the photo-generated holes combine with water to produce ·OH, and the ·OH in the system combines to generate H2O2; meanwhile, the photo-generated electrons reduce ferric chloride to ferrous chloride, and the ferrous chloride combines with H2O2 in the system to excite the light Fenton reaction, so that the degradation efficiency of the organic dye is improved.

Description

Technical Field

[0001] This invention belongs to the field of organic dye degradation, specifically relating to a microdroplet-photo-Fenton-photocatalysis synergistic method for organic dye degradation. Background Technology

[0002] Redox reactions involve the gain and loss of electrons and have wide applications in the degradation of organic pollutants. Photo-Fenton and photocatalysis technologies have made significant progress in converting solar energy into chemical energy to decompose environmental pollutants, and the synergistic effect of photocatalysis and photo-Fenton has been proven to greatly improve degradation efficiency. To date, researchers have made many efforts to improve the conversion efficiency of solar energy in photocatalytic reactions, mainly focusing on improving the performance of photoreaction materials, such as nano-semiconductors, metal doping, the construction of heterojunction structures, and noble metal deposition. Graphitic carbon nitride (g-C3N4) is considered a promising non-metallic semiconductor photocatalyst with great development potential in photocatalytic applications. g-C3N4 nanosheets are frequently used to improve the separation of photogenerated electron-hole pairs, and can degrade organic pollutants more efficiently than bulk g-C3N4.

[0003] However, the relatively slow reaction kinetics of photocatalysis and photoFenton remain a major obstacle to electron transfer. Hydroxyl radicals (·OH) are electron acceptors that play a crucial role in both photocatalysis and photoFenton reactions, and H₂O, acting as a solvent in these reactions, can serve as an effective source of ·OH. However, the inertness of H₂O at room temperature and pressure makes it difficult to generate ·OH in photocatalysis and photoFenton processes. Currently, the unique properties of droplets can be attributed to the different reaction environments between the droplets and the bulk solution, particularly the air-water interface, where interfacial enrichment and interfacial electric fields may occur.

[0004] Therefore, we combined microdroplets with photocatalysis and photo-Fenton to improve the availability of water as a reaction solvent during the photoreaction process and enhance the degradation efficiency of photo-Fenton and photocatalytic degradation of organic pollutants. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a microdroplet-photo-Fenton-photocatalysis synergistic method for the degradation of organic dyes, thus solving the problems in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A microdroplet-photoFenton-photocatalysis synergistic method for the degradation of organic dyes includes the following steps:

[0008] Construct a microdroplet generation device based on gas-assisted spraying;

[0009] An organic dye solution is premixed with a photo-Fenton reagent and a photocatalyst, and then passed through the microdroplet generating device to form microdroplets with a diameter of less than or equal to 70 μm.

[0010] An excitation light source is applied to the generated microdroplets to activate the photoreaction, resulting in a photoFenton-photocatalytic synergistic reaction to degrade organic dyes;

[0011] The reaction droplets are collected using an ice bath to form a degradation product solution.

[0012] Furthermore, the microdroplet generating device includes a three-way tube I and a three-way tube II connected to each other. The three-way tube I is used for premixing the organic dye solution with the photo-Fenton reagent and the photocatalytic reagent. Nitrogen gas is introduced into the upper end of the three-way tube II, and a quartz glass capillary tube is inserted parallel to each other in the middle channel between the left and right ends as a passage for the mixed solution.

[0013] By sealing the space on the left side of the three-way tube II, nitrogen gas flows out only from the right side of the three-way tube II. With the assistance of nitrogen gas, the mixed solution is dispersed into microdroplets.

[0014] Furthermore, the photo-Fenton reagent is a ferric chloride solution, and the photocatalytic reagent is a nitrogen carbide nanosheet dispersion.

[0015] Furthermore, the organic dye is: Rhodane Red B, Methylene Blue, Golden Orange, or Acid Fuchsin.

[0016] Furthermore, the preparation steps of the nitrogen carbide nanosheet dispersion include:

[0017] Step 1: Calcining melamine in a muffle furnace to obtain lumpy g-C3N4;

[0018] Step 2: Disperse the block-shaped g-C3N4 in deionized water and sonicate it; then centrifuge it multiple times. After each centrifugation, collect the supernatant to obtain the g-C3N4 nanosheet dispersion.

[0019] Furthermore, the melamine was heated to 550°C in a muffle furnace at a rate of 5°C / min and calcined for 4 hours.

[0020] Furthermore, each centrifugation process was performed at a speed of 8000 r / min for 30 min.

[0021] Furthermore, the excitation source is a 300W xenon lamp.

[0022] Furthermore, the quartz glass capillary has an outer diameter of 0.35 mm and an inner diameter of 0.2 mm; the liquid flow rate of the mixed solution injected into the quartz glass capillary is 120 μL / min. The nitrogen gas pressure is 0.2 MPa.

[0023] The beneficial effects of this invention are:

[0024] 1. Microdroplets with a diameter of 70 μm or less are obtained using a microdroplet generation device. These microdroplets possess unique physicochemical properties at the microscopic scale, such as high specific surface area, abundant charge density, and a strong electric field in the dielectric double layer. Using microdroplets as microreactors, based on their unique gas-liquid interface effect and the strong electric field at the gas-liquid interface (10... 9 (V / cm) causes water molecules to ionize and form free radicals ·OH. Irradiation excites the g-C3N4 nanosheets to undergo electron migration, generating photogenerated electrons (e electrons). - ) and photogenerated holes (h + Photogenerated holes combine with water to produce ·OH, which in turn combines to form H₂O₂. Simultaneously, photogenerated electrons reduce ferric chloride to ferrous chloride, which then combines with H₂O₂ to trigger the photo-Fenton reaction. The combination of photocatalysis / photo-Fenton and microdroplets creates a synergistic effect, enhancing the degradation efficiency of organic dyes.

[0025] 2. Compared with general photocatalytic and photo-Fenton degradation methods, the organic dye degradation method of the present invention utilizes the advantage of the high electric field at the gas-liquid interface of microdroplets to improve the availability of water as the reaction solvent during the photoreaction process, thereby enhancing the degradation efficiency of photo-Fenton and photocatalytic degradation of organic pollutants. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a reaction flow diagram of the organic dye degradation method of the present invention;

[0028] Figure 2 The results of the bulk phase reaction are shown in the diagrams for four cases: Rhodamine B, Rhodamine B + ferric chloride, Rhodamine B + carbon nitride nanosheets, and Rhodamine B + ferric chloride + carbon nitride nanosheets.

[0029] Figure 3 The graph shows the results of microdroplet reactions under four conditions: Rhodamine B, Rhodamine B + ferric chloride, Rhodamine B + carbon nitride nanosheets, and Rhodamine B + ferric chloride + carbon nitride nanosheets.

[0030] Figure 4 A schematic diagram illustrating the generation of ·OH in water droplets based on electron paramagnetic resonance verification.

[0031] Figure 5 A graph showing the relationship between the degradation rate and degradation time of microdroplets of different sizes;

[0032] Figure 6 Mass spectrometry results of Rhodamine B degradation products collected at different retention times after spraying;

[0033] Figure 7 This is a diagram showing the inferred degradation pathway of Rhodamine B. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be noted that the following ingredients used in this invention were purchased from Maclean's (Shanghai, China): melamine, ferric chloride (FeCl3), and rhodamine B. Ethanol was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All solutions were prepared with ultrapure water (impedance ≥18.2 MΩcm). The solutions were mixed using a shaker.

[0036] Example 1

[0037] like Figure 1 As shown, a microdroplet-photoFenton-photocatalytic synergistic method for the degradation of organic dyes includes the following steps:

[0038] S1, Construct a microdroplet generation device based on gas-assisted spray;

[0039] The microdroplet generating device includes two interconnected three-way tubes, I and II. Three-way tube I is used for premixing organic dye solution with photo-Fenton / photocatalytic reagent. Nitrogen gas is introduced into the upper end of three-way tube II, and a quartz glass capillary is inserted parallel to the middle channel of the left and right ends as a passage for the mixed solution.

[0040] By sealing the space from the outside of the quartz glass capillary on the left side of the three-way tube II to the inside of the three-way tube II, nitrogen gas flows out only from the right side of the three-way tube II, and the mixed solution flows out from the right side of the quartz glass capillary at the same time. With the assistance of nitrogen gas, the mixed solution is dispersed into micron-sized droplets.

[0041] It is worth mentioning that in this embodiment, the outer diameter of the quartz glass capillary is 0.35 mm and the inner diameter is 0.2 mm. The liquid flow rate of the mixed solution injected into the quartz glass capillary is 120 μL / min. Nitrogen gas at 0.2 MPa is applied to the spray end of the quartz glass capillary via a gas cylinder device to create a nitrogen atmosphere and generate microdroplets with a size less than 70 μm, thus achieving the reaction between the organic dye and the microdroplets. Under the above parameters, the generated microdroplets are small in size, and the aqueous solution per unit volume has a high specific surface area, increasing the contact probability between nitrogen gas and the gas-liquid interface. Simultaneously, from a temporal perspective, the reaction time between the organic dye and the microdroplet gas-liquid interface is prolonged. These spatial and temporal effects are beneficial to improving or enhancing the degradation rate and efficiency of the organic dye.

[0042] S2, the organic dye solution to be degraded is premixed with photoFenton reagent and photocatalyst, and then microdroplets with a diameter of less than or equal to 70 μm are formed through a microdroplet generating device;

[0043] In this embodiment, the organic dye to be degraded is Rhodamine B, the photo-Fenton reagent is ferric chloride (FeCl3) solution, and the photocatalyst is a nitrogen carbide (g-C3N4) nanosheet dispersion; of course, in some embodiments, the organic dye may also be methylene blue, golden orange, or acid fuchsin, etc.

[0044] Carbon nitride (g-C3N4) is a typical polymer semiconductor that can absorb blue-violet light with wavelengths less than 475 nm in the solar spectrum. It possesses highly suitable semiconductor band-edge positions, meeting the requirements for photodegradation of organic dyes. It is typically prepared using melamine or dicyandiamide as precursors through high-temperature calcination (550°C). Furthermore, compared to traditional photocatalysts, carbon nitride (g-C3N4) can effectively activate molecular oxygen, enabling photocatalytic conversion of organic functional groups and photocatalytic degradation of organic pollutants.

[0045] The preparation process of g-C3N4 nanosheet dispersion includes:

[0046] Step 1: Heat 5.0g of melamine to 550℃ in a muffle furnace at a rate of 5℃ / min, and calcine for 4h to obtain block g-C3N4;

[0047] Step 2: Disperse 250 mg of block g-C3N4 in 100 mL of deionized water, and then sonicate for 20 h to peel off the block g-C3N4; centrifuge at 8000 r / min for 30 min, repeat three times; after each centrifugation, collect the supernatant to obtain g-C3N4 nanosheet dispersion;

[0048] S3, during the formation of microdroplets, a 300W xenon lamp is applied to the generated microdroplets to activate the photoreaction, thereby causing a photo-Fenton-photocatalytic synergistic reaction to degrade organic dyes;

[0049] S4. The droplets after the reaction are collected by an ice bath to form a degradation product solution. By measuring the absorbance of the degradation product solution and comparing it with the absorbance of the organic dye solution before degradation, the degradation rate of the organic dye can be calculated.

[0050] Example 2

[0051] In this embodiment, under 300W xenon lamp illumination, four solutions—Rhodamine B, Rhodamine B + ferric chloride, Rhodamine B + carbon nitride nanosheets, and Rhodamine B + ferric chloride + carbon nitride nanosheets—were stirred for 1 hour each. The reaction solution was collected every ten minutes for UV absorbance measurement. Figure 2 As shown, Figure 2 In the table, (a)-(d) correspond to the UV absorbance detection results of four solutions: Rhodamine B, Rhodamine B + ferric chloride, Rhodamine B + carbon nitride nanosheets, and Rhodamine B + ferric chloride + carbon nitride nanosheets, respectively; from Figure 2 The results show that Rhodamine B itself cannot be degraded in bulk by light, but after adding ferric chloride / carbon nitride nanosheets, Rhodamine B is degraded to a certain extent in bulk under light conditions. This indicates that Rhodamine B can be degraded based on photo-Fenton and photocatalysis, and the synthesized carbon nitride nanosheets can be used as photocatalysts in this experiment.

[0052] The four reaction solutions described above were sprayed as microdroplets under both dark and light conditions. After ten minutes of reaction, the microdroplets were collected for ultraviolet absorbance measurement. The results are as follows: Figure 3 As shown, Figure 3 In the table, (a)-(d) correspond to the UV absorbance results of four solutions—Rhodamine B, Rhodamine B + ferric chloride, Rhodamine B + carbon nitride nanosheets, and Rhodamine B + ferric chloride + carbon nitride nanosheets—after being ejected through microdroplets. Figure 3 The effects of microdroplets on the degradation of organic dyes under different conditions were visually compared. After ten minutes of microdroplet reaction, the experimental results showed that microdroplets, whether combined with photocatalysis or photo-Fenton, significantly improved the degradation efficiency of Rhodamine B by photocatalysis / photo-Fenton itself. Furthermore, the degradation efficiency was most significantly improved under the microdroplet + photocatalysis + photo-Fenton condition, indicating a synergistic effect between photo-Fenton and photocatalysis based on the microdroplet reaction.

[0053] Example 3

[0054] This embodiment verifies the generation of hydroxyl radicals by microdroplets through the gas-liquid surface;

[0055] To visually verify the generation of ·OH during the microdroplet process, electron paramagnetic resonance (EPR) was used to detect both the bulk and microdroplet processes. First, two 2ml centrifuge tubes were used. DMPO (dihydroxyl radical scavenger), freshly thawed from the freezer, was added to each tube (10μL). Then, 1ml of water was added to one tube, and a 1ml water droplet was sprayed into the other tube using a microdroplet device, ensuring sufficient contact between the droplet and the DMPO. The two tubes were then quickly connected to a capillary tube, and X-ray diffraction was performed. Figure 4 As shown, ·OH can be clearly captured in water droplets compared to the bulk phase; this proves that water droplets can indeed spontaneously generate ·OH in the absence of an applied voltage.

[0056] Microdroplet reactions primarily rely on the formation of microdroplets with a size of 70 μm or less under external forces. Unlike bulk reactions, this disrupts the traditional understanding of water as a solvent at the macroscopic physicochemical scale, endowing them with unique physicochemical properties. These include increased surface area, strong interfacial electric fields, reduced reaction barriers, and special redox characteristics. Compared to the microscopic scale, microdroplets under microscopic conditions, and gas-liquid interfaces at the interfacial scale, possess unique electric field properties, with electric field strengths reaching 10⁻⁶. 9 V / cm. This electric field allows water to be electrolyzed into ·OH. The ·OH combines to produce H₂O₂, which is a powerful reducing agent for degrading organic dyes.

[0057] Example 4

[0058] This embodiment verifies the photodegradation effect of the microdroplet device on organic dyes.

[0059] 0.2 mL of Rhodamine B, 0.6 mL of ferric chloride, and 0.6 mL of g-C3N4 nanosheet dispersion were placed in a 2 mL centrifuge tube and mixed thoroughly. The mixture was then injected into a microdroplet device using a 1 mL syringe. The nitrogen cylinder (pressure 0.2 MPa) and the syringe pump (flow rate 120 μL / min) were turned on to allow the solution to be ejected under nitrogen gas, and a 300 W xenon lamp was turned on for illumination. Afterward, 1 mL of the degraded solution was analyzed by mass spectrometry. Figure 5 As shown, where Figure 5 In the figures (a)-(c), the degradation products of Rhodamine B are obtained at different retention times of 0.703 min, 0.717 min and 0.725 min, respectively.

[0060] Based on the degradation products, it can be inferred that RhB degradation mainly occurs through two pathways, such as... Figure 6As shown, one pathway involves the gradual removal of the ethyl group from the N molecule of RhB; another pathway involves the disruption of the conjugated structure of the RhB molecule. The molecular structure shows that the upper and lower conjugated structures are linked by single bonds, making them prone to breakage. Based on the mass spectrometry results, it is speculated that the RhB molecule is first deethylated, and due to the interaction between ·OH and RhB, certain groups are substituted.

[0061] Mechanism analysis:

[0062] The design mechanism of the invention lies in utilizing the large amount of ·OH generated by the system to degrade organic dyes. The sources of ·OH include the following three pathways: such as Figure 7 As shown, (1) by utilizing the high electric field characteristics of the water-gas interface of the microdroplets, the availability of the reaction solvent water during the photoreaction process is improved, and ·OH is spontaneously generated; (2) under light irradiation, the photocatalyst g-C3N4 nanosheets undergo charge separation, generating electron-hole pairs, in which the holes can oxidize the solvent water to ·OH; (3) in pathway (2), the photogenerated electrons can reduce the photo-Fenton reagent ferric chloride to ferrous chloride, and the ferrous chloride further reacts with the spontaneously generated H2O2 on the surface of the microdroplets to activate the Fenton reaction and generate ·OH. Through the synergistic effect of the above three pathways, a large amount of ·OH will be generated in the microdroplets, which is expected to enable the degradation process of organic dyes to achieve a higher degradation rate in a short time.

[0063] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0064] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for synergistically degrading organic dyes by microdroplet-photofenton-photocatalysis, characterized in that, The method comprises the following steps: constructing a microdroplet generating device based on gas-assisted spraying; premixing an organic dye solution with a photo-Fenton reagent and a photocatalytic reagent, and forming microdroplets with a diameter of less than or equal to 70 μm through the microdroplet generating device; applying an excitation light source to the generated microdroplets to activate a photo reaction, and causing a photo-Fenton-photocatalytic synergistic reaction to degrade the organic dye; collecting the droplets after the reaction through an ice bath to form a degradation product solution; the microdroplet generating device comprises a three-way pipe I and a three-way pipe II connected to each other, the three-way pipe I is used for premixing the organic dye solution with the photo-Fenton reagent and the photocatalytic reagent; the three-way pipe II is connected to nitrogen gas at the top, and a quartz glass capillary is inserted into the middle channel between the left and right openings of the three-way pipe II as a passage for the mixed solution; by sealing the left space of the three-way pipe II, nitrogen gas only flows out from the right side of the three-way pipe II, and under the assistance of nitrogen gas, the mixed solution is dispersed into microdroplets.

2. The method according to claim 1, wherein, The photo-Fenton reagent is a ferric chloride solution, and the photocatalytic reagent is a carbon nitride nanosheet dispersion liquid.

3. The method according to claim 1, wherein the microdroplet-photofenton-photocatalysis synergistic organic dye degradation method is characterized by, The organic dye is rhodamine B, methylene blue, aurine or acid fuchsin.

4. The method according to claim 2, wherein the microdroplet-photofenton-photocatalytic synergistic organic dye degradation method is characterized by, The preparation steps of the carbon nitride nanosheet dispersion liquid comprise: Step 1: calcining melamine in a muffle furnace to obtain blocky g-C3N4; Step 2: dispersing the blocky g-C3N4 in deionized water and performing ultrasonic treatment, and then performing multiple centrifugal treatments, and collecting the supernatant after each centrifugal treatment to obtain a g-C3N4 nanosheet dispersion liquid.

5. The method according to claim 4, wherein the microdroplet-photofenton-photocatalytic synergistic organic dye degradation method is characterized by, The melamine is heated in the muffle furnace at a rate of 5℃ / min to 550℃, and calcined for 4h.

6. The method according to claim 4, wherein the microdroplet-photofenton-photocatalytic synergistic organic dye degradation method is characterized by, The rotation speed of each centrifugal treatment is 8000r / min, and the time is 30min.

7. The method according to claim 1, wherein the microdroplet-photofenton-photocatalysis synergistic organic dye degradation method is characterized by, The excitation light source is a 300W xenon lamp.

8. The method according to claim 1, wherein the microdroplet-photofenton-photocatalysis synergistic organic dye degradation method is characterized by, The outer diameter of the quartz glass capillary is 0.35mm, and the inner diameter is 0.2mm; the liquid flow rate of the mixed solution injected into the quartz glass capillary is 120μL / min, and the nitrogen gas pressure is 0.2MPa.

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