Preparation method of microfiltration / nanofiltration double-layer catalytic membrane based on dual-site carbon nitride and its in-situ self-Fenton application

Abstract

The present invention belongs to the technical field of material preparation and environmental pollution control, and provides a preparation method and application of a microfiltration / nanofiltration double-layer catalytic membrane (i.e., a K / O-PCN double-layer catalytic membrane) based on dual-site carbon nitride, and the preparation method is as follows: Step 1, preparing a K / O-PCN catalyst; Step 2, preparing a K / O-PCN double-layer catalytic membrane. The present invention prepares a double-layer membrane, wherein the inner membrane fixes the K / O-PCN catalyst, which can generate a large amount of H2O2, so that the system realizes an in-situ Fenton reaction, and produces OH with strong oxidizing properties, thereby achieving a good degradation effect; the outer membrane separates the solution from the catalyst and other degradation products, and filters most of the pollutants, thereby achieving the purpose of water purification.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation and environmental pollution control, and relates to a preparation method and application of a microfiltration / nanofiltration double-layer catalytic membrane based on dual-site carbon nitride, specifically using the microfiltration / nanofiltration double-layer catalytic membrane based on dual-site carbon nitride (i.e., K / O-PCN double-layer catalytic membrane) as an in-situ Fenton degradation of pollutants in water. Background Art

[0002] In recent years, industrialization and urbanization have developed rapidly, producing a large amount of wastewater containing difficult-to-degrade organic pollutants, which poses a serious threat to the ecosystem and human health. Therefore, a low-cost and efficient solution is urgently needed. Among the many treatment methods currently available, the Fenton oxidation method has the advantages of low cost, strong oxidizing property, and high reliability, and can meet the industrial requirements for efficient treatment of difficult-to-degrade organic wastewater. However, it requires the additional addition of chemical oxidants (such as H2O2), which increases the complexity of the transportation process and the additional cost.

[0003] The coupling of Fenton oxidation with photocatalytic technology can realize the photo-Fenton catalytic system. This system can reduce oxygen in the air to H2O2 by using the photoreduction half-reaction of the photocatalytic material, and the photogenerated electrons can be quickly transferred to Fe 3+ and reduce it to Fe 2+ , promoting Fe 2+ The activated in-situ generated H2O2 produces a large amount of ·OH. In addition, the photogenerated holes can also effectively participate in the removal of pollutants. This system avoids the additional addition of H2O2, while greatly improving the oxidation removal capacity of pollutants, which is better than single advanced oxidation technology. Despite this, there are still some problems with the photo-self-Fenton system, such as: 1. The photocatalytic material has low oxygen adsorption efficiency, and electron holes are easy to recombine, resulting in low efficiency of self-produced H2O2; 2. After the reaction is completed, it is difficult to effectively separate the catalyst and other degradation products from the solution, and the operation process is complicated. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention firstly constructs a K / O-PCN catalyst by using salt-assisted heat shrinkage and method. The catalyst not only introduces potassium ions, which can effectively adsorb oxygen, but also contains abundant oxygen doping as active sites, which inhibits electron-hole recombination, accelerates the efficiency of H2O2 production, and realizes a photo-Fenton system, thereby improving the degradation of organic pollutants. Secondly, the present invention uses electrostatic spinning technology to fix the above catalyst on a fiber membrane to prepare a K / O-PCN double-layer catalytic membrane. This membrane material can effectively separate the catalyst and other degradation products from water, making subsequent operations easier.

[0005] Step 1: Preparation of K / O-PCN catalyst:

[0006] Take melamine and potassium chloride, add a certain amount of anhydrous sodium thiosulfate, grind them thoroughly at room temperature, place them in a porcelain crucible, and calcine them in a muffle furnace. The obtained yellow product is washed and dried with hot water, then ground again and washed with hot water. After filtering and drying, the product is K / O-PCN catalyst, which is ready for use;

[0007] Step 2: Preparation of K / O-PCN double-layer catalytic membrane:

[0008] The K / O-PCN catalyst obtained in step 1 is added to DMSO, ultrasonically dispersed, and then chitosan is added, mechanically stirred to obtain a uniform casting solution, and the bubbles generated by stirring are removed by vacuuming;

[0009] The prepared membranes are all prepared by electrospinning process. The casting liquid is loaded into a syringe installed on a syringe pump, the syringe needle tip is kept at a certain distance from the collector and voltage is applied to the syringe needle; after adjusting the flow rate of the casting liquid, the electrospun fibers are deposited on the glass, and the obtained composite membrane is washed and dried with ethanol and distilled water for multiple times; then the composite membrane is immersed in an aqueous solution of hexamethylenetetramine, taken out, washed and dried, and then immersed in an organic solution of trimesoyl chloride, and finally heat-treated. The obtained sample is a K / O-PCN double-layer catalytic membrane, that is, a microfiltration / nanofiltration double-layer catalytic membrane based on dual-site carbon nitride; the membrane is stored in deionized water at room temperature for standby use.

[0010] In step 1, the mass ratio of melamine, potassium chloride and anhydrous sodium thiosulfate is 3:3:0.8; the calcination time is 4 to 6 hours, the calcination temperature is 500 to 600°C, and the heating rate is 5 to 10°C / min; the hot water temperature is 60 to 70°C, the drying temperature is 60 to 80°C, and the drying time is 8 to 12 hours.

[0011] In step 2, when preparing the K / O-PCN double-layer catalyst membrane, the mass ratio of the K / O-PCN catalyst to DMSO is 0.1-0.4 g: 17.9-17.6 g;

[0012] In step 2, the mass fraction of chitosan in the casting solution is 5-20% of the casting solution, the mechanical stirring time is 4-6 hours, and the stirring temperature is 50-60°C; 10 mL of the casting solution loaded into the syringe is kept at a distance of 18-22 cm from the needle tip and the collector, and the voltage is 10-14 kV; the flow rate of the casting solution is 0.6-1.0 mL·h -1 ;

[0013] In step 2, the mass percentage concentration of hexamethylenetetramine in the aqueous solution is 1-8%; the mass percentage concentration of trimesoyl chloride in the organic solution is 0.05-1%; the immersion time in the two solutions is 5-20s, the heat treatment temperature is 20-45°C, and the heat treatment time is 1-2h.

[0014] The DMSO described in the above technical solution acts as a solvent to dissolve chitosan to prepare the casting solution.

[0015] The chitosan described in the above technical solution acts as a matrix.

[0016] The deionized water described in the above technical solution acts as a non-solvent.

[0017] The dual-site carbon nitride-based microfiltration / nanofiltration double-layer catalytic membrane prepared by the present invention is used for in-situ Fenton degradation of antibiotics in water.

[0018] Technical advantages of the present invention:

[0019] (1) The prepared K / O-PCN catalyst not only introduces potassium ions, which can effectively adsorb oxygen, but also contains abundant oxygen doping as active sites, which prevents the recombination of electrons and holes, improves the photocatalytic efficiency, and accelerates the efficiency of H2O2 production. It can be used for the later in-situ Fenton to degrade pollution, thus improving the disadvantage of the self-Fenton process that requires the additional addition of chemical oxidants.

[0020] (2) The prepared double-layer membrane has the advantages of both the inner and outer layers. The inner layer fixes the above-mentioned catalyst, and the subsequent Fenton reaction can produce a large amount of ·OH, thereby achieving a good degradation effect; the outer layer has a smaller pore size, which can not only effectively separate the solution from the catalyst and other degradation products, but also filter out most of the pollutants to a certain extent, thereby purifying the water body. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of K / O-PCN double-layer catalytic membrane. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with specific implementation examples.

[0023] The present invention takes the total mass of the casting liquid as 20g as an example.

[0024] Embodiment 1:

[0025] (1) Preparation of K / O-PCN catalyst:

[0026] 3g of melamine, 3g of potassium chloride and 0.8g of anhydrous sodium thiosulfate were ground at room temperature, placed in a porcelain crucible after sufficient grinding, and calcined in a muffle furnace for 4h, the calcination temperature was 550°C, the heating rate was 5°C / min, the obtained yellow product was washed with hot water and dried, ground again and washed with 60°C hot water, filtered and dried to obtain the product, the drying temperature was 70°C, the drying time was 12h, and the product was K / O-PCN catalyst;

[0027] (2) Preparation of K / O-PCN double-layer catalytic membrane:

[0028] 0.1 g K / O-PCN catalyst was added to 17.9 g DMSO and ultrasonically dispersed for 1 h. Then 2 g chitosan was added and mechanically stirred at 50 °C for 4 h to obtain a uniform casting solution. The bubbles generated by stirring were removed by vacuuming. The prepared membranes were prepared by electrospinning. 10 mL of the casting solution was loaded into a syringe installed on a syringe pump. The syringe needle tip was kept at a distance of 20 cm from the collector and a voltage of 12.5 kV was applied to the syringe needle. The casting solution flow rate was adjusted to 0.8 mL·h -1 , the electrospun fibers are deposited on glass, and the obtained composite membrane is washed and dried with ethanol and distilled water for multiple times; then the composite membrane is immersed in a 4% by mass concentration of hexamethylenetetramine aqueous solution for 15 seconds, taken out and immersed in a 0.6% by mass concentration of trimesoyl chloride organic solution for 10 seconds, and finally heat-treated at a temperature of 25°C. The obtained sample is a K / O-PCN double-layer catalytic membrane.

[0029] The K / O-PCN double-layer catalytic membrane constructed under the above conditions has a degradation effect of more than 90% on antibiotics within 120 minutes of visible light (λ>420nm) irradiation.

[0030] Embodiment 2:

[0031] While ensuring that other conditions remain unchanged, a comparative test was established as follows: When preparing the K / O-PCN catalyst, the degradation efficiency of the composite catalyst on antibiotics was investigated by changing the ratio of melamine and anhydrous sodium thiosulfate (3:0.6, 3:0.8, 3:1.0).

[0032] The experimental results show that the photocatalytic efficiency is optimal when the ratio of melamine to anhydrous sodium thiosulfate is 3:0.8, and the hydrogen peroxide production efficiency is 3069 μmol / h.

[0033] Embodiment 3:

[0034] When preparing the K / O-PCN double-layer catalytic membrane, (1) keep other conditions unchanged and only use the single-layer catalytic membrane on the glass for degradation experiments. The experimental results show that the degradation effect of the single-layer catalytic membrane on antibiotics within 120 minutes of visible light (λ>420nm) irradiation reaches more than 70%. (2) Keep other conditions unchanged and adjust the viscosity of the casting liquid by changing the amount of chitosan added (1g, 2g, 3g) to control the size of the composite membrane polymer fiber diameter and adjust the pore size. The experimental results show that when the amount of chitosan added is 2g, the membrane pore size is the smallest, which is 0.01μm. (3) Keep other conditions unchanged and adjust the thickness of the outer membrane by changing the immersion time in the liquid (6s, 8s, 10s, 12s, 15s, 18s) to screen the optimal amount. The experimental results show that the double-layer membrane has the best degradation efficiency after being immersed in a hexamethylenetetramine aqueous solution for 15 seconds and then immersed in a trimesoyl chloride organic solution for 10 seconds. The degradation effect of the catalytic membrane on antibiotics reaches more than 90% within 120 minutes of visible light (λ>420nm) irradiation.

Claims

1. A method for preparing a microfiltration / nanofiltration double-layer catalytic membrane based on dual-site carbon nitride, characterized in that: Here are the steps: Step 1: Preparation of K / O-PCN catalyst: Take melamine and potassium chloride, add a certain amount of anhydrous sodium thiosulfate, grind them thoroughly at room temperature, place them in a porcelain crucible, and calcine them in a muffle furnace. The obtained yellow product is washed and dried with hot water, then ground again and washed with hot water. After filtering and drying, the product is K / O-PCN catalyst, which is ready for use; The mass ratio of melamine, potassium chloride and anhydrous sodium thiosulfate is 3:3:0.8; Step 2: Preparation of K / O-PCN double-layer catalytic membrane: The K / O-PCN catalyst obtained in step 1 is added to DMSO, ultrasonically dispersed, and then chitosan is added, mechanically stirred to obtain a uniform casting solution, and the bubbles generated by stirring are removed by vacuuming; The prepared membrane is prepared by an electrospinning process, wherein a casting liquid is loaded into a syringe installed on a syringe pump, the syringe needle tip is kept at a certain distance from a collector and a voltage is applied to the syringe needle tip; after adjusting the flow rate of the casting liquid, the electrospun fibers are deposited on glass, and the obtained composite membrane is washed and dried with ethanol and distilled water for multiple times; then the composite membrane is immersed in an aqueous solution of hexamethylenetetramine, taken out, washed and dried, and then immersed in an organic solution of trimesoyl chloride, and finally heat-treated, and the obtained sample is a K / O-PCN double-layer catalytic membrane, that is, a microfiltration / nanofiltration double-layer catalytic membrane based on dual-site carbon nitride; the membrane is stored in deionized water at room temperature for standby use; In the aqueous solution of hexamethylenetetramine, the mass percentage concentration of hexamethylenetetramine is 1~8%; In the organic solution of trimesoyl chloride, the mass percentage concentration of trimesoyl chloride is 0.05~1%; The immersion time in both solutions was 5~20 s, the heat treatment temperature was 20~45 ℃, and the heat treatment time was 1~2 h.

2. The preparation method according to claim 1, characterized in that: In step 1, the calcination time is 4-6 h, the calcination temperature is 500-600 °C, and the heating rate is 5-10 °C / min.

3. The preparation method according to claim 1, characterized in that: In step 1, the hot water temperature is 60-70°C, the drying temperature is 60-80°C, and the drying time is 8-12 h.

4. The preparation method according to claim 1, characterized in that: In step 2, the mass ratio of the K / O-PCN catalyst to DMSO is 0.1-0.4 g: 17.9-17.6 g.

5. The preparation method according to claim 1, characterized in that: In step 2, in the casting solution, the mass fraction of the chitosan is 5-20% of the casting solution.

6. The preparation method according to claim 1, characterized in that: In step 2, the mechanical stirring time is 4-6 hours, and the stirring temperature is 50-60°C.

7. The preparation method according to claim 1, characterized in that: In step 2, 10 mL of the casting solution is loaded into the syringe, the needle tip is kept at a distance of 18-22 cm from the collector, and the voltage is 10-14 kV; the casting solution flow rate is 0.6-1.0 mL·h -1 .

8. Use of the dual-site carbon nitride-based microfiltration / nanofiltration double-layer catalytic membrane prepared by the preparation method according to any one of claims 1 to 7 as an in-situ Fenton degradation of antibiotics in water.

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