Heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process as well as preparation method and application of heterogeneous Fenton self-cleaning catalytic membrane

Abstract

The invention provides a heterogeneous Fenton self-cleaning catalytic membrane for a membrane distillation process as well as a preparation method and application of the heterogeneous Fenton self-cleaning catalytic membrane, and belongs to the technical field of wastewater purification. The preparation method comprises the following steps: by taking a polytetrafluoroethylene hydrophobic membrane as a base membrane, sequentially grafting a polydopamine bonding layer and a 3-aminopropyltriethoxysilane (APTES) coupling layer on the surface of the polytetrafluoroethylene hydrophobic membrane, and grafting an oxyferric chloride catalyst layer on the APTES coupling layer in a vacuum filtration manner, so as to prepare the heterogeneous Fenton self-cleaning catalytic membrane. The invention further provides the prepared membrane and application thereof in wastewater purification, the obtained self-cleaning catalytic membrane can efficiently intercept organic pollutants in wastewater and can also efficiently degrade the organic pollutants, self-cleaning of produced water and the membrane is achieved, the problem of membrane distillation concentrated waste liquid is solved while the anti-pollution performance of the membrane is improved, and the service life of the membrane is prolonged. The catalytic efficiency is high, and the operation stability is good.

Description

Technical Field

[0001] The present invention relates to a heterogeneous Fenton self-cleaning catalytic membrane for a membrane distillation process, a preparation method and an application thereof, belonging to the technical field of wastewater purification, and particularly to the technical field of catalytic membranes for coupling a membrane distillation process with a heterogeneous Fenton method for wastewater purification. Background Art

[0002] With the rapid advancement of global industrialization and urbanization, various toxic and harmful refractory organic compounds (such as dyes, antibiotics, and surfactants, etc.) enter the urban water supply system and natural water bodies through various channels, causing serious water pollution problems. Traditional sewage treatment technologies are usually limited by low efficiency and poor stability when treating complex pollutants, and are unable to effectively remove refractory organic compounds in wastewater. In contrast, membrane distillation (MD) technology has high pollutant removal efficiency, low energy consumption, is green and pollution-free, and is easy to realize sewage reuse. In recent years, it has shown good application potential in wastewater treatment and water resource reuse. MD uses a hydrophobic microporous membrane as the separation medium and the vapor pressure difference caused by the temperature difference on both sides of the membrane as the driving force. Water in the wastewater passes through the membrane pores in the form of vapor, is condensed and collected on the other side, and becomes reusable water, while organic pollutants and salts in the wastewater are intercepted, and the treated wastewater becomes a highly concentrated waste liquid with a greatly reduced volume (one of the inherent problems). At the same time, there will be a phenomenon that the intercepted pollutants accumulate on the membrane surface and block the membrane pores, thus significantly reducing the separation efficiency and service life of the membrane, that is, membrane fouling (the second inherent problem). Therefore, it is urgent to adopt innovative and efficient membrane fouling control strategies to degrade pollutants in wastewater while controlling membrane fouling, so as to fundamentally solve the inherent problems of the MD process for treating wastewater and promote its industrial application in wastewater treatment.

[0003] In recent years, the heterogeneous Fenton method, as a green advanced oxidation technology, has attracted much attention due to its strong degradation ability, wide pH application range, high stability, environmental friendliness, and simple operation. If the heterogeneous Fenton method can be combined with the membrane distillation technology and the heterogeneous Fenton catalyst is anchored on the membrane surface, the self-cleaning of the membrane and the degradation of pollutants can be realized, thus effectively solving the problems of difficult treatment of concentrated waste liquid and membrane fouling in the membrane distillation process, significantly improving the operation efficiency of the membrane distillation system, and having important practical value for wastewater treatment and environmental protection. Summary of the Invention

[0004] In view of some defects existing in the prior art, the present invention provides a heterogeneous Fenton self-cleaning catalytic membrane for a membrane distillation process, its preparation method and application. Specifically, the self-cleaning catalytic membrane provided by the present invention uses a polytetrafluoroethylene (PTFE) hydrophobic membrane as the base membrane, and successively grafts a polydopamine (PDA) bonding layer and a 3-aminopropyltriethoxysilane (APTES) coupling layer on its surface. Then, a ferric oxychloride (FeOCl) catalytic layer is grafted on the APTES coupling layer by vacuum filtration, thereby obtaining a heterogeneous Fenton self-cleaning catalytic membrane for the MD process.

[0005] To achieve the above technical objectives, the present invention provides the following technical solutions:

[0006] The present invention first provides a heterogeneous Fenton self-cleaning catalytic membrane for a membrane distillation process. The heterogeneous Fenton self-cleaning catalytic membrane uses a polytetrafluoroethylene (PTFE) hydrophobic membrane as the base membrane, and a polydopamine (PDA) bonding layer, a 3-aminopropyltriethoxysilane (APTES) coupling layer, and a ferric oxychloride (FeOCl) catalytic layer are successively grafted on the surface of the polytetrafluoroethylene hydrophobic membrane from bottom to top; it has the ability of self-cleaning.

[0007] The present invention also provides a preparation method for a heterogeneous Fenton self-cleaning catalytic membrane for a membrane distillation process. The method includes the following steps:

[0008] (1) Place the PDA solution under constant temperature conditions, add the PTFE hydrophobic membrane, so that the PTFE hydrophobic membrane floats on the surface of the PDA solution. After floating, wash and dry to obtain a membrane with a PDA bonding layer and a PTFE separation layer, denoted as the PDA / PTFE membrane.

[0009] Among them, the preparation method of the PDA solution includes: adding dopamine hydrochloride to a tris(hydroxymethyl)aminomethane buffer solution, stirring and mixing evenly to obtain the PDA solution.

[0010] Further, the dosage of dopamine hydrochloride and the tris(hydroxymethyl)aminomethane buffer solution is 400 mg: 200 mL; the pH value of the tris(hydroxymethyl)aminomethane buffer solution is 8.5, and the concentration is 10 mM; the stirring time is 30 min.

[0011] The temperature of the constant temperature treatment is 50 °C; the pore size of the PTFE hydrophobic membrane is 0.22 μm, and the thickness is 190 μm; the floating time of the PTFE hydrophobic membrane is 1.5 h.

[0012] (2) Float the PDA / PTFE membrane obtained in step (1) on the surface of an anhydrous ethanol solution of APTES. After floating, wash and dry to obtain a membrane with an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer, denoted as the APTES / PDA / PTFE membrane.

[0013] Among them, in the anhydrous ethanol solution of APTES, the dosage ratio of APTES to anhydrous ethanol is 40 mL: 400 mL; the floating time of the PDA / PTFE membrane is 1 h.

[0014] (3) Graft the anhydrous ethanol solution of FeOCl onto the surface of the APTES / PDA / PTFE membrane by vacuum filtration to obtain a membrane with a FeOCl catalytic layer, an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer, denoted as the FeOCl / APTES / PDA / PTFE membrane, which is the heterogeneous Fenton self-cleaning catalytic membrane for the membrane distillation process.

[0015] Among them, the specific operation method of the vacuum filtration includes: placing the APTES / PDA / PTFE membrane obtained in step (2) on the filter plate of the vacuum filtration device, ensuring that the membrane body is flat and completely fits the entire filter plate. Subsequently, start the vacuum pump to evacuate. After a stable negative pressure environment is formed in the vacuum filtration device, slowly pour the FeOCl anhydrous ethanol solution along the inner wall of the Buchner funnel. The solution quickly penetrates through the APTES / PDA / PTFE membrane under the drive of negative pressure, and FeOCl is grafted onto the surface of the APTES coupling layer of the APTES / PDA / PTFE membrane.

[0016] Furthermore, the FeOCl is prepared by a partial thermal decomposition method, and the specific operation is as follows: Take an appropriate amount of FeCl3·6H2O and grind it in an agate mortar for 30 min. After dividing it into crucibles, place it in a tube furnace. Set the heating rate of the tube furnace to 5 °C / min, the holding temperature to 220 °C, hold for 2 h, and then cool to room temperature. After taking it out and grinding, wash it thoroughly with anhydrous ethanol to remove the unreacted FeCl3, and then place it in a vacuum drying oven at 40 °C for 2 h, take it out and store it sealed.

[0017] The anhydrous ethanol solution of FeOCl is obtained by dissolving 80 mg of FeOCl in 300 mL of anhydrous ethanol and ultrasonically dispersing it for 30 min to make it uniform.

[0018] The present invention also provides the application of the heterogeneous Fenton self-cleaning catalytic membrane for the membrane distillation process in wastewater treatment, and the application is in the treatment of wastewater by the membrane distillation process.

[0019] Among them, during the process of treating wastewater by the membrane distillation process, add H2O2 to the wastewater, and then contact the side of the heterogeneous Fenton self-cleaning catalytic membrane loaded with the FeOCl catalyst layer with the wastewater.

[0020] The wastewater includes dye wastewater, antibiotic wastewater, or surfactant wastewater.

[0021] Preferably, in the membrane distillation process, the heterogeneous Fenton self-cleaning catalytic membrane for the membrane distillation process contacts the feed liquid on the side loaded with the FeOCl catalytic layer, and the other side is the permeate side; when starting the MD operation, H2O2 is added to the feed liquid. The feed liquid includes wastewater containing dyes (reactive brilliant blue), wastewater containing antibiotics (tetracycline), or wastewater containing surfactants (sodium dodecyl sulfate, containing NaCl).

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) The heterogeneous Fenton self-cleaning catalytic membrane of the present invention combines the advantages of the MD process and the FeOCl heterogeneous Fenton catalytic degradation: when used for MD treatment of wastewater, the membrane can not only efficiently intercept pollutants in the wastewater through the hydrophobic PTFE separation layer to produce water, but also activate H2O2 through the FeOCl catalytic layer to efficiently degrade pollutants. Compared with the traditional MD technology using PTFE membranes to treat wastewater, the heterogeneous Fenton self-cleaning catalytic membrane of the present invention has self-cleaning ability, does not require additional complex membrane cleaning, so MD can operate continuously with high production efficiency; at the same time, due to the self-cleaning effect of the membrane, the membrane is not easily contaminated and has a long service life. Through experimental verification, the service life of the heterogeneous Fenton self-cleaning catalytic membrane obtained in the present invention is more than five times that of the PTFE hydrophobic membrane, which can greatly reduce the operating cost.

[0024] (2) In the preparation process of the heterogeneous Fenton self-cleaning catalytic membrane of the present invention, an FeOCl catalytic layer is added, which can utilize FeOCl to activate H2O2 to generate hydroxyl radicals, thereby achieving the purpose of efficient degradation of pollutants. Compared with the traditional homogeneous Fenton method, this method is milder in reaction conditions, reduces the dependence on strong acid conditions, and effectively overcomes the disadvantages of generating a large amount of iron sludge, high consumption of H2O2, and difficulty in recycling and reusing the catalyst in the traditional homogeneous Fenton method; it can also efficiently treat various types of organic pollutant (such as dyes, antibiotics, surfactants, etc.) wastewater, effectively avoid environmental pollution, and at the same time reduce the cost of sewage reuse treatment, which is of great significance for promoting environmental protection and sustainable development.

[0025] (3) The modified materials used in the preparation of the heterogeneous Fenton self-cleaning catalytic membrane of the present invention are all environmentally friendly, do not require additional chemical agents, and there is no residue of high-concentration waste liquid, which can completely realize the harmlessness and resource utilization of wastewater without potential secondary pollution. When treating complex organic wastewater, the materials of the present invention show advantages such as high water production efficiency, high pollutant degradation ability, good self-cleaning and anti-pollution performance, good long-term operation stability, significant time and economic cost savings, etc., with higher practicality and economy, and at the same time greatly reducing the risk of secondary pollution, meeting the requirements of environmental protection and sustainable development. Description of the Drawings

[0026] Figure 1 The present invention is a schematic diagram of the structure of the heterogeneous Fenton self-cleaning catalytic membrane used in the membrane distillation process.

[0027] Figure 2 This is a permeation flux diagram of the membrane distillation treatment of reactive brilliant blue using a PTFE hydrophobic membrane and a heterogeneous Fenton self-cleaning catalytic membrane in the presence of H2O2 in Example 1.

[0028] Figure 3 This is a graph showing the concentration factor of the feed solution when the active brilliant blue is subjected to membrane distillation treatment using a PTFE hydrophobic membrane and a heterogeneous Fenton self-cleaning catalytic membrane in the presence of H2O2 in Example 1.

[0029] Figure 4 This is a permeation flux diagram of tetracycline when the PTFE hydrophobic membrane and the heterogeneous Fenton self-cleaning catalytic membrane are used for membrane distillation in the presence of H2O2 in Example 2.

[0030] Figure 5 This is a graph of feed liquid concentration factors when tetracycline is subjected to membrane distillation treatment using a PTFE hydrophobic membrane and a heterogeneous Fenton self-cleaning catalytic membrane in the presence of H2O2 in Example 2.

[0031] Figure 6 This is a permeation flux diagram of sodium dodecyl sulfate (containing NaCl) subjected to membrane distillation treatment using a PTFE hydrophobic membrane and a heterogeneous Fenton self-cleaning catalytic membrane in the presence of H2O2 in Example 3.

[0032] Figure 7 This is a graph of feed liquid concentration factors when sodium dodecyl sulfate (containing NaCl) is subjected to membrane distillation treatment using a PTFE hydrophobic membrane and a heterogeneous Fenton self-cleaning catalytic membrane in the presence of H2O2 in Example 3.

[0033] Figure 8 This is a graph showing the NaCl retention rate when sodium dodecyl sulfate (containing NaCl) is subjected to membrane distillation treatment using a PTFE hydrophobic membrane and a heterogeneous Fenton self-cleaning catalytic membrane in the presence of H2O2 in Example 3.

[0034] Specific embodiment

[0035] In order to better illustrate the purpose, technical solution and advantages of the present invention, the technical solution of the present invention will be explained in more detail in combination with several preferred embodiments and drawings. The specific embodiments described below are only used to further illustrate and explain the present invention, and are not intended to limit the present invention; all variations associated with or derived from the contents disclosed in the present invention are considered to be within the scope of protection of the present invention.

[0036] Except for the FeOCl catalyst which is prepared by partial thermal decomposition, the other raw materials in the present invention are purchased from commercial sources.

[0037] Unless otherwise specified, the operating temperature in the examples of the present invention is room temperature.

[0038] The calculation methods or measurement methods for the relevant performance indicators in the following examples are as follows:

[0039] (1) The calculation formula for the permeation flux (J) of the heterogeneous Fenton self-cleaning catalytic membrane during MD treatment of reactive brilliant blue, tetracycline, and sodium dodecyl sulfate (containing NaCl) in the presence of H2O2 is as follows:

[0040] J = Δm / AΔt; where Δm (kg) is the mass change of the permeate, A (m 2 ) is the effective membrane area, and Δt (h) is the operating duration.

[0041] (2) The calculation formula for the feed liquid pollutant concentration factor (R c ) of the heterogeneous Fenton self-cleaning catalytic membrane during MD treatment of reactive brilliant blue, tetracycline, and sodium dodecyl sulfate in the presence of H2O2 is as follows:

[0042] R c = A c / A m × 100%; where A c and A m are the absorbance values of the pollutants in the feed liquid after treatment and before treatment, respectively, measured with a UV-visible spectrophotometer.

[0043] (3) The calculation formula for the NaCl rejection rate (R r ) of the heterogeneous Fenton self-cleaning catalytic membrane during MD treatment of sodium dodecyl sulfate (containing NaCl) in the presence of H2O2 is as follows:

[0044] R r = (1 - C d / C f ) × 100%; where C d and C f are the conductivity values of the permeate and the feed liquid, respectively, measured with a conductivity meter.

[0045] Unless otherwise specified, the instruments used in the examples of the present invention are conventional instruments in the art.

[0046] Example 1: Preparation method of a heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process and its ability to degrade reactive brilliant blue

[0047] (1) Dissolve 400 mg of dopamine hydrochloride in 200 mL of pre-prepared tris(hydroxymethyl)aminomethane buffer with a pH of 8.5 and a concentration of 10 mM. Stir with a magnetic stirrer for 30 min until the solution is evenly mixed. Through the self-polymerization of dopamine hydrochloride, a PDA solution is obtained and set aside;

[0048] (2) Pour the PDA into a petri dish and place it in a constant temperature shaker at 50 °C. After the temperature of the PDA solution reaches 50 °C, float a PTFE hydrophobic membrane with a pore size of 0.22 μm and a thickness of 190 μm on its surface for 1.5 h to form a membrane with a PDA bonding layer and a PTFE separation layer (named PDA / PTFE). After washing and drying, set it aside;

[0049] (3) Add 40 mL of APTES to 400 mL of absolute ethanol and float the PDA / PTFE on the surface of the APTES absolute ethanol solution for 1 h to form a membrane with an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer (named APTES / PDA / PTFE);

[0050] (4) Prepare FeOCl by partial thermal decomposition method. The specific operation is as follows: Take an appropriate amount of FeCl3·6H2O and grind it in an agate mortar for 30 min. After dividing it into crucibles, place it in a tube furnace. Set the heating rate of the tube furnace to 5 °C / min, the holding temperature to 220 °C, hold for 2 h, and then cool to room temperature. After taking it out and grinding, wash it thoroughly with absolute ethanol to remove the unreacted FeCl3, and then place it in a vacuum drying oven at 40 °C for 2 h. Take it out and seal it for storage.

[0051] (5) Dissolve 80 mg of FeOCl in 300 mL of absolute ethanol and ultrasonically disperse it for 30 min to make it uniform. Place the APTES / PDA / PTFE membrane obtained in step (3) on the filter plate of the vacuum filtration device with tweezers, ensuring that the membrane body is flat, without wrinkles, gaps, and completely covers the filter plate. Then start the vacuum pump for vacuuming. After a stable negative pressure environment is formed in the vacuum filtration device, slowly pour the FeOCl absolute ethanol solution along the inner wall of the Buchner funnel. The solution quickly passes through the APTES / PDA / PTFE membrane under the drive of negative pressure, while FeOCl is grafted onto the surface of the APTES coupling layer of APTES / PDA / PTFE to form a membrane with a FeOCl catalytic layer, an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer (named FeOCl / APTES / PDA / PTFE), that is, a heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process.

[0052] The structural schematic diagram of the heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process described in the present invention is as Figure 1As shown in the figure, the heterogeneous Fenton self-catalytic membrane for the membrane distillation process has an FeOCl catalytic layer, an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer.

[0053] The performance of the obtained heterogeneous Fenton self-catalytic membrane was tested by a vacuum membrane distillation device. During the test, the side of the heterogeneous Fenton self-catalytic membrane loaded with the FeOCl catalytic layer was in contact with the feed liquid for heat measurement, while the other side was the permeate liquid on the cold side. The reactive brilliant blue wastewater with a concentration of 250 mg / L was used as the feed liquid, and the pH value of the wastewater was adjusted to 5. The temperature of the feed side was set at 60 °C. During operation, 187.5 mg / L of H2O2 was added to the feed liquid. At the same time, the PTFE membrane used for preparing the heterogeneous Fenton self-catalytic membrane was used as a control group for the experiment.

[0054] The test results are as Figure 2 and Figure 3 shown. The results show that the heterogeneous Fenton self-catalytic membrane (hereinafter referred to as the catalytic membrane for short) performs better than the traditional PTFE hydrophobic membrane in the membrane distillation process.

[0055] Specifically, Figure 2 it shows that in the presence of H2O2, the initial permeation flux of the catalytic membrane is 55.4 kg / m 2 ·h, while that of the PTFE membrane is 34.9 kg / m 2 ·h, and the former is 1.6 times that of the latter. Although the permeation flux of the catalytic membrane will decrease in the initial stage of operation, it will no longer decrease after 24 h of operation and stabilizes at 20.5 kg / m 2 ·h, and remains stable until 30 h. However, the permeation flux of the PTFE membrane decreases rapidly. After 6 h of operation, it drops to 20 kg / m 2 ·h, and after 10 h, it drops to 0 kg / m 2 ·h, completely stopping working. Therefore, if the permeation flux not lower than 20 kg / m 2 ·h is used as the minimum working permeation flux, the service life of the catalytic membrane is more than 5 times that of the PTFE membrane. This indicates that the catalytic membrane not only improves the permeation flux but also greatly extends the service life of the membrane, and at the same time shows good operational stability. Figure 3Further results showed that during the MD operation, the concentration factor of the feed solution using the catalytic membrane decreased significantly and tended to zero after 28 h, indicating that almost 100% of the pollutants in the feed solution were degraded. While the concentration factor of the feed solution using the PTFE membrane increased to 1.2 after 10 h (the PTFE membrane stopped working at 10 h and could no longer be tested continuously), indicating that it could not effectively degrade pollutants and there was concentrated waste liquid. The results showed that the FeOCl catalyst loaded on the surface of the catalytic membrane could effectively activate H2O2, efficiently degrade the reactive brilliant blue pollutants adsorbed on the membrane surface, thereby achieving self-cleaning of the membrane, endowing the membrane with strong anti-pollution performance, enabling stable operation, and effectively solving the problem of concentrated waste liquid residue in the membrane distillation process.

[0056] Example 2: Preparation method of heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process and its ability to degrade tetracycline

[0057] (1) Dissolve 400 mg of dopamine hydrochloride in 200 mL of pre-prepared tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 and a concentration of 10 mM, stir with a magnetic stirrer for 30 min until the solution is evenly mixed, and obtain a PDA solution through the self-polymerization of dopamine hydrochloride for standby.

[0058] (2) Pour the PDA into a petri dish and place it in a constant temperature shaker at 50 °C. After the temperature of the PDA solution reaches 50 °C, float a PTFE hydrophobic membrane with a pore size of 0.22 μm and a thickness of 190 μm on its surface for 1.5 h to form a membrane with a PDA bonding layer and a PTFE separation layer (named PDA / PTFE), wash and dry it for standby.

[0059] (3) Add 40 mL of APTES to 400 mL of absolute ethanol, and float the PDA / PTFE on the surface of the APTES absolute ethanol solution for 1 h to form a membrane with an APTES coupling layer, a PDA bonding layer and a PTFE separation layer (named APTES / PDA / PTFE).

[0060] (4) Prepare FeOCl by partial thermal decomposition method, and the specific operation is as follows: Take an appropriate amount of FeCl3·6H2O and grind it in an agate mortar for 30 min, then divide it into crucibles and place it in a tube furnace. Set the heating rate of the tube furnace to 5 °C / min, the holding temperature to 220 °C, hold for 2 h and then cool to room temperature. Take it out and grind it, then rinse it thoroughly with absolute ethanol to remove the unreacted FeCl3, and then place it in a vacuum drying oven at 40 °C for 2 h, take it out and seal it for storage.

[0061] (5) Dissolve 80 mg of FeOCl in 300 mL of absolute ethanol and ultrasonically disperse it for 30 min to make it uniform. Place the APTES / PDA / PTFE membrane obtained in step (3) on the filter plate of the vacuum filtration device with tweezers, ensuring that the membrane body is flat, without wrinkles, gaps, and completely covers the filter plate. Then start the vacuum pump for vacuum pumping. After a stable negative pressure environment is formed in the vacuum filtration device, slowly pour the FeOCl absolute ethanol solution along the inner wall of the Buchner funnel. The solution quickly passes through the APTES / PDA / PTFE membrane under the drive of negative pressure, while FeOCl is grafted onto the surface of the APTES coupling layer of APTES / PDA / PTFE, forming a membrane with a FeOCl catalytic layer, an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer (named FeOCl / APTES / PDA / PTFE), that is, a heterogeneous Fenton self-cleaning catalytic membrane for the membrane distillation process.

[0062] Perform performance tests on the obtained heterogeneous Fenton self-cleaning catalytic membrane through a vacuum membrane distillation device. During the test, the side of the heterogeneous Fenton self-cleaning catalytic membrane loaded with the FeOCl catalytic layer is in contact with the feed liquid for thermal measurement, while the other side is the permeate on the cold side. Use 250 mg / L tetracycline wastewater as the feed liquid, adjust the pH value of the wastewater to 5, and set the temperature on the feed side to 60 °C. During operation, add 187.5 mg / L of H2O2 to the feed liquid. At the same time, use the PTFE membrane used to prepare the heterogeneous Fenton self-cleaning catalytic membrane as a control group for the experiment.

[0063] The test results are as Figure 4 and Figure 5 shown. The results show that the heterogeneous Fenton self-cleaning catalytic membrane (hereinafter referred to as the catalytic membrane for short) performs better than the traditional PTFE hydrophobic membrane in the membrane distillation process.

[0064] Specifically, Figure 4 it shows that in the presence of H2O2, the initial permeation flux of the catalytic membrane is 54.9 kg / m 2 ·h, while that of the PTFE membrane is 36.8 kg / m 2 ·h, and the former is 1.5 times that of the latter. Although the permeation flux of the catalytic membrane will decrease in the initial stage of operation, it will no longer decrease after 20 h of operation and stabilizes at 30.6 kg / m 2 ·h, and remains stable until 30 h. However, the permeation flux of the PTFE membrane decreases rapidly. After 6 h of operation, it drops to 20 kg / m 2 ·h, and after 10 h, it drops to 0 kg / m 2 ·h and completely stops working. Therefore, if it is not less than 20 kg / m 2·Taking the permeation flux of ·h as the lowest working permeation flux, the service life of the catalytic membrane is more than 5 times that of the PTFE membrane. This indicates that the catalytic membrane not only improves the permeation flux but also can greatly extend the service life of the membrane, while showing good operation stability. Figure 5 Further indicated that during the MD operation, the concentration factor of the feed liquid using the catalytic membrane decreased significantly and tended to zero after 20 h, indicating that almost 100% of the pollutants in the feed liquid were degraded. While the concentration factor of the feed liquid using the PTFE membrane increased to 1.26 after 10 h (the PTFE membrane stopped working at 10 h and could no longer be tested continuously), indicating that it could not effectively degrade pollutants and there was concentrated waste liquid. This result shows that the FeOCl catalyst loaded on the surface of the catalytic membrane can effectively activate H2O2, efficiently degrade the tetracycline pollutants adsorbed on the membrane surface, thereby achieving self-cleaning of the membrane, making the membrane have strong anti-pollution performance, so that it can operate stably, and at the same time effectively solves the problem of concentrated waste liquid residue in the membrane distillation process.

[0065] Example 3: Preparation method of heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process and its ability test for degrading sodium dodecyl sulfate (containing 3.5 wt% NaCl)

[0066] (1) Dissolve 400 mg of dopamine hydrochloride in 200 mL of pre-prepared tris(hydroxymethyl)aminomethane buffer solution with a pH of 8.5 and a concentration of 10 mM, stir with a magnetic stirrer for 30 min until the solution is evenly mixed, and obtain a PDA solution through the self-polymerization of dopamine hydrochloride for standby;

[0067] (2) Pour the PDA into a petri dish and place it in a constant temperature shaker at 50 °C. After the temperature of the PDA solution reaches 50 °C, float a PTFE hydrophobic membrane with a pore size of 0.22 μm and a thickness of 190 μm on its surface for 1.5 h to form a membrane with a PDA bonding layer and a PTFE separation layer (named PDA / PTFE), wash and dry it for standby;

[0068] (3) Add 40 mL of APTES to 400 mL of absolute ethanol, and float the PDA / PTFE on the surface of the APTES absolute ethanol solution for 1 h to form a membrane with an APTES coupling layer, a PDA bonding layer and a PTFE separation layer (named APTES / PDA / PTFE);

[0069] (4) FeOCl was prepared by partial thermal decomposition method, and the specific operation is as follows: Take an appropriate amount of FeCl3·6H2O and grind it in an agate mortar for 30 min. After dividing it into crucibles, place it in a tube furnace. Set the heating rate of the tube furnace to 5 °C / min, the holding temperature to 220 °C, hold for 2 h, and then cool to room temperature. After taking it out and grinding, rinse it thoroughly with anhydrous ethanol to remove the unreacted FeCl3, and then place it in a vacuum drying oven at 40 °C for 2 h, take it out and store it sealed.

[0070] (5) Dissolve 80 mg of FeOCl in 300 mL of anhydrous ethanol and ultrasonically disperse it for 30 min to make it uniform. Place the APTES / PDA / PTFE membrane obtained in step (3) on the filter plate of the vacuum filtration device with tweezers, ensuring that the membrane body is flat, without wrinkles, gaps, and completely covers the filter plate. Then start the vacuum pump for vacuuming. After a stable negative pressure environment is formed in the vacuum filtration device, slowly pour the FeOCl anhydrous ethanol solution along the inner wall of the Buchner funnel. The solution quickly passes through the APTES / PDA / PTFE membrane under the drive of negative pressure, while FeOCl is grafted on the surface of the APTES coupling layer of APTES / PDA / PTFE, forming a membrane with a FeOCl catalytic layer, an APTES coupling layer, a PDA bonding layer, and a PTFE separation layer (named FeOCl / APTES / PDA / PTFE), that is, a heterogeneous Fenton self-cleaning catalytic membrane for the membrane distillation process.

[0071] The performance of the obtained heterogeneous Fenton self-cleaning catalytic membrane was tested by a vacuum membrane distillation device. During the test, the side of the heterogeneous Fenton self-cleaning catalytic membrane loaded with the FeOCl catalytic layer was in contact with the feed liquid for thermal measurement, while the other side was the permeate on the cold side. Use the wastewater of sodium dodecyl sulfate (containing 3.5 wt% NaCl) at 250 mg / L as the feed liquid, and adjust the pH value of the wastewater to 5. Set the temperature of the feed side to 60 °C. During operation, add 187.5 mg / L of H2O2 to the feed liquid. At the same time, use the PTFE membrane used to prepare the heterogeneous Fenton self-cleaning catalytic membrane as a control group for the experiment.

[0072] The test results are as Figure 6 、 Figure 7 and Figure 8 shown, and the results show that the heterogeneous Fenton self-cleaning catalytic membrane (hereinafter referred to as the catalytic membrane for short) performs better than the traditional PTFE hydrophobic membrane in the membrane distillation process.

[0073] Specifically, Figure 6 shows that in the presence of H2O2, the initial permeation flux of the catalytic membrane is 58.3 kg / m 2 ·h, while that of the PTFE membrane is 36.3 kg / m 2·h, and the former is 1.6 times that of the latter. Although the permeation flux of the catalytic membrane will decrease in the initial stage of operation, it will no longer decrease after 26 h of operation, and stabilizes at 42.5 kg / m 2 ·h (the decline rate is only 27%), which is significantly higher than the maximum flux of the PTFE membrane (6.3 kg / m 2 ·h), and remains stable until 30 h. The permeation flux of the PTFE membrane decreases rapidly. After 10 h of operation, it drops to 20 kg / m 2 ·h. After 16 h, it drops to 0 kg / m 2 ·h (the decline rate is 100%), and it completely stops working. Therefore, if the permeation flux of not less than 20 kg / m 2 ·h is used as the minimum working permeation flux, according to the trend of the flux change of the catalytic membrane, it will not drop to 20 kg / m 2 ·h within 60 h. Then, the service life of the catalytic membrane is more than 6 times that of the PTFE membrane. This shows that the catalytic membrane not only increases the permeation flux, but also can greatly extend the service life of the membrane, and at the same time shows good operation stability. Figure 7 It further shows that during the MD operation, the concentration factor of the feed liquid using the catalytic membrane decreases significantly and tends to zero after 24 h, indicating that almost 100% of the pollutants in the feed liquid are degraded. The concentration factor of the feed liquid using the PTFE membrane increases to 1.36 after 16 h (the PTFE membrane has stopped working at 16 h and cannot be tested further), indicating that it cannot effectively degrade pollutants and there is concentrated waste liquid. In addition, Figure 8 it shows that during the MD operation, the NaCl rejection rate when using the catalytic membrane remains above 99.9% within 30 h, indicating that the catalytic membrane can effectively prevent NaCl from passing through and has high salt rejection performance. When using the PTFE membrane, the NaCl rejection rate decreases rapidly and drops to 86.2% after 16 h, indicating that it has become wet. The results show that the FeOCl catalyst loaded on the surface of the catalytic membrane can effectively activate H2O2, efficiently degrade the sodium dodecyl sulfate (surfactant) pollutants adsorbed on the membrane surface, thereby achieving self-cleaning of the membrane and effectively preventing the membrane from getting wet, enabling the membrane to have strong anti-pollution and anti-wetting properties, so that it can operate stably for a long time, and at the same time effectively solve the problem of concentrated waste liquid residue in the membrane distillation process.

[0074] Example 4: Economic analysis of heterogeneous Fenton self-cleaning catalytic membrane

[0075] In this example, an economic analysis is carried out on the PTFE membrane and the heterogeneous Fenton self-cleaning catalytic membrane (referred to as the catalytic membrane) used in Example 1 for treating reactive brilliant blue, and the analysis results are shown in Table 1.

[0076] As can be seen from Table 1, the service life of the catalytic membrane described in the present invention is more than 5 times longer than that of the traditional PTFE membrane, significantly reducing the number of membrane replacements and reducing the comprehensive cost by about 67%. At the same time, due to the excellent self-cleaning and anti-pollution ability of the catalytic membrane, there is no additional membrane cleaning cost. Meanwhile, the pollutants in the wastewater are effectively degraded, and there is no cost for reprocessing the concentrated waste liquid (and the treatment of concentrated waste liquid is very difficult), further reducing the operating cost. In addition, in the MD process, based on the cumulative water production of the PTFE membrane in a single cycle (10 h) as the benchmark (286.2 g), the catalytic membrane can achieve a water production of 660.5 g under the same operating conditions, and the production efficiency is increased by 230.8%. Based on the advantages of extended membrane life, zero waste liquid treatment cost, and significantly reduced unit water production cost, the present invention not only solves the problem of flux decay caused by membrane pollution in the traditional MD process, but also synchronously optimizes the membrane life and treatment efficiency through the synergistic mechanism of "anti-pollution - self-cleaning - high productivity", forming an industrial-level solution of "cost reduction - efficiency increase - sustainability".

[0077] Table 1. Economic comparison between catalytic membrane and PTFE membrane

[0078] Membrane type Working cycle (h) Waste liquid treatment Water production (g) PTFE hydrophobic membrane 6 Required 286.2 Heterogeneous Fenton self-cleaning catalytic membrane ＞30 Not required 660.5

[0079] Note: Calculate the working cycle of the membrane based on the permeation flux of 20 kg / m 2 ·h as the minimum working permeation flux.

[0080] In summary, the heterogeneous Fenton self-cleaning catalytic membrane prepared in the present invention innovatively couples the MD process with the heterogeneous Fenton method. In the application of wastewater treatment, this membrane exhibits excellent performance. On the one hand, it can efficiently intercept organic pollutants to ensure the compliance of the effluent quality; on the other hand, with the effective activation of H2O2 by the FeOCl catalytic layer, it can efficiently degrade organic pollutants and achieve the self-cleaning function of the membrane, significantly extending the service life of the membrane. From the economic perspective, compared with the traditional PTFE hydrophobic membrane, the operating cost of the heterogeneous Fenton self-cleaning catalytic membrane is significantly reduced, the operating time is shortened, and there is no need to worry about the cost of concentrated waste liquid treatment, greatly reducing the overall operating cost and bringing higher economic benefits. In addition, as an efficient and low-consumption sewage reuse treatment technology, the present invention shows good applicability to various complex organic pollutants, is expected to be widely promoted and applied in the field of sewage treatment, provides a strong technical guarantee for alleviating water resource shortage and environmental pollution problems, and realizes a win-win situation of economic and environmental benefits.

[0081] The described embodiments are the preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Without departing from the essential content of the present invention, any obvious improvements, substitutions or modifications that those skilled in the art can make all belong to the protection scope of the present invention.

Claims

1. A heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process, characterized in that: The heterogeneous Fenton self-cleaning catalytic membrane uses a polytetrafluoroethylene hydrophobic membrane as a base membrane, and a polydopamine bonding layer, a 3-aminopropyltriethoxysilane coupling layer and an oxyferric chloride catalytic layer are sequentially grafted on the surface of the polytetrafluoroethylene hydrophobic membrane from bottom to top.

2. The method for preparing a heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process according to claim 1, characterized in that: The following steps are involved: (1) placing a polydopamine solution under a constant temperature condition, adding a polytetrafluoroethylene hydrophobic membrane to float it on the surface of the polydopamine solution, and washing and drying after the floating, thereby obtaining a PDA / PTFE membrane; (2) floating the PDA / PTFE membrane obtained in step (1) on the surface of an anhydrous ethanol solution of 3-aminopropyltriethoxysilane, and washing and drying after the floating is completed to obtain an APTES / PDA / PTFE membrane; (3) Grafting an anhydrous ethanol solution of ferric chloride oxychloride onto the surface of the APTES / PDA / PTFE membrane by vacuum filtration to obtain a FeOCl / APTES / PDA / PTFE membrane, i.e., the heterogeneous Fenton self-cleaning catalytic membrane for membrane distillation process.

3. The preparation method according to claim 2, characterized in that: In step (1), the preparation method of the polydopamine solution comprises: adding dopamine hydrochloride into a tris(hydroxymethyl)aminomethane buffer solution, stirring and mixing uniformly, to obtain the polydopamine solution.

4. The preparation method according to claim 3, characterized in that: The dosage ratio of dopamine hydrochloride to tris(hydroxymethyl)aminomethane buffer solution is 400 mg:200 mL; The pH value of the Tris buffer solution is 8.5, and the concentration is 10 mM.

5. The preparation method according to claim 2, characterized in that: In step (1), the constant temperature is 50° C.; and the floating time of the polytetrafluoroethylene hydrophobic membrane is 1.5 h.

6. The preparation method according to claim 2, characterized in that: In step (2), in the anhydrous ethanol solution of 3-aminopropyltriethoxysilane, the usage ratio of 3-aminopropyltriethoxysilane to anhydrous ethanol is 40mL:400mL; and the floating time of the PDA / PTFE membrane is 1h.

7. The preparation method according to claim 2, characterized in that: In step (3), in the anhydrous ethanol solution of oxyferric chloride, the dosage ratio of oxyferric chloride to anhydrous ethanol is 80 mg:300 mL.

8. Use of the heterogeneous Fenton self-cleaning catalytic membrane according to claim 1 or the heterogeneous Fenton self-cleaning catalytic membrane prepared by the method according to any one of claims 2 to 7 in wastewater treatment.

9. The use according to claim 8, characterized in that: The application is the application in treating wastewater by membrane distillation process; in the process of treating wastewater by membrane distillation process, H2O2 is added to the wastewater, and then one side of the heterogeneous Fenton self-cleaning catalytic membrane loaded with the oxyferric chloride catalyst layer is contacted with the wastewater.

10. The use according to claim 8 or 9, characterized in that: The wastewater includes dye wastewater, antibiotic wastewater or surfactant wastewater.

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