PVDF separation membrane and integrated process for treating printing and dyeing wastewater

Abstract

The present application relates to wastewater treatment technical field, specifically to a kind of PVDF separation membrane and integrated process for treating printing and dyeing wastewater.The method adopts six-step process:1) PVDF microporous membrane pretreatment and pore adjustment;2) polydopamine primer preparation;3) alternatively depositing sodium polystyrene sulfonate and zirconium oxychloride octahydrate;4) aminomethyl phosphonic acid graft modification;5) UiO-66-NH2 type MOF epitaxial growth, and insert repair treatment strengthen interlayer coordination anchoring;6) stabilization treatment, enhance structural compactness.The membrane shows excellent removal performance to multi-sulfonic acid group anionic dyes, still maintains higher removal rate and flux recovery rate under high salt, complex working condition, effectively solves the problem of structural relaxation and selective removal of traditional PVDF membrane in high salt environment, and has good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a PVDF separation membrane and an integrated process for treating dyeing and printing wastewater. Background Technology

[0002] As a traditional pillar industry, the dyeing and printing industry has generated dyeing and printing wastewater during its rapid development. Dyeing and printing wastewater is characterized by large volume, high concentration of organic pollutants, deep color, high salt content, and large pH fluctuations. The reactive dyes contained in it have complex molecular structures and large molecular weights. In particular, anionic dyes such as Reactive Black 5 exhibit strong hydrophilicity and high solubility due to the presence of multiple sulfonic acid groups, making them difficult to remove effectively using traditional biological and physicochemical treatment methods.

[0003] Membrane separation technology is widely used in the treatment of dyeing and printing wastewater due to its advantages such as high separation efficiency, simple operation, and relatively low energy consumption. Among them, polyvinylidene fluoride (PVDF) membranes have become an ideal substrate for dyeing and printing wastewater treatment due to their good chemical stability, thermal stability, and mechanical strength. However, traditional PVDF membranes face many technical challenges when treating high-salt dyeing and printing wastewater.

[0004] First, there is the issue of membrane structure stability. Dyeing and printing wastewater typically contains high concentrations of inorganic salts, such as sodium chloride and sodium sulfate. This high ionic strength environment leads to electrostatic double-layer compression, affecting the electrostatic repulsion of the membrane surface and consequently impacting the effective retention of pollutants. Simultaneously, ion exchange and displacement under high salinity conditions easily cause the leaching and deactivation of functional groups on the membrane surface, resulting in membrane structure relaxation and decreased separation performance.

[0005] Secondly, there is the issue of pollutant removal efficiency. Anionic dye molecules typically contain multiple sulfonic acid groups, which easily form aggregates in high-salt environments, increasing the complexity of separation. Traditional membrane materials often lack the ability to specifically recognize and capture these types of pollutants, resulting in low removal efficiency. Especially in simulated dyeing and printing wastewater containing salt, the electrostatic interaction between the membrane and dye molecules is weakened due to the shielding effect of salt ions, further reducing the separation effect.

[0006] In existing technologies, researchers have attempted to improve membrane separation performance through methods such as surface modification and the introduction of functional groups. However, these methods often suffer from problems such as short-lived modification effects and poor stability under complex operating conditions. The introduction of metal-organic framework materials provides a new approach to membrane modification, but traditional preparation methods are prone to random nucleation, resulting in discontinuous membrane layers that affect separation performance and the mechanical properties of the membrane.

[0007] Furthermore, membrane fouling is a significant factor limiting the industrial application of membrane technology. Dye molecules in dyeing and printing wastewater are prone to irreversible adsorption on the membrane surface, leading to decreased membrane flux and deteriorated separation performance. Although membrane performance can be restored through chemical cleaning, frequent cleaning not only increases operating costs but may also damage the membrane structure.

[0008] Therefore, there is an urgent need to develop a membrane treatment technology that can maintain structural stability in high-salt environments and efficiently remove anionic dyes to meet the actual needs of dyeing and printing wastewater treatment. Summary of the Invention

[0009] In view of this, the purpose of this invention is to propose a PVDF separation membrane and an integrated process for treating dyeing and printing wastewater, so as to solve the problems of structural instability and low pollutant removal efficiency of existing dyeing and printing wastewater treatment membranes in high-salt environments.

[0010] To achieve the above objectives, this invention provides a PVDF separation membrane and an integrated process for treating dyeing and printing wastewater, comprising the following steps:

[0011] (1) Pretreatment and pore adjustment of polyvinylidene fluoride membrane: The polyvinylidene fluoride microporous membrane was immersed in anhydrous ethanol, then transferred to a mixed solution of 1-methyl-2-pyrrolidone and deionized water, rinsed with deionized water, and finally immersed in a mixed solution of glycerol and deionized water. It was then taken out and air-dried until the surface was dry.

[0012] (2) Preparation of polydopamine base coating: Dissolve dopamine hydrochloride in tris(hydroxymethyl)aminomethane buffer, immerse the membrane prepared in step (1) in it, react on a shaker, then rinse with deionized water and dry with nitrogen;

[0013] (3) Prepare sodium polystyrene sulfonate aqueous solution and zirconium oxychloride octahydrate aqueous solution respectively. The membrane prepared in step (2) is treated for multiple complete cycles under room temperature conditions, with the process of impregnation with sodium polystyrene sulfonate aqueous solution, rinsing with deionized water, impregnation with zirconium oxychloride octahydrate aqueous solution, and rinsing with deionized water as one cycle. The time is shortened during the last zirconium ion impregnation.

[0014] (4) Aminomethylphosphonic acid grafting modification: Add aminomethylphosphonic acid to 2-morpholine ethane sulfonic acid buffer, stir at room temperature, immerse the membrane prepared in step (3) into it, take it out and rinse it with deionized water;

[0015] (5) UiO-66-NH2 epitaxial growth: Precursor solution A is a solution of zirconium tetrachloride and N,N-dimethylformamide, and precursor solution B is a solution of 2-aminoterephthalic acid and N,N-dimethylformamide. The membrane prepared in step (4) is sequentially immersed in precursor solution A, N,N-dimethylformamide rinse, precursor solution B, and N,N-dimethylformamide rinse to form one liquid phase epitaxial cycle. Multiple cycles are performed. After the liquid phase epitaxial cycle is completed, a short-term sodium polystyrene sulfonate-zirconium ion repair treatment is inserted.

[0016] (6) Stabilization treatment: The membrane prepared in step (5) is shaken in sodium chloride solution, then rinsed thoroughly with deionized water until the conductivity of the washing solution is less than 10 μS / cm, and dried with nitrogen to obtain PVDF separation membrane;

[0017] In step (3), the time for the last zirconium ion impregnation is 20-40s; in step (5), the sodium polystyrene sulfonate-zirconium ion repair treatment includes immersing the membrane in a sodium polystyrene sulfonate solution and then immersing it in an aqueous solution of zirconium oxychloride octahydrate.

[0018] Preferably, in step (1), the pore size of the polyvinylidene fluoride microporous membrane is 220 nm.

[0019] Preferably, in step (1), the soaking time in anhydrous ethanol is 8-12 min, the mass ratio of 1-methyl-2-pyrrolidone to deionized water is 50:50-90:10, the soaking time in the mixed solution is 20-40 min, and the concentration of glycerol is 8%-12%.

[0020] Preferably, in step (2), the concentration of the tris(hydroxymethyl)aminomethane buffer solution is 8-12 mmol / L, the pH value is 8.2-8.8, the concentration of dopamine hydrochloride is 1.5-2.5 mg / mL, the reaction temperature is 20-30℃, and the reaction time is 1.5-2.5 h.

[0021] Preferably, in step (3), the concentration of sodium polystyrene sulfonate is 3-7 mg / mL, the average molecular weight of sodium polystyrene sulfonate is 50,000-100,000 Da, the concentration of zirconium oxychloride octahydrate is 3-7 mmol / L, the number of coordination layer cycles is 3-7, the immersion time of sodium polystyrene sulfonate aqueous solution is 3-7 min, and the immersion time of zirconium oxychloride octahydrate aqueous solution is 1-3 min.

[0022] Preferably, in step (4), the concentration of the 2-morpholine ethane sulfonic acid buffer is 40-60 mmol / L, the pH value is 5.2-5.8, the amount of aminomethylphosphonic acid is 20-40 mg, the stirring time at room temperature is 20-40 min, and the membrane immersion time is 8-12 min.

[0023] Preferably, in step (5), the concentration of zirconium tetrachloride is 8-12 mmol / L, the concentration of glacial acetic acid in precursor solution A is 15-25 mmol / L, the concentration of 2-aminoterephthalic acid is 8-12 mmol / L, the epitaxial growth temperature is 45-55℃, the number of liquid phase epitaxial cycles is 3-7, and the immersion time of both precursor solution A and precursor solution B is 8-12 min.

[0024] Preferably, in the sodium polystyrene sulfonate-zirconium ion remediation treatment, the immersion time of the sodium polystyrene sulfonate solution is 1.5-2.5 min, the immersion time of the zirconium oxychloride octahydrate aqueous solution is 20-40 s, and the remediation treatment frequency is 1-3 times.

[0025] Preferably, in step (6), the concentration of sodium chloride is 0.8-1.2 mol / L, and the shaking time is 8-12 min.

[0026] Furthermore, the present invention also provides a PVDF separation membrane.

[0027] Furthermore, the present invention also provides an integrated process for treating dyeing and printing wastewater, using a PVDF separation membrane as the core physical filtration unit, comprising the following steps:

[0028] The dyeing and printing wastewater first passes through a screen to remove slag and then enters an equalization tank for water quality homogenization and pH adjustment before entering a coagulation and sedimentation unit. Inorganic polymeric flocculants and coagulants are added to achieve preliminary purification. The coagulated and sedimented wastewater then passes through a sand filter and an activated carbon fine filter in sequence, and then through a PVDF separation membrane for precision filtration. The filtered water then enters an advanced oxidation unit using ozone and hydrogen peroxide for oxidation. The clarified liquid after oxidation is disinfected by ultraviolet light and then collected in a clear water tank.

[0029] Preferably, the pH is maintained between 6.5 and 8.0.

[0030] Preferably, the dosage of the coagulant (PAC) is 60-100 mg / L, the dosage of the coagulant aid (PAM) is 1-2 mg / L, and the settling time is 20-30 min.

[0031] Preferably, the PVDF separation membrane operates at a pressure of 0.1-0.3 MPa, a temperature of 20-35°C, a transmembrane pressure difference of 0.04 MPa, and a membrane flux of 20-30 L·m⁻². -2 ·h -1 .

[0032] Preferably, the sand filter has a filtration rate of 8-10 m / h.

[0033] Preferably, the activated carbon layer is 1.0-1.5m high and the contact time is 15-20min.

[0034] Preferably, the ozone concentration is 30-50 mg / L; the molar ratio of hydrogen peroxide to ozone is 0.3; and the oxidation time is 15-25 min.

[0035] Preferably, the ultraviolet light wavelength is 254 nm, and the irradiation dose is 30-40 mJ / cm. 2 .

[0036] The beneficial effects of this invention are mainly reflected in the following aspects:

[0037] Significantly improved structural stability: The synergistic effect of the undercoordinated zirconium site retention strategy and the alternating chemical tandem reinforcement mechanism effectively solves the problem of structural relaxation of traditional membranes under high-salt environments. The undercoordinated zirconium sites, acting as endogenous nucleation centers, guide the directional epitaxial growth of the metal-organic framework material, avoiding discontinuities in the membrane layer caused by random nucleation. The alternating sodium polystyrene sulfonate-zirconium ion repair layer forms a reinforced anchoring network between the coordination layer and the metal-organic framework layer, significantly improving the stability of the membrane structure under complex operating conditions.

[0038] Excellent pollutant removal performance: The membrane prepared in this invention exhibits excellent removal performance for anionic dyes, especially high selectivity for polysulfonic acid dyes such as RB5. By introducing 2-aminoterephthalic acid to construct the UiO-66-NH2 structure, protonable sites are formed on the membrane surface. Even in the environment of high ionic strength dyeing wastewater, effective capture and removal of dye molecules can still be achieved through electrostatic attraction and hydrogen bonding synergistic effect.

[0039] Outstanding antifouling performance: The aminomethylphosphonic acid grafting modification technology provides stronger coordination anchoring force than traditional sulfonic acid groups through hard acid-hard base coordination, significantly improving the membrane's chemical stability and resistance to ion displacement. This enhanced interfacial bonding not only inhibits ligand leaching under high-salt conditions but also enables dye molecules to interact with the membrane surface primarily through reversible adsorption-desorption, greatly reducing irreversible fouling and ensuring the membrane's flux recovery capability during long-term operation.

[0040] Enhanced interfacial adhesion: The introduction of the polydopamine undercoat provides abundant adhesion sites for the membrane structure, significantly enhancing the interfacial adhesion between the functional layer and the polyvinylidene fluoride undercoat. This interfacial enhancement mechanism not only improves the overall structural stability of the membrane but also improves load transfer, enabling the membrane to maintain good structural integrity under mechanical stress.

[0041] High process adaptability: The membrane treatment method of this invention has good adaptability to the complex composition of dyeing and printing wastewater, and can maintain stable separation performance under various operating conditions such as pH fluctuations, high ionic strength, and the presence of surfactants. The stabilization treatment process makes the membrane structure more compact and stable through ionic strength-induced interfacial compaction and secondary coordination rearrangement, reducing leaching and defect regeneration in the early stage of operation.

[0042] Overall Performance Coordination: This invention successfully achieves a coordinated balance between membrane separation performance, antifouling performance, and mechanical properties, providing a technically feasible solution for the industrial treatment of dyeing and printing wastewater. The membrane material possesses both high dye removal rate and good flux recovery capability, while maintaining suitable mechanical strength, meeting multiple requirements for practical applications. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Example 1:

[0044] Step 1: Pretreatment and pore adjustment of polyvinylidene fluoride membrane. One polyvinylidene fluoride microporous membrane (pore size 220nm) with a diameter of 47mm was immersed in anhydrous ethanol for 8 minutes, then transferred to a mixed solution of 50mL 1-methyl-2-pyrrolidone and 50mL deionized water for 20 minutes, rinsed with deionized water for 8 minutes, and finally immersed in a mixed solution of 8mL glycerol and 92mL deionized water for 8 minutes. After that, it was removed and air-dried until the surface was dry.

[0045] Step 2: Preparation of polydopamine base coating: Dissolve 300 mg of dopamine hydrochloride in 200 mL of tris(hydroxymethyl)aminomethane buffer (8 mmol / L, pH 8.2), immerse the membrane prepared in Step 1 in it, and react in a shaker at 20 °C for 1.5 h, gently shaking every 30 min to ensure uniform deposition. Then rinse thoroughly with deionized water and dry with nitrogen.

[0046] Step 3: Prepare 200 mL of 3 mg / mL sodium polystyrene sulfonate (average molecular weight 50000 Da) aqueous solution and 200 mL of 3 mmol / L zirconium oxychloride octahydrate aqueous solution. Perform three complete cycles of treatment on the membrane prepared in Step 2 at room temperature, with the process consisting of immersion in sodium polystyrene sulfonate aqueous solution for 3 min, rinsing with deionized water for 1 min, immersion in zirconium oxychloride aqueous solution for 1 min, and rinsing with deionized water for 1 min. In the last zirconium ion immersion, shorten the time to 20 seconds.

[0047] Step 4: Aminomethylphosphonic acid grafting modification: Add 20 mg aminomethylphosphonic acid to 100 mL of 2-morpholine ethane sulfonic acid buffer (40 mmol / L, pH 5.2), stir at room temperature for 20 min, immerse the membrane prepared in step 3 for 8 min, and then rinse with deionized water.

[0048] Step 5: UiO-66-NH2 epitaxial growth. Precursor solution A is an 8 mmol / L zirconium tetrachloride N,N-dimethylformamide solution (containing 15 mmol / L glacial acetic acid). Precursor solution B is an 8 mmol / L 2-aminoterephthalic acid N,N-dimethylformamide solution. Under 45℃, the membrane prepared in Step 4 is sequentially immersed in precursor solution A for 8 min, rinsed with N,N-dimethylformamide for 1 min, then in precursor solution B for 8 min, and rinsed with N,N-dimethylformamide for 1 min, which constitutes one liquid phase epitaxial cycle. A total of 3 cycles are performed. After the second liquid phase epitaxial cycle, a short-term sodium polystyrene sulfonate-zirconium ion repair treatment is inserted, that is, the membrane is immersed in 3 mg / mL sodium polystyrene sulfonate solution for 1.5 min, then immersed in 3 mmol / L zirconium oxychloride octahydrate aqueous solution for 20 s, and then the subsequent liquid phase epitaxial growth continues.

[0049] Step 6: Stabilization treatment. The membrane prepared in step 5 is shaken in 0.8 mol / L sodium chloride solution for 8 min, then thoroughly rinsed with deionized water until the conductivity of the washing solution is less than 10 μS / cm, and dried with nitrogen to obtain the PVDF separation membrane. Example 2:

[0050] Step 1: Pretreatment and pore adjustment of polyvinylidene fluoride membrane. One polyvinylidene fluoride microporous membrane (pore size 220nm) with a diameter of 47mm was immersed in anhydrous ethanol for 10min, then transferred to a mixed solution of 70mL 1-methyl-2-pyrrolidone and 30mL deionized water for 30min, rinsed with deionized water for 10min, and finally immersed in a mixed solution of 10mL glycerol and 90mL deionized water for 10min. Remove and air dry until the surface is dry.

[0051] Step 2: Preparation of polydopamine base coating: Dissolve 400 mg of dopamine hydrochloride in 200 mL of tris(hydroxymethyl)aminomethane buffer (10 mmol / L, pH 8.5), immerse the membrane prepared in Step 1 in it, and react in a shaker at 25 °C for 2 h, gently shaking every 30 min to ensure uniform deposition. Then rinse thoroughly with deionized water and dry with nitrogen.

[0052] Step 3: Prepare 200 mL of 5 mg / mL sodium polystyrene sulfonate (average molecular weight 70000 Da) aqueous solution and 200 mL of 5 mmol / L zirconium oxychloride octahydrate aqueous solution. Perform 5 complete cycles of treatment on the membrane prepared in Step 2 at room temperature, with the following steps: immersion in sodium polystyrene sulfonate aqueous solution for 5 min, rinsing with deionized water for 1 min, immersion in zirconium oxychloride aqueous solution for 2 min, and rinsing with deionized water for 1 min. In the last zirconium ion immersion, shorten the time to 30 seconds.

[0053] Step 4: Aminomethylphosphonic acid grafting modification: Add 30 mg of aminomethylphosphonic acid to 100 mL of 2-morpholine ethane sulfonic acid buffer (50 mmol / L, pH 5.5), stir at room temperature for 30 min, immerse the membrane prepared in step 3 for 10 min to allow aminomethylphosphonic acid to coordinate and anchor with zirconium sites, and then rinse with deionized water.

[0054] Step 5: UiO-66-NH2 epitaxial growth. Precursor solution A is a 10 mmol / L zirconium tetrachloride N,N-dimethylformamide solution (containing 20 mmol / L glacial acetic acid). Precursor solution B is a 10 mmol / L 2-aminoterephthalic acid N,N-dimethylformamide solution. Under 50℃ conditions, the membrane prepared in Step 4 is sequentially immersed in precursor solution A for 10 min, rinsed with N,N-dimethylformamide for 1 min, then in precursor solution B for 10 min, and rinsed with N,N-dimethylformamide for 1 min, which constitutes one liquid phase epitaxial cycle. A total of 5 cycles are performed. After the 2nd and 4th liquid phase epitaxial cycles, a short-term sodium polystyrene sulfonate-zirconium ion repair treatment is performed, that is, the membrane is immersed in 5 mg / mL sodium polystyrene sulfonate solution for 2 min, and then immersed in 5 mmol / L zirconium oxychloride octahydrate aqueous solution for 30 s, and then the subsequent liquid phase epitaxial growth continues.

[0055] Step 6: Stabilization treatment. The membrane prepared in step 5 is shaken in a 1 mol / L sodium chloride solution for 10 min, then rinsed thoroughly with deionized water until the conductivity of the washing solution is less than 10 μS / cm, and dried with nitrogen to obtain the PVDF separation membrane. Example 3:

[0056] Step 1: Pretreatment and pore adjustment of polyvinylidene fluoride membrane. One polyvinylidene fluoride microporous membrane (pore size 220nm) with a diameter of 47mm was immersed in anhydrous ethanol for 12min, then transferred to a mixed solution of 90mL 1-methyl-2-pyrrolidone and 10mL deionized water and immersed for 40min. Then it was rinsed with deionized water for 12min. Finally, it was immersed in a mixed solution of 12mL glycerol and 88mL deionized water for 12min. After that, it was removed and air-dried until the surface was dry.

[0057] Step 2: Preparation of polydopamine base coating. Dissolve 500 mg of dopamine hydrochloride in 200 mL of tris(hydroxymethyl)aminomethane buffer (12 mmol / L, pH 8.8), immerse the membrane prepared in Step 1 in it, and react in a shaker at 30 °C for 2.5 h. During the reaction, gently shake every 30 min to ensure uniform deposition. Then rinse thoroughly with deionized water and dry with nitrogen.

[0058] Step 3: Prepare 200 mL of 7 mg / mL sodium polystyrene sulfonate (average molecular weight 100,000 Da) aqueous solution and 200 mL of 7 mmol / L zirconium oxychloride octahydrate aqueous solution. Perform 7 complete cycles of treatment on the membrane prepared in Step 2 at room temperature, with the following steps: immersion in sodium polystyrene sulfonate aqueous solution for 7 min, rinsing with deionized water for 1 min, immersion in zirconium oxychloride aqueous solution for 3 min, and rinsing with deionized water for 1 min. In the last zirconium ion immersion, shorten the time to 40 seconds.

[0059] Step 4: Aminomethylphosphonic acid grafting modification: Add 40 mg of aminomethylphosphonic acid to 100 mL of 2-morpholine ethane sulfonic acid buffer (60 mmol / L, pH 5.8), stir at room temperature for 40 min, immerse the membrane prepared in step 3 for 12 min to allow aminomethylphosphonic acid to coordinate and anchor with zirconium sites, and then rinse with deionized water.

[0060] Step 5: UiO-66-NH2 epitaxial growth. Precursor solution A is a 12 mmol / L zirconium tetrachloride N,N-dimethylformamide solution (containing 25 mmol / L glacial acetic acid). Precursor solution B is a 12 mmol / L 2-aminoterephthalic acid N,N-dimethylformamide solution. Under 55℃, the membrane prepared in Step 4 is sequentially immersed in precursor solution A for 12 min, rinsed with N,N-dimethylformamide for 1 min, then in precursor solution B for 12 min, and rinsed with N,N-dimethylformamide for 1 min, which constitutes one liquid phase epitaxial cycle. A total of 7 cycles are performed. After the 2nd, 4th, and 6th liquid phase epitaxial cycles, a short-term sodium polystyrene sulfonate-zirconium ion repair treatment is performed. That is, the membrane is immersed in 7 mg / mL sodium polystyrene sulfonate solution for 2.5 min, then immersed in 7 mmol / L zirconium oxychloride octahydrate aqueous solution for 40 s, and then the subsequent liquid phase epitaxial growth is continued.

[0061] Step 6: Stabilization treatment. The membrane prepared in step 5 is shaken in a 1.2 mol / L sodium chloride solution for 12 min, then thoroughly rinsed with deionized water until the conductivity of the washing solution is less than 10 μS / cm, and dried with nitrogen to obtain the PVDF separation membrane.

[0062] Comparative Example 1:

[0063] The difference between Comparative Example 1 and Example 2 is that in step 5, 2-aminoterephthalic acid is replaced with terephthalic acid to obtain UiO-66 instead of UiO-66-NH2. The other conditions are the same as in Example 2.

[0064] Comparative Example 2:

[0065] The difference between Comparative Example 2 and Example 2 is that the final zirconium ion impregnation time was extended to 2 minutes, while the other conditions were the same as in Example 2.

[0066] Comparative Example 3:

[0067] The difference between Comparative Example 3 and Example 2 is that sodium polystyrene sulfonate-zirconium ion repair treatment was not inserted in the liquid phase epitaxial cycle, and 5 complete liquid phase epitaxial cycles were performed directly, while the other conditions were the same as in Example 2.

[0068] Comparative Example 4:

[0069] The difference between Comparative Example 4 and Example 2 is that the aminomethylphosphonic acid grafting modification step is omitted, and UiO-66-NH2 epitaxial growth is carried out directly after step 3. The other conditions are the same as those in Example 2.

[0070] Comparative Example 5:

[0071] The difference between Comparative Example 5 and Example 2 is that step 6, the stabilization treatment (sodium chloride solution treatment), is omitted, while the other conditions are the same as in Example 2.

[0072] Performance testing:

[0073] Removal performance of RB5 dye: The membranes obtained in Examples 1-3 and Comparative Examples 1-5 were used as samples. RB5 solution (100 mg / L) and simulated dyeing wastewater containing salt (RB5 100 mg / L, Na2SO4 2 g / L, NaCl 1 g / L) were prepared at room temperature and used as feed solutions for single-component and compound evaluation, respectively. After pre-pressurization with pure water at 0.1 MPa for 30 min, filtration was performed under a transmembrane pressure difference of 0.1 MPa and a cross-flow velocity of 0.2 m / s, and samples were taken after 2 hours of continuous operation. The concentration of RB5 in the feed and permeate was determined by UV-Vis spectrophotometry at the maximum absorption peak, and the removal rate was calculated. The results are shown in Table 1.

[0074] Membrane antifouling performance: A dynamic fouling-washing cycle was used. Each sample was filtered through a 100 mg / L RB5 solution at 0.1 MPa for 4 hours, and flux decay was recorded. Subsequently, the membrane was rinsed with deionized water for 30 min, chemically washed with 0.1 mol / L NaOH for 15 min, and then replaced with pure water for 10 min. The pure water flux recovery rate was then measured. This cycle was repeated 10 times, and the flux recovery rate was calculated. To simulate the interference of salt / dye coexistence in the dyeing and printing process, the same cycle was performed with simulated saline wastewater, and the flux recovery rate was calculated again. The results are shown in Table 1.

[0075] Mechanical properties: Tensile strength and elongation at break were determined using a universal testing machine; the samples were cut into standard dumbbell-shaped specimens and tested at a clamping distance of 25 mm and a speed of 50 mm / min. The results are shown in Table 1.

[0076] Integrated Process Treatment: Using the PVDF separation membrane obtained in Example 2 as the core physical filtration unit, actual dyeing and printing wastewater with the following water quality indicators was used: COD 950 mg / L, color 600 times, SS 150 mg / L. The wastewater was treated using an integrated process: screen slag removal - equalization tank - coagulation sedimentation (PAC+PAM) - sand filtration - activated carbon adsorption - PVDF membrane filtration - ozone / hydrogen peroxide advanced oxidation - ultraviolet disinfection. The process parameters were: pH between 6.5 and 8.0, coagulant dosage 80 mg / L, coagulant aid (PAM) dosage 2 mg / L, settling time 25 min; PVDF separation membrane operating pressure 0.2 MPa, temperature 25℃, transmembrane pressure difference 0.04 MPa, membrane flux 25 L·m³. -2 ·h -1 Sand filtration rate: 9 m / h; activated carbon layer height: 1.0 m; contact time: 15 min; ozone concentration: 40 mg / L; hydrogen peroxide to ozone molar ratio: 0.3; oxidation time: 20 min; ultraviolet wavelength: 254 nm; irradiation dose: 35 mJ / cm². 2 COD, color, and SS in the water were measured again, and the test results are shown in Table 2.

[0077] Table 1 Performance Test Results

[0078]

[0079] Table 2. Changes in water quality before and after integrated treatment of dyeing and printing wastewater

[0080]

[0081] Data Analysis:

[0082] As can be seen from the data in Examples 1-3 in Table 1, the prepared membranes maintained high removal rates and flux recovery rates in both RB5 single-component solutions and simulated dyeing wastewater containing inorganic salts, while also maintaining tensile strength and elongation at break, demonstrating adaptability to conditions such as high ionic strength, surfactants, and pH fluctuations. This may be due to the shortening of the final zirconium ion impregnation time to retain undercoordinated zirconium sites, which serve as endogenous nucleation centers to guide the directional epitaxy of the metal-organic coordination network constructed by zirconium tetrachloride and 2-aminoterephthalic acid at the interface, reducing the risk of discontinuity caused by random nucleation; the insertion of sodium polystyrene sulfonate-zirconium ions for short-term repair during the liquid-phase epitaxy cycle to strengthen the anchoring of grain boundaries and uncovered domains, inhibiting leaching and interlayer relaxation under high salt conditions; the grafting of aminomethylphosphonic acid to improve anchor point density and ion exchange resistance through hard acid-hard base coordination, allowing the separation layer to remain dense and hydrophilic even when the electrical double layer is compressed; and the polydopamine undercoating layer to enhance interfacial adhesion and load transfer with the polyvinylidene fluoride undercoating. The aforementioned synergy enables parallel control of RB5 screening and reversible weak interactions, thereby achieving high flux recovery and stable retention even after long-term dynamic contamination-cleaning cycles.

[0083] As can be seen from Table 2, the integrated treatment process of this invention produces transparent, colorless, and odorless effluent with a COD removal rate of 95.3% and a color removal rate of 97.5%. All indicators meet and exceed the Class I standard requirements of the "Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry".

[0084] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, the removal rates of both are similar in the RB5 single-component system. However, in terms of the salt-containing compound system and flux recovery rate, Example 2 performs better (compound removal rate 97.8%, flux recovery rate 97.3%). Based on this, it can be inferred that after replacing terephthalic acid with 2-aminoterephthalic acid, protonable sites are formed on the separation layer surface. Under typical dyeing salt conditions (sodium chloride and sodium sulfate cause electro-bilayer compression), it can still provide electrostatic attraction and reversible capture of Reactive Black 5 with polysulfonic acid groups through hydrogen bonding, thereby reducing irreversible contamination while maintaining high selectivity.

[0085] As can be seen from the data in Table 1 for Example 2 and Comparative Example 2, extending the final zirconium ion impregnation time to 2 minutes in Comparative Example 2 resulted in a simultaneous decrease in both the compound removal rate and flux recovery rate (compound removal rate 86.9%, flux recovery rate 86.8%), indicating that this variable is sensitive to the stability of the interlayer structure and the reversibility of contamination. Based on this, it is speculated that: a shorter impregnation time helps retain the density of undercoordinated zirconium sites, promoting the directional epitaxy of subsequent organic ligands at the interface and reducing random nucleation on the solution side; extending the time may lead to oversaturation and recoordination of surface zirconium sites, weakening active anchor points and epitaxial orientation, and resulting in insufficient grain boundary splicing and the formation of soft defects.

[0086] As can be seen from the data in Table 1 for Example 2 and Comparative Example 3, Comparative Example 3 did not have the alternating repair setting, and the compound removal rate and flux recovery rate in Table 1 were both lower than those of Example 2 (compound removal rate 82.4%, flux recovery rate 83.5%). Inserting sodium polystyrene sulfonate-zirconium ion short-term repair between each round of liquid phase epitaxy can directionally fill uncovered domains and grain boundaries, constructing a high-density coordination anchoring network between layers, thereby reducing the propagation of micro-defects and interlayer leaching under high ionic strength; without this step, the intergranular overlap and interface compactness are insufficient, and under the action of salt crossflow and cleaning stress, interface micro-cracks and local desorption are more likely to occur, forming bypass channels and contamination anchors for RB5, resulting in a simultaneous decrease in compound selectivity and cleaning reversibility.

[0087] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, after omitting the aminomethylphosphonic acid grafting in Comparative Example 4, the compound removal rate and flux recovery rate decreased (90.8% and 88.7%, respectively). It is speculated that aminomethylphosphonic acid forms a strong hard acid-hard base coordination with zirconium ions. Compared with the sulfonic acid anchoring of sodium polystyrene sulfonate alone, it can improve the anchor point density and the resistance to ion replacement, and inhibit the interlayer relaxation and ligand leaching induced by sodium chloride, sodium sulfate and other ions. At the same time, the grafting improves the hydrophilicity and energy uniformity of the interface, so that RB5 mainly acts on the surface in a reversible adsorption-desorption manner during the operation and cleaning stages, reducing the proportion of irreversible pollution, thereby achieving higher flux recovery after circulation.

[0088] As can be seen from the data in Table 1 for Example 2 and Comparative Example 5, after omitting the stabilization treatment in Comparative Example 5, the compound removal rate and flux recovery rate in Table 1 were further reduced (88.9% and 84.2%, respectively), indicating that short-term salt stabilization has a positive effect on structural shaping under complex matrices. Stabilization in an appropriate concentration of sodium chloride solution induces interfacial compaction and secondary coordination rearrangement by ionic strength, making the anchoring of the sodium polystyrene sulfonate-zirconium and 2-aminoterephthalic acid-zirconium networks more stable, and replacing weakly bound small molecules and residual ion sources, reducing leaching and defect regeneration in the early stages of operation. Without this step, the weak interlayer coordination is more easily destroyed under cross-flow shearing and cleaning chemistry, forming propagable micro-defects and contamination anchors. The bypass transport and irreversible contamination of RB5 in saline dyeing wastewater are amplified, thus leading to a synergistic decrease in selectivity and flux recovery.

[0089] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a PVDF separation membrane, characterized in that, Including the following steps: (1) Pretreatment and pore adjustment of polyvinylidene fluoride membrane: The polyvinylidene fluoride microporous membrane was immersed in anhydrous ethanol, then transferred to a mixed solution of 1-methyl-2-pyrrolidone and deionized water, rinsed with deionized water, and finally immersed in a mixed solution of glycerol and deionized water. It was then taken out and air-dried until the surface was dry. (2) Preparation of polydopamine base coating: Dissolve dopamine hydrochloride in tris(hydroxymethyl)aminomethane buffer, immerse the membrane prepared in step (1) in it, react on a shaker, then rinse with deionized water and dry with nitrogen; (3) Prepare sodium polystyrene sulfonate aqueous solution and zirconium oxychloride octahydrate aqueous solution respectively. The membrane prepared in step (2) is treated for multiple complete cycles under room temperature conditions, with the process of impregnation with sodium polystyrene sulfonate aqueous solution, rinsing with deionized water, impregnation with zirconium oxychloride octahydrate aqueous solution, and rinsing with deionized water as one cycle. The time is shortened during the last zirconium ion impregnation. (4) Aminomethylphosphonic acid grafting modification: Add aminomethylphosphonic acid to 2-morpholine ethane sulfonic acid buffer, stir at room temperature, immerse the membrane prepared in step (3) into it, so that aminomethylphosphonic acid coordinates and anchors with the zircon sites in the intermediate layer, and rinse with deionized water after taking it out. (5) UiO-66-NH2 epitaxial growth: Precursor solution A is a solution of zirconium tetrachloride and N,N-dimethylformamide, and precursor solution B is a solution of 2-aminoterephthalic acid and N,N-dimethylformamide. The membrane prepared in step (4) is sequentially immersed in precursor solution A, N,N-dimethylformamide rinse, precursor solution B, and N,N-dimethylformamide rinse to form one liquid phase epitaxial cycle. Multiple cycles are performed. After the liquid phase epitaxial cycle is completed, a short-term sodium polystyrene sulfonate-zirconium ion repair treatment is inserted. (6) Stabilization treatment: The membrane prepared in step (5) is shaken in sodium chloride solution, then rinsed thoroughly with deionized water until the conductivity of the washing solution is less than 10 μS / cm, and dried with nitrogen to obtain PVDF separation membrane; In step (3), the time for the last zirconium ion impregnation is 20-40s; in step (5), the sodium polystyrene sulfonate-zirconium ion repair treatment includes immersing the membrane in a sodium polystyrene sulfonate solution and then immersing it in an aqueous solution of zirconium oxychloride octahydrate.

2. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the tris(hydroxymethyl)aminomethane buffer is 8-12 mmol / L, the pH value is 8.2-8.8, the concentration of dopamine hydrochloride is 1.5-2.5 mg / mL, the reaction temperature is 20-30℃, and the reaction time is 1.5-2.5 h.

3. The preparation method according to claim 1, characterized in that, In step (3), the concentration of sodium polystyrene sulfonate is 3-7 mg / mL, the average molecular weight of sodium polystyrene sulfonate is 50,000-100,000 Da, the concentration of zirconium oxychloride octahydrate is 3-7 mmol / L, the number of coordination layer cycles is 3-7, the immersion time of sodium polystyrene sulfonate aqueous solution is 3-7 min, and the immersion time of zirconium oxychloride octahydrate aqueous solution is 1-3 min.

4. The preparation method according to claim 1, characterized in that, In step (4), the concentration of the 2-morpholine ethane sulfonic acid buffer is 40-60 mmol / L, the pH value is 5.2-5.8, the amount of aminomethylphosphonic acid is 20-40 mg, the stirring time at room temperature is 20-40 min, and the membrane immersion time is 8-12 min.

5. The preparation method according to claim 1, characterized in that, In step (5), the concentration of zirconium tetrachloride is 8-12 mmol / L, the concentration of glacial acetic acid in precursor solution A is 15-25 mmol / L, the concentration of 2-aminoterephthalic acid is 8-12 mmol / L, the epitaxial growth temperature is 45-55℃, the number of liquid phase epitaxial cycles is 3-7, and the immersion time of both precursor solution A and precursor solution B is 8-12 min.

6. The preparation method according to claim 1, characterized in that, In the sodium polystyrene sulfonate-zirconium ion remediation treatment, the immersion time of the sodium polystyrene sulfonate solution is 1.5-2.5 min, the immersion time of the zirconium oxychloride octahydrate aqueous solution is 20-40 s, and the remediation treatment frequency is 1-3 times.

7. The preparation method according to claim 1, characterized in that, In step (6), the concentration of sodium chloride is 0.8-1.2 mol / L, and the shaking time is 8-12 min.

8. A PVDF separation membrane, characterized in that, It is prepared according to any one of claims 1-7.

9. An integrated process for treating dyeing and printing wastewater, characterized in that, Using the PVDF separation membrane of claim 8 as the core physical filtration unit, the method includes the following steps: The dyeing and printing wastewater first passes through a screen to remove slag and then enters an equalization tank for water quality homogenization and pH adjustment before entering a coagulation and sedimentation unit. Inorganic polymeric flocculants and coagulants are added to achieve preliminary purification. The coagulated and sedimented wastewater then passes through a sand filter and an activated carbon fine filter in sequence, and then through a PVDF separation membrane for precision filtration. The filtered water then enters an advanced oxidation unit using ozone and hydrogen peroxide for oxidation. The clarified liquid after oxidation is disinfected by ultraviolet light and then collected in a clear water tank.

10. The integration process according to claim 9, characterized in that, The PVDF separation membrane operates at a pressure of 0.1-0.3 MPa, a temperature of 20-35℃, a transmembrane pressure difference of 0.04 MPa, and a membrane flux of 20-30 L·m. -2 ·h -1 .

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