A photocatalytic membrane based on coordination of tannic acid and zinc ions, and a preparation method and application thereof

Abstract

The application discloses a kind of based on tannic acid and zinc ion coordination photocatalytic membrane and its preparation method and application, using the method of coordination pretreatment and ultrasonic assisted growth in combination prepares a kind of new multifunctional photocatalytic hollow fiber ultrafiltration membrane, under the condition of strong alkali environment and ultrasonic vibration, zinc ion can in situ growth between molecules under the coordination of tannic acid, so as to be fixed on tannic acid membrane tightly, not only obtain good hydrophilicity and antibacterial ability, but also effectively avoid the problem of easy to fall off and block membrane hole caused by directly loaded zinc oxide particles.The flux of the multifunctional photocatalytic hollow fiber ultrafiltration membrane (TA-ZnO membrane) prepared by the application is increased by 30% compared with the original membrane, and the highest reaches 170 L m ‑2 h ‑1 , and the rejection effect of bovine serum albumin always remains above 95% in long-term stability test, and has wide application prospect in complex wastewater purification treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic membranes, and particularly relates to a photocatalytic membrane based on tannic acid and zinc ion coordination and a preparation method and application thereof. BACKGROUND

[0002] Water is one of the indispensable elements in human daily life, however, water resource shortage and water pollution hinder the sustainable development of human economy and society. Among them, the slaughter wastewater produced by large-scale slaughter plants has become an important source of water pollution because of its large water quantity, uneven drainage, high concentration, and many impurities and suspended solids. In water environment treatment, hollow fiber ultrafiltration membrane technology has attracted the attention of many researchers because of its simple operation, high efficiency and low cost. At the same time, hollow fiber ultrafiltration membrane has the advantages of small occupied area, easy cleaning and convenient disassembly, and is more suitable for treating complex wastewater produced by large-scale slaughter industry. Many materials are used to construct hollow fiber ultrafiltration membrane to achieve better separation effect, such as polyvinylidene fluoride, polypropylene, polyether sulfone, etc.

[0003] However, no matter what material is used to prepare the membrane, the problem of irreversible pollution in the water purification process cannot be avoided. Irreversible pollution is the filter cake layer produced by the accumulation of pollutants in the membrane holes during long-term operation of the membrane. It is worth noting that the filter cake layer is extremely harmful to traditional ultrafiltration membranes, and the cleaning methods adopted can only remove the relatively loose reversible pollutants on the surface of the membrane, so it is particularly important to develop a new type of ultrafiltration membrane that can efficiently clean the membrane surface pollution.

[0004] Photocatalytic membrane and intelligent response type self-cleaning membrane are the most popular two kinds of multifunctional separation membranes at present. Among them, the photocatalytic membrane can generate O 2- and OH - under ultraviolet irradiation while ensuring the basic separation performance, which has shown significant advantages in pollutant degradation. In the work of Liuxin Li et al., a new type of multifunctional photocatalytic separation membrane based on single-component seaweed g-C3N4 was prepared, which showed excellent photocatalytic degradation, oil-water separation and antibacterial capacity, and the maximum flux reached 3114.0±113.0L m -2 h -1 bar -1For RhB, MB and CV, the photocatalytic degradation rate is up to 100%, and the degradation rate of bacteria is 100%. For example, the nitrogen-doped GO / TiO2 nanocomposite ultrafiltration membrane researched by Hang Xu et al. has excellent antifouling performance under ultraviolet light and natural light conditions, and the maximum FRR value under sunlight is 90.1%, and the maximum FRR value under ultraviolet light is 94.6%. The traditional photocatalytic membrane modification usually uses blending, deposition and nano-spraying technology, but the above modification methods will produce problems such as unstable membrane structure, membrane hole blockage or photocatalytic particle separation. SUMMARY

[0005] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification of the present application to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0006] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0007] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of a photocatalytic membrane based on coordination of tannic acid and zinc ions.

[0008] To solve the above technical problems, the present application provides the following technical scheme: comprising,

[0009] The polyvinylidene fluoride, lithium chloride and tannic acid after drying treatment are dissolved in N,N-dimethylacetamide to obtain a casting solution;

[0010] The coating solution after high-pressure degassing is moved to a volume pump for next dry-wet spinning treatment, and the spinning is finished after post-treatment to obtain a tannic acid hollow nanofiber membrane;

[0011] The tannic acid hollow nanofiber membrane is inserted into a cross-flow device, and zinc chloride solution is introduced for coordination reaction to realize the coordination of zinc ions and tannic acid, that is, to obtain the photocatalytic membrane based on the coordination of tannic acid and zinc ions.

[0012] As a preferred scheme of the preparation method of the photocatalytic membrane based on the coordination of tannic acid and zinc ions, the mass concentration of tannic acid in the coating solution is 0.5-2wt%.

[0013] As a preferred scheme of the preparation method of the photocatalytic membrane based on the coordination of tannic acid and zinc ions, the mass concentration of polyvinylidene fluoride in the coating solution is 12-14wt%, the mass concentration of lithium chloride is 1-2wt%, and the mass concentration of N,N-dimethylacetamide is 82-84wt%.

[0014] As a preferred scheme of the preparation method of the tannic acid and zinc ion coordination based photocatalytic membrane, in the dry-wet spinning process, the rotation speed of the volume pump is 8-14 rpm.

[0015] As a preferred scheme of the preparation method of the tannic acid and zinc ion coordination based photocatalytic membrane, in the dry-wet spinning process, the rotation speed of the volume pump is 8-14 rpm.

[0016] As a preferred scheme of the preparation method of the tannic acid and zinc ion coordination based photocatalytic membrane, in the dry-wet spinning process, the rotation speed of the volume pump is 8-14 rpm.

[0017] As a preferred scheme of the preparation method of the tannic acid and zinc ion coordination based photocatalytic membrane, in the dry-wet spinning process, the rotation speed of the volume pump is 8-14 rpm.

[0018] As a preferred scheme of the preparation method of the tannic acid and zinc ion coordination based photocatalytic membrane, in the dry-wet spinning process, the rotation speed of the volume pump is 8-14 rpm.

[0019] Another object of the present application is to provide a tannic acid and zinc ion coordination based photocatalytic membrane.

[0020] Another object of the present application is to provide a tannic acid and zinc ion coordination based photocatalytic membrane in slaughter wastewater separation.

[0021] The present application has the following advantages:

[0022] The present application adopts a method of coordination pretreatment and ultrasonic assisted growth to prepare a new type of multifunctional photocatalytic hollow fiber ultrafiltration membrane. Under the conditions of strong alkali environment and ultrasonic vibration, zinc ions coordinated with tannic acid can grow in situ between molecules, thereby being tightly fixed on the tannic acid membrane. Not only good hydrophilicity and antibacterial ability are obtained, but also the problems of easy falling and blocking of membrane pores caused by direct loading of zinc oxide particles are effectively avoided.

[0023] The flux of the multifunctional photocatalytic hollow fiber ultrafiltration membrane (TA-ZnO membrane) prepared by the present application is increased by 30% compared with the original membrane, and the highest flux reaches 170 L m -2 h -1And the rejection effect of bovine serum albumin always keeps above 95% in long-term stability test, effectively removes ammonia nitrogen, organic pollutants and suspended solids in slaughterhouse wastewater in long-term separation experiment, and the inhibition rate of TA-ZnO film on escherichia coli reaches 100% in terms of bacterial inhibition, so that the persistent multifunctional separation membrane has broad application prospect in the purification treatment of complex wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0025] Figure 1 The preparation flow chart of the photocatalytic membrane of embodiment 1 of the present application.

[0026] Figure 2 The SEM diagram of the surface of the TA-ZnO membrane prepared in embodiment 1 of the present application.

[0027] Figure 3 The ATR-FTIR spectrum characterization diagram of the TA-ZnO membrane prepared in embodiment 1 of the present application.

[0028] Figure 4 The surface, cross-sectional morphology and crystal growth state diagram of the tannic acid membrane with different zinc ion contents in embodiment 2 of the present application.

[0029] Figure 5 The surface morphology diagram of the PVDF in comparative example 2 of the present application.

[0030] Figure 6 The porosity comparison diagram of the TA-ZnO membrane obtained by in-situ growth of different coordination time in embodiment 2 and the membranes prepared in comparative example 1 and comparative example 2.

[0031] Figure 7 The performance comparison result diagram of the TA-ZnO membrane obtained by in-situ growth of different coordination time in embodiment 2 and the membranes prepared in comparative example 1 and comparative example 2.

[0032] Figure 8 The photocatalytic performance comparison result diagram of the TA-ZnO membrane obtained by in-situ growth of different coordination time in embodiment 2 and the membranes prepared in comparative example 1 and comparative example 2.

[0033] Figure 9 The photocatalytic cycle performance comparison diagram of the membranes prepared in embodiment 2 and comparative example 2 with bovine serum albumin as pollutants.

[0034] Figure 10The rejection flux and rejection rate results of the PVDF membrane of Comparative Example 2 in the photocatalytic circulation experiment.

[0035] Figure 11 The FRR graph of the PVDF membrane of Comparative Example 2 after 5 times of photocatalytic circulation.

[0036] Figure 12 The antibacterial effect comparison graph of the PVDF membrane, the TA membrane and the TA-ZnO membrane.

[0037] Figure 13 The membrane surface characterization graph of the PVDF membrane, the TA membrane and the TA-ZnO membrane after antibacterial.

[0038] Figure 14 The photocatalytic circulation performance test result graph of the TA-ZnO membrane of Example 1 with slaughter wastewater as the pollutant.

[0039] Figure 15 The slaughter wastewater before and after filtration of the TA-ZnO membrane of Example 1.

[0040] Figure 16 The electron microscope graphs of the surface and cross section of the TA membrane under different concentrations in Comparative Example 3.

[0041] Figure 17 The performance comparison graph of the TA membrane under different concentrations in Comparative Example 3.

[0042] Figure 18 The surface and interface graphs of the TA membrane obtained under different spinning conditions.

[0043] Figure 19 The performance comparison graph of the TA membrane obtained under different spinning conditions filtering bovine serum albumin solution.

[0044] Figure 20 The performance comparison graph of the TA membrane obtained under different spinning conditions filtering carbon ink. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below in combination with the description of the embodiments.

[0046] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be practiced in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the scope of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0047] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0048] Unless otherwise specified, all raw materials used in this invention are commercially available in the art, wherein:

[0049] Polyvinylidene fluoride (PVDF) was purchased from Solvay; N,N-dimethylacetamide (DMAC) was purchased from Shanghai Lingfeng and used as a polymer and solvent, respectively; tannic acid (TA) and sodium hydroxide (NaOH) were purchased from Shanghai Lingfeng; zinc chloride (ZnCl2) was purchased from Shanghai Maclean; bovine serum albumin (BSA) was purchased from Aladdin; and the slaughterhouse wastewater used in the application effect test came from a slaughterhouse in Beijing.

[0050] The performance of the membrane prepared in this invention was evaluated using the following method:

[0051] Permeation flux and repulsion properties

[0052] The pure water flux (PWF) and repulsion performance of the membrane were tested using a cross-flow filtration device under a transmembrane pressure (TMP) of 1 bar.

[0053] Before testing, the membrane was pre-pressed with pure water at a pressure of 2 bar for 20 minutes to ensure its stability.

[0054] The formula for calculating permeation flux is:

[0055] PWF = Q / (A×t)

[0056] Where Q is the infiltration volume (liters), A is the effective area (square meters), and t is the filtration time (minutes). In this experiment, A is the total area used, which is 17.5212 cm². 2 Two membrane filaments, each 15cm in length;

[0057] Retention performance was tested using a cross-flow system at a transmembrane pressure of 1 bar to assess the membrane's retention of bovine serum albumin (BSA). The retention rate was calculated using the following formula:

[0058] R = (1-C) p / C f )×100%

[0059] Where R is the retention rate (%), C p It is the permeate concentration (g / L), C f This is the concentration of the original solution (g / L).

[0060] Anti-pollution performance test

[0061] The tested membrane was rinsed with deionized water for 1 min, and then tested in pure water after soaking or light exposure for 1 hour;

[0062] The calculation formula of flux recovery rate is:

[0063] FRR = (J r / J w ) x 100%

[0064] Wherein, J w is the original membrane pure water flux (L / m 2 h), J r is the pure water flux after soaking or light exposure (L / m 2 h);

[0065] The calculation formula of reversible contamination rate R r is:

[0066] R r = [(J r -J L ) / J w ] x 100%

[0067] Wherein, J w is the original membrane pure water flux (L / m 2 h), J r is the pure water flux after soaking or light exposure (L / m 2 h), J L is the water flux when filtering bovine serum albumin (L / m 2 h);

[0068] The calculation formula of irreversible contamination rate R ir is:

[0069] R ir = [(J w -J r ) / J w ] x 100%

[0070] J w is the original membrane pure water flux (L / m 2 h), J r is the pure water flux after soaking or light exposure (L / m 2 h);

[0071] Antibacterial performance

[0072] The plate count method is used to inoculate the thawed E. coli into 50 ml of LB medium solution and cultivate in a 37°C and 200 rpm shaker for 14 hours. Subsequently, the cultured bacteria solution is diluted 100 times in a sterile physiological saline solution. 100 μL of the diluted bacteria solution is dropped onto the surface of the intercepted hollow fiber membrane, covered with a glass slide and sealed in a 37°C incubator for 1-2 hours. The cultured membrane and glass slide are immersed in 10 mL of physiological saline solution taken in advance, and shaken. 100 μL of the shaken and diluted bacteria solution is spread on the LB medium and inverted into a 37°C incubator for 12 hours. After the bacteria incubation, the number of bacteria colonies in the medium is observed.

[0073] Example 1

[0074] Reference Figure 1 The present embodiment provides a preparation method of a photocatalytic membrane based on tannic acid and zinc ion coordination, specifically:

[0075] 1) Polyvinylidene fluoride powder (PVDF) and lithium chloride powder (LiCl) are placed in a 70°C oven for 24 hours to remove moisture, and then dissolved in N,N-dimethylacetamide (DMAC) with tannic acid (TA), stirred at 75°C for 12 hours until completely dissolved to obtain a coating solution. In terms of mass concentration, the PVDF concentration in the coating solution is 14wt%, the DMAC is 83wt%, the LiCl is 2wt%, and the TA is 1wt%;

[0076] 2) The coating solution obtained in step 1) is poured into an autoclave and vacuum degassed, and the autoclave is pressurized to 3 bar using nitrogen, and the casting solution is pushed to the volume pump for the next dry-wet spinning process;

[0077] The roller speed is adjusted to 4.5 m / min, the volume pump speed is 10 rpm, the temperature is 75°C, the first stage coagulation bath temperature is 40°C, the roller coagulation bath temperature is 35°C, and the spinneret distance from the water surface is 40 cm, and the spinning is carried out;

[0078] After the spinning is completed, the membrane filaments on the roller are cut, soaked in ultrapure water for 15 hours, then soaked in a 20wt% glycerol solution for 12 hours, and finally the membrane filaments are dried to obtain TA hollow fiber membrane, denoted as TAHF.

[0079] 3) The TAHF is inserted into a cross-flow device, and 20 ppm ZnCl2 solution is introduced at a pressure of 1 bar for 30 minutes to coordinate zinc ions with tannic acid. Finally, the obtained TA-Zn 2+ is placed in a sodium hydroxide solution with pH = 11.5 for ultrasonic treatment for 3 hours to obtain a photocatalytic membrane based on tannic acid and zinc ion coordination, denoted as TA-ZnO.

[0080] Figure 2SEM images of TA-ZnO films surface were taken at 20K magnification, which showed that the in-situ grown ZnO nanoparticles were well embedded on the TA film surface. This structure made the ZnO nanoparticles not easy to fall off, and could maintain long-term photocatalytic ability.

[0081] Figure 3 The interaction between tannic acid and nano-ZnO was investigated by ATR-FTIR spectra, Figure 3 a peak at 3000-3500 cm -1 corresponding to the stretching vibration of tannic acid hydroxyl, the stretching vibration of TA-ZnO film hydroxyl gradually disappeared with the increase of the number of nano-ZnO, which was attributed to the strong interaction between zinc ions and hydrogen bonds. In addition, the peaks at 1650 and 1550 cm -1 also meant the interaction between tannic acid and zinc ions.

[0082] In order to identify the presence of ZnO in the complex, XRD spectrum was recorded in Figure 3 b. Because ZnO was embedded in the tannic acid film, the XRD pattern only showed some weak peaks at 31.7°(100), 47.5°(102), so TA-ZnO film was further studied by XPS in Figure 3 c. In addition to C1s, O1s and F1s peaks, Zn 3d, Zn 2p peaks were identified, which indicated that TA-ZnO film was successfully established. And the Zn 2p spectrum showed a doublet with binding energy of 1021.48 and 1044.78 eV Figure 3 (d), which could be identified as Zn 2p3 / 2 and Zn 2p1 / 2 lines respectively. The binding energy difference between the two lines was 23.3 eV, which was very close to the standard reference value of ZnO. In summary, according to the binding energy and binding energy difference calculated by XPS study, it was shown that Zn atoms existed in the form of ZnO.

[0083] Example 2

[0084] This example was used to explore the influence of different zinc ion loadings on the performance of TA-ZnO. By adjusting the loading time of zinc ions, the loading amount was controlled. Specifically, the difference from Example 1 was that the time of passing ZnCl2 solution in step 3) of Example 1 was adjusted to 30, 60 and 90 min, and TA-ZnO with different zinc ion loadings was obtained.

[0085] As Figure 4The surface, cross-section morphology and crystal growth state of the tannic acid membranes with different zinc ion contents were observed and studied by scanning electron microscopy (SEM) after ultrasonic treatment in a sodium hydroxide solution with pH = 11.5 for 3 hours. a~b are the surface morphologies of TA-ZnO with coordination times of 30, 60, and 90 min, respectively. a1~b1 are the cross-sectional morphologies of TA-ZnO with coordination times of 30, 60, and 90 min, respectively. In a strong alkaline environment, the high-frequency energy provided by ultrasonic waves can convert Zn(OH)2 or Zn(OH)4 2- The hydrolysis-generated nano-zinc oxide particles are firmly fixed and uniformly distributed on the membrane surface. Figure 4 a,b,c). It was also observed that the density of nanoparticles on the membrane surface increased with increasing loading time.

[0086] Comparative Example 1

[0087] This comparative example uses a TA membrane as a comparison. Unlike Example 1, step 3) is omitted, and the TA membrane of this comparative example is denoted as TA.

[0088] Comparative Example 2

[0089] This comparative example uses a PVDF membrane as a comparison. Specifically, the preparation method includes:

[0090] 1) Polyvinylidene fluoride powder (PVDF) and lithium chloride powder (LiCl) were placed in an oven at 70°C for 24 hours to remove moisture, then dissolved in N,N-dimethylacetamide (DMAC), stirred at 75°C for 12 hours until completely dissolved, to obtain a coating solution. In terms of mass concentration, the PVDF concentration in the coating solution is 14wt%, the DMAC is 84wt%, and the LiCl is 2wt%;

[0091] 2) The coating solution obtained in step 1) was poured into an autoclave and vacuum degassed, and the autoclave was pressurized to 3 bar using nitrogen, and the casting solution was pushed to a volume pump for the next step of spinning;

[0092] The spinning was carried out by adjusting the roller speed to 4.5 m / min, the volume pump speed to 10 rpm, the first-stage coagulation bath temperature to 40°C, the roller coagulation bath temperature to 35°C, and the spinneret distance from the water surface to 40 cm.

[0093] After the spinning was completed, the membrane filaments on the roller were cut, soaked in ultrapure water for 15 hours, then soaked in a 20wt% glycerol solution for 12 hours, and finally the membrane filaments were dried to obtain a PVDF hollow fiber membrane, denoted as PVDF.

[0094] 3) The PVDF was inserted into a cross-flow device, and a 20ppm ZnCl2 solution was introduced at a pressure of 1 bar for 30 minutes.

[0095] Figure 5 The image shows the surface morphology of PVDF after step 3) of the comparative example. It can be seen that the polyvinylidene fluoride film does not have the ability to coordinate with metal ions, and no nano zinc oxide particles grow on the film surface after ultrasonication.

[0096] Figure 6 The porosity comparison diagram shows the TA-ZnO membranes, TA membranes, and PVDF membranes obtained by in-situ growth at different coordination times in Example 2.

[0097] Application testing

[0098] Photocatalytic performance

[0099] Figure 7 The figures show the performance comparison of TA-ZnO membranes, TA membranes, and PVDF membranes obtained by in-situ growth at different coordination times in Example 2. (a) Permeation flux of the TA-ZnO membrane, (b) Bovine serum albumin (BSA) rejection performance, (c) Antifouling performance, (d) Contact angle, and (e) Preparation process and mechanism of the TA-ZnO membrane. It can be seen that the permeation flux (PWF) of the TA-ZnO membrane first increases and then decreases with increasing coordination time. This is related to the amount of ZnO grown. After 60 min of coordination, the ZnO grown increases the hydrophilicity of the membrane surface. Figure 7 c) Excessive ZnO growth after 90 min of coordination led to membrane pore blockage and a decrease in porosity, thus reducing photocatalytic flux (PWF). With a 0.35 g / L BSA solution as the feed, the flux rejection of the TA-ZnO membrane remained essentially unchanged with increasing coordination time, while the rejection rate decreased from 97% to 92%. This was due to slight surface damage caused by excessive zinc oxide growth. The optimal PWF recovery was observed for TA-ZnO membranes grown after 30 min of coordination. At this parameter, the TA-ZnO membrane exhibited the highest rejection rate and best hydrophilicity, thus preventing significant pollutant accumulation and minimizing its impact on photocatalytic performance.

[0100] The photocatalytic performance of the TA-ZnO membrane, PVDF membrane, and TA membrane prepared in Comparative Examples 1, 1, and 2 is compared with that of the TA-ZnO membrane, PVDF membrane, and TA membrane, and the results are as follows: Figure 8 As shown, (a) represents the permeation flux of polyvinylidene fluoride, tannic acid, and TA-ZnO membranes, (b) represents the bovine serum albumin retention performance, and (c) represents the antifouling performance. It can be seen that the performance of PWF is best with TA-ZnO membrane, followed by TA membrane, and lowest with PVDF membrane. This is due to the difference in hydrophilicity of the membranes, which is well shown in the contact angle test.

[0101] When the feed liquid is a 0.35 g / l BSA solution, the rejection flux of the membrane is best for the TA membrane due to its good hydrophilicity and relatively clean membrane surface, while the TA-ZnO membrane has a slight decrease in rejection flux due to the growth of metal oxide particles on the membrane surface, which makes it easier to trap contaminants. In terms of rejection rate, TA-ZnO has a higher rejection rate than TA and PVDF membranes because the ZnO particles can compensate for the defects in the pores of the hollow fiber membrane caused by stretching during production, as the ZnO particles are grown in situ on the membrane surface. In terms of PWF recovery, the static recovery effect of the modified membrane and the original membrane is basically the same, while the photocatalytic FRR of the TA-ZnO membrane reaches more than 80%, which is much higher than that of the original membrane.

[0102] In summary, the TA-ZnO membrane grown in situ after 30 minutes of coordination time can not only maintain a pure water flux of 150 L m -2 h -1 Above, and the rejection rate of bovine serum albumin reaches 96.98%. It is worth noting that compared with natural recovery, the photocatalytic flux recovery rate of the TA-ZnO membrane increases by 47.48%, and the irreversible pollution decreases by 47.39%. In contrast, the photocatalytic flux recovery rate of PVDF and TA membranes only increases by 17%.

[0103] Photocatalytic cycle performance

[0104] Figure 9 (a, b) show the comparison of the photocatalytic cycle performance of the TA-ZnO membrane and the PVDF membrane with bovine serum albumin as the contaminant. It can be seen that the TA-ZnO membrane prepared in five photocatalytic cycles has a FRR of more than 60%, and the rejection rate of the TA-ZnO membrane is always maintained at more than 95%, so the membrane has long-term stable photocatalytic performance. Compared with the TA-ZnO membrane, the PVDF membrane does not show an improvement in BSA flux and recovery effect after multiple cycles Figure 10 、 Figure 11 ). Finally, the surfaces of the polyvinylidene fluoride membrane and the TA-ZnO membrane after photocatalysis are photographed and compared Figure 9 c, d, e, f), by comparing the membrane surface before and after photocatalysis, it can be found that the photocatalytic cleaning effect of the TA-ZnO membrane is better than that of the PVDF membrane, and the contaminants on the membrane surface are degraded by photocatalysis, while the PVDF membrane surface shows a filter cake layer generated by the accumulation of contaminants. In summary, the TA-ZnO membrane prepared by the in-situ reduction method can complete the separation task and obtain stable photocatalytic degradation effect in long-term stability test, so the membrane has the potential for large-scale practical application in wastewater treatment.

[0105] Bacteriostatic effect

[0106] Slaughter wastewater can breed a large number of E. coli in the natural state, so the ability to effectively remove bacteria is also a necessary condition for multifunctional separation membranes today. For example Figure 12 It is shown that the inhibition rates of PVDF, tannic acid and TA-ZnO membranes on E. coli are 0%, 30% and 100%, respectively. Therefore, the TA-ZnO membrane has good antibacterial activity. After visible light irradiation for 5 min, the photo-generated e- and h+ can react with hydroxyl and adsorbed oxygen to produce reactive oxygen species (·O 2- , ·OH and H2O2). The combined action of these reactive oxygen species and holes (h + ) destroys the cell membrane of bacteria, and then enters the cell interior to further oxidize nucleic acids and proteins, thereby achieving a bactericidal effect. Figure 13 Photographing the membrane surface after antibacterial treatment shows that E. coli grows on the surface of all membranes except the TA-ZnO membrane.

[0107] Slaughter wastewater separation application

[0108] Figure 14 The photocatalytic recycling performance test of the TA-ZnO membrane with slaughter wastewater as the pollutant and Figure 15 (left before filtration, right after filtration) shows the slaughter wastewater before and after filtration by the TA-ZnO membrane. In eight slaughter wastewater separation experiments, the TA-ZnO membrane has stable performance and shows excellent separation capacity for solid suspended matter (SS), total carbon and ammonia nitrogen, especially the separation rate of SS reaches 100%. Importantly, the pure water recovery rate is maintained at 95%. In summary, the TA-ZnO membrane can meet the long-term application to slaughter wastewater and guide the industrialization of water treatment.

[0109] Comparative Example 3

[0110] This comparative example is used to compare the influence of different tannic acid concentrations on the performance of the prepared TAHF. Specifically, the difference from Example 1 is that the concentration of TA in the casting solution of step 1) of Example 1 is adjusted to 0, 1, 1.5 and 2 wt%, and the concentration of DMAC is adjusted accordingly. The specific casting solution formula is shown in Table 1.

[0111] Table 1 Different casting solution formulas

[0112]

[0113] Spinning is carried out according to the procedure of Example 1 step 2) to obtain the hollow fiber membranes prepared with different tannic acid concentrations in this comparative example.

[0114] Figure 16 The surface and cross-sectional morphology of the TA membrane at different concentrations are studied by electron microscopy, Figure 16(a)~(d) correspond to hollow fiber membranes with tannic acid concentration of 0, 1, 1.5, 2 wt% respectively. It can be seen that the membrane surface pores gradually increase with the increase of tannic acid concentration. At the same time, the asymmetric structure of ultrafiltration membrane is observed in the cross-section, including the skin layer, finger-like pores and the bottom sponge layer. The finger-like pores gradually increase with the increase of tannic acid concentration, which is due to the strong attraction of tannic acid to water, which promotes the exchange rate between solvent and ultra-pure water, accelerates the phase inversion.

[0115] Figure 17 (a) shows the effect of TA concentration change on the filtration performance of the membrane. The PWF of the modified membrane is significantly higher than that of the original PVDF membrane, and the PWF of the TA membrane continues to rise with the increase of TA concentration. When the TA concentration is 2wt%, the best PWF is obtained, which is nearly 50L m -2 h -1 The significant increase in PWF is mainly due to the increase in the proportion of finger-like pores of the membrane caused by the hydrophilicity of TA, thereby increasing the liquid permeability.

[0116] When using 0.35g / L BSA solution as the feed solution, the trend of rejection flux is basically consistent with that of PWF with the increase of TA membrane concentration, however, the rejection rate decreases from 90% to 30%, which is mainly due to the large amount of small molecule protein permeating caused by the increase of membrane surface pores. After soaking overnight, the PWF of the membrane is recovered to different degrees, and the FRR of 1wt% and 2wt% TA membranes is higher (more than 60%). Among them, the 1wt% TA membrane forms a hydration layer on the membrane surface due to its hydrophilicity, which improves the anti-pollution performance. The 2wt% TA membrane has no rejection ability. The FRR of the TA membrane with a concentration of 1.5wt% is the lowest, which is because the membrane pores are blocked. The TA membrane with a concentration of 1.5wt% neither has the rejection ability of 1wt% nor the large amount of permeation of pollutants of 2wt%, so it belongs to the pollution of the membrane pores, and it is more difficult to remove the BSA pollutants by simple soaking.

[0117] The comprehensive analysis shows that the effect of tannic acid concentration of 1wt% is the best. Among them, the pure water recovery effect reaches 68.83%, which is about 15.7% higher than that of the PVDF membrane. And the rejection flux and rejection rate of the tannic acid hollow fiber membrane with a concentration of 1wt% are higher than those of other concentrations.

[0118] Example 3

[0119] This embodiment is based on Comparative Example 3, comparing the performance of TA-ZnO films prepared with different concentrations of tannic acid. Specifically, the concentration of tannic acid was adjusted to 1, 1.5, and 2 wt%, while the remaining process steps were the same as in Example 1. The resulting TA-ZnO films were tested for their performance, and the results are shown in Table 2.

[0120] Table 2 Performance of TA-ZnO films prepared with different concentrations of tannic acid

[0121]

[0122]

[0123] From the effects of Comparative Example 3 and Example 3, it can be seen that not all amounts of added tannic acid can improve the performance of the film. When the amount of added tannic acid is 1 wt%, the comprehensive performance of the obtained film is optimal.

[0124] Comparative Example 4

[0125] This comparative example is used to compare the effects of different TAHF spinning parameters on the performance of the obtained TAHF. Specifically, the rotational speed of the volumetric pump in step 2) of Example 1 was adjusted to 8, 10, 12, and 14 rpm, while the casting solution formulation was the same as in Example 1. The TAHF obtained under different spinning parameters was denoted as 10-8, 10-10, 10-12, and 10-14.

[0126] Figure 18 The surface and interface images of the TA films obtained under different spinning conditions are shown in a1-d1, which represent the surface morphology of 10-8, 10-10, 10-12, and 10-14, respectively, and a2-d2, which represent the cross-sectional morphology of 10-8, 10-10, 10-12, and 10-14, respectively. It can be seen that as the spinning time increases, the thickness of the film increases.

[0127] The anti-fouling performance of the film was evaluated by filtering bovine serum albumin solution and carbon ink. The results are shown in Figure 19 and Figure 20 In the PWF test, as the rotational speed of the volumetric pump increases, the permeation flux of the TA film gradually decreases, which is attributed to the slowing down of the phase transition speed due to the increase in film thickness, and the resulting thicker sponge layer;

[0128] When the feed liquid is changed to a 0.35 g / l BSA solution, the rejection flux of the TA film has the same trend as the PWF, while the rejection rate increases from 78% to 98%. This is because the thicker the film, the worse the liquid permeability, resulting in a large amount of pollutants accumulating on the surface of the film, which blocks the membrane pores. This also affects the FRR of the TA film, Figure 3cIt is observed that FRR presents a trend of first increasing and then decreasing with the increase of membrane thickness, which is also due to the large accumulation of BSA on the membrane surface without hydration layer at low flux, so the recovery effect is poor.

[0129] In summary, the best performance is obtained at 10-10, at which the TA membrane has good rejection performance, and the pure water recovery effect reaches 70%. In the carbon ink filtration experiment, the hydrophilicity of the TA membrane is well demonstrated, the FRR reaches nearly 80%, and the rejection rate reaches 100%.

[0130] Example 4

[0131] In this example, the performance of TA-ZnO membranes prepared by different membrane spinning parameters is compared based on Comparative Example 3. Specifically, the volume pump speed in the spinning process is adjusted to 8, 10, 12, and 14 rpm, and the other steps are the same as in Example 1. The TA-ZnO membranes of this example are obtained, and the related performance of the membranes is tested, and the results are shown in Table 3.

[0132] Table 3 Performance of TA-ZnO membranes prepared based on different membrane spinning parameters

[0133]

[0134] It can be seen that the membrane spinning parameters also have a significant impact on the performance of the finally prepared TA-ZnO membranes. Consistent with Comparative Example 4, when the volume pump speed is 10 rpm, the TA-ZnO membrane prepared has the best comprehensive performance.

[0135] In summary, a new type of multifunctional photocatalytic hollow fiber ultrafiltration membrane is prepared by the method of coordination pretreatment combined with ultrasonic assisted growth. Under the conditions of strong alkali environment and ultrasonic vibration, zinc ions coordinated with tannic acid can grow in situ between molecules, and are tightly fixed on the tannic acid membrane. Not only good hydrophilicity and antibacterial ability are obtained, but also the problem of easy falling off and blocking of membrane pores caused by direct loading of zinc oxide particles is effectively avoided.

[0136] The flux of the multifunctional photocatalytic hollow fiber ultrafiltration membrane (TA-ZnO membrane) prepared by the present application is increased by 30% compared with the original membrane, and the highest flux reaches 170 L m -2 h -1 In the long-term stability test, the rejection effect of bovine serum albumin is always maintained at more than 95%, and in the long-term separation experiment of slaughter wastewater, ammonia nitrogen, organic pollutants and suspended solids are effectively removed. In terms of bacterial inhibition, the inhibition rate of TA-ZnO membrane to Escherichia coli reaches 100%. This persistent multifunctional separation membrane has broad application prospects in the purification treatment of complex wastewater.

[0137] It should be noted that the above examples are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced, without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions, characterized in that: include, After drying, polyvinylidene fluoride, lithium chloride, and tannic acid are dissolved in N,N-dimethylacetamide to obtain a casting solution. After high-pressure degassing, the casting solution is transferred to a volumetric pump for the next step of dry and wet spinning. After spinning, the solution undergoes post-treatment to obtain a tannic acid hollow nanofiber membrane. A hollow nanofiber membrane of tannic acid is inserted into a cross-flow device, and a zinc chloride solution is introduced to carry out a coordination reaction. After the reaction, the membrane is placed in a strong alkaline solution for ultrasonic treatment to achieve coordination between zinc ions and tannic acid, thus obtaining a photocatalytic membrane based on the coordination of tannic acid and zinc ions.

2. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 1, characterized in that: The mass concentration of tannic acid in the casting solution is 0.5–2 wt%.

3. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 2, characterized in that: The casting solution contains 12-14 wt% polyvinylidene fluoride, 1-2 wt% lithium chloride, and 82-84 wt% N,N-dimethylacetamide.

4. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 1, characterized in that: During the dry-wet spinning process, the rotation speed of the volumetric pump is 8 to 14 rpm.

5. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 4, characterized in that: The wet-dry spinning process includes a drum rotation speed of 4-5 m / min, a first-stage coagulation bath temperature of 35-45℃, a drum coagulation bath temperature of 30-40℃, and a spinneret height of 35-40 cm above the water surface.

6. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 1, characterized in that: The post-processing includes immersing the membrane fibers in ultrapure water and then in a 15-25 wt% glycerol solution, wherein the immersion time in ultrapure water is 15-20 h and the immersion time in glycerol is 10-15 h.

7. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 1, characterized in that: The coordination reaction was carried out by continuously passing 20 ppm of ZnCl2 solution through the reactor for a reaction time of 0–90 min.

8. The method for preparing a photocatalytic membrane based on the coordination of tannic acid and zinc ions as described in claim 1, characterized in that: The ultrasonic power of the ultrasonic treatment is 40-45 kHz, and the reaction time is 3-4 h.

9. The photocatalytic membrane based on the coordination of tannic acid and zinc ions prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the photocatalytic membrane based on tannic acid and zinc ion coordination as described in claim 9 in the separation of slaughterhouse wastewater.

Images