Preparation method of nano titanium dioxide modified ultrafiltration membrane

Abstract

The invention discloses a preparation method of a nano titanium dioxide modified ultrafiltration membrane. The preparation method comprises the following specific preparation steps: 1) preparing casting liquid; (2) casting liquid containing nano titanium dioxide is prepared through centrifugation; (3) coating; 4) drying; and finally obtaining the nano titanium dioxide composite ultrafiltration membrane. According to the nano titanium dioxide modified ultrafiltration membrane disclosed by the invention, the modified nano titanium dioxide is uniformly dispersed in the PES ultrafiltration membrane, so that the pore size and the surface roughness of the ultrafiltration membrane are improved, and the retention rate of the membrane on dye molecules is greatly improved under the condition that the flux of the ultrafiltration membrane is slightly lost; meanwhile, the anti-pollution regeneration performance of the membrane is improved.

Description

Technical Field

[0001] The invention belongs to the field of membrane technology, and specifically relates to a preparation method of a nano titanium dioxide modified ultrafiltration membrane by a surface casting method and application thereof. Background Art

[0002] Water shortage has become a serious global challenge, as more than one-third of the world's population lives in water-stressed areas. This problem has further worsened with the increase in industrialization, population and pollution. Water resources are precious resources, an important natural resource that cannot be replaced in development, and play an important role in the construction of human society. Water accounts for about 70% of the earth's surface area, but only 2.5% of the world's total water is available to humans. Nearly two-tenths of the world's people do not have access to safe drinking water. According to statistics from the World Health Organization in 2022, nearly four thousand children die every day from diseases caused by unsafe water or poor sanitation. Because some freshwater resources (such as freshwater frozen in polar regions and deep underground) are difficult to exploit and use based on current technology, the global available freshwater resources are very limited. my country's per capita water resources are far below the world average, and with the rapid development of industrialization, water bodies have been severely damaged and polluted, posing great challenges to my country's water safety. In the context of environmental protection and sustainable use of resources, dye wastewater recycling has become the focus of attention in the industrial and scientific communities. The wanton discharge of dye wastewater has brought a heavy burden to the ecological environment. Its composition is complex, including various dyes, additives and a large amount of organic matter. It not only has high chroma and high chemical oxygen demand, but also has problems such as poor biodegradability and strong toxicity, which seriously threatens water safety and ecological balance. Therefore, dye wastewater treatment is imminent and is a key link in achieving sustainable development. Nowadays, with the advancement of technology, dye wastewater recycling is not only a necessary environmental protection measure, but also a key strategy to achieve resource recycling and reduce production costs.

[0003] Driven by the dual needs of modern industry and environmental protection, dye treatment has become a key link in ecological balance and sustainable resource utilization. With the continuous expansion of dye production and application, if the large amount of wastewater generated is directly discharged without effective treatment, it will cause extremely serious pollution to the water environment and destroy the stability and balance of the ecosystem. At present, a variety of technologies are used in dye wastewater treatment. Biological treatment uses the metabolism of microorganisms to decompose organic matter, but the effect is limited for dyes with complex structures. Chemical oxidation methods such as ozone oxidation and Fenton oxidation can effectively degrade dyes, but the cost is high and may cause secondary pollution. Membrane separation technology has gradually become a research hotspot with its unique advantages. Membrane processes such as ultrafiltration, nanofiltration, and reverse osmosis can separate dyes and impurities according to molecular size and properties, and achieve wastewater purification and resource recovery. As an efficient and advanced separation method, membrane separation and water treatment technology is gradually emerging in the field of dye treatment and plays an irreplaceable and important role. It is like a precise pair of "molecular scissors" that can finely separate and purify various impurities in dyes and wastewater based on differences in molecular size, charge properties, etc., providing a highly innovative and feasible solution to dye treatment problems, and has huge potential and broad application prospects in promoting the green development of the dye industry.

[0004] Ultrafiltration membrane is a pressure-driven membrane, that is, under a certain pressure, when the filtrate passes through the ultrafiltration membrane, particles larger than the pore size of the membrane surface (such as colloids, bacteria, proteins, etc.) are retained on one side of the membrane, while particles smaller than the surface pore size (ions, small molecules, etc.) pass through the membrane surface and penetrate to the other side of the membrane. The selective permeability of the ultrafiltration membrane realizes the separation, concentration and purification of some impurities in the water. Ultrafiltration membranes need to have good chemical stability to cope with feeds of different chemical properties. It can tolerate a certain range of pH values ​​and work normally in acidic or alkaline environments. At the same time, it has good tolerance to many common chemical solvents and reagents, ensuring that the performance of the membrane will not decline rapidly in complex chemical environments, such as solutions containing acids, bases, oxidants, reducing agents and other components, thereby extending its service life.

[0005] Nano-titanium dioxide can be used for photocatalytic or thermal catalytic degradation of organic pollutants. For example, it can be used to degrade methylene blue solution. Incorporating nano-titanium dioxide into membrane materials is expected to improve the membrane's regeneration ability and the ability to separate dye wastewater.

[0006] In the previously published patents (publication number CN 117771975 A), (publication number CN 117899671A), (publication number CN 113230889 A), it is reported that composite nanofiltration by doping triphenylamine-based covalent organic frameworks, zwitterionic covalent organic frameworks, copper hydroxide nanowires, etc. can achieve good separation effects on dyes, and all achieve good interception performance and flux. However, there is no literature report on the ultrafiltration membrane prepared by composite modification and its separation ability for dye wastewater. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a nano titanium dioxide modified ultrafiltration membrane, which has small pore size, strong regeneration ability and strong ability to separate methyl orange dye molecules.

[0008] To solve the above problems, the present invention adopts the following technical solutions:

[0009] A nano-titanium dioxide modified ultrafiltration membrane, the composite ultrafiltration membrane is prepared by a surface coating method for a flat membrane, characterized in that the specific preparation steps can be divided into:

[0010] 1) preparing a casting solution: weighing a certain amount of polyethersulfone (PES), adding it to a mixed solution of N,N-dimethylformamide (DMF) and polyethylene glycol, and adding polyvinylpyrrolidone (PVP) particles after dissolving; stirring the solution in a water bath at a certain temperature for a period of time to prepare a casting solution;

[0011] 2) preparing a casting solution containing nano titanium dioxide: taking a certain amount of the modified nano titanium dioxide solution and adding it to the original casting solution obtained in step 2), and centrifuging it at room temperature, so that the nano titanium dioxide solution will gradually disperse evenly in the casting solution under centrifugation to obtain a casting solution containing nano titanium dioxide;

[0012] 3) Coating: The casting solution obtained in step 2) is placed in a dark place at room temperature for a period of time to remove bubbles, and then coated on a non-woven fabric, with the film thickness controlled to be 200 μm. After coating, the casting solution is quickly placed in deionized water for film-forming reaction;

[0013] 4) Drying: The membrane obtained in step 3) is placed at 50° C. and dried under normal pressure to finally obtain a nano-titanium dioxide composite ultrafiltration membrane.

[0014] Furthermore, the modified nano-titanium dioxide is used as the modified material, and PES is used as the film-forming material.

[0015] Furthermore, the casting solution is composed of DMF and PEG solution in which PES particles are dissolved, wherein DMF is used as the main solvent; the concentration of polyethersulfone in the casting solution is 0.238 mg-S / g; the feed ratio (mass ratio) of DMF to PEG is 1:3, the feed ratio (mass ratio) of PES to PVP is 10:1, the temperature during the formation of the casting solution is 90°C, and the rotation speed is 100-300 r / min, preferably 200 r / min.

[0016] Furthermore, in step 2), nano-titanium dioxide needs to be dispersed in the casting liquid by centrifugation.

[0017] Furthermore, in step 3), a coating rod is used to control the film thickness to be 200 microns.

[0018] Furthermore, in step 4), the coated ultrafiltration membrane is placed in a vacuum oven at a reaction temperature of 50-80° C. for a reaction time of 12 h.

[0019] Furthermore, the film-forming material is PES, and the average molecular weight is 3,000.

[0020] Furthermore, the present invention adopts DMF as the main solvent.

[0021] Furthermore, the porogen and plasticizer used in this method is PEG, and the molecular weight is between 280-320.

[0022] Furthermore, the method uses polyvinyl pyrrolidone (PVP) with an average molecular weight of 58,000 to increase the viscosity of the film and enhance the adhesion of the membrane, so that the ultrafiltration membrane can be better attached to the non-woven fabric.

[0023] Furthermore, the nano titanium dioxide used in this method is purchased from Ningbo Jiwei Nano New Material Technology Co., Ltd., and its crystal form is anatase type with a grain size of 3-5nm. Before use, the nano titanium dioxide powder is first soaked in 5MH2SO4 at 80°C and stirred for 2h, and the solid powder is vacuum dried after filtration. The solid powder after pretreatment is soaked in glacial acetic acid again, ultrasonicated at 40°C for 1h, and then freeze-dried to finally obtain the modified nano titanium dioxide powder.

[0024] The specific steps of the method for preparing the nano-titanium dioxide modified ultrafiltration membrane of the present invention are as follows: 1) weighing the chemicals required for the original casting solution: weighing 0.5-5g of PES, 0.02-0.2g of PVP particles are added to a mixed solution consisting of 2.0-10.0g of DMF and 1.0-5.0g of PEG, and the mixed solution is stirred in a 90°C water bath for 1-10h to prepare a casting solution; 2) Nano-titanium dioxide modified casting solution: 0.05-0.5g of modified nano-titanium dioxide powder is added to the casting solution prepared in step 1), stirred at room temperature for 12h and then centrifuged for 0.2-2h to uniformly disperse the nano-titanium dioxide in the casting solution, and finally a casting solution containing nano-titanium dioxide is obtained; 3) Surface coating: The nano-titanium dioxide modified casting solution obtained in step 2) is allowed to stand at room temperature in the dark for 6-36h to remove bubbles, and then coated on a glass plate with a non-woven fabric with a scraper, and the film thickness is controlled to be 50-400 microns. After coating, it is quickly placed in deionized water to form a film; 4) Drying: The film obtained in step 3) is placed in an oven at 50°C for drying and cross-linking, and finally a nano-titanium dioxide modified ultrafiltration membrane is obtained.

[0025] The beneficial effects of the present invention are as follows: the nano-titanium dioxide modified ultrafiltration membrane of the present invention improves the pore size and surface roughness of the ultrafiltration membrane by uniformly dispersing nano-titanium dioxide in the PES ultrafiltration membrane, and the ultrafiltration membrane has a greatly improved retention rate of dye molecules with a slight loss of ultrafiltration membrane flux, and the anti-pollution regeneration performance of the membrane is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 Schematic diagram of the separation performance of PES original ultrafiltration membrane for methyl orange;

[0028] Figure 2 This is a schematic diagram of the separation performance of a nano-titanium dioxide modified ultrafiltration membrane for methyl orange in the present invention. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0030] Example:

[0031] A method for preparing a nano-titanium dioxide modified ultrafiltration membrane:

[0032] Take 10g of anatase nano-titanium dioxide powder with an average grain size of 4nm, soak the nano-titanium dioxide powder in 200mL of 5M H2SO4 solution at 80o and stir for 2h. After filtering, the solid powder is vacuum dried. The solid powder after pretreatment is soaked in 100mL of glacial acetic acid solution, ultrasonicated at 40℃ for 1h and then freeze-dried to finally obtain the modified nano-titanium dioxide powder.

[0033] At room temperature, 1g PES and 0.1g PVP were weighed in turn and dissolved in a mixed solution of 4.2g DMF and 2.8g polyethylene glycol PEG, stirred in a 90°C water bath for 4h, and after cooling, 0.1g modified nano-titanium dioxide powder was added, and the mixture was centrifuged in a centrifuge for 0.5h; the mixture was allowed to stand for 12h to completely eliminate bubbles to obtain a modified casting solution, and a scraper was used to coat the obtained modified casting solution on a non-woven fabric, and the film thickness was controlled to be 200 microns. The non-woven fabric was immersed in deionized water to form a film, and after the film formation was completed, it was placed in an oven at 50°C for drying and cross-linking to obtain a nano-titanium dioxide modified ultrafiltration membrane.

[0034] Comparative Example:

[0035] Preparation of PES original ultrafiltration membrane: At room temperature, weigh 1g PES) and 0.1g PVP in turn and dissolve them in a mixed solution of 4.2g DMF and 2.8g PEG, stir in a 90°C water bath for 4h, put it in a centrifuge for centrifugation for 0.5h after cooling, and let it stand for 12h to completely eliminate bubbles to obtain the original membrane casting liquid; use a scraper to coat the obtained original membrane casting liquid on a glass plate fixed with a non-woven fabric, control the membrane thickness to 200 microns, immerse the glass plate in deionized water to form a film, and after the film formation is completed, put it in an oven at 50°C for cross-linking reaction for 12h to obtain a PES original ultrafiltration membrane as a comparison.

[0036] 4) Test methods and results:

[0037] The membrane was cut into a square with a side length of 4 cm and placed in a membrane pool. A methyl orange solution with a concentration of 0.1 g / L was prepared. A simulated dye was passed through a homemade membrane testing device at a pressure of 4 bar. The filtrate and stock solution samples were collected each time, and the time required for the filtrate per unit volume was recorded.

[0038] The obtained samples are sequentially placed in an ultraviolet analysis spectrometer for testing, and the absorbance of the filtrate and the original solution is measured at a predetermined wavelength.

[0039] 5) Calculate flux and retention:

[0040] Flux J W (L / m 2 h)

[0041]

[0042] m is the mass of pure water permeating the membrane (g); V is the volume of filtrate per unit time (ml); A is the membrane area (m2); t is the permeation time (h)

[0043] Retention rate R(%)

[0044]

[0045] C p is the concentration of methyl orange in the permeate (g / L), C F is the concentration of methyl orange in the feed liquid side of the ultrafiltration membrane (g / L)

[0046] The separation performance of the prepared nano-titanium dioxide modified ultrafiltration membrane for the dye methyl orange is shown in the attached Figure 2 As shown in the figure, for comparison, the separation performance of the original PES ultrafiltration membrane for the dye methyl orange is shown in the attached Figure 1 As shown in the figure, it can be seen that compared with the original PES ultrafiltration membrane, the retention rate of the nano-titanium dioxide modified ultrafiltration membrane for the dye methyl orange is increased by 80%, so it has a better ability to separate methyl orange.

[0047] The above embodiment is only an example of the present invention and is not intended to limit the implementation and scope of rights of the present invention. Any technical solution that is identical or equivalent to the content described in the claims of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a nano-titanium dioxide modified ultrafiltration membrane, wherein the composite ultrafiltration membrane is prepared by a surface coating method as a flat membrane, characterized in that: The specific preparation steps can be divided into: 1) preparing a casting solution: weighing a certain amount of polyethersulfone (PES), adding it to a mixed solution of N,N-dimethylformamide (DMF) and polyethylene glycol, and adding polyvinylpyrrolidone (PVP) particles after dissolving; stirring the solution in a water bath at a certain temperature for a period of time to prepare a casting solution; 2) preparing a casting solution containing nano titanium dioxide: taking a certain amount of the modified nano titanium dioxide solution and adding it to the original casting solution obtained in step 2), and centrifuging it at room temperature, so that the nano titanium dioxide solution will gradually disperse evenly in the casting solution under centrifugation to obtain a casting solution containing nano titanium dioxide; 3) Coating: The casting solution obtained in step 2) is placed in a dark place at room temperature for a period of time to remove bubbles, and then coated on a non-woven fabric, with the film thickness controlled to be 200 μm. After coating, the casting solution is quickly placed in deionized water for film-forming reaction; 4) Drying: The membrane obtained in step 3) is placed at 50° C. and dried under normal pressure to finally obtain a nano-titanium dioxide composite ultrafiltration membrane.

2. The method for preparing a nano-titanium dioxide modified ultrafiltration membrane according to claim 1, characterized in that: Nano titanium dioxide is used as a modified material and PES is used as a membrane-forming material. Before using the modified nano titanium dioxide, the nano titanium dioxide powder needs to be soaked in 5M H2SO4 at 80°C and stirred for 2 hours, and the solid powder is vacuum dried after filtration, and the solid powder after pretreatment is soaked in glacial acetic acid again, and then freeze-dried after ultrasonic treatment at 40°C for 1 hour to finally obtain the modified nano titanium dioxide powder, which can be used to prepare the nano titanium dioxide modified ultrafiltration membrane according to the method of the present invention.

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