CN107174950A - The positive osmosis composite membrane of high-performance and preparation method that a kind of graphene oxide is modified - Google Patents

Abstract

The positive osmosis composite membrane of high-performance and preparation method being modified the invention discloses a kind of graphene oxide, belong to water-treatment technology field.Comprise the following steps：First by blending method, polysulfones, graphene oxide, Macrogol 600, Tween 80 and solvent are added in flask, casting solution is prepared, using phase inversion, graphene oxide/polysulfone supporting layer is made.Then the positive osmosis composite membrane of graphene oxide/polyamide is obtained in support layer surface composite polyamide active layer using interfacial polymerization mode.The positive osmosis composite membrane of graphene oxide/polyamide prepared by the present invention has the advantages that flux is high, reverse flux salt is small, resistance tocrocking is strong, its water flux is up to 9 12LMH, reverse flux salt is 2 4gMH, in antifouling property test, the flux fall caused by pollution is only 30% the 50% of unmodified membrane.

Description

A high-performance forward osmosis composite membrane modified by graphene oxide and its preparation method

technical field

The invention relates to a high-performance forward osmosis composite membrane modified by graphene oxide and a preparation method thereof, in particular to a preparation method of a high-performance forward osmosis composite membrane.

Background technique

my country is a country that is extremely scarce in water resources, and the per capita water resources are only a quarter of the world's average level. The increasing population and the rapid development of industry make the problem of water shortage increasingly serious. The development of water treatment technology provides a direction for people to solve the problem of water shortage. As a new separation technology with high efficiency, environmental protection and energy saving, membrane separation technology occupies an important position in water treatment technology. It mainly includes microfiltration, ultrafiltration, nanofiltration, reverse osmosis, forward osmosis, etc. Among them, reverse osmosis is more mature than other technologies, but due to its high operating pressure, high energy consumption, and serious membrane fouling, it has certain limitations in practical application. The nanofiltration membrane can intercept small molecular organic matter and salts, and the operating pressure is low, but the pollution problem is also relatively serious. Compared with membrane separation technologies such as reverse osmosis and nanofiltration, forward osmosis technology has the advantages of low energy consumption, high desalination rate, and strong anti-pollution ability, and has attracted widespread attention in recent years.

At present, the research of forward osmosis technology mainly focuses on two aspects: the preparation of high-performance membrane materials and the selection of high-efficiency draw liquid. Membranes are the core of the entire forward osmosis separation process, so the preparation of high-performance membrane materials is crucial to improving the overall performance of the system. Polysulfone and cellulose acetate are the most commonly used membrane materials. Among them, polysulfone is widely used because of its good chemical stability, thermal stability, and film-forming mechanical properties. However, in practical applications, the conventional polysulfone membrane has large pore size, small porosity, and rough membrane surface, resulting in problems such as low water flux, poor desalination effect, and easy pollution. Therefore, it is of great significance to develop and prepare high-performance forward osmosis membranes.

The polyamide composite membrane has an asymmetric special structure, which is formed by polymerizing the amine-containing functional groups of the water phase (m-phenylenediamine) and the acid chloride groups of the oil phase (trimesyl chloride) on the surface of the porous support layer. The polyamide composite layer can reduce the surface roughness of the membrane and improve the hydrophilicity, thereby increasing the water flux and anti-pollution performance of the membrane. In addition, the polyamide composite membrane can achieve bidirectional optimization of the porous support layer and the ultra-thin active layer, and the overall performance of the membrane can be improved by using the respective optimal conditions.

Modifying the porous support layer is another important way to improve the performance of the forward osmosis membrane. The commonly used modification methods include: blending modification, surface graft modification, coating modification, and plasma modification. Among them, blending modification refers to adding solid phase substances into the casting solution to form a three-phase space to prepare the forward osmosis membrane. The method is simple to operate and the effect is obvious. It can directly change the matrix structure of the membrane, such as the pore size and the roughness of the pore wall. Degree, etc., in order to improve the performance of the membrane.

In recent years, nanomaterials have become a research hotspot in the field of membrane technology due to their high specific surface area and excellent physical and chemical properties. Among them, graphene oxide, as a sheet-like nanomaterial composed of carbon atoms, has a large number of hydrophilic functional groups such as carboxyl groups, hydroxyl groups, and epoxy groups. At the same time, graphene oxide can destroy cell membranes or induce oxidative stress to kill bacteria, and the contained hydroxyl radicals can also intensify the lipid peroxidation of biological cells, which has a significant inhibitory effect on the formation of biofilms on the membrane surface. Therefore, based on the special structure of the polyamide composite membrane and the hydrophilicity and antibacterial properties of graphene oxide, the forward osmosis support layer was prepared by blending graphene oxide and membrane materials, and then the polyamide layer was polymerized through the interface to effectively improve the forward osmosis. The permeability and desalination performance of the permeable membrane, as well as the anti-fouling property of the membrane, provide technical support for the extensive use of membrane technology in water treatment.

Contents of the invention

The object of the present invention is to prepare a high-performance forward osmosis composite membrane and provide a preparation method for the problems of low flux, poor desalination effect and low anti-pollution performance of the existing forward osmosis membrane.

A high-performance forward osmosis composite membrane modified by graphene oxide and its preparation method, the specific operation steps are as follows:

1. Preparation of graphene oxide/polysulfone support layer

The composition of the high-performance planar graphene oxide/polysulfone blended forward osmosis membrane casting liquid formula is as follows: the membrane material is polysulfone, 8.0%-25.0wt%; the additive is polyethylene glycol 600, 0-20.0wt%; The modifier is graphene oxide, 0-1.5wt%, the solvent is N,N-dimethylformamide, 65.0%-80.0wt%, and the solubilizer is Tween 80, 0.5%-2wt%.

First, add N,N-dimethylformamide, polyethylene glycol 600, and Tween 80 into a three-necked flask according to a certain ratio, and then add a certain amount of graphene oxide into the solution, and ultrasonicate for 10 to 60 minutes to make Graphene oxide is uniformly dispersed in the solution; after ultrasonication, move the solution to a magnetic stirrer, stir for 3-10 minutes, add polysulfone material, stir and dissolve at 50-70°C for 6-10 hours, and obtain uniform graphite oxide ethylene/polysulfone casting solution; then, the casting solution was left to stand still at the reaction temperature for 4 to 8 hours to remove the air bubbles in the casting solution; finally, a certain amount of casting solution was poured into the Use a scraper with a thickness of 50-200 μm to form a film on a glass plate of 120 polyester mesh, immerse in ultra-pure water to solidify to form a film, and after the film is automatically separated from the glass plate, soak in ultra-pure water for 24-24 μm After 72 hours, the water was changed every 6 hours to obtain a flat graphene oxide/polysulfone support layer.

2. Preparation of graphene oxide/polyamide composite membrane

The polyamide layer was synthesized on the support layer by interfacial polymerization. First, immerse the base film in 2-4wt% m-phenylenediamine (MPD) water phase for 3-5 minutes, take the base film out of the water phase, wash off the solution on the back of the support layer with ultrapure water, and then absorb it with filter paper. Water stains on both sides of the dry film; then soak the film in the oil phase, that is, the n-hexane solution of trimesoyl chloride (TMC) with a concentration of 0.15 to 0.25 wt%, take it out after 1 to 3 minutes, and remove the excess oil phase . That is, the graphene oxide/polyamide forward osmosis composite membrane is obtained. In order to make the polyamide composite layer polymerized more firmly, heat-treat the composite film in a drying oven at 40-80°C for 5-10 minutes, take it out, and store it in deionized water for later use.

In the preparation process of the high-performance forward osmosis composite membrane modified by graphene oxide, by controlling the mixing ratio of polysulfone, polyethylene glycol 600, and graphene oxide in the casting solution and the stirring and dissolving temperature of the casting solution, the The preparation conditions were optimized to control the structure and performance of the prepared blended forward osmosis membrane. The prepared forward osmosis composite membrane was tested in a cross-flow filtration system to investigate the water flux, reverse salt flux and anti-pollution performance of the graphene oxide modified forward osmosis composite membrane.

Beneficial effect:

The advantage of the graphene oxide/polyamide composite membrane in the present invention is that the polysulfone support layer blended with graphene oxide has the characteristics of stable structure, high porosity, small membrane pores, and high hydrophilicity, which can simultaneously ensure that the composite membrane has Higher membrane flux and lower reverse salt flux. In addition, according to existing research reports, graphene oxide has a bactericidal effect and improves the hydrophilicity of the membrane, so that the prepared graphene oxide/polyamide composite membrane has strong anti-biological fouling properties.

detailed description

In the following, the technical solutions of the present invention will be verified in combination with specific embodiments of the present invention, and the verified embodiments are only part of the embodiments of the present invention. Based on the embodiments of the present invention, other embodiments obtained by researchers in the field without any creative effort all belong to the protection scope of the present invention.

Example 1

First, N,N-dimethylformamide, polyethylene glycol 600, and Tween 80 were added to a three-necked flask at the ratio of 70wt%, 13.3wt%, and 1wt%, respectively, and then 0.2wt% of a single-layer ultrapure Graphene oxide was added to the solution, and the graphene oxide was fully and uniformly dispersed in the solution by ultrasonication for 30 minutes. After the ultrasonication was over, the solution was moved to a magnetic stirrer, and polysulfone material was added after stirring for 5 minutes, and stirred and dissolved at a temperature of 70°C. 8h to obtain a uniform graphene oxide/polysulfone casting solution; then, the casting solution was left at the reaction temperature for 5h to remove the air bubbles in the casting solution; finally, a certain amount of casting solution was poured into a Use a scraper with a thickness of 50 μm to form a film on a glass plate with 100 polyester screens, immerse in ultrapure water to solidify to form a film, and after the film is automatically detached from the glass plate, immerse in ultrapure water for 72 hours. Change the water every 6 hours to obtain a flat graphene oxide/polysulfone support layer.

The prepared support layer was first immersed in the water phase of 3.5wt% m-phenylenediamine (MPD) for 5min, after the base film was taken out from the water phase, the solution on the back of the support layer was washed away with deionized water, and then Filter paper blots the water stains on both sides of the film; then the film is soaked in the oil phase, i.e. the n-hexane solution of trimesoyl chloride (TMC) with a concentration of 0.15wt%, is taken out after 2min, and the excess oil phase is removed to obtain Graphene oxide/polyamide forward osmosis composite membrane (GO/TFC membrane). Using 2M NaCl solution as the driving solution and deionized water as the raw material solution, the average water flux of the prepared membrane reached 11.29LMH and the reverse salt flux was 2.1gMH during the test time of 1h.

In order to test the anti-pollution performance of the graphene oxide forward osmosis composite membrane, this example uses Pseudomonas aeruginosa as the polluting microorganism, and uses synthetic wastewater to simulate the secondary effluent (water composition: 1.2mM sodium citrate, 0.8mM NH ₄ Cl , 0.5mM NaHCO ₃ , 0.2mM K ₂ HPO ₄ , 8.0mM NaCl, 0.2mM CaCl ₂ ·H ₂ O, 0.15mM MgSO ₄ ·7H ₂ O, the microbial concentration is 5×10 ⁷ CFU/L), the membrane was tested Experimental research on anti-pollution. 2M NaCl was used as the driving solution, and synthetic wastewater was used as the raw material solution. After running the pollution experiment for two consecutive days, it was calculated that the decrease in water flux caused by biofouling was 11%.

Example 2

Based on the modification method in Example 1, the only difference is that graphene oxide is not added during the preparation of the support layer to obtain a polysulfone polyamide forward osmosis composite membrane (TFC membrane). Similarly, the prepared forward osmosis membrane was tested. In the test time of 1h, the average water flux of the membrane was 5.9LMH, and the reverse salt flux was 8gMH; In the pollution experiment, the water flux decreased by 25% due to biofouling.

Example 1-2 The detailed comparison of the test data of the forward osmosis composite membrane modified by graphene oxide and the forward osmosis composite membrane without graphene oxide is shown in Table 1.

Table 1

Classification of membranes Water flux/LMH Reverse salt flux/gMH Contact angle/° Porosity Decrease in flux after pollution GO/TFC membrane 11.29 2 60.6 33% 11% TFC membrane 5.9 8 47.32 53% 25%

It can be seen from the table that the water flux of the forward osmosis composite membrane modified by graphene oxide is greatly increased, and the reverse salt flux is reduced; while the contact angle is reduced, indicating that the hydrophilicity of the membrane modified by GO is improved; The increase in porosity indicates that the pore structure of the membrane is greatly improved; through the anti-fouling test, the anti-fouling performance of the GO/TFC membrane is better than that of the traditional TFC membrane.

Claims (9)

1. A high-performance forward osmosis composite membrane and preparation method modified by graphene oxide, is characterized in that, comprises the steps: (1) Preparation of graphene oxide/polysulfone support layer Add N,N-dimethylformamide, polyethylene glycol 600, and Tween 80 into a three-necked flask according to a certain ratio, then add a certain amount of graphene oxide into the solution, ultrasonicate until completely dispersed, add poly The sulfone material is stirred at a certain temperature to obtain a uniform graphene oxide/polysulfone casting solution; then, the casting solution is kept at the reaction temperature until it is completely defoamed; finally, a certain amount of casting solution is poured into the Scrape the film with a scraper of a certain thickness on a glass plate with a polyester screen, immerse in ultra-pure water to solidify to form a film, and after the film is automatically detached from the glass plate, soak in ultra-pure water until the solvent is completely precipitated to obtain Flat graphene oxide/polysulfone support layer; (2) Preparation of graphene oxide/polyamide composite membrane The polyamide layer was synthesized on the support layer by interfacial polymerization. The basement membrane is first immersed in a certain concentration of m-phenylenediamine (MPD) in the water phase. After the basement membrane is taken out of the water phase, the solution on the back of the support layer is washed away with ultrapure water, and then both sides of the membrane are blotted dry with filter paper. Then soak the membrane in the oil phase, that is, a certain concentration of trimesoyl chloride (TMC) in n-hexane, take it out, and remove the excess oil phase to obtain a graphene oxide/polyamide forward osmosis composite membrane. In order to make the polyamide composite layer polymerized more firmly, the composite film is heat-treated in a drying oven, taken out, and stored in deionized water for later use; In order to investigate the performance of the membrane, the prepared forward osmosis composite membrane was tested in a cross-flow filtration system to investigate the water flux, reverse salt flux and anti-pollution performance of the graphene oxide modified forward osmosis composite membrane. 2. a kind of graphene oxide modified high-performance forward osmosis composite membrane and preparation method according to claim 1, it is characterized in that in step (1), the material of preparing graphene oxide/polysulfone support layer has: membrane The material is polysulfone, 8.0%-25.0wt%; the modifier is graphene oxide, 0-1.5wt%; the solvent is N,N-dimethylformamide, 65.0%-80.0wt%; the additive is polyethylene glycol Alcohol 600, 0-20.0wt%; solubilizer Tween 80, 0.5%-2wt%. 3. The modification method according to claim 1, characterized in that before adding the polysulfone material in step (1), it is necessary to disperse graphene oxide uniformly in the solution by ultrasonic, the ultrasonic time is 10-60min, and then move to Stir on a magnetic stirrer for 3 to 10 minutes. 4. The modification method according to claim 1, characterized in that in step (1) after the polysulfone material is added, the stirring condition is: stirring and dissolving at a temperature of 50-70° C. for 6-10 hours. 5. The modification method according to claim 1, characterized in that in step (1) during film casting, the mesh of the polyester screen is 80-120, and the thickness of the scraper is 50-200 μm. 6. a kind of graphene oxide modified high-performance forward osmosis composite membrane and preparation method according to claim 1, it is characterized in that the synthesis of polyamide active layer is through the m-phenylenediamine of water phase in the step (2) Two solutions of trimesoyl chloride and oil phase are obtained by interfacial polymerization reaction on the membrane surface, and the concentrations of the two solutions are respectively 2-4wt% and 0.15-0.25wt%. 7. modification method according to claim 1, it is characterized in that after base film is taken out from aqueous phase in step (2), all there is m-phenylenediamine in the support layer both sides after the impregnation and cause double-sided For the problem of polymerization, it is necessary to wash off the solution on the back of the support layer with ultrapure water, then use filter paper to blot the water stains on both sides of the membrane, and then soak the membrane in the oil phase to complete further polymerization. 8. The modification method according to claim 1, characterized in that in step (2), in order to make the polyamide composite layer polymerized more firmly, the composite film is heat-treated in a drying oven at 40-80°C for 5-10min. 9. The modification method according to claim 1, characterized in that for the performance of the test membrane, the prepared forward osmosis composite membrane is placed in a cross-flow filtration system for testing, and the forward osmosis composite membrane modified by graphene oxide is investigated. The water flux, reverse salt flux and anti-pollution performance of the membrane, the results show that the water flux can reach 9-12LMH, and the reverse salt flux is 2-4gMH. In the anti-pollution test, the water flux caused by pollution The decrease in amount was 30%-50% of the unmodified membrane.