PLA rGO nanofiber membrane for oil-water separation and preparation method of PLA rGO nanofiber membrane

Abstract

The invention discloses a PLA rGO nanofiber membrane for oil-water separation and a preparation method of the PLA rGO nanofiber membrane. According to the invention, graphene oxide is prepared by using an improved hummers method, and the graphene oxide is reduced by using ascorbic acid to prepare rGO with hydrophobic performance. The PLA rGO nanofiber membrane is prepared by using an electrostatic spinning method. The preparation process is simple to operate, shows better oil-water separation performance and commercial application value, is suitable for popularization and application, has very good potential in practical application, and can be used for water purification and the like.

Description

Technical Field

[0001] The present invention relates to the technical fields of functional materials and oil-water separation technology, and particularly relates to a PLArGO nanofiber membrane for oil-water separation and a preparation method thereof. Background Art

[0002] Electrospinning is one of the common methods for preparing nanofiber membranes. It relies on the voltage generated by a high-voltage electric field to stretch polymer solutions into nanofibers at the nanoscale. The nanofiber membranes prepared by electrospinning have a large specific surface area, high porosity, etc. Some studies have shown that electrospun nanofiber membranes are more hydrophobic than membrane materials prepared by other methods.

[0003] Polylactic acid (PLA) is a polyester polymer. It is inexpensive and widely sourced. It has excellent biodegradability and biocompatibility. As a thermoplastic material, PLA exhibits excellent processability and can be made into various shaped functional materials through various processing methods such as melting, dry spinning, and electrospinning. And due to the ester groups contained in PLA itself, it has excellent hydrophobic properties. Currently, electrospun polylactic acid nanofiber membrane materials are widely used in the field of biomedical materials, but there is relatively little research in the field of oil-water separation. Graphene is a novel material with excellent properties. It has excellent electrical conductivity, antibacterial properties, and a large specific surface area, etc. These excellent properties make it also have great research prospects in the field of oil-water separation. However, the internal space of the pure graphene framework can be used for both oil and water, resulting in poor oil-water separation performance. Therefore, it needs to be hydrophobically modified. The hydrophobicity of graphene materials is closely related to the reduction degree of its oxidation groups. Reduced graphene oxide (rGO) has excellent hydrophobic properties.

[0004] In addition, currently, the electrospinning method is used to prepare PLA rGO nanofiber membranes. By adding rGO to improve the hydrophobic properties and oil-water separation ability of PLA nanofiber membranes, the exploration of the application of such membranes in the field of water pollution treatment is relatively less. Summary of the Invention

[0005] The purpose of the present invention is to provide a PLArGO nanofiber membrane for oil-water separation and a preparation method thereof in view of the deficiencies of the prior art.

[0006] In the first aspect, the present invention provides a preparation method of a PLArGO nanofiber membrane for oil-water separation, which is characterized by including:

[0007] Step 1: Weigh 2 g of flake graphite, 1 g of sodium nitrate, and 46 mL of concentrated sulfuric acid into a beaker. Place the beaker in an ice-water mixture and stir magnetically. Then, add 2 g of potassium permanganate to the beaker quantitatively every 15 minutes for a total of three times. After adding, continue the reaction for 1 h, and then the low-temperature reaction stage ends.

[0008] After the low-temperature reaction stage ends, transfer the beaker to a 35 °C constant-temperature water bath and continue stirring for 2 h, then the medium-temperature reaction stage ends.

[0009] After the medium-temperature reaction stage ends, change the temperature of the constant-temperature water bath to 95 °C, continue magnetic stirring, and slowly add 100 mL of deionized water drop by drop. After the temperature of the reaction system rises to 95 °C, wait for another 5 min and then continue to slowly add 200 mL of deionized water and 50 mL of hydrogen peroxide. At this time, a dispersion with a bright yellow metallic luster is obtained. Continue the reaction for 15 min, and then the high-temperature reaction stage ends.

[0010] After the high-temperature reaction stage ends, remove the beaker from the water bath, ultrasonically disperse the obtained dispersion for 30 min, add hydrochloric acid and stir for 3 min. Finally, dilute the obtained GO dispersion with deionized water to 10 L, and pour off the supernatant by natural gravity precipitation. Repeat this step three times until the pH of the GO dispersion is neutral, and then an aqueous dispersion of graphene oxide is obtained.

[0011] Step 2: Add 6 g of ascorbic acid to the aqueous dispersion of graphene oxide, and then stir magnetically to obtain a reduced graphene oxide dispersion; place the above dispersion in an oven for further reduction to obtain reduced graphene oxide powder.

[0012] Step 3: Add rGO to a solution of 10 g of N,N-dimethylformamide and ultrasonically disperse for 3 h; then add 7 g - 12 g of dichloromethane and 1.3 g - 2 g of polylactic acid powder to the above rGO dispersion and stir magnetically to prepare a spinning precursor solution of PLA / rGO.

[0013] Use a 10 mL sterile syringe and an electrospinning device. Set the voltage to: positive high voltage 18 V, negative high voltage 2 V, the temperature is kept constant at 25 °C, and the feeding speed is 0.05 mL / min; use a flat receiver, and cover the flat plate on the receiver with tin foil to facilitate peeling off the spun nanofiber membrane.

[0014] Furthermore, in Step 1, stir magnetically for 0.5 h during the low-temperature reaction stage.

[0015] Furthermore, in Step 2, stir magnetically for 12 h.

[0016] Furthermore, in Step 3, stir magnetically for 12 h.

[0017] Further, in step three, the dichloromethane is 9 g - 10 g.

[0018] Further, in step three, the polylactic acid powder is 1.3 g - 2 g.

[0019] In a second aspect, the present invention provides a PLA rGO nanofiber membrane for oil-water separation, which is characterized in that it is prepared by using the preparation method of the PLA rGO nanofiber membrane for oil-water separation described above.

[0020] The beneficial effects of the present invention are as follows: The present invention uses the improved Hummers method to prepare graphene oxide, and uses ascorbic acid to reduce the graphene oxide to obtain rGO with hydrophobic properties. The PLA rGO nanofiber membrane is prepared by electrospinning, and the effect of the addition amount of rGO on the performance of the PLA nanofiber membrane is explored. The PLA rGO nanofiber membrane is characterized by infrared spectroscopy and Raman spectroscopy. The characterization shows that rGO and PLA are only physically mixed and no chemical change occurs during the electrospinning process. The contact angle of the PLA rGO nanofiber membrane is characterized, and it is found that when the addition amount of rGO is 0.14%, the contact angle of the PLA / 0.14% rGO nanofiber membrane can reach 139.2°. At the same time, this membrane has good acid and alkali corrosion resistance, and the contact angle can reach more than 125° when titrating the contact angles of different pH values. The oil-water separation performance of the PLA rGO nanofiber membrane is tested, and it is found through experiments that when the addition amount of graphene is 0.14%, the oil flux can reach 141.3 L / (m 2 ·h), and the oil-water separation efficiency can reach 98.6%, showing good oil-water separation ability. The preparation process of the present invention is simple in operation, exhibits good oil-water separation performance and commercial application value, is suitable for popularization and application, has great potential in practical applications, and can be used for water purification, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the infrared spectrogram of PLA, rGO, and PLA rGO nanofiber membranes in Example 4;

[0022] Figure 2 It is the Raman spectrogram of rGO and PLA rGO nanofiber membranes in Example 4;

[0023] Figure 3 It is the scanning electron micrograph of the PLA nanofiber membrane in Example 1 and the PLA rGO nanofiber membrane in Example 4. (a) and (b) are the PLA nanofiber membranes; (c) and (d) are the PLA rGO nanofiber membranes;

[0024] Figure 4Contact angles of PLA rGO nanofiber membranes with different rGO dosages in Examples 1 - 8

[0025] Figure 5 Contact angles of the PLA rGO nanofiber membrane in Example 4 titrated with water of different pH values

[0026] Figure 6 Oil - water separation efficiency and oil flux of PLA rGO nanofiber membranes with different rGO dosages in Examples 1 - 8 Detailed implementation manners

[0027] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Specific conditions not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0028] The technical solution adopted by the present invention is as follows: Graphene oxide was prepared using the improved Hummers method, and reduced graphene oxide (rGO) with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid. The PLA rGO nanofiber membrane was prepared by electrospinning, and the effect of the rGO dosage on the hydrophobicity of the PLA nanofiber membrane was explored. The infrared spectrum and Raman spectrum of the PLA rGO nanofiber membrane show that PLA and rGO are physically mixed and no chemical change occurs during the electrospinning process. It is found that when the rGO dosage is 0.14%, the contact angle of the nanofiber membrane increases from 118° to 139.2°, and experiments prove that this membrane has good acid - base resistance. When titrated with solutions of different pH values, the contact angle of this membrane can reach more than 125°. From the oil - water separation experiment, it is found that the oil flux of the PLA rGO nanofiber membrane can reach 141.3 L / (m 2 ·h), and the oil - water separation efficiency can reach 98.6%.

[0029] The preparation method of the PLA rGO nanofiber membrane for oil - water separation of the present invention includes the following steps:

[0030] I. Prepare graphene oxide (GO) using the improved Hummers method, and the specific steps are as follows.

[0031] 1) Low - temperature stage

[0032] Weigh 2 g of flake graphite, 1 g of sodium nitrate, and 46 mL of concentrated sulfuric acid (98%) into a beaker. Place the beaker in an ice-water mixture and stir magnetically for 0.5 h. Then, add 2 g of potassium permanganate to the beaker at regular intervals of 15 min, for a total of three times. After adding, continue the reaction for 1 h, and then the low-temperature reaction stage ends.

[0033] 2) Medium-temperature stage

[0034] After the low-temperature reaction stage ends, transfer the beaker to a 35 °C constant-temperature water bath and continue stirring for 2 h, then the medium-temperature reaction stage ends.

[0035] 3) High-temperature stage

[0036] After the medium-temperature stage reaction ends, change the temperature of the constant-temperature water bath to 95 °C, continue magnetic stirring, and slowly add 100 mL of deionized water drop by drop. After the temperature of the reaction system rises to 95 °C, wait for another 5 min and then continue to slowly add 200 mL of deionized water and 50 mL of hydrogen peroxide. At this time, a dispersion with a bright yellow metallic luster is obtained. Continue the reaction for 15 min, and then the high-temperature reaction stage ends.

[0037] 3) Washing

[0038] After the high-temperature reaction stage ends, remove the beaker from the water bath, ultrasonically disperse the obtained dispersion for 30 min, add hydrochloric acid and stir for 3 min. Finally, dilute the obtained GO dispersion to 10 L with deionized water, and pour off the supernatant by natural gravity precipitation. Repeat this step three times until the pH of the GO dispersion is neutral. At this time, an aqueous dispersion of graphene oxide is obtained.

[0039] II. Preparation of reduced graphene oxide

[0040] Add 6 g of ascorbic acid to the aqueous dispersion of graphene oxide, and then stir magnetically for 12 h to obtain a reduced graphene oxide dispersion. Place the above dispersion in an oven for further reduction to obtain reduced graphene oxide powder.

[0041] III. Preparation of PLA rGO nanofiber membrane

[0042] 1) Preparation of spinning precursor solution

[0043] Add a certain amount of rGO to a solution of 10 g of N,N-dimethylformamide and ultrasonically disperse for 3 h. Then, add 7 - 12 g (optimized to 9 - 10 g) of dichloromethane and 1.3 - 2 g (optimized to 1.5 - 1.7 g) of polylactic acid powder to the above rGO dispersion, and stir magnetically for 12 h to prepare a spinning precursor solution of PLA rGO.

[0044] 2) Preparation of PLA rGO nanofiber membrane

[0045] Using a 10 mL sterile syringe, an electrospinning device produced by Jiangsu Yongkang Leye was used. The voltage was set as follows: positive high voltage 18 V, negative high voltage 2 V, the temperature was kept constant at 25 °C, and the feeding speed was 0.05 mL / min. A flat receiver was used, and tinfoil was covered on the flat plate of the receiver to facilitate peeling off the spun nanofiber membrane.

[0046] The methods for characterizing the prepared rGO and characterizing and testing the properties of the PLA / rGO nanofiber membrane in this application include:

[0047] (1) Infrared spectroscopy characterization: A Fourier transform infrared spectrometer was used to detect and analyze the samples.

[0048] (2) Raman spectroscopy characterization: A Raman spectrometer was used to detect the wavelength of the samples.

[0049] (3) Scanning electron microscopy characterization: A field emission scanning electron microscope was used to characterize the samples.

[0050] (4) Contact angle characterization: At room temperature, a droplet of a certain size was titrated on the nanofiber membrane, and a high-power microscope was used for characterization. ImageJ was used to calculate the contact angle of the nanofiber membrane.

[0051] (5) Oil-water separation performance test: Tetrachloroethylene was used as the oil phase and was stained with Rhodamine B. Pure water was used as the water phase and was stained with Methyl Blue. A sand filter was used for the oil-water separation experiment. The specific experimental steps are as follows: 50 mL of the oil phase and 50 mL of the water phase were each poured into a 200 mL beaker. The membrane was fixed in the filter, and the oil-water mixture was poured into the filtration device at the same time. Timing started when the first drop of oil dripped. Each membrane sample was tested 2 times, and the average value was taken.

[0052] Oil flux: F = V / (ΔS·ΔT) (1)

[0053] In the formula: F is the oil flux, L / m 2 ·h; V is the volume of oil passing through the oil-water separation membrane, L; ΔS is the surface area of the oil-water separation membrane, m 2 ; ΔT is the filtration time, h.

[0054] Separation efficiency: η = V 1 / V 2 × 100% (2)

[0055] In the formula; η is the separation efficiency, %; V 1 is the volume of oil before filtration, L; V 2 is the volume of oil after filtration, L. The above formulas (1) and (2) are used to calculate the oil flux and separation efficiency.

[0056] It should be understood that the above test methods and test equipment are common methods in the industry for evaluating the relevant properties of hydrophobic and oleophilic membranes, and are only a means to characterize or evaluate the technical solutions and technical effects of the present invention. Other test methods and test equipment can also be used, which will not affect the final results.

[0057] The following will specifically describe in detail the preparation method of the PLA rGO nanofiber membrane for oil-water separation of the present invention with reference to specific embodiments.

[0058] Example 1:

[0059] Graphene oxide was prepared using the improved Hummers method, and graphene oxide was reduced with ascorbic acid to prepare rGO with hydrophobic properties.

[0060] 1) Preparation of the spinning precursor solution

[0061] A certain amount of rGO (addition amount: 0%) was added to a solution of 10 g of N,N-dimethylformamide and ultrasonicated for 3 h. Then, 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetically stirred for 12 h to obtain the spinning precursor solution of PLA-rGO.

[0062] 2) Preparation of the PLA rGO nanofiber membrane

[0063] Using a 10 mL sterile syringe, with an electrospinning device, the voltage was set as: positive high voltage 18 V, negative high voltage 2 V, the temperature was kept constant at 25 °C, and the feeding speed was 0.05 mL / min. A flat receiver was used, and tinfoil was covered on the flat plate of the receiver to facilitate peeling off the spun nanofiber membrane.

[0064] Example 2:

[0065] Graphene oxide was prepared using the improved Hummers method, and graphene oxide was reduced with ascorbic acid to prepare rGO with hydrophobic properties.

[0066] 1) Preparation of the spinning precursor solution

[0067] A certain amount of rGO (addition amount: 0.06%) was added to a solution of 10 g of N,N-dimethylformamide and ultrasonicated for 3 h. Then, 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetically stirred for 12 h to obtain the spinning precursor solution of PLA-rGO.

[0068] 2) Preparation of the PLA rGO nanofiber membrane

[0069] Using a 10 mL sterile syringe and an electrospinning device, set the voltage to: positive high voltage 18 V, negative high voltage 2 V, keep the temperature constant at 25 °C, and the feeding speed at 0.05 mL / min. Use a flat receiver, and cover the flat plate on the receiver with tin foil so as to peel off the spun nanofiber membrane.

[0070] Example 3:

[0071] Graphene oxide was prepared using the improved Hummers method, and reduced graphene oxide (rGO) with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid.

[0072] 1) Preparation of the spinning precursor solution

[0073] A certain amount of rGO (added amount 0.1%) was added to a solution of 10 g of N,N-dimethylformamide and ultrasonically dispersed for 3 h. Then 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetically stirred for 12 h to obtain the spinning precursor solution of PLA-rGO.

[0074] 2) Preparation of the PLA-rGO nanofiber membrane

[0075] Using a 10 mL sterile syringe and an electrospinning device, set the voltage to: positive high voltage 18 V, negative high voltage 2 V, keep the temperature constant at 25 °C, and the feeding speed at 0.05 mL / min. Use a flat receiver, and cover the flat plate on the receiver with tin foil so as to peel off the spun nanofiber membrane.

[0076] Example 4:

[0077] Graphene oxide was prepared using the improved Hummers method, and reduced graphene oxide (rGO) with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid.

[0078] 1) Preparation of the spinning precursor solution

[0079] A certain amount of rGO (added amount 0.14%) was added to a solution of 10 g of N,N-dimethylformamide and ultrasonically dispersed for 3 h. Then 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetically stirred for 12 h to obtain the spinning precursor solution of PLA-rGO.

[0080] 2) Preparation of the PLA-rGO nanofiber membrane

[0081] Using a 10 mL sterile syringe and an electrospinning device, set the voltage to: positive high voltage 18 V, negative high voltage 2 V, keep the temperature constant at 25 °C, and the feeding speed at 0.05 mL / min. Use a flat receiver, and cover the flat plate on the receiver with tin foil so as to peel off the spun nanofiber membrane.

[0082] Example 5:

[0083] Graphene oxide was prepared using the improved Hummers method, and reduced graphene oxide (rGO) with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid.

[0084] 1) Preparation of the spinning precursor solution

[0085] A certain amount of rGO (added amount: 0.2%) was added to a 10 g solution of N,N-dimethylformamide, and ultrasonic dispersion was carried out for 3 h. Then, 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetic stirring was carried out for 12 h to obtain the spinning precursor solution of PLA-rGO.

[0086] 2) Preparation of the PLA-rGO nanofiber membrane

[0087] A 10 mL sterile syringe was used, and with an electrospinning device, the voltage was set as follows: positive high voltage 18 V, negative high voltage 2 V, the temperature was kept constant at 25 °C, and the feeding rate was 0.05 mL / min. A flat receiver was used, and tinfoil was covered on the flat plate of the receiver to facilitate peeling off the spun nanofiber membrane.

[0088] Example 6:

[0089] Graphene oxide was prepared using the improved Hummers method, and reduced graphene oxide (rGO) with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid.

[0090] 1) Preparation of the spinning precursor solution

[0091] A certain amount of rGO (added amount: 0.25%) was added to a 10 g solution of N,N-dimethylformamide, and ultrasonic dispersion was carried out for 3 h. Then, 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetic stirring was carried out for 12 h to obtain the spinning precursor solution of PLA-rGO.

[0092] 2) Preparation of the PLA-rGO nanofiber membrane

[0093] A 10 mL sterile syringe was used, and with an electrospinning device, the voltage was set as follows: positive high voltage 18 V, negative high voltage 2 V, the temperature was kept constant at 25 °C, and the feeding rate was 0.05 mL / min. A flat receiver was used, and tinfoil was covered on the flat plate of the receiver to facilitate peeling off the spun nanofiber membrane.

[0094] Example 7:

[0095] Graphene oxide was prepared using the improved Hummers method, and reduced graphene oxide (rGO) with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid.

[0096] 1) Preparation of spinning precursor solution

[0097] A certain amount of rGO (added amount is 0.3%) was added to a solution of 10 g of N,N-dimethylformamide and ultrasonically dispersed for 3 h. Then 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetically stirred for 12 h to obtain a spinning precursor solution of PLA-rGO.

[0098] 2) Preparation of PLA-rGO nanofiber membrane

[0099] A 10 mL sterile syringe was used, and with an electrospinning device, the voltage was set as: positive high voltage 18 V, negative high voltage 2 V, the temperature was kept constant at 25°, and the feeding rate was 0.05 mL / min. A flat receiver was used, and tinfoil was covered on the flat plate of the receiver so as to peel off the spun nanofiber membrane.

[0100] Example 8:

[0101] Graphene oxide was prepared using the improved Hummers method, and rGO with hydrophobic properties was prepared by reducing graphene oxide with ascorbic acid.

[0102] 1) Preparation of spinning precursor solution

[0103] A certain amount of rGO (added amount is 0.35%) was added to a solution of 10 g of N,N-dimethylformamide and ultrasonically dispersed for 3 h. Then 10 g of dichloromethane and 1.7 g of polylactic acid powder were added to the above rGO dispersion, and magnetically stirred for 12 h to obtain a spinning precursor solution of PLA-rGO.

[0104] 2) Preparation of PLA-rGO nanofiber membrane

[0105] A 10 mL sterile syringe was used, and with an electrospinning device, the voltage was set as: positive high voltage 18 V, negative high voltage 2 V, the temperature was kept constant at 25°, and the feeding rate was 0.05 mL / min. A flat receiver was used, and tinfoil was covered on the flat plate of the receiver so as to peel off the spun nanofiber membrane.

[0106] From Figure 1 It can be seen that: the binary infrared spectrum shows that the peaks at 3800 and 3700 cm -1 indicate that there are still a small amount of oxygen-containing functional groups in the infrared spectrum of rGO. The peak corresponding to the -C=O bond characteristic absorption peak of polylactic acid is at 1744 cm -1 , and the bending vibration peak of -C-C- is at 1390 cm -1 , and 1079 cm -1This is the stretching vibration peak of -C-O-C-. From the infrared spectrogram of the PLA rGO nanofiber membrane, it can be found that after adding reduced graphene oxide, the infrared spectrogram of the composite nanofiber membrane is basically the same as that of PLA, and no new characteristic absorption peaks appear. This proves that PLA and rGO are only physically mixed during the electrospinning process and no chemical reaction occurs.

[0107] From Figure 2 it can be seen that: The Raman spectrogram shows that the G peak and D peak of rGO appear at 1300 and 1600 cm -1 respectively. Among them, the D peak is a disordered vibration peak used to characterize the defects of the carbon atom lattice, and the G peak is caused by the in-plane vibration of sp 2 hybridized carbon atoms. The PLA rGO nanofiber membrane shows the same G peak and D peak as rGO, indicating that rGO is successfully loaded onto the PLA nanofiber membrane.

[0108] From Figure 3 it can be seen that: The scanning electron micrograph shows that the fibers of the pure PLA nanofiber membrane and the PLA rGO nanofiber membrane are uniform in thickness, and the morphology of the nanofiber membrane is good. And from the scanning electron micrograph of the PLA rGO nanofiber membrane, some convex structures can be seen, which are speculated to be the existence form of rGO in the nanofiber membrane.

[0109] From Figure 4 it can be seen that: The contact angle of the pure PLA nanofiber membrane is 118.8°. As the amount of rGO added increases, the water contact angle of the nanofiber membrane gradually increases. When the amount of rGO added is 0.14%, the water contact angle reaches the maximum value of 139.2°. However, as the amount of rGO added increases, the contact angle of the PLA rGO nanofiber membrane gradually decreases. This phenomenon can be explained from two aspects: First, many groups such as hydroxyl groups and carboxyl groups disappear after GO is reduced by ascorbic acid, thus making rGO hydrophobic. Many studies have shown that the wettability of materials mainly depends on the surface chemical structure and surface roughness. On the other hand, rGO increases the surface roughness of the PLA nanofiber membrane, making the contact angle of the polylactic acid nanofiber membrane larger and the hydrophobicity improved. However, as the amount of rGO added increases, the rGO particles agglomerate on the surface of the fiber membrane, making the roughness smaller, resulting in a smaller contact angle.

[0110] From Figure 5 it can be seen that: When titrating solutions with different pH values, the water contact angle of the PLA rGO nanofiber membrane remains above 125°, proving that this membrane has good acid and alkali corrosion resistance.

[0111] It can be seen from the oil-water separation experiment of the PLA rGO nanofiber membrane in Example 4 that when the oil-water ratio is 1:1, the oil and water in the beaker do not mix and naturally separate. After filtration, the water is isolated above the membrane, while the oil phase can permeate through the membrane. After testing, it is found that the water isolated above the membrane does not permeate through the membrane after 48 hours, indicating that this membrane has the ability of selective filtration.

[0112] Without applying any external force to the membrane, the separation efficiency of the pure PLA membrane is 92.2%. As the addition amount of rGO increases, the separation efficiency of the PLA rGO nanofiber membrane reaches 98.6%. The oil flux of the pure PLA nanofiber membrane is 63.9 L / m 2 ·h. When the addition amount of rGO is 0.14%, its oil flux reaches the maximum of 141.3 L / m 2 ·h, which is 2.2 times higher than that of the pure PLA nanofiber membrane. As a kind of lipophilic and hydrophobic porous membrane material, the separation mechanism of the PLA rGO nanofiber membrane is similar to that of general lipophilic and hydrophobic membranes. When the oil phase contacts the interface of the PLA rGO porous membrane, the oil phase coalesces into a liquid layer on the surface of the membrane. Under the action of the transmembrane pressure difference, the oil phase preferentially passes through the porous membrane interface, thus achieving the effect of oil-water separation. At the same time, the oil flux of the nanofiber membrane has a great relationship with its fiber diameter and hydrophobicity. Generally speaking, the larger the fiber diameter, the greater the flux of the membrane. Although the conductivity of the spinning solution increases after adding rGO, which makes the fibers stretched into finer fibers during the spinning process. However, the high hydrophobicity of rGO plays a dominant role, ultimately resulting in a significant increase in the oil flux of the membrane.

[0113] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a PLA rGO nanofiber membrane for oil-water separation, characterized in that: include: Step 1: Weigh 2 g of flake graphite, 1 g of sodium nitrate, and 46 mL of concentrated sulfuric acid in a beaker, place the beaker in an ice-water mixture and stir it magnetically, then quantitatively add 2 g of potassium permanganate to the beaker every 15 minutes for three times, and continue to react for 1 hour after the addition is completed, and then the low-temperature reaction stage ends; After the low temperature reaction stage, the beaker was transferred to a 35°C constant temperature water bath and stirred for 2 hours before the medium temperature reaction stage ended; After the reaction at the medium temperature stage, the temperature of the constant temperature water bath was changed to 95°C, magnetic stirring was continued, and 100 mL of deionized water was slowly added drop by drop. After the temperature of the reaction system rose to 95°C, 200 mL of deionized water and 50 mL of hydrogen peroxide were slowly added after waiting for 5 minutes. At this time, a dispersion with a bright yellow metallic luster was obtained. After the reaction was continued for 15 minutes, the high temperature reaction stage was ended. After the high temperature reaction stage, the beaker was removed from the water bath, the obtained dispersion was ultrasonically dispersed for 30 min, hydrochloric acid was added and stirred for 3 min, and finally the obtained GO dispersion was diluted to 10 L with deionized water, and the upper clear liquid was poured off by natural gravity precipitation. After repeating this step three times, the pH of the GO dispersion was neutral, and an aqueous dispersion of graphene oxide was obtained. Step 2: adding 6 g of ascorbic acid to the aqueous dispersion of graphene oxide, and then stirring with a magnetic force to obtain a reduced graphene oxide dispersion; placing the dispersion in an oven for further reduction to obtain reduced graphene oxide powder; Step 3, add rGO to a solution of 10g N-N-dimethylformamide and disperse it by ultrasonic for 3h; then add 7g-12g of dichloromethane and 1.3g-2g of polylactic acid powder to the above rGO dispersion and stir it by magnetic stirring to obtain a spinning precursor solution of PLArGO; Use a 10mL sterile syringe and an electrospinning device, set the voltage to: positive high voltage 18V, negative high voltage 2V, constant temperature at 25°, and a propulsion speed of 0.05mL / min; use a flat plate receiver, and cover the flat plate on the receiver with tin foil to facilitate the removal of the spun nanofiber membrane.

2. The method for preparing a PLA rGO nanofiber membrane for oil-water separation according to claim 1, characterized in that: In step 1, magnetic stirring was performed for 0.5 h during the low temperature reaction stage.

3. The method for preparing a PLA rGO nanofiber membrane for oil-water separation according to claim 1, characterized in that: In step 2, magnetic stirring was performed for 12 h.

4. The method for preparing a PLA rGO nanofiber membrane for oil-water separation according to claim 1, characterized in that: In step 3, magnetic stirring was performed for 12 h.

5. The method for preparing a PLA rGO nanofiber membrane for oil-water separation according to claim 1, characterized in that: In step 3, the dichloromethane is 9g-10g.

6. The method for preparing a PLA rGO nanofiber membrane for oil-water separation according to claim 1, characterized in that: In step three, the polylactic acid powder is 1.3g-2g.

7. A PLA rGO nanofiber membrane for oil-water separation, characterized in that: It is prepared by the method for preparing the PLA rGO nanofiber membrane for oil-water separation according to any one of claims 1 to 6.

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