An ultrahydrophilic / underwater superoleophobic oil-water separation membrane and a preparation method thereof

Abstract

A method for preparing a superhydrophilic / underwater superoleophobic oil-water separation membrane involves hydrolyzing chitin powder with sulfuric acid to obtain chitin nanocrystals (ChNCs), then mixing them with attapulgite (PGS) to form a mixed suspension. This suspension is then filtered onto the surface of a porous membrane substrate and dried to obtain a PGS / ChNC oil-water separation membrane. The superhydrophilic / underwater superoleophobic membrane prepared by this invention achieves a contact angle of 156.3°, exhibiting excellent interfacial oleophobic properties. After seven cycles, the water flow rate and oil rejection rate of the membrane remain essentially unchanged, indicating that the composite membrane is recyclable and possesses certain durability and antifouling properties. After 40 cycles of repeated abrasion, its underwater oil contact angle remains above 150°, indicating that the PGS / ChNC oil-water separation membrane retains good oil repellency even after abrasion. Simultaneously, the removal rate of methylene blue reaches as high as 99.92%, while the removal rate of Mn... 2+ Ni 2+ Cr 3+ and Fe 3+ The removal rate of all of them reached over 95%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super-oleophobic materials, and particularly relates to a super-hydrophilic / underwater super-oleophobic oil-water separation membrane and a preparation method thereof. BACKGROUND

[0002] Due to the rapid development of global industry, a large amount of oil-containing wastewater is generated in industrial processes, which has become a major challenge to the ecological environment and human health. In particular, water-soluble pollutants (such as dyes and heavy metal ions) in oil-containing wastewater have caused an increasingly serious threat to water resources and ecosystems. Traditional separation technologies, such as air floatation, chemical coagulation and adsorption, have been used for the treatment of oil-containing wastewater. However, these methods have their own disadvantages, such as low efficiency and high cost, which seriously limit their practical application in the field of oil-water separation. In addition, these technologies are ineffective in separating surfactant-stabilized emulsions or breaking emulsions after adding chemicals, resulting in high energy consumption and secondary pollution.

[0003] Membrane separation technology has attracted much attention in the field of oil-containing wastewater purification due to its simple operation process, high removal efficiency, low operation cost and avoidance of secondary pollution. Although oil-containing wastewater always contains water-soluble pollutants, most of the reported works only focus on the remediation of oil-containing wastewater without the ability to remove toxic ingredients (soluble metal ions or dyes). It has become increasingly necessary to remove organic pollutants during oil-water separation, so multifunctional super-wetting composite membranes capable of separating oil phase and water-soluble pollutants are needed.

[0004] The construction of such super-hydrophilic / underwater super-oleophobic membrane materials in the prior art is limited by expensive raw materials, toxic chemicals and complex preparation processes. On the other hand, these membrane materials are only used for oil-water separation, and the effect of removing other common wastewater pollutants such as heavy metal ions and dyes is not ideal. Therefore, it is crucial to develop low-cost, environmentally friendly multifunctional separation membranes. SUMMARY

[0005] In view of this, the present application provides a low-cost, green, super-hydrophilic / underwater super-oleophobic composite membrane and a preparation method thereof. Attapulgite and biodegradable chitin nanocrystals are used as raw materials to develop a super-hydrophilic / underwater super-oleophobic oil-water separation membrane through a vacuum-assisted filtration strategy.

[0006] The obtained oil-water separation membrane exhibits multifunctional separation performance, which not only can separate emulsified oil / water mixture in harsh environments, but also can remove soluble pollutants in the water phase, especially for the removal of heavy metal ions, showing great potential for wastewater purification.

[0007] In order to achieve the above purpose, the present application provides a preparation method of an oil-water separation membrane, which can simultaneously remove dye molecules and heavy metal ions when performing oil-water separation.

[0008] The application aims to realize the technical scheme as follows:

[0009] The application discloses a preparation method of an ultrahydrophilic / ultra-oleophobic oil-water separation membrane.

[0010] Further, the porous membrane substrate material is a mixed cellulose ester membrane, and the pore size is 0.22 μm.

[0011] Further, the vacuum-assisted filtration is performed, and the negative pressure in the vacuum-assisted filtration is 0.2-1.0 bar.

[0012] Further, the drying is performed in a drying box at 40-80 ℃ for 3-10 min.

[0013] Further, the hydrolysis temperature is 90 ℃, the concentration of H2SO4 is 3 mol / L, the stirring speed is 5000-6000 rpm, and the hydrolysis time is 6 h.

[0014] Further, the mass-volume ratio of the chitin powder and H2SO4 is 1 g:30 mL.

[0015] Further, after the hydrolysis is completed, distilled water is added to dilute the solution, and centrifugal precipitation is performed to remove supernatant; the dilution and centrifugal precipitation are repeated until H2SO4 in the supernatant is completely removed; after dialysis, the ChNC is obtained through centrifugal drying.

[0016] Further, the repeated centrifugal precipitation is performed at 6000-9000 rpm for 10-30 min.

[0017] Further, the dialysis bag used in the dialysis has a molecular weight cut-off of 8000-14000 KDa, and the dialysis is performed until the pH is 7.

[0018] Further, the mixed suspension is prepared by adding the ChNCs into deionized water, then adding 0.5 M NaOH into the suspension until the pH of the suspension is 10 to obtain a ChNC suspension, and then adding the attapulgite powder.

[0019] Further, in the mixed suspension, the mass-volume ratio of the ChNCs, the attapulgite and the deionized water is 3-9 mg:3-9 mg:25 mL, and the mass ratio of the ChNCs and the attapulgite is 1:1.

[0020] Further, the mixed suspension is subjected to ultrasonic treatment, and the ultrasonic power is 300-360 W, and the ultrasonic treatment is performed for 3-4 min.

[0021] Considering that the chitin nanocrystal has excellent antibacterial property and biodegradability, it is used as a raw material to be compounded with PGS, but in the preparation process, it is found that the chitin nanocrystal (ChNCs) and PGS have obvious agglomeration and sedimentation, resulting in uneven dispersion of ChNCs and PGS, poor thickness and structural uniformity of the prepared film, and poor overall performance, which cannot achieve the effect of super oil-repellent, and due to the influence of agglomeration, the removal effect of PGS on heavy metal ions, organic dyes and other pollutants is greatly reduced.

[0022] In the present application, by adding NaOH to the ChNC suspension and adjusting the pH to 10, the surface charge of ChNCs is reversed, ChNCs and PGS form hydrogen bonds, and the agglomeration and aggregation of ChNCs and PGS in the solvent are preliminarily inhibited, and then the system is subjected to ultrasonic treatment in an alkaline environment, which further promotes the uniformity of dispersion of ChNCs and PGS, and at the same time, through the combined action of NaOH and ultrasonic, the removal efficiency of the prepared separation membrane for metal ions is significantly improved.

[0023] Most specifically, a preparation method of a super-hydrophilic / underwater super-oleophobic oil-water separation membrane, characterized in that the following steps are performed:

[0024] Step 1: Preparation of chitin nanocrystals (ChNCs)

[0025] (1) Chitin powder is hydrolyzed with 3 M H2SO4 at 90 °C under stirring at 5000-6000 rpm for 6 h, and the mass-volume ratio of chitin powder and H2SO4 is 1 g:30 mL;

[0026] (2) After dilution with distilled water, centrifuge at 6000-9000 rpm for 10-30 min to remove the supernatant, and repeat the dilution and centrifugation until the supernatant is free of H2SO4, and obtain the suspension for standby use;

[0027] (3) The suspension is dialyzed using a dialysis bag with a molecular weight cut-off of 8000-14000 KDa until the pH is 7, and then centrifuged at 7000-10000 rpm for 10-30 min, and dried to obtain ChNCs;

[0028] Step 2: Preparation of attapulgite / chitin nanocrystal (PGS / ChNC) composite membrane

[0029] (1) adding ChNCs into deionized water, adding 0.5 M NaOH to adjust pH to 10, then adding PGS powder to form a mixed suspension, and performing ultrasonic treatment on the mixed suspension, wherein the ultrasonic power is 300-360 W, the ultrasonic treatment time is 3-4 min, the mass ratio of ChNCs to PGS is 1:1, and the mass / volume ratio of ChNCs, PGS and deionized water is 3-9 mg:3-9 mg:25 mL;

[0030] (2) performing vacuum-assisted filtration on the mixed suspension to the surface of a mixed cellulose ester membrane substrate with a pore size of 0.22 μm under a negative pressure of 0.2-1.0 bar;

[0031] (3) placing the mixed cellulose ester membrane substrate in a drying box at 40-80 ℃ for drying for 3-10 min to obtain a PGS / ChNC oil-water separation membrane.

[0032] The application further provides an ultra-hydrophilic / ultra-oleophobic oil-water separation membrane prepared by the above method.

[0033] The application has the following technical effects:

[0034] The application discloses an ultra-hydrophilic / ultra-oleophobic oil-water separation membrane and a preparation method thereof. The ultra-hydrophilic / ultra-oleophobic membrane is prepared from biodegradable chitin nanocrystals and attapulgite as raw materials under the double treatment of sodium hydroxide and ultrasonic waves. The contact angle of the ultra-hydrophilic / ultra-oleophobic membrane reaches 156.3°, and good oil-repellent performance of the surface interface is provided. After 7 cycles, the water flow flux and the oil rejection rate of the filter membrane remain basically unchanged, wherein the water flow flux basically maintains at about 540 L m -2 h -1 bar -1 , and the oil rejection rate is stably about 99.1%, indicating that the composite membrane can be recycled, has certain durability and anti-pollution performance. After 40 times of abrasion, the underwater oil contact angle still maintains above 150°, indicating that the PGS / ChNC oil-water separation membrane still has good oil-repellent performance after abrasion, and the removal rate of methylene blue reaches as high as 99.92%, and the removal rates of Mn 2+ , Ni 2+ , Cr 3+ and Fe 3+ all reach more than 95%. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 : a transmission electron microscope (TEM) image of the raw material chitin nanocrystals prepared in the application.

[0036] Figure 2 : a scanning electron microscope (SEM) image of the oil-water separation membrane prepared in the application.

[0037] Figure 3 : The underwater oil contact angle (OCA) diagram of the oil-water separation membrane prepared by the present application.

[0038] Figure 4 : The effect diagram of the mixed suspension after ultrasonic treatment in Example 1 and Comparative Example 2 of the present application.

[0039] Figure 5 : The separation effect diagram of the oil-water emulsion by the oil-water separation membrane prepared by the present application.

[0040] Figure 6 : The cycle performance diagram of the oil-water separation effect of the oil-containing wastewater containing oil by the oil-water separation membrane prepared by the present application.

[0041] Figure 7 : The separation effect diagram of the oil-containing wastewater containing methylene blue solution by the oil-water separation membrane prepared by the present application.

[0042] Figure 8 : The mechanical wear cycle performance diagram of the oil-water separation membrane prepared by the present application.

[0043] Figure 9 : The removal effect diagram of heavy metal ions by the oil-water separation membrane prepared by the present application. Embodiment

[0044] The present application will be described in detail below by examples. It is necessary to point out here that the following examples are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above content of the present application. Example

[0045] A preparation method of a super-hydrophilic / underwater super-oleophobic oil-water separation membrane, which is carried out according to the following steps:

[0046] Step 1: Preparation of chitin nanocrystals (ChNCs)

[0047] (1) Chitin powder is hydrolyzed with 3 M H2SO4 at 90 °C under stirring at 5500 rpm for 6 h, and the mass-volume ratio of chitin powder and H2SO4 is 1 g:30 mL;

[0048] (2) After dilution with distilled water, centrifugation is carried out at 8000 rpm for 20 min to remove the supernatant, and then the dilution and centrifugation are repeated until there is no H2SO4 in the supernatant, and the suspension is obtained for standby use;

[0049] (3) The suspension was dialyzed against deionized water with a dialysis bag with a molecular weight cut-off of 8000-14000 KDa until the pH was 7, and then centrifuged at 9000 rpm for 20 min, and dried to obtain ChNCs;

[0050] Step 2: Preparation of Attapulgite / chitin nanocrystal (PGS / ChNC) composite membrane

[0051] (1) ChNCs were added to deionized water, 0.5 M NaOH was added to adjust the pH to 10, and then PGS powder was added to form a mixed suspension, which was ultrasonically treated at a power of 360 W for 3 min, with a ChNCs:PGS mass ratio of 1:1 and a ChNCs:PGS:deionized water mass:volume ratio of 6 mg:6 mg:25 mL;

[0052] (2) The mixed suspension was filtered by vacuum-assisted filtration at a negative pressure of 0.5 bar to the surface of a mixed cellulose ester membrane substrate with a pore size of 0.22 μm;

[0053] (3) The mixed cellulose ester membrane substrate was placed in a drying oven at 40°C for 3 min to obtain a PGS / ChNC oil-water separation membrane.

[0054] During the preparation process, after adjustment with NaOH, if the ultrasonic treatment is not properly controlled, for example, when the ultrasonic treatment is 10 min, not only will it not promote dispersion, but it will also have a counterproductive effect, causing the mixed suspension, which has improved dispersion performance under the action of NaOH, to return to the aggregated and agglomerated state before NaOH adjustment.

[0055] Figure 1 A transmission electron microscope (TEM) image of the chitin nanocrystals prepared in Example 1, Figure 2 A scanning electron microscope (SEM) image of the PGS / ChNC oil-water separation membrane prepared in Example 1, Figure 3 An underwater oil contact angle (OCA) image of the PGS / ChNC oil-water separation membrane prepared in Example 1. From Figure 1 It can be seen that the morphology of the chitin nanocrystals exhibits a uniform needle-like structure, with a length of 200-600 nm and a diameter of 10-80 nm, and an average aspect ratio of 9.4. Figure 2 A scanning electron microscope (SEM) image of the PGS / ChNC oil-water separation membrane, in which there is no aggregation or agglomeration phenomenon, and the chitin nanocrystal fiber structure and the rod-like structure of attapulgite are uniformly dispersed and stacked with each other, forming a porous and rough surface. These unique microstructures are beneficial to the separation of oil droplets and water in an oil-water emulsion. From Figure 3 It can be seen that the contact angle of the PGS / ChNC oil-water separation membrane is 156.3°, providing good oil-repellent properties at the surface interface.

[0056] Comparative Example 1:

[0057] Compared with Example 1, in the preparation process, ChNCs were added to deionized water, no NaOH was added, but PGS powder was directly added to form a mixed suspension, and the mixed suspension was subjected to ultrasonic treatment; the remaining steps were completely consistent with Example 1.

[0058] As shown in Figure 4 , it was found during the preparation process that the mixed suspension prepared by the application was uniformly dispersed after ultrasonic treatment, and there was no phenomenon of aggregation and sedimentation ( Figure 4 left), while in the mixed suspension of Comparative Example 1, obvious aggregation and sedimentation occurred between ChNCs and PGS after ultrasonic treatment, and the dispersion uniformity of the whole system was poor ( Figure 4 right), which led to poor thickness uniformity of the finally prepared PGS / ChNC oil-water separation membrane, and the distribution of ChNCs and PGS in the membrane was also extremely uneven. The contact angle of the PGS / ChNC separation membrane prepared in Comparative Example 1 was 134.2°, which did not meet the requirement of super-oil-repellent.

[0059] Comparative Example 2

[0060] Compared with Example 1, in the preparation process, in step 2 (1), ChNCs were added to deionized water, 0.5 M NaOH was added to adjust the pH to 10, and then PGS powder was added to form a mixed suspension, without ultrasonic treatment; the remaining steps were the same as Example 1.

[0061] It was found during the preparation process that the dispersion of ChNCs and PGS in the prepared mixed suspension had improved to some extent compared with Comparative Example 1, but there was still a small amount of aggregation between ChNCs and PGS, and the dispersion uniformity was poorer than that of the application but better than that of Comparative Example 1. The contact angle of the finally prepared PGS / ChNC oil-water separation membrane was 147.2°.

[0062] Performance tests of the PGS / ChNC oil-water separation membrane prepared by the application:

[0063] (1) Oil-water separation experiment:

[0064] With the help of surfactants, soybean oil, n-hexane, petroleum ether and isooctane were dispersed into water respectively to prepare four kinds of micron-sized emulsions containing oil droplets. The pre-wetted PGS / ChNC oil-water separation membrane was placed on the filtration device (filter core diameter: 4 cm), and then the obtained emulsion was slowly poured into the vacuum-assisted filtration device (0.5 bar). Water quickly passed through the membrane, but oil droplets were trapped. After 5 minutes of filtration, the oil-water separation efficiency was tested, and the oil-water separation efficiency was calculated according to the following formula: R1 = (1− C fC0) x 100%, wherein C f (mg mL -1 ) and C0(mg mL -1 ) are the concentrations of oil in the filtrate and the original emulsion, respectively. The results are shown in Figure 5 : photographs of the surfactant-stabilized emulsion and the collected filtrate after separation. The prepared emulsion appears milky white because of the presence of a large number of micron-sized oil droplets that flood the entire imaging field of the optical microscope. After the oil-water emulsion is separated by the vacuum filtration system, the collected filtrate appears clear and transparent, and no droplets can be observed under the optical microscope, indicating that the composite membrane can effectively remove the oil droplets and the oil-water emulsion can be effectively separated.

[0065] (2) Durability experiment

[0066] From the environmental protection point of view, durability is also very important. The durability of the composite filtration membrane was detected by detecting the changes of water flux and oil rejection rate during the oil-water separation process. The specific results are shown in Figure 6 : After 7 cycles, the water flux and oil rejection rate of the filtration membrane remained basically unchanged, in which the water flux basically maintained at about 540 L m -2 h -1 bar -1 , and the oil rejection rate was stable at about 99.1%, indicating that the composite membrane can be recycled, and has certain durability and anti-pollution performance.

[0067] (3) Dye molecule removal experiment

[0068] In order to remove water pollutants such as methylene blue during oil / water separation, a 10 ppm aqueous solution was prepared. The oil / water mixture containing pollutants was poured into the PGS / ChNC oil-water separation membrane prepared by the application for filtration. The initial and final concentrations of dyes after filtration were measured using a UV spectrophotometer. The removal rate formula is R2 = (1− C b / C a ) x 100%, wherein C a (ppm) and C b (ppm) are the initial concentration and the concentration of the filtrate, respectively. The specific results are shown in Figure 7 , Figure 7 : Methylene blue is shown to be used as a water-soluble pollutant of the emulsion. The separation effect diagram of the PGS / ChNC oil-water separation membrane fixed in the filtration system, it is very obvious that the initial emulsion is blue, while the filtrate is transparent and colorless, and its removal rate is as high as 99.92%.

[0069] (4) Mechanical wear experiment

[0070] The mechanical stability of the composite film was evaluated by mechanical abrasion test, sandpaper abrasion test: PGS / ChNC oil-water separation film was placed on 2000 mesh sandpaper, a 50 g weight was added on top of it, an external force was applied to make the composite film move 10 cm along the ruler in the horizontal direction, then another 10 cm in the vertical direction, back to the starting point, this process was defined as an abrasion cycle. The durability after different abrasion times (0, 10, 20, 30, 40) was tested by measuring the underwater oil contact angle. The specific results of Example 6 are shown in Table 2. Figure 8 Figure 8 After 40 times of sandpaper abrasion test, the PGS / ChNC oil-water separation film prepared in the present application still maintained an underwater oil contact angle of more than 150°, indicating that the PGS / ChNC oil-water separation film still had good oil repellency after abrasion.

[0071] (5) Heavy metal ion removal experiment:

[0072] In the above oil-water separation experiment, micron-sized emulsion of n-hexane was added into Mn 2+ , Ni 2+ , Cr 3+ and Fe 3 + , and the concentration of metal ions was 50 ppm. The micron-sized emulsion containing metal ions was poured into the PGS / ChNC oil-water separation film prepared in the present application for filtration, and the same experiment was also conducted on the filtration membranes prepared in Comparative Example 1 and Comparative Example 2, and the filtration membranes prepared by the same procedure as Example 1 without NaOH treatment and ultrasonic treatment were used as the control group. The results are shown in Table 3. Figure 9 In Comparative Example 1, no NaOH was used for adjustment, and the ultrasonic treatment was carried out in a neutral environment. The removal effect of the prepared oil-water separation film on each metal ion was basically the same as that of the control group without ultrasonic treatment, i.e., the ultrasonic treatment alone did not improve the removal of heavy metal ions. In Comparative Example 2, only NaOH was used for adjustment, and no ultrasonic treatment was carried out afterwards. The removal rate of each metal ion was further improved compared with Comparative Example 1. In the present application, on the basis of NaOH adjustment, ultrasonic treatment was carried out alone, and the PGS / ChNC oil-water separation film prepared had a removal rate of Mn 2+ , Ni 2+ , Cr 3+ and Fe 3+ ​The removal rates of the heavy metal ions were 95.1%±0.1%, 96.3%±0.2%, 98.0%±0.5%, 96.9%±0.7% and 98.9%±0.4%, respectively, reaching the Integrated Wastewater Discharge Standard (GB 8978-1996). These results show that the PGS / ChNC oil-water separation membrane can also reduce the concentration of various pollutants in the water phase during the oil-water separation process. It is further shown that the removal performance of heavy metal ions of the PGS / ChNC oil-water separation membrane prepared by compounding chitin nanocrystals with attapulgite and ultrasonic treatment in an alkaline environment is significantly improved. Embodiment

[0073] A preparation method of a super-hydrophilic / underwater super-oleophobic oil-water separation membrane, which is performed according to the following steps:

[0074] Step 1: Preparation of chitin nanocrystals (ChNCs)

[0075] (1) Chitin powder is hydrolyzed with 3 M H2SO4 at 90 °C, stirred at 6000 rpm, and hydrolyzed for 6 h. The mass-volume ratio of chitin powder and H2SO4 is 1 g:30 mL;

[0076] (2) After dilution with distilled water, the hydrolyzate is centrifuged at 9000 rpm for 10 min to remove the supernatant, and then repeated dilution and centrifugation are performed until the supernatant is free of H2SO4. A suspension is obtained for use;

[0077] (3) The suspension is dialyzed using a dialysis bag with a molecular weight cut-off of 8000-14000 KDa until the pH is 7, and then centrifuged at 7000 rpm for 30 min. ChNCs are obtained by drying;

[0078] Step 2: Preparation of attapulgite / chitin nanocrystal (PGS / ChNC) composite membrane

[0079] (1) ChNCs are added to deionized water, 0.5 M NaOH is added to adjust the pH to 10, and then PGS powder is added to form a mixed suspension. The mixed suspension is subjected to ultrasonic treatment, with a specific ultrasonic power of 320 W and ultrasonic treatment for 4 min. The mass-volume ratio of PGS and deionized water is 3 mg:3 mg:25 mL;

[0080] (2) The mixed suspension is filtered by vacuum-assisted filtration at a negative pressure of 1.0 bar to the surface of a mixed cellulose ester membrane substrate with a pore size of 0.22 μm;

[0081] (3) The mixed cellulose ester membrane substrate is placed in a drying box at 60 °C and dried for 10 min to obtain a PGS / ChNC oil-water separation membrane. Embodiment

[0082] A method for preparing a super-hydrophilic / underwater super-oleophobic oil-water separation membrane, which is carried out according to the following steps:

[0083] Step 1: Preparation of Chitin Nanocrystals (ChNCs)

[0084] (1) Hydrolysis of chitin powder with 3 M H2SO4 at 90 °C under stirring at 5000 rpm for 6 h, the mass-volume ratio of chitin powder and H2SO4 being 1 g:30 mL;

[0085] (2) After dilution of the hydrolysate with distilled water, centrifugation at 6000 rpm for 30 min was performed to remove the supernatant, and the dilution and centrifugation were repeated until the supernatant was free of H2SO4, obtaining a suspension for use;

[0086] (3) The suspension was dialyzed against distilled water with a dialysis bag having a molecular weight cut-off of 8000-14000 KDa until the pH was 7, followed by centrifugation at 10000 rpm for 10 min, and drying to obtain ChNCs;

[0087] Step 2: Preparation of PGS / ChNC composite membrane

[0088] (1) ChNCs were added to deionized water, 0.5 M NaOH was added to adjust the pH to 10, and then PGS powder was added to form a mixed suspension, which was subjected to ultrasonic treatment at a power of 300 W for 3 min, the mass-volume ratio of ChNCs, PGS and deionized water being 9 mg:9 mg:25 mL;

[0089] (2) The mixed suspension was filtered onto a mixed cellulose ester membrane substrate with a pore size of 0.22 μm by vacuum-assisted filtration at a negative pressure of 0.2 bar;

[0090] (3) The mixed cellulose ester membrane substrate was placed in a drying oven at 80 °C for 5 min to obtain a PGS / ChNC oil-water separation membrane.

Claims

1. A method for preparing a superhydrophilic / underwater superoleophobic oil-water separation membrane, characterized in that, The following steps are taken: Step 1: Preparation of Chitin Nanocrystals (ChNCs) (1) Chitin powder is hydrolyzed with 3 M H2SO4 at 90 °C under stirring at 5000-6000 rpm for 6 h; (2) After dilution with distilled water, the hydrolysate is centrifuged at 6000-9000 rpm for 10-30 min to remove the supernatant, and the dilution and centrifugation are repeated until the supernatant is free of H2SO4, obtaining a suspension for use; (3) The suspension is dialyzed against distilled water using a dialysis bag with a molecular weight cut-off of 8000-14000 KDa until the pH is 7, then centrifuged at 7000-10000 rpm for 10-30 min, and dried to obtain ChNCs; Step 2: Preparation of Attapulgite / Chitin Nanocrystals (PGS / ChNCs) Composite Membrane (1) Chitin nanocrystals are added to deionized water, 0.5 M NaOH is added to adjust the pH to 10, and then attapulgite powder is added to form a mixed suspension. The mixed suspension is subjected to ultrasonic treatment, with a specific ultrasonic power of 300-360 W and ultrasonic treatment time of 3-4 min. The mass ratio of chitin nanocrystals to attapulgite is 1:1, and the mass / volume ratio of chitin nanocrystals, attapulgite, and deionized water is 3-9 mg:3-9 mg:25 mL; (2) The mixed suspension is filtered onto a mixed cellulose ester membrane substrate with a pore size of 0.22 μm by vacuum-assisted filtration at a negative pressure of 0.2-1.0 bar; (3) The mixed cellulose ester membrane substrate is placed in a drying oven at 40-80 °C for 3-10 min to obtain an attapulgite / chitin nanocrystal oil-water separation membrane.

2. The oil-water separation membrane with superhydrophilic / underwater superoleophobicity prepared by the preparation method of claim 1, characterized in that: The needle-like chitin nanocrystals and the rod-like attapulgite structures in the separation membrane are stacked on each other.

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