Nanosheet-based microspheres nanofiber membrane for separating oil-water emulsion and preparation method thereof

Abstract

The application discloses a nanosheet-based microsphere nanofiber membrane for oil-water emulsion separation and a preparation method thereof, and belongs to the technical field of functional micro-nano fiber materials.The nanosheet-based microsphere nanofiber membrane has a core-shell structure, and comprises a hydrophilic nanofiber core layer and a two-dimensional nanosheet microsphere shell layer.The hydrophilic nanofiber core layer is obtained by an electrospinning method.The two-dimensional nanosheet microsphere shell layer is composed of interlaced and vertically arranged bismuth oxyhalide nanosheets, and the microsphere diameter is micron level.When the membrane is used for oil-water emulsion separation, the membrane has high separation efficiency, and has good separation effect on diesel oil, gasoline, edible oil and engine oil in water, and the separation efficiency is greater than 99.6%.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of nanosheet-based microspheres nanofiber membrane for oil-water emulsion separation and preparation method thereof, belong to functional micro-nano fiber material technical field. BACKGROUND

[0002] Due to industrial emissions, offshore oil production, marine oil transportation and frequent oil spill accidents, oily wastewater pollution has caused waste of oil resources, threatened the life safety of animals and plants and seriously damaged the ecological environment, therefore, in recent years, purification of oily wastewater has become one of the research hotspots that people pay close attention to.

[0003] According to the size of the dispersed phase, oil / water mixture can be divided into three types: free oil / water mixture (> 150 μm), dispersed oil / water mixture (20 μm-150 μm), emulsified oil / water mixture (< 20 μm). Free and dispersed state oil / water mixture can be easily removed by adsorbent material. In contrast, due to small particle size and high stability, emulsified oil / water mixture is more difficult to handle than other types of oil / water mixture.

[0004] Traditional oil / water separation methods such as skimming, sedimentation, air flotation, centrifugation, etc. have the common shortcomings of complex equipment, high energy consumption and low efficiency, while membrane separation method is concerned by academia and industry due to its simple process and low cost. Among them, electrospinning nanofiber membrane has high porosity (> 80%), good pore connectivity, small pore size, large specific surface area and easy surface modification, making it a research hotspot in the field of oil / water separation. However, the average pore size of electrospinning nanofiber membrane is mostly above 2 μm, which is difficult to effectively separate emulsified oil droplets with particle size below 1 μm, and the electrospinning nanofiber membrane is easily contaminated by oil, with poor antifouling property, which seriously limits its development and application.

[0005] To improve the separation performance of nanofiber membranes, some researchers have regulated the wettability of the fiber membrane surface to impart hydrophilic / underwater superoleophobic properties to the fiber membrane, and further impart ultra-low underwater oil adhesion to increase the rolling performance of emulsified oil droplets on the surface to induce coalescence, thereby increasing the emulsion separation performance of nanofiber membranes. In the prior art Superhydrophilic and underwater superoleophobic nanofibrous membrane with hierarchical structured skin for effective oil-in-water emulsion separation (Journal of Materials Chemistry A, 2017, 5, 497), a layer of microspheres is constructed on the surface of the nanofiber membrane by electrostatic spraying to increase the separation performance of the nanofiber membrane, but the bonding strength of the microsphere layer and the nanofiber membrane is weak, which leads to easy separation of the microsphere layer from the base membrane, thereby limiting its practical application.

[0006] Therefore, it is necessary to develop a new type of high-performance oil-water emulsion separation membrane. SUMMARY

[0007] In view of the low separation efficiency of the nanofiber membrane for treating oil-water emulsion in the prior art, the present application provides a nanosheet-based microsphere nanofiber membrane for oil-water emulsion separation and a preparation method thereof. The nanosheet-based microsphere nanofiber membrane has stable ultra-low underwater oil adhesion, can increase the rolling performance of emulsified oil droplets on its surface to induce coalescence, and further improve the emulsion separation performance of the nanofiber membrane.

[0008] The first object of the present application is to provide a nanosheet-based microsphere nanofiber membrane for oil-water emulsion separation, which has a core-shell structure comprising a hydrophilic nanofiber core layer and a two-dimensional nanosheet microsphere shell layer. The hydrophilic nanofiber core layer is obtained by electrospinning. The two-dimensional nanosheet microsphere shell layer is composed of interlaced and vertically arranged bismuth oxyhalide nanosheets, and the microsphere diameter is microns.

[0009] In one embodiment, the hydrophilic nanofiber shell layer is an electrospun nanofiber membrane with hydrophilic properties.

[0010] In one embodiment, the electrospun nanofiber membrane is one or more of PAN nanofiber membrane, PVA nanofiber membrane, and PU cellulose nanofiber membrane.

[0011] In one embodiment, the oil-water emulsion separation refers to the separation of emulsified oil / water mixture (<20 μm).

[0012] In an embodiment, the hydrophilic nanofiber membrane has a water contact angle of 0-10° and an average pore size of 2.1-5 μm.

[0013] In an embodiment, the microspheres have a diameter of 0.5-5 μm and are closely arranged.

[0014] In an embodiment, the nanosheet-based microsphere nanofiber membrane has a water contact angle of 0° and a water spreading time of less than 1 s; an underwater oil contact angle of 160-170°; an underwater oil adhesion of less than 1 μN; and an average pore size of about 0.5-1.3 μm. The nanosheet-based microsphere nanofiber membrane has a separation efficiency of greater than 99.6% for diesel, gasoline, edible oil and engine oil in water.

[0015] A second object of the present application is to provide a method for preparing a nanosheet-based microsphere nanofiber membrane for separating oil-water emulsion, the method comprising the following steps:

[0016] (1) dissolving a hydrophilic monomer in a solvent to obtain a spinning solution, and stirring to obtain a hydrophilic nanofiber membrane by electrospinning;

[0017] (2) placing the hydrophilic nanofiber membrane prepared in step (1) in a Bi(NO3)3·5H2O aqueous solution for ultrasonic immersion; then placing the membrane in a halide salt solution for ultrasonic immersion; the two immersion processes are regarded as one complete SILAR cycle, and the nanosheet-based microsphere nanofiber membrane is obtained after 1-6 cycles.

[0018] In an embodiment, the hydrophilic monomer in step (1) is one or more of PAN, PVA, PU and cellulose; and the solvent is one or more of DMF, DMAc, acetone, water and chloroform.

[0019] In an embodiment, the electrospinning parameters in step (1) are as follows: a perfusion speed of 1-1.5 mL / h, an applied voltage of 20-25 kV, an ambient temperature of 25±3 °C and a humidity of 50±5%.

[0020] In an embodiment, the Bi(NO3)3·5H2O aqueous solution in step (2) has a concentration of 1-100 mmol / L; preferably 10-15 mmol / L.

[0021] In an embodiment, the ultrasonic power for ultrasonic immersion in step (2) is 10-300 W; preferably 30-90 W; and the immersion time is 30-210 s; preferably 90-180 s.

[0022] In an embodiment, the number of cycles in step (2) is 4-6.

[0023] In one embodiment, the halide salt solution in step (2) is a KX solution with a concentration of 1 to 100 mmol / L; wherein X is any one of Cl, Br and I.

[0024] A third objective of this invention is to provide an application of the nanosheet-based microsphere nanofiber membrane described above in oily wastewater.

[0025] The fourth objective of this invention is to provide a method for separating oil-water emulsions, wherein the method uses the aforementioned nanosheet-based microsphere nanofiber membrane to treat the oil-water emulsion.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) This invention employs microwave-assisted continuous ion layer adsorption reaction technology. By adding ultrasonic vibration during the adsorption reaction to induce local overheating of the fibers, BiOX nanosheets are induced to assemble into tightly packed microspheres on the surface of the nanofiber membrane. On the one hand, this increases the roughness of the fiber membrane. On the other hand, the microspheres are composed of vertically interlaced nanosheets and have semi-closed cavities, exhibiting hydrophilic and oleophobic wettability, thus demonstrating stable water retention. This serves as the core of the nanofiber membrane for separating emulsified oil. Both of these properties can impart stable ultra-low underwater oil adhesion to the hydrophilic nanofiber membrane, thereby increasing the rolling performance of emulsified oil droplets on its surface and inducing aggregation, thus achieving oil-water separation and improving the emulsion separation performance of the nanofiber membrane.

[0028] (2) The nanosheet-based microsphere nanofiber membrane prepared by this invention has a water contact angle of 0° and a water spreading time of less than 1s; the underwater oil contact angle can reach 160-170°, the underwater oil adhesion force is less than 1μN, and the average pore size is about 0.5-1.3μm. It has a very good separation effect on diesel, gasoline, edible oil and engine oil in water, with a separation efficiency of more than 99.6%. Attached Figure Description

[0029] Figure 1 The images show the microstructure of the PAN / BiOBr nanofiber membranes prepared in Example 1 and Comparative Example 1; (a) is Example 1; (b) is Comparative Example 1. Detailed Implementation

[0030] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to examples. However, the present invention is not limited to the examples listed, but should also include any other known modifications within the scope of the claims of the present invention.

[0031] The testing method involved in this invention:

[0032] 1. Morphology: The morphology of the fiber membrane sample was characterized by scanning electron microscopy (SEM, SU-8010, Hitachi, Japan).

[0033] 2. Pore size: The pore size distribution of the membrane was determined using a capillary flow porometer (CFP-1100A, PMI, USA).

[0034] 3. Contact angle: The water contact angle in air and the oil contact angle under water of the sample were tested at room temperature using a contact angle measuring instrument (Powereach JC2000D1), and the types of oil were 1,2-dichloroethane, diesel, gasoline, cooking oil, and engine oil. Considering the convenience of measurement, the present application is mainly illustrated by taking 1,2-dichloroethane with a density greater than water as an example.

[0035] 4. Adhesion: The underwater oil adhesion of the fiber membrane was determined using a DCAT25 surface tension meter, and considering the convenience of measurement, the present application is mainly illustrated by taking 1,2-dichloroethane with a density greater than water as an example.

[0036] 4. Separation performance:

[0037] Preparation of oil-in-water emulsion: The oil and water were mixed at a volume ratio of 1:99, and an oil-in-water emulsion was prepared by ultrasonic treatment at a power of 560 W for 30 min. The oil can be diesel, gasoline, cooking oil, or engine oil, and the particle size of the emulsified oil in the obtained oil-in-water emulsion is less than 1 μm.

[0038] The membrane was placed in a dead-end filtration device for emulsion separation experiment,

[0039] After the emulsion was separated, the filtrate was collected to test the total organic carbon content (TOC content, mg L -1 ), and the separation efficiency of the membrane was calculated according to formula (1):

[0040]

[0041] Example 1

[0042] A preparation method of a PAN / BiOBr nanofiber membrane, comprising the following steps:

[0043] (1) 0.3 g of PAN was dissolved in 3 g of DMF, and after stirring for 8 h, a PAN spinning solution was obtained; then spinning was carried out under the conditions of a perfusion speed of 1.5 mL / h and an external voltage of 25 kV, and the environmental temperature and humidity during electrospinning were 25±3℃ and 50±5%, respectively, to obtain a PAN nanofiber membrane; the water contact angle of the PAN nanofiber membrane was 8°, and the average pore size was 2.2 μm;

[0044] (2) The PAN nanofiber membrane prepared in step (1) was placed in an 8 mmol / L Bi(NO3)3·5H2O aqueous solution and immersed for 150 s under 60 W ultrasound to adsorb Bi. 3+ Ions were then added to the membrane, which was then immersed in an 8 mmol / L KBr solution and sonicated for 150 s under 60 W ultrasound to adsorb Br. - Ions are added to generate BiOBr nanosheets; the two soaking processes mentioned above are considered as one complete SILAR cycle. After 6 cycles, a PAN / BiOBr-6 nanofiber membrane with nanosheet microspheres is obtained.

[0045] The PAN / BiOBr nanofiber membrane prepared in this embodiment has nanosheets and microspheres with a diameter of 1.8–2.5 μm. The water contact angle of the PAN / BiOBr nanofiber membrane is 0°, and the water spreading time is 0.1 s. When this fiber membrane is used for oil-water emulsion separation, the underwater oil contact angle can reach 162°, the underwater oil adhesion force is 0.4 μN, and the average pore size is about 1.2 μm. It has a very good separation effect on emulsified diesel, gasoline, edible oil, and engine oil in water, with a separation efficiency greater than 99.7%.

[0046] Example 2

[0047] A method for preparing a PAN / BiOBr nanofiber membrane includes the following steps:

[0048] (1) 0.3g PAN was dissolved in 3g DMF and stirred for 8h to obtain PAN spinning solution; then spinning was carried out under the conditions of pouring speed of 1.5mL / h and applied voltage of 25kV. The ambient temperature and humidity during the electrospinning process were 25±3℃ and 50±5%, respectively, to obtain PAN nanofiber membrane; the water contact angle of PAN nanofiber membrane was 8° and the average pore size was 2.2μm;

[0049] (2) The PAN nanofiber membrane prepared in step (1) was placed in an 8 mmol / L Bi(NO3)3·5H2O aqueous solution and immersed for 150 s under 60 W ultrasound to adsorb Bi. 3+ Ions were then added to the membrane, which was then immersed in an 8 mmol / L KBr solution and sonicated for 150 s under 60 W ultrasound to adsorb Br. - Ions are added to generate BiOBr nanosheets; the two immersions are considered as one complete SILAR cycle. After four cycles, a PAN / BiOBr-4 nanofiber membrane with nanosheet microspheres is obtained.

[0050] The PAN / BiOBr nanofiber membrane prepared in the embodiment has a nanosheet microsphere diameter of 1-1.5 μm; the water contact angle of the PAN / BiOBr nanofiber membrane is 4°, and the water spreading time is 0.9 s; when the nanofiber membrane is used for oil-water emulsion separation, the underwater oil contact angle can reach 160°, the underwater oil adhesion is 0.8 μN, and the average pore size is about 1.3 μm; the nanofiber membrane has a very good separation effect on emulsified diesel oil, gasoline, edible oil and engine oil in water, and the separation efficiency is greater than 99.6%.

[0051] Example 3

[0052] A preparation method of a PAN / BiOI nanofiber membrane, comprising the following steps:

[0053] (1) 0.3 g of PAN is dissolved in 4 g of DMF, and after stirring for 8 h, a PAN spinning solution is obtained; then spinning is performed under the conditions of a perfusion speed of 2 mL / h and an applied voltage of 25 kV, and the environmental temperature and humidity during electrospinning are 25±3 ℃ and 50±5%, respectively; a PAN nanofiber membrane is obtained; the water contact angle of the PAN nanofiber membrane is 5°, and the average pore size is 2.1 μm;

[0054] (2) The PAN nanofiber membrane prepared in step (1) is soaked in an 8 mmol / L Bi(NO3)3·5H2O aqueous solution, and under the action of 30 W ultrasonic waves, the soaking time is 120 s, so as to adsorb Bi 3+ ions; then the soaked membrane is soaked in an 8 mmol / L KI solution, and under the action of 30 W ultrasonic waves, the soaking time is 120 s, so as to adsorb I - ions, and generate BiOI nanosheets; the above two soaking processes are regarded as one complete SILAR cycle, and after 6 SILAR cycles, a PAN / BiOI-6 nanofiber membrane with nanosheet microspheres is obtained.

[0055] The PAN / BiOI nanofiber membrane prepared in the embodiment has a microsphere diameter of 0.9-1.6 μm; the water contact angle of the PAN / BiOI nanofiber membrane is 0°, and the water spreading time is 0.1 s; when the nanofiber membrane is used for oil-water emulsion separation, the underwater oil contact angle can reach 167°, the underwater oil adhesion is 0.3 μN, and the average pore size is about 1.2 μm; the nanofiber membrane has a very good separation effect on emulsified diesel oil, gasoline, edible oil and engine oil in water, and the separation efficiency is greater than 99.8%.

[0056] Example 4

[0057] A preparation method of a PVA / BiOCl nanofiber membrane, comprising the following steps:

[0058] (1) 0.8 g PVA was dissolved in 5 g water, after stirring for 6 h, PVA spinning solution was obtained; then spinning was carried out under the conditions of perfusion speed 2 mL / h and applied voltage 28 kV, and the environmental temperature and humidity during electrospinning were 24±3℃ and 52±5% respectively, PVA nanofiber membrane was obtained, then the PVA nanofiber membrane was placed in a dry dish containing 50 mL glutaraldehyde, and crosslinking was carried out by using the steam volatilized from glutaraldehyde at room temperature; the water contact angle of the PVA nanofiber membrane was 8°, and the average pore size was 3.3 μm;

[0059] (2) The PVA nanofiber membrane prepared in step (1) was immersed in 8 mmol / L Bi(NO3)3·5H2O aqueous solution, and Bi 3+ ions were adsorbed under the action of 80 W ultrasound for 120 s, then the immersed membrane was placed in 8 mmol / L KCl solution, and Cl - ions were adsorbed under the action of 80 W ultrasound for 120 s, to generate BiOCl nanosheets, and the above two immersions were regarded as one complete SILAR cycle, after 6 SILAR cycles, PAN / BiOCl-6 nanofiber membrane was obtained;

[0060] The PAN / BiOCl nanofiber membrane prepared in this example had microspheres with a diameter of 1.8-2.1 μm; the water contact angle of the PAN / BiOCl nanofiber membrane was 0°, and the water spreading time was 0.2 s; when the fiber membrane was used for oil-water emulsion separation, the oil contact angle under water could reach 168°, the oil adhesion under water was 0.2 μN, and the average pore size was about 1.1 μm; the PAN / BiOCl nanofiber membrane had a very good separation effect on emulsified diesel oil, gasoline, edible oil and engine oil in water, and the separation efficiency was greater than 99.8%.

[0061] Comparative Example 1 (without ultrasonic treatment)

[0062] A preparation method of a PAN / BiOBr nanofiber membrane, comprising the following steps:

[0063] (1) 0.3 g PAN was dissolved in 3 g DMF, after stirring for 8 h, PAN spinning solution was obtained; then spinning was carried out under the conditions of perfusion speed 1.5 mL / h and applied voltage 25 kV, and the environmental temperature and humidity during electrospinning were 25±3℃ and 50±5% respectively, PAN nanofiber membrane was obtained; the water contact angle of the PAN nanofiber membrane was 8°, and the average pore size was 2.2 μm;

[0064] (2) The PAN nanofiber membrane prepared in step (1) was immersed in 8 mmol / L Bi(NO3)3·5H2O aqueous solution for 150 s to adsorb Bi 3+ ions, then the immersed membrane was placed in 8 mmol / L KBr solution to adsorb Br- ions to generate BiOBr nanosheets; the above two immersions are regarded as one complete SILAR cycle, and after 6 cycles, PAN / BiOBr nanofiber membrane is obtained.

[0065] The PAN / BiOBr nanofiber membrane prepared in the present comparative example has sheet-shaped BiOBr in the membrane; the water contact angle of the PAN / BiOBr nanofiber membrane is 2°, and the water spreading time is 0.1 s; when the nanofiber membrane is used for oil-water emulsion separation, the oil contact angle under water can reach 152°, the oil adhesion under water is 20 μN, and the average pore size is about 1.2 μm; the separation effect of the nanofiber membrane on emulsified diesel, gasoline, edible oil and engine oil in water is poor, and the separation efficiency is about 85%.

[0066] Results determination

[0067] The nanofiber membranes prepared in Examples 1-4 and Comparative Example 1 are applied to oil-water emulsion separation; wherein the oil-in-water emulsion is prepared by mixing oil and water at a volume ratio of 1:99, and ultrasonic treatment at a power of 560 W for 30 min to prepare 0.5 g / L oil-in-water emulsion. -1 The oil can be diesel, gasoline, edible oil or engine oil, and the particle size of the emulsified oil in the obtained oil-in-water emulsion is less than 1 μm. The separation efficiency is shown in Table 1:

[0068] Table 1. Separation efficiency of different fiber membranes

[0069] Diesel / water emulsion Gasoline / water emulsion Cooking oil / water emulsion Engine oil / water emulsion Example 1 99.9％ 99.7％ 99.8％ 99.7％ Example 2 99.7％ 99.6％ 99.6％ 99.9％ Example 3 99.8％ 99.8％ 99.8％ 99.9％ Example 4 99.9％ 99.8％ 99.8％ 99.9％ Comparative Example 1 84.6％ 85.2％ 85.7％ 85.1％

[0070] The examples provided above are not intended to limit the scope of the present application, and the described steps are not intended to limit the execution order. Those skilled in the art can make obvious improvements to the present application in combination with the existing common knowledge, which also falls within the protection scope defined by the claims of the present application.

Claims

1. A nanosheet-based microspheres nanofiber membrane for separating oil-water emulsion, characterized in that, The nanosheet-based microsphere nanofiber membrane has a core-shell structure, comprising a hydrophilic nanofiber core layer and a two-dimensional nanosheet microsphere shell layer; the hydrophilic nanofiber core layer is obtained by an electrospinning method; the two-dimensional nanosheet microsphere shell layer is composed of halogenated bismuth nanosheets arranged in a staggered and vertical manner, and the microspheres have a diameter of 0.5-5 μm and are closely arranged; The preparation of the nanosheet-based microsphere nanofiber membrane for separating oil-water emulsion comprises the following steps: (1) dissolving a hydrophilic monomer in a solvent, stirring to obtain a spinning solution, and obtaining a hydrophilic nanofiber membrane by electrospinning; (2) placing the hydrophilic nanofiber membrane prepared in step (1) into a Bi(NO3)3·5H2O aqueous solution for ultrasonic immersion, and then placing it into a halide salt solution for ultrasonic immersion; the above two immersion processes are regarded as one complete SILAR cycle, and the nanosheet-based microsphere nanofiber membrane is obtained after 1-6 cycles.

2. The nanoplatelet-based microspheres nanofiber membrane according to claim 1, wherein, The hydrophilic nanofiber shell layer is an electrospun nanofiber membrane with hydrophilic properties.

3. The nanoplatelet-based microspheres nanofiber membrane according to claim 2, wherein, The electrospun nanofiber membrane is one or more of a PAN nanofiber membrane, a PVA nanofiber membrane, and a PU cellulose nanofiber membrane.

4. The nanoplatelet-based microspheres nanofiber membrane of claim 1, wherein, The hydrophilic nanofiber has a water contact angle of 0-10° and an average pore size of 2.1-5 μm.

5. A method for preparing a nanosheet-based microspheres nanofiber membrane for separating oil-water emulsion, characterized in that, The method comprises the following steps: (1) dissolving a hydrophilic monomer in a solvent, stirring to obtain a spinning solution, and obtaining a hydrophilic nanofiber membrane by electrospinning; (2) placing the hydrophilic nanofiber membrane prepared in step (1) into a Bi(NO3)3·5H2O aqueous solution for ultrasonic immersion, and then placing it into a halide salt solution for ultrasonic immersion; the above two immersion processes are regarded as one complete SILAR cycle, and the nanosheet-based microsphere nanofiber membrane is obtained after 1-6 cycles.

6. The method of claim 5, wherein, In step (1), the hydrophilic monomer is one or more of PAN, PVA, PU, and cellulose; and the solvent is one or more of DMF, DMAc, acetone, water, and chloroform.

7. The method of claim 5, wherein, In step (1), the electrospinning parameters are as follows: a perfusion speed of 1-1.5 mL / h, an applied voltage of 20-25 kV, an ambient temperature of 25±3°C, and a humidity of 50±5%.

8. Application of the nanosheet-based microsphere nanofiber membrane according to any one of claims 1-4 to oil-containing wastewater.

9. A method of separating an oil-water emulsion, characterized by, The method is to treat an oil-water emulsion with the nanosheet-based microsphere nanofiber membrane according to any one of claims 1-4.

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