Preparation method and application of PVDF/GO @ PDA @ HNTs composite membrane
Technical Field
The invention belongs to the technical field of preparation of environment functional materials, and particularly relates to a preparation method and application of a PVDF/GO @ PDA @ HNTs composite membrane.
Background
In recent years, a great deal of oily wastewater caused by crude oil exploitation, offshore oil leakage accidents, domestic sewage and the like becomes a great challenge to the environment. The oily wastewater can cause great harm to the environment, for example, petroleum floats on the sea surface, and rapidly diffuses to form an airtight oil film to block the reoxygenation of the water body, so that the oxygen deficiency of the marine water body is caused, the growth of marine plankton is influenced, and the ecological balance of the sea is damaged. The oily sewage is also extremely difficult to treat, the efficiency is low, the cost is high, and the oil in the sewage is divided into four types according to the physical state: free oil, dispersed oil, emulsified oil and dissolved oil.
The membrane separation method is commonly used at present, and has the advantages of low energy consumption, high single-stage separation efficiency, flexible and simple process, low environmental pollution, strong universality and the like; however, the efficiency of membrane separation applications is limited by inherent factors such as membrane fouling resistance, thermal stability, chemical stability, etc., and by extrinsic factors such as membrane module form, operating conditions, etc. With the development of material science, the research and development of surface materials based on special wettability are rapid in recent years, the surface materials mainly comprise super-hydrophilic, super-hydrophobic, super-oleophilic, super-oleophobic, super-amphiphobic, super-amphiphilic surfaces and the like, and a series of applications are achieved in the aspects of self-cleaning surfaces, anti-fog coatings, anti-fouling coatings, anti-fingerprint coatings, micro-droplet transfer technologies, oil-water separation and the like. The polyvinylidene fluoride (PVDF) film has excellent performances of good chemical stability, high mechanical strength, high toughness and the like, and has good application prospect in the field of wastewater oil removal; however, the hydrophobic PVDF membrane has the problems of low surface energy, small permeation flux, easy pollution and the like, and the application of the PVDF membrane in the field of membrane separation is restricted.
The essence of oil-water separation is the interface problem, and the super-oleophobic or super-hydrophobic separation material is obtained by designing the special wettability of the surface of the material, which is undoubtedly the most effective means for improving the oil-water separation performance; however, the application of the membrane material based on the special wettability has many problems, such as poor swelling resistance, poor chemical resistance, fast flux attenuation, limited types of treating oily sewage, low separation efficiency, and the like, and the problems need to be solved urgently.
Disclosure of Invention
In view of the above-mentioned deficiencies in the prior art, the present invention is directed to solving one of the problems; the preparation method of the halloysite-modified super-hydrophilic/underwater super-oleophobic polyvinylidene fluoride/graphene oxide composite membrane comprises the following specific steps:
(1) preparing a vinylidene fluoride/graphene oxide blend membrane: dissolving Graphene Oxide (GO) and polyvinylidene fluoride (PVDF) powder, polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) into N-methyl pyrrolidone (NMP), mechanically stirring to obtain a casting solution, uniformly coating the casting solution on a glass plate, and putting the glass plate into deionized water to prepare a PVDF/GO membrane;
(2) firstly, preparing a dopamine hydrochloride solution, then dissolving Halloysite (HNTs) in the dopamine hydrochloride solution, adding the PVDF/GO membrane obtained in the step (1), and carrying out sealed oscillation reaction to obtain the PVDF/GO @ PDA @ HNTs composite membrane.
Further, in the step (1), the dosage ratio of the graphene oxide to the polyvinylidene fluoride to the polyvinyl alcohol to the polyvinylpyrrolidone to the N-methylpyrrolidone is 0.15-0.6 g: 1.5-6 g: 0.25-1 g, 0.1-0.4: 30 mL.
Further, the temperature of the mechanical stirring in the step (1) is 50 ℃, and the mechanical stirring time is 24 hours.
Further, the concentration of the dopamine hydrochloride solution in the step (2) is 2 mg/L.
Further, the dosage ratio of the halloysite to the dopamine hydrochloride solution in the step (2) is 0.05-0.2 g: 100 mL.
Further, the oscillation reaction time in the step (2) is 6-24 hours.
The super-hydrophilic composite membrane has super-hydrophilic/underwater super-oleophobic property, is strong in stability and simple to prepare, and has potential applications, such as the application in the aspects of separating oil stains in oily sewage, purifying water and the like.
Has the advantages that:
(1) the PVDF material used in the invention has low price and wide source, and the preparation method of the film is simple and has low energy consumption, thus being capable of producing PVDF film in large scale and being applied to the field of film separation.
(2) According to the invention, a dopamine bionic adhesion technology is utilized, natural mineral halloysite is loaded on a PVDF/GO membrane through a one-step method, the defect that inorganic nanoparticles loaded on the PVDF/GO membrane by a conventional suction filtration method are easy to fall off is overcome, and a PVDF/GO @ PDA @ HNTs composite membrane is prepared; through a contact angle test, the contact angle on water of the composite membrane is close to 0 degree, the contact angle under water is 153 degrees, and the composite membrane has super-hydrophilic/super-oleophobic performance under water; for the prepared PVDF @ PDA @ NiCo2(OH)6The composite membrane is subjected to various oil-water emulsion separation experiments, and the separation efficiency can reach 99.5 percent only under the gravity condition. And after 10 cycles of experimentThen, the flux recovery ratio reaches 87%, which shows that the composite membrane has good reproducibility and dirt resistance; and the filtered scanning electron microscope image shows that the halloysite nanoparticles are still firmly connected to the surface of the membrane, which shows that the composite membrane has stable structure and can effectively separate sewage.
(3) The invention adopts the membrane separation technology, has short flow, easy operation control, resource saving and no secondary pollution, conforms to the green chemical concept and is suitable for wide popularization and use.
Drawings
FIG. 1 is a scanning electron microscope image of a PVDF/GO @ PDA @ HNTs composite membrane.
FIG. 2 is a photograph of the oil contact angle of a PVDF/GO membrane.
FIG. 3 is a photograph of the oil contact angle of a PVDF/GO @ PDA @ HNTs film.
FIG. 4 is a photograph of the contact angle on water of a PVDF/GO membrane.
FIG. 5 is a photograph of the contact angle on water of PVDF/GO @ PDA @ HNTs film.
FIG. 6 is a graph of pure water flux and petroleum ether/water emulsion flux under gravity alone for PVDF/GO membrane and PVDF/GO @ PDA @ HNTs composite membranes prepared with different amounts of halloysite.
FIG. 7 is a graph of the separation efficiency of petroleum ether/water emulsion under gravity alone for PVDF/GO membrane and PVDF/GO @ PDA @ HNTs composite membranes prepared with different amounts of halloysite.
FIG. 8 is a graph of the separation efficiency of PVDF/GO @ PDA @ HNTs composite membrane for separating various oil-water emulsions.
FIG. 9 is a scanning electron microscope image after the PVDF/GO @ PDA @ HNTs composite membrane flux.
FIG. 10 is a graph of the cycling flux recovery ratio for PVDF/GO membrane and PVDF/GO @ PDA @ HNTs composite membrane.
Detailed Description
The invention is further described below with reference to specific examples:
example 1:
(1) preparation of PVDF/GO membranes: weighing 0.15g of graphene, 1.5g of polyvinylidene fluoride powder, 0.25g of polyvinyl alcohol and 0.1g of polyvinylpyrrolidone, adding the mixture into 30mL of N-methylpyrrolidone, mechanically stirring the mixture at 50 ℃ for 24 hours to obtain a casting solution, uniformly coating the casting solution on a glass plate, and putting the glass plate into deionized water to prepare a PVDF/GO composite membrane;
(2) preparing 100mL of 2mg/L dopamine hydrochloride solution, adding 0.05g of halloysite, performing ultrasonic homogenization, adding a PVDF/GO membrane, performing sealed oscillation reaction for 6 hours, taking out the membrane, washing with deionized water, and drying to obtain the PVDF/GO @ PDA @ HNTs membrane.
Example 2:
(1) preparation of PVDF/GO membranes: weighing 0.3g of graphene, 3g of polyvinylidene fluoride powder, 0.5g of polyvinyl alcohol and 0.3g of polyvinylpyrrolidone, adding the mixture into 30mL of N-methylpyrrolidone, mechanically stirring the mixture at 50 ℃ for 24 hours to obtain a membrane casting solution, uniformly coating the membrane casting solution on a glass plate, and putting the glass plate into deionized water to prepare a PVDF/GO composite membrane;
(2) preparing 100mL of 2mg/L dopamine hydrochloride solution, adding 0.1g of halloysite, performing ultrasonic homogenization, adding a PVDF/GO membrane, performing sealed oscillation reaction for 24 hours, taking out the membrane, washing with deionized water, and drying to obtain the PVDF/GO @ PDA @ HNTs membrane.
Example 3:
(1) preparation of PVDF/GO membranes: weighing 0.6g of graphene, 6g of polyvinylidene fluoride powder, 1g of polyvinyl alcohol and 0.4g of polyvinylpyrrolidone, adding the weighed materials into 30mL of N-methylpyrrolidone, mechanically stirring the materials at 50 ℃ for 24 hours to obtain a casting solution, uniformly coating the casting solution on a glass plate, and putting the glass plate into deionized water to prepare a PVDF/GO composite membrane;
(2) preparing 100mL of 2mg/L dopamine hydrochloride solution, adding 0.2g of halloysite, uniformly performing ultrasonic treatment, adding a PVDF/GO membrane, performing sealed oscillation reaction for 18 hours, taking out the membrane, washing with deionized water, and drying to obtain the PVDF/GO @ PDA @ HNTs membrane.
FIG. 1 is a scanning electron microscope image of the super-hydrophilic PVDF/GO @ PDA @ HNTs composite membrane prepared in example 2, and it can be seen from the image that a layer of rod-shaped nanoparticles is distributed on the surface of the membrane, so that the roughness of the surface of the membrane is increased.
FIG. 2 is the oil contact angle of the PVDF/GO membrane prepared in example 2, where the oil contact angle can be seen to be 123 deg., showing the underwater oleophobic property.
FIG. 3 is the oil contact angle of the superhydrophilic PVDF/GO @ PDA @ HNTs membrane prepared in example 2, where the underwater oil contact angle is 153 ° (> 150 °), showing the superhydrophobic property under water, and it can be seen that polyenerite enhances the oleophobicity of the membrane.
Fig. 4 is an on-water contact angle of the super-hydrophilic PVDF/GO composite membrane prepared in example 2, in which it can be seen from the graph that the oil contact angle is 94 °, exhibiting a hydrophobic property.
FIG. 5 is a water contact angle of the PVDF/GO @ PDA @ HNTs composite membrane prepared in example 2, and it can be seen that the water contact angle is close to 0 degree, and the super-hydrophilic performance is shown.
FIG. 6 is a graph of pure water flux and petroleum ether/water emulsion flux under gravity alone for PVDF/GO @ PDA @ HNTs composite membranes prepared in example 2 and different amounts of halloysite (0.05g, 0.1g, 0.2 g); as can be seen from the figure, the water flux of the PVDF/GO membrane is 546L.m-2.h-1(ii) a The water flux of halloysite used in the amount of 0.05g, 0.1g and 0.2g was 808L.m-2.h-1、1492L.m-2.h-1、1095L.m-2.h-1(ii) a Oil flux for PVDF/GO membranes is 325L.m-2.h-1(ii) a The oil fluxes of halloysite used at 0.05g, 0.1g and 0.2g were 447L.m respectively-2.h-1、895L.m-2.h-1、667L.m-2.h-1(ii) a The flux of 0.1g is the largest, and the flux is reduced on the contrary because the halloysite grafted on the surface of the membrane is too much, so that the pore diameter of the surface of the membrane is blocked, and the flux of the membrane is greatly reduced.
FIG. 7 is a graph of the separation efficiency of petroleum ether/water emulsions under gravity alone for PVDF/GO @ PDA @ HNTs composite membranes prepared in example 2 and different amounts of halloysite (0.05g, 0.1g, 0.2 g); the oil-water separation efficiency of the PVDF/GO membrane under the gravity condition is 78.92%; the oil-water separation efficiency of PVDF/GO @ PDA @ HNTs films prepared by different halloysite dosages (0.05g, 0.1g and 0.2g) under the gravity condition is 93.31%, 99.75% and 99.85% respectively; is far superior to the separation efficiency of PVDF/GO membranes and conforms to the principle of green chemistry.
FIG. 8 is a graph showing the separation efficiency of PVDF/GO @ PDA @ HNTs composite membrane prepared in example 2 for separating various oil-water emulsions, oil-water emulsions without emulsifier and emulsions with emulsifierThe oil-water emulsion separation efficiency of the reagent is up to more than 99.5 percent, which shows that the prepared PVDF @ PDA @ NiCo2(OH)6The composite membrane has wide applicability.
FIG. 9 is a scanning electron microscope image of the PVDF/GO @ PDA @ HNTs composite membrane prepared in example 2 after flux, and it can be seen from the scanning image that a layer of rod-shaped nanoparticles still exists on the surface of the membrane after an oil-water separation experiment, which illustrates that the prepared PVDF/GO @ PDA @ HNTs composite membrane has a stable structure.
FIG. 10 is a graph of the cycling flux recovery ratio of the PVDF/GO membrane and the PVDF/GO @ PDA @ HNTs composite membrane prepared in example 2. After 10 times of oil-water separation experiments, the flux recovery ratio of the PVDF/GO @ PDA @ HNTs membrane still reaches 87% and is far higher than that of the PVDF/GO membrane (78%), which indicates that the PVDF/GO @ PDA @ HNTs membrane has good stain resistance and regeneration performance.
Description of the drawings: the above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention; thus, while the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.