CN112933980A - Thiophene selective MoSe2-rGO foam composite membrane, preparation method thereof and method for separating thiophene - Google Patents

Thiophene selective MoSe2-rGO foam composite membrane, preparation method thereof and method for separating thiophene Download PDF

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CN112933980A
CN112933980A CN202110127871.XA CN202110127871A CN112933980A CN 112933980 A CN112933980 A CN 112933980A CN 202110127871 A CN202110127871 A CN 202110127871A CN 112933980 A CN112933980 A CN 112933980A
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mose
rgo
thiophene
solution
pebax
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CN112933980B (en
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彭平
兰永强
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Sanming University
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Sanming University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
    • B01D61/362—Pervaporation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0079—Manufacture of membranes comprising organic and inorganic components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/34—Polyvinylidene fluoride
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/76—Macromolecular material not specifically provided for in a single one of groups B01D71/08 - B01D71/74
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D333/00—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom
    • C07D333/02—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings
    • C07D333/04—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings not substituted on the ring sulphur atom
    • C07D333/06—Heterocyclic compounds containing five-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings not substituted on the ring sulphur atom with only hydrogen atoms, hydrocarbon or substituted hydrocarbon radicals, directly attached to the ring carbon atoms
    • C07D333/08—Hydrogen atoms or radicals containing only hydrogen and carbon atoms
    • C07D333/10—Thiophene

Abstract

The invention provides thiophene selective MoSe2-rGO foam composite membrane, preparation method thereof and method for separating thiophene, wherein the preparation method of the composite membrane comprises the following steps: firstly synthesizing MoSe2rGO and physical blending method is adopted to blend MoSe2-rGO as filler into Pebax matrix to obtain casting solution. And finally, coating the casting solution on a polyvinylidene fluoride micro-filtration membrane by taking polyvinylidene fluoride as a supporting layer and adopting a spin-coating methodObtaining MoSe2-rGO/Pebax/PVDF composite membranes. The composite film of the invention adopts MoSe2The rGO is used as a filler, so that the free volume in the composite membrane can be increased, more transfer promoting sites can be provided for thiophene, the pervaporation desulfurization performance of the Pebax membrane can be effectively improved, and the composite membrane has better thiophene separation capability.

Description

Thiophene selective MoSe2-rGO foam composite membrane, preparation method thereof and method for separating thiophene
Technical Field
The invention relates to the technical field of pervaporation composite membranes, and in particular relates to MoSe2-rGO foam composite membrane, preparation method thereof and separation deviceA process for producing a thiophene.
Background
With the increasing amount of automobile reserves, the use of gasoline has become an important cause of environmental pollution. Therefore, the development of efficient gasoline desulfurization technology is urgently needed. The existing gasoline desulfurization technology mainly comprises selective oxidation, selective extraction, catalytic extraction, alkylation extraction, adsorption, Pervaporation (PV) membrane separation and the like. Compared with other separation methods, the PV method is a desulfurization technology with wide application prospect, and is generally regarded by people because of the advantages of low operation cost, high separation efficiency, simple operation steps, easy amplification, adaptation to process flow change and the like.
According to the solubility parameter theory, thiophene and its derivatives are used as the main sulfur-containing compounds in gasoline, and the solubility parameter of thiophene is very close to that of polyether block amide (Pebax). Pebax has high hydrophobicity, strong physical and mechanical strength and good thermal stability, and is a common membrane material. It can be used to separate gas and liquid mixtures, and has particular advantages in the separation of aromatics. However, the current Pebax membrane separation mechanism is only a pure physical mechanism based on dissolution and diffusion, and therefore, innovation and improvement are needed.
Disclosure of Invention
The invention aims to provide MoSe2The preparation method of the-rGO foam composite membrane is simple, easy to operate and suitable for industrial production.
Another object of the present invention is to provide a MoSe2-rGO foam composite membranes using MoSe2The rGO serving as a filler is added into a Pebax matrix, so that the free volume in the composite membrane can be increased, more transfer promoting sites can be provided for thiophene, and the thiophene separation capacity is better.
The third purpose of the invention is to provide a method for separating thiophene, which adopts the composite membrane to separate the mixed solution of thiophene and normal octane and has better separation effect.
The technical problem to be solved by the invention is realized by adopting the following technical scheme.
The invention provides thiophene selective MoSe2-a method of making rGO foam composite membranes comprising the steps of:
S1、MoSe2-synthesis of rGO: dissolving selenium powder in hydrazine hydrate, magnetically stirring for 11-13 h to obtain a hydrazine hydrate-selenium mixed solution, and adding Na into the hydrazine hydrate-selenium mixed solution2MoO4Obtaining molybdenum diselenide (MoSe) in the solution2) A precursor, then adding said MoSe2Mixing the precursor with a Graphene Oxide (GO) solution, carrying out ultrasonic treatment for 0.5-1.5 h to obtain a mixture, and finally sealing the mixture in a stainless steel autoclave with a polytetrafluoroethylene lining for hydrothermal treatment, cooling, washing and freeze drying to obtain the MoSe2-rGO；
S2, dissolving Pebax in n-butanol at the temperature of 65-75 ℃ to obtain a first solution;
s3 MoSe2-rGO is ultrasonically dispersed in n-butanol to obtain a second solution;
s4, mixing the first solution and the second solution, and stirring for 3.5-4.5 hours at 70-80 ℃ to obtain a casting solution;
s5, coating the casting solution on the polyvinylidene fluoride micro-filtration membrane by taking the polyvinylidene fluoride micro-filtration membrane as a supporting layer and adopting a spin coating method to obtain MoSe2-rGO/Pebax/PVDF composite membranes.
The invention provides thiophene selective MoSe2-rGO foam composite membranes, prepared according to the above preparation method.
The invention also provides a method for separating thiophene, which uses the composite membrane to separate mixed liquor of thiophene and normal octane.
Thiophene selective MoSe of embodiments of the invention2the-rGO foam composite membrane, the preparation method thereof and the method for separating thiophene have the beneficial effects that:
the polyether block amide (Pebax) has high hydrophobicity, strong physical and mechanical strength and good thermal stability, and can be used for separating gas and liquid mixtures. The invention uses MoSe2-preparation of MoSe by filling rGO nano composite material into Pebax2-rGO/Pebax/PVDF composite membranes. MoSe2the-rGO structure can provide a transmission carrier and a large number of mesoporous structures for the composite membrane, so that the pervaporation desulfurization performance of the Pebax membrane can be effectively improved, and MoSe can be obtained2the-rGO/Pebax/PVDF composite membrane has better thiophene separation capability.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 shows MoSe obtained in example 4 of the present invention2-XRD pattern of rGO;
FIG. 2 shows MoSe obtained in example 4 of the present invention2-raman spectrogram of rGO;
FIG. 3 shows MoSe obtained in example 4 of the present invention2-SEM picture of rGO;
FIG. 4 shows MoSe obtained in example 4 of the present invention2-SEM images of surface and cross-section of rGO/Pebax/PVDF composite membrane;
FIG. 5 shows Pebax films of comparative example 1 and MoSe of example 42-AFM images of rGO/Pebax/PVDF composite films;
FIG. 6 shows MoSe2-rGO/Pebax/PVDF composite membrane swelling resistance and MoSe2-graph of rGO addition;
FIG. 7 shows MoSe obtained in example 4 of the present invention2-rGO and MoSe2-TGA curves for rGO/Pebax/PVDF composite membrane and Pebax membrane in comparative example 1;
FIG. 8 shows MoSe2-amount of added rGO to MoSe2-graph of the effect of pervaporation desulfurization performance of rGO/Pebax/PVDF composite membranes;
FIG. 9 shows the concentration of thiophene in a mixed solution of thiophene and n-octane versus MoSe2-effect plot of permeation flux and enrichment factor of rGO/Pebax/PVDF composite membranes;
FIG. 10 is operating temperature vs. MoSe2Influence of permeation flux and enrichment factor of rGO/Pebax/PVDF composite membranesA drawing;
FIG. 11 is operating time vs. MoSe2Graph of the effect of the pervaporation performance of rGO/Pebax/PVDF composite membranes.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Thiophene-selective MoSe for the following examples of the invention2the-rGO foam composite membrane, the preparation method thereof and the method for separating and purifying thiophene are concretely explained.
The embodiment of the invention provides thiophene selective MoSe2-a method of making rGO foam composite membranes comprising the steps of:
S1、MoSe2-synthesis of rGO: dissolving selenium powder in hydrazine hydrate, magnetically stirring for 11-13 h to obtain a hydrazine hydrate-selenium mixed solution, and adding Na into the hydrazine hydrate-selenium mixed solution2MoO4In solution to obtain MoSe2A precursor, then adding said MoSe2Mixing the precursor with a graphene oxide solution, carrying out ultrasonic treatment for 0.5-1.5 h to obtain a mixture, and finally sealing the mixture in a stainless steel autoclave with a polytetrafluoroethylene lining for hydrothermal treatment, cooling, washing and freeze drying to obtain the MoSe2-rGO。
Graphene, molybdenum disulfide (MoS)2) The material is a two-dimensional material with high specific surface area, and can establish a proper plane for thiophene transportation in the Pebax composite membrane, provide a proper transportation carrier and improve the desulfurization performance of the composite membrane. MoSe prepared by the invention2the-rGO nano composite material has a multi-layer porous structure and a high specific surface area, can improve the free volume in the composite membrane, and provides more transfer promotion sites for thiophene, so that the pervaporation desulfurization performance of the Pebax membrane can be effectively improved. Further, the freeze-drying treatment can be performedMoSe storage2The three-dimensional structure of rGO facilitates the preparation of subsequent composite membranes.
Further, in a preferred embodiment of the present invention, the molar concentration of selenium in the hydrazine hydrate-selenium mixed solution is 0.6 to 1mol/L, and the Na is2MoO4In solution, Na2MoO4The molar concentration of the inorganic oxide is 0.08-1.2 mol/L, and the MoSe is2In the precursor, the molar ratio of molybdenum to selenium is 1: 1.5-2. MoSe2The precursor is a transparent dark brown solution, preferably the MoSe2The molar ratio of molybdenum to selenium in the precursor was 1: 2.
Further, in the preferred embodiment of the present invention, the MoSe is2The volume ratio of the precursor to the graphene oxide solution is 1: 4.5-5.5, wherein the mass concentration of the graphene oxide solution is 1.5-2.5 mg/mL-1。
Further, in a preferred embodiment of the present invention, the temperature of the hydrothermal treatment is 180 to 220 ℃, the time is 22 to 26 hours, the volume of the stainless steel autoclave is 95 to 110mL, the mixture is cooled to room temperature after the hydrothermal treatment, and then deionized water and ethanol are used for washing for multiple times.
S2, dissolving Pebax in n-butanol at 65-75 ℃ to obtain a first solution.
Further, in a preferred embodiment of the invention, the mass ratio of the Pebax to the n-butanol is 1: 6-6.5.
S3 MoSe2-ultrasonic dispersion of rGO in n-butanol to obtain a second solution.
And S4, mixing the first solution and the second solution, and stirring for 3.5-4.5 hours at 70-80 ℃ to obtain a casting solution.
S5, coating the casting solution on the polyvinylidene fluoride micro-filtration membrane by taking the polyvinylidene fluoride micro-filtration membrane as a supporting layer and adopting a spin coating method to obtain MoSe2-rGO/Pebax/PVDF composite membranes. The separation capacity of a membrane depends on the dissolution and diffusion of the osmotic components inside the membrane, which depend on the chemical and physical properties of the membrane material. Pebax has a solubility parameter of 19.51 (J/cm)3)1/2Solubility parameter with thiophene 20: (J/cm3)1/2In close proximity. Thus, Pebax has a strong affinity for thiophene. According to the solubility parameter theory, the smaller the difference between the solubility parameters of two materials, the better their interaction. The solubility of thiophene in the Pebax layer is higher due to the affinity between thiophene and the Pebax material. With thiophene in MoSe2Binding energy on the nanoscale is in the range of reversible chemical complexation, thus MoSe2Can be used as a transportation carrier of the thiophene.
Further, in the preferred embodiment of the present invention, the MoSe is2-rGO/Pebax/PVDF composite membranes, said MoSe2-0.01-0.25 wt.% of rGO. Preferably, MoSe2-0.15-0.25 wt.% of rGO. Adding MoSe into Pebax matrix2Larger two-phase interface areas are obtained with rGO. At the same time, MoSe2rGO is able to disrupt the regular arrangement of Pebax segments, providing greater free volume. MoSe compared to Pebax films2The enrichment factor of the rGO/Pebax composite membrane is obviously improved. Thus, with MoSe2An increase in rGO content, an increasing pervaporation flux and enrichment factor of the membrane. But MoSe2Too high a rGO content leads to a decrease in the enrichment factor.
Further, in a preferred embodiment of the invention, the spin coating is carried out at a rotating speed of 490-510 rpm for 25-35 s, and the coating is dried overnight at 25-35 ℃ and then treated at 55-65 ℃ for 22-26 h. Coating the casting solution on a polyvinylidene fluoride micro-filtration membrane by a spin coating method to obtain MoSe with stable performance2-rGO/Pebax/PVDF composite membranes.
Further, in a preferred embodiment of the present invention, the polyvinylidene fluoride micro-filtration membrane is pretreated in a pretreatment solution for 2.5 to 3.5 hours, wherein the pretreatment solution is deionized water.
According to the invention, the reduced graphene oxide and the MoSe grown on the reduced graphene oxide are firstly subjected to a hydrothermal method2Nano layer synthesis of MoSe2-rGO nano composite material, and then preparing MoSe by adopting physical blending method2-rGO/Pebax/PVDF composite membranes. The preparation method is simpleEasy operation and low operation cost, and is suitable for industrial production.
The invention also provides thiophene selective MoSe2-rGO foam composite membranes, prepared according to the above preparation method. The composite film adopts MoSe2The rGO serving as a filler is added into a Pebax matrix, so that the free volume in the composite membrane can be increased, more transfer promoting sites can be provided for thiophene, and the thiophene separation capacity is better.
The invention also provides a method for separating thiophene, and the MoSe is used2Separating thiophene-octane mixed liquor by using an rGO/Pebax/PVDF composite membrane. The concentration and the operating temperature of the thiophene in the mixed solution of the thiophene and the octane can be adjusted to MoSe2-rGO/Pebax/PVDF composite membranes, preferably MoSe2When the-rGO/Pebax/PVDF composite membrane is used for thiophene separation, the concentration of selected thiophene is 1312-2512 ppm, and the operating temperature is 30-70 ℃.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a MoSe2-rGO/Pebax/PVDF composite membrane, made according to the following method:
(1) pretreatment of the support layer: the polyvinylidene fluoride micro-filtration membrane is soaked in deionized water for 3 hours before use.
(2)MoSe2-synthesis of rGO: in flask A, 8mmol selenium powder was dissolved in 10mL hydrazine hydrate and magnetically stirred for 12h at constant temperature. Simultaneously adding 4mmol of Na2MoO4·2H2O was dispersed in 40mL of distilled water in flask B. Then slowly adding 10mL of hydrazine hydrate-selenium mixed solution into 40mL of Na at room temperature2MoO4In solution. Finally obtaining a transparent dark brown solution with the mol ratio of Mo to Se of 1:2, namely MoSe2A precursor.
Adopts a hydrothermal method to synthesize MoSe2-rGO nanocomposites. 2mL of MoSe2Precursor and 10mL of 2 mg/mL-1The GO solution of (a) was mixed and sonicated for 1 hour. The resulting mixture was then sealed in a 100mL Teflon lined stainless steel autoclaveAnd hydrothermal treatment is carried out at 200 ℃ for 24 hours. After cooling to room temperature, the product was thoroughly washed several times with deionized water and ethanol and freeze-dried to preserve MoSe2-rGO three-dimensional structure.
(3) Preparing a casting solution: 0.7g of Pebax was dissolved in 4.5g of n-butanol at 70 ℃ under stirring to obtain a first solution. A certain amount of MoSe is added by ultrasonic waves2-rGO dispersed in 4.5g n-butanol to give a second solution. And mixing the first solution and the second solution, and stirring at 75 ℃ for 4 hours to obtain the membrane casting solution. In the film casting solution, MoSe2-rGO content 0.05 wt.%.
(4)MoSe2-preparation of rGO/Pebax/PVDF composite membrane: after cooling to room temperature, the casting solution was coated on the PVDF ultrafiltration membrane by treating for 30 seconds at 500rpm by a spin coating method. The membrane was dried at 30 ℃ overnight and treated at 60 ℃ for 24 hours to remove residual solvent. The obtained film is MoSe2-rGO/Pebax/PVDF composite membranes.
MoSe obtained in this example2The pervaporation desulfurization performance of the-rGO/Pebax/PVDF composite membrane is measured by a mixed solution of thiophene and n-octane with the thiophene concentration of 1312ppm, and the pervaporation flux of the composite membrane is 4334 g.m-2·h-1The enrichment factor was 4.36.
Example 2
The embodiment provides a MoSe2-rGO/Pebax/PVDF composite membrane, which differs from example 1 in that: MoSe2-rGO content 0.1 wt.%.
MoSe obtained in this example2The pervaporation desulfurization performance of the-rGO/Pebax/PVDF composite membrane is measured by a mixed solution of thiophene and n-octane with the thiophene concentration of 1312ppm, and the pervaporation flux of the composite membrane is 5085 g.m-2·h-1The enrichment factor was 4.80.
Example 3
The embodiment provides a MoSe2-rGO/Pebax/PVDF composite membrane, which differs from example 1 in that: MoSe2-rGO content 0.15 wt.%.
MoSe obtained in this example2rGO/Pebax/PVDF composite membranes at 1312The pervaporation desulfurization performance is measured by ppm mixed solution of thiophene and n-octane, and the pervaporation flux is 5709 g.m-2·h-1The enrichment factor was 5.26.
Example 4
The embodiment provides a MoSe2-rGO/Pebax/PVDF composite membrane, which differs from example 1 in that: MoSe2-rGO content 0.2 wt.%.
MoSe obtained in this example2The pervaporation desulfurization performance of the-rGO/Pebax/PVDF composite membrane is measured by 1312ppm of thiophene and n-octane mixed solution, and the pervaporation flux is 6645 g.m-2·h-1The enrichment factor was 5.61.
Example 5
The embodiment provides a MoSe2-rGO/Pebax/PVDF composite membrane, which differs from example 1 in that: MoSe2-rGO content 0.25 wt.%.
MoSe obtained in this example2The pervaporation desulfurization performance of the-rGO/Pebax/PVDF composite membrane is measured in 1312ppm mixed solution of thiophene and n-octane, and the pervaporation flux is 7582 g.m-2·h-1The enrichment factor was 5.16.
Comparative example 1
This comparative example provides a Pebax film, the method of making which differs from examples 1-5 in that in the Pebax matrix, MoSe is present2-a rGO content of 0.
The Pebax membrane prepared by the comparative example is used for measuring the pervaporation desulfurization performance in 1312ppm of mixed solution of thiophene and n-octane, and the pervaporation flux is 3532 g.m-2·h-1The enrichment factor was 3.54.
FIG. 1 shows MoSe provided in example 4 of the present invention2-XRD pattern of rGO. It can be seen from figure 1 that there is a broad diffraction peak at about 26 ° corresponding to the (002) plane of rGO, indicating that trace amounts of rGO are present in the sample. The other XRD diffraction peaks at 14.2 °, 36.5 °, 43.9 °, 56.1 ° and 73.4 ° correspond to MoSe of (002), (102), (006), (110) and (200), respectively2(JCPDS: 77-1715) Single Crystal faces, indicating that the prepared materials haveThe nature of the crystal.
FIG. 2 shows MoSe provided in example 4 of the present invention2-raman spectrum of rGO. From FIG. 2, it can be seen that the Raman spectrum is at 240cm-1And 280cm-1The nearby characteristic peaks correspond to 2H-MoSe respectively2A of (A)1gAnd E1 2gA vibration mode. E1 2gThe characteristic peak corresponds to the vibration of selenium atom in the horizontal plane, A1gThe characteristic peak corresponds to the vibration of the selenium atom in the vertical plane direction. Thus, A1gAnd E1 2gProvides MoSe grown on graphene nanoplatelets2The structural information of (1). MoSe in FIG. 22-A of rGO nanocomposite1g/E1 2gIs close to 1:1, indicating that the MoSe is prepared2The molybdenum diselenide in rGO is randomly oriented.
FIG. 3 shows MoSe provided in example 4 of the present invention2SEM picture of rGO. From FIG. 3, MoSe can be seen2rGO has a flower-like structure consisting of ultrathin nanosheets with rich folded edges, exhibiting little lamellar structure. The porous structure with atomic scale lamellae suggests that this structure is composed of stacked graphene nanoplatelets.
FIG. 4 shows MoSe provided in example 4 of the present invention2SEM picture of surface and section of rGO/Pebax/PVDF composite membrane, wherein FIG. 4a is MoSe2SEM picture of-rGO/Pebax/PVDF composite membrane surface, FIG. 4b is MoSe2SEM picture of cross section of rGO/Pebax/PVDF composite membrane. As can be seen from FIG. 4a, MoSe2The surface of the-rGO/Pebax/PVDF composite membrane is free from any obvious holes and cracks, and the Pebax and MoSe are proved2Good compatibility between rGO. And the active layer has a compact structure and is the basis of selective permeation. From FIG. 4b, MoSe can be seen2The addition of rGO does not introduce significant non-selective defects.
Shown in FIG. 5 are the Pebax film and MoSe of comparative example 12AFM image of rGO/Pebax/PVDF composite film, in which FIG. 5a is MoSe2AFM of rGO/Pebax/PVDF composite membranes, FIG. 5b is an AFM of Pebax membranes. Separation of composite membranesThe performance is related to the surface roughness, the rougher the surface, the higher the composite membrane flux. From a comparison of FIGS. 5a and 5b, it can be seen that MoSe is added2rGO can increase the roughness of the composite membrane surface.
As shown in FIG. 6, different MoSe were studied using a swelling experiment2-amount of added rGO to MoSe2-impact of anti-swelling properties of rGO/Pebax/PVDF composite membranes. The degree of swelling of the membrane can be used to evaluate the affinity of the membrane for the thiophene component. FIG. 6 shows different compositions containing MoSe2-MoSe in rGO addition2-room temperature swelling behaviour of rGO/Pebax/PVDF composite membranes in thiophene n-octane mixed liquor solutions. From FIG. 6, MoSe can be seen2the-rGO/Pebax/PVDF composite membrane has good thiophene adsorption performance. Furthermore, with MoSe2Increasing the addition amount of rGO and continuously enhancing the anti-swelling capacity of the composite membrane. Indicating MoSe2The rGO/Pebax/PVDF composite membrane does not have obvious performance reduction along with the prolonging of the service time when thiophene is separated. Therefore, the mixed solution of thiophene and octane can remove thiophene by preferential adsorption of the composite membrane. This confirmed that MoSe2the-rGO/Pebax/PVDF composite membrane has potential in the aspect of application of gasoline desulfurization.
As shown in FIG. 7, the MoSe of example 4 was separately treated by TGA2-rGO and MoSe2Characterization of thermal stability of rGO/Pebax/PVDF composite membranes and Pebax membranes in comparative example 1, where MoSe is shown in FIG. 7a2TGA profile of rGO, FIG. 7b Pebax film and MoSe2-TGA profile of rGO/Pebax/PVDF composite membranes. As shown in FIG. 7a, MoSe2Composition of GO and MoSe2，MoSe2-TGA profile of rGO decreases with increasing temperature. As can be seen from FIG. 7b, the thermal weight loss temperature (453 ℃) of the composite film was reduced by only 5 ℃ compared to the PDMS film (458 ℃), indicating that MoSe2Incorporation of rGO hardly results in a decrease in the thermal stability of the membrane. The sample is decomposed at a temperature higher than 400 ℃, which is far higher than the operating temperature (40-70 ℃) for desulfurization of pervaporation gasoline, so that the performance of the Pebax composite membrane can be kept stable in the separation process.
As shown in FIG. 8, MoSe was tested using 1312ppm of thiophene and n-octane as a simulated gasoline system2The pervaporation desulfurization performance of the rGO/Pebax/PVDF composite membrane, wherein 1 is a variation trend line of permeation flux, and 2 is a variation trend line of enrichment factor. In FIG. 8, following MoSe2The increase in rGO content, the pervaporation flux of the membrane increases continuously, while the enrichment factor tends to increase and then decrease. When MoSe2At an rGO content of 0.2 wt.%, the enrichment factor reaches a maximum of 5.61. Adding MoSe into Pebax matrix2Larger two-phase interface areas are obtained with rGO. At the same time, MoSe2rGO is able to disrupt the regular arrangement of Pebax segments, providing greater free volume. Thus, MoSe is comparable to Pebax films2The enrichment factor of the rGO/Pebax/PVDF composite membrane is obviously improved. MoSe2The effect of rGO addition on the separation performance of the composite membranes is due to: first, graphene and MoSe2The pi-electron enrichment surface can be reversibly complexed with the aromatic ring of the thiophene to form pi-pi interaction. Thus, thiophenes can pass through Pebax and MoSe2-interface fast transport between rGO. Secondly, due to thiophene and MoSe2Continuous reversible reaction between rGO, thiophene in MoSe2The regional concentration near the rGO surface fluctuates instantaneously, resulting in higher chemical potential gradients and higher thiophene fluxes. As can be seen from FIG. 8, when MoSe is present2When the addition amount of the rGO is 0.2 wt.%, the prepared composite membrane has the best desulfurization performance, the enrichment factor is 5.61, and the corresponding permeation flux is 6645 g.m-2·h-1。
As shown in FIG. 9, the concentration of thiophene in the mixture of thiophene and n-octane versus MoSe was examined at 40 deg.C2-effect of permeation flux and enrichment factor of rGO/Pebax/PVDF composite membrane, wherein 1 is the variation trend line of permeation flux and 2 is the variation trend line of enrichment factor. When the temperature of the feed liquid is 40 ℃, the total flux is from 6750 g.m as the concentration of the thiophene is increased from 1312 to 2512ppm-2·h-1Increased to 9843 g.m-2·h-1. This is because thiophene causes the composite membrane to swell to some extent, thereby increasing the permeability of the composite membrane. Furthermore, as can be seen from FIG. 9, as the thiophene concentration increased from 1312ppm to 2512ppm, the permeation flux tended to increase, while the enrichment factor decreased from 5.10 to3.79。
As shown in FIG. 10, the operation temperature vs. MoSe was investigated in a mixed solution of thiophene and n-octane having a thiophene concentration of 1312ppm2-effect of permeation flux and enrichment factor of rGO/Pebax/PVDF composite membrane, wherein 1 is the variation trend line of permeation flux and 2 is the variation trend line of enrichment factor. At the feed liquid concentration of 1312ppm, when the temperature of the feed liquid is increased from 30 ℃ to 70 ℃, the permeation flux is from 6598 g.m-2·h-1To 12823 g.m-2·h-1The enrichment factor decreased from 5.07 to 3.94. The saturated vapor pressure of the downstream components increases with increasing feed solution temperature. Thus, to achieve vapor-liquid equilibrium, the osmotic component is continually vaporized until the pressure equals its saturated vapor pressure, thereby increasing the mass transfer driving force. Furthermore, according to the law of thermal motion, the thermal motion of molecules increases with increasing temperature. The increase in thermal motion results in a simultaneous increase in free volume and osmotic molecular diffusion coefficient in the polymer matrix. Thus, as the operating temperature increases, the increase in total flux is a result of the combined effect of increased mobility of the permeating molecules and increased mobility of the polymer segments. In addition, the swelling degree of the membrane increases with increasing temperature, resulting in a decrease in thiophene selectivity. This is due to the fact that the free volume increases as the temperature increases, and n-octane molecules, which are small in size, permeate the membrane more easily than thiophene molecules.
As shown in FIG. 11, the operation time vs. MoSe was investigated in a mixed solution of thiophene and n-octane having a thiophene concentration of 1312ppm2-effect of pervaporation performance of rGO/Pebax/PVDF composite membrane, wherein 1 is the variation trend line of permeation flux and 2 is the variation trend line of enrichment factor. The experimental result shows that the enrichment factor is gradually reduced with the increase of the operation time, but the reduction amplitude is small, and the enrichment factor is kept at 5.0 after 168 hours. In addition, the total flux was maintained at a high level after 168 hours of continuous operation. The results show that the composite membrane has good separation performance under long-term operating conditions.
The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims (10)

1. Thiophene selective MoSe2-a process for the preparation of rGO foam composite membranes, characterized in that it comprises the following steps:
S1、MoSe2-synthesis of rGO: dissolving selenium powder in hydrazine hydrate, magnetically stirring for 11-13 h to obtain a hydrazine hydrate-selenium mixed solution, and adding Na into the hydrazine hydrate-selenium mixed solution2MoO4Obtaining a molybdenum diselenide precursor in the solution, then mixing the molybdenum diselenide precursor with the graphene oxide solution, carrying out ultrasonic treatment for 0.5-1.5 h to obtain a mixture, finally sealing the mixture in a stainless steel autoclave with a polytetrafluoroethylene lining for hydrothermal treatment, cooling, washing and freeze drying to obtain the MoSe2-rGO；
S2, dissolving polyether block amide in n-butanol at the temperature of 65-75 ℃ to obtain a first solution;
s3 MoSe2-rGO is ultrasonically dispersed in n-butanol to obtain a second solution;
s4, mixing the first solution and the second solution, and stirring for 3.5-4.5 hours at 70-80 ℃ to obtain a casting solution;
s5, coating the casting solution on the polyvinylidene fluoride micro-filtration membrane by taking the polyvinylidene fluoride micro-filtration membrane as a supporting layer and adopting a spin coating method to obtain MoSe2-rGO/Pebax/PVDF composite membranes.
2. The preparation method according to claim 1, wherein the molar concentration of selenium in the hydrazine hydrate-selenium mixed solution is 0.6 to 1 mol/L; the Na is2MoO4In solution, Na2MoO4The molar concentration of the compound is 0.08-1.2 mol/L; the MoSe is2In the precursor, the molar ratio of molybdenum to selenium is 1: 1.5-2.
3. According to claim 1The preparation method is characterized in that the volume ratio of the molybdenum diselenide precursor to the graphene oxide solution is 1: 4.5-5.5, wherein the mass concentration of the graphene oxide solution is 1.5-2.5 mg/mL-1。
4. The preparation method according to claim 1, wherein in step S1, the temperature of the hydrothermal treatment is 180 to 220 ℃ and the time is 22 to 26 hours, and the mixture is cooled to room temperature after the hydrothermal treatment, and then washed with deionized water and ethanol for a plurality of times.
5. The preparation method according to claim 1, wherein the mass ratio of the polyether block amide to n-butanol is 1: 6-6.5.
6. The method of claim 1, wherein the MoSe is present2-rGO/Pebax/PVDF composite membranes, said MoSe2-0.01-0.25 wt.% of rGO.
7. The preparation method according to claim 1, wherein the spin coating is performed at a rotation speed of 490 to 510rpm for 25 to 35 seconds, and the coating is performed at 25 to 35 ℃ overnight after drying and then at 55 to 65 ℃ for 22 to 26 hours.
8. The preparation method of claim 1, wherein the polyvinylidene fluoride microfiltration membrane is pretreated in a pretreatment solution for 2.5-3.5 hours, wherein the pretreatment solution is deionized water.
9. Thiophene selective MoSe2-rGO foam composite membrane, characterized in that it is prepared according to the preparation process of any one of claims 1 to 8.
10. A process for the isolation of thiophenes, characterized in that the thiophene-selective MoSe according to claim 9 is used2-rGO foam compositesAnd (3) membrane combination separation of a mixed solution of thiophene and octane.
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