Preparation method of two-dimensional bimetallic MOF intercalated g-C3N4 composite film

Abstract

The application discloses a preparation method of a two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane, and belongs to the technical field of two-dimensional material membrane preparation. The method solves the problems of low permeation flux and membrane pollution after long-term operation caused by small interlayer spacing and unstable layer structure of the existing two-dimensional membrane. The method comprises the following steps: S1, preparing NiFe-MOF; and S2, preparing the composite membrane through vacuum-assisted self-assembly. The two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane has larger interlayer spacing in the membrane, faster mass transfer rate and more stable and suitable membrane flux. The reasonable construction of the two-dimensional NiFe-MOF nanosheet can support the interlayer channel of the g-C3N4 membrane, improve the separation precision of the two-dimensional membrane, realize selective screening, and the composite membrane with fixed interlayer spacing has good selectivity and excellent water flux. The raw material of the application is easy to obtain and cheap, and the application does not need gas protection and is suitable for industrial production. The application is used for treating water bodies containing organic pollutants.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of two-dimensional material film preparation, and particularly relates to a preparation method of a two-dimensional bimetallic MOF intercalated g-C3N4 composite film. BACKGROUND

[0002] Membrane separation technology is widely used in water treatment and other fields due to its simple operation process, rapid processing, low energy consumption and environmental friendliness. However, in the practical application of membrane separation technology, there are still key technical problems such as membrane pollution, membrane permeability and selectivity contradiction (i.e. Trade-off effect). In the operation process, inorganic, organic pollutants and microorganisms will gradually deposit on the surface or in the pores of the membrane, causing reversible or irreversible membrane pollution, resulting in the decline of membrane flux and service life. The permeability and selectivity of traditional membrane materials are often difficult to improve simultaneously, and there is a technical bottleneck that one goes up and the other goes down. With the rapid development of graphene (Gr), graphene oxide (GO) and other graphene materials, and graphite phase carbon nitride (g-C3N4), molybdenum disulfide (MoS2), two-dimensional transition metal carbide / nitride (MXene) and many other emerging two-dimensional nanomaterials, two-dimensional nanomaterials have attracted research interest in many fields such as environment, energy, materials and life sciences. In new membrane materials, two-dimensional nanomaterials have a unique sheet structure with an atomic size thickness as a nanoscale building block of functional membranes, and through ordered stacking and self-assembly in the membrane, regular water channels are constructed. This kind of new membrane material based on two-dimensional nanomaterials has adjustable separation performance, which can break through the trade-off effect and is called "new generation of membrane materials".

[0003] For the two-dimensional layered membrane composed of stacked nanosheets, the mass transfer mainly occurs in the lateral channel between the nanosheets, and in order to meet the complex requirements of more advanced water separation process, different regulation and construction strategies need to be adopted for the two-dimensional layered membrane. Limiting the interlayer channel can improve the separation precision and realize the selective screening of specific ions and molecules, and the membrane with fixed interlayer distance has good selectivity and excellent water flux. Therefore, the reasonable construction of the two-dimensional nanochannel is an important factor to determine the performance of the separation membrane, and it is of great significance for the conversion of two-dimensional materials into ion and molecule separation membranes. The flux of water molecules in the interlayer channel of the two-dimensional membrane is small, and at present, most studies choose to insert some guest materials as "support" in the interlayer, such as larger zero-dimensional materials and one-dimensional materials, to increase the interlayer distance, which can expand the mass transfer space between the layers to some extent and improve the permeability. It is worth noting that due to the size of the intercalated "support", the effective interlayer distance of the two-dimensional membrane after intercalation may increase, which may reduce the mass transfer resistance of the substances to be intercepted based on size screening, and may sacrifice some selectivity. Therefore, the selection of appropriate size and dimension of the guest intercalation material is crucial to maintain the permeability and selectivity of the two-dimensional membrane.

[0004] In addition to the need for good permeability and selectivity of the two-dimensional membrane, it is also very important for practical application to maintain stable operation for a long time during the separation process. The stability of the membrane is reflected in the stability of the structure of the membrane during the separation process, and the stability of the separation performance (including permeability and selectivity) does not decrease significantly. Another big challenge faced by the two-dimensional membrane is the instability in the water treatment process. The large number of water molecules between adjacent nanosheets weaken the van der Waals force of the interlayer attraction, which makes the interlayer distance expand and even the structure of the membrane is destroyed, and the separation performance is lost. Strengthening the interaction force between the layers in the two-dimensional membrane to improve the stability of the membrane helps the two-dimensional membrane to maintain structural stability and separation performance under harsh operating conditions such as liquid phase separation. SUMMARY

[0005] The purpose of the present application is to solve the problems of low permeation flux, poor selectivity and membrane pollution after long-term operation caused by the difficulty in regulating the interlayer distance and the instability of the layered structure of the existing two-dimensional membrane, and to provide a preparation method of a two-dimensional double-metal MOF intercalated g-C3N4 composite membrane.

[0006] A preparation method of a two-dimensional double-metal MOF intercalated g-C3N4 composite membrane, which is carried out according to the following steps:

[0007] One, preparation of bimetallic layered MOF (NiFe-MOF): mix aqueous solution of nickel acetate tetrahydrate (Ni(OAc)2·4H2O) and ferrous sulfate heptahydrate (FeSO4·7H2O) with N,N-dimethylacetamide solution of terephthalic acid, carry out hydrothermal reaction, wash and dry after cooling to room temperature, to obtain NiFe-MOF;

[0008] Two, preparation of two-dimensional bimetallic MOF intercalated g-C3N4 composite film: disperse NiFe-MOF and g-C3N4 nanosheet into deionized water by ultrasonic, then vacuum filter onto microporous polyether sulfone film, after heat fixation, obtain two-dimensional bimetallic MOF intercalated g-C3N4 composite film, namely complete the preparation method.

[0009] Further, the mass-volume ratio of nickel acetate tetrahydrate, ferrous sulfate heptahydrate and deionized water in the aqueous solution of nickel acetate tetrahydrate and ferrous sulfate heptahydrate in step one is (0.1-0.2) g:(0.04-0.05) g:(20-40) mL.

[0010] The mass-volume ratio of terephthalic acid and N,N-dimethylacetamide in the N,N-dimethylacetamide solution of terephthalic acid is (0.04-0.05) g:(20-40) mL.

[0011] Further, the hydrothermal reaction in step one: the container is a polytetrafluoroethylene inner liner stainless steel autoclave, the reaction temperature is 120-150℃, and the reaction time is 3-5h.

[0012] Further, the washing and drying in step one: stir in 150-300 mL of deionized water and anhydrous ethanol respectively for 3-5h, then centrifuge at a speed of 7000-8000r / min for 5-10min, then take the precipitate and dry at 65-85℃ for 8-12h.

[0013] Further, the preparation process of g-C3N4 nanosheet in step two is as follows: put the organic nitrogen-containing compound into the crucible and calcine in the muffle furnace at high temperature to obtain blocky g-C3N4, then pour into concentrated sulfuric acid and stir to obtain a solid-liquid mixture, then add deionized water and ultrasonic treatment to obtain a light yellow dispersion liquid, after two times of centrifugal purification and drying, obtain g-C3N4 nanosheet.

[0014] Further, the total mass of NiFe-MOF and g-C3N4 nanosheet in step two is 0.5-1mg, and the mole fraction of NiFe-MOF is 25-75%.

[0015] Further, the mass ratio of the total mass of NiFe-MOF and g-C3N4 nanosheets to the mass of deionized water in step two is 1:(10000-20000); and the ultrasonic dispersion time is 1-2h.

[0016] Further, the average pore size of the microporous polyether sulfone membrane used for vacuum filtration in step two is 0.1-0.45μm, and the vacuum filtration pressure is 0.05-0.1MPa.

[0017] Further, the temperature of the heat fixation in step two is 65-85℃, and the heat fixation time is 8-12h.

[0018] Further, the application of the obtained two-dimensional double-metal MOF intercalated g-C3N4 composite membrane in step two is: the two-dimensional double-metal MOF intercalated g-C3N4 composite membrane is used for filtering water bodies containing organic pollutants under a certain pressure.

[0019] In the application, NiFe-MOF and g-C3N4 nanosheets are dispersed in an aqueous solution, and the assembly of the two-dimensional double-metal MOF intercalated g-C3N4 composite membrane under vacuum assistance is controlled by electrostatic interaction. The positively charged amino groups on the g-C3N4 nanosheets interact with the negatively charged carboxyl groups on the NiFe-MOF to form a continuous and orderly arranged heterostructure membrane with molecular attraction between adjacent layers. On the one hand, the insertion of the multi-fold NiFe-MOF can introduce additional interlayer water channels without significantly expanding the interlayer distance, which can more accurately control the interlayer channels for size screening. On the other hand, the Ni-Fe double active center can receive O2· - provides electrons and generates more HO·, effectively alleviating the membrane pollution problem after long-term operation.

[0020] Compared with the prior art, the application has the following advantages and beneficial effects:

[0021] (1) The application uses raw materials that are easy to obtain and inexpensive, does not require inert gas protection (all preparation processes are carried out in an air atmosphere), has a low synthesis temperature, and has relatively simple production equipment, process conditions and steps, and is easy to adjust the composition of the composite membrane, suitable for industrial production.

[0022] (2) The two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane has a faster mass transfer rate and a more stable membrane flux than the previously reported g-C3N4 membrane, and the reasonable construction of the two-dimensional NiFe-MOF nanosheet can introduce more water transport channels in the g-C3N4 membrane, improve the separation precision of the two-dimensional membrane, realize selective screening, and the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane with a fixed interlayer spacing has good selectivity and excellent water flux.

[0023] (3) The Ni-Fe bimetallic intercalation can realize the rapid reduction of Fe(III) through the synergistic effect between the metal centers, and as an electronic buffer system, it can receive O2· - Provided electrons, promote Fe(III) / Fe(II) cycle, produce more HO·. The strengthened in-situ degradation process makes the two-dimensional membrane have excellent catalytic self-cleaning performance.

[0024] (4) The stable intercalation can also improve the mechanical strength of the membrane structure, ensuring the stability of the water channel. The two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane prepared by the present application can have a stable layered structure, higher water flux and good anti-pollution performance, which can alleviate the membrane pollution problem after long-term operation and prolong the effective service life of the membrane.

[0025] The present application inserts a bimetallic layered MOF (NiFe-MOF) material between the g-C3N4 nanosheets through vacuum-assisted self-assembly, realizes the precise regulation of the nanochannel in the traditional g-C3N4 two-dimensional membrane. On the one hand, the layered NiFe-MOF intercalation realizes the increase of the permeation flux without sacrificing the selectivity; on the other hand, the synergistic effect mechanism of the Ni-Fe double center can strengthen the electron transfer of the Fenton-like process, effectively alleviate the membrane pollution problem after long-term operation by in-situ catalytic degradation of the pollution layer on the membrane surface. The composite membrane of the present application has a stable layered structure, higher water flux, better interception effect on organic pollutants and good anti-pollution performance.

[0026] The total thickness of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane prepared by the present application is 0.2-1.0 μm, and the water flux is 73.2 L·m -2 ·h -1 Above.

[0027] The two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane in the present application is suitable for treating water bodies containing organic pollutants. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a scanning electron microscope image of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane in Examples 1-3 and the g-C3N4 membrane in Comparative Example 1 after vacuum-assisted self-assembly.

[0029] Figure 2 Flux plot of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membranes in Examples 1-3 and the g-C3N4 membrane in Comparative Example 1 after continuous filtration of deionized water at 1 bar pressure for 180 min; where ▲ represents Example 1, ♦ represents Example 2,

[0030] ▼ represents Example 3, and ● represents Comparative Example 1.

[0031] Figure 3 Flux plot of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membranes in Examples 1-3 and the g-C3N4 membrane in Comparative Example 1 after continuous filtration of 1 g / L bovine serum albumin aqueous solution at 1 bar pressure for 180 min after the addition of 5 mM H2O2; where ▲ represents Example 1, ♦ represents Example 2, ▼ represents Example 3, and ● represents Comparative Example 1. DETAILED DESCRIPTION

[0032] The technical solution of the present application is not limited to the following specific embodiments, but also includes any combination of the specific embodiments.

[0033] Specific embodiment one: a preparation method of a two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane, which is carried out according to the following steps:

[0034] I. Preparation of bimetallic layered MOF (NiFe-MOF): a water solution of nickel acetate tetrahydrate (Ni(OAc)2·4H2O) and ferrous sulfate heptahydrate (FeSO4·7H2O) and a N,N-dimethylacetamide solution of terephthalic acid are mixed to perform a hydrothermal reaction, and after cooling to room temperature, washing and drying, NiFe-MOF is obtained;

[0035] II. Preparation of two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane: NiFe-MOF and g-C3N4 nanosheets are dispersed into deionized water by ultrasonic, and then vacuum filtered onto a microporous polyether sulfone membrane, and after thermal fixation, a two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane is obtained, and the preparation method is completed.

[0036] Specific embodiment two: different from specific embodiment one, the mass-volume ratio of nickel acetate tetrahydrate, ferrous sulfate heptahydrate and deionized water in the water solution of nickel acetate tetrahydrate and ferrous sulfate heptahydrate in step I is (0.1-0.2) g:(0.04-0.05) g:(20-40) mL.

[0037] The mass-volume ratio of terephthalic acid and N,N-dimethylacetamide in the N,N-dimethylacetamide solution of terephthalic acid is (0.04-0.05) g:(20-40) mL. Other steps and parameters are the same as in the first embodiment.

[0038] The third embodiment is different from the first or second embodiment in that the hydrothermal reaction in step one is carried out in a stainless steel autoclave with a polytetrafluoroethylene liner, the reaction temperature is 120-150°C, and the reaction time is 3-5 h. Other steps and parameters are the same as in the first or second embodiment.

[0039] The fourth embodiment is different from any one of the first to third embodiments in that the washing and drying in step one is carried out by stirring in 150-300 mL of deionized water and anhydrous ethanol for 3-5 h, then centrifuging at a speed of 7000-8000 r / min for 5-10 min, and then drying the precipitate at 65-85°C for 8-12 h. Other steps and parameters are the same as in any one of the first to third embodiments.

[0040] The fifth embodiment is different from any one of the first to fourth embodiments in that the preparation of g-C3N4 nanosheets in step two is carried out as follows: placing the organic nitrogen-containing compound in a crucible and calcining at high temperature in a muffle furnace to obtain bulk g-C3N4, then pouring into concentrated sulfuric acid and stirring to obtain a solid-liquid mixture, then adding deionized water and ultrasonic treatment to obtain a light yellow dispersion liquid, and then purifying by centrifugation twice and drying to obtain g-C3N4 nanosheets;

[0041] The high-temperature calcination is carried out at a rate of 1-5°C / min to 500-600°C, and the calcination time is 3-5 h;

[0042] The mass of the organic nitrogen-containing compound is 5-10 g;

[0043] The organic nitrogen-containing compound is urea, dicyanamide, or melamine;

[0044] The mass-volume ratio of bulk g-C3N4 and concentrated sulfuric acid is (1-2) g:(10-20) mL, and the mass fraction of the concentrated sulfuric acid is 95%-98%;

[0045] The stirring speed is 100-200 r / min, and the time is 5-10 h;

[0046] The volume ratio of deionized water to solid-liquid mixture is 1:(5-10), and the ultrasonic treatment time is 4-6 h;

[0047] The twice centrifugal purification and drying: the first centrifugal purification is centrifuged at a speed of 8000-10000 r / min for 5-10 min, and the second centrifugal purification is centrifuged at a speed of 8000-10000 r / min for 10-20 min for the supernatant after the first centrifugal purification, to obtain a light yellow precipitate, which is then dried at 65-85℃ for 8-12 h.

[0048] The other steps and parameters are the same as one of the first to fourth embodiments.

[0049] Embodiment six: different from one of the first to fifth embodiments, the total mass of the NiFe-MOF and g-C3N4 nanosheet in step two is 0.5-1 mg, and the mole fraction of the NiFe-MOF is 25-75%. The other steps and parameters are the same as one of the first to fifth embodiments.

[0050] Embodiment seven: different from one of the first to sixth embodiments, the mass ratio of the total mass of the NiFe-MOF and g-C3N4 nanosheet to the deionized water in step two is 1:(10000-20000); and the ultrasonic dispersion time is 1-2 h. The other steps and parameters are the same as one of the first to sixth embodiments.

[0051] Embodiment eight: different from one of the first to seventh embodiments, the vacuum filtration in step two is onto a microporous polyether sulfone membrane, and the average pore size of the microporous polyether sulfone membrane is 0.1-0.45 μm, and the vacuum filtration pressure is 0.05-0.1 MPa. The other steps and parameters are the same as one of the first to seventh embodiments.

[0052] Embodiment nine: different from one of the first to eighth embodiments, the heat fixation temperature in step two is 65-85℃, and the heat fixation time is 8-12 h. The other steps and parameters are the same as one of the first to eighth embodiments.

[0053] Embodiment ten: different from one of the first to ninth embodiments, the application of the obtained two-dimensional double-metal MOF intercalated g-C3N4 composite membrane in step two: the two-dimensional double-metal MOF intercalated g-C3N4 composite membrane is used to filter and treat water containing organic pollutants under a certain pressure;

[0054] The organic pollutants are any one or a combination of several of natural organic matter, dye, and medicine in any ratio;

[0055] The pressure is 0.05-0.1 MPa. The other steps and parameters are the same as one of the first to ninth embodiments.

[0056] The beneficial effects of the present application are verified by the following examples:

[0057] Example 1:

[0058] A preparation method of a two-dimensional bimetallic MOF intercalated g-C3N4 composite film, which is carried out according to the following steps:

[0059] I. Preparation of bimetallic layered MOF (NiFe-MOF): mix an aqueous solution of nickel acetate tetrahydrate (Ni(OAc)2·4H2O) and ferrous sulfate heptahydrate (FeSO4·7H2O) with an N,N-dimethylacetamide solution of terephthalic acid, perform a hydrothermal reaction, wash and dry after cooling to room temperature to obtain NiFe-MOF;

[0060] II. Preparation of two-dimensional bimetallic MOF intercalated g-C3N4 composite film: disperse NiFe-MOF and g-C3N4 nanosheets into deionized water by ultrasonic, then vacuum filter onto a microporous polyether sulfone film, and obtain a two-dimensional bimetallic MOF intercalated g-C3N4 composite film after heat fixation, thus completing the preparation method.

[0061] The mass-volume ratio of nickel acetate tetrahydrate, ferrous sulfate heptahydrate and deionized water in the aqueous solution of nickel acetate tetrahydrate and ferrous sulfate heptahydrate in step I of the present example is 0.124g:0.042g:30mL;

[0062] The mass-volume ratio of terephthalic acid and N,N-dimethylacetamide in the N,N-dimethylacetamide solution of terephthalic acid is 0.042g:30mL.

[0063] The hydrothermal reaction in step I of the present example: the container is a stainless steel autoclave with a polytetrafluoroethylene liner, the reaction temperature is 150℃, and the reaction time is 3h.

[0064] The washing and drying in step I of the present example: after stirring in 150mL of deionized water and anhydrous ethanol for 3h, centrifugation is performed at a speed of 8000r / min for 10min, then the precipitate is dried at 65℃ for 12h.

[0065] The preparation process of g-C3N4 nanosheets in step II of the present example is as follows: place the organic nitrogen-containing compound in a crucible and calcine at high temperature in a muffle furnace to obtain blocky g-C3N4, then pour into concentrated sulfuric acid and stir to obtain a solid-liquid mixture, then add deionized water and ultrasonic treatment to obtain a light yellow dispersion liquid, and after two times of centrifugal purification and drying, g-C3N4 nanosheets are obtained;

[0066] The high-temperature calcination: calcine at a rate of 2.5℃ / min to 550℃, and the calcination time is 5h;

[0067] The mass of the organic nitrogen-containing compound is 5 g;

[0068] The organic nitrogen-containing compound is urea;

[0069] The mass-volume ratio of the block-shaped g-C3N4 to concentrated sulfuric acid is 1 g:10 mL, and the mass fraction of the concentrated sulfuric acid is 98%;

[0070] The stirring speed is 150 r / min, and the time is 8 h;

[0071] The volume ratio of the deionized water to the solid-liquid mixture is 1:10, and the ultrasonic treatment time is 4 h;

[0072] The two times of centrifugal purification and drying: the first time of centrifugal purification is centrifugation at a speed of 8000 r / min for 5 min, the second time of centrifugal purification is centrifugation of the supernatant after the first time of centrifugal purification at a speed of 10000 r / min for 10 min, to obtain a light yellow precipitate, and then drying at 65℃ for 12 h.

[0073] The total mass of the NiFe-MOF and the g-C3N4 nanosheet in step two of the embodiment is 1 mg, wherein the mole fraction of the NiFe-MOF is 25%.

[0074] The mass ratio of the total mass of the NiFe-MOF and the g-C3N4 nanosheet in step two of the embodiment to the deionized water is 1:10000; and the ultrasonic dispersion time is 1 h.

[0075] The vacuum filtration in step two of the embodiment is onto a microporous polyether sulfone membrane: the average pore size of the microporous polyether sulfone membrane is 0.45 μm, and the vacuum filtration pressure is 0.1 MPa.

[0076] The heat fixation temperature in step two of the embodiment is 65℃, and the heat fixation time is 12 h.

[0077] The application of the obtained two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane in step two of the embodiment: the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane is used to filter and treat water bodies containing organic pollutants under a certain pressure.

[0078] The two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane obtained in the embodiment is denoted as NiFe@CN-1.

[0079] Example 2:

[0080] The mole fraction of the NiFe-MOF in the embodiment is 50%; and the others are the same as in Example 1.

[0081] The two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane obtained in the embodiment is denoted as NiFe@CN-2.

[0082] Example 3:

[0083] In this embodiment, the molar fraction of NiFe-MOF is 75%; the rest is the same as in Example 1.

[0084] The two-dimensional bimetallic MOF intercalated g-C3N4 composite film obtained in this example is recorded as NiFe@CN-3.

[0085] Comparative Example 1:

[0086] In this embodiment, the molar fraction of NiFe-MOF is 0%; the rest is the same as in Example 1.

[0087] The g-C3N4 film obtained in this example is denoted as CN.

[0088] like Figure 1 As shown, the two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 1 can obtain a typical two-dimensional layered film morphology after vacuum-assisted self-assembly, and the thickness of the film is about 450 nm.

[0089] The two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 2 can obtain a typical two-dimensional layered film morphology after vacuum-assisted self-assembly, and the thickness of the film is about 720 nm.

[0090] The two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 3 can obtain a typical two-dimensional layered film morphology after vacuum-assisted self-assembly, and the thickness of the film is about 720 nm.

[0091] The g-C3N4 film prepared in Comparative Example 1 can obtain a typical two-dimensional layered film morphology after vacuum-assisted self-assembly, and the thickness of the film is about 250 nm.

[0092] like Figure 2 As shown in the figure, the flux change diagram of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane prepared in Example 1 continuously filtered deionized water for 180 min at a pressure of 1 bar, and the flux was stable at 73.2 L·m -2 ·h -1 .

[0093] Flux variation of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane prepared in Example 2, which continuously filtered deionized water for 180 min at a pressure of 1 bar, with the flux stable at 81.2 L·m -2 ·h -1 .

[0094] The flux change diagram of the two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 3 in continuous filtration of deionized water for 180 min under 1 bar pressure, and the flux is stable at 91.4 L·m -2 ·h -1 .

[0095] The flux change diagram of the g-C3N4 film prepared in Comparative Example 1 in continuous filtration of deionized water for 180 min under 1 bar pressure, and the flux is stable at 8.8 L·m -2 ·h -1 .

[0096] As shown in Figure 3 , the flux decline diagram of the two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 1 in continuous filtration of 1 g / L bovine serum protein aqueous solution for 180 min under 1 bar pressure after adding 5 mM H2O2, and the flux decreased by 44.3% after 120 min.

[0097] The flux decline diagram of the two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 2 in continuous filtration of 1 g / L bovine serum protein aqueous solution for 180 min under 1 bar pressure after adding 5 mM H2O2, and the flux decreased by 10.4% after 120 min.

[0098] The flux decline diagram of the two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared in Example 1 in continuous filtration of 1 g / L bovine serum protein aqueous solution for 180 min under 1 bar pressure after adding 5 mM H2O2, and the flux decreased by 23.5% after 120 min.

[0099] The flux decline diagram of the g-C3N4 film prepared in Comparative Example 1 in continuous filtration of 1 g / L bovine serum protein aqueous solution for 180 min under 1 bar pressure after adding 5 mM H2O2, and the flux decreased by 28.9% after 120 min.

[0100] In summary, the two-dimensional bimetallic MOF intercalated g-C3N4 composite film prepared by the application has a high and stable permeation flux, and can be prepared by self-assembly of two-dimensional NiFe-MOF and g-C3N4 nanosheets. The performance of the two-dimensional bimetallic MOF intercalated g-C3N4 composite film can be regulated by the molar mass ratio of NiFe-MOF and g-C3N4 nanosheets. When the molar fraction of two-dimensional NiFe-MOF is close to 50%, the two-dimensional bimetallic MOF intercalated g-C3N4 composite film has the best comprehensive performance.

[0101] Although the present application has been described above with reference to specific embodiments, the above embodiments are merely illustrative and not restrictive, and many modifications and other embodiments of the present application can occur to those skilled in the art upon reading the foregoing description, which modifications and other embodiments fall within the scope of the present application.

Claims

1. A method for preparing a two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane, characterized in that It proceeds as follows: Preparation of a two-dimensional bimetallic layered MOF: An aqueous solution of nickel acetate tetrahydrate and ferrous sulfate heptahydrate was mixed with a solution of terephthalic acid in N,N-dimethylacetamide, and subjected to a hydrothermal reaction. The mixture was cooled to room temperature, washed, and dried to obtain NiFe-MOF.

2. Preparation of a two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane: NiFe-MOF and g-C3N4 nanosheets were ultrasonically dispersed in deionized water, then vacuum filtered onto a microporous polyethersulfone membrane. After thermal fixation, a two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane was obtained, completing the preparation method. The mass volume ratio of nickel acetate tetrahydrate, ferrous sulfate heptahydrate and deionized water in the aqueous solution of nickel acetate tetrahydrate and ferrous sulfate heptahydrate described in step 1 is (0.1-0.2) g: (0.04-0.05) g: (20-40) mL; The mass volume ratio of terephthalic acid to N,N-dimethylacetamide in the N,N-dimethylacetamide solution of terephthalic acid is (0.04-0.05) g: (20-40) mL; The hydrothermal reaction in step 1: the container is a stainless steel autoclave with a polytetrafluoroethylene liner, the reaction temperature is 120-150 ° C, and the reaction time is 3-5 h; Wash and dry as described in step 1: Stir in 150-300 mL of deionized water and anhydrous ethanol for 3-5 h, centrifuge at 7000-8000 rpm for 5-10 min, and then dry the precipitate at 65-85°C for 8-12 h; The preparation process of g-C3N4 nanosheets described in step 2 is as follows: an organic nitrogen-containing compound is placed in a crucible and calcined at high temperature in a muffle furnace to obtain blocky g-C3N4, and then concentrated sulfuric acid is poured into it and stirred to obtain a solid-liquid mixture, and then deionized water is added and ultrasonicated to obtain a light yellow dispersion. After two centrifugal purifications and drying, g-C3N4 nanosheets are obtained; The total mass of the NiFe-MOF and g-C3N4 nanosheets in step 2 is 0.5-1 mg, wherein the molar fraction of NiFe-MOF is 25-75%; In step 2, the mass ratio of the total mass of NiFe-MOF and g-C3N4 nanosheets to deionized water is 1:(10000~20000); the ultrasonic dispersion time is 1~2 h; The vacuum filtration in step 2 is performed onto a microporous polyethersulfone membrane: the average pore size of the microporous polyethersulfone membrane is 0.1-0.45 μm, and the vacuum filtration pressure is 0.05-0.1 MPa; The heat fixation temperature in step 2 is 65-85°C and the heat fixation time is 8-12 hours; Application of the two-dimensional bimetallic MOF intercalated g-C3N4 composite membrane obtained in step 2: filtering and treating water containing organic pollutants under a certain pressure, wherein the certain pressure is 0.05-0.1 MPa; The organic pollutants are dyes and / or drugs.

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