CN114870657B

CN114870657B - Graphene oxide film for in-situ growth of porous MOF intercalation, preparation method and application

Info

Publication number: CN114870657B
Application number: CN202210309584.5A
Authority: CN
Inventors: 刘公平; 茆羊羊; 金万勤
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2022-03-28
Filing date: 2022-03-28
Publication date: 2023-08-22
Anticipated expiration: 2042-03-28
Also published as: CN114870657A

Abstract

The application discloses an in-situ grown porous MOF intercalated graphene oxide film, a preparation method and application thereof. The hydrophobic graphene oxide membrane prepared by the method is used for membrane distillation desalination, has good hydrophobicity, high membrane flux and salt rejection rate, and has excellent separation performance.

Description

Graphene oxide film for in-situ growth of porous MOF intercalation, preparation method and application

Technical Field

The application belongs to the technical field of graphene, and particularly relates to a preparation method and application of a hydrophobic graphene oxide film.

Background

Shortage of water resources and safety issues are one of the greatest challenges in the 21 st century. Water is the most precious resource for life on earth, but is becoming increasingly scarce. The rapid population growth, industrialized rapid development, climate change and other problems cause great pressure on the safety of water resources, and further worsen the global water resource crisis.

Desalination of sea water is the most commonly used method to solve the shortage of water resources, especially drinking water. To address this challenge, there is an urgent need to develop low cost, low energy consumption, environmentally safe desalination technologies to obtain a continuous supply of clean water resources. Compared with the traditional desalination technology, the membrane separation desalination technology has obvious advantages: less space is used compared to conventional adsorption methods; has excellent separation efficiency and selectivity, and can obtain higher water quality.

Membrane distillation, a typical membrane separation desalination technology, combines membrane separation and distillation with the temperature difference at two sides of the membrane as driving force, water in raw material liquid evaporates on the surface of the membrane, water in the form of steam permeates through porous channels of a hydrophobic membrane and is condensed at the permeation side, and salt ions are trapped on the surface of the membrane, so that separation is realized. In the sea water desalination field, compared with the filter pressing membrane technology, the membrane distillation has the advantages of mild operation condition, high theoretical salt rejection rate and the like, and has important research potential.

Graphene is used as an emerging carbon material, and has excellent electric and heat conduction, high strength, high light transmittance and other performances, so that the graphene is widely developed and applied in the fields of composite materials, energy sources, biology and the like. In recent years, two-dimensional materials represented by graphene have unique layered structures, easy modification, intrinsic hydrophobicity and anisotropic heat conduction properties, and thus have become ideal materials for constructing high-performance membrane distillation separation membranes. However, when the graphene film is prepared, the gaps and flux are small due to the extrusion between the sheets ^[1,2] The method comprises the steps of carrying out a first treatment on the surface of the Combining patent content and reported results from prior literature ^[3,4] If some particles are directly mixed between the sheets to fill the sheets, the porosity of the membrane can be improved to some extent, but the intercalation is also easily uneven, so that problems such as mass transfer blocking, poor porosity, poor separation effect and the like are caused.

Reference is made to:

[1]CHEN L,SHI G,SHEN J,et al.Ion sieving in graphene oxide membranes via cationic control of interlayer spacing[J].Nature,2017,550(7676):415-8；

[2]JOSHI R K,CARBONE P,WANG F C,et al.Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes[J].Science,2014,343(6172):752-4；

[3]LU X,GENG Y,WU G,et al.Preparation of metal organic frameworks/graphene oxide composite membranes for water capturing from air[J].Materials Today Communications,2021,26.[4]CN111450711A。

disclosure of Invention

The technical problem that this patent will solve is: in the process of preparing the separation membrane by filling graphene sheets with particles, the problems of poor mass transfer effect and poor separation effect caused by insufficient distribution and intercalation of nano particles among the sheets are solved.

In order to achieve the above object, the present application adopts the following technical scheme:

the graphene oxide membrane comprises a support layer and a selective separation layer, wherein the selective separation layer is formed by a plurality of layers of graphene oxide nano sheets, MOF-801 nano particles are distributed on the surfaces of the graphene oxide nano sheets, the MOF801 nano particles are positioned between adjacent graphene oxide nano sheets, and a hydrophobic modification layer is further covered on the surfaces of the selective separation layer.

Preferably, the MOF-801 nanoparticle has a porous structure.

Preferably, the material of the hydrophobic modification layer is PDMS.

Preferably, the support layer is a porous inorganic material or a porous polymer material.

The preparation method of the hydrophobic graphene oxide film comprises the following specific steps:

s1, providing MOF-801@GO dispersion liquid with in-situ grown porous nano particles;

s2, mixing the MOF-801@GO dispersion liquid with an organic solvent, performing vacuum suction filtration on the mixture to a hydrophobic PVDF support body after ultrasonic treatment, and drying at room temperature to obtain a MOF-801@GO membrane;

s3, spin-coating an ethylene-based Polydimethylsiloxane (PDMS) -oil phase solution on the MOF-801@GO film, and performing heat treatment after drying to obtain the hydrophobic MOF-801@GO-PDMS film.

Preferably, the oil phase solution uses hydrocarbons as the solvent.

Preferably, the MOF-801@GO dispersion comprises the following preparation steps:

(1) Providing a GO dispersion;

(2) ZrOCl ₂ ·8H ₂ Mixing O, a dispersion solvent, an acid agent and GO dispersion liquid uniformly, and stirring;

(3) C is C ₄ H ₄ O ₄ Uniformly mixing the dispersion solvent and the acid agent, and stirring;

(4) Slowly pouring the mixed solution in the step (3) into the step (2), uniformly mixing, stirring, centrifuging, and vacuum drying at room temperature to obtain MOF-801@GO powder, and then adding a dispersing solvent for dispersing to obtain MOF-801@GO dispersion liquid.

Preferably, the preparation steps of the GO dispersion are: and uniformly mixing GO and a dispersing solvent, and fully stripping the GO sheet layer by ultrasonic to obtain GO dispersion liquid.

Preferably, the dispersing solvent is deionized water or N' N-Dimethylformamide (DMF).

Preferably, the acid agent comprises one of acetic acid, formic acid, hydrochloric acid or phosphoric acid.

Preferably, the MOF-801@GO membrane is subjected to an activation treatment after spin-coating the PDMS-oil phase solution.

Preferably, the activation treatment step is: and soaking the MOF-801@GO membrane in an activating agent, standing for a period of time, taking out, and drying at room temperature to activate the MOF-801 nano holes.

Preferably, the activator is an alcohol, preferably methanol or ethanol.

Preferably, the spin-coating operation conditions are spin-coating 6 times, 1 mL/time, 1500rpm, spin-coating 30s.

The application of the hydrophobic graphene oxide membrane is used for membrane distillation desalination.

The application has the advantages that: according to the application, the porous hydrophobic graphene film is prepared by adopting in-situ grown porous nano particles to cooperatively coat the hydrophobic polymer, so that the desalination performance of the porous hydrophobic graphene film can be obviously improved; compared with the direct mixing of nano particles, the in-situ growth can lead the particles to be more uniformly dispersed on the surface of the polymer and better embedding stability, thereby ensuring the intercalation effect; meanwhile, as the MOF801 nano particles have a porous structure, the intrinsic porous structure of the MOF801 nano particles can provide an additional water vapor mass transfer path to improve the water vapor permeation rate, and the prepared porous hydrophobic graphene film can show excellent desalination performance and operation stability;

the interior of the MOF-801@GO membrane can be physically coated and modified by spin-coating the PDMS-n-heptane solution, so that the PDMS is fully adhered to the surfaces of all the sheets of the MOF-801@GO membrane, good hydrophobicity of the surfaces of the membrane and the interior of the pore canal is further ensured, and the membrane flux and the salt rejection rate are effectively improved;

according to the preparation method, the MOF-801 intrinsic pores are subjected to activation treatment, so that the porosity of the MOF-801 intrinsic pores can be improved, pore channels are activated, the total porosity and the permeation flux of the membrane are improved, and the flux and the salt interception rate of the membrane are kept at higher levels.

Drawings

FIG. 1 is a technical schematic of the present application;

FIG. 2 is an AFM image of GO dispersion in the present application;

FIG. 3 is a SEM surface and cross-section of the GO membrane (a-a), GO-PDMS membrane (b-b), MOF-801@GO membrane (c-c ') and MOF-801@GO-PDMS membrane (d-d') of the present application;

FIG. 4 is an AFM three-dimensional topography of the surface of the GO film (a), GO-PDMS film (b), MOF-801@GO film (c) and MOF-801@GO-PDMS film (d) of the present application; root mean square roughness and water contact angle plot (e) for each film;

FIG. 5 is a SEM image of the surface and cross section of a MOF-801@GO film prepared by spin coating with different PDMS concentrations (0 wt%,0.5wt%,1wt%,2wt%,5 wt%) in the present application;

FIG. 6 is an XRD spectrum of a GO membrane, a GO-PDMS membrane, a MOF-801@GO-PDMS membrane and a support according to the present application;

FIG. 7 is a FT-IR spectrum of a GO membrane, a GO-PDMS membrane, a MOF-801@GO-PDMS membrane and a support according to the application;

FIG. 8 is XPS C1s spectra of GO film (a) and MOF-801@GO film (b) of the present application; SEM section characterization graph and EDS surface scanning Si element characterization graph (d) of MOF-801@GO-PDMS film (c);

FIG. 9 shows the average DCMD desalting performance (a) of the GO-PDMS film, MOF-801@GO film and MOF-801@GO-PDMS film of the present application; overall porosity (b); DCMD desalination performance (c) within 20 h;

FIG. 10 shows the contact angle of MOF-801@GO film (a) prepared by spin-coating PDMS solutions of different concentrations according to the present application; overall porosity (b); average DCMD desalination performance (c) and flux and permeate side salt concentration (d) of the membrane within 20 h;

FIG. 11 is a SEM surface map (a) of a MOF-801@GO (DMF) film before activation in the present application; SEM cross-section (b) of MOF-801@go (DMF) membrane before activation; FT-IR spectra (c) of GO membrane, MOF-801@GO (DMF) membrane before Activation (Before Activation), MOF-801@GO (DMF) membrane After Activation (After Activation of the After); overall porosity (d) of MOF-801@go (DMF) film before Activation (Before Activation) and MOF-801@go (DMF) film After Activation (After Activation); average DCMD desalting performance (e) before MOF-801@GO (DMF) -PDMS film Activation (Before Activation) and After MOF-801@GO (DMF) -PDMS film Activation (After After Activation); DCMD desalination performance (f) within 20 h;

FIG. 12 is an SEM surface view of a MOF-801@GO-FAS porous hydrophobic film of the present application and a water contact angle (a); SEM cross-section (b) of MOF-801@GO-FAS porous hydrophobic membrane; the FT-IR spectrum (c) of a MOF-801@GO membrane, a MOF-801@GO-FAS membrane, a GO membrane and a support; DCMD desalination performance (10 h) of MOF-801@GO-FAS porous hydrophobic membrane (d);

FIG. 13 shows the desalting performance (a) and continuous desalting performance (b) of a MOF-801@GO-1wt% PDMS porous hydrophobic membrane according to the present application at different feed temperatures.

Detailed Description

The application is described in detail below with reference to the drawings and the specific embodiments.

Example 1

The preparation method of the hydrophobic graphene oxide film comprises the following specific steps of:

s1, providing an MOF-801@GO aqueous dispersion liquid with in-situ grown porous nano particles:

(1) Uniformly mixing 40mg of GO with 20mL of deionized water, and fully peeling the GO sheets by ultrasound (90 min) to prepare GO aqueous dispersion (2 mg/mL);

(2) 0.0396g ZrOCl was taken ₂ ·8H ₂ O, 15mL of deionized water, 1mL of acetic acid and 8mL of GO aqueous dispersion (namely 16mg GO) are uniformly mixed, and then stirred for 1h at 60 ℃;

(3) Take 0.0143g C ₄ H ₄ O ₄ Uniformly mixing 15mL of deionized water with 1mL of acetic acid, and stirring for 1h at 60 ℃;

(4) C in (3) ₄ H ₄ O ₄ Slowly pouring the aqueous solution into the step (2), uniformly mixing, stirring for 3 hours at 60 ℃, centrifuging, washing with deionized water for 3 times, vacuum drying at room temperature to obtain MOF-801@GO powder, and adding deionized water for dispersion to prepare 2mg/mL MOF-801@GO aqueous dispersion;

s2, preparing a MOF-801@GO film:

mixing 0.5mL of MOF-801@GO aqueous dispersion (namely 1mg of MOF-801@GO) with 158g of methanol, carrying out ultrasonic treatment for 60min, vacuum-filtering to a hydrophobic PVDF support, and drying at room temperature for 12h to obtain a MOF-801@GO membrane;

s3, preparing a hydrophobic MOF-801@GO-PDMS film:

(1) Preparing PDMS-n-heptane solutions with mass fractions of 0.5wt%,1wt%,2wt% and 5wt%, and stirring at room temperature for 2h;

(2) The MOF-801@GO film was spin-coated with PDMS-n-heptane solutions of different concentrations (spin-coated 6 times, 1 mL/time, 1500rpm, spin-coated 30 s), dried at room temperature, and then placed in an oven at 70℃for heat treatment for 4 hours to prepare a hydrophobic film, which was labeled as [email protected]% PDMS film, MOF-801@GO-1wt% PDMS film (hereinafter labeled as MOF-801@GO PDMS film for simplicity of description), MOF-801@GO-2wt% PDMS film, and MOF-801@GO-5wt% PDMS film, respectively, according to the concentration of the PDMS solution.

Example 2

The process was substantially similar to that of example 1, except that DMF was used as the dispersing solvent, and the deionized water of example 1 was replaced entirely with DMF, with the procedure and reagent levels remaining unchanged.

Comparative example 1

This comparative example is substantially the same as example 2, except that the MOF-801 intrinsic nanopore is activated in step S3, specifically:

s1, providing MOF-801@GO (DMF) dispersion liquid with in-situ grown porous nano particles;

s2, preparing a MOF-801@GO (DMF) film;

s3, preparing a hydrophobic MOF-801@GO (DMF) -PDMS film:

(1) Soaking the MOF-801@GO (DMF) film in methanol, standing for 72 hours, taking out, and drying at room temperature to activate MOF-801 nano holes; MOF-801@GO (DMF) films before and After methanol soaking and drying are respectively marked as MOF-801@GO (DMF) films before Activation (Before Activation) and After Activation (After Activation);

(2) The activated MOF-801@GO (DMF) film is spin-coated with 1wt% PDMS-n-heptane solution (spin-coated for 6 times, 1 mL/time, 1500rpm, spin-coated for 30 s), dried at room temperature and then placed in an oven for heat treatment at 70 ℃ for 4 hours to prepare the hydrophobic MOF-801@GO (DMF) -PDMS film.

Comparative example 2

This comparative example is identical to the preparation steps S1 and S2 in example 1, except that spin coating treatment is not performed in step S3, specifically:

s1, providing MOF-801@GO aqueous dispersion liquid with in-situ grown porous nano particles;

s2, preparing a MOF-801@GO film;

s3, preparing a hydrophobic MOF-801@GO-FAS film:

(1) Preparing a 1H, 2H-perfluoro decyl triethoxysilane (FAS) -n-hexane solution with the mass fraction of 2wt%, and stirring for 2 hours at room temperature;

(2) And soaking the prepared MOF-801@GO film in a 2wt% FAS-n-hexane solution for 2 hours, taking out, washing with n-hexane to take out superfluous FAS on the surface, drying at room temperature, and then placing in an oven for heat treatment at 70 ℃ for 4 hours to obtain the hydrophobic MOF-801@GO-FAS film.

Comparative example 3

This comparative example is similar to the preparation procedure in example 1, except that the porous nanoparticles were not synthesized and grown in situ, as follows:

s1, providing GO aqueous dispersion liquid:

uniformly mixing 40mg of GO with 20mL of deionized water, and fully peeling the GO sheets by ultrasound (90 min) to prepare GO aqueous dispersion (2 mg/mL);

s2, preparing a GO film:

mixing 0.5mL of GO aqueous dispersion with 158g of methanol, carrying out vacuum suction filtration on the mixture to a hydrophobic PVDF support after ultrasonic treatment for 60min, and drying at room temperature for 12h to obtain a GO membrane;

s3, preparing a hydrophobic GO-PDMS film:

spin-coating 1wt% PDMS-n-heptane solution (spin-coating 6 times, 1 mL/time, 1500rpm, spin-coating 30 s) on the surface of the GO film, drying at room temperature, and heat-treating in an oven at 70 ℃ for 4h to obtain the hydrophobic GO-PDMS film.

Characterization and testing

Test method

1. Porosity of the membrane

The porosity epsilon of the composite film was tested using archimedes method. Taking the total mass of the dry film as m (the mass of the film layer as m) ₁ The mass of the support body is m ₂ ) After a sample is soaked in isopropanol for 12 hours, the isopropanol fully enters the inside of a membrane hole, the wet membrane is taken out to wipe excessive isopropanol on the surface of the membrane, the mass of the wet membrane is M, the density of a membrane layer material is p, the density of a support body is q, the density of the isopropanol is n, and the porosity epsilon of the composite membrane is expressed as:

2. desalination performance of membranes

A laboratory-self-made Direct Contact Membrane Distillation (DCMD) device was used to evaluate the desalination performance of porous hydrophobic graphene oxide membranes. The membrane feeding side adopts a gear pump to circulate high-concentration NaCl salt solution (35 g/L) with a circulation flow rate of 104L/h; the membrane permeation side circulation adopts a gear pump to circulate deionized water, and the circulation flow rate is 13L/h. The temperature of the feed brine was controlled at 40 ℃,50 ℃,60 ℃ and 70 ℃ and the temperature of the permeate side deionized water was controlled at 25 ℃. The conductivity meter monitors the salt concentration and the temperature of deionized water at the permeate side in real time every 1min, and the balance monitors the change of the deionized water mass in real time every 1 min. The following definitions are provided: the salt concentration of the feed is C _f A permeate side salt concentration of C _p The water volume at the permeation side is V _p The effective test area of the membrane is A, the test time is t, the mass of the circulating deionized water on the permeate side in the test time for collecting the added water is Q, and the flux J and the salt interception rate R of the membrane are respectively expressed as:

(II) characterization and test results

1. AFM characterization of the GO aqueous dispersion prepared in example 1

The specific operation steps are as follows: 1mL of GO aqueous dispersion is diluted into 200mL (the concentration of GO aqueous dispersion is diluted to 0.01 mg/mL) of deionized water, after stirring, one drop of diluted GO aqueous dispersion is removed to a mica sheet, and after drying for 24 hours at room temperature, the mixture is used for AFM characterization, and the result is shown in FIG. 2.

As can be seen from fig. 2, the range of GO feedstock sheet radial dimensions used for the composite synthesis is: the thickness of the lamellar layers is about 1.2nm and 0.4-1 μm, which indicates that the prepared GO raw material is fully peeled off, thereby being beneficial to fully in-situ growth of porous nano particles between the GO lamellar layers.

2. Characterization of film physicochemical Properties

(1) SEM, AFM and surface water contact angle characterization were performed on the GO film and the GO-PDMS film in comparative example 3 and the MOF-801@go film and MOF-801@go-PDMS film in example 1, respectively, to observe the micro-morphology, film thickness and hydrophobic properties of the films, and the results are shown in fig. 3 and 4.

From the analysis of fig. 3, it is known that: the pure GO film shows typical fold morphology and film thickness of 347+ -3 nm; the surface appearance of the hydrophobic GO-PDMS film prepared by spin-coating PDMS is slightly changed, the folds are thickened, the surface has obvious polymer adhesion and smoothness trend, but the whole surface of the GO-PDMS film still shows the fold appearance due to the obvious folds appearance of GO and the influence of lower PDMS concentration, the film thickness is about 342+/-13 nm when analyzed from the section, and the layer structure of the section is clear, so that the layer porous structure of the GO film is not changed due to the spin-coating of low-concentration PDMS; the MOF-801@GO membrane surface is continuously defect-free, the in-situ grown MOF-801 nano particles have the size of about 30-50 nm, macropores appear on the membrane surface, the section is in a layered porous structure, and the MOF-801 nano particles are uniformly distributed on the membrane surface and the section; the MOF-801@GO-PDMS film prepared by spin-coating low-concentration PDMS has slightly reduced surface pores, and the section still maintains an obvious porous layered structure, which shows that the introduced low-concentration PDMS does not change the porous structure of the film basically.

From the analysis of fig. 4, it is known that: comparing the three-dimensional AFM morphology, roughness and water contact angle of the surfaces of the GO film, the GO-PDMS film, the MOF-801@GO film and the MOF-801@GO-PDMS film, the following is found: compared with a pure GO film, the GO-PDMS film maintains the original basic fold morphology, and the roughness change is small; compared with the GO film, the fold morphology of the MOF-801@GO film is replaced by the nanoparticle morphology, and the roughness is obviously reduced; the MOF-801@GO-PDMS film roughness was slightly reduced compared to the MOF-801@GO film, but the overall change was not great. In addition, the contact angle of the surface of the GO film is 38.6+/-3.3 degrees, the contact angle of the surface of the GO-PDMS film is 105.3+/-1.6 degrees, the contact angle of the surface of the MOF-801@GO film is 28.6+/-1.2 degrees, and the contact angle of the surface of the MOF-801@GO-PDMS film is 114.6+/-2.3 degrees. The introduction of the PDMS with extremely low concentration is shown to basically not change the appearance of the original film, and the GO film or the MOF-801@GO film is subjected to hydrophobic modification.

(2) The MOF-801@GO film and the [email protected]% PDMS film, MOF-801@GO-1wt% PDMS film, MOF-801@GO-2wt% PDMS film and MOF-801@GO-5wt% PDMS film prepared by spin coating with different PDMS concentrations in example 1 were subjected to surface and cross-section SEM characterization, respectively, and the results are shown in FIG. 5.

As can be seen from the analysis of fig. 5: compared with MOF-801@GO film without spin coating PDMS (0 wt%), the surface of the hydrophobic film prepared by spin coating PDMS with the concentration of 0.5wt% and 1wt% still maintains the porous nano structure, and a clear porous lamellar structure is still observed from the section; but for films prepared by spin coating PDMS at a concentration of 2wt%, the film surface and film cross section are coated with polymer, so that the number of surface nano-macropores is reduced, the film tends to densify, and even for films prepared by spin coating of 5wt% PDMS, the film surface is completely covered with polymer, exhibiting typical PDMS film morphology. Therefore, it is known that spin coating of films prepared from PDMS at different concentrations causes changes in hydrophobicity and interlayer porosity of the film surface, which in turn has an important influence on the desalting performance of the film.

(3) XRD, FT-IR, XPS and EDS characterization were performed on the GO film prepared in comparative example 3, the GO-PDMS film and the MOF-801@GO-PDMS film prepared in example 1, respectively, to analyze the chemical properties of the film materials, and the results are shown in FIGS. 6, 7 and 8.

As can be seen from the analysis of fig. 6: for the GO film, a diffraction angle at 11.5℃was detected corresponding to the GO film 002 characteristic peak (interlayer channel size 0.77 nm); for the GO-PDMS film, the diffraction angle at 11.3 degrees is detected to correspond to the GO film 002 characteristic peak (the interlayer channel size is 0.78 nm), and the typical characteristic peak of PDMS is not detected because the concentration of PDMS is low and the content of spin-coating deposited in the film is low; for MOF-801@GO films, diffraction angles at 8.5℃and 9.7℃were detected corresponding to the 111 and 200 characteristic peaks, respectively, of MOF-801 crystals, indicating successful growth of MOF-801 nanoparticles on the GO sheets. Because the content of the nano particles is more, the GO characteristic peak is too strong and weak, and no obvious characteristic peak appears; for MOF-801@GO-PDMS films, diffraction angles at 8.5℃and 9.7℃were also detected corresponding to the 111 and 200 characteristic peaks, respectively, of MOF-801 crystals, indicating that the incorporation of PDMS polymer did not disrupt the crystalline form of the MOF-801 nanoparticles.

As can be seen from the analysis of fig. 7: for pure GO membranes, a typical characteristic peak-OH (3228 cm ^-1 )、C＝O(1740cm ^-1 )、C＝C(1644cm ^-1 )、C-OH(1403cm ^-1 ) C-O-C (1067 cm) ^-1 ) The method comprises the steps of carrying out a first treatment on the surface of the For GO-PDMS film, the-CH is detected ₃ (2965cm ^-1 )、C-Si(1261cm ^-1 ) Si-O-Si (1019 cm) ^-1 ) Indicating successful incorporation of PDMS onto GO, while detecting-OH (3218 cm ^-1 ) The peak position is obviously red shifted, which indicates that PDMS mainly interacts with-OH on GO in a hydrogen bond form; for MOF-801@GO, the-OH (3355 cm ^-1 ) Asymmetric carboxylate (1579 cm) ^-1 ) Symmetrical carboxylate (1403 cm) ^-1 ) Zr-O (659 cm) ^-1 ) It was shown that MOF-801 successfully grew in situ within and on the surface of the GO sheets. At the same time, c=c on MOF-801@go aromatics was detected (1658 cm ^-1 ) Compared with GO, the method has obvious blue shift, which indicates that in the in-situ synthesis process, the zirconium oxychloride and GO generate metal ion-pi interaction in the premixing process, thereby causing electron cloud density on the carbon six ring of the graphemeThe degree varies. In addition, compared with pure GO, the epoxy group peak on MOF-801@GO is obviously weakened, which indicates that ring opening can occur; for MOF-801@GO-PDMS film, compared to MOF-801@GO, the-CH was detected ₃ (2963cm ^-1 )、C-Si(1261cm ^-1 ) Si-O-Si (1022 cm) ^-1 ) Indicating that PDMS was successfully incorporated onto MOF-801@GO.

As can be seen from the analysis of fig. 8: comparison of typical C element characteristic peaks (C=C/C-C, -284.8 eV, -C-O, -286.9 eV, -C=O, -288.2 eV, -COOH, -288.9 eV) of GO shows that the C-O ratio in MOF-801@GO film is remarkably reduced, and the conclusion is consistent with the previous literature report that positively charged Zr metal ions firstly interact with epoxy groups on the GO surface in the synthesis process of MOF-801@GO. Further, EDS surface scanning characterization of Si element is carried out on the prepared MOF-801@GO-PDMS membrane section, the Si element is found to be uniformly distributed on the membrane section and is permeated into the supporting layer, and the fact that the spin-coating low-concentration PDMS solution in the section can carry out physical coating modification on the inside of the MOF-801@GO membrane, so that PDMS is fully adhered to the surfaces of all the sheets of the MOF-801@GO membrane, and good hydrophobicity of the membrane surface and the inside of the pore channel is guaranteed.

3. Influence of nanoparticle and PDMS concentration on membrane desalination Performance

(1) In constructing a hydrophobic graphene oxide membrane for use in membrane distillation, the effect of nanoparticles (MOF-801) on membrane desalination performance was tested and the results are shown in FIG. 9 (feed temperature 60 ℃ C., feed salt concentration 35 g/L).

As shown in fig. 9 (a), it is known that: when the film thickness is controlled to be proper, the flux of the GO-PDMS hydrophobic film is only 15.51 kg.m when the feeding temperature is 60 ℃ and the feeding salt concentration is 35g/L ^-2 ·h ^-1 The salt interception rate is about 99.995%; for the designed and prepared porous hydrophobic MOF-801@GO-PDMS membrane, the flux is 22.94 kg.m ^-2 ·h ^-1 The salt interception rate is 99.996%, the performance is obviously improved compared with the GO-PDMS hydrophobic membrane, and the flux is mainly attributed to that the overall porosity of the MOF-801@GO PDMS membrane is larger than that of the GO-PDMS membrane (fig. 9 (b)), so that the porous MOF-801 nano particles grown in situ can improve the porosity of the membrane to promote water vapor transmissionAnd the membrane maintained a stable water flux over a 20h test time (fig. 9 (c)).

(2) The contact angle, the overall porosity, the average DCMD desalination performance and the DCMD desalination performance of the MOF-801@GO film prepared by spin-coating PDMS solutions with different concentrations were respectively tested, and the results are shown in FIG. 10 (the feeding temperature is 60 ℃ C., and the feeding salt concentration is 35 g/L).

As can be seen from fig. 10 (a) and (b): the surface water contact angles of MOF-801@GO films prepared by spin coating with PDMS concentrations of 0wt%,0.5wt%,1wt%,2wt% and 5wt% are respectively: 28.6+/-1.2 degrees, 114.8+/-0.2 degrees, 114.6+/-2.3 degrees, 105.4+/-0.9 degrees and 104.7+/-0.7 degrees, namely when 2wt percent of PDMS is spin-coated, the roughness of the nano protrusions on the surface is reduced due to the fact that the polymer with higher concentration is coated on the surface of the MOF-801@GO film, the surface gradually tends to be smooth, and then the water contact angle is reduced; the overall porosity of the MOF-801@GO films prepared by spin coating at 0wt%,0.5wt%,1wt%,2wt% and 5wt% PDMS concentrations were: 69.1.+ -. 5.7%, 68.4.+ -. 4.7%, 66.5.+ -. 7.2%, 61.2.+ -. 10.2% and 55.0.+ -. 2.1%, i.e. when spin-coating 0.5% by weight of PDMS and 1% by weight of PDMS, the overall porosity of the membrane is slightly reduced from 69.1.+ -. 5.7% to 68.4.+ -. 7.7% and 66.5.+ -. 7.2%, respectively, whereas when spin-coating 2% by weight of PDMS and 5% by weight of PDMS, the introduction of higher concentration of polymer gradually plugs the MOF-801@GO channels, such that the overall porosity is reduced.

As can be seen from fig. 10 (c) and (d): compared with a hydrophilic MOF-801@GO membrane without spin coating PDMS (0 wt%), the membrane flux prepared by spin coating 0.5wt% PDMS can reach 31.3+/-1.0 kg.m ^-2 ·h ^-1 The salt cutting rate is improved to 99.953 +/-0.015 percent; the flux of the membrane prepared by spin coating 1wt% PDMS is reduced to 23.1+ -1.3 kg.m ^-2 ·h ^-1 However, the salt rejection rate is further improved to 99.971 +/-0.012 percent, and for the membrane, the porosity is slightly reduced, a certain flux is sacrificed, but the salt crystallization trend of the membrane interface can be reduced, so that the salt rejection rate is improved; the flux of the membrane prepared by spin coating 2wt% PDMS is reduced to 18.4+/-0.7 kg.m ^-2 ·h ^-1 The salt rejection rate also decreases to 99.885 ±0.023 due to the decrease in porosity and surface hydrophobicity of the membrane; the membrane prepared by spin coating 5wt% of PDMS has a salt interception rate as high as 99.973 +/-0.024%, but the membrane structure with compact low porosity enables the membrane flux to be only 11.3+/-0.6kg·m ^-2 ·h ^-1 . This section concludes: when the [email protected]% PDMS film prepared by spin coating of 0.5wt% PDMS has higher flux, and the salt interception rate of more than 99.9% is maintained; when the MOF-801@GO-1wt% PDMS film prepared by spin coating of 1wt% PDMS has higher salt interception rate, and the film flux is kept stable within 20h of test time.

4. Comparison of MOF-801 nanoparticle intrinsic pore versus Membrane desalination Performance

The mass transfer effect of MOF-801@GO (DMF) before and after MOF-801 pore activation on the membrane distillation desalination process is further characterized by using DMF as a solvent to prepare a hydrophilic MOF-801@GO (DMF) membrane before and after MOF-801 pore activation and a hydrophobic MOF-801@GO (DMF) -PDMS membrane before and after MOF-801 pore activation (0.48-0.74 nm), and the result is shown in FIG. 11 (the feeding temperature is 50 ℃ C., and the feeding salt concentration is 35 g/L).

Analysis from SEM characterization of pre-activation MOF-801@go (DMF) films: the MOF-801 nano particle size in the MOF-801@GO compound synthesized in situ by taking DMF as a solvent is about 20nm and smaller than that in the MOF-801@GO compound synthesized by taking water as a solvent, and the prepared film thickness is 177+/-17 nm.

Analysis of the FT-IR spectrum shown in (c) of FIG. 11 revealed that: for MOF-801@GO (DMF) membranes before and after activation, both-OH (3364 cm before activation) ^-1 3362cm after activation ^-1 ) Asymmetric carboxylate (1575 cm before activation) ^-1 1575cm after activation ^-1 ) Symmetrical carboxylate (1403 cm before activation) ^-1 1405cm after activation ^-1 ) Zr-O (655 cm before activation) ^-1 652cm after activation ^-1 ) The MOF-801 successfully grows in situ in and on the surface of the GO sheet layer when DMF is taken as a solvent, and the structure of the MOF-801@GO (DMF) is not damaged by the treatment of methanol soaking activation. Comparison of MOF-801@GO (DMF) membrane before methanol activation shows that the overall porosity of the membrane after activation is increased from 58.8+/-3.9% to 63.2+/-4.7% (the surface water contact angle is 106.9+/-2.4 ℃), and the methanol-activated MOF-801 subnano-pores are beneficial to improving the overall porosity of the membrane. Further, the MOF-801@GO (DMF) -PDMS hydrophobic membrane DCMD desalting performance before and after methanol activation was tested, and it was found that the flux of the membrane after methanol activation was from 14.2.+ -. 0.6 kg.m at 50℃feed temperature ^-2 ·h ^-1 Raised to 17.5+/-1.4 kg.m ^-2 ·h ^-1 The salt cutting rate is maintained above 99.9%. The flux and salt interception rate of the MOF-801@GO (DMF) -PDMS membrane before and after activation are kept stable within 20h of test time.

From the above characterization and performance results, it is known that: the present work in-situ grown porous MOF-801 nanoparticles can provide additional water vapor mass transfer channels (fig. 11 (g)) compared to in-situ grown solid MOF-801 nanoparticles to further enhance the water vapor permeation flux of the hydrophobic graphene oxide membrane.

5. Desalination Properties of FAS hydrophobically modified Membrane

The FAS hydrophobically modified MOF-801@GO porous hydrophobic membrane was further analyzed and characterized and the results are shown in FIG. 12 (feed temperature 60 ℃ C., feed salt concentration 35 g/L).

As can be seen from fig. 12: the microstructure of the MOF-801@GO-FAS film is similar to that of the MOF-801@GO film, the surface water contact angle is 111.8+/-1.3 degrees, and the FT-IR spectrum characterization proves that FAS is successfully introduced into the surface and the interlayer of the film. DCMD desalination performance of the prepared MOF-801@go-FAS film was found: the flux and salt rejection rate of the membrane are both slowly reduced with test time, indicating that a more severe wetting phenomenon (partial wetting) of the membrane occurs. The reason may be that the FAS long-chain hydrophobic modification is unstable to fall off during the test, resulting in a decrease in the hydrophobicity of the film surface: the MOF-801@GO-FAS film prepared by FAS modification has the advantages that after the performance is tested, the water contact angle of the film surface is reduced to 85.0+/-3.8 degrees; and the MOF-801@GO-PDMS film prepared by PDMS modification has the same contact angle with water on the surface of the film after testing the performance (FIG. 12 (e)). Therefore, compared with FAS modification, in the PDMS coating method provided by the application, due to the excellent winding cohesiveness of PDMS, the designed MOF-801@GO-PDMS film maintains stable film structure and desalting performance in the test process, and meanwhile, the PDMS is nontoxic, harmless and low in price, so that the uniqueness and practicality of the research method are further proved.

6. Different feed temperatures and continuous desalination performance

The MOF-801@GO-1wt% PDMS porous hydrophobic membrane was tested for desalination performance (40-70 ℃ C., feed salt concentration of 35 g/L) and continuous desalination performance (60 ℃ C., feed salt concentration of 35g/L,72 h) at different feed temperatures, and the results are shown in FIG. 13.

As can be seen from fig. 13: with the increase of the temperature of the feed salt solution, the vapor pressure of the interface of the feed membrane is gradually increased, and the driving force on the two sides of the membrane is increased, so that the flux of the MOF-801@GO-1wt% PDMS membrane is 14.5+/-1.0 kg.m ^-2 ·h ^-1 Increased to 29.2+ -1.6 kg.m ^-2 ·h ^-1 And the salt interception rate is kept high. In a 72h continuous desalting performance test, the flux of the MOF-801@GO-1wt% PDMS membrane is stably maintained at 22.9 kg.m ^-2 ·h ^-1 The salt cut rate is always kept above 99.9%, and good stability is shown.

Claims

1. The hydrophobic graphene oxide membrane is characterized by comprising a supporting layer and a selective separation layer, wherein the selective separation layer is formed by a plurality of layers of graphene oxide nano sheets, MOF-801 nano particles are distributed on the surfaces of the graphene oxide nano sheets, the MOF-801 nano particles are positioned between adjacent graphene oxide nano sheets, and the surfaces of the selective separation layer are also covered with a hydrophobic modification layer;

the MOF-801 nano particles have a porous structure;

the material of the hydrophobic modification layer is PDMS; the supporting layer is a hydrophobic PVDF supporting body;

uniformly mixing 40mg of GO with 20mL deionized water, and fully stripping the GO sheets by ultrasound to prepare GO aqueous dispersion;

step (2) 0.0396g ZrOCl is taken ₂ ·8H ₂ Mixing O, 15mL deionized water, 1mL acetic acid and 8mL GO aqueous dispersion uniformly, and stirring at 60 ℃ for 1h;

step (3) 0.0143g of C ₄ H ₄ O ₄ Uniformly mixing 15mL deionized water and 1mL acetic acid, and stirring at 60 ℃ for 1h;

step (4) C obtained in step (3) ₄ H ₄ O ₄ Slowly pouring the aqueous solution into the solution obtained in the step (2), uniformly mixing, stirring at 60 ℃ for 3h, centrifuging, washing with deionized water for 3 times, vacuum drying at room temperature to obtain MOF-801@GO powder, and adding deionized water for dispersion to prepare 2mg/mL of MOF-801@GO aqueous dispersion;

s2, preparing a MOF-801@GO film:

mixing 0.5mL of MOF-801@GO aqueous dispersion with 158g methanol, performing ultrasonic treatment for 60min, vacuum-filtering to obtain a hydrophobic PVDF support, and drying at room temperature to obtain a 12h MOF-801@GO membrane;

s3, preparing a hydrophobic graphene oxide film:

preparing PDMS-n-heptane solution with mass fraction of 0.5wt% or 1wt%, stirring at room temperature for 2h;

step (2), spin-coating PDMS-n-heptane solution on the MOF-801@GO film, wherein spin-coating parameters are as follows: spin-coating 6 times, 1 mL/time, 1500rpm, spin-coating 30 s; and drying at room temperature, and then placing the dried graphene film in an oven to perform heat treatment at 70 ℃ for 4h to prepare the hydrophobic graphene oxide film.

2. Use of the hydrophobic graphene oxide membrane according to claim 1 for membrane distillation desalination.