CN114931864A - Two-dimensional material composite separation membrane, preparation method and application - Google Patents
Two-dimensional material composite separation membrane, preparation method and application Download PDFInfo
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Abstract
The invention relates to a two-dimensional material composite separation membrane, a preparation method and application, and belongs to the technical field of membrane separation. Two-dimensional material composite componentThe separation membrane is composed of a two-dimensional material and a nano material loaded on the two-dimensional material, wherein the two-dimensional material is g-C 3 N 4 Nanosheets, the nanomaterial being MoS 2 Nanosheets or nano ZnO. And g-C 3 N 4 Pure film and MoS 2 Compared with a pure membrane, the composite membrane has the advantages that the phenol interception performance and the visible light catalytic degradation performance are improved, and the stability of the composite membrane is good. The nano ZnO can effectively fill in g-C 3 N 4 The performance of the film is greatly improved due to cracks and cavities. The retention rate of the composite membrane exceeds 88 percent, and the photocatalytic performance is g-C 3 N 4 /MoS 2 2 times of the composite membrane.
Description
Technical Field
The invention relates to a two-dimensional material composite separation membrane, a preparation method and application, and belongs to the technical field of membrane separation.
Background
Two-dimensional graphite phase carbon nitride (g-C) 3 N 4 ) Material [1,2] Have been explored as very promising candidates for the field of photocatalytic chemistry and separation membranes. g-C 3 N 4 The nano-sheet is metal-free, nontoxic and easy to be in realityLarge scale preparation in laboratory. Importantly, g-C 3 N 4 Is a material of a two-dimensional sheet laminated structure taking a trithiotriazine ring as a basic structural unit, g-C 3 N 4 The layers of the material have Van der Waals force and a pi-pi conjugated structure, and the material has special electronic and photocatalytic performance compared with the traditional TiO 2 The photocatalyst has a wider absorption spectrum range, and only does not need ultraviolet light under common visible light to play a photocatalysis role. g-C 3 N 4 Unique lattice defects and layered structures in nanosheets [3] Is very suitable for the formation of membrane channels for selective water transport. Zhao et al [4] Study of the composite g-C 3 N 4 Permeability of the photocatalytic film. The results show that g-C is responsible for 3 N 4 The high photocatalytic efficiency, rhodamine B removal efficiency and permeation flux of the compound are improved. These high separation and permeation properties are attributed to g-C 3 N 4 The function of the nano-sheet. But due to the body g-C 3 N 4 The specific surface area of the photo-induced carrier is small, and the photo-induced electron holes are easy to recombine, so that the transport speed of the photo-induced carrier is low, and the photocatalytic activity of the photo-induced carrier is limited. Thus, g-C is increased 3 N 4 The photocatalytic activity of the photocatalyst has important significance.
In recent years, researchers have found that g-C can be prepared by a certain method 3 N 4 The block is stripped, and 2D g-C with better photocatalytic activity can be obtained 3 N 4 Nanosheets. Common methods are thermal oxidation etching exfoliation, chemical intercalation exfoliation and liquid exfoliation. However, thermal oxide etch spalling method 2D g-C 3 N 4 The interface of the nanosheet has many defects. In the stripping process of the chemical intercalation, the chemical intercalation can destroy the two-dimensional g-C of a single layer 3 N 4 The structure of the nano-sheet and the process are complex. The liquid stripping method is to prepare two-dimensional g-C 3 N 4 One of the most commonly used methods for nanosheets is a higher photocatalytic activity and higher mass yield than thermal oxidation, etch stripping and chemical intercalation stripping. However, there are still some problems with this approach. Use of organic solvents during exfoliation and require long periods of ultrasonic assistance. Thus, the process may generate a large amount of organic waste liquid with a large energy consumption. Therefore, it is important to find a stripping method which is green and environment-friendly and can meet the requirements of high yield and photocatalytic activity.
Self-supporting ultrathin membranes have been a hotspot in research and industrial applications for decades, since such self-supporting membranes have a width of a few centimeters and a thickness of a few nanometers, i.e. have both macroscopic material and single molecule properties. Ran et al [5] By MoS in two dimensions 2 Zn-BTC nano-wire is inserted into the film, and Zn-BTC/MoS is successfully prepared 2 The composite film shows that Zn-BTC/MoS 2 Organic solvent flux ratio MoS of composite membrane 2 The membrane is improved by 6 times, and meanwhile, the composite membrane keeps excellent sieving capacity and can completely intercept dye molecules with the size larger than 0.42 nm.
Albeit g-C 3 N 4 In the application of membrane materials, a plurality of problems still exist in the application of self-membrane formation. First g to C 3 N 4 Self film-forming property is poor, and g-C is prepared 3 N 4 Once the pure film is oversize, the film surface has a plurality of obvious defect cracks. Meanwhile, in the self-film-forming process, more cavities are formed in the film. The presence of these cavities, greatly influences g-C 3 N 4 Separation performance of the membrane. Second g-C 3 N 4 The natural product has certain photocatalytic performance, and how to utilize the characteristic is also a hotspot of current research.
[1]S Li,L Zhang,X Zhong,et al.Nano-subsidence-assisted precise integration of patterned two-dimensional materials for high-performance photodetector arrays[J].ACS Nano,2019.
[2]Y Zhe,J D Benck,Y Eatmon,et al.Stable,temperature-dependent gas mixture permeation and separation through suspended nanoporous single-layer graphene membranes[J].Nano Letters,2018,18(8):5057-5069.
[3]Y Wang,L Li,Y Wei,et al.Water transport with ultralow friction through partially exfoliated g-C 3 N 4 nanosheet membranes with self-supporting spacers[J].Angewandte Chemie International Edition,2017,56(31):8974-8980.
[4]H Zhao,S Chen,X Quan,et al.Integration of microfiltration and visible-light-driven photocatalysis on g-C3N4 nanosheet/reduced graphene oxide membrane for enhanced water treatment[J].Applied Catalysis B Environmental,2016,194:134-140.
[5]Beautiful line, Huangqiang, Aixinyu, etc. Zn-BTC/MoS 2 Composite two-dimensional membrane construction and organic solvent nanofiltration performance study [ J]Journal of chemical engineering, 2021,04: 2148-.
Disclosure of Invention
The first technical problem to be solved by the invention is as follows: existing g-C 3 N 4 Self film-forming property is poor, and g-C is prepared 3 N 4 Once the pure film is oversize, the film surface has a plurality of obvious defect cracks. Meanwhile, in the self-film-forming process, more cavities are formed in the film. The presence of these cavities greatly affects g-C 3 N 4 Separation performance of the membrane. By mixing MoS 2 And nano ZnO with g-C 3 N 4 Compounding nano sheets to prepare MoS 2 /g-C 3 N 4 Film g-C 3 N 4 The @ ZnO film is prepared by the method, and the performance of the prepared film is researched, so that the phenol interception performance and visible light catalytic degradation performance of the composite film are effectively improved.
The second technical problem to be solved by the invention is: solves the problem of 2D g-C prepared in the prior art 3 N 4 The method of the nano-sheet has the problems of low yield, high energy consumption and the like. Proposed the preparation of g-C by gas phase exfoliation 3 N 4 A method of nanosheet. Exfoliated g-C 3 N 4 The nano sheet layer is thin, and the thickness of part of the nano sheet layer can reach the thickness of a single sheet layer. The structure is complete and the size is large.
The technical scheme is as follows:
a first object of the present invention is to provide:
two-dimensional g-C 3 N 4 Nanosheets produced by a vapor phase exfoliation method.
A second object of the present invention is to provide:
two-dimensional g-C as described above 3 N 4 The preparation method of the nanosheet comprises the following steps:
The heating in step 1 means heating to 300-500 ℃, and step 1 is repeated for 1-20 times.
The first centrifugation treatment in step 2 was repeated 1-10 times at a rotation speed of 4000-5500 rpm.
The centrifugation rotation speed of 10000-.
Said g-C 3 N 4 The powder is prepared by thermal polymerization.
The thermal polymerization method comprises the following steps: calcining melamine, grinding, cleaning and drying the product to obtain g-C 3 N 4 And (3) powder.
The calcination process is calcination at 500-600 ℃ for 1-10 h.
The cleaning process is to clean by using deionized water and absolute ethyl alcohol in sequence.
The drying is carried out for 1-48h at 60-100 ℃.
A third object of the present invention is to provide:
two-dimensional g-C as described above 3 N 4 The nano-sheet is used for photocatalytic degradation of organic matters.
The organic matter is phenol.
In the photocatalytic degradation, a visible light source is adopted for irradiation.
A fourth object of the present invention is to provide:
a two-dimensional composite separating membrane is composed of two-dimensional materialThe material and the nano material loaded on the two-dimensional material, wherein the two-dimensional material is g-C 3 N 4 Nanosheets, the nanomaterial being MoS 2 Nano-sheets or nano-ZnO.
In one embodiment, the weight ratio of the two-dimensional material to the nanomaterial is in the range of 1: 9-9: 1.
a fifth object of the present invention is to provide:
a preparation method of a two-dimensional material composite separation membrane comprises the following steps:
In one embodiment, the two-dimensional g-C in step 2 3 N 4 Nanosheet and two-dimensional MoS 2 The weight ratio of the nano sheets is 1: 9-9: 1.
in one embodiment, in step 1, the two dimensions g-C 3 N 4 Nanosheet or two-dimensional MoS 2 The preparation method of the nano sheet comprises the following steps:
step a, mixing g-C 3 N 4 Or MoS 2 Heating the powder, and adding the product into liquid nitrogen;
step b, dispersing the product obtained in the step a in an ethanol water solution, uniformly stirring, and then performing first centrifugal treatment to obtain a supernatant;
step C, carrying out second centrifugal treatment on the supernatant obtained in the step b to obtain a precipitate, and drying to obtain the two-dimensional g-C 3 N 4 Nanosheet or two-dimensional MoS 2 A nanosheet.
The heating in step a refers to heating to 300-500 ℃, and step 1 is repeated for 1-20 times.
The first centrifugation treatment in step b was repeated 1-10 times at a rotation speed of 4000-5500 rpm.
The centrifugation rotation speed of the second centrifugation treatment in the step c is 10000-.
A sixth object of the present invention is to provide:
a preparation method of a two-dimensional material composite separation membrane comprises the following steps:
In one embodiment, Zn (NO) 3 ) 2 And g-C 3 N 4 The weight ratio of the nano sheets is 5-15: 1.
in one embodiment, in step 3, Zn (NO) 3 ) 2 The concentration of the solution is 1-50mg/ml, and the concentration of the NaOH solution is 0.1-2 mol/L.
A seventh object of the present invention is to provide:
the two-dimensional material composite separation membrane is applied to filtering and/or photocatalytic decomposition of an organic matter-containing solution.
An eighth object of the present invention is to provide:
ZnO and/or MoS 2 Use of nanoplatelets in g-C repair 3 N 4 Use in the surface defect of a film.
A ninth object of the present invention is to provide:
ZnO and/or MoS 2 Use of nanoplatelets for increasing g-C 3 N 4 Use of a membrane for the rejection of organic matter in solution.
Advantageous effects
(1) Preparation of g-C 3 N 4 In the nanosheet method, the vapor exfoliation method requires heating of the material. The high temperature can accelerate the vibration of the sheets of material, thereby increasing the spacing between the sheets. When the super-cooled liquid gas enters between the sheets, it vaporizes violently and expands rapidly. The gas molecules collide with the sheet, creating a force that separates the sheets. Tong (Chinese character of 'tong')Liquid nitrogen is often used as the vaporizing medium. Because liquid nitrogen is very cold and inexpensive. The gas-phase peeling method is simpler and more environment-friendly to prepare the nano sheet.
(2) Exfoliated g-C 3 N 4 The nano sheet has thinner layers, and the thickness of partial layers can reach that of a single layer. The structure is complete and the size is large. The vapor phase exfoliation method is at g-C compared to conventional exfoliation methods 3 N 4 The performance of the nano-sheet structure is obviously improved.
(3) Preparation of g-C by different heating temperature versus vapor phase exfoliation 3 N 4 The effect of the nanoplatelets is different. The higher the heating temperature, the higher the effect of exfoliation and the yield. When the temperature reaches 500 ℃, the peeling effect and the yield are obviously increased.
(4)g-C 3 N 4 Can be used for photocatalytic degradation of phenol at room temperature. g-C 3 N 4 The nanosheet catalytic rate is non-exfoliated g-C 3 N 4 2-3 times of the total weight of the product. Preparation of g-C by vapor phase exfoliation 3 N 4 g-C effectively improved by nanosheets 3 N 4 Photocatalytic performance.
(5) And g-C 3 N 4 Pure film and MoS 2 Compared with a pure membrane, the composite membrane has the advantages that the phenol interception performance and the visible light catalytic degradation performance are improved, and the stability of the composite membrane is good.
(6) When g-C 3 N 4 And MoS 2 g-C when the mass ratio is 1:1 3 N 4 /MoS 2 The composite membrane has the best improved performance. The retention rate is greatly improved compared with that of a pure membrane, and the retention rate of phenol is 42.1%. Simultaneously the visible light catalytic performance is the same as g-C 3 N 4 Compared with the pure film, is g-C 3 N 4 1.5 times of pure membrane, same as MoS 2 Compared with pure film, is MoS 2 3 times that of the pure membrane.
(7) The nano ZnO can effectively fill in g-C 3 N 4 The performance of the film is greatly improved due to cracks and cavities. The retention rate of the composite membrane exceeds 88 percent, and the photocatalytic performance is g-C 3 N 4 /MoS 2 2 times of the composite membrane.
Drawings
FIG. 1 is a gas phase exfoliation method for preparing g-C 3 N 4 Schematic diagram of nanosheet principle.
FIG. 2 shows a block g-C 3 N 4 And g-C 3 N 4 Nanoplate infrared spectrogram.
FIG. 3 is an X-ray diffraction analysis of bulk g-C 3 N 4 And g-C 3 N 4 Crystal structure of nanosheet
FIG. 4 is a particle size distribution diagram.
FIG. 5 is a block g-C 3 N 4 And a standing comparison of g-C3N4 nanosheets (60 days)
FIG. 6 is a UV fluorescence test chart (left: block g-C) 3 N 4 (ii) a And (3) right: CN-500)
FIG. 7 shows blocks g-C of (a) and (b) 3 N 4 SEM picture of (1); (c) is in the form of block g-C 3 N 4 A TEM image of (B); (d) is g-C 3 N 4 TEM image of nanosheets
FIG. 8 is light time vs. block g-C 3 N 4 And the influence of CN-500 on the photocatalytic degradation of phenol
FIG. 9: g-C 3 N 4 /MoS 2 Flow chart of composite membrane preparation
FIG. 10: g-C 3 N 4 Static distribution map
FIG. 11: g-C 3 N 4 /MoS 2 Composite membrane preparation flow chart
FIG. 12: process flow diagram for pervaporation
FIG. 13: g-C 3 N 4 /MoS 2 SEM image and EDS elemental analysis of composite membrane surface and section
FIG. 14: g-C 3 N 4 SEM image and EDS elemental analysis of surface and section of @ ZnO composite membrane
FIG. 15: different MoS 2 g-C of content 3 N 4 /MoS 2 Effect of composite membranes on phenol rejection
FIG. 16: g-C 3 N 4 And MoS 2 g-C with mass ratio of 1:1 3 N 4 /MoS 2 Circulation test chart for phenol retention performance of composite membrane
FIG. 17: g-C 3 N 4 @ ZnO composite membrane cycle test chart for cycle test of phenol interception performance
FIG. 18 is a schematic view of: performance diagram for visible light catalytic degradation of phenol
FIG. 19: the preparation method of the composite membrane is shown in a mechanism diagram. (a) The method comprises the following steps g-C 3 N 4 /MoS 2 Compounding film; (b) the method comprises the following steps g-C 3 N 4 @ ZnO composite film
Detailed Description
Preparation of g-C in a gas phase stripping process 3 N 4 The reagents and instruments used in the nanosheet experiments are shown in tables 1 and 2, respectively:
TABLE 1 test reagents
TABLE 2 Experimental instruments
Preparation of g-C by thermal polymerization 3 N 4
Experiment adopts thermal polymerization method to prepare a large amount of g-C 3 N 4 And (3) powder. The specific experimental steps are as follows: firstly, weighing 10g of melamine and placing the melamine in an alumina crucible with a cover; then placing the crucible in a tube furnace, and calcining for 4 hours at 550 ℃ (the heating rate is 5 ℃/min); the calcined product is a light yellow block solid, and is washed for three times by deionized water and absolute ethyl alcohol after being ground by a mortar to remove unreacted impurities; then dried at 80 ℃ for 24h to give g-C 3 N 4 And (3) powder.
Preparation of g-C by vapor phase exfoliation 3 N 4 Nano-sheet
Weighing 5g of prepared g-C 3 N 4 The powder was placed in a crucible. The tube furnace was then warmed to 300C. The crucible was placed in a heated tube furnace and heated for 10 min. Pouring into 100ml liquid nitrogen in 500ml polytetrafluoroethylene beaker, heating the g-C 3 N 4 The powder was quickly added to liquid nitrogen. The beaker was shaken until the liquid nitrogen had completely vaporized. This is a complete exfoliation process. The above experimental procedure was repeated until the end of the 10 th exfoliation. 500ml of ethanol/water solution (volume ratio 1:1) was added to a beaker of polytetrafluoroethylene. Stirring with a glass rod for 5min, and ultrasonically dispersing for 30 min. The dispersion was centrifuged using an electric precipitation centrifuge. The rotational speed was 4800 rpm. Taking supernatant, continuing to centrifuge under the same conditions and repeating for 5 times to obtain g-C 3 N 4 A nanosheet dispersion. Taking g-C 3 N 4 And (4) carrying out high-speed centrifugation on the nanosheet dispersion. The rotation speed was 12000 rpm. Vacuum drying the precipitate at 80 deg.C for 12h to obtain g-C 3 N 4 The powder of nanoplatelets was used for subsequent sample characterization. The sample was designated CN-300. The heating temperatures were varied to 400 ℃ and 500 ℃ and the samples were designated CN-400 and CN-500, respectively. FIG. 1 is a gas phase exfoliation method for preparing g-C 3 N 4 Schematic diagram of nanosheet principle.
Infrared analysis
By detecting blocky g-C 3 N 4 Powders and g-C 3 N 4 FT-IR spectrum of nanosheets. The peak positions of the samples are basically consistent, which indicates that the g-C is prepared by the vapor phase exfoliation method 3 N 4 The nanosheets did not alter g-C 3 N 4 The chemical microstructure of (1). g-C 3 N 4 The existence of a large amount of primary amine and secondary amine at the edge part causes the stretching vibration of N-H bonds, and the stretching vibration occurs at 3600- -1 A broad peak region of (a). And g-C 3 N 4 Structures with a large number of 3-s-triazine rings inside, 813cm -1 The peak at (a) is caused by the vibration of the structure. And 1650 + 1240cm -1 The peaks between correspond to the tensile vibrations of the C-N bond and the C-NH-C bond, respectively. FIG. 2 shows a block g-C 3 N 4 And g-C 3 N 4 Nanoplate infrared spectrogram.
XRD analysis
Analysis of bulk g-C by X-ray diffraction 3 N 4 And g-C 3 N 4 Crystal structure of the nanoplatelets (fig. 3). It is apparent from the figure that g-C is observed 3 N 4 Two characteristic peaks (003) and (100) in the XRD spectrum of (1). Conjugated aromatic compounds like graphiteA flat packed structure will show a strong peak around 28 °. While the repeat units inside the sheet show strong peaks at the 13 deg. position. The intensity of the (003) and (100) peaks decreased with increasing temperature, indicating that g-C could be prepared 3 N 4 A nanosheet. The peak areas at 500 ℃ are obviously less than 300 ℃ and 400 ℃, which shows that the stripping effect is better when the heating temperature is 500 ℃.
Particle size analysis
As is clear from the results of the examination, the g-C after the exfoliation 3 N 4 The particle size of the nano-sheets is smaller than that of the un-peeled g-C 3 N 4 . Meanwhile, the particle size of CN-500 is obviously smaller than that of CN-300 and CN-400. Indicating that the heating temperature has a significant effect on the exfoliation effect. Meanwhile, the particle size of CN-500 reaches 290nm, which is far smaller than that of g-C prepared by the traditional stripping process 3 N 4 The particle size of the nanosheet (about 300 nm). FIG. 4 is a particle size distribution diagram.
g-C 3 N 4 Dispersibility and fluorescence property of nanosheet
As is evident from comparison of the dispersion after standing for 2 months (FIG. 5), only CN-500 was well dispersed in the dispersion. And CN-300, CN-400 and unexfoliated g-C 3 N 4 The powder had settled to the bottom of the reagent bottle. The results show that g-C is produced in a vapor phase exfoliation process 3 N 4 In the process of nanosheet, good peeling effect is achieved only when the heating temperature is higher than a certain degree. As can be seen from the experimental results, the CN-500 structural performance is the best, so that the subsequent characterization test is mainly used for detecting the CN-500. As can be seen from the fluorescence function test, under the irradiation of ultraviolet light, CN-500 has obvious fluorescence effect (FIG. 6).
SEM and TEM analysis
Observation of g-C by SEM 3 N 4 The powder structure can be found to have a pronounced lamellar stacking structure. Non-exfoliated g-C 3 N 4 Presents a bulk stacking state, seriously affecting g-C 3 N 4 And (4) performance. The stripped g-C can be seen through TEM 3 N 4 The nanosheets have thinner lamellae, and a portion of the nanosheets can reach the single lamellae. Exfoliated g-C 3 N 4 Nanosheet structureComplete and large in transverse dimension. The electron microscope test result shows that the gas phase exfoliation method can prepare g-C 3 N 4 The nano-sheet and the nano-sheet structure performance prepared by the method are greatly improved.
g-C 3 N 4 And g-C 3 N 4 Photocatalytic performance of nanoplatelets
First, an aqueous phenol solution having a concentration of 10mg/ml was prepared. 0.1g of non-exfoliated g-C is weighed 3 N 4 The powder was added to an aqueous phenol solution. Ultrasonically dispersing in dark for 5min, and stirring in dark for 25min to obtain g-C 3 N 4 The particles reach adsorption equilibrium. The solution was then illuminated with a visible light source. The light source is white in color and has a power of 100 w. Sampling every 0.5h, and removing g-C in the solution by using a high-speed centrifuge with the rotating speed of 12000rpm 3 N 4 . The phenol concentration was measured with an ultraviolet-visible spectrophotometer at a wavelength of 213nm in an ethanol/water solution (volume ratio 1: 1). The phenol standard curve was determined prior to the start of the experiment. The entire experiment was run at room temperature (25 ℃ C.). The same procedure was used for CN-500 photocatalytic performance.
As can be seen in FIG. 8, the block shape g-C 3 N 4 And g-C 3 N 4 The nano-sheets have certain photocatalytic performance. g-C 3 N 4 The catalytic rate of the nano-sheet is larger than that of the blocky g-C 3 N 4 . The results show that g-C produced by the vapor phase exfoliation method 3 N 4 The nano sheet effectively improves the photocatalytic performance. The experimental result also shows that under certain illumination conditions, g-C 3 N 4 VOCs can be catalytically degraded at room temperature.
g-C 3 N 4 /MoS 2 Preparation of composite membranes
First, a two-dimensional MoS is prepared 2 The nanosheet is prepared by a vapor exfoliation method, and the experimental operation steps of the preparation are as follows: weighing 5g of prepared g-C 3 N 4 The powder was placed in a crucible. The tube furnace was then warmed to 500 ℃. And (3) placing the crucible in a tubular furnace with a well-heated temperature for heating for 10 min. Pouring 100ml of L-N into a 500ml polytetrafluoroethylene beaker 2 . Heating the heated g-C 3 N 4 Powder is added rapidlyInto L-N 2 In (1). Shaking the beaker until L-N 2 And completely vaporized. This is a complete exfoliation process. The above experimental procedure was repeated until the end of the 10 th exfoliation. 500ml of ethanol/water solution (volume ratio 1:1) was added to a beaker of polytetrafluoroethylene. Stirring with a glass rod for 5min, and ultrasonically dispersing for 30 min. The dispersion was centrifuged using an electric precipitation centrifuge. The rotational speed was 4800 rpm. Taking supernatant, continuing to centrifuge under the same conditions and repeating for 5 times to obtain g-C 3 N 4 A nanosheet dispersion. Taking g-C 3 N 4 And (4) performing high-speed centrifugation on the nanosheet dispersion. The rotation speed was 12000 rpm. Vacuum drying the precipitate at 80 deg.C for 12h to obtain g-C 3 N 4 A powder of nanoplatelets. The sample was designated CN-500.
In addition, the MoS to be purchased is also required 2 Powder is peeled off to MoS 2 The nano-sheet is prepared by a gas phase peeling method, and the steps are as follows: 5g of the prepared MoS are weighed 2 The powder was placed in a crucible. The tube furnace was then warmed to 400 ℃. The crucible was placed in a tube furnace heated for 15 min. Pouring 100ml of L-N into a 500ml polytetrafluoroethylene beaker 2 . The heated MoS 2 Powder is rapidly added to L-N 2 In (1). Shaking the beaker until L-N 2 And completely vaporized. This is a complete exfoliation process. The above experimental procedure was repeated until the 8 th exfoliation was complete. 500ml of ethanol/water solution (volume ratio 1:1) was added to a beaker of polytetrafluoroethylene. Stirring with a glass rod for 5min, and ultrasonically dispersing for 30 min. The dispersion was centrifuged using an electric precipitation centrifuge. The rotation speed was 4000 rpm. Taking supernatant, continuing to centrifuge under the same conditions and repeating for 5 times to obtain MoS 2 A nanosheet dispersion. Get MoS 2 And (4) carrying out high-speed centrifugation on the nanosheet dispersion. The rotation speed was 10000 rpm. Taking the precipitate, and vacuum drying at 85 ℃ for 10h to obtain MoS 2 A powder of nanoplatelets.
Respectively adding the above-mentioned g-C 3 N 4 Nanosheet and MoS 2 Dispersing the nano-sheet in deionized water to obtain a dispersion liquid.
Next, a composite membrane was prepared by the following steps: mixing the dispersion of CN-500 with MoS 2 The nano-sheet dispersion liquid is prepared according to a certain mass proportionMixing, and ultrasonically dispersing for 30 min. And (3) performing vacuum filtration to form a membrane, wherein a PVDF membrane with the diameter of 0.22 mu m is adopted in the filtration process, and after the nanosheets are intercepted, the PVDF membrane is simultaneously used as a supporting layer and a composite membrane. g-C for preparing membrane material 3 N 4 Nanosheet (CN-500) and MoS 2 The total content of the nano sheets is 10 mg. g-C 3 N 4 Nanosheets and MoS 2 The weight ratio of the nano sheets is set to 10:0, 9:1, 8:2, 6:4, 5:5, 4:6, 2:8, 1:9 and 0: 10. FIG. 9 shows g-C 3 N 4 /MoS 2 A flow chart of composite membrane preparation.
In the following description, 10:0 and 0:10 of pure g-C in each case 3 N 4 Membranes and pure MoS 2 And (3) a membrane.
g-C 3 N 4 Preparation of @ ZnO composite film
The preparation method of the nano ZnO has a plurality of methods, and g-C with good performance can be prepared by selecting a proper mode 3 N 4 @ ZnO composite film. How to introduce the zinc source is of great importance. By molecular simulation, for g-C 3 N 4 The charge distribution and electrostatic potential distribution of (2) were calculated, and it was found that g-C 3 N 4 The unique crystal plane defect pores exhibit a negative potential around them. By introducing Zn-bearing 2+ By an electrostatic potential of Zn 2+ And forming nano ZnO through subsequent reaction. In addition, Zn can be adsorbed by the multi-channel adsorption of the membrane itself 2+ . Fig. 10 is an electrostatic distribution diagram, 1 being a positive potential, 2 being a negative potential, and 3 being neutral. Selection of Zn (NO) 3 ) 2 As a zinc source, due to Zn (NO) 3 ) 2 The highest degree of dissociation in ethanol/water solution.
Taking a certain amount of g-C 3 N 4 Nanosheet (CN-500) dispersion, the CN-500 content being 10 mg. 0.1g of Zn (NO) is weighed 3 ) 2 And added to the dispersion of CN-500. Stirring magnetically for 30 min. And then, preparing a membrane by vacuum filtration, wherein a PVDF membrane with the diameter of 0.22 mu m is adopted in the filtration process, and after the nanosheets are intercepted, the PVDF membrane is simultaneously used as a supporting layer and a composite membrane. Soaking the membrane prepared by suction filtration in Zn (NO) with concentration of 10mg/ml 3 ) 2 Soaking in 0.5mol/L NaOH solution for 4 hr, and soaking for 2 hrThe membrane after NaOH is placed for a period of time to allow the water to evaporate. The dry film was calcined in a tube furnace. The calcined film is g-C 3 N 4 @ ZnO composite film.
Comparative examples 1 g-C 3 N 4 Preparation of/ZnO composite film
Compared with example 2, the difference is that: directly mixing ZnO powder (average particle size 90nm) with g-C 3 N 4 The nanosheets are mixed and then calcined to form a membrane. Taking a certain amount of g-C 3 N 4 Nanosheet (CN-500) dispersion, the CN-500 content being 10 mg. 0.05g of ZnO was weighed and added to the dispersion of CN-500. Stirring magnetically for 30 min. Then, the membrane is prepared by vacuum filtration. And putting the membrane dry membrane prepared by suction filtration into a tubular furnace for calcination. The calcined film is g-C 3 N 4 A/ZnO composite film.
SEM and EDS analysis of composite membranes
Observation of g-C by scanning Electron microscopy 3 N 4 /MoS 2 Composite film and g-C 3 N 4 The microstructure of the @ ZnO composite membrane. Observation of g-C by elemental analysis of EDS 3 N 4 /MoS 2 Composite film and g-C 3 N 4 The @ ZnO composite film has N, Mo and Zn element distribution.
Observation of g-C by SEM 3 N 4 /MoS 2 Composite film and g-C 3 N 4 The microstructure of the surface and cross section of the @ ZnO composite film was analyzed by EDS element analysis, and the results are shown in FIGS. 13 and 14.
From FIGS. 13 and 14, g-C can be seen 3 N 4 /MoS 2 Composite film and g-C 3 N 4 The @ ZnO composite film effectively repairs the defects of a pure film and g-C 3 N 4 The improved effect of the @ ZnO composite membrane is better. g-C 3 N 4 /MoS 2 Minor defect cracks still exist on the surface of the composite film. From the EDS analysis, at g-C 3 N 4 /MoS 2 In the composite film, g-C 3 N 4 And MoS 2 Are dispersed relatively uniformly. In g-C 3 N 4 In the @ ZnO composite film, although the surface is repaired completely, the distribution of elements shows that the nano ZnO is in the filmThe surface and the inside are loaded and uniformly dispersed, but the amount is lower than MoS 2 。
Separation performance research and visible light catalysis performance research of composite membrane
Detection of g-C 3 N 4 /MoS 2 Composite film and g-C 3 N 4 The separation performance of the @ ZnO composite membrane. Firstly, preparing a phenol solution, wherein the total amount is 40g, and the mass fraction is 50%. Sampling to detect benzene concentration as a benchmark. And detecting the separation performance of the composite membrane on phenol/water by a vapor permeation device. The total time is 1 h. After the experiment is finished, the concentration of phenol in the cold hydrazine is detected, and g-C is calculated 3 N 4 The interception rate of the @ ZnO composite membrane to phenol.
In order to test the stability of the composite membrane, g-C with the mass ratio of 1:1 is added 3 N 4 /MoS 2 Composite film and g-C 3 N 4 @ ZnO composite films were tested for 5 cycles.
With g-C 3 N 4 /MoS 2 Composite film and g-C 3 N 4 The @ ZnO composite membrane degrades phenol under visible light so as to detect the visible light catalytic performance of the composite membrane. A phenol solution was prepared at room temperature to a concentration of 10 mg/ml. And fixing the composite membrane on the bracket. The scaffolds with membranes were placed in a phenol/water solution. Magnetic stirring in dark place for 30min, and irradiating with white visible light source. Samples were taken every 0.5h and the phenol concentration was determined spectrophotometrically, with the total time remaining at 4.5 h.
FIG. 15 shows the difference g-C 3 N 4 And MoS 2 Influence of the content composite membrane on phenol retention performance. As is clear from the figure, when the mass ratio is 1:1, the retention rate of the composite membrane to phenol reaches the highest. At the same time, it is found that when g-C 3 N 4 Pure film and MoS 2 The pure membrane flux is extremely high, the retention rate is extremely low, and the g-C is shown at the moment 3 N 4 Pure film and MoS 2 Pure membranes do not meet the rejection performance. FIG. 16 shows g-C 3 N 4 And MoS 2 g-C at a mass ratio of 1:1 3 N 4 /MoS 2 And (5) a composite membrane cycle test chart. Can clearly see that the interception and flux of the membrane are changed slightly, and the stability of the membrane is relativelyIs good. g-C 3 N 4 The flux of the @ ZnO composite film is 22356.42 g.m -2 ·h -1 The retention rate is 88.25%; while in comparative example 1, ZnO nanoparticles and g-C were directly passed through 3 N 4 The rejection rate of the composite film obtained by mixing the nano-sheets to phenol is only 9.2 percent, and the phenol rejection rate is equal to that of pure g-C 3 N 4 Compared with the retention rate of the nano-sheet film, the retention rate of the nano-sheet film has no substantial difference, which indicates that ZnO directly contacts g-C through the nano-particles 3 N 4 The entrapment performance of the nano-sheet mixed membrane on phenol cannot be improved. The results show that g-C 3 N 4 The performance of the @ ZnO composite film is higher than that of the g-C 3 N 4 /MoS 2 The composite membrane is more prominent. FIG. 17 is g-C 3 N 4 @ ZnO composite membrane cycle test chart.
The results of the above experiments show that g-C is modified 3 N 4 /MoS 2 And g-C 3 N 4 The @ ZnO composite membrane has greatly improved separation performance. As can be seen from the results of photocatalytic degradation of phenol, the modified g-C 3 N 4 /MoS 2 And g-C 3 N 4 The visible light catalytic performance of the @ ZnO composite film is greatly improved, g-C 3 N 4 The @ ZnO composite membrane has the best visible light catalysis performance. FIG. 18 is a graph of the performance of visible light photocatalytic degradation of phenol.
From the results of the experiment, it was found that g-C 3 N 4 Pure film and MoS 2 The pure film has poor performance, which is caused by the characteristic of the 2D nanosheet material that a large number of cavities are formed in the film due to the vacuum filtration of the film, so that the performance of the film is reduced. But when g-C 3 N 4 And MoS 2 When the content is similar, the rejection rate of the composite membrane is low, and the composite membrane is still improved. This may be due to g-C 3 N 4 Nanosheet and MoS 2 The nano sheets have different sizes and different surface charges, so that in the film forming process, the composite film has fewer cavities, and the performance of the film is improved. It can be seen from the elemental analysis chart of EDS that the reason is that when a zinc source is introduced, Zn 2+ Mainly adsorbed on the surface and the inner cavity of the film, effectively reduced defect cracks and greatly improved film propertyCan be used. The mechanism is illustrated in FIG. 19.
Claims (10)
1. A two-dimensional material composite separation membrane is characterized by comprising a two-dimensional material and a nano material loaded on the two-dimensional material, wherein the two-dimensional material is g-C 3 N 4 Nanosheets, the nanomaterial being MoS 2 Nano-sheets or nano-ZnO.
2. The two-dimensional material composite separation membrane according to claim 1, wherein the weight ratio of the two-dimensional material to the nanomaterial is in the range of 1: 9-9: 1.
3. the method for preparing the two-dimensional material composite separation membrane according to claim 1, comprising the steps of:
step 1, preparation of two-dimensional g-C 3 N 4 Dispersion of nanosheets and two-dimensional MoS 2 A nanosheet and a dispersion;
step 2, mixing two-dimensional g-C 3 N 4 Dispersion of nanosheets and two-dimensional MoS 2 And mixing the nanosheet and the dispersion liquid, and then carrying out suction filtration to obtain the membrane layer.
4. The method for preparing a two-dimensional material composite separation membrane according to claim 3, wherein the two-dimensional g-C in step 2 3 N 4 Nanosheet and two-dimensional MoS 2 The weight ratio of the nano sheets is 1: 9-9: 1.
5. the method for preparing a two-dimensional material composite separation membrane according to claim 3, wherein in step 1, the two-dimensional g-C 3 N 4 Nanosheets or two-dimensional MoS 2 The preparation method of the nano sheet comprises the following steps:
step a, mixing g-C 3 N 4 Or MoS 2 Heating the powder, and adding the product into liquid nitrogen;
step b, dispersing the product obtained in the step a in an ethanol water solution, uniformly stirring, and then performing first centrifugal treatment to obtain a supernatant;
step C, carrying out second centrifugal treatment on the supernatant obtained in the step b to obtain a precipitate, and drying to obtain the two-dimensional g-C 3 N 4 Nanosheet or two-dimensional MoS 2 Nanosheets.
6. The method for preparing a two-dimensional composite separation membrane according to claim 5, wherein the temperature rise in step a is a temperature rise to 500 ℃ at 300-;
the first centrifugal treatment in the step b is repeated for 1 to 10 times, and the rotating speed is 4000-;
the centrifugation rotation speed of the second centrifugation treatment in the step c is 10000-15000 rpm.
7. A preparation method of a two-dimensional material composite separation membrane is characterized by comprising the following steps:
step 1, preparation of two-dimensional g-C 3 N 4 A dispersion of nanoplatelets;
step 2, adding Zn (NO) into the dispersion liquid 3 ) 2 Filtering and forming a film;
step 3, soaking the film layer obtained in the step 2 in Zn (NO) 3 ) 2 And soaking in NaOH solution, taking out and calcining to obtain the composite separation membrane.
8. The method for preparing a two-dimensional material composite separation membrane according to claim 7, wherein Zn (NO) 3 ) 2 And g-C 3 N 4 The weight ratio of the nano sheets is 5-15: 1; in step 3, Zn (NO) 3 ) 2 The concentration of the solution is 1-50mg/ml, and the concentration of the NaOH solution is 0.1-2 mol/L.
9. Use of the two-dimensional material composite separation membrane according to claim 1 for filtration and/or photocatalytic decomposition of an organic-containing solution.
ZnO and/or MoS 2 Use of nanoplatelets for increasing g-C 3 N 4 Film for in solutionThe use of retention of organic matter.
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