CN115105976A - Carbon quantum dot photocatalytic multi-separation-layer composite nanofiltration membrane and preparation method thereof - Google Patents
Carbon quantum dot photocatalytic multi-separation-layer composite nanofiltration membrane and preparation method thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 13
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- UWCPYKQBIPYOLX-UHFFFAOYSA-N benzene-1,3,5-tricarbonyl chloride Chemical compound ClC(=O)C1=CC(C(Cl)=O)=CC(C(Cl)=O)=C1 UWCPYKQBIPYOLX-UHFFFAOYSA-N 0.000 claims description 9
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/66—Polymers having sulfur in the main chain, with or without nitrogen, oxygen or carbon only
- B01D71/68—Polysulfones; Polyethersulfones
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/40—Polymers of unsaturated acids or derivatives thereof, e.g. salts, amides, imides, nitriles, anhydrides, esters
- B01D71/42—Polymers of nitriles, e.g. polyacrylonitrile
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
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Abstract
The invention discloses a preparation method of a carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane, which comprises the steps of carrying out multiple alternate dynamic layer-by-layer self-assembly on carbon quantum dots and cationic polyelectrolyte on the surface of a base membrane to obtain a membrane coated with multiple layers of cationic polyelectrolyte-carbon quantum dots, generating a polypiperazine amide layer on the surface of the membrane coated with multiple layers of cationic polyelectrolyte-carbon quantum dots by an interfacial polymerization method, and carrying out heat treatment to obtain the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane. The multi-separation layer composite nanofiltration membrane prepared by the method has the advantages of high membrane preparation efficiency, good membrane stability, high membrane flux, good interception capability and good pollution resistance, and can degrade organic matters by photocatalysis.
Description
Technical Field
The invention relates to a carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane and a preparation method thereof, belonging to the technical field of membrane separation.
Background
Nanofiltration is a pressure driven membrane separation process with separation capacity intermediate between reverse osmosis and ultrafiltration. The aperture of the nanofiltration membrane is about a few nanometers, and the nanofiltration membrane has higher removal rate on bivalent or multivalent ions and organic matters with the molecular weight between 200 Da and 1000 Da. Layer-by-layer self-assembly is a method for spontaneously assembling a polymer film with a special layered structure under the combined action of electrostatic attraction, van der waals force, hydrogen bond force, covalent bond and the like by polyelectrolytes with opposite charges. The electrostatic repulsion action can be formed between the membrane surface and the separated substance by directionally regulating and controlling the charge condition of the formed membrane surface, thereby achieving the purpose of selective separation. The dynamic layer-by-layer self-assembly method is an improved method based on the static layer-by-layer self-assembly method, and the method is a method for alternately depositing the polyelectrolytes with opposite charges on the surface of the base membrane in a filtering mode under a certain pressure, so that the deposition speed of the polyelectrolytes is higher, and the combination with the base membrane is firmer.
The carbon quantum dots are carbon nano materials with the size less than 10nm, contain a large amount of epoxy groups, carboxyl groups and hydroxyl groups on the surface, and have the advantages of low toxicity, good water dispersibility, easy preparation, functionalization and the like. The carbon quantum dots are used as raw materials to carry out layer-by-layer self-assembly, so that the interception performance of the polyelectrolyte layer is improved, and the carbon quantum dots can provide water molecule channels, so that the flux of the polyelectrolyte membrane is improved. Because the carbon quantum dots have photocatalytic property, the film containing the carbon quantum dots has self-cleaning capability under visible light, so that the anti-pollution performance of the film is improved.
The interfacial polymerization method is characterized in that two monomers with high reaction activity are respectively dissolved in two solvents which are not mutually soluble, the polycondensation reaction is carried out at the interface of two liquid phases, and the obtained polymer is insoluble in the solvent and has better stability. The method for preparing the composite nanofiltration membrane has simple process, but has higher requirement on the performance of the base membrane, more side reactions in the interfacial polymerization reaction, and difficult effective control because the film forming process is completed within 1min, so the prepared nanofiltration membrane has poorer anti-pollution performance.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to provide a method for improving the interception capability of a nanofiltration membrane, which combines an interfacial polymerization method and a layer-by-layer self-assembly method, and uses a cationic polyelectrolyte-carbon quantum dot layer formed by alternately and dynamically self-assembling cationic polyelectrolyte and carbon quantum dots on the surface of a basement membrane as a bottom separation layer. The top separation layer prepared by the interfacial polymerization method has good stability, the defect of poor stability of a polymer layer prepared by a layer-by-layer self-assembly method is overcome, and meanwhile, amino groups in the polypiperazine amide layer prepared by the interfacial polymerization method have absorption capacity to light and can activate photocatalytic reaction sites in carbon quantum dots under visible light, so that the top separation layer has certain self-cleaning capacity. Therefore, the multi-separation layer composite nanofiltration membrane with high flux, high interception and strong pollution resistance can be prepared.
The invention is realized by the following technical scheme.
The invention provides a preparation method of a carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane, which comprises the following steps:
(1) fixing a base membrane in a membrane pool of a dynamic layer-by-layer self-assembly system filled with a cationic polyelectrolyte solution, operating under a pressure condition, changing the cationic polyelectrolyte solution into deionized water, and cleaning the membrane surface to obtain a membrane coated with the cationic polyelectrolyte;
(2) changing deionized water into a carbon quantum dot solution, operating under a pressure condition, changing the carbon quantum dot solution into the deionized water, and cleaning the membrane surface to obtain a membrane coated with 1 polyelectrolyte-carbon quantum dot double layer;
(3) repeating the steps (1) and (2) for n-1 times on the membrane coated with 1 cationic polyelectrolyte-carbon quantum dot double layer, so that the cationic polyelectrolyte and the carbon quantum dot are alternately and dynamically self-assembled, and repeating the step (1) for 1 time to obtain a membrane coated with n +0.5 cationic polyelectrolyte-carbon quantum dot double layers, wherein the membrane is marked as a multi-layer cationic polyelectrolyte-carbon quantum dot membrane;
(4) contacting the membrane coated with multiple layers of cationic polyelectrolyte-carbon quantum dots with a piperazine aqueous solution, and then draining off membrane surface liquid to obtain a polyelectrolyte-carbon quantum dot + piperazine loaded membrane;
(5) contacting the surface of a polycation polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane electrolyte-carbon quantum dot + piperazine load membrane with trimesoyl chloride organic phase solution to obtain a cation polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane;
(6) and (3) carrying out heat treatment on the cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane, and washing with water to obtain the carbon quantum dot photocatalytic multi-separation-layer composite nanofiltration membrane.
Preferably, the base membrane is an ultrafiltration membrane prepared by taking one of polyacrylonitrile, polysulfone, polyethersulfone or sulfonated polyethersulfone as a raw material.
Preferably, the cationic polyelectrolyte solution is a chitosan solution with the solution concentration of 0.5-2.5 g/L.
Preferably, the carbon quantum dots are obtained by pyrolyzing citric acid at 180-220 ℃ for 25-35min, dialyzing, purifying and freeze-drying.
Preferably, the concentration of the carbon quantum dot solution is 0.5-2.5 g/L.
Preferably, in the steps (1) and (2), the time of dynamic layer-by-layer self-assembly is 5-20 min, and the pressure of a dynamic self-assembly system is 0.1-0.4 MPa.
Preferably, the concentration of the piperazine aqueous phase solution is 1.0-3.0 wt%.
Preferably, the concentration of the trimesoyl chloride organic phase solution is 0.1-0.2 wt%, and the solvent is n-hexane.
Preferably, the temperature of the heat treatment is 70-80 ℃, and the time is 3-10 min.
In another aspect of the invention, the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane prepared by the method is provided.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
1. the dynamic layer-by-layer self-assembly method is carried out under the assistance of pressure, so that compared with the static layer-by-layer self-assembly method, the deposition speed of polyelectrolyte is higher, and the combination between the cationic polyelectrolyte-carbon quantum dot layers is firmer. The interfacial polymerization method has high reaction speed, the prepared polymer has good stability, and the film preparation efficiency and the stability of the film by the layer-by-layer self-assembly method are improved by organically combining the prepared polymer with the layer-by-layer self-assembly method; meanwhile, the existence of the cationic polyelectrolyte-carbon quantum dot layer improves the integral interception performance of the nanofiltration membrane.
2. The carbon quantum dots and the cationic polyelectrolyte layer are self-assembled layer by layer, and the carbon quantum dots can provide additional water molecule channels, so that the good interception capability of the polyelectrolyte layer is kept, and the flux of the polyelectrolyte layer is improved.
3. The composite nanofiltration membrane with the cationic polyelectrolyte-carbon quantum dot layer and the polypiperazine amide layer is prepared by organically combining a layer-by-layer self-assembly method and an interfacial polymerization method. The photosensitive amino in the polypiperazine amide layer has the light absorption capacity, and can activate photocatalytic reaction sites in the carbon quantum dots under visible light, so that the polypiperazine amide layer has certain self-cleaning capacity, and the anti-pollution performance of the nanofiltration membrane is improved. In addition, the polypiperazine amide layer can also serve as a protective layer, so that the polyelectrolyte layer is prevented from being polluted, and the catalytic activity of the carbon quantum dots is guaranteed.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention:
fig. 1 is a schematic diagram of a preparation system of the composite nanofiltration membrane.
Detailed Description
The present invention will now be described in detail with reference to the drawings and specific embodiments, wherein the exemplary embodiments and descriptions of the present invention are provided to explain the present invention without limiting the invention thereto.
The embodiment of the invention provides a preparation method of a carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane, which comprises the following steps:
step 1, using an ultrafiltration membrane prepared by taking one of polyacrylonitrile, polysulfone, polyethersulfone or sulfonated polyethersulfone as a base membrane, fixing the base membrane in a membrane pool of a dynamic layer-by-layer self-assembly system filled with a cationic polyelectrolyte chitosan solution with the concentration of 0.5-2.5 g/L, operating for 5-20 min under the condition of the pressure of 0.1-0.4 MPa, changing the cationic polyelectrolyte solution into deionized water, and cleaning the membrane surface for 3min to obtain a membrane coated with cationic polyelectrolyte;
step 2, changing deionized water into a carbon quantum dot solution with the concentration of 0.5-2.5 g/L, operating for 5-20 min under the condition that the pressure is 0.1-0.4 Mpa, changing the carbon quantum dot solution into the deionized water, and cleaning the membrane surface for 3min to obtain a membrane covered with 1 polyelectrolyte-carbon quantum dot double layer;
the carbon quantum dots are prepared by pyrolyzing citric acid at 180-220 ℃ for 25-35min, dialyzing, purifying and freeze-drying.
Step 3, repeating the step 1 and the step 2 for n-1 times to enable the cationic polyelectrolyte and the carbon quantum dots to be alternately and dynamically self-assembled, and repeating the step 1 for 1 time to obtain a membrane covered with n +0.5 cationic polyelectrolyte-carbon quantum dot bilayers and marked as a multi-layer cationic polyelectrolyte-carbon quantum dot membrane;
step 4, contacting the membrane coated with the multiple layers of cationic polyelectrolyte-carbon quantum dots with a 1.0-3.0 wt% piperazine aqueous solution for 3-6 min, and draining the membrane surface liquid to obtain a polyelectrolyte-carbon quantum dot + piperazine loaded membrane;
step 5, contacting the surface of the electrolyte-carbon quantum dot and piperazine load membrane of the poly-cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane with trimesoyl chloride organic phase solution with the concentration of 0.1-0.2 wt% for 40-80 s, wherein the solvent is n-hexane, so as to obtain a cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane;
and 6, carrying out heat treatment on the cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane at the temperature of 70-80 ℃ for 3-10 min, and washing with water to obtain the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane.
The main components of the dynamic self-assembly system of the invention comprise a stock solution tank, a pump, a pressure gauge, a flowmeter, a valve and a self-assembly device. The working principle diagram of the dynamic self-assembly system is shown in figure 1, the specific working process is that polyelectrolyte solution or deionized water is pumped into the self-assembly device after being pressurized, cross flow flows out from the other end of the self-assembly device after passing through the surface of the membrane and flows back into the raw liquid tank, the system pressure can be regulated and controlled through a pressure gauge and a valve, and the flow rate of the material liquid can be regulated and controlled through a flow meter and a valve.
The invention is further illustrated by the following specific examples.
Example 1:
(1) the method comprises the steps of taking an ultrafiltration membrane obtained after hydrolysis modification of a polyacrylonitrile membrane as a base membrane, fixing the base membrane in a self-assembly device of a dynamic self-assembly system, adding 1.5g/L of Chitosan (CTS) solution into the system, operating the dynamic self-assembly system for 20min under the operation pressure of 0.3MPa, then changing the CTS solution into deionized water, cleaning the membrane surface for 3min, and obtaining the membrane covered with CTS, which is marked as a CTS membrane.
(2) Changing the deionized water into 0.8g/L Carbon Quantum Dots (CQDs) solution, operating the dynamic self-assembly system for 15min under the operating pressure of 0.2MPa, then changing the CQDs solution into the deionized water, cleaning the film surface for 3min to obtain a film covered with 1 CTS-CQDs double layer, and marking as (CTS-CQDs) 1 And (3) a membrane.
The carbon quantum dots are prepared by pyrolyzing citric acid at 200 ℃ for 30min, dialyzing, purifying and freeze-drying.
(3) Will (CTS-CQDs) 1 The membrane was repeated 2 times for the operations of step 1 and step 2, allowing CTS and CQDs to alternately self-assemble dynamically, and then repeated 1 more time for the operation of step 1, to obtain a membrane coated with 3.5 double layers of CTS-CQDs, denoted as (CTS-CQDs) 3.5 And (3) a membrane.
(4) Will (CTS-CQDs) 3.5 The film is removed from the self-assembled device and then (CTS-CQDs) 3.5 Contacting the membrane surface with 1.5 wt% piperazine aqueous solution for 6min, and draining off the membrane surface liquid to obtain (CTS-CQDs) 3.5 + piperazine supported membranes.
(5) Will (CTS-CQDs) 3.5 Contacting the + piperazine load membrane with 0.10 wt% trimesoyl chloride in hexane for 65s to obtain (CTS-CQDs) 3.5 Polypiperazine amide composite membrane.
(6) Will (CTS-CQDs) 3.5 And (3) placing the polypiperazine amide composite membrane at 75 ℃ for heat treatment for 5min, and then repeatedly washing the composite membrane by using deionized water to obtain the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane.
Example 2:
(1) the method comprises the steps of fixing a polysulfone membrane as a base membrane in a self-assembly device of a dynamic self-assembly system, adding 0.5g/L Chitosan (CTS) solution into the system, operating the dynamic self-assembly system for 16min under the operation pressure of 0.1MPa, then changing the CTS solution into deionized water, and cleaning the membrane surface for 3min to obtain a membrane covered with CTS, and marking as a CTS membrane.
(2) Changing the deionized water into 1.2g/L Carbon Quantum Dots (CQDs) solution, operating the dynamic self-assembly system for 10min under the operation pressure of 0.4MPa, then changing the CQDs solution into the deionized water, cleaning the film surface for 3min to obtain a film covered with 1 CTS-CQDs double layer, and marking as (CTS-CQDs) 1 And (3) a membrane.
The carbon quantum dots are prepared by pyrolyzing citric acid at 180 ℃ for 35min, dialyzing, purifying and freeze-drying.
(3) Will (CTS-CQDs) 1 Repeating the operations of step (1) and step (2) 2 times to allow alternating dynamic self-assembly of CTS and CQDs, and repeating the operation of step (1) 1 more times to obtain a film coated with 3.5 double layers of CTS-CQDs, denoted as (CTS-CQDs) 3.5 And (3) a membrane.
(4) Will (CTS-CQDs) 3.5 The film is removed from the self-assembled device and then (CTS-CQDs) 3.5 Contacting the membrane surface with 1.0 wt% piperazine aqueous solution for 5min, and draining off the membrane surface liquid to obtain (CTS-CQDs) 3.5 + piperazine loaded membrane.
(5) Will (CTS-CQDs) 3.5 Contacting the piperazine load membrane with 0.16 wt% trimesoyl chloride in hexane for 55s to obtain (CTS-CQDs) 3.5 Polypiperazine amide composite membrane.
(6) Will (CTS-CQDs) 3.5 And (3) carrying out heat treatment on the polypiperazine amide composite membrane at 70 ℃ for 9min, and then repeatedly washing the polypiperazine amide composite membrane with deionized water to obtain the carbon quantum dot photocatalytic multi-separation-layer composite nanofiltration membrane.
Example 3:
(1) the method comprises the steps of taking a polyether sulfone membrane as a base membrane, fixing the base membrane in a self-assembly device of a dynamic self-assembly system, adding 2.3g/L Chitosan (CTS) solution into the system, enabling the dynamic self-assembly system to operate for 5min under the operation pressure of 0.3MPa, then changing the CTS solution into deionized water, and cleaning the membrane surface for 3min to obtain a membrane coated with CTS, wherein the membrane is marked as a CTS membrane.
(2) Changing the deionized water into 2.5g/L Carbon Quantum Dot (CQDs) solution, operating the dynamic self-assembly system for 5min under the operation pressure of 0.1MPa, then changing the CQDs solution into the deionized water, cleaning the film surface for 3min to obtain a film coated with 1 CTS-CQDs double layer, and marking as (CTS-CQDs) 1 And (3) a membrane.
The carbon quantum dots are prepared by pyrolyzing citric acid at 220 ℃ for 2min, dialyzing, purifying and freeze-drying.
(3) Will (CTS-CQDs) 1 Repeating the operations of step (1) and step (2) 1 time to make CTS and CQDs alternately self-assemble dynamically, and repeating the operation of step (1) 1 time to obtain a film coated with 2.5 double layers of CTS-CQDs, denoted as (CTS-CQDs) 2.5 And (3) a membrane.
(4) Will (CTS-CQDs) 2.5 The film is removed from the self-assembled device and then (CTS-CQDs) 2.5 Contacting the membrane surface with 2.8 wt% piperazine aqueous solution for 3min, and draining off membrane surface liquid to obtain (CTS-CQDs) 2.5 + piperazine supported membranes.
(5) Will (CTS-CQDs) 2.5 Contacting the + piperazine load membrane with 0.20 wt% trimesoyl chloride in n-hexane for 40s to obtain (CTS-CQDs) 2.5 Polypiperazine amide composite membrane.
(6) Will (CTS-CQDs) 2.5 And (3) placing the polypiperazine amide composite membrane at 80 ℃ for heat treatment for 10min, and then repeatedly washing the composite membrane by using deionized water to obtain the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane.
Example 4:
(1) the method comprises the steps of taking sulfonated polyether sulfone as a base membrane, fixing the base membrane in a self-assembly device of a dynamic self-assembly system, adding 2.5g/L of Chitosan (CTS) solution into the system, enabling the dynamic self-assembly system to operate for 10min under the operation pressure of 0.4MPa, then changing the CTS solution into deionized water, cleaning the membrane surface for 3min, and obtaining the membrane covered with CTS, and marking as the CTS membrane.
(2) Changing the deionized water into 0.5g/L Carbon Quantum Dots (CQDs) solution, operating the dynamic self-assembly system for 20min under the operating pressure of 0.25MPa, then changing the CQDs solution into the deionized water, cleaning the film surface for 3min to obtain a film covered with 1 CTS-CQDs double layer, and marking as (CTS-CQDs) 1 And (3) a membrane.
The carbon quantum dots are prepared by pyrolyzing citric acid at 210 ℃ for 30min, dialyzing, purifying and freeze-drying.
(3) Will (CTS-CQDs) 1 The membrane was repeated 1 time for the operations of step (1) and step (2), with alternating dynamic self-assembly of CTS and CQDs, followed by 1 more repetition of the operation of step (1), i.e.a membrane coated with 2.5 double layers of CTS-CQDs, noted (CTS-CQDs), was obtained 2.5 And (3) a membrane.
(4) Will (CTS-CQDs) 2.5 The film is removed from the self-assembled device and then (CTS-CQDs) 2.5 Contacting the membrane surface with 3.0 wt% aqueous solution of piperazine for 5min, and draining off the membrane surface liquid to obtain (CTS-CQDs) 2.5 + piperazine supported membranes.
(5) Will (CTS-CQDs) 2.5 Contacting the + piperazine load membrane with 0.1 wt% trimesoyl chloride in n-hexane for 80s to obtain (CTS-CQDs) 2.5 Polypiperazine amide composite membrane.
(6) Will ((CTS-CQDs) 2.5 And (3) placing the polypiperazine amide composite membrane at 70 ℃ for heat treatment for 3min, and then repeatedly washing the composite membrane by using deionized water to obtain the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane.
The nanofiltration membrane prepared in the embodiment has the following properties:
1. flux and rejection rate of nanofiltration membrane
And under the conditions of 0.6MPa of operating pressure and 20 ℃, 2g/L of magnesium sulfate solution is adopted to measure the flux and the rejection rate of the nanofiltration membrane. The flux and rejection results of the nanofiltration membranes prepared in examples 1-4 are shown in table 1.
Table 1 flux and rejection of nanofiltration membranes on magnesium sulfate solution prepared in example
2. Anti-pollution performance of membrane
Under the visible light with the illumination intensity of 1000lx and the operation pressure of 0.6MPa, 10mg/L bovine serum albumin solution is used for performing a membrane pollution experiment for 24 hours, deionized water is used for performing a membrane cleaning experiment after the membrane pollution experiment is finished, the flux of the cleaned nanofiltration membrane is measured by using the deionized water, and the flux attenuation rate and the flux recovery rate of the nanofiltration membrane are calculated.
Table 2 performance of nanofiltration membranes prepared in the examples of membrane fouling and membrane cleaning experiments
As can be seen from tables 1 and 2, the composite nanofiltration membrane prepared by the method has good flux and rejection rate, and the flux to magnesium sulfate solution is not lower than 45.47 (L.m) -2 ·h -1 ) The rejection rate of the magnesium sulfate solution is not lower than 95.32 percent; the flux attenuation rate is not more than 21.28%, and the flux recovery rate is not less than 86.10%.
The invention makes up the defects of more side reactions in the interfacial polymerization reaction, difficult effective control of the film forming process and poor pollution resistance of the film, and is a high-performance multi-separation-layer composite nanofiltration film with good preparation performance and capable of degrading organic matters by photocatalysis.
The present invention is not limited to the above embodiments, and based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some technical features without creative efforts based on the disclosed technical contents, and these substitutions and modifications are all within the protection scope of the present invention.
Claims (10)
1. A preparation method of a carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane is characterized by comprising the following steps:
(1) fixing a base membrane in a membrane pool of a dynamic layer-by-layer self-assembly system filled with a cationic polyelectrolyte solution, operating under a pressure condition, changing the cationic polyelectrolyte solution into deionized water, and cleaning the membrane surface to obtain a membrane coated with the cationic polyelectrolyte;
(2) changing deionized water into a carbon quantum dot solution, operating under a pressure condition, changing the carbon quantum dot solution into the deionized water, and cleaning the membrane surface to obtain a membrane covered with 1 polyelectrolyte-carbon quantum dot double layer;
(3) repeating the steps (1) and (2) for n-1 times on the membrane coated with 1 cationic polyelectrolyte-carbon quantum dot double layer, so that the cationic polyelectrolyte and the carbon quantum dot are alternately and dynamically self-assembled, and repeating the step (1) for 1 time to obtain a membrane coated with n +0.5 cationic polyelectrolyte-carbon quantum dot double layers, wherein the membrane is marked as a multi-layer cationic polyelectrolyte-carbon quantum dot membrane;
(4) contacting the membrane coated with multiple layers of cationic polyelectrolyte-carbon quantum dots with a piperazine aqueous solution, and then draining off membrane surface liquid to obtain a polyelectrolyte-carbon quantum dot + piperazine loaded membrane;
(5) contacting the surface of a poly-cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane electrolyte-carbon quantum dot + piperazine load membrane with trimesoyl chloride organic phase solution to obtain a cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane;
(6) and (3) carrying out heat treatment on the cationic polyelectrolyte-carbon quantum dot polypiperazine amide composite membrane, and washing with water to obtain the carbon quantum dot photocatalytic multi-separation-layer composite nanofiltration membrane.
2. The method for preparing the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane according to claim 1, wherein the base membrane is an ultrafiltration membrane prepared from one of polyacrylonitrile, polysulfone, polyethersulfone or sulfonated polyethersulfone.
3. The method for preparing the carbon quantum dot photocatalytic type multi-separation layer composite nanofiltration membrane according to claim 1, wherein the cationic polyelectrolyte solution is a chitosan solution with a solution concentration of 0.5-2.5 g/L.
4. The preparation method of the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane according to claim 1, wherein the carbon quantum dots are prepared by pyrolyzing citric acid at 180-220 ℃ for 25-35min, dialyzing, purifying and freeze-drying.
5. The method for preparing the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane according to claim 1, wherein the concentration of the carbon quantum dot solution is 0.5-2.5 g/L.
6. The method for preparing the carbon quantum dot photocatalytic type multi-separation layer composite nanofiltration membrane according to claim 1, wherein in the steps (1) and (2), the dynamic layer-by-layer self-assembly time is 5-20 min, and the pressure of a dynamic self-assembly system is 0.1-0.4 Mpa.
7. The method for preparing the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane according to claim 1, wherein the concentration of the piperazine aqueous phase solution is 1.0-3.0 wt%.
8. The method for preparing the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane according to claim 1, wherein the concentration of the trimesoyl chloride organic phase solution is 0.1-0.2 wt%, and the solvent is n-hexane.
9. The method for preparing the carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane according to claim 1, wherein the temperature of the heat treatment is 70-80 ℃ and the time is 3-10 min.
10. A carbon quantum dot photocatalytic multi-separation layer composite nanofiltration membrane prepared by the method of any one of claims 1 to 9.
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