CN114797471A - Crustacean charcoal/sodium alginate composite gel nanofiltration membrane as well as preparation method and application thereof - Google Patents
Crustacean charcoal/sodium alginate composite gel nanofiltration membrane as well as preparation method and application thereof Download PDFInfo
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- CN114797471A CN114797471A CN202210510805.5A CN202210510805A CN114797471A CN 114797471 A CN114797471 A CN 114797471A CN 202210510805 A CN202210510805 A CN 202210510805A CN 114797471 A CN114797471 A CN 114797471A
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- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
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- 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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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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Abstract
The invention discloses a crustacean biochar/sodium alginate composite gel nanofiltration membrane as well as a preparation method and application thereof, wherein the method comprises the following steps: cleaning and drying a shell of the crustacean, then pyrolyzing the shell at high temperature in a nitrogen atmosphere, cooling, cleaning and drying to obtain crustacean charcoal; performing ball milling modification on the crustacean charcoal to obtain modified crustacean charcoal; uniformly mixing the modified crustacean charcoal with an absolute ethyl alcohol solution to obtain a mixed solution, and then carrying out suction filtration on the mixed solution to load the modified crustacean charcoal on a basement membraneObtaining a base film loaded with biochar; uniformly coating a sodium alginate solution on the surface of the base membrane loaded with the biochar, and transferring the base membrane to CaCl 2 Soaking in the solution to fully crosslink, cleaning and airing to obtain the crustacean biochar/sodium alginate composite gel nanofiltration membrane. The separation effect is good, the aggregation phenomenon of materials in the separation layer can be effectively avoided, and the pressure resistance is good.
Description
Technical Field
The invention relates to the technical field of sodium alginate hydrogel nanofiltration membranes, and particularly relates to a crustacean biochar/sodium alginate composite gel nanofiltration membrane as well as a preparation method and application thereof.
Background
Dye wastewater is one of the most difficult wastewater to treat due to the characteristics of high organic content, high chroma, high salt content and the like. The main reason that dye wastewater is difficult to treat comes from high concentration of dye molecules, and most of the dye molecules have carcinogenic, teratogenic and mutagenic capabilities, and seriously threaten the ecological environment and water safety. With the increasing environmental protection of the country, the harmless and resource treatment of dye wastewater and the acquisition of more high-quality recycled water become great challenges to meet the continuously upgraded environmental protection requirements. Because dye molecules have strong acid resistance, alkali resistance and oxidation resistance, the traditional water treatment methods including a coagulating sedimentation method, an advanced oxidation method, adsorption and the like are difficult to completely remove the dye molecules. In contrast, the membrane separation technology can efficiently separate and recover useful dye molecules from the dye wastewater without causing secondary pollution to the environment, thereby truly realizing sustainable treatment of the dye wastewater. Among a plurality of membrane separation technologies, the nanofiltration membrane separation technology can effectively recover water, dye and inorganic salt components from dye wastewater, thereby realizing zero emission of wastewater and furthest exerting the economic benefit of wastewater. However, conventional commercial nanofiltration membranes typically trap both dye molecules and inorganic salt ions in the dye wastewater, thereby greatly reducing the purity of the recovered dye.
In order to solve this problem, researchers have developed various high performance nanofiltration membranes with "loose" functional layers, which have high retention of dye molecules and high permeability of inorganic salt ions, resulting in ultra high dye/salt separation efficiency. However, most "loose" nanofiltration membrane surfaces are hydrophobic, which can result in irreversible deposition of dye molecules on the membrane surface or in the pores of the membrane, reducing the useful life of the membrane.
Sodium alginate is a linear, naturally occurring anionic polysaccharide which can be crosslinked with certain divalent cations (e.g., Ca) by ionic crosslinking of the polymer chains 2+ 、Ba 2+ Ions, etc.) to form a hydrogel. The sodium alginate hydrogel has good performanceAre considered suitable materials for the construction of filtration membranes. However, the sodium alginate hydrogel nanofiltration membrane formed by the method has the balance problem of selectivity and permeability when being applied, and meanwhile, the self-supporting calcium alginate hydrogel membrane has poor pressure resistance. Therefore, further improvement in the separation and pressure resistance of the nanofiltration membrane is required.
Common modification methods of sodium alginate hydrogel nanofiltration membranes comprise the following five methods: 1) the hydrophilicity of the membrane surface is increased through surface modification, and the water mass transfer process is promoted; 2) an organic/inorganic material doped intermediate layer; 3) the effective contact area of the membrane surface is increased by constructing a nanofiltration membrane with a 'wrinkle' structure; 4) reducing the thickness of the nanofiltration membrane separation layer; 5) the pore diameter distribution of the nanofiltration membrane is narrowed. In contrast, doping with organic/inorganic materials can provide more water molecule channels for the nanofiltration membrane while retaining the rejection properties of the nanofiltration membrane. In addition, partial materials can also endow partial special functions to the modified nanofiltration membrane so as to further improve the performance of the membrane. The common doping materials at present are mainly carbon materials such as carbon nanotubes, graphene oxide, reduced graphene, MXenes and the like. The addition of the carbon materials improves the performance of the sodium alginate hydrogel nanofiltration membrane to a certain extent, but also has some disadvantages, for example, the aggregation phenomenon of the carbon materials in a membrane separation layer may affect the stability of the membrane, and the production process of the carbon materials is generally complex, and the cost in practical application is generally high.
Therefore, there is a need to develop a modified sodium alginate hydrogel nanofiltration membrane to solve the problems of the existing sodium alginate/Ca alginate 2+ The separation effect and the pressure resistance of the gel nanofiltration membrane are poor.
Disclosure of Invention
The invention aims to provide a crustacean biochar/sodium alginate composite gel nanofiltration membrane as well as a preparation method and application thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect of the invention, a preparation method of a crustacean biochar/sodium alginate composite gel nanofiltration membrane is provided, and the method comprises the following steps:
cleaning and drying a shell of the crustacean, then pyrolyzing the shell at high temperature in a nitrogen atmosphere, cooling, cleaning and drying to obtain crustacean charcoal;
performing ball milling modification on the crustacean charcoal to obtain modified crustacean charcoal;
uniformly mixing the modified crustacean charcoal with an absolute ethyl alcohol solution to obtain a mixed solution, and then carrying out suction filtration on the mixed solution to load the modified crustacean charcoal on a basement membrane to obtain a basement membrane loaded with the charcoal;
uniformly coating a sodium alginate solution on the surface of the base membrane loaded with the biochar, and transferring the base membrane to CaCl 2 Soaking in the solution to fully crosslink, cleaning and airing to obtain the crustacean biochar/sodium alginate composite gel nanofiltration membrane.
Further, the temperature of the high-temperature pyrolysis is more than or equal to 800 ℃.
Further, the ball milling modification of the crustacean biochar is carried out to obtain modified crustacean biochar, and the method comprises the following steps:
mixing the crustacean biochar and agate balls according to a mass ratio of 1: (90-110), alternately modifying for (10-14) h under the condition of forward and reverse circulation rotating speed (250-350) rpm, wherein each time of forward circulation and reverse circulation modification lasts for (9-11) min, and the operation is stopped (4-6) min when each time of forward circulation and reverse circulation are alternately performed.
Further, the basement membrane is made of polyvinylidene fluoride (PVDF).
Further, the mass ratio of the modified crustacean biochar to the absolute ethyl alcohol solution is 1: (90-110).
Further, the concentration of the sodium alginate solution is 2-4% (w/v).
Further, in the bar coating, the coating thickness is 100 to 300 μm.
Further, the CaCl 2 Concentration of the solutionThe degree is 2-4% (w/v).
In a second aspect of the invention, a crustacean biochar/sodium alginate composite gel nanofiltration membrane obtained by the method is provided.
In a third aspect of the invention, the application of the crustacean biochar/sodium alginate composite gel nanofiltration membrane in separation and recovery of dye molecules/inorganic salt ions in dye wastewater is provided.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
1. the invention provides a crustacean biochar/sodium alginate composite gel nanofiltration membrane and a preparation method and application thereof. Then adding CaCl 2 And crosslinking the solution and a sodium alginate solution containing crayfish shell biochar to prepare the composite membrane. The whole process is simple to operate, easy to control, low in cost and high in efficiency.
2. According to the invention, the characteristic that the hydroxy calcium component in the high-temperature crawfish shell biochar can be crosslinked with a sodium alginate solution is utilized, and the biochar can be doped into the separation layer of the contrast membrane. Because the doping is carried out through chemical reaction, the method can effectively avoid the aggregation phenomenon of materials in the separation layer, and therefore, the separation effect of the crustacean biochar/sodium alginate composite gel nanofiltration membrane is good. The doping of the biochar plays a role of a separation layer framework of the composite membrane, so that the compressive capacity of the composite membrane is stronger.
3. The doping of the biochar can improve the adsorption performance of the composite membrane, so that the removal efficiency of dye molecules is further improved compared with that of a contrast membrane. Due to the porous structure of the crayfish shell biochar, more water molecules and inorganic salt ion channels can be provided for the composite membrane, and therefore the composite membrane has higher water outlet flux and lower inorganic salt ion interception efficiency. The preparation method has simple process and easy popularization, and simultaneously, the composite membrane has higher dye molecule retention rate and lower inorganic salt ion retention rate, so that the composite membrane has higher selectivity for separating and recovering dye molecules/inorganic salts in dye molecules, thereby being more suitable for practical application.
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In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is an SEM image of a crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
FIG. 2 is a graph comparing the performance of example 1 and comparative example 1 in filtering five dye molecules according to the present invention.
FIG. 3 is a graph showing a comparison of the performance of example 1 and comparative example 1 in filtering four inorganic salt ions according to the present invention.
FIG. 4 is a graph showing a comparison of the compression resistance and the selection property in filtration between example 1 and comparative example 1 in the present invention.
FIG. 5 is a stability test of separation performance upon filtration of example 1 and comparative example 1 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be obtained by an existing method. The steps S1, S2, and S3 … … in the present invention do not represent a strict order relationship, and the order may be appropriately adjusted as necessary.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
according to a typical embodiment of the invention, a preparation method of a crustacean biochar/sodium alginate composite gel nanofiltration membrane is provided, which comprises the following steps:
step S1, cleaning and drying the shell of the crustacean, then pyrolyzing the shell at high temperature in a nitrogen atmosphere, cooling, cleaning and drying to obtain the crustacean charcoal;
in the step S1, in the above step,
the crustacean charcoal comprises at least one of crayfish, pig bone, ox bone, crab shell and other biochar.
The temperature of the high-temperature pyrolysis is more than or equal to 800 ℃.
The mineral component on the surface of the crayfish shell biochar prepared at the temperature of 800 ℃ and above mainly comprises hydroxyl calcium, and can generate cross-linking reaction with a sodium alginate solution; the mineral components on the surface of the crayfish shell biochar prepared at the temperature below 800 ℃ mainly comprise calcium carbonate and cannot generate cross-linking reaction with a sodium alginate solution.
Step S2, performing ball milling modification on the crustacean biochar to obtain modified crustacean biochar;
in step S2, the method specifically includes:
mixing the crustacean biochar and agate balls according to a mass ratio of 1: (90-110), alternately modifying for (10-14) h under the condition of forward and reverse circulation rotating speed (250-350) rpm, wherein each time of forward circulation and reverse circulation modification lasts for (9-11) min, and the operation is stopped (4-6) min when each time of forward circulation and reverse circulation are alternately performed.
If the mass ratio of the crustacean biochar to the agate balls is too small, the biochar with sufficient quality is not obtained, and if the mass ratio of the crustacean biochar to the agate balls is too large, the ball-milling modification effect is not obtained.
The reason for the alternate modification of the positive cycle and the reverse cycle is as follows: the ball milling reaction energy is reduced to prevent excessive aggregation of the crustacean biochar.
Preferably, the mass ratio of the biochar particles to the agate balls is 1: 100, alternately modifying for 12 hours at the forward and reverse circulation rotating speed of 300rpm, wherein each time lasts for 10min during the forward and reverse circulation modification, and the device stops running for 5min during each forward and reverse circulation to avoid excessive accumulation of the biochar in the modification process.
Step S3, mixing the modified crustacean charcoal and an absolute ethyl alcohol solution uniformly to obtain a mixed solution, and then carrying out suction filtration on the mixed solution to load the modified crustacean charcoal on a basement membrane to obtain a basement membrane loaded with the charcoal;
in the step S3, in the above step,
the purpose of mixing the biochar with absolute ethanol is to prevent aggregation of biochar particles, which may affect the effect if the medium is replaced with water.
The mass ratio of the modified crustacean charcoal to the absolute ethyl alcohol solution is 1: (90-110). If the mass ratio is too small, the composite finished film is not beneficial to doping a sufficient amount of biological carbon particles, and if the mass ratio is too large, the composite finished film is not beneficial to dispersing the biological carbon particles.
The base film is made of polyvinylidene fluoride (PVDF).
Step S4, uniformly coating a sodium alginate solution on the surface of the biochar-loaded basement membrane by a bar, and transferring the biochar-loaded basement membrane to CaCl 2 Soaking in the solution to fully crosslink, cleaning and airing to obtain the crustacean biochar/sodium alginate composite gel nanofiltration membrane.
In the step S4, in the above step,
the concentration of the sodium alginate solution is 2-4% (w/v). If the concentration is too low, the preparation of the composite membrane in the rod coating process is adversely affected; if the concentration is too large, the water permeability of the composite membrane is adversely affected;
in the bar coating, the coating thickness is 100-300 μm. The thickness range is beneficial to doping of the ball-milling biochar; preferably 200 μm.
The CaCl is 2 The concentration of the solution is 2-4% (w/v). If the concentration is too low, the crosslinking of the nanofiltration membrane is adversely affected; if the concentration is too high, the crosslinking process is too fast to regulate;
the preparation method of the crustacean biochar/sodium alginate composite gel nanofiltration membrane provided by the invention utilizes the characteristic that the cross-linking of the crayfish shell biochar and sodium alginate can be carried out, and the crayfish shell biochar and the sodium alginate are fixed in a sodium alginate gel solution in advance. And then crosslinking the CaCl2 solution with a sodium alginate solution containing crawfish shell biochar to prepare the composite membrane. The whole process is simple to operate, easy to control, low in cost and high in efficiency.
According to another typical embodiment of the invention, the crustacean biochar/sodium alginate composite gel nanofiltration membrane obtained by the method is provided. The shellfish biochar/sodium alginate composite gel nanofiltration membrane has a good separation effect. The doping of the biochar plays a role of a separation layer framework of the composite membrane, so that the compressive capacity of the composite membrane is stronger.
According to another typical embodiment of the invention, the application of the crustacean biochar/sodium alginate composite gel nanofiltration membrane in separation and recovery of dye molecules/inorganic salt ions in dye wastewater is provided.
Existing sodium alginate/Ca 2+ The gel nanofiltration membrane has the problems of low selectivity and low water flux when being used for separating and recovering dye molecules and inorganic salt ions in dye wastewater, and the crustacean biochar/sodium alginate composite gel nanofiltration membrane has the advantages of high selectivity recovery and high water flux on the dye molecules and the inorganic salt ions in the dye wastewater, and particularly: the doping of the biochar can improve the adsorption performance of the composite membrane, so that the removal efficiency of dye molecules is further improved compared with that of a contrast membrane. Due to the porous structure of the crayfish shell biochar, more water molecules and inorganic salt ion channels can be provided for the composite membrane, and therefore the composite membrane has higher water outlet flux and lower inorganic salt ion interception efficiency.
The crustacean biochar/sodium alginate composite gel nanofiltration membrane, and the preparation method and application thereof according to the present application will be described in detail below with reference to examples, comparative examples and experimental data.
Example 1
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower limit oxygen pyrolysis for 2h at 800 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of anhydrous ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 2% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole membrane obtained in step (4) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Example 2
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower-limit oxygen pyrolysis for 2h at 900 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of absolute ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 2% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole membrane obtained in step (4) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Example 3
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower limit oxygen pyrolysis for 2h at 1000 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of absolute ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 2% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole of the membrane obtained in step (4) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Example 4
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower limit oxygen pyrolysis for 2h at 800 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of absolute ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 3% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole membrane obtained in step (4) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Example 5
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower limit oxygen pyrolysis for 2h at 800 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of absolute ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 4% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole membrane obtained in step (4) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Example 6
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower limit oxygen pyrolysis for 2h at 800 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of absolute ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 2% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole of the membrane obtained in step (4) to 3% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive Ca on the surface of the membrane by using ultrapure waterCl 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Example 7
(1) Repeatedly cleaning and drying the collected crayfish shell waste, performing lower limit oxygen pyrolysis for 2h at 800 ℃ in a muffle furnace in a nitrogen environment, stopping heating the muffle furnace after pyrolysis is completed, taking out a sample after natural cooling, and repeatedly cleaning and drying the sample by using ultrapure water to obtain the crayfish shell biochar.
(2) And (2) mixing 1g of the biochar in the step (1) with 100g of agate balls, placing the mixture in a ball milling tank, alternately modifying for 12 hours by using a planetary ball mill under the condition of forward and reverse circulation rotating speed of 300rpm, wherein each time of forward and reverse circulation modification lasts for 10min, and stopping the operation of the instrument for 5min when each time of forward and reverse circulation is performed so as to avoid excessive aggregation of the biochar in the modification process.
(3) And (3) mixing 0.1g of the biochar obtained in the step (2) with 10mL of absolute ethanol solution, and loading the biochar in the mixed solution on a PVDF basement membrane by using a suction filtration device.
(4) And (4) paving the base membrane loaded with the biochar in the step (3) on a full-automatic mini-type coating machine, and uniformly coating a sodium alginate solution with the concentration of 2% w/v on the surface of the membrane by using a rod coating method, wherein the thickness of the membrane is 200 mu m.
(5) Transferring the whole membrane obtained in step (4) to 4% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 And airing the solution at room temperature to obtain the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane.
Comparative example 1
(1) The PVDF base membrane was spread on a fully automatic mini-coater and a uniform bar coating of sodium alginate solution at a concentration of 2% w/v was applied to the membrane surface to a thickness of 200 μm using a bar coating method.
(2) Transferring the whole membrane obtained in step (1) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 The solution is dried at room temperature to obtain the sodium alginate/Ca 2+ Gel nanofiltration contrastAnd (3) a membrane.
Comparative example 2
(1) The PVDF base membrane was spread on a fully automatic mini-coater and a uniform bar coating of sodium alginate solution at a concentration of 3% w/v was applied to the membrane surface to a thickness of 200 μm using a bar coating method.
(2) Transferring the whole membrane obtained in step (1) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 The solution is dried at room temperature to obtain the sodium alginate/Ca 2+ Gel nanofiltration comparative membrane.
Comparative example 3
(1) The PVDF base membrane was spread on a fully automatic mini-coater and a uniform bar coating of sodium alginate solution at a concentration of 4% w/v was applied to the membrane surface to a thickness of 200 μm using a bar coating method.
(2) Transferring the whole membrane obtained in step (1) to 2% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 The solution is dried at room temperature to obtain the sodium alginate/Ca 2+ Gel nanofiltration comparative membrane.
Comparative example 4
(1) The PVDF base membrane was spread on a fully automatic mini-coater and a uniform bar coating of sodium alginate solution at a concentration of 2% w/v was applied to the membrane surface to a thickness of 200 μm using a bar coating method.
(2) Transferring the whole membrane obtained in step (1) to 3% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 The solution is dried at room temperature to obtain the sodium alginate/Ca 2+ Gel nanofiltration comparative membrane.
Comparative example 5
(1) The PVDF base membrane was spread on a fully automatic mini-coater and a uniform bar coating of sodium alginate solution at a concentration of 2% w/v was applied to the membrane surface to a thickness of 200 μm using a bar coating method.
(2) Transferring the whole membrane obtained in step (1) to 4% w/v CaCl 2 Soaking in the solution for 2h, fully crosslinking, and cleaning excessive CaCl on the surface of the membrane by using ultrapure water 2 Solution and at room temperatureDrying in the air to obtain sodium alginate/Ca 2+ Gel nanofiltration comparative membrane.
Experimental example 1
1. Comparison of the performances of the biological nanofiltration membranes used for filtering five dye molecules in example 1 and comparative example 1
Five dye molecule solutions with the same concentration are prepared to investigate the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane (composite membrane for short in the figure) and the sodium alginate/Ca in the example 1 and the comparative example 1 2+ And (3) the separation and permeation performance of a gel nanofiltration comparison membrane (which is abbreviated as a comparison membrane in the figure). The specific operation is as follows: using ultrapure water to prepare methylene blue, acid fuchsin, amino black, congo red and methyl blue solutions with the concentration of 100mg/L respectively, filtering the five solutions by using a composite membrane and a comparison membrane respectively under the condition of the operating pressure of 0.1MPa, and recording the water flux and the interception and adsorption performance of the membranes. The results are shown in FIG. 2.
As can be seen from fig. 2, the removal rate of the composite film according to the example of the present invention was higher for the same type of dye molecules than that of the comparative example 1. This is because the adsorption performance of the crayfish shell biochar is enhanced due to the doping of the crayfish shell biochar in the composite membrane. In addition, the composite membrane also has higher water flux during filtration.
2. Example 1 and comparative example 1 comparison of Performance in Filtering four inorganic salt ions
The crayfish shell biochar/sodium alginate composite gel nanofiltration membrane (composite membrane for short in the figure) and the sodium alginate/Ca in the example 1 and the comparative example 1 are examined by preparing four inorganic salt ion solutions with the same concentration 2+ And (3) the separation and permeation performance of a gel nanofiltration comparison membrane (which is abbreviated as a comparison membrane in the figure). The specific operation is as follows: NaCl and Na were prepared using ultrapure water at a concentration of 500mg/L 2 SO 4 、MgCl 2 And MgSO 4 The solutions were filtered using composite and comparative membranes, respectively, at an operating pressure of 0.1MPa, and the flux and rejection of the membranes were recorded. The results are shown in FIG. 3;
as can be seen from fig. 3, the removal rate was lower and the effluent flux was higher for the same type of inorganic salt ions as in comparative example 1. This is because the doping of crayfish shell biochar in the composite membrane provides more water molecules and salt ion channels, so that the composite membrane has lower inorganic salt ion rejection rate and higher water flux.
3. Comparison of compression resistance and selection Performance during filtration of example 1 and comparative example 1
By preparing a Congo red molecule and NaCl ion mixed solution, the crayfish shell biochar/sodium alginate composite gel nanofiltration membrane (composite membrane for short in the figure) and the sodium alginate/Ca in the example 1 and the comparative example 1 are examined under different pressure conditions 2+ The separation, permeation and pressure resistance of the gel nanofiltration comparison membrane (referred to as the comparison membrane in the figure) are improved. The specific operation is as follows: the Congo red solution of 100mg/L and NaCl solution of 500mg/L were mixed using ultrapure water, the mixed solution was filtered using a composite membrane and a comparative membrane, respectively, at operating pressures of 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30MPa, and the flux change and membrane rejection performance were recorded. The results are shown in FIG. 4;
as can be seen from FIG. 4, the composite membrane of the embodiment of the invention shows good anti-compression effect in the whole operation pressure test range (0.05-0.35MPa), the water flux is gradually increased along with the increase of the pressure, and the retention capacity of Congo red molecules and sodium chloride ions is almost maintained. However, the comparative membrane of comparative example 1 broke after the operating pressure exceeded 0.25MPa, indicating that the addition of biochar was effective in improving the pressure resistance of the membrane. In addition, the selective separation indexes of the composite membrane and the comparative membrane are 149.2 and 34.8 respectively when the composite membrane and the comparative membrane operate at 0.1MPa, and the fact that the composite membrane has better selective separation capacity of Congo red molecules/sodium chloride ions due to the doping of the biochar is proved.
4. Stability test of separation Performance during filtration of example 1 and comparative example 1
Cray shell biochar/sodium alginate composite gel nanofiltration membrane (composite membrane for short in the figure) and sodium alginate/Ca in example 1 and comparative example 1 are examined by preparing Congo red molecule and NaCl ion mixed solution 2+ Stability of separation performance of a gel nanofiltration comparative membrane (in the figure, the comparative membrane is abbreviated as a reference membrane) under a long-time operation condition. The specific operation is as follows: using ultrapure waterPreparing a Congo red solution of 100mg/L and a NaCl solution of 500mg/L, mixing, filtering the mixed solution by using a composite membrane and a comparison membrane respectively under the condition of 0.1MPa of operating pressure, and recording the change of water flux and the membrane interception performance. The results are shown in FIG. 5;
as can be seen from FIG. 5, in 48h of operation, the composite membrane of the embodiment of the invention always maintains higher Congo red molecule rejection rate (> 97.5%) and lower sodium chloride ion rejection rate (< 5%), thereby having more stable separation performance. And in the long-term operation process, the final flux of the polluted biochar composite membrane is still higher than that of the comparative membrane of the comparative example 1.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A preparation method of a crustacean biochar/sodium alginate composite gel nanofiltration membrane is characterized by comprising the following steps:
cleaning and drying a shell of the crustacean, then pyrolyzing the shell at high temperature in a nitrogen atmosphere, cooling, cleaning and drying to obtain crustacean charcoal;
performing ball milling modification on the crustacean charcoal to obtain modified crustacean charcoal;
uniformly mixing the modified crustacean charcoal with an absolute ethyl alcohol solution to obtain a mixed solution, and then carrying out suction filtration on the mixed solution to load the modified crustacean charcoal on a basement membrane to obtain a basement membrane loaded with the charcoal;
uniformly coating a sodium alginate solution on the surface of the base membrane loaded with the biochar, and transferring the base membrane to CaCl 2 Soaking in the solution to fully crosslink, cleaning and airing to obtain the crustacean biochar/sodium alginate composite gel nanofiltration membrane.
2. The preparation method of the crustacean biochar/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the temperature of high-temperature pyrolysis is more than or equal to 800 ℃.
3. The preparation method of the crustacean charcoal/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the ball milling modification of the crustacean charcoal is performed to obtain the modified crustacean charcoal, and the preparation method comprises the following steps:
mixing the crustacean biochar and agate balls according to a mass ratio of 1: (90-110), alternately modifying for (10-14) h under the condition of forward and reverse circulation rotating speed (250-350) rpm, wherein each time of forward circulation and reverse circulation modification lasts for (9-11) min, and the operation is stopped (4-6) min when each time of forward circulation and reverse circulation are alternately performed.
4. The method for preparing a crustacean biochar/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the basement membrane is made of polyvinylidene fluoride (PVDF).
5. The preparation method of the crustacean charcoal/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the mass ratio of the modified crustacean charcoal to the absolute ethanol solution is 1: (90-110).
6. The preparation method of the crustacean charcoal/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the concentration of the sodium alginate solution is 2-4% (w/v).
7. The preparation method of the crustacean biochar/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the coating thickness in the bar coating is 100-300 μm.
8. The method for preparing a crustacean charcoal/sodium alginate composite gel nanofiltration membrane according to claim 1, wherein the CaCl is added 2 The concentration of the solution is 2-4% (w/v).
9. A crustacean biochar/sodium alginate composite gel nanofiltration membrane prepared by the method of any one of claims 1-8.
10. An application of the crustacean biochar/sodium alginate composite gel nanofiltration membrane of claim 9 in separation and recovery of dye molecules/inorganic salt ions in dye wastewater.
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