CN111672339B

CN111672339B - Ceramic composite nanofiltration membrane for dye removal and preparation method thereof

Info

Publication number: CN111672339B
Application number: CN202010365129.8A
Authority: CN
Inventors: 高能文; 张燕; 梁富杰; 王洪; 毕亚非
Original assignee: Chongqing University of Technology
Current assignee: Chongqing University of Technology
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2022-01-25
Anticipated expiration: 2040-04-30
Also published as: CN111672339A

Abstract

The invention relates to a preparation method of a ceramic composite nanofiltration membrane for dye removal, belonging to the field of membrane separation. The invention adopts a tubular or sheet ceramic substrate as a carrier, firstly, dopamine compound and polyethyleneimine form a codeposition layer on the surface of the carrier, and then TiO is loaded on the codeposition layer₂And finally, crosslinking with gallic acid to obtain the composite nanofiltration membrane. The preparation process is simple, the reaction conditions are mild, and the prepared ceramic composite nanofiltration membrane is high in mechanical strength, good in stability, large in permeation flux and high in rejection rate. Is suitable for removing the dye in the wastewater and is also suitable for removing the dye in the organic solvent.

Description

Ceramic composite nanofiltration membrane for dye removal and preparation method thereof

Technical Field

The invention relates to a preparation method of a ceramic composite nanofiltration membrane, in particular to a method for chelating TiO generated by hydrolysis of titanium tetrafluoride by utilizing a codeposition layer constructed by dopamine compound and polyethyleneimine₂And then cross-linked with gallic acid to obtain the ceramic composite nanofiltration membrane for dye removal, belonging to the field of membrane separation.

Background

The textile industry generates a great deal of dye wastewater with high salinity every year, and has the characteristics of high toxicity, complex components, great treatment difficulty and the like. The conventional dye wastewater treatment methods comprise flocculation precipitation, adsorption, biodegradation, advanced oxidation and the like, and have certain limitations. The flocculation precipitation method can play a certain role in decoloring, but can only play a role in part of dyes. The adsorbent is also selective to dye molecules, and the adsorbent is difficult to regenerate. Biodegradation methods, although less difficult to operate, tend to run for long periods. The advanced oxidation process is easy to cause secondary pollution, and the oxidant is expensive; moreover, the purpose of oxidation and degradation is to dispose of the pollutants, and the recovery of resources cannot be realized.

A large amount of organic solvents are used in the production of petrochemical products. If the organic solvents can be recycled, the harm to the environment and human beings can be reduced, and the production cost can be reduced, so that the method is a very favorable project. Conventional organic solvent recovery is usually achieved by extractive distillation, which is energy-intensive, solvent-consuming and environmentally friendly. With the rapid development of membrane separation technology, considering factors such as energy consumption and environmental protection, membrane separation technology gradually becomes an effective way for solvent recovery and separation.

The nanofiltration membrane technology is used as a pressure-driven membrane separation process, has the advantages of high efficiency, energy conservation, mild working conditions and the like, the operating pressure is generally between 0.5MPa and 1.5 MPa, and small molecules with the molecular weight of 200-1000 Da can be effectively intercepted. Nanofiltration membranes are widely used in dye separation. Lin et al (J. Membr. Sci., 477 (2015)) used commercial membranes Sepro NF 6 and Sepro NF 2A to separate different dyes and salt mixed solutions, and found that the commercial membranes have good retention (99.9%) for dyes and certain permeability for salt. Zhang et al (ACS appl. mater. Interfaces, 2017, 9(12): 11082) used isophorone diisocyanate (IPDI) and Tannic Acid (TA) for interfacial polymerization, and Graphene Oxide Quantum Dots (GOQDs) as water phase additives to prepare the composite nanofiltration membrane, wherein the rejection rate of methylene blue in a water solution is 97.6%, and the rejection rate of NaCl is 17.2%. Liu et al (chem. Eng. Res. Des., 153 (2020) 572-581) deposit hydroxyethylcellulose on a polypropylene membrane with a pore size of 90 nm, and cross-link with glutaraldehyde to obtain a nanofiltration membrane with retention rates of 95.4% and 84.2% for methyl blue and Congo red in ethanol, respectively, and a permeation flux of 4.6L/(m.m.²H.bar). Li et al (J. Membr. Sci., 601 (2020) 117951) coated a self-microporous polymer on the surface of a polyacrylonitrile carrier membrane with a molecular weight cut-off of 5 ten thousand, and the obtained nanofiltration membrane has a cut-off rate of 93.7% for methyl orange in ethanol and a permeation flux of 4.3L/(m m.m.²H.bar). At present, the nanofiltration membrane material mainly takes an organic nanofiltration membrane as a main material. However, organic nanofiltration membranes generally have the characteristics of poor mechanical strength, poor chemical stability and short service life. Therefore, the preparation of the nanofiltration membrane with good stability and excellent separation performance has important significance.

Researches find that amino groups, catechol groups and catechol groups in Dopamine (DA) molecules enable the dopamine to have the universality of deposition substrates and rich post-functionalization capability, so that a new way is opened for the preparation of composite membranes, and the dopamine can be used for preparing organic-inorganic composite membranes. In the existing report, chinese patent CN102614789A discloses a method for preparing a nanofiltration separation layer by depositing polydopamine on an organic or inorganic base membrane and then subsequently grafting and crosslinking; however, the method has long time for constructing the membrane layer and low water flux. Chinese patent CN105289336A discloses a method for preparing a nanofiltration separation layer on the surface of an organic membrane by co-deposition of catechol and polyethyleneimine; however, the composite nanofiltration membrane prepared by the method cannot realize the efficient separation of the dye and the inorganic salt in the dye wastewater.

Disclosure of Invention

In order to obtain a nanofiltration membrane with better performance, the invention provides a method for chelating TiO generated by hydrolysis of titanium tetrafluoride by using a codeposition layer constructed by dopamine compound and Polyethyleneimine (PEI)₂And then cross-linking with gallic acid (PG) to prepare the ceramic composite nanofiltration membrane. Wherein, in the PDA/PEI codeposition layer, the PDA is used for tightly connecting the codeposition layer with the base film by utilizing the characteristic that molecules are easy to adhere to the codeposition layer, so that the codeposition layer is more tight, and then the PDA is connected with TiO₂After the chelating and the cross-linking with gallic acid (PG) are carried out, the roughness of a separation layer on the surface can be obviously reduced, so that the nanofiltration membrane has better pollution resistance in the separation process of organic matters; in addition, the catechol group in the PDA molecule can chelate metal oxide for further modification. PEI was added because low molecular weight PEI contained a large number of amino groups that could react with DA, accelerating the deposition process and resulting in a more dense interlayer. TiO 2₂The low price, the prepared separation layer has good compactness and strong hydrophilicity, and has a self-cleaning function and is introduced. Meanwhile, PG can form a host-guest inclusion compound with PEI, and PG is utilized to crosslink the deposition skin layer, so that the stability and compactness of the membrane layer can be further improved, and the ceramic composite nanofiltration membrane with good stability and excellent separation performance is obtained.

And (2) placing the ceramic membrane in a dopamine compound/polyethyleneimine buffer solution, carrying out oscillation reaction for a certain time, taking out, soaking in a mixed solution of dilute hydrochloric acid, ammonia water and titanium tetrafluoride for a certain time, taking out, continuously soaking in a gallic acid solution for a certain time, airing and cleaning to obtain the dye desalination ceramic composite nanofiltration membrane.

In a first aspect of the present invention, there is provided:

a preparation method of a dye desalination ceramic composite nanofiltration membrane comprises the following steps:

step 1, soaking a ceramic membrane in deionized water for prewetting;

step 2, preparing 40-60mM aqueous solution of trihydroxymethane, and adjusting the pH value to 7.5-9.0; adding dopamine compound and polyethyleneimine, and uniformly mixing;

step 3, placing the ceramic membrane obtained in the step 1 in the first mixed solution obtained in the step 2, reacting, and taking out after the reaction is finished;

step 4, adding dilute hydrochloric acid and ammonia water into deionized water, adjusting the pH value to 2-4, adding titanium tetrafluoride to enable the concentration of the titanium tetrafluoride to be 0.01-0.07M to obtain a second mixed solution, placing the ceramic membrane obtained in the step 3 into the second mixed solution, reacting, and taking out after the reaction is finished;

and 5, placing the ceramic membrane obtained in the step 4 in 1-3mg/mL of trihydroxymethane water solution of gallic acid for reaction, and taking out after the reaction is finished to obtain the composite nanofiltration membrane.

In one embodiment, in the step 1, the pre-wetting time is more than 1 h; the ceramic membrane is a porous ceramic membrane prepared from an oxide at least containing one element of Al, Zr, Ti and Si, the average pore diameter of the ceramic membrane is 0.5-200 nm, and the ceramic membrane is a tubular membrane or a flat membrane.

In one embodiment, in the step 2, the mass concentration of the dopamine compound is 1-5mg/mL, the mass ratio of the polyethyleneimine to the dopamine compound is 1:0.5-1.5, and the molecular weight of the polyethyleneimine is 400-800 Da; the dopamine compound is dopamine, catechol, tannic acid or derivatives.

In one embodiment, in step 3, the reaction time is 4 to 8 hours and the reaction conditions are room temperature.

In one embodiment, in the step 4, the reaction temperature is 20-100 ℃ and the reaction time is 0.5-6 h.

In one embodiment, in step 5, the concentration of the aqueous trihydroxymethane solution is 40-60mM, and the pH range is 8.0-9.0; the reaction time is 5-120min, and the reaction temperature is room temperature.

In one embodiment, said steps 1 to 5 are repeated from 1 to 20 times.

In a second aspect of the present invention, there is provided:

the composite nanofiltration membrane obtained by the method is used for the dye desalination treatment.

In one embodiment, the dye desalting refers to separation of the dye from the inorganic salt.

In one embodiment, the dye is selected from Congo Red, methyl blue, reactive Brilliant Red, methyl orange, or methylene blue.

In one embodiment, the inorganic salt is selected from NaCl or Na₂SO₄。

In a third aspect of the present invention, there is provided:

application of dopamine compound in preparing nanofiltration membrane modifier.

In one embodiment, the modifier is used to reduce the surface roughness of the separation layer of the nanofiltration membrane, reduce the molecular weight cut-off, increase the separation factor of the nanofiltration membrane from dyes and inorganic salts, or increase the fouling resistance of the nanofiltration membrane.

Advantageous effects

1. The invention utilizes a codeposition method to construct a polydopamine/polyethyleneimine codeposition layer, and prepares metal oxide particles required by deposition through hydrolysis reaction. The catechol group in the polydopamine can form a coordination bond with metal ions in metal oxide, so that metal oxide particles are induced to deposit and mineralize on the surface of the basement membrane to form a compact metal oxide mineral layer, and then cross-linking is carried out, so that the high-performance ceramic composite nanofiltration membrane is constructed.

2. The ceramic composite nanofiltration membrane obtained by the method has a good dye interception effect and good stability. Can be used for concentrating and desalting the aqueous dye and can also be used for removing the dye in the organic solvent.

3. According to the method, titanium tetrafluoride is hydrolyzed to generate titanium oxide nanoparticles in situ, on one hand, the titanium oxide nanoparticles can show high organic solvent resistance, on the other hand, the titanium oxide nanoparticles can be crosslinked with monomers such as dopamine and the like, the stability of a composite selective separation layer of the nanofiltration membrane is improved, particularly, the titanium oxide nanoparticles can show good solvent resistance in a filtering process under the condition of an organic solvent, and the effect of removing the dye can still be maintained after long-time filtering.

4. The method has simple and controllable preparation process and mild reaction condition.

Drawings

Fig. 1 is a scanning electron microscope characterization of the surface (a) of the ceramic carrier membrane and the surface (b) of the composite nanofiltration membrane according to example 1 of the present invention.

FIG. 2 is an FTIR spectrum of the surface of the ceramic carrier membrane prepared in example 1 of the present invention.

FIG. 3 is an atomic force microscope photomicrograph of the ceramic films obtained in inventive example 1 and comparative example 1.

FIG. 4 is a gel chromatography molecular weight cut-off characterization pattern of the ceramic membranes prepared in example 1 and comparative example 1 of the present invention.

Fig. 5 is a graph showing the flux recovery rate of the ceramic membranes prepared in example 1 and comparative example 1 according to the present invention during the filtration of BSA solution.

Fig. 6 shows the effect of the ceramic membrane composite nanofiltration membrane prepared in example 1 of the present invention on the rejection of congo red.

FIG. 7 is a cross-linking reaction formula in the process of preparing the nanofiltration membrane.

Detailed Description

The cross-linking reaction in the nanofiltration membrane preparation process of the invention is shown in fig. 7:

the characterization methods in the following examples are as follows:

testing the membrane separation performance:

the determination method of the permeation flux comprises the following steps: fixing a nanofiltration membrane sample with a certain area in a membrane component, performing a filtration experiment at room temperature and 0.6 MPa, and measuring the permeation flux of the nanofiltration membrane after 30 min, wherein the calculation formula is as follows:

wherein J is permeation flux, Q is volume of permeate, A is effective membrane area, and t is filtration time.

The rejection of the membrane is calculated according to the formula:

in the formula C_pAnd C_fRespectively representing the dye or salt concentration in the permeate and the stock solution.

Example 1

First, ZrO with an average pore diameter of 3 nm was added₂The membrane is soaked in deionized water for prewetting for 3 h, and then taken out and wiped dry. Then, 50 mM of a trihydroxymethane solution having a pH of 8.5 was prepared at room temperature, and 2 mg/mL of Dopamine (DA) and 2 mg/mL of polyethyleneimine having a molecular weight of 600 Da were added to the trihydroxymethane solution, followed by uniform mixing. Soaking the pre-wetted ceramic membrane in the mixed solution, performing oscillation reaction for 6 hours, and then taking out, cleaning and drying; then soaking the titanium tetrafluoride in 0.01M titanium tetrafluoride solution with the temperature of 50 ℃ and the pH value of 3 for 0.5 h, taking out, cleaning and drying; then soaking in trihydroxymethane solution (50 mM, pH 8.5) containing 2 mg/mL gallic acid for 20min, taking out the obtained membrane, and drying to obtain the ceramic composite nanofiltration membrane.

Example 2

Firstly, SiO with the average pore diameter of 20 nm₂The membrane is soaked in deionized water for prewetting for 3 h, and then taken out and wiped dry. Then, 50 mM of a trihydroxymethane solution having a pH of 8.5 was prepared at room temperature, and 2 mg/mL of tannic acid and 2 mg/mL of polyethyleneimine having a molecular weight of 600 Da were added to the trihydroxymethane solution, followed by uniform mixing. Soaking the pre-wetted ceramic membrane in the mixed solution, performing oscillation reaction for 6 hours, and taking out, cleaning and drying;then soaking the titanium tetrafluoride in 0.07M titanium tetrafluoride solution with the temperature of 20 ℃ and the pH value of 4 for 1 hour, taking out, cleaning and drying; then, the membrane was immersed in a trihydroxymethane solution (50 mM, pH 8.5) containing 2 mg/mL of gallic acid for 120min, and the resulting membrane was taken out and dried. The preparation process is a preparation process, and the process is operated circularly for 10 times to obtain the ceramic composite nanofiltration membrane.

Example 3

Firstly, SiO with the average pore diameter of 5 nm₂The membrane is soaked in deionized water for prewetting for 3 h, and then taken out and wiped dry. Then 50 mM of trihydroxymethane solution with the pH value of 8.5 is prepared at room temperature, and 2 mg/mL of catechol and 2 mg/mL of polyethyleneimine with the molecular weight of 600 Da are added into the trihydroxymethane solution and mixed evenly. Soaking the pre-wetted ceramic membrane in the mixed solution, performing oscillation reaction for 6 hours, and taking out, cleaning and drying; then soaking the titanium tetrafluoride in 0.04M titanium tetrafluoride solution with the temperature of 70 ℃ and the pH value of 5 for 3 hours, taking out, cleaning and drying; then, the membrane was immersed in a trihydroxymethane solution (50 mM, pH 8.5) containing 2 mg/mL of gallic acid for 5 min, and the resulting membrane was taken out and dried. The preparation process is a preparation process, and the process is circularly operated for 4 times to obtain the ceramic composite nanofiltration membrane.

Comparative example 1

The difference from example 1 is that: in the soaking process of the middle layer of the nanofiltration membrane, dopamine compound is not added.

First, ZrO with an average pore diameter of 3 nm was added₂The membrane is soaked in deionized water for prewetting for 3 h, and then taken out and wiped dry. Then 50 mM of trihydroxymethane solution with the pH value of 8.5 is prepared at room temperature, 2 mg/mL of polyethyleneimine with the molecular weight of 600 Da is added into the trihydroxymethane solution, and the mixture is uniformly mixed. Soaking the pre-wetted ceramic membrane in the mixed solution, performing oscillation reaction for 6 hours, and then taking out, cleaning and drying; then soaking the titanium tetrafluoride in 0.01M titanium tetrafluoride solution with the temperature of 50 ℃ and the pH value of 3 for 0.5 h, taking out, cleaning and drying; then soaking in trihydroxymethane solution (50 mM, pH 8.5) containing 2 mg/mL gallic acid for 20min, taking out the obtained membrane, and drying to obtain the ceramic composite nanofiltration membrane.

Comparative example 2

The difference from example 1 is that: the titanium oxide nano particles are not generated in an in-situ hydrolysis mode in the preparation of the nano-filtration membrane.

First, ZrO with an average pore diameter of 3 nm was added₂The membrane is soaked in deionized water for prewetting for 3 h, and then taken out and wiped dry. Then, 50 mM of a trihydroxymethane solution having a pH of 8.5 was prepared at room temperature, and 2 mg/mL of Dopamine (DA) and 2 mg/mL of polyethyleneimine having a molecular weight of 600 Da were added to the trihydroxymethane solution, followed by uniform mixing. Soaking the pre-wetted ceramic membrane in the mixed solution, performing oscillation reaction for 6 hours, and then taking out, cleaning and drying; then soaking in trihydroxymethane solution (50 mM, pH 8.5) containing 2 mg/mL gallic acid for 20min, taking out the obtained membrane, and drying to obtain the ceramic composite nanofiltration membrane.

SEM characterization

The SEM photograph of the nanofiltration membrane prepared in example 1 is shown in fig. 1, and it can be seen from the figure that the composite nanofiltration membrane prepared by the present invention has a complete and dense surface.

Characterization by FTIR

The FTIR spectrum of the surface of the nanofiltration membrane prepared in example 1 is shown in fig. 2. As can be seen from the figure, at 3200-^-1The characteristic peak of (A) is the vibration peak of-OH-and-NH-generated after self-polymerization of dopamine oxidation, and the characteristic peak of-OH-and-NH-in PEI, and is at 1585cm^-1The characteristic peaks are the vibration peaks of-NH 2-and-NH-of PEI, and the PEI and DA are proved to be crosslinked to introduce a large number of secondary amine and primary amine groups; at the same time 1648^-1And 1534cm^-1There appears a characteristic absorption peak of the amide group without successful crosslinking of the suberic acid with PEI.

AFM characterization

The atomic force microscope photographs of the composite nanofiltration membranes prepared in example 1 and comparative example 1 are shown in fig. 3, the AFM photographs of the nanofiltration membranes in example 1 are shown in the region (a), and the AFM photographs of the nanofiltration membranes in comparative example 1 are shown in the region (b), and the surface roughness of the nanofiltration membranes are shown in the following table:

according to the scheme, the dopamine compound is crosslinked in the preparation of the middle layer to obtain a compact middle deposition layer, and then the deposition layer is relatively flat when the gallic acid is crosslinked on the surface, so that a smoother nanofiltration membrane can be obtained; because the surface finish of the nanofiltration membrane affects the accumulation of contaminants on the membrane surface, smoother nanofiltration membranes exhibit better contamination resistance.

Characterization of molecular weight cut-off

The retention rates of the nanofiltration membranes in example 1 and comparative examples 1-2 in PEG retention experiments with different molecular weights were measured by gel chromatography, the GPC molecular weight cut-off curve is shown in FIG. 4, the molecular weight at 90% cut-off is defined as the molecular weight cut-off, and the molecular weight cut-off of the nanofiltration membranes in example 1 and comparative examples 1-2 is shown as follows:

as can be seen from the figure, the retention performance of the nanofiltration obtained in the comparative example 1 is lower, which is mainly due to the fact that the dopamine can form a dense film layer in the middle of the codeposited layer, so that the nanofiltration obtained by crosslinking is more dense; similarly, the nanofiltration membrane obtained in comparative example 2 also has a higher molecular weight cut-off, mainly because titanium oxide nanoparticles are generated in situ in the intermediate layer, and can form a complex reaction with dopamine to further induce metal oxide to generate a compact deposition layer, so that the membrane pores are reduced, and the cut-off performance is improved.

Characterization of stain resistance

Preparing a BSA solution containing 0.5wt%, performing a filtration experiment under the condition of 0.5MPa by using the nanofiltration membranes in the embodiment 1 and the comparative example 1, recording the flux, controlling the filtration temperature at 25 ℃, filtering for 40min, taking out the ceramic membrane, repeatedly washing for 3 times by using deionized water, and testing the pure water flux again. And flux recovery was calculated with respect to the new membrane as shown in fig. 5. It can be seen that the nanofiltration membrane obtained in example 1 was subjected to filtration of the protein solution and then washed with water, and that the flux of 88.2% was recovered, whereas the nanofiltration membrane of comparative example 1 was only 57.9% recovered. This is mainly due to the high surface roughness, the tendency of proteins to adsorb and deposit on the surface, and the low recovery rate of flux after washing with water.

Separation of dyes and salts in aqueous systems

Mixed solutions of different dyes of 0.5 g/L and inorganic salts of 1 g/L are prepared, the nanofiltration membranes prepared in the above examples and comparative examples are used for separation experiments, and the retention performances obtained under different solution conditions are shown in the following table:

as can be seen from the table, the nanofiltration membrane prepared by the method can effectively perform desalination treatment on the dye.

Dye separation in organic solvent systems

0.5 g/L of mixed solution of alcoholic solutions of different dyes is prepared, the nanofiltration membranes prepared in the above examples and comparative examples are used for separation experiments, and the retention performances obtained under different solution conditions are shown in the following table:

as can be seen from the table, the nanofiltration membrane prepared by the method can be used for trapping dye under the condition of alcoholic solution.

In order to test the solvent resistance of the nanofiltration membrane obtained by the method of the present invention, the nanofiltration membrane prepared in the above example is soaked in DMF solvent for 12h at room temperature before use, and after being taken out and washed with deionized water to remove the solvent, the rejection performance of the nanofiltration membrane on 0.5 g/L dye is tested according to the same method, as shown in the following table:

the nanofiltration membrane prepared by the invention is suitable for dye separation in an organic solvent system, has better organic solvent resistance, and can still keep better retention rate on the dye after surface soaking; the rejection rate of the nanofiltration membrane in the comparative examples 1 and 2 is obviously reduced after the nanofiltration membrane is soaked in DMF; on the other hand, the nanofiltration membranes prepared in the comparative examples 1 and 2 have low stability in an organic solvent system because the dopamine cannot effectively crosslink with PEI, and the crosslinking property of a nanofiltration membrane separation layer is influenced; on the other hand, titanium oxide generated by in-situ hydrolysis of titanium tetrafluoride can also effectively crosslink with dopamine, and can also improve the stability of the separation layer.

Claims

1. The application of the ceramic composite nanofiltration membrane in the dye desalination treatment in aqueous solution is characterized in that the preparation method of the ceramic composite nanofiltration membrane comprises the following steps:

step 1, soaking a ceramic membrane in deionized water for prewetting;

step 2, preparing 40-60mM aqueous solution of trihydroxymethane, and adjusting the pH value to 7.5-9.0; adding a dopamine compound and polyethyleneimine into the mixture, and uniformly mixing to obtain a first mixed solution;

step 5, placing the ceramic membrane obtained in the step 4 in a trihydroxymethane aqueous solution containing 1-3mg/mL of gallic acid for reaction, and taking out the ceramic membrane after the reaction is finished to obtain a composite nanofiltration membrane;

in the step 1, the prewetting time is more than 1 h; the ceramic membrane is a porous ceramic membrane prepared from an oxide at least containing one element of Al, Zr, Ti and Si, the average pore diameter of the ceramic membrane is 0.5-200 nm, and the ceramic membrane is a tubular membrane or a flat membrane;

in the step 2, the mass concentration of the dopamine compound is 1-5mg/mL, the mass ratio of the polyethyleneimine to the dopamine compound is 1:0.5-1.5, and the molecular weight of the polyethyleneimine is 400-800 Da; the dopamine compound is dopamine, catechol, tannic acid or derivatives;

in the step 5, the concentration of the trihydroxymethane aqueous solution is 40-60mM, and the pH range is 8.0-9.0; the reaction time is 5-120min, and the reaction temperature is room temperature.

2. The use according to claim 1, wherein in the step 3, the reaction time is 4-8h, and the reaction condition is room temperature;

in the step 4, the reaction temperature is 20-100 ℃, and the reaction time is 0.5-6 h.

3. The use according to claim 1, wherein said steps 1 to 5 are repeated from 1 to 20 times.

4. Use according to claim 1, characterized in that the desalting of the dye in aqueous solution is the separation of the dye from the inorganic salt.

5. Use according to claim 4, characterized in that the dye is selected from Congo Red, methyl blue, reactive Brilliant Red, methyl orange or methylene blue.

6. Use according to claim 4, characterized in that the inorganic salt is selected from NaCl or Na₂SO₄。