CN108159902B - Preparation method of chelate polyacrylonitrile hollow fiber membrane - Google Patents
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Abstract
The invention discloses a preparation method of a chelate Polyacrylonitrile (PAN) hollow fiber membrane, which comprises the steps of mixing polyacrylonitrile resin pretreated by sodium hydroxide with a diazo resin solution for electrostatic adsorption, then mixing with an ethylene diamine tetraacetic acid disodium solution for electrostatic adsorption, drying and carrying out ultraviolet exposure on an obtained product to obtain the polyacrylonitrile hollow fiber membrane, and repeating the steps of diazo resin electrostatic adsorption, ethylene diamine tetraacetic acid disodium electrostatic adsorption and subsequent ultraviolet exposure for multiple times to obtain the polyacrylonitrile hollow fiber membrane with multiple layers of diazo resin and ethylene diamine tetraacetic acid disodium modified layers, namely the chelate polyacrylonitrile hollow fiber membrane. The method for preparing the fiber membrane by adopting the process has the characteristics of simple process, water as a solvent, energy consumption saving, good environmental protection and easy realization of industrial production, and the obtained chelate polyacrylonitrile hollow fiber membrane has good hydrophilicity, has good adsorption function on various heavy metal ions in the solution, can be repeatedly regenerated and used, and still keeps good heavy metal ion adsorption performance.
Description
Technical Field
The invention relates to the field of Polyacrylonitrile (PAN) hollow fiber membranes, in particular to a preparation method of a chelate polyacrylonitrile hollow fiber membrane with a good adsorption effect on various metal ions.
Background
Wastewater produced in chemical laboratories, steam power plants, metallurgy, mineral processing, combustible industries, etc. contains a large amount of heavy metal ions, which are usually present in acidic solutions and are difficult to remove, and they cause great pollution to water, soil, etc.
The current methods for removing heavy metal ions from wastewater mainly include adsorption, electroplating, ion exchange, membrane separation, precipitation, etc., among which adsorption is considered to be an effective and environmentally friendly method in the field of water treatment.
In recent years, related researchers have conducted a great deal of research work on preparation and modification due to the excellent performance of electrospun nanofiber membranes in the aspect of heavy metal ion adsorption, and in the textile industry, Polyacrylonitrile (PAN) hollow fiber membranes are not only cheap, but also chemically stable, excellent in mechanical properties, corrosion-resistant, mildew-resistant and characteristic-resistant solvents have become one of the most widely used polymers in the modern times.
Recently, people have been exploring modification of polyacrylonitrile membrane to remove heavy metal ions in water, and patent CN102140705A discloses a preparation method of thioamide chelate nanofiber for adsorbing heavy metal ions, which is to obtain nanofiber through electrostatic spinning, pre-crosslinking and thioamidation to obtain chelate nanofiber for adsorbing heavy metal ions. Patent CN105568423A discloses an amidoximated polyacrylonitrile spinning solution and a nano-scale ion exchange fiber prepared from the same, wherein hydroxylamine hydrochloride and a catalyst are added into a polyacrylonitrile solution, the mixture is stirred at a high temperature, filtered, added with a crosslinking inhibitor to obtain the spinning solution, a nano-fiber membrane is prepared by adopting an electrostatic spinning technology, and the nano-scale ion exchange fiber which can adsorb heavy metal ions is obtained by post-treatment. Patent 105195110a discloses an amine modified fiber membrane-shaped adsorbing material and a preparation method thereof, wherein polyacrylonitrile powder is used as a matrix, a liquid matrix is prepared through solid-phase graft polymerization and amination reaction, and a novel fiber membrane-shaped adsorbing material is prepared through electrostatic spinning. The obtained membrane-shaped adsorption material has a high water absorption surface and can effectively adsorb various heavy metal ions in water, but spinning is carried out after amination by the method, the method is complicated and wastes raw materials, and only surface amination groups chelate metals, so that the adsorption capacity of the adsorption material on the metals is not high.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of a chelate Polyacrylonitrile (PAN) hollow fiber membrane, which has the advantages of easily available raw materials, simple process and easy operation, and simultaneously, the prepared chelate polyacrylonitrile hollow fiber membrane has good adsorption effect on various metal ions.
The invention utilizes diazo resin grafted Ethylene Diamine Tetraacetic Acid (EDTA) to modify Polyacrylonitrile (PAN) hollow fiber membrane, and the modification method comprises the following steps: mixing the polyacrylonitrile hollow fiber membrane pretreated by the sodium hydroxide aqueous solution with a diazo resin aqueous solution for electrostatic adsorption, mixing the polyacrylonitrile hollow fiber membrane adsorbed with the diazo resin with an ethylene diamine tetraacetic acid aqueous solution for electrostatic adsorption, drying the obtained product, and exposing by using ultraviolet light to obtain a chelate-type PAN hollow fiber membrane with a modified layer; the membrane is subjected to the two-step electrostatic adsorption and exposure treatment to obtain the chelate polyacrylonitrile hollow fiber membrane with a plurality of modified layers.
The preparation method of the chelating polyacrylonitrile hollow fiber membrane provided by the invention comprises the following steps:
1. preparation of respective raw material solutions
(1) Aqueous sodium hydroxide solution: mixing and stirring sodium hydroxide and water to obtain a sodium hydroxide aqueous solution;
(2) diazo resin solution: mixing and stirring diazoresin and water to obtain a diazoresin aqueous solution;
(3) EDTA solution: EDTA and water are mixed and stirred to obtain EDTA aqueous solution.
The concentration of the sodium hydroxide aqueous solution is 0.5-2.5 mol/L;
the concentration of the diazoresin aqueous solution is 0.5-2 mg/mL;
the concentration of the EDTA aqueous solution is 1-4 mg/mL.
2. Pretreating a polyacrylonitrile hollow fiber membrane:
(1) cutting the polyacrylonitrile hollow fiber membrane into small sections, washing with water and drying for later use;
(2) putting the polyacrylonitrile hollow fiber membrane obtained in the step (1) into 0.5-2.5mol/L sodium hydroxide aqueous solution at the temperature of 40-60 ℃, reacting for 1-5h, then taking out, washing with water, and drying in vacuum; the concentration of the sodium hydroxide aqueous solution is preferably 1-2mol/L, and the reaction time is preferably 2-4 h;
(3) and (3) drying the polyacrylonitrile hollow fiber membrane obtained in the step (2) in a vacuum drying oven to obtain the pretreated polyacrylonitrile hollow fiber membrane.
3. The layer-by-layer self-assembly of the polyacrylonitrile hollow fiber membrane modified layer and the preparation of the chelate polyacrylonitrile hollow fiber membrane are as follows:
(1) putting the pretreated polyacrylonitrile hollow fiber membrane obtained in the step 2 into the diazo resin aqueous solution prepared in the step 1 for first-step electrostatic adsorption, wherein the concentration of the diazo resin aqueous solution is 0.5-2mg/mL, and preferably 0.8-1.5 mg/mL; the adsorption time is 5-50h, preferably 20-30 h.
(2) And (2) washing the PAN hollow fiber membrane adsorbed with the diazo resin obtained in the step (1) with water, and then putting the PAN hollow fiber membrane into an ethylene diamine tetraacetic acid disodium aqueous solution for second-step electrostatic adsorption. The concentration of the ethylene diamine tetraacetic acid disodium solution is 1-4mg/mL, preferably 1.2-1.8 mg/mL; the adsorption time is 5-50h, preferably 20-30 h; the number of water washes is preferably 2-3.
(3) And (3) washing the hollow fiber membrane obtained in the step (2) with water, drying, and placing under an ultraviolet lamp for ultraviolet exposure treatment after drying. The exposure time is 1-6h, preferably 2-4 h; the number of water washes is preferably 2 to 3.
(4) Repeating the steps (1), (2) and (3) for multiple times on the chelate polyacrylonitrile hollow fiber membrane with a modified layer obtained in the step (3), carrying out electrostatic adsorption and exposure for two times in the same way, and adding multiple layers of diazo resin and ethylene diamine tetraacetic acid modified layers to obtain the chelate polyacrylonitrile hollow fiber membrane with multiple modified layers. The number of times of repeating steps (1), (2) and (3) is preferably 1 to 5 times.
According to the preparation method of the chelate polyacrylonitrile hollow fiber membrane, the operation in the step 3 is carried out in a dark environment except for the ultraviolet exposure operation.
According to the preparation method of the chelate polyacrylonitrile hollow fiber membrane, the first step of electrostatic adsorption and the second step of electrostatic adsorption are preferably carried out at room temperature.
According to the preparation method of the chelate polyacrylonitrile hollow fiber membrane, water used in each step of operation is preferably distilled water or deionized water.
The molecular weight of the diazo resin is 500-6000, preferably 1000-4000.
The invention prepares the chelate polyacrylonitrile hollow fiber membrane with good adsorption effect on various heavy metal ions in water by grafting diazo resin and ethylene diamine tetraacetic acid to the polyacrylonitrile hollow fiber membrane, and has the advantages of simple process, energy saving, good environmental protection and easy realization of industrial production, and the process takes water as a solvent.
Because the adopted diazo resin contains a large amount of diazo groups, after the diazo resin is adsorbed on the polyacrylonitrile hollow fiber membrane by utilizing electrostatic adsorption, the diazo groups provide access sites of a large amount of chelating groups, disodium Ethylene Diamine Tetraacetate (EDTA) containing a large amount of carboxyl is accessed on the diazo resin adsorbed on the polyacrylonitrile hollow fiber membrane through the electrostatic adsorption of the carboxyl and the diazo groups, and then ultraviolet exposure is carried out, the diazo resin and the polyacrylonitrile hollow fiber membrane simultaneously generate light cross-linking reaction to generate chemical bonds, so that the diazo resin and the EDTA are successfully introduced on the polyacrylonitrile hollow fiber membrane, the EDTA has excellent chelating capacity to heavy metal ions, and simultaneously a large amount of amine groups in the diazo resin also have certain capacity to heavy metal ions, therefore, the polyacrylonitrile hollow fiber membrane simultaneously accessed with the diazo resin and the EDTA on the surface has good adsorption capacity to the heavy metal ions, meanwhile, the fiber membrane obtained by the preparation method has the advantages that due to the introduction of a large number of hydrophilic groups in the modification layer, the hydrophilicity of the fiber membrane is remarkably enhanced, and the heavy metal adsorption capacity of the fiber membrane in a water environment is further improved.
Meanwhile, after the chelate polyacrylonitrile hollow fiber membrane prepared by the invention is used, the chelate polyacrylonitrile hollow fiber membrane can be reused through a simple desorption process, and a good adsorption effect is still kept.
Drawings
FIG. 1 is a layer-by-layer self-assembly schematic diagram of a multi-layer modified layer of a polyacrylonitrile hollow fiber membrane.
FIG. 2 is a scanning electron microscope photograph and an atomic force microscope photograph of a polyacrylonitrile hollow fiber membrane, in which (a) (b) (c) are polyacrylonitrile hollow fiber membranes without a modified layer; (d) and (e) and (f) are chelate polyacrylonitrile hollow fiber membranes with three layers of diazo resin and EDTA modified layers.
FIG. 3 is an infrared spectrum before and after modification of a polyacrylonitrile hollow fiber membrane. Wherein (a) is a polyacrylonitrile hollow fiber membrane without a modified layer, and (b) is a chelate-type polyacrylonitrile hollow fiber membrane with a diazo resin and an EDTA modified layer.
Fig. 4 is a water contact angle of the chelate type polyacrylonitrile hollow fiber membrane having different numbers of modified layers.
FIG. 5 shows (a) the copper adsorption amount of the DR (diazo resin) -EDTA layer number modified fiber membrane, (b) the water flux of the DR-EDTA layer number modified polyacrylonitrile hollow fiber membrane, (c) the copper adsorption amount of the 3 layers of DR-EDTA modified polyacrylonitrile hollow fiber membrane under different pH conditions, and (d) the copper adsorption amount of the 3 layers of DR-EDTA modified polyacrylonitrile hollow fiber membrane under different temperature conditions.
FIG. 6 is the color change and energy spectrum of chelate polyacrylonitrile hollow fiber membrane after absorbing copper ion, mercury ion, cadmium ion, lead ion and their mixed liquid.
FIG. 7 shows the adsorption amount of copper ions after repeated desorption and adsorption of 3 DR-EDTA modified chelate polyacrylonitrile hollow fiber membranes.
Detailed Description
Example 1
Preparation of chelate polyacrylonitrile hollow fiber membrane with single-layer diazoresin and EDTA (ethylene diamine tetraacetic acid) modified layer
(1) Preparation of raw material solutions:
a: aqueous sodium hydroxide solution: mixing sodium hydroxide and distilled water at normal temperature, stirring and preparing into a sodium hydroxide solution with the concentration of 1 mol/L.
b: diazo resin solution: the diazoresin is mixed with distilled water at normal temperature, and stirred to prepare a diazoresin solution with the concentration of 1mg/mL, and the molecular weight of the diazoresin is 1248-.
c: ethylene diamine tetraacetic acid disodium solution: disodium ethylenediamine tetraacetate is mixed and stirred with distilled water at normal temperature to prepare disodium ethylenediamine tetraacetate water solution with the concentration of 1.5 mg/mL.
(2) Pretreating a polyacrylonitrile hollow fiber membrane:
a: cutting the polyacrylonitrile hollow fiber membrane into small sections of 3-5 cm, washing with distilled water, and drying for later use.
And b, placing the polyacrylonitrile hollow fiber membrane obtained in the step (a) in a sodium hydroxide solution for reacting for 4 hours at 40 ℃. After the reaction is finished, the reaction product is taken out and washed by water to be neutral.
c: drying the polyacrylonitrile hollow fiber membrane obtained in the step (b) in a vacuum drying oven for 24 hours.
(3) Preparing a chelate polyacrylonitrile hollow fiber membrane:
and a, adding the pretreated polyacrylonitrile hollow fiber membrane into a beaker filled with diazo resin solution, and performing electrostatic adsorption at normal temperature for 24 hours.
And b, washing the polyacrylonitrile hollow fiber membrane adsorbed with the diazo resin obtained in the step a with distilled water for 2-3 times.
c: and (c) adding the polyacrylonitrile hollow fiber membrane obtained in the step (b) into a beaker containing ethylene diamine tetraacetic acid solution, and performing electrostatic adsorption at normal temperature for 24 hours.
And d, washing the polyacrylonitrile hollow fiber membrane obtained in the step c with distilled water for 1-2 times.
e: and d, drying the polyacrylonitrile hollow fiber membrane in the air, then placing the dried polyacrylonitrile hollow fiber membrane under an ultraviolet lamp for exposure for 3 hours to obtain the chelate polyacrylonitrile hollow fiber membrane with a single layer of diazo resin and an EDTA modified layer, wherein the experiment processes except the ultraviolet lamp exposure process are all operated under the condition of keeping out of the sun.
Example 2
Preparation of chelate polyacrylonitrile hollow fiber membrane with two layers of diazo resin and EDTA modified layer
The experimental process is the same as that of example 1, but after the step e in (3) is completed, the fiber membrane obtained is subjected to the operations of (3) a-e again, and the chelate-type polyacrylonitrile hollow fiber membrane with two layers of diazo resin and EDTA modified layers is obtained.
Example 3
Preparation of chelate polyacrylonitrile hollow fiber membrane with three layers of diazo resin and EDTA modified layer
The chelate-type polyacrylonitrile hollow fiber membrane having two modified layers obtained in example 2 was treated in accordance with the operations a to e in (3) in example 1 to obtain a chelate-type polyacrylonitrile hollow fiber membrane having three layers of diazo resin and EDTA modified layers.
Example 4
Preparation of chelate polyacrylonitrile hollow fiber membrane with four layers of diazo resin and EDTA modified layer
(1) Preparation of raw material solutions: the preparation method is the same as example 1 to obtain
2mol/L sodium hydroxide solution,
Diazoresin solution with concentration of 1.8 mg/mL.
The concentration is 1.8mg/mL disodium ethylene diamine tetraacetate aqueous solution.
(2) Pretreating a polyacrylonitrile hollow fiber membrane:
a: cutting the polyacrylonitrile hollow fiber membrane into small sections of 3-5 cm, washing with distilled water, and drying for later use.
And b, placing the polyacrylonitrile hollow fiber membrane obtained in the step (a) in a sodium hydroxide solution for reacting for 2 hours at 60 ℃. After the reaction is finished, the reaction product is taken out and washed by water to be neutral.
c: drying the polyacrylonitrile hollow fiber membrane obtained in the step (b).
(3) Preparing a chelate polyacrylonitrile hollow fiber membrane:
and a, adding the pretreated polyacrylonitrile hollow fiber membrane into a beaker filled with diazo resin solution, and performing electrostatic adsorption at normal temperature for 15 hours.
And b, washing the polyacrylonitrile hollow fiber membrane adsorbed with the diazo resin obtained in the step a with deionized water for 2-3 times.
c: and (c) adding the polyacrylonitrile hollow fiber membrane obtained in the step (b) into a beaker containing ethylene diamine tetraacetic acid solution, and performing electrostatic adsorption at normal temperature for 15 hours.
And d, washing the polyacrylonitrile hollow fiber membrane obtained in the step c with deionized water for 1-2 times.
e: d, drying the polyacrylonitrile hollow fiber membrane in the air, and then placing the dried polyacrylonitrile hollow fiber membrane under an ultraviolet lamp for exposure for 4 hours to obtain a chelate polyacrylonitrile hollow fiber membrane with a single layer of diazo resin and an EDTA modified layer; the operation before ultraviolet exposure is carried out under the condition of keeping out of the sun. Repeating the steps a-e for three times to obtain the chelating polyacrylonitrile hollow fiber membrane with four modified layers.
Example 5
Preparation of chelate polyacrylonitrile hollow fiber membrane with five layers of diazo resin and EDTA modified layer
The chelate-type polyacrylonitrile hollow fiber membrane having four modified layers obtained in example 4 was treated in accordance with the operations a to e in (3) in example 4 to obtain a chelate-type polyacrylonitrile hollow fiber membrane having five layers of diazo resin and EDTA modified layers.
Example 6
Analysis and comparative Performance test of the chelate-type Polyacrylonitrile hollow fiber membranes obtained in examples 1 to 5 and unmodified Polyacrylonitrile
(1) The scanning electron microscope image and the atomic force electron microscope image of each polyacrylonitrile hollow fiber membrane are analyzed, and the result is shown in figure 2. FIG. 2(a) is a polyacrylonitrile hollow fiber membrane without modification, whose surface pores have an average size of about 1.44 um; FIG. 2(b) (c) is an atomic force microscope showing that the pure PAN hollow fiber membrane is smooth and neat with a surface roughness of 15.9nm, and (d) is a three-layer DR-EDTA modified PAN membrane with surface pores having an average size of about 0.92 um; fig. 2(e) (f) is an atomic force microscope, and it can be seen that the three-layer DR-EDTA-modified PAN film surface shows a rough peak with a surface roughness of 57.6um, indicating that the DR-EDTA layer was introduced on the PAN film surface, changing the roughness. Surface roughness increases the contact area between the membrane and water, which can indirectly increase the adsorption of copper and the penetration of water by the membrane.
(2) Infrared spectrum (IR) analysis was performed on the polyacrylonitrile hollow fiber membrane before and after modification, and the results are shown in FIG. 3. Fig. 3(a) is a fiber membrane without a modified layer, and fig. 3(b) is a three-layer modified chelate polyacrylonitrile hollow fiber membrane. As can be seen, FIGS. 3(a) and (b) are each 2245cm in length-1And an absorption peak appears, which is a characteristic peak of the nitrile group. 1646cm of vibration attributed to C ═ O in fig. 3(b)-1Peak at and 3031cm due to stretching vibration of unsaturated C-H-1The presence of a benzene ring is confirmed by the peaks at (a). At 3388cm-1The characteristic peaks of secondary amino groups of (a) further demonstrate successful grafting of the diazo resin onto polyacrylonitrile hollow fiber membranes. At about 3400cm-1O-H vibration was observed. In addition to the presence of C ═ O, grafting of EDTA was also confirmed. Thus, it was confirmed that diazo resin and EDTA were successfully grafted to the polyacrylonitrile hollow fiber membrane.
(3) The water contact angles of the polyacrylonitrile hollow fiber membrane before and after modification are analyzed, the result is shown in figure 4, in the figure, the water contact angle graphs from left to right on the curve are sequentially the fiber membranes with 0 layer, 1 layer, 2 layer, 3 layer, 4 layer and 5 layer diazo resin and EDTA modified layer, the change trend of the water contact angle can be obviously seen, when no modified layer is arranged, the water contact angle of the membrane is 87.8 ℃, while the water contact angle of the polyacrylonitrile hollow fiber membrane coated with 5 layers diazo resin and EDTA modified layer is reduced to 63.45 ℃, and the reduction of the hydrophilic angle shows that the fiber membrane added with the diazo resin and EDTA modified layer has better hydrophilicity, which is due to the effect of introducing a large amount of hydrophilic groups in the modified layer.
(4) The adsorption test of the fiber membranes to copper ions before and after modification was analyzed using a membrane mass of 0.006g, the membrane was immersed in a copper ion solution of a certain concentration, 1mL of the solution was taken out at regular intervals to measure the concentration, using the principle that copper ions can form a complex with sodium diethyldithiocarbamate, which can be extracted by chloroform and detected by UV, and the concentration and change of copper ions were detected by this method, and the amount of adsorbed copper ions was calculated, and the result is shown in FIG. 5a, in which pure fiber PAN, PAN- (DR-EDTA)1- PAN-(DR-EDTA)5Respectively represent polyacrylonitrile hollow fiber membranes without modified layers and with 1-5 DR-EDTA modified layers. From FIG. 5a, the adsorption capacity of PAN fiber membrane to copper ion can be seen, from FIG. 5a, the unmodified PAN hollow fiber membrane has a small chelating capacity to copper and an ability to adsorb copper, and as the DR and EDTA layers are increased, the adsorption capacity of copper is increased from 21.9mg/g to 50.3mg/g, and the increase is up to 230%, while PAN- (DR-EDTA)3The adsorption amount of copper was 37.5mg/g, which was increased by 171%, and the increase in the adsorption amount of copper was attributed to the introduction of the DR-EDTA layer, which contained a large amount of chelating groups, so that it can be seen from the figure that the adsorption capacity of copper ions was increased somewhat for each additional DR-EDTA layer. The result of water flux measurement of the polyacrylonitrile hollow fiber membrane is shown in FIG. 5b, and it can be seen that PAN fiber membrane without a modified layer, PAN- (DR _ EDTA) was formed under a pressure of 19.79kp1-5Has a water flux of 733.30, 1049.80, 1085.94, 1068.85, 679.30, 350.30g · m-1·h-1,PAN-(DR-EDTA)1The increase in water flux was attributed to the introduction of hydrophilic groups on the surface of the polyacrylonitrile hollow fiber membrane, since both DR and EDTA are hydrophilic groups. And PAN- (DR-EDTA)1-3The trend of the water bucket amount to be stable is mainly caused by two reasons: 1, introduction of hydrophilic groups can increase water flux of the membrane, and 2. introduction of DR-EDTA chains to the surface of the polyacrylonitrile hollow fiber membraneThe pores of the surface have certain plugging effect, and the water flux basically tends to be stable by combining the two factors. PAN- (DR-EDTA)3-5The water flux decreased because with the introduction of DR-EDTA, the blocking effect of the polymer chains on the pores of the membrane surface had far exceeded the enhancement of water flux by the hydrophilic groups. In order to investigate the adsorption capacity of the modified membrane to copper under different environments, we tested the effect of pH and temperature on adsorption, and we can see from fig. 5c that the adsorption capacity of the modified fiber membrane to copper ions increases with increasing pH (4.0-6.5) and flattens with increasing pH (6.5-7.0), and the results show that the modified PAN can absorb copper better in neutral environment, and it can be demonstrated that the acidic environment can make the ion-ligand reaction proceed toward desorption direction due to the fact that the N atom on the amino group is combined with proton to lose coordination in the acidic environment, so that the chelating capacity of the membrane is reduced. As can be seen from fig. 5d, the amount of copper adsorbed increases with increasing temperature, which is attributed to the fact that the free volume of the polymer chains increases after increasing temperature, more copper ions can enter the polymer chains, thus causing more copper absorption by the modified film, and the structure of the film changes when the temperature reaches 70 ℃ to 80 ℃, which is not suitable for adsorbing copper ions.
(5) And (3) carrying out adsorption analysis on various heavy metal ions by the modified chelate polyacrylonitrile hollow fiber membrane, respectively soaking a plurality of groups of membranes with the same mass into a mixed solution of copper ions, chromium ions, mercury ions, lead ions and the ions, taking out the membranes after absorbing for 12 hours, washing the membranes with distilled water, washing the residual ions on the surface, drying, and measuring the absorption result of various ions by using an energy spectrum, wherein the absorption result is shown in figure 6. It can be seen from the figure that after the heavy metal ions of copper, chromium, mercury and lead are respectively and independently adsorbed, a large amount of corresponding heavy metal example adsorption can be respectively detected on the membrane, and after the heavy metal ion mixed solution of copper, chromium, mercury and lead is adsorbed, the existence of various heavy metal ions can also be detected on the membrane. It can be known that the modified polyacrylonitrile hollow fiber membrane has good adsorption effect on heavy metal ions such as copper, chromium, mercury, lead and the like.
(6) In order to study the chelate type polypropyleneThe stability of the adsorption performance of the alkene nitrile hollow fiber membrane to heavy metal ions is measured, and the repeated adsorption and desorption test of copper ions is 720 h. Fig. 7 shows the copper adsorption capacity after repeated desorption. The results show that PAN-DR (EDTA)3The membrane still can keep stronger adsorption capacity after 720h of adsorption and desorption, and can still reach 37.12mg/g compared with the first adsorption capacity of 37.47 mg/g. The chelating polyacrylonitrile hollow fiber membrane has good stable absorption capacity for copper ions, and can be reused.
Claims (9)
1. A preparation method of a chelate polyacrylonitrile hollow fiber membrane is characterized in that a polyacrylonitrile hollow fiber membrane pretreated by a sodium hydroxide aqueous solution is mixed with a diazo resin aqueous solution for first-step electrostatic adsorption, the polyacrylonitrile hollow fiber membrane adsorbed with the diazo resin is then mixed with an ethylene diamine tetraacetic acid aqueous solution for second-step electrostatic adsorption, and an obtained product is washed and dried and then is exposed by ultraviolet light to obtain the chelate polyacrylonitrile hollow fiber membrane with a modified layer; the fiber membrane is repeatedly and sequentially subjected to the electrostatic adsorption of the first step and the second step, product washing, drying and ultraviolet exposure treatment to obtain the chelate polyacrylonitrile hollow fiber membrane with the multilayer modified layer.
2. The method for preparing a chelating polyacrylonitrile hollow fiber membrane according to claim 1, characterized by comprising the following steps:
(1) pretreating a polyacrylonitrile hollow fiber membrane: cutting polyacrylonitrile hollow fiber membrane into small segments, washing with water, drying, placing in 0.5-2.5mol/L sodium hydroxide aqueous solution at 40-60 deg.C, reacting for 1-5h, taking out, washing with water, and drying;
(2) electrostatic adsorption and ultraviolet exposure of polyacrylonitrile hollow fiber membrane: placing the polyacrylonitrile hollow fiber membrane obtained in the step (1) in a diazo resin aqueous solution with the concentration of 0.5-2mg/mL for first-step electrostatic adsorption, wherein the reaction time is 5-50h, then washing the polyacrylonitrile hollow fiber membrane with water, then placing the polyacrylonitrile hollow fiber membrane in an ethylene diamine tetraacetic acid solution with the concentration of 1-4mg/mL for second-step electrostatic adsorption, carrying out the reaction for 5-50h, then washing the polyacrylonitrile hollow fiber membrane with water and drying, and exposing with an ultraviolet lamp after the drying is finished, thereby obtaining the polyacrylonitrile hollow fiber membrane with a modified layer;
(3) layer-by-layer self-assembly of the polyacrylonitrile hollow fiber membrane modified layer: repeating the operation of the step (2) on the polyacrylonitrile hollow fiber membrane obtained in the step (2) to obtain a modified polyacrylonitrile hollow fiber membrane coated with multiple layers of diazo resin and ethylene diamine tetraacetic acid, and completing the preparation of the chelate polyacrylonitrile hollow fiber membrane;
the operations in the step (2) are carried out under the condition of keeping out of the sun before ultraviolet exposure;
the water in each step is distilled water or deionized water.
3. The method for preparing a chelate-type polyacrylonitrile hollow fiber membrane according to claim 2, wherein the operation of the step (2) in the step (3) is repeated 1 to 5 times.
4. The method for preparing a chelating polyacrylonitrile hollow fiber membrane according to claim 2, characterized in that the concentration of the sodium hydroxide aqueous solution used in the step (1) is 1-2mol/L, and the reaction time is 2-4 hours.
5. The method for preparing a chelating polyacrylonitrile hollow fiber membrane according to claim 2, wherein the concentration of the aqueous solution of diazo resin in the step (2) is 0.8-1.5 mg/mL, the concentration of the aqueous solution of disodium edetate is 1.2-1.8mg/mL, and the time for electrostatic adsorption in the first and second steps is 20-30 hours.
6. The method for preparing a chelate type acrylonitrile hollow fiber membrane according to claim 2, wherein the operating temperature of the first step electrostatic adsorption and the second step electrostatic adsorption in the step (2) is room temperature.
7. The method for preparing a chelate type acrylonitrile hollow fiber membrane according to claim 2, wherein the time for exposing the fiber membrane after completion of adsorption in the step (2) to an ultraviolet lamp is 1 to 6 hours.
8. The method for preparing a chelate type acrylonitrile hollow fiber membrane according to claim 7, wherein the time for exposing the fiber membrane after completion of adsorption in the step (2) to an ultraviolet lamp is 2 to 4 hours.
9. The use of the chelate polyacrylonitrile membrane prepared by the preparation method according to any one of claims 1 to 8 for adsorbing heavy metal ions in wastewater.
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