CN114570336A - Metal adsorption fiber membrane and preparation and application thereof - Google Patents

Metal adsorption fiber membrane and preparation and application thereof Download PDF

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CN114570336A
CN114570336A CN202011374347.4A CN202011374347A CN114570336A CN 114570336 A CN114570336 A CN 114570336A CN 202011374347 A CN202011374347 A CN 202011374347A CN 114570336 A CN114570336 A CN 114570336A
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pvdf
solution
pan
fiber membrane
metal
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CN114570336B (en
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陈仰
蒋兰英
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Central South University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B01J20/26—Synthetic macromolecular compounds
    • B01J20/265—Synthetic macromolecular compounds modified or post-treated polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D15/00—Separating processes involving the treatment of liquids with solid sorbents; Apparatus therefor
    • B01D15/08—Selective adsorption, e.g. chromatography
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0081—After-treatment of organic or inorganic membranes
    • B01D67/0093—Chemical modification
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/34—Polyvinylidene fluoride
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/40—Polymers of unsaturated acids or derivatives thereof, e.g. salts, amides, imides, nitriles, anhydrides, esters
    • B01D71/42—Polymers of nitriles, e.g. polyacrylonitrile
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28033—Membrane, sheet, cloth, pad, lamellar or mat
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/3085—Chemical treatments not covered by groups B01J20/3007 - B01J20/3078
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/288—Treatment of water, waste water, or sewage by sorption using composite sorbents, e.g. coated, impregnated, multi-layered
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/12—Adsorbents being present on the surface of the membranes or in the pores
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/24—Mechanical properties, e.g. strength
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Abstract

The invention belongs to the technical field of heavy metal sewage treatment, and particularly relates to a heavy metal adsorption fiber membrane which is formed by interlacing and weaving PVDF @ PAN composite fibers; the PVDF @ PAN composite fiber comprises a PVDF core fiber and a PAN shell layer coated on the PVDF core fiber, wherein the outer surface of the PAN shell layer is a functional layer subjected to oximation and/or carboxylation modification treatment. In addition, the invention also provides a preparation method of the fiber membrane. The invention provides a PVDF @ PAN composite fiber with a brand-new structure and a fiber membrane material obtained by interweaving the fiber. Researches show that the membrane material disclosed by the invention has excellent metal adsorption performance, and also has excellent mechanical properties and cyclic adsorption stability.

Description

Metal adsorption fiber membrane and preparation and application thereof
Technical Field
The invention relates to the technical field of environmental management, in particular to a fiber membrane material for adsorbing metal ions.
Background
The fiber membrane material has a multi-communicated pore channel structure due to high porosity, and is an ideal adsorption material. The fiber membrane is widely concerned by researchers at home and abroad for treating wastewater containing metal ions. The main reason is that compared with the traditional adsorbing material, the active sites of the membrane material are positioned on the surface or the pore wall of the membrane, so that the contact between the material and metal ions can be greatly increased, the reaction time is shortened, the reaction process is shortened, and the volume of the reactor is controlled. Commonly used methods for making fibrous membranes include: stretching, template synthesis, phase separation, self-assembly and electrostatic spinning, wherein the electrostatic spinning is the only method capable of continuously preparing the nano-scale fiber membrane.
At present, the nanofiber prepared by electrostatic spinning has the advantages of simple operation, adjustable structure, high porosity, large specific surface area and the like, and is widely applied to the fields of water treatment and the like. The amidoxime nanofiber membrane has high affinity and selectivity to metal ions, is particularly outstanding in the aspect of metal adsorption separation, and has poor mechanical strength and durability, so that the problem of large-scale application is challenged. A large number of researchers find that with the increase of the surface modification and the oximation degree, the fiber inevitably has the phenomena of shrinkage, agglomeration, embrittlement and the like, and the chemical modification generates irreversible damage to the material, so that the currently prepared amidoxime nanofiber is difficult to consider both the adsorption performance and the mechanical strength.
To solve the above problems, the prior art proposes some solutions, which mainly include: hot pressing, solvent annealing treatment, non-woven fabric support and the like. The methods have respective defects, for example, the hot pressing treatment needs to be carried out at a temperature of more than 90 ℃ and then the fiber membrane is hot pressed, which is a waste for the current large environment with the energy resource up; the solvent annealing treatment is to treat the fiber membrane by generating solvent steam which is undoubtedly harmful to people and environment; nonwoven fabrics have good mechanical properties, but how to make the fibrous membrane adhere to the surface more firmly is still a breakthrough.
Disclosure of Invention
In order to solve the problem that the adsorption performance and the structural stability of the existing metal adsorption fiber membrane (metal adsorption membrane) are difficult to be considered at the same time, the first purpose of the invention is to provide a metal adsorption fiber membrane with a brand-new structure, and to provide a fiber membrane material with good metal adsorption performance and mechanical stability.
The second object of the present invention is to provide a method for producing a metal-adsorbing fibrous membrane, which is intended to produce a fibrous membrane material having both excellent mechanical properties and metal-adsorbing properties.
The third purpose of the invention is to provide the application of the metal adsorption fiber membrane in metal adsorption.
For a metal-adsorbing fiber membrane, in order to obtain good metal adsorption performance, structural modification is usually required to be performed on the membrane, however, functional modification can perform etching reconstruction on the surface of a fiber structure to a great extent, which easily causes technical problems of fiber structure collapse, shrinkage, agglomeration, embrittlement and the like, and a strong image influences the structural integrity and mechanical properties of the membrane, and can influence the adsorption performance, structural stability and adsorption stability of the membrane to a great extent, and for the technical problems, the invention provides the following improvement scheme, specifically:
a metal adsorption fiber membrane is formed by interlacing and weaving PVDF @ PAN composite fibers;
the PVDF @ PAN composite fiber comprises a PVDF core fiber and a PAN shell layer coated on the PVDF core fiber, wherein the outer surface of the PAN shell layer is a functional layer subjected to oximation and/or carboxylation modification treatment.
The invention provides a PVDF @ PAN composite fiber with a brand-new structure and a fiber membrane material obtained by interweaving the fiber. Researches show that the membrane material disclosed by the invention has excellent metal adsorption performance, and also has excellent mechanical properties and cyclic adsorption stability.
The synergy of the material component characteristics of the fiber and the characteristics of the core-shell (PAN shell) -shell (active layer on the outer side of PAN) double-shell structure is the key to improve the metal adsorption performance, the membrane structure stability and the adsorption stability of the fiber membrane material. The study also found that the PAN is compounded on the surface of the PVDF, no gap exists between the surface of the PVDF and the PAN is subjected to functional modification on the outer surface, and the active layer does not penetrate through the whole PAN layer, so that the metal adsorption and the mechanical structure stability are improved.
Preferably, the PVDF core fiber has a diameter of 0.36 to 0.45. mu.m.
The thickness of the PAN shell layer is 0.24-0.32 μm.
Preferably, in the outer-layer PAN, the proportion (volume proportion) of the functional layer is 50-85%; preferably 70 to 80%.
The invention also provides a preparation method of the metal adsorption fiber membrane, which comprises the following steps:
step (1):
obtaining a solution A dissolved with PVDF and a solution B dissolved with PAN; performing coaxial electrostatic spinning treatment on the solution A serving as core liquid and the solution B serving as outer layer casting solution to obtain a PVDF @ PAN base film; the concentration of PVDF in the solution A is 6-12 wt%; the concentration of PAN in the solution B is 10-14 wt%;
the voltage of the electrostatic spinning process is 13-15 KV;
step (2):
performing functional modification treatment on the outer surface of the PAN of the PVDF @ PAN base film, and then performing freeze drying to obtain the PVDF @ PAN base film;
the functionalization is oximation and/or carboxylation.
The research of the invention finds that in order to successfully construct the fiber membrane with the double-shell structure and improve the structural stability and the adsorption performance of the fiber membrane, the problems of the composite form of PVDF and PAN and the activity modification degree of the PAN outer surface need to be properly solved. Research shows that the coaxial electrostatic mode means of the invention is matched with the spinning solution and the combined control of the voltage, the modification treatment mechanism and the freeze drying means in the electrostatic mode process, so that the synergy can be generated, the contact tightness of PAN and PVDF interfaces can be controlled, the modification treatment degree can be controlled, and the double-shell structure can be maintained, thus the fiber membrane with the double-shell structure and excellent structural stability and metal adsorption performance can be prepared unexpectedly. In addition, the fibrous membrane prepared by the preparation method has good double-shell structure appearance and no broken silk chain beads.
In the invention, PVDF is sprayed from the core hole and PAN is sprayed from the outer hole by adopting the coaxial electrostatic spinning needle head, the PVDF @ PAN basal membrane which takes PVDF as the inner core fiber and uniformly coats PAN on the surface of the inner core fiber can be obtained, and researches also find that the surface composite state of PVDF and PAN can be improved and the separation of the interface of PVDF and PAN to form a gap can be avoided based on the cooperative control of the concentration and the voltage in the spinning solution, thereby being beneficial to further improving the metal adsorption performance of the fiber membrane.
According to the method, the base membrane is prepared by using a coaxial electrostatic spinning method through the matching of materials with the mass in the membrane casting solution, and a freeze drying method is combined, so that the flexible aminated fiber membrane with good appearance, high strength and excellent adsorption performance is obtained.
Preferably, the molecular weight of the PVDF is 15-25 ten thousand; preferably, the PVDF is PVDF 6020.
Preferably, the solvent in the solution a is a solvent capable of dissolving PVDF, preferably at least one of N, N-dimethylacetamide (DMAc) and N, N-Dimethylformamide (DMF);
researches show that the PAN membrane casting solution is matched with the PVDF membrane casting solution, so that the fibers with complete core-shell structures are facilitated; however, when the concentration of PVDF is too high (e.g., higher than the upper limit), the viscosity of the dope solution increases, which may affect the electrospinning process and the performance of the fiber membrane.
Preferably, the content of PVDF in the solvent A is 10-12 wt.%. In the present invention, the balance of the solution A is a solvent.
The preparation method of the PVDF-containing solution A is as follows: adding PVDF into solvent such as N, N-dimethylacetamide, and mixing at 40-60 deg.C.
Preferably, the molecular weight of the PAN is 13-16 ten thousand; more preferably 14 to 15 ten thousand.
Preferably, the solvent in the solution B is a solvent capable of dissolving PAN, and is preferably at least one of N, N-dimethylacetamide and N, N-dimethylformamide.
Preferably, the PAN-containing solution B is prepared in the following manner: adding PAN into solvent such as N, N-dimethylacetamide, and mixing at 40-60 deg.C.
Preferably, the PAN content in the solvent B is 11 to 13 wt.%; further preferably 11.5 to 12.5 wt.%. In the present invention, the balance of the solution B is a solvent. The research finds that the preferable proportion can help to cooperate with other conditions to unexpectedly improve the strength and the adsorption performance of the fiber membrane, and particularly can help to further improve the strength and the adsorption performance retention rate after the circulation.
The research of the invention finds that the accurate control of the voltage is beneficial to the smooth proceeding of the spinning process, can improve the form of the base film and is beneficial to improving the metal adsorption performance and the structural stability of the obtained fiber film. However, when the voltage is too high, the electrostatic stretching is too large to cause separation of the inner and outer layers, and when the voltage is too small, the electrostatic force is insufficient to draw the dope solution into fibers.
Preferably, in the electrostatic process, the spinning voltage is 13.5-14.5 KV; further preferably 14 to 14.5 KV. It was found that at the preferred voltages, the metal adsorption properties and the structural stability of the worthwhile fiber membranes can be surprisingly further improved.
According to the invention, on the basis of controlling the proportion and voltage of the casting solution, the flow speed regulation is further controlled, so that the nanofiber membrane with small fiber diameter, large pore volume and complete core-shell shape can be further prepared.
Preferably, in the electrostatic process, the distance between the coaxial spinneret and the receiving plate is 14-16 cm; further preferably 15 cm. The flow rate of PAN is 0.5-1 mL/h; preferably 0.5-0.6 mL/h, and the flow rate of PVDF is 0.5-1 mL/h; preferably 0.5-0.6 mL/h.
The preferable test process of the invention comprises the steps of respectively filling the PAN and PVDF casting solution into an injector, connecting a coaxial spinning needle head by a conduit, controlling the inner aperture of the needle head to be 374 mu m, the concentric aperture to be 534 mu m, adjusting the distance between the needle head and a roller to be 15cm, connecting 14kv high-voltage static electricity at the needle head, controlling the flow rate of the casting solution to be 0.5-1mL/h, controlling the winding speed of the roller to be 300-450rn/min, and continuing for 1-3h to obtain the base membrane.
In the invention, under the control of the spinning means and conditions, the surface modification treatment means is further controlled, which is beneficial to further generating synergy and further ensuring that the prepared fiber membrane has good metal adsorption performance and structural stability.
Preferably, the oximation surface treatment step is:
placing the PVDF @ PAN base film into a modified solution a in which hydroxylamine and alkali are dissolved, and carrying out surface oximation treatment;
preferably, the alkali is at least one of anhydrous sodium carbonate and anhydrous sodium bicarbonate;
in the modified solution a, the molar ratio of hydroxylamine to alkali is 1:1-2.5: 1;
preferably, in the modified solution a, the molar concentration of hydroxylamine is 0.4-0.6 mol/L;
preferably, the temperature of the oximation modification process is 60-80 ℃;
preferably, the time of the oximation modification process is 60-180 min; further preferably 110 to 140 min.
The step of the carboxylation surface treatment comprises the following steps:
placing the PVDF @ PAN base membrane into a modified solution b in which alkali is dissolved, and performing surface carboxylation treatment;
preferably, the alkali is at least one of sodium hydroxide and potassium hydroxide;
preferably, in the modified solution b, the molar concentration of the alkali is 1-5 mol/L;
preferably, the temperature of the oximation modification process is 60-80 ℃;
preferably, the time for the oximation modification process is 30-120 min.
In the present invention, the modified polycarbonate resin composition is obtained by subjecting the resin composition to modification treatment, followed by washing (washing the modifying material, for example, with water), and freeze-drying.
Preferably, the freeze-drying time is 4-7 h.
In the present invention, the molding may be carried out at a low temperature, for example, at-20 to 5 ℃ before the freeze-drying.
In a preferred embodiment of the present invention, the following steps are included: preparing a base film from the PAN membrane casting solution and the PVDF membrane casting solution through coaxial electrostatic spinning, and freeze-drying after amidoximation modification to obtain a flexible amidoximation fiber membrane; the PAN casting solution comprises 10-14 wt% of PAN (preferably 11.5-12.5%), and the balance of a polar solvent, and the PVDF casting solution comprises 6-12 wt% of PVDF (preferably 10-12%), and the balance of a solvent; the voltage of the spinning process is 13.5-14.5 KV.
The amidoxime functional group has excellent ion exchange capacity and selectivity, and the fiber damage caused by the amidoxime functional group is irreversible. The core-shell fiber membrane is prepared by coaxially and electrostatically spinning two solutions by taking PAN as an outer layer and PVDF as an inner layer for the first time. The inventor finds that after PVDF is added as an inner layer material, the mechanical strength of the fiber after the oximation reaction basically maintains the condition before the oximation reaction, and the freeze drying enables the morphology of the fiber to be retained to the maximum extent, which has great significance for improving the service performance of the oximation fiber material. Meanwhile, the inventor discovers through a great deal of research that the flexible aminated fiber membrane with good appearance, high strength and good lead ion adsorption performance can be unexpectedly prepared by matching the membrane casting solution with the membrane forming mode.
The invention also provides an application of the metal adsorption fiber membrane, which is used for adsorbing lead metal ions;
preferably, for adsorbing lead metal ions (Pb) in an aqueous solution2+)。
Advantageous effects
1. The invention provides a metal adsorption fiber membrane with a brand-new double-shell structure, and finds that the performance of the membrane material in metal adsorption can be unexpectedly improved based on the synergistic control of the substances and the structure, for example, the adsorption performance of metal can be improved, the adsorption stability of the metal can be improved, and the structural stability of the material can be improved, and the attenuation degree of mechanical performance can be controlled.
2. The invention also provides a preparation method of the metal adsorption fiber membrane, which takes PVDF as core liquid and PAN as outer membrane casting liquid, adopts a coaxial electrostatic mode, and is matched with the spinning liquid and the combined control of the voltage, the modification treatment mechanism and the freeze drying mode of the electrostatic mode process, so that the synergy can be generated, the contact tightness of the PAN and the PVDF interface can be controlled, and the modification treatment degree can be controlled, thus the fiber membrane with the double-shell structure and excellent structural stability and metal adsorption performance can be prepared unexpectedly.
3. In the invention, by combining the characteristics of the fiber membrane with the double-shell structure, amidoxime modification treatment is further preferably adopted, the shape of the flexible nanofiber membrane can be effectively maintained, amidoxime functional groups not only have excellent chelating effect on metal ions, but also have unique selectivity, and the inventor finds that the core-shell fiber structure can keep the shape of fibers subjected to amidoxime, maintain the original strength and improve the service performance of the fiber membrane, and the flexible aminated membrane still has very good metal ion capture capacity and selectivity.
4. The preparation method of the invention has simple operation, good film forming performance and complete core-shell shape, the strength of the modified material is basically not changed to 80 percent of that before modification, and the composite fiber film is used for Pb2+The adsorption capacity of the membrane reaches 89.3mg/g, 45 percent of adsorption capacity of the original membrane is still kept after repeated use for 5 times, the mechanical strength of the membrane is unchanged after repeated use for many times, the original appearance is basically maintained, and the membrane has an industrial application prospect.
Drawings
FIG. 1 is a TEM image and an SEM image of a spinning pattern of a composite nanofiber membrane prepared in example 2; wherein a is a spinning picture of a prepared fiber membrane, b is a TEM picture of the fiber, and c is an SEM picture; as can be seen in fig. a, there is a droplet build up at the tip of the needle, which results in an increase in beading on the surface of the fiber (as shown in fig. b and c), and a decrease in the strength of the fiber structure.
FIG. 2 is a TEM image and an SEM image of a spinning pattern of the composite nanofiber membrane prepared in example 1; wherein a is a spinning picture of a prepared fiber membrane, b is a TEM picture of a fiber, and c is an SEM picture; as can be seen from fig. a, the spinning process is uniform and stable, and a complete core-shell structure fiber membrane is formed (as shown in fig. b and c).
FIG. 3 is a TEM image and an SEM image of a spinning pattern of the composite nanofiber membrane prepared in example 3; wherein a is a spinning picture of a prepared fiber membrane, b is a TEM picture of a fiber, and c is an SEM picture; as can be seen from the graph a, two Taylor cones are formed near the needle tip, which means that the inner and outer layers are separated to form a single-layer structure (as shown in the graphs b and c, the core-shell separation condition exists), resulting in the strength reduction of the modified fiber membrane.
FIG. 4 is a macro topography of the composite nanofiber membranes prepared in example 1 and comparative example 1; wherein a is the macro topography of the fiber membrane of comparative example 1, it can be seen that the fiber membrane without the PVDF support layer has severe shrinkage after modification; b is the macro topography of the fiber membrane of example 1, c is the flexibility map of example 1, and it can be seen that the fiber membrane with core-shell structure maintains intact morphology and structural stability.
Detailed Description
PAN: the molecular weight is 13-15 ten thousand.
PVDF: model number 6020.
With a coaxial needle, the inner diameter of the bore in the needle is 374 μm and the inner diameter of the outer bore is 534 μm.
Example 1
(1) Preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand of polyacrylonitrile with molecular weight and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the membrane casting solution obtained in the steps (1) and (2) into 10mL syringes, connecting coaxial needles by Teflon guide tubes, adjusting the distance between the needle and the roller to be 15cm, connecting 14kv high-voltage static electricity at the needle, wherein the flow rate of the membrane casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base membrane is obtained after 2 h.
(4) Preparation of composite nanofiber membrane
And (3) treating the base membrane obtained in the step (3) with 100mL of mixed solution of hydroxylamine hydrochloride and anhydrous sodium carbonate (wherein the molar concentration of hydroxylamine is 0.5M, and the molar ratio of hydroxylamine to anhydrous sodium carbonate is 2: 1) at 70 ℃ for 2h to obtain the amidoxime nanofiber membrane. The obtained modified fiber membrane is frozen and molded at the temperature of minus 20 ℃, and then the modified fiber membrane is obtained by freezing and vacuum drying; the volume ratio of the modified layer is 80%.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+
Adding the fiber film to lead (Pb)2+) The solution (2) was subjected to oscillatory adsorption for 10 hours, and the supernatant in the solution was taken and subjected to ICP-OES measurement of the concentration before and after the adsorption reaction of the solution to calculate the Pb content of the fiber membrane2+The amount of adsorption of (3).
The test shows that the mechanical strength of the fiber membrane (referring to the base membrane) before modification is 3.567MPa, the mechanical strength of the modified composite fiber membrane (referring to the composite membrane modified in the step 4) is 80% before modification, the lead ion adsorption amount in the aqueous solution is 89.3mg/g, after repeating for 5 times, the lead ion adsorption amount is 40.2mg/g, and the mechanical strength is 79% before modification.
Example 2
Compared with example 1, the difference is mainly that the voltage of the spinning process is adjusted:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the casting solution obtained in the steps (1) and (2) into 10mL syringes, connecting coaxial needles by Teflon guide tubes, adjusting the distance between the needle and the roller to be 15cm, connecting 13kv high-voltage static electricity at the needle, wherein the flow rate of the casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base film is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber membrane. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
The fiber membrane was added to an aqueous solution containing lead, the solution was subjected to adsorption under shaking for 10 hours, and the supernatant of the solution was taken, and the concentrations before and after the adsorption reaction of the solution were measured by ICP-OES, to calculate the adsorption amount of Pb2+ by the fiber membrane.
The mechanical strength of the fiber membrane before modification was 3.567MPa (the strength before modification was similar to that of example 1), the mechanical strength of the composite fiber membrane after modification was 55% before modification, the lead ion adsorption amount in the aqueous solution was 85.7mg/g, and after repeating the above steps 5 times, the lead ion adsorption amount was 39.6mg/g, and the mechanical strength was 26% before modification. As compared with the examples, it was found that the adsorption performance was decreased and the structural stability as well as the cycle stability were decreased.
Example 3
Compared with example 1, the difference is mainly that the voltage of the spinning process is adjusted:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the casting solution obtained in the steps (1) and (2) into a 10mL injector, connecting a coaxial needle by a Teflon guide tube, adjusting the distance between the needle and the roller to be 15cm, introducing 15kv high-voltage static electricity at the needle, wherein the flow rate of the casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base film is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoximated fiber membrane2+(same as example 1)
The fiber membrane was added to an aqueous solution containing lead, the solution was subjected to adsorption under shaking for 10 hours, and the supernatant of the solution was taken, and the concentrations before and after the adsorption reaction of the solution were measured by ICP-OES, to calculate the adsorption amount of Pb2+ by the fiber membrane.
The mechanical strength of the fiber membrane before modification is 3.61MPa, the mechanical strength of the modified composite fiber membrane is 16% before modification, the adsorption amount of lead ions in an aqueous solution is 36.6mg/g, and after repeating for 5 times, the adsorption amount of lead ions is 11.7mg/g, and the mechanical strength is 15% before modification. As compared with the examples, it was found that the adsorption performance was decreased and the structural stability as well as the cycle stability were decreased.
Example 4
Compared with the embodiment 1, the difference is mainly that the concentration of the PAN membrane liquid is controlled, specifically:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 14 wt% and 86 wt% of polyacrylonitrile with the molecular weight of 15 ten thousand and solvent N, N-dimethylacetamide at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the membrane casting solution obtained in the first step and the second step into a 10mL injector, connecting a coaxial needle by a Teflon conduit, adjusting the distance between the needle and a roller to be 15cm, introducing 14kv high-voltage static electricity at the needle, wherein the flow rate of the membrane casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base membrane is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
The fiber membrane was added to an aqueous solution containing lead, the solution was subjected to adsorption under shaking for 10 hours, and the supernatant of the solution was taken, and the concentrations before and after the adsorption reaction of the solution were measured by ICP-OES, to calculate the adsorption amount of Pb2+ by the fiber membrane.
The base film strength was found to be similar to that of example 1, but the mechanical strength of the modified composite fiber film was 42% before modification, the lead ion adsorption amount in the aqueous solution was 83.2mg/g, and after repeating 5 times, the lead ion adsorption amount was 40.5mg/g and the mechanical strength was 21% before modification. As compared with the examples, it was found that the adsorption performance was decreased and the structural stability as well as the cycle stability were decreased.
Example 5
Compared with the embodiment 1, the difference is mainly that the concentration of the PAN membrane liquid is controlled, specifically:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and solvent N, N-dimethylacetamide according to the weight percentage of 10 wt% and 90 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the membrane casting solution obtained in the first step and the second step into a 10mL injector, connecting a coaxial needle by a Teflon conduit, adjusting the distance between the needle and a roller to be 15cm, introducing 14kv high-voltage static electricity at the needle, wherein the flow rate of the membrane casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base membrane is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (3) treating the base film obtained in the step (4) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
The fiber membrane was added to an aqueous solution containing lead, the solution was subjected to adsorption under shaking for 10 hours, and the supernatant of the solution was taken, and the concentrations before and after the adsorption reaction of the solution were measured by ICP-OES, to calculate the adsorption amount of Pb2+ by the fiber membrane.
The base film was found to have a strength similar to that of example 1, but the mechanical strength of the modified composite fiber film was 49% before modification, the amount of lead ion adsorption in the aqueous solution was 73.5mg/g, and after repeating the procedure 5 times, the amount of lead ion adsorption was 32.1mg/g and the mechanical strength was 19% before modification. As compared with the examples, it was found that the adsorption performance was decreased and the structural stability as well as the cycle stability were decreased.
Example 6
Compared with the embodiment 1, the difference is mainly that the concentration of the PAN membrane solution and the PVDF membrane solution is controlled, and the specific steps are as follows:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide as solvent in the weight percentage of 10 wt% and 90 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the membrane casting solutions obtained in the steps (1) and (2) into a 10mL injector, connecting a coaxial needle by a Teflon guide tube, adjusting the distance between the needle and a roller to be 15cm, introducing 14kv high-voltage static electricity at the needle, wherein the flow rate of the membrane casting solutions is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base membrane is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
Adding the fiber membrane into a lead-containing aqueous solution, performing oscillatory adsorption for 10h, taking the supernatant of the solution, measuring the concentration of the solution before and after adsorption reaction by ICP-OES, and calculating the Pb content of the fiber membrane2+The amount of adsorption of (3).
The base film before modification was found to have a strength similar to that of example 1, and the mechanical strength of the modified composite fiber film was 76% before modification, the lead ion adsorption amount in the aqueous solution was 92.4mg/g, and after repeating 5 times, the lead ion adsorption amount was 50.6mg/g and the mechanical strength was 75% before modification. Compared with the examples, the adsorption performance, the structural stability and the cycle stability are not greatly changed.
Example 7
Compared with the embodiment 1, the difference is mainly that the voltage of the spinning process is adjusted, specifically:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the casting solution obtained in the steps (1) and (2) into a 10mL injector, connecting a coaxial needle by a Teflon guide tube, adjusting the distance between the needle and the roller to be 15cm, introducing 13.5kv high-voltage static electricity at the needle, wherein the flow rate of the casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base film is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
Adding the fiber membrane into a lead-containing aqueous solution, oscillating and adsorbing for 10h, taking the supernatant in the solution, measuring the concentration of the solution before and after adsorption reaction by ICP-OES, and calculating the Pb pair of the fiber membrane2+The amount of adsorption of (3).
The base film before modification was found to have a strength similar to that of example 1, and the mechanical strength of the composite fiber film after modification was 70% before modification, the lead ion adsorption amount in the aqueous solution was 80.3mg/g, and after repeating 5 times, the lead ion adsorption amount was 44.2mg/g and the mechanical strength was 58% before modification. Compared with the example, the change of the adsorption performance, the structural stability and the cycling stability is not large, but the strength attenuation after the cycling treatment is more obvious than that of the example 1.
Example 8
Compared with the embodiment 1, the difference is mainly that the voltage of the spinning process is adjusted, specifically:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the casting solution obtained in the steps (1) and (2) into a 10mL injector, connecting a coaxial needle by a Teflon guide tube, adjusting the distance between the needle and the roller to be 15cm, introducing 14.5kv high-voltage static electricity at the needle, wherein the flow rate of the casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base film is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was freeze-molded at-20 ℃ and then dried by freeze-vacuum.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
Adding the fiber membrane into a lead-containing aqueous solution, performing oscillatory adsorption for 10h, taking the supernatant of the solution, measuring the concentration of the solution before and after adsorption reaction by ICP-OES, and calculating the Pb content of the fiber membrane2+The amount of adsorption of (3).
The base film before modification was found to have similar strength to example 1, and the mechanical strength of the composite fiber film after modification was 74% before modification, the amount of adsorption of lead ions in the aqueous solution was 85.6mg/g, and after repeating 5 times, the amount of adsorption of lead ions was 50.4mg/g, and the mechanical strength was 72% before modification. Compared with the examples, the adsorption performance, the structural stability and the cycle stability are not greatly changed.
Comparative example 1
The only difference compared to example 1 is that the double-shell structure according to the invention (without PVDF as inner support) is not constructed, as follows:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of base film
And (2) filling the casting solution obtained in the step (1) into a 10mL syringe, connecting a No. 22 needle with a Teflon catheter, adjusting the distance between the needle and the roller to be 15cm, introducing 14kv high-voltage static electricity at the needle, wherein the flow rate of the casting solution is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base film is obtained after 2 h.
(3) Modification of composite nanofiber Membrane (same as example 1)
And (3) treating the base film obtained in the step (2) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film.
The modified composite fiber membrane shrinks seriously, and the fiber membrane is embrittled, so that the mechanical strength of the composite fiber membrane cannot be measured, and the use value is lost, as shown in figure 4 a. Experiments show that the oximation modification degree exceeds 35 percent, the PAN without the core-shell structure can shrink and deform, the oximation modification degree exceeds 80 percent, and the fiber membrane with the core-shell structure still keeps complete morphology.
Comparative example 2
The only difference from example 1 is that the inner layer support material was changed as follows:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PSF solution
The PSF solution is prepared by uniformly mixing 12 ten thousand molecular weight polysulfone and 88 wt% solvent N, N-dimethylacetamide at normal temperature.
(3) Preparation of base film
Respectively filling the membrane casting solutions obtained in the steps (1) and (2) into a 10mL injector, connecting a coaxial needle by a Teflon guide tube, adjusting the distance between the needle and a roller to be 15cm, introducing 14kv high-voltage static electricity at the needle, wherein the flow rate of the membrane casting solutions is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base membrane is obtained after 2 h.
(4) Preparation of composite nanofiber Membrane (same as example 1)
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film.
(4) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
The fiber membrane was added to an aqueous solution containing lead, the solution was subjected to adsorption under shaking for 10 hours, and the supernatant of the solution was taken, and the concentrations before and after the adsorption reaction of the solution were measured by ICP-OES, to calculate the adsorption amount of Pb2+ by the fiber membrane.
The mechanical strength of the modified composite fiber membrane was 62% before modification, the lead ion adsorption amount in the aqueous solution was 73.8mg/g, and after repeating the modification 5 times, the lead ion adsorption amount was 32.5mg/g, and the mechanical strength was 33% before modification. Therefore, the PVDF is adopted, and the structure and the control of the conditions are matched, so that the strength and the adsorption performance of the material can be unexpectedly improved, and the strength retention rate after multiple cycles is improved.
Comparative example 3
Compared with the example 1, the difference is mainly that the spinning mode is changed, specifically:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of spinning solution
Uniformly stirring the casting solution obtained in the steps (1) and (2) according to the volume ratio of 1:1 until a homogeneous solution is formed
Respectively loading into 10mL syringes, connecting coaxial needles with Teflon guide tubes, adjusting the distance between the needles and the roller to be 15cm, introducing 14kv high-voltage static electricity at the needles, controlling the flow rate of the casting solution to be 0.5mL/h, controlling the winding speed of the roller to be 300rn/min, and continuing for 2h to obtain the basement membrane.
(4) Preparation of nanofiber Membrane (same as example 1)
And (3) putting the spinning solution obtained in the step (3) into a 10mL syringe, connecting a No. 22 needle by using a Teflon conduit, adjusting the distance between the needle and the roller to be 15cm, connecting 14kv high-voltage static electricity at the needle, wherein the flow rate of the casting solution is 1mL/h, the winding speed of the roller is 300rn/min, and the base film is obtained after 2 h.
In subsequent modification experiments, the modification solution cannot soak the base film, and the modification is ineffective; the desired adsorption film cannot be obtained.
Comparative example 4
The difference from example 1 is mainly that the drying method was changed, specifically:
(1) preparation of PAN solution
The PAN solution is prepared by uniformly mixing 15 ten thousand molecular weight polyacrylonitrile and a solvent N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at 60 ℃.
(2) Preparation of PVDF solution
The PVDF solution is prepared by uniformly mixing 6020 PVDF and N, N-dimethylacetamide according to the weight percentage of 12 wt% and 88 wt% at normal temperature.
(3) Preparation of base film
Respectively filling the membrane casting solutions obtained in the steps (1) and (2) into a 10mL injector, connecting a coaxial needle by a Teflon guide tube, adjusting the distance between the needle and a roller to be 15cm, introducing 14kv high-voltage static electricity at the needle, wherein the flow rate of the membrane casting solutions is 0.5mL/h, the winding speed of the roller is 300rn/min, and the base membrane is obtained after 2 h.
(4) Preparation of composite nanofiber membrane
And (4) treating the base film obtained in the step (3) with 100mL of hydroxylamine hydrochloride and anhydrous sodium carbonate at 70 ℃ for 2h to obtain the amidoxime nanofiber film. The resulting modified fiber membrane was dried at 60 ℃.
(5) Adsorption of Pb in water by amidoxime fiber membrane2+(same as example 1)
Adding the fiber membrane into a lead-containing aqueous solution, performing oscillatory adsorption for 10h, taking the supernatant of the solution, measuring the concentration of the solution before and after adsorption reaction by ICP-OES, and calculating the Pb content of the fiber membrane2+The amount of adsorption of (3).
The strength before modification was found to be similar to that of example 1, but the amount of adsorption of lead ions in the aqueous solution of the modified composite fiber membrane was 51.7mg/g, and after repeating the modification 5 times, the amount of adsorption of lead ions was 22.5 mg/g. Researches find that the adsorption performance has a large influence.

Claims (10)

1. A metal adsorption fiber membrane is characterized in that the membrane is formed by interlacing and weaving PVDF @ PAN composite fibers;
the PVDF @ PAN composite fiber comprises a PVDF core fiber and a PAN shell layer coated on the PVDF core fiber, wherein the outer surface of the PAN shell layer is a functional layer subjected to oximation and/or carboxylation modification treatment.
2. The metal-adsorbing fiber membrane according to claim 1, wherein the PVDF core fiber has a diameter of 0.36-0.45 μ ι η;
preferably, the thickness of the PAN shell layer is 0.24-0.32 μm;
preferably, in the outer-layer PAN, the proportion of the functional layer is 50-85%.
3. A method for preparing a metal-adsorbing fibrous membrane according to claim 1 or 2, comprising the steps of:
step (1):
obtaining a solution A dissolved with PVDF and a solution B dissolved with PAN; performing coaxial electrostatic spinning treatment on the solution A serving as core liquid and the solution B serving as outer layer casting solution to obtain a PVDF @ PAN base film; the concentration of PVDF in the solution A is 6-12 wt%; the concentration of PAN in the solution B is 10-14 wt%;
the voltage of the electrostatic spinning process is 13-15 KV;
step (2):
performing functional modification treatment on the outer surface of the PAN of the PVDF @ PAN base film, and then performing freeze drying to obtain the PVDF @ PAN base film;
the functionalization is oximation and/or carboxylation.
4. The method for preparing a metal-adsorbing fiber membrane according to claim 3, wherein the molecular weight of PVDF is 15 to 25 ten thousand; preferably, the PVDF is PVDF 6020;
preferably, the solvent in the solution a is a solvent capable of dissolving PVDF, preferably at least one of N, N-dimethylacetamide and N, N-dimethylformamide;
preferably, the content of PVDF in the solvent A is 10-12 wt.%.
5. The method for producing a metal-adsorbing fibrous membrane according to claim 3,
the molecular weight of the PAN is 13-16 ten thousand;
preferably, the solvent in the solution B is a solvent capable of dissolving PAN, preferably at least one of N, N-dimethylacetamide and N, N-dimethylformamide;
preferably, the PAN content in the solvent B is 11 to 13 wt.%; further preferably 11.5 to 12.5 wt.%.
6. The method for preparing a metal-adsorbing fiber membrane according to claim 3, wherein the spinning voltage is 13.5-14.5 KV in the electrostatic process.
7. The method for preparing a metal-adsorbing fiber membrane according to claim 3, wherein in the electrostatic process, the distance between the coaxial spinneret and the receiving plate is 14-16 cm; the flow rate of PAN is 0.5-1mL/h and the flow rate of PVDF is 0.5-1 mL/h.
8. The method for preparing a metal-adsorbing fibrous membrane according to claim 3, wherein the oximation surface treatment comprises the steps of:
placing the PVDF @ PAN base film into a modified solution a in which hydroxylamine and alkali are dissolved, and carrying out surface oximation treatment;
preferably, the alkali is at least one of anhydrous sodium carbonate and anhydrous sodium bicarbonate;
in the modified solution a, the molar ratio of hydroxylamine to alkali is 1:1-2.5: 1;
preferably, in the modification solution a, the molar concentration of hydroxylamine is 0.4-0.6 mol/L;
preferably, the temperature of the oximation modification process is 60-80 ℃;
preferably, the time for the oximation modification process is 60-180 min.
9. The method for preparing a metal-adsorbing fibrous membrane according to claim 3, wherein the step of the carboxylated surface treatment comprises:
placing the PVDF @ PAN base membrane into a modified solution b in which alkali is dissolved, and performing surface carboxylation treatment;
preferably, the alkali is at least one of sodium hydroxide and potassium hydroxide;
preferably, the molar concentration of the alkali in the modification solution b is 1-5 mol/L;
preferably, the temperature of the oximation modification process is 60-80 ℃;
preferably, the time of the oximation modification process is 30-120 min;
preferably, the metal adsorption fiber membrane is obtained by freeze drying after surface modification;
preferably, the freeze-drying time is 4-7 h.
10. Use of a metal-adsorbing fiber membrane according to any one of claims 1 to 2 or a metal-adsorbing fiber membrane prepared by the method according to any one of claims 3 to 9 for adsorbing lead metal ions;
preferably for adsorbing lead metal ions in an aqueous solution.
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