Mn-mof modified single-cone nanochannel pet film and preparation method and application thereof

Abstract

The application discloses a Mn-MOF modified single-cone nanochannel PET film and a preparation method and application thereof, the PET film is etched with single-cone nanochannels, and Mn-MOF is fixed on the inner surface of the single-cone nanochannel of the PET film after ammonia treatment through a nanointerface in-situ growth method.The preparation method comprises the following steps: step 1, etching a single-cone nanochannel of a PET film; step 2, ammonia treatment is performed on the PET film obtained in step 1; and step 3, Mn-MOF modification is performed on the single-cone nanochannel of the PET film in step 2.The obtained Mn-MOF modified single-cone nanochannel PET film is applied to thallium ion selective transmission and thallium metal extraction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heavy metal extraction, and particularly relates to a Mn-MOF (metal-organic frameworks) modified single-cone nanochannel PET film and a preparation method and application thereof. BACKGROUND

[0002] Thallium is a typical rare element, and the global pure thallium production is very low. However, with the rapid development of contemporary industrial technology, the demand for thallium is increasing. At present, thallium pollution mainly comes from mineral exploitation and plant kongen combustion. About 5000 tons of thallium are released into the environment every year. After these thalliums enter the water environment, they participate in the water cycle, and finally accumulate in organisms through the food chain, leading to poisoning. The existing methods for treating thallium-containing wastewater mainly include ion exchange, solvent extraction, oxidation precipitation, coagulation and adsorption. However, these treatment technologies have the problems of waste of thallium resources and great pollution to the water environment. Therefore, it is particularly important to develop a method for selective extraction of thallium ions.

[0003] In recent years, more and more researchers have paid attention to the application of solid-state nanochannels in intelligent regulation of ion and molecule transport. Among various solid-state nanochannels, the nanochannel prepared by chemical etching of ion tracks in polymer film is widely used due to its simple process, controllable channel shape and size, good mechanical properties, easy chemical modification and other advantages. It has been used to construct many ion separation and detection platforms, especially for selective screening of alkali metal ions such as lithium, sodium and potassium. However, there is no report on selective separation and extraction in solid-state nanochannels. +

[0004] Chinese patent document CN 113041860 A discloses a water system nanochannel separation membrane for ionophilic and hydrophobic molecules and a preparation method and application thereof. The nanochannel separation membrane is prepared by filling a liquid organic compound which is immiscible with water and has high polarity into the nanochannel of a polymer film. The liquid organic compound is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, chloroform and carbon tetrachloride. The nanochannel separation membrane can promote the transmission of ions and effectively inhibit the transmission of water molecules. The pore size of the nanochannel in the membrane can be used for selective transmission of various ions.

[0005] The patent has the following disadvantages: only the accelerated transmission of alkali metal ions such as Li+, Na+or K+ions in the water-based electrolyte battery is completed, the transmission of water molecules to the electrode direction is effectively inhibited, the electrolysis of water molecules is inhibited, the water-based battery with high discharge voltage is obtained, and the cost of the water-based electrolyte battery is reduced. However, the nanochannel separation membrane does not have the functions of selective transmission and separation of Tl + ions.​

[0006] Chinese patent document CN 109459481 B published on September 18, 2020 discloses a modification method of biomimetic nanochannel and application of biomimetic nanochannel, which places the substrate with biomimetic nanochannel between utility polyelectrolyte solution and matching polyelectrolyte solution, and under the induction of electric field, self-assembly is realized in the biomimetic nanochannel through electric crosslinking, and the modification of the biomimetic nanochannel is completed. The substrate material with biomimetic nanochannel comprises polyethylene terephthalate, and the modification method greatly widens the selection range of utility polyelectrolyte, has the advantages of short modification time, good response effect, and reversible modification process, and the prepared biomimetic nanochannel can be applied to nanofluidic devices, but it does not mention how to modify Mn-MOF in situ in the single-cone nanochannel, and it does not mention its responsiveness to metal thallium.

[0007] Therefore, in order to overcome the problem of waste of thallium resources, it is of great importance to develop a solid-state nanochannel for selective screening and extraction of thallium ions. SUMMARY

[0008] In view of the problems existing in the prior art thallium ion extraction technology, the technical problem to be solved by the present application is to provide a Mn-MOF modified single-cone nanochannel PET film which can selectively enrich and extract thallium ions. The present application also provides a preparation method and application of the nanochannel PET film.

[0009] In order to solve the above technical problems, the technical scheme of the present application is:

[0010] The Mn-MOF modified single-cone nanochannel PET film provided by the present application comprises a polyethylene terephthalate (PET) film, the PET film is etched with a single-cone nanochannel, and Mn-MOF is fixed on the inner surface of the single-cone nanochannel of the ammoniated PET film by a nanointerface in-situ growth method.

[0011] The preparation method of the Mn-MOF modified single-cone nanochannel PET film provided by the present application comprises the following steps:

[0012] Step 1, etching a single-cone nanochannel of a PET film

[0013] The PET film is clamped between the left and right chambers of an etching tank, a stopping solution is added to the left chamber of the etching tank, an etching solution is added to the right chamber, platinum sheet electrodes are respectively inserted into the left and right chambers, an external voltage is constant at 1V, the current change of the current-time (i-t) curve is observed, the current is suddenly changed and maintained for a period of time, then the voltage is turned off to suck out the etching solution, the stopping solution is added to the right chamber for flushing, then the PET film is taken out from the etching tank and repeatedly washed with distilled water to obtain a single-cone nanochannel PET film.

[0014] Step 2, ammoniation is performed on the PET film obtained in step 1

[0015] The carboxyl group of the PET film is activated by using a mixed solution of carbodiimide and N-hydroxysuccinimide to contact the reverse side of the PET film, and then the PET film is treated with an ethylenediamine solution overnight to obtain an amino-functionalized nanochannel;

[0016] Step 3, Mn-MOF modification of the single-cone nanochannel of the PET film in step 2

[0017] The PET film in step 2 is placed in the middle of an electrolytic cell, 2,4,6-benzoic acid aqueous solution is added to the tank contacted by the tip surface of the single-cone nanochannel of the PET film, manganese nitride aqueous solution is added to the other tank, the two preheated solutions are sealed in a reaction kettle, the reaction kettle is placed in an oven for reaction, after the reaction is completed, the PET film is taken out after cooling to room temperature, washed with distilled water, and dried with N2 to obtain a single-cone nanochannel PET film modified by Mn-MOF.

[0018] The application also provides an application of the single-cone nanochannel PET film modified by Mn-MOF in selective transmission of thallium ions and extraction of thallium metal.

[0019] The technical effects of the application are:

[0020] The application fills the MOF structure uniformly in the inner surface of the single-cone nanochannel on the PET film by combining manganese and organic ligands, and the Tl + specifically binds to the MOF structure in the single-cone nanochannel, showing high selective one-way transmission characteristics for Tl + , and the extraction effect of thallium reaches 87.3%. The application can separate and extract thallium from a solution of multiple metal ions. BRIEF DESCRIPTION OF DRAWINGS

[0021] The brief description of the drawings of the application is as follows:

[0022] Figure 1 It is a structural schematic diagram of an etching tank;

[0023] Figure 2 It is a current change of the PET film etched into a conical nanochannel;

[0024] Figure 3 It is a scanning electron microscope image of the PET film;

[0025] (a) unetched PET film, (b) porous PET film after etching;

[0026] Figure 4 It is a comparison test diagram of thallium ion drift diffusion experiments of three ion channel membranes;

[0027] Figure 5 It is a K+ Na + 、Tl + IV characteristic curves of three ion selectivity experiments. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0029] Example: Preparation of Mn-MOF-modified single-cone nanochannel PET membrane

[0030] Step 1: Etching single-cone nanochannels in PET film

[0031] A chemical etching method was used, in which the front and back sides of a PET film bombarded by single ion tracks were sensitized under ultraviolet light for 1 hour and then placed in an etching bath. Figure 1 As shown, the etching tank includes a left chamber, a right chamber, and a PET film held in place at the central connection. 10 mL of stop solution (1 mol / L HCOOH + 1 mol / L KCl) is added to the left chamber, and 10 mL of etching solution (9 mol / L NaOH + 0.025% sodium dodecyl diphenyl ether disulfonate) is added to the right chamber. A platinum electrode is inserted into each of the left and right chambers, and the applied voltage is kept constant at 1 V. The change in current in the current-time (it) curve is observed using an ammeter. Figure 2 As shown, a sudden increase in current indicates the formation of nanochannels during etching. The current was maintained at 10. -8 After 30 minutes of continuous etching, the voltage is disconnected and the etching solution is extracted. A stop solution is added to the right chamber and rinsed for 15 minutes to neutralize the etching solution on the surface of the PET film. Then, the PET film is removed from the etching tank and rinsed three times with distilled water to clean the stop solution off the surface of the PET film, thus obtaining a single-cone nanochannel PET film. The side of the PET film that is in contact with the etching solution and forms the large opening of the nanochannel is called the front side of the PET film, also known as the PET film substrate. The side that is in contact with the stop solution and forms the small opening of the nanochannel is called the back side of the PET film, also known as the tip of the PET film nanochannel.

[0032] Step 2: Ammoniation of the PET film obtained in Step 1

[0033] The carboxyl groups were activated by contacting the reverse side of a PET film with a mixed solution of carbodiimide (EDC) and N-hydroxysuccinimide (NHSS) for 1 h, and then the PET film was treated overnight with 0.1 mol / L ethylenediamine (EDA) solution to obtain amino-functionalized nanochannels (abbreviated as PET@NH2).

[0034] Step 3: Mn-MOF modification of the PET membrane single-cone nanochannels from step 2

[0035] Using a nano-interface growth method, 360 mg of 2,4,6-benzoic acid (H3BTC) was dissolved in 10 mL of distilled water and stirred for 30 min, denoted as solution A; a 50% (w / w) manganese nitride aqueous solution was prepared, denoted as solution B. The amino-functionalized nanochannel PET membrane was placed in an H-type electrolytic cell (the structure of which is similar to...) Figure 1 (The etching tank structure is the same as that without electrodes) In the middle, solutions A and B are heated to 90°C on a preheating plate and then placed on the channel tip and both sides of the substrate of PET@NH2, respectively. Then, the H-type electrolytic cell is sealed in a reaction vessel with a polytetrafluoroethylene liner and the reaction vessel is placed in an oven at 100°C for 48 hours. After cooling to room temperature, the PET membrane is taken out, rinsed three times with distilled water, and dried with N2 to obtain the Mn-MOF-PET@NH2 membrane single conical nanochannel, that is, the Mn-MOF modified single conical nanochannel PET membrane (abbreviated as Mn-MOF-PET@NH2).

[0036] Comparative example: used to measure the size of a single conical nanopore

[0037] Since a single conical nanopore membrane has only one pore, it is difficult to pinpoint its exact location even under electron microscopy magnification of tens of thousands of times. Therefore, the size of the single pore is inferred from the dimensions of the multi-porous conical membrane.

[0038] The preparation process of porous conical nanochannel PET membranes differs from that of the PET membranes prepared by single-ion track bombardment in that the current stabilizes at 2 × 10⁻⁶ after a sudden increase. -7 A.

[0039] Figure 3 (a) is an unetched single-ion track PET film; Figure 3 (b) is a scanning electron microscope (SEM) image of the porous conical nanochannel PET film after etching. Based on the SEM images, the average size of the macropores at the ends of the porous conical nanochannels was calculated to be 159 nm. At 0.1 V, an inert electrode (Ag / AgCl electrode) was used to test the IV curve of the nanochannels in 1 M KCl solution (voltage scan range ±0.1 V, step size 0.01 V / s, within which the IV characteristic curve exhibits obvious ohmic behavior). The nanochannel conductance G = nG0 = I / U, where G0 is the conductance of a single nanochannel, n is the number of nanopores within the effective film contact area, and I is the current measured using a Keithley 6487 picoammeter. After obtaining the response values, according to the literature "Study on Ion Transport and Magnetron Effect in PET Nanochannels," Li Yaning, University of Chinese Academy of Sciences (Institute of Modern Physics, Chinese Academy of Sciences), page 25, the formula for calculating the size of the nanochannel tip is:

[0040]

[0041] Where k(c) is the conductivity of 1M KCl solution at 298K, which is 0.11173Ω. -1 cm -1 D base Let L be the diameter of the large opening of the nanopore and L be the thickness of the PET film. The calculated tip size of the single conical nanochannel is approximately 3.4 nm.

[0042] Therefore, it is possible to etch single-conical nanopores on a polyethylene terephthalate (PET) film, with an average size of 159 nm at the large end and 3.4 nm at the small end, and a PET film thickness of 7.0–7.3 μm.

[0043] Channel charge selectivity verification

[0044] To determine the charge selectivity of the PET membrane ion channels of the present invention, three membrane materials prepared in the examples—single-cone nanochannel PET, PET@NH2, and Mn-MOF-PET@NH2—were compared.

[0045] The three membrane materials were placed in the middle of an H-type electrolytic cell (which includes electrodes). The left and right chambers of the H-type electrolytic cell were filled with equal volumes of thallium nitrate solution at concentrations of 0.1 mmol / L and 1.0 mmol / L, respectively. The low-concentration electrolyte and the positive voltage electrode corresponded to the PET membrane substrate. Using an Ag / AgCl electrode, a scanning voltage (-2V to +2V) was applied across the membrane in steps of 0.05V / s, and the current was measured using a Keithley 6487 picoammeter.

[0046] Prior to the drift diffusion IV measurement, multiple IV scans were performed on the electrolyte at a lower concentration to eliminate the possible influence of cation exchange. Specifically, at least four IV measurements of 0.1 mmol / L thallium nitrate were performed in two electrolytic cells. Then, the 0.1 mmol / L thallium nitrate solution in the chamber on the reverse side of the PET membrane was replaced with 1.0 mmol / L thallium nitrate for the 1.0 mmol / L TlNO3 / 0.1 mM TlNO3 drift diffusion experiment.

[0047] Experimental results are as follows Figure 4 As shown, using I -2V / I +2V The ratio can be expressed as the selectivity of an ion channel for cations versus anions. For the PET ion channel, this value is 0.615, indicating that this channel preferentially transports NO3. - The value for PET@NH2 is 1.126 (≈1), indicating that this channel does not have strong charge selectivity; the value for Mn-MOF-PET@NH2 is 2.09, indicating that this channel preferentially transports Tl. + .

[0048] Cation selectivity experiment

[0049] To determine the effect of Mn-MOF-PET@NH2 membrane single-conical nanochannels on Tl + To assess the specificity of cation selection, the Mn-MOF-PET@NH2 prepared in Example 1 was placed in the middle of an H-type electrolytic cell. The left cell contained a 0.1 mmol / L solution of sodium nitrate, potassium nitrate, and thallium nitrate as the electrolyte, while the right cell contained an equal volume of distilled water. Using an Ag / AgCl electrode, with the positive electrode aligned with the tip of the PET nanochannel and the electrolyte solution, the scanning voltage was increased from -2V to +2V in steps of 0.05V / s. IV characteristic curves were plotted to determine the cation selection characteristics of Mn-MOF-PET@NH2. Simultaneously, inductively coupled plasma mass spectrometry (ICP-MS) was used to analyze the changes in cation concentration in the solutions on both sides, allowing for comparison of the ion channel's selective transport performance for sodium, potassium, and thallium cations.

[0050] Experimental results are as follows Figure 5 As shown, from Figure 5 The conductivities of the three ion solutions obtained in this ion channel were 0.28173 μS, 0.10718 μS, and 2.06215 μS, indicating that the Mn-MOF-PET@NH2 ion channel has a positive effect on Tl. + It exhibits high selectivity. Tl is obtained from the aqueous solution on the right. + The ion concentration was 17.84 mg / L, and the residual rate on the left side was only 12.7%. 87.3% of the thallium ions were selectively transported unidirectionally and extracted to the right side through the PET membrane of the present invention under the action of electric field force.

Claims

1. A Mn-MOF-modified single-cone nanochannel PET membrane, comprising a PET membrane, characterized in that: The PET film is etched with single-conical nanochannels, and Mn-MOF is fixed on the inner surface of the single-conical nanochannels on the ammoniated PET film by in-situ growth of nano-interfaces.

2. A method for preparing a Mn-MOF-modified single-cone nanochannel PET membrane, characterized in that, Includes the following steps: Step 1: Etching single-cone nanochannels in PET film The PET membrane was sandwiched between the left and right chambers of the etching tank. Stop solution was added to the left chamber and etching solution was added to the right chamber. Platinum electrodes were inserted into the left and right chambers respectively. The applied voltage was kept constant at 1V. The current change of the it curve was observed. After the current changed abruptly and was maintained for a period of time, the voltage was disconnected and the etching solution was extracted. Stop solution was added to the right chamber for rinsing. Then the PET membrane was taken out of the etching tank and rinsed repeatedly with distilled water to obtain a single cone-shaped nanochannel PET membrane. Step 2: Ammoniation of the PET film obtained in Step 1 The carboxyl groups of a PET membrane were activated by contacting the reverse side of the membrane with a mixed solution of carbodiimide and N-hydroxysuccinimide, and then the PET membrane was treated overnight with an ethylenediamine solution to obtain amino-functionalized nanochannels. Step 3: Mn-MOF modification of the PET membrane single-cone nanochannels from Step 2 The PET membrane from step 2 is placed in the middle of an electrolytic cell. 2,4,6-benzoic acid aqueous solution is added to the cell in which the tip of the single-cone nanochannel of the PET membrane is in contact, and manganese nitride aqueous solution is added to the other cell. After preheating the two solutions, the electrolytic cell is sealed in a reaction vessel, which is then placed in an oven for reaction. After the reaction is completed and cooled to room temperature, the PET membrane is removed, rinsed with distilled water, and dried with N2 to obtain the Mn-MOF modified single-cone nanochannel PET membrane.

3. The method for preparing the Mn-MOF-modified single-cone nanochannel PET membrane according to claim 2, characterized in that: in In step 1, the stopping solution is a mixture of 1 mol / L HCOOH and 1 mol / L KCl; the etching solution is a mixture of 9 mol / L NaOH and 0.025% sodium dodecyl diphenyl ether disulfonate.

4. The method for preparing the Mn-MOF-modified single-cone nanochannel PET membrane according to claim 2 or 3, characterized in that: In step 2, the concentration of the ethylenediamine solution is 0.1 mol / L.

5. The method for preparing the Mn-MOF-modified single-cone nanochannel PET membrane according to claim 4, characterized in that: The concentration of the 2,4,6-benzoic acid aqueous solution is 36 g / L.

6. The application of the Mn-MOF modified single-cone nanochannel PET membrane according to claim 1 in the selective transport and extraction of thallium ions.

7. The application according to claim 6, characterized in that: A Mn-MOF-modified single-cone nanochannel PET membrane was placed in the middle of an H-type electrolytic cell. One side of the cell was filled with thallium-containing electrolyte waste liquid, and the other side was filled with distilled water. An Ag / AgCl electrode was used, with the positive voltage electrode corresponding to the tip of the PET membrane nanochannel and the electrolyte waste liquid, and a DC voltage was applied.

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