CN118371133A - Preparation of a positively charged two-dimensional MXene-PEI membrane and its application in acid recovery - Google Patents

Abstract

The invention discloses preparation of a positively-modified two-dimensional MXene-PEI membrane and application thereof in acid recovery, and belongs to the technical field of membrane separation. The preparation method of the positively modified two-dimensional MXene film comprises the following steps: mixing lithium salt, acid and MAX phase raw materials to obtain mixed solution, and reacting to obtain a single-layer MXene nanosheet solution; mixing the MXene nano-sheet solution with positively charged polyelectrolyte to obtain a mixed system, and reacting to obtain a positively-modified MXene nano-sheet solution; and coating the positively-modified MXene nano-sheet solution into a film shape, and drying to obtain the positively-modified two-dimensional MXene film. The membrane material designed by the invention well solves the problem that the existing separation membrane can not achieve both the acid diffusion capacity and the membrane selectivity, and has excellent stability in the acid recovery cyclic permeation test and good application prospect.

Description

Preparation of a positively charged two-dimensional MXene-PEI membrane and its application in acid recovery

Technical Field

The present invention relates to the field of membrane separation technology, and in particular to the preparation of a positively charged modified two-dimensional MXene-PEI membrane and its application in acid recovery.

Background technique

In the industrial production process such as metal smelting, electroplating, etching and mining, a large amount of inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, etc. are needed to clean the metal surface or leach metal components. During this process, waste acid with strong acidity and corrosiveness will be produced. If this substance is directly discharged without treatment, it will have a huge impact on the surrounding ecological environment, such as changing the pH value of the water body, interfering with the self-purification of the water body, and endangering the growth of aquatic organisms. If the inorganic acids and various metal ions contained in these waste acids are directly discharged, it will also lead to serious waste of resources. Therefore, waste acid resource recovery has gradually become the mainstream way of waste acid treatment.

Traditional methods for treating waste acid include: neutralization precipitation, distillation, solvent extraction, etc., but these methods have problems such as secondary pollution, high energy consumption, and cumbersome operation. Membrane treatment technology has the advantages of low energy consumption, small equipment footprint, and high separation efficiency, and is widely used in wastewater treatment. Separation membrane is the core of the entire membrane treatment technology. The membrane materials currently reported for acid recovery are mainly organic polymer membranes based on organic polymer materials such as polysulfone (PSf), polyvinyl alcohol (PVA), and polyphenylene ether (PPO). However, due to the characteristics of organic polymers themselves, they are insufficient in thermal stability and mechanical stability. When the operating time is long, waste acid will cause partial degradation of membrane materials and greatly reduce separation performance. In addition, there is a restrictive relationship between the permeability and separation performance of polymer membranes. Therefore, developing high-performance new separation membrane materials, achieving a balance between high permeability and high selectivity, and improving the operational stability of the membrane are the focus of promoting membrane treatment technology for acid recovery.

The two-dimensional membrane is assembled from two-dimensional nanosheets and relies on the two-dimensional channels formed between the sheets to achieve mass transfer. It is a high-precision separation at the molecular and ionic levels and is an ideal alternative to traditional polymer membranes. At present, some researchers have tried to use two-dimensional membranes for acid recovery, showing good acid permeability and selectivity, proving that two-dimensional membrane materials have broad prospects in the field of acid recovery. For example, the Journal of Membrane Science (618 (2021) 118692) reported an imidazolium cation-modified graphene oxide membrane, which adjusted the size and chemical environment of the interlayer channels of the two-dimensional graphene oxide membrane by imidazolium cations, significantly improving the H ⁺ dialysis coefficient and selectivity of the graphene oxide membrane. However, compared with high-performance commercial membranes, there is still a certain gap, and there is still room for improvement in acid permeability and selectivity, which still needs further improvement.

Summary of the invention

In order to solve the problem that the acid dialysis coefficient and selectivity of the current acid recovery separation membrane still need to be further improved and high acid diffusion capacity and high selectivity cannot be achieved at the same time, the purpose of the present invention is to provide a preparation method of a positively charged modified two-dimensional MXene membrane and its application in diffusion dialysis acid recovery. The positively charged modified two-dimensional MXene membrane of the present invention has high acid diffusion capacity and high selectivity, and shows good stability in the cycle performance test.

To achieve the above object, the present invention provides the following technical solutions:

One of the technical solutions of the present invention is to provide a positively charged modified two-dimensional MXene film, wherein the MXene film is composed of a two-dimensional MXene film with a positively charged polyelectrolyte inserted between layers, and has a thickness of 500 nm.

The second technical solution of the present invention is to provide a method for preparing the above-mentioned positively charged modified two-dimensional MXene film, comprising the following steps:

(1) mixing a lithium salt, an acid and a MAX phase raw material to obtain a mixed solution, reacting the mixture to obtain a single-layer MXene nanosheet solution;

(2) mixing the MXene nanosheet solution with a positively charged polyelectrolyte to obtain a mixed system, and reacting to obtain a positively charged modified MXene nanosheet solution;

(3) coating the positively charged modified MXene nanosheet solution into a thin film and drying it to obtain the positively charged modified two-dimensional MXene film.

Preferably, in step (1), the acid is hydrochloric acid with a concentration of 7-12 mol/L, the ratio of the lithium salt, the acid and the MAX phase raw material in the mixed solution is 1.5-3 g:80 mL:1.5-3 g, the reaction temperature is 30-50° C., and the reaction time is 12-72 h.

Preferably, the MAX phase raw material is one or more of Ti ₂ AlC, V ₂ AlC, Ti ₃ SiC ₂ , Ti ₃ AlC ₂ , Ti ₃ AlN ₃ and Nb ₄ AlC ₃ .

Preferably, in step (2): in the mixed system, the mass ratio of MXene nanosheets to positively charged polyelectrolyte is 1:1-1:8; and the reaction is carried out under a protective atmosphere for 24 hours.

Preferably, the positively charged polyelectrolyte is one or more of polyethyleneimine (PEI), polydiallyldimethylammonium chloride (PDDA) and poly 4-vinylpyridine (P4VP).

Preferably, the drying is vacuum drying at 80° C. for 24 hours; the method of coating into a thin film is to filter the positively charged modified MXene nanosheet solution onto a nylon substrate through a vacuum filtration device.

The third technical solution of the present invention is to provide an application of the above-mentioned positively charged modified two-dimensional MXene membrane in the field of waste acid recovery.

The fourth technical solution of the present invention is to provide a method for recovering waste acid, comprising the following steps:

The above-mentioned positively charged modified two-dimensional MXene membrane was placed in an ion separation test device, waste acid was added to the raw material side, and water was added to the permeate side, and hydrogen ions and metal ions were selectively separated by driving the concentration difference.

Waste acid contains both inorganic acids and metal salts. The positively charged modified two-dimensional MXene membrane of the present invention can treat inorganic acids such as HCl, H ₂ SO ₄ , HNO ₃ , and the H ⁺ concentration can be 1-5 mol/L; it can also treat metal salts such as NaCl, KCl, CuCl ₂ , FeCl ₂ , FeSO ₄ , CuSO _{4 , AlCl 3 ,} Al ₂ (SO ₄ ) ₃ , Al(NO ₃ ) ₃ , and the concentration of metal cations is 0.1 mol/L.

The beneficial technical effects of the present invention are as follows:

The present invention inserts a positively charged polyelectrolyte into the interlayer channel of the two-dimensional MXene membrane. On the one hand, the introduction of the polyelectrolyte expands the interlayer distance of the MXene membrane and the interlayer mass transfer channel, which makes the H ⁺ permeation rate of the modified membrane much greater than that of the original membrane, and the diffusion rate of the acid is significantly enhanced. On the other hand, the positively charged polyelectrolyte modifies the interlayer channel of the two-dimensional MXene membrane, which was originally negatively charged, into positively charged, thereby enhancing the membrane's repulsion performance to metal cations and effectively improving the membrane selectivity.

The positively charged modified two-dimensional MXene membrane obtained by the present invention has excellent acid recovery performance in waste acid systems of different types and concentrations, and can efficiently intercept various metal ions such as Cu ²⁺ , Fe ²⁺ , Al ³⁺ , etc., to achieve efficient separation.

The membrane material designed in the present invention solves the problem that the existing separation membranes cannot achieve both acid diffusion and membrane selectivity, and exhibits excellent stability in acid recovery cycle permeation tests. It has the characteristics of simple preparation method, easy implementation, good repeatability, a large number of functional groups on the surface as reaction sites, and an inorganic high-stability structure, and has good application prospects in the field of acid recovery.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

Figure 1 is a SEM image of the membrane surface and the membrane cross section of the membrane material of Example 1. Among them, (a) is a SEM image of the membrane surface, and (b) is a SEM image of the membrane cross section.

FIG. 2 is a graph showing the acid recovery performance test results of the products of Examples 1-5 and Comparative Example 1.

FIG. 3 is a graph showing the results of the cyclic permeation test of the product of Example 4.

FIG. 4 is a graph showing the acid recovery performance test results of the membrane material of Example 4 in acid systems of different concentrations.

Detailed ways

Now, various exemplary embodiments of the present invention are described in detail, which should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the invention.

The words “include,” “including,” “have,” “contain,” etc. used in the present invention are all open-ended terms, meaning including but not limited to.

All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

Example 1

Preparation of positively charged two-dimensional MXene film:

(1) Preparation of MXene nanosheet solution: 1.5 g LiF was mixed with 80 mL 8 M hydrochloric acid solution, and then 2 g MAX phase raw material (Ti ₃ AlC ₂ ) was slowly added to the mixed solution and stirred at 40 °C for 24 h. The suspension after the reaction was centrifuged and washed several times at 5000 rpm until the supernatant was neutral. The lower layer of nanosheet precipitate was dispersed in 120 mL deionized water, and ultrasonicated for 10 min in an argon atmosphere. The volume was fixed to obtain a single-layer MXene nanosheet solution with a nanosheet concentration of 4.5 mg/mL.

(2) PEI positively modified MXene nanosheets: 10 mL of a single-layer MXene nanosheet solution and 9 mL of a 5 mg/mL PEI solution were mixed, wherein the mass ratio of MXene nanosheets to PEI was 1:1. The mixture was magnetically stirred in an argon atmosphere for 24 h, and then the resulting solution was centrifuged to remove the PEI that was not grafted onto the MXene nanosheets, thereby obtaining a positively modified MXene nanosheet solution.

(3) Vacuum filtration to form a membrane: The positively charged modified MXene nanosheet solution was filtered onto a nylon substrate through a vacuum filtration device and vacuum dried at 80° C. for 24 h to obtain a positively charged modified two-dimensional MXene membrane (denoted as MXene-PEI ₁ ).

Figure 1 is a SEM image of the membrane surface and the membrane cross section of the membrane material of Example 1. Among them, (a) is a SEM image of the membrane surface, and (b) is a SEM image of the membrane cross section.

Example 2

Preparation of positively charged two-dimensional MXene film:

The relevant operations of step (1) are shown in Example 1.

(2) PEI positively modified MXene nanosheets: 5 mL of single-layer MXene nanosheet solution and 9 mL of PEI solution with a mass concentration of 5 mg/mL were mixed, where the mass ratio of MXene nanosheets to PEI was 1:2. The mixture was magnetically stirred in an argon protection environment for 24 h, and then the reacted solution was centrifuged and washed to remove the PEI that was not grafted onto the MXene nanosheets in the system, thereby obtaining a positively modified MXene nanosheet solution.

The relevant operations of step (3) are shown in Example 1, and a positively charged modified two-dimensional MXene film (denoted as MXene-PEI ₂ ) is prepared.

Example 3

Preparation of positively charged two-dimensional MXene film:

The relevant operations of step (1) are shown in Example 1.

(2) PEI positively modified MXene nanosheets: 2.5 mL of single-layer MXene nanosheet solution and 9 mL of 5 mg/mL PEI solution were mixed, where the mass ratio of MXene nanosheets to PEI was 1:4. The mixture was magnetically stirred in an argon atmosphere for 24 h, and then the reacted solution was centrifuged and washed to remove the PEI that was not grafted onto the MXene nanosheets in the system, thereby obtaining a positively modified MXene nanosheet solution.

The relevant operations of step (3) are shown in Example 1, and a positively charged modified two-dimensional MXene film (denoted as MXene-PEI ₄ ) is prepared.

Example 4

Preparation of positively charged two-dimensional MXene film:

The relevant operations of step (1) are shown in Example 1.

(2) PEI positively modified MXene nanosheets: 6 mL of single-layer MXene nanosheet solution and 32.4 mL of 5 mg/mL PEI solution were mixed, where the mass ratio of MXene nanosheets to PEI was 1:6. The mixture was magnetically stirred in an argon atmosphere for 24 h, and then the reacted solution was centrifuged and washed to remove the PEI that was not grafted onto the MXene nanosheets in the system, thereby obtaining a positively modified MXene nanosheet solution.

The relevant operations of step (3) are shown in Example 1, and a positively charged modified two-dimensional MXene film (denoted as MXene-PEI ₆ ) is prepared.

Example 5

Preparation of positively charged two-dimensional MXene film:

The relevant operations of step (1) are shown in Example 1.

(2) PEI positively modified MXene nanosheets: 2.5 mL of a single-layer MXene nanosheet solution and 18 mL of a 5 mg/mL PEI solution were mixed, wherein the mass ratio of MXene nanosheets to PEI was 1:8. The mixture was magnetically stirred in an argon atmosphere for 24 h, and then the reacted solution was centrifuged and washed to remove the PEI that was not grafted onto the MXene nanosheets in the system, thereby obtaining a positively modified MXene nanosheet solution.

The relevant operations of step (3) are shown in Example 1, and a positively charged modified two-dimensional MXene film (denoted as MXene-PEI ₈ ) is prepared.

Comparative Example 1

The only difference from Example 1 is that no positive charge modification is performed, and the single-layer MXene nanosheet solution of step (1) is directly filtered to form a membrane to obtain a two-dimensional MXene membrane (denoted as MXene).

Effect verification

(1) The films prepared in Examples 1-5 and Comparative Example 1 were placed in an ion permeation device, wherein the effective area for diffusion dialysis was 1.76 cm ² . A mixed solution of 1 mol/L HCl+0.1 mol/L FeSO ₄ was added to the raw material chamber to simulate waste acid, and an equal amount of deionized water was added to the permeation chamber. The ion permeation test was performed for 5 hours, during which the two chambers were stirred with an electromagnetic to prevent concentration polarization. After 5 hours, the solutions in the two chambers were taken out respectively, and the concentration of H ⁺ was determined by acid-base titration, and the concentration of Fe ²⁺ was determined by inductively coupled plasma mass spectrometry (ICP-MS), and the dialysis coefficient U and selectivity S of the corresponding ions were calculated. The test results are shown in FIG2 .

The calculation formula of the dialysis coefficient U is:

Wherein, M represents the molar number of ion diffusion (mol); A represents the effective area for diffusion dialysis (m ² ); t represents time; ΔC represents the logarithmic mean concentration between the two chambers (mol/m ³ ).

The calculation formula of ΔC is:

Where _Cf0 and _Cft represent the concentrations of the solution in the feed chamber at time 0 and t, respectively (mol/L), and _Cdt represents the concentration of the solution in the permeate chamber at time t (mol/L). It should be noted that ( _Cf0 - _Cdt - _Cft ) is not equal to zero, because water is transferred through the membrane, resulting in a change in the volume of the solutions in the two chambers.

The calculation formula of selectivity S is:

In the formula, _UH+ represents the dialysis coefficient of H ⁺ , and _UFe2+ represents the dialysis coefficient of ^Fe2+ .

Figure 2 is a graph showing the acid recovery performance test results of the products of Examples 1-5 and Comparative Example 1. As shown in Figure 2, the H ⁺ dialysis coefficient and membrane selectivity of the membrane modified by PEI positive charge are significantly better than those of the original membrane, and the positively charged modified membrane can effectively enhance its selectivity while increasing its acid diffusion coefficient.

(2) The film prepared in Example 4 was placed in an ion permeation device, and a mixed solution of 1mol/L HCl+0.1mol/L _FeSO4 was added to the raw material chamber to simulate waste acid, and an equal amount of deionized water was added to the permeation chamber. The ion permeation test was performed for 5 hours, during which the two chambers were stirred with an electromagnetic to prevent concentration polarization. After 5 hours, the solutions in the two chambers were taken out for measurement, and then the membrane surface and the inner walls of the two chambers were cleaned with deionized water. Then, 1mol/L HCl+0.1mol/ _LFeSO4 solution was added to the raw material chamber again, and an equal amount of deionized water was added to the permeation chamber for the next round of ion permeation test, and this was repeated. The method for determining the ion concentration in the solution and the method for calculating the performance were consistent with those in effect verification (1). The test results are shown in Figure 3.

Figure 3 is a graph showing the results of the cyclic permeation test of the product of Example 4. As can be seen from the figure, in multiple rounds of cyclic tests, the H ⁺ dialysis coefficient and selectivity of the membrane did not fluctuate significantly, indicating that the positively charged modified membrane has good stability.

(3) The film prepared in Example 4 was placed in an ion permeation device, and a mixed solution of 0.5, 1, 1.5, 2, and 3 mol/L HCl+0.1 mol/L FeSO ₄ was added to the raw material chamber, and the test was carried out in sequence. An equal amount of deionized water was added to the permeation chamber, and the ion permeation test was carried out for 5 hours. During the test, the two chambers were stirred with an electromagnetic to prevent concentration polarization. After 5 hours, the solutions in the two chambers were taken out for measurement. The method for measuring the ion concentration in the solution and the method for calculating the performance were consistent with those in effect verification (1). The test results are shown in Figure 4.

Figure 4 is a graph showing the acid recovery performance test results of the membrane material of Example 4 in acid systems of different concentrations. As shown in Figure 4, the membrane material exhibits high acid diffusivity and selectivity in acid systems of different concentrations, indicating that the positively charged modified membrane is suitable for acid separation systems of various concentrations.

The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims (9)

1. A positively-modified two-dimensional MXene film, characterized in that the MXene film consists of a two-dimensional MXene film with a thickness of 500nm intercalated between layers of positively-charged polyelectrolyte.

2. A method of preparing the positively modified two-dimensional MXene film of claim 1 comprising the steps of:

(1) Mixing lithium salt, acid and MAX phase raw materials to obtain mixed solution, and reacting to obtain a single-layer MXene nanosheet solution;

(2) Mixing the MXene nano-sheet solution with positively charged polyelectrolyte to obtain a mixed system, and reacting to obtain a positively-modified MXene nano-sheet solution;

(3) And coating the positively-modified MXene nano-sheet solution into a film shape, and drying to obtain the positively-modified two-dimensional MXene film.

3. The method according to claim 2, wherein in step (1): the acid is hydrochloric acid with the concentration of 7-12mol/L, the ratio of the lithium salt to the acid to the MAX phase raw material in the mixed solution is 1.5-3g, 80mL and 1.5-3g, the reaction temperature is 30-50 ℃, and the reaction time is 12-72h.

4. The method of claim 2, wherein the MAX phase feedstock is one or more of Ti₂AlC、V₂AlC、Ti₃SiC₂、Ti₃AlC₂、Ti₃AlN₃ and Nb ₄AlC₃.

5. The method according to claim 2, wherein in step (2): in the mixed system, the mass ratio of the MXene nano-sheet to the positively charged polyelectrolyte is 1:1-1:8; the reaction is carried out for 24 hours under a protective atmosphere.

6. The method of claim 2, wherein the positively charged polyelectrolyte is one or more of polyethylenimine, polydiallyldimethyl ammonium chloride, and poly 4-vinylpyridine.

7. The method of claim 2, wherein the drying is vacuum drying at 80 ℃ for 24 hours; the method for coating the membrane is to carry out suction filtration on the MXene nano-sheet solution subjected to positive modification on a nylon substrate through a vacuum suction filtration device.

8. Use of the positively modified two-dimensional MXene film of claim 1 in the field of spent acid recovery.

9. A method for waste acid recovery, comprising the steps of:

the positively-modified two-dimensional MXene membrane of claim 1 in which spent acid is added on the raw material side and water is added on the permeate side, and hydrogen ions and metal ions are selectively separated by driving the concentration difference.