WO2022217906A1

WO2022217906A1 - Modified multi-walled carbon nanotube, low-pressure membrane thereof, preparation method therefor and use thereof

Info

Publication number: WO2022217906A1
Application number: PCT/CN2021/130182
Authority: WO
Inventors: 郭瑾; 王钰
Original assignee: 北京工业大学
Priority date: 2021-04-14
Filing date: 2021-11-12
Publication date: 2022-10-20
Also published as: CN113104839A

Abstract

Provided is a preparation method for a modified multi-walled carbon nanotube, the method comprising: subjecting a multi-walled carbon nanotube and a humic acid solution to ultrasonic treatment to obtain a modified multi-walled carbon nanotube dispersion; and removing the solvent from the modified multi-walled carbon nanotube dispersion to obtain the modified multi-walled carbon nanotube. Furthermore, the modified multi-walled carbon nanotube dispersion is subjected to solid-liquid separation by using a microfiltration porous membrane to obtain a modified multi-walled carbon nanotube low-pressure membrane. The preparation method does not cause any damage to the structure and properties of the multi-walled carbon nanotube; and in addition, the ecological risk of a multi-walled carbon nanotube entering a water environment is avoided. The modified multi-walled carbon nanotube and the low-pressure membrane thereof are used for removing a methylene blue dye from an aqueous solution, and the removal method is simple, easy to implement, low-cost and highly efficient.

Description

A kind of modified multi-walled carbon nanotube and its low pressure membrane and preparation method and application

This application claims the priority of the Chinese patent application filed on April 14, 2021, with the application number of 202110401717.7 and the invention titled "A modified multi-walled carbon nanotube and its low-pressure membrane and its preparation method and application" , the entire contents of which are incorporated herein by reference.

technical field

The invention relates to the technical field of multi-walled carbon nanotubes, in particular to a modified multi-walled carbon nanotube and a low-pressure membrane thereof, as well as a preparation method and application thereof.

Background technique

Dyes are commonly found in wastewater from industries such as textiles, leather, paper, printing and cosmetics. Dye wastewater has the characteristics of large chroma, complex composition, high biological toxicity and refractory degradation, which brings great difficulties to the treatment of dye wastewater. The increasing discharge of dye wastewater into the aquatic environment will seriously harm biodiversity and the natural activities of aquatic systems. Many physical, chemical and biological methods, such as adsorption, membrane separation, ozone treatment, coagulation/flocculation, photocatalytic degradation, ion exchange, biosorption and biodegradation, have been used to remove wastewater from wastewater of dyes. Activated carbon is the most widely used conventional adsorbent in dye wastewater adsorption treatment. The pore structure of activated carbon is uneven, the pore size is widely distributed, the proportion of micropores and macropores is high, and the proportion of mesopores is small. Most of the dye molecules are larger in size, such as methylene blue, which is larger than 1.3 nm, and can only enter mesopores or micropores with larger pore sizes, which leads to low utilization efficiency of activated carbon. In addition, activated carbon contains a large proportion of inner pores, and the process of dye molecules diffusing from the liquid phase into the inner pores of activated carbon and being adsorbed is relatively slow. Using activated carbon to adsorb and purify dye wastewater requires a long equilibrium time, which is not conducive to the regeneration of saturated activated carbon. The removal effect of polar organics is relatively poor.

Carbon nanotubes (CNTs) have attracted much attention due to their ultra-high specific surface area and excellent mechanical, electrical and thermal properties. CNT has a clear structure, uniform surface, open adsorption surface and mesoporous structure, and CNT also has a good treatment effect on polar organics. The special structure of CNT enables its surface to be functionalized to remove pollutants of different properties. Among them, the multi-walled carbon nanotube (MWCNT) has a simple production process, a relatively cheap price and a wider range of applications. However, MWCNTs are prone to agglomeration when put into water, which reduces the available adsorption sites on the surface of MWCNTs and seriously affects the adsorption efficiency of MWCNTs. At the same time, it is difficult to separate MWCNTs from water after the adsorption is saturated, and there is a certain ecological risk. The non-covalent functionalization of MWCNTs can effectively improve the dispersibility of MWCNTs without destroying the structure of carbon nanotubes. Dispersants for non-covalent functionalization of MWCNTs include surfactants, peptides and proteins, and polysaccharides. Humic acid (HA) exists in almost all water sources, and its content accounts for 40-90% of the total dissolved organic carbon in water. Similar to surfactants, HA is also amphiphilic, containing both hydrophilic groups (carboxyl groups, phenolic groups) and hydrophobic groups (aromatic rings, aromatic hydrocarbons). Studies have shown that HA improves the dispersibility of CNTs. In addition, HA-encapsulated CNTs have lower toxicity, which will reduce the ecological risk of CNT release into the environment.

At present, there is no report on the preparation of modified MWCNT materials using HA non-covalent functionalized MWCNTs.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing a modified multi-walled carbon nanotube and a low pressure membrane thereof in order to overcome the deficiencies of the prior art. The preparation method of the invention does not cause any damage to the structure and performance of the multi-walled carbon nanotubes, and simultaneously avoids the ecological risk of the multi-walled carbon nanotubes entering the water environment. The modified multi-walled carbon nanotube low-pressure membrane of the present invention maintains the operation range of the low-pressure membrane in the methylene blue dye removal process, has low cost, high efficiency, simple removal method and easy realization.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a preparation method of modified multi-walled carbon nanotubes, comprising the following steps:

1) ultrasonically treating the multi-walled carbon nanotubes and the humic acid solution to obtain a modified multi-walled carbon nanotube dispersion;

2) removing the solvent in the modified multi-walled carbon nanotube dispersion to obtain modified multi-walled carbon nanotubes.

The present invention also provides a preparation method of the modified multi-walled carbon nanotube low-pressure film, comprising the following steps:

2) The modified multi-wall carbon nanotube dispersion liquid is subjected to solid-liquid separation using a microfiltration porous membrane to obtain a modified multi-wall carbon nanotube low-pressure membrane.

Preferably, the outer diameter of the multi-walled carbon nanotubes in step 1) is 30-50 nm, the inner diameter is 8-15 nm, and the length is less than or equal to 10 μm; the concentration of the humic acid solution is 0.1-50 mg/mL.

Preferably, the power of the ultrasonic treatment in step 1) is 100-200 W, and the time is 10-20 min; the concentration of the modified multi-walled carbon nanotube dispersion liquid is 0.5-2 mg/mL.

The present invention also provides the modified multi-walled carbon nanotubes obtained by the preparation method described in the above scheme.

Preferably, the pore size of the microfiltration porous membrane is 0.4-0.5 μm, and the pressure of the solid-liquid separation is 0.08-0.12 MPa.

The present invention also provides the modified multi-walled carbon nanotube low pressure film obtained by the preparation method described in the above scheme.

Preferably, the loading amount of the modified multi-walled carbon nanotubes on the low-pressure film of the modified multi-walled carbon nanotubes is ≥22.39 g/m ² .

The present invention also provides an application of the modified multi-wall carbon nanotubes or the low-pressure membrane of the modified multi-wall carbon nanotubes described in the above technical solution in removing methylene blue from water.

The present invention also provides a method for removing methylene blue from water using the modified multi-walled carbon nanotube low-pressure membrane described in the above technical solution, and using the modified multi-walled carbon nanotube low-pressure membrane to filter an aqueous solution containing methylene blue dye under constant flow; The time of flow filtration is 180-220 min, the flow rate is 60-80 L·m ^-2 ·h ^-1 , and in the constant flow filtration, the rotational speed of the peristaltic pump is 0.4-0.6 r/min.

The beneficial effects of the present invention include:

1) The preparation process of the modified multi-walled carbon nanotubes and the low-pressure membrane thereof of the present invention is simple, does not cause any damage to the structure and performance of the multi-walled carbon nanotubes, and simultaneously avoids the ecological risk of the multi-walled carbon nanotubes entering the water environment.

2) The modified multi-walled carbon nanotube low-pressure membrane of the present invention is kept in the operating range of the low-pressure membrane in the methylene blue dye removal process, with low cost, high methylene blue removal efficiency, and the removal effect is hardly affected by the concentration of Na ⁺ and Ca ²⁺ . The removal method is simple and easy to implement.

Instruction drawings

Fig. 1 is the modified multi-walled carbon nanotube low pressure film of embodiment 1;

Figure 2 is a comparison diagram of pure water flux under different pressures of the modified multi-walled carbon nanotube low-pressure membrane, the 0.45 μm polyethersulfone-based membrane and the original multi-walled carbon nanotube membrane of Example 1;

Figure 3 is a graph showing the effect of different concentrations of methylene blue solutions on the removal of methylene blue from the modified multi-walled carbon nanotube low-pressure membrane, 0.45 μm polyethersulfone-based membrane and original multi-walled carbon nanotube membrane of Example 1;

Figure 4 is a graph showing the change of the transmembrane pressure difference when the modified multi-walled carbon nanotube low-pressure membrane, the 0.45 μm polyethersulfone-based membrane and the original multi-walled carbon nanotube membrane of Example 1 filter 50 mg/L methylene blue solution;

5 is a graph showing the effect of different pH values on the removal of methylene blue from the modified multi-walled carbon nanotube low-pressure film and the original multi-walled carbon nanotube film of Example 1;

6 is a graph showing the effect of different Na concentrations on the removal of methylene blue from the modified multi ^- walled carbon nanotube low-pressure film and the original multi-walled carbon nanotube film of Example 1;

7 is a graph showing the effect of different Ca ²⁺ concentrations on the removal of methylene blue from the modified multi-walled carbon nanotube low-pressure film and the original multi-walled carbon nanotube film of Example 1.

Detailed ways

2) The modified multi-walled carbon nanotube dispersion liquid is subjected to solid-liquid separation using a microfiltration porous membrane to obtain a modified multi-walled carbon nanotube low-pressure membrane.

In the preparation method of modified multi-walled carbon nanotubes and the preparation method of the modified multi-walled carbon nanotube low-pressure film of the present invention, the outer diameter of the multi-walled carbon nanotubes in step 1) is preferably 30-50 nm, more preferably 35 to 45 nm, more preferably 40 nm; the inner diameter of the multi-walled carbon nanotubes is preferably 8 to 15 nm, more preferably 10 to 12 nm; the length of the multi-walled carbon nanotubes is preferably ≤ 10 μm, more preferably 1 to 9 μm ; The concentration of the humic acid solution is preferably 0.1-50 mg/mL, more preferably 3-40 mg/mL, and more preferably 10-20 mg/mL.

In the preparation method of modified multi-walled carbon nanotubes and the preparation method of the modified multi-walled carbon nanotube low-pressure film of the present invention, the multi-walled carbon nanotubes are subjected to ultrasonic treatment with a humic acid solution and multi-walled carbon nanotubes. non-covalent modification; the power of the ultrasonic treatment in step 1) is preferably 100-200W, more preferably 120-180W, more preferably 140-160W; the ultrasonic treatment time is preferably 10-20min, more preferably 12-18 minutes, more preferably 14-16 minutes; the concentration of the modified multi-walled carbon nanotube dispersion is preferably 0.5-2 mg/mL, more preferably 1-1.5 mg/mL.

In the preparation method of the modified multi-wall carbon nanotube low-pressure membrane, the present invention preferably adopts the pressure filtration method to make the modified multi-wall carbon nanotube dispersion liquid pass through the microfiltration porous membrane, and in the process of solid-liquid separation, the modified multi-wall carbon nanotubes are separated The walled carbon nanotubes are deposited on the surface of the microfiltration porous membrane; the pore size of the microfiltration porous membrane of the present invention is preferably 0.4-0.5 μm, more preferably 0.42-0.48 μm, more preferably 0.44-0.46 μm; The membrane is preferably a polyethersulfone membrane; the pressure of the solid-liquid separation is preferably 0.08-0.12 MPa, more preferably 0.1 MPa.

In the method for preparing the modified multi-walled carbon nanotube low-pressure membrane of the present invention, after the solid-liquid separation in step 2), the modified multi-walled carbon nanotube low-pressure membrane is preferably washed and dried; the washing is preferably ultrapure water. Rinse several times until the TOC value of the effluent is less than or equal to 0.2mg/L.

The loading amount of modified multi-walled carbon nanotubes on the low-pressure membrane of the present invention is preferably ≥22.39 g/m ² .

The present invention also provides the application of the modified multi-walled carbon nanotubes described in the above scheme or the low-pressure membrane of the modified multi-walled carbon nanotubes described in the above scheme in removing methylene blue from water.

The present invention also provides a method for removing methylene blue from water by using the modified multi-walled carbon nanotube low-pressure membrane described in the above scheme, and using the modified multi-walled carbon nanotube low-pressure membrane to filter an aqueous solution containing methylene blue dye under constant flow; The filtering time is preferably 180-220min, more preferably 190-210min, more preferably 200min; the flow rate of the constant-flow filtration is preferably 60-80L·m ^-2 ·h ^-1 , more preferably 65-75L·m ^-2 ·h ^-1 , more preferably 75L·m ^-2 ·h ^-1 ; in the constant flow filtration, the rotational speed of the peristaltic pump is preferably 0.4 to 0.6 r/min, more preferably 0.5 r/min.

In the process of removing methylene blue in an aqueous solution using the modified multi-walled carbon nanotube low-pressure membrane in the present invention, the influence of Na ⁺ and Ca ²⁺ concentrations is very small and can be ignored; the concentration of Na ⁺ in the methylene blue aqueous solution is preferably 0 ~10 mmol/L, the concentration of Ca ²⁺ is preferably 0 to 5 mmol/L.

In the present invention, in the aqueous solution containing methylene blue dye, the concentration of methylene blue is preferably 10-50 mg/L. The higher the concentration of the dye, the shorter the time it takes to penetrate the low pressure membrane, and the easier it is for the low pressure membrane to reach adsorption saturation; the present invention The acidity and alkalinity of the aqueous solution have obvious effects on the removal of methylene blue, and the alkaline solution is more conducive to the removal of methylene blue.

The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the protection scope of the present invention.

Example 1

30 mg of multi-walled carbon nanotubes with an outer diameter of 35 nm, an inner diameter of 10 nm, and a length of 8 μm were added to a humic acid solution with a concentration of 0.3 mg/mL and a volume of 50 mL, and the solution was subjected to ultrasonic treatment with an ultrasonic crusher to obtain The modified multi-walled carbon nanotube dispersion liquid with a concentration of 0.6 mg/mL was ultrasonically treated for 15 min and the power was 150 W.

The multi-walled carbon nanotube dispersion was passed through a polyethersulfone membrane with a pore size of 0.45 μm by a pressure filtration method (the pressure was 0.1 MPa), and then the modified multi-walled carbon nanotube low-pressure membrane was washed with ultrapure water through the membrane until the water was discharged. The TOC value is lower than 0.2mg/L, and the low-pressure membrane is dried for use. According to the effective area of the polyethersulfone-based membrane and the amount of multi-walled carbon nanotubes, the modified multi-walled carbon nanotubes low-pressure membrane can be calculated, and the loading amount of the modified multi-walled carbon nanotubes is 22.39 g/m ² .

The modified multi-walled carbon nanotube low-pressure film of Example 1 is shown in FIG. 1 .

The pure water flux comparison of the modified multi-walled carbon nanotube low-pressure membrane of Example 1, the 0.45 μm polyethersulfone-based membrane and the unmodified original multi-walled carbon nanotube membrane at different pressures is shown in Figure 2 (Fig. In 2, Virgin is the polyethersulfone-based membrane, P-MWCNT is the unmodified original MWCNT membrane, and HA-MWCNT is the modified MWCNT low-pressure membrane of Example 1, Figures 3 to 7 In , the meanings of Virgin, P-MWCNT and HA-MWCNT are the same as those in FIG. 2 , and will not be repeated hereafter). It can be seen from Figure 2 that under the same pressure, the pure water flux of the modified multi-wall carbon nanotube low-pressure membrane of the present invention is lower than that of the 0.45 μm polyethersulfone-based membrane and the original multi-wall carbon nanotube membrane.

Example 2

75 mg of multi-walled carbon nanotubes with an outer diameter of 50 nm, an inner diameter of 15 nm, and a length of 10 μm were added to a humic acid solution with a concentration of 25 mg/mL and a volume of 50 mL, and the solution was ultrasonically treated with an ultrasonic crusher to obtain a concentration of It is 1.5mg/mL modified multi-walled carbon nanotube dispersion, the ultrasonic treatment time is 20min, and the power is 180W.

The multi-walled carbon nanotube dispersion was passed through a polyethersulfone membrane with a pore size of 0.5 μm by the pressure filtration method (the pressure was 0.12 MPa), and then the modified multi-walled carbon nanotubes low-pressure membrane was washed with ultrapure water through the membrane until the water was discharged. The TOC value is lower than 0.2mg/L, and the low-pressure membrane is dried for use. According to the effective area of the polyethersulfone-based membrane and the amount of multi-walled carbon nanotubes, the modified multi-walled carbon nanotubes low-pressure membrane can be calculated, and the loading amount of the modified multi-walled carbon nanotubes is 28 g/m ² .

Example 3

50 mg of multi-walled carbon nanotubes with an outer diameter of 40 nm, an inner diameter of 8 nm, and a length of 5 μm were added to a humic acid solution with a concentration of 12 mg/mL and a volume of 50 mL, and the solution was ultrasonically treated with an ultrasonic crusher to obtain a concentration of It is 1 mg/mL modified multi-walled carbon nanotube dispersion, the ultrasonic treatment time is 20 min, and the power is 120 W.

The multi-walled carbon nanotube dispersion was passed through a polyethersulfone membrane with a pore size of 0.4 μm by a pressure filtration method (the pressure was 0.08 MPa), and then the modified multi-walled carbon nanotube low-pressure membrane was washed with ultrapure water through the membrane until the water was discharged. The TOC value is lower than 0.2mg/L, and the low-pressure membrane is dried for use. According to the effective area of the polyethersulfone-based membrane and the amount of multi-walled carbon nanotubes, the modified multi-walled carbon nanotubes low-pressure membrane can be calculated, and the loading amount of the modified multi-walled carbon nanotubes is 24 g/m ² .

Application example 1

The modified multi-walled carbon nanotube low-pressure membrane prepared in Example 1 was used to filter the aqueous solutions with methylene blue dye concentrations of 10 mg/L, 20 mg/L, 30 mg/L and 50 mg/L using a constant current filter device, respectively. In the process of constant flow filtration, the flow rate was 70L·m ^-2 ·h ^-1 , the filtration time was 200min, the speed of the peristaltic pump was 0.5r/min; the pH value of the methylene blue dye-containing aqueous solution was 7.

Application Comparative Example 1-1

The aqueous solutions with methylene blue dye concentrations of 10 mg/L, 20 mg/L, 30 mg/L and 50 mg/L were filtered using a polyethersulfone-based membrane with a pore size of 0.45 μm (the polyethersulfone-based membrane was exactly the same as in Example 1), and the constant current The filtering conditions are the same as in Application Example 1.

Application Comparative Example 1-2

The unmodified original multi-walled carbon nanotube membranes (multi-walled carbon nanotubes were the same as those in Example 1) were used to filter aqueous solutions with methylene blue dye concentrations of 10 mg/L, 20 mg/L, 30 mg/L and 50 mg/L, respectively. The conditions for stream filtering are the same as in Application Example 1.

The effect of methylene blue concentration on the removal of methylene blue from modified MWCNT low-pressure membranes, polyethersulfone-based membranes and unmodified pristine MWCNT membranes is shown in Figure 3. As the methylene blue concentration gradually increased from 10 mg/L to 50 mg/L, the time for methylene blue to penetrate the low-pressure membrane of modified multi-walled carbon nanotubes became shorter. In the first few minutes of filtration, the ratio C/C ₀ of the effluent dye concentration to the influent dye concentration of the polyethersulfone-based membrane increased to more than 0.9, indicating that the removal of methylene blue by the polyethersulfone-based membrane was basically negligible. Compared with the original multi-walled carbon nanotube film, the modified multi-walled carbon nanotube low-pressure film of the present invention has a significantly enhanced removal effect on methylene blue, and the continuous effective removal time of methylene blue is prolonged.

Application example 2

In Application Example 1, the change of the transmembrane pressure difference of the modified multi-walled carbon nanotube low pressure membrane when filtering 50mg/L methylene blue dye was monitored in real time by a pressure sensor, and the operating pressure of the membrane was evaluated through the change of the transmembrane pressure difference.

Application Comparative Example 2-1

When filtering 50 mg/L methylene blue dye in Comparative Example 1-1, the change of the transmembrane pressure difference of the polyethersulfone-based membrane was monitored in real time by a pressure sensor.

Application Comparative Example 2-2

The change of the transmembrane pressure difference of the unmodified pristine multi-walled carbon nanotube membrane when filtering 50 mg/L methylene blue dye in Comparative Examples 1-2 was monitored in real time by a pressure sensor.

Figure 4 shows the changes in the transmembrane pressure difference of the modified multi-wall carbon nanotube low-pressure membrane, the polyethersulfone-based membrane, and the unmodified pristine multi-wall carbon nanotube membrane. Compared with polyethersulfone-based membranes and pristine MWCNTs, the transmembrane pressure difference of the modified MWCNTs low-pressure membrane for filtration of methylene blue dye is higher, but much lower than that of nanofiltration and reverse osmosis membranes Pressure difference, the transmembrane pressure difference of the modified multi-walled carbon nanotube low pressure membrane of the present invention still belongs to the operation category of the low pressure membrane.

Application example 3

The modified multi-walled carbon nanotube low-pressure membrane prepared in Example 1 was used to filter the aqueous solutions containing methylene blue dye with pH values of 3.38, 5.93 and 10.2, respectively. ^-2 ·h ^-1 , the filtration time was 200 min, the rotational speed of the peristaltic pump was 0.5 r/min, and the concentration of methylene blue was 50 mg/L.

Application Comparative Example 3

Using unmodified original multi-walled carbon nanotube membrane (multi-walled carbon nanotubes are the same as in Example 1) to filter aqueous solutions containing methylene blue dye with pH values of 3.38, 5.93 and 10.2, respectively, conditions and application examples of constant flow filtration 3 is the same.

The effect of the concentration of methylene blue dye on the removal of methylene blue from the modified MWCNT low-pressure film and the pristine MWCNT film is shown in Figure 5. It can be seen from Figure 5 that the pH value has a great influence on the removal of methylene blue from the modified multi-walled carbon nanotube low-pressure membrane and the original multi-walled carbon nanotube, and the removal of methylene blue is more favorable under alkaline conditions.

Application example 4

The modified multi-walled carbon nanotube low-pressure membrane prepared in Example 1 is used to filter the methylene blue aqueous solution containing Na ⁺ (Na ⁺ from NaCl) with a concentration of 0, 5mmol/L and 10mmol/L using a constant current filter device. , the concentration of methylene blue was 50mg/L, and the pH value was 10.2. In the process of constant flow filtration, the flow rate was 70L·m ^-2 ·h ^-1 , the filtration time was 200min, and the speed of the peristaltic pump was 0.5r/min.

Application Comparative Example 4

The unmodified original multi-walled carbon nanotube membrane (multi-walled carbon nanotubes are the same as in Example 1) was used to filter methylene blue aqueous solutions containing Na ⁺ concentrations of 0, 5 mmol/L and 10 mmol/L, respectively, under constant flow filtration conditions Same as application example 4.

The effect of Na ⁺ concentration on the removal effect of methylene blue is shown in FIG. 6 . It can be seen from FIG. 6 that the effect of Na ⁺ concentration on the removal effect of methylene blue by the modified multi-walled carbon nanotube low-pressure membrane of the present invention is very small, indicating that the modification of the present invention The removal of methylene blue by the low-pressure membrane of multi-walled carbon nanotubes is not limited by the concentration of Na ⁺ in the solution.

Application example 5

The modified multi-walled carbon nanotube low-pressure membrane prepared in Example 1 was used to filter the methylene blue aqueous solution containing Ca ²⁺ (Ca ²⁺ from CaCl ₂ ) with a concentration of 0, 1 mmol/L and 5 mmol/L using a constant-current filter device, In the methylene blue aqueous solution, the concentration of methylene blue is 50 mg/L, and the pH value is 10.2. In the process of constant flow filtration, the flow rate was 70L·m ^-2 ·h ^-1 , the filtration time was 200min, and the speed of the peristaltic pump was 0.5r/min.

Application Comparative Example 5

The unmodified original multi-walled carbon nanotube membranes (multi-walled carbon nanotubes were the same as those in Example 1) were used to filter methylene blue aqueous solutions containing ^Ca concentrations of 0, 1 mmol/L and 5 mmol/L, respectively. The conditions are the same as in Application Example 5.

The effect of Ca ²⁺ concentration on the removal effect of methylene blue is shown in Figure 7. It can be seen from Figure 7 that the effect of Ca ²⁺ concentration on the removal effect of methylene blue by the modified multi-walled carbon nanotube low pressure film of the present invention is very small, indicating that the The removal of methylene blue by the modified multi-walled carbon nanotube low-pressure membrane is not limited by the concentration of Ca ²⁺ in the solution.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims

A method for preparing modified multi-walled carbon nanotubes, comprising the steps of:

1) ultrasonically treating the multi-walled carbon nanotubes and the humic acid solution to obtain a modified multi-walled carbon nanotube dispersion;

2) removing the solvent in the modified multi-walled carbon nanotube dispersion to obtain modified multi-walled carbon nanotubes.
A preparation method of a modified multi-walled carbon nanotube low-pressure membrane, characterized in that, comprising the following steps:

1) ultrasonically treating the multi-walled carbon nanotubes and the humic acid solution to obtain a modified multi-walled carbon nanotube dispersion;

2) The modified multi-walled carbon nanotube dispersion liquid is subjected to solid-liquid separation using a microfiltration porous membrane to obtain a modified multi-walled carbon nanotube low-pressure membrane.
The preparation method according to claim 1 or 2, wherein in step 1) the outer diameter of the multi-walled carbon nanotubes is 30-50 nm, the inner diameter is 8-15 nm, and the length is ≤ 10 μm; the humic acid solution The concentration of 0.1 ~ 50mg/mL.
The preparation method according to claim 1 or 2, wherein the power of the ultrasonic treatment in step 1) is 100-200 W, and the time is 10-20 min; the concentration of the modified multi-walled carbon nanotube dispersion liquid is 0.5～2mg/mL.
The modified multi-walled carbon nanotubes obtained by the preparation method of claim 1, 3 or 4.
The preparation method according to claim 2, wherein the pore size of the microfiltration porous membrane is 0.4-0.5 μm, and the pressure of the solid-liquid separation is 0.08-0.12 MPa.
The preparation method according to claim 2 or 6, wherein the microfiltration porous membrane is a polyethersulfone membrane.
The preparation method according to claim 2, characterized in that, after the solid-liquid separation, further comprising washing and drying the modified multi-walled carbon nanotube low-pressure membrane.
The preparation method according to claim 8, wherein the rinsing adopts ultrapure water for several times until the TOC value of the effluent is less than or equal to 0.2 mg/L.
The modified multi-walled carbon nanotube low-pressure membrane obtained by the preparation method described in any one of claims 2 to 4 and claims 6 to 9 is composed of a microfiltration porous membrane and a modified multi-walled membrane deposited on the surface of the microfiltration porous membrane. Walled carbon nanotubes.
The modified multi-walled carbon nanotube low-pressure membrane according to claim 10, wherein the loading amount of modified multi-walled carbon nanotubes on the modified multi-walled carbon nanotube low-pressure membrane is ≥22.39 g/m 2 .
Application of the modified multi-walled carbon nanotubes of claim 5 or the low-pressure membrane of the modified multi-walled carbon nanotubes of claim 10 or 11 in removing methylene blue from water.
The method for removing methylene blue from water using the modified multi-walled carbon nanotube low-pressure membrane according to claim 10 or 11, characterized in that, the modified multi-walled carbon nanotube low-pressure membrane is used to filter the aqueous solution containing methylene blue dye under constant flow; The time of flow filtration is 180-220 min, the flow rate is 60-80 L·m -2 ·h -1 , and in the constant flow filtration, the rotational speed of the peristaltic pump is 0.4-0.6 r/min.
The method according to claim 13, wherein the aqueous solution containing methylene blue dye is alkaline.
The method according to claim 13, wherein the pH value of the methylene blue dye-containing aqueous solution is 10.2.