Preparation method of ceramic-based polyamide nanofiltration membrane regulated and controlled by molybdenum oxide middle layer

Abstract

The invention discloses a preparation method of a ceramic-based polyamide nanofiltration membrane regulated and controlled by a molybdenum oxide interlayer, which comprises the following steps: (1) carrying out ultrasonic cleaning and strong alkali activation on a ceramic membrane, and loading a silane coupling agent to obtain a silane grafted ceramic membrane; (2) reacting the silane grafted ceramic membrane with an aqueous solution containing piperazine and a polyamine catalyst at room temperature; (3) reacting the material obtained in the step (2) with an n-hexane solution containing O-MoS2 and CTAB (cetyltrimethyl ammonium bromide) at room temperature; (4) reacting the material obtained in the step (3) with an n-hexane solution of trimesoyl chloride at room temperature; and (5) carrying out air drying and heat treatment on the material obtained in the step (4). The O-MoS2 / CTAB amphiphilic intermediate layer is introduced to the surface of the silane modified ceramic membrane, so that the wetting and diffusion behaviors of an organic phase monomer on the hydrophilic ceramic surface are effectively improved, and a polyamide separation layer is more uniform and compact.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a method for preparing a ceramic-based polyamide nanofiltration membrane with a molybdenum disulfide intermediate layer regulated by oxidation. Background Technology

[0002] Nanofiltration membranes, due to their advantages such as low operating pressure, low energy consumption, and good selectivity, have been widely used in seawater desalination, industrial wastewater treatment, and heavy metal ion removal. Among them, composite nanofiltration membranes with polyamide as the active separation layer have become the mainstream commercial product due to their excellent separation performance. The separation layer of this type of membrane is usually prepared by the interfacial polymerization reaction of piperazine and trimesoyl chloride on the surface of the support layer.

[0003] However, traditional interfacial polymerization reactions are extremely fast and difficult to control precisely. The localized heat released during the reaction tends to accumulate at the interface, leading to defects or uneven thickness in the polyamide layer, thus creating a "trade-off" effect between flux and rejection rate. Furthermore, when a highly hydrophilic inorganic ceramic membrane is used as the support, the poor wettability and uneven diffusion of the organic monomers on the ceramic surface further exacerbate the inhomogeneity of the separation layer structure, limiting the overall performance of the ceramic-based polyamide composite nanofiltration membrane.

[0004] In recent years, researchers have attempted to introduce amphiphilic nanomaterials as interlayers during interfacial polymerization to improve monomer diffusion behavior and reaction heat transfer. Molybdenum disulfide (MoD) has attracted attention in the field of membrane materials due to its excellent thermal conductivity and layered structure. However, there are currently no reports on the application of a composite of MoD with cationic surfactants to form an amphiphilic interlayer for the regulation of polyamide interfacial polymerization on ceramic supports. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing a ceramic-based polyamide nanofiltration membrane with a molybdenum disulfide intermediate layer regulated by oxidation.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a ceramic-based polyamide nanofiltration membrane with a molybdenum disulfide interlayer modulated by the following steps:

[0008] (1) After ultrasonic cleaning and strong alkali activation, the ceramic membrane is loaded with silane coupling agent to obtain silane-grafted ceramic membrane;

[0009] (2) The silane-grafted ceramic membrane obtained in step (1) is reacted with an aqueous solution containing piperazine and polyamine catalyst at room temperature, and then the unreacted aqueous solution is removed.

[0010] (3) The material obtained in step (2) is reacted with a hexane solution containing O-MoS2 and CTAB (hexadecyltrimethylammonium bromide) at room temperature, and then the unreacted hexane solution is removed.

[0011] (4) After reacting the material obtained in step (3) with a hexane solution of trimesoyl chloride at room temperature, the unreacted hexane solution is removed.

[0012] (5) The material obtained in step (4) is air-dried and heat-treated to obtain the ceramic-based polyamide nanofiltration membrane with molybdenum disulfide intermediate layer regulation.

[0013] In a preferred embodiment of the present invention, the ceramic membrane is made of alumina, titanium dioxide, or zirconium oxide.

[0014] In a preferred embodiment of the present invention, the strong base in the strong base solution is sodium hydroxide or potassium hydroxide, with a concentration of 1-10 mol / L and an activation time of 10-24 h.

[0015] In a preferred embodiment of the present invention, the silane coupling agent is 3-aminopropyltriethoxysilane, diethyltrimethoxysilane, or diethyltrimethoxysilane.

[0016] In a preferred embodiment of the present invention, the aqueous solution in step (2) contains: piperazine at a concentration of 0.05-0.5 wt% and polyamine catalyst at a concentration of 0.1-0.3 wt%.

[0017] More preferably, the polyamine catalyst is diethylamine or triethylamine.

[0018] In a preferred embodiment of the present invention, in the hexane solution of step (3), the total concentration of O-MoS2 and CTAB is 0.025-0.05 wt%, and the mass ratio of O-MoS2 to CTAB is 2:1.

[0019] In a preferred embodiment of the present invention, the concentration of pyromellitic amide in the hexane solution of step (4) is 0.05-0.3 wt%.

[0020] In a preferred embodiment of the present invention, the reaction time in step (2) is 1-10 min, the reaction time in step (3) is 1-10 min, and the reaction time in step (4) is 1-10 min.

[0021] More preferably, the temperature of the heat treatment in step (5) is 50-80 °C.

[0022] The beneficial effects of this invention are:

[0023] 1. This invention introduces an O-MoS2 / CTAB amphiphilic intermediate layer on the surface of a silane-modified ceramic membrane, which effectively improves the wetting and diffusion behavior of organic phase monomers on the hydrophilic ceramic surface, making the polyamide separation layer more uniform and dense.

[0024] 2. The high thermal conductivity of the molybdenum disulfide nanosheets in this invention can quickly conduct the local heat generated by interfacial polymerization, significantly reducing film defects caused by heat accumulation during reaction.

[0025] 3. The synergistic effect of the cationic surfactant and molybdenum disulfide oxide in this invention endows the intermediate layer with good amphiphilicity, while introducing a moderate negative charge, which further regulates the diffusion rate of amine monomers into the organic phase and alleviates the problem of difficult control in traditional interfacial polymerization.

[0026] 4. The preparation process of this invention is simple and mild, and is completed entirely at room temperature. It is applicable to various ceramic substrates such as alumina, titanium dioxide, and zirconium oxide, and has good prospects for industrialization.

[0027] 5. The ceramic-based polyamide nanofiltration membrane prepared by the present invention maintains an extremely high salt rejection rate while significantly increasing the pure water flux, effectively breaking through the "trade-off" limitation between flux and rejection rate. Attached Figure Description

[0028] Figure 1 This is an electron microscope image of the ceramic-based polyamide nanofiltration membrane prepared in Comparative Example 3 of the present invention.

[0029] Figure 2 This is an electron microscope image of the ceramic-based polyamide nanofiltration membrane prepared in Example 2 of the present invention. Detailed Implementation

[0030] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0031] The molybdenum disulfide (O-MoS2) in the following examples and comparative examples was prepared by a modified Hummers method, as detailed below:

[0032] (1) Take a 1000 mL beaker, wash and dry it, add 3 g of molybdenum disulfide, and slowly add 360 mL of concentrated sulfuric acid (98% H2SO4) and 40 mL of concentrated phosphoric acid (95% H3PO4) under magnetic stirring. Then slowly add 18 g of potassium permanganate (KMnO4) in batches. Transfer the beaker to a 50℃ oil bath and stir for 12 h. Remove the beaker and let it cool naturally to room temperature. Slowly pour the reaction solution onto ice cubes containing 400 mL of dilute hydrogen peroxide (containing 18 mL of 30% H2O2). The solution turns bright yellow.

[0033] (2) The above solution was filtered by cross-flow filtration using a tubular ceramic membrane with a pore size of 0.05 μm to remove impurities, and the purified material was obtained.

[0034] (3) Freeze-dry the material obtained in step (2) according to the required concentration to obtain molybdenum disulfide oxide.

[0035] Comparative Example 1 (Organic Support Polyamide Nanofiltration Membrane)

[0036] (1) Immerse a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 10,000 Da in an aqueous solution containing 0.1 wt% piperazine and 0.1 wt% diethylamine, react at room temperature for 10 min, remove it, and blow off the residual liquid on the surface with an air gun;

[0037] (2) The material obtained in step (1) is immersed in a hexane solution containing 0.2 wt% trimesoyl chloride (TMC), reacted at room temperature for 1 min, removed, rinsed with hexane and dried with an air gun;

[0038] (3) After the material obtained in step (2) is placed in a cool place to air dry naturally, it is placed in a 50 ℃ oven for heat treatment for 15 min and cooled with the oven to obtain the polyamide composite nanofiltration membrane as a comparison.

[0039] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux is 45 L·m³. -2 ·h -1 The rejection rate for 0.2% sodium sulfate solution was 97%.

[0040] Comparative Example 2 (Low-Temperature Organic Phase Interfacial Polymerization)

[0041] The process is basically the same as in Example 1, except that the hexane solution in step (3) is frozen at -20 °C for 12 h before use.

[0042] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux is 70 L·m³. -2 ·h -1 The rejection rate for 0.2% sodium sulfate solution was 92%.

[0043] Comparative Example 3 (Direct interfacial polymerization of silane-modified ceramic membranes without intermediate layer)

[0044] 1. Ceramic membrane pretreatment

[0045] Titanium oxide ceramic membrane tubes with an average pore size of 50 nm were cut to a length of approximately 50 cm, ultrasonically cleaned for 2 h, then activated by immersion in a 1 mol / L potassium hydroxide solution for 10 h, and dried at 100 ℃ for 24 h. After cooling, the membrane was immersed in an ethanol solution of 0.1 wt% 3-aminopropyltriethoxysilane (KH-550) and reacted at room temperature for 12 h. The membrane was then rinsed with ethanol and deionized water sequentially, dried at 150 ℃ for 12 h, and cooled in the furnace to obtain a silane-grafted ceramic membrane.

[0046] 2. Preparation of composite nanofiltration membranes

[0047] (1) The above silane-grafted ceramic membrane was immersed in an aqueous solution containing 0.1 wt% piperazine and 0.1 wt% diethylamine, reacted at room temperature for 10 min, and then removed and dried with an air gun;

[0048] (2) Immerse the material obtained in step (1) in a hexane solution containing 0.2 wt% trimesoyl chloride (TMC), react at room temperature for 1 min, rinse with hexane and dry with an air gun;

[0049] (3) After the material obtained in step (2) is air-dried at room temperature, it is placed in a 50 ℃ oven for heat treatment for 15 min, and then cooled with the oven to obtain the desired product. Figure 1 The ceramic-based polyamide nanofiltration membrane shown for comparison has a membrane thickness of 120 nm.

[0050] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux is 75 L·m³. -2 ·h -1 The retention rate for 0.2% sodium sulfate solution is 95%.

[0051] Comparative Example 4 (only molybdenum disulfide intermediate layer introduced, no CTAB)

[0052] Step 1 is the same as in Comparative Example 3, and Step 2 is as follows:

[0053] (1) The above silane-grafted ceramic membrane was immersed in an aqueous solution containing 0.1 wt% piperazine and 0.1 wt% diethylamine, reacted at room temperature for 10 min, and then removed and dried with an air gun;

[0054] (2) Immerse the material obtained in step (1) in a hexane solution containing 0.025 wt% O-MoS2, react at room temperature for 1 min, and then dry it with an air gun;

[0055] (3) Immerse the material obtained in step (2) in a hexane solution containing 0.2 wt% trimesoyl chloride (TMC), react at room temperature for 1 min, rinse with hexane and dry with an air gun;

[0056] (4) After the material obtained in step (3) is air-dried at room temperature, it is placed in a 50 ℃ oven for heat treatment for 15 min and cooled with the oven to obtain the ceramic-based polyamide nanofiltration membrane for comparison.

[0057] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux is 75 L·m³. -2 ·h -1 The retention rate for 0.2% sodium sulfate solution is 95%.

[0058] Comparative Example 5 (only CTAB intermediate layer introduced, no O-MoS2)

[0059] Step 1 is the same as Comparative Example 3.

[0060] Step 2 is basically the same as Comparative Example 4, except that a 0.025 wt% hexane solution of cetyltrimethylammonium bromide (CTAB) is used instead of a 0.025 wt% hexane solution of O-MoS2.

[0061] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux is 115 L·m³. -2 ·h -1 The rejection rate for 0.2% sodium sulfate solution was 97.5%.

[0062] Example 1

[0063] Step 1 is the same as in Comparative Example 3, and Step 2 is as follows:

[0064] (1) The above silane-grafted ceramic membrane was immersed in an aqueous solution containing 0.1 wt% piperazine and 0.1 wt% diethylamine, reacted at room temperature for 10 min, and then removed and dried with an air gun;

[0065] (2) Immerse the material obtained in step (1) in a hexane solution containing 0.025 wt% O-MoS2 / CTAB (mass ratio 2:1), react at room temperature for 1 min, and then dry with an air gun;

[0066] (3) Immerse the material obtained in step (2) in a hexane solution containing 0.2 wt% trimesoyl chloride (TMC), react at room temperature for 1 min, rinse with hexane and dry with an air gun;

[0067] (4) After the material obtained in step (3) is air-dried at room temperature, it is placed in a 50 ℃ oven for heat treatment for 15 min and cooled with the oven to obtain a ceramic-based polyamide nanofiltration membrane with molybdenum disulfide intermediate layer regulation.

[0068] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux was 148 L·m³. -2 ·h-1 The rejection rate for 0.2% sodium sulfate solution was 98.5%.

[0069] Example 2

[0070] Step 1 is the same as in Example 1, and Step 2 is as follows:

[0071] Step 2 is basically the same as in Example 1, except that: a 0.03 wt% O-MoS2 / CTAB (mass ratio 2:1) hexane solution is used instead of a 0.025 wt% O-MoS2 / CTAB (mass ratio 2:1) hexane solution. The prepared film layer is as follows: Figure 2 As shown, the film thickness is 58.8 nm, and the film surface is denser and thinner.

[0072] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux was 156 L·m³. -2 ·h -1 The rejection rate for 0.2% sodium sulfate solution was 99.3%.

[0073] Example 3

[0074] Step 1 is the same as in Example 1, and Step 2 is as follows:

[0075] Step 2 is basically the same as in Example 1, except that a 0.025 wt% O-MoS2 / CTAB (mass ratio 2:1) hexane solution is used instead of a 0.05 wt% O-MoS2 / CTAB (mass ratio 2:1) hexane solution.

[0076] Performance testing: At room temperature and an operating pressure of 0.69 MPa, the pure water flux was 161 L·m³. -2 ·h -1 The rejection rate for 0.2% sodium sulfate solution was 97.1%.

[0077] The following list compares the embodiments with the comparative examples:

[0078] Table 1

[0079] Group Support type Silane modification Intermediate layer material and concentration (n-hexane dispersion) TMC concentration Key process differences Pure water flux (LHM) <![CDATA[Sodium sulfate rejection rate (%)]]> Comparative Example 1 Organic PES base film none none 0.2 wt% Traditional organic membrane interface polymerization 45 97 Comparative Example 2 Organic PES base film none None (TMC solution pre-cooled at -20 ℃ for 12 h) 0.2 wt% Low-temperature organic phase inhibition reaction 70 92 Comparative Example 3 <![CDATA[50 nm TiO2 ceramic tube]]> have none 0.2 wt% Direct interfacial polymerization of silane-modified ceramic membranes 75 95 Comparative Example 4 <![CDATA[50 nm TiO2 ceramic tube]]> have <![CDATA[O-MoS20.025 wt%]]> 0.2 wt% Only the molybdenum disulfide interlayer is oxidized 122 96.2 Comparative Example 5 <![CDATA[50 nm TiO2 ceramic tube]]> have CTAB 0.025 wt% 0.2 wt% Only cationic surfactant intermediate layer 115 97.5 Example 1 <![CDATA[50 nm TiO2 ceramic tube]]> have <![CDATA[O-MoS2 / CTAB(2:1)0.025 wt%]]> 0.2 wt% This invention (low-concentration composite intermediate layer) 148 98.5 Example 2 <![CDATA[50 nm TiO2 ceramic tube]]> have <![CDATA[O-MoS2 / CTAB(2:1)0.03 wt%]]> 0.2 wt% This invention (optimal concentration) 156 99.3 Example 3 <![CDATA[50 nm TiO2 ceramic tube]]> have <![CDATA[O-MoS2 / CTAB(2:1)0.05 wt%]]> 0.2 wt% This invention (high-concentration composite intermediate layer) 161 97.1

[0080] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing a ceramic-based polyamide nanofiltration membrane with a molybdenum disulfide interlayer controlled by an oxide molybdenum disulfide interlayer, characterized in that: Includes the following steps: (1) After ultrasonic cleaning and strong alkali activation, the ceramic membrane is loaded with silane coupling agent to obtain silane-grafted ceramic membrane; (2) The silane-grafted ceramic membrane obtained in step (1) is reacted with an aqueous solution containing piperazine and polyamine catalyst at room temperature, and then the unreacted aqueous solution is removed. (3) The material obtained in step (2) is reacted with a hexane solution containing O-MoS2 and CTAB at room temperature, and then the unreacted hexane solution is removed. (4) After reacting the material obtained in step (3) with a hexane solution of trimesoyl chloride at room temperature, the unreacted hexane solution is removed. (5) The material obtained in step (4) is air-dried and heat-treated to obtain the ceramic-based polyamide nanofiltration membrane with molybdenum disulfide intermediate layer regulation.

2. The preparation method according to claim 1, characterized in that: The ceramic membrane is made of alumina, titanium dioxide, or zirconium oxide.

3. The preparation method according to claim 1, characterized in that: The strong base in the strong alkaline solution is sodium hydroxide or potassium hydroxide, with a concentration of 1-10 mol / L and an activation time of 10-24 h.

4. The preparation method according to claim 1, characterized in that: The silane coupling agent is 3-aminopropyltriethoxysilane, diethyltrimethoxysilane, or diethyltrimethoxysilane.

5. The preparation method according to claim 1, characterized in that: In the aqueous solution of step (2), the concentration of piperazine is 0.05-0.5 wt%, and the concentration of polyamine catalyst is 0.1-0.3 wt%.

6. The preparation method according to claim 5, characterized in that: The polyamine catalyst is diethylamine or triethylamine.

7. The preparation method according to claim 1, characterized in that: In the hexane solution of step (3), the total concentration of O-MoS2 and CTAB is 0.025-0.05 wt%, and the mass ratio of O-MoS2 to CTAB is 2:

1.

8. The preparation method according to claim 1, characterized in that: In the hexane solution of step (4), the concentration of pyromellitic amide is 0.05-0.3 wt%.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The reaction time in step (2) is 1-10 min, the reaction time in step (3) is 1-10 min, and the reaction time in step (4) is 1-10 min.

10. The preparation method according to claim 9, characterized in that: The heat treatment temperature in step (5) is 50-80 ℃.

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