A graphene oxide-doped reverse osmosis mixed matrix membrane and preparation method thereof

Abstract

The present invention belongs to the technical field of composite membrane preparation and specifically discloses a graphene oxide-doped reverse osmosis mixed matrix membrane and its preparation method. The membrane is prepared by doping graphene oxide into a polymeric organosilicon sol and forming the graphene oxide / organosilicon mixed matrix membrane on the surface of a prefabricated ceramic tube support through vacuum filtration. The graphene oxide-doped reverse osmosis mixed matrix membrane prepared by the present invention exhibits good water permeability (≥4.8×10 ‑4 mol / (m 2 h Pa) and salt rejection (NaCl: ≥96%), and exhibited excellent stability during reverse osmosis desalination of brackish water with a salt content of 2000-10000 ppm.

Description

Technical Field

[0001] The invention belongs to the technical field of composite membrane preparation, and specifically discloses a graphene oxide-doped reverse osmosis mixed matrix membrane and a preparation method thereof. Background Art

[0002] In recent years, graphene oxide membrane (GOM) has become a research hotspot in the field of membrane materials due to its ultra-thin thickness, excellent molecular sieving ability, high chemical stability and high mechanical strength. The interlayer spacing of graphene oxide (GO) itself is about 0.35-0.45nm, while the interlayer spacing of GO membrane formed by stacking GO sheets is between 0.78-0.80nm. This spacing allows water molecules to pass freely and excludes most molecules and ions. It has broad application prospects in the fields of nanofiltration and reverse osmosis. The basal plane or edge of graphene oxide (GO) contains a large number of hydrophilic oxygen-containing functional groups (carboxyl, hydroxyl, carbonyl, etc.). These groups give GO excellent dispersibility, hydrophilicity and other properties. Therefore, the GO membrane formed by a large number of stacked GO sheets has excellent separation performance.

[0003] However, existing graphene oxide membranes will swell in water, resulting in a significant decrease in material separation performance, which seriously restricts its membrane preparation process and practical application; therefore, it is extremely difficult to precisely control the interlayer spacing of GO nanosheets. It is necessary to overcome the swelling phenomenon under humidity conditions and ensure the stability of the physical and chemical properties at the interface, ultimately achieving precise control of the interlayer spacing at the sub-nanometer scale.

[0004] The network structure of silicone is simple and amorphous, which easily forms a dense layer and affects the water transmission rate. The current methods for preparing silicone membranes mainly include wiping, spin coating and drop coating. When the wiping method is used to prepare GO / silicone mixed matrix membranes, the GO nanosheets mixed in the silicone sol are more easily adsorbed on the wiping cotton sheet, resulting in the inability to attach GO to the support body; if the spin coating method is used to prepare the GO / silicone mixed matrix membrane, the solvent is required to have a certain viscosity to better disperse into the film; if the drop coating method is used to prepare the GO / silicone mixed matrix membrane, the GO / silicone mixed sol is dispersed too slowly and unevenly. Summary of the Invention

[0005] In order to overcome the deficiencies in the prior art, the present invention provides a GO-doped reverse osmosis mixed matrix membrane and a preparation method thereof.

[0006] The preparation method of the GO-doped reverse osmosis mixed matrix membrane provided by the present invention comprises the following specific steps:

[0007] (1) hydrolyzing and polymerizing a silicon source precursor and a hydrochloric acid catalyst in an ethanol solution with water to obtain an organosilicon polymer sol;

[0008] The silicon source precursor includes 1,2-Bis(triethoxysilyl)ethylene (BTESEthy) or 2,2′,2″-[(vinylsilyl)tri(oxy)]triethylamine (2,2′,2″-[(ethenylsilylidyne)tris(oxy)]tris-Ethanamine, hereinafter abbreviated as ETOTE).

[0009] The molar ratio of the silicon source precursor, water and hydrochloric acid is 1:60-180:0.2.

[0010] The hydrolysis polymerization reaction temperature is 25° C., and the hydrolysis polymerization reaction time is 2 h.

[0011] (2) stirring and dispersing graphene oxide (GO) nanosheets in water to obtain a dispersion, and then uniformly dispersing the dispersion into the organosilicon polymer sol obtained in step (1) by mixing and stirring to prepare a GO / unsaturated organosilicon polymer sol;

[0012] The size of graphene oxide (GO) nanosheets is 0.5-0.8 μm, the stirring and dispersion time is 10-30 min, and the obtained dispersion concentration is 0.1-1 mg / ml.

[0013] The weight ratio of graphene oxide (GO) to silicon source precursor (GB-n) in the polymer sol is 0.25-1:1, and the mixing time is 10-30 minutes.

[0014] (3) Cutting a ceramic tube, pre-treating it by grinding and boiling it in water, and coating it with a particle layer and an intermediate layer to obtain a ceramic support body.

[0015] The ceramic tube is an α-Al2O3 asymmetric ceramic tube with a pore size of 120nm;

[0016] The particle layer is a silica-zirconia particle sol layer containing α-Al2O3, the α-Al2O3 particle size is 0.2μm, 3-5 layers are applied, the drying temperature is 200℃, the drying time is 20min, the calcination temperature is 550℃, and the calcination time is 20min;

[0017] The middle layer of coating is silicon dioxide-zirconia particle sol, which is coated in 8-10 layers, with a calcination temperature of 550° C. and a calcination time of 20 minutes.

[0018] (4) The GO / organosilicon mixed sol was adsorbed onto a ceramic support by vacuum filtration and dried in an oven to obtain a GO / organosilicon mixed matrix membrane.

[0019] The filtration is dead-end filtration, the filtration time is 20-30min, the filtration vacuum degree is 260-400Pa, and the filtration temperature is 30-60℃.

[0020] The drying temperature is 80-100℃ and the drying time is 20min.

[0021] The graphene oxide (GO) / organic silicon mixed matrix membrane prepared by the present invention is used for reverse osmosis desalination.

[0022] Beneficial effects of the present invention:

[0023] (1) The graphene oxide (GO) / organic silicon mixed matrix membrane prepared in the present invention exhibits good water permeability (≥4.8×10 -4 mol / (m 2 hPa) and salt rejection (NaCl: ≥96%), and the membrane structure is stable over a long period of time during high-concentration desalination treatments with NaCl concentrations of 2000-10000 ppm. The selected graphene oxide (GO) basal plane or edge contains a large number of hydrophilic oxygen-containing functional groups (carboxyl, hydroxyl, carbonyl, etc.). These groups impart excellent dispersibility and hydrophilicity to the GO / organosilicon hybrid matrix membrane. By incorporating graphene oxide nanosheets into the organosilicon network, the dispersion of the nanosheets stretches the agglomerated network structure of the organosilicon membrane, unblocking the agglomerated organosilicon and forming new transport channels. The synergistic effect of graphene oxide and organosilicon creates more, newer, and more expansive water channels, significantly improving the desalination performance of the reverse osmosis membrane.

[0024] (2) The vacuum filtration method is used to prepare reverse osmosis membranes, which can produce highly interlocked and orderly stacked GO / organic silicon mixed matrix membranes. When the GO aqueous dispersion is assembled into a layered structure during liquid phase membrane formation, the graphene oxide nanosheets are interspersed in the network structure of the organosilicon and stretched out, which ensures the stability of the organosilicon network structure. At the same time, it also ensures that the layer spacing can freely pass water molecules and ions are trapped in the middle of the channel, thereby increasing the water flux and improving the retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, wherein:

[0026] Figure 1 This is a schematic diagram of the preparation process of the GO-doped reverse osmosis mixed matrix membrane in Example 1 of the present invention.

[0027] Figure 2These are SEM images of the cross section of the GO / BTESEthy mixed matrix membrane in Example 1 of the present invention (the three images are magnified electron microscope images of the same position).

[0028] Figure 3 This is a test diagram of the stability performance of the GO / BTESEthy mixed matrix membrane in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0030] Example 1

[0031] (1) Bis(triethoxysilyl)ethylene (BTESEthy) was used as a silicon source precursor and hydrochloric acid was used as a catalyst. A hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 h. The molar ratio of BTESEthy, water, and hydrochloric acid was 1:60:0.2, resulting in a 5 wt% BTESEthy polymer sol.

[0032] (2) 5 wt% BTESEthy polymer sol was diluted to 2 wt%, 0.1 mg / ml graphene oxide dispersion was added (the mass ratio of GO graphene oxide and polymer sol was 1:0.25), and stirred for 20 min to uniformly disperse to prepare GO / BTESEthy polymer sol. The GO / BTESEthy sample was designated as GB-0.25.

[0033] (3) The ceramic tube is an α-Al2O3 asymmetric ceramic tube with a pore size of 120 nm. 0.2 μm α-Al2O3 and silica-zirconia sol (the preparation process refers to Example 1 of patent CN105272370A) are mixed in a mass ratio of 1:3 and ultrasonically coated on the ceramic tube in three layers as a particle layer (thickness is about 2 μm). The drying temperature is 200°C, the drying time is 20 min, the calcination temperature is 550°C, and the calcination time is 20 min. Then, eight layers of silica-zirconia particle sol are coated on the particle layer as an intermediate layer (thickness is about 4 μm). The calcination temperature is 550°C, and the calcination time is 20 min.

[0034] (4) The GO / BTESEthy polymer sol was filtered by suction onto the α-Al2O3 asymmetric ceramic tube in step (3) as a separation layer (thickness of about 200 nm), wherein the filtration was dead-end filtration, the filtration time was 20 min, the filtration vacuum was 300 Pa, and the filtration temperature was 30°C. After filtration, the GO / BTESEthy mixed matrix membrane was obtained by drying at 80°C for 20 min. The prepared membrane was applied to the reverse osmosis desalination system. The water flux of the membrane under this condition was measured to be 2.9 mol / (m 2h Pa), and the rejection rate was 98.24%.

[0035] Example 2

[0036] (1) Bis(triethoxysilyl)ethylene (BTESEthy) was used as a silicon source precursor and hydrochloric acid was used as a catalyst. A hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 h. The molar ratio of BTESEthy, water, and hydrochloric acid was 1:120:0.2, resulting in a 5 wt% BTESEthy polymer sol.

[0037] (2) 5 wt% BTESEthy polymer sol was diluted to 2 wt%, 0.1 mg / ml graphene oxide dispersion was added (the mass ratio of GO graphene oxide and polymer sol was 1:0.25), and stirred for 30 min to uniformly disperse to prepare GO / BTESEthy polymer sol. The GO / BTESEthy sample was designated as GB-0.25.

[0038] Steps (3)-(4) are the same as those in Example 1. The prepared membrane is applied to a reverse osmosis desalination system. The water flux of the membrane under this condition is measured to be 3.3 mol / (m 2 h Pa), and the rejection rate was 97.21%.

[0039] Example 3

[0040] (1) Bis(triethoxysilyl)ethylene (BTESEthy) was used as a silicon source precursor and hydrochloric acid was used as a catalyst. A hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 h. The molar ratio of BTESEthy, water, and hydrochloric acid was 1:180:0.2, resulting in a 5 wt% BTESEthy polymer sol.

[0041] (2) 5 wt% BTESEthy polymer sol was diluted to 2 wt%, 0.1 mg / ml graphene oxide dispersion was added (the mass ratio of GO graphene oxide and polymer sol was 1:0.25), and stirred for 30 min to uniformly disperse to prepare GO / BTESEthy polymer sol. The GO / BTESEthy sample was designated as GB-0.25.

[0042] Steps (3)-(4) are the same as those in Example 1. The prepared membrane is applied to a reverse osmosis desalination system. The water flux of the membrane under this condition is measured to be 4.8 mol / (m 2 h Pa), and the rejection rate was 96.42%.

[0043] Example 4

[0044] (1) Using 2,2′,2″-[(vinylsilyl)tri(oxy)]triethylamine as a silicon source precursor and hydrochloric acid as a catalyst, a hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 hours. The molar ratio of ETOTE, water, and hydrochloric acid was 1:60:0.2, and a 5 wt% ETOTE polymer sol was obtained.

[0045] Steps (2) to (4) are the same as in Example 1. The water flux of the membrane under this condition was measured to be 3.1 mol / (m 2 hPa), and the rejection rate was 97.74%.

[0046] Example 5

[0047] (1) Bis(triethoxysilyl)ethylene (BTESEthy) was used as a silicon source precursor and hydrochloric acid was used as a catalyst. A hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 h. The molar ratio of BTESEthy, water, and hydrochloric acid was 1:120:0.2, resulting in a 5 wt% BTESEthy polymer sol.

[0048] (2) Dilute 5 wt% BTESEthy polymer sol to 2 wt%, add 0.5 mg / ml graphene oxide dispersion (the mass ratio of GO graphene oxide and polymer sol is 1:0.5), stir for 20 min to uniformly disperse and prepare GO / BTESEthy polymer sol. The GO / BTESEthy sample is designated as GB-0.5.

[0049] Steps (3) to (4) are the same as in Example 2. The water flux of the membrane under this condition was measured to be 4.6 mol / (m 2 hPa), and the rejection rate was 96.91%.

[0050] Example 6

[0051] (1) Bis(triethoxysilyl)ethylene (BTESEthy) was used as a silicon source precursor and hydrochloric acid was used as a catalyst. A hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 h. The molar ratio of BTESEthy, water, and hydrochloric acid was 1:180:0.2, resulting in a 5 wt% BTESEthy polymer sol.

[0052] (2) 5 wt% BTESEthy polymer sol was diluted to 2 wt%, 1.0 mg / ml graphene oxide dispersion was added (the mass ratio of GO graphene oxide and polymer sol was 1:1), and stirred for 20 min to uniformly disperse to prepare GO / BTESEthy polymer sol. The GO / BTESEthy sample was designated as GB-1.

[0053] Step (3) to step (4) are the same as in Example 3. The water flux of the membrane under this condition was measured to be 3.0 mol / (m2 hPa), and the rejection rate was 98.54%.

[0054] Example 7

[0055] (1) Using 2,2′,2″-[(vinylsilyl)tri(oxy)]triethylamine as a silicon source precursor and hydrochloric acid as a catalyst, a hydrolysis polymerization reaction was carried out in ethanol at 25°C with water and stirring for 2 hours. The molar ratio of ETOTE, water, and hydrochloric acid was 1:120:0.2, and a 5 wt% ETOTE polymer sol was obtained.

[0056] (2) 5 wt% ETOTE polymer sol was diluted to 2 wt%, and 0.5 mg / ml of graphene oxide dispersion was added (the mass ratio of graphene oxide to polymer sol was 1:0.5). The mixture was stirred for 20 min to uniformly disperse and prepare GO / ETOTE polymer sol. The GO / ETOTE sample was designated as GE-0.5.

[0057] Steps (3) to (4) are the same as in Example 1. The water flux of the membrane under this condition was measured to be 3.2 mol / (m 2 hPa), with a rejection rate of 97.89%.

[0058] Example 8

[0059] (1) Using 2,2′,2″-[(vinylsilyl)tri(oxy)]triethylamine as a silicon source precursor and hydrochloric acid as a catalyst, a hydrolysis polymerization reaction was carried out in ethanol at 25°C with stirring with water for 2 hours. The molar ratio of ETOTE, water, and hydrochloric acid was 1:180:0.2 to obtain a 5wt% ETOTE polymer sol.

[0060] (2) 5 wt% ETOTE polymer sol was diluted to 2 wt%, 0.5 mg / ml of graphene oxide dispersion was added (the mass ratio of graphene oxide to polymer sol was 1:1), and the mixture was stirred for 20 min to uniformly disperse and prepare GO / ETOTE polymer sol. The GO / ETOTE sample was designated as GE-1.

[0061] Step (3) to step (4) are the same as in Example 1. The water flux of the membrane under this condition was measured to be 3.8 mol / (m 2 hPa), and the rejection rate was 95.33%.

[0062] Comparative Example 1

[0063] Steps (1)-(2) are the same as in Example 1.

[0064] (3) The ceramic tube is an α-Al2O3 asymmetric ceramic tube with a pore size of 120 nm. The support body is calcined at a temperature of 550°C for 20 min.

[0065] (4) The GO / BTESEthy polymer sol was filtered onto an α-Al2O3 asymmetric ceramic tube by suction filtration, wherein the filtration was dead-end filtration, the filtration time was 30 min, the filtration vacuum was 300 Pa, and the filtration temperature was 30°C. After filtration, the GO / BTESEthy mixed matrix membrane was obtained by drying at 80°C for 20 min. The prepared membrane was applied to a reverse osmosis desalination system. The water flux of the membrane under this condition was measured to be 11.6 mol / (m 2 h Pa), and the rejection rate was 27.18%.

[0066] The results of the above embodiments and control tests are shown in Table 1.

[0067] Table 1

[0068] membrane <![CDATA[Flux mol / (m 2 h Pa)]]> Retention rate (%) Example 1 2.9 98.24 Example 2 3.3 97.21 Example 3 4.8 96.42 Example 4 3.1 97.74 Example 5 4.6 96.91 Example 6 3.0 98.54 Example 7 3.2 97.89 Example 8 3.8 95.33 Comparative Example 1 11.6 27.18

[0069] According to the experimental test results of Examples 1-7, the maximum flux of the prepared GO / unsaturated organosilicon mixed matrix membrane is 4.8 mol / (m 2 h Pa), the maximum retention rate was 98.54%.

[0070] According to the control example 1, a different silicon source precursor, 2,2′,2″-[(vinylsilyl)tri(oxy)]triethylamine, was used to measure the flux of GO / unsaturated organosilicon mixed matrix membrane, which was 2.2 mol / (m 2 h Pa), with a retention rate of 95.33%; it can be seen that the performance of this precursor is not as good as that of the bis(triethoxysilyl)ethylene (BTESEthy) organosilicon precursor. In subsequent studies, it is recommended to use bis(triethoxysilyl)ethylene (BTESEthy) as the precursor of the organosilica sol.

[0071] Stability test method: The prepared GO / unsaturated silicone mixed matrix membrane was continuously measured under the same environment (25°C, 2000ppm NaCl raw material solution, 1.0MPa) for 50h. Samples were taken every 1h for the first 10h (the first 10h was unstable and the sampling frequency was high), and samples were taken every 5 hours thereafter to calculate its water flux and retention rate.

Claims

1. A graphene oxide-doped reverse osmosis mixed matrix membrane, characterized in that: The reverse osmosis mixed matrix membrane is prepared by doping graphene oxide into an organosilicon polymer sol having unsaturated bridging groups, and forming a GO / organosilicon mixed matrix membrane on the surface of a prefabricated ceramic support by vacuum filtration; The steps of preparing the graphene oxide-doped reverse osmosis mixed matrix membrane are as follows: (1) The silicon source precursor and the hydrochloric acid catalyst are subjected to a hydrolysis polymerization reaction with water in an ethanol solution to obtain an organosilicon polymer sol; The silicon source precursor is bis(triethoxysilyl)ethylene (BTESEthy) or 2,2′,2″-[(vinylsilyl)tri(oxy)]triethylamine (ETOTE); (2) stirring and dispersing the graphene oxide nanosheets in water to obtain a dispersion, and then uniformly dispersing the dispersion into the organosilicon polymer sol obtained in step (1) under stirring to prepare a GO / unsaturated organosilicon polymer sol; (3) Cutting the ceramic tube, pre-treating it by grinding and boiling it in water, and then coating it with a particle layer and an intermediate layer to obtain a ceramic support body; (4) The GO / organosilicon polymer sol is adsorbed onto a ceramic support by vacuum filtration and dried in an oven to obtain a GO / organosilicon mixed matrix membrane.

2. The graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, wherein: In step (1), the molar ratio of the silicon source precursor, water, and hydrochloric acid is 1:60-180:0.2, the hydrolysis polymerization reaction temperature is 25° C., and the hydrolysis polymerization reaction time is 2 h.

3. The graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, wherein: The graphene oxide nanosheets in step (2) have a size of 0.5-0.8 μm, the stirring and dispersion time is 10-30 min, and the obtained dispersion concentration is 0.1-1 mg / ml.

4. The graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, wherein: The mass ratio of graphene oxide to silicon source precursor in the GO / unsaturated organosilicon polymer sol in step (2) is 0.25-1:

1.

5. The graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, wherein: The ceramic tube described in step (3) is an α-Al2O3 asymmetric ceramic tube with a pore size of 120nm; the particle layer is a silica-zirconia particle sol layer containing α-Al2O3, the α-Al2O3 particle size is 0.2µm, 3-5 layers are coated, the drying temperature is 200℃, the drying time is 20min, the calcination temperature is 550℃, and the calcination time is 20min; the coated intermediate layer is a silica-zirconia particle sol, 8-10 layers are coated, the calcination temperature is 550℃, and the calcination time is 20min.

6. The graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, wherein: The filtration in step (4) is dead-end filtration, the filtration time is 20-30 min, the filtration vacuum degree is 260-400 Pa, and the filtration temperature is 30-60°C.

7. The graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, wherein: The drying temperature of step (4) is 80-100°C and the drying time is 20 minutes.

8. A use of the graphene oxide-doped reverse osmosis mixed matrix membrane according to claim 1, characterized in that: Graphene oxide-doped reverse osmosis mixed matrix membrane for reverse osmosis desalination.

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