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NANOCOMPOSITE MEMBRANE FOR HEAVY METAL REJECTION AND PREPARATION METHOD THEREOF

20200330930 ยท 2020-10-22

    Inventors

    Cpc classification

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    Abstract

    The present invention discloses a nanocomposite membrane for heavy metal rejection and a preparation method thereof. The nanocomposite membrane comprises a porous membrane prepared from a two-dimensional sheet material and a hydrophilic inorganic nanomaterial distributed between the sheets of the two-dimensional material. The effective pore size of the nanocomposite membrane under wet conditions is not greater than 1.2 nm. The static water contact angle of the nanocomposite membrane is not greater than 45. The preparation method of the nanocomposite membrane comprises: adding reactants on both sides of a nanoporous membrane to carry out an interfacial synthesis reaction to obtain the nanocomposite membrane. The method is simple and controllable. Driven by lower pressure, heavy metal ions in water are rejected by a pore size screening function, thereby achieving the purpose of deep removal. The nanocomposite membrane can be used to quickly remove heavy metal ions from water.

    Claims

    1. A nanocomposite membrane for heavy metal rejection, comprising: (1) a nanoporous membrane; and (2) a hydrophilic inorganic nanomaterial distributed in the interior and on the surface of the nanoporous membrane; and the average effective pore size of the nanocomposite membrane under wet conditions is not greater than 1.2 nm.

    2. The nanocomposite membrane for heavy metal rejection according to claim 1, wherein the static water contact angle of the nanocomposite membrane is not greater than 45.

    3. The nanocomposite membrane for heavy metal rejection according to claim 1, wherein the average effective pore size of the nanocomposite membrane under wet conditions is less than 1.2 nm.

    4. The nanocomposite membrane for heavy metal rejection according to claim 3, wherein the hydrophilic inorganic nanomaterial is synthesized from reactants through an interfacial reaction by using a nanoporous membrane as an interface.

    5. The nanocomposite membrane for heavy metal rejection according to claim 1, wherein the nanoporous membrane is prepared from a two-dimensional sheet material and a polymer base membrane, and the two-dimensional sheet material comprises any one or a combination of two or more of molybdenum sulfides, molybdenum selenides, tungsten sulfides, tungsten selenides, platinum selenides, rhenium selenides, tin sulfides, graphenes, graphene derivatives, C.sub.3N.sub.4, Ti.sub.4N.sub.3, and layered double hydroxides.

    6. The nanocomposite membrane for heavy metal rejection according to claim 5, wherein the hydrophilic inorganic nanomaterial comprises, but is not limited to any one or a combination of two or more of silicates, phosphates, metal sulfides, metal oxides and metal hydroxides.

    7. A preparation method of the nanocomposite membrane for heavy metal rejection according to claim 1, comprising the following steps: (1) dispersing a two-dimensional sheet material in water to prepare a two-dimensional sheet material dispersion, and then, pouring the dispersion into a suction flask in which a polymer base membrane is placed in advance, to carry out suction filtration and washing to obtain a nanoporous membrane; and (2) fixing the nanoporous membrane in a reaction tank, adding reactant A and reactant B on both sides of the nanoporous membrane so that the reactant A and the reactant B interfacially synthesize a hydrophilic inorganic nanomaterial, and washing to obtain a nanocomposite membrane.

    8. The preparation method of the nanocomposite membrane for heavy metal rejection according to claim 7, wherein in the step (1), the two-dimensional nanosheet dispersion is prepared by ultrasonic dispersion, ultrasonic time is 0.02-10 h, and the concentration of the two-dimensional nanosheet dispersion is 0.0001-200 mg/L.

    9. The preparation method of the nanocomposite membrane for heavy metal rejection according to claim 8, wherein the suction filtration in the step (1) is carried out at a pressure of 0.01-1 bar for 0.01-15 h.

    10. The preparation method of the nanocomposite membrane for heavy metal rejection according to claim 9, wherein the time of the interfacial synthesis reaction in the step (2) is 0.1-24 h.

    11. The nanocomposite membrane for heavy metal rejection according to claim 2, wherein the average effective pore size of the nanocomposite membrane under wet conditions is less than 1.2 nm.

    12. The nanocomposite membrane for heavy metal rejection according to claim 11, wherein the hydrophilic inorganic nanomaterial is synthesized from reactants through an interfacial reaction by using a nanoporous membrane as an interface.

    13. The nanocomposite membrane for heavy metal rejection according to claim 2, wherein the nanoporous membrane is prepared from a two-dimensional sheet material and a polymer base membrane, and the two-dimensional sheet material comprises any one or a combination of two or more of molybdenum sulfides, molybdenum selenides, tungsten sulfides, tungsten selenides, platinum selenides, rhenium selenides, tin sulfides, graphenes, graphene derivatives, C.sub.3N.sub.4, Ti.sub.4N.sub.3, and layered double hydroxides.

    14. The nanocomposite membrane for heavy metal rejection according to claim 13, wherein the hydrophilic inorganic nanomaterial comprises, but is not limited to any one or a combination of two or more of silicates, phosphates, metal sulfides, metal oxides and metal hydroxides.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0036] FIG. 1 is a schematic view showing the preparation of a nanocomposite membrane of the present invention;

    [0037] FIG. 2 is a schematic cross-sectional (sectional) view of the nanocomposite membrane prepared in Example 1 of the present invention;

    [0038] FIG. 3 is a scanning electron micrograph of the surface of the nanocomposite membrane prepared in Example 1 of the present invention;

    [0039] FIG. 4 is an atomic force micrograph of the nanocomposite membrane prepared in Example 1 of the present invention;

    [0040] FIG. 5 is an X-ray diffraction pattern of the nanocomposite membrane prepared in Example 1 of the present invention;

    [0041] FIG. 6 is a comparison diagram of water contact angles of the nanocomposite membranes prepared in Example 1 and Comparative Example 1 of the present invention;

    [0042] FIG. 7 is a graph showing the rejection data of five kinds of heavy metal ions by the nanocomposite membrane prepared in Example 1 of the present invention.

    DETAILED DESCRIPTION

    [0043] The present invention is further described below with reference to specific embodiments.

    Example 1

    [0044] The nanocomposite membrane in this example was prepared by the steps as follows.

    [0045] 1) Preparation of a two-dimensional sheet material dispersion: Commercially available single-layer molybdenum diselenide was purchased and prepared by chemical vapor deposition into a two-dimensional sheet material with a diameter of 20-50 m and a thickness of 0.6-0.8 nm. The two-dimensional sheet material was dispersed in deionized water and ultrasonicated for 5 h to prepare the dispersion having a concentration of 0.02 g/L.

    [0046] 2) Preparation of a molybdenum diselenide porous membrane: A hydrophilic PVDF membrane (pore size: 0.22 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 10 mL of the dispersion prepared in step 1) was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 0.01 h at a pressure of 1 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the obtained membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the molybdenum diselenide porous membrane was obtained.

    [0047] 3) Interfacial reaction synthesis of the nanocomposite membrane: The molybdenum diselenide porous membrane was fixed in a reaction tank. 20 mL of a potassium phosphate solution having a concentration of 0.01 mol/L and 15 mL of a calcium chloride solution having a concentration of 0.01 mol/L were successively added. A reaction was carried out at 351 C. for 10 h. The porous membrane was taken out and placed in deionized water for soaking and washing, and the nanocomposite membrane was prepared and stored in deionized water.

    [0048] As shown in FIG. 1, during the interfacial synthesis reaction, the molybdenum diselenide porous membrane was positioned in the middle of the reaction tank, reactant 1 was the potassium phosphate solution, and reactant 2 was the calcium chloride solution.

    [0049] A schematic cross-sectional (sectional) diagram of the nanocomposite membrane of the present invention is shown in FIG. 2. According to FIG. 2, the hydrophilic calcium phosphate generated by the interfacial reaction is stably dispersed between the molybdenum diselenide sheets. The scanning electron micrograph of the surface of the composite membrane is shown in FIG. 3. According to FIG. 3, the surface of the nanocomposite membrane is smooth, and no obvious defects are found. The atomic force micrograph of the composite membrane is shown in FIG. 4. According to FIG. 4, the thickness of the nanocomposite membrane is 18015 nm. The X-ray diffraction pattern (FIG. 5) of the composite membrane has a diffraction peak at 8.87. According to the Bragg equation, the nanocomposite membrane has an interlayer spacing of 0.99 nm.

    [0050] The contact angle of the porous membrane of this example was measured. The water contact angle was measured to be 22.43.2, and the pore size was 0.65 nm (under wet conditions). The manner in which the pore size was measured under wet conditions employs an universal ion calibration method for nanomembranes in the prior art.

    [0051] According to the Yang-Laplace equation, as the hydrophilicity increases, the Laplace additional pressure of nanopores increases. Therefore, the nanocomposite membrane has a larger water flux at a low pressure.

    [0052] Filtration and rejection of heavy metals using the nanocomposite membrane:

    [0053] The nanocomposite membrane prepared above was fixed in an ultrafiltration cup, and different concentrations of heavy metal ions aqueous solutions were added to carry out a filtration and rejection test at an operating pressure of 1 bar.

    [00001] L = V A .Math. t .Math. .Math. .Math. p .Math. .Math. Rejection .Math. .Math. % = c 0 - c t c 0 100 .Math. % .Math. .Math. ,

    [0054] where L is the water flux, V is the filtration volume, A is the effective area of the membrane, t is the filtration time, p is the operating pressure, Rejection % is the rejection rate of heavy metal ions of the nanocomposite membrane, and C.sub.0 and C.sub.t are the concentrations of heavy metal ions in water before and after filtration respectively. The rejection test of heavy metal ions by the composite membrane prepared in Embodiment 1 at an operating pressure of 1 bar is shown in Table 1. FIG. 7 is a graph showing the rejection data of five kinds of heavy metal ions by the nanocomposite membrane prepared in Example 1 of the present invention.

    TABLE-US-00001 TABLE 1 Rejection test of heavy metal ions by composite membrane prepared in Example 1 (operating pressure: 1 bar) Rejection Heavy metal L (L/m.sup.2h) C.sub.0 (mg/L) C.sub.t (mg/L) rate (%) Pb.sup.2+ 35 2 0.02 99.0 Cd.sup.2+ 37 2 0.04 98.1 Cu.sup.2+ 50 2 0.01 99.2 Zn.sup.2+ 21 2 0.08 95.6 Cr.sup.3+ 31 2 0.03 98.6

    Example 2

    [0055] The nanocomposite membrane in this example was prepared by the steps as follows.

    [0056] Commercially available single-layer tungsten disulfide was purchased and prepared by chemical vapor deposition into a two-dimensional sheet material with a diameter of 20-30 m and a thickness of 0.6-0.8 nm. The two-dimensional sheet material was dispersed in deionized water and ultrasonicated for 10 h to prepare the dispersion having a concentration of 200 mg/L.

    [0057] A hydrophilic PVDF membrane (pore size: 0.22 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 10 mL of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 2 h at a pressure of 0.05 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the tungsten disulfide porous membrane was obtained.

    [0058] The tungsten disulfide porous membrane was fixed in a reaction tank. 20 mL of a 0.02 mol/L zirconium oxychloride solution and 20 mL of a 0.02 mol/L potassium carbonate solution were successively added. A reaction was carried out at 351 C. for 24 h. Zirconium hydroxide nanoparticles were formed inside the porous membrane by an interfacial reaction and stably dispersed between the sheets of the two-dimensional material. After the reaction, the porous membrane was taken out and placed in deionized water for soaking and washing, and the nanocomposite membrane was prepared and stored in deionized water.

    [0059] The contact angle of the porous membrane of this example was measured to be 8.22, and the pore size was 0.60 nm (under wet conditions).

    Example 3

    [0060] The nanocomposite membrane in this example was prepared by the steps as follows.

    [0061] Graphene oxide was prepared by the Hummers method, and the preparation method refers to a patent with the patent application No. 201810242893.6. The graphene oxide has a diameter of 0.2-10 m and a thickness of 1.2-1.8 nm. The graphene oxide was dispersed in deionized water and ultrasonicated for 5 h to prepare the dispersion having a concentration of 10 mg/L.

    [0062] A hydrophilic PVDF membrane (pore size: 0.22 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 50 ml of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 15 h at a pressure of 0.01 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the graphene oxide porous membrane was obtained.

    [0063] The graphene oxide porous membrane was fixed in a reaction tank. 20 mL of a 0.02 mol/L potassium sulfide solution and 20 mL of a 0.02 mol/L lanthanum nitrate solution were successively added. A reaction was carried out at room temperature (221 C.) for 10 h. Lanthanum sulfide nanoparticles were formed inside the porous membrane by an interfacial reaction and stably dispersed between the sheets of the two-dimensional material. After the reaction, the porous membrane was taken out and placed in deionized water for soaking and washing, and the nanocomposite membrane was prepared and stored in deionized water.

    [0064] The contact angle of the porous membrane of this example was measured to be 392.6, and the pore size was 0.82 nm (under wet conditions).

    Example 4

    [0065] The nanocomposite membrane in this example is prepared by the steps as follows.

    [0066] Preparation of CoAl-LDHs: CoCl.sub.3.6H.sub.2O and AlCl.sub.3.6H.sub.2O were mixed in a molar ratio of 1:2 to prepare a salt solution. With stirring, a 0.5 M aqueous ammonia solution was added until a precipitate was formed completely. Filtration was carried out using a Buchner funnel to obtain the precipitate. The precipitate was thermally insulated at 901 C. for 24 h and then dried to obtain the CoAl-LDHs. Observed by scanning electron microscopy, the particle size of the CoAl-LDHs was 200-300 nm. The CoAl-LDHs was dispersed in deionized water and ultrasonicated for 0.02 h to obtain the dispersion having a concentration of 0.0001 mg/L.

    [0067] A hydrophilic PVDF membrane (pore size: 0.1 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 20 ml of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 2 h at a pressure of 0.05 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the CoAl-LDHs porous membrane was obtained.

    [0068] The CoAl-LDHs porous membrane was fixed in a reaction tank. 20 mL of a 0.02 mol/L sodium silicate solution and 25 mL of a 0.02 mol/L cerium chloride solution were successively added. A reaction was carried out at 421 C. for 0.1 h. Cerium silicate nanoparticles were formed inside the porous membrane by an interfacial reaction and stably dispersed between the sheets of the two-dimensional material. After the reaction, the porous membrane was taken out and placed in deionized water for soaking and washing, and the nanocomposite membrane was prepared and stored in deionized water.

    [0069] The contact angle of the porous membrane of this example was measured to be 20.61.6, and the pore size was 0.69 nm (under wet conditions).

    Example 5

    [0070] The nanocomposite membrane in this example is prepared by the steps as follows.

    [0071] Preparation of C.sub.3N.sub.4: 5 g of urea was placed in a crucible, and reacted at 550 C. for 10 h in a tube furnace to obtain a C.sub.3N.sub.4 sheet material. Observed by scanning electron microscopy, the particle size of the C.sub.3N.sub.4 sheet material was 100-500 nm. The C.sub.3N.sub.4 sheet material was dispersed in deionized water and ultrasonicated for 2 h to obtain the dispersion having a concentration of 0.05 g/L.

    [0072] A hydrophilic PVDF membrane (pore size: 0.1 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 20 ml of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 2 h at a pressure of 0.05 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the C.sub.3N.sub.4 porous membrane was obtained.

    [0073] The C.sub.3N.sub.4 porous membrane was fixed in a reaction tank. 10 mL of a 0.02 mol/L metatitanic acid solution and 55 mL of a 0.02 mol/L hydrochloric acid solution were successively added. A reaction was carried out at 601 C. for 2 h. Titanium dioxide nanoparticles were formed inside the porous membrane by an interfacial reaction and stably dispersed between the sheets of the two-dimensional material. After the reaction, the porous membrane was taken out and placed in deionized water for soaking and washing, and the nanocomposite membrane was prepared and stored in deionized water.

    [0074] The contact angle of the porous membrane of this example was measured to be 15.00.9, and the pore size was 1.1 nm (under wet conditions).

    Comparative Example 1

    [0075] The nanoporous membrane in this comparative example is prepared by the steps as follows.

    [0076] Commercially available single-layer molybdenum diselenide was purchased and prepared by chemical vapor deposition into a two-dimensional sheet material with a diameter of 20-50 m and a thickness of 0.6-0.8 nm. The two-dimensional sheet material was dispersed in deionized water and ultrasonicated for 5 h to prepare the dispersion having a concentration of 0.02 g/L.

    [0077] A hydrophilic PVDF membrane (pore size: 0.22 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 10 ml of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 0.01 h at a pressure of 1 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the molybdenum diselenide porous membrane was obtained.

    [0078] The contact angle of the porous membrane of this comparative example was measured to be 65.63.1, and the pore size was 1.67 nm (under wet conditions). FIG. 6 is a comparison diagram of water contact angles of the nanocomposite membranes prepared in Example 1 and Comparative Example 1 of the present invention. The rejection test of heavy metal ions by the porous membrane prepared in Comparative Example 1 is shown in Table 2.

    TABLE-US-00002 TABLE 2 Rejection test of heavy metal ions by porous membrane prepared in Comparative Example 1 (operating pressure: 1 bar) Rejection Heavy metals L (L/m.sup.2h) C.sub.0 (mg/L) C.sub.t (mg/L) rate (%) Pb.sup.2+ 3 2 0.94 53.0 Cd.sup.2+ 3 2 1.16 42.1 Cu.sup.2+ 5 2 1.26 37.6 Zn.sup.2+ 2 2 1.44 28.4 Cr.sup.3+ 3 2 1.28 36.1

    [0079] According to Table 1 and Table 2, the nanocomposite membrane prepared by the present invention has a higher water flux, reaching 21-50 L/m.sup.2h, and has a rejection rate of heavy metals reaching 96%-99%. The nanoporous membrane in the prior art has a water flux of only 2-5 L/m.sup.2h, and a rejection rate of heavy metals reaching only 28%-53%.

    Comparative Example 2

    [0080] The nanoporous membrane in this comparative example is prepared by the steps as follows.

    [0081] Graphene oxide was prepared by the Hummers method with reference to a preparation method in a patent with the application No. 201810242893.6. The prepared graphene oxide has a diameter of 0.2-10 m and a thickness of 1.2-1.8 nm. The graphene oxide was dispersed in deionized water and ultrasonicated for 5 h to prepare the dispersion having a concentration of 10 mg/L.

    [0082] A hydrophilic PVDF membrane (pore size: 0.22 m) was fixed in a suction filter flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 50 ml of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 15 h at a pressure of 0.01 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the graphene oxide porous membrane was obtained.

    [0083] The contact angle of the porous membrane of this comparative example was measured to be 60.32.0, and the pore size was 1.34 nm (under wet conditions).

    Comparative Example 3

    [0084] The nanoporous membrane in this comparative example is prepared by the steps as follows.

    [0085] Preparation of CoAl-LDHs: CoCl.sub.3.6H.sub.2O and AlCl.sub.3.6H.sub.2O were mixed in a molar ratio of 1:2 to prepare a salt solution. With stirring, a 0.5 M aqueous ammonia solution was added until a precipitate was formed completely. Filtration was carried out using a Buchner funnel to obtain the precipitate. The precipitate was thermally insulated at 901 C. for 24 h and then dried to obtain the CoAl-LDHs. Observed by scanning electron microscopy, the particle size of the CoAl-LDHs was 200-300 nm. The CoAl-LDHs was dispersed in deionized water and ultrasonicated for 0.02 h to obtain the dispersion having a concentration of 0.0001 mg/L.

    [0086] A hydrophilic PVDF membrane (pore size: 0.1 m) was fixed in a suction flask, and the effective area of the hydrophilic PVDF membrane was 2.01 cm.sup.2. 10 mL of the above dispersion was taken and poured into a glass tube over the membrane of the suction flask. A vacuum circulating water pump was used for suction filtration for 2 h at a pressure of 0.05 bar. After water in the dispersion was completely extracted from the bottom of the membrane, the membrane (together with the PVDF membrane) was taken out, and soaked and washed in deionized water. After 24 h, the CoAl-LDHs porous membrane was obtained.

    [0087] The contact angle of the porous membrane of this comparative example was measured to be 59.05.3, and the pore size was 1.80 nm (under wet conditions). Comparison of the pore size and contact angle of the membranes prepared in examples and comparative examples is shown in Table 3.

    TABLE-US-00003 TABLE 3 Comparison of pore size and contact angle of membranes prepared in examples and comparative examples Hydrophilic Water inorganic Nanoporous contact Pore Name Reactant A Reactant B nanomaterial membrane angle size* Example 1 Potassium Calcium Calcium Molybdenum 22.4 3.2 0.65 nm phosphate chloride phosphate diselenide Example 2 Zirconium Potassium Zirconium Tungsten 8.2 2 0.60 nm oxychloride carbonate hydroxide disulfide Example 3 Lanthanum Potassium Lanthanum Graphene .sup.39 2.6 0.82 nm nitrate sulfide sulfide oxide Example 4 Cerium Sodium Cerium CoAl-LDHs 20.6 1.6 0.69 nm chloride silicate silicate Example 5 Metatitanic Hydrochloric Titanium C.sub.3N.sub.4 15.0 0.9 1.1 nm acid acid dioxide Comparative Molybdenum 65.6 3.1 1.67 nm example 1 diselenide Comparative Graphene 60.3 2.0 1.34 nm example 2 oxide Comparative CoAl-LDHs 59.0 5.3 1.80 nm example 3 Note: The pore size here is the pore size of the nanomembrane under wet conditions.