CN111841340A

CN111841340A - Filtering assembly with porous carbon film, filtering device and application

Info

Publication number: CN111841340A
Application number: CN201910333600.2A
Authority: CN
Inventors: 力小安; 艾承颖; 罗伯特·梅耶尔; 维尔拉·博斯
Original assignee: Nanjing Momentum Material Technology Co ltd
Current assignee: Nanjing Momentum Material Technology Co ltd
Priority date: 2019-04-24
Filing date: 2019-04-24
Publication date: 2020-10-30

Abstract

The invention discloses a filter assembly and a filter device and application, which comprises one or more layers of porous carbon films with an interconnected porous open network structure, wherein holes are formed by removing inorganic particles with specific sizes from carbonized precursor films containing carbon and inorganic particles with specific sizes. The filter assembly or the filter device is suitable for filtering nano and submicron-sized particles such as nano particles, viruses, bacteria and the like, can select the size of the filter holes according to the size of the particles, and is suitable for various filtering processes. In addition, the filter assembly or filter device of the present invention is prepared from relatively low cost raw materials, and has the advantages of simple process, high mechanical strength, high conductivity, high porosity, continuous nanopores, pore-controlled orientation, and easy mass production.

Description

Filtering assembly with porous carbon film, filtering device and application

Require priority

The present patent application claims the benefit of priority of U.S. provisional application No. US/2018.62715085 entitled "FILTRATION assembly USING NANOPOROUS CARBON membrane (FILTRATION USING membrane MEMBRANES)" filed on 8/6/2018, which is hereby incorporated by reference in its entirety.

Technical Field

The present invention relates to a filter assembly and a filter device, in particular to the use of a porous carbon membrane (also referred to herein as a membrane) as a filter material and a filter apparatus comprising one or more layers of such porous carbon membranes; belongs to the technical field of filtration.

Background

The filtration is a unit operation belonging to the fluid dynamic process, wherein fluid in a liquid-solid or gas-solid mixture is forced to pass through a porous filter medium, suspended solid particles in the fluid are intercepted, and the separation of the mixture is realized. With the development of technology, membrane filtration, which is a precision separation technology for realizing molecular-level filtration, has been developed in recent years, and is a technology for performing two-phase separation by utilizing the selective permeability of membrane pores. The pressure difference between two sides of the membrane is used as driving force to make solvent, inorganic ions, small molecules and the like permeate the membrane to intercept particles and macromolecules. Membrane filtration technology is beginning to be used frequently in various devices, especially in devices such as gas-liquid filtration screens.

The core element of the membrane filter is a filter membrane, which is a thin film with more tiny pores distributed on a micropore supporting layer (supporting body). There are many materials for making filtration membranes, including organic membranes (such as polysulfone hollow fiber membranes) and inorganic membranes. The filter membrane is used as a filter element, and has the structural characteristic that a filter layer is very thin, so the filter mechanism of the filter membrane is mainly a screening effect, and the adsorption effect is very small. Therefore, the membrane filter has high filtration precision, stable particle size control and easy back washing recovery performance. However, if the water contains oil, it is easily clogged and is not easily backwashed. Many researchers at home and abroad hope to treat produced water by ceramic membranes based on the hydrophilic property of ceramic materials, but after the research, the membrane pollution problem is generally considered to be difficult to solve.

Carbon materials having a nano structure have been widely researched and widely used. This is because it has the following advantages: low specific gravity, good electrical conductivity, high surface area, ease of surface modification, and suitability for large-scale production. Such materials are carbon black, carbon nanotubes, carbon nanofibers, ordered mesoporous carbon, and the like. Porous colloidal-imprinted carbon (CIC) powders have also been prepared, with narrow pore size distribution and three-dimensionally connected nanopores. These nanomaterials are applied to many aspects such as electrochemical devices including batteries, capacitors and fuel cells. Most of these carbon materials are only available in powder form, limiting their range of applications. The orientation of individual nanoporous carbon particles is different, mass transfer through the nanopores is influenced, and the reproducibility of product performance is poor. In addition, particulate contamination has been viewed as an increasing problem and the use of carbon powders can cause health concerns. If the carbon material with the nano structure can be applied to the technical field of filtration, the better development of the industry is certainly driven.

The core element filter membrane of the membrane filter in the prior art mainly depends on outsourcing, has the problems of unadjustable size range, uncontrollable pore density and the like, and can not be effectively and timely clarified after membrane pollution, thereby influencing the filtering effect. In view of the above, it is necessary to conduct more intensive research on the membrane filter.

Disclosure of Invention

In order to solve the defects of the prior art, the invention aims to provide a filtering component or a filtering device with a nano-porous carbon film, and also discloses an application direction of the filtering component or the filtering device.

In order to achieve the above object, the present invention adopts the following technical solutions:

a filter assembly having a porous carbon film comprising one or more layers of porous carbon film having an open network and interconnected pore structures within the porous carbon film formed by removing inorganic particles from a carbonized non-porous precursor film.

Preferably, the pore diameter of the pore structure of the at least one layer of porous carbon film is 2 nm-100 nm; more preferably, pores smaller than 2nm or between 0.1 and 100 μm are formed in the porous carbon film.

Preferably, the at least one porous carbon membrane has a specific surface area of 1m²/g-2000m²(ii)/g; in some embodiments, at least one of the films has a specific surface area of 10 to 1000m²/g。

Still preferably, wherein the at least one porous carbon film is on a porous support. The thickness of the porous carbon film is substantially less than its lateral dimension, and thus, in some embodiments, the lateral dimension has a macroscopic dimension (e.g., greater than 1mm or 1 cm), while the thickness dimension is on a nanometer or micrometer scale. In some embodiments, the membrane has sufficient mechanical strength to be self-supporting, i.e., to support its structure without a support. In other embodiments, the membrane is supported by a suitable support.

More preferably, the porous support is selected from any one of metal, glass, ceramic, carbon paper or carbon fiber.

Further preferably, when the porous carbon film is a plurality of layers, a porous structure separator, such as glass fiber paper, is further disposed between two adjacent layers of the porous carbon film to ensure the filtering effect.

Still further preferably, the aforementioned filter assembly having a porous carbon film, at least one layer of the porous carbon film:

(a) comprising a gradient of porosity through the thickness of the film, and/or

(b) Is electrically conductive; and/or

(c) Surface functional group modification is carried out, and the functional groups can be positively charged or negatively charged; surface-modifying groups include pentafluorophenyl, aminophenyl, nitrophenyl, benzenesulfonic acid groups, and combinations thereof.

Still further preferably, the aforementioned porous carbon film is a nanoporous carbon film, which is a previous scientific research result of the present applicant, and PCT publication No. WO 2015/135069. PCT application WO2015/135069, published 9/17/2015, relates to a method of preparing a porous carbon film, and WO2015/135069 is incorporated by reference in its entirety for the description of porous carbon films therein and methods of preparing the same. These membranes comprise nanoporous carbon films composed of an open network of interconnected channels, wherein the network comprises a three-dimensional network of interconnected channels. In some embodiments, the membrane comprises channels having a size of 2nm to 100nm (nano-pore size); in other embodiments, the pores are macropores (pore size greater than 100nm but less than 1 μm). The pore size of these membranes can be selected during membrane preparation by selecting the size of the inorganic particles (particle templates) incorporated into the membrane, and removing the inorganic particles after membrane formation to obtain a porous carbon membrane. In other embodiments, the film comprises pores having a broader range of size distribution, for example from <2nm to >100 nm. In some embodiments, a pore gradient may also be formed across the thickness of the film.

The nanoporous carbon film described in WO2015/135069 is more advanced than the nanoporous carbon film in the prior art because it is prepared from relatively low cost raw materials, by less complex, cumbersome or time consuming processes and exhibits the following advantages: higher mechanical strength, higher conductivity, high porosity, continuous nanopores, controllable pore orientation, uniform pore diameter, controllable size range and pore density, stable property and the like, is a filter material which can carry out expected size separation and has enough mechanical strength, and is easy for mass production.

The invention also discloses a filtering device with the porous carbon film, which comprises the nano porous carbon film and a filter shell for placing the nano porous carbon film, wherein the filter shell comprises an upper shell, a port for connecting an inflow end and a lower shell for supporting the porous carbon film, the upper shell and the lower shell are hermetically connected through threads, a lead is arranged on a support of the lower shell and is in contact with the nano porous carbon film to form a first electrode, a conductor material is arranged on the surface of the upper shell to serve as a second electrode, and voltage is applied between the first electrode and the second electrode when the filtering device is used. The conductor material is a metal material such as Ni, Pt, gold, or a non-metal material such as carbon, graphite, and may be in the form of wire, net, or sheet, or a nanoporous carbon film.

The filter assembly having the porous carbon membrane as described above is applied to nanoparticle filtration, bacterial or viral filtration, and may employ any one of gravity filtration, pressure filtration, vacuum filtration, direct flow filtration or cross flow filtration.

The invention has the advantages that:

(1) the filter assembly and the filter device comprise one or more layers of porous carbon films, wherein the porous carbon films are provided with open networks and interconnected pore channel structures, and the pore channel structures are formed by removing inorganic particles from carbonized nonporous precursor films, so that the pore orientation, the pore density and the pore size are controllable, and the proper size of filter pores can be selected according to substances to be filtered;

(2) the filtering component and the filtering device have wide application range, are not only suitable for filtering conventional particle impurities, but also suitable for filtering nano particles and nano/submicron-sized particles such as bacteria or viruses, and can adopt any one of gravity filtration, pressure filtration, vacuum filtration, direct-current filtration or cross-flow filtration as required;

(3) the filtering component and the filtering device are prepared from relatively low-cost raw materials, have the advantages of simple process, high mechanical strength, high conductivity, high porosity, continuous nano pores, pore control orientation, easiness in large-scale production and the like, and have good market popularization prospect.

Drawings

FIG. 1 is a schematic structural view of a filter assembly of example 2 of the present invention;

FIG. 2 is a schematic structural view of a filtration apparatus according to example 3 of the present invention;

FIG. 3 is a schematic view of a multi-layer membrane filtration module composed of the two-layer nanoporous carbon membrane of example 4;

FIG. 4 is a schematic diagram of a multi-layer membrane filtration assembly of example 5 in which multiple nanoporous carbon membranes are arranged in series;

FIG. 5 is a schematic of the cross-flow filtration mode of example 6;

FIG. 6A is a graph showing the comparative effect before and after filtration of the silica suspension of application example 1;

FIG. 6B is an EDX spectrum of the filtrate after filtration;

FIG. 7 is a graph showing the comparative effect before and after filtration of the gold nanoparticle suspension of application example 2;

FIG. 8 is a graph showing the comparative effect before and after filtration of the suspension of Vulcan Carbon particles of application example 3;

FIG. 9A is a graph showing the comparative effect before and after filtration of Escherichia coli of application example 4;

FIG. 9B is a graph showing the comparative effect of the M13 virus of application example 4 before and after filtration;

FIG. 10 is a schematic view of a filter device with an electric pulse function according to example 7;

FIG. 11 is a comparative graph of the filtering effect before and after the application of an electric pulse to a nanocarbon film;

FIG. 12A is an SEM image of a cross-section of an NCS-22 membrane after filtration of a 22nm silica colloid;

FIG. 12B is a graph showing the distribution of Si elements in the NCS-22 film after filtering 22nm silica gel;

FIG. 13A is an SEM image of a cross-section of an NCS-22 membrane after filtration of an 8nm silica colloid;

FIG. 13B is a graph of Si distribution in the NCS-22 film after filtering 8nm silica gel;

FIG. 14 is an SEM image of an NCS-22 film showing a 7nm connection hole (arrow in the figure);

FIG. 15A is an SEM image of an NCS-85 film showing a 15nm connection hole (arrow in the figure);

fig. 15B is a partially enlarged view of fig. 15A.

Detailed Description

The invention is described in detail below with reference to the figures and the embodiments.

As indicated previously, the nanoporous carbon films used in the present application were a preliminary scientific effort by the present team, and the specific preparation thereof was disclosed in detail in PCT application WO2015/135069, the entire content of which is incorporated herein by reference.

The synthesis principle of the porous carbon film is as follows: the porous carbon film is formed by first forming a mixture containing particles of an inorganic material, a carbon precursor material and water, other solvent, or a mixture of other solvent and water, then forming a layer of the mixture on a substrate, then removing the water or other solvent from the layer of the mixture to form a non-porous film containing inorganic particles, heating (carbonizing) the film to convert the carbon precursor therein to carbon, thereby forming a composite film containing carbon and the particle material, and finally removing the particle material from the composite film. The particulate material acts as a sacrificial template for pore formation in porous carbon film synthesis. In an embodiment, the film has been peeled off from the substrate before it is carbonized. As described in this document, the carbon film is mainly composed of carbon, and the mass fraction of the elements other than carbon in the carbon film is less than 20%, 10%, 5%, 2%, or 1%, respectively. When the pores in the porous carbon film are in the size range of 2 nm to 100 nm, the porous carbon film may be referred to as a Nanoporous Carbon Film (NCF). The mixture for forming the porous nanocarbon film is also referred to as a synthesis mixture. In embodiments, the mass fraction of water in the synthesis mixture is in the range of 1% to 99% or 40% to 90%. In some embodiments, the synthesis mixture further comprises a non-aqueous solvent (e.g., an organic solvent), or a mixture of one or more solvents, including a mixture of water and one or more organic solvents.

The resultant mixture containing the inorganic particulate template material, carbon precursor, and water may also be referred to as an ink slurry. In embodiments, the inorganic particles used as pore-forming templates may be any inorganic material that does not react with carbon and its precursors during the preparation process. The template material may be a metal oxide, and the metal oxide particles may be suspended in an aqueous solution or a mixed solvent, or in an aqueous solution or a mixed solvent to which a stabilizer (e.g., an ionic stabilizer) is added. Suitable metal oxides include, but are not limited to, silica-based materials, alumina-based materials, titania-based materials, and magnesia-based materials. Suitable silica-based templates include, but are not limited to, colloidal silica. In embodiments, the inorganic template material has an average particle size of 2nm to 100nm, 5nm to 50nm, 5nm to 25nm, 25nm to 50nm, or 50nm to 100 nm. In some embodiments, inorganic particles having a particle size outside of the above ranges will result in a carbon film having a pore size greater than 100nm or less than 2 nm. In further embodiments, the average particle size of the inorganic particles may be 0.5 nm to 100 μm, 0.5 nm to 2nm, or 100nm to 10 μm. Various shapes of inorganic particles, including spherical, are suitable for use in the process of the invention. Nanostructures of various inorganic materials are also suitable for use in the methods of the present invention. In the specific implementation process, a proper template agent can be selected according to the pore size requirement.

Suitable carbon precursors include, but are not limited to, Mesophase Pitch (MP). In an embodiment, the mesophase pitch carbon precursor may be selected from the group consisting of naphthyl pitch, coal-based pitch, petroleum-based pitch, and pitch based on other feedstocks. Other suitable carbon sources include, but are not limited to, carbohydrates (e.g., sucrose), polymers (e.g., phenolic resins, etc.), oligomers, alcohols, and polycyclic aromatic hydrocarbons (e.g., anthracene and naphthalene). Of course, mesophase pitch is the preferred carbon precursor for use as a filter material. In the examples, the mass ratio of the carbon precursor to the inorganic particulate material is 1/20-2/1, 1/20-1/5, or 1/10-1/1. The mass ratio of MP to colloidal silica in the synthesis mixture is 1/20-2/1, 1/20-1/5, or 1/10-1/2.

In addition, the synthesis mixture further comprises at least one of a surfactant, a binder, or a plasticizer. In one embodiment, the synthesis mixture comprises a surfactant, the surfactant being thermally decomposable selected from the group consisting of: poly (ethylene oxide) -poly (propylene oxide) -poly (ethylene oxide) block copolymers (PEO-PPO-PEO), polysorbate 80, partially hydrolyzed polyvinyl alcohol (PVA), and combinations thereof. The mass ratio of the surfactant to the carbon precursor is 1/100-100/1 or 1/10-10/1.

In another embodiment, the resultant mixture further comprises a binder, the binder being water soluble or comprising a water soluble moiety; further, the binder is thermally decomposable and is selected from the group consisting of: poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate), polyacrylamide, polyvinyl alcohol (PVA), partially hydrolyzed polyvinyl alcohol (PVA), and combinations thereof, with a mass ratio of inorganic material to binder of 1/10 to 10/1.

In another embodiment, the synthetic mixture further comprises a plasticizer selected from the group consisting of: water, polyethylene glycol, polyol, polyamine or a combination thereof, wherein the mass ratio of the plasticizer to the inorganic material is 1/10-10/1, 1/5-5/1 or 1/1-3/1.

In another embodiment, the synthesis mixture comprises polyvinyl alcohol (PVA) which acts as both a surfactant and a binder, the polyvinyl alcohol being partially hydrolyzed. In the examples, the synthesis mixture also included 1, 3-Propanediol (PD), which served as both a dispersant and a plasticizer.

In the examples, the mass ratio of silica colloid to polyvinyl alcohol in the synthesis mixture was 1/10-50/1 or 1/5-5/1. In the examples, the mass ratio of silica colloid to 1, 3-propanediol in the synthesis mixture was 1/10-100/1, 1/5-5/1. In addition, other agents are added to the synthesis mixture to improve the properties of the intermediate and final products.

In embodiments, the mixture further comprises one or more additional additives, the additives being liquid or solid. Solid additives include, but are not limited to, particulate materials and fibrous materials. Fibrous additives include, but are not limited to, carbon fibers and glass fibers, among others. The additive may be selected from the group consisting of: alcohols, phenols (e.g., phenol), iron compounds, silicon compounds other than silicon dioxide, titanium compounds other than titanium dioxide, carbon nanotubes, graphene oxide, carbon nanofibers, polymers, plastics, and the like. The additive may also be an alcohol, such as n-butanol. It should be noted that the weight percentage of additives in the mixture is less than 50%.

In the examples, a carbon precursor mixture consisting of a carbon precursor and a first additional component, and an inorganic particle mixture consisting of an inorganic particle material and water were separately prepared, and then the two mixtures were mixed. The carbon precursor material and the first additional component are both solids and are mechanically milled together to form a carbon precursor mixture, the carbon precursor material being in particulate form and having its particle size reduced during the mechanical milling process, the first additional component comprising a water-soluble polymer. In further embodiments, the polymer molecular weight (Mw) is 5,000-50,000 or 10,000-40,000. In the examples, the water-soluble polymer is polyvinyl alcohol (PVA) or partially hydrolyzed PVA, and the water-soluble polymer functions as a binder of the composite film. In a further embodiment, the water-soluble polymer also serves some additional function in the synthesis mixture, for example acting as a surfactant. In a specific embodiment, the binder is substantially removed from the composite film during carbonization, leaving less than 5% or less than 10% by mass of the original binder after carbonization. In the examples, the mass ratio of carbon precursor to water-soluble polymer in the synthesis mixture was 1/100-100/1 or 1/10-10/1.

In an embodiment, the aqueous inorganic particle mixture further comprises a second additional component, the second additional component being an alcohol, the second additional component being less than 50% by mass.

In an embodiment, the aqueous inorganic particulate mixture comprised of inorganic particulate material and water further comprises a third additional component selected from the group consisting of polyethylene glycol, polyols or polyamines. In one example, the third additional component is a polyol. In the examples, the polyol is 1, 3-propanediol. In the examples, the mass ratio of plasticizer to inorganic material in the synthetic mixture is 1/10-10/1, or 1/5-5/1, or 1/1-3/1.

In a further embodiment, the aqueous inorganic particle mixture further comprises a component for stabilizing the suspension or slurry, the stabilizer being a cationic stabilizer or an anionic stabilizer.

The resultant mixture is coated on the substrate by casting, spin coating (spin coating), dip coating, spray coating, screen printing, roll coating, gravure coating, or other means known in the art. When the casting method is used, the thickness of the coating layer (film) can be adjusted by adjusting the component concentration of the ink slurry and by adjusting the gap between the blade and the substrate, and the thickness of the film is 0.1 μm to 10 mm. Suitable substrates include, but are not limited to, glass, plastic, metal, or ceramic. In embodiments where a reinforcement material (such as a grid or fabric) is also incorporated, it may be incorporated into the carbon film by coating the composite mixture directly onto the reinforcement material.

In practice, the coated film is exposed to air at room temperature (15-25 ℃) to remove moisture therefrom, and the coated ink slurry may also be dried at various temperatures, in a range of humidity or other vapor environments. Not all of the water or solvent needs to be removed from the membrane during the drying step. The film after drying and before carbonization is in the form of gel or plastic, and the film is separated from the substrate after drying and before subsequent processing. In embodiments for filtration, the porous carbon film is formed on a porous substrate having a larger pore size than it, and the substrate is used with the porous carbon film during filtration, the substrate providing additional support and mechanical strength during filtration.

In some embodiments, heating the dried film produces a composite film of carbon and inorganic particulate material, and carbonizing the film is carried out at a temperature between 500 ℃ and 1500 ℃. The film is maintained at this temperature for 0.1 to 48 hours or about two hours for carbonization, and the film needs to be preheated before reaching the carbonization temperature, and the preheating temperature of the film is gradually increased to the carbonization temperature. In an embodiment, the film may be exposed to a temperature between 500 ℃ and 1500 ℃ for 0.1-48 hours. In a further embodiment, the film is exposed to a temperature of 100 ℃ to 500 ℃ for 0.1 to 48 hours and then heated to 500 ℃ to 1500 ℃ at a rate of temperature increase from room temperature of between 0.1 to 100 ℃/minute or between 1 ℃/minute to 10 ℃/minute. In another embodiment, the heating step is performed in a stepwise fashion and held at one or more intermediate temperatures for a period of time (e.g., 400 ℃ for 0.1 to 10 hours). The film may need to be partially pressed during preheating and carbonization to avoid deformation, and thus, the film may be placed between two clamping plates, which are porous. It is also possible to subject a plurality of carbon films together to preheating and carbonizing processes in which one film is placed between the other two films. In an embodiment, the carbonization of the membrane may also be performed under pressure, which varies with the carbonization process. In the embodiment, the heat treatment is preferably performed in a non-oxidizing atmosphere, such as nitrogen, helium, argon or a mixture thereof. In some embodiments, the heat treatment may also be performed in an oxidizing atmosphere (e.g., air) for a period of time, and the resulting composite film may be cooled prior to post-treatment.

In embodiments, at least a portion of the particle "template" is removed from the composite membrane by a dissolution process. The size and shape of the pores in the film can be adjusted by selecting a size and shape of the removable template material. In various embodiments, the template material is dissolved using an acidic or basic solution, and the composite membrane is immersed in the solution for a sufficient time to dissolve a majority (90% or more by volume or 95%) of the template. The synthesized porous carbon film needs to be washed, and the porous carbon film after washing or after removing the template needs to be dried.

In an embodiment, a porous carbon film useful for filtration is composed of carbon and includes less than about 20% non-carbon components. The non-carbon components may include the additives described herein or the amount of residues thereof, residues of carbon precursors, residues of inorganic particle templates, and the like. The porous carbon film is substantially composed of carbon, and contains only a small amount of residues of materials used in the process of producing the thin film, such as residues of precursors of carbon, residues of inorganic particle templates, and residues of additives. Of course, the porous carbon film may also be composed entirely of carbon.

In general, porous carbon films are prepared by forming a mixture comprising selected sizes of inorganic particles and a carbon precursor material in water, other solvents, or a mixture of water and other solvents. The mixture is laid down in a layer and water or other solvent is removed to form a precursor film, which is heated to convert the carbon precursor to carbon, and the inorganic particles are removed to form a porous carbon film. The inorganic particles serve as sacrificial templates for pore formation. The pore size and distribution of the membrane is determined by the selection of the size (e.g., average particle size) and size distribution of the inorganic particles used. In a preferred embodiment, the carbon precursor is mesophase pitch and the inorganic particles are colloidal silica. The mixture for preparing the porous carbon film may further include a surfactant, a binder, a dispersant and/or a plasticizer. The surfactant/binder is partially hydrolyzed polyvinyl alcohol (PVA) and the dispersant and/or plasticizer is 1, 3-Propanediol (PD).

Example 1

In order to make the preparation method of the porous carbon film more clear to those skilled in the art, the preparation process thereof will be briefly described below with reference to examples.

The process for preparing nanoporous carbon films with x-nanometer pore size (x = 7, 12, 22, 50 or 80) is as follows:

first, 0.100 g of Mesophase Pitch (MP) and 0.200 g of n-butanol were mixed in a 20 mL bottle of Low Density Polyethylene (LDPE) and then ball milled for 2 hours (70 rpm with 32 g of alumina balls each 4 mm in diameter). 5 g of a 10% by weight aqueous solution of polyvinyl alcohol (PVA, Alfa Aesar, 86-89% hydrolyzed, low molecular weight) was then added to the bottle and the new mixture was ball milled for 3 h to produce a homogeneous MP/PVA ink slurry.

Then, one part of a sol-gel silica suspension (Ludox-HS-40, Ludox-AS-40, Nanosol-5050S, or Nanosol-5080S, average particle size of x nm, x = 12, 22, 50, or 80) containing 0.5 g of silica gel was added to a mixed solution of 1 g of 1, 3-Propanediol (PD) and water (mass ratio of 1: 1) to produce a new silica suspension. To obtain a suspension of 7nm sized silica particles, 1.66 g of Ludox-SM-30 colloidal suspension was dispersed into 5 g of a 30% PD/water solution (note: all colloids were stabilized with sodium ions except Ludox-AS-40 was stabilized with ammonium stabilizer AS shown in their MSDS table).

Next, this silica/PD/aqueous suspension was added to the MP/PVA ink slurry prepared previously, mixed, and ball-milled for 4 hours to obtain MP/PVA/PD/silica ink slurry (or slurry). Before use, the ink slurry was degassed under vacuum for 15 minutes to remove bubbles entrapped therein, to obtain a slurry.

Finally, the slurry was cast onto a glass substrate with a gap of 0.010 inches (0.254 mm) between the blade and the substrate. After drying, a fresh MP/PVA/PD/silica composite membrane is obtained. The composite membrane was cut into small pieces and placed between two carbon coated alumina plates. This assembly was inserted into an alumina tube furnace and carbonized at 900 ℃ for 2 hours in a nitrogen atmosphere at a temperature rise rate of 1-2 ℃/min. The temperature is maintained at 400 ℃ for 2 hours before reaching 900 ℃. After cooling, the carbonized film was immersed in 3M sodium hydroxide at 80 ℃ for 2 days to remove the silica template. After this, the film was washed several times with deionized water untilNeutral state, and soaking in dilute hydrochloric acid for one day to remove Na still attached to carbon surface⁺Ions. After rinsing several more times with deionized water, the film was placed in an oven at 80 ℃ and dried overnight. The resulting self-supporting nanoporous membrane is stored in a conductive container (e.g., an aluminum foil covered petri dish) to avoid the effects of static electricity.

The nanoporous carbon film prepared by the method of this example is collectively referred to as NCS-x, with "x" corresponding to the template silica particle size x nm.

In the thin film preparation process, the pore size is controlled by selecting the size of inorganic particles (particle templates) incorporated in the thin film, and the inorganic particles are removed after the thin film is formed to obtain a porous carbon film. In embodiments, the porous carbon film comprises a three-dimensionally connected porous open network having pore sizes in the range of 2nm to 100nm, 5nm to 100nm, 10nm to 50nm, or 15 to 40nm, and the like. In a further embodiment, the membrane comprises macropores having a size greater than 100nm and less than 1 μm, such pore size being suitable for the selected filtration application. In addition, the porous carbon film may also contain pores of a larger size range distribution, for example less than 2nm, or greater than 100 nm. Preferably, the porous carbon film has a gradient in porosity in the thickness direction.

In one embodiment of a filter or filter device, the porous carbon film is prepared from a precursor film comprising carbon formed by carbonization of a carbon precursor and inorganic particles of a specified size. Inorganic particles of a particular size are removed from a non-porous precursor by acid or base dissolution. In filtration applications, the thickness of porous carbon films is typically less than their lateral dimensions, which are macroscopic dimensions (e.g., greater than 1 millimeter or 1 centimeter), while the thickness dimensions are on the nm or μm scale. In some embodiments, the porous carbon film is free standing and does not adhere to a support material or backing. In some embodiments, the porous carbon film is a self-supporting thin film material, the porous carbon film is capable of supporting itself without a support material, and the self-supporting carbon film has sufficient mechanical strength that it can be easily transferred without breakage. In the application herein, the porous carbon membrane has sufficient mechanical strength to be used for filtration, and is flexible enough to be rolled or bent without breaking or damaging the membrane itself.

In embodiments, the porous carbon film for filtration applications is not composed of graphene, graphene oxide, graphene flakes, graphene oxide flakes, fullerenes or carbon nanotubes, nor is it composed of carbon black, carbon nanofibers or ordered mesoporous carbon. The film making mixture is deposited on a suitable substrate by casting, spin coating, dip coating, spray coating, screen printing, roll coating, gravure coating, or by other methods known in the art. In one embodiment, the film has a thickness of 0.1 μm to 10 mm. After removal of the solvent, the dried film layer is heated (carbonized) to produce a composite film comprising carbon and inorganic particulate material, the film is carbonized by heating to a temperature of 500 ℃ to 1500 ℃, and at least a portion of the inorganic particulate "template" material is removed from the composite film by dissolving the template material from the composite film. In an embodiment, the porous carbon film is heat treated at a temperature up to 3000 ℃ in an inert atmosphere. Further, the porous carbon film in the present embodiment is conductive, and the conductivity is 0.001 to 1000S/cm or 2 to 10S/cm.

FIG. 14 is an SEM image of an NCS-22 film we prepared according to example 1, showing the 7nm connection hole (indicated by the arrow in the figure).

Fig. 15A and 15B are SEM images of NCS-85 films we prepared according to example 1, and fig. 15B is a partially enlarged image of fig. 15A showing a 15nm connection hole (arrow in the figure).

The above characterization results show that: in the present invention, connection holes are present between nanopores in the nanoporous carbon film. As previously mentioned, this feature affects the particle size selectivity of filtration.

The nanoporous carbon films used in the following examples were all the products obtained by the method of example 1.

Example 2

Fig. 1 is a schematic view of the filter assembly of the present embodiment, and the specific structure thereof is as follows: the nanoporous carbon film 1 is located on a porous support 2. Wherein the nanoporous carbon film 1 is an NCS-22 film, and can be produced as described above with reference to the production method of example 1; the porous support 2 may be selected from commercial carbon paper (carbon fiber paper) with pores larger than the nanoporous carbon membrane 1 for filtration, ensuring that filtrate flow through is not impeded.

When manufacturing the filter assembly, the nanoporous carbon membrane 1 is first cut to the desired size and then the membrane is fixed to the support 2 by applying pressure or using a sealant/adhesive at the edges, the adhesive being selected from epoxy (two-component epoxy), it being noted that the central area cannot be coated with sealant or adhesive to avoid affecting the filtering effect.

In specific application, the filter assembly of the embodiment can be used in various filtering places such as gravity filtration, pressure filtration or vacuum filtration.

Example 3

Fig. 2 is a schematic structural diagram of the pressurized nanofiltration device according to this embodiment, in which the nanoporous carbon film 3 is mounted or positioned on the support 4 to form a filtration assembly, and then placed in the filter housing, and pressure is applied to the top inlet of the housing to realize filtration, so that the influences of different pressures, different pore sizes of the nanoporous carbon film, and physical dimensions on the filtration effect can be detected.

The syringe filter is purchased from Sigma-Aldrich company, and comprises an upper shell 5, a port 6 for connecting the syringe and a lower shell 7 for supporting a membrane, wherein the upper shell 5 and the lower shell 7 are hermetically connected in the form of threads 8 and the like, and it is noted that a support body with a porous structure is arranged on the lower shell 8, and a nano-porous carbon membrane can be mounted on the support body in the form of an O-ring and the like, so that the nano-porous carbon membrane is fixedly arranged between the upper shell 5 and the lower shell 7 to form a pressurizing nanofiltration device, and an effective filtration effect is achieved.

In practice, pressure is applied to the top inlet of the syringe filter housing to increase the flow rate. The influence of different pressures, the pore size and the physical size of the nano porous carbon membrane on the filtration can be tested.

Example 4

Fig. 3 is a schematic diagram of a two-layer membrane filtration module comprising two stacked nanoporous carbon membranes, wherein the membrane 9 may be located between two porous supports 10, and a separator 11 (e.g., glass fiber paper) may be located between two adjacent membranes. Of course, it is also possible to provide no spacers, i.e. to stack the membranes one after the other.

In practical application, after liquid containing impurities to be removed enters the multilayer film filtering component, impurity particles and the like are filtered, and filtrate flows out of the filter.

Example 5

Fig. 4 is a schematic structural diagram of a multi-layer membrane filtration module constructed from a series arrangement of multiple nanoporous carbon membranes, in which the nanoporous carbon membranes are sequentially designated 2a, 2b, 2c. The application method is the same as that of example 3, and the nanoporous carbon film has more layers, so that the nanoporous carbon film is suitable for application places with higher requirements on the filtering effect.

Example 6

Fig. 5 shows a specific filtration mode using the filter of example 1: cross-flow filtration process, i.e.: the top film surface of the nano porous carbon film is parallel to the flowing direction of the feed liquid, and the filtered filtrate flows out of the filter from the direction vertical to the flowing direction of the feed liquid. The filtering method can effectively utilize the shearing force generated when the feed liquid flows through the membrane surface to take away the particles retained on the membrane surface, thereby keeping the pollution layer at a thinner level, prolonging the service life of the filter and optimizing the filtering effect.

Example 7

Fig. 10 is a schematic view of a filter device with an electrical pulse function. The concrete structure is as follows: the nanoporous carbon membrane 15 is placed in a filter housing 16, and a first electrode and a second electrode are both connected to the filter, in particular, an electrical contact is provided as a first electrode by means of a steel wire 17 in the lower housing of the filter, and the second electrode is a Ni mesh 19 with an outgoing contact wire 18. A Ni mesh 19 is sealed on top of the filter housing 16 and a voltage is applied across the electrodes and the membrane.

The principle is as follows: the steel wire 17 (first electrode) is woven on a support (e.g., a steel mesh) for supporting the nanoporous carbon film. When a voltage pulse is applied, the steel wire conducts current to the nanoporous carbon film, and when the top of the carbon film is pressed, it is tightly pressed together with the wire to form a stable electrical connection.

See fig. 11 for effects:

single NCS-22 membrane a 0.1m nacl solution containing 85nm silica colloid (0.1% w/v) was filtered using the filtration unit of fig. 10, and as with the general filtration unit, the flow rate decreased with time, as shown by the dark line of fig. 11, due to the build-up of silica colloid as a filter cake on the membrane surface.

Since the nanoporous carbon film in the present application is electrically conductive, electricity can be applied to the film. During filtration of the aqueous suspension, periodic application of electricity to the membrane (2V pulse to the Ni mesh) can increase the flow rate as shown in fig. 11 (light line). This is because the bubbles generated on the surface of the nanoporous carbon film by electricity effectively reduce the accumulation of the filter residue on the surface of the film. Applying electricity to the filter unit reduces the build-up of filter residue, which is much simpler and more efficient than applying counter pressure, which is common in industrial production. In addition, the method has the advantage of eliminating filter membrane clogging without stopping the filtration, rather than stopping the filtration to allow clogged particles to come out of the filter membrane, as is required when applying back pressure.

Application example 1: removal of silica colloids

Two NCS-12 carbon films (prepared with silica particles having a particle size of 12nm, nominal pore size of 12 nm) and porous glass fiber paper were stacked together in the manner shown in FIG. 3, and a colloidal suspension of silica having a mass fraction of 0.1% was filtered through a double membrane filter.

The filtration effect is shown in FIG. 6A, the filtrate is clear and transparent, and no silica colloid is visually observed in the filtrate. Further, it was confirmed by an EDX/SEM energy dispersive X-ray spectrum attached to a Scanning Electron Microscope (SEM) system that the filter completely removed the silica, as shown in fig. 6B without a characteristic peak of Si in the EDX spectrum.

Application example 2: removal of Au nanoparticles from aqueous solutions

An aqueous Au nanoparticle solution (nominal size of about 10nm, pink solution) was filtered using a single NCS-22 carbon membrane filter. As shown in fig. 7, Au nanoparticles were completely removed, and the filtrate was a colorless transparent liquid. It should be noted that in the present application example, the NCS-22 film prepared by using 22nm silica colloid as the template successfully filtered out Au nanoparticles with a nominal size of about 10nm, and the applicant speculates that this may be due to the existence of the connecting holes with a size of about 7nm in the NCS-22 film, and the SEM characterization result of fig. 14 effectively verifies this. It can be seen that the nanoporous carbon film is able to filter out particles smaller than the inorganic particle templates used in its preparation.

Application example 3: removal of Vulcan Carbon nanoparticles from Hexane suspensions

The hexane suspension (black) containing Vulcan Carbon nanoparticles was filtered using a single NCS-22 Carbon membrane filter. As shown in fig. 8, Vulcan Carbon nanoparticles were completely removed and the filtrate was a clear transparent liquid.

Application example 4: filtering bacteria and viruses

The filtration performance of the nanoporous carbon membrane was further tested with bacteria and viruses. As shown in FIG. 9A, the solution containing E.coli was filtered using a single NCS-22 carbon membrane filter, and E.coli was found to be 100% removed (as measured by colony forming units).

Similar results were obtained when the M13-containing virus solution was filtered using an NCS-22 carbon membrane filter, as shown in FIG. 9B, with 99.999% of the M13 virus being filtered out (as measured by plaque forming unit assay). Minute amounts (0.001%) of M13 virus were able to penetrate the NCS-22 membrane, probably because of the small diameter of the M13 virus (about 6.5 nm) and its mutability as a cylindrical viral structure.

Application example 5: examples of imaging of filtered nanoporous carbon films

Figure 12A is an SEM image of a cross section of the NCS-22 membrane after filtration of 22nm silica colloid, the direction of filtration being from the top to the bottom of the image. FIG. 12B is a graph showing the distribution of Si elements in the NCS-22 membrane after filtration of 22nm silica colloid, and it can be seen that 22nm silica particles do not penetrate into the filtration membrane.

FIG. 13A is an SEM image of a cross-section of the NCS-22 membrane after filtration of an 8nm silica colloid. The filtering direction is from the top to the bottom of the image. FIG. 13B is a distribution diagram of Si element in the NCS-22 film after filtering 8nm silica colloid, and it can be seen that 8nm silica particles permeate into the filter film. This further demonstrates the size selectivity of the nanoporous carbon membrane filtration modules or filters of the invention.

In each of the above applications, the filtration effect is related to the selection of materials, the selection of pore sizes, the selection of filtration methods (direct or cross flow, gravity, pressure or vacuum). The selection of these materials, pore sizes and methods can be selected by one of ordinary skill based on the particular filtration needs without undue disclosure of the present application. In practice, the size of the pores of the porous carbon film of the filter element or device is selected according to the size of the microorganisms, including bacteria and viruses, to be removed in the liquid to be filtered/the size of the nanoparticles to be removed/the size of the nanoparticles to be separated from the solution.

In summary, porous carbon films, particularly nanoporous carbon films (also referred to as NC films), are suitable for use in filtration technology because of their relatively good pore uniformity and controllable pore size (the size selectivity results from the pore size of the pores into which they are introduced). The prepared nanoporous carbon membrane is cut to a desired size and can be placed in a housing of a conventional filter, such as the filter housing shown in fig. 2, to impart excellent filtration performance to the filter, and can successfully filter out nanoparticles in aqueous and organic suspensions. The organic solvent can be simultaneously applied to water and organic solvents, fills the blank of the prior art, can be suitable for multiple industries, and has good market prospect.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It should be understood by those skilled in the art that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by using equivalent alternatives or equivalent variations fall within the scope of the present invention.

Claims

1. A filter assembly having a porous carbon film comprising one or more layers of porous carbon film having an open network of interconnected pore structures formed by removing inorganic particles from a carbonized non-porous precursor film.

2. The filter assembly with a porous carbon film according to claim 1, wherein at least one layer of the porous carbon film has a pore structure with a pore diameter of 2nm to 100nm, and preferably, pores smaller than 2nm or between 0.1 μm and 100 μm are further formed in the porous carbon film.

3. The filter assembly of claim 1, wherein the at least one porous carbon membrane has a specific surface area of 1m²/g-2000m²/g。

4. A filtration module having a porous carbon membrane according to claim 1, wherein at least one layer of porous carbon membrane is on a porous support.

5. A filtration module having a porous carbon membrane according to claim 4, wherein the porous support is selected from any of metal, glass, ceramic, carbon paper or carbon fiber.

6. The filter assembly of claim 1, wherein when the porous carbon membrane is a plurality of layers, a porous spacer is further disposed between two adjacent layers of the porous carbon membrane.

7. A filter assembly having a porous carbon membrane according to claim 1, wherein at least one layer of porous carbon membrane:

(a) comprising a gradient of porosity through the thickness of the film, and/or

(b) Is electrically conductive; and/or

(c) Surface functional group modification is performed, and the surface modified group comprises pentafluorophenyl, aminophenyl, nitrophenyl, benzenesulfonic acid group and combination thereof.

8. A filtration module having a porous carbon membrane according to claim 1, wherein the porous carbon membrane is a nanoporous carbon membrane, which is a prior scientific effort of the present applicant, PCT publication No. WO 2015/135069.

9. A filtering apparatus with a porous carbon film, comprising a nano-porous carbon film and a filter housing for placing the nano-porous carbon film, wherein the filter housing comprises an upper housing, a port for connecting an inflow end and a lower housing for supporting the porous carbon film, the upper housing and the lower housing are hermetically connected by screw threads, a lead is arranged on a support of the lower housing and is in contact with the nano-porous carbon film to form a first electrode, a conductor material is arranged on the surface of the upper housing to serve as a second electrode, and a voltage is applied between the first electrode and the second electrode when the filtering apparatus is used; the conductor material is a metal material such as Ni, Pt, gold, or a non-metal material such as carbon, graphite, and may be in the form of wire, net, or sheet, or a nanoporous carbon film.

10. A filtration module with a porous carbon membrane according to any one of claims 1 to 9, for use in nanoparticle filtration, bacterial or viral filtration, using any one of gravity filtration, pressure filtration, vacuum filtration, direct flow filtration or cross-flow filtration.