POROUS MATERIALS AND SYSTEMS AND METHODS OF FABRICATING THEREOF

Abstract

A porous material with a specific surface area higher than 10/mm, and methods and system for manufacturing such a porous material. The porous material includes a plurality of pores having a substantially uniform size with a variation of less than about 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm. A system including the porous material can be configured as one of a desalination system, a super-fine bubble generation system, a capacitor system, or a battery system.

Claims

1. A porous material with a specific surface area higher than 10/mm, the specific surface area depending on different pore sizes, wherein the porous material comprises a plurality of pores having a substantially uniform size with a variation of less than about 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm.

2. The porous material of claim 1, wherein the porous material is substrateless membrane.

3. The porous material of claim 1, comprising a plurality of grain boundary regions filled with a solid material to increase a mechanical strength of the porous material, wherein the specific surface area is higher than 4100/mm, wherein the size variation is less than about 10%, and wherein the grain boundary regions have a size of about 5 μm-15 cm.

4. A system configured to fabricate a porous material, the system comprising: a particle template formation portion configured to fabricate a particle template; an infiltration portion configured to infiltrate the particle template with an infiltrant substance, and a template removal portion configured to remove the particle template and keep the infiltrant substance substantially intact, to thereby form a sub strateless porous material with a specific surface area higher than 10/mm, wherein the porous material comprises a plurality of pores having a substantially uniform size with a variation less than 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm.

5. The system of claim 4, further comprising a baking portion configured to dry the particle template fabricated through the particle template formation portion to thereby enhance mechanical strength of the colloidal particle template.

6. The system of claim 5, wherein the particle template formation portion comprises an electrophoresis assembly apparatus including: an electrophoresis tank; a DC power supply; a magnetic stirrer; a reference electrode; and a working electrode; wherein: an electrophoresis solution containing a suspension of particles is disposed in the electrophoresis tank; the reference electrode and the working electrode are substantially vertically arranged in the electrophoresis tank; and the working electrode provides a surface for electrophoretically fabricating the particle template.

7. The system of claim 6, wherein the reference electrode has a shape of a round rod and is disposed adjacent to an air-liquid interface or lower than the interface by about 0-5 cm.

8. The system of claim 7, wherein the working electrode comprises a flexible and movable conductive tape, and a leak-proof inlet is arranged on a sidewall of the electrophoresis tank such that the flexible and movable conductive tape can be fed into the electrophoresis tank.

9. The system of claim 4, wherein the infiltration portion comprises an electrophoretic deposition (EPD) apparatus including: an EPD tank; a DC power supply; a reference electrode; and a working electrode; wherein: an EPD solution is placed in the EPD tank; and the working electrode is configured to carry the colloidal particle template, the colloidal particle template providing a surface for electrophoretic deposition of the infiltrant substance on the colloidal particle template inside the EPD tank.

10. The system of claim 4, wherein the template removal portion comprises a chemical etching apparatus including an etching tank having an etching solution disposed therein, whereby the particle template is removed by the etching solution to only keep the infiltrant substance.

11. The system of claim 10, wherein a leak-proof inlet and a leak-proof outlet are arranged at sidewalls of the etching tank for leak-free feeding of a flexible and movable conductive tape carrying the colloidal particle template and the infiltrant substance into and out of the etching tank, respectively.

12. The system of claim 11, further comprising a blade configured to separate the infiltrant substance from the flexible and movable conductive tape to obtain the porous material and to recycle the flexible and movable conductive tape.

13. A method of fabricating a porous material, comprising: (1) fabricating, with a particle template formation portion, a particle template; (2) infiltrating, with an infiltration portion, the particle template with an infiltrant substance; and (3) removing, with a template removal portion, the particle template and keep the infiltrant substance intact to thereby form a substrateless porous material with a surface-area-to-volume ratio higher than about 10/mm, wherein the porous material comprises a plurality of pores having a substantially uniform size with a variation of less than about 20%, wherein the size is larger than about 100 nm and smaller than about 5 mm.

14. The method of claim 13, further comprising baking the particle template immediately after the step (1) and before the step (2) to enhance mechanical strength of the particle template, wherein said baking is performed at a temperature of about 90-500° C., a relative humidity of >75, for a duration of about 0.5-2 hrs.

15. The method of claim 14, wherein: an electrophoresis solution containing a suspension of colloidal particles is disposed in an electrophoresis tank; a reference electrode and a working electrode are substantially vertically disposed in the electrophoresis tank; the reference electrode has a shape of a round rod; the working electrode provides a surface for electrophoretically fabricating the particle template; and an electric field between the reference electrode and the working electrode is in a range of about 0.1 V/cm-1000 V/cm.

16. The method of claims 15, further comprising providing the suspension of particles including a powder substance selected from at least one of polystyrene, SiO.sub.2, or PMMA, wherein the power substance has a particle size of about 100 nm-5 mm, and wherein the electrophoresis solution comprises an ionic solution configured to provide electrical charges to surfaces of the colloidal particles.

17. The method of claim 16, wherein the electrophoresis solution comprises at least one of: an ethanol solution with a pH value of about 4-9, NH.sub.4OH/HNO.sub.3, or SDS.

18. The method of claim 17, wherein the working electrode is static or configured to move at a speed of about 100 nm/sec-10 cm/sec.

19. The method of claim 13, further comprising heating the particle template carrying the infiltrant substance to about 500° C. for less than 24 hours to thereby thermally remove the colloidal particle template while keeping the infiltrant substance substantially intact and oxidizing metal structure surfaces, wherein the particle template comprises polymers.

20. The method of claim 14, further comprising chemically removing the particle template while keeping the infiltrant substance substantially intact and avoiding oxidizing metal structure surfaces, and wherein said chemically removing comprises etching at a temperature of about 40-80° C. for about 1-4 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 illustrates an OM (Optical Microscope) image of a metal foam.

[0040] FIG. 2 is a flow chart of the method to fabricate a conventional porous material.

[0041] FIG. 3 is a schematic diagram of an embodiment of the system used to manufacture a large-dimension macroporous film using a flexible and movable conductive tape as the working electrode.

[0042] FIG. 4A is a top view SEM image of a fine-array porous structure.

[0043] FIG. 4B is a side view SEM image of the structure of FIG. 4A.

[0044] FIG. 4C is another side view SEM image of the structure of FIG. 4A.

[0045] FIG. 4D is a top view SEM image of stacked nanospheres.

[0046] FIG. 4E is a low resolution (200×) top view SEM image of the inverse structure, wherein the sketches show the grain boundaries forming grain domains, which can provide mechanical strengths of the porous material.

[0047] FIG. 4F is a magnified view (500×) of the structure in FIG. 4E.

[0048] FIG. 4G is a further magnified view (2500×) of the structure in FIG. 4E.

DETAILED DESCRIPTION

[0049] Some approaches of manufacturing highly porous materials can be complex and costly, and may have difficulties producing porous materials with high purity with high specific surface areas.

[0050] FIG. 1 illustrates the microstructure of a metal foam, comprising an interconnected matrix of metallic ligaments 101 with varying lengths and orientations, and individual void spaces (pores) 100 of different shapes and sizes formed between adjacent ligaments. Typical metal foams may have pore sizes of 0.5-8 mm.

[0051] In addition to the specific area, uniformity of the pore sizes is another important factor. In the conventional metal foam illustrated in FIG. 1, the pore sizes have variations higher that 100%.

[0052] A fabrication system according to some embodiments disclosed herein can fabricate a porous material with more superior performances. The system can include a colloidal particle template formation portion configured to fabricate a colloidal particle template; an infiltration portion configured to infiltrate the colloidal particle template with an infiltrant substance; and a template removal portion configured to remove the colloidal crystal template and keep the infiltrant substance substantially intact.

[0053] FIG. 2 illustrates a process flow of manufacturing a fine-array porous material according to some embodiments using the system. The manufacture process may include: step (1), surface-charged particle deposition forming an array (assembly process), step (2), deposition/infiltration, and step (3), template removal. The system can include portions (e.g., modules) 310, 320, 330 to respectively realize these steps. A movable conductive tape can be used to transport the colloidal particle template between the waterproof inlet and outlet of each tank. Each portion can have functions as shown in FIG. 3 and as described in detail below.

[0054] FIG. 3 illustrates a system configured to fabricate large-area, fine-array porous films according to some embodiments. The system can include an electrophoresis portion 310, a deposition/infiltration portion 320, and a colloidal particle template removal portion 330.

[0055] The electrophoresis portion 310 can include an electrophoresis tank 311, a power supply 312, a reference electrode 313, a working electrode 314, a magnetic stirrer 315, a leak-proof inlet 316, and an oven/RTA 319. An electrophoresis solution 317 containing a monodispersed colloidal nanosphere suspension can be disposed in the electrophoresis tank 311; the leak-proof inlet 316 can be disposed at a side wall of the electrophoresis tank 311; the working electrode 314 can comprise a movable continuous conductive tape 318 configured to feed into the electrophoresis tank 311 via the leak-proof inlet 316, provide a surface for the formation of a colloidal particle template in the electrophoresis tank 311, move out of the electrophoresis tank 311 if the electrophoresis self-assembly of the colloidal particle template is complete, and transport the colloidal template through the oven/RTA 319 for drying.

[0056] The deposition/infiltration portion 320 can include a deposition tank 321, a power supply (not shown), a DC power source, a reference electrode 323, a working electrode 324, a leak-proof inlet 325, and a leak-proof outlet 326. An electrodeposition solution 327 can be disposed in the deposition/infiltration tank 321. The leak-proof inlet 325 and the leak-proof outlet 326 can respectively be disposed at two opposite side walls of the deposition tank 321.

[0057] The working electrode 324 can have a electrode position suspension solution 327 disposed thereover. The tape that comes from the electrophoresis portion 310 carrying the dried colloidal particle template can be fed into the deposition tank 321 via the leak-proof inlet 325. A surface for formation of a fine-array porous film over the colloidal particle template can be provided in the deposition tank 321. Upon completion of electrodeposition of the fine-array porous film, the tape can be moved out of the electrodeposition tank 321 via the leak-proof outlet 326.

[0058] The colloidal particle template removal portion 330 can include an etching tank 331, a leak-proof inlet 332, and a leak-proof outlet 333. An etching solution 334 can be disposed in the etching tank 331. The leak-proof inlet 332 and the leak-proof outlet 333 can be respectively disposed at two opposite sidewalls of the etching tank 331. The tape carrying the colloidal particle template and the fine-array porous film that comes from the deposition portion 320 can be moved into the etching tank 331 via the leak-proof inlet 332, for removal of the colloidal particle template. The tape can be moved out of the etching tank 331 via the leak-proof outlet 333 if etching of the colloidal particle template is complete. The fine-array porous film 335, referred to as the porous material or membrane of the claimed embodiments, can be separated from the movable continuous conductive tape after the tape comes out of the etching tank 331.

[0059] For example, a separation blade (not shown) can be disposed between the conductive substrate tape 337 and the porous film 335 to separate them, allowing the porous film 335 to form a roll on a first roller (not shown), and a second roller (not shown) is used to recycle the tape 337.

[0060] In some embodiments, the apparatus as shown in FIG. 3 can be used to manufacture a Nickel film with a fine-array porous structure. The process may include, for example, 1) preparation of monodispersed polystyrene (PS) colloidal suspension; 2) assembly of PS colloidal crystal template; 3) electrodeposition of Nickel; and 4) removal of PS nanosphere templates by heating or etching using ethyl acetate.

[0061] In contrast to conventional metal foams that have relatively low specific surface areas and lack of uniformity in pore sizes, the fine-array porous material has larger specific areas, and the pores therein are also highly uniform.

[0062] Table 1 below compares parameters, as defined in association with Equation (1) above, of conventional metal forms with those of the fine-array porous materials disclosed herein. As shown, the specific surface areas of the fine-array porous materials can be higher than 3130/mm, such as higher than 4100/mm. However, specific surface areas of the fine-array porous materials can also be in the range of 10/mm and 3130/mm, and would still have superb properties for various applications resulting from other properties unmatched by metal forms. For example, fine-array porous materials according to some embodiments, with a specific surface area >10/mm, can have very uniform pore sizes, such as <20% as measured by the standard deviation, or <10% as measured by the standard deviation.

TABLE-US-00001 TABLE 1 d Sv (mm) 281.8/d θ (1-θ){circumflex over ( )}0.5 1-Q (1-θ){circumflex over ( )}0.4 (mm2/mm3) Metal 1 281.8 0.95 0.224 0.05 0.302 14.760 Foams 0.5 563.6 0.95 0.224 0.05 0.302 29.521 0.5 563.6 0.90 0.316 0.10 0.398 48.516 0.5 563.6 0.85 0.387 0.15 0.468 62.618 0.01 28180 0.95 0.224 0.05 0.302 1476.032 0.01 28180 0.90 0.316 0.10 0.398 2425.786 0.01 28180 0.85 0.387 0.15 0.468 3130.922 Fine- 0.01 28180 0.74 0.510 0.26 0.583 4108.658 array 0.005 56360 0.74 0.510 0.26 0.583 8217.316 porous 0.001 281800 0.74 0.510 0.26 0.583 41086.578

[0063] FIG. 4A is a top view SEM image of a fine-array porous structure.

[0064] FIG. 4B is a side view SEM image of the structure of FIG. 4A.

[0065] FIG. 4C is another side view SEM image of the structure of FIG. 4A.

[0066] FIG. 4D is a top view SEM image of stacked nanospheres.

[0067] FIG. 4E is a low resolution (200×) top view SEM image of the inverse structure, wherein the sketches show the grain boudaries forming grain domains, which can provide mechanical strengths of the porous material.

[0068] FIG. 4F is a magnified view (500×) of the structure in FIG. 4E.

[0069] FIG. 4G is a further magnified view (2500×) of the structure in FIG. 4E

[0070] In some embodiments, the apparatus as shown in FIG. 3 can be used to make fine-array porous ZnO films. For example, a process can include: 1) preparation of monodispersed polystyrene (PS) colloidal suspension; 2) assembly of PS colloidal crystal template and drying of the template at about 90-100° C. in the ambient atmosphere, for example for about 30 minutes; 3) electrodeposition of ZnO in the Zn(NO.sub.3).sub.2 electroplating solution with a constant electrical current (e.g. 1 mA/cm.sup.2) at about 70° C.; and 4) removal of PS nanosphere templates by heating in the ambient at about 500° C. for <2 hours. A well array prouos ZnO film with controllable periodic layers can thus be fabricated.

[0071] In some embodiments, the colloidal particle template formed by the assembly process can be made of polystyrene (PS), SiO.sub.2, PMMA (Poly(methyl methacrylate)), or any powder substance with a sphere shape, with a particle size in the range of about 100 nm-5 mm and diameter variation (e.g., standard deviation) within about ±20%, optimally within about ±10%. For example, in an embodiment, the particle size is about 200 nm ±40 nm; in another example, the particle size is about 300 nm ±60 nm. The particles can have spherical shapes, and can be hollow or solid spheres. In some other embodiments, non-spherical shapes can be employed.

[0072] In some embodiments, the solution used has a pH value in the range of 4-9, a temperature in the range of about −10˜45° C., a DC electrical field in the range of about 0.1 V/cm-1 kV/cm, and an electrode tip withdraw velocity in a range of about 100 nm/sec-10 cm/sec.

[0073] In some embodiments, the baking temperature for the removal of colloidal crystal template can depend on the nanosphere material, and can be in a range of about ±10% of the material's glass transition temperature.

[0074] In some embodiments, the grain domain of the fine-array porous films (planar/monolithic) can be in a range of about 5 μm-5 mm, and the pore size can be in the range of about 100 nm-5 mm.

[0075] In some embodiments, the solution can have a density higher than the nanospheres, allowing the nanospheres to float on the solution. Alternatively, the solution can have a density lower than that of the nanospheres, such that the nanospheres can disperse in the solution uniformly, wherein the liquid can be specified by density.

[0076] In some embodiments, the assembly apparatus can have a vertical structure such that film thickness can be controlled, and the film can be dissembled from the apparatus.

[0077] The porous materials disclosed herein can be used in many areas of applications. For example, in some embodiments, a water purifier can employ a filter composed of a porous material of the present disclosure. The filter can be a membrane, and the high surface-area-to-volume ratio of the porous membrane as described above allows contaminated water to be purified effectively.

[0078] In some other embodiments, a salt water desalination system can be provided employing a membrane with a high surface-area-to-volume ratio. The membrane can facilitate a reverse osmosis or an ion exchange process for desalination.

[0079] In some other embodiments, a super-fine bubble generation system can be provided employing a membrane with a high surface-area-to-volume ratio. The porous structure can facilitate bubble generation in various types of liquids.

[0080] In yet some other embodiments, a capacitor or a battery can be provided employing a porous material with a high surface-area-to-volume ratio. The large surface area provided by the porous material of the present disclosure can facilitate a higher capacitance for a capacitor, or a higher rate of ion exchanges for a battery thereby improving the battery's efficiency.

[0081] In some other embodiments, the porous materials can be used in application areas such as vibration and sound absorption, impact protection, heat exchange, membranes, filtration, ion exchange, photonics, gas sensing, catalysis, biomedical engineering, etc.

[0082] Although specific embodiments have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects described above are not intended as required or essential elements unless explicitly stated otherwise. Various modifications of, and equivalent acts corresponding to, the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of the present disclosure, without departing from the spirit and scope of the disclosure defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.