Photocatalytic filter, method for manufacturing the same, and method for reactivating the same

Abstract

The devices, systems and techniques disclosed in this patent document include photocatalytic filter devices and can be used to provide a method for manufacturing a photocatalytic filter with improved adhesion. In addition, the present disclosure of this patent document includes technology to provide a method for reactivating a photocatalytic filter. Using the disclosed techniques, even if a photocatalytic filter is contaminated, the contaminated photocatalytic filter is easily reactivated while maintaining improved adhesion.

Claims

1. A photocatalytic filter, including; a catalyst portion including a porous support and dispersed TiO.sub.2 particles coated on the porous support; and cells formed in the catalyst portion and providing an air flow path, wherein the photocatalytic filter has a height between 8 to 10 mm, wherein a frame between the cells has a thickness of 0.3 to 1.2 mm, and wherein each of the cell has a width of 2 to 4 mm.

2. The photocatalytic filter of claim 1, wherein the porous support includes ceramic material.

3. The photocatalytic filter of claim 1, wherein the porous support has a honeycomb shape.

4. The photocatalytic filter of claim 1, wherein the porous support has a check lattice pattern.

5. The photocatalytic filter of claim 1, further comprising a bumper covering the catalyst portion.

6. The photocatalytic filter of claim 1, wherein a density of the cells is of 30 to 260 cells/inch.sup.2.

7. A photocatalytic filter device, comprising: a photocatalytic filter that includes a catalyst portion including a porous support and dispersed TiO.sub.2 particles coated on the porous support and cells formed in the catalyst portion and providing an air flow path; and an ultraviolet light (UV) light emitting device (LED) located to irradiate UV light toward the catalyst portion for photocatalytic activation, and wherein the photocatalytic filter has a height between 8 to 10 mm, wherein a frame between the cells has a thickness of 0.3 to 1.2 mm, and wherein each of the cell has a width of 2 to 4 mm.

8. The photocatalytic filter device of claim 7, further comprising a substrate on which the UV LED is disposed.

9. The photocatalytic filter device of claim 8, further comprising an additional UV LED disposed on the substrate and configured to irradiate UV light toward the catalyst portion for photocatalytic activation.

10. The photocatalytic filter device of claim 7, wherein the porous support includes ceramic material.

11. The photocatalytic filter device of claim 7, wherein the porous support has a honeycomb shape.

12. The photocatalytic filter device of claim 7, wherein the porous support has a check lattice pattern.

13. The photocatalytic filter device of claim 7, further comprising a bumper covering the catalyst portion.

14. The photocatalytic filter device of claim 7, wherein a density of the cells is of 30 to 260 cells/inch.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view showing an arrangement of an exemplary photocatalytic filter and a UV LED substrate.

(2) FIG. 2 is a top view of an exemplary photocatalytic filter.

(3) FIG. 3 is a graph showing the change in removal rate of acetaldehyde with a change in the height of a photocatalytic filter.

(4) FIG. 4 is a graph showing the change in removal rate of acetic acid with a change in the height of a photocatalytic filter.

(5) FIG. 5 is a photograph showing the state of a conventional photocatalytic filter and a photocatalytic filter provided according to the present disclosure.

(6) FIG. 6 and FIG. 7 are graphs showing the transmittance of water boiled with each of various filters added thereto.

(7) FIG. 8 is a graph showing the results of cleaning air by filters reactivated using boiling water.

(8) FIG. 9 is a graph showing the results of cleaning air by a photocatalytic filter before and after contamination of the filter.

(9) FIG. 10 is a graph showing the results of cleaning air by a photocatalytic filter before and after contamination of the filter and after reactivating the filter by treating the filter with boiling water.

(10) FIG. 11 is a graph showing the results of cleaning air by a photocatalytic filter before and after contamination of the filter and after reactivating the filter by treating the filter with boiling water and microwaving the treated filter.

DETAILED DESCRIPTION

(11) The devices, systems and techniques disclosed in this patent document provide photocatalytic filter devices and a method of manufacturing a photocatalytic filter with improved adhesion.

(12) In addition, the present disclosure of this patent document includes technology to provide a method for reactivating a photocatalytic filter. Using the disclosed techniques, even if a photocatalytic filter is contaminated, the contaminated photocatalytic filter is easily reactivated while maintaining improved adhesion.

(13) The devices, systems and techniques in this patent document are disclosed by examples in the following descriptions and claims.

(14) Hereinafter, embodiments of the disclosed technology will be described in detail with reference to implementation examples, including those illustrated in the accompanying drawings.

(15) The following embodiments are provided by way of examples so as to facilitate the understanding of various implementations of the disclosed technology to those skilled in the art.

(16) Accordingly, the present disclosure is not limited to the embodiments disclosed herein and can be implemented in different forms. In the drawings, widths, lengths, thicknesses, and the like of elements may be exaggerated for convenience and illustrative purposes.

(17) Photocatalytic Filter—Device

(18) Hereinafter, an example of a photocatalytic filter is provided. The photocatalytic filter includes a support, and dispersed TiO.sub.2 nanoparticles coated on the support.

(19) The support may include a metal, activated carbon, or ceramic. In one implementation, a porous ceramic honeycomb support may be used as the support. In this case, the porous ceramic honeycomb support helps TiO.sub.2 nanoparticles to permeate the ceramic pores during the coating process. Further, TiO.sub.2 nanoparticles are anchored through the drying process that will be discussed later in detail, and thus, adhesion of the TiO.sub.2 nanoparticles to the support is enhanced.

(20) If a metal material is used as the support, TiO.sub.2 nanoparticles are not as easily attached to the photocatalytic support as the porous ceramic honeycomb support. Further, although activated carbon has pores, the activated carbon may be easily damaged during the sintering process.

(21) As will be discussed later in detail, the support may be coated with dispersed TiO.sub.2 nanoparticles, thereby providing a photocatalytic filter with improved adhesion.

(22) FIG. 1 is a perspective view showing the arrangement of the photocatalytic filter 80 and the UV LED substrate 55, and FIG. 2 is a top view of the photocatalytic filter 80.

(23) Referring to FIG. 1, the UV LED 56 for sterilization is disposed on the central portion of the UV LED substrate 55, and three UV LEDs 57 for photocatalytic activation are disposed around the UV LED 56. In some implementations, the UV LEDs 57 for photocatalytic activation will irradiate UV light toward the photocatalytic filter 80.

(24) As shown in FIG. 2, the photocatalytic filter 80 includes a catalyst portion 81 obtained by sintering TiO.sub.2 (titanium dioxide) coated on a ceramic porous material having a check lattice pattern, and an elastic bumper 82 covering the side of the catalyst portion.

(25) FIG. 3 is a graph showing removal rates of acetaldehyde of two photocatalytic filters that have different heights (h), and FIG. 4 is a graph showing removal rates of acetic acid of two photocatalytic filters that have different height (h).

(26) The results of the experiment indicated that, in the case of the photocatalytic filter having the shape shown in FIG. 2, the surface area of the photocatalyst, which increases due to the thickness (t) of the frame between the cells of the photocatalytic filter, did not substantially influence the deodorization efficiency of the photocatalytic filter, but the height (depth) of the photocatalytic filter influenced the inner wall area of the internal air flow path, thus directly influencing the area of contact with air.

(27) Thus, it could be seen that, when the height of the photocatalytic filter was 5-10 mm, the deodorization efficiency of the photocatalytic filter was the highest. In addition, when the height decreases to 2 mm or less, the photocatalytic filter is difficult to use, due to its weak strength, and when the height is 15 mm or more, air resistance merely increases, UV light does not reach the rear portion of the photocatalytic filter or the intensity thereof becomes very weak, and thus only the cost increases without increasing the deodorization efficiency.

(28) Also, it could be seen that, when the width (g) of each cell 83 was 2 mm, the air resistance did not increase, and the rate of shadowed area of the inner wall of the photocatalytic filter, which is generated by the shape of the filter itself blocking UV light irradiated thereto, was not high, suggesting that the cell width of 2 mm is most suitable for maximizing the rate of UV light irradiated area of the inner wall of the photocatalytic filter. Meanwhile, when the cell width decreased to 1 mm or less, the air resistance increased, and the amount of UV light reaching the inner wall decreased, suggesting that the efficiency of deodorization was low. In addition, when the cell width was 4 mm or more, the whole area of the inner wall decreased due to low cell density, which suggests that the efficiency of deodorization was low.

(29) Regarding the density of cells in view of width (g) of each cell above mentioned, when the density of cells was lower than 30 cells/inch.sup.2 or less, that is, the cell width increased to 4 mm or more, the area of the inner wall decreased. This indicates that the efficiency of deodorization was low. When the density of cells was 260 cells/inch.sup.2 or more, that is, the cell width decreased to 1 mm or less, the air resistance increased and the amount of UV light reaching the inner wall decreased. This indicates that the efficiency of deodorization was low. When the density of cells was about 100 cells/inch.sup.2, the air resistance did not increase, and the rate of shadowed area of the inner wall of the filter, which is generated by the shape of the filter itself blocking UV light irradiated thereto, was not high. This suggests that the efficiency of deodorization was the highest.

(30) The results of an experiment on the thickness (t) of the cell frame indicated that, when the frame thickness was 0.3 mm or less, the TiO.sub.2 layer became too thin, and thus the photocatalytic efficiency decreased and the strength was insufficient. When the frame thickness was 1.2 mm or more, the material cost increased without increasing the photocatalytic efficiency. In addition, the photocatalytic efficiency was the highest when the frame thickness was 0.6 mm.

(31) Photocatalytic Filter—Fabrication Process

(32) Hereinafter, an example of a method of manufacturing a photocatalytic filter will be discussed.

(33) The photocatalytic filter may be provided by dispersing titanium dioxide (TiO.sub.2) nanoparticles, coating a support with the dispersed TiO.sub.2 nanoparticles, drying the coated support and sintering the dried support.

(34) As one example, the dispersing process is performed using P25 TiO.sub.2 nano-powders commercially available from Evonik Degussa. For example, P25 TiO.sub.2 nano-powders may be added into water into which silicon dispersing agent with a concentration between 0.1 and 10% may be dissolved. After dispersing P25 TiO.sub.2 nano-powders using a mill, a solid TiO.sub.2 nano solution with a concentration from 20 to 40% may be obtained. The dispersing agent including one or more types of components may be used.

(35) During the coating process, if the porous ceramic honeycomb support is selected, the porous ceramic honeycomb support is dip-coated with the prepared TiO.sub.2 dispersion liquid. At the time of dip-coating, one to five minutes suspension may be applied such that TiO.sub.2 dispersion liquid is sufficiently absorbed by the pores of the porous ceramic honeycomb support.

(36) The drying process may be performed for a predetermined time in a condition that the coated support is maintained at a predetermined temperature. In one implementation, if the porous ceramic honeycomb support is selected, the coated porous honeycomb ceramic support may be maintained in a drying unit at a temperature between 150° C. to 200° C. for three to five minutes.

(37) The sintering process may be performed by maintaining the dried support at a predetermined temperature for a predetermined time. In one implementation, if the porous ceramic honeycomb support is selected, the sintering process may be performed for from two to three hours at between 400° C. and 500° C. Upon our experiments, if the sintering temperature is lower than 300° C., the coated TiO.sub.2 photocatalyst is separated easily from the support. If the sintering temperature is higher than 500° C., the crystal structure of the coated TiO.sub.2 photocatalyst changes and thus, the photocatalyst activation deteriorates. Thus, in order to provide a photocatalytic filter with improved adhesion and photocatalyst activation, the sintering process may be performed at between 400° C. and 500° C.

(38) Reactivated Photocatalytic Filter

(39) FIG. 5 shows the results of an experiment conducted to examine the adhesion of a catalytic material to a support in a TiO.sub.2 photocatalytic filter. In the experiment, each of sintered and unsintered photocatalytic filters was dipped in distilled water, and then sonicated.

(40) As can be seen in FIG. 5, unlike the case of the sintered photocatalytic filter, TiO.sub.2 attached to the unsintered photocatalytic filter was eluted into water by sonication.

(41) FIG. 6 shows the transmittance of distilled water, which was measured at various wavelengths in each of the following cases: sonicating distilled water only; adding to distilled water a porous ceramic material not coated with a TiO.sub.2 photocatalytic material and then sonicating the distilled water; adding to distilled water a porous ceramic material coated with a TiO.sub.2 photocatalytic material and sintered and then sonicating the distilled water; and adding to distilled water a porous ceramic material coated with a TiO.sub.2 photocatalytic material but not sintered and then sonicating the distilled water. The transmittance was measured by UV-Vis Spectroscopy (detector: Analytik Jena).

(42) As can be seen in FIG. 6, the transmittance of the water containing the porous ceramic material, which was coated with the TiO.sub.2 photocatalytic material and sintered, was nearly similar to that of distilled water. This suggests that the photocatalytic material had excellent adhesion to the porous ceramic material, and that the photocatalytic material was not substantially eluted.

(43) This result indicates that the photocatalytic filter manufactured according to the method of the present disclosure maintains the adhesion of the photocatalytic material to the surface of the photocatalytic filter even when the photocatalytic filter is sonicated.

(44) FIG. 7 shows the transmittance of water measured as a function of sonication time in each of the following cases: sonicating distilled water only; adding to distilled water a porous ceramic material not coated with a TiO.sub.2 photocatalytic material and then sonicating the distilled water; and adding to distilled water a porous ceramic material coated with a TiO.sub.2 photocatalytic material and sintered and then sonicating the distilled water.

(45) As can be seen in FIG. 7, in the case in which the porous ceramic material, coated with the TiO.sub.2 photocatalytic material and sintered, was added to distilled water and sonicated, the transmittance of the distilled water showed a tendency to decrease as the sonication time increased, but this decrease in transmittance was not visually distinguishable from distilled water only.

(46) FIG. 8 shows the results of measuring the acetaldehyde removal activities of the two samples (see the arrows in FIG. 7) showing the greatest difference in transmittance therebetween among the samples of FIG. 7, after naturally drying the two samples for use as photocatalytic filters. As can be seen in FIG. 8, there was little or no difference in photocatalytic activity between the two samples showing different transmittances as shown in FIG. 7.

(47) The reactivative characteristics of the TiO.sub.2 nanoparticle-coated photocatalyst are shown in FIG. 9 to FIG. 11. The two graphs (marked Filter 1 and Filter 2) on FIG. 9 show two sets of experiments to irradiate a contaminated TiO.sub.2 nanoparticle coated filter and a fresh uncontaminated TiO.sub.2 nanoparticle coated filter, by using a UV LED source for a period of 3 hours so as to remove acetaldehyde. In both Filter 1 and Filter 2 figures, the contaminated TiO.sub.2 nanoparticle coated filter is contaminated with chemicals including formaldehyde, acetic acid, NH.sub.3, toluene, CH.sub.3—S—SCH.sub.3, or commercial air freshener (aromatic).

(48) As can be seen in FIG. 9, the uncontaminated filter normally degraded acetaldehyde (see the plot marked as Fresh TiO.sub.2 in FIG. 9). However, when an experiment was performed using a photocatalytic filter contaminated after used in the above-described acetaldehyde removal experiment, it could be seen that the amount of acetaldehyde did not decrease (see the plot marked as contaminated TiO.sub.2 in FIG. 9), suggesting that the photocatalytic activity of the filter was poor.

(49) FIG. 10 shows reactivation of the contaminated TiO.sub.2 nanoparticle coated on filters after being treated with boiling water and FIG. 11 shows reactivation of the contaminated TiO.sub.2 nanoparticle coated on filters after being treated a combination of boiling water and microwave exposure. The reactivity properties of the contaminated TiO.sub.2 nanoparticle coated on filters are compared against fresh uncontaminated TiO.sub.2 nanoparticle coated on filters.

(50) As can be seen in FIG. 10, when the contaminated filter was treated with boiling water, the function of the filter was significantly restored. As shown in FIG. 11, when the contaminated filter was treated with boiling water and then microwaved, the filter was reactivated so that it would show performance nearly similar to that of its original state.

(51) As described above, the present disclosure provides the photocatalytic filter including the photocatalytic material attached securely to the support. Thus, the photocatalytic material is not detached from the photocatalytic filter during reactivation, and thus can be repeatedly reactivated. Thus, the photocatalytic filter can be used semi-permanently. This is different from The conventional photocatalytic filters where the reactivation via boiling cannot be achieved since the photocatalytic material is not so securely attached to the support as it is not eluted from the support into water while being treated with boiling water.

(52) In addition, according to the present disclosure, the photocatalytic filter can be reactivated in a simple manner without using a troublesome washing process.

(53) Though only a few embodiments, implementations and examples are described, other embodiments and implementations, and various enhancements and variations can be made based on what is described and illustrated in this document.