CN113134289A - Method for purifying air and air purification device - Google Patents
Method for purifying air and air purification device Download PDFInfo
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- CN113134289A CN113134289A CN202010066941.0A CN202010066941A CN113134289A CN 113134289 A CN113134289 A CN 113134289A CN 202010066941 A CN202010066941 A CN 202010066941A CN 113134289 A CN113134289 A CN 113134289A
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- 238000004887 air purification Methods 0.000 title claims abstract description 26
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- 229910052739 hydrogen Inorganic materials 0.000 claims description 13
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/32—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by electrical effects other than those provided for in group B01D61/00
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M14/00—Electrochemical current or voltage generators not provided for in groups H01M6/00 - H01M12/00; Manufacture thereof
- H01M14/005—Photoelectrochemical storage cells
Abstract
The present disclosure relates to a method for purifying air, and an air purification device usable in combination with the method, the method comprising: providing a photo-electrochemical cell comprising an anode and a cathode separated by a proton-conducting interlayer; supplying photons from a photon source to the surface of the anode and/or cathode, thereby generating electron holes and electrons by means of the photoelectric effect; providing water on said surface of the anode; oxidizing molecules of the water by electron holes to produce hydroxyl radicals, electrons, and protons; allowing an air stream to flow over the surface of the anode; oxidizing one or more volatile compounds, particles and/or microorganisms present in the air with the generated electron holes and/or the hydroxyl radical and directing electrons through an electron conducting circuit and protons through a proton conducting interlayer, forming hydrogen gas at the cathode, thereby increasing the lifetime of the hydroxyl radical at the anode.
Description
Technical Field
The present invention relates to a method for purifying air. The invention also relates to an air cleaning device which can be used in combination with the method for cleaning air.
Background
Indoor air, where people spend more and more time at home or at work, contains pollutants and Volatile Organic Compounds (VOCs), particulates, and building materials in outdoor air, as well as microorganisms produced by human beings and other biological activities. These contaminants constitute a serious health risk in many places and situations, and clean indoor air is considered an effective investment to improve quality of life, increase productivity, and reduce healthcare costs.
Air purifiers and conditioners may contain particulate and microbial filters, adsorbent materials, or generate free radicals such as hydroxyl (OH)*) Ozone (O)3) The oxidizing agent or charged ion of (2) is generally used in combination with humidification or dehumidification. They all have advantages and disadvantages. For example, filters and adsorbent materials are simple and inexpensive, but require cleaning or replacement and thus constitute a hazard in themselves. Ozone is harmful and can only be used in unmanned rooms, and the cleaning and disinfecting efficiency of charged ions is questionable. In contrast, hydroxyl radicals are very strong oxidants and are therefore safe to use, as they cannot be present at any great distance outside the generator. However, to date, hydroxyl radicals have been inefficient because they react immediately with the co-produced hydrogen to form water, limiting their effective concentration for reacting with air pollutants.
US 7,373,351 discloses a photoelectrochemical air cleaner comprising a system comprising a plurality of photocatalyst surfaces fixed to a solid surface, with which a fluid is brought into contact for disinfection. This patent provides a structure for removing a portion of the photo-generated electrons in contact with the photocatalyst layer, thereby reducing the rate of recombination of the photo-generated electrons and electron holes, and thus improving the removal rate of microorganisms or chemical accompaniments from the fluid undergoing cleaning.
Applied Catalysis B, Environmental, vol.38,2002, pages 215-. For most of the contaminants studied, the formation of carbon deposits during decomposition deactivates the photocatalyst, which can be regenerated when humid air is introduced into the contaminant stream.
Atmospheric environmental, vol.43,2009, pages 3168-. It is reported that after 50 to 85 seconds of residence time, the mineralization rate of all air pollutants is 90% and there is no catalyst deactivation. The presence of humid conditions adversely affects the performance of the system.
International Journal of hydrogen Energy, vol.44,2019, pages 587-. The production of hydrogen is carried out in a solid-state photoelectrochemical cell comprising a photoanode, a substrate
A membrane-separated photocathode. It is noted that the only requirements for hydrogen production are humidity and sunlight. Air purification is not mentioned.
Photochem, Photobiol, Sci, 2017,16,10-16 discloses a water-splitting agent with TiO2Nanotube solid-state Photoelectrochemical (PEC) cells. In the photoelectrochemical cell, the aqueous electrolyte is hydrated by proton conduction
Polymer film instead, the film being sandwiched between TiO2Between the base photo-anode and the Pt/C base cathode. It is said that solid-state battery PEC cells minimize electrode distance and device volume and provide a compact practical application method for solar water splitting. Air purification is not mentioned.
Thus, there remains a need for improvements in air purification methods and apparatus.
Disclosure of Invention
The invention aims to provide a method for safely and efficiently purifying air. Further, it is an object of the present disclosure to provide an air purification device that can be used in combination with the above air purification method.
Thus, there is provided a method for purifying air, the method comprising:
-providing a photo-electrochemical cell comprising an anode and a cathode separated by a proton-conducting interlayer,
-supplying photons from a photon source to the surface of the anode and/or cathode, thereby generating electron holes and electrons by means of the photoelectric effect,
-providing water on the surface of the anode,
-oxidizing molecules of said water by said electron holes to produce hydroxyl radicals, electrons and protons,
-allowing the air flow to flow over the surface of the anode,
-oxidizing one or more volatile compounds, particles and/or microorganisms present in the air with the generated electron holes and/or the hydroxyl radical, and
-directing the electrons through an electron conducting circuit and the protons through the proton conducting intermediate layer, forming hydrogen at the cathode separate from the anode, thereby increasing the lifetime of the hydroxyl radicals at the anode.
Further, there is provided an air purification apparatus, comprising:
-a housing having at least one air inlet and at least one air outlet,
a photoelectrochemical cell having an anode and a cathode separated by a proton-conducting interlayer, and
a photon source configured to provide photons to a surface of the anode and/or the cathode, thereby generating electron holes and electrons by a photoelectric effect,
-water present on the surface of the anode,
wherein the photoelectrochemical cell and/or the photon source is located in the housing such that a flow of air from the at least one air inlet to the at least one air outlet flows over the surface of the anode.
Surprisingly, it has been found that air can be purified using the method described herein, optionally in combination with the air purification device described herein. Unexpectedly, recombination of photogenerated electrons and electron holes is prevented, while hydrogen generated by the electrons is prevented from reacting with hydroxyl radicals generated from the reaction of the electron holes and adsorbed water, thereby improving the generation of active hydroxyl radicals and thus improving the cleanliness of air.
More specifically, the method for air purification and/or the operation of the air purification device described herein is based on three main principles; namely: the photoelectric effect, the presence of an adsorbed water layer on the anode, and a proton-conducting electrochemical cell that separates the hydrogen formed from the active hydroxyl radicals.
The photoelectric effect comprises materials, in particular semiconductors, which absorb photons, which are subsequently converted into energy carriers in the form of electron holes and electrons. When a semiconductor is illuminated with light that matches its bandgap energy, electrons are optically excited from the Valence Band (VB) to the Conduction Band (CB), leaving electron holes in VB. In the typical case of photoelectrochemical cells, the anode where oxidation occurs is such a semiconductor. The photogenerated electron holes are attracted to the surface of the material, while the photogenerated electrons are transferred to the cathode through external wiring. These electron holes are capable of non-selective oxidation, i.e. degradation of any type of volatile organic compounds or particles or microorganisms on the surface of the anode.
Furthermore, in the presence of water absorbed from the laden atmospheric moisture on the anode surface, the water molecules are oxidized to hydroxyl radicals (OH)*) And proton (H)+) They are hydrated with hydronium ions (H) in an aqueous environment3O+) Exist in the form of (1). In this disclosure, the hydroxyl radical is named or depicted as OH*Or HR. Hydroxyl radicals are the second largest oxidizing element next to fluorine and are also capable of non-selectively degrading any volatile organic compounds, particles and microorganisms. In the present disclosure, the photocatalyst may be TiO2A nanotube.
The cathode receives electrons from the anode and protons through the proton-conducting membrane and generates hydrogen H2. Advantageously, the photoelectrochemical process is preferred over the photocatalytic process because the voltages applied across the two electrodes are such as to suppress electronsThe strong driving force for the recombination of holes and electrons improves the generation of Hydroxyl Radicals (HRs) of clean air. In contrast, in a simple photocatalytic process, the same charge carriers are generated, but both the electron hole and the electron reach the same surface, where the electron hole oxidizes water to HRs or directly oxidizes volatile organic compounds/microorganisms, but the electron reduces the proton to hydrogen, which reacts with HRs and reduces its concentration and effect.
In the methods described herein, the water on the surface of the anode is present in the form of a physisorbed layer, which may have a particular thickness. For example, the thickness may be in a range of about 0.8 to about 2 nanometers (nm). This water thickness can be achieved by performing the method at a Relative Humidity (RH) equal to or greater than 50%. The thickness and/or relative humidity of the water layer may be provided by cooling the air flow before and/or at the anode surface. Cooling may be achieved by using peltier elements. For example, the peltier element may be of the type used in consumer products, such as peltier elements used for camping, portable radiators, cooling electronic elements and/or small instruments.
The air purification methods described herein may operate on the humidity present in the incoming air to be purified. If the air is too dry, sufficient water content in the air described herein can be achieved by using a humidifier, for example, by bubbling a stream of air through a water saturator.
The relative humidity level of air passing over the surface of the anode can be monitored using a sensor for Relative Humidity (RH) and feedback provided to control the power to the peltier elements. For example, the relative humidity may be controlled to be equal to or greater than 50%, such as 60% or 70%.
The air stream, which is air-purified using the methods and/or apparatus described herein, may be moved over the surface of the anode by a fan. Additionally or alternatively, the air stream that has been air-purified using the methods and/or apparatus described herein may be moved over the surface of the anode by natural attraction or brownian motion using the temperature difference of the air stream as it passes through the cooler and the light-emitting electrochemical cell.
The hydrogen gas formed in the air purification apparatus and/or method for air purification described herein may be mixed with the air stream after passing through the photo-anode, and then reacted with and reduced by any ozone and/or oxidizing radicals remaining in the air.
The methods described herein may also include applying a voltage, such as a voltage in the range of 0.1V to 10V, between the anode and the cathode of the photoelectrochemical cell.
The anode and/or cathode and/or proton conducting intermediate layer described herein may be partially or completely transparent.
The anode described herein may include a mesh, a perforated plate, and/or a porous layer. Additionally or alternatively, the anode of the photoelectrochemical cell described herein may include a first photocatalyst configured to oxidize water molecules of the water to generate hydroxyl radicals, electrons, and protons. The first photocatalyst may be a porous and/or earth-rich material, such as TiO on a Ti substrate2A nanotube.
The proton conducting intermediate layer of the photoelectrochemical cell described herein may comprise or consist of:
(i) polymers, such as sulfonated tetrafluoroethylene based fluoropolymer copolymers, and/or
(ii) Porous ceramics, such as pure or doped SiO2、TiO2And/or ZrO2。
The cathode of the photoelectrochemical cell described herein may include or consist of a second photocatalyst configured to reduce protons to form hydrogen and/or oxygen to water. The second photocatalyst may be porous and/or comprise an earth-rich material, such as carbon nitride. For example, the second photocatalyst may comprise or consist of graphite-carbon nitride. In this document, graphite-carbon nitride may be named g-C or graphitic phase-C3N4。
The photon source may be a UV LED or a UV-VIS LED, such as a pulsed UV LED or a UV-VIS LED. Additionally or alternatively, the photon source may include other types of lights or daylight.
The air purification apparatus described herein may further include:
-a humidifier and/or cooler configured to provide a relative humidity to the air sufficient to provide water on the surface of the anode to generate hydroxyl radicals, electrons and protons by oxidizing molecules of the water,
a sensor configured to measure Relative Humidity (RH) over the anode,
-a fan configured to move the air flow over the surface of the anode of the photoelectrochemical cell,
an integrated circuit configured to apply a voltage, such as a voltage of 0.1 to 10V, between the anode and the cathode of the photoelectrochemical cell,
-a filter, such as a high efficiency particulate trap filter, and/or
-an electrochemical sensor configured to measure the amount of hydroxyl radicals generated.
It should be understood that the aforementioned components may be located within the housing. Additionally or alternatively, the aforementioned components may not be located within the housing, e.g., in close proximity to the housing.
The air purification devices described herein may be portable. This is particularly advantageous, especially for consumer applications where convenient transport is required.
The present invention also provides for the use of a photoelectrochemical cell (such as the one described herein) to decontaminate air by allowing electron holes and/or hydroxyl radicals generated by the photocatalyst in the photoelectrochemical cell to non-selectively oxidize any type of volatile compound, particle or microorganism present in the air.
Definition of
nm nanometer
UV ultraviolet ray
UV-VIS
UV LED ultraviolet light emitting diode
UV-VIS LED
Drawings
Fig. 1 shows a photoelectrochemical cell for air purification subjected to a photon source lamp according to the present disclosure, equipped with a humidifier, a cooler, a fan and a filter stage.
FIG. 2 shows nanostructured TiO on a solid-state electrochemical cell with and without a 1V driving force applied to the cell as a function of time2An example of photoelectrochemical generation of hydroxyl radicals on a nanotube photoanode (measured by the decolorization of a remotely placed dye, methylene blue).
Detailed Description
See figure 1 for a description of the reference numerals with brackets. Photoelectrochemical (PEC) cells are constructed from gas-tight protons (H)3O+) A conductive electrolyte (4) and a porous photoanode (3) and a porous cathode (5) and is driven by a voltage from a DC power supply (10), the DC power supply (10) extracting electrons e from the anode-(15) And supplies it to the cathode. UV-VIS light (12) is directed from the LED or other photon source lamp (2) to the anode where the UV-VIS light (12) adsorbs water vapor H in the incoming air stream (11)2Reaction of O to form hydroxyl radical OH*(13). Some photons may also be transmitted through the anode and electrolyte and excite the light cathode to provide additional driving force to the cell. Air (11) containing impurities such as Volatile Organic Compounds (VOCs) (11) is fed into the cell, whereby the VOCs react with hydroxyl radicals to form CO in the outgoing gas stream (17)2And H2And O. A humidifier (6) and/or peltier cooler (7) is provided at the inlet to ensure that the relative humidity at the anode is high enough to obtain a liquid water film on the anode.
Hydrogen H generated at the cathode2(16) Can be flushed with purified air and will react with and eliminate any remaining oxidizing radicals or ozone. A particulate filter (8) may be added at the outlet to capture any VOC oxidised to particles, and a fan (9) may be provided to ensure sufficient air flow through the device. For PEC battery, lamp, cooler and fan and sensor and control electronicsThe direct current power supply is provided by an alternating current power line (1).
Sensors (not shown) for RH and radicals may be installed to provide control feedback to the humidifier, cooler, lights and PEC battery power supply.
Examples of the invention
We performed a model contaminant Methylene Blue (MB) decomposition experiment placed 2cm from the anode to demonstrate the generation of hydroxyl radicals from the photoanode surface of a Photoelectrochemical (PEC) cell. The PEC cell was made of Ti sheets with TiO grown by an anodic oxidation process in a glycerol-based electrolyte containing 10% water and 0.5% ammonium fluoride2A nanotube. The proton-conducting intermediate layer is
And the photocathode is carbon nitride. Air containing 80% RH was supplied to the anode, while the cathode was in ambient air and separated from the anode. The air flow over the anode was 0.73ml/min of the humid air. Fig. 2 shows the remote decomposition of MB measured in terms of discoloration.
We investigated two cases. In the first case, no voltage was applied to the photoelectrochemical cell and 11% of the MB decomposed after one hour. In this case, without the voltage, the photoelectrochemical cell functions as a typical photocatalyst system, and hydrogen gas is also generated in the anode. In the second case, we apply a voltage of 1V to the photoelectrochemical cell, 21% of the MBs are decomposed after one hour. These experiments show that the generation of hydrogen at the cathode, rather than at the anode, improves the efficiency of the air purifier. They also show that hydroxyl radicals or radicals are able to reach a distance of at least 2cm from the photocatalyst of the anode from their initial action. After the first hour in both cases, the efficiency of the system decreases. In the first hour, the photon source is turned off every ten minutes, which is advantageous for maintaining the decomposition efficiency (growth trend). Thereafter, the light source was turned off every 1 hour. The higher initial efficiency results from more frequent cooling, leaving the adsorbed water layer intact. The peltier element can be used to cool the air and/or PEC cell when the photon source is kept on for more than 10 minutes, for example, the light source is turned off every hour from the 2 nd hour for both experiments in fig. 2.
Claims (19)
1. A method for purifying air, the method comprising:
-providing a photo-electrochemical cell comprising an anode and a cathode separated by a proton-conducting interlayer,
-supplying photons from a photon source to the surface of the anode and/or cathode, thereby generating electron holes and electrons by means of the photoelectric effect,
-providing water on the surface of the anode,
-oxidizing molecules of said water by said electron holes to produce hydroxyl radicals, electrons and protons,
-allowing the air flow to flow over the surface of the anode,
-oxidizing one or more volatile compounds, particles and/or microorganisms present in the air with the generated electron holes and/or the hydroxyl radical, and
-directing the electrons through an electron conducting circuit and the protons through the proton conducting intermediate layer, forming hydrogen gas at the cathode, thereby increasing the lifetime of the hydroxyl radicals at the anode.
2. The method of claim 1, comprising:
(i) maintaining the thickness of the water at the anode surface in the range of 0.8 to about 2nm, and/or
(ii) The method is performed at the anode at a relative humidity equal to or greater than 50%.
3. The method according to claim 2, wherein the thickness and/or relative humidity of the water layer is provided by cooling the air flow before and/or at the anode surface.
4. The method of claim 3, wherein the cooling is accomplished using a Peltier element.
5. The method of any one of the preceding claims, comprising achieving a desired relative humidity using a relative humidity sensor.
6. The method according to any of the preceding claims, comprising moving the air flow over the surface of the anode by means of a fan.
7. The method of any one of the preceding claims, further comprising mixing the hydrogen gas with the air stream after passing through the anode and then reacting with and reducing any ozone and/or oxidizing radicals remaining in the air.
8. The method of any one of the preceding claims, comprising applying a voltage, such as a voltage in the range of 0.1 to 10V, between the anode and the cathode of the photoelectrochemical cell.
9. An air purification device, comprising:
-a housing having at least one air inlet and at least one air outlet,
a photoelectrochemical cell having an anode and a cathode separated by a proton-conducting interlayer, and
a photon source configured to provide photons to a surface of the anode and/or the cathode, thereby generating electron holes and electrons by a photoelectric effect,
-a humidifier and/or cooler to provide a relative humidity at the surface of the anode equal to or higher than 50%,
wherein the photoelectrochemical cell and/or the photon source and/or the humidifier and/or the cooler are located in the housing such that a flow of air from the at least one air inlet to the at least one air outlet flows over the surface of the anode.
10. The air purification device according to claim 9, wherein the anode and/or the cathode and/or the proton conducting intermediate layer are partially or completely transparent.
11. An air cleaning device according to claim 9 or 10, wherein the anode comprises a mesh, a perforated plate and/or a porous layer.
12. The air purification apparatus according to any one of claims 9 to 11, wherein the anode of the photoelectrochemical cell may include a first photocatalyst configured to oxidize water molecules of the water to produce hydroxyl radicals, electrons and protons.
13. An air purification device according to claim 12, wherein the first photocatalyst is porous and/or earth rich material, such as TiO on Ti substrate2A nanotube.
14. The air purification device according to any one of claims 9 to 13, wherein the proton conducting intermediate layer of the photoelectrochemical cell comprises or consists of:
(i) polymers, such as sulfonated tetrafluoroethylene based fluoropolymer copolymers, and/or
(ii) Porous ceramics, such as pure or doped SiO2、TiO2And/or ZrO2。
15. The air purification apparatus according to any one of claims 9 to 14, wherein the cathode of the photoelectrochemical cell comprises a second photocatalyst configured to reduce protons to form hydrogen and/or oxygen to water.
16. An air purification apparatus as claimed in claim 15, wherein the second photocatalyst is porous and/or comprises an earth-rich material such as carbon nitride.
17. An air cleaning device according to any one of claims 9 to 16, wherein the photon source is a UV LED or a UV-VIS LED, such as a pulsed UV LED or a UV-VIS LED.
18. The air purification device according to any one of claims 9 to 17, further comprising:
-a humidifier configured to provide relative humidity to the air to provide water on a surface of the anode to allow generation of hydroxyl radicals, electrons and protons by oxidation of molecules of the water,
a sensor configured to measure a relative humidity at the surface of the anode,
-a fan configured to move the air flow over the surface of the anode of the photoelectrochemical cell,
an integrated circuit configured to apply a voltage, such as a voltage of 0.1 to 10V, between the anode and the cathode of the photoelectrochemical cell,
-a filter, such as a high efficiency particulate trap filter, and/or
-a sensor configured to measure the amount of hydroxyl radicals generated.
19. An air cleaning device according to any one of claims 9 to 18, wherein the housing is portable.
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