JP4521558B2 - Photocatalytic device using light emitting diode - Google Patents

Description

  The present invention relates to a photocatalytic device that performs deodorization and the like by combining a light emitting diode and a photocatalyst.

  The photocatalyst is activated by a light source to cause a photocatalytic reaction, exhibits deodorization / deodorization, antibacterial / sterilization, antifouling / antifogging effects, and is used for malodor removal, air purification, sterilization, sterilization, and the like. Conventionally, mercury lamps, black lights, and germicidal lamps have been used as light sources in addition to sunlight. However, since these light sources have a lifetime of several thousand hours, they need to be replaced in about one year when used in continuous lighting. In addition, the electro-optical conversion efficiency is about 20%, the heat generation amount is large, and the energy consumption is large. In contrast, in recent years, attempts have been made to use light-emitting diodes (LEDs) as light sources for photocatalytic reactions. For example, an ultraviolet light emitting diode (UV-LED) has a very long life of about 50,000 hours, and more than 80% of the power consumption is converted to light. Therefore, it has low power consumption and is expected as a future light source to replace fluorescent lamps. Has been. Further, the LED has an advantage that pulse irradiation and current control are possible. In addition, since it is a small element, it leads to flexibility in device design from the point that design is diverse.

  Examples of the semiconductor used as the photocatalyst include gallium phosphide (GaP) and gallium arsenide (GaAs). When most of these semiconductors are put in water and exposed to light, a photodissolution reaction occurs in which cations and anions are dissolved and the semiconductor is eluted and disappears. On the other hand, titanium oxide is chemically very stable and does not cause such dissolution. There is no other material that does not cause a dissolution phenomenon, but such a material has a band gap energy greater than that of titanium oxide. That is, higher energy ultraviolet rays are required for the photocatalytic action. Titanium oxide does not absorb visible light, but can absorb ultraviolet light that is close to visible light, and is advantageous as a photocatalyst in that it can utilize the slight ultraviolet light contained in sunlight and fluorescent lamps.

From such a viewpoint, in recent years, an air cleaner that combines a semiconductor photocatalyst with a light emitting diode as a light source and activates the photocatalyst by light emission from the light emitting diode has been proposed (see Patent Document 1). For example, a photocatalyst layer having a photocatalyst material that purifies the airflow that flows through the air flow path of the air cleaner is disposed, and the photocatalyst material of the photocatalyst layer is activated by a light emitting diode, and the odorous substance in the air is decomposed. ,Remove.
JP 2002-98375 A

  Conventionally, in a deodorizing apparatus that combines a semiconductor photocatalyst such as a titanium oxide-based semiconductor and a semiconductor element such as a light-emitting diode, it has been considered that the output of the light-emitting diode should be improved in order to improve the deodorizing ability. However, according to research conducted by the present inventors, it has been found that sufficient photocatalytic ability cannot be exhibited simply by continuously irradiating a light emitting diode. The reason for this is considered that the photocatalyst exhibits the photocatalytic effect when the target gas is adsorbed, and the effect of deodorization or the like is not sufficiently exhibited when sufficient adsorption is not performed.

  In addition, such a deodorization / deodorization method has a problem in that when the target gas has a low concentration, the removal efficiency is remarkably lowered due to the boundary film diffusion resistance. When the target gas has a low concentration, the adsorption driving force is also lowered due to the concentration gradient caused by the concentration difference, so that the adsorption speed of the target gas with respect to titanium dioxide is slow and the removal efficiency is deteriorated. This tendency becomes more prominent as the concentration decreases. For this reason, in the conventional processing method using the conventional titanium dioxide, since the removal efficiency per one stage is low, methods such as processing of several to ten or more stages and circulation use in a closed space are usually employed. However, the configuration in which the catalyst layers are multi-stages requires a large space, and the arrangement of light sources for irradiating each catalyst layer with excitation light also becomes a problem and costs are high. In addition, circulation use in a closed space has problems such as the need for a circulation facility and a configuration of the closed space, and the conditions that can be used are limited. For this reason, there is a need for a photocatalytic device capable of causing a photocatalytic reaction by bringing the photocatalyst into contact with an object to be decomposed such as malodorous gas more efficiently.

  The present invention has been made to solve such problems. A main object of the present invention is to provide a photocatalytic device using a light emitting diode that can efficiently excite a photocatalyst with a light emitting diode and exhibit a photocatalytic effect.

  In order to achieve the above object, a photocatalytic device using a light emitting diode according to the first aspect of the present invention activates a photocatalytic layer made of or carrying a photocatalytic material, and the photocatalytic material of the photocatalytic layer. A photocatalytic device having a light emitting diode capable of irradiating light, a driving circuit for driving the light emitting diode, and a pulse control circuit capable of controlling a lighting time of the light emitting diode by controlling the driving circuit, the pulse control circuit However, the driving circuit is controlled so that the lighting time of the light emitting diode when using the photocatalytic device is pulsed at 30 ms or less and at a duty ratio of 50% or less. Thus, the photocatalytic reaction can be promoted by turning on / off the light emitting diode by providing the light-off time with the same or shorter lighting time.

  In the photocatalyst device using the light emitting diode according to the second aspect of the present invention, the pulse control circuit controls the drive circuit so that the lighting time of the light emitting diode is pulse-lit with a duty ratio of 10% or less. By shortening the lighting time in this way, a new reactant can be supplied during the light-off time, and the photocatalytic reaction can be performed efficiently. Further, by reducing the duty ratio, power saving can be achieved and battery driving can be realized.

  Furthermore, in the photocatalyst device using the light emitting diode according to the third aspect of the present invention, the pulse control circuit controls the drive circuit so that the lighting cycle of the light emitting diode is pulsed at a frequency of 50 Hz to 5 kHz. Thus, the photocatalytic reaction can be promoted by performing pulse lighting with a short lighting time and lighting ON / OFF.

  Furthermore, the photocatalyst device using the light emitting diode according to the fourth aspect of the present invention further includes a solar cell as a drive source of the drive circuit. Thereby, driving power can be secured in the daytime with the solar cell, and can be driven with power saving. Moreover, a photocatalyst apparatus can be used day and night by using together with a commercial power source.

  Furthermore, the photocatalyst device using the light emitting diode according to the fifth aspect of the present invention further includes vibration applying means for vibrating the photocatalyst layer. Thereby, the surface area of the photocatalyst layer and the target of the photocatalytic reaction can be increased, and the photocatalytic reaction can be further promoted.

  Furthermore, in the photocatalyst device using the light emitting diode according to the sixth aspect of the present invention, the light emitting diode is an ultraviolet irradiation light emitting diode.

  Furthermore, in the photocatalyst device using the light emitting diode according to the seventh aspect of the present invention, the photocatalytic substance is titanium dioxide.

  According to the photocatalyst device using the light emitting diode of the present invention, it is possible to efficiently generate a photocatalytic reaction and obtain a highly efficient photocatalyst device by controlling the lighting timing of the light emitting diode that irradiates the excitation light that excites the photocatalyst. it can. In particular, the adsorption of organic substances on the photocatalyst surface is more efficient when turned off than when turned on, and based on the knowledge that photolysis is performed in a short time, it is superior to continuous lighting by suppressing the lighting time. It is possible to achieve a long-life and highly reliable photocatalyst device that can achieve efficiency, consumes less power, and generates less heat.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a photocatalyst device using a light emitting diode for embodying the technical idea of the present invention, and the present invention uses a photocatalyst device using a light emitting diode as follows. Not specified. Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, but are merely described. It's just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.

  As a result of investigating the relationship between the degree of photocatalytic effect in such a photocatalytic device and the light irradiation, the present inventors have obtained knowledge showing that the pulse irradiation is better than the continuous irradiation of the light source to the photocatalyst. The present invention has been achieved. Hereinafter, the mechanism will be described with reference to FIG.

  When light is irradiated onto a photocatalytic substance such as titanium oxide, radicals are generated and the radicals decompose organic substances. In this decomposition reaction, the photocatalytic substance itself needs to be in contact with an object to be decomposed. When the light source is continuously turned on and continuously irradiated, decomposition occurs at the contact portion between the photocatalyst substance and the organic substance, but there is little adsorption of new organic substance due to the influence of the resulting gas. Less adsorption results in less photocatalytic reaction, resulting in lower processing capacity. On the other hand, in the case of pulse lighting, since there is a period during which the light source is turned off, the decomposition reaction does not occur during this period, and as a result, new organic substances are easily adsorbed. When more organic substances are adsorbed on the photocatalytic substance, the photocatalytic reaction becomes active and decomposition is promoted. Further, according to the test conducted by the present inventors, it was found that a sufficient catalytic effect can be obtained even if the ON time is momentary because the photocatalytic reaction is performed with a short irradiation. Therefore, by shortening the ON time and setting the OFF time to a length that sufficiently adsorbs the organic matter of the decomposition target, the light source can emit light and a photocatalytic reaction can be obtained. In addition, shortening the ON time also leads to reduction of power consumption of the light source, suppressing the amount of heat generation, extending the life of the light emitting diode element of the light source, and leading to reliable use over a long period.

Utilizing this property, it is possible to achieve high efficiency of photocatalytic devices such as deodorizing / deodorizing devices, sterilizing devices, and antifouling devices using the decomposition and sterilizing action of organic substances using photocatalytic reactions. Hereinafter, as an embodiment of the present invention, an example in which the present invention is applied to a malodor purification apparatus that purifies malodors will be described by paying attention to a deodorizing / air cleaning function widely used as a photocatalytic device.
(Embodiment 1)

FIG. 2 shows the malodor purification apparatus according to Embodiment 1 of the present invention. The photocatalyst device 100 includes a photocatalyst layer 10 made of or carrying a photocatalyst material, a plurality of light-emitting diodes 12 and light-emitting diodes 12 as light sources fixed at positions where the photocatalyst layer 10 can be irradiated with light. A driving circuit 14 for driving, a pulse control circuit 16 capable of controlling the lighting time of the light emitting diode 12 by controlling the driving circuit 14, and a power source 18 for driving them.
(Light emitting diode 12)

As the light emitting diode 12, a light emitting diode that emits light including ultraviolet rays of 360 to 400 nm can be used. The emission wavelength is selected according to the wavelength of the excitation light of the photocatalyst used. Examples of the material of such a light emitting diode include various semiconductors such as BN, SiC, ZnSe, GaN, InGaN, InAlGaN, AlGaN, BAlGaN, and BInAlGaN. Similarly, these elements can contain Si, Zn, or the like as an impurity element to serve as a light emission center. In particular, a nitride semiconductor (eg, a nitride semiconductor containing Al or Ga, a nitride semiconductor containing In or Ga, or In _X as a material for a light emitting layer capable of efficiently emitting a short wavelength in the ultraviolet region that can excite a photocatalyst efficiently. Al _Y Ga _1-XY N (0 <X <1, 0 <Y <1, X + Y ≦ 1) is more preferable, and the semiconductor structure includes a MIS junction, a PIN junction, a pn junction, and the like. Preferred examples include those having a homo structure, a hetero structure, or a double hetero structure, and various emission wavelengths can be selected depending on the material of the semiconductor layer and its mixed crystal ratio. The output can be further improved by forming the single quantum well structure or the multiple quantum well structure, and the number of the light emitting diodes 12 may be one or a large number may be arranged in parallel. In the specification, a light-emitting diode does not necessarily need to emit light including a visible light component, and includes a diode capable of outputting a short wavelength in the ultraviolet region, and is used as a high-power power LED or semiconductor laser ( LD) is used in the concept including.
(Photocatalytic substance)

As the photocatalytic substance, a semiconductor-based substance is used, and preferably, a substance having a small effect of elution by a photodissolution reaction and a high effect sustainability is used. Here, titanium oxide was used as a photocatalytic substance having a relatively small band gap energy and capable of being excited by ultraviolet rays close to visible light.
(Titanium oxide)

The reaction mechanism of titanium oxide will be described below. Titanium oxide has three crystal forms: rutile, anatase, and brookite. Brookite is unstable compared to others and it is difficult to synthesize pure crystals. Rutile is widely used as a pigment in paints, and anatase is mainly used as a photocatalyst. Titanium oxide exhibits n-type semiconductivity, and its application to solar energy conversion materials has attracted attention as a material for photoelectrodes and photocatalysts. A general photochemical reaction occurs by photoexcitation of a reaction substrate. On the other hand, the photocatalytic reaction of titanium oxide absorbs light (ultraviolet light) energy over a band gap of about 3 to 3.2 eV, and in the conduction band, the electron (e ⁻ ) Holes (h ⁺ ) are generated.

[Chemical 1]
TiO ₂ + near UV → e ^- (electron) + h ⁺ (holes)

The electrons reduce oxygen to produce superoxide ions (O ²⁻ ). Thereafter, superoxide ions react with moisture to generate hydroxyl radicals through hydrogen peroxide. Holes are also involved in hydroxyl radical generation. This is shown in the following equation.

[Chemical 2]
O2 + e ⁻ → O ²⁻
O ^2- + 2H ⁺ → H ₂ O ₂
H ₂ O ₂ + e ⁻ + H ⁺ → OH + H ₂ O
h ⁺ + H ₂ O → OH + OH ⁻

Hydroxyl radicals, superoxide ions, and the like are called active oxygens, and hydroxyl radicals have the highest reactivity and the strongest oxidizing power. Therefore, it breaks down any organic matter and changes it into water and carbon dioxide.
(Photocatalyst layer 10)

The photocatalyst material itself is granulated and fired, or the photocatalyst material is supported on other members such as cloth, ceramics, and metal to form the photocatalyst layer 10. For carrying, for example, a binder can be used.
(Drive circuit 14)

The LED drive circuit 14 is a switching circuit for turning on / off the LED, and is composed of an FET or the like. The pulse control circuit 16 controls the drive circuit 14 to adjust the amount of current supplied to the LED and the lighting cycle. Further, PWM control capable of adjusting the duty ratio that defines the LED ON time is performed. The duty ratio is the ratio of the LED irradiation time to the pulse period (lighting time / cycle). For example, the pulse control circuit 16 can change the pulse period from 120 μs to 999 s, the maximum current amount per LED element is 100 mA, and the timer can be changed from 0.5 to 9.5 h at intervals of 0.5 h. In this photocatalytic device, the photocatalytic substance is activated by driving the light emitting diode 12 with the drive circuit 14 and irradiating the photocatalytic substance with excitation light. The photocatalytic efficiency is improved by adjusting the lighting cycle and the duty ratio.
(Power supply 18)

The drive circuit 14 is connected to a power source 18. The power source 18 may be a primary battery, a secondary battery, or the like in addition to a commercial power source. In general, LEDs consume less power than ordinary ultraviolet lamps or ultraviolet fluorescent lamps. However, even when an LED is used, power supply such as a commercial power source is required for continuous irradiation or pulse irradiation with a high duty ratio. On the other hand, in the present embodiment, pulse driving with the duty ratio suppressed to 1 to 50% can suppress power consumption and drive with a portable power source such as a battery. Thereby, it is possible to realize a photocatalyst device that does not require connection of a power supply line and is easy to handle, and a portable photocatalyst device that can be used in a place without power supply equipment. Further, a solar cell can be used as the power source 18. In the daytime, it is possible to drive continuously by day and night by using the ultraviolet light contained in the sunlight to excite light and storing the electric power in the solar cell and using the stored electric power in the nighttime. Needless to say, it is possible to employ a configuration in which either a commercial power source, a storage battery, or a solar cell is used in combination as the power source 18 or these can be switched for use.
(Embodiment 2)

Moreover, you may add the vibration provision means 20 which vibrates the photocatalyst layer 10 to photocatalyst apparatuses, such as a malodor purification apparatus. In FIG. 3, the malodor purification apparatus which added the vibration provision means 20 is shown as the photocatalyst apparatus 200 which concerns on Embodiment 2 of this invention. The same members as those shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The vibration applying means 20 shown in FIG. 3 is a low frequency vibrator and can vary the frequency from 0 to 300 Hz. By adding fine vibrations, the contact probability between the photocatalyst layer 10 and the target of the photocatalytic reaction can be increased, and the photocatalytic reaction can be further promoted. In particular, it is possible to improve the removal rate in a low concentration region where it is difficult to decompose and remove organic substances such as malodorous gases.
Example 1

Hereinafter, using the malodor purification apparatus of FIG. 2 as Example 1, the target gas containing the malodorous substance was allowed to flow, LED pulse irradiation and continuous irradiation were performed, the gas concentration was measured, and the respective removal rates were calculated.
(Gas concentration measurement)

Here, a gas detector tube (detector tube type gas measuring device) was used as an instrument for measuring and analyzing the gas concentration. A gas detector tube is a device that measures the concentration of the target gas. The surface of the glass tube is filled with a granular detector that changes color in response to the target gas and is tightly packed into a glass tube with a constant inner diameter. Is printed with a density scale. The detection agent to be filled is coated with each reagent on a granular material such as silica gel or alumina as a desiccant, and the reagent reacts only with the gas to be measured to show a clear discoloration layer and is stable over a long period of time. What is used is used.
(Odorous substance)

In this example, two types of malodorous substances, acetaldehyde and formaldehyde, were used.
(Acetaldehyde)

Acetaldehyde (CH ₃ CHO) is a colorless chemical substance with an irritating odor, has a boiling point of 20.8 ° C. and a melting point of −123.3 ° C., and is synthesized by a method such as oxidizing ethylene, acetic acid, butanol, synthetic high It becomes a raw material for producing molecules and the like. Emissions to the atmosphere include acetaldehyde production processes, production processes of substances using acetaldehyde as a raw material, automobile exhaust gas and cigarette smoke. It is designated as a specific malodorous substance as a substance causing bad odor. The concentration at which odor can be detected (detection threshold concentration) is 0.002 ppm, and the concentration range (odor intensity 2.5 to 3.5) that can be established as a regulation standard by the prefectural governor by the Odor Control Act is 0.05 to 0.00. 5 ppm.
(Formaldehyde)

Formaldehyde (HCHO) is a colorless gas with an irritating odor and has a boiling point of −19.3 ° C. and a melting point of −118.3 to −117.8 ° C. What is dissolved in about 40% water is an aqueous solution called formalin, which is widely used in antiseptic and sterilizing agents such as phenolic resin, melanin resin, urea resin, adhesives, paints, and formalin samples. Yes. Even at low concentrations, some people may experience disorders such as sick house syndrome. It is a kind of VOC (volatile organic compound).
(LED malodor purification device)

  The malodor purification apparatus using the LED as the light source is a continuous contact purification apparatus in which the target gas passes through the photocatalyst layer 10 as shown in FIG. In the examples, NSHU550 manufactured by Nichia Corporation was used as the UV-LED. Its peak wavelength is 375 nm, and the maximum rating of the pulse forward current is 50 mA. Six UV-LEDs were installed above and below the photocatalyst layer 10 respectively.

Also as a photocatalytic substance, using anatase type titanium dioxide (TiO ₂₎ PC-500 powder MILLENNIUM Corporation. As pretreatment for application to the apparatus, the mixture was granulated by kneading with water and then subjected to baking treatment at 500, 600 and 800 ° C. In addition, a sample prepared by adding 10% gypsum and drying at 70 ° C. was also prepared.

The particles of the sample produced as described above are microspherical and contain titanium dioxide as a main component. This photocatalytic substance was supported by a 60 mesh stainless steel mesh to form a photocatalytic layer 10. The area of the photocatalyst layer 10 is about 4.32 cm ² , the thickness of the photocatalyst layer 10 is about 2 mm, and the amount of photocatalyst is about 1.1 g. The distance between the LED and the photocatalyst layer 10 was about 9 mm, and the average illuminance was 0.6 mW / cm ² . The pulse period and duty ratio are changed by the LED pulse control circuit 16 of this purification device to control the pulse output.

  A pump 26 was attached to the outlet side of the purification device in order to pass the gas before treatment through the purification device. A mini pump (0.05 to 3 l / min) was used as the pump 26. Moreover, in order to diverge the heat | fever by LED irradiation in the photocatalyst layer vicinity, a fan is installed as needed. Since the oxidation reaction by the photocatalyst is influenced by the environmental temperature, the test was performed in a constant temperature room at 20 to 25 ° C.

  The measurement was performed by the following procedure using the purification apparatus of FIG. First, acetaldehyde was diluted with air using a test gas preparation Tedlar bag 22 to produce a concentrated acetaldehyde gas (about 6000 ppm). This rich gas was diluted to a concentration according to the purpose, put into the Tedlar bag 22, and used as a gas before treatment. The gas flow rate and ultraviolet LED irradiation method are set according to the measurement purpose. After the purification device was started, the gas in the device (dead space) was removed in another bag, and a test gas sampling tedlar bag 24 was newly attached. This recovered gas was used as a gas after the test. And the density | concentration of the collect | recovered gas after the process was measured. Based on the measured concentration, the performance was evaluated by the removal rate using the following formula 1.

The test was conducted in the same manner for formaldehyde, which is another malodorous component.
(Influence of titanium dioxide due to firing)

The XRD results of titanium dioxide and the results of specific surface area measurement by the BET method are shown in FIGS. Anatase was observed from the unfired sample (raw material) to the sample at a firing temperature of 900 ° C. However, for the sample fired at 1000 ° C., rutile was also confirmed in addition to anatase. As the firing temperature increased, the specific surface area of titanium dioxide decreased to 77 at 500 ° C., 43 at 600 ° C., and 13 m ² / g at 800 ° C.

The SEM photograph of the sample surface used for FIGS. 6-7 is shown. (A) of FIG. 6 is an unbaked powder, (b) is extruded and granulated using gypsum, and (c) and (d) are granulated with a granulator. In (b), the particles are enlarged by gypsum, and it can be seen that (c) and (d) have a similar granular appearance. Furthermore, although the magnification is different, it can be seen in detail in FIG. 7 that the voids decrease and the particles are clogged as the firing temperature increases. It can also be seen that (d) is grain-grown and sintered as compared with (c) (photocatalytic performance evaluation by powder sample).

FIG. 8 shows the removal rate of acetaldehyde by the gas bag B method. Only in the experiment of FIG. 8, black light was used as the ultraviolet light source, and the ultraviolet intensity was 1.0 mW / cm ² . There was no significant difference in the photocatalytic activity from uncalcined titanium dioxide to titanium dioxide calcined at 700 ° C., and the removal rate was slower from that of the sample having a calcining temperature of 800 ° C. or higher. This is because there is no direct relationship between the specific surface area and the photocatalytic activity, and it is considered that the decomposition reaction occurs if there is a sufficient specific surface area for adsorption and decomposition.
(Effect of LED malodor purification device for acetaldehyde)

FIG. 9 shows changes in the removal rate of acetaldehyde with respect to the pulse period. As test conditions, titanium dioxide baked at 600 ° C. with a gas concentration of 20 ppm, a current value of 20 mA, a linear velocity of 0.0042 m / s, a temperature of 20 ° C., a duty ratio of 50%, and an ultraviolet intensity of 0.6 mW / cm ² was used. The removal rate was about the same as or higher than that of continuous irradiation up to a period of about 0.2 to 2 ms. After a period of about 2 ms, the removal rate gradually decreased, and after about 10 ms, it was about ½ of continuous irradiation.

  From these things, it is thought that the removal mechanism of acetaldehyde follows FIG. 1 mentioned above. That is, when the pulse period is around 1 ms, the amount of adsorption when the LED is turned off is sufficiently larger than the processing amount when the LED is turned on, so that the removal efficiency is equal to or higher than that of continuous lighting. On the other hand, since decomposition occurs at the time of lighting, adsorption is reduced due to the influence of the generated gas. The reason why the removal rate becomes about 1/2 when the pulse period is about 10 ms is considered that the adsorption on the photocatalyst layer is saturated and the adsorption effect at the time of extinction is lost. Thus, acetaldehyde is mainly removed by simultaneous adsorption and decomposition when the LED is turned on and only adsorption when the LED is turned off. Although the adsorption at the time of turning off is larger than that at the time of turning on, it decreases rapidly with the passage of time. On the other hand, even if lighting is instantaneous, sufficient decomposition can be obtained. For this reason, the lighting cycle of the LED is set to a time during which the extinguishing time becomes dominant and the adsorption effect of the organic matter on the photocatalytic substance can be exhibited. Preferably, the turn-off time is shorter than the time when the adsorption is saturated. On the other hand, from the viewpoint of saving power consumption, it is preferable to shorten the lighting time. However, from the viewpoint of increasing the switching speed of the LED drive circuit 14 and cost, 0.1 ms to 30 ms, preferably 1 to 20 ms, More preferably, it is 2 ms to 5 ms. The lighting cycle is about 50 Hz to 5 kHz. Furthermore, the duty ratio is 50% or less, preferably 10% or less. The lighting time and lighting cycle are optimally adjusted according to the photocatalyst material used, the output of the LED, the type of power source, and the like.

  In the examples described below, LED irradiation was performed at a linear velocity of 0.0042 m / s and a temperature of 20 ° C. using titanium dioxide baked at 600 ° C., unless otherwise specified.

  First, the removal rate when the gas ratio of acetaldehyde was 20 ppm, the pulse period was 1 ms, and the duty ratio was changed was measured. The result is shown in FIG. The decomposition of acetaldehyde showed better removal efficiency than continuous irradiation in the duty ratio range of 10-80%. The reason why the removal efficiency superior to continuous irradiation was exhibited even when the duty ratio was 10% was presumed to be that the titanium oxide was decomposed with respect to acetaldehyde because of its excessive ability to decompose. Therefore, it can be confirmed that efficient decomposition is not performed. Therefore, if it is devised to make sufficient contact with the titanium oxide on the surface, it is possible to process a chemical amount about 10 times this. When the duty ratio was 80% or more, the removal rate was comparable to that of continuous irradiation. This is presumably because the decomposition occurs when the LED is lit as described above, and the adsorption is hindered by the influence of the gas generated by the decomposition.

Next, the change in removal rate with respect to the pulse period when the concentration of acetaldehyde was 5 ppm was measured. The result is shown in FIG. The duty ratio here is 50%. As a result of the measurement, unlike the case of 20 ppm acetaldehyde shown in FIG. 9, the removal rate of acetaldehyde decreased as the pulse width became 70 to 1 ms. Compared to the case of the 20 ppm test, the concentration gradient is small, the amount of adsorption when the LED of the above-mentioned model is turned off is small, and it is considered that the gas passed as it is. Note that the variation in the graph seems to be an error due to the fact that the value of the detector tube is difficult to distinguish because of its low concentration.
(Example 2)

  Next, in order to improve the adsorption efficiency at a low concentration, the removal rate of the target gas was measured using the second embodiment shown in FIG. In general, in the deodorization / deodorization system as in the first embodiment, when the target gas has a low concentration, the removal efficiency is significantly reduced due to the boundary film diffusion resistance. Therefore, a low-frequency vibrator was installed as a vibration imparting means 20 at the lower part of the apparatus through which acetaldehyde passes through the catalyst, and the effect of improving the adsorption efficiency at a low concentration was confirmed by increasing the contact probability between the photocatalyst and the target gas. .

As Example 2, FIG. 12 shows the results of measuring the acetaldehyde removal ability by applying a fine vibration with a frequency of 60 Hz in a low concentration region and changing the duty ratio. As a comparative example, the ability to remove acetaldehyde in the case of continuous irradiation was around 60%. On the other hand, when the pulse period was around 1 ms as Example 2, the removal rate was better than that in the continuous irradiation test. This is considered to be because when the pulse period is short, the concentration gradient at the time of turning on the LED is the same as that immediately after the turning off, and the larger adsorption at the time of turning off the light works effectively. On the other hand, as the pulse period becomes longer, the concentration gradient becomes smaller, so the adsorption amount when the LED is turned off also becomes smaller. Therefore, it was proved that application of fine vibration and pulse irradiation of around 1 ms are effective for removing acetaldehyde at a low concentration.
(Relationship between specific surface area of photocatalytic substance and pulse period)

  Furthermore, the relationship between the specific surface area of titanium dioxide used in the acetaldehyde removal test and the optimum pulse period was investigated. The results are shown in FIGS. FIG. 13 shows the removal rate when an LED is irradiated at a room temperature of 20 ° C. with a duty ratio of 50% by flowing acetaldehyde with a gas concentration of 20 ppm at a linear velocity of 0.0042 m / s on a titanium dioxide sample dried at 70 ° C. Is shown. 14 shows the removal rate when using a titanium dioxide sample calcined at 500 ° C. as a sample under the same conditions, and FIG. 15 shows the removal rate when using a titanium dioxide sample calcined at 800 ° C. Yes. In each sample, a portion where the pulse irradiation showed a better removal rate than the continuous irradiation was found. FIG. 16 shows the pulse period at which the removal rate reaches a peak in the tests of FIGS. As shown in this figure, the pulse periods at which the removal rate peaks were 50, 30, and 5 ms for samples of 70 ° C., 500 ° C., and 800 ° C., respectively. In the case of pulse irradiation, adsorption / desorption of the target gas as shown in FIG. 1 occurs. In these examples, it can be seen that the photocatalytic substance having a large specific surface area and a large adsorption amount can be removed even if the pulse period is increased.

  On the other hand, in the continuous irradiation performed as a comparative example, the removal rate decreased to 65, 60, and 30% as the processing temperature was increased to 70, 500, and 800 ° C. Further, there was no significant difference in removal efficiency between the 70 ° C. dried sample and the 500 ° C. fired sample. This is the same phenomenon as FIG. 8 in which there is no direct relationship between the specific surface area and the removal of acetaldehyde in the case of LED continuous irradiation, and the decomposition reaction occurs if there is a sufficient specific surface area for adsorption and decomposition. It appears to be.

  The 800 ° C. calcined sample has low photocatalytic activity but high mechanical strength. A high mechanical strength is advantageous for use as a device. However, the removal rate is about 30%. Then, the improvement of the removal rate of acetaldehyde was tried by giving a low frequency vibration.

Here, under the same conditions as in FIG. 15, the duty cycle was changed by applying a vibration with a pulse period of 10 ms and a vibration frequency of 180 Hz. The result is shown in FIG. Comparing this result with FIG. 15, when the pulse period was 10 ms, the removal rate was improved more than twice by applying vibration. As a result of the application of vibration, the contact probability between the acetaldehyde and the sample is increased and the adsorption is promoted. Moreover, a value better than continuous irradiation was shown when the duty ratio was in the range of 20 to 60%. This seems to be because the amount of adsorption when the LED was turned off was larger than when the LED was turned on, and the processing amount as a whole increased. The reason why the removal efficiency is reduced when the duty ratio is 80% or more is thought to be that gas is generated due to decomposition of acetaldehyde, adsorption becomes difficult to occur, and adsorption amount is reduced.
(Effect of LED malodor purification device for formaldehyde)

  Next, the removal test which used formaldehyde instead of acetaldehyde as a malodorous substance was done. In recent years, air pollution in a low concentration range such as sick house syndrome has become a problem, and formaldehyde, which is the main component of VOC, is first picked up as a target of priority efforts. Here, the test was performed with gas concentrations of 0.5 ppm, 3 ppm, and 4 ppm, a frequency of 200 Hz, a 70 ° C. dry sample used in FIG. 13, and a duty ratio of 100%. The results are shown in FIG. From this figure, the removal rate was 80% or more when the gas concentration was 3 ppm or more. The reason why the removal efficiency of 3 ppm is higher than that of 4 ppm seems to be a measurement error due to the use of a detector tube with a wide concentration range. At 0.5 ppm, the removal rate was about 40%, which was reduced to 1/2 of 4 ppm. This is probably because the concentration gradient is small and the adsorption of titanium dioxide is small as in the case of acetaldehyde of 5 ppm.

  Furthermore, in order to improve the removal efficiency of formaldehyde at a low concentration, the removal rate was measured when the pulse period was changed at a gas concentration of 0.5 ppm, a duty ratio of 50%, and a vibration frequency of 200 Hz. The result is shown in FIG. As shown in this figure, it was shown that by applying pulse irradiation and vibration, a removal rate of about 80% can be achieved even with a low concentration of formaldehyde. This is considered to be because the adsorption amount when the LED is turned off is sufficiently larger than the processing amount when the LED is turned on by performing pulse irradiation as in the case of the acetaldehyde described above. However, the removal rate when the pulse period was 1 ms was only 20%, which was 1/2 of the LED continuous irradiation.

  Therefore, the influence on the removal rate was examined by changing the duty ratio in the test of FIG. 25 at a pulse period of 1 ms. The result is shown in FIG. The removal rate when the duty ratio is 1% is higher than that when the duty ratio is 20 to 80%. This is considered to be because the amount of adsorption when the LED is turned off is large. It was also found that a high removal rate can be obtained even if the duty ratio is reduced if the adsorption ability of titanium oxide is sufficient with respect to the test gas concentration. Accordingly, it has been shown that, as a countermeasure against sick house syndrome, if the duty ratio is set small, the power consumption can be reduced and the life of the LED can be extended.

  As described above, a high removal rate can be maintained even if the pulse period is increased and the duty ratio is decreased. In the decomposition test of acetaldehyde and formaldehyde, the removal rate was better when pulse irradiation with a period of several to several tens of milliseconds was performed than continuous irradiation. Further, a good removal rate was exhibited at a duty ratio of 1 to 50%. In addition, for the titanium oxide used in the malodor purification apparatus that can be used for a long period of time, a material that can be adsorbed and desorbed in a short time during LED pulse irradiation and that has high photocatalytic activity is effective. Specifically, when acetaldehyde was 20 ppm, when titanium dioxide baked at 600 ° C. was used as the photocatalytic substance, a removal rate of 80% was achieved in the LED continuous irradiation test. Further, in the LED pulse irradiation test with a duty ratio of 50%, a processing capability comparable to that of continuous irradiation can be obtained in a cycle of about 0.2 to 2 ms. The removal rate of titanium dioxide tends to decrease as the firing temperature increases. For this reason, it became clear that target gas adsorb | sucks to a titanium oxide, so that it is a high specific surface area. Furthermore, when fine vibration is imparted to the photocatalyst substance, the contact probability between the target gas and the photocatalyst substance is increased and the adsorption is promoted. As a result, the reactivity is improved. For example, when fine vibration is applied to titanium dioxide baked at 800 ° C., the acetaldehyde removal rate is improved. By applying vibration, the removal rate was improved more than twice when the pulse period was 10 ms. In addition, when the target gas concentration is low, a high removal rate is exhibited even if the duty ratio is set small, and the life of the LED can be extended with low power consumption. For example, as a result of measuring the removal rate when applying 200 Hz vibration to titanium dioxide dried at 70 ° C. in 0.5 ppm formaldehyde and changing the duty ratio, the duty ratio is 40% even when the duty ratio is 1%. %, The removal rate was comparable. In this way, by using an LED as a light source for irradiating titanium dioxide and performing pulse irradiation with an appropriately set duty ratio, the adsorption power of titanium dioxide to the target gas can be improved and the processing capacity can be increased. it can. Further, by shortening the lighting period, the amount of power consumption is remarkably reduced, and use with a battery or a secondary battery is also possible. At the same time, it can be combined with a solar cell to enable operation at night.

  The photocatalyst device using the light emitting diode of the present invention is not limited to the deodorization / deodorization device, and can be suitably applied to a sterilization device, an antifouling device, and the like.

It is explanatory drawing which shows the process in which the photocatalytic effect is expressed by pulse irradiation. It is a block diagram of the photocatalyst device using the light emitting diode which concerns on Embodiment 1 of this invention. It is a block diagram of the photocatalyst apparatus using the light emitting diode which concerns on Embodiment 2 of this invention. It is a graph which shows the XRD result of titanium dioxide. It is a graph which shows the result of the specific surface area measurement by BET method of titanium dioxide. It is an image figure which shows the SEM photograph of the sample surface. It is an image figure which shows the SEM photograph of the sample surface. It is a graph which shows the removal rate of acetaldehyde by the gas bag B method. When a sample of titanium dioxide fired at 600 ° C is irradiated with acetaldehyde with a gas concentration of 20 ppm at a linear velocity of 0.0042 m / s, the duty ratio is 50% at room temperature of 20 ° C, and the pulse period is changed to irradiate the LED It is a graph which shows the removal rate of. When a sample of titanium dioxide fired at 600 ° C. is irradiated with acetaldehyde having a gas concentration of 20 ppm at a linear velocity of 0.0042 m / s, a pulse period of 1 ms at a room temperature of 20 ° C., and a duty ratio is changed to irradiate an LED. It is a graph which shows a removal rate. When a sample of titanium dioxide fired at 600 ° C is flowed with acetaldehyde with a gas concentration of 5 ppm at a linear velocity of 0.0042 m / s, the duty ratio is 50% at a room temperature of 20 ° C, and the pulse period is changed to irradiate the LED. It is a graph which shows the removal rate of. A titanium dioxide sample fired at 600 ° C. was given a fine vibration of a frequency of 60 Hz, acetaldehyde with a gas concentration of 5 ppm was flowed at a linear velocity of 0.0042 m / s, and the duty ratio was changed at room temperature of 20 ° C. to irradiate the LED. It is a graph which shows the removal rate in a case. It is a graph showing the removal rate when acetaldehyde with a gas concentration of 20 ppm is flowed at a linear velocity of 0.0042 m / s on a titanium dioxide sample dried at 70 ° C., and the LED is irradiated at a duty ratio of 50% at a room temperature of 20 ° C. is there. It is a graph showing the removal rate when acetaldehyde with a gas concentration of 20 ppm is flowed at a linear velocity of 0.0042 m / s on a titanium dioxide sample fired at 500 ° C., and the LED is irradiated at a duty ratio of 50% at a room temperature of 20 ° C. is there. A graph showing the removal rate when a 20% acetaldehyde gas was flowed at a linear velocity of 0.0042 m / s on a titanium dioxide sample fired at 800 ° C., and the LED was irradiated at a duty ratio of 50% at a room temperature of 20 ° C. is there. 12 to 15 are graphs showing pulse periods at which the removal rate reaches a peak. A vibration with a frequency of 180 Hz was applied to a titanium dioxide sample calcined at 800 ° C., and acetaldehyde with a gas concentration of 20 ppm was flowed at a linear velocity of 0.0042 m / s as in FIG. 15, and the duty ratio was changed at a room temperature of 20 ° C. It is a graph which shows the removal rate at the time of irradiating LED. A titanium dioxide sample dried at 70 ° C. was given a vibration at a frequency of 200 Hz, and formaldehyde with a gas concentration of 0.5 ppm, 3 ppm, and 4 ppm was flowed at a linear velocity of 0.0042 m / s, and the LED was continuously irradiated at a room temperature of 20 ° C. It is a graph which shows the removal rate in a case. A titanium dioxide sample dried at 70 ° C. is given a vibration of 200 Hz, formaldehyde with a gas concentration of 0.5 ppm is flowed at a linear velocity of 0.0042 m / s, a duty ratio is 50% at a room temperature of 20 ° C., and a pulse cycle is set. It is a graph which shows the removal rate at the time of changing and irradiating LED. A titanium dioxide sample dried at 70 ° C. is given a vibration at a frequency of 200 Hz, formaldehyde with a gas concentration of 0.5 ppm is flowed at a linear velocity of 0.0042 m / s, a pulse period is 1 ms at a room temperature of 20 ° C., and a duty ratio is set. It is a graph which shows the removal rate at the time of changing and irradiating LED.

DESCRIPTION OF SYMBOLS 100, 200 ... Photocatalyst apparatus 10 ... Photocatalyst layer 12 ... Light emitting diode 14 ... Drive circuit 16 ... Pulse control circuit 18 ... Power supply 20 ... Vibration applying means 22 ... Preparation Tedlar bag 24 ... Extraction Tedlar bag 26 ... Pump

Claims (7)

A photocatalytic layer made of or carrying a photocatalytic material;
A light emitting diode capable of irradiating light for activating the photocatalytic substance of the photocatalytic layer;
A drive circuit for driving the light emitting diode;
A pulse control circuit capable of controlling the driving circuit to control the lighting time of the light emitting diode;
A photocatalytic device comprising:
The photocatalyst device , wherein the pulse control circuit controls the drive circuit so that the lighting time of the light emitting diode when using the photocatalyst device is 30 ms or less and the duty ratio is 50% or less . A photocatalytic device using the light-emitting diode according to claim 1,
The photocatalyst device characterized in that the pulse control circuit controls the drive circuit so that the light emitting diode is pulse-lit with a lighting time of 10% or less. A photocatalytic device using the light emitting diode according to claim 2 ,
The photocatalyst device, wherein the pulse control circuit controls the drive circuit so that the lighting cycle of the light-emitting diode is pulse-lit at a cycle of 50 Hz to 5 kHz. A photocatalytic device using a light emitting diode according to any one of claims 1 to 3, further
A photocatalyst device comprising a solar cell as a drive source of the drive circuit. A photocatalytic device using a light emitting diode according to any one of claims 1 to 4, further
A photocatalyst apparatus using a light emitting diode, comprising vibration imparting means for vibrating the photocatalyst layer. A photocatalytic device using a light emitting diode according to any one of claims 1 to 5,
A photocatalytic device using a light emitting diode, wherein the light emitting diode is an ultraviolet light emitting light emitting diode. A photocatalytic device using the light-emitting diode according to claim 1,
A photocatalytic device using a light emitting diode, wherein the photocatalytic substance is titanium dioxide.