JP5217561B2 - Photocatalyst regeneration method - Google Patents

Description

  When carrying out photochemical reaction treatments such as oxidative decomposition of organic matter in water, warm bath water, pool water, drinking water, seawater, industrial water, decomposition of bacteria, decomposition of fungi, decomposition of viruses, decomposition of algae, etc. The present invention relates to a method for regenerating a photocatalyst that is contaminated by components contained in a liquid and whose activity decreases.

  In recent years, attention has been focused on the strong oxidizing power of photocatalysts, and it is no exception in the field of water purification. The oxidative degradation mechanism of photocatalyst is due to OH radicals in which holes generated by excitation light oxidize OH groups, and organic impurities in water and organic impurities such as bacteria, fungi, viruses and algae have been used in the past Unlike germicidal lamps, ozone, chlorine, etc., it does not persist and oxidatively decomposes. In addition, among active species, OH radicals have the strongest oxidizing power, and it has been clarified that even refractory substances that could not be dealt with until now can be decomposed.

  However, if photochemical reaction treatment that oxidizes organic matter, decomposes bacteria, decomposes fungi, decomposes viruses, or decomposes algae is performed for a long period of time, the photocatalyst is contaminated with the treated water component, and the photocatalytic activity rapidly decreases. However, it has been clarified that the result of the photochemical reaction treatment suddenly deteriorates.

  In the past, the photochemical reaction treatment was interrupted before the photocatalytic activity decreased, and the photocatalyst with the remaining activity was discarded early to prevent deterioration of the liquid quality of the processing solution. Disposing a photocatalyst that can be regenerated and replacing it with a new one, especially disposing of a photocatalyst that remains active, is an expensive material, so the cost of organic photochemical reaction treatment is high. In addition, there were problems in terms of effective use of resources and generation of industrial waste.

In addition, there is a method of regenerating a photocatalyst having a reduced activity, for example, a complex on the surface of catalyst fine particles used for the decomposition or sterilization treatment of organic matter in water to be treated, such as pure or tap water. Patent Document 1 discloses a method of cleaning and regenerating while performing ultrasonic vibration in cleaning water and aeration with ozone or air. In addition, in the process of performing photochemical reaction treatment such as oxidative decomposition of organic matter in liquid and sterilization of bacteria, in order to remove calcium and magnesium, which are hardness components in liquid, adhere to the surface of the photocatalyst over time, Patent Document 2 reports a method for regenerating a photocatalyst that is washed and removed with a weakly acidic solution.
Japanese Patent Laid-Open No. 7-185340 JP-A-10-151354

  Ultrapure water, excluding ion exchange water, clean water, warm bath water, pool water, drinking water, seawater, oxidative decomposition of organic matter in industrial water, decomposition of bacteria, decomposition of fungi, decomposition of viruses, decomposition of algae, etc. That is, in the case of decomposing organic impurities, since the treatment is performed continuously, it is very difficult to clearly determine the photocatalyst contamination status. It was confirmed that it was caused by both undecomposed organic matter. In the above-mentioned Patent Document 1 and Patent Document 2, it is not assumed that a metal compound and an organic impurity exist simultaneously as contaminants that reduce the conventional activity of the photocatalyst, and these contaminants exist simultaneously. In this case, it is difficult to regenerate the conventional activity by the above-described photocatalyst regeneration method, and it is considered that the conventional activity is easily lost again due to the residual adhered contaminants. Therefore, if there is a method in which the photocatalyst is regenerated from contamination of both the metal compound and the undecomposed organic matter, that is preferable.

  Therefore, the object of the present invention is to provide organic, such as oxidative decomposition of organic matter in drinking water, warm bath water, pool water, drinking water, seawater, industrial water, bacterial decomposition, fungal decomposition, virus decomposition, and algal decomposition. It is intended to provide a method for efficiently regenerating a photocatalyst that causes a decrease in activity due to contamination during photochemical reaction treatment of a volatile impurity.

  Thus, it is possible to provide a low-cost photochemical reaction process by continuously using an expensive photocatalyst without discarding it.

  When the inventors perform oxidative decomposition of organic matter in water, warm bath water, pool water, drinking water, seawater, industrial water, bacterial decomposition, fungal decomposition, virus decomposition, algae decomposition, etc. for a long time Thus, a method for regenerating a photocatalyst that is contaminated and impairs conventional activity has been studied. As a result, as a pollutant that impairs the photocatalytic activity, it is confirmed that there is a metal compound and an undecomposed organic impurity, not one of them, and after washing with an acidic solution, washing with an alkaline solution, It has been found that the above problems can be solved.

That is, the present invention is a method for regenerating a photocatalyst used for purification of water containing organic impurities and deteriorated due to contamination by the metal compound and undecomposed organic matter during the water purification treatment. A fiber composed of a composite oxide phase of an oxide phase (first phase) mainly composed of a component and a metal oxide phase (second phase) containing titanium, and titanium of a metal oxide constituting the second phase Is a silica-based composite oxide fiber having a photocatalytic function, which gradually increases toward the surface layer of the fiber, and the photocatalyst is washed and regenerated with an acidic aqueous solution, and then washed and regenerated with an alkaline aqueous solution. The present invention relates to a method for regenerating a photocatalyst. The acidic aqueous solution is preferably a strong acidic aqueous solution. The alkaline aqueous solution is preferably a strong alkaline aqueous solution. In one embodiment of the present invention, the washing is performed by immersing the photocatalyst in an acidic aqueous solution or an alkaline aqueous solution. Further, it is preferable to wash the photocatalyst by causing forced convection in the acidic aqueous solution or alkaline aqueous solution.

  The method for regenerating a photocatalyst in the present invention is to perform cleaning with an alkaline aqueous solution after cleaning with an acidic aqueous solution in order to regenerate a photocatalyst that has been contaminated with a metal compound and an undecomposed organic substance and has originally lost activity. It is possible to regenerate up to near the original activity.

  Since the photocatalyst regeneration method in the present invention can be regenerated and used for photochemical reaction treatment without discarding the photocatalyst whose activity has been impaired due to contamination, the cost of photochemical reaction treatment with an expensive photocatalyst can be reduced.

Examples of the organic impurities include bacteria, fungi, viruses, algae and other organic substances, and also include organic compounds which are decomposed by a photocatalyst upon irradiation with ultraviolet rays. The photocatalyst that is the subject of the present invention is a catalyst that decomposes organic substances, bacteria, fungi, viruses, and algae contained in water. Titanium oxide (TiO ₂ ), strontium titanate (SrTiO ₂ ), cadmium sulfide (CdS), Single semiconductors such as molybdenum sulfide (MoS ₂ ), zinc oxide (ZnO), tungsten oxide (WO ₃ ), copper oxide (CuO ₂ ), iron oxide (Fe ₂ O ₃ ), silicon (Si), or single semiconductors thereof Metal or metal oxide such as gold (Au), platinum (Pt), copper (Cu), tin (Sn), palladium (Pd), rhodium (Rh), nickel oxide (NiO), rhodium oxide (RhO ₂ ) And the like on which is supported. As for the shape of the photocatalyst, the form of the photocatalyst particles alone, supported on a round or plate-shaped substrate, fibrous, supported on a honeycomb-shaped substrate is not limited, but the contact efficiency to the processing fluid, the photocatalyst It is preferable to use a fibrous material having the best ultraviolet irradiation efficiency and having a photocatalytic function on the surface. In particular, the silica-based composite oxide fiber having a photocatalytic function disclosed in Japanese Patent No. 3465699 and the like has an increase in the proportion of the second phase having a photocatalytic function in an inclined manner toward the surface layer of the fiber. It is firmly held in the oxide phase mainly composed of the silica (SiO ₂ ) component as the first phase, and there is almost no dropout of the photocatalyst that has been a problem in water purification, so the shape is non-woven fabric. It is often used as a catalyst for water purification.

  In the silica-based composite oxide fiber suitably used as the object of the present invention, the oxide phase (first phase) mainly composed of the silica component may be amorphous or crystalline. You may contain the metal element or metal oxide which can form a solid solution or a eutectic compound with a silica. The metal element (A) that can form a solid solution with silica or its oxide is not particularly limited as the metal element (B) that can form a compound with a specific composition with silica. For example, (A) is titanium, Examples of (B) include aluminum, zirconium, yttrium, lithium, sodium, barium, calcium, boron, zinc, nickel, manganese, magnesium, iron and the like.

  This first phase forms the internal phase of the fiber obtained in the present invention and plays an important role in bearing the mechanical properties. The ratio of the first phase to the entire fiber is preferably 98 to 40% by weight, and in order to sufficiently develop the target second phase function and also to exhibit high mechanical properties, It is preferable to control the existence ratio of one phase within the range of 50 to 95% by weight.

  On the other hand, the metal oxide constituting the second phase plays an important role in developing the photocatalytic function. An example of the metal constituting the metal oxide is Ti. The metal oxide may be a simple substance, or may be a compound in which a substitutional solid solution is formed with the eutectic compound or a specific element. The abundance ratio of the second phase constituting the surface layer portion of the fiber is preferably 2 to 60% by weight, although it varies depending on the type of the oxide, in order to fully exhibit its function and simultaneously exhibit high strength. It is preferable to control within the range of 5 to 50% by weight. The crystal grain size of the metal oxide containing Ti of the second phase is preferably 15 nm or less, particularly preferably 10 nm or less.

  The proportion of Ti in the metal oxide constituting the second phase increases in a gradient toward the fiber surface, and the thickness of the region where the composition gradient is clearly recognized is in the range of 5 to 500 nm. However, it may be about 1/3 of the fiber diameter. In the present invention, the “existence ratio” of the first phase and the second phase means the metal oxide constituting the first phase and the whole metal oxide constituting the second phase, that is, the first phase relative to the whole fiber. The weight percent of metal oxide and second phase metal oxide is shown.

  Examples of water containing organic impurities such as organic substances, bacteria, fungi, viruses and algae in which the photocatalyst of the present invention is used include clean water, warm bath water, pool water, drinking water, sea water, industrial water and the like.

  In such water purification, the photocatalyst is contaminated by metal compounds and undecomposed organic substances contained in the treated water due to long-term use, and the initial activity is significantly reduced.

  The contaminated photocatalyst has a metal compound and an undecomposed organic substance partially attached to the surface. Originally, oxidative decomposition that occurs only on the surface by OH radicals in which holes generated by excitation light oxidize OH groups, The excitation light is partially absorbed by contaminants that are absorbed. This results in a decrease in photocatalytic activity. That is, the photocatalyst loses its activity by blocking the excitation light due to contamination. Thus, the photocatalyst is regenerated by removing the adhering contaminants and restoring the area that receives the excitation light before contamination.

  In the present invention, the contaminated fiber is washed with an acidic aqueous solution, and then washed with an alkaline solution. If this order is changed, sufficient activity cannot be obtained.

  Examples of the acidic aqueous solution used for washing include aqueous solutions of sulfuric acid, hydrochloric acid, citric acid, phosphoric acid and the like, but a strong acidic aqueous solution is particularly preferable in order to obtain a greater degree of regeneration faster. Examples of the strongly acidic aqueous solution include sulfuric acid and hydrochloric acid. Among strong acidic solutions, hydrochloric acid that has little influence on the photocatalyst such as dissolution is preferable, and its concentration avoids dissolution and shortens the washing time. Therefore, it is more preferable to use 0.5 to 1M.

  Examples of the alkaline aqueous solution used for washing include sodium carbonate, potassium carbonate, sodium percarbonate, sodium hypochlorite, and the like, but a strong alkaline aqueous solution is particularly preferable in order to obtain a greater degree of regeneration faster. Examples of strong alkaline aqueous solutions include sodium percarbonate and sodium hypochlorite, but among the strong alkaline aqueous solutions, it is also effective in inactivating various bacteria and viruses. Sodium hypochlorite, which can be easily oxidatively decomposed even if it remains, is preferable, and its concentration should be 2 to 6% effective chlorine concentration in order to affect the human body and shorten the cleaning time. Is more preferable.

  As a cleaning, leave in a container not affected by acidic or alkaline aqueous solution using a contaminated photocatalyst, put a predetermined amount of acidic or alkaline aqueous solution adjusted to any concentration, and soak for a predetermined time to increase the degree of regeneration It is preferable to use immersion cleaning. Also, in order to obtain a large regeneration rate faster than immersion cleaning, as with immersion cleaning, forced convection is applied by applying a flow rate to these aqueous solutions with a pump or the like when a predetermined amount of acidic or alkaline aqueous solution is added. It is more preferable to circulate and circulate by raising and circulating. In the present invention, “immersion cleaning” means that the contaminated photocatalyst is immersed in a fixed amount of an acidic or alkaline aqueous solution for a predetermined time. It means that the photocatalyst is immersed in a fixed amount of acidic or alkaline aqueous solution, and the fixed amount of aqueous solution is sucked from the upper part of the aqueous solution, for example, with a pump, and discharged to the lower part of the aqueous solution, thereby causing forced convection and circulating for a predetermined time. .

  Hereinafter, the present invention will be described with reference to examples.

(Reference Example 1)
A 5-liter three-necked flask was charged with 2.5 liters of anhydrous toluene and 400 g of metallic sodium, heated to the boiling point of toluene with a nitrogen gas stream, and 1 liter of dimethyldichlorosilane was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was heated to reflux for 10 hours to form a precipitate. The precipitate was filtered, washed with methanol and then with water to obtain 420 g of white powder of polydimethylsilane. Polydimethylsilane (250 g) was charged into a three-necked flask equipped with a water-cooled reflux condenser, and heated and reacted at 420 ° C. for 30 hours in a nitrogen stream to obtain polycarbosilane having a number average molecular weight of 1200.

  To 16 g of the synthesized polycarbosilane, 100 g of toluene and 64 g of tetrabutoxytitanium were added, preheated at 100 ° C. for 1 hour, then slowly heated to 150 ° C. and reacted for 5 hours to synthesize modified polycarbosilane. In order to intentionally allow the low molecular weight organometallic compound to coexist with the modified polycarbosilane, 5 g of tetrabutoxytitanium was added to obtain a mixture of the modified polycarbosilane and the low molecular weight organometallic compound.

  After the mixture of the modified polycarbosilane and the low molecular weight organometallic compound was dissolved in toluene, the mixture was charged into a melt blow spinning apparatus, the interior was sufficiently purged with nitrogen, and the temperature was raised to distill off the toluene. Spinning was performed. The spun nonwoven fabric was heated to 150 ° C. stepwise in air and infusible, and then fired in air at 1200 ° C. for 1 hour to obtain a titania / silica fiber nonwoven fabric.

As a result of X-ray diffraction, the obtained fiber (average diameter: 5 μm) was composed of amorphous silica and anatase titania, and the Ti / Si (molar ratio) of the entire fiber was 0.17. Further, when the distribution state of the constituent atoms by EPMA was examined, Ti / Si (molar ratio) = 0.90 in the region of 0.5 μm from the outermost periphery, and Ti / Si (molar) in the region of 1 to 2 μm from the outermost periphery. Ratio) = 0.12 and Ti / Si (molar ratio) = 0.04 at the center, confirming that the structure has an inclined structure in which titanium increases toward the surface. The tensile strength of the fiber was 1.8 GPa, which was extremely high compared to the anatase-type titania / silica fiber obtained by the conventionally known sol-gel method. The resulting nonwoven fabric had a basis weight of 100 g / m ² and a thickness of 1 mm.

(Examples 1-18)
As shown in FIG. 1, in a glass container 1 having an internal volume of 1 L, an upper valve 2 and a lower valve 3 are attached, water, warm bath water, pool water, drinking water, seawater, and organic water in industrial water. Two sheets of the titania / silica fiber nonwoven fabric obtained in Reference Example 1 used for photochemical reaction treatment of oxidative degradation, bacterial degradation, fungal degradation, virus degradation, and algal degradation, with metal compounds and undegraded organic substances attached Stacked to a thickness of about 2 mm, hollow conical shape molding with a stainless steel wire mesh (wire diameter 1 mm, 3 mesh) as a supporting member, a diameter of about 85 mm, a height of 130 mm, and a hole with a diameter of 20 mm in the center The product and the photocatalyst cartridge 4 were allowed to stand.

  As an acidic solution for washing, 1 L of hydrochloric acid was adjusted at a concentration of 0.5 M so that the photocatalyst cartridge 4 placed in the glass container 1 was completely immersed and the water level was above the upper valve 2. The acidic solution prepared from the upper part of the glass container 1 was poured, the photocatalyst cartridge 4 was immersed, and left to stand for 1, 2 or 3 hours, thereby performing immersion cleaning with the acidic solution (Examples 1 to 9). Moreover, it was set as the circulation washing | cleaning by an acidic solution by circulating the acidic solution for 1, 2, and 3 hours at 20 L / min in the state which immersed the photocatalyst cartridge using the pump 5 (Examples 10-18).

  After washing with the acidic aqueous solution, the acidic aqueous solution was discharged from the lower valve 3, and after discharging, the tap water was introduced from the lower valve 3 and discharged from the upper valve 2 to remove the residual acidic aqueous solution. After discharging tap water from the lower valve 3, sodium hypochlorite was adjusted so as to have an effective chlorine concentration of 2% as an alkaline solution serving as a cleaning solution so as to have the same volume as the acidic solution. The alkaline solution prepared from the upper part of the glass container 1 was poured, the photocatalyst cartridge 4 was immersed, and allowed to stand for 1, 2 or 3 hours, thereby performing immersion cleaning with the alkaline solution (Examples 1 to 9). Moreover, with the photocatalyst cartridge immersed in the pump 5, the alkaline solution was circulated at a rate of 20 L / min for 1, 2, and 3 hours for circulation cleaning with the alkaline solution (Examples 10 to 18).

  After the washing, the alkaline solution was discharged from the lower valve 3, and after discharging, the tap water was introduced from the lower valve 3 and discharged from the upper valve 2 to remove the residual alkaline waste liquid. The photocatalyst retained in the photocatalyst cartridge after all washing operations were taken out, dried at 100 ° C. for 12 hours, and sized to Φ40 mm and a weight of 0.05 g.

  As a means of measuring the activity of the photocatalyst, DMSO (dimethyl sulfoxide) that reacts with OH radical, which is the main active species of the photocatalyst, produces a product, and the amount of MSA (methanesulfonic acid) produced as a product with the OH radical The method of quantifying was used.

A sample sized in a petri dish of Φ40 mm was charged, a DMSO solution adjusted to a concentration of 100 ppm was poured into a 10 ml petri dish, and irradiated with UV light at a UV intensity of 2.5 mW / cm ² for 60 min under black light, and the MSA produced in the DMSO aqueous solution The photocatalytic activity (MSAm) was measured by IC (ion chromatograph), and the degree of regeneration was expressed in 100 fractions using the photocatalytic activity (MSAref) measured in the same manner before the photochemical reaction treatment as a denominator. The results are shown in Table 1. As can be seen from Table 1, in Examples 7-18, 100% regeneration was achieved, and in circulation cleaning, it was revealed that large regeneration was obtained in a short time compared to immersion cleaning. .

(Comparative Examples 1-3)
As described in Patent Document 1, the photocatalyst cartridge 4 used for the photochemical reaction treatment under the same conditions as in the examples was placed in a glass container 1 and injected with 1 L of tap water, and then air was supplied from the lower valve 3 at 1 L / min. The mixture was aerated and subjected to washing for 1, 2, and 3 hours by applying ultrasonic vibration while stirring. After washing, the amount of MSA produced was measured in the same manner as in Example, and the photocatalytic activity after washing was determined. The results are shown in Table 1. From Table 1, it became clear that the degree of regeneration was considerably low compared with the Examples, and almost no cleaning effect was observed.

(Comparative Example 4)
As described in Patent Document 2, the photocatalyst cartridge 4 used for the photochemical reaction treatment under the same conditions as in the examples was placed in a glass container 1 and injected with 1 L of 1N citric acid, and then the flow rate of 1 L / hr was set with a pump. Washed for 12 hours. After washing, the amount of MSA produced was measured in the same manner as in Example, and the photocatalytic activity after washing was determined. The results are shown in Table 1. As can be seen from Table 1, despite the fact that it was washed for a long time, a large regeneration rate was not obtained as compared with the Examples.

(Comparative Examples 5-19)
When the operations of Examples 1 to 9 are only acidic solution cleaning (Comparative Examples 5 to 7), only the alkaline solution (Comparative Examples 8 to 10), and the cleaning order of the acidic solution and the alkaline solution are reversed. (Comparative Examples 11 to 19) are shown in Table 1. As can be seen from Table 1, when the cleaning is performed individually, the degree of regeneration does not increase, the value tends to converge, and it does not become 100% if the time is extended. Further, it was found that when the order was reversed, the degree of regeneration with respect to the cleaning time was low as compared with the example.

It is the schematic of the washing tank used for one Embodiment of the regeneration method of the photocatalyst of this invention.

Explanation of symbols

1 Washing tank 2 Upper valve 3 Lower valve 4 Photocatalyst cartridge 5 Pump

Claims (6)

A method for regenerating a photocatalyst used for purifying water containing organic impurities and deteriorated due to contamination by a metal compound and undecomposed organic matter during the water purification treatment, wherein the photocatalyst is an oxidation mainly composed of a silica component. It is a fiber composed of a composite oxide phase of a physical phase (first phase) and a metal oxide phase (second phase) containing titanium, and the presence ratio of titanium in the metal oxide constituting the second phase is A photocatalyst, which is a silica-based composite oxide fiber having a photocatalytic function, increasing in a slanting manner toward the surface layer, wherein the photocatalyst is washed and regenerated with an acidic aqueous solution and then washed with an alkaline aqueous solution How to play.   The method for regenerating a photocatalyst according to claim 1, wherein the acidic aqueous solution is a strong acidic aqueous solution.   The method for regenerating a photocatalyst according to claim 1, wherein the alkaline aqueous solution is a strong alkaline aqueous solution.   The method for regenerating a photocatalyst according to claim 1, wherein the acidic aqueous solution is an aqueous hydrochloric acid solution, and the alkaline aqueous solution is an aqueous sodium hypochlorite solution.   The method for regenerating a photocatalyst according to claim 1, wherein the washing is performed by immersing the photocatalyst in an acidic aqueous solution or an alkaline aqueous solution. 6. The method for regenerating a photocatalyst according to claim 5, wherein forced convection is caused in the acidic aqueous solution or the alkaline aqueous solution to wash the photocatalyst.

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