Hexavalent-chromium-reducing photocatalyst composition and method for reducing hexavalent chromium

Abstract

Provided are a hexavalent-chromium-reducing photocatalyst composition having exceptional properties for reducing hexavalent chromium irrespective of pH, and a method for reducing hexavalent chromium.　This hexavalent-chromium-reducing photocatalyst composition contains a photosensitizer (A) and a sacrificial agent (B).

Description

Hexavalent chromium reducing photocatalytic composition and method for reducing hexavalent chromium

[0001] The present invention relates to a hexavalent chromium reducing photocatalytic composition and a method for reducing hexavalent chromium.

[0002] Hexavalent chromium is known as a water-soluble hazardous metal that exhibits strong biological toxicity. Therefore, hexavalent chromium contained in waste, such as wastewater, is treated by, for example, reducing it to trivalent chromium and precipitating it. The following methods are known as methods for treating hexavalent chromium: (1) A method in which sulfuric acid or the like is added to a solution containing hexavalent chromium to create an acidic condition, and then a reducing agent such as sodium bisulfite is added to reduce it to trivalent chromium, and then sodium hydroxide or the like is added to make the solution alkaline, thereby precipitating chromium hydroxide; and (2) A method in which ferrous sulfate (iron(II) sulfate) is added as a reducing agent to minerals, such as those used for concrete, soil, ash, sludge, etc., containing hexavalent chromium, thereby reducing the hexavalent chromium in the waste (e.g., Patent Document 1).

[0003] As another method, Patent Document 2 describes a hexavalent chromium reducing agent obtained by mixing predetermined amounts of ascorbic acid or the like, glucose, and aluminum sulfate.

[0004] JP 2001-121109 A JP 2019-131780 A

[0005] For example, the above-mentioned method (1) requires the use of a large amount of acid and alkali, which results in an increase in secondary waste. In addition, the above-mentioned method (2) and the like tend to leave the reducing agent in the environment. Therefore, there is a demand for a method for treating hexavalent chromium with less environmental impact.

[0006] The reducing agent in Patent Document 2 is presumed to be composed of ascorbic acid or the like and glucose, which act as a reducing agent for hexavalent chromium. However, these compounds have low reducing power for hexavalent chromium, and even when a high concentration of the reducing agent is used, a long reaction time is required. Furthermore, the reducing agent in Patent Document 2 needs to be adjusted to an acidic condition.

[0007] An object of the present disclosure is to provide a hexavalent chromium reducing photocatalyst composition that has excellent hexavalent chromium reducing properties regardless of pH, and a method for reducing hexavalent chromium.

[0008] One embodiment of the hexavalent chromium reducing photocatalyst composition according to the present disclosure contains a photosensitizer (A) and a sacrificial agent (B).

[0009] In one embodiment of the method for reducing hexavalent chromium according to the present disclosure, the hexavalent chromium-reducing photocatalyst composition is sprayed or added to an article or solution containing hexavalent chromium, and then irradiated with light.

[0010] The present disclosure provides a hexavalent chromium reducing photocatalyst composition that has excellent hexavalent chromium reducing properties regardless of pH, and a method for reducing hexavalent chromium.

[0011] Hereinafter, embodiments of the present invention will be described. In this disclosure, the expression "to" indicating a range of values ​​includes the lower limit and the upper limit unless otherwise specified.

[0012] [Hexavalent Chromium Reducing Photocatalytic Composition] The hexavalent chromium reducing photocatalytic composition (hereinafter simply referred to as the photocatalytic composition) of the present disclosure contains a photosensitizer (A) and a sacrificial agent (B). When the photocatalytic composition is irradiated with light, the photosensitizer (A) absorbs the light and is first reduced through an oxidation-reduction reaction with the sacrificial agent (B). The reduced photosensitizer (A) undergoes an oxidation-reduction reaction with hexavalent chromium, and is oxidized to produce trivalent chromium. In this way, the photocatalytic composition can reduce hexavalent chromium without adjusting the pH, thereby suppressing the generation of secondary waste and reducing environmental impact. Furthermore, reducing compounds may be capable of reducing hexavalent chromium by themselves. However, the activation energy of the hexavalent chromium reduction reaction was high, resulting in poor reaction efficiency. On the other hand, it was found that the reduced photosensitizer (A) has a high reducing power for hexavalent chromium, and the reduction reaction proceeds much more easily than when, for example, ascorbic acid itself is used as a hexavalent chromium reducing agent. Furthermore, even if the sacrificial agent (B) of the present photocatalytic composition does not itself have the reducing power to directly reduce hexavalent chromium, it can reduce hexavalent chromium by combining it with the photosensitizer (A). Furthermore, as shown in the examples, the present photocatalytic composition exhibits excellent hexavalent chromium reduction properties even when a light source with a relatively low output, such as an LED, is used.

[0013] The present photocatalytic composition contains at least a photosensitizer (A) and a sacrificial agent (B), and may further contain other components as necessary. Each component that may be contained in the present photocatalytic composition will be described below.

[0014] <Photosensitizer (A)> The photosensitizer (A) may be any agent that can generate a reduced photosensitizer by the action of light and the sacrificial agent (B). Examples of such photosensitizers (A) include compounds having a skeleton such as naphthalene, anthracene, phenanthrene, pyrene, perylene, benzophenone, fluorene, naphthoquinone, anthraquinone, xanthene, thioxanthene, xanthone, isoalloxazine, alloxazine, phenoxazine, fluorescein, phloxine, thioxanthone, coumarin, ketocoumarin, cyanine, merocyanine, oxonol, benzothiazole, acridine, thiazine, oxazine, indoline, azulene, azulenium, porphyrin, triarylmethane, phthalocyanine, phenothiazine, spiropyran, and spirooxazine; unsaturated ketones such as acridone, chalcone, and dibenzalacetone; 1,2-diketones such as benzil and camphorquinone; azo compounds; and organometallic complexes. The photosensitizers (A) may be used singly or in combination of two or more. In the compounds having the above various skeletons, the carbon atoms, nitrogen atoms, etc. that constitute the skeleton may have a substituent. Examples of the substituent include a halogen atom, a hydroxyl group, an acidic group such as a carboxy group or a sulfo group, an amino group, an organic group, etc. The acidic group and the amino group may form a salt, and the organic group may further have a substituent.

[0015] The photosensitizer (A) is preferably one having a tricyclic fused ring (tricylic) because it can provide excellent hexavalent chromium reduction properties and is relatively easy to obtain. Examples of the tricyclic fused ring include compounds having a skeleton such as anthracene, phenanthrene, fluorene, anthraquinone, xanthene, thioxanthene, xanthone, isoalloxazine, alloxazine, phenoxazine, fluorescein, thioxanthone, acridine, and phenothiazine. Among them, compounds having a skeleton selected from isoalloxazine, alloxazine, phenothiazine, fluorescein, anthraquinone, and acridine are preferred. Furthermore, compounds having an isoalloxazine skeleton or alloxazine skeleton are more preferred because they have excellent hexavalent chromium reduction properties under visible light and have a small environmental impact. Specific examples of compounds having a phenothiazine skeleton include perfeazin, chlorpromazine, acepromazine, phenothiazine, methylphenothiazine, methylene blue, etc., with perfeazin, chlorpromazine, or acepromazine being preferred in terms of hexavalent chromium reduction. Specific examples of compounds having a fluorescein skeleton include fluorescein, phloxine, dibromofluorescein, eosin Y, eosin B, rhodamine B, rhodamine 6G, rose bengal, and acid red 92, with fluorescein, phloxine, dibromofluorescein, eosin Y, eosin B, or rose bengal and acid red 92 being preferred in terms of hexavalent chromium reduction. Specific examples of compounds having an anthraquinone skeleton include anthraquinonesulfonic acid, anthraquinonedisulfonic acid, anthraquinonecarboxylic acid, 2-anthraquinonesulfonic acid, and alkali metal salts thereof. Specific examples of compounds having an acridine skeleton include acridine orange and acridine carboxylic acid.

[0016] Examples of compounds having an isoalloxazine skeleton or an alloxazine skeleton include compounds represented by the following general formula (1) and compounds represented by the following general formula (2).

[0017] In formula (1), R １ , R ２ , R３ and R ４ are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group which may have a substituent, and R ５ and R ６ are each independently a hydrogen atom or a hydrocarbon group which may have a substituent, and in formula (2), R １１ , R １２ , R １３ and R １４ are each independently a hydrogen atom, a halogen atom, or a hydrocarbon group which may have a substituent, and R １５ and R １６ are each independently a hydrogen atom or a hydrocarbon group which may have a substituent.

[0018] R １ ~R ４ , R １１ ~R １４ Examples of the halogen atom in R include a fluorine atom, a chlorine atom, and a bromine atom. １ ~R ４ , R １１ ~R １４ Examples of the hydrocarbon group in R include a linear or branched alkyl group having 1 to 6 carbon atoms, a cycloalkyl group or aryl group having 6 to 12 carbon atoms which may have a linear or branched alkyl group as a substituent. Examples of the linear or branched alkyl group include a methyl group, an ethyl group, an n-butyl group, a tert-butyl group, and a hexyl group. Examples of the cycloalkyl group include a cyclohexyl group. Examples of the aryl group include a phenyl group and a naphthyl group. １ ~R ４ , R １１ ~R １４ Examples of the substituent that the hydrocarbon group in R may have include a hydroxy group, a carboxy group, a halogen atom, etc., and the hydroxy group and the carboxy group may be further esterified derivatives. １ , R ４ , R １１ and R １４ are preferably each independently a hydrogen atom. ２ , R３ , R １２ and R １３ are each independently preferably a linear or branched alkyl group having no substituent, more preferably an alkyl group having 1 to 4 carbon atoms, and even more preferably a methyl group.

[0019] R ６ , R １５ and R １６ The hydrocarbon group in R １ In terms of photocatalytic activity, R ６ , R １５ and R １６ are each independently preferably a hydrogen atom.

[0020] R ５ The hydrocarbon group in R １ and the like. ５ Examples of the substituent that the hydrocarbon group in R may have include a hydroxy group or an esterified product thereof. ５ In particular, the substituents in ２ -CHOH-CHOH-CHOH-CH ２ OH) or an esterified product of the ribityl group is preferred.

[0021] Furthermore, the compound having an isoalloxazine skeleton or an alloxazine skeleton is preferably riboflavin or a riboflavin derivative. Riboflavin, also known as vitamin B2, is highly safe and has a reduced environmental impact. Specific examples of riboflavin derivatives include riboflavin tetrabutyrate, riboflavin tetraacetate, lumichrome (7,8-dimethylalloxazine), riboflavin phosphate ester, and salts thereof (such as sodium salt and potassium salt), and flavin adenine dinucleotide.

[0022] Among these, the photosensitizer (A) is preferably riboflavin, riboflavin tetrabutylate, lumichrome, riboflavin sodium phosphate, methylene blue, acridine orange, Acid Red 92, or 2-anthraquinonesulfonic acid from the viewpoint of hexavalent chromium reducing ability.

[0023] <Sacrificial Agent (B)> In the present photocatalytic composition, the sacrificial agent (B) is a compound capable of reducing the photosensitizer (A). The sacrificial agent (B) does not need to have the reducing power to reduce hexavalent chromium. The present photocatalytic composition can obtain hexavalent chromium reducing properties by using the sacrificial agent (B) in combination with the photosensitizer (A). Note that the sacrificial agent (B) is usually decomposed during the progress of the hexavalent chromium reduction reaction.

[0024] Examples of the sacrificial agent (B) include ascorbic acids, alkanolamines, polyols, polyphenols, polyamines, polycarboxylic acids, polysaccharides, and the like. One type can be used alone or two or more types can be used in combination.

[0025] Examples of ascorbic acids include ascorbic acid, isoascorbic acid (erythorbic acid), and salts thereof. The counter ions of the salts are not particularly limited, but examples include lithium ions, sodium ions, potassium ions, calcium ions, magnesium ions, and iron ions.

[0026] Alkanolamines include compounds having one or more hydroxy groups and one or more amino groups in one molecule, and compounds in which the amino group of the compound forms a salt with an acid such as an organic acid or an oxoacid. Specific examples of alkanolamines include triethanolamine, diethanolamine, triethanolamine, methanolamine, triisopropanolamine, diisopropanolamine, isopropanolamine, butylethanolamine, 2,2'-(cyclohexylimino)bisethanol, N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine, bis(2-hydroxypropyl)alkylamine, dibutylpropanolamine, N-tert-butyldiethanolamine, dimethylaminoethanol, N-piperidineethanol, N-morpholineethanol, 2-(methylamino)ethanol, and 2-[(hydroxymethyl)amino]ethanol. Examples of acids that form salts with alkanolamines include organic acids such as acetic acid, lactic acid, succinic acid, salicylic acid, citric acid, gluconic acid, tartaric acid, fumaric acid, malic acid, phosphoric acid, ascorbic acid, erythorbic acid, malic acid, oleic acid, phytic acid, and octylphosphonic acid; and oxo acids such as phosphoric acid, boric acid, sulfuric acid, nitric acid, polyphosphoric acid, and silicic acid.

[0027] The polyols include compounds having two or more hydroxy groups in one molecule. Among them, compounds having the composition formula C are preferred because of their high electron donating properties. ｎ H ２ｎ－２ O ｎ (n is an integer of 2 or more) is preferred. Specific examples of polyols that satisfy this composition formula include glycerin, threitol, arabitol, xylitol, ribitol, and polyethylene glycol, and examples of polyethers thereof include polyglycerin. Polyols that are liquid at the temperature of use (e.g., 25°C) also function as solvents.

[0028] Examples of polyphenols include compounds having two or more phenolic hydroxyl groups in one molecule, and the hydroxyl groups may be in the form of a salt. Polyphenols are preferably naturally derived polyphenols because they have low environmental impact and are highly safe for living organisms. Specifically, ferulic acid, tannic acid, catechin acid, epigallocatechin gallate, gallic acid, chlorogenic acid, caffeic acid, ellagic acid, curcumin, lignan, rutin, hesperidin, kaempferol, quercetin, isoflavone, anthocyanin, theaflavin, theaflavin gallate, cyanidin, resveratrol, chalconic acid, ellagic acid, quercitrin, isoquercitrin, myricitrin, myricetin, delphinidin, delphin, nasunin, peonidin, peonin, neo Examples include hesperidin, hesperetin, naringin, lingenin, prunin, astragalin, apiin, apigeni, daidzein, daidzin, glycitein, glycitin, genistein, genistin, malvidin, malvin, enine, leucocyanidin, cyanin, chrysanthemin, keracyanin, idein, mecocyanin, pelargonidin, callistephin, p-coumaric acid, sesamin, sesaminol, sesamolin, and sodium, potassium, and calcium salts thereof.

[0029] The polyamines include compounds having two or more amino groups in the molecule, and the amino groups may form salts. Specific examples of the polyamines include spermine, spermidine, putrescine, ethylenediamine, and polyethyleneimine.

[0030] Polyethyleneimine is -CH ２ -CH ２ Structural units represented by —NH— and —CH ２ -CH ２It is a compound having two or more types of structural units selected from structural units represented by -N< in one molecule. The polyethyleneimine may be a linear polyethyleneimine (amines other than the terminals are secondary amines), a dendrimer-type polyethyleneimine (amines other than the terminals are tertiary amines), or a branched polyethyleneimine (containing both secondary amines and tertiary amines). The polyethyleneimine is a compound having two or more types of structural units selected from structural units represented by -CH ２ -CH ２ -NH- or -CH ２ -CH ２ The polyethyleneimine may have a structural unit other than the structural unit represented by -N<. ２ -CH ２ -NH- or -CH ２ -CH ２ The proportion of the structural units represented by -N< is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on the total mass of polyethyleneimine.

[0031] In the present invention, the polyethyleneimine may contain a polyethyleneimine derivative. Examples of the polyethyleneimine derivative include hydroxyalkylene polyethyleneimines such as hydroxyethyl polyethyleneimine obtained by reacting the polyethyleneimine with an alkylene oxide such as ethylene oxide or propylene oxide; carboxymethylated polyethyleneimine obtained by reacting the polyethyleneimine with (1) monochloroacetic acid or (2) reductive amination of glyoxalic acid; and polyethyleneimines having a crosslinked structure obtained by reacting the polyethyleneimine with a dichloride such as adipic acid dichloride.

[0032] The peak top molecular weight (Mp) of the polyethyleneimine is preferably 1,000 or more, more preferably 10,000 or more, and even more preferably 25,000 or more from the viewpoint of hexavalent chromium reducibility, while the weight average molecular weight of the polyethyleneimine is preferably 1,000,000 or less, more preferably 800,000 or less, and even more preferably 500,000 or less from the viewpoint of ease of synthesis.

[0033] Polyethyleneimine can be synthesized, for example, by ring-opening polymerization of aziridine. Alternatively, commercially available polyethyleneimine may be used.

[0034] Examples of polycarboxylic acids include compounds having two or more carboxylic acids in one molecule, and the carboxylic acids may form acid anhydrides. Specific examples of polycarboxylic acids include oxalic acid, citric acid, tartaric acid, malic acid, succinic acid, maleic acid, itaconic acid, adipic acid, and fumaric acid.

[0035] Polysaccharides include compounds having a structure in which two or more groups are bonded together. Specific examples of polysaccharides include starch, glycogen, agarose, agaropectin, carrageenan, pectin, xanthan gum, locust bean gum, guar gum, gellan gum, gum arabic, alginic acid, hemicellulose, tara gum, tamarind seed gum, chitin, chitosan, glucomannan, and the like, and may also include agar, which is a mixture of agarose and agaropectin.

[0036] Chitosan is a compound having two or more glucosamine-derived structural units, and may also have a structural unit derived from acetylglucosamine, and may further have other structures. Furthermore, in the present disclosure, chitosan may be a relatively low molecular weight compound that can be classified as a chitosan oligosaccharide. From the viewpoint of photocatalytic activity, chitosan (poly-1,4-β-D-glucosamine) or chitosan oligosaccharide, in which multiple D-glucosamines are polymerized by bonding at the 1- and 4-positions, is preferred as the chitosan. Chitosan may be a polyglucosamine consisting only of glucosamine-derived structural units, or may have a structural unit derived from N-acetylglucosamine.

[0037] The chitosan can be obtained by deacetylating chitin, which is obtained from the cell walls of shrimp, crab, mushroom, insect, or fungus, with alkali. The degree of deacetylation of chitosan is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more, in terms of photocatalytic effect and the durability of the photocatalytic effect. The degree of deacetylation of chitosan is expressed as {number of glucosamine-derived structural units / (number of glucosamine-derived structural units + number of acetylglucosamine-derived structural units)} × 100 (%), and can be measured, for example, by colloid titration using polyvinyl potassium sulfate (PVSK).

[0038] The chitosan of the present disclosure may contain a chitosan derivative, such as hydroxyalkylene chitosan, obtained by reacting the chitosan with an alkylene oxide, such as ethylene oxide or propylene oxide; carboxymethylated chitosan, obtained by reacting the chitosan with (1) monochloroacetic acid or (2) reductive amination of glyoxalic acid; or chitosan having a crosslinked structure, obtained by reacting the chitosan with a dichloride, such as adipic acid dichloride.

[0039] From the viewpoint of hexavalent chromium reducibility, the molecular weight of chitosan is preferably 350 or more, more preferably 5,000 or more, even more preferably 30,000 or more, and particularly preferably 40,000 or more. On the other hand, from the viewpoint of viscosity, the molecular weight is preferably 1,000,000 or less, more preferably 500,000 or less, and even more preferably 200,000 or less. In the present disclosure, the molecular weight is the peak top molecular weight (Mp) determined as a standard pullulan equivalent value by aqueous gel filtration chromatography (Chromaster (registered trademark), manufactured by Hitachi High-Tech Science Corporation).

[0040] In this photocatalytic composition, the ratio of the photosensitizer (A) to the sacrificial agent (B) is not particularly limited. It may be appropriately adjusted, taking into consideration that the sacrificial agent (B) is consumed, but the photosensitizer (A) is not. For example, the mass ratio (A / B) of the photosensitizer (A) to the sacrificial agent (B) may be appropriately adjusted within the range of 1 / 0.1 to 1 / 500,000, preferably 1 / 0.2 to 1 / 200,000, and more preferably 1 / 0.3 to 1 / 100,000. Furthermore, if necessary, the sacrificial agent (B) may be replenished during the hexavalent chromium reduction reaction.

[0041] In addition, in order to suppress side reactions, the content of iron ions in the present photocatalytic composition is preferably 50 mol% or less, more preferably 30 mol% or less, more preferably 10 mol% or less, even more preferably 5 mol% or less, and particularly preferably 1 mol% or less, relative to the photosensitizer (A). In addition, in order to suppress side reactions and to reduce the impact on humans and the environment, the total amount of heavy metal ions in the present composition is preferably 50 mol% or less, more preferably 30 mol% or less, even more preferably 10 mol% or less, even more preferably 5 mol% or less, particularly preferably 1 mol% or less, relative to the photosensitizer (A), and it is extremely preferable that they are substantially free (0.1 mol% or less). Here, heavy metal is a general term for metals with a specific gravity of 4 or more.

[0042] The ratio of the photosensitizer (A) to the hexavalent chromium to be reduced is not particularly limited, but from the viewpoint of reaction rate, etc., it is preferably 0.01 to 500 mol%, more preferably 0.05 to 200 mol%, and more preferably 0.1 to 100 mol% relative to the hexavalent chromium. The ratio of the sacrificial agent (B) to the hexavalent chromium to be reduced is not particularly limited, but from the viewpoint of sufficiently reducing the hexavalent chromium, it is preferably 10 to 1000 mol%, more preferably 50 to 500 mol%, and more preferably 90 to 200 mol% relative to the hexavalent chromium.

[0043] <Method for preparing hexavalent chromium reducing photocatalytic composition> The method for preparing the photocatalytic composition may be any method that uniformly mixes the photosensitizer (A) and the compound (B). When preparing a powder composition, the photosensitizer (A) and the compound (B) may be blended and mixed in any ratio. When preparing a liquid composition, the photosensitizer (A) and the compound (B) may be added to a solvent and stirred. Alternatively, a highly concentrated liquid composition may be prepared and diluted with a solvent before use. The preparation is preferably carried out in a dark place.

[0044] The solvent can be appropriately selected from those capable of dissolving or dispersing each component of the photocatalytic composition. From the viewpoint of facilitating dissolution or dispersion of each component, the solvent preferably contains one or more solvents selected from water and water-soluble solvents, and more preferably contains water. Examples of water-soluble solvents include alcohol-based solvents such as ethanol, isopropanol, ethylene glycol, propylene glycol, glycerin, dipropylene glycol, and diethylene glycol. When a mixed solvent of water and a water-soluble solvent is used, the amount of the water-soluble solvent is preferably 10% by mass or less, and more preferably 5% by mass or less, of 100% by mass of the solvent. Furthermore, the solvent may be a solvent consisting essentially of water alone.

[0045] [Method for reducing hexavalent chromium] The method for reducing hexavalent chromium according to the present disclosure is characterized in that the hexavalent chromium-reducing photocatalyst composition is sprayed or added to an article or solution containing hexavalent chromium, and then irradiated with light.

[0046] Examples of materials containing hexavalent chromium include concrete minerals, soil, ash, sludge, and other industrial waste. Materials containing hexavalent chromium generated in chromate films are also included. Solutions containing hexavalent chromium are primarily, but not limited to, industrial waste.

[0047] The method for spraying the photocatalytic composition is not particularly limited, and either a powder composition or a liquid composition may be used. If the target object is particulate, such as soil or ash, the target object may be mixed with the photocatalytic composition. Furthermore, if a portion containing hexavalent chromium, such as a chromate film, is clearly identified, the photocatalytic composition may be applied to that portion. If the target object is a solution, the photocatalytic composition may be added to the solution and stirred as necessary. In addition, in this reduction method, the pH is not particularly limited, and pH adjustment is not necessary. The light source for light irradiation is not particularly limited, and may be selected taking into account the absorption wavelength of the photosensitizer (A). Examples include an LED light source, an incandescent light bulb, and sunlight.

[0048] If necessary, trivalent chromium may be precipitated as chromium hydroxide, which can be achieved by known methods, such as by making the solution alkaline or by using a flocculant.

[0049] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, "ppm" represents "μg / g" and "%" represents "% by mass".

[0050] Example 1 Preparation of Photocatalytic Composition A composition was prepared by mixing 10 ppm of riboflavin with 0.1 mass % of N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine (ADEKACARPOL MD-100, manufactured by ADEKA Corporation, hereinafter also referred to as "MD-100"). In the table, the concentration of each component is expressed as mass % unless otherwise specified as ppm. The concentrations in Table 1 represent the concentration of each component after mixing with an aqueous hexavalent chromium solution, which will be described later.

[0051] <Examples 2 to 18, Comparative Examples 1 to 4, Reference Examples 1 to 7> In Example 1, the types and amounts of the photosensitizer (A), sacrificial agent (B), and other components were changed as shown in Table 1 to prepare each composition. Note that Examples 1 to 2, 4 to 7 and Reference Examples 1 to 2, 4 to 7 have the same composition in this order, and Examples 3-1, 3-2, and Reference Example 3 have the same composition. Note that "PEG" in the table represents polyethylene glycol monomethyl ether (molecular weight: 550).

[0052] [Evaluation] The composition of the above example was added to an aqueous hexavalent chromium solution to adjust the hexavalent chromium concentration to the "initial concentration" in Table 1 and the concentration of each component to the concentration shown in Table 1. Next, light irradiation was performed under the light irradiation conditions shown in Table 1. Reference Examples 1 to 7 were left standing for the time shown in Table 1 without light irradiation. Next, as a post-treatment, 2.4 ml of sulfuric acid (1+9) was added to 50 ml of the irradiated solution, followed by the addition of 200 ppm equivalent of diphenylcarbazide. Five minutes later, the hexavalent chromium concentration was measured. Reference Example 3 was diluted after post-treatment and then measured. The hexavalent chromium concentration was determined from the absorbance at a wavelength of 540 nm. The residual hexavalent chromium concentration (concentration after photocatalytic treatment) is a value converted to the solution before post-treatment. The lower limit of quantitation is 0.1 ppm. The results are shown in Table 1.

[0053] (Evaluation criteria) A: The residual hexavalent chromium concentration was less than the lower limit of quantification. B: The residual hexavalent chromium concentration was 0.1 ppm or more and less than 0.5 ppm. C: The residual hexavalent chromium concentration was 0.5 ppm or more and less than 0.8 ppm. D: The residual hexavalent chromium concentration was 0.8 ppm or more and less than 1.0 ppm. E: The residual hexavalent chromium concentration was 1.0 ppm or more.

[0054]

[0055] As shown in Examples 1 to 18, it was demonstrated that hexavalent chromium can be reduced by irradiating a hexavalent chromium-reducing photocatalyst composition containing a photosensitizer (A) and a sacrificial agent (B) with light. Comparisons between Examples 1 to 7 and Reference Examples 1 to 7 demonstrate that light is involved in the reduction of hexavalent chromium. As shown in Comparative Examples 1 and 2, it was demonstrated that hexavalent chromium is not reduced by using the photosensitizer (A) or the sacrificial agent (B) alone. It was also demonstrated that hexavalent chromium is not reduced by photocatalysts such as titanium oxide. Furthermore, as shown in Comparative Example 4, a reducing agent combining ascorbic acid, glucose, and aluminum sulfate was confirmed to reduce hexavalent chromium, but the reaction rate was low. As shown in Examples 2, 3-1, and 3-2, even with high concentrations of hexavalent chromium, excellent hexavalent chromium reduction was demonstrated by adjusting the amount of this composition added and the light irradiation intensity.

[0056] The hexavalent chromium-reducing photocatalyst composition of the present disclosure exhibits excellent hexavalent chromium reduction properties even when a light source with a relatively low output is used, and it also suppresses the generation of secondary waste and reduces the environmental load. Furthermore, it can be used in the form of a solution or powder, and can be used in any application requiring the removal of hexavalent chromium.

[0057] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention.

[0058] This application claims priority based on Japanese Patent Application No. 2023-168518, filed September 28, 2023, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A hexavalent chromium reducing photocatalyst composition comprising a photosensitizer (A) and a sacrificial agent (B).

2. The hexavalent chromium reducing photocatalyst composition according to claim 1, wherein the photosensitizer (A) comprises a photosensitizer having a tricyclic condensed ring.

3. The hexavalent chromium reducing photocatalyst composition according to claim 1, wherein the sacrificial agent (B) comprises one or more selected from ascorbic acids, alkanolamines, polyols, polyphenols, polyamines, polycarboxylic acids and polysaccharides.

4. The hexavalent chromium reducing photocatalyst composition according to claim 1, further comprising water.

5. The hexavalent chromium reducing photocatalyst composition according to claim 1, wherein the content of iron ions is 50 mol % or less relative to the photosensitizer (A).

6. A method for reducing hexavalent chromium, comprising spraying the hexavalent chromium reducing photocatalyst composition according to any one of claims 1 to 5 onto an article containing hexavalent chromium, and irradiating the article with light.

7. A method for reducing hexavalent chromium, comprising adding the hexavalent chromium reducing photocatalyst composition according to any one of claims 1 to 5 to a solution containing hexavalent chromium, and irradiating the solution with light.

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