JPH0134921B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hydrogen,
More specifically, it relates to a method for producing hydrogen by photolyzing water in the presence of a reducing agent, an electronic medium, and a platinum colloid using a cationic polymer having a polycyclic aromatic hydrocarbon or the like in its side chain as an optical medium. be.

In recent years, with the depletion of petroleum resources, various forms of exploration and research have been conducted to develop alternative energy sources, and among these, the generation of hydrogen through photolysis of water using light energy is considered to be an attractive option due to its clean nature. This is also a field with great expectations for the future. Photolysis of water through modeling reactions of photosynthesis or photolysis of water using inorganic semiconductor electrodes and metal complexes has been studied so far, but they lack photostability and durability, as well as low energy efficiency. Furthermore, it is not at a stage where it can be put into practical use due to cost problems.

Conventionally, poly-1-vinylnaphthalene, poly-
Polymers having polycyclic aromatic hydrocarbon groups in their side chains, such as 1-vinylpyrene, are well known. These known compounds are generally
It is used as a probe to obtain knowledge related to the molecular motion and conformational changes of polymer chains in dilute solutions, or to understand the mechanism of photodegradation reactions. It is also considered to be a precursor for carrier generation of photoconductive polymers, and application systems for dry electrophotography and photosensitive resins using the photodimerization reaction of anthracene are also based on polymers with anthryl groups in their side chains. It is being considered. However, there are almost no examples of focusing on the large π-electron conjugated system of a polycyclic aromatic hydrocarbon group and utilizing it as a polymer photosensitizer, that is, as an optical medium, in an electron transfer reaction. This is because the electron transfer reaction proceeds in a diffusion-controlled manner, so the effects of polymers could not be expected with known homopolymers.

In addition, regarding electron transfer reactions, viologen has recently attracted a lot of attention as an electron medium for the production of hydrogen through the reduction of water. That is, it is well known that when platinum colloid and a reducing agent are made to coexist with cation radicals obtained by electrochemically or photoreducing viologen, water is reduced and hydrogen is produced.

Attempts have been made to generate hydrogen by decomposing water using metal complexes such as ruthenium trisdipyridyl complexes and zinc porphyrin complexes as photocatalysts in the presence of reducing agents such as ethylenediaminetetraacetic acid disodium salt and ascorbic acid. In this case, these metal complexes are visible light (450-500 nm)
It has the advantage of being able to be irradiated. However, this method has disadvantages in that hydrogen production efficiency is low, metal complexes are expensive, and they are poor in stability, so they cannot be used repeatedly.

In view of the current situation, the present inventors have conducted intensive research with the aim of providing a method for efficiently and economically producing hydrogen by photolysis of water. We have discovered that the above object can be achieved by using as a photocatalyst a cationic polymer having a polycyclic aromatic hydrocarbon group selected from the group consisting of a quaternary ammonium salt in its side chain, and have arrived at the present invention. It is something.

That is, the present invention provides a method for producing hydrogen by photolyzing water in the presence of a reducing agent, an electronic medium, a platinum colloid, and an optical medium. This is a method for producing hydrogen by photolysis of water, which is characterized by using a cationic polymer (hereinafter abbreviated as cationic polymer) having a ring aromatic hydrocarbon group in a side chain containing a quaternary ammonium salt.

Examples of the cationic polymer used as a photocatalyst in the present invention include the following (a):
(b) and (c) are listed.

(a) A vinyl copolymer having a degree of polymerization of 50 to 10,000 and consisting of 1 to 90 mol% of the structural units represented by the following formula () and 99 to 10 mol% of the structural units represented by the following formula ().

(However, A in the formula is a polycyclic aromatic hydrocarbon group,
R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms, R ₂ ,
R ₃ and R ₄ represent an alkyl group having 1 to 12 carbon atoms, X represents a halogen, and n represents an integer of 1 to 5. ) (b) A vinyl copolymer having a degree of polymerization of 50 to 50,000 and comprising 1 to 90 mol% of the structural unit represented by the following formula () and 99 to 10 mol% of the structural unit represented by the following formula ().

[A, R ₂ , R ₃ , R ₄ , X, and n in the formula are the same as in formula () and formula (). (c) A polyionene with a molecular weight of 1,000 to 100,000 that is substantially composed of repeating units represented by the following formula ().

_{[ In the} formulas, A _, represents an integer. ] In formulas (), () and (), the polycyclic aromatic hydrocarbon group represented by A is a polycyclic aromatic hydrocarbon group selected from the group consisting of naphthyl group, anthryl group and pyrenyl group, Specific examples thereof include 1-naphthyl group, 2-naphthyl group, 2-anthryl group, 9-anthryl group, and 1-pyrenyl group, but 1-naphthyl group, 9-anthryl group, and 1-pyrenyl group are preferable. Among these, 1-pyrenyl group is particularly preferred from the viewpoint of photostability and long life of photoexcited species.

The vinyl copolymer shown in (a) is, for example, the following formula (): [A, R ₁ and n in the formula are the same as in the formula (). ] Vinyl monomer shown by and the following formula () [R ₂ , R ₃ , R ₄ , and X in the formula are the same as in the formula (). ] It can be obtained by adding a radical polymerization initiator to the cationic vinyl monomer shown in the following in the presence of a solvent, purging with nitrogen or vacuum degassing, and then heating. Typical examples of vinyl monomers represented by the formula include acrylic acid-(1-pyrenyl)methyl,
2-(1-pyrenyl)ethyl acrylate, 3-(1-pyrenyl)propyl acrylate, 1-(1-pyrenyl)methyl methacrylate, 2-(1-pyrenyl)ethyl methacrylate, methacrylic acid (meth)acrylic acid derivatives having a pyrenyl group such as -3-(1-pyrenyl)propyl; -(1-naphthyl)methyl acrylate, -2 acrylic acid
-(1-naphthyl)ethyl, acrylic acid-3-(1
(meth) having a naphthyl group such as -naphthyl)propyl, -(1-naphthyl)methyl methacrylate, -2-(1-naphthyl)ethyl methacrylate, and -3-(1-naphthyl)propyl methacrylate.
Acrylic acid derivatives; acrylic acid-(9-anthryl)methyl, acrylic acid-2-(9-anthryl)
Anthryl such as ethyl, 3-(9-anthryl)propyl acrylate, methyl methacrylate, 2-(9-anthryl)ethyl methacrylate, and 3-(9-anthryl)propyl methacrylate. groups (methacrylic acid derivatives), etc. In addition, typical examples of cationic vinyl monomers represented by formula () include:
Examples include vinylbenzyltrimethylammonium chloride and vinylbenzyltriethylammonium chloride. In the copolymer represented by (a) above, the structural unit represented by the formula () is 1
If it is less than 90 mol % or more than 90 mol %, it will not be possible to exhibit the desired excellent effect as a polymeric photocatalyst. On the other hand, the degree of polymerization
If it is smaller than 50, no effect as a polymer can be expected, and if the degree of polymerization exceeds 10,000, it is difficult to manufacture.

The vinyl copolymer shown in (b) is, for example, the following formula [A and n in the formula are the same as in the formula (). ] It can be obtained by adding a radical polymerization initiator to the vinyl monomer represented by the following formula and the cationic vinyl monomer represented by the above formula () in the presence of a solvent, purging with nitrogen or vacuum degassing, and then heating. Typical examples of vinyl monomers represented by formula () include vinylbenzyl[(1-pyrenyl)methyl]ether, vinylbenzyl[2-(1-pyrenyl)ethyl]ether, and vinylbenzyl[3-
(1-pyrenyl)propyl] ethervinylbenzyl[(1-naphthyl)]ether, vinylbenzyl[2-(1-naphthyl)methyl]ether, vinylbenzyl[3-(1-naphthyl)propyl]
Ether, vinylbenzyl [(9-anthril)
Ether, vinylbenzyl [2-(9-anthryl)ethyl] ether, vinylbenzyl [3-
Examples include (9-anthril)propyl]ether.

Furthermore, the vinyl copolymer shown in (b) can also be produced by a polymer reaction using polystyrene as a starting material. That is, after polystyrene is chloromethylated with chloromethyl ether in the presence of a solvent and a Friedel-Crafts catalyst, the following formula () A-(CH ₂ ) n-OH () (However, A in the formula ring aromatic hydrocarbon group, n
represents an integer from 1 to 5. ) After reacting with a compound represented by the formula () N (R ₁ ) (R ₂ ) (R ₃ ) () (However, R ₁ , R ₂ , and R ₃ in the formula have 1 to 12 carbon atoms. represents an alkyl group). Examples of the compound represented by the formula () include 1-hydroxymethylpyrene, 2-
Hydroxyethylpyrene, 3-hydroxypropylpyrene, 1-hydroxymethylnaphthalene, 2
-Hydroxyethylnaphthalene, 3-hydroxypropylnaphthalene, 9-hydroxymethylanthracene, 9-hydroxyethylanthracene,
9-hydroxypropylanthracene and the like are preferably used. Further, as the amines represented by the formula (), for example, trimethylamine and triethylamine are preferably used. In the copolymer represented by (b) above, if the constituent unit represented by the formula () is less than 1 mol% or exceeds 90 mol%, it will not have the desired excellent effect as a polymer photocatalyst. unable to perform. On the other hand,
If the degree of polymerization is less than 50, no effect as a polymer can be expected, and if the degree of polymerization exceeds 50,000, it is difficult to manufacture.

The polyionene shown in (c) is, for example, the following ()
formula [A, X, and n in the formula are the same as in formula () and formula (). ] Dihalides represented by the following formula (XI) (R ₅ ) (R ₆ ) N (CH ₂ ) mN (R ₇ ) (R ₈ )
(XI) (In the formula, R ₅ , R ₆ , R ₇ , R ₈ are alkyl groups having 1 to 3 carbon atoms, and m is an integer of 1 to 12.) It can be manufactured by
Representative examples of dihalides represented by the formula ( Propyl]trimethylene dibromide 2-[(1-naphthyl)methyl]trimethylene dibromide, 2-
[(1-naphthyl)ethyl]trimethylene dibromide, 2-[(1-naphthyl)propyl]trimethylene dibromide, 2-[(9-anthryl)methyl]trimethylene dibromide, 2-[(9-anthryl) ) Ethyl]trimethylene dibromide, 2
-[(9-Anthryl)propyl]trimethylene dibromide and the like. Representative examples of the tetraalkyldiamines represented by formula (XI) include N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,
4-tetramethylenediamine, N,N,N',
Examples include N'-tetramethyl-1,6-hexamethylene diamine.

The molecular weight of the polyionene shown in (c) above is
If the molecular weight is less than 1,000, no effect as a polymer can be expected, and if the molecular weight exceeds 100,000, it is difficult to manufacture.

As the reducing agent used in the present invention, those having an oxidation-reduction potential of 0 to +0.81 eV are preferably used, and among such reducing agents, ethylenediaminetetraacetic acid and its metal salts, and ethylenediaminetetraacetic acid are particularly preferred. Examples include ammonium acetate, ascorbic acid, and triethanolamine.

Examples of electronic media used in the present invention include viologens, rhodium tris dipyridyl complex, rhodium tris (4,4'-dimethyl-2,
2'-bipyridine), etc., but the following formula (XII) is preferred. (However, R ₁ and R ₂ in the formula represent an alkyl group having 1 to 15 carbon atoms, and X represents a halogen.) The selection of the viologens used in combination with a sensitizer is Although different, methyl viologen and hexyl viologen are generally preferred.

As the platinum colloid used in the present invention, platinum colloidally dispersed in a water-soluble polymer is preferably used, but polyvinyl alcohol Alternatively, platinum colloidally dispersed in polyvinylpyrrolidone is particularly preferably used.

According to the method of the present invention, hydrogen can be produced, for example, as follows. First, a cationic polymer was added 1× to a reaction vessel consisting of a quartz cell with an optical path length of 1 cm and a Pyrex tube with a volume of 10 ml.
10 ⁻⁵ to 1×10 ⁻³ M, preferably 5×10 ⁻⁵ to 5×
1×10 ⁻³ to 1× reducing agent so that the concentration is 10 ⁻⁴ M.
10 ^-1 M, preferably 5 x 10 ^{-3 to 5} x ^{10 -2 M} ; ^-2M , platinum was further colloidally dispersed in a 2% polyvinyl alcohol aqueous solution so that the platinum concentration was 5 x 10 ^-3 ~
Add 5 x 10 ^-1 M, preferably 1 x 10 ^-3 to 5 x 10 ^-2 M, deaerate by bubbling argon for 20 minutes, then plug with a two-way stopper and place into an irradiator. It can be irradiated with monochromatic light excitation at room temperature using spectroradiation (CRM-FA).The amount of hydrogen produced can be determined by connecting the reaction vessel to a gas sampler and performing gas chromatography (column: Molecular Sieve 5A). , column temperature: 50℃, carrier gas: argon).

The reason why hydrogen can be produced efficiently by the method of the present invention is not clear, but it is probably because the uptake of the reducing agent into the cation field consisting of quaternary ammonium is promoted by electrostatic effect and because of photosensitization. This seems to be because the electron transfer reaction of the viologen cation radicals to viologen generated by this is suppressed by the effect of the cation field, thereby increasing the accumulation of viologen radicals as an electron medium.

According to the method of the present invention using a cationic polymer as a photocatalyst, the photocatalyst is stable against light irradiation, can be used repeatedly, and is relatively inexpensive. It can be manufactured as follows.

The present invention will be explained in more detail below by giving examples.

Example 1 3-(1-pyrenyl)propyl methacrylate
0.16g, vinylbenzyltriethylammonium chloride 1.14g and azobisisobutyronitrile
0.01g dimethylamide-water (10:1, volume ratio)
Dissolved in 5 c.c. of mixed solvent, vacuum degassed, and heated to 70°C.
Polymerization was carried out for 10 hours. After the reaction, the resulting viscous solution was poured into 100 c.c. of tetrahydrofuran to obtain a precipitate. The precipitate was washed with acetone, filtered and dried to obtain a white powdery polymer.
1.15g was obtained.

This copolymer was confirmed to contain 7.3 mol% of the structural unit 3-(1-pyrenyl)propyl methacrylate based on elemental analysis (Cl: 12.7%), and the average content was determined by light scattering method. The degree of polymerization is 1100
It was hot. Also, the infrared absorption spectrum is 3450cm ^-1
They exhibited characteristic absorptions based on quaternary ammonium groups or ester groups, respectively, near 1720 cm ^-1 .

In a reaction vessel with a volume of 10 ml, add 4 x 10 ^-4 M (concentration converted to pyrene units) of the above copolymer aqueous solution, 8 x
10 ^-2 M ethylenediaminetetraacetic acid disodium salt aqueous solution, 4 x 10 ^-2 M methyl viologen aqueous solution, and 4 x 10 ^-3 M (concentration converted to platinum) platinum/polyvinyl alcohol colloid (molecular weight
6000, 2% polyvinyl alcohol aqueous solution), and after purging with argon for 20 minutes, stopper with a two-way stopper, and use an irradiator (Jiyasco Spectrum Irradiation CRM-FA).
Monochromatic light excitation was performed at 345 nm. The amount of hydrogen produced after 1 hour of irradiation was 110μ. However, the light intensity of the irradiator under the same conditions as determined by a chemical photometer was 3.40×10 ^-6 quanta/sec.

Example 2 0.35 g of vinylbenzyl[(1-pyrenyl)methyl]ether, 1.90 g of vinylbenzyltrimethylammonium chloride and 0.01 g of benzoyl peroxide.
g was dissolved in 10 c.c. of dimethylacetamide-water (10:1, volume ratio) mixed solvent, and after purging with nitrogen, 70
Polymerization was carried out in a sealed tube at ℃ for 8 hours. After the reaction was completed, the obtained viscous solution was poured into 100 c.c. of tetrahydrofuran to obtain a precipitate. The obtained precipitate was washed with acetone, filtered and dried to obtain a white powdery polymer 2.03. I got g.

This copolymer was confirmed to contain 9.2 mol% of vinylbenzyl [(1-pyrenyl) methyl] ether, which is a structural unit, based on elemental analysis (Cl: 14.3%), and the average polymerization rate determined by light scattering was The temperature was 2000 degrees.

4 x 10 ^-4 M (concentration converted to pyrene units) of the above copolymer aqueous solution, 8 x 10 ^-2 M ascorbic acid aqueous solution, 4 x 10 ^-2 hexyl viologen aqueous solution and 4 x 10 ^-3 M (platinum platinum concentration (concentration converted to
Polyvinyl alcohol colloid (molecular weight 10,000,
1% polyvinyl alcohol aqueous solution)
After replacing the tube with argon for 20 minutes, the tube was stopped with a two-way stopper and excited with monochromatic light at 345 nm using an irradiator (Jasco Spectral Irradiation CRM-FA). The amount of hydrogen produced after 5 hours of irradiation was 300μ.

Example 3 0.327 g of 2-[(1-pyrenyl)methyl]trimethylene dibromide and 0.172 g of N,N,N',N'-tetramethyl-1,6-hexamethylene diamine
and dissolved in 5 c.c. of dimethylformamide and heated at 60°C.
Heated for 24 hours. After the reaction is complete, the resulting viscous solution is
The mixture was poured into 50 c.c. of ether to obtain a precipitate, and the precipitate obtained was washed with ether and dried to obtain 0.450 g of a white powdery polymer. The average molecular weight of this polyionene determined by light scattering method is 8500.
It was hot.

In a reaction vessel with a volume of 10 ml, the above polyionene aqueous solution of 6 × 10 ^-4 M (concentration converted to pyrene units),
6×10 ^-4 M aqueous solution of ethylenediaminetetraacetic acid disodium salt, 4×10 ^-3 M aqueous methylviologen solution, and 4×10 ^-3 M (value converted to platinum concentration) platinum/polyvinylpyrrolidone colloid ( Molecular weight 8000, 2% polyvinylpyrrolidone aqueous solution)
After putting 1 ml of each into the tubes and purging with argon for 20 minutes, the tubes were stopped with a two-way stopper and excited with monochromatic light at 345 nm using an irradiator. The amount of hydrogen produced after 1 hour of irradiation was 90μ.

Example 4 3-(1-pyrenyl)propyl methacrylate
A copolymer was obtained in the same manner as in Example 1, except that 0.10 g of acrylic acid-3-(1-naphthylmethyl) was used instead of 0.16 g.

This copolymer was confirmed to contain 5.0 mol% of the structural unit acrylic acid-3-(1-naphthylmethyl) based on elemental analysis (Cl: 13.4%), and the average content was determined by light scattering method. The degree of polymerization was 1200.

Next, this copolymer was irradiated with light under exactly the same conditions as in Example 1, and the amount of hydrogen generated after 1 hour of irradiation was 100μ.

Example 5 3-(1-pyrenyl)propyl methacrylate
A copolymer was obtained in the same manner as in Example 1, except that 0.14 g of methacrylic acid-(9-anthryl)methyl was used instead of 0.16 g.

This copolymer was confirmed to contain 4.5 mol% of the structural unit methyl methacrylate (9-anthryl) methacrylate based on the elemental analysis value (Cl: 13.3%), and the average degree of polymerization determined by light scattering method was It was 1000.

Next, this copolymer was irradiated with light under exactly the same conditions as in Example 1, and the amount of hydrogen generated after 1 hour of irradiation was 130μ.

Example 6 0.270 g of 2-[(1-naphthyl)methyl]trimethylene dibromide instead of 0.327 g of 2-[(1-pyrenyl)methyl]trimethylene dibromide
Polymer was prepared in the same manner as in Example 3 except that
0.400g was obtained. The average degree of polymerization of this polyionene was determined by light scattering method to be 700.

Next, using this polyionene, Example 3
When light was irradiated under exactly the same conditions as above, the amount of hydrogen generated after 1 hour of irradiation was 100μ.

Comparative Example 1 A copolymer was synthesized in exactly the same manner as in Example 1, except that sodium p-styrenesulfonate was used instead of vinylbenzyltriethylammonium chloride. This copolymer was irradiated with light under exactly the same conditions as in Example 1, but no hydrogen generation was observed.

Comparative Example 2 Instead of using a copolymer obtained from 3-(1-pyrenyl)propyl methacrylate and vinylbenzyltriethylammonium chloride, (1
Light irradiation was carried out under exactly the same conditions as in Example 1, except that pyrenyl)methyltriethylammonium chloride was used. The amount of hydrogen produced at this time is
It was 50μ.

Claims (1)

[Claims] 1. When producing hydrogen by photolyzing water in the presence of a reducing agent, an electronic medium, a platinum colloid, and a photocatalyst, a polycyclic aromatic hydrocarbon selected from the group consisting of a naphthyl group, anthryl group, and pyrenyl group is used as a photocatalyst. A method for producing hydrogen by photolysis of water, which comprises using a cationic polymer containing a quaternary ammonium salt having a group in its side chain.