JP7548499B2 - Photocatalyst and method for producing hydrogen peroxide using the photocatalyst - Google Patents

Description

The present invention relates to a photocatalyst and a method for producing the same, as well as a method for producing hydrogen peroxide using a photocatalyst.

Hydrogen peroxide is a powerful oxidizing agent that is easy to handle, easy to store, and environmentally safe, and is widely used as a bleaching agent, cleaning agent, disinfectant, etc.

In recent years, the anthraquinone method has been mainly used as a method for producing hydrogen peroxide (Patent Document 1). The anthraquinone method is a method in which anthrahydroquinone dissolved in a solvent is reacted with oxygen to oxidize the anthrahydroquinone and reduce the oxygen, thereby generating hydrogen peroxide water together with anthraquinone. However, the anthraquinone method has problems such as the need to remove the organic solvent and the need to regenerate the anthraquinone that has undergone a side reaction, which makes the production process complicated.
Besides the anthraquinone method, a direct synthesis method for producing hydrogen peroxide by directly reacting hydrogen with oxygen has been studied (Non-Patent Document 1). However, this direct synthesis method has a problem of the risk of explosion associated with the reaction between hydrogen and oxygen.

As a method for producing hydrogen peroxide that can avoid the problems associated with the above two methods, research is being conducted on a method using photocatalyst-based hydrogen peroxide synthesis.
However, when using inexpensive water as a raw material in the synthesis of hydrogen peroxide using this photocatalyst, the yield is low, making it necessary to use an organic solution such as an acetic acid solution or an aqueous 2-propanol solution (Patent Document 2).In addition, the catalyst is oxidized by the high oxidizing ability of hydrogen peroxide, resulting in problems of a decrease in yield and a complicated manufacturing process.

_C3N4 has attracted attention as _a photocatalyst for producing hydrogen peroxide from water and oxygen as raw materials.
For example, methods have been reported in which hydrogen peroxide is generated from water and oxygen as raw materials by using, as a photocatalyst, C ₃ N ₄ modified with molecules (Non-Patent Documents 2 and ₃ ) and C ₃ N ₄ reduced with NaBH 4 (Non-Patent Document 4). However, all of these methods have the problem of extremely low yields and low efficiency.

JP 2018-135230 A JP 2010-188240 A

Dr. Richard J. Lewis, Prof. Graham J. Hutchings, ChemCatChem, 11, 298-308 (2019) Yusuke Kofuji, Takayuki Hirai, et al., ACS Catalysis, 6, 7021-7029 (2016) Shiraishi Y, Hirai T, et al., Angewandte Chemie, 53, 13454-13459 (2014) Zedong Zhu, et al., Applied Catalysis B, 232, 19-25 (2018)

In order to solve the above problems, the present invention aims to provide a photocatalyst and a method for producing the same that can provide a method for producing hydrogen peroxide continuously and with high efficiency without using organic solvents, and a method for producing hydrogen peroxide using the catalyst.

The present inventors have found that the above problems can be solved by supporting a specific element on a photocatalyst, and have arrived at the present invention.
That is, the gist of the present invention is as follows.
[1] A photocatalyst comprising carbon nitride carrying at least one element selected from the group consisting of Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum.
[2] The photocatalyst according to [1], wherein the content of the element relative to 100% by weight of the carbon nitride is 1% by weight or more and 80% by weight or less.
[3] The photocatalyst according to [1] or [2], wherein the element is at least one element selected from phosphorus, arsenic, and antimony.
[4] A method for producing hydrogen peroxide, comprising the steps of: using water and oxygen as raw materials; and using the photocatalyst according to any one of [1] to [3] as a catalyst; and reacting the water and the oxygen by light irradiation.
[5] The method for producing hydrogen peroxide according to [4], wherein the raw material is water containing oxygen.
[6] The method for producing hydrogen peroxide according to [5], further comprising a step of releasing an oxygen-containing gas into water.
[7] A method for producing a photocatalyst according to any one of [1] to [3],
a reaction step of reacting a raw material containing nitrogen, carbon, and at least one element selected from the group consisting of Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum to produce the carbon nitride,
a content of at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum in the raw material is 1% by weight or more and 80% by weight or less with respect to 100% by weight of the carbon nitride.
[8] The method for producing a photocatalyst according to [7], wherein the raw material contains a compound containing nitrogen and carbon, and a compound containing at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum.

The present invention provides a photocatalyst and a method for producing the same that can provide a method for producing hydrogen peroxide continuously and with high efficiency without using organic solvents, etc., as well as a method for producing hydrogen peroxide using the catalyst.

1 is a graph showing the change over time in the amount of hydrogen peroxide produced when the pH of an aqueous solution in which a catalyst is suspended is set to 1.7 in Examples 1 to 4 and Comparative Example 1. 1 is a graph showing the change over time in the amount of hydrogen peroxide produced when the pH of an aqueous solution in which a catalyst is suspended is set to 7 in Examples 1 to 4 and Comparative Example 1. 1 is a graph showing the change over time in the amount of hydrogen peroxide produced when the pH of the aqueous solution in which the catalyst was suspended was set to 7 or 13 in Example 3 and Comparative Example 1. 1 is a graph showing the change over time in the amount of hydrogen peroxide produced when the pH of the aqueous solution in which the catalyst was suspended was set to 7 in Examples 5 to 7 and Comparative Examples 1 to 3.

The following describes in detail the embodiments of the present invention, but these descriptions are merely examples (representative examples) of the embodiments of the present invention, and the present invention is not limited to these contents as long as they do not exceed the gist of the invention.

<1. Photocatalyst>
A photocatalyst (hereinafter, also simply referred to as "photocatalyst") according to one embodiment of the present invention is a photocatalyst in which at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum are supported on carbon nitride.
A photocatalyst is a substance that can be excited by light and promote chemical reactions.

Carbon nitride is a compound whose main structure is represented by the chemical formula _C3N4 . This compound whose main structure is represented by the chemical formula _C3N4 means that the compound may have a structure in which a part of _{the C3N4} crystal lattice is missing, a structure in which a part is replaced by another element, a structure other than _{the C3N4 structure} , or the like, within the scope _of the effects of _the present invention.

The form of carbon nitride is not particularly limited, and for example, graphite carbon nitride (graphite C ₃ N ₄ , g-C ₃ N ₄ ), α-C ₃ N ₄ , cubic C ₃ N ₄ , pseudo-cubic C ₃ N ₄ or other polymeric carbon nitride can be used. In particular, graphite carbon nitride is preferable from the viewpoints of high absorption efficiency of visible light and near-ultraviolet light and ease of production.
When the above-mentioned carbon nitride is supported with an element described below, active sites are formed, and the effect of the present invention is achieved, that is, the efficiency of generating hydrogen peroxide is thought to be improved. Here, "supporting" refers to, for example, attaching the element as a single cation, as a salt, or as a complex to the base material carbon nitride. The element may be attached in advance, or the base material and the element may be added separately to a reaction vessel and attached within the reaction vessel.

The group 15 elements other than nitrogen (N) supported on carbon nitride are phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi), the group 14 elements other than carbon (C) and silicon (Si) are germanium (Ge), tin (Sn), and lead (Pb), and the group 13 elements other than boron (B) and aluminum (Al) are gallium (Ga), indium (In), and thallium (Tl), with P, As, and Sb being preferred, and Sb being particularly preferred. Sb is considered to have particularly high activity in the state of Sb ⁵⁺ or Sb ³⁺ , in which the outermost shell electron configuration is d10.
The element supported on the carbon nitride may be one selected from these elements, or two or more of them may be used in any combination and ratio.

The content of the above- _mentioned supported elements can be evaluated, for example, by performing inductively coupled plasma (ICP) emission spectroscopy after washing 60 mg of the element-supported photocatalyst with 100 mL of hot water at 80 to 100° C. ₃ to 5 times in order to remove elements not supported on g-C 3 N 4. When carbon nitride (carbon nitride itself excluding the above-mentioned supported elements, etc.) is taken as 100% by weight, the content of the above-mentioned supported elements is usually 1% by weight or more, preferably 5% by weight or more, more preferably 20% by weight or more, and even more preferably 40% by weight or more, from the viewpoint that the density of active sites is preferably high and, on the other hand, the decrease in the amount of light reaching the photocatalyst due to covering the photocatalyst (carbon nitride) needs to be suppressed. Washing to remove elements not supported on g-C ₃ N ₄ may be repeated three times with room temperature water instead of five or more times with hot water. When washing with room temperature water, the amount of metal supported may be measured to be slightly higher than when washing with hot water. It should be noted that the amount of added elements is assumed to be almost the same as the amount added, unless a large amount is added.

Carbon nitride may support elements other than those listed above, such as boron, oxygen, silicon, and aluminum.

The shape of the photocatalyst is not particularly limited and can be, for example, particulate, film, net, fiber, etc. It may be used alone or in aggregate. It may also be fixed to a support.

When the photocatalyst is particulate, its average particle size is not particularly limited, but high crystallinity is advantageous in suppressing light scattering, and therefore the average particle size is large, but on the other hand, it is advantageous to increase the specific surface area in order to increase the active sites, and therefore it is desirable for the average particle size to be small. From this viewpoint, it is usually 0.02 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.3 μm or more, and is usually 30 μm or less, preferably 10 μm or less, more preferably 3 μm or less, and even more preferably 1 μm or less.
The average particle size can be measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification at which the particles can be confirmed, for example, at a magnification of 10,000 to 100,000 times, the longest intercept value of a horizontal line formed by the left and right boundary lines of the particles is determined for any 50 primary particles, and the average value is calculated.

The specific surface area of the photocatalyst is not particularly limited, but for reasons similar to those for the preferred range of the average particle diameter described above, it is usually 0.1 m ² /g or more, preferably 1 m ² /g or more, more preferably 3 m ² /g or more, and even more preferably 5 m ² /g or more, and is usually 500 m ² /g or less, preferably 200 m ² /g or less, more preferably 100 m ² /g or less, and even more preferably 50 m ² /g or less.
The specific surface area can be measured by a known method.

The method for producing the photocatalyst is not particularly limited, and any known method capable of supporting a specific element on carbon nitride can be used. For example, the photocatalyst can be produced by the photocatalyst production method described below, which is another embodiment of the present invention.
A method for producing a photocatalyst (also simply referred to as a "method for producing a photocatalyst") according to another embodiment of the present invention includes a reaction step of producing the carbon nitride by reacting a raw material containing nitrogen, carbon, and at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum (also referred to as a "supported element" or a "supported element");
In the reaction step, the content of at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum in the raw material is 1% by weight or more and 80% by weight or less, based on 100% by weight of the carbon nitride. The production method may include any step other than the reaction step.
The above-mentioned manufacturing method will be described in detail below. Specifically, for example, raw materials including a compound containing the above-mentioned supported element and a compound containing nitrogen and carbon such as melamine are dissolved in an organic solvent such as ethanol, mixed, and then calcined at 500° C. or higher and 570° C. or lower, preferably 530° C. or higher and 570° C. or lower, to produce a photocatalyst.

The photocatalyst manufacturing method may include a raw material preparation step of preparing raw materials. The raw materials are not particularly limited as long as they contain at least nitrogen, carbon, and a supporting element, and usually contain two or more types of compounds. For example, the raw materials may be in an embodiment in which a compound containing nitrogen and carbon and a compound containing a supporting element are used (included), or the raw materials may be in an embodiment in which a compound containing nitrogen and carbon, a compound containing one type of supporting element, and a compound containing another supporting element different from the carbon element are used (included).

2. Method for producing hydrogen peroxide
Another embodiment of the present invention, a method for producing hydrogen peroxide (H ₂ O ₂ ) (hereinafter also referred to simply as a "method for producing hydrogen peroxide"), is a method for producing hydrogen peroxide that uses water and oxygen as raw materials, and the above-mentioned photocatalyst as a catalyst, and includes a step (reaction step) of reacting the water and the oxygen by light irradiation. Note that oxygen generated from water by a photocatalytic reaction can also be used as part of the oxygen.
In the reaction step, it is essential to use the above-mentioned photocatalyst, but other catalysts can also be used at the same time.

The form of the water as a raw material is not particularly limited, but it is preferably a liquid from the viewpoint of increasing the number of molecules that come into contact with the photocatalyst.
The form of oxygen as a raw material is not particularly limited, but is preferably in the form of a gas from the viewpoint of convenience of storage, transportation, and introduction at room temperature.
In addition, a step of releasing an oxygen-containing gas into water (oxygen releasing step into water) may be included prior to the above reaction step. By introducing this step, water containing oxygen can be used as a raw material, which is advantageous. As a gas other than oxygen contained in the oxygen-containing gas, a gas that can be used as an atmospheric gas, which will be described later, can be used.
The flow rate of oxygen when releasing oxygen-containing gas into water is not particularly limited, but from the viewpoint of increasing the number of molecules that come into contact with the photocatalyst, the flow rate is usually 0.1 L/min or more, preferably 0.3 L/min or more, more preferably 1 L/min or more, and even more preferably 3 L/min or more, per 1 L of water, calculated under standard conditions, and is usually 150 L/min or less, preferably 50 L/min or less, more preferably 20 L/min or less, and even more preferably 12.5 L/min or less.

The pH of the water may be adjusted with a pH adjuster or the like. In this case, the pH of the pH-adjusted aqueous solution in which the catalyst is suspended is not particularly limited, but from the viewpoint of increasing the amount of hydrogen peroxide produced and from the viewpoint of the degree of freedom in the materials used in the reactor, it is usually 1 to 14, preferably 5 to 11, more preferably 6 to 8, and even more preferably 7 to 8. The above pH adjusters and the like include not only materials added for the purpose of adjusting the pH, but also materials added for other purposes that change the pH as a result of their addition.

The reactor is not particularly limited as long as it can react water and oxygen and can transmit light, and a general reactor can be used. Regarding the transmission of light, the reactor may be entirely or partially transparent.
The handling of water and oxygen during the reaction is not particularly limited, and may be an embodiment in which water and/or oxygen are constantly flowed into the reactor from the outside of the reactor during the reaction, or an embodiment in which water and oxygen are sealed in the reactor before the reaction and then reacted.
The temperature inside the reactor during the reaction is not particularly limited, but is usually 0° C. or higher, preferably 5° C. or higher, more preferably 10° C. or higher, and even more preferably 20° C. or higher, and is usually 100° C. or lower, preferably 90° C. or lower, more preferably 60° C. or lower, and even more preferably 40° C. or lower.
The pressure in the reactor during the reaction is not particularly limited, but from the viewpoint of safety, it is usually 0.001 Pa or more, preferably 0.01 Pa or more, more preferably 0.03 Pa or more, and even more preferably 0.1 Pa or more, and is usually 0.9 Pa or less, preferably 0.5 Pa or less, more preferably 0.3 Pa or less, and even more preferably 0.2 Pa or less.

In a mode in which oxygen is constantly flowed into the reactor from outside the reactor during the reaction, when oxygen is used as a gas, the flow rate of oxygen gas into the reactor is not particularly limited, but is usually 0.1 L/min or more, preferably 0.3 L/min or more, more preferably 1 L/min or more, and even more preferably 3 L/min or more, per 1 L of water, calculated under standard conditions, and is usually 150 L/min or less, preferably 50 L/min or less, more preferably 20 L/min or less, and even more preferably 12.5 L/min or less.

The atmosphere in the reactor is not particularly limited, and may be air or may be filled with oxygen gas, or an atmospheric gas other than oxygen gas may be introduced. As the atmospheric gas, an inert gas such as argon gas is preferable.

The ratio of water to photocatalyst in the reaction vessel is not particularly limited, but from the viewpoint of efficiently obtaining hydrogen peroxide from a reactor of a fixed volume, the weight ratio is usually 10 or more, preferably 30 or more, more preferably 100 or more, and even more preferably 200 or more, and is usually 30,000 or less, preferably 10,000 or less, more preferably 5,000 or less, and even more preferably 2,000 or less.

The volume ratio of water to the reaction vessel is not particularly limited, but when oxygen is used as the gas, from the viewpoint of efficiently obtaining hydrogen peroxide from a reactor of a certain volume, it is usually 10 vol.% or more, preferably 20 vol.% or more, more preferably 40 vol.% or more, and even more preferably 60 vol.% or more, and is usually 99.9 vol.% or less, preferably 99 vol.% or less, more preferably 95 vol.% or less, and even more preferably 90 vol.% or less.

The type of light used for the light irradiation is not particularly limited, and for example, ultraviolet light, visible light, etc. may be used.
The type of light source is not particularly limited, but when ultraviolet light or visible light is used, for example, sunlight, a xenon lamp, an ultra-high pressure UV lamp, an ultra-high pressure mercury UV lamp, a metal halide UV lamp, a low pressure mercury UV lamp, a UV-LED, an excimer lamp, etc. Furthermore, the light source may be used alone or in combination of two or more types.

The wavelength of the light is not particularly limited, but since the optical absorption edge of g-C ₃ N ₄ is at 450 nm, it is usually 250 nm or more, preferably 300 nm or more, and more preferably 375 nm or more, and is usually 600 nm or less, preferably 500 nm or less, and more preferably 450 nm or less.

The intensity of the light beam is not particularly limited, but is usually 10 mW/ ^cm2 or more, preferably 30 mW/ ^cm2 or more, and more preferably 80 mW/ ^cm2 or more, and is usually 5000 mW/cm2 or ^less , preferably 1000 mW/ ^cm2 or less, and more preferably 200 mW/ ^cm2 or less.
The intensity of the light can be appropriately changed depending on the progress of the hydrogen peroxide production reaction.

The method for producing hydrogen peroxide may include a step of recovering hydrogen peroxide (recovery step) after the reaction step, and the hydrogen peroxide produced in the reaction step can be recovered as it is by this step.
After the reaction in the reaction step is completed, the unreacted water and oxygen, as well as the photocatalyst, can be recovered and reused in another reaction system.

<3. Hydrogen peroxide production system>
A hydrogen peroxide production system according to another embodiment of the present invention is a hydrogen peroxide production system that uses the above-mentioned photocatalyst and is capable of reacting water and oxygen by irradiation with light.
The embodiment of the system is not particularly limited, but an example of the system is a system that uses water and oxygen as raw materials and the above-mentioned photocatalyst as a catalyst, and can react the water and oxygen by irradiating them with light.
The raw materials, reactor, and reaction conditions may be the same as those described above in <2. Method for producing hydrogen peroxide>.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

<Production of photocatalyst>
[Example 1]
0.5 mmol of NaSbF ₆ was dissolved in ethanol (50 mL) and ultrasonicated for 1 hour, and then 4 g of melamine was added to the solution. After ultrasonication for another hour, the solvent was removed by rotary evaporation, and the temperature was raised from 20 ° C to 560 ° C at a temperature increase rate of 2.2 ° C / min in a nitrogen atmosphere, and held at 560 ° C for 4 hours. The prepared yellow product was washed three times with demineralized water and then dried overnight in a vacuum drying oven to obtain a photocatalyst. For the following Examples 2, 3, 4 and Comparative Example 1, it was confirmed by X-ray diffraction that g-C ₃ N ₄ was formed, and it is presumed that g-C ₃ N ₄ was also formed for Examples 5 to 9 and Comparative Examples 2 and 3.

A photocatalyst was produced in the same manner as in Example 1, except that the amount of _NaSbF6 was changed to 1 mmol.

[Example 3]
A photocatalyst was produced in the same manner as in Example 1, except that the amount of _NaSbF6 was changed to 3 mmol.

[Example 4]
A photocatalyst was produced in the same manner as in Example 1, except that the amount of _NaSbF6 was changed to 5 mmol.

[Example 5]
A photocatalyst was produced in the same manner as in Example 1, except that the amount of _NaSbF6 was changed to 15 mmol.

[Example 6]
A photocatalyst was produced in the same manner as in Example 1, except that 0.5 mmol of NaSbF ₆ was changed to 15 mmol of NaAsF ₆ .

[Example 7]
A photocatalyst was produced in the same manner as in Example 1, except that 0.5 mmol of NaSbF ₆ was changed to 15 mmol of NaPF ₆ .

[Example 8]
A photocatalyst was produced in the same manner as in Example 1, except that the amount of _NaSbF6 was changed to 10 mmol.

[Example 9]
A photocatalyst was produced in the same manner as in Example 1, except that the amount of _NaSbF6 was changed to 20 mmol.

[Comparative Example 1]
4 g of melamine was heated in a nitrogen atmosphere from 20° C. to 560° C. at a temperature increase rate of 2.2° C./min and held at 560° C. for 4 hours. The prepared product was washed three times with demineralized water and then dried overnight in a vacuum drying oven.

[Comparative Example 2]
A photocatalyst was produced in the same manner as in Example 1, except that 0.5 mmol of _NaSbF6 was changed to 15 mmol of NaF.

[Comparative Example 3]
A photocatalyst was produced in the same manner as in Example 1, except that 0.5 mmol of NaSbF ₆ was changed to 15 mmol of NaCuF ₆ .

<Evaluation of Sb Support Amount>
60 mg of the photocatalysts of Examples 1, 2, 3, 4, 8, 5, Comparative Example 1, and Comparative Example 2 were washed 3 to 5 times or more with 100 mL of hot water at 80 to 100°C, and then inductively coupled plasma (ICP) emission spectrometry was performed to evaluate the amount of Sb supported on the carbon nitride. The weight of Sb relative to the total weight of the catalyst and the weight of Sb relative to the carbon nitride carrier were as shown in Table 1 below. Note that free Sb ions remaining on the surface of the photocatalyst were removed by washing 3 to 5 times or more as described above.

<Production of Hydrogen Peroxide>
In a quartz reactor (volume 50 ml), a catalyst (60 mg) was added to water or pH-adjusted water (40 ml), and the reactor was sealed with a rubber septum. The pH adjustment will be described later. After dispersing the catalyst by ultrasonic treatment for 15 minutes, the water in the reactor was bubbled with oxygen gas for 30 minutes. Oxygen gas was introduced at a flow rate of 0.5 L/min, and the total amount introduced in 30 minutes was 15 L. Thereafter, the introduction of oxygen gas was stopped, and light from a xenon lamp (intensity before passing through the filter was 100 mW/cm ² ) was introduced into the reactor through a long-wavelength transmission (780 nm>λ>420 nm) filter to react water and oxygen to generate hydrogen peroxide. The reaction was carried out at a pressure of 1 atmosphere and at room temperature (20 to 30° C.) in the reactor. The amount of hydrogen peroxide was quantified by oxidation-reduction titration using KMnO ₄ and colorimetric analysis using 4-aminoantipyrine.

<Experiment 1-1>
An experiment was carried out to examine the change over time in the amount of hydrogen peroxide produced from the start of light irradiation using the photocatalysts of Examples 1 to 4 and Comparative Example 1. The results of this experiment are shown in FIG.
The pH-adjusted water used was prepared by adding a 0.1 M NaOH aqueous solution and a 0.1 M HCl aqueous solution to water so that the pH of the aqueous solution in which the catalyst was suspended was adjusted to 1.7.
From FIG. 1, it can be seen that in Examples 1 to 4, which used a photocatalyst carrying an element according to the present application, the amount of hydrogen peroxide produced was greater than in Comparative Example 1, which used a photocatalyst not carrying the element.
Furthermore, a comparison of Examples 1 to 4 revealed that the amount of hydrogen peroxide produced increased with an increase in the amount of _NaSbF6 charged, that is, with an increase in the amount of Sb supported on carbon nitride.

<Experiment 1-2>
Using the photocatalysts of Examples 5, 8, and 9, we investigated how the amount of hydrogen peroxide generated under light irradiation depends on the amount of _NaSbF6 added. However, pure water was used as the aqueous solution in producing hydrogen peroxide. The amount of hydrogen peroxide generated after 120 minutes of light irradiation is as shown in Table 2 below. From these results, it was found that the optimal amount of _NaSbF6 to generate hydrogen peroxide is about 15 mmol of _NaSbF6 per 4 g of melamine.

<Experiment 2>
An experiment was carried out to examine the change over time in the amount of hydrogen peroxide produced from the start of light irradiation using the photocatalysts of Examples 1 to 4 and Comparative Example 1. The results of this experiment are shown in FIG.
The pH-adjusted water used was prepared by adding a 0.1 M NaOH aqueous solution and a 0.1 M HCl aqueous solution to water to adjust the pH of the aqueous solution containing the catalyst suspended therein to 7.
As seen from FIG. 2, similarly to Experiment 1, Examples 1 to 4, which used a photocatalyst carrying an element according to the present application, produced a greater amount of hydrogen peroxide than Comparative Example 1, which used a photocatalyst not carrying the element.
Moreover, as in Experiment 1, a comparison of Examples 1 to 4 revealed that the amount of hydrogen peroxide produced increased with an increase in the amount of _NaSbF6 charged, that is, with an increase in the amount of Sb supported on carbon nitride.
Comparing Experiments 1 and 2, when the amount of _NaSbF6 charged was 0.5 mmol, no difference in the amount of hydrogen peroxide generated due to differences in pH was observed, but when the amount of _NaSbF6 charged was 1 to 5 mmol, the amount of hydrogen peroxide generated was greater at pH = 7 than at pH = 1. In addition, in Comparative Example 1, no difference in the amount of hydrogen peroxide generated due to differences in pH was observed.

<Experiment 3>
An experiment was carried out to examine the change over time in the amount of hydrogen peroxide produced from the start of light irradiation using the photocatalysts of Example 3 and Comparative Example 1. The results of this experiment are shown in FIG.
As the pH-adjusted water, water whose pH was adjusted to 7 and 13 by adding a 0.1 M aqueous NaOH solution and a 0.1 M aqueous HCl solution was used.
From FIG. 3, a comparison of pH=7 and pH=13 in Example 3 shows that the amount of hydrogen peroxide produced was greater at pH=7 than at pH=13.
Referring to the comparison results between Experiments 1 and 2, the amount of hydrogen peroxide produced was greater at pH = 7 than at pH = 1.7 and pH = 13. In other words, it was found that it is preferable for the pH-adjusted water to be neutral rather than acidic or alkaline.

<Experiment 4>
An experiment was carried out to examine the change over time in the amount of hydrogen peroxide produced from the start of light irradiation using the photocatalysts of Examples 5 to 7 and Comparative Examples 1 to 3. The results of this experiment are shown in FIG.
However, in producing hydrogen peroxide, pure water was used as the aqueous solution.
As seen from FIG. 4, similarly to Experiment 1, Examples 1 to 4, which used a photocatalyst carrying an element according to the present application, produced a greater amount of hydrogen peroxide than Comparative Example 1, which used a photocatalyst not carrying the element.
Furthermore, a comparison of Examples 5 to 7 revealed that the elements supported on carbon nitride were most abundant in the order P, As, and Sb.

<Experiment 5>
An experiment was carried out to examine the pH dependency of the amount of hydrogen peroxide produced, using the photocatalyst of Example 5 as the photocatalyst. However, in the production of hydrogen peroxide, a 0.1 M aqueous NaOH solution and a 0.1 M aqueous HCl solution were added to pure water to adjust the pH of the aqueous solution. The amount of hydrogen peroxide produced after 120 minutes of light irradiation is shown in Table 3 below. From this result, it was confirmed that, as described in the above description of the method for producing hydrogen peroxide, a pH of 6 to 11 is preferable in the production of hydrogen peroxide with this catalyst.

<Experiment 6>
An experiment was carried out using the photocatalyst of Example 5 as the photocatalyst and a phosphate buffer solution or a 0.1M _NaHCO3 aqueous solution as the aqueous solution. The amount of hydrogen peroxide produced after 120 minutes of light irradiation is shown in Table 4 below. From this result, it was found that a phosphate buffer solution is suitable for producing hydrogen peroxide using this photocatalyst.

From Experiments 1 to 6 above, it was found that by using the photocatalyst according to the present application, hydrogen peroxide can be produced continuously and efficiently without using organic solvents, etc.

Claims (10)

A photocatalyst comprising carbon nitride carrying at least one element selected from arsenic and antimony . The photocatalyst according to claim 1, wherein the content of the element relative to 100% by weight of the carbon nitride is 1% by weight or more and 80% by weight or less. A method for producing hydrogen peroxide, comprising the steps of: using water and oxygen as raw materials; and using a photocatalyst as a catalyst , the photocatalyst being carbon nitride carrying at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum, and reacting the water with the oxygen by light irradiation. 4. The method for producing hydrogen peroxide according to claim 3, wherein the content of the element in the photocatalyst is 1% by weight or more and 80% by weight or less relative to 100% by weight of the carbon nitride. 5. The method for producing hydrogen peroxide according to claim 3, wherein the element in the photocatalyst is at least one element selected from the group consisting of phosphorus, arsenic, and antimony. The method for producing hydrogen peroxide according to any one of claims 3 to 5 , wherein the raw material is water containing oxygen. 7. The method for producing hydrogen peroxide according to claim 6 , further comprising the step of releasing an oxygen-containing gas into water. A method for producing a photocatalyst , comprising the steps of:
The photocatalyst is a carbon nitride having a group 15 element other than nitrogen and a group 14 element other than carbon and silicon.
and at least one element selected from the group consisting of boron, aluminum, and group 13 elements excluding boron and aluminum;
a reaction step of reacting a raw material containing nitrogen, carbon, and at least one element selected from the group consisting of Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum to produce the carbon nitride,
a content of at least one element selected from Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum in the raw material is 1% by weight or more and 80% by weight or less with respect to 100% by weight of the carbon nitride. 9. The method for producing a photocatalyst according to claim 8, wherein the raw material comprises a compound containing nitrogen and carbon, and a compound containing at least one element selected from the group consisting of Group 15 elements excluding nitrogen, Group 14 elements excluding carbon and silicon, and Group 13 elements excluding boron and aluminum. The method for producing a photocatalyst according to claim 8 or 9, wherein the element is at least one element selected from the group consisting of phosphorus, arsenic, and antimony.

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