TWI804230B - An organic-photocatalytic thin film, the corresponding preparation method, and application in photocatalytic hydrogen-producing system - Google Patents

Abstract

The present invention provides a preparation method for organic-photocatalytic thin film, and its corresponding application in photocatalytic hydrogen production. The preparation for manufacturing an organic-photocatalytic thin film includes several steps: preparing a 0.6wt% pBTTT-C14 solution; preparation of thin films through spin-coating the pBTTT-C14 solution on a substrate; annealing the thin film at 265 ^oC for 1 minute under vacuum environment; spin coating a layer of PCBM on the thin film, where the concentration of the PCBM is 3 mg/ml; annealing the prepared thin film with a layer of PCBM molecules at 210 ^oC for 1 hour. Therefore, the organic-photocatalytic thin films with evolved structure of donors and acceptors are achieved. Moreover, the organic-photocatalytic thin film exhibits improved efficiency in hydrogen production.

Description

Organic photocatalyst thin film, its preparation method and its photohydrogen production system

The invention relates to an organic photocatalyst film, a preparation method thereof and a photohydrogen production system using the same, in particular to an organic photocatalyst film using a polymer.

In recent years, fossil energy has been depleted day by day, and the energy crisis is serious, so exploring alternative energy is the current trend and goal. In order to solve the above problems, hydrogen energy, which has a high calorific value, is clean and does not produce any greenhouse gases, has gradually become an energy source with great development potential. In addition, solar energy is environmentally friendly and inexhaustible, and has become a new choice of energy source.

Accordingly, the development of photocatalysts and photocatalyst thin films has been common, and it is expected to effectively split water and produce hydrogen after being irradiated with sunlight.

However, due to its large energy gap, traditional photocatalysts can only be excited to generate electron-hole pairs under ultraviolet light irradiation. Since ultraviolet light only accounts for about 4% of sunlight energy, there is still room for improvement in the utilization efficiency of solar energy. The materials synthesized in the prior art mostly use inorganic materials as the main body, and the photocatalyst film is mainly prepared by chemical synthesis, so complicated synthesis steps and harsh synthesis environment are required, such as: high temperature, high pressure and high pH value. [Prior Technical Literature] [Patent Document]

[Patent Document 1] Japanese publication JP 6471299 B2

[Technical problem to be solved by the invention]

Accordingly, the present invention provides an organic photocatalyst film and a preparation method thereof which can improve the utilization efficiency of solar energy and enhance the efficiency of water splitting and hydrogen production, and apply it to a photohydrogen production system. [Technical means]

The invention provides an organic photocatalyst film, which uses pBTTT-C14 (poly[2,5-bis(3-tetradecylthiophen-2-yl)thiophene\[3,2-bthiophene]) as a donor material, Carbon nanosphere derivative (PCBM) is the acceptor material, and the PCBM is embedded into the gap between side chains and side chains in the pBTTT-C14 to form ordered fine stripes.

Wherein, the preparation method of the organic photocatalyst thin film may include the following steps: (A) configuring a pBTTT-C14 solution with a concentration of 0.6 wt% by weight; (B) spinning the pBTTT-C14 solution by spin coating Apply on a substrate to prepare a film; (C) Keep the film at 265 ^o C for 1 minute in a vacuum environment; (D) Spin coat the film after holding the temperature in step (C) In the way of coating a layer of PCBM, wherein the solution concentration of the PCBM is 3mg/ml; (E) the film coated with the PCBM in the step (D) is kept at a temperature of 210 ^o C for 1 hour, that is An organic photocatalyst film was obtained.

Wherein, the solvent of the pBTTT-C14 solution in step (A) can be chlorobenzene.

Wherein, the conditions of the spin coating in the step (B) can be: first carry out 20 seconds at a rotating speed of 500 rpms, and then carry out 30 seconds at a rotating speed of 2000 rpms.

Wherein, the condition of the spin coating in the step (D) can be: 40 seconds at a rotation speed of 3000 rpms.

Wherein, the substrate in step (B) may be a glass substrate or an indium tin oxide substrate.

On the other hand, the present invention also provides a method for preparing an organic photocatalyst film, which includes the method of using heat treatment to crystallize the polymer, which can control and distribute the material with hydrogen ion reactivity in the polymer film, and simultaneously produce an ordered array The thin film can also achieve the effect of promoting the decomposition of water to produce hydrogen.

The preparation method may include the following steps: (A) configuring a pBTTT-C14 solution with a concentration of 0.6 wt% by weight; (B) spin-coating the pBTTT-C14 solution on a substrate by spin coating, Prepare a thin film; (C) hold the film at 265 ^o C for 1 minute in a vacuum environment; (D) spin coat the film after holding the temperature in step (C) on One layer of PCBM, wherein the solution concentration of the PCBM is 3mg/ml; (E) The film coated with the PCBM in step (D) is kept at a temperature of 210 ^o C for 1 hour to obtain an organic photocatalyst film.

Further, the solvent of the pBTTT-C14 solution in step (A) can be chlorobenzene.

Further, the conditions of spin coating in step (B) can be: firstly carry out 20 seconds at a rotating speed of 500 rpms, and then carry out 30 seconds at a rotating speed of 2000 rpms.

Further, the condition of spin coating in step (D) may be: 40 seconds at a rotation speed of 3000 rpms.

Further, the substrate in step (B) may be a glass substrate or an indium tin oxide substrate.

The present invention also provides a photohydrogen production system, which can use the above-mentioned organic photocatalyst film as the hydrogen production film. [Effect of the invention]

The present invention utilizes polymers to synthesize organic photocatalyst films. Compared with most inorganic materials, conjugated polymers have a wide range of visible light absorption, so the combination with conjugated polymers can improve the use efficiency of solar energy.

In addition, the present invention also improves the efficiency of water splitting and hydrogen production by regulating the structural evolution of polymers and hydrogen ion reactive materials.

In addition, compared with the method of chemically synthesizing photocatalysts, the present invention physically regulates the film that is beneficial to the hydrogen production efficiency, so that the preparation environment is simple and safe, and does not require harsh conditions or complicated synthesis steps. An organic photocatalyst thin film with high hydrogen production efficiency is obtained.

The preparation steps, identification methods and analysis results of the present invention are described below by means of exemplary embodiments. It should be noted that the following exemplary embodiments are only used to illustrate the present invention, but not to limit the scope of the present invention.

The operating mechanism of the organic photocatalyst prepared by the present invention is shown in FIG. 1 . The process of using sunlight to produce hydrogen can be simply divided into three reaction steps: photocatalyst material absorbs sunlight to generate photoelectrons, photoelectrons diffuse to the interface between photocatalyst and water, and photoelectrons react with hydrogen ions in water to generate hydrogen. Both donor and acceptor materials play an indispensable role in the development of hydrogen-producing photocatalyst materials, and since common donor materials have the problem of easy recombination of photoelectrons, the coupling of acceptor materials can effectively solve this problem. situation.

However, in order to efficiently transfer the photoexcited electrons from the donor material to the acceptor material, the distribution of the acceptor material in the donor material will dominate the overall hydrogen production efficiency.

Accordingly, the main purpose of the present invention is to develop an optimized organic photocatalyst film. In the selection of the donor material, the present invention uses a conjugated polymer pBTTT-C14 (trade name pBTTT-C14 or Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3, 2-b]thiophene], https://www.sigmaaldrich.com/TW/en/product/aldrich/753971); due to the high molecular mobility of liquid crystal phase polymers, there will be Potential for optimal distribution of receptor material. The acceptor material is to choose a nanomaterial with high electron harvesting ability: carbon nanosphere derivative PCBM (trade name [6,6]-Phenyl C71 butyric acid methyl ester, https://www.sigmaaldrich.com/TW /en/product/aldrich/684465). In addition, such a combination of materials is also suitable for the transition process of optoelectronics in terms of the matching of electronic energy levels.

Exemplarily, the preparation method of the organic photocatalyst thin film of the present invention includes the following steps: (A) Prepare a solution of pBTTT-C14 with a concentration of 0.6wt% by weight, and its solvent is chlorobenzene. (B) The pBTTT-C14 solution was spin-coated on the substrate by spin-coating to prepare a thin film. The parameters of the spin coater (GSSP-03A) are: the first stage rotation speed is 500 rpms for 20 seconds, and the second stage rotation speed is 2000 rpms for 30 seconds. (C) The pBTTT-C14 film was kept at 265 ^o C for 1 minute under vacuum. This step allows pBTTT-C14 to pre-develop a very large-scale liquid crystal phase alignment. (D) Coat the film prepared in step (C) with a layer of PCBM film by spin coating. The solution concentration of PCBM is 3mg/ml; the parameters of the spin coater are 3000 rpms, 40 seconds. (E) Next, keep the spin-coated film of PCBM molecules at 210 ^o C for 1 hour to obtain an organic photocatalyst film.

The substrate in step (B) can be a glass substrate or an indium tin oxide substrate (ITO); Figure 2 shows the film structure of an organic photocatalyst film containing pBTTT-C14 and PCBM developed on a glass substrate, and Figure 3 shows the film structure containing The thin film structure of organic photocatalyst thin film of pBTTT-C14 and PCBM developed on indium tin oxide substrate (ITO).

Organic photocatalyst film prepared by X-ray diffraction analysis (D8 DISCOVER with GADDS (Bruker AXS Gmbh, Karlsruhe, Germany)). As shown in Figure 4 is the X-ray diffraction pattern, it can be found that the layered stacking distance of pBTTT-C14 tends to move to a lower angle; this trend is due to the fact that the acceptor material PCBM will be embedded in the Gap between side chains in pBTTT-C14. The schematic diagram of the embedding relationship between pBTTT-C14 and PCBM is shown in Figure 5, where the spherical molecule is PCBM and the chain molecule is pBTTT-C14.

In addition, the prepared organic photocatalyst film was observed with an electron microscope (JEM-1400 Transmission electron microscope, JEOL). As shown in Figure 6, the embedding of PCBM in the liquid crystal phase of pBTTT-C14 will form ordered thin stripes. This is because the gaps between the side chains of pBTTT-C14 will develop channels along the direction of the b-axis of the molecular chain; the thin stripes It is an extremely important structure of the organic photocatalyst film prepared by the present invention. It shows that under the heat treatment conditions of step (E), the pBTTT-C14 and PCBM of the present invention can form a good electron transmission channel and greatly improve the hydrogen production efficiency. .

Therefore, it can be found that the organic photocatalyst film prepared by the preparation method of the organic photocatalyst film of the present invention, especially after the heat treatment in step (E), not only can make the donor pBTTT-C14 and the acceptor PCBM form a large amount of mutual help The heterojunction that separates photoelectrons and holes also enables the two materials to develop continuous crystal phases in the thin film that are conducive to the transfer of photoelectrons. Therefore, such a thin film structure will help to improve the reaction efficiency of photoelectrons participating in hydrogen production and thus improve the performance of hydrogen production.

In order to evaluate the hydrogen production efficiency of the thin film, the prepared thin film was evaluated by photocurrent experiment. Use a vitamin C electrolyte with a pH value of 4, place a film in it and place it at a light intensity equal to the size of a sunlight intensity, and measure the light generated when the light irradiates the sample with a constant current meter (Autolab PGSTAT30) Current density; when the photocurrent density is higher, it means that the number of electrons that can provide hydrogen ions to be reduced to hydrogen gas is more, so the efficiency of hydrogen production is better. As shown in Figure 7, when a layer of PCBM molecules is deposited on the surface of pBTTT-C14, the photocurrent density of the pure PBTTT-C14 film is higher due to the establishment of heterojunction; however, at 210 ^o C After heat treatment, a further increase in photocurrent density can be observed. This is due to the structure of PCBM molecules embedded in the pores of pBTTT-C14 after heat treatment, so that the heterojunction between the donor and the acceptor can be established on a smaller scale, so the separation of electron holes can be more efficient, so there is more Good hydrogen production efficiency.

Accordingly, the organic photocatalyst film of the present invention has a heterojunction that facilitates the separation of photoelectrons and holes, and applying the organic photocatalyst film of the present invention to a photohydrogen production system can also achieve extremely high hydrogen production efficiency.

[Figure 1] The operating mechanism of the organic photocatalyst prepared by the present invention. [Fig. 2] The film structure of the organic photocatalyst film including pBTTT-C14 and PCBM developed on the glass substrate. [Fig. 3] The film structure of the organic photocatalyst film including pBTTT-C14 and PCBM developed on the indium tin oxide substrate (ITO). [Figure 4] X-ray diffraction pattern of organic photocatalyst film. 〔Figure 5〕Schematic diagram of the embedded relationship between PCBM and pBTTT-C14. [Fig. 6] Electron microscope observation diagram of organic photocatalyst thin film. [Fig. 7] Results of photocurrent experiments.

Claims (6)

A preparation method of an organic photocatalyst thin film is characterized in that it comprises the following steps: (A) pBTTT-C14 (poly[2,5-bis(3-tetradecylthiophene-2 -base) thiophene\[3,2-bthiophene]) solution; (B) spin-coat the solution of pBTTT-C14 on a substrate by spin coating to prepare a thin film; (C) place the thin film on In a vacuum environment, keep the temperature at 265°C for 1 minute; (D) apply a layer of carbon nanosphere derivatives (PCBM) to the film after the temperature in step (C) by spin coating, wherein The solution concentration of the PCBM is 3 mg/ml; (E) The film coated with the PCBM in step (D) is kept at 210° C. for 1 hour to obtain an organic photocatalyst film. The preparation method of the organic photocatalyst film as described in Claim 1, wherein, the solvent of the pBTTT-C14 solution in step (A) is chlorobenzene. The preparation method of the organic photocatalyst thin film as described in Claim 1, wherein, the spin-coating condition in the step (B) is: first carry out 20 seconds with rotating speed 500rpms, then carry out 30 seconds with rotating speed 2000rpms. The method for preparing an organic photocatalyst thin film as claimed in Claim 1, wherein the spin coating condition in step (D) is: 40 seconds at a rotating speed of 3000rpms. The method for preparing an organic photocatalyst thin film according to claim 1, wherein the substrate in step (B) is a glass substrate or an indium tin oxide substrate. A photohydrogen production system, characterized in that it uses the organic photocatalyst film prepared by the method for preparing an organic photocatalyst film described in any one of claims 1 to 5 as a hydrogen production film.

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