Research Results

Development of a safe and high-yield solution synthesis method for next-generation materials of black phosphorus ~Dream technology: Accelerating artificial photosynthesis~

Smmary

 A group led by Professor Tomoko Yoshida (Deputy Director, Center for Artificial Photosynthesis, Osaka City University) and Akiyo Ozawa (Osaka City University), and Sakai Chemical Industry Co., Ltd. have jointly developed a method to synthesize black phosphorus, which acts as a catalyst for the production of hydrogen from water, using solar energy to synthesize black phosphorus in high yield and simplicity using a solution method. Black phosphorus is one of the allotropes of phosphorus and is attracting attention as a material that can absorb most of the visible light range of sunlight, but it has been difficult to synthesize it in large quantities, which is required for industrial purposes. This time, we succeeded in synthesizing black phosphorus in high yield by the solution method, using safe and harmless red phosphorus as a starting material, paving the way for mass synthesis.

 This article was published on the online page of a chemical journal published by the Royal Society of Chemistry (RSC) on March 12, 2020 (Japan time).

Research Background

 Global warming has become a serious social problem, and hydrogen is attracting attention as a new energy source to replace fossil fuels such as oil and coal, which generate carbon dioxide, which is the causative agent of global warming. Until now, research has been actively conducted on the production of hydrogen on photocatalysts using familiar materials such as solar energy and water. Black phosphorus is a very promising photocatalytic material that can be used from ultraviolet light to near-infrared light in solar energy, but its synthesis methods are generally synthesis methods such as high-temperature and high-pressure methods and chemical vapor deposition, and it has been difficult to synthesize them in large quantities at low cost.

 It is expected to be synthesized in large quantities of black phosphorus at a lower cost, and it has recently been reported that black phosphorus can be synthesized from white phosphorus by a special method called the sorbothermal method^*1, which synthesizes solids using a high-temperature or high-pressure solvent. However, since white phosphorus is highly poisonous, it was necessary to develop a method to obtain black phosphorus in high yields from red phosphorus, which is safe and harmless.

*1: A method of synthesizing materials by heating a solvent.

Outline of Research

 In this study, we found a method to synthesize red phosphorus to black phosphorus in high yields by the sorbothermal method using ethylenediamine^*2 as a solvent, and clarified the reaction mechanism by making full use of various spectroscopic methods. We clarified the reaction mechanism in which red phosphorus is dissolved as trivalent phosphorus in ethylenediamine, and then a certain amount of phosphorus is collected to form a zero-valent polyline, which is stacked in solution to form black phosphorus. The obtained sample contains a very high content of black phosphorus, and we have succeeded in significantly improving the yield from about 10% to about 90%. In addition, when the obtained sample was supported with a cocatalyst^*3, it showed high hydrogen production activity under visible light irradiation from an aqueous methanol solution, demonstrating that it is also promising as a photocatalyst for water splitting. (This result is patent pending)

*2: An organic compound that mixes with water and alcohol at will. It is widely used in chemical synthesis.
*3: Attaching fine particles of metal used as a catalyst to a carrier.

Expected effect

 Black phosphorus is a layered compound like graphite, and since the wavelength of light that can be absorbed can be changed depending on the thickness of the layer, it is expected to be a two-dimensional material that can be used from visible light to near-infrared light. However, due to the lack of established synthesis methods, few examples of its use in the industrial field have been reported. This research is expected to obtain a high yield of black phosphorus from safe red phosphorus, and further accelerate photocatalytic research using black phosphorus.

 In addition, black phosphorus single-layer film (phosphorine) is a substance related to graphite single-layer film (graphene^*4), which was the topic of discussion at the 2010 Nobel Prize in Physics, and is a semiconductor material that exhibits excellent electrical conductivity and has a band gap that graphene does not have. For this reason, numerous research papers have been reported in the field of materials such as two-dimensional transistors and sensors. It is expected that the results of this research will be applied not only in the field of photocatalytic chemistry but also in the field of electronic materials.

*4: A thin-film polymer with a thickness of one carbon atom. It has a hexagonal lattice structure like a honeycomb made of carbon atoms and their bonds.

Future Developments

 Black phosphorus is difficult to synthesize and has low stability in the atmosphere. Based on the black phosphorus synthesis guidelines obtained in this study, we plan to develop a method to increase the layered area of black phosphorus and to develop a formulation that improves stability.

Joint research, funding, etc.

 This research is a joint research between Osaka City University and Sakai Chemical Industry Co., Ltd. In addition, it was carried out with the following financial support:
• Grants-in-Aid for Scientific Research on Innovative Areas "Creation and Functions of Complex Anionic Compounds" Research Project 16H06440

Publication Information

All Press Release (PDF:348KB)

Article source: Osaka City University website