Green Science Alliance Succeeded in Artificial Photosynthesis with Quantum Dot – MOF Composite Material

KAWANISHI-CITY, Japan, April 12, 2022 /PRNewswire/ — Environmental problems such as global warming, natural resource depletion, plastic pollution due to population explosion, are getting severe in the world. CO2 increase is one of the major reasons for global warming. Plants are the planet’s lungs, but they’re struggling from deforestation. Artificial photosynthesis is one of the innovative technologies to solve this problem. Just like plants, from sun light energy, CO2 and water, this innovative technology can produce organic raw materials for fuels and chemicals.

This time, Dr. Ryohei Mori and Tetsuro Kajino at Green Science Alliance have succeeded in making formic acid at a ratio of 216 µmolh-1g-1cat, from water, CO2, and light energy. They have used their original catalyst composed of quantum dot and MOF (metal organic framework).

MOFs are the super porous material composed of inorganic metal cluster and organic linker. They can be controlled in molecular level at nanometer range with large surface area. From these features, MOF can be applied to gas storage, gas separation, metal absorption, catalysis, drug delivery, water treatment, sensor, electrode and filter etc… Recently, MOF has been found to possess CO2 capturing ability and MOF can even produce organic substances by CO2 photo reduction reaction, and that is artificial photosynthesis.

As for artificial photosynthesis materials, MOF could be more preferable than other materials including oxide, metal complex, nitride, enzymes etc…, due to their super porous structure for CO2 capturing, and the fact that optical absorption range can be optimized by modifying the synthesis procedure.

On the other hand, quantum dots are super tiny materials (0.5 – 9 nm) with optical properties which follows the rules of quantum chemistry and quantum mechanics. They are called "artificial atom or artificial molecules" because each quantum dot is composed of only several to several thousand number of atoms or molecules. At this size range, energy levels of electrons are no longer continuous and become separated due to physical phenomenon called quantum confinement effect. In this circumstance, wavelength of emission light will depend on the size of quantum dot.

This quantum dots also can be used for artificial photosynthesis because they possess high optical absorption ability, multiple exciton generation ability, with large surface area. However, the low durability and water resistance have been problems.

Both MOF and quantum dots have been synthesized within Green Science Alliance and this time, they have created quantum dot – MOF composite material which can be used for artificial photosynthesis. By making composite, durability and water resistance of quantum dot can be improved because they can be encapsulated within MOF. It is also suggested that excited electrons in quantum dots were transferred to metal catalyst in MOF which resulted in enhancing the catalytic activity. In the experiment, LED light with average wavelength of 460 nm was used as light source.

Formic acid can be the replacement for hydrogen fuel. One of the major reasons for preventing world wide spread of hydrogen based society is that it is difficult to store hydrogen because they are the smallest atoms in the universe, and it will be very expensive to make hydrogen tank with high sealing effect. Also, hydrogen can be explosive and have safety issue concern. It is much easier to store formic acid as fuel because they are liquid. If necessary, hydrogen can be made from formic acid with catalytic reaction. Some fuel cell can produce electrical energy directly from formic acid too.

Therefore, Green Science Alliance is promoting to make formic acid for their artificial photosynthesis technology. They will further try to improve artificial photosynthesis efficiency and try to create artificial photosynthesis business.

Ryohei Mori

SOURCE Green Science Alliance Co., Ltd.