KAWANISH, Japan, Nov. 15, 2022 /PRNewswire/ — Environmental issues such as climate change, resource depletion, species extinction, plastic pollution and deforestation caused by the world’s population surge are becoming more pressing.
        Carbon dioxide (CO2) is a greenhouse gas and one of the main causes of climate change. In this regard, a process called “artificial photosynthesis (photoreduction of carbon dioxide)” can produce organic raw materials for fuel and chemicals from carbon dioxide, water and solar energy, as plants do. At the same time, they reduce CO2 emissions, which are used as feedstock for energy and chemical production. Therefore, artificial photosynthesis is known as one of the most advanced green technologies.
        MOFs (metal-organic frameworks) are superporous materials composed of clusters of inorganic metals and organic linkers. They can be controlled at the molecular level in the nano range with a large surface area. Due to these properties, MOFs can be applied in gas storage, separation, metal adsorption, catalysis, drug delivery, water treatment, sensors, electrodes, filters, etc. MOFs have recently been found to have the ability to capture CO2, which can be used to produce organic substances through CO2 photoreduction, also known as artificial photosynthesis.
        Quantum dots, on the other hand, are ultra-tiny materials (0.5–9 nanometers) with optical properties that obey the rules of quantum chemistry and quantum mechanics. They are called “artificial atoms or artificial molecules” because each quantum dot consists of only a few to thousands of atoms or molecules. In this size range, the energy levels of the electrons are no longer continuous and become separated due to a physical phenomenon known as the quantum confinement effect. In this case, the wavelength of the emitted light will depend on the size of the quantum dot. These quantum dots can also be applied in artificial photosynthesis due to their high light absorption capacity, ability to generate multiple exciton and large surface area.
        Both MOFs and quantum dots have been synthesized by the Green Science Alliance. Previously, they have successfully used MOF-quantum dot composites to produce formic acid as a special catalyst for artificial photosynthesis. However, these catalysts are in powder form and these catalyst powders must be collected by filtration in each process. Therefore, it is difficult to apply it to real industrial use because these processes are not continuous.
        In response, Mr. Kajino Tetsuro, Mr. Iwabayashi Hirohisa, and Dr. Mori Ryohei of Green Science Alliance Co., Ltd. used their technology to immobilize these special artificial photosynthesis catalysts on an inexpensive textile fabric and opened a new formic acid plant. The process can be run continuously for practical industrial applications. After the completion of the artificial photosynthesis reaction, the water containing formic acid can be taken out and extracted, and then new fresh water can be added to the container to continue the resumption of artificial photosynthesis.
        Formic acid can replace hydrogen fuel. One of the main reasons holding back the worldwide adoption of a hydrogen-based society is that hydrogen, the smallest atom in the universe, is difficult to store, and it would be very expensive to build a well-sealed reservoir of hydrogen. In addition, hydrogen gas can be explosive and pose a safety hazard. It is much easier to store formic acids as a fuel because they are liquid. If necessary, formic acid can catalyze the reaction to produce hydrogen in situ. In addition, formic acid can be used as a raw material for various chemicals.
       Even if the efficiency of artificial photosynthesis is currently still very low, the Green Science Alliance will continue to fight to increase efficiency and introduce truly applied artificial photosynthesis.