Environmental problems such as climate change, natural resource depletion, extinction of species, plastic pollution and deforestation etc. because of human population explosion, are getting severe in the world. Carbon dioxide (CO2) is a greenhouse gas and one of the major reasons for climate change. In this regard, the process called “artificial photosynthesis (photo-reduction of CO2)” can produce organic raw materials for fuels and chemicals, from CO2, water and sun light energy, just like plants. At the same time, they can reduce CO2 because CO2 is utilized as raw materials to produce resources for energy and chemicals. Therefore, artificial photosynthesis is said to be one of the ultimate green technology.
MOFs (Metal Organic Frameworks) 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. Owing to these features, MOF can be applied to gas storage, separation, metal absorption, catalysis, drug delivery, water treatment, sensor, electrode and filter etc. Recently, MOF has been found to possess CO2 capturing ability and can produce organic substances by CO2 photo reduction, and that is artificial photosynthesis.
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. These quantum dots also can be applied for artificial photosynthesis because they possess high optical absorption ability, multiple exciton generation ability, with large surface area.
Both MOF and quantum dots have been synthesized within Green Science Alliance company. They have succeeded in creating formic acid with MOF – quantum dot composite material as artificial photosynthesis special catalyst, previously. However, those catalysts were in powder form and those catalysts powders need to be collected by filtration at each process. Therefore, it was difficult to be applied for real industrial usage because those process were not continuous.
Even the artificial photosynthesis efficiency is still low, Green Science Alliance will keep challenging to improve efficiency to set up artificial photosynthesis for real application.