Researchers from the Tokyo Institute of Technology have helped to create an efficient light-harvesting system which could be used to build better photocatalysts.
The new and efficient light-harvesting system is based on the principles of natural photosynthesis and could be used to build better photocatalysts which can be used for a number of purposes including CO2 reduction and water oxidation photocatalysis.
Scientists have been trying to emulate the way in which plants harvest energy from the sun through photosynthesis for many years. Plants absorb photons from even weak sunlight through light antennae made from chlorophyll molecules in their leaves. The absorbed energy is then converted into sugars which plants use as food. So far, artificial systems built to try and replicate this have been limited to a single reaction centre with a few light absorbers, being largely unable to absorb enough energy from light sources with low photon levels.
Now, Osamu Ishitani at the Tokyo Institute of Technology, along with researchers from Toyota Central R&D Labs, Inc., has created an efficient, artificial light-harvesting system based on the natural two-step process of photosynthesis. The new system uses man-made 'leaves' as light absorbers, which relay energy through a metal complex to feed a final energy acceptor.
“It is difficult to make an efficient solar-energy converter using molecular devices such as so-called photocatalysts because the molecules are so small and solar light is so dilute” said Ishitani. “Such systems would require huge numbers of molecular devices, which are expensive and time-consuming to make. Introducing devices with the ability to harvest light into solar-energy conversion would be one possible solution.”
Ishitani and his team realized that building a system with multiple light absorbers feeding a smaller number of energy relay 'antennae' linked to an energy acceptor would allow more photons to be absorbed from dilute light, with less energy being lost along the way.
The researchers created a device with 440 'leaves' using tubes made from so-called periodic mesoporous organosilica (PMO) and light-absorbing biphenyl (Bp). The PMO-Bp complexes were linked to five connected rhenium metal sticks, which transferred the light energy harvested by PMO-Bp directly to a central ruthenium sphere. In this way, the photons from the light source were concentrated very efficiently, first through the rhenium sticks and then into the ruthenium reaction center, with little loss of energy en-route.
In a series of tests using the new system, Ishitani and his team found that the reaction center of their device was capable of emitting a strong light powered by the photonic energy from the man-made 'leaves'.
The new system could be used to build better photocatalysts, which can be used for a range of purposes including conversion of water to hydrogen gas by photocatalytic water splitting, conversion of carbon dioxide into gaseous hydrocarbons, decontamination of water and various ways in which to reduce carbon dioxide.
However, Ishitani and co-workers state that it will be some time before artificial photosynthesis becomes commonplace in such systems, because the process requires considerable further research and development.