Artificial Photosynthesis: Nexus of Photon Energy and Bioreactors

The rising energy demands of the rapidly growing population are a major challenge, involving science and geopolitics. Fossil fuels are diminishing at a faster pace, leading to rising greenhouse gases and temperature. Artificial photosynthesis can contribute to reduce greenhouse gas emissions and dependence on fossil fuels by harnessing solar energy. The key to achieving solar-driven water splitting is to create a light-absorbing material that captures a solar photon and generates a wireless current harnessed by catalysts. The artificial Mn4CaO4-complex, which contains a Mn3CaO4 cubane attached with a satellite Mn ion, has been found to mimic the atomic structures of the OEC. The oxidation states of the four manganese ions of the Mn4CaO4-complex are similar to the S1 state, and the redox transitions suggest that the artificial Mn4CaO4-cluster could serve as a catalyst for the water-splitting reaction. The size of the light-harvesting antenna has evolved greatly among photosynthetic organisms, and the size is inversely proportional to light intensity. The CpSRP protein plays a role in reducing antenna size, improving photosynthetic efficiency and growth rates under intense light conditions. Another advantage of photolytic systems is to produce biohydrogen through direct photolysis, involving light reactions of photosynthesis. Biohydrogen can be produced from microalgae through indirect photolysis under sulfur deprivation, which causes an imbalance in photosynthesis and respiration. Strategies to improve biohydrogen production include downregulating photosystem complex proteins and upregulating ATP synthase subunits to divert excess hydrogen ions towards the stroma. However, photodamage to photosystem complexes needs to be addressed through developing an efficient photobioreactor. This chapter gives a basic understanding of the principles and techniques of harnessing of solar energy through artificial antennae for value addition.