Photocatalytic Systems of Pt Nanoparticles and Molecular Co Complexes for NADH Regeneration and Enzyme-coupled CO2Conversion

Abstract

Natural photosynthesis utilizes solar energy to convert carbon dioxide and water to energy-rich carbohydrates. Substantial use of sunlight to meet world energy demands requires energy storage in useful fuels via chemical bonds because sunlight is intermittent. Artificial photosynthesis research focuses the fundamental natural process to design solar energy conversion systems. Nicotinamide adenine dinucleotide (<TEX>$NAD^+$</TEX>) and <TEX>$NADP^+$</TEX> are ubiquitous as electron transporters in biological systems. Enzymatic, chemical, and electrochemical methods have been reported for NADH regeneration. As photochemical systems, visible light-driven catalytic activity of NADH regeneration was carried out using platinum nanoparticles, molecular rhodium and cobalt complexes in the presence of triethanolamine as a sacrificial electron donor. Pt nanoparticles showed photochemical NADH regeneration activity without additional visible light collector molecules, demonstrating that both photoactivating and catalytic activities exist together in Pt nanoparticles. The NADH regeneration of the Pt nanoparticle system was not interfered with the reduction of <TEX>$O_2$</TEX>. Molecular cobalt complexes containing dimethylglyoxime ligands also transfer their hydrides to <TEX>$NAD^+$</TEX> with photoactivation of eosin Y in the presence of TEOA. In this photocatalytic reaction, the <TEX>$NAD^+$</TEX> reduction process competed with a proton reduction.