Artificial Photosynthesis: Visible Light-Activated TiOCl2/2-Phenyl Indole Complexes for Atmospheric CO2 and H2O Capture and Long-Chain Organic Products Generation

Abstract

We present a novel self-organized chemical "living" system that mimics natural photosynthesis by capturing CO₂ and H₂O from the atmosphere at ambient conditions. This system autonomously reduces CO₂ with H₂O protons to produce long-chain aliphatic oxygenated products. Starting with 2-phenyl indole (PI) complexes with TiCl₄, the hydrolyzed complexes react with CO₂ to form organotitanium carbonates. The 2:1 PI/TiCl₄ complex was found to be the most effective. Key findings include: Photocatalytic Reduction: Visible light reduces Ti^IV to Ti^III and Ti^II, forming peroxotitanium complexes and releasing OH radicals. CO₂ Reduction: CO₂ is reduced to CO, H₂CO, and CH₃OH, which couple to form HOCH₂CH₂OH. Organic Compound Synthesis: The system generates oxygenated organic compounds with carbon chains from C₂ to C₁₆. Ligand Exchange: The PI ligand exchanges with donor molecules, forming adducts involved in the photocatalytic process. PI Oligomerization: Contributes to the formation of PI oligomers. These processes were monitored using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) spectra, proton and Carbon-13 nuclear magnetic resonance (¹³C NMR), and infrared (IR) spectra, identifying over two dozen intermediates and products. This system offers a prototype for new applications with potential improvements using other metals and ligands.