Artificial photosynthesis of methanol from carbon dioxide and water via a Nile red-embedded TiO2 photocathode

Abstract

The conversion of carbon dioxide into useful chemicals is a prospective strategy for alleviating the greenhouse effect and the depletion of energy. Herein, we report an artificial photosynthetic system composed of a photoanode and a photocathode comprised of NR_x@TiO₂ functionalized with Nile red via covalent linkage or Pd/NR_x@TiO₂ with additional palladium nanoparticles. The new Nile red derivatives and organic–inorganic composite electrodes were steadily prepared and well characterized using NMR, HRMS, UV-vis, FTIR, TEM, XPS, XRD and SEM. Methanol and oxygen were the products that could be detected in the liquid and gas phase. The main active species in this artificial photosynthesis system were proven using EPR spectroscopy to be hydroxy radicals releasing O₂ gas via H₂O₂. Moreover, the carbon source of methanol was validated using a ¹³CO₂ labeling experiment; ¹⁸O₂ was determined to come from H₂O using GC-MS. The optimal photoelectrocatalytic CO₂ reduction was carried out using Pd/NR₂@TiO₂ as the working electrode yielding methanol at a rate of 106 μM h⁻¹ cm⁻² with high light quantum efficiency (Φ_cell = 0.95).