Photocatalytic reduction of gaseous and solution CO₂ to energy products using Ag/TiO₂ and Cu/TiO₂ in CuCl₂ solution

This study investigates the surface modification of photocatalysts and the photoreduction of CO₂ to convert to useful fuels or chemicals under ultraviolet (UV) illumination. The photocatalysts used in this study are Ag/TiO₂ and Cu/TiO₂ made by the impregnation method, and the wavelength of UV irradiation is 254 nm. An X-ray single crystal diffractometer, scanning electron microscope, energy dispersive spectrometer, X-ray photoelectron spectroscopy or Electron Spectroscopy for Chemical Analysis and BET surface measurement devices are used for the characterization of Cu/TiO₂ and Ag/TiO₂. These analyses prove that the elements of Ag and Cu are all in the form of a zero charge, such as Ag⁰ and Cu⁰. The photocatalytic reductions of CO₂ are performed for three different cases. The major product in the Na₂CO₃ solution with the photocatalysts is methanol, and the gas product is methane with the yield 125 µg g^-1 at 1 M CuCl₂ and 0.1 M Na₂CO₂. For the reaction mechanism, CO₂ is assumed to be adsorbed on the surface of the photocatalysts and combines with the electron which is excited from the photocatalytic reaction via the forming of ·CO₂^-. After the forming of ·CO₂^-, the intermediates of ·CO⁺ and OH^- produce the products of CH₃OH and CH₄. The results obtained from this study contribute to a better understanding of the UV/photocatalytic process for the reduction of CO₂. The technology for the reduction of CO₂ to useful fuels and chemicals as elucidated in this study is also environmentally beneficial.