Photocatalytic reduction of CO2 with H2O over modified TiO2 nanofibers： Understanding the reduction pathway

Nanosized metal （Pt or Pd）-decorated TiO2 nanofibers （NFs） were synthesized by a wet impregnation method. CdSe quantum dots （QDs） were then anchored onto the metal-decorated TiO2 NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO2 under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO2 NFs were found to exhibit enhanced performance compared to Pt-decorated TiO2 NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO2 NFs exhibited higher selectivity for methanol, typically producing -90 ppmg^-1.h^-1 methanol. The CO2 photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.