Role of chlorophyll in Spirulina on photocatalytic activity of CO sub(2) reduction under visible light over modified N-doped TiO sub(2) photocatalysts

The combination of TiO sub(2) nanoparticles and chlorophyll molecules is promising to provide potential new composite materials for improving photocatalytic CO sub(2) reduction by merging the ability and features of both material types. In this research, the visible light reactive N-doped TiO sub(2) (N-TiO sub(2)) catalysts were synthesized using a simple sol-gel method, and chlorophyll in Spirulina was consequently loaded onto the N-doped TiO sub(2) catalysts (Sp/N-TiO sub(2)) in an attempt to enhance the photocatalytic efficiency. The effects of nitrogen and chlorophyll in Spirulina, and their loading amount on CO sub(2) photoreduction with water under visible light of Sp/N-TiO sub(2) catalysts were investigated. The activities of catalysts were in the order undoped TiO sub(2) < N-TiO sub(2) < Sp/N-TiO sub(2). The addition of Spirulina was found to significantly improve the photocatalytic stability and C sub(2+) (C sub(2)H sub(4) and C sub(2)H sub(6)) product selectivity. The 0.5Sp/10N-TiO sub(2) catalyst exhibited approximately 21.3 times and 1.9 times higher total production yield compared with undoped TiO sub(2) and 10N-TiO sub(2), respectively. This outstanding photocatalytic activity could be attributed to the enhancement in visible light harvesting, the surface oxygen vacancies (V sub(O)) facilitating reactants adsorption and dissociation, and the synergistic effect between N-TiO sub(2) and chlorophyll in Spirulina.