Role of chlorophyll in Spirulina on photocatalytic activity of CO2 reduction under visible light over modified N-doped TiO2 photocatalysts

Abstract

The combination of TiO2 nanoparticles and chlorophyll molecules is promising to provide potential new composite materials for improving photocatalytic CO2 reduction by merging the ability and features of both material types. In this research, the visible light reactive N-doped TiO2 (N–TiO2) catalysts were synthesized using a simple sol–gel method, and chlorophyll in Spirulina was consequently loaded onto the N-doped TiO2 catalysts (Sp/N–TiO2) in an attempt to enhance the photocatalytic efficiency. The effects of nitrogen and chlorophyll in Spirulina, and their loading amount on CO2 photoreduction with water under visible light of Sp/N–TiO2 catalysts were investigated. The activities of catalysts were in the order undoped TiO2<N–TiO2<Sp/N–TiO2. The addition of Spirulina was found to significantly improve the photocatalytic stability and C2+ (C2H4 and C2H6) product selectivity. The 0.5Sp/10N–TiO2 catalyst exhibited approximately 21.3 times and 1.9 times higher total production yield compared with undoped TiO2 and 10N–TiO2, respectively. This outstanding photocatalytic activity could be attributed to the enhancement in visible light harvesting, the surface oxygen vacancies (VO) facilitating reactants adsorption and dissociation, and the synergistic effect between N–TiO2 and chlorophyll in Spirulina.