Activation of MCM-41 mesoporous silica by transition-metal incorporation for photocatalytic hydrogen production

Abstract

A series of transition metal incorporated MCM-41 mesoporous silica is successfully synthesized by hydrothermal method, and all of them display optical absorption in ultraviolet-visible light region. Analysis results from different characterization techniques demonstrate that the transition metal ions are well dispersed in the silica framework and mainly in tetrahedral coordination. In comparison to Co and Ni incorporated MCM-41, Fe-MCM-41 shows considerable photocatalytic activity for hydrogen production, without loading any noble metal as cocatalyst. The activation for photocatalytic reaction is induced by the ligand-to-metal charge-transfer (LMCT) excitation of the monometallic centers in the framework-substituted MCM-41. Bimetal co-incorporation is found to be effective for the enhanced photocatalytic activity. For instance, Fe/Ni co-incorporated MCM-41 shows much higher photocatalytic activity for hydrogen production than either Fe or Ni incorporated MCM-41 indicating synergistic effect of co-doping with Fe and Ni. The main reason for the enhanced activity is attributed to the metal-to-metal charge–transfer (MMCT) excitation creating oxo-bridged bimetallic redox sites, which results in efficient charge separation and creation of long-lived electrons and holes to initiate redox reaction.