In natural photosynthesis, water oxidation reaction is catalyzed by μ-oxido-Mn₄Ca cluster in photosystem II (PSII). It has been reported that the active site for natural PSII is CaMn₄O₅ cluster with three Mn and one Ca forming a distorted CaMn₃O₄ cubane and the fourth Mn ion bonding to this cubane by additional μ-oxido ligand. In order to reveal the mechanism of oxygen formation, synthesis of CaMn₄O₅ cluster mimetic is very important. A team from sate key laboratory of catalysis of Dalian institute of chemical physics has developed one-pot synthesis method for CaxMnOy nanoparticles and investigated water oxidation mechanism. Their research has been published on March 29^th, 2016 in J. Mater. Chem. A.

The team identified that CaxMnOy nanoparticles have similar structural motifs to the catalytic active site for water oxidation in PSII. Water oxidation experiments for both chemical and photocatalytic systems suggest that the disordered structure of calcium manganese oxides and a modest valence state of Mn (+3.7 ~ +3.8) are necessary for achieving high activity.

Using synchrotron radiation at BSRF, the local structure of CaxMnOy has been clarified. Calcium manganese oxides have similar structural motifs to the catalytic active site for water oxidation in PSII. The content of Ca and the concentration of H₂O₂ in initial mixture could affect the crystallinity and the average Mn valence state of calcium manganese oxides.

The research provides developed a novel method for the synthesis of CaMn₄O₅ cluster mimetic and provided new clues for understanding the water oxidation mechanism, synchrotron sources have helped the team to unveil the local structure of CaxMnOy nanopaticles.

Article:  Feng Rong, Jiao Zhao, Zheng Chen, Yuxing Xu, Yaopeng Zhao, Qihua Yang* and Can Li*, Highly active water oxidation on nanostructured biomimetic calcium manganese oxides catalysts, J. Mater. Chem. A (4) 2016, 6585-6594.