Nanocrystalline spinel LiMn2O4 has been prepared and treatment of LiMn2O4 with dilute nitric acid solution resulted in the delithiation of the framework, while maintaining the spinel structure, λ-MnO2. LiMn2O4 is not a catalyst for water oxidation. Upon removal of the lithium, the cubical Mn 4O4 cores become active sites for oxidizing water to molecular oxygen, which was investigated with the photochemical [Ru 2+(2,2′-bpy)3]/persulfate system at pH 5.8. The nanosize λ-MnO2 obtained from the nanocrystalline LiMn 2O4, which was synthesized by the citrate route, shows a significantly higher water oxidation catalytic activity (Turnover Frequency: 3 × 10-5 mol O2/s/mol Mn) than that obtained via solid state reaction with micrometer and irregular particle sizes (Turnover Frequency: 5 × 10-6 mol O2/s/mol Mn).
ASJC Scopus subject areas
- Colloid and Surface Chemistry