title: Water oxidation by lambda-MnO2: catalysis by the cubical Mn4O4 subcluster obtained by delithiation of spinel LiMn2O4.
abstract: Nanocrystalline spinel LiMn(2)O(4) has been prepared and treatment of LiMn(2)O(4) with dilute nitric acid solution resulted in the delithiation of the framework, while maintaining the spinel structure, lambda-MnO(2). LiMn(2)O(4) is not a catalyst for water oxidation. Upon removal of the lithium, the cubical Mn(4)O(4) 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 lambda-MnO(2) obtained from the nanocrystalline LiMn(2)O(4), which was synthesized by the citrate route, shows a significantly higher water oxidation catalytic activity (Turnover Frequency: 3 x 10(-5) mol O(2)/s/mol Mn) than that obtained via solid state reaction with micrometer and irregular particle sizes (Turnover Frequency: 5 x 10(-6) mol O(2)/s/mol Mn).
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Robinson
authors.forename: Yong Bok
authors.initials: YB
authors.lastname: Go
authors.forename: Martha
authors.initials: M
authors.lastname: Greenblatt
authors.forename: G Charles
authors.initials: GC
authors.lastname: Dismukes
mesh_terms: D002384:Catalysis; D008094:Lithium / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D017895:Manganese Compounds / Q000737:chemistry*; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D017895:Manganese Compounds; D010087:Oxides; C488552:lithium manganese oxide; D014867:Water; D008345:Manganese; C027424:manganese oxide; D008094:Lithium; C016552:manganese dioxide